Document Sample

IEA Bioenergy
Task 24: Energy from biological
conversion of organic waste
2                                                         BIOGAS UPGRADING AND UTILISATION

                Table of Contents
                Introduction                                                         3

                Biogas Composition                                                   4
Flotec water
scrubbing       Gas Utilisation                                                      5
                Heating                                                              5
                CHP-engines                                                          5
                Vehicle fuel                                                         6
                Fuel cells                                                           7

                Gas upgrading technologies                                           10

                Carbon dioxide removal                                               10
Kompogas        Water scrubbing                                                      10
carbon          Polyethylene glycol scrubbing                                        11
molecular       Carbon molecular sieves                                              11
sieves          Membranes                                                            12
                High pressure gas separation                                         12
                Gas-liquid absorption membranes                                      13

                Hydrogen sulphide removal                                            13
                Biological desulphurisation                                          14
                Iron chloride dosing to digester slurry                              15
                Iron oxide                                                           15
Cirmac          Iron oxide wood chips                                                16
Membrane        Iron oxide pellets                                                   16
Gas upgrading   Impregnated activated carbon                                         16
                Water scrubbing                                                      17
                Selexol scrubbing                                                    17
                Sodium hydroxide scrubbing                                           17

                Halogenated hydrocarbon removal                                      17

                Siloxane removal                                                     17

                Removal of oxygen and nitrogen                                       17

Selexol         List of reference plants                                             18
BIOGAS UPGRADING AND UTILISATION                                                                                                   3

Anaerobic digestion (AD) has successfully been used for many applications that have
conclusively demonstrated its ability to recycle biogenic wastes. AD has been suc-
cessfully applied in industrial waste water treatment, stabilisation of sewage sludge,
landfill management and recycling of biowaste and agricultural wastes as organic ferti-
lisers. Increasingly the AD-process is applied for degrading heavy organic pollutants
such as chlorinated organic compounds or materials resistant to aerobic treatment.

Today, farm-based manure facilities are perhaps the most common use of AD-techno-
logy. Six to eight million family-sized low-technology digesters are used in the far East
(Peoples Republic of China and India) to provide biogas for cooking and lighting. The-
re are now over 800 farm-based digesters operating in Europe and North America.
Thousands of digesters help to anaerobically stabilise and thicken sewage sludge be-
fore it is either used on agricultural land, dried and incinerated or landfilled. More than
1 000 high-rate anaerobic digesters are operated world-wide to treat organic polluted
industrial waste water including processors of beverages, food, meat, pulp and paper,          1 000 high-rate anaerobic digesters
milk among others.                                                                                 are operated world-wide to treat
Gas recovery from landfills has become a standard technology in most of the indu-                 organic waste water and 120 AD
strialised countries for energy recovery, environmental and safety reasons. Increasingly      plants to digest totally 5 million tons
the gas is used in combined heat and power (CHP) engines or as a supplement to                                   of MSW and other
natural gas.                                                                                                biogenic solid wastes.
There are more than 120 AD plants operating or under construction using the organic
fraction of source separated municipal solid waste to produce a high quality compost
or mechnically separated MSW to stabilise the organic fraction before landfilling. The
total installed capacity is close to five million tonnes.
The product of anaerobic digestion is a mixed gas primarily composed of methane
CH4 and carbon dioxide which commonly is called biogas. In small scale installations
the gas is primarely utilised for heating and cooking. In larger units CHP’s are fueled
with biogas. In any case, the driving force for the gas utilisation was to economise fos-
sil fuels or wood as in developing countries.
More recently, as discussed at the conferences of Rio and Kyoto, various airborne
emissions have caused serious concern about climatic, environmental and health im-
pacts. Discharges of acid and green house gases are actually at levels that require im-
mediate actions to counter severe future problems. This is particularly true for the
transport sector. Alternative fuels might help considerably to reduce emissions. This
has been recognised by a number of governements which brought forward programs
(such as the EU ZEUS project which stands for Zero Emission vehicles in Urban So-
ciety) and legislations (e.g. the Californian clean fuel act).
In particular, biogas as a fuel could bring substantial reductions in green house gases,
particles and dust or nitrogen oxide emissions. This has been acknowledged among
others by by the Swedish Ministry of Environment who suggest to fully free biogas from
fuel taxes as the only biofuel before methanol and ethanol from bio-based origin or ra-
pemethylester (RME). In Switzerland biogas is exempt of all fuel taxes for a limited pilot
period. There are good chances that it will be fully freed in the near future.
                                                                                               From Arthur Wellinger, Switzerland
When biogas is used as a vehicle fuel it has to be upgraded and compressed. A num-
                                                                                                    and Anna Lindberg, Sweden.
ber of technologies have been developed during the passed ten years. This brochure
provides an insight of the 1999 status of biogas upgrading and utilisation.
4                                                                                       BIOGAS UPGRADING AND UTILISATION

                                           Biogas Composition
                                           Biogas produced in AD-plants or landfill     maximal workplace concentration is 5
                                           sites is primarily composed of methane       ppm). When biogas is burned SO2/SO3
                                           (CH4) and carbon dioxide (CO2) with          is emitted which is even more poiso-
                                           smaller amounts of hydrogen sulphide         nous than H2S. At the same time SO2 lo-
                                           (H2S) and ammonia (NH3). Trace               wers the dew point in the stack gas. The
                                           amounts of hydrogen (H2), nitrogen (N2),     sulphurous acid formed (H2SO3) is high-
                                           carbon monoxide (CO), saturated or ha-       ly corrosive.
                                           logenated carbohydrates and oxygen
                                           (O2) are occasionally present in the bio-    • Removal of water because of potential
                                           gas. Usually, the mixed gas is saturated     accumulation of condensate in the gas
                                           with water vapour and may contain dust       line, the formation of a corrosive acidic
                                           particles and siloxanes.                     solution when hydrogen sulphide is dis-
                                                                                        solved or to achieve low dew points
                                                                                        when biogas is stored under elevated
    Characteristics of different fuel gases                                             pressures in order to avoid condensati-
                                                                                        on and freezing.
    Parameter                     Unit     Natural Gas Town Gas         Biogas
                                                                      (60% CH 4 , 38%
                                                                                        • Removal of CO2 will be required if the
                                                                      CO2, 2% Other)
                                                                                        biogas needs to be upgraded to natural
    Calorific value (lower)       MJ/m3    36.14         16.1           21.48
                                                                                        gas standards or vehicle fuel use. It dilu-
    Density                       kg/m3    0.82          0.51           1.21            tes the energy content of the biogas but
                                                                                        has no significant environmental impact.
    Wobbe index (lower)           MJ/m3    39.9          22.5           19.5
                                                                                        • Landfill gas often contains significant
    Max. ignition velocity        m/s      0.39          0.70           0.25
                                                                                        amounts of halogenated compounds
    Theor. air requirement        m3air/
                                                                                        which need to be removed prior to use.
                                  m3gas    9.53          3.83           5.71            Occasionally the oxygen content is high
                                                                                        when too much air is sucked in during
    Max. CO2-conc. in stack gas   vol%     11.9          13.1           17.8            collection of the landfill gas.

    Dew point                     °C       59            60             60-160

                                           The characteristics of biogas are some-
                                           where in-between town gas (deriving
                                           from cracking of cokes) and natural gas.
                                           The energy content is defined by the
                                           concentration of methane. 10 % of CH4
                                           in the dry gas correspond to approx. one
                                           kWh per m3.

                                           For many applications the quality of bio-
                                           gas has to be improved. The main pa-
                                           rameter that may require removal in an
                                           upgrading systems are H2S, water, CO2
                                           and halogenated compounds:
                                           • Desulphurisation to prevent corrosion
                                           and avoid toxic H2S concentrations (the
BIOGAS UPGRADING AND UTILISATION                                                                                                  5

Gas utilisation
Biogas can be used for all applications       Requirements to remove gaseous components depending on
designed for natural gas. Not all gas ap-     the biogas utilisation
pliances require the same gas stan-
dards. There is a considerable diffe-         Application                    H2S           CO2                  H2O
rence between the requirements of sta-
tionary biogas applications and fuel gas      Gas heater (boiler)            < 1000 ppm    no                   no

or pipeline quality.
                                              Kitchen stove                  yes           no                   no

                                              Stationary engine (CHP)        < 1’000 ppm   no                   no condensation
                                              Vehicle fuel                   yes           recommended          yes
Boilers do not have a high gas quality
                                              Natural gas grid               yes           yes                  yes
requirement. Gas pressure usually has
to be around 8 to 25 mbar. It is recom-
mended to reduce the H2S concentrati-
ons to values lower than 1.000 ppm           Gas engines do have comparable requi-
which allows to maintain the dew point       rements for gas quality as boilers except
around 150°C. The sulphurous acid for-       that the H2S should be lower to guaran-
med in the condensate leads to heavy         tee a reasonable operation time of the
corrosion. It is therefore recommended       engine. Otto engines designed to run on
to use stainless steel for the chimneys      petrol are far more susceptible to hydro-
or condensation burners and high tem-        gen sulphide than the more robust die-
perature resistant plastic chimneys.         sel engines. For large scale applicati-
Most of the modern boilers have tin-la-      ons (> 60 kWel) diesel engines are the-
minated brass heat exchangers which          refore standard. Occasionally, organic
corrode even faster than iron chimneys.      silica compounds in the gas can create
Where possible, cast iron heat ex-           abrasive problems. If so, they should be
changers should be utilised.                 removed.
It is also advised to condense the water
vapour in the raw gas. Water vapour can      A diesel engine can be rebuilt into a
cause problems in the gas nozzles.           spark ignited gas engine or a dual fuel
Removal of water will also remove a lar-     engine where approx. 8-10 % of diesel
ge proportion of the H2S, reducing the       are injected for ignition. Both type of en-    Boilers and CHP-engines are reliable
corrosion and stack gas dew point pro-       gines are often applied. The dual fuel         gas utilisers. They do not have a high
                                                                                                  gas quality requirement. Usually
blems.                                       engine has a higher electricity efficiency.
                                                                                                      upgrading is limited to water
                                             The requirements for the gas upgrading              condensation and eventually H2S
                                             are the same; small CHP (< 45 kWel)                                            control.
The utilisation of biogas in internal com-
bustion engines is a long established
and extremely reliable technology. Thou-
sands of engines are operated on se-
wage works, landfill sites and biogas in-
stallations. The engine sizes range from
45kW (which corresponds to approx. 12
kWel ) on small farms up to several MW
on large scale landfill sites.
6                                                                                     BIOGAS UPGRADING AND UTILISATION

                                                                                      natural carbon cycle.
                                                                                      Best results are achieved with lean burn
                                                                                      engines. At air-fuel ratios (λ) of 1.5, NOx
                                                                                      and CO concentrations of less than 500
                                                                                      ppm can be achieved.

                                                                                      A promising application of electrical ge-
                                                                                      neration is the use of gas turbines. Mo-
                                                                                      dern engines are equally efficient as in-
                                                                                      ternal combustion engines and very ro-
                                                                                      bust. They allow recovery of the heat in
                                                                                      form of valuable steam. Unfortunately,
                                                                                      the efficient turbines are available only
                                                                                      at scales greater than 800 kWel. Their
                                                                                      gas requirements are comparable to
                                                                                      those of CHP engines.

                                                                                      Vehicle fuel
                                                                                      The utilisation of biogas as vehicle fuel
                                                                                      uses the same engine and vehicle con-
Transportation of the biowaste with      achieve practical electric efficiencies of   figuration as natural gas. In total there
biogas operated trucks allows to fully   29 % (spark ignition) and 31 % (dual         are more than 1 million natural gas ve-
close the natural carbon cycle: No non   fuel). Larger engines have efficiencies of   hicles all over the world, this demon-
renewable energy is required
                                         up to 38 %.                                  strates that the vehicle configuration is
                                         In biogas engines NOx emissions are          not a problem for use of biogas as ve-
                                         usually low because of the CO2 in the        hicle fuel. However, the gas quality de-
                                         gas. CO-concentration is often more of a     mands are strict. With respect to these
                                         problem. Catalysts to reduce the CO are      demands the raw biogas from a dige-
                                         difficult to use because of the H2S in the   ster or a landfill has to be upgraded.
                                         gas. However, from an environmental          Through upgrading we obtain a gas
Replacement of diesel or petrol by       point of view CO is a far smaller pro-       which:
biogas reduces the emissions and         blem than NOx because it is rapidly oxi-     • has a higher calorific value in order to
also the engine noise considerably.      dised to CO2 which makes part of the         reach longer driving distances,
                                                                                      • has a regular/constant gas quality to
                                                                                      obtain safe driving,
                                                                                      • does not enhance corrosion due to
                                                                                      high levels of hydrogen sulphide, am-
                                                                                      monia and water,
                                                                                      • does not contain mechanically dama-
                                                                                      ging particles,
                                                                                      • does not give ice-clogging due to a
                                                                                      high water content,
                                                                                      • has a declared and assured quality.

                                                                                      In practice this means that carbon dioxi-
                                                                                      de, hydrogen sulphide, ammonia, partic-
BIOGAS UPGRADING AND UTILISATION                                                                                                 7

les and water (and sometimes other tra-
ce components) have to be removed so
that the product gas for vehicle fuel use
has a methane content above 95 vol%.
In different countries different quality
specifications for vehicle fuel use of bio-
gas and natural gas are applied.

Upgraded biogas is actually the clea-
nest vehicle fuel possible with respect to
environment, climate and human health.
A 1995 Swedish report on alternative
fuels classified biogas on top long befo-
re bio-based methanol and ethanol
(resp. their tertiary butylesters) as well
as rapemethylester (RME).                     in an electrochemical reaction. There is        The four steps of biogas upgrading to
In 1998 two Swiss studies confirmed           no intermediate process which first con-                                 vehicle fuel.
the Swedish findings. Different methods       verts fuel into mechanical energy and
of environmental rating gave natural          heat. Therefore fuel cells have extremely
gas a 75 % over all advantage over die-       low emissions. The reaction is similar
sel and a 50 % advantage over petrol.         to a battery however, fuel cells do
Human toxicity gave a 70 % lower value,       not store the energy with chemicals in-
the ozone potential was reduced by 60         ternally.
to 80 %, acid formation by more than 50
%. Parallel monitoring of comparable          In a first step the fuel is transformed into
car engines fueled with either petrol, die-   hydrogen either by a catalytic steam re-
sel or natural gas in a town cycle (EU        forming conversion or by a (platinum)
standard) demonstrated a reduced NOx          catalyst. The H2 is converted to direct
emission for gas of 57 % resp. 88 %           electrical current. The by-products of the
when compared to petrol resp. diesel, a       reaction are water and CO2.
96 % reduction of the ozone potential
and virtually no emission of canceroge-       Conversion efficiency to electricity is ex-
nic compounds. Non methanogenic hy-           pected to exceed 50 %. FC’s demon-
drocarbon emission was reduced by 73          strate relatively constant efficiencies over
%. Only the methane emission was              a wide range of loads. There are five ty-
increased with the gas fueled engines         pes of fuel cells, classified by the type of    Different methods of environmental
which reduced the advantage of green          electrolyte: Alkaline (AFC), Phosphoric         rating gave natural gas a 75% over
house gas emission to 25 %.                   Acid (PAFC), Molten Carbonate (MCFC),          all advantage over diesel and a 50%
                                              Solid Oxide (SOFC) and Proton Ex-                            advantage over petrol.
                                              change Membrane (PEM) fuel cells.

Fuel cells                                    Alkaline fuel cell technology is used ex-
                                              tensively in NASA’s space shuttle pro-
Fuel cells (FC)are power generating sy-       gram but is more difficult to use for terre-
stems that produce DC electricity by          strial applications because of its intole-
combining fuel and oxygen (from the air)      rance to carbon oxides.
8                                                                                        BIOGAS UPGRADING AND UTILISATION

     Quality demands in different countries for utilisation of bio-                      that a PACF can be operated on biogas
     gas as vehicle fuel                                                                 without CO2 removal however, with care-
                                                                                         full cleaning of halogens and hydrogen
                                   Unit      France 1)     Switzerland 1) Sweden         sulphide.

     Wobbe indexlower              MJ/nm3                                 45,5

     Wobbe indexupper              MJ/nm3                                 48,2           Molten-Carbonate Fuel Cells are a type
                                                                                         of direct fuel cell that eliminate external
     Water dewpoint                °C                      5° lower than the lowest      fuel processors. Methane (from natural
                                                           ambient temperature
                                                                                         gas) and steam are converted into hy-
                                                                                         drogen-rich gas in the reforming anode
     Energy content upper          kWh/nm3   10.7
                                                                                         which is part of the fuel cell stack.
     Water content, maximum        mg/nm3    100           5              32             MCFC pilot plants have demonstrated
                                                                                         up to 50 % electric efficiency. They can
     Methane minimum               vol%                    96             97             operate from 25 up to 125 % of the no-
                                                                                         minal plant design. They are far more
     Carbon dioxide, maximum       vol%                                   3
                                                                                         compact than PAFC’s.
     Oxygen, maximum               vol%      3.5           0.5            1              At the end of 1999 a first demonstration
                                                                                         project of an MCFC using digester gas
     Carbon dioxide, + oxygen +                                                          as a fuel will be completed near Seattle
     nitrogen, maximum             vol%      3             3              3
                                                                                         at the King County’s waste water treat-
                                                                                         ment plant.
     Hydrogen, maximum             vol%                                   0,5

     Hydrogen sulphide, maximum    mg/nm3    7             5              23
                                                                                         Solid Oxide Electrolyte Fuel Cells
     Total sulphure                mg/nm3                  14.3                          usually are utilising doped zirconia or yt-
                                                                                         trium as the electrolyte. It operates at at-
     Particles or other solid
     contaminants, max. diameter   mm                                     5              mospheric pressure or slight overpres-
                                                                                         sure at temperatures above 900°C.
     Halogenated hydrocarbons      mg/m3     1             0                             There are several features of SOFC that
                                                                                         make the technology attractive: One is
                                                                                         the high tolerance to fuel contaminant
  Basically there are no specific            All the other technologies could be app-    and two, the high temperature does not
requirements for fuel gas. The               lied with upgraded biogas.                  require expensive catalyst and permits
requirements are valuable for biogas
                                                                                         direct fuel processing.
introduction into the grid from where it
is also used for fuel gas. In Switzer-       Currently, phosphoric acid fuel cells are   Sulzer Hexis has developed a ZrO2-Ce-
land the gas quality corresponds to          the only commercialised technology. Uti-    ramic fuel cell. One of two test stacks of
natural gas quality type H.                  lity-scale PACF have been in operation      1 kW electrical power has over 10.000
                                             since 1983. A number of power plants in     hours of operation with H2. 10 pilot
                                             the 200 kW to 2 MW range are operated       plants of 2 kW are in operation at poten-
                                             in Japan and the USA. A 200 kW plant is     tial clients. With an expected electric ef-
                                             also running in Switzerland. The largest    ficiency of 40 % and low emissions, they
                                             unit of 11 MW is operated by the Tokyo      are thought to have a role as heat and
                                             Electric Power Company. The practical       power plants in living areas.
                                             electric efficiency is 41 %.
                                             A number of PAFCs have been installed
                                             on water treatment plants, such as Port-    Proton Exchange Membrane Fuel Cells
                                             land, USA. A feasibility study has shown    are the most compact technology and
BIOGAS UPGRADING AND UTILISATION                                                             9

 Types of fuel cells

 Fuel Cell and                 PAFC              MFC                 SOFC       PEM

 Electrolyte                   Phosphoric       Molten Carbo- Solid Oxide   Membranes
                               Acid H3PO4       nate LiKCO3   Y2O3 and ZrO2

 Operating Temperature         200°C             650°C               1000°C     50-120°C

 System Efficiency (%)         40-45%            50-57%              45-50%

 Module Size                   200 kW-          2 MW                 3-100 kW
                               2 MW

 Fuel type                     Natural, coal or landfill gas, etc.              Gases MeOH

 Commercial Availability       now               1999                2001       2004

the only ones which operate at tempera-
tures below boiling point of water.
They are therefore particularly interesting
for vehicles. All the major car industries
are heavily investing in the development
of the PEMFC technology. Two major
improvements made the success pos-
One, the amount of the platinum catalyst
                                                         Gazelle, a 200 kW natural gas
could be reduced by a factor of 30 and
                                                  operated phosphoric acid fuel cell has
two, new membranes are boosting PEM                been in operation since 1995 with an
performance at lower cost.                                   electric efficiency of 41 %.
10                                                                                     BIOGAS UPGRADING AND UTILISATION

                                          Gas upgrading technologies
                                                                                       driving distances with a fixed gas stora-
                                                                                       ge volume. Removal of carbon dioxide
                                                                                       also provides a consistent gas quality
                                                                                       with respect to energy value. The latter is
                                                                                       regarded to be of great importance from
                                                                                       the vehicle manufacturers in order to re-
                                                                                       ach low emissions of nitrogen oxide.
                                                                                       At present four different methods are
                                                                                       used commercially for removal of car-
                                                                                       bon dioxide from biogas either to reach
                                                                                       vehicle fuel standard or to reach natural
                                                                                       gas quality for injection to the natural
                                                                                       gas grid.
                                                                                       These methods are:
                                                                                       • water absorption,
                                                                                       • Polyethylene glycol absorption,
                                                                                       • carbon molecular sieves,
                                                                                       • membrane separation.
                                                                                       Below the methods are described in
                                                                                       more detail.

                                                                                       Water scrubbing
                                                                                       Water scrubbing is used to remove car-
                                                                                       bon dioxide but also hydrogen sulphide
                                                                                       from biogas since these gases are
                                                                                       more soluble in water than methane.
                                                                                       The absorption process is purely physi-
                                                                                       cal. Usually the biogas is pressurised
                                                                                       and fed to the bottom of a packed co-
                                                                                       lumn where water is fed on the top and
                                                                                       so the absorption process is operated
Water scrubbing of carbon dioxide         A number of gas upgrading technolo-
and hydrogen sulphide is often            gies have been developed for the treat-      Water scrubbing can also be used for
applied in Sweden, France and the         ment of natural gas, town gas, sewage        selective removal of hydrogen sulphide
U.S.A. The process is especially
simple and usefull in sewage and          gas, landfill gas etc. However, not all of   since hydrogen sulphide is more solu-
industrial waste water treatment plants   them are recommended for the applica-        ble than carbon dioxide in water. The
where the water does not have to be       tion with biogas because of price and/or     water which exits the column with absor-
regenerated and recycled. The picture     environmental concerns.                      bed carbon dioxide and/or hydrogen
shows the Renton plant (Seattle,
                                                                                       sulphide can be regenerated and recir-
U.S.A.) with a capacity of 4.000 nm3
per day.                                                                               culated back to the absorption column.
                                          Carbon dioxide removal                       The regeneration is made by de-pressu-
                                                                                       rising or by stripping with air in a similar
                                          For an effective use of biogas as vehicle    column. Stripping with air is not recom-
                                          fuel it has to be enriched in methane.       mended when high levels of hydrogen
                                          This is primarily achieved by carbon di-     sulphide are handled since the water
                                          oxide removal which then enhances the        will soon be contaminated with elemen-
                                          energy value of the gas to give longer       tary sulphur which causes operational
BIOGAS UPGRADING AND UTILISATION                                                                                                     11

problems. The most cost efficient me-                                                            upgraded biogas     Dryer
thod is not to recirculate the water if                                                          ~90 % CH4
cheap water can be used, for example,
                                                                                                        CO2 + H2S
outlet water from a sewage treatment
plant.                                                                                                                       Water

                                                                              Absorbtion tower                      Desorption tower
Polyethylene glycol scrubbing
                                                                                                                    (regeneration of
Polyethylene glycol scrubbing is like wa-                                                                           water)
ter scrubbing a physical absorption pro-                               Compression 10 bar
cess. Selexol is one of the trade names
used for a solvent. In this solvent, like in
water, both carbon dioxide and hydrogen              Digester
sulphide are more soluble than metha-                                                             Water pump
ne. The big difference be-tween water
and Selexol is that carbon dioxide and
hydrogen sulphide are more soluble in          produced from coke rich in pores in the              Schematic flow sheet for water
Selexol which results in a lower solvent       micrometer range. The pores are then                absorption with recirculation for
                                                                                                 removal of carbon dioxide and/or
demand and reduced pumping. In addi-           further reduced by cracking of the hydro-
                                                                                                  hydrogen sulphide from biogas.
tion, water and halogenated hydrocar-          carbons.
bons (contaminants in biogas from              In order to reduce the energy consumpti-
landfills) are removed when scrubbing          on for gas compression, a series of ves-
biogas with Selexol.                           sels are linked together. The gas pres-
                                               sure released from one vessel is sub-
Selexol scrubbing is always designed           sequently used by the others. Usually
with recirculation. Due to formation of        four vessels in a row are used filled with
elementary sulphur stripping the Selexol       molecular sieve which removes at the
solvent with air is not recommended            same time CO2 and water vapour.
but with steam or inert gas (upgraded          After removal of hydrogen sulphide, i.e.
biogas or natural gas). Removing hydro-        using activated carbon and water con-
gen sulphide on beforehand is an alter-        densation in a cooler at 4°C, the biogas
native.                                        flows at a pressure of 6 bars into the ad-     Pressure swing adsorbtion of biogas
                                                                                               on activated carbon with removal of
                                               sorption unit. The first column cleans
                                                                                            H2S (right), halogenated hydrocarbons
Carbon molecular sieves                        the raw gas at 6 bar to an upgraded bio-                    (middle) and 4-bed CO2
Molecular sieves are excellent products        gas with a vapour pressure of less than                             adsorption (left).
to separate specifically a number of dif-
ferent gaseous compounds in biogas.
Thereby the molecules are usually loo-
sely adsorbed in the cavities of the car-
bon sieve but not irreversibly bound. The
selectivity of adsorption is achieved by
different mesh sizes and/or application
of different gas pressures.
When the pressure is released the com-
pounds extracted from the biogas are
desorbed. The process is therefore of-
ten called “pressure swing adsorption”
(PSA). To enrich methane from biogas
the molecular sieve is applied which is
12                                                                                   BIOGAS UPGRADING AND UTILISATION

                                                                  upgraded biogas    There are two basic systems of gas
                                                                                     purification with membranes: a high
                                                                         (CH4)       pressure gas separation with gas pha-
                                                                                     ses on both sides of the membrane,
                   Condensation                                   4-bed              and a low-pressure gas liquid absorpti-
     Compressor    Cooler                                         adsorber           on separation where a liquid absorbs
  Biogas                                                                             the molecules diffusing through the
                                                                  Vacuum pump        membrane.

                    H2 O
                                                                                     High pressure gas separation
                                                                                     Pressurised gas (36 bar) is first cleaned
                                                                                     over for example an activated carbon
                                                                                     bed to remove (halogenated) hydrocar-
                                                                                     bons and hydrogen sulphide from the
Schematic flow sheet for upgrading of    10 ppm H2O and a methane content of         raw gas as well as oil vapour from the
biogas to vehicle fuel standards with    96 % or more.                               compressors. The carbon bed is follo-
carbon molecular sieves.                 In the second column the pressure of 6      wed by a particle filter and a heater.
                                         bar is first released to approx. 3 bar by   The membranes made of acetate-cellu-
                                         pressure communication with column 4,       lose separate small polar molecules
                                         which was previously degassed by a          such as carbon dioxide, moisture and
                                         slight vacuum. In a second step the         the remaining hydrogen sulphide. The-
                                         pressure is then reduced to atmosphe-       se membranes are not effective in sepa-
                                         ric pressure. The released gas flows        rating nitrogen from methane.
                                         back to the digester in order to recover    The raw gas is upgraded in 3 stages to
                                         the methane. The third column is eva-       a clean gas with 96 % methane or more.
                                         cuated from 1 bar to 0.1 bar. The desor-    The waste gas from the first two stages
                                         bed gas consists predominantly of car-      is recycled and the methane can be re-
                                         bon dioxide but also some methane and       covered. The waste gas from stage 3
                                         is therefore normally released to the en-   (and in part of stage 2) is flared or used
                                         vironment. In order to reduce methane       in a steam boiler as it still contains 10 to
                                         losses the system can be designed with      20 % methane.
                                         recirculation of the desorbed gases.        First experiences have shown that the
                                                                                     membranes can last up to 3 years
                                         The product gas of column 1 is monito-      which is comparable to the lifetime of
                                         red continuously for CH4 by an infrared     membranes for natural gas purification -
First experiences have shown that        analyser. If the required Wobbe index is    a primary market for membrane techno-
the high pressure gas seperation         not maintained the gas flows back to        logy - which last typically two to five
membranes can last up to 3 years         PSA. If the methane content is high         years. After 1½ years permeability has
which is comparable to the liefetime     enough, the gas is either introduced into   decreased by 30 % due to compaction.
of membranes for natural gas             the natural gas net or compressed in a      The clean gas is further compressed up
                                         3 stage compressor up to 250 bar.           to 3.600 psi (250 bar) and stored in
                                         Continuous monitoring of a small-scale      steel cylinders in capacities of 276 m3
                                         installation (26 m3/hr) demonstrated ex-    divided in high, medium and low pres-
                                         cellent results of gas cleaning, energy     sure banks.
                                         efficiency and cost.
                                                                                     The membranes are very specific for gi-
                                                                                     ven molecules, i.e. H2S and CO2 are se-
BIOGAS UPGRADING AND UTILISATION                                                                                                 13

parated in different modules. The utilisa-
tion of hollow-fibre membranes allows
the construction of very compact modu-                                      liquid
les working in cross flow.

Gas-liquid absorption membranes                            H2S
Gas-liquid absorption using membra-
nes is a separation technique which
was developed for biogas upgrading
only recently. The essential element is a                  H2S

microporous hydrophobic membrane
separating the gaseous from the liquid
phase. The molecules from the gas
stream, flowing in one direction, which
are able to diffuse through the membra-
                                                                                                   Gas-liquid absorption using
ne will be absorbed on the other side by                                                   hydrophobic membranes is a recent
the liquid flowing in counter current.                    membrane                         development working at atmospheric
The absorption membranes work at ap-                                                          pressures which allows a low-cost
prox. atmospheric pressure (1 bar)                                                                                construction.
which allows low-cost construction.
The removal of gaseous components is         in order to avoid corrosion in compres-
very efficient. At a temperature of 25 to    sors, gas storage tanks and engines.
35°C the H2S concentration in the raw        Hydrogen sulphide is extremely reactive
gas of 2 % is reduced to less than 250       with most metals and the reactivity is en-
ppm. The absorbent is either Coral or        hanced by concentration and pressure,
NaOH.                                        the presence of water and elevated tem-
                                             peratures. Due to the potential problems
                                             hydrogen sulphide can cause, it is re-       The cross-flow gas absorption
H2S saturated NaOH can be used in wa-
                                                                                          membrane is particularly well adapted
ter treatment to remove heavy metals.        commended to remove it early in the
                                                                                          for the removal of H2S with NaOH or
The H2S in Coral can be removed by           process of biogas upgrading. Experi-         coral as an absorbant. The latter can
heating. The concentrated H2S is fed         ence has also shown that two of the          be regenerated.
into a Claus reaction or oxidised to ele-
mentary sulphur. The Coral solution can
then be recycled.
CO2 is removed by an amine solution.
The biogas is upgraded very efficiently
from 55% CH4 (43 % CO2) to more than                                                                                     inlet

96% CH4. The amine solution is regene-                                          outlet

rated by heating. The CO2 released is
pure and can be sold for industrial app-

Hydrogen sulphide removal
Hydrogen sulphide is always present in
biogas, although concentrations vary
with the feedstock. It has to be removed
14                                                                                       BIOGAS UPGRADING AND UTILISATION

                                            most commonly used methods for hy-           For the microbiological oxidation of sulp-
                                            drogen sulphide removal are internal to      hide it is essential to add stoichiometric
                                            the digestion process: 1) air/oxygen do-     amounts of oxygen to the biogas. De-
                                            sing to digester biogas and 2) iron chlo-    pending on the concentration of hydro-
The simplest method of desulphuri-          ride dosing to digester slurry. The most     gen sulphide this corresponds to 2 to 6
sation is the addition of air into a        common commercial methods for hy-            % air in biogas.
storage tank serving at the same            drogen sulphide removal are described        Air/oxygen dosing to digester biogas.
time as gas holder. Microorganisms          below:                                       The simplest method of desulphurisati-
reduce the H2S concentration by             • air/oxygen dosing to digester biogas,      on is the addition of oxygen or air directly
95 % to less than 50 ppm.                   • iron chloride dosing to digester slurry,   into the digester or in a storage tank ser-
                                            • iron sponge,                               ving at the same time as gas holder.
                                            • iron oxide pellets,                        Thiobacilli are ubiquitous and thus sy-
                                            • activated carbon,                          stems do not require inoculation. They
                                            • water scrubbing,                           grow on the surface of the digestate,
                                            • NaOH scrubbing,                            which offers the necessary micro-aero-
                                            • biological removal on a filter bed,        philic surface and at the same time the
                                            • air stripping and recovery.                necessary nutrients. They form yellow
                                                                                         clusters of sulphure. Depending on the
                                            Biological desulphurisation                  temperature, the reaction time, the
                                            Desulphurisation of biogas can be per-       amount and place of the air added the
                                            formed by micro-organisms. Most of the       hydrogen sulphide concentration can be
                                            sulphide oxidisin g micro-organisms          reduced by 95 % to less than 50 ppm.
                                            belong to the family of Thiobacillus. Most   Measures of safety have to be taken to
                                                                                         avoid overdosing of air in case of pump
                                                                                         failures. Biogas in air is explosive in the
Addition of 2 to 6 % of air to the biogas                                                range of 6 to 12 %, depending on the
allows the indigenous Thiobacilli to
                                                                                         methane content). In steel digesters wit-
oxidise the H2S to natural sulfure
adhering to the digester surface or the                                                  hout rust protection there is a small risk
digestate.                                                                               of corrosion at the gas/liquid interface.

                                                                                         Biological filters
                                                                                         In large digesters there is often a combi-
                                                                                         ned procedure of water scrubbing (ab-
                                                                                         sorption) and biological desulphurisati-
                                                                                         on applied. Either raw waste water or
                                                                                         press-separated liquor from digestate is
                                                                                         dispensed over a filter bed. In the bed, li-
                                                                                         quor and biogas meet in counterflow
                                                                                         manner. In the biogas 4 to 6 % air is ad-
                                                                                         ded before entering the filter bed. The fil-
                                                                                         ter bed offers the required surface for
                                            of them are autotrophic i. e. they are       scrubbing as well as for the attachment
                                            using carbon dioxide from the biogas to      of the desulphurisation micro-orga-
                                            cover their carbon need. The products        nisms.
                                            formed are predominantly elementary          The system is applied in several instal-
                                            sulphur but also sulphate. The latter        lations for industrial waste water treat-
                                            forms in solutions sulphuric acid which      ment and in many of the Danish agricul-
                                            may cause corrosion.                         tural and co-digestion plants.
BIOGAS UPGRADING AND UTILISATION                                                                                                   15

Iron chloride dosing to dige-                   Therefore, there is always a chance that
ster slurry                                     the mass is self-ignited. The elementary
Iron chloride can be fed directly to the di-    sulphur formed remains on the surface
gester slurry or to the feed substrate in a     and covers the active iron oxide surface.
pre-storage tank. Iron chloride then re-        After a number of cycles depending on
acts with produced hydrogen sulphide            the hydrogen sulphide concentration the
and form iron sulphide salt (particles).        iron oxide or hydroxide bed has to be ex-     Iron chloride dosing to digester slurry
This method is extremely effective in re-       changed.                                         is an extremely efficient method to
ducing high hydrogen sulphide levels                                                           reduce hydrogen sulphide levels, but
but less effective in attaining a low and       Usually an installation has two reaction           does not allow to achieve vehicle
stable level of hydrogen sulphide in the        beds. While the first is desulphurising                               fuel demands.
range of vehicle fuel demands. In this          the biogas, the second is regenerated
respect the method with iron chloride           with air.
dosing to digester slurry can only be re-       The desulphurisation process works
garded as a partial removal process in          with plain oil free steel wool covered with
order to avoid corrosion in the rest of the     rust. However, the binding capacity for
upgrading process equipment. The me-            sulphide is relatively low due to the low
thod need to be complemented with a fi-         surface area.
nal removal down to about 10 ppm.
The investment cost for such a removal          Iron oxide wood chips
process is limited since the only invest-       Wood chips covered with iron oxide have
ment needed are a storage tank for iron         a somewhat larger surface to volume ra-
chloride solution and a dosing pump.            tio than plain steel. Their surface to
On the other hand the operational cost          weight ratio is excellent thanks to the low
will be high due to the prime cost for iron     density of wood. Roughly 20 grams of
chloride.                                       hydrogen sulphide can be bound per
                                                100 grams of iron oxide chips.
Iron oxide
Hydrogen sulphide reacts easily with            The application of wood chips is very po-
iron hydroxides or oxides to iron sulphi-       pular particularly in the USA. It is a low
de. The reaction is slightly endothermic,       cost product, however, particular care
a temperature minimum of approximate-           has to be taken that the temperature
ly 12°C is therefore required to provide        does not rise too high while regenera-
the necessary energy. The reaction is           ting the iron filter.                           Hydrogen sulphide reacts with iron
                                                                                                   oxide (rust) to iron sulphide. The
optimal between 25 and 50°C. Since the
                                                                                              latter can be reoxidised with air. The
reaction with iron oxide needs water the        Iron oxide pellets
                                                                                                     product is again iron oxide and
biogas should not be too dry. However,          The highest surface to volume ratios are
                                                                                                               elementary sulphure.
condensation should be avoided becau-           achieved with pellets made of red mud,
se the iron oxide material (pellets,            a waste product from aluminium pro-
grains etc.) will stick together with water     duction. However, their density is much
which reduces the reactive surface.             higher than that of the wood chips. At hy-
                                                drogen sulphide concentrations bet-
The iron sulphides formed can be oxi-           ween 1.000 ppm and 4.000 ppm totally
dised with air, i. e. the iron oxide is reco-   50 grams can be loaded on 100 grams
vered. The product is again iron oxide or       of pellets. Most of the German and
hydroxide and elementary sulphur. The           Swiss sewage treatment plants without
process is highly exothermic, i.e. a lot of     dosing of iron chloride are equipped
heat is released during regeneration.           with an iron oxide pellet installation.
16                                                                                    BIOGAS UPGRADING AND UTILISATION

Hydrogen sulphide reacts easily with                                                  be considered for the simultaneous
iron oxide or hydroxide which is                                                      removal of carbon dioxide in order to
usually bound on wood chips or red
                                                                                      meet vehicle fuel demands on biogas
mud pellets to increase the reation
surface. In a two-column plant one                                                    quality.
column binds H2S where as the other
is regenerated.                                                                       Selexol scrubbing
                                                                                      Selexol scrubbing is like water absorpti-
                                                                                      on a purely physical absorption process
                                                                                      described above. Selexol is one of the
                                                                                      trade names for a solvent mainly consti-
                                                                                      tuting of a dimethylether of polyethylene
                                                                                      glycol (DMPEG). The cost for selective
                                                                                      hydrogen sulphide removal has not yet
                                                                                      shown to be competitive and so Selexol
                                                                                      scrubbing will probably only be conside-
                                                                                      red for simultaneous removal of carbon
                                                                                      dioxide and hydrogen sulphide in order
                                                                                      to meet vehicle fuel demands on biogas
                                       Impregnated activated carbon                   quality.
                                       With PSA systems H2S usually is remo-
                                       ved by activated carbon doted with po-         Sodium hydroxide scrubbing
                                       tassium iodide (KI). Like in biological fil-   Absorption in a water solution of sodium
                                       ters in presence of air which is added to      hydroxide (NaOH) enhances the absorp-
                                       the biogas, the hydrogen sulfide is cata-      tion capacity of the water and the ab-
                                       lytically converted to elementary sulphur      sorption process is no longer purely
                                       and water. The sulphur is adsorbed by          physical but chemical. Sodium hydroxi-
                                       the activated carbon. The reaction works       de reacts with hydrogen sulphide to
                                       best at a pressure of 7 to 8 bar and a         form sodium sulphide or sodium hydro-
                                       temperature of 50 to 70°C. The gas tem-        gen sulphide. Both these salts are inso-
                                       perature is easy to achieve through the        luble and the method is not regenerati-
                                       heat formed during compression.                ve. Since the absorption capacity of wa-
                                       Usually, the carbon filling is adjusted to     ter is enhanced lower volumes are nee-
                                       an operation time of 4.000 to 8.000            ded and pumping demands are redu-
                                       hours. If a continuous process is requi-       ced. The main disadvantage is the dis-
                                       red the system consists of two vessels.        posal of the large volumes of water con-
                                       At H2S concentrations above 3.000 ppm          taminated with sodium sulphide.
                                       the process is designed as a regenera-
                                       tive system.

                                       Water scrubbing
                                       Water scrubbing is a purely physical ab-
                                       sorption process, described above,
                                       which can be used for selective removal
                                       of hydrogen sulphide. The cost for sel-
                                       ective removal has not yet been shown
                                       to be competitive with other hydrogen
                                       sulphide removal methods.
                                       Thus water scrubbing probably only will
BIOGAS UPGRADING AND UTILISATION                                                                                             17

Halogenated hydrocar-                        CHP engines claim maximum limits of
bon removal                                  siloxanes in biogas.
                                             It is known that the organic silicon com-
Higher hydrocarbons as well as haloge-       pounds in biogas is in the form of linear
nated (FHC) hydrocarbons, particularly       and cyclic methyl siloxanes.
chloro- and fluoro-compounds are pre-        These compounds are widely used in
                                                                                                  Halogenated hydrocarbons
dominantly found in landfill gas. They       cosmetics and pharmaceutical pro-              predominantly found in landfill gas
cause corrosion in CHP engines, in the       ducts, and as anti-foaming agents in de-        cause corrosion in CHP engines.
combustion chamber, at spark plugs,          tergents.                                           They have to be removed by
valves, cylinder heads, etc. For this rea-   Siloxanes can be removed by absorpti-                 specific activated carbon.
son CHP engine manufacturers claim           on in a liquid medium, a mixture of hy-
maximum limits of halogenated hydro-         drocarbons with a special ability to ab-
carbons in biogas.                           sorb the silicon compounds. The absor-
                                             bent is regenerated by heating and des-
They can be removed by pressurised           orption. A full scale removal plant for bio-
tube exchangers filled with specific acti-   gas from a landfill is in operation in Dort-
vated carbon. Small molecules like CH4,      mund-Huckarde since 1993.
CO2, N2 and O2 pass through while lar-
ger molecules are adsorbed. The size of
the exchangers are designed to purify        Removal of oxygen
the gas during a period of more than 10      and Nitrogen
hours. Usually there are two parallel
vessels. One is treating the gas while       Oxygen and in part also nitrogen in the
the other is desorbed. Regeneration is       biogas is a sign that air has been su-
carried out by heating the activated car-    cked in. This occurs quite often in land-
bon to 200°C, a temperature at which all     fills where the gas is collected through
the adsorbed compounds are evapora-          permeable tubes by applying a slight
ted and removed by a flow of inert gas.      underpressure. Low concentrations of             Organic silicon compounds are
                                             oxygen is not a problem. Higher concen-          occasionally present in biogas.
                                             tration however bear a risk of explosion.           They are used in cosmetics,
Siloxane removal                             Biogas with a methane content of 60 %,             pharmaceutical products and
                                             the rest being predominantly carbon di-        detergents. They can be removed
Organic silicon compounds are occa-          oxide, is explosive in concentrations                    by liquid hydrocarbons.
sionally present in biogas which can         between 6 and 12 % in air.
cause severe damage to CHP engines.          Oxygen and nitrogen can be removed by
During incineration they are oxidised to     membranes or low temperature PSA
silicon oxide which deposits at spark        however, removal is expensive. Preven-
plugs, valves and cylinder heads abra-       ting the introduction of air by carefully
ding the surfaces and eventually             monitoring the oxygen concentration is
causing serious damage. Particularly in      far cheaper and more reliable than gas
Otto engines this might lead to major re-    treatment.
pairs. Dual fuel engines are less su-
ceptible because the temperature of the
entire motor body is much higher than
with Otto engines.
Because of the increased wearing of
combustion chambers caused by silica
deposits nowadays manufacturers of
18                                                                                              BIOGAS UPGRADING AND UTILISATION

           List of selected reference plants with full gas
 Country       City            Product          Biogas                 CH4    CO 2- removal H 2S- removal Raw gas       In operation
                               gas              Production             Requi- (technique)   (technique)   flow          since
                               utilisation                             rement
                               gas grid or      (landfill/ sewage      %
                               vehicle fuel     sludge/waste/

 Czech Rep.    Bystrany/       Vehicle fuel     Sewage sludge          95     Water scrub.     Water scrub.     368     1985
               Bystrica        Vehicle   fuel   Sewage     sludge      95     Water   scrub.   Water   scrub.   186     1990
               Chanov/Most     Vehicle   fuel   Sewage     sludge      95     Water   scrub.   Water   scrub.   186     1990
               Liberec         Vehicle   fuel   Sewage     sludge      95     Water   scrub.   Water   scrub.   368     1988
               Zlin/Tecovice   Vehicle   fuel   Sewage     sludge      95     Water   scrub.   Water   scrub.   186     1990

 France        Chambéry        Vehicle fuel     Sewage sludge          96,7   Water scrub.     Biol. filter/    30
                                                                                               water scrub.
               Lille           Vehicle fuel     Sewage sludge                 Water scrub.     Water scrub.     100     1995
               Tours           Vehicle fuel     Landfill                      Water scrub.     Water scrub.     200     1994

 The Nether-   Collendorn      Natural gas      Landfill               88     Membranes        Activated        375     1991
 lands                                                                                         carbon
               Gorredijk       Natural gas      Landfill               88     Membranes        Activated        400     1994
               Nuenen          Natural gas      Landfill               88     Carbon           Activated        1 500   1990
                                                                              molecular        carbon
               Tilburg         Natural gas      Sewage sludge          88     Water scrub.     Iron oxide       2 100   1987
                                                Landfill                                       pellets
                                                Green waste
               Wijster         Natural gas      Landfill               88     Carbon           Activated        1 150   1989
                                                                              molecular        carbon

 New Zeeland Christchurch      Vehicle fuel                                   Water scrub.

 Sweden        Eslöv           Vehicle fuel     Sewage sludge          97     Water scrub.     Water scrub.     40      1998
                                                Vegetable waste
               Göteborg        Vehicle fuel     Sewage sludge          97     Carbon           Activated        6       1992
                                                                              molecular        carbon
               Helsingborg     Vehicle fuel     Slaughterhouse waste   97     Carbon           Activated        16      1996
                                                                              molecular        carbon
               Kalmar          Vehicle fuel     Sewage sludge          97     Water scrub.     Water scrub.     30      1998
                                                 + manure + slaugh-
                                                terhouse waste
               Linköping       Vehicle fuel     Sewage sludge          97     Water scrub.     Iron chloride    700     1997
                                                + manure + slaugh-                             dosing +
                                                terhouse waste                                 water scrub
                               Vehicle fuel                                   Carbon                            200     1991
               Stockholm       Vehicle fuel     Sewage sludge          97     Water scrub.     Water scrub.     45      1997
               Trollhättan     Vehicle fuel     Sewage sludge          97     Water scrub.     Water scrub.     200     1996
                                                + fish waste
BIOGAS UPGRADING AND UTILISATION                                                                                                  19

upgrading to natural gas/vehicle fuel standards
 Country       City            Product         Biogas            CH4       CO2- removal H2S- removal Raw gas          In operation
                               gas             Production        Requi-    (technique)  (technique)  flow             since
                               utilisation                        rement
                               gas grid or     (landfill/ sew.      %
                               vehicle fuel    sludge/waste/

 Sweden        Uppsala         Vehicle fuel    Sewage sludge       97      Water scrub.   Water scrub.   200          1997
                                               + manure

 Switzerland   Bachenbülach Vehicle fuel       Biowaste            96      Carbon         Activated
                                                                           molecular      carbon
               Otelfingen      Vehicle fuel    Biowaste            96      Carbon         Activated
                                                                           molecular      carbon
               Rümlang         Vehicle fuel    Biowaste            96      Carbon         Activated
                                                                           molecular      carbon
               Samstagern      Natural gas     Biowaste            96      Carbon         Activated
                                                                           molecular      carbon

 USA           Croton landfill, Vehicle fuel   Landfill            90      Selexol        Selexol        120          1993 (reused
               Westchester                                                 scrubbing      scrubbing                   from Tork
               Co. (NY)                                                                                               Landfill Wisc.
               Fresh Kills,    Natural gas     Landfill                    Selexol        Selexol        13 000       1981
               Staten Island                                               scrubbing      scrubbing
               Puente Hill     Vehicle fuel    Landfill            96      Membranes      Activated      2 600        1993
               Landfill, Los                                                              carbon
               Angeles (CA)
               Renton (WA)     Natural gas     Sewage sludge       98      Water scrub.   Water scrub.   4 000        1984 + 1998
               Mc Carty        Natural gas     Landfill                    Selexol        Selexol        9 400        1986
               Road (NY)                                                   scrubbing      scrubbing

                                                                                          Text:     Arthur Wellinger and
                                                                                                    Anna Lindberg,
                                                                                                    Member IEA, Task 24
                                                                                          Layout:   Gaby Roost,
                                                                                                    Nova Energie GmbH,
                                                                                          Pictures: Manufacturers
                                                                                                    Nova Energie GmbH
                                                                                                    Verband der
                                                                                                    Schweiz. Gasindustrie

                                                                                          Printer:       Sailer Druck, Winterthur

                                                                                          Cartoon by JTI
20                                            BIOGAS UPGRADING AND UTILISATION

     Task 24: Energy from biological
     conversion of organic waste

     Task 24 Participants

     Task Leader                              Denmark
     Pat Wheeler                              Jens Bo Holm-Nielsen
     AEA Technology Environment               The Biomass Institute, SUC
     E6 Culham Laboratory                     Niels Bohrs vej 9
     Abingdon                                 DK 6700, Esbjerg
     Oxfordshire                              Denmark
     OX14 3DB                                 Tel +45 79 14 11 11
     UK                                       Fax +45 79 14 11 99
     Tel. +44 1235 463135                     e-mail:
     Fax +44 1235 463010
     e-mail:       Switzerland
                                              Arthur Wellinger
     Finland                                  Nova Energie
     Terho Jaatinen                           Elggerstr. 36
     Eco-Tecnology JVV OY                     8356 Ettenhausen
     Valkärventie 2                           Switzerland
     SF-02130 Espoo                           Tel. +41 52 368 34 70
     Finland                                  Fax +41 52 365 43 20
     Tel. +358 9 4357 7477                    e-mail:
     Fax +358 9 4357 7488
     e-mail:   UK
                                              Alastair Pettigrew
     Sweden                                   Onyx Waste Management
     Anna Lindberg                            Onyx House
     Sweco/VBB Viak                           401 Mile End Rd.
     P.O Box 34044                            London, E3 4PB
     S-100 26 Stockholm                       UK
     Sweden                                   Tel. 0181 983 5945
     Tel +46 8 695 62 39                      Fax 0181 983 0100
     Fax +46 8 695 62 30                      e-mail:

     Simon Lundeberg
     RVF/Swedish Association of Waste