In the cleaning of soot and fly ash from the combustion plants, much has changed in the history. While the ancestors had to deal mainly with soot in the flue gas, the present-day furnaces are mainly confronted with fly ash in
In the cleaning of soot and fly ash from the combustion plants, much has changed in the history. While the ancestors had to deal mainly with soot in the flue gas, the present-day furnaces are mainly confronted with fly ash in the flue gas thanks to the controlled firing. The «soot», resulting from insufficient combustion is not known to modern combustion technology, because this organic carbon content is burned out to the state of inorganic residue, namely to the fly ash.
The waste triangle demonstrates that an adequate amount of ash must always be expected in the waste.
Various cleaning processes have become established in industrial technology and the former chimney sweeper is rarely seen anymore. At present, modern combustion plants are largely kept in continuous operation by means of various cleaning systems.
Fig. 1: The good chimney sweeper of the past days
This is how our grandparents treated the waste
Already our ancestors have had the idea to treat the unneeded waste by burning it. Over time, it became clear that the released heat should be used. Soon, the most diverse stoves for heating and cooking were developed, in which, in addition to the actual fuel wood or coal, combustible waste was also burned.
Fig. 2: An “omnivore” of days gone by. [www.kaminofen-store.de/kuechenherd]
During industrialization and densification of the population, it has become clear that such a kind of unregulated combustion is highly uneconomical and furthermore due to the various fuels – in addition to the soot and fly ash – many toxic substances are emitted. The environment around each fireplace not only smelled of «burnt», but also made it difficult to breathe. Not aware were the negative effects on people and nature due to the halides and heavy metals contained in the flue gas.
«Although mankind has known fire as a blessing or a terror for thousands of years, the physico-chemical process of combustion is still quite little scientifically penetrated»
[W. Bioe 1901-1978, Chair of Thermal Engineering TH Dresden]
As materials have become more diverse, waste has become more energy containing, which has shifted the focus from disposal to energy recovery for the generation of electrical energy, process heat or district heating.
How to measure the energy content of the waste?
The waste triangle can be used to illustrate the relationship between waste qualities, which is based on the following relationship: [Tanner Triangle for Assessment of Combustibility of MSW: World bank technical guidance report or H. Hämmerli: Grundlagen zur Berechnung von Müllfeuerungen]
where the combustible* also contains the inert components such as nitrogen as well as oxygen and is therefore marked with an asterisk (*).
Fig. 3: Waste-Triangle by Hämmerli, Tanner Triangle for Assessment of Combustibility of MSW [World Bank Technical Guidance Report]
Unfortunately, the anhydrous calorific value of the waste, which means the energy-bearing calorific value, cannot be calculated from the waste triangle. For practical calculation, only the water- and ash-free calorific value Hi,waf (= water-ash-free) characterizes the mass fraction of the combustible.
The amount of heat that is released as usable heat during the complete combustion of a substance (released heat minus the energy lost for the evaporation of the water produced during combustion) is called the calorific value.
The calorific value Hi (inferior; formerly lower calorific value Hu) is thus the maximum amount of heat that can be utilized in 