**4. Discussion**

The development of Kartigen® was started from our previous study using atelocollagenembedded chondrogenic BMSCs to repair the full thickness of cartilage defect in miniature pigs [51]. The promising results encouraged us to initiate a case series study to test the safety and efficacy of Kartigen® for treating cartilage defects. In the 9 years of followup study, improvement of knee functions was satisfactory and sustainable [34]. Most importantly, infection, inflammation, joint adhesion, loose body, and tumor formation were not found in the Kartigen®-implanted knees. However, in the case series study, the contralateral knees of the same patients were used as a control group. To further validate the therapeutic efficacy of Kartigen® in comparison with standard surgical treatments, such as microfracture, a new controlled and randomized phase I clinical trial was conducted. As expected, no severe adverse events were found, and all the TEAEs were not treatment-related. Although clinical outcome was similar for Kartigen implantation and microfracture in 1-year follow-up, a sustained improvement of knee functions was found in the Kartigen® group in the 2 years follow-up.

Microfracture was introduced for focal articular cartilage repair in the 1980s and soon became a standard treatment for cartilage defects [9,46,52]. However, its results are usually associated with fibrocartilage production [12,13], and its long-term efficacy remains poor [16,53]. Mosaicplasty provides a better improvement than microfracture, but there are still several disadvantages, such as the donor-site morbidity for autografts [54], limited sources of grafts, a technical challenge in leveling the graft during operation [55], and poor integration of the implant into host tissue [56,57]. On the contrary, the procedure of Kartigen® implantation is technically simple and can be carried out with a small arthrotomy or using arthroscope. Furthermore, there is no donor site morbidity, and sources of cells are not limited.

The ability of engrafted cells to integrate into the recipient site and participate in the repair process is crucial for successful clinical outcomes. It has been reported that intra-articular injection of autologous MSCs reduced the degeneration of cartilage defects and provided pain relief [58], but integration of injected MSCs into damaged cartilage defects is unclear and doubtful. On the contrary, using atelocollagen as a cell carrier, Kartigen® prevents cell loss, is easy for implantation for cartilage defects of any shape, and achieves uniform cell distribution at the recipient site. These advantages contribute to the efficacy and durability of Kartigen® implantation. In addition, atelocollagen has been proven to enable a gradual proliferation and matrix synthesis of chondrocytes, which allow chondrocytes to maintain their phenotype for up to 4 weeks in vitro [40]. Atelocollagen gel can also support cell proliferation, matrix synthesis, and chondrogenic differentiation of MSCs [42]. Recently, the Adachi group reported the efficacy of repairing osteochondral defects with minced cartilage embedded in atelocollagen gel [41]. Our previous clinical trial with 9 years of follow-up also demonstrated the safety and efficacy of atelocollagen in repairing cartilage defects together with CPs [34].

Unlike previous studies using mature chondrocytes for cartilage repair in ACI [59], our study showed CPs in Kartigen® exhibiting sufficient integration capacity. Under arthroscopic examination, the integration between the graft and the recipient site was complete (Figure 3). The histological analyses of the biopsy specimens also demonstrated the integration of the implanted tissue into the surrounding articular cartilage (Figure 4). The accumulation of GAG and collagen type II was confirmed in the biopsy specimens (Figure 4). However, there are several limitations to this study. Because this is a phase I study, the sample size number is small. The 2 years of follow-up are not long enough to reach a final conclusion for cartilage defect repair.

Recent advances in 3D bioprinting [60–63] have enabled reconstructions of functional living cartilage to recapitulate the complexity and architecture [64,65] of an articular surface. We are looking into partnerships to integrate that technology and potentially further improve the outcome with Kartigen® implantation. This may result in more favorable biomechanical properties at the recipient sites and allow earlier weight-bearing and range

of motion without concern of graft detachment. Since MSCs are multipotent, additional biochemical and biomechanical stimulations can delicately manipulate the chondrogenic differentiation and maturation of seeded cells [66,67] to improve the functional properties of the derived neo-cartilage tissues [29]. The integration of 3D bioprinting and biomimetic in vitro chondrogenesis will drive advanced therapeutic innovations for cartilage repairs.


**2.1 Operationalization**

As part of process operationalization, a rice husk supply analysis is necessary, which ensures the raw materials meet production demands. For example, San Martín is the region with the highest economic participation in terms of rice industries in Peru, representing 18.49% of annual production in the 2013 agricultural campaign, with a total of 563.99 tonnes of paddy rice. Of the total amount produced, 20% will be converted into husk, meaning large volumes of this agricultural waste product will be burnt, due to limited recycling. **Figure 5** shows the various current uses of rice husk [16], reflecting its potential demand for companies or mills within the regional market. In many agricultural areas of the San Martín region, policies have been established to raise awareness and encourage recycling in other activities, regulated by municipal ordinances prohibiting burning. In addition, from a survey of 100 families in the region, the study concluded that 70% of the population would be willing to substitute firewood for an ecological product, 50% would pay a price equal to that of firewood, and 70% agree that briquettes should be delivered to their homes.

On the other hand, energy model sustainability revolves around the acceptance of demand variability in any successful scenario for briquette sales. For this reason, certain production programs were designed based on briquette machine production capacity. For example, if the market focus is 23% of the firewood-consuming population, mills or companies should produce 69,000 briquettes per month for a total of 92 families, using 13,248 kg of rice husk and 552 kg of cassava starch. Within a supply–demand analysis, the final stock estimate is 36,000 briquettes, which may be distributed monthly to low-income households or be sent to poulterers or bakeries as an alternative source for embers in their ovens.

**115**

for sale.

**2.2 Method**

first semester.

**Figure 5.**

firewood.

with the mixing process of binder and husk.

*Sustainable Energy Model for the Production of Biomass Briquettes Based on Rice Husks…*

However, if at the end of the year a briquette production program is not desired, a second production program can be designed, without the need to change the market focus completely. For example, 20% of the market should initially be addressed

between January and July, with a monthly production of 60,000 rice husk briquettes. Subsequently this would increase by 40% from July to December, to supply a total of 112 families with 84,000 briquettes, using the briquette machine's maximum production capacity. Including the final inventories from January to June, this would deplete resources to zero in December. It bears noting that the second production scenario must consider approval and sales success during the

*Utilization of rice husks in agricultural areas of the San Martín region.*

Note that the proposed briquette machine is of Italian origin—model E60, ECO by Prodeco—which has been used in similar briquette production projects. Its processing capacity is 60 kg of cassava starch and rice husk mix, for a total production of 300 briquettes per hour. Thus, the briquette machine processes a maximum of 2400 briquettes per day. In addition, these machines work 8 hours a day, transforming 1 kg into five briquettes for a market which consumes an average of 5 kg per family. Therefore, a total 25 briquettes per family must be produced for daily consumption, considering the yield equivalence between husk briquettes and

The briquette production program must consider a processing plant design (see **Figure 6**), with the purpose of strategically distributing the machines and resources corresponding to briquette production. For example, mixing and grinding areas should be separated, because smoke from the grinder must not come into contact

The production process begins with the selection of raw material, which is comprised of two stages. First, sand, spikes, and residue of different sizes are eliminated using sieves, in the granulometric analysis. The "weighing" process follows, wherein the various resources used during the entire production process are weighed. Next, the "mixing" process, by means of the agglomeration method, combines the rice husk in different quantities. Finally, the mixture is compacted by the briquette machine and passed through the "drying" area, to then be packaged

One of the most relevant methods for briquetting is the granulometric method,

which is a process of compaction or briquetting by using a piston and a press to reduce mixture structures. However, a briquette machine may also be used,

*DOI: http://dx.doi.org/10.5772/intechopen.81817*

**Figure 4.** *Sustainable energy model design.*

*Sustainable Energy Model for the Production of Biomass Briquettes Based on Rice Husks… DOI: http://dx.doi.org/10.5772/intechopen.81817*

However, if at the end of the year a briquette production program is not desired, a second production program can be designed, without the need to change the market focus completely. For example, 20% of the market should initially be addressed between January and July, with a monthly production of 60,000 rice husk briquettes. Subsequently this would increase by 40% from July to December, to supply a total of 112 families with 84,000 briquettes, using the briquette machine's maximum production capacity. Including the final inventories from January to June, this would deplete resources to zero in December. It bears noting that the second production scenario must consider approval and sales success during the first semester.

Note that the proposed briquette machine is of Italian origin—model E60, ECO by Prodeco—which has been used in similar briquette production projects. Its processing capacity is 60 kg of cassava starch and rice husk mix, for a total production of 300 briquettes per hour. Thus, the briquette machine processes a maximum of 2400 briquettes per day. In addition, these machines work 8 hours a day, transforming 1 kg into five briquettes for a market which consumes an average of 5 kg per family. Therefore, a total 25 briquettes per family must be produced for daily consumption, considering the yield equivalence between husk briquettes and firewood.

The briquette production program must consider a processing plant design (see **Figure 6**), with the purpose of strategically distributing the machines and resources corresponding to briquette production. For example, mixing and grinding areas should be separated, because smoke from the grinder must not come into contact with the mixing process of binder and husk.

The production process begins with the selection of raw material, which is comprised of two stages. First, sand, spikes, and residue of different sizes are eliminated using sieves, in the granulometric analysis. The "weighing" process follows, wherein the various resources used during the entire production process are weighed. Next, the "mixing" process, by means of the agglomeration method, combines the rice husk in different quantities. Finally, the mixture is compacted by the briquette machine and passed through the "drying" area, to then be packaged for sale.

#### **2.2 Method**

One of the most relevant methods for briquetting is the granulometric method, which is a process of compaction or briquetting by using a piston and a press to reduce mixture structures. However, a briquette machine may also be used,

*Green Energy Advances*

preparation.

**2.1 Operationalization**

respiratory and lung disease incidence rates decreased, from the reduction of CO2 produced by burning rice husks and firewood in the domestic sector. **Figure 4**

by burning rice husk in paddy fields or around the city and by the minimization of greenhouse gases (GHGs) from substituting wood for briquettes in food

Finally, environmental impact was measured by the reduction of CO2 produced

As part of process operationalization, a rice husk supply analysis is necessary, which ensures the raw materials meet production demands. For example, San Martín is the region with the highest economic participation in terms of rice industries in Peru, representing 18.49% of annual production in the 2013 agricultural campaign, with a total of 563.99 tonnes of paddy rice. Of the total amount produced, 20% will be converted into husk, meaning large volumes of this agricultural waste product will be burnt, due to limited recycling. **Figure 5** shows the various current uses of rice husk [16], reflecting its potential demand for companies or mills within the regional market. In many agricultural areas of the San Martín region, policies have been established to raise awareness and encourage recycling in other activities, regulated by municipal ordinances prohibiting burning. In addition, from a survey of 100 families in the region, the study concluded that 70% of the population would be willing to substitute firewood for an ecological product, 50% would pay a price equal to that of

firewood, and 70% agree that briquettes should be delivered to their homes.

ies as an alternative source for embers in their ovens.

On the other hand, energy model sustainability revolves around the acceptance of demand variability in any successful scenario for briquette sales. For this reason, certain production programs were designed based on briquette machine production capacity. For example, if the market focus is 23% of the firewood-consuming population, mills or companies should produce 69,000 briquettes per month for a total of 92 families, using 13,248 kg of rice husk and 552 kg of cassava starch. Within a supply–demand analysis, the final stock estimate is 36,000 briquettes, which may be distributed monthly to low-income households or be sent to poulterers or baker-

shows the energy model proposed for rice husk briquette production.

**114**

**Figure 4.**

*Sustainable energy model design.*

**Figure 6.** *Design of briquette processing plant.*

**Figure 7.** *Granulometry of rice husk particle composition.*

optimizing man-hours and increasing production rates. Development methods were performed in the laboratory at the Peruvian University of Applied Sciences (UPC).

The granulometric method is important for proper mixture compaction, since there is a range indicating optimum mixture state; for example, the lower limit indicates a mixture with a larger proportion of finer rice husk, whereas the upper limit indicates a mixture with larger grains. However, if the mixture falls outside the established range, the fine grain mixture will hinder oxygen flow and combustion, whereas if it exceeds the upper limit, the excess oxygen will produce more pollutant gases [17]. **Figure 7** shows the ratio of rice husk particle size necessary for adequate composition. Generally, particle size ranges from 0.10 to 3.00 mm. Composition depends directly on use, for the mixture can be composed of small or large particles, but must fall within this range [13].

The granulometric distribution of the best briquette prototype elaborated in the UPC laboratory is shown in **Figure 8**. This prototype had the greatest energy efficiency, both in terms of correct combustion and heating capacity. This briquette

**117**

*Sustainable Energy Model for the Production of Biomass Briquettes Based on Rice Husks…*

is composed of 0.850 mm particles, as well as smaller particles, making it perfect for briquette compaction using an experimental artisanal method. However, as mentioned above, briquette composition should include particles of different sizes, especially for industrial production, because the briquette machine can compact

Another method within the energy model that will provide sustainability from a technical perspective is agglomeration, which will generate value to briquette production. Agglomeration is the initial mixing stage of cassava starch and water. One liter of water and 200 g of cassava starch were used for this experiment, producing approximately 15 briquettes. The agglomeration process for this type of briquette production was the following, considering the percentage of each input in each stage:

1.Twenty-five percent of cold water is mixed with 200 g of cassava starch and

The agglomeration process can be seen in the left section of **Figure 9**, where the entire sequence of general rice husk briquette production processes is also shown, beginning with the "selection" of raw material, comprised of two stages, wherein sand, spikes, and residue of different sizes are eliminated by filtering. The "weighing" sub-process follows, in which the various resources used throughout the production process are weighed. Next, the "mixing" sub-process is performed, by agglomeration of water and cassava starch, which is later combined with rice husk in different quantities. The mixture is then compacted, either by a briquette machine for industrial purposes, or a hydraulic press for experimental artisanal purposes. Finally, the briquettes pass through the "drying" area and are packaged for sale. It is important to note that both methods—granulometry and agglomeration produce optimum values regarding combustion efficiency and heating capacity, thus both variables will be measured through the "boiling water test" (BWT), which measures the amount of energy transferred from the biofuel to a pot or container with a certain volume of water [19]. Below are some basic characteristics of the BWT:

• Sufficient quantities of water and fuel for the experiment. The fuel must be

larger rice husk grains correctly, with an average size of 2.36 mm [18].

2.Seventy-five percent of the total water is boiled to 100°C.

4.The adhesive mixture is then added to the rice husk container.

3.While boiling, the mixture is stirred until adhesive.

*DOI: http://dx.doi.org/10.5772/intechopen.81817*

*Granulometric distribution of rice husk particles.*

stirred for 2 minutes.

**Figure 8.**

uniform and completely dry.

*Sustainable Energy Model for the Production of Biomass Briquettes Based on Rice Husks… DOI: http://dx.doi.org/10.5772/intechopen.81817*

**Figure 8.**

*Green Energy Advances*

**116**

ticles, but must fall within this range [13].

*Granulometry of rice husk particle composition.*

(UPC).

**Figure 7.**

**Figure 6.**

*Design of briquette processing plant.*

optimizing man-hours and increasing production rates. Development methods were performed in the laboratory at the Peruvian University of Applied Sciences

The granulometric method is important for proper mixture compaction, since there is a range indicating optimum mixture state; for example, the lower limit indicates a mixture with a larger proportion of finer rice husk, whereas the upper limit indicates a mixture with larger grains. However, if the mixture falls outside the established range, the fine grain mixture will hinder oxygen flow and combustion, whereas if it exceeds the upper limit, the excess oxygen will produce more pollutant gases [17]. **Figure 7** shows the ratio of rice husk particle size necessary for adequate composition. Generally, particle size ranges from 0.10 to 3.00 mm. Composition depends directly on use, for the mixture can be composed of small or large par-

The granulometric distribution of the best briquette prototype elaborated in the UPC laboratory is shown in **Figure 8**. This prototype had the greatest energy efficiency, both in terms of correct combustion and heating capacity. This briquette *Granulometric distribution of rice husk particles.*

is composed of 0.850 mm particles, as well as smaller particles, making it perfect for briquette compaction using an experimental artisanal method. However, as mentioned above, briquette composition should include particles of different sizes, especially for industrial production, because the briquette machine can compact larger rice husk grains correctly, with an average size of 2.36 mm [18].

Another method within the energy model that will provide sustainability from a technical perspective is agglomeration, which will generate value to briquette production. Agglomeration is the initial mixing stage of cassava starch and water. One liter of water and 200 g of cassava starch were used for this experiment, producing approximately 15 briquettes. The agglomeration process for this type of briquette production was the following, considering the percentage of each input in each stage:

The agglomeration process can be seen in the left section of **Figure 9**, where the entire sequence of general rice husk briquette production processes is also shown, beginning with the "selection" of raw material, comprised of two stages, wherein sand, spikes, and residue of different sizes are eliminated by filtering. The "weighing" sub-process follows, in which the various resources used throughout the production process are weighed. Next, the "mixing" sub-process is performed, by agglomeration of water and cassava starch, which is later combined with rice husk in different quantities. The mixture is then compacted, either by a briquette machine for industrial purposes, or a hydraulic press for experimental artisanal purposes. Finally, the briquettes pass through the "drying" area and are packaged for sale.

It is important to note that both methods—granulometry and agglomeration produce optimum values regarding combustion efficiency and heating capacity, thus both variables will be measured through the "boiling water test" (BWT), which measures the amount of energy transferred from the biofuel to a pot or container with a certain volume of water [19]. Below are some basic characteristics of the BWT:

• Sufficient quantities of water and fuel for the experiment. The fuel must be uniform and completely dry.

Another BWT characteristic was biofuel moisture content calculation. This observation is related to that mentioned by Michael Lubwama and Vianney Yiga, in the paper "Characteristics of Briquettes Developed from Rice and Coffee Husks for Domestic Cooking Applications in Uganda" in which they state that the moisture content of any type of biomass must oscillate between 10 and 15%, with a compression force of 230 MPa. In addition, humidity values should oscillate between 9 and 10%, to obtain efficient combustion with fewer gas emissions. However, biomass compression is not the only moisture reduction process; a drying process must also be carried out, in which an electric heater is used to reduce humidity before the mixing process. Calculations referring to different means of calculating moisture content will be shown in the following formulae [20]:

$$\text{LOL} \ge \frac{\text{LOL} \left( \text{sexM [n:]} - \text{last} \left( \text{newM [n:]} \right) }{ \text{test} \left( \text{newM [n:]} \right)} = \text{(\text{?} \text{val} \mid \text{"R"} \text{"R"})}$$

$$\text{(MOL\\_VALUE\\_\% \text{ (drug\\_IF\\_)} = \text{(Juel Mean\\_level\\_models)} = \text{(Juel)} \times \text{(Juel)} \times \text{(Juel)})}$$

$$\text{MOISITORE } \% \text{ (wet)} = \frac{\text{MOISITORE } (\text{dry})}{\text{MOISITORE } (\text{dry}) + 1} \tag{3}$$

Eqs. 1 and 2 are important in analyzing briquette and firewood moisture content in different states, but the equation that was used, which is more frequent in this type of experimental method, corresponds to a dry base humidity calculation, due to better energy efficiency during combustion. Eq. (3) shows the different moisture content calculations.

As mentioned previously, rice husk moisture content is determined using an electric stove, after having passed the grinding process. Subsequently it is weighed and compared with the value obtained in drying. In Eq. 4 it observes the relationship between rice husks mass in different states of humidity:

$$\text{UNDIINI} \left( \text{"{}^{\text{\tiny\text{\tiny\text{\tiny\text{\tiny\text{\tiny\text{\tiny\text{\tiny\text{\tiny\text{\tiny\text{\tiny\text{\tiny\text{\tiny\text{\tiny\text{\text}}}}}}}}}} \right)} \right) \left( \text{\text{\tiny\text{\text{\tiny\text{\text{\tiny\text{\text{\tiny\text{\text{\tiny\text{\text{\tiny\text{\text}}}}}}}}}} \right) \right) \left( \text{\text{\text{\textquotedblleft}}} \right) \text{\textquotedblright} \left( \text{\textquotedblleft} \right) \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblleft} \right) \left( \text{\textquotedblright} \right) \left$$

As mentioned above, humidity calculations are important for optimal briquette combustion, based on combustion efficiency and heating capacity. In the study "Briquette Production for Use as a Power Source for Combustion, Using Charcoal Thin Waste and Sanitary Sewage Sludge," the authors describe the relationship between heat lost from the fuel and the heat of the water; thus Eqs. 5 and 6 show the calculations for both variables, including some theoretical values [21].

A 150 convective factor ("H" air-water) was considered for heat loss calculations, denominated "Q lost," since it is the most commonly used value with respect to thermal experiments [22]. Regarding water heat, denominated "Q water," the theoretical value for the specific heat of the water, was considered to be 4.18 J/g°C under normal conditions [23]; this value is represented by the "Cp." In addition, the container in which the test was performed had a diameter of 0.12 m and a height of 0.1 m, so the volume container is denominated "A." The equations necessary to estimate briquette heating values are shown below:

Q lost (J) = A × H × (final temperature − initial temperature) (5)

**119**

**Table 1.**

**Figure 9.**

Container volume (m3

*Rice husk briquette production process.*

H air–water (W/m2

*Experiment characteristics.*

in Eq. 9.

*Sustainable Energy Model for the Production of Biomass Briquettes Based on Rice Husks…*

under normal conditions and boiling point as final temperatures.

**Characteristic Value** Final temperature (°C) 100 Initial temperature (°C) 22 Cp water (J/g.°C) 4.18

) 0.012

.K) (20–300)

of the briquette. Eq. 7 calculates heating capacity (HC):

Qwater (J) = Cpwater×(final temperature−initial temperature) ×water mass (6)

**Table 1** presents values used in the experiment, considering initial temperatures

The difference between these equations allows us to calculate the approximate amount of heat emitted during combustion, which is divided by the charred mass

HC (kcal/kg) = (Q water − Q lost)/burned mass (7)

The equation developed by Estela Assureira [24] was used to calculate heating capacity, in which the resultant briquette mass is related to the mass of the inputs used for its production and the ash content representing each component. In Eqs. 8 and 9, the mass of the inputs added to the composition of the briquette is called "M bc." Note that in the experiment, the addition of another binder is necessary. The proportion of this input and its percentage of ash must be included

Finally, it bears mentioning that from the equations shown above, it was possible to calculate estimated heating capacity, humidity, and efficiency values, without the need for heating pumps or other laboratory instruments. However, if the focus

*DOI: http://dx.doi.org/10.5772/intechopen.81817*

*Sustainable Energy Model for the Production of Biomass Briquettes Based on Rice Husks… DOI: http://dx.doi.org/10.5772/intechopen.81817*

Qwater (J) = Cpwater×(final temperature−initial temperature) ×water mass (6)

**Table 1** presents values used in the experiment, considering initial temperatures under normal conditions and boiling point as final temperatures.

The difference between these equations allows us to calculate the approximate amount of heat emitted during combustion, which is divided by the charred mass of the briquette. Eq. 7 calculates heating capacity (HC):

$$\text{HC (kcal/kg)} = \text{(Q water - Q lost)/burned mass} \tag{7}$$

The equation developed by Estela Assureira [24] was used to calculate heating capacity, in which the resultant briquette mass is related to the mass of the inputs used for its production and the ash content representing each component. In Eqs. 8 and 9, the mass of the inputs added to the composition of the briquette is called "M bc." Note that in the experiment, the addition of another binder is necessary. The proportion of this input and its percentage of ash must be included in Eq. 9.

Finally, it bears mentioning that from the equations shown above, it was possible to calculate estimated heating capacity, humidity, and efficiency values, without the need for heating pumps or other laboratory instruments. However, if the focus

**Figure 9.**

*Green Energy Advances*

experiment.

content calculations.

• The volume of cold water must be at least 10% of the total water used for the

• Temperature is measured at boiling point, because at that moment, tempera-

Another BWT characteristic was biofuel moisture content calculation. This observation is related to that mentioned by Michael Lubwama and Vianney Yiga, in the paper "Characteristics of Briquettes Developed from Rice and Coffee Husks for Domestic Cooking Applications in Uganda" in which they state that the moisture content of any type of biomass must oscillate between 10 and 15%, with a compression force of 230 MPa. In addition, humidity values should oscillate between 9 and 10%, to obtain efficient combustion with fewer gas emissions. However, biomass compression is not the only moisture reduction process; a drying process must also be carried out, in which an electric heater is used to reduce humidity before the mixing process. Calculations referring to different means of calculating moisture

Eqs. 1 and 2 are important in analyzing briquette and firewood moisture content in different states, but the equation that was used, which is more frequent in this type of experimental method, corresponds to a dry base humidity calculation, due to better energy efficiency during combustion. Eq. (3) shows the different moisture

As mentioned previously, rice husk moisture content is determined using an electric stove, after having passed the grinding process. Subsequently it is weighed and compared with the value obtained in drying. In Eq. 4 it observes the relation-

As mentioned above, humidity calculations are important for optimal briquette combustion, based on combustion efficiency and heating capacity. In the study "Briquette Production for Use as a Power Source for Combustion, Using Charcoal Thin Waste and Sanitary Sewage Sludge," the authors describe the relationship between heat lost from the fuel and the heat of the water; thus Eqs. 5 and 6 show the calculations for both variables, including some theoretical values [21].

A 150 convective factor ("H" air-water) was considered for heat loss calculations, denominated "Q lost," since it is the most commonly used value with respect to thermal experiments [22]. Regarding water heat, denominated "Q water," the theoretical value for the specific heat of the water, was considered to be 4.18 J/g°C under normal conditions [23]; this value is represented by the "Cp." In addition, the container in which the test was performed had a diameter of 0.12 m and a height of 0.1 m, so the volume container is denominated "A." The equations necessary to

Q lost (J) = A × H × (final temperature − initial temperature) (5)

ship between rice husks mass in different states of humidity:

estimate briquette heating values are shown below:

(1)

(2)

(3)

(4)

ture can no longer vary nor the amount of transferrable energy.

content will be shown in the following formulae [20]:

**118**

*Rice husk briquette production process.*

#### **Table 1.** *Experiment characteristics.*

of the briquette production proposal was industrial and with a business vision, it would be necessary to use a briquette machine and sophisticated measuring instruments.

```
 combustion efficiency (%) = (initial mass − final mass)/mass bc (8)
```

```
 mass bc (kg) = [mass husk × (1 − %ash)] + [mass binder × (1 − %ash)](9)
```


**Acknowledgements**

To investigate further the performance of the quantum wells solar cells and control solar cells, the conversion efficiency and dark currents have been combined under the assumption of additives and a low aerosol optical depth spectrum, as shown in Figure 22. The red dots show an improved tandem solar cells structure where the top control solar cell with high disorder is grown on the quantum well bottom solar cell. Such solar cells structure should achieve a

In this chapter, the structure characteristics and optoelectronic properties of InGaN/GaN multiple quantum wells solar cells with In content about 0.3 and 0.4 are analyzed and studied, the phase separation of GaN and InN are not observed in the InGaN alloy materials with all kinds of In content when the InGaN alloys materials are packaged by InGaN/GaN multiple quantum wells heterojunction. The open circuit voltage of InGaN/GaN multiple quantum wells solar cells with In content about 0.3 and 0.4 are measured by 2 V and 1.8 V, respectively, when InGaN alloys materials are irradiated by monochromatic light under the same white light source. The InGaN/GaN multiple quantum wells are used as solar cells excitation region, the fill factor of this solar cell is about 0.6. The external quantum efficiency of this solar cell is 40% at the wavelength 420 nm, but external quantum efficiency drops to only 10% at the

The performance of InP/InGaAsP quantum wells solar cells can be greatly improved by integration of dielectric or metal nanoparticles into the surface of the tandem solar cells devices structure in order to couple incident light into the lateral propagation paths which can confine the slabby waveguide formed by the multiple quantum wells intrinsic layer. This approach can also improve the inherent conflict in achieving both efficient photon absorption which mandated a thick multiple quantum wells layer and efficient collection of the photo-generate carriers which required a thin multiple quantum wells layer, and could further realize the high optoelectronic conversion efficiency predicted for InP/InGaAsP quantum wells tandem solar

It has been known that quantum wells can tailor bandedges absorption, which also provides the flexibility to currently match InGaP/GaAs tandem solar cells under any defined spectrum. The device conversion efficiency has been achieved to 30.6% under the concentrator spectrum. This is a new record for any nanostructure solar cells devices. Strain balanced quantum wells solar cells with optimized conventional top solar cells should achieve the conversion efficiency of 34%. A new high efficiency consisting of quantum wells tandem solar cells have been proposed in both the GaAs and InGaP solar cells. This solar cells devices structure has the advantage to achieve higher efficiency comparable to the current lattice mismatched multi-

conversion efficiency of over 34%.

354 Solar Cells - New Approaches and Reviews

**5. Conclusions**

wavelength of 450 nm.

junction tandem solar cells.

cells.

In this chapter, the research was sponsored by the National Nature Science Foundation of China (Project No. 61178030) and Center for Collaborative Innovation of Functional Polymer Materials in Foshan University.