Thermo-chemical conversion

The most widely spread use of solid biomass is the provision of heat released during combustion. During combustion, solid biofuels are oxidized primarily to carbon dioxide and water by releasing heat. Equation 7.1 shows the approximate process for wood, which can be described as C H ,Op. 

Fixed carbon (char) and ash are the by-products that are not vaporized. Gasification. It is obvious that solid earbon neeessarily remains as a product of the pyrolytic decomposition. In order to eonvert this solid carbon into a gas, an oxygen-containing agent such as air or pure oxygen is required. At a temperature range between 700 and 1,500 °C the solid carbon as well as gaseous products (CO, H2, CH4) are oxidized as follows  

Additionally, balance reactions take place. The most important are the reduction of CO2 to CO (Boudouard reaction) and of H2O to H2 (heterogeneous water gas reaction). Simultaneously, carbon can be transformed to CH4. 

If equation (7.1) occurs in one step, we speak of full oxidation. Under these conditions the excess air ratio is 1.0 or above (the exeess air ratio is defined as the ratio between the amoimt of oxidizing agent fed to the eonversion process and the amount of oxidizing agent needed to fully oxidize all reaetion products per definition the excess ratio is 1.0 if the conversion process is realized exactly as shown in equation (7.1)). 

Oxidation can also be realized in two steps in which the excess air ratio of the first step is below 1.0. Under these conditions the reaction products can be further oxidized in a second step releasing the rest of the available energy. Carbon monoxide and/or hydrocarbons are typically produced at the first step and transported to another device for full oxidation. Within such processes the procedure described above is paused for example after the gasification step e.g. within a gasifier) is performed, the oxidizing step is realized at another time and at another place e.g. within the engine). 

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He, R, Gu, G., Shao, E., Zhang, Y. 2000. Research on low temperature thermo-chemical conversion to oil process from sewage sludge. Water Sci Tech 42 301-308. 

Emission reduction for all types of thermo-chemical conversion of biomass. Ash recycling and cleaning. 

Size press starch may be non-ionic, from in-mill enzymatic conversion or thermo-chemical conversion of native starch. It may be anionie if an oxidised starch is used. (Note this refers to chemically modified oxidised starch. Many American texts wrongly refer to any viscosity-reduced starch - including enzyme-converted and thermo-chetnically converted stareh - as oxidised stareh. Such processes do not form any carboxyl or carbonyl groups on the starch.) Furthermore, cationic and amphoteric starches are frequently tpplied on multi-purpose office paper for improved ink-jet printability. 

Thermo-chemical conversion summarizes all conversion processes of biomass into a solid, liquid or gaseous fuel based on heat. Therefore... 

Thermo-chemical conversion mixed cultivation of different lignocellulosic plants for the provision of solid biofuels ... 

Figure 7.4 Example of thermo-chemical conversion for wood." ...

Oxidation. Within this last step of the thermo-chemical conversion, the gaseous products produced during the steps already performed are fully oxidized to carbon dioxide and water releasing energy i.e. they are exothermic). 

Biomass Sources Biomass Production and Supply Thermo-Chemical Conversion Physico-Chemical Conversion Blo-Chemical Conversion Outlook... 

The most widely use of biomass is the provision of heat released during combustion of solid biofuels. But combustion is only one conversion process among others based on a heat-induced chemical conversion of the organic material. Therefore within the following explanations we first discuss the basics of such thermo-chemical conversion processes. Then we focus on the technical implementation of these principles in conversion plants. 

FIGURE 4 Example of thermo-chemical conversion of wood. [From Kaltschmitt, M., and Hartmann, H. (2001). "Energy from Biomass, Springer, Berlin, Heidleberg, Germany. (In German.)]... 

TABLE III Excess Air Ratio and Reaction Product Composition for Thermo-Chemical Conversion Processes... 

Szuha J, WasUewski P, Mikolajska U, Bal S, Swierczek R. Method and apparatus for thermo-chemical conversion of coal. Polish Patent No. 83,271, 1976. 

Zhang, L., Xu, C., Champagne, P. Overview of recent advances in thermo-chemical conversion of biomass. Energy Conversion and Management 51 (2010) 969-982. 

Panwar, N.L., Kothari, R., Tyagi, V.V., 2012. Thermo chemical conversion of biomass — eco friendly energy routes. Renewable and Sustainable Energy Reviews 16 (4), 1801—1816. 

Amen-Chen C, Pakdel H, Roy C. Production of monomeric phenols by thermo-chemical conversion ofbiomass a review. Bioresour Technol. 2001 79 277-299. 

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