Cofiring is a direct combustion method by combining coal and biomass to produce energy. Applying this method reduces emissions during the combustion process. This will also reduce the impact of global warming causing by greenhouse gases. Moreover, the combination of coal and biomass will increase 33-37% efficiency of gas turbines. This was disclosed by the National Energy Laboratory.
The advantages of using this method are reducing carbon dioxide and sulfur oxide. Sulphur oxide can cause acid rain, haze, and ozone pollution. Meanwhile, carbon dioxide will cause global warming. Contribution of biomass in this method supports carbon neutral effects meaning that it will re-absorb of carbon dioxide by plants for photosynthesis reaction.
Gasification is a method that converts carbonaceous feedstock into gas fuels using high temperatures. Gasification process produces synthetic gases such as carbon dioxide, carbon monoxide, methane, and hydrogen. Gasification products flow to several stages before it is used for energy production. Heat exchanger and scrubber are used to cool and clean.
Gasification products can be converted into energy by direct combustion such as in gas turbines. Gas is burned in this equipment and produces turbine rotation. Generator is connected to convert into electrical energy. In the system of fuel cells, synthetic gas such as hydrogen and methane are used as fuel cell feedstock. Chemical processes take place in the fuel cell stack and produce electricity. Another conversion process of synthetic gas is Fischer-Tropsch, which is extracted from gas into liquid fuel.
Anaerobic digestion is a decomposition of organic matter to produce gas that occurs in the absence of oxygen. Over 50% gas produced is methane. Initially, organic material such as biomass, cow dung accumulates in digester (reactor). Bacteria will extract it into gas through two stages.
First stage, organic material is degraded into weak acid using acid forming bacteria. These bacteria decompose the garbage at the level of hydrolysis and acidification. Hydrolysis is a decomposition of complex compounds or long chain compound such as fat, protein, carbohydrate into simple-compound. Meanwhile, acidification is created simple-compounds from acid. It changes material into amino-acid. Second stage is anaerobic digestion, which forms methane from methane forming bacteria. This methane gas can be converted into electrical energy by gas turbines or fuel cells.
Synthetic gas such as hydrogen and methane are used as feedstock for fuel cells. Chemical processes take place in the fuel cell stack and produce electricity. Another conversion process of synthetic gas is Fischer-Tropsch process, which is extracted the gas into liquid fuel.