Why Produce Electricity From Biogas Using Gas Engine Generators? Not With Gas Turbine Generators Or Steam Turbine Generators

  

The need for this type of power plant is always related to capacity, a number of technical factors and the investment costs required. Turbine with generator is a type of generator which is commonly used in industry, especially steam turbine and gas turbine. The grouping of turbine types above is based on the principle of operation and the fluid that moves them. At a palm oil mill, almost all of the electricity is generated from a steam turbine generator. In addition to electricity production, the steam generated from the boiler is also used to process fresh fruit bunches (FFB) to produce crude palm oil or CPO.

Processing of palm oil mill effluent (POME) into biogas and subsequently mostly used for power generation. Almost all of the electricity from biogas is used to meet the needs outside the palm oil mill and the surrounding community. With the potential for palm oil mills in Indonesia that are estimated at more than 1000 units supported by 15 million hectares of palm oil plantations, the potential for electricity generated will be more than 1.5 GW. Approximately 0.7 m3 of liquid waste is produced by the palm oil mill from each tonne of FFB processed. Biogas usually consists of 50-75% methane (CH4), 25-45% carbon dioxide (CO2), and a number of other gases. If wastewater management is not controlled, methane in biogas is released directly into the atmosphere. As a greenhouse gas (GHG) methane has a 21 times greater effect than CO2. The production of electricity from biogas from palm oil mill effluent (pome) is also an effort to reduce environmental hazards. The electricity production from the biogas all uses a gas engine generator and none of them uses a steam engine generator. This is because the production of electricity with steam turbines is not only more complex but also less efficient. The gas engine generator is a power plant that is most suitable for the conversion of biogas to electricity. Gas engines whose engines are similar to gasoline engines, with only the change of fuel into gas (biogas) or similar to vehicle engines such as public buses that run on gas fuel are also more familiar to most people. 

Gas turbine generators are generally used for large capacity power plants. Gas power plants in Indonesia generally use gas turbine generators. Gas turbines are equipment that uses high pressure combustion gases to turn a turbine that can be connected to a generator to generate electricity. Apart from generating power, gas turbines are also used in boats, racing cars and jet planes. The main parts of gas turbines include: compressor, combustion chamber, gas turbine and workload. Each part or segment has a number of critical components which are connected in one axis. During the operation of the gas turbine, some of the power generated by the turbine is used to drive the compressor. The large capacity and technical factors of gas turbine generators make the unit expensive and not used for the production of electricity from biogas. The electricity capacity of biogas from wastewater treatment like POME is not too large, that is, for a palm oil mill with a capacity of 30 tonnes / hour of FFB it will produce about 1 MW of electricity and its multiples. This is the reason why gas engine generators are used in biogas power plants, especially in the palm oil industry.

Rice Husk Pellets or Rice Husk Briquettes?

 

Rice husk truck, photo taken from here

Indonesia's rice production in 2008 is estimated to reach 59.9 million tons of milled dry unhulled rice with a composition of 25% husk, which means that the potential for husks reaches 15 million tons / year. Although the amount is abundant but generally the utilization is still not optimal, this is because the rice husks have low bulk density and low calorific value due to the high ash content. So that the rice husks can be utilized optimally, one solution is densification. With this compacted rice husks can be easier to use, economical in transportation and facilitate storage. A large pile of rice husks also has a strong tendency to burn. The dry husks easily fly like dust so that high concentrations in the room will be flammable and dangerous. Compaction of rice husks will make rice husks larger, denser and heavier so that they do not fly easily or in other words, reduce the risk of the fire.

The need for biomass fuel has increased recently. This encourages the use of agricultural and wood processing industrial wastes. These wastes were initially not utilized and tended to pollute the environment, but now they are being processed a lot for the production of biomass fuels. A positive effort, of course, because in addition to minimizing environmental problems caused by waste, it is also a profitable business activity. Production of biomass fuel can start from medium capacity to large capacity, from a capacity of several hundred tons or thousands of tons per month to hundreds of thousands of tons per month. Although the potential in Indonesia is large, generally the use of these wastes is not maximized so that commercial biomass fuel production is generally still low. 

 Briquettes and pellets are the products of the biomass densification technology. Basically, briquettes and pellets have their own characteristics, although physically they can be easily recognized by the size of the briquette that are bigger than the pellets. The briquette technology is also more diverse than pellets, so that is the case with the output in the form of the briquette product, for more details, please read here. For rice husks for use as industrial fuel, industrial production of briquette with a mechanical press is most suitable. This is because it is technically easier and economically cheaper. Although the rice husk can also be pelleted, it will cost more. This is because rice husks are very abrasive due to the large ash content with the main constituent component in the form of silica. The ring die and roller press on the pelletiser will wear out quickly due to the abrasive material. Production of rice husk briquettes with a screw extruder is also possible and possible, even a number of countries such as Pakistan, Nepal, Bangladesh, Vietnam and Thailand have also done so. But with these abrasive materials the production costs are also high. The briquettes produced by the screw extruder are also long so they usually need to be cut into pieces for use so that the use of the screw extruder also becomes less practical. With a mechanical press, the briquette size can be cut into small pieces easily, making it easier to use.