Increasing Biogas Production With Biomass Briquettes

For example, activated carbon which has much more pores than ordinary charcoal, or one spoon of activated charcoal is estimated to have a surface area like the area of ​​a football field. With this surface area, activated carbon can adsorb much more molecules than ordinary charcoal. That is what makes activated carbon used by many industries, for more details, you can read it here. The activation process is the process of creating or opening the pores of charcoal so that it has a large surface area. Likewise with the biomass briquetting process, due to the strong pressure and high temperature of the briquetting process with a mechanical press, the micro pores of the biomass will open. The opening of the biomass pores will increase its absorption power. It turns out that according to research at Aarhus University Denmark, the use of biomass briquettes, especially straw briquettes, has been able to significantly increase biogas production. Every 1 tonne of straw briquettes added has increased the biogas production by an average of 400 cubic meters. With a biogas caloric value of around 4500 kcal / m3, each tonne of addition of straw briquettes will increase calories by 1,800,000 kcal in the form of biogas. Meanwhile, every 1 m3 of POME will produce about 25 m3 of biogas.

The research was conducted on a continous stirred tank reactor (CSTR) biogas type so that the effort to maximize the substrate mixture of biogas was carried out mechanically. CSTR for biogas production is still rare in Indonesia and the Southeast Asia region today, but is common in Europe. The addition of briquettes to the biogas reactor also means adding organic material as raw material for biogas production. But with this form of briquette which has the ability to absorb much more water or 10 times that of bulk straw without be briquetted, which causes microbes to penetrate far more through the micro pores of the straw briquettes, as a result the fermentation process is more perfect. Based on these experiments, the biogas production reached the optimum level at the addition of 10% straw briquettes to the reactor volume. The addition of straw briquettes of up to 10% apparently did not interfere with the performance of the stirrer motor and the straw briquettes because the micro pores absorbed water optimally and did not create floating material that covered the surface of the reactor. 

For biogas factories in Indonesia, especially Southeast Asia in general, especially those that use CSTR for biogas production, of course the above can be a reference and guide for trials to increase biogas production by adding biomass briquettes. In the above case, the straw used in Denmark uses straw from the wheat plant because it is abundantly available there, while in Indonesia and Southeast Asia, rice straw is widely available. The properties of wheat straw and rice straw are so similar that it is also predicted that they will produce almost the same volume of biogas. But if the biogas unit is for example in palm oil mills, biomass sources such as mesocarp fiber, empty bunches and palm leaves can be used as raw material for the briquettes. The biogas unit commonly used in palm oil mills in Indonesia and Southeast Asia using palm oil mill effluent as raw material is a covered lagoon which is not equipped with a mixer. For this type of reactor, one of the efforts to increase biogas production is by making the operating conditions thermophilic. The heat from the biogas power plant can be used to reach this temperature. Can biomass briquettes increase biogas production in covered lagoon reactors? The answer still needs further research.

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.

Urgency of the Biogas Unit in the Palm Oil Mills

In palm oil mills with a big vision, business development is important and always receives special attention. Palm oil mills which generally only produce CPO (crude palm oil) and only a few produce PKO (palm kernel oil). Biomass wastes generated such as empty fruit bunches (EFB), fiber and palm kernel shells (PKS) have great potential to be developed into businesses. In addition, the kernel (palm kernel) which has only been sold to other parties can actually be processed by ownself into a PKO. Even CPO itself can also be developed into various derivative products such as cooking oil, stearin, olein and various other oleochemical products. To process the above material, will always need energy and the availability of energy especially those which become a major obstacle to various business developments in the palm oil mill.

Biogas from POME or palm oil mill effluent is a potential energy source that can be created to support a number of business developments based on the palm oil mill. Liquid waste in the form of POME is generally not utilized and is still a problem for most palm oil mills today. By processing it into biogas, it can then be converted to heat and electricity so that it can be utilized for business development that mentioned above. Under certain conditions the biogas produced can even be upgraded to CBG (Compressed Biomethane Gas) with the use as a substitute for fuel in trucks used in the palm oil industry.

There are two types of biogas reactors being developed at this time, namely by maing then covering the pool with a special rubber material (covered lagoon) and a continous stirred tank reactor (CSTR). Although it requires a wider area, the type of covered lagoon is more widely used because in addition to being simpler it can also accommodate more biogas volume. A palm oil mill using centrifugal oil separator will produce a lot of sludge which increases the COD (Chemical Oxygen Demand) thereby increasing the amount of biogas produced. While palm oil mills use decanters, the sludge will be separated so that the COD is low and so is the biogas product produced.

Biogas Water Absorber

The use of biogas to convert to thermal energy (in external combustion engines such as furnaces and boilers) is simpler than the conversion to electrical energy with a gas engine (typical of internal combustion engine). When biogas is converted into heat, the gas purification process is not even carried out and directly burned in the gas burner, so existing boiler of the palm oil can be used. But when it converted into electricity with a gas engine , the biogas purification process becomes important, because the quality of the gas is very influential on the performance and durability of the gas engine and automatically the electricity product produced. Biogas with a lot of H2S content will be corrosive so as to damage the gas engine unit and biogas with high CO2 content will reduce the calorific value so that the gas engine performance will decrease.