Cogeneration in Palm Oil Mills with Pyrolysis, Initial Steps in Biochar Production and Implementation

The analogy is like cofiring carried out in coal-fired power plants by mixing biomass fuels with a certain ratio as an effort to decarbonize the energy sector in power plants. While in palm oil mills, cogeneration with pyrolysis is an innovative initial step to enter the carbon negative era with the application of biochar, the main product of pyrolysis. And because all palm oil mills use biomass fuel for their mill operations, they are already based on carbon neutral fuel, unlike coal-fired power plants which are based on carbon positive fuels because they come from fossils.

Unlike cofiring which mixes coal and biomass fuels with a certain ratio and then burns them together in a furnace such as pulverized combustion, cogeneration is done by producing energy separately but the energy output is for the same use or especially the same boiler. This is done because the types of fuels may be different, such as solid fuels with liquid fuels or the technology for producing the energy is different. With this cogeneration, it means that not all energy is produced from one energy source or energy from cogeneration is a secondary energy source to meet total energy needs, and in the case of cogeneration in this palm oil mill, energy from combustion is still the primary energy.

Then why not just do full pyrolysis? It is easier, gradually for palm oil mills to adopt pyrolysis technology and its characteristics. Because (slow) pyrolysis aims to maximize solid / biochar, the by-products in the form of excess energy (syngas and biooil) as a source of boiler fuel, the calorific value is not as much as combustion which is indeed intended to maximize heat. Only about 1/3 of the excess energy contributes (cogeneration) as boiler fuel. In other words, if full pyrolysis is carried out directly, the amount of biomass as raw material for pyrolysis becomes 3 times greater or the pyrolysis unit becomes very large so that all palm oil mill biomass waste is used, and the mill cannot sell its palm kernel shells.

What are the benefits obtained by palm oil mills if they carry out cogeneration with pyrolysis for biochar production? Among the biochar products, it can save fertilizer use in oil palm plantations, overcome the problem of empty oil palm bunches (EFB) so that palm oil mills can achieve zero waste, palm kernel shells (PKS) that have been used for boiler fuel can be sold to increase income, the productivity of fresh fruit bunches (FFB) of palm oil increases, the application of biochar in palm oil plantations is also a climate solution (carbon sequestration / carbon sink) so that it can get carbon credit compensation and with good waste management, even zero waste and the application of biochar in palm oil plantations, palm oil companies will get a good image in terms of the environment and sustainability.  

Biochar to Increase Biogas Production

Charcoal (biochar) is the raw material for the production of activated carbon. The production of activated charcoal itself goes through two main processes, namely carbonization (pyrolysis) and activation. The surface area of charcoal (biochar) is also smaller than that of activated carbon, but larger than the raw biomass. The carbonization process increases the surface area of the raw biomass. The ratio of surface area between raw biomass, charcoal and activated charcoal is approximately 25 m2 / gram, 200 m2 / gram, 2000 m2 / gram. The larger the surface area of the biomass material that is inserted into the biogas reactor, the greater the penetration of bacteria into the substrate so that the fermentation process that occurs is more perfect so that biogas production will increase. Biochar itself does not participate in fermentation because the main component is stable carbon, while hemicellulose, cellulose and lignin have been decomposed during the carbonization process.

Another example is the addition of biomass briquettes to the biogas reactor, briquetting processs with high pressure and heat also open pores or expand the surface of the biomass, so that biogas production also increases, for more details, read here. The addition of biomass briquettes to the biogas reactor will also increase the C / N ratio, even biochar and activated charcoal have high carbon (C) content.

Charcoal (biochar) has been widely used in the agricultural world to repair damaged soil / soil amendment and thus increase fertility. Good soil fertility will also increase agricultural production. The biochar becomes a home for soil microbes, so that organic materials or compost will break down more completely and be absorbed by plants more as plant nutrients. The charcoal (biochar) pores are the home for these microbes. The more pores, the more microbes will inhabit the biochar as their “house”. The same principle applies to the biogas unit. Another bonus of using biochar is that it absorbs CO2 from the atmosphere, thereby contributing to lowering the greenhouse gases that cause climate change and global warming.

Research in Germany shows that adding 5% biochar to a biogas reactor increases methane production by 5% - based on the dry matter of biochar to the substrate. But when the amount of biochar became 10%, it turned out that no more methane was added. This shows that the optimum condition for adding biochar is the amount of 5%. The microbes in the biochar increase the volume of microbes in the reactor so that the production of biogas or especially methane also increases up to 5%. Biochar itself is not decomposed in the fermentation process. 

Meanwhile, the addition of biomass briquettes per 1 tonne of briquettes will increase biogas production by 400 Nm3. This is because in the biomass briquettes, both cellulose, hemicellulose and lignin have not been decomposed, thus adding to the substrate in the biogas reactor. Whereas in biochar, both cellulose, hemicellulose and lignin have been decomposed during the thermal carbonization process, so there is practically no additional substrate, but only microbial addition occurs in the biochar pores.

The important thing about the addition of biochar is that the compost or digestate produced is of better quality with the addition of the biochar. Biochar will make the compost which is produced as a slow release organic fertilizer. This further encourages biochar production, especially for palm oil companies that care about environmental issues and even strive for zero waste conditions.

 Palm oil mills have the potential to apply biogas and biochar units. Solid wastes such as empty bunches and mesocarp fiber can be used for biochar production. Palm oil mills can even replace the furnace in the boiler with a gasifier or pyrolyser. This becomes more profitable because in addition to heat energy being used for production of steam which is used for power generation and sterilization of fresh fruit, biochar will also be produced. The biochar produced is then used to increase biogas production and improve the quality of the compost, as well as a fertilizer mixture in palm oil plantations. And even the potential use of biochar to save fertilizer on large palm oil plantations, for more details can be read here.     

Which is Better, Efficient Boiler or Pyrolysis System ?

Fiber and palm kernel shells (PKS) are palm oil mill solid wastes that are produced in CPO production in that mill. The amount of fiber and PKS waste is quite a lot, which is around 20% of each fresh fruit bunch (FFB) or almost the same as the CPO produced. A palm oil mill with a capacity of 60 tons / hour FFB can produce fiber as much as 8.1 tons per hour or 194.4 tons per day and PKS of 3.3 tons / hour per hour or 79.2 tons per day. And because both of them are waste, generally the utilization of the waste is not initially considered, including for use as fuel in boilers in palm oil mills for the production of electricity and steam. The use of fiber and PKS for boiler fuel generally uses 100% fiber and about 30% of the PKS. Under these conditions the remaining 70% of the PKS can be used for other things including being sold or even exported.

When the shell becomes a commercial commodity and demand is greater, palm oil mills replace their old inefficient boilers with new boilers that have a high level of efficiency. In this way, 100% of the PKS is no longer used to boiler fuel and only requires fiber as fuel. In this condition a paradigm shift in thinking begins to occur, that is when the solid waste is almost unnoticed and tends to be considered a problem, then it becomes an important part of earning additional income and it can even be estimated that if the shell is successfully sold then it is sufficient to cover the operational costs of the palm oil mill. Certainly something interesting if the production of CPO (crude palm oil) with 0% operational costs so that profit is increasingly attractive especially amid the recent decline in CPO prices.

Another thing that can be done is to use a pyrolysis unit, to run the boiler. With pyrolysis, not only fiber is used but also the empty fruit bunch (EFB). EFB are solid palm oil mill waste which to date have generally not been utilized. Besides producing energy, pyrolysis also produces products in the form of charcoal (biochar). Although charcoal (biochar) can also be used for energy sources, but in the business of palm oil companies the use of biochar for plantations can be more compatible. The use of biochar in palm oil plantations is mainly to  fertilizer saving, which is one of the major cost components (around 30%) in the CPO production business. With an area of ​​20 thousand hectares of oil palm plantations, fertilizer costs are estimated to reach Rp. 71.50 billion (around US$ 5 million) per year or Rp. 35.75 billion (around US$ 2.5 million) per year for every 10,000 hectares, for more details, please read here. Palm oil mills with big vision certainly try to maximize their potential with the aim of maximizing profits from upstream to downstream production activities. With Biochar can also target the increase in productivity of FFB, for more details, please read here.

The application of biochar will be easier to do in Indonesia than in Malaysia, this is because almost all palm oil mills in Indonesia also have palm oil plantations while in Malaysia the mills generally do not have their own palm oil plantations. The palm oil industry also has an important role for the two countries because Indonesia and Malaysia are the largest CPO producers and owners of biggest palm oil plantations in the world today. The palm oil industry contributes around 7% of Malaysian GDP and 3% of Indonesian GDP, so its role cannot be ignored. Both with pyrolysis and high efficient boilers, biomass waste can be used as an energy source and 100% of the PKS can be commercialized, but with pyrolysis is better because waste of EFB can also be processed, there are biochar product (while only ash if only with regular combustion) for Fertilizers saving in the palm oil plantations and the exhaust gases from the palm oil mill boilers are also clean because they burn gas (syngas) produced from the pyrolysis process.