Charcoal Production for Activated Carbon Raw Material

Charcoal characteristics are influenced by the raw materials used and the conditions of the production process. The use of charcoal for certain applications or industries also requires certain specifications or characteristics. For example, charcoal used for fuel can have different specification requirements from charcoal specifications for agriculture (biochar), or charcoal used as raw material for activated carbon. A number of parameters that are acceptable in certain applications may not be acceptable in other applications.

Charcoal products used as raw materials for activated carbon production are also the same. Parameters in the form of high fixed carbon (~80%), high hardness, low ash content (~3%) and low volatile matter (<10%) are prerequisites for the specifications or quality of charcoal as a raw material for activated carbon. As a comparison, charcoal for agriculture (soil amendment) or commonly called biochar has a wide range of quality or specifications, namely lower fixed carbon (FC), higher ash content and higher volatile matter, especially in agro type biochar according to WBC (World Biochar Certificate), while premium type biochar according to WBC has a higher or highest quality and can be used for various purposes. While the material type biochar according to WBC has the lowest quality with use mainly in certain industries such as cement, asphalt, plastic, electronics, and composite materials or cannot be used for agriculture, soil applications and consumer products.

 Raw materials for charcoal production for activated carbon production because it requires stricter parameters, especially high fixed carbon, low ash content and high hardness so that raw materials suitable for this purpose are more limited or not all biomass can be used for charcoal production for activated carbon raw materials. This is what makes coconut shells the best and most popular raw material for charcoal production as activated carbon raw materials today. And palm kernel shell raw materials (especially from dura variety) are expected to be the next candidate. The availability of abundant palm kernel shells (PKS) is a special attraction. But indeed with this palm kernel shell (PKS) charcoal raw material, there is still the smell of palm oil, so it is a challenge for activated carbon producers.

Become the Trendsetter of the World's Vegetable Oil Producers

In the vegetable oil market, there are 4 types of vegetable oils that are widely consumed around the world, namely soybean oil, sunflower oil, palm oil and rapeseed oil. Based on USDA data (2018) the total area of the 4 vegetable oil-producing plants in 2017 was around 208 million hectares. Soybean plantations have the largest proportion of area, namely 126 million hectares (61 percent), while the area of palm oil plantations is only 21 million hectares (10 percent). However, with an area of 126 million hectares, soybeans are only able to produce 56 million tons of oil or only 32 percent of the production of the world's 4 main vegetable oils. In contrast, palm oil with an area of 21 million hectares is capable of producing 73 million tons or 42 percent of the production of the world's 4 main vegetable oils.

The high level of palm oil production is obtained from the productivity of palm oil plantations which is much higher than the productivity of other vegetable oil producing plants. According to Oil World (2018), the average productivity of oil palm is 4.27 tons/hectare, while the productivity of other vegetable oil-producing plants is only 0.4 – 0.6 tons/ha. The productivity of palm oil is much higher, around 8-10 times compared to other types, making palm oil have a comparative advantage over other vegetable oils. This comparative advantage can be interpreted as saving deforestation in various regions of the world if palm oil is consumed by the global community or to produce the same amount of oil, the land needed for oil palm is 8-10 times smaller than other crops.

With an average annual productivity of 4.27 tons/hectare of palm oil or 17 tons of FFB/year, this is actually still quite low and productivity can be increased up to around 30 tons of FFB/hectare or 7.5 tons/hectare of oil. Increasing the productivity of palm oil is primarily by increasing soil fertility so that fertilization efficiency increases. Slow release fertilizer (SRF) is an efficient fertilizer that is economical and environmentally friendly. In addition, the use of biochar, apart from being a slow release agent in the fertilizer, will also improve soil quality or fertility by increasing soil porosity, providing organic carbon, raising soil pH, retaining water and nutrients so that they are more available to plants and as a medium for soil microbial colonies. By increasing the productivity of palm oil, followed by saving fertilizer due to increased efficiency, minimizing environmental pollution so that production costs can be reduced, it means that it is equivalent to increasing land efficiency by 76%. This means that the productivity of palm oil per year is 30 tons of FFB/hectare, or 7.5 tons/hectare oil and when compared to other vegetable oils it is 15 times more land-efficient or per tonne of palm oil requires 0.13 hectares while other vegetable oils require 2 hectares of land.

The climate solution in the form of carbon sequestration / carbon sink can also be done simultaneously with the biochar application. Every 1 ton of biochar will store or reduce CO2 (carbon dioxide) in the atmosphere by approximately 3 tons. Carbon credit from the application of biochar is a significant additional income apart from fertilizer efficiency and increased crop productivity, including palm oil yields. Moreover, the value of carbon credit tends to increase and the carbon (CO2) removal mechanism with biochar will become a trend in the future. The amount of income from carbon credit is proportional to the number of biochar applications in the oil palm plantation which will also be proportional to the area of the palm oil plantation.

The area of palm oil plantations ranging from thousands to tens of thousands of hectares owned by a company is common in Indonesia. This indicates the business potential that can be done. With the current area of palm oil plantations in Indonesia reaching around 15 million hectares, as much as 40% (6 million hectares) are smallholder plantations so that the company's plantation area is 60% (9 million hectares) which is divided into owned by Large Private Plantations (PBS), which is 8 .42 million ha (55.8%) and State Large Plantations (PBN) covering an area of 579.6 thousand ha (3.84%), for more details read here. Palm oil trees themselves can only produce well in the tropics because the temperature factor affects production through the rate of biochemical and generative reactions in the plant's body. To some extent, higher temperatures lead to increased fruit production. The temperature of 20°C is referred to as the minimum limit for generative growth and an annual average temperature of 22-23°C is required for continued fruit production. That is why not all locations on earth can be cultivated for palm oil even though the productivity of the oil is the largest compared to other plants, so that it becomes a comparative advantage in itself.

Meanwhile, from biochar production technology, it is also possible to reduce the use of solid fuels such as palm kernel shells (pks) which are commonly used in boilers at palm oil mills. Palm kernel shell which is a biomass fuel and used as boiler fuel in palm oil mills besides fiber (mesocarp fiber), can then be sold directly for both the domestic market (local) and the international market (export). The palm kernel shells can also be further processed into charcoal or activated carbon. The use of energy from biochar production technology (pyrolysis) will also increase the efficiency of boilers at palm oil mills, in addition to additional income from selling palm kernel shells or further processing. Becoming a trendsetter in the world's vegetable oil producers is very possible based on the reasons mentioned above. With Indonesia's current condition in particular, or other palm oil producing countries, with a little improvement, it is very possible to do this. Moreover, the palm oil industry produces a lot of biomass waste which is very potential as raw material for making biochar.

Drying Palm Kernel Shells (PKS) by Utilizing Waste Heat from Palm Oil Mills and POME Biogas Units

The need for palm kernel shells or PKS is getting bigger because its use is increasing and diversifying. PKS can be used as boiler fuel in industry and in power plants. In addition, it can also be used as a raw material for activated carbon whose needs are also increasing, for more details, read here. The global trend to decarbonize or replace fossil fuels with renewable energy including biomass fuels, especially PKS is the main driving force for the increasing demand for PKS. Even oil-rich countries with economies driven from oil (petrodollars) are also gradually implementing the decarbonization program.

To be used as fuel or further processed into a number of derivative products such as torrified PKS, PKSC or palm kernel shell charcoal and activated carbon, the PKS must be dried first. The process of drying or reducing the moisture content to a certain level requires energy. PKS, which are palm oil mill waste, are generally just piled up in the backyard of the palm oil mill, so they are usually dirty and wet, resulting in a low selling price. If the palm oil mill can dry and clean its PKS, the selling price will also increase, so that there is added value as well as additional income for the palm oil mill. A number of energy sources from waste heat from palm oil mills can be used for the drying process.

Heat is an energy source that can be used for various purposes, either heat generated directly from the combustion process or from waste heat which is the residual heat from the combustion or other sources such as electricity and so on. In palm oil mill operations there is a certain amount of waste heat that can be extracted or harvested or recovered as a heat source for drying such as heat from combustion in the boiler, heat from steam turbine and heat from the FFB sterilization process. If the palm oil mill also processes its liquid waste for electricity production, the waste heat from burning biogas in the generator can also be used as a heat source for drying the PKS. A number of heat sources which are waste heat when integrated, the amount is large so that it can be sufficient for drying the PKS.

In addition to producing CPO (Crude Palm Oil) as the main product, palm oil mills generally also produce palm kernel. Currently, there are still a few palm oil mills (CPO mills) that also have PKO (Palm Kernel Oil) mills , meaning that there are palm oil mills that process fiber for CPO production and palm kernel for PKO production. The palm kernel is produced from the separation of palm kernel with its shell (PKS). Separation is done by breaking the palm kernel shell in a nut cracker drum, then it can be separated between the palm kernel shell and the kernel or core based on differences in specific gravity. If the palm oil mill wants to get added value from its palm kernel shells (PKS), then as soon as it leaves the palm oil mill it goes straight into the dryer (with waste heat as the heat source) after which it is cleaned with a sieve (screening) so that it becomes the final product in the form of dry and clean PKS, so that higher sale value. The size of the shell and fibers that pass the sieve (undersize), can also be used as boiler fuel. Palm oil mill boilers currently operate using fiber fuel (mesocarp fiber) and part of the palm kernel shell (PKS). The rejected material in the form of undersize can be used as boiler fuel so that less PKS are used.

PKSC For Activated Carbon Production

The production of palm kernel shells (PKS) in Indonesia and Malaysia is very large, with more than 15 million tons annually which comes from palm oil mill waste. There are about 20 million hectares of palm oil plantation from these two countries (Indonesia and Malaysia) as sources of crude palm oil and are the largest in the world today. Utilization of PKS can be optimized for the production of activated carbon. The demand for activated carbon is predicted to increase by around 10% per year and the demand will reach nearly 4 million tons in 2021 worth 8.12 billion USD, while data in 2015 recorded global activated carbon production of around 2.7 million tons worth 4.74 billion USD. Powdered activated carbon (PAC) has the largest market share followed by granular activated carbon (GAC). The high demand for PAC is mainly driven by the need in a number of industries such as chemical, petrochemical, food and beverage for decolorizarion and deodorization applications. More specifically, the use in the liquid phase has the largest portion.

However, it is recognized that coconut shell is the current favorite material for activated charcoal production, and PKS is likely to be the next priority. The area of ​​Indonesian coconut plantations is estimated at around 3.7 million hectares so that the number of coconut shells that can be used as activated carbon is also not as much as PKS because the area of Indonesian palm oil plantations has also reached approximately 15 million hectares. With a coconut plantation area of 3.7 million hectares, coconut shells have a composition of 12% of coconuts so that the total coconut shells that can be produced are around 23,000 tons/year. This is in stark contrast to PKS which have the potential to reach tens of millions of tons every year.

The characteristics of coconut shells are also almost the same as PKS. Likewise for the use of activated carbon which emphasizes factors such as hardness and ash content. The harder the material and the smaller the ash content, the better the quality of activated carbon produced. Currently there is a need for palm kernel shell charcoal / PKSC  of 20,000 tons / year for the raw material for the production of activated carbon. Groups of palm oil companies that have a number of palm oil mills (1 group of palm oil companies having 5 palm oil mills is common in Indonesia) or other private parties by taking raw material for PKS from these palm oil mills to be able to produce PKSC to be exported as raw material for the activated production. The use of a large capacity carbonization (pyrolysis) equipment that works continuously is needed to meet these needs. This will be a business development for the palm oil companies and will be more environmentally friendly because less solid biomass waste is produced.

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.

Activated Carbon For Flue Gas Desulphurisation (FGD) Process

Exhaust gas emissions, especially from coal power plants, must be made environmentally friendly. About 60% of the world's electricity currently depends on coal, this is because coal power plants can provide electricity at low prices. The exhaust gases that pollute and endanger the environment need to be treated in such a way that they no longer endanger the environment. Coal is a fuel that contains a high enough sulfur content, namely 0.5% (5 kg / ton of coal) so that when it is burned, it will cause SO2 and SO3 gas emissions or the SOx gas group. If these gases are emitted in the atmosphere, they will cause acid rain. The acid rain will damage agricultural land, forests due to imperfect photosynthesis, the death of marine life and corrosion of metal objects such as vehicles, buildings and so on, even human health in the form of respiratory problems such as asthma, chronic bronchitis to permanent lung damage. 

For example, China says more than half of the country's cities experience acid rain and only a few have fresh air. One sixth of the major rivers are so polluted that their water is deemed unsuitable for agriculture. Pollution watchdogs say 16.4% of China's major rivers do not even meet agricultural irrigation standards. Water from big cities such as Shanghai, Tianjin and Guangzhou is said to be highly polluted. Only the tourist island area of Hainan and parts of the northern coast are considered truly healthy. Only 3.6% of the 471 cities monitored received the top ranking in terms of air cleanliness.

 

Efforts to minimize SOx gas emissions (including sulfur dioxide (SO2), sulfur monoxide (SO), and sulfur trioxide (SO3)) are carried out by treating flue gas desulphurisation or the term FGD (Flue Gas Desulphurisation). As of June 1973, there were 42 FGD units operating, 36 in Japan and 6 in the United States, with capacities ranging from 5 MW to 250 MW. Between 1999 and 2000, FGD units were in use in 27 countries, and there were 678 FGD units operating at a total power generation capacity of about 229 gigawatts. About 45% of the FGD capacity is in the US, 24% in Germany, 11% in Japan, and 20% in various other countries. Approximately 79% of the units, representing about 199 gigawatts of capacity, use wet limestone. About 18% (or 25 gigawatts) use spray-dry scrubbers or sorbent injection systems. The use of these FGDs has now been introduced to various places that use fossil fuels such as coal incinerators and waste incinerators.

Basically there are several types of FGD techniques but in general they can be divided into 2, namely the wet method, for example by absorption of wet lime or sea water solutions, dry methods such as activated carbon and semi-dry methods. The wet method is the method most widely used. The "gypsum lime method", which is one of the wet methods, has become a mainstream in the world as a large capacity exhaust gas treatment process especially for thermal power plants. The considerations for selecting the FGD technique include scale, cost, types of by-products, and their application. The lime-gypsum method complicates the gypsum recovery process and the wastewater treatment process, so it is not suitable for application in small boilers. Therefore, in small-scale plants, the "magnesium hydroxide method" which uses magnesium hydroxide, which is a cheap alkaline in addition to lime, is often used. The soda method was a wet method commonly used in pulp mills and small-scale equipment in the second half of the 1960s, but because caustic soda as an absorber is expensive and operating costs are high, a method using magnesium hydroxide, which is a cheaper absorber, has been adopted. 

In the 1960s, Japan developed a lot of dry FGD techniques and since the 1980s wet FGD techniques have been widely used until now. Currently, Japan has all installed the FGD equipment, but it is certain that the need in China and Southeast Asia will increase in the future. Therefore, in recent years, most FGD equipment manufacturers have realized the technological developments being applied to overseas markets, and the development of simple desulphurisation devices suitable for developing countries that are easy to operate and low cost is underway. There is also a by-product from the FGD which has economic value, namely the gypsum FGD. In Indonesia, there is only one coal power plant that uses FGD with wet limestone and produces a gypsum FGD, namely at PLTU Tanjung Jati, Jepara, Central Java. Meanwhile, other coal power plants still use wet technique with sea water absorbtion.

The desulphurisation method with activated carbon is also simultaneous with denitration and functions to remove other components such as removing dioxins and removing heavy metal elements. The activated carbon adsorption method consists of an adsorption tower, a desorption tower, and an activated carbon circulation transfer device. When other components such as NOx are also adsorbed, a module consisting of a number of activated carbon cells forms an adsorption tower, and each component in the exhaust gas is removed as it passes through each module.

Activated carbon which has adsorbed SOx, etc. In the adsorption tower it is sent to the desorption tower, heated to 350 ° C or higher, and regenerated. The regenerated activated carbon is cooled to 150 ° C or lower in the cooling section, then the dust is removed by filtration and reused in the adsorption tower. Instead, the concentrated SO2 gas obtained is washed and purified, then oxidized or reduced, and finally recovered as sulfuric acid, elemental sulfur, or the like.

 Activated carbon has a large surface area because of the many pores on its surface. These pores are intentionally made to increase the efficiency of adsorption. The more pores are formed, the wider the activated carbon surface area. Based on the size of the pores, they are divided into macropore, mesopore and micropore. Activated carbon from coconut shells has many micropores, while activated carbon from wood is dominated by mesopore and macropore (micropore only has a small portion) because the wood structure is also more open. For activated carbon from coal, the distribution of micropore, mesopore and macropore is almost evenly distributed. Based on the above characteristics, coconut shell activated carbon is widely used to absorb small molecules from gas and liquid. Activated carbon from coconut shells and palm kernel shells (PKS) is thought to be the most suitable for the FGD (flue gas desulphurisation) process.