Ash From Palm Oil Waste Combustion As A Biomaterial In Concrete Construction

Palm kernel shells (PKS) and mesocarp fibres are commonly used as fuel for palm oil mills for the production of electricity and steam for sterilizers. The byproduct of combustion in the form of ash a lot produced by the process. A palm oil mill can produce 5 tons / day or more of the ash depending on the amount burned because the average ash content of the palm oil waste is around 5%. Most of the palm oil mills do not make use of the residual ash from the combustion but just throw it away. Though the ash can actually be used for various purposes, one of which is as a biomaterial substitute for sand in various building construction projects. The locations of palm oil mills or surrounding communities usually in the remote areas difficult to obtain a supply of sand for the construction of various buildings, so that the presence of ash as a substitute for sand will be helped.

Typical boiler in palm oil mill

At present, a number of domestic industries have started to use biomass fuel, as an environmentally friendly fuel. Palm kernel shell or PKS is one of the favorite biomass fuels at this time. One of the interesting things about palm kernel shells is that they are  almost similar properties to wood pellets, but at a lower price. Ash from the palm kernel shells as well as ash from the palm oil mills can also be used for sand substitution for various building construction projects. The location of industries in urban areas so that the use of ash can also be in line with various city construction constructions such as the construction of roads, high rise buildings and aircraft runways. Although the ash cannot replace 100% sand but it will help save costs by around 25% substituted with the ash.

Main chemical compounds content in sand

Main chemical compounds content in boiler bottom ash

The palm kernel shell ash itself contains high silica which is around 60%, while the ash mixture from the shell and palm fiber in the boiler furnace contains about 30% SiO2. SiO2 functions as a filler in the manufacture of concrete which will affect the strength of the concrete. While the composition of the main compounds in the sand can be seen that SiO2 has a relatively large composition. Mud in sand is impurity so that the mud content in sand cannot exceed 5%. Mud levels of more than 5% result in the hydrogen bonding of cement paste and sand being reduced due to the influence of sludge as impurities. Boilers ash from palm oil mills can be used as a substitute for sand in making concrete because it has compounds that play a role in making concrete. If it is to be used as a cement substitution material, a material must contain a relatively large amount of lime compounds because cement basically functions as a binder and mainly functions as lime. The content of SiO2, Al2O3, and CaO is contained in boiler scale ash (bottom ash) which is needed in making concrete.

The yield of ash density is 2.11 g / cm3, lower than the density of sand. According to ASTM C128-93, the good density for making concrete is above 2.50% so it includes rough aggregate. The absorption value of water produced by boiler scale ash fulfills the requirements of preventing or reducing empty voids in concrete. The maximum limit of SiO2 content contained in sand for making concrete is around 30%, so that the boiler bottom ash is included in a good aggregate and meets the standard for partial sand replacement. Based on the composition of the chemical content, boiler bottom ash is superior to sand because CaO in ash plays a role in helping cement as a binding material. Similarly Al2O3 is very influential in accelerating hardening of concrete.

Comprehensive concrete strength tester

If calculated the potential ash from the waste of palm oil is also quite large potential. Say with 1,000 palm oil mills now operating in Indonesia with each mill producing 5 tons / day of ash then 5,000 tons of ash a day or 150,000 tons of ash a month. While the excess of palm kernel shells from palm oil mills that can be utilized by other industries in Indonesia is estimated to reach 11 million tons, which means that the ash potential that can be produced is 550 thousand tons. In addition, the difference between ash from palm oil waste classified as biomass ash and coal ash is palm kernel shell ash excluding B3 (hazardous) waste so handling is easier while coal ash including B3 (hazardous)waste whose handling is more difficult. Palm kernel shell ash also comes from biomass which is a renewable resource while coal is from non-renewable resource group.

Higher Power Plant Efficiency Demands Higher Fuel Quality

When we want to refuel our vehicle at a gas station, of course we choose what fuel is most suitable for our vehicle. Our vehicles will be able to run optimally when using the appropriate fuel. Over spec fuel quality or too low (under spec) will only provide less optimal performance. Technically, the vehicle has been designed with a certain pressure ratio on the combustion system, if the quality of the fuel is too high then low compression is difficult to burn perfectly, and vice versa. In the operation of vehicles, even fuel that burns prematurely or after time will produce a performance that is not optimal. High-quality fuels also have higher prices so that they are economically also not profitable, as are low quality fuels, although they are cheaper but performance is also below standard.

The analogy above is also more or less the same for electricity generation. The higher the level of efficiency the higher the quality of the fuel required because the operating conditions are also above the average, for example compression, temperature and so on. If the quality of gasoline is expressed by octane numbers, or on diesel oil the quality is stated by cetan numbers, then in solid fuels such as wood pellets the size of quality is expressed as a caloric value. Other elements that are also considered in fuel are elements that can damage the equipments or machines used. Especially for wood pellets, high potassium and chlorine content can have a bad effect on the power plant. Potassium will be a deposit / fouling on boiler pipes thereby reducing its efficiency, while corrosive chlorine will shorten the life of the power plant.

In 2030, Japan will implement the use of power plants with higher efficiency, which is a minimum of 41%, while most of the efficiency of coal power plants currently ranges from 30-35%. To achieve an efficiency level of more than 41% the technology used is ultra supercritical pulverized coal. Ultra supercritical pulverized coal technology is basically a further development of pulverized coal technology that is most widely used by coal power plants or more than 95% in the entire world today. The difference in ultra supercritical pulverized technology with pulverized is the use of higher pressure and temperature so that its efficiency is also higher. Modification of the power plant can also be done to increase the efficiency. The use of biomass fuels such as wood pellets can be done by cofiring or full firing (100% wood pellets). The characteristics of the fuel used will also affect the boiler technology used.

The ash of wood pellet required for industries such as electricity generation can be up to 6% according to the American pellet fuel institute (PFI). But chemical ash is an important consideration in the use of the power plant. South Korea for example currently requires a maximum chlorine level of 500 ppm (500 mg / kg) or Japan requires a maximum potassium level of 1000 ppm (1000 mg / kg). This makes the production of wood pellets follow these specifications if the specifications are not appropriate. A number of special pretreatments need to be done to achieve these specifications. The potential of wood pellets from energy plantations in Indonesia is very large, as are pellet fuels from agricultural or plantation waste such as palm oil empty fruit bunches which are estimated to reach approximately 38 million tons per year. But once again the specifications of the pellets (wood pellets or agro waste pellets) produced need to be adjusted to the needs of power plants in Japan or South Korea - two countries that are highly energy dependent - of course if the pellet producers are export oriented. What are the next pretreatment questions that need to be done on the production of the pellet? InsyaAllah, we discussed on another occasion.