Oil palm kernel shells, a solid waste from the production of Crude Palm Oil (CPO) and derivatives, are usually only used as a boiler fuel or exported but a team of researcher has managed to turn it into a promising combustion gas to heat hot-mixed asphalt to replace diesel oil or coal gas.
The team, from the Research and Public Service Institute (LPPM) of the Sebelas Maret University in Solo, Central Java, has managed to show that this solid waste could be used to heat up aggregates in the production of Hot-mixed asphalt, through a gasification process.
“This gasification process of the oil palm kernel shells produces a combustible gas that is used as a fuel to heat up the aggregates in the production of hot-mixed asphalt,” said Sunu H Pranolo, a leading member of the LPPM team of researchers.
In a written reply to queries, Pranolo said that the heating process was necessary to allow the aggregates to mix with the asphalt.
“One of our aims is the wish to make oil palm kernel shells as one of the fuels that can provide the energy needed for heating up the aggregates, besides of natural gas and gasified coal,” he said.
Pranolo said that so far, the shells which are in abundant supply were currently merely burned to fuel boilers or exported as raw material for renewable energy production overseas. These exports, he lamented, meant that the nutrients in the kernels also would be enjoyed by other countries.
“These exports are because of the unavailability of system that made use of the kernels shells in the country that could absorb kernel shell production in Indonesia, So, this innovation has the potential of opening up a domestic market for palm kernel shells,” he said.
One ton of oil palm fresh fruit bunch will produce some 65 kilogram of kernel waste and data from the Indonesian Palm Kernel Shell Association (APCASI) showed that in 2019, Indonesia produced 9.97 million tons of kernel shells while its export volume reached 1.72 million ton or about 17.25 percent of the total produced.
Kernel shells had the highest calorific value compared other side products from the CPO production process from the fresh fruit bunch (up to 16-18 MJ/kg) such as oil palm fibers, empty fruit bunches and others, Pranolo said. The research also showed that the use of the shells in the production process did not affect the quality of the asphalt produced.
The combustible gas is produced from the kernel shells through the use of a gasification reactor, a gas cooler and cleaner, a gas burner and its instrumentation system, almost all of them could be produced domestically.
“The capabilities of our workshops can really support the production of these equipment and the Domestic Component Content (TKDN) of this system could reach 70 percent, with the exception being the electrical motor and its instruments,” Pranolo said.
He admitted that there was a capital investment needed to produce the equipment and the salary of the manpower to operate the process of using the kernel shells as fuel to heat the asphalt mixture, but he added that this initial investment could quickly be recouped if there was an adequate demand for the production of the hot-mixed asphalt.
“We estimate that within two to three years, the initial capital could be recouped if the production proceeds for at least four to six months per year,” Pranolo said, explaining that the production of the hot-mixed asphalt was dependent on the number of new roads to be built, or the maintenance of old ones.
He said that the production of one ton of hot-mixed asphalt needed about 35-40 kilograms of dried kernel shells.
According to harga.web.id, the price of kernel shells stood at between Rp 500 and Rp 1,800 per kilogram in August 2020, making it a relatively cheap raw material for fuel making.
In terms of mass and energy balance, one liter of diesel oil to process the heating of the aggregates was equivalent to three to four kilograms of dry kernel shells. The use of this solid waste from the CPO production process could thus reduce the cost of heating up the aggregates compared to the use of diesel oil or gasified coal and also reduce their use.
At the Rp 1,800 ceiling price, the cost of using oil palm kernel shells was still below that of one liter of diesel oil/ In August 2020, Bio Solar cost Rp 9,400 the liter while Dexlite was at Rp 9,400 and Dex at Rp 10,200.
The research involved two private companies, one as a fabricant of the gasification reactor and the other as the would-be consumer of this technology, Pranolo said without giving further details.
The research and development of the use of kernel shells as material to heat up the hot-mixed asphalt which also involved three other team members — Joko Waluyo, Ary Setyawan, and Prabang Setyono – has obtained funding from the Palm Oil Plantation Fund Management Agency (BPDPKS) since 2018. The funding will expire at the end of this year.
Pranolo said that the fund was used to conduct shell quality testing, the planning and manufacture of the gasification equipment, transportation and commissioning of the gasification equipment, the provision of the shells and a number of aggregates for equipment and instrument testing and quality testing of the gasification results.
Some of the fund was also used to conduct the promotion and publication of the process through focus group discussions, international seminars, international journals as well as for patent submission.
“These activities are part of our roadmap to achieve a Green Asphalt Mixing Plant that gradually uses renewable fuels,” Pranolo said.