Biomass Boiler Testing and Selection of Suitable Biomass Fuel

In line with the trends toward decarbonization and sustainability across various sectors of life, particularly in the processing industries (manufacturing/process industries), the use of biomass boilers has become a realistic option today among boilers that utilize other renewable energy sources. Fossil-fuel-fired boilers—such as solid-fuel boilers (coal), liquid-fuel boilers (industrial diesel), and gas-fired boilers (natural gas)—must be replaced with renewable fuel boilers, namely biomass boilers. Apart from technical factors in the form of operational adjustments from previous fossil-based fuels, the suitability and availability of biomass fuels are important factors. Suitability refers to the technical aspect and availability refers to the economic aspect.

Combustion technology for biomass boilers also continues to develop so that efficiency continues to increase. From the beginning in the form of static grates to dynamic moving grates such as chain grates and reciprocating grates, even fluidized beds. And to get optimal performance, biomass fuel specifications must also match the shape, size, calorific value and dryness. If the specifications do not meet the requirements of the combustion technology in the boiler then of course the performance will not be optimal. For example, chain grates are suitable for using fuel that has a uniform size and low water content such as palm kernel shells, wood chips and wood pellets. Apart from that, biomass fuel with ash content which has a high melting point is highly preferred so that the ash does not melt and clog the chain lattice cavity.

Meanwhile, using a reciprocating grate, this system is very reliable for burning biomass with high moisture content (up to 60%), non-uniform size, and high ash content, such as empty oil palm fruit bunches (EFB), bark, and municipal solid waste (MSW). The combustion system moves back and forth periodically (like a moving staircase that moves back and forth) which functions to mechanically turn and stir the fuel. And for fluidized beds, this system has the highest thermal efficiency (>89%) and is very suitable for biomass with very small size (powder/dust), low calorific value, or fluctuating chemical content such as rice husks, sawdust, and coffee grounds. The biomass particle size must be maintained within certain limits so that it can float and fluidize perfectly with the sand bed media. The ideal particle size for a fluidized bed boiler (FBC) generally ranges from 0.1 mm to 10 mm (maximum 30–50 mm for certain components), depending on the specific type of technology used.

As a country located on the equator with a tropical climate, Indonesia is a biomass paradise in the world; read more here. A wide variety of biomass fuels in large volumes can be sourced in Indonesia. The most readily available biomass fuels in Indonesia today are wood chips, palm kernel shells, and wood pellets. Wood briquettes are also available but in limited quantities. Choosing the right biomass fuel will ensure optimal boiler performance, but of course, the economic factors for each metric ton of high-pressure steam produced are equally important. 

Ideally, biomass fuel is available in large quantities, ensuring affordability and high quality. The price of biomass fuel is influenced by various factors, including availability, location, logistics infrastructure, and transportation costs. Furthermore, if the biomass fuel undergoes processing, such as wood pellets and briquettes, production costs also contribute. Palm kernel shells for industrial boiler use in Indonesia require almost no processing; they are simply collected from palm oil mills or CPO mills, which produce waste in the form of palm kernel shells (PKS).

There is a case study regarding the selection of this biomass fuel involving a multinational company. In a certain country, the company’s boilers operate using wood briquettes—specifically, industrial briquettes produced by a mechanical press. This approach was also planned for the company’s plant in Indonesia. However, because producers of wood briquettes are still very scarce in Indonesia—making it impossible to secure a supply—the company ultimately conducted various experiments and trials with different types of biomass fuels and now operates its boilers using wood pellets. Thus, in addition to technical factors, economic factors are also crucial for ensuring optimal and sustainable biomass boiler operations. The trial phase is a critical step in achieving these conditions. 

EFB Pellets as Biomass Fuel Transition from PKS to Wood Pellet Energy Plantations?

The high demand for palm kernel shells or PKS makes their availability or supply increasingly limited. The properties of palm kernel shells or PKS which have many similarities to wood pellets make them the main competitor for biomass fuel in the global market. The high demand for palm kernel shells is not only because the price is usually cheaper than wood pellets, but also the large availability can be achieved because of the large number of palm oil mills, also especially the many new biomass power plant developments that can use 100% palm kernel shells, namely biomass power plants with fluidized bed combustion (CFBC or BFBC) technology, read more details here. 

Under these conditions, efforts to obtain new biomass fuel become important. The palm oil industry itself produces a lot of biomass waste so it has potential as raw material for new biomass fuel. One of the biomass wastes that has not yet been utilized and is large in volume and has the potential to pollute the environment is palm oil empty bunches or EFB (empty fruit bunch). Every ton of crude palm oil or CPO production will produce approximately 1 ton of EFB waste. This means that with an average palm oil mill capacity of 45 tonnes of FFB/hour, around 10 tonnes/hour of crude palm oil (CPO) will be produced and 10 tonnes/hour of EFB waste. So, for example, if a palm oil mill operates 20 hours/day, approximately 200 tons of EFB waste will be produced/day. And with the number of palm oil mills in Indonesia estimated at 1,000 units, the amount of EFB waste will also huge.

PKS and EFB are both biomass waste from palm oil mills. Both can be easily obtained from palm oil mills in abundant quantities. PKS can even be used directly as biomass fuel, whereas EFB requires pre-treatment first. The EFB that comes out of the palm oil mill is very wet and the shape and size still need to be adjusted to make the follow-up process easier. EFB pellet production is a solution for EFB waste. But apart from that, so that this EFB pellet product can be used more widely or like wood pellets in general, there is an additional process to reduce the amount of mineral content in the ash.

Meanwhile, wood pellets from energy plantations could become the next source of biomass fuel, although currently someone has already started doing so. Because the raw material for EFB pellets is palm oil mill waste and is abundant, it requires a smaller investment, so EFB pellets can be used as transitional biomass fuel before biomass fuel in the form of wood pellets from energy plantations. Investing in land and its preparation as well as creating an energy plantation costs a lot of money. But the advantage of wood pellets from this energy plantation is that the availability of raw materials, even in very large volumes, can be more guaranteed. Apart from that, there are also other benefits from using the leaves as animal feed, especially ruminants and the flowers for honey bee farming.