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.

Potassium and Chlorine, 2 Elements Need More Attention at Wood Pellet

Most of the current power plants use pulverized combustion technology which operates at temperatures greater than 1400 C. The high operating temperature makes the requirements for the fuel used quite tight, meaning that not all fuels can be received immediately. The standard power plant fuel is designed using coal, so that when using biomass fuels it might be necessary to modify it. In the ratio of small cofiring, for example, 5% of the power plant is likely to operate on a standard basis without modification. The big question is why the pulverized combustion technology power plant whose capacity can be hundreds or even thousands of MW can not directly use biomass up to 100% without obstacles? That's what we will try to review in the article below.

The main difference between biomass fuel and coal in terms of the power plant is the chemical ashes. The chemistry of coal ash is composed of inorganic materials which have very high melting points and tend not to be corrosive to metals at high temperatures. This makes technically coal fuel more friendly to pulverized combustion technology. Although reviewed environmentally, coal fuel is not friendly because there are many fly ash, ash waste is classified as hazard material / B3 and SOx emissions cause acid rain. While a review of climate change and global warming, it is clear that coal is a fossil fuel and is a carbon positive that increases the concentration of CO2 which is a greenhouse gas in the atmosphere. Many countries now reduce their use of coal in their policies.

While biomass fuels have a chemical content of ash consisting of inorganic materials that have low melting points and tend to be corrosive so that it becomes an obstacle to the pulverized combustion technology. Potassium is one of the chemical elements of ash in biomass which is in the spotlight, this is because potassium has a low melting point and in a large amount of biomass. The melted potassium ash will cover and be deposited on the heat exchanger pipes in the generator boiler. These deposits make heat transfer efficiency decrease so that fuel consumption will increase. This is indicated by the increased chimney temperature which means that there is a large heat loss.

Another element that is the main highlight besides potassium is chlorine. This chlorine is corrosive and is like a ghost for the pulverized combustion power plant. Corrosive properties will shorten the life span or operating life of the power plant, for example with high chlorine content in the fuel, making the operating life of the power plant to be half or a quarter of what it should be. Of course this is very detrimental, for more details can be read here. In addition to the two things above which are considered unfavorable from the use of biomass fuels, but along with the problem of environmental damage in the form of climate change and global warming, biomass fuels are the solution to the problem. This is because biomass fuels are renewable, sustainable, carbon neutral and various other environmental benefits.

The most popular biomass fuel today is wood pellets. When it turned out that wood pellet which is a biomass fuel containing potassium and high chlorine, it became less desirable and was even rejected by the pulverized combustion power plant. Wood pellet producers must pay attention to this issue if the market segment is electricity generation. Ensuring wood pellet products with chlorine and potassium content according to technical requirements are mandatory for these producers. When wood pellets have been produced but the specifications cannot meet the requirements, it is necessary to change the market or improve the quality of the wood pellets.

Basically to overcome the content of chlorine and potassium it can be in two ways, namely from the production side of wood pellets and from the user side. Wood pellet producers can choose raw materials that can meet the specifications requested or even do a number of treatments so that the specifications can be achieved. Whereas from the user side, that is by using electricity generation technology with lower operating temperatures so that the problem of potassium and chlorine can be reduced and even eliminated. The technology of electricity generation with fluidized beds and gasification can be a solution to this.

Ash Problem Up to Modification of Power Plant in the Framework of Coal Substitution to Wood Pellet on Pulverized System

The ash of various biomass in combustion causes a number of problems in the pulverized system. That's because the pulverized system is designed to burn coal. Does not the coal also produce ash after burning even more quantity? Yeah right, but the chemical content of coal ash is different from that of biomass. The difference is that coal ash contains a lot of heavy metals such as arsenic, cadmium, mercury, selenium, lead, and nickel which have high melting point so it does not cause problems to the pulverized, whereas biomass ash mainly contains alkali metals such as potassium and alkaline earths are calcium, which has a low melting point so it creates a problem on the pulverized. The content of coal ash is also much larger compare with biomass ash content.

Ash Slagging: Melt ash deposits on boilers or generally on radiant exposed surfaces in a furnace at temperatures above
1,000 C

High-temperature fouling (around 1000 ° C) while low-temperature fouling (300-600 ° C) usually occurs in boiler pipes

What is the problem with the biomass ash chemistry? There are several problems caused by the ash chemistry on the pulverized system, namely slagging and fouling. How to avoid it? There are several ways to avoid it, namely first, determine the exact percentage of biomass fuel in the pulverized system or co-firing. At the appropriate percentage of biomass fuel can be used simultaneously (co-firing) with coal. The type of biomass fuel also determines its percentage, eg wood pellets will have a larger portion than agro-waste pellets. Secondly, by modifying the coal-fired power plant so that it can even be 100% with biomass fuel such as wood pellets.

Burning biomass fuel in addition to environmentally friendly or carbon neutral, fewer CO2 emissions, SO2 emissions are also very small, very little fly ash even does not occur, and the ash is rich in potassium, and phospur so it becomes a good fertilizer for plants. While coal ash is otherwise and even categorized as dangerous waste due to the heavy metal content. Based on these things, it is natural that the use of biomass fuel continues to be improved even has become government policy in some countries.

The entry point for massive biomass fuel usage is co-firing with coal. The modification of the coal-fired power plant has become an opportunity, so a number of companies have emerged to capture such opportunities as Ramboll and Doosan Babcock. While in Indonesia it seems still long enough to make biomass fuel has a large portion as a source of energy, especially in power plants, because there is no policy that supports it.