EFB pellet is pelletized by the byproduct of EFB, as a new biomass, it is friendly to the environment. However, EFB contains a large variety of different fuels with different chemical composition and combustion characteristics. If making it into pellet in the case of unpretreament, which may lead to slagging, fouling and corrosion when combustion.
Problems Occurred During the Combustion of EFB pellet
The Main Chemical Composition in EFB Pellet
Chlorine is a special minimal nutrition elements, and it widely exists in nature. In the seven kinds of necessary trace elements, plants contain the highest chlorine content. Such as rice straw, EFB etc. EFB still contains large quantity of alkali metals, such as, K, Na, Ca, Mg, etc, and it still contains inorganic element, such as N, etc. It can generate KCl, NaCl, NOx, HCl, etc easily under high temperature(>450°C). These ingredients will generate slagging and corrosion.
Slagging and Low Ash Fusion Temperature Problems
Firstly, during the EFB pellet combustion process, its raw material composition, the parameters(furnace temperature, contact to the air, heating surface temperature ) and fuel shape has a certain impact on the deposition. High chlorine content in the raw materials can promote the liquidity of alkali, and easily to form alkali metal chlorine, then deposit on heating surface; if the furnace temperature rises, it is contributed to the escape of alkali metal from fuel. The alkali metals condensate on the fly ash, and reduced its melting point, which are more likely to cause slagging problems.
Moreover, caused by alkali corrosion mechanism, the furnace temperature, chlorine content and deposit volume are the important factors affecting corrosion. In the process of corrosion caused by solid alkali metal oxide, furnace temperature and the deposit volume’s increasing will obviously increase the oxidation rate of boiler steel. And the rise of temperature will accelerate the response to the corrosion; and the increasing of chlorine content in EFB pellet will also cause corrosion.
Solution of Problems Which Occur at Combustion of EFB Pellet
1. Use multi-fuel boiler which is suitable for burning EFB pellets.
2. Using washed method to remove part of alkali metal before pelletization. Most of the alkali metal elements in EFB are water-soluble, so washed method can be used as an effective method to eliminate alkali metal problem. After washing, the ash has different degrees of decline, and ash melting has been improved, and reduced the corrosion problem caused by alkali metal.
3. Using additives when pelletizing. Such as, kaolin clay, activated alumina, dolomite, silica and diatomite. It can solve the problem of chloride content and corrosion effectively.
4. Co-firing with fossil fuel will solve the problem of low ash fusion temperature and reduce the chloride content.
5. Lower combustion temperature is also the effective way to solve the problem of low ash fusion in the EFB pellet burning.