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Mining, pelletizing and gasifying waste at Philippine landfill

A Philippines-based waste to energy company, True Green Energy Group (TGEG), has successfully tested the Material Recycling Facility (MRF), shedder and pelletizng machine at the country’s San Fernando landfill site.

According to the company its facility will reduce landfill waste and create a pelletized feedstock for its gasification based waste to energy system.

First, waste materials that are combustible, such as paper, plastic, food, wood, and agricultural materials, are dried and shredded. The company said that while metal are removed for recycling, the gasification system will still work if some contamination from these materials is present in the feedstock.

Next, the shredded trash is turned into fuel pellets which TGEG said is done by using a special high temperature gasification process to decompose the pellets in a controlled manner.

The company claimed that while about 5 per cent of the pelletized material ends up as ash, the rest is converted into a syngas (mostly hydrogen and carbon monoxide) that is similar to natural gas, but with a lower energy content. The resulting gas is burned in a highly efficient micro turbine to generate electricity.

Pelletizing waste

According to the company, the process of manufacturing fuel pellets involves placing ground biomass under high pressure and forcing it through a round opening called a “die.”

When exposed to the appropriate conditions, the biomass “fuses” together, forming a solid mass. This process is known as “extrusion.” Some biomass (primarily wood) naturally forms high-quality fuel pellets, while other types of biomass may need additives to serve as a “binder” that holds the pellet together.

A roller is used to compress the biomass against a heated metal plate called a “die.” The die includes several small holes drilled through it, which allow the biomass to be squeezed through under high temperature and pressure conditions.

If the conditions are right, the biomass particles will fuse into a solid mass, thus turning into a pellet. A blade is typically used to slice the pellet to a predefined length as it exits the die. Some biomass tends to fuse together better than other biomass.

The proper combination of input material properties and pelleting equipment operation may minimise or eliminate this problem. The company said that it is also possible to add a “binder” material - as it is doing with its biomass to help it stick together.

As they leave the die the pellets are quite hot (around 150 degrees C) and fairly soft. Therefore, they must be cooled and dried before they are ready for use. This is usually achieved by blowing air through the pellets as they sit in a metal bin. The final moisture content of the pellets should be no higher than 8 per cent.

The standard shape of a TGEG fuel pellet is cylindrical, with a diameter of 6 to 8 millimetres and a length of no more than 38 millimetres.

Most common pellets currently on the market must have an ash content of less than 1 per cent, whereas “standard” pellets may have as much as 2 per cent ash, explained the company. All pellets should have chloride levels of less than 300 parts per million and no more than 0.5 per cent of fines (dust).

The company said that 1 tonne of its biomass pellets will cost approximately $165 and that it estimates that the facility at the landfill site in San Fernando is capable of pelletizing between 300 to 1000 tonnes per day.

Additionally, the company said that waste already stored below ground at the landfill will be mined and additional pelletizing equipment installed at the landfill.

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