Waste to Energy Gasification Fuels

 

Characteristics of the various waste materials to be used as fuel are extremely important to take into account when designing waste to energy gasification facilities. EPR maintains analytical capability, as well as high temperatures process engineering and development capability at the University of Washington in Seattle. Shown here in some detail are some of the materials that are used as fuel in a typical mixed fuel gasification system. Analysis of both the fuel materials and the ash that results from the gasification of the materials is of great value in optimization of system design and operating parameters for the gasification equipment.

 

Source separated commercial waste shown here in bulk makes an excellent gasifier fuel. If sent to landfill,  the wood and shredded paper components of this waste will slowly degrade anaerobically, forming carbon dioxide and methane gas. As a greenhouse gas, methane is more than 20 times as harmful as carbon dioxide.

Light construction and demolition waste are shown to the right is another clean dry waste stream that can be processed to form refuse derived fuel for gasification. This waste material typically contains a great deal of plastic sheeting and wood and makes an excellent medium to high Btu fuel for gasification.

In the gasifier this material is converted cleanly and efficiently to a clean burning fuel gas that is used to fire a heat recovery boiler that produces steam to drive a steam turbine generator.

Municipal solid waste (MSW) is normally placed into landfill where it decomposes producing methane gas and noxious odors, as well as a leachate that can contaminate local ground water.

MSW can be cleanly and efficiently gasified to produce thermal energy which can be used to  generate electricity or for district heating or other beneficial uses. Gasification reduces the volume of material that is eventually placed into landfill by as much as 90%. The solid residue from gasification with EPR equipment is an inert non-hazardous, carbon free material that can be used for landfill daily cover or in construction.

 Waste tires can also be used as a high BTU fuel component for gasification. After de-beading to remove the relatively heavy gauge bead steel, the tires are shredded with the belt materials left in. These shreds have more heating value per pound than coal and can be gasified cleanly. The sulfur oxides that are produced during incineration of these tires are largely avoided during the gasification process. Analysis shows that much of the sulfur comes out as sulfate in the ash.

 

Sewage sludge such as that shown here is comprised of approximately 20% solids and 80% water. On a dry weight basis it can have a calorific value as high as 5000 Btu/lb. Sewage sludge can be added to the gasifier fuel mix in proportions of between approximately 10% and15% by weight. Sewage sludge causes odor problems when disposed of in a land fill. In the gasification process the odor causing compounds in sewage sludge are converted to a fuel gas which is burned to generate heat and energy.