Use of Waste for Energy Applications

Abstract

In Sweden the utilization of household waste for energy purposes is quite significant already today. Individuals sort the household waste in different fractions where the organic biologically degradable material is separated into one fraction, while other type of combustible materials into one or more fractions. The rest of the waste is normally going to recycling, like metal, glass and paper. Concerning industrial waste we have a similar situation.

In Vastmanland and eastern Uppland a collection system with sorting of waste into many fractions has been in operations for 15 years. This has led to a situation, where most waste is sorted in a very good way. Just 1-2 % of the waste is put into the wrong container. At the central waste recycling plant at Gryta in Vasteras, the biologically degradable organic waste is mixed with fat sludge from restaurants and lay crops like clover and grass into a large biogas reactor. This now has been in operations for four years. It has been proven that the residue from the reactor is not causing any problems with heavy metals or organic toxics when used as fertilizer, and the residue is actually even CERALIA and KRAV certified.

When it comes to extension of biogas production, we are running into a shortage of feed stocks generally in most cities in Sweden. It therefore becomes more interesting to utilize more agricultural wastes like straw, but also to introduce high temperature gasification for e.g. methane production. Today most recycled wood and similar is combusted. This gives heat, but unfortunately no organic materials to the farmlands. We also see a trend towards low energy buildings reducing the need for heat, while the wish to replace fossil fuels for
transportations is increasing. In Västmanland and other parts of Sweden high temperature gasification processes with circulated fluidized beds (750-900 oC) as well as CORTUS high temperature processes using steam for the actual gasification at 1100 oC are investigated. These techniques are also discussed in the paper.