Economic possibilities of HTAG compared to grate fire incineration, using MSW and rejected plastic as fuel

University essay from KTH/Energiteknik; KTH/Energiteknik

Author: Jonathan Guzman; Björn Jonsson; [2015]

Keywords: ;

Abstract:

Energy is one of the most required products. Grate Fire Incineration is an old technique where waste is incinerated to produce heat and electricity. High Temperature Air Gasification is a new technique there rejected plastics can be used as fuel to produce syngas which can be used in a gas turbine to produce heat and electricity. The objective of this thesis is to compare those two and determine which is more profitable.

The LHV of the waste that is transported to Högdalen have been calculated to be 9.44 MJ/kg. Only plastic rejects will be used as fuel for HTAG and for simplicity, only six of the most common plastic sorts will be the ones assumed to form the plastic rejects. Those plastic types are; PVC, PS, PUR, ABS, Nylon 66 and Nylon 6. GFI calculations are based on Högdalen CHP-plant boiler number 4, which produces an effect of 86 MWh and has an incineration capacity of 36 ton/h. The boiler has an efficiency of 90% where electricity makes up for 16% and heat the remaining 74%. Most if the information about HTAG comes from articles based on the HTAG prototype in KTH. It is assumed that an HTAG facility with gas combined cycle gas turbines in cold countries have an efficiency of 95%. Syngas, which is the fuel produced from HTAG to be used in gas turbines, is assumed to only be made of H2 and CO. The LHV for H2 is 119.96 MJ/kg while for  CO it is 10.12 MJ/kg. The initial investment for and GFI facility is assumed to be 77000 kr/kWEl while it is lower for HTAG, 57000 kr/kWEl. The fixed yearly cost for GFI is 2200 kr/kWEl and about the same for HTAG, 2300 kr/kWEl. The moving cost which depends on how much energy is produced is 54 kr/kWhGr for GFi and 65 kr/kWhGr. GFI, which takes care of waste, gets paid 350 kr/ton for doing so.

The HTAG process involves the gasification of plastic using steam with the goal of producing syngas. According to the assumptions, the mass of the plastic stands for half of the reactant mass while the mass of the syngas stands for more than 9/10 of products mass. H2 represents 10.1% of the syngas mass while CO represents 89.9%. In this scenario 200 kg plastic and 1000 kg of MSW will be used as fuel. That results in 362.3 kg of syngas which produces 0.961 MWh of heat and 1.069 MWh of electricity in a combined cycle. The incineration of the MSW yields 1.94 MWh of heat and 0.38 MWh of electricity. According to the results HTAG has almost the same payback period as GFI. If the heat and electricity price increase HTAG will have a shorter payback period than GFI. But if the prices decrease HTAG will have a much longer payback period.

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