Foreground system:
The data set represents the generation of electricity in waste-to-energy plants (WtE) for the thermal treatment of municipal solid waste (MSW) with dry flue gas cleaning and selective non-catalytic reduction (SNCR) for NOx-removal to meet the legal requirements. Environmental impacts for waste collection, transport or any pre-treatment of the waste are not included in the data set. The modeled average plant consists of an incineration line fitted with a grate and a steam generator.
The average efficiency of the process steam production is about 82%. Produced steam is used internally as process steam and the balance is used to generate electricity or exported as heat or process steam to industry or households. The energy balance for the plant is modeled, using specific data from the "CEWEP Energy Report 2004-2007" (2008) representing 231 waste-to energy plants in Europe. Per ton of treated MSW 0.02 GJ electricity and 0.04 GJ of fuels and thermal energy are (are imported. Per ton of treated MSW (net calorific value: 10.0 GJ/t) 1.12 GJ electricity and 3.43 GJ thermal energy are feeded to the electricity grid, industrial customers and households. This results in a net efficiency of 44.2% of the average plant.
The flue gas treatment system uses a dry technology with adsorbent and a SNCR system for NOx-reduction. The NOx reducing agent ammonia is directly injected into the furnace and reacts with the NOx to nitrogen and water. The flue gas is conditioned, adsorbents added and filtered with fabric filters. Lime milk and small parts of hearth furnace coke are used as adsorbents; a part of the adsorbents is re-circulated. The fly ash together with the adsorbent is mixed together with the boiler ash (treatment of APC residues see below).
For the emissions HCl, HF, NOx, VOC, N2O, CO, NH3, SO2, dust, dioxins and the heavy metals As, Cd, Co, Cr, Ni and Pb mean emission values per cubic meter of cleaned flue gas published in the BREF document "Waste Incineration" of the European Commission are used. Due to the wide range of emissions for some elements and substances the mathematical mean values are adjusted with additional real plant data. The emission of all other elements and the distribution of all elements and substances into the different residues are calculated by means of transfer coefficients.
The bottom ash, approximately 220 -250kg/t of MSW, is quenched, ferrous scrap and partly non-ferrous metals (aluminum, copper, brass, zinc, lead) are recovered and a three month ageing process is done to stabilize the bottom ash. The produced bottom ash after metal recovery and ageing is re-used as construction material (and will leave the system as bottom ash for re-use). The APC residues (approximately 40-45kg/t of MSW) including boiler ash, filter cake and slurries are disposed in underground deposits salt mines. The disposal in underground deposits without free water and contact to ground water reservoirs is modeled as emission free. The operation of the underground deposit is included. Transports for bottom ash and APC residues independent of the different routes are considered.
All important utilities and auxiliaries used in the waste incineration plant are included in the system. To calculate the credits for the recovered ferrous metal scrap a "value of scrap" data set was used, i.e. the environmental burdens for the remelting and processing of the scrap are taken into account in the system boundaries. Credits for an eventual recovery of non-ferrous metals are not given.
Background system:
Electricity: Electricity is modelled according to the individual country-specific situations. The country-specific modelling is achieved on multiple levels. Firstly, individual energy carrier specific power plants and plants for renewable energy sources are modelled according to the current national electricity grid mix. Modelling the electricity consumption mix includes transmission / distribution losses and the own use by energy producers (own consumption of power plants and "other" own consumption e.g. due to pumped storage hydro power etc.), as well as imported electricity. Secondly, the national emission and efficiency standards of the power plants are modelled as well as the share of electricity plants and combined heat and power plants (CHP). Thirdly, the country-specific energy carrier supply (share of imports and / or domestic supply) including the country-specific energy carrier properties (e.g. element and energy content) are accounted for. Fourthly, the exploration, mining/production, processing and transport processes of the energy carrier supply chains are modelled according to the specific situation of each electricity producing country. The different production and processing techniques (emissions and efficiencies) in the different energy producing countries are considered, e.g. different crude oil production technologies or different flaring rates at the oil platforms.
Thermal energy, process steam: The thermal energy and process steam supply is modelled according to the individual country-specific situation with regard to emission standards and considered energy carriers. The thermal energy and process steam are produced at heat plants. Efficiencies for thermal energy production are by definition 100% in relation to the corresponding energy carrier input. For process steam the efficiency ranges from 85%, 90% to 95%. The energy carriers used for the generation of thermal energy and process steam are modelled according to the specific import situation (see electricity above).
Transports: All relevant and known transport processes are included. Ocean-going and inland ship transport as well as rail, truck and pipeline transport of bulk commodities are considered.
Energy carriers: The energy carriers are modelled according to the specific supply situation (see electricity above).
Refinery products: Diesel fuel, gasoline, technical gases, fuel oils, lubricants and residues such as bitumen are modelled with a parameterised country-specific refinery model. The refinery model represents the current national standard in refining techniques (e.g. emission level, internal energy consumption, etc.) as well as the individual country-specific product output spectrum, which can be quite different from country to country. The supply of crude oil is modelled, again, according to the country-specific situation with the respective properties of the resources.