Conversion of a lignite-fired power plant into a waste-to-energy plant using the example of the ZMS Schwandorf, Germany

With the establishment of the Zweckverband ZMS Schwandorf 40 years ago and the associated decision to convert the existing lignite-fired power plant into a waste-to-energy plant, approx. 8.25 million tons of CO2 equivalents were saved in the period from 1982 to 2018.

ZMS Schwandorf

This is due to the fact that, by ensuring the safety of waste disposal through thermal recycling, the landfills of the Association members were gradually closed, thus avoiding methane emissions from the previously open landfills.  Significant emission credits also result from the separation of metals from ashes.

Today - in the year 2020 - seventeen towns and districts are united in ZMS.  The Association's area covers 15,000 km² and ensures the disposal of household, bulky and commercial waste of about 1,856,000 citizens.  The Association operates a bulky waste processing plant and uses the energy from the combined heat and power plant to supply the nearby aluminium industry with process steam, to generate electricity, to operate a district heating network and to dry sewage sludge.

Calculation of climate relevance

The study compared the climate-relevant emissions from waste treatment in the waste-to-energy plant with the emissions that would have resulted from the continued operation of the lignite-fired power plant and the emissions from open landfills.

The climate-relevant emissions from waste treatment to be taken into account result from the combustion of the fossil components of the waste, from the combustion of auxiliary fuels, which are mainly used during the start-up and shut-down phases and in the area of waste gas purification, and from the provision of operating materials, e.g. in waste gas purification.

Prior to the establishment of the ZMS, the industrial heat supply at the present location was ensured by a lignite-fired combined heat and power plant.  The resulting emissions can be estimated at about 240,000 tons of CO2 equivalents in the years before 1983.  Due to the successive replacement of lignite by waste, half of which is regenerative, the annual emissions in the following years changed to a net reduction of up to 150,000 tons of CO2 equivalents.

Very strong additional greenhouse gas reduction effects occurred in the years 1982 to 2005 due to the avoided release of landfill gases, since during this period waste could still be landfilled untreated under German law.

By generating electricity from surplus steam from waste incineration, partially regenerative electricity is fed into the public grid.  The associated relief effects are also significant, but are losing importance over time due to the increasing share of renewable energy sources in the German electricity sector.  A similar effect can be seen with district heating, which has been provided by the waste-to-energy plant since 1996.

The construction of the sewage sludge drying plant enables the process steam not required in industry to be used profitably as surplus heat and, in addition, saves greenhouse gases.

By recycling ferrous and non-ferrous metals (here mainly aluminium and copper) from the incineration residues, almost 600,000 tons of CO2 equivalents can be saved, assuming recovery rates according to the state of the art.

The sum of all effects leads to calculated savings of 8.25 million tons of CO2 equivalents in the period from 1982 to 2018.  3.1 million tons of CO2 equivalents were saved in this period, even without taking into account avoided landfill gas emissions.

The delivery of 80% of the waste by rail and the thus resulting reduction in road traffic of around 13 million tons of load capacity on trucks results in a further reduction in emissions of around 385 tons of CO2 equivalents.

International significance

The advantage of changing the lignite-fired power plant into a waste-to-energy plant was particularly high until 2015, because landfilling was permitted in Germany until then.  In many countries of the world landfilling is still permitted and common practice, so that when calculating the international significance, a comparison must be made between open landfilling and waste-to-energy power plants.  The climate relevance here is thus much higher than in Schwandorf.

History

May 21, 1979:  Constituent meeting of the Association Assembly, founding meeting with 13 Association members in Schwandorf
April 1980:  Contracting of the construction work for the waste power plant
August12,1982: First waste train from Regensburg and Straubing; construction of eight reloading stations in advance, specially designed for transport by rail
October 1, 1982: Start of the four-month trial operation of the first incineration line
August 5, 1983: Transfer of the waste power plant to the operator Vereinigte Aluminiumwerke AG (VAW)
March 31,1989: Start of the planning approval procedure for the expansion of the waste power plant by a 4th furnace line.
End of July 1989: Contract award for flue gas cleaning line and expansion of the waste-to-energy plant
End of January 1990:  Laying of the foundation stone for the new flue gas cleaning plant
March 1992: Approval for retrofitting the flue gas cleaning systems on kiln lines 1-3
August 1996:   Approval of the denitrification and dedioxination plant and kiln line 4
In 2006:   The city and district of Landshut were admitted to the ZMS
2010 to 2012:  Fundamental modernisation of the transfer stations
November 16, 2011: Final closure of the Landshut waste incineration plant.  As a result, expansion of the rail transport network from 369 to 467 km
 
Technical Data

The waste transported by rail and road is tipped into the waste storage pit at the unloading station. It is filled into the feed hoppers with large grippers. From there the waste is fed into one of the four kiln lines. 

At temperatures between 850° and 1000°C, the waste is rotated by a counter-rotating transfer grate system through the furnace in just under two hours and burns during the process. The heating value of the waste is so high that the burning process does not require any additional fuels. Only light fuel oil is required to heat up the furnace. In kiln line 4, approx. 28 tons of waste are burned per hour, in kiln lines 1-3, approx. 12.5 tons of waste per hour each, depending on the heating value. The resulting slag is cooled by a wet slag remover. A conveyor belt transports it to the slag bin. Various magnet systems are used to separate the ferrous and some of the non-ferrous parts from the slag. 

The scrap is recycled in the steel industry. After processing, the remaining slag is used for external landfill construction measures. The residual slag corresponds to about one tenth of the original waste volume. The thermal energy recovered from the incineration process is used to generate steam in the boiler. Part of it is released as process steam to neighbouring industrial plants. Electrical energy is generated by three turbines and fed into the public grid.

Since 1996, the waste-to-energy plant has also been supplying district heating to the district heating network of the Schwandorf municipal water and district heating utility. Its use saves primary energy, reduces emissions and contributes to climate protection.

Waste bunker:
Capacity:   16,000 cubic meters
Crane systems:  3 (two in operation, one in reserve)
Grab load:  approx. 3.5t
Extinguishing system: ceiling foam, foam, water cannon

Kiln lines (KL):
Average annual throughput:  450,000 t
Quantity:    4
Throughput per hour:  KL 1-3 =12.5 t/h, KL 4 = 28 t/h (calorific value 10.5 MJ/kg)
Fire grate:    counter-flow transfer grate, partially water-cooled
Combustion chamber temperature: 850 to 1000 °C
Steam generation:   72 bar at 410°C, KL 1 - 3= each 42.8 t/h, KL4= 88.0 t/h,
2018 steam generation.  1.63 million t

Turbines:
Type:   Extraction condensation
Quantity:  3
Output:  2x11 MW, 1x32 MW
Steam processing 2018: approx. 1,500,000 t
Power generation 2018: approx. 220,000 MWh

District heating:
Heating condensers
Quantity:  3
Power:  12 MW each
Decoupling in 2018: approx. 73,300 MWh

Flue gas cleaning:
CDAS reactors:  5
Fabric filters:  4
DeNOx lines:   3
Catalyst volume:  3 x 43 m³
 
 Building of the 4th kiln line

Contact
ZMS Zweckverband Müllverwertung Schwandorf
Alustr. 7
D - 92421 Schwandorf

phone:+49 9431 631500

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