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Walheim sewage sludge treatment plant

How a sewage sludge combined heat and power plant works

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A schematic diagram of the sewage sludge recycling plant in Walheim (subject to change until completion). (Only available in German)

The planned plant essentially consists of a closed storage bunker, a fluidized bed furnace for incinerating the sewage sludge with a downstream waste heat boiler and a flue gas cleaning system.

The flue gas produced during incineration flows into a waste heat boiler. This generates hot steam that drives a downstream steam turbine and in turn generates electricity. The cooled flue gas then reaches the multi-stage flue gas cleaning system. This is also where the ash is separated, from which the phosphorus is later recovered.

Any potential extraction for district heating takes place in the so-called vapor processing area. The vapors produced during the drying of the sewage sludge are cleaned and condensed here. Up to four megawatts can be extracted for district heating, enough to supply around 300 households with sustainable energy..

The plant does not smell

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One important issue concerns questions around potential odor pollution. This can be 100 percent ruled out with the state-of-the-art plant: The combustion air is sucked out via a reception and storage bunker during operation of the plant, creating a vacuum, which, together with an airlock system, prevents odors from escaping outside.

Even if the plant is idle or out of service for an overhaul, the exhaust air is guided through a filter system. In such cases, odor pollution will also be reliably prevented.

Following storage, the sewage sludge is dried. Its water content is reduced to such an extent that it can be burned in an autothermal process in a so-called fluidized bed furnace at temperatures of up to 950 degrees Celsius. Organic matter is also completely incinerated at these temperatures.

Incineration as the method of choice

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Sewage sludge is already being incinerated and added to the fuel in coal power plants. Special incineration plants, such as those planned for Walheim, are notably superior to this method. For one thing, they are designed for low-emission processing (in other words, they significantly cut carbon emissions). Furthermore, the ash produced during incineration contains valuable phosphorus that can be recycled – as even required by legislators from 2029/2030. In modern plants, the ash containing the phosphorus can be better treated after the incineration process and then sent to specialized companies for further processing. As things currently stand, this is not possible when the sewage sludge is incinerated with other fuels in a coal power plant.

Technical data for Walheim sewage sludge recycling plant

Function
Specific figure
Function
Plant capacity
Specific figure
Around 180,000 t/a of dewatered sewage sludge (equivalent to 50,000 t/a of dry matter) and around 5,000 t/a of dried sewage sludge
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Dry matter content of delivered sewage sludge
Specific figure
20–30% dry matter
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Throughput
Specific figure
approx. 20 metric tons of dewatered sewage sludge per hour
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Operating time
Specific figure
Over 8,000 hours per year
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Electrical outputv
Specific figure
approx. 1.5 megawatts electrical
Function
Local heating
Specific figure
up to 4 megawatts thermal
Contact

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