Our first Stirling CHP was successfully put into operation at the central sewage plant Niederfohna (Saxony) by the company WUDAG. The sewage plant can serve 40,000 residents and cleans domestic and industrial wastewater biologically according to the SBR procedure (Sequencing Batch Reactor).

WUDAG bought the engine, combustion chamber and operating controls from Stirling Denmark and independently designed the burner management system. WUDAG then had the task of building a sewage gas line and integrating the plant into the existing heating and process control system. The plant was successfully put into operation in May 2010 at the sewage plant Niederfrohna.

The generated sludge is stabilised anaerobically. The sewage gas generated contains between 50 and 60% methane. On its way from the gas storage to the Stirling CHP it only passes through a biological desulphurisation and two condensate separators even though it is rich in siloxanes. Due to the external combustion of the Stirling CHP no further sewage gas treatment, e.g. with an activated carbon filter, is necessary.

The combustion air is preheated according to the counter-current principle in the combustion chamber and therefore the waste gasses reach a medium temperature of about 425°C at the exit of the combustion chamber. A downstream waste gas heat exchanger cools the waste gasses further down to about 100°C. The cooling of the Stirling engine, the combustion chamber as well as of the waste gasses generates up to 120 kWtherm of thermic power. The heat is mainly used for the temperature control of the mesophilic run sewage sludge reactor fermenter and also for heating the company building.  The electricity generated according to the Stirling principle of about 35 kWel is solely used to cover the energy demand of the sewage plant.  

The operation of the Stirling CHP is laid out for a base load protection. Due to the high efficiency even in partial load operation the Stirling CHP can be run continuously. The control of the sewage gas range fed into the plant, regulation of the combustion air as well as the whole plant operation is done automatically. It is integrated into the guidance system of the whole plant. 

Stirling - Engine

Typ: SD4
Fuel: sewage gas
Methane content: 60-70 (%)
Energy input: 200 (kW)
Electrical output: 35 (kW)
Heating output: 120 (kW)
Electrical efficiency: 22-25 (%)
Plant efficiency: 90-94 (%)