Significant increase in overall efficiency + + + CHP unit equipped with SCR catalytic converters

The CHP specialists from ETW Energietechnik in Moers have delivered two new cogeneration units for the municipal biogas plant in Backnang-Neuschöntal, Germany. The two old Rems-Murr waste management gas engines (AWRM) were replaced after 65,000 operating hours and over eight years of operation.

Significant increase in efficiency
ETW dismantled the used CHP engines, each with 800 kilowatts, for this purpose. Two new, larger gas engines with an electrical output of 1560 and 1200 kilowatts were installed at the same location. Compared with the replaced old units, the change means a significant increase in efficiency: while the used CHP units still had an electrical efficiency of 40.4 percent, this is now 42 percent. The overall efficiency is now around 85 percent.

Admixture of fermentation residue exhaust air into the combustion air
„A further leap in efficiency is achieved by adding fermentation residue exhaust air to the combustion air of the gas engines. This was the first time that we have equipped an ETW system in this way,“ reports Alexander Szabo, the responsible sales manager at ETW Energietechnik. The processed fermentation residue exhaust air extracted from the liquid fertilizer storage tanks and the sedimentation basin of the biogas plant is fed into the combustion air supply of the gas engines and used especially for this pilot project. To avoid an ignitable mixture in the combustion air, the fermentation residue exhaust air is continuously monitored with a gas analysis. In addition, expected legislative changes with regard to the mandatory use of residual methane in the fermentation residue exhaust air are already being met. This system was designed by the planning company Ingenieurgruppe RUK GmbH from Stuttgart.

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Equipped with SCR catalysts
According to the current 44th BImSchV (Federal Immission Control Act) of 13 June 2019, CHP plants must comply with a NOx limit value of
<100 mg/Nm3 with 5 percent reference oxygen from 2023 onwards. In order to avoid later, costly conversions of the exhaust system, both block-type thermal power stations have already been equipped with modern SCR catalytic converters. In order to comply with the stricter limit values, only minor retrofitting will have to be carried out later as a result of modern exhaust gas purification.>
Surcharge for process, measurement and control technology
AWRM hopes that the exchange will enable it to make CHP operation more variable in the future by increasing engine output while maintaining the same amount of gas throughout the day. In addition, the waste management company is expecting an increase in the amount of electricity fed into the public grid.
In addition to the CHP plants, ETW was also awarded the contract for the entire pro- cess, measurement and control technology (EMSR). In addition, ETW will also supply the gas wash drying plant for the fermentation residue exhaust air. If both lots are combined, this is one of the largest orders in ETW Energietechnik‘s 20-year history.