Combined heat and power (CHP) and biogas upgrading technology specialists ETW Energietechnik GmbH has delivered two new cogeneration units complete with NOx abatement and process, measurement, and control technology for a 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.
ETW dismantled the used CHP engines, each with an 800 kW power output, for this purpose. Two new, larger gas engines with an electrical output of 1560 and 1200 kW respectively were installed instead.
Significant efficiency increase
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.
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, said Alexander Szabo, Sales Manager at ETW Energietechnik and responsible for the project.
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 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.
Equipped with SCR
According to the current 44th BImSchV (Federal Immission Control Act) of June 13, 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 Selective Catalytic Reduction (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.
Enable variable CHP operation
AWRM hopes that the new cogeneration units 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.
Along with the CHP plants, ETW was also awarded the contract for the entire process, measurement, and control technology (EMSR). Furthermore, ETW will supply the gas wash drying plant for the fermentation residue exhaust air.
Though the value of the orders has not been disclosed, the combination of the order lots makes it one of the largest orders in ETW Energietechniks 20-year history.