Project E-MinBHKW: Development of an aftertreatment system to minimize emission of micro and nano CHP plants

 

 

 

At the beginning of 2020, the joint project funded by the Sächsische AufbauBank (SAB) started to develop an aftertreatment system to minimize the pollutant emissions of micro and nano CHP plants. Project partners are the Chair of Reaction Engineering at the IEC, Argomotive GmbH (Dresden) and Autotechnik GmbH from Johanngeorgenstadt.

Combined heat and power units (CHP) are modularly designed systems for the simultaneous generation of electrical energy and heat, which are preferably operated at the location of heat consumption. Combined heat and power plants use the principle of combined heat and power generation (CHP). The advantage of CHP plants is the high degree of utilisation (up to 90%) of the fuel used. CHP plants are divided according to the electrical output into the following classes: nano (up to 2.5 kW), micro (up to 20 kW), mini (up to 50 kW) and large scale CHP. Modules of the nano and micro CHP class are used for applications in single and multi  family houses or for supplying several objects by means of a local heating network.

Cogeneration plants in the nano and micro range have become increasingly important in recent years. A large number of manufacturers with different types of cogeneration units (fuel, engines) have established themselves on the market, partly due to numerous subsidy programmes.

Combined heat and power plants with a capacity of 1 MW or more are generally subject to the Technical Instructions on Air Quality Control (TA Luft), which define the emission limits. The TA Luft does not apply to cogeneration plants with a capacity of less than 1 MW, but general requirements for cogeneration plants are applied to plants not subject to licensing. According to these, all measures must be taken that are possible according to the state of the art in order to avoid air pollution through the emission of pollutants. For this reason, subsidy programmes often assume that in order to receive state subsidies, emissions must be minimised in accordance with the state of the art. Special bonus payments for CHP plants with particularly low pollutant emissions are based on the 50% value of the TA Luft specifications for NOx and CO.

One possible way of reducing pollutant emissions and thus improving the immission situation at the operating site of the CHP plant is to use efficient exhaust gas aftertreatment systems. As a rule, current CHP units are equipped with a maximum of one diesel oxidation catalyst (DOC). With a general tightening of the emission limits, it can be assumed that even micro and nano CHP units will not be able to meet the required limits in the future without efficient four-stage exhaust aftertreatment. Here, the applicants want to break new ground and achieve an innovation in the form of a combined cleaning system that simultaneously reduces the pollutants CO, HC, NOx and particles (4-way system). The innovative character is based in particular on the development of a denitrification technology (SCR), which has not existed in the CHP classes under consideration up to now, coupled with particle reduction by means of filters. A major focus is the research, development and testing of a novel SCR coating, which is preferably applied to a filter substrate.