Numerical and experimental development of integrated electrostatic precipitator concepts for small-scaled biomass furnaces

Abstract

Downstream electrostatic precipitators (ESP) represent the state of the art separation technology in medium and large biomass combustion plants. However, these technologies are often difficult to implement in smaller furnaces due to economic aspects and space constraints. This study deals with the integration of ESP systems into the heat exchanger of a small-scale biomass furnace. In order to accelerate the costly and time-consuming development process, preliminary numerical investigations of different ESP configurations were conducted using computational fluid dynamics (CFD). A prototype of the most promising variant were manufactured based on the results of the CFD simulations and experimentally tested with regard to the collection efficiency. In addition to the full load behaviour of the firing system, further test arrangements with several partial-load situations were tested to analyse the particle precipitation under realistic plant conditions with regard to flue gas properties and flow conditions. Furthermore, the collection efficiency for the combustion of different types of biomass was evaluated. Both discontinuous and time-resolved aerosol measuring methods are used to determine particulate matter (PM) emissions. Discontinuous measurements show that at least 55% of the PM2.5 particles are separated with the integrated ESP, both at full and partial load operation of the boiler, irrespective of the fuel used. In the partial load range, collection efficiencies for PM2.5 can be increased by up to 75%, depending on the fuel being fired. In order to enable a more precise observation of the separation behaviour with regard to particle size, additional continuous high-resolution aerosol measurements were carried out for a selected fuel (wood chips w=20%). The results show that over 50% (full load) and over 80% (part load) of small particles (PM1) can be separated.