Planning of a urea injection system for nitrogen oxide reduction using the SNCR process in decentralized biomass burners

This study examines concepts for the dosing and injection of urea solution for the selective non-catalytic reduction (SNCR) of nitrogen oxides in small- and medium-sized biomass combustion systems. The goal is to develop a cost-effective and energy-efficient urea injection system for a combined flue gas cleaning system. To this end, the requirements for the dosing and injection system for a pilot plant with a thermal output of 25 kW were first derived. For the operating condition under consideration, the required AdBlue flow rate is approximately 0.62 to 1.85 ml/min. Based on a review of the literature and market research, various concepts for the direct and indirect atomization of urea solution, as well as for the external generation of ammonia, were examined. The options were evaluated in terms of cost, energy consumption, droplet distribution, controllability, and their susceptibility to deposits and clogging. A discontinuous, pulsed urea injection using a single-component nozzle and external ammonia generation from a urea solution in an electrically heated reactor were identified as particularly suitable. Test setups were developed for both concepts, which can be used to experimentally investigate, in particular, dosing accuracy, atomization, thermal stability, and the tendency to form deposits.