Facility studies of novel sodium bicarbonate and urea dry sorbent injection system for low-cost adaptation of peak power boilers to low NO_X and SO_X emission limit operation

The transition period in the energy transition towards zero emissions means that, especially in the case of district heating plants, there is a problem of temporarily using the existing solid fuel boilers for peak operation in order to ensure the reliability of heat supply. The potential of the dry sorbent injection method (DSI) utilizing sodium bicarbonate and dry urea to reduce SO₂ and NO_X emissions from a coal-fired boiler for peak operation with an emission limit of <200 mg/Nm³ was investigated. NaHCO₃ was injected into the second boiler pass and a non-standard high-temperature area - directly into the combustion chamber and the non-operating mill feeder. The maximum SO₂ reduction achieved, with a base level of approx. 717 mg/Nm³ down to 38 mg/Nm³ for a average capacity of 45.6 MW_th, was 94.70 %. The reduction achieved through the use of dry urea mainly proceeded from a value of approx. 400 to as low as 135 mg/Nm³, while maintaining a low level of NH₃ slip. The principal advantage of dry denitrification is the absence of water injection, which minimizes corrosion risk and does not reduce boiler efficiency. The chemical properties of fly ash were determined to ensure its safe storage and potential use in accordance with the circular economy rules. The content of Na₂SO₄ as a desulfurization product was indicated. An economic analysis of the investment and operating expense of a low-cost installation, adapting power boilers to peak operation with NO_X and SO_X emission limits <200 mg/Nm³ using dry sorbents was carried out.