Biomass Co-Firing Retrofit with ROFA for NOx Reduction
Brian Higgins1, Li Yan1, Hani Gadalla1, John Meier1, Tore Fareid1, Guisu Liu1, Mirosław Milewicz2, Arkadiusz Repczyński2, Michael Ryding3, Włodzimierz Blasiak3
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1Nalco Mobotec, 2540 Camino Diablo, Walnut Creek, CA 94597 USA
2Zespół Elektrociepłowni Wrocławskich, KOGENERACJA S.A., Łowiecka 24, 50-220 Wrocław, Poland
3Nalco Mobotec Polska, Przemyslowa 55, 43-110 Tychy, Poland
Pol. J. Environ. Stud. 2010;19(6):1185–1197
Nalco Mobotec’s Rotating Opposed Fired Air (ROFA®) system has been installed on a RAFAKO OP-230 boiler to facilitate the co-firing of biomass by improving combustion performance and biomass burnout in the upper furnace. High velocity air is injected through multiple nozzles, resulting in strong turbulent mixing between the flue gas and fuel. The intention of this high-pressure ROFA air system is to provide better chemical interaction, increased volumetric utilization, and improved combustion. The boiler is a 50-MW corner-fired boiler burning Polish hard coal with sulfur content around 0.6% and fuel-bound-nitrogen content around 1.1%.
Prior to the ROFA installation, there was an existing SOFA system. At the same time as the ROFA installation, RAFAKO installed new low-NOx burners (LNB) and a Nalco Mobotec consortium installed a complete biomass handling system with the capability of firing 45% of the energy input as biomass. EDF’s motivation to co-fire biomass is to reduce greenhouse gas emissions. Electricity produced from renewable fuel sources is eligible for a rate increase in Poland.
The combined effect of LNB, SOFA, and ROFA results in NOx emissions below 200 mg/Nm3, a reduction of 43% from the LNB/SOFA operation (350 mg/Nm3) and 63% from the pre-LNB with the SOFA-only baseline (540 mg/Nm3). The improved combustion due to the mixing introduced by ROFA maintains loss-onignition (LOI) below 5%, required for continued fly-ash sales. Simultaneously, the CO emissions were held below 100 mg/Nm3 with ROFA.
Biomass co-firing results in displacing as much as 45% of CO2 from nonrenewable fuels. The ROFA system allows the combustion of the biomass with no noticeable increase of CO and LOI. NOx emission is lower with biomass co-firing. Similarly, because of the lower sulfur content in biomass, co-firing results in a 36% reduction in SO2 emissions when firing 45% biomass.