A proposal for SO2 abatement in existing power plants using rich in calcium lignite

Abstract Under current European legislation for the abatement of SO 2 emissions and the strict ELV after 2016, existing power plants need to apply flue gas desulphurization technologies. For the majority of the units operating in Northern Greece and elsewhere in the Balkans, wet FGD is not the desired option due to the high capital investment involved and the limited service life of the units (less than 20 years). The answer to the dilemma (opt out or new investment) seems to be a solution that comes from the rich calcium lignite of the region. Although local lignite is of low calorific value and loaded with mineral matter and high moisture, it carries a high calcium oxide content part of which is in the form of limestone. The calcareous fly ash is rich in free lime and under certain conditions full desulphurization of the flue gas is already achievable. The desulphurization efficiency of the flue gas due to calcium in lignite is at an average of 80% and it only needs to be boosted to 96% in order to achieve SO 2 emission levels below 200 mg/Nm 3 (dry, 6% reference oxygen). The scope of this research work is an effort to study the effect of the so called “natural desulphurization” and have its efficiency characterized in terms of certain lignite physical parameters. Under proper mixing and homogenization of the lignite feed to the power plants, the peak SO 2 emissions can be smoothed out. Further desulphurization of the flue gas can be achieved by several dry FGD techniques already investigated in Greece and elsewhere [1] . Dry FGD is reported to have an efficiency limitation of 80% in the cool side of the combustion process (after LUVO). SO 2 emission concentrations in the vicinity of 1.000 mg/Nm 3 can by cooped with low investment dry FGD installation (with multiple injection points if required). Actual operation data show a clear relation between power load and flue gas velocities in the ducts as well as SO 2 emission concentrations. A feasibility study carried out for a dry FGD installation is compared to wet FGD technology. It turns out that if lignite feed homogenization is employed, power plants can afford a compromising solution with power load losses in case of peak SO 2 emissions and dry FGD installations instead of the classic and expensive wet FGD solution.