Conversion of Sulfur during Pulverized Oxy-coal Combustion

Abstract

On the basis of experiments in the Chalmers 100 kW th oxy-fuel test facility, this study presents an analysis of sulfur chemistry of pulverized lignite combustion, comparing oxy-fuel and air-fired conditions. Four test cases were investigated: an air-fired case, two oxy-fuel cases with dry recycling (30 and 35 vol % O 2 ), and one oxy-fuel case with wet recycling (43 vol % O 2 on a dry basis). The amounts of sulfur in the flue-gas, ashes, and condensed water from the condenser were quantified, and a sulfur mass balance was established. The composition of the ashes and the ash-forming matter in the fuel was analyzed. The ashes were investigated by X-ray diffraction, while the size of fuel and ash particles was determined by laser diffraction. In general, the results show that the lignite has a high sulfur self-retention by ash, especially in oxy-fuel combustion. The experiments also show that the conversion of fuel S to SO 2 from oxy-fuel combustion is around 35% lower compared to air-fired conditions, whereas the flue-gas concentration of SO 2 is higher in oxy-fuel combustion because of the absence of air-borne nitrogen.

Measurement and Modeling of Particle Radiation in Coal Flames

“…The lignite is pre-dried and milled to an average diameter of 40 μm; details on the fuel and ash are presented by Fleig et al 30 All measurements were performed in the high-temperature zone of the flame, 384 mm from the burner. Total radiation intensity, spectral intensity, temperature, and gas composition profiles were measured by traversing the water-cooled probes radially through the furnace.…”

The influence of air and oxy-fuel combustion on fly ash and deposits

“…This increase is caused by higher SO 2 concentrations in oxy-fuel combustion without recycle desulfurization, compared to conventional air-fired conditions. The increased SO 2 partial pressures in the oxy-fuel flue gas stabilize sulfates (most importantly: CaSO 4 ) which leads to higher sulfur capture in ash and deposits and lower energy based SO 2 emissions [14][15][16][17][18]. Assuming no air ingress and the same O 2 exit concentrations for air and oxy-fuel combustion, the expected rise of the SO 2 concentrations when switching from air to oxy-fuel combustion can be calculated (equations can be found in [4]): For example with an exit O 2 of 4 vol%, for the "OxyPP" lignite ( Table 1) an increase of the SO 2 level (on dry basis) by a factor of 6 can be expected.…”

Particle composition and size distribution in coal flames – The influence on radiative heat transfer

“…The black colour corresponds well with soot particles, which mainly consist of carbon. The ash from the Lausitz lignite has a fairly high iron content [20], which gives it a brown-red colour which also can be seen in fly ash or bottom ash samples from the same fuel. Primary soot particles, i.e.…”

“…It was also concluded that it is important to treat the gas and particle temperatures separately for accurate predictions of the heat transfer. In previous works at Chalmers a 100 kW th oxy-fuel test facility has been used in studies related to large scale combustion of solid fuels [17][18][19][20]. In one of these studies [19] a methodology based on combined measurements with a FTIR system and detailed radiation modelling was used to estimate the amount of particles and the particle temperature in a lignite flame similar to the one examined here.…”