Reducing Power Production Costs by Utilizing Petroleum Coke

Abstract

EXECUTIVE SUMMARYThe effects of blending petroleum shot cokes with Powder River Basin (PRB) subbituminous coals on grindability, combustion reactivity, fouling/slagging, and electrostatic precipitator (ESP) fly ash collection efficiency were investigated over a 2-year period. Testing was conducted using three different laboratory-scale downfired combustion systems. Fly ash and deposit samples were analyzed using a variety of techniques, including inductively coupled plasma-atomic emission spectroscopy, x-ray diffraction, x-ray absorption fine-structure spectroscopy, wavelengthdispersive x-ray fluorescence spectrometry, scanning electron microscopy, electron probe microanalysis, and digital image analysis.A PRB subbituminous coal with a Hardgrove grindability index (HGI) of about 56 at 26 wt% moisture and a petroleum shot coke with an average HGI of 38 were used for testing the effects of parent fuel hardness on PRB coal-petroleum coke blend grindability. Samples of the PRB coal, petroleum shot coke, and coal-coke blends of 95:5 and 85:15 (on a weight basis) were pulverized under identical conditions. Ni and V analyses of three size fractions (<45 µm, $45 µm but <75 µm, and $75 µm) for each pulverized fuel indicate that the finest particle-size fraction of the petroleum coke is significantly enriched in V and Ni, whereas V and Ni are uniformly distributed among the three particle-size fractions of the pulverized PRB coal. The finest particle-size fractions of the coal-coke blends are not enriched in V and Ni relative to their coarser size fractions, suggesting that the softer Ni-and V-depleted coal particles are preferentially fractioned into the finest size fractions during pulverization.Combustion kinetic testing in a drop-tube furnace of a PRB coal, petroleum coke, and an 80 wt% PRB coal-20 wt% petroleum coke blend indicates that the parent fuels essentially burn independently of each other. It was demonstrated that the combustion kinetics of a given coalpetroleum coke blend in the drop-tube furnace can be predicted from those of the parent fuels because of the two-stage combustion process.Measurements of deposits (i.e., initial slagging temperatures, crushing strengths, and ash fouling deposition rates) produced from burning PRB coal-petroleum coke blends (coke blends of 0%, 10%, and 20% on a weight basis) in a drop-tube furnace under slagging and high-temperature fouling conditions indicate that petroleum coke blending with PRB coal impedes the rate of fouling deposit growth but promotes slagging and slag deposit strength. Although petroleum coke blending slows the rate of ash fouling deposition, it promotes ash sulfation and the formation of an anhydrite-rich base layer on tube surfaces.Testing of a PRB coal and two (95:5 and 85:15) coal-coke blends in a 42-MJ/hr (40,000 Btu/hr) downfired combustion system indicates that the primary effect of petroleum coke blending on flue gas composition is a significant increase in sulfur concentration. Sulfur speciation analyses using U.S. Environmental Protection Agenc...