(Fiona Austin, Sarah Forrest, Jane McTavish, Steve McGahey, Sven Raz, Josh Evans)
SULFUR REMOVAL BEFORE FUEL COMBUSTION
By removing sulfur before burning the fuel, one can achieve two benefits: (a) convert S into H2S (instead of SO2) and thereby facilitate S capture (because the acidic H2S is easily absorbed in a basic solution); and (b) increase the overall efficiency of the power cycle, e.g., using IGCC (integrated gasification/combined cycle) technology. Amid concerns about both global warming and conventional air pollution, this may well be the predominant trend in electricity generation in the 21st century.
Problem 5.7 in Benítez (op. cit.) illustrates the high efficiency of S capture in such a power cycle, whose overall efficiency (i.e., (electricity produced)/(heating value of gasifying primary fuel) is said to be 40%. Here is a summary of the solution.
Feed rate of primary fuel (orimulsion, 2.7% S, 27.2 MJ/kg):
Sulfur entering the process:
Sulfur leaving the process:
Sulfur removal efficiency = (75,060–37.8)/75,060 = 99.95% (very high indeed...)
Sulfur production: 75.06-0.038 = 75.0 tons/day
FLUIDIZED BED COMBUSTION
This is an attractive technology because it can minimize both NOx emissions (by virtue of lower combustion temperatures made possible by enhanced heat transfer) and SOx emissions. The latter objective is achieved by using a sulfur capture agent in the fluidizing medium. The key issue here is the efficiency of sulfur capture, which is best expressed as moles of capture agent (e.g., a Cu-, Na- or Ca-containing compound) per mole of S captured.
Problem 5.21 in Benítez (op.cit.) addresses this issue for the case of copper-impregnated alumina particles. The summary of the solution to parts (a) and (c) is presented in this Mathematica notebook.
FLUE GAS DESULFURIZATION: GENERAL DISCUSSION
Analysis of the stoichiometry of the reactions of sulfur capture is a powerful tool for preliminary screening of the various options that are commercially available. Problem 5.17 in Benítez (op.cit.) illustrates the key concepts. See Task 3 report for the solution.
lrr3@psu.edu (revised 11/3/98)