Sulfur removal in advanced two stage pressurized fluidized bed combustion. Technical report, March 1--May 31, 1995 Page: 2 of 28
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EXECUTIVE SUMMARY
Second generation staged combustion processes for power generation systems such as
Advanced Two Stage Fluidized-Bed Combustion (PFBC) combined cycle plants can
achieve higher thermal efficiencies and a lower cost of electricity than a conventional
pulverized coal-fired (PC fired) plant equipped with flue gas desulfurization. Because
two-stage PFBC plants incorporate coal gasification and combustion and can use high
sulfur coals in an environmentally acceptable manner, they have the potential to expand
the marketability of high sulfur Illinois coals. Projected costs for two-stage PFBC plants
are substantially lower than comparable pulverized-coal (PC) combustion plants, especially
if air emission regulations were to require much lower SO2 emissions.
In the two-stage PFBC processes supported by the United Stated Department of Energy,
calcium-based sorbents such as limestone and dolomite are added to the first stage reactor
to capture hydrogen sulfide as calcium sulfide (CaS) in the reducing atmosphere of the
carbonizer. The partially sulfided calcium-based sorbent is transferred to the second stage
(combustor) where the unreacted calcium carbonate is reacted with SO2 and oxygen in the
oxidizing atmosphere of the combustor to produce calcium sulfate. The calcium sulfide is
also expected to react with oxygen and convert to calcium sulfate.
The partial pressure of C02 in the carbonized usually exceeds the equilibrium value for
calcination of calcium carbonate. Under such conditions, the removal of sulfur
compounds takes place through the reaction of hydrogen sulfide and calcium carbonate
(direct sulfidation reaction). The rates of direct sulfidation reaction at carbonizer
conditions were determined in an earlier ICCI-funded project (Ref. No. R93-1/2.1A-1M).
This project is a follow-up of the earlier project to determine the rates and the extent of
sulfation reactions involving partially sulfided Ca-based sorbents (containing CaS and
CaCO3), at the operating conditions prevailing in the second stage (combustor) of the
advanced PFBC processes.
A systematic study of the sulfation reactions occurring in the combustor stage of the two-
stage PFBC is necessary to improve the economic and environmental advantages of two-
stage PFBC processes by maximizing the utilization of calcium-based sorbents and
minimizing the production of solid waste materials by such processes.
The objective of this investigation is to obtain data on the rates and the extent of sulfation
reactions involving partially sulfided calcium-based sorbents, sulfur dioxide, and oxygen
under operating conditions expected in the combustor stage of the two-stage PFBC
processes.
This study will focus on the determination of the effects of sorbent type (i.e. limestone or
dolomite), sorbent particle size; SO2 and 02 partial pressures, as well as reactor
temperature and pressure, on the sulfation reactions. The rate of reaction with fully
calcined sulfided sorbents at near equilibrium C02 partial pressure will also be measured
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Abbasian, J. Sulfur removal in advanced two stage pressurized fluidized bed combustion. Technical report, March 1--May 31, 1995, report, December 31, 1995; Chicago, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc671808/m1/2/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.