Sulfur Removal During Combustion of Solid Fuels In A Fluidized Bed of Dolomite

Abstract

Sulfur removal during combustion of coal or low-temperature coal char using excess air in a fluidized bed of dolomite has been demonstrated in a continuous benchscale unit. The SO 2 produced during the combustion is fixed as CaSO4 by reaction with CaO in the dolomite as follows: CaO + SO 2 + Yz O 2 = CaSO 4. The ranges of conditions explored were calcium oxide-to-feed sulfur mol ratios in the range of 1 to 8, fluidizing velocities of 1.5 and 3.0 ft/sec, superficial gas residence times of 1 and 2 sec, and temperatures from 1700° to 1900°F, with 120% stoichiometric air at the operating pressure of 8 psig. The process was operable at all conditions studied using a highly caking Pittsburgh seam coal as well as two low-temperature chars. Desulfurization efficiency with a Ca-to-S mol ratio of 1 was 78%; at Ca-to-S ratios of 2 or higher desulfurization efficiency exceeded 90%. Continuous regeneration of the sulfated dolomite using partial combustion of carbon monoxide gas at 1950°F was also demonstrated. As high as 97% of the sulfur in the dolomite was liberated as SO 2 by this treatment giving a gas that contained SO 2 concentrations as high as 23 times that in the combustion gases. Dolomite life was investigated, with the dolomite subjected alternately to SO 2absorption during combustion and subsequent regeneration. It was demonstrated that by regeneration and re-use of the dolomite, the ultimate SO 2 capacity can be extended in excess of four times that for a once-through process. Regeneration also permits recovery of elemental sulfur by processing the SC>2-rich regenerator off-gas.

Nonisothermal Kinetics Studies of the Hydrodesulfurization of Coal

“…We have not succeeded in resolving the lowtemperature H2S evolution peak into its components at the heating rates used. Since we know two or more processes are involved, and since it is generally accepted (Batchelor, et al, 1960;Blayden, 1958; Brewer and Ghosh, 1949;Chapman and Jones, 1955;Chowlhury, et al, 1952;Curran, et al, 1958;Fuchs, 1951;Gray, et al, 1970;Mahmoud, et al, 1969;Mason, 1959;Ode, 1963;Powell, 1920;Snow, 1932;Thiessen, 1945;Wandless, 1955; Wibaut and Stoffel, 1919; Zielke, et al, 1954Zielke, et al, , 1970, that organically bound sulfur and pyritic sulfur are released as H2S at the lowest temperature in hydrodesulfurization, we designate this low temperature H2S evolution peak as Organic I and Organic II. It has been shown by Jiintgen and coworkers that application of eq 5-8 to peaks that comprised more than one process leads to kinetic parameters that are averages of the individual processes.…”

“…An excellent review of work done on this subject prior to 1932 is given by Snow (1932), while a summary of work done to about 1945 is presented by Thiessen (1945). Reports of desulfurization studies have continued to appear to the present time (Batchelor, et al, 1960;Blayden, 1958;Brewer, 1949;Chapman, 1955;Chowlhury, et al, 1952;Curran, et al, 1958;Fuchs, 1951;Gray, et al, 1970; Mahmoud, et al, 1969;Mason, 1959;Zielke, et al, 1954Zielke, et al, , 1970.…”

Reaction of sulfur dioxide with limestone and the grain model

“…The fluidized bed, with its excellent mass and heat transfer characteristics, offers attractive possibilities for efficient contact between gas and solid and complete combustion of fuel. Two most attractive schemes would be passing combustion gases through the fluidized bed of limestone or actually burning fuel within such a bed (Zielke et al, 1970). The latter alternative seems to be more attractive.…”

Simulation of desulfurization in a fluidized‐bed limestone reactor

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One of the most promising techniques of sulfur dioxide removal from flue gas is sorption using a fluidized bed of limestone. Two commonly considered schemes are the passing of combustion gases through the fluidized bed of limestone or actually burning fuel, e.g., coal, within such a bed (Zielke et al, 1970). Although the latter alternative seems to be more attractive and has been under intensive investigation (Horio and Wen, 1976;Zheng et at., 1982) the former scheme is also desirable since it can be designed to operate in conjunction with existing combustors.

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