Manganese-based sorbents for coal gas desulfurization Page: 4 of 13
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The intent of this study is to perform a preliminary screening on a particular Mn-based
sorbent, CST-939 (from Chemetals), for hot gas desulfurization. The purpose of the pre-
liminary screening is to determine which temperature and type of coal gas this sorbent
demonstrates the greatest capacity and efficiency for sulfur removal.
The first two sets of experiments, tests CST1 and CST2, were conducted with simulated
KRW gas containing 2,000 ppmv H2S and 871 and 343 C (1,600 and 650 F), respectively.
Due to the tremendous capacity of the sorbent, these experiments required as long as 75 hours
to achieve breakthrough (breakthrough is defined as 200 ppmv H2S in the outlet gas). There-
fore, the later experiments were conducted with simulated KRW gas (or Shell gas) containing
30,000 ppmv H2S to decrease the time required for breakthrough. A set of six experiments,
three with KRW gas and three with Shall gas, were conducted for 1.5 cycles each at tempera-
tures of 343, 538, and 871 C (650, 1,000, and 1,600 F). A fresh sample of the sorbent was
used for each set of experiments.
During one of the early experiments (test CST2) using 2,000 ppmv H2S, the regeneration tem-
perature was ramped from 343 C (650 F) to 871 C (1,600 F) to determine the lowest tem-
perature that may be sufficient for regeneration with 50 mol percent air/50 mol percent steam.
The extent of regeneration was indicated by the amount of SO2 given off at each temperature.
Sulfur dioxide as high as 3.0 volume percent was given off after 1/2 hour on-stream at
343 C (650 F), as shown by gas chromatographic analysis, but the concentration then
dropped off rapidly and regeneration was not sustained at this temperature. A relatively small
amount of SO2 was released at 538 C (1,000 F). The rate of regeneration finally increased
at 649 C (1,200 F), at which temperature concentrations as high as 23.8 percent by volume
SO2 were measured. The additional SO2 that was released at 760 C (1,400 F) was minimal.
Finally, when the sorbent bed was raised to a temperature of 871 C (1,600 F), significant
quantities of SO2 were released, giving a concentration as high as 2.2 percent by volume.
Since MnSO4 decomposes in air at an atmospheric pressure of 850 C (1,562 F), it is not
surprising that additional sulfur was released after heating the sorbent to 871 C (1,600 F).
It was concluded that 871 C (1,600 F) would be the best temperature for air-steam regenera-
tion of the sorbent.
During the second sulfidation of the CST2 series of experiments described above, it was
noted that a significant amount of SO2 was released during the first hour on-stream. This
indicated that regeneration was not complete, even after using the air-steam mixture at 871 0C
(1,600 F). Another set of experiments (CST3) was conducted in which the first regeneration
was conducted with air-steam at 871 0C (1,600 F) and the second regeneration was per-
formed in the same manner, except the oxidative regeneration step was followed by a reduc-
tive regeneration step. Reductive regeneration was carried out with simulated KRW gas with-
out H2S for 11 hours. The result of the reductive regeneration was that no SO2 was detected
during the first 2-1/2 hours on-stream and no higher than 3.0 ppmv was detected afterward.
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Gasper-Galvin, L.D.; Fisher, E.P. & Goyette, W.J. Manganese-based sorbents for coal gas desulfurization, report, December 31, 1996; Morgantown, West Virginia. (digital.library.unt.edu/ark:/67531/metadc687536/m1/4/: accessed September 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.