Desulfurization of Low Temperature Char by Partial Gasification

Abstract

A considerable amount of literature has developed on the desulfurization of coke by treatment with hydrogen, steam, and other gases.The published work has been concerned largely with the desulfurization of high temperature coke in contradistinction to the work recorded here on low temperature char.The previous investigators were chiefly interested in the development of procedures for desulfurizing hot coke before it was pushed from the oven. These procedures were empirical, and no systematic investigation has been made of the effect of process variables on the kinetics of the desulfurization process. In particular, the effecte of three important variables have been lackingnamely, pressure, carbon burnoff, and hydrogen-steam ratio.Some of the more pertinent of the previous work is reviewed below.Gurarii (4) investigated the effect of temperature over the range of 800" to 1200" C. and particle size over the range of 2 to 15 mm. on the removal of sulfur from coke with steam and hydrogen. The efficiency of removal of sulfur increased with increasing temperature and decreasing particle size but in no case was more than 54% of the original sulfur removed.Mirev ( 6 ) showed the desulfurization of coke vas less effective with hydrogen than with hydrogen-steam mixtures.Monkhouse and Cobb (7) removed 94% of the sulfur from coke a t 1000" C. with hydrogen. They were able to desulfurize coke Pexton and Cobb (8) investigated the effect of carbon burnoff on the desulfurization of 1/3~ X inch coke with steam-nitrogen inlet gas mixtures in the temperature range of 800" to 1000" C. Their work showed that, a t low carbon burnoffs, pure steam is an efficient agent for the removal of sulfide sulfur but not for the removal of organic sulfur.The present investigation is concerned with a study of the effect of the process variables on char desulfurization by partial gasification with steam-hydrogen mixtures and pure hydrogen. The extrapolation technique described earlier ( 2 ) in connection with the original char-steam kinetics work was also employed in this work. Data were thus obtained that relate the efficiency of desulfurization to a definite value of the gas composition and that are independent of the physical characteristics of the equipment employed.The variables studied and ranges over which they were investigated are as follows:This work has been reviexed by Lowry (6). c to the same extent at 800' C. with steam and hydrogen.

Rate of reduction of pyrrhotite in hydrogen

“…This can be tested by using the following mass-transfer equation, assuming a negligible amount of H2S in the H2 stream. ~j q%s )e JH2S = D12 2r o RT [1] where JHzS ~ flux of HzS through the gas-film boundary, Dlz = interdiffusivity of H a-HzS , r o = average radius of the pyrrhotite spheroids, (p H2S) e = equilibrium partial pressure of H2S for the iron-pyrrhotite equilibrium at 1 arm Ha, R = gas constant, T = temperature, Nu = average Nusselt number.…”

“…7 The loss of sulfur calculated from Eq. [1], for masstransfer control, is shown by the broken lines in Figs.…”

“…E x p r e s s i n g Eq. [1] in t e r m s of f r a c t i o n a l sulfur r e m o v a l , and r e p l a cing (PH2S) e by (PHzS)s, gives F 3 Dzz lq~ t -2 pr2oR-----~ /(PH2S)s dt [5] Differentiating Eqs. [3], [4], and [5] with r e s p e c t to…”

Evolution of hydrogen sulfide in a fluidized bed coal gasification reactor

“…Coal decomposition and secondary gasification reactions also lead to the formation of other sulfur gas species including carbonyl sulfide (COS), carbon disulfide, and various thiophenes and mercaptans. Studies of coal desulfurization chemistry have been reported by Zielke et al (1954) (1977), Huang and Pulsifer (1977), Attar (1978Attar ( , 1979, Torrest and VanMeurs (1980), and Yeboah et al (1982), and kinetic studies of H2S evolution have been performed for coal pyrolysis (Solomon, 1977;Lester et al, 1982;Attar and Messenger, 1983) and coal hydrogasification (Vestal et al, 1969(Vestal et al, ,b, 1972; ; Yergey et al, 1974).…”

Desulfurization of Coal in a Fluidized-Bed Reactor

“…Unfortunately the hydrodesulfurization of coal is inhibited by hydrogen sulfide in the gas phase which severely limits the concentration build-up of hydrogen sulfide (5,8,9,10).…”