GB1408888A - Manufacture of combustible gases - Google Patents

Abstract

1408888 Sulphur-free fuel gas EXXON RESEARCH & ENG CO 8 Nov 1972 [12 Nov 1971] 52656/71 Heading C5E Sulphur-free combustible fuel gas is produced at a predetermined superatmospheric pressure from a sulphur-containing fuel, e.g. powdered coal, coal slurry, or fuel oil, by feeding the fuel into a bed of particles comprising alkaline earth metal oxide contained within a reactor, the particles being fluidized by an upwardly flowing stream of an oxygen-containing gas under a pressure substantially equal to the predetermined superatmospheric pressure, the rate of supply of the oxygen-containing gas and the partial pressure or concentration of oxygen therein being so adjusted in relation to the fuel feed rate that the oxygen supplied is insufficient for complete combustion of the fuel, whereby the fuel is partially combusted at 800‹ to 1000‹ C. to form substantially sulphur-free combustible gas and sulphur of the sulphur-containing fuel is fixed in particles of the bed as alkaline earth metal sulphide by reaction with alkaline earth metal oxide in the particles, recovering substantially sulphur-free combustible gas from the reactor bed, transferring sulphide-containing particles from a first region of the reactor bed to a first region of a regenerator wherein particles are contained and contacted with an upwardly flowing stream of an oxygen-containing gas whereby the sulphide is converted to oxide with the liberation of sulphur dioxide, the rate of supply of oxygen-containing gas and the partial pressure or concentration of oxygen therein being such that the temperature in the regenerator bed is between 1035‹ and 1300‹ C., monitoring the temperature of the regenerator bed and deriving a signal representative of the temperature, providing a heat sink material in the regenerator bed at a rate which increases with increasing temperature in the bed and which decreases with decreasing temperature therein whereby to maintain the bed temperature between 1035‹ and 1300‹ C., transferring oxidecontaining particles from a second region of the regenerator bed to a second region of the reactor bed whereby the transferred particles may be re-used in the reactor bed, and releasing offgases from the regenerator bed. The superficial gas velocity in the reactor and regenerator beds is below the superficial velocity at which substantial entrainment or elutriation of particles from the bed occurs. The reactor bed temperature is monitored and a heat sink fluid is provided in the reactor bed at. a rate which increases as the reactor bed temperature rises towards 1000‹ C. and which decreases as the temperature falls towards 800‹ C. The heat sink fluid may be water, water vapour, steam, flue gas or mixtures thereof, and may be in direct and/or indirect heat exchange with the reactor bed. The fuel feed rate may be varied in dependence with a signal representative of the demand for substantially sulphur-free combustible fuel gas, and the temperature in the, reactor bed is maintained between 800- 1000‹ C. by relatively increasing and decreasing the fuel supply rate with respect to the partial pressure of oxygen in the oxygen-containing gas supplied to the bed as the reactor bed temperature respectively increases towards 1000‹ C. and decreases towards 800‹ C. A signal representative of the temperature in the regenerator bed is employed to regulate the initiation of, and rate of, provision of heat sink fluid in the reactor bed. The heat sink material provided in the regenerator bed may comprise particles containing alkaline earth metal carbonate transferred from the reactor bed, the carbonate being formed in the reactor bed by so regulating the reactor bed temperature employing heat sink fluid that the reactor bed temperature falls to a temperature at which alkaline earth metal oxide can be carbonated by carbon dioxide in the reactor bed. The particles may be transferred from the bottom region of the reactor bed and contain alkaline earth metal sulphate from the reaction of alkaline earth metal sulphide with oxygen in the bottom region of the reactor bed, and may be passed into the regenerator bed at or near the bottom region thereof. The transfer of particles from the reactor bed to the regenerator may vary with the sulphur-containing fuel feed rate and the transfer rate may be regulated in accordance with the amount of sulphur in the fuel. The transfer of particles from the second region of the regenerator bed to the second region of the reactor bed may vary with the temperature of the regenerator bed. The composition of the regenerator off-gas is monitored, and the rate of supply of oxygencontaining gas to the regenerator bed is regulated according to the off-gas composition to control the composition of the regenerator offgas. The concentration of O 2 and/or SO 2 in the off-gases leaving the regenerator bed is monitored, and the oxygen-containing gas supplied into the regenerator bed comprises an inert diluent gas, the concentration or partial pressure of inert diluent gas being varied in accordance with the concentration of O 2 and/or SO 2 in the regenerator bed off-gases, substantially to control the concentration or partial pressure of O 2 and/or SO 2 in the regenerator off-gases. The concentration of inert diluent gas, e.g. regenerator off-gas from which SO 2 has been removed, is varied directly with any excess concentration of SO 2 over a predetermined concentration of SO 2 in the regenerator off-gas, or is a fixed proportion of the oxygen-containing gas supplied to the regenerator bed, or is supplied to the regenerator bed at, a substantially fixed rate. The superficial velocity of gas in the regenerator bed is at least sufficient to maintain the particles in the bed in a state of fluidization. The heat sink material provided in the regenerator bed may be a fluid in indirect heat exchange relationship with the regenerator bed.