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Plant hikes sulfur recovery with sub-dew point modification
Existing three-stage sulfur plants can be modified to a sub-dew point mode with a minimum of capital investment and a recovery improvement of 2-4%.
Modifications of a conventional two-stage Claus plant would involve addition of a new converter, thus increasing capital investment. But the recovery improvement would be as high as 6-7%. The Esso Quirk Creek conventional three-stage sulfur plant, built in 1971 to recover 96%, was modified in late 1987 to meet a sulfur-recovery demand of 98%. Current operations approach 300 ton/day.
Claus-plant configuration. The existing Claus plant consisted of three converter stages.
Total acid gas is oxidized to the correct level in a combustion chamber and heat is removed through a water-tube boiler. A hot gas (600|-610| C.) takeoff from the boiler is used to reheat the first and second Claus converters. Steam (400 psig) is generated in the waste-heat boiler (WHB).
Gases not used for reheat are cooled to approximately 275| C. in a shell and tube condenser, generating 55-psig steam.
The third converter used a gas/gas exchange for reheat, with the outlet from the second converter as the source of reheat. Steam (55 psig) was generated in the second and third condensers (effluent for No. 1 and No. 2 converters) and boiler feed-water (BFW) preheat was used for the final condenser from No. 3 converter.
Cold-bed configuration. The MCRC ("Maximum Claus Recovery Concept") process was selected as the scheme for increasing the recovery. The conventional two-bed scheme, consisting of one bed operating as a conventional Claus converter and the two remaining beds alternating between adsorption and regeneration, was selected. Position 2 and 3 alternate on a time cycle of 18 hr.
The existing plant, as physically laid out, did not lend itself to the conventional MCRC scheme. It was desirable to use the existing gas/gas exchanger as the source of reheat for the regeneration mode.
This exchanger, however, being located between the second and third beds, did not physically fit the MCRC layout where the gas/gas exchanger would be between the first and second converter. Also it was necessary to operate two condensers at a lower temperature for final cooling of effluent from the regeneration bed and the outlet for the bed on the adsorption mode.
The existing BFW exchanger would function for one case condition; however, the other condenser was used to generate 55-psig steam (150| C.) and as such would be much too hot for the desired cooling from the regeneration bed or …