Case Analysis of Energy-saving Retrofit for Steam Superheater in Styrene Plant
With the advancement of the national energy conservation and emission reduction policies,the desulfurization measures for fuel gas are becoming increasingly popular,making it possible to further reduce the exhaust gas temperature of the heating furnace and improve the overall thermal efficiency.The energy-saving retrofit scheme for the steam superheater in the styrene plant proposed in this paper utilizes the reserved space in the convection section of the original steam superheater.Combining with the plant process flow,by adding furnace tubes to the boiler water preheating section of the steam superheater,the heat transfer area between the boiler water and the flue gas is increased,while the feed temperature of the boiler water is reduced,thereby reducing the exhaust gas temperature of the steam superheater and further recovering the waste heat in the flue gas.The reduction of the feed temperature of the boiler water is achieved by installing a second preheater,which uses the boiler water to heat the process condensate feed of the condensate stripping tower.The increase in the temperature of the process condensate can also reduce the steam consumption injecting to the mixer.Taking a 300,000 tons/year styrene plant as an example,compared with the conventional waste heat recovery method for flue gas,the investment in this energy-saving retrofit scheme can be reduced by approximately two-thirds,with a static investment payback period of about 22.5 months.This retrofit scheme has important reference for similar styrene plants.
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