Large Volume Inorganic Chemicals - Ammonia ... - ammk-rks.net

Chapter 44.4.15 Energy recovery and exportDescriptionTable 4.18 shows energy considerations for double contact plants with different plant setup incomparison with a single contact plant. Table 4.17, Table 4.19 and Table 4.20 show examplesfor energy balances of double contact processes. Please note that the examples given in Table4.17 and Table 4.19 include energy release from production of the inlet gas (sulphur burning),the other examples are based on cooled inlet gas.The input of the starting materials provides the energy for the production of sulphuric acid. Anessential feature of the double contact process is the autothermal operation of the plant, which ispossible in modern plants with a minimum inlet SO 2 concentration of 4 – 4.5 % v/v. Up to 67 %of the process waste heat, which is released from a double contact plant on the basis of sulphurburning, is recovered as high pressure steam from burning gases and from the reaction heat ofthe contact process. Waste heat released from acid cooling represents about 30 – 40 % of thetotal process waste heat. A thermal efficiency of 85 – 90 % can be achieved by using waste heatreleased from the acid cooling for drying processes or for the production of low pressure steamwith a special heat recovery system.For a modern single contact plant, the minimum requirement for autothermal operation is a SO 2inlet concentration of >2 % v/v [59, Outukumpu, 2005].If gas cleaning processes are required (e.g. metallurgical off-gases), the cold raw gases arereheated to the reaction temperature of the catalyst by using waste heat from the contact tower.Achieved environmental benefits• a modern double contact plant (sulphur burning) can export about 6 GJ/ tonne H 2 SO 4• roasting of ZnS: production of 0.6 – 1 tonne HP steam (40 bar/400 ºC) per tonne rawmaterial.Cross-media effectsNone believed likely.Operational data• input of electrical power: 35 – 50 kWh/tonne H 2 SO 4• pyrite roasting with air releases 13 GJ/tonne pyrite.ApplicabilityGenerally applicable. The amount of recoverable energy and export options depend on theindividual situation (mainly SO 2 source and process). If no energy consumer is available,recovered energy can be partially converted into electrical power.For recovered heat from acid cooling, there are three main applications [59, Outukumpu, 2005]:• delivering hot water for municipal/domestic heat supply systems• phosphoric acid concentration• delivering hot water for industrial utilisation, such as filter washing, sea water distillation.Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 195