Example PFD 1: double absorption Sulfur Burning Sulfuric Acid Plant
Example PFD 2: double absorption Metallurgical Sulfuric Acid Plant
Gas HEAT Exchanger Applications in Sulfuric Acid PlanT
Cold Exchanger
- Application: Generally metallurgical plant as shown in PFD 2.
- Basis: Low SO2 strength or autothermal case.
- Heating medium: Last cooling stage for hot SO3 gas to FAT.
- Cooling medium: 1st heating stage for incoming cold SO2 gas.
- Gas flow: Preferably SO3 down the tubes if condensation is a problem.
- Material: Carbon steel or 304/304L dual certified Stainless Steel (preferably SS).
- Design considerations: Acid condensation at cold end, minimum metal temperature, material selection
Intermediate Exchanger
- Application: Generally metallurgical plant as shown in PFD 2.
- Basis: High SO2 strength.
- Heating medium: SO3 gas between bed 2 and 3.
- Cooling medium: Incoming SO2 gas from Cold HX to bed 1.
- Gas flow: SO3 up or down the tube depending on duct layout.
- Material: 304 or 304H stainless steel.
- Design considerations: Low allowable strength at high temperature
Hot Exchanger
- Application: Generally metallurgical plant as shown in PFD 2.
- Basis: High SO2 strength.
- Heating medium: SO3 gas between bed 1 and 2.
- Cooling medium: Partly heated SO2 gas from Cold HX to bed 1.
- Gas flow direction: Up or down the tube depends on duct layout.
- Material: 304H or 304 stainless steel w/ minimum carbon content of 0.04%.
- Design considerations: Low allowable strength at high temperature, material selection.
- Notes: Aluminizing hot sections/tubes for carbon steel material are not practical anymore and it is a costly method. Surface aluminizing of hot channel and tubesheet with tube-end welds may last only couple of years and needs repeated application every shutdown. Use of stainless steel is the right choice.
Hot Interpass Exchanger
- Application: Generally DA plant.
- Basis: High SO2 strength.
- Heating medium: SO3 gas between bed 2 and 3.
- Cooling medium: SO2 gas between IPAT via Cold HX and bed 4.
- Gas flow: Hot SO3 up or down the tubes depends on duct layout.
- Material: 304 or 304H stainless steel
- Design considerations: Low allowable strength at high temperature.
Cold Interpass Exchanger
- Application: generally DA plant.
- Basis: low SO2 strength or autothermal case.
- Heating medium: SO3 from bed 3 to IPAT.
- Cooling medium: SO2 from IPAT to bed 4.
- Gas flow: SO3 down the tubes if condensation is a problem.
- Material: Carbon steel or 304/304L dual certified Stainless Steel (preferably SS).
- Design factor: Condensation at cold end, minimum metal temperature, material selection.
SO3 Cooler
- Application: Generally DA plant.
- Basis: high gas strength with excess heat generated in converter.
- Heating medium: SO3 gas between bed 4 and FAT.
- Cooling medium: Ambient air.
- Gas flow: SO3 down the tubes.
- Material: Carbon steel / 304 or 316L Stainless steel (preferably SS).
- Design considerations: Acid condensation at cold end, minimum metal temperature, material selection, hot air recycle.
Preheater
- Application: metallurgical plant as shown in PFD 2 or waste acid regeneration plant.
- Basis: process gas side heat duty and plant heat-up time.
- Heating medium: Flue gas from burning fuel e.g. natural gas.
- Cooling medium: process gas.
- Gas flow: flue gas entering via top vestibule to ensure heat shield stability.
- Material: 304H stainless steel, high alloy (e.g. alloy 230) steel for tube ferrules
- Design considerations: Protection from high temperature furnace gas, low allowable strength at high temperature, counter and co -current flow combination to reduce hot end temperature, tube ferrule location and stability
effect of tube plugging for a specific application
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