PROCESS DESCRIPTION
1. Sulfur-melting section
Solid sulfur in bulk is transferred with a belt conveyor and melted in an accelerated sulfur-melting tank. The melted sulfur overflows into filter-acid tank and then enters filtration machine by pumps. The sulfur stream after filtration of impurities is stored in the refined sulfur tank and pumped into the sulfur burner for combustion by sulfur pump and through liquid sulfur flow meter. The liquid sulfur tanks are indirectly heated by steam (0.4~0.5Mpa) to keep sulfur in the melting state (135~148℃).
2. Sulfur combustion and conversion section
Liquid sulfur is pressured by pumps, sprayed through the nozzles into the sulfur burner and burns after mechanical atomization. Air needed for sulfur combustion is blown into the sulfur burner by a blower after filtrated in a filter, dried in drying tower.
The outgoing gas from the sulfur burner with high temperature enters into a boiler for recovery of heat with its temperature dropping from 1050℃ to 410℃ (convertor is 3+1 sections) and then into the first stage of catalyst beds in the converter for conversation of SO2 to SO3 its temperature rises to about 600℃.
After reaction and falls to 440℃ after high temperature super heater. Then the gas enters into the second stage of catalyst beds, heat exchange (I), the third stage of catalyst beds and heat exchanger (II), economizer (II) successively the gas goes into the first absorbing tower with its temperature 170℃ and SO3 in the gas is absorbed. The gas after absorption of SO3 goes through a highly-efficient fiber demister on the top of the tower for elimination of acid mist inside. The gas is heated to 410℃ after twice heat exchanged and enters the fourth stage of catalyst beds for the second conversation. The outgoing gas finally enters the second absorbing tower with temperature 160℃ after heat exchange in a low temperature after super heat exchange in a low temperature super heater and economizer (II). In the second absorbing tower, SO3 in the tail gas is absorbed and mist is eliminated through a demister on the top of the tower. The tail gas out of the tower is discharged to the air from the chimney.
3. Drying, absorbing and product section
The air blower is located behind the drying tower. The circulating system of tower-tank-pump is adopted. The air needed for sulfur combustion enters drying tower after filter. The moisture inside is absorbed by 98% H2SO4 spraying from the top of the tower which comes from the cooler of the drying tower. The dried air with its moisture of below 0.1g/Nm3 is blown into the sulfur burner after elimination of acid foam in the demister on the top of the drying tower and pressured by air blower. The first converted from the third stage of catalyst beds enters the first absorbing tower after cooled in heat exchanger (III) and economizer (II), in which the gas is sprayed by H2SO4(98%, 75℃) from the acid cooler of the first absorbing tower. H2SO4 after absorbing SO3 and flowing from the bottom of the tower enters circulating tank, and the then acid is pumped to the top of the first absorbing tower after cooled by acid cooler.
The second converted gas from the fourth stage catalyst beds enters the bottom of the second absorbing tower after cooled through low temperature super-heater and economizer, in which SO3 is absorbed by H2SO4(about 98.2%) from the outlet of the drying tower. H2SO4 after absorbing of SO3 flows into the acid circulating tank from the bottom of the tower, then back to the top of the tower by pumps for spraying after cooled through drying acid cooler. Product acid is pumped to underground tan by circulating pump after cooled by product acid cooler, and the temperature is below 45℃ and then pumped to storage tanks.
4. Heat recovery
Large amount of heat can be recovered in the production of sulfuric acid with the raw material of sulphur. In this plant a waste heat boiler (3.82MPa) at the outlet of the sulfur burner, high and low temperature super-heaters at the outlets of the first
And fourth stages of the converter are installed respectively to heat steam up to 450 ℃. A heat pipe economizer is installed at the outlets of the heat exchanger of the third stage and low temperature super-heater respectively to heat in series DM water (104℃) and the heat water obtained is transferred to the drum to produce 3.82 MPa saturated steam in the boiler. The saturated steam coming from the drum is transferred to the steam turbine after heated through low and high temperature super heaters up to 450℃, 3.8MPa. Low and medium pressure steam from the steam turbine is used for the use of melting sulfur, insulating, de-aerating and other unit.
5. DM water station
According to the requirements of supplied water quality for boilers in “The quality standards of water and steam for thermal power units and steam power equipment” (GB 12145), the DM-water process flow is shown as follows:
Raw water→ Raw water tank→ Water pump →Quartz sand filter→ Activated carbon filter → Cartridge filter→ High pressure pump→ RO unit→CO2-removal tower→ Clean water tank→ Clean water pump→ Mixed-bed exchanger→ DM water tank→ DM water pump→ De-oxygen unit. The capacity of DM water station is defined as 12t/h.
6. Auto-control system
Based on the requirements and characteristics of the process, the DCS is adopted for the sulfuric acid system and steam turbine system.