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Sulfur-based Sulfuric Acid Solution

Sulfur-based sulfuric acid plantuses conversion and dry absorption process. It produce sulfuric acid throughsulfur melting, sulfur burning, conversion, dry absorption and other steps bytaking sulfur as raw materials. The heat generated by burning sulfur istransported to waste heat boiler, water goes into the boiler and generatessteam through deaerator, and then it is transported to steam turbine powerplant for power generation through low-temperature superheater,high-temperature superheater and steam header. In addition to supply power forthe operation of electric motors and pumps, the power generated can also supplypower to users, which not only saves energy, but also reduces pollution.

I.Introduction of Sulfur-based Sulfuric Acid Process Flow

Solid sulfur is transported to quick sulfurmelting tank through belt conveyor and hoist, and then transported to crudesulfur tank. Some goes into refine sulfur tank and is transported to sulfurburning furnace through sulfur transferring pump for burning, and some goesinto horizontal liquid sulfur filter and then is processed in pre-coating tankafter filtering. The sulfur after burning generates high temperature gas (SO2,SO3), and then goes into gas filter through boiler heat exchange. At thebeginning of the operation, electric furnace needs to be started, and theconverters will carry out catalytic conversion after being heated by electricfurnace. The converter is divided into five sections, it goes into drying towerfor drying after sufficient heat exchange, and then goes through primaryabsorption tower, secondary absorption tower, 105 acid absorptiontower, goes through 98 acid, 105 acid cooler and then respectively goes into 98acid, 105 acid circulating tank to generate 98 acid and 105 acid, and then itis transported to finished tank area. There are drying tower circulation pump,secondary tower circulation pump, 105 acid circulation pump at dry absorptionsection, and exhaust fan carries out air exhaust for the entire section. Inaddition, there are air blower, circulating water station and other auxiliaryequipments.

II. WasteHeat Recovery Process

First deoxidize the water through deaerator,transport it to the steam drum of the first waste steam boiler thorough thefirst coal economizer E-504 and the second coal economizerE-505, heat water into steam there through a lot of heat, make the steam gointo high temperature superheater F-502 after heating up through lowtemperature superheater F-503, go into steam header after going out from hightemperature superheater, and then transport it to turbine power plants forpower generation.

III. KeyControl Circuit

The control loop of sulfur-based sulfuric acidsystem is relatively simple, mainly composed of 13 sets of single-loop controland one set of boiler steam drum level three-impulsecontrol, instrument selection is mainly conventional transmitters, specialinstruments mainly include 3 concentrated acid meters, four PH meters and 1 SO2analyzer, and the thermocouple of sulfur burning furnace must select hightemperature resistant model.

1. Conventional control

Generate appropriate control action to changemanipulated variable according to its signal, so as to make the controlledvariable is maintained at a given value. Combine it with feedback control, soas to make control system stable.

The system uses conventional control based onthe control of liquid sulfur feeding and acidity. Take feeding amount FI109 ascontrol signal.

2. Three-impulseboiler drum level control

The water level of boiler drum is an importantfactor to affect safe operation. In the implementation of control, attentionshould be paid to the phenomenon of “false water level”. That is, when thesteam quantity of boiler increases suddenly (e.g., emptying), the bubblecapacity also increases quickly, the water level not only did not decline, butit will rise quickly. Therefore, if automatic control is carried out accordingto conventional volume, the feedwater quantity will be reduced, severevolatility will be caused at water level and it may lead to accidents inserious conditions. To this end, three-impulse control must be carried out fordrum level LI501, feedwater quantity FI501Aand steam quantity FI501B for automatic control system of water supply.