Method of controlling the suction gas pressure of a sulfuric acid plant for treatment of smelter exhaust gas

In a system which includes an intermittently operating converter furnace, a constantly operating smelting furnace, a sulfuric acid-producing stage, a converter furnace exhaust gas flue for leading exhaust gases from the converter furnace away therefrom via a converter furnace exhaust gas fan, a smelting furnace exhaust gas flue for leading exhaust gases from the smelting furnace away therefrom via a smelting furnace exhaust gas fan, wherein said exhaust gas flues join together and a further gas flue leads to generated exhaust gases, sequentially through a gas-cleaning stage, a sulfuric acid plant main blower, and onto said sulfuric acid-producing stage, wherein a first damper is provided in the converter furnace exhaust gas flue between the converter furnace exhaust gas fan and the location where said exhaust gas flues join together, wherein a second damper is provided in the further gas flue between the gas-cleaning stage and the sulfuric acid plant main blower, and wherein a gas pressure transmitter is located on the further gas flue between the location where said exhaust gas flues join together and said gas-cleaning stage, the method of controlling the suction gas pressure in said further gas flue such that the rotation speed of the sulfuric acid plant main blower and the degree of the opening of the second damper are controlled automatically so as to maintain a predetermined value by signals from the gas pressure control unit wherein:

• (A) When the converter furnace operation is commenced, in sequence:
• the first damper is opened, the rotational speed of the sulfuric acid plant main blower is increased, the degree of the opening in the second damper is reduced such that the gas pressure in the further gas flue between the location where the exhaust gas flues join together and the gas-cleaning stage will maintain a constant value, the blowing of air through the converter furnace is started, the degree of the opening in the second damper is made larger such that an increase in the gas pressure in said further gas flue will be compensated for and be maintained at a predetermined value, and the degree of the opening in the second damper and the rotation speed of the sulfuric acid plant main blower are controlled so as to maintain a predetermined gas pressure in the further gas flue when both the converter furnace and the smelting furnace are in normal operation,
• (B) When the converter furnace operation is stopped, in sequence:
• the degree of the opening in the second damper is reduced such that the gas pressure in said further gas flue will maintain a constant value, when the amount of exhaust gas entering from said converter furnace exhaust gas flue is decreased, the first damper is closed, the rotation speed of the sulfuric acid plant main blower is reduced, the degree of the opening in the second damper is made larger such that an increase in the gas pressure in said further gas flue will be compensated for and be maintained at a predetermined value, and the degree of the opening in the second damper and the rotation speed of the sulfuric acid plant main blower are controlled so as to maintain a predetermined gas pressure in the further gas flue when only the smelting furnace is in normal operation.