October 27, 2008
A trainer again
Originally published August 31, 2005
Let me tell you how a sulfuric acid plant operates. Very simply, and I'm not going into much detail.
You start with a giant blower that pulls in outside air and runs it through a Drying Tower, where 1,800 gallons per minute of 93% sulfuric acid cascades through a maximum contact ABSORBTION system that removes any moisture from the air. The dry air is then fed into a Sulfur Furnace, where it provides oxygen to combust molten sulfur, carefully melted and heated to 380 degrees F before it is atomized in the furnace.
It burns and produces SO2 gas.
The SO2 gas is passed through a converter filled with vanadium pentoxide catalyst that converts the SO2 to SO3 gas as rapidly as possible. Maintaining temperature control is essential to make this reaction happen. Therefore, the gas passes through a series of waste-heat boilers and gas-to-gas heat exchangers before it hits the Interpass Tower, where the gas is ADSORBED (not ABSORBED) in a steam of 98% sulfuric acid, pumped at a rate of up to 3,600 gallons per minute.
The temperature of the recirc acid is just as important as the temperature of the gas. Interpass acid MUST be between 170 and 190 degrees F or it won't ADSORB, and your fumes go right out the stack.
As your 93% acid keeps ABSORBING moisture from the air, it gets weaker. As your 98% acid ADSORBS more SO3, it gets stronger. So, you cross-breed the 98% with the 93% and add water through dip legs that extend almost all the way to the bottom of a pump tank. That's how you ADD WATER TO ACID without causing an explosion. You do it from the bottom in a brick-lined tank.
The gas leaving the Interpass tower makes one more pass through the converter, where any remaining SO2 is converted to SO3 and ADSORBED in another acid-bath. Ideally, at the end, you have nothing but nitrogen leaving the stack with a trace amount of unconverted SO2 gas (less than 3 pounds per ton of acid, according to our operating permit, and we ALWAYS beat that standard if things were working right).
If you don't believe me about this shit, just ask catfish. He operated the acid plant for a long, long time. I was his boss for several good years.
It's been a while since I trained anybody on how to do this (it's a complicated job), but I still remember how.
Some things you just don't forget.
All content © Rob Smith