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Contact Section -
Stacks
- Spitting
May 22, 2003
Introduction |
Associated Links |
Stack spitting, fall-out and rain are terms that refer to the phenomenon of liquid or solid particles being emitted from a stack.
Condensation will occur in the stack as the hot, acid saturated gas leaving the absorber tower cools down as it passes along the duct going to the stack and then up the stack. A liquid film forms on the inside walls of the stack and then drains down to the base. As the liquid drains down the stack, the film becomes thicker and the liquid may begin to flow in streams. If the upward velocity of gas is high enough, liquid droplets can be sheared from the liquid film and will be carried up the and out of the stack.
Solids and iron
sulphate can also be blown out of the stack, particularly during startups.
The most obvious
sign of stack rain is the discolouration of paint on buildings and cars.
Stack rain can be a costly problem for plant operators if they must repair the
damage to employee cars and those in the surrounding neighbourhood.
The fall out from a stack can be monitored by placing a board on top of pole. The board is painted white so any acid droplet landing on the horizontal board will discolour the paint. This monitoring method will help to determine the degree of fallout and assist in settling or dismissing claims of damage to personal property due to stack fallout. The board should be examined periodically to help pinpoint when incidences of stack rain occur.
Stack rain can
be avoided by keeping the gas velocity in the stack low, reducing the vapour
pressure of the acid in the absorber tower, ensuring stack drains and candle
drains are open and ensuring candle drain cups are sealed.