Can a screw be used for slag discharge in a waste heat boiler?
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I have a question: can a screw be used for slag discharge from sulfuric acid waste heat boilers? It was tested last year during the slag treatment upgrade of a 150,000-ton sulfuric acid plant at our unit, but the feeding screw stopped working immediately. I would like to know if plants of similar scale in China use screws as well, and what the results are
Based on our factory’s experience, spiral types were used in the past and required frequent repairs; switching to star-type ash discharge devices has yielded better results.
Waste heat boilers rarely use spirals. Star-type ash discharge valves or plug valves are generally used.
A screw conveyor was used, mainly when the boiler was not in use (for historical reasons, which will not be explained in detail here). The flue gas cooler was operated in bypass mode, but the slag cooling drum was located on the boiler’s axis. In order to transfer the ash from the flue gas cooler to the cooling drum, a custom-made screw conveyor for ash discharge was created. After several modifications, it proved to be effective, and maintenance requirements were not high.
The slag from the boiler is first discharged using a slag discharge valve, and then transported to the ash hopper via a screw conveyor or a grate conveyor
Our original residual heat boilers used double flap valves that were manufactured by us, and their gas-locking performance was poor. In 1993, it was modified to a screw auger ash discharger. The main problems were large pieces of hard ash adhering to the pipe walls, as well as the falling and getting stuck of anti-wear plates, refractory materials, and refractory bricks; these issues were extremely difficult to deal with. Even though there were two manholes, it remained very troublesome, especially during startup and ignition. In the end, we solved this problem by installing four cast iron grating plates on top of the screw conveyor! For the second phase in 2003, an star-shaped ash discharger was chosen, and it seemed to work much better. The gas locking performance, lifespan, operating costs, and so on are all easy to manage!
We have been using ash discharge screws in our waste boilers; the screws in flue 1 and 2 wear out more quickly, so they need to be replaced every six months or so. Especially when the slag discharge system is shut down for maintenance, the screws stop working as soon as they are started, and it’s only possible to restart them after all the ash has been removed. 3.4 The flue spiral performs well and can last for over a year. A stainless steel grating should be installed at the spiral inlet.