Problem Investigation

The Background.

Flue gas is treated with powdered lime and other additives to remove acid gases and other combustion by-products in three streams from multiple boilers to stringent standards.

Spent lime is separated from the exhaust gas in a large filtration houses and removed for off-site disposal. The filtration system and conveyors have been plagued by persistent blockage problems requiring potentially hazardous manual intervention as well as corrosion to equipment resulting in downtime and significant replacement costs. With increased scrutiny and pressure to improve the safety, BW were engaged to investigate and identify root causes and recommend improvements. This is a typical and recent example of a smaller, focused study or investigation with limited outlay to the client who lacks the specific expertise to identify a clear way forward before embarking on potentially significant investment.

The Client

Utility company based in a metropolitan environment operating a large Domestic Waste Incineration to Energy facility

The Solution.

A critical control parameter for the lime treatment process is lowering the temperature of the flue gas as it enters the lime addition and spent recovery system, principally to protect the filters from being overheated.

On investigation of the water addition system in the quench tower which directly controls the temperature as well as humidifying the flue gas, the control regime to prevent blockage in the nozzles under no or low flow conditions was also periodically resulting in water not being fully evaporated. Carry-over of moisture can in turn result in consolidation of lime powder and also corrosion from being locally acidified where powdered lime is not present. A number of small modifications were identified and proposed.