Selective Catalytic Reduction (SCR) catalysts are vulnerable to plugging by high ash contents in flue gas streams generated during combustion of coal, particularly in thermal power plants. High dust flue gases can contain dust concentrations over 60 mg/Nm3 in firing coal with high ash content, and with high ash coals and lignites from countries such as India, flue gas dust concentrations can be as high as 90-100 mg/Nm3. The problem can also be encountered in other applications like cement kilns where dust concentrations of 80 to 100 gm/Nm3 are not uncommon. The high ash phenomenon can also give rise to erosion problems depending on the characteristics of the dust particles and chemicals.
Catalyst plugging is one of the major issues that needs to be addressed in the application of all SCR Catalysts be they of honeycomb, plate, or corrugated design. Though the ash particles are considerably smaller than the Catalysts cells, ash pluggage can occur due to combination of reasons.
A major cause of ash pluggage can be attributed to the presence of large particle ash (LPA) in the flue gas. LPA can collect in the upstream portions of the SCR reactor in ducts, turning vanes, and splitters and, when the ash deposits are dislodged, the accumulated solids plug the catalyst. Other factors affecting pluggage may include poor distribution of ash flow in the flue gas, flue gas flow anomalies such as low velocity, angular flow, recirculation flow, and even ash collection on soot blowers. Further complications can arise when reactor leakage allows moisture to enter causing formation of sticky ash which can build up along boiler walls.
Solutions to the ash plugging problem lie in correcting the gas and ash flow distribution, preventing ash build up at upstream of the reactor, and frequent operation of cleaning devices. Equally important is the suitable design of the SCR reactor with proper catalyst pitch and suitable geometry.
Cormetech, the world’s leading SCR Catalyst Manufacturer, has developed an innovative honeycomb catalyst which greatly mitigates the problems of ash pluggage. Cormetech’s Dust Buster™SCR catalyst consists of optimized channel geometries that facilitate the flow of ash-laden flue gas through catalytic surfaces with high DeNOx activity. The Dust Buster high pitch design and uniform cell geometry makes the catalyst less susceptible to plugging and erosion. Hybrid design of different pitches near the wall as well as at other portions of the reactor can also be incorporated to overcome the local pluggage issues. Like all of Cormetech’s SCR catalyst products, Dust Buster provides high DeNOx performance, low ammonia slip, low pressure drop and mercury removal co-benefits.