Use of catalysts
With stringent environmental regulations for carbon monoxide and nitrogen oxides, the use of catalysts for controlling emissions is becoming commonplace. Steam and water injection and modifications to the gas turbine combustor can reduce NOx levels to 30-40 ppm. However, some states require that NO, be reduced further to 9-15 ppm. Catalysts, in the form of selective catalytic reduction (SCR) systems (9), can be used in the HRSG to achieve this lower emission level,
Catalyst performance is affected by gas temperature at the catalyst. Catalysts operate efficiently over a narrow range of gas temperatures. For NOx catalysts, the gas temperature range is typically 600-750°F; for CO catalysts it is 900- 1,200°F. The catalyst supplier specifies this temperature window, which depends on the materials used. In order to achieve temperatures within this window at all loads of the HRSG, the heat-transfer surfaces may have to be split to find a good location for the SCR (Figure).
Provision should be made for an ammonia injection grid upstream of the NOx catalyst. The catalyst also has a high gas pressure drop, in the range of 2-4 in. w.c., which must be considered in the overall design and performance evaluation.
With stringent environmental regulations for carbon monoxide and nitrogen oxides, the use of catalysts for controlling emissions is becoming commonplace. Steam and water injection and modifications to the gas turbine combustor can reduce NOx levels to 30-40 ppm. However, some states require that NO, be reduced further to 9-15 ppm. Catalysts, in the form of selective catalytic reduction (SCR) systems (9), can be used in the HRSG to achieve this lower emission level,
Catalyst performance is affected by gas temperature at the catalyst. Catalysts operate efficiently over a narrow range of gas temperatures. For NOx catalysts, the gas temperature range is typically 600-750°F; for CO catalysts it is 900- 1,200°F. The catalyst supplier specifies this temperature window, which depends on the materials used. In order to achieve temperatures within this window at all loads of the HRSG, the heat-transfer surfaces may have to be split to find a good location for the SCR (Figure).
Provision should be made for an ammonia injection grid upstream of the NOx catalyst. The catalyst also has a high gas pressure drop, in the range of 2-4 in. w.c., which must be considered in the overall design and performance evaluation.