The energy mix is evolving towards a lower carbon, more sustainable future. This evolution is slow and is predicted to take many decades – even in the more mature economies in the developed world. In many parts of the developing world the combustion of carbon based fuels is predicted to grow (in some cases rapidly) over the next few decades. There is growing pressure to mitigate the impact this might have on Air Quality Coal Fired Boilers continue to make a significant contribution to our growing need for power. Often very large (of the order of hundreds of MW installed), their combustion processes also make significant quantities of acidic gasses SOx and NOx. SOx emissions relate directly to the sulphur content in the fuel and can be removed in a scrubber. NOx is a process pollutant and can be prevented/removed via a number of methods, but the most efficient is SCR. The installation of SCR Reactors on coal fired and co-fired boilers have now become routine in many parts of the world, particularly in North America, Western Europe and China.
Depending on plant requirements (new plant, retrofit or space availability), SCR catalysts have been installed in High-Dust, Low-Dust or Tail end configurations to meet NOx reduction requirements.
Durable plate type SCR catalysts are ideally suited for high-dust environments in Waste-To-Energy and Biomass-To-Energy power plants.
By changing the pitch of the catalyst low pressure drop and very low dust accumulation is achieved. Soot blowers can be installed, if required, to remove dust from the face of the catalyst and maintain maximum catalyst activity.
The following diagrams illustrate the different configuration options for SCR on a coal fired boiler.
A key concern of operators is ensuring that the emissions from their power plant are compliant with the requirements of their licence to operate. Catalysts are installed in layers and each has a definitive lifetime of compliant operation – determined by their design and the conditions they face during installation and operation.
The decay in performance can be modelled and used to predict when a catalyst layer should be replaced with new or regenerated catalyst.
After replacement activity can be monitored and modelled to appreciate the next timeframe for catalyst recharge / replacement. All this allows the operator to manage the maintenance cycle of the SCR reactor with that of the rest of the Power plant.