AirProtekt Limited

Newton Hall
Newton
Cambridge CB2 5PE
UK

Phone: (+44) 0 1223 872933

Fax: (+44) 0 1223 872934

Web:
airprotekt.co.uk

E-mail:
john.moore@airprotekt.co.uk

AirProtekt operates in the field of industrial air pollution control systems. Worldwide the company has supplied more than one thousand air pollution control systems using catalytic and thermal oxidation technology. The strength of AirProtekt is the considerable breadth of market knowledge and technical experience gained from over thirty years in catalyst technology and applied engineered solutions to air pollution control business. One key area of our products and services is exhaust catalyst treatment systems for stationary engines and turbines.

Catalysed Particulate Filter

On diesel engine generator applications exhaust emissions can cause a localised problem when direct venting introduces fumes into street or other populated areas. For this reason, expensive and often unsightly chimneys are installed to disperse the engine emissions into the atmosphere. This problem can be overcome by the use of a catalysed particulate filter to not only eliminate the need for a high chimney, but also treats the engine emissions rather than just dispersing them. The dual stage wall flow filter firstly collects the exhaust gases and soot, then it only allows the gases to pass through the porous wall whereas the carbon soot remains trapped within the structure. The next stage in the process is to remove the soot by regeneration of the filter. As the soot progressively builds up in the filter honeycomb it creates addition back pressure which must be reduced so that the filter can work continuously and efficiently while the engine is in operation. A precious metal based oxidation catalyst is coated onto the filter. The catalyst initiates an oxidation reaction with the carbon soot at a temperature of around 350°C.

Photo: AirProtekt Ltd Catalysed Particulate Filter and electrical pre heater for 800 kVA diesel standby generator.

The benefits of the wall flow filter in a stationary engine application are that they are by far the most effective method of high performance particulate reduction, they are not consumed and they can achieve good sound attenuation eliminating the need for additional silencing. In addition to dealing with the particulate the catalyst will also reduce the Carbon Monoxide, Hydrocarbon and the unwanted diesel odours in the exhaust gases. The consequences of this are that vast lengths of exhaust pipework can be reduced or eliminated as vents from gensets can be located in basements or discharge at low levels into the atmosphere. These advantages offer capital cost reductions to the engineer and better aesthetics to the architect.

Specific care has to be taken in the design of a stationary diesel generator when incorporating a particulate wall flow filter system.The back pressure generated by the filter is considerable and it will account for 50-75% of the total allowable back pressure on a typical stationary diesel engine exhaust installation.The catalyst & filter option requires that the engine must run on load (exhaust temperature >350°C) for at least 20% of its cycle. This will create uncertainty because it relies on the site maintenance engineer when starting the engine on a weekly check to bring the system onto load, if the engine is idling the temperature regime can not be achieved. If the temperature regime is not reached the filter will not regenerate and this could lead to filter blockage and eventual engine stalling. This can be overcome by including pre heater /loadbank as an integral part of the original system, therefore allowing the engineer to freely test the engine on load without the unwanted concern of bring the system online.

The type of fuel should be considered, as each system is susceptible to different levels of sulphur in the diesel fuel.

DeNOx & Oxidation Systems

Photo: AirProtekt Ltd Catalytic Exhaust Purifier for 5MW gas powered engine.

AirProtekt’s DeNOx units for natural gas and LPG-fuelled engines simultaneously reduce emissions of NOx, CO and HC by employing a so-called “Three-Way” catalyst. As a result the unwanted engine emissions are decomposed into non-toxic nitrogen, carbon dioxide and water vapour. DeNOx systems convert up to 98% of NOx, CO and Non-methane hydrocarbon (NMHC) emitted by a rich-burn IC engine.

For lean-burn diesel engines emission control is generally limited to removal of CO, Hydrocarbon and particulate. The oxidation catalyst unit is simply installed into the exhaust system and no additional engine stoichiometry control is required. Oxidation systems convert up to 98% of CO and 85% of HC.

Our converters consist of three basic components: the catalyst material, a metal monolith, (which supports the catalyst material) and a corrosion resistant housing. The catalyst, which employs Platinum Group Metals (PGMs) to achieve the highest catalytic activity and best poison resistance. The PGM catalysts provide high efficiency with catalyst inlet temperature as low as 375°C and will withstand up to 720°C without degradation. The metal monolith is special stainless steel foil honeycomb-like structure.