Catalytic Converter Price for Large Power Generation Engines

Catalytic converter price for large power generation engines can vary significantly depending on the type of catalyst, substrate material, exhaust flow, and required emissions performance. Generators or combined heat and power plants driven by internal combustion engines are often fitted with catalytic converters to reduce their emissions, in order to comply with local air quality requirements or permits. They may be fuelled by Diesel, natural gas, syngas, biogas, biodiesel, HVO (hydrotreated vegetable oil) or electrofuels.

When considering catalytic converter price, it is important to look beyond the initial cost of the equipment and consider how substrate design, flow distribution, durability, and catalyst loading affect the overall value.

What Determines Catalytic Converter Price?

The two most common types of catalytic converters installed on this equipment are:

• Oxidation catalysts: These are designed to oxidise carbon monoxide and hydrocarbons
  
• SCR systems: The purpose of these is to reduce NOx emissions

A common feature of both types is that the starting point is one or more ‘substrates’ (meaning a structure made from either a ceramic extrusion or metal foil which has a very high surface area), which is subsequently coated with catalytic material.

The volume of the substrates is normally calculated by the supplier in relation to the mass of exhaust gas that will flow through it in a given time. This is known as the ‘space velocity’. Although this calculation appears scientific, in reality it fails to take account of one very important factor which is the flow distribution.

Catalytic converters are always a bigger diameter than the exhaust pipe leading into and out of them, and unless the cones transitioning between the pipes and the catalytic converter are designed using aerodynamic principles, most of the gas flow passes through the middle, meaning that the perimeter serves little purpose.

How Catalytic Substrate Design Can Reduce Costs

The first way to reduce catalytic converter price is to optimise the design of the inlet and outlet cones, improve flow distribution, and thereby reduce the diameter of the diameter of the catalytic substrate.

The next suggestion is to replace square catalytic converters with round ones. Large-engine units based on ceramic substrates usually rely on 150 x 150 mm square-section substrates, which are built up into a grid.

However, with a grid which is square or rectangular overall, it is extremely difficult to equalise the flow distribution, even with carefully designed inlet and outlet cones, so it may be more economical to opt for round substrates which have a smaller volume but achieve the same results due to better flow distribution.

Round substrates on large engines are normally made from metal foil, and are generally more expensive than the ceramic type when equal volumes are compared. It should be possible to use a smaller volume round catalytic substrate compared to a square or rectangular one, due to the better flow distribution, and this will offset some or all of the cost difference. This illustrates why catalytic converter price should be considered alongside substrate volume, material, and flow performance rather than viewed in isolation.

Another way to economise when specifying metal substrates is to use one of a lower quality. Top quality metal substrates are made using a process called vacuum-brazing in which every point of contact between the adjacent layers of metal foil are joined together. This results in a very robust catalytic substrate which is able to withstand powerful exhaust gas pulses, vibration and temperature changes for thousands of hours.

Vacuum brazing is an expensive process though because it requires special ovens and a lot of energy. Therefore, some suppliers use a cheaper method to hold their substrates together, which is to rely on the coating to act as an adhesive. This results in a more fragile catalytic substrate which is not suitable for intensive use, but may be acceptable for applications where the generator is not used much such as in an emergency standby role.

Optimising Catalyst Loading to Reduce the Price

The next money saving idea concerns the precious metals which are the standard materials used on oxidation catalytic converters. Precious metals can be applied at varying densities, which are usually expressed in grams per cubic foot.

Customers often assume that there is a correlation between the density of the precious metal loading and its effectiveness at reducing pollution, but this is vague at best. There are other factors which have more influence on the activity of an oxidation catalytic converter than the precious metal content. To explain these, it is important to understand that precious metals are only a part of the coating, typically making up about 1-3% of the total.

The standard method of coating a catalytic converter is to mix all the ingredients together and then apply them in a single stage. This is quicker but has the disadvantage that most of the precious metal ends up buried amongst the other ingredients where it is not in contact with the flue gas, and therefore serves no purpose. An alternative approach is to apply the coating in two stages, so that the precious metals end up on the surface. This can lead to a saving of 50-75% in precious metal costs. As a result, optimising the coating process can have a significant impact on catalytic converter price without necessarily compromising emissions performance.

Finally, the other ingredients of the coating (mainly metal oxides and rare earths) play an important role in its activity, and they are much less expensive than precious metals, so optimising these can mean that the precious metals loading can be reduced further whilst still achieving the target emissions reduction.