Converting an existing power station to DRAIG technology is straight forward, as all components of a conventional power station basically remain the same.

When a pulveriser mill is being used for coal, or an alternative biomass burner is being used for biomass,  these can be replaced by DRAIG’s RPX burners as shown in this diagram.

All solid fuels can be burnt cleanly in the RPX2000, these fuels include:- Anthracite, bituminous coals, lignite, peat, pelletised coal dust and petroleum coke.

Many sources of Biomass such as:- forestry waste, pelletised sawdust, bamboo, reeds and grasses.

Bio-fuels such as Wood chips, reclaimed wood (Chipped), Chipped bamboo, pelletised sawdust and certain types of WDF.

The RPX range of DRAIG solid fuel burners operate on almost any solid fuel, especially coal, anthracite, or any dry biomass. Unlike many other forms of combustion, they operate with very low emission figures within any of the world-wide clean air regulations, without the need for additional external gas cleaning equipment (though these can be employed to capture various biproducts for resale).

• The DRAIG combustion system can be part of a custom designed power station, or can be used to convert an existing ‘dirty’ power station to operate within the clean air regulations, thus extending the life of the power station.

Solid fuel, such as coal is introduced at the top of the RPX burner from a fuel storage hopper and when the fuel enters the RPX burner, it passes through the gasification zone, where, due to the very high temperature burn, the solid fuel releases a large quantity of its volatile gases. These volatile gases are ignited and expelled from the RPX unit through the fire tube into the steam raising boiler, as a clean 3-4m flame.

Solid fuel, such as coal is introduced at the top of the RPX burner from a fuel storage hopper and when the fuel enters the RPX burner, it passes through the gasification zone, where, due to the very high temperature burn, the solid fuel releases a large quantity of its volatile gases. These volatile gases are ignited and expelled from the RPX unit through the fire tube into the steam raising boiler, as a clean 3-4m flame.

The DRAIG RPX 2000 burner stands vertically and works in a similar way to a coke oven by providing a very high temperature combustion zone, acting as a gasification zone. The burner unit has a water- cooled jacket surrounding the combustion chamber and the water that is pre-heated by the burner is then passed into a steam boiler for further heating to raise steam.

The combustion process is simple. The solid fuel, ideally between 15mm and 30mm, is delivered from a storage hopper which sits above the DRAIG combustor and the pre-heated primary air is delivered horizontally and efficiently to the combustion chamber. The fuel then passes through the gasification zone, all volatile gases are released and the fuel then continues to fall onto the fire bed where all remaining carbon is combusted.

The clean flame from the volatile gases is then blown like a rocket flame, through the fire tube into the boiler. This clean flame, up to 4m long, heats the boiler to steam point.

The key to clean combustion, is the DRAIG control system, which is constantly monitoring the input of primary air and fuel. Unwanted excess air is eliminated, as excess air combines with nitrogen, sulphur and carbon to make the unwanted and environmentally damaging gases

The DRAIG control systems balance the quantity of oxygen to achieve 98-99% optimum combustion. With optimum combustion there is little, or no carbon left in the fuel, and with no excess air to combine with any element to form unwanted gases, the result is cleaner emissions. 

Pictured to the right is a DRAIG RPX2000 chimney during a full firing sequence at the 3F Pellets site in Lincoln in the UK. This burner was being run on wood, but you would get the same results no matter the type of fuel. There is no visible smoke. There will sometimes be water vapour in the chimney gases, if the fuel source is wet when introduced to the combustion chamber.

Smoke is only present in  flue gases when the carbon in the fuel is not fully combusted. This is eliminated in the DRAIG RPX units due to the very high combustion temperature, and the constant computer control of the oxygen entering the combustion chamber. 

The greater the quantity of excess air, the greater the reactions between oxygen and the elements contained in the coal, resulting in greater quantities of CO (Carbon Monoxide) and CO₂ (Carbon Dioxide).

The reason the RPX 2000 runs without smoke is due to the very high temperature burn, which can be up to 2000°C precipitating the gasification of the solid fuel. This temperature is determined by the fuel type being combusted.

The DRAIG computer system controls the air flow into the combustion chamber virtually no excess air is delivered, thereby ensuring 98-99% combustion. When optimum combustion is achieved, there is no carbon left to react with the air and the gaseous emissions are so much cleaner. The image to the right shows the emissions readings achieved on wood at the Lincoln site.

An additional benefit of firing the primary air horizontally into the circular combustion chamber is that any particulate matter is naturally cycloned down towards the fire bed. In all other types of solid fuel combustion processes employed in power stations the air is being driven upwards through a fire bed under high pressure, thus lifting any particulate matter into the boiler or up the chimney stack.