A new generation of water-cooled wear zones
Greater waste capacity, increased energy production and reduced operating and maintenance costs are some of the main benefits of water-cooled wear zones in furnaces.
Over the past 6-7 years, Babcock & Wilcox Vølund have installed water-cooled wear zones in both existing furnaces and completely new plants - and in the past few years our company has developed a new advanced wear zone which has now been patented.
Good experience with water-cooled wear zones
More people are realising the many benefits involved in using water-cooled wear zones in furnaces in waste-to-energy plants.
The benefits are numerous: A greater waste flow, increased calorific value, greater energy production, reduced maintenance, fewer operational stoppages and less wear and tear to the refractory.
Experiences from the 15 plants where Babcock & Wilcox Vølund have installed water-cooled wear zones show that the total annual energy production has increased significantly - in many cases by as much as 25-30%. A single plant can even handle 40% more waste after a conversion which the new wear zone concept is part of.
The costs for a wear zone are quickly covered with a payback time of as little as two years.
New patented generation of water-cooled wear zones
Since 2005, Babcock & Wilcox Vølund have upgraded nine existing plants and commissioned six new plants with water-cooled wear zones.
Thomas Norman, Manager of Technology Design at Babcock & Wilcox Vølund, explains: "Every plant is unique. In close collaboration with our client, our specialists provide a tailor-made solution."
All plants containing water-cooled wear zones have increased their energy production and reduced their operating costs. One example of this is the Aars District Heating Plant in Denmark. A successful furnace line upgrade at the Aars District Heating Plant in 2009 has increased energy production by approx. 25%.
Aars District Heating Plant is the first plant to incorporate Babcock & Wilcox Vølund's new patented wear zone where we developed holes in the panels for injection of cooling air for the side walls.
The computational fluid dynamics illustration shows the temperature in the walls in a furnace. Here you can see two generations of water-cooled wear zones
On the left: A traditional water-cooled wear zone
On the right: A new, advanced water-cooled wear zone with integrated cooling air.
No slag - no operational stoppages
On standard refractory without water-cooled wear zones the slag can quickly build up. With growing slag deposits on the sides the incineration capacity is reduced and thereby affects the entire energy production.
A common problem can be that the furnace has to be shut down completely every 4-8 weeks for 2-3 days to remove the slag.
With the water-cooled wear zones these expensive operational stoppages are avoided, and the furnace retains its active grate area. By cooling the sides of the furnace slag deposits are avoided as the wear zone is relatively cold.
Utilisation of the heat absorption
The water-cooled wear zones can be connected to the plant in three different ways depending on the plant: Directly connected to the boiler circuit, indirectly connected or externally connected.
Wear zone directly connected to the boiler circuit
The heat absorption of the wear zone can be directly incorporated in the plant's power production by connecting the wear zone directly to the boiler circuit, i.e. in circulation with the boiler drum, and thereby making the wear zone an integrated part of the boiler. Due to the high operating temperature, the wear zone must be covered with Inconel®, a chrome and nickel alloy capable of withstanding very high temperatures.
Wear zone indirectly connected
In indirect connections the heat absorption for the air or condensate preheater is utilised so that the heat absorption of the wear zone is incorporated directly into the plant's power production. The wear zone is made up of standard boiler tubes.
Wear zone externally connected
An external connection uses the heat absorption for district heating. The wear zone is made up of standard boiler tubes.
Conversion of existing furnace rooms takes place by removing the refractory of the side walls and installing the water-cooled wear zones along the entire length of the grate. The volume of the furnace will therefore remain unchanged after the installation.
Maintenance on directly connected Inconel covered wear zones is limited. Over longer periods of time, local renewal of the Inconel coating in some exposed areas should be expected.
In some cases, the addition of refractory or Inconel in the most exposed areas will be necessary on indirectly or externally connected wear zones. Previously, the refractory deteriorated due to the high temperatures, but as the wear zone is cooled and also made of durable metal tubes, minimal maintenance is required.
"If maintained correctly, the wear zones will last for at least ten years," says Allan Hedegaard Olesen, an engineer at Babcock & Wilcox Vølund, who has worked on the development and adjustment of the water-cooled wear zones since 2005.
Here you can see a furnace with the new, patented water-cooled wear zone. Babcock & Wilcox Vølund have installed water-cooled wear zones in 15 plants, and experience shows that the total annual energy production has risen significantly - in many cases by as much as 25-30%.
The rear of a furnace after 14 weeks of operation. The holes for cooling air can be seen in the bottom right-hand corner. By cooling the sides of the furnace slag deposits are avoided as the wear zone is relatively cold. The costs for a wear zone are quickly covered with a payback time of as little as two years.
Aars District Heating Plant: 25% increased energy production and lower operating costs
Water cooled wear zones
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