Water-cooled wear zones
Water-cooled wear zones are a revolutionary, efficient, and economical way to improve operational accessibility and productivity for waste-fired power plants.
Experiences from the 15 plants where we 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 that includes the new wear zone technology.
Unlike many of our competitors, our new waste-to-energy plants are fully equipped with the best and most future-proof technology. We also have vast experience with upgrading existing plants and installing water-cooled wear zones.
Reducing maintenance costs by reducing refractory volume
Our water-cooled wear zone was developed to reduce the area of uncooled refractory in the furnace of our waste-to-energy boilers. The disadvantage of uncooled refractory is that because of high surface temperature it tends to build up large volumes of slag. This will often disturb the plant’s operation. Build-up of slag, especially on the lower part of the furnace side walls, can interrupt the waste flow and therefore heavily influence the combustion process. In serious cases this can shut down the plant. A great advantage of reducing the refractory volume is the resulting reduction in maintenance costs.
Constructed to ensure stability and withstand pressure
The wear zone itself is fully welded construction with relatively thick-walled tubes and plates. This is primarily to ensure structural stability, but also to provide a large allowance for erosion in the wear zone. The wear zone is either part of the evaporator or part of a separate circuit, such as a district heating circuit. The circulation principle depends on whether the wear zone is part of the evaporator (natural or, in some cases, forced circulation) or part of a separate circuit (forced circulation). In cases where the wear zone coolant temperature is above 230° C, the wear zone is protected with Inconel®, a nickel-based metal with outstanding characteristics regarding high temperature corrosion in waste-to-energy boilers.
Water-cooled wear zone.
Water-cooled wear zone and DynaGrate®.
Three ways to increase overall efficiency
The heat absorption from the wear zone can be used in three different ways:
- Direct connection to the boiler circuit. The wear zone is connected in natural circulation with the boiler drum, and constitutes an integrated part of the boiler. This coupling increases the overall efficiency of the plant. Due to the high operational temperature, the wear zone must be covered with Inconel®.
- Indirectly connected. The heat absorption is used for air or condensation preheating so the plant’s efficiency is increased. The wear zone is executed in standard black boiler pipe.
- Externally connected: The heat absorption is used for district heating.
Wear zones with direct connection and external conncetion setup
A typical system can receive 1.5 - 2.8 MW of extra energy
One of the many advantages of a water-cooled wear zone is that it absorbs approximately 80-100 KW per m2, compared to only 20-40 kW per m2 in a standard plant. This means that a typical system can receive 1.5-2.8 MW of extra energy. With our water-cooled wear zone it is possible to reduce the total amount of surface area in the radiant part of the boiler. There are no slag deposits as the wear zone is a relatively cold 150-300° C. The system therefore retains its active grate area throughout the operational period.
Less down time with water-cooled wear zones
There’s no need for operational stoppages due to slag removal. Heat absorption is five to 10 times higher than in the boiler’s two radiation passes. Heat absorption in the wear zone reduces the furnace temperature and therefore allows increased heating value and maintains waste capacity.
The water-cooled wear zone replaces the refractory lining in the system’s most heavily used area and experience shows that a water-cooled wear zone has a longer life than refractory lining. If you have an existing waste-to-energy plant, we can build in a water-cooled wear zone during a standard maintenance stoppage.
The water-cooled wear zone works actively as an expansion segment between boiler and grate. No jamming occurs due to the base plate being pressed over the outer beams of the grate.
Our continuous research guarantees you cutting-edge technology
Unlike many of our competitors, our new waste-to-energy plants are fully equipped with the best and most future-proof technology. We also have vast experience upgrading existing plants and installing water-cooled wear zones.
During the last 7 years we have upgraded nine existing plants and commissioned six new plants with water-cooled wear zones.
Our new generation of water-cooled wear zones has been patented. Aars District Heating Plant is the first plant to incorporate our new patented wear zone, which has holes in the panels for injection of cooling air for the side walls.
Installation of wear zones at the existing waste-to-energy facility, in Thorshavn, Faroe Islands
Operational problems due to slag deposits in the furnace are critical in small plants with narrow grates as the waste flow is hindered by even small amounts of slag deposit.
The waste-to-energy plant in Torshavn is an example of this type of system. The plant had problems with capacity and operating time and it was often necessary to stop the plant to remove slag from the furnace.
With new wear zones results show a 50% reduction in down time and 10% capacity increase
In 2006 we installed a water-cooled wear zone. After the installation the plant owner experienced an increased accessibility of 100%, an overall improvement in the working environment without dust at the ash conveyor, and down time for cleaning was reduced by 50% from two weeks to one week.
The Thorshavn Plant
Developing new technology for a 25-year-old furnace line at the Aars District Heating Plant in Denmark
Furnace line 1 at the Aars District Heating Plant dated back to 1985-86 and required an excessive amount of down time due to clinker build-up. The plant was forced to close for two to four days every fifth or sixth week to clean the furnace room, losing valuable production time.
After exploring a system that was right for this plant, we redesigned both the water-cooled wear zone and secondary air system, and upgraded the grate to a new DynaGrate®. Wear zones were heightened using extra tubes and new, proprietary technology featuring cooling air inlet holes in the side walls and side panels was developed and implemented.
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.
With new wear zones: Energy production increased from an output of 6.5-7 MW to 8.5 MW.
The resultant minimal refractory wear and only minor clinker accumulation has led to an increase in productivity and a decrease in operating costs. Down time has dropped dramatically. Output has increased from 6.5-7 MW to 8.5 MW. This reflects 7.5 MW coming from the boiler and the remaining 1 MW coming from the wear zones themselves.
The new systems were so successful they have been patented.
For further information on water-cooled wear zones for existing plants, please contact our Service Department, (+45) 76 14 34 00.
Here you can see a furnace with the new, patented water-cooled wear zone.
We 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.
A new generation of water-cooled wear zones
Aars District Heating Plant: 25% increased energy production and lower operating costs