Vibration grate (HVB) water-cooled
The water-cooled vibrating grate (HVB) was developed for combustion of biomass with little or almost no ash content. The grate has proved its effectiveness over more than 10 years of commercial operation.
Very high availability, low maintenance cost and low consumption of spare parts
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Design:
The grate design
Simple mechanical design and few movable parts
The grate consists of two or four panel walls mounted on leaf springs. The panels are placed at an angle of 6º to the horizontal and each panel is activated by a vibrating unit via a connecting rod. The panels are vibrated in pairs in counter-phase in order to balance external forces.
The fuel moves from the top of the grate to the lower end towards the slag hopper. The vibrating frequency is adjustable by means of a v-belt wheel. The start/stop sequence is controlled by the DCS and can be freely adjusted to the condition of the fuel. Commonly used limits are 15 sec. every 5. min and 5 sec. every 40. min., depending on the condition of the fuel.
High flexibility through multiple cooling options
The preferred method, which is always used when both boiler and grate are supplied by Babcock & Wilcox Vølund, is to connect the grate as a boiler floor, cooled by natural circulation, together with the other evaporator heating surfaces.
Advantages:
- The heat input is utilised for steam generation
- The grate temperature is high and contributes to the drying and pyrolysis of the fuel
- Alternative methods are incorporation as an economiser in the high pressure system or as a feed water preheater in the low pressure system
Possibility of high preheating temperature of under-grate air
There are no mechanical joints or moving parts under the vibration grate that need lubrication. As it is thus only the strength of the construction materials that set the limit, the under-grate air can be preheated to 300°C without any problems.
Advantages:
- High heat release rate with medium wet fuel
- Stable combustion with wet fuel
- Stable combustion at low load
Size and location of air holes can be custom-designed
The holes for the under-grate air are bored in the fin material The hole pattern and size can be chosen according to the condition of the fuel and the required turn-down ratio.
For plants that operate mainly at 100% load, good air distribution can be ensured at a low pressure drop. If a high turn-down ratio is required, the pressure must be optimized to achieve good distribution, also at low load.
This will ensure efficient combustion and good emission control.
