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DRYCONTM - a steel plate conveyor - is used to automatically convey and cool the bottom ash by means of ambient air. The plate conveyor is designed for operation under difficult conditions, like extreme temperatures and strongly fluctuating quantities of bottom ash. Due to impact beams below and special damping mechanisms, DRYCONTM can cope with large quantities of slag suddenly landing from a height of 30 meters without suffering lasting deformation. DRYCON™ can be retrofitted into existing facilities where space is at a premium.
The steel plate conveyor has a direct drive provided by two round link chains and a frequency controlled drive station. Ambient air is induced into the DRYCON™ at the top end and along the length of the conveyor. Air travels in a counter flow direction along the surface of the ash and cools the same. In addition a re-burning process of the glowing ash is activated which reduces the unburned carbon level and frees up additional heat that adds further thermal energy to the steam generating process within the boiler. The system can transport material to a silo with an incline of up to 45°, making the use of a second conveyor dispensable.
In some process applications very large clinker lumps are produced and there is a danger that these will block the onward conveying system. To protect the system, Clyde Bergemann has designed an isolation gate with a jaw crusher function, which fits at the bottom of the transition hopper.
A mesh grid with 250 x 250 mm spacing is fitted to the bottom of each transition hopper outlet upon which any large clinker lumps will sit. These are crushed by hydraulically actuated jaw crushers, allowing them to drop through the mesh grid.
By reducing the ash particle size before entering the DRYCON, the cooling effect as well as the post-combustion will be improved. In addition the downstream equipment such as crusher are facing a defined particle size.
The isolating gates with jaw crusher function can be also used to isolate the DRYCON from the transition hopper. In this case the bottom ash can be stored up to 8 hours in the transition hopper while the boiler is in operation.
To maximize the value of the dry bottom ash, it needs to be crushed or pulverized to appropriate particle sizes for recirculation back into the boiler, onward conveying and/or discharge into silos or lorries. Roll crushers and hammer mills are the most common means of ensuring appropriate particle size.
Roll crushers will not generally reduce particle size to less than 2 mm. Dependent upon the incoming maximum particle size, two roll crushers may be used in series to achieve the required reduction ratio. Where smaller particle sizes are required, hammer mills will be used. Again depending on the process, a series of hammer mills or roll crushers and hammer mills can be installed to achieve the required reduction ratio.