About the water-cooled DynaGrate®
The grate bar is machined as a hollow section with channels designed to convey the cooling water to the areas with the highest heat load.
The large quantity of water circulating through the individual grate bars results in a small temperature difference over the individual grate bar, minimising the risk of local boiling. The last grate shaft in each grate section is not equipped with water-cooled grate bars since the thermal stress on this axle does not require water-cooling.
Temperatures
The individual grate sections are equipped with separate cooling circuits, dimensioned for max 10 bar and 110° C. The temperatures in the cooling circuit are controlled in order to obtain a constant outlet temperature from the grate, resulting in a fluctuation of the differential temperature over the grate. The maximum differential temperature is approx. 25° C.
Cooling circuit
The cooling circuit is dimensioned for the maximum possible heat flux from the hot flue gases. The normal heat transfer lies between 15-20 kW per square metre. During normal operation, the energy transferred from the grate can be used to preheat the air. Boiler efficiency and electricity production will thus be maintained when using a water-cooled grate.
Each cooling circuit is equipped with circulating pumps, a flow and energy meter, a pressure expansion tank and a heat exchanger. Transferred energy is exchanged in a heat exchanger to air preheating or district heating. In order to set an equal flow for each axle, a combined flow indicator / flow guard is installed on the individual grate shafts.
The cooling water flow is led from each axle through two concentrically placed pipes in the shaft. These pipes duct the water through a fixed piping system in the middle section of the shaft to the individual grate bars. The individual grate bars are connected in series. The water is also returned from the grate bars through the piping system. Standard steam hoses are used for ducting the water from the fixed piping system outside the furnace and to the shafts, which move over a 60º angle. The hoses are placed outside the furnace in order to avoid exposure to hot ashes, molten tin, aluminium, etc. which could damage the hoses. This construction means that there are no sensitive connections inside the furnace.
The quantity of water circulating through the cooling circuit is constant, as is the quantity circulating through the individual grate bars.
