Overfire air control
Secondary air, or overfire air, is important for the flames to mix well and gases to oxidize completely. The air is supplied through nozzles placed in the furnace walls above the fuel bed, the flow rate is then changed by adjusting the pressure. The control variable for secondary air is steam demand and is automatically controlled as a function of this, i.e. the overfire air flow rate is varied in proportion to the boiler load. To set the correct values for overfire air supply the combustion must be studied according to a few points. The visual flames may never reach higher than the ceramic protective coating, flue gases above the flames must be clear and transparent and CO values in the flue gases should be kept as low as possible. The set-points for the overfire air flow rate can be changed by the operator in case of varying waste composition, varying the pressure within certain limits (MARTIN GmbH, 2008a, 2008b).
Overfire air controlSecondary air, or overfire air, is important for the flames to mix well and gases to oxidize completely. The air is supplied through nozzles placed in the furnace walls above the fuel bed, the flow rate is then changed by adjusting the pressure. The control variable for secondary air is steam demand and is automatically controlled as a function of this, i.e. the overfire air flow rate is varied in proportion to the boiler load. To set the correct values for overfire air supply the combustion must be studied according to a few points. The visual flames may never reach higher than the ceramic protective coating, flue gases above the flames must be clear and transparent and CO values in the flue gases should be kept as low as possible. The set-points for the overfire air flow rate can be changed by the operator in case of varying waste composition, varying the pressure within certain limits (MARTIN GmbH, 2008a, 2008b).
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