When the burner is tilted upward, the flue gas temperature towards the superheater zone is raised and the temperature of the water wall is reduced.
When the burner is tilted downward, the flue gas temperature towards the superheater zone is reduced and the temperature of the water wall is raised. And the burners are designed in such a way that they can be tilted upward or downward.ĭepending upon the requirement, the burner may be tilted upward or downward In this case, the burner is tilted or adjusted to control the superheated steam temperature. The draft loss is less when the damper is opened so that the flue gas path is bypassed. The draft loss is more when the damper is closed so that flue gas flows through the superheater. The draft loss in the flue gas path varies periodically. The damper has to operate at a high temperature and in an erosive environment. During higher load, the damper is closed and the entire flue gas is allowed to flow through the superheater.Īccording to the desired temperature at a certain load, the damper is set at a certain position. As less volume of hot flue gas flows through the superheater, the temperature of steam can be maintained constant during lower load conditions. During low load when the steam flow is less in the superheater, the bypass damper is kept open. In this method, the damper is used to bypass the flue gas path so that some quantity of flue gas does not flow through the superheater. This type of control is mostly used where a convective superheater is used. Heat contents in the flue gas decrease and the heat transfer to the superheater decreases as well. If the combustion air is reduced the steam temperature decreases and heat absorption at the water wall increases. The flue gas temperature is raised by supplying excess air through mechanical draught systems and the heat absorption rate of the furnace water wall is reduced. If excess air is supplied more heat transfer takes place at the superheater tube and the steam temperature increases. To increase the superheated steam temperature the air supply must be increased. The air supply to the furnace can be varied accordingly to control the temperature of the superheated steam. This is done by controlling the mechanical draught systems. in between the main boiler furnace and superheater furnace, the rise in superheated steam temperature depends upon the firing rate in the furnace. The radiant superheater is placed in another furnace and the convective superheater is placed in between the common flue gas path of both furnaces, i.e. In this method, there are two superheaters and two furnaces. To control the temperature of the superheated steam the following methods are adopted. What methods are adopted to control the temperature of the superheated steam? When steam demand rises, the flow in the superheater increases, and steam temperature decreases. When steam demand drops, the steam temperature increases, and flow in the superheater reduces. And to minimize thermal stress, the temperature must be maintained within its limits. To drive the steam turbine, the superheated steam temperature must be equal to the rated design value. The main steam temperature must be equal to the set point or the design temperature. The superheated steam temperature of the boiler is required to maintain within the limit. Why is superheated steam temperature controlled? This type of superheater is called a drainable superheater. In a horizontal superheater, the tubes are arranged on a slope so that the condensate can be drained out easily. This type of superheater is called a non-drainable superheater, and the vent of this superheater is kept open during start-up so that the condensate can evaporate easily. In a vertical superheater, the condensate cannot be drained out completely, when the boiler is in shut-off condition. In some boilers, the superheater tubes are arranged vertically and horizontally. One header of the superheater is connected to the steam drum to receive saturated steam and another header of the superheater is connected to the outgoing pipe followed by the main steam stop valve (MSSV).
And to absorb all the water and moisture content present in the saturated steam. The purpose of a superheater in the boiler is to raise the temperature of the saturated steam. What is a Superheater? Why is it used in the boiler?Ī superheater is a set of parallel tubes connected between the two headers to minimize the pressure drop.
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