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#BoilerManual #AirAndGasFlow #Section3 #Page30
Normally,steam temperature is lower than design at low boiler loads due to the reduced convection heat transfer which exists with low gas flows. This is shown in Figure 23. With a constant level of gas recirculation, steam temperature would increase throughout the load range, as shown in Figure 24. By running with high levels of gas recirculation at low loads, and gradually reducing gas recirculation as load increases, a constant steam temperature can be obtained over a wide load range, as shown in Figure 25.
When both main steam and reheat steam temperatures must be controlled, additional measures are required. Normally, without gas recirculation, reheat temperatures are lower than main steam temperatures, as shown in
Figure 26. With the proper levels of gas recirculation required to bring reheat steam temperatures to design
levels, main steam temperatures would be high as shown in Figure 27.
FLUE GAS TEMPERING
Another method of steam temperature control is by use of flue gas tempering. Tempering gas is introduced into the furnace near the furnace outlet so it mixes with the gaseous products of combustion to reduce the gas temperature leaving the furnace. Generally, gas tempering has little effect on steam temperature.
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#BoilerManual #AirAndGasFlow #Section3 #Page30
Normally,steam temperature is lower than design at low boiler loads due to the reduced convection heat transfer which exists with low gas flows. This is shown in Figure 23. With a constant level of gas recirculation, steam temperature would increase throughout the load range, as shown in Figure 24. By running with high levels of gas recirculation at low loads, and gradually reducing gas recirculation as load increases, a constant steam temperature can be obtained over a wide load range, as shown in Figure 25.
When both main steam and reheat steam temperatures must be controlled, additional measures are required. Normally, without gas recirculation, reheat temperatures are lower than main steam temperatures, as shown in
Figure 26. With the proper levels of gas recirculation required to bring reheat steam temperatures to design
levels, main steam temperatures would be high as shown in Figure 27.
FLUE GAS TEMPERING
Another method of steam temperature control is by use of flue gas tempering. Tempering gas is introduced into the furnace near the furnace outlet so it mixes with the gaseous products of combustion to reduce the gas temperature leaving the furnace. Generally, gas tempering has little effect on steam temperature.
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#BoilerManual #FluidCirculation #Section2 #Page30
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Alt = A full page but sideways illustration of pipe connections with the bottom on the right side and the top on the left. Labeled Fig. 24 Convection pass supply circuitry. When the page is turned 90 degrees, one sees a manifold of tubes on the left, connecting by two tubes the manifold on the right which has a large vertical pipe labeled Convection pass supply downcomer. The two connecting tubes connect to that. At the bottom of the downcomer are two opposite arrows originating at the downcomer and pointing away from it along a tube that connects with the rightmost manifold with 3 branches on the right and 5 branches on the left, all of which connect together again to a slightly larger tube labeled Convection pass enclosure header.On the left side of that header is a long arrow pointing straight up toward what's labeled as F.W. convection pass screen tubes, but along the way, in the middle of the image, the arrow passes through a circle labeled Convection pass intermediat header, to which an arrow from the leftmost end of one of the two connecting tubes points back to it. That end of the tube is labeled Pendant convection pass inlet header. The arrow bends at a point labeled Furnace arch; it further continues to a point labeled Pendant convection pass floor, before the arrow arrives at the Convection pass intermediate header.
The leftmost manifold of tubes is joined at the bottom by the other connecting tube in a set of 2, then 3, then 3, then 2 tubes, and the larger tubes which connect them in sets at the top is labeled Pendant convection pass side wall headers.
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#BoilerManual #FluidCirculation #Section2 #Page30
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Alt = A full page but sideways illustration of pipe connections with the bottom on the right side and the top on the left. Labeled Fig. 24 Convection pass supply circuitry. When the page is turned 90 degrees, one sees a manifold of tubes on the left, connecting by two tubes the manifold on the right which has a large vertical pipe labeled Convection pass supply downcomer. The two connecting tubes connect to that. At the bottom of the downcomer are two opposite arrows originating at the downcomer and pointing away from it along a tube that connects with the rightmost manifold with 3 branches on the right and 5 branches on the left, all of which connect together again to a slightly larger tube labeled Convection pass enclosure header.On the left side of that header is a long arrow pointing straight up toward what's labeled as F.W. convection pass screen tubes, but along the way, in the middle of the image, the arrow passes through a circle labeled Convection pass intermediat header, to which an arrow from the leftmost end of one of the two connecting tubes points back to it. That end of the tube is labeled Pendant convection pass inlet header. The arrow bends at a point labeled Furnace arch; it further continues to a point labeled Pendant convection pass floor, before the arrow arrives at the Convection pass intermediate header.
The leftmost manifold of tubes is joined at the bottom by the other connecting tube in a set of 2, then 3, then 3, then 2 tubes, and the larger tubes which connect them in sets at the top is labeled Pendant convection pass side wall headers.
