Zhangjiagang Dehai Boiler Co., Ltd
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Steam Superheaters And Reheaters Anto Corrosion Erosion Long Life Time
Steam Superheaters and Reheaters
1. The superheaters and reheaters are tube bundles located in the flue gas stream that increase the temperature of the saturated steam, which is produced in the furnacewaterwalls.
2. These tubes are constructed from steel alloy material because of their high operating temperature. The main difference between superheaters and reheaters is the steam pressure.
3. In a typical drum boiler, the superheater outlet pressure might be 2700 psig while the reheater outlet pressure might only be 580 psig. They are used to help control steam temperatures, control steam flow pressure loss, and optimize heat recovery.
Reheater Function
1. Therefore the number of reheat stages can not be many as the pressure drop will reduce efficiency of thermal cycle.The steam pipes and reheater coils are to be so designed to limit the drop to 2–3%.
2. The control valves in reheat steam path is not desirable.Systems using HP LP bypass require these valves to control steam flow during bypass operation.
3. The efficiency of the Reheat cycle can be improved by increasing the pressure and temperature of steam entering into the turbine. As the initial pressure increases the expansion ratio of the turbine also increases and the steam becomes quite wet at the end of expansion.
Details
1. Convection superheater/reheater heating surfaces are placed above or behind the banks of water tubes at the rear of the radiant heatingsurfaces to protect them from combustion flames and high temperatures.
2. The main mode of heat transfer between the flue gasesand the convection superheater/reheater tubes is convection. With an increase in steam demand, both fuel and air flow increase, resulting in an increase in flue-gas flow.
3. As a result, convective heat transfer coefficients increase both inside and outside the tubes. The overall heat transfer coefficient between gas and steam hence increases faster than the increase in mass flow rate of steam.
Differences
| Type | Advantages | Disadvantages | Supporting method |
| Pendant-type | 1.Firm structural support | 1. Flow blockage by condensed steam 2. Needs slow restart to purge the water that accumulates in the bottom. | supported from above |
| Inverted-type | 1.Proper drainage of the condensed steam | 1. Lack the structural rigidity, especially in high speed gas flow | Supported from below |
| Horizontal -type | 1. Proper drainage 2. Good structural rigidity. | 1. They do not view the flam directly so they are mainly from the convective type | Usually supported in the vertical gas ducts parallel to the main furnace. |
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