Carbon Steel Coils Superheater And Reheater Processing Plant Ball Passing U-Bending Ovality Test
Carbon steel coils superheater and reheater processing plant ball passing U-bending ovality test
Description
| 1 | The efficiency of the steam cycle is improved by higher steam pressure and temperature as well as reheating. |
| 2 | Both superheating and reheating of steam have to be as high as possible. At a steam pressure of 120 bar and higher, the cycle efficiency improves by —1% for every 20°C rise in superheat. |
| 3 | Therefore, high superheats are desired for each band of pressure consistent with the metallurgy of the turbine. |
Superheater(SH)
| In a subcritical boiler, the SH is between the main-steam header and the steam drum and consists of |
| • Saturated tubes that transport steam from the drum to the SH inlet header (when the SH tubes are not directly connected to the drum) |
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• Superheater banks with their respective inlet and outlet headers |
| • Attemperator station for STC |
| • Main-steam header with all fittings and terminating with the main-steam stop valve (MSSV) |
| Steam from the steam drum flows toward the main-steam header, and there should be no valve between the two to ensure flow in SH tubes under all conditions to prevent overheating and failure. |
Reheater(RH)
Reheating of steam involves withdrawal of partly expanded steam (at the end of the high — pressure cylinder of the turbine), taking it back to the boiler in cold reheat pipes, heating to the same or higher temperature as the superheated steam, and returning to the turbine in hot reheat pipes. In terms of hardware, an RH system comprises
| • Cold reheat pipe from turbine to boiler |
| • Safety valves on the cold reheat pipe |
| • Emergency spray-water attemperator system on a cold reheat pipe or interconnecting pipe |
| • Reheater bank complete with inlet and outlet headers |
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• Hot reheat pipe from boiler to turbine |
Superheater and Reheater Design Principles
1.Superheater and reheater are the tube banks that attain the highest temperatures in a boiler and consequently require the greatest care in the design, fabrication, and O&M to ensure that the permissible metal temperatures are never exceeded.
2.The final sections of both SH and RH must be placed in the highest gas temperatures, which calls for adopting the most appropriate high-temperature alloy for the tubing from considerations of the following information.
| • Metal temperatures |
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• Fouling due to ash compounds |
| • Corrosion due to salts in ash |
The three most important aspects of the design of both SH and RH are:
| 1 | Uniform distribution of steam and gas across all the sections to minimize unbalance of flows. |
| 2 | Optimally high steam velocity in all the tubes to keep the metal temperatures as low as possible. |
Product
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