Desuperheater
Desuperheater
(OP)
While looking for a desuperheater that provides a very low superheat degree (per process design), I came across the Komax desuperheater that offers a simple equipment and to be within 5°F of the saturated temperature. For the specific applications, they offered to be within 1°F of saturation. Anybody has experience/comments about this equipment?
(http://www.komax.com/products/desuperheater.html)
(http://www.komax.com/products/desuperheater.html)





RE: Desuperheater
In the case of steam dumps into a surface condenser, the outlet steam volumentric flowrate is directly proportional to the outlet steam pressure. For some toher control valves ( such as Lesley valves), the valve stem position and the dp across the inlet to the valve vena contracta can be combined to yield the apparent inlet steam flowrate. The water flowrate is monitored by an orifice plate flow element.
RE: Desuperheater
RE: Desuperheater
If you are going to use a 1 F superheat, better make sure the ratio of water to steam flow may not exceed 0.35 :1 ; this is a backup safety measure to avoid water hammer and/or other damage due to excess water flow entering teh steam devices. I ahve seen temperature controlled desuperheaters overpsray to the level of very high water in the steam line.
RE: Desuperheater
Above guidelines are from an old Fisher spray attemporator design book, and confimred by techpapers published by Deutsche Babcock design engineers in the 1980's. Based on expereience with damage caused by not meeting these guidelines, I concur with their accuracy.
RE: Desuperheater
reviewing old notes, the transit time from spray nozzle to thermocouple to be GT 0.35 sec, and to downstream elbow GT 0.15 sec.
brain cells are retiring at a fast rate now.
RE: Desuperheater
Every time I have used the ideal gas laws to calculate Mach, steam came out with its speed of sound somewhere around 1500 ft/sec. (I know that's variable according to temp, but it's still a rule-of-thumb number)
If the discharge from the valve expands to 1/3 Mach velocity, then that's 1500/3=500 ft/sec, so the 0.35 sec transit time to the T/c occurs 175 feet downstream!..
RE: Desuperheater
I2I
RE: Desuperheater
The large difference in inlet enthalpy to the individual tubes of the next heat exchanger results in large heat exchanger outlet tube -to- tube temperature differences and resulting loss in hottest tube creep life and high thermal stress at tube to header weld interfaces.
One way the boiler mfrs try to skirt this issue is to limit the range of boiler loads for which you can use the spray, and mandate a minimum 20 F superheat measured at the downstream thermowell.
On HRSG's we have seen faiulures of large 12" F22 forged nozzles on P91 intermediate reheater inlet headers ; the combination of the 2:1 step change in pressure part wall thickness combined with a rapidly alternating steam temperature hitting the nozzle to header weld ( due to alternating impaction of liquid water from the spray) had lead to a prompt fatigue failure in about 18 months.
On LP bypass /dumps from the HRSG reheater to condenser we have seen gross failures of the spray outlet pipe due to waterhammer when there was inadequate transit time from spray nozzle to monitoring thermowell and outlet temperature control was used to control spray water flow. Relocating the thermowell downstream onto the condenser nozzle , upgrading the spray nozzle type, converting to enthalpy control with overide to prevent the ratio of water flow to steam flow from exceeding 0.4:1 ended the waterhammer issue.
RE: Desuperheater
- Buy the most expensive one you can afford.
- Buy the one with the largest pressure drop you can accommodate.
- Install the TI way, way, way down the pipe.
- Clearly specify your turndown requirements.
- Design the rest of the plant assuming the desuperheater does not work.
RE: Desuperheater
rmw