4 replies to this topic

[chetanghotekar@gmail.com]

For desuperheating of steam, will it work if i use water temperature which is higher than the downstream required steam temperature?

When i do an heat and mass balance, there seems to be nothing wrong and its perfect. But i do not have practical experience of this. I do not have a specific process but following example can help us to investigate which i have used.

Let me know if any more details are required on this.

Description Maximum Qs (kg / hr) = 10000 Inlet Pr. (Bar A) 2.5 Inlet Temp. (Deg C) 350 H1 ( kJ / kg) = 3172 Outlet Pr (Bar a) 2.5 Outlet Temp (Deg C) 140 H2 ( kJ / kg) = 2743 Water Pr. (Bar A) 15 Water Temp (Deg C) 180 Hw ( k J / kg) = 763 Qw (kg / hr) = 2166.67

[ankur2061]

Chetan,

Your desuperheating water temperature cannot be more than the outlet steam temperature of the desuperheater or in other words you cannot achieve a steam temperature at the desuperheater outlet below the spray water temperature. Refer the link below for doing a desuperheater calculation.

http://www.cheresour...__fromsearch__1

Hope this helps.

Regards,
Ankur.

[kkala]

Attached "stdes.xls" complies with your calculations, supporting the view that required desuperheating under the specific conditions is possible.
It is noted that desuperheating occurs at 2.5 bara. Water of 15 bara and 180 oC can be assumed as transformed into water and steam of 127 oC, when throttled to 2.5 bara (see stdes.xls).
This fluid (vapor+liquid) of 127 oC is mixed with the steam of 350 oC, to result in 140 oC steam. A physical interpretation can be so.
Evidently steam temperature cannot go below 127 (precisely 127.4) oC under the operating pressure of 2.5 bara.

Attached Files

•  stdes.xls   31.5KB   75 downloads

Edited by kkala, 24 April 2012 - 09:29 AM.

[chetanghotekar@gmail.com]

Thanks Ankur / kkala,

I guess, i am more in agreement with kkala on this issue as i believe that the desuperheating is possible with warmer water than the required downstream temperature. The only physical limitation comes up about the nozzles / spray valve that will be used here. If we are not worried about flashing damage on nozzles and spray valve, then i guess this will work fine.


kkala,

regarding your limit on how low we can go for desuperheating, won't that be true even with water having less temperature than downstream steam temperature. In the above case at 2.5 bar A, the saturation temperature is 127.4 deg C, if we try to desuperheat below that we will never achieve the lower temperature and there will be lot of condensate flowing in the pipe line.

[kkala]

For operating pressure = 2.5 bara, corresponding temperature of saturated steam is 127.4 oC. We cannot have steam at lower temperatures.
On the contrary injected water of 15 bara can have any temperature between 0 oC and 198 oC (saturation temperature at 15 bara). For temperatures above 127.4 oC, throttling to 2.5 bara would result in water and flash steam (theoretically of 127.4 oC), to be used for desuperheating. Lower than 127.4 oC temperatures would result in no flash steam.

Edited by kkala, 25 April 2012 - 04:31 PM.