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Steam Desuperheater Performance Analysis

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1. Superheated Steam Properties
a. Pressure: 185 psig (199.696 psia)
b. Temperature: 525 F
c. Enthalpy: 1282.51 Btu/lb
d. Specific Volume: 2.8156 ft3/lb
e. Mass Flow: 120,000 lb/hr
f. Energy Flow: 153,901,200 Btu/hr

2. Cooling Water Properties
a. Pressure: 325 psig (339.696 psia) A rule of thumb is that the cooling water must be at least 75 psi higher than the pressure of the steam being desuperheated. Also the pressure of the water before the control valve needs to be around 60 psi higher for the control valve pressure drop. Thus the pressure before the control valve needs to be 185psig + 75 +60 = 320 psig minimum.
b. Temperature: 217 F
c. Enthalpy: 185.02 Btu/lb
d. Specific Volume: 0.01684 ft3/lb
e. Mass Flow: Must be calculated
f. Energy Flow: Must be calculated

3. Desuperheated Steam Properties
a. Pressure: 185 psig (199.696 psia)
b. Temperature: 415 F
c. Enthalpy: 1219.80 Btu/lb
d. Specific Volume: 2.4229 ft3/lb
e. Mass Flow: Must be calculated
f. Energy Flow: Must be calculated

4. Equation & Calculation
a. Equation:
mss(lb/hr) x hss (Btu/lb) + mwater (lb/hr) x hwater (Btu/lb) = (mss + mwater)lb/hr x hdesuperheated steam

(120,000 x 1282.51) + (mwater x 185.02) = (120,000 x 1219.80) + (mwater x 1219.80)

153,901,500 + 185.02 mwater = 146,376,000 + 1219.80 mwater

7,525,500 = 1034.78 mwater

mwater = 7,272.56 lb/hr

GPMcooling water = 7,272.56 lb/hr x 0.01684 ft3/lb x 7.4805195 gal/ft3 x 1.0 hour/60min
= 15.27 gal/min

mdesuperheated steam = msuperheated steam + mcooling water
= 120,000 lb/hr + 7272.56 lb/hr
= 127,272.56 lb/hr

5. Computer Program Answers
a. Mass Flow of Cooling Water: 7253 lbs/hr
b. GPMcooling water = 15.10 gal/min

Steam Desuperheater Computer Program Printout
DESUPER

1. Superheated Steam Input Data
a. Pressure: 185 psig
b. Temperature: 525 F
c. Mass Flow: 120,000 lb/hr
2. Cooling Water Input Data
a. Temperature: 217 F
3. Desired Desuperheated Steam Properties Input Data
a. Pressure: 185 psig
b. Temperature: 415 F
4. Program Output Data – Required Cooling Water
a. Cooling Water Mass Flow: 7253 lb/hr
b. Cooling Water Volume Flow: 15.10 gal/min




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