8.6-1. Water Consumption and Pressure in Barometric Condenser. The concentration

Question

8.6-1. Water Consumption and Pressure in Barometric Condenser. The concentration of NaOH solution leaving the third effect of a triple-effect evaporator is 50 wt %. The vapor flow rate leaving is 5670 kg/h and this vapor goes to a barometric condenser. The discharge water from the condenser leaves at 40.5°C. Assuming that the condenser can maintain a vacuum in the third effect corresponding to a saturated vapor pressure of 2.78°C above 40.5°C, calculate the pressure in the third effect and the cooling water flow to the condenser. The cooling water enters at 29.5°C. (Note: The vapor leaving the evaporator will be superheated because of the boiing-point rise.) Ans. Pressure8.80 kPa abs, W 306 200 kg water/h

Explanation / Answer

Saturated temperature Ts = 2.78°C + 40.5°C = 43.28°C

From the steam table

At Ts = 43.28 °C

Saturated vapor pressure = 8.80 kPa abs

Boiling point of water = 43.28 °C

Boiling point of 50% NaOH solution = 83.3°C

BPR = 83.3 - 43.28 = 40°C

Enthalpy of solution at 83.3°C, Hs = enthalpy at 43.3°C + Cp x BPR

= 2577 kJ/kg + 1.86 kJ/kg-K x 40K

= 2652 kJ/kg

Average temperature in condenser = (40.5 + 29.5)/2 = 35°C

W/V = kg water/kg vapor = [Hs - Cp ( T2 - 0)]/Cp(T2-T1)

W/5670 = [2652 - 4.184 (40.5 - 0)]/4.184(40.5 - 29.5)

W /5670 = 54

W = 306200 kg water/h

Related Questions

Navigate

• Browse (All)
• Browse 8
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.