Problem 6.9: A deaerator normally heats boiler feedwater to

From Chapter 6 Problem Set. Level 3: System Integration.

Question

A deaerator normally heats boiler feedwater to 220°F, removing nearly all oxygen. The steam valve fails and feedwater drops to 140°F. If the system flows 50,000 lb/hr, how many pounds of dissolved oxygen per hour are now entering the boiler? Assume the feedwater is exposed to air and reaches approximately air-saturated dissolved oxygen at 140°F.

Answer

Show answer

At 140°F, dissolved O₂ ≈ 4.4 mg/L = 4.4 ppm. 1 ppm = 1 lb O₂ per million lb water. 50,000 lb/hr ÷ 1,000,000 × 4.4 = 0.22 lb O₂/hr entering the boiler.