Problem 11.4: A feedwater tank normally receives 80
From Chapter 11 Problem Set. Level 2: Applied Thinking.
Question
A feedwater tank normally receives 80% condensate return at 180°F and 20% makeup at 65°F. Suddenly the condensate return drops to 35%, while total flow remains unchanged. Explain qualitatively what happens to:
- Feedwater temperature
- Conductivity
- Dissolved oxygen load
- Sulfite demand
Then explain why increasing sulfite feed alone may not solve the problem.
Answer
Show answer
When condensate return collapses and makeup rises:
- Feedwater temperature decreases
- Conductivity increases
- Dissolved oxygen load increases
- Sulfite demand increases
Increasing sulfite feed addresses one symptom, but the deeper problem is the change in the system’s mass and heat balance. The correct diagnosis is not simply “the sulfite program is failing,” but “the feedwater system has shifted to a different input balance.”