The Blueprint of Water

Heating Things Up: Problem Set

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⟵ 13 Heating Things Up (Engineering Notes) · Contents · 13 Heating Things Up (Answer Key) ⟶

Heating Things Up: Problem Set

“These are only provided to reinforce understanding. The Engineering Notes contain some of the information that will be required. Make sure to employ dimensional analysis for all unit conversions.”

Level 1: Conceptual Mastery

  1. At 140°F, feedwater contains roughly 4 mg/L dissolved oxygen - half of what it held at room temperature. Explain why corrosion risk is higher at 140°F, not lower.

  2. A boiler burns 100 billion BTU per year. If 1/32” of calcium carbonate scale reduces efficiency by 2%, estimate the annual cost of that inefficiency at $10/MMBTU.

  3. A facility reports water hammer every weekday morning at 7 AM but never on weekends. The boiler chemistry is within ASME limits. Is the problem more likely priming or foaming? Explain.

  4. List four consequences of losing 50% of condensate return, and for each, identify which link in the boiler circuit is affected.

Level 2: Applied Thinking

  1. Feedwater contains 3 ppm dissolved oxygen. (a) Calculate the stoichiometric sulfite requirement. (b) If the boiler is operating at 10 cycles of concentration and the target boiler residual is 30 ppm, what total sulfite concentration would you target in the boiler feedwater?

  2. A plant returns 8,000 lb/hr of condensate at 170°F. Cold makeup is 60°F. Boiler efficiency is 82%. Natural gas costs $12/MMBTU. The plant operates 8,000 hours per year. (a) Calculate the hourly energy savings from condensate return. (b) Calculate the annual fuel savings in dollars.

  3. A boiler produces 20,000 lb/hr of steam. Feedwater conductivity = 50 µS. (a) At 40 cycles, what is the boiler water conductivity? (b) If cycles drop to 10 due to lost condensate, and feedwater conductivity rises to 200 µS, what is the new boiler water conductivity? (c) Using the ASME table, is this still within guidelines for a 150 psig boiler? Explain why conductivity alone does not tell the full story.

Level 3: System Integration

  1. Your blowdown conductivity controller reads 2,000 µS. Your handheld meter reads 3,800 µS on a cooled grab sample. The blowdown valve has been closed for hours. (a) What has happened? (b) Estimate the actual cycles if feedwater conductivity is 80 µS. (c) Using the ASME table, is this boiler (300 psig) at risk? For what?

  2. A technician reports: sulfite residual is zero in the boiler, scale inhibitor is depleted, and condensate pH has dropped to 5.5. Instead of increasing all three chemical pumps, describe the diagnostic sequence you would follow to identify the root cause. What single failure could explain all three symptoms?

  3. Using the Perfect Storm scenario (90% condensate return dropping to 37%), estimate the fuel cost of heating the additional cold makeup water. Assume: steam production = 25,000 lb/hr, condensate returns at 180°F, makeup temperature = 55°F, boiler efficiency = 80%, gas cost = $10/MMBTU, 8,760 hours/year operation. Show your work using dimensional analysis.

Problem notes

Each problem as its own linked note.

13.1 · 13.2 · 13.3 · 13.4 · 13.5 · 13.6 · 13.7 · 13.8 · 13.9 · 13.10

⟵ 13 Heating Things Up (Engineering Notes) · Contents · 13 Heating Things Up (Answer Key) ⟶

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