Commissioning boiler blowdown heat recovery
Blowdown heat recovery commissioning is the bringing-into-service of equipment that captures heat from continuous boiler blowdown — a flash vessel and a heat exchanger — so its energy preheats feedwater or makeup instead of going to drain. It proves the system recovers heat reliably while still controlling boiler water dissolved solids.
What it is
Continuous blowdown removes a stream of hot, high-solids water from the boiler to control its chemistry, and that stream carries significant heat. Recovery equipment flashes the blowdown to a low-pressure vessel for steam recovery, then passes the remaining hot liquid through a heat exchanger to warm incoming makeup water. Commissioning verifies that the flash steam and the heat exchanger both perform, and that the blowdown rate still does its chemistry job.
Why it is done
Sending hot blowdown straight to drain wastes both its heat and the treated water, and the loss runs continuously whenever the boiler fires. Recovered flash steam can feed a deaerator and the recovered liquid heat can preheat makeup, cutting fuel and water. But the recovery system must not compromise the blowdown's primary purpose of controlling boiler dissolved solids, so commissioning has to confirm both the energy recovery and the maintained water chemistry.
How it is done
Commissioning begins by confirming the blowdown control — continuous rate set on conductivity — still holds boiler dissolved solids within limits with the recovery equipment in line. The flash vessel is brought up and its recovered low-pressure steam routed to its intended load, with level control on the residual liquid verified. The makeup preheat heat exchanger is then commissioned, checking approach temperature and that makeup is genuinely warmed. Recovered heat and the displaced energy are measured against expectation, and the controls are tuned so recovery never starves the chemistry control.
- Confirm blowdown control
- Commission flash vessel
- Route recovered steam
- Commission preheat HX
- Measure recovered heat
- Tune to protect chemistry
What to watch for
The key risk is letting heat recovery override the blowdown's chemistry duty — throttling blowdown to recover more heat lets boiler solids climb toward carryover. Neglecting the flash-vessel level control floods it or loses the liquid heat, and a fouled or undersized preheat exchanger quietly delivers little benefit. Routing recovered flash steam to a load that is not always present means the vessel simply vents.
Related practices
Running a compressed-air leak survey programme
Retrofitting waste-heat recovery
Retrofitting variable-speed drives
Related topics
Waste Heat Recovery in Industry: Methods and Where It Pays · Boiler Efficiency
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