Steam Generators
From fire-tube package boilers to water-tube high-pressure units.
Steam generators produce saturated or superheated steam for process, heating or power. Common designs: fire-tube (package), water-tube, and once-through coil-type steam generators.
How it works
- 1
Feed water is pumped from deaerator into the boiler drum.
Treated feed water is deaerated at 105 °C to strip oxygen and CO₂, dosed with oxygen scavenger and amines, then pumped by the multistage boiler feed pump through the economizer into the steam drum. Level is controlled by a three-element scheme (drum level + steam flow + feed flow) so swell and shrink during load changes do not trip the boiler.
- 2
Fuel (gas/oil/solid) burns in the furnace, heating water in tubes.
Fuel and combustion air mix at the burner (or on the grate) and burn in the furnace at 1200–1600 °C. Radiant heat passes to the water walls; the risers carry the steam-water mixture up to the drum while the downcomers return water, driving natural circulation. Flue gas O₂ is trimmed to 3–4 % — excess air cools the furnace and wastes fuel, too little makes CO and soot.
- 3
Steam separates in drum; superheater raises temperature.
Inside the drum, cyclone separators and chevron dryers separate water droplets from steam so that only dry saturated steam leaves. In a water-tube boiler it then passes through the superheater to 400–540 °C, with an attemperator (spray desuperheater) holding final temperature within ±5 K. Continuous blowdown from the drum controls dissolved solids and prevents carryover.
- 4
Economizer preheats feed water using flue gas.
The economizer recovers flue gas heat into the feed water, typically lifting it 40–70 K and adding 4–6 % to boiler efficiency. It is placed after the superheater where gas is cooler; skin temperature must stay above the acid dew point to avoid cold-end corrosion.
- 5
Air preheater improves efficiency; ID/FD fans handle draft.
The air preheater (tubular or regenerative) heats combustion air with the remaining flue gas, raising furnace temperature and efficiency by another 2–4 %. The FD fan supplies air, the ID fan maintains furnace draft slightly negative (−2 to −5 mm WC) so hot gas cannot puff out, and both are interlocked so the ID always leads.
Key components
Gas/oil burner with pilot, flame scanner, air register and modulating fuel valve, or a solid-fuel grate/FBC bed. Purge and light-off sequence, flame failure trip and low/high fuel pressure trips are the mandatory burner management interlocks.
Thick-walled pressure vessel holding the water/steam interface, internal cyclones and dryers, feed distribution pipe, chemical dosing line and continuous blowdown pipe. Two independent level gauges plus low-water trips — the low-water trip is the single most important protection on any boiler and must never be bypassed.
Membrane-welded tube panels forming the furnace enclosure, plus riser and downcomer circuits for natural circulation. Failures come from waterside scale (poor feed water), overheating and flue-side erosion; ultrasonic thickness surveys at every annual shutdown map the wear.
Convective and/or radiant tube banks that dry and heat steam above saturation, with an interstage spray attemperator for temperature control. Superheated steam raises turbine efficiency and prevents condensate erosion in long steam lines.
Finned or bare-tube economizer for feedwater preheat, tubular or rotary (Ljungström) air preheater for combustion air. Together they typically pull stack temperature from 300 °C to 150–170 °C. Watch for cold-end corrosion and soot blocking — rising stack temperature is the alarm.
Spray/tray or spray-only vessel at 0.2 bar(g) / 105 °C that heats condensate with steam and vents non-condensables, cutting dissolved oxygen to <7 ppb before the chemical scavenger. Also acts as the feed water storage tank giving NPSH to the BFP.
Typical operating parameters
Problem solving videos
Safety notes
- •IBR compliance mandatory (India).
- •Test safety valves, level gauges & interlocks per schedule.
- •Never bypass low-water trip.
Maintenance schedule
- •Daily: TDS, pH, hardness, blowdown log.
- •Weekly: burner tuning, flue gas O₂/CO.
- •Annual: hydro test, IBR inspection, tube thickness.
Problem solving matrix
| Issue | Likely cause | Fix |
|---|---|---|
| Carryover | High TDS / level swing | Blowdown, tune level control |
| Low efficiency | Excess air / fouling | Tune burner, clean tubes |
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