Generating bank

A generating bank is an evaporator tube bank between the steam drum and mud drum of a two-drum boiler, especially in kraft recovery boilers and older industrial boilers. It generates steam by absorbing heat from flue gas after the furnace and superheater sections.

Operating role

Water and steam circulate through the bank by natural circulation or assisted circulation depending on design. Hot gas crosses the tubes and transfers heat to the water-steam mixture inside. The generating bank sits in the transition between high-temperature radiant and lower-temperature convective duty, so it is both a heat-transfer surface and a gas-path restriction.

Fouling behaviour

In recovery boilers, sodium-rich fume and carry-over can deposit on generating-bank tubes. Deposits may be powdery at first but can sinter, bridge between tubes and restrict gas flow. Fouling reduces heat absorption, raises gas temperature to downstream economisers, increases draft loss and can force more aggressive sootblowing.

Failure modes and maintenance

Generating-bank issues include external fouling, tube erosion from gas lanes, under-deposit corrosion, circulation problems, drum-level sensitivity and access difficulty. Because the tube pitch can be tight, inspection must look for internal bridging, not only deposits visible from the edges. Sootblower alignment and steam conditions matter because badly aimed blowing can erode tubes.

Acoustic cleaning relevance

Sonic horns can support generating-bank cleanliness where deposits are dry and friable enough to respond. They are most useful as a supplement to sootblowers, reducing the rate at which deposits bridge between tubes and helping maintain gas flow between more forceful cleaning events.

Inspection notes

Generating-bank inspections should note which lanes are open, which are bridged and whether deposits are soft, sintered or chemically sticky. Tube spacing makes partial plugging easy to miss. Sootblower lanes, alignment marks and erosion scars should be checked together, because aggressive cleaning can create tube damage while still leaving shadowed regions dirty. Acoustic horns should be evaluated by whether they slow bridge formation across the bank, not only by whether deposits fall during a short demonstration.

Operating and inspection context

A generating bank transfers heat from flue gas to the steam-water mixture, so gas-side cleanliness, water circulation and tube integrity are linked. Key variables include gas temperature, tube spacing, baffle arrangement, circulation ratio, drum level stability, feedwater quality and ash loading. In older industrial boilers, generating banks can be difficult to inspect because tubes are closely spaced and access lanes are limited.

Common problems include ash bridging between tubes, sootblower erosion, under-deposit corrosion, oxygen pitting during layup, tube leaks, poor circulation and vibration. Operators infer fouling from rising gas-side pressure drop, falling steam generation, higher exit gas temperature or draught limitation. Acoustic cleaning can help keep dry ash mobile in the gas lanes, but it must be applied early. Once deposits are baked between tube rows or wetted by a leak, outage cleaning is usually needed.

Safety context

Generating-bank access usually means working near confined spaces, hot surfaces, ash deposits and pressure parts that may have leaked. Washing or lancing should be planned so debris can drain or be removed without loading lower hoppers or blocking gas lanes. Tube leaks found in the bank should trigger checks for secondary corrosion where wet ash sat against neighbouring tubes.