Winter operation checklist for activation furnaces

Look outside the furnace first: three winter failure paths

The activation zone itself runs at 850–1100 °C (site caliber), so winter problems almost always start in the auxiliary systems. Three paths dominate: water and steam freezing in stagnant line sections, bursting valves or blocking flow; flue-gas walls dropping below the dew point, pasting the baghouse and wetting the stack; and moisture uptake inside a furnace at rest, which then cracks the lining during the next warm-up. Any one of these means an unplanned stop, and the repair always costs more time than the pre-winter inspection.

Freeze protection is not only about water pipes. Take the site's utility figures for the 1 t/h activation line: 1.8 t/h of steam at 0.8 MPa, 12 m³/h of cooling water and 1.2 m³/min of compressed air — all three circuits need a winter pass. The refractory itself is protected by its own temperature, but the insulation gaps at roof manholes, feed ports and shaft seals decide both heat loss and local condensation; see the site page on furnace lining and insulation.

What follows is a checklist you can tick off: a pre-winter inspection table by location, separate actions for steam, water and air, dew-point control for the baghouse, and two different protection routines for short and long shutdowns. Figures that reflect general engineering practice rather than site caliber are marked as such.

Steam, cooling water, compressed air: actions per system

• Steam: the site-caliber activation steam figure is 1.5–2.2 kg per kg of carbon (duty-dependent); what winter actually tests is the idle time — drain or keep tracing standby lines, regeneration lines and purge connections. There is no universal tracing set-point; common practice is to enable tracing before ambient temperature approaches 0 °C and confirm by hand along the line on cold nights (general practice, adjust to local climate).
• Cooling water: the killer is "stopped by day, frozen by night". Keep a trickle circulating or drain completely during even short pump stops; outdoor valve pits and water meters are the two most-missed spots.
• Compressed air: condensate is the direct source of ice. Blow down the receiver every shift and drain line low points regularly; what freezes is usually not the main line but end devices such as the filter-regulator in front of a valve positioner.
• Instruments: impulse-line tracing tends to fail together on cold-snap nights. Carry a local gauge on night rounds; if the remote reading diverges, treat it as freeze-plugging first before touching the zero.

Dew point and the baghouse: the flue-gas risk on cold days

The winter problem on the gas side is always "wall below dew point". Afterburner exit sits at 850–1100 °C (site caliber) and the gas is cooled by heat recovery before it reaches the bags; any insulation gap that only wastes heat in summer becomes a condensation point in winter. Water in a baghouse cakes the dust, raises the pressure drop, and ends in either a shutdown to clean or a full bag change. Worse, off-gas from the 450–550 °C carbonization zone (site caliber) carries tars, and tar mixed with dust is far harder to clean out than plain water.

Common practice keeps the baghouse wall at least 20 °C above the gas dew point (general practice; set per fuel moisture and duty). Two levers matter: complete the duct and equipment insulation before winter, focusing on flanges, expansion joints and supports where insulation tends to break; and on cold-snap days raise the low-temperature alarm at the bag inlet — spend a little more heat rather than letting the bag area hover near the dew point.

If a long winter shutdown is unavoidable, the furnace cools and the lining absorbs moisture; the reheat must then follow the refractory supplier's dry-out curve stage by stage. The site article on the 72-hour dry-out curve after relining is written for the relining case, but its staged water-removal logic applies equally to restarting a furnace that sat cold through winter.