AQ Series (Exhaust Gas Economiser)
The Aalborg AQ Series is the world's most widely distributed exhaust gas economiser on ocean-going vessels. Installed in the funnel, it utilises the exhaust heat from the main engine for steam generation or fresh water pre-heating. Sootfires in economisers are one of the most frequent and dangerous causes of fire on ocean-going vessels — SOLAS and ISM Code require strict maintenance protocols. The AQ Series is present in every ship size, from Coastal to ULCC.
Components & Design
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Technical Data
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Common failures & inspection points
Visual inspection of gas side for soot buildup, exhaust temperature measurement: >10-20°C above setpoint indicates sludging; perform water flushing kit application (50 l/min, 0.4-0.6 MPa pressure); operate Soot-Blower daily 3x (caution: In case of uptake fire DO NOT blow down with steam due to H₂ fire hazard)
Internal inspection test (opening of sight glasses/hand ports): inspect tubes for wear, pitting, thinning; external inspection for soot deposits, blistering, sag; perform hydraulic pressure test at 1.25 × operating pressure for maximum 10 minutes
Class surveyor: Inspect all boilers >3.5 bar working pressure and >4.65 m² heating surface. Frequency: DNV/LLOYDS every 2 years up to 8 years old, then annually; 2 comprehensive internal inspections per 5-year period, interval maximum 36 months. Inspect internal surfaces (drums, headers) for sludging, corrosion, cracks.
Safety valve test: opening at ≤3% above working pressure; test pressure 15% above working pressure for maximum 10 minutes (feedwater only for water level safety); pressure rise during test maximum 10% above design pressure at full load firing with stop valves closed.
Sight glass visual inspection for highest, lowest, normal water level markings; protective devices without sight obstruction; test water cushion safety ball valve for function; check drain line for safety.
For Aalborg OL/D and similar burner boilers: inspect refractory material (membrane walls, furnace floor) for cracks, deformation, separation; remove carbon deposits. For XS-TC7A: clean helix tube bundle with water flush kit (7–8 hours on similar ships), if necessary add cleaning chemicals before discharge to slop tank.
Type-general inspection and maintenance points for this equipment category — not model-specific.
Service & Maintenance
Soot blowing MINIMUM daily when running on HFO. Exhaust gas temperature differential monitoring (rise = soot buildup = fire risk). Water-side treatment per boiler standards. Complete tube inspection at drydock. Tube thickness measurement with ultrasound.
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