Duct Air Heaters

Pre-Start Checks

• Inspect ductwork, heater flanges and vessel welds for air leakage.
• Remove debris and dust to prevent deposits and local hot spots.
• Verify main dampers, bypass and inspection covers against the startup procedure; ensure covers are sealed.
• Check inlet/outlet temperature, pressure, airflow and element surface-temperature instruments.
• Check cable insulation, protective earth and phase sequence; verify interlocks.
• Set target temperature and approved overtemperature, overload and low-flow protection values.
• Check insulation, cooling arrangements and access seals.

Startup Sequence

• Start the supply/exhaust fan first and establish stable airflow; heating is prohibited with no or insufficient flow.
• Verify flow above the minimum and provide heating permission; a fan-running signal alone is insufficient.
• Once heating is permitted, air passes through the elements via the specified flow-distribution arrangement and heats by forced convection.
• Deliver heated air to drying, curing, space heating or assessed exhaust-pretreatment duties.
• PID adjusts power from outlet temperature; confirm PLC or other control configuration for the project.
• Monitor static pressure as designed; blockage or abnormal pressure triggers alarms and protection.

Operating Monitoring

• Monitor inlet/outlet temperatures, static pressure, flow and element temperature; adjust power for flow and inlet-temperature changes.
• Disconnect heating on low/no flow; continued fan cooling depends on the fault and must not be assumed safe during fan failure or hazardous-atmosphere conditions.
• Gas or element overtemperature alarms and disconnects heating; pressure interlocks and relief measures follow duct design.
• After shutdown, isolation and cooling, remove dust and oil deposits under the maintenance plan to prevent local overheating.

Normal Shutdown

• Disconnect heating first; keep the fan running to remove residual heat where safe.
• Stop the fan when temperatures reach the safe range specified in the manual; operate dampers as instructed.
• Before cleaning for extended shutdown, confirm electrical isolation, cooling and safe maintenance conditions.

Emergency Shutdown

Leakage, overtemperature, blockage, fan failure or electrical faults trigger heating isolation and alarms. Determine fan operation from the fault and manual; do not restart before resolving the fault and rechecking protection.

Process Flow

Fresh air → fan → duct heater → heated air → process station → exhaust/return duct. Monitor outlet temperature, static pressure, airflow and element temperature; protect with minimum-flow, outlet/element overtemperature and designed pressure/relief measures.

• Drying: production-line materials, foods, medicinal herbs, wood veneers, paper, coated parts and grain.
• Coating: spray-booth circulation, paint/powder curing and workpiece preheating; assess solvents and combustible dust.
• Composites: glass-fibre curing, carbon-fibre thermoforming and insulation-panel curing ovens.
• Food/pharmaceuticals: clean air, ingredient drying and packaging drying; stainless steel alone does not establish hygienic suitability.
• Rubber/plastics: rubber preheating, pellet drying and extrusion-line circulating-air heating.
• Exhaust treatment: RCO/RTO pretreatment, catalytic-oxidation preheating and odour-gas heating, subject to specific safety assessment.
• HVAC/buildings: factory heating, cleanroom ventilation preheating and mine-entry freeze protection.
• Other industries: mould preheating, feed gases, laboratory hot air and pipeline heating-air supply.

Assess construction, materials and complete hazardous-area suitability for corrosive, dusty or combustible gases.

Selection Checklist

Design Features

• Atmospheric-duty design: assess forced-convection heating. The document’s 800°C value is a potential special-design target, not a verified product rating. Pressure-equipment applicability depends on actual pressure, construction and local requirements.
• PID control: validate response and accuracy against flow, thermal inertia, sensing and controls.
• Flow distribution: appropriate arrangements improve heat transfer and reduce hot spots; uniformity is not guaranteed for every installation.
• Protection: confirm minimum-flow, element-temperature and outlet-overtemperature interlocks to reduce, not eliminate, risk.
• Modular integration: review the supply scope for heater, sensing and PLC control panel.
• Materials: select vessel and sheath for temperature, corrosion, humidity and dust.
• Interfaces: verify duct standard, dimensions and loads rather than assume universal compatibility.
• Communication: operating, fault, temperature and pressure signals may be provided to PLC/DCS.

Core Functions

• Gas heating: continuously heat flowing air or compatible inert gases.
• Temperature measurement and control: configure multiple sensing points and adjust output to maintain the target.
• Flow interlock: monitor flow or a validated airflow signal and disconnect heating below the protective threshold.
• Overtemperature protection: alarm and disconnect the heating circuit as designed.
• Pressure monitoring: abnormal static-pressure alarms/interlocks; confirm relief devices through system design.
• Status: operating, fault and alarm feedback to central controls.
• Distribution: specified flow plates support uniform element heat transfer.
• Dust protection: review filtration and cleaning access; monitor filter pressure drop/blockage.

Final ratings and supplied functions follow the technical agreement, drawings and acceptance.