Natural Gas Heated Process Air Duct Heater for Ethanol Plant Air Preheating

This oven was developed for an ethanol plant application requiring the preheating of process air before use in downstream operations. This equipment was not intended to thermally process discrete parts or products inside an oven chamber. Instead, the customer required a dedicated air-heating module capable of delivering a controlled temperature rise across a large airstream under cold ambient inlet conditions.

APPLICATION REQUIREMENT

• The equipment had to heat a continuous process airstream for ethanol plant service.
• The system had to take 0°F inlet air and raise it to 40°F.
• The unit had to support downstream plant processes requiring a warmed airflow stream rather than direct product heating.
• This project is one of multiple Precision Quincy systems built for ethanol plant process-air heating.

AIRFLOW / THROUGHPUT REQUIREMENT

• Required process airflow: 27,000 ACFM.
• Required temperature rise: 0°F to 40°F.
• The air stream passes through the unit in one pass and is then used by downstream equipment.

CONSTRUCTION / INTEGRATION REQUIREMENT

• The heater had to be built as a skid-mounted duct section for integration into the customer’s larger air-handling system.
• The process-air blower is remote and supplied by others.
• The system required a combustion and controls package that could be integrated into plant utilities and ductwork.

SAFETY REQUIREMENT

• The heater was designed as a gas-fired Class A duct heating system with flame safety, airflow proving, gas-pressure supervision, excess-temperature protection, and purge sequencing.
• The combustion controls package had to support safe startup, burner supervision, and fault shutdown in accordance with the project control and safety architecture.

UTILITY / SITE REQUIREMENT

• Required electrical service: 575V / 3PH / 60Hz.
• Required fuel: natural gas.
• Natural gas inlet pressure: 2 PSI minimum design, with gas train design maximum of 5 PSI.
• Natural gas flow basis: 1,500 CFH.
• Design elevation: below 1,000 ft.

INSTALLATION / SHIPMENT REQUIREMENT

• The unit was designed as a preassembled skid-mounted duct section.
• Approximate shipped weight: 6,500 lb.
• Approximate overall dimensions: 98 in W × 150 in L × 100.88 in H.
• Required dock / access basis: 12 ft W × 16 ft H.

These thermal process requirements were established from the customer’s need to heat a high-volume ethanol-plant process airstream under cold inlet-air conditions.

TEMPERATURE CAPABILITY

• Inlet air basis: 0°F.
• Outlet air basis: 40°F.
• Temperature rise basis: 40°F.
• Maximum stated operating temperature basis: 40°F, assuming 0°F inlet temperature.

PROCESS BASIS

• The thermal process basis is once-through heating of a process airstream, not batch heating of product inside a work chamber.
• The heated air is delivered to downstream plant processes after passing through the duct heater.

HEAT INPUT REQUIREMENT

• Heat source: natural gas.
• Burner: Selas Superflame 1500.
• Burner capacity: 1,500,000 BTU/hr.
• Natural gas flow basis: 1,500 CFH.
• Fuel inlet pressure basis: 2 PSI minimum design, 5 PSI maximum design.
• Regulated gas pressure at gauge: 30 in. W.c.

AIRFLOW DELIVERY REQUIREMENTS

• Process airflow basis: 27,000 ACFM supplied by others.
• Burner combustion blower basis: NYB 2306A7.5 blower.
• Combustion blower performance: 287 CFM at 42 in. W.c.
• Combustion blower motor: 7.5 HP.
• Airflow path: one-pass duct heating with internal mixing section and vanes.

EXHAUST / VENTILATION BASIS

• Exhaust fan: supplied by others.
• The overall system requires exhaust capacity sufficient to remove combustion products from the duct-heating process.

THERMAL INSTRUMENTATION / CONTROL BASIS

• Primary temperature controller: WATLOW F4T with Ethernet connectivity.
• Upstream and downstream duct temperature protection: Gefran 650L excess-temperature controllers.
• Thermocouple basis shown in the wiring package: Type K for duct sensing.
• Burner modulation signal: 4–20 mA.

SAFETY / CLASSIFICATION BASIS

• The gas train and burner system include double safety shutoff valves, proof of closure, high and low gas pressure switches, airflow proving, flame safeguard controls, and UV flame detection.
• The system includes purge sequencing and burner interlocks tied to blower and airflow status.

To deliver the customer and thermal process requirements for this oven, Precision Quincy developed the following equipment concept and architecture.

OVERALL CONCEPT

• One skid-mounted natural-gas-heated duct heater.
• Designed for heating a 27,000 ACFM process airstream from 0°F to 40°F for ethanol plant service.
• The design uses a cylindrical insulated duct section with an integrated burner package and internal mixing section.

HEATING ARCHITECTURE

• Heat source: natural gas.
• Burner: Selas Superflame 1500.
• Burner capacity: 1,500,000 BTU/hr.
• Gas train manufacturer: Karl Dungs.
• Gas valve actuator: Siemens VA40.25 / SQM4-series actuator architecture.
• Burner supervision includes direct spark ignition, flame safeguard, and UV flame detection.

AIRFLOW / MIXING ARCHITECTURE

• Process airflow through duct: 27,000 ACFM supplied by others.
• Combustion blower: NYB 2306A7.5.
• Combustion blower performance: 287 CFM at 42 in. W.c. With 7.5 HP motor.
• The duct section includes internal mixing vanes to blend burner heat into the process air stream.
• The process blower and exhaust fan are provided by others as part of the larger plant system.

DUCT / CONSTRUCTION ARCHITECTURE

• Inner duct diameter: 46 in.
• Duct outer diameter: 66.50 in.
• Overall unit length: 150 in.
• Overall width: 98 in.
• Overall height: 100.88 in.
• Construction style: double-wall cylindrical duct section on a skid frame.
• Inner shell: rolled steel inner duct shell.
• Inner shell thickness: 0.25 in rolled steel.
• Wall thickness: 4 in.
• Insulation: 4 in of 8 lb Superwool / ceramic-fiber insulation.
• The unit includes mounting flanges, forklift lifting points, and anchor locations for installation.

CONTROLS ARCHITECTURE

• Control enclosure: remote-mounted NEMA 4 control enclosure.
• Controller: WATLOW F4T with Ethernet connectivity.
• The control panel is identified as a UL 508A open industrial control panel.
• The system includes burner enable logic, remote run fan logic, purge indication, flame fault indication, and temperature monitoring.
• The controls package can receive remote commands from an external PLC via Ethernet/IP.

SAFETY / COMPLIANCE ARCHITECTURE

• Applicable standards shown in the electrical package: NFPA 79, NFPA 86, UL 508A.
• Gas train includes double blocking safety shutoff valves, proof of closure, pressure switches, regulator, test ports, and visual indication.
• Safety devices include airflow switches, high- and low-gas-pressure switches, upstream and downstream excess-temperature limits, flame safeguard logic, and manual reset functions.

SHIPPING / INSTALLATION ARCHITECTURE

• The equipment is configured as a skid-mounted preassembled duct heater section.
• Approximate shipping weight: 6,500 lb.
• The design supports unloading and installation using the structural frame and forklift access points shown on the GA.