HEM Indirect Fired Process Air Heater
Designed to fire applications where process air is to be heated from ambient temperatures up to the process plant's heat requirements.
The Selas HEM series of indirect-fired process air heaters have robust construction making them an ideal heat source for many industrial oven and process heating applications including spray booths and drying rooms.
The outer casing of the HEM air heater is manufactured from standard carbon steel and is double skinned, and thermally insulated. Insulation is available either 50mm or 100mm thickness depending on application requirements. The complete inner assembly can be withdrawn on its front plate for repair or servicing and the tube banks are fitted with an end inspection cover to facilitate cleaning.
Operating Air Temperatures up to 300C
Heater capacities of thermal outputs from 60kW to 1000kw are available; special units to meet the requirements of a particular application can be supplied. The standard HEM heaters consist of a heat exchanger mounted inside a flanged and insulated steel duct section. The heat exchanger section is generously rated for heat transfer surface area and consists of a stainless steel combustion chamber and tube assembly. The combustion chamber and the tube bank assembly are independently mounted to cater for differential expansion.
Burner Assemblies
Each HEM unit is supplied with a pre-packaged and pre-wired burner assembly which includes all of the necessary burner fuel safety valves, pressure switches and automatic ignition and flame safety equipment. Most types of flame failure and automatic ignition control units can be supplied, utilizing flame rectification, photo cell or ultra-violet flame sensing equipment. Air heating burners built to specific applications and country of installation can be fitted. All Burner packages are fully tested and the operation of all components are checked before dispatch from the factory.
Fuel Supply 
Burners can be fitted for operation with natural gas, LP gases or light fuel oils. All gas burners are sized to suit an inlet gas pressure of 17.5mbar (natural gas) or 30mbar (LP gases) unless otherwise specified. Burners can be supplied to suit other fuel types and supply pressures.
Direction of Air Flow
Standard HEM process air heaters are arranged to fire horizontally in the direction of air flow from left to right. (SF)
Heater units can be supplied for firing into duct systems with vertical upwards or downwards air flow. Air flow should be uniform across the air duct, both upstream and downstream of the heater.
Types of Control Available
Heaters supplied with oil burners are normally for high-low operation. (On-off on small units) Most gas burner applications are fitted with modulation burners although high-low can be supplied.
Electrical Supply
The HEM units can be supplied fitted with burners to suit almost all types of electrical supply; including all common industrial three phase (50 or 60Hz) power supplies and with 110/120v or 220/240v control circuits. Burners to suit other electrical supply voltages can be supplied specially to suit specific application requirements.
In general, HEM heaters are designed to provide a nominal temperature rise of 45C at the specified nominal process air flow; however this will depend on application and heater selection (see information sheets) If in doubt concerning the suitability of a HEM unit for a specific application – consult sales office.
