Indirect Fired Heaters — Bath Heaters and Process Heating Systems

An indirect fired heater uses a combustion system to heat an intermediate bath fluid — typically water or glycol-water mixture — contained in a vessel. Process coils containing the fluid to be heated are immersed in this heated bath, and heat is transferred from the bath fluid to the process fluid through the coil wall.

The indirect heating arrangement limits the maximum process fluid temperature to below the bath fluid boiling point and eliminates the risk of hot spots that could cause overheating or decomposition of the process fluid. This makes indirect heaters well suited to heating streams that are sensitive to high temperatures or where safe heat input is important.

In upstream oil and gas production, glycol bath heaters are widely used to heat wellhead fluids — including wet natural gas, crude oil and multiphase streams — to prevent hydrate formation and reduce the viscosity of waxy crude oils for pipeline flow.

The glycol-water bath provides a stable heat source even when the process stream flow rate varies or is intermittent, which is common in wellhead applications. The heater fire tube is typically a U-tube or helical coil burner submerged in the bath.

Line heaters are indirect fired heaters used to heat gas or liquid streams in pipelines and gathering systems, typically to prevent hydrate formation or wax deposition. They are compact, skid-mounted units designed for remote or unattended operation in upstream field applications.

Indirect fired heaters are used in gas processing and refinery applications where a controlled, moderate heat input is required. Applications include preheating of regeneration gas in adsorption systems, heating of feed streams to separation units and heating of heat transfer fluid circuits.

In TSA and PSA adsorbent regeneration duties, indirect fired heaters provide clean, temperature-controlled heating of the regeneration gas without the combustion products that would be present with a direct-fired heater.

Indirect fired heater design covers the combustion system (burner, fire tube and flue), bath vessel design, process coil design and the control and safety systems. Safety systems typically include high-temperature cutouts, low-level protection for the bath fluid and burner management systems.

Heat duty calculation must account for the thermal properties of both the bath fluid and the process stream, heat losses from the vessel, and the required process outlet temperature across the full operating range.

Howe Baker designs and supplies indirect fired heaters for wellhead, pipeline and process plant applications. Engineering scope covers thermal design, mechanical design, burner specification and integration with process and safety systems.