An exhaust gas heat exchanger recovers heat from the exhaust of a stationary engine, generator set, or other combustion equipment. In a common gas-to-water design, exhaust passes through a tube core while water circulates inside the shell. Heat crosses the tube walls without the two media normally mixing.
This equipment is not an air-cooled heat exchanger. An air cooler rejects heat from oil, water, or another fluid to ambient air through finned tubes and fans. An exhaust heat exchanger captures waste heat for another duty. It is also not necessarily a gas-to-gas exchanger; the second medium discussed here is liquid.
How Does an Exhaust Gas Heat Exchanger Recover Heat?
Hot exhaust flows across a metal heat-transfer surface. Water or another specified liquid flows on the opposite side. The exhaust leaves cooler, while the liquid carries the recovered energy to a hot-water or process circuit.
The approved design defines the flow path. Exhaust often flows through tubes arranged for inspection and cleaning, with liquid in the surrounding shell, but other constructions are possible. Our guide to shell-side and tube-side fluid allocation explains why media placement should be reviewed rather than assumed.
More heat recovery is not automatically better. Excessive exhaust gas cooling can cause condensation and corrosion; restricted passages can increase backpressure. The engine supplier or project engineer should define allowable backpressure, exhaust outlet limits, thermal duty, and operating range. These limits must be considered with heat exchanger pressure drop.
Soot, combustion deposits, and condensate also affect performance. Tube size, gas velocity, drains, inspection access, and the specified cleaning method therefore matter.
Where Are Exhaust Gas Heat Exchangers Used?
Industrial exhaust heat exchangers are considered for stationary diesel or gas generator sets, CHP systems, biogas engines, marine auxiliary generators, and industrial engine packages. A heat exchanger for diesel engine exhaust may range from a compact hot-water unit to a larger engineered recovery system.
Recovered heat may serve process water, building heating, feedwater preheating, drying, or absorption cooling. The value depends on whether the site needs heat while the engine operates. A heat exchanger cannot save energy if the recovered heat has no useful destination.
Pumps, valves, bypasses, controls, expansion provision, drains, safety devices, and the liquid circuit remain part of the wider system. For related equipment, see JED’s power-generation auxiliary cooling and marine heat exchangers.
What Must an Exhaust Gas Heat Exchanger Drawing Specify?
A drawing-based manufacturer needs more than engine power. The approved drawing and specification should define:
- Service: Engine type, fuel, exhaust composition, liquid medium, and corrosion or contamination concerns.
- Conditions: Flow rates, inlet and required outlet temperatures, design temperature and pressure, and allowable backpressure.
- Construction: Shell, tube, and tubesheet materials; thickness; corrosion allowance; welding; gaskets; and insulation. See heat exchanger material selection.
- Interfaces: Orientation, dimensions, nozzles, flanges, supports, drains, bypass connections, and maintenance clearance.
- Inspection: Code, material certificates, dimensional checks, pressure or leakage testing, VT/UT/PT, witness points, and documents.
For the calculation logic, see how to size a heat exchanger. JED does not determine the engine’s safe backpressure or operating limits. The customer’s engine supplier or engineering team must specify or approve these requirements before manufacturing documents are finalized.
Have an Exhaust Gas Heat Exchanger Drawing for Manufacturing Review?
JED manufactures custom shell-and-tube heat exchangers and industrial coolers from customer-approved drawings and technical specifications.
Send the available drawing, materials, dimensions, connections, design conditions, inspection requirements, quantity, and document list. We will review the construction, manufacturing scope, material availability, testing, and required certificates before quotation. Missing or conflicting details must be resolved before production approval.
Exhaust Gas Heat Exchanger FAQ
Is an exhaust gas heat exchanger the same as an EGR cooler?
No. An EGR cooler cools part of the exhaust before it returns to the engine. An exhaust gas heat recovery exchanger captures energy for a separate thermal load.
Can an exhaust gas heat exchanger replace an exhaust silencer?
Not automatically. Some engineered units combine both functions, but acoustic performance must be included in the approved specification.
Can seawater be used on the liquid side?
It may be possible in a marine unit. Seawater changes material, corrosion, fouling, cleaning, and service-life requirements, so the medium and materials must be specified.
Can only the tube bundle be replaced?
Possibly, if the existing shell remains suitable. Tubesheet dimensions, sealing surfaces, supports, materials, clearances, and shell interfaces must first be verified.
Does exhaust heat recovery increase engine electrical output?
Not necessarily. Its main purpose is to use heat that would otherwise be rejected. Any effect on electrical output depends on the complete engine and recovery-system design.
