Heat Recovery for Jenbacher 620 GS NL Gas Engine

Heat Recovery for Jenbacher 620 GS NL Gas Engine

When a gas engine (e.g. natural gas engine, biogas engine) is running, only about 30%-40% of the fuel combustion energy is converted into mechanical work or electrical energy, and the remaining 60%-70% is dissipated in the form of waste heat (exhaust gas accounts for 35%-45%, cooling water accounts for 20%-30%, and lubricating oil, etc., accounts for 5%-10%). Heat recovery technology recovers this waste heat through high-efficiency heat exchanger equipment and converts it into usable thermal energy (such as hot water, steam, hot air), which increases the energy utilization rate to 70%-90% and reduces the carbon emission at the same time, which is applicable to “Combined Heat and Power (CHP)” or “Cooling, Heating, and Power (CCHP) “ systems.

Heat Recovery Main Methods and Equipment

1. Exhaust Heat Recovery

Core equipment:

Exhaust Waste Heat Boiler: High-temperature exhaust gas (400-600°C) is passed into the boiler tube bundle to heat water to generate steam (pressure 0.5-2.5MPa), which is used to drive steam turbines for power generation, industrial steaming or heating.

Plate / Tube Heat Exchanger: Low temperature exhaust gases (<300°C) are passed through a heat exchanger to heat water or air, e.g. to provide domestic hot water for buildings or to preheat combustion air (to improve engine efficiency).

Example: a 1MW gas generator set, exhaust heat recovery can produce 1.5t/h, 0.8MPa steam to meet the steam demand of the plant.

2. Cooling water heat recovery

Recovery object: engine cylinder liner water, intercooler cooling water (temperature 80-120 ℃).

Equipment and application:

Tube heat exchanger: Heating domestic water (50-60℃) for hotel and hospital heating; or preheating process materials (e.g. chemical reactor feed).

Absorption heat pump / lithium bromide unit: Utilizing high temperature cooling water (>90℃) to drive the heat pump to raise the heat to a higher temperature (e.g. 70-90℃) for district heating or cooling.

3. Lube oil heat recovery

Recovery object: lubricating oil temperature is usually 60-90℃, heating low temperature water (e.g. 30-40℃ to 50-60℃) through oil-water heat exchanger, used for preheating boiler feed water or domestic hot water pre-treatment.

Key components of a heat recovery system

Heat exchanger selection:

High-temperature exhaust: use temperature-resistant stainless steel tube heat exchanger or finned tube heat exchanger (heat transfer coefficient 200-400W/m2・K).

Low and medium temperature water/oil: plate heat exchanger (heat transfer coefficient 2000-4000W/m2/K), compact and easy to clean.

Heat distribution and control:

Temperature control valve: Adjust the waste heat flow into the heat exchanger according to the heat load demand to avoid overheating.

Heat storage devices: such as hot water storage tanks (volume 5-50m³), balancing the heat load fluctuations (e.g., storage of heat at night when heating demand decreases).

Auxiliary systems:

Circulating water pump: to drive the cooling water or heat medium water circulation, the head is designed according to the system resistance (usually 10-30m).

Flue gas purification: some scenarios require the addition of dust removal and desulphurization devices before exhaust heat recovery (e.g., when the gas contains sulfur) to prevent heat exchanger corrosion.