How Printed Circuit Heat Exchanger Optimize LNG Waste Heat
Introduction
Liquefied Natural Gas (LNG) is a vital clean energy source with significant potential for energy optimization in its industry chain. LNG power systems generate substantial medium-to-high-temperature waste heat, while the gasification process releases a vast amount of high-quality cold energy. Efficiently recovering and utilizing this otherwise wasted heat and cold energy is crucial for improving the energy efficiency of the LNG industry, reducing operational costs, and minimizing environmental impact.
LNG Power Waste Heat Recovery: ORC Technology
In LNG ships or power generation units, engines or gas turbines typically achieve thermal efficiencies of 40%-45%, with turbine efficiencies around 40%-43%. Over 50% of the energy is lost as high-temperature exhaust gases or jacket water waste heat. Organic Rankine Cycle (ORC) technology effectively recovers this medium-to-low-temperature waste heat and converts it into electricity.
Compared to traditional steam cycles, ORC uses low-boiling-point organic working fluids (e.g., cyclopentane, R245fa), offering simpler system structures, stable operation, high safety, and adaptability to a wide range of heat source temperatures. With optimized working fluid selection and system configuration, ORC systems can achieve a 10%-15% waste heat-to-electricity conversion rate. The performance of internal heat exchange equipment is critical for efficient and stable ORC operation.
- Evaporator: Absorbs heat from the waste heat source to vaporize the organic working fluid.
- Recuperator: Recovers residual heat from the working fluid after expansion to preheat the liquid entering the evaporator, improving overall efficiency.
- Condenser: Condenses the low-pressure gaseous working fluid into a liquid, releasing latent heat and providing inlet conditions for the working fluid pump.
High-Efficiency Heat Exchangers for ORC Stability
Plate-Fin Heat Exchangers (PFHE) and Shell-Plate Heat Exchangers (Shell Plate HX) are compact, offer excellent heat transfer performance, and have strong pressure resistance, making them ideal for use as evaporators, recuperators, and condensers in ORC systems.
Shell-Plate Heat Exchangers enhance heat transfer through their corrugated plate bundle structure and offer a variety of metal material options for superior corrosion and high-temperature resistance. Their welded design eliminates the risk of fatigue failure under high temperatures, pressures, and alternating stresses, unlike traditional detachable plate heat exchangers.
In an LNG ship project, a PFHE preheater provided by Shen-Tech was successfully applied in a 240°C/40 Bar condition, efficiently handling a 12,000 kW cyclopentane evaporation process. The PFHE core, manufactured using advanced diffusion welding, eliminates the risk of gasket leaks, while its enhanced plate design meets both high heat transfer efficiency and high-pressure reliability requirements.
Efficient Utilization of LNG Cold Energy
Traditional LNG gasification stations use simple heat exchanger structures for basic heat exchange between LNG and seawater or ambient media. In advanced LNG/ethane cold energy utilization systems, heat exchangers must handle complex conditions, including efficient heat transfer between ultra-low-temperature fluids (LNG as low as -162°C) and intermediate media, as well as multi-stream, multi-temperature heat transfer processes involving various media (air, organic working fluids, water/glycol solutions) in different phases (liquid, gas, two-phase). This demands superior performance, optimized structural design, and high reliability.
Shen-Tech’s Printed Circuit Heat Exchangers (PCHE) and Shell-Plate Heat Exchangers meet the stringent technical requirements for efficient, compact, and reliable heat exchange in LNG and ethane cold energy applications. PCHEs, with their microchannel design (up to 99 MPa design pressure), offer high surface-area-to-volume ratios and compactness, reducing footprint while enhancing internal turbulence for significantly improved heat transfer efficiency. They are ideal for high-pressure, multi-stream coupled low-temperature conditions.
Shell-Plate Heat Exchangers combine the efficiency of plate heat exchangers with the high-pressure and wide-temperature-range capabilities of shell-and-tube heat exchangers. They offer excellent pressure resistance, large flow handling, and material options for corrosion and high-temperature resistance, making them suitable for medium-to-large flow and medium-to-high-pressure cold energy recovery scenarios.
Cold Energy Applications and Thermal Management Solutions
LNG Gasification Cold Energy Recovery
(Recommended: PCHE or Shell-Plate Heat Exchangers)
District Cooling and Aquaculture
Using PCHE or Shell-Plate Heat Exchangers, the cold energy released during LNG gasification is transferred to an intermediate cooling medium (e.g., glycol-water solution). After multi-stage temperature regulation, this medium provides a stable, controllable low-temperature source for district cooling systems or low-temperature aquaculture facilities, reducing energy consumption from traditional electrically driven refrigeration compressors.
Direct LNG Cold Energy Use for Glycol Cooling
Efficient, compact PCHEs transfer LNG cold energy directly to glycol solutions, which can be used in processes requiring medium-to-low-temperature cooling or as a secondary cooling medium for cold energy distribution, enabling efficient cold energy recovery.
Cold Energy Utilization in Fuel Gas Supply Systems (FGSS)
In LNG-fueled ships, cold energy released during LNG gasification for engine combustion can be recovered using PCHE or Shell-Plate Heat Exchangers. This cold energy can directly cool refrigerants or indirectly cool them via a cooling medium, providing cooling for ship air conditioning or refrigeration systems, reducing compressor loads, and improving overall ship energy efficiency.
Ethane Gasification Cold Energy Recovery
(Recommended: Shell-Plate Heat Exchangers)
In chemical plants like ethane cracking units, gaseous ethane needs to be liquefied. Shen-Tech’s Shell-Plate Heat Exchangers, with excellent pressure resistance and large flow handling, enable efficient heat exchange between LNG and gaseous ethane for liquefaction. During the subsequent gasification stage, the released cold energy is recovered to cool process fluids like propylene, achieving multi-temperature cascade utilization and minimizing overall energy consumption.
