GREEN MATTERS Using pressure exchange
technology to boost CO2 refrigeration effi ciency
Jimmy McLean, senior director of product and sustaining engineering at Energy Recovery looks at the advantages of using a pressure exchanger with a CO2
system. F
or decades, industries and commercial refrigeration applications have used carbon dioxide (CO2
) as a natural refrigerant. Its
growing global popularity has increased as more businesses look to replace synthetic refrigerants and harmful HFCs with a safe, low global warming potential (GWP) alternative. However, despite its numerous advantages, CO2
refrigeration systems
still present some engineering challenges that the refrigeration industry must address to ensure their success. High compression ratio: Carbon dioxide
operates at a much higher compression ratio than synthetic refrigerants. Higher compression ratios result in higher power consumption and reduced effi ciency. They can also stress components, resulting in issues such as wear and tear, leaks, and equipment failure. High discharge temperature: CO2
refrigeration
systems have a high discharge temperature, which measures the heat generated during refrigeration. These temperatures can lead to increased energy consumption, decreased system effi ciency, and shortened component lifespan, and make these systems more vulnerable to failure when ambient temperatures rise. High operating pressure: The high operating refrigeration systems can
pressure of CO2
be challenging, as it requires high-pressure components and specialized equipment. As CO2
refrigeration grows in popularity, the
refrigeration industry is developing myriad solutions to address these challenges, including new system architectures and components. Pressure exchanger technology from Energy Recovery, which has provided signifi cant energy and emissions savings to the water desalination industry for decades, has now been adapted to address these challenges in CO2
refrigeration.
This article will provide an inside look at how the pressure exchanger was developed and the
18 June 2024 •
www.acr-news.com
benefi ts it brings to CO2 refrigeration systems. In short, the PX G1300 pressure exchanger
(PX) is a positive displacement compressor. It acts as a fl uid piston, effi ciently transferring energy between high-pressure and low-pressure liquid and gas through continuously rotating ducts. In other words, the PX captures energy in the system that would otherwise be lost and reintroduces it to the system. A pressure exchanger has two fl uid fl ow paths
through a highly engineered ceramic rotor. The fi rst is the motive fl uid fl ow path and the second is the driven fl uid path. The motive fl uid comes in at the highest pressure inside the PX while the driven fl uid enters from the other side at a lower pressure. The motive fl uid enters the system, pressurizes the driven fl uid to high pressure, and then leaves the rotor as a low-pressure fl uid. The driven fl uid is then compressed or pumped to a higher pressure due to energy exchange with the motive fl uid.
An easy way to think about the pressure
exchanger is that there is a valve and compressor side. The valve side acts like the HPV to control the gas cooler pressure and create liquid CO2
that can
be used in the cooling process. The compressor side can compress CO2
from anywhere in the
system to a higher pressure. Energy Recovery’s PX Pressure Exchanger
fi rst entered the market over 30 years ago as an energy-saving solution for the seawater reverse osmosis (SWRO) desalination industry. Since then, the PX has made the SWRO treatment process commercially viable and has become that industry’s gold standard energy recovery device. The PX is able to reduce energy consumption in an SWRO desalination system by as much as 60%. The PX G1300 is a revolutionary pressure
exchanger application that provides energy-saving benefi ts to high-pressure CO2
systems. The project
began when the United States Department of Energy asked Energy Recovery to explore if the pressure exchanger technology could be applied to CO2 power generation. When transitioning from desalination to CO2
refrigeration, the engineering team at Energy Recovery foresaw the primary challenge was adapting the pressure exchanger, initially designed for pumping liquids only, to operate seamlessly across both liquid and gas phases.
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