Reintroduction of Cryogenic Refrigeration for Cold Transport (2010)

The refrigerated product transport industry is actively looking for alternative approaches to present day diesel fueled, electro-mechanical refrigeration systems. Alternative systems look to reduce CO2 emissions to meet operational criteria of minimal use of fossil fuels and for compliance with Kyoto Protocol criteria for elimination of HCFCs and their derivatives. Ideally the approaches should also minimize noise generation and be cost competitive. Forty years ago there was a significant attempt to move to on-board cryogenic refrigeration alternatives. At the time the driver was not environmental sustainability issues as it is today, rather that cryogenic systems offered simpler more reliable functionality. The movement failed for several reasons, namely: -(1) Cost of cryogenic fluids compared to cost of fossil fuels (fossil fuels were less than $1.00 /gal in the U.S.), (2) Limited reliable availability to cryogenic fluids in the U.S. (3) Limited operational capability. (single temperature control or operation) (4) Limited capacity. (8-hour operation without refill maximum) (5) Safety. No preclusion to inadvertent or premature entry to an O2 depleted trailer atmosphere. Presently there is a new move back to cryogenic refrigeration. Today, designs for cryogenic refrigerated systems are significantly safer, more user-friendly, completely adaptable to operational requirements and are fully capable of long haul demand. Cryogenic refrigeration designs incorporate both direct and indirect injection of nitrogen, the later offering significant safety advantages over direct nitrogen injection. The cryogenic manufacturing industry has expanded its production and distribution capability, with reliable, cost effective nitrogen supply in the 50 U.S. states and virtually every country in the developed world. The cost of cryogenic fluids has proven to be extremely stable in a global economy which has seen the cost of fossil fuels increase and vary significantly. Domestic supply of liquid nitrogen minimizes dependence on foreign suppliers of fossil fuels. Cryogenic production costs are based predominately on the cost of electricity. Most importantly, the use of cryogenic fluids has a significantly lower effect on the environment from both global warming and ozone depletion standpoints. This includes the total effects resulting from the production of the fluids. There is data which provides a comparison of carbon footprints for a diesel driven vs. nitrogen refrigerated trailer cooling system on an annualized basis. Annual consumptions of diesel, refrigerant and liquid nitrogen and CO2 emissions: Total CO2 emissions 31.8 tons eqCO2/an for mechanical diesel systems and 13.9 tons eqCO2 /an for LIN a savings of 56% based on US EPA estimate. (http://www.epa.gov/oms/climate/420f05001.htm#carbon). This data is based on a refrigerated trailer at 37F, 8 hours/d, 300 days/y. Assumed diesel consumption at 4 liters/hr; nitrogen consumption at 30 liters/hr. Both ‘Direct’ and ‘Indirect’ nitrogen refrigeration systems quietly vent spent nitrogen vapor back to the atmosphere after cooling the trailer. Since the source for cryogenic fluids is our atmosphere, and nitrogen is totally recycled, 100% of the fluid used to cool the trailer is returned to the atmosphere with zero greenhouse effect.