CO.sub.2 vehicle refrigeration support systems

A system for filling vehicle tanks with low pressure liquid carbon dioxide. A holding chamber is supplied with high pressure liquid CO.sub.2 from a storage vessel system, and the pressure of liquid CO.sub.2 is reduced to about 60 psig or below to create CO.sub.2 vapor and CO.sub.2 snow and form a low-temperature coolant reservoir in the holding chamber. CO.sub.2 vapor from the chamber is compressed and returned to the storage vessel system. Liquid CO.sub.2 from the storage vessel system can be supplied simultaneously to several vehicle tanks at below about 125 psig, and vapor created as a result thereof is condensed by melting CO.sub.2 snow in the holding chamber. Standby cooling of vehicle compartments is provided by vaporizing liquid CO.sub.2 from a vehicle tank in a heat exchanger for vaporization therein, expanding the vapor to cool it and then passing the expanded vapor through a second heat exchanger. An auxiliary compressor withdraws the expanded vapor from the second heat exchanger and compresses withdrawn vapor sufficient to inject it into the holding chamber where it is condensed by melting the snow.

This invention relates to the carbon dioxide cooling of refrigerated 
vehicles, and more specifically to an arrangement for efficiently and 
economically filling the storage tanks of such vehicles with liquid carbon 
dioxide and for providing standby cooling for such vehicles. 
Although both mechanical and cryogenic systems have been developed in the 
past for cooling refrigerated vehicles, the industry has continued to 
search for better and improved versions of vehicle cooling systems. For 
example, U.S. Pat. No. 3,802,212, issued Apr. 9, 1974 and No. 3,374,640, 
issued Mar. 26, 1968 illustrate the use of liquid nitrogen cooling units 
for trucks and like refrigerated vehicles. My co-pending application Ser. 
No. 708,268, now U.S. Pat. No. 4,045,972 filed July 23, 1976, illustrates 
a vehicle cooling system utilizing liquid carbon dioxide which is believed 
to have significant advantages over prior art cooling systems of this 
general type. 
It is an object of the present invention to provide an improved support 
arrangement for filling vehicle tanks with low pressure liquid carbon 
dioxide. A further object of the invention is to provide an improved 
system for simultaneously filling the tanks of a number of refrigerated 
vehicles with liquid carbon dioxide. Another object is to provide an 
efficient system for cooling of the cargo compartments of such vehicles on 
a standby basis while filling of vehicle tanks is simultaneously 
occurring. These and other objects of the invention will be apparent from 
the following detailed description of a preferred embodiment of an 
installation embodying the invention, particularly when read in 
combination with the single FIGURE of the appended drawing. 
An efficient and economical installation for supplying refrigerated trucks 
with low pressure liquid carbon dioxide has been created which is capable 
of supplying the peak demand of a number of trucks simultaneously, without 
the requirement of an expensive, large capacity compressor and its 
associated high horsepower electric motor and power supply. By creating 
and preserving a reservoir of carbon dioxide snow, a ready sump is 
provided for the carbon dioxide vapor which will be created during the 
time of the peak demand, and as a result the installation allows both the 
simultaneous filling multiple vehicle tanks with low pressure carbon 
dioxide and the standby cooling of their cargo compartments with recovery 
of substantially all of the carbon dioxide vapor created. 
Depicted in the FIGURE is a system which is designed to store refrigerant 
for supply to refrigerated vehicles that employ liquid carbon dioxide for 
coolant. The basic refrigeration system for the vehicle is described in 
detail in my above-mentioned patent application Ser. No. 708,268, the 
disclosure of which is incorporated herein by reference. The system for 
filling the truck storage tanks is sometimes referred to as a ground 
support system, and it is designed to minimize the cost of operating such 
an overall, carbon dioxide, vehicle refrigeration system by (1) minimizing 
the cost of installed equipment and (2) recovering carbon dioxide vapor 
for compression and reliquefication whenever feasible.

Basically, the vehicle refrigeration system utilizes a liquid carbon 
dioxide storage tank 5, which may be mounted underneath the truck frame, 
and includes a liquid inlet line 7 that is equipped with a shut-off valve 
9 and a coupling 11a for connection to the ground support system. A vapor 
return line 13 extends from an upper region of the tank 5. It includes a 
pressure relief valve 15 and similarly includes a shut-off valve 17 and a 
coupling 19a for connection to the ground support system. 
A liquid feed line 21 runs from a lower portion of the storage tank 5 
through a shut-off valve 23 to a heat exchanger 25, which is located in 
the cargo compartment 27 of the vehicle. The heat exchanger 25 is of 
sufficient length so that all of the liquid carbon dioxide turns to vapor 
therein, and the vapor exits through a line 29 which includes a back 
pressure regulator 31 that is set to maintain a pressure of at least 65 
psig in the heat exchange coil to prevent the formation of solid carbon 
dioxide therein. The carbon dioxide vapor flowing through the line 29 
enters a gas motor 33 which is drivingly connected to a blower fan 35 that 
causes circulation of the atmosphere throughout the cargo compartment 27 
and in particular past the heat exchanger 25. Isentropic expansion takes 
place in the gas motor 33 and results in both a lowering of the pressure 
of the vapor as well as a lowering of its temperature. 
The cold vapor then passes through a second heat exchanger 37, which may be 
arranged so that it also lies in the circulation path of the blower 35, 
and advantage is thus taken of the cooling capacity of this expanded 
vapor. The vapor exiting from the heat exchanger 37 travels through a line 
39 to a tee connection 41. One leg of the tee 41 leads to a second gas 
motor 43, which is drivingly connected to a second blower 45, wherein 
further isentropic expansion occurs. The other leg of the tee 41 connects 
to a branch line 47 which contains a shut-off valve 49 and leads to a 
coupling 51a for connection to an auxiliary vapor return line 53 of the 
ground support system. The re-cooled vapor from the second motor 43 flows 
through a third heat exchanger 55 which lies in the circulation path of 
the second blower 45. After the cooling capacity of this re-cooled vapor 
is extracted, it is vented to the atmosphere exteriorly of the cargo 
compartment 27. 
The ground support system includes a main storage vessel 61 together with a 
freon condenser 63 of appropriate size. A supply line 65 from a lower 
portion of the storage vessel 61 is directed to a tee connection 67, the 
left hand leg of which leads, via a solenoid-controlled valve 69 to an 
intermediate tank 71 which is provided with a liquid level control 73. A 
liquid outlet 75 from the intermediate tank 71 is branched, and each 
branch line includes a shut-off valve 77 and a coupling 11b for connection 
via coupling 11a to the liquid inlet 7 of a selected vehicle storage tank 
5. A vapor outlet line 81 of the intermediate tank 71 contains a back 
pressure regulator 83 which is set to maintain a predetermined pressure, 
e.g., 95 psig., in the intermediate tank and which thus determines the 
amount of expansion and pressure drop that takes place as the high 
pressure liquid from the main storage vessel 61 is expanded thereto. The 
vapor line 81 is connected through a tee 84 to another pressure regulator 
85, set at, for example, 65 psig., to a vapor inlet line 88 which leads to 
the bottom of a holding tank 89. The pressure regulator 85 prevents the 
formation of solid carbon dioxide in the lines and devices upstream 
thereof. The other leg of the tee 84 contains a relief valve 86 and leads 
to a branched line which includes pairs of shut-off valves 87 and the 
mating couplings 19b. 
The holding tank 89 is supported on a balance 91, and a weight switch 93 is 
connected to a control system 95. When the holding tank 89 is being 
filled, liquid CO.sub.2 flows through the right-hand line leading from the 
tee 67 via a solenoid-operated valve 96 until a predetermined weight is 
reached, which indicates that the holding tank is filled to the desired 
extent with high pressure liquid carbon dioxide. A vapor line 97 leads 
from the upper portion of the holding tank 89 and is branched to provide 
two parallel paths leading to a compressor 99 that is controlled by a 
pressure switch 101 that will cause the compressor to run whenever there 
is a minimum amount of vapor present. 
During the initial filling of the holding tank 89, the vapor passes through 
a back pressure regulator 103 which may be set at about 65 psig. (which is 
above the triple point of carbon dioxide, i.e., about 60 psig and 
-70.degree. F.), and the compressor automatically begins to run, as the 
pressure switch may be set for about 50 psig. The compressed vapor is 
raised to a pressure sufficient to cause it to flow through a return line 
105 and bubble through a submerged inlet into the liquid portion of the 
main storage vessel 61. 
As soon as the weight switch 93 indicates that the holding tank 89 has been 
filled with the desired amount of liquid, the control system 95 opens a 
solenoid-controlled valve 107 that provides a parallel path to the 
compressor 99 through a back-pressure regulator 109 that is set at the 
triple point or below, e.g., 55 psig. and thus allows the formation of 
solid CO.sub.2 in the holding tank 89. As the compressor 99 slowly lowers 
the pressure, first slush is created, and then eventually the entire 
contents of the holding tank 89 is converted to CO.sub.2 snow. This takes 
place over a number of hours, usually during the night or some other 
period of low demand, and the ground system is then fully charged and 
ready for operation. The compressor 99 runs continuously until the entire 
reservoir in the holding tank 89 has turned to snow, and when the 
compressor 99 shuts off, the control system 95 closes the valve 107 so the 
pressure in the tank 89 is allowed to slowly rise to the triple point. 
The ground support system is coupled to a vehicle refrigeration system via 
connection of appropriate couplings 11a and b, 19a and b and 51a and b. 
The valves 9 and 17 are opened along with appropriate valves 77 and 87, 
and the cold liquid CO.sub.2 from the intermediate tank 71 flows into the 
vehicle storage tank 5 through the line 75 and the coupling 11a, 11b. Flow 
occurs as the result of pressure differential, and the pressure in the 
vehicle tank is preferably controlled by a back-pressure regulator 111 
which is set a few pounds below the regulator 83. The vapor from the tank 
5 flows through the line 13 and the tee 84 where it enters the main vapor 
return line 81 which leads to the bottom of the holding tank 89. 
Shortly after liquid CO.sub.2 begins to flow from the intermediate storage 
tank 71, the liquid level controller 73 opens the solenoid-operated supply 
valve 69, via the control system 95 which also actuates the 
solenoid-operated valve 107 in the vapor line 97 to open the parallel path 
to the compressor 99 through pressure regulator 109, which is set at about 
10 psi. below pressure regulator 103. Opening of the valve 107 allows the 
compressor 99 to get a head start, anticipating that vapor will soon be 
flowing to the holding tank 89, where the latent heat of the refrigeration 
reservoir of solid CO.sub.2 stands available to assist the compressor 99 
in condensing the incoming vapor. As soon as the flow of vapor through the 
line 88 reaches the tank 89, melting of the CO.sub.2 snow to slush begins 
accompanied concurrently with liquefication of the incoming vapor. The 
compressor is of course working to remove vapor and convert the liquid 
back to snow; however, a net increase in liquid in the tank occurs when 
the rate of vapor inflow exceeds the capacity of the compressor 99. 
When it is desired to cool the cargo compartment 27 of a vehicle while the 
vehicle is still coupled to the ground support system, the valve 23 in the 
liquid feed line 21, the valve 49 and a valve 115 in the secondary vapor 
recovery line 53 are opened. As a result, liquid carbon dioxide at, for 
example, a pressure of about 90 psig. flows into the main heat exchanger 
25 and vaporizes. The vapor is expanded and cooled in the first air motor 
33, and then provides further cooling for the cargo compartment 27 as it 
passes through the second heat exchanger 37. In order to recover the 
carbon dioxide vapor that is being used for this standby cooling of the 
cargo compartment 27, the branch line 47 is utilized. Thus, the vapor from 
the second heat exchanger 37 is sucked through coupling 51a, b and through 
the auxiliary vapor recovery line 53 to a small auxiliary compressor 117, 
which is sized to take the vapor, that may be at about 25 psig. and raise 
it to a sufficient pressure, i.e., in the neighborhood of about 60-70 
psig., so that it will flow through a check valve 119 and into the main 
vapor recovery line 88 leading to the holding tank 89. Thus, this 
compressed vapor is condensed to liquid by the snow or slush reservoir 
that has been built up in the tank; and accordingly, the system provides 
for standby cooling of the cargo compartments 27 of vehicles without 
expending liquid carbon dioxide. 
As indicated by the plural couplings 11b, 19b and 51b, the ground support 
system is designed to supply liquid carbon dioxide at cold temperatures 
and relatively low pressure simultaneously to a plurality of vehicles. In 
the preferred form, all of the fluid flow is by pressure differential, and 
no auxiliary pumping equipment is required. As a part of the design of the 
system, a low temperature low pressure liquid reservoir is preferably 
built up in the tank 71 which is ready for prompt flow at any time to the 
individual vehicle tanks 5. More importantly, either during off periods or 
at night, the large holding tank 89 full of carbon dioxide snow is 
created, which then stands ready to condense the vapor which will be 
created during a peak time of filling individual vehicle tanks and/or 
cooling still coupled vehicles. 
All of the foregoing is accomplished without the need for a large 
horsepower motor to drive a high capacity compressor, that would otherwise 
be needed to handle all of the vapor that would be created during peak 
demand periods. Instead, a relatively small sized compressor 99 can 
adequately handle the job because its period of operation is stretched out 
over a good deal of the 24-hour day. However, should a peak demand of 
unusually long duration occur, so that all the snow in the holding tank 89 
is melted and the pressure in the tank 89 climbs past a set upper limit of 
about 70 psig., a spring-loaded relief valve 121 opens and vents the 
ground support system, as needed, to keep the pressure within the working 
design so as to allow the continued filling of vehicle tanks 5 and the 
standby cooling of the cargo compartments 27. Should such venting occur, 
the control system 95 senses the condition via the weight switch 93, after 
an "at rest" position is later reached, and automatically refills the 
tank 89 to the desired level. Thus, the ground support system provides a 
relatively low cost installation, from an equipment standpoint, yet is 
extremely economical in use because it stands ready to supply cold liquid 
carbon dioxide to the storage tanks of multiple vehicles with 
substantially no expenditure of carbon dioxide during the filling of the 
vehicle tanks or during stand-by cooling of their cargo compartments. 
Various of the features of the invention are set forth in the claims which 
follow.