Refrigeration – Automatic control – Of external fluid or means
Reexamination Certificate
1999-11-19
2001-04-10
McDermott, Corrine (Department: 3744)
Refrigeration
Automatic control
Of external fluid or means
C062S434000
Reexamination Certificate
active
06212895
ABSTRACT:
CROSS REFERENCES TO RELATED APPLICATIONS
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
BACKGROUND OF THE INVENTION
The present invention relates to refrigeration systems in general, and more particularly to refrigeration systems which provide cooling for air as well as machinery fluids.
Many industrial processes require control of the temperature of the material being processed and often of the machines handling the material. Particularly in the food industry an entire plant may be cooled to prevent spoilage and the growth of bacteria in foodstuffs. This is particularly a concern with meat, where it is important to control bacterial growth to assure product safety.
In an industrial setting, ammonia is often employed as a refrigerant. Ammonia is low cost and an efficient refrigerant for the temperature range of interest in many industrial processes. The hazards associated with ammonia: flammability and toxicity if inhaled, are safely handled in an industrial setting where safety practices and monitoring equipment can be reliably employed. Thus, for industrial processes, ammonia is one of the most widely used refrigerants.
Ethylene glycol is a widely used coolant. When used alone or mixed with water it has excellent heat absorbing characteristics, good thermal conductivity, and remains liquid over a broad temperature band. Whereas ammonia is used in a refrigerator or heat pump to transport heat energy from a cool reservoir to a warm reservoir, ethylene glycol transports heat from a warm reservoir to a cool reservoir.
In industrial plants, merely keeping the air at a desired temperature will not typically ensure that a material being handled within the plant remains near the air temperature. Machines which perform work convert energy stored as hydraulic pressure into mechanical motion. Most of the energy, however, is eventually converted into heat. Where a material is worked by a machine, the machine and the material may become undesirably heated. For machines employing hydraulic fluid to transfer energy, a typical process is to cool the hydraulic oil used by individual machines by passing water through a heat exchanger so that heat from the oil is given up to the cooling water.
Ground water is sometimes used as a low cost source of cooling fluid to extract heat from hydraulic oil. Water has a high specific heat and when pumped from below the ground typically has a temperature, determined principally by latitude, which in the Midwest is typically in the neighborhood of 55 degrees Fahrenheit. In the past this ground water could be obtained at the cost of pumping it from the ground.
Modern industrial plants, particularly those handling organic material, are typically connected to their own or to a municipal sewage treatment plant. Particularly when connected to a municipal sewage treatment plant, the cost of treatment is based on the amount of water consumed. Thus the use of an open loop water cooling system can have considerable negative economic consequences.
What is needed is an efficient method and apparatus for closed loop cooling of machine hydraulic fluids.
SUMMARY OF THE INVENTION
The cooling system of this invention employs an ethylene glycol coolant transport loop which is cooled by the existing plant ammonia-based air conditioning or other refrigeration system. The coolant loop, which employs an ethylene glycol or a water ethylene glycol solution, moves through an ammonia evaporator where the coolant is lowered to a set point temperature, typically around 50 degrees Fahrenheit. The coolant then flows to a supply header. The supply header is connected to a return side header by one or more individual cooling loops which pass through one or more associated heat exchangers mounted on individual machines for cooling the hydraulic fluid employed by each machine. The supply header is also connected to the return header by a regulating valve which is set to maintain a constant pressure drop between the supply header and the return header. Fluid flow networks such as those involved in cooling many different machines in parallel are not subject to analytical solution, with the result that a change in one loop of a network changes flows in all other loops of the same network.
This problem is solved by maintaining a fixed pressure drop between the supply header and the return header. Thus each machine coolant fluid flow can be adjusted by a regulating valve which is adjusted by reference to a flow meter on a particular coolant loop. As each individual coolant loop is adjusted, the regulating valve between the supply header and the return header will require adjusting either automatically or manually to maintain a constant pressure drop between the supply header and the return header. However, every other coolant loop maintains a constant flow so long as the pressure drop between the supply header and the return header remains constant. This allows simple machine by machine adjustment of coolant flows. The return header is connected through an isolation valve to a surge tank and to a pump which returns the fluid to the ammonia heat exchangers where the ethylene glycol coolant is again cooled and sent to the supply header.
It is an object of the present invention to provide a lower cost method of cooling industrial machinery.
It is a further object of the present invention to provide a method of regulating the cooling of a plurality of machines without introducing ammonia into the factory floor.
It is a still further object of the present invention to eliminate open loop cooling within a manufacturing facility handling foodstuffs.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.
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Emmpak Foods Inc.
Jiang Chen-Wen
Lathrop & Clark LLP
McDermott Corrine
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