Experts Appraisal on DY Cold Storage

DY Refrigeration Technique will replace large and medium-sized refrigeration warehouse

Mr. Hanchun Song
Hunan Province Food General Company Member,
Hunan Province Refrigeration Association

I have engaged in the career of refrigeration warehouse design, manufacturing and administration for more than thirty years. Now I have the honor to be invited by the "DY project production administration office" to chair the meeting for the application of DY refrigeration system, a pioneering invention which had been studied for more than eighteen years, into the large and medium scale refrigerated warehouse, the design of with possesses a refrigerated warehouse, the design of with possesses a crucial importance and significance, it will not only yield a great economical benefit, but will create a shaking admiration in the field of commercial refrigerated warehouse as well; certainly it is a revolution in the field of refrigeration.

The reasons are that, at present, cold warehouse consumes a large amount of energy while the DY refrigeration consumes much less. For many years, in the trade of food the compressor refrigeration has been adopted (mostly ammonia compressor refrigerator) for keeping the foodstuffs frozen, stored and in fresh states.
Nowadays the compressor refrigerator generally used in the piston type that possesses the crank transmission is very expensive, if it is continuously applied under the condition with shortage of energy, while it is not competent enough to solve the problem of freezing food. For instance, building a low temperature cold storage with a capacity of 500T, with the temperature of -20¡ãC, if the freezing capacity is fixed at 10T,there should be 3 sets of compressors, one is the S8-12.5 type with a power of 75KW; altogether power of these three sets will be totally 185KW/hr. According to the price in the mainland of 1watt=0.84 yuan RMB, then the cost per hour will be 155 yuan or 3729.5 yuan per day or 112,300 yuan per month. As for the DY refrigeration system with similar refrigeration capacity, since it is heated in the way of >0.3Kg/cm2 with saturated steam, the cost per hour only 0.633T/h. According to the price of steam of per ton 60 yuan per day or 35,990 yuan per month, which is less that half the cost of the other one.

Another thing worthwhile to be mentioned is that the generator used by the DY refrigeration system needs only water cooling, then a cooling water of 70¡ãC or more could be obtained this water could be utilized again, and the cost will be further reduced.

The cold storage equipment of ammonia compressor refrigeration is even more complicated, the investment is high, while equipment for DY refrigeration is simpler with a low investment. Because of the fact that currently large quantity of ammonia compressor refrigeration has been adopted by the cold storage while the physic change of ammonia is mainly through mechanical motion, but DY refrigeration is by way of heating to achieve the aim, the former possesses motion parts while the latter none. This radically has determined that ammonia compression refrigeration surpasses DY refrigeration system in its complexity efficiency.

For example, the compressor adopts cold freezing oil to lubricate the motion parts. Though an oil and ammonia separator is adopted to have a part of the cold freezing oil separated out, but due to the fact during the operation of the compressor, temperature expelled out of is may be as high as 90--140¡ãC, a part of the cold freezing oil is gasified to become very tiny particles of 5-50 micrometer in size which follows the refrigeration agent gas to enter into the refrigeration system, while on the other hand, the speed of gas expulsion of the compressor may be high up to 24-30m/s, this will easily bring the cold freezing oil into the refrigeration system and bring to the latter bad influence , such as, (1)It makes the condensing temperature raise and the condensing pressure is raised correspondingly. (2) It makes the evaporation temperature fall down. After the oil enters into the evaporator of the system and forms a thin layer of oil membrane of 0.1 mm on the surface will make the evaporation temperature fall by 2.5 ¡ãC, thus consumption of power will also be increased. For this, a large amount of cold freezing oil should be added into the machine during its motion; besides, oil used for the compressor should be consistent with the demands proposed by the refrigerator manufactory. According to general requirements, for home-made compressor with 360 reaper min No.14 oil is used, or may be No.40, but the cost is higher. In order trying to reduce the amount of the freezing oil to enter the refrigeration system during the course of the expulsion of the compressor.

As for the ammonia compressor refrigerator used in cold storage of 500T, it will cost 7,000 yuan RMB. Again for the ammonia compressor refrigerator used in cold storage of 500T, it will nee 5-6T of liquid ammonia, while DY refrigeration system needs only 1T. According to the primary estimate, total investment in the adoption of DY refrigeration system requires less than 2/3 of it. The problem of security in the cold storage compressor refrigeration system is very conspicuous, while in the DY refrigeration system such a problem has never appeared. The present ammonia compressor refrigeration system not only problem of safety exists not only exits not only exists in the pressure container, but there are other problem of safety as well. Accidents easily take place during the course of revolution if operation of the machine is wrong; those usually occur are "frost back". When the compressor absorbs moist steam, there appears frosting on the wall of the cylinder, then the absorption temperature and expulsion air temperature will fall significantly, when the frost back appears to be serious, more amount of solution will be adsorbed into the crankshaft tank, at this time, even at the exit of the expulsion gas there may appear frosting; the compressor would produce abnormal sound which will break the valve plates; sometimes even the filler of the cylinder lid may be broken to let the refrigerating agent leak out. In addition, due to the fall of the temperature of the wall of the cylinder to contract abruptly so much so that an accident of "biting cylinder". When frosting back becomes further serious, large amount of liquid get into the cylinder and the crankshaft tank, thus the viscosity of the freezing oil is increased, the oil cannot be pressed up, the axis tile and the crank get burned and bite together, and this even results into a serious accident-explosion of the compressor. Besides, when the ammonia compressor refrigerator under the condition when the whole unit does not work will have 5-6T liquid ammonia (as to A COLD STORAGE of 500T) deposited, this will offer a hidden point of risk with the presence of liquid ammonia under pressure.

By summarizing the above points, in techniques of refrigeration, compressor is not consistent with the present production. Especially in the cities with dense population, for noises produced by the compressor as well as pollution brought about by the leaked ammonia liquid, the use of them is strictly prohibited by the department of public security and environmental protection. However, there is no existence of such problems mentioned above. Though it also belongs to the type of compressor and its operational pressure is also up to around 10kg/cm2, the equipment itself has increased its security because the heating media used is water and saturated steam, and ammonia is highly soluble in water. It is especially worthwhile to be mentioned here when the whole system stops to perform, there is no existence of liquid ammonia in the system, pressure on the system is zero, so there is no such problem concerning safety. This could never be equaled by the compressor refrigeration system with ammonia.

Currently large amount of maintenance and repair is required by the ammonia compressor refrigeration system while that required by DY refrigeration system is far much less. The piston type of refrigerator depends on the cylinder, gas valve and the to-and-from motion of the piston to complete the absorption of the working substance and steam with the procedures of compression and expulsion. Therefore, any of the breakable parts inside the machine need frequent cleaning and replacement. If an overhaul is performed, assembly and adjustment should be needed, even a modification is required. Therefore the repair will become a heavy burden to the enterprise so far as economical benefits as well as manpower and material are concerned. As for the DY refrigeration system, because there is no motion parts, and as DY generator-the one which is to replace the compressor, need no repair for nearly ten years.

As an old worker with the registration system, after studying the DY system, I sincerely hope that the new products will soon enter into the market; I believe that this DY system will be a challenge to the old system of refrigerator.