RU2084780C1 - Method of providing cold air flows and design of turbo-refrigerating plant - Google Patents

Abstract

FIELD: refrigerating engineering; turbo-refrigerating plants of high power rating (removal of heat up to 2000 kcal/s) for quick freezing of large amounts of products. SUBSTANCE: compressed air flow is built in two steps with intermediate cooling by water in heat exchanger (refrigerator) between two stops. Degree of pressure rise at second step is selected to provide equality of compression in compressor and expansion in turbine mounted on common drive shaft and operating on cold compressed air. Gas turbine engine is used as drive of first compressor. Exhaust device of engine is connected to turbine of first turbocompressor. Air only is used as cold carrier. No electric power is required. Turbojet aircraft engines removed from aircraft after expiration of their service life are used as both turbocompressors operating at ratings close to designed one. EFFECT: enlarged operating capabilities. 4 cl, 2 dwg

Description

The invention relates to the field of refrigeration equipment, in particular to high-power turbo-refrigeration units with heat dissipation up to 2000 kcal / s (≈8000 kW) at a temperature of cold air flow (-80) - (-170) ^o C. These parameters are necessary for quick freezing tens of tons of products for no more than 20-60 minutes (optimally 15-30 minutes), for example freshly caught fish, up to t = -80 ^o C, which significantly increases its quality and cost. It is known that liquid nitrogen is currently used for this purpose (see Appendix No. 1, for technical data on a standard English container for freezing products with liquid nitrogen). Similar parameters of refrigeration devices are required to quickly freeze large quantities of meat, vegetables and fruits, to obtain solid CO ₂ , as well as in a number of technical fields, for example, in the cryogenic separation of gas mixture components and for other purposes. Widely used chillers with conventional refrigerants (ammonia, freons) cannot provide such low temperatures [1] Such parameters are obtained in air-powered turbochargers (a combination of a turbine and a compressor on one shaft) with an electric drive. At the same time, it is important not only that the air that performs the functions of the refrigerant is quickly cooled in the blade machines, but it becomes possible to blow cold objects into the air to create intense convective heat exchange between the refrigerated products and the flow of refrigerant (air), since the latter is harmless to the products. With other refrigerants, cooling occurs by natural convection, when the heat flux is many times smaller.

 In turbo-refrigerating machines, compressed air after cooling in the heat exchanger is sent to the turbine expander, where, when the pressure drops, the air temperature decreases, and the turbine generates power by reducing the internal energy of the air flow. However, the turbine power is 1.5-2.5 times less than that required to compress the air flow in one compressor (in gas turbine engines, the air after the compressor is heated in the combustion chamber by 2.5-3.5 times, which provides a corresponding increase turbine power); in this regard, in turbo-refrigerating machines, as well as in piston refrigerators, power supply is required to drive the turbocompressor, which is carried out using an electric motor (see [2] and also appendix N 2; "Technical installations with air turbo-refrigerating machines" (turbo expanders) , Ministry of Heavy Engineering, SKTBA NPO NIIKHIMMASH, 1991; since 1993 SKB Turboholod see Appendix No. 3). Currently, these SKBs produce low-power turbo-refrigerating machines with an air flow rate of 0.5-2.5 kg / s and a heat sink of 5-20 kcal / s. The closest technical solution to the proposed below method for producing cold air are the method and installation described in [2] on page 365, which we take as a prototype of the claimed invention.

 A disadvantage of the known schemes of turbo-refrigerating machines and methods for producing cold air streams in them is that to obtain machines of high power, for example, with a heat sink of up to 2000 kcal / s, with an air flow of up to 200 kg / s, an electric motor with a power of 20-40 MW is required, and the weight of the machine will be 100-300 tons, i.e. in terms of parameters, such a machine will be close to powerful exhauster blowers used in research centers for testing aircraft engines in high-altitude conditions. An electric drive of the indicated power requires a special electrical substation, and the mode will be on the order of 30-60 minutes (for the gradual heating of the cases), and it is rather difficult to coordinate the speed of the electric motor and compressor.

 The technical result of the claimed invention is to obtain large volumes of cold air flow without the use of electricity, which increases the mobility of the installation, significantly reduces the weight and reduces the cost of the structure, makes the entire structure easier to manufacture and reduces the cost of freezing, because cooling occurs when air is blown, i.e. with intensive heat dissipation, for 15-30 minutes, and access to the mode takes a few minutes at the machine.

This technical result is achieved by the fact that atmospheric air is sucked in by the first compressor (Fig. 1), after which it is cooled in a heat exchanger (up to 15-25 ^o C), then compressed air (with a pressure of 2-4 atm, depending on the set temperature entering the consumer of cold) is pressurized in a second compressor (up to 2.5-5.5 ata), at the outlet of which it is again cooled and dried in the heat exchanger with cold air leaving the consumer of cold; after the second heat exchanger, compressed air enters the turbine, in which excess pressure is triggered, and then the air (coolant), acquiring a predetermined low temperature, is supplied at atmospheric pressure to the cold consumer, and then through the heat exchanger to the atmosphere, while not using the first compressor an electric motor, and a gas turbine located on the same shaft with it and connected to an exhaust device of a turbojet engine, for example, a serial aircraft engine that has performed a flight LAS.

 The introduction of two turbochargers from serial aircraft engines into the device of a turbo-refrigerating machine allows the use of a simple and cheap gas-turbine drive, reducing the work of compression due to intermediate cooling between the two compressors and using ready-made turbocompressors, which are the main components of any turbo-refrigerating device in terms of complexity and cost, and allow quick start-up characteristic of aircraft.

The costs of heat removal using a cold air stream generated, for example, by the TMHZ-5 machine (see Appendix N 2), are an order of magnitude lower than the costs of liquid nitrogen for the same heat removal, despite the fact that the energy consumption per unit the heat removed from turbo-refrigerators operating in air is two to four times greater than in ammonia or freon coolers due to lower temperatures (-80 -170 ^o C) and the absence of changes in the state of aggregation of the refrigerant (air) during refrigeration cycle.

The present invention is illustrated by the general scheme of a turbo-refrigeration machine for producing a cold air flow shown in FIG. 1. The proposed method for producing cold air is that the atmospheric air is sucked in by the first compressor (1), after which it is cooled in the first water-air heat exchanger (2) to 15-25 ^o C; then compressed air with a pressure of 2-4 ata (depending on the set temperature at the inlet to the cold consumer) is compressed in the second compressor (3) to 2.5-5.5 ata, at the outlet of which it is first cooled in a water-air heat exchanger (4) to 15-24 ^o C, after which it is cooled and dried in the heat exchanger (5) with cold air leaving the consumer of cold, as is usually done in turbo-refrigerating machines; after heat exchanger (5), compressed air enters the turbine-expander (6), in which excess pressure is triggered, and then the air cooler, having acquired a predetermined low temperature, is supplied at atmospheric pressure to the cold consumer (7) and exits through the heat exchanger (5) into the atmosphere . Below are the main parameters of the state of the coolant for three of the possible modes of operation of the turbo-refrigerating machine described above with an air flow rate of 150-200 kg / s, heat removal in an amount up to 1300-2000 kcal / s and a gas turbine drive power of 20-30 mW. If both turbocompressors (I) and (II) (Fig. 1) are gas turbine engines (for example, RD-3M or VD-7, the air flow on them, respectively, 160 and 210 kg / s) with the exhausted air resource, then the main the nodes that need to be designed and manufactured anew during the production of a turbo-refrigeration machine are only heat exchangers, gas paths, a cold consumer and a control system. In this regard, the cost of such a turbo-refrigerating machine based on the experience of creating a turbo-refrigerating machine and several two-stage exhausters, consisting, like the pipe refrigerating machine described above, of two turbochargers from aircraft engines, heat exchangers and one turbojet engine (8) (Fig. 1) of the source there will be about two million dollars of hot gases [3, 4, 5] entering the turbine (9), and it can even be installed on large fishing vessels, since its weight is 15–25 tons, and the required area for placement is about 200 m ² . A stationary blower (exhauster) with an electric drive and similar parameters costs $ 10-20 million.

 Thus, the introduction of two turbochargers from serial aircraft engines in the device of a turbo-refrigerating machine allows using a simple and cheap gas-turbine drive, reducing the compression work and using ready-made turbocompressors, which are the main components of the frontal turbo-refrigerating device in terms of complexity and cost.

 It should be noted that using a turbo-compressor from a turbojet engine from a turbojet engine is only possible with low efficiency, because a cold-air turbine should operate at half the design speed (flow temperature about 4 times lower) than in a turbojet engine, but then the compressor will be in completely unsatisfactory conditions, and the drive should still be based on powerful electric motors. engines. The use of two turbochargers (Fig. 1) makes it possible for all four blade machines to work in modes close to the calculated ones. The compressor (3) of the second compression stage, having a degree of pressure increase of 1.3-1.8, should consist only of the last 2-3 stages (the remaining wheels of the multistage axial compressor together with the guide devices are removed).

With such a small degree of pressure increase and a small number of stages, an axial compressor, if a calculated ratio of the axial flow rate to the peripheral speed of the wheel is provided, works satisfactorily regardless of the absolute value of the speed. Then the turbine (5), in which cold air flows, can operate at the same number of revolutions at which its mode will be close to the calculated one. At the first turbocharger (1) (Fig. 1), the speed slightly differs from those at which it operates in the aircraft engine system, as hot gases come to the turbine, and the compressor in this case also appears at the design speed. The decrease in the degree of increase in pressure in the compressor (1) of the first compression stage from conventional π _to 6-12 to 2-4 is achieved by removing the last few stages of the axial compressor or by adjusting the stator rotary blades in the first and last stages of the compressor. Some axial compressors of gas turbine engines have rotary blades on the compressor stator.

где T_IIк и Т_IIт температуры воздуха на входе соответственно в компрессор (3) и турбину (6);
π_кII, π_тII степени повышения во втором компрессоре (3) и понижения давления во второй турбине (6);
η_кII, η_тII кпд компрессора (3) и турбины (6).The above ratio of the degrees of pressure increase of the first and second stages follows from the equality of the compression work in the compressor (3) (Fig. 1) and the expansion in the turbine (6) of the second turbocompressor (II) for the average air temperature in front of the turbine (6) -100 -130 ^o C:

where T _IIk and T _IIt are the inlet air temperatures to the compressor (3) and turbine (6), respectively;
π _kII , π _tII degree of increase in the second compressor (3) and pressure decrease in the second turbine (6);
η _kII , η _tII efficiency of the compressor (3) and turbine (6).

где 0,85⁴ потери полного напора в трех теплообменниках (2), (4), (5) (теплообменник (5) воздух проходит дважды), в воздушных трактах и ресиверах на выходе из компрессоров, где числа М бывают обычно достаточно велики.If a

where 0.85 is the ⁴ total pressure loss in the three heat exchangers (2), (4), (5) (the heat exchanger (5) passes air twice), in the air ducts and receivers at the outlet of the compressors, where the numbers M are usually quite large.

и, следовательно, при перепаде температур на стенках теплообменника в 10^o температура воздуха на входе в холодную турбину будет -30^oC.The degree of pressure increase in the first compressor (I) at the highest temperature of the cold air flow, which was taken above t _h.p. -60 ^o C, heating of cold air in an amount of 210 kg / s in a cold consumer (7) by 40 ^o C, which corresponds to q = 2000 kcal / s, should be π _кI = 2.5. In this case, the air temperature at the outlet of the consumer will be cold

and therefore, when the temperature difference on the walls of the heat exchanger is 10 ^o, the air temperature at the inlet to the cold turbine will be -30 ^o C.

The value of π _kII is again obtained from the equality of the compressor (3) and turbine (6) operations with the necessary decrease in the air temperature in the turbine (6) [-80 ^o (-30 ^o )] - 50 ^o C and the pressure at the outlet of the cold turbine 1, 1 ata:
π _kI = 2.5; π _tII = 2.58; π _kII = 1.54.
When t ^o cold flow -80 ^o C and a decrease in heat volume to 1500 kcal / s π _kI = 2,05; π _kII = 1.35; π _tII = 2.
The technical effect of this invention is that the introduction of two turbocompressors and two heat exchangers into the system of the turbo-refrigerating machine, splitting the compression process into two stages with intermediate cooling, choosing different peripheral speeds (speed) for two turbocompressors in accordance with the temperatures of the gas flows passing through the turbines , you can reduce the work of compression, get a harmless coolant (air) with t ^o = (- 80 ^o ) (-170 ^o ) C in the amount of 100-200 kg / s, use a gas turbine drive instead of an electric drive and use ready-made turbochargers from serial aircraft engines with exhausted air resources to create turbo-refrigerating machines, without which large-capacity turbo-refrigerating machines with an air coolant are so heavy, expensive, with a longer start-up time and tied to electric power lines of greater power, which for these reasons the production of powerful turbo-refrigerating machines is irrational, and for the rapid removal of large quantities of heat q = 500-2000 kcal / s at t ^o = (- 80 ^o ) (-170 ^o ) C use nitrogen (see Appendix N 1).

If necessary, produce carbon dioxide (CO ₂ ) simultaneously with the heat sink to the inlet of the first compressor (I), the products of combustion cooled to 15-20 ^o C are fed (leaving the first turbine (9), Fig. 2), in which for every kg of fuel combustion depending on the type of fuel 2.8-3.2 kg of CO ₂ . Carbon dioxide will precipitate in the first part of the consumer of cold (7) in the solid phase. With a drive power of 20-35 mW (fuel consumption of 4600-9000 kg / h), CO ₂ production will be 13-28 tons / hour and 10-23 tons of water. The cost of carbon dioxide is 3-7 times higher than fuel. When producing CO _2, along with the cold gas flow, a third water-gas heat exchanger (10) is added to the turbo-refrigeration machine system, and the heat removal is reduced by an average of 50% due to condensation of 2.8-3.2 kg / s CO ₂ . Since in the proposed installation through the turbine of the first compressor the weighted gas flow rate is less than through the first compressor, because in the turbojet engine the pressure at the outlet of the compressor (P _kI ) ₂ and at the inlet to the turbine (P _tI ) ₁ are equal, and in the turbo-refrigerating system machines (P _KI ) ₂ > (P _TI ) ₁ , then at the entrance to the compressor when producing CO ₂ it is necessary to supply not only the combustion products that have passed through the turbine, but also the air from the atmosphere. If a turbo-refrigerating machine works in conjunction with a gas turbine power plant (GTE), then it is advisable to also supply combustion products from a GTE to the entrance to the turbo-refrigerating machine to increase the production of CO ₂ .

 In the air turbo-refrigerating machines described in Appendix No. 2, the air is first cooled in a heat exchanger, then it enters a cooled object, and from there it goes to a turbine, where it is again cooled, it goes from a turbine with a pressure of 0.3-0.5 ata to the heat exchanger to cool the suction from the atmosphere and through the compressor is emitted into the atmosphere. In the proposed refrigeration turbomachine (Fig. 1), the air is first compressed (in two compressors), then it is cooled by cold air coming from the cold consumer, then it goes to the turbine, and from there to the cold consumer and to the atmosphere.

In the circuit described in Appendix N 2, the compressor and heat exchanger operate with inlet pressure 2-3 times lower than in the application proposed by the author. In this regard, devices operating according to this scheme have a large weight and dimensions with the same heat sink. The advantage of such a scheme is lower air temperature at the inlet to the compressor and lower energy consumption for air compression with the same heat sink compared to the proposed scheme. At flow rates of 0.5-2 kg / sec of air, the increased dimensions of the compressor and heat exchanger do not play a big role, and preference is given more often to improving efficiency. However, in air conditioners, a scheme with the best weight and overall parameters is used [1] The changes proposed by the authors in the processes occurring in a turbomachine and in its device can equally be used in both schemes of a refrigeration machine made on the basis of a turbocompressor. From the point of view of thermodynamic processes, the difference of one circuit from another is that, working on the same cycle, in one circuit, the cycle starts at point 0, and in the second at point 4, but at P = 1 ata (see cycle in appendix N 2). When the volumes of the consumer of the cold are hundreds of m ^{3 of} air, a reduced pressure, determined by the pressure loss in the heat exchanger and turbine, is undesirable, which is a drawback of the cycle starting at point 0.

Literature
1. ND Kochetkov, Refrigeration, ed. "Mechanical Engineering", Moscow, 1966.

 2. Refrigerators. / Ed. I.A. Sakuna, Leningrad, ed. "Mechanical Engineering", 1985.

 3. V. B. Vologodsky, K.V. Chashchin-Semenov, Multistage continuous exhauster for variable-density supersonic wind tunnels, ed. testimonial. N 27216, 1963.

 4. V. B. Vologodsky, K.V. Chashchin-Semenov, Supersonic continuous wind tunnel using turbojet engines, ed. testimonial. N 29314, 1964.

 5. V. B. Vologodsky, R.M. Pushkin, K.V. Chashchin-Semenov. The method of heat recovery and environmental cleaning of exhaust gases in a gas turbine engine with a free turbine, patent N 20428417, 07.08.93.

Claims (4)

 1. The method of obtaining streams of cold air, namely, that the air compressed in the compressor is cooled in a heat exchanger, expanded in a turbine, then sent to a consumer of cold, then the air is heated in a heat exchanger and removed into the atmosphere, characterized in that the air from the atmosphere first sent to the first additional compressor with independent drive and compressed sequentially in two stages with intermediate cooling in an additional heat exchanger (refrigerator) between the first and second compressors, while the second th stage, the compression ratio is selected from the condition of equality of compression work in the compressor and expansion in the turbine located on the same shaft without an external drive and working in cold compressed air, and this equality is provided by choosing the total compression ratio close to the expansion ratio in the turbine, the number of stages and the installation angles of the compressor stator vanes and the number of revolutions corresponding to the design mode of the turbine and compressor.  2. The method according to claim 1, characterized in that the first stage of air compression provides a greater degree of compression than the second, and to drive the compressor of the first stage of compression use an additional turbine that runs on exhaust gases coming from a gas turbine engine, and with a number revolutions corresponding to the design mode of the additional compressor and its turbine.  3. Turbo-refrigeration unit containing a compressor and a turbine on a common shaft driven by an external power source, a heat exchanger, a consumer of cold, while the exhaust path of the turbine is connected to the consumer of cold and then connected through the heat exchanger to the atmosphere, characterized in that the installation is equipped with an additional compressor with an independent drive and an additional heat exchanger, while the input of the additional compressor is connected to the atmosphere, and the output through the additional heat exchanger with the entrance to the compressor, finding Drive on a common shaft with a turbine without drive from an external power source.  4. The installation according to claim 3, characterized in that as an independent drive of the additional compressor, an additional turbine is installed at the first stage of compression, the entrance to which is connected by a gas path to the exhaust of a separately installed gas turbine engine.

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