RU2498176C1 - Method of cold generation in cryogenic compressor-expander unit for air separation - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: method implies compression of atmospheric air to the pressure below the critical one, precooling of the compressed air, integrated treatment, separation of the compressed treated air into direct expander and process flows, cooling of direct compressed flows by the cold of reverse flows, adiabatic expansion of the direct expander air flow, liquefaction, throttling of the direct process air flow. At that the temperature and the pressure of the direct expander air flow before and after the adiabatic expansion is monitored, the said expansion is ended in the wet vapour region under the moisture content of not more than 20% and under the pressure close to the atmospheric one, liquid phase is separated from the wet-vapour expander air flow and is vapourised, at the same time the liquefied direct process air flow is cooled down to the subcooled liquid state, the latter flow is directed for throttling and separation into the productional liquid nitrogen and oxygen. The obtained productional liquid nitrogen and oxygen are sent for isothermal storage, liquid oxygen is compressed and gasified and the heat of its vapourisation cools one of the previously formed direct flows of compressed treated air.

EFFECT: improvement of economy efficiency and specific refrigerating power of a compressor-expander cryogenic unit.

2 dwg

Description

The invention relates to a cryogenic technique and, in particular, to cryogenic gas-liquid air separation plants, as well as to liquid cryogenic systems for storing air separation products in a state of an unheated liquid.

There is a known method of operation of a cooling device in which the gas supplied in the initial thermodynamic state is separated, depending on temperature, into hot and cold flows using a two-stream vortex tube [1]. A relatively hot stream is fed to the inlet of the direct flow of the regenerative heat exchanger, and the cold stream of the vortex tube is fed to the input of the return flow or to the output of the direct recuperative heat exchanger. In this case, the hot stream is pre-cooled before being fed to the regenerative heat exchanger. The disadvantage of this method of producing cold is the limited functionality of cooling the working fluid to temperatures significantly higher than cryogenic.

The closest known technical solution as a prototype is a method of producing cold, which includes compressing atmospheric air to a pressure higher than critical, subsequent pre-cooling of compressed air, complex purification, separation of compressed purified air into direct expander and process streams, cooling compressed direct streams with cold return flows, adiabatic expansion of direct expander air flow, liquefaction and throttling of direct process air flow [2]. Due to the separation of the direct flow into the main and additional parts, of which the additional part of the stream is used to compensate for irreversible losses, and the main part of the stream is adiabatically expanded sequentially in three expanders, the refrigerant of the main part of the stream is liquefied in the expander of the lower cooling stage, and the additional stream after expansion from supercritical pressure to intermediate pressure, liquefy in the heat exchanger of the throttle cooling stage. The resulting liquid refrigerant is discharged to the consumer, and the vapors are used to cool the main and additional parts of the direct flow.

The disadvantage of the prototype is the complexity of the technical implementation of technological processes for producing cold, as well as the low operational reliability associated with the structural complexity of the installation scheme. The latter, in turn, is associated with loss of installation performance due to long (up to several tens of hours to restore the turbo-expander) installation downtime caused by accidental failure of the turbo-expanders. In addition, the complete liquefaction of the refrigerant in the turbine expander of the lower cooling stage of the installation leads to a significant decrease in the efficiency of the expander, which occurs when the degree of humidity is more than 7% [3]. These disadvantages significantly reduce the efficiency of the installation.

The purpose of the invention is to increase the efficiency and specific refrigeration capacity of the compressor-expander cryogenic unit due to the use in the refrigeration cycle of the heat of vaporization of the liquid phase of the refrigerant obtained by expanding the refrigerant into the wet steam region.

This goal is achieved by the fact that in addition to the well-known and general operations on a material object (air), namely: compression of atmospheric air to a pressure below critical, subsequent preliminary cooling of compressed air, complex purification, separation of compressed purified air into direct expander and process flows, cooling compressed direct flows by cold return flows, adiabatic expansion of the direct expander air flow, liquefaction and throttling of the direct process air flow, in the proposal of the proposed method for producing cold in a cryogenic compressor-expander air separation unit, the temperature and pressure of the direct expander air stream are monitored before and after its adiabatic expansion, which is completed in the area of wet steam at a humidity level of not more than 20% and liquid is separated at a pressure close to atmospheric phase from the wet-steam expander air stream and it is evaporated, while cooling to a state of an unheated liquid, the liquefied direct process air stream, which is directed to throttling and separation into production liquid nitrogen and oxygen, direct the obtained production liquid nitrogen and oxygen to isothermal storage, compress and gasify liquid oxygen, cooling one of the previously formed direct flows of compressed purified air due to the heat of evaporation.

The novelty of the invention lies in the fact that in the proposed method for producing cold in a cryogenic compressor-expander air separation unit, the temperature and pressure of the direct expander air stream are monitored before and after its adiabatic expansion, which is completed in the area of wet steam at a humidity degree of not more than 20% and at close to atmospheric pressure, the liquid phase is separated from the wet-steam expander air stream and it is evaporated, while cooling to the state of an unheated liquid, the liquefied direct technol the chemical air stream, which is directed to throttling and separation into production liquid nitrogen and oxygen, directs the obtained production liquid nitrogen and oxygen to isothermal storage, compresses and gasifies liquid oxygen, cooling one of the previously formed direct flows of compressed purified air due to the heat of vaporization, which provides increased efficiency and specific refrigeration capacity of the compressor-expander cryogenic installation.

Figure 1 presents a diagram of T-s implementation of a method of producing cold in a cryogenic air separation unit using an air compressor-expander refrigeration machine with a recuperative heat exchanger, a choke and a wet-steam expander. Figure 2 shows a functional diagram of one of the possible installations with which the proposed method for producing cold can be implemented. In figure 1 is indicated:

Ta is the temperature of the direct flow at the inlet to the recuperative (main) heat exchanger;

Ti is the return temperature of the air at the outlet of the main heat exchanger;

Te is the temperature of the beginning of condensation of compressed air;

Tn is the temperature of the compressed air in the state of an unheated liquid;

Td is the return temperature of the air in a saturated vapor state;

process (bc) - wet steam expansion;

process (b'-d) - gas vapor expansion;

configuration (a-b-e-m-n-f-c-d-i) of the refrigeration cycle with wet steam expansion;

configuration (a-b'-e-m-n-f-c-d-i) of the refrigeration cycle with gas vapor expansion.

In figure 2 is indicated: 1 - air compressor; 2 - water scrubber; 3 - adsorption block of complex air purification (BKO); 4 - the main recuperative heat exchanger; 5 - wet steam expander; 6 - expander collector-liquid separator; 7 and 8 - immersion heat exchangers-coolers; 9, 10, 11 and 12 - heat exchangers-coolers; 13, 14 and 15 - throttles; 16 - lower distillation column; 17 - upper distillation column; 18 - condenser-evaporator; 19 and 20 - production cryogenic vessels; 21 - electric heater BKO; 22 - pump of liquid oxygen; 23 - heat exchanger-evaporator; 24 - consumer compressed gaseous oxygen; 25 - differentiating pressure gauge; 26 and 27 - blocks for measuring temperature and pressure; 28 - atmospheric air; 29 - coolant (water); 30 - column of two extreme distillation; 31 - nitrogen discharged into the atmosphere.

An example of a technical implementation of the proposed method for the production of cold works as follows.

Compressor 1 compresses atmospheric air 28 to a pressure lower than critical and pumps it through a water scrubber 2 into a complex cleaning unit 3 (BKO). At the output of BKO 3, the flow of dried and purified compressed air is divided into two direct flows: direct expander and direct process, then both of these flows are sent to the main (recuperative) heat exchanger 4, in which these two direct flows are cooled due to the cold of two return flows: nitrogen low pressure from the top 17 of the distillation column 30 through the heat exchanger-cooler 12 and the circulating stream of low pressure expander air from the output of the expander collector-liquid separator 6.

The direct expander stream cooled in the heat exchanger 4 is detanated in the expander 5 into the region of wet steam, and then from the expanded expander stream in the expander collector - liquid separator 6, the following is obtained: the liquid phase is oxygen-enriched air in a saturated liquid state and the vapor phase is nitrogen-enriched air in a state of saturated steam. Using a differential pressure gauge 25, the pressures of the liquid and vapor phases are compared. Cooled in the heat exchanger 4 direct process stream of compressed air in a saturated steam state is sent for separation in the lower 16 distillation column 30. In the upper part of the lower column 16, nitrogen vapor is sent to the condenser 18, where the nitrogen is condensed, forming nitrogen reflux. This liquid nitrogen is partially directed directly to the irrigation of the plates of the bottom 16 of the distillation column 30 and partially through the heat exchanger-cooler 12 in the state of under-heated liquid is sent through the throttle 15 to irrigation of the upper 17 of the distillation column 30. The bottom liquid is also sent from the bottom column 16 through the throttle 13. in a state of saturation and through the inductor 14 in a state of unheated liquid from the heat exchanger - cooler 10. From the bottom of the upper column 17, liquid oxygen in the form of a product is fed through a heat exchanger the heat exchanger cooler 9 in the state of underheated liquid in the production cryos vessel 20 of liquid oxygen.

Liquid nitrogen from the bottom column 16 in the form of a product through a heat exchanger - cooler 11 in a state of underheated liquid is sent to a production cryos vessel 19 of liquid nitrogen. In order to cool the production liquid nitrogen, liquid oxygen, bottoms liquid to cryostat, and also to cryostat liquid oxygen and liquid nitrogen in cryo vessels 20 and 19, the liquid air taken from the expander collector - liquid separator 6 is evaporated at a pressure close to atmospheric, respectively heat exchangers 11, 9 and 10 and coolers 8 and 7.

Thus, in the proposed method for producing cold, the processes presented in the T-s diagram of FIG. 1 are implemented, where line (b-c) corresponds to the process of expanding into the wet steam region of a part of the direct air stream compressed to a pressure below critical. The line (g-f) displays the throttling process of liquid air cooled to a state of underheated liquid. Line (m-j) corresponds to the process of throttling liquid air in a saturated liquid state, where the degree of air humidity at the end of the expansion is determined by the value (i-xc). The proposed processes of expansion and throttling compares favorably with the expansion process shown in the prototype, shown in Fig. 1 by a thick dashed line, in that they are technically implemented at low operating pressure.

In the proposed method, using the temperature and pressure measuring units 26 and 27, the temperature and pressure of the direct expander air stream are monitored before and after its adiabatic expansion, which is completed in the area of wet steam at a moisture degree of not more than 20% and at a pressure close to atmospheric.

An additional reduction in energy costs for the operation of a cryogenic air separation unit that implements the proposed method for producing cold is achieved by the fact that the output of the heat exchanger 12 is connected through an electric heater 21 of the complex cleaning unit 3 to increase its performance.

The industrial feasibility of the proposed method for the production of cold in a cryogenic air separation unit is justified by the fact that well-known units, mechanisms and units specified in the analogue and prototype are involved in its technical implementation for their intended purpose. The applicant organization has developed a mathematical model of a cryogenic compressor-expander unit.

The positive effect of the use of the invention is that it increases by at least 25 ... 30% the cooling capacity of turbomachine gas-liquid units for separating low-pressure air into oxygen and high-power nitrogen, while reducing specific energy costs by at least 15 ... 20%.

Information sources

1. The method of operation of the cooling device and the cooling device, RF patent 2193739, IPC F25B 9/02, priority: 03.03.2000, author and patent holder: Belostotsky Yu.T. (analogue).

2. Method for the production of cold. Author's certificate No. 606042 of the USSR, IPC F25B 9/02, F25J 1/00, priority: 03.03.1976, authors: Korsakov-Bogatkov S.M. and others, the applicant: Enterprise "Mailbox M-5096", (prototype).

3. Davydov A.B., Kobulashvili A.Sh. Calculation and design of turbo expanders. M.: Mechanical Engineering, 1987, 232 pp.

Claims (1)

Method for producing cold in a cryogenic compressor-expander air separation unit, including compressing atmospheric air to a pressure below critical, subsequent preliminary cooling of compressed air, complex purification, separation of compressed purified air into direct expander and process flows, cooling of compressed direct flows by cold return flows, adiabatic expansion of direct expander air flow, liquefaction and throttling of direct process air flow, characterized by we note that the temperature and pressure of the direct expander air stream are monitored before and after its adiabatic expansion, which ends in the region of wet steam at a moisture degree of not more than 20% and at a pressure close to atmospheric, the liquid phase is separated from the wet-vapor expander air stream and it is evaporated, while cooling to a state of an unheated liquid, the liquefied direct process air stream, which is sent to throttling and separation into production liquid nitrogen and oxygen, direct the products obtained liquid nitrogen and oxygen for isothermal storage, compress and gasify liquid oxygen, cooling one of the previously formed direct flows of compressed purified air due to the heat of vaporization.

Images