SU1453129A1 - Operating pair of substances for absorption refrigerating machine - Google Patents

Abstract

The invention relates to the field of refrigeration and can be used to generate cold at temperatures up to minus on the basis of heat waste. The purpose of the invention is to increase the performance characteristics of an absorption chiller (by reducing working pressure drops, eliminating the need for rectifying devices and by reducing toxicity. The goal is achieved by using AHM as a refrigerant of tetrahydrofuran in the working pair, and 2-60 as an absorbent % solution of tetrahydrofuran in phosphoric acid. The proposed pair of substances ensures the achievement of the goal without a significant reduction in thermodynamic efficiency and AXl I. 2-yl., 1 tab. with S

Description

The invention relates to the field of refrigeration, in particular, to working substances of absorbent cooling machines (AHM) and can be used to produce cold in the chemical industry, for example, in the production of tetrahydrofuran (THF).

A working pair of AHM substance water-methyl lithium / 1 / is known, which provides high thermodynamic efficiency and good performance characteristics of AHM.

However, this working pair of substances does not allow cold temperatures to be negative in AHM due to the freezing of the refrigerant (water).

Also known is a working pair of substances AHM am iac-water / 2 /, which also provides high thermodynamic efficiency and, in addition, allows to produce cold negative temperatures in AHM.

However, a pair of substances, / 2 / in a number of cases does not provide sufficiently good performance1; ion characteristics of AXM.

The fact is that at condensing temperatures: and refrigerant, which usually occur in practice (25-40 0), the pressure of the saturated ammonia vapor (refrigerant in the working vapor / 2 /) is very high (1000-1500 kPa), which determines the operation of the AXM generator with a comparatively large pressure and, as a consequence, the operation of the AX1-I with a rather significant pressure drop between

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g generator and absorber. All this with | lowers the performance characteristics of the AXM, forcing it to increase the strength of a number of units and apparatus.

In addition, the difference between .normal and the boiling point of the refrigerant lit. absorbent in / 2 / (ammonia and water) is not large enough, as in / 1 /. Causes the formation of a two-component working fluid in the generator during boiling, which requires the presence in AXM / 2 / of rectifying apparatuses and other elements to ensure acceptable thermodynamic efficiency of AX14, but at the same time, the performance of AXtl decreases.

 Finally, the refrigerant in / 2 / is a chemically active substance, and its presence (in the form of leaks) in some chemical industries is undesirable, and in a number of cases it is inadmissible. In addition, the refrigerant in / 2 / is a highly toxic substance with a sharp physiological effect, this also reduces the performance characteristics of the AHM.

The purpose of the invention is to increase the performance characteristics of AHM by reducing the operating pressure drops, eliminating the need for rectifying devices and by reducing toxicity.

The goal is achieved by using THF in the working pair of substances as a coolant, and as an absorbent 2-60% solution of THF in phosphoric acid.

FIG. Figure 1 shows the graphical dependence of the saturated vapor pressure on temperature for THF and. ammonia FIG. Figure 2 shows the P, T, diagram of the THF – phosphoric acid system, where the nodal points of the AXM cycle are shown, the parameters of which are given in the table.

THF has a set of properties that allows it to be used as AXli refrigerant. Parameters of the Liquid-vapor Equilibrium state correspond to the conditions of the refrigeration cycle (Fig. 1). The crystallization temperature is minus 108 well below the temperature in the AXM evaporator. The heat of condensation is 437.3 kJ / kg at 20 ° C. THF is a colorless liquid with almost no odor with a boiling point of 65.6 ° C and a surface

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887.6 kg / m at 2 (fC. The concentration and temperature parameters of ignition in air are 1, 84-1 1 .8 vol.%. and (-20) - (+ 1GS, respectively. THF is thermally stable, low toxicity (HSPC 100 mg / m, whereas in ammonia MPC 20 mg / m), it does not exert a corrosive effect on construction materials. Being a product of domestic large-scale production, THF is a cheap and affordable substance.

The use of a solution of THF in phosphoric acid as an absorbent is based primarily on the experimentally obtained temperature dependence of the pressure of a saturated pair of THF on solutions. From the consideration of the pj j diagrams (Fig. 2), it can be seen that, depending on the circuit design of the AXM and the temperatures of external sources, the THF – phosphoric acid system can be used in a rather wide concentration range. However, it has been established experimentally that the presence of a solution of tetrahydrofuran above 60%. impractical due to a sharp drop in the rate of vapor absorption. In addition, it is undesirable to decrease the concentration of THF during boiling in the generator below 2%, because, otherwise, the crystallization zone may shift to the positive region of the first temperature. It was experimentally verified that the addition of pure tetrahydrofuran to pure phosphoric acid (crystallization temperature of 42.35 ° C) in amounts of 2% and more brings the process of crystallisation into the region of negative temperatures, i.e. safe in terms of performance AHM. The limits of phosphoric acid concentrations () are determined by the content of THF in the binary solution by the formula% H, PO 100% THF.

The calculation of theoretical thermal coefficients of selectively taken AHM cycles showed that, when operating in the same temperature mode, the thermodynamic efficiencies of the AXI-1 words with the proposed working pair of substances and c / 2 / are comparable (see table). The calculation for AHM / 2 / was made taking into account the presence of a distillation column, de-floater and a solution heat exchanger (B AHM with the proposed working pair only solution heat exchanger).

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A study of the corrosive effects of THF - HjP04 solutions on various steel grades showed that, under the conditions of operation of AHM, steel X18H1.0T or other materials with anti-corrosion properties is preferable. Phosphoric acid is a cheap and affordable product, at temperatures up to 200 ° C, it is thermally stable and practically does not form a vapor phase. The absence of the compatibility of phosphoric acid during heating of the THF solution is verified experimentally.

An example of a specific use of the invention can be seen in the process of obtaining cold minus 10 ° C in AXli with a solution of THF — phosphoric acid as a working pair of substances. The pressure corresponding to the boiling of THF in the evaporator at minus 10 ° C is maintained by absorbing its vapor with a weak solution entering the absorber from the generator. The concentration of the solution, boiled in% THF, increases. When cooling the absorbing solution to 40 ° C, it reaches 13.2% THF. If the solution is cooled to O C (such cooling can be obtained in a two-stage process), its concentration increases to 60% THF. The strong solution from the absorber is transported to the generator, the pressure in which is determined by the condensation temperature of the refrigerant. If it is equal, then, in accordance with the P, T, diagram, a solution of 13.2% THF in phosphoric acid will boil at 96 ° C, and a 60% solution will be boiled at. As the THF evaporates from the strong solution, the boiling point of the solution rises and the THF content in it decreases. For example, a teNmeparype of 110 ° C corresponds to a concentration of 5% THF. If the evaporation process is continued, the THF content in the solution can be brought up to 2%, which corresponds to boiling at l5 ° C. Further evaporation is impractical for the reason indicated above. By supplying a weak solution to the absorber, the mortar cycle closes.

In the described example, the variant of using the working solution is shown.

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in the range (with the zone of decontaminating) from 13.2% THF to 5% with a possible expansion of the boundaries to 60% THF and 2%.

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0

35

40

Temperature, ° С: Refrigerant in the evaporator

Refrigerant condenser Strong solution at the outlet of the absorber

Weak solution at the exit of the generator

Strong solution at the outlet of the heat exchanger Pressure, KPA: in the evaporator (absorber) in the condenser (generator) Concentration (% by weight of the coolant) of the strong solution at the outlet from the absorber

weak solution at the generator output degassing zone Multiplicity n ipKy-tion (kg / kg) Theoretical thermal coefficient

-10 40

40

110

45

-10 40

40

110

45

3.801 290.9 40.55 1557.0

13.2

5.0 8.2

11.6 0.50

39.2

35.0 4.2

15.4 0.53

Claims (1)

Invention Formula five A working pair of substances for the absorption- cooling machine consisting of a refrigerant and an absorbent, characterized in that, in order to improve the performance characteristics of an absorption refrigeration machine, tetrahydrofuran is used as a refrigerant, and a 2-60% solution of tetrahydro- furan in phosphoric acid.  0 3.8 3.6 FOR 3.2 D g Figure 2; Compiled by D. Plachendovsky Editor E.Girinska Tehred L.OliynykKorrektor A, Obruchar v : | order 2557 Circulation 335 Subscription VNIIPI State Committee for Inventions and Discoveries at the State Committee on Science and Technology of the USSR 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and Publishing Combine Patent, Uzhgorod, st. Gagarin, 101