JPH0633911B2 - Absorption refrigeration - Google Patents

Description

Description: TECHNICAL FIELD The present invention is a highly efficient refrigeration system driven by low grade heat and operated at pressures substantially below atmospheric pressure to provide cooling at temperatures as low as about −10 ° C. And about the method. Solutions of normally liquid, mutually soluble components having substantially different boiling points are used as refrigerant and absorbent. Typically, the absorbent will have a high boiling point component of about 65-65.
The distillation bottoms fraction comprises about 95 mol% and the refrigerant comprises a distillation overhead fraction containing about 93 to about 99 mol% low boiling components. Multiple effect forms can be used.

BACKGROUND ART Absorption cooling methods generally allow the thermal energy to be directly converted into a cooling effect, and thus provide the basis for an economical method. However, in practice, although many ingredients have been suggested based on theoretical considerations of their respective physical properties and absorption cycles, the absorption cycle is
Only used in the case of a small number of absorbent-refrigerant combinations. In this cycle, the refrigerant is first vaporized to provide a cooling effect, then the refrigerant vapor is absorbed by the absorbent to generate heat, and finally the rich absorbent solution:
Fractionated to regenerate the refrigerant as a condensing overhead stream and recycle to the evaporation process.

Absorption cooling methods are usually operated at or near atmospheric pressure. An ideal refrigerant would be boiling at about 5-10 ° C and about 3
It is specified to allow absorption above 8 ° C.
The ideal absorbent should be a liquid with a relatively high boiling point. A suitable refrigerant-absorbent combination should exhibit a significant negative deviation in vapor pressure from the ideal solution. Commercial use is generally limited to two systems, one using water as the refrigerant with lithium bromide brine as the absorbent and the other using ammonia as the refrigerant with aqueous ammonia as the absorbent.

Theoretically, the efficiency of the absorption cycle depends only on the temperature levels achieved in the evaporator, absorber, regenerator and condenser parts of the cycle. However, acceptable operating temperatures for these parts exhibit interdependencies that help limit the effective performance of the system. For example, the partial pressure of the refrigerant in the absorber will determine the operating temperature in the evaporator. Similarly, the partial pressure of the refrigerant in the regenerator will determine the temperature in the condenser. The operating temperature in the evaporator and condenser is
Fixed by the temperature and concentration maintained in the absorber and regenerator.

Existing refrigerant-absorbent systems are limited by their physical properties or by the relatively low thermal efficiencies achieved. For example, the lithium bromide-water system is susceptible to crystallization of the salt phase if the temperature is set too low; and in the evaporator section, at the lowest temperature in the cycle, this temperature is zero.
If it reaches around ℃, icing may occur. Ammonia-aqueous ammonia systems are often used despite their generally low coefficient of performance. These systems have greater flexibility in choosing operating conditions and are not susceptible to crystallization and ice accretion potential. In the choice of absorption refrigeration as an alternative to electric drive or steam turbine driven mechanical refrigeration, the choice is generally limited by economic considerations involving the selective use of a particular form of energy rather than another. .

Suitable prior art includes the Institute of Gas Technology Research Bulletin No. 14 "Absorption Cooling", which gives an extensive review of the literature until 1957. Refrigerant-absorption combinations are fully discussed,
And it is evaluated in terms of practical and theoretical considerations. Such combinations include ammonia-ammonia water, water-
Includes aqueous lithium bromide, dichloromethane-dimethoxytetraethylene glycol.

Two papers, W. R. Hynsworth "Refrigerants and Absorbents", Part I, Refrig . Eng . ，
48 , 97-100 (1944); Part II, ibi.
d , 48 , 201205 (1944), a comprehensive review of the field is presented, which is based on the properties described as desirable in each component, and the boiling point of the system water-diethylenetriamine as a promise of development. There is. In addition, Hansworth, R. S. Taylor, Re
frig . Eng . , 17, 135-143, 149
(1929) and presents a circular chart displaying some 66 compounds from carbon dioxide to glycerin in the order of increasing the normal boiling point. This list includes both water and ethylene glycol. In the appendix table of refrigerant-absorbent combinations, ethylene glycol is often designated as the absorbent (eg, with methyl alcohol, ethyl alcohol, n-propyl alcohol-ethylenediamine, n-amylamine, morpholine, and N-methylmorpholine). , And one of the only 27 compounds proposed as an absorbent in combination with water as a refrigerant.

In publications of the same period R. S. Taylor, "Heating Operation Absorption Unit), Reftig . Eng . 49 , 1
88-193, 207 (1945) presents a detailed review of advances in absorption refrigeration system design.
Water is often mentioned as a refrigerant, but ethylene glycol as an absorbent in combination with water as a refrigerant is not mentioned there.

U.S. Pat. No. 1,734,278 discloses an improvement over the ammonia-water absorption system, in which methylamine is used as the refrigerant and glycerin is used as the absorbent, especially when metal salts of calcium, barium or lithium are dissolved. The use of alcohols such as is disclosed. U.S. Pat. No. 1,914,222 discloses ethylene glycol alone or as a mixture with water as an absorbent in combination with methylamine as a refrigerant. Hydrogen is present as an auxiliary gas. U.S. Pat. No. 1,953,329 discloses means for avoiding freezing of the refrigerant by mixing it with a trace amount of absorbent in the evaporation zone. U.S. Pat. No. 1,955,345 discusses problems with ammonia-water systems, such as evaporation of water with ammonia and the resulting loss of efficiency.

U.S. Pat. No. 1,961,297 discloses a device used for water-glycerin mixtures at pressures below atmospheric pressure. U.S. Pat. No. 2,308,665 discloses water or low boiling alcohols as refrigerants, polyamines or polyamides as absorbents, and cites the methylamine-ethylene glycol system. U.S. Pat. No. 2,963,875 describes
Disclosed is a heat pump system that uses a high temperature miscible liquid such as triethylamine-water. Water and glycols are also considered examples of high boiling liquids.

U.S. Pat. No. 3,296,814 uses a lithium salt solution as absorbent, typically lithium bromide in ethylene glycol-water. U.S. Pat. No. 3,38
No. 8,557 claims a solution of lithium iodide in ethylene glycol-water as an absorbent. U.S. Pat. No. 3,524,815 describes lithium bromide,
Water is disclosed as a refrigerant together with an absorbent from lithium iodide, water and ethylene glycol or glycerin. U.S. Pat. No. 3,643,555 claims a specific proportion of lithium salt.

U.S. Pat. No. 4,127,010 discloses a heat pump device which maximizes utilization of the available heat by preheating the absorbent liquid by heat exchange with the effective internal flow as it passes through the evaporator. There is. U.S. Pat. No. 4,193,268 describes
Disclosed is an evaporation device that allows a controlled evaporation rate in response to an internal differential pressure. The heat carrier can consist of water containing traces of ethylene glycol. Preferred refrigerants include various chlorofluoromethanes and ammonia. Provisions for the injection of evaporator bottoms into the precooler, which otherwise contains the refrigerant to be passed to the absorber, are provided.

Current economic conditions call for more efficient and more complete use of available energy sources. There is a real need for more efficient absorption refrigeration cycle components. There is a similar need for the economics inherent in refrigeration systems that can utilize waste heat as their driving force.

DISCLOSURE OF THE INVENTION The system of the present invention is a circulating absorption refrigeration system that uses mutually soluble, normally liquid compounds in each of the absorbent and refrigerant components, comprising: (a) a first low subatmospheric pressure. An evaporation zone operating at (b) an absorption zone operating at a pressure above the first low atmospheric pressure,
And (c) operating at a second, subatmospheric pressure, with a fractionation zone having an equivalent separation efficiency of at least about 2 theoretical plates; the liquid compound has a normal boiling point that differs by at least about 50 ° C. A sorbent component comprising about 65 to about 95 mol% of high boiling point compounds; and a refrigerant component comprising about 93 to about 99 mol% of low boiling point compounds.

The present invention additionally relates to the inclusion of dual effect fractionation zones, each effect having at least two theoretical plates (as in subparagraph (c) above), and the operating pressure of the first effect is
The latent heat of condensation released in the first-effect overhead distillate condenser is sufficiently higher than the second-effect operating pressure to be used to reboil the second-effect bottoms.

The vaporization and absorption zones are preferably operable at about 2 to about 13 mm Hg absolute pressure, therefore the vaporization zone is desirably about -12.
Temperatures in the range of 0 ° C to about + 15 ° C can be maintained. The reboiler portion of the fractionation zone is desirably heated through a heat exchange surface with a waste heat stream, such as low pressure steam or a warm process stream.

The low boiling point compound used in the present invention is water, methanol,
And acetone. Suitable high boiling compounds include ethylene glycol, propylene glycol, ethanolamine, diethylene glycol, butyrolactone, and dimethylformamide.

The invention additionally relates to a refrigeration process and to a modified process using the system outlined above in continuous operation with an ammonia-ammonia water refrigeration process.

Still other features and advantages of the present invention will be apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings which illustrate, without limitation, the operating mode characteristics of the methods and systems of the present invention.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 shows a simplified schematic of the equipment and tubing used in a variant of the invention which uses one sorting effect.

FIG. 2 shows a similar diagram using two fractionation effects.

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 schematically illustrates a simplified flow sheet illustrating one variation of the method or system of the present invention. The container 1 contains an evaporation zone 2 and an absorption zone 3. Second main container 4
Consists of a segregation zone.

The cooled liquid refrigerant component is transferred from the evaporation zone 2 to the line 21,
The external fluid flowing through 22 and 23 to the heat exchanger 6 where it passes through lines 75 and 76 is indirectly cooled. The liquid refrigerant component thus warmed by a few degrees is returned to the upper part of the evaporation zone 2 through lines 24 and 25, where a part of the stream is flash evaporated at the equilibrium temperature and pressure of the evaporation zone 2. The vapor separated in this process then flows into the absorption zone 3 where it is mixed with the absorbent components present therein.

The absorbent component rich in the refrigerant component in the absorption zone 3 is the line 3
9, pump P-1, and line 39a, and line 57, heat exchanger 8, and lines 58,5.
5, 56, the throttle valve V-1, and after passing through the line 56a,
It is partially recycled to the absorption band 3. The remaining portion is line 40, heat exchanger 10, and lines 41, 42 and 4
It is directed to the sorting zone 4 through 3. A portion of the rectification tower bottoms is reboiled by passing through lines 33, 34, 35, heat exchangers 8 and 36 and 37,
The reboil is performed indirectly in exchanger 7 with the waste steam entering through line 70 and exiting as condensate through line 71. Instead of waste steam, line 70
Any warm stream entering through and leaving at a lower temperature through line 71 can be used. A part of the refrigerant component is lines 21, 22, 26, 27, pump P-2, line 2
7a and 28, heat exchanger 11, and lines 29, 3
It is directed to the top of the fractionation zone 4 as reflux through 0, 31, and 32.

The bottoms from the separation zone 4 consisting of the absorbent component are sequentially lines 50, 51 and 52, the heat exchanger 10, and lines 53, 54, 55, 56, valve V-1, and line 5.
It is returned to the absorption band 3 by passing 6a.

The overhead from the separation zone 4 composed of the refrigerant component is sequentially supplied to the lines 44, 45 and 46, the heat exchanger 9, the lines 47 and 48, the heat exchanger 11, the line 49 and the throttle valve V.
-2, and is returned to the evaporation zone 2 by passing through the line 49a. Cooling is performed by line 61, exchanger 8,
Heat exchanger 8 by indirect cooling with water flow from source 60 through line 62, exchanger 9 and effluent line 63.
And 9 are performed.

If desired, the pump (not shown) may cause lines 34 and 51 to move due to the relative positions of the various components of the device and due to the driving force required to pass flow through the device and lines.
Can be used in.

FIG. 2 schematically illustrates a simplified flowsheet illustrating a variation of the method or system of the present invention that uses two fractionation effects, or steps. The evaporation zone 102 is in the container 101.
And an absorption band 103. Another primary container contains a first fractionation effect 104 and a second fractionation effect 105.

The cooled liquid refrigerant component is transferred from the evaporation zone 102 to line 1
External fluids flowing through 21, 122 and 123 to heat exchanger 106, line 123a and heat exchanger 106a, where they pass through lines 175 and 176, or lines 175a and 176a, are indirectly cooled.
The refrigerant component additionally passes through lines 124 and 125 back to the top of the evaporation zone 102 to mix with the vapor rising in the vessel 101 and then into the absorption zone 103 where the absorbent present therein. Mix with the ingredients.

The refrigerant-rich absorbent component in absorption zone 103 is passed through line 139, pump P-101, and line 139a, and line 157, heat exchanger 108, and lines 158, 155, 156, throttle valve V. -101,
And after passing through the line 156a, it is partially recycled to the absorption band 103. The rest is line 140, heat exchanger 1
10 and the lines 141, 142, and 143, the heat exchanger 113, and the line 143a through the separation zone 1
Turned to 04. A part of the rectification tower bottoms from the separation zone 4 is connected to the lines 133, 134, 135 and the heat exchanger 10.
7, and re-boiling by passing through lines 136 and 137, the re-boiling entering waste steam through line 170 and exiting as condensate through line 171 or a warm process exiting through line 171 at a lower temperature than in line 170. Flow is performed indirectly in exchanger 107. A part of the refrigerant component is the lines 121, 122, 126, 127 and the pump P-10.
2, through lines 127a and 128, heat exchanger 111, and lines 129, 130, 131, and 132 as reflux to the top of fractionation zone 104.

Bottoms from the separation zone 104 are sequentially line 150,1
51 and 152, heat exchanger 113, and line 1
It is directed to the second sorting zone 105 by passing through 91 and 191a.

A portion of the fractionator bottoms from fractionation zone 105 is reboiled by passing lines 195, 196, 197, heat exchanger 112, and lines 198 and 198a, which reboil through lines 138 and 138a. The overhead vapor from the first rectification column 104 entering and exiting through lines 138b, 144 and 145 is done indirectly in exchanger 112.

Bottoms from the separation zone 105 composed of an absorbent component are sequentially line 192, 193, 194, heat exchanger 110, and lines 153, 154, 155, 156, throttle valve V.
It is returned to absorption band 103 by passing through -101 and line 156a.

Overhead vapor flow from fractionation zone 105 is line 1
81, through line 145, conjoining with the liquid stream from exchanger 112, and the confluence of refrigerant components
Sequential lie 145a, 146, heat exchanger 109, line 1
47,182,183, heat exchanger 114, line 14
8, 148a, the heat exchanger 111, the line 149, the throttle valve V-102, and the line 149a to be returned to the evaporation zone 103.

Cooling is provided by line 161, exchanger 108, lines 162 and 162a, exchanger 109, and water effluent line 1
Performed in heat exchangers 108 and 109 by indirect cooling with a water stream from a water source 160 passing through 63.
A portion of the water flow is in lines 164 and 165, exchanger 1
14, and through lines 166 and 167, finally confluent with mainstream in line 162, and continue to flow through line 162a.

As in FIG. 1, depending on the operating conditions and the relative position of the equipment, if necessary, the pump may be operated in lines 134,15.
1, 193 and 196 can be used in all or all.

The present invention relates to a circulating absorption refrigeration system driven by low grade heat and operated at a pressure substantially below atmospheric pressure, and a refrigeration process using said system. About -10
Cooling to temperatures as low as ℃ can be realized, while about -5 ℃
The temperature of is easily reached. Broadly speaking, the present invention is a circulating absorption refrigeration system that uses mutually soluble, normally liquid compounds in each of the absorbent and refrigerant components, comprising: (a) a first lower subatmospheric pressure. Evaporation zone operated (b) absorption zone operated at a pressure below the first low atmospheric pressure,
And (c) operating at a second, subatmospheric pressure, with a fractionation zone having an equivalent separation efficiency of at least about 2 theoretical plates; the liquid compound has a normal boiling point that differs by at least about 50 ° C. A sorbent component comprising about 65 to about 95 mole% of high boiling point compound; and a refrigerant component comprising about 93 to about 99 mole% of low boiling point compound. Here, the theoretical plate (theoretical plate) is a term generally used in a distillation system, and refers to a virtual plate used for convenience in calculating the required number of plate columns and the height of a packed column. The theoretical stage is assumed to produce vapor with a composition that is in equilibrium with the composition of the liquid descending from that stage. To find the actual number of plate columns, first find the number of theoretical plates required and divide by the column efficiency.

The invention makes it possible to use absorption refrigeration as a tool for energy storage, whereby waste heat is converted into usable refrigeration. Additionally, the current significant increase in energy costs makes the systems and methods of the present invention particularly attractive for petroleum processing and incorporation into petrochemical manufacturing.

In the system of the present invention, the evaporation and absorption zones are
Generally, low subatmospheric pressures within the range of about 2 to about 13 mmHg absolute pressure, and preferably within the range of about 3 to about 9 mmHg absolute pressure are maintained. Consistent with these zones, the fractionation zone is maintained at a higher subatmospheric pressure, generally within the range of about 30 to about 150 mmHg absolute pressure, and preferably within the range of about 30 to about 100 mmHg absolute pressure.

Using such a pressure constraint on the system, about −
Maintaining temperature within the absorption band of 12 ° C to about + 15 ° C, preferably about -5 ° C to about + 10 ° C (flash refrigeration level)
An absorbent and refrigerant component composition that allows for can be achieved. The corresponding temperature in the absorption band is generally maintained in the range of about 20 to about 60 ° C, preferably about 30 ° C to about 40 ° C.
To provide the desired absorbent and refrigerant component composition, the fractionated zone reboiler portion is in the range of about 65 to about 110 ° C, preferably about 75 to about 9 by indirect heat exchange with an external heat source.
Maintained at a temperature of 5 ° C.

Since high purity is not essential for the absorbent and refrigerant components in the present invention, the fractionation zone need not be highly efficient, a separation efficiency of about 3 or 4 theoretical plates is sufficient. Some reflux is provided at the top of the rectification column with a barge stream taken from the evaporation zone.

If desired, improved particle size effectiveness may be achieved by the incorporation of a second fractionation zone. When this is done, the rich absorbent component is directed to a first rectification column operating at a higher pressure, usually in the range of about 250 to about 760 mm Hg absolute, preferably about 300 to about 650 mm Hg absolute. . Bottoms from the first rectification column are fed to a second rectification column operating substantially as described above except that its reboiler duty is provided by heat exchange with overhead vapor from the first rectification column. . As before, the first rectification column typically has about 1 unit due to indirect heat exchange with an external heat source.
Within the range of 10 to about 150 ° C., preferably about 120 to about 1.
Heat is obtained from the reboiler system, which is now maintained at a temperature of 40 ° C. Two would be sufficient, but if desired,
Still other sorting effects may be used.

Effect 1 or 2 In the rectification column arrangement, the temperature level achieved in the evaporation zone is such that the indirect heat exchange with the cooling liquid refrigerant component allows the external flow to be in the range of about -8 ° C to about + 20 ° C, It is preferably frozen to a temperature of about -3 ° C-about + 15 ° C. In practice, such an external stream is ammonia,
It may include brine, petrochemical or petroleum process streams and the like.

A limited number of normally liquid compounds are generally suitable for use in the systems and orientations of the present invention. All are
It must be stable, not corrosive, and fully miscible with each other. For the preferred operation of the refrigeration cycle of the present invention, the normal boiling points of the selected low boiling and high boiling compounds should differ by at least about 50 ° C. The low boiling point compound is preferably water, although acetone, methanol, or a mixture of any of these can be used. 1,3-propylene glycol,
The high boiling point compound is preferably ethylene glycol, although compounds such as 1,2-propylene glycol, diethylene glycol, butyrolactone, dimethylformamide, monoethanolamine and the like or mixtures thereof can be used. In addition to the water-ethylene glycol system, other promising systems include acetone-butyrolactone, methanol-1,2-propylene glycol, and methanol-1,3-propylene glycol.

The attractive practicality of this refrigeration system does not, in part, require that both the given absorbent and refrigerant components consist of compounds that are substantially pure water, thus limiting fractionation requirements and traditionally efficient and economical. It stems from the discovery that it allows the selection of compound combinations that are only speculative without the identification of effective means for successful utilization. According to the present invention, the refrigerant component comprises about 93 to about 99 mol% of the low boiling point compound,
Preferably, it need only consist of about 96 mol%. Similarly, the absorbent component may comprise about 65 to about 9 high boiling compounds.
It need only consist of 5 mol%, preferably about 75 to about 90 mol%.

In addition to using waste heat for reboil, ambient temperature cooling water is also used to remove heat from overhead vapors from the fractionation zone or from the recirculating absorbent component (Figure 1, respectively). Heat exchangers 9 and 8 as described in 1).

Thermal efficiency of absorption cycle, or coefficient of performance (C.O.
P. ) Is defined as the ratio of the cooling effect to the energy input to ensure such effect. In other words, C.I. O. P. Is the ratio of the refrigeration by the evaporator to the energy input to the generator or rectification column.

In one preferred embodiment of the invention a combination of ethylene glycol and water is used. In the contemplated practice of this embodiment, a refrigerant component containing about 98 mol% water and about 2 mol% ethylene glycol is flashed in the evaporation zone at about 3 mm Hg absolute pressure to produce a flash refrigeration level of about -5 ° C. . At this temperature level in the evaporation zone bottoms, the external stream can be cooled to a temperature of about -3 ° C by indirect heat exchange. The possible freezing of water in the bottoms is advantageously avoided by the presence of ethylene glycol. The flashed vapor, primarily water, is admitted to the absorption zone and is absorbed at the same pressure by an absorbent component containing about 15 mol% water and about 85 mol% ethylene glycol. The temperature of the water-rich absorbent component is about 35 ° C. A portion of the rich absorbent component is recycled to the absorption zone after removing the heat of absorption to cooling water at about 32 ° C.

The majority of the water-rich absorbent component was reconcentrated in a fractionation zone consisting of one theoretical stripping stage and two theoretical rectification stages at a pressure of about 52 mmHg and a reboiler temperature of about 81 ° C to give about 98 moles of water. % And ethylene glycol about 2
The refrigerant component consisting of mol% is recovered as overhead distillate and returned to the evaporation zone. Reflux to the fractionation zone is provided by directing the slip stream from the evaporation zone bottoms to the top of the rectification column. The heat of condensation of overhead is
It is removed by cooling water at about 34 ° C. The heat to the reboiler is provided by heat exchange with low pressure steam available at about 110 ° C. A rectification column bottoms or absorbent component consisting of about 85 mol% ethylene glycol and about 15 mol% water is returned to the absorption zone after heat exchange with the water-rich effluent from the absorption zone.

In a second preferred embodiment, a second fractionation step or effect is added, one step operating at the above conditions. In this embodiment, the additional rectification column is operated at a higher pressure of about 440 mm Hg and the overhead vapor is cooled by reboiling the first rectification column. Bottoms from the second rectification column are at a temperature of about 131 ° C. The reboiler duty is provided by high quality waste steam available at about 135 ° C. The overhead vapors from the two fractionation zones are combined and returned to the distillation zone.

In this second preferred embodiment, only one of the rectification columns is reboiled with an external heat source, such as low pressure steam, and therefore the heat of regeneration is reduced by at least about 40%.

The process calculations for operations performed substantially as described above exhibit extremely high coefficient of performance, as described below.

The astonishing advantage of the dual effect operation is that regeneration is acceptable using low pressure steam derived from the back pressure steam turbine at about 3.5-4.0 atmospheres or extracted from a fully condensing steam turbine at such pressure. It is possible. In such reproduction, C.I. O. P. 1.47 is so high that in turbine systems (about 0.10 to 0.15
(Atmospheric pressure) The mechanical energy lost by not condensing any of the regenerated steam would be the machine that would be needed to provide a refrigeration load of 1,000,000 BTU / hr at -4 ° C when using a mechanical refrigeration unit. Less than half the target energy.

The widely used absorption cooling cycle consists of ammonia as a refrigerant and aqueous ammonia as an absorbent, with hydrogen gas sometimes present as a third phase. For effective applications such as in industrial air conditioning, water must be removed from the refrigerant components recovered as overhead vapors from the generator or rectification tower zone.
In a typical ammonia cycle, ammonia is boiled from solution at about 140 ° C. and about 175 p.sia. Ammonia is condensed at about 35 ° C. and squeezed to about 760 mm Hg absolute pressure before being transferred to the evaporation zone. The flash evaporation temperature achieved under these conditions is about -3.
It is 3 ° C. After absorbing the vapor, the absorbent solution, now about 35 ° C., is pumped back to the rectification column and recycled. Heat is removed from both the fractionation zone condenser and the absorption zone effluent by indirect heat exchange with cooling water. In a typical unit, the coefficient of performance (COP) is in the range of about 0.1 to about 0.3.

The hybrid process of the present invention effectively combines the novel process detailed above with the ammonia-ammonia water process by drawing heat from the ammonia process fractionation zone overhead and absorption zone effluent using the novel process cooling refrigerant component. . This effectively removes the heat of condensation of the refrigerant component (ammonia) and the heat of solution in the absorbent component (ammonia water). For example, referring to FIG. 1 as applied to a process that uses ammonia-ammonia water, the coolant supplied by the cooling source 60 may be, for example, a refrigeration zone from the ethylene glycol-water process rather than a cooling water stream. Bottoms.
Thus, the coolant temperature may be, for example, about 35 ° C to about 5 ° C.
Can be lowered to

This heat exchange temperature drop is due to the lower sorting zone or generator,
Allows temperature and pressure. This tends to limit the reboiler duty required. When combined with improved refrigeration duty, as well as refrigeration quality, a significantly increased coefficient of performance is achieved.

The process calculations for extracting heat from the ammonia-water system by the hybrid method of the present invention show a significant improvement in the coefficient of performance compared to that achieved with the conventional ammonia, ammonia water method. This is shown in Examples A and B for two low refrigeration levels.

Although the discussion and examples of practice of the invention discuss the use of low pressure waste steam as an external heat source and ambient cooling water for removal of heat of absorption and condensation, any source of low value heating and cooling can be used. It should be emphasized. The present invention makes efficient use of waste energy in providing highly desirable and accessible levels of refrigeration.

Also, the refrigeration system of the present invention can be continuously used with any suitable mechanical refrigeration system to provide an economically and technically attractive means of achieving abnormally low temperatures.

Claims (17)

[Claims] 1. A circulating absorption refrigeration system which utilizes compounds that are mutually soluble and normally liquid and that differ in normal boiling point by at least about 50 ° C. for each of the absorbent component and the refrigerant component. Evaporation zone (2,102) operating at a pressure below atmospheric pressure, an absorption zone (3,103) operating at a pressure below a first atmospheric pressure, and a second high pressure below atmospheric pressure. Equipped with a separation zone (4, 104),
The fractionation zone (4, 104) has a reboiler zone (7, 107) bound at this bottom, the fractionation zone having a separation efficiency corresponding to at least about two theoretical plates, and the fractionation zone containing about 60 65 to about 95 mol% absorbent component and low boiling point compound about 93 to about 9
The separation condition of the system is lightened by separating the refrigerant component consisting of 9 mol%, and the pressure below the first atmospheric pressure is substantially lower than the atmospheric pressure, and the separation zone (4, 104)
The system, wherein the reboiler portion (7,107) of is continuously warmed by indirect heat exchange with any low quality external heat source, including low pressure steam. 2. The circulating absorption system is used continuously with a second circulating absorption refrigeration system, the second system comprising substantially anhydrous ammonia as a refrigerant and about 30-60% by weight ammonia as an absorbent and water. Characterized by having aqueous ammonia containing about 40-70% by weight,
Further, heat is removed from the second ammonia-ammonia water system to the first mentioned circulating absorption refrigeration system, whereby heat is extracted from the second system at substantially the refrigerant cooling temperature of the first mentioned system. The system according to claim 1. 3. The first low, subatmospheric pressure is about 267.
It is maintained within the range of Pa (2mm) to about 1733Pa (13mmHg absolute pressure), and the second high, subatmospheric pressure is about 400.
0Pa (30mm) ~ 20,000Pa (150mmHg absolute pressure)
The system according to claim 1 or 2, characterized in that it is maintained within the range. 4. The purge flow from the evaporation zone (2,102) comprises:
The separation zone (4, 1) as the reflux (32, 132, 132a)
04,105) is introduced continuously into the reflux section of the system according to claim 1 or 2. 5. The evaporation zone (2,102) is from about -10 ° C. to about 1.
The absorption zone (3,103) is maintained at a temperature in the range of 2 ° C, the absorption zone (3,103) is maintained at a temperature in the range of about 20 ° C to about 60 ° C, and the separation zone (4,104) containing the reboiler portion (7,107) is System according to claim 1 or 2, characterized in that it is maintained at a temperature in the range of about 65 ° C to about 110 ° C. 6. The external fluid is indirect heat exchange with the refrigerant components from the evaporation zone (4,104) to about -8 ° C to about + 20 ° C.
Characterized by being continuously cooled to a temperature in the range of
The system according to claim 5. 7. The high boiling point compound is ethylene glycol,
Selected from the class consisting of 1,3-propylene glycol, 1,2-propylene glycol, diethylene glycol, butyrolactone, dimethylformamide, monoethanolamine and mixtures thereof,
On the other hand, the system according to claim 1 or 2, characterized in that the low-boiling compound is selected from the class consisting of water, methanol, acetone and mixtures thereof. 8. The sorting belts (4, 104) are arranged continuously,
A third highest, sub-atmospheric pressure operating first rectification column (104), and a second, higher, sub-atmospheric pressure operating second rectification column (105), An overhead stream (138) from the rectification column (104) by indirect heat exchange to provide the reboiler heat duty required for operation of the second rectification column (105). The system according to item 2. 9. A third highest, subatmospheric pressure of about 3
3,331 Pa (250 mm) to about 101,325 Pa (76
Maintained within the range of 0 mmHg absolute pressure, and the first rectification column (10
The system according to claim 8, characterized in that the reboiler section (107) of 4) is maintained at a temperature in the range of about 110 ° C to about 150 ° C by indirect heat exchange with an external heat source. 10. A circulating absorption refrigeration method which utilizes compounds which are mutually soluble and normally liquid and which differ in normal boiling point by at least about 50 ° C. for the absorbent component and the refrigerant component. In the separation zone (4,104) having the separation efficiency equivalent to the theoretical stage, the separation zone (4,104)
Is a reflux zone (32, 132, 132
Reboiler band bound to a) at this bottom (7,107)
And rectifying the refrigerant-rich absorbent component to provide an overhead refrigerant component stream and a bottom absorbent component stream, an overhead refrigerant by indirect heat exchange with any external coolant stream containing water or air. Cooling the component stream, cooling the cooled overhead refrigerant component stream to the evaporation zone (2,10
2), cooling the bottom absorbent component stream by indirect heat exchange with a refrigerant-rich absorbent component stream, transferring the cooled bottom absorbent component stream to the absorption zone (3, 103), evaporation Evaporating a substantial portion of the refrigerant component in the zone (2, 102), an absorption zone (3, 102) for mixing the evaporated portion of the refrigerant component with the absorbent component to provide the refrigerant rich absorbent component.
103), the step of separating the absorbent component rich in refrigerant into the separation zone (4, 104, 10
5), and a small amount of the refrigerant component is continuously led out from the evaporation zone (2, 102), and the refrigerant component is returned to the reflux zone (32, 13).
2,132a) and about 4,000 Pa (30 mm) to about 22,000 Pa (150
mmHg absolute pressure) and a reboiler zone temperature in the range of about 65 ° C to about 110 ° C (reboiler zone (7,107) by indirect heat exchange by any low external grade including low pressure steam). Heated from a heat source)
And the overhead refrigerant component stream is about 93
To about 99 mol% and about 1 to about 7 mol% of high boiling compounds and the bottom absorbent component stream comprises about 65 to about 95 mol% of high boiling compounds and about 5 to about 35 mol% of low boiling compounds. Operate the separation zone in the following manner to set the evaporation zone to about 267 Pa (2 mm) to about 1733 Pa (13 mmHg
Absolute pressure) to achieve a temperature of the residual portion of the refrigerant component in the range of about −12 ° C. to about + 15 ° C. and circulate the residual portion of the refrigerant component to the refrigeration zone (6, 106),
Thereby, by indirect heat exchange, the external refrigeration heat exchange fluid is cooled to a temperature in the range of about -8 ° C to about 20 ° C, and a portion of the refrigerant rich absorbent component in indirect heat exchange with the external coolant stream. By maintaining the absorption zone (3, 103) at the same pressure as the evaporation zone (2, 102) and at a temperature in the range of about 20 ° C. to about 60 ° C. 11. Adopting substantially anhydrous ammonia as the refrigerant component and ammonia water containing about 40 to about 70% by weight of water as the absorbent, respectively, and enriching the ammonia-water effluent mixture from the second cycle absorption zone. An overhead refrigerant component stream (138) consisting of substantially anhydrous ammonia, which is collected as a sorbent and the ammonia-water mixture is rectified in the second cycle fractionation zone (105).
Claim 10 including a second absorption refrigeration cycle providing a bottom absorbent component stream consisting of
The method according to paragraph 1, wherein the remaining portion of the refrigerant component is transferred to the first cycle refrigeration zone (105).
Cooling the ammonia-water effluent mixture at a temperature in the range of about -8 ° C to about + 20 ° C, by circulating the solution to an indirect heat exchange therethrough to condense the second cycle ammonia overhead, and Evaporating a substantial portion of anhydrous ammonia in the cycle evaporation zone (104) to achieve a temperature of the remaining liquid ammonia of about -15 ° C to about -60 ° C, and circulating the remaining liquid ammonia to the second cycle refrigeration zone. And then cooling the external heat exchange fluid to within the range of about −10 ° C. to about −55 ° C. by indirect heat exchange. 12. The low boiling point compound is selected from the class consisting of water, methanol, acetone and mixtures thereof, and the high boiling point compound is ethylene glycol, 1,3-propylene glycol, 1,2. -Claim 10 or 1 characterized in that it is selected from the class consisting of propylene glycol, diethylene glycol, butyrolactone, dimethylformamide, monoethanolamine and mixtures thereof.
The method according to item 1. 13. The evaporation zone (2, 102) is about 400 Pa (3
mm) to about 1200 Pa (9 mmHg absolute pressure). The method according to claim 10 or 11, characterized in that the pressure is maintained. 14. A fractionation zone (4, 104, 105) consisting of a plurality of effects or stages, operating sequentially at higher reboiler temperatures, with additional effects provided by a low-grade heat source external to the reboiler duty of maximum pressure effect. And the highest pressure effect treats the refrigerant rich absorbent from the absorption zone (3, 103) and the reboiler duty (112) for each successive lower pressure effect is the overhead refrigerant component flow from the previous effect. (138) characterized by collecting the overhead stream from each effect and transferring it to the evaporation zone (2,102) and the bottom stream from the lowest pressure effect to the absorption zone (3,103). The method according to claim 10 or 11. 15. The refrigerant rich bottom component in the fractionation zone is a water-ethylene glycol mixture, at about 6666 Pa.
At a reflux pressure of (50 mmHg absolute) and a reboiler temperature of about 85 ° C, the overhead refrigerant component is about 95% water.
Mol% and about 2 mol% ethylene glycol,
And wherein the bottom absorbent component comprises about 85 mol% ethylene glycol and about 15 mol% water.
The method according to claim 10 or 11, wherein the evaporation zone (2,1) is applied at a pressure of about 400 Pa (3 mmHg absolute pressure).
02) the step of maintaining the refrigerant component, cooling the external cooling heat exchange fluid to about -3 ° C.
The temperature of the absorption zone (3,103) is maintained at a pressure of about 400 Pa (3 mmHg absolute pressure) and a temperature of about 35 ° C. Water-ethylene glycol production of the absorption zone (3,103) after evaporation The step of returning the substances to the separation zone (4, 104, 105), and the residual portion of the refrigerant component that has undergone heat exchange after cooling is returned to the reflux zone (3, 132, 132) of the separation zone (4, 104, 105).
The method further comprising the steps of injecting into a). 16. At a reflux pressure of about 6666 Pa (50 mmHg absolute pressure) and a reboiler temperature of about 85 ° C., the first cycle overhead refrigerant component is about 98 mol% water.
And about 2 mol% ethylene glycol, the first cycle bottom absorbent component comprises about 85 mol% ethylene glycol and about 15 mol% water, a reflux pressure of about 57,000 Pa (75 p.sia) and about 60 mol. At a reboiler temperature of ° C, the second cycle overhead refrigerant component consists essentially of anhydrous ammonia, the second cycle bottom refrigerant component consists of about 38 mol% ammonia and about 62 mol% water, and the first cycle evaporation zone ( 2,102) is about 400Pa (3mm
Hg absolute pressure) is maintained and a temperature level is given in the residual portion of the first cycle evaporation zone at about -5 ° C, and the first cycle absorption zone (3,103) is set at about 667 Pa (5 mm
Hg absolute pressure) and a temperature of about 35 ° C., the second cycle ammonia overhead refrigerant is cooled to a temperature of about 0 ° C., and the second cycle evaporation zone (2,102) is about 101,325.
Maintaining a pressure of Pa (760 mmHg absolute pressure), approx.
The freezing temperature of the second cycle is applied to the remaining portion of the second cycle evaporation zone of, and the second cycle absorption zone is about 101,325 Pa (760 mmHg
12. Absolute pressure) and is maintained at 0 ° C. by indirect heat exchange of the absorbent component rich in the residual refrigerant component of the first cycle evaporation zone. the method of. 17. A second cycle freezing temperature is provided within the range of about -15 ° C to about -40 ° C.
16. The method according to claim 15.