WO2009053908A1

WO2009053908A1 - A low-temperature absorption refrigerator

Info

Publication number: WO2009053908A1
Application number: PCT/IB2008/054345
Authority: WO
Inventors: Alberto Sassi; Marco Sassi
Original assignee: Agecoserv S.R.L.
Priority date: 2007-10-23
Filing date: 2008-10-22
Publication date: 2009-04-30
Also published as: BRPI0818882A2; EP2210050A1; AR068954A1; ITTO20070751A1; WO2009053908A8

Abstract

A refrigeration system operating with a mixture of water and ammonia, comprising a distillation unit (SD), a heat exchange unit (SE), an ejector device (PJ) and an absorber (A1).

Description

A low-temperature absorption refrigerator

The present invention relates to a refrigeration system operating with a mixture of water and ammonia.

A system of this type comprises a distillation unit which produces ammonia gas when a mixture of water and ammonia passes through it. This gas is used as a coolant fluid which is sent in succession to a condenser, an expansion valve, and finally an evaporator associated with a cold chamber.

The depleted mixture of water and ammonia leaving the distillation unit is sent to an absorber, to which the ammonia gas returning from the evaporator is also directed, in order to produce the original mixture of water and ammonia at the inlet of the separation unit.

The object of the present invention is to maximize the efficiency of a system of the type described above.

In order to achieve the aforesaid object, the system according to the invention has all the characteristics claimed in Claim 1.

hi particular, the refrigeration system according to the present invention is designed to exploit the "waste" thermal energy of external systems adjacent to it. These adjacent systems may, for example, be internal combustion engines, air conditioning systems, turbine systems, or the like. The "waste" thermal energy of the adjacent systems is exploited for the production of the ammonia gas used as the coolant fluid in the system.

The system according to the present invention also has an ejector device which is used to increase the pressure of the ammonia gas returning from the evaporator, and to mix this gas with the mixture of water and ammonia leaving the distillation unit. The ejector device considerably simplifies the structure of the system and makes the thermodynamic cycle of the working fluid highly efficient. Further features and advantages will be made clear with reference to the appended drawings, provided purely by way of a non-limiting example, in which

Figures 1 and 2 are schematic illustrations of a refrigeration system according to the invention;

Figure 3 A is a view from above of an ejector device of the system of Figs. 1 and 2; and '

Figure 3B shows a sectional view of the ejector device of Fig. 3B.

With reference to Figure 1, a refrigeration system according to the invention comprises a distillation unit SD made up of a first stage Cl forming an enriching column, a second stage C2 forming a depleting column, and a reflux reservoir (not shown). In the following description, reference will be made from time to time to numerical values of certain parameters: these numerical values are to be interpreted simply as preferred values of the parameters, without any limiting effect on the present invention.

The depleting column Cl is formed by a vertical cylindrical structure containing Raschig rings, and comprises a horizontal cylindrical boiler B placed under the aforesaid vertical structure.

The boiler B is supplied with the waste heat from an external system G: for example, the boiler B can have fumes from a furnace or gases from a gasifier passed through it, these fumes or gases heating a mixture of water and ammonia entering the boiler B as indicated by the line Ll. A flow of vapour indicated by the line Vl, containing both water and ammonia, is generated from the incoming water and ammonia mixture, this vapour flow rising up the depleting column C2 and being sent to the enriching column Cl .

The enriching column Cl is formed by a cylindrical structure with a domed cap, containing 25 mm Raschig rings with a surface area: volume ratio of 606 m²/m³. The velocity of the steam in the enriching column is preferably in the range from 2000 to 4000 m³/m²/h.

An ammonia gas, indicated by the line Gl, and a discharge liquid with a 43% ammonia content, indicated by the line L2, are formed in the enriching column Cl at a temperature of 66⁰C and a pressure of 7 bar. The gas produced in the enriching column Cl is used as the coolant fluid of the system and is sent to a condenser Dl which converts it to a liquid at a temperature of 27⁰C and a pressure of 7 bar. Some of this liquid is recycled into the enriching column Cl, as indicated by the line L3, while the remainder, indicated by the line L4, is sent to an expansion valve VL (shown in Fig. 2) and then to an evaporator EV (shown in Fig. 2) associated with a user device (shown in Fig. 2) such as a cold chamber. Figure 2 shows the complete system, including the part shown in Fig. 1, which is indicated as a whole by DE, the expansion valve VL, and the evaporator EV.

The liquid produced in the enriching column Cl has a velocity in the range from 10,000 to 40,000 m³/m²/h at the output of this column (line L2), from where it is sent to a heat exchange unit SE.

The heat exchange unit is formed by heat exchangers El, E4, E5 for heating the liquid flows flowing towards the depleting column C2 of the distillation unit SD.

In detail, the liquid (line L2) leaving the enriching column Cl is sent to a first heat exchanger El in which it is heated by the heat given up by an external heat-yielding liquid, for example the coolant of an internal combustion engine AM, which is made to circulate in the exchanger El .

At the outlet of this first heat exchanger El, the ammonia-containing liquid, indicated by a line L4, has reached a temperature of 8O⁰C, and is combined with the flow of liquid (line L5) leaving a second heat exchanger E4, described more fully below, which is also supplied by the aforesaid external liquid and has the same thermodynamic conditions.

The resulting flow, indicated by a line L6, is then directed to a third heat exchanger E5 which heats it by means of the heat supplied by the liquid (line L7) leaving the depleting column C2 and passing through the exchanger E5, and is then directed to the depleting column C2, as indicated by the line Ll . The liquid leaving the depleting column C2 (line L7) has an ammonia content of 10% and a temperature of 133⁰C, and passes through the exchanger E5 where it is cooled to a temperature of 90⁰C by the liquid (line L6) sent to the depleting column C2. The liquid is then sent to an air-type exchanger E3 with finned tubes, and then to a tube bundle heat exchanger E6 which is supplied with external water, the liquid being cooled in these stages to a temperature of 25 ° C.

The liquid is then directed to an ejector device PJ, shown in detail in Figures 3A and 3B.

As shown in Figure 3B, the ejector device PJ is formed by a body 1 provided with three branches located in the same plane, in which a first inlet branch 2 is provided with a nozzle 2a, a second inlet branch 3, substantially perpendicular to the first, is formed by a suction pipe 3 which has a conical portion 3 a diverging in the direction of the flow passing through it, and which directly faces the outlet of the aforesaid nozzle 2a, and in which an outlet branch 4 extends in the opposite direction to that of the first branch with respect to the second branch 3, thus forming an extension of the first branch, and has a further conical portion 4a diverging in the direction of the flow passing through it.

The liquid from the heat exchanger E6 (line L8) passes through the first branch 2, while the ammonia gas leaving the evaporator EV (line G2) on its return from the user device U, at a temperature of -25°C and apressure of 0.9 bar, is sent to the second branch 3 of the ejector device PJ. '

The ejector device PJ has the function of compressing the ammonia gas returning from the evaporator EV, while simultaneously mixing it with the liquid entering the ejector device PJ.

The nozzle 2a of the first branch 2 acts in such a way that it increases the kinetic energy of the liquid while also reducing its pressure, so that the ammonia gas is sucked through the second branch 3 and is mixed with the liquid, and a mixture of ammonia gas and liquid with a 22-23% content of ammonia, at a temperature of 45⁰C and a pressure of 3 bar, flows out through the third branch 4.

This mixture is then sent, as indicated by a line L9, to a post-ejector heat exchanger E2 which cools the mixture, using external water, to a temperature of 33⁰C. The mixture is then directed from the exchanger E2 to an absorber Al .

The absorber Al has the function of mixing the ammonia in the gas phase uniformly with the aforesaid ammonia-containing liquid, in order to produce a liquid with a 33% ammonia content at a temperature of 34-35⁰C. The pressure of the liquid is then raised from 3 to 7 bar by means of a pump PCl which sends it to the second heat exchanger E4. This additional heat exchanger heats the liquid from 75⁰C to 8O⁰C, using the thermal energy of the cooling liquid leaving the first exchanger El (line Rl) after it has been used to heat the mixture in this first exchanger El. As described above, the liquid mixture (line IA) leaving the first exchanger El and the liquid mixture (line L5) leaving the second exchanger E4 are sent in a single flow to the third exchanger E5, which then passes through the circuit of the system as described above.

Clearly, the details of construction and the embodiments of the invention can be varied widely from those described and illustrated herein, without departing from the scope of the present invention as defined in the claims below.

Claims

1. A refrigeration system operating with a mixture of water and ammonia, characterized in that it comprises:

- a distillation unit (SD) for producing, from a incoming mixture of water and liquid ammonia, an ammonia gas for use as a coolant fluid for a user device (U), said distillation unit comprising a first stage (C2) for producing a mixture of water and ammonia in vapour from said mixture of water and ammonia, and a second stage (Cl) for producing said ammonia gas from said mixture of water and ammonia in vapour, with the interposition between said first and second stages of a first, a second and a third heat exchanger (El, E4, E5) , in which said first heat exchanger (El) is capable of heating a liquid mixture of water and ammonia which is discharged from said second stage (Cl)₅ said second heat exchanger (E4) is capable of heating a liquid mixture of water and ammonia which enters the distillation unit (SD), and said third heat exchanger (E5) is capable of receiving a combination of the heated mixtures which leave the first and second heat exchangers (El, E4) and heating them additionally by exchanging heat with a liquid mixture of water and ammonia which is discharged from the first stage (C2) of said separation unit, this first stage (C2) of said distillation unit being designed to receive as its incoming mixture the said combined and additionally heated mixtures leaving said third exchanger (E5), and said third exchanger (E5) being designed to receive said liquid mixture of water and ammonia discharged from the first stage (C2) of the separation unit and to send it out of said distillation unit (SD) in the form of a cooled liquid mixture of water and ammonia;

- at least one cooling heat exchanger (E3, E6) for additionally cooling the cooled mixture of water and liquid ammonia leaving said distillation unit;

- an ejector device (PJ) for receiving said ammonia gas after it has been used as the coolant fluid by said user device (U), and for compressing it and mixing it with said additionally cooled mixture of water and ammonia leaving said at least one cooling heat exchanger (E3, E6);

- a post-ejector heat exchanger (E2) for cooling the compressed mixture of water and ammonia leaving said ejector device;

- an absorber (Al) for converting the cooled mixture of water and ammonia leaving the post-ejector exchanger (E2) into a liquid solution, which forms the liquid mixture of water and ammonia entering the distillation unit (SD).

2. A refrigeration system according to Claim 1, in which the first and second heat exchangers (El, E4) are designed to exchange heat between the corresponding mixtures of water and ammonia and an external heat-yielding liquid, preferably a coolant liquid of an internal combustion engine (AM).

3. A refrigeration system according to Claim 1 or 2, in which said at least one cooling heat exchanger (E3, E6) comprises, in succession, an air-type cooling heat exchanger (E3) designed to exchange heat between the corresponding mixture of water and ammonia and external air, and a water-type cooling heat exchanger (E6) designed to exchange heat between the corresponding mixture of water and ammonia and external water.

4. A refrigeration system according to any one of the preceding claims, in which said first stage (C2) of the distillation unit comprises a boiler (B) for said incoming mixture, said boiler being supplied with waste heat from an external system (G).

5. A refrigeration system according to Claim 1, in which said ejector device (PJ) is formed by a body (1) provided with three branches located in the same plane, in which a first inlet branch (2) is provided with a nozzle (2a), a second inlet branch (3), substantially perpendicular to the first, is formed by a suction pipe which has a conical portion (3 a) diverging in the direction of the flow passing through it, and which directly faces the outlet of the aforesaid nozzle (2a), and in which an outlet branch (4) extends in the opposite direction to that of the first branch with respect to the second branch, thus forming an extension of the first branch, and has a further conical portion (4a) diverging in the direction of the flow passing through it.

6. A refrigeration system according to Claim 5, in which said additionally cooled mixture of water and ammonia leaving said at least one cooling heat exchanger (E3, E6) can be passed through said first inlet branch (2); said ammonia gas used as a coolant fluid by said user device (U) can be passed through said second inlet branch (3); and a mixture formed by said additionally cooled mixture of water and ammonia leaving said at least one cooling heat exchanger (E3, E6) and said ammonia gas used as a coolant fluid by said user device (U) can be passed through said outlet branch (4).