EP1169606A1

EP1169606A1 - Absorber for use in absorption refrigeration and heat pump systems

Info

Publication number: EP1169606A1
Application number: EP00921831A
Authority: EP
Inventors: Benjamin A. Phillips
Original assignee: Phillips Engineering Co
Current assignee: Phillips Engineering Co
Priority date: 1999-04-08
Filing date: 2000-04-07
Publication date: 2002-01-09
Also published as: AU4209700A; WO2000061998A9; CA2368918A1; MXPA01010130A; WO2000061998A1

Abstract

Apparatus designs for ammonia-water generator-absorber-heat exchange (GAX) systems. Embodiments include knurled (20) inner housing surfaces, flow deflectors (30), and various heat transfer heating coil designs and configurations, all of which are intended to improve and increase heat and mass transfer in ammonia-water GAX systems.

Description

ABSORBER FOR USE IN ABSORPTION REFRIGERATION AND HEAT PUMP

SYSTEMS

BACKGROUND OF THE INVENTION

Field Of The Invention

The present invention relates to refrigeration and heat pump systems and, more particularly, to improved apparatus designs for generator-absorber-heat exchange ("GAX") systems. Description Of Related Art

The absoφtion refrigeration and heat pump systems disclosed by U.S. Patent Nos. 5,367,884, 5,271,235, 5,570,584, 5,579,652 and 5,782,097, the disclosures of which are incorporated by reference herein, utilize generator- absorber-heat exchange ("GAX") systems. These systems include an absorber having a section with operating temperatures that overlap with temperatures in the generator such that the heat output of the absorber section can serve as heat input to the temperature overlap section of the generator. As disclosed in the aforementioned patents, the temperature overlap sections of the generator and absorber are referred to as the "heat transfer regions."

To reach its full effectiveness, the absorber heat output must be produced over the full range of the absorber overlap temperatures and must be transferred to the generator overlap section such that each element of heat from the absorber at any specific temperature is transferred to the generator at a location that is at a temperature only a few degrees below the temperature of the region in the absorber where the heat was extracted. The above patents describe various ways of transferring the heat from the absorber to the generator in that manner.

This invention relates to improved apparatus designs for use in the absoφtion process that enable mass and heat transfer to be carried out very efficiently. While the present invention is of most importance to the GAX overlap section of the absorber, it is also useful for the rich liquor cooled (absorber heat exchange, or AHE) section and the hydronically cooled section of the absorber. It is also well suited to the GAX overlap section of the generator.

To achieve maximum performance, the absorber must produce the heat of absoφtion at each and all the temperatures along the overlap range and transfer each element of heat to the heat transfer medium with the lowest temperature differences possible. This invention relates to new means by which the absorption process can be carried out with lower temperature differences from the absorption surface to the coolant than is possible with the prior art.

In the prior art, such as shown in Fig. 1 , the liquid 12 introduced into the top of the absorber 10 was dripped over coils 14 of tubing, flowing downward as a falling film over the tubes, while the vapor 16 to be absorbed flowed upwards alongside and between coils 14. The use of falling films of this type are among the most effective of known heat and mass transfer methods. Yet, in the absorption of ammonia into an ammonia-water solution, we have found that this use of concentric coils has significant limitations.

One limitation of concentric coils is the difficulty in consistently distributing the liquid on the tops of coils so the flows on both the inner and outer surfaces of the coils are equal or, preferably, in proportion to the inner and outer coil surface areas. Another limitation of the prior art coiled tubing is that heat transfer from the coiled tube to the coolant flowing inside is often low, requiring high velocity coolant and/or more than one concentric coil. A third limitation is that the flow rate of the absorbent may be so low that the absorbent flowing downward does not wet the surfaces of the cooling coils uniformly or completely. Instead, rivulets of the absorbent flowing downward contact only part of the coils. A fourth limitation is that the vapor flowing upward along the outside and inside of a coil may not always flow in proportion to the absorption rates at the two sides. It may flow upward more rapidly through one passage than through another, resulting in variable vapor compositions, and in incomplete absorption and heat transfer.

In the GAX cycle, the absorbent liquid, e.g., water, entering the top of the absorber has a low concentration of ammonia, commonly below 7% and often down to about 1%, and is referred to herein as "weak liquor." As the weak liquor liquid travels down the absorber, it absorbs ammonia, the concentration of ammonia increases, and under mild operating conditions the weak liquor may reach 50% ammonia or more at the absorber bottom outlet. This liquid at the absorber outlet is herein referred to as "rich liquor." Generally, the larger the difference in concentration between the rich liquor and the weak liquor, the better the performance of the GAX apparatus. The temperature range between the two ends of the absorber may be 200°F or more.

To produce the best performance, the ammonia vapor should flow in a counterflow manner relative to the absorbent liquid. The counterflow is especially important in the overlap (GAX) section of the absorber and in the section of the absorber cooled by rich liquor (AHE section).

The vapor generally enters the bottom of the absorber at a concentration of about 99% ammonia and 1 % water. As the vapor flows upward in counterflow with the liquid, the composition of the vapor changes, preferably being as close to equilibrium with the liquid that it is contacting as possible. In the pressure- temperature-diagram of Fig. 2, each point on the solid lines represents the concentration of ammonia in the liquid at the temperature and pressure of that point. Similarly, the dashed lines represent the concentration of ammonia in the vapor that is in equilibrium with the liquid at the same temperature and pressure. As can be seen in Fig. 2, the concentrations of ammonia in the equilibrium vapors are always greater than the concentrations of ammonia in the liquids with which they are in equilibrium. Also, the amount of equilibrium ammonia in the vapor relative to that in the liquid changes upwards and downwards with the pressure.

As shown in Fig. 2, the ammonia concentration in the vapor that is in equilibrium with the liquid changes in the same direction as the liquid, but to different extents, across the ammonia to water temperature range. As an example, the concentration of ammonia in the vapor, (shown by the light dotted lines and at the top of the plot) changes slowly at the left hand side of the range and faster at the right hand side. The liquid ammonia concentration changes the opposite way, rapidly at the left and more slowly at the right.

Thus, in the absorber, when the 99% ammonia vapor enters the absorber and flows upward, ammonia vapor first absorbs into the liquid, but soon, water from the liquid must evaporate into the vapor. Ultimately, the water evaporation ends and, near the top, absorption of both ammonia and water vapors occurs, until the vapor is all absorbed. It is therefore very important that the flows of both the vapor and the liquid be carefully controlled. As one part of that control, the absorber of the invention uses only one surface for absorption, the inside surface of the absorber housing.

Additional features and advantages of the invention will be set forth in the drawings and written description which follow, and in part will be apparent from the drawings and written description or may be learned from the practice of the invention. The advantages of the invention will be realized and attained by the generator-absorber heat exchange apparatus particularly pointed out in the drawings, written description and claims hereof.

SUMMARY OF THE INVENTION

To achieve these and other advantages, and in accordance with the purpose of the invention as embodied and broadly described herein, the present invention, in one aspect, provides a generator-absorber heat exchange apparatus that includes a generator and an absorber. Each of the generator and absorber includes a generally cylindrical housing having inner wall surfaces. The absorber is configured so that weak liquor ammonia-water liquid entering the top of the absorber flows downward along the inner wall surface of the absorber thereby contacting in a generally counterflow manner the rich liquor vapor entering the bottom of the absorber and flowing upward through the absorber. The inner wall surface of the absorber includes a plurality of spaced knurls configured to increase the transfer of ammonia from the vapor flowing upward through the absorber to the liquid flowing downward along the inner wall surface of the absorber and to increase the transfer of heat from the liquid to the knurled inner wall surface.

In accordance with another aspect of the invention, as embodied and broadly described herein, a generator-absorber heat exchange apparatus including a generator and an absorber is provided. The absorber has an interior pressure lower than the pressure of the generator interior, and the generator and absorber each includes a generally cylindrical housing having inner wall surfaces forming a hollow interior. The absorber is configured so that weak liquor ammonia- water liquid entering the top of the absorber flows downward along the inner wall surface of the absorber thereby contacting in a generally counterflow manner the rich liquor vapor entering the bottom of the absorber and flowing upward through the absorber. The hollow interior of the absorber housing includes a plurality of flow deflectors. Each of the flow deflectors includes a base directing liquid flowing downward through the absorber toward the absorber inner wall surface, and a rim extending from the base to a skirt forming an open end. The rim skirt and the absorber inner wall surface form a pathway for liquid flowing down the inner wall surface of the absorber to pass from one flow deflector to an adjoining flow deflector. The pathway is impervious to the upward flowing vapor. The rim includes a plurality of perforations allowing the vapor flowing upward through the absorber to flow horizontally toward the inner wall surface. The perforations together with the pressure drop from the flowing liquid cause the vapor to impinge on the liquid flowing downward along the inner wall surface to increase the transfer of ammonia from the vapor flowing upward through the absorber to the liquid flowing downward along the inner wall surface of the absorber and to increase the transfer of heat from the liquid to the knurled surfaces.

In accordance with a preferred embodiment of the invention, the generator- absorber heat exchange apparatus includes an absorber having both the knurled inner surface and plurality of flow deflectors described above.

In accordance with another preferred embodiment of the invention, the generator-absorber heat exchange apparatus includes an absorber having a secondary fluid cooled section proximate the bottom of the absorber, an absorber heat exchange section proximate the middle of the absorber, and a generator- absorber heat exchange section proximate the top of the absorber. The apparatus includes three helical heat exchange coils extending around the outer surface of the absorber housing. The first helical coil extends around the outer surface of the absorber housing adjacent to the secondary fluid cooled section. The second helical coil extends around the outer surface of the absorber housing adjacent to the absorber heat exchange section. The third helical coil extends around the outer surface of the absorber housing adjacent to the generator-absorber heat exchange section.

The above and other advantages and features of this invention will become apparent upon review of the following desription in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a prior art heat transfer configuration;

FIG. 2 is a pressure-temperature-composition diagram (P-T-X) of ammonia- water compositions;

FIG. 3a is a front view of one embodiment of the knurls of the invention;

FIG. 3b is a cross-sectional view of one embodiment of the knurls of the invention;

FIG. 4 is a cross-sectional view of an embodiment of the invention illustrating the knurls, flow deflectors, and heat transfer coils of the invention;

Fig. 5 is a schematic of an absorber illustrating the flow deflectors and heat transfer coils in one embodiment of the invention;

FIG. 6 illustrates an embodiment of the invention relating to attachment of heat transfer coils to the absorber;

FIG. 7 is a schematic of an absorber illustrating the flow deflectors and heat transfer coils in an embodiment of the invention wherein the absorber is a component of a heat pump;

FIG. 8 is a graph showing heat transfer results obtained using two types of knurls in accordance with the invention; and

FIG. 9 is a flow diagram of a heat pump using a generator-absorber-heat exchange apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with a first embodiment of the invention, to provide good and continuous wetting of all of the inner surface of the absorber shell, that surface is preferably knurled, as shown in Fig. 3. The knurls improve the flow of the absorbent liquid, which has been distributed around the inner surface of the shell, and maintain the even distribution of the liquid by causing it to constantly split the little streams that flow around each knurl pyramid. The knurls also increase the effective surface area of the inside of the shell.

The knurls can be of different sizes and shapes. A preferred shape of the knurls is a diamond shape, as shown in Fig. 3a. The present inventor has experimented with three different types of diamond shaped knurls. Vertical diamond shaped knurls 20, as shown in Fig. 3a, have a 60° angle at the top, as shown. Horizontal diamond shaped knurls (not shown) have a 120° angle at the top, i.e., the configuration illustrated in Fig. 3a after rotating the Figure 90°. Square diamond shaped knurls (not shown) have a 90° angle. The number of knurls/horizontal inch preferably ranges from between about 8 to about 15. The inventor has found from testing done to date that 12 knurls/horizontal inch may provide the best performance of those tested. Preferably, the knurls have a depth 22 as shown in Fig. 3b ranging from about .015 to about .06 inch, more preferably about .03 inch, depending on the number of knurls/horizontal inch. Generally, the fewer the knurls/inch, the greater the depth of the knurls should be, and the more knurls/inch, the shallower the preferred depth.

Experimental results with diamond shaped knurls have generally shown that the higher the liquid flow rate the better the heat transfer coefficient. Fig. 8 shows the heat transfer results obtained with square diamond shaped knurls (data points shown as black dots) and horizontal diamond shaped knurls (data points shown as x) each having a pitch of 12 knurls/horizontal inch and a depth of about .03 inch. In Fig. 8, U is the heat transfer coefficient and A is the heat transfer superficial area. For the testing of horizontal and square diamond shaped knurls, the superficial area of heat transfer was the same. The data in Fig. 8 depicted with triangles represents testing of an early design that worked better than previous absorbers, but had a low heat transfer superficial area because various design parameters had not been optimized. With horizontal diamond shaped knurls, the curve at the top left was moved upward and somewhat to the left giving better results with lower flows. Horizontal knurls have been the best of the three at lower flow rates. Thus, for a 5 ton heat pump system, vertical diamond shaped knurls may work best, square diamond shaped knurls may work best for a 4 ton system, while horizontal diamond shaped knurls may perform best in a 3 ton system.

The tests done to date have used a uniform knurl type and size over the full height of the GAX and rich liquor cooled sections of the absorber. However, absorption of ammonia into the liquid causes the flow rate of the liquid to increase as it flows downward through the absorber, almost doubling the flow rate at the outlet of the absorber. The improvements shown in Fig. 8 are averages of gains that occurred over the full heights and over the range of flow rates. The inventor believes that by modifying the knurled shapes and sizes along the height of the absorber, each to be a best fit to the liquid flow rate at that particular point, much better performance could be obtained.

Another embodiment of the invention, as shown in Figs. 4 and 5, enables control of the vapor flowing upward through the absorber by keeping it as essentially one stream rather than two or more. More importantly, in this embodiment, contact of the vapor with the liquid is greatly improved. Rather than slow vertical flow of the ammonia vapor across the liquid surface, as in Fig. 1 , in this embodiment the vapor is impinged on the liquid surface at much higher velocities by causing it to flow as jets of the ammonia vapor at right angles onto the cylindrical liquid surface.

In this embodiment of the invention, the impingement is used to increase absorption rates by the velocity of the vapor jets impinging on the liquid, by causing mixing of the absorbent liquid on which the vapor impinges, and by causing greater liquid movement on the inner surface of the shell. This impingement also causes the concentrations of ammonia in the vapor and the liquid to come closer to the equilibrium concentrations shown in Fig. 2.

In this embodiment, the above described flow of the vapor relative to the liquid is achieved by an inner structure within the absorber shell, shown in Figs. 4 and 5. The purpose of this structure is to cause the vapor to go through a sequence of impingements against the liquid flowing downward on the inner surface of the shell. This embodiment creates a stream of vapor that is self controlling and a single stream of liquid, which enhances overall control of the process.

The absorber of Fig. 4 is composed of a vertical group of radially perforated steel cups, or flow deflectors 30, positioned within the absorber 10, which are upside down and spaced apart to allow flow of vapor 32 from one to another. Flow deflectors 30 include a base 34 and a rim 36. Rim 36 extends from base 34 to a skirt 38 at the end of rim 36. Skirt 38 forms a pathway with the inner wall surface for the liquid 39 flowing downward through the absorber along the inner wall surface. Vapor 32 enters the inside of the bottom flow deflector 30 and is separated into the many small streams that flow radially through perforations 40 (orifices) in the cylindrical wall of flow deflector 30. The vapor jets leaving the orifices created by perforations 40 flow radially toward the surface of the absorber shell, each to impinge on the liquid on the knurled surface of the absorber shell. In each impingement step, some of the vapor is absorbed rapidly by the impingement process. Another amount is absorbed by contact with the other liquid on the shell surface. The non-absorbed vapor, of a new composition, then flows upward into the next flow deflector through the open end 42 between the top of the bottom flow deflector and the bottom of the second flow deflector immediately above it.

A portion of the ammonia vapor is thus absorbed into the liquid by flow through each impingement flow deflector. The vapor is reduced in volume at each flow deflector and ultimately is absorbed completely at the top. The vapor and the liquid are thus brought close to equilibrium with each other at each impingement step.

The compositions and the masses of the vapor and the liquid thus change at each impingement step. Ideally, the number of impingement steps would be very large, but tests performed to date have shown that practical quantities, perhaps up to about 36 for a complete absorber, are sufficient to achieve very efficient absorption. For absorbers having a height ranging from about 3 to about 6 feet, it is believed that the preferred number of flow deflectors, i.e., the preferred number of impingement steps, ranges from about 14 to about 36.

It is preferable that in each flow deflector 30, perforations 40 be of the proper diameter and number to produce the proper velocity and momentum of the jets relative to the vapor volume flowing through each flow deflector. The perforations must also be properly spaced, generally in a staggered arrangement rather than in line, to produce the best absorption. At this stage in the development of absorbers, various dimensions for the perforations (in the GAX and absorber heat exchange sections) have been tested by trial and error and visualization trials with air and water. In the inventor's testing to date, circular perforations have been used, although other shaped perforations could also be used in the invention.

The visualization trials led to the conclusion that an optimum velocity of vapor through each perforation may be on the order of about 4 feet/sec. Various designs were tried in order to obtain this desired velocity. After developing a design configuration that achieved this desired velocity, subsequent testing on an ammonia/water absorber confirmed that the design based on the 4 feet/sec. flow through the perforations in fact produced better heat transfer than other designs tested.

The diameter of the flow deflector perforations may range from about 1/32 to about 5/16 inch. The inventor has found from testing that, for a 6 inch ID absorber tube, perforations of about 3/16 inch in diameter may perform best for flow deflectors at or near the bottom of the AHE section of the absorber. At or near the top of the absorber, smaller perforations on the order of about 1/32 to about 1/16 inch in diameter may work best. Thus, from the bottom to the top of the absorber, the diameter of the perforations should preferably gradually change from about 3/16 to about 1/16 inch, more preferably from about 3/16 to about 1/32 inch. The number of rows of perforations per flow deflector can range from about 1 to about 6. It has been found that 4 rows of perforations per flow deflector may provide the best performance. The number of perforations/row around the circumference of the flow deflector may range from about 20 to about 50. The inventor has found that about 30 perforations/row around the circumference of the flow deflector may be best. The height of each flow deflector preferably ranges from about 1 to about 3 inches, with the preferred height being about 1.75 inches, depending on the height of the absorber. It is preferable that the flow deflectors be composed of a metal or alloy, such as steel, that is thin enough to provide a sharp-edged orifice, such as a thickness of about .02 to about .05 inch, more preferably about .035 inch. However, the flow deflectors may also be composed of polymeric or other suitable materials.

The open end 42 of the flow deflectors 30, the bottom, is enlarged as shown in Fig. 4, to form the peripheral opening for vapor 32 to flow from a lower flow deflector into an upper one. That larger diameter at the lip is designed to be in contact, or close to contact, with the inner wall surface of the absorber, which is preferably knurled (not shown), so it can serve as a means for establishing a liquid seal 44 at the knurled surface. Liquid seal 44 has three purposes. It prevents vapor from leaking upwards through the knurls, it serves as a pressure head to provide the necessary pressure to pull the vapor through perforations 40, and it is a pathway for the liquid to the lower level. The seal is formed by close contact of the flow deflector's skirt to the knurls. The height of the skirt in contact with the knurls should be sufficient to allow for a head of liquid of approximately 0.1 - 0.1875 inch high to cause the vapor to be pulled through perforations 40 of flow deflectors 30. Flow deflectors 30 can be fixed in place within the hollow interior of the absorber housing, for example, by utilizing spacers 46 as shown in Fig. 4. Other suitable means known in the mechanical arts for fixing work pieces in place could also be used.

As shown in Fig. 5, to transfer the GAX absorption heat from the shell of the absorber 10 to the heat transfer liquor (which may be weak liquor, boiling rich liquor, or an intermediate concentration liquor), a GAX heat transfer tube or tubes 50 for the transfer liquor are tightly wound around the GAX section 52 of the absorber shell. Similarly, rich liquor tube coils 54 are wound around the rich liquor cooled section 56 (AHE section) and secondary fluid tube coils 58 are wound around the hydronically cooled (usually an antifreeze secondary fluid) section 60 of the absorber. See Fig. 5. All of those coils are then attached to the shell of the absorber 10 to obtain good heat transfer to the three fluids serving as coolants. This metallic attachment has been done very successfully by dipping the fully sealed complete assembly in molten tin. It could also be dipped in molten solder. Other methods such as brazing and welding are also possibilities.

The tinning, soldering, brazing, welding, etc. is intended to provide a continuous metallic path for the heat being transferred from the absorbent fluid to the fluid being heated as shown in Figure 5 and, more specifically, by Figure 6. The solder, or braze etc. should preferably be done in a manner that forms fillets 76 of the joining metal between the shell 77 and the tubes 78 to provide a wide path for heat flow, as opposed to the line contact that would occur by merely wrapping the tube on the shell.

Mechanically, the coils of small tubes serve as hoops around the shell, increasing the strength of the shell to withstand internal pressure. Thus, the thickness of the shell wall may be reduced, reducing weight and cost.

All the GAX heat transfer fluids disclosed in the patents identified on page 1 and incorporated by reference herein can be used for heat transfer from the GAX section of this absorber design. Fig. 5 shows the absorber divided into three sections, the upper section 52 being the GAX section. The middle section 54, the AHE section, is used for heating the rich liquor that must be heated from the absorber outlet temperature to the temperature for inlet to the generator. The bottom section 60 in Fig. 5 is the heat output section of the absorber. This section heats secondary fluid that is used for space heating in the winter and used to dissipate the heat output to the outside air in the summer, as shown in Fig. 9.

The rich liquor and the secondary fluid streams can flow in parallel paths through more than one coil, as shown in Fig. 5. In the embodiment shown in Fig. 5, the secondary fluid enters two parallel secondary fluid tube coils 58 through two secondary fluid parallel inlets 62 and exits through secondary fluid parallel outlets 64. Similarly, the rich liquor enters two parallel rich liquor tube coils 54 through two rich liquor parallel inlets 66 and exits through two rich liquor parallel outlets 68. The purpose of using parallel tube coils for one stream is to improve the heat transfer through the metal wall of the tubes to the fluid being heated.

The top section (the GAX section) of the absorber in Fig. 5 is cooled by, and transfers heat to, the GAX heat transfer fluid. There, the number of tube coils on the outer surface of the shell can vary as desired or required by the heat transfer fluid. Fig. 5 shows three parallel GAX heat transfer fluid tube coils 50 constituting one stream of weak liquor that flows through the three passages in sequence as described in one embodiment (Fig. 3) of U.S. Patent No. 5,367,884 ("'884 patent"). In this embodiment of the invention, GAX heat transfer fluid tube coils 50 have three inlets 70 that receive weak liquor that has circulated through the heat transfer region of the generator (not shown) and three outlets 72, two of which circulate weak liquor out of the absorber and back to the generator, and one that returns weak liquor up to the absorber inlet 73. In many tests conducted by the inventor, three passages have been very effective. However, as disclosed in the '884 patent, there can also be a sequence of four parallel tube coils in the GAX section for four passages of weak liquor (Fig. 3A of '884 patent); 1 tube coil for one passage of weak liquor (Fig. 4 of '884 patent) or one passage of rich liquor (Figs. 7, 7A, 8, 8A of '884 patent); no tube coil (Figs. 5 and 6 of '884 patent); or two tube coils for two passages of rich liquor (Fig. 9 of '884 patent).

Other tube coil arrangements can be used for the GAX section of the absorber as disclosed in U.S. Patent Nos. 5,271 ,235, 5,570,584, 5,579,652 and 5,782,097. For example, for the combination of weak liquor and boiling rich liquor of U.S. Patent No. 5,579,652 ('"652 patent"), one weak liquor coil and one rich liquor coil (Figs. 4 and 6 of '652 patent) may be preferred, but other embodiments have one rich liquor coil only (Figs. 3 and 5 of '652 patent. For the intermediate liquor GAX system of U.S. Patent No. 5,570,584 ('"584 patent"), one coil (Figs. 4, 6, 7, and 9-11 of '584 patent) two coils (Fig. 3 of '584 patent), or three coils (Fig. 12 of '584 patent) carrying intermediate liquor can be used. For the rich liquor embodiment of U.S. Patent No. 5,782,097 ('"097 patent"), one coil carrying rich liquor (Figs. 3 and 4 of '097 patent) is preferably used. For the embodiments of U.S. Patent No. 5,271 ,235, one or two coils can be used for the GAX section.

The division of the absorber into three sections can also be made as shown in Fig. 7, in which the bottom low temperature section 80 of absorber 10 heats both the secondary fluid in a secondary fluid coil 82 and the rich liquor in a rich liquor coil 84. In the embodiment of Fig. 7, secondary fluid is introduced to secondary fluid coil 82 through two secondary fluid parallel inlets 81 and exits through two secondary fluid parallel outlets 83. Rich liquor is introduced into rich liquor coil 84 through two rich liquor parallel inlets 85 and continues upward to be heated further in the middle section 86, before exiting through two rich liquor parallel outlets 87. The GAX heat transfer fluid is heated by GAX heat transfer coil 88 adjacent to GAX section 90. ln Fig. 7, unlike Fig. 5, the rich liquor enters rich liquor coil 84 at the bottom of absorber 10 at rich liquor parallel inlets 85 where it is heated by heat that in Fig. 5 was transferred to the secondary fluid. To ensure that the secondary fluid is heated to the desired temperatures in the Fig. 7 embodiment, secondary fluid coil 82 could be extended beyond bottom low temperature section 80 of absorber 10 to middle section 86 (not shown). Alternatively, the flow rate of the secondary fluid through secondary fluid coil 82 could be reduced to allow the secondary fluid to be heated to the desired temperature at secondary fluid parallel outlets 83. The design of Fig. 7 can also serve to produce two streams of secondary fluid, one hotter than the other, by using two secondary coils of different heights.

Distribution of the liquid at the top of the absorber around the inner walls of the absorber can be accomplished in ways known in the art. Preferably, a spray nozzle 74 as shown in Figs. 5 and 7 is used to spray the hot liquid into the top of the absorber after it has been circulated between the heat transfer regions of the absorber and generator. Spray nozzle 74 preferably introduces the liquid in the form of fine droplets into the hot vapor at the top of the absorber. In their radial paths to the cylindrical inner wall of the absorber, the droplets absorb the hot vapor in that space and are also heated by that absorption to very near the equilibrium temperature before contacting the inner wall of the absorber. Thus, the top of the absorber is heated to very near the peak temperature of the absorber, depicted as point F in Fig. 2 of U.S. Patent No. 5,367,884.

It will be apparent to those skilled in the art that various modifications and variations can be made in the generator-absorber heat exchange apparatus of the invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided that they come within the scope of the appended claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. An ammonia-water generator-absorber heat exchange apparatus comprising a generator and an absorber, each including a generally cylindrical housing having inner wall surfaces, the absorber configured so that weak liquor ammonia-water liquid entering the top of the absorber flows downward along the inner wall surface of the absorber thereby contacting in a generally counterflow manner the rich liquor vapor entering the bottom of the absorber and flowing upward through the absorber, wherein the inner wall surface of the absorber includes a plurality of spaced knurls configured to increase the transfer of ammonia from the vapor flowing upward through the absorber to the liquid flowing downward along the inner wall surface of the absorber and to increase the transfer of heat from the liquid to the knurled surfaces.

2. The apparatus of claim 1 , wherein the knurls have a generally diamond shape.

3. The apparatus of claim 1 , wherein the knurls have a generally vertical diamond configuration.

4. The apparatus of claim 1 , wherein the knurls have a generally horizontal diamond configuration.

5. The apparatus of claim 1 , wherein the knurls have a generally square diamond configuration.

6. The apparatus of claim 1 , wherein some of the knurls have a generally vertical diamond configuration and some of the knurls have a generally square diamond configuration.

7. The apparatus of claim 1 , wherein the knurls in the upper portion of the absorber have a generally horizontal diamond configuration and the knurls in the lower portion of the absorber have a generally square diamond configuration.

8. The apparatus of claim 1 , wherein the knurls in the upper portion of the absorber have a generally horizontal diamond configuration and the knurls in the lower portion of the absorber have a generally vertical diamond configuration.

9. The apparatus of claim 1 , wherein the knurls in the upper portion of the absorber have a generally square diamond configuration and the knurls in the lower portion of the absorber have a generally vertical diamond configuration.

10. The apparatus of claim 1 , wherein the knurls in the upper portion of the absorber have a generally horizontal diamond configuration, the knurls in the middle portion of the absorber have a generally square diamond configuration, and the knurls in the bottom of the absorber have a generally vertical diamond configuration.

11. The apparatus of claim 1 , wherein the number of knurls/horizontal inch of absorber surface ranges from about 8 to about 15.

12. The apparatus of claim 11 wherein the number of knurls/horizontal inch of absorber surface is about 12.

13. The apparatus of claim 1 , wherein the knurls have a depth ranging from about .015 to about .06 inch.

14. The apparatus of claim 13, wherein the knurls have a depth of about .03 inch.

15. The apparatus of claim 1 , further comprising means for directing the vapor flowing upward through the absorber to the liquid flowing downward along the inner wall surface of the absorber.

16. The apparatus of claim 1 , wherein the generator is configured so that rich liquor ammonia-water liquid entering the top of the generator flows downward along the inner wall surface of the generator thereby contacting in a generally counterflow manner the weak liquor ammonia-water vapor flowing upward from the bottom of the generator, wherein at least a portion of the inner wall surface of the generator includes a plurality of spaced knurls configured to increase the transfer of ammonia from the liquid flowing downward along the inner wall surface of the generator to the vapor flowing upward through the generator and to increase the transfer of heat from the knurled surfaces to the liquid.

17. An ammonia-water generator-absorber heat exchange apparatus comprising: a generator and an absorber, the absorber having an interior pressure lower than the pressure of the generator interior, each including a generally cylindrical housing having inner wall surfaces forming a hollow interior, the absorber configured so that weak liquor ammonia-water liquid entering the top of the absorber flows downward along the inner wall surface of the absorber thereby contacting in a generally counterflow manner the rich liquor vapor entering the bottom of the absorber and flowing upward through the absorber; wherein the hollow interior of the absorber housing includes a plurality of flow deflectors, said flow deflectors including: a base directing liquid flowing downward through the absorber toward the inner wall surface; and a rim extending from the base to a skirt forming an open end; wherein the rim skirt and the absorber inner wall surface form a pathway for liquid flowing down the inner wall surface of the absorber to pass from one flow deflector to an adjoining flow deflector, the pathway being impervious to the upward flowing vapor; wherein the rim includes a plurality of perforations allowing the vapor flowing upward through the absorber to flow toward the inner wall surface, said perforations together with the pressure drop from said flowing liquid causing the vapor to impinge on the liquid flowing downward along the inner wall surface to increase the transfer of ammonia from the vapor flowing upward through the absorber to the liquid flowing downward along the inner wail surface of the absorber and to increase the transfer of heat from the liquid to the inner wall surface.

18. The apparatus of claim 17, wherein the base is disc shaped and the rim is annular shaped.

19. The apparatus of claim 17, wherein the flow deflectors are stacked along the length of the housing so that adjacent pairs of flow deflectors include a base of one of the flow deflectors positioned in the open end of another flow deflector, and wherein the flow deflectors are positioned to allow flow of the vapor sequentially through each of the flow deflectors.

20. The apparatus of claim 17, wherein the number of flow deflectors ranges from about 14 to about 36.

21. The apparatus of claim 17, wherein the perforations in the flow deflector rims are generally circular in shape.

22. The apparatus of claim 17, wherein the diameter of the perforations in the flow deflector rims ranges from about 1/32 to about 5/16 inch.

23. The apparatus of claim 22, wherein the diameter of the perforations in the flow deflector rims gradually increases from about 3/16 inch at the bottom of the absorber to about 1/32 inch at the top of the absorber.

24. The apparatus of claim 17, wherein the perforations in the flow deflectors are arranged in rows ranging from about 1 to about 6 rows/flow deflector.

25. The apparatus of claim 24, wherein the number of perforations/row around the circumference of each flow deflector ranges from about 20 to about 50.

26. The apparatus of claim 17, wherein the height of each flow deflector ranges from about 1 to about 3 inches.

27. The apparatus of claim 17, wherein the flow deflectors are composed of a metal or alloy having a thickness ranging from about .02 to about .05 inch.

28. The apparatus of claim 17, wherein the perforations in the flow detector rims are configured in a generally staggered arrangement around the perimeters of the flow detectors.

29. The apparatus of claim 17, further comprising a spray nozzle at the top of the absorber for introducing weak liquor ammonia-water liquid into the absorber toward the inner wall surface in the form of a fine mist.

30. The apparatus of claim 17, wherein the generator is configured so that rich liquor ammonia-water liquid entering the top of the generator flows downward along the inner wall surface of the generator thereby contacting in a generally counterflow manner the weak liquor ammonia-water vapor flowing upward from the bottom of the generator; wherein the hollow interior of the generator housing includes a plurality of flow deflectors, said flow deflectors including: a base directing liquid flowing downward through the generator toward the inner wall surface; and a rim extending from the base to a skirt forming an open end; wherein the rim skirt and the generator inner wall surface form a pathway for liquid flowing down the inner wall surface of the generator to pass from one flow deflector to an adjoining flow deflector, the pathway being impervious to the upward flowing vapor;

wherein the rim includes a plurality of perforations allowing the vapor flowing upward through the generator to flow toward the inner wall surface, said perforations together with the pressure drop from said flowing liquid causing the vapor to impinge on the liquid flowing downward along the inner wall surface to increase the transfer of ammonia from the liquid flowing downward along the inner wall surface of the generator to the vapor flowing upward through the generator and to increase the transfer of heat from the knurled surfaces to the liquid.

31. The apparatus of claim 17, wherein the inner wall surface of the absorber includes a plurality of spaced knurls configured to increase the transfer of ammonia from the vapor flowing upward through the absorber to the liquid flowing downward along the inner wall surface of the absorber and to increase the transfer of heat from the liquid to the knurled surfaces.

32. The apparatus of claim 17, wherein the inner wall surface of the generator includes a plurality of spaced knurls configured to increase the transfer of ammonia from the liquid flowing downward through the generator to the vapor flowing upward through the generator and to increase the transfer of heat from the knurled surfaces to the liquid.

33. The apparatus of claim 31 , wherein the absorber includes a secondary fluid cooled section proximate the bottom of the absorber, an absorber heat exchange section proximate the middle of the absorber, and a generator- absorber heat exchange section proximate the top of the absorber.

34. The apparatus of claim 33, further comprising a first helical heat exchange coil extending around the outer surface of the absorber housing adjacent to the secondary fluid cooled section, a second helical heat exchange coil extending around the outer surface of the absorber housing adjacent to the absorber heat exchange section, and a third helical heat exchange coil extending around the outer surface of the absorber housing adjacent to the generator- absorber heat exchange section.

35. The apparatus of claim 34, wherein the first helical coil contains a secondary heat transfer fluid, the second helical coil contains a rich ammonia- water liquor, and the third helical coil contains an ammonia-water liquor selected from a rich liquor, a weak liquor, and an intermediate liquor.

36. The apparatus of claim 34, wherein the helical coils are attached to the outer surface of the absorber housing by means that forms fillets between the coils and the absorber housing to provide a continuous path for heat being transferred from the absorber to the fluid being heated.

37. The apparatus of claim 36, wherein the helical coils increase the strength of the absorber housing.

38. The apparatus of claim 33, further comprising a first helical heat exchange coil extending around the outer surface of the absorber housing adjacent to the secondary fluid cooled section, a second helical heat exchange coil extending around the outer surface of the absorber housing adjacent to the secondary fluid cooled section and the absorber heat exchange section, and a third helical heat exchange coil extending around the outer surface of the absorber housing adjacent to the generator-absorber heat exchange section.

39. The apparatus of claim 38, wherein the first helical coil contains a secondary heat transfer fluid, the second helical coil contains a rich ammonia- water liquor, and the third helical coil contains an ammonia-water liquor selected from a rich liquor, a weak liquor, and an intermediate liquor.

40. The apparatus of claim 38, wherein the helical coils are attached to the outer surface of the absorber housing by means that forms fillets between the coils and the absorber housing to provide a continuous path for heat being transferred from the absorber to the fluid being heated.

41. The apparatus of claim 40, wherein the helical coils increase the strength of the absorber housing.

42. The apparatus of claim 34, wherein said vapor impinging on the liquid flowing downward along the inner wall surface of the absorber increases the turbulence of the flowing liquid to increase the transfer of ammonia from the vapor to the liquid and to increase the transfer of heat from the liquid to the knurled surfaces.

43. The apparatus of claim 42, wherein the flow deflectors are designed and configured so that the impinging vapor does not cause the liquid flowing along the inner wall of the absorber to be displaced from the knurled inner wall surface.