FIELD

The present disclosure relates to a system and a method for generating low pressure steam. DEFINITIONS As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.

Low pressure steam - refers to steam having a pressure in the range of 0.3 bar to 0.9 bar. BACKGROUND

The multiple effect evaporation/distillation process is widely used in a variety of industries including pharmaceuticals, chemical, paper & pulp, sugar manufacturing, food & beverage industries. In these processes, multiple effect evaporation is done to evaporate off water from an aqueous solution or slurry so as to concentrate it before further treatment.

Particularly, in the food industry, to avoid thermal damage of the feed, the evaporation has to be done under reduced pressures such that the maximum temperature of the feed does not exceed 70 to 75°C across the effects. Thus, the required heat source is normally low pressure steam (approximately 75-95°C).

Like a food industry, desalination is also characterized by low boiling points approximately 70°C, to avoid the metastable state of the salt during the evaporation process.

Desalinated seawater can be used to overcome the shortage of fresh water required for human consumption. About 97% of water contained in the oceans can be tapped to produce desalinated water by different conventional systems and conventional methods, such as multi-stage flash evaporation, multi-effect distillation, reverse osmosis, vapor recompression, and the like. From the above mentioned systems and methods, the multi- stage flash (MSF) evaporation, and the multi-effect distillation (MED) are widely used for the production of desalinated water.

Multi-effect distillation (MED) comprises a series of 8 to 16 columns or effects operating at decreasing levels of pressures and temperatures. At least one of the series of effects requires a heated fluid, particularly steam, from an external source to heat the contents or the seawater contained in the series of effects and produce desalinated water.

Boilers are used as the external source to generate and provide the heated fluid, particularly steam, in at least one of the series of effect of the MED. However, following are limitations associated with the use of boilers: · pressure of the steam generated from the boilers is quite high, as such the pressure of the steam has to be first reduced by some mechanism before it is taken to the MED process. The pressure reducing process will have its own associated energy losses, thereby deteriorating the thermal performance of the MED. Also, higher pressure steam is more expensive;

· as huge amount of water needs to be evaporated ,the energy requirement is also huge, thereby making the entire operation of producing desalinating water energy intensive.

Further, attempts have been made in the prior art to produce desalinated water.

For example, CN102992532 suggests an air type immersed multiple-effect evaporation desalination unit in which the waste heat is used to partly evaporate incoming seawater and partly as a heat source for a vapor absorption heat pump. The intention of this document is to enable the use of exhausted heat for desalination. In contrast, GB 1134130 suggests a multi-flash evaporator system where the feed is heated to a high temperature and flashed in lower pressure stages. The vapor flashed in the last stage is absorbed in a vapor absorption cycle. The vapor condensed in every stage is collected as a fresh product. This document does not deal with the heat rejected in the absorbed. The absorption process suggested reduced the pressure of the last stage as it is coupled to an absorber instead of a condenser.

Still further, US8910477 suggests a method of using the vapor absorption cycle to produce electricity or mechanical energy. In the suggested cycle of this document, vapor in the distillation column is superheated and expanded to generate energy while the working stream is in closed circulation. The heat rejected in the absorber assembly is rejected in the cooling water.

Yet further, CN101435615 suggests a method of cooling and dehumidification of air using a Li-Br based vapor absorber system. The refrigerant is regenerated using a membrane with lower temperature heat sources.

Therefore, there is felt a need for a system and a method for generating low pressure steam. Further, there is felt a need for a system and a method for generating low pressure steam that obviates the above mentioned limitations.

OBJECTS Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:

An object of the present disclosure is to provide a system for generating low pressure steam.

Another object of the present disclosure is to provide a method for generating low pressure steam.

Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure. SUMMARY

The present disclosure envisages a system for generating low pressure steam for a distillation unit. The system comprises a distillation unit, a vapor absorption unit comprising of an evaporator chamber, an absorber chamber,a first heat exchanger, a heat reclaimer, a first generator and a flash tank.

In accordance with the present disclosure, the distillation unit has a plurality of effects and a condenser in operative communication with at least one effect configured to generate a warmed fluid.

In accordance with the present disclosure, the evaporator chamber is configured for absorbing the heat from the warmed fluid to convert a refrigerant (water) into vapor. The vapor is then allowed to enter the absorber chamber to absorb the vapor in a cooled concentrated Li-Br solution (absorbent solution) to dilute the cooled concentrated Li-Br solution and generate a dilute Li-Br solution and heat of dilution which is for absorbed in a circulating heated absorbing fluid. In accordance with the present disclosure, the first heat exchanger is configured to provide the cooled concentrated Li-Br solution to the absorber chamber.

In accordance with the present disclosure, the first heat exchanger is further configured to receive a first stream of said dilute Li-Br solution from the absorber chamber for cooling a received hot concentrated Li-Br solution and generate a first stream of warmed dilute Li- Br solution.

In accordance with the present disclosure, the heat reclaimer is configured to receive a condensate stream from the first generator and a second stream of the dilute Li-Br solution from the absorber chamber to generate a second stream of warmed dilute Li-Br solution;

In accordance with the present disclosure, the first generator is configured to receive the first stream of warmed dilute Li-Br solution, second stream of warmed dilute Li-Br solution and a heating fluid, for generating the hot concentrated Li-Br solution for supplying to the first heat exchanger, the condensate for supplying to the heat reclaimer and a hot refrigerant vapor. In accordance with the present disclosure, the flash tank is fitted with a pump for circulating the heated absorbing fluid between itself and the absorber chamber and receiving the hot refrigerant vapor from the first generator and generating low pressure steam. In accordance with the present disclosure, the system also includes optionally a second heat exchanger and a second generator.

In accordance with the present disclosure, a method for generating low pressure steam for a distillation unit is also provided.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

A system and a method for generating low pressure steam will now be described with the help of the accompanying drawing, in which:

Figure 1 and Figure 2 illustrate a system for generating low pressure steam in accordance with the present disclosure.

DETAILED DESCRIPTION

Generally, boilers are used to generate steam. The steam generated by the boilers is used as a heating medium in multi-effect distillation (MED) for varied purposes such as desalination of seawater, and the like. However, there are certain limitations associated with the use of boilers, for example: · pressure of the steam generated from the boilers is quite high, as such the pressure of the steam has to be first reduced by some mechanism before it is taken to the MED process. The pressure reducing process will have its own associated energy losses, thereby deteriorating the thermal performance of the MED. Also, higher pressure steam is more expensive; and

· as huge amount of water needs to be evaporated, the energy requirement is also huge, thereby making the entire operation of producing desalinating water energy intensive. The present disclosure, therefore, provides a system and a method for generating low pressure steam for a distillation unit that obviates the above mentioned drawbacks.

In accordance with one embodiment of the present disclosure, the system of the present disclosure is described with respect to Figure 1. The system (100) includes: o a distillation unit (18) having a plurality of effects and a condenser (32) in operative communication with at least one effect configured to generate a warmed fluid;

• a vapor-absorption unit (10) comprises a shell (S) including:

o an evaporator chamber (26);

o an absorber chamber (28); and

o a perforated plate (24) disposed between the evaporator chamber (26) and the absorber chamber (28);

o a first heat exchanger (12);

o a heat reclaimer (14);

o a first generator (G); and

o a flash tank(16)

Typically, the distillation unit (18) is a multi-effect distillation unit.

The system (100) also includes a collecting tank (T) and a plurality of pumps (PI, P2, P3, P4 and P5).

A method for generating low pressure steam using the system (100) is described herein below.

Low pressure steam, from the flash tank is introduced into the distillation unit (18). In accordance with the present disclosure, there may be a single effect or a plurality of effects. The low pressure steam is circulated through tubes of a first effect (30) of the plurality of distillation effects. Due to this, a fluid contained in the first effect (30) is heated to obtain a heated fluid, wherein at least a portion of the heated fluid is in vapor form. In accordance with the present disclosure, the fluid includes, but is not limited to, seawater. The vapors of the heated fluid are further circulated through tubes of consecutive effects of the plurality of effects to heat the fluid contained in the consecutive effects of the plurality of effects to obtain a heated fluid, wherein at least a portion of the heated fluid is in vapor form. A last effect (31) of the plurality of effects is in operative communication with the condenser (32). A cooling fluid having a temperature in the range of 25 to 34°C is circulated through tubes of the condenser. The vapors of the heated fluid leaving the last effect (31) of the plurality of effects are introduced into the condenser (32). Due to heat exchange between the low pressure steam and the cooling fluid circulated through the tubes of the condenser (32), the low pressure steam is condensed to generate low pressure steam condensate having a temperature in the range of 70 to 75°C. In accordance with the present disclosure, the low pressure steam condensate is collected in the collecting tank (T). The cooling fluid leaving the tubes of the condenser (32) is the warmed fluid having a temperature in the range of 31 to 40°C.

In order to utilize unused heat of the warmed fluid, it is necessary to circulate the warmed fluid through tubes of the evaporator chamber (26). In accordance with one embodiment of the present disclosure, the warmed fluid is circulated through the tubes of the evaporator chamber (26) by the pump (PI).

A refrigerant having a temperature in the range of 20 to 30°C is sprinkled by a first sprinkler (20) on the tubes of the evaporator chamber (30). The refrigerant is converted into vapor due to heat exchange between the warmed fluid and the refrigerant. Further, due to heat transfer, the warmed fluid is cooled to obtain a cooled fluid having a temperature in the range of 25 to 35°C.

In accordance with one embodiment of the present disclosure, the refrigerant is water.

In accordance with one embodiment of the present disclosure, the refrigerant is continuously circulated in the evaporator chamber (26) by the pump (P2).

In accordance with one embodiment of the present disclosure, the low pressure steam condensate collected in the collecting tank (T) can be pumped into the evaporator chamber (26) by the pump (P5) and used as a refrigerant. The vapor from the evaporator chamber (26) enters into the absorber chamber (28) via the perforated plate (24). A cooled concentrated Li-Br solution having a temperature in the range of 85 to 90°C and a concentration in the range of 61 to 64% from the first heat exchanger (12) is sprinkled by a second sprinkler (22) on tubes of the absorber chamber (28). The vapor is absorbed by the cooled concentrated Li-Br solution and due to this the concentration of the cooled Li-Br solution is reduced to obtain a diluted Li-Br solution having a concentration in the range of 56 to 59% and a temperature in the range of 75 to 80°C. Moreover, heat of dilution is generated during the absorption of the vapor in the cooled concentrated Li-Br solution. In order to maintain uniform temperature in the absorber chamber (28), it is necessary to absorb the heat of dilution. The heat of dilution is absorbed by circulating a heated absorbing fluid having a temperature in the range of 70 to 75°C from the flash tank (16) through the tubes of the absorber chamber (28), thereby increasing the temperature of the heated absorbing fluid to a temperature in the range of 76 to 80°C. The heated absorbing fluid is recycled into the flash tank (16). In accordance with one embodiment of the present disclosure, the heated absorbing fluid from the flash tank (16) is circulated through the tubes of the absorber chamber (28) by the pump (P4).

In accordance with one embodiment of the present disclosure, the heated absorbing fluid is heated water having a temperature in the range of 70 to 75°C. In accordance with the present disclosure, the diluted Li-Br solution obtained in the absorber chamber (28) is passed through a series of heat exchangers to regain a desired concentration of the Li-Br solution.

In the present case, a first stream of the diluted Li-Br solution from the absorber chamber (28) is introduced into the first heat exchanger (12). In accordance with one embodiment of the present disclosure, a first stream of the diluted Li-Br solution from the absorber chamber (28) is introduced into the first heat exchanger (12) by the pump (P3). In the first heat exchanger (12), a hot concentrated Li-Br solution having a desired concentration i.e. a concentration in the range of 61 to 64% and a temperature in the range of 131 to 134°C is introduced into the first heat exchanger (12) from the first generator (G). In the first heat exchanger (12) there is heat exchange between the hot concentrated Li-Br solution and the diluted Li-Br solution, thereby obtaining a first stream of warmed diluted Li-Br solution having a temperature in the range of 120 to 130°C and decreasing the temperature of the hot concentrated Li-Br solution to a temperature in the range of 85 to 90°C. In short, in the first heat exchanger (12), the hot concentrated Li-Br solution is converted into the cooled concentrated Li-Br solution, which is sprinkled in the absorber chamber (28) by the second sprinkler (22).

In accordance with the present disclosure, a second stream of the diluted Li-Br solution from the absorber chamber (28) is introduced into the heat reclaimer (14), wherein a condensate stream having a temperature in the range of 140 to 150°C is introduced into the heat reclaimer (14). There is heat exchange between the condensate stream and the second stream of the diluted Li-Br solution in the heat reclaimer (14), thereby obtaining a second stream of warmed diluted Li-Br solution and decreasing the temperature of the condensate stream to a temperature in the range of 85 to 95°C. In accordance with the present disclosure, the first stream of warmed diluted Li-Br solution and the second stream of warmed diluted Li-Br solution are pre-mixed i to obtain a pre-mixed mixture having a temperature in the range of 135 to 140°C. The pre-mixed mixture is then introduced into the generator (G). A heating fluid (high pressure steam) having a temperature in the range of 140 to 150°C and a pressure of 4 bar to 5 bar is generated from an external source and introduced into the first generator (G). In the first generator (G) there is heat exchange between the pre-mixed mixture and the heating fluid, due to which the refrigerant vapor is separated from the pre-mixed mixture and introduced into the flash tank (16). Due to heat exchange, the heating fluid (high pressure steam) condenses to obtain the condensate stream, and the pre-mixed mixture is bolied to obtain the hot concentrated Li-Br solution.

In accordance with the present disclosure, the heated absorbing fluid circulated in the absorber (28) and the refrigerant vapor from the first generator (G) are flashed to generate the low pressure steam i.e. a steam of desired pressure (0.35 bar). The low pressure steam is re-circulated in the distillation unit, because the low pressure facilitates heating of the fluid (seawater) at a low temperature, to produce desalinated water.

In accordance with one embodiment of the present disclosure, the low pressure steam condensate collected in the collecting tank (T) is circulated to the flash tank i.e. the low pressure steam condensate is used as make-up source for the flash tank (16).

In accordance with another embodiment of the present disclosure, the system of the present disclosure is described with respect to Figure 2. The system (200) includes:

• a second Heat exchanger (52), the heat reclaimer (14), a first generator (G), a second generator (Lg) and the flash tank (16).

The system (200) also includes the collecting tank (T) and the plurality of pumps (PI, P2, P3, P4 and P5) as depicted in Figure 2.

The function of the collecting tank (T) and the plurality of pumps (PI, P2, P3, P4 and P5) are described herein above.

A method for generating low pressure steam using the system (200) is described herein below.

A method for obtaining the diluted Li-Br solution is same as that obtained using the system (100). The difference in obtaining the diluted Li-Br solution using the system (200) is that the vapour absorption portion is double effect, that is concentration of the LiBr solution is done in two stages.

In accordance with the present disclosure, a first stream of the diluted Li-Br solution from the absorber chamber (28) is introduced into the first heat exchanger (12). Also, the hot concentrated Li-Br solution is introduced into the first heat exchanger (12) from the second generator (Lg). There is heat exchange between the first stream of the diluted Li-Br solution and the hot concentrated Li-Br solution due to which diluted Li-Br solution is heated and the temperature of the hot concentrated Li-Br solution is reduced to obtain the cooled concentrated Li-Br solution. The heated first stream of diluted Li-Br solution is introduced into the second heat exchanger (52). An intermediate concentrated Li-Br solution having a concentration in the range of 58 to 60% and a temperature in the range of 186 to 195°C is also introduced into the second heat exchanger (52) from the first generator (G). Due to heat exchange between the heated diluted Li-Br solution and the intermediate concentrated Li-Br solution, a first stream of warmed having a temperature in the range of 175 to 185°C is obtained and the temperature of the intermediate concentrated Li-Br solution is reduced to a temperature in the range of 135 to 145°C.

In accordance with the present disclosure, a second stream of the diluted Li-Br solution is introduced into the heat reclaimer (54), wherein a condensate stream having a temperature in the range of 195°C to 210°C is introduced from the first generator (G) for heating the second stream of the diluted Li-Br solution. Due to heat exchange between the second stream of the diluted Li-Br solution and the condensate stream, a second stream of warmed diluted Li-Br solution having a temperature in the range of 175 to 185°C is obtained and the temperature of the condensate stream is reduced to a temperature in the range of 85 to 95°C.

In accordance with the present disclosure, the first stream of warmed diluted Li-Br solution and the second stream of warmed diluted Li-Br solution is pre-mixed ito obtain a pre-mixed mixture having a temperature in the range of 175 to 185°C. The pre-mixed mixture is introduced into the first generator (G) and a third heated fluid (high pressure steam) having a temperature in the range of 195 to 210°C and a pressure in the range of 10 bar to 16 bar is also introduced into the first generator (G) from a second external source, for boiling the pre-mixed mixture. Due to heat exchange between the third heated fluid and the pre-mixed mixture, the refrigerant vapor having a temperature in the range of 135 to 145°C is separated from the pre-mixed mixture and introduced into the second generator (Lg). During the heat exchange between the third heated fluid and the pre-mixed mixture, the pre-mixed mixture boils the third heated fluid, the high pressure steam condenses to obtain the:

• the intermediate concentrated Li-Br solution; and • the condensate stream.

In the second generator (Lg), there is heat exchange between the refrigerant vapor fluid introduced from the first generator and the intermediate concentrated Li-Br solution introduced from the low temperature heat exchanger (50). Due to this, the LiBr solution boils and the concentration of the intermediate concentrated Li-Br solution is increased to obtain the concentrated Li-Br solution and the refrigerant vapor having a temperature in the range of 70°C to 75°C. The refrigerant vapour leaving the second generator (Lg) is introduced into the flash tank (16).

In the flash tank (16), the heated absorbing fluid from the absorber chamber (28) and the vaporized fluid from the second generator (Lg) are flashed to generate the low pressure steam. The low pressure steam is then re-circulated in the distillation unit (18) for producing desalinated water.

Application of the systems (100 and 200) of the present disclosure is not limited to the production of desalinated water. The systems (100 and 200) of the present disclosure can generate steam up to 0.9 bar depending upon the unused heat available at an outlet of the condenser (32) of the distillation unit (18) and the external heat source available. Moreover, a part of the waste heat rejected in the condenser (32) of the MED (18) is absorbed by the evaporator chamber (26) of the vapor absorption unit (10), the amount of energy required is less than that of the boiler steam used directly in the MED (18).

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE

The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a system and a method that:

• generates low pressure steam; and

· utilizes unused heat effectively from outlet fluid of a condenser of MED. The disclosure has been described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein.

The foregoing description of the specific embodiments so fully revealed the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application. In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only. While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principle of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.