FIELD

The present disclosure relates to the field of mechanical engineering and more particularly, the present invention relates to the field of regenerative feed water heating.

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.

Anergy: The term "Anergy" hereinafter in the complete specification refers to destroyed exergy. Exergy: The term "Exergy" hereinafter in the complete specification refers to the maximum useful work possible during a process that brings a system in equilibrium with its surroundings.

BACKGROUND

In a power generating cycle, regenerative feed heating is done in order to increase the temperature of the feed water. This is done so as to minimize the sensible heat required to heat the water using external heat usually from fossil fuel. Therefore, steam is extracted from a turbine and is condensed in the heater to heat the feed water. However, the extraction pressure of the steam limits the temperature up to which the feed water can be heated as the theoretical maximum temperature achievable by direct or indirect heating is the saturation temperature of the corresponding extraction pressure of the steam. Therefore, multiple extractions are taken at various stages of the turbine at different pressures to increase the feed water temperature that is closer to the saturation temperature of a steam generator. But, the down-side of extraction of steam for regenerative feed heating is that it deprives the turbine of the equivalent amount of steam to generate mechanical power. The steam required by a low pressure heater for heating the feed water is less, and therefore the amount of steam required for generating the power using the turbine is not affected.

The possibility of providing feed water heating not limited by the extraction pressure of steam necessitates reduced steam extraction quantity at the subsequent higher pressure extraction. This saved quantity of steam performs work in the turbine by expanding to low pressure. Therefore, with the same heat as an input to the steam generator, the power output of the turbine increases, or for the same power output, the input heat requirement reduces, thereby improving the heat rate of the regenerative power cycle. However, such a scheme would require external work or external heating which is not economical. The external work can be provided by heat pumps.

Heat pumps are equipment that pump heat from low temperature to high temperature with the aid of external inputs. Heat pumps are broadly classified as vapor compression heat pumps and vapor absorption heat pumps. The vapor compression heat pump uses a mechanical drive such as a compressor to provide the external input required to increase the temperature. The vapor absorption heat pump is a thermally activated device that uses a combination of generator-absorber to provide external input. The generator and absorber arrangement can be analogous to the steam generator and the condenser in a power plant.

Therefore, there is felt a need for a regenerative feedwater heating system for a boiler that alleviates the above-mentioned drawbacks.

OBJECTS

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

It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.

An object of the present disclosure is to provide a regenerative feedwater heating system for a boiler.

Another object of the present disclosure is to provide a system for increasing a temperature of the feed water above the saturation temperature of a heat source steam extracted from a turbine.

Still another object of the present disclosure is to provide a system by which exergy of a medium temperature heat source steam extraction can be used to pump the heat to a higher temperature. Yet another object of the present disclosure is to disclose a system by which the destroyed exergy of a heat transformer can be utilized for regenerative feed heating.

Another object of the present disclosure is to disclose a system for improving the regenerative power cycle efficiency. SUMMARY

The present disclosure envisages a regenerative feedwater heating system. The system comprises a steam turbine, a condenser, a low pressure (LP) heater, a deaerator, and a vapour absorption machine (VAM). The steam turbine is configured to receive high pressure steam for providing a mechanical drive and provide low pressure expanded steam subsequent to the expansion of the high pressure steam thereon. The condenser is configured to receive a first stream of expanded steam from the steam turbine and facilitate the condensation of the first stream of expanded steam therewithin to probide a condensate.

The LP heater is configured to receive the condensate and a second stream of expanded steam from the steam turbine. The LP heater has an arrangement that permits thermal communication between the condensate and the second stream of expanded steam. The condensate and the second stream of expanded steam facilitate heating of the condensate to provide a heated condensate. The deaerator is configured to receive the heated condensate and facilitate removal of dissolved oxygen from the heated condensate. The deaerator is further configured to receive a third stream of expanded steam from the steam turbine. The deaerator has a configuration that permits thermal communication between the heated condensate and the third stream of steam, thereby further heating the heated condensate to provide a vaporized condensate.

The vapour absorption machine (VAM) of the present invention comprises a VAM condenser and a VAM absorber. The VAM condenser is disposed downstream of the condenser and upstream of the LP heater. The VAM condenser is configured to facilitate heating of the condensate prior to entering within the LP heater. The VAM absorber is disposed downstream of the LP heater and upstream of the deaerator. The VAM absorber is configured to facilitate heating of the heated condensate prior to entry within the deaerator.

In accordance with another embodiment of the present disclosure, a regenerative feedwater heating system for a boiler comprises a steam turbine, a condenser, a low pressure (LP) heater, a deaerator, a high pressure (HP) heater, a first vapour absorption machine (VAM I), and a second vapour absorption machine (VAM II). Typically, the boiler is used in power plants for generating steam.

The high pressure (HP) heater is configured to receive vaporized condensate from the deaerator and a fourth stream of expanded steam from the steam turbine. The HP heater has a configuration that permits thermal communication between the vaporized condensate and the fourth stream of expanded steam, thereby heating said vaporized condensate to provide heated vaporized condensate.

The first vapour absorption machine comprises a first VAM condenser and a first VAM absorber. The first VAM condenser is disposed downstream of the condenser and upstream of the LP heater. The first VAM condenser is configured to facilitate heating of the condensate prior to entering within the LP heater. The first VAM absorber is disposed downstream of the LP heater and upstream of the deaerator. The first VAM absorber is configured to facilitate heating of the heated condensate prior to entry within the deaerator. a second vapour absorption machine comprises a second VAM condenser and a second VAM absorber. The second VAM condenser is disposed downstream of the first VAM condenser and upstream of the deaerator. The second VAM condenser is configured to facilitate further heating of the heated condensate prior to entry within the deaerator. The second VAM absorber is disposed downstream of the deaerator and upstream of HP heater. The second VAM absorber is configured to facilitate heating of the vaporized condensate prior to entry within said HP heater.

In an embodiment, a condensate collection tank is in fluid communication with the condenser, and is configured to collect the condensed fluid therewithin.

In another embodiment, the system further includes a condensate extraction pump that is in fluid communication with the condensate collection tank. The condensate extraction pump is configured to extract said condensed fluid from the condensate collection tank and pump the condensed fluid downstream.

In still another embodiment, the drain of the LP heater is configured to reject the condensed fluid formed in the low pressure heater to the condensate collection tank. In yet another embodiment, the system includes a boiler feed pump that is disposed downstream of the deaerator and upstream of the HP heater. The boiler feed pump is configured to pressurize the vaporized condensate prior to entry within the HP heater.

In still another embodiment, the drain of the HP heater is configured to reject condensed fluid formed in the HP heater to the deaerator.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING

A regenerative feedwater heating system, of the present disclosure, will now be described with the help of the accompanying drawing in which: FIGURE 1 illustrates a partial view of a regenerative feedwater heating system implementing a conventional regenerative feed heating power cycle in power plants.

FIGURE 2 illustrates a regenerative feedwater heating system implementing a regenerative feed heating power cycle with a heat transformer.

FIGURE 3 illustrates a regenerative feed heating system in accordance with an embodiment of the present disclosure.

The present disclosure will now be described with reference to the following non-limiting embodiments.

LIST OF REFERENCE NUMERAL

100 - Conventional regenerative feedwater heating system 102 - Steam turbine

104 - Exhaust steam duct

106 - Condenser

108 - Condensate storage tank

110 - Condensate extraction pump 112, 114 - Conduit

116 - LP heater 118 - Deaerator 120, 122 - Conduit 124, 126 - Conduit

200, 300 - Regenerative feedwater heating system 202 - VAM condenser/ First VAM condenser 204 - VAN absorber/ First VAM absorber 206, 212 - Conduit 208 - Second VAM condenser 210 - Second VAM absorber 214 - High pressure heater DETAILED DESCRIPTION

Figure 1 illustrates a partial view of a conventional regenerative feedwater heating system 100 (hereinafter referred as "conventional system 100")· The conventional system 100 includes a steam turbine 102, a condenser 106, a condensate extraction pump, a low pressure heater 116 (hereinafter referred as "LP heater"), and a de-aerator 118. The steam turbine 102 is configured to generate steam of low pressure and low temperature. The condenser 106 is in fluid communication with the steam turbine 102 via an exhaust steam duct 104, and is configured to receive the steam from the steam turbine 102. The condenser is further configured to generate a condensate. In an embodiment, the condensate corresponds to saturation temperature of 40-60°C depending upon ambient conditions and the type of media used for condensation. The condensed fluid (feed water) is routed and collected in a condensate storage tank 108. In an embodiment, the condensate is a condensed fluid. Further, a condensate extraction pump 110 pumps the feed water from the condensate storage tank 108 to the de-aerator 118 via the LP heater 116. A conduit 112 connects the condensate extraction pump to the LP heater 116 and a conduit 120 connects the de-aerator 118 to the LP heater 116. The LP heater 116 increases the temperature of the feed water by indirect heating and condensing the steam extracted from the steam turbine 102. The steam from the steam turbine 102 is fed to the LP heater 116 via a conduit 122. Further, a conduit 114 provides fluid communication between a drain (not exclusively labelled in the figures) of the LP heater 116 and the condensate storage tank 108 thereby adding the condensed fluid generated from the LP heater 116 with the feed water contained in the condensate storage tank 108. In addition, in the de-aerator 118, the steam transferred via a conduit 124 is used for direct heating of the feed water apart from removing the dissolved oxygen in the condensate. As the de-aerator 118 is directly heated, the condensate extraction pump 110 pumps the feed water at a tank pressure of the de-aerator 118. Post heating, in the de-aerator 118, the feed water is provided to a boiler feed pump via a conduit 126. The extraction quantity of the steam for the LP heater 116 is governed by the condensing temperature and heat transfer area of the LP heater 116 as the feed water can be heated to a temperature only so much below the condensing temperature of the LP steam extraction as the heat transfer area of the LP heater 116 allows. An increase in the temperature of the feed water above the condensing temperature is thermodynamically not possible by increasing the heat transfer area of the LP heater 116.

In order to overcome the afore-stated drawbacks, the present disclosure envisages a system and method for improving regenerative heating in power.

A preferred embodiment of a system and method for improving regenerative heating in power, of the present disclosure, will now be described in detail with reference to the accompanying drawing. The preferred embodiment does not limit the scope and ambit of the disclosure.

FIGURE 2 illustrates a regenerative feedwater heating system 200 (hereinafter referred as "system 200") implementing a regenerative feed heating power cycle with a heat transformer in accordance with one embodiment of the present disclosure. FIGURE 3 illustrates a regenerative feedwater heating system 300 (hereinafter referred as "system 300") in accordance with a second embodiment of the present disclosure. The system 200, in addition to components of the conventional system 100 as discussed above, in the Figure 1, includes a vapor absorption machine (not exclusively labelled in the figures).

The vapor absorption machine (VAM) can be classified into Type I and Type II heat pump. The type II heat pump can also be called a heat transformer. In the type I heat pump, a low temperature heat source is pumped to a medium temperature sink using a high temperature heat source. Whereas in the heat transformer that is type II, a medium temperature heat source is pumped to a high temperature source with the aid of a low temperature sink. Since the external energy for pumping heat to a higher temperature is given in the form of heat input at medium temperature, by the Kelvin-Plank's statement of the second law of thermodynamics, heat needs to be rejected at a low temperature. The co-efficient of performance of the heat transformer ranges between 0.42-0.5 for a single stage and single lift design. Generally, the heat transformer finds application where medium temperature waste heat that is usually rejected to the environment is recovered to provide high temperature useful output. The requirement of low temperature cooling water and the resulting low coefficient of performance of the heat transformer prevents the use of external energy.

The present disclosure envisages a regenerative feed water heating system 200). The system 200 comprises a steam turbine 102, a condenser 106, a low pressure (LP) heater 116, a deaerator 118, and a vapour absorption machine (VAM). The steam turbine 102 is configured to receive high pressure steam for providing a mechanical drive and provide low pressure expanded steam subsequent to the expansion of the high pressure steam thereon. The condenser 106 is configured to receive a first stream of expanded steam from the steam turbine 102 and facilitate the condensation of the first stream of expanded steam therewithin to provide a condensate (hereinafter also referred as "feed water"). The LP heater 116 is configured to receive the condensate and a second stream of expanded steam from the steam turbine 102. The LP heater 116 has an arrangement that permits thermal communication between the condensate and the second stream of expanded steam. The condensate and the second stream of expanded steam being in thermal communication facilitate heating of the condensate to provide a heated condensate. The deaerator 118 is configured to receive the heated condensate and facilitate removal of dissolved oxygen from the heated condensate. The deaerator is further configured to receive a third stream of expanded steam from the steam turbine 102. The deaerator 118 has a configuration that permits thermal communication between the heated condensate and the third stream of steam, thereby further heating the heated condensate to provide a vaporized condensate.

In accordance with an aspect of the present disclosure, the vapor absorption heat transformer or simply a heat transformer is used to pump heat to a higher temperature to improve the regenerative feed heating of a feed water inlet to a boiler. Typically, the boiler is used in power plants for generating steam. In particular, using the regenerative feed heating scheme as described herein below, a feed water temperature is raised above a saturation temperature of extracted steam from the steam turbine 102, or in other words, above the temperature of a heat source used for feed heating, which entails the heat transformer to provide a system benefit that would improve the regenerative power cycle efficiency. The heat transformer uses the exergy in a medium temperature steam to provide for the work used for pumping heat to high temperatures. The system utilizes the anergy to heat the feed water at low temperature, thus providing an overall system performance co-efficient (CoP) of 1.0.

The vapour absorption machine VAM) of the present invention comprises a VAM condenser 202 and a VAM absorber 204. The VAM condenser 202 is disposed downstream of the condenser 106 and upstream of the LP heater 116. The VAM condenser 202 is configured to facilitate heating of the condensate prior to entering within the LP heater 116. The VAM absorber 204 is disposed downstream of the LP heater 116 and upstream of the deaerated 118. The VAM absorber 204 is configured to facilitate heating of the heated condensate prior to entry within the deaerator 118.

More specifically, the VAM condenser 202 is operatively placed in between the condensate extraction pump 110 and the LP heater 116 that in the flow path of the conduit 112. The VAM absorber 204 is operatively placed in between the LP heater 116 and the de-aerator 118 that is in the flow path of the conduit 120 to increase the feed water temperature prior to heating in the de-aerator 118. The LP steam extraction from the steam turbine 102 is provided in parallel with the LP heater 116, the generator, and the evaporator of the heat transformer. The steam is condensed to provide for the heating and the resulting condensate is routed to the condensate storage tank 108. The low temperature feed water is heated in the VAM condenser 202 of the heat transformer and then provided to the LP heater 116. After being heated by the LP heater 116, the feed water is provided to the VAM absorber 204 where the heat of dilution of the heat transformer is rejected in the VAM absorber 204 to further heat it. The heating provided with the help of low pressure steam in the generator and the evaporator of the heat transformer helps reduce the high pressure steam requirement in the de-aerator 118. The quantum of steam saved in the de-aerator 118 is allowed to expand in the steam turbine 102, thereby generating more mechanical work using the same quantity and enthalpy of inlet steam. Else, to generate the same power, lesser quantity of steam is required. This reduces a turbine heat rate, which in turn translates to substantial savings in terms of fuel quantity. In case of regenerative feed heating using single extraction, the heating provided by the absorber 204 of the heat transformer reduces the energy required in the steam turbine 102.

In accordance with an embodiment of the present disclosure Figure 3 illustrates the use vapour absorption machine (VAM) (also referred as "heat transformer") in multiple locations of the regenerative stages to achieve improved regenerative cycle efficiency. As explained above in Figure 2, the heat transformer reduces the steam required by the de-aerator 118 for feed heating. Similarly, if a second heat transformer is introduced post the de-aerator 118 that can reduce the steam requirement of a corresponding high pressure stage extraction. A regenerative feed water heating system 300 for a boiler comprises a steam turbine 102, a condenser 106, a low pressure (LP) heater 116, a deaerator 118, a high pressure (HP) heater 214, a first vapour absorption machine (VAM I), and a second vapour absorption machine (VAM II). In an embodiment, the first vapour absorption machine (VAM I) is a low temperature heat transformer. In another embodiment, the second vapour absorption machine (VAM II) is a high pressure heat transformer.

The first vapour absorption machine comprises a first VAM condenser 202 and a first VAM absorber 204. The first VAM condenser 202 is disposed downstream of the condenser 106 and upstream of the LP heater 116. The first VAM condenser 202 is configured to facilitate heating of the condensate prior to entering within the LP heater 116. The first VAM absorber 204 is disposed downstream of the LP heater 116 and upstream of the deaerator 118. The first VAM absorber is configured to facilitate heating of the heated condensate prior to entry within the deaerator 118.

The second vapour absorption machine (VAM II) comprises a second VAM condenser 208 and a second VAM absorber 210. The second VAM condenser 208 is disposed downstream of the first VAM condenser 202 and upstream of the deaerator 118. The second VAM condenser 208 is configured to facilitate further heating of the heated condensate prior to entry within the deaerator 118. The second VAM absorber 210 is disposed downstream of the deaerator 118 and upstream of HP heater 214. The second VAM absorber 210 is configured to facilitate heating of the vaporized condensate prior to entry within said HP heater 214.

The high pressure (HP) heater 214 is configured to receive vaporized condensate from the deaerator 118 and a fourth stream of expanded steam from the steam turbine. The HP heater 214 has a configuration that permits thermal communication between the vaporized condensate and the fourth stream of expanded steam, thereby heating said vaporized condensate to provide heated vaporized condensate.

The first vapour absorption machine (VAM I) requires steam in its generator and evaporator and the same is provided from the low pressure extraction in the conduit 122. Similarly, the second vapour absorption machine (VAM II) requires steam in its generator and evaporator and the same is provided from the de-aerator extraction in the conduit 124. A conduit 212 connects a drain of a high pressure heater 214 (also referred as "HP heater 214") to the deaerator 118. Post heating in the HP heater 214, the steam is fed to the steam generator/turbine 102. In an embodiment, a condensate collection tank 108 is in fluid communication with the condenser 106, and is configured to collect the condensed fluid therewithin.

In another embodiment, the system 200, 300 further includes a condensate extraction pump 110 that is in fluid communication with the condensate collection tank 108. The condensate extraction pump 110 is configured to extract said condensed fluid from the condensate collection tank and pump the condensed fluid downstream.

In an embodiment, the drain of the LP heater is configured to reject condensed fluid formed in said LP heater 116 to the condensate collection tank 108. In another embodiment, a boiler feed pump is disposed downstream of the deaerator 118 and upstream of the HP heater 214, said boiler feed pump is configured to pressurize the vaporized condensate prior to entry within the HP heater 214. The drain of the HP heater 214 is configured to reject condensed fluid formed in the HP heater 214 to the deaerator 118.

The VAM II reduces the heat duty of the high pressure (HP) heater 214, thereby reducing a steam requirement of the HP extraction in a conduit 206. This scheme can be extended to multiple stages of extraction to provide a regenerative feed heating scheme with increased efficiency. The maximum temperature to which the heating can be provided is limited by the working temperatures of the absorbent solution.

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 for improving regenerative heating in power plants that:

- increases the regenerative feed heating of a feed water inlet to a boiler.

- increases the overall performance co-efficient of a thermal power plant.

- efficiently utilizes waste heat in the heating stages. 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 examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of 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 disclosure 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 disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application. While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure 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 disclosure and not as a limitation.