Title of Invention

A WATER PRE-HEATER DEVICE IN A HEAT RECOVERY SYSTEM GENERATOR SYSTEM FOR ENHANCING THE PERFORMANCE OF HRSG

Abstract

There is provided a water pre-heater device for reducing the exist gas temperature in a heat recovery gas generator (HRGS) 19, having super heater (12), evaporator (13), an economizer (14), and condense water pre-heater (15) connected to a gas turbine (10) through an exhaust duct (11) through which combustion gas flows and gets entry to a HRSG (19) system for heat recovery and combustion gas passes through the stack (20), the device comprising ; plurality of coated tubes (22) connected between headers (21), the inlet pipe supplying cold water to the pre-heater and outlet pipe (23) supplying hot water using the exhaust gases, wherein the plurality of tubes (22) and headers (21) are coated with coated materials.

Full Text

FIELD OF INVENTION The present invention generally relates to a co generation or a combined cycle power plant. In particular the invention relates to a Heat recovery steam generator (HRSG) system in a combined cycle/ cogeneration plant, adaptable to downstream of Gas Turbine, which employs a condensate/ makeup water heater which are being placed as a last stage heat transfer section of the heat recovery.. steam generator system. The provision of the condensate pre-heater or makeup water heater increases the overall heat recovery from the HRSG. The present invention further relates to a method of enhancing the performance of the condensate pre heater or makeup water heater by cooling the exhaust gases below the dew point. More particularly, the present invention relates to a water pre-heater device in a heat recovery steam generator system for enhancing the performance of HRSG. BACKGROUND OF THE INVENTION It is known that combined or cogeneration power plants which convert fossil fuel energy into electrical energy is efficient in comparison to coal fired power plants and they are relatively easy and inexpensive to construct. In a typical combined cycle /cogeneration plant gaseous /liquid fuels are fired in gas turbine and HRSG. The exhaust gases leave the gas turbine at about 600 degree and contain a significant source of energy. To recover this energy, the typical combined cycle or cogeneration plant has a heat recovery steam generator through which the hot exhaust gases is caused pass to produce steam for the process or for use in steam turbine. The exhaust gases leave the HRSG between 100 to 200 degree. The steam generated in the HRSG passes through the steam turbine and then into a condenser where it is converted into liquid water at a relatively low temperatures of around 30 to 50 degc. This low temperature water enters the water pre heater of HRSG where it gets heated to a near-feed-water temperature. To enhance the performance of HRSGs, water pre heaters are generally installed as the last stage heat recovery section in the Heat Recovery Steam Generators. These water pre heaters generally operate at low metal temperatures, thereby increasing their susceptibility to corrosion by acid gases .In order to deter the formation of sulfuric acid, these water heaters are designed to recover limited quantity of heat energy in the exhaust of the gas turbine and the water enters the water heaters at a temperature higher than acid dew point temperatures. Hence the extent of heat recovery is dictated by the amount of sulphur present in the fuels being fired in the Gas turbines and in the supplementary firing system of the HRSGs. Whenever any of the fossil fuels containing sulfur are fired in Gas turbine or in the supplementary firing system of the Heat Recovery Steam Generator, sulfur dioxide, and to a small extent sulfur trioxide, are formed in addition to C02 and water vapour. The S03 combines with water vapor in the flue gas of the gas turbine exhaust to form sulfuric acid and condenses on the last stage heat transfer sections, which are at or below the dew point of the acid gas. This could lead to corrosion and destruction of the last stage heat recovery surfaces or water heaters, which are made up of metallic surfaces. However with the reduction in exit gas temperature the thermal efficiency of the equipment is increased. The prior art concept of protecting the water heater or back end heat transfer surfaces from dew point corrosion is by maintaining a higher cold end temperature by adopting a recirculation system as depicted in Fig 1. In this configuration a recirculation pump draws off some of the outlet heated water from water heater outlet and mixed with the inlet colder condensate or makeup water. The temperature of the mixed water entering the water heater is elevated to a level higher than the dew point temperature to avoid corrosion of the cold end surfaces. US 6508206 Bl dated January 21, 2003 (Fig2) discloses a system for maintaining a higher water inlet temperature entering the cold end sections by initially heating the cold water in an external water heat exchanger (1), and using an outlet(4), the heated water from one of the parallel sections(3) located inside the HRSG, the cooled water is then fed to an inlet(5) of a second parallel heat transfer section(6) located inside the HRSG for further heating, thus maintaining wall temperatures higher than dew point temperatures as depicted in Fig 2.In this arrangement the water heater has two sections(3&6) which are located in parallel in so far as the flow of exhaust gases is concerned. As far as the water flow is concerned the preheated water flow is in series which enters at a bottom (2) of the first parallel section gets heated by the flue gases, then enters the external heat exchanger where it gets cooled to the original entry temperature of the first section,thereafter enters a bottom(5) of the second parallel section located inside the HRSG and gets heated by the flue gases to the final required temperature at the outlet(7). The major disadvantages of the prior art is that the heat recovery potential is limited by the amount of sulphur content in the fuel being fired in GT or HRSG. Another disadvantage of the prior art is that the reduction in exit gas temperature is not possible beyond a limit, which limits the thermal efficiency of the equipment. Further there is a possibility of production of sulphuric acid as a by-product by condensation of acid gases. OBJECTS OF THE INVENTION It is therefore an object of the present invention to propose a water preheater device to reduce the exit gas temperature in HRSG, which eliminates the disadvantages of prior art. Another object of the present invention is to propose a'water pre heater device in HRSG for increasing the efficiency of the HRSG, which is compact and easy to operate. A still another object of the present invention is to propose a water pre heater device in HRSG; which facilitates condensing the acid gases in HRSG. A further object of the present invention is to propose a /'water heater device in HRSG, which is environment friendly and does not allow exit of pollutant gases to the atmosphere. A still further object of the present invention is to propose a water pre heater device in HRSG, which enables production of sulphuric acid as a by-product. Yet another object of the present invention is to propose a water pre heater device in HRSG, which enables protection of the last-stage heat transfer surfaces from cold back end corrosion. SUMMARY OF THE INVENTION Accordingly, there is provided a water pre heater device for reducing the exit gas temperature in a heat recovery steam generator (HRSG) system, the HRSG being fiowably connected to a gas turbine via a transition duct acting as a passage for exhaust gas from the gas turbine, the HRSG comprising: a super heater formed of a plurality of tubes; an evaporator consisting of a plurality of configured tubes; an economizer adjacently located to the evaporator; and a water pre heater/makeup water heater adjacently located to the economizer, the exhaust gases from the economizer/condensate pre heater/makeup water heater emitting via a stack, the water pre heater device comprising an inlet water entry line from condenser ; a set of finned or bare tubes coated with corrosion resistant material along with a water outlet line, and disposed as a last stage heat transfer section in the HRSG. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Fig-1 is a schematic presentation of a water pre heater in HRSG as per prior art. Fig-2 is a schematic presentation of a water pre heater in HRSG as per prior art. Fig-3 is a schematic view of a power system that incorporates an HRSG provided with corrosion resistant condensing water heater constructed in accordance with the present invention. Fig-4 is a schematic view of the water pre heater of HRSG of the present invention. DETAILED DESCRIPTION OF A PREFERRRED EMBODIMANT OF THE INVENTION Figure 3 shows a Gas turbine (10) discharging exhausting gases at a high temperature of around 600 degc through an inlet transition duct (11) of the complete Heat recovery steam generator (19). The system comprises a Gas Turbine (10) connected by a inlet transition duct (11) to a heat recovery steam generator (19). The HRSG (19) has a plurality of devices arranged in the following order namely a super heater (12), an evaporator (13), an economizer (14) and a condensate water pre heater (15). The exhaust gases leave the economizer/condensate water pre heater of HRSG (19) through and then via a stack (20). The steam from the superheater (12) is delivered to a steam turbine (18) or to process headers for electric power generation or process use. The steam turbine (18) discharges steam at a low temperature/pressure into a condenser (17) where it gets condensed into condensate. The condenser (17) is connected to a condensate pump (16), which delivers the water into the water pre heater (15) of the HRSG (19) This is heated by the exhausted gases and delivers the preheated water to a deaerator (not shown) or to the required system. According to the present invention, as shown in Figure 3, exhaust gases from the Gas turbine entering the HRSG (19) at a higher temperature before the last stage heat recovery section namely corrosion resistant coated water pre heater device (15) and the condensate entering into the water pre heater (15) from the condensate /makeup water pump (16) at a lower temperature in the range of 30 to 60 degc which results in the metal temperatures falling below the acid dew point of the gases and reduces the gas temperature leaving the HRSG (19) . The finned or bare tubes^of the water pre heater and headers are coated with any of the corrosion resistant polymer or metal or refractory based materiaIsTiased on the. ~~ "~~ ---------"--^'-^—--—_-— level of concentration of the sulphuric acid formation for protecting the HRSG (15). The coated water pre heater (15) of the HRSG (19) reduces the gas temperature leaving the HRSG which increases the efficiency of the overall system, reduces the atmospheric pollution and further facilitates generation of sulphuric acid as a by product. Referring to figure 4, in another aspect of the present invention, the thickness of the protective coating of the tubes (22) aad_hejdersT(21) of the water pre heater can be varied for obtaining the required conductivity as well as corrosion protection. According to the present invention, the method of coating on the water pre heater finned/bare tubes (22) and headers (21) can be any one of the types of spraying or painting or dip processing based on the coating material and functional performance requirements. Another advantage of the present invention with the application of a refractory based protective coating, is that the outside surface metal temperature of the finned tubes (22) of the water pre heater (15) can be increased which comparatively reduces the condensation of acid gases on the water heater with marginal reduction in efficiency as compared to Metal or polymer based coating materials. A further advantage of the present invention with the corrosion resistant precoated tubes (22) and headers (21) of the water pre heater is that it allows condensation of acid gases into sulphuric acid as a by product. A still further advantage of the present invention with the corrosion resistant precoated tubes (22) and headers (21) of the water pre heater is that, the coating can be on either bare or finned tubes. The coating is applied with required finish, which eliminates sticking of the soot on the tubes (22) and headers (21) of the waterpreheater (15). A still another advantage of the present invention with the corrosion resistant precoated water pre heaters (15), is that the Tubes and headers (22&21) eliminate the use of recirculation pump of Fig 1 of the prior art. Yet another advantage of the present invention with the coated water pre heater (15), is that the, tubes and headers (22&21) eliminates the use of external water-to-water heat exchanger of Fig 2 of the prior art. The water pre heater (15) device consisting of tubes and headers (22,21) are coated with any of the corrosion resistant polymer or metal or refractory based materials based on the level of concentration of the sulphuric acid formation. Yet further advantage of the present invention with the coated water pre heater (15),is that the performance of the coating can be varied by selecting coating material with good permeance property. Permeance determines the rate and the extent to which a particular coating will be penetrated by the exposure medium. Materials with lowest permeance will offer the best corrosion protection. Thus, the invention provides a device, which facilitates achieving higher efficiency of power plant and reduces the life cycle cost of the plant. WE CLAIM 1. A water pre-heater (15) device in a HRSG system, the system (19) having a super heater (12), an evaporator (13), an economizer (14) and at least one condensate water pre-heater (15) connected to a gas turbine (10) through an exhaust gas duct (11) through which combustion gas flows and gets entry to at least one HRSG (19) for heat recovery, and combustion gas further passing through a stack (20), the device comprising; - a plurality of tubes (22) connected between a plurality of headers (21), an inlet pipe (20) supplying cold water to the pre-heater and an outlet pipe (23) supplying hot water using the exhaust gases, wherein the plurality of tubes (22) and the headers (21) are coated with coating materials that facilitates formation of H2S04 in the exhaust gases at low temperature as well as increases the efficiency of equipment by enhancing increased heat recovery. 2. The device as claimed in claim 1, wherein the coating material comprises corrosion resistant polymer or metal or refractory based material selected according to the concentration level of sulphuric acid formation. 3. The device as claimed in claim 1 wherein the tubes (22) can be either bare or finned tubes. 4. The device (15) as claimed in claim 1, wherein the thickness of the protective coating of the water pre-heater tubes (22) and header (21) is variable. 5. The device (15) as claimed in claim 1 or 4, wherein the coating on the water pre-heater finned/ bare tubes (22) and headers (21) is achieved by any one of the process like spraying or painting or dip processing based on the coating material and functional performance requirements. ABSTRACT A water pre-heater device in a heat recovery steam generator system for enhancing the performance of HRSG There is provided a water pre-heater device for reducing the exist gas temperature in a heat recovery gas generator (HRGS) 19, having super heater (12), evaporator (13), an economizer (14), and condense water pre-heater (15) connected to a gas turbine (10) through an exhaust duct (11) through which combustion gas flows and gets entry to a HRSG (19) system for heat recovery and combustion gas passes through the stack (20), the device comprising ; plurality of coated tubes (22) connected between headers (21), the inlet pipe supplying cold water to the pre-heater and outlet pipe (23) supplying hot water using the exhaust gases, wherein the plurality of tubes (22) and headers (21) are coated with coated materials.

Documents:

01640-kol-2007-abstract.pdf

01640-kol-2007-claims.pdf

01640-kol-2007-correspondence others.pdf

01640-kol-2007-description complete.pdf

01640-kol-2007-form 1.pdf

01640-kol-2007-form 2.pdf

01640-kol-2007-form 3.pdf

01640-kol-2007-gpa.pdf

1640-KOL-2007-(10-07-2014)-ABSTRACT.pdf

1640-KOL-2007-(10-07-2014)-AMENDED ABSTRACT.pdf

1640-KOL-2007-(10-07-2014)-AMENDED CLAIMS.pdf

1640-KOL-2007-(10-07-2014)-CLAIMS.pdf

1640-KOL-2007-(10-07-2014)-CORRESPONDENCE.pdf

1640-KOL-2007-(10-07-2014)-OTHERS.pdf

1640-KOL-2007-(10-07-2014)-REPLY TO EXAMINATION REPORT.pdf

1640-KOL-2007-(23-08-2013)-ABSTRACT.pdf

1640-KOL-2007-(23-08-2013)-CLAIMS.pdf

1640-KOL-2007-(23-08-2013)-CORRESPONDENCE.pdf

1640-KOL-2007-(23-08-2013)-DESCRIPTION (COMPLETE).pdf

1640-KOL-2007-(23-08-2013)-DRAWINGS.pdf

1640-KOL-2007-(23-08-2013)-FORM-1.pdf

1640-KOL-2007-(23-08-2013)-FORM-2.pdf

1640-KOL-2007-(23-08-2013)-OTHERS.pdf

1640-KOL-2007-CANCELLED PAGES.pdf

1640-KOL-2007-CORRESPONDENCE 1.1.pdf

1640-KOL-2007-CORRESPONDENCE.pdf

1640-KOL-2007-EXAMINATION REPORT.pdf

1640-KOL-2007-FORM 18-1.1.pdf

1640-kol-2007-form 18.pdf

1640-KOL-2007-GPA.pdf

1640-KOL-2007-GRANTED-ABSTRACT.pdf

1640-KOL-2007-GRANTED-CLAIMS.pdf

1640-KOL-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

1640-KOL-2007-GRANTED-DRAWINGS.pdf

1640-KOL-2007-GRANTED-FORM 1.pdf

1640-KOL-2007-GRANTED-FORM 2.pdf

1640-KOL-2007-GRANTED-FORM 3.pdf

1640-KOL-2007-GRANTED-SPECIFICATION-COMPLETE.pdf

1640-KOL-2007-REPLY TO EXAMINATION REPORT.pdf

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