Patent ID: 12203393

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, it should be noted that the present disclosure is not limited thereto, and may include all modifications, equivalents, or substitutions within the spirit and scope of the present disclosure.

Terms used herein are used to merely describe specific embodiments, and are not intended to limit the present disclosure. As used herein, an element expressed as a singular form includes a plurality of elements, unless the context clearly indicates otherwise. Further, it will be understood that the term “comprising” or “including” specifies the presence of stated features, numbers, steps, operations, elements, parts, or combinations thereof, but does not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, parts, or combinations thereof. Hereinafter, a vertical type once-through heat recovery steam generator (HRSG) and a combined power generation system including the same according to embodiments of the present disclosure will be described with reference to the accompanying drawings.

FIG.1is a diagram illustrating a combined power generation system according to an embodiment of the present disclosure.

Referring toFIG.1, the combined power generation system100may include a gas turbine110, a steam turbine120, a generator130, and a heat recovery steam generator (HRSG)1000. The steam turbine120may include a low-pressure steam turbine120a, a medium-pressure steam turbine120b, and a high-pressure steam turbine120c.

The gas turbine110may serve to suck atmospheric air, compress the air to a high-pressure, burn an air-fuel mixture in static pressure conditions to release thermal energy, expand high-temperature combustion gases for conversion into kinetic energy, and then discharge exhaust gases containing the residual energy to the atmosphere.

The gas turbine110may include a compressor111, a combustor112, and a turbine section113. The compressor111of the gas turbine110may suck and compress external air. The compressor111may serve both to supply the compressed air generated by compressor blades to the combustor112and to supply the cooling air to a high temperature region of the gas turbine110. Here, since the sucked air undergoes an adiabatic compression process in the compressor111, the air passing through the compressor111increases in pressure and temperature.

The compressor111is usually designed as a centrifugal compressor or an axial compressor, wherein the centrifugal compressor is applied to a small-scale gas turbine, whereas a multi-stage axial compressor is applied to a large-scale gas turbine.

The combustor112may mix compressed air supplied from an outlet of the compressor111with fuel and combust the air-fuel mixture at a constant pressure to produce high-energy combustion gases.

High temperature, high-pressure combustion gases generated by the combustor112is supplied to the turbine section113. A fuel preheater112areceives fuel from a fuel supply via a fuel supply pipe, heats the fuel, and supplies the heated fuel to the combustor112.

In the turbine section113, the combustion gases undergo adiabatic expansion and impact and drive a plurality of blades arranged radially around a rotary shaft of the turbine section113so that heat energy of the combustion gases is converted into mechanical energy with which the rotary shaft is rotated. A portion of the mechanical energy obtained from the turbine section113is supplied as the energy required to compress the air in the compressor111, and the rest is utilized as an available energy to drive the generator130to produce electric power.

The combustion gases discharged from the turbine section113is cooled through the HRSG1000and then discharged to the outside. The HRSG1000serves to not only cool the combustion gases, but also generate high-temperature and high-pressure steam using the heat of the combustion gases and deliver same to the steam turbine120.

The steam generated in the HRSG1000is transmitted to the steam turbine120through a steam feed line L1, and feedwater cooled in the steam turbine120is transmitted to the HRSG1000through a turbine feedwater recovery line L2.

The steam turbine120rotates blades using the steam generated by the HRSG1000and transmits the rotational energy to the generator130. The steam turbine120supplies the cooled steam back to the HRSG1000.

Although the gas turbine110and the steam turbine120are exemplified inFIG.1as being connected to one generator130, the present disclosure is not limited thereto. Rather, the gas turbine110and the steam turbine120may be disposed in parallel and/or connected to different generators.

The turbine feedwater recovery line L2is connected with a condenser121for condensing steam, a condensate storage tank122for storing condensed feedwater, and a condensate pump123for supplying the condensed feedwater stored in the condensate storage tank122to the HRSG1000.

The steam flowing in the HRSG1000may have at least two or three levels of pressure, and accordingly, the feedwater is pressurized to at least two or three pressure levels. In this embodiment, the HRSG1000is exemplified as having three levels of pressure.

FIG.2is a diagram illustrating a vertical type once-through heat recovery steam generator (HRSG) according to an embodiment of the present disclosure.

Referring toFIG.2, the HRSG1000may include a low-pressure section1100having a relatively low-pressure, a medium-pressure section1200having a medium-pressure, and a high-pressure section1300having a relatively high-pressure.

The high-pressure section1300may be disposed adjacent to an inlet side of the HRSG, through which combustion gases are introduced, and may be heated by high-temperature combustion gases, and the low-pressure section1100may be disposed adjacent to an outlet side of the HRSG, through which the combustion gases are discharged, and may be heated by low-temperature combustion gases. The low-pressure section1100may be disposed vertically upward than the high-pressure section1300.

The low-pressure section1100includes a condensate preheater1110, a low-pressure drum1120, a low-pressure evaporator1130, a low-pressure superheater1140, and a condensate preheater bypass1150.

The condensate stored in the condensate storage tank122is transferred to the condensate preheater1110by a condensate pump123, and the condensate preheater1110heats the condensate through heat exchange with combustion gases. The feedwater heated in the condensate preheater1110is supplied to the low-pressure drum1120.

The low-pressure evaporator1130is connected to the low-pressure drum1120to heat the feedwater stored in the low-pressure drum1120. The steam separated in the low-pressure drum1120is heated in the low-pressure superheater1140, and then supplied to the low-pressure steam turbine120a.

The condensate preheater bypass1150allows a portion of the condensate transferred from the condensate storage tank122bypass the condensate preheater1110and to flow directly to the low-pressure drum1120. The bypassing portion of the condensate may be diverted from a pipe between the condensate pump123and the condensate preheater1110to a pipe between the condensate preheater1110and the low-pressure drum1120. By letting a portion of the condensate bypass the condensate preheater1110, the temperature of gases discharged through the outlet of the HRSG may be raised and thereby can prevent a large amount of white smoke from being produced.

The medium-pressure section1200includes a medium-pressure economizer1210, a medium-pressure drum1220, a medium-pressure evaporator1230, a medium-pressure superheater1240, a first reheater1251, a second reheater1252, a first desuperheater1261, and a second desuperheater1262. The medium-pressure section may further include a low-temperature reheating steam line L6that reheats low-temperature steam discharged from the steam turbine120. The first reheater1251, a second reheater1252, a first desuperheater1261, and a second desuperheater1262of the medium-pressure section1200may be referred to as the first medium-pressure reheater1251, a second medium-pressure reheater1252, a first medium-pressure desuperheater1261, and a second medium-pressure desuperheater1262.

A portion of feedwater heated by the condensate preheater1110, and/or a portion of the condensate that bypassed the condensate preheater1110through the condensate preheater bypass1150is supplied, by and through the medium-pressure pump P1, to the medium-pressure economizer1210. The medium-pressure economizer1210heats the feedwater or condensate supplied from the medium-pressure pump P1(hereinafter collectively referred to as “feedwater”) through heat exchange with combustion gases. The feedwater heated in the medium-pressure economizer1210is supplied to the medium-pressure drum1220. The medium-pressure evaporator1230is connected to the medium-pressure drum1220to heat the feedwater stored in the medium-pressure drum1220. Specifically, the medium-pressure evaporator1230receives the feedwater from the medium-pressure drum1220, heat the feedwater through heat exchange with combustion gases, and returns the heated feedwater to the medium-pressure drum1220. The heated steam is separated from the medium-pressure drum1220and then heated in the medium-pressure superheater1240. Then, the heated steam is supplied to the medium-pressure steam turbine120b. While the heated steam is supplied from the medium-pressure superheater1240to the medium-pressure steam turbine120b, the heated steam may pass through the first reheater1251, the first desuperheater1261, and the second reheater1252, consecutively. The first reheater1251, the first desuperheater1261, and the second reheater1252regulate and adjust the temperature of the steam entering the medium-pressure steam turbine120b. Between the medium-pressure superheater1240and the first reheater1251, reheated steam from the medium-pressure superheater1240may be joined by the low-temperature reheating steam line L6, which reheats the low-temperature steam discharged from the steam turbine120.

During rapid startup, the temperature of the steam entering the medium-pressure steam turbine120bfrom the second reheater1252may rise rapidly, and this rapid rise is one of the factors that reduces the operational stability and the lifetime of the steam turbine during rapid startup. Thus, according to the present disclosure, a second desuperheater1262is additionally installed to reduce and adjust the temperature of the steam entering the medium-pressure steam turbine120bfrom the second reheater1252during rapid startup. The second desuperheater1262is installed between the second reheater1252and the medium-pressure steam turbine120b. According to an embodiment, the second desuperheater1262may not need to operate continuously throughout the entire operation of the HRSG, instead, it may be activated solely during rapid startup, and subsequently turned off after the rapid startup process is completed.

In addition, the feedwater line L3between the medium-pressure drum1220and the medium-pressure superheater1240may be joined by steam heated by an external heater124. The external heater124allows to generate steam through heat exchange of a portion of the feedwater supplied provided from the medium-pressure pump P1using high-temperature compressed air compressed by the compressor111, and the thereby generated steam is supplied to the feedwater line L3. The compressed air heat-exchanged in the external heater124is cooled to low temperature and returned to the gas turbine110to cool at least one of the compressor111and the turbine section113. In this sense, the external heater124may also functions as an external cooler for the gas turbine110.

The high-pressure section1300includes a high-pressure economizer1310, a multi-stage once-through evaporator1330, a high-pressure superheater1340(1341,1342), a first desuperheater1361, and a second desuperheater1362. The first desuperheater1361and the second desuperheater1362of the high-pressure section1300may be referred to as the first high-pressure desuperheater1361, and the second high-pressure desuperheater1362.

A portion of feedwater heated by the condensate preheater1110, and/or a portion of the condensate that bypassed the condensate preheater1110through the condensate preheater bypass1150is supplied, by and through a high-pressure pump P2, to the high-pressure economizer1310, which heats the feedwater through heat exchange with combustion gases. According to an embodiment, the high-pressure economizer1310may be formed in multiple stages to heat the feedwater sequentially.

The feedwater heated by the high-pressure economizer1310is supplied to the multi-stage once-through evaporator1330. The multi-stage once-through evaporator1330includes an inlet part1331into which feedwater flows in, and a heat transfer tube1332having a front end connected to the inlet part and a rear end out of which steam is discharged such that the feedwater from the inlet part1331is evaporated through heat exchange with combustion gases while flowing from the front end to the rear end. The heat transfer tube1332is formed such that an inner diameter of the rear end is larger than that of the front end. According to an embodiment, the heat transfer tube1332may be formed such that the inner diameter gradually increases from the front end toward the rear end. Such a multi-stage once-through evaporator1330may prevent static instability or Ledinegg instability caused by two-phase flow. The multi-stage once-through evaporator1330will described below furthermore in detail with reference toFIGS.4through6.

Steam heated by the multi-stage once-through evaporator1330is supplied to the high-pressure steam turbine120cthrough the first high-pressure superheater1341, the first desuperheater1361, and the second high-pressure superheater1342, consecutively. The first high-pressure superheater1341, the first desuperheater1361, and the second high-pressure superheater1342regulate and adjust the temperature of the steam entering the high-pressure steam turbine120c.

During rapid startup, the temperature of the steam entering the high-pressure steam turbine120cfrom the second high-pressure superheater1342may rise rapidly, and this rapid rise is one of the factors that reduces operational stability and power generation efficiency during rapid startup. Therefore, according to the present disclosure, a second desuperheater1362may be additionally installed to reduce the temperature of the steam entering the high-pressure steam turbine120cduring rapid startup. The second desuperheater1362is installed between the second high-pressure superheater1342and the high-pressure steam turbine120c. According to an embodiment, the second desuperheater1362may not need to operate continuously throughout the entire operation of the HRSG, instead, it may be activated solely during rapid startup, and subsequently turned off after the rapid startup process is completed.

During the rapid startup process, the multi-stage once-through evaporator1330may not convert all of the incoming feedwater to steam immediately. Instead, at the beginning of the rapid startup, only a portion of the feedwater may be converted to steam, while the remaining portion may still exist in a liquid form. Therefore, a steam separator1370may be installed at the rear end of the multi-stage once-through evaporator1330and before the first high-pressure superheater1341for steam-water separation at the beginning of the rapid startup.

That is, during a predetermined period of time at the beginning of the rapid startup, the feedwater that has flowed through the multi-stage once-through evaporator1330may flow through the steam separator1370and, after that, into the first high-pressure superheater1341. After a predetermined period of time when the startup process is completed, only steam is supplied to the steam separator1370, so the steam separator1370may function only as a connection channel between the multi-stage once-through evaporator1330and the first high-pressure superheater1341.

A portion of the feedwater heated in the high-pressure economizer1310may be supplied to the fuel preheater112aof the combustor112via the fuel preheating feedwater line LA. The high-temperature feedwater supplied to the fuel preheater112amay be converted to cold feedwater after heating fuel through a heat exchange process, and returned to the condensate preheater1110through a return line L5.

The second desuperheater1262of the medium-pressure section1200and the second desuperheater1362of the high-pressure section1300serve to prevent a rapid temperature increase during rapid startup. This not only enhances operational reliability but also help protect the lifetime of the steam turbine from being reduced.

Next, a vertical type once-through heat recovery steam generator (HRSG) according to another embodiment of the present disclosure will be described with reference toFIG.3.FIG.3is a diagram illustrating the HRSG according to the embodiment of the present disclosure.

In the embodiment according toFIG.2, the feedwater supplied to the medium-pressure economizer1210and the feedwater supplied to the high-pressure economizer1310are illustrated as being supplied from the front end of the low-pressure drum1120(in other words, from condensate preheater1110without the feedwater being entering the lower-pressure drum1120) by and through the medium-pressure pump P1or high-pressure pump P2, respectively.

However, alternatively, according to an embodiment as illustrated inFIG.3, the feedwater supplied to the medium-pressure economizer1210and the feedwater supplied to the high-pressure economizer1310may be supplied from the rear end of the low-pressure drum1120(in other words, after the feedwater passing through the low-pressure drum1120) to the medium-pressure economizer1210or the high-pressure economizer1310, respectively and through by the medium-pressure pump P1or high-pressure pump P2.

Next, a multi-stage perfusion-type evaporator1330will be described more in detail with reference toFIGS.4through6.

FIG.4is a diagram illustrating a multi-stage once-through evaporator according to an embodiment of the present disclosure,FIG.5is an enlarged cross-sectional view of the multi-stage once-through evaporator ofFIG.4, andFIG.6is a diagram illustrating a variant of the multi-stage once-through evaporator.

Referring toFIGS.4and5, the multi-stage once-through evaporator1330includes an inlet part1331and a heat transfer tube1332, wherein the inlet part1331includes a small-diameter tube portion1331a.

The inlet part1331is in a form of a tube through which feedwater is introduced from the high-pressure economizer1310. An inlet header1330amay be disposed at the inlet part1331, which has an inner diameter (D-in). The small-diameter tube portion1331amay be a slender tube, an inner diameter of which may be the same with the inner diameter (D-in) of the inlet part. As the small-diameter tube portion1331ais disposed, the pressure characteristic curve of the multi-stage once-through evaporator1330may change, which may improve flow instability within the multi-stage once-through evaporator1330.

The heat transfer tube1332is a tube having a front end connected to the rear end of the inlet part1331and a rear end out of which steam is discharged. An outlet header1330bmay be disposed at the rear end of the heat transfer tube1332. The front end of the heating tube1332is supplied with feedwater from the inlet part1331, and the feedwater is evaporated by heat exchange with a flow of combustion gases stream MF while flowing to the rear end of the heat transfer tube1332and then discharged. The heat transfer tube1332may be formed such that the inner diameter of the rear end is larger than that of the front end.

Further, the inlet-side inner diameter D-in, which is the inner diameter of the small-diameter tube portion1331a, may be configured to be smaller than the inner diameter of the heat transfer tube1332. In other words, in the multi-stage once-through evaporator1330, the inlet-side inner diameter D-in of the small-diameter tube portion1331aof the inlet part1331may be smaller than the inner diameter of the front end of the heat transfer tube1332, which in turn may be smaller than the inner diameter of the rear end of the heat transfer tube1332.

The heat transfer tube1332may include a plurality of heat transfer parts having different inner diameters, each of which may be formed to increase stepwise from the front end of the heat transfer tube1332to the rear end of the heat transfer tube1332. The heat transfer tube1332may include a first heat transfer tube part1332aand a second heat transfer tube part1332b.

The first heat transfer tube part1332ais a heat transfer tube that has a first inner diameter D1and whose front end is connected to the rear end of the inlet part1331. The first inner diameter D1is formed to be larger than the inlet-side inner diameter D-in. The second heat transfer tube part1332bis a heat transfer tube that has a second inner diameter D2and whose front end is connected to the rear end of the first heat transfer tuber part1332a. The second inner diameter D2is formed to be larger than the first inner diameter D1. That is, the inner diameter of the multi-stage once-through evaporator1330may progressively increase in sequential steps from the inlet part1331to the first heat transfer tube part1332a, and further to the second heat transfer tube part1332b.

A tapered part1333may be disposed between the small-diameter tube portion1331aand the first heat transfer tube part1332a, and between the first heat transfer tube part1332aand the second heat transfer tube part1332b. Specifically, a first tapered part1333amay be disposed between the small-diameter tube portion1331aand the first heat transfer tube part1332a, and a second tapered part1333bmay be disposed between the first heat transfer tube part1332aand the second heat transfer tube part1332b. The tapered part1333has an inner diameter that increases gradually and gently toward a rear end thereof. The inclusion of the tapered part1333helps prevent a sudden and discontinuous increase in the inner diameter, which in turn prevents flow delamination and improve flow stability within the multi-stage once-through evaporator1330. Furthermore, the tapered part1333may be formed in the form of a straight line or a rounded curve when viewed in its cross-section.

Further, according to an embodiment as illustrated inFIG.6, the heat transfer tube1332may further include a third heat transfer tube part1332c. The third heat transfer tube part1332cis a heat transfer tube having a front end connected to a rear end of the second heat transfer tube part1332band whose inner diameter is a third inner diameter D3. The third inner diameter D3is formed to be larger than the second inner diameter D2. In this case, the inner diameter of the multi-stage once-through evaporator1330may progressively increase in sequential steps from the inlet part1331to the first heat transfer tube part1332aand the second heat transfer tube part133band further to the third heat transfer tube part1332c. In addition to the two or three heat transfer tube parts described earlier, the heat transfer tube1332may include four or more heat transfer tube parts, each having a sequentially increasing inner diameter toward the rear end thereof. In other words, a heat transfer tube part disposed more rearward has a diameter larger than the one disposed more forward.

The flow stability of the multi-stage once-through evaporator1330will now be described in detail with reference toFIG.7.

There may occur a pressure difference between the flow at the front end and the flow at the rear end of the multi-stage once-through evaporator1330. This is referred to as a ‘system pressure drop’ or ‘internal pressure drop’. The system pressure drop varies with a mass flow rate (i.e., a mass velocity-W). However, since water evaporates inside the multi-stage once-through evaporator1330, a two-phase flow phenomenon may occur where water and steam flow together. The change in pressure drop of steam, which is a gas phase, is greater than the change in pressure drop of water, which is a liquid phase.

As a result, the system pressure drop curve is formed to have a ridge and a valley where the slope varies from positive to negative value and then to a positive value (see the thin solid line inFIG.7) as the mass flow rate increases.

Meanwhile, a flow rate in the multi-stage once-through evaporator1330is determined by a pressure drop curve of the evaporator outer head. Here, the outer head is the head that provides a flow driving force, which may be determined by a height difference between the inlet header1330aand the outlet header1330b, or by a circulation pump or the like (see dashed line A inFIG.7). More specifically, a flow rate in the multi-stage once-through evaporator1330is determined at the intersection between the system pressure drop curve and the pressure drop curve of the outer head.

In the two-phase flow condition, there may be three intersections such as 1, 2, and 3, as illustrated inFIG.7. In this case, a flow rate in the multi-stage once-through evaporator1330may be determined at any of the intersections 1 to 3. If a plurality of multi-stage once-through evaporators1330are arranged in parallel, a flow rate in the multi-stage once-through evaporators1330may be arbitrarily determined at any one of the intersection points of 1 to 3, rather than determined at a specified one intersection.

Accordingly, a mass flow rate different from an initially designed flow rate (intersection 1) may flow in the multi-stage once-through evaporator1330. This flow instability is referred to as static instability (or Ledinegg instability). If a flow rate is less than an initially designed flow rate, a problem may arise in that steam may overheat excessively at the rear end of the multi-stage once-through evaporator1330.

The multi-stage once-through evaporator1330according to the embodiments of the present disclosure may have a more gentle system pressure drop curve because the heat transfer tube1332is formed such that the inner diameter of the rear end is larger than that of the front end (see the bold solid line inFIG.7). In this case, only one intersection (intersection 1) is formed between the system pressure drop curve and the pressure drop curve of the outer head, which may prevent static instability. Furthermore, as the inlet part1331includes the small-diameter tube portion1331a, the system pressure drop curve is formed more gently so that the static instability phenomenon can be more reliably prevented.

While the embodiments of the present disclosure have been described, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure through addition, change, omission, or substitution of components without departing from the spirit of the disclosure as set forth in the appended claims, and such modifications and changes may also be included within the scope of the present disclosure. Also, it is noted that any one feature of an embodiment of the present disclosure described in the specification may be applied to another embodiment of the present disclosure.