ES2336455T3 - STEAM REGENERATOR WITH HEAT RECOVERY. - Google Patents

Abstract

A heat recovery steam generator (10, 110, 210) comprises a heat exchange unit (12) in which, in normal operative conditions, is defined a hot portion (16), with high metal temperatures and high temperatures of the water/steam mixture enclosed there, and a relatively cool portion (18, 20), with lower metal temperatures and lower temperatures of the water/steam mixture enclosed there, with respect to those of said hot portion (16); substantially shutter-shaped means (32, 132, 232) are interposed between said hot portion (16) and said relatively cool portion (18, 20) in order to thermally insulate said hot portion (16) from said relatively cool portion (18, 20), said substantially shutter-shaped means (32, 132, 232) being at least partially removable in order to put said hot portion (16) and said relatively cool portion (18, 20) again in fluid communication with each other.

Description

Steam generator with recovery hot.

Scope

The present invention, in its most aspect In general, it refers to a steam generator with recovery of heat (also indicated by the acronym RSG, Recovery Steam Generator (Recovery steam generator), or HRSG, Heat Recovery Steam Generator heat) or HRB, Heat Recovery Boiler heat) comprising a heat exchange unit in fluid communication with at least one separation chamber of water-steam and is directed in particular although not exclusively for use in thermoelectric plants of the type called combined gas / steam cycle.

In the rest of the description it will be done reference, only as a non-limiting example, to the technological field concerning the combined cycle thermoelectric plants of gas / steam, that is, plants where two cycles are planned technological, one carried out by air and fuel (cycle gas or Joule) and the other one carried out by water and steam (steam or Rankine cycle), both aimed at producing energy electrical with high performance (normally greater than 55%) and / or electrical energy and thermal energy that can be directed to users such as, for example, remote heating networks, desalination plants and steam distribution networks for industrial processes.

Prior art

It is known that the gas cycle of a plant combined cycle thermoelectric of the type considered essentially  it comprises a compressor, a combustion chamber, a turbine of gas and an alternator. The compressor takes air from the atmosphere bringing it to a predetermined high pressure; the air so compressed it is injected into the combustion chamber together with a fuel, which It usually consists of natural gas; the mixture that forms is ignites and causes high and high pressure gases to expand temperature produced in the gas turbine that moves the alternator, which generates electrical energy.

The steam cycle of the thermoelectric plant mentioned above, on the other hand, comprises a generator of steam, a steam turbine and an additional alternator. The unit of heat exchange of said steam generator, comprising generally heat exchangers of the type with water pipes, it is placed in a heat exchange relationship by discharging the hot gases through the gas turbine of the gas cycle mentioned above, with the consequent great and fast water heating and steam generation. Steam like this produced is sent to the steam turbine that makes the alternator respective function to generate electric power.

A steam generator used in the manner mentioned previously called steam generator with recovery of heat precisely because to generate steam you "take advantage" of the heat of hot gases (at approximately 600 ° C) discharged by the gas turbine.

An HRSG is known from the prior art of US-A-5189988. A boiler known to produce steam is disclosed in the document CH-A-174774.

In modern combined cycles the steam is preferably produces at different pressure levels in order of being able to optimize energy recovery.

In particular, the plant configuration more used for high power realizations provides three levels pressure (high, medium and low) plus additional superheating of the medium pressure steam returning from the steam turbine, is say, of what is called superheated steam further.

As is known, the steam generator with recovery, for each level of pressure, deals with three well-defined heat exchange operations:

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liquid water preheating from a feed pump or an extraction pump of condensate, carried out in a section of the unit heat exchange known as economizer or preheater;

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water evaporation for generation of saturated steam, carried out in a section of the unit heat exchange known as evaporator;

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steam superheat, led to out in a section of the known heat exchange unit As superheater.

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The tube bundles that deal with the three Different operations are structurally independent.

In the presence of several levels of pressure, the steam generator with recovery has several stages of evaporation (two or three), at different pressures and as consequence at different saturation temperatures.

Therefore, there is a high steam production pressure (and therefore at high temperature, which can develop a lot of energy in its subsequent expansion in the steam turbine) in which gas turbine gases are hotter, followed of steam production at lower pressures in which the gases They cool progressively.

From the aforementioned, therefore distinguishes, inside the generator heat exchange unit  of steam, different sections or parts at a temperature progressively decreasing In particular, in the unit of heat exchange, under normal operating conditions, always a hot part can be defined, with high metal temperatures and high temperatures of the water / steam mixture contained in the same, and a relatively cold part, with metal temperatures lower and lower temperatures of the water / steam mixture contained therein, with respect to those of said party hot.

To be precise, in this application for patent, it is intended that the phrase "metal temperatures" indicate the average temperature of the metal with which they are made the components of the heat exchange unit itself, in particular, the average temperature of the tubes through which pass the water / steam mixture.

The steam generator with recovery described previously has recognized drawbacks, which include that of require relatively long periods of time to take it to normal operating conditions of pressure and temperature. A inconvenience of this kind is particularly serious considering the present need to have a great flexibility of operation of the thermoelectric plant.

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Summary of the invention

The technical problem that underlies this invention is to conceive and provide a steam generator with recovery of the type considered, which can overcome, so simple and economical, limitations and / or inconveniences mentioned in reference to the known technique; in particular reduce the reset time of the steam generator after a stop, that is, the possibility of carrying out stops and frequent starts of the plant considered, restarting at intervals as small as possible while respecting the permissible thermal gradients for the major components thickness.

This problem is resolved, according to the present invention, by means of a steam generator with recovery of heat, which comprises a heat exchange unit in which, Under normal operating conditions, a hot part is defined, with high metal temperatures and high temperatures of the mixture of water / steam contained therein, and a relatively cold part, with lower metal temperatures and lower temperatures of the water / steam mixture contained therein, with respect to those of said hot part, wherein means substantially in the form of shutter are interposed between said hot part and said relatively cold part in order to thermally insulate said hot part of said relatively cold part, being able to at least partially removing said means substantially in shutter form in order to put said hot part and said relatively cool part again in fluid communication between yes, and said shutter-shaped means comprise a shutter roller or folding.

Other features and advantages of steam generator according to the present invention will be the result of the following description of a preferred embodiment by way of example of this, provided for indicative purposes and not limiting in reference to the attached drawings.

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Brief description of the drawings

Figure 1 schematically represents a side elevation view of a steam generator with recovery according to the present invention.

Figure 2 schematically represents a side elevation view of a second embodiment of a generator of steam with recovery according to the invention.

Figure 3 schematically represents a side elevation view of a third embodiment of a generator of steam with recovery according to the invention.

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Detailed description of a preferred embodiment

Referring to Figure 1, a generator of steam with heat recovery is shown according to the present invention and is indicated globally with 10.

The steam generator 10 with recovery comprises a heat exchange unit 12, comprising a plurality of tube bundles in which, under operating conditions normal, a hot part is defined, with high temperatures of metal and high temperatures of the water / steam mixture contained in the same, and a relatively cold part, with metal temperatures lower and lower temperatures of the water / steam mixture contained therein, with respect to those of said party hot.

The heat exchange unit 12 is in fluid communication with one (or more) separation chambers 14 of water-steam, which are also referred to in the art cylindrical bodies (Figure 1 shows three bodies cylindrical, which work at different pressures).

The heat exchange unit 12 is supported in a flue pipe 13, for example, substantially parallelepipedic, with a face or section 13a in communication of fluids with the exhaust gases of a gas turbine and with a section 13b or opposite side in fluid communication with a chimney duct 13c. The cylindrical bodies 14 are placed above said smoke tube 13.

The heat exchange unit 12 of the Figure 1 comprises a high pressure section 16, which performs said hot part and sections 18 of medium pressure and 20 of low pressure, which perform said relatively cold part. Values of example pressure is 130 bars for the high section pressure, 30 bars for the medium pressure section and 5 bars for The low pressure.

The hot part, at high temperature, comprises a high pressure evaporator and several bundles of tubes additional superheat / superheat and possibly a high pressure economizer.

The relatively cold part, to relatively low temperature, includes the levels of medium and low pressure, the preheater and possibly a part of the economizer high Pressure.

According to the present invention, substantially shutter-shaped means 32 are interposed between said hot part and said relatively cold part in order to thermally insulate said hot part from said relatively cold part. Said means 32 substantially in the form of a plug can be extracted at least partially in order to put said hot part and said relatively cold part back into fluid communication between
yes.

According to a preferred embodiment, such means 32 they comprise a roller shutter 34, with a width substantially equal to the width of the smoke pipe 13.

Preferably, the winding roller 36 corresponding of the roller shutter 34 is arranged in the face, or side, upper, or upper part 13e of the tube 13 of smoke

Shutter 34 can descend, so substantially vertical, to the face, or side, bottom or base 13d of substantially parallel parallelepiped smoke pipe 13, insulating therefore the two said parts of said exchange unit 12 of heat with each other.

Figure 2 shows a second embodiment of a steam generator 110 according to the invention, in which the components similar to those of steam generator 10 are indicated by The same reference number.

In this case, means 132 substantially in shutter form are interposed between said hot part and said relatively cold part in order to thermally insulate said hot part of said relatively cold part. Sayings substantially shutter-shaped means 132 can be removed at less partially in order to put said hot part and said relatively cool part again in fluid communication between yes.

Such means 132 comprise a shutter 134 roller, with a width substantially equal to the width of the tube 13 of smoke

Preferably, the roll roller 136 Corresponding shutter 134 is disposed in the face, or side, bottom, or base 13d of the smoke pipe 13 substantially parallelepipedic.

Shutter 134 may ascend, by means of a actuator 138 provided with cables 140, substantially vertical, to the upper face 13e of the smoke pipe 13 substantially parallelepipedic, thereby isolating said two parts of said heat exchange unit 12.

Figure 3 shows a third embodiment of a steam generator 210 according to the invention, in which the components similar to those of steam generator 110 are indicated by The same reference number.

In this case, means 232 substantially in shutter form are interposed between said hot part and said relatively cold part in order to thermally insulate said hot part of said relatively cold part. Sayings substantially shutter-shaped means 232 may be removed at less partially in order to put said hot part and said relatively cool part again in fluid communication between yes.

Such means 232 comprise a shutter 234 folding, with a width substantially equal to the width of the tube 13 of smoke

A lower end 236 of the shutter 234 folding is limited to the lower face 13d of the smoke pipe 13 substantially parallelepipedic.

The shutter 234 can ascend, by means of a actuator 238 provided with cables 240, substantially vertical, to the upper face 13e of the smoke pipe 13 substantially parallelepipedic, thereby isolating said two parts of said heat exchange unit 12.

The operation of generators 10, 110 and 210 of steam with recovery is detailed below.

Shutters 34, 134 and 234, which can actuated automatically or manually, they isolate these two parts of the heat exchange unit 12 preferably immediately after starting the stop procedure generator and after having stopped the flow of gas from the turbine.

In this way, the internal convection of the generator is limited between the hottest tube beams and the coldest, that is, heat transfer is limited from the hot part to the relatively cold part by convection and irradiation.

As an example, in a three steam generator pressure levels with additional superheating, placed water below a 250 MW gas turbine, at the time of carrying make a stop starting from the nominal load is given approximately the following situation:

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part hot (superheater, additional superheater and evaporator high pressure): approximately 900 t of metal and 30 t of mixture of water / steam at the average temperature of approximately 360-380 ° C.

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part relatively cold: approximately 1,600 t of metal and 180 t of water / steam mixture at the average temperature of approximately 190-200 ° C.

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Therefore it is evident that, for example, in 8 hours of a night stop (in the case of two shifts each day) or within 48 hours of a possible stop during the end of week, the transfer of a considerable amount of heat is limited, from the hot part (which consequently cools and decreases its own pressure) to the relatively cold part: put than the high pressure evaporator and more precisely the body cylindrical steam-water separation chamber related, is the element that limits the starting gradient, it it follows that such reduction in cooling leads to a shortening of the boot transition period.

Shutters must be in a position fully open during normal operation of the generators, so as not to generate pressure drops and therefore energy dissipations

The location of the shutter is preferably between the inlet of the high pressure evaporator and the medium pressure evaporator outlet for generators illustrated in the figures (three pressure level generators) or the low pressure evaporator inlet for two generators pressure levels (not illustrated).

In the case of a possible realization of four pressure levels, the shutter can be located in a downstream position of the high pressure evaporator and water below the evaporator of the third pressure level.

In all the cases mentioned above, Installation with more than one shutter can be provided.

In the case of an embodiment with a single level pressure, the shutter may be located downstream of the evaporator.

The shutter can be made with materials Metallic (stainless steel) or textile materials. Preferably The shutter is covered with thermally insulating materials. The form indicated in the figures is merely indicative and not limiting

In an alternative, the media substantially in the form of a shutter can comprise devices of type bulkhead.

The levers and / or motorizations for the actuators can be of different types and are arranged inside or outside the smoke pipe. In cases of contingency, a manual type drive can also be provided.

From the above description it results from obvious way that the steam generator with recovery according to the invention achieves numerous advantages, the first is in fact that restart times are unusually short, allowing significant improvements in operating times at full load of the thermoelectric plant.

In fact, at the time of restarting each time the steam generator according to the invention after a stop of limited duration (for example, less than 72 hours), it is possible to start at higher pressures and by consequently higher temperatures in the high pressure circuit, thus reducing the starting time accordingly, being same the thermomechanical stresses induced in the components of the most critical steam generator, that is, in the components thicker such as high cylindrical bodies Pressure.

Another advantage of the steam generator according to the invention is that, during the shutdown, the flow of cold air inside of the generator is limited, which, in the absence of the shutter, is would produce due to the chimney pipe shot, which leads to a additional cooling of the generator during shutdown.

Obviously, one skilled in the art can make numerous modifications and variants of the generator steam with recovery described above, in order to meet contingent and specific requirements, which are included in any case within the scope of protection of the present invention, as defined in the following claims.

Claims (3)

1. Steam generator (10, 110, 210) with heat recovery, comprising a heat exchange unit (12) in which, under normal operating conditions, a hot part (16) is defined, with high temperatures of metal and high temperatures of the water / steam mixture contained therein, and a relatively cold part (18, 20), with lower metal temperatures and lower temperatures of the water / steam mixture contained therein, with respect to those of said hot part (16), in which means (32, 132, 232) substantially in the form of a shutter are interposed between said hot part (16) and said relatively cold part (18, 20) in order to thermally insulate said hot part (16) of said relatively cold part (18, 20), said means (32, 132, 232) being substantially in the form of a shutter at least partially so as to put said hot part (16) and said part (18, 20) relatively cold again in communication n of fluids with each other, characterized in that said means (32, 132) substantially in the form of a shutter comprise a shutter (34, 134, 234) that can be rolled or folded. 2. Steam generator (10, 110, 210) with heat recovery according to claim 1, characterized in that said shutter (32, 132, 232) is made of textile or metallic materials. 3. Steam generator (10, 110, 210) with heat recovery according to claim 2, characterized in that said shutter (32, 132, 232) is covered with thermally insulating material.