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Title:
IMPROVEMENT AND CONTROL OF THE HIGH PRESSURE SUPERHEATED STEAM DIRECTLY PRODUCED BY A SOLAR FIELD. DESCRIPTION
Document Type and Number:
WIPO Patent Application WO/2015/159310
Kind Code:
A1
Abstract:
A method for operating a combined cycle power plant comprising a gas turbine, a solar field and a high pressure steam turbine, wherein the hot flue gas flowing from the gas turbine enters into a heat recovery unit to heat a molten salt to be used as heat transfer fluid to adjust the flow rate and the temperature of the superheated high pressure steam produced by the solar field depending on the environmental conditions. For conducting such a method, an Integrated Solar Combined Cycle is disclosed, wherein the basic elements are: a gas turbine, a high pressure steam turbine, which is connected to a steam generator, and a solar thermal field, that, together with a steam super heater, is provided between the exit of the gas turbine and the inlet of the steam turbine, wherein the hot flue gases flowing from the gas turbine heat up a molten salt that, as heat transfer fluid, is stored in a first storage tank and used to adjust the temperature of the superheated high pressure steam produced by the solar field and to superheat the steam produced by the steam generator. Furthermore the flue gases coming out from the molten salt heating section are used to preheat the water feeding the solar field and the steam generator.

Inventors:
PIZZI ROBERTO (IT)
LEHMANN ROBERTO (IT)
AGUILERA PEDRO (CO)
Application Number:
IT2014/000111
Publication Date:
October 22, 2015
Filing Date:
April 16, 2014
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
TECHNIP ITALY SPA (IT)
International Classes:
F01K3/12; F01K23/10; F22B1/00
Domestic Patent References:
WO2013185909A12013-12-19
Foreign References:
US20120102950A12012-05-03
US20110127773A12011-06-02
EP2604858A22013-06-19
DE4409197A11995-09-21
Other References:
None
Attorney, Agent or Firm:
SARPI, Maurizio (Via Collina 36, - Rome, IT)
Download PDF:
Claims:
CLAIMS

1) Method for operating a combined cycle power plant comprising a gas turbine (4), a solar field (8) and a high pressure steam turbine (14), characterized in that the hot flue gases flowing from the gas turbine (4) heat up in a heating recovery unit (6) a molten salt that, as heat transfer fluid, is stored in a first storage tank (18) and used to adjust the temperature of the superheated high pressure steam produced by the solar field (8) through a solar steam super-heater (10) and to superheat the saturated steam produced by a steam generator (12), whenever the sun irradiation changes .

2) Method for operating a combined cycle power plant according to claim 1, characterized in that the flue gases coming out from the molten salt heating recovery unit (6) are used to preheat the water feeding the solar field (8) and the steam generator (12) so achieving an acceptable temperature of the flue gases discharged from the stack (58) of the plant to the atmosphere .

3) Method for operating a combined cycle power plant according to claim 1 characterized in that the steam generator (12) comprises an economizer section (12a) , a vaporization section (12b) and a super heater section (12c) .

4) Method for operating a combined cycle power plant according to claim 1 characterized in that, the temperature of the steam produced by the solar field (8) through the solar steam super-heater (10) is controlled by acting on a control valve (23) modulating the hot molten salt flow rate and in the same way the steam produced by the vaporization section (12b) of the steam generator (12) passes through the super heater section (12c) and its temperature is controlled by acting on a control valve (30) .

5) Method for operating a combined cycle power plant according to claim 1 characterized in that, the steam generator (12) is used:

to produce additional high pressure steam in case of the production from the solar field drops below the value assumed as minimum for the steam turbine (14) to maintain an acceptable efficiency;

to produce the total amount of the steam required to operate the steam turbine (14) for a limited time after sunset.

6) Method for operating a combined cycle power plant according to claim 1 and characterized in that, the solar steam super heater (10) and the super-heater section (12c) of the steam generator (12) are directly connected by means of a high pressure steam line (15) to the steam turbine (14) .

7) Method for operating a combined cycle power plant according to claim 1 characterized in that, the molten salt coming out from the solar steam super heater (10) is stored into a second tank (26) and used as heating medium in the steam generator (12) passing first through the vaporizer section (12b) and after through the economizer section (12a) trough a line (41) . 8) Method for operating a combined cycle power plant according to claims 1 and 7 characterized in that, the molten salt coming out from the super heater (12c) of the steam generator (12) enters the vaporization section (12b) jointly with the molten salt pumped from the second storage tank (26).

9) Method for operating a combined cycle power plant according to claim 1 and 3 characterized in that, the cold molten salt coming out from the economizer section (12a) of the steam generator (12) is stored into a third tank (36) from where it is pumped to the heat recovery unit (6) connected to the gas turbine (4).

10) Method for operating a combined cycle power plant according to claim 1 and 7 characterized in that, the flow rate of the molten salt from the second tank (26) to the steam generator (12) is automatically controlled by a pressure control valve (28) to maintain the proper pressure of the high pressure steam feeding the steam turbine (14) .

11) Method for operating a combined cycle power plant according to preceding claims characterized in that, it is provided a hot molten salt line (40) from the output of the second tank (26), before said control valve (28) , to said third tank (36) through a temperature control valve (38), to maintain the temperature of the cold molten salt in said third tank (36) always far from its solidification automatically.

12) Method for operating a combined cycle power plant according to preceding claims characterized in that, it is provided a cold molten salt line (46) from the output of the third tank (36) to the inlet of the second tank (26) to add cold molten salt under a temperature control valve (48) .

13) Method for operating a combined cycle power plant according to preceding claims characterized in that, in order to reintegrate the level of the molten salt into the second tank (26) it is provided a molten salt line (22, 50) from the first tank (18) to add molten salt to second tank (26) by opening a level control valve (52) .

14) Integrated Solar and Combined Cycle Power Plant for conducting a method according to claim 1, comprising a gas turbine (4), with a heat recovery unit (6), a solar field (8) and a high pressure steam turbine (14), characterized in that :

said solar field (8) is connected with a steam super heater (10), between the exit of the gas turbine (4) and the inlet of the steam turbine (14);

it is provided a steam generator (12), connected by high pressure steam line with the inlet of the steam turbine (14) ;

the flue gases coming out from the heat recovery unit (6) preheat the water feeding the solar field (8) as well as the water feeding the steam generator (12) ; in the heat recovery unit (6) the hot flue gases flowing from the gas turbine (4) heat up a molten salt that, as heat transfer fluid, through an hot molten salt line, is stored in a first storage tank (18) and used to adjust the temperature of the superheated high pressure steam produced by the solar super heater (10) and to superheat the saturated steam produced by the steam generator (12), whenever the sun irradiation changes, modulating the hot molten salt flow rate.

15) Integrated Solar and Combined Cycle Power Plant according to preceding claim, characterized in that the cold molten salt coming out from the steam generator (12) enters the tank (18) jointly with the cold molten salt coming out from the steam super heater (10) .

16) Integrated Solar and Combined Cycle Power

Plant according to one of claims 14,15, characterized in that it is provided a cold molten salt line in order to return back the cold molten salt coming out from tank (18) to the heat recovery unit (6) connected to the gas turbine (4) .

17) Integrated Solar and Combined Cycle Power Plant according claim 14, characterized in that:

the steam generator (12), comprises an economizer section (12a), a vaporization section (12b) and a super heater section (12c), which is connected by high pressure steam line (15) with the steam turbine (14) ; the molten salt that, as heat transfer fluid, through a line (16), is stored in the storage tank (18), is used to adjust by means of a line (22) the temperature of the superheated high pressure steam produced by the solar super heater (10) and to superheat the saturated steam produced by the vaporizer section (12b) in the super-heater section (12c) of the steam generator (12), whenever the sun irradiation changes; the steam produced by the solar field passes into a line (15) through the super heater (10) and its temperature is controlled by acting on a control valve (23) modulating the hot molten salt flow rate in a line (22) and in the same way the steam produced by the vaporization section (12b) of the steam generator (12) passes through the super heater section (12c) and its temperature is controlled by acting on a control valve (30);

it is provided a second tank (26) to store the molten salt coming out from the solar steam super heater (10), said second tank (26) being connected by a line (32) with the vaporizer section (12b) in order to use said molten salt as heating medium in the steam generator (12) passing first through said vaporizer section and after through the economizer section.

18) Integrated Solar and Combined Cycle Power Plant according to claim 17, characterized in that, the molten salt coming out from the super heater (12c) of the steam generator (12) enters the vaporization section (12b) jointly with the molten salt pumped from the second storage tank (26) trough a line (32) .

19) Integrated Solar and Combined Cycle Power Plant 14, according to claim 17 characterized in that it is provided a cold line (42) in order to store the cold molten salt coming out from the economizer section (12a) of the steam generator into a third tank (36) from where is pumped to the heat recovery unit (6) connected to the gas turbine (4) . 20) Integrated Solar and Combined Cycle Power Plant according to claim 17, characterized in that, in order to reintegrate the level of the molten salt into the second tank (26) it is provided a molten salt line (22,50) from the first tank (18) to add molten salt to second tank (26) by opening a level control valve (52) .

21) Integrated Solar and Combined Cycle Power Plant according to claim 17, characterized in that it is provided a line (56) of flue gases coming out from the heat recovery unit (6) to preheat the water feeding the steam generator (12) as well as a line (54) to preheat the water feeding the solar field (8) .

Description:
IMPROVEMENT AND CONTROL OF THE HIGH PRESSURE SUPERHEATED STEAM DIRECTLY PRODUCED BY A SOLAR FIELD.

DESCRIPTION

FIELD OF THE INVENTION

The present invention relates to thermodynamic solar and to its integration with a gas turbine generator. More specifically, it relates to a method for operating a combined cycle power plant comprising a gas turbine, a solar field and a high pressure steam turbine, wherein the hot flue gas flowing from the gas turbine enters into a heat recovery unit to heat a molten salt to be used as heat transfer fluid to adjust the flow rate and the temperature of the superheated high pressure steam produced by the solar field depending on the environmental conditions. STATE OF THE ART

The demanded reduction of the C0 2 emission to the atmosphere requires to produce electricity by maximizing the use of renewable energy.

One of the most attractive is the solar energy used to produce steam that drives a steam turbine generator .

The sun radiation heats a thermal fluid that may be synthetic oil, molten salt or water.

The direct superheated steam generation technologies produce solar energy at less cost when compared with thermal oil and molten salt based technologies . The limit of those technologies is that there is no possibility to provide a thermal storage to compensate fluctuation in the production from the solar field and/or to extend the operation of the power plant after the sunset.

In addition to the above any disturbance in the sun radiation may generate important sudden variation in the steam temperature that will negatively affect the proper and safe operation of the steam turbine.

The present invention is intended to overcome the above mentioned weakness of the direct high pressure superheated steam generation by integrating the solar with a gas turbine generator. SUMMARY OF THE INVENTION

This invention is intended to be applied to an integrated Solar and Combined Cycle Power Plant in case of direct superheated steam generation from the Solar field.

The scope is to ensure a proper and stable operation of the Steam Turbine Generator using the steam as motive fluid.

The stability of the steam production in quantity and quality affects the operation of the Steam Turbine and depends from the sudden change of the weather conditions .

The object of the invention is a method for using the hot flue gases produced by the Gas Turbine to provide an adequate thermal storage of heat transfer fluid (molten salts) to be used to adjust the flow rate and the temperature of the superheated steam produced by the solar field, whenever the sun irradiation changes .

It is a further object of the invention to provide a ISCC (Integrated Solar Combined Cycle) for conducting such a method.

According to the invention, the basic elements of said ISCC are: a gas turbine, a high pressure steam turbine, which is connected to a steam generator, and a solar thermal field, that, together with a steam super heater, is provided between the exit of the gas turbine and the inlet of the steam turbine, wherein the hot flue gases flowing from the gas turbine heat up a molten salt that, as heat transfer fluid, is stored in a first storage tank and used to adjust the temperature of the superheated high pressure steam produced by the solar field and to superheat the steam produced by the steam generator. Furthermore the flue gases coming out from the molten salt heating section are used to preheat the water feeding the solar field and the steam generator .

According to a further feature of the invention, the steam generator comprises an economizer section, a vaporization section and a super heater section.

According to a further feature of the invention the flue gases used to preheat the water feeding the solar field and the steam generator pass first through said economizer section.

According to a further feature of the invention, the solar steam super heater and the super-heater section of the steam generator are directly connected by means of a high pressure steam line to the steam turbine .

According to a further feature of the invention, the steam generator is used to produce additional high pressure steam during unplanned weather perturbations or the total amount of the steam for a limited time after sunset.

According to a further feature of the invention, the molten salt coming out from the solar steam superheater is stored into a second tank and used as heating medium in the steam generator passing first through the vaporizer section and after through the economizer section .

According to a further feature of the invention the molten salt coming out from the super heater of the steam generator enters the vaporization section jointly with the molten salt pumped from the second storage tank.

According to a further feature of the invention the cold molten salt coming out from the economizer section of the steam generator is stored into a third tank from where it is pumped to a heat recovery unit connected to the gas turbine.

According to a further feature of the invention the flow rate of the molten salt from the second tank to the steam generator is automatically controlled by a pressure control valve to maintain the proper pressure of the high pressure steam feeding the steam turbine generator . According to a further feature of the invention it is provided a hot molten salt line from the output of the second tank, after said control valve, to said third tank through a temperature control valve, to maintain the temperature of the cold molten salt in said third tank always far from its solidification automatically .

According to a further feature of the invention it is provided a cold molten salt line from the output of the third tank to the inlet of the second tank to add cold molten salt under a temperature control valve.

According to a further feature of the invention in order to reintegrate the level into the second tank it is provided a molten salt line from the first tank to add molten salt to second tank by opening a level control valve.

With these features the system of the present invention make attractive the use of cheaper heat solar collection as the direct steam generation with respect to thermal oil and molten salt.

DESCRIPTION

As already mentioned, some solar technologies use water as thermal fluid to collect the solar heat, the water is vaporized and superheated to have superheated high pressure steam suitable to be expanded into a steam turbine to generate electricity.

The quality of such steam is strongly affected by the weather conditions and its instability may affect the proper and safe operation of the steam turbine. The integration of the solar field and steam turbine with a gas turbine generator will consistently improve the steam characteristics in terms of quality and quantity and consequently make reliable the operation of the plant.

The foregoing and other features of the present invention will become apparent to one skilled in the art to which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, wherein :

Figure 1 shows a basic scheme of an Integrated Solar and Combined Cycle Power Plant according to the invention;

Figure 2 shows a preferred simplified embodiment of an ISCC including all features of the invention;

Figure 3 shows the simplified scheme of Fig.2 with

Heat and Material Balance during insolation design sun radiation according to operation mode A;

Figure 4 is a graphic of the stored volume inside tank TK-01 and tank TK-02 for normal operation;

Figure 5 shows the simplified scheme of Fig.2 with Heat and Balance Operation according to operation mode B;

Figure 6 shows the Heat and Material Balance according to operation mode C;

Figure 7 is a graphic of the Stored Volume for Molten Salt Tank in operation mode C;

Figure 8 shows the Heat and Material Balance in Operation Mode D. List of reference numerals

4: gas turbine generator;

6: heat recovery unit;

8: solar field;

10: super-heater of the steam produced by the solar field;

12: steam generator with three sections: an Economizer section 12a, a vaporization section 12b and a super-heater 12c;

14: steam turbine;

15: high pressure steam line at controlled temperature ;

16: molten salt heated line coming out from 6;

118: first tank to store the hot molten salts;

20: molten salt line to superheat the saturated steam produced by the vaporization section 12b of the steam generator 12;

21: steam line from solar field 8 to super-heater

10;

22: hot molten salt line to adjust through the super heater 10, the temperature of the superheated high pressure steam produced by the solar field 8;

23: temperature control valve;

24: molten salt line coming out from the solar super heater 10;

26: second tank to store the molten salt coming out from 10;

27: molten salt line from 26 to 28;

28: pressure control valve to automatically control the flow rate of the molten salt from the tank 26 to the vaporization section 12b of the steam generator 12;

30: temperature control valve to control the temperature of the steam produced by the vaporization section of the steam generator 12 through modulation of the hot molten salt flow rate;

32: molten salt line between the control valve 28 and the vaporization section 12b;

34: molten salt line between the super-heater section 12c and line 32;

36 : third tank of cold molten salt;

38 : temperature automatic valve to control the inlet of hot molten salt from tank 26 to tank 36;

40: hot molten salt line from tank 26 to tank 36; 42: cold molten salt line coming out from economizer section 12a to tank 36;

44: molten salt line from tank 36 to the unit recovery unit 6;

46: cold molten salt line from the tank 36 to tank 26;

48: valve to control automatically the temperature inside the tank 26 by adding if necessary cold molten salt from tank 36;

50: hot molten salt line to reintegrate the minimum level into the tank 26 from tank 18;

52: valve to control automatically the level into the tank 26 by adding hot molten salt from tank 18;

54: line of flue gases coming out from the heat recovery unit 6 to preheat the water feeding the solar field 8; 56: line of flue gases coming out from the heat recovery unit 6 to preheat the water feeding the steam generator 12;

57: control valve

58: stack;

A conceptual scheme of the invention is shown in fig. 1 wherein:

the solid line is a feed water line for the solar field and the steam generator;

the dotted line is a cold molten salt line;

the broken line is a high pressure steam line from solar field;

the fine line is a high pressure line for the steam turbine;

the chain line is a hot molten salt line.

The combined cycle power plant comprises: a gas turbine 4, a high pressure steam turbine 14, which is connected to a steam generator 12, and a solar thermal field 8, that, together with a steam super heater 10, is provided between the exit of the gas turbine and the inlet of the steam turbine, wherein the hot flue gases flowing from the gas turbine heat up a molten salt that, as heat transfer fluid, is stored in a first storage tank 18 and used to adjust the temperature of the superheated high pressure steam produced by the solar field through the steam super heater 10 and to superheat the steam produced by a steam generator 12.

According to the other figures 2-8, described below is a preferred embodiment of the invention including all features of the invention, which must not be regarded as limiting the present invention.

With reference to fig.2 and 3, the hot flue gases flowing from the gas turbine 4 enter into a heat recovery unit 6 to heat up a molten salt (a blend of Sodium Nitrate and Potassium Nitrate) from 280 °C to 530 °C.

The flue gases coming out from the molten salt heating section are used to preheat the water feeding the solar field 8 and the steam generator 12 so achieving an acceptable temperature of the flue gases discharged from the stack 58 to the atmosphere.

The hot molten salts are stored into the tank 26 and will be used both to adjust the temperature of the superheated high pressure steam produced by the solar field 8 and to superheat the saturated steam produced by the vaporization section 12b of the steam generator 12.

The steam generator 12 will be used:

· To produce additional high pressure superheated steam in case of the production from the solar field 8 drop below the value assumed as minimum for the steam turbine 14 to maintain an acceptable efficiency.

· To produce the total amount of the steam required to operate the steam turbine generator 12 at the design load for a limited time after sunset.

The steam produced by the solar field 8 pass through the super heater 10 (shell side) and its temperature is controlled by acting on the control valve 23 modulating the hot molten salt flow rate and in the same way the steam produced by the vaporization section 12b of the steam generator 12 pass through the super heater section 12c and its temperature is controlled by acting on the control valve 30.

The molten salt coming out from the solar steam super heater 10 through the line 24 will be stored into the tank 26 and used as heating medium in the steam generator 12 passing first through the vaporizer section 12b and after through the economizer section 12a.

The molten salt coming out from the super heater 12c of the steam generator 12, by means of lines 34 and 32, enter the vaporization section 12b jointly with the molten salt pumped from the storage tank 26.

The flow rate of the molten salt from the tank 26 to the steam generator 12 on the line 32, is automatically controlled by control valve 28 to maintain the proper pressure of the high pressure steam feeding the steam turbine generator 12.

The cold molten salt coming out from the economizer section 12a of the steam generator 12, through the line 42 will be stored into the tank 36 from where it is pumped to the heat recovery unit 6 through line 44.

In order to maintain into the tank 36 the temperature of the cold molten salt always far from its solidification, automatic adding of hot molten salt from the tank 26 is provided by means of a line 40 through a control valve 38 on the molten salt out from the economizer 12a. The temperature inside the tank 26 is controlled by adding if necessary cold molten salt from tank 36 under automatic control of a temperature valve 48 on line 46

In the case that the level into the tank 26 drops below a minimum level it will be reintegrated by molten salt from tank 18 by opening the level control valve 38 on the line 40.

APPLICATION CASE

The advantage of . the present invention will be better considered from an example of the proposed system.

The following are the basis of the case used as example :

a) Flue gases from gas turbine :

• Flow rate: 391.5 ton/h

• Temperature 545 °C

b) Steam from solar field:

• Flow rate (at the design insolation): 152.4

ton/h

• Temperature: 460 °C

• Pressure: 112 bar

c) Steam to steam turbine:

• Flow rate: 152.4 ton/h

• Temperature: 480 °C

• Pressure: 110 bar

d) Steam from steam generator:

• Flow rate: 152.4 ton/h (Case C) , 61 ton/h (Case D)

• Temperature: 480 °C

• Pressure: 110 bar Twelve hours have been assumed as design time of insolation.

Four operation modes are considered:

1. The first is the normal condition during insolation design sun radiation (Operation mode A) ;

2. The second is the condition with the power block receives coldest steam from the solar field but still at the design flow rate (Operation mode B) ;

3. The third is the operation after sunset when the storage is used to operate the power plant at the design output using the heat storage (Operation mode C) ;

4. The forth is the operation with the steam from the solar field reduced in temperature and flow rate and compensated with steam produced by the steam generator using the thermal storage (Operation mode D)

Operation Mode A

Reference is made to the heat and material balance according to Figure 3.

The flue gases coming out from the gas turbine 4 through line 56 heat the molten salt pumped from the cold storage tank 36 from 280 °C to 530°C.

The flue gases outlet from the molten salt heating section 6 heat the boiler feed water from 110 °C (operating temperature of the deaerator) to 225 °C.

The solar high pressure steam is produced at a pressure of 112 bar and a temperature of 460 °C and is heated up to 482 °C using the hot molten salt (530 °) . The steam generator 12 is not in operation.

The hot molten salt in excess to the one used to heat the solar steam is accumulated into the tank 18 and the molten salt outgoing from the super heater is accumulated into the tank 26.

The steam turbine 14 receives steam at stable conditions, 110 bar and 480 °C.

The volume of the tank 18 will be adequate to accumulate the hot molten salt produced by the heating system during the day of the year having the maximum insolation.

Figure 4 indicates the stored volume inside 18 and TK-02 for this operation mode.

Operation mode B

Reference is made to the heat and material balance

( figure 5 ) .

The difference with respect to the operation mode A is the temperature of the steam produced in the solar field that is reduced to 400 °C.

The steam super heater 10 increases the temperature of the steam to 482 °C so maintaining the same condition at the inlet of the steam turbine 14.

The solar steam temperature of 400 °C maintaining the maximum steam flow rate is considered as an extreme design condition for the super heater 10, in fact when temperature decreases it is also expected a decrease of the steam flow rate.

The system can also handle high pressure steam at temperature lower than 400 °C up to the saturation provided that the steam flow rate is reduced to match the super heater duty design.

Operation Mode C

Reference is made to the heat and material balance (Figure 6)

The hot molten salt from the tank 18 provides the super heating of the saturated steam produced by the steam generator vaporizer 12b that is using the hot molten salt pumped from tank 26 in combination with the one outgoing from the super heater 10.

The steam generator 12 is designed to produce the steam flow rate necessary to operate the steam turbine 14 at design conditions

Figure 7 indicates the variation in the stored volume inside the three molten salts 18, 26, and 36 tanks during this operation mode.

The operation time in Mode C refers to twelve hours of insolation, less insolation reduces the extension of the operation after sunset.

Operation Mode D

Reference is made to the heat and material balance ( Figure 8 ) .

This operation is a combination of the mode B and C with the difference that the flow rate from the solar field 8 is reduced to 60% and the flow rate from the steam generator 12 compensates in order to provide to the steam turbine 14 the design flow rate.

This mode of operation reduces the operation time after sunset.