CH718340A2 - Increasing the performance of gas and steam turbine systems with a new additional pre-firing. - Google Patents

Abstract

The invention relates to a gas and steam turbine plant or combined cogeneration plant consisting essentially of at least one gas turbine group (50) with at least one compressor (1), at least one GT combustor (3) and at least one gas turbine (2) with a simple or sequential combustion, a steam turbine group (51), a steam circuit (52), with a steam generator (5) connected after the gas turbine, a condenser (9) and a feedwater tank deaerator (11). The system is designed in such a way that an air flow (35) is tapped off at the end of the compressor (1) and cooled by at least one air cooler (34), a cooled air flow (35b) is heated through a pre-combustion chamber (41), is heated by a gas cooler (42) can be cooled before the cooled gas stream (36) is fed into the GT combustor (3). In the case of a gas turbine (2) with sequential combustion, a second air stream (40) is bled at an MD stage of the compressor and cooled by at least one air cooler, a cooled partial air stream is fed into the gas turbine for cooling GT parts of the MD stage and preferably a cooled partial air flow is heated by an MD pre-combustion chamber and cooled by an MD gas cooler before the cooled gas flow is fed into the MD combustor of the gas turbine (2).

Description

TECHNICAL AREA

Thermal power plants are used to generate electricity. These include steam turbine plants (DTA), gas and steam turbine plants (GDTA), i.e. combi-plants and combi-cogeneration plants.

A gas and steam turbine plant or combination plant consists of at least one gas turbine (GT), at least one steam turbine (DT) and a waste heat or heat recovery steam generator (HRSG), the steam generator being connected downstream of the gas turbine. In such a heat recovery steam generator, the evaporation, steam overheating and reheating of the feed water on the secondary side takes place by cooling the hot gas on the primary side from the gas turbine. The steam process uses the flue gas heat and dissipates the waste heat of the process to near the ambient temperature. The invention relates to gas turbines and heat recovery steam generators HRSG in gas and steam turbine systems or combined systems and combined cogeneration systems.

STATE OF THE ART

The gas turbine is designed for a specific power. The performance is determined by the air flow, the compression pressure by the compressor and the combustion chamber temperature. The air flow depends on the air temperature at the compressor inlet. On hot summer days, the air flow at the compressor inlet and the output of the gas turbine will decrease significantly, and the aim is to regain the lost megawatts, especially when there is high demand for power plant output.

[0004] In gas turbines, combustion takes place within the combustion chamber with a large excess of air. The excess air factor is so high because the maximum temperature in the combustion chamber and the temperature at the inlet of the turbine must not exceed 1400 °C (or up to 1500 °C).

Because of the high excess air in the combustion chamber, there is a high oxygen content in the exhaust gas from the gas turbine. In a gas turbine with a natural gas fuel, the oxygen content in the gas turbine exhaust gas is 12 to 15% by volume. The reason for the remaining oxygen in the GT exhaust is on the one hand the limited heating in the combustion chamber from approx. 500 °C to approx. 1400 °C and on the other hand the cooling air flow which flows through the turbine blades and thus bypasses the combustion chamber. The remaining oxygen content at the gas turbine exit is sufficient to burn an auxiliary fuel in the exhaust duct and to increase the temperature of the gas turbine exhaust gases.

The additional firing (ZsF) is realized by installing burners in the exhaust gas duct of the gas turbine or in the inlet duct of the HRSG. This additional firing is therefore an additional post-firing (ZNF) and is an effective measure for utilizing the residual oxygen content of the gas turbine exhaust gases. Post-firing is a commonly used method to increase output in combined cycle power plants on hot summer days when gas turbine output drops significantly. However, the use of post-firing does not increase the efficiency of the combined plant. Supplemental firing is most commonly used in combi-cogeneration plants where the process steam flow needs to be varied independently of the electrical power generated. In this case, the additional firing controls the amount of process steam generated.

[0007] By afterburning in the HRSG intake port, the GT exhaust gas temperature can be increased up to 780°C. This requires special alloys in the reheater and superheater heating surfaces to withstand the elevated temperatures.

The burners in the exhaust gas duct of the gas turbine can be put into operation in two cases and the exhaust gases can be increased to a maximum temperature of approx A second unit failed through the Fresh Air Firing (FLF) to generate steam flow.

[0009] For higher air mass flow and GT production in warm climate regions, air cooling at the compressor inlet is a useful technique. The more cost-effective system of these air cooling systems is water injection at the compressor inlet and the use of water evaporation.

PROBLEM

[0010] Post-firing problems of the known additional post-firing ZNF due to channel burners: The requirements must be met by the duct burner Post-firing takes place at a low exhaust gas pressure and the combustion behavior of the duct burner can therefore be incomplete, so that soot can form Compliance with the CO limit values is the main problem The duct burner increases the NOx level and leads to a negative impact on the environment Special alloys are required in the superheater and intermediate superheater so that the heating surfaces can withstand the increased exhaust gas temperatures (from approx. 600 °C to approx. 780 °C). The large inlet duct must be long enough to ensure complete combustion and to avoid direct flame contact on the heat transfer surfaces It is not possible or an easy solution to build post-firing ZNF for existing plants that are not designed for channel firing.

The following publications are known from the prior art for combined cycle power plants: "Combined-Cycle Gas & Steam Turbine Power Plants" Chapter 6 & 10 by R. Kehlhofer, R. Bachmann, PennWell, Tusla, Oklahoma 1999 "Supplementary Duct Firing for Combined Cycle Power Plants" by Stellar Energy Masch 28, 2016 http://stellarenergy.rfgdemo.com/blog/2016/03/28/supplementary-duct-firing-for-combined-cycle-power-plants-how -it-compares-to-tiac/ Duct burner as additional firing for the gas and steam turbine process, November 13, 2007 Univ.-Prof. Dr.-Ing. Klaus Görner Co-referee: Univ.-Prof. Dr.-Ing. Viktor Scherer https://duepublico2.unidue.de/servlets/MCRFileNodeServlet/duepublico_derivate_00018881/Koesters_Dissertation.pdf Sequential supplementary firing in combined cycle power plant 13<th>International Conference on Greenhouse Gas Control Technologies, GHGT-13, 14-18 Nov 2016, Lausane, Switzerland

PRESENTATION OF THE INVENTION

The object of the invention is now to provide a method for increasing the plant output and avoiding operational problems. In the present invention, the excess air in the gas turbine flow is used to increase the combustion output after the compressor at the same combustion chamber temperature of approx. 1400°C. This is possible if an air flow is tapped at the compressor outlet and heated outside of the gas turbine by a pre-combustion chamber, cooled by a gas cooler (flue gas cooler) and fed into the gas turbine in front of the combustion chamber for further firing. To increase the additional firing, the air heating by the precombustion chamber and the gas cooling by the gas cooler can be repeated.

This new additional firing is referred to as additional pre-firing (ZVF). Thus, the additional firing (ZsF) can be subdivided as follows: Known supplementary post-firing (ZNF) (state of the art) New additional pre-firing (ZVF) (according to the invention)

BRIEF EXPLANATION OF THE FIGURES

The invention will be explained in more detail with reference to two exemplary embodiments in a simplified representation by drawings. The new air/gas and water/steam circuit and the corresponding diagrams show in the figures, according to the invention, the tapping of an air flow for cooling and heating outside the gas turbine and the recirculation into the GT combustion chamber. Bl. 1: Fig. 1 circuit of the new gas/steam circuit of a combination plant with a single or a sequential combustion of the gas turbine according to the present invention Fig.2: Simple circuit of the new cycle of a combination plant with a single or sequential combustion of the gas turbine Bl. 2: Fig.3a Diagram for the air/gas temperature as a function of the entropy T(s) Fig.3b Diagram for the air/gas temperature and water/steam temperature as a function of the heat flow ratio vQ (vQ = QK/Qzu0) QK = cooling heat flow in the air and gas coolers Bl.3: Fig.1w and Fig. 2w for new ZVF with repeat pre-firing Fig.1s and Fig. 2s for new ZVF at GT with sequential combustion Fig.4 Circuit of a gas and steam turbine system with LP and HP steam pressure circuit, simple GT burner and additional post-firing ZNF (prior art).

The figures are shown only as examples of the implementation of the invention.

CARRYING OUT THE INVENTION

Depending on the gaseous or oily fuel, i.e. with low or high sulfur content, a corresponding W/D cycle (single steam pressure, two steam pressure or three steam pressure cycles HD, MD, ND) is switched on. In Fig. 4 (Bl. 3) a simple gas and steam circuit of a combined system with two steam pressure circuits is shown (prior art). A steam generator (HRSG) (5) is connected downstream of the gas turbine group (50). The steam generator consists of LP and HP feedwater preheaters, LP and HP evaporators, an HP superheater (21) and a reheater. The air is compressed by the compressor and a GT cooling air flow is bled from the compressor and cooled by a cooling air cooler (30) (or two coolers in sequential combustion). The cooled cooling air flow (31) is fed into the gas turbine to cool the GT parts. A portion of the cooling airflow passes through the GT blade, bypassing the combustor and retaining an oxygen content. To cool the GT cooling air (30), a water flow (32) is tapped from the preheated HP feed water and is evaporated and superheated by the cooling air cooler (30). The superheated steam flow (33) generated is added to the HP steam flow at the appropriate point in the superheater heating surface (21). In a gas turbine with sequential combustion (i.e. with HP combustor, HP turbine, HP combustor and HP turbine), HP and HP cooling air coolers (30) are switched. Fig. 4 in Bl. 3 shows the afterburner (45) and the afterburner duct (44) between the gas turbine and the steam generator (5) (prior art).

shows an example of the implementation of the invention in gas and steam turbine systems with simple combustion in the gas turbine and a new additional pre-combustion ZVF. An air stream (35) is tapped at the compressor outlet and divided into two streams. The cooling air flow (35a) is cooled to a temperature of approx. 330° C. by a cooling air cooler KLK (30) and fed into the gas turbine to cool the gas turbine parts. The air stream (35b) is cooled to a temperature of, for example, 300°C or lower by an air cooler LK (34). The cooled air flow is heated by one or more burners in a pre-combustion chamber (41) to a temperature between 500° and 600°C. The combustion chamber is relatively small, but must be long enough to ensure ideal combustion.

The heated gas flow is cooled by the flue gas or gas cooler (42) to a temperature of approx. 300°C and the cooled gas flow (36) is introduced into the gas turbine for cooling the GT combustion chamber (3) and firing. Because the gas flow is cooled to approx. 300 °C at the outlet of the gas cooler (42), the gas is heated through the combustion chamber (3) from approx. 300 °C instead of approx. 500 °C (compressor outlet temperature) to the combustion chamber temperature i.e. part of the additional combustion will take place through the GT combustion chamber (3) (see also Ts diagram Fig. 3a and TQ diagram Fig. 3b). Supplemental heating by the GT burner (3) is shown by line 4-1 as part of line 4-5).

The cooling of the air flow (35b) by the air cooler (34) and the gas cooler (42) can be done by at least one tap of the feed water or steam flow from the HRSG. The tapping point is determined according to the cooling temperature at the outlet of the individual coolers. The feedwater can be taken from the feedwater preheater (17) and through the valve (32v) or from the HP water vapor tank (19) and through the valve (37v) and fed into the cooling surfaces of the air and gas coolers (34 and 42), vaporized and superheated and added to the main steam stream in HP superheater (21). The point at which the steam is introduced into the superheater (21) depends on the steam temperature at the outlet of the two gas coolers.

The increase in system performance results from the steam turbine as a result of the increase in steam generation in the air and gas cooler.

Fig. 2 shows a variant of the implementation of the invention with the new additional pre-firing (ZVF) and one with simple combustion in the gas turbine. An air flow (35) is bled at the compressor outlet and cooled by the cooling air cooler (30). A cooled partial air flow (31) is fed into the gas turbine to cool the GT blade. The residual air flow (35b) is guided through the slider (43) and heated to a temperature between 500 °C and 600 °C by the pre-combustion chamber (41) and cooled by a gas cooler (34). The cooled gas stream (36) is introduced into the gas turbine for combustor wall cooling and combustion. The cooling of the air and the gas stream in the cooling air cooler (30) and the gas cooler (34) can take place by at least one tapping of the feed water or steam stream from the HRSG. The cooling can be tapped through the cooling water flow (32) from the feedwater preheater (17) and introduced into the cooling surfaces through the valve (32v). The cooling can also be taken from the feedwater preheater (17) or from the HP steam tank (19) by a water flow and fed into the cooling surfaces of the air and gas coolers (34 and 42). The flow of superheated steam generated is introduced into the superheater (21).

Fig. 3a shows the temperature-entropy diagram T(s) for air and gas through a gas turbine of the new combination plant according to Fig. 1 or Fig. 2. The air is compressed by the compressor from ambient temperature (0) to a temperature of approx. 500 °C (0-1). The tapped air flow (35) is cooled in the air cooler (34) or (30) (line 1-2), heated (2-3) by the pre-combustion chamber (41), cooled (3-4) by the gas cooler (42) and mixed with the residual air flow after the compressor and heated (4-5) by the GT combustion chamber (3).

3b shows the temperature over the heat flow ratio T(vQ) for the gas and water/steam flow through the air cooler KLK (30), LK (34) and the gas cooler GK (42) of the new combination plant according to FIG 1 or 2. vQ = heat flow ratio vQ = QK/Qzu0 QK = cooling heat output, Qzu0 = supplied GT heat output

For the purpose of greater steam generation and/or reduction of the bleed air flow, the precombustion chamber and gas cooler can be repeated after the first gas cooler (34) (Fig. 1w & 2w) in sheet 3.

To cool the gas turbine parts in a gas turbine with sequential combustion (Fig. 1s), two cooling air flows (MP and HP cooling air flow) are tapped from the compressor and cooled by two cooling air coolers (30). To use the new ZVF additional pre-firing in such gas turbines, one or two additional MD and HP air streams can be taken from the compressor and each heated by the pre-combustion chamber, cooled by the gas cooler and introduced into the corresponding MD or HP combustion chamber of the gas turbine . In Fig. 1s, in a gas turbine with sequential combustion, an MD bleed air stream is cooled by an MD air cooler (34), heated by a precombustion chamber (41), cooled by the MD gas cooler (42) and returned to the MD gas turbine combustor .

In Fig. 2s, in a gas turbine with sequential combustion, two MD and HP cooling air streams are tapped from the compressor and each cooled by two air coolers (30), heated by two precombustion chambers (41), cooled by two gas coolers (42). and introduced into the corresponding MD or HP combustor of the gas turbine.

Because of the series connection of two or more air and gas coolers, measures to overcome the flow resistance or pressure loss are required. Depending on the number of coolers connected, a pressure loss of between 250 and 500 mbar is estimated. The following methods are possible for this task: 1- The position of the two connections of the air bleed and the gas inlet can be implemented in the gas turbine in such a way that the flow pressure loss is overcome by using the dynamic pressure and a bleed air flow is achieved. 2- Compensation of the pressure difference through a constriction or through a pressure loss effect in the gas turbine. 3- Activation of a fan (46) before the pre-combustion chamber (41 in Fig. 1) or after the gas cooler (42 in Fig. 2). In this case, the air or gas is cooled to a temperature of 250 - 300 °C in front of the fan. The fan housing is loaded by the HP air pressure from the compressor. The fan can be powered by an electric motor or by a steam turbine.

As a result of additional firing or additional heat output, the steam turbine output increases with unchanged GT output, which would lead to a reduction in the system efficiency. Because of the increasing HP feed water flow, the LP water flow will be reduced or lost depending on the additional capacity. This leads to a compensation of the efficiency losses and thus the efficiency remains practically unchanged both with the additional post-firing (ZNF) and with the additional pre-firing (ZVF).

[0029] A new bleed of air flow from a gas turbine and recirculation needs modification for further openings on the gas turbine. Such changes can be made during the design and manufacture of the gas turbine. In the existing gas turbine, bleed openings for the GT cooling air flow are already present and therefore no change in the gas turbine is required.

According to FIG. 2, the change is only carried out outside of the gas turbine and can be carried out during an inspection and when the system is shut down. The variant according to FIG. 2 is better suited for existing gas turbines.

[0031] In GT operation with an additional pre-firing ZVF, the GT exhaust gas temperature will not rise above 650°C. Therefore, no special alloy is necessary in the heating surfaces of the reheater and superheater. Since an oxygen content in the GT exhaust gas is still present despite additional pre-firing, another additional post-firing ZNF can be carried out in the GT exhaust gas duct. In this case, the GT exhaust gas temperature will rise above 650 °C. The GT exhaust gas temperature can be increased to a maximum value of 780 °C by the ZNF additional post-firing in the GT exhaust duct. This requires a special alloy for the superheater heating surfaces. The post-firing burner can also be used for FL firing if the gas turbine fails.

A simultaneous supply of additional heat output by a pre-firing ZVF and a conventional post-firing FNF can lead to a double additional steam generation. A gas turbine with a pre-firing ZVF and a post-firing FNF is particularly suitable for combined cogeneration plants.

ADVANTAGES OF THE INVENTION

The comparison between combined systems with new additional pre-firing (ZVF) according to the invention and combined systems with conventional additional post-firing (ZNF) is characterized by the following advantages: The new additional pre-combustion ZVF takes place through the pre-combustion chamber (41) at high compression pressure and oxygen content and thus the combustion behavior of the pre-combustion chamber is complete and without soot formation As a result of the better combustion by the pre-combustion chamber, an increase in the CO content and the NOx level in the exhaust gas is less to be expected compared to post-firing ZNF and thus a more positive impact on the environment No special alloys are required for the superheater and reheater due to the ZVF pre-firing, as the gas temperature at the HRSG inlet does not exceed 650 °C The precombustion chamber (41) is small, has an air temperature of up to approx. 600 °C and is cooled by the cooled air at the inlet of approx. 300 °C If the new ZVF pre-firing and conventional ZNF post-firing are switched on simultaneously in GT operation, the additional heat output can be increased more than with conventional post-firing (by approx. twice), which leads to double the additional steam generation. Special alloys in the superheater and Zue are necessary because of ZNF An additional pre-firing ZVF can be retrofitted for an existing system with or without an additional post-firing ZNF.

REFERENCE LIST

1 GT air compressor 2 Gas turbine GT 3 GT combustor 4 GT generator 5 Steam generator (DE), (HRSG) 6 HP steam turbine 7 IP/LP steam turbine 8 DT generator 9 Condenser 10 Condensate pump 11 Feedwater tank deaerator SWB 12 LP feedwater pump 13 HP feedwater pump 14 GT exhaust flow 15 Exhaust flow from HRSG 16 LP heating coil 17 HP feedwater heater, HP heating coil 18 HP evaporator heating coil 19 HP steam tank, HP W/D tank 20 Water circulation pump 21 HP Superheater heating surface 22 Reheater (Zue) 23 Condensate flow from the condenser 24 Extraction steam flow to the deaerator 25 LP steam flow to the LP turbine 26 Live steam flow 27 Steam flow from the HP-DT to the Zue 28 Steam flow to the MP/LP steam turbine 29 Air flow at the compressor outlet (HP stage) 30 GT cooling air cooler KLK 31 Cooled GT cooling air flow from cooling air cooler 32 Cooling water from the HP preheater (17) 32v valve, slide 33 Steam from the GT cooling air cooler 34 Air cooler LK before the precombustion chamber 35 Bleed air flow from the compressor (35a+35b) 35a air flow through the air cooler (30) 35b air flow through the air cooler (34) 36 cooled (flue gas) gas flow from gas cooler (42) 37 cooling water from HP steam tank (19) 37v valve, slide 39 Steam from air or gas cooler 40 MD bleed airflow at GT with sequ. Combustion 41 Pre-combustion chamber, pre-combustion space 42 Gas cooler GK after the pre-combustion chamber (41) 43 Slider 44 Afterburner duct 45 Afterburner 46 Fan 50 Gas turbine group: compressor, BK, GT and G 51 Steam turbine group: HP-DT, MD/LP-DT and G 52 DE, condenser and SWB degasser GT gas turbine with single or sequ. Combustion GDTA Gas and DT system or combination system MD, HD Medium pressure, high pressure for gas or steam QK Cooling heat flow in the air and gas cooler Qzu0 Heat flow supplied through the GT burner (3) TBK Flue gas temperature at the combustion chamber outlet vQ vQ = QK /QzuO W/D water and steam G/D gas and steam L/G air and gas ZsF additional firing ZVF additional pre-firing in the pre-combustion chamber ZNF additional post-firing in the entry channel of HRSG FLF fresh air firing in the entry channel in front of the HRSG HRSG "Heat Recovery Steam Generator", steam generator

Claims (8)

1. A gas and steam turbine plant or combined cogeneration plant consisting essentially of at least one gas turbine group (50) with at least one compressor (1), at least one GT combustor (3) and at least one gas turbine (2) with a single or a sequential combustion, a steam turbine group (51), a steam circuit (52), with a steam generator (5) connected after the gas turbine, a condenser (9), a feed water tank deaerator (11) is characterized in that an air flow (35 ) at the end of the compressor (1) is bled and cooled by at least one air cooler, a cooled air flow (35b) is heated by a pre-combustion chamber (41), cooled by a gas cooler (42) before the cooled gas flow (36) enters the GT Combustion chamber (3) is performed and, in the case of a gas turbine with sequential combustion, a second air stream (40) is tapped at an MD stage of the compressor and cooled by at least one air cooler, a ge cooled partial airflow for cooling GT parts of the MD stage into the gas turbine and preferably a cooled partial airflow is heated by a MD precombustor and cooled by a MD gas cooler before the cooled gas stream is fed into the MD combustor of the gas turbine ( figure 1, fig. 2 or fig. 2s). 2. A gas and steam turbine plant with single combustion in the gas turbine according to claim 1, characterized in that an air flow (35) is bled at the end of the compressor, a partial air flow (35a) is cooled by a cooling air cooler (30) and used for cooling gas turbine parts into the gas turbine and a partial air flow (35b) is cooled by an air cooler (34), heated by the pre-combustion chamber (41), cooled by the gas cooler (42) and the heating and cooling are preferably repeated by at least one further pre-combustion chamber and one further gas cooler , before the cooled gas stream (36) is fed into the GT combustion chamber (3), with the air and gas cooling in the air and gas cooler being taken from the steam generator by feed water or steam, depending on the cooling temperature, and fed into the steam generator as superheated steam (Fig. 1, Fig. 1w). 3. A gas and steam turbine plant with single combustion in the gas turbine according to claim 1, characterized in that an air flow (35) is bled at the end of the compressor and cooled by an air cooler (30), a cooled partial air flow (31) for cooling of Gas turbine parts are fed into the gas turbine and a cooled partial air flow (35b) is heated through a pre-combustion chamber (41), cooled by a gas cooler (42) and the heating and gas cooling are preferably repeated by at least one further pre-combustion chamber and one further gas cooler and the cooled gas flow (36 ) is fed into the GT combustion chamber (3), whereby the air and gas cooling in the air and gas cooler is taken from the steam generator by feed water or steam, depending on the cooling temperature, and fed into the steam generator as superheated steam (Fig. 2, Fig .2w). 4. A gas and steam turbine plant according to claim 1, 2 or 3, characterized in that an HP air flow (35) is tapped at the compressor outlet and an LP air flow (40) from an intermediate pressure stage of the compressor (1) of a gas turbine with sequential combustion an HP air flow (35) or MD air flow (40) is cooled by at least one air cooler, a cooled partial air flow is fed into the gas turbine for cooling parts of the gas turbine of the affected pressure stage, and a cooled partial air flow of the pressure stage is heated through a pre-combustion chamber by a gas cooler cooled and the cooled gas flow is guided into the GT combustion chamber of the affected pressure stage (Fig. 1s). 5. A gas and steam turbine plant according to Claim 4, characterized in that both the HP air flow (35) and the MD air flow (40) are each cooled by at least one air cooler, a cooled partial air flow for cooling gas turbine parts of the affected pressure stage in guided through the gas turbine and a cooled partial air flow is heated through a pre-combustion chamber, cooled by a gas cooler and the cooled gas flow is guided into the GT combustion chamber of the affected pressure stage (Fig. 2s). 6. A gas and steam turbine plant according to claims 1 to 5, characterized in that in gas turbines with closed steam cooling of the gas turbine blades, the air flow (31) fails in (Fig. 2) and the air cooler (30) and the air flow (31) in ( Fig. 1) fail. 7. A gas and steam turbine system according to Claims 1 to 6, characterized in that a fan can be switched on for each partial air flow (35b) routed through the pre-combustion chamber (41) for pre-firing, the fan preferably being installed before the pre-combustion chamber (41) or after the gas cooler (42) is arranged. 8. A gas and steam turbine system according to claims 1 to 7, characterized in that the cooling surface of an air cooler (34) and/or a gas cooler (42) is divided into at least two coolers and these are connected in series or in parallel.