RU2809894C1 - Steam turbine unit with switchable low-pressure steam supply point of waste heat boiler - Google Patents

Abstract

FIELD: power engineering.

SUBSTANCE: used on condensing and heating steam turbines of two or more pressures. The technical problem is a general decrease in the efficiency and power of the CCGT unit when the equipment operates during periods with a significant deviation in outside air temperatures relative to the accepted design value, on the basis of which the main equipment is designed for the nominal operating mode. The technical result is achieved by the claimed steam turbine unit, which includes a steam turbine of two or more pressures, connected by pipelines to the pressure circuits of the waste heat boiler. A distinctive feature of such a steam turbine unit is that in the steam turbine there are two chambers for supplying steam to the low-pressure circuit through one stage, or a group of stages from each other, the supply of low-pressure steam to which is carried out through pipelines with control devices that switch the place of supply of low-pressure steam pressure from the waste heat boiler depending on the values of steam pressure in the low pressure circuit of the waste heat boiler and along the turbine flow path.

EFFECT: increasing the maximum electrical power of a steam turbine unit when operating in condensing mode compared to a similar CCGT unit without switching the LP steam supply, and the efficiency of the steam turbine and the entire CCGT unit.

3 cl, 1 dwg

Description

The invention relates to power engineering and can be used on condensing and heating steam turbines of two or more pressures.

Known, accepted as a prototype, are steam turbine units as part of combined cycle gas units, operating in a block with a waste heat boiler, having only one point for supplying steam to the low pressure circuit from the waste heat boiler (Book “Steam turbines and turbine units of the Ural Turbine Plant”, 3rd edition , under the general editorship of Yu.M. Brodov and A.Yu. Kultyshev, 2017, p. 41, Fig. 2.2). The disadvantage of such solutions is that in winter, along with a decrease in the electrical power of gas turbine units (GTU), there is also a decrease in the efficiency and steam output of the waste heat boiler, resulting in a decrease in the power of the steam turbine, and a general decrease in the power and efficiency of the entire combined cycle gas plant (CCP). . At the same time, CCGT-CHP plants equipped with heating turbines and waste heat boilers without afterburning devices, during the period of highest heating loads, are forced to maintain the most optimal operating mode of the CCGT unit with reference to the process of steam expansion in the flow part of the steam turbine, to the detriment of the potential for increasing cogeneration and increasing efficiency cycle.

One of the key features of waste heat boilers (HRBs) compared to energy boilers is that HRSGs almost always operate in off-design modes, because in most cases, they are a “passive” part in energy production and depend on the parameters of the exhaust gases behind the gas turbine plant. Taking into account the year-round operation of CCGT units in a wide range of outside air temperatures (in some regions from -40°C to +40°C), the temperature of the flue gases along the waste heat boiler path changes significantly and forced maintenance of steam pressure in the drums leads to a decrease in steam production, especially in low pressure circuit. (Book “Gas turbine and combined cycle power plants”, Tsanev SV. MPEI, 2002, p. 314).

By reducing the water pressure in the heating surfaces of the waste heat boiler (low pressure circuit), deeper utilization of the heat of the flue gases is achieved. (Book “Steam turbines and turbine installations of the Ural Turbine Plant for CCGT Units”, under the general editorship of A.Yu. Kultyshev. Yekaterinburg, 2015, p. 11).

This phenomenon becomes most relevant for turbines with district heating extractions, where, due to the increased steam flow, a larger amount of steam that has passed through the cogeneration cycle enters the low-pressure circuit of the turbine, and then into the heating extractions, and thus, an increase in the efficiency of thermal energy production is achieved ( Book “Gas turbine and combined cycle thermal power plants”, MPEI, 2002, formula 9.15 on page 393, and 9.51 on page 419).

However, in known CCGT schemes, significant uncoupled changes in steam pressure between the high pressure (HP) and low pressure (LP) circuits of the waste heat boiler are not allowed, because this leads to off-design modes of steam flow in the blade channels of the turbine flow section and significantly reduces the internal efficiency of the compartments, and, accordingly, the turbine power. (Book “Thermal Power Plants”, Ryzhkin V.Ya., M., Energoatomizdat, 1987, pp. 58-61).

To avoid the occurrence of this phenomenon in the flow part of the turbine, as well as to increase the efficiency of the waste heat boiler, solutions were developed with the installation of a two-stage burner (Book “Gas turbine and combined cycle thermal power plants”, Tsanev SV., MPEI, 2002, p. 420). The disadvantage of this solution is that it is more expensive and complex to manufacture and operate compared to the proposed invention.

The technical problem to which the claimed invention is aimed is a general decrease in the efficiency, economy and power of the CCGT unit, and in particular the waste heat boiler and the power of the steam turbine, when the equipment operates during periods with a significant deviation in outside air temperatures relative to the accepted design value, on the basis of which The design of the main equipment for the nominal operating mode is carried out.

The technical result of the claimed invention is to achieve higher annual thermal efficiency of the CCGT unit, reduce the specific heat consumption for electrical energy generation, increase the maximum electrical power of the steam turbine unit when operating in condensing mode compared to a similar CCGT unit without switching the LP steam supply, increase the efficiency of the steam turbine and throughout PSU.

In addition to increasing the efficiency of CCGT operation in heating modes, while maintaining high economic indicators when operating in condensing modes, the following advantages are achieved:

- improvement of the annual thermal efficiency indicators of CCGT units;

- the possibility of eliminating the afterburning device to optimize operating modes in winter, and a corresponding reduction in capital and operating costs, as well as simplifying the design of the waste heat boiler;

- increasing the supplied thermal load of the turbine from the heating plant using the cogeneration principle;

- fuel economy.

The highest economic effect is achieved by implementing this technical solution at a CCGT with cogeneration steam turbines, which provide for operation both in backpressure modes and with full steam passage into the condensing unit.

The technical result is achieved by the claimed steam turbine installation, which includes a steam turbine of two or more pressures, connected by pipelines to the pressure circuits of the waste heat boiler. A distinctive feature of such a steam turbine installation is that in the steam turbine there are two chambers for supplying steam to the low-pressure circuit through one stage, or a group of stages from each other, and the supply of low-pressure steam to these chambers is carried out through pipelines with control devices. The supply of low pressure steam to the steam supply chambers of the LP circuit can be carried out either through individual pipelines with an installed group of shut-off and control valves, or through a pipeline and a three-way valve device rigidly connected to the cylinder body, for example, by welding. Switching the location of the low pressure steam supply from the waste heat boiler is carried out depending on the values of steam pressure in the low pressure circuit of the waste heat boiler and along the flow path of the turbine.

During the development of the invention, a double-circuit CCGT unit without an afterburning device with a heating steam turbine and two-stage heating of network water was considered as a basic example of the application of this technical solution.

Depending on the expected operating mode, the supply chamber is switched: in the condensing operating mode (heating unit is turned off, increased pressure in the LP circuit of the waste heat boiler), LP steam is supplied to the upper supply chamber; in heating mode of operation (with steam supplied to boilers), low pressure steam is supplied to the lower supply chamber.

The claimed solution can also be applied to condensation-type turbines as part of CCGT units, which also do not require the use of afterburning devices. At the same time, the greatest economic effect will be achieved in regions where CCGT units are located with significant fluctuations in outside air temperatures throughout the year (for example, regions of sharply continental and subarctic climates).

The efficiency of the operating modes of the entire CCGT unit throughout the year will be increased both due to a more optimal process of steam expansion in the flow part of the turbine in condensing operating modes in the summer, and on heat consumption in the winter due to an increase in the supply of thermal energy and a more optimal operating mode of the boiler -utilizer depending on the outside air temperature. In this case, the total economic effect from the application of the claimed invention, taking into account the operational characteristics of the CCGT unit, can be calculated using a well-known method (Book “Gas turbine and combined cycle power plants”, Tsanev S.V., MPEI, 2002, p. 414).

The calculations performed for the project of the cogeneration steam turbine Tp-96/185-9.5, intended for operation as part of a double-circuit CCGT unit, showed an increase in the efficiency of the steam turbine up to 6% of electrical energy generation from thermal consumption in the event of a decrease in pressure in the LP circuit and switching of the location of the steam supply compared to a similar CCGT with a decrease in steam pressure in the LP circuit without switching the supply location.

During the patent information search, no information was identified that became publicly available in the world before the priority date, which contains a set of essential features specified in the independent claim of the claimed invention. Consequently, the claimed invention meets the patentability criterion of “novelty”.

In the course of the analysis of known steam turbine plants, including steam turbines of two or more pressures, carrying out calculations and non-standard methods for solving problems, a fundamentally new thermal circuit was developed with variable pressure of the LP circuit of the waste heat boiler, and a switchable location for supplying LP steam to the flow part of the steam turbine, which led to an unexpected technical result. Thus, the claimed solution meets the patentability criterion of “inventive step”.

The claimed invention can be implemented on condensing and heating steam turbines of two or more pressures. This is most relevant for highly efficient CCGT units operating in the basic mode (in winter - with rated electrical and heating loads, in summer - with maximum electrical power). Therefore, the solution meets the patentability criterion of “industrial applicability”.

The claimed invention is illustrated by the attached figure, which shows an example of the implementation of a thermal circuit of a steam turbine installation with the supply of LP steam to the steam supply chambers of the LP circuit through individual pipelines with an installed group of shut-off and control valves.

The following positions are indicated on the figure:

1 - steam supply to the HP circuit;

2 - steam supply to the LP circuit;

3 - block of HP stop and control valves;

4 - block of LP stop and control valves;

5 - high pressure cylinder of a steam turbine;

6 - group of shut-off and control valves on the pipelines to the steam inlet pipes of the low pressure steam supply chambers;

7 - stage compartment in front of the upper LP steam supply chamber;

8 - intermediate group of steps between the LP steam supply chambers;

9 - stage compartment behind the lower LP steam supply chamber;

10 - upper heating water heater;

11 - lower heating water heater;

12 - boiler condensate cooler;

13 - return network water;

14 - direct network water;

15 - condensation unit;

16 - main condensate.

The steam turbine plant includes a two-pressure steam turbine, a waste heat boiler and auxiliary equipment. Auxiliary equipment consists of a condensing unit 15, an upper 10 and lower 11 network water heater, a boiler condensate cooler 12. When a steam turbine unit is operating with the heating unit turned on, the condensate of a pair of network heaters after the boiler condensate coolers 12 is pumped into the main condensate line 16. The main condensate 16 is supplied into the gas condensate heater (GCH) of the waste heat boiler. The steam turbine is connected by pipelines to the high and low pressure circuits of the waste heat boiler, through which steam is supplied to circuit HP 1 through the block of stop and control valves HP 3 and steam is supplied to circuit LP 2 through the block of stop and control valves LP 4. In the high pressure cylinder 5 steam turbine there are two chambers for supplying steam to the LP circuit: after the stage compartment 7 there is an upper chamber for supplying LP steam, then along the flow path there is an intermediate group of stages 8, immediately behind which there is a lower chamber for supplying LP steam. On the LP steam supply pipelines near the high pressure cylinder 5, a group of shut-off and control valves 6 is installed, which passes and regulates the steam supply to the steam inlet pipes of the low pressure steam supply chambers, and switches the location of the low pressure steam supply from the waste heat boiler depending on the steam pressure values in the low pressure circuit of the waste heat boiler and along the turbine flow path.

The claimed invention works as follows.

1. The turbine operates in condensing mode without releasing steam to the upper 10 and lower 11 heating water heaters. At the same time, pressure is provided in the low pressure circuit of the waste heat boiler

Where - pressure in the upper steam supply chamber LP;

- reserve pressure for the resistance of the LP steam supply pipeline and some excess pressure corresponding to the design characteristics of the turbine flow path.

The supply of steam to circuit HP 1 from the waste heat boiler is carried out through the block of stop-control valves HP 3 to the high-pressure cylinder 5, and the supply of steam to circuit LP 2 is carried out through the block of stop-control valves LP 4 to the upper chamber of the steam supply LP, in which the flow-through design parts provide nominal pressure

2. When the outside air temperature decreases and the heating plant is turned on (steam extraction to the upper 10 and lower 11 network heaters), a natural decrease in the temperature of the flue gases behind the gas turbine occurs, which leads to a decrease in pressure or steam production in the circuits of the waste heat boiler. For multi-circuit HRSGs, it is planned to install individual groups of electric feed pumps (FEP), which provide the necessary pressure in the drum of the corresponding circuit. Taking into account the high energy value of steam, the pressure in the HP circuit is maintained close to the nominal pressure, and in the LP circuit the pressure is set by means of frequency control of the LP PEN

Where - pressure in the lower steam supply chamber LP;

ΔР ₂ is the pressure reserve for the resistance of the LP steam supply pipeline and some excess pressure corresponding to the design characteristics of the turbine flow path.

3. The procedure for switching the LP steam supply from the upper chamber to the lower chamber is carried out in the following order.

The heating installation is turned on with the minimum pressure in the lower heating chamber set. Then, an automated process control system supplies a control signal to the frequency regulator PEN ND, and at the same time a control signal to the electrohydraulic control and protection system (ECSRiP) of the steam turbine to a group of shut-off and control valves on the pipelines to the steam inlet pipes of the low-pressure steam supply chambers 6 to close the valve at the steam inlet into the upper supply chamber and opening the valve at the steam inlet into the lower LP steam supply chamber when the specified conditions for the pressure difference ΔР ₁ and ΔР ₂ are met between the pressures in the LP circuit and in the corresponding chambers of the turbine flow path. Then, in normal mode, the steam turbine unit is controlled based on heat consumption. An increased amount of low-pressure steam is activated in the stage compartment behind the lower steam supply chamber ND 9, after which it is partially taken to the upper network heater 10, to the lower network heater 11, and the rest is sent to the condensing unit 15. Return network water 13 is sequentially supplied to the cooler condensate from 12 boilers, then to the lower 11 and upper 10 network water heaters. From the top 10 of the network water heater, direct network water 14 comes out for heating and hot water supply needs.

4. The procedure for switching the LP steam supply from the lower chamber to the upper one is carried out in the following order.

The heating installation is turned off. Then, an automated process control system supplies a control signal to the frequency regulator PEN ND, and at the same time a control signal in the ECHSRiZ of the steam turbine to the group of shut-off and control valves on the pipelines to the steam inlet pipes of the low pressure steam supply chambers 6 to open the valve at the steam inlet into the upper supply chamber and closing the valve at the steam inlet into the lower LP steam supply chamber when the specified conditions for the pressure difference ΔР ₁ and ΔР ₂ are met between the pressures in the LP circuit and in the corresponding chambers of the turbine flow path. Then, in normal mode, the steam turbine unit is controlled in condensing operating modes.

Thus, the claimed invention makes it possible to implement a circuit design of a combined cycle gas plant with variable pressure in the LP circuit and improve the level of technology in the domestic industry.

Claims (3)

1. A steam turbine installation, including a steam turbine of two or more pressures, connected by pipelines to the pressure circuits of a waste heat boiler, characterized in that the steam turbine has two chambers for supplying steam to a low-pressure circuit through one stage, or a group of stages from each other, low pressure steam is supplied to which is carried out through pipelines with control devices that switch the location of the low pressure steam supply from the waste heat boiler depending on the steam pressure values in the low pressure circuit of the waste heat boiler and along the flow path of the turbine. 2. Steam turbine installation according to claim 1, characterized in that low pressure steam is supplied to the steam supply chambers of the low pressure circuit through individual pipelines with an installed group of shut-off and control valves. 3. Steam turbine installation according to claim 1, characterized in that low-pressure steam is supplied to the steam supply chambers of the low-pressure circuit through a pipeline and a three-way valve device rigidly connected to the cylinder body.

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