RU2529296C2 - Two-rotor air compressor for combined-cycle plants - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: two-rotor air compressor for combined-cycle plants is proposed, its common housing hosts a low-pressure rotor coupled with a recovery steam turbine set on the side of the atmospherical air suction into the compressor and a high-pressure rotor coupled with a gas turbine set on the compressor discharge side. The air compression rate in the low-pressure compressor ε₁ is defined on the condition that the recovery steam turbine output is equal to the low-pressure compressor output, and the air compression rate in the high-pressure compressor ε₂ is equal to $${\epsilon }_2=\raisebox{1ex}{$\epsilon $}\!\left/ \!\raisebox{-1ex}{${\epsilon }_1$}\right.,$$

where ε stands for the total rate of air compression in the two-rotor compressor.

EFFECT: invention is aimed at increasing the maximal output of combined-cycle plants.

3 dwg

Description

The invention relates to the field of power engineering and, in particular, to the problem of improving the equipment of combined cycle plants (PTU).

A steam-gas unit is known, which is a mechanical combination of a gas turbine unit (GTU) and a steam turbine unit (PTU) using water vapor generated in a waste heat boiler based on the heat of gases leaving a gas turbine (Tsanev S.V., Burov V.D., Remizov AN Gas-turbine and steam-turbine installations of thermal power plants. M., MEI Publishing House, 2002).

The main task solved by the present invention is to increase the ultimate power of combined cycle plants (CCGTs) made on the basis of single-shaft CCGTs with one electric generator and one gas turbine, which entails a decrease in specific mass and size indicators, the cost of capital costs when creating these CCGTs.

With the indicated combination of gas turbine and steam turbine installations, the main disadvantage of gas turbines, consisting in the low value of the coefficient of useful work, remains. more than half the power of the gas turbine is spent on the compressor drive, and with an increase in the initial temperature of the gases in front of the gas turbine, which increases the efficiency of the gas turbine, there is a decrease in the coefficient of useful work, because an increase in the initial temperature entails an increase in the optimal degree of air compression in the compressor. As a result, almost all energy gas turbines operate at reduced, against optimal values, degrees of air compression, which leads to a decrease in the thermodynamic efficiency of gas turbines. However, in this case, the useful work of a gas turbine does not exceed 50% of the power developed by a gas turbine.

In other words, a gas turbine is the only engine where half of all the power generated by a gas turbine is spent on its own needs.

When using a gas turbine in a gas turbine circuit, part of the power lost by the gas turbine to the compressor drive is returned in the form of power generated by the steam turbine based on the utilization of the relatively low potential heat of the gases leaving the gas turbine.

From a thermodynamic point of view, such a scheme for utilization of thermal energy is not entirely successful, because To ensure their own needs (compressor drive), the high-temperature potential of the working fluid is used, and the generation of additional useful power occurs at a lower temperature level.

In addition, the low efficiency of GTU ultimately leads to a significant limitation of the maximum useful power of these plants.

Now these GTU capacities do not exceed 350 MW. Recall that the ultimate power of steam turbine plants has long exceeded 1000 MW at significantly lower (2-2.5 times) initial temperatures of the working fluid (steam).

As a result, the limiting capacities of technical and vocational schools on the basis of a single gas turbine do not exceed 550 MW, and while maintaining the existing schemes of technical colleges, these power values cannot be exceeded.

In addition, most modern vocational schools with a single gas turbine are twin-shaft, where not only gas, but also steam turbines are used to drive electric generators. The use of two generators inevitably increases the cost and weight and size characteristics of technical and vocational schools.

This disadvantage is absent in single-shaft vocational schools with a linear arrangement of equipment, shown in figure 1.

The following notation is used in this figure.

Figure 1:

1 - steam supply to the recovery steam turbine

2 - recovery steam turbine

3 - release coupling

4 - compressor

5 - combustion chamber

6 - gas turbine

7 - capacitor

8 - thrust bearings

9 - thrust bearings

10 - line exhaust gas to the waste heat boiler

11 - air supply line to the compressor

12 - generator.

As follows from the above layout of the main equipment, in this case, the electric generator 12 is located between the gas turbine unit, consisting of a gas turbine 6 and compressor 4, and a steam turbine 2, and the steam turbine 2 is connected to the shaft of the electric generator 12 using a split clutch 3.

Single-shaft vocational school works as follows.

When starting the gas turbine 6 (Fig. 1), the disconnect clutch 3 disconnects the steam turbine from the compressor 4 and the starting device spins the gas turbine 6 together with the compressor 4, thereby creating air movement through the flow parts of the compressor and turbine.

When the air pressure in front of the gas turbine is equal to 2 ÷ 3 bar, the ignition is turned on and the combustion chamber 5 enters into operation, which ensures the gas turbine goes to idle mode and then connects the generator 12 to the electric network. Hot gases after the gas turbine are sent to a waste heat boiler (the boiler is not shown in figure 1), which generates steam entering the steam turbine along line 1. After its heating, the turbine goes to operating speed (3000 rpm) and after synchronization with the speed a gas turbine using a trip clutch 3, the steam turbine 2 is connected to the generator 12. Next, the speed of the entire unit is synchronized with the frequency of the network and the generator is connected to the network. Through the influence of the control system on the fuel supply, the electrical load of the entire unit is set.

Compared to the multi-shaft configuration, the single-shaft circuit of the PTU has a significantly greater compactness, and its undoubted advantage is the presence of only one electric generator.

In this case, however, single-shaft vocational schools have limited power, because exclude the possibility of parallel connection of two or more gas turbines. In addition, the trip clutch 3 (figure 1) has significant limitations on the amount of transmitted power.

For these reasons, the maximum power of a single-shaft technical and vocational school with a release clutch is at the level of 60 MW.

The disadvantages of the considered technical specifications also include the complexity and very high cost of the coupler, commensurate with the cost of the electric generator.

The installation cost also increases as a result of the use of a non-standard electric generator with two-way connection of power units.

GENERAL ELECTRIC uses single shaft systems without a coupler. In this case, the power of single-shaft anti-tank missiles increases, however, their mobility is lost and difficulties arise in ensuring the vibration reliability of a single long rotor of the installation.

The noted drawbacks are absent in the vocational school scheme considered in the patent GE EP 1245805 A2 F02C 6/00 02/10/2002. In this case, the gas turbine compressor consists of two independent parts - a low pressure compressor connected to a steam turbine and a high pressure compressor connected to a gas turbine.

The above solution not only retains all the advantages of single-shaft gas turbines, but also allows to reduce the power of the gas turbine starter and significantly improves the operation of the gas turbine in variable modes, since in the considered solution the change in the power of the gas turbine is achieved not only by changing the initial gas temperature in front of the gas turbine, but due to the ability to change the speed of a steam turbine connected to a low-pressure compressor in a wide range and change the flow rate of air entering the combustion chambers of a gas turbine.

A serious drawback of the proposed solution is the spatial separation of the low-pressure compressor into an independent steam-turbo-compressor unit, since this loses the compactness inherent in a single-shaft anti-friction unit, additional difficulties are created in the air supply from the low-pressure compressor to the high-pressure compressor, which ultimately causes a noticeable increase in pressure losses in the gas-air installation path.

The noted disadvantages can be eliminated by using twin-shaft compressors, which are widely used in aircraft gas turbine engines, but are absent in power engineering. Closest to the proposed invention is a twin-shaft compressor, shown in figure 2 (Skubachevsky G.S. Aircraft gas turbine engines, structures and calculation of parts. M: Mechanical Engineering, 1981, 552 S.).

Figure 2:

13 - low pressure compressor (LPC)

14 - high pressure compressor (HPC)

15 - internal shaft of the compressor

16 - external shaft of the compressor.

It consists of a low-pressure compressor 13, which is driven by the inner shaft 15, and a high-pressure compressor 14, connected to the outer shaft 16. A distinctive feature of all known two-rotor aircraft compressors is that both compressors: low pressure compressor (LPC) and compressor high pressure (HPC) are driven in rotation from a single twin-shaft gas turbine located on one side of a two-rotor compressor (Chigrin BC, Tikhomirov AE Design and layout schemes of gas turbine engines. Kharkov: VAIU, 1991, 26 pp.).

The disadvantages of such a two-rotor compressor are the impossibility of its use in combined-cycle plants with a dedicated steam-turbocompressor unit while maintaining the basic layout of single-shaft technical and vocational schools, the structural complexity and the inability to change the RPV speed regardless of the RPM speed.

These disadvantages of the prototype, as well as the above-mentioned disadvantages of single-shaft PTUs, are easily eliminated by using a two-rotor compressor with rotor drive from two independent turbines - steam and gas, located on both sides of the compressor, as shown in figure 3, where the following notation is adopted:

Figure 3:

1 - steam supply line to the recovery turbine

2 - recovery steam turbine

5 - combustion chamber

6 - gas turbine

7 - capacitor

8 - thrust bearings

9 - thrust bearings

10 - line exhaust gas to the waste heat boiler

11 - air supply line to the compressor

12 - generator

13 - low pressure compressor (LPC)

14 - high pressure compressor (HPC)

17 - line for supplying air to the HPC when starting a gas turbine

18 - rigid coupling.

где εIn the above scheme, a low-pressure compressor 13 of a single two-rotor compressor is driven by a steam turbine 2, and the high-pressure compressor 14 uses part of the gas turbine 6 power for its work. As in the prototype (Patent GE EP 1245805 A2, F02C 6/00, 10/02/2002) the rotors of the HPH and gas turbine are a single rotor of a gas turbine installation. In this case, the degree of air compression in the low-pressure compressor ε ₁ is determined from the condition that the power of the utilizing steam turbine is equal to the power of the low-pressure compressor, and the degree of air compression ε in the high-pressure compressor ε ₂ is $${\mathrm{<figure-callout\; id="2"\; label="\epsilon "\; filenames="00000005.png,00000007.png"\; state="\{\{state\}\}">\epsilon </figure-callout>}}_2=\frac{\epsilon }{{\epsilon }_{\mathrm{one}}},$$

where ε

- the total compression ratio in the compressor.

With this design of the compressor, all the advantages of a single-shaft PTU, made according to the scheme depicted in figure 1, and the advantages that the PTU considered in the above patent have, without the inherent disadvantages of these schemes, are preserved. in the new vocational school there is no disconnect clutch and there are no additional hydraulic resistance between the low and high pressure compressor.

In addition, when a new two-rotor compressor with two-sided drive of its rotors is used in a vocational school, the rotational speed of the rotor of the low-pressure compressor associated with a steam turbine can be either greater or less than 50 Hz, since this unit is not connected to an electric generator.

The technical result of the invention is as follows.

1. The use of a two-rotor compressor allows you to dramatically increase the capacity of combined cycle gas turbines based on one gas turbine while maintaining all the advantages of a single-shaft layout of the main equipment.

2. The separation of the compressor rotor into two parts with the drive of the low pressure stages from the steam turbine provides the ability to change the speed of these stages in a wide range, which allows either to sharply increase the compressor performance while reducing its rotor speed from 50 Hz to 25 Hz, or to reduce it metal consumption with increasing frequency up to 75-100 Hz.

3. Separation of a single rotor of single-shaft plants into two parts using a two-rotor compressor significantly increases vibrational reliability.

Thus, an axial compressor for combined cycle plants is proposed, comprising a single housing, inside which is located the rotor of the low-pressure compressor and the rotor of the high-pressure compressor with corresponding guide devices, thrust bearings and thrust bearings, characterized in that the compressor rotors are driven by fundamentally different turbines - steam and gas located on different sides of the compressor (steam - from the intake side of atmospheric air, and gas - from the discharge side), m degree of air compression in the low pressure compressor ε ₁ is determined from the condition that the capacity utilization of the steam turbine power the low pressure compressor, and the degree of air compression in the compressor high

где ε - общая степень сжатия воздуха в двухроторном компрессоре.pressure ε ₂ is equal to $${\mathrm{<figure-callout\; id="2"\; label="\epsilon "\; filenames="00000005.png,00000007.png"\; state="\{\{state\}\}">\epsilon </figure-callout>}}_2=\raisebox{1ex}{$\epsilon $}\!\left/ \!\raisebox{-1ex}{${\epsilon }_{\mathrm{one}}$}\right.,$$

where ε is the total degree of air compression in the two-rotor compressor.

Such a solution allows increasing the rotational speed of the low-pressure compressor rotor to 75 ÷ 100 Hz at air flow rates not exceeding the maximum flow rates in existing powerful gas turbines, which dramatically reduces the overall dimensions of the steam turbo compressor unit.

At high air flow rates exceeding its marginal flow rates in existing single-shaft compressors, to pass air through the first stages of the low-pressure compressor, the rotational speed of the low pressure rotor should be reduced to 25 Hz in order to increase the allowable from the standpoint of strength passage areas of the first compressor stages.

Claims (1)

An air two-rotor compressor mainly for combined cycle plants, containing a single housing, inside which there is a rotor of a low-pressure compressor and a rotor of a high-pressure compressor with corresponding guide devices, thrust bearings and thrust bearings, characterized in that the compressor rotors are driven by fundamentally different turbines - steam and gas located on different sides of the compressor (steam - from the intake side of atmospheric air, and gas - from the discharge side), moreover, the compression ratio of air in the low-pressure compressor ε ₁ is determined from the condition of equality of power of the recovery steam turbine power of the low-pressure compressor, and the compression ratio of air in the high-pressure compressor ε ₂ is equal to $${\epsilon }_2=\raisebox{1ex}{$\epsilon $}\!\left/ \!\raisebox{-1ex}{${\epsilon }_{\mathrm{one}}$}\right.,$$

where ε is the total degree of air compression in the two-rotor compressor.

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