GB2479001A

GB2479001A - Compressor with atomised cryogenic liquefied gas injection

Info

Publication number: GB2479001A
Application number: GB201005169A
Authority: GB
Inventors: Edward Christopher Atkinson
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2010-03-26
Filing date: 2010-03-26
Publication date: 2011-09-28
Also published as: GB201005169D0

Abstract

A compressor and a method of operating a compressor 4 comprising at least one compression stage, wherein a cryogenic liquefied gas is atomised internally of the compression stage so as to reduce the temperature of the gas being compressed. The primary gas may be air which contains water vapour and the cryogenic liquefied gas can be liquid air or liquid nitrogen. Preferably the compressor is a rotary compressor with a plurality of stages which may be used in the generation of power such as part of a gas turbine engine 2. The cryogenic liquefied gas may be injected continuously or only during periods of peak power demand. A flow control valve 22 may be located in the cryogenic liquefied gas pipeline 20 before the atomiser 26 and the flow control value responds to a temperature sensor 24 which measures the temperature of the gas to be compressed.

Description

COMPRESSORS

This invention relates to a method of operating a compressor, particularly an air compressor, and to the compressor itself.

It has long been known that the performance of an air compressor (or a compressor of any gas) decreases with increasing inlet temperature. It is therefore difficult to maintain at relatively high ambient temperatures the performance of plant which depends on the air compressor. A notable example of this problem arises in a cryogenic air separation plant for separating air by rectification. The rate of production of the products of separation have been found to fall markedly with increasing ambient temperature. A second notable example is in the operation of a gas turbine.

The power generated by the gas turbine is found to fall markedly with increasing ambient temperature.

According to EP-A-O 855 518 there is provided a method of controlling the inlet temperature of an air compressor, comprising the step of vaporising in the air upstream of its entry into the compressor a sufficient flow of cryogenic liquid to maintain the inlet temperature at or below a chosen value, wherein the cryogenic liquid is nitrogen or comprises a mixture of oxygen and nitrogen.

EP-A-O 855 518 also provides apparatus for controlling the inlet temperature of an air compressor, comprising the air compressor and a * mixing chamber having an outlet communicating with the air compressor, a first inlet communicating with the atmosphere, and a second inlet * communicating with a source of liquid nitrogen or a source of cryogenic liquid comprising oxygen and nitrogen. * 30 S. * * S *

* A potential disadvantage of the method and apparatus according to EP-A-O 855 518 is the local formation of the particles in the mixing chamber.

Such ice particles may be of sufficient size to endure in particulate form within the compressor and to be therefore a potential source of damage to rotary parts of the compressor.

According to the present invention there is provided a method of operating a compressor comprising at least one compression stage to compress a primary gas, including the step of atomising a cryogenic liquefied gas internally of the said compression stage so as to reduce the temperature of the primary gas being compressed.

The invention also provides a rotary compressor comprising at least one compression stage for compressing a primary gas, the rotary compressor having an inlet for a primary gas to be compressed, the said compression stage having at least one atomiser communicating with a source of a cryogenic liquefied gas, the said atomiser having an outlet communicating directly with an internal volume of the said compression stage upstream of a rotor of the compressor.

The method and compressor according to the invention are particularly suitable for operating a compressor to compress a primary gas which typically carries water vapour and which is introduced into the compressor at a temperature of at least 10°C and typically in the range from 15 to 50°C. The primary gas may be air. *S

The compressor may be used in the generation of power. For S..

* example, it may form part of a gas turbine. *. ** *e S * *

The compressor typically comprises a plurality of compression stages.

One or more of the compression stages may be selected for the introduction of the atomised cryogenic liquefied gas. The selected compression stage * may be the most upstream stage, but, if desired, atomised cryogenic liquefied gas may be introduced into one or more downstream stages. The atomised cryogenic liquefied gas may be introduced intermittently into the or each compression stage.

The cryogenic liquefied gas may be formed by liquefaction of a permanent gas during periods of relatively low power demand and used in the method and apparatus according to the invention during periods of higher power demand. The atom ised cryogenic liquefied gas has the effect of reducing the temperature of the primary gas. As a result, more power can be generated for example from a gas turbine of which the compressor forms a part.

If the primary gas is air, the cryogenic liquefied gas is preferably also (liquid) air. The air may be liquefied directly, or a synthetic liquefied air may be formed by mixing liquid oxygen and liquid nitrogen. In the example of the primary gas being air, it is also possible to use liquid nitrogen as the (sole) cryogenic liquefied gas.

The atoniiser may comprise a nozzle having a suitable atomising configuration. In general, the finer the particle size produced, the less is the risk of Iocalised freezing of any water vapour in the primary gas. Because the cryogenic liquefied gas is atomised in compressor itself, the period of time in which any localised particles of ice, which may cause damage to rotary part of the compressor, can be formed is kept down in comparison with operation of the method and apparatus according to EP-A-855 518. Moreover, the atomised particles of cryogenic liquefied gas tend to vaporise almost s...

* instantaneously, thereby minimising the risk of damage to rotary parts of the compressor as a result of impact of such particles against such rotary *. particles. ***.

The cryogenic liquefied gas may be pressurised in order to achieve a * desired degree of atomisation and to overcome the pressure at the injection point in the compressor. For example, the cryogenic liquefied gas may be raised in pressure to 20 to 50 bar upstream of its atomisation.

In the example of operation of a gas turbine a part of the flow of the air to the compressor may be bled off to form a feed to a liquefier in which the liquefaction of the cryogenic liquefied gas is performed.

The rotary compressor according to the invention may include a flow control system operatively associated with a temperature sensor. The temperature sensor may be arranged to sense the temperature of the primary gas, for example, upstream of its compression in the selected compression stage. Such an arrangement enables excessive cooling of the primary gas by the atomised cryogenic liquefied gas to be avoided, for example, by holding constant the outlet temperature of the selected compression stage. In one example of a suitable flow control system there may be a flow control valve in a pipe along which the cryogenic liquefied gas is fed to the atomiser, the flow control valve being operatively associated with a temperature sensor arranged so as to sense the temperature of the primary gas upstream of its compression in the selected compression stage.

In another example, the compressor may form part of an air separation plant.

The method and apparatus according to the present invention will now * S S...

be described by way of example with reference to the accompanying drawing * ** * .* * which is a schematic flow diagram of a plant for the generation of electrical power including a turbine having a compressor adapted for operation in accordance with the invention. * S*.

Thedrawingisnottoscale.

Referring to the drawing, the illustrated plant has a gas turbine comprising an air compressor 4, a combustion chamber 6 and a turboexpander, otherwise known as an expansion turbine 8. The compressor 4 draws in air, in operation, and send compressed air, typically at a pressure of 20 to 40 bar, to a combination chamber in which it is used to support combustion of fuel, for example a fuel gas or a fuel oil. Resulting gaseous combustion products flow into the expansion turbine 8 with the performance of external work, in this case the driving of an alternator forming part of generator 10 of electrical power.

The air compressor 4 typically has a plurality of rotary compression stages and an in inlet 12 for air. If desired, the most upstream compression stage may be selected for the introduction of atomised cryogenic liquefied gas, but instead or in addition, one or more of the other compression stages may be so selected.

Most aspects of the configuration and operation of the gas turbine 2 and the generator 10 are well known to those versed in the art of power generation. The ensuing description will therefore be confined to those aspects which are not known.

The illustrated plant also includes an air liquefier 14. The components, arrangement and operation of the air liquefier may be as described with reference to the drawing accompanying EP-A-856 713 (which is incorporated into this document by way of reference). * *

The resulting liquefied air is stored in at least one storage tank 16. At ** least some of the resulting liquefied air is employed to improve the power * output of the gas turbine 2 either continuously or only for periods of peak demand for electrical power. When the liquefied air is so required a pump 18 * withdraws liquefied air from the storage tank 16 and raises the liquefied air to a pressure suitable for its atomisation (typically, a pressure in the range 2 to bar). The pressured liquid air is sent by the pump 18 along a pipeline 20 to an atomiser 26 which injects atomised liquefied air, typically having a mean particle size of less than 5Opm, into a chamber in the first or other compression stage of the compressor 4 upstream of a first rotor (not shown) thereof. The atomised liquid air encounters air at approximately ambient temperature (typically in the range 10 to 50C). The atomised liquid air vaporises almost instantaneously on contact with the ambient temperature air.

The atomised liquefied air has a cooling effect on the ambient temperature air and reduces its temperature by a chosen amount. As a result of this cooling the maximum electrical power output of the generator 10 is enhanced.

There is typically a flow control valve 22 disposed along the pipeline 20. The flow control valve 22 is operatively associated with a temperature sensor 24 located in the inlet 12 of the air compressor. The arrangement is such that the position of a valve member (not shown) of the flow control valve 22 is adjusted so as to adjust the rate of flow of liquefied air into the air compressor 2 in accordance with variations in the sensed temperature of the ambient air in such a way that excessive cooling of the ambient air is avoided.

If there is, say, a fall in the sensed ambient temperature of the air, the flow control valve 22 automatically reduces the flow rate of liquefied air so as to compensate for this fall and keep the temperature of the cooled air constant.

If on the other hand the temperature of the air rises, the flow control valve 22 automatically increases the flow rate of liquefied air into the air compressor 4.

* **** * * There are various options for the operation of the plant shown in the drawing. Normally the gas turbine 2 and the generator 10 are operated continuously. Similarly, the air liquefier may be operated continuously and resulting liquefied air supplied continuously through the atomiser26 to the air * compressor 4.

Alternatively, the supply of the liquefied air to the air compressor 4 may be intermittent, typically for periods of peak power demand only. In this example, the air liquefier may be sized so as to produce liquefied air at a constant rate less than that at which the liquefied air is supplied to the air compressor in the periods of peak power demand, but sufficient to ensure that the storage tank or tanks 16 are not exhausted of liquid air by the demands of the air compressor 4.

Instead of forming liquefied air, the liquefier 14 may form liquid nitrogen instead. The burners (not shown) associated with the combustion chamber 6 may be adapted to operate with a combustion-supporting gas which contains less than 20.9% by volume-supporting gas which contains less than 20.9% by volume of oxygen so that dilution of the ambient or primary air by the nitrogen will not adversely affect the operation of the gas turbine 2. Typically the nitrogen liquefier is integral with or forms part of a variable demand air separation unit. The advantage of this arrangement is that production of liquid nitrogen can be maximised during periods of lower power demand and minimised during periods of high power demand.

If desired, one of the later stages of compression may additionally or alternatively be selected for the introduction therein of atomised cryogenic liquefied gas. Cooling of the later stages of compression may offer the additional advantage of improving the balance of the compressor and maintaining its surge margin if output is temporarily increased during, say, * I peak operation. * I

If desired, the liquefer 14 and storage tank or tanks 16 may be operatively associated with a further turboexpander (not shown), the liquefied gas pressurised and vaporised at elevated pressure, and the resulting vaporised gas expanded in the further turboexpander with the performance of * external work, which may be the generation of electrical power. Such generation of electrical power may be performed at periods of peak demand for the power. The vaporisation of the liquefied gas may be effected by heat exchange with a source of low grade heat, such as a flue gas, sea water, river water or ambient air. S. * **.*

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Claims

CLAIMS1. A method of operating a compressor comprising at least one compression stage to compress a primary gas, including the step of atomising a cryogenic liquefied gas internally of the said compression stage so as to reduce the temperature of the primary gas being compressed.
2. A method according to claim 1, wherein the compressor comprises a plurality of compression stages and the cryogenic liquefies gas is atomised internally of the most upstream of the compression stages.
3. A method according to claim 1 or claim 2, wherein the compressor comprises a plurality of compression stages and the cryogenic liquefied gas is atomised internally of one or more compression stages downstream of the most upstream compression stage.
4. A method according to claim 1, in which the primary gas carries water vapour.
5. A method according to any one of the preceding claims, in which the primary gas is introduced into the said compression stage at a temperature of at least 10°C.
6. A method according to claim 5, in which said temperature is in * * *.S* the range of 1 5 to 50 C. *..*I* * *
7. A method according to any one of the preceding claims, in which the primary gas is air.
8. A method according to any one of the preceding claims, in which * ** the compressor is used in the generation of power.
9. A method according to claim 8, in which the compressor forms part of a gas turbine.
10. A method according to any one of the preceding claims, in which the cryogenic liquefied gas is liquid air.
11. A method according to any one of claims 1 to 9, in which the cryogenic liquefied gas is liquid nitrogen.
12. A method according to any one of the preceding claims, in which the cryogenic liquefied gas is pressurised upstream of its atomisation to a pressure in the range from 20 to 50 bar.
13. A method according to any one of the preceding claims, in which the cryogenic liquefied gas is atomised and introduced into the said compression stage only during periods of peak power demand.
14. A method according to any one of claims 1 to 12, in which the cryogenic liquefied gas is atomised and introduced into said compression stage continuously.
15. A rotary compressor comprising at least one compression stage for compressing a primary gas, the rotary compressor having an inlet for a primary gas to be compressed, the said compression stage having at least one atomiser communicating with a source of a Cryogenic liquefied gas, the said atomiser having an outlet communicating directly with an internal volume of the said compression stage upstream of a rotor of the compressor.
16. A rotary compressor according to claim 15, wherein the S...compressor comprises a plurality of compression stages and the outlet of the said atomiser communicates directly with an internal volume of the most upstream of the compression stages. -Il-17. A rotary compressor according to claim 15 or claim 16, wherein the compressor comprises a plurality of compression stages and the outlet of the said atomiser communicates directly with an internal volume of one or more compression stages downstream of the most upstream of the compression stages.18. A rotary compressor according to any one of claims 15 to 17, forming part of a gas turbine.19. A rotary compressor according to any one of claims 15 to 18, wherein the said atomiser comprises a nozzle.20. A rotary compressor according to any one of claims 15 to 19, wherein there is a pump for supplying the cryogenic liquefied gas form the source thereof to the atomiser.21. A rotary compressor according to any one of claims 15 to 20, including a flow control valve communicating at one end with the source of the cryogenic liquefied gas and at another end of the atomiser, the flow control valve being operatively associated with a temperature sensor arranged to sense, in operation, the temperature of the primary gas at a chosen location in relation to the said compression stage. * * ***. S.. * .i-'. S. * S S a SI 5'.I a... * I S as S S. I * .. $ .*