WO2017143408A2

WO2017143408A2 - Gas expansion device and method for expanding gas

Info

Publication number: WO2017143408A2
Application number: PCT/BE2017/000011
Authority: WO
Inventors: Henrik Öhman
Original assignee: Atlas Copco Airpower, Naamloze Vennootschap
Priority date: 2016-02-23
Filing date: 2017-02-13
Publication date: 2017-08-31
Also published as: WO2017143408A3

Abstract

Gas expansion device (1) for expanding a gas or a gas-liquid mixture, whereby the gas expansion device (1) comprises a gas expansion element (2) with an inlet port (4) tor the gas to foe expanded and an inlet pipe (5) for the gas to be expanded, whereby the inlet pipe (5) is connected to the inlet port (4), whereby the gas expansion device (1) comprises a first liquid Injection point (13) for the injection of liquid, whereby the first liquid injection point (13) is at a position level with the inlet port (4) or upstream from the inlet port (4).

Description

s ex ns n device and method for. expandina

T present .invention relates to a gas e nsi n device nd method for expanding gas_*

Applications for multiphase fluid expansion- in a volumetric ex ansio element h t is coupled to a generator for electrical energy present a wide range of characteristics and limitations.

In seise applications the pressure and gas compositions are relatively stable over time, which enablas constant operating characteristies and a l w control level,

In other applications the operating conditions can vary su s ant ally, which leads to inefficiency and/or re!lability problems♦ Some pplications, such as pressure reduction stations for natural g s,. generally maintain a constant pressure downstream from the pressure reduction stations but a variable pressure upstream. The constant pressure downstream is needed for the correct distribution of ga to the end customers while the varying pressure upstream is determined by effects such as variations in the supply and an unstabl control.♦

In such cases the energy generated by the expansion device is strongly influenced by the inlet pressure, There are two reasons fo this, Firstly a higher inlet pressure leads to an i c e sed essu e ratio and co sequenti a greater enthalpy drop per unit of ex anded mass, secondly a higher inlet pressure leads to a greater mass low on acc u t of a higher qas densi y.

As it is of vi a importance for the s stem that the downst eam pressure is maintained, the expansion machine isay only expand a mass low that is equivalent to the instantaneous demand for gas at the endpoints of the gae network.

This leads to requi ements for a com le variability of the volu flow at the inlet in a volumetric exp nsio machine with variable inlet pressure.

Existing solutions to control the ol e flow in a volumetric expansion device include VSD, i.e. variable speed drive , flow reductio at the inlet_f and mechanical means to vary the stroke volume of the aia.chi*½«

Flow reduction at the inle means that the density of the gas can be adjusted to control the mass flow that is ex a ded_* The disadvantage is the cleat efficiency loss as the pressure ratio of the expansion device is substantially reduced at all times, except when a mn¾imum flow is required h c is rarely the case.

* To cont ol the stroke volume, a m vable sleeve valve or other lve mechanism that changes the stroke vol me of the machine is generally used. Such s lutio s can foe extremely efficient but are expensive and increase the complexity of the design and thereby o ardise the reliability.

^» & ¥S enables a precise control of the expanded mass volume and also preserves a high efficiency and low design complexity. But the torque of volumetric expansion m c nes is generally little dependent on the speed or even inversely dependent, This means that a VSD generator must be able to operate safely at a low speed and at a high torque, Moreo e , it means that f rces that act on the inside of the vo.lumet.ric^' expansion device will be defined by the nlet r ssure, and not by the generated power. In othe words the forces are directly dependent on the mechanical torque that is produced on the outgoing sha t .

In VSD applications, the risk of a structural overload of the expansion device is clear if the inlet pressure varies upwards. If an overdimensione expansion machine is used, the efficiency will suffer at every inlet pressure i normal operating conditions. If precisely dimensioned expansion device is used, the efficienc will be optimised at a normal inlet pressure* while structural damage can be expected at high peaks in the inlet pressure- Moreover, it is complex and expensive to control the speed in conditions with an exceptionally igh torque and a low speed, A related problem is the ex ensi e and com lex moderations of he problem of too high a speed . When the aking torque is lost, the ex si n m c ine will accelerate quickly and create aza dous operating conditions that jeopardise the reliability of the s stem and wi l result in a excessive su ly to the downstream gas network.

An often used moderation technique is to use quick-closing l es before the expansion devic * such that the mass flow and the torque are effectively cut. off in a fractio of a second.

Such quick-closing valves ca se a temporary vacuus* at the inlet of the expansio device on account of its rotation delay. The vacuum quickly brakes the expansion machine to a stop_* The use of quick-closing valves means very high transient loads o the mechanical sys em,

Moreover, the expansion machine remains out of operation until it is properly controlled, restarts and is synchronised again with the electricity network.

T e loss of braking torque can be due to a broken shaft connection, then a stoppage by a quick-closing valve can be adequate. But it can also foe due to short or long disruptions in the electricity network, an unstable speed control of the VS , or an overload of the brake generator.

The detection of real or supposed emergency situations, for example in auxiliary systems o by m a s of an emergency button, can lead to the need to use quick-closing valves. h s fe? elia le and quick way to limit tho torque in n ex ansi n d vice is h s desira l , and preferably a method that can operate continuousl without losing operating t e of the expansion mach ne, e en if an inlet ressu e is temporarily s o ed,

The purpose of the esen Invention is to provide a solution to the aforementioned and other disadvantages by providing a gas expansion device fo expanding a gas or gas-liquid mixt e, whereby t e gas expansion device comprises a gas expansion element with an inlet port for the ga to be exp ndd and an inlet pipe for the gas to be expanded, whereby the inlet pipe is connected to the inlet port? whereby the gas expansion device comprises a first liquid injection point for the Injection of liquid, whereby the first liquid injectio point is at a position level with the inlet port or upstream from the inlet port., and preferably upstream from the inlet port,

As a result, when too high a torque is detected, liquid can be injected in the gas flow upstream from the inlet port, or level with the inlet port, so that this liquid goes into an expansion chamber together with the gas,

When operating at high speed, the liquid that is injected ensures braking effect on the inlet gas. The energy needed to accelerate the liquid reduces the total pressure of the gaa_;, such that the pressure ratio of the expansion and volumetric inflow of the gas expansion device is reduced. As a result the torque is limited_* hen op&ratiag t l w s e d the liquid that is injected fills a l g proportion of the ch fer volume that w uld otherwise be occupied by inlet gas. Consequently the volumetric inflow of gas is reduced. Th pressure ratio remains res ed but the mass flow is reduced. As a result the or ue is limited.

Furthermore, when an emergency situation is detected that requires a rapid stoppage of the gas expansion device, liquid can he injected upstream from the inlet port.

The liq id then has the effect as described above, hut also substantially reduces the high speed that would otherwise briefly occur. This means that a protection valve, before the expansion device, can be closed with a slower operating speed than would otherwise he the case. Consequently an extremely fast a d expens e quick-closing valve is unnecess y, and a standard valve can e used for this, a p ssibl brief ov lo d does not occur and the gas expansion device is operational again more quickly after an erne e y sitnation .

Such an emergency situation can occur in the event of a technical fault, for exampl a disconnection of the energy n twork to which energy is supplied, or the loss of the mechanic l coupling between the expansion element and the generator, and can be detected in many ways know to a man skilled in the art. ?

Such an e e g nc situation can also occur if an auxiliary ratus, correctly or inco rect , issues an emergency signal, or if a» emergency stop procedure is activated by human intervention or by software«

In a preferred embodiment_* the gas e paneion device is provided with means for starting up or switching off flow of the said liquid to the first liquid injection p int, so that the first liquid injection point can d o otherwise according to eed.

Preferably these mea s are connected to a control urtit to control the ts a s, and the gas expansion element is mechanically coupled to a generator such that the expansion element can drive the generator, whereby the control unit is connected to the generator,

As a result operating conditions and meas red para eters of the generato can h used to control the said means.

Preferably the gas e ansio device is provided with a liquid separator for separating the liquid fross gas that is expand d in the gas expansion element, whereby the first liquid injection point la connected to a liquid outlet of the liquid separ tor, a result the same liquid that haa already been separated f om the gas, normally oil, can be used to supply the first liquid Injection point. Preferably the gas expansion device c m is s- a second liquid injection point that ia configured to inject the said liquid in the gas expansion ele ent at a position downstream from the inlet port, and the gas expansion device is provided with a reservoir or supply pipe for the said liquid, whereby the first liquid injection point and the second liquid injectio point are both connected to this s pl pipe or this reservoir. A a result the same liquid that is normally already injected via the second liquid injection point for cooling and/or lubrication can also [be injected] to the first liquid injection point so that the complexity of the device is reduced.

Preferably the said Mea s com ri e a three-wa valve with three connecting por s, whereby a fi st of the connecting ports is connected to the supply pipe or the reservoir and the other connecting ports are each connected to one of the said liquid injection points,

As a result,, the supply of the second liquid injection point, that is desirable in aoxml o eration, can easily fee diverted to the first liquid injection point if the operation i such that the use of the first liquid injection point is dealtable.

In a preferred embodiment, the first liquid injection point is positioned such that the injection direction is upstream, This ensures a massiimim braking af ect upon the occurrence of a high torque when operating at high speed. ec use tne direction of the liquid must t n be reve sed y the fl i g gas.

The invention urthe o cerns a m t od for ex nding gag in which this q&® is- fuided by g s expansion devic according to th invention, in w ich liquid is only injected via the first liquid injection oint upon the detection of an exceptional operating condition_*

Hereby first threshold value of a torque being exceeded indicates a first exceptional operating condition. is torque ia the torque of mechanically coupled s af s of the generator and the expansion element. This can be measured in various places, or derived in a know way by a man skilled in the art fro othe me sur d values such as speed of rotation and po*#er♦

Hereby the occurrence of an emergency situation that requires the stoppage of the gas expansion device indicates a second exceptional operating condition, for example.

Hereby a threshold value of the speed of rotation of the expansion element being exceeded for example, or a second threshold value of a torque being exceeded, or a first threshold value of generated electric power being exceeded indicates an emergency situation.

Alternatively the invention can foe defined by means of the follow!ng clauses : X. Gas expansion device com ris g a gas expansion lement wi h an inlet port connected to an inlet pipe for pressurised aa_f wh eb the gas expansion device com rises a liquid injectio point that is located before the inlet S port .

2. G s expansion device according to clause I, i which the gas expansion device further comprises a main liquid injection point that is configured to inject iiqnid in the0 gas xpansion element at a location after the inlet port,

3» Gas expansion device according to eleuses X and Z_t in which the liquid i jection point and the main liquid injection point are both connected vi liquid pipe to two5 connectinq po s: of & three-way alve, whereby the third connecting port of th three-way valve is connected to a liquid outlet of a liquid separator connected to the outlet of the gas expansion element. 4» Gas expansion devic according to clauses 1 and 2, in w ich injection control means are provided for controlling the flow of the liquid that is injected via the liquid injectio point and the flow of the liqnid injected via the main liquid in ection point,

5

5. Gas expansio device according to cla ses 3 and 4 in which the control meana comp ise the three-way v lv , β. Gas expansion device according to clause 3, in whichD the three-way valve is connected to a controller_* 7. G s ex ansi n de ice according to cl use 6, in which the controller is further connected to a g ner t r that is connected to the gas expansion element, such that the ex ansion i&iemant can drive the generator,

8, Method for operating a gas e pansion device according to clause 1, in which, the liquid injection s switched o during normal operation ?ia the liquid injection point. 9. Method for operating a gas ex nsion device according to clause 1, in which, w en operating at high speed, th liquid injection via the liquid injection point is activated when the torque or the inlet pressure exceeds a first preset threshold: value,

10. Method for operating gas expansion device according to clause 1, in which, when operating at low speed, the liquid injection via the liquid injection point is activated when the torque or the inlet pressure ex eeds a second preset threshold value,

11, Method fo operating a gas expansion device according to clause 1, in w ich during normal operation the liquid injection via the liquid injection point is activated when it goes below a power or torque limit; or when a speed limit is exceeded. The present invention relates to a method for registering the movements of the limbs: of an articulated foody. With the intention of better eho ing the characteristics of the invention, a preferred embodiment of a gas expansion device .according to t e invention and an accompanying method a e described he i af er toy s y of an m l without any limiting nature,. with reference to the acco yi g drawings_f wherein :

S

figure 1 schematicaliy shows a gas expansio device according to the invention?

figure 2 illnatrates te operating principle of the gas expansion device.

0

In this example the gas expansion device 1 is a double se e*? na ur l gas expansion device wit oil injection to the expansion. 5 However_f the invention can he similarly applied to other types of volumetric expansion machines and oth r fluids than oil and natural gas .

The gaa expansion device s shown in figure 1, com ises0 a dou e screw expansion element 2 and an electricity generator 3 that are mechanically coupled together,

The expansion element 2 campsi& an inlet port for natural gas that is connected to an inlet pipe S forS natural gae, A shut-off valve 6 is provided in the inlet pip 5,

A oil separator 7 for separating oil and gas is provided downstream from the expansion element 2. This has an outlet0 3 for expanded gas and an outlet for oil. The outlet 9 for oil s connec ed via an oil pasap 11 to a first c nn cting t of three-way alve 12.

The two other con ecti g ports of the three-way v lve 12 are co ected to liquid injection points.

More s eci ically this concerns « first liquid injection point 13 that is affixed just upstream from the inlet port 4 in the expansion element 2 or in the inlet pipe 5, and. a second liquid injection point 14 that is affixed downst e m f om the inlet po t .

The first liquid injection point 13 hereby has an injection direction that is opposite to the low direction of the gas.

The gas expansion d vice I is further provided with an electronic control unit 15 that is connected in a data- transferring way to the shut-off val^e &, the three-way alve 12 end the generator 3.

The operation of the gas expansion, device 1 is simple and s follows. In the event of normal operation,, i.e. when a higher torgue than desired is not detected, the three-way valve 12 is set uch that all oil is d ive to the second liquid injection point 14» The operation is then analogous to a traditional gas expansion device. This is schematically shown in figure 2. The horizontal axis indicates the progress of the rotation of a rotor of the expansion element 2. The vertical axis indicates the volume of an expansion chamber.

Hereby the inlet port 4 is open to the expansion chamber between the points indicated by A and B. Just after the inlet port 4 is closed, oil is injected via the second liquid injection point 14, schematically indicated by the interval from point C to point D.

This is done in this way because, for a cost efficient application of a screw expansion device, the peripheral speed of the rotors must be as high as possible. Hence the oil injection to the inlet of the machine must be minimised to limit the friction losses that reduce an optimum filling of the expansion chamber. Hence, the oil injection is generally controlled such that the oil gets in the expansion chamber after the inlet port is closed, when the oil has no further effect on the filling process of the chamber wit gas.

In order to obtain a good effect of the injected oil, it is often injected at high pressure, immediately after the inlet port is closed. The oil pressure is generally higher than the gas pressure at the inlet of the piping, despite the fact that the chamber pressure is reduced immediately after the inlet port closes. In a first exceptional, operating condition, i.e. if a higher than desired torque is measured or calculated in the 25 generator 3 b the control unit IS, the three-way ? .i¥e 12 is set such that all oil flows to the first liquid inj ction point 13_* This has two effects. The first effect is that upon .injection* the oil experiences a narrowing and change of direction doe to the gas flowing past so that the effective inlet pressure of the gas is reduced. The second effect is that the oil flows in the expansion chamber of the expansion element* so that there is less room for the gas. With a high speed of rotation in the first effect will significan ly gain the upper hand and at a low speed of rotation the second effect will significantly g in the upper hand,

In both cases the torque is ed ced so that an overload of the gae e&p&nsion device 1 is e e ted.

In a second exceptt.io.nal operating condition, upon detection of an emergenc situation, the three-way valve 12 is also set such that ell oil flows to the first liquid injection point 13, wit the above~ment.io.ned effects, and additionally the shut-off valve 6 is closed toy the control unit IS, so that the gas expansion device X quickly comes to a stop in a way that does not cause any damage to the gas ex ansion device 1.

In the above, downstream and upstream refer to the flow direction of the gas. he present inve i Is no means lim ted to the sia d me ts described as s example and ehovm in h drawings, but a ga expansion device and method according to the invention a be realised in all ki ds of forms and dimension i hout departing rom the sco e of h I ven ion_*

Claims

Claims..

X. - Gas e a sion devic D fo expanding a gas or a gas- liquid mixture whereby the gas ex ansio device (1) comp ises a g s expansion lem t (2) with a inlet port for the g s to be expanded and an inlet pipe (S) for the as to be expanded, whereby the inlet pipe (5} is connected to the inlet port |4) , whereby the gas expansion. d vice (II comprises a first liquid injection point (13) for the injection of liquid, whereby the first liquid injection point (13) is at a position level wit the inlet port ( ) or upstream from the inlet port (4) ,

2_*~ Gas expansion device (1) according to claim 1, characterised in that the liquid is oil.

3.™ Gas expansion, device (1) according to any one of the previous claims, characterised in that the gas expansion element is a double screw gas expansion ele ent £2) .

4>~ Ga expansio device {1} according to y one of the previous claims, characterised in that it is provided with a Iiguid separator (7) for separating Iiguid from g s that is expanded in the gas exp»9nsion element (21, whereby the first iiguid injectio point. (13) .is connected to a iiguid outlet £$) of the liguid separator (?) >

S.~ Sas expansion device (1) according to any one of the previous claims, characterised in that it is provided with means (12) for starting up and switching off a flow of the said liquid to the first liquid injection point (13) .

6. - Gas expansion device (1) according to claim 5, characterised in that the gas expansion device (1) comprises a control unit (15) to control the said means (12) .

7. Gas expansion device (1) according to claim 6, characterised in that het gas expansion element (2) is coupled to a generator (3), such that the expansion element (2) can drive the generator (3) , whereby the control unit (15) is connected in a data-transf rring way to the generator (3) .

8. - Gas expansion device (1) according to any one of the previous claims, characterised in that the gas expansion device (1) comprises a second liquid injection point {14} that is configured to inject the said liquid into the gas expansion element (2) at a position downstream from the inlet port (4) .

9. - Gas expansion device (1) according to claim 8, characterised in that it is provided with a reservoir or supply pipe for the said liquid, whereby the first liquid injection point (13) and the second liquid injection point (14) are both connected to this supply pipe or this reservoir .

10. Gas expansion device (1) according to claim 9 and any one of the claims 5 to 7, characterised in that the said me ns comprise a hree-w y ^aive {12} with three conn c i g ports^■, whereby a first of e connec in ports is connected to the supply pipe or the reservoir and other connecting ports are each connected to one of the said liquid injection points (13_r 14}♦

11. ~ Gas expansion device 11} according to any one of the reviou claims, characterised in that the first liquid injection point {13} is positioned such that the injection direction of the liquid ia upstream,.

12. Method for ex a ding gas in which this gas is guided by a gas ex sion device 11} according to any one of the previous claims, in which liquid is only injected via the first liquid injection point {13} upon the detection of an excep ion l operating condition.

13 Method according to claim IX, characterised in that a first threshold value of a torque feeing exceeded indicates a first exceptional operating condition.

14, Method according to claim 11 or 12, characterised in that the occurrence of an emergency situation that requires the stoppage of the g s expansion device {1} indicates a second exceptional operating condition.

15. Method according to any one of the claims 12 to 14, characterised In that the gas is natural gas_*