Patent Description:
Compressor devices are applied on large scale and in various forms for the purpose of increasing the pressure of gases. A known form is the piston compressor which draws gas in via an inlet valve during an inlet stroke by means of a reciprocally moving piston in a cylinder, and in a subsequent compression stroke compresses the gas and makes it available under increased pressure via another valve. The piston is here driven mechanically by for instance an electric motor, steam turbine or a combustion engine.

Other forms of known compressors are for instance a rotary-screw compressor and a roots blower wherein rotation of respectively two screws or lobes acting on each other reduces a mutual intermediate space, with the result that the intermediate gas is displaced and compressed. Another known compressor is a centrifugal compressor. To drive the relevant displacing members use is here also usually made of an electric motor, steam turbine or a combustion engine.

What these known forms of compressor have in common is that mechanical parts moving therein are applied as displacing means, which is unequivocally subject to wear and moreover produces sound. To counteract these disadvantages, <CIT> discloses a fluid piston compressor device of the type as described in the opening paragraph. According to this document, the displacing means comprise a liquid pump which is connected on the pressure side to an electronically switchable liquid feed. Such a compressor device is relatively quiet, subject to low-maintenance and may be particularly suitable for compressing a liquid vapour, such as particularly steam.

The present invention has inter alia for its object to provide such a liquid driven compressor device with an elevated energy efficiency.

In order to achieve the stated object a compressor device of the type described in the preamble of claim <NUM> has the feature according to the invention that that the compression chamber forms part of an assembly, comprising a number of corresponding compression chambers, particularly four compression chambers, which are coupled to shared respective liquid conduits and respective gas conduits, in that each of the compression chambers of the assembly is controlled individually by the control means, in that the compression chambers are each operated in an individual state of a series of a corresponding number of successive cycles, at least one of the compression chambers performing a compression stroke in each case, and in that the compression chambers are connected in pairs on the liquid side with interposing of a switch valve that is electronically controllable by the control means.

The compressor device according to the invention is a compressor of the positive displacement type whereby, in contrast to the known mechanical compressors where this is done with mechanical parts, the compression space is however alternately increased and reduced by repetitively letting a liquid into and out of the closed compression chamber. The inlet is here provided for by the liquid pump, which thereby supplies the energy required for the compression. Owing to this alternating evacuation and (partial) filling of the compression space, gas is drawn in and then compressed in the same order without moving mechanical parts acting on the gas for compressing for this purpose. The gas here particularly and preferably comprises the vapour phase of the liquid which is let into and discharged from the compressor space in order to alternately reduce and increase the compression space. Unless expressly stated otherwise, vapour or vapour phase will therefore in the following always be understood to mean the gaseous aggregation state of the liquid which is let into and evacuated from the compression space via respectively the liquid feed and liquid discharge. By means of, for instance, switch valves in the liquid feed and liquid discharge the liquid to be pumped can be alternately supplied in the compression chamber or evacuated therefrom. The gas inlet and outlet can also be electronically controlled in similar manner, or mechanical valves or non-return valves can be applied therein.

Compressing the gas will automatically cause an increase of the temperature of the gas in the compression space. This temperature increase or even overheating as a result of the compression can be countered by application of direct water injection into compression space. A preferred embodiment of the compressor device has for this purpose the feature according to the invention that the compression chamber comprises on the gas side a liquid inlet which is connected to a liquid conduit and which debouches in the compression space. A part of the injected liquid will here evaporate in the compression space and thereby already cool the space. In order to enhance this, a further preferred embodiment of the compressor device has the feature according to the invention that the liquid inlet comprises an atomizer which debouches in the compression space.

A part of the injected liquid may also remain behind in the form of heated liquid. The energy absorbed due to heating of the remainder of the injected liquid will cause this liquid to evaporate wholly or partially when the liquid is evacuated from the compression space. The developed vapour is then compressed during a subsequent compression cycle. The same medium as pumped by the liquid pump is then preferably also used as the injected liquid.

Although the liquid can be fed and discharged alternately, a further preferred embodiment of the compressor device has the feature according to the invention that the liquid discharge is connected to an inlet of the liquid pump. The liquid thus circulates in the device so as to be reused time and again.

The temperature of the pumped liquid will likewise increase due to the pump energy dissipated for the compression. This dissipated energy is supplied by the liquid pump. A particular embodiment of the compressor device according to the invention has the feature here that the liquid discharge is coupled to the inlet of the liquid pump in heat-exchanging contact with a heat exchanger. In this way the dissipated pump energy can be recovered at least partially, for instance to be used elsewhere.

A full operating cycle of the compressor device comprises a suction state and a compression state. After compression, the compression space can additionally go through a state in which a free expansion or compression is provided. In order to be able to provide at least a number of these states simultaneously, the compressor device has the feature according to the invention that the compression chamber forms part of an assembly of a number of corresponding compression chambers, particularly four compression chambers or a whole multiple thereof, which are coupled to shared respective liquid conduits and respective gas conduits, that each of the compression chambers of the assembly is controlled individually by the control means, wherein the compression chambers are each operated in an individual state of a series of a corresponding number of successive cycles, wherein in each case at least one of the compression chambers will perform a compression stroke.

In a preferred embodiment use is made here of four compression chambers, wherein alternately one chamber is in the compression state and the compression spaces in the other three chambers are respectively either expanding or compressing freely or being pumped empty forcibly. Four different states, i.e.:.

which are fulfilled successively by different compression chambers, therefore always prevail simultaneously then.

In order to allow a free expansion and/or free compression of the compression space the compressor device has the feature according to the invention that the compression chambers are connectable in pairs on the liquid side with interposing of a switch valve which is electronically controllable by the control means. After a compression in the one chamber of the set, the intermediate switch valve can thus be opened in order to allow a free (partial) expansion which results in a free (partial) compression in the coupled compression space. This part of the energy need therefore no longer be provided by the liquid pump, this contributing to the energy efficiency of the device.

The required energy is supplied by the liquid pump. The pump capacity will therefore be adapted to a desired flow rate on the gas side and a maximum pressure ratio between the compression state and the wholly evacuated underpressure state of the compression space. In order to be able to make allowance for this sometimes varying requirement, a further preferred embodiment of the compressor device has the feature according to the invention that the liquid pump comprises a controllable pump with a pump drive which is operatively coupled to the control means and which is able and configured to impose a variable pump capacity on the pump. The liquid pump is thus embodied with variable speed drive for the purpose of an adjustable capacity.

The capacity can for instance be controlled on the basis of availability of the low pressure gas (residual heat in the case of steam compression) at the gas inlet. On the other hand, the capacity can for instance be controlled on the basis of the desired high pressure (high temperature heat demand in the case of vapour compression) at the gas outlet. With a view thereto, a further particular embodiment of the compressor device has the feature according to the invention that the gas inlet and the gas outlet each communicate upstream with respectively an inlet pressure sensor and an outlet pressure sensor, which pressure sensors are operatively coupled to the control means. The control means can thus adapt the rotational speed of the liquid pump to the available inlet pressure at the inlet and/or the desired outlet pressure at the outlet.

By means of level measurements or level switches it is possible to indicate when a minimum or maximum level in a compression space has been reached. For the control means, this is the signal to switch from one state to another state in the compression chamber. A particular embodiment of the compressor device has for this purpose the feature that provided in the compression chamber is a liquid level sensor which is operatively coupled to an electronic control circuit, and more particularly that the control means comprise the control circuit. The control equipment of the control means will control the switch valves for liquid to or from the compression space to open or close depending on the state intended therein.

Both the supply of liquid to the compression space and the evacuation therefrom are in particular actively imposed by the control means. For this purpose a further embodiment of the compressor device has the feature that the liquid feed and the liquid discharge comprise a switch valve which is electronically controllable by the control means. Active valves which are controlled by the control means can likewise be applied on the gas side, although an autonomous, purely mechanical drive is instead also possible. This will then automatically follow the active drive imposed on the liquid side. For this purpose a further embodiment of the compressor device has the feature according to the invention that the gas inlet and the gas outlet each comprise a non-return valve or valve with operatively opposite orientation.

The above described compressor device according to the invention is particularly suitable for compressing a liquid vapour. For this purpose the invention also relates to a method for compressing a liquid vapour, particularly steam, with the feature that the above described compressor device according to the invention is applied for this purpose, wherein a liquid vapour, particularly steam, is supplied under a first pressure at the gas inlet and a liquid vapour, particularly steam, is taken off under an increased second pressure at the gas outlet, and wherein the corresponding liquid, particularly water, is opted for the liquid feed.

For a gas cooling use is in that case preferably likewise also made of the same medium as is applied for the liquid feed and discharge. A preferred embodiment of the method according to the invention therefore has the feature that the compression chamber comprises on the gas side a liquid inlet, particularly a water inlet, which is connected to a liquid conduit, particularly a water conduit, and which debouches in the compression space, particularly via an atomizer.

The invention will be further elucidated hereinbelow with reference to an exemplary embodiment and an accompanying drawing. In the drawing:.

It is otherwise noted here that the figures are purely schematic and not always drawn to (the same) scale. Some dimensions in particular may be exaggerated to greater or lesser extent for the sake of clarity. Corresponding parts are designated in the figures with the same reference numeral.

Part of an exemplary embodiment of a compressor device according to the invention is shown schematically in <FIG>. The compressor device comprises a substantially closed compression chamber <NUM> which provides on the gas side a compression space <NUM>. On the gas side the compression chamber comprises a gas inlet <NUM> and a gas outlet <NUM> in the form of valves <NUM>, <NUM> with opposite orientation. The inlet valve <NUM> lets a gas from a gas inlet <NUM> of relatively low pressure LP into the compression space <NUM> as soon as a lower pressure prevails therein, and closes in opposite direction. At a predetermined overpressure in compression space <NUM> the outlet valve <NUM> opens to a gas outlet <NUM> of relatively high pressure HP. In this embodiment steam is used as vapour phase of water which is applied in liquid form. This is for instance supplied at inlet <NUM> at a pressure LP of several tenths of a Bar and taken off at outlet <NUM> at an increased pressure HP in the order of <NUM> Bar at a temperature in the order of <NUM>.

On an opposite, liquid side the compressor chamber comprises a liquid feed <NUM> and a liquid discharge <NUM> which are coupled to respective liquid conduits <NUM>, <NUM>. Connected between liquid conduits <NUM>, <NUM> and the relevant liquid feed <NUM> or liquid discharge <NUM> is an electronically controllable switch valve <NUM>, <NUM> which is controlled by control means of a central control unit <NUM>. Also coupled thereto is a variable frequency drive <NUM> of liquid pump <NUM> whereby a liquid can be carried to liquid feed <NUM> under pressure. If desired, several liquid pumps can here also be placed parallel or in series, each having a variable frequency drive, which can then each be called upon in their own optimal range of operation. Unless explicitly stated otherwise, water is in this embodiment always used as the liquid, particularly sufficiently clean process water. Water is correspondingly also applied for the gas which is let in or let out under increased pressure on the gas side, albeit in the corresponding vapour phase as steam.

In the stage shown in <FIG> the compression chamber is not filled with water, or hardly so, which is indicated by the drawn low water level WL and the opened valve <NUM> to the outgoing liquid conduit <NUM>. In this state the compression space fills with steam from the low pressure feed <NUM> and the valve <NUM> opened to gas inlet <NUM> there. Once compression space <NUM> has completely filled with steam, control unit <NUM> sends a control signal to discharge valve <NUM> to close it and the control unit controls feed valve <NUM> to open, see <FIG>.

The pump <NUM> is also brought to the desired rotational speed by control unit <NUM> and variable frequency drive <NUM>. The liquid level in compression chamber <NUM> is thus elevated from feed conduit <NUM>, whereby the compression space decreases and the gas present therein is compressed. Valve <NUM> is now closed. In order to limit dead volume in the compression space a narrow hood <NUM> is provided thereon, this having a level switch <NUM> which generates a signal when a maximum filling level WH corresponding with a predetermined compression ratio is reached. When this level is reached, outlet valve <NUM> opens in order to release steam to pressure conduit <NUM> under the thus increased pressure. After this, the steps of <FIG> and <FIG> can be repeated in order to thus impart a pressure increase to the gas supplied from inlet <NUM> in steps and supply it under increased pressure, whereby the gas can be taken off at outlet <NUM>.

The compressor device described here is of the positive displacement type whereby, in contrast to most mechanical compressors where this is done with mechanical parts, the necessary increase and reduction of the compression space <NUM> is brought about by repetitively pumping a liquid into the compression space and evacuating it therefrom. Gas is here drawn in and then compressed to an increased pressure in the same order. The gas to be compressed is supplied to compression space <NUM> by means of valve <NUM> or a switch valve. The compressed gas is also supplied under a correspondingly increased pressure via a valve <NUM> or switch valve to be guided to for instance a pressure vessel or supply system for consumption. The liquid to be pumped is likewise alternately supplied to or evacuated from compression space <NUM> with valves <NUM>, <NUM>.

By means of level measurements with sensors or switches <NUM>, <NUM>, <NUM> provided for this purpose in or on compression chamber <NUM> it is possible to indicate when a minimum or maximum level in compression chamber <NUM> has been reached. These indicator signals are exchanged with control means <NUM> in order to switch between the different states of the compressor device. The control equipment will control the switch valves <NUM>, <NUM> to open or close depending on the state to be reached. The measured values are also shared with control equipment <NUM> in order to have them calculate how long the feed water control valve <NUM> must be controlled to open so that the desired level will be reached in the compression state.

Compressing the gas will automatically cause an increase of the temperature of the gas. The temperature of the pumped liquid will likewise increase due to the pump energy dissipated by pump <NUM>. This temperature increase (overheating) as a result of the steam compression can be countered by application of direct water injection into compression space <NUM>. For this purpose the compressor chamber <NUM> comprises on the gas side an atomizer <NUM> which is coupled via a switch valve <NUM> to a feed <NUM> for mains water. Switch valve <NUM> is coupled to a controller of control unit <NUM> provided for this purpose.

Controller <NUM> comprises a temperature sensor (not shown) in compression space <NUM>, at gas outlet <NUM> and/or in outlet conduit <NUM>. The measured values are transmitted to control equipment <NUM> which generates a signal to control unit <NUM> when a threshold value is exceeded, upon which signal the control unit controls switch valve <NUM> to open. Liquid, cold water will hereby be fed to the atomizer and then be supplied in compression space <NUM> in the form of a fine mist (aerosol). Controller <NUM> thus controls the injection water control valve <NUM> indirectly until the desired value has once again been reached.

A part of the injected water will evaporate in compression space <NUM>; a remaining part remains behind in the form of heated water. The energy absorbed for this heating and evaporation provides for a reduction of the ambient temperature in compression space <NUM>, so that overheating therein is avoided. The heated remainder of injected water that stays behind will cause this water to evaporate wholly or partially in a subsequent low pressure state of the device, as shown in <FIG>, which preferably forms part of a cycle as described below. The developed vapour is here compressed during the subsequent compression state.

<FIG> shows an assembly of four mutually co-acting compressor spaces <NUM>-<NUM> which are controlled collectively by control means <NUM> and together perform a full cycle. Compression chambers <NUM>-<NUM> of the assembly are connected to a shared low pressure inlet <NUM> and shared high pressure outlet <NUM>. A shared feed conduit <NUM> for injection water is also provided for the individual atomizers <NUM>. For the sake of clarity the compression chambers <NUM> in the figure are not further provided with a hood <NUM> and level switch <NUM> as shown in <FIG> and <FIG>, although these can also be advantageously applied here in order to limit dead volume therein to a minimum.

In each stage of a full operating cycle of the assembly of <FIG> a compression chamber <NUM> is in each case in a suction state, as described in <FIG>, and another compression chamber <NUM> in a compression state, as shown in <FIG>. In addition, in each stage of the assembly one of the compression chambers can expand freely <NUM> and another compression chamber can compress freely <NUM> following compression. For this purpose adjacent compression chambers <NUM>, <NUM> are coupled in pairs by means of a controllable intermediate valve <NUM> which is controlled by control means <NUM>.

Of the four vessels <NUM>-<NUM>, one compression chamber is thus in each case alternately in the compression state while another compression chamber suctions. In the shown stage of the assembly of <FIG> four different states thus prevail simultaneously, divided over the compression chambers <NUM>-<NUM>, i.e.: (i) compression (<NUM>), (ii) free expansion (<NUM>), (iii) inlet pressure (<NUM>), and (iv) free compression (<NUM>). The required energy will be supplied by a shared liquid pump <NUM>. The capacity, i.e. the rotational speed, thereof will be determined on the basis of the desired flow rate and the desired compression ratio between state (i) and (iii).

By means of level measurements with sensors or switches <NUM>, <NUM>, <NUM> provided for this purpose in or on compression chamber <NUM>-<NUM> it is possible to indicate when a minimum or maximum level in a compression chamber <NUM>-<NUM> has been reached. These indicator signals are exchanged with control means <NUM> in order to switch between different states of the compression chambers <NUM>-<NUM> in each stage per cycle. The control equipment will control the switch valves <NUM>, <NUM> to open or close depending on the state. The level of all compression chambers <NUM>-<NUM> will be measured. The measured values are transmitted to control equipment <NUM>. The control equipment calculates the average value of all compression chambers <NUM>-<NUM> and controls the relevant feed water control valve <NUM> so that the desired value will be reached.

The capacity can be controlled on the basis of availability of the low pressure gas, particularly residual heat in the case of steam compression. On the other hand, the capacity can be controlled on the basis of high pressure high temperature heat demand. For this purpose an inlet pressure sensor <NUM>, and outlet pressure sensor <NUM> and an outlet temperature sensor <NUM> are respectively coupled to the control means <NUM> in order to monitor respectively the low inlet pressure and high outlet pressure. The compression liquid pump <NUM> is embodied with variable speed drive <NUM> in order to be able to accommodate a changed demand. Control means <NUM> can thereby control the rotational speed of liquid pump <NUM> so that the desired value is reached.

Compression chambers <NUM>-<NUM> of the assembly of <FIG> are coupled to a shared feed conduit <NUM> and discharge conduit <NUM>. Pump <NUM> is received therebetween. Any residual heat can be recovered by means of a heat exchanger <NUM> provided for this purpose between feed conduit <NUM> and discharge conduit <NUM>.

Claim 1:
Compressor device, comprising an at least substantially closed compression chamber (<NUM>) which comprises on the gas side a compression space (<NUM>) with a gas inlet (<NUM>) and a gas outlet (<NUM>) for respectively receiving a supplied gas at a first pressure and delivering it at an increased pressure, and comprising energizable displacing means which are able and configured to alternately reduce and increase the compression space (<NUM>), wherein the compression chamber (<NUM>) comprises an electronically switchable liquid feed (<NUM>) and an electronically switchable liquid discharge (<NUM>), each in open communication with the compression space (<NUM>), wherein the displacing means comprise a liquid pump (<NUM>) which is connected on the pressure side to the liquid feed (<NUM>), and wherein control means (<NUM>) are provided which are connected operatively to the switchable liquid feed (<NUM>), the switchable liquid discharge (<NUM>) and the liquid pump (<NUM>) to mutually adapt operation thereof in order to alternately fill the compression space (<NUM>) at least partially with a liquid and evacuate the liquid therefrom, characterized in that the compression chamber (<NUM>) forms part of an assembly, comprising a number of corresponding compression chambers (<NUM>), particularly four compression chambers (<NUM>), which are coupled to shared respective liquid conduits and respective gas conduits, in that each of the compression chambers (<NUM>) of the assembly is controlled individually by the control means (<NUM>), in that the compression chambers (<NUM>) are each operated in an individual state of a series of a corresponding number of successive cycles, at least one of the compression chambers (<NUM>) performing a compression stroke in each case, and in that the compression chambers (<NUM>) are connected in pairs on the liquid side with interposing of a switch valve (<NUM>) that is electronically controllable by the control means (<NUM>).