Apparatus and Method for Transferring a Fluid from a Subcritical Gaseous State into a Supercritical State

The present invention relates to an apparatus and a method for transferring a fluid from a subcritical gaseous state into a supercritical state.

Separation units that separate a specific component from a mixed fluid stream of various components oftentimes return a fluid stream of the corresponding separated component in a subcritical gaseous state, i.e. in a gaseous state with a temperature below a critical temperature Tand with a pressure below a critical pressure p, wherein these critical values define the critical point. With a temperature and a pressure above the corresponding critical point the fluid would be in a supercritical state, in which distinct liquid and gaseous phases do no longer exist. Separation units of that kind can e.g. be COseparation units for separating a COstream from a mixed gas stream, oftentimes yielding the separated COin a fluid stream in a subcritical, gaseous state.

However, the subcritical gaseous state can oftentimes not be expedient for further use of the separated fluid, e.g. for storage or for long distance transportation e.g. in pipelines. For further use the corresponding fluid often is required to be in the supercritical state, i.e. with a temperature above the critical temperature Tand a pressure above the critical pressure p. It is therefore desirable to provide a possibility for transferring a fluid from its subcritical gaseous state into its supercritical state.

The present invention relates to an apparatus and a method for transferring a fluid from a subcritical gaseous state into a supercritical state with the features of the independent claims. Further advantages and embodiments of the invention will become apparent from the description and the appended figures.

Advantages and advantageous embodiments of the apparatus according to the present invention and the method according to the present invention shall arise from the present description in an analogous manner.

The apparatus comprises a compressor unit or compressor stage, a pump unit or pump stage, a drive unit and a liquefaction unit or liquefaction stage. The compressor unit can comprise one or several compressors. The pump unit can comprise one or several pumps. The compressor unit and the pump unit are commonly driven by the drive unit. The drive unit is thus provided as a common drive or engine coupled with both the compressor unit and the pump unit. The liquefaction unit is provided downstream of the compressor unit and upstream of the pump unit. The fluid, particularly CO, in its subcritical gaseous state is provided to the compressor unit.

The compressor unit is configured to compress the fluid from a first subcritical gaseous state, expediently from its initial state with an initial pressure level, to a first predetermined pressure level of a second subcritical gaseous state. This first predetermined pressure level is thus expediently below the corresponding critical pressure pc of the fluid. After this compression, the fluid can e.g. have a temperature level above the corresponding critical temperature T. The correspondingly compressed fluid in its second subcritical gaseous state is then transported to the liquefaction unit.

The liquefaction unit is configured to reduce the temperature of the correspondingly compressed fluid in the second subcritical gaseous state downstream of the compressor unit to a predetermined temperature level such that the fluid is transferred from the second subcritical gaseous state to a liquid state. The temperature of the fluid is thus reduced below a liquefaction temperature or condensation temperature at the first pressure level. In the course of this liquefaction process, the fluid is particularly kept at the first predetermined pressure level or at least essentially at the first predetermined pressure level. Before this liquefaction process, the fluid can for example have a temperature level above the critical temperature Tof the corresponding fluid. The predetermined temperature level after the liquefaction can expediently be below the corresponding critical temperature T. The correspondingly liquefied fluid is then transported to the pump unit.

The pump unit is configured to compress the correspondingly liquefied fluid in the liquid state downstream of the liquefaction unit to a second predetermined pressure level such that the fluid is transferred from the liquid state to the supercritical state. The pressure level is thus particularly increased above the critical pressure p. The temperature level is expediently increased above the critical temperature T. The fluid in its supercritical state can then be provided downstream of the pump unit for further use.

To characterise pressures and temperatures, the present application uses the terms “pressure level” and “temperature level”, which are intended to signify that corresponding pressures and temperatures do not necessarily have to be used as exact pressure and temperature values. However, such pressures and temperatures are typically within particular ranges which lie, for example ±1%, 5%, 10%, 20% or even 50% around an average. In this respect, corresponding pressure levels and temperature levels can lie within disjoint ranges or within overlapping ranges. In particular, for example pressure levels include pressure losses which are unavoidable or which are to be expected. The same applies accordingly to temperature levels. Pressure levels which are given here in bar are absolute pressures.

The present invention provides a single, highly integrated apparatus for compressing the subcritical fluid into its supercritical state in an effective, space saving, flexible manner with low footprint and low costs. In particular, commonly driving the compression unit and the pump unit with the same drive unit yields the possibility to consolidate corresponding compression steps and pumping steps into one single, integrated apparatus. It is therefore particularly not necessary to provide separate machines, especially separate pumps and compressors, independently driven by different engines. The present apparatus combines the compressor unit and pump unit into a common unit, thus reducing complexity and number of components and conserving energy and required space. The apparatus therefore requires little plot space and can easily be installed. The apparatus further allows to flexibly integrate the liquefaction process or liquefaction stage, thus increasing effectiveness and flexibility of the process of transferring the fluid into its supercritical state. The flexibility and the reduced plot space allows for the apparatus to be applied to a wide range of inlet and outlet fluid pressures and temperatures.

Combining or integrating the compression stage and pumping stage allows for an optimization of machinery technology. Fluid compression by means of the compression unit allows to pre-compress the fluid given its first subcritical gaseous starting state. Pumping by means of the pump unit is an efficient and simple way to further compress the pre-compressed fluid to the required process pressure for the supercritical state. Pre-compressing the subcritical fluid, liquefying the pre-compressed fluid by means of the liquefaction unit, and then compressing the liquefied fluid to a pressure level above the critical pressure pc provides an energetically efficient way to transfer the fluid into its supercritical state.

Advantageously, the liquefaction unit comprises or is provided as a cooling unit configured to perform liquefaction of the fluid by means of air and/or cooling water and/or refrigerated or chilled water and/or an external refrigeration medium. Depending on the site conditions of the apparatus location, e.g. in cold regions, ambient cooling can be performed, i.e. ambient air or water can be used to cool the fluid below its liquefaction temperature. In hot regions, refrigerated water or refrigeration medium can be used to cool down the fluid.

According to a preferred embodiment, the liquefaction unit is further configured to perform a process cooling of an external process unit. Thus, the liquefaction unit is particularly not only used for the liquefaction of the fluid in the present apparatus, but also for cooling process streams in another, external process unit, e.g. an LNG facility or plant. This external process unit can e.g. be a nearby apparatus of the same provider or operator as the present apparatus. This multiple use of the liquefaction unit is particularly beneficial in plants where a large refrigeration capacity is already available and the equipment is already installed.

According to a preferred embodiment, the liquefaction unit is provided as an open loop refrigerant system comprising a heat exchanging unit and a precooling unit. This open loop refrigerant system is preferably configured to extract a portion of the fluid from the compressor unit, for example upstream of the compressor unit or downstream of the compressor unit or from in-between the compressor unit itself. This extracted portion of the fluid is provided to the precooling unit in order to precool the extracted portion of the fluid. This precooling unit can preferably comprise an ambient (air or water) cooling unit and/or a valve unit, particularly for a cascade Joule-Thomson expansion. The precooled extracted portion of the fluid is provided as a refrigerant to the heat exchanging unit. Further, the compressed fluid in the second subcritical gaseous state downstream of the compressor unit is provided to the heat exchanging unit. The temperature of the compressed fluid in the second subcritical gaseous state is reduced to the predetermined temperature level by means of the heat exchanging unit. In the course of the corresponding heat exchange, the temperature of the extracted portion of the fluid is increased again. Downstream of the heat exchanging unit, the extracted portion of the fluid is returned to the compressor unit. Therefore, the liquefaction unit can be provided as an open loop refrigerant system using the process fluid (e.g. CO) as a refrigerant and using the compressor portion of the apparatus in combination with ambient (air or water) cooling and a cascade Joule-Thomson valve expansion of a side stream of the process fluid to provide the necessary refrigeration for the liquefaction. This will come at an energetic cost but will provide significant benefits in terms of installed equipment count and plot space if alternative refrigeration sources are not readily available.

Preferably, the liquefaction unit comprises or is provided as a hydrocarbon refrigerant unit configured to perform liquefaction of the fluid by means of a hydrocarbon refrigerant, especially using a cold hydrocarbon stream as a refrigerant. Preferably, a C3 refrigerant can be used, particularly propane CHor a fluid mixture comprising propane. Alternatively or additionally, a C4 refrigerant can preferably be used, particularly butane CHor a fluid mixture comprising butane. A hydrocarbon refrigerant unit of that kind can expediently be used for process cooling of an external process unit. For example, corresponding C3 or C4 refrigeration compressors can also be used for an LNG facility, utilising a cold hydrocarbon side stream as a refrigerant.

Advantageously, the liquefaction unit comprises or is provided as a coldbox. A coldbox or packaged unit is an assembly of various cryogenic components in a steel containment. For example, interconnecting piping, vessels, valves and instrumentation can be included in a packaged unit of that kind, expediently filled with insulation material, e.g. perlite. The coldbox can e.g. further be utilised for a wide range of applications for the treatment of cryogenic fluids and gases, e.g. for external process units like separation plants, liquefaction plants, chemical and petrochemical plants, etc.

According to a preferred embodiment, the drive unit is coupled to or connected with the compressor unit and the pump unit via a gearbox. The gearbox particularly distributes mechanical energy produced by the drive unit to the compressor unit and the pump unit. A driven shaft or output shaft of the drive unit is particularly coupled to the gearbox and the gearbox is particular coupled with both the compressor unit and the pump unit. Pinions of the pump unit and the compressor unit can expediently be integrated in this gearbox, driven by the drive unit.

According to a preferred embodiment, the drive unit comprises two output shafts or driven shafts. The drive unit is therefore expediently provided as a double-end drive unit. A first output shaft or driven shaft of the drive unit is preferably coupled with the compressor unit and a second output shaft or driven shaft of the drive unit is preferably coupled with the pump unit. Each output shaft can be coupled directly with the corresponding unit or via an individual gearbox. The output shafts can also be directly coupled with a common gearbox and this common gearbox can directly be coupled with each of the compressor unit and the pump unit.

Preferably, the drive unit is provided as an electric motor, a steam turbine, an expansion turbine, a hydraulic power recovery turbine (HPRT), a gas turbine or a combination thereof. The drive unit thus allows to realise high-pressure stages with pump casings and impellers.

Advantageously, the compressor unit is configured to perform centrifugal compression of the fluid in multiple stages with interstage cooling. The fluid is therefore compressed in a multitude of compressing steps, wherein after each compressing step a cooling step is performed in which the temperature of the compressed fluid is reduced, since each compression step particularly increases the temperature of the fluid. Centrifugal compressing with interstage cooling of that kind provides an expedient way to compress the fluid, depending on the starting pressure and temperature levels of its subcritical state, to the second pressure level and to prepare the fluid for subsequent liquefaction.

Advantageously, the pump unit is provided as a centrifugal pump. The pump unit is particularly configured to achieve an end pressure of the fluid required for subsequent use of the supercritical fluid. The centrifugal pump can expediently be provided without interstage cooling, especially since a temperature increase way above the critical temperature Tcan be desired. Thus, an overall efficiency of the apparatus can be increased. Costs and space requirements can be reduced.

According to an advantageous embodiment, the apparatus is provided as or used as a part of a heat recovery unit or waste heat recovery unit. For this purpose, the apparatus is preferably configured to use heat or waste heat to heat up the fluid in the supercritical state and expand it to a liquefaction pressure level. The apparatus can expediently be used to drive a refrigeration cycle in a corresponding refrigeration cycle unit, e.g. a Rankine cycle or an organic Rankine cycle. In a Rankine cycle, heat is supplied to a working fluid thereby bringing the working fluid in its gaseous state, which then drives a turbine. Afterwards, the working fluid is condensed back into its liquid state in the course of which waste heat is produced. This waste heat can partially be recovered by the present apparatus.

According to a preferred embodiment, the first predetermined pressure level is in a range between 50 bar and 70 bar, preferably between 55 bar and 65 bar. The subcritical fluid is thus expediently compressed from its initial pressure level to a medium pressure. The first predetermined pressure level can especially be in range between 60% and 95% of the critical pressure p, particularly between 75% and 90% of the critical pressure p.

According to a preferred embodiment, the predetermined temperature level is in a range between 10° C. and 30° C., preferably between 15° C. and 25° C. Expediently, the predetermined temperature level is below the liquefaction temperature at the first pressure level. Particularly, the liquefaction unit is configured to achieve a liquid state of the fluid with the highest possible temperature.

According to a preferred embodiment, the second predetermined pressure level lies above 100 bar, preferably above 125 bar, preferably above 150 bar. The second pressure level can especially be predetermined in dependence of an end pressure required for subsequent further use of the supercritical fluid.

According to a particularly advantageous embodiment, the fluid is COor a fluid mixture comprising CO. In particular, the fluid is dry COof high purity, especially >99% CO. The fluid can expediently be an azeotropic mixture of COand ethane CH. This fluid mixture can particularly address the topic of COfreeze in the case of rapid depressurization, further adding to the stable and reliable operation of the process.

Preferably, the fluid in the first subcritical gaseous state is provided or produced by a separation unit separating a specific component from a fluid mixture of various components. The apparatus can flexibly be adjusted to a variety of different input conditions of the subcritical, gaseous fluid. Expediently, the apparatus can therefore flexibly be provided downstream of different kinds of separation units. For example, the corresponding separation unit can use chemical or mechanical absorption, chemical or mechanical adsorption, pressure swing adsorption, temperature swing adsorption, membranes, cryogenic distillation, or a combination thereof to return a fluid stream of the separated component in the subcritical gaseous state. Since the subcritical gaseous state may not be expedient for further use of the separated fluid, the apparatus particularly provides the supercritical fluid with output conditions needed for further use.

Advantageously, the fluid in the supercritical state is used or provided for long distance transportation, pipeline transportation, storage, Enhanced Oil Recovery (EOR), sequestration or underground sequestration, or a combination thereof. For example, in the course of Enhanced Oil Recovery, crude oil can be extracted from oil fields by injecting the supercritical CO. For example, in the course of sequestration, the supercritical COcan be stored in carbon pools e.g. using subsurface saline aquifers, reservoirs, ocean water, aging oil fields, etc.

It should be noted that the previously mentioned features and the features to be further described in the following are usable not only in the respectively indicated combination, but also in further combinations or taken alone, without departing from the scope of the present invention.

schematically shows a preferred embodiment of an apparatusaccording to the present invention for transferring, transforming or converting a fluid in a subcritical gaseous state into a supercritical state.

The subcritical gaseous fluid, particularly dry COof high purity, can be provided by a separation unitfor separating a specific component from a fluid mixture of various components.

Supercritical COcan be further processed in a COutilising unit, e.g. for long distance transportation, pipeline transportation, storage, Enhanced Oil Recovery, sequestration, or a combination thereof.

For example, the COcan be provided by the separation unitin an initial or first subcritical gaseous state with a pressure pof ca. 5 bar and a temperature Tof ca. 35° C. The critical pressure pof COis 73.3 bar and the critical temperature Tis 304.1 K or 31° C.

In order to compress the COfrom this first subcritical gaseous state to its supercritical state, the apparatuscomprises a compressor unit or compressor stage, e.g. a centrifugal compressor. This compressor unitis configured to compress the fluid from its first subcritical gaseous state and from its initial pressure level pto a first predetermined pressure level pof a second subcritical gaseous state, i.e. such that fluid remains in a subcritical gaseous state. For example, this first predetermined pressure level pcan be in the range between 55 bar and 65 bar. After this compression, the fluid can have a temperature level Tabove its critical temperature.

A liquefaction unit or liquefaction stageis provided downstream of the compression unitand is configured to reduce the temperature of the compressed fluid in the second subcritical gaseous state to a predetermined temperature level Tsuch that the fluid is transferred from the second subcritical gaseous state to a liquid state. For example, this predetermined temperature level Tcan be in a range between 15° C. and 25° C. The pressure of the fluid during and after liquefaction can remain at least essentially at the first predetermined pressure level p.

The liquefaction unitcan for comprise a cooling unit configured for cooling and liquefying the fluid by means of air and/or cooling water and/or refrigerated water and/or an external refrigeration medium.

The liquefaction unitcan also be used for cooling purposes in an external process unit, e.g. for cooling process streams in a nearby LNG facility.

The liquefaction unitcan further comprise a hydrocarbon refrigerant unit configured to perform liquefaction of the fluid by means of a hydrocarbon refrigerant, e.g. a C3 refrigerant like propane CHand/or a C4 refrigerant like butane CH. For example, a C3 or C4 refrigeration of that kind can also be used for nearby LNG facilities.

It is also possible, that the liquefaction unitcomprises a coldbox, e.g. an assembly of various cryogenic components in a steel containment, which can further be used for the treatment of cryogenic fluids and gases in external process units.

A pump unit, e.g. a centrifugal pump, is provided downstream of the liquefaction unitand is configured to compress the fluid in the liquid state to a second predetermined pressure level psuch that the fluid is transferred from the liquid state to the supercritical state. This second predetermined pressure level pcan e.g. be above 150 bar.

A common drive unitis provided for commonly driving both the compressor unitand the pump unit, e.g. indirectly via a common gearbox. For this purpose, an output shaft or driven shaftof the drive unitis directly connected or coupled with the gearboxand the gearboxis directly connected or coupled with both the compressor unitand the pump unit. The drive unitcan e.g. be provided as an electric motor, a steam turbine, an expansion turbine, a hydraulic power recovery turbine (HPRT), a gas turbine or a combination thereof.

It is also possible that the drive unit is directly coupled with both the compressor unitand the pump unitas shall now be explained with reference to

In, a preferred embodiment of an apparatus according to the present invention is schematically shown and referred to as′. In, identical reference signs refer to identical elements or to elements of at least the same function.

As shown in, a corresponding drive unit′ is provided as a double-end drive unit with two driven shafts or output shafts′,′. A first output shaft or driven shaft′ of this drive unit′ is coupled with the compressor unitand a second output shaft or driven shaft′ of the drive unit′ is coupled with the pump unit.

schematically shows a pressure-temperature-diagramrepresenting the transfer of COfrom the subcritical, gaseous state into the supercritical state by means of the apparatusofor the apparatus′ of

Depending on its pressure and temperature, COcan exist in its solid state in a solid phase range, in the liquid state in a liquid phase range, and in the gaseous phase in a gaseous state range. A pressure pof 5.2 bar and a temperature Tof 216.6K or −56.6° C. represents the triple point of CO, at which the gaseous state, the liquid state, and the solid state exist in thermodynamic equilibrium. In a supercritical range, with pressures above the critical pressure pof COof 73.3 bar and with temperatures above the critical temperature Tof 304.1 K or 31° C., distinct liquid and gaseous phases do not exist anymore.

Pointrepresents the COin its first subcritical gaseous state as provided by the separation unitwith the initial pressure pof ca. 5 bar and the initial temperature Tof ca. 35° C.

Arrowrepresents the step of compressing the COin its first subcritical gaseous stateby means of the compressor unitfrom its initial pressure pto the first predetermined pressure level pof e.g. 65 bar.

Pointrepresents the COin the second subcritical gaseous state after compression step, still in its subcritical gaseous state, with the first predetermined pressure level pof e.g. 65 bar. For example, after the compression, the COcan have a temperature level Tof e.g. 40° C.