Patent Application
20170122660
The present invention relates to a de-superheater system for de-superheating a compressed vaporous discharge stream. In another aspects, the present invention relates to a compression system for producing a pressurized and at least partially condensed mixture of hydrocarbons, and to a method of producing a pressurized and at least partially condensed mixture of hydrocarbons.
A pressurized and at least partially condensed mixture of hydrocarbons is frequently produced in refrigeration cycles, wherein the pressurized and at least partially condensed mixture of hydrocarbons is typically expanded and brought into indirect heat exchanging contact with a product stream to extract heat from the product stream. In such application, the mixture of hydrocarbons is typically referred to a mixed refrigerant (MR) or mixed component refrigerant (MCR).
An example of a single mixed refrigerant cycle is disclosed in CN103216998A. The method in this example comprises the steps of performing compressor first-section compression and inter-cooling on the mixed refrigerant; then, entering a second section and a third section for continuous compression; then, cooling the mixed refrigerant in two steps, and forming a gas phase and a liquid phase in last-step cooling. A compression suction pot is provided at the suction inlet of the compressor train. Anti-surge lines are provided to recycle a portion of the de-superheated mixed refrigerant from between the first-step cooling and last-step cooling to the compression suction pot.
The temperature of the de-superheated mixed refrigerant between the first-step cooling and last step cooling is between 65 and 100° C., and the temperature of the gas phase and liquid phase after the last-step cooling is between 20 and 50° C. These temperatures are controlled by a control valve, which controls the flow rate of the cooling streams which absorb the heat in the first-step cooling and last step cooling heat exchangers.
The system and method of CN103216998A may not be suitable when an ambient stream, particularly an ambient air stream, is used as the cooling stream. Ambient water streams, and ambient air streams more so, are subject to relatively large and unpredictable temperature variations and variations in humidity (in case of air). Hence, in order to guarantee that the de-superheated mixed refrigerant between the first-step cooling and last step cooling is fully vaporous, a relatively large margin needs to be observed between the target temperature of the de-superheated mixed refrigerant between the first-step cooling and last step cooling and the dew point of the mixed refrigerant between the first-step cooling and last step cooling.
In one aspect, the present invention provides a de-superheater system for de-superheating a compressed vaporous discharge stream, comprising:
Such de-superheater system may be employed in a compression system and/or a method of producing a pressurized and at least partially condensed mixture of hydrocarbons.
Accordingly, in a further aspect the present invention provides a compression system for producing a pressurized and at least partially condensed mixture of hydrocarbons, comprising:
Optionally, the compression system comprises
Controlling the recycle flow rate is done to maintain a flow rate through the train of one or more compressors to keep the train of one or more compressors from surging.
Furthermore, the present invention provides a method of producing a pressurized and at least partially condensed mixture of hydrocarbons, comprising:
Optionally, establishing a recycle flow comprises establishing a recycle flow at a recycle flow rate from the de-superheater discharge conduit to the train of one or more compressors via a surge recycle valve and the compression suction scrubber, whereby controlling the recycle flow rate with the surge recycle valve.
Controlling the recycle flow rate is done to maintain a flow rate through the train of one or more compressors to keep the train of one or more compressors from surging.
The method includes the process step dealing with the compression suction scrubbing. Discharging a vaporous compressor feed stream from a compression suction scrubber therefore includes operating a compression suction scrubber, wherein operating the compression suction scrubber includes discharging the vaporous compressor feed stream from the compression suction scrubber.
Optionally, the method further comprises:
The invention will be further illustrated hereinafter by way of example only, and with reference to the non-limiting drawing in which;
For the purpose of this description, a single reference number will be assigned to a line as well as a stream carried in that line. Same reference numbers refer to similar components. The person skilled in the art will readily understand that, while the invention is illustrated making reference to one or more a specific combinations of features and measures, many of those features and measures are functionally independent from other features and measures such that they can be equally or similarly applied independently in other embodiments or combinations.
The present disclosure involves a de-superheater system and method, for de-superheating a compressed vaporous discharge stream. The de-superheater system comprises a de-superheater heat exchanger to remove excess heat from the compressed vaporous discharge stream which has been added during compression of a vaporous compressor feed stream. In the presently proposed de-superheater system, the temperature of the de-superheated stream as it is being discharged from the de-superheater system is controlled by allowing a bypass portion of the compressed vaporous discharge stream to bypass the de-superheater heat exchanger over a temperature-controlled valve. The bypass portion of the compressed vaporous discharge stream is re-joined with the portion that has passed through the de-superheater heat exchanger, and the rejoined stream is passed through a mixer. The presently disclosed temperature controlled bypass functionality in combination with the mixer provides a much more direct and complete temperature control of the de-superheated stream than is the case in the prior art system of CN103216998A. These measures facilitate that the de-superheated stream being discharged from the de-superheater system is kept at high enough temperature whereby formation of condensation liquids is avoided. The mixer ensures that the heat from the bypass portion is evenly absorbed in the portion of the compressed vaporous discharge stream that has passed through the de-superheater heat exchanger. With these measures, the heat transfer rate in the de-superheater heat exchanger is not a critical parameter any more. This facilitates the use of an ambient stream as the heat sink in the de-superheater heat exchanger, as the actual temperature of the ambient stream may fluctuate significantly over the seasons and the 24 hour cycle of each day.
Furthermore, employing the proposed de-superheater system allows maintaining a de-superheated stream in the vapour phase at a temperature much closer to the dew point temperature of the de-superheated stream being discharged from the de-superheater system.
The de-superheater system can be incorporated in a system for refrigerating a product stream, as will be illustrated herein below.
First, however,
The de-superheater system 1 further comprises a combiner 220, that is configured downstream of the de-superheater heat exchanger 170 for rejoining the bypass portion with the portion of the compressed vaporous discharge stream that has passed through the de-superheater heat exchanger 170. Together, these streams form a rejoined stream 70. Furthermore, a mixer 180 is configured downstream of the combiner 220, to receive and mix the rejoined stream 70, and to discharge the rejoined stream 70 into a de-superheater discharge conduit 80.
The de-superheater system 1 further comprises a temperature controller 56. The temperature controller 56 is functionally coupled to the temperature-controlled valve 52 to change a valve opening setting in response to a temperature of de-superheated stream in the de-superheater discharge conduit 80. The temperature controller 56 is programmed to keep the temperature of the de-superheated stream in the de-superheater discharge conduit 80 above a dew point temperature of the de-superheated stream in the de-superheater discharge conduit 80.
The temperature controller is preferably programmed to keep the temperature of the de-superheated hydrocarbon stream between 1° C. and 15° C. above said dew point temperature. More preferably, the temperature controller is programmed to keep the temperature of the de-superheated hydrocarbon stream between 1° C. and 10° C. above said dew point temperature. The most preferred target temperature for the temperature controller is (about) 5° C. above said dew point temperature.
Suitably, the heat transfer rate in the de-superheater heat exchanger 170 is controlled as well. To this end, the flow rate of the ambient stream 65 in the de-superheater heat exchanger 170 may also be controlled via said temperature controller 56, possibly in concert the temperature-controlled valve 52. In the case the ambient stream 65 is a stream of ambient air, this may be accomplished by varying the speed of a fan 172 which drives the stream of ambient air through the de-superheater heat exchanger 170. The speed of the fan 172 may suitably be varied by varying the motor speed of motor 174 which drives the fan 172. However, alternatives have been conceived, including varying air inlet vanes.
An advantage of the mixer 180 is that if inadvertently some condensation may have occurred in the de-superheater heat exchanger 170, and small droplets or mist of liquid particulates are discharged from the de-superheater heat exchanger 170, the mixer facilitates the direct heat transfer between the bypass portion and the small droplets or mist of liquid particulates are discharged from the de-superheater heat exchanger 170 so that these can evaporate prior to being discharged in the de-superheater discharge conduit 80 in the form of the de-superheated stream. The mixer may suitably be provided in the form of a static mixer. Static mixers as such are known in the art, and they typically comprise a conduit defining a flow path for the rejoined stream 70, with static (stationary) flow-disrupting internals configured in the flow path. The advantage of a static mixer is that it functions autonomously because it contains no moving parts. Commercially available examples for various flow regimes are described in for instance an information brochure “Mixing and Reaction Technology” published by Sulzer Chemtech Ltd.
The de-superheater system 1 can be used in a variety of industrial refrigeration processes to de-superheat a compressed vaporous discharge stream. Typically in such industrial refrigeration processes a hydrocarbon refrigerant is cycled in a refrigeration cycle. The compressed vaporous discharge stream 40 is obtained in such a refrigeration cycle by compressing a vaporous compressor feed stream in a train of one or more compressors to a higher pressure. The compression typically adds heat (enthalpy) to the vaporous compressor feed stream such that the compressed vaporous discharge stream 40 thus formed is typically superheated by more than 60° C. above the dew point temperature of the compressed vaporous discharge stream as it is being discharged from the last compressor (or last compression stage) in the train of one or more compressors.
The suction scrubber outlet 166 is in direct fluid communication with the train of one or more compressors. This train of one or more compressors is represented in
Regardless of the number of compressors or compression stages, the train of one or more compressors comprises 232 a suction inlet fluidly connected to the feed scrubber vapour outlet 166, as well as a compressor train discharge outlet 236.
The train of one or more compressors is configured to compress the vaporous compressor feed stream 30 from the compression suction scrubber 160 to a higher pressure, whereby forming the compressed vaporous discharge stream 40 at the discharge outlet 236. The discharge outlet 236 is in fluid communication with the de-superheater system 1 as described above.
A condenser 190 is arranged in fluid connection with the de-superheater system 1 via the de-superheater discharge conduit 80, which is configured between the de-superheater system 1 and the condenser 190, to receive at least a portion 85 of the de-superheated hydrocarbon stream 80. The condenser 190 is configured to further cool the portion of the de-superheated hydrocarbon stream 80, by allowing indirect heat exchanging against a cooling stream 165, whereby said portion 85 of the de-superheated hydrocarbon stream 80 is at least partly condensed to form a pressurized and at least partially condensed mixture of hydrocarbons 90. Suitably, the heat transfer rate in the condenser 190 is controlled by a temperature controller 196 on the at least partially condensed mixture of hydrocarbons 90. To this end, the flow rate of the ambient stream in the condenser 190 may be controlled via said temperature controller 196. In the case the ambient stream is a stream of ambient air, this may be accomplished by varying the speed of fan 192 which drives the stream of ambient air through the condenser 190. The speed of the fan 192 may suitably be varied by varying the motor speed of motor 194 which drives the fan 192. However, alternatives have been conceived, including varying air inlet vanes.
In embodiments wherein both the de-superheater heat exchanger 170 and the condenser 190 are provided in the form of air-cooled heat exchangers, the de-superheater heat exchanger may be referred to as first air-cooled heat exchanger cooled by a first stream of ambient air, while the condenser may be referred to as second air-cooled heat exchanger cooled by a second stream of the ambient air.
A compressor train surge recycle pathway is arranged between the de-superheater discharge conduit 80 and the suction scrubber inlet 162. Herewith a recycle flow consisting of a recycle portion 120 of the de-superheated hydrocarbon stream, at a recycle flow rate, can be conveyed from the de-superheater discharge conduit 80 to the suction inlet 232 of the train of one or more compressors 230 via the compression suction scrubber 160. A surge recycle valve 250 is configured in said compressor train surge recycle pathway, to control the recycle flow rate.
Optionally, a surge recycle separator drum 210 is configured in said compressor train surge recycle pathway in addition to the surge recycle valve 250. The optional surge recycle separator drum 210 is arranged to remove and drain liquid constituents from the recycle portion 120 of the de-superheated hydrocarbon stream via a liquid drain outlet 218 into a liquid drain conduit 140. A drain control valve 240 may be provided in the liquid drain conduit 140 to control the flow rate of the liquid constituents being drained. Suitably the drain control valve 240 is controlled by a level controller 246 to keep the level of liquid constituents that has accumulated in the surge recycle separator drum 210 within a predetermined range. The recycle vapour outlet 216 of the optional surge recycle separator drum 210 is fluidly connected with the compression suction scrubber 160 via the surge recycle valve 250 and suitably via the suction scrubber inlet 162 to allow vapour constituents of the recycle portion 120 to continue the journey along the compressor train surge recycle pathway and reach the suction scrubber inlet 162.
The suction scrubber inlet 162 may be connected directly to a feed vapour source via a feed line 10, for providing a mixture of hydrocarbons in vapour phase into the suction scrubber 160. Advantageously, however, an additional feed scrubber 150 separates the feed line 10 from the suction scrubber inlet 162. If provided, such feed scrubber 150 may comprise a feed drum provided with at least a feed scrubber inlet 152 connected to the feed line 10, and a feed scrubber vapour outlet 156. The feed vapour source may thus be connected to the feed drum via the feed scrubber inlet 152. The feed scrubber vapour outlet 156 is suitably connected with the suction scrubber inlet 162.
If the compression system 2 is provided with both the optional surge recycle separator drum 210 and the optional feed scrubber 150, the liquid drain outlet 218 of the surge recycle separator drum 210 is suitably fluidly connected via the liquid drain conduit 140 to the feed scrubber 150. The liquid constituents drained from the recycle portion of the de-superheated hydrocarbon stream may thus be fed into the feed drum, wherein these liquid constituents mix with the mixture of hydrocarbons in vapour phase and re-vaporize in direct heat exchange with the mixture of hydrocarbons in vapour phase. In such embodiments, the feed drum preferably comprises a liquid recycle inlet 154 as a separate inlet in addition to the feed scrubber inlet 152, whereby the liquid drain conduit fluidly connects the liquid drain outlet of the surge recycle separator drum 210 with the feed drum via the liquid recycle inlet 154. The liquid recycle inlet 154 is suitably configured gravitationally lower than the feed scrubber inlet 152.
Regardless of whether the optional feed scrubber 150 is provided or not, the compression system 2 may be incorporated in a refrigeration system. In such a refrigeration system, the feed line 10 is ultimately fed from the pressurized and at least partially condensed mixture of hydrocarbons 90.
In the example of
The feed vapour source further comprises a cryogenic heat exchanger 300. The expansion system 3 is optionally separated from the compression system 2 by the cryogenic heat exchanger 300, configured to further cool the pressurized and at least partially condensed mixture of hydrocarbons prior to expanding it. However, this is not a requirement. The cryogenic heat exchanger 300 is arranged to receive the at least one refrigeration stream (95, in
The feed line 10, as described above, is connected to the compression system 2 optionally via the optional feed scrubber 150 if provided.
In the example of
The expansion system 3 in
The expansion system 3 as shown in the example of
Regardless of the type of refrigeration system, the product stream 400 may be a hydrocarbon stream that for at least 80 mol. % consists of methane.
In operation, the compression system 2 may be used in a method of producing a pressurized and at least partially condensed mixture of hydrocarbons 90. A vaporous compressor feed stream 30 is discharged from the compression suction scrubber 160, and compressed to a higher pressure whereby forming the compressed vaporous discharge stream 40.
The vaporous compressor feed stream 30 and the compressed vaporous discharge stream 40 may comprise a mixture comprising two or more selected from N2, C1, C2, C3, C4, C5, whereby N2 denotes nitrogen, C1 denotes methane, C2 denotes ethane and/or ethylene, C3 denotes propane and/or propylene, C4 denotes i-butane and/or n-butane, and C5 denotes one or more of the pentanes, such as i-pentane and/or n-pentane. In one embodiment, between 20 and 80 mol. % consists of C2 and/or C3 of which at least 10 mol. % C3, and at least 20 mol. % consists of one or more selected from C1, C4, and C5. In another embodiment, between 20 and 60 mol. % consists of C1 and/or C2, supplemented with up to 20 mol. % of N2 and at least 20 mol. % selected from C3, C4, and C5. In all cases the total amount of N2, C1, C2, C3, C4, and C5 in the mixture is at least 98 mol. %, preferably at least 99 mol. %, of the total mixture, whereby the maximum amount of N2 is 20 mol. %. The pressure the compressed vaporous discharge stream 40 is suitably in pressure range of from 30 to 50 bara.
The compressed vaporous discharge stream 40 is then de-superheated in the de-superheater system 1. In the course of de-superheating, at least the portion 60 of the compressed vaporous discharge stream 40 is brought in indirect heat exchanging contact with the ambient stream 65 in the de-superheater heat exchanger 170. Hereby, heat is allowed to flow from the compressed vaporous discharge stream 40 to the ambient stream 65. However, the de-superheater heat exchanger 170 is selectively bypassed over the temperature-controlled valve 52 with the bypass portion 50 of the compressed vaporous discharge stream 40. The bypass portion 50 is rejoined with the portion 60 of the compressed vaporous discharge stream 40 that has passed through the de-superheater heat exchanger 170, thereby forming the rejoined stream 70. The rejoined stream 70 is subsequently passed through the mixer 180. This way, the de-superheated hydrocarbon stream 80 is formed out of the compressed vaporous discharge stream 40.
The de-superheated hydrocarbon stream 80, or at least a portion thereof, passes from the de-superheater system 1 to the condenser 190 via the de-superheater discharge conduit 80. The portion of the de-superheated hydrocarbon stream in the condenser 190 is further cooled by indirect heat exchanging said portion of the de-superheated hydrocarbon stream against the cooling stream 165. During the further cooling, the portion of the de-superheated hydrocarbon stream is at least partly condensed, to form the pressurized and at least partially condensed mixture of hydrocarbons 90. As stated above, the de-superheated hydrocarbon stream may be fully condensed or partially condensed in the condenser 190.
A recycle portion 120 may be split off from the de-superheated hydrocarbon stream 80 in the de-superheater discharge conduit, to establish a recycle flow at a recycle flow rate from the de-superheater discharge conduit 80 to the train of one or more compressors. The recycle flow passes via the surge recycle valve 250 and the compression suction scrubber 160. The recycle flow rate is controlled with the surge recycle valve 250. Typically the recycle flow rate is determined with the object to keep the train of one or more compressors from surging by ensuring there is sufficient flow rate through the train of one or more compressors.
This may for instance be done by known surge control techniques, such as by measuring the flow rate through the train of one or more compressors and monitoring the operation of the train of one or more compressors and controlling the recycle flow rate in response thereto.
The temperature-controlled valve 52 is preferably controlled in response to a temperature of de-superheated hydrocarbon stream in the de-superheater discharge conduit 80. Preferably, the temperature of the de-superheated hydrocarbon stream 80 is kept above a dew point temperature of the de-superheated hydrocarbon stream in the de-superheater discharge conduit 80. The dew point temperature depends on composition of the de-superheated hydrocarbon stream and the pressure in the de-superheater discharge conduit 80. The temperature of the de-superheated hydrocarbon stream is preferably kept between 1° C. and 15° C., more preferably between 1° C. and 10° C., above the dew point temperature. If desired a larger safety margin may be applied, whereby the temperature of the de-superheated hydrocarbon stream is kept at least 2 or 3° C. above the dew point temperature instead of only 1° C. The optimum temperature of the de-superheated hydrocarbon stream is conceived to be 5° C. (or about 5° C.) above the dew point temperature. About 5° C. above the dew point temperature is understood to include temperatures between 3 and 7° C. above the dew point temperature.
The method described above is preferably carried out surrounded by ambient air having an actual temperature. The ambient stream 65 may be a steam of the ambient air at the actual temperature.
The cooling stream 165 in the condenser 190 may be a chilled stream at a temperature below the actual temperature, or a second ambient air stream at the actual temperature. An approach temperature, in the condenser 190, between the temperature of the cooling stream 165 and the pressurized and at least partially condensed mixture of hydrocarbons 90 is suitably between 1° C. and 10° C. Preferably, the approach temperature is in a range of from 3° C. to 10° C., more preferably in a range of from 3° C. to 7° C. A typical optimum approach temperature for the condenser 190 is 5° C.
In one example carried out in Honeywell UniSim™ process simulation software, a pressurized and at least partially condensed mixture of hydrocarbons 90 was produced using the method described above. The vaporous compressor feed stream 30 had the following composition:
The resulting pressurized and at least partially condensed mixture of hydrocarbons 90, after compressing, de-superheating and partially condensing against an air stream having an actual temperature of 40° C., had a temperature of 45° C. and a pressure of 38.3 bara. A molar fraction of 0.76 was in vapour phase having an average molar mass of 28.67 g; a molar fraction of 0.24 was in liquid phase having an average molar mass of 52.84 g. This resulting pressurized and at least partially condensed mixture of hydrocarbons 90 was intended as refrigerant in a single mixed refrigerant process for liquefying a product stream of natural gas.
The method described above may form part of a method of refrigerating a product stream. In such method of refrigerating, a mixture of hydrocarbons in vapour phase is obtained from the pressurized and at least partially condensed mixture of hydrocarbons 90 and passed to the compression suction scrubber 160. To this end, the the pressurized and at least partially condensed mixture of hydrocarbons 90 is expanded, whereby forming at least one refrigeration stream, such as but not limited to the refrigeration stream 95 in
Regardless the precise nature of the at least one refrigeration stream, the at least one refrigeration stream is then passed through the cryogenic heat exchanger 300 where it is exposed to indirectly heat exchanging against the product stream. During this indirect heat exchanging, the at least one refrigeration stream absorbs heat from the product stream 400 whereby a phase transition occurs in the at least one refrigeration stream from liquid phase to vapour phase. The product stream 400 is thereby cooled and discharged from the cryogenic heat exchanger 300 as refrigerated product stream 450. Optionally, heat from the pressurized and at least partially condensed hydrocarbon stream 90 is simultaneously absorbed by the at least one refrigeration stream.
The at least one refrigeration stream is discharged in vapour phase from the cryogenic heat exchanger 300 in the form of the mixture of hydrocarbons in vapour phase.
The product stream may be a hydrocarbon stream that for at least 80 mol. % consists of methane. Examples of such a hydrocarbon stream include natural gas and pipeline gas from a natural gas grid. Synthetic gas
Regardless of the precise nature of the product stream 400, during or after said indirectly heat exchanging the at least one refrigeration stream against the product stream 400 the product stream may be allowed to condense to form a liquefied hydrocarbon product stream. The liquefied hydrocarbon product stream may be a liquefied natural gas stream.
Although not shown in the drawings, a pressure reduction system may be arranged in the refrigerated product stream 450 downstream of the cryogenic heat exchanger 300 and in fluid communication therewith, to receive refrigerated product stream 450 and to reduce its pressure. An end-flash separator may be arranged downstream of the pressure reduction system, and in fluid communication therewith, to receive the refrigerated product stream from the pressure reduction system. The pressure reduction system may comprise a dynamic unit, such as an expander turbine, a static unit, such as a Joule Thomson valve, or a combination thereof. If an expander turbine is used, it may optionally be drivingly connected to a power generator. Many arrangements are possible and known to the person skilled in the art.
With these provisions it is possible to pass the product stream 400 through the cryogenic heat exchanger 300 in pressurized condition, for instance at a pressure of between 30 and 120 bar absolute, or between 30 and 80 bar absolute, while storing any liquefied part of the refrigerated product stream at substantially atmospheric pressure, such as between 1 and 2 bar absolute.
Depending on the separation requirements, the end flash separator may be provided in the form of a simple drum which separates vapour from liquid phases in a single equilibrium stage, or a more sophisticated vessel such as a distillation column. Non-limiting examples of possibilities are disclosed in U.S. Pat. Nos. 5,421,165; 5,893,274; 6,014,869; 6,105,391; and pre-grant publication US 2008/0066492. In some of these examples, the more sophisticated vessel is connected to a reboiler whereby the refrigerated product stream 450, before being expanded in said pressure reduction system, is led to pass though a reboiler in indirect heat exchanging contact with a reboil stream from the vessel, whereby the refrigerated product stream 450 is caused to give off heat to the reboil stream.
The person skilled in the art will understand that the present invention can be carried out in many various ways without departing from the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14172746.1 | Jun 2014 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/062837 | 6/9/2015 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62010890 | Jun 2014 | US |
