NO342899B1

NO342899B1 - System adapted for heating a mixed hydrocarbon wellstream and a method for heating a mixed hydrocarbon wellstream

Info

Publication number: NO342899B1
Application number: NO20161104A
Authority: NO
Inventors: Pål Rushfeldt; Stig Karl Brustad
Original assignee: Kanfa Ingenium Process As
Priority date: 2016-07-01
Filing date: 2016-07-01
Publication date: 2018-08-27
Also published as: WO2018004351A8; WO2018004351A1; NO20161104A1

Abstract

The present application relates to a system adapted for heating a mixed hydrocarbon stream in a phase separation process at a processing facility, the system includes avapour compression heat pump cyclewhich is thermally connected with at least one heating consumer, for providing heat to the at least one heating consumer, and with at least one cooling consumer, for cooling and recovering heat from the at least one cooling consumer. The application also relates to a method for heating a mixed hydrocarbon stream in a phase separation process at an oil/gas processing facility, wherein the mixed hydrocarbon stream is heated by directly or indirectly heat exchanging with avapour compression heat pump cyclein at least one heating consumer, while recovering heat by heat exchanging in at least one cooling consumer. The present invention thus eliminates the need for hydrocarbon gas/oil fired heaters foroffshore and/or onshore field installations and oil processing plants. The invention also provides a considerable less power consuming alternative compared to electrical heaters, used for the same purpose, where electrical power transmitted from the national grid is required.The present application relates to a system adapted for heating a mixed hydrocarbon stream in a phase separation process at a processing facility, the system includes avapor compression heat pump cycle which is thermally connected with at least one heating consumer, for providing heat to the at least one heating consumer, and with at least one cooling consumer, for cooling and recovering heat from the at least one cooling consumer. The application also relates to a method for heating a mixed hydrocarbon stream in a phase separation process at an oil / gas processing facility, where the mixed hydrocarbon stream is heated by direct or indirect heat exchange with avapor compression heat pump cycle in at least one heating consumer , while recovering heat by heat exchanging in at least one cooling consumer. The present invention thus eliminates the need for hydrocarbon gas / oil fired heaters for offshore and / or onshore field installations and oil processing plants. The invention also provides a considerable less power consumption alternative compared to electrical heaters, used for the same purpose, where electrical power transmitted from the national grid is required.

Description

TECHNICAL FIELD

The present invention relates to a heating system adapted for heating a mixed hydrocarbon wellstream in a phase separation process at a processing facility. The invention also relates to a method for heating a mixed hydrocarbon wellstream in a phase separation process at a processing facility, in particular at an oil/gas processing facility.

BACKGROUND

To ensure petroleum production with low CO2emissions, government licenses to develop and operate a petroleum field may include requirements to use existing area electrical power supply. Electrical power transmitted from the national grid to an onshore or offshore installation will then replace power generated from the installations own gas turbines. For offshore installations, this would mean using electrical power from shore or from another external source. The report “Kraft fra land til norsk sokkel” published in January 2008 by Norwegian Petroleum Directorate, The Norwegian Water Resources and Energy Directorate, Petroleum Safety Authority Norway and Norwegian Pollution Control Authority, is a study related to electrifying existing installations offshore, technology and future perspectives.

On a typical oil and gas producing facility, mechanical equipment units are integral parts of the topside processing systems. The hydrocarbon stream (wellstream) received at the first production separator is a mixed stream comprising three main phases; oil, water and gas phase. The mixed stream is processed to separate the oil, water and gas phases according to strict sales or disposal specifications for all three phases. The gas/liquid phase separation process is mainly accomplished by a combination of heat addition and pressure reduction. The liquid oil/water separation is mainly accomplished by gravity separation (water at bottom and oil at top). The oil/water/gas phase separation process may require additional more complex processes, but both heating and cooling of the streams is in most scenarios required. The largest heaters are normally upstream one or several separator vessels. The largest coolers are normally in the gas stream, due to inter alia compressing and cooling of the gas, and at the downstream end of the stabilized oil stream and the water stream.

Current installations, with own power generation by gas turbines, provide heat for various consumers through a closed loop heating medium system, which receives heat from the gas turbine waste heat recovery unit (WHRU).

New installations, with power from the national grid, have dedicated gas-fired heaters to replace the above-mentioned WHRUs. Although the gas turbines are replaced with electrical power from efficient/low emission power plants, the gas-fired heaters will still constitute high CO2emissions from the petroleum field installation. Using electric power directly to produce heat is not considered good practice as electric power is considered a high value energy and should be used to power machines rather than as a heat source.

As an example, for fixed offshore installations the heating demand is typically in the range 10-30 MW. With gas-fired heaters, the consequential CO2emissions will be in the range 20.000-60.000 tons/year.

Cooling is normally done by either direct seawater cooling, direct air-cooling or from a separate closed loop cooling medium system (which again is cooled by seawater or by air coolers).

In “Energy-Efficient Technologies for Reduction of Offshore CO2Emmissions”, Marit J. Mazzetti et al., Oil and Gas Facilities, February 2014, pages 89-96, novel technologies for increasing the energy efficiency of offshore oil and gas platforms are discussed. The focus is on developing compact, novel bottoming cycles for recovery of waste heat from the gas turbine and heat recovery from the compressor train for gas export. It was concluded that the most effective means of improving energy efficiency on offshore oil and gas platforms was by applying compact bottoming cycles to the waste heat from the platform’s gas turbines with potential CO2reductions of up to 25%.

Chinese patent application CN101344348 relates to an oilfield produced water heat pump which is used for heating of outward transported crude oil, dehydration of the crude oil and the heat pump process of oilfield produced water for heating. However, CN101344348 does not related to heating of a mixed hydrocarbon wellstream in a phase separation process at a processing facility.

WO 2012/012153 and WO 2015/057514 concern process for recovering heat from the separation of hydrocarbons, by the use of a heat exchanger circle, which may comprise a heat pump compressor. None of WO 2012/012153 or WO 2015/057514 relate to heating of a mixed hydrocarbon wellstream in a phase separation process at a processing facility.

The present invention provides a solution for eliminating the need for hydrocarbon gas/oil fired heaters for offshore and/or onshore field installations and oil processing plants. The invention also provides a considerable less power consuming alternative compared to electrical heaters, used for the same purpose, where electrical power transmitted from the national grid is required. Thus, the present invention relates to a system adapted for providing heat for various heating consumers, where the heat is provided by a vapour compression heat pump cycle.

The system may be integrated into the topside processing facilities on a fixed or floating offshore field installation, or a floating vessel, e.g. a floating production, storage and offloading (FPSO) unit. The system may also be integrated in the processing facilities of onshore hydrocarbon production fields. The system is not limited to be used in processing facilities for produced streams from oil wells, as the system may also be used in further processing facilities e.g. partly treated hydrocarbon products, wherein further treatments or processing involve heat consumer(s) and cooling consumer(s). Common for such processes is the high demand for heat supply to the hydrocarbon process streams in order to separate the mixed streams. As stated above, the heat for such processes are normally supplied by gas fired boilers or a waste heat recovery unit (WHRU), e.g. from a gas turbine. The present invention provides the necessary heat to the heating consumer(s) in an oil/gas treatment process by using a vapour compression heat pump cycle. The vapour compression heat pump cycle may recover heat from cooling consumer(s) resulting in a high COP (Coefficient of Performance) of the heat pump cycle. This has never been done before for hydrocarbon separation processes.

As the present system will eliminate the need for hydrocarbon gas/oil fired heaters for offshore/onshore field installations the CO2emissions from fired heaters will thereby be eliminated. The power consumption will, compared to using electrical heaters for heat generation, be reduced by a factor of 4-5, or may even be almost fully eliminated in terms of heat generation.

SUMMARY OF THE INVENTION

The present invention relates to a system adapted for heating a mixed hydrocarbon wellstream in a phase separation process at a processing facility, the system includes a vapour compression heat pump cycle thermally connected with at least one heating consumer, for providing heat to the at least one heating consumer, where the at least one heating consumer includes one or more of; inlet heater(s) and oil separation train interstage heater(s), and thermally connected with at least one cooling consumer, for cooling and recovering heat from the at least one cooling consumers, where the said at least one cooling consumer is one or more of oil cooler(s) and/or gas cooler(s).

The vapour compression heat pump cycle should have a thermal heating duty from 2 to 100 MW.

The at least one heating consumer may further include other utility heater(s). The at least one cooling consumer may further include produced water cooler(s), and/or other utility cooler(s).

According to a first embodiment of the invention the vapour compression heat pump cycle is directly or indirectly thermally connected with the at least one heating consumer. According to a second embodiment of the invention the vapour compression heat pump cycle is indirectly thermally connected with the at least one heating consumer via a separate closed loop heating medium system.

According to a third embodiment of the invention the vapour compression heat pump cycle is directly or indirectly thermally connected with the at least one cooling consumer. According to a fourth embodiment the vapour compression heat pump cycle is indirectly thermally connected with the at least one cooling consumer via a separate closed loop cooling medium system.

Alternative configurations of the system according to the present invention include; the vapour compression heat pump cycle is

- directly thermally connected with the at least one heating consumer and directly thermally connected with the at least one cooling consumer, or

- directly thermally connected with the at least one heating consumer and indirectly connected with the at least one cooling consumer via a separate closed loop cooling medium system, or

- indirectly thermally connected with the at least one heating consumer via a separate closed loop heating medium system and directly connected with the at least one cooling consumer, or

- indirectly thermally connected with the at least one heating consumer via a separate closed loop heating medium system and indirectly connected with the at least one cooling consumer via a separate closed loop cooling medium system.

According to a fifth embodiment of the invention the processing facility is integrated in topside processing facilities on a fixed or floating offshore field installation, an onshore hydrocarbon production field or in an onshore hydrocarbon receiving process plant.

According to a sixth embodiment of the invention the mixed hydrocarbon stream is a wellstream produced from one or several well(s) offshore or onshore, crude oil or a partially processed hydrocarbon fluid.

According to a seventh embodiment of the invention the refrigerant is a high temperature refrigerant.

According to an eight embodiment of the invention the system comprises a combined heating and cooling closed loop, transferring heat recovered from cooling consumers, the cooling consumers being gas cooler(s), to the heating consumer(s).

In a second aspect, the present invention provides a method for heating a mixed hydrocarbon wellstream in a phase separation process at an oil/gas processing facility, wherein the mixed hydrocarbon wellstream is heated by directly or indirectly heat exchanging with a vapour compression heat pump cycle in at least one heating consumer, where the at least one heating consumer includes one or more of; inlet heater(s) (102) and oil separation train interstage heater(s), while recovering heat by heat exchanging in at least one cooling consumers, wherein the at least one cooling consumer is one or more oil cooler(s) and/or gas cooler(s).

In a first embodiment of the method the mixed hydrocarbon stream is a wellstream produced in at least one oil well offshore or onshore, crude oil or a partially processed hydrocarbon petroleum fluid.

In a second embodiment of the method the at least one heating consumer may further include other utility heater(s).

In a third embodiment of the method the at least one cooling consumer may further include produced water cooler(s), and/or other utility cooler(s).

In a fourth embodiment of the method the mixed hydrocarbon wellstream is separated into oil, water and natural gas.

In a fifth embodiment of the method the mixed hydrocarbon wellstream is heated by heat exchanging with a combined closed loop heating and cooling medium in at least one heating consumer, the heat being recovered from hot, compressed gas by heat exchanging the combined closed loop heating and cooling medium in at least one cooling consumer, the cooling consumer being gas cooler(s).

In the present context the mixed hydrocarbon wellstream should be understood as including a petroleum fluid stream comprising more than one phase, the phases being liquid hydrocarbons, water, natural gas and any common impurities, such as sand and corrosion products, present in a typical wellstream. The characteristics and phase composition of the mixed hydrocarbon stream may vary, depending inter alia on the temperature and the pressure. Normally such fluid is a mixed stream comprising three main phases; generally denoted oil, water and gas. Mixed hydrocarbon stream thus includes a hydrocarbon wellstream received at an inlet manifold, or from a single well/flowline of an oil and gas producing facility onshore or offshore. The mixed hydrocarbon stream may also be referred to as a produced fluid and/or a petroleum hydrocarbon stream. The mixed hydrocarbon stream may be unrefined or partially processed.

Heating consumer in the present context include any type of process heaters, typical examples are wellstream heaters, inlet heaters, oil separation train interstage heaters and various minor utility heaters (for instance fuel gas heater, freshwater maker heater, building/living quarter heating and winterization heating to prevent buildup of ice and snow). The heaters (heating consumers) should be individual heat exchanger(s), thermally communicating, directly or indirectly, via a separate closed loop, with the heat pump refrigerant. Each heating consumer may include one, two or several heat exchanger(s).

Cooling consumer in the present context include any type of process coolers, typical examples are oil coolers, produced water coolers and gas coolers. The coolers (cooling consumers) should be individual heat exchanger(s), thermally communicating, directly or indirectly, via a separate closed loop, with the heat pump refrigerant, as explained above. Each cooling consumer may include one, two or several heat exchanger(s).

The heat exchangers may be any type of heat exchangers, typical examples include shell and tube heat exchangers, plate and frame heat exchangers and compact/welded heat exchangers, which are generally known in the technical field.

In the present context the vapour compression heat pump cycle is an arrangement in which a working fluid (also commonly referred to as refrigerant) contained in a closed loop undergoes phase changes in order to transfer heat between different systems. The heat pump is a machine that can transfer heat from a low temperature heat source to a higher temperature sink/consumer. The working principle behind the basic vapor compression heat pump is that a boiling (evaporating)/condensing working fluid/refrigerant will boil (and thus evaporate) and condense at different temperatures at different pressures.

The pressure of the vapour-phase working fluid is increased in a compressor to allow the working fluid to be condensed at a high temperature. The hot vapour transfers heat to a heating consumer by condensing, i.e. releasing the heat of evaporation, in a heat exchanger (“Condenser”). The now liquid working fluid/refrigerant is reduced in pressure and thus cooled. This is typically done through a throttling valve in smallmedium scale vapour compression heat pump cycles. In large scale applications, an expander may be used for this purpose instead of a throttling valve. The reduction in pressure through the throttling valve or expander causes a reduction in working fluid temperature because the boiling temperature drops when the working fluid pressure is reduced. The cold liquid working fluid is then evaporated, i.e. consuming the heat of evaporation, in a heat exchanger (“Evaporator”) and thereby cools the cooling consumer. The vapour is then routed back to the compressor, thus completing the vapour compression heat pump cycle. The vapour compression heat pump cycle may comprise one, two or several stage compressor(s), which compresses the heat pump working fluid and circulates it in the heat pump cycle.

The vapour compression heat pump cycle (system) should, as stated above, have a thermal heating duty from 2 to 100 MW. In some embodiments the heating duty of the vapour compression heat pump cycle is from at least 5 MW, e.g. from at least 10, 15, 20 or 30 MW. The vapour compression heat pump cycle should deliver the total heat demand of the heating consumer(s) on an oil/gas processing facility, thus eliminating the need for hydrocarbon gas/oil fired heaters or electrical heaters.

The working medium should be selected such that a sufficient high temperature is reached in order to provide the necessary heat to the hydrocarbon stream to be processed, e.g. in an oil/gas/water separation process, while maintaining an adequate production rate. The hydrocarbon stream is typically heated to a temperature of 50 to 70 ºC in an inlet heater before introducing the stream into a separator. Further heating is often done in-between the separation stages (here referred to as “interstage heating”), typically to 70-90 ºC. However, the heating demand and processing temperatures of the hydrocarbon stream in such a processing facility may vary depending on the stream to be processed (composition, pressure, production rate, etc.). Such parameters are generally known to the skilled person. The working fluid/refrigerant used in the vapour compression heat pump cycle may be any mixture or pure component suitable for high temperature operation. Typical examples of suitable hydrocarbon based mixtures or pure components include refrigerants such as 1,1,1,3,3-Pentafluoropropane (R245fa), 1,1,1,2-Tetrafluoroethane (R134a), 1,1,1,2,3,3,3-Heptafluoropropane (R227ea), 1,1,1,3,3,3-Hexafluoropropane (R236fa), 1,1,1,3,3,-Pentafluorobutane (R365mfc), Ammonia (R717), H2O, i-Butane and/or n-Butane.

The expression “thermally connected” used herein should be understood as thermal communication between fluids, i.e. the transfer of heat between fluids via one, two or any required number of heat exchangers. The thermal connection (heat exchange) between the vapour compression heat pump cycle and the heating consumer(s) and cooling consumer, respectively, may be direct or indirect.

By the “direct thermal connection” arrangement the heating consumers are any required number of heat exchangers, in which the hydrocarbon stream to be processed is heated by directly heat exchanging with the hot refrigerant (working fluid) of the vapour compression heat pump cycle.

Correspondingly, the cooling consumers are any required number of heat exchangers wherein the cold refrigerant (working fluid) of the vapour compression heat pump cycle flows through the cooling consumer heat exchangers, thereby cooling the produced water, produced oil, compressed gas and/or other utility cooler.

By the “indirect thermal connection” arrangement the heating consumers are any required number of heat exchangers, as described above, for heating the hydrocarbon stream. In the indirect arrangement the heat from the hot refrigerant is transferred to the hydrocarbon stream via a separate heating medium. The separate heating medium is circulated in a closed loop, and heated by heat exchanging with the hot refrigerant (working fluid) of the vapour compression heat pump cycle in at least one heat exchanger, or any suitable number of heat exchangers. Thus, the hydrocarbon stream is indirectly heated by the heat pump refrigerant via a separate heating medium. The heating medium loop may be similar to a traditional heating medium loop, known in the field. The working (heating) medium in in the heating medium loop may be any known heating medium used in such traditional heating loops, e.g. hot oil, water or a water/glycol mixture.

Correspondingly, by indirect thermal connection the cooling consumers are any suitable number of heat exchangers, as described above, wherein a separate cooling medium flows through the cooling consumers heat exchangers. The separate cooling medium is circulated in a closed loop, and cooled by heat exchanging with the cold refrigerant (working fluid) of the vapour compression heat pump cycle in at least one heat exchanger, or any suitable number of heat exchangers. Thus, the cooling consumers are indirectly cooled by the heat pump refrigerant via a separate cooling medium. The cooling medium loop may be similar to a traditional cooling medium loop, known in the field. The working (cooling) medium may be any known cooling medium used in such traditional cooling loops, e.g. water or water/glycol mixture.

The inventors found that in situations with high gas compressor(s) outlet temperature, the downstream gas cooler(s), i.e. the cooling consumer heat exchangers, can be designed so that the temperature of the cooling medium is sufficiently high to be used directly as heating medium for the process heaters (heating consumers heat exchangers). This solution is a variation of the embodiment where a single heat pump cycle is directly thermally connecting the heating consumer(s) and the cooling consumers(s). In this embodiment the whole heating/cooling medium cycle may be in liquid phase, and supplying heat by heat pump cycle may not be necessary, thus electrical power consumption may be fully eliminated in terms of heat generation, the only electrical power required is for pumping the liquid used for the heating and cooling in the closed cycle. This system depicts in principle the merging of the cooling medium loop with the heating medium loop.

Thus, in this embodiment there is provided a system adapted for heating a mixed hydrocarbon stream in a phase separation process at a processing facility, the system includes a combined heating and cooling medium closed loop, thermally connected with at least one heating consumer, for providing heat to the at least one heating consumer, and thermally connected with at least one cooling consumer, for cooling and recovering heat from the at least one cooling consumer.

The combined heating and cooling closed loop system may provide for the total heat demand for the process heating consumers, in an oil/gas processing facility, as described above. In situation where the heat recovery downstream the gas coolers is not sufficient to provide the necessary heat to the heating consumers, additional heat supply to the combined heating/cooling closed loop may be needed. Such situations may arise during start-up, i.e. before the gas coolers can provide sufficient heat, or in any situations when the amount of heat recovered from the gas coolers is insufficient to cover the total heat demand to the heating consumers.

The heat pump may provide the necessary additional heat by heat exchanging (i.e. the heat pump condenser) with the combined heating/cooling closed loop, similar as described above in the cases of indirect heat exchanging with cooling medium loops or heating medium loops. The heat pump evaporator may be integrated, i.e. connected thermally, with the cold end of the combined heating/cooling closed loop. Additional heat may also be provided by an electrical heater integrated in the combined closed loop.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show a simplified depiction of a typical oil and gas treatment process.

Figure 1: Schematic process flow diagram illustrating the use of a heat pump inbetween cooling consumer(s) and heating consumer(s).

Figure 2: Schematic process flow diagram illustrating the use of a heat pump between cooling medium loop and heating consumer(s).

Figure 3: Schematic process flow diagram illustrating the use of a heat pump between cooling consumer(s) and heating medium loop.

Figure 4: Schematic process flow diagram illustrating the use of a heat pump between cooling medium loop and heating medium loop.

Figure 5: Schematic process flow diagram illustrating a closed combined heating and cooling loop containing a combined cooling and heating agent.

List of numeral references on drawings:

Fig.1 Fig.2 Fig.3 Fig.4 Fig.5

101 201 301 401 501 Inlet production stream

102 202 302 402 502 Inlet Heater

103 203 303 403 503 Upstream Separator

104 204 304 404 504 Interstage Heater

105 205 305 405 505 Mixed Phase Flow from Inlet Separator

106 206 306 406 506 Downstream Separator

107 207 307 407 507 Produced Oil

108 208 308 408 508 Produced Oil Cooler

109 209 309 409 509 Produced Water

110 210 310 410 510 Produced Water Cooler

111 211 311 411 511 Produced Gas

112 212 312 412 512 Gas Compressor

113 213 313 413 513 Gas Cooler

114 214 314 414 Heat Pump Compressor

115 215 315 415 Heat Pump Working Fluid (Gas)

116 216 316 416 Receiver Vessel

117 217 317 417 Heat Pump Working Fluid (Gas)

118 218 318 418 Heat Pump Working Fluid (Condensate)

119 219 319 419 Direct cross heat exchanger (optional)

220 423 518 Seawater

221 424 519 Cooling Medium Cooler (Seawater)

222 425 Cooling Medium Cooler (Heat Pump Working Fluid)

223 426 520 Cooling Medium Circulation Pump

224 427 521 Cooling Medium

320 420 Heating Medium

321 421 Heating Medium Circulation Pump

322 422 Heating Medium Heater (Heat Pump Working Fluid)

514 Break Tank

515 Temperature Control Valve (optional)

516 Level Control Valve

517 Electrical Heater (optional)

DETAILED DESCRIPTION

Embodiments of the invention will in the following be described in detail with reference to the accompanying drawings. It should be understood that the drawings represents a simplified schematic process diagram of a typical topside system, and the system may comprise other and additional individual units than those shown in the drawings. The main purpose of the drawings is to schematically depict various arrangement of the system according to the present invention.

(a) First arrangement; by use of a heat pump directly in-between cooling consumer(s) and heating consumer(s) (Fig. 1).

In a first arrangement, shown in Fig. 1, a heat pump is used directly in-between cooling consumer(s) and heating consumer(s), thus depicting a direct thermal connection arrangement. The vapour compression heat pump cycle comprises one or several stage compressor(s) (114) which compresses the heat pump working fluid/refrigerant (117) and circulates it in the heat pump cycle. A number of process heaters (102, 104) act as the heat pump circuit condensers. A number of process coolers (108, 110, 113) act as the heat pump circuit evaporators.

In the system shown in Fig. 1 the heat pump working fluid circulates through the loop, directly linking the heating and cooling consumers. The hot working fluid (115) is discharged from the compressor (114) and condenses in the process heaters (102, 104), thereby heating the process fluid. The condensate (118) is then routed to a receiver vessel (116). The receiver vessel (116) ensures that there in sufficient working fluid in the heat pump circuit. From the receiver vessel (116), the condensate (118) is routed to the cooling consumers and throttled upstream each process cooler (108, 110, 113). The cold working fluid evaporates in the process coolers (108, 110, 113), thereby cooling the process fluid. The working fluid is then routed back to the compressor (114), which discharges it back to the heat consumers (102, 104), thereby completing the loop.

In a method for processing an inlet hydrocarbon wellstream (101), which can be a mixture of oil, water and gas phase, in the system (arrangement) shown in Fig.1, the inlet stream (101) is heated, by heat exchanging with the hot refrigerant/working fluid (115), in a first inlet heater (102) to a temperature of typically 50-70 ºC before being introduced into the inlet separator (103), wherein gas is separated from the liquid phase. The liquid mixed phase (105) from the inlet separator (103) is further heated, by heat exchanging with the hot refrigerant/working fluid (115), in an interstage heater (104) and introduced into a downstream separator (106), wherein the oil and water phases are separated. The gas stream from separator (106), typically with cooling/scrubbing/ recompression, is left out from the figure for simplicity. All required heating for the separation process is supplied by the heat pump cycle and by recovering heat from the cooling consumers.

The produced oil (109) and produced water (107) are cooled in respective coolers (108) and (110), in which the produced oil and water are heat exchanged with the cold (condensed) heat pump working fluid (118) causing the working fluid to be evaporated, as described above. It should be noted that the oil separation train may include additional units and processing steps, e.g. any number of heaters and separators. Gas may be separated from the stream in additional separators in addition to the upstream separator (103) and produced water may be separated from the stream in additional separators in addition to the downstream separator (106). The method for processing the inlet stream may also include direct cross heat exchangers (119) transferring heat from e.g. the hot produced oil (109) and/or hot produced water (107) directly to the mixed phase flow from the inlet separator (103).

The gas phase (111), separated in the inlet separator (103), and in any later separating steps, is compressed in compressor (112) and cooled by heat exchanging with the cold (condensed) heat pump working fluid in gas cooler (113), thereby evaporating the refrigerant. It should be noted that the gas may be treated in additional compressing steps (112), each followed by interstage cooling (113). Each of said gas coolers should be integrated into the heat pump cycle, wherein the working fluid evaporates.

The condensing temperature of the hot working fluid (115), leaving the compressor (114), will be higher than any heater (102, 104) outlet temperature. The temperature of the hot working fluid (115) will thus depend on the composition and the pressure of the working fluid (115), which should be controlled with respect to the heat demands of mixed hydrocarbon stream to be processed. The working fluid/refrigerant used in the heat pump cycle may be any mixture or pure component suitable for high temperature operation, as indicated above.

In a startup situation where no heat can be recovered from the process coolers yet, i.e. the process cooling consumers (108, 110, 113), the heat supplied by the heat pump compressor (114) itself is sufficient to start the oil/gas processing, at reduced flowrates if necessary. Alternatively, extra heat may be provided by an electrical heater (not shown in Fig.1). The system may further include equipment for monitoring and controlling the temperatures, pressures and flowrates, and any additional process parameters generally known in an oil/gas processing system.

Possible variations of the system and method shown in Fig.1 include:

i. Any type of heat pump design may be utilized.

ii. The heat pump may be with or without any type of economizer.

iii. Removing the receiver vessel (116) and only utilizing the volume within the loop.

iv. Several circuits in a cascade arrangement, supplying the heat at different temperature levels.

v. Conventional direct cross heat exchangers (119) between hot and cold fluids.

Indicated locations in Fig.1 are typical examples only.

vi. Using supercritical working fluid in the heat pump circuit.

vii. Any process heaters or coolers (102, 104, 108, 110, 113) may be excluded from the heat pump circuit, if desirable. Heat/cold may then be supplied from other suitable sources, for example by process fluids (as per variation iv. above), hot return coolant or cold return heating medium.

(b) Second arrangement; by use of a heat pump between the cooling medium loop and the heating consumer(s) (Fig. 2)

In a second arrangement, which depicts a direct and indirect thermal connection arrangement, shown in Fig.2 a heat pump is used between a cooling medium loop and the heating consumer(s).

The system shown in Fig.2 is a variation of the system and method (a) shown in Fig.1, and described above. The heat pump shown in Fig.2 comprises, corresponding to the above described system (a), one or several stage compressor(s) (214) which compresses the working fluid (217) and circulates it, a number of process heaters (202, 204), which act as the heat pump circuit condensers and a receiver vessel (216) for the condensate (218). In this second arrangement, a cooling medium cooler (222) acts as the heat pump circuit evaporator.

In the system (arrangement) shown in Fig.2 the cooling consumers (208, 210 and 213) are part of a separate cooling medium loop (224). Like in the system (a), described above, the heating consumers, i.e. process heaters (202, 204) act as the heat pump circuit condensers. From the receiver tank (216), the working fluid (218) is throttled and routed to the cooling medium cooler (222). The cooling medium cooler (222) acts as the heat pump circuit evaporator and provides cooling for the cooling medium loop (224). It should be noted that cooling medium cooler (222) may consist of any number of heat exchangers. The evaporated working fluid (217) is routed to the compressor (214) which discharges compressed, hot working fluid (215) to the process heaters (202, 204), thereby completing the loop. The cooling medium loop (224) may be additionally cooled by heat exchanging with e.g. seawater (220) in an additional cooling medium cooler (221). The cooling medium loop (224) also comprises a circulation pump (223) to circulate the cooling medium throughout the loop.

Possible variations and working fluid considerations as established in the system and method described for the first arrangement (a) above are also valid for the system and method according to the second arrangement.

(c) Third arrangement; by the use of a heat pump between cooling consumer(s) and the heating medium loop (Fig. 3)

The system and method according to the third arrangement, which depicts another direct and indirect thermal connection arrangement, as shown in Figure 3, is a variation of the system and method (a) shown in Fig.1, described above. The heat pump shown in Figure 3 comprises, corresponding to the above described system (a), one or several stage compressor(s) (314) which compresses the working fluid (317) and circulates it, a receiver vessel (316) for the condensate (318) and a number of process coolers (308, 310, 313), which act as the heat pump circuit evaporators. In the third arrangement, a heating medium heater (322) acts as the heat pump circuit condenser.

In the system and method according to the third arrangement (c) all heating consumers (302, 304) are part of a separate heating medium loop (320). Like in the system and method (a), described above, the compressor (314) discharges compressed, hot working fluid (315), however in this arrangement the heat is exchanged/transferred to the process heating consumers (302, 304) via the heating medium heater (322). The heating medium heater (322) acts as the heat pump circuit condenser, transferring heat to the heating medium loop. It should be noted that heating medium heater (322) may consist of any number of heat exchangers. From the receiver vessel (316) the heat pump working fluid condensate (318) is throttled and routed to the cooling consumers (308, 310, 313) which act as the heat pump circuit evaporators. The evaporated working fluid (317) is routed back to the compressor (314) which discharges compressed, hot working fluid (315) to the heating medium heater (322), thereby completing the loop. The heating medium loop (320) also comprises a circulation pump (321) for circulating the heating medium through the loop (320).

Possible variations and working fluid considerations as established to the system and method in the first arrangement (a), described above, are also valid for the system and method according to the third arrangement.

(d) Fourth arrangement; by use of a heat pump between the cooling medium loop and the heating medium loop (Fig. 4)

The system and method according to the fourth arrangement, which depicts an indirect thermal connection arrangement, as shown in Figure 4, is a variation of the system and method (a), described above. The heat pump shown in Figure 4 comprises, corresponding to the above described system (a), one or several stage compressor(s) (414) which compresses the working fluid (417) and circulates it and a receiver vessel (416) for the condensate (418). A heating medium heater (422) acts as the heat pump circuit condenser, and a cooling medium cooler (425), acts as the heat pump circuit evaporator.

In the system according to the fourth arrangement all heating consumers (402, 404) are part of a heating medium loop (420), corresponding to the heating medium loop (320) in the third arrangement (c) described above, and all cooling consumers (408, 410, 413) are part of a cooling medium loop (427), corresponding to the cooling medium loop (224) in the second arrangement (b) as described above. Corresponding to the systems and methods (a) and (c), described above, the compressor (414) discharges the compressed, hot working fluid (415) providing heat to the heating medium loop (420) via the heating medium heater (422). The heating medium heater (422) acts as the heat pump circuit condenser and provides heat to the heating medium loop. It should be noted that heating medium heater (422) may consist of any number of heat exchangers. The condensed working fluid (418) is routed to the receiver vessel (416). The working fluid (418) is then throttled and routed to the cooling consumers, in this arrangement the cooling is performed by heat exchanging via the cooling medium cooler (425), correspondingly as described in arrangement (b) above. It should be noted that cooling medium cooler (425) may consist of any number of heat exchangers. The cooling medium cooler (425) acts as the heat pump circuit evaporator and is cooling the cooling medium loop (427). The evaporated working fluid (417) is routed back to the compressor (414) and discharged to the heating medium heater (422), thereby completing the loop. Both heating medium loop and cooling medium loop comprise circulations pumps (421, 426). The cooling medium loop (427) may comprise an additional cooler (424) for cooling with seawater (423).

Possible variations and working fluid considerations as established to the system and method in the first arrangement (a), described above, are also valid for the system and method according to the fourth arrangement. Also, possible variations described in arrangement related to the cooling medium loop (second arrangement (b)), and the heating medium loop (third arrangement (c)) above should be considered to be valid for the fourth arrangement.

(e) Fifth arrangement; combined cooling and heating medium closed loop (Fig.5).

The system according to the fifth arrangement, as shown in Figure 5, depicts the merging of a cooling medium loop with a heating medium loop. The inventors found that in situations with high gas compressor(s) (512) outlet temperature, the downstream the gas cooler(s) (513), can be designed so that the temperature of the cooling medium is sufficiently high to be used directly as heating medium for the process heaters. The system comprises a number of gas coolers (513), temperature control valve(s) (523), a break tank (514), a level control device (516) for said break tank (514), and a number of process heat consumers (502, 504).

Downstream the gas cooler(s) (513) the cooling medium has a high temperature and is routed to a break tank (514). From the break tank the hot cooling medium is routed to the heating consumers (502,504). Downstream the heating consumers (502, 504) the cooling medium is routed to the cooling medium return line. A level control device (516) for said break tank (514) will ensure that excess hot cooling medium is returned to the cooling medium circulation pump (520). The cooling medium loop (521) has an expansion drum/bladder (522) to absorb thermal expansions in the loop. A temperature control device (515) may be added for lowering the inlet temperature of the cooling medium cooler (519), to minimize scaling potential. The working medium in the combined cooling and heating medium loop may e.g. be water or a mixture of water/glycol.

The previously described heat pump vapour compression cycle may be thermally communicating with the combined heating and cooling closed loop for providing additional heat, e.g. if heat recovery from the gas coolers (513) is insufficient compared to the heating demand of the heating consumers (502, 504) and/or in start-up situations. An additional electrical heater (517) may also be used during start-up or to further increase the temperature, if required.

The heat exchangers in the combined heating/cooling closed loop should be of the same type as specified above. Surface areas of the relevant heat exchangers (513, 502, 504) are sufficiently sized for all operating cases.

A method for processing an inlet hydrocarbon wellstream (101), as described under the first arrangement (a) above, will in principle be identical using the fifth arrangement. However, the heating consumers and cooling consumers will in this arrangement thermally communicate with the combined heating/cooling closed loop. The combined heating and cooling closed loop will provide a thermal heating duty as specified above, i.e. 2-100 MW. This means that the total heat demand of the heating consumers may be supplied by the combined heating/cooling closed loop.

Possible variations of the system and method in the fifth arrangement include:

i. The electrical heater (517) may be removed, if the cooling medium temperature downstream the gas cooler (513) is already sufficient.

ii. The electrical heater (517) may be placed at another location if desirable, for example integrated into the break tank (514) or upstream one specific heating consumer such as 502 or 504.

iii. Additional control devices, for example downstream the heating consumers (502, 504), may be included.

iv. The electrical heater (517) may be replaced by a heat pump circuit condenser, the heat pump circuit evaporator should be located in the line downstream valve (516).

v. In addition to the electrical heater (517) a heat pump circuit condenser and evaporator may be positioned as indicated in iv above.

The system and methods described for the arrangements (a), (b), (c), (d) and (e) above can be adapted to any variations of said simplified oil and gas treatment process.

The separation train may consist of additional separation stages and each stage may consist of any type of two-phase separator or a three-phase separator. Associated heaters may be integrated into the heat pump cycle/loops described in arrangements (a), (b), (c), (d) and (e). The gas compression train may comprise any number of additional stages with associated coolers and any type of gas treatment systems such as gas dehydration and/or sweetening systems. Associated heaters and coolers may be integrated into the heat pump cycle and/or heating/cooling loops described in arrangements (a), (b), (c), (d) and (e).

In general, any heaters and coolers in systems not shown in the simplified oil and gas treatment process may be included. Examples include fuel gas heaters, heaters and coolers associated with still columns, freshwater maker heater, building heating, winterization heating to prevent buildup of ice and snow and others. These may be integrated into the heat pump cycle and/or heating/cooling loops described in arrangements (a), (b), (c), (d) and (e).

If deemed beneficial, direct cross heat exchange may be used between suitable streams, independent from the heat pump cycle and/or heating/cooling loops described in arrangements (a), (b), (c), (d) and (e). Typical examples are the use of hot produced oil or hot produced water to pre-heat the production stream between separation stages.

The heaters and coolers that are part of the heat pump cycle and/or heating/cooling loop described in arrangements (a), (b), (c), (d) and (e) may be any type of heat exchanger. Typical examples include shell and tube heat exchangers and plate and frame heat exchangers, compact/welded heat exchangers and others.

The system may be used for providing the required heat demand in oil/gas separating processes for separating mixed hydrocarbon fluids into at least a liquid oil phase, water phase (if present in the mixed hydrocarbon fluid) and natural gas phase (if present), as well as other present impurity phases. The system according to the present invention may be integrated in the processing facilities for separating the phases in a mixed phase production stream from one or more oil well(s) offshore and/or onshore. The system may be integrated into the topside processing facilities on a fixed or floating offshore field installation, or a floating vessel, e.g. a floating production, storage and offloading (FPSO) unit. The system may also be integrated in the processing facilities of onshore hydrocarbon production fields. The system is not limited to be used in processing facilities for produced oil well streams, as the system may also be used in further processing facilities e.g. partly treated hydrocarbon products, wherein further treatments/processing involve heat consumer(s) and cooling consumer(s) such as has been described herein.

Claims

C l a i m s

1. A system adapted for heating a mixed hydrocarbon wellstream (101) in a phase separation process at a processing facility, the system includes a vapour compression heat pump cycle which is thermally connected with at least one heating consumer (102,104), for providing heat to the at least one heating consumer, where the at least one heating consumer includes one or more of; inlet heater(s) (102) and oil separation train interstage heater(s) (204), and with at least one cooling consumer, for cooling and recovering heat from the at least one cooling consumer, where the said at least one cooling consumer is one or more of oil cooler(s) (108) and/or gas cooler(s) (113).

2. A system in accordance with claim 1, where the vapour compression heat pump cycle has a thermal heating duty from 2 to 100 MW.

3. A system in accordance with claim 1 or 2, where the at least one heating consumer further includes one or more of other utility heater(s).

4. A system in accordance with claim 1 or 2, where the at least one cooling consumer further includes one or more of; produced water cooler(s) (110) and other utility cooler(s).

5. A system in accordance with any of the preceding claims, where the vapour compression heat pump cycle is directly or indirectly thermally connected with the at least one heating consumer.

6. A system in accordance with claim 5, where the vapour compression heat pump cycle is indirectly thermally connected with the at least one heating consumer via a separate closed loop heating medium system (320).

7. A system in accordance with any of the preceding claims 1-4, where the vapour compression heat pump cycle is directly or indirectly thermally connected with the at least one cooling consumer.

8. A system in accordance with claim 7, where the vapour compression heat pump cycle is indirectly thermally connected with the at least one cooling consumer via a separate closed loop cooling medium system (224).

9. A system in accordance with any of the preceding claims, where the vapour compression heat pump cycle is

- directly thermally connected with the at least one heating consumer (102,104) and directly thermally connected with the at least one cooling consumers (108,110), or - directly thermally connected with the at least one heating consumer (102,104) and indirectly connected with the at least one cooling consumers (108,110), or

- indirectly thermally connected with the at least one heating consumer (102,104) and directly connected with the at least one cooling consumers (108,110), or

- indirectly thermally connected with the at least one heating consumer (102,104) and indirectly connected with the at least one cooling consumers (108,110).

10. A system according to any of the preceding claims, where the processing facility is integrated in topside processing facilities on a fixed or floating offshore field installation, an onshore hydrocarbon production fields or in an onshore hydrocarbon receiving process plant.

11. A system according to any of the preceding claims, where the mixed hydrocarbon wellstream is a wellstream (101) produced from one or several oil well(s) offshore or onshore, a crude oil or a partially processed hydrocarbon petroleum fluid.

12. A system according to any of the preceding claims, where the refrigerant (115,117) circulating in the vapour compression heat pump cycle is suitable for high temperature operation.

13 A system according to any of claims 1-4 and 10-12, comprising a combined heating and cooling closed loop, transferring heat recovered from cooling consumers, the cooling consumers being gas cooler(s) (513), to the heating consumer(s) (502,504).

14. A method for heating a mixed hydrocarbon wellstream (101) in a phase separation process at an oil/gas processing facility, wherein the mixed hydrocarbon wellstream is heated by directly or indirectly heat exchanging with a vapour compression heat pump cycle in at least one heating consumer (102, 104), where the at least one heating consumer includes one or more of; inlet heater(s) (102) and oil separation train interstage heater(s) (204), while recovering heat by heat exchanging in at least one cooling consumer, wherein the at least one cooling consumer is one or more of oil cooler(s) (108) and/or gas cooler(s) (113).

15. A method according to claim 14, wherein the mixed hydrocarbon wellstream is a wellstream (101) produced in at least one oil well offshore or onshore, a crude oil or a partially processed hydrocarbon petroleum fluid.

16. A method according to any of the preceding claims 14-15, wherein the at least one heating consumer further includes other utility heater(s).

17. A method in accordance with any of the preceding claims 14-16, wherein the at least one cooling consumer further includes one or more of; produced water cooler(s) (110) and/or other utility cooler(s).

18. A method according to any of the preceding claims 14-17, wherein the mixed hydrocarbon wellstream (101) is separated into oil, water and natural gas.

19. A method according to any of the preceding claims 14-18, wherein the mixed hydrocarbon wellstream (501) is heated by heat exchanging with a combined closed loop heating and cooling medium (521) in the at least one heating consumer (502,504), the heat being recovered from hot, compressed gas by heat exchanging with the combined closed loop heating and cooling medium (521) in at least one cooling consumer, the cooling consumer being gas cooler(s) (513).