System and method for heat removal using gas hydrates

Abstract

The present invention provides a system and method for heat removal. The system comprises a closed cooling loop with circulation of a cooling medium. The closed cooling loop includes a first pipeline in which the cooling medium comprising water and gas hydrate forming components is transported; a subsea cooler in which heat is removed from the cooling medium and gas hydrates are formed; a second pipeline in which the cooling medium from the subsea cooler is transported; a topside heat exchanger in which the cooling medium absorbs heat from an external source; and a means for circulating the cooling medium within the cooling loop.

Description

[0001] SYSTEM AND METHOD FOR HEAT REMOVAL USING GAS HYDRATES

[0002] Technical Field

[0003] The present invention relates to a system for cooling and a method of cooling with minimal use of electricity or other energy sources.

[0004] Background Art

[0005] The concept of “Free cooling” relates to the use of an available cold reservoir, such as water where energy in terms of heat can be discharged. Such cold water can be found in oceans, lakes, rivers or underground water basins. The cooling effect comes from absorbing heat by a cooling medium that can either be the cold reservoir itself or by heat exchanging with the cold reservoir through a heat exchanger. The cooled fluid, after discharging heat to the cold reservoir is then transferred to the distribution network and delivered to the customers as chilled fluid, such as water, for cooling a system inside a building. The main advantages of free cooling are the low costs and the sustainability in using a renewable energy source (RES).

[0006] Free cooling is also known as Deep water source cooling, as Seawater district cooling (SDC) or lake source district cooling (LSDC). Implementation of SDC principles in the design, development, or conversion of central air conditioning systems has proven to save in excess of 85 percent of the energy typically required for conventional air conditioning. Furthermore, the largest cities and several Data Centers are located at or close to the coastline and can gain from utilizing free subsea cooling.

[0007] The patent publication US8161759 B2 relates to a method of and apparatus for transferring heat energy between a heat exchanging subsystem installed above the surface of the Earth, and material beneath the surface of the Earth, by installing one or more coaxial-flow heat exchanging structures in the material beneath the surface of the Earth.

[0008] Gas hydrates as phase change material (PCM) for refrigeration purposes are known from the state of the art. Gas hydrates generate heat at the time of formation and absorb heat at the time of dissociation (melting). As an example, the patent publication GB2402732A discloses a refrigerating method and system utilizing gas hydrates. The patent publication US2020149787A1 relates to a land-based closed loop refrigeration system using a gas hydrate having a temperature below 0°C (273.15 K).

[0009] One object of the present invention is to provide an improved, reliable and close to electricity free cooling system for buildings, industrial applications and district cooling with high energy capacity. There is a desire to reduce the energy demand for cooling applications compared to existing cooling infrastructure.

[0010] Summary of invention

[0011] According to a first aspect of the present invention, there is provided a system for heat removal comprising a closed cooling loop with circulation of a cooling medium. The closed cooling loop includes: a first pipeline in which the cooling medium comprising water and gas hydrate forming components is transported; a subsea cooler in which heat is removed from the cooling medium and gas hydrates are formed; a second pipeline in which the cooling medium comprising the gas hydrates formed in the subsea cooler is transported; a topside heat exchanger in which the cooling medium absorbs heat from an external source; and a means for circulating the cooling medium within the closed cooling loop.

[0012] According to a second aspect of the invention there is provided a method for heat removal comprising circulating a cooling medium in a closed cooling loop, wherein the closed cooling loop comprises a first pipeline in which the cooling medium comprising water and gas hydrate forming components is transported; a subsea cooler in which heat is removed from the cooling medium and gas hydrates are formed; a second pipeline in which the cooling medium comprising the gas hydrates formed in the subsea cooler is transported; and a topside heat exchanger, and heat exchanging a warmer fluid from an external source with the cooling medium comprising gas hydrates in the topside heat exchanger. Brief description of Figures

[0013] Figure 1 is a general illustration of the disclosed system and process.

[0014] Figure 2 shows a basic design of a cooling loop, including a pump, topside heat exchanger and subsea cooler.

[0015] Figure 3 shows an embodiment with subsea recycling loop.

[0016] Figure 4 shows an embodiment with topside bypass.

[0017] Figure 5 shows an embodiment with gas separation and bypassing and recompression of separated gas.

[0018] Figure 6 shows an embodiment with pressure reduction unit upstream heat exchanger to reduce pressure.

[0019] Figure 7 shows an embodiment with pressure reduction unit upstream gas separator, bypassing of gas and gas hydrate slurry and over topside heat exchanger.

[0020] Figure 8 shows an embodiment with the inclusion of the main components in figures 2-7.

[0021] Figure 9 shows the gas hydrate curve for 90 mol% CO2 with 10 mol% N2 as the stippled line. The grey plot is the temperature plotted against the pressure for an experiment where a hydrate slurry produced by water and the abovementioned gas composition was exposed to external temperature changes in a cyclic manner which led to partly dissociation and re-formation of the gas hydrates.

[0022] Figure 10 shows temperature cycling for the torque plot in Figure 12. The stippled line is the temperature set-point for the system, the grey line is the temperature outside the pipe and the black line is the temperature inside the pipe where the hydrate slurry was flowing.

[0023] Figure 11 shows that the superficial velocity was 1 m / s indicated by the stippled line with units provided by the rightmost y-axis with label “Velocity [m / s]”. The figure also shows the same measured temperature profile from inside the pipe with label “Temperature [°C], as for Figure 10.

[0024] Figure 12 shows the torque profile measured during the temperature cycling indicated in Figure 10 and Figure 11 , for the velocity indicated in Figure 11 . Figure 13 shows calculated gas hydrate curves for systems with pure CO2 mixed with water with and without 5 volume percent ethanol. The arrow indicates the change in the experimentally determined gas hydrate melting temperature and pressure due to the addition of ethanol to the fluid system.

[0025] Figure 14 shows as sketch of the wheel flow loop applied in the production of the abovementioned results (Figures 9-13) with its main components.

[0026] Figure 15 is a photo of the wheel flow loop shown in Figure 14.

[0027] Detailed description of the invention

[0028] The present invention relates to free cooling, utilizing gas hydrate forming compounds, gas hydrates, and water as the energy carrier to transport heat from a waste heat source to a free cooling medium, such as the ocean, lake, river, or underground basin or onshore basin. These components, i.e. , the gas hydrate forming compounds, gas hydrates and water, are collectively referred to as the "cooling medium" in this description. The main idea involves using cold water from oceans, lakes, rivers, or underground basins to form gas hydrates, employing the subsea-cooling principle under high pressure in the presence of a gas hydrate forming gas mixture. In simplified terms, the industrial version includes a large-scale cooling unit submerged in the cold water (hereafter referred to as the subsea cooler) where heat is removed from the cooling medium by the cold water, and a topside heat exchanger where heat is absorbed by the cooling medium from a warm fluid provided by an external source, such as a district cooling unit, building or industry (for example data centers).

[0029] More specifically, the present invention relates to a system for heat removal that includes a closed cooling loop with continuous circulation and production of lean and rich gas hydrate phases, with heat absorption occurring in a topside heat exchanger and heat removal in a subsea cooler.

[0030] The idea is illustrated in Figure 1 , which depicts a basic design of a cooling loop. The cooling loop comprises a topside heat exchanger and a subsea cooler connected by large diameter pipelines (> ~5cm (2”)) for circulating the cooling medium from the topside heat exchanger to the subsea cooler and back. The heat exchanger design is not limited to pipes and can include any relevant design, such as plate-heat exchangers. The cooling medium within the cooling loop can consist of any combination of i) liquid and solids, ii) liquid and gas, and iii) liquid, solid, and gas. A "lean" gas hydrate phase (partly melted) or completely dissociated gas hydrate phase is transported from the topside heat exchanger via a first pipeline to the subsea cooler. Gas hydrates are produced in the subsea cooler, and a "rich" gas hydrate phase is transported via a second pipeline back to the topside heat exchanger, the first or second pipeline may be entirely or partly insulated.

[0031] The physical principle is that when a pressurized mixture of a gas hydrate forming compound (e.g., CO2, hydrocarbon gases) and water is cooled, gas hydrates form through an exothermic process (releasing heat), which is removed by the subsea cooler immersed in the cold water. Similarly, melting gas hydrates requires heat, which can be sourced from the external fluid. Thus, by exchanging heat between the warm fluid from the external source and the gas hydrate phase in the topside heat exchanger, the external fluid is cooled while the gas hydrates melt. The external source needing cooling can be any material, such as water, air, gas, another phase change material (PCM), another gas hydrate system, or even solids. The gas hydrate slurry in the cooling loop maintains a nearly constant temperature through the topside heat exchanger, and by avoiding complete melting, the remaining gas hydrate particles can enhance crystal growth in the subsea cooler. In such cases, the cooling loop thus recycles a phase change material with a very high heat capacity. The process can operate autonomously or as a "cooling battery." Since the system is pressurized, the subsea cooler can be located in shallow water if the temperature is suitable for gas hydrate formation. Even in warmer regions, sufficiently deep water can facilitate gas hydrate formation. For industrial systems, the subsea cooler could be a single-tube or multi-tube infrastructure. The subsea cooler may be a single uninsulated pipeline where gas hydrates form, or it may include an inlet manifold diverting to multiple smaller diameter pipes. When the subsea cooler comprises a plurality of pipes, the plurality of pipes is merged into the second pipeline having a larger diameter than the diameter of each of the plurality of pipes. Onshore or offshore single-phase or multiphase pumps can transport the gas hydrates, and compressors may be used for repressurizing the gas phase as needed. The singlephase or multiphase pumps may be located anywhere in the first or second pipeline or both. A dynamic control system would be relevant for adjusting efficiency. If no heat extraction is required from the gas hydrate slurry, the system can be recirculated or shut down, thus functioning as a fully autonomous system or a "cold storage battery." The topside heat exchanger will indirectly cool heat released from buildings using "district cooling" and cooling-demanding industries (including data centers). Direct contact heat exchanging is also a possibility.

[0032] The cooling loop, shown within the stippled area of Figure 2, includes a topside heat exchanger 1 for onshore / topside cooling and a subsea cooler for heat removal at the sea or lake floor. A cooling medium, a lean gas hydrate phase comprising water, gas hydrate forming components and optionally gas hydrates, is transported through a first pipeline 4 connecting the topside heat exchanger 1 with the subsea cooler 2. A pump 3 is used to pump the cooling medium to the subsea cooler at the sea floor. Alternatively, this pump 3 may be placed upstream of the topside heat exchanger, feeding the cooling medium in a second pipeline 5 to the topside heat exchanger. The system may include more than one pump.

[0033] The second pipeline 5 connects the subsea cooler with the topside heat exchanger 1 and may transport the cooling medium, a cold gas hydrate slurry, from the subsea cooler. The part outside the stippled area in Figure 2 shows the connection to the end user 14, where heat is discharged in the form of a warm fluid 12 to the topside heat exchanger 1 . Here, the cold gas hydrate slurry exchanges heat with the warm fluid 12 from the end user 14, which could be a building, district cooling, data center, or other units needing heat discharge. The gas hydrates melt either partially or completely, and the lean or gas hydrate-free phase returns to the subsea cooler 2 on the sea floor. The topside heat exchanger effectively cools the warm fluid 12 and returns a cold fluid 13 to the end user 14. Between the topside heat exchanger 1 and the end user 14, heat pumps or other energy transfer units can be used to create colder fluids (not shown in the figures).

[0034] Figure 3 shows an embodiment of the invention with a subsea recycling loop. The same components described for Figure 2 are shown in Figure 3. A first control valve 8 is used to recycle gas hydrate slurry back to the inlet of the subsea cooler 2, promoting gas hydrate formation or controlling pressure in the subsea cooler 2 and pipeline 5. A second control valve 9 may also be used to control pressure in the subsea cooler 2 and pipeline 5, working in conjunction with the first control valve 8 to control the recirculation of a portion of the rich gas hydrate phase back to pipeline 4.

[0035] Figure 4 shows an embodiment with a topside bypass line. The same components described for Figure 2 are shown in Figure 4. A portion of the gas hydrate-rich phase may bypass the topside heat exchanger 1 and be recycled using a second pump 10 directly to pipeline 4.

[0036] In Figure 5, an embodiment of the cooling loop with gas separation, bypassing, and recompression of the separated gas is shown. The same components described for Figure 2 are shown in Figure 4. A portion of the gas hydrate-rich phase may bypass the topside heat exchanger, be compressed by a gas compressor 7, and further recycled into pipeline 4. In Figure 5, it is shown that the recycled portion is injected directly after the multiphase pump 3. However, this injection may be done at any location along the pipeline. A gas separator 11 is arranged topside in the transport line 5, where gas is bypassed from the topside heat exchanger, compressed by a gas compressor 7, and further recycled into pipeline 4. The liquid, the gas hydrate-rich phase, is heat exchanged with warm fluid from the end user 14.

[0037] Figure 6 shows a further embodiment having the same components as shown in Figure 5. In addition to the natural reduction of pressure when transporting from below sea level to sea level or above sea level, forced reduction of the pressure through one or more expanders acting as a pressure reduction unit 6 may decrease the temperature of the gas hydrate slurry phase and increase the cooling potential of the rich gas hydrate slurry.

[0038] Figure 7 shows a combination of Figures 4, 5, and 6. This embodiment shows a pressure reduction unit upstream of the gas separator, bypassing of gas and gas hydrate slurry, and a heat exchanger topside.

[0039] Figure 8 shows an embodiment where a combination of main components is shown. This figure shows the system with all the components in the different versions of Figure 2-7 and thus constitutes the most complex set-up. The final set-up may deviate from the various suggested set-ups in Figures 2-8. A person skilled in the art of engineering will recognize that additional units and control systems may be required for the complete operation of such a process system. The main components are indicated in Figures 2-8 but do not exclude other useful units to ensure reliable and safe operation of the system.

[0040] The water depth between the topside heat exchanger and the subsea cooler may be whatever depth is appropriate for gas hydrate formation. The depth at which the subsea cooler will be located when submerged in the ocean will normally range from 50 to 1000 m.

[0041] The cooling medium may contain further components that modify gas hydrate formation temperature and kinetics and gas hydrate agglomeration. An example is an anti-agglomerant, a gas hydrate inhibitor preventing the deposition of gas hydrates on the pipe walls or clogging of the pipelines by gas hydrate lumping.

[0042] The gas hydrate forming compound may be selected from CO2, tetrahydrofuran, propane, methane, iso-butane, ethane, cyclo-pentane, and other gas hydrate forming components. Additionally, other phase change materials, including salt hydrates, may be part of the fluid system to improve the transport of the gas hydrate slurry or when it improves the overall efficiency of the system. The nature of the gas hydrate formers may be gas, liquid, or solids.

[0043] The production of gas hydrates at a higher pressure to a lower pressure downstream of the subsea cooler will lead to a reduction in temperature and an increased cooling effect. Furthermore, a forced reduction of the pressure through one or more pressure reduction units will decrease the temperature of the gas hydrate slurry phase and increase the cooling potential of the rich gas hydrate slurry.

[0044] Calculation of the additional cooling effect when transporting a gas hydrate slurry with 20% gas hydrate particles from 100 m below sea level with an initial pressure of 3650 kPa (36.5 bar) and temperature of 6.9 °C (283.35 K) to sea level with an operating pressure of 2650 kPa (26.5 barg) shows that the temperature of the fluid would drop 1 .9 °C (1 .9 K) to 5 °C (278.15 K).

[0045] The pump power for driving the fluid is low compared to the cooling effect. A 20 MW unit will demand around 120 kW of pump power. This depends on the overall viscosity and flow profiles of the system. The subsea cooler 2 may consist of an inlet manifold where the lean gas hydrate slurry enters from a larger diameter pipe and is diverted to several smaller diameter pipes that are not insulated (not shown in the figures). Alternatively, the subsea cooler 2 may consist of only one single uninsulated pipe. The single uninsulated pipe may have the same or a different pipe diameter than the first pipeline. Its dimensions will be determined from calculations of the overall efficiency as well as cost calculations. For the subsea cooler where the larger pipe is diverted to smaller, the smaller diameter pipes will transport the same volume of fluid per time, but the surface area of the pipes will be larger, which will give higher overall heat transfer. This high heat transfer will enable faster gas hydrate formation since the heat is removed faster. The smaller diameter pipes of the subsea cooler will be merged into a larger pipeline at the outlet of the unit, enabling efficient transport of the rich gas hydrate slurry to the topside heat exchanger.

[0046] The topside heat exchanger can be any efficient heat exchanger technology that fits the purpose, whether it be pipe-in-pipe, pipe-in-shell, plate heat exchanger, direct heat exchange, etc.

[0047] To increase the rate of gas hydrate formation, the gas hydrate phase may not be entirely melted in the topside heat exchanger. This will lead to a lean gas hydrate slurry phase containing gas hydrate particles that can act as seed particles for gas hydrate growth in the subsea cooler, which will both increase the rate of gas hydrate formation and reduce the plugging challenges.

[0048] Alternatively, a bypass stream of rich gas hydrate slurry can be diverted upstream of the topside heat exchanger and injected into the lean gas hydrate / water phase downstream of the topside heat exchanger to achieve the same seeding effect as described above.

[0049] One or several single-phase and / or multiphase liquid pumps may be used to transport the I iquid / slurry phase through the cooling loop. In addition to the transport, the pumps may also re-pressurize the flow after the pressure reduction when transporting from a lower height to a higher height (i.e. , from the subsea cooler to the topside heat exchanger) with additional reduction through reducers if such units are used.

[0050] Gas compressors may be used to re-compress free gas that cannot be transported by the pumps. The need for gas compressors will depend on the fluid system, the pumps used, multiphase flow properties, and heat exchanger type. The amount of gas hydrate particles in the liquid phase will affect the overall viscosity of the slurry (solid particles in a liquid phase). Also, possible formation of dispersions consisting of liquid water and other liquids (hydrocarbon, CO2, and other materials used for optimizing the process) may affect the viscosity of the fluid system. Therefore, it is important to control the amount of gas hydrates present in order to control the overall viscosity and thus the pressure drop during transport. The relative viscosity of a hydrate slurry will depend on the volume that the gas hydrates constitute relative to the total volume (hydrate volume fraction). Numerous experimental and simulation studies have shown that the relative viscosity depends on multiple factors. However, a common view is that a volume fraction of 20-30% of gas hydrate particles will not considerably increase the overall viscosity of the liquid phase. Moreover, a system may be transportable with a higher hydrate particle volume fraction as well, depending on factors such as pipe diameter, length of transport pipe, pump capacity and other factors. During the process the volume fraction of hydrates can vary from 0 vol% for a fully melted system downstream the topside heat exchanger, to 80 vol% which is deemed the absolute maximum amount of hydrate particles at any place in the system. For the transport pipe from the subsea cooler to the topside heat exchanger the most realistic concentration range will be 15-45 volume%, however improved flow assurance methods such as use of anti-agglomerants, optimized hydrate formation in the subsea cooler and other methods may increase the upper limit for a given system. Predicted and experimental values may deviate considerably, especially at higher volume fractions of hydrate particles, thus there are many factors that govern the overall viscosity and transport properties of gas hydrate slurries. Thus, for a given system, the optimal hydrate particle concentration must be determined from simulations and experiments.

[0051] Additional applications of this methodology include adding technology for water purification, hydrate-based gas separation (HBGS), gas storage, gas transport and other applications of gas hydrates. The present invention will contribute to making these additional technologies more energy efficient and commercially attractive by utilizing the sea or other cold basins for heat removal during the hydrate formation process. In this case, a portion of the rich hydrate slurry may be extracted. The extracted slurry will consist of liquids, gases and hydrate particles. During the separation of the gas hydrate particles, the hydrate particle fraction can approach or reach 100%. For such applications topside and subsea bypass lines in Figure 8 enables extracting a portion of the main flow (second pipeline, 5). The extracted hydrate slurry can then be further treated, for example, by separating the gas hydrate particles from the gases and liquids using appropriate process units or by transporting it to a subsequent treatment facility.

[0052] Experimental work

[0053] Results from Wheel Flow Loop tests on CO2 gas hydrate transportability during temperature cycling

[0054] Description of set-up of the “Wheel flow loop” or Wheel:

[0055] The wheel flow loop is a 2" stainless steel pipe shaped into the form of a wheel and mounted on a shaft in a vertical direction as shown in Figure 14. It is placed inside a climate chamber for temperature control. The stainless steel pipe can be operated at elevated pressures. Measured parameters are temperature, pressure, velocity, and torque values. In addition, a video camera is used to film through a sapphire optical section on the pipe. It can simulate transportation / flow, cool-down, shut-in, and restart conditions and is used to study the fluid system's behavior in a close to real- case scenario. A photo of the actual wheel is shown in Figure 15.

[0056] Experiment 1: Temperature cycling

[0057] A total of 8 wheel tests with CO2 and water were performed. The overall results were that:

[0058] • Flow occurred without plugging of the pipeline when gas hydrates were dispersed.

[0059] • A dispersed, well-transportable system was formed that stayed transportable during temperature cycling.

[0060] First, water and the gas phase were pumped into the Wheel in amounts precalculated to be able to form gas hydrates. The gas phase consisted of 90 mol% CO2 and 10 mol% nitrogen (N2). The wheel was cooled by reducing the temperature in the chamber (Figure 14-b), thus reducing the temperature of the fluids in the Wheel. After gas hydrates were formed, repetitive heating and partial melting followed by cooling and re-forming of gas hydrates was performed by changing the temperature in the chamber (Figure 14-b) in a cyclic manner as indicated in Figures 10 and 11 . The results from the torque plot (Figure 12) indicated that the gas hydrate slurry was stable and did not form any plugs during this temperature cycling.

[0061] Figure 9 shows the gas hydrate curve for 90 mol% CO2 in N2 as the stippled line. The black line is the temperature plotted against the pressure for an experiment where a gas hydrate slurry produced by water and the aforementioned gas composition was exposed to external temperature changes in a cyclic manner, which led to partial dissociation and re-formation of the gas hydrates. The temperature profiles for the set-point of the temperature control, the measured temperature in the chamber, and the measured temperature in the wheel are given in Figure 10. It shows that the fluid inside the pipe responds slowly to the temperature changes. This was due to the heat transmission through the steel pipe of the wheel and the phase transition of the gas hydrates in the wheel. The wheel was rotated at 1 m / s for this test as indicated by Figure 11. Figure 12 shows the measured torque data, which varies in a cyclic manner as a response to the gas hydrate content inside the wheel, which is an effect of the temperature inside the wheel. Lower temperature will give more gas hydrate particles, which will give a higher overall viscosity of the liquid phase, which will give a higher friction factor between the liquid and the pipe wall, which again will affect the torque on the shaft between the motor and the wheel.

[0062] Experiment 2: Addition of a thermodynamic inhibitor

[0063] A thermodynamic inhibitor for gas hydrate is normally added to the water phase and has the effect of reducing the temperature at which gas hydrates will form and dissociate. To show this, a system consisting of water with and without 5 volume-% ethanol and a pure CO2 phase was tested. The results from dissociation experiments showed that the ethanol reduced the gas hydrate melting temperature from 8.6 °C to 6.3 °C. This fits well with the thermodynamic calculations performed, as indicated in Figure 13. The change in melting point with 5 volume% ethanol present is indicated by the arrow in Figure 13. Advantages

[0064] The present invention will contribute considerably to meeting the increasing cooling demand worldwide, thus reducing CO2 emissions both nationally and globally. The global cooling energy consumption (housing + industries) was 3900 TWh in 2018 and is increasing every year. The main part of this is cooling for buildings with an expected increase of a factor of 3, and for the industry, where it is expected a factor of 7 increase in cooling demand for data centers alone.

[0065] List of reference signs in Figures 2-8

Claims

CLAIMS1 . A system for heat removal comprising a closed cooling loop with circulation of a cooling medium, the closed cooling loop including: a first pipeline in which the cooling medium comprising water and gas hydrate forming components is transported; a subsea cooler in which heat is removed from the cooling medium and gas hydrates are formed; a second pipeline in which the cooling medium comprising the gas hydrates formed in the subsea cooler is transported; a topside heat exchanger in which the cooling medium absorbs heat from an external source; and a means for circulating the cooling medium within the closed cooling loop.

2. The system according to claim 1 , wherein the cooling medium, when cooled in the subsea cooler, is transformed to a rich gas hydrate slurry.3 The system according to claim 2, further comprising a bypass line for bypassing parts of the rich gas hydrate slurry either for extraction or injection to the first pipeline.

4. The system according to any of the preceding claims, wherein the means for circulating the cooling medium is one or more single or multiphase pumps located anywhere in the first or second pipeline or both.

5. The system according to any of the preceding claims, wherein the first or second pipeline are entirely or partly insulated.

6. The system according to any of the preceding claims, wherein the subsea cooler comprises an inlet manifold diverted to a plurality ofpipes each having a smaller diameter than the first pipeline, and the plurality of pipes is not insulated.

7. The system according to claim 6, wherein the plurality of pipes is merged into the second pipeline having a larger diameter than the diameter of each of the plurality of pipes.

8. The system according to any of claims 1 to 5, wherein the subsea cooler comprises a single uninsulated pipe having the same or a different pipe diameter than the first pipeline.

9. A method for heat removal, comprising circulating a cooling medium in a closed cooling loop, wherein the closed cooling loop comprises a first pipeline in which the cooling medium comprising water and gas hydrate forming components is transported; a subsea cooler in which heat is removed from the cooling medium and gas hydrates are formed; a second pipeline in which the cooling medium comprising the gas hydrates formed in the subsea cooler is transported; and a topside heat exchanger, and heat exchanging a warmer fluid from an external source with the cooling medium comprising gas hydrates in the topside heat exchanger.

10. The method according to claim 9, wherein circulating the cooling medium is carried out by means of a single or multiphase pump located anywhere in the first or second pipeline or both.11 . The method according to claim 9 or 10, further comprising bypassing the topside heat exchanger a portion of gas hydrates in the second pipeline directly to the first pipeline or for extraction.

12. The method according to any of claims 9 to 11 , further comprisingbypassing a portion of gas hydrates from the second pipeline directly to the first pipeline comprising over the subsea cooler.

13. The method according to any of claims 9 to 12, further comprising controlling the pressure within the closed cooling loop.

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