LNG COLD ENERGY RECOVERY BY USING ICE SLURRY

Abstract

LNG cold energy can be recovered from the regasification process by using ice slurry. Ice slurry is used as a cold energy storage medium and heat transfer fluid. Currently, LNG at 162 C. is vaporized to city gas in heat exchange with sea water and the chilled sea water is disposed of into the sea. The cold energy recovered in a form of ice slurry at temperature of 45 C. is used for freeze and refrigeration warehouses, cooling data centers and HVAC of commercial buildings, cold energy industries, and CO.sub.2 liquefaction for CCUS. Ice slurry is produced in large capacities required for the LNG regasification process by direct contact heat transfer in the water layer with cold light solvent bubbles which are generated by the distributor nozzles being submerged in the heavy solvent layer. Toluene is used as the light solvent liquid and perfluorohexane or perfluoroheptane as the heavy solvent.

Claims

1. A LNG (liquified natural gas) cold energy recovery system 400 comprising: an LNG regasification heat exchanger 420, the LNG regasification heat exchanger receiving LNG 421 at 162 C. and vaporizing the LNG to natural gas 422; and an ice slurry production tank 401 having a top layer 405 having a light solvent, a middle layer 403 having water and a bottom layer 402 having a heavy solvent, wherein the middle layer comprises water, ice particles and a freezing point depressant, wherein the top, middle and bottom layers are different liquids with different densities and immiscible to each other, and wherein toluene 411 is chilled by the LNG regasification heat exchanger and fed into the bottom layer, thereby forming toluene bubbles having less density than the middle layer.

2. The LNG cold energy recovery system of claim 1, wherein the toluene bubbles are fed into the bottom layer by distributor nozzles, the bottom layer being more dense than the middle layer, thereby the middle layer prevented from reaching the distributor nozzles.

3. The LNG cold energy recovery system of claim 1, wherein the bottom heavy solvent layer is selected from a group consisting perfluorohexane (C.sub.6F.sub.14) and perfluoroheptane (C.sub.7F.sub.16).

4. The LNG cold energy recovery system of claim 1, wherein the freezing point depressant dissolves in water and is insoluble in the top light solvent and in said heavy solvent; wherein the freezing point depressant is a substance selected from a group comprising LiCl, NaCl, K.sub.2CO.sub.3, CaCl.sub.2), MgCl.sub.2, KAc (Potassium Acetate), and KCOOH (Potassium Formate).

5. The LNG cold energy recovery system of claim 1, wherein in the LNG regasification heat exchanger the flow rate of the toluene changes in response to the flow rate of the LNG while the temperature of the toluene is kept constant.

6. The LNG cold energy recovery system of claim 1, further comprising a superheater heat exchanger 430, a) wherein the natural gas from said LNG regasification heat exchanger is heated to a temperature above +2 C. in the natural gas superheater heat exchanger; b) wherein the heating medium for said superheater heat exchanger is an aqueous solution of a freezing point depressant which can be cooled to a temperature below 0 C. at an exit of the superheater heat exchanger; and c) wherein the freezing point depressant is a substance selected from a group consisting LiCl, NaCl, ethylene glycol, propylene glycol, KAc (potassium acetate) and potassium formate (KCOOH).

7. The LNG cold energy recovery system of claim 1, further comprising an ice slurry separation tank 451 for separating an ice slurry stream from a toluene stream from the ice slurry production tank; a. wherein the terminal velocity of a toluene bubble of 5 mm in diameter is Vt m/s whereas the hindered settling velocity of an ice particle of 1 mm in diameter Vs m/s; b. wherein, for the downward ice slurry flow at a bottom section of the ice slurry separation tank, the bulk flow velocity is maintained higher than Vs m/s but lower than Vt m/s; and c. wherein, for the upward toluene flow exiting through a nozzle located at the top section of the ice slurry separation tank, the nozzle is located where the level of the nozzle can prevent entrainment of blanketing nitrogen gas and the ice slurry.

8. The LNG cold energy recovery system of claim 7, further comprising an ice slurry storage tank 471 for receiving ice slurry from the ice slurry separation tank, wherein: a. the ice slurry storage tank operates continuously for LNG cold energy recovery while charging and discharging ice slurry at the same time; b. the ice slurry storage tank is charged with ice slurry from the ice slurry separation tank; c. the ice slurry storage tank discharges ice slurry at least to cold energy users and a CO.sub.2 liquefaction heat exchanger 481 for CCUS (Carbon Capture, Utilization, and Storage); and d. the ice slurry storage tank is sized for a capacity sufficiently large enough for the continuous operation by storing the excess ice slurry and discharging it during the peak hours for the deficient amount.

9. The LNG cold energy recovery system of claim 8, wherein: a. the CO.sub.2 liquefaction heat exchanger condenses CO.sub.2 gas by using the ice slurry generated with the LNG cold energy recovered; b. said CO.sub.2 gas 482 is fed from CO.sub.2 capture processes; c. said ice slurry is available for CO.sub.2 liquefaction from 45 C.; d. said CO.sub.2 gas is liquefied at 30 C. and 15 bar for transport; e. said ice slurry is supplied at temperatures higher than 45 C. in order to condense CO.sub.2 gas at higher pressures; f. said CO.sub.2 gas is liquefied for temporary storage for CCUS (Carbon Capture, Utilization, and Storage); and g. said recovered LNG cold energy is used to cool the CO.sub.2 gas during the compression process for CCUS.

10. The LNG cold energy recovery system of claim 1, wherein: a. the ice slurry is generated at the ice concentration up to 15% in weight; b. said ice slurry can be concentrated for various applications; c. for the ice slurry, ice particles of 1 mm to 100 micron in diameter are used.

11. The LNG cold energy recovery system of claim 1, wherein said LNG regasification heat exchanger is a closed system having an LNG side and a toluene side, wherein for the LNG side, stainless steel is used for the material of construction and for the toluene side, the material of construction is a substance selected from a group consisting stainless steel and carbon steel.

12. The LNG cold energy recovery system of claim 6, wherein said superheater heat exchanger is a closed system having a natural gas side and a heating medium side, wherein for the natural gas side, stainless steel is used for construction and for the heating medium side, the material of construction is a substance selected from a group consisting stainless steel and carbon steel.

13. The LNG cold energy recovery system of claim 7, wherein the ice slurry separation tank further comprises a pump to circulate the toluene stream from a top layer of the ice slurry separation tank to the LNG regasification heat exchanger and then to the bottom layer of the ice slurry production tank.

14. The LNG cold energy recovery system of claim 13, wherein the pump is explosion proof.

15. The LNG cold energy recovery system of claim 6, wherein: a. the natural gas superheater heat exchanger is used to heat the natural gas exiting the LNG regasification heat exchanger; b. a CO.sub.2 stream for a CCUS heats the natural gas as a heating medium; and c. said CO.sub.2 stream is condensed in a CO.sub.2 liquefaction heat exchanger.

16. The LNG cold energy recovery system of claim 1, wherein no nitrogen gas is entrained in the toluene stream fed to the LNG regasification heat exchanger.

17. The LNG cold energy recovery system of claim 1, wherein no ice slurry is entrained in the toluene stream fed to the LNG regasification heat exchanger.

18. The LNG cold energy recovery system of claim 1, wherein nitrogen blanketing is used for the ice slurry production tank to prevent leakage of the bottom layer of heavy solvent.

19. The LNG cold energy recovery system of claim 7, wherein each of the ice slurry production tank and the ice slurry separation tank has a safety valve leading to a flare system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The foregoing summary, as well as the following detailed description of presently preferred embodiments, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the embodiments, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the embodiments are not limited to the precise arrangements and instrumentalities shown.

[0031] FIG. 1 is a schematic flow chart of an ice slurry manufacturing process comprising an ice production tank, an ice slurry separation tank, and a chiller;

[0032] FIG. 2 is a schematic diagram of an ice slurry downcomer;

[0033] FIG. 3 is a schematic diagram of an ice slurry separation tank having an inverted cone at the bottom section;

[0034] FIG. 4 is a phase diagram of a eutectic system of NaClH.sub.2O;

[0035] FIG. 5 is a diagram of solubility of water in toluene;

[0036] FIG. 6a is a schematic diagram of a sessile water drop sitting on a smooth hydrophilic surface of uncoated base substrate in air;

[0037] FIG. 6b is a schematic diagram of Wenzel state where a water drop contacts the bottom of the ridges, with water replacing air in the spaces between the ridges, on a rough surface in air;

[0038] FIG. 6c is a schematic diagram of Cassie-Baxter state where a water drop sits on the top of the ridges, with the spaces between the ridges occupied with air, on a rough surface in air;

[0039] FIG. 6d is a schematic diagram of a water drop or an ice particle carried away by a chilled solvent flow from an icephobic surface that is completely submerged in a flowing immiscible solvent;

[0040] FIG. 7 is a schematic flow chart of an ice slurry manufacturing process of the present invention comprising an ice slurry production tank, an ice slurry separation tank, an ice slurry storage tank, a CO.sub.2 liquefaction heat exchanger, a LNG regasification heat exchanger, and a natural gas superheater heat exchanger; and

[0041] FIG. 8 is a phase diagram of a eutectic system of potassium formatewater.

[0042] To facilitate an understanding of the invention, identical reference numerals have been used, when appropriate, to designate the same or similar elements that are common to the figures. Further, unless stated otherwise, the features shown in the figures are not drawn to scale but are shown for illustrative purposes only.

DETAILED DESCRIPTION OF THE INVENTION

[0043] The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

[0044] Certain terminology is used in the following description for convenience only and is not limiting. The article a is intended to include one or more items, and where only one item is intended the term one or similar language is used. Additionally, to assist in the description of the present invention, words such as top, bottom, upper, lower, front, rear, inner, outer, right and left are used to describe the accompanying figures. The terminology includes the words above specifically mentioned, derivatives thereof, and words of similar import.

[0045] Ice slurry manufacturing process 100 of this invention in FIG. 1 generates an ice slurry stream 114 at 5 C. from a brine feed 108 at 1 C. in ice slurry production tank 101 using a chiller 120. The ice production tank 101 has two immiscible solvent layers; a layer 102 being heavier in density than water and the other layer 105 lighter than ice. The ice slurry is produced in direct contact heat transfer with the light solvent bubbles generated by distributor 107 in heavy solvent layer 102. The ice slurry product comprises of 15 wt. % ice particles in sizes ranging from around 100 microns to 1 mm, while the light solvent bubbles are in sizes from around 5 mm to 10 mm. The light solvent bubbles collect in immiscible light solvent layer 105 at the top of the ice slurry production tank. Ice slurry 114 produced in tank 101 is sent by pump 106 to ice slurry separation tank 151 through downcomer 109. The entrained light solvent bubbles are first separated in downcomer 109 and further in ice slurry separation tank 151 from the ice slurry stream by using buoyant forces.

[0046] From the ice slurry separation tank 151, stream 167 comprising of the entrained light solvent and the large ice particles is sent by pump 161 to be mixed with stream 166. The homogeneous ice slurry product stream 165 is supplied by pump 162 to the users 170 and 180. The brine stream 166 of the melted ice slurry is recycled to ice slurry production tank 101 from users 170 and 180 along with stream 167. At this time, the large ice particles in stream 167 are melted in stream 108 by mixing with warm returning stream 166. Agitator 163 in ice slurry production tank 101 operates in low speeds to push the ice slurry toward ice slurry downcomer 109, and agitator 168 in ice slurry separation tank 151 to push large ice particles to exit nozzle 112. The ice slurry manufacturing process 100 is a completely closed system requiring very small amount of fresh make-up brine 117.

[0047] The ice slurry mixture of 15 wt. % ice is fed into the inverted circular cone section of ice slurry separation tank 151, where it flows down at a specific velocity to carry the ice particles of wanted sizes with it but to release the light solvent bubbles to rise. This inverted cone keeps the ice slurry product to be homogeneous. By being homogeneous, it means that the particles are evenly distributed in the slurry flow without any segregated layer of particles. To form a homogeneous ice slurry mixture without this inverted cone, it usually needs appreciable agitation in a tank as ice tends to float. The entrained light solvent bubbles along with the large ice particles are also separated from the ice slurry product stream in this inverted cone. The ice slurry 191 may be exported when needed, and the used brine 192 returns to the process. The exported ice slurry can be used to produce pure ice particle blocks after the brine removal and water wash steps or stored for later use for the peak shaving of power consumption.

[0048] Recirculating cold light solvent stream 111 is continuously injected by distributor 107 into the immiscible heavy solvent layer 102 to generate bubbles of immiscible light solvent without ice clogging, and the bubbles ascend by buoyant forces through water layer 103 exchanging cold energy to produce ice. Returning brine stream 108, a mixture of streams 166 and 167, is continuously fed into the water layer 103. Ice slurry stream 114 of 15 wt. % ice, a Newtonian fluid, is continuously withdrawn through ice slurry downcomer 109. Stream 110 from the layer of collected light solvent is circulated by pump 115 through chiller 120. When this cold immiscible light solvent stream 111 is injected back into immiscible heavy solvent layer 102, ice clogging does not take place because there is no free liquid water available to freeze in the stagnant immiscible heavy solvent layer.

[0049] The phase diagram of water-NaCl binary system in FIG. 4 shows the operating conditions for the ice slurry production process. A brine feed at point A at 6.7 wt. % NaCl and 1 C. is continuously fed into the water layer in the ice slurry production tank. The feed brine is in direct contact heat exchange with the cold immiscible light solvent bubbles generated at 15 C. The feed is then cooled to 5 C. as shown at point B in the figure, where pure ice crystals are produced. It separates into point C of pure ice and point D of 7.9 wt. % brine. As a result, 15 wt. % of the feed brine is crystallized into pure ice and 85 wt. % of the feed remains as a brine solution of 7.9 wt. % NaCl. The pure ice produced is withdrawn in ice slurry stream 114 that contains 15 wt. % of ice.

[0050] In order to separate the light solvent bubbles entrained in the ice slurry stream being withdrawn from the ice slurry production tank 101, a downcomer 109 is installed at the wall of the tank. The downcomer system 200 is shown in detail in FIG. 2, which comprises a straight vertical wall 209, sloped wall 208, and outlet nozzle 207. The downcomer provides a disengaging space 206, where any entrained solvent droplets are separated from the ice slurry stream by buoyant forces. In order for the buoyant forces to work most effectively, the downward vertical velocity of the ice slurry flow in the disengaging space must be maintained below the terminal velocity of the light solvent bubbles but higher than the hindered settling velocity of the largest ice particle to recover. The terminal velocity for the solvent bubble in this case is defined as the vertically rising velocity of a bubble of the density lighter than the surrounding fluid owing to the buoyant forces overcoming the frictional drag forces in the quiescent fluid, when the solvent bubble does not interact with other solvent bubbles because the concentration of the bubble is low in the surrounding fluid. The hindered settling velocity for the ice particle is defined as the vertically rising velocity of a particle of the density lighter than the surrounding fluid owing to the buoyant forces overcoming both the frictional drag and interaction forces in the quiescent fluid, when the ice particle interact with other ice particles with its motion hindered by the interactions. The velocities are calculated by the methods well known to those who are familiar with the field of this art as explained in Perry's Chemical Engineers' Handbook (in the section of Particle Dynamics, Seventh Edition, 1999, McGraw Hill).

[0051] The terminal and the hindered settling velocities are calculated using toluene as a light solvent to produce a product of 15 wt. % ice slurry in NaCl brine. The velocities of a spherical toluene bubble of 5 mm in diameter are tabulated in Table 1. The velocities of the ice particles of 2 mm, 1 mm, 0.5 mm and 0.1 mm in diameter are also tabulated in the table. In the ice slurry downcomer 109 and the ice slurry separation tank 151, the surrounding fluid for the toluene bubbles is the ice slurry of 15 wt. % ice at 5 C. The surrounding fluid for the ice particles, on the other hand, is assumed to be the same as the brine of 7.9 wt. % NaCl at 5 C. neglecting the effects of toluene bubbles; based on the preliminary design of the ice slurry production tank made for this invention, the average density change of the surrounding fluid due to the existence of the liquid toluene bubbles is within a few percent so the density reduction has been neglected. For the toluene bubbles, the terminal velocity is more appropriate to use in the downcomer and the ice slurry separation tank because their concentrations must be low, but the hindered settling velocity is more representative in the brine layer of the ice slurry production tank. For the ice particles, the hindered settling velocities are used in all three places. The physical properties needed for the calculation are given in Table 3 and Table 4.

TABLE-US-00001 TABLE 1 Terminal and Hindered Settling Velocities Settling Object Size Reynolds Number Terminal Velocity Hindered Settling Velocity TolueneBubble 5 mm 137 0.102 m/s 0.072 m/s Ice Particle 2 mm 18.3 0.040 m/s 0.021 m/s Ice Particle 1 mm 5.2 0.023 m/s 0.011 m/s Ice Particle 0.5 mm 0.7 6.7 10.sup.3 m/s 2.9 10.sup.3 m/s Ice Particle 0.1 mm 0.02 3.4 10.sup.4 m/s 1.4 10.sup.4 m/s

[0052] As shown in the table, the terminal velocity of a toluene bubble of 5 mm in diameter is 0.102 m/s in an ice slurry of 15 wt. % ice at 5 C., and the hindered settling velocity of an ice particle of 1 mm is 0.011 m/s. Therefore, the downward ice slurry flow velocity in the downcomer must be maintained between these two velocities, because the ice slurry flow must carry the ice particles of 1 mm in diameter and smaller with it, while release the toluene bubbles of 5 mm in diameter and larger to float. The volume of disengaging space 206 in the straight vertical wall section depends on the width M and height L for a given circumferential length, and provides enough residence time for the withdrawing ice slurry flow so that the rising light solvent bubbles can escape. Also, the width M determines the cross sectional area of the flow passage for a given circumferential length, which will again determine the average velocity of the ice slurry flow. The height L of the disengaging space, on the other hand, determines the residence time for a solvent bubble to rise to the top of the ice slurry downcomer. For the disengaging height L, a height more than 0.3 m is typically provided. The downward ice slurry fluid then collects at space 210 of the sloped wall, and is discharged through nozzle 207 with no stagnant space. Agitator 263 operates in low RPM to push ice slurry 204 to downcomer 209 below interface 202 with light solvent layer 205.

[0053] The ice slurry separation tank system 300 is shown in FIG. 3. Stream 114 in FIG. 1 is sent to ice slurry separation tank 151 by pump 106, and fed into nozzle 354 in FIG. 3. The inlet nozzle 354 provides a horizontal cross-sectional area of the inverted circular cone through which the inlet ice slurry stream develops the flow velocity necessary to carry the ice particles of the desired sizes. When it is desired to carry the particles of larger sizes, the inlet slurry stream can be introduced into nozzle 355, which will provide a smaller cross-sectional area to carry the larger particles at a higher flow velocity. For example, the ice slurry stream of 110 LPM of 15 wt. % ice slurry with a production rate of 1 ton of ice/hr can be fed into the nozzle 354 that will develop the downward flow velocity of 0.011 m/s, which is the hindered settling velocity to carry the ice particles in diameter of 1 mm and less and release the toluene bubble of 5 mm and larger to rise at its terminal velocity of 0.102 m/s. When it is desired to carry ice particles of 2 mm and lower, the ice slurry stream is fed into nozzle 355 which will develop a flow velocity of 0.021 m/s the hindered settling velocity of the larger ice particle. Therefore, the light solvent bubbles are separated twice, once in the downcomer and again in the ice slurry separation tank. In the meantime, the ice slurry product can be kept homogeneous owing to this inverted cone section, and then pumped directly to the cold energy users 170 and 180 through the outlet nozzle 357. The toluene bubbles collected in the top layer 353 and the large size ice particles floating below the toluene layer are pumped in stream 167 through exit nozzle 356. Agitator 368 operates in low RPM to push the ice particles to exit nozzle 356 below the interface 358 between ice slurry layer 354 and toluene layer 353. The large ice particles are melted by mixing with the warm returning brine stream 166 in the line of stream 108, and the combined stream is fed into ice slurry production tank 101.

[0054] Returning brine stream 166 of 6.7 wt. % NaCl, combined with stream 167, is fed into ice slurry production tank 101 as a feed stream 108 at around 1 C. Since the agglomerating large ice particles melt at this time, no agglomeration of the ice particles takes place in the closed system of this ice slurry manufacturing process. In heat exchange with homogeneous ice slurry product stream 165, ice slurry user 170 cools a cold liquid HTF for use in the low temperature consumers, and user 180 generates a cold air stream for the cold air consumers. The number and types of the users can change while the ice slurry is supplied in series or parallel to the users between the supply stream 165 and the return stream 166.

[0055] The ice slurry manufacturing process of this invention needs two solvents one heavier in density than water and the other lighter than ice. The heavy solvent, light solvent and water are immiscible with each other. The freezing point depressant, on the other hand, must be soluble in water, but insoluble in the solvents. We have found that the system comprising perfluorohexane (C6F14), toluene, and water with NaCl as a freezing point depressant satisfies these requirements. By being immiscible, it means that the liquid solutions make distinct liquid phases after thorough mixing; the distinct liquid phases, however, can still dissolve the components between each other. The miscibility is strongly dependent on temperature. Therefore, an immiscible binary mixture at a low temperature may form a miscible mixture at higher temperatures. The mutual solubility of perfluorohexane (C.sub.6F.sub.14), toluene and water is illustrated in Table 2.

TABLE-US-00002 TABLE 2 Mutual Solubility of Solvents and Water (1) C.sub.6F.sub.14 Toluene Water in C.sub.6F.sub.14 N/A 2.0 (1) 10 ppm (2) in Toluene 1.2 (1) N/A 567 ppm (2) in Water <5 ppm (2) 520 ppm (3) N/A Note: (1) Solubility in volume % at room temperature (2) At 25 C. (3) At 20 C.

[0056] The relevant physical properties of the four components being used in the process of this invention perfluorohexane (C.sub.6F.sub.14), toluene, water and ice are listed in Table 3.

TABLE-US-00003 TABLE 3 Physical Properties of C.sub.6F.sub.14, Toluene, Water and Ice Property C.sub.6F.sub.14 Toluene Water Ice Molecular Weight 338 92.1 18 18 Density (Kg/M.sup.3) 1680 (1) 886 (2) 999.8 (3) 916.2 (2) Melting Point ( C.) 90 95 0 0 Boiling Point ( C.) 56 111 100 100 Flash Point ( C.) N/A 6 N/A N/A Auto Ignition N/A 530 N/A N/A Point ( C.) Specific Heat Capacity 1.1 (1) 1.6 (2) 4.2 (3) 2.05 (2) (KJ/Kg. C.) Therm. Cond. 0.057 (1) 0.144 (2) 0.57 (3) 2.22 (2) (W/M. C.) Viscosity (mPa .Math. s) 0.64 (1) 0.77 (2) 1.79 (3) N/A Note: (1) At 25 C. (2) At 0 C. (3) At 0.01 C.

[0057] Physical properties of the ice slurry must be known for process design of the ice slurry manufacturing plant. For density, specific heat capacity, thermal conductivity and viscosity, the following equations are used, where , Cp, k and stands for density in Kg/M3, specific heat capacity in KJ/Kg.Math.K, thermal conductivity in W/m.Math.K, and viscosity in Pa.Math.s, respectively, while subscripts b, i, and m for brine, ice, and mixture of ice slurry, respectively. For density p, the weight fraction averaged value is expressed by the following equation

[00001]${}_{m=1}/W_i/{}_i+\left(1-W_i\right)/{}_b]$

where Wi stands for weight fraction. For specific heat capacity, the following equation is used.

[00002]$\mathrm{Cpm}=\mathrm{WiCpi}+\left(1-\mathrm{Wi}\right)\mathrm{Cpb}$

For thermal conductivity k, the following equation is recommended, where Wiv stands for volumetric fraction.

[00003]$k_m=k_b\left\{[2k_b+k_i-2W_{\mathrm{iv}}\left(k_b-k_i\right)/\left[2k_b+k_i+W_{\mathrm{iv}}\left(k_b-k_i\right)\right]\right\}$

For dynamic viscosity p, the following equation is used.

[00004]${}_m={}_b\left(1+2.5W_{\mathrm{iv}}+10.05W_{\mathrm{iv}}^2+0.00273.Math.{10}^{-3}.Math.e^{16.6\mathrm{Wiv}}\right)$

The calculated values of the physical properties are given in Table 4.

TABLE-US-00004 TABLE 4 Physical Properties of Brine, Ice, Ice Slurry and Toluene at 5 C. 7.9 wt. % Property NaCl Brine Ice 15 wt. % Ice Slurry Toluene Density (Kg/M.sup.3) 1062 917.5 1037.7 890.5 Heat Capacity(KJ/Kg .Math. K) 3.76 2.07 3.51 1.61 Therm. Cond. (W/M .Math. K) 0.54 2.25 0.58 0.14 Viscosity (mPa .Math. s) 2.32 N/A 4.09 0.83 Heat of Fusion (KJ/Kg) N/A 333.6 (1) N/A N/A Note: (1) At 0 C.

[0058] In addition to perfluorohexane (C.sub.6F.sub.14) as an immiscible heavy solvent, the mixtures of a perfluorocarbon such as perfluorohexane(C.sub.6F.sub.14) and a hydofluoroether such as perfluorobutyl methyl ether(C.sub.4F.sub.9OCH.sub.3) make binary liquid solutions that are immiscible with toluene and water. For example, the binary mixture comprising perfluorohexan (C.sub.6F.sub.14) and 3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-trifluoromethyl hexane (C.sub.3F.sub.7CF(OC.sub.2H.sub.5)CF(CF.sub.3).sub.2) or perfluorohexane (C.sub.6F.sub.14) and perfluorohexylethyl 1,3-dimethylbuthyl ether also makes a miscible binary solution which is immiscible with toluene and water in certain concentrations. Therefore, the binary mixtures are good candidates for the heavy solvent. Especially, the hydrofluoroethers are lower in price than the perfluorocarbons.

[0059] For a proper operation of the ice slurry manufacturing process, the chiller must be designed such that the blockage does not take place due to the ice adhesion and accumulation. This problem is more significant when the amount of undissolving water in the solvent is high. For example, toluene dissolves water in a range of a hundred ppm at the operating temperatures, while perfluorohexanein around 10 ppm. When the toluene stream is chilled from 5 C. to 15 C. in the chiller, the solubility of water decreases from 152 ppm (point A) to 82 ppm (point B) as shown in FIG. 5. For production of 1 ton of ice/hr for 15 wt. % ice slurry product, the feed brine of 6.7 wt. % NaCl is cooled first in a precooler from 1 C. to 4 C., which is 0.2 C. warmer than the liquidus temperature, and then further chilled in the ice slurry production tank from 4 C. to 5 C. for ice formation. In order to supply cold energy for the ice formation, about 420 LPM of toluene must be recirculated through the chiller with the chiller inlet temperature of 5 C. and outlet temperature of 15 C. The recirculating toluene stream, in this case, generates about 1.6 Kg/hr of water. When this amount of water remains as solid ice in the chiller, it is a sufficient amount to block the passages of the solvent in a few hours.

[0060] Owing to the icephobicity of the coated surfaces in this invention, the undissolving water and the subsequent ice particles do not adhere on the cold surfaces, but are all carried away into the ice slurry production tank. The unique operation methods described below enable the coated surfaces to exhibit the icephobicity in actual applications in subzero conditions. According to an experiment for the drop shedding by Milne and Amirfazli, a water drop of 2 micro-liters (l) was carried away by an air stream at the velocities above 5 m/s from superhydrophobic surface and 20 m/s from the hydrophilic surface. This result suggests that, even with superhydrophobic surfaces, the water drop will possibly be sessile and then freeze into ice if there are not enough drag forces by the surrounding fluid. It also suggests that it is more probable with hydrophilic surfaces for the water drops to be sessile and freeze. This conclusion is consistent with the observations made by other researchers that icephobicity is not directly related with hydrophobicity. This is because the icephobicity also depends on other factors from the environment where the surfaces are exposed to. In this invention, therefore, all possible options are incorporated in order to prevent ice adhesion on the cold heat transfer surfaces.

[0061] In this invention, the hydrophobicity of the coated surfaces of the solvent side of the chiller is transferred to icephorbicity by submerging the surfaces in the flowing immiscible solvent. This icephorbicity ensures that the free water molecules undissolving in the chilled solvent are readily carried away by the main flow of the immiscible solvent stream by drag forces before the water droplets become sessile locally on the cold heat transfer surfaces. Hydrophobic coatings are known to form rough surfaces comprising of random ridges as shown in FIG. 6b to FIG. 6d; with air filled in the spaces between the ridges, this roughness makes water drops in micron sizes to sit on the top of the ridges as shown in FIG. 6c making a Cassie-Baxter state rather than being sessile on an untreated surface as shown in FIG. 6a in a completely wet state or in FIG. 6b on a treated surface in a Wenzel state. Those rough surfaces are produced by applying the hydrophobic coating material on the surfaces of a hydrophilic base substrate. The hydrophilic surfaces of such a base substrate are illustrated in FIG. 6a, where a water drop in air spreads out on a flat surface and become sessile with the contact angle less than 90.

[0062] The hydrophobic coating materials are readily available in marketplaces, being made from a wide range of different materials comprising of polymeric materials such as PTFE and silanes, inorganic materials such as silica and titania, or their combinations thereof. The hydrophobic surfaces as represented in FIG. 6c in a Cassie-Baxter state lose their water repelling capability, when the air in the pore spaces between the ridges is displaced by water as shown in FIG. 6b in a Wenzel state. For example, in nature, such hydrophobic surfaces lose their ability to repel water after they are exposed to a torrential rain or strong waves on a ship. Also, such hydrophobic surfaces lose their ability due to the loss of air molecules by diffusion into the water phase, when the surfaces are submerged in water. Another cause for the loss of hydrophobicity is the destruction of the ridge structure due to the repetition of freezing and deicing procedures. Therefore, for the ice slurry manufacturing process of this invention, the coated surfaces of the chiller is not allowed to contact the brine water directly for heat transfer. Instead, the brine is kept away from the coated surfaces, and only the flowing immiscible solvent is allowed to contact them. This unique operation method of this invention makes it possible to maintain the icephobicity on the coated surfaces, and consequently the free water molecules liberated in the chilled solvent stream do not become sessile on the cold heat exchange surfaces but are carried away with the main stream of solvent as shown in FIG. 6d.

[0063] Therefore, the equipment is designed to develop sufficient drag forces so that the water droplets forming from the undissolving free water molecules are readily carried away by the main flow of immiscible solvent stream. The circulation pump needs to perform adequately so that a sufficient velocity of the solvent flow can be maintained for generation of drag forces on the undissolving water droplets and the subsequent ice particles that form during chilling. Also, the tube bundles must be carefully designed so that no stagnant spaces develop in the passages of the solvent. Therefore, a design such as U-tube is preferred.

[0064] In summary, the problem of the blockage by ice adhesion in the chiller is overcome in this invention by providing the environments for the hydrophobic coated surfaces to exhibit the necessary icephorbicity while in operation. The environments are successfully provided by taking the following measures; firstly, the coated surfaces are let remain immersed in the flowing immiscible solvent all the time; secondly, sufficiently high velocity of the immiscible solvent flow is maintained in order for the free water droplets and ice particles to be carried away by drag forces; thirdly, no stagnant spaces are allowed in the solvent side of the chiller where otherwise water drops could possibly become sessile due to the stagnation of solvent flow.

[0065] The additional heat transfer resistance due to the coating layer must be carefully addressed in this invention. A coating layer of a thickness of 150 microns with a thermal conductivity of 0.2 W/m.K yields a 25% increase of heat transfer resistance on a regular shell and tube heat exchanger for such chilling services. Fortunately, some of the hydrophobic coating materials, for example PTFE (polytetrafluoroethylene), provide an excellent corrosion resistance against the aqueous solutions of many salts. Such corrosion resistant materials have been used throughout the industries for many decades. With the additional benefit of corrosion resistance, the coating material provides an opportunity to generate the ice slurry resolving the chronic problems of the ice adhesion and the corrosion by salt solutions at the same time.

[0066] In another embodiment, system 400 in FIG. 7 comprises of an ice slurry production tank 401, an ice slurry separation tank 451, an ice slurry storage tank 471, a CO.sub.2 liquefaction heat exchanger 481, a LNG regasification heat exchanger 420, and a natural gas superheater heat exchanger 430. The LNG regasification heat exchanger chills toluene stream 411, while it vaporizes LNG stream 421 at 162 C. to natural gas. Since the freezing point of toluene is 95 C., its flow rate must be maintained high enough to prevent it from freezing. In the ice slurry production tank 401, the chilled toluene is sprayed by distributor nozzles which are submersed in the cold heavy solvent layer 402. The heavy solvent layer prevents water drops from reaching the cold distributor nozzles and thereby from freezing in the cold heavy solvent layer. The cold light solvent bubbles rise by buoyant forces through the heavy solvent layer 402 and then through the water layer 403 generating ice crystals in direct contact heat transfer. The stream 415 and 416 of ice slurry collected at the interface with toluene layer 405 are combined and withdrawn to ice slurry separation tank 451 in stream 414. The toluene layer in tank 451 is withdrawn and recycled to the LNG regasification heat exchanger 420 by pump 452. The ice slurry layer in tank 451 is withdrawn and sent to ice slurry storage tank 471 by pump 462 in stream 465. The ice slurry in tank 471 is mixed with agitator 474 to maintain a uniform ice concentration of 15 wt %. The ice slurry stream 475 is sent by pump 472 to liquefy CO.sub.2 gas 482 to CO.sub.2 liquid 483 in CO.sub.2 liquefaction heat exchanger 481 at around 30 C. and 15 bar. The CO.sub.2 is condensed at 15 bar because the liquid CO.sub.2 storage tank in the liquid CO.sub.2 ocean carrier is designed at 15 bar. The saturation temperature of CO.sub.2 at 15 bar is 28.5 C. The ice slurry stream 491 is used as a low temperature coolant for other users such as the freeze and refrigeration warehouses at service temperatures from 40 C. to 5 C. It is also used as a low temperature coolant for industries at temperatures up to 45 C. It returns as a 38 wt % potassium formate brine of stream 492. Any water formed from melting ice is sent to the ice slurry production tank by pump 473. The combined returning brine stream 408 is fed to the water layer 403 containing ice in the ice slurry production tank. The natural gas exiting regasification heat exchanger 420 is heated by HVAC coolant stream 423 in supertheater heat exchanger 430 from around 65 C. to +2 C., and then natural gas stream 422 is sent to the natural gas users. The HVAC coolant stream is cooled to a temperature below 0 C., while it is used for cooling data centers and HVAC of commercial and apartment buildings.

[0067] In FIG. 8 is shown a phase diagram of a eutectic system of potassium formatewater. The brine at point A of 38 wt % and +1 C. is fed into the water layer in the ice slurry production tank and cooled to point B at 45 C. Point B, physically, separates into two phases comprising pure ice at point C and a solution of 45 wt % potassium formate at point D. The ice slurry represented by point B contains 15 wt % of ice particles. This ice slurry is withdrawn from ice slurry production tank 401 and sent to ice slurry separation tank 451.

[0068] This 15 wt % ice slurry is separated in ice slurry separation tank 451 from the toluene stream and then stored in ice slurry storage tank 471. The 15 wt % ice slurry can deliver two to three times higher enthalpy than the single phase HTF (Heat Transfer Fluid), when it is used as a coolant from 45 C. to 30 C. with a temperature rise of 15 C. This capability makes ice slurry more favorable to use, when the installation cost of the plant needs to be reduced. The ice slurry returns from the cold energy users as 38 wt % brine at +1 C. The potassium formatewater system has a eutectic point at 52 wt % and 60 C. For the freezing point depressant, a substance can be selected from a group composing LiCl, NaCl, K.sub.2CO.sub.3, CaCl.sub.2), MgCl.sub.2, KAc (potassium acetate) and KCOOH (potassium formate).

[0069] LNG vaporizes in LNG regasification heat exchanger 420 and then the vaporized natural gas is superheated in natural gas superheater heat exchanger 430. In the LNG regasification heat exchanger, the LNG stream at 162 C. at a pressure from 30 bar to 70 bar is vaporized in heat exchange with the toluene stream at a temperature of 45 C. at a pressure lower than 10 bar. The natural gas from the LNG regasification heat exchanger 420 is superheated by superheater heat exchanger 430 to a temperature higher than +2 C. by an aqueous solution which is used as a coolant for cooling data centers and HVAC of commercial and apartment buildings being maintained at a room temperature of around +20 C. The aqueous solution dissolves a freezing point depressant selected from a group composing LiCl, NaCl, K.sub.2CO.sub.3, CaCl.sub.2), MgCl.sub.2, ethylene glycol, propylene glycol, KAc (potassium acetate) and KCOOH (potassium formate). The aqueous solution is chilled to a temperature below 0 C. in natural gas superheater heat exchanger 430.

[0070] The LNG cold energy is recovered as much as around 160 kcal/kg, when it is vaporized from 162 C. to 65 C. at 30 bar in the LNG regasification heat exchanger. Additionally, the LNG cold energy is further recovered as much as 40 kcal/kg from 65 C. to +2 C. at 30 bar in the natural gas superheater heat exchanger. Typically, the LNG cold energy is recovered as much as 200 kcal/kg in total. At 65 C. and 30 bar, the LNG is completely vaporized. Since the behavior of LNG on the temperature and enthalpy diagram depends on the concentration of the heavier components such as ethane, propane and butane, the composition must be checked routinely prior to use.

[0071] For production of ice slurry in the ice slurry production tank, three liquids perfluorohexane (C.sub.6F.sub.14), toluene, and water being immiscible between each other are contacted by direct contact heat transfer in a cylindrical tank 401; firstly, the water mixture containing potassium formate as a freezing point depressant and ice particles of 1 mm to 100 microns in diameter at the middle layer, secondly the heavy solvent of perfluorohexane (C.sub.6F.sub.14) at the bottom layer, and thirdly the light solvent of toluene at the top layer. The distributor for toluene is submerged in the heavy solvent layer and sprays the cold toluene bubbles through the nozzles properly without clogging by freezing water. It is possible due to the fact that the immiscible heavy solvent layer prevents the water drops from contacting the cold distributor nozzles owing to the density difference. The cold toluene bubbles ascend through the heavy solvent layer, and then through the ice slurry layer generating ice particles. The toluene bubbles collect at the top layer. The ice slurry and toluene layers are maintained at 45 C.

[0072] The light solvent is fed to the LNG regasification heat exchanger at 45 C. and exits at temperatures around 65 C. LNG is fed into the LNG regasification heat exchanger at 162 C. and exits at temperatures around 65C The light solvent stream carries the cold energy from LNG, and transfers it to the ice slurry layer in the ice slurry production tank. The heavy solvent layer stays at the bottom of the ice slurry production tank at temperatures around 65 C. This temperature is determined with the optimum circulation flow rate of toluene for a given amount of cold energy recovered. The ice slurry is produced, separated and stored at 45 C. The ice slurry is used to condense the CO.sub.2 gas for CCUS (Carbon Capture, Utilization, and Storage) at around 30 C. and 15 bar. When the LNG flow rate fluctuates, the toluene flow rate changes in response to the fluctuation, while the inlet and outlet temperatures of toluene are kept constant in the LNG regasification heat exchanger.

[0073] In Table 5, the physical properties of the 45 wt. % potassium formate aqueous solution, ice, 15 wt. % ice slurry, and toluene at 45 C. are given.

TABLE-US-00005 TABLE 5 Physical Properties of Brine, Ice, Ice Slurry and Toluene at 45 C. Property 45 wt. % P. F. Brine Ice 15 wt. % Ice Slurry Toluene Density (Kg/M.sup.3) 1324 918.0 1085.8 930 Heat Capacity(KJ/Kg .Math. K) 2.7 2.45 2.66 1.55 Therm. Cond. (W/M .Math. K) 0.43 2.76 0.366 0.150 Viscosity (mPa .Math. s) 30 N/A 45.3 1.75 Heat of Fusion (KJ/Kg) N/A 247.2 N/A N/A

[0074] The terminal velocity and the hindered settling velocity of the toluene bubble in size of 5 mm and of the ice particles in sizes of 2 mm, 1 mm, 0.5 mm, and 0.1 mm are given in Table 6. The ice particles are produced in the 45 wt. % potassium formate aqueous solution in direct contact heat transfer at 45 C.

TABLE-US-00006 TABLE 6 Terminal and Hindered Settling Velocities at 45 C. Settling Object Size Reynolds Number Terminal Velocity Hindered Settling Velocity Toluene Bubble 5 mm 13.6 0.073 m/s 0.0029 m/s Ice Particle 2 mm 1.5 0.02 m/s 0.0096 m/s Ice Particle 1 mm 0.37 0.01 m/s 0.0048 m/s Ice Particle 0.5 mm 0.053 2.8 10.sup.3 m/s 1.2 10.sup.3 m/s Ice Particle 0.1 mm 0.0003 7.1 10.sup.5 m/s 3.2 10.sup.5 m/s

[0075] The ice slurry separation tank 451 separates the ice slurry stream from the toluene stream. The terminal velocity of a toluene bubble of 5 mm in diameter is about 0.073 m/s in the ice slurry mixture of 45 wt % potassium formate at 45 C. The hindered settling velocity of an ice particle of 1 mm in diameter is 0.0048 m/s in the water dissolving potassium formate in 45 wt % at 45 C. For the downward ice slurry flow at the bottom section of the tank, the bulk flow velocity is maintained higher than 0.0048 m/s but below 0.073 m/s so that all ice particles smaller than 1 mm in diameter can be withdrawn with the bulk ice slurry stream but all toluene liquid drops larger than 5 mm in diameter can be released from the ice slurry stream. For the upward toluene flow exiting through the nozzle located at the top section of the tank, the exit nozzle is located where the elevation of the nozzle can prevent the blanketing nitrogen gas and the ice slurry mixture from being entrained into the toluene stream, which will be chilled in the LNG regasification heat exchanger at 162 C. Otherwise, the entrainment will cause water freezing on the toluene side heat transfer surfaces, thus deteriorating heat transfer. Also, due to the low terminal velocity of the toluene bubbles and hindered settling velocities of the ice particles owing to the high viscosity of potassium formate solution, a cylindrical tank is provided for more effective separation of the ice slurry from the toluene stream with a sufficient residence time.

[0076] The ice slurry storage tank 471 stores ice slurry at 45 C. The capacity of the storage tank is determined by the two requirements; firstly, it must provide the cold energy users such as the freeze and refrigeration warehouses, cold energy industries, and CO.sub.2 liquefaction heat exchangers for CCUS with an enough residence time. For example, the cold energy to condense CO.sub.2 gas must be available whenever the CO2 gas is delivered to CO.sub.2 liquefaction heat exchanger 481. In the meantime, the storage tank must have enough capacity to store the excess cold energy being generated in the regasification process all the time. Since the cold energy users and the cold energy producers are working independently, the cold energy storage tank must provide enough buffer capacity for both sides to operate in coordination.

[0077] In another embodiment, a ternary system comprising perfluoroheptane (C.sub.7F.sub.16), toluene, and water can be used instead of the ternary system perfluorohexane (C.sub.6F.sub.14), toluene, and water for production of ice slurry. The C.sub.6F.sub.14 and C.sub.7F.sub.16 were marketed with the product name of FC-72 and FC-84, respectively, from 3M Corporation. Their solubilities with tolune are given in the brochure titled SOLUBILITY published by the company. From this reference, it has been found that the solubility of FC-72 (C.sub.6F.sub.14) and FC-84 (C.sub.7F.sub.16) in toluene is slightly soluble (1-5 g/100 g), respectively, while the solubility of toluene in FC-72 and FC-84 is slightly soluble (1-5 g/100 g), respectively, too. The binary system of C.sub.6F.sub.14 and toluene forms immiscible liquid phases as was found from the experiment of Chu et al. In addition, according to the solubility data of 3M Corporation, FC-84 and toluene will not form a miscible liquid mixture because of their solubilities being slight soluble. Therefore, the binary system of FC-84 and toluene will form immiscible liquid phases following the experimental results of Chu et al., where the binary system of FC-72 and toluene forms immiscible liquid phases while having the same solubilities being slight soluble as the binary system of FC-84 and toluene in the 3M brochure.

[0078] The physical properties of C.sub.6F.sub.14 (FC-72) and C.sub.7F.sub.16 (FC-84) are shown in Table 7. They have very close values for the physical properties required for a heavy solvent such as pour point, liquid density, viscosity, coefficient of expansion, specific heat, thermal conductivity, surface tension, water solubility, and solubility in water.

TABLE-US-00007 TABLE 7 Physical Properties of C.sub.6F.sub.14 (FC-72) and C.sub.7F.sub.16 (FC-84) at 25 C. C.sub.6F.sub.14 (FC-72) C.sub.7F.sub.16 (FC-84) Appearance Clear, Colorless Clear, Colorless Molecular Weight 338 388 Boiling Point, C. (1 atm) 56 80 Pour Point, C. 90 95 Critical Temperature, C. 176 202 Critical Pressure, Bar 18.3 17.5 Vapor Pressure at 25 C., Bar 0.31 0.11 Latent Heat of 88 90 Vaporization, J/g (2) Liquid density, kg/m3 1680 1730 Kinematic Viscosity, centistokes 0.38 0.53 Absoluto Viscosity, centipoises 0.64 0.91 Liquid Specific Heat, J/kg. C. 1100 1100 Liquid Thermal 0.057 0.060 Conductivity, W/m. C. Coefficient of Expansion, 1/( C.) 0.00156 0.0015 Surface Tension, dynes/cm 10 12 Refractive Index 1.251 1.261 Water Solubility, ppmw 10 11 Solubility in Water, ppmw <5 <5 Note: 1. Physical properties FC-72 and FC-84 are from product brochures of 3M Corporation. (2) At normal boiling point

[0079] For the alternative system, the mutual solubility is given in Table 8. The binary system comprising C.sub.7F.sub.16 (FC-84) and toluene will form immiscible phases as for the system comprising C.sub.6F.sub.14 (FC-72) and toluene. The mutual solubility of the binary pair of C.sub.7F.sub.16 (FC-84) and toluene was found from the brochure titled Solubility printed by 3M Corporation. The mutual solubility of C.sub.7F.sub.16 (FC-84) and water is given in Table 7. For the binary pair of toluene and water, their mutual solubility is the same as given in Table 2.

TABLE-US-00008 TABLE 8 Mutual Solubility of C.sub.7F.sub.16, Toluene, and Water C.sub.7F.sub.16 Toluene Water in C7F16 N/A 1-5 (1) 11 ppm (2) in Toluene 1-5 (1) N/A 567 ppm (2) in Water <5 ppm (2) 520 ppm (3) N/A Note: (1) Solubility in weight % at 25 C. (2) At 25 C. (3) At 20 C.

[0080] The relevant physical properties of the four components being used in the process of the alternative embodiment perfluoroheptane (C.sub.7F.sub.16), toluene, water and ice are listed in Table 9. For toluene, water and ice, their physical properties are the same as given in Table 3.

TABLE-US-00009 TABLE 9 Physical Properties of C.sub.7F.sub.16, Toluene, Water and Ice Property C.sub.7F.sub.16 Toluene Water Ice Molecular Weight 388 92.1 18 18 Density (Kg/M.sup.3) 1730 (1) 886 (2) 999.8 (3) 916.2 (2) Melting Point ( C.) 95 95 0 0 Boiling Point ( C.) 80 111 100 100 Flash Point ( C.) N/A 6 N/A N/A Auto Ignition N/A 530 N/A N/A Point ( C.) Specific Heat Capacity 1.1 (1) 1.6 (2) 4.2 (3) 2.05 (2) (KJ/Kg. C.) Therm. Cond. 0.060 (1) 0.144 (2) 0.57 (3) 2.22 (2) (W/M. C.) Viscosity (mPa .Math. s) 0.91 (1) 0.77 (2) 1.79 (3) N/A Note: (1) At 25 C. (2) At 0 C. (3) At 0.01 C.

[0081] For the fluctuations of the LNG flow rate of stream 421, the system consisting of ice slurry production tank 401, LNG regasification heat exchanger 420, and toluene circulation pump 452 is controlled by the following control scheme. When the fluctuation starts, the toluene flow rate in the LNG regasification heat exchanger changes in response to the fluctuation, while the inlet and outlet temperatures of toluene are kept constant. In this way, a faster response can be obtained in the direct contact heat transfer operation in space 403 in the ice slurry production tank. If the temperatures change instead of the flow rate for the fluctuation, it would require much longer response time because the temperature of the whole liquid in the ice slurry production tank must change in order to see the change of ice slurry production rate as a response. Whereas, with the toluene flow rate changing, it will make the change of ice slurry production rate faster, because the ice slurry production rate depends on the number of toluene bubbles delivered in space 403 for direct contact heat transfer operation, which will be again directly dependent on the toluene flow rate into the toluene distributor. For the toluene pump, a centrifugal pump can be used, because a large flow rate of several thousand GPM (3.785 liter/min/GPM) with low head below 10 bar are required. Also, for pumping toluene liquid, stainless steel or carbon steel can be used for material of construction of the pump with the explosion proof provisions.

[0082] To achieve the Net Zero by 2050, meaning that the net emission of CO.sub.2 into the atmosphere will be reduced to zero (0) by 2050, most countries in the world capture CO.sub.2 from the industrial activities such as stack gases of power plants which contain CO.sub.2 at a concentration of 10 to 14% in weight for CCUS. After the cleaning and purification processes in the capture step, the CO.sub.2 stream is at a concentration of more than 95%. For CCS, this CO.sub.2 stream must be stored in a liquid state before it is put into the geological formations. For CCU, some can be utilized in a gaseous state depending on the type of utilization process, while the rest must be stored in a liquid state until it is used in the utilization process. Liquefaction of this CO.sub.2 stream requires an appreciable amount of electrical energy for compression and condensation. Instead, the CO.sub.2 gas can be condensed by using the recovered LNG cold energy. In this case, the CO.sub.2 gas must be condensed immediately as soon as it is processed in the capture step, because it cannot be stored in a gaseous state. As an option, the CO.sub.2 gas from the capture step can be chilled first in the superheater heat exchanger 430 and then condensed in the CO.sub.2 liquefaction heat exchanger 481.

[0083] The LNG regasification heat exchanger can be constructed of less corrosion resistant material of construction. For example, the heat exchanger tubes contacting seawater were made of titanium, but now for toluene stream they can be constructed of stainless steel. Also, the parts contacting LNG can be constructed of stainless steel as they have been. The costs of the equipment unit have become much lower now. As for the natural gas superheater heat exchanger, stainless steel can be used for the natural gas side, and stainless steel or carbon steel can be used for the heating medium side depending on the corrosivity of the heat transfer fluid (HTF).

[0084] The ice slurry production tank and ice slurry separation tank contain toluene which is a flammable substance. Therefore, the tanks need blanketing with nitrogen to prevent air from leaking into the system. Also, they need safety valves for over pressure emergencies which will lead to a flare system for safe combustion. Also, since LNG makes combustible gas mixture at a concentration between 4-15 volume % in the atmosphere, all electricity users including motors, instrumentation and IT (Information Technology) servers must be designed for explosion proof.

[0085] The process is a closed system in order to prevent the fluorocarbon from leaking into the atmosphere. The heavy solvent, perfluorohexane (C.sub.6F.sub.14) and perfluoroheptane (C.sub.7F.sub.16), have GWP (Global Warming Potential) of 9300 and 7820, respectively, and will stay at the bottom of the ice slurry production tank all the time, preventing leakage of the component into the atmosphere. Vapor pressure of C.sub.6F.sub.14 at 45 C. is 0.007 bar and of C.sub.7F.sub.16 0.0014 bar, respectively, while they are immiscible with toluene and water having very low solubility with them. Also, the plant operates in a closed system securing safety by preventing the leakage of the heavy solvent component into the atmosphere.

[0086] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.