US3400545A

US3400545A - Use of cold-carriers in liquefaction and regasification of gases

Info

Publication number: US3400545A
Authority: US
Inventors: Willem P Hendal
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1965-05-31
Filing date: 1966-05-25
Publication date: 1968-09-10
Anticipated expiration: 1985-09-10
Also published as: DE1501749A1; ES327211A1; GB1082789A; FR1481495A; JPS4822892B1; SE334634B

Description

United States Patent 3,400,545 USE OF COLD-CARRIERS IN LIQUEFACTION AND REGASIFICATION 0F GASES Willem P. Hcndal, Amsterdam, Netherlands, assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed May 25, 1966, Ser. No. 552,712. Claims priority, application Netherlands, May 31, 1965,

6506843 24 Claims. (Cl. 62-9) ABSTRACT OF THE DISCLOSURE Method of liquefying a natural gas by bringing the gas into heat exchange with a cooled cold-carrier which coldcarrier is formed by introducing a carrier liquid which remains fluid during the process of heat exchange and having a boiling point higher than a temperature which is just below ambient temperature, and having particles evenly dispersed the-rein of a substance distinct from the carrier fluid which, during the process of heat exchange, undergo a phase change, the said even dispersion being accomplished by the addition of an emulsifying agent for the system of carrier fluid and particles.

The invention relates to use of cold-carriers in liquefaction and regasification of gases, in particular of methane or natural gas.

The invention relates more in particular to such use of cold-carriers in the transportation or in peak-shaving of gases.

In order to reduce the cost of cooling and liquefaction of gas in the transportation of gas in liquefied condition a method is known in which:

(a) At a production point the gas is liquefied by cooling and is passed in liquefied condition into a reservoir,

(b) The reservoir thus filled is transported to a consumption point,

(c) At the consumption point the liquefied gas is regasified by bringing it into heat exchange with a coldcarrier,

(d) The cold-carrier cooled 01f as a result of the stage described under (c) is passed into a reservoir,

(e) The reservoir filled with the cooled cold-carrier as described under (d) is transported to the production point,

(t) At the production point the gas is cooled according to stage (a) by bringing it in heat exchange with the cold-carrier supplied according to stage (e).

In the above-mentioned method the cold is thus passed back from the consumption point to the production point by means of a cold-carrier. In this respect it should be noted that by the production point is meant the place where the gas is liquefied for dispatch, while by the consumption point is meant the place where the liquefied gas is converted, on arrival, to the gaseous state for consumption.

As mentioned, the cold-carrier may also be used in the storage of gas, for example natural gas or methane, for peak-shaving purposes which may be described as follows. During periods of small demand for natural gas or methane this can be liquefied by passing it in heat exchange with the cold cold-carrier. The methane or natural gas thus liquefied can then be stored in suitable heat-insulated reservoirs and in periods of large demand for natural gas or methane the liquefied methane or natural gas is regasified by passing it in heat exchange with the warmed up cold-carrier so that the cold-carrier is cooled down. The cooled down cold-carrier is then stored temporarily in suitable heat-insulated reservoirs until a period of small demand for natural gas or methane arrives again.

3,400,545 Patented Sept. 10, 1968 Then the cooled down cold-carrier is used again for liquefying a quantity of methane or natural gas which is temporarily stored until the demand for natural gas or methane rises again.

It will be clear that it is desirable for the cold-carrier to be able to absorb a large amount of cold per unit of volume, so that the reservoir space required for storing or transporting the cold-carrier can be small. To this end the cold-carrier should possess among others a relatively high specific heat and a relatively high specific gravity.

The invention will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic view of an arrangement according to the present invention; and

FIGURE 2 is a schematic view of a detail of the arrangement of FIGURE 1.

Referring now to the drawings and particularly to FIGURE 1, it may be seen how natural gas may be transported in the liquid state between a production point and a consumption point. The gas is introduced into a heat exchange at the gas producing area where it is cooled by contact with a cooled cold-carrier. The liquefied gas is passed into a reservoir which is transported to the gas consuming area. At this point, the liquefied natural gas is converted back to the gaseous state by bringing it into contact with a warm cold-carrier in a heat exchanger at the gas consumption area. The natural gas is removed from the heat exchanger. The cold-carrier consists of a cooled carrier liquid having solid particles evenly dispersed therein as will be explained further hereinbelow. The cold-carrier, cooled down as a result of the foregoing, is passed into a reservoir for transportation back to the production area where the cooled cold-carrier is brought into contact with the natural gas introduced into the heat exchanger at the production area.

According to the invention it is proposed to use in the above transportation method or for peak-shaving purposes, a cold-carrier which is characterized by a carrierliquid not solidifying, i.e., remaining fluid, during the process of heat exchange and having a boiling point higher than, equal to or just below ambient temperature, i.e., a boiling point which is higher than a temperature which is just below ambient temperature, and containing particles of a substance, which, during the process of heat exchange, undergo a phase change.

In a suitable embodiment of the invention the substance of the particles is of such a nature that, during the process of heat exchange, it entirely or partly melts or solidifies, said substance having a boiling point higher than, equal to, or just below ambient temperature.

The liquid of the particles, which can be dispersed in the carrier-liquid, will solidify upon cooling, so that the heat of fusion thereof adds to the specific heat of the cold-carrier. Accordingly as more liquid solidifies, the effect will be larger.

During the solidification of the liquid of the particles the temperature of the coldcarrier remains constant. Heat is then transferred from the cold-carrier to the liquefied gas which is being regasified, without a simultaneous drop in temperature of the cold-carrier. This is favorable With respect to a high rate of the heat transfer.

Naturally, the advantages mentioned hereinbefore likewise exist when the cold cold-carrier is being heated up by passing it in heat exchange with gas in order to cool the gas down for liquefaction.

A large effect is obtained if the substance of the particles of the cold-carrier consists of water. Water has a high heat of fusion and a high specific gravity.

An even more favorable effect is obtained if the substance of the particles of the cold-carrier consists of water containing a freezing point depressant. As a result, the temperature range in which the substance of the particles remains liquid is increased. This is favorable with respect to increasing the specific heat of the cold-carrier, because the specific heat of the particles in liquid condition is higher than that of the particles in solid condition.

Suitable freezing point depressants are ammonia, hydrochloric acid, an alcohol, a mixture of alcohols, a glycol, a mixture of glycols.

By means known as such, the cold-carrier can be converted into a stable emulsion. Upon solidification of the dispersed particles a suspension is formed. A manageable emulsion or suspension can also be obtained by stirring, for instance by means of a jet of liquid or with the aid of mechanical means.

It is also possible to use a cold-carrier in which the particles, in addition, contain a solid capable of adsorbing or absorbing, i.e., picking up, the liquid of the particles. For this purpose use can be made of silica gel. With the aid of known means a heterogeneous cold-carrier of this type can be converted into a stable suspension.

Several liquids are suitable for use as carrier-liquid of the cold-carrier. A suitable liquid is for example isopentane. It is also possible to choose as a carrier-liquid a liquid containing a freezing point depressant. In this connection the eutectic mixtures of 88% isopentane and 12% normal pentane or 85% isopentane and 15% isohexane are attractive in view of their low melting point.

It has been found that the cold-carrier is still pumpable if the dispersed particles contain not more than 50% of liquid based on the total volume of the cold-carrier.

The gas can be liquefied and be transported in a reservoir at a pressure of 1 atmosphere, but in many cases it may be desirable to employ a higher pressure.

During the liqeufaction of the gas the cold-carrier is heated up, for example to ambient temperature. If desired, the heated-up cold-carrier can be used in the production point, for example in chemical industry. It is also possible for the heated-up cold carrier to be passed into a reservoir and thus to be transported to the consumption point, as illustrated in FIGURE 1. Generally, such transport will take place under a pressure of 1 atmosphere, but it is also possible to employ a higher pressure.

In many cases the cooled down cold-carrier can be transported from the consumption point to the production point in the same reservoir as that in which the liquefied gas has been transported in the opposite direction. An advantage of this is that the reservoir always remains in cold condition. Owing to the high specific heat and the generally high specific weight of the cold-carrier according to the invention the reservoir that has been used for the transport of the liquefied gas is as a rule large enough for the transpoit of the cold cold-carrier in the opposite direction.

In another very attractive embodiment of the invention use is made of a cold-carrier, in which the substance of the particles is of such a nature that, during the process of heat exchange, it shows one or more transitions between the solid-, the liquid-, or the vapor phase.

In this way an important contribution to the heat capacity of the cold-carrier is formed by the heat of vaporization or the heat of condensation of the substance of the particles. In this respect it is remarked that the heat of vaporization and the heat of condensation of a substance are always larger than the heat of fusion and the heat of solidification. Still, the last mentioned heat effects may also be utilized by decreasing the temperature of the cold-carrier during the cooling to a sufficiently low level. Said substance changes from the vapor phase via the liquid phase into the solid phase. The cooling may be extended so far, if desired, that the carrier-liquid of the cold-carrier also solidifies partly.

During a phase transition of the substance of the particles the temperature of the cold-carrier remains constant. Then heat is transferred from the cold-carrier to the liquefied gas which is being regasified or heat is transferred from the gas which is being liquefied to the coldcarrier without a simultaneous drop or rise in the temperature of the cold-carrier. This is favorable with respect to a high rate of heat transfer. The temperature at which the substance of the particles displays a phase transition naturally in the first instance depends on the nature of said substance. Furthermore, to said substance a material may be added for lowering the temperature of the phase transition. As a result, more freedom on the point of the mode of operation of the process is obtained.

Ina suitable embodiment the substance of the particles consists of carbon dioxide. For the sublimation of carbon dioxide approximately 135 cal./g. are required, which is already considerably more than the heat of fusion of water (approximately cal./g.), so that a considerably larger amount of gas can be liquefied with a specific amount by weight of a cold-carrier comprising a carrierliquid containing particles of solid carbon dioxide than with the same amount by weight of a cold-carrier comprising a carrier-liquid containing particles of ice instead. The ratio of the amount of useful load, i.e. the amount of liquefied methane or liquefied natural gas, to the amount of cold-carrier then becomes more favorable.

That ratio becomes more favorable still if the coldcarrier comprises a carrier-liquid containing particles of ammonia. For the transition of solid ammonia into vapor requires approximately 400 cal./g.

A suitable substance for addition to the substance of the particles is methane.

Owing to the low price of carbon dioxide it may be justified economically that the carbon dioxide, which during the liquefaction of the gas changes into vapor form, is discharged into the atmosphere. In that case each time a new amount of carbon dioxide has to be employed at the consumption point.

It is also possible, however, for the carbon dioxide, which changes into vapor form, to be bound in such a Way that it can be easily decomposed again. The carbon dioxide may then be used for a variety of purposes. The bound carbon dioxide may be stored or be transported to the consumption point so that it, after liberation, may be used again as the substance of the particles in the coldcarrier. Suitable compounds for binding the carbon dioxide are for instance bicarbonates or ammonium carbonate. These can be decomposed by little heat. It is advantageous if the ammonia, which during the cooling and liquefaction of the gas changes into vapor form, is bound and that in such a way that it may easily be decomposed again. A suitable way of binding the ammonia is by catching the released ammonia in water. The bound ammonia may be stored or be transported to the consumption point so that it, after liberation, may be used again as the substance of the particles in the cold-carrier. Ammonia is valuable and may for example be further processed to fertilizer in the neighborhood of the production point of the methane or the natural gas.

The vapor that forms the substance for the particles of the cold-carrier in cooled condition should at the consumption point together with the carrier-liquid form a heterogeneous system. A suitable process for obtaining this result is one by which during the heat exchange with the liquefied gas which is being regasified, first the carrierliquid of the cold-carrier is cooled and, next, the substance which is to form the particles is introduced in vapor form into the carrier-liquid, whereby said substance changes from the vapor phase into the liquidor into the solid phase so that an emulsion or a suspension, i.e., a non-homogeneous two-phase fiuid, is formed. The temperature of the carrier-liquid of the cold-carrier will in generaly be so low, during the introduction in vapor form of the substance which is to form the particles, that condensation or solidification of that vapor occurs at once. The introduction of said vapor into the carrier-liquid may take place for example by injecting the vapor into the carrier-liquid from one or more narrow openings and under pressure. Also, the vapor may already be cooled beforehand by heat exchange with the vaporizing natural gas or methane.

Various liquids can be used for the carrier-liquid of the cold-carrier. An example is isopentane. It is also possible to select a liquid containing a freezing point depressant. In this connection the eutectic mixtures consisting of 88% isopentane and 12% normal pentane or 85% isopentane and 15% isohexane are attractive on account of their low melting points.

In the liquefaction ofgas, such as natural gas or methane, the cold-carrier is raised in temperature, for instance to ambient temperature. If desired, the heatedup cold carrier may be used on the spot, for instance in a chemical industry. It is also possible for the components of the cold-carrier to be led to one or more reservoirs and thus to be transported to the consumption point.

The cooled down cold-carrier may be transported from the consumption point to the production point in the same reservoir as that in which the liquefied gas has been transported from the production point to the consumption point. This has the advantage that the reservoir always remains cold. Owing to the high specific heat of the coldcarrier according to the inventon, the reservoir that has een used for the transport of the liquefied gas is more than sufficiently large for the transport of the coldcarrier in the opposite direction.

The reservoirs for the transport of the liquefied gas and/or cold-carrier may be built in or form part of a ship, a railway truck, a road truck or any other means of conveyance.

The method according to the invention may be used for the transportation or for peak-shaving of natural gas, methane, ethane, propane, butane or other gases.

In cooling a cold-carrier comprising said carrier-liquid in which the particles of said substance are present, it is desirable that these particles are evenly dispersed in the carrier-liquid. If this cold-carrier is prepared a long time before the cooling down of the cold-carrier takes place, and if the substance of the particles is in liquid condition, for the stabilization of the dispersion addition of an emulsifier will be required. This addition of an emulsifier may have the disadvantage that the viscosity of the cold-carrier, in particular at low temperatures, will increase.

If the substance for the particles has a high -vapor pressure or if it is in the vapor phase, then a carrier-liquid containing a sufiicient quantity of the dispersed substance will form only under elevated pressure and/ or with thorough stirring.

Therefore it is proposed to prepare the above dispersion at a special moment and in a special Way, viz. by cooling the carrier-liquid by passing it in heat exchange with the liquefied gas which is being regasified and adding the said substance to the cooled down carrier-liquid. Thus, it is ensured that only a relatively short time elapses between the formation of the dispersion and the phase transition of the substance of the particles in dispersion. Consequently the risk of the dispersed liquid particles coalescing is small and, hence only a very small quantity of emulsifier will be required which has no adverse influence on the viscosity of the cold-carrier.

If the substance for the particles is a liquid with a high vapor pressure, then when said substance in liquid form is brought into contact with the cooled-down carrier-liquid, the vapor pressure of said substance will be considerably reduced, so that trouble encountered owing to vapor formation will be less.

In a suitable embodiment of the last mentioned method, the said substance is added to the carrier-liquid at the moment that the carrier-liquid has been cooled down to a temperature, equal to, or lower than the temperature at which said substance may, under the prevailing conditions, change into the liquid condition. Then, if the said substance is vapor, this will condense more easily when being brought into contact with the cooled down carrierliquid.

In another suitable embodiment, the said substance is added to the carrier-liquid at the moment that the carrierliquid has been cooled down to a temperature, equal to, or lower than the temperature at which said substance may, under the prevailing conditions, change into the solid condition. As a result the particles formed will hardly be in the liquid condition so that, even when a corrosive substance is used, the cold-carrier formed will have no corrosive properties and, hence the heat exchange apparatus used may be made of material meeting only low requirements as regards chemical resistance. In this case use of emulsifiers is not necessary.

If desired, it is possible to precool the substance for the particles, before adding it to the cooled down carrierliquid. In this Way vapors may be first converted to the liquid or the solid condition and then be added to the cooled down carrier-liquid.

During heating up of the cold cold-carrier when passing it in heat exchange with a gas to be liquefied, for example natural gas or methane, it is possible to separate the substance of the particles dispersed in the carrier-liquid from the carrier-liquid as soon as said substance is no longer in solid condition. In this way it is possible to store the said substance and the carrier-liquid each in separate reservoirs, which can be transported to the consumpticn point. This is advantageous if the said substance is corrosive and the carrier-liquid is not corrosive, since in that case only the reservoir in which the said substance is stored or transported needs to be made of a material resistant to chemicals, whereas the reservoir for the carrier-liquid can be made of a material having a low resistance to chemicals.

The requirements in relation to the boiling point of the substance of the particles in the carrier-liquid of the cold-carrier restrict the choice thereof. Also, precautions should be taken against substances of a corrosive nature, because the dispersed particles come into contact with the walls of reservoirs, lines and heat exchangers.

Therefore in a suitable embodiment of the cold-carrier according to the invention, at least some of the particles of the substance undergoing a phase change during the process of heat exchange are each enclosed within a wall.

In the process of heat exchange between the coldcarrier and the gas a heat flow occurs within the coldcarrier between the carrier-liquid and the substance of the particles, which heat flow goes through the walls enclosing the substance of the particles. This involves that the substance of the particles will display phase transitions. The latent heat absorbed or evolved thereby contributes greatly to an increase in the specific heat of the cold-carrier. During the phase transitions there will be little or no change in temperature of the carrier-liquid, which is favorable with respect to a rapid heat transfer.

As the substance of the particles which absorbs or evolves the latent heat is present in enclosed spaces, this substance cannot come into contact with the walls of reservoirs, heat exchangers or other equipment. Also, any vapor that may have formed will remain confined within said enclosed spaces, so that no vaporization losses will occur. This results in a high degree of independence of both the boiling point and the corrosive properties of the substance of the particles. The degree of this indepedence may be controlled by the choice of the mechanical properties of the walls in which the particles are enclosed and the chemical resistance thereof.

The rate of heat transfer between the gas to be liquefied or to be regasified and the cold-carrier is determined partly by the rate of heat transfer through the walls of the particles. The size of those walls as well as the shape thereof may be adapted to the requirements to be made in this respect. Quite a number of embodiments are of course possible. For instance a large number of hollow objects piled up in a reservoir in such a way that a good contact with the pumpable carrier-liquid is possible, may be used.

It may be advantageous to employ for the particles two or more different substances, for example a mixture of water and ammonia on the one hand and toluene on the other hand, which, each at a different temperature level can absorb or evolve latent heat, so that it is possible that the heat exchange with the gas to be liquefied or to be regasified takes place at various levels of constant or substantially constant temperature. These different substances may together be enclosed within a Wall or walls. However, it is also possible for one or more of those substances or combinations thereof to be each enclosed by walls so that they are separate from each other and from the carrier-liquid. This may be desirable, for instance, if these substances interact physically or chemically.

Finally, it is possible to use for the cold-carrier at least two reservoirs, each of which can contain, in addition to the carrier-liquid one of the said substances. The contents of these reservoirs may then separately be subjected to heat exchange with the gas to be liquefied or to be regasified, for instance at different temperature levels.

The walls which enclose the substance or substances of the particles may be made of a metal with a high conductivity, for instance aluminum. This is promotive of a rapid heat transfer. It is also possible for these walls to be made of a polymer, for instance high-pressure polyethene. This material has the advantage of possessing a high chemical resistance.

The walls of the particles may also consist of two or more different materials, for instance of a plurality of layers of different material, of a coated material or a material containing reinforcing elements of another material; this may be of importance when the requirements concerning, for instance, the tightness, the strength and the chemical resistance cannot be met by one material without resort to a wall thickness that is unacceptably large in relation to the heat transfer. Thus, for instance a polymer may be used for obtaining a tight wall with a high chemical resistance, while the mechanical strength is increased with the aid of a layer of plate metal. Often, the material serving stiffening purposes need consist only of a grid or a gauze.

The substance of the particles may be contained in enclosed receptacles resembling capsules as illustrated in FIGURE 2. Capsules enable a favorable ratio to be obtained between wall thickness and wall strength; they can be evenly distributed over the volume of a reservoir, while a close packing can also be obtained herewith in reservoirs which are shaped irregularly or which are provided on the inside with stiffening elements. They may also be suspended in the carrier-liquid and be introduced into the reservoir in suspended condition.

During the process of heat exchange between the coldcarrier and the gas to be liquefied or regasified the carrierliquid may circulate between the gas and the substance of the particles which are enclosed within walls and may alternately be subjected to heat exchange therewith. In this case the carrier-liquid may contact the gas at different temperature levels and if more than one reservoir is employed, enter into heat exchange with said particles at different temperature levels.

If the substance of the particles is contained in capsules, then the capsules may be suspended in the carrier-liquid during the process of heat exchange between the coldcarrier and the gas to be liquefied or regasified. In that case the cooled cold-carrier also may be transported from the consumption point to the production point in a reservoir in which liquefied gas has been transported to the consumption point. The advantage of this is that the reservoir always remains cold.

I claim as my invention:

1. A method of liquefying a gas, selected from the group consisting of methane and natural gas, by bringing the gas into heat exchange with a cooled cold-carrier which cold-carrier is formed by introducing a carrierliquid which remains fluid during the process of heat exchange and having a boiling point higher than a temperature which is just below ambient temperature, and having particles evenly dispersed therein of a substance, distinct from the carrier fluid which, during the process of heat exchange, undergo a phase change, the said even dispersion being accomplished by the addition of an emulsifying agent for the system of carrier fluid and particles.

2. The method as claimed in claim 1, in which the substance of the particles is water.

3. The method as claimed in claim 2, in which the substance of the particles is Water containing a freezing point depressant.

4. The method as claimed in claim 1, in which the coldcarrier is a stable emulsion of the dispersed particles in the carrier-liquid, the dispersed particles, upon solidification of the particles by cooling, remaining in suspension.

5. The method of claim 1 in which the particles, in addition, contain a solid capable of picking up the liquid of the particles.

6. The method of claim 5 in which the cold-carrier is a stable suspension.

7. The method of claim 1 in which the substance of the particles is of such a nature that, during the process of heat exchange, it shows transitions between the solid-, the liquidand the vapor phase.

8. The method as claimed in claim 7, in which the substance of the particles contains a material for lowering the temperature of the phase transition.

9. The method of claim 7 in which during regasification of the liquefied gas, the carrier-liquid of the cold-carrier is cooled down by heat exchange with the liquefied gas and that next the substance which is to form the particles is introduced in vapor form into the carrier-liquid, whereby said substance changes from the vapor phase into another phase, so that a non-homogeneous two-phase fluid is formed.

10. The method of claim 1 in which the carrier-liquid of the cold-carrier consists of isopentane.

11. The method of claim 1 wherein said substance is separated from said carrier-liquid subsequent to said phase change.

12. A method of transporting a gas selected from the group consisting of methane and natural gas, in liquefied condition, comprising the following steps:

(a) liquefying the gas at a production point by cooling and passing the gas in liquefied condition into a reservoir,

(-b) transporting the reservoir containing said liquefied gas to a consumption point,

(c) regasifying the liquefied gas at the consumption point by bringing it into heat exchange with a coldcarrier,

((1) passing said cold-carrier cooled off as a result of the stage described under (c) into a reservoir,

(e) transporting the reservoir, containing the cooled cold-carrier as described under (d) to the production point,

(f) cooling the gas at the production point according to stage (a) by bringing it in heat exchange with the coldcarrier supplied according to stage (0), the coldcarrier used being formed by introducing a carrierliquid which remains fluid during the process of heat exchange and: having a boiling point higher than a temperature which is just below ambient temperature, and having particles evenly dispersed therein of a substance, distinct from the carrier fluid which, during the process of heat exchange, undergo a phase change, the said even dispersion being accomplished by the addition of an emulsifying agent for the system of carrier fluid and particles.

13. The method of claim 12 in which the carrier-liquid of the cold-carrier consists of 88% isopentane and 12% n-pentane.

14. The method of claim 12 in which the carrier-liquid of the cold-carrier consists of 85% isopentane and 15% is ohexane.

15. The method of claim 12 in which the cold-carrier, after heating up according to step (t), is passed into a reservoir and is thus transported to the consumption point.

16. The method of claim 12 in which the cold-carrier, after cooling down according to step (c), is transported from the consumption point to the production point in the same reservoir as that in which the liquefied gas has been transported from the production point to the consumption point.

17. The method of claim 12 in which use is made of said cold-carrier comprising particles of said substance which are dispersed in said carrier-liquid wherein the dispersion is formed 'by cooling the carrier-liquid by passing it in heat exchange with the liquefied gas which is being regasified and adding the said substance to the cooleddown carrier-liquid.

18. The method as claimed in claim 17, in which the said substance is added to the carrier-liquid at the moment that the carrier-liquid has been cooled down to a temperature no greater than the temperature at which said substance may, under the prevailing conditions, change into the liquid condition.

19. The method as claimed in claim 17, in which the said substance is added to the carrier-liquid at the moment that the carrier-liquid has been cooled down to a temperature no greater than the temperature at which said substance may, under the prevailing conditions, change into the solid condition.

20. The method of claim 17 wherein said substance is 10 pre-cooled as a separate flow stream prior to mixture with said carrier-liquid.

21. The method of claim 12 in which, during cooling of the gas for liquefaction by passing the gas to be liquefied in heat exchange with the cold cold-carrier, the substance of the particles dispersed in the carrier-liquid, is separated from the carrier-liquid as soon as said substance is no longer in solid condition.

22. The method of claim 12 in which at least some of the particles of the substance undergoing a phase change during the process of heat exchange are each enclosed within a receptacle.

23. The method of claim 22 in which during the process of heat exchange between the cold-carrier and the gas, the carrier-liquid circulates between the gas and the particles enclosed within receptacles.

24. The method as claimed in claim. 22 in which the receptacles are suspended in the carrier-liquid.

References Cited UNITED STATES PATENTS 1,472,294 10/1923 Currne et al. 6240 XR 2,449,351 9/1948 White 62-52 2,496,380 2/1950 Crawford 6230 XR 2,975,604 3/1961 McMahon 629 3,018,632 1/1962 Keith 629 3,034,309 5/1962 Muck 629 XR 3,224,208 12/1965 Schlumberger 6212 3,283,521 11/1966 Harmens 6240 XR 3,306,057 2/ 1967 Harmens 6228 XR 3,331,214 7/1967 Proctor et al 6223 XR NORMAN YUDKOFF, Primary Examiner.

V. W. PRETKA, Assistant Examiner,