MXPA99006295A - Reducing void formation in curable adhesive formulations - Google Patents

Abstract

In accordance with the present invention, adhesive formulations have been developed which enable curing of adhesively bonded assemblies (i.e., assemblies which comprise devices which have been adhesively bonded to substrates) with dramatically reduced occurrence of void formation upon curing. In many instances, void formation can be eliminated employing invention compositions. In accordance with another aspect of the present invention, methods employing the above-described adhesive formulations are also provided, as are substantially void-free articles produced thereby.

Description

USE OF A TURBOEXPANSOR CYCLE IN THE PROCEDURE OF LIQUEFIED NATURAL GAS TECHNICAL FIELD The present invention relates generally to a process for the liquefaction of natural gas and, specifically, to the use of turboexpanders to increase the mechanical cooling effect used in such a process for the liquefaction of such natural gas.

ANTECEDENTS OF THE TECHNIQUE The liquefaction of natural gas is a technology that has been practiced widely important to convert the gas to a form in which it can be transported and stored easily and economically. There are numerous reasons for the liquefaction of gases and particularly natural gas. Perhaps the main reason is that liquefaction greatly reduces the volume of a gas, making the storage and transportation of liquefied gas in cheaper and better designed containers feasible. These economies are evident, for example, when considering gas transported by pipeline from a source of supply to a distant market. In these circumstances, it is desirable to operate under a high load factor. However, in practice the capacity may exceed the demand on some occasion or another, the demand may exceed capacity. It would be desirable to supplement such systems when demand exceeds supply by supplying additional materials for a storage source. For this purpose, it is desirable to provide gas in a liquefied state and vaporize the liquid as required by the demand for gas storage. Liquefaction of natural gas is also important in situations where gas must be transported from a full supply source to a distant market, particularly if the source of supply can not be connected directly to the market through a pipeline. In some cases, the method of transport is through containers that traverse the ocean. It is not economical to transport gaseous materials by ship unless the gaseous materials are highly compressed. Even when transportation is not economical due to the need to provide containers of adequate strength and capacity. Therefore, it is very desirable to store and transport the natural gas by first reducing the natural gas to a liquefied state by cooling the gas to a temperature in the range of about -151 ° C to -162 ° C and at atmospheric pressure. A reference number of the prior art teaches the procedures for the liquefaction of natural gas in which the gas liquefies by passing it sequentially through a plurality of gas cooling stages and successively lowering the temperatures until the liquefaction temperature is reached. . Cooling is generally achieved in such systems by indirect heat exchange with one or more refrigerants such as propane, propylene, ethane, ethylene and methane that expand in a closed cooling loop. Additionally, natural gas expands to an atmospheric pressure passed in liquefied gas through one or more expansion stages. During the course of the expansion, the gas is further cooled to a temperature suitable for storage or transport and the pressure is reduced to approximately atmospheric pressure. In this expansion at atmospheric pressure, important volumes of natural gas can be vaporized instantaneously. The instant vapors can be collected from the expansion stages and recycled or burned to generate energy for the liquid natural gas manufacturing facility. Many liquefied natural gas (LNG) liquefaction plants use a mechanical refrigeration cycle to cool the inlet gas flow of the cascade or mixed type refrigerant as described, for example, in the U.S. patent. do not. 3,548,606, issued December 22, 1970, and assigned to Phillips Petroleum Company. Plants with cascade cooling cycle type have expensive construction and maintenance and mixed refrigeration cycle plants require close attention to the composition of the flow during operation. Cooling equipment in particular is expensive due to the low temperature metallurgy requirements of the components. Therefore, it would be desirable to develop a liquefaction process that has a lower cost than traditional cascade or mixed refrigerant systems.

It would also be desirable to provide an improved method for the liquefaction of natural gas containing a hybrid design that combines a turbo expander cycle with mechanical cooling to liquefy natural gas in an efficient and economical manner. Specifically, it would be desirable to provide a method in which a mechanical refrigeration cycle provides cooling at the high temperature end of the process while a turboexpander cycle is provided to develop cooling at the relatively lower temperature end of the process.

DETAILED DESCRIPTION OF THE INVENTION Therefore, it is the object of the present invention to provide a more economical method for the liquefaction of natural gas. Another object of the present invention is to provide an improved process using a turbo expander cycle loop in a natural gas liquefaction process to increase a mechanical refrigeration cycle that provides a liquid natural gas manufacturing process more efficient and economical than cascade refrigeration cycles of the prior art. In accordance with the present invention there is provided a process for producing liquefied natural gas from a pressurized natural gas feed stream in which the feed flow contacts heat exchange in a mechanical refrigeration cycle to cool the flow of feeding at a first cooling temperature. At least a portion of the feed flow passes through a turboexpander cycle to provide an auxiliary cooling for the mechanical refrigeration cycle, thereby cooling the stream to a relatively lower second cooling temperature. Preferably, the feed stream is of natural gas deficient in pressurized fuel components, which is predominantly methane and has an initial pressure approximately greater than 56.24 kg / cm 2 gauge. The resulting liquefied natural gas stream has a reduced pressure in a flash vessel subsequent to the cooling passage to thereby produce a stream of liquefied natural gas product and a higher gas stream. Preferably, the upper gas stream is recycled to provide additional cooling to the process before recombining it with the feed stream that accesses the mechanical refrigeration cycle. A portion of the upper gaseous stream recycled from the flash vessel may be diverted to be used as fuel in the process. The liquefied natural gas stream leaving the flash vessel has an approximate atmospheric pressure and an approximate temperature of -151 ° C to -162 ° C. In the preferred embodiment, the turboexpansor cycle includes a turboexpander to reduce the pressure of the feed gas stream and to extract useful work therefrom during the pressure reduction, the turboexpander also produces an effluent stream.

The effluent stream of the turboexpander goes to a separator or distillation column that separates the effluent stream into a heavy liquid stream which subsequently expands to provide greater cooling to the process and a gas stream that is also used for a cooling effect higher. Both the expanded heavy liquid stream and the gas stream from the separator or column make indirect heat exchange contact with the incoming feed gas stream. The gas stream leaving the separator or column is compressed after making indirect heat exchange contact with the incoming feed gas stream and a combination and subsequent recycling with the feed gas stream entering the process. The gas stream leaving the separator or column can be compressed by a compressor that guides the work obtained from the turboexpander. The additional objectives, characteristics and advantages will be evident in the description written below.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a simplified flow diagram of a liquefaction process in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION The detailed description of the invention will be made with reference to the liquefaction of a natural gas deficient in fuel components and specific reference will be made to the liquefaction of a natural gas deficient in fuel components that has an initial pressure greater than 56.2 kg / cm2 gauge, having an ambient temperature. Preferably, the natural gas deficient in fuel components will have an initial pressure of approximately 63.27 to 70.3 kg / cm2 gauge at room temperature. In this analysis, the term "natural gas deficient in fuel components" will have a meaning of a gas that is predominantly methane, for example, 85% by volume of methane, with ethane being equilibrium, high hydrocarbon and nitrogen. With reference to Figure 1 of the drawings, the natural gas feed stream deficient in pressurized fuel components at room temperature is introduced to the process by a power supply line 11. In the illustrated embodiment, the feed gas stream It has an approximate pressure of 70.3 kg / cm2 gauge and an ambient temperature. The feed gas stream has been pretreated to remove acid gases, such as carbon dioxide, hydrogen sulfide, and the like, by methods known as desiccation, amine extraction, or the like. The feed stream 1 1 is also previously treated typically in a dehydrating unit of conventional design to remove water from the natural gas stream. In accordance with conventional practice, water is removed to prevent freezing and plugging of lines and heat exchangers at the temperature subsequently found in the process. Known dehydration techniques include the use of gas desiccants, such as molecular sieves. The pre-treated feed gas stream 1 1 passes through conduit 13 to the cooling section of the liquid natural gas manufacturing facility. In the cooling section 15, the feed gas stream is cooled by heat exchange contact with a closed-loop propane or propylene cooling cycle to cool the feed stream to a first cooling temperature. The mechanical cooling extract that is achieved in the cooling section 15 is typically provided by a cascade cooling cycle, such as that discussed with reference to the Phillips patent, cited above. Such cascade cooling cycles may only have an evaporation pressure and a single compression step for each refrigerant used, ie, methane, ethane, ethylene, propane / propylene. However, refrigeration is typically provided over many discrete temperatures. Any number of cooling steps may be employed, depending on the composition, temperature and pressure of the feed gas. In the embodiment of Figure 1, a closed-loop refrigeration cycle simplified by two "THERMOSIPHON" units, commercially available from ABB Randall Corporation of Houston, Texas, is provided. The THERMOSIPHON units 17, 19 have a circulating refrigerant, in this case propane or propylene, with closed loops 21, 23, respectively, between the compression section 25 and the expansion valves 25, 27 of the THERMOSIPHON containers. The expansion valves 25, 27 produce a cooling effect within the containers 17, 19, thereby cooling the refrigerant circulating through the conduits 29, 31 to produce a cooling effect within the cooling section 15 of the process . Although the THERMOSIPHON system is illustrated in the preferred embodiment of Figure 1, any other mechanical cooling system available can be used. The conduit 13 branches within the cooling section 15 within the downwardly extending conduit 33 and the branch conduit 35. The feed stream passes through the branch conduit 35, approximately presently at 70.3 kg / cm2. and - 9.4 ° C, passes through a turboexpansor cycle to provide an auxiliary cooling for the mechanical refrigeration cycle to cool the feed stream to a relatively lower second cooling temperature. The turboexpander cycle may consist of a commercially available turboexpander 37, as is commonly used in the industry for descent turbines, gas treatment, or in connection with water-based systems, these will be familiar to those skilled in the art. The turboexpander 37 is used in the process of the invention to extract work from the natural gas feed stream during the pressure reduction, so as to produce an effluent stream 39, which is predominantly gaseous but has a substantially reduced pressure. The resulting effluent stream will have an approximate pressure of 14.06 kg / cm2 gauge and a reduced temperature typically less than about -101.1 ° C. The effluent stream of the turboexpander 39 passes to a separator or column 41 which separates the effluent stream into a heavy liquid stream leaving the conduit 43 and a stream of upper gas leaving the conduit 45. While the separation unit 41 can assume a variety of forms , in the embodiment of Figure 1 includes a mass transfer section 47 in which a portion of liquids is evaporated and sent to the column to separate a portion of the lighter components from the incoming stream. The heavier components, for example propane, which exits through conduit 43 at about -73.3 ° C expand through the Joule-Thomson valve 49 and are sent back through the cooling section 15 in a flow of countercurrent to enter the feed stream 13 and provide an additional cooling effect. The output stream 51 from the cooling section 15 can be burned for, for example, energy compressors that are used in other parts of the process. The lighter components that exit the separator through the upper conduit 45 similarly pass in a countercurrent heat exchange relationship to the feed gas stream entering into the refrigeration unit 15, and then pass through the conduit 53 towards the impeller compressor 55, which in this case is guided by the turboexpander 37.

The output stream 57 from the compressor 55 passes through a chiller unit 59 and continues out of conduit 61. The combined effect of the mechanical refrigeration cycle and the expander tube cycle provides a cooling effect of approximately -9.44 ° C on the cross-sectional location "A" of the heat exchanger in the cooling section 15 in figure 1 and approximately -40 ° C below the location "B" in the cross section of the heat exchanger of figure 1. The current of liquefied natural gas leaving the cooling section 15 through the outlet conduit 63 is approximately -1 12.2 ° C and reduced to an approximate temperature of -147.2 ° C by means of the Joule-Thomson valve 65 or a liquid expander before passing through the conduit 67 to the flash vessel 69. The pressure of the liquefied natural gas stream is reduced within the flash vessel 69 to approximately 1.75 kg / cm2 gauge and a stream of liquid product LNG that can be removed through the discharge line 71. The LNG product exiting the flash vessel 69 through line 71 passes through the Joule-Thomson valve 77 where the temperature is reduced to about -162.2 ° C and at atmospheric pressure about then it can be sent for storage. An upper gaseous stream 73 is also produced in the flash vessel 69 and passes in a countercurrent heat exchange relationship to the incoming feed gas stream within the cooling section 15. The upper gas stream 73 is at approximately -147.22 ° C and is typically in the order of 40% of the LNG product sent to storage, but can be much smaller, for example, 15% if an immediate two-stage vaporization is used with liquid expanders between the vaporization vessels snapshot. At a volume of 40%, the upper vapor 73 from the flash vessel or containers constitutes an important source of cooling for the process. The upper gas stream leaving the cooling section 15 through the conduit 75 is approximately 1.4 kg / cm 2 gauge and -20 ° C and is sent through a conventional compressor-cooler section 79 having a series of on-line compressors 81, 83 and alternating cooling units 85, 87 to produce an output stream 89 with a pressure that is chosen to be adjusted to the approximate output pressure of the impeller compressor 55 of the turboexpander unit, in this case 19.6 kg / cm2 gauge. The arrangement of the compressor / cooler is chosen because the compressor seals generally have a limit of 149 ° C, necessitating the use of multi-stage compressor / chiller units. The combined streams in the conduits 61 and 89 are routed through the return conduit 91 through an additional compressor / cooler stage 93 to drive the pressure to approximately 70.3 kg / cm2 gauge. The outlet is passed to a compressor oil separator unit 95 to be combined again with the feed gas stream entering through a branch pipe 97. The other branch 99 can be used, for example, to form a gas stream of regeneration gas. dehydration system. Some of the gaseous stream 91 can be diverted through the conduit 101 to be burned to do additional work in the process. The volumetric flow through the branch conduit 97 is typically in the order of three times the flow of the incoming feed gas through the conduit 11. An invention is provided with various advantages. The "hybrid" liquefaction cycle of the process of the invention combines a turboexpander cycle with a mechanical cooling loop. The mechanical propane or propylene refrigeration loop provides cooling at one high temperature end of the process while the turboexpander cycle provides auxiliary cooling at the relatively lower temperature end of the cycle. The relatively higher temperature operation of the cooling section has the advantage that it can be built with more economical materials. After condensing the incoming power gas stream, it evaporates instantaneously at a pressure close to the final storage pressure with the liquid from the flash evaporation vessel sent to the storage tank LNG. The steam is recycled through the cooling section for an additional cooling effect and then recycled to the plant inlet. The effluent stream from the turboexpander is sent to a separator or column to remove heavy liquids that could solidify at lower temperatures. The liquids are also used to provide additional cooling to the process through a Joule-Thomson expansion. The gas leaving the separator provides cooling to the process and is then compressed by the impeller compressor, which is guided by the expander. The compressed stream is finally recycled to the entrance of the plant. The process of the invention provides a method for producing liquefied natural gas that is more economical than the mixed-type cascade cooling systems of the prior art. The process offers simplicity of design and economy of components. It is possible to use only one closed loop refrigeration cycle, instead of multiple cycles using mixed refrigerants. Only a portion, approximately 25% of the work in the inventive process, comes from a single closed loop cooling system. The rest of the cooling effect results from the heating of the return currents that are produced by a combination of the expansion of the feed through a turboexpansor and a Joule-Thomson valve or the pressure reduction of the liquid expander. The vaporization of the heavy hydrocarbons develops a significant additional cooling effect in the general process of the invention. The ability to recover the work of the turboexpander allows the reduction of the work requirement of the liquefaction process. While the invention has been shown only in one of its forms, it is not limited, but it is susceptible to various changes and modifications without separating from the spirit of the latter.

Claims (10)

1. NOVELTY OF THE INVENTION CLAIMS 1. - A process to produce a liquefied natural gas from a pressurized natural gas feed stream, the process consists of the steps of: introducing a supply current in heat exchange contact with a mechanical refrigeration cycle to cool the current of feeding at a first cooling temperature; and passing, at least a portion of the feed stream through a turboexpander cycle to provide an auxiliary cooling for the mechanical refrigeration cycle to thereby cool the feed stream to a relatively lower second cooling temperature. (2 .- The process according to claim 1, further characterized in that the feed stream is a natural gas feed stream deficient in fuel components that is predominantly methane and has an initial pressure greater than about 56.24 kg / cm2 gauge. 3. A process to produce liquefied natural gas from a pressurized natural gas feed stream, the process consists of the steps of: introducing the supply current into heat exchange contact with a mechanical refrigeration cycle to cool the feed stream at a first cooling temperature, and passing at least a portion of the feed stream through a turboexpander loop to provide auxiliary cooling for the mechanical refrigeration cycle to thereby cool the feed stream to a second lower cooling temperature, and condense the current of feed to produce a stream of liquefied gas; reduce the pressure of the stream of liquefied natural gas in a flash vessel to produce a stream of liquefied natural gas and a higher gas stream, compress the upper gas stream, and recycle the compressed upper gas stream to combine it with the feed stream which enters the mechanical refrigeration cycle. 4. The process according to claim 3, further characterized in that a portion of the upper recycled gaseous stream from the flash vessel, after passing at least some compression, is diverted to be used as fuel in the process. 5.- A process to produce liquefied natural gas from a natural gas feed stream deficient in predominantly fuel components is methane and has an initial pressure greater than 56.24 kg / cm2 gauge, the process consists of the steps of: introducing the supply current in heat exchange contact with a mechanical refrigeration cycle to cool the feed stream to a first cooling temperature; passing at least a portion of the feed stream through the passage of a turboexpander to provide auxiliary cooling for the mechanical refrigeration cycle to thereby cool the feed stream to a relatively lower second cooling temperature and to condense the feed to produce a liquefied natural gas stream; reducing the pressure of liquefied natural gas stream in a flash vessel to produce a product stream of liquefied natural gas and a higher gas stream; compress the upper gas stream; recycle the compressed upper gas stream to combine it with the feed stream entering the mechanical refrigeration cycle; further characterized in that the turboexpansor passage includes a turboexpander to reduce the pressure of the feed gas stream and to extract useful work therefrom during the pressure reduction, the turboexpander also produces an effluent stream; passing the effluent stream from the turboexpander to a separator or column that separates the effluent stream into a heavy liquid stream that subsequently expands to provide greater cooling to the process and a gas stream that is also used for a cooling effect, both the expanded heavy liquid stream and the separator or column gas stream based on indirect heat exchange contact with the incoming feed gas stream. 6. The process according to claim 5, further characterized in that the gas stream leaving the separator or column is compressed after making direct heat exchange contact with the incoming feed gas stream and subsequently recycled and recycled. It combines with the feed gas stream that enters the process. \ - 7. - The process according to claim 6, further characterized in that the gas stream leaving the separator or column is compressed by a compressor that guides the work obtained from the turboexpander. 8. The process according to claim 7, further characterized in that the heavy liquid stream leaving the separator or column is expanded by a Joule-Thomson expansion to provide greater cooling to the process. 9. The process according to claim 8, further characterized in that the liquefied natural gas stream leaving the flash vessel has approximately an atmospheric pressure and at a lower temperature of about -151 ° C to -162 ° C. 10. The process according to claim 9, further characterized in that the pressurized natural gas feed stream has a pretreatment before feeding it to the mechanical refrigeration cycle to remove the carbon dioxide, hydrogen sulfide and water.