KR100609186B1 - Method for removing aromatic compounds and medium molecular compounds from methane base feed by condensation and stripping and related apparatus - Google Patents

Abstract

DETAILED DESCRIPTION The present disclosure relates to a method and apparatus associated therewith for removing benzene, other aromatics and / or heavy hydrocarbon compounds from a methane base gas stream by condensation and stripping. The present application is preferably to remove benzene and other aromatics to prevent fouling and plugging of process equipment and preferably to recover other hydrocarbon components as needed. Cooled feed stream 118 is fed to column 60 and separated into methane rich vapor stream 120 and benzene / aromatic / heavys liquid 114. The liquid 114 is sent to a heat exchanger 62 where the freezing is restored. Warm dry gas 108 is cooled in heat exchanger 62 and distributed to strip 60 as stripping gas 109.

Description

Method for removing aromatic and heavy molecular compounds from methane base feed by condensation and stripping and related apparatus

The present invention relates to a process for removing benzene, other aromatics and / or heavy hydrocarbon compounds from a methane base gas stream by means of unique condensation and stripping processes and related apparatus.

Low temperature liquefaction of normal gaseous gases is used for the purpose of separating, purifying, storing and transporting the compounds in a more economical and stable form. Most liquefaction systems have many tasks in common that do not take into account the gases they contain, and as a result have many of the same problems. One problem that is commonly encountered in the liquefaction process, especially when there is an aromatic component, is that the settling of the material in the processing equipment and subsequent solidification leads to a decrease in process efficiency and reliability. Another common problem is the removal of small amounts of expensive, high molecular weight chemicals from the gas stream immediately prior to liquefaction of the gas stream in the major part. Thus, the present invention is applicable to gas processes in other systems that encounter similar problems, while being specifically described based on natural gas processes.

To methane (C ₂ +) than is commonly run on natural gas processing technique which the gas is subjected to a low temperature process for a hydrocarbon separation having a high molecular weight, useful C ₂ + stream with methane to a different purpose from natural gas It is to produce predominant pipeline gas. Frequently, C + ₂ stream, for example, _{C 2, C 3, C 4} , which will be separated into the individual compounds as shown in stream C ₅ +.

In addition, a process of liquefying natural gas at low temperature for transport and storage is generally carried out. The main reason for liquefying natural gas is that liquefaction can reduce its volume to about 1/600, allowing liquefied gas to be stored and transported in more economically and practically designed containers. For example, when gas is supplied from a source to a remote market by pipeline, it is desirable for the pipeline to operate under generally constant and high load elements. Frequently, the pipeline's distribution or capability exceeds the supply, while at some point the supply exceeds the pipeline's. To resolve peaks in places where demand exceeds supply, it is desirable to store excess gas in such a way that it is distributed when supply exceeds demand so that material from storage can meet future peaks in demand. Do. One practical means of doing this is to convert the gas into a storage liquefied state and then vaporize the liquid when demand is required.

Liquefaction of natural gas plays an important role in enabling gas to be transferred from the production site to the market when the production site and the market are remotely separated and pipelines are not available or practical. This is especially important where the movement is carried out by ships crossing the sea. Ship movement in an evaporated state is generally not practical because it requires adequate gas indentation that significantly reduces the specific volume of gas that requires the use of expensive storage vessels.

In order to store and transport the natural gas in the liquefied state, the natural gas is preferably cooled at -240 ° F to -260 ° F, where it has near-atmospheric vapor pressure. Numerous systems of the prior art for liquefaction of natural gas or the like, in which gas is sequentially liquefied at a pressure rising through a number of cooling stages while the temperature is continuously lowered and cooled until the gas reaches the liquefaction temperature. There is this. Cooling operations are generally accomplished by heat exchange with one or more refrigerants such as propane, propylene, ethane, ethylene, and methane or one or more compounds of the foregoing. In the art, refrigerants are arranged in a cascade fashion and each refrigerant is used in a closed refrigeration cycle. Cooling of the liquid is also possible by expansion of the liquefied natural gas to atmospheric pressure in one or more expansion stages. In each stage, the liquefied gas is flashed to the low pressure section to produce a two-phase gas liquid mixture at significantly lower temperatures. The liquid is recovered and reflashed. In this way, the liquefied gas is further cooled to a storage or transport temperature suitable for the liquefied gas at a pressure close to atmospheric pressure. At this expansion to near atmospheric pressure, an additional volume of some liquefied gas will flash. Flashed vapors from the expansion stage are generally collected and utilized as fuel gas for power generation or recycled for liquefaction.

As mentioned above, a major operational problem in the liquefaction of natural gas is the removal of residual benzene and other aromatic compounds from the natural gas stream immediately prior to the liquefaction of the main part of the stream and the precipitation and solidification of the pipes and keys. It causes fouling and potential plugging of processing equipment. For example, the fouling significantly reduces the heat transfer efficiency and throughput of heat exchangers, especially plate-fin heat exchangers.

For technical and economic reasons, there is no need to completely remove impurities such as benzene. However, there is a need to lower the concentration. Removal of debris from natural gas can be achieved with the same type of cooling operation used in the liquefaction process in which debris condenses, depending on their respective condensation temperatures. The basic cooling technique is the same as for liquefaction and separation, except that it must be cooled to liquefy to low temperatures as opposed to the separation of benzene foreign matter from the gas. Thus, in terms of residual benzene, it is only necessary to cool the natural gas to the temperature at which a portion of the feed gas condenses. This can be achieved in a low temperature separation column equipped at a suitable point in the LNG recovery process for separating condensed benzene from the main gas stream.

The effective operation of the low temperature separation column is to utilize the condensed liquid at low temperatures that must be withdrawn from the column for heat exchanged with the warm dry gas stream provided in the low temperature separation column. This heat exchange scheme, however, has a problem resulting from excessive temperature differences between the two streams supplied to the heat exchanger. Since the actual temperature difference exceeds 100 ° F., heat shock to the heat exchanger will shorten or damage the useful life of the heat exchanger device constructed of conventional materials.

Another consideration associated with validating the operation of the cold separation column is to provide a heat exchanger control that allows for automatic start-up of the column.

Another problem with the treatment of methane rich gas streams is the lack of economic means to recover high molecular weight hydrocarbons from the gas stream prior to returning the residual stream to a pipeline or other processing stage or liquefaction of the stream to the major part. Is that it is. In general, recovered high molecular weight hydrocarbons have a higher value per unit mass than residual components in the gas stream.

1 is a simplified flow diagram illustrating a low temperature LNG production process illustrating the method and apparatus of the present invention for removing benzene, other aromatics and / or high molecular weight hydrocarbon materials from a methane base gas stream.

FIG. 2 is a flow diagram briefly describing the method and apparatus described in FIG. 1 in more detail.

3 is a diagram illustrating the associated control system and cryogenic separation column of the present invention to maintain the required temperature ratio for the heat exchange fluid.

FIG. 4 is a diagram similar to FIG. 3 for temporarily selecting a temperature to allow automatic start-up of the cold separation column.

It is an object of the present invention to remove the residual amounts of benzene and other aromatics from the methane base gas stream which is liquefied in the major part.

Another object of the present invention is to remove high molecular weight hydrocarbons from the methane base gas stream.

Another object of the present invention is to remove high molecular weight hydrocarbons from the methane base gas stream which is liquefied in the major part.

Another object of the present invention is to remove benzene, other aromatics and / or high molecular weight hydrocarbons from the methane base gas stream in an energy efficient manner.

Another object of the present invention is to provide a process used to remove benzene, other aromatic compounds and / or high molecular weight hydrocarbons that can be incorporated and mixed in the techniques routinely used in gas plants.

Another object of the present invention is to provide a fairly simple, compact and inexpensive process and apparatus used for the removal of benzene, other aromatics and / or high molecular weight hydrocarbons from a methane base gas stream.

It is another object of the present invention to provide a technique in which the process used to remove benzene, other aromatics and / or high molecular weight hydrocarbons from the methane base gas stream to liquefy major fractions routinely used in plants producing liquefied natural gas. It is to be able to match and mix.

It is another object of the present invention to provide a heat exchanger controller which overcomes the problems associated with the treatment of cold fluids and the above mentioned problems.

It is another object of the present invention to provide an improved control method which lowers the initial device temperature requirements and reduces the cost of the heat exchanger device.

Another particular object of the present invention is to control the heat exchanger temperature to allow cooling of the warm fluid stream to the cold fluid stream without introducing heat shock into the heat exchanger device.

Another object of the present invention is to control the heat exchanger to facilitate automatic start-up of the low temperature separation column.

In one embodiment of the present invention, benzene and / or other aromatics are removed from the methane base gas stream in a process comprising: (1) the major portion of the gas stream is liquefied to produce a two-phase stream. Prior to condensing the minor portion of the methane base gas stream, (2) feeding the biphasic stream into the upper section of the stripping column, (3) degassing the gas stream depleted of aromatic compounds from the upper section of the stripping column. Removing (4) removing the aromatic compound rich liquid stream from the lower section of the stripping column, and (5) the aromatic compound rich liquid stream with the methane rich stripping gas stream is contacted via an indirect heat exchanger. Producing a warm aromatics containing stream and a cooled methane rich stripping gas stream, (6) Supplying a cooled methane rich stripping gas stream to the lower section of the stripping column and optionally (7) liquefying the aromatic compound depleted gas stream to produce liquefied natural gas where the gas stream is liquefied in the major portion. Feeding step by step.

In another embodiment of the present invention, the high molecular weight hydrocarbon is removed and condensed in the methane base gas stream in a process comprising: (1) condensing the minor portion of the methane base gas stream to produce a two-phase stream, (2) feeding the biphasic stream into the upper section of the stripping column, removing the gas stream depleted of the heavy compounds of (3) from the upper section of the stripping column, and the molecules of (4) Removing the compound rich liquid stream from the lower section of the stripping column, (5) the heavy molecular compound rich liquid stream with the methane rich stripping gas stream is contacted via an indirect heat exchanger, so that the molecular compound rich in warm Producing a stream and a cooled methane rich stripping gas stream, and (6) stripping the methane rich stripping gas stream. Supplying the lower section of the column.

In another embodiment of the invention, the invention is a device comprising: (1) a condenser that condenses the minor portion of the methane base gas stream to produce a two-phase stream, (2) feeds a two-phase stream and vapors therefrom. Stripping columns for producing streams and liquid streams, (3) heat exchangers incorporating indirect heat exchange means for providing a warm liquid stream and a cooled gas stream by providing an indirect heat exchanger between the gas stream and the liquid stream, (4) A conduit between the upper section of the stripping column and the condenser for flowing a two-phase stream, (5) a conduit connected to the upper section of the stripping column to remove the vapor stream, (6) the stripping column and the liquid A conduit between the heat exchanger and the heat exchanger for flowing the stream, (7) a conduit between the heat exchanger and the stripping column and the heat exchanger for flowing the cooled gas stream, A conduit connected to a heat exchanger to warm the flow of the liquid stream from the group, (9) a conduit connected to the heat exchanger so that the gas stream to flow to the heat exchanger.

In another embodiment of the present invention, the above and other objects and advantages are achieved by providing a bypass conduit for warming fluid to control a heat exchanger for treating warm and cold fluids, wherein the control in the bypass conduit The valve is operated in response to the temperature ratio of the heat exchange fluid. According to another aspect of the present invention, an automatic start-up control is a high selector that directs the flow of warm fluid to facilitate the start-up of the column and temporarily selects the temperature to be switched to the warm gas flow control for the next required temperature. It is to be provided.

The invention, which implements a preferred embodiment, comprises (1) removing molecular compounds in benzene and / or other aromatics from the methane base gas stream condensed in the major portion, and (2) from the methane base gas stream condensed in the major portion. While applicable to the removal of more useful high molecular weight hydrocarbon materials, the technique is also applicable to recovering the materials from the methane elementary stream (eg, removing natural gas liquids from natural gas). Benzene and other aromatic compounds pose special problems because of their high high melting point temperature. For example, benzene containing 6 carbon atoms has a melting point of 5.5 ° C. and a boiling point of 80.1 ° C. Hexane containing 6 carbon atoms also has a melting point of -95 ° C and a boiling point of 68.95 ° C. Thus, compared to other hydrocarbons of similar molecular weight, benzene and other aromatic compositions have a very large problem with fouling and / or plugging of process equipment and conduits. As used herein, an aromatic composition is a composition characterized by the presence of at least one benzene ring. As used herein, high molecular hydrocarbon materials are hydrocarbon materials that possess a molecular weight greater than ethane, and in this respect can be used interchangeably with heavy hydrocarbons.

For the purpose of clarity and simplicity of explanation, the following description is limited to using an inventive process and associated with an apparatus for cryogenically cooling a natural gas stream for producing liquefied natural gas. In particular, the following description is directed mainly to the removal of benzene and / or other aromatics and / or high molecular weight hydrocarbons (heavy hydrocarbons) in liquefaction designs in which cascaded refrigeration cycles are used. However, the inventive process described herein and its correlators are not limited to liquefied systems that exclusively process natural gas streams or utilize cascaded refrigerant cycles. The process and associated apparatus may comprise (a) benzene and / or heavy aromatics present in the methane base gas stream in concentrations which may foul or plug process equipment such as heat exchangers used to condense the stream, or (b) may be applied to any refrigeration system, which is necessary for reasons of removal and recovery of high molecular weight hydrocarbons from the methane base gas stream.

Natural Gas Stream Liquefaction

Low temperature plants have various forms; The most efficient and effective is the cascade type operation and this type combined with expansion type cooling operation. In addition, a method for generating a LNG (liquefied natural gas) by its claim having one hydrocarbon separation of larger molecular weight than the methane portion as a part, to the plant to a low temperature to produce LNG explanation is good for C ₂ + hydrocarbons from the natural gas stream Describe a similar plant for removal.

In a preferred embodiment using a cascaded refrigeration system, the present invention is directed to a multistage propane cycle, a multistage ethane or ethylene cycle, and (a) a single or multistage expansion cycle in which the same is further cooled to lower to near atmospheric pressure. Either a closed methane cycle, or an open methane cycle utilizing a portion of the feed gas, such as (b) a source of methane, and having a multistage expansion cycle therein in which the same is further cooled to lower the pressure to near atmospheric pressure. Cooling the gas stream sequentially by a passage through a cycle of sequential cooling, for example, sequentially cooling the natural gas stream at an elevated pressure of about 650 psia. In the sequence of cooling cycles, the refrigerant with the highest boiling point is first followed by the refrigerant with the intermediate boiling point and finally utilized according to the refrigerant with the lowest boiling point.

The pretreatment step provides a means for removing unwanted components such as acid gas, mercaptans, mercury and moisture from the natural gas feed stream distributed to the plant. The compounds of this gas stream can be very important. As used herein, a natural gas stream is basically an optional stream comprising methane starting in the major portion from the natural gas feed stream, the feed stream containing, for example, at least 85% by weight methane, Ethane, high hydrocarbons, nitrogen, carbon dioxide, and small amounts of mercury, hydrogen sulfide, and mercaptans are in balance. The pretreatment step is a separation step that is placed downstream of the early stage of the cooling operation in the initial cycle or upstream of the cooling cycle. The following does not include a list of some of the tools that are readily available to those skilled in the art. Acid gas and mecapcaptan are routinely removed by an adsorption process using an aqueous amine containing solution. This processing step is generally performed upstream of the cooling stage used in the initial cycle. The major part of the water is routinely removed as a liquid by gas compression and by two phase gas liquid separation which cools the downstream of the first cooling stage and the upstream of the initial cooling cycle in the initial cooling cycle. Mercury is routinely removed by mercury solvent beds. Residual amounts of water and acid gas are routinely removed using appropriately selected solvent beds, such as renewable molecular sieves. Processes using solvent beds are generally placed downstream of the first cooling stage in the initial cooling cycle.

The resulting natural gas stream is generally delivered to the liquefaction process at high pressure or compressed at high pressure, the high pressure being greater than 500 psia, preferably from about 575 to about 650 psia, most preferably at about 600 psia. Pressure. The stream temperature is generally the temperature of the surrounding atmosphere to slightly above the atmosphere. Representative temperature ranges are from 60 ° F to 120 ° F.

As is well known, the natural gas stream in this respect is cooled in a number of multi-stage (eg three) cycles or stages by means of a plurality of refrigerants, preferably three indirect heat exchangers. Although the overall effective cooling for a given cycle improves as the number of stages increases, this increase in efficiency correspondingly increases asset value and complicates the process. The feed gas comprises a well effective number of refrigeration stages, normally two, preferably two to four, and most preferably three stages in a first closed refrigeration cycle utilizing significant high boiling refrigerants. Passing through The refrigeration agent comprises propane, propylene or mixtures thereof in the major part, more preferably propane, and the best refrigerant is basically composed of propane. The treated feed gas is then subjected to a valid number of stages, normally two, preferably two to four, and more preferably two in a second closed refrigeration cycle in a heat exchanger with a low boiling point refrigerant. Flow through three or three stages. The refrigerant comprises ethane, ethylene or mixtures thereof in the major portion, preferably ethylene, and most preferably the refrigerant consists essentially of ethylene. Each of the aforementioned cooling stages for each refrigeration comprises a split cooling zone.

Generally, the natural gas feed stream containing C ₂ + C ₂ + a large amount of a rich component to result in the formation of liquid in the at least one cooling stage. This liquid is removed by gas-liquid separation means, preferably one or more conventional gas-liquid separators. In general, the sequential cooling of the natural gas at each stage is controlled to remove as much of the C ₂ and high molecular weight hydrocarbons as possible from the gas so as to contain a significant amount of ethane and heavier components. The liquid stream and the methane produce a dominant first gas stream. Gas / liquid separating means of the number of valid is downstream of the cooling zones for the removal of a liquid stream rich in C ₂ + components are placed in strategic areas. The exact number of zones and gas / liquid separators depends on the number of operating parameters. The operating parameters include the C ₂ + compounds in the natural gas feed stream, the BTU components required for the final product, the values of the C ₂ + components for other applications, and other considerations routinely considered by those skilled in the LNG plant and gas plant operating arts. There are elements. The C ₂ + hydrocarbon stream or streams can be demethane by a single stage flash or fractionation column. In the former case, the methane rich stream can be recompressed and recycled or used as fuel gas. In the latter case, the methane rich stream returns directly to the liquefaction process at pressure. C ₂ + hydrocarbon streams or streams or dimtan C ₂ + hydrocarbon streams can be used as fuel or produce individual stream riches in specific chemical compositions (eg C ₂ , C ₃ , C ₄ and C ₅ +) May be additionally handled by classification in one or more classification zones. In the final stage of the second cooling cycle, the gas stream dominated by methane condenses in the major part, preferably in its entirety. In one preferred embodiment, discussed in detail later, this process and zone is to use the inventive process and correlator to remove benzene, other aromatics and / or heavy hydrocarbons. The process pressure in this zone will be slightly lower than the pressure of the feed gas to the first stage of the first cycle.

The liquefied natural gas stream is then additionally cooled in a third stage or cycle in one of two embodiments. In one embodiment, the liquefied natural gas stream is additionally cooled by an indirect heat exchanger with a third closed refrigeration cycle, where the concentrated gas stream is a stage of effective water, normally two, preferably two to four And most preferably subcooled via a path through the three stages, the cooling operation being provided by a third refrigerant having a lower boiling point than the refrigerant used in the second cycle. Such refrigerants are preferably included in the major portion of methane, more preferably in the dominant portion of methane. In a second embodiment utilizing an open methane refrigeration cycle, the liquefied natural gas stream is subcooled by contact with the flash gas in economical main methane in the manner described below.

In the fourth cycle or step, the liquefied gas is further cooled by expansion and separation of the flash gas from the cooling liquid. In the manner described, the removal of nitrogen from the condensed product and the system is achieved at either part of this stage or at one stage of the separation continuous stage. The key elements that distinguish closed cycles from open cycles are the initial temperature of the liquefied stream before flashing to near atmospheric pressure, the relative amount of flash steam generated during the flashing, and the deposition of the flash steam. The majority of the fresh steam is recycled from the open cycle system to the methane compressor and the fresh steam in the closed cycle system is generally utilized as fuel.

In a fourth cycle or stage in either of the open or closed cycle methane systems, the liquefied product is cooled by at least one, preferably two to four, and more preferably three expansions, where each Expansion uses either a Joule-Thompson expansion valve or a hydraulic expander accompanied by the separation of the gas liquid product into the separator. When operating properly using a hydraulic expander in operation, some steam products during the flash stage, large reductions in stream temperature, and large efficiencies associated with power recovery are effective in terms of operating costs and increased importance associated with the expander. It is said to be. In one embodiment for use in an open cycle system, further cooling of the high pressure liquefied product prior to flashing may be performed via one or more hydraulic expanders to cool the high pressure liquefied stream prior to flashing and then using the flash stream. It is made possible by first flashing a portion of the stream via indirect heat exchange means. The flash product is then recycled in an open methane cycle by return to the appropriate zone based on temperature and pressure.

If the liquid product entering the fourth cycle is at a good pressure of about 600 psia, representative flash pressures for the three stage flash process are about 190,61 and 14.7 psia. In an open cycle system, the vapor flashed or fractionated in the above-described nitrogen separation step and the vapor flashed in the expansion flash step are used as cooling agents in the third step or cycle described. In a closed cycle system, vapor from the flash stage may also be used as a cooling agent prior to regeneration or use as fuel. In both open or closed cycle systems, the flashing of the nearby atmospheric liquefied stream produces an LNG product that is treated at temperatures between -240 ° F and -260 ° F. Nitrogen should be concentrated and removed in some areas of the process so that when the significant nitrogen is in the feed stream, the BTU content of the liquefied product is maintained to the extent possible. Various techniques suitable for this purpose are available to those skilled in the art. Here is an example: If an open methane cycle is used and the nitrogen concentration of the fuel is low, nitrogen removal, typically less than about 1.0 vol%, is typically achieved by removing small side streams at a high pressure inlet port or outlet port in the methane compressor. For a closed cycle at a nitrogen concentration of up to 1.5 vol.% In the feed gas, the liquefied stream is generally flashed from the processing state at near atmospheric pressure in a single step via a flash drum. Nitrogen-containing flash steam is generally used as fuel gas for gas turbines driving compressors. Nearly atmospheric atmospheric LNG products are routed and stored. An open cycle is used and at a nitrogen concentration in the inlet feed gas of about 1.0 to about 1.5 vol.%, The nitrogen is subjected to a liquefied gas stream from the third cooling cycle to the flash stage prior to the fourth cooling stage to be removed. The flash steam is one that contains an appropriate concentration of nitrogen and can then be used as fuel gas. Typical flash pressure for nitrogen removed at this concentration is about 400 psia. If the feed stream contains nitrogen concentrations greater than about 1.5 vol% and an open or closed cycle is used, the flash step will not be able to provide sufficient nitrogen removal. In this case, it can be used from a nitrogen rejection column producing a liquid stream and a nitrogen rich vapor stream. In a preferred embodiment using a nitrogen rejection column, the high pressure liquefied methane stream to the methane saver is split into first and second portions. The first portion is flashed to nearly 400 psia and the biphasic mixture is fed to the nitrogen rejection column as a feed stream. The second portion of the high pressure liquefied methane stream flows through the methane saver described below and is further cooled, which is then flashed to the next 400 psia, and the liquid portion or the resulting two-phase mixture functions as the flux stream as the flux. Is fed to the upper section of the column. The nitrogen rich vapor stream produced from the top of the nitrogen rejection column is generally used as fuel. The liquid stream produced from the bottom of the column is then fed to the methane expansion first stage.

Refrigeration cooling work for natural gas liquefaction

The liquefaction limit of natural gas in the cascade process is the use of one or more refrigerants that transfer heat energy from the natural gas stream to the refrigerant and transfer heat energy to the surroundings. Basically, a refrigeration system is one in which the stream is gradually cooled down to an increasingly low temperature to function as a heat pump by the removal of thermal energy from the natural gas stream.

Various types of cooling operations are employed, including but not limited to (a) indirect heat exchangers, (b) evaporators, and (c) expansion or compression reducers. As used herein, an indirect heat exchanger refers to a process in which a refrigeration or cooling agent cools the material to be cooled without substantial physical contact between the freezing agent and the material being cooled. Specific examples include a heat exchanger under a tube-and-cell heat exchanger, a core-in-kettle heat exchanger, and a brazed aluminum plate-fin heat exchanger. The physical state of the material and the refrigerant to be cooled can be changed depending on the type of heat exchanger selected and the requirements of the system. Thus, in the inventive process, cell-and-tube heat exchangers are generally utilized where there is a material that is cooled in the liquid or gaseous state and there is a refrigeration agent in the liquid state, and plate-pin heat exchangers are generally It is utilized when it is in the gaseous state and the material to be cooled is in the liquid state. Finally, a core-in-kettle heat exchanger is one in which the material to be cooled is a liquid or gas and the refrigerant can be utilized where the phase changes from liquid to gaseous phase during heat exchange.

Evaporative cooling refers to the cooling of a material by evaporation or vaporization of a portion of the material as a system maintained at a constant pressure. Thus, during vaporization, the portion of the material to be evaporated absorbs heat from the portion of the material that is in the liquid state and thus the liquid portion is cooled.

Finally, the expansion or pressure reduction cooling operation refers to the cooling operation that occurs when the pressure in the gas phase, liquid phase, or two-phase system passes through the pressure reduction means. In one embodiment, such expansion means is a Joule-Thompson expansion valve. In another embodiment, the expansion means is a hydraulic or gas expander. Since the expander recovers working energy from the expansion process, lower process stream temperatures are possible upon expansion.

In the following figures and descriptions, the descriptions or figures show the expansion of the refrigerant flowing through the throttle valve accompanied by the sequential separation of the gas and liquid portions in the refrigeration chillers or condensers where indirect heat exchange takes place. This simple design is good because it is workable and sometimes simple and inexpensive, and is more suitable for performing expansion and separation and partial evaporation in a separation step, such as a combination of flash drum and throttle valve, prior to indirect heat exchange to the chiller or condenser. It is effective. In another workable embodiment, the throttle or expansion valve is not a separate item and is an integral part of a refrigeration chiller or condenser (eg, a flash occurs upon entry of liquefied refrigerant into the chiller). In a similar manner, the cooling operation of the multiple streams for a given refrigeration stage can occur in a single vessel (eg chiller) or multiple vessels. The former is generally good in terms of major equipment costs.

In the first cooling cycle, the cooling operation delivers pressure at the place where it is liquefied by indirect heat transfer into a heat transfer medium which ultimately utilizes an atmosphere such as a heat sink, with the compression of a high boiling point gas refrigerant, preferably propane, The heat sink is generally at least two of the atmosphere, fresh water source, salt water source, earth or the like. The condensation refrigerant is then subjected to one or more expansion cooling steps by appropriate expansion means to produce a biphasic mixture having significant low temperatures. In one embodiment, the main stream is divided into at least two split streams, preferably two to four streams, and most preferably three streams, where each stream is separated and expanded to the designed pressure. Each stream then provides evaporative cooling by indirect heat transfer to one or more selected streams, one stream being the natural gas stream to be liquefied. The number of separate refrigeration streams corresponds to the number of refrigeration compressor stages. The vaporized refrigerant from each individual stream is then returned to the stage appropriate for the refrigeration compressor (eg, two separate streams correspond to two stage compressors). In a better embodiment, all the liquefied refrigerant is expanded to a pre-specified pressure and this stream is then used to provide vaporizable cooling by indirect heat transfer to one or more selected streams, the one stream being a liquefied natural gas stream. to be. A portion of the liquefied refrigerant is removed from the indirect heat transfer means and the expansion cooled by expansion to low temperatures and corresponding low temperatures provides vaporizable cooling by the indirect heat transfer means to one or more designated streams, the one stream being Natural gas stream to be liquefied. Normally, this embodiment uses two, preferably two to four, most preferably three expansion cooling / vaporizable cooling steps. Similar to the first embodiment, the frozen steam from each stage is returned to the inlet port suitable for the staged compressor.

In a preferred cascaded embodiment, most of the refrigeration cooling of the lower boiling point refrigeration (e.g., the refrigerant used in the second and third cycles) is passed through the indirect heat exchanger with the selected high boiling refrigeration stream. Cooling is made possible. This cooling scheme is referred to as "cascade cooling". In the high boiling refrigerant effect, which functions as a heat sink for low boiling refrigerants or other conditioned heat sinks, thermal energy is pumped from the liquefied natural gas stream to the low boiling refrigerant and then to an ambient heat sink (e.g. fresh flash). Water, salt water, atmosphere) is pumped (eg delivered) to one or more high boiling refrigerants prior to delivery to the surrounding atmosphere. In the first cycle, the refrigerant used in the second and third cycles is compressed by a multistage compressor at a preselected pressure. In a possible economical implementation, the compressed refrigeration vapor is first cooled via indirect heat exchange with one or more cooling agents (eg, air, salt water, fresh water) that are directly coupled with the surrounding heat sink. Such cooling is via mutual stage cooling between the cooling of the compressed product and / or with the compression stage. The compressed stream is then further cooled via indirect heat exchange with one or more cooling stages described above for the high boiling point refrigerant.

The second cycle refrigeration agent is preferably via indirect heat exchange with one or more cooling agents which are preferably bonded directly to ethylene, an ambient heat sink (eg, an intermediate-stage and / or post-cooling following compression). Firstly cooled and then sequentially contacted with the first and second or first, second and third cooling stages for the highest boiling point refrigerant used in the first cycle to further cool and finally liquefy. Preferred second and first cycle refrigerants are ethylene and propane, respectively.

If the three refrigerants use a cascade closed cycle system, the third cycle refrigerant is optionally by indirect heat transfer to a heat sink (eg, intermediate-stage and / or post cooling following compression) around it. It is compressed in a well-cooled stage manner and then cooled by indirect heat exchange in either the first and second cooling cycles or in one of the selected cooling stages, which makes good use of propane and ethylene as their respective refrigerants. Preferably, this stream is such that each progressive cooling stage is contacted in a sequential manner in the first and second cooling cycles.

In an open cycle cascade refrigeration system as described in FIG. 1, the first and second cycles are to operate in a manner similar to that described for the closed cycle. However, open methane cycle systems are easily distinguished from conventional closed refrigeration cycles. As noted above, a substantial portion of the liquefied natural gas stream originally given at high pressures is cooled to approximately -260 ° F by expansion cooling in a stepwise manner at near atmospheric pressure. In each step, a significant amount of methane rich vapor is produced at a given pressure. Each vapor stream preferably receives significant heat transfer in the methane economizer and returns well to the inlet port of the compression stage at a temperature close to ambient temperature. In the course of flowing through the methane economizer, the fresh steam is contacted with the warm stream in a reverse flow fashion and in an order designed to maximize cooling of the warm streams. The pressure selected for each expansion cooling stage is for each stage, the volume of gas produced by the addition of the volume of compressed steam from the adjacent lower stage results in the effective overall operation of the multistage compressor. Intermediate cooling and cooling of the final compressed gas are preferably achieved by indirect heat exchange with one or more cooling agents that are directly coupled to the ambient heat sink. The compressed methane rich stream is then in the first and second cycles, preferably in all stages associated with the refrigerant used in the first cycle, more preferably in the first two stages and most preferably in the first stage. Only at the stage, it is further cooled by indirect heat exchange with the refrigerant. The cooled methane rich stream is further cooled by indirect heat exchange with fresh steam to the main methane economizer, and then preferably the natural gas feed stream and the cooled methane rich stream enter the ethylene cooling stage, preferably most of the time. Immediately before the ethylene cooling stage where methane is liquefied (eg, ethylene condenser), it is combined with the natural gas feed stream in any zone in the liquefaction process, in a state of similar temperature and pressure.

Optimal utilization by intermediate stage and intermediate cycle heat transfer

In a preferred embodiment, the step may return the refrigeration gas stream to the inlet port of their respective compressor at or near ambient temperature to achieve more optimal process efficiency. This step not only improves the overall efficiency but also significantly reduces the difficulties associated with exposure of the compressor components to low temperatures. This is achieved by the use of an economizer, wherein one or more vapors prior to flashing and in which the stream comprised in most of the liquid is generated in a downstream expansion stage (eg stage) in a downstream cycle or the same. First cooled by indirect heat exchange into the stream. In closed systems, economizers are preferably used to obtain additional cooling from fresh steam in the second and third cycles. If an open methane cycle system is used, the fresh steam from the fourth stage is preferably returned to one or more economizers, where (1) the steam is cooled by indirect heat exchange with the liquefied product stream prior to each pressure reduction stage. And (2) the steam is cooled by indirect heat exchange of compressed steam from an open methane cycle prior to combining the main natural gas feed stream with the stream. The cooling step includes the cooling step of the third stage described above, which will be described in more detail with reference to FIG. 1. In one embodiment where ethylene and methane are used in the second and third cycles, the contacting operation is performed by a series of ethylene and methane economizers. In the preferred embodiment described in FIG. 1 and described in more detail below, the process utilizes a main ethylene economizer, a main methane economizer and one or more additional methane economizers. Said further economizer is referred to herein as the second methane economizer, the third methane economizer and the like and each of said additional methane economizers corresponds to a separate downstream fresh step.

Removal of benzene, other aromatics and / or heavy hydrocarbons

The inventive process of removing benzene, other aromatics and / or high molecular weight hydrocarbon materials from a methane base gas stream is of considerable energy efficiency and is simple in operation. Because of the way of operation, the column referred to herein as the stripping column is to perform both stripping and sorting functions. The process comprises cooling a methane base gas stream in which from 0.1 to 20 mol%, preferably from 0.5 to about 10 mol% and more preferably from about 1.75 to about 6.0 mol% of the total gas stream is condensed to form a two-phase stream. will be. The optimal mole percentage depends on the compound of the gas being liquefied and other parameters related to the process which are readily identified by processes generally known to those skilled in the art.

In one embodiment, the required two-phase stream is obtained by cooling the entire feed stream to the extent that the required liquid percentage is obtained. In a preferred embodiment, the gas stream is first cooled adjacent to the liquefaction temperature and then divided into a first stream and a second stream. The first stream is subjected to additional cooling and partial condensation and then combined with the second stream to produce a two-phase stream containing the required percentage of liquid. This latter approach is good because it facilitates associated motion and process control.

A two-phase stream is then fed to the upper section of the column, where the stream contacts the rising vapor stream from the lower part of the column, whereby heavy molecular compound-heavys-deplete vapor streams and reflux streams are produced from the column. It functions as a stream to produce a heavy molecular compound rich liquid stream. As used herein, “heavies” refers to organic compounds that are somewhat dominant with molecular weights greater than ethane. The column is unique, as described above, without the use of a flux generating condenser and additionally without the use of a steam generating reboiler.

As mentioned above, the methane rich stripping gas stream is fed to the column. This stream preferably starts from the upstream where the cooled methane base gas stream is subjected to some cooling and liquid removal. Prior to the inflow into the base of the column, this gas stream is cooled by indirect contact in a favorable reverse flow manner with the liquid product produced from the bottom of the column, such that a warm heavy molecular compound rich stream and a cold methane rich stripping gas stream Create The methane rich stripping gas is partially condensed upon cooling and the resulting cold methane rich stripping gas containing two phases is fed directly to the column.

Generally used in the methane-rich stripping gas cooling and containing a small amount of the C ₃ + components in place of the steam which is generated from a reboiler which contains a large amount of the C ₃ + components are the problems to do with the fluid in the column approaching critical conditions Significantly reduced, resulting in poor component separation. This factor is particularly pronounced when operating in the better pressure range of about 550 to about 675 psia. The critical temperatures and pressures of methane are -116.4 F and 673.3 psia. The critical temperatures and pressures of propane are 206.2 ° F. and 617.4 psia, and the critical temperatures and pressures of n-butane are 305.7 ° F. and 551.25 psia. Appropriate amount of presence of the C ₃ + components will (1) and the low approach to the preferred operating pressure of the process the critical pressure, (2) to raise the critical temperature. The result is an effect that makes the separation of components more difficult by the vapor / liquid contact action. A second element that distinguishes the use of cooled methane rich stripping gas over steam from the reboiler is the temperature difference between the liquid effluent from the final stage and each stream. Since it is preferred that the cooled methane rich stripping gas is warmer than similar vapors from the reboiler, this good stream retains a significant ability to strip the liquid phase of the lighter component. The temperature difference between the effluent liquid from the column and the effluent stripping gas to the column is preferably between 20 ° F. and 110 ° F., more preferably between 40 ° F. and 90 ° F., and most preferably between 60 ° F. and 80 ° F. .

The number of theoretical trays in a column depends on the compound, the temperature, the flow rate of the incoming vapor stream into the column, and the ratio of the compound, temperature, flow rate, and liquid to the vapor of the two-phase stream fed to the upper section of the column. Such a determination is easily made within the skills acquired by those skilled in the art. The theoretical number of trays may be provided by various types of column packings (pall rings, saddles, etc.) or separate contact stages (eg trays) in the column or combinations thereof. In general, two to fifteen theoretical stages are required, preferably three to ten, more preferably four to eight, and most preferably five theoretical stages. Trays are generally good if the column diameter is larger than 6 ft.

Good Open Cycle Example of Cascade Liquefaction Process

The flowchart of the apparatus shown in FIGS. 1 and 2 is a preferred embodiment of an open cycle cascade liquefaction process and is shown for illustrative purposes. Since the system depends on the nitrogen component of the feed gas, it is a nitrogen removal system that was deliberately omitted from the preferred embodiment. However, if one pays attention to the nitrogen removal technique described above, one skilled in the art will readily be able to utilize the systematic classification applicable to the preferred embodiment. 3 and 4, which are shown in more detail for the purpose of illustration, illustrate the inventive low temperature column, and in particular, illustrate a systematic classification method for cooling and controlling the temperature and stripping gas supplied to the low temperature column. One skilled in the art will appreciate that only Figures 1 through 4 are shown schematically so that the equipment of the various items required for a successful commercial plant is omitted for clarity of understanding. Examples of such items include compressor controls, flow and level measurement and response controllers, additional temperature and pressure controls, pumps, motors, filters, additional heat exchangers, valves, and the like. These items are installed according to general technical practice.

For ease of understanding of FIGS. 1 to 4, items numbered 1 to 99 have been generally assigned correspondingly to processes for processing vessels and equipment directly related to the liquefaction process. Items numbered from 100 to 199 were given mostly corresponding to methane-containing flow furnaces or conduits. Items numbered 200 to 299 were assigned correspondingly to flow conduits or conduits containing frozen ethylene or optionally ethane. Items numbered 300 to 399 were assigned corresponding to flow paths or conduits containing frozen propane. In order to extend the understanding as far as possible, the numbering system used in FIG. 1 was also used in FIGS. In addition, the accompanying numbering system has the addition of additional elements not described in FIG. Items numbered 400 to 499 were assigned corresponding flow lines or conduits. Items numbered 500 to 599 were assigned correspondingly to further process equipment such as vessels, columns, heat exchange means and valves having process control valves. Items numbered 600 to 799 relate to process control systems with the exception of control valves and in particular with sensors, transducers, controllers and setpoint inputs.

Nearly all control systems use some combination of electrical, pneumatic or hydraulic signals. However, any other type of signal carrier may be used that is compatible with the process and equipment used within the scope of the present invention. In the present invention illustrated in FIGS. 1 to 4, the line represented by the signal line is represented by a solid line in the drawing. The line is an electrical or pneumatic signal line. In general, the signal provided from any transducer is in the form of an electric wire. And the signal provided from the flow sensor is in the form of a pneumatic line. This signal conversion is simply not uniformly explained as it is known to those skilled in the art because if the flow is measured in pneumatic form it must be converted to electrical form if it is electrically transmitted by the flow transducer.

Referring to FIG. 1, the gas propane is compressed in a multistage compressor 18 driven by an undescribed gas turbine driver. The three stages of the compressor are in a single unit, but each stage of the compressor may be in a unit mechanically coupled to be driven by a split unit and a single driver. Upon compression, compressed propane passes through conduit 300 to cooler 20 where propane is liquefied. The pressure and temperature of the liquefied propane refrigerant prior to flashing represent about 190 psig and 100 ° F. Although not illustrated in FIG. 1, the dividing vessel is disposed upstream of the pressure reducing means described as expansion valve 12 and downstream of cooler 20 for removal of residual light components from liquefied propane. . The vessel may include a single stage gas-liquid separator or may be more complicated and includes an accumulator section, a condenser section and an absorber section, followed by two sections in succession to remove residual light components from propane. It is on-line that is operated or communicated periodically. In this case the stream from the cooler 20 or the stream from such a vessel passes through the conduit 302 by means of pressure reducing means described as expansion valve 12, where the pressure of the liquefied propane is reduced to evaporate a portion of it. Or flashing. The resulting biphasic product then flows into the high stage propane chiller 2 through conduit 304, where the gaseous methane refrigerant, introduced via conduit 152, feeds via conduit 100. Natural gas and gaseous ethylene refrigerant flowing through conduit 202 are cooled by indirect heat exchange means 4, 6, 8, respectively, and are produced separately via conduits 154, 102, 204. Produce a cooled gas stream. The gas in conduit 154 is fed to the main methane economizer 74 described in detail in the subsecret section, and the stream is cooled by indirect heat exchange means 98. The resulting cold compressed methane recycle stream produced via conduit 158 is combined with a heavy molecular compound depleted vapor stream from conduit 120 from heavy molecular removal column 60. And the methane condenser 68 is supplied.

Propane gas from chiller 2 is returned to compressor 18 through conduit 306. This gas is supplied to the high stage inlet port of the compressor 18. Residual liquid propane passes through conduit 308 and the pressure is further lowered by passages through the pressure reducing means described as expansion valve 14, in which state additional portions of liquefied propane are flashed. The resulting two-phase stream is fed to chiller 22 through conduit 310 to provide coolant for chiller 22. The cooled feed gas stream from chiller 22 flows through conduit 102 to knock-out vessel 10 where gas and liquid phases are separated. Liquid phase enriched in the C 3+ component is removed via conduit 103. The gaseous phase is removed via conduit 104 and then divided into two separate streams delivered via conduits 106 and 108. The stream in conduit 106 is fed to propane chiller 22. The stream in conduit 108 is the stream supplied to the heat exchanger 62 and eventually becomes a stripping gas to the heavy molecular compound removal column 60. The ethylene refrigerant from chiller 22 enters chiller 22 via conduit 204. In chiller 22, the feed gas stream and the ethylene refrigeration stream, also referred to herein as the methane rich stream, are individually cooled by indirect heat transfer means 24, 26 and cooled via conduits 110, 206. Produce rich and ethylene refrigeration streams. The evaporated portion of the propane refrigerant is thus split and passed through conduit 311 to the intermediate stage inlet of compressor 18. The liquid propane refrigerant from chiller 22 is removed via conduit 314 and flashed across the pressure reducing means described as expansion valve 16 and via the next conduit 316 to the third stage chiller. Supplied to (28).

As described in FIG. 1, the methane-rich stream flows from the intermediate stage propane chiller 22 to the low stage propane chiller / condenser 28 via conduit 110. In this chiller, the stream is cooled by indirect heat exchange means 30. In a similar manner, the ethylene refrigeration stream flows from the intermediate stage propane chiller 22 to the low stage propane chiller / condenser 28 via conduit 206. Here, the ethylene refrigerant is almost condensed as a whole by the indirect heat exchange means 32. The evaporated propane is removed from the low stage propane chiller / condenser 28 and returned to the low stage inlet to compressor 18 via conduit 320. Although FIG. 1 illustrates cooling of the stream provided by conduits 110, 206 occurring in the same vessel, chilling of stream 110 and cooling and condensation of stream 206 may occur in a split process vessel, respectively. In a similar manner (eg, in the split chiller and split condenser, respectively), a cooling step is introduced into the splitting vessel in which the multiple streams are cooled in a common vessel (eg chiller). The installation is a preferred embodiment because it requires little plant space and the cost of multiple vessels is low.

As shown in FIG. 1, the methane rich stream exiting the low stage propane chiller enters the high stage ethylene chiller 42 via conduit 112. Ethylene refrigerant exits low stage propane chiller (2) via conduit (208) and is well fed into a split vessel (37) where the light component is removed via conduit (209), and the condensed ethylene is It is removed via 210. The split container is a container similar to the one described above that removes the light component from the liquefied propane refrigerant, which may be a multiple stage operating unit or a single stage gas liquid separator that provides significant selectivity for removing light components from the system. In this zone of the process the ethylene refrigerant is generally subjected to a temperature of about -24 ° F. and a pressure of about 285 psia. The ethylene refrigerant by conduit 210 then flows to ethylene economizer 34 where it is cooled by indirect heat exchange means 38 and removed via conduit 211 and described as expansion valve 40. Passing through the pressure reducing means, wherein the refrigerant is flashed to a predetermined temperature and pressure and supplied to the high stage ethylene chiller 42 via the conduit 212. The vapor is removed from the chiller via conduit 214 and passed to ethylene economizer 34, where the steam functions as a coolant via indirect heat exchange means 46. Ethylene vapor is then removed from the ethylene economizer via conduit 216 and fed to the high stage inlet to ethylene compressor 48. Ethylene refrigerant, which does not evaporate in the high stage ethylene chiller 42, is removed via conduit 218, removed from the ethylene economizer via conduit 220, and in pressure reducing means described as expansion valve 52. Flashed, the biphasic product produced in this state is introduced into the low stage ethylene chiller 54 via conduit 222.

The methane rich stream is removed from the high stage ethylene chiller 42 via conduit 116. This stream is then partially condensed in the low stage ethylene chiller 54 by the cooling action provided by the indirect heat exchange means 56 and via the conduit 118 a benzene / aromatic / heavy molecular compound removal column ( 60) to a two-phase stream. As is well known, the methane rich stream in conduit 104 is split to flow through conduits 106 and 108. The contents of conduit 108, referred to as methane rich stripping gas, are first fed to heat exchanger 62, where this stream is cooled by indirect heat exchange means 66 to remove the benzene / heavy molecular compound removal column 60. This results in a cooled methane rich stripping gas stream flowing by conduit 109. Liquids containing significantly concentrated benzene, other aromatics and / or heavy hydrocarbon components are removed from the benzene / heavy molecular compound control via conduit 114 and preferably also function as pressure reducing means 97. By the control means, it is preferably flashed by a control valve and is transmitted to the heat exchanger 62 by conduit 117. Preferably, the stream flashed by the flow control means 97 is flashed to a pressure level of or greater than the pressure at the high stage inlet port with a methane compressor. Flashing also gives greater cooling capacity than the stream. In the heat exchanger 62, the stream distributed by the conduit 117 provides cooling capability via the indirect heat exchange means 64 and exits the heat exchanger via the conduit 119. In the benzene / aromatic compound / heavy molecular compound removal column 60, the two-phase stream entering via conduit 118 is contacted with the cooled methane rich stripping gas stream entering via conduit 109 in a countercurrent fashion. To produce a benzene / heavy molecular compound-depleted methane rich vapor stream via conduit 120 and a benzene / heavy molecular compound-condensed stream via conduit 117.

The stream in conduit 119 is rich in benzene, other aromatics, and / or other heavy hydrocarbon components. This stream is sequentially divided into liquid and vapor portions or flashed or fractionated in vessel 67. In each case, the liquid stream is rich in benzene, other aromatics and / or heavy hydrocarbon components, and is produced via conduit 123 and a second methane rich vapor stream is produced via conduit 121. In the preferred embodiment described in FIG. 1, the stream to conduit 121 is sequentially combined with a second stream distributed via conduit 128, the combined stream being conduit to the high pressure inlet port to methane compressor 83. It is supplied via 140.

Gas in conduit 154 is supplied to main methane economizer 74, where the stream is cooled via indirect heat exchange means 98. The cold compressed methane recycle or refrigeration stream produced in conduit 158 is in a preferred embodiment combined with a heavy molecular compound depleted vapor stream from heavy molecular compound removal column 60 distributed via conduit 120 and in a low stage. The ethylene condenser 68 is supplied. In the low stage ethylene condenser, this stream is cooled via the indirect heat exchange means 70 in which liquid effluent from the low stage ethylene chiller 54 which is passed through the conduit 226 to the low stage ethylene condenser 68 is cooled. To condense. Methane rich product condensed from the low stage condenser is produced via conduit 122. Vapor from the low stage ethylene condenser 68 withdrawn via conduit 228 and the low stage ethylene chiller 54 withdrawn via conduit 224 is combined with ethylene economizer 34 to conduit 230. Passed through, where the steam functions as a coolant via indirect heat exchange means (58). The stream then passes from the ethylene economizer 34 via the conduit 232 to the low stage side of the ethylene compressor 48.

As shown in FIG. 1, the compressor effluent from the steam flowing through the low stage side is removed via conduit 234, cooled via intermediate stage cooler 71, and given to conduit 216. Return to compressor 48 via conduit 236 for injection into the high stage stream. Preferably, the two stages are a single module where they can be modules that are mechanically coupled to each split module and a common driver. Compressed ethylene product from the compressor is routed to downstream cooler 72 via conduit 200. The product from the cooler flows through conduit 202 and enters the high stage propane chiller 22 as described above.

The liquefaction stream in conduit 122 is generally subjected to a temperature of about -125 ° F. and a pressure of about 600 psi. This stream passes through conduit 122 through main methane economizer 74, where the stream is cooled by indirect heat exchange means 76 as described below. From the main methane economizer 74, liquefied gas passes through the conduit 124 and the pressure is reduced by means of pressure reducing means described as expansion valve 78 which evaporates or flashes a portion of the gas stream. The fresh stream then passes to a methane high stage drum 80 which is separated into a gaseous phase released through conduit 126 and a liquid phase released through conduit 130. The gas phase is then delivered to the main methane economizer via conduit 126 where the steam functions as a coolant by indirect heat transfer means 82. The vapor exits the main methane economizer via conduit 128, which is coupled with a gas stream distributed by conduit 121. The stream is fed to the high pressure inlet port of the compressor (83).

The liquid phase in conduit 130 passes through a second methane economizer 87, where the liquid is further cooled by downstream fresh steam via indirect heat exchange means 88. The cooled liquid flows out of the second methane economizer 87 via conduit 132 and expands or flashes via the pressure reducing means described as expansion valve 91 to further reduce the pressure and at the same time the second liquid. Evaporate the part. This fresh stream passes through an intermediate stage methane fresh drum 92 where the stream separates into a gaseous phase passing through conduit 136 and a liquid phase passing through conduit 134. The gaseous phase flows through conduit 136 to a second methane economizer 87 and the vapor cools the liquid entering in 87 via conduit 130 via indirect heat exchange means 89. The conduit 138 serves as a flow conduit between the indirect heat exchange means 89 in the methethane methane economizer 87 and the indirect heat exchange means 95 in the main methane economizer 74. This vapor leaves the main methane economizer 74 via conduit 140 connected to the intermediate stage inlet to the methane compressor 83.

The liquid phase flowing out of the intermediate stage fresh drum 92 via the conduit 134 is further reduced in pressure by passages passing through the pressure reducing means described as the expansion valve 93. Again, the third portion of liquefied gas is evaporated or flashed. Fluid from expansion valve 93 passes through last or low stage fresh drum 94. In the fresh drum 94, the vapor phase is split and passed through the conduit 144 to the second methane economizer 87, where the steam functions as a coolant via the indirect heat exchange means 90. Exits the second methane economizer via conduit 146 connected to the first methane economizer 74, where the steam functions as a coolant via indirect heat exchange means 96 and ultimately the compressor 83 The first methane economizer leaves the conduit 148 via a conduit 148 connected to the low pressure port.

Liquefied natural gas product from fresh drum 94 at near atmospheric pressure passes through conduit 142 to a storage unit. The low pressure, low temperature LNG boil-off vapor stream from the storage unit and the vapor returning from the cool down of the rundown line correlated with the optional LNG loading system are preferably given in either of the conduits 144, 146, or 148. Low pressure fresh steam and the stream combine to recover well; The conduit selected is based on the conduit corresponding to the vapor stream temperature as closely as possible.

As shown in FIG. 1, the high, middle and low stages of the compressor 83 are preferably combined into a single unit. However, each stage is as a separate unit in which the units are mechanically coupled together to be driven by a single driver. Compressed gas from the low stage section passes through the intermediate stage cooler 85 and is coupled with the intermediate pressure gas to the conduit 140 prior to the compressed second stage. Compressed gas from the intermediate stage of the compressor 83 passes through the intermediate stage cooler 84 and is coupled with high pressure gas to the conduit 140 prior to the compressed third stage. Compressed gas is discharged from the high stage methane compressor through conduit 150, cooled in cooler 86 and sent to high pressure propane chiller via conduit 152 as described above.

FIG. 1 shows the expansion of a liquid phase in which a gas and a liquid portion are separated in sequence in a chiller or condenser and using an expansion valve. Although the figures are briefly shown to be operable in some cases, for example, the dividing step and the partial evaporation in the splitting equipment in which the expansion valve and the split flash drum are used prior to any flow of split steam or liquid to the propane chiller. It is more effective and effective in carrying out this. In a similar manner, any process stream subjected to expansion may advantageously use an hydraulic expander as part of the pressure reducing means to extract work energy and low two phase temperatures.

For the compressor / driver unit used in the process, FIG. 1 shows a separate compressor / driver unit (for example a single compression train) for propane, ethylene and open cycle methane compression stages. However, in a preferred embodiment for some cascade processes, process reliability is significantly improved by using multiple compression trains that include two or more compressor / driver combinations in parallel instead of the single compressor / driver unit shown. Even when the compressor / driver unit becomes ineffective, the process operates with reduced capacity.

Preferred Examples of Inventively Removed Processes and Equipment

2 is a preferred embodiment of a benzene, other aromatics, and / or heavy hydrocarbon component removal process and associated apparatus. As described above, the cooling section in which the two-phase stream supplied to the benzene / aromatic / heavy molecular compound removal column 60 via the conduit 118 is provided to the ethylene chiller 54 by the heat exchange means 56. Via conduits 116 result from cooling of the stream and partial condensation. In one embodiment, the entire stream is cooled in conduit 116. In the preferred embodiment described in FIG. 2, the two-phase stream is obtained by cooling and partially condensing a portion of the stream in conduit 116, and this portion is the remaining portion of the stream starting via conduit 116. Combined with

Referring to FIG. 2, the stream distributed via conduit 116 is divided into a first stream flowing in conduit 450 and a second stream flowing in conduit 452. The stream in conduit 532 flows to conduit 454 which distributes the first stream to ethylene chiller 54 via option valve 532 preferably hand control valve, where the stream is passed to indirect heat exchange means 56. There is at least partially condensation and exits the means via conduit 458. A second stream in conduit 452 flows through a valve 530, preferably through a control valve, into conduit 456, which is coupled with a first stream that is distributed via conduit 458. The combined stream, now a two-phase stream, is distributed to column 60 via conduit 118. In remote operation, the length of conduit 118 should be sufficient to ensure proper mixing of the two streams to approach equilibrium. The amount of liquid in the two-phase stream in conduit 118 is controlled by keeping the stream at the required temperature well. This is done in the following way. The temperature transfer device 688 in combination with a sensing device such as a thermal couple disposed in the conduit 118 provides an input signal 686 to the temperature controller 682. The set point temperature signal 684 is also provided to an operator or computer algorithm. The controller 682 responds to the difference between the two inputs, and the flow disposed in the conduit flowing through the portion of the stream distributed to the chiller 54 via the conduit 116 not cooled by the heat exchange means 56. The control valve 530 transmits a signal. The signal 680 transmitted is a scale indicating the position of the control valve 530 which requires maintaining the flow rate required to obtain the required temperature in the conduit 118.

The feed stream to the process step where benzene, other aromatics and / or heavy hydrocarbon components are removed is passed through ethylene chiller 54 and conduit 108 which is distributed via conduit 118 to the upper section of column 60. There is a two-phase process stream from the methane rich stripper gas being distributed. Although shown in FIG. 1 as starting from the feed gas stream from the first stage of propane cooling, this stream may be started from any zone in the process or may be an outer methane rich stream. As illustrated in FIG. 2, at least a portion of the methane rich stripper gas is subjected to cooling in the heat exchanger 62 by indirect heat exchange means 62 prior to entering the base of the column 60. The stream exiting the inventive process step is a heavy molecular compound depleted gas stream from column 60 produced via conduit 120 and a warm heavy molecular compound rich stream generated via conduit 119. As illustrated in FIG. 2, the heavy molecular compound rich stream is produced from column 60 and subjected to warm warming in heat exchanger 62 via indirect heat exchange means 66. This is the manner in which the column effluent generated via conduit 114 cools the stripping gas supplied to the column via conduit 109.

The number of theoretical stages in column 60 depends on the composition of the feed stream to the column. Generally two to fifteen theoretical stages are required. The good number of stages is 3 to 10, more preferably 4 to 8, and the best number is about 5 in terms of operating price. Theoretical stages can be made available by packing, plate / tray or combinations thereof. Generally, packing is about 6 feet. Columns less than diameter and about 6 feet. Plate / tray is good for columns larger than diameter. As illustrated in FIG. 2, the upper section of the column to which the two-phase stream is fed to conduit 118 is designed for easy gas / liquid separation. Preferably the top of the column contains means for removal from which the cycle is altered. This means is arranged between the outlet point of conduit 120 and the inlet point of conduit 118.

As illustrated in FIG. 2, the heavy molecular compound rich liquid stream generated via conduit 114 flows to heat exchanger 62 through control valve 97 and conduit 117, which stream is indirect heat transfer. It provides cooling by means 64 and is produced from heat exchanger 62 via conduit 119 of a warm heavy molecular compound rich stream. Depending on the operating pressure of the downstream process, the cooling capacity of this stream can be improved by flashing at low pressure in the flow through the control valve 97. This process stream produced by conduit 119 may be processed sequentially or directly utilized for removal of light components. In the preferred embodiment described in FIG. 2, the stream is fed to dimethanizer 67.

The flow rate of the heavy molecular compound rich liquid from the column 60 can be controlled by various classification methods that can be readily utilized by those skilled in the art. The control device described in FIG. 2 is a preferred device and includes a level controller device 600, a sensing device and a signal converter connected to the level controller device operatively arranged in the lower section of the column 60. Controller 600 stabilizes output signal 602 indicating a flow rate in conduit 114 required to maintain the required level in column 60 or indicating that the actual level exceeds a predetermined level. The transducer 604 and flow measurement device operatively disposed in the conduit 114 stabilize the output signal 606 representing the actual flow rate of the fluid in the conduit 114. The flow measurement device is preferably located upstream of the control valve so as to avoid sensing the two-phase stream. Signal 602 is provided to flow controller 608 as a set point signal. Signals 602 and 608 are compared separately at flow controller 608 and controller 608 stabilizes output signal 614 in response to the difference between signals 602 and 606. Signal 614 is provided to control valve 97 and valve 97 is manipulated in response to signal 614. A setting signal (not described) indicative of the required level in column 60 may be manually input to the level controller 600 by an operator or may optionally be subjected to computer control by a control algorithm. Depending on the operating state, operator or computer machine logic is used to determine if control is based on liquid level or flow rate. In response to the variable flow rate input of the selected setpoint signal and signal 606, the controller 608 provides an output signal 614 in response to the difference between the individual input and the setpoint signal. This signal is of a magnitude that indicates the position of the control valve 97 required to maintain a flow rate of fluid that is approximately the same liquid level or a flow rate that is generally the same as the required liquid level.

In heat exchanger 62, the molecular compound rich stream is routed to heat exchanger via conduit 117 while cooling the methane rich stripping gas stream. The heavy molecular compound rich stream flows through indirect heat exchange means 66 and is produced from the heat exchanger via conduit 119. The extent to which the methane rich stripping gas is cooled by the heavy molecular compound containing stream prior to entering the column can be controlled by various classification schemes that can be readily utilized by those skilled in the art. In one embodiment, the entire methane rich stripping gas stream is fed to a heat exchanger, the degree of cooling being a quantity of heavy molecular compound rich liquid stream made available for heat transfer, a heat transfer cotton zone available for heat transfer, And / or parameters such as the retention time of the fluid under heating or cooling which may be present. In a preferred embodiment, the methane rich stripping gas stream distributed via conduit 108 flows through control valve 500 into conduit 400, where the stream is split and via conduits 402, 403. Is delivered. The stream flowing through conduit 403 ultimately flows through indirect heat transfer means 64 in heat exchanger 62. Means for manipulating the relative flow rates of the fluid in the conduits 402 and 403 are provided in the conduits 402 or 403 or both. The means described in FIG. 2 is a simple hand control valve 502, 504 separately attached to conduits 404, 407. However, a control valve having a position input to the controller and controlled by the controller includes a set point and the signal indicative of flow in the conduit as described above for the heavy molecular compound containing stream is directed to one or two hand control valves. It can be replaced. In any case, the valve is operated so that the difference in temperature access of the stream to conduits 117 and 404 for heat exchanger 62 does not exceed 50 ° F., resulting in damage to the heat exchanger. The cooling fluid leaves the indirect heat transfer means 64 via the conduit 405 and is coupled at the junction with the uncooled methane rich stripping gas distributed via the conduit 407 via the conduit 109. A cooled methane rich stripping gas stream is formed which is distributed to the column.

A flow conversion device 616 in combination with the flow sensing device is operatively disposed in the conduit 109 such that the orifice plate (not described) stabilizes the output signal 618 representing the actual flow rate of the fluid in the conduit. Signal 618 is provided to flow controller 620 to variably process the input. In addition, a set point for the flow rate represented by signal 622 is provided to the computer or passive output. The flow controller then provides an output signal 624 that is responsive to the difference between each input and set point signal and is sized to indicate the position of the control valve needed to maintain the required flow rate in the conduit 109.

In another embodiment, the relative flow rate of the fluid through the conduits 402, 403 is a magnitude representative of the control valve position required to maintain the required flow rate in the conduit 109 and responds to the difference between the two signals. It uses the set point temperature and the output as inputs to the flow controller generating the output signal, and is controlled by placing a transducer and a temperature sensing device connected to the device in conduit 109 as needed. The control valve is to be replaced by hand valve 502 and / or 504.

In another embodiment shown in FIG. 3, the temperature of the stripping gas for the column 60 is controlled in the following manner. The temperature converter 704 in combination with a measuring device such as a thermocouple operatively disposed in the conduit 117 provides an output signal 708 representing the actual temperature of the liquid flowing in the conduit 117. Signal 708 is provided to ratio calculator 700 as a first input value. The ratio calculator 700 is also provided with a second temperature signal 706 that indicates the temperature of the fluid flowing into the conduit 109. Signal 706 begins at a temperature converter with an output signal 706 responsive to a sensing element such as a thermocouple operatively disposed within conduit 109. In response to signals 706 and 708, ratio calculator 700 provides an output signal 710 representing the ratio of signals 706 and 708. Signal 710 is provided as input to ratio controller 712. The ratio controller 712 is also provided with a set point signal 714 that indicates the required temperature ratio for the fluid flowing in the conduits 109, 114. In response to signals 710 and 714, ratio controller 712 provides an output signal 716 that responds to the difference between signals 710 and 714. Signal 716 is of a magnitude indicative of the position of control valve 534 operatively disposed in bypass conduit 714 necessary to maintain the required ratio represented by set point signal 714. The control valve 534 is manipulated in response to the signal 716.

According to the best control classification shown in FIG. 4 where the reference numerals used for the elements shown in the previous figures are used, automatic start-up of the column 60 is facilitated by the high selector 728. The set point of the temperature controller 722 is set to a temperature in the column 60 that can be mixed with the liquid. However, at start-up, the temperature in conduit 109 becomes the near ambient temperature. Thus, a signal 726 connected directly to the steering valve 536 closes the valve 536 and allows the flow of warm dry gas to the cold separation column 60 during startup. This problem is overcome by a temporary select signal 742 to the control valve 536 as described below.

In response to signals 706 and 724, temperature controller 722 provides an output signal 726 that responds to the difference between signals 706 and 724. Signal 726 indicates the location of control valve 536 operatively disposed in conduit 108 required to maintain the actual temperature of the fluid in conduit 109 generally at the same temperature required by signal 724. It is of size. In this state, the value needed for the set point signal 724 will not allow start-up of the column. Thus, signal 726 is provided to signal selector 728. In the signal selector 728 also, the position of the control valve 536 required to react to the difference between the signals 736 and 740 and to maintain the temperature of the fluid in the conduit 119 that is approximately equal to the required temperature indicated by the signal 740. A control signal 742 is provided that is sized to indicate. Upon start-up of the column, the actual temperature of the fluid in the conduit 119 will be lower than the required temperature indicated by the signal 740. Thus, the connection signal 742 to the valve 536 causes the valve 536 to open to lower the temperature represented by the signal 706. The high selector 728 determines the control signal 726, 742 that controls the valve 536.

Start-up progression is similar. The feed gas enters the top of the cold splitting column 60 in the upper section. When the temperature of the feed gas is cooled to the net concentrated temperature at which it is removed, the liquid begins to enrich the column 60. Level controller 600 senses a level and opens valve 97 whose output responds to signal 614. The cold liquid then passes through heat exchanger 62 and exchanges heat with a warm dry gas stream through valve 536 and conduit 108. Valve 536 is initiated to open by signal 742 at a set point temperature. After the dry gas flow is initiated, the temperature converter 702 senses the rapidly cooled temperature resulting in the signal 726 selected by the high selector 728. Start-up control helps to provide the operator with a gentle safety start-up, reducing the level of attention required.

The warm heavy molecular compound rich liquid stream from heat exchanger 62 is fed via conduit 119 to a dimethanizer column 67 containing both rectification and stripping sections. The commutation and stripping sections may provide continuous mass transfer by column packing (eg saddles, racking rings, woven wires) or combinations thereof or may contain separate stages (eg trays, plates). will be. In general, packing is preferred for columns with diameters less than about 6 feet, and discrete stages are preferred for columns with diameters greater than 6 feet. The number of theoretical stages in both the rectifying and stripping sections depends on the compound of the feed stream and the required compound of the final product. Preferably, the stripping or lower section contains 4 to 20 theoretical stages, more preferably 8 to 12 theoretical stages and most preferably about 10 theoretical stages. In a similar manner, the top or rectifying section of the column contains 4 to 20 theoretical stages, preferably 8 to 13 theoretical stages, and most preferably about 10 theoretical stages.

Conventional reboiler 524 is installed at its bottom to provide stripping steam. In the preferred embodiment shown in FIG. 2, liquid from the lowest stage to the dimethanizer is provided to the reboiler via conduit 428, where the fluid is indirect with a heating medium distributed via conduit 440. It is returned via a conduit 442 that is heated by heat transfer means 525 and connected to a flow control valve 526 that is in turn connected to a conduit 444. Vapor from the reboiler is returned to the dimethanizer column via conduit 430 and liquid is removed from the reboiler via conduit 432. The stream in conduit 432 is optionally combined in conduit 436 with a second liquid stream generated from the bottom of the dimethanizer via option conduit 434. The entire liquid stream generated from the dimethanizer via conduits 436 and / or 432 which may be selectively flows through cooler 520 and is produced via conduit 438. Means for controlling liquid flow are inserted into one or two of the conduits. In one embodiment described in FIG. 2, the flow control means includes a control valve 522 inserted between conduits 438 and 123. The position of the control valve 522 is a flow controller responsive to the difference between the actual flow rate of the fluid in the conduit 438 in response to the signal 631 and the set point input signal 628 from the level control device 626. 632. The set point flow rate 630 for the level controller 626 may be provided as an operator or computer algorithm input. The output from the controller 632 is a signal 634 sized to indicate the position of the control valve 522 required to maintain the required flow rate in the conduit 438 to maintain the required level.

Various control techniques can be readily used to control the flow rate of the stripping vapor for the column 67 via the conduit 430, although a good technique is based on the temperature of the return steam. Temperature conversion device 636 in combination with a sensing device such as a thermocouple disposed in conduit 430 provides an input signal 638 to temperature controller 642. In addition, a set point temperature signal 640 is provided to the controller by an operator or a computer algorithm. The controller 642 responds to the difference between the two inputs and signals to the flow control valve 526 disposed in the heating medium containing conduit, preferably conduit 440 or 444, most preferably conduit 444. 644). The transmitted signal 644 is of a magnitude that indicates the position of the control valve 526 required to maintain the flow rate needed to obtain the required temperature within the conduit 440.

A novel aspect of the dimethanizer column is the way to generate the reflux liquid. As described in FIG. 2, the overhead product exits the dimethanizer column 67 via conduit 410, wherein at least a portion of the stream is removed from the heavy molecular compound removal column 60. Partially condensed when flowing through indirect heat exchange means 510 in heat exchanger 62 which is cooled by molecular compound rich liquid product. In a preferred embodiment, the heavy molecular compound rich liquid product is first used to cool at least a portion of the overhead vapor system and then for cooling the methane rich stripping gas stream. The condensed liquid resulting from cooling by the heavy molecular compound rich liquid stream becomes the source of the reflux for the dimethanizer column 67. Preferably, heat exchange between the two designated streams takes place in a countercurrent manner. In one embodiment, the entire stream can flow to the heat exchanger 62 in the same way as cooling the entire methane stripping gas. In the preferred embodiment described in FIG. 2, the overhead vapor product in conduit 410 is split into a stream flowing in conduits 412 and 414. The stream in conduit 414 is cooled in heat exchanger 62 with the flow of said stream through indirect heat exchange means 510 in heat exchanger 62 and the resulting cooling stream is produced via conduit 418. . The relative flow rate of the steam stream in conduits 412 and 414 or 418 is controlled by flow control means, preferably flow control valves, via overhead steam that do not flow through the heat exchanger, thereby avoiding control of the two-phase fluid. do. Vapor flowing in conduit 412 flows through and is generated from flow control means 512 via conduit 416. Conduits 416 and 418 are then connected to generate a combined chilled two-phase stream flowing through conduit 420. Temperature Sensing Device disposed in Conduit 420 The temperature conversion device 646, preferably in combination with a thermocouple, sends a signal 648 to the temperature controller 652 indicating the actual temperature of the fluid flowing in the conduit 420. to provide. The required temperature 650 is also input to the controller 652 in either a manual or computer algorithm. Based on the input comparison by the conversion device 646 and the set point 650, the controller 652 is provided with a valve 512 that is sized to adjust the valve 512 in an appropriate manner to approach or maintain the set temperature. Provide an output signal 654. The two-phase fluid generated in conduit 420 is supplied to divider 514 to produce a methane rich vapor stream via conduit 422 and a reflux liquid stream via conduit 424. In another preferred embodiment, with the above classification, cooling of the stream distributed via conduit 414 prior to cooling the stream of heavy molecular compound rich stream in conduit 117 via conduit 414. It is used first. As described in FIG. 1, the methane rich vapor stream in conduit 121 is returned to a sequential open methane cycle for liquefaction. The pressure of the dimethanizer and the correlated equipment is controlled by an automatic steering control valve 518 responsive to the pressure conversion device 656 operatively disposed within the conduit 422. The control valve is connected at the inlet side to the conduit 121 and at the inlet side to the conduit 422 which is preferably directly or indirectly connected to the low pressure inlet port to the methane compressor, and the pressure converting device 656 in combination with the sensing device The conduit 422 provides a signal 658 to the pressure controller 660 that represents the actual pressure. A set point pressure signal 662 is also input to the pressure controller 660. The controller then generates a response signal 664 that responds to the difference between the pressure sensing device signal 658 and the set point signal 662. Signal 664 is measured in such a way as to activate valve 518 as it approaches and maintains the set point pressure. In one embodiment, the controller and control valve and optional pressure sensitive transducer 656 are installed in a single device, commonly referred to as back pressure regulator.

Reflux from the separator ultimately flows to the dimethanizer. In the preferred embodiment described in FIG. 2, the reflux exits separator 514 via conduit 9424 and flows through pump 516 to allow conduit 425, control valve 519 and conduit 426. Stream is introduced into the upper section of the dimethanizer column. In this embodiment, the flow rate of the reflux is controlled by the input from the level control device 666 responsive to the sensing device disposed in the lower section of the separator 514. The controller 666 generates a signal 668 representing the flow rate in the conduit 426 required to maintain the required level in the separator 514, and the signal 668 is a signal representing the actual flow rate in the conduit 425. 671 is provided as a set point input to the flow controller 670 to which it is supplied. The controller 670 then generates a signal 674 to the control valve 519 indicating the signal difference and the appropriate liquid flows through the flow control valve 519 in such a way that the liquid level is controlled in the separator 514. To be provided.

The controller described above is capable of using various known control modes such as proportional, proportional, or proportional-integral-derivative (PID). A digital computer with a backup regulator is good in the preferred embodiment shown in FIG. 4 for computation of required control signals based on measured process variables such as set points supplied to the computer. Any digital computer with software that allows operation in a real-time environment that sends signals to external devices and reads external variable values is suitable for use. 2 to 4 may utilize various control modes such as proportional, proportional integral, or proportional integral induction. In the preferred embodiment a proportional integral mode is utilized. However, the scope of the present invention includes any controller that possesses the ability to generate an output signal representing the contrast with two input signals and to accept two or more input signals.

Scaling of the output signal by the controller is well known in the art of control systems. Basically, the output of the controller is scaled to represent any necessary elements or variables. An example of this is where the required and actual temperatures are compared by the controller. The controller output should be a signal that indicates the rate of flow of the required "control" gas to make the required and actual temperatures the same. Alternatively, the same output signal should be a scale that represents the pressure required to make the required and actual temperatures the same. If the controller output is in the range of 0 to 10 units, the controller output signal is scaled such that an output with a level of 5 units corresponds to 50% or a specific temperature or a specific flow rate. The converting means are used to measure characteristic parameters which are processed into various signals to be generated and take various forms. For example, the control elements of such a system provide the means necessary for the use of electrical analog, digital electronic, hydraulic, pneumatic, mechanical or other similar types of instruments or combinations of such type instruments.

Selective control loops are used in various process situations to select the appropriate control action. In general, a normal control signal is covered with a second control signal having the highest priority in any process situation. For example, a dangerous condition may be avoided or a necessary advantage such as automatic start-up may be implemented by temporarily selecting the second control signal.

The particular hardware and / or software utilized in the feedback control system is a technique known in the field of process plant control. See, for example, Chemical Engineering's Handbook, 5th ED., McGraw-Hill, pgs 22-1 to 22-147.

Although certain low temperature methods, materials, materials, equipment items and controls have been described herein, these specific references are included without limitation for the purposes of explanation in accordance with the present invention.

Example 1

An example is computer simulation of the process efficiency describing removal of benzene and heavy molecular compounds from the methane base stream immediately prior to liquefaction of the methane base stream in the major portion. Flow rates represent those in a 2.5 million metric tonne / year LNG plant using the liquefaction technique described in FIGS. 1 and 2. Benzene condensation in the methane-base gas stream used in the examples is considered to indicate that it is owned by many selected natural gas streams at these locations in the process. However, the methane gas stream is considered to be relatively lean in the heavier hydrocarbon components (for example, C + ₃₎ of the. Simulation results are obtained using HiProtech's process simulation HYSIM (version 386 / C2.10, Prop. Pkg PR / LK).

Compounds, temperatures, pressures and phase states of the inlet and effluent streams to the heavy molecular compound removal column are shown in Table 1. The simulation is based on 5 theoretical stage containing columns. The partially condensed stream, also referred to as the two phase stream undergoing liquefaction in the major part, is first fed to the top stage (stage 1) in the column. The temperature of this stream is −112.5 ° F. and the pressure is 587.0 psia. As noted, this stream is partially condensed such that the stream is 98.24 mol% steam.

The cooled methane rich stripping gas fed into the bottom stage (stage 5) is taken from the upstream zone as shown in FIG. This stream is cooled to approximately 63 ° F. to −10 ° F. by countercurrent heat exchange with the heavy molecular compound rich liquid stream produced in stage 5. During the heat exchange as shown in FIG. 2, this stream is heated to approximately −78 ° F. to approximately 62 ° F. This stream is also used to cool the overhead vapor from the dimethanizer column. The relative flow rates, simulated temperatures, and pressures of each phase in the stage fabric in the column are shown in Table 2. Each liquid and vapor equivalent compound is shown in Table 3 for each stage.

The warm, heavy molecular compound rich stream is a ethanol column containing rectification and stripping that produces a stream rich in natural gas liquid and a methane / ethane rich stream that is recycled back to the methane compressor as a feed to the high stage inlet port. Supplied.

The efficiency of the process for the removal of aromatic / heavy molecular compounds is described by the contrast of the product from stage 1 with the mole percent nitrogen, methane, ethane bonded to the feed streams for stages 1 and 5. The percentages for each stream are 99.88, 99.89 and 99.94 mol%, respectively. The process thus produces a product stream richer in light components than either of the two gas feed streams.

The efficiency of the benzene and heavy aromatics removal process is in contrast to the enrichment ratio defined by the mole percent of the components in the liquid product from stage 5, which is divided by the mole percent of the components in the vapor product from stage 1. It is explained. For example, when using benzene, the molar fractions of each are 0.1616E-04 and 0.00352. This results in approximately 220 concentration costs.

Additional primary values to describe the efficiency of the process is the C ₃ + concentration ratio for the feedstream of the liquid product stream and a stage 1 and 5 produced from the first stage. This ratio varies from about 45 for propane to about 200 for n-octane. Each ratio between the product streams varies from about 50 for propane to about 20,000 for n-octane.

Example 2

The example is similar to the previous one, which shows, via computer simulation, the process efficiency describing removal of benzene and heavy molecular compounds from the methane base gas stream immediately prior to liquefaction of the stream in the major part. Flow rates represent those in a 2.5 million metric tonne / year LNG plant using the liquefaction technique described in FIGS. 1 and 2. Benzene condensation in the methane-rich feed stream used in the examples is considered to be a concentrate that exists for many selected natural gas streams at these locations in the process. However, the condensation of ethane and heavy molecular compounds in the gas stream has been significantly increased resulting in a significant burden on the process of removing both the component and benzene, resulting in a richer gas stream. This example illustrates in more detail the ability of the process to remove benzene and heavy hydrocarbon components simultaneously. This example also illustrates the benzene removal processability, which accepts significant process errors in a form that is significantly increased in ethane and heavy hydrocarbons without significantly affecting the efficiency and operation of the benzene removal process. In addition, the above example illustrates the processability of recovering heavy hydrocarbons in a separate liquefaction stream. Simulation results are obtained using HiProtech's process simulation HYSIM (version 386 / C2.10, Prop. Pkg PR / LK).

Compounds, temperatures, pressures and phase states of the inlet and effluent streams to the heavy molecular compound removal column are shown in Table 4. The simulation is based on 5 theoretical stage containing columns. The partial condensate stream, which is also referred to as the two-phase stream undergoing liquefaction in the major part, is first fed to the top stage (stage 1) in the column. The temperature of this stream is −91.2 ° F. and the pressure is 596.0 psia. As noted, this stream is partially condensed such that the stream is 94.04 mol% steam.

The cooled methane rich stripping gas fed into the bottom stage (stage 5) is taken from the upstream zone as shown in FIG. This stream is cooled to approximately −10 ° F. by countercurrent heat exchange with the liquid product stream produced in stage 5. As shown in Table 4, the stream receives partial condensation during the cooling process.

The relative flow rates, simulated temperatures and pressures of each phase in the stage base in the column are shown in Table 5. Each liquid and vapor equivalent compound is shown in Table 6 for each stage.

The efficiency of the process for heavy molecular compound removal is illustrated by the ratio of molar% of nitrogen, methane, ethane combined in the product stage from stage 1 and the feed streams for stages 1 and 5. The percentages are 97.85, 97.30 and 99.37 mol%, respectively. The process thus produces a product stream richer in these components than either of the two gas feed streams.

The efficiency of the process for removing benzene and heavy aromatics is described in contrast to the enrichment ratio for benzene as defined in Example 1. Each mole fraction is 0.003E-04 and 0.00923. This results in approximately 30 enrichment ratios.

Additional primary values to describe the efficiency of the process is the C ₃ + concentration ratio for the feedstream of the liquid product stream and a stage 1 and 5 produced from the first stage. This ratio varies from about 19 for propane to about 30 for n-octane. Each ratio between the product streams varies from about 67 for propane to about 19,000 for n-octane.

Claims (8)

(a) condensing the minor portion of the methane base gas stream to produce a two-phase stream; (b) feeding said two-phase stream to the upper section of the column; (c) removing the molecular compound depleted gas stream from the upper section of the column; (d) removing the molecular compound rich liquid stream in (d) from the lower section of the column; (e) contacting the methane rich stripping gas stream with the heavy molecular compound rich liquid stream by indirect heat exchange to produce a warm heavy molecular compound rich stream and a cooled methane rich stripping gas stream; (f) feeding the cooled methane rich stripping gas stream to the lower section of the column; (g) contacting the cooled, methane rich stripping gas stream with the two phase stream to produce a heavy molecular compound depleted gas stream and a heavy molecular compound rich liquid stream; (h) condensing the molecular compound depleted gas stream in to produce a liquefied natural gas stream; (i) freshening the liquefied product of step (h) close to atmospheric pressure in one or more stages to produce an LNG product stream and one or more methane vapor streams. A method of removing and concentrating high molecular weight hydrocarbon material from a methane-base gas stream comprising. The method of claim 1, (j) flowing the stream through at least one indirect heat exchange means in contact with the first refrigeration stream, thereby sequentially cooling the methane base gas stream prior to step (a) to produce a cooled methane base gas stream, and a second refrigeration stream. Flowing the cooled methane-base gas stream through at least one indirect heat exchange means in contact with the stream to produce a feed stream to step (a), the boiling point of the second refrigeration stream being the boiling point of the first refrigeration stream. Lower); (k) recovering the side stream from the methane-base gas stream in a downstream zone of one of the indirect heat exchange means and using the side stream as methane rich stripping gas in step (e); (l) feeding a warm heavy molecular compound rich stream of step (e) to a demethanizer comprising a fractionation column, a reboiler and a condenser to produce a heavy molecular compound rich liquid stream and a methane rich vapor stream Doing; (m) compressing the major stream of step (1) at a pressure of 3450-6210 kPa (500-9OOpsia); (n) cooling the compressed vapor stream of step (m); (o) combining the resulting cooling stream with a product from one of the indirect heat exchange means of step (j) or a methane base gas stream fed to step (a), (P) further comprising the step of freshening the heavy molecular compound rich liquid stream at low pressure to further reduce the temperature of the stream, between steps (d) and (e). The process of claim 2 wherein the pressure of the methane base feed gas and the gas stream from step (m) is 575 to 9650 psia and the column provides a gas liquid contacting operation of 2 to 15 theoretical stages. The benzene / aromatic depleted gas stream and the benzene / aromatic rich liquid stream according to claim 1, wherein the removed and concentrated high molecular weight hydrocarbon material comprises benzene and other aromatic compounds. This is the process by which it is generated. (a) a capacitor; (b) a column; (c) a heat exchanger providing indirect heat exchange between the two fluids; (d) a conduit between the condenser and the upper section of the column for flow into the column of a two-phase stream; (e) a second conduit connected to the upper section of the column for removal of the vapor stream from the column; (f) a conduit between said column and said heat exchanger for the flow of a cooled gas stream from a heat exchanger; (g) a conduit between said column and said heat exchanger for the flow of liquid stream from said column; (h) conduits connected to the heat exchanger for the flow of warm liquid strips from the heat exchanger; And (i) conduits connected to the heat exchanger for the flow of the gas stream to the heat exchanger; A device for removing and concentrating high molecular weight hydrocarbon material from a methane elementary gas stream comprising a. The method of claim 5, (j) (g) pressure reduction means located in the conduit; (k) classification column; (1) reboiler; (m) capacitors; (n) an overhead conduit connecting the upper section of the column to the condenser of the element for removal of overhead vapor, a reflux conduit connecting the condenser of the element to the column for the return of the reflux fluid, And (m) a vapor product conduit connected to the condenser of the element to remove uncondensed vapor; (p) bottoms conduit connecting the lower section of the column to the reboiler, steam conduit causing the stripping vapor to return to the column, and bottom product connected to the reboiler to remove non-vapor products from the reboiler. line Additionally includes, (h) The conduit of the element is connected to the fractionation column at a point between the upper and lower theoretical stages. The method of claim 6, (q) (a) a conduit connected to the capacitor of the element; (r) a compressor connected to the vapor product conduit of (n) element at the inlet port; and (s) a conduit connecting the outlet port of the compressor of element (r) to the conduit of element (q). 4. The method of any one of claims 1, 2, and 3, further comprising gasifying the LNG product.