Patent Application
20080264099
1. Field of the Invention
This invention relates to methods and apparatuses for liquefying natural gas. In another aspect, the invention concerns an LNG facility capable of simultaneously producing liquefied natural gas (LNG) and a domestic gas product.
2. Description of the Prior Art
Cryogenic liquefaction is commonly used to convert natural gas into a more convenient form for transportation and/or storage. Because liquefying natural gas greatly reduces its specific volume, large quantities of natural gas can be economically transported and/or stored in liquefied form.
Transporting natural gas in its liquefied form can effectively link a natural gas source with a distant market when the source and market are not connected by a pipeline. This situation commonly arises when the source of natural gas and the market for the natural gas are separated by large bodies of water. In such cases, LNG can be transported from the source to the market using specially designed ocean-going LNG tankers.
Storing natural gas in its liquefied form can help balance out periodic fluctuations in natural gas supply and demand. In particular, LNG can be “stockpiled” for use when natural gas demand is low and/or supply is high. As a result, future demand peaks can be met with LNG from storage, which can be vaporized as demand requires.
Several methods exist for liquefying natural gas. Some methods produce a pressurized LNG (PLNG) product that is useful, but requires expensive pressure-containing vessels for storage and transportation. Other methods produce an LNG product having a pressure at or near atmospheric pressure. In general, these non-pressurized LNG production methods involve cooling a natural gas stream via indirect heat exchange with one or more refrigerants and then expanding the cooled natural gas stream to near atmospheric pressure. In addition, most LNG facilities employ one or more systems to remove contaminants (e.g., water, acid gases, nitrogen, and ethane and heavier components) from the natural gas stream at different points during the liquefaction process.
In addition to LNG, some LNG facilities also produce a domestic gas product. As used herein, the term “domestic gas product” refers to any gaseous, predominantly methane stream originating from an LNG facility that is routed to a location external to the LNG facility for sale and/or use. Typically, domestic gas products from LNG facilities are transported via pipeline to the local natural gas market for subsequent sale. The domestic gas product from most LNG facilities originates as a slip stream of the natural gas feed entering the liquefaction portion of the LNG facility. In order to ensure the domestic gas product meets certain pipeline specifications (e.g., hydrocarbon dew point), the withdrawn natural gas stream is often subjected to further processing (e.g., distillation) in order to produce a compliant domestic gas product. Often, the remaining portion of the domestic gas stream is recombined with the natural gas feed stream entering the LNG facility, a practice which can cause in drastic changes in the composition of the natural gas feed. These drastic changes can adversely affect the operation of the LNG facility and can ultimately result in off-spec LNG product and/or reduced LNG production.
Thus, a need exists for an LNG facility that is capable of efficiently and consistently producing on-spec LNG and a pipeline-compliant domestic gas product without requiring additional process equipment in order to maximize facility production while minimizing capital and operating costs.
In one embodiment of the present invention, there is provided a process for liquefying a natural gas stream in an LNG facility, the process comprising: (a) cooling at least a portion of the natural gas stream in a first refrigeration cycle via indirect heat exchange with a predominantly methane refrigerant; (b) flashing at least a portion of the cooled natural gas stream to thereby provide a predominantly liquid product stream and a predominantly vapor refrigerant stream; (c) compressing at least a portion of the predominantly vapor refrigerant stream to thereby provide a compressed refrigerant stream; and (d) separating at least a portion of the compressed refrigerant stream into a domestic gas fraction and a compressed refrigerant fraction.
In another embodiment of the present invention, there is provided a process for liquefying a natural gas stream in an LNG facility, the process comprising: (a) cooling at least a portion of the natural gas stream in an upstream refrigeration cycle of the LNG facility via indirect heat exchange with an upstream refrigerant to thereby provide a cooled natural gas stream; (b) further cooling at least a portion of the cooled natural gas stream via indirect heat exchange with a predominantly methane refrigerant stream in a methane refrigeration cycle to thereby produce a further cooled natural gas stream and a warmed refrigerant stream; (c) separating at least a portion of the warmed refrigerant stream into a domestic gas fraction and a refrigerant fraction; and (d) cooling at least a portion of the refrigerant fraction in the upstream refrigeration cycle via indirect heat exchange with the upstream refrigerant.
In yet another embodiment of the present invention, there is provided a process for liquefying a natural gas stream in an LNG facility, the process comprising: (a) cooling the natural gas stream in a first refrigeration cycle via indirect heat exchange with a first refrigerant to thereby produce a cooled predominantly methane stream; (b) separating at least a portion of the cooled predominantly methane stream in a distillation column to thereby produce a heavies-rich stream and a heavies-depleted stream; (c) subjecting at least a portion of the heavies-depleted stream to expansion cooling to thereby produce LNG having a pressure in the range of from about 0 to about 40 psia; and (d) prior to at least a portion of the expansion cooling of step (c), withdrawing a domestic gas fraction from the heavies-depleted stream.
In a still further embodiment of the present invention, there is provided an LNG facility for liquefying a natural gas stream. The LNG facility comprises an open-loop refrigeration cycle operable to cool at least a portion of the natural gas stream via indirect heat exchange with a first refrigerant. The open-loop refrigeration cycle comprises a first heat exchanger defining a first cooling pass and a first refrigerant pass. The first heat exchanger is operable to cool at least a portion of the natural gas stream in the first cooling pass via indirect heat exchange with the first refrigerant in the first refrigerant pass. The open-loop refrigeration cycle also comprises an expander defining an expander inlet and an expander outlet. The expander inlet is in fluid communication with the first cooling pass. The open-loop refrigeration cycle further comprises a vapor-liquid separator defining a separator inlet, a lower liquid outlet, and an upper vapor outlet. The separator inlet is coupled in fluid flow communication with the expander outlet and the upper vapor outlet is coupled in fluid flow communication with the first refrigerant pass. The open-loop refrigeration cycle also comprises a first refrigerant compressor defining an inlet port and an outlet port. The inlet port is coupled in fluid flow communication with the first refrigerant pass. The open-loop refrigeration cycle additionally comprises a compressed refrigerant conduit for routing fluid flow from the outlet port of the compressor to a location within the LNG facility and a domestic gas conduit for routing fluid flow from the outlet port of the compressor and/or the compressed refrigerant conduit to a location outside the LNG facility.
Certain embodiments of the present invention are described in detail below with reference to the enclosed figures, wherein:
The present invention can be implemented in a facility used to cool natural gas to its liquefaction temperature to thereby produce liquefied natural gas (LNG). The LNG facility generally employs one or more refrigerants to extract heat from the natural gas and then reject the heat to the environment. Numerous configurations of LNG systems exist, and the present invention may be implemented many different types of LNG systems.
In one embodiment, the present invention can be implemented in a mixed refrigerant LNG system. Examples of mixed refrigerant processes can include, but are not limited to, a single refrigeration system using a mixed refrigerant, a propane pre-cooled mixed refrigerant system, and a dual mixed refrigerant system.
In another embodiment, the present invention is implemented in a cascade LNG system employing a cascade-type refrigeration process using one or more pure component refrigerants. The refrigerants utilized in cascade-type refrigeration processes can have successively lower boiling points in order to maximize heat removal from the natural gas stream being liquefied. Additionally, cascade-type refrigeration processes can include some level of heat integration. For example, a cascade-type refrigeration process can cool one or more refrigerants having a higher volatility via indirect heat exchange with one or more refrigerants having a lower volatility. In addition to cooling the natural gas stream via indirect heat exchange with one or more refrigerants, cascade and mixed-refrigerant LNG systems can employ one or more expansion cooling stages to simultaneously cool the LNG while reducing its pressure to near atmospheric pressure.
In accordance with one embodiment of the present invention, first, second, and third refrigeration cycles 13, 14, 15 can employ respective first, second, and third refrigerants having successively lower boiling points. For example, the first, second, and third refrigerants can have mid-range boiling points at standard pressure (i.e., mid-range standard boiling points) within about 20° F., within about 10° F., or within 5° F. of the standard boiling points of propane, ethylene, and methane, respectively. In one embodiment, the first refrigerant can comprise at least about 75 mole percent, at least about 90 mole percent, at least 95 mole percent, or can consist essentially of propane, propylene, or mixtures thereof. The second refrigerant can comprise at least about 75 mole percent, at least about 90 mole percent, at least 95 mole percent, or can consist essentially of ethane, ethylene, or mixtures thereof. The third refrigerant can comprise at least about 75 mole percent, at least about 90 mole percent, at least 95 mole percent, or can consist essentially of methane.
As shown in
First refrigerant chiller 18 can comprise one or more cooling stages operable to reduce the temperature of the incoming natural gas stream in conduit 100 by about 40 to about 210° F., about 50 to about 190° F., or 75 to 150° F. Typically, the natural gas entering first refrigerant chiller 24 via conduit 100 can have a temperature in the range of from about 0 to about 200° F., about 20 to about 180° F., or 50 to 165° F., while the temperature of the cooled natural gas stream exiting first refrigerant chiller 18 can be in the range of from about −65 to about 0° F., about −50 to about −10° F., or −35 to −15° F. In general, the pressure of the natural gas stream in conduit 100 can be in the range of from about 100 to about 3,000 pounds per square inch absolute (psia), about 250 to about 1,000 psia, or 400 to 800 psia. Because the pressure drop across first refrigerant chiller 18 can be less than about 100 psi, less than about 50 psi, or less than 25 psi, the cooled natural gas stream in conduit 101 can have substantially the same pressure as the natural gas stream in conduit 100.
As illustrated in
The natural gas feed stream in conduit 100 will usually contain ethane and heavier components (C2+), which can result in the formation of a C2+ rich liquid phase in one or more of the cooling stages of second refrigeration cycle 14. In order to remove the undesired heavies material from the predominantly methane stream prior to complete liquefaction, at least a portion of the natural gas stream passing through second refrigerant chiller 21 can be withdrawn via conduit 102 and processed in heavies removal zone 11, as shown in
Heavies removal zone 11 can comprise one or more gas-liquid separators operable to remove at least a portion of the heavy hydrocarbon material from the predominantly methane stream. Typically, heavies removal zone 11 can be operated to remove benzene and other high molecular weight aromatic components, which will freeze in subsequent liquefaction steps and plug downstream process equipment. In addition, heavies removal zone 11 can be operated to recover the heavy hydrocarbons as a natural gas liquids (NGL) product stream. Examples of typical hydrocarbon components comprising NGL streams can include ethane, propane, butane isomers, pentane isomers, and hexane and heavier components (i.e., C6+). The extent of NGL recovery from the predominantly methane stream can ultimately impact one or more final characteristics of the LNG product, such as, for example, Wobbe index, BTU content, higher heating value (HHV), ethane content, and the like. In one embodiment, the NGL product stream exiting heavies removal zone 11 can be subjected to further fractionation in order to produce one or more pure component streams. Often, NGL product streams and/or their constituents can be used as gasoline blendstock.
The predominantly methane stream exiting heavies removal zone 11 via conduit 103 can comprise less than about 1 weight percent, less than about 0.5 weight percent, less than about 0.1 weight percent, or less than 0.01 weight percent of C6+ material, based on the total weight of the stream. Typically, the predominantly methane stream in conduit 103 can have a temperature in the range of from about −140 to about −50° F., about −125 to about −60° F., or −110 to −75° F. and a pressure in the range of from about 200 to about 1,200 psia, about 350 to about 850 psia, or 500 to 700 psia. As shown in
As illustrated in
As shown in
Each expansion stage may additionally employ one or more vapor-liquid separators operable to separate the vapor phase (i.e., the flash gas stream) from the cooled liquid stream. As previously discussed, third refrigeration cycle 15 can comprise an open-loop refrigeration cycle, closed-loop refrigeration cycle, or any combination thereof. When third refrigeration cycle 15 comprises a closed-loop refrigeration cycle, the flash gas stream can be used as fuel within the facility or routed downstream for storage, further processing, and/or disposal. When third refrigeration cycle 15 comprises an open-loop refrigeration cycle, at least a portion of the flash gas stream exiting expansion section 12 can be used as a refrigerant to cool at least a portion of the natural gas stream in conduit 104. Generally, when third refrigerant cycle 15 comprises an open-loop cycle, the third refrigerant can comprise at least 50 weight percent, at least about 75 weight percent, or at least 90 weight percent of flash gas from expansion section 12, based on the total weight of the stream. As illustrated in
As shown in
As shown in
In addition to producing LNG in conduit 107, the LNG facility depicted in
In one embodiment shown in
Referring to
The operation of the LNG facility illustrated in
The cooled natural gas stream from high-stage propane chiller 33 (also referred to herein as the “methane-rich stream”) flows via conduit 114 to a separation vessel 40, wherein the gaseous and liquid phases are separated. The liquid phase, which can be rich in propane and heavier components (C3+), is removed via conduit 303. The predominately vapor phase exits separator 40 via conduit 116 and can then enter intermediate-stage propane chiller 34, wherein the stream is cooled in indirect heat exchange means 41 via indirect heat exchange with a yet-to-be-discussed propane refrigerant stream. The resulting two-phase methane-rich stream in conduit 118 can then be routed to low-stage propane chiller 35, wherein the stream can be further cooled via indirect heat exchange means 42. The resultant predominantly methane stream can then exit low-stage propane chiller 34 via conduit 120. Subsequently, the cooled methane-rich stream in conduit 120 can be routed to high-stage ethylene chiller 53, which will be discussed in more detail shortly.
The vaporized propane refrigerant exiting high-stage propane chiller 33 is returned to the high-stage inlet port of propane compressor 31 via conduit 306. The residual liquid propane refrigerant in high-stage propane chiller 33 can be passed via conduit 308 through a pressure reduction means, illustrated here as expansion valve 43, whereupon a portion of the liquefied refrigerant is flashed or vaporized. The resulting cooled, two-phase refrigerant stream can then enter intermediate-stage propane chiller 34 via conduit 310, thereby providing coolant for the natural gas stream and yet-to-be-discussed ethylene refrigerant stream entering intermediate-stage propane chiller 34. The vaporized propane refrigerant exits intermediate-stage propane chiller 34 via conduit 312 and can then enter the intermediate-stage inlet port of propane compressor 31. The remaining liquefied propane refrigerant exits intermediate-stage propane chiller 34 via conduit 314 and is passed through a pressure-reduction means, illustrated here as expansion valve 44, whereupon the pressure of the stream is reduced to thereby flash or vaporize a portion thereof. The resulting vapor-liquid refrigerant stream then enters low-stage propane chiller 35 via conduit 316 and cools the methane-rich and yet-to-be-discussed ethylene refrigerant streams entering low-stage propane chiller 35 via conduits 118 and 206, respectively. The vaporized propane refrigerant stream then exits low-stage propane chiller 35 and is routed via conduit 318 to the low-stage inlet port of propane compressor 31, wherein the stream is compressed and recycled as previously described.
As shown in
Turning now to ethylene refrigeration cycle 50 in
The remaining liquefied refrigerant in conduit 220 can re-enter ethylene economizer 56, wherein the stream can be further sub-cooled by an indirect heat exchange means 61. The resulting cooled refrigerant stream exits ethylene economizer 56 via conduit 222 and can subsequently be routed to a pressure reduction means, illustrated here as expansion valve 62, whereupon the pressure of the stream is reduced to thereby vaporize or flash a portion thereof. The resulting, cooled two-phase stream in conduit 224 enters intermediate-stage ethylene chiller 54, wherein the refrigerant stream can cool the natural gas stream in conduit 122 entering intermediate-stage ethylene chiller 54 via an indirect heat exchange means 63. As shown in
The vaporized ethylene refrigerant exits intermediate-stage ethylene chiller 54 via conduit 226, whereafter the stream can combine with a yet-to-be-discussed ethylene vapor stream in conduit 238. The combined stream in conduit 239 can then enter ethylene economizer 56, wherein the stream is warmed in an indirect heat exchange means 64 prior to being fed into the low-stage inlet port of ethylene compressor 51 via conduit 230. Ethylene compressor 51 can be driven by, for example, a gas turbine driver 51a. Ethylene compressor 51 comprises at least one stage of compression, and, when multiple stages are employed, the stages can exist in a single unit or can be separate units mechanically coupled to a common driver. Generally, when ethylene compressor 71 comprises two or more compression stages, one or more intercoolers (not shown) can be provided between subsequent compression stages. As shown in
The remaining liquefied ethylene refrigerant exits intermediate-stage ethylene chiller 54 via conduit 228 prior to entering low-stage ethylene chiller/condenser 55, wherein the refrigerant can cool the methane-rich stream entering low-stage ethylene chiller/condenser via conduit 128 in an indirect heat exchange means 65. In one embodiment shown in
The cooled natural gas stream exiting low-stage ethylene chiller/condenser in conduit 132 can also be referred to as the “pressurized LNG-bearing stream.” As shown in
The liquid phase exiting high-stage methane flash drum 82 via conduit 142 can enter secondary methane economizer 74, wherein the methane stream can be cooled via indirect heat exchange means 92. The resulting cooled stream in conduit 144 can then be routed to a second expansion stage, illustrated here as intermediate-stage expander 83, wherein the pressure of the stream can be reduced to thereby evaporate or flash a portion thereof. The resulting two-phase methane-rich stream in conduit 146 can then enter intermediate-stage methane flash drum 84, wherein the liquid and vapor portions of the stream can be separated and can exit the intermediate-stage flash drum via respective conduits 148 and 150. The vapor portion (i.e., the intermediate-stage flash gas) in conduit 150 can re-enter secondary methane economizer 74, wherein the stream can be heated via an indirect heat exchange means 87. The warmed stream can then be routed via conduit 152 to main methane economizer 73, wherein the stream can be further warmed via an indirect heat exchange means 77 prior to entering the intermediate-stage inlet port of methane compressor 71 via conduit 154.
The liquid stream exiting intermediate-stage methane flash drum 84 via conduit 148 can then pass through a low-stage expander 85, whereupon the pressure of the liquefied methane-rich stream can be further reduced to thereby vaporize or flash a portion thereof. The resulting cooled, two-phase stream in conduit 156 can then enter low-stage methane flash drum 86, wherein the vapor and liquid phases can be separated. The liquid stream exiting low-stage methane flash drum 86 can comprise the liquefied natural gas (LNG) product. The LNG product, which is at about atmospheric pressure, can be routed via conduit 158 downstream for subsequent storage, transportation, and/or use.
The vapor stream exiting low-stage methane flash drum 86 (i.e., the low-stage methane flash gas) in conduit 160 can be routed to secondary methane economizer 74, wherein the stream can be warmed via an indirect heat exchange means 89. The resulting stream can exit secondary methane economizer 74 via conduit 162, whereafter the stream can be routed to main methane economizer 73 to be further heated via indirect heat exchange means 78. The warmed methane vapor stream can then exit main methane economizer 73 via conduit 164, whereafter the stream can be split into two portions. The first portion in conduit 164 can enter the low-stage inlet port of methane compressor 71, which will be discussed in detail shortly. The second portion in conduit 164a can be routed to an inlet port of a sales gas compressor 91. The compressed gas product exiting sales gas compressor 91 via conduit 172e can then cooled (not shown) and routed to a location external to the LNG facility for use as a domestic gas product. Optionally, as shown in
As previously discussed, the warmed methane refrigerant stream in conduit 164 can enter the low-stage inlet port of methane compressor 71. Methane compressor 71 can be driven by, for example, a gas turbine driver 71a. Methane compressor 71 comprises at least one stage of compression, and, when multiple stages are employed, the stages can exist in a single unit or can be separate units mechanically coupled to a common driver. Generally, when methane compressor 71 comprises two or more compression stages, one or more intercoolers (not shown) can be provided between subsequent compression stages.
As shown in
Upon being cooled in propane refrigeration cycle 30, the compressed methane refrigerant fraction can be discharged into conduit 130 and subsequently routed to main methane economizer 73, wherein the stream can be further cooled via indirect heat exchange means 79. The resulting sub-cooled stream exits main methane economizer 73 via conduit 168 and can then combined with the heavies-depleted stream exiting heavies removal zone 95 via conduit 126, as previously discussed.
Turning now to heavies removal zone 95, the cooled, at least partially condensed effluent exiting intermediate-stage ethylene chiller 54 via conduit 124 can be routed into the inlet of first distillation column 96, as shown in
In one embodiment of the present invention, the LNG production systems illustrated in
The simulation results can then be used to manipulate the LNG system. In one embodiment, the simulation results can be used to design a new LNG facility and/or revamp or expand an existing LNG facility. In another embodiment, the simulation results can be used to optimize the LNG facility according to one or more operating parameters. In a further embodiment, the computer simulation can directly control the operation of the LNG facility by, for example, manipulating control valve output. Examples of suitable software for producing the simulation results include HYSYS™ or Aspen Plus® from Aspen Technology, Inc., and PRO/II® from Simulation Sciences Inc.
The present description uses numerical ranges to quantify certain parameters relating to the invention. It should be understood that when numerical ranges are provided, such ranges are to be construed as providing literal support for claim limitations that only recite the lower value of the range as well as claims limitation that only recite the upper value of the range. For example, a disclosed numerical range of 10 to 100 provides literal support for a claim reciting “greater than 10” (with no upper bounds) and a claim reciting “less than 100” (with no lower bounds).
As used herein, the terms “a,” “an,” “the,” and “said” means one or more.
As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.
As used herein, the term “cascade-type refrigeration process” refers to a refrigeration process that employs a plurality of refrigeration cycles, each employing a different pure component refrigerant to successively cool natural gas.
As used herein, the term “closed-loop refrigeration cycle” refers to a refrigeration cycle wherein substantially no refrigerant enters or exits the cycle during normal operation.
As used herein, the terms “comprising,” “comprises,” and “comprise” are open-ended transition terms used to transition from a subject recited before the term to one or elements recited after the term, where the element or elements listed after the transition term are not necessarily the only elements that make up of the subject.
As used herein, the terms “containing,” “contains,” and “contain” have the same open-ended meaning as “comprising,” “comprises,” and “comprise,” provided below.
As used herein, the term “domestic gas product” refers to any gaseous, predominantly methane stream originating from within an LNG facility that is routed to a location external to the LNG facility prior to sale and/or use.
As used herein, the terms “economizer” or “economizing heat exchanger” refer to a configuration utilizing a plurality of heat exchangers employing indirect heat exchange means to efficiently transfer heat between process streams.
As used herein, the terms “having,” “has,” and “have” have the same open-ended meaning as “comprising,” “comprises,” and “comprise,” provided above.
As used herein, the terms “heavy hydrocarbon” and “heavies” refer to any hydrocarbon component having a molecular weight greater than methane.
As used herein, the terms “including,” “includes,” and “include” have the same open-ended meaning as “comprising,” “comprises,” and “comprise,” provided above.
As used herein, the term “mid-range standard boiling point” refers to the temperature at which half of the weight of a mixture of physical components has been vaporized (i.e., boiled off) at standard pressure.
As used herein, the term “mixed refrigerant” refers to a refrigerant containing a plurality of different components, where no single component makes up more than 75 mole percent of the refrigerant.
As used herein, the term “natural gas” means a stream containing at least 85 mole percent methane, with the balance being ethane, higher hydrocarbons, nitrogen, carbon dioxide, and/or a minor amount of other contaminants such as mercury, hydrogen sulfide, and mercaptan.
As used herein, the terms “natural gas liquids” or “NGL” refer to mixtures of hydrocarbons whose components are, for example, typically heavier than ethane. Some examples of hydrocarbon components of NGL streams include propane, butane, and pentane isomers, benzene, toluene, and other aromatic compounds.
As used herein, the term “open-loop refrigeration cycle” refers to a refrigeration cycle wherein at least a portion of the refrigerant employed during normal operation originates from an external source.
As used herein, the terms “predominantly,” “primarily,” “principally,” and “in major portion,” when used to describe the presence of a particular component of a fluid stream, means that the fluid stream comprises at least 50 mole percent of the stated component. For example, a “predominantly” methane stream, a “primarily” methane stream, a stream “principally” comprised of methane, or a stream comprised “in major portion” of methane each denote a stream comprising at least 50 mole percent methane.
As used herein, the term “pure component refrigerant” means a refrigerant that is not a mixed refrigerant.
As used herein, the terms “upstream” and “downstream” refer to the relative positions of various components of a natural gas liquefaction facility along the main flow path of natural gas through the plant.
The preferred forms of the invention described above are to be used as illustration only, and should not be used in a limiting sense to interpret the scope of the present invention. Modifications to the exemplary embodiments, set forth above, could be readily made by those skilled in the art without departing from the spirit of the present invention.
The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any apparatus or process not materially departing from but outside the literal scope of the invention as set forth in the following claims.
