Dehydrogenation and pyrolysis product recovery with common refrigerant

Abstract

A method and apparatus cools a pyrolysis stream and a dehydrogenation stream in respective cold boxes by using refrigerant compressed by a common compressor. The refrigerant is compressed and used to cool the pyrolysis cold box and the dehydrogenation cold box.

Description

[0001] Priority Statement

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 384,931, filed on November 23, 2022, the entire content of which is incorporated herein by reference. Technical Field

[0003] This field relates to the recovery of light olefins, ethylene, and propylene, as well as the recovery and separation of light component by-products such as hydrogen, methane, ethane, and propane. Specifically, this field relates to the recovery of ethylene and propylene from pyrolysis effluents and dehydrogenation effluents. Background Art

[0004] The dehydrogenation of propane and the steam cracking of saturated and predominantly paraffinic hydrocarbons such as naphtha, butane, propane, and ethane are important commercial hydrocarbon conversion processes because they produce light olefins, which are building blocks for polyolefins and polymers with growing demand. Specifically, the demand for ethylene and propylene in the petrochemical industry has increased significantly due to their use as precursors in the production of polyethylene and polypropylene for many commercial products. One route for producing propylene is propane dehydrogenation. The main products from a steam cracker are ethylene and propylene; however, other by-products such as hydrogen, methane, and other heavier hydrocarbons can be further processed for other petrochemical processes.

[0005] A method for converting paraffins to olefins via a propane dehydrogenation process involves passing a propane feed stream through a highly selective catalyst to dehydrogenate propane to propylene in the dehydrogenation reactor effluent. The dehydrogenation reactor effluent is cooled and separated in a cryogenic separation system into a hydrocarbon-rich fraction and a hydrogen-rich vapor fraction (a portion of which is non-recycled net gas), and the cryogenic separation system requires refrigeration to cool the process stream in order to separate hydrogen from the light hydrocarbon liquid. Conventional cryogenic separation systems cool the process stream alone to remove hydrogen from the light hydrocarbons. However, further fractionation is required to separate C2 - materials from the C3 hydrocarbons in the dehydrogenation effluent in a deethanizer tower, which typically also requires a refrigeration package.

[0006] A large amount of the ethylene consumed in the production of plastics and petrochemicals such as polyethylene is produced by the thermal cracking or pyrolysis of hydrocarbons. Pyrolysis also produces a large amount of propylene, which can be used in the plastics industry for the preparation of polypropylene. Steam is typically mixed with the feed stream into the cracking furnace to reduce the hydrocarbon partial pressure and increase the olefin yield, and to reduce the formation and deposition of carbonaceous materials in the cracking reactor. Thus, this process is commonly referred to as steam cracking or pyrolysis.

[0007] Steam cracking produces lower value by-products such as pyrolysis gasoline (cracked gas) and fuel oil (cracked oil). The cracked gas contains a large amount of paraffins and aromatic compounds. The resulting paraffins include normal paraffins and non-normal paraffins that can be recovered or further processed. Aromatic compounds are very stable and difficult to crack in a steam cracker. Side chains of paraffins can be removed, but this results in the production of polycyclic aromatic compounds, which increases the yield of low-value fuel oil. Normal paraffins are more selectively pyrolyzed into olefins than non-normal paraffins.

[0008] Improvements in separation systems are necessary for recovering light olefins from dehydrogenation and pyrolysis effluents and other valuable by-products such as hydrogen and methane. Summary of the Invention

[0009] We have discovered an improved method that cools pyrolysis and dehydrogenation feed streams in respective cold boxes using a refrigerant compressed by a common compressor. The refrigerant is compressed and used to cool the pyrolysis cold box and the dehydrogenation cold box.

[0010] These and other features, aspects, and advantages of the present disclosure are further explained in the following detailed description, the drawings, and the appended claims. Brief Description of the Drawings

[0011] The figure is a schematic diagram of the method and apparatus of the present disclosure.

[0012] Definition

[0013] The following detailed description is merely exemplary in nature and is not intended to limit the application and use of the described embodiments. Additionally, there is no intention to be bound by any theory presented in the foregoing background or the following detailed description.

[0014] The term "in communication with" means that material flow is operably permitted between the enumerated components.

[0015] The term "downstream in communication with" means that at least a portion of the material flowing towards the main body in the downstream communication can flow operably from the object with which it is in communication.

[0016] The term "upstream in communication with" means that at least a portion of the material flowing out of the main body in the upstream communication can flow operably towards the object with which it is in communication.

[0017] The term "in direct communication with" means flowing from an upstream component into a downstream component without a change in composition due to physical fractionation or chemical transformation.

[0018] The term "bypass" means that the object loses downstream communication with the bypassed main body at least within the scope of the bypass.

[0019] As used herein, the term "separator" means a vessel having an inlet and at least one overhead vapor outlet and one bottoms liquid outlet, and may also have an aqueous stream outlet from a boot. A flash drum is a type of separator that can be in communication downstream of a separator that can operate at a higher pressure.

[0020] As used herein, the term "major" or "substantially" means greater than 50%, suitably greater than 75%, and preferably greater than 90%.

[0021] The term "C x " is to be understood to refer to a molecule having the number of carbon atoms indicated by the subscript "x". Similarly, the term "C x -" refers to a molecule containing less than or equal to x, and preferably x and fewer carbon atoms. The term "C x +" refers to a molecule having greater than or equal to x, and preferably x and more carbon atoms.

[0022] The term "column" means one or more distillation columns used to separate one or more components having different volatilities. Unless otherwise specified, each column includes a condenser at the top of the column for condensing a portion of the overhead stream and returning it to the top of the column, and a reboiler at the bottom of the column for vaporizing a portion of the bottoms stream and returning it to the bottom of the column. The feed to the column can be preheated. The top pressure is the pressure of the overhead vapor at the column outlet. The bottoms temperature is the liquid bottoms outlet temperature. Unless otherwise specified, the overhead line and the bottoms line refer to the net lines from downstream of the column that are refluxed or reboiled to the column. Alternatively, a stripping stream can be used for heat input near the bottom of the column.

[0023] As used herein, the term "rich component stream" or "component-rich stream" means a stream exiting a vessel that is identified as rich having a greater component concentration than the feed to the vessel.

[0024] As used herein, the term "lean component stream" or "component-lean stream" means a stream exiting a vessel that is identified as lean having a smaller component concentration than the feed to the vessel. Detailed Description

[0025] The present disclosure is a method and apparatus for recovering propylene from a propane dehydrogenation reactor and a pyrolysis reactor by using a common refrigerant. The method and apparatus can also use a common compression system. It has been found that by utilizing a propane dehydrogenation reactor and a pyrolysis reactor, additional production of propylene can be accompanied by a large amount of ethylene production by pyrolysis.

[0026] The method and apparatus 10 shown in Figure 1 processes the effluents from two conversion units, namely a propane dehydrogenation reactor 14 and a pyrolysis reactor 50. A propane feed stream in line 12 is prepared for charging to the propane dehydrogenation reactor 14. The propane feed stream comprises propane and may comprise other light paraffins such as ethane, n-butane, isobutane, pentane or isopentane. In some embodiments, the propane feed stream comprises at least one other paraffin having from 2 to 30 carbon atoms.

[0027] The propane feed stream in line 12 is cooled in the PDH cold box 16 or may bypass the cold box and be sent to a depropanizer fractionator (not shown) for purification and then warmed or slightly cooled to 25°C to 50°C, preferably 35°C to 40°C, in the dehydrogenation cold box 16 in line 20 and charged to the propane dehydrogenation reactor 14.

[0028] In the dehydrogenation reactor 14, propane is dehydrogenated to produce propylene. A dehydrogenation catalyst is used in the dehydrogenation reaction to catalyze the dehydrogenation of propane. The conditions in the dehydrogenation reactor may include a temperature of 500°C to 800°C, a pressure of 40 kPa to 310 kPa, and a catalyst-to-oil ratio of 5 to 100.

[0029] The dehydrogenation reaction can be carried out in a fluidized manner such that a gas with or without a fluidizing inert gas that may contain the reactant alkane is distributed to the reactor in a manner that lifts the dehydrogenation catalyst in the reactor vessel while catalyzing the dehydrogenation of the alkane. During the catalytic dehydrogenation reaction, coke deposits on the dehydrogenation catalyst, thereby causing a reduction in the activity of the catalyst. The dehydrogenation catalyst must then be regenerated in a regenerator. The regenerator can combust the coke from the dehydrogenation catalyst and a fuel gas to ensure sufficient enthalpy in the dehydrogenation reactor to promote the endothermic reaction.

[0030] The selected dehydrogenation catalyst should minimize the cracking reaction and favor the dehydrogenation reaction. Catalysts suitable for use herein include active metals that can be dispersed in a porous inorganic support material such as silica, alumina, silica-alumina, zirconia, or clay. Exemplary embodiments of the catalyst include alumina or silica-alumina containing gallium, a noble metal, and an alkali metal or alkaline earth metal.

[0031] The catalyst support comprises a support material, a binder, and optionally a filler material to provide physical strength and integrity. The support material may include alumina or silica-alumina. Silica sol or alumina sol can be used as the binder. Alumina or silica-alumina typically contains γ, θ, and / or δ phases of alumina. The nominal diameter of the catalyst support particles can be from 20 microns to 200 microns, and the average diameter is from 50 microns to 150 microns. Preferably, the surface area of the catalyst support is 85 m 2 / g to 140 m 2 / g.

[0032] The fluidized dehydrogenation catalyst may include a dehydrogenation metal on a support. The dehydrogenation metal may be one or a combination of transition metals. Noble metals may be preferred dehydrogenation metals, such as platinum or palladium. Gallium is an effective metal for paraffin dehydrogenation. The metal may be deposited on the catalyst support by impregnation or other suitable methods, or included in the support material or binder during catalyst preparation.

[0033] The acid functionality of the catalyst should be minimized to prevent cracking and favor dehydrogenation. Alkali metals and alkaline earth metals may also be included in the catalyst to attenuate the acidity of the catalyst. Rare earth metals may be included in the catalyst to control the activity of the catalyst. Metals may be incorporated into the dehydrogenation catalyst at a concentration of 0.001 wt% to 10 wt%. In the case of noble metals, noble metals in the range of 10 parts per million (ppm) by weight to 600 ppm by weight are preferably used. More preferably, noble metals in the range of 10 ppm to 100 ppm by weight are preferably used. The preferred noble metal is platinum. Gallium should be present in the range of 0.3 wt% to 3 wt%, preferably 0.5 wt% to 2 wt%. Alkali metals and alkaline earth metals may be present in the range of 0.05 wt% to 1 wt%.

[0034] The regenerated catalyst may be contacted with a propane feed stream, possibly in contact with a fluidizing gas, to lift the propane feed stream and the dehydrogenation catalyst into a riser when dehydrogenation occurs. Above the riser, the spent dehydrogenation catalyst and the propylene product may be separated by a centripetal separation device. The propylene product gas may be quenched with a cooling fluid to prevent overreaction to form undesired by-products. The separation of the propylene product may include quench contact and fractionation to produce a propylene product stream in line 22.

[0035] The paraffin dehydrogenation reactor 14 may alternatively employ a catalytic moving bed reactor. The reactor section may include several parallel or series radial flow reactors heated by chargers and interstage heaters. A propane feed stream, possibly with hydrogen added, flows through a screened central tube through an annular dehydrogenation catalyst bed to an outer effluent ring in each dehydrogenation reactor. The flow may be in the opposite direction. The dehydrogenation catalyst may include noble metals and their mixtures, modifiers selected from the group consisting of alkali metals or alkaline earth metals and their combinations, components selected from the group consisting of tin, germanium, lead, indium, gallium, thallium, and their combinations, and a porous support forming the catalyst particles. The catalyst support may include oil-drop alumina spheres.

[0036] The dehydrogenation conditions may include a temperature of 400 °C to 900 °C, a pressure of 0.01 absolute atmosphere to 10 absolute atmospheres, and 0.1 hr -1 to 100 hr -1The liquid hourly space velocity (LHSV). The pressure in the dehydrogenation reactor is maintained at the lowest feasible level consistent with equipment limitations to maximize the chemical equilibrium advantage. The spent dehydrogenation catalyst in the annular catalyst bed can be removed from the bottom of the bed and transferred to a regenerator to burn the coke from the catalyst in air at 450 °C to 600 °C. The noble metal on the catalyst can be redispersed, dried by an oxohalogenation method, and returned to the top of the dehydrogenation catalyst bed as a regenerated dehydrogenation catalyst.

[0037] The dehydrogenation feed stream in line 22 can include light hydrocarbons and hydrogen. Propylene must be separated from other light hydrocarbons such as unreacted propane and hydrogen. Propane can be recycled to the dehydrogenation reactor for propylene production. Hydrogen is a valuable by-product and can be used elsewhere in the refinery or in the dehydrogenation reactor 14 to control the dehydrogenation reaction.

[0038] Before hydrogen separation, the dehydrogenation feed stream in line 22 can be cooled, compressed, and dried. To effectively separate hydrogen from the light hydrocarbons, the dehydrogenation feed stream in line 22 is cryogenically cooled by passing it through the dehydrogenation cold box 16 to condense the hydrocarbons. In the dehydrogenation cold box 16, the dehydrogenation feed stream in line 22 is cooled by heat exchange with other streams (including the refrigerant stream passing through the dehydrogenation cold box 16 in line 25) to provide a cooled dehydrogenation feed stream in line 23, which is fed to the dehydrogenation separator 26. The refrigerant stream in line 25 may have passed through a first compression stage and be at a pressure of 1400 kPa to 1700 kPa. The refrigerant stream in line 25 can pass through the dehydrogenation cold box 16 and then be expanded through an expansion valve 24 to cool the refrigerant stream by the heat of vaporization and return through the dehydrogenation cold box 16. The dehydrogenation cold box 16 can be in downstream communication with the dehydrogenation reactor 14.

[0039] The cooled dehydrogenation feed stream in line 23 is separated in the dehydrogenation separator 26 to provide a net gas overhead stream rich in hydrogen in a dehydrogenation separator overhead line 28 extending from the top of the dehydrogenation separator 26, and a liquid dehydrogenation feed stream rich in hydrocarbons in a dehydrogenation separator bottom line 30 extending from the bottom of the separator. The dehydrogenation separator 26 can operate at a temperature between -100 °C (-150 °F) and 66 °C (150 °F) and more commonly between -95 °C (-138 °F) and -40 °C (-40 °F) and at a gauge pressure between 690 kPa (100 psig) and 1.4 MPa (200 psig).

[0040] By sufficiently condensing the hydrocarbons in the dehydrogenation separator 26, the net gas overhead stream in the separator overhead line 28 is sufficiently pure hydrogen from a separation stage. The net gas overhead stream can have a hydrogen purity of at least 94 mole%, suitably at least 95 mole%, preferably at least 96 mole% and most preferably at least 96.5 mole% molecular hydrogen. The net gas overhead stream in line 28 can be directed to the dehydrogenation cold box 16 for heating and to provide a product hydrogen stream that can be used elsewhere in a refinery or plant. The heated net gas stream in line 28 can be provided at a temperature of from 32 °C (90 °F) to 60 °C (140 °F) and a gauge pressure of from 760 kPa (110 psig) to 1.2 MPa (170 psig). A portion of the hydrogen-rich net gas overhead stream in line 28 is also mixed with the propane feed stream in line 20 and fed into the dehydrogenation reactor 14 to inhibit coke deposition reactions.

[0041] The liquid dehydrogenation stream in line 30 is rich in hydrocarbons that can be refined to obtain valuable products. The liquid dehydrogenation stream in the dehydrogenation separator bottom line 30 can be heated by passing it through the dehydrogenation cold box to vaporize the hydrocarbons. The vaporized hydrocarbons in line 30 are cooled by releasing the heat of vaporization and thus assist in cooling the dehydrogenation stream passing through the dehydrogenation cold box 16 in line 22. The necessary heat exchange in the dehydrogenation cold box 16 occurs between the cold and hot streams and the dehydrogenation refrigerant stream in line 25. The liquid dehydrogenation stream in line 30 is heated by passing it through the dehydrogenation cold box 16 and fed into the dehydrogenation stripper 34.

[0042] The liquid dehydrogenation feed stream in line 30 includes some light residues such as methane and ethane, which must be separated from larger hydrocarbons such as propylene and propane. Accordingly, the liquid dehydrogenation feed stream in line 30 is heated to a temperature of from 0 °C (30 °F) to 45 °C (115 °F) in the dehydrogenation cold box 16 and then transferred to the dehydrogenation stripper 34 for fractionation. The dehydrogenation stripper 34 separates the liquid dehydrogenation feed stream into a stripper top stream rich in methane and ethane together with slip C3 hydrocarbons in a stripper top line 36 extending from the top of the stripper 34, and a stripper bottom stream rich in C3 hydrocarbons in a stripper bottom line 38 extending from the bottom of the stripper 34. The light residues are stripped off, which have a limited amount of C3 hydrocarbons in the overhead vapor. However, the C3 hydrocarbons in the stripper top stream are recovered in a demethanizer 40, to which the stripper top stream is directed. The stripper top stream in line 36 is heat exchanged with the net demethanizer bottom stream in the net demethanizer bottom line 72 in a heat exchanger 37, thereby cooling the stripper top stream to provide a cooled stripper top stream and heating the net demethanizer bottom stream to provide a heated net demethanizer bottom stream. The cooled stripper top stream is fed as a demethanizer feed stream in a demethanizer feed line 39 to the demethanizer 40 to remove methane and lighter gases from the stripper top stream. The heated net demethanizer bottom stream in line 72 may be fed to a deethanizer 74.

[0043] The stripper bottom stream in the stripper bottom line 38 is split into a reboil stream that is boiled and returned to the paraffin dehydrogenation stripper 34, and a net stripper bottom stream is conveyed in a net stripper bottom line 42 to a propylene-propane splitter tower (not shown). The stripper 34 may be operated at a bottom temperature of from 30 °C (90 °F) to 60 °C (140 °F) and a top gauge pressure of from 1.5 MPa to 1.9 MPa (gauge). The stripper 34 may be in downstream communication with the dehydrogenation cold box 16 and the dehydrogenation separator 26.

[0044] The method and apparatus 10 omits the paraffin dehydrogenation deethanizer and the cryogenic cooling equipment associated with the paraffin dehydrogenation deethanizer required for olefin recovery. Instead, olefin recovery may occur downstream of the pyrolysis reactor 50.

[0045] To provide sufficient cooling to the dehydrogenation cold box 16 and the pyrolysis cold box 58, a refrigerant stream in line 202 is fed to a first refrigerant compressor 200, where the refrigerant stream is compressed to a pressure of 1500 kPa to 1750 kPa in a first compression stage to provide a first compressed refrigerant stream in line 206. The refrigerant stream can be a mixed refrigerant stream containing some or all of nitrogen and C1-C5 hydrocarbons. The mixed refrigerant can be a mixture of up to six components appropriately selected to meet the refrigeration requirements of the dehydrogenation stream and the pyrolysis stream. The mixed refrigerant composition can contain 0 mol% to 7 mol% inert gas, 11 mol% to 35 mol% methane, 25 mol% to 40 mol% C2 hydrocarbons, 20 mol% to 50 mol% C3 hydrocarbons, and 0 mol% to 15 mol% C5 hydrocarbons. The inert gas can be nitrogen, and the C5 hydrocarbon can be isopentane.

[0046] The reboiling refrigerant stream in line 204 and the dehydrogenation refrigerant stream in line 25 are taken from the first compressed refrigerant stream in line 206. The reboiling refrigerant stream in line 204 exchanges heat with the bottoms reboil stream in reboil line 79 taken from the bottoms reboil stream of the deethanizer tower in line 78 in the deethanizer bottoms reboiler 201 to boil the deethanizer bottoms reboil stream and cool the first compressed refrigerant stream in line 204, thereby providing a cooled first compressed refrigerant stream in line 205 and a boiling deethanizer bottoms reboil stream that is returned to the deethanizer tower. The cooled first compressed refrigerant stream in line 205 is further cooled to near ambient temperature in a cooler and separated in a second stage separator 208. If necessary, in addition to the heating provided by the first compressed refrigerant stream in line 204, supplementary deethanizer bottoms reboiling by a low level heat stream (not shown) may be required to provide sufficient heat to reboil the deethanizer bottoms reboil stream in line 79.

[0047] The second stage separator 208 separates the cooled first compressed refrigerant stream in line 205 into a second compressed vapor stream in the second stage separator overhead line 210 and a second compressed liquid stream in the second compressed refrigerant bottoms line 211. The second compressed liquid stream in line 211 converges with the second compressed refrigerant stream in the second compressed refrigerant line 215.

[0048] The dehydrogenated refrigerant stream in line 25 taken from the first compressed refrigerant stream in line 206 is cooled to near ambient temperature and delivered to the dehydrogenation cold box 16, where it undergoes heat exchange with the liquid dehydrogenated stream in the dehydrogenation column bottom line 30 to heat the liquid dehydrogenated stream and other streams in line 30 and cool the dehydrogenated refrigerant stream in line 25. The dehydrogenation cold box 16 may be in downstream communication with the first refrigerant compressor 200. After passing through the dehydrogenation cold box 16, the cooled dehydrogenated refrigerant stream in line 25 passes through an expansion valve 24 to vaporize the dehydrogenated refrigerant stream, thereby cooling it and providing a vaporized dehydrogenated refrigerant stream in line 207. The vaporized dehydrogenated refrigerant stream in line 207 returns through the dehydrogenation cold box 16 to further provide cooling to the streams passing through it, including the dehydrogenated stream in line 22. The heated vaporized dehydrogenated refrigerant stream in line 207 returns to provide a portion of the refrigerant stream in line 202.

[0049] In the second compression stage, the second compressed vapor stream in line 210 separated in the second stage separator 208 is compressed in the second compressor 212 to a pressure of 4500 kPa to 5500 kPa to provide a second compressed refrigerant stream in line 214. The second compressed refrigerant stream in line 214 undergoes heat exchange with the deethanizer side reboiler stream in line 75 from the deethanizer 74 in the deethanizer side reboiler exchanger 203 to boil the side reboiler stream and cool the second compressed refrigerant stream in line 214, and if necessary, is further cooled in an additional exchanger (not shown) to provide a cooled second compressed refrigerant stream in line 215 and a boiling side reboiler stream in line 75, which boiling side reboiler stream returns to the column. The cooled second compressed refrigerant stream in line 215 combines with the second compressed liquid stream in the second stage separator column bottom line 211 to provide a total second compressed refrigerant stream in line 220.

[0050] Then the total second compressed refrigerant stream in line 220 is passed to the pyrolysis cold box 58, where it exchanges heat with the main pyrolysis stream in line 233 to cool the main pyrolysis stream and other streams, and also cools the total second compressed refrigerant stream. After passing through the pyrolysis cold box 58, the cooled total second compressed refrigerant stream in line 220 is passed through an expansion valve 222 to vaporize the total second compressed refrigerant stream, thereby cooling it to provide a vaporized second compressed refrigerant stream in line 224. The vaporized second compressed refrigerant stream in line 224 can be returned through the pyrolysis cold box 58 to further provide cooling to the streams passing through it, including the main pyrolysis stream in line 233. The heated vaporized second compressed refrigerant stream in line 224 is returned to provide a portion of the refrigerant stream in line 202. The pyrolysis cold box 58 can be in downstream communication with the first refrigerant compressor 200 and the second refrigerant compressor 212.

[0051] The pyrolysis feed stream in the feed line 52 (optionally supplemented with recycled ethane) is charged to the pyrolysis reactor 50, which can be a steam cracker for cracking hydrocarbons under steam to produce a pyrolysis stream in the pyrolysis line 57. The pyrolysis feed stream can optionally be in the gas phase. The pyrolysis reactor 50 can preferably be operated at a temperature of 750 °C (1382 °F) to 950 °C (1742 °F). The pyrolysis feed stream can be one of a number of feed streams entering at the same or different points in the furnace to maximize the product yield. The pyrolysis feed stream can be an ethane stream or a naphtha stream.

[0052] The pyrolysis stream leaving the pyrolysis reactor 50 in the pyrolysis line 57 can be in a superheated state. One or more quench towers or other devices not shown but preferably an oil quench tower and / or a water quench tower can be used to quench the pyrolysis stream. The pyrolysis stream can be scrubbed with alkali in a scrubbing tower to remove acid gases, and the scrubbing gas is compressed to provide a treated pyrolysis gas stream in line 57, which is then cooled in the pyrolysis cold box 58. The pyrolysis cold box 58 can be in downstream communication with the pyrolysis reactor 50.

[0053] Although other streams can be recovered from the pyrolysis reactor 50, the treated pyrolysis stream in line 57 can be a gaseous pyrolysis stream. The gaseous pyrolysis stream can first be cooled in the waste gas exchanger 216 by exchanging heat with the cold purified hydrogen stream in line 230 and the cold volatile methane stream in line 232 (which is the waste gas generated in the pyrolysis reactor).

[0054] In the waste gas exchanger 216, the pyrolysis feed stream exchanges heat with the cold purified hydrogen feed stream in line 230 and the cold volatile methane feed stream in line 232 to heat them and cool the pyrolysis feed stream in line 57, thereby providing a cooled pyrolysis feed stream. The cooled pyrolysis feed stream in line 57 is separated in the pyrolysis separator 226 into a gaseous pyrolysis feed stream in line 228 and a liquid pyrolysis feed stream in line 229. The liquid pyrolysis feed stream in line 229 is fed to the demethanizer 40 to provide liquid near the bottom of the demethanizer. The demethanizer 40 can be in downstream communication with the dehydrogenation cold box 16, the pyrolysis cold box 58, and the stripper 34. The demethanizer 40 can also be in downstream communication with the paraffin dehydrogenation reactor 14 and the pyrolysis reactor 50.

[0055] The gaseous pyrolysis feed stream in line 228 is split into two feed streams: a main pyrolysis feed stream in line 233 and a bypass pyrolysis feed stream in line 234. The main pyrolysis feed stream in line 233 is cooled in the pyrolysis cold box 58 by exchanging heat with the total second compressed refrigerant feed stream in line 220 and the vaporized second compressed refrigerant feed stream in line 224 to provide a cooled main pyrolysis feed stream in line 233 and a heated vaporized second compressed refrigerant feed stream in line 224. The bypass pyrolysis feed stream in line 234 exchanges heat in the demethanizer reboiler 235 with the demethanizer bottom reboil feed stream in line 236 taken from the demethanizer bottom stream in line 64 of the demethanizer bottom, and the demethanizer bottom reboil feed stream cools the bypass pyrolysis feed stream to provide a cooled bypass pyrolysis feed stream in line 234 and boils the demethanizer bottom reboil feed stream in line 236, and the demethanizer bottom reboil feed stream returns to the demethanizer 40 boiling.

[0056] The demethanizer reboiler 235 is also used to provide side reboiling to the demethanizer. The demethanizer side reboil feed stream in the demethanizer side reboil line 254 from the demethanizer is withdrawn from a suitable tray and partially vaporized in the demethanizer reboiler 235 by exchanging heat with the bypass pyrolysis feed stream in the bypass line 234 to provide a cooled bypass pyrolysis feed stream and boil the demethanizer side reboil feed stream in line 254, and the demethanizer side reboil feed stream returns to the demethanizer 40 at least partially boiling in the demethanizer side reboil line 256. The heating in the demethanizer reboiler 235 is provided by the bypass pyrolysis feed stream in line 234, which is further cooled, thereby maximizing the heat exchange opportunity. The cooled bypass pyrolysis feed stream in line 234 recombines with the cooled main pyrolysis feed stream in line 233 to provide a recombined pyrolysis feed stream in line 238. Then the recombined cooled pyrolysis feed stream in line 238 is separated in the turbine expander tank 240.

[0057] The turbine expander vessel 240 separates the recombined cooled pyrolysis feed stream in line 238 into a gaseous recombined pyrolysis feed stream in line 242 and a liquid recombined pyrolysis feed stream in line 244. The gaseous cooled pyrolysis feed stream expands in the turbine expander 246 into an expanded gaseous cooled pyrolysis feed stream in line 248, thereby cooling the gaseous cooled pyrolysis feed stream due to polytropic gas expansion and also generating power from the turbine expander 246. The expanded gaseous pyrolysis feed stream in line 248 can be fed to the demethanizer 40, where it is demethanized.

[0058] The expanded gaseous pyrolysis feed stream in line 248 is fed to the top of the demethanizer 40, above the liquid recombined pyrolysis feed stream in line 244. The liquid recombined pyrolysis feed stream in line 244 can be fed to the demethanizer 40, above a partially boiled demethanizer side reboil stream in the demethanizer side reboil line 256. The take-off point of the demethanizer side reboil stream in line 254 is lower than the feed of the demethanizer side reboil stream in line 256, but both are higher than the feed height of the liquid pyrolysis feed stream in line 229. The feed height of the liquid pyrolysis feed stream in line 229 is higher than the height of the demethanizer feed stream in line 39. The demethanizer bottom reboil stream in line 236 is fed to the demethanizer at a height lower than the height of the demethanizer feed stream in line 239.

[0059] The stripper top stream rich in C2 - hydrocarbons and residual C3 hydrocarbons in the stripper top line 36 extending from the top of the stripper 34 can be heat - exchanged with the net demethanizer bottom stream in the net demethanizer bottom line 72 in the heat exchanger 37 and fed to the demethanizer 40. The heated net demethanizer bottom stream in the net demethanizer bottom line 72 can be fed to the deethanizer 74.

[0060] To provide further cooling and reflux to achieve the desired ethylene recovery rate in the demethanizer 40, a C2 - hydrocarbon - lean vapor side stream is taken from a suitable tray of the demethanizer into line 250 and can be compressed in the side compressor 252 to provide a compressed side stream in line 254. The compressed side stream in line 254 can be cooled by heat - exchanging with the total second - compressed refrigerant stream in line 220 in the pyrolysis cold box 58 to provide a cooled compressed side stream, which is refluxed to the demethanizer 40 at a height higher than the feed of the expanded gaseous pyrolysis feed stream in line 248 into the demethanizer 40, and this height can be the highest feed height of the tower. The take - off point of the vapor - lean side stream in line 250 can be at a height lower than the feed of the expanded gaseous pyrolysis feed stream in line 248 into the demethanizer 40.

[0061] In the demethanizer 40, the cooled stripper overhead stream rich in C2 - hydrocarbons and residual C3 hydrocarbons in line 39, the cooled pyrolysis stream containing the liquid pyrolysis stream in line 229, the expanded gaseous cooled pyrolysis stream in line 248, and the liquid recombined cooled pyrolysis stream in line 244 are fractionated together to provide a demethanizer overhead stream rich in methane and hydrogen in the demethanizer overhead line 62, and a demethanizer bottoms stream rich in C2+ hydrocarbons in the demethanizer bottoms line 64. By providing a cooled reflux and allowing the C1 - stream mainly of hydrogen and methane, which is the net overhead stream of the demethanizer 40, to slip, a demethanizer overhead stream with very little ethylene loss is achieved. The demethanizer overhead stream in line 62 is cooled by heat exchange with the net gas hydrogen stream in line 262 and the volatile methane stream in line 266 in the hydrogen - hydrocarbon exchanger 260 to provide a warm net hydrogen stream in line 230 and a warm volatile methane stream in line 232.

[0062] The condensed demethanizer overhead stream can be separated in the hydrogen - methane separator 66 to provide a hydrogen - rich hydrogen stream in the net overhead line 68 and a methane - rich net overhead liquid stream in the hydrogen - methane separator bottoms line 70. The methane stream in the net hydrogen - methane separator bottoms line 70 can be vaporized by expansion across the expansion valve 71 to provide a gaseous methane stream. The hydrogen split - off stream in line 263 can be withdrawn from the hydrogen stream in the net overhead line 68 to leave a net hydrogen stream in line 262. The hydrogen split - off stream in line 263 can be expanded across the expansion valve 264 and added to the expanded methane stream in the net liquid line 70 to provide a volatile methane stream in line 266. The added hydrogen will lower the evaporation temperature of methane in the net liquid line to increase its extracted heat of vaporization, thereby cooling the temperature in the hydrogen - methane separator 66 and increasing the hydrogen purity of the hydrogen stream in the net overhead line 68 from the hydrogen - methane separator.

[0063] The net hydrogen stream in line 262 and the volatile methane stream in line 266 can be heated by heat exchange with the demethanized overhead stream in the demethanizer overhead line 62 to provide a warm net hydrogen stream in line 230 and a warm volatile methane stream in line 232, respectively. The warm net hydrogen stream in line 230 and the warm volatile methane stream in line 232 can be heat exchanged with the main pyrolysis stream in line 233 and the total second compressed refrigerant stream in line 220 to further heat the warm net hydrogen stream and the warm volatile methane stream while cooling the main pyrolysis stream in line 233 and the total second compressed refrigerant stream in line 220. Then, the pyrolysis stream in line 57 can further heat the warm net hydrogen stream in line 230 and the warm volatile methane stream in line 232 and cool the pyrolysis stream in line 57 to provide a cooled pyrolysis stream fed to the pyrolysis separator 226.

[0064] The demethanizer bottoms reboil stream in line 64 is split into a reboiler bottoms stream in line 236 and a net demethanizer bottoms stream in the net demethanizer bottoms line 72, and the reboiler bottoms stream boils and returns to the demethanizer 40. The reboiler bottoms stream in line 236 boils by heat exchange with the bypass pyrolysis stream in line 234 in the demethanizer reboiler 235 to provide a boiling reboiler bottoms stream in line 236 and a cooled bypass pyrolysis stream in line 234. The stripper overhead stream in line 36 is heat exchanged in the heat exchanger 37 to heat the net demethanized stream in line 72 and cool the stripper overhead stream in line 36 before feeding the net demethanized stream to the deethanizer 74.

[0065] The deethanizer 74 fractionates the net demethanizer bottoms stream in line 72 into a deethanizer overhead stream rich in C2 hydrocarbons in line 76 and a deethanizer bottoms stream rich in C3+ hydrocarbons in line 78. The deethanizer overhead stream in line 76 is condensed in the deethanizer condenser 81. The condensed overhead stream in line 76 is fed to the deethanizer receiver 77, where it is separated into a liquid reflux stream that refluxes back to the deethanizer 74 and a net overhead stream in line 83, which can be further processed, for example, in a C2 separation column and / or a selective hydrogenation reactor not shown in the figure.

[0066] The bottoms stream of the deethanizer in line 78 provides the bottoms reboiler stream in line 79, which is reboiled by heat exchange with the first compressed refrigerant stream in line 204 in reboiler 201 and fed back to the deethanizer 74 in a boiling state. The bottoms stream of the deethanizer in line 78 also provides a net bottoms stream of the deethanizer, which can be fed to the depropanizer in line 82. The deethanizer 74 operates at a top temperature of -10 °C (15 °F) to -32 °C (-25 °F) and a bottom gauge pressure of 1.1 MPa (160 psig) to 2.5 MPa (360 psig).

[0067] The disclosed methods and apparatus use a single refrigerant to meet the refrigeration requirements of both the propane dehydrogenation cold box 16 and the pyrolysis cold box 58. From an energy perspective, a mixed refrigerant system is optimal, and the integrated method can also reduce the number of equipment and capital expenditure. The integrated method and apparatus 10 achieve hydrogen recovery of sufficient purity for processing in a pressure swing adsorption unit, with high purity of methane relative to ethylene and a very high degree of ethylene and propylene recovery. These objectives are achieved by minimizing the number of equipment such as exchangers and separation vessels and reducing energy use.

[0068] Example

[0069] We conducted a cost analysis of a conventional method in which a multi-stage cascade refrigeration system uses ethylene and propylene refrigeration circuits for pyrolysis and dehydrogenation recovery, including a methane compressor for pyrolysis recovery, and compared it with an integrated method that uses a mixed refrigerant compressor for dehydrogenation and pyrolysis and propylene refrigeration for pyrolysis. This integrated scenario also uses a methane compressor, an off-gas compressor, a PSA feed gas compressor, and a turbo expander. This analysis was performed for 500 thousand tons of propylene per year for the dehydrogenation unit and 500 thousand tons of propylene and 1500 thousand tons of ethylene per year for the pyrolysis unit.

[0070] We found that the integrated method reduced the compressor power by more than 7%, resulting in an annual reduction in utility costs of $9 million to $12 million, which is 8% to 11% of the base case.

[0071] The operating savings from the integration are shown in Table 1.

[0072] Table 1

[0073]

[0074]

[0075] The capital expenditure savings provided by the integrated method compared to the base method are shown in Table 2.

[0076] Table 2

[0077] Equipment Basic method Integrated process Tank 21 9 Compressor stage 11 8 Expander 0 1 Plate heat exchanger 10 4 Shell and tube and air cooler heat exchanger 14 7 Total 56 29

[0078] Surprisingly, the number of devices can be reduced by nearly half through integration. The capital expenditure is reduced by $44 million, which is 18% of the base case.

[0079] Specific implementation

[0080] Although the following is described in connection with specific embodiments, it should be understood that the description is intended to illustrate and not limit the scope of the foregoing description and the appended claims.

[0081] A first embodiment of the present disclosure is a method for cooling a feed stream, the method comprising cooling a dehydrogenation feed stream in a dehydrogenation cold box to provide a cooled dehydrogenation feed stream; cooling a pyrolysis feed stream in a pyrolysis cold box to provide a cooled pyrolysis feed stream; and providing a refrigerant feed stream to the dehydrogenation cold box and the pyrolysis cold box. An embodiment of the present disclosure is one, any, or all of the first embodiment to the previous embodiments of this paragraph, and further comprises compressing the refrigerant feed stream in a first compressor to provide a first compressed refrigerant feed stream, obtaining a dehydrogenation refrigerant feed stream from the first compressed refrigerant feed stream, and effecting heat exchange between the dehydrogenation feed stream and the dehydrogenation refrigerant stream. An embodiment of the present disclosure is one, any, or all of the first embodiment to the previous embodiments of this paragraph, and further comprises obtaining a second compressed refrigerant feed stream from the first compressed refrigerant feed stream and compressing the second compressed refrigerant feed stream to provide a second compressed refrigerant feed stream, and effecting heat exchange between the pyrolysis feed stream and the second compressed refrigerant feed stream. An embodiment of the present disclosure is one, any, or all of the first embodiment to the previous embodiments of this paragraph, and further comprises separating the cooled dehydrogenation feed stream into a net gas feed stream and a liquid dehydrogenation feed stream, and stripping the liquid dehydrogenation feed stream to provide a stripper overhead feed stream. An embodiment of the present disclosure is one, any, or all of the first embodiment to the previous embodiments of this paragraph, and further comprises separating the cooled pyrolysis feed stream into a gaseous cooled pyrolysis feed stream, expanding the gaseous cooled pyrolysis feed stream into an expanded gaseous cooled pyrolysis feed stream, and effecting demethanation of the expanded gaseous cooled pyrolysis feed stream and the stripper overhead feed stream in a demethanizer. An embodiment of the present disclosure is one, any, or all of the first embodiment to the previous embodiments of this paragraph, and further comprises separating the cooled pyrolysis feed stream into a gaseous cooled pyrolysis feed stream, expanding the gaseous cooled pyrolysis feed stream into an expanded gaseous cooled pyrolysis feed stream, and effecting demethanation of the expanded gaseous cooled pyrolysis feed stream in a demethanizer. An embodiment of the present disclosure is one, any, or all of the first embodiment to the previous embodiments of this paragraph, and further comprises compressing a demethanizer sidestream to provide a compressed sidestream, cooling the compressed sidestream in the pyrolysis cold box to provide a cooled compressed sidestream, and recycling the cooled compressed sidestream to the demethanizer. An embodiment of the present disclosure is one, any, or all of the first embodiment to the previous embodiments of this paragraph, and further comprises cooling a demethanated overhead feed stream from the demethanizer by heat exchange with a methane feed stream to provide a condensed demethanated overhead feed stream and a warm methane feed stream, and separating the condensed demethanated overhead feed stream in a hydrogen-methane separator to provide a methane feed stream and a hydrogen feed stream.One embodiment of the present disclosure is one, any, or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, further comprising mixing a portion of the hydrogen stream with the methane stream prior to the cooling step to provide a volatile methane stream, and the volatile methane stream is heat-exchanged with the top stream of the demethanizer to provide a warm methane stream and the condensed top stream of the demethanizer. One embodiment of the present disclosure is one, any, or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, further comprising cooling the top stream of the demethanizer from the demethanizer by also heat-exchanging with the hydrogen stream to provide a warm hydrogen stream. One embodiment of the present disclosure is one, any, or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, further comprising heating the warm methane stream by heat-exchange in the pyrolysis cold box. One embodiment of the present disclosure is one, any, or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, further comprising heating the warm hydrogen stream by heat-exchange in the pyrolysis cold box.

[0082] A second embodiment of the present disclosure is a method for separating methane from ethane, the method comprising cooling a hydrocarbon feed stream; separating the hydrocarbon feed stream into a gaseous hydrocarbon feed stream; expanding the gaseous hydrocarbon feed stream into an expanded gaseous hydrocarbon feed stream; demethanizing the expanded gaseous hydrocarbon feed stream in a demethanizer to provide a methane-rich overhead stream and an ethane-rich bottoms stream. One embodiment of the present disclosure is one, any, or all of the second embodiment to the previous embodiments of this paragraph, and further comprises compressing a demethanizer side stream to provide a compressed side stream, cooling the compressed side stream in a cold box to provide a cooled compressed side stream, and refluxing the cooled compressed side stream to the demethanizer. One embodiment of the present disclosure is one, any, or all of the second embodiment to the previous embodiments of this paragraph, and further comprises cooling the demethanized overhead stream from the demethanizer by heat exchange with a methane stream to provide a condensed demethanized overhead stream and a warmed methane stream, and separating the condensed demethanized overhead stream in a hydrogen-methane separator to provide a methane stream and a hydrogen stream. One embodiment of the present disclosure is one, any, or all of the second embodiment to the previous embodiments of this paragraph, and further comprises mixing a portion of the hydrogen stream with the methane stream prior to the cooling step to provide a volatile methane stream, the volatile methane stream being in heat exchange with the demethanized overhead stream to provide a warmed methane stream and the condensed demethanized overhead stream. One embodiment of the present disclosure is one, any, or all of the second embodiment to the previous embodiments of this paragraph, and further comprises cooling the demethanized overhead stream from the demethanizer by also heat exchanging with the hydrogen stream to provide a warmed hydrogen stream. One embodiment of the present disclosure is one, any, or all of the second embodiment to the previous embodiments of this paragraph, and further comprises heating the warmed methane stream and the warmed hydrogen stream by heat exchange in the cold box.

[0083] A third embodiment of the present disclosure is an apparatus for cooling a feed stream, the apparatus comprising a dehydrogenation reactor; a pyrolysis reactor; and a dehydrogenation cold box in downstream communication with the dehydrogenation reactor; a pyrolysis cold box in downstream communication with the pyrolysis reactor; a refrigerant compressor; the pyrolysis cold box and the dehydrogenation cold box in downstream communication with the refrigerant compressor. One embodiment of the present disclosure is one, any, or all of the third embodiment to the previous embodiments of this paragraph, and further comprises a stripper in downstream communication with the dehydrogenation cold box and a demethanizer in downstream communication with the pyrolysis cold box and the stripper.

[0084] Although no further elaboration is provided, it is believed that those skilled in the art can make the most of the present invention by using the foregoing description and can easily determine the basic features of the present invention without departing from the essence and scope of the present invention to make various changes and modifications thereto and adapt it to various uses and conditions. Accordingly, the foregoing preferred specific embodiments should be construed as merely illustrative and not in any way limiting the remainder of the disclosure, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0085] In the foregoing, all temperatures are shown in degrees Celsius and all parts and percentages are by weight unless otherwise indicated.

Claims

1. A method for cooling a material stream, the method comprising: cooling a dehydrogenation material stream in a dehydrogenation cold box to provide a cooled dehydrogenation material stream; cooling a pyrolysis material stream in a pyrolysis cold box to provide a cooled pyrolysis material stream; supplying a refrigerant material stream to the dehydrogenation cold box and the pyrolysis cold box.

2. The method according to claim 1, further comprising compressing the refrigerant material stream in a first compressor to provide a first compressed refrigerant material stream, obtaining a dehydrogenation refrigerant material stream from the first compressed refrigerant material stream, and performing a heat exchange between the dehydrogenation material stream and the dehydrogenation refrigerant material stream.

3. The method according to claim 2, further comprising obtaining a second compressed refrigerant material stream from the first compressed refrigerant material stream and compressing the second compressed refrigerant material stream to provide a second compressed refrigerant material stream, and performing a heat exchange between the pyrolysis material stream and the second compressed refrigerant material stream.

4. The method according to claim 1, further comprising separating the cooled dehydrogenation material stream into a net gas material stream and a liquid dehydrogenation material stream, and stripping the liquid dehydrogenation material stream to provide a stripper top material stream.

5. The method according to claim 4, further comprising separating the cooled pyrolysis material stream into a gaseous cooled pyrolysis material stream, expanding the gaseous cooled pyrolysis material stream into an expanded gaseous cooled pyrolysis material stream, and demethanizing the expanded gaseous cooled pyrolysis material stream and the stripper top material stream in a demethanizer.

6. The method according to claim 1, further comprising separating the cooled pyrolysis material stream into a gaseous cooled pyrolysis material stream, expanding the gaseous cooled pyrolysis material stream into an expanded gaseous cooled pyrolysis material stream, and demethanizing the expanded gaseous cooled pyrolysis material stream in a demethanizer.

7. The method according to claim 6, further comprising compressing a demethanizer side stream to provide a compressed side stream, cooling the compressed side stream in the pyrolysis cold box to provide a cooled compressed side stream, and recycling the cooled compressed side stream to the demethanizer.

8. A method for separating methane from ethane, the method comprising: cooling a hydrocarbon material stream; separating the hydrocarbon material stream into a gaseous hydrocarbon material stream; expanding the gaseous hydrocarbon material stream into an expanded gaseous hydrocarbon material stream; demethanizing the expanded gaseous hydrocarbon material stream in a demethanizer to provide a methane-rich top stream and an ethane-rich bottom stream.

9. The method according to claim 8, further comprising compressing a demethanizer side stream to provide a compressed side stream, cooling the compressed side stream in a cold box to provide a cooled compressed side stream, and recycling the cooled compressed side stream to the demethanizer.

10. An apparatus for cooling a material stream, the apparatus comprising: a dehydrogenation reactor; a pyrolysis reactor; and a dehydrogenation cold box in downstream communication with the dehydrogenation reactor; a pyrolysis cold box in downstream communication with the pyrolysis reactor; a refrigerant compressor; the pyrolysis cold box and the dehydrogenation cold box are in downstream communication with the refrigerant compressor.

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