Separation device and method for carbon three fraction in propane dehydrogenation to propylene reaction gas

Abstract

The application discloses a separation device and method for carbon three fraction in reaction gas generated by propane dehydrogenation to propylene, and the separation device comprises a cold box sequence, an expander, a carbon three booster pump, a liquid separation tank, a light component flash tower and a fractional condensation and fractional distillation tower; the device is connected into a loop for separating the reaction gas by using its own cold energy; the cold box sequence comprises a first-stage cold box, a second-stage cold box, a third-stage cold box and a fourth-stage cold box, and at least two-stage cold boxes are provided with a mixer and a circulating propane supplement inlet. In the technical scheme, the cold energy required by the cold energy gas is provided by the throttling expansion of the reaction gas itself, the circulating propane is quantitatively and batch-wise mixed with a part of the cold energy gas to provide the cold energy for the carbon three separation of the reaction gas, the technical scheme can reduce the heat exchange area by about 40%, and can provide a lower temperature, so that the purpose of fully recovering the propylene product is achieved in advance of reducing the equipment investment.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering, and more specifically, relates to a separation device and method for separating the C3 fraction in the product gas from the propane dehydrogenation to propylene reaction. Background Technology

[0002] Propylene is an important basic raw material for petrochemicals, with downstream products mainly including polypropylene, propylene oxide, cumene / phenol / acetone / bisphenol A, acrylic acid and esters, epichlorohydrin, etc. In recent years, global propylene demand has grown rapidly, and propylene produced by traditional processes such as naphtha cracking and refinery catalytic cracking has struggled to keep pace with this rapid growth. Among the few large-scale propylene production processes, propane dehydrogenation (PDH) has proven to be the most effective way to address propylene sourcing. The gas produced by propane dehydrogenation contains a large amount of light components such as hydrogen and alkanes, which typically need to be sent to cryogenic processing units for low-temperature separation.

[0003] The core of the entire propane dehydrogenation separation process lies in how to economically and efficiently separate the C3 fraction generated from the propane dehydrogenation reaction from the lighter components. Cryogenic separation requires a large amount of energy and necessitates the use of massive cryogenic heat exchangers. Typically, cryogenic refrigeration is employed, requiring refrigerant compressors, which consume significant amounts of energy, especially for reactions with large circulation volumes. Summary of the Invention

[0004] The inventors discovered in their research that during the separation of hydrogen from the byproduct gas in propane dehydrogenation, a method similar to mixed refrigerant refrigeration can be used to batch-mix the hydrogen diluent with the reaction feedstock propane (including fresh and recycled propane) to provide cooling for the cold box, thereby separating the hydrogen from the propylene product in the byproduct gas. The purpose of this invention is to provide a separation device and method for the byproduct gas in propane dehydrogenation to propylene production. This technical solution eliminates the need for an additional refrigeration compressor, utilizing heat exchange between the byproduct gas and the reaction products to achieve low-temperature separation of the byproduct gas, thus fully recovering the propylene product.

[0005] To achieve the above objectives, the first aspect of the present invention provides a separation device for the C3 fraction in the product gas from the propane dehydrogenation to propylene reaction, the device comprising: a cold box sequence, an expander, a C3 booster pump, a separator, a light component flash distillation tower, and a fractionation tower.

[0006] The cold box sequence includes a first-level cold box, a second-level cold box, a third-level cold box, and a fourth-level cold box;

[0007] The dispensing tank includes a first dispensing tank, a second dispensing tank, and a third dispensing tank;

[0008] The expander includes a first expander and a second expander;

[0009] The reaction product gas feed pipeline is sequentially connected with the first-stage cold box, the second-stage cold box, the third-stage cold box and the first-stage liquid separator.

[0010] The partial condensation and fractionation column is provided with a partial condensation and fractionation column condenser.

[0011] The first-stage liquid separator top is sequentially connected with the first-stage expander, the fourth-stage cold box and the second-stage liquid separator, and the bottom is connected with the lower inlet of the light component flash tower.

[0012] The second-stage liquid separator top pipeline is divided into two branches, one of which is connected with the second-stage expander inlet, and the other is connected with the lower inlet of the partial condensation and fractionation column, and the bottom is connected with the middle inlet of the light component flash tower.

[0013] The second-stage expander outlet is connected with the third-stage liquid separator inlet, the third-stage liquid separator top is connected with the partial condensation and fractionation column condenser inlet, and the bottom is connected with the upper inlet of the light component flash tower.

[0014] The light component flash tower top is provided with a gas phase extraction pipeline, and the bottom is sequentially connected with the carbon three booster pump, the third-stage cold box, the second-stage cold box, the first-stage cold box and the carbon three fraction extraction pipeline.

[0015] The partial condensation and fractionation column top is sequentially connected with the fourth-stage cold box, the third-stage cold box, the second-stage cold box, the first-stage cold box and the crude hydrogen extraction pipeline, the bottom is connected with the upper inlet of the light component flash tower, and the partial condensation and fractionation column condenser outlet is sequentially connected with the third-stage cold box, the second-stage cold box, the first-stage cold box and the reactor feed extraction pipeline.

[0016] The circulating propane feed pipeline is sequentially connected with the first-stage cold box, the second-stage cold box and the third-stage cold box, wherein the circulating propane pipelines at the outlets of at least two cold boxes and the reactor feed pipelines at the inlets are connected through interconnecting pipelines, and a mixer and a circulating propane supplement inlet are arranged on each interconnecting pipeline.

[0017] The second aspect of the present application provides a separation method of the carbon three fraction in the reaction product gas of the propane dehydrogenation to propylene, which comprises the following steps:

[0018] (1) the reaction product gas from the deep purification unit is sent into the cold box sequence through the reaction product gas feed pipeline, and is cooled to -90 o C~-110 o C in the first-stage cold box, the second-stage cold box and the third-stage cold box to obtain the cooled reaction product gas;

[0019] (2) the cooled reaction product gas is subjected to gas-liquid separation in the first-stage liquid separator, the liquid phase at the bottom is sent into the lower part of the light component flash tower, and the gas phase at the top is sent into the first-stage expander to be expanded and refrigerated, and then is sent into the fourth-stage cold box to be cooled to -110 o C~-130 o C to obtain the deep-cooled reaction product gas;

[0020] (3) The gas generated by the cryogenic reaction is sent to the second separator for gas-liquid separation. The liquid phase at the bottom of the separator is sent to the middle of the light component flash distillation tower, and the gas phase at the top of the separator is divided into two parts. One part of the gas phase is sent to the second expander as circulating hydrogen and then sent to the third separator. The other part of the gas phase is sent to the fractionation distillation tower. The liquid phase at the bottom of the third separator is sent to the top inlet of the light component flash distillation tower, and the gas phase at the top of the separator is sent to the condenser of the fractionation distillation tower. The liquid phase at the bottom of the fractionation distillation tower is sent to the upper inlet of the light component flash distillation tower, and the temperature at the top of the fractionation distillation tower is -123°C. o C~-143 o The fractional distillation reaction of C produces gas;

[0021] (4) The gas generated by the fractionation reaction is sent into the cold box sequence, and the cold energy is recovered step by step in the fourth-stage cold box, the third-stage cold box, the second-stage cold box and the first-stage cold box to obtain crude hydrogen. The crude hydrogen is extracted through the crude hydrogen extraction pipeline.

[0022] (5) The gas phase at the top of the light component flash tower is extracted through the gas phase extraction pipeline, and the liquid phase at the bottom of the tower is pressurized by the C3 booster pump and sent into the cold box sequence. The C3 fraction is obtained by recovering the cold energy in the third-stage cold box, the second-stage cold box and the first-stage cold box. The C3 fraction is extracted through the C3 fraction extraction pipeline.

[0023] (6) After the circulating hydrogen provides cooling in the condenser of the fractionation and distillation tower, it is sequentially sent to the third-stage cold box, the second-stage cold box, and the first-stage cold box. Before entering the inlet of each cold box, it is mixed with the countercurrent circulating propane and the supplementary circulating propane added by the circulating propane inlet. The cooling gas recovered through the stage-by-stage cooling is extracted through the reactor feed pipeline.

[0024] The effects of this invention are:

[0025] (1) In the technical solution of the present invention, no additional refrigeration compressor is required. The heat exchange between the reaction product gas and the reaction product is used to achieve low-temperature separation of the reaction product gas, thereby achieving the purpose of fully recovering propylene products.

[0026] (2) In the technical solution provided by the present invention, the reaction gas itself is throttled and expanded to provide the required cooling gas. The circulating propane is quantitatively and in batches mixed with a portion of the cooling gas to provide cooling for the C3 separation of the reaction gas. This technical solution can reduce the heat exchange area by about 40% and provide a lower temperature. With the reduction of equipment investment, the purpose of fully recovering propylene products can be achieved.

[0027] (3) In this invention, through the reasonable distribution of cooling capacity, the cold box exhibits excellent heat transfer performance, with the minimum heat transfer temperature difference at the low-temperature end being greater than 3. o C, The heat transfer temperature difference at the hot end is greater than 2.4. o C, with a smaller heat transfer area (UA value).

[0028] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0029] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0030] Figure 1 A schematic diagram of the C3 fraction separation process in Embodiment 1 of the present invention is shown.

[0031] Figure 2 A schematic diagram of the C3 fraction separation process in Embodiment 2 of the present invention is shown.

[0032] Figure 3 A schematic diagram of the C3 fraction separation process in Comparative Example 1 of the present invention is shown.

[0033] Explanation of reference numerals in the attached figures:

[0034] E-301X, Primary Cold Box; E-302X, Secondary Cold Box; E-303X, Tertiary Cold Box; E-304X, Quaternary Cold Box; D-301, First Separator; D-302, Second Separator; D-303, Third Separator; EXP1, First Expander; EXP2, Second Expander; P-301, C3 Booster Pump; C-301, Light Component Flash Distillation Tower; C-302, Fractionation and Distillation Tower; B-301, Primary Cold Box Circulating Propane Inlet; B-302, Secondary Cold Box Circulating Propane Inlet. Propane inlet; B-303, propane inlet for the third-stage cold box circulation; M-301, first-stage cold box mixer; M-302, second-stage cold box mixer; M-303, third-stage cold box mixer; DH-301, flow control valve for the first separator; DH-302, flow control valve for the second separator; DH-303, flow control valve for the third separator; CH-301, flow control valve for the light component flash distillation tower; CH-301, flow control valve for the fractionation and condensation tower; E-305X, condensation and condensation tower condenser. Detailed Implementation

[0035] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0036] This invention provides a separation device for the C3 fraction in the product gas from the propane dehydrogenation to propylene reaction, such as... Figure 1 As shown, the apparatus includes: a cold box sequence, an expander, a C3 booster pump P-301, a separator, a light component flash distillation tower C-301, and a fractionation distillation tower C-302.

[0037] The cold box sequence comprises a first cold box E-301X, a second cold box E-302X, a third cold box E-303X, and a fourth cold box E-304X;

[0038] The knock-out drum comprises a first knock-out drum D-301, a second knock-out drum D-302, and a third knock-out drum D-303;

[0039] The expander comprises a first expander EXP1 and a second expander EXP2;

[0040] The reaction gas feed pipeline is connected to the first cold box E-301X, the second cold box E-302X, the third cold box E-303X, and the first knock-out drum D-301 in sequence;

[0041] The partial condensation fraction column C-302 is provided with a partial condensation fraction column condenser E-305X;

[0042] The first knock-out drum D-301 is connected to the first expander EXP1, the fourth cold box E-304X, and the second knock-out drum D-302 in sequence at the top, and is connected to the lower inlet of the light component flash tower C-301 at the bottom;

[0043] The pipeline at the top of the second knock-out drum D-302 is divided into two branches, one of which is connected to the inlet of the second expander EXP2, and the other is connected to the lower inlet of the partial condensation fraction column C-302, and the bottom is connected to the middle inlet of the light component flash tower C-301;

[0044] The outlet of the second expander EXP2 is connected to the inlet of the third knock-out drum D-303, the top of the third knock-out drum D-303 is connected to the inlet of the partial condensation fraction column condenser E-305X, and the bottom is connected to the top inlet of the light component flash tower C-301;

[0045] The light component flash tower C-301 is provided with a gas phase outlet pipeline at the top, and is connected to the carbon three booster pump P-301, the third cold box E-303X, the second cold box E-302X, the first cold box E-301X, and the carbon three fraction outlet pipeline in sequence at the bottom;

[0046] The partial condensation fraction column C-302 is connected to the fourth cold box E-304X, the third cold box E-303X, the second cold box E-302X, the first cold box E-301X, and the crude hydrogen outlet pipeline in sequence at the top, and is connected to the upper inlet of the light component flash tower C-301 at the bottom, and the outlet of the partial condensation fraction column condenser E-305X is connected to the third cold box E-303X, the second cold box E-302X, the first cold box E-301X, and the reactor feed outlet pipeline in sequence;

[0047] The circulating propane feed pipeline is connected with the first cold box E-301X, the second cold box E-302X and the third cold box E-303X in sequence, wherein the circulating propane pipeline at the outlet of at least two cold boxes and the reactor feed pipeline at the inlet are connected through an interconnecting pipeline, and a mixer and a circulating propane supplement inlet are arranged on each interconnecting pipeline.

[0048] According to the present application, each interconnecting pipeline is provided with at least one circulating propane supplement inlet and one mixer, and the circulating propane supplement inlet and the mixer are independently controlled.

[0049] Preferably, the flow control valves at the bottoms of the knock-out drum, the light component flash tower C-301 and the partial condensation fractionating tower C-302 are independently controlled.

[0050] The present application also provides a method for separating the carbon fraction in the reaction gas generated by the dehydrogenation of propane to propylene, which comprises the following steps:

[0051] (1) The reaction gas from the deep purification unit is sent to the cold box sequence through a reaction gas feed pipeline, and is cooled to -90 o C~-110 o C to obtain a cooled reaction gas;

[0052] (2) The cooled reaction gas is subjected to gas-liquid separation in the first knock-out drum D-301, and the liquid phase at the bottom of the drum is sent to the lower part of the light component flash tower C-301, and the gaseous phase at the top of the drum is sent to the fourth cold box after being expanded to refrigerate at -110 o C~-130 o C to obtain a deeply cooled reaction gas;

[0053] (3) The deeply cooled reaction gas is sent to the second knock-out drum D-302 for gas-liquid separation, and the liquid phase at the bottom of the drum is sent to the middle part of the light component flash tower C-301, and the gaseous phase at the top of the drum is divided into two parts, one part of the gaseous phase is sent to the third knock-out drum D-303 after being expanded by the second expander EXP2, and the other part of the gaseous phase is sent to the partial condensation fractionating tower C-302; the liquid phase at the bottom of the third knock-out drum D-303 is sent to the top inlet of the light component flash tower C-301, the gaseous phase at the top of the third knock-out drum D-303 is sent to the partial condensation fractionating tower condenser E-305X, the liquid phase at the bottom of the partial condensation fractionating tower C-302 is sent to the upper inlet of the light component flash tower C-301, and the fractionated reaction gas at the top of the partial condensation fractionating tower C-302 has a temperature of -123 o C~-143 o C;

[0054] (4) The fractionation reaction gas is sent to the cold box sequence, and the crude hydrogen is obtained by recovering the cold energy in the fourth-stage cold box, the third-stage cold box E-303X, the second-stage cold box E-302X and the first-stage cold box E-301X in sequence, and the crude hydrogen is extracted through the crude hydrogen extraction pipeline;

[0055] (5) The light component flash tower C-301 overhead gas is extracted through the gas phase extraction pipeline, and the bottom liquid phase is pressurized by the carbon three booster pump P-301 and then sent to the cold box sequence, and the carbon three fraction is obtained by recovering the cold energy in the third-stage cold box E-303X, the second-stage cold box E-302X and the first-stage cold box E-301X in sequence, and the carbon three fraction is extracted through the carbon three fraction extraction pipeline;

[0056] (6) The circulating hydrogen gas provides cold energy in the condenser E-305X of the condensing fractionation tower, and then is sent to the third-stage cold box E-303X, the second-stage cold box E-302X and the first-stage cold box E-301X in sequence, and is mixed with the countercurrent circulating propane and the supplement circulating propane added by the supplement circulating propane supplement inlet in the mixer before entering the inlet of each cold box, and the cold energy gas recovered by the cold energy in sequence is extracted through the reactor feed pipeline.

[0057] In the present application, the circulating propane includes newly added circulating propane and circulating propane in the cold box, and the ratio of the two is set by the reaction unit.

[0058] The liquefaction rate of the reaction gas changes greatly above -40°C, and most of the carbon three components have been condensed at around -40°C. After further cooling, the condensation rate slows down due to the high hydrogen content in the gas phase and the low carbon three component partial pressure, and the condensation amount changes little after cooling to below -100°C.

[0059] The liquid phase of the first liquid separation tank D-301, the liquid phase of the second liquid separation tank D-302, the liquid phase of the third liquid separation tank D-303 and the liquid phase of the condensing fractionation tower C-302 are separated in the light component flash tower C-301.

[0060] The cold energy of the crude hydrogen product at the top of the condensing fractionation tower C-302 is used to cool the stream after the expansion of the first expander EXP1 to recover the cold energy.

[0061] The condensing fractionation tower C-302 separates hydrogen and carbon three fraction, and the cold energy of the condensing fractionation tower C-302 is provided by the twice-expanded crude hydrogen.

[0062] According to the present application, the number of supplement inlets of the supplement circulating propane is not less than 2.

[0063] Preferably, the third-stage cold box, the second-stage cold box and the first-stage cold box are all added with supplement circulating propane;

[0064] The temperature of the supplement circulating propane added to the third-stage cold box is -110o C - 90 o C, 0-20% of the total circulating propane, preferably 5-12%.

[0065] The temperature of the make-up circulating propane added to the secondary cold box is -90 o C - 40 o C, 10-25% of the total circulating propane, preferably 12-18%.

[0066] The temperature of the make-up circulating propane added to the primary cold box is -60 o C - 0 o C, 65-87% of the total circulating propane, preferably 70-83%.

[0067] According to a preferred embodiment of the present application, make-up circulating propane is added to the tertiary cold box and the primary cold box.

[0068] The temperature of the make-up circulating propane added to the tertiary cold box is -110 o C - 90 o C, 5-50% of the total circulating propane, preferably 15-40%.

[0069] The temperature of the make-up circulating propane added to the primary cold box is -90 o C - 0 o C, 50-95% of the total circulating propane, preferably 60-85%.

[0070] According to the present application, the mass ratio of the reaction product gas fed to the carbon three fraction withdrawn is 0.5-2:1, preferably 0.8-1.35:1.

[0071] Preferably, the operating temperature of the carbon three booster pump is -90 to -115°C and the operating pressure is 1.7-4.3 MPaG.

[0072] The operating temperature of the first expander outlet is -105 to -125°C and the operating pressure is 0.45-0.75 MPaG.

[0073] The operating temperature of the second expander outlet is -120 to -140°C and the operating pressure is 0.35-0.60 MPaG.

[0074] The operating temperature of the first knock-out drum is -90 to -110°C and the operating pressure is 0.8-1.35 MPaG.

[0075] The operating temperature of the second knock-out drum is -105 to -125°C and the operating pressure is 0.45-0.75 MPaG.

[0076] The third liquid separation tank operates at a temperature of -120 to -140 DEG C and a pressure of 0.35 to 0.60 MPaG.

[0077] The light component flash tower operates at a temperature of -90 to -125 DEG C and a pressure of -0.08 to 0.35 MPaG, and the bottom temperature is -90 to -125 DEG C.

[0078] The fractionating column operates at a temperature of -120 to -140 DEG C and a pressure of 0.45 to 0.75 MPaG, and the bottom temperature is -120 to -130 DEG C.

[0079] The application is described in more detail below by way of examples.

[0080] Example 1

[0081] The separation device for the reaction gas generated by the propane dehydrogenation to propylene reaction shown in the drawing is used, which comprises a cold box sequence, an expander, a carbon three booster pump P-301, a liquid separation tank, a light component flash tower C-301, and a fractionating column C-302. Figure 1

[0082] The cold box sequence comprises a first cold box E-301X, a second cold box E-302X, a third cold box E-303X, and a fourth cold box E-304X.

[0083] The liquid separation tank comprises a first liquid separation tank D-301, a second liquid separation tank D-302, and a third liquid separation tank D-303.

[0084] The expander comprises a first expander EXP1 and a second expander EXP2.

[0085] The reaction gas feed line is connected to the first cold box E-301X, the second cold box E-302X, the third cold box E-303X, and the first liquid separation tank D-301 in sequence.

[0086] The fractionating column C-302 is provided with a fractionating column condenser E-305X.

[0087] The first liquid separation tank D-301 is connected to the first expander EXP1, the fourth cold box E-304X, and the second liquid separation tank D-302 in sequence at the top, and is connected to the lower inlet of the light component flash tower C-301 at the bottom.

[0088] The second liquid separation tank D-302 is divided into two branches at the top, one of which is connected to the inlet of the second expander EXP2, and the other is connected to the lower inlet of the fractionating column C-302, and the bottom is connected to the middle inlet of the light component flash tower C-301.

[0089] ​The outlet of the second expander EXP2 is connected to the inlet of the third separator D-303. The top of the third separator D-303 is connected to the inlet of the condenser E-305X of the fractionation distillation tower, and the bottom of the tank is connected to the top inlet of the light component flash distillation tower C-301.

[0090] A gas phase extraction pipeline is installed at the top of the light component flash distillation tower C-301, and the bottom of the tower is connected in sequence to the C3 booster pump P-301, the third-stage cold box E-303X, the second-stage cold box E-302X, the first-stage cold box E-301X, and the C3 fraction extraction pipeline.

[0091] The top of the fractionation distillation tower C-302 is connected sequentially to the fourth-stage cold box E-304X, the third-stage cold box E-303X, the second-stage cold box E-302X, the first-stage cold box E-301X, and the crude hydrogen extraction pipeline. The bottom of the tower is connected to the upper inlet of the light component flash distillation tower C-301. The outlet of the fractionation distillation tower condenser E-305X is connected sequentially to the third-stage cold box E-303X, the second-stage cold box E-302X, the first-stage cold box E-301X, and the reactor feed extraction pipeline.

[0092] The circulating propane feed line is connected sequentially to the primary cold box E-301X, the secondary cold box E-302X, and the tertiary cold box E-303X. The circulating propane lines at the outlets of each cold box and the reactor feed lines at the inlets are connected by interconnecting lines. Each of the primary cold box E-301X, the secondary cold box E-302X, and the tertiary cold box E-303X is equipped with its own circulating propane inlet mixer.

[0093] The main steps of the separation method for the gas produced in the propane dehydrogenation to propylene reaction in this embodiment are as follows:

[0094] (1) The reaction product gas from the deep purification unit is sent into the cold box sequence through the reaction product gas feed pipeline, and cooled to -90°C in the first-stage cold box E-301X, the second-stage cold box E-302X, and the third-stage cold box E-303X. o C~-110 o C reacts upon cooling to produce gas;

[0095] (2) The gas generated by the cooling reaction is separated into gas and liquid in the first separator D-301. The liquid phase at the bottom of the separator is sent to the lower part of the light component flash distillation tower C-301, and the gas phase at the top of the separator is sent to the first expander EXP1 for expansion and cooling, and then sent to the fourth-stage cold box for cooling to -110°C. o C~-130 o C undergoes a cryogenic reaction to produce gas;

[0096] (3) The cryogenic reaction gas is sent to the second liquid separator D-302 for gas-liquid separation, the liquid phase at the bottom of the tank is sent to the middle of the light component flash tower C-301, and the gas phase at the top of the tank is divided into two parts, one part of the gas phase is sent to the second expander EXP2 after expansion and then to the third liquid separator D-303, and the other part of the gas phase is sent to the fractionating condensing tower C-302; the liquid phase at the bottom of the third liquid separator D-303 is sent to the top inlet of the light component flash tower C-301, the gas phase at the top of the tank is sent to the fractionating condensing tower condenser E-305X, the liquid phase at the bottom of the fractionating condensing tower C-302 is sent to the upper inlet of the light component flash tower C-301, and the top of the fractionating condensing tower C-302 obtains the fractionating reaction gas of the fractionating condensing tower C-302 at a temperature of -123 o C~-143 o C.

[0097] (4) The fractionating reaction gas is sent to the cold box sequence, and the crude hydrogen is obtained by gradually recovering cold energy in the fourth cold box, the third cold box E-303X, the second cold box E-302X and the first cold box E-301X, and the crude hydrogen is obtained through the crude hydrogen extraction pipeline;

[0098] (5) The gas phase at the top of the light component flash tower C-301 is extracted through the gas phase extraction pipeline, and the liquid phase at the bottom is pressurized by the carbon three booster pump P-301 and then sent to the cold box sequence, and the carbon three fraction is obtained by gradually recovering cold energy in the third cold box E-303X, the second cold box E-302X and the first cold box E-301X, and the carbon three fraction is extracted through the carbon three fraction extraction pipeline;

[0099] (6) The circulating hydrogen gas provides cold energy in the fractionating condensing tower condenser E-305X, and is sequentially sent to the third cold box E-303X, the second cold box E-302X and the first cold box E-301X, and is mixed with the countercurrent circulating propane and the supplementary circulating propane added through the supplementary inlet before entering the cold energy gas inlet of each cold box. The cold energy gas recovered by stages is extracted through the reactor feed pipeline.

[0100] The circulating propane outlet temperature of the third cold box E-303X in the embodiment is -100 o C, the supplementary circulating propane accounts for 6.9% of the total circulating propane, and the temperature after mixing with the cold energy gas is -119 o C; the circulating propane outlet temperature of the second cold box E-302X is -50 o C, the supplementary circulating propane accounts for 16.3% of the total circulating propane, and the temperature after mixing with the cold energy gas is -55 o C; the circulating propane outlet temperature of the first cold box E-301X is -25 o C, the supplementary circulating propane accounts for 76.8% of the total circulating propane, and the temperature after mixing with the cold energy gas is -33 o C.

[0101] The data of the cold box operation of Example 1 is shown in Table 1. As can be seen from Table 1, by adding make-up circulating propane at the circulating propane outlet of each cold box, the cold box shows excellent heat transfer performance, and the minimum heat transfer temperature difference at the low temperature end is greater than 3 o C, and the heat transfer temperature difference at the high temperature end is greater than 2.4 o C, and the heat transfer area (UA value) is small.

[0102] Table 1: Cold box operation data of Example 1

[0103]

[0104] Example 2

[0105] A separation device for reaction gas generated by the propane dehydrogenation to propylene reaction is adopted as shown in Figure 2 The separation device comprises: a cold box sequence, an expander, a carbon three booster pump P-301, a liquid separation tank, a light component flash tower C-301, a partial condensation and fractional distillation tower C-302.

[0106] The cold box sequence comprises a first cold box E-301X, a second cold box E-302X, a third cold box E-303X, and a fourth cold box E-304X.

[0107] The liquid separation tank comprises a first liquid separation tank D-301, a second liquid separation tank D-302, and a third liquid separation tank D-303.

[0108] The expander comprises a first expander EXP1 and a second expander EXP2.

[0109] The reaction gas feed line is connected to the first cold box E-301X, the second cold box E-302X, the third cold box E-303X, and the first liquid separation tank D-301 in sequence.

[0110] The partial condensation and fractional distillation tower C-302 is provided with a partial condensation and fractional distillation tower condenser E-305X.

[0111] The first liquid separation tank D-301 is connected to the first expander EXP1, the fourth cold box E-304X, and the second liquid separation tank D-302 in sequence at the top, and is connected to the lower inlet of the light component flash tower C-301 at the bottom.

[0112] The second liquid separation tank D-302 is divided into two branches at the top, one branch is connected to the inlet of the second expander EXP2, and the other branch is connected to the lower inlet of the partial condensation and fractional distillation tower C-302, and the bottom is connected to the middle inlet of the light component flash tower C-301.

[0113] The outlet of the second expander EXP2 is connected with the inlet of the third knock-out drum D-303, the top of the third knock-out drum D-303 is connected with the inlet of the condenser E-305X of the partial condensation fraction column, and the bottom is connected with the inlet of the top of the light component flash tower C-301;

[0114] The top of the light component flash tower C-301 is provided with a gas phase outlet pipeline, and the bottom is sequentially connected with a carbon three booster pump P-301, a third stage cold box E-303X, a second stage cold box E-302X, a first stage cold box E-301X, a carbon three fraction outlet pipeline;

[0115] The top of the partial condensation fraction column C-302 is sequentially connected with a fourth stage cold box E-304X, a third stage cold box E-303X, a second stage cold box E-302X, a first stage cold box E-301X, a crude hydrogen outlet pipeline, and the bottom is connected with the inlet of the upper part of the light component flash tower C-301; the outlet of the condenser E-305X of the partial condensation fraction column is sequentially connected with the third stage cold box E-303X, the second stage cold box E-302X, the first stage cold box E-301X, and a reactor feed outlet pipeline;

[0116] A circulating propane feed pipeline is sequentially connected with the first stage cold box E-301X, the second stage cold box E-302X and the third stage cold box E-303X; the circulating propane pipeline at the outlet of the first stage cold box E-301X and the third stage cold box E-303X and the reactor feed pipeline at the inlet are connected through an interconnecting pipeline; the interconnecting pipeline of the first stage cold box E-301X is provided with a first stage cold box circulating propane supplement inlet B-301 and a first stage cold box mixer M-301; and the interconnecting pipeline of the third stage cold box E-303X is provided with a third stage cold box circulating propane supplement inlet B-303 and a third stage cold box mixer M-303.

[0117] The main steps of the separation method of the reaction gas in the embodiment are as follows:

[0118] (1) The reaction gas from the deep purification unit is sent into the cold box sequence through a reaction gas feed pipeline, and is cooled to -90 o C~-110 o C in the first stage cold box E-301X, the second stage cold box E-302X and the third stage cold box E-303X in sequence to obtain a cooled reaction gas;

[0119] (2) The cooled reaction gas is subjected to gas-liquid separation in the first knock-out drum D-301, the liquid phase at the bottom is sent into the lower part of the light component flash tower C-301, and the gas phase at the top is sent into the first expander EXP1 to be expanded and refrigerated, and then is cooled to -110 o C~-130 o C in the fourth stage cold box to obtain a deep-cooled reaction gas;

[0120] (3) The cryogenic reaction gas is sent to the second liquid separator D-302 for gas-liquid separation, the liquid phase at the bottom of the tank is sent to the middle of the light component flash tower C-301, and the gas phase at the top of the tank is divided into two parts, one part of the gas phase is sent to the third expansion machine EXP2 after expansion and then to the third liquid separator D-303, and the other part of the gas phase is sent to the fractionating condensing tower C-302; the liquid phase at the bottom of the third liquid separator D-303 is sent to the top inlet of the light component flash tower C-301, the gas phase at the top of the tank is sent to the fractionating condensing tower condenser E-305X, the liquid phase at the bottom of the fractionating condensing tower C-302 is sent to the upper inlet of the light component flash tower C-301, and the top of the fractionating condensing tower C-302 obtains the fractionating reaction gas of C at a temperature of -123 o C~-143 o C.

[0121] (4) The fractionating reaction gas is sent to the cold box sequence, and the crude hydrogen is obtained through the cold energy recovery of the fourth cold box, the third cold box E-303X, the second cold box E-302X and the first cold box E-301X in sequence, and the crude hydrogen is obtained through the crude hydrogen extraction pipeline;

[0122] (5) The gas phase at the top of the light component flash tower C-301 is extracted through the gas phase extraction pipeline, and the liquid phase at the bottom is pressurized by the carbon three booster pump P-301 and then sent to the cold box sequence, and the carbon three fraction is obtained through the cold energy recovery of the third cold box E-303X, the second cold box E-302X and the first cold box E-301X in sequence, and the carbon three fraction is extracted through the carbon three fraction extraction pipeline;

[0123] (6) The circulating hydrogen gas provides cold energy in the fractionating condensing tower condenser E-305X, and then is sent to the third cold box E-303X, the second cold box E-302X and the first cold box E-301X in sequence, and before entering the cold energy gas inlets of the first cold box E-301X and the third cold box E-303X, is mixed with the countercurrent circulating propane and the supplementary circulating propane added by the circulating propane supplement inlet in the mixer, and the cold energy gas after the cold energy recovery in sequence is extracted through the reactor feed pipeline.

[0124] The circulating propane outlet temperature of the third cold box E-303X in the embodiment is -100 o C, the supplementary circulating propane accounts for 23.2% of the total circulating propane amount, and the temperature after mixing with the cold energy gas is -112 o C; the circulating propane outlet temperature of the second cold box E-302X is -50 o C; the circulating propane outlet temperature of the first cold box E-301X is -25 o C, the supplementary circulating propane accounts for 76.8% of the total circulating propane amount, and the temperature after mixing with the cold energy gas is -33 o C.

[0125] The data of the cold box operation of Example 2 is shown in Table 2. As can be seen from Table 2, by adding make-up circulating propane at the circulating propane outlet of the first cold box E-301X and the third cold box E-303X, the cold box shows good heat transfer performance, the minimum heat transfer temperature difference at the low temperature end is greater than 2.6 o C, the heat transfer temperature difference at the hot end is greater than 2.4 o C, and the heat transfer area (UA value) is small.

[0126] Table 2: Data of the cold box operation of Example 2

[0127]

[0128] Comparative Example 1

[0129] A separation device for reaction gas generated by the propane dehydrogenation to propylene reaction is used as shown in Figure 3 The separation device comprises a cold box sequence, an expander, a carbon three booster pump P-301, a liquid separation tank, a light component flash tower C-301, and a partial condensation and fractionation tower C-302.

[0130] The cold box sequence comprises a first cold box E-301X, a second cold box E-302X, a third cold box E-303X, and a fourth cold box E-304X.

[0131] The liquid separation tank comprises a first liquid separation tank D-301, a second liquid separation tank D-302, and a third liquid separation tank D-303.

[0132] The expander comprises a first expander EXP1 and a second expander EXP2.

[0133] The reaction gas feed line is connected to the first cold box E-301X, the second cold box E-302X, the third cold box E-303X, and the first liquid separation tank D-301 in sequence.

[0134] The partial condensation and fractionation tower C-302 is provided with a partial condensation and fractionation tower condenser E-305X.

[0135] The first liquid separation tank D-301 is connected to the first expander EXP1, the fourth cold box E-304X, and the second liquid separation tank D-302 in sequence at the top, and is connected to the lower inlet of the light component flash tower C-301 at the bottom.

[0136] The second liquid separation tank D-302 is divided into two branches at the top, one branch is connected to the inlet of the second expander EXP2, and the other branch is connected to the lower inlet of the partial condensation and fractionation tower C-302, and the bottom is connected to the middle inlet of the light component flash tower C-301.

[0137] The outlet of the second expander EXP2 is connected with the inlet of the third knock-out drum D-303, the top of the third knock-out drum D-303 is connected with the inlet of the condenser E-305X of the partial condensation fraction column, and the bottom is connected with the inlet of the top of the light component flash tower C-301;

[0138] The top of the light component flash tower C-301 is provided with a gas phase outlet pipeline, and the bottom is sequentially connected with a carbon three booster pump P-301, a third stage cold box E-303X, a second stage cold box E-302X, a first stage cold box E-301X, and a carbon three fraction outlet pipeline;

[0139] The top of the partial condensation fraction column C-302 is sequentially connected with a fourth stage cold box E-304X, a third stage cold box E-303X, a second stage cold box E-302X, a first stage cold box E-301X, and a crude hydrogen outlet pipeline, the bottom is connected with the upper inlet of the light component flash tower C-301, and the outlet of the condenser E-305X of the partial condensation fraction column is sequentially connected with the third stage cold box E-303X, the second stage cold box E-302X, the first stage cold box E-301X, and a reactor feed outlet pipeline;

[0140] A circulating propane feed pipeline is sequentially connected with the first stage cold box E-301X, the second stage cold box E-302X, and the third stage cold box E-303X, wherein the circulating propane pipeline at the outlet of the third stage cold box E-303X and the reactor feed pipeline at the inlet are connected through an interconnection pipeline, and a third stage cold box mixer M-303 is arranged on the interconnection pipeline.

[0141] The main steps of the separation method of the reaction gas generated by the propane dehydrogenation reaction in the example are as follows:

[0142] (1) The reaction gas from the deep purification unit is sent into the cold box sequence through a reaction gas feed pipeline, and is cooled to -90 o C~-110 o C in the first stage cold box E-301X, the second stage cold box E-302X, and the third stage cold box E-303X in sequence to obtain a cooled reaction gas;

[0143] (2) The cooled reaction gas is subjected to gas-liquid separation in the first knock-out drum D-301, the liquid phase at the bottom is sent into the lower part of the light component flash tower C-301, and the gas phase at the top is sent into the first expander EXP1 to be expanded and refrigerated, and then is cooled to -110 o C~-130 o C in the fourth stage cold box to obtain a deep-cooled reaction gas;

[0144] (3) The cryogenic reaction generated gas is sent to the second liquid separator D-302 for gas-liquid separation, the liquid phase at the bottom of the tank is sent to the middle of the light component flash tower C-301, and the gas phase at the top of the tank is divided into two parts, one part of the gas phase is sent to the second expander EXP2 after expansion and then to the third liquid separator D-303, and the other part of the gas phase is sent to the fractionating condensing tower C-302; the liquid phase at the bottom of the third liquid separator D-303 is sent to the top inlet of the light component flash tower C-301, the gas phase at the top of the tank is sent to the fractionating condensing tower condenser E-305X, the liquid phase at the bottom of the fractionating condensing tower C-302 is sent to the upper inlet of the light component flash tower C-301, and the top of the fractionating condensing tower C-302 obtains the fractionating reaction generated gas of C-143 o C. o C.

[0145] (4) The fractionating reaction generated gas is sent to the cold box sequence, and the crude hydrogen is obtained by recovering the cold energy in the fourth cold box, the third cold box E-303X, the second cold box E-302X and the first cold box E-301X in sequence, and the crude hydrogen is obtained through the crude hydrogen extraction pipeline;

[0146] (5) The gas phase at the top of the light component flash tower C-301 is extracted through the gas phase extraction pipeline, and the liquid phase at the bottom is pressurized by the carbon three booster pump P-301 and then sent to the cold box sequence, and the carbon three fraction is obtained by recovering the cold energy in the third cold box E-303X, the second cold box E-302X and the first cold box E-301X in sequence, and the carbon three fraction is extracted through the carbon three fraction extraction pipeline;

[0147] (6) The circulating hydrogen gas provides cold energy in the fractionating condensing tower condenser E-305X, and then is sent to the third cold box E-303X, the second cold box E-302X and the first cold box E-301X in sequence, and is mixed with the countercurrent circulating propane in the third cold box mixer M-303 before entering the cold energy gas inlet of the third cold box E-303X, and the cold energy gas after recovering the cold energy in sequence is extracted through the reactor feed pipeline.

[0148] The circulating propane outlet temperature of the third cold box E-303X in the example 1 is-100 o C, and all the circulating propane is mixed with the cold energy gas and then supplemented into the cold box, and the temperature of the cold box is-103 o C.

[0149] The cold box operation data of the comparative example 1 is shown in Table 3. As can be seen from Table 3, the heat transfer of the cold box of the comparative example 1 is poor, and the minimum heat transfer temperature difference of the third cold box E-303X is only 1.46 o C. The heat transfer area of the cold box is very large, and the UA value of the example 1 and the example 2 is only 58.6 and 62.3% of that of the comparative example 1.

[0150] Table 3 Cold box operation data of comparative example 1

[0151]

[0152] In summary, the propane dehydrogenation to propylene reaction gas separation device and separation method of Example 1 and Example 2 have very significant effects, which can reduce the cooling temperature of the carbon three stream, reduce the heat exchange area of the heat exchanger, at the same time, the cold energy utilization of Example 1 and Example 2 is more reasonable, the thermodynamic efficiency is higher, and the energy consumption is lower.

[0153] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A separation apparatus for separating carbon trimers from a propane dehydrogenation to propylene reaction product gas, characterized by, The apparatus includes: a cold box sequence, an expander, a C3 booster pump, a separator, a light component flash distillation tower, and a fractionation distillation tower; The cold box sequence includes a first-level cold box, a second-level cold box, a third-level cold box, and a fourth-level cold box; The dispensing tank includes a first dispensing tank, a second dispensing tank, and a third dispensing tank; The expander includes a first expander and a second expander; The reaction gas feed line is connected in sequence to the primary cold box, the secondary cold box, the tertiary cold box, and the first liquid separator; The fractionation distillation tower is equipped with a fractionation distillation tower condenser; The top of the first separatory tank is connected in sequence to the first expander, the fourth-stage cold box, and the second separatory tank, while the bottom of the tank is connected to the lower inlet of the light component flash evaporator. The top pipeline of the second separator is divided into two branches: one branch is connected to the inlet of the second expander, and the other branch is connected to the lower inlet of the fractionation and distillation tower. The bottom of the tank is connected to the middle inlet of the light component flash tower. The outlet of the second expander is connected to the inlet of the third separator, the top of the third separator is connected to the inlet of the condenser of the fractionation distillation tower, and the bottom of the tank is connected to the top inlet of the light component flash distillation tower. A gas phase extraction pipeline is installed at the top of the light component flash evaporator, and the bottom of the tower is connected in sequence to the C3 booster pump, the third-stage cold box, the second-stage cold box, the first-stage cold box, and the C3 fraction extraction pipeline. The top of the fractionation distillation tower is connected in sequence to the fourth-stage cold box, the third-stage cold box, the second-stage cold box, the first-stage cold box, and the crude hydrogen extraction pipeline. The bottom of the tower is connected to the upper inlet of the light component flash distillation tower. The condenser outlet of the fractionation distillation tower is connected in sequence to the third-stage cold box, the second-stage cold box, the first-stage cold box, and the reactor feed extraction pipeline. The circulating propane feed line is connected sequentially to the primary cold box, the secondary cold box, and the tertiary cold box. The circulating propane lines at the outlets of at least two cold boxes and the reactor feed lines at the inlets are connected by interconnecting lines. Each interconnecting line is equipped with a mixer and a circulating propane inlet.

2. The apparatus of claim 1, wherein, Each of the interconnecting pipelines is provided with at least one of the circulating propane inlets and one of the mixers, the circulating propane inlets and the mixers being independently controlled.

3. The apparatus of claim 1, wherein, The bottom of the liquid separator, the light component flash evaporator, and the fractionation distillation tower are all equipped with flow control valves, which are independently controlled.

4. A process for separating the carbon trimers from the product gas of the dehydrogenation of propane to propylene using the apparatus of any one of claims 1 to 3, characterized in that, The method includes the following steps: (1) The reaction gas from the deep purification unit is sent to the cold box train via the reaction gas feed line, and is cooled to -90°C, -110°C, and -130°C in the first stage cold box, the second stage cold box, and the third stage cold box, respectively, to obtain a cooled reaction gas; o C~-110 o C cooled reaction gas; (2) The cooling reaction gas is subjected to gas-liquid separation in a first separation tank, the tank bottom liquid phase is sent to the lower part of the light component flash tower, and the tank top gas phase is sent to the first expander for expansion refrigeration and then to the fourth stage cold box for cooling to -110 o C~ -130 o C The deep cooling reaction gas is obtained; (3) the cryogenic reaction generated gas is sent into the second liquid separator for gas-liquid separation, the liquid phase at the bottom of the tank is sent into the middle of the light component flash tower, the gas phase at the top of the tank is divided into two parts, one part of the gas phase is sent into the third liquid separator after being expanded by the second expander, the other part of the gas phase is sent into the fractionating column; the liquid phase at the bottom of the third liquid separator is sent into the top inlet of the light component flash tower, the gas phase at the top of the third liquid separator is sent into the condenser of the fractionating column; the liquid phase at the bottom of the fractionating column is sent into the upper inlet of the light component flash tower, and the temperature of the gas phase at the top of the fractionating column is-123 o C~-143 o C fractionating reaction generated gas; (4) The gas generated by the fractionation reaction is sent into the cold box sequence, and the cold energy is recovered step by step in the fourth-stage cold box, the third-stage cold box, the second-stage cold box and the first-stage cold box to obtain crude hydrogen. The crude hydrogen is extracted through the crude hydrogen extraction pipeline. (5) The gas phase at the top of the light component flash tower is extracted through the gas phase extraction pipeline, and the liquid phase at the bottom of the tower is pressurized by the C3 booster pump and sent into the cold box sequence. The C3 fraction is obtained by recovering the cold energy in the third-stage cold box, the second-stage cold box and the first-stage cold box. The C3 fraction is extracted through the C3 fraction extraction pipeline. (6) After the circulating hydrogen provides cooling in the condenser of the fractionation and distillation tower, it is sequentially sent to the third-stage cold box, the second-stage cold box, and the first-stage cold box. Before entering the inlet of each cold box, it is mixed with the countercurrent circulating propane and the supplementary circulating propane added by the circulating propane inlet. The cooling gas recovered through the stage-by-stage cooling is extracted through the reactor feed pipeline.

5. The method of claim 4, wherein, The number of inlets for replenishing the circulating propane is not less than 2.

6. The method of claim 4, wherein, All three cold boxes (stage 3, stage 2, and stage 1) are replenished with circulating propane. The temperature of the supplemental circulating propane added by the third cold box is -110 o C ~ -90 o C, 0 ~ 20% of the total circulating propane The temperature of the supplementary circulating propane added into the secondary cold box is -90 o C~ -40 o C, 10%~25% of the total circulating propane The temperature of the supplemental circulating propane added to the primary cold box is -60 o C~0 o C, accounting for 65%~87% of the total circulating propane.

7. The method of claim 6, wherein, The circulating propane added by the third cold box accounts for 5-12% of the total circulating propane; The circulating propane added by the second cold box accounts for 12-18% of the total circulating propane; The circulating propane added by the first cold box accounts for 70-83% of the total circulating propane.

8. The method of claim 4, wherein, The circulating propane added by the third cold box and the first cold box; The temperature of the supplemental circulating propane added into the third cold box is -110 o C ~ -90 o C, 5~50% of the total circulating propane The temperature of the supplemental circulating propane added to the primary cold box is -90 o C0 o C, 50%~95% of the total circulating propane.

9. The method of claim 8, wherein, The circulating propane added by the third cold box accounts for 15-40% of the total circulating propane; The circulating propane added by the first cold box accounts for 60-85% of the total circulating propane.

10. The method of claim 4, wherein, The mass ratio of the circulating propane added to the mass of the condensed carbon three fraction in the reaction gas is 0.5-2:

1.

11. The method of claim 4, wherein, The mass ratio of the circulating propane added to the mass of the condensed carbon three fraction in the reaction gas is 0.8-1.35:

1.

12. The method of claim 4, wherein, The operating temperature of the carbon three booster pump is -90--115℃, and the operating pressure is 1.7-4.3 MPaG; The operating temperature of the first expander outlet is -105--125℃, and the operating pressure is 0.45-0.75 MPaG; The operating temperature of the second expander outlet is -120--140℃, and the operating pressure is 0.35-0.60 MPaG.

13. The method of claim 4, wherein, The operating temperature of the first liquid separation tank is -90--110℃, and the operating pressure is 0.8-1.35 MPaG; The operating temperature of the second liquid separation tank is -105--125℃, and the operating pressure is 0.45-0.75 MPaG; The operating temperature of the third liquid separation tank is -120--140℃, and the operating pressure is 0.35-0.60 MPaG; The overhead temperature of the light component flash tower is -90--125℃, the pressure is -0.08-0.35 MPaG, and the bottom temperature is -90--125℃; The overhead temperature of the partial condensation fractionating tower is -120--140℃, the pressure is 0.45-0.75 MPaG, and the bottom temperature is -120--130℃.

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