RU2483783C1 - Method of gas separation - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to separation of gases of different-origin gas oil catalytic cracking and may be used to increased yield of commercial propylene. Proposed method comprises separation in two absorbers, one with circulation sprinkling, and distribution of heat removal over circulation irrigations performed in three steps in compliance with premade calculations. Note here that, at first step, conditional dependence of temperature variation at plates upon absorption heat proper is determined. Share of heat removal in circulation irrigations is determined. Third step consists in accurate definition of relationship between heat removal distribution between circulation irrigation and its position of circulation removal from absorber. Optimum heat removal is defined proceeding from the balance between extra costs of organising circulation irrigations and extra yield of increased extraction of propylene.

EFFECT: increased yield of propylene.

2 cl, 4 dwg, 6 tbl, 5 ex

Description

The invention relates to the field of oil and gas processing, in particular to the separation of gases of catalytic cracking of gas oil of various origins, and can be used to increase the selection of propylene as a commercial product from potentially formed propylene in the cracking process.

A known method for the extraction of propylene from gas products of catalytic cracking, which consists in the fact that the feedstock, consisting of chilled products of catalytic cracking, enters the separator, where it is divided into two streams: the lower hydrocarbon stream enters the fractionating absorber, and the upper hydrogen-containing gas stream passes through the membrane separation device, where hydrogen is extracted, and the concentrated hydrocarbon portion is fed to the same plate of the fractionating absorber, onto which the lower hydrocarbon stream is supplied, fresh absorbent is fed to the top of the fractionating absorber for mixing with the gas stream discharged from the fractionating absorber to the condenser, and after partial condensation, the mixture obtained in the second separator is separated into dry gas and the condensate supplied to the top of the fractionating absorber as an absorbent. Spent absorbent saturated with propylene and other components extracted from the feedstock is discharged from the bottom of the fractionating absorber to the subsequent regeneration of the absorbent and separation of components extracted from the feedstock (Patent US 6723231 B1 “Propylene recovery” C10G 7/02; C10G 7/00; B01D 3/3 fourteen). The disadvantage of this method is that the extraction of hydrogen from the gas mixture is carried out using a membrane process, the use of which in large-scale industries is not economically feasible. In addition, when implementing the absorption process in the process of gas absorption in the fractionating absorber, the heat of absorption is released, which leads to an increase in the temperature of liquid and gas flows on the plates of the absorber, which reduces the degree of absorption on the plates, prevents the absorption of propylene and reduces the degree of extraction of propylene from gas products, which leads to the irretrievable loss of a substantial part of the propylene produced in the catalytic cracking process with dry gas discharged from the second separator.

There is also known a method of energy-efficient gas separation using low-temperature heat flows. In this method, a fractionating absorber is used, in the middle part of which a raw material is fed, vapors from the top of the fractionating absorber are sent to the condenser, non-condensing gas is separated from the condensation products, and a liquid stream - reflux - is fed to the top of the absorber as irrigation. As an absorbent, a gasoline fraction of C ₄ or higher is fed to the top of the fractionating absorber. The bottom liquid from the fractionating absorber enters the riboiler, from which the evaporated part of the bottom liquid is returned to the fractionating absorber, and the other, balance part, is withdrawn from the column to regenerate the absorbent and isolate the components extracted from the feedstock. In this method of separating raw materials in a fractionating absorber, a constant temperature zone is provided located between the input of the raw materials and the absorbent in the fractionating absorber. A constant temperature in this area is maintained using a heat pump (circulating irrigation), in which the cold product is transferred to the lower part of the absorber (US Pat. No. 4,444,576, “Energy-Saving Gas Separation Using Low-Temperature Heat Flows” B01D 3/40). The disadvantage of this method is that the constant-temperature zone is practically not realized, since in this zone, consisting of a series of mass transfer plates, as a result of the release of heat of absorption, counterpropagating flows of liquid and vapor phases will inevitably occur, which will lead to a decrease in the absorption efficiency. In this regard, the unit circulating irrigation system proposed in this method, which covers almost the entire package of plates in the upper part of the fractionating absorber, is irrational and contradicts the physics of the absorption process, since due to the release of heat of absorption in this part of the fractionating absorber it is impossible to ensure the temperature constancy of the vapor and liquid phases. A proof of this is the example cited by the authors, according to which the value of temperatures in the "zone of constant temperatures" practically increases by 2-3 times.

There is also a known method for the separation of liquid hydrocarbons, in which the gaseous products of catalytic cracking are compressed, condensed and fed into the absorber, while the gas from the top of the absorber, after washing, drying and cooling, is sent to the deethanation column, after which the gas phase of the column condenses, and the resulting non-condensed after cooling, the gas fraction is fed to the head of the second absorber, and the condensed liquid fraction is returned to the deethanation column. The bottom liquid from the absorber is sent to the debutanization column, the gas fraction formed in it is condensed, after condensation the non-condensed gas fraction is mixed with the feedstock after compression, and the condensed liquid fraction is sent to the debutanation column (Patent RU 2014343 “Method for the separation of liquid hydrocarbons and installation for it implementation "C10G 5/06). The disadvantage of this method is that when absorption occurs in a conventional absorber, a significant amount of recoverable components are lost with the gas fraction due to the lack of clarity in the separation of the components of the gas phase due to the lack of fractionation effect in the apparatus.

Closest to the claimed method for separating gases obtained in the process of catalytic cracking of gas oil of various origin is a method for separating gases obtained in the process of catalytic cracking of hydrocarbons, in which catalytic cracking gas extracted from catalytic cracking products is compressed by a compressor to form non-condensing fatty gas and compression condensate enters the fractionating absorber with a circulating irrigation system. Stable gasoline is supplied as absorbent to the top of the fractionating absorber, and unstable gasoline is introduced into the middle part between the injection of stable gasoline and raw materials (compression gas and compression condensate) as a second absorbent; bottom liquid of the fractionating absorber is drained into the stabilizer, on top of which propane is taken propylene and butane-butylene fractions, which goes further to the separation of C ₃ and C ₄ fractions, and from below - stable gasoline, which is returned upward of the fractionating absorber. Dry gas containing C ₁ -C ₂ hydrocarbons leaves from the top of the absorber, and C ₃ -C ₄ hydrocarbons are removed from the bottom along with a saturated absorbent. The temperature in the absorption part is maintained by intermediate cooling of the absorbent, and two circulation irrigation is used (Erich VN, Rasina MG, Rudin MG “Chemistry and technology of oil and gas”, Leningrad, “Chemistry”, 1985, 408 p.). The disadvantages of this method of gas separation of catalytic cracking are:

- low depth of extraction of propylene in the fractionating absorber with respect to the propylene potentially generated during cracking due to the fact that in accordance with the laws of phase equilibrium in the fractionating absorber it is impossible to absorb all the propylene contained in the feedstock (potential propylene content), and part propylene will leave with "dry gas" from the top of the fractionating absorber;

- the content of propylene in the "dry gas" leaving the top of the fractionating absorber is determined by the operating mode of the circulation irrigation, there is no theoretically justified relationship between the content of propylene in the "dry gas", the amount of circulation irrigation, the distribution of heat removal between the circulation irrigation of the fractionating absorber, leading to private suboptimal operating modes of the fractionating absorber and unjustified loss of some part of propylene with "dry gas";

- it is not taken into account that the depth of extraction of propylene in the fractionating absorber is not a determining factor in the efficiency of the functioning of the fractionating absorber, since when trying to increase the depth of extraction of propylene economically unjustified modes of operation of the fractionating absorber are possible, leading to the cost of increasing the depth of extraction of propylene exceed the cost of additionally extracted propylene.

The aim of the invention is to increase the depth of extraction of propylene from potentially generated propylene in the cracking process and to ensure optimal heat removal in the system of circulating irrigation of the fractionating absorber.

This goal is achieved by the fact that in the method of separation of gases obtained in the process of catalytic cracking of gas oil of various origins and isolated in the form of fatty gas and compression condensate from above the main fractionating distillation column, including their subsequent separation in a fractionating absorber with a circulation irrigation system, to the top of which as absorbent, stable gasoline, and in the middle part between the introduction of stable gasoline and fatty gas together with compression condensate ditsya unstable gasoline as the second absorbent bottom fractionating absorber is given bottoms liquid in the stabilizer, on top of which shown in propane-propylene and butane-butylene fraction entering further separation of fractions of C ₃ and C _4, and bottom - stable gasoline returned upwards fractionating absorber ; light hydrocarbon gases are discharged from the top of the fractionating absorber to a second absorber, to the top of which a product is discharged as absorbent, which is removed from the main fractionation distillation column as circulation irrigation, dry gas is distilled off from the top of the second absorber, and bottom residue is returned to the main circulation fractionation distillation column, the distribution of heat removal by the circulation irrigation of the absorption heat removed in the circulation irrigation is performed by p by the counting method in three stages, while the first stage calculates the temperature of the liquid and vapor on I plates of the upper part of the fractionating absorber T _{1, I} , on top of which the absorbent is introduced, in the absence of heat removal in the circulation irrigation, the conditional dependence of the temperature change on the plates T is clarified _{A, I} = T _{1, I} -T ₀ due to the actual heat of absorption on the plates, where T _{0 is the} temperature on the absorbent input plate, in the second stage, the temperature value T _{A, F-1} on the F-1 plate is divided by the raw material input plate closest to the top on N equal cut Cove, multiple fractions of heat removal in pumparound, with one or two lobes heat removal are removed in the first top pumparound and the remaining fraction is distributed between the remaining pumparound and the dependence of T _{A, I} of the number of trays is the pumparound location approximate position adjustment top parts of the fractionating absorber, while if the approximate position of the location of the circulation irrigation is between the plates, then the selection of the product in the circulation irrigation is accepted It is removed from one of the nearest plates and at the third stage, the ratio of the heat removal distribution between the circulation irrigation is refined. It is advisable to determine the optimal actual heat sink in the circulation irrigation system by the ratio

, $${\text{(G}}_{\text{BTSO}}\times {\text{FROM}}_{\text{BTSO}}-{\text{G}}_{\text{CO}}\times {\text{C}}_{\text{CO}}{\text{) C}}_{\text{P}}-{\text{Ts}}_{\text{AT}}{\displaystyle {\sum }_{\text{J}=\text{one}}^{\text{Z}}\text{(}\frac{{\text{G}}_{\text{CO}\text{, J}}\times {\text{c}}_{\text{CO}\text{, J}}{\text{(t}}_{\text{O}\text{, J}}-{\text{t}}_{\text{J}}\text{)}}{{\text{c}}_{\text{B}}{\text{(t}}_{\text{K}\text{, J}}-{\text{t}}_{\text{B}\text{0}}\text{)}}-}\frac{{\text{G}}_{\text{BTSO}\text{, J}}\times {\text{c}}_{\text{BTSO}\text{, J}}{\text{(t}}_{\text{BO}\text{, J}}-{\text{t}}_{\text{J}}\text{)}}{{\text{c}}_{\text{B}}{\text{(t}}_{\text{K}\text{, J}}-{\text{t}}_{\text{B}\text{0}}\text{)}}\text{)}>\text{0}$$

,

where G _BCO is the estimated number of vapors discharged from the top of the fractionating absorber in the basic version of its operation with specific quantitative values of circulating irrigation, kg / h;

With _BCO - the concentration of propylene in the vapors removed from the top of the fractionating absorber in the basic version of its operation with specific quantitative values of circulating irrigation, mass. shares;

G _ЦО - estimated amount of vapors discharged from the top of the fractionating absorber when it is operated with variable increasing quantitative values of circulating irrigation, kg / h;

C _CO - the concentration of propylene in the vapors discharged from the top of the fractionating absorber during its operation with variable increasing quantitative values of circulating irrigation, mass. shares;

C _P - the cost of propylene, rub / t;

C _B - the cost of recycled water, rub / t;

Z is the number of circulating irrigation;

G _{ЦО, J} - the amount of variable J-th circulating irrigation in the fractionating absorber, kg / h;

G _{BCO, J} - the amount of basic J-th circulating irrigation in a fractionating absorber, kg / h;

with _{central heating, J} is the heat capacity of the variable Jth circulating irrigation, J / kg · deg;

with _{BCO, J} - heat capacity of the basic J-th circulating irrigation, J / kg · deg;

t _{O, J} is the temperature of the variable J-th circulating irrigation supplied to the cooling from a fractionating absorber, ° C;

t _{BO, J} is the temperature of the base J-th circulating irrigation supplied for cooling from a fractionating absorber, ° C;

t _J is the temperature of the Jth circulating irrigation entering the fractionating absorber after cooling, ° C;

c _B is the heat capacity of the cooling circulating water, J / kg · deg;

t _{K, J} is the final heating temperature of the cooling circulating water supplied to the cooling of the Jth circulating irrigation, ° C;

t _{B, O} is the temperature of the circulating water, ° C.

Figure 1 shows a diagram illustrating the proposed method of gas separation.

The catalytic cracking products are fed through pipeline 1 to the lower part of the main distillation column 2, above which gasoline vapor, water vapor and hydrocarbon gas are cooled through line 3 in the refrigerator-condenser 4 and fed through line 5 to the gas separator 6, from where gas is pumped out by pump 7 8, while one part of the flow through line 9 is fed to the main distillation column 2 in the form of sharp irrigation on the upper plate, and the balance amount of unstable gasoline as the second absorbent through line 10 is fed into the medium nyuyu part fractionating the absorber 11 between the input stability of gasoline (first absorber) and wet gas compression in conjunction with condensation. From the bottom of the gas separator 6, water along line 12 is discharged from the installation. Gas through line 13 from the top of the gas separator 6 is supplied to the compressor 14, the gas compressed in the compressor is then fed through the pipeline 15 to the condenser-cooler 16 and through the line 17 to the gas separator 18, where the fatty gas is separated from the gas condensate and process water. The gas condensate through line 20 enters the pump 21 and through line 22 enters the middle part of the fractionating absorber 11 together with the fatty gas entering line 23 from the gas separator 18 to extract C ₃₊ hydrocarbons, and water through line 24 is discharged from the gas separator 18 to the sewer industrial stocks.

The temperature of the bottom of the fractionating absorber 11 is maintained by heating part of the bottoms liquid of the fractionating absorber 11, which enters the riboiler 25, by the average circulation irrigation of the main distillation column 2, which enters the riboiler 25 through line 26. Hot irrigation of the bottom of the fractionating absorber 11 comes from riboilera 25 to the bottom of the fractionating absorber 11 along line 27. The balance portion of the bottom liquid of the fractionating absorber 11 through line 28 enters the stabilizer 29 to separate the propane-propylene and butane-butylene fractions from stable gasoline returned to the fractionating absorber 11 as an absorbent. Vapors from the top of the stabilizer 29 via line 30 enter the refrigerator-condenser 31, from which propane-propylene and butane-butylene fractions are removed via line 32 for further separation, and part of the condensate from the refrigerator-condenser 31 via line 33 is returned to the stabilizer 29 as irrigation. The stabilizer bottoms liquid through line 34 enters the riboiler with steam space 35, from which the vapor on line 36 returns to the bottom of the stabilizer 29, and the stable gasoline from the riboiler 35 passes through line 37 to the pump 38, from which the stable gasoline is fed to the top via line 39 fractionating absorber 11 as a first absorbent.

Non-absorbed light hydrocarbon gases in a fractionating absorber 11 containing propylene in a certain amount are fed through line 40 to the bottom of the second absorber 41, to the top of which, through line 42, the product is removed from the main fractionation distillation column 2 as circulation irrigation. Dry gas is distilled off from the top of the second absorber 41 through line 43, from the bottom of the second absorber 41 through line 44, the bottom residue is returned to the circulation irrigation of the main fractionation distillation column 2.

The fractional absorber 11 is equipped with a circulating irrigation system 45, providing heat removal of hydrocarbon absorption, leading to intensification of the absorption of light hydrocarbons from the liquid absorbent flowing down the plates of the fractionating absorber 11.

The main distillation column 2 is equipped with upper 46, middle 47 and lower 48 circulation irrigation. From the bottom of the main distillation column 2, bottoms liquid containing heavy hydrocarbons is discharged via line 49. The average circulating irrigation 47 is formed by heat removal from the stream of light catalytic gas oil (the internal stream of the main distillation column 2 with its simultaneous circulation as absorbent supplied to the second absorber 41 and the coolant supplied to the reboiler 25. The stream of hot light catalytic gas oil from the main distillation columns 2 through line 47 enters the pump 50 and is fed through line 26 to the riboiler 25, after which through line 51 it enters the refrigerator 52. After the refrigerator 52, the stream of chilled of the catalytic gas oil is divided into two parts, while the first part along line 42 as an absorbent is fed to the top of the second absorber 41, and the second part along line 53 is returned to the circulation irrigation zone 47, pre-mixed with the bottom liquid withdrawn from the second absorber 41 line 44.

Figure 2 and 3 as an example 1 shows the steps of the calculation of the distribution of heat removal between the circulating irrigation of the fractionating absorber with the supply of raw materials to 11 plate and absorbent to 1 plate.

Based on the calculation of the base absorber, which is the top of the fractionating absorber with the entire absorbent fed to the top of the absorber, the temperatures T _{1, I of the} equilibrium vapor and liquid on each i-plate are taken from plate to plate, taking into account the heating of the absorbent due to heat absorption of light hydrocarbons by absorbent, in the absence of circulating irrigation. Figure 2, row 1, presents the temperature profile on the plates of the base absorber. At the first stage of the analysis of the solution of the problem of the heat removal distribution between the circulating irrigation of the fractionating absorber in order to take into account the contribution of the actual absorption heat to the fixed temperature of the absorbent, the specified conditional dependence of the temperature change on the plates T _{A, I} = T _{1, I} -T _{0 is found} due to the actual absorption heat plates, where T _{0 the} temperature on the plate absorbent input. Figure 2, row 2, presents the refined conditional dependence of the temperature change on the plates T _{A, I} = T _{1, I-} T ₀ .

Next, the conditional heat removal rate N, equal to 5-10, is taken, and in the second stage, the temperature value T _{A, F-1} on the F-1 plate is divided into N equal segments in multiples of the heat removal parts in circulation irrigation, the same as the fraction of heat removal in the circulation irrigation, the top one or two parts of the heat removal are allocated in the first circulation irrigation from above, and the remaining shares are distributed between the rest of the circulation irrigation, and according to the dependence of T _{A, I} on the number of plates, there is an approximate position of the location of the circulation irrigation along the height of the upper part of the fra positioning absorber. If the approximate position of the location of the circulation irrigation is between the plates, then the selection of the product for circulation irrigation is taken from one of the nearest plates. In Fig. 3, curve 1 shows the refined conditional dependence of the temperature change on the plates T _{A, I} = T _{1, I} -T ₀ due to the actual heat of absorption on the plates, identical to Fig. 2, row 2, and options for the location of circulating irrigation at N = 6. In this case, the temperature value T _{A, 10} per 10 plate, which is closest to the input plate of raw materials, is divided into 6 equal segments that are multiples of the heat removal parts in circulation irrigation (Fig. 3, distribution of heat removal 2). For the proposed three circulation irrigation with a pre-accepted distribution of heat removal by circulation irrigation (counting from the top of the absorber) 1: 2: 3 (Fig. 3, distribution of heat removal 3) we obtain that the first circulation irrigation should be taken from the 3rd plate, the second circulation irrigation should be selected between 7 and 8 plates, and the third circulation irrigation should be selected from the 10th plate. Due to the fact that the second circulation irrigation can be selected only from 7 or 8 plates, figure 3 shows two options for the selection of the second circulation irrigation. When selecting the second circulation irrigation from 7 plates, the distribution ratio of the heat removal between the circulation irrigation 1: 1,7: 3,3 is formed (Fig. 3, the distribution of heat removal 4), and when selecting the second circulation irrigation from 8 plates, the distribution ratio of the heat removal between the circulation irrigation is formed 1: 2.3: 2.7 (Fig. 3, distribution of heat sinks 5).

Example 2. Mathematical modeling of the method of gas separation of catalytic cracking was performed in a circuit operating at one of the refineries. In this scheme, the fractionating absorber had 19 theoretical plates and one circulation irrigation in the amount of 39 t / h on the third theoretical plate from above. The characteristics of the feed streams (fatty gas and gas condensate), as well as the calculated data for the dry gas discharged from the absorber 41, the gas stream discharged from the fractionating absorber 11, and the bottom residue of the fractionating absorber 11 are shown in Table 1. At the time of the survey, the total supply of fatty gas and gas condensate into the fractionating absorber at a separation temperature of 56.5 ° C in the separator 18 was 51.26 t / h, and the absorber 41 functioned as an intermediate tank without supplying absorbent material. As follows from table 1, the propylene content in the gas leaving the fractionating absorber 11 was 29.1% wt. or the degree of extraction from the potential of 54.7%. Table 2 shows the results of mathematical modeling of fractionating absorber 11 under the following conditions: fatty gas and gas condensate are served on a fifth plate with a temperature of 46.5 and 56.5 ° C, respectively, and a temperature of stable and unstable gasolines, respectively, 17.5 and 40 ° C, which showed that the achieved results of the extraction of propylene are provided by the heat removal value in the circulation irrigation of 0.3339 Gcal / h. Table 3 shows a comparison of the calculated and actual compositions of the gas stream discharged from the fractionating absorber 11, indicating the adequacy of mathematical modeling of the operation of the gas separation scheme. The low degree of extraction of propylene from the incoming feed is explained by the high temperature of the hydrocarbon feed at the inlet to the fractionating absorber 11 and the idle second absorber 41.

Example 4. A mathematical simulation of a number of variants of the method of gas separation of catalytic cracking according to the claimed invention. The characteristics of the feed streams (fatty gas and gas condensate) and absorbents (stable and unstable gasolines) are given in table 1. The fractionating absorber accepts 19 theoretical plates, the input of raw materials to 11 theoretical plates at a temperature of all incoming external flows of 40 ° C, and circulation irrigation 35 ° C. Table 4 shows:

a) the results of mathematical modeling of the basic version (option 1) of a fractionating absorber 11 with one circulating irrigation with a total supply of fatty gas and gas condensate to the fractionating absorber 11 at a separation temperature in the separator 18 40 ° C of 51.26 t / h, including the amount of fatty gas 19.47 t / h and gas condensate 31.79 t / h. The amount of circulating irrigation supplied from the third to the second plate was 39 t / h. The heat removal value in circulation irrigation was 0.110 Gcal / h, the loss of propylene with gases from the fractionating absorber 11 and the second absorber 41 was 1.260 and 1.017 t / h, respectively, providing a degree of recovery of 89.70% from the potential;

b) the results of mathematical modeling of a number of work options (options 2-4) of the fractionating absorber 11 with three circulation irrigations with a total supply of fatty gas and gas condensate to the fractionating absorber 11 at a separation temperature in the separator 18 of 40 ° C, also of 51.26 t / h, including fatty gas 19.47 t / h and gas condensate 31.79 t / h. Previously, the heat removal ratio for circulation irrigation was adopted, starting from the top of the fractionating absorber, 1: 1.7: 3.3 similarly to the explanation of the essence of the method of calculating heat removal (figure 2 and 3) given above in example 1, while the output positions of the corresponding circulation irrigation 3, 7, and 10 theoretical plates corresponded to the cooling system, and the introduction of cooled circulating irrigation into the fractionating absorber amounted to 2, 6, and 9 theoretical plates, respectively.

Mathematical modeling of the gas separation method in order to determine the operation mode of the installation with ensuring the optimal depth of propylene extraction from the feedstock was carried out by varying the costs of circulation irrigation in the fractionating absorber 11 while maintaining the heat removal ratio for circulation irrigation, starting from the top of the fractionating absorber, 1: 1.7: 3 , 3 with comparison with the base case (table 4, option 1). The total consumption of circulating irrigation was taken as a multiple of the base and ranged from 1-10. As follows from the calculation data given in table 4, the transition to three circulating irrigation allowed to reduce the loss of propylene with gases leaving the fractionating absorber 11 and the second absorber 41, respectively, from 13.25 to 9.39% and from 12.72 to 8. 79%, while the degree of propylene extraction increased from 89.70 to 93.30% with an increase in the total heat removal in circulation irrigation from 0.110 to 0.528 Gcal / h.

Example 5. For options 2-4 of example 4 (table 4), the costs of additional heat removal in circulation irrigation are calculated with an increase in the irrigation rate from 1 to 10 at a cooling water price of 4 rubles / t and the additional income from providing additional selection of propylene with an increase in the multiplicity irrigation at a price of 2000 rubles / t. Figure 4 presents the calculation results: row 1 characterizes the costs of additional heat removal, row 2 - additional income from providing additional selection of propylene.

Zone 1 corresponds to the condition of expediency of increasing the flow rate of circulating irrigation as compared with the base case due to the possibility of economical production of additional propylene, zone 2 corresponds to the condition of the inadvisability of increasing the flow rate of circulating irrigation as compared with the base case due to the increase in the cost of water consumption with increasing amount of circulating irrigation . The dashed line in figure 4 with a multiplicity of consumption of circulating irrigation of 2.7 compared with the base case characterizes the optimal heat removal mode in the system of circulating irrigation of the fractionating absorber 11, which ensures balancing the additional costs of creating circulating irrigation and additional profit from the maximum allowable extraction of propylene from the feedstock, while the degree of extraction of propylene will be 93%.

Example 6. The results of the absorption extraction of propylene in the system fractionating absorber 11 and the second absorber 41 can be significantly improved by increasing the number of theoretical plates in the fractionating absorber 11. Table 5 shows the calculation results of the scheme according to the claimed invention for the following initial conditions:

- the number of theoretical plates 30;

- temperature of raw materials and absorbents 40 ° C,

  circulating irrigation - 35 ° C;

- the total consumption of fatty gas and gas condensate is 51.26 t / h (as in the previous calculation examples);

- raw materials are served on 21 theoretical plates;

- absorbents - stable and unstable gasolines - are served on 1 and 7 theoretical plates, respectively;

- circulating irrigation is discharged from 3, 15 and 20 theoretical plates and fed into the absorber for 2, 14 and 19 theoretical plates, respectively, in the amount of 55, 38 and 40.2 t / h, respectively, providing heat removal in the ratio 1: 1.7: 3.3 .

The degree of propylene recovery was 98.93%. With a further increase in the flow rate of circulating irrigation, it is possible to increase the degree of propylene extraction to 99.02% (table 6).

Thus, the above examples indicate the usefulness of the claimed invention for forming the creation of an optimal circulating irrigation system in a fractionating absorber when implementing a method for the separation of catalytic cracking gases.

Table 3 Stream name Gas from the absorber 11 calculated Absorber actual gas 11 Calculation error Total weight % of the mass. H ₂ 0.48 0.49 -0.01 N ₂ 9.45 9.48 -0.03 O ₂ 0.61 0.61 0 CO 0.37 0.41 -0.04 CH ₄ 11.72 11.76 -0.04 C ₂ H ₅ 9.27 9.31 -0.04 C ₂ H ₆ 9.57 9.09 +0.48 CO ₂ 2.94 2.95 -0.01 H ₂ s 0.85 0.85 0 C ₃ H ₆ 29.07 27,20 +1.87 C ₃ H ₈ 7.07 7.17 -0.1 iC ₄ H ₁₀ -C ₄ H ₆ 9.81 17.25 -7.44 C ₅ H ₁₂ and above boiling 8.80 3.46 +5.34

Claims (2)

1. The method of separation of gases obtained in the process of catalytic cracking of gas oil of various origin and isolated in the form of fatty gas and compression condensate on top of the main fractionating distillation column, including their subsequent separation in a fractionating absorber with a circulation irrigation system, on top of which stable gasoline is supplied as absorbent , and in the middle part between the injection of stable gasoline and fatty gas together with the compression condensate, unstable gasoline is introduced as a second of the absorber, bottom liquid of the fractionating absorber is discharged into the stabilizer, on top of which propane-propylene and butane-butylene fractions are taken, which are then transferred to the separation of fractions C ₃ and C ₄ , and from the bottom is stable gasoline, which is returned upward of the fractionating absorber; light hydrocarbon gases are discharged from the top of the fractionating absorber to a second absorber, to the top of which the product is discharged as an absorbent, which is removed from the main fractionation distillation column as circulation irrigation, dry gas is distilled off from the top of the second absorber, and bottom residue is returned to main irrigation fractionating distillation column, characterized in that, in order to increase the depth of extraction of propylene from potentially formed in the cracking process ropilena and optimum heat removal system pumparound fractionating absorber, distribution of heat removal by pumparound withdrawn in pumparound absorption of heat is performed by calculation in three stages, with the first stage calculated temperature of the liquid and vapor on the I-x trays top of the fractionating absorber T _{1, I} , on the top of which an absorbent is introduced, in the absence of heat removal in the circulation irrigation, the conditional dependence of the temperature change is specified trays on plates T _{A, I} = T _{1, I} -T ₀ due to the actual heat of absorption on the plates, where T ₀ is the temperature on the plate of the absorbent input, at the second stage, the temperature T _{A, F-1} on the F-1 plate, the raw material input plate closest to the top is divided into N equal segments that are multiples of the heat removal parts in the circulation irrigation, with one or two heat removal parts being allocated in the first circulation irrigation from above, and the remaining shares are distributed between the remaining circulation irrigations, and according to the dependence of T _{A, I} on number of plates is the approximate position of the races the position of the circulation irrigation along the height of the upper part of the fractionating absorber, while if the approximate position of the location of the circulation irrigation is between the plates, then the selection of the product for circulation irrigation is taken from one of the nearest plates and at the third stage the distribution of the heat removal between the circulation irrigation is refined. 2. The method of gas separation according to claim 1, characterized in that the optimal actual heat sink in the circulating irrigation system is determined by the ratio
$${\text{(G}}_{\text{BTSO}}\times {\text{FROM}}_{\text{BTSO}}-{\text{G}}_{\text{CO}}\times {\text{C}}_{\text{CO}}{\text{) C}}_{\text{P}}-{\text{Ts}}_{\text{AT}}{\displaystyle {\sum }_{\text{J}=\text{one}}^{\text{Z}}\text{(}\frac{{\text{G}}_{\text{CO}\text{, J}}\times {\text{c}}_{\text{CO}\text{, J}}{\text{(t}}_{\text{O}\text{, J}}-{\text{t}}_{\text{J}}\text{)}}{{\text{c}}_{\text{B}}{\text{(t}}_{\text{K}\text{, J}}-{\text{t}}_{\text{B}\text{, O}}\text{)}}-}\frac{{\text{G}}_{\text{BTSO}\text{, J}}\times {\text{c}}_{\text{BTSO}\text{, J}}{\text{(t}}_{\text{BO}\text{, J}}-{\text{t}}_{\text{J}}\text{)}}{{\text{c}}_{\text{B}}{\text{(t}}_{\text{K}\text{, J}}-{\text{t}}_{\text{B}\text{, O}}\text{)}}\text{)}>\text{0}\text{,}$$

where G _BCO is the estimated number of vapors discharged from the top of the fractionating absorber in the basic version of its operation with specific quantitative values of circulating irrigation, kg / h;
With _BCO - the concentration of propylene in the vapors removed from the top of the fractionating absorber in the basic version of its operation with specific quantitative values of circulating irrigation, wt., Fraction;
G _ЦО - estimated amount of vapors discharged from the top of the fractionating absorber when it is operated with variable increasing quantitative values of circulating irrigation, kg / h;
With _CO - the concentration of propylene in the vapors discharged from the top of the fractionating absorber during its operation with variable increasing quantitative values of circulating irrigation, wt., Fraction;
C _P - the cost of propylene, rubles / t;
C _B - the cost of recycled water, rubles / t;
Z is the number of circulating irrigation;
G _{ЦО, J} - the amount of variable J-th circulating irrigation in the fractionating absorber, kg / h;
G _{BCO, J} - the amount of basic J-th circulating irrigation in a fractionating absorber, kg / h;
with _{central heating, J} is the heat capacity of the variable Jth circulating irrigation, J / kg · deg;
With _{BCO, J} is the heat capacity of the base J-th circulating irrigation, J / kg · deg;
t _{О, J} is the temperature of the varied J-th circulating irrigation supplied to cooling from a fractionating absorber, ° С;
t _{BO, J} is the temperature of the base J-th circulating irrigation supplied to the cooling from a fractionating absorber, ° C;
t _J is the temperature of the Jth circulating irrigation, which, after cooling, enters the fractionating absorber, ° C;
with _In - the heat capacity of the cooling circulating water, J / kg · deg;
t _{K, J} is the final heating temperature of the cooling circulating water supplied to the cooling of the J-th circulating irrigation, ° С;
t _{B, O} - temperature of circulating water, ° С.

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