Be rich in the separation method of propylene, propane catalytically cracked gas
Technical field
The present invention relates to the separation method of splitting gas, particularly a kind ofly in the petrochemical complex industry, be used to be rich in the separation method that carbon three is formed the catalytically cracked gas of (comprising propylene and propane etc.).
Background technology
In the petrochemical complex industrial chain, tube cracking furnace thermal cracking gas, liquid phase feed are mainly adopted in the production of basic organic ethene, propylene, as: ethane, propane and lighter hydrocarbons, and a part of normal pressure diesel oil or hydrogenated diesel oil, and the component that cracking obtains separated.Separate the method that adopts the compression cryogenic rectification usually, the method that oil absorbs and transformation is adsorbed of using is also arranged, but greatly the full scale plant of part is the flow process that adopts the compression cryogenic rectification, its process characteristic is: the splitting gas of pyrolyzer outlet is by refrigerated separation part liquid phase component, and after reclaiming a part of heat, arrive certain pressure with compressor pressurizes, be generally about 38atm, dry then, cooling, deep cooling is progressively isolated ethene with the method for rectifying, propylene product, method with alkali cleaning and hydrogenation is removed impurity, can isolate as requested simultaneously and respectively organize byproduct such as hydrogen, methane, ethane, propane and carbon four and carbon four above blending fractions.The catalytically cracked gas that obtains with catalytic cracking process (as FCC, DCC technology) processing heavy oil contains propylene and small amount of ethylene usually, and propylene is wherein reclaimed as byproduct with the method for compression rectification usually.
Recent years is because the technical development of catalytic pyrolysis, and the raising of propylene product price, and producing ethene, propylene product with Deep Catalytic Cracking process is that the technology of purpose has enlarged in industrial application, and the device industrial scale enlarges day by day.The composition of catalytically cracked gas is different from the gas composition of tube cracking furnace, it is light form as hydrogen, methane, ethene, ethane less, and relative heavier compositions such as propylene, propane are more, and because the characteristics of Deep Catalytic Cracking process, catalytically cracked gas is different with the splitting gas impurities that tube cracking furnace obtains, and the activity change owing to catalyzer or contact substance causes the composition of catalytically cracked gas slightly to change in continuous flow procedure; Catalytically cracked gas contains N usually
2, NO
x, CO
2Deng impurity, and the splitting gas that thermo-cracking obtains does not contain these impurity usually, in order to remove these impurity, needs to increase trace impurity hydrogenation reaction bag.
Along with the required raw material of tubular type cracking technology raising up of shortage and price increase and propylene price day by day, Deep Catalytic Cracking process based on catalytic cracking process (FCC) is developed, the technology of new development such as DCC, HCC, CPP, SHMP etc., contain more carbon three (being mainly propylene and propane) in its splitting gas, a certain amount of ethene and ethane are also arranged.According to selection of process parameters such as the difference of raw material component characteristic, catalyzer (contact substance), temperature of reaction, reaction pressure, water oil ratios, can obtain different products and distribute, but the yield of two alkene (propylene and ethene) be a height than FCC all.
Existing separation process is described below:
Adopting the conventional rectification method, is purpose with the separation of propylene, its characteristics be middle pressure, in cold.Tail gas is generally known as catalysis drying gas, as fuel, or makes industrial chemicals to utilize ethene wherein.This technology is in industrial more application, generally at refinery with the gas separation unit setting, obtain propylene with separation.
In order further to obtain the ethylene fraction in the splitting gas, also can further separate catalysis drying gas, because the catalysis drying gas ethylene concentration is lower, impurity is more, therefore hydrogen and methane and ethane are higher to the ratio of ethene, adopt investment of low temperature separation process flow process and the process cost can be very high.Also have and adopt the suction of oil receipts to separate with the method that transformation is adsorbed, but generally only be used for the device of small-scale, its main drawback is that oily absorption flowsheet synthesis energy consumption is higher, and transformation adsorption process unit is too much, complicated operation.
In addition, if distribution of the composition of catalytically cracked gas and tube cracking furnace is approaching, also there is suggestion to adopt general ethylene unit low temperature separation process flow process commonly used.
Chinese patent application 00113109.5 has been introduced a kind of " method of separating and reclaiming ethylene, ethane, propylene and hydrogen from the gas mixture that contains hydro carbons ", this invention adopts pickling, absorption, low temperature separation process to obtain cuts such as ethene, ethane, propylene, has the comparatively complicated defective of technology equally.
Chinese patent application 01132960.2 has been introduced " a kind of improved light hydrocarbon deep cooling separating method ", it be with compression and refrigerative light hydrocarbon feedstocks gas after knockout drum separates, gaseous component enters the component distribution device, make whole carbon three, most of carbon two and a spot of methane change component distribution device bottom liquid phases over to, this inventive method has reduced the load of ice chest and demethanizing tower, reduced energy consumption, but since enter the component distribution device have only the gas phase part, make the sepn process of component once not finish, removing methane also needs two towers to finish, and technology is comparatively complicated.
Summary of the invention
The purpose of this invention is to provide a kind of separation method that is rich in propylene, propane catalytically cracked gas that is applicable to, the technical issues that need to address are: simplify the separating technology that is rich in propylene, propane catalytically cracked gas, cut down the consumption of energy and facility investment, improve the adaptability of raw material.
Technical scheme of the present invention is: be rich in the separation method of propylene, propane catalytically cracked gas, catalytically cracked gas enters cracking gas compressor, when being compressed to 10-14atm for three sections, enter the alkali cleaning unit and carry out alkali cleaning, remove sour gas, enter the drying unit drying then, behind drying unit, set up C
3Presort tower, adopt fuzzy cutting and separating method, C
3Presorting the pressure of tower is decided (to be generally 10~20atm), to control the cat head condensing temperature simultaneously and be not less than-40 ℃ (can use propylene refrigerant as refrigerant), C by upstream and downstream pressure
3Presorting the column overhead cut is light constituents such as hydrogen, methane, ethene, ethane, propylene, and tower bottom distillate is propylene, propane, carbon four and carbon four above heavy constituent; C
3The overhead fraction of presorting tower is after trace impurity hydrogenation reaction bag hydrogenation reaction is removed impurity, further compression, be pressurized to 36-40atm, lighting end after compression enters ice chest, carry out low temperature separation process, isolate hydrogen and low-pressure methane, enter demethanizing tower through the isolating cut of ice chest, the overhead fraction of demethanizing tower is a high pressure methane, the tower bottom distillate of demethanizing tower enters deethanizing column, and the overhead fraction of deethanizing column enters ethylene rectification tower, and the tower bottom distillate of deethanizing column enters propylene rectification tower, the overhead fraction of ethylene rectification tower is a polymer grade ethylene, and the tower bottom distillate of ethylene rectification tower is an ethane.C
3The tower bottom distillate of presorting tower enters depropanizing tower, and the depropanizing tower overhead fraction enters propylene rectification tower, and the tower bottom distillate of depropanizing tower is C
4And C
4Above heavy constituent, the overhead fraction of propylene rectification tower is a polymerization-grade propylene, the tower bottom distillate of propylene rectification tower is a propane.
C
3The principle of presorting the fuzzy cutting of tower is to make propylene in the splitting gas at C
3Distribute cutting at the bottom of presorting the cat head of tower and tower, separation requirement is that cat head gently consists of hydrogen, methane, ethene, ethane and propylene, reorganization becomes propylene, propane, carbon four and carbon and forms four or more at the bottom of the tower, and the distribution of propylene can be formed any adjusting according to splitting gas, and the adjusting target is C
3Presort column overhead and do not contain propane, cryogen can the low and propylene in position, propane is sent at the bottom of tower as far as possible.The propylene boiling point is lower than propane, control C
3Presort the column overhead produced quantity, promptly control C
3Presort the column overhead temperature, then cat head just can not contain propane; If C
3It is many to presort the column overhead produced quantity, i.e. C
3Presort column overhead temperature height, then propane also has part from the cat head extraction, the extraction at the bottom of the tower of some propane.Hence one can see that, by control C
3Presort the column overhead temperature, the may command propylene is at C
3Presort the distribution at the bottom of the Tata head tower, and then the may command cat head does not contain propane.
Work as C
3Presort the overhead fraction of tower and be not with propane, the tower stilling branch of the deethanizing column cat head that can enter propylene rectification tower refluxes like this, effectively reduces the load of propylene rectification tower, has also reduced the reflux ratio of propylene rectification tower, can be energy-conservation significantly and save facility investment.
The invention has the beneficial effects as follows: the technical program and prior art contrast, because used the operational condition of middle pressure, adopt the isolation technique of fuzzy cutting, carbon three is formed at the bottom of cat head and tower, distributed, like this, can under the condition of middle pressure, isolate most of carbon three and more last running, saved a large amount of compression works, because cat head has kept a part of carbon three, the required freezing grade of overhead condenser is descended simultaneously, make the turndown ratio of this tower bigger simultaneously.Because oneself has removed most carbon three and more last running overhead light-end, so the flow that continues to pressurize reduces significantly, back secondary compression work is reduced significantly, the load of low temperature separation process is significantly reduced.In lighting end, keep a part of carbon three to form, also make the freezing loads at different levels of further deep cooling more even, help engineering construction.Catalytically cracked gas contains various trace impurities usually in addition, generally walks with lighting end in sepn process, in the hydrogenator treating processes, can only handle the lighting end in the flow process of the present invention, has saved the energy consumption of the investment and the processing of hydrogenator.
Description of drawings
Accompanying drawing is a process flow diagram of the present invention
Embodiment
Embodiment 1: with reference to accompanying drawing, the present invention uses the separation of being rich in propylene, propane catalytically cracked gas in conjunction with ethylene unit and SHMP catalytic pyrolysis novel process in Shanghai Petrochemicals Company Ltd.The SHMP catalytically cracked gas enters cracking gas compressor C-201 system, when catalytically cracked gas is arrived 12atm by 1,2,3 section compressor compresses, enter the alkali cleaning unit and carry out alkali cleaning, the alkali cleaning unit is soda-wash tower T-201, remove sour gas, enter the drying unit drying then, drying unit is moisture eliminator inlet jar V-204, sets up C behind drying unit
3Presort tower (T-1201), C
3Presorting tower is general distillation tower, 43 ℃ of tower still temperature, tower top temperature is-26 ℃, tower still working pressure 10.5atm, the cat head working pressure is 11.1atm, overhead fraction is light constituents such as hydrogen, methane, ethene, ethane, propylene, and tower bottom distillate is propylene, propane, carbon four and carbon four above heavy constituent; C
3The overhead fraction of presorting tower is after trace impurity hydrogenation reaction bag hydrogenation reaction is removed impurity, enter the compression of process gas compression machine, hydrogenation reaction wraps into mouthful temperature 60-90 ℃, temperature out is 135 ℃ to the maximum, pressure is 9-30atm, be compressed to 37.4atm through process gas compression machine, cut after the compression enters ice chest and carries out low temperature separation process, five plates are installed in the ice chest stick up the formula interchanger, isolate hydrogen and low-pressure methane, enter demethanizing tower V-301 through the isolating cut of ice chest, 5.2 ℃ of tower still temperature, tower top temperature-86.4 ℃, tower still working pressure 32.1atm, the cat head working pressure is 31.6atm, the overhead fraction of demethanizing tower is a high pressure methane, the tower bottom distillate of demethanizing tower enters deethanizing column T-302,64.6 ℃ of tower still temperature, tower top temperature-10.9 ℃, tower still working pressure 28.7atm, the cat head working pressure is 27.4atm, the overhead fraction of deethanizing column enters ethylene rectification tower T-303, tower still temperature-6.8 ℃, tower top temperature-28.9 ℃, tower still working pressure 21.1atm, the cat head working pressure is 19.5atm, the tower bottom distillate of deethanizing column enters propylene rectification tower T-304, and the overhead fraction of ethylene rectification tower is a polymer grade ethylene, and the tower bottom distillate of ethylene rectification tower is an ethane.C
3The tower bottom distillate of presorting tower enters depropanizing tower, 70.7 ℃ of tower still temperature, and 12.6 ℃ of tower top temperatures, tower still working pressure 9.2atm, the cat head working pressure is 8.4atm, and the depropanizing tower overhead fraction enters propylene rectification tower, and the tower bottom distillate of depropanizing tower is C
4And C
5Heavy constituent, 55.1 ℃ of propylene rectification tower tower still temperature, 46.2 ℃ of tower top temperatures, tower still working pressure 19.6atm, the cat head working pressure is 21.2atm, the overhead fraction of propylene rectification tower is a chemical grade propylene, the tower bottom distillate of propylene rectification tower is a propane.
Embodiment 2, and catalytically cracked gas is arrived 13atm, C by 1,2,3 section compressor compresses
3Presort column overhead temperature-32 ℃, tower still working pressure 12.3atm, the cat head working pressure is 12.8atm, through 4,5 sections compressions, is pressurized to 38.5atm, all the other are identical with embodiment 1.
The present invention also can be applicable on the capacity expansion revamping of ethylene unit, along with successively going up of propylene product price Rise, existing ethylene unit can improve third by adopting the technology such as catalytic pyrolysis, propane freshening and Olefin conversion The alkene yield increases propylene product. Adopt C of the present invention3The pre-tower that divides makes the propylene, propane fraction of increase from C3Pre-come out at the bottom of dividing Tata, like this, " three machines " and the ice chest of existing ethylene unit, domethanizing column, Dethanizer, ethylene rectifying column and debutanizing tower just do not need to transform, and it is minimum that improvement cost is dropped to, and reaches Maximum economic benefit.