CN1020898C - Process for separating unconverted raw materials - Google Patents

Abstract

In the process of CO2 _- stripping urea, the optimal operating conditions used in the synthesis, stripping, carbamate condensation and decomposition steps at medium pressure have been obtained in order to reduce the amount of high-pressure steam required. These conditions need to be Selected according to the molar ratio of total _NH3 to total _CO2 in the synthesis procedure. The method of reducing the above-mentioned vapors is to directly recover the heat generated by the condensation of the carbamate in the said condenser and use it in the decomposition process at moderate pressure. In this way, the excess amount of low-pressure vapor produced which cannot be efficiently reused is also reduced.

Description

Process for separating unconverted raw materials

The part that the present invention relates to the urea synthesis method is improved.

The present invention relates to improve the thermo-efficiency of urea synthesis method key step particularly.

More specifically the present invention relates to the compression system of major tuneup urea synthesis, comprises CO ₂Gas is carried, and wherein the carbonic acid gas of part supply is used to the raw material of separating unconverted one-tenth urea, and these characteristics of improving one's methods are, unconverted raw materials separator exhaust gas discharged is carried out condensation again, makes the heat that produces can obtain efficient recovery and utilization.

Fig. 1 is according to synthesis process of urea schema of the present invention, and wherein the solid line representative wherein has the liquid material mobile to connect each unitary pipeline, and the two point dotted line is then represented wherein has the gas material mobile to connect each unitary pipeline.15 in pipeline is a pipeline of supplying with steam for heated separator 16.

Containing conventional CO ₂In the key step of the urea technique flow process that gas is carried, be at least 10 atmospheric high compressed steam heating by pressure, and equal synthesis pressure (for the peak pressure in the flow process) at pressure and carry out gas with the atmospheric carbon dioxide raw material of supply down and carry, make the raw material that does not change urea as yet into be decomposed into gaseous mixture.The gaseous mixture that gas puts forward from liquid phase, be substantially equal to condensation formation ammonium carbamate under the synthesis pressure at pressure, and the generation heat that produces is usually being that several atmospheric low-pressure steams are recovered at the most, and the low pressure steps that is used for urea synthesis goes, and for example is used for the decomposition of unconverted raw materials under low pressure or has been used to separate concentrating of resulting aqueous solution of urea behind the unconverted raw materials.

Although the low-pressure steam that reclaims is used for some steps of urea technique flow process, but still can remains excessive low-pressure steam, use it for urea technique suitable occasion in addition at present, for example be used for general heating.

The thermo-efficiency that it is believed that urea technique is high, even used a large amount of high compressed steam.As if but owing to generate the amount of the low-pressure steam that ammonium carbamate reclaimed also is very big, remedies used high compressed steam from the superfluous low-pressure steam that reclaims, and the amount of its deficiency is that less this point be it seems, used steam total amount is little in urea technique.

For example in 20 pages of " Kagaku Binran, applying portion " third editions, reveal: comprise solution recirculation, but do not comprise the urea technique that reclaims low-pressure steam that urea product per ton needs 0.9 to 1.2 ton of high compressed steam, and comprises conventional CO ₂The technology that gas is carried then requires 1.0 to 1.1 tons high compressed steam.

Superfluous low-pressure steam amount from system's discharging in one technology of back is 0.25 ton, therefore comprises conventional CO ₂The technology steam demand that gas is carried is situated between by mistake and is seemingly 0.75 to 0.85 ton, and this is to deduct 0.25 ton of resulting amount for 1.0 to 1.1 tons from total amount.

By above-mentioned high compressed steam and low-pressure steam being utilized the careful research of situation, the institute that considers urea technique confirms: conventional CO in steps ₂It is uneconomic that gas is put forward technology.

Certainly, problem is that the expense of high compressed steam is the expense that is higher than low-pressure steam.In addition, find suitable use to effectively utilize superfluous low-pressure steam, also be difficult actually.

In addition, the vapor volume that produces in the system is very big, and this fact means that the material volume that needs to handle also is very big in technology, and this just requires to adopt jumbo operating unit in each step.

In addition, comprise conventional CO in order to improve ₂The urea technique that gas is carried also need be taked an important measures, should reduce the amount of required expensive high compressed steam exactly, is worth even the superfluous low-pressure steam that reclaims also reduces to some extent.

Determining the principal element of required high compressed steam amount, is that ammonium carbamate is to the urea transformation rate.After the ratio of ammonia in the reactor for synthesis of urea and carbonic acid gas was given, transformation efficiency was high more, was used to decompose with the amount of the required high compressed steam of separating unconverted raw materials just few more.

Yet, in fact transformation efficiency on be limited to 70 to 75%, therefore, must reduce the amount of required high compressed steam, and can not realize the ratio of carbonic acid gas by improving ammonia with additive method.

In urea synthesis, when the mol ratio of total ammonia and total CO 2 in the synthesis stage is no more than about 3.5 the time, because synthesis pressure is low, make that can carry out gas to unconverted raw materials with high-level efficiency carries, after carrying, stays in gas therefore that the content of ammonia and carbonic acid gas is low in the urea synthesis solution.

When total ammonia in the synthesis stage to the molar ratio of total CO 2 as far as possible near 2.8 the time, required synthesis pressure is quite low, so gas is carried just more effective.Yet gas is proposed the in addition condensation of gaseous mixture of generation, fall too lowly to generate the required temperature of ammonium carbamate, so that can't on high level, reclaim heat energy.

As mentioned above, comprise conventional CO ₂The urea technique that gas is carried there is no need to liquefy and reclaim superfluous ammonia, when the pressure of urea synthesis solution is reduced to medium value, also seldom is necessary to take steps to come separating unconverted raw material.So this technology is in a kind of like this level: only with regard to the amount of the low-pressure steam that reclaims is big this point, be good to the evaluation of technology, although the amount of required high compressed steam is also big.Therefore this technology is not considered fully and can adopt the step of working under middle pressure, removes separating unconverted raw material, and the heat that reclaims is used for this step, and required high compressed steam amount is minimized.

In the synthesis technique of urea, when total ammonia is about 3.5 or it is when above to the mol ratio of total CO 2 in synthesis stage, the value of mol ratio is high more, it is big more that synthesis pressure just becomes, thereby the gaseous mixture of being proposed generation by gas is condensed also higher to form the required temperature of ammonium carbamate, therefore can on high level, reach recovery to heat, also more difficult although gas is carried.

By to reduce required high compressed steam total amount and improve in the key step at urea technique (decomposition that comprises synthesis stage, unconverted raw materials with separate and the generation of ammonium carbamate) recovery of heat carried out detailed research after, finished the present invention.

That is to say, the invention is characterized in the decomposition of having used the unconverted raw materials that under middle pressure, carries out and separate and absorption step that this middle pressure is to carry between the pressure (low pressure) of the pressure (equaling synthesis pressure) of step and decomposition and separating step between gas; The heat that produces when pressure is equaled to generate ammonium carbamate under the synthesis pressure, pass to decomposition and separating step under the middle pressure, do not adopt the heat-transfer medium of steam and so on, but directly by the heat exchange tube wall, and the heat that will transmit like this is used for decomposition and separating step under middle pressure.Like this, according to the present invention, those are also stipulated in the top condition (these steps influence the process of the whole technology of urea synthesis significantly) that is not less than the series of steps of being carried out under the middle pressure.

These top conditions are by designing many urea plants, and their various data and experience that actual motion obtained obtains later on.

According to the present invention, the reaction of ammonia and carbonic acid gas is carried out in synthesis stage, and the temperature and pressure that high-pressure reactor had wherein is to being optimum for the synthesis process of urea that obtains urea synthesis solution.

This solution that contains amino first ammonium, ammonia, water and urea emits from synthesis stage.Carry out gas by carbonic acid gas and carry with the part supply, and heating (being substantially equal to urea synthesis pressure) under certain pressure, from this solution, can obtain the gaseous mixture that some are called " waste gas ", and it is separated from urea synthesis solution.

Separated after the waste gas, the pressure of remaining urea synthesis solution is reduced to 12 to 24 kilograms per centimeter ²The medium value of (gauge pressure).In addition, the remaining unconverted raw materials of part contained in urea synthesis solution has become gaseous mixture, separates from resulting solution as second gaseous mixture with middle pressure.

After having separated second gaseous mixture, remaining urea synthesis solution passes through step-down and heating again, and the unconverted raw materials that part is residual is separated as the 3rd gaseous mixture.Remaining urea synthesis solution after having separated the 3rd gaseous mixture is carried out last step-down, residual unconverted raw materials is almost completely separated.The aqueous solution of urea that obtains like this is transported to purifying and concentration section goes.

For the feedstock recycle that will not change is got back to synthesis stage, second gaseous mixture contacted with the solution of pressurization (this solution contains the 3rd gaseous mixture, that is substantially equal under the second separation of gaseous mixture pressure its absorption at pressure), thereby be absorbed in the solution.

Second solution that contacts with second gaseous mixture and generate is pressurized to the pressure that is substantially equal to urea synthesis at least, and gaseous mixture of itself and synthesis stage discharging is contacted, and then contacts with above-mentioned waste gas (that is first gaseous mixture).At this moment there is first gaseous mixture of q.s to be absorbed in second solution.

The 3rd solution that first gaseous mixture of q.s is absorbed second solution into and form, and unabsorbed part in first gaseous mixture all are recirculated to synthesis stage.

(this solution is substantially equal to generate under the pressure of second gaseous mixture at pressure when the solution of second gaseous mixture and pressurization, absorbed the 3rd gaseous mixture) contact, so that the heat that mixed gas is generated when being absorbed in the solution is recovered and utilizes.

When first gaseous mixture when pressure equals under the urea synthesis pressure to contact with second solution substantially, in solution, generate ammonium carbamate thereby produced heat energy, the part of this heat is directly passed to the urea synthesis solution of middle pressure by heat exchanger wall, to be used for separating second gaseous mixture, simultaneously, remaining that part of heat then is used to produce steam.

When urea synthetic is that total ammonia is when carrying out under 2.8 to 3.4 the situation to the mol ratio of total CO 2 in synthesis stage, the pressure-controlling of synthesis stage is in 140 to 170 kilograms per centimeter ²In (gauge pressure) scope, unconverted raw materials decomposed with separating to form the temperature required and pressure of first mixed gas then should control like this, so that after having separated first gaseous mixture, the ammonia and the total carbon dioxide content that remain in the urea synthesis solution remain on 13 to 24%(weight) scope in.In addition, second separation of gaseous mixture is to be 12 to 18 kilograms per centimeter at pressure ²Carry out under (gauge pressure), decompose with separating unconverted raw materials with generate the required temperature of second gaseous mixture then like this control so that the ammonia and the total carbon dioxide content that remain in after having separated second gaseous mixture in the urea synthesis solution remain on 5 to 11%(weight) scope within.

When urea synthesis is the molar ratio of total ammonia and total CO 2 in synthesis stage when carrying out under greater than 3.4 to 4.2 situation, the pressure-controlling of synthesis stage is in 160 to 190 kilograms per centimeter ²In (gauge pressure) scope, unconverted raw materials decomposed with separating to form the required temperature and pressure of first gaseous mixture then should control like this, so that after having separated first gaseous mixture, the ammonia and the total carbon dioxide content that remain in the urea synthesis solution remain on 20 to 30%(weight) scope in.In addition, second separation of gaseous mixture is to be 14 to 20 kilograms per centimeter at pressure ²Carry out under (gauge pressure), decompose with separating unconverted raw materials and then should control like this, remain on 6 to 12%(weight so that separated the ammonia and the total carbon dioxide content that remain in the urea synthesis solution after second gaseous mixture to generate the required temperature of second gaseous mixture) scope in.

When urea synthesis is that the pressure-controlling of synthesis stage is in 180 to 210 kilograms per centimeter when the mol ratio of total ammonia of synthesis stage and total CO 2 is carried out under greater than 4.2 to 5.0 situation ²In the scope of (gauge pressure), unconverted raw materials decomposed with the temperature and the pressure that separate to form first gaseous mixture then should control like this, so that after having separated first gaseous mixture, the ammonia and the total carbon dioxide capacity that remain in the urea synthesis solution remain on 25 to 35%(weight) scope in.In addition, second separation of gaseous mixture is to be 16 to 24 kilograms per centimeter at pressure ²Carry out under (gauge pressure), decompose with separating unconverted raw materials and then should control like this, so that separated the ammonia that remains in behind second gaseous mixture in the urea synthesis solution and the total content of carbonic acid gas remains on 7 to 13%(weight with the temperature that generates second gaseous mixture) scope in.

For synthesis system being controlled under the above-mentioned various condition, take the general automatic control system of feedback-type to suit, can certainly adopt the automatic control system of direct digital control formula.

According to the present invention, the mol ratio of total ammonia and total CO 2 can both reach high thermo-efficiency to fixing in 2.8 to 5.0 the scope in synthesis stage.In addition, the present invention has improved the recovery of heat and utilization, and these heats are to carry the waste gas that obtains in the pressure therapeutic method to keep the adverse qi flowing downward that pressure is substantially equal to synthesis stage to produce when condensation becomes ammonium carbamate, and in 12 to 20 kilograms per centimeter ²Under the middle pressure of (gauge pressure), the waste gas that generates from urea synthesis solution produces when condensation.

According to method of the present invention, the temperature and pressure of each step is Be Controlled all, so that required high compressed steam amount reduces, in addition, the limited low-pressure steam output of operability has also reduced.

According to the present invention, with the gas formulation unconverted raw materials is decomposed and separates and generate ammonium carbamate (according to prior art, these two all is to carry out under pressure equals the pressure of synthesis stage fully), partly under middle pressure, its decomposition and separation and absorption are replaced, like this, the part assembly of forming condenser (ammonium carbamate generates therein) can use as well heater, therein the decomposition of unconverted raw materials is carried out with separating under middle pressure, volume with the well heater that reduces the middle pressure device, in addition, temperature head between two kinds of fluids of heat-shift has strengthened mutually, thereby having reduced the heat exchange area of well heater, this has just caused the reduction of equipment manufacturing cost.

Embodiment 1

Hereinafter, all amounts of representing with kilogram are all by per hour calculating, simultaneously, come out from reactor 3 tops via pipeline 24 that contained ammonia and the amount (representing with kilogram) of carbonic acid gas all omit the gaseous mixture of to be recycled and recirculation, the situation of embodiment 2 and embodiment 3 is also identical.

In Fig. 1, add 23611 kilograms of liquid ammonias to be used for urea synthesis via pipeline 1 to reactor 3, respectively via pipeline 12 and 13, the adding temperature is that the aqueous solution and the temperature of 178 ℃ unconverted raw materials are the gaseous mixture of 178 ℃ unconverted raw materials in reactor 3 simultaneously.

Is 90266 kilograms via pipeline 12 and 13 via the unconverted raw materials total amount of answering device 3 to add, and amount of water is 10833 kilograms simultaneously.Total ammonia is 3.2 to the mol ratio of total CO 2 in the reactor 3.

Amount increase owing to the ammonium carbamate aqueous solution that adds via pipeline 12, and the amount of the gaseous mixture that adds via pipeline 13 reduces, and the amount that makes in the reactor 3 the carboxylamine ammonia that generates is when reducing, the heat that produces in reactor 3 has also just reduced, thereby has reduced the temperature in the reactor 3.Otherwise, amount minimizing owing to the ammonium carbamate aqueous solution that adds via pipeline 12, and the amount of passing through the gaseous mixture of pipeline 13 addings increases, and when the ammonium carbamate amount that generates is increased, the heat that produces in reactor 3 also just increases, thereby has improved the temperature in the reactor 3.Like this, just the temperature in the reactor 3 is remained on prescribed value.

The reactor 3 of urea synthesis remains on 145 kilograms per centimeter ²Under the state of (gauge pressure) and 185 ℃, so that ureagenetic transformation efficiency is 60%.

Contain 41667 kilograms urea, 59708 kilograms of raw materials that do not change and 23333 kilograms water from the urea synthesis solution that reactor 3 is discharged, this solution is added to the top that gas is carried device 5 via pipeline 4, and the pressure that gas is carried device equals the internal pressure of reactor 3.

The rare gas element that is collected in reactor 3 tops contains aerobic (it is in order to prevent the corrosion of equipment that oxygen is added reactor 3) and other components (being brought in the reactor 3 as being contained in impurities in raw materials), this rare gas element is drained from the pipeline 24 at reactor 3 tops with the gaseous mixture form together with ammonia, carbonic acid gas and water.

Be added to gas and carry the urea synthesis solution at device 5 tops and flow downward, carry the internal surface of the many vertical heating tubes in the device 5 and flow down with filminess along being contained in gas.

As mentioned above, when urea synthesis solution flows downward, by adding 17 kilograms per centimeter via pipeline 6 ²The heating of the outside surface of the high-pressure steam of (gauge pressure) heating heating tube and be that 140 ℃ 30588 kilograms carbonic acid gas carries out gas and carries via the temperature that pipeline 2 adds makes wherein contained unconverted raw materials be decomposed into gaseous mixture.So the gaseous mixture that generates is separated from liquid phase, rises to enter vertical heating tube.

Carry the urea synthesis solution that device 5 bottoms emit from gas and contain 41667 kilograms of urea, 16917 kilograms of unconverted raw materials (wherein containing materials such as ammonia, carbonic acid gas) and 20042 kg of water, temperature is 170 ℃, at reducing valve 9 places pressure is reduced to 15.5 kilograms per centimeter by pipeline 8 ²(gauge pressure).Then, the urea synthesis solution after the step-down is heated by the heat exchangers that are located in the condenser 10, be contained in part unconverted raw materials in the urea synthesis solution with decomposition, so generated gas-liquid mixture.This mixture is added in the separator 16, use the steam that adds via pipeline 15 to be heated, contain 41667 kilograms in urea, ammonia and 6000 kilograms of carbonic acid gas (total amount) and 18625 kg of water in the rough aqueous solution of urea that gives off, 152 ℃ of solution temperatures are discharged by pipe 17 from the bottom of separator.

Rough aqueous solution of urea, is transported in follow-up purifying and the enrichment step again and goes in the decompression of reducing valve 18 places by pipeline 17, and this part does not show in Fig. 1.

Contain 10917 kilograms of ammonia and carbonic acid gas (total amount) from the gaseous mixture of separator 16 top discharges, and 1417 kilograms water, add resorbers 20 via pipeline 19, the pressure of resorber keeps the middle pressure identical with separator 16.

In reducing valve 18 downstream recovery 12125 kilograms of unconverted raw materials aqueous solution of 50 ℃, and be added in the resorber 20, to absorb 113 ℃ the gaseous mixture of coming in via pipeline 19 via pipeline 21.

The current most of heat that produces that absorbs is used to the concentrating urea aqueous solution.

Owing to contain 16917 kilograms of unconverted raw materials and 7542 kg of water in the aqueous solution that above-mentioned absorption step generates, be pressurized to through pump 22 and equal synthesis pressure at least, be transported to scrubber tower 25 via pipeline 23 then, to absorb contained ammonia and carbonic acid gas in the rare gas element that adds via pipeline 24.The aqueous solution that produces is transported to condenser 10 via pipeline 11.

Carry at gas and to separate in the device 5 and to be condensed in the aqueous solution of above-mentioned unconverted raw materials via the portion gas mixture that pipeline 7 is transported to condenser 10, to form ammonium carbamate, degree of condensation depends on the temperature of reactor 3.

The heat part that current regeneration is produced, that is be equivalent to that part of of 9988 kilograms of steams, be used for heating from gas carry device 5 and by step-down urea synthesis solution, and the remainder of heat to be used to produce 32410 kilograms, pressure be 4 kilograms per centimeter ²The low-pressure steam of (gauge pressure) is reclaimed through pipeline 14.

The aqueous solution of the unconverted raw materials that generates in condenser 10 returns reactor 3 via pipeline 12 recirculation, and is added to uncooled part in the gaseous mixture that goes in the condenser 10, then returns in the reactor 3 via pipeline 13 recirculation.

At conventional CO ₂Gas is carried in the technology, no matter is the condenser 10 that is used for directly reclaiming heat, or separator 16 these kind equipments, all less than adopting.Therefore, carry in the device 5 at gas and will consume a certain amount of high compressed steam, in an amount equivalent to the required heat of separator 16, and along with gas is proposed the increase of the high compressed steam amount that consumes in the device 5, the amount that the low-pressure steam that using value is lower produces has also increased.

Can from numerous condensers, select the structure of condenser 10, temperature difference between the liquid reaction mixture after will considering institute's heat requirements in the separator 16 during selection and reclaiming ratio, the condenser 10 of heats through pipeline 14 and pass through reducing valve 9 or the like factor.For example, by after the reducing valve 9, urea synthesis solution can resemble as shown in Figure 1 by the inside of heat exchanger tube, also can adopt the structure by the outside of pipe.

Embodiment 2

23611 kilograms liquefied ammonia is added in the reactor 3 via pipeline 1, adds reactor 3 via pipeline 12 and 13 gaseous mixture with the unconverted raw materials of the aqueous solution of 180 ℃ unconverted raw materials and 180 ℃ respectively simultaneously.Via pipeline 12 and 13 ammonia and the total carbon dioxide capacities that add is 90766 kilograms, and the water yield of adding is 11042 kilograms.Reactor 3 remains on 175 kilograms per centimeter ²Under the state of (gauge pressure) and 190 ℃, be 68% so that wherein generate the urea transformation rate.Contain 23542 kilograms in 41667 kilograms in urea, 60208 kilograms of unconverted raw materials and water in the urea synthesis solution of discharging via pipeline 4.In reactor 3, the mol ratio of total ammonia and total CO 2 is 4.0.

Via pipeline 6 with 19 kilograms per centimeter ²The high compressed steam of (gauge pressure) adds gas and carries device 5, simultaneously 30558 kilograms (identical with embodiment 1 consumption) 140 ℃ carbon dioxide pressurized is added wherein via pipeline 2.

The temperature of proposing device 5 bottoms dischargings from gas is 175 ℃ a urea synthesis solution, contains the water of 41667 kilograms urea, 21458 kilograms of unconverted raw materials and 20667 kilograms, and this solution stream piping 8 also drops to 17 kilograms per centimeter at reducing valve 9 places with pressure ²(gauge pressure).Urea synthesis solution after the step-down is delivered to the heat exchanger in the condenser 10.

The temperature of discharging from separator 16 bottoms is 160 ℃ a urea synthesis solution, contains 41667 kilograms urea, 6000 kilograms unconverted raw materials and 18625 kilograms water, and this solution is reducing pressure at reducing valve 18 places by pipeline 17 backs.

From the gaseous mixture of separator 16 top discharges, contain 15458 kilograms unconverted raw materials and 2042 kilograms water, it is reinforced to resorber 20 via pipeline 19.

12125 kilograms of temperature have been reclaimed from reducing valve 18 downstreams (not drawing Fig. 1) and are 55 ℃ the unconverted raw materials aqueous solution.This unconverted raw materials aqueous solution is fed to resorber 20 via pipeline 21, to absorb 110 ℃ the gaseous mixture that feeds in raw material via pipeline 19.

The current aqueous solution that generates that absorbs contains 21458 kilograms of not converting substances and 8167 kg of water, makes its pressure equal synthesis pressure through pressurization, is used for absorbing contained useful component in the gaseous mixture that adds in the scrubber tower 25 via pipeline 24.The aqueous solution that produces is added in the condenser 10 via pipeline 11.

Condensation is to produce heat in condenser 10 to carry the gaseous mixture that device 5 carries via pipeline 7 by gas, and degree of condensation depends on the temperature of reactor 3.Part heat, that is the heat that is equivalent to 13340 kilograms of steams is used for separator 16, remaining heat then is recovered as 20603 kilograms 5 kilograms per centimeter via pipeline 14 ²The low-pressure steam of (gauge pressure).

Embodiment 3

Add 23611 kilograms of liquid ammonias via pipeline 1 to reactor 3, simultaneously in reactor 3, add the gaseous mixture of unconverted raw materials and the aqueous solution of unconverted raw materials via pipeline 12 and 13, that is to add total amount be 101885 kilograms ammonia and carbonic acid gas and 13125 kg of water, and both temperature are 181 ℃.Reactor 3 is 200 kilograms per centimeter at pressure ²(gauge pressure) and temperature are under 190 ℃, and the transformation efficiency with 71% generates urea, and the urea synthesis solution that discharges from reactor 3 via pipeline 4 contains 41667 kilograms in urea, 25625 kilograms in 71297 kilograms of unconverted raw materials and water.The mol ratio of total ammonia and total CO 2 is 5.0 in the reactor 3.

Urea synthesis solution is added to the top that gas is carried device 5 via pipeline 4, and gas is carried utensil the pressure identical with reactor 3, urea synthesis solution 21 kilograms per centimeter of sending into via pipeline 6 ²The high compressed steam heating of (gauge pressure), and carried from 30558 kilograms of carbon dioxide pressurized gas of 140 ℃ of pipeline 2 addings.

The urea synthesis solution of proposing device 5 bottoms dischargings from gas contains 41667 kilograms of urea, 30334 kilograms of unconverted raw materials and 22667 kg of water, and solution temperature is 187 ℃, by pipeline 8 and at reducing valve 9 places pressure is reduced to 18.5 kilograms per centimeter ²(gauge pressure).Urea synthesis solution after the step-down is sent in the heat exchanger in the condenser 10.

Give off urea synthesis solution from separator 16 bottoms via pipeline 17, wherein contain 19458 kilograms in 41667 kilograms in urea, 6000 kilograms of unconverted raw materials and water, solution temperature is 164 ℃.

Contain 24334 kilograms of unconverted raw materials, 3209 kilograms in water from the top expellant gas mixture of separator 16, be added to resorber 20 via pipeline 19, the pressure that the latter has is identical with the pressure of separator 16.

Reclaimed 12958 kilograms of the aqueous solution of 58 ℃ unconverted raw materials from the downstream (Fig. 1 does not draw) of reducing valve 18, be added to resorber 20 via pipeline 21, to absorb 107 ℃ the gaseous mixture that adds via pipeline 19.

The high concentrated aqueous solutions that generates in resorber 20 contains 30334 kilograms of unconverted raw materials and 10167 kg of water, through be pressurized to equal synthesis pressure at least after, being delivered to scrubber tower 25 again, to remove to absorb unconverted raw materials contained in the gaseous mixture that adds via pipeline 24 complete to basic absorption.The aqueous solution that obtains is added in the condenser 10.Gaseous mixture is added to via pipeline 7 and carries out condensation in the condenser 10, and to produce heat, degree of condensation depends on the temperature of reactor 3.Part in the heat, that is be equivalent to that part of separator 16 that is used for of 19755 kilograms of steams.Remaining heat part reclaims via pipeline 14, and obtaining 5044 kilograms, pressure is 5 kilograms per centimeter ²The low-pressure steam of (gauge pressure).

Claims (1)

1. A method for separating unconverted raw materials, the method comprising: feed ammonia and carbon dioxide to the synthesis section, the temperature and pressure of this synthesis section are suitable for the synthesis of urea, to generate a urea synthesis solution, which contains urea, carbamic acid Ammonium, ammonia, carbon dioxide and water; from this synthesis solution, that part of the raw material which has not been converted to urea is separated as a first gas mixture by stripping and degassing with part of the carbon dioxide feedstock at a pressure substantially equal to the urea synthesis pressure Heating; After the first gas mixture is separated, the remaining synthetic solution is decompressed; the unconverted raw material is separated as the second gas mixture from the obtained urea synthetic solution by means of heating; Under pressure of the second gas mixture, the second gas mixture is contacted with the first solution returned by the remaining unconverted raw material to be recycled to the synthesis section to generate the second solution; recovery and utilization of the generated second solution in the process Heat; contacting the first gas mixture with the second solution at a pressure substantially equal to that of urea synthesis to form ammonium carbamate, transferring a portion of the heat generated during the formation of ammonium carbamate directly to the urea through the walls of the heat exchanger tubes Synthesis of a solution to separate the second gas mixture and use the remaining heat partly to generate steam; the mixture obtained by contacting the first gas mixture with the second solution is sent to the synthesis section; characterized in that: When the mol ratio of total ammonia and total carbon dioxide fed to the synthesis section is controlled in the range of 2.8 to 3.4, the pressure of the synthesis section is controlled in the range of 140 to 170 kg/ ^cm2 (gauge pressure), and the first gas is separated The ^total amount of ammonia and carbon dioxide in the remaining urea synthesis solution after the mixture is controlled in the range of 13 to 24% (weight), and the separation of the second gas mixture is at a pressure of 12 to 18 kg/cm (gauge pressure) Carry out under, at the same time, the total amount of ammonia and carbon dioxide in the remaining urea synthesis solution after separating the second gas mixture is controlled within the scope of 5 to 11% (weight), When the mol ratio of total ammonia and total carbon dioxide fed to the synthesis section is controlled in the scope greater than 3.4 to 4.2, the pressure of the synthesis section is controlled in the scope of 160 to 190 kg/ ^cm (gauge pressure), and the first The total amount of ammonia and carbon dioxide in the remaining urea synthesis solution after the gas mixture is controlled within the scope of 20 to 30% (weight), and the separation of the second gas mixture is at a pressure of 14 to 20 kg/cm (gauge ^pressure ), simultaneously, the total amount of ammonia and carbon dioxide in the remaining urea synthesis solution after separating the second gas mixture is controlled within the scope of 6 to 12% (weight), When the mol ratio of total ammonia and total carbon dioxide fed to the synthetic section was controlled in the scope greater than 4.2 to 5.0, the pressure of the synthetic section was controlled in the scope of 180 to 210 kg/ ^cm (gauge pressure), separated the first The total amount of ammonia and carbon dioxide in the remaining urea synthesis solution after the gas mixture is controlled in the range of 25 to 35% (weight), and the separation of the second gas mixture is at a pressure of 16 to 24 kg/cm (gauge ^pressure ) The total amount of ammonia and carbon dioxide in the remaining urea synthesis solution after separating the second gas mixture is controlled within the range of 7 to 13% (weight).