RU2373148C2 - Pipe reactor and device for producing composition of urea and ammonium sulphate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: pipe reactor for producing a composition of urea and ammonium sulphate includes a pipe-like housing and a head, where the head of the reactor has a device for axial introduction of acid, device for introducing ammonia, device for introducing urea and a reaction chamber, in which reaction of acid with ammonia before getting in contact with urea is intensified by creating incipient turbulence when introducing said reagents. In addition to the pipe reactor, the device for producing a composition of urea and ammonium sulphate includes a separator for separating vapour, formed from suspension of urea and ammonium sulphate, and a device for receiving this vapour.

EFFECT: provision for conditions for reacting an acid and a base in a stream of a component which is sensitive to heating and acid action without decomposition.

26 cl, 2 dwg, 4 tbl

Description

Field of Invention

The present invention relates to the design of a selective tubular reactor and installation for the production of various mixtures, allowing to solve the general problem of the preferred reaction of the acid and base in the stream of a component or mixture of components that are sensitive to heat and / or acid, without decomposition or with the preferred decomposition of one of components. More specifically, a reactor is used to produce a composition of urea and ammonium sulfate (MCA).

State of the art

Tubular reactors for the production of ammonium salts are described, for example, in US Pat. No. 2,568,901, US Pat. No. 2,755,176 and US Pat.

Currently, the commercial production of the urea and ammonium sulfate (MCA) composition is carried out by physically mixing the two compounds by introducing powdered solid ammonium sulfate into the molten urea in the granulation step, for example, using drums or vats, as described in US 3785796. This method can call the "hard way." This method is quite simple. Nevertheless, it has a number of serious drawbacks both from an economic point of view and from the point of view of process efficiency.

No. 3,928,015 describes a two-step reaction for the synthesis of ammonium sulfate (CA) in a urea solution. The bisulfate solution and ammonia react in a urea solution to form a substantially anhydrous CA in a mixture with molten urea; this process is carried out in a simple and inexpensive tank or tube type reactor.

Bisulfate corresponds to the product obtained by the reaction of one mole of sulfuric acid with one mole of ammonia, while ammonium sulfate corresponds to the product obtained by the reaction of one mole of sulfuric acid with two moles of ammonia. The first ammonization of sulfuric acid (which results in bisulfate) is more exothermic than the second.

On the other hand, obtaining CA in urea solution in situ (in place) is rather difficult, since the acid quickly reacts with urea, which leads to loss of urea. If the losses are too high, this circumstance significantly limits the advantages of any liquid method in comparison with the solid method for the production of MSA. Bisulfate is less aggressive with urea than sulfuric acid. According to US Pat. No. 3,928,015, bisulfate is synthesized separately to minimize urea decomposition. In this case, there is an incomplete use of the heat released during the first ammonization.

Disclosure of invention

The problem to which the present invention is directed, is to create a reactor design designed to carry out the reaction between the acid and the base in the flow of a component that is sensitive to heat and / or acid, without decomposition. Another task is to create a reactor designed for the production of ISA. Another objective is to create an installation, especially for the production of ISA.

In accordance with the invention, the solution of these and other problems is achieved by creating a reactor, described below; The invention is defined and characterized in detail in the attached claims.

Brief Description of the Drawings

The invention is further illustrated with reference to the figures, where:

figure 1 shows a tubular reactor with a preliminary reactor, mixer and scrubbers;

figure 2 shows a standard reactor with a crosshair of pipes.

The implementation of the invention

Thus, the present invention relates to a tubular reactor, in particular for the production of MSA, and comprising a tubular body and a reactor head, the reactor head including an axial acid introduction device and an ammonia introduction device. Ammonia can be in free and / or bound form and / or as part of a mixture. In addition, there is a urea injection device and a reaction chamber in which the acid reaction with ammonia is intensified before contact with urea. The tubular reactor can also be used to react a different acid and another base with a component that is sensitive to heat and / or acid, other than urea.

Preferably, upstream of the reactor head is a pre-reactor for pre-neutralizing the acid. The pre-reactor may be a tubular reactor or a tank type neutralizer. Preferably, the pre-reactor is part of the main tubular reactor and has an inlet for ammonia or another base. Ammonia can be in free and / or bound form and / or as part of a mixture. Upstream of the head of the reactor may also be a mixer for diluting the acid. The head of the reactor preferably has a narrowing at its outlet end. The ammonia or other base introduction device has an inlet in communication with an annular chamber surrounding the acid introduction device. The inlet is preferably located tangentially. The annular chamber at the outlet end has the shape of a cone or an open end. A device for introducing urea or another sensitive component has an inlet and an annular chamber surrounding an injection device (injector) of ammonia or another base.

The invention also relates to an apparatus for producing a composition of urea and ammonium sulfate and comprising a tubular reactor consisting of a tubular body and a reactor head, wherein the reactor head includes an axial acid injection device, an ammonia injection device, a urea injection device and a reaction chamber in which the reaction of acid and ammonia can take place before they are brought into contact with urea, a separator for separating the vapor generated from the MCA suspension, and a device for receiving this wow couple. Ammonia may be in a free and / or bound state and / or as part of a mixture.

Preferably, a pre-reactor is located in front of the reactor head, which has an ammonia introducer, an acid introducer and a reaction chamber. Upstream in front of the reactor head can be a mixer for diluting the acid. The steam receiving device is preferably a scrubber, which may have a two-stage structure. The scrubber preferably has a washing solution recirculation device in the urea inlet 7 and / or in the acid injection device (injector). An evaporator tank may be located behind the separator. The production of the urea and ammonium sulfate composition is preferably the final process in the operation of the urea plant.

The following description is based on the production of ammonium urea sulfate (MCA), i.e. urea and ammonium sulfate compositions. Urea is sensitive to heat and to the effects of sulfuric acid. Ammonium sulfate is formed in the urea solution as a result of the reaction of sulfuric acid with ammonia with the maximum possible protection of the urea component from severe destruction.

However, the same principles and equivalent concepts can be used for other mixtures in any case where such in situ synthesis is used, which is of greater interest compared to a single synthesis and the subsequent stage of simple mixing.

In situ synthesis has several advantages. The tubular reactor is simple enough to control, as well as start it and complete its work. The heat generated during the synthesis of ammonium sulfate (CA) allows the use of water evaporation from a urea solution, which makes it possible to exclude the stage of evaporation, as well as the consumption of the substance (in particular, steam). In situ synthesis makes it possible to obtain very small CA crystals, especially suitable for the subsequent granulation process, and to obtain a more homogeneous product compared to the product obtained by the solid method. Finally, the use of in situ synthesis of MCA in an installation with full or partial urea recirculation can significantly increase the efficiency of urea use.

Description of the method of obtaining ISA in situ

Of particular interest is the in situ production of ISA as the final process for the urea plant.

Components and reagents are introduced into the tubular reactor. The stream leaving the reactor is fed to a separator to separate the vapor obtained from the MCA slurry. Rapid evaporation of the liquid solution can be carried out immediately or subsequently in vacuum to obtain the required water content required for the subsequent granulation process, while the vapor is absorbed by the acid until, for example, condensation.

The washing solution from the steam scrubber and the washing solution from the granulation section are recycled to the inlet of the reaction section or used for other purposes outside the installation (batteries limit, BL) (i.e. outside the process in question).

Four components must be present in the tubular reactor: sulfuric acid (free or pre-neutralized as ammonium bisulfate), ammonia (free or bound as carbamate), urea and water (BL and / or washing solution, in addition to the water contained in the feed substances, acid, ammonia, urea).

Sulfuric acid reacts with ammonia and forms CA in a urea solution, while the heat released during the synthesis evaporates water to produce steam.

A certain proportion of urea decomposes due to heating and the presence of acid and is either polymerized to carbamylurea and other substances, or hydrolyzed to carbon dioxide and ammonia. Such ammonia is neutralized by sulfuric acid and, as a result, is taken into account in the mass balance to obtain the correct final ratio of N-NH ₃ to N-urea in the final product.

Water is added to the reactor to balance the balance of heat and water depending on the amount of synthesized CA, the concentration of the urea solution supplied to the tubular reactor, the desired final water content and the amount of washing solution to be recycled.

The product from the tubular reactor is sent to the separator tank to separate the process steam from the MCA solution.

To limit the high temperature that stimulates the undesired decomposition of urea, as well as to achieve the required water content in the solution, which, for example, is sprayed into a granulator with a fluidized bed (usually ~ 2-5% water), the MCA solution is preferably quickly evaporated in vacuum.

Such evaporation can be carried out directly in the separator of the tubular reactor or in a second tank, the so-called evaporation tank. The use of such an evaporation tank avoids the complication of the vacuum system (necessary for the extraction of condensate and non-condensable components), but requires duplication of the scrubber of the process steam and the condensation system in case the steam from the separator must condense. Therefore, such a configuration of the separator in combination with an evaporation tank should be studied in each case; nevertheless, it is highly advisable to use it when using a high-capacity plant and consuming the outgoing gaseous ammonia by a urea plant in the presence of a large amount of non-condensable components (such as СО ₂ released during the decomposition of carbamate).

The steam generated in the reactor and separated in the separator contains mainly steam itself, but also includes some unreacted ammonia, carbon dioxide, air and droplets of the MCA solution.

Depending on the quality of the introduced components, minor proportions of various non-condensable components (NOx, SOx ...) may be present, which are not formed in the reactor in significant quantities.

The scrubber is a wet scrubber. Drops of solution are captured by the wash solution. The scrubber is partially acidified with sulfuric acid to capture ammonia in parallel.

The design of the scrubber preferably provides for two separate processing steps: in the first stage, the urea drops are captured by a sufficiently neutral washing solution, and in the second stage, ammonia is captured by acid. Such an implementation avoids increased decomposition of urea due to the strong acidification of urea containing a washing solution.

If the scrubber has the indicated two-stage structure, the washing solution for the second stage is preferably systematically recycled to the sulfuric acid line feeding the reactor, since there is almost no urea in this solution. Urea containing a washing solution after the first stage is preferably not recycled directly to sulfuric acid in order to avoid an increased degree of decomposition of urea. This solution can be mixed with the washing solution from the granulation section and introduced into the urea solution supplied to the tubular reactor. Alternatively, it can be recycled to the urea concentration section, withdrawn from the system, or used as additional water in the scrubber of the granulation section.

TUBULAR REACTOR DESCRIPTION

The tubular reactor is characterized by strong and short turbulence for mixing the reactants, allowing them to be immediately brought into contact and the reaction can be carried out. The residence time of reagents in such equipment, as a rule, should not be more than 0.2 s.

The design should provide selective interaction of the reagents without decomposition of urea, and also exclude the possibility of destruction of the tubular reactor material by acid or any other reagent. Therefore, the acid is introduced into the reactor along the axis of the reactor, the initial turbulence increases to immediately begin the reaction.

A quick reaction minimizes the risk of free small droplets of acid coming into contact with the wall of the tubular reactor, leading to steel corrosion or the appearance of hot spots that can damage, for example, the Teflon coating.

To increase the initial turbulence, ammonia is preferably introduced in gaseous form. Its speed is high, its direction is tangential to the dispersion of acid in order to improve its atomization and increase initial turbulence.

To limit the loss of urea, it is necessary to soften the acid if possible by providing more complete contact between the acid and ammonia without contact with urea, if possible, first neutralize the acid by converting it to ammonium bisulfate, which is much less aggressive for urea, and to keep the temperature as low as possible. those. provide as low a pressure drop as possible while maintaining a high degree of turbulence.

In order to be efficient, a tube reactor of an optimal design requires high turbulence and, consequently, pressure reduction. If the reactor is not fully loaded (i.e., there is a low flow in each section of the reactor), its efficiency decreases rapidly. In the case of MSA, this means higher losses of urea and ammonia, which fall into the scrubber.

On the contrary, if the capacity of a normally loaded reactor (see above) is slightly increased, then its efficiency will increase and the pressure decrease will also increase. However, this causes an increase in the temperature in the reactor, which can lead to destruction of the material of the reactor, as well as some components, for example, urea, in the case of in situ preparation of MCA

Thus, the tubular reactor has an ideal design for a given loading range, preferably from 80% to 110%.

The tubular reactor for the production of MSA includes several components that depend on the method and raw materials used. It is further described with reference to FIG. 1.

1 shows a tubular reactor including a pre-mixer, a preliminary reactor, a reactor head and a reactor vessel. The head and body of the reactor are present in all varieties of the reactor, while the use of a pre-mixer and pre-reactor depends on the conditions of the process.

The head part 1 of the reactor has a reaction chamber. It is the zone between the end of the acid introduction cone 3A and the end of the ammonia introduction cone 2A, in which ammonia and acid come into contact and react. The head part has a tubular shape, at its output end there is a narrowing 1A. It includes an axial acid injector 3, 3A. Ammonia is introduced tangentially through the inlet 8 into the ammonia injector 2, forming a first annular chamber surrounding the acid injector. At the output end of the ammonia injector there is a cone 2A. Urea is fed through an inlet 7 into a second annular chamber surrounding the ammonia injector. The reactor vessel 14 is straight across and ends with a constriction of 1A.

In some cases, as described below, before the introduction of urea, the acid can be partially neutralized with some ammonia in a separate reactor called a pre-reactor. The preliminary reactor is located upstream in front of the reactor head 1 and has an inlet 9 for introducing ammonia into the annular chamber surrounding the axial acid injection device, where the acid injector 4 has a conical end 4A.

The pre-mixer 12 is located upstream in front of the pre-reactor and can be used on the sulfuric acid line to dilute the acid 5 with water 13 or with a washing solution 11.

Figure 1 also shows a two-stage purification, where urea is captured in the first stage S1, ammonia is captured by acid 6 in the second stage S2.

Design optimization of the ISA tubular reactor

The design of the tubular reactor MSA can be optimized in accordance with the balance of ammonia, taking into account the water balance of the installation and the optimization of the energy balance.

Ammonia balance

When choosing the design of a tubular reactor, it is necessary to consider the following two cases.

CASE A: Ammonia must be partially or completely supplied in the process in addition to the urea solution to obtain the required class of MCA.

CASE B: the urea solution contains ammonia in the form of carbamate or free ammonia in an amount to obtain the required class of MCA.

Water balance

Water balance is mainly a function of the following parameters:

- the water content in the urea solution supplied to the tubular reactor;

- heat of reaction;

- the ratio between SA synthesized in the reactor and CA synthesized in a steam scrubber (see below);

- vacuum created in the evaporation tank;

- recirculation of washing solutions.

Energy balance

The energy released in the tubular reactor during the synthesis allows you to evaporate more water and, therefore, to supply a less concentrated urea solution to the tubular reactor, which is more favorable from an energy point of view.

On the contrary, the energy released during the reaction in the steam scrubber does not contribute to the concentration of the MCA solution, but requires the introduction of additional water into the scrubber.

The more SA is synthesized in the reactor (and not in the scrubber), the better the energy balance and water balance.

CASE A - ammonia is supplied separately from urea, in whole or in part

If ammonia is supplied partially or completely separately, it is possible to provide a more complete contact of the acid with ammonia before they are brought into contact with urea.

Typically, the molar excess of ammonia relative to sulfuric acid in the tubular reactor is 2%, mainly to compensate for flow changes due to fluctuations in the control valves.

Feeding gaseous ammonia to the reactor is more preferable than liquid ammonia. The volume flow in this case is much higher, therefore, the initial turbulence is higher and the onset of the reaction is more intense.

Thus, if ammonia in the plant is present in liquid form, it is preferably vaporized in a heat exchanger used, for example, to condition the air in the plant, usually in the cooling zone of the final product. Ammonia in this case can be preheated, for example, due to process steam generated in the tubular reactor.

Ammonia can also be supplied as a mixture of gases, usually a mixture of ammonia, carbon dioxide and water vapor, resulting from the distillation of carbamate in the urea treatment step upstream or in the form of exhaust ammonia gases. In this case, water vapor and carbon dioxide work as inert compounds. They increase turbulence in the reactor and, therefore, to some extent its efficiency.

Case A can be divided into two cases, described in detail below:

- either the water supplied with the urea solution and with concentrated washing solutions containing urea is able to absorb most of the heat released during in situ synthesis (case A1);

- either this water is not enough (case A2), and additional water is required.

Case A2 may occur, in particular, with a high proportion of ammonium sulfate with respect to urea; in such a situation, a preliminary reagent, bisulfate, is preferably added, which is unacceptable in the case of A1.

CASE B - ammonia is supplied in a urea solution in the form of carbamate and ammonia

The starting ammonia is completely mixed with the urea solution; sulfuric acid can come into contact with both urea and the starting ammonia for the reaction. At the same time, the risk of decomposition of urea is high. To prevent the decomposition of urea, an alkaline environment is favorable, the process conditions are set accordingly: the excess molar fraction of ammonia is higher than in case A

(usually 5-20%).

Said alkalinity in combination with the design of the reactor itself reduces urea loss. In this case, the washing solution of the steam scrubber (from the second stage, if the urea and ammonia are cleaned separately) is preferably recycled to sulfuric acid on a line equipped, for example, with a static mixer, which increases the homogeneity of the mixture and prevents the appearance of heating points. This method allows the introduction of softer acid into the MCA tubular reactor, since, on the one hand, it is diluted with a certain amount of water and, on the other hand, ammonium sulfate from the washing solution is converted to ammonium bisulfate, which is less aggressive for urea than sulfuric acid itself.

In this case, however, it is necessary to supply an additional amount of acid to the steam scrubber, which then functions as a second reactor.

DESCRIPTION OF REACTORS

Table 1 Case A1 Case A2 Case B Mixer Recommended Recommended Strongly recommended Pre reactor Not required Strongly recommended Not required Head part Yes Yes Yes Body Yes Yes Yes

The head part and the reactor vessel are the same in all cases, while the first part of the reactor is different.

Reactor vessel

The case design in cases A and B is the same. The body is a straight pipe segment with a certain diameter and length. The length of the tubular reactor is designed taking into account the fact that the reactants must have sufficient time for contact and reaction; the diameter of the reactor is determined by a certain degree of turbulence, increasing the degree of mixing and efficiency.

In the case of MSA, the heat flux (taking into account the heat released during the chemical reaction) should be more than 5000 kcal / h / cm ² and less than 150,000 kcal / h / cm ² , preferably from 25,000 to 90,000 kcal / h / cm ² , and the residence time - less than 1 s, preferably less than 0.2 s.

If the heat flux is too low, there is insufficient contact between the reagents, ammonia is lost, which is neutralized in the steam scrubber, and the acid remaining in the urea solution decomposes a certain amount of urea.

If the residence time is too long, two cases are possible depending on the loading of the reactor:

- if the residence time is too long, since the reactor is not sufficiently loaded, the urea decomposes due to insufficient turbulence, as described above;

- if the reactor is sufficiently loaded, but has an excessive length, the additional residence time has a negative effect, since it causes an excessive pressure drop and, as a consequence, a higher temperature in the first part of the reactor, which leads to loss of urea.

To maintain the temperature in the reactor at an acceptable level while maintaining a sufficient pressure drop for efficient mixing, the pressure drop should be more than 0.5 bar, preferably more than 1 bar, and the back pressure on the reactor, for example, the ammonia pressure after the control valve immediately before entering the reactor, preferably should be less than 10 bar, preferably less than 5 bar.

MSA reactor head

The design of the head of the ISA reactor should meet the following tasks.

Urea is sensitive to decomposition, but contains most of the water, which allows you to control the temperature. In some cases, urea also contains a base, which is subsequently neutralized, for example, a urea-carbamate solution.

Therefore, the design of the head should provide the most complete contact between the reagents, and not between urea and unreacted acid, in addition, in any case, it is desirable to soften the acid before it comes in contact with urea. In addition, it is necessary to prevent contact of small drops of acid with the wall of the reactor.

Thus, taking into account the above conditions, the head of the ISA tubular reactor should be designed to provide immediate contact and turbulence to obtain a homogeneous and neutralized mixture. Any remaining un-neutralized acid in the form of a jet or any drop of free acid adversely affects the efficiency of the tubular reactor and the decomposition of urea. Initial turbulence is associated with the method of introducing reagents and increases due to the heat of reaction, causing the evaporation of water and, therefore, additional mixing and turbulence.

In cases A and B, a similar design principle of the head of the reactor is applied: acid is introduced into the center (directly from the pre-mixer or through the pre-reactor), around it in the first ring there can be an ammonia source (if required), and an external ring flow is used containing urea.

Acid is introduced axially relative to the reactor vessel. The introduction is carried out centrally by means of an injector 4 / 4A, at the end of which there is preferably an injector 4A in the case of a preliminary reactor, or directly through an injector 3 / 3A, at the end of which there is preferably an injector 3A. As a rule, the nozzle is a simple cone spraying the flow and thereby increasing the contact area between the reactants and, as a consequence, the reaction rate.

Sulfuric acid, dissolved sulfuric acid or pre-neutralized sulfuric acid, i.e. a mixture of sulfuric acid, ammonium bisulfate, etc. Usually it is in a liquid state, but may contain some vapors, for example, when using a preliminary reactor (see below).

In addition, the acid should be softened as much as possible before entering the head of the MCA reactor. The best way to soften the acid before contact with urea is to completely neutralize it with ammonium sulfate. However, complete ammonization of sulfuric acid before contact with urea is not possible.

The reasons for this are as follows:

- firstly, the solution of ammonium sulfate should contain a large amount of water to maintain a liquid state, therefore, the synthesis of ammonium sulfate with subsequent mixing with urea does not allow achieving the water balance necessary to maintain the required water content at the outlet of the reactor;

- secondly, the synthesis of ammonium sulfate is highly exothermic. Water that absorbs such heat of reaction, which allows maintaining the temperature in an acceptable range, is contained mainly in the urea solution. Therefore, synthesis and mixing should be performed almost simultaneously; ammonium sulfate (CA) cannot be fully synthesized when the stream of reagents enters the urea;

- thirdly, the ammonia to be neutralized (free ammonia and / or carbamate), in some cases, is already contained in the urea stream; this means that ammonium sulfate must be synthesized directly in the urea stream and cannot be synthesized before contact with urea.

Design and principle of operation of the reactor for case A1

In this case, an ammonia stream 8, for example gaseous ammonia or a carbamate solution, is fed into the first ring around the central acid injector [zone between 2 and 3].

Due to the design of the ammonia injector 2 / 2A, the acid is sprayed into the urea-free region of the reaction chamber [between 3A and 2A]. The design of this chamber forms a double conical structure in the reactor: the first cone 3A (or nozzle) for acid, the second cone 2 for ammonia, as well as the narrowing 1A for urea.

A large amount of heat is generated in this reaction chamber. With this in mind, the chamber should be sufficiently open to allow reacting droplets to be removed from the chamber into the urea stream, which absorbs heat. On this path, before contact with urea, the acid passes through an ammonia curtain.

In the area of contact with urea, there is a particularly high turbulence [zone between 1A and 2A], providing heat dissipation and homogeneous mixing of products; thus, the reaction mixture is preferably sprayed from the reaction chamber in the constriction 1A into the reactor vessel 14, where various liquids converge, further increasing turbulence.

The convergence angle 1A is equal to the usual angle determined by hydrodynamics, preferably the opening angle is from 30 to 90 °, which avoids local back-mixing and at the same time improves circulation efficiency in the reactor vessel.

The exit diameter of the cone 2A is preferably less than or equal to the diameter of the reactor vessel 1A, which avoids the appearance of heated areas on the wall of the reactor, especially in the area of narrowing. On the other hand, the cone 2A can also be fully open, i.e. replaced by the direct part of the injector 2.

The design of the reaction chamber 2A / 3A can be unambiguously determined by the design of the air pneumatic nozzles.

Unreacted acid at this stage reacts along the reactor vessel 14, mainly with ammonia, as well as with some of the urea that decomposes.

Irrigated solutions are recycled at all convenient times. If they contain urea, it is preferable to direct them into the urea stream. If they do not contain urea or contain a small amount of it (for example, if there is a second stage of technological steam purification [S2]), then it is preferable to recycle them into sulfuric acid in line.

Case A2

If, during the synthesis of ammonium sulfate, more heat is released than urea can be absorbed at the moment due to the water content, then in addition to this water, a certain amount of additional water must be added to the urea solution and it makes sense to use a preliminary reactor.

For example, such a case occurs during the synthesis of a mixture containing 50% CA and 50% urea when using a 70% urea solution as a starting material.

Such a preliminary reactor may be a tank type neutralizer or a tubular reactor.

If the reaction takes place in a separate container designed as a neutralizer, it may be preferable to maintain a certain pressure in it, which, in combination with gravity, allows the substance to be fed into the reactor without using a pump to pump a substance that is sufficiently corrosive. Such a system with a separate pre-catalyst has the advantage of obtaining, if necessary, a small amount of steam under pressure, but requires a higher investment compared to the version with a tubular reactor.

As described below, the pre-reactor may be simpler, be integrated into the same tubular reactor, which is the MCA reactor, and be an additional extension of the MCA tubular reactor in front of the urea injection zone 1A / 2A.

This reaction proceeds particularly quickly, and the continuation of the preliminary reactor is a kind of jet nozzle in zone 3A / 4A.

Water 13 is first added to ammonia through an inlet 9 or to acid 5. When added to an acid, for example, a PTFE coated pipe (polytetrafluoroethylene) is preferably provided with a static mixer 12 to prevent the appearance of any heating points that could damage Teflon. The mixture is fed into a nozzle for spraying in an axial or, preferably, tangential flow of ammonia from the inlet 9 directly to the acid injector 3 / 3A.

This configuration of the preliminary reactor allows to increase the overall economic efficiency of the entire urea complex. Water is formed in the urea plant in accordance with the following stoichiometry:

Therefore, water is available directly in the installation, and additional water for the reactor can be supplied from the urea plant in the form of a weak solution of carbamate or N-containing effluents, which require expensive treatment before release into the environment, for example, thermal hydrolysis.

Case B

This case is usually the case of a urea-carbamate solution present in any urea complex.

The modes of processes are selected taking into account the work with a high excess of alkali in the reactor and the capture of a large amount of ammonia in an acid steam scrubber. Therefore, the steam cleaning solution contains a large amount of ammonium sulfate. 5-20% acid is usually added to a steam scrubber.

In this case, it is strictly recommended to use a two-stage scrubber [S1; S2]: in the first stage [S1], small drops of urea are captured, in the second stage [S2] it is ammonia that is processed.

Thus, the washing solution 11 in the second stage, which is almost free of urea, is directly recycled to the sulfuric acid line to soften it without destroying the purified urea. The acid line is preferably equipped with a static mixer 12 to mitigate through a preliminary reaction. Thus, from 10% to ~ 50% of sulfuric acid is converted to bisulfate before any contact with urea, which allows to achieve a generally acceptable level of urea destruction.

The washing solution from the dry part together with the washing solution from the first stage of the scrubber 10, the steam is usually recycled to the first ring of the MCA reactor, designed for case A, or directly to the urea stream 7.

SEPARATOR DESIGN

A three-phase mixture flows from a tubular reactor to a separator (not shown): liquid (urea, water, dissolved ammonium sulfate ...), gas (steam obtained due to the heat of reaction) and even solid fractions (supersaturated CA crystals). The purpose of the separator is to separate the MSA solution / suspension and process steam. Due to the possible presence of crystals and a high flow rate in the reactor, the separator must be wear resistant.

The design of the separator will depend on the location, especially in the case of modernization of the installation. The reactor can be installed horizontally, vertically or in any intermediate position. Several options can be listed for the separator, taking into account separation efficiency and wear resistance.

Preferably, the separator is a container with an inner skirt. The steam inlet is located on the upper part of the tank in a tangential position to obtain a vortex effect that increases the separation efficiency.

In the lower part, the separator has a conical or concave shape, preferably with a reduced diameter, which allows more precise level control with a reduced residence time. For the same purpose of level adjustment, an anti-vortex device is preferably installed.

At the top of the separator, a droplet separation device (for example, a woven mesh, a device such as a cap plate, ceramic filter or bag) can preferably be mounted to separate most of the remaining droplets.

In this case, a water or condensate atomizer is preferably used to periodically clean the droplet separator when the pressure drop increases due to the formation of deposits, crystallization, and growing clogging.

SCRUBBER PAIR

The steam generated in the tubular reactor contains a certain amount of unreacted ammonia, as well as small drops of the MCA solution that did not separate in the separator.

This steam is further cleaned in an acid scrubber. The latter may be a column with a nozzle, a disk column, a venturi scrubber, or a combination of such devices to achieve the required characteristics.

In addition, such a scrubber has the advantage that it saturates the process steam, increasing the overall efficiency of the capacitor. The scrubber can be a separate container or a sequence of independent elements that implement successive cleaning steps to achieve the same result, it can also be integrated into the upper part of the tubular reactor separator and form a single structure with it.

The scrubber is preferably designed to perform two stages: in the first stage, urea / MCA droplets are captured by a relatively neutral washing solution, in the second stage an acid that captures ammonia is used. This avoids the increased destruction of urea due to the strong acidification of urea containing a washing solution.

The invention is further illustrated with reference to the following examples.

Examples

Example 1 - Illustration of Case A1

The experiments were conducted on a small scale experimental setup. Firstly, acid is fed into the conventional standard crosshair reactor shown in FIG. 2 along axis 15 of the reactor, a 78% carbamate-free urea solution through inlet 16 and gaseous ammonia through inlet 17.

Secondly, in the reactor according to the present invention, corresponding to case A1, the acid is introduced axially, the urea solution is supplied through the inlet 7, the ammonia gas is supplied through the inlet 8. The goal was to obtain an MCA containing 77% urea and 23% CA. Ammonia was fed with a molar excess of 2%.

Rapid evaporation was carried out in vacuum at an absolute pressure of 0.5 bar and a temperature of about 135 ° C, the water content in the solution exiting the reactor was approximately 5%. The washing solution was not recycled in this experiment.

The conditions and results are shown below in table 2.

table 2 Head part with a crosshair of pipes The reactor according to the invention The introduction of urea into the reactor (kg / h) (expressed for 100% urea) 500 500 Urea exit from the reactor (in ISA and condensates) (kg / h) 452 490 Entering NH ₃ into the reactor (kg / h) 39 39 Sulfuric acid injection into the reactor (kg / h) 111 111 Ammonium sulfate in the obtained MSA (kg / h) 149 149 The growth of carbamylurea (%) 0.5 0.4 Destroyed urea (%) (due to hydrolysis or formation of carbamylurea) 9.6 2.1

Example 2 - illustration of case A2

The experiments were carried out in order to obtain the composition MCA 65/35 wt./wt. (urea / ammonium sulfate) when using a 78% urea solution. Therefore, additional water was required to absorb the heat of reaction. In the first experiment, water was introduced by diluting a urea solution 7; 13, in the second experiment, the advantages of a preliminary reactor were investigated, with one quarter of the amount of ammonia fed through inlet 9, three quarters of ammonia fed through inlet 8, and additional water 13 was added to acid 5 through a pre-mixer 12.

Rapid evaporation was performed at an absolute pressure of 0.5 bar in a separate vessel after the tube reactor separator.

The results and conditions are shown in table 3.

Table 3 Without pre reactor With pre-reactor The introduction of urea into the reactor (kg / h) (expressed for 100% urea) 500 500 Urea exit from the reactor (in ISA and condensates) (kg / h) 483 488 Entering NH ₃ into the reactor (kg / h) 71 71 Sulfuric acid injection into the reactor (kg / h) 200 200 Ammonium sulfate in the obtained MSA (kg / h) 269 269 The growth of carbamylurea (%) 0.5 0.5 Urea destruction (%) (due to hydrolysis or formation of carbamylurea) 3.4 2,4

Example 3 - Illustration of Case B

Tests with urea-carbamate were performed with a molar excess of ammonia of 2% and a molar excess of ammonia of 10% and 20%, respectively. A urea melt at a concentration of 99.5% was mixed in line with a suspension of ammonium bicarbonate and gaseous ammonia to simulate a urea-carbamate solution. The goal was to obtain 35% CA in the ISA.

Recirculation of the washing solution corresponding to the second stage of the scrubber was simulated by an additional stream of a solution of ammonium sulfate at a concentration of 30% in a pre-mixer. Such a CA stream corresponds to neutralizing the excess ammonia fed to the reactor, with the exception of ammonia generated by the destruction of urea.

A regulating water flow was added to the urea solution to achieve the same water content of about 5% in the MCA solution at the outlet of the evaporation tank. The results and conditions are shown in table 4.

Table 4 Excess 2% Excess 10% Excess 20% The introduction of urea into the reactor (kg / h) (expressed for 100% urea) 500 500 500 Urea exit from the reactor (in ISA and condensates) (kg / h) 446 459 489 Ammonium bicarbonate injection into urea (kg / h) fifty fifty fifty Enter NH ₃ in urea (kg / h) 59 59 59 The input of sulfuric acid into the reactor in the form of H ₂ SO ₄ (kg / h) 196 180 160 CA in the pre-mixer (kg / h) (expressed as 100% CA) 5 27 54 Ammonium sulfate in the obtained MSA (kg / h) 269 269 269 The growth of carbamylurea (%) 0.5 0.4 0.5 Urea destruction (%) (due to hydrolysis or formation of carbamylurea) 10.8 8.2 2,3

Claims (26)

1. A tubular reactor for the production of a composition of urea and ammonium sulfate, including a tubular body (14) and a reactor head (1), the reactor head having an axial acid introduction device (3, 3A) and an introduction device (2, 2A) ammonia, a urea injection device (7) and a reaction chamber (zone 3A, 2A), in which the reaction of the acid with ammonia before contact with urea is intensified by creating initial turbulence with the introduction of these reagents. 2. The tubular reactor according to claim 1, characterized in that it contains a preliminary reactor for preliminary neutralization of the acid, located upstream in front of the head of the reactor. 3. The tubular reactor according to claim 2, characterized in that the preliminary reactor is a tubular reactor or tank type neutralizer. 4. The tubular reactor according to claim 3, characterized in that the preliminary reactor is part of the main tubular reactor, and the ammonia introduction device has an inlet (9). 5. The tubular reactor according to claim 1, characterized in that it contains a mixer (12) for diluting the acid, located upstream in front of the reactor head. 6. The tubular reactor according to claim 1, characterized in that the head of the reactor has a narrowing (1A) at its output end. 7. The tubular reactor according to claim 1, characterized in that the ammonia introduction device has an inlet (8) in communication with the annular chamber surrounding the acid introduction device (3, 3A). 8. The tubular reactor according to claim 7, characterized in that the annular chamber at the outlet end has the shape of a cone (2A) or an open end. 9. The tubular reactor according to claim 1, characterized in that the urea injection device includes an urea inlet (7) and an annular chamber surrounding the ammonia injection device (2, 2A). 10. A tubular reactor for carrying out a reaction between an acid, a base and a component sensitive to heat and / or acid, including a tubular body (14) and a reactor head (1), the reactor head having an axial device (3, 3A) the introduction of acid, the device (2, 2A) the introduction of the base, the device (7) the introduction of a component that is sensitive to heat and / or acid, and a reaction chamber (zone 3A, 2A), in which the reaction of the acid with the base before contact with heat-sensitive and / or acid component intensifiers It was created by creating initial turbulence during the introduction of these reagents. 11. The tubular reactor of claim 10, characterized in that it contains a preliminary reactor for pre-neutralizing the acid, located upstream in front of the head of the reactor. 12. The tubular reactor of claim 10, wherein the preliminary reactor is a tubular reactor or tank type neutralizer. 13. The tubular reactor according to claim 11, characterized in that the preliminary reactor is part of the main tubular reactor, and the base introduction device has an inlet (9). 14. The tubular reactor according to claim 10, characterized in that it contains a mixer (12) for diluting the acid, located upstream in front of the head of the reactor. 15. The tubular reactor according to claim 10, characterized in that the head of the reactor has a narrowing (1A) at its output end. 16. The tubular reactor according to claim 10, characterized in that the base introduction device has an inlet (8) in communication with the annular chamber surrounding the acid introduction device (3, 3A). 17. The tubular reactor according to clause 16, wherein the annular chamber at the outlet end has the shape of a cone (2A) or an open end. 18. Tubular reactor according to claim 10, characterized in that the device for introducing a heat and / or acid sensitive component includes an inlet (7) for the sensitive component and an annular chamber surrounding the base introduction device (2, 2A). 19. Installation for the production of urea and ammonium sulfate compositions, including a tubular reactor containing a tubular body (14) and a reactor head (1), where the reactor head contains an axial acid introduction device (3, 3A), device (2, 2A) the introduction of ammonia, the device (7) the introduction of urea, the reaction chamber (zone 3A, 2A), in which the reaction of the acid with ammonia before they contact the urea, a separator for separating the vapor formed from a suspension of urea and ammonium sulfate, and a device for receiving this steam . 20. Installation according to claim 19, characterized in that in front of the head part (1) of the reactor there is a preliminary reactor, which contains an ammonia introduction device (9), an acid introduction device (4) and a reaction chamber (4A). 21. Installation according to claim 19, characterized in that it contains a mixer (12) for diluting the acid, located upstream in front of the reactor head. 22. Installation according to claim 19, characterized in that the steam receiving device is a scrubber (S1, S2). 23. The apparatus of Claim 22, wherein the scrubber design comprises two separate processing steps (S1, S2). 24. Installation according to claim 22 or 23, characterized in that the scrubber has a device (11) for recirculating the washing solution into the urea inlet (7) and / or into the acid injection device (3). 25. Installation according to claim 19, characterized in that the evaporator tank is located behind the separator. 26. Installation according to claim 19, characterized in that it is the final part of the installation of receiving urea.

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