KR100266557B1 - Method for treating ammonia and urea condensates - Google Patents

Abstract

Ammonia plant process concentrate with ammonia, carbon dioxide and methanol mixed with urea, ammonia, carbon dioxide, and other forms of urea plant concentrate combined with ammonia and carbon dioxide in a single treatment vessel, substantially and continuously It is a method of simultaneously changing the vapor phase flow with a lot of carbon dioxide and methanol and the liquid phase flow with ammonia, carbon dioxide, methanol and urea. The vapor phase flow so produced is recycled and used as raw material in the reforming zone of the ammonia plant.

Description

Treatment of Ammonia and Urea Concentrates

1 is a schematic process flow diagram illustrating the practice of the present invention in simultaneously processing process concentrates produced in a facility where both ammonia and urea are manufactured.

* Explanation of symbols for main parts of the drawings

2, 16, 22, 32, 34, 38, 40, 42: conduits 4, 24: heat exchanger

6: lower stripping zone

8: upper part (of lower stripping area) 9, 10, 12: liquid / vapor contact

14: lower part (of the lower stripping area) 18, 36: valve

20: treatment vessel 26: lower hydrolysis zone

28: upper end (of upper hydrolysis zone) 30: upper end (of upper hydrolysis zone)

The present invention relates to a process for the simultaneous treatment of a concentrate stream of each by-product produced and recovered in a plant where both ammonia and urea are produced. More specifically, the present invention provides a single vapor phase product stream with a high amount of ammonia, methanol, and carbon dioxide and a single low amount of streams by simultaneously hydrolyzing and stripping the process concentrate stream of the byproduct in a single process vessel. A method for producing a liquid product stream.

In the production of ammonia and urea, it is known that process concentrates of large quantities of by-products are produced. In the production of urea, for example, one mole of byproduct water is produced for each mole of urea produced. If the water of such by-products is taken into account with other water used and / or produced in the urea process, the total amount of process concentrate and the other water combined is 40 to 60% by weight of the total weight of the urea produced. Similarly, in the production of ammonia, the amount of concentrate of the resulting process by-products is generally from 100 to 135% by weight of the total weight of the ammonia produced.

Unfortunately, process concentrates of the ammonia and by-products generated and recovered at the urea manufacturing facilities generally contain contaminants of that nature that cannot be easily recycled or disposed of into the environment for reuse in the manufacturing process. Generally, contaminants found in public concentrates produced and recovered in the manufacture of urea contain not only 1.0 to 1.5% by weight of urea, but also 4 to 8% by weight of ammonia and 2.0 to 5.5% by weight of carbon dioxide. can do. Process concentrates typically produced and recovered from the production of ammonia contain 0.05-0.1% by weight ammonia, 0.2-0.3% by weight carbon dioxide and 0.05-0.2% by weight methanol, in addition to higher alcohols, amines and other It may contain a trace amount of a hydrocarbon component.

In order to allow the process concentrates of the by-products to be recycled for use in the manufacturing process or to be easily disposed of in the environment, it is common to apply certain treatments to these process concentrates to remove as much of the contaminants as possible. Thus, for example, U. S. Patent No. 4, 552, 979 contains urea using both steam and hydrocarbon fuel gas to hydrolyze urea and stream ammonia and carbon dioxide from this hydrolyzed concentrate. One-element plant process A continuous process for treating concentrates is introduced. The water present in this concentrate is converted to steam for use in this process. A gaseous stream consisting of steam, hydrocarbon fuel gas, ammonia and carbon dioxide is recovered as the end product of the process. If the urea plant comprises an ammonia plant reformer integrally, the stream can be used as feed to the reformer. U.S. Patent No. 4,341,640 describes an improved treatment of urea plant process concentrates, wherein the treatment comprises at least one treatment cell comprising an inner cylinder located in a vessel having an inner and outer surface, and an outer surface of the cylinder. There is a need for use of a container having a liquid holding area located between the container and the container and at least one striping tray connected to the inner surface. The zone remains substantially separate from the vapor stream passing through the vessel.

The processing of the by-product concentrates produced during the production of ammonia is illustrated by US Pat. No. 3, 970, 739. This patent discloses a process for simultaneously treating flue gas and process wastewater generated from an ammonia synthesis process plant. The process involves stripping ammonia and organics as gas from the process wastewater and stripping using a first catalyst suitable for cracking methanol to produce carbon dioxide and water or gases containing carbon dioxide, water and hydrogen. Decomposing methanol contained in the gas. In addition, the resulting gas, which also contains undecomposed ammonia, is mixed with the flue gas generated in the ammonia plant, the gaseous mixture being in contact with a second catalyst capable of reducing the nitrogen oxides contained in the gaseous mixture to nitrogen and water. Done. Finally, the resulting gaseous mixture is brought into contact with the third and last catalyst capable of decomposing unreacted ammonia by oxidation with nitrogen and water.

Typical processes for removing urea, ammonia and carbon dioxide from process concentrates from combined ammonia and urea synthesis are illustrated in US Pat. No. 4,410,503. According to this patent, the process concentrates produced during urea synthesis are first processed in a desorption or stripping column to remove as much of the carbon dioxide and ammonia contained therein as possible to produce ammonia-lean concentrates. The ammonia lean process concentrate is then introduced into a separate reaction column together with the process concentrate produced in the ammonia synthesis and the combined concentrate treated with steam. A gas mixture rich in ammonia, carbon dioxide and water vapor is removed from the top of the reaction column, and an aqueous solution of urea, ammonia and carbon dioxide lean is removed from the bottom of the reaction column. A disadvantage of this process is that the process concentrate from urea synthesis must now be treated before the concentrate, which is now lean in ammonia, is combined with the process concentrate from ammonia synthesis in a separate reaction column. Costly equipment is needed to perform this separate first step treatment.

It is an object of the present invention to provide an improved process for treating process concentrates of by-products generated and recovered in plants where both ammonia and urea are produced. Another object is to provide an improved process by simultaneously processing the process concentrate of the byproduct in a single treatment vessel, thereby reducing the additional costs associated with the additional equipment required for the process described in US Pat. No. 4,410,503. It is.

According to the invention, in a plant synthesizing both ammonia and urea from which process concentrates of the first and second by-products are produced, the process is carried out in a single vertically located treatment vessel having an upper hydrolysis zone and a lower stripping zone. Continuous methods for simultaneously treating the concentrates are provided. The process of the present invention comprises the steps of preheating the first process concentrate produced in the ammonia synthesis process comprising a dilute aqueous stream consisting of water, ammonia, carbon dioxide, methanol and traces of higher alcohols, amines and other hydrocarbon components as essential components. And introducing this preheated first process concentrate to the top of the stripping region. Within the upper end of the stripping zone, the preheated first process concentrate is mixed with a lean lean first liquid stream which is collected and recovered at the lower end of the upper hydrolysis zone in fluid communication with the upper end of the lower stripping zone. The resulting mixed stream then comes into contact with the steam introduced at the lower end of the stripping region in a counterflow relationship. This contact strips a portion of the ammonia, carbon dioxide and methanol contained in the mixed stream and is also rich in ammonia, carbon dioxide and methane and also in a vapor phase stream containing traces of higher alcohols, amines and other hydrocarbon components, and Ammonia, carbon dioxide and methanol are made under temperature and pressure conditions effective to produce a second lean liquid stream. The vapor phase stream emerges from the top of the stripping zone of the treatment vessel and is introduced into the bottom of the hydrolysis zone in fluid communication with the stripping zone.

A second process concentrate stream comprising a dilute aqueous stream consisting essentially of water, urea, ammonia and carbon dioxide is also introduced to the top of the hydrolysis zone of the treatment vessel. In the hydrolysis zone, the second process concentrate is further heated to introduce into the bottom of the hydrolysis zone by contacting the vapor phase stream recovered from the top of the stripping zone with the second process concentrate in a countercurrent relationship, In some cases, new process steam is also introduced into the lower end of the hydrolysis zone. The contact between the preheated second process concentrate stream and the vapor phase stream, and optionally the new process vapor introduced into the lower end of the hydrolysis zone, substantially reduces the urea present in the second process concentrate to ammonia and carbon dioxide. And under temperature and pressure conditions effective to produce a first liquid stream that is lean in urea and rich in ammonia and carbon dioxide. The first liquid stream collected at the lower end of the hydrolysis zone is introduced from there into the upper end of the stripping zone.

Finally, the vapor phase stream is recovered through the upper end of the hydrolysis zone, while the second liquid phase stream, which is lean in ammonia, carbon dioxide and methanol, is recovered through the lower end of the stripping zone of the treatment vessel.

In another embodiment of the present invention, the vapor phase stream recovered in the hydrolysis zone is used for transfer to a reforming stage at the ammonia synthesis site of the ammonia and urea plant. In another embodiment of the present invention, the second liquid stream preheats both the ammonia synthesis process concentrate and the urea synthesis process concentrate by passing the ammonia synthesis process concentrate and the urea synthesis process concentrate in heat exchange relationship with the effluent stream. It can be used to

Referring to the drawings, the ammonia synthesis process concentrate produced in the plant producing both ammonia and urea is passed through conduit 2 and heat exchanger 4 under elevated pressure in the range of about 3.8 MPa to about 7.5 MPa. It is delivered to (20), where it is preheated to a temperature of about 220 ° C to about 285 ° C. The processing vessel 20 is provided with a lower stripping region 6 having an upper end 8 and a lower end 14 and an upper hydrolysis region 26 having an upper end 28 and a lower end 30. In the figure, the lower stripping area 6 is provided with multiple liquid / vapor contacts 9, 10, 12, which are filled, for example, using known "beveled" or "in alignment" packing material. Site may be included. Representative examples of aligned filler materials are Flexpak, Hyperfil, Kloss packing, and representative examples of inclined packing materials are Berl saddles, Intalox saddles. saddles, Fall rings, etc. Descriptions and / or examples of these two types of packing materials are found in Chapter 18, pages 19-26 of the Ferry Handbook for Chemical Engineers, 6th edition (1984).

The preheated ammonia synthesis process concentrate flowing through the conduit 2 is introduced at its upper end 8 into the stripping region 6 of the treatment vessel 20. Upon entering the upper end 8 of the stripping zone 6, the process concentrate stream is lean in urea and rich in ammonia and carbon dioxide streams collected at the lower end 30 of the upper hydrolysis zone 26 and discharged therefrom. It is mixed with the first liquid stream. This mixed stream flows down past the stripping region 6 and the contacts 9, 10, 12 in the region, past the stripping region 6 and the contacts 9, 10, 12. It is in intimate contact with the process steam flowing upward. The process steam is stripped at the lower end 14 via the steam conduit 16 and the valve 18 at a pressure in the range as mentioned for the ammonia synthesis process concentrate, ie from about 3.8 to about 7.5 MPa. (16) flows into. This process steam is introduced into the stripping region 6 at the lower end 14 at a flow rate sufficient such that the weight ratio of process vapor to the total process concentrate stream introduced into the treatment vessel 20 is from about 0.4 to about 0.6. .

The process vapor from the lower portion 14 flows upwardly through the stripping region 6 and the contacts 9, 10, 12, and thus is different from the ammonia, carbon dioxide and methanol contained in the mixed stream. Hydrocarbon components are stripped from the process vapor and also entrained in the process vapor, ammonia. It forms a vaporous stream rich in carbon dioxide, methanol and also containing trace amounts of higher alcohols, amines and other hydrocarbon components. The stripped mixed stream or the second liquid stream has a reduced content of ammonia and methanol and is also substantially free of carbon dioxide. The second liquid stream is collected at the bottom 14 of the stripping region 6.

This second liquid stream is removed from the lower end 14 of the stripping region 6 via the conduit 42. The heat energy contained in the stripped mixed stream or the second liquid stream is used to preheat the ammonia synthesis process concentrate which is fed to the stripping zone 6 of the treatment vessel 20, thus concentrating the ammonia synthesis process in the heat exchanger 4. It can be passed through a heat exchange relationship with water.

While treating the mixed stream of the ammonia synthesis process concentrate and the first liquid stream in the stripping zone of the treatment vessel 20, the urea synthesis process concentrate is hydrolyzed in the hydrolysis zone 26 in the treatment vessel 20. Can be. Referring to the figures, the urea synthesis process concentrate stream is conveyed through conduit 22 and heat exchanger 24 under elevated pressure between about 3.8 MPa and about 7.5 MPa to be hydrolyzed at the top 28 of the hydrolysis zone. It is introduced into 26. Depending on the concentration of ammonia and carbon dioxide contained in the urea synthesis process concentrate in conduit 22, at least a portion of the ammonia and carbon dioxide is removed from the process concentrate prior to introducing the process concentrate into the hydrolysis zone 26. For this purpose, it may be desirable for this process concentrate (by means not shown) to be fractionally distilled. The ammonia and carbon dioxide thus removed can be transported to the urea synthesis site of the ammonia and urea manufacturing facilities. The urea synthesis process concentrate, preheated to a temperature of about 130 ° C. to about 195 ° C. in the heat exchanger 24, descends from the upper end 28 through the hydrolysis zone 26 provided with a plurality of liquid and gas contact trays 27. To flow. Above the plurality of liquid and gas contact trays 27, the downward flowing preheated urea synthesis process concentrate is directed upwardly in the vapor phase which is produced and discharged in the stripping region 6 through the upper end 8 of the stripping region. It is in intimate contact with steam.

In another embodiment of the present invention, the vapor phase stream may be combined with the fresh process vapor and the mixture obtained in a counterflow contact with the urea synthesis process concentrate.

In this embodiment, the new process steam is passed through conduits 16, 32, 34 and valve 36 under the same pressure as previously mentioned for the urea synthesis process concentrate, that is, from about 3.8 to about 7.5 MPa. It is introduced into the hydrolysis zone 26 at the lower end 30 of the hydrolysis zone 26. When used, this new process steam is produced in the hydrolysis zone (at the lower end 30) at a flow rate sufficient such that the weight ratio of the process steam to the urea synthesis process concentrate fed to the hydrolysis zone 26 is at most about 0.2. 26) is introduced into.

From the bottom 30, the vapor phase stream and optionally fresh process steam flows upwards and flows through the hydrolysis zone 26 and a number of contact trays 27 installed therein, thus urea synthesis process The urea contained in the concentrate is in intimate contact with the vaporous stream and, optionally, with the new process steam, substantially converting it to ammonia and carbon dioxide. In general, the flow rate of the vapor phase stream and the urea synthesis process concentrate to the counter flow through the hydrolysis zone 26 is adjusted such that the contact time between the concentrate stream and the first vapor phase stream is about 1-5 minutes. The ammonia and carbon dioxide produced by the hydrolysis of the urea synthesis process concentrate are substantially contained in the liquid stream produced during the hydrolysis of this concentrate stream, ie the first liquid phase stream. The liquid stream is collected at the bottom 30 of the hydrolysis zone 26. Ammonia and carbon dioxide contained in the two-liquid stream are continuously stripped in the stripping region 6.

The vapor phase stream produced in the stripping zone 6 and passed through the hydrolysis zone 26 in a counterflow relationship with the urea synthesis process concentrate is conduit 38, via an upper end 28 of the hydrolysis zone 26. 40 is removed from the processing vessel 20 through. This vapor phase stream is suitable for use in the production of ammonia and other synthesis gases used in the ammonia synthesis site of the urea plant, and therefore through conduit 40 directly to the steam reforming site (not shown) of the ammonia synthesis site of the plant. Can be transported.

Further describing the implementation of the method of constructing the present invention according to the process flow diagram shown in the figures, process concentrates obtained in a plant for producing both ammonia components are treated in the manner mentioned below. Unless stated otherwise, all quantities are expressed in parts or parts / hour.

The process concentrate recovered from the ammonia synthesis site of the plant making both ammonia and urea is continuously flowed through conduit 2 at a flow rate of 57, 297 parts / hour. This concentrate contains 172 parts of carbon dioxide, 57 parts of ammonia, 57 parts of methanol and 57, 011 parts of water and is recovered from the plant under a temperature of about 93 ° C. and a pressure of about 4.2 MPa. This process concentrate is heated in the heat exchanger 4 to a temperature of about 241 ° C. and introduced into the stripping region 6 of the treatment vessel 20 at the upper end 6. There, the process concentrate is lean in urea, rich in ammonia and carbon dioxide, and mixed with the first liquid phase stream produced in the hydrolysis zone 26 of the treatment vessel 20. The resulting mixed stream flows downwardly through the stripping region 6 with multiple liquid / vapor contacts 9, 10, 12, where the mixed stream passes through the conduit 16 and the valve 18. At the lower end 14, the process steam comes into contact with the process steams 36 and 056 introduced into the stripping region 6. This process vapor is continuously introduced into the stripping zone 6 at a pressure of about 4.2 MPa and a temperature of about 374 ° C., so that ammonia, carbon dioxide, methanol and the first liquid phase present in the process concentrate from the ammonia synthesis site of the plant. A vapor phase stream is produced which contains both ammonia and carbon dioxide contained in the stream as essential components.

Simultaneously with the stripping of the mixed stream of the process concentrate from the ammonia synthesis site of the plant and the first liquid phase stream, the process concentrate from the urea synthesis site of the ammonia and urea production plant was flowed at a flow rate of 29, 189 parts / hour Flow continuously through 22). This concentrate contains 282 parts of urea, 553 parts of carbon dioxide, 1,278 parts of ammonia, 27, 076 parts of water and is recovered from the plant under a pressure of about 4.2 MPa. This process concentrate is preheated in heat exchanger 24 from an initial temperature of about 56 ° C. to a temperature of about 152 ° C. The preheated process concentrate is then introduced at the top 28 into the hydrolysis zone 26 of the treatment vessel 20. The preheated process concentrate flows downwardly from the top 28 through the hydrolysis zone 26 in which the vapor phase stream generated in the stripping zone 6 of the treatment vessel 20 and, in the case of In some cases, the vapor phase mixture of fresh process steam is in intimate contact with each other in a countercurrent relationship. This vapor phase mixture is formed by introducing a first vapor phase stream generated in the stripping region 6 and optionally a new process vapor at a pressure of about 4.2 MPa and about 374 ° C. into the bottom 28, The mixture is combined and flows upward through the hydrolysis zone 26. In some cases new process steam is introduced into the lower end 30 via conduits 16, 32, 34 and the valve 36, while the vapor phase stream is fed from the upper end 8 of the stripping region 6 to the tray. Passes directly to the lower end 30 of the hydrolysis zone 26 in direct fluid communication through a passage or riser 31 located at 29.

In the hydrolysis zone 26, the urea present in the process concentrate from the urea synthesis section is substantially hydrolyzed with ammonia and carbon dioxide. The ammonia and carbon dioxide contained in the first liquid stream obtained from the hydrolysis of the urea containing process concentrate are continuously stripped in the stripping zone 6 of the treatment vessel 20. The first vapor phase stream recovered from the hydrolysis zone 26 at the upper end 28 via conduit 38 at a flow rate of 36,410 parts / hour contains 1492 parts of ammonia, 932 parts of carbon dioxide, and 53 parts of methanol. In the preferred embodiment of the present invention, as shown in the figure, the vapor phase stream is conveyed to the process steam flowing through conduit 32 and to the steam reforming site of the ammonia synthesis site of the ammonia and urea plant (both not shown). Is combined with the balance of the obtained mixed steam.

While the preferred embodiments of the present invention have been described so far, it will be appreciated that various modifications and improvements can be made within the foregoing and following claims.

Claims (8)

In a facility for producing both ammonia and urea from which the first process concentrate and the second process concentrate are produced, the process concentrates are simultaneously placed in a single vertically placed treatment vessel having an upper hydrolysis zone and a lower stripping zone. A continuous process of treatment comprising the steps of: a) preheating a first process concentrate consisting of a dilute aqueous stream consisting of ammonia carbon dioxide and methanol, and introducing the preheated first concentrate into an upper end of the lower stripping region. ; b) mixing the preheated first concentrate in the upper end of the stripping zone with the first liquid stream produced and recovered in the upper hydrolysis zone; c) by removing a portion of the ammonia, carbon dioxide and methanol from the mixed stream to a temperature sufficient to produce a vapor phase stream with the ammonia, carbon dioxide and methanol and a second lean liquid stream with the ammonia, carbon dioxide and methanol; Contacting the mixed stream in a counterflow relationship with the vapor introduced into the bottom of the stripping region under pressure; d) recovering the vaporous stream from the upper end of the stripping zone and introducing the vaporous stream into the lower end of the upper hydrolysis zone; e) preheating a second process concentrate consisting of a dilute aqueous stream of which urea, ammonia and carbon dioxide are essential and introducing the preheated second concentrate into the upper end of the hydrolysis zone; f) said preheated agent in said hydrolysis zone at a temperature and pressure sufficient to hydrolyse urea contained in said preheated second concentrate to ammonia and carbon dioxide to produce a first liquid stream rich in ammonia and carbon dioxide. 2 contacting the concentrate in a counterflow relationship with the vapor phase stream produced in the lower stripping region; And g) recovering said vapor stream from said hydrolysis zone and said second stream from said stripping zone. The ammonia and urea concentrate of claim 1 further comprising the step of recycling said vapor phase stream enriched with ammonia, carbon dioxide and methanol to a steam reforming stage to produce an ammonia syngas used in the ammonia production. Water treatment method Ammonia and urea according to claim 1, wherein the first process concentrate is provided under a pressure of about 3.8 MPa to 7.5 MPa and the first concentrate is preheated to a temperature of about 220 ° C. to 285 ° C. 7. Method of treatment of concentrates. The method of claim 1 wherein the second process concentrate is provided under a pressure of about 3.8 MPa to 7.5 MPa and is preheated to a temperature of about 130 ° C. to 195 ° C. 7. 2. The ammonia as claimed in claim 1, wherein the contact between the mixed stream and the steam in the stripping zone is carried out with a weight ratio of 0.4 to 0.6 of the vapor to the total process concentrate treated in the processing vessel. And a method of treating urea concentrate. 2. The method of claim 1 wherein said contact between said preheated second concentrate and vapor phase stream in said hydrolysis zone lasts 1-5 minutes. 7. A method according to claim 6, wherein the contacting is carried out further in the presence of additional steam. The ammonia and urea concentrates as claimed in claim 1, wherein the first process concentrate and the second process concentrate are preheated by indirect heat exchange with the second liquid stream recovered at the bottom of the stripping zone. Water treatment method