Optimized process condensate preparation
Patent Information
- Application Number
- EP2023704159
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-02-18
- Filing Date
- 2023-02-14
- Publication Date
- 2024-12-25
AI Technical Summary
The existing process condensate treatment in urea synthesis is complex and energy-intensive, requiring high purity for most applications but being energetically disadvantageous for lower-purity requirements like exhaust gas scrubbing in urea formation processes, such as granulation or prilling, due to the need for identical separation processes in the first and third stages.
A system network with separate process condensate purification and coarse process condensate purification devices, allowing for high-purity condensate production while reducing energy consumption by using a simpler, one-stage coarse purification process for applications like exhaust gas scrubbing, and enabling flexible capacity expansion and efficient ammonia adjustment.
This approach achieves high-purity condensate for standard uses while minimizing energy consumption, simplifying process control, and allowing for efficient use of process condensate in scrubbing applications, with reduced steam requirements and easier capacity expansion.
Smart Images
Figure 1.1
Abstract
Description
[0001] Optimized process condensate treatment
[0002] The invention relates to the treatment of the process condensate resulting from urea synthesis.
[0003] The process condensate resulting from urea synthesis contains both ammonia and urea as impurities. Therefore, it is purified in a three-stage process before further use. In a first step, ammonia is removed at temperatures often around 115 to 140 °C. This is followed by hydrolysis at temperatures around 190 to 200 °C and usually more than 15 bar for a time of 60 to 120 minutes, during which urea decomposes into ammonia and carbon dioxide. The resulting ammonia and carbon dioxide are then removed in a third step. The separation processes in the first and third steps are identical, so these two steps are usually carried out in one column that is only split in the middle to accommodate the second step.
[0004] This three-stage process ensures that the entire process condensate stream is extremely pure, containing less than 3 ppm ammonia and less than 3 ppm urea. This is correspondingly complex and requires a lot of energy. There are also applications with less stringent purity requirements, particularly in the exhaust gas scrubbing required for urea formation, particularly urea granulation or urea prilling, where urea is introduced as a contaminant from the exhaust gas.
[0005] Therefore, it is energetically advantageous to use less purified process condensate for such flue gas scrubbing. US 2019 / 0177180 A1 proposes separating a partial stream after the first stage and feeding it to the flue gas scrubbing. However, this results in the streams in the first and third stages, which are located in a common column, having very different volumes, which can have a detrimental impact on design and operation.
[0006] US 4,652,678 A discloses a process for recovering valuable components from a urea synthesis off-gas stream. US 4,410,503 A discloses a process for removing urea, ammonia, and carbon dioxide from a dilute aqueous solution.
[0007] The object of the invention is to provide a process condensate treatment which has both high purity for the usual uses and a lower purity for the exhaust gas scrubbing, thereby enabling optimal process control with minimal energy consumption.
[0008] This object is achieved by the system assembly having the features specified in claim 1. Advantageous further developments emerge from the subclaims, the following description, and the drawing.
[0009] The plant complex according to the invention serves to produce a urea molding material, in particular a urea granulate or a urea prill. The terms "granulate" or "prill" are commonly used; this refers to particulate, agglomerated material which has a particle size suitable for application as a fertilizer and is usually produced in a subsequent shaping step, namely granulation or prilling. The plant complex comprises at least one urea synthesis device and one urea molding device. The plant complex usually also comprises a device for synthesizing ammonia and, in many cases, a reformer for producing hydrogen. Ammonia is produced from hydrogen and nitrogen in the ammonia synthesis device.Urea is produced from this ammonia using carbon dioxide in the urea synthesis device. It is then partially processed with other components, such as ammonium nitrate, sulfur compounds, lime, and the like, in the urea forming device to form granules, which are widely used, in particular, as fertilizers. The plant complex can optionally also comprise a nitric acid synthesis device and, optionally, additionally an ammonium nitrate synthesis device. In this case, ammonium nitrate, for example, can be mixed with the urea as a further component and formed, in particular granulated, together. The plant complex has a process condensate purification device, wherein the process condensate purification device is designed to separate ammonia and urea from the process condensate of the urea synthesis device.This enables further use of the water within or outside the plant network, or even its disposal. The process condensate purification device has a purification stream up to the process condensate outlet. The purification stream typically leads the process condensate through three stages to achieve a high level of purity in the process condensate. This means that the purified process condensate can be used in a variety of ways. The plant network has a forming exhaust air scrubber that is connected to the urea forming device and serves to clean its exhaust gases. The forming exhaust air scrubber serves to remove the urea that has entered the exhaust air by washing it with water, thus reducing nitrogen emissions. The forming exhaust air scrubber often has a second stage in which ammonia is removed by washing with an acidic medium.
[0010] According to the invention, the system assembly comprises a coarse process condensate purification device in addition to the process condensate purification device. The coarse process condensate purification device has a coarse purification stream. In the coarse purification stream, purification is simpler than in the process condensate purification device, so that the coarsely purified process condensate has a lower purity, but the effort required for the coarse purification is correspondingly reduced. The coarse purification stream is separate and distinct from the purification stream. The coarse process condensate purification device and the process condensate purification device are thus two separate devices, and the coarse process condensate purification device is not merely, for example, the first stage of the process condensate purification device.The urea synthesis device is connected to the process condensate purification device and the coarse process condensate purification device for transferring process condensate. The coarse process condensate purification device is connected to the.
[0011] Forming exhaust air scrubbing device. Thus, according to the invention, the process condensate stream from the urea synthesis device is divided into two substreams. A first substream goes to the process condensate purification device according to the prior art. Since this stream is completely purified, the first and third stages are designed for the same volume flow and are also operated accordingly. The new coarse process condensate purification device, into which a second substream is fed, is arranged parallel to the conventional process condensate purification device. Depending on the ambient conditions, for example, the demand for the first substream and the second substream can be approximately equal. The water flow required for the forming exhaust air scrubbing device, for example, granulation or prilling, is purified sufficiently in the coarse process condensate purification device only for this application and is therefore much more energy-efficient.Removing the urea from the process condensate is not necessary for its use in exhaust air scrubbing. In particular, the coarse process condensate purification device has only one stage and therefore, above all, no hydrolysis in a second step. The amount of ammonia in the process condensate can be specifically adjusted using the separate coarse process condensate purification device. According to the state of the art, the ammonia released during the forming process, particularly during granulation or prilling, is preferably removed from the exhaust air by acid scrubbing, for example, with nitric acid or sulfuric acid. Depending on the acid used, the corresponding ammonia salt is produced, which can also be used as a fertilizer or as a feedstock for further processes, for example, for the production of urea ammonium nitrate (UAN).The ammonia remaining in the process condensate stream used for exhaust air scrubbing after the coarse process condensate purification device is scrubbed out in the acidic scrubbing stage of the exhaust air scrubbing system. According to the state of the art, the heat required for the process condensate purification device is provided in the form of steam, which is predominantly fed directly into the process and thus itself becomes process condensate. If the process condensate purification is carried out in a more energy-efficient manner, the amount of steam fed in can be reduced. This leads to a reduction in the amount of process condensate generated, since the saved steam prevents the introduction of additional water, which would otherwise increase the amount of process condensate.
[0012] The strict separation of the process condensate purification device and the purification stream from the coarse process condensate purification device and the coarse purification stream results in two fundamental advantages. The first advantage is that the process condensate purification device, in particular, is designed for a constant continuous purification stream. Thus, all stages are designed for an identical volume flow, which is advantageous. The second advantage is that retrofitting as part of a capacity expansion is easily possible.For example, if a corresponding existing plant network is converted to expand production capacity, an existing process condensate purification device can continue to operate, while a new, additional and separate coarse process condensate purification device is installed. This device purifies the process condensate stream resulting from the capacity expansion in a simple and reduced manner and makes it available for corresponding applications, particularly the forming exhaust air scrubber. This advantageously eliminates the need for a capacity expansion of the process condensate purification device.
[0013] In a further embodiment of the invention, the coarse process condensate purification device is designed as a single-stage device for removing ammonia. In particular, the coarse process condensate purification device is designed in the form of a column, in particular a tray column or a packed column. A second stage for hydrolyzing urea to ammonia and CO2 is therefore preferably not part of the coarse process condensate purification device.
[0014] In a further embodiment of the invention, the coarse process condensate purification device comprises a first heat exchanger. The first heat exchanger is designed to preheat the process condensate stream coming from the urea synthesis device. This is achieved by the heat exchanger being designed to cool the coarsely purified process condensate stream exiting the coarse process condensate purification device. Thus, the process heat can be retained in the coarse process condensate purification device.
[0015] In a further embodiment of the invention, the coarse process condensate purification device comprises a second heat exchanger. The second heat exchanger is designed to condense the gas stream exiting the coarse process condensate purification device. In particular, the gas mixture, which contains, in particular, water, ammonia, and carbon dioxide, can be condensed here. This process condensate can also be referred to as a carbamate solution, since the ammonia and carbon dioxide contained therein partially react with each other in aqueous solution, among other things to form carbamate. Preferably, the second heat exchanger and the coarse process condensate purification device are connected to a carbamate return line. This allows a partial stream of the carbamate solution to be recirculated to the coarse process condensate purification device.This recirculation allows the water content in the carbamate solution to be reduced as needed to increase the concentration of ammonia and carbon dioxide. This is advantageous because this carbamate solution is fed to the urea synthesis device, where a low water input is beneficial for the reaction process.
[0016] In a further embodiment of the invention, the coarse process condensate purification device comprises a third heat exchanger. The coarse process condensate purification device further comprises a recirculation line for a partial stream of the coarsely purified process condensate stream. The third heat exchanger is arranged in the recirculation line and designed to heat the recirculated partial stream. To supply the required heat to the coarse process condensate purification device, steam could alternatively be introduced directly. However, this direct steam feed increases the water quantity of the coarsely purified process condensate stream. However, the indirect heat input through a heat exchanger leaves the total quantity unchanged. In the third heat exchanger or downstream, for example, after a corresponding pressure valve, evaporation of the partial stream can also take place.
[0017] In a further embodiment of the invention, the plant network comprises a process condensate storage tank. The process condensate storage tank is arranged downstream of the urea synthesis device and upstream of the process condensate purification device and the coarse process condensate purification device.
[0018] In a further embodiment of the invention, the coarse process condensate purification device and the urea synthesis device are connected via a first line for recirculating the carbamate solution produced in the coarse process condensate purification device. In particular, the process condensate purification device and the urea synthesis device are connected via a second line for recirculating the carbamate solution exiting the process condensate purification device. The first line and the second line are connected to each other. In particular, they can flow into each other and be routed as a common line into the urea synthesis device.
[0019] In a further embodiment of the invention, the urea forming device comprises one or more fine exhaust air scrubbing devices, for example, a droplet separator using a demister. Since this is the final purification step before the exhaust air is released into the environment, special purity requirements are placed on the scrubbing solution used. If this requirement is not met by the coarsely purified process condensate from the coarse process condensate purification device, a different source for the scrubbing solution must be selected for this final purification step. Typically, the clean process condensate from the process condensate purification device is then used as before. The water quantity of the fine exhaust air scrubbing device is usually small compared to the total water requirement for the scrubbing. Therefore, the listed positive effects of the coarse process condensate purification device are also retained in this embodiment.
[0020] The system combination according to the invention is explained in more detail below using an embodiment shown in the drawing.
[0021] Fig. 1 exemplary embodiment
[0022] The illustration is purely schematic and greatly simplified to clarify the invention. Conventional components such as valves, heat exchangers, conveying devices such as pumps and the like have been omitted for simplicity and are sufficiently known to those skilled in the art for such systems. The aim of the illustration is to clarify the inventive concept. Fig. 1 shows a section of a plant network. Ammonia and carbon dioxide are fed to the reactant inlet 30 of the urea synthesis device 1 and converted there to urea. The urea is then transferred to the urea forming device 2. The exhaust air from the urea forming device 2 is transferred to the forming exhaust air scrubbing device 4. The process condensate, which is produced during the synthesis of urea from ammonia and carbon dioxide, is transferred from the urea synthesis device 1 to a process condensate storage tank 3.Here, the process condensate stream is divided according to the invention. A partial stream, for example 50%, is transferred to the process condensate purification device 10, as is known and customary from the prior art for such a plant network. The process condensate is first passed through the fourth heat exchanger 14 into the first stage 11, where ammonia is separated at, for example, 140 °C and 3 bar. After passing through the first stage 11, the process condensate passes through the fifth heat exchanger 15 into the second stage 12, for example for 60 minutes at 200 °C and 16 bar. This converts the urea with water into ammonia and carbon dioxide. The process condensate passes through the fifth heat exchanger 15 into the third stage 13, where ammonia is separated under the same conditions as in the first stage 11 (in a common column). This then returns to the urea synthesis device 1 via a second line 41.The cleaned process condensate passes from the third stage 13 through the fourth heat exchanger 14 to the process condensate outlet 32 and can be transferred to other processes.
[0023] A further partial stream, for example 50%, of the process condensate is transferred from the process condensate reservoir 3 to the coarse process condensate purification device 20. There, the process condensate initially enters the first heat exchanger 22, where it is preheated and transferred to the column 21, for example a packed column. The gas stream exiting the upper end of the column 21 is passed through the second heat exchanger 23 and condensed. A partial stream of this is fed back into the column 21, and the remaining partial stream is fed through the first line 40 into the urea synthesis device 1. The coarsely purified process condensate exiting the lower end of the column is divided, and a partial stream is heated through the process condensate return line and the third heat exchanger 24, at least partially evaporated, and fed back to the column 21.The remaining partial flow of the roughly cleaned process condensate is passed through the first heat exchanger 22 to recover the heat and then into the molding exhaust air washing device 4 to absorb further urea from the exhaust air.
[0024] Reference symbol
[0025] 1 urea synthesis device
[0026] 2 Urea forming device
[0027] 3 process condensate storage tanks
[0028] 4 Forming exhaust air washing device
[0029] 10 Process condensate purification device
[0030] 11 first stage
[0031] 12 second stage
[0032] 13 third stage
[0033] 14 fourth heat exchanger
[0034] 15 fifth heat exchanger
[0035] 20 Coarse process condensate purification device
[0036] 21 Column
[0037] 22 first heat exchanger
[0038] 23 second heat exchanger
[0039] 24 third heat exchanger
[0040] 30 reactant inlet
[0041] 31 Product output
[0042] 32 Process condensate outlet
[0043] 40 first line
[0044] 41 second line
Claims
Patent claims 1. Plant system for the production of a urea forming material, wherein the plant system comprises at least one urea synthesis device (1) and one urea forming device (2), wherein the plant system comprises a process condensate purification device (10), wherein the process condensate purification device (10) is designed for separating ammonia and urea from the process condensate of the urea synthesis device (1), wherein the process condensate purification device (10) has a purification stream up to the process condensate outlet (32), wherein the plant system comprises a forming exhaust air scrubber (4), characterized in that the plant system comprises, in addition to the process condensate purification device (10), a coarse process condensate purification device (20), wherein the coarse process condensate purification device (20) has a coarse purification stream,wherein the coarse purification stream is separate and distinct from the purification stream, wherein the urea synthesis device (1) is connected to the process condensate purification device (10) and the coarse process condensate purification device (20) for transferring process condensate, wherein the coarse process condensate purification device (20) is connected to the molding exhaust air scrubber (4).
2. Plant assembly according to claim 1, characterized in that the coarse process condensate purification device (20) is designed as a single-stage device for the removal of ammonia.
3. Plant assembly according to one of the preceding claims, characterized in that the coarse process condensate purification device (20) has a first heat exchanger (22), wherein the first heat exchanger (22) is configured for preheating the process condensate stream coming from the urea synthesis device (1), and wherein the first heat exchanger (22) is configured for cooling the coarsely purified process condensate stream exiting the coarse process condensate purification device (20).
4. System assembly according to one of the preceding claims, characterized in that the coarse process condensate purification device (20) has a second heat exchanger (23), wherein the second heat exchanger (23) is used for condensing the condensate from the The coarse process condensate purification device (20) is designed for the outgoing gas stream.
5. System assembly according to claim 4, characterized in that the second heat exchanger (23) and the coarse process condensate purification device (20) are connected to a carbamate return line.
6. System assembly according to one of the preceding claims, characterized in that the coarse process condensate purification device (20) has a third heat exchanger (24), wherein the coarse process condensate purification device (20) has a recirculation line for a partial flow of the coarsely purified process condensate flow, wherein the third heat exchanger (24) is designed in the recirculation line for heating the recirculated partial flow.
7. Plant assembly according to one of the preceding claims, characterized in that the plant assembly has a process condensate storage tank (3), wherein the process condensate storage tank (3) is arranged after the urea synthesis device (1) and before the process condensate purification device (10) and the coarse process condensate purification device (20).
8. Plant assembly according to one of the preceding claims, characterized in that the coarse process condensate purification device (20) and the urea synthesis device (1) are connected via a first line for the return of the carbamate stream exiting the coarse process condensate purification device (20).
9. Plant assembly according to claim 8, characterized in that the process condensate purification device (10) and the urea synthesis device (1) are connected via a second line for the return of the condensate exiting the process condensate purification device (10). are connected to the carbamate current, with the first line and the second line being connected to each other.