A urea-to-ammonia product gas treatment device and method

Abstract

The present invention discloses a urea-to-ammonia product gas treatment device and method. The device includes: a urea hydrolyzer in which urea solution reacts to generate product gas; a drying device for drying the product gas from the urea hydrolyzer; a heating device for evaporating the moisture absorbed by the desiccant from the drying device and returning it to the drying device; a decarbonization device for decarbonizing the product gas from the drying device; and a reaction device for providing quicklime powder to the decarbonization device. In the present invention, the drying and decarbonization processes do not require two-way parallel switching, and the removal process is continuous, ensuring the stability of the product gas pressure, avoiding the banded peaks of H2O and CO2 in the product during the switching process, and obtaining a product gas containing only NH3. The product gas can be transported without heat tracing, and has the characteristics of energy conservation, consumption reduction, low carbon environmental protection, and recycling, which is of great significance and value for the new construction, renovation, and safe operation of urea hydrolysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of ammonia production from urea, and particularly relates to a device and method for treating product gas produced from urea to ammonia. Background Art

[0002] In the SCR denitration reaction, ammonia is used as a reducing agent. Ammonia can be sourced from direct heating and vaporization of liquid ammonia, or indirectly prepared through evaporation of ammonia water or decomposition of urea. According to national policy requirements, the denitration reducing agent must be changed from liquid ammonia to urea. Urea is not a dangerous good, which is convenient for transportation and storage, and can be decomposed by heating to produce ammonia. There are mainly two mature technologies for ammonia production from urea: urea pyrolysis and hydrolysis. The main equipment of the urea hydrolysis ammonia production system includes a urea dissolution tank, a urea dissolution pump, a urea solution storage tank, a urea solution transfer pump, and a urea hydrolysis reactor, etc. Urea particles are added to the urea dissolution tank and dissolved into a urea solution with a mass fraction of about 40% - 60% with water. It is transported to the urea solution storage tank through the urea dissolution pump. Then, the urea solution enters the urea hydrolysis reactor through the urea solution transfer pump, and decomposes in the urea hydrolysis reactor to generate NH3, H2O, and CO2. The product gas from the hydrolysis of the urea solution is sent to the furnace side by its own pressure, mixed with dilution air, and then sprayed into the SCR inlet flue through an ammonia injection device. Different from liquid ammonia, the product gas from hydrolysis needs to maintain a temperature above 140°C to avoid the reverse reaction of ammonia and carbon dioxide at low temperatures to form carbamate, which will cause blockage of equipment such as the downstream ammonia injection branch pipes. Therefore, the product gas transmission pipeline of hydrolysis needs to be steam traced to ensure that the whole process temperature is not lower than 140°C. Using steam tracing, on the one hand, the energy consumption is relatively high, especially when the transmission pipeline is long, a large amount of steam needs to be consumed; on the other hand, local tracing is prone to low temperature, resulting in reverse reaction of the product gas and affecting the safe operation of the system.

[0003] Chinese invention patent, publication number CN113788484B, discloses a purification treatment device and method for product gas from hydrolysis. This method uses two parallel processes for dehydration and decarbonization. One process uses an absorbent for dehydration and decarbonization, and the other process is for desorption of the absorbent to restore its absorption capacity. However, this patent has obvious deficiencies:

[0004] The product gas from hydrolysis needs to maintain a stable pressure. Using a two-way switching method is prone to cause fluctuations in the pressure of the product gas in the pipeline, seriously affecting the stability of ammonia supply. The discrimination criterion for the switching point is the appearance of H2O and CO2 in the treated product gas, which will cause banded peaks of H2O and CO2 in the product, affecting the treatment effect. Moreover, this patent also needs to consume additional energy to desorb the absorbent to restore its absorption capacity. The waste gas generated during the desorption process contains a small amount of ammonia, which pollutes the environment and is not suitable for direct discharge. Summary of the Invention

[0005] To solve the technical problems existing in the prior art, the object of the present invention is to provide a urea-to-ammonia product gas treatment device and method.

[0006] To achieve the above object and reach the above technical effects, the technical solution adopted by the present invention is as follows:

[0007] A urea-to-ammonia product gas treatment device includes:

[0008] A boiler;

[0009] A urea hydrolyzer, in which urea solution reacts to generate product gas, and the product gas includes NH3, H2O, and CO2;

[0010] A drying device, connected to the urea hydrolyzer, for drying the product gas from the urea hydrolyzer;

[0011] A heating device, connected to the drying device, for evaporating the water absorbed by the desiccant from the drying device and returning it to the drying device;

[0012] A decarbonization device, connected to the drying device, for decarbonizing the product gas from the drying device;

[0013] A reaction device, connected to the decarbonization device, for supplying quicklime powder to the decarbonization device;

[0014] Urea solution reacts in the urea hydrolyzer to generate product gas, the product gas enters the drying device for drying, the dried product gas contains NH3 and CO2, and then enters the decarbonization device for CO2 removal to obtain product gas containing only NH3.

[0015] Further, the device further includes a quicklime powder storage tank, in which quicklime powder is stored. The quicklime powder storage tank is connected to the decarbonization device through a delivery pump c, and the quicklime powder storage tank and the delivery pump e are connected to the reaction device.

[0016] Further, the drying device is a sealed three-compartment housing structure, including a desiccant compartment, a dehumidifying and drying compartment, and a desiccant to be treated compartment arranged in sequence from top to bottom. The desiccant compartment is connected to the dehumidifying and drying compartment through a regulating valve b, the dehumidifying and drying compartment is connected to the desiccant to be treated compartment through a regulating valve c, the desiccant compartment and the desiccant to be treated compartment are respectively connected to the bottom and top of the heating device, and the desiccant can flow between the desiccant compartment, the dehumidifying and drying compartment, the desiccant to be treated compartment, and the heating device.

[0017] Further, a regulating valve a is provided at the top of the desiccant bin, a level gauge a and a regulating valve b are provided at the bottom. The level gauge a is used to monitor the quantity of the desiccant in the desiccant bin. The opening degree of the regulating valve b is adjustable and is used to control the flow rate of the desiccant flowing into the dehumidifying and drying bin. A regulating valve c is provided at the bottom of the dehumidifying and drying bin. The opening degrees of the regulating valve b and the regulating valve c are always kept consistent to ensure that there is always a certain stock of desiccant in the dehumidifying and drying bin. A humidity sensor is arranged at the exhaust port of the dehumidifying and drying bin. A level gauge b is provided at the top of the desiccant bin to be processed, and a regulating valve d is provided at the bottom of the desiccant bin to be processed.

[0018] Further, the decarbonization device includes a decarbonization reaction tower. A quicklime powder spraying device is provided at the top of the decarbonization reaction tower for evenly spraying quicklime powder into the decarbonization reaction tower. A regulating valve e is provided at the bottom, and a CO2 sensor is arranged at the exhaust port. The bottom of the decarbonization reaction tower is connected to the reaction device through the regulating valve e, a delivery pump d and a regulating valve h in sequence. The top of the decarbonization reaction tower is connected to a quicklime powder storage tank through the quicklime powder spraying device and a delivery pump c. Quicklime powder is stored in the quicklime powder storage tank.

[0019] Further, the bottom of the heating device is connected to the desiccant bin through a regulating valve g, a delivery pump b and a regulating valve a in sequence. The top of the heating device is connected to the desiccant bin to be processed through a regulating valve f, a delivery pump a and a regulating valve d in sequence.

[0020] Further, the heating device includes a heating evaporation tower. A regulating valve f is provided at the top of the heating evaporation tower, a regulating valve g is provided at the bottom, and heating coils are arranged inside. The gas in the heating coils is isolated from the gas in the heating device. The inlet of the heating coils is connected to the inlet flue of the air preheater, and the exhaust is connected to the outlet flue of the air preheater. The flue gas pressure at the inlet of the air preheater is 1 - 2 kPa higher than the flue gas pressure at the outlet of the air preheater, and the flue gas temperature is 300 - 400 °C. The temperature inside the heating evaporation tower is always higher than 100 °C.

[0021] Further, the heating evaporation tower is connected to a compressed air storage tank. Compressed air is introduced into the heating evaporation tower through the compressed air storage tank to take away the evaporated moisture, and the exhaust is connected to the outlet flue of the air preheater.

[0022] Further, the reaction device includes a high-temperature pyrolysis tower. The high-temperature pyrolysis tower is connected to a boiler. The high-temperature flue gas in the boiler enters the high-temperature pyrolysis tower. The limestone powder in the high-temperature pyrolysis tower decomposes into CaO and CO2 under high temperature. The gaseous CO2 circulates with the boiler flue gas and is not discharged externally, and the CaO returns to the quicklime powder storage tank.

[0023] The present invention also discloses a method for treating product gas in urea-to-ammonia production, which adopts a device for treating product gas in urea-to-ammonia production as described above. The method includes the following steps:

[0024] 1) Product gas drying:

[0025] Regulating valve a and regulating valve d are closed, regulating valve b and regulating valve c are opened, and the opening degrees of regulating valve b and regulating valve c are the same. The opening degree can be dynamically adjusted. According to the monitoring of the humidity sensor, if H2O is detected, the opening degrees of regulating valve b 34 and regulating valve c are further increased until the treated product gas is completely dry and there is a certain margin. At this time, the desiccant in the desiccant bin flows into the dehumidifying and drying bin, and the water-absorbed desiccant flows into the desiccant bin to be treated. The product gas in the urea hydrolyzer enters from the lower air inlet of the dehumidifying and drying bin and exits from the upper exhaust port, so that the desiccant that first contacts the product gas preferentially flows into the desiccant bin to be treated. When level gauge a detects that the desiccant bin is insufficient, at this time, regulating valve b and regulating valve c are closed, and regulating valve a is opened. Delivery pump b quickly transports the desiccant that has been heat-treated to restore its drying capacity to the desiccant bin. This process takes a short time and the desiccant bin can be quickly filled in a short time. Subsequently, regulating valve a and delivery pump b are closed, and regulating valve b and regulating valve c are reopened. When level gauge b detects that the desiccant bin to be treated reaches the upper limit value, at this time, regulating valve b and regulating valve c are closed, regulating valve d and regulating valve f are opened, and delivery pump a quickly transports the water-absorbed desiccant to the heating evaporation tower. This process takes a short time and all the desiccant in the desiccant bin to be treated can be quickly transported to the heating evaporation tower in a short time. Subsequently, regulating valve f, regulating valve d and delivery pump a are closed, and regulating valve b and regulating valve c are reopened;

[0026] 2) Product gas decarbonization:

[0027] After the product gas is dried by the drying device and no longer contains H2O, it exits from the upper exhaust port of the dehumidifying and drying bin and flows into the decarbonization device to remove CO2:

[0028] The product gas flows in from the lower part of the decarbonization reaction tower and is discharged from the upper part. The delivery pump C continuously delivers the quicklime powder in the quicklime powder storage tank to the quicklime powder injection device. The output power of the delivery pump C is adjusted according to the CO2 content in the product gas monitored by the CO2 sensor. If CO2 is detected, the output power of the delivery pump C is quickly increased to ensure the decarbonization effect and leave enough margin. The quicklime powder injection device on the top of the decarbonization reaction tower sprays quicklime powder into the decarbonization reaction tower. The quicklime powder settles downward under the action of gravity and can fully react with the countercurrent product gas to absorb the CO2 in it. The limestone powder is formed into limestone powder, and the decarbonization effect can be improved through countercurrent contact reaction. The limestone powder is accumulated at the bottom of the decarbonization reaction tower. The regulating valve e is set to open at a fixed time. When it is opened, the delivery pump d and the regulating valve h are opened, and the limestone powder can be quickly transported to the high-temperature pyrolysis tower for pyrolysis reaction to generate CaO and CO2. The reaction time is short, and the gaseous CO2 circulates with the boiler flue gas. After the set time, the regulating valve i is opened, and the delivery pump e is turned on to transport the quicklime powder to the quicklime powder storage tank. In this way, it can be recycled and reused, but there will still be a small amount of loss. The quicklime powder can be regularly added to the quicklime powder storage tank;

[0029] The product gas after treatment by the decarbonization device is NH3 gas, which flows into the denitrification inlet flue through pipelines and ammonia injection devices without the need for heating to achieve the denitrification function.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention discloses a device and method for treating product gas produced from urea to ammonia. Through a drying device and a decarbonization device, H2O and CO2 in the product gas produced from urea to ammonia are continuously and stably removed. The product gas can be transported without being accompanied by heat. On the one hand, it can reduce the consumption of heat accompanying energy, and on the other hand, it can also improve the reliability of the system, avoiding the problem of crystallization blockage caused by low temperature of the product gas. The drying and decarbonization processes do not need to adopt two-way parallel switching, and the removal process is continuous, ensuring the stability of the product gas pressure and avoiding the band-shaped peaks of H2O and CO2 in the product during the switching process. By using the high-temperature flue gas of the boiler to form a high-temperature atmosphere, the desiccant is heated to evaporate water, realizing the reuse of the desiccant. With the differential pressure of the boiler flue gas itself, spontaneous flow is achieved without adding a driving device. There are no any pollutants discharged during the whole drying process, and the evaporated water vapor also returns to the boiler cycle. By using the heat of the boiler, the decarbonization product limestone powder is pyrolyzed to realize the reuse of the decarbonizing agent quicklime powder. There are no any pollutants discharged during the whole decarbonization process, the treated CO2 returns to the boiler cycle, and the decarbonizing agent returns to the storage bin for reuse. After drying and decarbonizing, the hydrolyzed product gas only remains NH3, and NH3 can be transported at normal temperature without being accompanied by heat. The present invention not only realizes the dehydration and decarbonization treatment of the urea hydrolysis product gas and cancels the heat accompanying of the product gas, but also has the characteristics of energy conservation and consumption reduction, low-carbon environmental protection, and recycling use, which can improve the system stability and has important significance and value for the new construction, transformation, and safe operation of urea hydrolysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic structural diagram of the present invention;

[0033] Figure 2 is a schematic structural diagram of the boiler of the present invention;

[0034] Wherein: 1. Boiler; 2. Urea hydrolyzer; 3. Drying device; 4. Humidity sensor; 5. Decarbonization device; 6. CO2 sensor; 7. Quicklime powder storage tank; 8. Heating device; 9. Reaction device; 10. Compressed air storage tank; 11. Delivery pump a; 12. Delivery pump b; 13. Delivery pump c; 14. Delivery pump d; 15. Delivery pump e; 31. Control valve a; 32. Desiccant bin; 33. Level gauge a; 34. Control valve b; 35. Dehumidifying and drying bin; 36. Control valve c; 37. Level gauge b; 38. Desiccant bin to be treated; 39. Control valve d; 51. Quicklime powder injection device; 52. Decarbonization reaction tower; 53. Control valve e; 81. Control valve f; 82. Heating and evaporation tower; 83. Heating coil; 84. Control valve g; 91. Control valve h; 92. High-temperature pyrolysis tower; 93. Control valve i; 16. Air preheater inlet flue; 17. Air preheater outlet flue. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The present invention will be described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making the scope of protection of the present invention more clearly defined.

[0036] A brief overview of one or more aspects is given below to provide a basic understanding of these aspects. This overview is not an exhaustive survey of all contemplated aspects, and is neither intended to identify key or decisive elements of all aspects nor to attempt to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that follows.

[0037] As Figure 1-2 shown, a urea-to-ammonia product gas treatment device includes:

[0038] A boiler 1;

[0039] A urea hydrolyzer 2, in which urea solution reacts to generate product gas, and the product gas includes NH3, H2O, and CO2;

[0040] A drying device 3, which is connected to the urea hydrolyzer 2 and has a sealed three-compartment housing structure, including a desiccant bin 32, a dehumidifying and drying bin 35, and a desiccant bin 38 to be processed, which are arranged in sequence from top to bottom; wherein, desiccant is stored in the desiccant bin 32, the desiccant is fine-grained silica gel with good fluidity, a regulating valve a 31 is provided at the top of the desiccant bin 32, a level gauge a 33 and a regulating valve b 34 are provided at the bottom, the regulating valve a 31 is opened when replenishing desiccant and closed under normal circumstances, the level gauge a 33 can monitor the quantity of desiccant in the desiccant bin 32, when the desiccant drops to the lower limit value, the regulating valve a 31 needs to be opened for desiccant replenishment, the opening degree of the regulating valve b 34 can be adjusted to control the flow rate of desiccant flowing into the dehumidifying and drying bin 35; a certain stock of desiccant is always maintained in the dehumidifying and drying bin 35 for dehydration and drying, the product gas enters from the air inlet at the lower part of the dehumidifying and drying bin 35 and exits from the air outlet at the upper part, the top of the dehumidifying and drying bin 35 communicates with the desiccant bin 32 through the regulating valve b 34, a regulating valve c 36 is provided at the bottom of the dehumidifying and drying bin 35 for communicating with the desiccant bin 38 to be processed, and the opening degrees of the regulating valve b 34 and the regulating valve c 36 are always kept consistent to ensure that the quantity of desiccant entering and leaving the dehumidifying and drying bin 35 is the same, so as to ensure that a fixed stock of desiccant is always maintained inside; the water-absorbed desiccant is stored in the desiccant bin 38 to be processed, the top of the desiccant bin 38 to be processed communicates with the dehumidifying and drying bin 35 through the regulating valve c 36, a regulating valve d 39 is provided at the bottom of the desiccant bin 38 to be processed, and a level gauge b 37 is provided at the upper part of the desiccant bin 38 to be processed. When the level gauge b 37 monitors that the water-absorbed desiccant accumulates to the upper limit value, the water-absorbed desiccant is timely output to the heating device 8;

[0041] The decarbonization device 5 has a decarbonization reaction tower 52 as its main body. The decarbonization reaction tower 52 is a sealed housing structure. There is a quicklime powder spraying device 51 at the top, which can evenly spray quicklime powder, and a regulating valve e 53 at the bottom.

[0042] A quicklime powder storage tank 7;

[0043] The heating device 8 has a heating and evaporation tower 82 as its main body. The heating and evaporation tower 82 is a sealed housing structure. There is a regulating valve f 81 at the top, a regulating valve g 84 at the bottom, and a heating coil 83 inside. The gas inside the heating coil 83 is isolated from the gas inside the heating device 8. The inlet of the heating coil 83 is connected to the inlet flue of the air preheater 16, and the exhaust is connected to the outlet flue of the air preheater 17. The boiler 1, the denitration device, and the air preheater are arranged in sequence. The flue gas pressure at the inlet of the air preheater is 1 - 2 kPa higher than that at the outlet of the air preheater, and the flue gas temperature is 300 - 400 °C. The above flue gas can flow spontaneously without a pumping device, without adding a power device and energy consumption. In this way, the temperature inside the heating and evaporation tower 82 can always be kept higher than 100 °C, and the water absorbed by the desiccant can be evaporated. Compressed air is introduced into the heating and evaporation tower 82 through the compressed air storage tank 10, and the evaporated water is carried away by the compressed air. The exhaust is connected to the outlet flue of the air preheater 17. Since the compressed air is at positive pressure and the outlet of the air preheater is at negative pressure, the above gases can flow spontaneously, and the evaporated waste gas returns to the boiler 1 for circulation and is treated by the boiler environmental protection equipment;

[0044] The reaction device 9 has a high-temperature pyrolysis tower 92 as its main body. The high-temperature pyrolysis tower 92 is connected to the furnace of the boiler 1. The product gas flows into the lower part of the decarbonization device 5 and is discharged from the upper part. A filter screen is set at the exhaust port to prevent a large amount of powder from being carried out by the airflow and causing loss. The CO2 sensor 6 is located at the exhaust port to monitor the CO2 in the treated product gas. Quicklime powder (CaO) is stored in the quicklime powder storage tank 7. The quicklime powder can be transported to the quicklime powder spraying device 51 through the delivery pump c 13. The limestone powder (CaCO3) after absorbing CO2 is sent to the reaction device 9. Using the high-temperature flue gas (>1000 °C) in the boiler 1 to form a high-temperature reaction atmosphere, the limestone powder (CaCO3) decomposes into CaO and CO2 under high temperature. The gaseous CO2 circulates with the boiler flue gas and is not discharged externally. The quicklime powder (CaO) returns to the quicklime powder storage tank 7 again.

[0045] The chemical equation for the urea hydrolysis to produce ammonia is:

[0046]

[0047] The concentration of the urea solution in the urea hydrolysis reactor is about 40 - 60%, the pressure of the gas-liquid two-phase equilibrium system is about 0.4 - 0.6 MPa, and the temperature is about 140 - 170 °C.

[0048] A method for treating product gas produced from urea to ammonia, comprising the following steps:

[0049] 1) Product gas drying:

[0050] Regulating valve a 31 and regulating valve d 39 are closed, regulating valve b 34 and regulating valve c 36 are opened, and the opening degrees of regulating valve b 34 and regulating valve c 36 are the same. The opening degree can be dynamically adjusted. According to the monitoring of humidity sensor 4, if H2O is detected, the opening degrees of regulating valve b 34 and regulating valve c 36 are further increased until the treated product gas is completely dry with a certain margin. At this time, the desiccant in desiccant bin 32 flows into dehumidifying and drying bin 35, and the water-absorbed desiccant flows into the desiccant bin to be treated 38. The product gas enters from the lower air inlet of dehumidifying and drying bin 35 and exits from the upper air outlet. This design enables the desiccant that first contacts the product gas to flow into the desiccant bin to be treated 38 preferentially, because the desiccant that first contacts the product gas absorbs the most water and is also the part that first loses its drying ability. When level gauge a 33 monitors that the desiccant bin 32 is insufficient, at this time, regulating valve b 34 and regulating valve c 36 are closed, regulating valve a 31 is opened, and transfer pump b 12 quickly transports the desiccant that has been heat-treated to restore its drying ability to desiccant bin 32. This process takes a short time and can quickly fill desiccant bin 32 in a short time. Subsequently, regulating valve a 31 and transfer pump b 12 are closed, and regulating valve b 34 and regulating valve c 36 are reopened. Because the replenishment time is very short, it basically does not affect the treatment effect of the desiccant in dehumidifying and drying bin 35. When level gauge b 37 monitors that the desiccant bin to be treated 38 reaches the upper limit value, at this time, regulating valve b 34 and regulating valve c 36 are closed, regulating valve d 39 and regulating valve f 81 are opened, and transfer pump a 11 quickly transports the water-absorbed desiccant to heating evaporation tower 82. This process takes a short time and can quickly transport all the desiccant in the desiccant bin to be treated 38 to heating evaporation tower 82 in a short time. Subsequently, regulating valve f 81, regulating valve d 39 and transfer pump a 11 are closed, and regulating valve b 34 and regulating valve c 36 are reopened. Because the discharging time is very short, it basically does not affect the treatment effect of the desiccant in dehumidifying and drying bin 35;

[0051] 2) Product gas decarbonization:

[0052] After being dried by the drying device 3, the product gas no longer contains H2O and is discharged from the upper exhaust port of the dehumidifying and drying bin 35 and flows into the decarbonization device 5 to remove CO2: The product gas flows in from the lower part of the decarbonization reaction tower 52 and is discharged from the upper part. The conveying pump c13 continuously conveys the quicklime powder (CaO) in the quicklime powder storage tank 7 into the quicklime powder injection device 51. The output power of the conveying pump c13 is adjusted according to the CO2 content in the product gas monitored by the CO2 sensor 6. If CO2 is detected, the output power of the conveying pump c13 is quickly increased to ensure the decarbonization effect and leave enough margin. The quicklime powder injection device 51 at the top of the decarbonization reaction tower 52 sprays the quicklime powder into the decarbonization reaction tower 52. The quicklime powder deposits downward under the action of gravity and can fully react with the countercurrent product gas to absorb the CO2 therein and generate limestone powder (CaCO3). The decarbonization effect can be improved through countercurrent contact reaction. The limestone powder accumulates at the bottom of the decarbonization reaction tower 52. The regulating valve e53 is set to open regularly. When it opens, the conveying pump d14 and the regulating valve h91 open, and the limestone powder can be quickly conveyed into the high-temperature pyrolysis tower 92 for pyrolysis reaction to generate CaO and CO2. The reaction time is short. The gaseous CO2 is recycled with the boiler flue gas. After a set time, the regulating valve i93 opens and the conveying pump e15 starts to convey the quicklime powder (CaO) into the quicklime powder storage tank 7. In this way, it can be recycled repeatedly, but there will still be a small amount of loss, and quicklime powder can be regularly replenished into the quicklime powder storage tank 7;

[0053] The product gas treated by the decarbonization device 5 is NH3 gas, which flows into the denitration inlet flue through the pipeline and the ammonia injection device under the condition of no need for heat tracing to realize the denitration function.

[0054] Compared with the prior art, the present invention has at least the following technical effects:

[0055] 1. Through the drying and decarbonization treatment of the product gas, the present invention realizes the purpose of transporting the product gas without heat tracing, greatly saves energy consumption, and improves the reliability of system operation;

[0056] 2. The present invention realizes the repeated recycling of the desiccant and the decarbonizing agent by using the heat of the boiler flue gas, reduces the consumption of resources and energy and the generation of by-products, greatly saves costs and causes no environmental pollution;

[0057] 3. The present invention separately sets the absorption treatment and the restoration treatment processes of the desiccant and the decarbonizing agent, ensuring the continuous and stable drying and decarbonization process and the stable pressure of the product gas.

[0058] For the parts or structures not specifically described in the present invention, the prior art or existing products can be adopted and will not be elaborated here.

[0059] The above are only embodiments of the present invention, and do not thus limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall similarly be included within the patent protection scope of the present invention.

Claims

1. An ammonia production gas treatment device using urea, characterized in that, Comprising: A boiler; A urea hydrolyzer, in which a urea solution reacts to generate a product gas, and the product gas includes NH3, H2O, and CO2; A drying device, connected to the urea hydrolyzer and used to dry the product gas from the urea hydrolyzer; A heating device, connected to the drying device and used to evaporate the moisture absorbed by the desiccant from the drying device and return it to the drying device; A decarbonization device, connected to the drying device and used to decarbonize the product gas from the drying device; A reaction device, connected to the decarbonization device and used to supply quicklime powder to the decarbonization device; The urea solution reacts in the urea hydrolyzer to generate a product gas, the product gas enters the drying device for drying, the dried product gas contains NH3 and CO2, and then enters the decarbonization device for CO2 removal to obtain a product gas containing only NH3; The heating device includes a heating evaporation tower, a control valve f is provided at the top of the heating evaporation tower, a control valve g is provided at the bottom, and a heating coil is provided inside. The gas in the heating coil is isolated from the gas in the heating device. The inlet of the heating coil is connected to the inlet flue of the air preheater, and the exhaust is connected to the outlet flue of the air preheater. The flue gas pressure at the inlet of the air preheater is 1-2 kPa higher than the flue gas pressure at the outlet of the air preheater, and the flue gas temperature is 300-400 °C. The temperature inside the heating evaporation tower is always higher than 100 °C.

2. The ammonia production product gas treatment device according to claim 1, wherein It also includes a quicklime powder storage tank, in which quicklime powder is stored. The quicklime powder storage tank is connected to the decarbonization device through a delivery pump c, and the quicklime powder storage tank and the delivery pump e are connected to the reaction device.

3. The ammonia production product gas treatment device according to claim 1, characterized in that, The drying device is a sealed three-compartment housing structure, including a desiccant chamber, a dehumidifying and drying chamber, and a desiccant chamber to be treated, which are arranged in sequence from top to bottom. The desiccant chamber is connected to the dehumidifying and drying chamber through a control valve b, the dehumidifying and drying chamber is connected to the desiccant chamber to be treated through a control valve c, the desiccant chamber and the desiccant chamber to be treated are respectively connected to the bottom and the top of the heating device, and the desiccant can flow between the desiccant chamber, the dehumidifying and drying chamber, the desiccant chamber to be treated, and the heating device.

4. The ammonia production product gas treatment device according to claim 3, wherein A control valve a is provided at the top of the desiccant chamber, a level gauge a and a control valve b are provided at the bottom. The level gauge a is used to monitor the quantity of the desiccant in the desiccant chamber. The opening degree of the control valve b is adjustable and used to control the flow rate of the desiccant flowing into the dehumidifying and drying chamber; a control valve c is provided at the bottom of the dehumidifying and drying chamber. The opening degrees of the control valve b and the control valve c are always kept consistent to ensure that there is always a certain stock of desiccant in the dehumidifying and drying chamber. A humidity sensor is provided at the exhaust port of the dehumidifying and drying chamber; a level gauge b is provided at the top of the desiccant chamber to be treated, and a control valve d is provided at the bottom of the desiccant chamber to be treated.

5. The ammonia production product gas treatment device according to claim 1, characterized in that, The decarbonization device includes a decarbonization reaction tower. A quicklime powder spraying device is provided at the top of the decarbonization reaction tower for evenly spraying quicklime powder into the decarbonization reaction tower. A regulating valve e is provided at the bottom, and a CO2 sensor is arranged at the exhaust port. The bottom of the decarbonization reaction tower is sequentially connected to the reaction device through the regulating valve e, the delivery pump d, and the regulating valve h. The top of the decarbonization reaction tower is connected to the quicklime powder storage tank through the quicklime powder spraying device and the delivery pump c. Quicklime powder is stored in the quicklime powder storage tank.

6. The ammonia production product gas treatment device according to claim 1 or 3, characterized in that, The bottom of the heating device is sequentially connected to the desiccant bin through the regulating valve g, the delivery pump b, and the regulating valve a. The top of the heating device is connected to the desiccant bin to be treated through the regulating valve f, the delivery pump a, and the regulating valve d in sequence.

7. A urea-to-ammonia product gas treatment device according to claim 1, characterized in that, The heating evaporation tower is connected to the compressed air storage tank. Compressed air is introduced into the heating evaporation tower through the compressed air storage tank, and the evaporated moisture is carried away by the compressed air. The exhaust gas is connected to the outlet flue of the air preheater.

8. The ammonia production product gas treatment device according to claim 1, wherein The reaction device includes a high-temperature pyrolysis tower. The high-temperature pyrolysis tower is connected to the boiler. The high-temperature flue gas in the boiler enters the high-temperature pyrolysis tower. The limestone powder in the high-temperature pyrolysis tower decomposes into CaO and CO2 under the action of high temperature. The gaseous CO2 circulates with the boiler flue gas and is not discharged externally. The CaO returns to the quicklime powder storage tank.

9. A method for treating product gas produced from urea to ammonia, characterized in that, Using a urea-to-ammonia product gas treatment device according to any one of claims 1-8, the method includes the following steps: 1) Product gas drying: The regulating valves a and d are closed, the regulating valves b and c are opened, and the opening degrees of the regulating valves b and c are the same. The opening degree can be dynamically adjusted. According to the monitoring of the humidity sensor, if H2O is detected, the opening degrees of the regulating valves b34 and c are further increased until the treated product gas is completely dried with a certain margin. At this time, the desiccant in the desiccant bin flows into the dehumidifying and drying bin, and the water-absorbed desiccant flows into the desiccant bin to be treated. The product gas in the urea hydrolyzer enters from the lower air inlet of the dehumidifying and drying bin and exits from the upper exhaust port, so that the desiccant that first contacts the product gas preferentially flows into the desiccant bin to be treated. When the level gauge a detects that the desiccant bin is insufficient, at this time, the regulating valves b and c are closed, the regulating valve a is opened, and the delivery pump b quickly conveys the desiccant that has been heated and treated to restore its drying ability to the desiccant bin. This process takes a short time and can quickly fill the desiccant bin in a short time. Subsequently, the regulating valve a and the delivery pump b are closed, and the regulating valves b and c are reopened. When the level gauge b detects that the desiccant bin to be treated reaches the upper limit value, at this time, the regulating valves b and c are closed, the regulating valves d and f are opened, and the delivery pump a quickly conveys the water-absorbed desiccant to the heating evaporation tower. This process takes a short time and can quickly convey all the desiccant in the desiccant bin to be treated to the heating evaporation tower in a short time. Subsequently, the regulating valve f, the regulating valve d, and the delivery pump a are closed, and the regulating valves b and c are reopened; 2) Product gas decarbonization: After being dried by the drying device, the product gas no longer contains H2O and is discharged from the upper exhaust port of the dehumidifying and drying bin and flows into the decarbonization device to remove CO2: The product gas flows in from the lower part of the decarbonization reaction tower and is discharged from the upper part. The conveying pump c continuously conveys the quicklime powder in the quicklime powder storage tank into the quicklime powder injection device. The output power of the conveying pump c is adjusted according to the CO2 content in the product gas monitored by the CO2 sensor. If CO2 is detected, the output power of the conveying pump c is quickly increased to ensure the decarbonization effect and leave enough margin. The quicklime powder injection device at the top of the decarbonization reaction tower sprays the quicklime powder into the decarbonization reaction tower. The quicklime powder deposits downward under the action of gravity and can fully react with the counter-flowing product gas to absorb the CO2 in it and generate limestone powder. The decarbonization effect can be improved through counter-flow contact reaction. The limestone powder accumulates at the bottom of the decarbonization reaction tower. The regulating valve e is set to open regularly. When it opens, the conveying pump d and the regulating valve h open, and the limestone powder can be quickly conveyed into the high-temperature pyrolysis tower for pyrolysis reaction to generate CaO and CO2. The reaction time is short. The gaseous CO2 circulates with the boiler flue gas. After a set time, the regulating valve i opens and the conveying pump e starts to convey the quicklime powder into the quicklime powder storage tank. In this way, it can be recycled repeatedly, but there will still be a small amount of loss, and quicklime powder can be regularly added to the quicklime powder storage tank; The product gas treated by the decarbonization device is NH3 gas, and it flows into the denitration inlet flue through the pipeline and the ammonia injection device under the condition of no need for heat tracing to achieve the denitration function.

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