A system and method for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea

Abstract

The invention discloses a system and method for preparing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea, the system comprising a urea solution storage tank (1), a urea solution delivery pump A (2), a heterogeneous hydrolysis reactor (3) and a steam pipeline (4), wherein the heterogeneous hydrolysis reactor (3) adopts a tubular fixed bed reactor; the urea solution storage tank (1) is connected to the heterogeneous hydrolysis reactor (3) by a urea solution delivery pump A (2) and a pipeline, and the steam pipeline (4) is connected to the heterogeneous hydrolysis reactor (3). The hydrolysis ammonia system of the present invention has a simple structure, adopts a fixed bed tubular reactor, and the urea solution is hydrolyzed to generate ammonia and carbon dioxide under the action of a solid catalyst, which belongs to a liquid-solid two-phase reaction. When the device corresponding to the current most urea homogeneous catalytic hydrolysis process reaction is modified, the system responsiveness can be improved, the system operation cost can be reduced, and the waste liquid discharge can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas denitration, and in particular to a system and method for preparing ammonia by heterogeneous catalytic hydrolysis of SCR denitration urea, belonging to the technical field of air pollution control. Background Art

[0002] Selective catalytic reduction (SCR) denitrification technology has been widely used at home and abroad due to its high efficiency. Commonly used reducing agents for SCR denitrification technology are liquid ammonia, ammonia water and urea. Liquid ammonia and ammonia water are hazardous chemicals, which pose great safety hazards to transportation and unloading. If a leak occurs, it will affect the safe production of power plants, surrounding residents and the ecological environment. Urea is a non-toxic and harmless chemical product with good performance indicators and operational control safety. Its chemical properties are stable and will not explode suddenly, and it is completely non-hazardous. It is imperative for coal-fired power plants to upgrade the denitrification reducing agent from liquid ammonia to urea.

[0003] Urea ammonia production technology mainly includes urea thermal decomposition ammonia production technology and urea hydrolysis technology. Urea hydrolysis technology has been increasingly used in flue gas denitrification of coal-fired power plants due to its low energy consumption, safe, stable and reliable operation. Urea hydrolysis ammonia production technology is generally divided into two types: ordinary urea hydrolysis technology and urea catalytic hydrolysis technology. Compared with ordinary urea hydrolysis technology, urea catalytic hydrolysis technology has the advantages of low reaction temperature, fast reaction speed and short response time. However, urea catalytic hydrolysis technology currently generally uses liquid acid or alkali as a catalyst. The homogeneous catalyst has the problems of being difficult to recycle, requiring regular investment, high operating costs, and corrosive to equipment.

[0004] Patent application No. 201510236369.7 discloses a three-phase fluidized urea catalytic hydrolysis ammonia production equipment and method, in which a three-phase fluidized reaction occurs in the hydrolysis ammonia production equipment, and the three phases involved in the reaction are composed of a solid catalyst, a liquid urea solution and a gas phase steam. Although this method can solve the problem of catalyst recovery, it still has the following disadvantages: 1. Using a three-phase fluidized reaction, in addition to indirectly heating the feed liquid in the reactor, the steam is also used as the fluidizing medium of the reactor and enters the reactor directly from the bottom. The urea solution is sprayed from the top, which will cause the entrainment of mist and foam, making the mass transfer and heat transfer in the reactor worse, and the chemical The reaction takes a long time, which makes the system take a long time to respond to the ammonia demand signal; it also increases steam consumption, reduces the urea hydrolysis conversion rate and increases the system operating cost; 2. Activated carbon is used as a carrier of the catalyst. The activated carbon itself does not have catalytic properties, which makes its catalytic activity relatively general, resulting in a slow catalytic hydrolysis reaction rate, causing the system to take a long time to respond to the ammonia demand signal, and there is no interaction between the activated carbon and the active components, which makes the active components easy to lose; 3. The three-phase fluidized hydrolysis reaction device has a complex structure, and the three-phase fluidized reaction aggravates the disturbance in the reactor, which is easy to cause the reactor to vibrate, and has high requirements for the base, resulting in high manufacturing and installation costs. Summary of the invention

[0005] The object of the present invention is to provide a system and method for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea. The hydrolysis reactor adopts a tubular fixed bed reactor, so that the system urea hydrolysis conversion rate is high, the response time to the ammonia demand signal is short, and the system energy consumption, investment cost and operation cost are reduced.

[0006] In order to solve the above technical problems, the present invention adopts the following technical scheme: a system for producing ammonia by heterogeneous catalytic hydrolysis of urea using SCR denitration, comprising: a urea configuration system, a urea heterogeneous hydrolysis reaction system, a residual liquid discharge and recovery system and a hydrophobic recovery system; the urea heterogeneous hydrolysis reaction system comprises a urea solution storage tank, a urea solution delivery pump A, a heterogeneous hydrolysis reactor and a steam pipeline, and the heterogeneous hydrolysis reactor adopts a tubular fixed bed reactor; the urea solution storage tank is connected to the heterogeneous hydrolysis reactor through a urea solution delivery pump A and a pipeline, and the steam pipeline is connected to the heterogeneous hydrolysis reactor; the urea solution storage tank is connected to the urea configuration system through a pipeline; the heterogeneous hydrolysis reactor is respectively connected to the residual liquid discharge and recovery system and the hydrophobic recovery system, and the residual liquid discharge and recovery system is connected to the urea configuration system.

[0007] Preferably, the urea configuration system comprises: a urea dissolving tank, a desalted water pump and a B urea solution delivery pump, wherein the desalted water pump is connected to the urea dissolving tank; the urea dissolving tank is connected to a urea solution storage tank via the B urea solution delivery pump and a pipeline, so that urea can be dissolved in advance and pumped into the urea solution storage tank.

[0008] After dissolution, the urea solution at a temperature of 30 to 65° C. is transported to a urea solution storage tank, thereby facilitating a hydrolysis reaction.

[0009] Preferably, the residual liquid discharge and recovery system includes: a residual liquid storage tank and a residual liquid circulation pump. The residual liquid storage tank is connected to the heterogeneous hydrolysis reactor through a pipeline, and the residual liquid storage tank is connected to the urea dissolution tank through the residual liquid circulation pump and the pipeline. The residual liquid discharge and recovery system can reduce the waste of water resources, realize the recycling of urea residual liquid, and reduce the discharge of system waste liquid.

[0010] Preferably, the steam pipeline is divided into three routes, one route is connected to the heterogeneous hydrolysis reactor, and the other two routes are respectively connected to the inlet of the urea solution storage tank and the inlet of the urea dissolution tank, and are used for cleaning the urea dissolution tank and the urea solution storage tank.

[0011] Preferably, the drain recovery system comprises: a drain tank and a drain pump, the drain pump is connected to the drain tank, and the drain tank is connected to the heterogeneous hydrolysis reactor through a pipeline, so that the condensate generated after steam heat exchange enters the drain tank and is drained back to the plant by the drain pump.

[0012] Preferably, the heterogeneous hydrolysis reactor is further provided with a demister, which eliminates the liquid by using the demister, thereby avoiding the entrainment of mist when the target product ammonia escapes from the fixed bed reactor, and bringing the liquid urea solution out of the reactor.

[0013] Preferably, the demisting device adopts but is not limited to a Venturi demisting device or a wire mesh demisting device.

[0014] Preferably, the droplet content is reduced to less than 10 mg / m 3 If the droplet content is higher than 10mg / m 3 , which will cause excessive loss of urea solution and waste of water resources.

[0015] Preferably, the interior of the heterogeneous hydrolysis reactor is also provided with an integrated ammonia buffer space, thereby improving the responsiveness of the heterogeneous hydrolysis reactor to changes in unit load.

[0016] Preferably, the volume of the integrated ammonia buffer space is 1 / 20 to 1 / 3 of the volume of the heterogeneous hydrolysis reactor. The size of the buffer space is determined by factors such as the change in the load of the power plant unit and the volume of the heterogeneous hydrolysis reactor. When it is set to 1 / 20 to 1 / 3, the heterogeneous hydrolysis reactor can have sufficient buffer space when the unit load changes.

[0017] Preferably, the heterogeneous hydrolysis reactor is further provided with a spraying device, and the urea solution is sprayed into the heterogeneous hydrolysis reactor through the spraying device, thereby achieving uniform spraying of the urea solution and improving the conversion rate of the urea solution.

[0018] Further preferably, the angle α between the spray direction of the nozzle in the spray device and the axial direction of the tubes of the tube-in-tube fixed bed reactor is 0-60°, so that uniform spraying of the urea solution can be achieved, resulting in a higher conversion rate of the urea solution.

[0019] Preferably, the inner diameter of the tube of the shell-and-tube fixed bed reactor is 0.05-1.00 m, and the number of inner tubes is 3-100. The inner diameter of the tube and the number of inner tubes of the shell-and-tube fixed bed reactor are determined by factors such as the filling amount of the solid catalyst, the bulk density of the catalyst, the porosity of the catalyst, the volume flow rate of the urea solution, the urea conversion rate, the reactor floor area, and the reactor cost. When the inner diameter of the tube is less than 0.05, the flow rate of the urea solution is too fast, which will shorten the reaction time and reduce the reaction conversion rate; when the inner diameter of the tube is greater than 1 m, it is not conducive to the heat exchange between water vapor and the reactants in the tube; and when the inner diameter of the tube of the shell-and-tube fixed bed reactor is 0.05-1.00 m, it can be conducive to the heat exchange between steam and the reactants in the tube, and the flow rate of the urea solution will not be too fast, which can increase the reaction time, thereby improving the reaction conversion rate. In addition, when the number of inner tubes is less than 3, the tube wall area is too small, which is not conducive to the heat exchange between the steam outside the tube and the reactants inside the tube; when the number of inner tubes is greater than 100, the cost will be greatly increased. When the number of inner tubes is 3 to 100, the tube wall area can be increased, which is conducive to the heat exchange between the steam outside the tube and the reactants inside the tube, and the cost can be effectively controlled.

[0020] Preferably, the tube length is 0.1 to 5 m. The tube length is determined by the catalyst filling amount, the number of inner tubes and the inner diameter of the tube. The design of the tube length also needs to consider the actual situation on site, such as the floor space and the designable height. By setting the tube length to 0.1 to 5 m and considering other factors, the actual catalytic reaction effect can be better.

[0021] The method for producing ammonia by catalytic hydrolysis of SCR denitrification urea using the aforementioned SCR denitrification urea heterogeneous catalytic hydrolysis system comprises the following steps: placing a solid catalyst in a tube of a tubular fixed bed reactor, and then pumping in a urea solution; after heating, the urea solution undergoes a hydrolysis reaction under the action of the solid catalyst to produce ammonia and carbon dioxide; wherein the reaction pressure in the tubular fixed bed reactor is 0.3-0.6 MPa, and the reaction temperature is 120-150°C.

[0022] Preferably, the reaction pressure in the tubular fixed bed reactor is 0.5 MPa and the reaction temperature is 135° C. This can further improve the reaction conversion rate of the urea solution.

[0023] Preferably, the solid catalyst is prepared by loading a metal oxide on a porous material having an acidic or basic functional group on the surface, wherein the metal oxide loading is 5% to 60%; if the metal oxide loading is less than 5%, the active components exposed on the catalyst surface are few, making the reaction activity of the catalyst low; if the metal oxide loading is greater than 60%, the active components will accumulate on the catalyst surface, which will slightly increase the reaction activity of the catalyst, but the manufacturing cost of the catalyst will increase significantly, causing waste. When the metal oxide loading is 5% to 60%, it will not cause waste, but also improve the reaction activity of the catalyst, so that the catalytic hydrolysis reaction rate is fast and the response time to the ammonia demand signal is short.

[0024] Preferably, the solid catalyst is a catalyst prepared by loading 25% MgO on η-Al2O3, thereby further improving the reaction conversion rate of the urea solution, making the catalytic hydrolysis reaction rate faster and the response time to the ammonia demand signal shorter.

[0025] Preferably, the urea solution is injected into the reactor through a nozzle and flows along the catalyst bed in the reactor tube, so that the reactor tube is filled with the urea solution.

[0026] Preferably, the mass fraction of urea in the urea solution is 25% to 75%. If the urea content in the urea solution is too low (≤25%), the reaction rate will be reduced and the energy consumption of the system will be increased; and if the urea content is too high (≥75%), urea crystals are easily precipitated during transportation and block the pipeline.

[0027] Preferably, the urea aqueous solution is heated by feeding steam at a pressure of 0.2-0.8 MPa and a temperature of 130-180°C into a tubular fixed bed reactor to cause a catalytic hydrolysis reaction. If the temperature and pressure of low-quality steam provided by the power plant are too low (pressure less than 0.2 MPa, temperature less than 130°C), the temperature required for the reaction cannot be reached; if the temperature and pressure are too high (pressure greater than 0.8 MPa, temperature greater than 180°C), the system energy consumption will be too high, increasing the operating cost.

[0028] Preferably, steam with a pressure of 0.2-0.8 MPa and a temperature of 130-180°C is sent into the tubular fixed bed reactor to heat the urea solution. If the temperature and pressure of the low-quality steam provided by the power plant are too low (pressure less than 0.2 MPa, temperature less than 130°C), the temperature required for the reaction cannot be reached; if the temperature and pressure are too high (pressure greater than 0.8 MPa, temperature greater than 180°C), the system energy consumption will be too high, increasing the operating cost.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. The system of the SCR denitrification urea heterogeneous catalytic hydrolysis to produce ammonia of the present invention comprises a urea configuration system, a urea heterogeneous hydrolysis reaction system, a residual liquid discharge and recovery system and a hydrophobic recovery system; the urea heterogeneous hydrolysis reaction system comprises a urea solution storage tank, a urea solution delivery pump A, a heterogeneous hydrolysis reactor and a steam pipeline, and the heterogeneous hydrolysis reactor adopts a tubular fixed bed reactor, and the urea solution undergoes a liquid-solid two-phase reaction under the action of a solid catalyst to generate a target product ammonia. The reactor in the present invention has faster heat transfer, fast chemical reaction rate, high urea conversion rate, so that the system's response time to ammonia demand signals is also shorter, and the steam usage is small, so that the system's operating cost is lower; in addition, the reactor in the present application makes the catalyst mechanical loss small, and has a simple structure, low manufacturing cost, high reliability, and low waste liquid discharge, which can not only realize the recycling of solid catalysts, but also reduce system energy consumption and investment and operating costs.

[0031] 2. The SCR denitrification urea heterogeneous catalytic hydrolysis system for producing ammonia of the present invention is highly compatible with the process flow of the current urea homogeneous catalytic hydrolysis system and the ordinary urea hydrolysis system, has high system operation reliability, is suitable for the transformation of the current urea hydrolysis system, has low transformation cost, and can improve system responsiveness, reduce system operating costs and reduce waste liquid discharge.

[0032] 3. The solid catalyst in the present invention is prepared by loading a metal oxide on a porous material having acidic or alkaline functional groups on the surface. The surface of the porous material has acidic or alkaline functional groups. The acidic site is conducive to stabilizing the active components of the alkaline metal oxide, making it difficult to lose, and the alkaline site is conducive to promoting the occurrence of catalytic hydrolysis reactions. Therefore, the solid catalyst has the advantages of high catalytic activity, long service life, and high hydrothermal stability. It can also greatly improve the conversion rate of urea solution and the reaction rate of catalytic hydrolysis, shorten the system response time, and especially when the solid catalyst is a catalyst prepared by loading 25% MgO on η-Al2O3, the conversion rate of urea solution is higher, the catalytic hydrolysis reaction rate is faster, and the response time to the ammonia demand signal is shorter.

[0033] In order to verify the above technical effects, the inventors also conducted the following experiments (but it should be understood that these descriptions are only to further illustrate the characteristics and advantages of the present invention, rather than to limit the claims of the present invention):

[0034] Experimental method: a solid catalyst is placed in the tube of a tube-in-tube fixed bed reactor, and a urea aqueous solution is filled in the tube; after heating, the urea aqueous solution undergoes a hydrolysis reaction under the action of the solid catalyst to produce ammonia and carbon dioxide. Specifically, the inner diameter of the tube of the tube-in-tube reactor is 0.10m, the number of inner tubes is 5, and the tube length is 0.5m. The reactor is filled with 10% MgO-loaded γ-Al2O3 (10% of the 10% MgO represents the loading amount of MgO in the catalyst), 10% MgO-loaded η-Al2O3, 10% MnO2-loaded γ-Al2O3, and 25% MgO-loaded η-Al2O3, respectively, and the catalyst filling height is 0.5m; the one without adding catalyst is used as the control group. A urea solution with a urea mass fraction of 50% and a temperature of 35°C is transported to a urea solution storage tank 1 after raw material dissolution, and then transported to a heterogeneous hydrolysis reactor 3 by a raw material delivery pump, and the volume flow rate of the urea solution is 3L / min; steam with a pressure of 0.5MPa and a temperature of 130°C is sent into the heterogeneous hydrolysis reactor to heat the urea solution and perform a catalytic hydrolysis reaction. The reaction pressure in the heterogeneous hydrolysis reactor 3 is 0.5MPa and the reaction temperature is 130°C; the product gas containing a mixture of ammonia and carbon dioxide generated after the reaction flows out from the outlet at the top of the reactor after passing through a demisting device. Detect the urea concentration in the urea residual liquid. The performance parameters of the catalyst are shown in Figure 1 (the catalyst specific surface area and the catalyst bulk density are the characteristics of the catalyst itself), and the hydrolysis reaction performance is shown in Table 2.

[0035] Table 1 Performance parameters of catalysts

[0036]

[0037]

[0038] Table 2 Hydrolysis reaction performance

[0039]

[0040] It can be seen from Table 1 and Table 2 that (compared with the control group) the catalyst of the present invention (porous material catalyst loaded with basic metal oxide) can greatly improve the reaction conversion rate of catalytic hydrolysis; and different porous materials loaded with different basic metal oxides and different loading amounts will also lead to different final reaction conversion rates. Among them, when the solid catalyst is a catalyst prepared by loading 25% MgO on η-Al2O3, the final reaction conversion rate is the highest, reaching 99.7%.

[0041] In addition, the inventors also tested the reusability of the catalyst used in the present invention, and the results are shown in Table 3:

[0042] Table 3 Reusability of catalyst

[0043]

[0044] According to Table 3, the porous material catalyst supported by the alkaline metal oxide used in the present invention is placed in the tube of the tubular fixed bed reactor to catalyze the reaction with the urea aqueous solution filled in the tube. After repeated use for many times, the catalyst still has a high catalytic activity, indicating that the porous material catalyst supported by the alkaline metal oxide used in the present invention has high reusability and long service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a process flow diagram of an embodiment of the present invention;

[0046] Figure 2 is a schematic structural diagram of a tube-in-tube fixed bed reactor in one embodiment of the present invention;

[0047] Figure 3 is the cross section of the shell-and-tube reactor;

[0048] Figure 4 This is a schematic diagram of the internal tubes of a tube-in-tube reactor;

[0049] Figure 5 It is a schematic diagram of the cross section of the tubes in the tube-in-tube reactor;

[0050] Figure 6 Schematic diagram of the spray direction of the nozzle in the spray device.

[0051] Figure numerals: 1-urea solution storage tank, 2-A urea solution delivery pump, 3-heterogeneous hydrolysis reactor, 4-steam pipe, 5-urea dissolution tank, 6-deionized water pump, 7-B urea solution delivery pump, 8-residual liquid storage tank, 9-residual liquid circulation pump, 10-drain tank, 11-drain pump, 12-demist device, 13-filled catalyst tubes, 14-spherical catalyst particles, 15-integrated ammonia buffer space, 16-spraying device; a-deionized water; b-urea particles; c-water vapor; dA urea solution; eB urea solution; f-condensed water; g-water vapor; h-product gas; i-residual liquid; j-condensed water.

[0052] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0053] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below. DETAILED DESCRIPTION

[0054] Embodiment 1:

[0055] A system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea. Figure 1-Figure 5 As shown, a system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea includes: a urea configuration system, a urea heterogeneous hydrolysis reaction system, a residual liquid discharge and recovery system and a hydrophobic recovery system; the urea heterogeneous hydrolysis reaction system includes a urea solution storage tank 1, a urea solution delivery pump A 2, a heterogeneous hydrolysis reactor 3 and a steam pipeline 4, and the heterogeneous hydrolysis reactor 3 adopts a tubular fixed bed reactor; the urea solution storage tank 1 is connected to the heterogeneous hydrolysis reactor 3 through the urea solution delivery pump A 2 and a pipeline, and the steam pipeline 4 is connected to the heterogeneous hydrolysis reactor 3; the urea solution storage tank 1 is connected to the urea configuration system through a pipeline; the heterogeneous hydrolysis reactor 3 is respectively connected to the residual liquid discharge and recovery system and the hydrophobic recovery system, and the residual liquid discharge and recovery system is connected to the urea configuration system.

[0056] Example 2: A system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea. Figure 1-Figure 5As shown, a system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea includes: a urea configuration system, a urea heterogeneous hydrolysis reaction system, a residual liquid discharge and recovery system and a hydrophobic recovery system; the urea heterogeneous hydrolysis reaction system includes a urea solution storage tank 1, a urea solution delivery pump A 2, a heterogeneous hydrolysis reactor 3 and a steam pipeline 4, and the heterogeneous hydrolysis reactor 3 adopts a tubular fixed bed reactor; the urea solution storage tank 1 is connected to the heterogeneous hydrolysis reactor 3 through the urea solution delivery pump A 2 and a pipeline, and the steam pipeline 4 is connected to the heterogeneous hydrolysis reactor 3; the urea solution storage tank 1 is connected to the urea configuration system through a pipeline; the heterogeneous hydrolysis reactor 3 is respectively connected to the residual liquid discharge and recovery system and the hydrophobic recovery system, and the residual liquid discharge and recovery system is connected to the urea configuration system. The residual liquid discharge and recovery system may include: a residual liquid storage tank 8 and a residual liquid circulation pump 9, wherein the residual liquid storage tank 8 is connected to the heterogeneous hydrolysis reactor 3 through a pipeline, and the residual liquid storage tank 8 is connected to the urea dissolution tank 5 through the residual liquid circulation pump 9 and a pipeline. The residual liquid discharge and recovery system may also be formed by the cooperation of other devices.

[0057] In order to efficiently recycle the residual liquid, the residual liquid after the reaction in the heterogeneous hydrolysis reactor 3 can also read its pH value through an online pH monitor. When the pH value is ≤7, it is discharged from the system as a waste liquid (the residual liquid is acidic because a side reaction occurs during the reaction to produce isocyanic acid or biuret); when the pH value is greater than 7, it can be sent to the residual liquid storage tank 8.

[0058] In order to save energy, when the residual liquid in the residual liquid storage tank 8 is stored to more than one third, the urea concentration can be detected, and the residual liquid can be sent to the urea dissolution tank 5 by the residual liquid circulation pump 9 for preparing new urea solution.

[0059] Example 3: A system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea. Figure 1-Figure 5As shown, a system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea includes: a urea configuration system, a urea heterogeneous hydrolysis reaction system, a residual liquid discharge and recovery system and a hydrophobic recovery system; the urea heterogeneous hydrolysis reaction system includes a urea solution storage tank 1, a urea solution delivery pump A 2, a heterogeneous hydrolysis reactor 3 and a steam pipeline 4, and the heterogeneous hydrolysis reactor 3 adopts a tubular fixed bed reactor; the urea solution storage tank 1 is connected to the heterogeneous hydrolysis reactor 3 through the urea solution delivery pump A 2 and a pipeline, and the steam pipeline 4 is connected to the heterogeneous hydrolysis reactor 3; the urea solution storage tank 1 is connected to the urea configuration system through a pipeline; the heterogeneous hydrolysis reactor 3 is respectively connected to the residual liquid discharge and recovery system and the hydrophobic recovery system, and the residual liquid discharge and recovery system is connected to the urea configuration system. The steam pipe 4 is divided into three paths, one of which is connected to the heterogeneous hydrolysis reactor 3, and the other two are respectively connected to the inlet of the urea solution storage tank 1 and the inlet of the urea dissolving tank 5, so as to conveniently and quickly clean the urea solution storage tank 1 and the urea dissolving tank 5. The urea solution storage tank 1 and the urea dissolving tank 5 can also be cleaned by other existing methods.

[0060] Example 4: A system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea. Figure 1-Figure 5 As shown, a system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea includes: a urea configuration system, a urea heterogeneous hydrolysis reaction system, a residual liquid discharge and recovery system, and a hydrophobic recovery system; the urea heterogeneous hydrolysis reaction system includes a urea solution storage tank 1, a urea solution delivery pump A 2, a heterogeneous hydrolysis reactor 3, and a steam pipeline 4, and the heterogeneous hydrolysis reactor 3 adopts a tubular fixed bed reactor; the urea solution storage tank 1 is connected to the heterogeneous hydrolysis reactor 3 through a urea solution delivery pump A 2 and a pipeline, and the steam pipeline 4 is connected to the heterogeneous hydrolysis reactor 3; the urea solution storage tank 1 is connected to the urea configuration system through a pipeline; the heterogeneous hydrolysis reactor 3 is respectively connected to the residual liquid discharge and recovery system and the hydrophobic recovery system, and the residual liquid discharge and recovery system is connected to the urea configuration system. The heterogeneous hydrolysis reactor 3 is also provided with an integrated ammonia buffer space 15, and the volume of the integrated ammonia buffer space 15 is preferably 1 / 20 to 1 / 3 of the volume of the heterogeneous hydrolysis reactor 3.

[0061] Example 5: A system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea. Figure 1-Figure 6As shown, a system for preparing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea includes: a urea configuration system, a urea heterogeneous hydrolysis reaction system, a residual liquid discharge and recovery system, and a hydrophobic recovery system; the urea heterogeneous hydrolysis reaction system includes a urea solution storage tank 1, a urea solution delivery pump A 2, a heterogeneous hydrolysis reactor 3, and a steam pipeline 4, and the heterogeneous hydrolysis reactor 3 adopts a tube-type fixed bed reactor; the urea solution storage tank 1 is connected to the heterogeneous hydrolysis reactor 3 through the urea solution delivery pump A 2 and a pipeline, and the steam pipeline 4 is connected to the heterogeneous hydrolysis reactor 3; the urea solution storage tank 1 is connected to the urea configuration system through a pipeline; the heterogeneous hydrolysis reactor 3 is respectively connected to the residual liquid discharge and recovery system and the hydrophobic recovery system, and the residual liquid discharge and recovery system is connected to the urea configuration system. The heterogeneous hydrolysis reactor 3 is also provided with a spray device 16, and the urea solution is sprayed into the heterogeneous hydrolysis reactor 3 through the spray device 16. Preferably, the angle α between the spray direction of the nozzle in the spray device 16 and the axial direction of the tubes of the tube-in-tube fixed bed reactor is 0-60°.

[0062] Example 6: A system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea. Figure 1-Figure 5 As shown, a system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea includes: a urea configuration system, a urea heterogeneous hydrolysis reaction system, a residual liquid discharge and recovery system, and a hydrophobic recovery system; the urea heterogeneous hydrolysis reaction system includes a urea solution storage tank 1, a urea solution delivery pump A 2, a heterogeneous hydrolysis reactor 3, and a steam pipeline 4, and the heterogeneous hydrolysis reactor 3 adopts a tube-type fixed bed reactor; the urea solution storage tank 1 is connected to the heterogeneous hydrolysis reactor 3 through the urea solution delivery pump A 2 and the pipeline, and the steam pipeline 4 is connected to the heterogeneous hydrolysis reactor 3; the urea solution storage tank 1 is connected to the urea configuration system through a pipeline; the heterogeneous hydrolysis reactor 3 is respectively connected to the residual liquid discharge and recovery system and the hydrophobic recovery system, and the residual liquid discharge and recovery system is connected to the urea configuration system. The inner diameter of the tube of the tube-type fixed bed reactor is 0.05-1.00m, the number of inner tubes is 3-100, and the tube length is 0.1-5m.

[0063] Example 7: A system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea. Figure 1-Figure 5As shown, a system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea includes: a urea configuration system, a urea heterogeneous hydrolysis reaction system, a residual liquid discharge and recovery system and a hydrophobic recovery system; the urea heterogeneous hydrolysis reaction system includes a urea solution storage tank 1, a urea solution delivery pump A 2, a heterogeneous hydrolysis reactor 3 and a steam pipeline 4, and the heterogeneous hydrolysis reactor 3 adopts a tubular fixed bed reactor; the urea solution storage tank 1 is connected to the heterogeneous hydrolysis reactor 3 through the urea solution delivery pump A 2 and a pipeline, and the steam pipeline 4 is connected to the heterogeneous hydrolysis reactor 3; the urea solution storage tank 1 is connected to the urea configuration system through a pipeline; the heterogeneous hydrolysis reactor 3 is respectively connected to the residual liquid discharge and recovery system and the hydrophobic recovery system, and the residual liquid discharge and recovery system is connected to the urea configuration system. The urea configuration system may include: a urea dissolution tank 5, a desalted water pump 6 and a B urea solution delivery pump 7, wherein the desalted water pump 6 is connected to the urea dissolution tank 5; the urea dissolution tank 5 is connected to the urea solution storage tank 1 through the B urea solution delivery pump 7 and a pipeline. The urea configuration system may also be formed by the cooperation of other devices. The residual liquid discharge and recovery system may include: a residual liquid storage tank 8 and a residual liquid circulation pump 9, wherein the residual liquid storage tank 8 is connected to the heterogeneous hydrolysis reactor 3 through a pipeline, and the residual liquid storage tank 8 is connected to the urea dissolution tank 5 through the residual liquid circulation pump 9 and a pipeline. The residual liquid discharge and recovery system may also be formed by the cooperation of other devices. In order to efficiently recycle the residual liquid, the residual liquid after the reaction of the heterogeneous hydrolysis reactor 3 can also read its pH value through an online pH online monitor, and when the pH value is ≤7, it is discharged from the system as a waste liquid (the residual liquid is acidic because a side reaction occurs during the reaction process, producing isocyanic acid or biuret); when the pH value is greater than 7, it can be sent to the residual liquid storage tank 8. In order to save energy consumption, when the residual liquid in the residual liquid storage tank 8 is stored to more than one third, the urea concentration can be detected, and the residual liquid can be sent to the urea dissolution tank 5 by the residual liquid circulation pump 9 for preparing new urea solution. The steam pipe 4 is divided into three routes, one of which is connected to the heterogeneous hydrolysis reactor 3, and the other two routes are respectively connected to the inlet of the urea solution storage tank 1 and the inlet of the urea dissolution tank 5, which are used to conveniently and quickly clean the urea solution storage tank 1 and the urea dissolution tank 5. The urea solution storage tank 1 and the urea dissolution tank 5 can also be cleaned by other existing methods. The hydrophobic recovery system includes: a hydrophobic tank 10 and a hydrophobic pump 11, the hydrophobic pump 11 is connected to the hydrophobic tank 10, and the hydrophobic tank 10 is connected to the heterogeneous hydrolysis reactor 3 through a pipeline. The hydrophobic recovery system can also be composed by the cooperation of other devices. A demisting device 12 is also provided in the heterogeneous hydrolysis reactor 3. An integrated ammonia buffer space 15 is further provided inside the heterogeneous hydrolysis reactor 3 . Preferably, the volume of the integrated ammonia buffer space 15 is 1 / 20 to 1 / 3 of the volume of the heterogeneous hydrolysis reactor 3 .The heterogeneous hydrolysis reactor 3 is further provided with a spray device 16, and the urea solution is sprayed into the heterogeneous hydrolysis reactor 3 through the spray device 16. Preferably, the angle α between the spray direction of the nozzle in the spray device 16 and the axial direction of the tubes of the tube-in-tube fixed bed reactor is 0-60°. The tube inner diameter of the tube-in-tube fixed bed reactor is 0.05-1.00 m, the number of inner tubes is 3-100, and the tube length is 0.1-5 m.

[0064] Embodiment 8: A method for producing ammonia by catalytic hydrolysis of SCR denitrification urea using the system described in any one of Embodiments 1-7, comprising the following steps: placing a solid catalyst in a tube of a tubular fixed bed reactor, and then pumping in a urea solution; after heating, the urea solution undergoes a hydrolysis reaction under the action of the solid catalyst to produce ammonia and carbon dioxide; wherein the reaction pressure in the tubular fixed bed reactor is 0.3-0.6 MPa, and the reaction temperature is 120-150°C. Preferably, the reaction pressure is 0.5 MPa, and the reaction temperature is 130°C.

[0065] The reaction equation of urea solution reacting under the action of solid catalyst is:

[0066] CO(NH2)2→2NH3+CO2.

[0067] Embodiment 9: A method for producing ammonia by catalytic hydrolysis of SCR denitrification urea using the system described in any one of Embodiments 1-7, comprising the following steps: placing a solid catalyst in a tube of a tubular fixed bed reactor, and then pumping in a urea solution; after heating, the urea solution undergoes a hydrolysis reaction under the action of the solid catalyst to produce ammonia and carbon dioxide; wherein the reaction pressure in the tubular fixed bed reactor is 0.3-0.6 MPa, and the reaction temperature is 120-150°C. Preferably, the reaction pressure is 0.5 MPa, and the reaction temperature is 130°C.

[0068] The reaction equation of urea solution reacting under the action of solid catalyst is:

[0069] CO(NH2)2→2NH3+CO2.

[0070] The solid catalyst is prepared by loading metal oxide on a porous material with acidic or alkaline functional groups on the surface, wherein the loading amount of the metal oxide is 5% to 60%.

[0071] The catalyst may be spherical in shape with a diameter of 5 to 25 mm.

[0072] The metal oxides include but are not limited to one or more of insoluble alkaline earth metal oxides, MnO2, Co2O3, V2O5, WO3, and NiO; the carriers include but are not limited to one or more of alumina, silica gel (porous silicon dioxide), and molecular sieves, wherein the crystal form of alumina includes but is not limited to one or more of γ-alumina, η-alumina, θ-alumina, and ɑ-alumina.

[0073] The inventors found in their research that the catalyst required for urea hydrolysis is an alkaline substance. In order to prevent the active components from being lost into the urea solution during the reaction, insoluble alkaline earth metal oxides or broadly alkaline metal oxides (such as Mn, Co, V, etc.) are selected as active components, and alumina, silica gel (porous silica) or molecular sieves are used as carriers. The surface of the carrier has acidic or alkaline functional groups, and the alkaline sites can play a catalytic role. There is a weak interaction between the acidic sites and the alkaline oxide active components, which is conducive to the loading and dispersion of the alkaline active components.

[0074] Preferably, the solid catalyst is a catalyst prepared by loading 25% MgO on η-Al2O3, so that the conversion rate of the urea solution is higher and the reaction time is shorter.

[0075] Embodiment 10: A method for producing ammonia by catalytic hydrolysis of SCR denitrification urea using the system described in any one of Embodiments 1-7, comprising the following steps: placing a solid catalyst in a tube of a tubular fixed bed reactor, and then pumping in a urea solution; after heating, the urea solution undergoes a hydrolysis reaction under the action of the solid catalyst to produce ammonia and carbon dioxide; wherein the reaction pressure in the tubular fixed bed reactor is 0.3-0.6 MPa, and the reaction temperature is 120-150°C. Preferably, the reaction pressure is 0.5 MPa, and the reaction temperature is 130°C.

[0076] The reaction equation of urea solution reacting under the action of solid catalyst is:

[0077] CO(NH2)2→2NH3+CO2.

[0078] The urea solution can be added to the tubular fixed bed reactor in various conventional ways. Preferably, the urea solution is sprayed into the reactor through a nozzle and flows along the catalyst bed in the reactor tube to fill the reactor tube with the urea solution.

[0079] Embodiment 11: A method for producing ammonia by catalytic hydrolysis of SCR denitrification urea using the system described in any one of Embodiments 1-7, comprising the following steps: placing a solid catalyst in a tube of a tubular fixed bed reactor, and then pumping in a urea solution; after heating, the urea solution undergoes a hydrolysis reaction under the action of the solid catalyst to produce ammonia and carbon dioxide; wherein the reaction pressure in the tubular fixed bed reactor is 0.3-0.6 MPa, and the reaction temperature is 120-150°C. Preferably, the reaction pressure is 0.5 MPa, and the reaction temperature is 130°C.

[0080] The reaction equation of urea solution reacting under the action of solid catalyst is:

[0081] CO(NH2)2→2NH3+CO2.

[0082] The solid catalyst is prepared by loading metal oxides on porous materials with acidic or alkaline functional groups on the surface, wherein the loading amount of metal oxides is 5% to 60%. The metal oxides include but are not limited to one or more of insoluble alkaline earth metal oxides, MnO2, Co2O3, V2O5, WO3, and NiO; the carrier includes but is not limited to one or more of alumina, silica gel (porous silica) and molecular sieves, wherein the crystal form of alumina includes but is not limited to one or more of γ-alumina, η-alumina, θ-alumina and α-alumina.

[0083] Preferably, the solid catalyst is a catalyst prepared by loading 25% MgO on η-Al2O3, so that the conversion rate of the urea solution is higher and the reaction time is shorter.

[0084] The urea solution can be added to the tubular fixed bed reactor in a variety of conventional ways. Preferably, the urea solution is sprayed into the reactor through a nozzle, flows along the catalyst bed in the reactor tube, and fills the reactor tube with the urea solution. The angle α between the spray direction of the nozzle in the spray device and the axial direction of the tubular fixed bed reactor can be 0-60°.

[0085] Optionally, the mass fraction of urea in the urea solution is 25% to 75%, preferably 50%.

[0086] Optionally, the urea aqueous solution is heated by sending steam with a pressure of 0.2 to 0.8 MPa and a temperature of 130 to 180° C. into a shell-and-tube fixed bed reactor to cause a catalytic hydrolysis reaction; preferably, steam with a pressure of 0.5 MPa and a temperature of 130° C. is sent into a heterogeneous hydrolysis reactor to heat the urea solution.

[0087] The working principle of an embodiment of the present invention:

[0088] The bagged urea is delivered to the urea dissolving tank 5 by the unpacking machine and bucket elevator. The desalted water is pumped into the urea dissolving tank 5 by the desalted water pump 6 to prepare a urea solution with a mass concentration of about 50%, and then delivered to the urea solution storage tank 1 by the B urea solution delivery pump 7 for temporary storage. When making ammonia, the urea solution is delivered to the heterogeneous hydrolysis reactor 3 by the A urea solution delivery pump 2. After the reaction, a product gas composed of ammonia and carbon dioxide is generated. The gas is discharged from the top of the heterogeneous hydrolysis reactor 3 after the entrained water droplets are removed by the demisting device 12. The urea residual liquid left by the reaction is delivered to the residual liquid storage tank 8. After the residual liquid is stored to a certain amount, the urea concentration in the urea residual liquid is detected, and then it is delivered to the urea dissolving tank 5 by the residual liquid circulation pump 9 for preparing urea solution, realizing the recycling of the urea residual liquid. The low-pressure steam provided by the power plant flows in the shell side. The low-pressure steam transfers heat to the urea aqueous solution through the steam pipe 4 through the partition heat exchange method, providing heat for the catalytic hydrolysis reaction. The condensate produced after the heat exchange enters the drain tank 10 and is drained back to the plant by the drain pump 11; the medium-pressure steam also needs to be sent to the urea dissolution tank 5 and the urea solution storage tank 1 for cleaning the dissolution tank and the storage tank. The heterogeneous hydrolysis reactor 3 used in this application is a tubular fixed bed reactor, in which the solid catalyst is placed in the tubular, and the urea aqueous solution is filled in the tube, and ammonia and carbon dioxide are produced by reaction under the action of the catalyst.

[0089] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, all equivalent changes made according to the structure, method, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea, characterized in that: include: A urea configuration system, a urea heterogeneous hydrolysis reaction system, a residual liquid discharge and recovery system, and a hydrophobic recovery system; the urea heterogeneous hydrolysis reaction system comprises a urea solution storage tank (1), a urea solution delivery pump (2), a heterogeneous hydrolysis reactor (3), and a steam pipeline (4); the heterogeneous hydrolysis reactor (3) is a tubular fixed bed reactor; The urea solution storage tank (1) is connected to the heterogeneous hydrolysis reactor (3) through a urea solution delivery pump (2) and a pipeline, and the steam pipeline (4) is connected to the heterogeneous hydrolysis reactor (3); the urea solution storage tank (1) is connected to the urea configuration system through a pipeline; the heterogeneous hydrolysis reactor (3) is respectively connected to the residual liquid discharge and recovery system and the hydrophobic recovery system, and the residual liquid discharge and recovery system is connected to the urea configuration system; the residual liquid discharge and recovery system comprises: a residual liquid storage tank (8) and a residual liquid circulation pump (9), the residual liquid storage tank (8) is connected to the heterogeneous hydrolysis reactor (3) through a pipeline, and the residual liquid storage tank (8) is connected to the heterogeneous hydrolysis reactor (3) through the residual liquid circulation pump (9) and the pipeline. The urea dissolving tank (5) is connected to the urea dissolving tank (5) by a road; the pH value of the residual liquid after the reaction of the heterogeneous hydrolysis reactor (3) is read by an online pH monitor, and when the pH value is ≤7, it is discharged from the system as waste liquid; when the pH value is greater than 7, it is sent to a residual liquid storage tank (8); when the residual liquid in the residual liquid storage tank (8) is stored to more than one third, the urea concentration is detected, and the residual liquid is sent to the urea dissolving tank (5) by a residual liquid circulation pump (9) for preparing new urea solution; the heterogeneous hydrolysis reactor (3) is also provided with an integrated ammonia buffer space (15), and the volume of the integrated ammonia buffer space (15) is 1 / 20 to 1 / 3 of the volume of the heterogeneous hydrolysis reactor (3).

2. The SCR denitrification urea heterogeneous catalytic hydrolysis system for producing ammonia according to claim 1, characterized in that: The urea configuration system comprises: a urea dissolving tank (5), a desalted water pump (6) and a B urea solution delivery pump (7), wherein the desalted water pump (6) is connected to the urea dissolving tank (5); the urea dissolving tank (5) is connected to a urea solution storage tank (1) via the B urea solution delivery pump (7) and a pipeline; the drain recovery system comprises: a drain tank (10) and a drain pump (11), wherein the drain pump (11) is connected to the drain tank (10), and the drain tank (10) is connected to a heterogeneous hydrolysis reactor (3) via a pipeline.

3. The SCR denitrification urea heterogeneous catalytic hydrolysis system for producing ammonia according to claim 1, characterized in that: The steam pipeline (4) is divided into three paths, one of which is connected to the heterogeneous hydrolysis reactor (3), and the other two are respectively connected to the inlet of the urea solution storage tank (1) and the inlet of the urea dissolution tank (5).

4. The SCR denitrification urea heterogeneous catalytic hydrolysis system for producing ammonia according to claim 1, characterized in that: The heterogeneous hydrolysis reactor (3) is further provided with a spraying device (16), through which the urea solution is sprayed into the heterogeneous hydrolysis reactor (3); the angle α between the spraying direction of the nozzle in the spraying device (16) and the axial direction of the tubes of the tube-in-tube fixed bed reactor is 0-60°.

5. The SCR denitrification urea heterogeneous catalytic hydrolysis system for producing ammonia according to claim 1, characterized in that: The inner diameter of the tubes of the tube-in-tube fixed bed reactor is 0.05-1.00 m, the number of inner tubes is 3-100, and the tube length is 0.1-5 m.

6. A method for producing ammonia by catalytic hydrolysis of SCR denitrification urea using the system for producing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea according to any one of claims 1 to 5, characterized in that: The following steps are involved: The solid catalyst is placed in the tube of the tube-in-tube fixed bed reactor, and then the urea solution is pumped into it; After heating, the urea solution undergoes a hydrolysis reaction under the action of a solid catalyst to produce ammonia and carbon dioxide; wherein the reaction pressure in the tubular fixed bed reactor is 0.3-0.6 MPa, and the reaction temperature is 120-150°C.

7. The method for preparing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea according to claim 6, characterized in that: The solid catalyst is prepared by loading metal oxide on a porous material with acidic or basic functional groups on the surface, wherein the metal oxide loading amount is 5% to 60%; the solid catalyst is a catalyst prepared by loading 25% MgO on η-Al2O3.

8. The method for preparing ammonia by heterogeneous catalytic hydrolysis of SCR denitrification urea according to claim 6, characterized in that: The mass fraction of urea in the urea solution is 25% to 75%. Steam with a pressure of 0.2 to 0.8 MPa and a temperature of 130 to 180° C. is sent into a tubular fixed bed reactor to heat the urea solution.

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