Urea hydrolysis method and system

Abstract

The invention discloses a urea hydrolysis method and system, and relates to the technical field of environment-friendly denitration urea hydrolysis synthesis ammonia, the method comprises the following steps: a unit is utilized to assist hydrophobic heating of a preposed heat exchanger group and preheating of a urea solution, and the preposed heat exchanger group is provided with at least one preposed heat exchanger; heating a rear heat exchanger connected with the urea hydrolyzer by using unit auxiliary steam to hydrolyze urea; the unit auxiliary drain water is condensate water generated by the unit auxiliary steam passing through the rear heat exchanger. The unit auxiliary steam is fully utilized for denitration, a temperature and pressure reduction device does not need to be arranged, hydrophobic energy generated by the unit auxiliary steam can be extracted, the hydrolysis efficiency can be improved, energy saving can be achieved, when the hydrolyzer is in a standby or overhaul state, a urea solution in the hydrolyzer is recycled, the urea solution is prevented from being directly discharged into a sewage pit, and waste is avoided. And the operation flexibility, safety and environmental friendliness of the hydrolyzer are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of environmentally friendly denitrification urea hydrolysis and ammonia synthesis, in particular to a urea hydrolysis method and system. Background Art

[0002] In coal-fired power plants, the process of synthesizing ammonia by urea hydrolysis has replaced liquid ammonia. Although it solves the danger of transporting and storing liquid ammonia, the process of synthesizing ammonia is an endothermic reaction, and the urea solution is very easy to crystallize. Therefore, 3 to 10 t / h of steam is required for the preparation of urea solution, hydrolysis and product steam heating. The steam is generally taken from the auxiliary steam of the unit with a pressure of 1.0 to 1.5 MPa and a temperature of 250 to 350 ° C. The general design value of the hydrolyzer is about 0.8 MPa and a temperature of about 180 ° C. It is necessary to set a temperature and pressure reduction device to achieve the desired effect. to meet the design parameters; and the water discharged from the auxiliary steam condensation of the unit reaches 90-100℃, and contains a large amount of heat inside. If it is not utilized, the denitrification operation cost will be seriously increased; and when the hydrolyzer is shut down for some reason, if the remaining urea solution is directly discharged into the sewage pit, ammonia will be produced, which will seriously affect the safety and environmental protection of the production environment; because the power plant has a small number of production personnel and a large number of equipment, the urea hydrolysis and ammonia synthesis process is only a small part of the power plant's production, and it is impossible to invest more manpower and material resources. Therefore, a high degree of automation is needed to solve these problems.

[0003] Therefore, a urea hydrolysis method and system are needed to solve all the above-mentioned problems of urea hydrolysis to synthesize ammonia. And ensure the safe and economical operation of the denitrification system. The present application eliminates the temperature reduction and pressure reduction device, and sets a urea solution preheating system at the entrance of the urea hydrolyzer. The urea solution is preheated by using the steam hydrophobic heat, which can not only preheat the urea solution to improve the hydrolysis efficiency, but also extract the heat in the hydrophobic state to achieve energy-saving effects. At the same time, the system is also provided with a urea solution recovery and transportation system. When the hydrolyzer is switched from operation to standby or maintenance state, the urea solution in the hydrolyzer is recovered to the urea solution storage tank to avoid discharging the urea solution directly into the sewage pit, thereby achieving energy-saving effects. The low-concentration urea solution produced after cleaning the urea hydrolyzer can also be recovered, which reduces the time it takes for the hydrolyzer to switch from operation to standby or maintenance, making the operation of the hydrolyzer more flexible, safe, and environmentally friendly. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is that when using unit-assisted steam denitrification, a temperature reduction and pressure reduction device needs to be set up, and the returned drain temperature is high, and a large amount of energy is not utilized.

[0005] The above technical problems are solved by the following technical solutions:

[0006] The present invention provides a urea hydrolysis method, which comprises preheating a urea solution and hydrolyzing the urea.

[0007] In a preferred embodiment of the urea hydrolysis method of the present invention: the urea solution is preheated by using a unit-assisted hydrophobic heating front heat exchanger group, wherein the front heat exchanger group includes at least one front heat exchanger;

[0008] The auxiliary steam of the unit is used to heat the post-heat exchanger connected to the urea hydrolyzer to hydrolyze urea;

[0009] The auxiliary drain of the unit is condensed water generated by the auxiliary steam of the unit passing through the post-heat exchanger.

[0010] In a preferred embodiment of the urea hydrolysis method of the present invention, the auxiliary hydrophobic unit performs countercurrent heat exchange with the urea solution in the front heat exchanger group.

[0011] In a preferred embodiment of the urea hydrolysis method of the present invention: the auxiliary steam pressure of the unit is 1.0-1.5 MPa and the temperature is 250-350°C;

[0012] The auxiliary drain temperature of the unit is 90-100°C.

[0013] In a preferred embodiment of the urea hydrolysis method of the present invention: preheating the urea solution, preheating the 50% concentration urea solution from 40-50° C. to 70-80° C.;

[0014] The temperature of the auxiliary drain of the unit is reduced to 50-70°C after passing through the front heat exchanger group.

[0015] In a preferred embodiment of the urea hydrolysis method of the present invention: the front heat exchanger group includes at least two groups of the front heat exchangers;

[0016] The front heat exchangers in the front heat exchanger group are connected in series.

[0017] In a preferred embodiment of the urea hydrolysis method of the present invention: the urea solution is hydrolyzed in the urea hydrolyzer to generate urea hydrolysis product steam;

[0018] The urea hydrolysis product steam includes ammonia, water vapor and carbon dioxide.

[0019] The present invention also provides a urea hydrolysis system, which includes a front heat exchanger group, a rear heat exchanger and a urea hydrolyzer.

[0020] In a preferred embodiment of the urea hydrolysis system of the present invention: a pre-heat exchanger group is provided to preheat the urea solution by using the unit to assist in hydrophobic preheating;

[0021] A rear heat exchanger connected to the front heat exchanger group, using the auxiliary steam of the unit to heat the preheated urea solution;

[0022] The urea hydrolyzer is connected to the post-exchange heat exchanger and hydrolyzes the urea solution heated by the post-exchange heat exchanger.

[0023] In a preferred embodiment of the urea hydrolysis system of the present invention, the auxiliary steam of the unit is generated into the auxiliary drain of the unit after passing through the post-heat exchanger.

[0024] In a preferred embodiment of the urea hydrolysis system of the present invention, the auxiliary drain of the unit is passed through the front heat exchanger group to generate the cooled auxiliary drain of the unit, which is recovered by the auxiliary steam system of the unit.

[0025] In a preferred embodiment of the urea hydrolysis system of the present invention: a hydrolyzer urea solution recovery pump is connected to the urea hydrolyzer and is used to discharge upper suspended matter and bottom sediment in the urea hydrolyzer;

[0026] a hydrolyzer urea solution recovery pump, one end of which is connected to the urea hydrolyzer and is used to recover the solution in the urea hydrolyzer;

[0027] a urea solution storage tank connected to the urea solution recovery pump of the hydrolyzer and configured to receive the clean urea solution in the urea hydrolyzer;

[0028] The urea dissolving tank is connected to the urea solution recovery pump of the hydrolyzer and is used to receive the low-concentration urea solution generated after cleaning the urea hydrolyzer.

[0029] The beneficial effects of the present invention are: full use of the auxiliary steam of the unit for denitrification, no need to set up a cooling and pressure reduction device, and the hydrophobic energy generated by the auxiliary steam of the unit can be extracted, thereby improving the hydrolysis efficiency and achieving energy saving. When the hydrolyzer is transferred to the standby or maintenance state, the urea solution in the hydrolyzer is recovered, avoiding the direct discharge of the urea solution into the sewage pit, thereby improving the flexibility, safety and environmental protection of the operation of the hydrolyzer. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments of the present invention. Obviously, the drawings described below only relate to some embodiments of the present invention, and are not intended to limit the present invention.

[0031] Figure 1 A flow chart of a urea hydrolysis process is shown;

[0032] Figure 2 A schematic diagram of the urea hydrolysis system is shown. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the present invention, the present invention is further described in detail below with reference to specific embodiments and the accompanying drawings.

[0034] The terms used in the present invention are those commonly used in the art in view of the functions of the present invention, but these terms may vary according to the intentions of those skilled in the art, precedents, or new technologies in the art. In addition, specific terms may be selected by the applicant, and in such cases, their detailed meanings will be described in the detailed description of the present invention. Therefore, the terms used in the specification should not be understood as simple names, but rather as the meanings of the terms and the overall description of the present invention.

[0035] Example 1, reference Figure 1 , this embodiment provides a urea hydrolysis method, including preheating a urea solution and hydrolyzing urea.

[0036] Specifically, the auxiliary drain 5 of the unit is used to heat the preheater group to preheat the urea solution 6. The preheater group includes at least one preheater 3. When the auxiliary steam 4 of the unit is used as heat for hydrolysis of the urea solution 6, the drain temperature generated by the auxiliary steam 4 of the unit is about 100°C, which also contains a large amount of unused energy. Therefore, the auxiliary drain 5 of the unit is introduced into the preheater group to heat the urea solution 6 at a temperature of about 50°C, thereby extracting the heat of the auxiliary drain 5 of the unit and avoiding energy waste.

[0037] The auxiliary steam 4 of the unit is used to heat the afterheat exchanger 2 connected to the urea hydrolyzer 1 to hydrolyze urea. The pressure of the auxiliary steam 4 of the unit is 1.0-1.5 MPa and the temperature is 250-350°C, which exceeds the design values ​​of pressure of about 0.8 MPa and temperature of about 180°C required for general hydrolysis. Therefore, the afterheat exchanger 2 is installed to indirectly increase the temperature of the urea solution 6. The generated auxiliary hydrophobic water 5 of the unit is used to circulate through the front heat exchanger group to preheat the urea solution 6.

[0038] The auxiliary drain 5 is the condensate generated by the auxiliary steam 4 after it passes through the post-heat exchanger 2. The temperature of the auxiliary drain 5 is around 100°C, and directly recycling it in the auxiliary steam system would waste a lot of energy. Therefore, it is used to preheat the urea solution 6 through the pre-heat exchanger group.

[0039] Example 2, reference Figure 1 , this embodiment provides a urea hydrolysis method, including preheating a urea solution and hydrolyzing urea.

[0040] Specifically, the auxiliary drain 5 of the unit is used to heat the preheater group to preheat the urea solution 6. The preheater group includes at least one preheater 3. When the auxiliary steam 4 of the unit is used as heat for hydrolysis of the urea solution 6, the drain temperature generated by the auxiliary steam 4 of the unit is about 100°C, which also contains a large amount of unused energy. Therefore, the auxiliary drain 5 of the unit is introduced into the preheater group to heat the urea solution 6 at a temperature of about 50°C, thereby extracting the heat of the auxiliary drain 5 of the unit and avoiding energy waste.

[0041] The auxiliary steam 4 of the unit is used to heat the afterheat exchanger 2 connected to the urea hydrolyzer 1 to hydrolyze urea. The pressure of the auxiliary steam 4 of the unit is 1.0-1.5 MPa and the temperature is 250-350°C, which exceeds the design values ​​of pressure of about 0.8 MPa and temperature of about 180°C required for general hydrolysis. Therefore, the afterheat exchanger 2 is installed to indirectly increase the temperature of the urea solution 6. The generated auxiliary hydrophobic water 5 of the unit is used to circulate through the front heat exchanger group to preheat the urea solution 6.

[0042] The auxiliary drain 5 is the condensate generated by the auxiliary steam 4 after it passes through the post-heat exchanger 2. The temperature of the auxiliary drain 5 is around 100°C, and directly recycling it in the auxiliary steam system would waste a lot of energy. Therefore, it is used to preheat the urea solution 6 through the pre-heat exchanger group.

[0043] Specifically, the auxiliary drain 5 and the urea solution 6 undergo countercurrent heat exchange in the preheat exchanger group. The preheat exchanger group includes several preheat exchangers 3 connected in series. This countercurrent heat exchange between the auxiliary drain 5 and the urea solution 6 improves heat exchange efficiency and further extracts energy from the auxiliary drain 5.

[0044] Specifically, the auxiliary steam 4 has a pressure of 1.0-1.5 MPa and a temperature of 250-350°C; the auxiliary drain 5 has a temperature of 90-100°C. After passing through the post-heat exchanger 2, the auxiliary steam 4 becomes the auxiliary drain 5. The heat of the auxiliary steam 4 is used to hydrolyze urea, and the auxiliary drain 5 is used to preheat the urea solution 6.

[0045] Specifically, the urea solution 6 is preheated from 40-50°C to 70-80°C at a 50% concentration. The temperature of the auxiliary drain 5 is reduced to 50-70°C after passing through the preheater group. Increasing the number of preheaters 3 in the preheater group increases the heat exchange between the auxiliary drain 5 and the urea solution 6, but also increases the time required to preheat the urea solution 6.

[0046] Specifically, the urea solution 6 is hydrolyzed in the urea hydrolyzer 1 to produce urea hydrolysis product vapor 7; the urea hydrolysis product vapor 7 includes ammonia, water vapor, and carbon dioxide, and the temperature of the urea hydrolysis product vapor 7 is about 150 degrees.

[0047] Example 3, reference Figure 2 This embodiment provides a urea hydrolysis system, including a front heat exchanger group, a rear heat exchanger 2 and a urea hydrolyzer 1.

[0048] Specifically, the preheat exchanger group includes several preheat exchangers 3, which use the auxiliary hydrophobic unit 5 to preheat the urea solution 6; the several preheat exchangers 3 are connected together in series, and the auxiliary hydrophobic unit 5 and the urea solution 6 are subjected to countercurrent heat exchange.

[0049] The rear heat exchanger 2 is connected to the front heat exchanger group, and uses the auxiliary steam 4 of the unit to heat the preheated urea solution 6; the auxiliary steam 4 of the unit is cooled to the temperature of urea hydrolysis, and also generates the auxiliary hydrophobicity 5 of the unit to preheat the urea solution 6.

[0050] The heat exchanger is divided into two chambers by the end cap: the upper chamber is the steam inlet chamber, and the lower chamber is the steam outlet (or drain outlet). The heat exchanger also contains multiple heat exchange tube bundles. The tube bundles are made of 316L stainless steel, and the heat exchanger shell is made of 304 stainless steel. The tube bundles are welded using the expansion welding process.

[0051] The urea hydrolyzer 1 is connected to the post-exchange heat exchanger 2 to hydrolyze the urea solution 6 heated by the post-exchange heat exchanger 2. The urea hydrolyzer 1 hydrolyzes the urea solution 6 to produce urea hydrolysis product steam 7.

[0052] Specifically, the auxiliary drain 5 of the unit passes through the preheat exchanger group 3 to generate cooled auxiliary drain 5, which is then recovered by the auxiliary steam system. The auxiliary steam system in a coal-fired power plant provides auxiliary steam. Auxiliary steam is drawn from various extraction points of the steam turbine. The steam turbine is the core equipment of a coal-fired power plant, used to convert the thermal energy of the steam into mechanical energy, thereby driving the generator to generate electricity. To improve energy efficiency, power plants extract a portion of steam from various locations of the steam turbine for other production or living needs.

[0053] Specifically, the hydrolyzer urea solution recovery pump 11 is connected to the urea hydrolyzer 1 and is used to discharge the upper suspended matter and bottom sediment in the urea hydrolyzer 1; one end of the hydrolyzer urea solution recovery pump 11 is connected to the urea hydrolyzer 1 and is used to recover the solution in the urea hydrolyzer 1.

[0054] The urea solution storage tank 13 is connected to the hydrolyzer urea solution recovery pump 11 and is used to receive the clean urea solution 6 in the urea hydrolyzer 1 .

[0055] The urea dissolving tank 12 is connected to the hydrolyzer urea solution recovery pump 11 and is used to receive the low-concentration urea solution generated after cleaning the urea hydrolyzer 1 .

[0056] When the urea hydrolyzer 1 needs to be switched to standby or shut down for emergency reasons, the 12 tons of 50% urea solution in the urea hydrolyzer 1 need to be drained and cleaned urgently. To ensure the recovery of clean 50% urea solution, the top suspended matter is first drained away, and then the bottom sediment is drained away to the wastewater pit 9; the temperature of the 150° C. 50% urea solution is reduced to 50° C. and recovered to the urea solution storage tank 13, recovered to the low level, and stopped; then the urea hydrolyzer 1 is repeatedly cleaned, and the low-concentration urea solution is recovered to the urea dissolution tank 12, and the 50% urea solution can be continued to be prepared, thereby achieving the effects of saving raw materials and reducing environmental pollution.

[0057] The implementation process is divided into three steps: sewage discharge, recovery of clean urea solution and recovery of urea hydrolyzer 1 washing water, that is, low-concentration urea solution.

[0058] Discharge of sewage: Open the sewage gate from urea hydrolyzer 1 to wastewater pit 9; open the upper sewage gate of urea hydrolyzer 1, and after discharging the upper suspended solids, close the upper sewage gate of urea hydrolyzer 1; open the lower sewage gate of urea hydrolyzer 1, and after discharging the bottom sediment, close the lower sewage gate of urea hydrolyzer 1; after the sewage discharge is completed, close the sewage gate from urea hydrolyzer 1 to wastewater pit 9.

[0059] Recovery of clean urea solution: When the temperature of the 150°C, 50% urea solution drops to 50°C, open the lower sewage discharge door of the urea hydrolyzer 1, and the recovery door from the urea hydrolyzer 1 to the urea solution storage tank 13 forms a recovery passage, start the hydrolyzer urea solution recovery pump 11, and the clean urea solution is recovered to the urea solution storage tank 13. When the urea solution level in the urea hydrolyzer 1 reaches a low level, stop the hydrolyzer urea solution recovery pump 11 and close the urea hydrolyzer 1 to the urea solution storage tank 13.

[0060] Recovery of urea hydrolyzer 1 rinse water, i.e., low-concentration urea solution: Urea hydrolyzer 1 is rinsed with water. When the urea solution 6 level in urea hydrolyzer 1 reaches a high level, the lower drain valve of urea hydrolyzer 1 and the recovery valve from urea hydrolyzer 1 to urea dissolving tank 12 are opened to form a recovery path. The hydrolyzer urea solution recovery pump 11 is started to recover clean urea solution 6 to urea dissolving tank 12. When the urea solution 6 level in urea hydrolyzer 1 reaches a low level, the hydrolyzer urea solution recovery pump 11 is stopped. Water is then refilled for rinsing and recovery is continued. Once rinsing is complete, the hydrolyzer urea solution recovery pump 11 is stopped and the lower drain valve of urea hydrolyzer 1 and the recovery valve from urea hydrolyzer 1 to urea dissolving tank 12 are closed.

[0061] Finally, it should be pointed out that the methods and devices described in detail above are merely embodiments, and those skilled in the art can modify these embodiments in different ways without departing from the scope of the present invention.

Claims

1. A urea hydrolysis method, characterized in that: The steps are as follows, including, Using the auxiliary hydrophobic heating unit to preheat the urea solution, the front heat exchanger group includes at least one front heat exchanger; The auxiliary steam of the unit is used to heat the post-heat exchanger connected to the urea hydrolyzer to hydrolyze urea; The auxiliary drain of the unit is condensed water generated by the auxiliary steam of the unit passing through the post-heat exchanger.

2. The urea hydrolysis method according to claim 1, wherein: The auxiliary hydrophobicity of the unit and the urea solution are countercurrently exchanged with each other in the front heat exchanger group.

3. The urea hydrolysis method according to claim 1, wherein: The auxiliary steam pressure of the unit is 1.0-1.5 MPa and the temperature is 250-350°C; The auxiliary drain temperature of the unit is 90-100°C.

4. The urea hydrolysis method according to claim 3, wherein: Preheating the urea solution, preheating the 50% concentration urea solution from 40-50° C. to 70-80° C.; The temperature of the auxiliary drain of the unit is reduced to 50-70°C after passing through the front heat exchanger group.

5. The urea hydrolysis method according to claim 4, wherein: There are at least two groups of the front heat exchanger groups; The front heat exchangers in the front heat exchanger group are connected in series.

6. The urea hydrolysis method according to claim 5, wherein: The urea solution is hydrolyzed in the urea hydrolyzer to generate urea hydrolysis product steam; The urea hydrolysis product steam includes ammonia, water vapor and carbon dioxide.

7. A urea hydrolysis system, characterized in that: include, The front heat exchanger group uses the unit to assist in hydrophobic preheating of urea solution; A rear heat exchanger connected to the front heat exchanger group, using the auxiliary steam of the unit to heat the preheated urea solution; The urea hydrolyzer is connected to the post-exchange heat exchanger and hydrolyzes the urea solution heated by the post-exchange heat exchanger.

8. The urea hydrolysis system according to claim 7, characterized in that: The auxiliary steam of the unit is passed through the post-heat exchanger to generate the auxiliary drain of the unit.

9. The urea hydrolysis system according to claim 8, characterized in that: The auxiliary drain of the unit is passed through the front heat exchanger group to generate the cooled auxiliary drain of the unit, and is recovered by the auxiliary steam system of the unit.

10. The urea hydrolysis system according to claim 9, characterized in that: Also includes, a hydrolyzer urea solution recovery pump connected to the urea hydrolyzer and used for discharging upper suspended matter and bottom sediment in the urea hydrolyzer; a hydrolyzer urea solution recovery pump, one end of which is connected to the urea hydrolyzer and is used to recover the solution in the urea hydrolyzer; a urea solution storage tank connected to the urea solution recovery pump of the hydrolyzer and configured to receive the clean urea solution in the urea hydrolyzer; The urea dissolving tank is connected to the urea solution recovery pump of the hydrolyzer and is used to receive the low-concentration urea solution generated after cleaning the urea hydrolyzer.

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