Device and method for reducing saturated steam consumption in urea production

Abstract

The invention belongs to the technical field of urea production, and particularly relates to a device and method for reducing saturated steam consumption in urea production, and the device comprises a carbon dioxide heater, a hydrolysis stripping tower, a high-pressure steam pocket, a medium-pressure steam pocket, a low-pressure steam pocket, a carbon dioxide stripping tower, a two-stage evaporation heater, a medium-pressure decomposition tower and a high-pressure total condensation reactor. The high-pressure steam pocket is respectively connected with the medium-pressure steam pocket and the carbon dioxide stripping tower, and the medium-pressure steam pocket is respectively connected with the low-pressure steam pocket, the medium-pressure decomposition tower and the two-section evaporation heater. The steam of 1.5 MPa, 0.8 MPa and 0.6 MPa is sequentially flashed out, so that the steam of different pressure grades is matched with the heating requirements of equipment such as a carbon dioxide stripping tower, a medium-pressure decomposition tower and a two-section evaporation heater, the low-efficiency direct use of high-grade steam is avoided, and the steam energy utilization rate is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of urea production technology, specifically a device and method for reducing saturated steam consumption in urea production. Background Technology

[0002] The mainstream urea processing technologies today mainly include CO2 stripping, ammonia stripping, and ACES21. With the development of urea industry technology, these urea processes are roughly equivalent in terms of raw material consumption, and can all reach a level that is close to the theoretical value. The main difference lies in steam consumption, with the lowest 2.5MPa saturated steam consumption being about 650kg / tur.

[0003] At present, although the traditional stripping process for urea production has become quite mature and has certain advantages in terms of production stability, it still has significant shortcomings in steam consumption control and faces the problem of high steam consumption.

[0004] Since steam consumption accounts for a significant portion of the cost structure of urea production, high steam consumption directly leads to further increases in the production cost of the plant. In the current increasingly competitive market environment of the urea industry, plants with high steam consumption lack advantages in cost control and are easily eliminated in market competition. Therefore, reducing steam consumption in urea plants has become an important requirement for the industry's development.

[0005] Therefore, the present invention provides an apparatus and method for reducing saturated steam consumption in urea production. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0007] The technical solution adopted by the present invention to solve its technical problem is: a device for reducing saturated steam consumption in urea production, the device comprising a carbon dioxide heater, a hydrolysis stripping tower, a high-pressure steam boiler, a medium-pressure steam boiler, a low-pressure steam boiler, a carbon dioxide stripping tower, a two-stage evaporation heater, a medium-pressure decomposition tower and a high-pressure total condensation reactor.

[0008] Preferably, the high-pressure steam boiler is connected to the medium-pressure steam boiler and the carbon dioxide stripping tower, respectively, and the medium-pressure steam boiler is connected to the low-pressure steam boiler, the medium-pressure decomposition tower and the second-stage evaporation heater, respectively.

[0009] Preferably, the low-pressure steam boiler is connected to the high-pressure total condensation reactor, and the low-pressure steam boiler is connected to the medium-pressure decomposition tower and the second-stage evaporation heater respectively.

[0010] A method for reducing saturated steam consumption in urea production, the method comprising the following steps:

[0011] S1. The 2.5MPa steam in the boundary zone is directly supplied to the carbon dioxide heater and the hydrolysis stripping tower as a heating source. At the same time, the 2.5MPa steam is introduced into the high, medium and low pressure steam bunkers for depressurization flash evaporation, which produces 1.5MPa, 0.8MPa and 0.6MPa steam for system use. The 1.5MPa high pressure steam is used to heat the carbon dioxide stripping tower, and the 0.8MPa medium pressure steam is used to power the medium pressure decomposition tower and the second-stage evaporation heater. The liquid phase of the medium pressure steam bunker is discharged to the low pressure steam bunker to produce low pressure steam. The high pressure tubular total condensation reactor also produces low pressure steam as a byproduct of the exothermic reaction.

[0012] S2. The 1.5MPa steam from the high-pressure steam bunker is heated by the carbon dioxide stripping tower and then becomes steam condensate, which is returned to the high-pressure steam bunker. The liquid phase from the high-pressure steam bunker is introduced into the medium-pressure steam bunker, and after depressurization and flash evaporation, about 0.8MPa steam is produced for use in the medium-pressure decomposition tower and the second-stage evaporation heater. The liquid phase from the medium-pressure steam bunker enters the low-pressure steam bunker and is depressurized and flash evaporated to produce steam at an even lower pressure level.

[0013] S3. The heat released by the strongly exothermic reaction in the high-pressure total condensation reactor is carried away by the condensate in the low-pressure steam package on the shell side, and low-pressure steam is produced as a by-product.

[0014] S4. Use the low-pressure steam produced as a byproduct of the high-pressure total condensation reactor for heating the medium-pressure decomposition tower;

[0015] S5. The low-pressure steam produced by the high-pressure total condensation reactor is used simultaneously for heating in the second-stage evaporation heater.

[0016] The beneficial effects of this invention are as follows:

[0017] 1. The apparatus and method for reducing saturated steam consumption in urea production, as described in this invention, achieves stepped depressurization flash evaporation of 2.5MPa steam by setting up a graded connection structure of high-pressure steam, medium-pressure steam, and low-pressure steam, thereby sequentially flashing out 1.5MPa, 0.8MPa, and 0.6MPa steam. This allows steam of different pressure levels to match the heating requirements of equipment such as the carbon dioxide stripping tower, medium-pressure decomposition tower, and two-stage evaporation heater, avoiding the inefficient direct use of high-grade steam and significantly improving steam energy utilization.

[0018] 2. The apparatus and method for reducing saturated steam consumption in urea production as described in this invention collects steam from a low-pressure steam drum and directly supplies it to the medium-pressure decomposition tower and the second-stage evaporation heater, converting the waste heat of the reaction into usable energy, reducing the demand for 2.5MPa fresh steam in the inlet zone, and realizing the recycling of energy.

[0019] 3. The apparatus and method for reducing saturated steam consumption in urea production as described in this invention improves the conversion rate of the high-pressure synthesis system and reduces the content of unreacted substances by adding a liquid ammonia preheater to the liquid ammonia process, thereby reducing the steam consumption of the recovery system; at the same time, the medium-pressure system is diverted to the carbon dioxide stripping tower, directly reducing the 2.5MPa steam consumption of this major steam consumer, and the steam consumption is significantly reduced through the synergistic effect of multiple links. Attached Figure Description

[0020] The invention will now be further described with reference to the accompanying drawings.

[0021] Figure 1 This is a flowchart from the present invention. Detailed Implementation

[0022] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0023] like Figure 1 As shown in the figure, an embodiment of the present invention provides an apparatus for reducing saturated steam consumption in urea production. The apparatus includes a carbon dioxide heater, a hydrolysis stripping tower, a high-pressure steam boiler, a medium-pressure steam boiler, a low-pressure steam boiler, a carbon dioxide stripping tower, a two-stage evaporation heater, a medium-pressure decomposition tower, and a high-pressure total condensation reactor.

[0024] The high-pressure steam boiler is connected to the medium-pressure steam boiler and the carbon dioxide stripping tower, while the medium-pressure steam boiler is connected to the low-pressure steam boiler, the medium-pressure decomposition tower, and the second-stage evaporation heater.

[0025] The low-pressure steam boiler is connected to the high-pressure total condensation reactor, and the low-pressure steam boiler is connected to the medium-pressure decomposition tower and the second-stage evaporation heater.

[0026] A method for reducing saturated steam consumption in urea production, the method comprising the following steps:

[0027] S1. The 2.5MPa steam in the boundary zone is directly supplied to the carbon dioxide heater and the hydrolysis stripping tower as a heating source. At the same time, the 2.5MPa steam is introduced into the high, medium and low pressure steam bunkers for depressurization flash evaporation, which produces 1.5MPa, 0.8MPa and 0.6MPa steam for system use. The 1.5MPa high pressure steam is used to heat the carbon dioxide stripping tower, and the 0.8MPa medium pressure steam is used to power the medium pressure decomposition tower and the second-stage evaporation heater. The liquid phase of the medium pressure steam bunker is discharged to the low pressure steam bunker to produce low pressure steam. The high pressure tubular total condensation reactor also produces low pressure steam as a byproduct of the exothermic reaction.

[0028] S2. The 1.5MPa steam from the high-pressure steam bunker is heated by the carbon dioxide stripping tower and then becomes steam condensate, which is returned to the high-pressure steam bunker. The liquid phase from the high-pressure steam bunker is introduced into the medium-pressure steam bunker, and after depressurization and flash evaporation, about 0.8MPa steam is produced for use in the medium-pressure decomposition tower and the second-stage evaporation heater. The liquid phase from the medium-pressure steam bunker enters the low-pressure steam bunker and is depressurized and flash evaporated to produce steam at an even lower pressure level.

[0029] S3. The heat released by the strongly exothermic reaction in the high-pressure total condensation reactor is carried away by the condensate in the low-pressure steam package on the shell side, and low-pressure steam is produced as a by-product.

[0030] S4. Use the low-pressure steam produced as a byproduct of the high-pressure total condensation reactor for heating the medium-pressure decomposition tower;

[0031] S5. The low-pressure steam produced by the high-pressure total condensation reactor is used simultaneously for heating in the second-stage evaporation heater.

[0032] Working principle:

[0033] Urea production involves two reversible steps: the reaction of ammonia with carbon dioxide to produce ammonium carbamate, and the dehydration of ammonium carbamate to produce urea. Since the reaction cannot proceed completely, unreacted materials must be treated in a subsequent recovery section. The unit adds a liquid ammonia preheater before the liquid ammonia enters the high-pressure synthesis system to increase the feed temperature, promoting the forward reaction within the high-pressure synthesis system and improving the urea conversion rate. This increased conversion rate reduces the content of unreacted ammonium carbamate, thus lowering the steam consumption required for heating and decomposing unreacted materials in the recovery section.

[0034] The device constructs a steam cascade utilization system through a hierarchical connection structure of high-pressure steam bunkers, medium-pressure steam bunkers, and low-pressure steam bunkers. The 2.5MPa steam in the boundary zone is divided into two parts:

[0035] A portion is directly supplied to the carbon dioxide heater and the hydrolysis stripping tower;

[0036] The other part enters the high-pressure steam bath and is reduced and flashed to 1.5MPa high-pressure steam, which is then supplied to the carbon dioxide stripping tower.

[0037] The liquid phase from the high-pressure steam bunker enters the medium-pressure steam bunker and flashes into 0.8MPa medium-pressure steam. The medium-pressure system reduces the dependence of the carbon dioxide stripping tower on medium-pressure steam by load diversion.

[0038] The liquid phase from the medium-pressure steam drum enters the low-pressure steam drum and flashes to produce 0.6MPa low-pressure steam, thus matching the steam pressure level with the equipment requirements.

[0039] The heat generated by the exothermic reaction in the high-pressure total condensation reactor is absorbed by the condensate in the low-pressure steam bunker on the shell side, producing low-pressure steam as a byproduct. The unit adds steam lines from the low-pressure steam bunker to the heating lines of the medium-pressure decomposition tower and the second-stage evaporator heater, replacing the traditionally relied-upon medium-pressure steam with byproduct low-pressure steam and flash steam from the low-pressure steam bunker.

[0040] The condensate from the high-pressure steam drum is recycled, while the medium-pressure and low-pressure steam drums form an energy ladder of liquid-phase flash evaporation. The low-pressure steam drum and the high-pressure total condensation reactor work together to collect waste heat steam. Through the synergistic system of "source reduction - ladder utilization - waste heat recovery - substitution and consumption reduction", the consumption of 2.5MPa saturated steam is reduced.

[0041] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A device for reducing saturated steam consumption in urea production, characterized in that, The device includes a carbon dioxide heater, a hydrolysis stripping tower, a high-pressure steam boiler, a medium-pressure steam boiler, a low-pressure steam boiler, a carbon dioxide stripping tower, a two-stage evaporation heater, a medium-pressure decomposition tower, and a high-pressure total condensation reactor.

2. The apparatus for reducing saturated steam consumption in urea production according to claim 1, characterized in that: The high-pressure steam boiler is connected to the medium-pressure steam boiler and the carbon dioxide stripping tower, respectively. The medium-pressure steam boiler is connected to the low-pressure steam boiler, the medium-pressure decomposition tower and the two-stage evaporation heater, respectively.

3. The apparatus for reducing saturated steam consumption in urea production according to claim 1, characterized in that: The low-pressure steam boiler is connected to the high-pressure total condensation reactor, and the low-pressure steam boiler is connected to the medium-pressure decomposition tower and the second-stage evaporation heater.

4. A method for reducing saturated steam consumption in urea production, comprising an apparatus for reducing saturated steam consumption in urea production as described in any one of claims 1-3, characterized in that, The method includes the following steps: S1. The 2.5MPa steam in the boundary zone is directly supplied to the carbon dioxide heater and the hydrolysis stripping tower as a heating source. At the same time, the 2.5MPa steam is introduced into the high, medium and low pressure steam bunkers for depressurization flash evaporation, which produces 1.5MPa, 0.8MPa and 0.6MPa steam for system use. The 1.5MPa high pressure steam is used to heat the carbon dioxide stripping tower, and the 0.8MPa medium pressure steam is used to power the medium pressure decomposition tower and the second-stage evaporation heater. The liquid phase of the medium pressure steam bunker is discharged to the low pressure steam bunker to produce low pressure steam. The high pressure tubular total condensation reactor also produces low pressure steam as a byproduct of the exothermic reaction. S2. The 1.5MPa steam from the high-pressure steam bunker is heated by the carbon dioxide stripping tower and then becomes steam condensate, which is returned to the high-pressure steam bunker. The liquid phase from the high-pressure steam bunker is introduced into the medium-pressure steam bunker, and after depressurization and flash evaporation, about 0.8MPa steam is produced for use in the medium-pressure decomposition tower and the second-stage evaporation heater. The liquid phase from the medium-pressure steam bunker enters the low-pressure steam bunker and is depressurized and flash evaporated to produce steam at an even lower pressure level. S3. The heat released by the strongly exothermic reaction in the high-pressure total condensation reactor is carried away by the condensate in the low-pressure steam package on the shell side, and low-pressure steam is produced as a by-product. S4. Use the low-pressure steam produced as a byproduct of the high-pressure total condensation reactor for heating the medium-pressure decomposition tower; S5. The low-pressure steam produced by the high-pressure total condensation reactor is used simultaneously for heating in the second-stage evaporation heater.

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