Method and system for synthesizing urea based on nitrogen fixation and carbon fixation process of fossil fuel combustion system

Abstract

The invention relates to the field of energy conservation and emission reduction and recycling of fossil fuel combustion pollutants, in particular to a method for synthesizing urea based on a fossil fuel combustion system nitrogen fixation and carbon sequestration process, and the fossil fuel combustion system comprises an air separation device, an oxygen-enriched combustion system, a dust removal device, a desulfurization device, a CO2 recovery device and a water treatment device. According to the invention, CO2 recovered from a combustion system is used as a raw material for synthesizing urea; meanwhile, air is separated by means of an air separation device to obtain N2, wastewater discharged from a combustion system is recycled, H2 is obtained by electrolyzing water, nitrogen and H2 react to obtain ammonia gas which serves as another raw material for synthesizing urea, and the ammonia gas and CO2 react to synthesize urea. Material circulation and energy circulation in a fossil fuel combustion system are fully utilized, resource utilization of waste water and waste gas emissions of the fossil fuel combustion system is achieved, and the purposes of energy conservation, emission reduction, quality improvement and efficiency improvement are achieved.

Description

Technical Field

[0001] The present invention relates to the field of energy conservation and emission reduction and recycling of pollutants from fossil fuel combustion, and in particular to a method and system for synthesizing urea based on a nitrogen and carbon fixation process in a fossil fuel combustion system. Background Art

[0002] The pollutants produced by the combustion of fossil fuels mainly include carbon dioxide, sulfur dioxide, nitrogen oxides, inhalable particulate matter, etc. In order to reduce the emission of pollutants, humans have adopted a variety of pollutant control and prevention measures. Among them, recycling and utilizing pollutants in the flue gas emitted after the combustion of fossil fuels is a new idea for energy conservation and emission reduction.

[0003] Urea is a chemical nitrogen fertilizer used in large quantities in the agricultural field. In industry, urea is often synthesized by reacting ammonia and carbon dioxide under certain conditions.

[0004] As for the raw materials of carbon dioxide and ammonia used in the synthesis of urea, the flue gas after the combustion of fossil fuels contains a large amount of carbon dioxide. For the purpose of energy conservation and emission reduction, actively exploring the recovery and utilization of carbon dioxide in flue gas is the goal pursued in this field. As for ammonia, in line with the idea of ​​making the best use of everything, exploring the synthesis pathway of ammonia from the fossil fuel combustion system is an important measure to improve the resource utilization rate of the combustion system. Summary of the invention

[0005] The present invention aims to solve the technical problems existing in the prior art and provide a method for synthesizing urea based on the nitrogen and carbon fixation process of a fossil fuel combustion system. The method recovers CO2 from the flue gas after the combustion of fossil fuels as a raw material for synthesizing urea; at the same time, the wastewater discharged by the fossil fuel combustion system is recycled and utilized, hydrogen is prepared by electrolysis of water, and ammonia is then prepared by the hydrogen. Ammonia is used as a raw material for synthesizing urea, and urea is synthesized by the reaction of ammonia and CO2. The method provided by the present invention realizes the comprehensive resource utilization of wastewater and waste gas emissions from the fossil fuel combustion system, and achieves the purpose of energy conservation and emission reduction.

[0006] In order to achieve the purpose of the present invention, the technical solution provided by the present invention is as follows:

[0007] A method for synthesizing urea based on a nitrogen and carbon fixation process in a fossil fuel combustion system, characterized in that:

[0008] The fossil fuel combustion system includes an air separation device, an oxygen-enriched combustion system, a dust removal device, a desulfurization device, a CO2 recovery device and a water treatment device;

[0009] The air separation device, oxygen-enriched combustion system, dust removal device, desulfurization device, and CO2 recovery device are connected in sequence via pipelines;

[0010] The air separation unit is used to separate air into O2 and N2, and O2 is supplied to the oxygen-enriched combustion system to support the combustion of fossil fuels;

[0011] The flue gas after burning fossil fuels passes through the dust removal device and desulfurization device, and then enters the CO2 recovery device to recover CO2; CO2 is used as a raw material to prepare urea;

[0012] The desulfurization device is connected to the water treatment device. After the wastewater is treated, it is used for electrolysis to produce H2 and O2. The H2 obtained by electrolysis of water reacts with the N2 obtained by separating air from the air separation device to produce ammonia, which is used as the raw material for synthesizing urea.

[0013] Ammonia reacts with CO2 to synthesize urea.

[0014] The fossil fuel includes any form of fossil fuel, such as coal, oil, natural gas, etc.

[0015] The present invention utilizes an air separation device to separate air into N2 and O2, controls nitrogen entering the combustion system from the source, and uses the N2 gas obtained after separation to synthesize ammonia, thereby significantly reducing the emission of nitrogen oxides in the oxygen-rich combustion system, truly achieving the technical effect of fixing nitrogen from the source.

[0016] The air separation device described in the present invention adopts common equipment in the field, and the present invention does not limit this. Preferably, the air separation device disclosed in the CN105823074A application is adopted, and oxygen and nitrogen can be obtained by using methods such as "air pressure swing adsorption method", "air membrane filtration method", and "air deep cold processing method".

[0017] The O2 obtained by separating air from the air separation unit is used to support the combustion of fossil fuels in the oxygen-rich combustion system. Under oxygen-rich conditions, the fuel burns more completely, and since there is no nitrogen input, the volume fraction of CO2 in the flue gas can reach more than 80%, which is beneficial to the recovery of CO2.

[0018] The present invention does not limit the oxygen-enriched combustion system. Preferably, the oxygen-enriched combustion system disclosed in the CN105823074A application is adopted.

[0019] The dust removal device described in the present invention adopts common equipment in the art, and the present invention does not limit this. Preferably, an electrostatic dust removal device is adopted.

[0020] The desulfurization device of the present invention is used to remove sulfides in flue gas and recover SO2; the recovered SO2 can be used to react with ammonia to synthesize ammonium sulfate, or to prepare sulfuric acid.

[0021] The desulfurization device belongs to the commonly used equipment in this field, and the present invention does not limit this. Preferably, the desulfurization device includes two parts: absorption and analysis of SO2. Amine liquid is used as the absorbent. After the dust-removed flue gas enters the desulfurization device, in the absorption section, the SO2 in the flue gas contacts and is absorbed by the amine liquid, and the flue gas after desulfurization enters the CO2 recovery system. The amine liquid that absorbs SO2 enters the desorption part for regeneration, and the regenerated amine liquid is recycled in the system. This process reduces the consumption of chemicals such as limestone or caustic soda, almost completely eliminates the generation of solid waste, avoids the white feather phenomenon caused by gypsum desulfurization, and at the same time, the recovered SO2 brings certain economic benefits.

[0022] The desulfurization device is connected to a water treatment device. The wastewater discharged from the desulfurization device is used to electrolyze water to prepare H2 and O2 after water treatment; the prepared H2 is used as a raw material for synthesizing ammonia; and the synthesized ammonia is used as a raw material for synthesizing urea.

[0023] The water treatment device adopts common equipment in the field. Preferably, a mechanical vapor compression (MVC) water treatment system is adopted, and the wastewater is treated by MVC water treatment technology, and the water quality index is excellent, and it can be directly used for electrolysis of water, or for boiler replenishment or system circulating cooling water replenishment.

[0024] The CO2 recovery device is a common device in this field, and the present invention does not limit this. The present invention increases the oxygen content entering the oxygen-enriched combustion system through an air separation device, thereby increasing the concentration of CO2 in the flue gas (CO2 content is more than 80%), which can be directly used to recover CO2; by recycling CO2, the carbon fixation effect is achieved, carbon emissions are reduced, and it is used as a raw material for synthesizing urea, realizing the recycling of flue gas pollutants.

[0025] The wastewater is treated by the water treatment device and then enters the water electrolysis hydrogen production device. The water electrolysis hydrogen production device is a common device in the art and the present invention does not limit this.

[0026] Preferably, the present invention uses valley electricity as power supply to alleviate the power supply pressure during peak power consumption periods. Valley electricity is also called low valley electricity, which is a way of expressing electricity relative to peak power consumption periods. Using electricity during valley periods not only reduces power losses but also reduces power load during peak periods, thereby achieving the purpose of peak shaving and valley filling and peak capacity expansion.

[0027] Preferably, the O2 generated by the electrolysis of water is connected to the inlet of the oxygen-enriched combustion system via a pipeline to support the combustion of fossil fuels; and the H2 prepared by the electrolysis of water is used as a raw material for synthesizing ammonia.

[0028] When H2 prepared by electrolysis of water is used to synthesize ammonia, N2 is obtained by separating air in an air separation device as a raw material, and N2 and H2 are input together into an ammonia synthesis device to prepare ammonia; the ammonia synthesis device is a common equipment in this field, and the present invention does not limit this.

[0029] The prepared ammonia is used as a raw material for synthesizing urea. When synthesizing urea, the recovered CO2 is used as a raw material, and the ammonia and CO2 are sent together to a urea synthesis device; the urea synthesis device is a common equipment in this field, and the present invention does not limit this.

[0030] According to the technical solution of the present invention, preferably, SO2 recovered by the desulfurization device is used to prepare sulfuric acid, or reacts with ammonia to prepare ammonium sulfate.

[0031] The present invention uses CO2 recovered from the flue gas after the combustion of fossil fuels as a raw material for synthesizing urea; at the same time, air is separated by an air separation device to obtain N2, and wastewater discharged from the fossil fuel combustion system is recycled and utilized, H2 is obtained by electrolyzing water, and ammonia is obtained by reacting N2 with H2 as another raw material for synthesizing urea. The present invention fully explores and utilizes the material cycle and energy cycle in the fossil fuel combustion system, realizes the resource utilization of wastewater and waste gas emissions from the fossil fuel combustion system, and achieves the purpose of energy conservation, emission reduction, quality improvement and efficiency enhancement.

[0032] According to the technical solution of the present invention, preferably, the fossil fuel combustion system also includes a flue gas reflux device, and part of the flue gas exhausted from the oxygen-enriched combustion system is transported to the inlet of the oxygen-enriched combustion system through the flue gas reflux device, and mixed with the oxygen output by the air separation device, and recycled flue gas is used instead of nitrogen as a diluent for oxygen, thereby improving the completeness of combustion, significantly reducing the exhaust volume of the oxygen-enriched combustion system, reducing the emission of pollutants, reducing exhaust heat loss, and significantly improving the thermal efficiency of the oxygen-enriched combustion system.

[0033] The present invention has no particular limitation on the smoke reflow device. Preferably, the smoke reflow device disclosed in the CN105823074A application is adopted.

[0034] Preferably, the present invention further comprises a cold recovery device, which recovers cold from liquid O2 and / or liquid N2 obtained by separating air in the air separation device, and uses the cold to recover CO2 in the CO2 recovery device.

[0035] Further preferably, the present invention further comprises a flue gas heat recovery device for recovering heat from the flue gas, and using the recovered heat for decomposing the amine solution in the desulfurization device to achieve SO2 recovery. The flue gas heat recovery device is a common device in the art, and the present invention does not limit this.

[0036] From the perspective of material utilization:

[0037] Air is separated by an air separation device to obtain N2 and O2. N2 is used to react with H2 obtained by electrolysis of water to synthesize ammonia. The synthesized ammonia is used as a raw material for synthesizing urea.

[0038] The oxygen-enriched combustion system and air separation device are used to control the input of N2 from the source, so that the nitrogen oxides in the flue gas after the combustion of fossil fuels are ultra-low emissions, reducing the impact on the environment. At the same time, the volume fraction of CO2 gas in the flue gas is significantly increased (CO2 content is more than 80%), which can be directly used to recover CO2;

[0039] The CO2 recovery device is used to recover CO2 from flue gas, reducing carbon emissions and lowering the greenhouse effect; the recovered CO2 is used to synthesize urea;

[0040] By purifying the wastewater, the treated wastewater is used for electrolysis to produce H2 and O2, thus achieving wastewater purification and recycling, reducing wastewater discharge and saving water;

[0041] The H2 produced by electrolysis of water is used as a raw material to react with the N2 obtained by separating air in an air separation device to synthesize ammonia, which is used as a raw material for synthesizing urea.

[0042] Furthermore, the present invention protects a fossil fuel combustion system for carrying out the method for synthesizing urea, the system comprising an air separation device, an oxygen-enriched combustion system, a dust removal device, a desulfurization device, a CO2 recovery device and a water treatment device;

[0043] The air separation device, oxygen-enriched combustion system, dust removal device, desulfurization device, and CO2 recovery device are connected in sequence via pipelines;

[0044] The air separation unit is used to separate air into O2 and N2, and O2 is supplied to the oxygen-enriched combustion system to support the combustion of fossil fuels;

[0045] The flue gas after burning fossil fuels passes through the dust removal device and desulfurization device, and then enters the CO2 recovery device to recover CO2; the recovered CO2 is used as the raw material for synthesizing urea;

[0046] The desulfurization device is connected to the water treatment device. After the wastewater is treated, it is used for electrolysis to produce H2 and O2. The H2 obtained by electrolysis of water reacts with the N2 obtained by separating air from the air separation device to produce ammonia, which is used as the raw material for synthesizing urea.

[0047] CO2 reacts with ammonia to synthesize urea in a urea synthesis unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 : A schematic diagram of a fossil fuel combustion system architecture for executing a urea synthesis method provided by a first embodiment of the present invention.

[0049] Figure 2 : A schematic diagram of a fossil fuel combustion system architecture for executing a urea synthesis method provided by a second embodiment of the present invention.

[0050] Figure 3 : A schematic diagram of a fossil fuel combustion system architecture for executing a urea synthesis method provided in a third embodiment of the present invention.

[0051] Figure 4 : A schematic diagram of a fossil fuel combustion system architecture for executing a urea synthesis method provided in a fourth embodiment of the present invention.

[0052] Description of reference numerals:

[0053] Air separation device 1, oxygen-enriched combustion system 2, dust removal device 3, desulfurization device 4, CO2 recovery device 5, water treatment device 6, water electrolysis hydrogen production device 7, ammonia synthesis device 8, urea synthesis device 9, flue gas reflux device 10, cold recovery device 11, flue gas heat recovery device 12. DETAILED DESCRIPTION

[0054] The present invention will now be further described in conjunction with the accompanying drawings, but the following embodiments do not constitute a limitation of the present invention.

[0055] Figure 1-4 A schematic diagram of a fossil fuel combustion architecture for carrying out the method for synthesizing urea according to the present invention is shown.

[0056] in, Figure 1 A schematic diagram of a fossil fuel combustion system architecture for executing a urea synthesis method provided by a first embodiment of the present invention is shown.

[0057] like Figure 1 As shown, the fossil fuel combustion system comprises:

[0058] Air separation device 1, oxygen-enriched combustion system 2, dust removal device 3, desulfurization device 4, CO2 recovery device 5 and water treatment device 6;

[0059] The air separation device, oxygen-enriched combustion system, dust removal device, desulfurization device, and CO2 recovery device are connected in sequence via pipelines;

[0060] The air separation device is used to separate air to obtain O2 and N2, and the O2 is supplied to the oxygen-enriched combustion system to support the combustion of fossil fuels; the N2 is used to prepare ammonia;

[0061] The flue gas after burning fossil fuels passes through the dust removal device and desulfurization device, and then enters the CO2 recovery device to recover CO2; CO2 is used as a raw material to prepare urea;

[0062] The desulfurization device is connected to the water treatment device. After the wastewater is treated, it is transported to the water electrolysis hydrogen production device 7 for electrolytic production of H2 and O2. The H2 produced by electrolysis and the N2 obtained by separating air from the air separation device are transported to the ammonia synthesis device 8 to prepare ammonia. The prepared ammonia is used as a raw material for synthesizing urea.

[0063] Ammonia and CO2 are sent together into the urea synthesis device 9 to react and synthesize urea.

[0064] Figure 2 FIG. 1 shows a schematic diagram of a fossil fuel combustion system architecture for executing a urea synthesis method provided by a second embodiment of the present invention. Figure 1 The difference between the two is that, Figure 2 A flue gas reflow device 10 is added.

[0065] Part of the flue gas exhausted from the oxygen-enriched combustion system is transported to the inlet of the oxygen-enriched combustion system through the flue gas reflux device, mixed with the oxygen output by the air separation device, and the recycled flue gas is used instead of nitrogen as the diluent of oxygen to improve the completeness of combustion, significantly reduce the exhaust volume of the oxygen-enriched combustion system, reduce the emission of pollutants, reduce the heat loss of the exhaust, and significantly improve the thermal efficiency of the oxygen-enriched combustion system.

[0066] Figure 3 FIG. 1 shows a schematic diagram of a fossil fuel combustion system architecture for executing a urea synthesis method provided by a third embodiment of the present invention. Figure 2 The difference between the two is that, Figure 3 A cold recovery device 11 is further added.

[0067] Recover cold from liquid O2 and / or liquid N2 obtained by separating air from the air separation unit through a cold recovery unit 11, and use the cold to recover CO2 in a CO2 recovery unit;

[0068] Figure 4 FIG. 4 shows a schematic diagram of a fossil fuel combustion system architecture for executing a urea synthesis method provided by a fourth embodiment of the present invention. Figure 3 The difference between the two is that, Figure 4 A flue gas heat recovery device 12 is further added.

[0069] The flue gas heat recovery device is used to recover heat from the flue gas, and use the recovered heat for the analysis of amine liquid in the desulfurization device to achieve SO2 recovery.

[0070] The present invention utilizes CO2 recovered from flue gas after fossil fuel combustion as a raw material for synthesizing urea; at the same time, air is separated by means of an air separation device to obtain N2, and wastewater discharged from the fossil fuel combustion system is recycled and utilized, H2 is obtained by electrolyzing water, and N2 and H2 are reacted to obtain ammonia as another raw material for synthesizing urea; the material cycle and energy cycle in the fossil fuel combustion system are fully explored and utilized, the resource utilization of wastewater and waste gas emissions from the fossil fuel combustion system is realized, and the purpose of energy conservation, emission reduction, quality improvement and efficiency enhancement is achieved.

[0071] The present invention has been introduced in detail above. Specific examples have been used in the specification to illustrate the principles and implementation methods of the present invention. However, the examples are only used to help understand the present invention and should not be construed as limiting the present invention.

Claims

1. A method for synthesizing urea based on a nitrogen and carbon fixation process in a fossil fuel combustion system, characterized in that: The fossil fuel combustion system includes an air separation device, an oxygen-enriched combustion system, a dust removal device, a desulfurization device, a CO2 recovery device and a water treatment device; The air separation device, oxygen-enriched combustion system, dust removal device, desulfurization device, and CO2 recovery device are connected in sequence via pipelines; The air separation unit is used to separate air into O2 and N2, and O2 is supplied to the oxygen-enriched combustion system to support the combustion of fossil fuels; The flue gas after burning fossil fuels passes through the dust removal device and desulfurization device, and then enters the CO2 recovery device to recover CO2; CO2 is used as the raw material for synthesizing urea; The desulfurization device is connected to the water treatment device. The wastewater is used for electrolysis to produce H2 and O2 after treatment. H2 reacts with N2 obtained by separating air from the air separation device to produce ammonia, which is used as the raw material for synthesizing urea. Ammonia reacts with CO2 to synthesize urea.

2. The method according to claim 1, characterized in that: The fossil fuel combustion system further comprises a flue gas reflux device, and part of the flue gas exhausted from the oxygen-enriched combustion system is transported to the inlet of the oxygen-enriched combustion system through the flue gas reflux device.

3. The method according to claim 1, characterized in that: The fossil fuel combustion system also includes a cold recovery device, which recovers cold from the liquid O2 and / or liquid N2 separated by the air separation device, and uses the cold to recover CO2 in the CO2 recovery device.

4. The method according to claim 1, characterized in that: The desulfurization device is used to remove sulfides in flue gas and recover SO2.

5. The method according to claim 4, characterized in that: The fossil fuel combustion system also includes a flue gas heat recovery device for recovering heat from the flue gas, and using the recovered heat for decomposing the amine liquid in the desulfurization device to achieve SO2 recovery.

6. The method according to claim 5, characterized in that: The recovered SO2 is used to prepare sulfuric acid, or is used to react with ammonia to prepare ammonium sulfate.

7. The method according to claim 1, characterized in that: The water treatment device adopts a mechanical vapor compression (Mechanical Vapor Compression) water treatment system.

8. The method according to claim 1, characterized in that: The O2 produced by electrolysis of water is connected to the inlet of the oxygen-enriched combustion system through a pipeline to support the combustion of fossil fuels.

9. A fossil fuel combustion system for carrying out the method of any one of claims 1-8.

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