Condensate water preheating system of nitric acid production device

Abstract

The utility model provides a nitric acid production device condensate water preheating system which comprises a first condensate water preheating unit and a second condensate water preheating unit which are connected in sequence, the first condensate water preheating unit is connected with a tail gas exhaust port of an ammonia reduction reaction unit and used for providing cold energy for tail gas generated by the ammonia reduction reaction unit, and the second condensate water preheating unit is connected with the tail gas exhaust port of the ammonia reduction reaction unit. The second condensate water preheating unit is connected with the energy saver of the heat recovery unit and used for providing cold energy needed by heat exchange for high-temperature NOx gas at an outlet of the energy saver, and the condensate water supply unit provides low-temperature condensate water for the first condensate water preheating unit. The system can overcome the defect that in the prior art, energy waste is caused due to the fact that energy of high-temperature NOx gas at an outlet of an economizer and energy of high-temperature tail gas exhausted by a tail gas turbine are not fully recycled.

Description

Technical Field

[0001] The utility model relates to the technical field of nitric acid production devices, in particular to a condensed water preheating system for a nitric acid production device. Background Art

[0002] At present, when the double pressure method is used to produce nitric acid, the air pressurized by the axial flow compressor and the gaseous ammonia evaporated by the ammonia evaporator are mixed and enter the oxidation furnace. Under the action of the platinum catalyst, an oxidation reaction occurs in the oxidation furnace, and the temperature of the oxidation furnace is generally maintained at 870-890°C. The NOx gas generated by the reaction is able to recover part of the heat when passing through the steam superheater and heat recovery device installed at the bottom of the oxidation furnace, and the temperature of the NOx gas at the outlet of the oxidation furnace drops to about 415°C. The NOx gas leaving the oxidation furnace flows through the tail gas reheater and the economizer, and its outlet temperature is reduced to about 280°C and 160°C respectively. The NOx mixed gas enters the low-pressure reaction water condensation separation bleaching device and is cooled to 40°C with circulating water, where the NOx gas reacts with the condensed water and generates dilute nitric acid. The acid / gas mixture is sent to the nitrogen oxide separator, where the dilute nitric acid is separated, and the separated NOx gas is compressed to 1.0MPa in the nitrogen oxide compressor. The pressurized NOx gas is cooled to 40°C in the tail gas preheater and high-pressure reaction water condenser, and then enters from the bottom of the absorption tower, and contacts with the process water added from the top of the absorption tower in reverse to generate dilute nitric acid. The temperature of the tail gas after absorption is increased to 360°C after heat exchange, and then enters the tail gas turbine to recover energy, and finally the high-temperature tail gas of 110°C is discharged into the atmosphere through the exhaust pipe.

[0003] From the perspective of the double-pressure nitric acid production process: (1) the temperature of the NOx gas at the economizer outlet is about 160°C, and a large amount of circulating water is required to cool it to 40°C before it enters the condensation separation bleaching device; (2) the high-temperature tail gas (about 110°C) discharged by the tail gas turbine is directly discharged into the atmosphere through the exhaust pipe. In the above process, a large amount of heat is not fully recovered and utilized. Utility Model Content

[0004] Therefore, the utility model provides a condensate preheating system for a nitric acid production device, which can overcome the defect in the prior art that the high-temperature NOx gas at the economizer outlet and the high-temperature exhaust gas emitted by the exhaust turbine are not fully recovered and utilized, resulting in energy waste.

[0005] In order to solve the above problems, the utility model provides a condensate preheating system for a nitric acid production device, comprising a first condensate preheating unit and a second condensate preheating unit connected in sequence, the first condensate preheating unit being connected to the exhaust gas exhaust port of an ammonia reduction reaction unit, for providing cold energy for the exhaust gas generated by the ammonia reduction reaction unit, the second condensate preheating unit being connected to the economizer of the heat recovery unit, for providing cold energy required for heat exchange for the high-temperature NOx gas at the outlet of the economizer, and the condensate supply unit providing low-temperature condensate for the first condensate preheating unit.

[0006] In some embodiments, the condensate supply unit includes a steam turbine unit and a desalted water self-pipeline unit arranged in parallel, the steam turbine unit includes a steam turbine and a condenser, the desalted water self-pipeline unit includes a desalted water tank, and the drain outlets of the condenser and the desalted water tank are respectively connected to the condensate inlet of the first condensate preheating unit.

[0007] In some embodiments, the ammonia reduction reaction unit includes an ammonia reduction reactor and a tail gas turbine connected in sequence, and the exhaust port of the tail gas turbine is connected to the air inlet of the first condensed water preheating unit.

[0008] In some embodiments, the first condensate preheating unit includes a first condensate preheater, which is an external fin-tube heat exchanger, and the second condensate preheating unit includes a second condensate preheater, which is a shell-and-tube heat exchanger.

[0009] In some embodiments, the first condensate preheater is further provided with a first condensate bypass pipeline, and the opening and closing of the first condensate preheater is controlled by a manual shut-off valve.

[0010] The second condensate preheater is also provided with a second condensate bypass pipeline, and the temperature of the condensate entering the second condensate preheater is adjusted by a temperature regulating valve. The temperature of the NOx gas at the outlet of the second condensate preheater is higher than 120°C.

[0011] In some embodiments, the condensate preheating system of the nitric acid production device also includes a deaerator, the drain outlet of the deaerator is connected to the economizer for heat exchange with the exhaust gas discharged from the economizer, and the drain outlet of the second condensate preheating unit is connected to the water inlet of the deaerator.

[0012] The utility model provides a condensate preheating system for a nitric acid production device, which recovers the waste heat of NOx gas at the economizer outlet and the exhaust gas discharged at the exhaust turbine outlet through a first condensate preheating unit and a second condensate preheating unit, and uses the heated condensate to increase the condensate temperature entering a deaerator, thereby reducing the consumption of low-pressure steam for deoxidation and improving the comprehensive heat recovery and utilization rate of the entire nitric acid device, thereby achieving the purpose of energy saving and consumption reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a process flow chart of a condensate preheating system for a nitric acid production device according to an embodiment of the utility model.

[0014] The reference numerals are:

[0015] 1. Desalted water tank; 2. Desalted water pump; 3. Steam turbine; 4. Condenser; 5. Condensate pump; 6. Deaerator; 7. Boiler feed pump; 8. Economizer; 9. Steam drum; 10. Tail gas reheater; 11. Low-pressure reaction water condensation bleacher; 12. Nitrogen oxide separator; 13. Nitrogen oxide compressor; 14. Ammonia reduction reactor; 15. Tail gas turbine; 16. Tail gas silencer; 17. Tail gas exhaust pipe; a. First condensate preheating unit; b. Second condensate preheating unit; 201. First condensate preheater; 202. Second condensate preheater; A. Manual shut-off valve; B. Temperature regulating valve. DETAILED DESCRIPTION

[0016] See also Figure 1 As shown, according to an embodiment of the utility model, a condensate preheating system for a nitric acid production device is provided, comprising a first condensate preheating unit a and a second condensate preheating unit b connected in sequence, the first condensate preheating unit a is connected to the tail gas exhaust port of the ammonia reduction reaction unit, and is used to provide cold energy for the tail gas generated by the ammonia reduction reaction unit, the second condensate preheating unit b is connected to the economizer 8 of the heat recovery unit, and is used to provide the cold energy required for heat exchange for the high-temperature NOx gas at the outlet of the economizer, and the condensate supply unit provides low-temperature condensate for the first condensate preheating unit a. The waste heat of the high-temperature NOx gas at the outlet of the economizer of the heat recovery unit and the exhaust gas discharged from the outlet of the tail gas turbine are recovered through the first condensate preheating unit a and the second condensate preheating unit b, so as to improve the comprehensive heat recovery and utilization rate of the entire nitric acid device, thereby achieving the purpose of energy saving and consumption reduction.

[0017] Specifically, the condensed water generated by condensing the exhaust steam from the steam turbine 3 through the condenser 4 is transported to the first condensed water preheating unit a through the condensed water pump 5, and the desalted water stored in the desalted water tank 1 from the desalted water network is transported to the first condensed water preheating unit a through the desalted water pump 2, and enters the second condensed water preheating unit b after heat exchange in the first condensed water preheating unit a, and is heated to the set temperature and then sent to the deaerator 6. The deaerator 6 performs thermal deoxidation with low-oxygen steam from the low-pressure steam self-pipeline, and the deoxygenated water after deoxidation is transported to the economizer 8 through the boiler feed water pump 7 to exchange heat with the high-temperature NOx gas, and the boiler feed water after heat exchange is sent to the steam drum 9 to produce medium-pressure saturated steam as a by-product.

[0018] Specifically, the high-temperature exhaust gas of the self-heating system and the NOx gas in the exhaust gas react with the gaseous ammonia (reducing agent) in the ammonia reduction reactor 14 under the action of the SCR catalyst to generate harmless N2 and H2O, thereby achieving the purpose of reducing the NOx gas content in the exhaust gas. The treated hot exhaust gas is recovered through the exhaust turbine 15, and the exhaust gas is finally discharged into the atmosphere through the exhaust muffler 16, the first condensed water preheating unit a and the exhaust pipe 17.

[0019] In a specific embodiment, the condensate supply unit includes a steam turbine unit and a desalted water self-pipeline unit arranged in parallel, the steam turbine unit includes a steam turbine 3 and a condenser 4, the desalted water self-pipeline unit includes a desalted water tank 1, and the drain outlets of the condenser 4 and the desalted water tank 1 are respectively connected to the condensate inlet of the first condensate preheating unit a.

[0020] In a specific embodiment, the ammonia reduction reaction unit includes an ammonia reduction reactor 14 and a tail gas turbine 15 which are connected in sequence, and the exhaust port of the tail gas turbine 15 is connected to the air inlet of the first condensed water preheating unit a.

[0021] In a specific embodiment, the first condensate preheating unit a includes a first condensate preheater 201, which is an external fin-tube heat exchanger, and the second condensate preheating unit b includes a second condensate preheater 202, which is a shell-and-tube heat exchanger. The first condensate preheater 201 is an external fin-and-tube heat exchanger, and the second condensate preheater 202 is a shell-and-tube heat exchanger, so as to ensure sufficient heat exchange and reduce the space occupied by the heat exchange equipment.

[0022] Specifically, the first condensate preheater 201 is provided with a heat source inlet, a heat source outlet, a cold source inlet and a cold source outlet. The medium of the heat source inlet is the high-temperature exhaust gas at the outlet of the exhaust turbine 15, and the medium of the cold source inlet is the condensed water mixed with the condensed water produced by the steam turbine 3 and the desalted water at the ambient temperature. The high-temperature exhaust gas at the heat source inlet exchanges heat with the condensed water at the cold source inlet, and the condensed water is heated to a set temperature and the exhaust gas after heat exchange is transported to the exhaust gas discharge tube 17 for discharge. The second condensate preheater 202 is provided with a heat source inlet, a heat source outlet, a cold source inlet and a cold source outlet. The medium of the heat source inlet is the high-temperature NOx gas at the outlet of the economizer 8, and the medium of the cold source inlet is the condensed water heated by the first condensate preheater 201. The high-temperature NOx gas at the heat source inlet exchanges heat with the condensed water at the cold source inlet, and the condensed water is heated to a set temperature and then sent to the thermal deaerator 6. The NOx gas after heat exchange is sent to the low-pressure reaction water condensation separation bleaching device 11 and continues to be cooled to a set temperature by circulating water.

[0023] In a specific embodiment, the first condensate preheater 201 is further provided with a first condensate bypass pipeline, and the opening and closing of the first condensate preheater 201 is controlled by a manual shut-off valve A.

[0024] The second condensate preheater 202 is also provided with a second condensate bypass pipeline, and the temperature of the condensate entering the second condensate preheater 202 is adjusted by the temperature regulating valve B, and the temperature of the NOx gas at the outlet of the second condensate preheater 202 is higher than 120° C. The amount of condensate entering the second condensate preheater 202 is adjusted by the temperature regulating valve B to control the temperature of the NOx gas at the outlet of the second condensate preheater 202 to be higher than 120° C. (i.e., higher than the dew point temperature of the NOx gas by more than 30° C.), so as to prevent a large amount of hot condensed acid from being generated in the second condensate preheater 202, which will cause corrosion to the equipment.

[0025] In a specific embodiment, the condensate preheating system of the nitric acid production device further includes a deaerator 6, the drain port of the deaerator 6 is connected to the economizer 8, and is used to perform heat exchange with the tail gas discharged from the economizer 8, and the drain port of the second condensate preheating unit b is connected to the water inlet of the deaerator 6. After heating by the first condensate preheating unit a and the second condensate preheating unit b which are connected in sequence, the low-pressure steam consumption of the deaerator 6 can be reduced, and the comprehensive heat recovery rate of the entire nitric acid device can be improved.

[0026] Specifically, the high-temperature NOx mixed gas from the oxidation furnace exchanges heat with the exhaust gas through the exhaust reheater 10, exchanges heat with the deoxygenated water through the economizer 8, and exchanges heat with the condensed water through the second condensed water preheating unit b, and the temperature of the NOx mixed gas gradually decreases. When the temperature decreases, the NO in the NOx mixed gas begins to be oxidized. Then the NOx mixed gas enters the low-pressure reaction water condensation separation bleaching device 11 and continues to be cooled to the set temperature by circulating water. In the low-pressure reaction water condensation separation bleaching device 11, the NOx gas reacts with the condensed water to generate a certain concentration of dilute nitric acid, and the generated dilute nitric acid is pumped to the absorption tower through the dilute acid pump; the NOx gas is sent to the nitrogen oxide separator 12 to separate the entrained dilute nitric acid, and then sent to the nitrogen oxide compressor 13 for pressurization treatment.

[0027] Taking a domestic 270kt / a double-pressure nitric acid unit as an example, before the transformation, the exhaust gas temperature at the outlet of the exhaust turbine was about 110℃, and the exhaust gas volume was 124544Nm3 / h, which was directly sent to the exhaust pipe for high-altitude discharge; the NOx gas temperature at the outlet of the economizer was about 160℃, and the gas volume was 147206Nm3 / h, which directly entered the low-pressure reaction water condensation separation bleaching device and was cooled to 40℃ with circulating water; the condensate temperature entering the deaerator was 55℃, the flow rate was 43130kg / h, and the consumption of 0.6MPa, 160℃ low-pressure steam for deoxygenation was 3910kg / h.

[0028] After the transformation, the condensed water passes through the first condensed water preheater 201 arranged at the outlet of the tail gas turbine and the second condensed water preheater 202 arranged at the outlet of the economizer 8, and is preheated to about 110°C before entering the deaerator 6. The exhaust temperature of the tail gas is expected to drop to about 63°C, and the temperature of the NOx gas at the outlet of the economizer 8 is expected to drop to about 130°C before entering the condensation separation bleaching device 11. After the transformation, the low-pressure steam consumption of the deaerator is less than 900kg / h.

[0029] After the transformation, the 270kt / a double-pressurized nitric acid unit can save about 3t / h of 0.6MPa, 160℃ low-pressure steam consumption. The utility model can be implemented without affecting the normal operation of the unit and process system. By installing heat exchange equipment and carrying out process transformation, the waste heat of the process system can be utilized on the basis of the existing device, with significant energy-saving effect and economic benefits.

[0030] The above is only a preferred embodiment of the utility model, and is not intended to limit the utility model. Any modifications, equivalent replacements and improvements made within the spirit and principles of the utility model should be included in the protection scope of the utility model. The above is only a preferred implementation of the utility model. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the utility model, and these improvements and variations should also be regarded as the protection scope of the utility model.

Claims

1. A condensate preheating system for a nitric acid production device, characterized in that: It comprises a first condensate preheating unit (a) and a second condensate preheating unit (b) which are connected in sequence, wherein the first condensate preheating unit (a) is connected to the exhaust gas outlet of the ammonia reduction reaction unit and is used to provide cold energy for the exhaust gas generated by the ammonia reduction reaction unit, and the second condensate preheating unit (b) is connected to the economizer (8) of the heat recovery unit and is used to provide the cold energy required for heat exchange for the high-temperature NOx gas at the outlet of the economizer (8), and the condensate supply unit provides low-temperature condensate for the first condensate preheating unit (a).

2. The condensate preheating system for nitric acid production equipment according to claim 1, characterized in that: The condensate supply unit comprises a steam turbine unit and a desalted water self-pipeline unit arranged in parallel, the steam turbine unit comprises a steam turbine (3) and a condenser (4), the desalted water self-pipeline unit comprises a desalted water tank (1), and the drain outlets of the condenser (4) and the desalted water tank (1) are respectively connected to the condensate inlet of the first condensate preheating unit (a).

3. The condensate preheating system for nitric acid production equipment according to claim 1, characterized in that: The ammonia reduction reaction unit comprises an ammonia reduction reactor (14) and an exhaust gas turbine (15) which are connected in sequence, and the exhaust port of the exhaust gas turbine (15) is connected to the air inlet of the first condensate preheating unit (a).

4. The condensate preheating system for nitric acid production equipment according to claim 1, characterized in that: The first condensate preheating unit (a) comprises a first condensate preheater (201), which is an external fin-tube heat exchanger; the second condensate preheating unit (b) comprises a second condensate preheater (202), which is a shell-and-tube heat exchanger.

5. The condensate preheating system for nitric acid production equipment according to claim 4, characterized in that: The first condensate preheater (201) is also provided with a first condensate bypass pipeline, and the opening and closing of the first condensate preheater (201) is controlled by a manual shut-off valve (A); The second condensate preheater (202) is also provided with a second condensate bypass pipeline, and the temperature of the condensate entering the second condensate preheater (202) is adjusted by a temperature regulating valve (B). The temperature of the NOx gas at the outlet of the second condensate preheater (202) is higher than 120°C.

6. The condensate preheating system for nitric acid production equipment according to claim 1, characterized in that: It also includes a deaerator (6), the drain outlet of the deaerator (6) is connected to the economizer (8) for heat exchange with the exhaust gas discharged from the economizer (8), and the drain outlet of the second condensate preheating unit (b) is connected to the water inlet of the deaerator (6).

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