CN113683066B - Process for producing dilute nitric acid by medium-pressure method - Google Patents
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- C01B21/00—Nitrogen; Compounds thereof
- C01B21/20—Nitrogen oxides; Oxyacids of nitrogen; Salts thereof
- C01B21/38—Nitric acid
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Abstract
The invention discloses a process for producing dilute nitric acid by a medium-pressure method, belonging to the field of full medium-pressureThe technical field of preparation of dilute nitric acid. The invention relates to a high-efficiency low-emission process method with the acid concentration of finished products of 0.17 to 0.65MPa being up to 55 to 65 percent. The method comprises the following steps: oxygen ammonia ratio is 1.85 to 2.0, and O in tail gas 2 The content is 5.1 to 5.5 percent, secondary air is added step by step to improve the concentration of the condensed acid to 45 to 55 percent, the total oxidation degree of an inlet of the absorption tower is 90 to 98 percent, and a system heat exchange network is optimized by a 'pinch point' analysis method to fully recover cold and heat. Aiming at the full medium-pressure process, the invention mainly improves the energy utilization rate through the optimization of the heat exchange network, solves the problems of high energy consumption and low effective energy, simultaneously improves the concentration of acid finished products and the service life of equipment, and reduces the equipment investment and the tail gas treatment cost.
Description
Technical Field
The invention relates to a process for producing dilute nitric acid by a medium-pressure method, belonging to the field of nitric acid manufacture.
Background
The industrial production method of dilute nitric acid is characterized by that it uses liquid ammonia as raw material, adopts air oxidation to produce nitric oxide, then makes the nitric oxide undergo the process of oxidation treatment to produce nitrogen dioxide, then uses water to absorb nitrogen dioxide to produce dilute nitric acid, finally makes the dilute nitric acid undergo the processes of bleaching and degassing to produce finished product acid.
The ammonia oxidation and nitrogen oxide absorption pressures may be the same or different, and may be carried out at low pressure (< 0.17 MPa), or at medium pressure (0.17 to 0.65MPa) or high pressure (0.65 to 1.3 MPa). Typical production processes are the double low/medium pressure process (L/M), the single medium/medium pressure process (M/M), the double medium/high pressure process (M/H) and the single high/high pressure process (H/H). With the enlargement of production scale, the improvement of the requirements on the concentration of finished acid and the operation economy and the limitation on the emission of tail gas nitrogen oxides, the current double medium pressure/high pressure method (M/H) becomes the mainstream of development, and meanwhile, the single medium pressure/medium pressure (M/M) process has the advantages of investment saving, strong adaptability to medium and small scales, moderate concentration of finished products and the like, thereby becoming the effective supplement of the market.
The full-medium pressure (M/M) technology generally adopts the oxidation pressure of 0.45MPa, produces steam with the pressure of less than 2.5MPa as a byproduct, preheats tail gas to recover the heat of nitrogen oxide, and produces finished acid after double-tower absorption and bleaching. The process has the following problems:
(1) Because the oxidation pressure of NO is low, the degree of oxidation at the inlet of the absorption tower is only about 68 percent, so that the absorption volume coefficient is large; the investment is increased after the double-tower series connection mode is adopted, and the oxidation reaction heat in the tower cannot be utilized, so that the heat loss is caused;
(2) The oxidation degree of the front part of the rapid cooler is not enough, and only about 25 percent of dilute nitric acid is formed, so that the equipment is seriously corroded;
(3) The energy utilization is unreasonable, the energy consumption is high, and the efficiency loss is large especially at high temperature;
(4) Tail gas NO x High content and high treating cost.
Chinese patent CN207435029U discloses a system for producing dilute nitric acid from medium-pressure nitrogen oxides, which improves the recovery power of a tail gas turbine by tail gas reinforced heating so as to reduce the power consumption of a device, and has the defects of sacrificing by-product steam as a cost, and does not solve the problems of large volume coefficient of an absorption tower, serious equipment corrosion, low energy utilization rate, large effective energy loss and the like. Chinese patent CN106744746A discloses an environment-friendly and efficient nitric acid production method, which adopts a process of first oxidation and then cooling, greatly improves the degree of oxidation in an absorption tower to solve the problems of large absorption volume coefficient and equipment corrosion, partially improves the energy utilization problem by utilizing the heat of secondary air, and still has the problems of high industrial energy consumption and large effective energy loss.
Disclosure of Invention
The invention aims to provide a process for producing dilute nitric acid by a medium-pressure method, which only relates to a technology for producing dilute nitric acid by a single medium-pressure/medium-pressure (M/M) or full medium-pressure method.
Aiming at the oxidation heat and different temperature rises in the production process of the dilute nitric acid, the invention utilizes the 'pinch point' technology to analyze the system heat energy, designs and optimizes a cold-heat exchange network, strengthens the utilization of the medium-low temperature heat energy (especially the NO oxidation heat) and the recovery of cold energy, and integrally reduces the energy consumption of the system.
The invention provides a process for producing dilute nitric acid by a medium-pressure method, which comprises the following steps:
(1) Air enters the gas ammonia preheater through an air filter and an air compressor;
(2) Liquid ammonia enters a liquid ammonia evaporator, the liquid ammonia is heated by low-temperature circulating cooling water and absorption liquid (desalted water) of an absorption tower, gas ammonia is evaporated, the gas ammonia is recovered and filtered by the cold energy of condensed acid, a gas ammonia preheater is preheated to 120 ℃ by secondary air, the gas ammonia preheater is mixed with compressed air at 0.17 to 0.65MPa and 220 to 280 ℃ in an ammonia air mixer, and then the mixture is subjected to fine filtration by mixed air and enters an oxidation furnace for ammoxidation at 850 to 950 ℃;
the molar ratio of oxygen to ammonia in the ammoxidation process is 1.85-2.0, the molar concentration of ammonia is 9.5-10.19%, and the ammoxidation rate is 96-97.5%;
(3) After ammoxidation reaction, adding a certain amount of secondary air into the NO mixed gas, recovering heat through a waste heat boiler, a tail gas third preheater, a boiler water supply heater, a rapid cooling condenser and a desalted water preheater, cooling to 40 ℃ through the rapid cooling condenser, allowing the mixture to enter a condensed acid separator to generate condensed acid, adding the rest secondary air into the condensed acid separator, allowing the mixed gas added with the secondary air to enter an oxidation tower to continuously oxidize NO to 90-95%, and then cooling to 30-35 ℃ through a tail gas first preheater, allowing the mixed gas to enter an absorption tower; carrying out oxidation absorption operation under the cooling of circulating cooling water and low-temperature water to produce 58 to 68 percent dilute nitric acid; bleaching the secondary air cooled by the gas ammonia preheater in a bleaching tower to form finished acid;
in the step (3), the proportion of secondary air added twice is 10-20%:80 to 90 percent.
(4) And the tail gas of the absorption tower enters an NOx reduction reactor after passing through a first tail gas preheater, a second tail gas preheater and a third tail gas preheater, and the treated tail gas is discharged after passing through a tail gas turbine and heat recovery.
The temperature of an NOx mixed gas outlet of the tail gas third preheater ranges from 260 ℃ to 325 ℃, and the oxidation degree ranges from 23% to 38%;
the temperature of the tail gas after the third tail gas preheater ranges from 360 ℃ to 390 ℃, and the heat recovery efficiency of the tail gas turbine ranges from 45% to 72%.
The desalted water and the steam condensate are heated by a rapid cooling condenser and a desalted water preheater, then enter a deoxidizing tank for treatment, and are heated by a boiler water supply heater and then are sent to a waste heat boiler to generate high-pressure superheated steam.
The desalted water and the condensed acid are respectively sent to the top and the middle of the absorption tower for absorption operation after being cooled by a liquid ammonia evaporator and a dilute acid cooler.
The innovation points of the invention are as follows:
(1) The invention expands the operating pressure of the medium pressure method to 0.17-0.65 MPa to meet different environment and market demands, supplements secondary air by sections at different pressures to ensure that the concentration of condensed acid reaches 45-50%, the conductivity is reduced by 15-20%, reduces the corrosion of a quick cooler (quick cooling condenser), simultaneously ensures that the degree of oxidation at the inlet of an absorption tower reaches 90-98%, reduces the absorption volume coefficient and improves the concentration of finished acid by 58-68%.
(2) The invention changes the high-temperature cooling section of the quick cooler into a desalted water preheating section, recovers the oxidation heat of the mixed gas under the condition of controlling the dew point of the mixed gas, and adds a cooling acid spraying section after the section to quickly cool and saturate the gas, thereby preventing interface corrosion through the reduction of the conductivity of the condensed acid and the disappearance of a phase interface, and simultaneously reducing the increase of NO due to the increase of the concentration of the condensed acid x Dissolution and the influence on the absorption tower.
(3) The invention uses the low-temperature tail gas with the temperature of 20-25 ℃ at the outlet of the absorption tower as a cooling medium, and adopts the high-efficiency heat pipe heat exchanger to recover the oxidation heat of the oxidation tower, so that the temperature of the gas entering the tower (70-80 ℃) can be reduced by 30-40 ℃, and the tail gas can be preheated to 50-60 ℃, thereby further improving the absorption rate and the energy recovery rate.
(4) The invention uses the cold energy of liquid ammonia to pre-cool the absorption liquid (desalted water) at the top of the absorption tower to 10-15 ℃, so as to greatly reduce NO in the tail gas x The content is 350-400 ppm, and the treatment cost is reduced.
(5) The invention utilizes the cold energy of the gas ammonia at 10-12 ℃, reduces the condensed acid from 40 ℃ to 25-30 ℃, reduces the temperature by 10-15 ℃, further improves the absorption and oxidation rate of the absorption tower, and simultaneously further improves the preheating temperature of the gas ammonia.
(6) The invention starts from the utilization of effective energy, achieves the great improvement of high-temperature effective energy by improving the grade of waste boiler byproduct steam, and improves the effective energy output by 10 to 35 percent from the current 1.0 to 2.5MPa to 4.0 to 10.0 MPa.
(7) Because the concentration of the cooling acid is 10-20% higher than that of the traditional concentration, 45-55% and 58-68% of grade product acid can be directly output by carrying out secondary bleaching in a condensed acid separator, and different market demands and full coverage of the product acid concentration range can be met.
The invention has the beneficial effects that:
aiming at the full medium-pressure process, the invention mainly improves the energy utilization rate through the optimization of the heat exchange network, solves the problems of high energy consumption and low effective energy, simultaneously improves the concentration of acid finished products and the service life of equipment, and reduces the equipment investment and the tail gas treatment cost. By the method, the capacity utilization coefficient of the absorption tower can be reduced by 40 to 50 percent, and NO in tail gas is remarkably reduced x The content of the nitrogen-containing organic compound in the tail gas is greatly reduced, the corrosion rate of the quick cooler is greatly reduced, the heat recovery rate can reach 75 to 85 percent, the energy recovery rate of tail gas can reach 45 to 75 percent, and the efficiency output of unit heat is increased by 10 to 35 percent compared with that of the traditional process.
Drawings
FIG. 1 is a flow chart of the process for producing nitric acid according to the present invention.
Detailed Description
The present invention is further illustrated by, but is not limited to, the following examples.
The implementation process of the invention corresponds to the flow of the attached figure 1: the system comprises an ammonia oxidation unit, a heat recovery and NO high-temperature oxidation unit, a quick cooling and separator, an NO oxidation tower and cooling unit, an absorption tower and a tail gas treatment unit;
the ammonia oxidation unit comprises an air filter, an air compressor, a liquid ammonia evaporator, a dilute acid cooler, an ammonia gas preheater, an ammonia air mixer, a mixed gas fine filter and an oxidation furnace;
the heat recovery and NO high-temperature oxidation unit comprises a third tail gas preheater and a boiler water supply heater;
the quick cooling and separating device comprises a quick cooling condenser and a nitrogen oxide separator;
the NO oxidation tower and cooling unit comprises an oxidation tower and a tail gas first preheater;
the absorption tower and the tail gas treatment unit comprise an absorption tower, a first tail gas preheater, a second tail gas preheater, a third tail gas preheater, a reduction reactor, a tail gas turbine and a desalted water preheater.
The invention provides a process for producing dilute nitric acid by a medium-pressure method, which comprises the following steps:
(1) Air enters the gas ammonia preheater through an air filter and an air compressor;
(2) After the cold energy of the condensed acid is recovered and filtered, a gas ammonia preheater is preheated to 120 ℃ by secondary air, and is mixed with air with the temperature of 0.17 to 0.65MPa and 220 to 280 ℃ after being compressed in an ammonia-air mixer, and then the mixture enters an oxidation furnace for ammoxidation at the temperature of 850 to 950 ℃ after being subjected to fine filtration;
the molar ratio of oxygen to ammonia in the ammoxidation process is 1.85-2.0, the molar concentration of ammonia is 9.5-10.19%, and the ammoxidation rate is 96-97.5%;
(3) After ammoxidation reaction, adding a certain amount of secondary air into the NO mixed gas, recovering heat through a waste heat boiler, a tail gas third preheater, a boiler water supply heater, a rapid cooling condenser and a desalted water preheater, cooling to 40 ℃ through the rapid cooling condenser, allowing the mixture to enter a condensed acid separator to generate condensed acid, adding the rest secondary air into the condensed acid separator, allowing the mixed gas added with the secondary air to enter an oxidation tower to continuously oxidize NO to 90-95%, and then cooling to 30-35 ℃ through a tail gas first preheater, allowing the mixed gas to enter an absorption tower; carrying out oxidation absorption operation under the cooling of circulating cooling water and low-temperature water to produce 58 to 68 percent dilute nitric acid;
in the step (3), the proportion of secondary air added twice is 10-20%:80 to 90 percent.
(4) Bleaching the secondary air cooled by the ammonia gas preheater in a bleaching tower to form finished acid;
(5) And the tail gas of the absorption tower enters an NOx reduction reactor after passing through a first tail gas preheater, a second tail gas preheater and a third tail gas preheater, and the treated tail gas is discharged after passing through a tail gas turbine and heat recovery.
The temperature of an NOx mixed gas outlet of the tail gas third preheater ranges from 260 ℃ to 325 ℃, and the oxidation degree ranges from 23% to 38%;
the temperature of the tail gas after the third tail gas preheater ranges from 360 to 390 ℃, and the recovery efficiency of the turbine heat of the tail gas ranges from 45 to 72%.
The desalted water and the steam condensate are heated by a rapid cooling condenser and a desalted water preheater, then enter a deoxidizing tank for treatment, and are heated by a boiler water supply heater and then are sent to a waste heat boiler to generate high-pressure superheated steam.
The desalted water and the condensed acid are respectively sent to the top and the middle of the absorption tower for absorption operation after being cooled by a liquid ammonia evaporator and a dilute acid cooler.
The following describes the practice of the present invention through specific operations.
Example 1:
the ammonia oxidation unit controls the oxygen-ammonia ratio to be 1.92, the ammonia content to be 9.85 percent, the temperature in the oxidation furnace to be 860 ℃, the pressure to be 0.45MPa and the ammonia oxidation rate to be 96.7 percent; a heat recovery and NO high-temperature oxidation unit controls the adding proportion of secondary air to be 10 percent; the oxygen content at the outlet of the oxidation furnace reaches 7.8 percent (V/V), the outlet temperature of NOx mixed gas of a tail gas third preheater is 280 ℃, and the degree of oxidation is 25 percent; the outlet temperature of the boiler feed water heater is 180 ℃, and the oxidation degree is 40%; the outlet temperature of the quick cooling and separating device is 40 ℃, the oxidation degree is 65 percent, and the concentration of the condensed acid is 50 percent; the outlet temperature of the NO oxidation tower and the cooling unit is 35 ℃, and the oxidation degree is 90%; the concentration of the acid of the finished product of the absorption tower and the tail gas treatment unit is 58%, the NOx content of the tail gas is 550ppm, and the oxygen content is 5.5% (v/v). The temperature of the tail gas after the third preheater of the tail gas is 380 ℃, and the heat recovery efficiency of the tail gas turbine is 60 percent.
Example 2
The ammonia oxidation unit controls the oxygen-ammonia ratio to be 2.0, the ammonia content to be 9.5 percent, the temperature in the oxidation furnace to be 880 ℃, the pressure to be 0.65MPa and the ammonia oxidation rate to be 96 percent; a heat recovery and NO high-temperature oxidation unit controls the adding proportion of secondary air to be 10 percent; the oxygen content at the outlet of the oxidation furnace reaches 7.5 percent (V/V), the outlet temperature of the NOx mixed gas of the tail gas third preheater is 325 ℃, and the oxidation degree is 38 percent; the outlet temperature of the boiler feed water heater is 240 ℃, and the oxidation degree is 55%; the temperature of the outlet of the quick cooling and separator is 40 ℃, the oxidation degree is 75 percent, and the concentration of the condensed acid is 55 percent; the outlet temperature of the NO oxidation tower and the cooling unit is 35 ℃, and the oxidation degree is 98%; the concentration of the acid of the finished product of the absorption tower and the tail gas treatment unit is 65%, the NOx content of the tail gas is 400ppm, and the oxygen content is 5.2% (v/v). The temperature of the tail gas after the third preheater of the tail gas is 390 ℃, and the heat recovery efficiency of the tail gas turbine is 72%.
Example 3
The ammonia oxidation unit controls the ratio of oxygen to ammonia to be 1.85, the ammonia content to be 10.19 percent, the temperature in the oxidation furnace to be 850 ℃, the pressure to be 0.17MPa and the ammonia oxidation rate to be 97.5 percent; a heat recovery and NO high-temperature oxidation unit, wherein the adding proportion of secondary air is controlled to be 15%; the oxygen content at the outlet of the oxidation furnace reaches 8.0 percent (V/V), the outlet temperature of the NOx mixed gas of a tail gas third preheater is 280 ℃, and the oxidation degree is 25 percent; the outlet temperature of the boiler feed water heater is 180 ℃, and the oxidation degree is 38%; the temperature of the outlet of the quick cooling separator is 40 ℃, the oxidation degree is 63 percent, and the concentration of the condensed acid is 48 percent; the outlet temperature of the NO oxidation tower and the cooling unit is 35 ℃, and the oxidation degree is 91%; the concentration of finished acid in the absorption tower and the tail gas treatment unit is 56%, the NOx content in the tail gas is 600ppm, and the oxygen content is 5.8% (v/v). The temperature of the tail gas after the third tail gas preheater is 360 ℃, and the heat recovery efficiency of the tail gas turbine is 48%.
Example 4
The ammonia oxidation unit controls the oxygen-ammonia ratio to be 1.92, the ammonia content to be 9.85 percent, the temperature in the oxidation furnace to be 860 ℃, the pressure to be 0.45MPa and the ammonia oxidation rate to be 96.7 percent; a heat recovery and NO high-temperature oxidation unit, wherein the adding proportion of secondary air is controlled to be 15%; the oxygen content at the outlet of the oxidation furnace reaches 7.8 percent (V/V), the outlet temperature of the NOx mixed gas of a tail gas third preheater is 300 ℃, and the oxidation degree is 30 percent; the outlet temperature of the boiler feed water heater is 200 ℃, and the oxidation degree is 42%; the temperature of the outlet of the quick cooling separator is 40 ℃, the oxidation degree is 70 percent, and the concentration of the condensed acid is 53 percent; the outlet temperature of the NO oxidation tower and the cooling unit is 35 ℃, and the oxidation degree is 93%; the concentration of the finished acid of the absorption tower and the tail gas treatment unit is 59 percent, the NOx content of the tail gas is 500ppm, and the oxygen content is 5.5 percent (v/v). The temperature of the tail gas after the third preheater of the tail gas is 380 ℃, and the heat recovery efficiency of the tail gas turbine is 62%.
Example 5
The ammonia oxidation unit controls the ratio of oxygen to ammonia to be 2.0, the ammonia content to be 9.5 percent, the temperature in the oxidation furnace to be 880 ℃, the pressure to be 0.65MPa and the ammonia oxidation rate to be 96 percent; a heat recovery and NO high-temperature oxidation unit controls the adding proportion of secondary air to be 10 percent; the oxygen content at the outlet of the oxidation furnace reaches 7.5 percent (V/V), the outlet temperature of the NOx mixed gas of a tail gas third preheater is 300 ℃, and the oxidation degree is 30 percent; the outlet temperature of the boiler feed water heater is 200 ℃, and the oxidation degree is 45%; the temperature of the outlet of the quick cooling separator is 40 ℃, the oxidation degree is 70 percent, and the concentration of the condensed acid is 52 percent; the outlet temperature of the NO oxidation tower and the cooling unit is 35 ℃, and the oxidation degree is 95%; the concentration of the finished acid of the absorption tower and the tail gas treatment unit is 60%, the NOx content of the tail gas is 500ppm, and the oxygen content is 5.2% (v/v). The temperature of the tail gas after the third preheater of the tail gas is 390 ℃, and the heat recovery efficiency of the tail gas turbine is 65%.
Example 6
The ammonia oxidation unit controls the oxygen-ammonia ratio to be 1.92, the ammonia content to be 9.85 percent, the temperature in the oxidation furnace to be 860 ℃, the pressure to be 0.45MPa and the ammonia oxidation rate to be 96.7 percent; a heat recovery and NO high-temperature oxidation unit, wherein the adding proportion of secondary air is controlled to be 20%; the oxygen content at the outlet of the oxidation furnace reaches 7.8 percent (V/V), the outlet temperature of the NOx mixed gas of a tail gas third preheater is 320 ℃, and the oxidation degree is 35 percent; the outlet temperature of the boiler feed water heater is 210 ℃, and the oxidation degree is 45%; the temperature of the outlet of the quick cooling and separator is 40 ℃, the oxidation degree is 72 percent, and the concentration of the condensed acid is 55 percent; the outlet temperature of the NO oxidation tower and the cooling unit is 35 ℃, and the oxidation degree is 95%; the concentration of the acid of the finished product of the absorption tower and the tail gas treatment unit is 60%, the NOx content of the tail gas is 450ppm, and the oxygen content is 5.5% (v/v). The temperature of the tail gas after the third preheater of the tail gas is 380 ℃, and the heat recovery efficiency of the tail gas turbine is 65%.
Example 7
The ammonia oxidation unit controls the oxygen-ammonia ratio to be 1.85, the ammonia content to be 10.19 percent, the temperature in the oxidation furnace to be 850 ℃, the pressure to be 0.17MPa and the ammonia oxidation rate to be 97.5 percent; a heat recovery and NO high-temperature oxidation unit, wherein the adding proportion of secondary air is controlled to be 20%; the oxygen content at the outlet of the oxidation furnace reaches 8.0 percent (V/V), the outlet temperature of the NOx mixed gas of a tail gas third preheater is 300 ℃, and the oxidation degree is 30 percent; the outlet temperature of the boiler feed water heater is 200 ℃, and the oxidation degree is 40%; the outlet temperature of the quick cooling and separating device is 40 ℃, the oxidation degree is 68 percent, and the concentration of the condensed acid is 50 percent; the outlet temperature of the NO oxidation tower and the cooling unit is 35 ℃, and the oxidation degree is 93%; the concentration of the acid of the finished product of the absorption tower and the tail gas treatment unit is 58%, the NOx content of the tail gas is 550ppm, and the oxygen content is 5.8% (v/v). The temperature of the tail gas after the third tail gas preheater is 360 ℃, and the heat recovery efficiency of the tail gas turbine is 50%.
Example 8
The ammonia oxidation unit controls the ratio of oxygen to ammonia to be 2.0, the ammonia content to be 9.5 percent, the temperature in the oxidation furnace to be 880 ℃, the pressure to be 0.65MPa and the ammonia oxidation rate to be 96 percent; a heat recovery and NO high-temperature oxidation unit controls the adding proportion of secondary air to be 10 percent; the oxygen content at the outlet of the oxidation furnace reaches 7.5 percent (V/V), the outlet temperature of the NOx mixed gas of a tail gas third preheater is 315 ℃, and the oxidation degree is 35 percent; the outlet temperature of the boiler feed water heater is 220 ℃, and the oxidation degree is 50%; the temperature of the outlet of the quick cooling separator is 40 ℃, the oxidation degree is 72 percent, and the concentration of the condensed acid is 53 percent; the outlet temperature of the NO oxidation tower and the cooling unit is 35 ℃, and the oxidation degree is 96%; the concentration of finished acid in the absorption tower and the tail gas treatment unit is 62%, the NOx content in the tail gas is 450ppm, and the oxygen content is 5.2% (v/v). The temperature of the tail gas after the third preheater of the tail gas is 390 ℃, and the heat recovery efficiency of the tail gas turbine is 68%.
Example 9
The ammonia oxidation unit controls the oxygen-ammonia ratio to be 1.85, the ammonia content to be 10.19 percent, the temperature in the oxidation furnace to be 850 ℃, the pressure to be 0.17MPa and the ammonia oxidation rate to be 97.5 percent; a heat recovery and NO high-temperature oxidation unit controls the adding proportion of secondary air to be 10 percent; the oxygen content at the outlet of the oxidation furnace reaches 8.0 percent (V/V), the outlet temperature of the NOx mixed gas of the tail gas third preheater is 260 ℃, and the oxidation degree is 23 percent; the outlet temperature of the boiler feed water heater is 160 ℃, and the oxidation degree is 35%; the outlet temperature of the quick cooling and separator is 40 ℃, the oxidation degree is 60 percent, and the concentration of the condensed acid is 45 percent; the outlet temperature of the NO oxidation tower and the cooling unit is 35 ℃, and the oxidation degree is 90%; the concentration of the finished acid of the absorption tower and the tail gas treatment unit is 55%, the NOx content of the tail gas is 650ppm, and the oxygen content is 5.8% (v/v). The temperature of the tail gas after the third tail gas preheater is 360 ℃, and the heat recovery efficiency of the tail gas turbine is 45%.
Claims (5)
1. A process for producing dilute nitric acid by a medium-pressure method is characterized by comprising the following steps:
(1) Air enters the gas ammonia preheater through an air filter and an air compressor;
(2) Liquid ammonia enters a liquid ammonia evaporator, the liquid ammonia is heated by low-temperature circulating cooling water and absorption liquid of an absorption tower to evaporate gas ammonia, the gas ammonia is recovered and filtered by cold energy of condensed acid, a gas ammonia preheater is preheated to 120 ℃ by secondary air, the gas ammonia preheater is mixed with compressed air in an ammonia-air mixer, and then the mixture is subjected to fine filtration by mixed gas and enters an oxidation furnace to carry out ammonia oxidation at 850-950 ℃;
(3) After ammoxidation reaction, adding secondary air into the NO mixed gas, recovering heat through a waste heat boiler, a tail gas third preheater, a boiler water supply heater, a rapid cooling condenser and a desalted water preheater, cooling to 40 ℃ through the rapid cooling condenser, allowing the cooled gas to enter a condensed acid separator to generate condensed acid, adding the residual secondary air into the condensed acid separator, allowing the mixed gas added with the secondary air to enter an oxidation tower to continuously oxidize NO to 90-95%, and then cooling to 30-35 ℃ through a tail gas first preheater, allowing the mixed gas to enter an absorption tower; carrying out oxidation absorption operation under the cooling of circulating cooling water and low-temperature water to produce dilute nitric acid; bleaching the secondary air cooled by the ammonia gas preheater in a bleaching tower to form finished acid; the proportion of secondary air added twice is 10-20%:80-90%; the concentration of the finished acid reaches 58% -68%;
(4) The tail gas of the absorption tower enters NO after passing through a first tail gas preheater, a second tail gas preheater and a third tail gas preheater x The reduction reactor is used for emptying the treated tail gas after the tail gas is subjected to tail gas turbine and heat recovery;
the temperature of an NOx mixed gas outlet of the tail gas third preheater ranges from 260 ℃ to 325 ℃, and the oxidation degree ranges from 23% to 38%; the temperature of the tail gas after the third tail gas preheater ranges from 360 ℃ to 390 ℃, and the heat recovery efficiency of a tail gas turbine ranges from 45% to 72%;
reducing the temperature of the condensed acid from 40 ℃ to 25-30 ℃ by using the cold energy of the gaseous ammonia at 10-12 ℃, and reducing the temperature by 10-15 ℃; the tail gas with the temperature of 20-25 ℃ at the outlet of the absorption tower is used as a cooling medium, the high-efficiency heat pipe exchanger is used for recovering the oxidation heat of the oxidation tower, the temperature of the gas entering the tower is reduced by 30-40 ℃, and the tail gas is preheated to 50-60 ℃.
2. The process for the production of dilute nitric acid according to claim 1, wherein: the absorption liquid is desalted water, the desalted water and the steam condensate are heated by a rapid cooling condenser and a desalted water preheater and then enter a deoxidizing tank for treatment, and the desalted water and the steam condensate are heated by a boiler water supply heater and then are sent to a waste heat boiler to generate high-pressure superheated steam;
the desalted water and the condensed acid are respectively sent to the top and the middle of the absorption tower for absorption operation after being cooled by a liquid ammonia evaporator and a dilute acid cooler.
3. The process for the production of dilute nitric acid according to claim 1, wherein: the molar ratio of oxygen to ammonia in the ammoxidation process is 1.85-2.0, the molar concentration of ammonia is 9.5-10.19%, and the ammoxidation rate is 96-97.5%.
4. The process for the production of dilute nitric acid according to claim 1, wherein: the compressed air entering the ammonia air mixer is 0.17 to 0.65MPa and 220 to 280 ℃.
5. The process for the production of dilute nitric acid according to claim 1, wherein: bleaching for the second time in a condensed acid separator to finally prepare 45-55 percent and 58-68 percent of grade product acid.
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| CN104016317A (en) * | 2014-06-18 | 2014-09-03 | 天脊煤化工集团股份有限公司 | Method and device for preparing high-concentration dilute nitric acid |
| CN111689480A (en) * | 2020-07-10 | 2020-09-22 | 济南双硝技术开发有限公司 | Full-medium-pressure dilute nitric acid production system |
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| CN102502541A (en) * | 2011-10-21 | 2012-06-20 | 天津华景化工新技术开发有限公司 | Production method of high-concentration dilute nitric acid |
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| CN103011102B (en) * | 2012-12-21 | 2014-09-03 | 贵州开磷（集团）有限责任公司 | Cooling process for desalted water conveyed to nitric acid absorbing tower |
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| CN207175470U (en) * | 2017-07-18 | 2018-04-03 | 河北冀衡赛瑞化工有限公司 | A kind of residual heat using device of dilute nitric acid production system |
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| CN110540178B (en) * | 2019-09-10 | 2024-02-02 | 中国成达工程有限公司 | Medium-pressure nitric acid production process and production equipment thereof |
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| CN111689480A (en) * | 2020-07-10 | 2020-09-22 | 济南双硝技术开发有限公司 | Full-medium-pressure dilute nitric acid production system |
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