CN102003867A - Method for producing high-purity nitrogen and low-purity oxygen - Google Patents

Abstract

The invention relates to a method for producing high-purity nitrogen and low-purity oxygen by utilizing air separation, comprising the following steps of: feeding air cooled to a saturated condition into a lower tower and separating into nitrogen and liquid air; and then cooling the nitrogen into liquid nitrogen, respectively feeding the liquid nitrogen and the liquid air into a nitrogen tower for rectification to obtain the high-purity nitrogen and oxygen-enriched liquid, and feeding the oxygen-enriched liquid into an oxygen tower for rectification to obtain the low-purity oxygen. The method is used for simultaneously producing the high-purity nitrogen and the low-purity oxygen with pressure by adopting three towers, has high production efficiency and low energy consumption, and can be used for continuously producing nitrogen and oxygen required by float glass and other industries.

Description

A method for producing high-purity nitrogen and low-purity oxygen

technical field

The invention relates to a method for gas separation through liquefaction, in particular to a method for separating high-purity nitrogen and low-purity oxygen from air.

Background technique

With the rapid development of float glass and chemical industries, the demand for high-purity nitrogen and low-purity oxygen has increased sharply. Usually, the pressure of high-purity nitrogen used in the float glass industry is 0.2-0.5MPa, and the purity of nitrogen is 99.999%. (O ₂ concentration ≤ 3ppm); because the melting of glass raw materials requires air or oxygen combustion, and with the implementation of national energy conservation and emission reduction policies and the rise in fuel costs, oxygen combustion has a broader application prospect. The use of oxygen combustion can greatly reduce the emission of nitrous oxide and carbon dioxide, and can save fuel and improve the grade of glass products. The oxygen purity required for oxygen combustion is greater than 80%, preferably greater than 90%, and the pressure should be greater than 0.1MPa.

The main gas components in the air are nitrogen and oxygen, the volume fractions of nitrogen and oxygen are 78.12% and 20.95%, respectively, and air is ubiquitous as a cheap resource, so the production of nitrogen and oxygen by separating air is the most traditional method.

Cryogenic air separation nitrogen production technology has a history of nearly 100 years, but this method has complex process flow, high infrastructure costs, low yield, and many operators. Therefore, people have been trying to find a simpler air separation method for a long time. Adsorption (Pressure Swing Adsorption, PSA) technology is the result of this effort, but so far, general enterprises can only produce nitrogen with a purity of 99.9% using PSA technology, and only a few domestic companies can produce nitrogen with a concentration of 99.99%. Currently, only the United States Air Products can produce ≥99.999% nitrogen with PSA technology, but it is expensive. Therefore, liquefaction and rectification are still commonly used methods for producing nitrogen.

The production of low-purity oxygen generally adopts full low-pressure double-tower rectification to produce low-pressure nitrogen and oxygen. The power consumption is generally 0.38-0.5KWh/m ³ , and the energy consumption is relatively high. The by-product low-pressure nitrogen cannot be directly transported, and nitrogen compression needs to be increased. Machine, nitrogen purity can not meet the needs of high-end float glass. At the same time, the oxygen pressure produced is less than 0.1MPa, while the float glass and chemical industries need a large amount of high-purity nitrogen and low-purity oxygen under pressure, and the pressure of nitrogen and oxygen is required to be greater than 0.15MPa. At the same time, in order to meet the requirements of energy saving and emission reduction, it is very valuable to directly produce high extraction rate, high-purity nitrogen and low-purity oxygen under pressure from the air separation process.

Patent US006079223A discloses a low-temperature air separation system, which separates air into nitrogen-rich vapor and oxygen-rich liquid, rectifies in a reflux condenser including a rectification section and a stripping section to obtain a medium-purity nitrogen product, and strips to obtain a medium-purity nitrogen product Oxygen products, the nitrogen and oxygen products produced by this method have low purity. Patent US006230519B1 discloses a low-temperature air separation method for producing gaseous nitrogen and gaseous oxygen. The air is cryogenically rectified and separated into oxygen-rich fluid and secondary nitrogen fluid in the low-pressure tower, and then nitrogen and nitrogen are recovered from the upper and lower parts of the low-pressure tower according to the density. Oxygen, the cooling and cooling process of this method is complicated. Patent CN1038514A discloses an air separation process for producing high-pressure oxygen and high-pressure nitrogen. The air is compressed, adsorbed and impurity-removed, and rectified through a two-stage rectification tower. Since both nitrogen and oxygen are rectified in the same tower, the production efficiency Low.

Contents of the invention

The invention provides a method for simultaneously producing high-purity nitrogen and low-purity oxygen using air as a raw material. Three towers are used to produce nitrogen and oxygen. Nitrogen and oxygen are rectified in different towers, and nitrogen and oxygen are extracted from the air at the same time Separation overcomes the defects of traditional methods, saves equipment investment, reduces energy consumption, increases product added value, and realizes the effect of circular economy.

The method for producing high-purity nitrogen and low-purity oxygen of the present invention, the steps are as follows:

Step 1, the purified and dried air is cooled to a saturated state, and then sent to the lower tower to be separated into nitrogen and liquid air, and then the separated nitrogen is sent to the nitrogen tower, condensed into liquid nitrogen by the condensing evaporator, and then refluxed to the lower tower top;

Step 2, the liquid nitrogen refluxed to the lower tower and the liquid air separated from the lower tower are respectively entered into the nitrogen tower for rectification, separated into pressurized nitrogen and oxygen-enriched liquid, and the nitrogen is extracted from the top of the tower to obtain a purity greater than 99.999%. High-purity nitrogen; oxygen-enriched liquid is drawn from the bottom of the tower and sent into the oxygen tower from the upper end;

Preferably, the oxygen-enriched liquid enters the oxygen tower at least one tray above the oxygen tower;

Step 3, the oxygen-enriched liquid is rectified in the oxygen tower, the oxygen-enriched liquid and liquid nitrogen are separated into low-purity oxygen and dirty nitrogen with a purity of 80% to 95%, and the low-purity oxygen is cooled and drawn out from the bottom of the tower.

Preferably, the dirty nitrogen is extracted from the top of the tower and sent to a turbo expander to be expanded to atmospheric pressure for refrigeration to supplement the cooling capacity.

Among them, the number of trays in the lower column is preferably 50-130, and the operating pressure is preferably 0.6MPa-1.1MPa.

Among them, the number of trays in the nitrogen tower is preferably 45-120, and the operating pressure is preferably 0.15MPa-0.5MPa.

Among them, the number of oxygen tower trays is preferably 20-90, and the operating pressure is preferably ≥0.08 MPa.

According to a preferred implementation of the production method, wherein the liquid air enters the nitrogen column from one of the first to tenth theoretical trays at the upper part of the nitrogen column, or enters the nitrogen column from the bottom of the column.

According to another preferred implementation of the production method, in the step 1, while the nitrogen gas is sent into the nitrogen tower, part of the nitrogen gas is sent into the oxygen tower, condensed into liquid nitrogen by the condensing evaporator in the oxygen tower, and then refluxed to the lower tower.

Preferably, the nitrogen is extracted in the middle of the lower tower and sent to the oxygen tower, and then the liquid nitrogen condensed by the condensing evaporator in the oxygen tower enters the lower tower in the middle of the lower tower.

According to a further preferred embodiment of the production method, wherein, while the liquid nitrogen is refluxed to the top of the lower tower, part of the liquid nitrogen is sent to the top of the oxygen tower as rectification reflux liquid.

Through the above design, the present invention has the following advantages compared with conventional techniques:

1) The present invention adopts three-tower continuous production, which can produce high-purity nitrogen and low-purity oxygen at the same time, and the production capacity is greatly improved.

2) The nitrogen pressure produced by the present invention can reach 0.15～0.45MPa, the purity reaches 99.999% (oxygen content is less than 5ppm), and the nitrogen extraction rate is 63～72%; the oxygen purity produced simultaneously can reach 80%～95%, and the pressure reaches 0.02-0.25MPa, the oxygen extraction rate is 70-95%; the comprehensive power consumption is low, 0.19-0.23KWh/NM ³ (N ₂ +O ₂ ).

Description of drawings

Fig. 1 is the flowchart of embodiment 1 of the present invention;

Fig. 2 is the flowchart of embodiment 2 of the present invention;

Fig. 3 is the flowchart of embodiment 3 of the present invention;

Among them, 1 is the lower tower, 2 is the oxygen tower, 3 is the nitrogen tower, 4 is the upper section of the main heat exchanger, 5 is the lower section of the main heat exchanger, 6 is the subcooler, 7, 71, 72 are throttle valves, 8 9 is the condensing evaporator of the nitrogen tower, 10 is the condensing evaporator of the nitrogen tower, 11 is compressed air, 12 is the nitrogen extracted from the lower tower, 13 is liquid air, 14 and 141 are condensed and evaporated into the oxygen tower 15 is the liquid nitrogen after the oxygen tower is condensed, 16 is the nitrogen that enters the nitrogen tower condensing evaporator, 17 is the liquid nitrogen after the nitrogen tower is condensed, 18 is the liquid nitrogen sent from the lower tower, and 181 is the nitrogen gas that enters the nitrogen tower Liquid nitrogen, 182 is the liquid nitrogen entering the oxygen tower, 19 is high-purity nitrogen, 20 is dirty nitrogen, 201 is the dirty nitrogen after expansion, 21 is oxygen-enriched liquid, 22 is low-purity oxygen, 30 is high-purity liquid nitrogen, 40 For low-purity liquid oxygen.

Detailed ways

The method for producing high-purity nitrogen and low-purity oxygen of the present invention adopts the design of three towers of lower tower, oxygen tower and nitrogen tower. Choose from the following ranges:

Number of trays in the lower column: 50-130 pieces, operating pressure: 0.6MPa-1.1MPa;

Number of trays in the nitrogen tower: 45 to 120, operating pressure: 0.15MPa to 0.5MPa;

Oxygen tower tray number: 20 to 90, operating pressure: ≥0.08MPa.

Implementation mode 1:

With reference to Fig. 1, the method that the present invention produces high-purity nitrogen and low-purity oxygen is as follows:

The nitrogen tower 3, the oxygen tower 2 and the lower tower 1 are connected by pipelines according to the method shown in Figure 1, wherein, 45 trays are installed in the nitrogen tower 3, and the operating pressure is 0.29MPa; 20 trays are installed in the oxygen tower 2, and the operating pressure is 0.17MPa ; 50 trays are installed in the lower tower 1, and the operating pressure is 0.8MPa.

After carbon dioxide and water are removed by molecular sieve adsorption, the air 11 is cooled to a saturated state through the upper section 4 and the lower section 5 of the main heat exchanger, and sent to the lower tower 1 for separation to obtain nitrogen and liquid air; nitrogen 12 is drawn from the top of the tower and sent to Enter the nitrogen tower and cool it into liquid nitrogen through the condensing evaporator 9, and then return to the lower tower 1.

In order to improve the nitrogen extraction rate, and in order to further remove the oxygen in the nitrogen, the nitrogen 12 can also be selected to be divided into two nitrogen streams 14 and 16, which are passed through the condensation evaporator 10 in the oxygen tower 2 and the condensation evaporator 3 in the nitrogen tower respectively. Cool to liquid nitrogen 15 and 17, then reflux to the lower column.

The liquid nitrogen 18 is sent to the top of the nitrogen tower 3 through the throttle valve for rectification, and the liquid air 13 enters the nitrogen tower at the 10th tray on the upper part of the nitrogen tower through the throttle valve 71 for rectification to obtain pressurized nitrogen and Oxygen-enriched liquid, nitrogen gas 19 is extracted from the top of the tower, reheated through the cooler 6 and the lower section 5 and upper section 4 of the main heat exchanger to obtain high-purity nitrogen with a purity of greater than 99.999% and a pressure of 0.25 MPa for users.

The oxygen-enriched liquid 21 is extracted from the bottom of the nitrogen tower, and the oxygen-enriched liquid 21 is sent to the oxygen tower 2 at least one tray away from the upper part of the oxygen tower, and rectified to obtain low-purity oxygen with a purity of 90%, and the low-purity oxygen 22 is extracted from the bottom of the tower , after expansion, it is reheated by the main heat exchanger and then exits the cold box.

The remaining dirty nitrogen in the oxygen tower is extracted from the top of the tower, and then reheated in the cooler 6 and the lower section of the main heat exchanger 5 and enters the turbo expander 8 to be expanded to atmospheric pressure or close to atmospheric pressure for refrigeration to supplement the cooling capacity of the device.

Implementation mode 2:

With reference to Fig. 2, the method that the present invention produces high-purity nitrogen and low-purity oxygen is as follows:

80 trays are installed in the nitrogen tower 3 with an operating pressure of 0.43MPa; 50 trays are installed in the oxygen tower 2 with an operating pressure of 0.18MPa; 90 trays are installed in the lower tower 1 with an operating pressure of 0.83MPa.

After carbon dioxide and water are removed by molecular sieve adsorption, the air 11 is cooled to a saturated state through the upper section 4 and the lower section 5 of the main heat exchanger, and then sent to the lower tower 1 for separation to obtain nitrogen and liquid air. The nitrogen gas 12 is extracted from the top of the tower and divided into Two streams 14 and 16, nitrogen streams 14 and 16 enter the oxygen tower 2 and nitrogen tower 3 respectively, and are cooled by the condensing evaporator 10 in the oxygen tower and the condensing evaporator 9 in the nitrogen tower respectively to become liquid nitrogen and then flow back to the lower tower 1. At the same time, part of the refluxed liquid nitrogen is divided into two liquid nitrogen streams 181 and 182 and sent to the top of the nitrogen tower and the oxygen tower respectively as the reflux liquid. The liquid air 13 in the lower column is sent to the nitrogen column at the 5th tray from the top of the nitrogen column for rectification. Liquid nitrogen and liquid air are separated into high-purity nitrogen and oxygen-enriched liquid after rectification.

According to the method described in Embodiment 1, the nitrogen gas is extracted to obtain nitrogen gas with a purity greater than 99.999% and a pressure of 0.4 MPa. The oxygen-enriched liquid is sent to the oxygen tower for rectification to obtain 90% pure oxygen.

Implementation mode 3:

With reference to Fig. 3, the method that the present invention produces high-purity nitrogen and low-purity oxygen is as follows:

120 trays are installed in the nitrogen tower 3 with an operating pressure of 0.52MPa; 90 trays are installed in the oxygen tower 2 with an operating pressure of 0.2MPa; 130 trays are installed in the lower tower 1 with an operating pressure of 1.0MPa.

After carbon dioxide and water are removed by molecular sieve adsorption, the air 11 is cooled to a saturated state through the upper section 4 and the lower section 5 of the main heat exchanger, and sent to the lower tower 1 for separation to obtain nitrogen and liquid air.

Nitrogen gas 141 is extracted from the middle of the lower tower and sent to the oxygen tower to be cooled into liquid nitrogen by the condensing evaporator 10, and then refluxed to the lower tower 1 in the middle of the lower tower. Nitrogen is extracted from the middle of the lower tower and sent to the oxygen tower for cooling, which can make full use of the lower-purity nitrogen separated from the lower tower to increase the extraction rate of nitrogen and oxygen.

According to the method described in Embodiment 1, nitrogen with a purity greater than 99.999% and a pressure of 0.5 MPa and oxygen with a purity of 95% are produced.

The specific embodiments of the present invention have been described in detail above, but they are only examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions to the present invention are also within the scope of the present invention. Therefore, equivalent changes and modifications made without departing from the spirit and scope of the present invention shall fall within the scope of the present invention.

Claims (9)

1. A method for producing high-purity nitrogen and low-purity oxygen, characterized in that the steps are as follows: Step 1, the purified and dried air is cooled to a saturated state, and then sent to the lower tower to be separated into nitrogen and liquid air, and then the separated nitrogen is sent to the nitrogen tower, condensed into liquid nitrogen by the condensing evaporator, and then refluxed to the lower tower top; Step 2, the liquid nitrogen refluxed to the lower tower and the liquid air separated from the lower tower are respectively entered into the nitrogen tower for rectification, separated into pressurized nitrogen and oxygen-enriched liquid, and the nitrogen is extracted from the top of the tower to obtain high-purity nitrogen; The oxygen-enriched liquid is drawn from the bottom of the tower and sent into the oxygen tower from the upper end of the oxygen tower; Step 3, the oxygen-enriched liquid is rectified in the oxygen tower, the oxygen-enriched liquid is separated into low-purity oxygen and dirty nitrogen, and the low-purity oxygen is cooled and extracted from the tower kettle. 2. The method according to claim 1, characterized in that, the number of trays in the lower column is 50-130, and the operating pressure is 0.6-1.1 MPa. 3. The method according to claim 1, characterized in that, the number of trays in the oxygen tower is 20-90, and the operating pressure is ≥0.08MPa. 4. The method according to claim 1, characterized in that, the number of trays in the nitrogen tower is 45-120, and the operating pressure is 0.15MPa-0.5MPa. 5. The method according to claim 4, wherein the liquid air enters the nitrogen tower at the bottom of the nitrogen tower, or at one of the first to tenth trays above the bottom of the nitrogen tower. 6. The method according to claim 1, characterized in that the dirty nitrogen gas is extracted from the top of the oxygen tower, and the dirty nitrogen gas is expanded to atmospheric pressure through a turbo expander to refrigerate and replenish cooling capacity. 7. The method according to claim 1, characterized in that, in said step 1, while the nitrogen is sent into the nitrogen tower, part of the nitrogen is sent into the oxygen tower, refluxed after being condensed into liquid nitrogen by the condensing evaporator in the oxygen tower To the next tower. 8. The method according to claim 8, characterized in that nitrogen is taken out in the middle of the lower tower and sent to the oxygen tower, and the liquid nitrogen condensed in the oxygen tower is refluxed to the lower tower in the middle of the lower tower. 9. The method according to claim 1 or 8, characterized in that, while the liquid nitrogen is refluxed to the lower tower, part of the liquid nitrogen is transported to the top of the oxygen tower as a reflux liquid.

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