CN113797700A

CN113797700A - Integrated unit and method for separating air and producing carbon dioxide-rich product

Info

Publication number: CN113797700A
Application number: CN202111106802.7A
Authority: CN
Inventors: 阿兰·布里格利亚; 陆中皓
Original assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2021-09-22
Filing date: 2021-09-22
Publication date: 2021-12-17

Abstract

An integrated unit and method for separating air and producing a carbon dioxide rich product is disclosed. The integrated unit includes an air separation plant that produces an oxygen-enriched gas and a dirty nitrogen gas; an oxycombustion vessel for combusting at least a portion of the oxygen-enriched gas from the air separation plant and a supplied fuel to produce a high temperature flue gas; the heat exchange equipment is used for heating the polluted nitrogen by the high-temperature flue gas; and the compression and purification unit is used for conveying the flue gas subjected to heat exchange by the heat exchange equipment to obtain a carbon dioxide-rich product. The invention comprehensively considers the requirements of the regenerative heat source of the air separation equipment and the requirements of the output oxygen or carbon dioxide products, and realizes high-efficiency energy utilization and carbon dioxide recovery.

Description

Integrated unit and method for separating air and producing carbon dioxide-rich product

Technical Field

The invention belongs to the field of air separation, relates to an integrated unit capable of adjusting carbon dioxide emission, and particularly relates to an integrated unit and a method for separating air and generating a carbon dioxide-rich product.

Background

Cryogenic air separation technology is currently the most widely and mature method of producing high purity oxygen and nitrogen. The technical process of cryogenic air separation technology is generally as follows: air enters an air compressor after being filtered, and then enters a molecular sieve purifier to remove impurities such as water, carbon dioxide and trace hydrocarbons in the air after being cooled to about 13 ℃ by an air cooling system. The purified air can be further pressurized, then the air is cooled in a main heat exchanger and is continuously expanded or throttled to obtain liquefied raw material air, and the air is separated in a rectifying tower by utilizing the characteristics of different boiling points of oxygen, nitrogen, argon and the like to prepare gases of oxygen, nitrogen, argon and the like. In order to improve the product purity and reduce the volume of the rectifying tower, the general air separation device discharges polluted nitrogen.

The molecular sieve purifier can effectively remove impurities such as carbon dioxide in the air, and during the adsorption process of the molecular sieve purifier, firstly, moisture is adsorbed, and then, carbon dioxide and other hydrocarbons are adsorbed. The adsorbed molecular sieve needs to be regenerated, and the gas source for regenerating the molecular sieve is sewage Nitrogen (Waste Nitrogen) output by an air cryogenic separation system. The heat sources currently used in the prior art to heat the contaminated nitrogen gas used to purify molecular sieves typically employ steam or electricity. If most of energy is from coal for power generation, with the development of large-scale air separation plant equipment, the energy consumption of the molecular sieve purification process and the heat required by regeneration from polluted nitrogen are greatly increased, and the coal is combusted for power generation to generate flue gas containing a large amount of carbon dioxide.

Accordingly, those skilled in the art have been devoted to developing apparatus and methods for providing a more efficient and energy efficient source of heat for heating the contaminated nitrogen gas, and for reducing carbon dioxide emissions from flue gases.

Disclosure of Invention

In order to overcome the above technical problems in the prior art, the present invention provides a system integrating an air separation device, an adaptive oxycombustion burner, and a compression and purification unit, wherein oxygen generated by the air separation device is introduced into the oxycombustion burner to be combusted to generate heat, and the heat can properly satisfy the heat required for heating the polluted nitrogen; at the same time, the carbon dioxide rich flue gas produced by the oxycombustion reactor may be treated in a subsequent compression and purification unit to produce a carbon dioxide rich product. The emission of the carbon dioxide-rich products can be adjusted according to the requirements, not only can meet the more and more strict carbon emission standard, but also can be applied to industries such as food industry and the like which have requirements on high-purity carbon dioxide.

To achieve the above object, a first aspect of the present invention discloses an integrated unit for separating air and producing a carbon dioxide rich product, comprising:

(1) an air separation plant that produces an oxygen-enriched gas and a nitrogen-contaminated gas, the air separation plant comprising a molecular sieve purifier, the nitrogen-contaminated gas being a source of gas for regeneration of molecular sieves in the molecular sieve purifier;

(2) an oxycombustion vessel for combusting at least a portion of the oxygen-enriched gas from the air separation plant and a supplied fuel to produce a high temperature flue gas;

(3) the heat exchange equipment is used for heating the polluted nitrogen by the high-temperature flue gas; and

(4) and the compression and purification unit is used for conveying the flue gas subjected to heat exchange by the heat exchange equipment to the compression and purification unit so as to obtain a carbon dioxide-rich product.

Further, the fuel is a gaseous fuel.

Further, the gaseous fuel is natural gas.

Further, the volume ratio of the fuel supplied in the oxycombustion burner to the nitrogen pollution is in the range of 1: 230 to 300.

Further, a portion of the carbon dioxide rich product is delivered from the compression and purification unit to an oxycombustion.

Further, the integrated unit comprises a line for conveying oxygen-enriched gas from the air separation unit to the oxycombustion unit, and a line for conveying flue gas after heat exchange by the heat exchange unit to the compression and purification unit.

Further, the temperature range of the flue gas after heat exchange of the heat exchange equipment is 160-200 ℃.

In a second aspect the present invention provides a method of separating air and producing a carbon dioxide rich product comprising the steps of:

(a) generating oxygen-enriched gas and dirty nitrogen gas in air separation equipment, wherein the air separation equipment comprises a molecular sieve purifier, and a gas source for regenerating a molecular sieve in the molecular sieve purifier is the dirty nitrogen gas;

(b) directing at least a portion of the oxygen-enriched gas from the air separation plant into an oxycombustion reactor for combustion with a supply of fuel to produce a high temperature flue gas;

(c) the high-temperature flue gas heats the polluted nitrogen by utilizing a heat exchange device;

(d) the flue gas after heat exchange by the heat exchange equipment is conveyed to a compression and purification unit to obtain a carbon dioxide-rich product.

Further, the method further comprises a step (e): 5 to 95 vol%, preferably 10 to 80 vol%, more preferably 20 to 70 vol% of the carbon dioxide-rich product is fed to the oxycombustion burner.

Further, the carbon dioxide-rich product refers to a product containing at least 40% carbon dioxide by volume, at least 60% carbon dioxide by volume, at least 80% carbon dioxide by volume, or at least 90% carbon dioxide by volume.

Compared with the prior art, the technical scheme provided by the invention has the following advantages:

1. the high-purity oxygen-enriched gas obtained by means of the air separation device is provided with a special oxygen-enriched combustor, so that the heat provided by the special oxygen-enriched combustor is matched with the heat for heating the waste nitrogen gas for molecular sieve regeneration, the energy efficiency of the oxygen-enriched combustor is fully utilized, and the volume of flue gas is reduced.

2. The heat generated by the combustion of the oxygen-enriched combustor completely replaces steam or electric power for heating the polluted nitrogen, so that the combustion efficiency is improved, the generation of nitrogen pollutants in flue gas is reduced, the consumption of coal power generation is reduced, and the coal power generation device is cleaner.

3. After the flue gas which is subjected to heat exchange with the waste nitrogen and thus has a reduced temperature subsequently enters the compression and purification unit, the compression and purification unit needs to provide less cold, and is more energy-saving.

4. The carbon dioxide-rich flue gas from the combustion process can be treated by a compression and purification unit to obtain a carbon dioxide-rich product with high purity, even to a food grade with a purity of 99.99%; in addition, a portion of the carbon dioxide rich product can be fed back to the oxycombustion for adjusting the combustion rate and temperature to avoid reaching excessive temperatures in the oxycombustion, with a higher adjustment efficiency than with flue gas-regulated combustion processes.

5. The technical scheme of the application integrates the requirements of a heat source for regenerating the molecular sieve in the air separation equipment and the requirements of outputting oxygen or carbon dioxide products, and realizes efficient energy utilization and recycling of carbon dioxide.

Drawings

The advantages and spirit of the present invention can be further understood by the following detailed description of the invention and the accompanying drawings.

FIG. 1 is a flow diagram illustrating one embodiment of exchanging heat from flue gas with dirty nitrogen gas to heat the dirty nitrogen gas.

In the figure: 101-an air separation plant; 102-a portion of oxygen-enriched gas; 103-another part of oxygen-enriched gas; 104-an oxygen-enriched burner; 105-natural gas; 106 a-high temperature flue gas; 106b — unused high temperature flue gas; 107-flue gas after heat exchange by heat exchange equipment; 108-Compression and Purification Unit (CPU); 109-a first portion of the carbon dioxide-rich product; 110-a second portion of the carbon dioxide rich product; 111-nitrogen off-gas; 112-heat exchange means; 113-heated waste nitrogen; 1011-molecular sieve purifier; 1012-rectification column of an air separation plant.

Detailed Description

Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention should be understood not to be limited to such an embodiment described below, and the technical idea of the present invention may be implemented in combination with other known techniques or other techniques having the same functions as those of the known techniques.

In the following description of the embodiments, for purposes of clearly illustrating the structure and operation of the present invention, directional terms are used, but the terms "front", "rear", "left", "right", "outer", "inner", "outward", "inward", "axial", "radial", and the like are to be construed as words of convenience and are not to be construed as limiting terms.

In the following description of the specific embodiments, it is to be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in an orientation or positional relationship indicated in the drawings for convenience in describing the invention and to simplify the description, but are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are not to be construed as limiting the invention.

Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not intended to limit the temporal order, quantity, or importance, but are not intended to indicate or imply relative importance or implicitly indicate the number of technical features indicated, but merely to distinguish one technical feature from another technical feature in the present disclosure. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically stated otherwise. Similarly, the appearances of the phrases "a" or "an" in various places herein are not necessarily all referring to the same quantity, but rather to the same quantity, and are intended to cover all technical features not previously described. Similarly, unless a specific number of a claim recitation is intended to cover both the singular and the plural, and embodiments may include a single feature or a plurality of features. Similarly, modifiers similar to "about", "approximately" or "approximately" that occur before a numerical term herein typically include the same number, and their specific meaning should be read in conjunction with the context.

It should be understood that in the present application, "at least one" means one or more, "a plurality" means two or more. "and/or" is used to describe the association relationship of the associated objects, meaning that there may be three relationships, for example, "a and/or B" may mean: only A, only B and both A and B are present, wherein A and B may be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single item(s) or plural items. For example, at least one (one) of a, b, or c, may represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", wherein a, b, c may be single or plural.

The terms "unit", "piece", "object", and "module" described in the present specification denote units for processing at least one of functions and operations, and may be implemented by hardware components or software components, and a combination thereof.

Unless clearly indicated to the contrary, each aspect or embodiment defined herein may be combined with any other aspect or embodiments. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

Description of the terms

As used herein, "oxycombustion burner", "combustion unit" may refer to any boiler or incinerator.

The energy necessary for the operation of the units herein comes from the combustion unit itself, at least partially fed by the oxygen produced, or from another power generation unit via a power transmission network, or directly from a renewable source (solar, wind, hydroelectric, etc.).

The fuel herein may be a gaseous fuel such as natural gas, propane or other gaseous hydrocarbons, hydrogen, CO, or combinations thereof.

Replacing air with a high purity oxygen-enriched gas can effectively improve the energy efficiency of the burner and reduce the flue gas volume, producing a flue gas with a high carbon dioxide concentration and a low nitrogen concentration. Wherein the oxygen-enriched gas may have at least 80 vol% oxygen, at least 90 vol% oxygen, at least 98 vol% oxygen, or at least 99 vol% oxygen.

By "carbon dioxide-rich" is meant that the gas stream in question contains at least 40% by volume carbon dioxide, at least 60% by volume carbon dioxide, at least 80% by volume carbon dioxide or at least 90% by volume carbon dioxide.

In the present invention, the high temperature flue gas (about 1000-1500 ℃) generated by the oxycombustion burner mainly comprises carbon dioxide, water vapor and "non-condensable" gas, i.e. gas from chemical processes which is not easily condensed by cooling, such as oxygen, nitrogen, argon and acid gas (e.g. SO generated from components in the fuel as oxidation products or by combination of nitrogen and oxygen at high temperature) which are excessively combusted and/or leaked from any air into the system₃、SO₂HCl, NO and NO₂). The exact concentration of gaseous impurities present in the flue gas depends on a number of factors, such as the fuel composition, the amount of nitrogen in the burner, the combustion temperature and the design of the burner.

In the compression and purification unit 108(CPU), the flue gas 107 after heat exchange by the heat exchange device may be compressed and water and acid gases removed by phase separation and/or distillation. The CPU includes at least one heat exchanger and a distillation column system. In the heat exchanger of the CPU, the carbon dioxide gas is cooled and condensed by refrigerant indirect heat exchange, leaving non-condensable gases as vapors, and then the condensed carbon dioxide gas is separated from the non-condensable gases in a phase separator, producing carbon dioxide liquid and overhead vapors. In general, the final purified carbon dioxide-rich stream should ideally be produced as a high pressure fluid stream that is sent to a pipeline for storage or use.

Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In an Air Separation Unit (ASU)101, air is compressed, cooled, and purified as a feed gas, and enters a main heat exchanger of the ASU, and after being cooled by the main heat exchanger, the air enters a rectifying column 1012. ASUs typically comprise a high pressure column (operating at about 5 to 6.5 bar) and a low pressure column (operating at about 1.1 to 1.5 bar). Within the higher pressure column, the feed gas is rectified so that it forms an oxygen-rich liquid stream near the bottom and nitrogen-rich streams of various purities at the various distillation trays. Depending on customer needs, the ASU of a double column may produce a gaseous or liquid nitrogen product stream at the top of the higher or lower pressure column, a gaseous or liquid oxygen product stream at the bottom of the lower pressure column, and/or a nitrogen purge below the top of the lower pressure column. And the polluted nitrogen is led out from the rectifying tower, is heated by a cooler and a main heat exchanger and is discharged to the air or the molecular sieve is regenerated.

Air inevitably contains impurities such as water and carbon dioxide, and therefore, a purifier for removing these impurities is required. The purifier may be of double-bed structure, with the lower part of the double-bed being active alumina with high mechanical strength and high adsorption capacity for water, and the upper part being molecular sieve adsorbent with good adsorption capacity for carbon dioxide and hydrocarbon impurities. During the adsorption process, moisture is first adsorbed, followed by carbon dioxide and other hydrocarbons. In order to release the adsorbate from the surface of the adsorbent and recover the adsorption capacity of the adsorbent, the adsorbent must be regenerated, and the regenerated air source is the waste nitrogen output by the air separation equipment. The temperature of the polluted nitrogen is increased from the initial 4-8 ℃ to 160-200 ℃ by heating.

The piping that carries the oxygen-enriched gas produced by the ASU is designed so as to divide the oxygen-enriched gas into a portion of oxygen-enriched Gas (GOX)102 and another portion of oxygen-enriched Gas (GOX) 103. The flow ratio of the two parts of oxygen-enriched gas can be adjusted by a flow dividing device (such as a valve). Another portion of the oxygen-enriched gas 103 is coupled to the oxycombustion 104 as the sole oxidant, while natural gas 105 is supplied to the oxycombustion 104 as fuel. The combustion of the natural gas 105 and another part of the oxygen-enriched gas 103 takes place in the oxycombustion burner 104, the heat of combustion being trapped in the high

temperature flue gases

106a and 106b generated and bringing the temperature in the oxycombustion burner to around 1500 ℃. The heating method for the polluted nitrogen with the initial temperature of 4-8 ℃ includes but is not limited to indirect heat exchange between part or all of the high-temperature flue gas 106a and the polluted nitrogen 111 by adopting heat exchange equipment 112 and the like, or heating the polluted nitrogen by using the high temperature of a burner in the heating equipment by adopting conduction, radiation and the like, and the method is used for regenerating a molecular sieve in an Air Separation Unit (ASU), so that the use of other energy sources such as electric power and the like is saved. The flow rate of the high-temperature flue gas 106a can be adjusted according to the flow rate of the dirty nitrogen gas to be heated, the temperature of the heated dirty nitrogen gas 113 is raised to 160-200 ℃, and the heated dirty nitrogen gas is conveyed into a molecular sieve purifier 1011 to desorb and regenerate the molecular sieve. Accordingly, the proportion of the unused high-temperature flue gas 106b to the entire high-temperature flue gas can be arbitrarily adjusted.

FIG. 1 illustrates one embodiment of exchanging heat from high temperature flue gas with the dirty nitrogen gas, thereby heating the dirty nitrogen gas.

After the heat exchange with the nitrogen pollution is completed, the flue gas 107 after the heat exchange by the heat exchange device 112 is sent to a Compression and Purification Unit (CPU) 108. Because part of O still exists in the flue gas after oxygen-enriched combustion₂、N₂、H₂O and typical pollutants (SO) from combustion₂And NO_xEtc.), this portion of the impurity gas may cause CO₂Pipeline corrosion, icing, blockage and the like in the transportation process seriously harm the stable operation of equipment and CO₂The quality of the product. In the compression and purification unit 108, the flue gas is passed through NO_x、SO_xAbsorption and desorption of and CO₂Can realize high-purity CO₂And (4) preparation. Removal of NO_xAnd SO_xThe process of (a) is not limited in the present invention and can be carried out using a washing column well known to those skilled in the art. In the CPU, the flue gas firstly enters a compressor to be pressurized to about 50bar, and enters a low-Temperature separation process after being dehydrated by TSA (Temperature Swing Adsorption) so as to purify CO₂. Cryogenic separation is achieved by partial condensation of flue gas in a heat exchanger (e.g., an aluminum brazed heat exchanger) against a refrigerant, CO in the flue gas₂Is condensed. Subsequently separating the liquid phase and the gas phase (non-condensable gases, mainly N) in a gas-liquid separation tank₂) Is vented to the atmosphere. The liquid phase is expanded and sent to the top of a rectifying tower for rectification and purification so as to remove all light impurities and produce CO meeting the requirements₂And (5) producing the product. Since the temperature of the flue gas 107 entering the compression and purification unit 108 after heat exchange by the heat exchange means has been substantially reduced, the amount of cold to be supplied in the compression and purification unit is also substantially reduced.

With respect to the resulting carbon dioxide-rich product, a first portion of the carbon dioxide product 109 can be returned to the oxycombustion 104 to condition the combustion process, and a second portion of the carbon dioxide product 110 can be used as a raw material in another process. The recycled carbon dioxide can realize the temperature regulation and control in the oxygen-enriched combustion process and the CO in the flue gas₂And (4) enriching.

In the oxygen-enriched combustor, the combustion process of the natural gas can be simplified as follows: CH (CH)₄+2O₂＝CO₂+2H₂O, i.e. 1Nm³Natural gas combustion theoretically requires 2Nm³Pure oxygen of (3). In this embodiment, in order to control NO of high temperature type_xThe combustion temperature is generally required to be controlled below 1500 ℃, so as to avoid the increase of material selection cost of the combustor caused by the overhigh combustion temperature. The excess air coefficient alpha (namely the ratio of the actual air consumption to the theoretical air consumption) of the burner taking natural gas as fuel needs to be controlled between 1.1 and 1.25. If the excess air coefficient is too small, incomplete combustion and fuel waste can be caused; if the coefficient of the excess air is too large, too much oxidant enters the combustor, the temperature of a hearth can be reduced, the heat transfer result is poor, the heat taken away by flue gas is large, and a furnace tube is easy to oxidize and peel.

The combustion temperature at 1500 ℃ and the excess air ratio of 1.1 to 1.25 are calculated from Table 1, and it is necessary to control the feed gas ratio of the combustor to 1 Nm/1 Nm³Natural gas corresponding to 2.4Nm³About 8.9Nm of oxygen gas is simultaneously doped³Carbon dioxide (c). The inlet pressure of the natural gas was controlled at about 0.5 bar.

TABLE 1 air excess index and air oxygen content relation table

The regeneration temperature of the molecular sieve is about 150 ℃, the design of the oxygen-enriched combustor is matched with the scale of the molecular sieve to be regenerated, and the volume ratio of natural gas to polluted nitrogen is set to be 1: 230 to 300.

The following is an example of a typical 2000tpd air separation plant:

if only the electric heater is used for regenerating the molecular sieve in the air separation equipment, the total power is about 2500kW, and the total power consumption is 2500kW multiplied by 9h multiplied by 365 which is 8,212,500 kW.h each year when the air separation equipment works for 9 hours each day.

If the molecular sieve in the air separation equipment is regenerated by adopting natural gas combustion to replace an electric heater, the total power is 2500kW, the heat value of 1 kW.h power consumption is 3.6MJ, and 1Nm³The heating value of natural gas is 36 MJ. So that 821250Nm is needed³The natural gas replaces 8212500 kW.h of electric energy.

Regarding the emission of carbon dioxide, the emission of CO2 is about 0.92kg for every 1 kW.h of electricity generated, estimated from the emission of carbon generated per kilowatt hour.

If the molecular sieve regeneration in the air separation plant only uses an electric heater, the annual CO₂The discharge was 8,212,500kW · h × 0.92kg/KW · h ═ 7,555,500 kg.

If the molecular sieve in the air separation equipment is regenerated by adopting natural gas combustion to replace an electric heater, the annual CO₂The discharge was 821250Nm³×1.997kg/m³+60kW×24h×365×0.92kg/KW·h＝2,123,588kg。

If the invention completely replaces the traditional steam or electric energy with the heat generated by the oxygen-enriched combustion to heat the polluted nitrogen, the generated enriched carbon dioxide can be partially or completely converted into a high-purity carbon dioxide product, and the additional carbon dioxide can not be released like the traditional electricity generation process adopting an electric heater.

In conclusion, the technical scheme of the application integrates the requirements of a molecular sieve regeneration heat source of the air separation equipment and the requirements of output oxygen or carbon dioxide products, and realizes efficient energy utilization and carbon dioxide recycling by combining the oxygen-enriched combustion technology.

The embodiments described in the specification are only preferred embodiments of the present invention, and the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the present invention. Those skilled in the art can obtain technical solutions through logical analysis, reasoning or limited experiments according to the concepts of the present invention, and all such technical solutions are within the scope of the present invention.

Claims

1. An integrated unit for separating air and producing a carbon dioxide-rich product, comprising:

(3) heat exchange equipment, by which the high temperature flue gas heats the contaminated nitrogen gas; and

2. The integrated unit of claim 1, wherein the fuel is a gaseous fuel.

3. The integrated unit of claim 2, wherein the gaseous fuel is natural gas.

4. The integrated unit of claim 2, wherein the volumetric ratio of fuel supplied in the oxycombustion burner to the dirty nitrogen gas is in the range of 1: 230 to 300.

5. The integrated unit of claim 1, wherein a portion of the carbon dioxide rich product is delivered from the compression and purification unit to an oxycombustion.

6. The integrated unit of claim 1, comprising a line for delivering oxygen-enriched gas from the air separation plant to the oxycombustion unit, and a line for delivering flue gas after heat exchange by the heat exchange plant to the compression and purification unit.

7. The integrated unit according to claim 1, wherein the temperature of the flue gas after heat exchange by the heat exchange device is in the range of 160-200 ℃.

8. A method of separating air and producing a carbon dioxide-rich product, comprising the steps of:

9. The method of claim 8, further comprising step (e): 5 to 95 vol%, preferably 10 to 80 vol%, more preferably 20 to 70 vol% of the carbon dioxide-rich product is fed to the oxycombustion burner.

10. The method of claim 8, wherein the carbon dioxide-rich product is a product containing at least 40% carbon dioxide by volume, at least 60% carbon dioxide by volume, at least 80% carbon dioxide by volume, or at least 90% carbon dioxide by volume.