ES2658550T3 - Process for cryogenic air separation - Google Patents

Abstract

Low temperature air separation process to produce pressurized gaseous product in an air separation unit using a distillation column system (10, 11), comprising the following steps: a) cooling a stream of compressed air in a heat exchange line (30) to form a stream of compressed cooled air, b) send at least part of the stream of compressed cooled air to a column (10) of the system, c) in a first period of time, liquefy a stream process to form a first liquid product (49) and store at least part of the first liquid product, d) in a second period of time, send the first liquid product stored above to the air separation unit as one of the feeds , e) pressurizing at least a second stream (6, 13) of liquid product, f) vaporizing the second stream of pressurized liquid product mentioned above to form a product Pressurized gaseous gas (7) in the heat exchange line, g) during the second period of time mentioned above, extract a cold gas (40) from the air separation unit and compress the cold gas into a compressor (70) that it has an inlet temperature between -180 ° C and -50 ° C and an outlet temperature of at most -20 ° C to form a pressurized gas, characterized in that step c) is carried out only if the price of electricity is below a predetermined threshold and why steps d) and g) are carried out only if the price of electricity is above a predetermined threshold.

Description

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DESCRIPTION

Process for cryogenic air separation

This invention relates to a process of separating air at low temperature.

Air separation is a technology that requires a huge amount of energy, consuming thousands of kilowatts or several megawatts of electrical energy to produce large quantities of industrial gases for tonnage applications such as chemicals, refineries, steelworks, etc.

A typical process of pumped liquid is illustrated in Figure 1. In this type of process atmospheric air is compressed by means of a main air compressor (Main Air Compressor (MAC)) up to a pressure of approximately 6 bar absolute, then said air is purified in an adsorber system 2 to remove impurities such as moisture and carbon dioxide, which can be frozen at cryogenic temperature, to obtain a purified feed air. A part 3 of this purified feed air is then cooled to almost its dew point in a heat exchanger 30 and introduced into a high pressure column 10 of a double column system in gaseous form for distillation. At the top of this high pressure column, nitrogen-rich liquid 4 is extracted, and a part is sent to the top of the low pressure column 11 as a reflux stream. The liquid stream 5 enriched with oxygen from the bottom of the high pressure column is also sent to the low pressure column as feed. These liquids 4, 5 are subcooled before an expansion against cold gases in subcoolers not shown in the figure for greater simplicity. From the lower part of the low pressure column 11 an oxygen liquid 6 is extracted, which is pressurized by a pump to a required pressure and then vaporized in the exchanger 30 to form the gaseous oxygen product 7. Another part 8 of the purified feed air is subsequently compressed in a booster air compressor 20 (Booster Air Compressor (BAC)) to a high pressure for a condensation in the exchanger 30 against the stream enriched with vaporization oxygen. Depending on the pressure of the oxygen-rich product, the reinforced air pressure may be around 65 bars or sometimes more than 80 bars. The condensed reinforced air 9 is also sent to the column system as a feed for distillation, for example to the high pressure column. Some of the liquid air can be removed from the high pressure column and sent to the low pressure column after subcooling and expansion. It is also possible to extract nitrogen-rich liquid from the top of the high pressure column and then pump it at high pressure (stream 13) and vaporize it in the exchanger in the same way as with the oxygen liquid. In addition, a small part of the feed air (stream 14) is compressed and expanded in column 11 to provide cooling of the unit. Optionally, alternative or additional means can be used to provide cooling, such as Claude expansion devices or nitrogen expansion devices.

The residual nitrogen is removed from the top of the low pressure column and heated in the exchanger 30. Argon is produced using a standard argon column whose upper condenser is cooled with liquid enriched with oxygen.

A typical 3000 T / D oxygen plant that produces gaseous oxygen under pressure for industrial uses can typically consume approximately 50 MW. A network of oxygen plants for pipeline operation would require a power supply capable of providing several hundred megawatts of electrical power. In fact, electric power is the main operating cost of an air separation plant, since its raw material is atmospheric air and is basically free. Electric power is used to drive compressors to compress air or products. Therefore, energy consumption, or the efficiency of the process, is one of the most important factors in the design and operation of an air separation unit (USA). The price of energy, usually expressed in $ / kWh, is not constant throughout the day, but varies widely depending on peak hours or valley hours. It is known that during the day the price of energy is maximum when there is a high demand - or during the period of peak hours - and minimum during the low demand - or period of valley hours. Public utilities tend to offer a considerable cost reduction if an industrial energy user can cut their energy consumption during peak hours. Therefore, companies that operate air separation units always have great incentives to adjust the operating conditions of the plants in order to follow the demand for energy so that they can reduce the cost of the service. It is clear that a solution is needed to provide an economic answer to this question of the variable price of energy.

It is useful to point out that the periods in which the energy peaks take place may differ totally from the product demand peaks, for example, warm weather would generate a great demand for energy due to the air conditioning equipment, and meanwhile the demand of products would remain at a normal level. In some places, peaks occur during daylight hours in which the industrial production of manufacturing plants, the main users of industrial gases, is normally at the highest level, which combined with the great energy use of others activities will cause a very large demand in the power grid. This great use of energy creates a potential shortage and utility companies have to allocate other sources of energy supply, which causes a temporarily high energy price. In addition, normally, at night the demand for energy is lower and energy is available in abundance, so that the companies of

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public services will reduce the price of energy to encourage use and to keep power plants running efficiently with reduced load. The price of energy at peak times may be two or several times greater than the price of energy at peak hours. In the subsequent paragraphs, the term "tip" describes the period in which the price of energy is high and the term "valley" means the period in which the price of energy is low.

For industrial energy users, energy prices are negotiated and defined in advance in energy contracts. In addition to the daily variation in energy prices, there are sometimes provisions or concessions for an interruptible energy supply: during periods of high demand for energy in the energy grid, utility companies can reduce the supply to users with a relatively short notice and in return the total price of the energy offered may be considerably below the normal price of energy. This type of arrangement provides additional incentives for users to adapt their consumption according to the network management of the energy providers. Therefore, it is possible to achieve a considerable cost reduction if the plant team can perform such flexibility. Based on the energy cost structure set forth in the energy contracts, users can define a threshold or several predetermined energy price thresholds to trigger the energy reduction mechanism:

- when the price of energy is above the predetermined threshold, the use of energy to reduce the cost is reduced,

- when the price of energy is below the predetermined threshold, the use of energy is increased to a normal level or even higher if desired.

A simple approach to address the problem of the variable price of energy is to reduce the energy consumption of the plant during peak hours, while maintaining product production to meet customer needs. However, the cryogenic process of air separation plants is not very flexible, since it implies distillation columns and product specifications require quite high purities. Attempts to decrease the production of the plant in a very short time or to increase the production of the plant quickly to meet product demand can have detrimental effects on the stability of the plant and the integrity of the product. Some prior art documents suggest how to solve the difficulties associated with the variable demand for a cryogenic plant product:

US-A-3,056,268 teaches the technique of storing oxygen and air in liquid form and vaporizing liquids to produce gaseous products to meet the variable demand of customers such as metallurgical plants. Liquid oxygen vaporizes when demand is high. This vaporization is compensated by a condensation of liquid nitrogen through the main condenser of the double column air separation unit.

US-A-4,529,425 teaches a technique similar to that of US-A-3,056,268 to solve the problem of variable demand, but liquid nitrogen is used instead of liquid air.

Document US-A-5,082,482 offered an improved version of document US-A-3,056,268 in which a constant flow of liquid oxygen is sent to a container and a variable flow of liquid oxygen is removed from it to meet the requirement of a demand oxygen variable The liquid oxygen removed is vaporized in an exchanger by condensing a corresponding flow of incoming air.

Document US-A-5,084,081 teaches yet another method of document US-A-4,529,425 where another intermediate liquid is used, the liquid enriched with oxygen, in addition to the traditional liquid oxygen and the liquid nitrogen as intermediate stored products to satisfy the variable demand The use of enriched oxygen liquid allows stabilizing the argon column during periods of variable demand.

In yet another approach to address variable product demand, US-A-5,666,823 teaches a technique for effectively integrating the air separation unit with a high pressure combustion turbine. Air extracted from the combustion turbine during periods of low product demand is fed to the air separation unit and a part is expanded to produce liquid. When the demand for the product is high, less air is drawn from the combustion turbine and the previously produced liquid is fed back to the system to meet the highest demand. The cooling provided by the liquid is compensated by not operating the expansion device for the lack of air extracted from the combustion turbine during high product demand.

Previous publications addressed the technical problems of variable demand, especially the techniques used to maintain the stability of distillation columns during the time when the demand for product varies widely. However, none of the above directly addressed the aspect of potential savings and the economy when the air separation plants are adapted to the energy price structure of the peak and valley periods to achieve a cost reduction. The prior art also did not solve the technical problems associated with the adjustment of the air separation units during periods of high energy cost and with a relatively unchanged product demand. In fact, these two aspects of

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The operation of the air separation units are quite different in nature: one is governed by the variable demand of the customers and the other is governed by the variable cost of energy with a relatively constant demand.

Therefore, there is a need to present a configuration for air separation plants that allows a reduction in energy consumption during peak hours, while maintaining a supply of products to meet customer demand. To compensate for this reduction in energy, it may be provided that additional energy consumption takes place during valley periods, at a much lower price of energy.

Therefore it is possible to achieve considerable savings in the price of energy, since a part of the products are produced at a low energy price and are supplied to customers during periods with a high energy price.

This invention offers a technique to solve the problems associated with the reduction of energy consumption during peak periods and is still able to maintain the same product production, so that energy cost savings can be achieved:

a) liquefying a process stream in valley periods to produce a first liquid liquefied product;

b) feed the first liquid liquefied liquid product to the air separation unit in the peak periods;

c) reduce the air supply provided by the air compressor to keep essentially the total amount of oxygen contained in the feed streams;

d) removing at least one product from the column system and raising its pressure by pumping it to vaporize it in the heat exchanger in order to form a gaseous product;

e) remove a cold gas from the cryogenic temperature system; Y

f) cryogenically compress the cold gas produced to a higher pressure with a cold gas compressor.

For a better understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which similar elements have been provided with the same or similar reference numbers and where :

- Figure 1 illustrates the prior art,

 - Figure 2 illustrates the predetermined invention,

 when the price of electricity is below a threshold level

 - Figure 2A illustrates the predetermined invention,

 when the price of electricity is above a threshold level

- Figure 3 illustrates an embodiment of the invention and the equipment used in the liquefaction of air in the valley periods,

- Figure 4 illustrates another embodiment with an independent blender connected to the air separation unit

used in the liquefaction of air in the valley periods,

- Figure 5 illustrates the equipment used to produce liquid air inside the air separation unit,

- Figure 6 illustrates the mode of liquid feeding during peak periods,

- Figure 7 illustrates that cold compression of cold gas can be carried out in one step,

- Figure 8 illustrates an air separation unit based on that of Figure 2A in which cold nitrogen at low pressure is compressed to a pressure between 10 and 20 bar abs.,

- Figure 9 illustrates how the pressurized cold gas can, after a cold compression in a cold compressor, be heated and sent to a hot expansion device for energy recovery or energy production,

- Figure 10 illustrates an application of the invention in which the compressed cold gas is sent to a gas turbine for energy recovery,

- Figure 11 illustrates a CCGI application,

- Figure 12 illustrates a general procedure for extracting cold gas from the process when a liquid is fed to the system during peak periods,

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- Figure 13 illustrates an operation mode of the air separation unit when energy peaks occur.

According to the invention, a low temperature air separation process according to claim 1 is provided.

A process according to the preamble of claim 1 is known from DE-A-24 34 238.

According to additional optional aspects of the invention:

- the pressurized gaseous product is an oxygen product;

- the pressurized gaseous product is a nitrogen product;

- the process stream of step c) contains any proportion of oxygen, nitrogen and argon;

- the process current of step c) is at least one of the following: pure nitrogen, air, oxygen containing at least 37 mol% oxygen, oxygen containing at least 65 mol% oxygen, oxygen which it contains at least 85 mol% oxygen, and oxygen containing at least 99.5 mol%;

- the cold gas of step g) is selected from the group consisting of a gas rich in nitrogen, pure nitrogen, air, a gas having a composition similar to air, a gas rich in oxygen and a product of pure oxygen;

- The cold gas is compressed to a pressure between 35 and 80 bar abs. in the compressor;

- at least part of the pressurized gas is heated and expanded in a hot expansion device to recover energy;

- at least a part of the pressurized gas is injected into a gas turbine for energy recovery;

- at least a part of the pressurized gas is recirculated back to the column system of the air separation unit;

- the air separation unit supplies a pressurized gaseous oxygen product to a CCGI installation;

- The CCGI installation comprises a gas turbine that also includes the following steps:

a) extract air from the gas turbine if the price of electricity is below a predetermined threshold,

b) feed the aforementioned extracted air to the air separation unit

- the process includes the step of injecting the pressurized cold gas into the gas turbine if the price of electricity is greater than a predetermined threshold;

- the process includes the steps of:

a) heat the pressurized gas on the heat exchange line;

b) cooling additional gas in the heat exchange line to form additional cold gas;

c) cryogenically compress additional cold gas to a higher pressure

- both gases are compressed to a pressure between 10 and 20 bar abs .;

- the vaporization LNG refrigeration is recovered to reduce the cost of liquefying the first liquid product;

- the process comprises reducing the flow of compressed air in the heat exchange line if the price of electricity is above a predetermined threshold, compared to the volume of air cooled in the heat exchange line if the price of electricity is below a predetermined threshold;

- the cold gas is removed from the cold box of the air separation unit without being heated in the heat exchange line;

- the cold gas is removed from the cold box of the air separation unit after being partially heated in the heat exchange line;

- the cold gas is removed from the cold box of the air separation unit after being cooled by passing it through the hot end of the heat exchange line only;

- the process includes the step of heating the pressurized gas on the heat exchange line;

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- the air separation unit is contained within a cold box and the cold gas is extracted from the cold box at a temperature between -195 ° C and -20 ° C.

The invention is described in more detail below with reference to the Figures.

Figures 2 to 13 show air separation processes according to the invention.

The invention is particularly suitable for the process of separating liquid pumped air.

The process has at least two modes of operation, one corresponding to the periods in which the price of electricity is below a predetermined threshold (Figure 2) and one corresponding to the periods in which the price of electricity is per above a predetermined threshold (Figure 2A).

When the price of electricity is below a predetermined threshold, the appliance operates according to Figure 2 as follows. Atmospheric air is compressed by a main air compressor 1 (MAC) to a pressure of approximately 6 bar absolute, then said air is purified in an adsorber system 2 to remove impurities such as moisture and carbon dioxide, which can be frozen at cryogenic temperature, to obtain a purified feed air. A part 3 of this purified feed air is then cooled to almost its dew point in a heat exchanger 30 and introduced into a high pressure column 10 of a double column system in gaseous form for distillation. At the top of this high pressure column, nitrogen-rich liquid 4 is extracted, and a part is sent to the top of the low pressure column 11 as a reflux stream. The liquid stream 5 enriched with oxygen from the bottom of the high pressure column is also sent to the low pressure column as feed. The two liquids 4, 5 are subcooled before being subjected to an expansion. From the lower part of the low pressure column 11 an oxygen liquid 6 is extracted, which is pressurized by a pump to a required pressure and then vaporized in the exchanger 30 to form the gaseous oxygen product 7. Another part 8 of the purified feed air is subsequently compressed in a booster air compressor 20 (BAC) to a high pressure for a condensation in the exchanger 30 against the stream enriched with vaporization oxygen. Depending on the pressure of the oxygen-rich product, the reinforced air pressure is typically about 65 to 80 bars for oxygen pressures of about 40-50 bars or sometimes more than 80 bars. As an indication, the flow of the stream 8 represents approximately 30-45% of the total flow of the compressor 1. The condensed reinforced air 9 is also sent to the column system as a feed for distillation, for example to the high pressure column. Some of the liquid air (stream 62) can be removed from the high pressure column and sent to the low pressure column. It is also possible to extract nitrogen-rich liquid from the top of the high pressure column and then pump it at high pressure (stream 13) and vaporize it in the exchanger in the same way as with the oxygen liquid. In addition, a small part of the feed air (stream 14) is compressed and expanded in column 11 to provide cooling of the unit. Optionally, alternative or additional means can be used to provide cooling, such as Claude expansion devices or nitrogen expansion devices.

The residual nitrogen or low pressure nitrogen is removed from the top of the low pressure column, and the entire current is heated in the exchanger 30.

Optionally, argon 80 is produced using a standard argon column whose upper condenser is cooled with oxygen-enriched liquid 5.

The nitrogen gas can be compressed to a high pressure as necessary by means of compressors 45, 46 to obtain a stream 48 of nitrogen product.

During this period, only if the price of electricity is below a predetermined threshold, air is liquefied by any of the means described in Figures 3 to 5. For example, in Figure 2, after adsorber 2 is air taken gaseous tablet free of moisture and CO2 (stream 47), which is sent to an external blender 60 to produce a stream 49 of liquid air. This liquid air is stored in a tank 50. During this period liquid air from the storage tank 50 is not sent to the column.

Only if the price of electricity is above the predetermined threshold, does the device operate according to Figure 2A as follows.

Liquid air flows from the storage tank 50 to the high pressure column 10 through a conduit 60 connected to the conduit 9, and to the low pressure column 11 through a conduit 61. During these periods, an air liquefaction does not take place. in the blender.

When liquid air from the reservoir 50 is sent to the column system, the flow rate of the main air compressor 1 can be reduced by an amount essentially equal to the amount of liquid air, so that the total oxygen balance of the feeds to the feed can be maintained. unity. As indicated above, the flow rate 14 of the expansion device 44 is quite small and can be optionally eliminated, thereby adjusting the flow rate of the compressor 1. The lost refrigeration work resulting from the omission of the expansion device can be easily compensated by the amount of the aforementioned liquid air. For the

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Therefore, by replacing the flow of the stream 8 with a flow of liquid air through 60, it is possible to stop the compressor 20 and reduce the flow of the compressor 1 by 20-55%. These reductions result in a sharp decrease in the unit's energy consumption. Since the flow of the various streams that feed the column system remains similar, the distillation operation will not be altered by these changes and the product purities will not be affected. However, by feeding a significant amount of liquid air and eliminating the reinforced air part 9 and reducing the flow of the compressor 1, the main exchanger 30 is unbalanced in terms of incoming and outgoing flow rates and cooling. In order to restore the flow and cooling balances, a flow of outgoing cold gas at cryogenic temperature must be extracted from the system. Figure 2A illustrates a possible arrangement of such operation, in which part 40 of the residual nitrogen from the low pressure column is removed from the system without being heated in the exchanger 30 or in any other exchanger. The current 40 is compressed in a compressor 70 whose input is at cryogenic temperature. The cold gas stream can be any cold gas with a suitable flow rate and temperature, including the gaseous oxygen product from the bottom of the low pressure column 11. The temperature of the cold gas leaving the cold box is between -180 ° C and -50 ° C. The main exchanger 30, and other cryogenic heat exchangers such as subcoolers, constitute a thermal exchange system, sometimes referred to as a thermal exchange line, of an air separation system. This thermal exchange line promotes the transfer of heat between incoming feed gases and outgoing gaseous products to cool the feed gases to almost their dew points before feeding them to the columns and to heat the gaseous products to room temperature.

The energy required to liquefy air is generally very high and normally the use of liquid air to replace the reinforced air stream as described above cannot be economically justified. However, since there is a large difference in the price of energy between peak periods and valley periods, as explained previously, it is planned to carry out the high energy consumption step of the air liquefaction only during periods in which those that the price of energy is low, for example at night, in such a way that the cost caused by this liquefaction step is not excessive. Therefore, it becomes clear that only during the peak periods is this liquid, previously produced economically, used to power the system and reduce the flow rates or energy consumed by the unit. Such a maneuver greatly reduces the power consumption of the unit. Therefore, it is possible to minimize the expense of paying the high price of energy during peak periods. In essence, this new invention makes it possible to produce the gas molecules necessary for distillation during periods of low energy prices and then effectively use those molecules during periods of high energy prices to achieve overall cost savings.

Cold gas extracted from the system during peak hours is economically compressed at low temperature to a higher pressure. The energy consumed by this cold compression is low compared to a hot compression performed at room temperature. In fact, the energy consumed by a vane wheel of a compressor is directly proportional to its absolute inlet temperature. A vane wheel of a compressor with an intake at -173.15 ° C (100 K) would consume approximately 1/3 of the energy of a vane wheel of a compressor with an intake at room temperature of 26.85 ° C ( 300K) Therefore, using cold compression it is possible to further improve the energy value of a gas by increasing its pressure at the expense of a relatively small need for energy. It is evident that the cold gas extracted from the process, instead of being directly subjected to a cold compression process, can be used for other purposes, for example to cool another process, to cool another gas, etc. Therefore, depending on the applications, instead of cold compressing the cold gas directly, it is possible to heat the cold gas slightly by means of some other external recovery heat exchangers to another temperature, still cryogenic (less than -50 ° C) , and then compress it using the cold compressor.

It is useful to note that traditional air separation units also constantly discharge small cold streams into the atmosphere such as a non-consensible purge of condensers or a liquid purge of containers or columns. These purge streams normally have a very small flow rate, usually less than 0.2% of the total air supply. Unless there is a rare gas recovery unit (neon, krypton, xenon, etc.) that can use these purge streams as feeds, they are rejected without any cold recovery, since their flow range is too much small. Meanwhile, the cold gas recovered from this invention has a much higher flow rate: its minimum flow rate is approximately 4% of the minimum gas supply to the system and it can be up to 70% of the total air flow rate.

The liquefaction of air in the valley periods can be carried out in another cryogenic plant, using a different equipment, as illustrated in Figure 3. In this, the air is compressed in a compressor 100, sent to a blender 200 and then to the tank 50 of storage. Liquid air is sent from the storage tank 50 to an USA as described in Figure 2A during peak periods, the storage tank being outside the cold box.

The liquefaction can also be carried out using an independent blender connected to the air separation unit as illustrated in Figure 4, where the air from the main air compressor 1 is divided, a part being sent to the blender 200 and the rest to he uses it. Next, the air coming from the blender is sent to the storage tank 50 and from it back to the USA during the peak periods.

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As an alternative, liquid air can be produced within the USA using the same equipment as in the cases of the integrated blender, as described in Figure 5. Figure 6 illustrates the mode of liquid feeding during peak periods.

The liquid storage tank can be a container located externally with respect to the cold box or a container located inside the cold box. It is also possible to use an oversized lower part of a distillation column as a liquid storage tank, in which case the stored liquid has a composition similar to that of the liquid being produced in the lower part of the container. During filling, the liquid level is allowed to rise at the bottom of the column or container.

Some additional operating conditions of various process parameters related to the invention are described below:

• The amount of liquid air to be produced in the valley hours depends on the relative duration of the valley period with respect to the duration of the peak period. The shorter the valley period, the higher the required liquefaction rate and vice versa. In peak mode, the liquid air feed rate can be approximately 20-30% of the total air supply under normal conditions.

• Figure 12 can be used to provide a general guideline for extracting cold gas from the process when a liquid 30 is fed to the system during peak periods: as shown, the column system 71 is connected to the exchange line 65, and the liquid products 15, 16 are supplied by the pumps 20, 21 to the exchange line 65 for vaporization. The entire pressurized liquid product that is vaporized in the exchanger 65 is called Total Vaporized Liquid. Pressurized gases 31, 32 are cooled and condensed in the exchanger 65 against the vaporization products 15, 16 to obtain liquid feeds 25, 26, which are then subjected to an expansion in the column system 71. The total flow of all condensed pressurized streams is called Total Incoming Liquid. The cold gas 11 can be extracted from the system according to the following guideline: its flow rate is approximately 1.6 to 2.6 times the Total Vaporized Liquid minus the Total Incoming Liquid:

Cold gas flow rate = k [Total Vaporized Liquid - Total Incoming Liquid] with k = 1.6 to 2.6

• It is also possible to extract liquid product (oxygen, nitrogen or argon) or a combination of these liquid products together with the cold gas described above increasing the amount of liquid air feed, thereby providing the necessary cooling for the production of liquid product or liquid products.

The cold compression of the cold gas can be carried out in a single step, as illustrated above in Figure 2A. When the final pressure of the compressed cold gas is relatively low, that is to say that the temperature of the compressed gas remains at a low level, then it is possible to increase the flow of compressed gas, as illustrated in Figure 7, by cooling additional air 85 from the main air compressor 1 (or nitrogen gas) with the compressed cold gas from the cold compressor 70 on the exchange line 30 and then compressing the additional gas to a higher pressure in the cold compressor 75. Then, the Two compressed cold streams are mixed upstream with respect to the heat exchange line 30 to form stream 95. This exchanger can be combined with the main exchanger 30 of Figure 2A. Figure 8 also describes this embodiment.

Figure 8 shows an USA based on that of Figure 2A, in which cold nitrogen 40 is compressed at low pressure to a pressure between 10 and 20 bar abs., Preferably 15 bar abs. The compressed gas in the cold compressor 70 is heated only at the hot end of the heat exchanger 30. Part of the compressed feed air in the main air compressor 1 is purified, cooled in the exchanger 30 to an intermediate temperature and then it is compressed in the cold compressor 75 to the same pressure as that of the cold compressor outlet 70. Next, the two compressed streams in the cold compressors 70, 75 are mixed and sent, for example, to the chamber of combustion of a gas turbine, where the mixed current is heated and then expanded into a turbine for energy recovery.

In Fig. 9 another embodiment is described in which the pressurized cold gas can, after a cold compression in the cold compressor 70, be heated and sent to a hot expansion device 110 for energy recovery or production of energy This energy produced during peak hours can be very valuable and can be exported to generate additional income. The nitrogen from the cold compressor 70 is heated in an exchanger 80 and subsequently heated by the heater 90 before being subjected to an expansion in the expansion device 110. The exhaust gas of the expansion device 110 is sent to the exchanger 80 and is used to heat the compressed cold nitrogen.

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Figure 10 illustrates the application in which the compressed cold gas is sent to a gas turbine for energy recovery. Here, the nitrogen from the cold compressor 70 is sent to the combustion chamber 150 of the gas turbine, after mixing it with air from the compressor 120 of the gas turbine. Fuel 140 is also sent to the combustion chamber, and the exhaust gas is subjected to an expansion by means of the expansion device 130 to form gas 160. In this application a compression arrangement similar to that illustrated in Figure 8 could also be used. or 9, use two compressors and mix compressed cold air with compressed cold nitrogen.

This is a field in which the new invention can be used to improve the economy of this type of process.

In fact, the CCGI process (cycle combined with integrated gasification) is based on the concept of gasifying coal, petroleum coke, etc. using oxygen gas to produce synthetic gas (syngas), which is then burned in a gas turbine to generate energy. A steam generation subsystem is added to form a combined cycle for additional power generation. Since the CCGI's energy demand normally fluctuates widely between day and night and the gasifier is not very flexible in terms of production capacity variations, it is problematic to achieve a stable mode of operation. In addition, the equipment is rarely used during valley hours. The problem is further aggravated by the fact that at night, with a lower ambient temperature, the gas turbine compressor can generate a higher flow to the turbine system. However, the latter cannot use this additional capacity due to lower demand. Similarly, during the day, when the ambient temperature is higher, the gas turbine compressor sees its reduced flow, and this during the time when additional power generation is desirable. By incorporating the characteristics of this new invention to a CCGI plant we can significantly improve the performance of the unit, thanks to the synergy of the air separation plant and the CCGI:

• At night, as shown in Figure 11, when the energy demand is low and a higher compressor flow rate is available, air from the gas turbine compressor 120 can be diverted to the air separation plant to provide the less part of the flow and energy for air liquefaction. A high pressure USA could also be advantageously used, since it can directly use the high pressure air from the gas turbine. By taking a higher flow and consuming more energy, and therefore more synthetic gas for the gas turbine, to liquefy the air during the valley hours, the CCGI part can be kept relatively constant during the night hours. In Figure 11, block 170 represents the gasifier and block 180 represents treatment, filtration, compression, etc. of synthetic gas / fuel.

• During the day, the capacity of the gas turbine air compressor 120 is reduced due to the higher ambient temperature. Air extraction from night mode stops. The liquid air produced at night and sent to storage 50 is then used in the air separation plant and the energy consumption of the latter is reduced, so that, therefore, more energy can be diverted to meet the high demand of the daytime hours. In addition, the cold gas extracted from the USA is economically compressed in the cold compressor 70 to a higher pressure to inject it into the gas turbine and to compensate for the lack of flow, thus generating even more energy.

For applications involving injecting compressed gas into a combustion turbine or a gas turbine, the cold compression arrangements of Figures 7 and 8 are well adapted: the need for pressure for the injected gas is approximately 15-20 bar, which is exactly the range of pressures required by the process of these figures, and by mixing the flow of compressed cold air with the gas rich in compressed cold nitrogen, as shown, it is possible to ensure a good supply of oxygen necessary for the combustion process .

The new invention can be advantageously used to improve the efficiency of an air separation unit. An embodiment of this feature is illustrated in Figure 13, which describes a mode of operation of the air separation unit when power peaks occur. The liquid air 30 produced during the valley periods is fed to the column system 30 ', 31. The cold gas 10 extracted from the top of the distillation column 31 is cold compressed 60, 61 to a higher pressure in the form of stream 13. A portion of this gas at higher pressure (stream 14) is recirculated back to the main exchanger 65, where it is liquefied to form a liquid stream 15 and fed to the column system. This recirculation and liquefaction improves the vaporization of the compressed liquid stream 23 in the main exchanger 65 and it is possible to slightly reduce the flow rate of the liquid feed 30. In addition, the presence of this liquid stream 15 at the cold end of the exchanger 65 would balance the cold terminal part of the plant and prevent liquefaction of the stream 2, which could be detrimental to the heat transfer in the exchanger 65 and could cause problems distillation in column 30 '.

If necessary, a part of the compressed gas (stream 12) can also be cooled and recirculated to the top of the high pressure column 30 'to improve distillation of the column system following cooling in the heat exchange line 65 to form the current 16.

5

10

fifteen

twenty

25

30

35

40

During the valley periods, the air separation plant operates in accordance with the process described in Figure 2 (for clarity of the drawing, the expansion devices and the valley mode compressors are not shown). The process of Figure 2 is a typical process for separation plants of pumped liquid air and it will be obvious to the person skilled in the art that other pumped liquid processes, such as a cold reinforcement process, can also be used for the valley mode. or a process of liquid pumped with Claude expansion device, etc. The liquid air necessary for the peak periods could be produced by an external blender, as shown in Figure 2. Of course, as previously mentioned, an integrated blender can also be implemented.

A further embodiment can be used in the recovery of refrigerators from the vaporization of LNG. Cryogenic plants have been used to recover the cold released from the vaporization of LNG in LNG plants terminal vaporization or leveling of tip loads. This refrigeration is used to reduce the cost of producing liquid products in air separation plants. With this invention, vaporized LNG refrigeration can be used to reduce the cost of liquefying liquid air in valley periods and therefore result in greater cost savings when the liquid is fed back to the USA in peak periods, such as It has been described in this concept.

The above embodiments describe the use of liquid air as an intermediate liquid to transfer refrigeration and gas molecules between the peak and valley periods. It will be obvious to one skilled in the art that any liquid with various compositions of air components can be used to apply this technique. For example, the liquid may be an oxygen-rich liquid extracted at the bottom of the high pressure column containing approximately 35 to 42 mol% of oxygen, or a liquid extracted near the bottom of the column of Low pressure with a content of 70-97 mol% of oxygen, or even a pure oxygen product. The liquid can also be a stream rich in nitrogen with little oxygen content. It is useful to note that when this nitrogen-rich liquid stream that contains almost no oxygen is fed back to the air separation unit during peak periods, the air supply rate will not be reduced, but must be kept constant to satisfy The supply of oxygen molecules. In this situation, energy saving can be achieved, for example, by turning off the nitrogen product compressors (compressors 45, 46 of Figure 2) and supplying the nitrogen product by cold compressors, which consume considerably less energy. In other words, the concept is applicable to an intermediate liquid with any composition of air components.

The invention has been developed for a constant product demand under a structure of variable energy prices. It is clear that the invention can also be extended to a system with a variable product demand. For example, during periods with low oxygen demand, the concept can be applied by feeding liquid air to the system and reducing the supply air flow. Unused oxygen can be stored in the form of a liquid oxygen product, so that it is possible to keep the distillation columns unchanged. This liquid oxygen can be fed back to the system when the oxygen demand is large. By adjusting the flow rate of liquid air, oxygen liquid, cold gas extraction and gaseous air supply, or other liquid such as liquid nitrogen, it is possible to provide an optimal process that satisfies the restrictions imposed by both variable product demand as per the variable price of energy.

Claims (9)

5 10 fifteen twenty 25 30 35 1. Low temperature air separation process to produce pressurized gaseous product in an air separation unit using a distillation column system (10, 11), comprising the following steps: a) cooling a stream of compressed air in a heat exchange line (30) to form a stream of compressed cooled air, b) send at least part of the compressed cooled air stream to a column (10) of the system, c) in a first period of time, liquefy a process stream to form a first liquid product (49) and store at least part of the first liquid product, d) in a second period of time, send the first liquid product stored above to the air separation unit as one of the feeds, e) pressurize at least a second stream (6, 13) of liquid product, f) vaporize the second stream of pressurized liquid product mentioned above to form a pressurized gaseous product (7) in the heat exchange line, g) during the second period of time mentioned above, extract a cold gas (40) from the air separation unit and compress the cold gas into a compressor (70) having an inlet temperature between -180 ° C and -50 ° C and an outlet temperature of at most -20 ° C to form a pressurized gas, characterized in that step c) is carried out only if the price of electricity is below a predetermined threshold and that steps d) and g) are carried out only if the price of electricity is above a default threshold. 2. The process according to claim 1, wherein the pressurized gaseous product is an oxygen product. 3. The process according to claim 1, wherein the pressurized gaseous product is a product of nitrogen. 4. The process according to claim 1, wherein the process stream of step c) contains any proportion of oxygen, nitrogen and argon. 5. The process according to claim 1, wherein the process current of step c) is at least one of the following: pure nitrogen, air, oxygen containing at least 37 mol% oxygen, oxygen containing at least 65 mol% oxygen, oxygen containing at least 85 mol% oxygen, and oxygen containing at least 99.5 mol%. 6. The process according to claim 1, wherein the cold gas from step g) is selected from the group consisting in a gas rich in nitrogen, pure nitrogen, air, a gas that has a composition similar to air, a gas rich in oxygen and a pure oxygen product. 7. The process according to claim 1, wherein the cold gas is compressed to a pressure between 35 and 80 bar abs. in the compressor (60, 61, 70). 8. The process according to claim 1, wherein at least a part of the pressurized gas is heated and expanded in a hot expansion device (130) to recover energy. 9. The process according to claim 1, wherein at least a part of the pressurized gas is injected into a gas turbine (130, 150) for energy recovery. image 1 Figure 1 - PREVIOUS TECHNIQUE image2 image3 Figure 2 image4 Figure 2A AIR USES ► cox and not 1 HOUR LIQUEFIER TO Air liquid image5 STORAGE image6 Figure 3 image7 ■ + «jx - + anger

 LIQUEFIER

 G Air

 liquid

STORAGE Figure 4 image8 AIR USES > otj: + HS _ Air liquid or ► STORAGE Figure 5 image9 Figure 6 7D image10 Figure 7 ■ * image11 Figure 8 image12 ESCAPE Figure 9 image13 Figure 10 GAS TURBINE SYSTEM i image14 Figure 11 image15 Figure 12 image16 Figure 13