1. CO based on iodine-sulfur semi-open type cycle hydrogen production₂A zero emission ammonia synthesis system, comprising: air separation device for separating nitrogen and method for preparing H₂H of S₂S preparation device and method for preparing SO₂SO of (A)₂Preparation device, Bunsen reaction device for preparing sulfuric acid and hydrogen iodide, HI decomposition device for preparing hydrogen and iodine, and device for synthesizing NH₃NH of (2)₃A synthesizing device;

the NH₃A synthesis unit in communication with the air separation unit for receiving the separated nitrogen, the NH, from the air separation unit₃The synthesis device is communicated with the HI decomposition device to receive the hydrogen prepared by the HI decomposition device;

said H₂An S preparation device is communicated with the HI decomposition device to receive hydrogen from the HI decomposition device;

the SO₂Preparation apparatus and the same₂S preparation device connected to receive the said H₂S preparation of H prepared by device₂S; the SO₂A preparation device is communicated with the Bunsen reaction device to receive sulfuric acid from the Bunsen reaction device;

the Bunsen reaction device is communicated with the HI decomposition device to receive iodine prepared by the HI decomposition device, sulfuric acid prepared by the Bunsen reaction device is divided into two parts, the first part of sulfuric acid is output as a product, and the second part of sulfuric acid is introduced into the SO₂Preparing a device; and introducing the HI prepared by the Bunsen reaction device into the HI decomposition device.

2. CO based on iodine-sulfur semi-open type cycle hydrogen production₂The zero-emission ammonia synthesis method is characterized by comprising the following steps:

s101: introducing air into an air separation device to obtain nitrogen, mixing the nitrogen with an HI decomposition device to obtain hydrogen, mixing part of the hydrogen and introducing NH₃A synthesis device for preparing ammonia gas;

s102: introducing H into the rest of the hydrogen and the sulfur source₂S preparation device for preparing H₂S, the H₂Introducing SO into the sulfuric acid prepared by the S and Bunsen reaction device₂Preparation apparatus to obtain SO₂And water, said SO₂And introducing iodine prepared by the water and HI decomposition device into the Bunsen reaction device to prepare sulfuric acid and HI, dividing the sulfuric acid into two parts, wherein the first part of sulfuric acid is taken as a product to be output, and the second part of sulfuric acid is introduced into the SO₂Preparing a device; introducing HI into the HI decomposition device to prepare hydrogen and iodine, dividing the hydrogen into two parts, introducing the first part of hydrogen as a raw material into the NH₃A synthesis device, a second part of raw materials is introduced into the H₂S, preparing a device; and introducing the iodine into the Bunsen reaction device.

3. CO for hydrogen production based on iodine-sulfur semi-open cycle according to claim 2₂The method for zero emission ammonia synthesis is characterized in that in the step S102, the sulfur source is at least selected from iron disulfide and ferrous sulfideOne of ferric trisulfide and sulfur.

4. CO for iodine-sulfur based semi-open cycle hydrogen production according to claim 2 or 3₂Zero-emission ammonia synthesis process, characterized in that, in step S102, the H₂Introducing SO into the sulfuric acid prepared by the S and Bunsen reaction device₂When preparing the apparatus, said H₂The molar ratio of S to the sulfuric acid is 1: (2.8-3.2).

5. CO for hydrogen production based on iodine-sulfur semi-open cycle according to claim 4₂Zero-emission ammonia synthesis process, characterized in that, in step S102, the H₂Introducing SO into the sulfuric acid prepared by the S and Bunsen reaction device₂When preparing the apparatus, said H₂The molar ratio of S to the sulfuric acid is 1: 3.

6. CO for iodine-sulfur based semi-open cycle hydrogen production according to any of claims 2-5₂The zero emission ammonia synthesis method is characterized in that in the step S102, the first part of sulfuric acid accounts for 1/5-1/3 of the total volume of sulfuric acid.

7. CO for iodine-sulfur based semi-open cycle hydrogen production according to any one of claims 2-6₂The zero-emission ammonia synthesis method is characterized in that in the step S102, the first part of sulfuric acid accounts for 1/4 of the total volume of the sulfuric acid.

8. CO for iodine-sulfur based semi-open cycle hydrogen production according to any of claims 2-7₂The zero-emission ammonia synthesis method is characterized in that in the step S102, the first part of hydrogen accounts for 5/8-7/8 of the total volume of hydrogen.

9. CO for iodine-sulfur based semi-open cycle hydrogen production according to any of claims 2-8₂The zero-emission ammonia synthesis method is characterized in that the CO for hydrogen production based on iodine-sulfur semi-open cycle₂Zero-emission synthetic ammoniaThe hydrogen production energy utilization rate of the method is not lower than 50%.

10. CO for hydrogen production based on iodine-sulfur semi-open cycle as claimed in claim 1₂Zero emission ammonia synthesis system and/or iodine sulfur semi-open cycle hydrogen production based CO of any of claims 2 to 9₂The zero-emission ammonia synthesis method is applied to the field of hydrogen production.

Background

The realization of carbon peak reaching and carbon neutralization is a hard layer, and under the aim of 'double carbon', the coalThe rise and decay of the base energy are related to the upstream and downstream related plates of coal, coal electricity and coal chemical industry, and the influence is very heavy. Due to the structure and the reaction process of coal, 2-3 tons of carbon dioxide are discharged from 1 ton of coal, and high carbon is just one of the main problems of long-term scaling in the coal chemical industry. In this context, hydrogen energy is considered as an important pathway for achieving carbon neutralization, and is classified as a national strategy by a plurality of countries. Firstly, hydrogen energy is used as a raw material, and is used for reducing steel making by hydrogen to replace a reducing agent CO in the steel making process so as to reduce CO discharged in the coking process₂(ii) a Secondly, the method is used for synthesizing ammonia to replace coal gasification hydrogen production; thirdly, the hydrogen is used for petroleum refining and coal chemical production chemicals to replace coal gasification followed by water gas shift hydrogen production or natural gas reforming hydrogen production so as to reduce CO discharged in the shift or reforming process₂. Secondly, hydrogen energy is used as fuel to replace fossil energy to realize CO₂Emission reduction, namely cement calcination, heat supply and power generation; secondly, the fuel cell is used for traffic and power generation; and thirdly, the energy storage device is used for storing energy, so that the flexibility of a power system is enhanced, and the development of a higher proportion of renewable energy in an energy structure can be promoted.

According to the analysis, the hydrogen energy can promote the transformation and upgrading of the traditional synthetic ammonia, and nitrogen prepared by air separation can be combined with hydrogen to generate ammonia, so that CO of the system is realized₂And (4) zero emission.

Thermochemical iodine sulfur closed cycle hydrogen production is considered to be the most efficient process which can realize large-scale production. The iodine-sulfur closed cycle hydrogen production process mainly comprises the following three chemical reactions: bunsen reaction (Bunsen reaction) SO₂+I₂+2H₂O＝2HI+H₂SO₄，H₂SO₄Thermal decomposition reaction H₂SO₄＝H₂O+SO₂HI decomposition reaction 2HI ═ I₂+H₂. Wherein, the decomposition temperature of the sulfuric acid is about 850 ℃, the decomposition temperature of the hydrogen iodide is about 400 ℃, and a large amount of high-temperature heat sources are consumed. Because the fourth generation advanced nuclear energy technology, a high-temperature gas cooled reactor (outlet temperature is 700-950 ℃) and an ultra-high temperature gas cooled reactor (outlet temperature is more than 950 ℃) are the most ideal heat sources for hydrogen production by high-temperature electrolysis at present, hydrogen production by thermochemical iodine-sulfur closed cycle is realized by introducingAre often associated with nuclear hydrogen production. But is limited by the installed scale of nuclear power, and the total amount of hydrogen produced by thermochemical iodine-sulfur closed cycle hydrogen production related to nuclear power is difficult to meet the hydrogen demand under the carbon neutralization target.

Disclosure of Invention

The invention aims to solve the technical problem of providing CO for hydrogen production based on iodine-sulfur semi-open cycle aiming at the defects of the prior art₂The zero-emission ammonia synthesis system realizes the preparation of hydrogen by decomposing water by a chemical method, is mild in reaction conditions, widens the scenes of application in industrial practice, reduces energy consumption, improves system energy efficiency, and is low in energy consumption and CO₂Zero emission and large-scale industrial application.

In a first aspect, the invention provides CO based on iodine-sulfur semi-open cycle hydrogen production₂A zero-emission ammonia synthesis system, comprising: air separation device for separating nitrogen and method for preparing H₂H of S₂S preparation device and method for preparing SO₂SO of (A)₂Preparation device, Bunsen reaction device for preparing sulfuric acid and hydrogen iodide, HI decomposition device for preparing hydrogen and iodine, and device for synthesizing NH₃NH of (2)₃A synthesizing device;

the NH₃A synthesis unit in communication with the air separation unit for receiving the separated nitrogen, the NH, from the air separation unit₃The synthesis device is communicated with the HI decomposition device to receive the hydrogen prepared by the HI decomposition device;

said H₂An S preparation device is communicated with the HI decomposition device to receive hydrogen from the HI decomposition device;

the SO₂Preparation apparatus and the same₂S preparation device connected to receive the said H₂S preparation of H prepared by device₂S; the SO₂A preparation device is communicated with the Bunsen reaction device to receive sulfuric acid from the Bunsen reaction device;

the Bunsen reaction device is communicated with the HI decomposition device to receive the iodine prepared by the HI decomposition deviceThe first part of sulfuric acid is taken as a product to be output, and the second part of sulfuric acid is introduced into the SO₂Preparing a device; and introducing the HI prepared by the Bunsen reaction device into the HI decomposition device.

In the invention, the air separation device is used for mixing the prepared nitrogen and the hydrogen prepared by the HI decomposition device and then mixing the mixture with NH through a pipeline₃Connecting a synthesis device; production of hydrogen sulfide H₂The hydrogen sulfide prepared by the S preparation device passes through the pipeline and the SO₂Preparation plant connection, SO₂The sulfur dioxide and the water prepared by the preparation device are respectively connected with the Bunsen reaction device through pipelines; the sulfuric acid produced by the Bunsen reaction device for producing sulfuric acid and hydrogen iodide is divided into two parts, one part is used as a reactant and is communicated with SO through a pipeline₂The preparation device is connected, and the other part is output as a product; hydrogen produced by HI decomposition device for producing hydrogen and iodine is divided into two parts, one part is used as reactant and H is passed through pipeline₂The S preparation device is connected, and the other part of the S preparation device is adjusted with nitrogen to meet the requirement of ammonia synthesis.

CO for preparing hydrogen based on iodine-sulfur semi-open cycle₂The zero-emission synthetic ammonia system directly mixes the nitrogen generated by the air separation device and the hydrogen generated by the iodine-sulfur semi-open cycle in proportion to prepare ammonia gas, thoroughly changes the traditional synthetic ammonia production process taking fossil energy such as coal and the like as main raw materials, omits the processes of coal gasification, water gas shift, purification and the like, simplifies the process flow and reduces the system investment; meanwhile, as the hydrogen comes from the HI decomposition device, CO is not generated in the whole production process₂CO for realizing the production process of synthetic ammonia₂And (4) zero emission.

The process of preparing sulfur dioxide by thermal decomposition of sulfuric acid is converted into the process of preparing sulfur dioxide by chemical reaction of sulfuric acid and hydrogen sulfide, and a high-temperature heat source required by thermal decomposition of sulfuric acid is saved. Hydrogen is produced by iodine-sulfur semi-open cycle, four main chemical reactions are adopted, hydrogen is produced by decomposing water by a chemical method, the reaction conditions are mild, the scenes of industrial practice are widened, the energy consumption is reduced, the system energy efficiency is improved, and the hydrogen production system is low in energy consumption and CO₂Zero emission and large-scale industrial applicationThe hydrogen production system and the process method.

In a second aspect, the invention provides CO for hydrogen production based on an iodine-sulfur semi-open cycle₂The zero-emission ammonia synthesis method comprises the following steps:

s101: introducing air into an air separation device to obtain nitrogen, mixing the nitrogen with an HI decomposition device to obtain hydrogen, mixing part of the hydrogen and introducing NH₃A synthesis device for preparing ammonia gas;

s102: introducing H into the rest of the hydrogen and the sulfur source₂S preparation device for preparing H₂S, the H₂Introducing SO into the sulfuric acid prepared by the S and Bunsen reaction device₂Preparation apparatus to obtain SO₂And water, said SO₂And introducing iodine prepared by the water and HI decomposition device into the Bunsen reaction device to prepare sulfuric acid and HI, dividing the sulfuric acid into two parts, wherein the first part of sulfuric acid is taken as a product to be output, and the second part of sulfuric acid is introduced into the SO₂Preparing a device; introducing HI into the HI decomposition device to prepare hydrogen and HI, dividing the hydrogen into two parts, introducing the first part of hydrogen as a raw material into the NH₃A synthesis device, a second part of raw materials is introduced into the H₂S, preparing a device; and introducing the iodine into the Bunsen reaction device.

As a specific embodiment of the present invention, in the step S101, the sulfur source is at least one selected from the group consisting of iron disulfide, ferrous sulfide, ferric trisulfide, and sulfur.

By introducing iron disulfide, ferrous sulfide or ferric trisulfide or sulfur and by-producing a part of sulfuric acid, the traditional process for preparing sulfuric acid by oxidizing iron disulfide, ferrous sulfide, ferric trisulfide or sulfur is changed; when the iron disulfide, the ferrous sulfide or the ferric trisulfide are used as a sulfur source, hydrogen sulfide is generated through hydrogen reduction, and iron can be generated as a byproduct, so that the problems of low iron content and harmful element sulfur content when the iron disulfide, the ferrous sulfide or the ferric trisulfide is used for iron making are solved. Therefore, the process method of the system can produce hydrogen with low energy consumption, simultaneously can produce sulfuric acid and iron as by-products, realizes the semi-open type cycle hydrogen production process of iodine and sulfur, improves the energy utilization efficiency of the system, and reasonably and fully utilizes resources.

As a specific embodiment of the present invention, in the step S102, the molar ratio of the hydrogen sulfide to the sulfuric acid is 1: (2.8-3.2), for example, 1: 2.8,1: 3,1: 3.2 and any combination thereof; preferably 1: 3.

In step S102, the first portion of sulfuric acid accounts for 1/5 to 1/3 of the total volume of sulfuric acid, for example, 1/5, 1/4, 1/3 and any combination thereof, preferably 1/4.

In step S102, the first portion of hydrogen gas accounts for 5/8 to 7/8 of the total volume of hydrogen gas, such as 5/8, 2/3, 7/8 and any combination thereof, preferably 2/3.

As a specific embodiment of the invention, the CO for hydrogen production based on iodine-sulfur semi-open cycle₂The hydrogen production energy utilization rate of the zero-emission ammonia synthesis method is not lower than 50%, preferably not lower than 55%.

In a third aspect, the invention provides CO based on iodine-sulfur semi-open cycle hydrogen production₂Zero emission ammonia synthesis system and/or the CO for hydrogen production based on iodine-sulfur semi-open cycle₂The zero-emission ammonia synthesis method is applied to the field of hydrogen production.

The process flow of the invention is as follows:

air enters an air separation device to prepare nitrogen and oxygen, the nitrogen is mixed with hydrogen prepared from an HI decomposition device to form hydrogen-nitrogen reaction gas, the hydrogen-nitrogen ratio is adjusted to be 3:1, and the hydrogen-nitrogen reaction gas enters NH₃The synthesis device prepares ammonia which can be used as a product and also can be used as a raw material for producing other chemicals such as urea, sodium carbonate and the like.

The iron disulfide, ferrous sulfide, iron trisulfide or sulfur and hydrogen produced by HI decomposition device enter H₂S, a preparation device, which performs the following reduction reaction according to different raw materials: FeS₂+2H₂＝Fe+2H₂S，FeS+H₂＝Fe+H₂S，Fe₂S₃+3H₂＝2Fe+3H₂S，S+H₂＝H₂S; if it is iron disulfide, ferrous sulfide or ferric sulfideThe iron disulfide is used as a raw material and is reduced into iron 2, and simultaneously, the sulfur element in the iron disulfide, ferrous sulfide or ferric trisulfide or sulfur is converted into hydrogen sulfide; hydrogen sulfide and sulfuric acid generated from the Bunsen reaction device enter SO₂A manufacturing apparatus, in which the following redox reaction occurs: 3H₂SO₄+H₂S＝4SO₂+4H₂And O, sulfuric acid and hydrogen sulfide react according to a molar ratio of 3:1, the sulfuric acid is reduced into sulfur dioxide, the hydrogen sulfide is oxidized into sulfur dioxide, sulfur dioxide and water are generated, and the sulfur dioxide and the water, the iodine from the HI decomposition device and water supplemented from the outside enter the Bunsen reaction device together to perform the following redox reaction: SO (SO)₂+2H₂O+I₂＝H₂SO₄+2HI to produce sulfuric acid and hydrogen iodide, with part of the sulfuric acid produced as product and the other part entering SO₂Preparing a device as a reactant; hydrogen iodide enters an HI decomposition device, and the following thermal decomposition reaction is carried out at about 400 ℃: 2HI ═ I₂+H₂Hydrogen and iodine are generated, a part of hydrogen generated by the reaction is used as a raw material to be mixed with nitrogen to adjust the hydrogen-nitrogen ratio, and the other part of hydrogen enters H₂And the S preparation device is used as a reactant, and the iodine is returned to the Bunsen reaction device for cyclic utilization.

The invention has the following beneficial effects:

1) according to the invention, the nitrogen generated by the air separation device and the hydrogen generated by the iodine-sulfur semi-open cycle are directly mixed in proportion to prepare the ammonia gas, so that the traditional synthetic ammonia production process taking fossil energy such as coal and the like as main raw materials is thoroughly changed, the processes such as coal gasification, water gas shift, purification and the like are omitted, the process flow is simplified, and the system investment is reduced; meanwhile, as the hydrogen comes from the HI decomposition device, CO is not generated in the whole production process₂CO for realizing the production process of synthetic ammonia₂And (4) zero emission.

2) The invention converts the process of preparing sulfur dioxide by thermal decomposition of sulfuric acid into the process of preparing sulfur dioxide by chemical reaction of sulfuric acid and hydrogen sulfide, thereby saving a high-temperature heat source required by thermal decomposition of sulfuric acid. The hydrogen is produced by iodine-sulfur semi-open cycle, the reaction condition is mild, the scenes of application in industrial practice are widened, and the hydrogen production rate is reducedEnergy consumption, improved system energy efficiency, low energy consumption and CO₂A hydrogen production system and a process method which have zero emission and can be applied in large-scale industry.

3) By introducing iron disulfide, ferrous sulfide or ferric trisulfide or sulfur and by-producing a part of sulfuric acid, the traditional process for preparing sulfuric acid by oxidizing iron disulfide, ferrous sulfide, ferric trisulfide or sulfur is changed; when the iron disulfide, the ferrous sulfide or the ferric trisulfide are used as a sulfur source, hydrogen sulfide is generated through hydrogen reduction, and iron can be generated as a byproduct, so that the problems of low iron content and harmful element sulfur content when the iron disulfide, the ferrous sulfide or the ferric trisulfide are used for iron making are solved; because trace elements such as cobalt, nickel, copper, gold, selenium and the like also exist in the components of pyrite such as pyrite and the like, when the content is higher, the trace elements can be comprehensively recovered and utilized in the process of realizing sulfur conversion, so that resources are reasonably and efficiently utilized.

4) The invention has low energy consumption and CO₂When ammonia is produced in zero discharge, sulfuric acid and iron can be produced as by-products, the semi-open type circulating chemical hydrogen production process of iodine and sulfur is realized, the comprehensive energy utilization efficiency of the system is improved, and resources are reasonably and fully utilized.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings.

FIG. 1 shows the CO produced by the iodine-sulfur semi-open cycle hydrogen production method₂A process flow diagram of a zero-emission ammonia synthesis system;

wherein: 1-air; 2-nitrogen gas; 3-oxygen; 4-nitrogen-hydrogen reaction gas; 5-ammonia; 6-a source of sulfur; 7-iron; 8-hydrogen sulfide; 9-hydrogen; 10-sulfur dioxide; 11-water; 12-sulfuric acid; 13-water; 14-sulfuric acid; 15-hydrogen iodide; 16-iodine; 17-hydrogen; 21-an air separation unit; 22-NH₃A synthesizing device; 23-H₂S, preparing a device; 24-SO₂Preparing a device; 25-a Bunsen reaction device; 26-HI decomposition device.

Detailed Description

In order that the invention may be more readily understood, the following detailed description of the invention is given, with reference to the accompanying examples and drawings, which are given by way of illustration only and are not intended to limit the scope of the invention.

As shown in figure 1, the CO for hydrogen production based on iodine-sulfur semi-open cycle of the invention₂A zero-emission ammonia synthesis system, comprising:

1) an air separation unit 21 for mixing the nitrogen gas 2 obtained by the air separation unit with the hydrogen gas 17 obtained by the HI decomposition unit and then feeding the mixture to NH₃The synthesizing device 22 is connected;

2) h for producing hydrogen sulfide₂S preparation device 23, hydrogen sulfide 8 prepared by the device passes through a pipeline and SO₂The preparation device 24 is connected;

3) SO for producing sulfur dioxide₂The preparation device 24 is used for respectively connecting the sulfur dioxide 10 and the water 11 prepared by the device with the Bunsen reaction device 25 through pipelines;

4) a Bunsen reaction apparatus 25 for producing sulfuric acid and hydrogen iodide, the apparatus producing sulfuric acid divided into two parts, one part 12 as reactant passing through the pipeline and SO₂The preparation device is connected, and the other part 14 is output as a product;

5) a HI decomposition unit 26 for producing hydrogen and iodine, the hydrogen produced by the unit being divided into two parts, one part 9 being fed as reactant via a conduit to H₂The S preparation device 23 is connected, and the other part 17 and the nitrogen gas 2 are used for adjusting the hydrogen-nitrogen ratio to meet the requirement of ammonia synthesis.

CO for preparing hydrogen based on iodine-sulfur semi-open cycle₂The zero-emission ammonia synthesis process method comprises the following steps:

1) air 1 enters an air separation device 21 to prepare nitrogen 2 and oxygen 3, the nitrogen 2 is mixed with hydrogen 17 from an HI decomposition device 26 to form reaction gas 4, and the reaction gas enters NH₃The synthesis device 22 obtains ammonia 5 which can be used as a product and also can be used as a raw material for producing other chemicals such as urea, sodium carbonate and the like.

2) Hydrogen 9 and a sulfur source (iron disulfide, ferrous sulfide, iron trisulfide or sulfur) 6 from the HI decomposition device 26 enter the H₂S preparation device 23, iron disulfide, ferrous sulfide or ferric trisulfide are reduced to iron 7, and meanwhile, sulfur in sulfur source 6 is converted to hydrogen sulfide 8; hydrogen sulfide 8 with hydrogen from the Bunsen reactionThe sulfuric acid 12 generated in the device 25 enters SO₂The preparation device 24, sulfuric acid and hydrogen sulfide react to generate sulfur dioxide 10 and water 11, the sulfur dioxide and water are fed into the Bunsen reaction device 25 together with iodine 16 from the HI decomposition device 26 and externally supplemented water 13 to generate sulfuric acid and hydrogen iodide 15, one part of the sulfuric acid is used as a product 14, and the other part of the sulfuric acid is fed into SO₂Preparation apparatus 24 as reactant 12; hydrogen iodide 15 is fed into HI decomposition device 26 to generate hydrogen and iodine 16, one part of the hydrogen is used as raw material 17 to be mixed with nitrogen 2, and the other part is fed into H₂The S preparation device 23 is used as a reactant 9, and the iodine 16 is returned to the Bunsen reaction device 107 for recycling.

The present invention will be described in more detail below with reference to examples and the accompanying drawings, but the present invention is not limited to the examples.

Example 1

The above method was used to calculate the overall system performance at base load for example 1 based on 30 million tons/year of methanol produced. Generally, the comprehensive energy utilization efficiency of the synthetic ammonia prepared from coal is about 50% -55%, and the coal is used as CO in the raw material production process₂The discharge amount is about 60 ten thousand tons per year, and the consumption of raw material coal is about 30 ten thousand tons per year. The system of embodiment 1 of the invention has an energy utilization efficiency of about 59%, and CO in the production process₂The discharge amount is 0, and the coal consumption is reduced by 30 ten thousand tons per year.

Table 1 example bulk performance data

Wherein, the calculation formula of the synthetic ammonia energy utilization efficiency eta is as follows:

wherein, HHV_Ammonia-the higher calorific value of ammonia, MJ/kg;

m_ammonia-mass of ammonia, kg;

q_pyrite-the calorific value of pyrite, MJ/kg;

m_pyrite-mass of pyrite, kg;

W_{air separation}Power consumption of air separation, MJ;

η_{air separation}-efficiency of air separation heat energy conversion to useful work;

∑Q_iheat directly input by the system, MJ.

It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.