POWER EFFICIENT HYDROGEN LIQUEFACTION SYSTEM AND PROCESS THEREOF USING GREEN TECHNOLOGY

FIELD OF INVENTION

The present invention relates to the process engineering of Industrial gases. More particularly, it relates to an improved low-pressure and power efficient process of hydrogen liquefaction which involves use of only hydrogen as refrigerant in a closed loop cycle with improved liquefaction process efficiency and without the need of external pre-coolant and refrigerant gas.

DEFINITIONS

ASU: The acronym relates to Air Separation Unit and the “ASU” used hereinafter in the specification refers to the unit employed to extract one or all of the main constituents of atmospheric air. It provides important feed stocks to several industries.

CAPEX: The acronym relates to Capital Expenditure and the “CAPEX” used hereinafter in the specification refers to the long term expenses incurred by a company to acquire, upgrade and maintain physical assets such as ASU, compressors, expanders, exchangers, etc.

GREEN TECHNOLOGY : It refers to avoiding environmental damage at the source through use of materials, processes or practices to eliminate or reduce the creation of carbon dioxide, other pollutants and excessive heat responsible for global warming.

Clean technology has been achieved in the present invention by optimising the number of expanders, exchangers and compressors, generating power using renewable source of energy such as solar energy, carrying out the entire process from hydrogen generation till transportation of hydrogen using sustainable technology resulting in energy conservation, thereby enhancing process efficiency and minimizing negative effects on the environment.

JT VALVE: The acronym relates to Joule-Thomson Valve and the “JT Valve” used hereinafter in the specification refers to a flow control valve which operates on the principle of Joule Thomson effect to cool down a compressed gas by throttling its flow and causing rapid expansion.

MINIMUM TEMPERATURE APPROACH: The term “Minimum Temperature Approach” used hereinafter in the specification refers to the minimum allowable difference between the temperatures of cold and hot streams across which heat transfer occurs in the heat exchanger networks (HEN). It is used for designing an energy efficient HEN and is based on Pinch analysis.

OPEX: The acronym relates to Operating Expenses and the “OPEX” used hereinafter in the specification refers to the day-to-day expenses a company incurs to keep its business operational with respect to power consumption.

SEC: The acronym relates to Specific Energy Consumption and the “SEC” used hereinafter in the specification is defined as the ratio of kWh of energy consumed to the unit weight of product produced by this energy. It is used to portray how much energy is used for liquefying a unit of hydrogen gas.

BACKGROUND OF THE INVENTION

A future economy is awaiting in which the primary form of stored energy will be in the form of hydrogen which will replace all the fossil fuels. A hydrogen economy is proposed to solve some of the issues related to negative effects of using hydrocarbon fuels such as rise in carbon footprint. Since 1970, the interest in finding alternatives to fossil fuel have emerged and the efforts have been taken in that direction particularly towards use of hydrogen gas in the form of fuel.

Hydrogen fuel unlike other combustion fuels produces only water as a byproduct. The study by the World Energy Council (WEC) has reported that combusting one kilo of hydrogen released three times more energy than a kilo of gasoline and only water as a byproduct. Hydrogen fuel that converts the chemical energy of hydrogen and oxygen into electricity also produces water as the only waste product.

Whereas in the current hydrocarbon economy, transportation is fueled primarily by petroleum and burning of hydrocarbon fuels emits carbon dioxide and other pollutants. Tire supply of economically usable hydrocarbon resources in the world is limited and the demand for hydrocarbon fuels is increasing, particularly in China, India and other developing countries. By moving to a hydrogen economy, these developing countries particularly India can not only reduce imports of oil, coal and natural gas, but will also be able to export hydrogen to other countries in Europe and Asia. According to reports, India has the potential to produce 210 Mtpa (598 Mtoe) of hydrogen from solar and wind energy and can meet 32% of Asia-Pacific’s (APAC's) hydrogen demand in future due to the prevailing geographical features. While green hydrogen was expensive in 2020, within next decade cost-competitiveness will be achieved by technology improvement and policy support. Green hydrogen has a key role to play in India's energy transition.

Currently, India spends over Rs 12 lakh crore on importing energy. The government aims to make India an energy-independent country before 100 years of independence is completed. The Prime Minister of India, Shri Narendra Modi on August 15, 2021, launched the National Hydrogen Mission on India’s 75th Independence Day. The Mission aims to aid the government in meeting its climate targets and making India a green hydrogen hub.

Transportation and storage of hydrogen are critical to its large-scale adoption and hence, hydrogen is most commonly transported and delivered as a liquid when high-volume transport is needed in the absence of pipelines. The liquefaction and storage processes must, however, be both safe and efficient for liquid hydrogen to be viable as an energy carrier. Identifying the most promising liquefaction processes and associated transport and storage technologies is therefore crucial. Gaseous hydrogen is liquefied by cooling it to below' -253°C (20°K). The Ideal liquefaction work required to turn hydrogen gas into liquid (energy) is thermodynamically determined by the state quantity at the start and the end of the liquefaction process. Assuming a start point of atmospheric pressure and 600 K and an end point of saturated liquid hydrogen at atmospheric pressure, the ideal liquefaction work is approximately 3.90 kWh/kg (0.35 kWh/Nm ³ ). The conventionally available liquefaction methods require substantially higher energies typically in the range 9-13 kWli/kg liquid hydrogen for Claude and Brayton cycles, depending on the equipment efficiencies, cooling cycle and size of tire liquefaction operation. There is no such process available with the optimum equipment efficiencies and power consumption approaching the value of 3.90 kWh/kg.

Currently available hydrogen liquefaction plants operate with a relatively modest thermody namic energy efficiency of 30 to 35%. lire cost of the hydrogen liquefaction process needs to be lowered down by improving the thermodynamic energy efficiency and reducing the total work input of the compression system. Additionally, costs can be significantly lowered by reducing the electrical power requirements by the liquefaction plant.

There is a need of a hydrogen liquefaction system and process involving optimal CAPEX and OPEX which consumes overall less pow er or SEC.

The present invention speaks about the system for liquefaction of hydrogen using GREEN TECHNOLOGY which consumes less overall power required for hydrogen liquefaction. Additionally, the invention also offers a process for liquefaction of hydrogen which is capable of functioning on power generated using renewable sources of energy such as solar energy and without use of refrigerants such as liquid natural gas, liquid nitrogen, nitrogen, neon thereby reducing the carbon footprint. Tire use of gases such as Helium or mix refrigerants leads to emission of the greenhouse gases. The components such as compressors which radiate heat in the atmosphere are used at their minimal count to prevent releasing heat in the atmosphere. Since the number of components used is optimized, OPEX is reduced. Additionally, there is no need of continuous supply of cooling gases since the process involves circulation of refrigerant gas in closed loop cycle, thus saving the CAPEX.

OBJECTS OF THE INVENTION

The primary object of the present invention is to provide a power efficient system and process for liquefaction of Industrial gases such as hydrogen with GREEN TECHNOLOGY.

Another object of the present invention is to provide a system and process for liquefaction of GREEN hydrogen gas generated using processes like electrolysis which is carried out using electrical energy generated from renewable sources.

Yet another object of the present invention is to provide a power efficient system and process for liquefaction of hydrogen gas with the help of refrigerant hydrogen gas circulated in a close loop cycle at right mass, pressure and temperature value.

Another object of the present invention is to provide a system and process for liquefaction of hydrogen gas and GREEN transportation of the same. The liquefied hydrogen gas is transported using means which are operated using hydrogen gas as fuel instead of fossil fuel. Yet another object of the present invention is to provide a power efficient process for liquefaction of hydrogen gas where the mass ratio of the only refrigerant hydrogen gas used has been optimised to enable the operation of the process with a smaller number of compressors and heat exchangers which further reduces the cost of the process.

Yet another object of the present invention is to provide a power efficient process for liquefaction of feed hydrogen gas where the pressure values at which the hydrogen is circulated in a closed loop as a refrigerant are adjusted to low values, which further reduces the risk of operation of the plant.

Y et another object of the present invention is to provide a power efficient hydrogen liquefaction process with reduced overall work in single multistep process by using only hydrogen refrigerant in closed loop.

Another object of the present invention is to provide a power efficient hydrogen liquefaction system with reduced number of liquefaction components such as compressors and heat exchangers which effectively reduces the CAPEX and OPEX.

Another object of the present invention is to provide a system and process for liquefaction of hydrogen gas which works at less operating power and thus results into 32% reduction in SEC.

Further object of the present invention is to provide a power efficient process for liquefaction of hydrogen gas with improved process efficiency.

Another object of the present invention is to provide a power efficient process for liquefaction of hydrogen gas which is simplified in terms of refrigerant gas and its management.

Y et another object of the present invention is to provide a power efficient hydrogen liquefaction process without the need of continuous supply of external pre-coolant and refrigerant gas.

Yet another object of the present invention is to provide a power efficient process for liquefaction of hydrogen gas with better energy mapping.

The overall object of the present invention is to provide a power efficient hydrogen liquefaction process with GREEN TECHNOLOGY having improved efficiency, optimal power consumption with less OPEX and CAPEX due to the use of only hydrogen gas as refrigerant in closed loop cycle. The proposed invention works on GREEN TECHNOLOGY from start to end i.e. from generation of feed gas to be liquefied to the GREEN transportation of the liquefied hydrogen gas thus reducing carbon footprint.

SUMMARY OF THE INVENTION

This section is provided to introduce certain objects and aspects of the present disclosure in a simplified form that are further described below in the detailed description. This summary is not intended to identify the key features or the scope of the claimed subject matter.

Embodiments of the present disclosure may relate to a power efficient hydrogen liquefaction system using Green Technology comprised of a feed gas circulation unit and a refrigerant gas circulation unit, both of which are communicatively connected to plurality of liquefaction components including a JT valve, a separator, a storage tank and plurality of compressors, coolers, expanders and heat exchangers. The expanders, exchangers, JT valve and separator operate in a thermally and adiabatically insulated atmosphere and are placed in a canister.

The feed gas circulation unit is comprised of plurality of interlinked feed gas circulation passages which include a feed gas inlet passage, a recycled compressed gas passage, a combined feed gas passage and a compressed feed gas passage which is split into first feed gas passage and second feed gas passage. These two passages enable the splitting of feed gas stream into pre-defined split ratio. The first feed gas passage progresses as a pre-cooled first feed gas passage, a refrigerant first feed gas passage and an outlet passage A whereas the second feed gas passage progresses as a pre-cooled second feed gas passage, a cryo-cooled second feed gas passage, a liquefied feed gas passage and a liquid- vapour mixture passage which separates as a vapour hydrogen passage and a liquefied hydrogen product passage. The vapour hydrogen passage further continues as a cryo-coolant vapour hydrogen passage A, a recycled vapour hydrogen passage and a combined recycled gas passage. The outlet passage A and recycled vapour hydrogen passage fitted with non-retum valves are communicatively connected to combined recycled gas passage.

The refrigerant gas circulation unit forms a closed loop cycle and comprises plurality of refrigerant gas passages which include a refrigerant gas passage progressing as a compressed refrigerant passage which splits into three passages namely first split passage, second split passage and third split passage. These three passages split the refrigerant gas stream into three split streams in a pre-defined ratio. Plurality of flow control valves are used to control pressure and keep a check on the split ratio. The first split passage is progressing into a refrigerant passage A and an outlet passage B, the second split passage continues as a pre-cooled outlet passage A, a cryo-coolant passage B, a refrigerant passage B and an outlet passage C whereas the third split passage progresses as a pre-cooled outlet passage B, a refrigerant passage C, a cryo-coolant passage C and an outlet passage D. Plurality of non-retum valves are fitted at the outlet passage B, the outlet passage C and the outlet passage D to prevent the backflow of the gas. The outlet passage B, outlet passage C and outlet passage D are communicatively connected to the refrigerant gas passage and form a closed loop.

The compressors increase the temperature of the gas stream flowing through it and hence to bring down the temperature of the said gas stream, a water cooler is placed immediately after every compressor in the entire liquefaction system. Accordingly, the plurality of compressors including booster compressor, refrigerant compressor and recycle compressors are followed by respective water coolers.

The plurality of expanders include an expander A which is communicatively connected to the pre-cooled first feed gas passage on one end and the refrigerant first feed gas passage on another end, an expander B communicatively connected to the first split passage on one side and the refrigerant passage A on other side, an expander C which is communicatively connected to the pre-cooled outlet passage A on one end and the cryo-coolant passage B on another end and an expander D is communicatively connected to the pre-cooled outlet passage B on one end and the refrigerant passage C on another end.

The plurality of heat exchangers is comprised of exchanger A, exchanger B, exchanger C and exchanger D. The exchanger B and exchanger D are additionally provided with a catalyst to ensure complete conversion of o-hydrogen to p-hydrogen. The JT valve is communicatively connected to the liquefied feed gas passage at one end and the liquid- vapour mixture passage at another end. The liquid vapour mixture passage then runs into the separator which is communicatively connected to vapour hydrogen passage and the liquefied hydrogen product passage. The storage tank is communicatively connected to an outlet of the liquefied hydrogen product passage.

Embodiments of the present disclosure may relate to a hydrogen liquefaction process with improved efficiency and with only hydrogen refrigerant in a closed loop cycle without the need of continuous supply of external pre-coolant and refrigerant gas. Embodiments of the present disclosure may encompass power efficient process of hydrogen liquefaction which operates at pre-defined value of SEC of 7.3 kWh/kg of liquefied hydrogen gas by using plurality of heat exchangers working on principle of minimum temperature approach. The feed gas inlet stream flowing through said feed gas inlet passage comprising hydrogen and having an initial temperature of 303 - 313K and a pressure of 15 - 20 bar is combined with a recycled compressed gas stream flowing through recycled compressed gas passage to yield a combined feed gas stream in combined feed gas passage. This combined feed gas stream is compressed in booster compressor to a pre-defined pressure between 25-30 bar and it is then cooled in cooler A to its initial temperature to yield a compressed feed gas stream in the compressed feed gas passage. The obtained compressed feed gas stream is transmitted to heat exchanger A, where it splits to yield two streams namely first feed gas stream flowing through first feed gas passage and second feed gas stream which flows through second feed gas passage in a pre-defined split ratio of 0.12 : 0.88.

The first feed gas stream exchanges heat and pre-cools to a temperature between 135-148K in heat exchanger A against plurality of refrigerant streams from closed loop cycle and yields a pre-cooled first feed gas stream flowing through pre-cooled first feed gas passage. This stream expands in expander A to a pressure 1.113 bar followed by its cooling and yields a refrigerant first feed gas stream in the refrigerant first feed gas passage having a temperature of 65 K. The refrigerant first feed gas stream re-circulates in the heat exchanger A and yields an outlet stream A. Then the outlet stream A flows through outlet passage A and mixes with a recycled vapour hydrogen stream flowing through recycled vapour hydrogen passage to yield a combined recycled gas stream to flow through combined recycled gas passage. The obtained combined recycled gas stream compresses in recycle compressor followed by cooling in water cooler C to form a recycled compressed gas stream which flows through recycled compressed gas passage and having a pressure between 15 - 20 bar.

The second feed gas stream is precooled to a temperature between 77 - 83 K in heat exchanger A by plurality of refrigerant streams and yields a pre-cooled second feed gas stream flowing through pre-cooled second feed gas passage. This pre-cooled second feed gas stream is then fed to heat exchanger B where it undergoes catalytic conversion of o-hydrogen to p-hydrogen and exchanges heat by a cryo-coolant stream B through flowing cryo-coolant passage B to yield a cryo-cooled second feed gas stream having a temperature of 63K which flows in a cryocooled second feed gas passage. The cryo-cooled second feed gas stream is allowed to pass to heat exchanger D to ensure the optimum o-hydrogen to p-hydrogen catalytic conversion and gets liquefied by refrigerant streams to a liquefied feed gas stream which flows through liquefied feed gas passage having a temperature of 25K and same pressure of 30 bar. The pressure of liquefied feed gas stream is reduced in JT valve to yield a liquid-vapour mixture stream flowing through liquid -vapour mixture passage and having temperature 19 K and reduced pressure of 1.113 bar. The liquid-vapour mixture stream is separated by the separator into a vapour hydrogen stream and a liquefied hydrogen product stream. Out of which, the liquefied hydrogen product stream flows through liquefied hydrogen product passage and is collected into a storage tank, while the vapour hydrogen stream flows through vapour hydrogen passage and is re-circulated by converting to the recycled vapour hydrogen stream flowing through recycled vapour hydrogen passage having a temperature of 303 K and pressure 1.113 bar.

Closed loop cycle: A refrigerant gas stream having a mass fraction of 3-4 kg per 1 kg of feed gas is fed through the refrigerant gas passage to the refrigerant compressor where it is compressed to a pressure of 25-30 bar followed by its cooling to the initial temperature of 303- 313 K by using water cooler B and yields a compressed refrigerant stream flowing through compressed refrigerant passage. This compressed refrigerant stream then splits into three streams namely first split stream flowing through first split passage, second split stream flowing through second split passage and third split stream flowing through third split passage in a pre-defined ratio of 0.3: 0.3: 0.4.

First split stream expands in expander B and yields a refrigerant stream A which is fed through refrigerant passage A in heat exchanger A where it exchanges heat from the feed gas streams (3a and 3b) and yields an outlet stream B flowing through outlet passage B.

Second split stream is pre-cooled in heat exchanger A and gives a pre-cooled outlet stream A flowing through pre-cooled outlet passage A which is then expanded in expander C to yield a cryo-coolant stream B flowing through cryo-coolant passage B. The obtained cryo-coolant stream B is fed in the heat exchanger B where it cryo-cools the pre-cooled second feed gas stream to a temperature of 63-70 K and yields a refrigerant stream B. Then, the refrigerant stream B through refrigerant passage B is further fed in heat exchanger A where it pre-cools the splitted feed gas streams (3a and 3b) and yields an outlet stream C which flows through outlet passage C. Third split stream is pre-cooled in the heat exchanger C to a temperature in range of 63 - 70K and yields a pre-cooled outlet stream B in pre-cooled outlet passage B. The obtained stream B is then expanded in expander D to give a refrigerant stream C which flows through refrigerant passage C and acts as a refrigerant in heat exchangers C and D. The refrigerant stream C is fed in the heat exchanger D where it enables liquefaction of the cryo-cooled second feed gas stream at a temperature of 24-26 K and yields a cryo-coolant stream C. This cryo-coolant stream C is transmitted to heat exchanger C through cryo-coolant passage C where it cools third split stream and gives an outlet stream D flowing through outlet passage D.

The three outlet streams (B, C and D) obtained above mix together and yield the refrigerant gas stream, which re-circulate in the closed loop cycle.

The vapour hydrogen stream obtained above is fed in the heat exchanger D where it enables liquefaction of the cryo-cooled second feed gas stream and gets converted into a cryo-coolant vapour hydrogen stream A. The obtained cryo-coolant vapour hydrogen stream A flowing through cyro-coolant vapour hydrogen passage is then allowed to pass to heat exchanger C where it enables cryo-cooling of third split stream and yields recycled vapour hydrogen stream which then mixes with outlet stream A flowing through outlet passage A and forms the combined recycled gas stream. This combined recycled gas stream flows through combined recycled gas passage and mixes with the feed gas inlet stream and is subjected to the liquefaction process in a cyclic manner.

The hydrogen liquefaction system and process of the present invention is an advantageous one since it operates at low pressure, is power efficient with better energy mapping and with less OPEX and CAPEX.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention will best be understood from the following exemplary accompanying drawing. This drawing, which is incorporated herein, and constitutes a part of this disclosure, illustrates exemplary embodiments of the disclosed system and method with respect to sequential liquefaction of hydrogen gas.

FIG. 1 depicts a three dimensional view of power efficient hydrogen liquefaction system (600) of the present invention. FIG. 2a depicts an interior sectional view of cold insulated canister (500) showing front interpretation of exchangers (63 and 64).

FIG. 2b depicts an elaborate view of heat exchanger (61) showing split passages such as first feed gas passage (103a) and second feed gas passage (103b) of compressed feed gas passage (103).

FIG. 2c depicts an interior sectional view of cold insulated canister (500) showing front interpretation of exchangers (61 and 62).

FIG. 3 depicts a schematic illustration of power efficient hydrogen liquefaction process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, or components, but do not preclude or rule out the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof. The process steps, method steps, protocols, or the like may be described in a sequential order, such processes, methods, and protocol may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. The steps of processes described herein may be performed in any order practical. Further, some steps may be performed simultaneously, in parallel, or concurrently. The aim of this specification is to describe the invention without limiting the invention to any one embodiment or specific collection of features. A person skilled in the relevant art may realize the variations from the specific embodiments that will nonetheless fall within the scope of the invention, and such variations are deemed to be within the scope of the current invention. It may be appreciated that various other modifications and changes may be made to the embodiment described without departing from the spirit and scope of the invention. Before the present invention is described, it is to be understood that this invention is not limited to particular methodologies described, as these may vary as per the person skilled in the art. It is also to be understood that the terminology used in the description is for the purpose of describing the particular embodiments only and is not intended to limit the scope of the present invention. Throughout this specification, the word “comprises”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired obj ects or results.

This will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its essential characteristics. The present embodiments are, therefore, to be considered as merely illustrative and not restrictive, the scope of the invention being indicated by the claims rather than the foregoing description, and it will be appreciated that many variations in detail are possible without departing from the scope and spirit of the invention and all such variations therefore intended to be embraced therein.

In the following description, for the purposes of explanation, various specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent, however, that embodiments of the present disclosure may be practiced without these specific details. Several features described hereafter can each be used independently of one another or with any combination of other features. An individual feature may not address any of the problems discussed above or might address only one of the problems discussed above. Some of the problems discussed above might not be fully addressed by any of the features described herein. Example embodiments of the present disclosure are described below, as illustrated in various drawings in which like reference numerals refer to the same parts throughout the different drawings.

Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by the way of explanation of the invention and not meant as limitation of the invention, e.g. features illustrated or described as part of one embodiment to yield still third embodiment. It is intended that the present invention includes these and other modifications and variations. The hydrogen liquefaction system of the proposed invention incorporating various components such as compressors, heat exchangers, expanders and water coolers and variation in their arrangement for performing industrial liquefaction process shall not limit the scope of the invention.

Climate change is one of the greatest challenges we are facing now a days. Transportation and energy sectors are the largest contributors to pollution and greenhouse gases emissions. In response to the urgency of dealing with climate change, a number of countries have plans to switch to carbon-free energy technologies. In addition to adopting solar power and wind energy, the use of hydrogen as an alternate fuel is getting significant attention and has been implemented in some parts of the world. Using hydrogen can reduce pollution, greenhouse gases emissions and the economic dependence on fossil fuels.

The “hydrogen economy” refers to the vision of using hydrogen as a GREEN, low-carbon energy resource to meet the world’s energy needs, replacing traditional fossil fuels in various applications, and forming a substantial part of a GREEN ENERGY portfolio. Hydrogen is emerging as one of the most promising energy carriers for a decarbonised global energy system. Transportation and storage of hydrogen are critical to its large-scale adoption and to these ends, liquid hydrogen is being widely considered. The liquefaction and storage processes must, however, be both safe and efficient for liquid hydrogen to be viable as an energy carrier. Identification of the most promising liquefaction processes, associated transport and storage technologies is therefore crucial. Considering these factors, the cautious efforts of the inventors have resulted into an invention which proposes a unique system and process of hydrogen liquefaction which is power efficient with GREEN TECHNOLOGY and operating at a reduced OPEX and CAPEX. The proposed invention employs hydrogen as a feed gas produced by electrolysis where the electrical energy is generated using renewable source instead of fossil fuel. The liquefaction of feed hydrogen gas is carried out at optimum SEC values with the help of refrigerant hydrogen gas circulated in closed loop cycle. The power generated from liquefaction components such as expanders is reutilised which leads to power conservation. The liquefied hydrogen is transported by containers driven using hydrogen as a fuel, thus the entire process including generation, liquefaction and transportation of hydrogen contributes to GREEN technology.

The present invention describes a simulated power efficient system and process of hydrogen liquefaction using only hydrogen gas as a refrigerant circulated in a closed loop cycle. The software used for the purpose of simulation is Aspen HYSYS Software which is a chemical simulator used to mathematically model chemical processes.

DETAILED DESCRIPTION OF DRAWINGS

FIG. 1 depicts a three dimensional view of power efficient hydrogen liquefaction system (600) of the present invention including plurality of compressors namely booster compressor (31), refrigerant compressor (32) and recycle compressor (33) followed by plurality of respective water coolers (41, 42, 43), plurality of feed gas passages (101, 102, 103, 113b, 114) and refrigerant passages (215 and 216), a canister (500) which is thermally and adiabatically insulated encasing plurality of liquefaction components such as plurality of exchangers and expanders. The canister (500) also encases plurality of feed gas passages and refrigerant gas passages. The storage tank (91) collecting the liquefied hydrogen gas is also shown.

FIG. 2a depicts an interior sectional view of cold insulated canister (500) showing front interpretation of exchangers (63 and 64), JT valve (71), separator (81), rear interpretation of exchangers (61 and 62) and top display of plurality of expanders (51, 52, 53 and 54) interlinked with plurality of feed gas passages and refrigerant gas passages. The figure also elaborates progression of compressed feed gas passage (103) through said exchangers and expanders via plurality of gas passages. The figure shows plurality of flow control valves (421, 422 and 423) and non-retum valves (311, 312, 313, 314 and 315) fitted with appropriate refrigerant gas passages and feed gas passages.

FIG. 2b depicts an elaborate view of heat exchanger (61) where compressed feed gas passage (103) progresses through heat exchanger (61) and splits into first feed gas passage (103a) and second feed gas passage (103b) continuing as pre-cooled first feed gas passage (104) and precooled second feed gas passage (107) respectively.

FIG. 2c depicts an interior sectional view of cold insulated canister (500) showing front interpretation of exchangers (61 and 62), rear interpretation of exchangers (63 and 64) and top display of plurality of expanders (51, 52, 53 and 54) interlinked with plurality of feed gas passages and refrigerant gas passages. The JT valve (71) and separator (81) are seen sideways. The figure also elaborates progression of compressed refrigerant passage (216) through the said exchangers and expanders via plurality of gas passages. Also, plurality of flow control valves (421, 422 and 423) fitted at refrigerant gas passages (217, 220 and 225) respectively. FIG. 3 illustrates the simulated process flow diagram of a power efficient process of hydrogen liquefaction using GREEN TECHNOLOGY. The drawing elaborately explains the sequential flow of the feed gas, it’s splitting into first feed gas stream (3a) and second feed gas stream (3b) and then subsequent liquefaction of the second stream (3b) into the product stream (30) through processes such as pre-cooling, cryo cooling followed by separation of the vapour hydrogen not liquefied and collection of the liquid hydrogen (30). The vapour hydrogen stream (11) which is not liquefied is recirculated and mixed with the fresh feed gas stream (101). During the course, it passes through exchangers acting as a refrigerant.

The refrigerant hydrogen gas stream (15) is circulated in a closed loop thereby preventing the need of continuous external supply of coolant and refrigerant gases. The refrigerant gas stream (15) is split into plurality of sub streams (17, 20, 25) which are circulated in the plurality of exchangers effecting pre-cooling, cryo cooling and liquefaction of the feed hydrogen gas.

The present invention offers a system and process for power efficient liquefaction of hydrogen gas using as a refrigerant circulated in closed loop cycle with minimal SEC and at lower pressure range thereby reducing the risk of operation. The entire process is operated using GREEN TECHNOLOGY wherein the generation of hydrogen gas takes place electrolytically employing the electricity generated using renewable sources. The liquefaction takes place using hydrogen itself circulated in a closed loop and the liquefied hydrogen gas is GREEN transported using vehicles driven on hydrogen as a fuel instead of fossil fuel. The said system is innovatively fabricated to achieve a characteristic split ratio of feed gas stream and refrigerant gas stream as well. The different components of said system are as described in the table given below:

Table 1

PREFERRED EMBODIMENTS OF THE INVENTION

Embodiments of the present disclosure relates to the process engineering of the industrial gases. More specifically, it pertains to a power efficient system and process for carrying out liquefaction of hydrogen gas utilizing a closed loop refrigeration cycle thereby minimizing the power consumption by nearly 32% of SEC as compared to the available industrial benchmark contributing to GREEEN TECHNOLOGY. The research is carefully carried out by inventors using simulation techniques. An aspect of the present invention pertains to a process of liquefaction of hydrogen gas operated at optimum power as compared to the industrial benchmark at present.

One or more embodiments are now described more fully hereinafter with reference to the accompanying drawings in which example embodiments are shown. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various embodiments. However, the various embodiments can be practiced without these specific details.

According to one embodiment of the present invention refers to the power efficient system (600) for hydrogen liquefaction using GREEN Technology comprising a feed gas circulation unit (100) with plurality of interlinked feed gas circulation passages such as feed gas inlet passage (101), recycled compressed gas passage (114), combined feed gas passage (102), compressed feed gas passage (103). The compressed feed gas passage (103) is split into two passages (103a and 103b) wherein, the first feed gas passage (103a) progressively forms precooled first feed gas passage (104) followed by a refrigerant first feed gas passage (105) and an outlet passage A (106) whereas the second feed gas passage (103b) progresses through passages such as pre-cooled second feed gas passage (107), cryo-cooled second feed gas passage (108), liquefied feed gas passage (109), liquid-vapour mixture passage (110), vapour hydrogen passage (111), cryo-coolant vapour hydrogen passage A (112) continued as recycled vapour hydrogen passage (113a), combined recycled gas passage (113b) and liquefied hydrogen product passage (130) carrying the liquid hydrogen. The recycled vapour hydrogen passage (113a) and outlet passage A (106) fitted with respective non-retum valves (311 and 312) are communicatively connected to combined recycled gas passage (113b) to carry out the liquefaction process in a cyclic manner.

A refrigerant gas circulation unit (200) is comprised plurality of refrigerant gas passages and forms a closed loop cycle. The plurality of refrigerant gas passages include a refrigerant gas passage (215) progressing as a compressed refrigerant passage (216) wherein, said compressed refrigerant passage (216) splits into first split passage (217) progressing as refrigerant passage A (218) followed by an outlet passage B (219), second split passage (220) progressing sequentially as pre-cooled outlet passage A (221), cryo-coolant passage B (222), refrigerant passage B (223) and outlet passage C (224) and third split passage (225) progressing as pre- cooled outlet passage B (226), refrigerant passage C (227), cryo coolant passage C (228) and outlet passage D (229). The plurality of flow control valves (421, 422 and 423) are placed at respective split passages such as first split passage (217), second split passage (220) and third split passage (225) which enable to maintain the pre-defined split ratio of the refrigerant hydrogen gas whereas the three outlet passages such as outlet passage B (219), outlet passage D (229) and outlet passage C (224) are fitted with respective non-retum valves (313, 314 and 315) to prevent the back flow of the gas and are communicatively connected to refrigerant gas passage (215) for continued circulation of refrigerant gas in the closed loop.

Both the feed gas circulation unit (100) and refrigerant gas circulation unit (200) are communicatively connected to plurality of compressors each followed by a cooler and to plurality of liquefaction components such as a JT valve (71), a separator (81), a storage tank (91), expanders and heat exchangers. The said liquefaction components are encased in a canister (500) and are operated in thermally and adiabatically insulated environment.

The compressors increase the temperature of the gas stream flowing through it and hence to bring down the temperature of the said gas stream, a water cooler is placed immediately after every compressor in the entire liquefaction system. Accordingly, the plurality of compressors including booster compressor (31), refrigerant compressor (32) and recycle compressors (33) are followed by respective water coolers as cooler A (41), cooler B (42) and cooler C (43). The booster compressor (31) is communicatively connected to combined feed gas passage (102) at one end and a cooler A (41) at another end, the refrigerant compressor (32) is communicatively connected to refrigerant gas passage (215) at one end and to a cooler B (42) at another end whereas the recycle compressor (33) communicatively connected to an outlet of combined recycled gas passage (113b) at one end and a cooler C (43) at another end.

The plurality of expanders include an expander A (51) which is communicatively connected to the pre-cooled first feed gas passage (104) on one end and the refrigerant first feed gas passage (105) on another end, an expander B (52) communicatively connected to the first split passage (217) on one side and the refrigerant passage A (218) on other side, an expander C (53) which is communicatively connected to the pre-cooled outlet passage A (221) on one end and the cryo- coolant passage B (222) on another end and an expander D is communicatively connected to the pre-cooled outlet passage B (226) on one end and the refrigerant passage C (227) on another end.

The plurality of heat exchangers is comprised of exchanger A (61), exchanger B (62), exchanger C (63) and exchanger D (64). The exchanger B (62) and exchanger D (64) are additionally provided with a catalyst to ensure complete conversion of o-hydrogen to p- hydrogen. The JT valve (71) is communicatively connected to the liquefied feed gas passage ( 109) at one end and the liquid- vapour mixture passage ( 110) at another end. The liquid-vapour mixture passage (110) then runs into the separator (81) which is communicatively connected to vapour hydrogen passage (111) and the liquefied hydrogen product passage (130). The outlet of the liquefied hydrogen product passage (130) is further communicatively connected to storage tank (91) to collect and store the liquid hydrogen.

According to another embodiment of the present invention refers to the power efficient process for liquefying hydrogen using Green Technology, wherein said process comprising steps of:

The hydrogen liquefaction process is carried out at pre-defined value of SEC of 7.3 kWh/kg of liquefied hydrogen gas by operating plurality of exchangers, plurality of expanders, JT valve and separator in adiabatically and thermally insulated environment inside the canister (500). The plurality of exchangers operates on principle of minimum temperature approach. Renewable sources of energy such as Solar energy are used in generating power used for carrying out this process.

A feed gas inlet stream (1) comprising hydrogen at an initial temperature of 303K - 313K and a minimal pressure value of 15 - 20 bar flowing through feed gas inlet passage (101) is combined with a recycled compressed gas stream (14) flowing through recycled compressed gas passage (114) to yield a combined feed gas stream (2) which flows in combined feed gas passage (102). This combined feed gas stream (2) is compressed in a booster compressor (31) to a pre-defined pressure between 25-30 bar followed by cooling in a cooler A (41) to bring back the feed gas stream to the initial temperature of 303K - 313K in the form of a compressed feed gas stream (3).

The obtained compressed feed gas stream (3) through compressed feed gas passage (103) is transmitted to heat exchanger A (61) where it splits and yields two feed gas streams namely first feed gas stream (3a) flowing through first feed gas passage (103a) and second feed gas stream (3b) flowing through second feed gas passage (103b) in a pre-defined split ratio of 0.12:0.88. Precooling of First Feed Gas Stream (3a):

The first feed gas stream (3a) is pre-cooled to a temperature between 135-143K by exchanging heat in heat exchanger A (61) against plurality of refrigerant streams (5, 18 and 23) from closed loop cycle to yield a pre-cooled first feed gas stream (4) in pre-cooled first feed gas passage (104).

Cryo-cooling of Pre-cooled First Feed Gas Stream (4):

The pre-cooled first feed gas stream (4) is expanded in an expander A (51) followed by cooling and yields a refrigerant first feed gas stream (5) having a temperature of 65 K and pressure 1.113- 1.5 bar.

The refrigerant first feed gas stream (5) flows through refrigerant first feed gas passage (105), re-circulates in heat exchanger A (61) and gives an outlet stream A (6) in outlet passage A ( 106) . A non-retum valve (312) fitted at outlet passage A (106) which prevents the back flow of outlet stream A (6) and this stream mixes with recycled vapour hydrogen stream (13a) flowing through recycled vapour hydrogen passage (113a) to yield a combined recycled gas stream (13b) to flow through combined recycled gas passage (113b).

The combined recycled gas stream (13b) is compressed in recycle compressor (33) followed by cooling in a water cooler C (43) to form the recycled compressed gas stream (14) flowing through recycled compressed gas passage (114) and has temperature in the range of 303-313 K and a pressure between 15 - 20 bar .

Pre-cooling of Second Feed Gas Stream (3b):

The second feed gas stream (3b) is pre-cooled to a temperature between 77-83K in heat exchanger A (61) by plurality of refrigerant streams (5, 18 and 23) and gives a pre-cooled second feed gas stream (7).

Cryo-cooling of Pre-cooled Second Feed Gas Stream (7):

This pre-cooled second feed gas stream (7) flowing through pre-cooled second feed gas passage (107) is transmitted to heat exchanger B (62) where it exchanges heat with cryo-coolant stream B (22) and is cryo-cooled to yield a cryo-cooled second feed gas stream (8). In this particular step, catalytic conversion of o-hydrogen to p-hydrogen takes place.

Liquefaction of Cryo-cooled Second Feed Gas Stream (8):

The obtained cryo-cooled second feed gas stream (8) flows through cryo-cooled second feed gas passage (108) and is allowed to pass to heat exchanger D (64) where it is liquefied by vapour hydrogen stream (11) flowing through vapour hydrogen passage (111) and refrigerant stream C (27) flowing through refrigerant passage C (227) to a liquefied feed gas stream (9) flowing in liquefied feed gas passage (109) having a temperature of 25K. The liquefaction is accompanied by effective catalytic conversion of o-hydrogen to p-hydrogen. The pressure of liquefied feed gas stream (9) is reduced in JT valve (71) up to storage pressure of liquid hydrogen which causes vaporization of some liquid hydrogen and thus results in a liquid-vapour mixture stream (10) which flows through liquid-vapour mixture passage (110).

The liquid- vapour mixture stream (10) is separated by separator (81) into vapour hydrogen stream (11) and liquefied hydrogen product stream (30), both having temperature 20K.

The liquefied hydrogen product stream (30) flows through liquefied hydrogen product passage (130) and is collected into the storage tank (91), while the vapour hydrogen stream (11) flows through vapour hydrogen passage (111) re-circulates in heat exchanger C (63) and heat exchanger D (64) to act as a refrigerant and yields the recycled vapour hydrogen stream (13a) flowing through recycled vapour hydrogen passage (113a). The back flow of recycled vapour hydrogen stream (13a) is prevented via a non-retum valve (311) fitted with recycled vapour hydrogen passage (113a).

Circulating Refrigerant gas through Closed Loop Cycle:

The hydrogen refrigerant gas stream (15) flowing through refrigerant gas passage (215) having a mass fraction of 3-4 kg per 1 kg of feed gas is fed and compressed in refrigerant compressor (32) to a pressure between 25-30 bar.

It is then cooled to the initial temperature in the range of 303-313 K by using a water cooler B (42) and yields a compressed refrigerant stream (16) flowing through compressed refrigerant passage (216).

This cooled and compressed refrigerant stream (16) splits at controlled pressure via plurality of flow control valves (421, 422, 423) into three streams namely first split stream (17) flowing through first split passage (217), second split stream (20) flowing through second split passage (220) and third split stream (25) flowing through third split passage (225) in a pre -calculated split ratio of 0.3:0.3:04.

Cooling of First split stream (17):

The first split stream (17) is expanded and cooled in expander B (52) and yields a refrigerant stream A (18) to flow in refrigerant passage A (218).

The obtained refrigerant stream A ( 18) is transmitted to heat exchanger A (61 ) to carry out heat exchange from split feed gas streams (3a and 3b) and gives an outlet stream B (19) which flows through outlet passage B (219). The back flow of outlet stream B (19) flowing through the outlet passage B (119) is prevented via a non-retum valve (313).

Pre-cooling of Second split stream (20):

The second split stream (20) is pre-cooled in heat exchanger A (61) to a temperature in the range of 130 - 132K and yields a pre-cooled outlet stream A (21) flowing through pre-cooled outlet passage A (221).

Cryo-cooling of Pre-cooled Outlet Stream A (21):

The pre-cooled outlet stream A (21) is then expanded in expander C (53) to yield a cryo-coolant stream B (22) to flow in cryo-coolant passage B (222).

This cryo-coolant stream B (22) is fed in the heat exchanger B (62) where it cryo-cools the pre- cooled second feed gas stream (7) to a temperature of 63-70 K and forms a refrigerant stream B (23).

The refrigerant stream B (23) is further fed in heat exchanger A (61) through refrigerant passage B (223) where it pre-cools the split feed gas streams (3a and 3b) and converts to an outlet stream C (24) which flows through outlet passage C (224). A non-retum valve (315) fitted at outlet passage C (224) prevents the back flow of outlet stream C (24).

Pre-cooling of Third split stream (25):

The third split stream (25) is pre-cooled in heat exchanger C (63) to a temperature in range of 63-70 K and yields a pre-cooled outlet stream B (26).

The pre-cooled outlet stream B (26) flows through pre-cooled outlet passage B (226), expands in expander D (54) and gives a refrigerant stream C (27) flowing through refrigerant passage C (227) which acts as a refrigerant stream in heat exchanger C (63) and heat exchanger D (64).

The refrigerant stream C (27) is fed in heat exchanger D (64) where it enables liquefaction of the cryo-cooled second feed gas stream (8) up to a temperature of 24-26 K and yields a cryo- coolant stream C (28).

This cryo-coolant stream C (28) is fed in the heat exchanger C (53) through cryo-coolant passage C (228), cools the third split stream (25) and yields an outlet stream D (29) which flows through outlet passage D (229). The back flow of outlet stream D (29) is prevented via non-retum valve (314) fitted at outlet passage D (229). The above obtained three outlet streams namely: outlet stream B (19) flowing through outlet passage B (219), outlet stream C (24) flowing through outlet passage C (224) and outlet stream D (29) flowing through outlet passage D (229) mix together and yield the refrigerant gas stream (15) which flows through refrigerant gas passage (215), re-circulates in the closed loop cycle thereby eliminating the need of external ASU and reduces required number of compressors thereby contributing to GREEN TECHNOLOGY.

Recirculating vapour hydrogen stream (11):

The vapour hydrogen stream (11) is fed in the heat exchanger D (64) through vapour hydrogen passage (111) to enable liquefaction of the cryo-cooled second feed gas stream (8) to yield a cryo-coolant stream A (12).

The cryo-coolant stream A (12) flows through cryo-coolant passage A (112) and is then fed in heat exchanger C (63) where it enables cryo-cooling of the third split stream (25) to yield the recycled vapour hydrogen stream (13a) flowing through recycled vapour hydrogen passage (113a) to continue the process of liquefaction of hydrogen gas.

The obtained recycled vapour hydrogen stream (13a) mixes with outlet stream A (6) to form the combined recycled gas stream (13b) which further combines with the feed gas inlet stream (1) and is subjected to the liquefaction process in a cyclic manner.

ADVANTAGES OF PRESENT INVENTION

The present invention provides a power efficient hydrogen liquefaction process with improved process efficiency and GREEN TECHNOLOGY.

The present invention describes the process for liquefaction of hydrogen to enable the large- scale transport and storage of hydrogen gas.

The present invention describes the process for liquefaction of hydrogen gas wherein, the entire process from hydrogen generation till transportation of hydrogen is carried out using sustainable technology which results in energy conservation, thereby contributes towards GREEN TECHNOLOGY.

The present invention provides a power efficient hydrogen liquefaction process with a closed loop system using hydrogen as the only refrigerant with optimised mass, pressure and temperature values. In the present invention due to closed loop system and use of hydrogen as a refrigerant, there is no need of continuous supply of external pre-coolant and refrigerant gas.

In the present invention, the process of liquefaction of hydrogen gas occurs in a closed loop system which delineates the requirement of installation of ASU. Hence, it is helpful in reducing CAPEX.

In the proposed invention, the liquefaction of hydrogen feed stream is carried out by only hydrogen refrigerant stream of optimized mass. Therefore, requirement of compressor and heat exchanger count is less that demands less operating power which ultimately reduces OPEX.

The present invention offers a carefully planned process which operates with less numbers of compressors thereby minimizing the heat generated and released to the atmosphere and thus contributes to GREEN TECHNOLOGY.

The power efficient hydrogen liquefaction process of present invention operates on a renewable source of energy such as solar energy which is easily accessible, affordable and don’t run out as compared to fossil fuels and hence contributes to the GREEN TECHNOLOGY.

The present invention proposes a process for liquefaction of hydrogen gas which operates with 32% less power with respect to present industrial benchmark of 9-13 kWh/kg.

The entire process of the present invention operates at low pressure such as 15-20 bar which further reduces the risk of operation of the plant.

INVENTIVE CONCEPT

The process for liquefaction of hydrogen gas as devised in the proposed invention utilizes hydrogen gas itself as only refrigerant in a closed loop at predefined mass, pressure and temperature for better energy mapping.

The process of hydrogen liquefaction operates on following parameters: a. The refrigerant hydrogen gas with a pre-calculated mass fraction of 3-4 kg per 1kg of feed gas is utilized to effectively convert the feed gas into liquid. b. The refrigerant feed gas is split into three streams with a split ratio of 0.3:0.3:0.4 per unit of total refrigerant gas stream. c. The feed gas stream splits into two partial streams in a split ratio 0.12:0.88 per unit of feed hydrogen gas stream. d. The overall liquefaction process operates at 7.3 kWh/kg of liquefied hydrogen gas which is 32% less as compared to the industrial benchmark of 9-13kWh/kg of feed gas. e. The power generated from liquefaction components such as expanders is reutilised which leads to power conservation.

The hydrogen liquefaction process of the present invention operates with reduced overall work in single multistep process by using only hydrogen refrigerant in closed loop.

The proposed invention offers compactness of the system due to reduced number of compressor and heat exchangers. This is due to the employment of only hydrogen spirited from the feed gas itself as a refrigerant stream for the liquefaction of hydrogen feed stream.

In proposed invention, hydrogen feed gas stream is liquefied by using only hydrogen refrigerant in a closed loop cycle at low to medium pressure in the range of 15 - 20 bar with high energy efficiency in view of present technical machinery advancement.