 In the previous class we have seen compressed hydrogen tanks, depending upon what material they are made up of they were divided into type 1, type 2, type 3 and type 4 tanks. Type 1 were all metallic, type 2 with an inner metallic liner and hoop ramped with fiber resin composite, type 3 where there is metallic liner and a fully ramped fiber resin composite and the type 4 tank which had an inner polymer liner with an outside fiber, carbon fiber composite. So, this is what we have seen in the previous class. In a type 4 tank this is an inner liner which provides the gas tightness as well as reduces the permeability. Then there is a carbon fiber composite, there is a carbon fiber wrapping and there after a resin. Now this composite provides strength to the tank against the environmental challenges. Now this tank other than the carbon fiber and liner, there are other components like a port which is having a bosh here, a port which has a valve and then there are several other accessories which are there in with the tank, this is like the in tank regulator. Then there are pressure sensors to measure the pressure, then there is interfacing with the refuelling station for filling in at the same time for dispensing, for releasing the hydrogen for the utilization purpose. Then there are thermally activated pressure relief devices, so refuelling port, vent line port. So, all these accessories are there other than the remaining accessories outside the tank which are like the tubings, other walls, flow regulators, so all these are the components of the type 4 tank. So, with today we will look at the liquefied hydrogen storage. Now by liquefied hydrogen storage it means like the temperatures are in the cryogenic range. Now the cryogenic term itself was coined from a Greek term and that means ice cold. Now here the temperatures are below minus 150 degrees centigrade and the gas in the process the gas at ambient conditions is cooled down to temperatures which are cryogenic temperature and at ambient pressure. Now if we look briefly onto the history of liquefaction it started way back in 1812 when Michael Faraday he carried out certain small scale experiments in a test tube to experiment with the different gases to liquefy them and he was successfully able to liquefy ammonia and carbon dioxide. In 1840 Gauri he was able to produce ice by means of air expansion engine. In 1844 there were experiments being carried out on large scale for liquefying gases and that was by Trilorin and he used mechanical compressor for this purpose. In 1845 with the use of hydraulic pump large quantities of liquid and solid carbon dioxide was produced. Now the major landmark in the history of liquefaction was the invention of Joule-Thompson effect that was in 1852. Thereafter Kirk he came up with a sterling cooling system in 1860. 1863 was another landmark when critical temperature was introduced at that time. Thereafter 1877 Pictet and Calitat they individually were able to produce mist of liquid oxygen. This was not completely liquefied which was later on completely liquefied in 1883 by Robelski and Olszwecki and they liquefied oxygen and nitrogen. So Robelski he liquefied and Olszwecki he confirmed that liquefaction by the process which was given by him. In 1884 Robelski he created mist of hydrogen and again he confirmed it was another landmark that was in 1892 when Dewar he developed the vacuum insulated vessels for storing cryogenic liquid and thereafter came the term 1894 the cryogenic term was coined. In 1895 Linde he patented the air liquefaction using expansion wall and then he started producing the various gases at industrial scale. He also established the well-known company for liquefaction Linde in 1895 started the recuperative heat exchangers and that was first time introduced by Hampson. In 1898 Sir James Dewar he liquefied hydrogen and that was in a very small capacity liquefaction device. In 1902 Claude he developed a system which was for air liquefaction and that used expanders and he also established a company which is now also known as air liquidy. In 1908 Owens he first time liquefied helium in 1910 onwards there were large sized liquefiers which were constructed and thereafter large capacity applications where applications where large capacity of liquid hydrogen and oxygen is used were developed after 1930. So, we can say that in the period 1850 to 1900 the thermodynamics of liquefaction was developed while in the period 1900 to 1950 the various technologies for liquefactions were developed and thereafter started the large scale production of these liquefied gases. So, this is how the cryogenics liquefaction of various gases have advanced in past. Now coming back to liquefaction of hydrogen in liquefying hydrogen there are several challenges involved. The first and foremost is we know that and we have also seen thermodynamics of hydrogen liquefaction in earlier classes that the liquefaction of hydrogen can be done by reducing its temperature to 20 k minus 253 degree centigrade and this is a very low temperature for liquefaction requires a lot of energy. The another challenge is ortho to para conversion and this conversion has to be has to be occur and at the same time this conversion is exothermic. So, we have to also remove the heat of conversion from the process of liquefaction and the third major challenge that lies is that the inversion temperature of hydrogen is below ambient temperature. This we have earlier seen when we have studied the thermodynamics of expansion the Joule-Thompson effect what is the Joule-Thompson coefficient when it is positive then if it is positive in that case with the reduction of pressure temperature also reduces that means with expansion cooling is observed if it is negative reverse of it happens that means if the expansion occurs or pressure reduction then temperature will increase Joule-Thompson coefficient which is negative at ambient temperature and in order to cool it down we have to cool down below the inversion temperature so as to use the throttling process. So, these are the three major challenges which are observed in hydrogen liquefaction. Now, if we look these challenges one by one the major challenge is the ortho-to-para conversion. Now, this was in 1912 that while measuring the heat capacity of hydrogen it was observed that the warming and the cooling curve they have shown a hysteresis and that hysteresis it was proposed in 1927 that it was arising because of the two different spin isomers of hydrogen and this presence of these two spin isomers was experimentally proven in 1929. Now, what this conversion is what these spins are so if the two spins the nuclear spins proton spins are parallel then it is ortho-hydrogen if however the two spins are anti-parallel then it is para-hydrogen. Now, there is a difference in the calorimetric properties of ortho-hydrogen and para-hydrogen at the same time the energy levels of these two isomers are also different. So, ortho-hydrogen is an excited state it is in a higher energy state compared to the para-hydrogen. So, when we are liquefying hydrogen this conversion which occurs ortho-to-para-hydrogen that extra amount of energy is released in the process. Just to explain in more detail the normal hydrogen which is under ambient condition at the ambient normal temperature pressure condition it consists of 75 percent of normal hydrogen consists of 75 percent of ortho-hydrogen and 25 percent of para-hydrogen. However, during liquefaction at the boiling temperature at the boiling point of 20 k the equilibrium composition of hydrogen is 99.8 percent of para-hydrogen and the remaining is ortho-hydrogen and that is the equilibrium composition at its boiling point. That means if we are reducing the temperature of hydrogen in that case the ortho-hydrogen which was 75 percent under normal condition has to convert in such a way that we get 99.8 percent of para-hydrogen from the normal hydrogen that is the equilibrium hydrogen. Now, in this conversion process since ortho-hydrogen is its in higher energy state so the excess energy is released thus the process is exothermic process. So, this release or this conversion of ortho-to-para-hydrogen this is an exothermic process and that heat which is released that needs to be removed during the liquefaction process. Now, if we see the concentration of para-hydrogen with temperature we can see that it has a very strong dependence on temperature. However, it has negligible dependence on pressure. So, there is a strong dependence on temperature specifically we can see in this region but no pressure dependence. Now, when we want complete conversion of hydrogen from the ortho-to-para so from complete ortho-to-complete para-conversion that releases heat that releases energy approximately 703 kilo joule per kg. However, normal hydrogen which is 75 percent ortho 25 percent para when converts it into equilibrium hydrogen then the amount of heat which is released is 527 kilo joule per kg. Now, we can see that these both these energy is higher than the latent heat of vaporization for hydrogen which is 446 kilo joule per kg. Now, that means when we are converting when we are liquefying when we are reducing the temperature of hydrogen this amount of heat which is released in this ortho-to-para conversion is sufficient enough to evaporate certain amount of liquid hydrogen as well. So, because this latent heat of vaporization is less compared to the heat released during this process. Now, this process wherein the stored liquid which contains ortho hydrogen and with the reduction of temperature when it converts to para-hydrogen causes evaporation of hydrogen this process is known as boil-off and what is required is that this boil-off should be as low as possible. So, we need to minimize this evaporation in the storage tank and thus we need to minimize this ortho-para conversion which is very important when we are considering long term storage. The reason being if at normal temperature pressure hydrogen if it is very fastly cooled in that case the hydrogen may convert or may liquefy but then in that case the concentration will be again same as the normal hydrogen and when it is being stored at that temperature 20 Kelvin then slowly this ortho-to-para conversion will occur will release heat and the liquid hydrogen will start to evaporate and that will be resulting into boil-off loss. Also we need to understand that ortho-to-para conversion this process is a very slow process this is a second order reaction which takes place very slowly and it can take about several days or a week time to convert without catalyst from ortho-to-para. Now if we want to increase the rate of this conversion we have to use a catalyst in the presence of catalyst depending upon what catalyst what is the temperature what is the pressure this conversion is a first order reaction. However at the liquid hydrogen temperature at 20 Kelvin this conversion is a 0th order reaction and takes place very fast. So once we have cooled down the system to liquid hydrogen temperature in that case this ortho-to-para conversion takes place very fast and is an exothermic reaction leading to boil-off and that is not required when we are storing hydrogen for long term because that will result into evaporation of hydrogen and then we will have to release that hydrogen which is evaporated. So liquefaction process have ortho-to-para conversion and most of the cycles liquefaction cycles they have this ortho-to-para conversion systems and that reduces the boil-off. Another important characteristic that we need to consider in liquefaction of hydrogen is throttling. Now throttling we have studied in more detail what is the Joule-Thompson effect what is the Joule-Thompson coefficient when is it positive and it is negative. Now important when we are liquefying hydrogen is the throttling which is common to most of the cycle and this is created after we create a sort of non-ideality and this non-ideality condition is carried out by other increasing the pressure by compressing or lowering down the temperature that is pre-cooling or it can be done using both. Now the problem with gas like hydrogen is its inversion temperature is below ambient and if we want to get the maximum cooling effect we have to cool it down below the maximum inversion temperature so that we can get a maximum cooling benefit. As such because of this inversion temperature being below ambient pre-cooling of the gas becomes essential so that it can be cooled down before throttling below its inversion temperature and then only we will be able to get a cooling effect on expansion. So pre-cooling becomes essential because of the negative inversion temperature of hydrogen above the ambient temperature. If we look at the hydrogen liquefaction process then before 1895 the process which was considered was compression followed by chilling reduction in the temperature and finally an expansion by means of throttling. So prior to 1895 this was the process flow that was followed here in the working media used to be hydrogen and the saturated vapor was not returned as a coolant after the throttling. So after the throttling process that we will see in the subsequent slides that after the throttling a certain amount of liquid will be obtained however vapor will be at a lower temperature. So that vapor which was formed after throttling that was not returned back as a coolant into the stream. But after 1895 the recuperative cooling was employed and here the liquefaction fluid that was itself acting as a coolant. Now if we look at the process thermodynamics we have also studied earlier that thermodynamic effect which is used for expanding is that we had do a adiabatic expansion. So if we look at the complete process it should be an isothermal compression and an adiabatic expansion. So expansion is adiabatic. Now this adiabatic expansion can be done either by mechanically extracting the energy from the fluid which is being expanded. So the fluid which is being expanded from there the energy is extracted mechanically then the process is isoentropic process and the component used is an expanding machine or an expander or an expanding device. However if this extraction is not done so without extracting the energy in that case the process is isoentropic and that is what happens in the throttling process. So if we quickly see what are the processes or what are the steps that occurs in hydrogen liquefaction is first of all since finally we have to do an expansion we have to increase the pressure so as to expand. So first step involved is a compression step where the hydrogen is the gaseous hydrogen is compressed to a higher pressure. This higher pressure should be such that it should be higher than the critical pressure. Thereafter once compression is done cooling is carried out to reduce its temperature. Now this cooling can be done in two steps first is a pre-cooling. So from the temperature ambient or after the compression it will be at a higher temperature. So from the ambient or to a higher temperature we have to cool it down to 80 k or slightly higher or lower temperature depending upon that depends on several other parameters that means liquid nitrogen cooling is done which is also known as pre-cooling. The another step could be a final cooling. So this is at a temperature which is much lower than the liquid nitrogen temperature and that can be achieved using recuperative cooling where the vapor after throttling itself acts as a coolant. And finally the step involved is an expansion step where the gas which is at a higher pressure pH it is expanded to PL using the Joule-Thompson wall. In this process the hydrogen partially gets liquefied and that amount which is getting liquefied is collected. So the liquid hydrogen in this process which is obtained can be collected. The remaining which is in the vapor from or the vapor fraction of the gas which has got liquefied or the flash gas also known as flash gas this is allowed to exchange heat in a heat exchanger in such a way that it cools down the hydrogen stream in a heat exchanger and finally it is again fed back to the main stream to the feed stream before compressor. So in a in general these are the three major steps which occurs in hydrogen liquefaction. Now there are several ways of doing that there are several components which can be used depending upon what are their what are their energy consumption we can have even to reduce their energy consumption we can have complicated cycles we can have cascading hybridization. So we will see all those cycles now. So for large-scale liquefaction the well-known cycles are the simple Claude process, Capitza process which is a modification it can be a dual pressure Claude process, it can be pre-cooled Lind-Hamson cycle or it can be pre-cooled Duel pressure Lind-Hamson cycle it could be helium pre-cooled Claude cycle or a pre-cooled mixed refrigerated cycle or cascaded cycle. So these are several options depending upon what are the components used they are in fact classified into these type of liquefaction methods. Starting with the simple Claude cycle here if we see how the liquefaction occurs the gaseous hydrogen it is compressed in a cooled compressor. So there is an intercooling involved in the compressor. So the gaseous hydrogen undergoes cool this gaseous hydrogen undergoes compression then it goes through a series of heat exchangers such that its temperature reduces finally it undergoes throttling. Now between one of the heat exchangers is an expander or an expanding device. So what happens is the part of the compressed gas it goes through an expanding device reducing its temperature and that gas which is cooled then mixes with the hydrogen stream returning hydrogen stream in that way the temperature of the gas further cools down. Now this expander or this expanding device cannot condense because if it condenses then that is detrimental for the hardware. So it only lowers down the temperature of the gas. Now in this process it undergoes the gas compressed gas passes through a number of heat exchangers reducing its temperature below the inversion temperature which is the requirement for the throttling process. Once its temperature reduces below the throttling below the inversion temperature it passes through a throttle valve undergoes expansion such that certain amount of a small amount of liquid is or gas gets liquefied or liquid hydrogen is obtained. Now in this vessel the liquid hydrogen is collected while the gas which is not liquefied or is still in the vapor form or the vapor fraction of this gas is further recirculated back through these heat exchangers so that it can reduce the temperature of the feed gas stream to the throttle process. Now once it has exchanged its heat with the feed gas finally it is fed back before the compressor. So this is how the process takes place. Now this expansion device which is used before the throttling process is to reduce the temperature of the gas. Now if we see thermodynamics of this simple Claude cycle now we can do the energy and mass balance considering the different points we can do the mass balance of the control volumes. So the gas it enters into the compressor leaves the compressor goes into the heat exchanger and the same goes into the expander after the heat exchanger 2 after the heat exchanger 3 goes to the throttle valve certain amount of the gas gets liquefied the remaining still is in the vapor form that again goes back to the heat exchanger. Now this at this point it gets mixed with the gas which is coming from the expander and as such this is 0.89 and finally 10. Now if we write a mass balance for the control volume at steady state. So at this point after the compressor m2 dot is equal to m1 dot and let say it is m dot this is the first equation at 0.3 this is same as me dot after the expanding device so after the expander. Now the gas which is at the exit at 0.10 m10 dot is it this is m1 dot which is entering and some amount which has already been liquefied so m1 m10 dot is m dot minus mf dot. So the amount which gets liquefied is subtracted and this is m dot minus mf dot because m1 dot is same as m dot. Now m dot is in general represented for the mass flow rate of stream x and this is expressed in kilojoules per second. Same we can write the energy balance energy balance between the different outlets. So the energy balance is written at the outlets of compressor expander considering the different components compressor heat exchangers expander and separator. So the energy balance is m10 dot h10 plus m3 dot h3 mf dot hf and that is equal to m dot h2 plus me dot he. Now if we substitute these values for m10 dot it is m dot minus mf dot h1 because h10 is h1 considering h10 equal to h1. So this is m10 dot h10 which is m dot minus mf dot h1 m3 dot is me dot so me dot h3 plus mf dot hf and that is equal to m dot h2 plus me dot he. So this is the energy balance where h is specific enthalpy of the stream. Now if we see how much is the mass fraction at the expander this is at the expander. So the mass fraction at the expander which is e which is exiting from the expander in that case the ratio is me dot over m dot and the amount of which which get liquefied or the liquid yield is given by mf dot upon m dot and that is h1 minus h2 upon h1 minus hf plus x times the mass fraction at expander times h3 minus he divided by h1 minus hf. We can also calculate the net work which is required per unit mass of the compressed gas and this is the net work or the net energy consumption in the cycle W which is expressed in kilojoules per kg and this is given by the net power consumption in the cycle divided by the mass flow rate and that is equal to temperature T1 s1 minus s2 minus h1 minus s2 minus x of h3 minus he where the s is standing for specific entropy of the stream x and that is kilojoules per kg Kelvin. We can also calculate the specific energy consumption which is expressed as the energy consumed divided by the mass which gets liquefied. So, the energy consumption per unit mass liquefied it is in kilojoules per kg this is W dot upon mf dot and that is W dot upon m times y from this expression m f dot is y times m dot. So, the specific energy consumption is the power net power consumption divided by m dot y. So, the y is the fraction which got liquefied and the mass flow rate. We can also find the coefficient of performance that is the cooling which is provided by the working fluid to the net input power in the cycle. So, that is the COP and that is given by m dot times the enthalpy in the enthalpy of the feed minus hf of the liquefied hydrogen divided by the net power consumption. Now, this was the thermodynamics or the energy consumption in a simple Claude cycle. There are several variations to the simple Claude cycle. The variation to simple Claude cycle is the Capitza process wherein we can use reciprocating expansion engines instead of the instead of that expander. So, that expander is in fact the reciprocating expansion engine and this particular process is specially used when large-scale hydrogen production is required. We can also have dual pressure Claude process. So, instead of one pressure compression to one pressure before a throttling we can have two pressure, two pressure levels or two compressors being added. This is because the minimum work is proportional to pressure ratio. So, minimum work in compression that is proportional to the pressure ratio and not the pressure difference in the cycle. Now, we know also know that the compression energy this is this varies with the logarithmic of the compression ratio. For example, if it is a simple Claude cycle with a primary compressor with a compressor having a compression ratio of 200 is to 1 we can get the logarithmic value of 5.3 as a compression energy. So, that logarithmic term is 5.3. However, if we use a dual pressure cycle or a dual pressure Claude process then this compression ratio there are two compressors. So, the main compressor that will have a compression ratio of 200 by 5 and that can reduce the logarithmic term to 1.8 and that clearly shows the improvement in the performance and the energy consumption reduction. Now, in an ideal simple Claude cycle the pressure as it increases the minimum work of compression that reduces and as we know because it is proportional to the pressure ratio and then the expander flow rate is at is corresponding to the minimum work that also reduces. But the major problem with the Claude process is because we are using several components there is a expander which is being used there are several heat exchangers being used. In fact, two heat exchanger in the simple Claude process that adds up to the capital cost of the simple Claude cycle. So, the next cycle we will see will be the Lind-Hamson cycle which compared to the Claude cycle has a lower capex, capital investment. But compared to Claude cycle it has a higher operational cost. So, operational cost of Claude is lower compared to the Lind-Hamson the reason being the lower power consumption in the Claude process. So, we have seen that in the Claude cycle there is a expander or an expanding device which is used but the Lind-Hamson cycle that has a pre-cooling step which is by means of liquid nitrogen. And this pre-cooling step is introduced the reason because the inversion temperature of hydrogen is below the ambient temperature. So, that becomes inevitable. So, it can be either by means of an expander which is done in case of the Claude cycle while in case of pre-cooled Lind-Hamson cycle this is by means of a liquid nitrogen system through a heat exchanger the hydrogen is being cooled. Now in the addition of this pre-cooling not only reduces the temperature of hydrogen below its inversion temperature but it also improves the yield of liquid which we are getting. So, the yield of liquid hydrogen which is being collected this is because it improves the it decreases in fact the enthalpy of high pressure gas at the warm end of the heat exchanger. So, this reduces the enthalpy of the gas which is entering into the heat exchanger by cooling that. And also the high pressure which is required the requirement of high pressure can still be reduced. If we cool it down we pre-cool it using a liquid nitrogen network and this can be done by reducing the temperature before it undergoes the throttling. So, inclusion of this liquid nitrogen cooling has several benefits it reduces hydrogen gas temperature below its inversion temperature it reduces the enthalpy of the gas entering in the heat exchanger at the same time it reduces the pressure requirement before throttling. Now the pre-cooled Lind-Hamson cycle is where the gaseous hydrogen it gets compressed in a cool compressor once it is compressed it passes through a heat exchanger wherein its temperature is dropped below the inversion temperature by means of liquid hydrogen cooling. After that it is throttled through a Joule-Thompson wall undergoes an isoentropic expansion. In this process some amount of liquid hydrogen is formed which is being collected the remaining which is still in the vapor form that is allowed to exchange heat or that itself acts as a coolant cooling down the inlet hydrogen gas stream from the compressor to the throttle wall. So, in the way back to the compressor that passes through the heat exchanger and undergoes or it acts as a coolant for the feed gas to the throttle wall. After this heat exchanger it is fed back to the compressor. So, this is the simple pre-cooled Lind-Hamson cycle. Now performance wise this pre-cooling improves the performance of the entire process and we have seen the various reasons why it improves the performance. Now if we compare the Claude cycle with the Lind-Hamson cycle the specific energy consumption for a ideal Lind-Hamson cycle is 16.24 kilowatt hour per kg but for Claude cycle it is 22.1 kilowatt hour per kg. So, it is less in case of Lind-Hamson cycle. Now this performance can further be improved if instead of one stage compression if we include two pressure levels before throttling. So, by we can have two pressure levels included and then it becomes dual pressure pre-cooled Lind-Hamson cycle and the energy requirement can be reduced not only by means of pre-cooling but by increasing by increasing one more component the one more compressor and then we can have dual pressure levels included. Now if we consider that dual pressure ideal Lind-Hamson cycle then the specific energy consumption it reduces to 12.12 kilowatt hour per kg of liquid hydrogen being produced. While if the same we apply to dual pressure we apply to the Claude process it reduces to 6.66 kilowatt hour per kg. There are many other cycles which are possible there are several other variations like one of the variation is Collins process wherein we have further added one more expander and then there are several a series of heat exchangers which have been employed in the process. Now other variations to the pre-cooled system this is for the pre-cooled system there are many variations possible one is like helium pre-cooled. Now we know that the major component of the cost is also a compressor in the liquefaction system. Higher the size of compressor which is being used higher will be the cost associated. Now in order to reduce the size of compressor then the flow rate will also reduce the pressure will also reduce and that can still work well if we use helium for pre-cooling. So that helium acts as a working fluid here and the cycle becomes helium pre-cooled cycle. Another possibility is the joule Brayton pre-cooled cycle where again helium cycle it acts as a the helium system it acts as a refrigerant while the final expansion this is done by means of an expansion engine. And this working fluid this is not liquefied however its temperature is reduced to below the hydrogen temperature. Another possibility is with the use of different refrigerants and then we can have mixed refrigerant pre-cooled cycle. So there can be mixtures of gases and vapors which acts as working fluid in the refrigeration cycle. Now this mixed refrigerant cycle that acts as a pre-cooler for the expansion for the remaining cycle or we can superimpose or make an we can have a hybrid. So we can have a cascaded system wherein different independent cycles they pre-cool the other refrigeration cycle and with this particular system it approaches very close to the ideal reversible liquefaction process reducing the amount of net amount of energy consumption. But as we keep on adding the different components the complexity of the entire process increases. And this cascaded system is specially important when we have to use it for wide temperature range and there it improves not only the yield of the liquid which we are getting but also it improves the efficiency. So to summarize this part there have been several hydrogen liquefaction plants which are operational in the world these are located in various regions it is in USA, Japan, Canada, Holland, Finland, France, China, Germany, India. Now if we see some of the these representative examples like the one which is at being installed by Praksher this is having a specific energy consumption between in the range of 12.5 to 15 kilowatt hour per kg. Another one in Germany Ingolstadt that has 13 to 15 kilowatt hour per kg of specific energy consumption the plant that has about 13.5 that is 4.4 tons per day of hydrogen being produced liquid hydrogen being produced and it operates on the principle of pre-cooled clod cycle. This specific energy consumption is still very high the US DOA targets are to achieve a specific energy consumption of 6 kilowatt hour per kg for a large sized plant of 300,000 kg of hydrogen liquefaction per day and still it is way far off compared to the plants which are operational today. So we have to reduce the requirement is to reduce the specific energy consumption because the liquefaction is a highly energy intensive process we have to reduce the energy requirement and that can be carried out by several process integrations and many improvements in the cycle but with integration processing integration including more and more components to reduce the specific energy consumption the entire cycle becomes more and more complicated. Out of the total liquefaction cost considering a fives of 100 tons of liquefaction per day about 40 to 50 percent is the capital cost of the capital cost involved in the plant. So there have been improvements there have been models wherein large size plants have been modeled and also develop like a fives of 50 tons per day with liquid helium cooling and that had 4 ortho to para converter systems which has reduced the specific energy consumption to 8.73 kilowatt hour per kg. Another one which is being modeled is pre-cooled Claude and Joule-Breton cycle and that has a specific energy consumption of 5.85 kilowatt hour per kg. So as we are looking at the reduction in the specific energy consumption the process gets more and more complicated then 4 Joule-Breton cycles being cascaded together and then used the mixed refrigerant cycle as well for the refrigeration and that reduces the specific energy consumption to 5.35 kilowatt hour per kg. So the major challenges which we can see with the liquefaction processes the high capital cost the high specific energy consumption boil off losses inversion temperature of hydrogen which is in fact lower than the ambient temperature conversion from ortho to para all these leads to a complicated hydrogen liquefaction process. Thank you.