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We keep reading it that way, and we think that that is the only point boil temperature at which water will boil that is correct that is the temperature at which water will boil under 1-atmosphere pressure, that 1-atmosphere pressure is something it will be there in your textbook, but I don’t think you would have paid attention to it if you think about it carefully you will find it will go and look up this information it will always say the boiling point of something at this pressure it will say that. We somehow don’t the pressure part of it does not register to us because we went only looking for the boiling point. And the pressure is always assumed to be one atmosphere because most of the time our operation is at one atmosphere. So, the boiling point of water is 100 degrees C at one atmosphere. You drop the pressure significantly you can decrease the boiling point if you increase the pressure you can increase the boiling point. So, this is, so the boiling point is variable and depends on the pressure and so if you decrease the pressure you can decrease the boiling point and then the same the I mean the steam at the same temperature is now, superheated relative to what it’s the boiling point. So, that is what is done and this idea of you know lowering the boiling point by adjusting the pressure. It is called flashing. So, what happens is steam comes out before it enters the turbine it will enter a chamber where it is allowed to expand. If it is allowed to expand then it’s boiling point comes down and therefore, it becomes superheated and once it becomes superheated because the pressure has decreased pressure has suddenly decreased and therefore, it becomes superheated and at that point, you can send it into the turbine. (Refer Slide Time: 36:04) So, this is basically what we do. So, from the production well it’s the same process you pull up the steam and you send it into this tank called the flash tank. So, here flashing is done and this, this concept is called flashing where you suddenly decrease the pressure and because it is decreased suddenly you have superheated steam and then that superheated steam is sent into the turbine. And then that rotates the turbine then you get the generator to operate and then after that you can send it back into the injection. And again you know it depends if you have if it is still you know it is still in the steam condition you can again put a condenser and again drop it to vacuum conditions to get the liquid water to form, and then you can send that liquid water down the injection well. So, this is how you would handle a situation where you have you have saturated steam coming into the becoming available to you coming from the location where you have done this prospecting okay. (Refer Slide Time: 37:02) The third possibility is hot water. So, we saw superheated steam, we saw saturated steam. Now, we are looking at hot water. So, this is the third possibility that we have which is hot water. This is found in many many places. So, when you do the prospecting this is what you are most likely to find most commonly you end up finding this hot water in which case the process that is used as I mentioned is similar. So, we saw in the OTEC plant discussion that we had a couple of classes ago that there you are only looking at a difference of about 25 degrees centigrade, you are looking at the water coming from the bottom of the ocean which is sitting at about 3, 4 or 5 degrees centigrade and you are looking at the water on the top of the top surface of the ocean which is sitting at about 25-30 degree centigrade. So, the temperature difference is only about 25-degree centigrade maybe even less 15 to 25 degrees centigrade is the difference that you are looking at with that itself we are running a generator right. So, with that, it is we are running a generator. So, when you get hot water when you do geothermal prospecting and get hot water then clearly you can use the same concept that you are using in an OTEC plant. So, typically to do that you need to do something called a binary fluid cycle and the different again the idea is the same if you have some you know vapour going through the turbine you can get it to rotate and so you look at liquids which have low boiling points. So, you can take butane which is the minus 1-degree centigrade boiling point. isobutane is minus 11.7 degrees centigrade boiling point pentane which is 36.1 degrees C boiling point. So, you can use these as liquids as opposed to using water which is 100 degrees C boiling point. So, to use water and then get steam from it and then run the turbine you would have to be past 100-degree centigrade temperature, but if you have got hot water, that hot water may be reasonably hot it may be you know 80-degree centigrade, 90-degree centigrade or something like that and therefore, you may have a considerable amount of heat available in it, it is just that it is not yet past the boiling point it is not in the scheme. So, you use some other fluid and you exchange heat with this water and using that process you run the turbine. (Refer Slide Time: 39:47) So, for example, it would look something like this. Again you would have a production well. So, from this, you pick up the hot water and it goes into a heat exchanger. So, this is very important. So, we have a heat exchanger that is out there. So, in this heat exchanger, this water enters hot. So, you come here with hot water and what is coming out here is cold water okay. So, cold water is exiting from the condenser from the heat exchanger and goes down. So, there is another fluid which is running between, so this is the fluid that is running from the well from the production well to the injection well through the heat exchanger. So, your water does not see the turbine it only sees the heat exchanger it goes in goes enters the heat exchanger hands-off heat and goes down cold. Then you take the take another fluid which could be any of these that we spoke about butane isobutane pentane etc you find a fluid which is the low boiling point and has you know the correct range of temperatures with which we can operate it in this situation and that fluid enters here cold picks up heat and then exits out here hot ok. So, it enters in cold exits out hot vapour form it will and exit out that hot you know a gaseous form of that liquid of that you know pentane or butane or whatever you have taken fluid is now going to run the turbine. So, you complete running the turbine and then you exit the fluid will exit out and it is now, cold again and goes this way ok. So, you have 2, 2 fluids here the fluid that is coming from the underground and that’s this loop that we just saw which is how the heat exchanger is you know picking up that heat and handing it off to this second fluid, which is the binary and hence this is called this binary fluid cycle because there are two fluids involved here and the second fluid is what runs the generator runs the turbine. So, the turbines are here and then that runs the generator and from here you get the electricity okay. So this is the basic idea of this process where you could be running using hot water ok. So, and that is how this system is set to run. (Refer Slide Time: 42:28) Now, if you look at it as I said you know the geothermal energy is available with differing levels of heat. So, we saw that you know based on the location you could have either supersaturated steam, superheated steam you could have or you could have saturated steam or you can have hot water. So, these are the 3 that you would get based on your prospecting. So, you do prospecting and you could get one of these 3. And therefore, this is a very from location to location you get this and then based on this you run a turbine with a condenser, you do flashing in this case, and in this case, you use a binary fluid ok. So, so these are all the options that you have available to you and in that process, you can generate the electricity from the turbine. And therefore, the geothermal plant has to be designed to account for the differing prevalent conditions. So, whatever the condition is as I said you know you have 3 possibilities here which could be distinctly different in how their behaviour is concerning the turbine. And a lot of this as I said has got to do with you know in all these cases you are looking for efficiency and you are also looking of life, the life of turbine blades turbine etcetera. So, the life of turbine blades etcetera, that efficiency and life are the two criteria that you are using when you decide what is the design that you need to use. And it also tells you that given that this is geothermal and you don’t have significant control on what is coming out from underground significant variation is going to be there from site to site, both in terms of I mean this temperature is just one variation that we are talking of that decides there is a very important parameter because the design of this plant itself will be based on this variation of temperature that, clearly you know you have three different designs that have to be put in place. So, you cannot just you know force-fit one design to all locations of this plant. So, this, you have to do some initial design understanding of that location to decide what kind of a plant you have to use. But if you look at the life of the turbine you have to keep in mind that what comes out is not going to be pure steam, you are likely to have other things that are coming out. So, your system should be capable of you know keeping track of track of that to ensure that you know whatever is coming out is not dealing with the turbine which is incapable of handling what is coming out and therefore, this turbine material is a know fair amount of material science is there concerning turbine blades and a lot of coatings are given often ceramic coatings. So, ceramic coatings are often given for turbine blades primarily to ensure that you know the turbine blade doesn’t directly get impacted by what is heating it, ok so and that dramatically increases the life of the turbine blade. So, sometimes you know Zirconia based coatings are used, etcetera and they are used to create this thermal barrier coating they are called and that helps handle the temperature plus also the fact that it’s a ceramic kind of coating usually make means it is much more resistant to attack from corrosion and so on, and so those coatings are very significant. Even, even if you can you know the actual blade if it sees a temperature that is you know 5-10 degrees lower than the temperature of the gas that is hitting the turbine blade then that itself will greatly increase the life of the turbine. On top of it you know if any particles are coming by chance from underground etcetera which you don’t have control on the ceramic material will take the impact from those fine particulate material that may be present and in that case, that again helps protect the turbine blades. So, the coating or the study of those coatings is a very significant activity because not only do they have to understand which material to use you would also figure out what is the best way to apply that material on top of the blade. So, that that you know coating is uniform and has some predictable properties so that you can say safely say that you know for a certain range of operation of temperatures certain range of you know compositions the turbine blade will be safe. So, even though we draw you know diagrams like this where you have just put in a turbine system here clearly, since this is not you know typical thermal power plant where you have a lot of control on what liquid is being used, I mean what’s the quality of water that is being used we cannot just like that put whatever is available in a typical thermal power plant cannot directly be used here. It’s a good starting point and that is probably where people will start, but you have to account for all these things, you have to account for what is available locally in terms of what is coming out from underground and figure out if you need to put in additional coatings to make it run. So, there are these conditions that we have to look at people actively look at it, but as I said the geothermal energy as an overall area of activity has all of those positives. The first thing is you are not depending on a particular kind of oil of any nature. So, in a sense, it puts almost all nations on even footing. So, many of them you know political aspects associated with energy are you know blunted when you look at the energy of this nature when you look at say solar energy, wind energy and geothermal energy they get blunted and if it is geothermal energy to some degree I mean early you don’t even need access to the coast. So, OTEC for example needs access to the coast. So, even within the, within a, within a nation like India, only the coastal areas can you know immediately attempt to benefit from the OTEC kind of activity. Even there you have all this you know flowing water and you have difficulty in controlling the pipes and the lifetime of the pipes. Whereas here it is it’s primarily a hole in the ground and so to some degree, it puts everybody on an even footing you can do this at various places, although as I said based on prospecting they tend to pick specific locations in preference to other locations ok. So, those are our conclusions for today’s class. Geothermal energy is available with differing levels of heat at different locations and plants have to be designed to account for the various prevalent conditions, conditions prevalent primarily looking at efficiency and lifetime of the turbine. And with that cont you know aspects taken into account this is a technology that is very clean and can be used at multiple locations. So, we will halt this discussion with this today and we will pick it up in our next class. Thank you. So, I mean to the extent that you can handle it this itself is not a major issue, but you can think about at least you need to apply thought in the process right. So, so that we know that we are not pushing the society into a corner, where suddenly you may have a shortage which you may not be able to control in the short term and food is something that we need daily. So, even if you have a sudden shortage of food for let’s say 2 months or 3 months, that’s not something that you can easily handle for a large population right. So, that is significant. So, it is in direct competition with food resources that’s the point we have to remember right. So, its in direct competition with food resources especially when you do farming of this nature, exclusively for the sake of the energy industry. So, there is a competition with food resources. So, we have to be aware of it aware of the say the extent of it the magnitude of it so, that we can keep it manageable and still says secure both from the energy perspective as well as from the food perspective. There is also some biomass agriculture is one aspect of it, the other issue is also that you can use biowastes. So, as part of normal agriculture, so if you were to use bio-waste then you are not impacting the normal agriculture; normal agriculture in the sense agriculture for the perspective of food right. So, agriculture for food is a waste product, from this is a waste product from agriculture for food. So, to the extent that it is only a waste product from the agricultural process, it does not affect the food supply chain okay. So, it does not affect. So, it does not affect food supply because you have grown some crop and you have harvested that crop. So, that crop has already been harvested and sent you to the food cycle for people to buy, it is going to you know wherever the wholesale distributors are etcetera it goes that way. So, that is not being affected, but after the cross main part of the crop is gone, do you have a lot of waste associated with just regular agricultural process. So, that waste you can use as a biofuel, in that case, the first issue that we were discussing off which is competition with food resources is not an issue ok. So, that is something that we can look at. (Refer Slide Time: 20:50) So, for example, the straw that would be an excellent example of this bio-based. So, to speak. So, So, as I said you know biomass is often a byproduct of or waste product from agriculture. So, straw is a major by-product from grain production ok. So, any grain you produce you have plenty of straw that comes along with it. So in fact, if you look at the weight percentage, that is very significant you look at this weight per cent almost 40 per cent of the weight of the overall product is the straw. So, if you have a 1-ton total product that you make right. So, 1000 kilograms you make the total product. So, of which 600 kilograms would be the grain, 400 kilograms will be straw. So, for every, you know a ton of the total product 600 kilograms is the grain which we will take for eating purposes 400 kilograms of straw is just going to be sitting around right. So, if you can use that 400 kilograms that’s a great thing to do so. If you look at it globally billions of tons are being produced every year of straw billions of tons of straw is being produced every year globally. However, only 100 million tones or so, roughly about 100 million tones seem to be getting used in the form of biofuel or in the form of biomass that is this you know 100 million tones of straw or any other ways that are being generated is getting converted into a fuel that is then being put into the energy sector. The rest very, unfortunately, the rest of it is being burnt in the open or allowed to rot ok. So, this is a huge waste I mean we just burn it or you allow it rot. So, when you burn it you do damage in two way two different ways, the first thing is you are releasing you are burning it and you are releasing carbon dioxide into the atmosphere right in carbon dioxide much particulate matter a lot of stuff is being released into the atmosphere when you burn you know straw. Most importantly and very unfortunately, in this case, you are not even using that energy you are just burning it in open that’s it you are just burning it, destroying it, throwing the energy throwing the waste, throwing you know particulate matter everything into the atmosphere and nothing you are gaining from it only all the negatives you put together and handoff to society that’s all happens when you just burn it out in the open without any other purpose being served. So, this is what is happening unfortunately internationally. Only about 100 million tons is being used properly to generate energy and you know billions of tons out of the billions of tons that are available all the rest of it is just being destroyed in a manner that is a highly self-destructive for us right. So, that’s something we have to look at. So, for example, in India one of the things that keep coming to our news very regularly, every year we have this thing coming to our news that if you look around October November you will see that pollution in Delhi shoots upright pollution in our capital shoots up in a very significant way. Pollution in Delhi goes up in a very significant way typically you will hear this news around October November. Now and there will be a major spike, and the pollution is terrible we are not just talking of a slight increase in pollution, we are looking at situations where the amount of particulate matter in the air is 16 times ok. So, 15 to 20 times the upper permissible limit ok. Is the upper permissible limit itself is a high limit, but they say you know up if you cross this limit it is no it is fairly dangerous to the health. Now you are not crossing you are not just. So, most of the time you want to be well below that limit, you don’t want to cross say 10 per cent of the limit or some such thing you want to stay well below that limit. Now not only you are not staying below the limit you are crossing it by an order of magnitude more than an order of magnitude. So, you are crossing it by a factor of 15 or 20 that’s a huge you know you have suddenly change the scenario of a place from being you know the livable city to something that you know is extremely toxic, you cannot be there extremely dangerous. So, many times in October November last few years we have the situation that you have major shutdown in Delhi okay. So, schools are all shut down many things are shut down, people are asked to stay indoors a people are asked to use some kind of mask to cover their noses and so on and even staying indoors, I don’t know to what degree it helps because ultimately the ashes come in. So, that tissue is there, but you have a lot of particulate matter at least if you put something or around your nose to that extent you can avoid the particulate matter, but this is happening, why is this happening? A very significant reason this is happening is that there are a lot of agricultural activities that go on in areas that are neighbouring Delhi ok. So, in states our neighbouring Delhi, you have various places where there are a lot of agricultural farms and it is this season when they change from one crop to another crop and when they have harvested a crop, there’s a lot of the waste of the crop that is sitting there in that form, and they need to clear that waste and then start the next crop. So, it turns out that for many of them it economically and time-wise it works out very conveniently if they just like the fire, and then they just burn that burned the place down burn the farm all the waste in the farm is just burnt. So, unfortunately, the economic reality and you know the convenience of quick disposal creates this situation, where the large number of farms that are burning their waste and this seems to be fairly well documented. They seem to be a lot of reports saying that at that point a huge number of farms were burning, and it's a strictly there are rules which prohibit this kind of activity, but unfortunately, the ground reality is that you know due to economic reasons you know pressures various pressures etcetera this seems to be the ground reality that many people are burning their the waste in the farm. And as a result, a huge amount of pollution comes up and this is dangerous even for those people because whatever you may say even though maybe the wind eventually takes the pollution into Delhi, wherever those farms are wherever that burning is happening with all these farms neighbouring farms burning, people who live in those places their families they are all breathing that highly toxic air I mean highly injurious here they are breathing for several days. So, there can be nothing good about it and maybe it is you know a lack of understanding of the situation that and also the circumstances their circumstances that even if they understand it is not good for the health, they are in a corner where they need to do something and they end up doing this and this is a pretty bad situation and a lot of efforts have to be made to know to educate them to stop this kind of burning and give them not just educate them, to give you an avenue give them an avenue. So, for example, the straw that is the waste material that is generated there, all you know by-product of this the farming process that is lying there. So, most mostly in the form of straw, for example, that can easily be bundled and sent off to a plant where it can be burnt in a controlled manner and you can generate a huge amount of electricity right. So, this can be done, but for that to happen this has to be economical. So, many times the report suggests that you know if they have to bundle this up and take it and go and give it to a plant which will accept it, that process of bundling it the process of transporting it and going and selling it will cost them a lot more than what the companies are willing to pay them for the right for that. So, you take one kilogram of the straw and go and go and hand it off, if they are only going to give you a 100 rupees for it, but it is going to take you 500 rupees to know to make that bundle put it on a truck take the truck to that place and hand it off. So, you are going to spend 500 rupees delivering it and they are going to give you 100 rupees for it. If nobody who is you know running any kind of business we will see this as economically viable and so on. So, governments need to assist them in some process to you know to take care of this kind of waste disposal and then try to do something more you know effective concerning this. But the point being this is a reality not just in some remote international location this is a reality in our country in our nation's capital ok. So, it affects our nation's capital every year and in a manner that is very dramatic very visible and affects a lot of people every year you are going to see I mean you see you end up seeing this just you will see newspaper reports that you know it is just full of smog full of smoke particulate partner matter. You take a photograph you can barely see you know 100 meters ahead of you. It is so, heavily ridden with we smoke that has come into the city. So, this is something that needs are just argent addressing, and it has got to do exactly with this idea of biomass right. So, this biomass, in this case, being destroyed recklessly being destroyed we just because the circumstances are like that and so, something needs to be done about it. And so so in terms of biowaste straw is there, unfortunately, it is not being used. So, if you choose to use biowaste and you can find a way to do it economically, at least you won’t affect the food supply you can stick to waste. I mean in a more comprehensive way you can use the entire cycle of the agricultural process from you know end to end. So, this is something that we need to keep in mind ok. (Refer Slide Time: 29:50) So, what kind of substitutions are people talking about when we talk of biomass in what ways is biomass being used. So, that’s something that we will briefly look at. So, we do know that coal is being used extensively in thermal power plants. So, many times biomass is used as a substitute for coal and in fact, this is a major activity, because as I said the power industry is where the pressure is to say that you know we have shifted to renewable because then that can be something that is reported. See the general public if you have somebody who is I mean poor and is using some twigs to do some cooking, it is difficult to document to what degree they are using what and then see if to what degree it has affected our power sources so, to speak whereas, the major part of our power comes from power plants. So, if you impact how the power plant generates the power, that is how you report that you know you have made a change to the energy sector and you have made a change to make it cleaner or whatever it is that you are trying to project. So, the governments put pressure on power plants and power plants find this is a nice way to proceed. So, they use coal instead of coal where they had been using previously coal, they can now additionally add wood and add. So, you have some percentage of coal some percentage of wood. So, to the extent that they add wood, they have now added say 20 you put 20 per cent of by mass of wood then 20 per cent substitution you have done with a renewable source. So, we will talk about this idea of renewable shortly, but you would treat it for the moment that it is renewable. So, we put it in as 20 per cent substitution. And again as a substitute for coal instead of directly using the wood, you can convert wood to charcoal which is wood heated in the absence of air. So, you first heat would in the absence of air, it will remove a lot of volatile materials from it various other unnecessary things should be removed from it, what will remain would be primarily carbon and it is twice the energy content per unit mass ok. So, you can get much higher you know the energy in unit mass and therefore, that is much more useful for us when we try to get you to know some useful power out of it. So, therefore, you can convert. So, you can either use the wood directly as a substitute for coal or you can take the wood to convert it to charcoal and then use that as the substitute. So, this is how we are dealing with solid, solid fuel coal either as charcoal or wood is the substitute. Then we have a liquid form which is petrol or diesel. So, for petrol typically ethanol is used as a substitute and this is largely obtained by fermentation of corn and sugarcane anaerobic fermentation. So, again the absence of air. So, fermentation of corn and sugar is done and from that we get ethanol, and that ethanol can be used as a substitute for petrol and people have demonstrated and in fact, many patrol mixes that are out there usually have some maybe 10 per cent of ethanol already mixed in it. So, each government has you know put in some rule from how much of this kind of ethanol should be there already added to the fuel, and to that degree reduces dependence on the incoming supply of petrol right. So, so far petrol the substitute is you know biomass substitute is ethanol. Similarly, for diesel, there is something called biodiesel, which is which can be derived from vegetable oils such as soybean oil. So, a large amount of it is coming from vegetable oils, soybean oils, some animal fats etcetera you can all be used to create the biodiesel and this can be used directly in you know as a substitute for diesel. So, with varying levels of percentages, you can use you know this ethanol for petrol biodiesel for diesel etcetera and therefore, to that degree you change the mix of the fuel. So, this is. So, petrol and diesel in this case our biomass being used in I mean biomass substitutes are being used for petrol and diesel. So, that is biomass substitutes in the form