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Module 1: Biomass and Waste

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Energy from Biomass and Waste - Physical Route

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Hi friends, now we will discuss on the topic renewable energy, biomass and waste part 3.So, previously we have discussed on biomass and waste in part 1 and part 2 and chemicalroutes and biological routes we have discussed, and here will discuss on physical routes whichis used for making the biomass and waste suitable for its application in reactors or in saythermal applications like if I want to use the biomass and waste incinerator or in gasifiers,then we need to make it in a usable form. That means, normally the biomass and wasteare having less density and it is difficult to handle in reactive system. So, this physicalprocess helps to make it harder to give some particular strength and save also and it becomeseasy to use in the conversion process like incineration, gasification, etc.So, the content of this class is the physical conversion of biomass and waste for energyuse and that will be giving some focus on the densification of biomass and waste. So,our objective will be to densify the biomass and waste to give certain strength, certainproperties, which are more desirable for applications in energy production by this feedstock.So the definition of densification will be like this. The densification is the processof increasing the density of something, it makes a fuel denser and gives more uniformproperties with respect to the raw form. So, this is the main objective of the densificationand densification can be done by some mechanism that is your compaction or compression, andconcentrations and concretion. So, these are the steps which help to perform the densificationprocess.So, here we will put some material here and we press it, then it will be densified. Advantageof this process is that this is very simplified mechanical handling and feeding, and uniformcombustion in boilers, the feed will be having almost uniform properties, then reduced dustproduction, reduced possibility of spontaneous combustion in storage, then simplified storageand handling infrastructure, lowering capital requirements at the combustion plant, andreduced cost of transportation due to increased energy density.So, these are the advantage. Disadvantage is that the major disadvantage to biomassdensification technologies is the high cost associated with some of the densificationprocesses. So, we will see that densification processes are costlier in some cases. In somecases, it is not that costlier and people use that also.Then we will see the mechanism. So, you see the figure here. The molecular forces, vander waal’s forces can be responsible for the binding, electrostatic forces can be responsiblefor the binding or interlocking, there will be some particles and those can be under pressurethat can be interlocked or there will be some, if we add some additives, then hardening bindershighly viscous binders, then also makes some adsorption layer and binders connect the particlesof the biomass and waste and makes them strong. So, these are different processes, which areresponsible for the densification of the biomass and waste.So, for this process, for densification process, we need some pressure, high pressure is requiredor we may add some binder. When we use binder, then the pressure requirement is less, andwhen we do not use binder, then pressure requirement is high. So, when the material is compactedwith low to moderate pressure, then the space between the particles is reduced. If pressureis increased at certain stage particular to each material, the cell walls of the celluloseconstituent are collapsed.Then the pressures required to achieve such high densities are typically 100 megapascal.So if we apply very high pressure, then the cellulosic materials maybe coming out andthey can help for binding the particles. A binding agent is necessary to prevent thecompressed material from springing back and eventually returning to its original form.If we do not use binders for at low pressure if it is initially, the particulars may becompressed and again it will be springing back. So, that is why binder is required.Additives of high viscous bonding media such as tar, molasses, and other molecular weightorganic liquid can from bonds very similar to solid bridges, so these the mechanism andadhesive forces at solid liquid interface and cohesion forces with the solid are usedfor binding. So, there are if it is a solid and liquid interface, there are adhesive forcesand solid-solid interface, there will be some cohesive forces. So, these forces are responsiblefor the binding.The binding agent can be either be added to the process or when compressing ligneous material,be part of the material itself in the form of lignin, that we are talking about thatif we apply very high pressure, then lignin material can help to bind the biomass andwaste particles.So, after the application of pressure, we will be getting the dense biomass and wasteand that will be either in pellet forms or maybe in briquettes forms. The pellets arerelatively smaller diameter, smaller size, and briquettes are bigger size. So, that istypical definition or we can say there is a typical limit of the diameter on the basisof which this can be said as briquettes or pellets that is equal to 30 millimeter. Ifdiameter is greater than 30 millimeter, we can say it is briquettes, and if it is lessthan 30 millimeter, it is pellets, but this is the rough distinction and it is arbitraryalso.So, the factors which influence the densification we will discuss now. Under the physical properties,there is moisture content, bulk density, void volume as well as thermal properties of thebiomass are the most important factors in the binding process or the biomass densification.So, what are the moisture content, bulk density, void volume and the thermal properties alsoare responsible for this.The ultimate density of a briquette will depend on to some extent on a range of factors includingmost importantly the nature of the original material and the machine used for this operationand the conditions we have used.On that basis, we can have 3 types of briquetting process. One is your low pressure compactionwith a binder, then medium pressure compaction with a heating, and high pressure compaction.So, there are 3 options the people have used for this binding process. In case of low pressureup to 5 megapascal, then up to intimidate it is 5-100 megapascal and high pressure means100 megapascal pressure or more. So, when we use a high pressure, then sufficient ligninis released which helps to agglomerate the particles to and from the briquette.An intermediate pressure machines may or may not require binders depending on the natureof the material, and low pressure machines positively require binders. So, these are3 types of briquetting machines and briquetting processes.So, high and medium pressure operation if you consider, then high and medium pressurecompaction normally does not use any additional binder as we have discussed. Then the briquettingprocess is based either on piston press or screw press. So mostly, piston press or screwpress. Apart from these, there are some other also, roller press and pellet mill. So rollerpress and pellet mill can also be used, but these are having initial high investment cost,these require high initial investment costs and that is why this is not implemented indeveloping countries.So these are also having high capacity, but biomass and waste are scattered source, sothese are collection of these and then to convert it into this, that is not practicesin a small sector, these collected and produce. So bigger scale machines is not used in developingcountries. In this case, we get the piston press or screw press based machines.Now we will see the piston press. So here the figure shows the piston press. So thisis the piston, so here if we put the feedstock, so feedstock under gravity it will go downand when it will come entering here, so this piston will have back and forth movement andthis will be pressed here. So this, we are getting the briquette. So here, the pistoncan give us very high pressure. So the density of this material will be very high with respectto other method.Something piston press punch the feed material into a die with very high pressure, eithermechanically by reciprocating ram powered by the massive flywheel or by hydraulic drivenpiston. So, hydraulic driven pistons any mechanical arrangement is made and in this pressure developedhere, and we get the briquette.Now we will see the screw press. So, this is a figure which shows the operation of screwpress. So we will feed the feedstock here and then the screw is moving. So, when thescrew moves, then it gives some forward movement to the materials and materials moves towardsthis where the die is there. So, here the material is coming and pressure is developed.So, high pressure developed, then here, there is some briquette arrangement. So, briquetteis going out due to the pressure.Here, the diameter is high, here diameter is less, so there is some pressure. So, thispressure will also help to get the material out, we will get the briquette here. So, thisis the mechanism of the operation of the screw press or the screw extruder. In a screw press/screwextruder, the rotating screw takes the material from feed port through the barrel and compactsit against a die which assists the buildup of a pressure gradient along the screw.So, that we have discussed just now. It consist 3 distinct zones, here we are getting thefeeding zone, then it is your transport zone and this zone is our extrusion zone here,this extrusion zone.Now, the performance of the process will depend upon some factors that is your the abilityand cohesion of the feed material, then the particle size and its distribution, surfaceforces and adhesiveness. So, these are the factors which influence the performance ofthe process. The screw presses produce high quality briquettes, this also produce highquality briquettes with a homogeneous structure and good combustibility and require only littlemaintenance.So, the main disadvantage is that the wear of the screw leads to elevate the cost ofthe spare parts okay. So, the operating costs may be higher because of that wear of thescrew.Then we are coming to low pressure operation. So under low pressure operation as we havementioned that, we need to add some binder. So, here biomass and waste will be mixed withsome binder and then initially some step will be given and then there will be some curingtime. So that way, we have to use some binder and organic binders may be used or inorganicbinders may be used.So, different types of organic binders are provided here that is bitumen, molasses, starch,coal tar, and resin and inorganic cement, lime, clay, and sulphite liquor. So, thesehave been reported and used for the briquette formation. During the compaction process,the briquettes are brought into shape without giving them substantial strength, and afterthat, a subsequent curing step, drying, burning, chemical reaction, etc., the green briquettesare formed. So, these green briquettes developed and with the required strength and stability.Now, we will see the comparison of different machines. So, we have screw press, we havepiston press, we have roller press, we have pellet mills. So, these two mills are highinitial cost, but these can be used for the production of very large amount of productsalso. The throughput is high in these two cases. When we compare, then we see the pistonpress, we see the density, bulk density her, piston press we are having less than 0.1 andhere it is having 0.5-0.6, and there is 0.7-0.8.If we see the specific energy consumption, then this is 37-150, 37-77 here, here 30-83and 16 to 75. So, this is also different for all the machines. So, these machines energyrequirement you see also comparable, here it is higher, but these are comparable withthis also, screw press also. These are advantage, but this will be producing more product andinitial cost is high. Now if you see about the output of the machine, so this screw pressis continuous, this is also continuous, pellet mill also continuous, but piston is our instrokes, that works in strokes.So particle size, you see 2-6 millimetre, here 6-12 millimetre, less than 4, less than3 millimetre, so are giving bigger particles in this case. The maintenance is low, hereit is high, low, low. So, these are the different process for the densification which have beenused and this is a comparison.Now, when the briquettes are formed, the briquettes will be densified, it is fine, but still itwill be having more volatile matter. So, when we will be using it, then it will be producingmore smokes and we need to remove that, so carbonization of the briquettes is done. So,carbonization process is required. As we have mention that it increases the smoke generation,it also reduced ignition and burning properties, then low heat value and not suitable underwet condition.These are the demerits of the briquettes and carbonization if we do, then these demeritswill be reduced. The carbonization is the partial pyrolysis process, is heated up to600 degrees centigrade and burnable gases like CO, CH4, CH2, formaldehyde, methanol,formic and acetic acid as well as non-burnable gases like CO2, H2O and liquid tar are released.So if we heat it in absence of oxygen, then it will be converted to char along with theseproducts.So, why we do this? By this carbonization, carbon content increases in the briquettesand volatile metal reduces. So when we will use in combustion process, some smoke formationand tar formations will be reduced.The off-gas of the process is of high energetic value and can be used to balance the energyand heat demand of the carbonization and this carbonization process can be done either afterbriquette formation or before briquette formation also the biomass and waste can be convertedto char and then it will be made into briquette. So here either carbonization followed by grindingand briquetting or grinding followed by briquetting and carbonization both are possible.Now we will see how the property changes due to the briquette formations and char formation.So here the pine needle, so then pine needle char, then char to pine needle briquette.So, you see the basically volatile matter content, in the pine needle we are having70.03%, when it is converted to char it is 17.96%, and then briquette it is 29.04%. So,briquetting process is helping us to reduce the volatile matter content.Now, we see the fixed carbon. So, here 15.83 for pine needle, for char it is 69.150, andhere it is 52.85. So, briquetting process again helping us to get more fixed carbonin it. So when it will burned further in the combustion unit, it will be less amount ofmaterial will be required to release same amount of energy also and you see the howthe material changes as this is your pine needle and this is your char and then theseare the briquettes. The ash content also changes here 4.37, 5.390, and 11.21 because it isconverted into briquette form.Now briquette characteristics. There are some properties the briquette should have becausebriquettes have to be transported from one place to other place. So, one will be thereis handling characteristics and another will be fuel characteristics. Our main objectivefor the production of briquettes is to get energy from it, so use it as a fuel in combinations.So heating value, size and shape.Heating value is the fuel property, size and shape is also the fuel properties, and italso helps to achieve the performance of the reactor system. Then the handling characteristicsare bulk density, friability, resistance to humidity, these are very important properties.Now, both are important, but if I want to get one type of property in higher extent,then the other property may be compensative. So the distinction is not always clear, thatis these handling properties and fuel characteristic, this distinction is not always clear and sometimesthey interfere with each other.For example, improving the handling characteristics by making a more dense briquette, if I producemore dense briquette so that it will be easy to transport but or easy to handle, but atthe same time, it will be detrimental on its combination, because combustion requires porousmaterial, so more combustion we will get, so in that case, we have to compromise.Then we will see the manual briquette machines which are used in small scale, they are smallmachines and anybody can use it easily. So, here different parts are there. We have onebase plate. So, these are base plates and base plates will having some ejection piston.So, if we see here, we have one hydraulic jack here. So, then the pistons are there,and ejection pistons and transmission rod.So, ejection piston and transmission rod will help the transition of the force from thishydraulic machine to the plate and ejection piston will help to press the materials inthe die and when the lid will be opened, it will help to get the material out from it.So, then briquette die is also there. So, these are the briquette die here and thenhydraulic jack as I have discussed. So, hydraulic jack, then transmission rod, then your ejectionpiston, and then we have base plate on it and the lid or just say the cover of it.So, then it will be covered and then from the bottom, hydraulic jack will work and thenthat will be pressed, after that, that will be taken out by the ejection piston. So, inthis case, if we have say 20 briquettes at a time it can produce, so 20 transmissionrod and 20 ejection piston if we have, then the area requirement will be 20 x pie r square,so pi/4 x d square where d is the diameter of the die diameter. So, if the die diameterof each is 28 millimetre for example, then it will be 0.28 metre, the number of mouldis equal to 20, so total area = 20 x pie r square or pi d square/4, that is equal to0.0123 metre square. So, this is the area requirement.Then in this case, so how much weight the hydraulic jack has to be lifted. Let us see.So mass of one pressure transmission rod equal to say 450 gram, we are assuming this, andthe number of pressure transmission rod = 20. So total mass of 20 transmission rod = thisx this, 9000 gram = 9 kg. Then mass of ejection piston 20 numbers we have. So 100 gram ofit we are assuming, so that 20 x 100, so 2000, that is equal to 2 kg we are getting here.Mass of the base plate is 4.5 kg, we are assuming.So, maximum mass of one wet briquette sample is equal to 50 gram we are assuming it. So,the total mass of briquette samples that will be number of briquette sample x mass of onesample, that is equal to 20 x 50 = 1000 gram = 1 kg.So, total mass to be lifted by the hydraulic jack is the total mass of the transmissionrod, mass of base plate, total mass ejection piston, and total mass of briquette samples.So, we have got 9 kg + 2 kg + 4.5 kg + 1 kg, so 16.5 kg. So, if g = 9.81 kg per secondsquare. So, then, we are getting weight to be lifted equal to 16.5 x 9.81, that is equalto 161.87 Newton. So, this is the weight we need to lift by the hydraulic jack.Then what is the force that we have to calculate. How can you calculate the force that we willdiscuss now. Say a 10 tonnes hydraulic jack, we are using a 10 tonnes hydraulic jack thatis equal to 10,0000 Newton hydraulic jack was used to lift the missing components andcompress the briquettes. So if this is the situation, then compaction force can be calculatedusing the pressure. So, what would be compaction force that can also be calculated?So, read from the pressure gauge connected to the hydraulic jack is equal to say 17.5kilo Newton per metre square, that is one example that this is the pressure press thepressure gauge is showing this reading and the machine has 20 moles, then we can calculatewhat is the compaction force. We are getting the pressure here. So what is the compactionforce that I am interested to calculate? So, in that case, what we will do, we will usethe formula pressure equal to force area. So, pressure is given here.So, you have to calculate the area and we get the force. So, in this case area Ac = 20,now 20 number of moles we have. So 20 x pi/4 x d square. So that is equal to 0.0123 metresquare. So if Fc is equal to this, Ac x P, which is given here, so that we are getting0.2153 kilo Newton that is equal to 215.3 Newton. So that way we can calculate whatis the preset requirement. So up to this in this class. Thank you very much for your patience.