TECHNICAL REPORT

ON

BIOGAS, HYDROGEN AND HYTHANE

FUELS

Submitted to

Prof. Kumar G N

Mechanical department

NITK

MANOJ – 13ME237

KARTHIK KUMAR K –13ME238

KOUSHIK – 13ME239

KISHAN R - 13ME240

MANISH K-13ME241

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Acknowledgement

As a part of completion of Mechanical lab course, writing a technical report on biogas, hythane and hydrogen fuel was indeed knowledge gaining experience. This report gave an insight of current scenario of the usage of fuels both in India and Internationally. Composition of fuels, Production, Utilisation of fuels leads to deeper understanding of their applications and research in the areas.

We would like to express our heartfelt gratitude to Prof. Kumar G N, Mechanical engineeringdepartment, National Institute of Technology, Karnataka – NITK, for providing an opportunity to conduct a technical survey of fuels and construct a technical report of our understanding about the fuels.

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INDEX

1) Biogas ………………………………………………………………………………4

2) Hydrogen …………………………………………………………………………...10

3) Hythane……………………………………………………………………………. 18

4) References…………………………………………………………………………. 23

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BIOGAS

Biogas typically refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste or food waste. It is a renewable energy source and in many cases exerts a very small carbon footprint.

Biogas can be produced by anaerobic digestion with anaerobic bacteria, which digest materialinside a closed system, or fermentation of biodegradable materials.

Biogas is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts ofhydrogen sulfide (H2S), moisture and siloxanes. The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.

Biogas can be compressed, the same way natural gas is compressed to CNG, and used to power motor vehicles. In the UK, for example, biogas is estimated to have the potential to replace around 17% of vehicle fuel. It qualifies for renewable energy subsidies in some parts of the world. Biogas can be cleaned and upgraded to natural gas standards, when it becomes bio methane.

PROPERTIES

The composition of biogas varies depending upon the origin of the anaerobic digestion process. Landfill gas typically has methane concentrations around 50%. Advanced waste treatment technologies can produce biogas with 55%–75% methane, which for reactors with free liquids can be increased to 80%-90% methane using in-situ gas purification techniques. As produced, biogas contains water vapor. The fractional volume of water vapor is a functionof biogas temperature; correction of measured gas volume for water vapor content and thermal expansion is easily done via simple mathematics which yields the standardized volume of dry biogas.

In some cases, biogas contains siloxanes. They are formed from the anaerobic decomposition of materials commonly found in soaps and detergents. During combustion of biogas containing siloxanes, silicon is released and can combine with free oxygen or other elements in the combustion gas. Deposits are formed containing mostly silica (SiO2) or silicates (SixOy) and can contain calcium, sulphur, zinc, phosphorus. Such white mineral deposits accumulate to a surface thickness of several millimetres and must be removed by chemical or mechanical means.

Practical and cost-effective technologies to remove siloxanes and other biogas contaminants are available.

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For 1000 kg (wet weight) of input to a typical bio-digester, total solids may be 30% of the wet weight while volatile suspended solids may be 90% of the total solids. Protein would be 20% of the volatile solids, carbohydrates would be 70% of the volatile solids, and finally fats would be 10% of the volatile solids.

PRODUCTION

International Scenario

With the many benefits of biogas, it is starting to become a popular source of energy and is starting to be used in the United States more. In 2003, the United States consumed 147 trillion BTU of energy from "landfill gas", about 0.6% of the total U.S. natural gas consumption. Methane biogas derived from cow manure is being tested in the U.S. Accordingto a 2008 study, collected by the Science and Children magazine, methane biogas from cow manure would be sufficient to produce 100 billion kilowatt hours enough to power millions of homes across America.

Initiated by the events of the gas crisis in Europe during December 2008, it was decided to launch the EU project "SEBE" (Sustainable and Innovative European Biogas Environment) which is financed under the CENTRAL programme. The goal is to address the energy dependence of Europe by establishing an online platform to combine knowledge and launch pilot projects aimed at raising awareness among the public and developing new biogas technologies.

In February 2009, the European Biogas Association (EBA) was founded in Brussels as a non-profit organisation to promote the deployment of sustainable biogas production and use in Europe. EBA's strategy defines three priorities: establish biogas as an important part of Europe’s energy mix, promote source separation of household waste to increase the gas potential, and support the production of bio-methane gas vehicle fuel. In July 2013, it had 60 members from 24 countries across Europe

Germany is Europe's biggest biogas producer and the market leader in biogas technology. In 2010 there were 5,905 biogas plants operating throughout the country; Lower Saxony, Bavaria and the eastern federal states are the main regions. Most of these plants are employedas power plants. Usually the biogas plants are directly connected with a CHP which produces electric power by burning the bio methane. Biogas in Germany is primarily extracted by the co-fermentation of energy crops (called ‘NawaRo’, an abbreviation of ‘nachwachsende Rohstoffe’, which is German for renewable resources) mixed with manure. The main crop used is corn. Organic waste and industrial and agricultural residues such as waste from the food industry are also used for biogas generation.

India Scenario

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Biogas in India has been traditionally based on dairy manure as feed stock and these "gobar" gas plants have been in operation for a long period of time, especially in rural India. In the last 2-3 decades, research organisations with a focus on rural energy security have enhanced the design of the systems resulting in newer efficient low cost designs such as the Deenabandhu model.

The Deenabandhu Model is a new biogas-production model popular in India. (Deenabandhu means "friend of the helpless.") The unit usually has a capacity of 2 to 3 cubic metres. It is constructed using bricks or by a ferrocement mixture. In India, the brick model costs slightly more than the ferrocement model; however, India's Ministry of New and Renewable Energy offers some subsidy per model constructed.

In India, Nepal, Pakistan and Bangladesh biogas produced from the anaerobic digestion of manure in small-scale digestion facilities is called gobar gas; it is estimated that such facilities exist in over 2 million households in India, 50,000 in Bangladesh and thousands in Pakistan, particularly North Punjab, due to the thriving population of livestock. The digester is an airtight circular pit made of concrete with a pipe connection. The manure is directed to the pit, usually straight from the cattle shed. The pit is filled with a required quantity of wastewater. The gas pipe is connected to the kitchen fireplace through control valves. The combustion of this biogas has very little odour or smoke. Owing to simplicity in implementation and use of cheap raw materials in villages, it is one of the most environmentally sound energy sources for rural needs. One type of these systems is the Sintex Digester. Some designs use vermiculture to further enhance the slurry produced by thebiogas plant for use as compost.

To create awareness and associate the people interested in biogas, the Indian Biogas Association was formed. It aspires to be a unique blend of nationwide operators, manufacturers and planners of biogas plants, and representatives from science and research. The association was founded in 2010 and is now ready to start mushrooming. Its motto is "propagating Biogas in a sustainable way".

Some Gas Production Figures

If the daily amount of available dung (fresh weight) is known, gas production per day in warm tropical countries will approximately correspond to the following values:

1 kg cattle dung 40 litres biogas

1 kg buffalo dung 30 litres biogas

If the live weight of all animals whose dung is put into the biogas plant is known, the daily gas production will correspond approximately to the following values:

cattle, buffalo and chicken: 1,5 litres biogas per day per 1 kg live weight.

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pigs, humans: 30 litres biogas per day per 1 kg weight

STORAGE

There are two basic reasons for storing biogas or bio methane: storage for later on-site usage and storage before and/or after transportation to off-site distribution points or systems. The least expensive and easiest to use storage systems for on-farm applications are low-pressure systems; these systems are commonly used for on-site, intermediate storage of biogas. The energy, safety, and scrubbing requirements of medium- and high-pressure storage systems make them costly and high-maintenance options for on-farm use. Such extra costs can be bestjustified for biome thane, which has a higher heat content and is therefore a more valuable fuel than biogas.

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Low-Pressure Storage of Biogas

Floating gas holders on the digester form a low-pressure storage option for biogas systems. These systems typically operate at pressures up to 10-inch water column (less than 2 psi). Floating gas holders can be made of steel, fibreglass, or a flexible fabric. A separate tank maybe used with a floating gas holder for the storage of the digestate and also storage of the raw biogas. Medium-Pressure Storage of Cleaned Biogas Biogas can also be stored at medium pressure between 2 and 200 psi, although this is rarely, if ever done, in the USA. To prevent corrosion of the tank components and to ensure safe operation, the biogas must first be cleaned by removing H2S. Next, the cleaned biogas must be slightly compressed prior to storage in tanks. Typical propane gas tanks are rated to 250 psi. Compressing biogas to this pressure range uses about 5 kWh per 1,000 ft3. Assuming the biogas is 60% methane and a heat rate of 13,600 Btu/kWh, the energy needed for compression is approximately 10% of the energy content of the stored biogas.

UTILISATION

Biogas can be used for electricity production on sewage works, in a CHP gas engine, where the waste heat from the engine is conveniently used for heating the digester; cooking; space heating; water heating; and process heating. If compressed, it can replace compressed natural gas for use in vehicles, where it can fuel an internal combustion engine or fuel cells and is a much more effective displacer of carbon dioxide than the normal use in on-site CHP plants.

Biogas upgrading

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Raw biogas produced from digestion is roughly 60% methane and 29% CO2 with trace elements of H2S it is not of high enough quality to be used as fuel gas for machinery. The corrosive nature of H2S alone is enough to destroy the internals of a plant.

Methane in biogas can be concentrated via a biogas up-grader to the same standards as fossil natural gas, which itself has had to go through a cleaning process, and becomes bio-methane. If the local gas network allows, the producer of the biogas may use their distribution networks. Gas must be very clean to reach pipeline quality and must be of the correct composition for the distribution network to accept. Carbon dioxide, water, hydrogen sulfide, and particulates must be removed if present.

There are four main methods of upgrading: water washing, pressure swing adsorption, selexoladsorption, and amine gas treating. In addition to these, the use of membrane separation technology for biogas upgrading is increasing, and there are already several plants operating in Europe and USA.

The most prevalent method is water washing where high pressure gas flows into a column where the carbon dioxide and other trace elements are scrubbed by cascading water running counter-flow to the gas. This arrangement could deliver 98% methane with manufacturers guaranteeing maximum 2% methane loss in the system. It takes roughly between 3% and 6% of the total energy output in gas to run a biogas upgrading system.

Biogas gas-grid injection

Gas-grid injection is the injection of biogas into the methane grid (natural gas grid). Injections includes biogas until the breakthrough of micro combined heat and power two-thirds of all the energy produced by biogas power plants was lost (the heat), using the grid to transport the gas to customers, the electricity and the heat can be used for on-site generation resulting in a reduction of losses in the transportation of energy. Typical energy losses in natural gas transmission systems range from 1% to 2%. The current energy losses on a large electrical system range from 5% to 8%.

Biogas in transport

If concentrated and compressed, it can be used in vehicle transportation. Compressed biogas is becoming widely used in Sweden, Switzerland, and Germany. A biogas-powered train, named Biogaståget Amanda (The Biogas Train Amanda), has been in service in Sweden since2005. Biogas powers automobiles. In 1974, a British documentary film titled Sweet as a Nut detailed the biogas production process from pig manure and showed how it fueled a custom-adapted combustion engine. In 2007, an estimated 12,000 vehicles were being fueled with upgraded biogas worldwide, mostly in Europe.

Electricity Production

Whereas using the gas for direct combustion in household stoves or gas lamps is common, producing electricity from biogas is still relatively rare in most developing countries. In Germany and other industrialised countries, power generation is the main purpose of biogas plants; conversion of biogas to electricity has become a standard technology.

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This document will discuss the potentials, obstacles and necessary framework conditions for the utilisation of biogas for small and medium scale electricity generation in developing countries. This paper will not address the biogas production process in general but focus uniquely on electricity generation.

The findings presented here are based mainly on available experience from GTZ-related pilotbiogas power plants in different countries. They focus on more or less well-documented existing country cases even though little extensive documentation of practical long term operating experience is available. Besides the cases described here, we know of further examples from other GTZ projects (e.g. Bolivia, Tunisia and the Ivory Coast). However, there is not yet sufficient information concerning these to merit inclusion in this assessment.

HYDROGEN

FUEL PROPERTIES

On reacting with oxygen, hydrogen releasesenergy explosively in combustion engines or quietly in fuel cells to produce water as its onlyby-product.

Energy ContentHydrogen has the highest energy content per unit mass of any fuel. For example, on a weightbasis, hydrogen has nearly three times the energy content of gasoline (140.4 MJ/kg versus48.6 MJ/kg). However, on a volume basis the situation is reversed: 8,491 MJ/m3 for liquidhydrogen versus 31,150 MJ/m3 for gasoline. The low volumetric density of hydrogen resultsin storage problem, especially for automotive applications. The energy density of hydrogen isalso affected by the physical nature of the fuel, whether the fuel is stored as a liquid or asa gas; and if a gas, at what pressure. Energy-related properties of hydrogen are comparedwith other fuels in Tables 1.3 through 1.5.One of the important and attractive features of hydrogen is its electrochemical property,which can be utilized in a fuel cell? At present, H2/O2 fuel cells are available operating atan efficiency of 50–60% with a lifetime of up to 3000 h. The current output range from 440to 1720 A/m2 of the electrode surface, which can give a power output ranging from 50 to2500 W.

Wide Range of FlammabilityIn ambient air, hydrogen is fl ammable in 4–75% concentrations (which is much broader thangasoline range, 1–7.6%) and is explosive in 15–59% concentration range [9,13]. However, forinternal combustion engines, it is more meaningful to define fl ammability range in terms ofequivalence ratio (φ), defined as the mass ratio of actual fuel/air ratio to the stoichiometricfuel/air ratio. Then, the fl ammability range for hydrogen is 0.1 < φ < 7.1, and that forgasoline is 0.7 < φ < 4, which indicates that H2 internal combustion engine is amenable to

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stable operation even under highly dilute conditions. In fact, the wider range gives additionalcontrol over the engine operation for emissions and fuel metering [25]. The engineoperation at hydrogen-lean mixture (i.e., hydrogen amount less than the theoretical or stoichiometric amount needed for combustion with a given amount of air) allows an easeof start. Also, due to the complete combustion, the fuel economy is good. In addition, thefinal combustion temperature is generally lower with hydrogen fuel than with gasoline,reducing the amount of pollutants, such as nitrogen oxides, emitted in the exhaust.

Low Ignition EnergyThe amount of energy needed to ignite hydrogen is 0.02 mJ, which is about 10-fold lessthan that required for gasoline (0.24 mJ). The low ignition energy enables hydrogenengines to ensure prompt ignition even for lean mixtures. Unfortunately, the low ignitionenergy means that hot gases and hot spots on the cylinder can serve as sources of ignition,creating problems of premature ignition and fl ash back. Prevention of hot spots is one ofthe challenges associated with running an engine on hydrogen, which is further exacerbateddue to the wide fl ammability range.

Small Quenching DistanceHydrogen has a smaller (0.64 mm) quenching distance than that for gasoline (~2 mm).Consequently, hydrogen flames travel closer to the cylinder wall than other fuels beforeextinguishing. Thus, it is more difficult to quench a hydrogen flame than a gasoline flame.The smaller quenching distance can also increase the tendency for backfire since the flamefrom a hydrogen–air mixture can more readily pass a nearly closed intake valve, than ahydrocarbon–air flame.

Auto ignition TemperatureThe auto ignition temperature is the minimum temperature required to initiate self sustainedcombustion in a combustible fuel mixture in the absence of an external ignition.For hydrogen, the auto ignition temperature is relatively high—585oC. This makes it difficultto ignite a hydrogen–air mixture on the basis of heat alone without some additional ignitionsource. The auto ignition temperatures of various fuels are shown in Table 1.3. Thistemperature has important implications when a hydrogen–air mixture is compressed. Infact, the auto ignition temperature is an important factor in determining what maximumcompression ratio an engine can use, since the temperature rise during compression isrelated to the compression ratio. The temperature should not exceed the auto ignition temperatureof hydrogen to avoid premature ignition. Thus, the absolute final temperaturelimits the compression ratio. The high auto ignition temperature of hydrogen facilitateshigher compression ratios than those in hydrocarbon engines. The higher compressionratio is important, since it is related to the thermal efficiency of the system. However, thedrawback of a high auto ignition temperature is that hydrogen is difficult to ignite in acompression ignition or diesel engine because the temperatures needed for these types ofignitions are relatively high.

High Flame SpeedAt stoichiometric ratio, hydrogen flame speed (3.46 m/s) is nearly an order of magnitudehigher (faster) than that of gasoline (0.42 m/s). Hence, due to the high flame speed,hydrogen engines can more closely approach the thermodynamic engine cycle. However,

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at leaner mixtures, the flame velocity decreases significantly.

Hydrogen EmbrittlementConstant exposure to hydrogen causes hydrogen embrittlement in many materials, whichcan lead to leakage or catastrophic failures in both metal and non-metallic components.Factors known to influence the rate and severity of hydrogen embrittlement includehydrogen concentration, purity, pressure, temperature, type of impurity, stress level,stress rate, metal composition, metal tensile strength, grain size, microstructure, and heattreatment history. Additionally, moisture content in the hydrogen gas may lead to metalembrittlement through the acceleration of the formation of fatigue cracks. Chapters 10 and16 discuss various embrittlement aspects in detail.

PRODUCTION

Indian scenario

Steam Methane Reforming of Natural Gas

Steam methane reforming (SMR) is the most common and least expensive method ofproducing hydrogen (almost 48% of the world’s hydrogen is produced from SMR). There aretwo basic steps in steam methane reforming. The first one involves the mixing of methanewith steam to produce a gaseous mixture that is mostly hydrogen with about 12% CO and10% CO2. This process occurs at about 800o C. The next step is called water gas shiftreaction which involves combining the carbon monoxide with water to produce hydrogen gasand carbon dioxide. The shift conversion may be conducted in either one or two stagesoperating at three temperature levels. High temperature (350°C) shift utilizes an iron-basedcatalyst, whereas medium and low (205°C) temperature shifts use a copper based catalyst.Assuming a 76% SMR efficiency coupled with CO shift, the hydrogen yield from methaneon a volume is 2.4:1. This process results in mostly CO2 and H2 as gas outputs with smalleramounts of carbon monoxide, methane, water and other gases. CO is removed by absorptionor membrane separation. Hydrogen is separated from carbon dioxide and other gases usingPressure Swing Absorption (PSA), which results in pure (>99.9%) hydrogen.

Coal Gasification

The first step in hydrogen production from coal is to basify it by combining it with steam andoxygen to produce a raw gas mixture. After the ash is removed, the raw gas is de-sulfurizedto produce synthetic gas (often called “syn gas”) which contains mostly hydrogen, carbonmonoxide and carbon dioxide. Carbon monoxide is converted to carbon dioxide andhydrogen using water gas shift reaction and hydrogen is separated from the carbon dioxideusing PSA (Pressure Swing Absorption) or other separation techniques. The drawback in thecost of hydrogen produced by coal gasification is the cost of CO2 abatement. Hydrogenproduction from gasification releases about 38 kg of carbon per GJ of hydrogen.

Electrolysis of Water

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A small amount (4%) of the world’s hydrogen is produced by electrolysis of water.Electrolysis process uses electricity to split water into hydrogen and oxygen atoms. In theseprocess two electrodes, one positive and another negative, are submerged in pure water thathas been made more conductive by the addition of an electrolyte. When direct current (DC) isapplied, hydrogen bubbles up at negatively charged electrodes and oxygen at positivelycharged electrode. Alkaline water electrolysis is the most common technology used in largerproduction capacity units (0.2 kg/day). Electrolysis is an energy intensive process. The powerconsumption at 100% efficiency is about 40 kWh/kg hydrogen; however, in practice it iscloser to 50 kWh/kg. Since electrolysis units operate at relatively low pressures (10atmospheres), higher compression is needed to distribute the hydrogen by pipelines or tubetrailers compared to other hydrogen production technologies. This process offers the potentialto produce hydrogen with almost no pollution or greenhouse gas production. Theenvironmental effects of renewable electrolysis depend on the technique that is used toproduce electricity. Nuclear energy can also produce carbon free electricity that can be usedto split water into hydrogen and oxygen.

International Scenario

Photo electrochemical Water Splitting

Nonporous black silicon photocathode for H2 production by photoelectrochemical water splitting.

Nanostructure Si eliminates several critical problems with Si photocathode and dramaticallyimproves a photo electrochemical (PEC) reaction important to water-splitting. Thenanostructure black Si photocathode's improve the H2 production by providing (1) near-idealanti-reflection that enables the absorption of most incident light and its conversion tophotogene rated electrons and (2) extremely high surface area in direct contactwith water that reduces the over potential needed for the PEC hydrogen half-reaction.Application of these advances would significantly improve the solar H2 conversion efficiencyof an ideal tandem PEC system. Finally, the nanostructure Si surface facilitates bubbleevolution and therefore reduces the need for surfactants in the electrolyte.

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Fermentation:

Hydrogen production from cellulose in a two-stage process combining fermentation andelectrohydrogenesis.

A two-stage dark-fermentation and electrohydrogenesis process can be used to convert therecalcitrant lignocellulosic materials into hydrogen gas at high yields and rates. Fermentationusing Clostridium thermocellum produced 1.67 mol H2/mol-glucose at a rate of 0.25 L H2/L-dwith a corn Stover lignocelluloses feed, and 1.64 mol H2/mol-glucose and 1.65 L H2/L-d witha cellobiose feed. The lignocelluose and cellobiose fermentation effluent consisted primarilyof: acetic, lactic, succinic, and formic acids and ethanol. An additional 800 ± 290 mL H2/g-COD was produced from a synthetic effluent with a wastewater inoculum (fermentationeffluent inoculum; FEI) by electrohydrogensis using microbial electrolysis cells (MECs).Hydrogen yields were increased to 980 ± 110 mL H2/g-COD with the synthetic effluent bycombining in the inoculum samples from multiple microbial fuel cells (MFCs) each pre-acclimated to a single substrate (single substrate inocula; SSI). Hydrogen yields andproduction rates with SSI and the actual fermentation effluents were 980 ± 110 mL/g-CODand 1.11 ± 0.13 L/L-d (synthetic); 900 ± 140 mL/g-COD and 0.96 ± 0.16 L/L-d (cellobiose);and 750 ± 180 mL/g-COD and 1.00 ± 0.19 L/L-d (lignocellulose). A maximum hydrogenproduction rate of 1.11 ± 0.13 L H2/L reactor/d was produced with synthetic effluent. Energyefficiencies based on electricity needed for the MEC using SSI were 270 ± 20% for thesynthetic effluent, 230 ± 50% for lignocellulose effluent and 220 ± 30% for the cellobiose

effluent. COD removals were ∼90% for the synthetic effluents, and 70–85% based on VFA

removal (65% COD removal) with the cellobiose and lignocellulose effluent. The overallhydrogen yield was 9.95 mol-H2/mol-glucose for the cellobiose.

Solar Thermal Water SplittingThe High-Flux Solar Furnace reactor is used to concentrate solar energy and generatetemperatures between 1,000 and 2,000 degrees Celsius. Ultra-high temperatures are requiredfor thermo chemical reaction cycles to produce hydrogen. Such high-temperature, high-flux,solar-driven thermo chemical processes offer a novel approach for the environmentallybenign production of hydrogen. Very high reaction rates at these elevated temperatures giverise to very fast reaction rates, which significantly enhance production rates and more thancompensate for the intermittent nature of the solar resource

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STORAGE

Compressed Gas Storage

Compressed gas storage of hydrogen is the simplest storage solution. The equipmentsrequired are a compressor and a pressure vessel. The main problem with compressed gasstorage is the low storage density which depends on the storage pressure. High storagepressure results in higher capital and operating costs. At low production rates, the capital costof the pressure vessel dominates while at higher volumes the critical factor is the electricitycost for compression. As storage time increases, the capital cost of the pressure vessel beginsto dictate the cost. One option is to increase the operating pressure of the system (smaller,lower cost tank; higher compressor capital and compression running costs): for short times,there is a balance between these costs, at longer times the capital cost reduction is thedominant factor resulting in an optimum at maximum operating pressure.

Liquid Hydrogen Storage

Liquefaction is done by cooling a gas to form a liquid. A combination of compressors, heatexchangers, expansion engines, and throttle valves are used in liquefaction processes toachieve the desired cooling. The simplest liquefaction process is the linde cycle or JouleThompson expansion cycle. In this process, the gas is compressed at ambient pressure, andthen cooled in a heat exchanger, before passing through a throttle valve where it undergoes anisenthalpic Joule-Thompson expansion, producing some liquid. This liquid is removed andthe cool gas is returned to the compressor via the heat exchanger. An alternative to thisprocess is to pass the high-pressure gas through an expansion engine which consists of anisothermal compressor, followed by an isentropic expansion to cool the gas and produce aliquid. It is used as a theoretical basis for the amount of energy required for liquefaction andalso to compare liquefaction processes. In practice, an expansion engine can be used only tocool the gas stream, not to condense it because excessive liquid formation in the expansionengine would damage the turbine blades.

Metal Hydride Storage

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Metal hydrides store hydrogen by chemically bonding it to metal or metalloid elements andalloys. Hydrides are unique because they can absorb hydrogen at or below atmosphericpressure and then release at significantly higher pressures when heated—the higher thetemperature, the higher the pressure. There is a wide operating range of temperatures andpressures for hydrides depending on the alloy chosen. Each alloy has different performancecharacteristics, such as cycle life and heat of reaction. When the partial pressure of hydrogenis increased, it dissolves in the metal or alloy and then begins to bond to the metal. During thebonding period the equilibrium or plateau pressure remains constant from the time that 10%of hydrogen has been stored until about 90% of the storage capacity is reached. After the 90%point, higher pressures are required to reach 100% of the hydride storage capacity. Heatreleased during hydride formation must be continuously removed to prevent the hydride fromheating up. If the temperature is allowed to increase the equilibrium pressure will increaseuntil no more bonding occurs. If hydrogen is being recovered from another gas, somehydrogen can be allowed to escape or blow off; taking away any contaminants that did notbond to the hydride. To recover the hydrogen from the metal hydride, heat must be added tobreak the bonds between the hydrogen and the metal. Again, the higher the temperature, thehigher the release pressure. Initially the pressure of the gas is high as any free hydrogen isreleased, and then the pressure plateaus as the hydride bonds are broken. When only about10% of the hydrogen remains the equilibrium pressure drops off. This last bit of hydrogendissolved in the metal matrix is difficult to remove, and represents strongly bonded hydrogenthat cannot be recovered in the normal charge/discharge cycle. Metal hydride storage isperceived to have no economy of scale (high capital cost of storage alloy). So it does notcompete with other options at high production rates or long storage times, but may be ideal atlow flow rates and short storage times. Since it is considered as the safest storage option, thismakes it a leading candidate for on-vehicle storage, subject to achieving satisfactory energydensities.

Underground Storage

Depending on the geology of an area, underground storage of hydrogen gas may be possible.Underground storage of natural gas is common and underground storage of helium, whichdiffuses faster than hydrogen, has been practiced successfully in Texas. For undergroundstorage of hydrogen, a large cavern or area of porous rock with an impermeable cap rockabove it is needed to contain the gas. A porous layer of rock saturated with water is anexample of a good cap rock layer. Other options include abandoned natural gas wells;solution mined salt caverns, and manmade caverns. Underground storage is the cheapestmethod at all production rates and storage times (due to low capital cost of the cavern):biggest cost item is electricity cost for compression; relatively insensitive to changes inproduction rate and storage time; additional transport cost to consumer may be high, butunderground storage may have applications for seasonal storage or security of supply.

UTILIZATION

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Using hydrogen in Internal Combustion Engines

Conventional combustion engines require modification to burn hydrogen. The provencommercially available technology to use natural gas in combustion engines is similar to theone needed to use hydrogen. Hydrogen combustion releases no carbon monoxide,hydrocarbons, particulate pollution, or carbon dioxide but there is emission of nitrogen oxideswhich are very low. Use of hydrogen in an internal combustion engines has several potentialadvantages, like increased efficiency (25%-30%), a wide range of ignition limits, and highflame and diffusion speeds.

Using hydrogen in fuel cells

Hydrogen and oxygen merge in a fuel cell, forming water and releasing electricity. Becausefuel cells require no lubricating oil, and no combustion to generate high temperatures thatlead to the formation of nitrogen oxides, fuel cell-powered electric vehicles offer the cleanestway of using hydrogen (they are zero-emission vehicles). Fuel cells are two to three times asenergy efficient as combustion engines. An internal combustion engine loses more than 80%of energy it generates, either as waste heat or friction. When a hydrogen fuel cell is used, theenergy loss is 40 to 60%, so the percent of energy that is delivered as movement is muchgreater. However, various technological hurdles must be overcome before fuel cells can 10compete effectively, in terms of overall performance and cost, with internal combustionengines in automotive applications. Fuel cell demonstration projects now under way aroundthe world will likely yield improved solutions to these technical challenges.

Hydrogen Electric Hybrid vehicles

By combining onboard engines or fuel cells that generate power with electrical systems thatstore power, electric hybrids may offer greater market potential than vehicles powered solelyby single systems. Demonstrations of hybrid technology, involving hydrogen, indicate thatthese vehicles may be lighter, smaller, more versatile, and offer better performance thanvehicles running solely on hydrogen engines, fuel cells, or batteries. There are two primarytypes of hydrogen hybrid electric vehicles that are proposed ─ parallel and series. In parallelhybrid vehicle, both electric motor and the ICE are coupled through the transmission to thewheels. In series, the ICE is not connected to the wheels and the power to the wheels comesfrom the electric motor. The overall efficiencies for these vehicles are estimated at 39% forICE series version and 35% for the fuel cell series version. Efficiency of series hybrid ICEvehicles ranges between 38 and 39%, for parallel hybrid ICE vehicles it is 25%.

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HYTHANE

Hydrogen and methane are the two main gaseous energy carriers and also are widely used in the chemical industry. Each has independently attracted broad commercial interest and is highly valued. Hydrogen is regarded as the cleanest fuel. The hydrogen-based economy is described as a developing trend of future society with zero carbon emissions (Turner, 2004), as it is clean and sustainable compared with the current fossil fuel-based economy. However, the development of a hydrogen-based society has been restricted mainly by its cost-intensive processes and operations. Methane is being commonly used, not only in the chemical industry but also in transport as compressed natural gas (CNG), which has been regarded as the clean energy carrier in comparison to gasoline or diesel.

A mixture of hydrogen and methane is called hythane, which was trademarked by Eden (2010), HCNG or methagen (Ljunggren and Zacchi, 2010). Typically, the suggested hydrogencontent in hythane is 10–25% by volume (Fulton et al., 2010). By combining the advantages of hydrogen and methane, hythane is considered one of the important fuels involved in achieving the transition of technical models from a fossil fuel-based society to a terminal Hydrogen based society. Hythane has been used commercially as vehicle fuel in the USA andIndia (Das et al., 2000; Eden, 2010) and has also received much attention from many individual companies such as Volvo, Fiat, Air products and others.

PROPERTIES

When used in an internal combustion engine, even the addition of small amount of hydrogen to natural gas (5-30% by volume) leads to many advantages, because of some particular physical and chemical properties .They developed a new HCNG premixed system which wasused to blend desired amount of hydrogen into CNG. According to Dalton’s partial pressure law, hydrogen fraction was decided by the partial pressure of these two fuels in HCNG tank. The influence of gas composition on engine behaviour can be adequately characterized by Wobbe index. If the Wobbe index remains constant, change in the gas composition will not lead to a noticeable change in the air-fuel ratio and combustion rate. The overall comparison of properties of Hydrogen, CNG, 5% HCNG blend is given in tabs. 1 and 2 show the characteristic values of the HCNG fuels with different hydrogen fractions. Also, these confirm that the properties of HCNG lie in between those of hydrogen and CNG. There are a number of unique features associated with HCNG that make it remarkably well suited in principle to engine applications. Addition of hydrogen increases the H/C ratio of the fuel. A higher H/C ratio results in less CO2 per unit of energy produced and thereby reduces greenhouse gas emissions. When excess air ratio is much higher than the stoichiometric condition, the combustion of natural gas is not as stable as HCNG. The problem encountered using natural gas is that the engine will experience incomplete combustion (misfire) before sufficient NOx reductions are achieved. Adding hydrogen to the fuel extends the amount of charge dilution that can be achieved while still maintaining efficient combustion .Hydrogen

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also has a very low energy density per unit volume and as a result, volumetric heating value of the HCNG mixture decreases.

PRODUCTION

INDIAN SCENARIO

H-CNG requires blending of hydrogen and natural gas. While CNG is available in the city, hydrogen has to be produced. The cost of hydrogen production is high. There are various processes by which hydrogen can be produced. At the Dwarka station, hydrogen for H-CNG fuel is being produced through electrolysis. Electrolysis is the decomposition of water into hydrogen and oxygen. The hydrogen produced is blended with CNG to fuel vehicles. In addition to the electrolyser, the station has a compressor along with a buffer storage facility. The station which will enable the IOC to continue its R&D for use of hydrogen as a transport fuel has capacity to fuel nearly fifteen three-wheelers. Initially, CNG vehicles will be targetedwhich will run on a mixture of hydrogen fuel with little modification.

Hythane meets from Euro I to Euro V emission standards. Says John Nadeau, business development manager, Hythane company, ‘Regarding the engine modifications, the electronics in the engine will have to be re-tuned to take advantage of the lower emissions of hythane. This is only a software modification, and does not require any change in hardware toan existing natural gas engine.

INTERNATIONAL SCENARIOThrough the pyrolysis process, developed by Eden with the University of Queensland and which Eden now owns 100%, and which is being commercialised in Colorado, USA at Hythane Company’s facility, methane (natural gas) is broken down into its constituents of hydrogen gas and carbon, without the production of carbon dioxide. The carbon is produced as a solid as either carbon nano fibres or carbon nano-tubes that each are many times stronger, in certain applications, than steel, whilst each also has a great a capacity to conduct both electricity and heat.

Low-cost hydrogen production without the production of carbon dioxide as a by-product that could help facilitate the more rapid spread of both hydrogen as a vehicle fuel and also Eden’s

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Hythane® technology as an ultra-clean, highly efficient premium blend of hydrogen and natural gas that it is marketing in India and USA.

Additionally, the only other major by-product from Eden’s pyrolysis process is hydrogen, the real cost of which will be dependent upon the value of the carbon produced. The quantity of hydrogen produced will be 33.33% (by weight) of the quantity of carbon produced. This hydrogen can be either captured and fed into the various hydrogen/Hythane® applications that Eden has been developing around the world, with the intention of accelerating the commercial rollout of these downstream hydrogen applications based on the prospect of relatively low cost hydrogen, or else it can be used to help fuel the pyrolysis reactor.

There are various methods of hydrogen production; however, some of them are not especiallyrelevant in the UK context e.g., geothermal energy. Therefore, this analysis will be restricted to the production sources, shown in Fig. 1. Renewable electricity, biomass energy crops, suchas short rotation coppice SRC, and miscanthus were identified the major potential renewable hydrogen energy sources for UK 1,3. The hydrogen production technologies, currently at research and demonstration stage e.g., photosynthesis, fermentation, photochemi-cal, and thermochemical processes could be important in future. The cost of different renewable hydrogen fuel options, including distribution and 5% profit margin, by the year 2020 is shown in Fig. 2. The cost of supplying renewable hydrogen from wind or biomass resources are likely to lie above the current pump price of untaxed petrol and diesel, though some costs are very close to this level. It is also expected that, based on mature technologies, the production costs of hydrogen from biomass will be lower than hydrogen from wind electricity. The production costs of hydrogen from biomass may be close to those of hydrogenproduced from the steam reforming of natural gas. However, GHG and other emissions are likely to be higher for hydrogen produced from biomass than that produced from wind energy.

STORAGE

Carbons with slitlike pores can serve as effective host materials for storage of hythane fuel, a bridge between the petrol combustion and hydrogen fuel cells. We have used grand canonical Monte Carlo simulation for the modeling of the hydrogen and methane mixture storage at 293K and pressure of methane and hydrogen mixture up to 2 MPa. We have found that these pores serve as efficient vessels for the storage of hythane fuel near ambient temperatures and low pressures. We find that, for carbons having optimized slitlike pores of size H 7 Å (pore ≅width that can accommodate one adsorbed methane layer), and bulk hydrogen mole fraction ≥0.9, the volumetric stored energy exceeds the 2010 target of 5.4 MJ dm-3 established by the U.S. FreedomCAR Partnership. At the same condition, the content of hydrogen in slitlike carbon pores is 7% by energy. Thus, we have obtained the composition corresponding to ≅hythane fuel in carbon nanospaces with greatly enhanced volumetric energy in comparison to the traditional compression method.

Storage vessels with pressure capabilities ranging from 3,600 to 10,000 psi, (25 to 69 MPa) are available in both cylindrical and spherical configurations. All tanks are manufactured to ASME pressure vessel standards and are approved for Hythane® use.

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UTILISATION

INTERNATIONAL SCENARIO

Results of a test project for the US electricity market show that a 400kW Cummins diesel generator can run on a mixture of Eden Energy’s Hythane (a hydrogen-CNG mix) and diesel fuel to reduce the cost of electricity production from 10.97 to 6.5 Rupees per kilowatt hour (US$0.26 to $0.15 per kWh). The savings result from a 78% reduction of diesel in the fuel mix.

In tests performed at Eden’s Hythane Company test facility in Colorado, US, a dual-fuel kit was developed to enable the generator to run on a combination of petroleum diesel and either natural gas or Hythane. The natural gas and diesel mixture also showed a significant cost decrease (US$0.26 to $0.21 per kWh). Savings were calculated using recent prices for naturalgas and petroleum diesel in India.

Products like compressors, dispensers in bunks, Optiblend, hythane reformers are the devices which could be used from hytane. Every project based on hythane is unique.

INDIAN SCENARIO

It is advantageous for India to use the existing CNG infrastructure for investigating the feasibility of using HCNG as an automotive and gain experience in handling the new fuel. Furthermore, no major engine modifications are required. Government of India has taken decision to treat up to 20% HCNG blend on par with CNG. Government has also constituted a committee to frame regulations for HCNG blends above 20% hydrogen. ISO standards for HCNG and hydrogen kit component testing are being framed in ISO.

A number of research and development programs have been initiated on the use of H2-CNG blends with the Ministry of New of Renewable Energy (MNRE), Automotive Research Association of India (ARAI) and automobile manufacturers R&D centre of Indian oil corporation has taken major steps towards using HCNG as a fuel in automotive engines. Numerous experiments were conducted in three - wheelers with different HCNG blends and 18% HCNG blend is selected for further optimization. Field trials are in progress to study the long term effect of HCNG fuel. Vehicle optimization for suitable HCNG blends in LCV and buses are in progress. Further experimental optimization is in progress at ARAI to convert thedeveloped CNG injection engine to run on HCNG blends and to achieve Euro-IV norms.

EFFECTS OF HCNG ON DIESEL ENGINE EMISSIONS Considering emissions, when HCNG fuel is compared with gasoline and diesel it appears to be a very appealing alternative fuel. When compared with diesel, it nearly eliminates the particulate matter which is often of great concern. Methane has a relatively stable chemical structure, therefore making it difficult to reduce emissions by after treatment. For this reason, the engine fueled with HCNG has a large advantage regarding the hydrocarbon emissions

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than that of CNG fueling. Probably the largest advantage to running the engine on lean burn is that it has the ability to greatly reduce the NOx emissions. The reduction in NOx emissionsare due to the increased airflow which causes the engine to run at a lower temperature, therefore reducing the NOx emissions. Emissions can also be improved with the addition of hydrogen. Compared to pure natural gas, HCNG reduces the HC emissions, which is in part due to the increased combustion stability that comes with the addition of hydrogen. However,due to the increased temperature and combustion duration that accompanies the hydrogen addition, an increase in NOx emissions is observed [6]. A report which has an experimental investigation and reinforced with Figure1, Figure 2 an Figure 3; mentioned that, when excess air ratio changed from 1.2 to 2.0, NOx emission could research to an extremely low level. When excess air ratio was about 1.8, maximum cylinder pressure and maximum heat release have got more significance rise due to hydrogen addition compared to excess air ratio was 1.2. It has been suggested that, when adding more than 20% volume into CNG, lean mixture combustion and ignition timing optimization could significantly decrease NOx emission and maintain relatively higher thermal efficiency under certain fixed engine conditions[8]. Figure 1 and 2 shows the gas consumption and green house gases emissions for different contents of hydrogen in HCGN and local emissions of different volumes of hydrogen in HCNG, respectively.

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