This application note defines some of the terms associated with use of transducers and electrical equipment in areas which are defined as hazardous by national rating agencies. It also outlines Setra products which have Factory Mutual approvals for use in hazardous areas.
Explosion-Proof
“Explosion-proof” products are capable of containing an explosion. The term “explosion-proof” does not indicate that the product is capable of withstanding an external explosion, but only of withstanding an internal explosion without allowing flames or hot gases to escape from the transducer housing to trigger an explosion in the surrounding atmosphere.
The “explosion-proof” term is assigned to those products which are certified by the national rating agencies such as Underwriters Laboratories and Factory Mutual Research after meeting their specifications and passing their tests. Unless certified by one of these agencies, the product does not meet the “explosion-proof” requirements of the National Electrical Code.
Intrinsically Safe
“Intrinsically safe” products receive their classification because their electrical power usage is below the level of power required to set off an explosion within a given hazardous area. In addition, “intrinsically safe’” products are incapable of storing large amounts of energy which might spark an explosion when discharged.
Hazardous Areas
Both national rating agencies, as well as the American National Standards Institute adhere to the same definitions of what contributes a hazardous area. These areas are defined as Class I (combustible gas and liquids), Class II (combustible dust), and Class III (combustible fibers). Class I is subdivided into groups A (acetylene), B (Hydrogen and butadiene), C (diethyl ether, ethylene, isoprene, and UDMH), and D (acetone, gasoline, lacquer solvent, styrene, propane, and natural gas). Class II is divided into Groups E (metal dust), F (carbon black, coal, and coke), and G (flour, starch, and grain dusts).
All classes include two divisions. Division I covers electrical equipment directly exposed in an explosion atmosphere of the material of a specific group. Division II covers electrical equipment in an explosive atmosphere only when accident or fallout occurs, or in a properly vented direct exposure.
Qualification for a rating automatically qualifies the equipment for a lower class and group. For example: Class I equipment can be used in Class II and Class III applications with no restrictions.
An “explosion-proof” rating is given only to a single piece of equipment for a specific class, division, and group. Equipment installation is the sole responsibility of the end user, and the National Electrical Code clearly defines the requirements of this installation. For example, a piece of equipment can carry a Class I rating and qualify only for a Class II rating after installation and inspection if the installation is not up to the original rating requirements. The National Electrical Code allows no modification of the rated equipment.
A single piece of equipment, a system, or parts of a system can receive an “intrinsically safe” rating for a class, group, and division. The rating agencies usually test the equipment as a system, and all parts of the system receive the highest class and group reached by the system regardless of any previous “explosion-proof” rating. The entire system also receives a collective rating, which will generally be that of the lowest rated piece within the system. If the system is not modified by the end user, it retains the rating. The end user must install the equipment as supplied, and installation procedures are not specified by the National Electrical Code.
Reference: National Electrical Code of the American National Standards Institute
CUSTOM TRANSDUCER SOLUTION HELPS UNIT INSTRUMENTS REDUCE SPACE, INCREASE RELIABILITY OF NEW GAS FLOW CONTROL PANEL
Retooling for the next generation of wafer processing equipment makes cleanliness in semiconductor fabrication more critical than ever. It will also improve the efficiency of IC chip production by processing more 300mm (12-inch) diameter wafers than 200 mm (8-inch) diameter wafers in each process load. A self-contained, automobile-sized unit called a semiconductor process tool handles the complete operation of fabricating patterns on wafers, from the loading of pure silicon wafers to outputting a patterned wafer.
Due to the costly premium on workspace for these process tools, wafer fabrication laboratories are telling process tool makers to minimize any increase in their tool size, while accommodating their redesign for larger loads of 300 mm wafers. In response, the fabrication support industry is seeking ways to reduce the volume of all subsystems and components where possible, while simultaneously increasing their reliability to reduce the cost of downtime.
A semiconductor process tool contains many subsystems. Key examples are wafer transporting, loading chamber, wafer process chamber, gas delivery system, and vacuum system. Specialized subsystems include: light projection systems (photolithography tool), plasma generator (plasma etch/CVD), ionization system (ion implant) and coat/develop system (tracking system).
The gas delivery system is critical to the IC pattern development and must deliver clean and controlled gases in a reliable and maintainable manner. Although taking up only 10% to 20% of the process tool volume, any reduction in the size of the gas delivery system is beneficial. This reduction helps offset the necessary expansion of other process tool components for the 300 mm wafer production, such as wafer transport and the process chamber.
In response to present retooling pressures for compactness, cleanliness and easy maintenance, manufacturers have devised a gas delivery system based on gas sticks constructed in the form of channeled stainless steel blocks. These gas stick designs are referred to as top-mounted or flat-bottom systems. The gas flow control components need only be attached directly to the channeled block on one side to complete the gas flow channels that are drilled into the blocks. The ability to better drill channels into stainless steel blocks and improvements made in metal seals over the past 20 years, have made this approach to gas stick design viable.
Unit Instruments, Inc., of Yorba Linda, California, a leading manufacturer of mass flow controllers, ultra-high purity gas isolation boxes, and ultra clean gas panels for semiconductor processing tools, recently introduced its own version of this gas stick design: the Z-Bloc Modular Gas System. This top-mounted gas stick design not only addresses volume reduction issues, but utilizes seals and components that make it extremely compact, clean and accurate.
Pressure sensors are key components in any gas flow control system. When the idea for the modular gas system was developed, Unit began working with Setra Systems, Inc., of Boxborough, Massachusetts, a designer and manufacturer of highly accurate capacitive-based pressure sensors. David Sheriff, Vice President and General Manager of the Z-Bloc Modular Gas Group, said, “Setra’s involvement in the early research and development of the Z-Bloc, and their willingness to work with us and adapt their product to fit our needs, allowed us to enhance the cleanliness, accuracy and compactness of the product.”
Tiago Anes, National Sales Manager at Setra, explained that working with a customer in the development stage of their product and providing a customized transducer solution is far from unusual for Setra. “Before spending millions of dollars, our customers generally need the assurance that the solution we provide will meet their requirements,” he said. “The amount of time varies, but we are quite accustomed to working with them well before their product enters final development and full production. In addition, we cater to many different industries and provide a tremendous volume of custom products,” he added. “If you look at our top customers, probably seven out of ten are using products that were customized to meet their specialized requirements.”
Before explaining in greater detail how Setra’s custom solution played such a key role in the development of the Z-Bloc, it is important to understand how the design and characteristics of the Z-Bloc itself will accommodate the current demands of semiconductor process retooling – that is, increased reliability with decreased component size.
First, Z-Bloc makes use of 316L VIM/VAR stainless steel for its block with its internal channels passivated by a chromium oxide layer to minimize specialty gas corrosion. Components on a single “stick” are top-mounted and consecutively positioned along it’s extended steel block. The “in” and “out” ports of each component are positioned to the block’s internal “V-shaped” channel configuration (see Figure 1). This allows internal connections of each neighboring component to complete the flow path through the gas stick and eliminates the need for the space required for tubing and fittings. As a result, the size of the gas panel decreases up to 75%. This configuration still allows access to each component directly. Mounting and removing components require only a hex key “Allen” wrench. With direct access to components, it is also possible to make repairs simply by removing only the damaged component, thereby reducing downtime. Since component mounts are standardized, the Z-Bloc design is able to preserve the design flexibility inherent in conventional welded systems, in which the user has the flexibility to position components anywhere on the stick.
Second, increased reliability depends on improving the intricate sealing techniques of conventional face seal fittings. Unit developed Z seal joints which are effectively sealed simply by tightening four socket-head capscrews without any complicated tightening sequence or torquing. In the sealing process, both the component mount and the block incorporate machined glands, which compress a malleable nickel seal to produce a leak-free system. Under installation, the seal produces no particles greater than 0.1 microns and less than 10 particles greater than 0.02 microns. Furthermore, these particles are typically purged out of the system in less than one minute.
Unit Instruments incorporates components of high stability, accuracy and cleanliness into their Z-Bloc Modular Gas System to enhance reliability. “Pressure transducers were critical and Setra’s Model 215 Ultra High Purity Pressure Transducer offers the kind of stability, accuracy and cleanliness that ensures our highest quality product,” states Sheriff. “And, the Model 215 offers superior stability and accuracy of a quarter percent full scale, which goes a long way to reducing maintenance downtime to recalibrate.” According to Anes, “We modified the 215 pressure transducer for Unit by welding the transducer to a flange, so that it would easily mount to the Z-Bloc.” Eric Redemann, Technical Director at Unit Instruments, said, “Setra’s willingness to redesign their pressure transducer to adapt to the Z-Bloc also enhances our product for our customers, since they see that more component manufacturers support our product.”
The Model 215 incorporates Setra’s patented variable capacitance sensor technology, which features a 316L stainless steel diaphragm and an insulated electrode plate. A variable capacitor is formed between the diaphragm and the electrode plate. When pressure is applied, it causes a slight deflection of the diaphragm which decreases the capacitance. The change in capacitance is detected and converted to a highly accurate linear analog signal by Setra’s unique custom integrated circuit, which utilizes a patented charge balance principle. The pressure transducer’s output signal is fed to the process tool computer, which monitors the status of all gas sticks. With such monitoring, the computer can shut down the wafer processing when pressure status throughout the gas delivery system implies a malfunction. If a malfunction occurs, the repair technician can analyze the pressure status and determine the location of the component failure. The repair technician can also view local pressure readings on Setra’s swivel-base LD330 display, which is directly mounted to the Model 215 Pressure Transducer.
With the cooperative help of Setra in modifying its high purity, stable, and accurate transducers to the Z-Bloc design, Unit is better able to fulfill the semiconductor retooling needs by producing a leading-edge, compact gas delivery system. According to Anes, “The cooperative effort, as was exhibited by Unit Instruments and Setra, is the key to future technological innovations and improvements in this industry.”
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SYNOPSIS
The main condition that all countries have agreed about the future of the earth is to keep it clean and free of pollution .The solution is to use alternate fuels and among them Hydrogen would be a good choice. Hydrogen can be produced in different ways. Hydrogen should be produced in such a way to obtain maximum efficiency and should be at a affordable cost. Various strategies are adopted to obtain the above conditions. There are different methods for Hydrogen storage and distribution and various strategies should be adopted to obtain optimum condition. Hydrogen has got wide variety of applications. They are stationary applications, transportation applications, portable applications etc… Here we discuss about the strategies to develop Hydrogen as an energy carrier.
INTRODUCTION
The main condition that all countries have agreed on about the future of the earth is to keep it clean and free of pollution. For using energy and still keeping the earth clean, the final solution is to use alternative fuels. These fuels must satisfy at least three requirements:
Being clean, meaning that no by-products harmful to the environment will be produced
Being abundant
Being economic
Hydrogen, as an alternative fuel, would be a good choice in this respect. Using Hydrogen as alternative fuel rests mainly upon the fact that it is both abundant and not harmful to the environment (its oxidation gives water). The only problem seems to be the fact that hydrogen may not be produced so easily. Hydrogen production is defined as a series of processes from its generation from an available energy source, its purification and other conditioning for subsequent distribution and use. From the following figure Hydrogen is most abundant element in the earth. It is the main element in plants and water. Hydrogen occupies almost two third of water composition and half of plants composition.
F
Figure 1.Relative abundance of Hydrogen
HYDROGEN PRODUCTION
Figure 2. Hydrogen production methods
CENTRALIZED HYDROGEN PRODUCTION
A general issue encountered with centralized hydrogen production is hydrogen transport to the point of use. Of the three primary modes of transportation, pipeline, high pressure and liquid road transport ,the third one can be considered as a part of production process.
CHEMICAL CONVERSION
Large-scale industrial production from the full range of fossil energy sources coal, oil natural gas is considered as commercially mature technology. This includes a wide range of gas phase processes referred to as gasification processes for oil and coal as well as catalytic processes, including steam reforming, auto thermal reforming, natural gas and light hydrocarbons. Important post processing steps include water gas shift (WGS) process and hydrogen separation and purification using pressure swing absorption (PSA). In biomass gasification co2 capture must be given emphasis because of the co2 intensity of coal based hydrogen production, also coal may offer prospects for novel options for the integration of mining, hydrogen production and carbon sequestration.
ELECTROLYSIS
Centralized hydrogen production through electrolysis is a niche application, since electricity is generally more easily transportable than hydrogen and electrolysis works well in distributed applications. Large-scale electrolysis requires a huge scale up in the size of electrolysers. The largest electrolysers have a capacity of approximately1000kg/day. Its application is fond in association with “standard renewable”, such as offshore wind parks energy. Large scale hydrogen production from renewable electricity could be achieved either by transmission of the dispersedly produced Renewable energy sources (RES) electricity, followed by hydrogen production at a central electrolyser or by dispersed, on site production of hydrogen from (RES) at remote locations with subsequent transportation of hydrogen. High temperature electrolysis is an attractive modification of existing low
temperature electrolysis as it boosts the efficiency of hydrogen production through a reduction of the electricity demand.
THERMOLYSIS
It’s a multi step thermo chemical process that uses high temperature heat to split water into hydrogen and oxygen. The process would convert high temperature heat into hydrogen with 50% efficiency., thereby offering an alternative to electrolysis for renewable hydrogen generation. Thermolysis is proposed in the context of advanced nuclear reactors .The future of the thermolysis is not promising as the practical conversion efficiency is less than 35%. It involves chemical operations involving large inventories of hazardous chemicals. The chemical industry is as far as possible trying to phase out.
PHOTO – ELECTROLYSIS
Photo – electrolysis of water also referred to as photo catalytic water splitting is the combination of photovoltaic (PV) cells with in- situ electrolysis of water. The photovoltaic effect of semiconductor materials is not used to generate electricity as in PV, but to split water electrochemically. Photo – electrolysis and PV are by nature dispersed and much of the cost is associated with the manufacturing of large devices. As electricity is more easily collected than gases which requires additional cover and sealing of the device, the limit capital and maintenance cost for photo – electrolysis will remain higher than PV.
HYDROGEN AS AN INDUSTRIAL BYPRODUCT
In some industrial processes intrinsically emits emit hydrogen as a byproduct and it is released to the atmosphere. This considerable amount of gas is able to cover demands arising in short and medium term.
BENCHMARKS OF HYDROGEN PRODUCTION
1. The pathway energy efficiency
2. The carbon intensity of hydrogen production
3. The cost of delivered hydrogen
4. Hydrogen purity
DECENTRALIZED HYDROGEN PRODUCTION
The big advantage of hydrogen production at the point of use is that it avoids the need for hydrogen transport. In the case of hydrogen production from any hydrocarbon feedstock, the penalty that is paid is that carbons capture and its sequestration is no longer an economically viable option. An additional issue is the need for operation and control of many and small hydrogen production units, requiring such varied things as cheap process control, high safety standards.
CHEMICAL CONVERSION
In the long run hydrogen will be directly delivered through pipelines to filling stations or to fuel cells used in small scale distributed power generation. The decentralized hydrogen production will take the advantage of the existing natural gas infrastructure. Small-scale CHP plants convert natural gas into a hydrogen rich gas whereas the production of hydrogen at the retail site can be done by on-site or forecourt reforming.
ELECTROLYSIS
Hydrogen production using electrolysis is ideally suited for decentralized hydrogen production. It is because electricity is transported easier and cheaper than hydrogen production .The main applications for this mode of production are forecourt hydrogen production for transport, hydrogen production coupled to renewable electricity production in off-grid situations.
SMALL SCALE PHOTOELECTROLYSIS
The potential of photo-electrolysis appears primarily in small scale, stand-alone applications where the cost of the electrolysers would be prohibitively high. Competition would be on the basis of energy cost and system cost will be important as efficiency. The benchmarking of decentralized hydrogen is similar to that of centralized hydrogen production.
PHOTOMICROBIOLOGICAL ELECTROLYSER AS BIOFUEL CELL
`Among the methods for producing hydrogen one promising method is electrolysis of water by sun in the device called photoelectrolyser (Pe). Main problem with photoelectrolyser is that it must be pre-activated so that it can absorb light and decompose water into hydrogen and oxygen. In this case a microbial cell would be used to pre-activate the photoelectrolyser. Theoretical aspects of such combination of photoelectrolyser and microbial cell are called “GREEN ENGINE”.
MICROBIAL CONCEPTS OF GREEN ENGINE
Sulphur-oxidising bacteria (SOB) are a family of bacteria that require oxygen for their growth (aerobic bacteria). SOB can produce sulphuric acid with very low pH values down to one even. A type of these bacteria known as Colourless SOB produces sulphuric acid by either of the reactions given below.
H2S + 2O2 H2SO4
2S0 + 3O2 2H2SO4
Colourless SOB can be found everywhere in the nature and be isolated from almost every aquatic system. A genus of SOB known as Thiobacillus Ferrooxidan is capable of producing 10% concentrated sulphuric acid with pH less than 2.5.
Sulphate reducing bacteria (SRB) that grow anaerobically (no oxygen) are known for their capability of reducing sulphate to sulphide where in absence of metallic ions such as iron they produce H2S gas. SRB may be found everywhere from soil to seawater. Both SRB and SOB are examples of corrosion-enhancing bacteria, which cause a lot of destruction to a country’s economy.
ELEECTROCHEMICAL COCEPTS OF GREEN ENGINE
It is known in electrochemistry that when two dissimilar metals are placed into an electrolyte, an electrochemical galvanic cell with a certain voltage is produced. For instance, if two electrodes of copper and zinc were placed in an aqueous solution with SO-24 (eg, sulphuric acid), they would produce a voltage difference of about 1.1 volts; in case of using other types of electrochemical cells voltages more than 1.2 volts may be reached.
PHOTOELECTROLTSIS OF WATER
A photoelectrolyser is a device that by using sunlight dissociates water into
hydrogen and oxygen, for which 62.3 Kcal must be consumed,
A part of this consumed energy is deposited in hydrogen molecules, as water cannot absorb the ultraviolet radiation that accounts for 50% of the sunlight. To solve this problem, an n-type semi-conductor known as photo anode is used. The photo anode absorbs sunlight and gets excited so that emits electron. The cathode for decomposition of water molecules and hydrogen production will use these electrons:
At the same time, as photo anode has sent off electron and lacks it now, it will attract the soluble hydroxyl ions that are oxidized and oxygen is given off:
Cathode: 2H2O + 2e- H2 + 2OH-
Anode: 2OH- ½ O2 + 2e-
Photo anodes are made up of materials such as Titanium Oxide (TiO2-x). It is very important to note that TiO2-x photo anodes must be “pre-excited” by an external voltage shock of about 0.2 V to become active and ready for electron emission. At IBARAKI national industrial chemistry laboratories in Japan, researchers have found out that if sodium carbonate is added to the water and TiO2 + 0.3% platinum is used as the catalyst, the best result is achieved: with only 0.3 gr of that catalyst, hydrogen with a rate of 0.2 ml. H2/hour will be produced. One tone of such catalyst would produce 75000 liters hydrogen gas (or 100 liters of liquid H2) which is enough for running a car for a distance of 300 Km. The energy efficiency of an advanced electrolyser is 75% where using hydrogen in running an electrical engine-by a fuel cell, for instance- would yield an efficiency of 60% which is much better than internal combustion engines being only 35%
ACTIVATING A Pe BY MICROBIALLY ACTIVATED CELL
In absence of metallic ions, colourless SOB to produce sulphuric acid constantly and naturally may use the H2S produced by SRB as a source. The acid would be used as electrolyte in an appropriate electrochemical cell (like a galvanic cell or an oxygen aeration cell) to produce a voltage of about 1.2 volts. Such a voltage would be high enough to run at lease six Pe`s simultaneously. If we take a galvanic cell having copper and zinc as electrodes and sulphuric acid as the electrolyte, for a copper sulphate and zinc sulphate concentrations of 10 mol/lit, and 0.1 mol/lit, respectively, and a Zn+2/Cu+2 ratio of 0.01, the output voltage of the cell would be 1.16 volts. This means that as long as polarisation is not taking place and the bacteria are alive and active, at least six Titanium oxide photo anodes corresponding to six Pe`s could be running (remember that each photo anode would require a “push” of 0.2 volt whereas the available voltage from an electrochemical cell with microbial electrolyte would be about 1.2 volts).
Calculations show that [9] considering 300 sunny days in a year and a day-length of 12 hours, a surface area of 1 cm2 would receive an energy amount of 0.033 Watts/hour from the sun so that the amount of hydrogen produced by the sun in a Pe having a photoanode area of just 1 cm2 would be 0.01 litre/hour/photoanode surface area. By increasing the photoanode surface area to 4 cm2, the hydrogen then-produced would be about 0.05 lit. H2/hour. On the other hand, if for just one Pe, the photoanode is TiO2-x of the type octahedrite with a density of 3.9 kg/m3 ,a titanium oxide sample of 0.3 gr would have a volume of more than 70 cm3 suggesting that the anode surface area could be taken much more than 1 cm2 so receiving much more sunlight and energy. In this way, six Pe`s working together would receive more energy so that more water could be decomposed and, therefore, more hydrogen would be produced. The oxygen produced in this way could be used for many applications as well.
If a combined microbial cell containing SRB and SOB were used, theoretically they would produce the voltage necessary for running at least six photoelectrolysers simultaneously. This combination of electrochemical cells having microbial electrolytes with photoelectrolysers is defined as a “Green Engine”,
Figure 4. Components of a “Green Engine”
HYDROGEN STORAGE AND DISTRIBUTION
Hydrogen storage and distribution covers the supply chain between the production sites and hydrogen consumption in all kinds of applications. This involves:
All transportation pathways: water, rail, road, and pipeline
All storage option: gaseous, liquid, novel storage media
All storage issues at production sites, local filling stations and transmission sites, in transport applications, stationary systems or portable systems
All kind of fuelling stations
In each case hydrogen management in terms o energy efficiency, environmental friendliness safety, reliability and cost, must be taken into consideration.
HYDROGEN TRANSMISSION TO STATIONARY SYSTEMS
PIPELINES
A strategy has to be found to use these systems for first hydrogen infrastructures and to combine hydrogen production stations of today with new pipelines to create first small hydrogen supply clusters. After 2015 hydrogen will be supplied to the customers by pipeline than making use of road, rail, waterways. Research should be done on new materials, novel construction techniques and gradual adaptation of the existing natural gas grid to 100% hydrogen. Specific work has to be done in terms of safety, risk assessment and low-pressure infrastructure at the end user side. Regulation and standards must be defined and questions of public acceptance should be studied.
LIQUID SUPPLY AND GASEOUS SUPPLY
The strategy to bring hydrogen to the customer includes pathways based on gaseous and liquid hydrogen with the relevant transport and storage constraints. Different energy demands and costs arise when comparing liquefied and pressurized hydrogen: higher specific energy demand and cost for liquefaction than for pressurization on one side and lower specific costs for transportation of liquefied hydrogen on the other side. At the filling station a higher capital investment is necessary for supplying pressurized hydrogen .On the other hand liquid hydrogen supply involves additional energy loss due to boil off. Overall the primary energy and greenhouse (CHG) emission balances have to be evaluated.
STATIONARY STORAGE
Stationary storage means either storage in a secondary distribution center e.g. a cylinder filling center or in a transmission site along pipelines or in a stationary power application above 10 KW where a supply by CHG cylinders become impractical. The possibility to establish underground facilities depends upon regulatory improval, but might be of strategic importance to match hydrogen production and demand and to ensure reliability. Applied research is needed to evaluate long-term behavior of hydrogen confinement.
On the contrary for reasons of safety in enclosed areas, stationary storage based on hydride materials needs to be examined in terms of reactor design for relatively large hydrogen flows. Moreover the management of the supply chain of the hydride materials, including refilling or recycling of the dehydrogenated product needs to be considered.
HYDROGEN SUPPLY FOR TRANSPORT SYSTEMS
FUELLING STATIONS
Hydrogen must be delivered to a car within a few minutes only and has to be safe enough for public self-service operations in various climates and operation conditions. This requires optimization of components such as hydrogen dispensers and nozzles, hydrogen sensors, metrology of hydrogen mass-flow delivered to the vehicle, and basic engineering for rapid refueling and energy management in compression and gas cooling.(CGH2), or cryogenics or boil-off(LH2) , and in heat transfer. This should reflect on the specific hydrogen delivery to the user.
The space requirement for a fuelling station and the scalability of its hydrogen fuelling capacity has to be optimized and anticipated. This may require scalable on-site production units, e.g. electrolysers or reformers and eventually small liquefaction units. All components of future fuelling stations must be compact to avoid complex space requirements. Underground storage must be accepted for future infrastructure. Such important developments call for an evolution of hydrogen regulations and standards and should be driven by the development strategy.
ON-BOARD STORAGE
Storage tanks in current hydrogen vehicles are still bulky. The need for increased driving range (500 to 600 km) with a fuel – cell engine requires an estimate of 5 kg of hydrogen. This corresponds to a LH2 volume of 71 liters or a CGH2 volume of 128 liters at 700 bars and at 20 degree Celsius. In order to confine this H2 quantity in an overall volume smaller than 150 liters, developers have to achieve a volumetric energy density grater than 1.1 kWh/l. For CGH2 storage at 700 bars the filling pressure should exceed 800 bars in order to compensate gas and tank heating for the adiabatic compression. Cryogenic LH2 tank needs further research to reduce size, cost and to minimize and manage boil-off.
Eventually improved storage area may be necessary to improve the net volumetric energy density (kWh/l) and usable gravimetric energy density (kWh/kg) or usable mass fraction (%kgH2/kg) when the overall tank volume and weight is considered. This may be achieved using alternative hydrogen storage media based either on H2 reversible physical or chemical H2 adsorption. The storage system should match further criteria pertaining to car usage in terms of fuel stability.
1. Operating temperature ranging from -40 to 60 degree Celsius
2. Minimum and maximum temperature ranges from –40 to 85 degree Celsius
3. More than 1500 cycles
4. Kinetics and transient response
HYDROGEN SUPPLY FOR PORTABLE SYSTEMS
CYLINDERS AND CATRIDGES
Hydrogen in private customer use requires a new quality of handling, safety and acceptance that includes refilling procedures at special locations or in combination with fuelling stations for vehicles as well as operating small energy converters less than 5 kW. The storage medium consists of CGH2 cylinders or metal hydride tanks. In this case refilling or recyclability of the tank or the storage medium or product is necessary.
Improved storage systems are necessary for micro and mini fuel cells (up to 100 W) where non-refillable cartridges can be used. These cartridges have special requirements regarding specific and volumetric energy density, kinetics, cycle life, temperature stability, interfaces, safety equipments, sensors and test procedures. The storage medium can be CGH2 but chemical hydrides or reversible adsorption/desorption systems based on metal hydrides may be preferred.
REFILLING AND RECYCLING CENTERS
The development of a collection of specific stationary and portable application requires adaptation of existing industrial gas filling plants in order to manage the corresponding cylinder or cartridge logistics. This also needs engineering effort to optimize the refilling process of reversible H2 adsorption/desorption systems based metal hydrides, as well as recycling of chemical hydride byproducts.
STATIONARY APPLICATIONS
Stationary fuel – systems can be either connected to the power grid or stand-alone and through their very high potential efficiencies offer reductions in CO2 emissions. Such systems are likely to be fuelled by natural gas or liquefiable hydrocarbon fuels in the first applications with biofuels and hydrogen coming more important as technology matures. The primary technology development track is for decentralized power applications with a gradual transition from fossil fuels to CO2 neutral fuels.
LONG TERM PERSPECTIVE
By 2050 cheaper oil will no longer be available and all internal reserves will be exhausted. An increasing proportion of primary energy production will be from renewables such as solar, wind, tidal and tidal and biomass possibly supplemented by nuclear, natural gas and coal. We must rely on new energy carriers: biogas or synthetic fuels such as gas-to-liquid products and liquid biofuels. These carriers will complement the main energy vectors electricity enabling optimization of energy efficiency for a range of system scales. A decentralized electricity generation infrastructure powered a broad spectrum of renewable and clean technologies with a strong fuel cell component will have been created. The power network will be largely based upon self-constrained nodes, each consisting of renewable or fuel cell systems. A high value network powered by advanced thermal or nuclear systems, hydropower and buffered wind power and fuel cell systems will support the nodes. Advantages of this decentralized system can arise from lower transmission losses, higher total energy efficiency and improved energy security. Stationary deployment is expected to involve both high and low temperature fuel cells. High temperature fuel cells will be applied where carbon-containing fuels, including pure hydrogen, is available and for large-scale systems, particularly when high value heat is demanded. Low temperature fuel cells will be applied where clean hydrogen is available.
DECENTRALIZED POWER GENERATION
These applications involve long annual operation times. High efficiency and low cycle costs are very important. The possibilities to use combined heat power or trigeneration, low noise, and fuel flexibility are also of great importance as well as reliability and long lifetime. These applications will predominately utilize natural gas or liquefied gases like LPG or LNG, with later introduction of hydrogen and biogas.
RESIDENTIAL 1-10 KW AND COMMUNITY 5-50 KW
The existing technologies will require significant improvement to improve cost and reliability for small residential fuel cells to become competitive in world. Stand-alone units working on liquefied gases, or diesel oil, can offer a particularly important application in remote areas and especially outside the remote world where grid isolation is the norm. For much of the third world fuel cell units of les s than 1kW could be particularly enabling, providing household needs such as communication, lighting and refrigeration using fuels such as liquefied hydrocarbons or for groups of such households using gas from renewably generated hydrogen.
Combined heat and power (CHP) and trigeneration will be important in the developed world. High efficiency fuel-cell micro-CHP appliances for residential and small commercial would reduce the consumption of fossil fuels by up to 50% and emission of CO2 by up to 50%. Such fuel cell micro – CHP appliances in the 1-5kw range have already shown the validity of this concept. All project teams are faced with big challenges concerning the cost and design of key components as well as robustness, durability and reliability of the system.
A community with a large number of households and also some common use of electricity and cooling /heating is well suited for fuel- cell installation. This may be achieved by means of integration of residential systems .The operation time will be longer than for residential fuel cells and the peaks will be more evened out. Grid parallel operation would give better handling of load variations.
PUBLIC AND COMMERCIAL BUILDINGS AND INDUSTRIAL 50 TO 500 KW
This application is an important market for fuel cells in terms of volume and revenue. Several countries are developing plants with these size or even larger. Long operation times are an essential performance target and there will be a strong requirement of combined heat and power operation. High efficiency and use of alternative fuels such as waste gases from industry are important. High temperature fuel cells will probably be most competitive as they offer high efficiency and high value heat especially for industrial processes.
LARGE SCALE, 1MW AND ABOVE
The large fuel cell plants above one megawatt are still far away. A combination with a gas turbine increases the efficiency of the fuel cell process. The demand for high efficiency favors the high temperature fuel cells in this power range. Low temperature fuel cells may be deployed where large volumes of hydrogen are available.
RENEWABLE FUEL CELL APPLICATIONS
Fuel cells play an important role in the conversion of biofuels to electricity at a high efficiency and low emissions. Biofuels can be used in high temperature fuel cells at high efficiency benefiting from the fuel flexibility of the system. A high degree of integration is important for achieving the highest efficiencies and low cost investment. Impurity tolerance and high temperature fuel clean up are important are key aspects for developing these system. Emphasis of the development should be on direct internal reforming in high temperature fuel cells; contaminant tolerance and low temperature fuel clean up
Low temperature fuel cells require processing the raw gas from bio-gasification to hydrogen and low temperature clean up to high purity. Fermentation gas requires low temperature clean up ,high temperature reforming, CO removal and additional clean up before it can be fed into low temperature fuel cell.
Excessive electricity produced by renewable sources can be used to produce hydrogen electrolysis that can be either used for transport or for production of electricity on demand. Reversible fuel cells can provide an efficient storage technology to use it with intermittent renewables. High temperature Electrolysers can be developed with high electrical conversion efficiencies.
Figure 5. Applications of Hydrogen
NICHE AND PREMIUM POWER APPLICATIONS
Fuel cells provide flexible, low environmental impact solutions to quality power needs. The requirements for a premium power include quick response time, flexibility and safe utilization by non-experts, availability and reliability at moderate investment cost.
UPS AND BACK-UP SYSTEMS
Uninterruptible power supplies (UPS) requires an instantaneous response to a power failure to ensure continuity of supply over a fairly short time scale. The fuel costs are not sensitive and efficiency is not given prime importance. A high system cost is tolerable. This can be achieved either by using a hybrid system with a storage device or with a fuel cell operating in a standby mode. A polymer fuel cell operated on hydrogen offers advantages in terms of responsiveness especially for UPS applications.
QUALITY POWER
Fuel cell systems offer the potential of very high quality, stable power supply for applications that have an extremely low tolerance of frequency or voltage variations such as precision engineering or secure data systems. This is of particular importance in areas where grid is unreliable.
LEISURE
For leisure applications such as camping, luxury boats and caravans the easy handling of both system and fuel are of high importance. The investment costs are probably more sensitive than the running costs so efficiency and flexibility are of less importance. It is essential to have transportable fuel sources, probably involving direct hydrogen low temperature fuel cells or high temperature fuel cells utilizing more complex fuels such as propane
DEFENSE
In defense applications, particularly for generation at temporary or semi-permanent installations, the possibilities to use logistic fuels are of great importance. Low noise and thermal radiation are highly desirable, giving significant advantage to lower fuel cells in certain modes of application. Size and weight are also very important.
The device is not so sensitive to impurities in the fuel or cathode gas.
TRANSPORTATION APPLICATIONS
Transportation application deals with ground, air and marine transportation. The focus for ground transportation is on propulsion for passenger cars as well as auxiliary power units for passenger cars, light duty vehicles, and heavy trucks. As a very high power level is required in case of marine and air propulsion the primary focus is on auxiliary power units.(APU).
The potential for higher efficiency and zero emission vehicles has created more and more interest in fuel cells for alternative propulsion and onboard electricity generation as long term sustainable solutions for the rapidly growing transportation market. Various vehicles have already demonstrated this potential worldwide using hydrogen as fuel both from onboard storage and from reforming of hydrocarbons.
Hydrogen internal combustion engines are used in cars. In the long term fuel cell option is considered as the ultimate solution due to its inherent higher efficiency and ability to zero emission. An essential technology especially for high power and long range is the onboard fuel processing of liquid fuels to hydrogen using today’s fossil fuels until liquid renewable synthetic fuels and bio fuels are available.
SYSTEM FOR PROPULSION APPLICATIONS
High power and high dynamic response operation are essential for most propulsion applications. The propulsion of passenger cars is the most demanding application of fuel cells regarding cost, size, ambient conditions and dynamic response. Today’s fuel propulsion systems, successfully demonstrated in safety operating and comfortable driving cars, are characterized by system costs above 4000 EUR/kw, lifetime below 2000 hour and system power density of about 3 l/kw.
The short-term targets for the second generation of fuel cells are
• Operation under all ambient conditions over a wide range of temperature.
• Maximum overall efficiency above 40%, low-pressure air supply, low humidification and hybrid system architecture using small electrical storage devices.
• Operating range of vehicles above 400 km
• Cost reduction down to 100 EUR/kw, projection for grater than 150000 units per year
• Lifetime of at least 5000hours.
• Compact fuel cell systems with 1.5 kg/kw and 1.5 l/kw for 100kw systems, without electric drive and H2 storage.
• Capability of start/stop processes
Hydrogen internal combustion engines are used inside cars recently.
Main development targets are
• Improved refueling and storage systems for Hydrogen.
• Engine efficiency of least 22% for an acceptable vehicle range.
• Low NOx production
Figure 6. Hydrogen the future fuel
CONCLUSION
Hydrogen as an alternative fuel is extremely useful in meeting the energy scarcity. There should be research strategy in the field of Hydrogen production storage, distribution, its applications in order to develop Hydrogen as an energy carrier for the future.
REFERENCES
J.E.FUNK, Thermochemical Hydrogen production past and present. Vol 26 June 2001
J.I.Vy, Summary of electrolytic hydrogen production Vol 4 April 2004
W.IWASKI, Hydrogen energy Vol 28 April 2003
M.N.HUGHES, Metals and Micro organisms , Chapman and Hall New York 1989
R.JAVAHERDASTHI, A review of some characteristics of M I C by S R B past ,present and future. Vol 46 March 1999
JOHN .A. TURNER, Hydrogen production path ways Vol 15 Sept: 2000
SRA for Hydrogen production conference proceedings June 2004
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