Hydrogen is considered an important fuel for future use in transportation, central and distributed electric power, portable power and combined heat and power for industrial development. The plethora of sources for hydrogen production, along with the variety of methods to extract it, makes hydrogen a very promising fuel. The introduction of hydrogen can be feasible in both industrialised and developing countries.
Chemically bound hydrogen is found everywhere on Earth: in water, fossil fuels and all living things. Yet, it rarely exists free floating in nature. Instead, it has to be extracted from water or from hydrocarbons. Today, nearly half the hydrogen produced in the world is derived from natural gas via a steam reforming process. The natural gas reacts with steam in a catalytic converter. The process strips away the hydrogen atoms, leaving carbon dioxide as the byproduct (and, unfortunately, releasing it to the atmosphere as a global warming gas). Coal can also be reformed through gasification to produce hydrogen, but this is more expensive than using natural gas and also releases CO2, which scientists hope to keep earthbound through a process called “carbon sequestration.” Hydrogen can also be processed from gasoline or methanol, though again CO2 is an unwanted by-product.
Hydrogen is a fuel for future use in transportation, central and distributed electric power, portable power and combined heat and power for industrial development (Lymberopoulos, 2005). It can be made in several different processes and the plethora of sources for hydrogen production, along with the variety of methods to extract it, makes hydrogen a very promising fuel. The introduction of hydrogen can be feasible in both industrialised and developing countries.
Hydrogen is the most abundant element in nature, accounting for 90% of the universe by weight (Lymberopoulos, 2005). However, it is always found in the form of compounds and its production for energy purposes is energy intensive. Hydrogen can mainly be produced from water through electrolysis or from fossil fuels through the process of reforming, whereby water (H2O) is dissolved into oxygen (O) and hydrogen (H). The hydrogen can be stored and transported and used as energy source elsewhere and/or at a later time. Potential other ways to produce hydrogen are biogenic production, thermolysis and pyrolysis. The energy required for these processes can be obtained from various sources, such as fossil fuels, nuclear energy and renewable energy sources, including bio-fuels.
This plurality in terms of energy sources is one of the main advantages of the hydrogen energy vector. In order to introduce and apply hydrogen in the marketplace, it has to be conditioned, i.e. transformed into a transportable and/or storable form. For transportation in gas pipelines, hydrogen must be compressed or admixed to natural gas. For long-distance transport in smaller quantities, the most practical as well as economical way is to transport hydrogen in liquid form at cryogenic temperatures. If hydrogen needs to be stored for longer periods (e.g. for seasonal storage), it can be transformed into liquid hydrides (methanol, methyl-cyclohexane, ammonia) or stored as pressurised gas in underground caverns. For mobile as well as stationary small-scale storage, hydrogen has to be conditioned preferably to either pressurised gaseous hydrogen, bound to metal hydrides, liquefied at cryogenic temperatures or cryo-adsorbed at an optimised pressure/temperature balance.
Hydrogen has several important properties that have an impact on its applicability as a fuel (see http://www.chfcc.org):
- It combines with oxygen to form water.
- It has a high energy content per weight (nearly three times as high as gasoline).
- It is highly flammable – it only takes a small amount of energy to ignite it and make it burn – and it has a wide flammability range so that it can burn when it makes up 4 to 74 % of the air by volume.
- The combustion of hydrogen does not produce CO2, particulate, or sulphur dioxide (SO2) emissions. It can produce nitrous oxide (NOX) emissions under some conditions.
- Hydrogen can also be produced from renewable resources, such as by reforming ethanol (this process emits some CO2) and by the electrolysis of water.
As stated above, one advantage of hydrogen is that it can be produced with different energy sources. Consequently, hydrogen can also be produced in remote parts in the world, regardless of the level of economic development and the quality of local infrastructure. Indeed, vast quantities of hydrogen as an industrial gas are nowadays produced around the world. Total annual production amounts to 500 billion normal cubic meters per year (Nm3/yr), which is equivalent to around 10% of the world oil production in 2002. Almost all of this hydrogen is produced by using fossil fuels. Only 5% of hydrogen production is commercially used and distributed, whereas the remainder is consumed internally in refineries or chemical plants. The US space programme has been the only case where hydrogen was used as a fuel. Hydrogen can very well be burned in suitably modified boilers, gas turbines and internal combustion engines. However, it is the development of fuel cells with which hydrogen can be combusted with minimal or no emissions that has opened new horizons for its energetic use in transport, mobile, portable and stationary applications, spanning all types of human activities (Lymberopoulos, 2005).
In industrialised countries hydrogen can be used in conventional power generation technologies, such as automobile engines and power plant turbines, or in fuel cells, which are relatively clean and more efficient than conventional technologies. Examples of applying hydrogen are:
- Transport – Transportation applications for hydrogen include buses, trucks, passenger vehicles, aircrafts, and trains, with technologies being developed to use hydrogen in both fuel cells and internal combustion engines, including methanol systems. Almost all major carmakers have a hydrogen-fuelled vehicle demonstration programme. Hydrogen-fuelled, internal-combustion engine vehicles are viewed by some as a near-term, lower-cost option that could assist in the development of hydrogen infrastructure and hydrogen storage technology (Sapru et al., 2002). A key advantage of this option is that hydrogen-fuelled internal-combustion engines vehicles can be made in larger numbers. Since the early 1990s, several car makers (BMW, Daimler-Benz, Mazda) have developed and tested prototype hydrogen-powered passenger cars with internal combustion engines (piston, rotary). In addition, first fuel-cell hydrogen passenger cars are under development (e.g. Renault/Volvo - France/Sweden) (see http://www.fuelcells.org). To date, first city bus prototypes are under development. Hydrogen application in the aerospace sector occurs only in space applications due to its specific energy/weight ratio. In aircrafts no commercial use has occurred yet. In the Russian Federation, in a modified Tupolew 154 experimental aircraft, the starboard jet engine was successfully operated with liquid hydrogen over the full operating range during several test flights.
- Stationary power generation – Stationary power applications include back-up power units, grid management, power for remote locations, stand-alone power plants for towns and cities, distributed generation for buildings, and co-generation (in which excess thermal energy from electricity generation is used for heat). Although some commercial fuel cells are on the market, the industry is still in its infancy. Most existing fuel-cell systems are used in commercial settings and operate on reformatted natural gas. Widespread availability of hydrogen would allow the introduction of direct hydrogen units (simpler systems with lower cost and increased reliability). In general, combustion-based processes, such as gas turbines and reciprocating engines, can be designed to use hydrogen either alone or mixed with natural gas. These technologies tend to have applications in the higher power ranges of stationary generation.
- Portable power generation – Portable applications for fuel cells include consumer electronics, business machinery, and recreational devices. Many participants in the US fuel cell industry are developing small-capacity units for a variety of portable and kilowatt systems for critical commercial and medical functions. Most of these portable applications will use methanol or hydrogen as the fuel. In addition to consumer applications, portable fuel cells may be well suited for use as auxiliary power units in military applications.
- Other industrial sectors - Hydrogen is used in ammonia (NH3) production that in turn is used for the production of fertilisers. In refineries, hydrogen is used for the upgrading of fuels, mostly for the removal of sulphur. Hydrogen becomes the single most important product of the refinery; however it remains an internally consumed product and rarely exits the refinery (Lymberopoulos, 2005). The petrochemical industry uses hydrogen to produce methanol, which is sometimes used in fuel cells where it is reformed to release its hydrogen content. Hydrogen is also used in the food industry for the hydrogenation of fats. Some other uses derive from the physical properties of hydrogen, like lubrication, heat transfer (cooling of power plant generators) or buoyancy (meteorological balloons).
Hydrogen is considered an important fuel for future use in transportation, central and distributed electric power, portable power and combined heat and power for industrial development (Lymberopoulos, 2005). The plethora of sources for hydrogen production, along with the variety of methods to extract it, makes hydrogen a very promising fuel. The introduction of hydrogen can be feasible in both industrialised and developing countries. For the success of implementing hydrogen technology, it is needed that it can be produced in an economically and environmentally acceptable manner and that hydrogen end-use technologies can gain a significant market share (see http://www.nyserda.org). Reaching this goal, however, will require addressing several technical, social, regulative, and policy challenges:
- Public acceptance: The use of hydrogen is well established in chemical industry. Its use, starting in first niche markets, with selected automotive and utility applications will introduce the handling and application of hydrogen into the public sector step by step. Similar concepts and standards as for natural gas may be developed and introduced for gaseous and liquid hydrogen, thereby creating confidence in its safe, efficient and environmentally compatible application among its users as well as acceptance of the public and authorities.
- Technological and technical challenges: The four fundamental technological and technical challenges related to hydrogen are: to develop and introduce economic, durable, safe, and environmentally acceptable fuel cells and hydrogen storage systems; to develop the infrastructure to provide hydrogen for the light-duty vehicle user; to reduce the costs of hydrogen production from renewables over the next few decades; and, if politically feasible and acceptable, to capture and store the CO2 by products of hydrogen production from coal (National Academy of Engineering 2004).
- The challenge of transition: The transition period to a hydrogen fuel system is likely to be lengthy. It will probably best be accomplished at first by distributed production of hydrogen using small natural gas reforming and electrolysis units, possibly using distributed renewable energy (e.g. wind or direct solar). A distributed system can allow time for development of the new technologies and concepts needed for widespread use of hydrogen. Such an approach, however, cannot yet be fully defined.
- Infrastructure requirements: Hydrogen as a fuel will not be widely used until a nation-wide safe and efficient infrastructure is in place. The main infrastructural components are pipelines, compression, liquefaction, tube trailers, liquid and gaseous tanks, geologic storage, separation/purification, dispensers, carriers and carrier charging and discharging (Freedom Car Fuel Partnership 2005). There are significant opportunities for large improvements in infrastructure and delivery, and nations should put greater emphasis on storage requirements, hydrogen purity, pipeline materials, compressors, leak detection, and permitting (National Academy of Engineering 2004). In addition, exploratory research on new hydrogen deliver concepts needs additional funding.
- Safety challenges and requirements: Safety will be a major issue for commercialisation of hydrogen applications and this requires an early discussion of safety policy goals with stakeholder groups, continuing work with standards development organizations, the inclusion of safety in systems analysis, a physical testing program to resolve safety issues, and public education focusing on hydrogen safety.
- Regulatory issues: In the special case of hydrogen, existing codes and regulations usually do not include or reflect hydrogen as a product itself. For instance, the codes for the maritime transportation of liquid gases as established by the International Maritime Organisation only refer to liquefied petroleum gas (LPG) or liquefied natural gas (LNG), but not to liquefied hydrogen (LH2). For a successful and efficient planning and design process for a new technology or concept to be applied on a worldwide basis as well as for a successful marketing, an extension of such codes to the technology or concept in question is needed.
Several researchers have argued that the implementation of hydrogen technologies in developing countries should start in remote areas or countries that do not have access to the electricity grid (Lymberopoulos, 2005). Specific support (economic and technological) to implement new energy technologies in developing and transition countries can be the starting point to create a market which also can be progressively extended to developed countries. Another favourable factor for the transfer of hydrogen technology to the developing countries is the local availability of bio-resources which can be exploited this way and which could also be a solution for waste disposal problems in many of such countries, e.g. with developed agriculture and forestry. Therefore, there is a great opportunity to foster the transition to more sustainable energy use by combining hydrogen technology promotion and aid to developing and transition-economy countries to the necessity of creating the market incentives, to the use of these new sustainable energy technologies, such as sustainable and decentralised production of hydrogen and integration of fuel cells for transportation, housing, and other applications.
All in all, hydrogen may be a good long-term option for certain types of trucks, depending in part on the evolution of hydrogen storage technologies. For medium and heavy trucks, natural gas (eventually partly substituted by bio-synthetic gas, bio-SG) gains some market share by 2050, as do hydrogen fuel cells. Diesel engines and diesel fuel remain dominant, particularly for long-haul trucks. For these trucks, refuelling needs to be high-capacity, quick and available on motorway networks. These factors limit the viability of fuels such as natural gas or hydrogen, given their low energy density and long refuelling times (IEA 2010).
Driven by recent technical advances in hydrogen and fuel cell technologies and the need for diversified and sustainable technologies, OECD governments are intensifying their R&D efforts (Lymberopoulos, 2005). Almost € 1 billion per year are invested globally in hydrogen and fuel cells research, mainly in the USA, Japan, and Europe. Half of this amount is spent on fuel cells R&D and the rest on technologies to produce, store and use hydrogen in other energy conversion devices like internal combustion engines. The respective investment from the private sector is considerably larger (approx. € 3-4 billion/yr), including major oil and gas companies, car manufacturers, electrical utilities, power plant component developers, and a number of small and medium enterprises in the current hydrogen and fuel cell market. According to the IEA (2010), hydrogen can be introduced globally after 2030, with almost 200 Mtoe used in transport.
For EU countries in particular, hydrogen and fuel cells have received increased attention in order to meet policy objectives at the EU or member state level. For instance, in the 6th Framework Programme (FP6), the EC has approved for funding the following projects (see Figure below), with an indicative EU funding of € 60.8 million.
In the field of hydrogen and fuel cells the European Commission has helped the launch of the hydrogen and fuel cells technology platform. This platform has been a major instrument for steering EU efforts in this field and it is expected that in the context of FP7, the platform will evolve into a Joint Technology Initiative, a new kind of framework for fostering technological development through public private partnerships.
In developing countries, R&D in hydrogen technologies is mainly carried out within individual nations’ planning and not in the framework of a joint initiative. The main aim of this R&D is to develop deliberate, socially acceptable strategies to stimulate and sustain institutional R&D in the perspective of commercial hydrogen applications. For instance, China’s R&D programme aims at developing advanced hybrid-electric and fuel-cell vehicles and involves a large number of universities, public sector research institutes and private firms (Lymberopoulos, 2005). India too is rolling out hydrogen-fueled two- and three-wheeler vehicles, while at the same time exploring ways of tapping hydrogen for stationary power. South Africa’s R&D programme covers a range of alternative applications, with a major emphasis on exploring opportunities to exploit its vast platinum reserves in fuel cell catalysts. Nigeria has put in place a comprehensive energy strategy aimed at expanding its production of natural gas, which among others serves as a basis for creating methanol and hydrogen. Finally, Malaysia has adopted a dual strategy to simultaneously develop hydrogen and solar energy as alternative fuel sources.
While most fuel cell and hydrogen activities are taking place in countries that experience a sustained economic development, such as Japan, USA and the EU, there are some hydrogen activities that take place in developing countries (Lymberopoulos, 2005). Research on fuel-cell and related technologies is being carried out in several developing countries, e.g. Brazil, China, India, Malaysia, Singapore and South Africa, and a few of these are also developing demonstration projects for fuel-cells in buses and cars, as well as hydrogen stations. At present, China carries out fuel cell vehicle and refuelling station demonstration projects in Shanghai and Beijing, and the country also undertakes its own national research and development activities. India has developed a clean fuel motorbike driven by metal hydride, which is presently a rather expensive technology, but in the longer run may become cheaper due to the lower cost for hydrogen fuel and durable storage tanks for metal hydride. Besides that, India has made progress with research on powering/fuelling cooking stoves, generators and illuminations with hydrogen. In Mexico, the potential of hydrogen as a major component in the Mexican energy scene has been acknowledged both by researchers and the academic community. Since its creation in 1999, the Hydrogen Mexican Society has promoted the potential benefits that the inclusion of hydrogen in the Mexican energy sector could represent (Lymberopoulos, 2005).
Indicative case studies of hydrogen technologies’ applications are:
- Utsira, Norway – Norske Hydro in co-operation with Enercon developed a combined wind and hydrogen energy system as a pilot demonstration project on the island of Utsira, whose municipality has an ambition to be self-sufficient with renewable energy (Eide et al., 2004). Utsira is located a one hour and a half by boat from the western coast of the Norwegian mainland. It has the smallest population of all municipalities in Norway (about 230 inhabitants) and a total area of only 6.15 km2. The island is presently connected to the main land through a sea cable, but it used to produce its energy with diesel electric generation. The wind-hydrogen option was examined in order for Utsira to become self-sufficient with renewable energy and independent of a cable to the main land. The autonomous system developed on the island aimed to cover the loads of ten customers both in terms of peak load and energy consumption, with the same power quality as the energy delivered through the cable. Under these constraints and after detailed simulations, the system consisted of the following components.
- Hysolar, Saudi Arabia – The HYSOLAR project was carried out by German Aerospace Center (DLR) and the University of Stuttgart, Germany, in co-operation with three Saudi universities. Phase I of the programme lasted from 1985 to 1989 and consisted of the following activities:
- Design and installation of a 350 kW demonstration plant in the ‘Solar Village’ near Riyadh, Saudi Arabia, consisting of a concentrating photovoltaic (PV) power system, an advanced electrolyser system with power supply system, a grid operated rectifier, and the necessary gas handling and storage system in order to collect experience in technical scale application.
- Design and installation of a 10 kW test and research facility in Stuttgart, consisting of a multi-crystalline photovoltaic generator system, a power conditioning system, two electrolysers of 10 kWe and one electrolyser of 2 kWe and a PV-simulator in order to do systems development for advanced hydrogen equipment.
- Basic research and system studies to assess the HYSOLAR project and a utilisation programme for the evaluation of safety, reliability and environmental aspects of the selected hydrogen application technologies, as well as of an educational and training programme.
Phase II lasted from 1992 to 1995 and its major focus was on hydrogen production and utilisation. In particular, the 350 kW electrolysis demonstration plant in Riyadh was put into continuous solar-connected operation. From the long-term experience thus accumulated, performance data were obtained for optimisation and scaling up of the system. In the 10 kW research and test centre in Stuttgart, several different electrolyser concepts were investigated. For solar operation the electrolysers could be connected to the photovoltaic generator with or without power a conditioning unit. Furthermore, the electrolysers could be operated with any other controllable current or power profile fed by grid connected power supplies, thus simulating wind energy profiles from wind turbines located at different sites worldwide. A comprehensive simulation code to calculate system efficiency and annual hydrogen production rate from individual characteristics of components and climatic data has been developed.
In the field of hydrogen utilisation technologies, basic theoretical and laboratory research was performed on alkaline fuel cell concepts (e.g. characterisation of gas diffusion electrodes), as well as on catalytic burners (reaction kinetics of H2/air mixtures). Experimental investigation of instationary combustion phenomena was performed. Practical tests were carried out on internal combustion engines, also of the compression ignition type.
In OECD countries, multi-annual programmes have been announced for hydrogen development, including a USD 1.7 billion over 5 years in the USA, € 2 billion in the EU 6th Framework Programme and the Growth Initiative of the EC and ¥ 30 billion per fiscal year in Japan, as well as programmes in Canada, Germany, and Italy. These efforts are complimented by three major international co-operation initiatives (Lymberopoulos, 2005):
- The IEA has formed in April 2003 the Hydrogen Co-ordination Group to enhance co-ordination among national R&D programmes, building on the IEA co-operation framework, including the Implementing Agreements on Hydrogen, Advanced fuel cells and others.
- In November 2003, sixteen countries including the non-OECD countries Russia, Brazil, India and China formed the International Partnership for the Hydrogen Economy (IPHE).
- In January 2004, the EC established the European Hydrogen and Fuel cells technology platform (HFP), which is a cluster of public and private initiatives aiming to co-ordinate and promote the development and application of hydrogen energy technologies including fuel cells.
Apart from those initiatives under development in Europe, many developing nations also share an interest in hydrogen and have invested in hydrogen R&D. Significant momentum for the introduction of hydrogen energy systems is currently being generated by government policy developments, capital market participation and industry programmes.
Hydrogen could be an important energy carrier in the future, largely due to its unique physical properties and ability to convert energy to useful work cleanly and efficiently. A great deal of work has been undertaken on the integration of hydrogen into transport and power generation, but more opportunities exist beyond these sectors. The new and sustainable technologies of hydrogen production, such as gasification of biomass, reforming of fossil fuels, transformation solar and other types of renewable energy, coupled to the technologies of hydrogen use as an alternative green fuel, e.g. in fuel cells, now constitute the cutting edge topics of R&D for sustainable energy production and a cleaner environment. Many hydrogen technologies still need to be improved in terms of performance and cost reduction in order to be considered best available options.
Currently, there are large, small, portable, mobile and stationary hydrogen applications operational. Some are based on mature, proven technologies and others are evolving as conceptual hydrogen projects across an expanding number of research centres around the globe (Lymberopoulos, 2005). The combustion-based hydrogen conversion technologies developed during the 1980s showed a high degree of maturity and displayed a broad range of practical applicability. Yet, their global advancement in response to the need for improved air quality was rivalled by the development of low-cost emission reduction strategies, and the very low costs of fossil fuels. The technical progress of fuel-cell technologies over the past fifteen years, however, has given the electrochemical hydrogen conversion path a significant foundation to become a versatile, clean and ultramodular future technology option. However, besides the technical challenges, the economic viability of hydrogen as an energy carrier must be proven. Europe has been the leader in technologies like electrolysers and reformers and similarly in technologies related to renewable energy sources. For a successful uptake of the technology in developing countries it is important that economic and non-techno-economic barriers to hydrogen’s penetration into the energy and fuel markets will be overcome. In general thus the success of a sustainable hydrogen application depends on the following key factors:
- A scientific and technical basis for approved codes and standards;
- Reduction of hydrogen production cost;
- Promotion of hydrogen infrastructure for supply, maintenance and operation of the technology;
- Pursue technologies that will lead to increased market penetration for hydrogen; and
- Initiate safety-related educational and technology assessment activities.
Regardless of the above mentioned evolutions in the sector, according to the IEA (2008), the development of a hydrogen infrastructure will depend on developments in the transportation sector. It seems unlikely that a hydrogen network will develop solely for stationary applications.
Regarding the structure of the existing energy economy, hydrogen could contribute to sustainable development objectives in four main ways:
- The use of hydrogen reduces pollution and improves air quality: When hydrogen is combined with oxygen in a fuel cell, energy in the form of electricity is produced which can be used in several economic sectors. The advantage of using hydrogen as an energy carrier is that when it combines with oxygen the only by-products are water and heat. No GHGs or other particulates are produced by the use of hydrogen fuel cells.
- Hydrogen can be produced locally from numerous sources: Hydrogen can be produced either centrally, and then distributed, or decentrally for on-site use (see http://www.hydrogenenergycenter.org). Hydrogen gas can be produced from methane, gasoline, biomass, coal, or water. Each of these sources brings with it different amounts of pollution, technical challenges, and energy requirements, but would also contribute to diversifying energy infrastructures.
If hydrogen is produced from water, the production system would be sustainable: Since electrolysis (to separate water into hydrogen and oxygen) uses electricity as an input, it does not have the geographical restrictions that alternative ways of producing energy do. It also allows flexible and remote siting of hydrogen generators, providing distributed generation of this energy carrier, without requiring physical transport and large scale storage. Renewable energy can be used to power electrolysers which would provide a sustainable system that is independent of petroleum products and free of pollution.
When hydrogen is produced through the reforming of fossil fuels, then CO2 is released. Nuclear energy, although CO2-free, still faces nuclear waste disposal. When hydrogen is produced through water electrolysis, then the GHG emissions related are those associated with the power used. According to the IEA (2008), the contribution of hydrogen in the reduction of GHG emissions in the transport sector (estimated to 12.5 GtCO2 if all technologies are implemented) for the year 2050, can be quite substantial. In order to achieve these savings, R&D expenditures for the hydrogen fuel cell vehicles can amount from 3,500 to 4,500 billion USD.
For calculation of these GHG emission reductions, it is recommended to apply the approved methodologies for switching fossil fuels and hydrogen production using methane extracted from biogas project (large scale activities) which has been developed under the Clean Development Mechanism of the UNFCCC Kyoto Protocol (CDM). This methodology helps to determine a baseline for GHG emissions in the absence of the project (i.e. business-as-usual circumstances), how emission reductions below this baseline can be calculated, and how these reductions can be monitored. General information about how to apply CDM methodologies for GHG accounting can be found at: http://cdm.unfccc.int/methodologies/PAmethodologies/approved.html.
The costs of hydrogen technologies refer mainly to the processes necessary to produce, distribute, and dispense the hydrogen. Currently, most hydrogen is produced with natural gas close to where it is needed for industrial purposes. However, as mentioned before there are other pathways of producing hydrogen as well. The major factors that will affect the cost of delivered hydrogen are the following:
- The feedstock and/or the major energy source with which the hydrogen is produced,
- The size of the facility at which the hydrogen is produced and the transportation requirements to deliver it to the customer,
- The state of the technology used and future improvements, and
- Whether or not the CO2 by-product is sequestered when hydrogen is produced using fossil fuel.
However, it should be noted that there remains significant uncertainty about the actual costs of the technologies under current conditions. Costs are site-specific, particularly for wind and solar-based technologies. Moreover, the uncertainty about possible future technologies is substantially greater. Concerning the hydrogen production, storage and distribution, some indicative costs are presented in the table below.
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