H2 : The Long-Term Candidate for Energy Production and Storage from Renewable Sources : www.reein.org

H2 : The Long-Term Candidate for Energy Production and Storage from Renewable Sources

Dr. Shahida Rafique, Hasan Sarwar

Department of Applied Physics, Electronics and Communication Engineering

University of Dhaka

Dhaka-1000, Bangladesh

Abstract

The lightest, simplest and most abundant element in the universe is hydrogen, having a symbol H of atomic no. 1, atom wt. 1.00797, a melting point ~2590C, and a boiling point ~2530C. It is found in nature as a colorless, odorless, highly flammable gas in the molecular form H2. Its two isotopes are 2H (deuterium) and 3H (tritium).

The potential prospect of this H2 as major future energy vector has been analyzed. It has been realized that H2 can address the issues of environment protection and energy security. It can be a source of sustainable energy on the basis of quality and economically efficient energy services. It can also provide a fundamental means for energy production and storage from intermittent energy sources and has full potential as a renewable energy source. It offers flexibility in terms of energy volume and power stored and released.

There are a wide range of potential options for production of H2 from renewables in terms of scale, installations and distributions. The main supply option of H2 from renewables has been found to be wind-generated electricity, biomass from woody energy crops, agricultural and forestry residues, biodegradable municipal solid waste, wave, tidal and photovoltaic.

Onshore and offshore winds are considered to have the great potential for direct renewable hydrogen generation. Wind farms could be 30 MW for onshore and 60 MW for offshore. The electricity generated could be used either to power on-site electrolysis to produce hydrogen directly. It requires hydrogen transport infrastructure.

Large-scale alkaline electrolysis is the mature commercial technology. Small-scale electrolysers are also commercially available. There are number of possible routes for hydrogen from woody energy crops, such as, electrolytic hydrogen production using biomass electricity, biomass liquid fuel reforming to hydrogen and on-site reforming of biomass gases from gasification.

Gasification and gas cleaning equipment is still at the pre-commercial stage. Reforming, shift reaction and PSA equipment is commercially available at large-scale, and is widely used for industrial hydrogen production, mainly from natural gas.

The main storage options for hydrogen are as compressed gas at low and high pressure, or as liquid hydrogen. Underground storage is suitable for very large gas volumes. Compressed hydrogen can be stored above ground in pressure vessels at various ranges of sizes and pressures.

Hydrogen can be transported as a compressed gas either in dedicated pipelines or by container or as liquid hydrogen by tanker. Transport of both compressed and liquid hydrogen by road is used in industry. Liquid hydrogen is favored for long distances and compressed gas is suitable for short distances.

Hydrogen can be used as fuel in internal combustion engine vehicles (ICEV), in fuel cell vehicles (FCV). Hydrogen and its use in fuel cell are likely to play a major role in a sustainable energy future.

Introduction

• In the new millennium, hydrogen is considered as the key solution for enabling clean, efficient production of energy from a range of primary energy sources.

• On the technology front, hydrogen is not a primary energy source but a clean energy carrier, which can be produced from any primary energy source and fuel cells, are very efficient energy conversion devices.

• Sources of renewable energy, such as, solar, wind, or geothermal potential can become hydrogen factories.

• Renewable energy resources may produce hydrogen, a clean energy when burned. The energy from these resources can be converted to fuel for on-demand clean energy applications.

• It is expected that the economic and societal values of both the hydrogen and the renewable energy resources will be enhanced by the synergy between hydrogen development and application of the RE technologies.

• The renewable hydrogen energy production does need to wait for further major new developments in other technologies. It is speculated that the widespread and large-scale application of energy storage may not be needed until 2020 or 2030.

• The development of hydrogen fuel and applications will proceed independently of RE transition. Pulled by the economic benefits of the hydrogen transition and pushed by government programs, so that the hydrogen technology and infrastructure can be expected to be sufficiently ready to support higher penetration levels of the intermittent RE resources.

• The environmental success of the hydrogen transition depends entirely on the utilization of RE resources to produce hydrogen. ‘As mentioned by the President of the EC, it is our declared goal of achieving a step-by-step shift towards a fully integrated hydrogen economy, based on renewable energy by the middle of this century.’

Hydrogen Production

• Hydrogen can be produced in many different ways using a wide range of technologies.

• Some technologies are well established involving industrial processes; others are still in the laboratory stage.

• Some need considerable research and development. Hydrogen production is mostly at a large-scale.

• Small-scale production technologies include electrolysis, stationary and on-board reformers that extract hydrogen from gaseous and liquid fuels like natural gas, gasoline and methanol.

• Hydrogen production technologies are shown in Table 1.

Production of Hydrogen by Gasification Process

· The biomass feedstock is first dried and sized.

· The feedstock is then gasified to produce syngas, mainly composed of CO, hydrogen, CO2, steam, some methane and small quantities of hydrocarbons.

· The syngas is then cleaned, and hydrocarbons are converted to CO and hydrogen by steam reforming.

· The reformed gas then undergoes shift reactions. Two shift reactors in series, the first at 4500C and the second at 2300C are used to react the CO with steam to form hydrogen.

· Hydrogen is then recovered from the gas steam by pressure swing absorption (PSA - PSA desorbs all the gases except hydrogen).

· 97% of the hydrogen passing through the PSA is recovered which has 99.999% purity.

· The hydrogen can then be liquefied or compressed for transport.

Schematic diagram of gasification and liquefaction plant. Organic waste are introduced into a coil that is heated using a downdraft burner. This causes the material to decompose into hydrogen and carbon monoxide, which, after cleanup, is catalytically combined into a liquid fuel such as ethanol or diesel. Residual heat from the downdraft burner is first used to generated superheated steam, which is injected with the organic material. Remaining heat is used to pre-dry the organic waste. Ash remaining after gasification is collected using a cyclone.

Steam Reforming System

Hydrogen Storage

· The main storage options for hydrogen are as compressed gas at low and high pressure, or as liquid hydrogen.

· Underground storage is suitable for very large gas volumes.

· Compressed hydrogen can be stored above ground in pressure vessels at various ranges of sizes and pressures.

Hydrogen storage technologies are shown in Table 2.

Hydrogen Transport

· Hydrogen can be transported as a compressed gas either in dedicated pipelines or by container or as liquid hydrogen by tanker.

· Transport of both compressed and liquid hydrogen by road is used in industry. Liquid hydrogen is favored for long distances and compressed gas is suitable for short distances.

Hydrogen Infrastructure

Infrastructure is required for hydrogen production, storage, and distribution and, in the case of transport; special facilities will be required for vehicle refueling. This has implications for land use planning as well as for the safe operation and maintenance of hydrogen equipment. Other issues must also be addressed. Trained maintenance personnel, specifically trained researchers; accepted codes and standards all form part of a successful support infrastructure for any product or service, and will be vital for the successful introduction of hydrogen and fuel cells.

Fuel cell systems

There are five types of fuel cells classified according to their electrolyte:

Solid Oxide Fuel Cell (SOFC)
Molten Carbonate Fuel Cell (MCFC)
Phosphoric Acid Fuel Cell (PAFC)
Direct Methanol Fuel Cell (DMFC)

Fuel cells convert fuel and air directly to electricity, heat and water in an electrochemical process, as shown in the diagram below. Unlike conventional engines, they do not burn the fuel and run pistons or shafts, and so have fewer efficiency losses, low emissions and no moving parts. The diagram shows how a single fuel cell works.

Their advantages are:

• high efficiency;

• zero emissions when using hydrogen, and very low emissions when using other fuels (e.g. NOx, CO…);

• mechanical simplicity, low vibration and noise, low maintenance requirements;

• a high ratio of electricity to heat compared with conventional combined heat and power plants.

Benefits of transport fuel cells:

• Efficiency: Fuel cell cars have demonstrated very high efficiencies when operated with hydrogen, compared both to internal combustion engines and fuel cells coupled with onboard reforming of methanol or gasoline;

• CO2 emissions and energy security: Fuel cell vehicles using hydrogen offer the greatest benefits over internal combustion engines of the future and over fuel cell vehicles using other fuels, especially when viewed in the context of a longer term transition to renewable hydrogen;

• Regulated emissions: Fuel cell cars have very low emissions, and even zero emissions at the point of use when fuelled by hydrogen;

• Power: Fuel cells can provide on-board electricity with high efficiency. Fuel cell cars could produce (back-up) power for homes, offices, or remote locations;

• Performance and convenience: Hydrogen and fuel cell vehicles could provide similar or improved qualities in terms of performance and convenience;

• Congestion: Silent vehicles could deliver goods at night, taking traffic off roads during the day;

• Comfort: Fuel cell vehicles have a very smooth, refined ride and emit low noise.

Benefits of stationary fuel cells:

• Efficiency: Fuel cells are highly efficient, whatever the size, and have high power quality.

• Emissions: Very low to zero carbon emissions and no emissions of harmful ambient air pollutants such as nitrogen dioxide, sulphur dioxide or carbon monoxide.

• Environment: Low levels of noise and emissions mean fuel cells can be sited in sensitive areas.

• Convenience: Fuel cells can provide both heat and power from a range of fuels; compared to

conventional Combined Heat and Power (CHP) systems they operate at a higher power to

heat ratio.

Defence and aerospace applications:

Fuel cells have large potential in defence applications, providing silent power in place of diesel generators, as auxiliary power units for tanks, or producing high levels of power for advanced soldier uniforms. Defence markets are less cost sensitive than private markets, and can provide an excellent opportunity for technology development and verification. Likewise, aerospace offers the potential for fuel cells in spaceships, where they are already used, and in aircraft for fly-by-wire or auxiliary power requirements.

Challenges for fuel cells:

• Cost: Except in premium applications such as back-up power generation for major financial institutions, fuel cells are generally today too expensive for commercial introduction.• Lifetime: Some fuel cell systems have been demonstrated for thousands of hours, but the majority must still be proven.• Reliability: Not only fuel cells, but also supporting equipment such as fuel processors, must be proven.• Novelty: In most conservative markets, any new technology requires significant support and public understanding in order to compete.• Technological breakthroughs are needed for simultaneously improving fuel cell performance, reliability and cost.• Infrastructure: Refueling, large-scale manufacturing processes and support infrastructures, such as trained personnel, are not yet available for fuel cell systems.

Hydrogen-based Energy System

The wide-range of options for sources, converters and applications are shown in Figure 1 and 2.

The figures illustrate the flexibility of hydrogen and fuel cell energy systems.

· Hydrogen is not a primary energy source like coal and gas, it is an energy carrier.

· It is produced using existing energy systems based on different conventional primary energy carriers and sources.

· RE sources is the most important source for the production of hydrogen.

· Regenerative hydrogen, and hydrogen produced from nuclear sources and fossil-based energy conversion systems with capture, and safe storage (sequestration) of CO2 emissions are completely carbon-free energy pathways.

· Renewable energy such as, biomass, solar, wind and ocean energy are viable according to regional, geographic and climatic conditions.

Concentrated solar thermal energy is a potentially affordable and secure option for large-scale hydrogen production (especially for Bangladesh).

Benefits of Hydrogen and Fuel Cells

The use of hydrogen in fuel cells systems, there are zero-carbon emission and no emission of harmful ambient air substances like NO2, SO2 and CO.

• Due to their low-noise and high-power qualities, fuel cell systems are ideal for use in hospitals, IT centers or for mobile applications.

• Due to high efficiency and small size, fuel cell can be used in electric-drive trains.

• It can be used auxiliary power units in combination with internal combustion engines, in stationary backup systems.

• It can be used in portable devices such as, mobile phones, laptops, etc.

• It can be used in automobiles like cars, vehicles, buses and ships.

• It can be used to heat and power generators in the domestic and industrial sectors.

Future energy systems may include

• Improved conventional energy converters running on hydrogen such as, internal combustion engine, Stirling engines, turbines, etc.

• Energy carriers such as direct heat and electricity from renewable energy, bio-fuels for transport, etc.

•

Table 3: The reduction of average greenhouse emission in a hydrogen-oriented economy.

High Level Group on Hydrogen and Fuel Cells Technologies

A Renewables Timeline

Conclusion

·Renewable energy transition will happen region-by-region, country-by-country.

·This will happen when people governments, regulators, utilities, and the financial community have all become familiar with the technologies.

·The RE transition must start now before it is too late.

·Governments, cities, companies and people must cooperate in moving it beyond the first difficult steps, knowing that great societal, environmental and personal rewards will come.

·Let RE, the source of all life on earth, be the sustainable, safe and sane energy for us all.