Environmental Science & Engineering - www.esemag.com - May 2005
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Renewable solar hydrogen production

By Jamie Bakos, P.Eng.

Rendering of the Fleet Street Landfill Project that is scheduled to begin in Canada in July 2005.

Notwithstanding Episode 2F 19 of a popular, long-running cartoon series (Lisa Simpson's perpetual motion machine), the first law of thermodynamics is difficult to disobey. You simply cannot get more energy out of a system compared to the energy that you put in.

Based in Saskatoon, Solar Hydrogen Energy Corporation (SHEC Labs) has recently constructed and demonstrated a Dry Fuel Hydrogen Generation System that is powered primarily by sunlight-focusing mirrors. The system comprises a solar mirror array and advanced solar concentrator and shutter system, and two thermo-catalytic reactors to convert methane, carbon dioxide, and water into hydrogen. SHEC has designed and constructed a solar hydrogen generation system that, when utilizing sunlight, appears to deliver more energy than it receives.

Demonstration unit.

Why produce hydrogen? The current market for hydrogen is approximately 42 billion kg per year and growing, and is used primarily in ammonia fertilizer manufacturing, for hydrogenation in the food and beverage industry, and in petroleum refining to reduce the sulphur content of fossil fuels.

Hydrogen is also an energy carrier and is recognized by many as the fuel of the future. When hydrogen is consumed by a fuel cell, its only significant emissions are water and heat. A clean source of hydrogen will lead to energy self-sufficiency and clean air and clean water.

Traditional hydrogen production More than 95% of hydrogen produced today is by the Steam Methane Reformation (SMR) of fossil fuels such as oil, coal, and natural gas, a process that liberates massive amounts of carbon dioxide and other pollutants to the atmosphere. The SMR process provides a net energy loss of 30 to 35% when converting methane into hydrogen since a great deal of fossil energy or electrical power is required to operate the process. Hydrogen is also produced by electrolysis, a process that uses electricity to convert water into hydrogen and oxygen. Although electrolysis itself can be quite efficient in converting electricity into hydrogen, the electricity used for electrolysis is often primarily generated from fossil fuels. Therefore, traditional hydrogen production methods result in a net increase in air pollution and are highly inefficient from an energy conversion perspective.

The value proposition for solar hydrogen Solar hydrogen production provides a net energy gain when converting methane into hydrogen since the energy used to drive the process is from the sun. Since SMR is not typically costeffective at small to moderate production levels, SHEC's technology is particularly attractive for smaller and distributed hydrogen production. The environmental benefits of generating hydrogen using renewable energy include significant greenhouse gas reductions, and the reduction of smog precursors, acid gases, and mercury as a result of reduced local need for oil, coal, and natural gas.

To add even greater value, the process has the ability to use a renewable source of methane and carbon dioxide, such as biogas from municipal wastewater plants and landfill gas. Renewable methane generated from biomass results in no net increase of carbon dioxide levels in the atmosphere when the methane is converted into hydrogen by SHEC's solar hydrogen generator. Technology and process description The unit produces hydrogen with solar energy as the primary energy input and has the following general chemistry:

Methane (CH₄) and carbon dioxide (CO₂) are reacted to form hydrogen gas (H₂) and carbon monoxide (CO):
The carbon monoxide is reacted with water to produce more hydrogen and carbon dioxide:

Carbon dioxide (CO₂) and methane gas (CH₄) are fed into a reactor heated by a solar mirror array. The intermediate products from Reaction 1 feed into a water gas shift reactor (WGSR), controlled at near atmospheric pressure. The resulting gas stream is H₂ and CO₂ and is saturated with water.

Solar energy provides the driving force for the endothermic Reaction 1. A water cooled iris dilates to control the amount of radiant energy directed to Reaction 1. Reaction 2 is exothermic and requires cooling to maintain the optimum temperature.

Gas Production SHEC’s solar hydrogen generator has now operated for approximately 1,200 hours with no noticeable coking or degradation of the catalysts. Hydrogen production is near the theoretical maximum at approximately 66% in the product gas stream with a 98.2% mol conversion of the feed methane. The estimated maximum hydrogen production with the unit is approximately 3,500 kg per year with minor modifications to the operating pressure and reactor configuration and an increase in the solar mirror area.

Energy Balance The system does not produce more energy than it receives. It does, however, produce more energy in the form of hydrogen than the energy input in the form of methane.

When energy is converted from one form to another, a great deal of energy is typically lost (i.e. 10 kW of methane produces approximately 3 kW of electricity in a reciprocating engine). With the SHEC process, there are two sources of hydrogen (methane, CH4 and water, H₂O). The process of SHEC Labs uses ‘free’ solar energy to produce hydrogen from both methane and water.

In bulk terms, every 1 m³ of methane feed produces approximately 3.9 m³ of hydrogen in the process. Put in common energy terms at 1 bar pressure and 25°C, 1 m³ of methane equals approximately 40 MJ of thermal energy and 3.9 m³ of hydrogen equals approximately 45.7 MJ of thermal energy, which is a net energy gain of over 14% for the demonstration unit.

Considering the total energy (from the sun and from the methane), the overall energy balance has a less than 100% conversion efficiency and obeys the laws of thermodynamics. In fact the SHEC system is quite inefficient at present in that a great deal of the solar energy is lost in the form of heat. And since we know nothing is free, this heat loss translates into additional cost for the solar mirror array. A few well placed heat exchangers and some added insulation will help reduce the amount of heat loss and allow more of the mirror area to be dedicated to driving the chemical reactions.

Controls system for the demonstration unit.

Cost analyses Cost analyses and models have been prepared based on the use of the various feed gases (i.e. landfill gas, natural gas, flare gas, etc.) and based on empirical data for the cost of the demonstration unit, current gas production, and current size of the solar array. The cost analyses show that the hydrogen production costs based on using landfill gas are lower than traditional hydrogen production methods that use natural gas. It is important to note that the overall cost competitiveness of hydrogen extends beyond hydrogen production to hydrogen compression, storage, and distribution. The cost models are currently being expanded to include these elements and involve some innovative hydrogen distribution cost savings.

What’s next? The next stage of development is anticipated to be a commercial-scale demonstration at a landfill gas site in Canada using 40,000 kg per year hydrogen production modules. This one project (a small-to-medium sized landfill gas project) will prevent more than 1.6 million tonnes of carbon dioxide equivalent (CO₂e) from entering the atmosphere over the next twenty years and will significantly improve local air quality and reduce smog.

The next generation of solar hydrogen involves direct water splitting with only water as the primary feed component. According to SHEC, six of the ten steps needed for this process are already integrated into the current system.

Conclusion Hydrogen production from renewable methane, such as biogas from municipal wastewater treatment plants and landfill gas is ideally suited to SHEC’s solar hydrogen production system. Their solar hydrogen generator produces hydrogen from methane and carbon dioxide feed gases in a reactor maintained at temperature by solar thermal energy (directed by mirrors). A demonstration unit indicates that solar hydrogen generation is feasible, and appears to be cost-competitive with traditional methods.

And yes, it does obey the laws of thermodynamics.

Jamie Bakos, P.Eng., is Manager of Environmental Services with Ingenium Group Inc. (Giffels Associates Limited) in Toronto.
Contact e-mail: jamie.bakos@giffels.com.

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