May 2005
Renewable Solar Hydrogen Production
Environmental Science & Engineering
Jamie Bakos, P.Eng.
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.
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 sulfur 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 cost-effective 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:
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.
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.
