11-09-28 Bioenergy and the Hydrogen Economy

Bioenergy and the Hydrogen Economy

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28 Sep 2011PDF (557 kb)

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11-09-28 Bioenergy and the Hydrogen Economy

It seems an almost panacea-like notion that an abundant source of energy could be found in our own human waste, but modern anaerobic digesters and wastewater treatment plants are beginning to harness the energy potential of municipal waste. An exponentially expanding world population intrinsically creates an ever-growing energy demand; with energy security and environmental issues rife the opportunity to transform local waste into essentially free energy is an exciting prospect.

Waste streams from sewerage systems and agricultural activities create environmental pollution issues of varying severity. To mitigate this, anaerobic digestion (AD) utilises the natural decomposition processes of various microorganisms accelerated by heat to produce, in most instances, methane gas. This gas may then be fed into on-site, local, or wider gas networks for use. This may not necessarily be the best use of the methane: many domestic gas distribution networks are dated and suffer from leakage issues. In addition, as we integrate an increasing number of renewable energy systems into the grid and move away from fossil-fuel derived energy, we are likely to see electrical demand increasingly outpace gas demand. As such, more merit may be found in utilising the methane for the production of electricity. This is an area of increasing industrial interest and one in which fuel cells could play a key role.

If AD-derived methane is fed into a high temperature fuel cell, either MCFC or SOFC, then electricity can be produced with by-products of just water and heat. This process offers the double benefit of removing environmental pollution concerns from management of the waste stream whilst generating sustainable electricity.

FuelCell Energy has been providing MCFC units for several such deployments including a multi-site San Diego wastewater project, a poultry ranch and a wastewater plant in California. Bloom Energy’s popular SOFC Energy Servers can also run on biogas. A deployment of five 100 kW units by IT service provider NTT America at its Californian data centre are fed using biogas captured from local dairy farms.

The production of electricity from human waste facilitates the distributed generation of electricity at its point of use, population centres, allowing for partial independence from sometimes problematic centralised transmission networks. There is also the potential for biogas-derived electricity to be integrated into feed-in tariff schemes. Of course, simple economies of scale work in the favour of this approach: the larger the population centre, the more municipal waste, and thus the more potential energy.

In the MCFC electrochemical reaction methane (CH4) enters the cell and is split into carbon and hydrogen at the anode catalyst. In standard operation hydrogen will pair at the anode with oxygen from carbonate ions arriving from the cathode side and leave the unit as water. However, the opportunity exists to extract the hydrogen before it reacts for use externally.

The number of fuel cell deployments is set to increase dramatically in the coming years; with thousands of ~100 kW automotive units and several multi-megawatt, even up to 65 MW, stationary units appearing there will be a surge in demand for hydrogen. Current industrial hydrogen production is sourced almost entirely from steam methane reforming; however there is not a large surplus in the current system. To meet demand, production methods will need to be expanded and hydrogen production via biogas offers the same double benefit here as it does with electricity: distributed energy production and environmental pollution mitigation.

Air Products, the world’s largest hydrogen producer with a daily output of more than five million kilograms of hydrogen, recently made its first foray into biogas hydrogen production with a wastewater treatment plant in the Californian Orange County Sanitation District (pictured above). Methane from the wastewater is purified and fed through a MCFC where electricity to power the plant is produced and hydrogen is extracted, purified to vehicle grade and piped to a nearby hydrogen refuelling station. The plant produces 175 kg hydrogen, enough for 25 to 50 vehicle refuellings, and 250 kW electricity daily at a claimed efficiency of 80%.

With the successes of this project the company has announced plans for its HESTON project – an upscaled biogas to hydrogen energy station in London that will mark Europe’s first megawatt MCFC deployment. Planning to operate at 1.1 to 1.4 MW, the plant would produce 635 kg hydrogen per day at approximately €10 per kilo, providing a step change in European hydrogen production. Supported by the London Hydrogen Partnership and the EU JTI (Joint Technology Initiative), the project is pending legislative approval.

Projects such as HESTON will contribute to the beginning of distributed hydrogen production networks, serving the hydrogen demands, and some of the electrical demands, of large population areas using the very waste they produce.

Jonathan Wing     Market Analyst



Image: Air Products’ Orange County municipal wastewater treatment plant (Source: Air Products)


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