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A bio-energy future?

Neil Crumpton has outlined an ambitious bio-energy future, based on solar driven bio (algae) oil production, and the use of Carbon Capture and Storage (CCS) to achieve carbon-negative energy generation.

While he sees Concentrated Solar Power and wind power as major global energy solutions, he believes that combining desert-based algae production with CCS could become a global scale carbon-negative climate solution.

He sees Seawater Greenhouses or similar desert-based low-tech structures as potentially ideal for algae production in photo bio-reactors.

The ‘Seawater Greenhouse’ is a solar-driven technology which uses adapted greenhouses (low-cost polytunnels) to desalinate seawater in arid regions to provide suitable growing conditions for food – or energy crops like algae.

Seawater is evaporated by drawing the hot desert air through a wetted cardboard wall in one side of the greenhouse. The cooled humid air passes over the crops and condenses to provide water for the crops. The humid air is then expelled from the greenhouse and can be used to improve the growing conditions for nearby outdoor plants: www.seawatergreenhouse.com. Sunny locations near the sea would obviously help, but the cost of piping sea-water long distances inland may not be significant.

The ‘Sahara Forest project’ is a supercharged variant of this concept, which would link huge greenhouses, potentially for growing algae, with concentrated solar power (CSP), which uses mirrors to focus the Sun’s rays and generate heat and electricity. The combination of these desert technologies would provide more energy for evaporation, pumping and algae production – and desalinated water for mirror cleaning, CSP cooling and algae production.

Further potential synergies could lead to higher bio-oil yields, says Crumpton. The thermo-chemical liquefaction and the trans-esterification of the algae ‘soup’ to produce bio-diesel could be achieved by heating some algae types to 300 °C under pressure for 30 minutes – just the job for CSP technology: www.futurity.org/earth-environment/pressure-cook-algae-to-make-better-biofuel/. Also, reject CSP heat could be used in power direct CO₂ air-capture devices and the CO₂ could be bubbled through the algae soup to enhance production.

Crumpton says that by 2040 bio-oil from such desert-based bio-energy systems, if proven, could be shipped to gas turbine or fuel cell/CCS gasification schemes in countries with more variable renewable energy resources (e.g. Europe), to provide reliable and carbon-negative daily grid back-up and strategic energy reserves.

By 2040, bio-oil importing countries could have extensive CCS infrastructure, deployed initially to abate gas and coal power stations and industry in the 2020s. A recent study of North Sea CCS deployment and storage potential estimated that there might be about 450 mt CO₂ per year injection capability by 2050. Crumpton estimates that this could equate to a carbon-negative potential of up to 2 tonnes per UK resident per year. He sees coal and gas CO₂ sequestration as paving the way for, and potentially being replaced by, CO₂ sequestration from bio-energy gasification, including imported algae.

It sounds pretty ambitious, but many of the components are in place or under development. CSP technology is moving ahead rapidly. New CSP technology, such as the ‘Mulk’ curved aluminium sheet mirror system, may achieve significantly lower costs compared to conventional glass troughs, by reductions in system weight and other design and construction benefits: www.mulkre.com.

Several experimental Seawater Greenhouse projects have been tried and tested. Soon the world’s first commercial Seawater greenhouse will be completed in Australia: www.seawatergreenhouse.com/australia.html.

Also algae production is picking up, for example Argentine company Oilfox has opened the country’s first plant to make biodiesel from algae, which it claims can be grown using seawater. There have been reports that a Texan company, Petrosun, has developed an algae-to-biofuels facility using a series of saltwater ponds spanning 1,100 acres.

CCS in geological strata remains unproven at large scale, and is sometimes seen as undesirable if it simply facilitates unchecked fossil fuel use, but the carbon negative bio-oil application proposed by Crumpton might give CCS a new renewable direction. Trials are also underway to enhance algae production by bubbling captured carbon dioxide through the algae ‘soup’. The Carbon Trust has launched a major algae R&D project funded by DECC.

Using deserts, algae and seawater would certainly avoid most of the land-use and biodiversity conflicts that have bedevilled biofuels so far, although there could still be conflicts with food growing that might otherwise be done in the seawater greenhouses.

Neil Crumpton has worked for Friends of the Earth and more recently the Bellona Foundation, which is a partner in the Sahara Forest project. He is currently a consultant to B9 Coal, which is a fuel cell/gasification CCS power-station project development company.

Posted by Dave Elliott on January 8, 2011 1:52 PM | Permalink