by Graeme » Tue 13 Jan 2015, 19:23:45
The Economics of Waste to Energy -- Part I
$this->bbcode_second_pass_quote('', 'F')uel cell manufacturers worldwide have been examining waste-to-energy applications (WtE, also referred to as EfW, energy from waste, and more specifically hydrogen from waste) since the early 1990s. During that time, proton-exchange membrane (PEMFC), alkaline (AFC), molten carbonate and direct carbonate (MCFC/DFC), solid oxide (SOFC), and phosphoric acid fuel cells (PAFC) have been demonstrated. Recent, promising WtE economics are resulting from biogas-fueled fuel cells that can generate multiple revenue streams at MW scale.
Compared to the hydrocarbon-based ‘dirty’ fuel options (such as flaring methane and burning coal), WtE conversion of biohydrogen (bioH2) for use in fuel cells offers the cleanest electrical power available. In many cases, fuel cell WtE installations can produce combined heat and power (CHP) onsite along with excess electricity, hydrogen, and carbon dioxide (CO2) that can be sold back to the grid and other customers.
Granted, there may still be a ‘dirty’ connotation associated with various non-hydrocarbon feedstocks, based on their unique origins in the organic waste realm. From hog farms in China to dairies in Minnesota (think manure management), food and manufacturing waste in Japan, forestry dross in Pennsylvania, to agricultural silage (such as grasses and molasses), potato peel, onion skins, pond scum (algae), chicken litter, and sewage sludge, this stuff can be mighty stinky. Yet there's no garbage in the fact that such solid waste material (some 11.2 billion tonnes per annum collected worldwide) can be converted into biomass – and from that, renewable bioH2 as a reliable fuel resource for powering fuel cells.
Beyond solid waste, existing landfills, wastewater treatment plants (WWTPs), and chemical and manufacturing plants currently emit by-product hydrogen directly or as a component of waste methane gas. Although regulated, by-product methane is often flared (burnt off), making it an unused asset and creating pollutants such as nitrous oxides. The US Department of Energy (DOE) reports that, if captured, annual domestic methane emissions from these facilities could provide an estimated 12.9 million tonnes per annum as a biofuel source, and in turn, generate around 8.3 million kg of bioH2 per day.
Furthermore, the 40 000 anaerobic digesters already operating in the US industrial sector could provide 300 million m3 (10.8 trillion cubic feet) of bioH2 and another 200 million m3 (7 trillion cubic feet) of bioH2 from landfill gas. [Anaerobic digestion occurs in oxygen-free, sealed reactors where micro-organisms break down biomass.] An estimated 15% – or 216 000 tonnes per annum – of excess hydrogen produced annually from chlor-alkali manufacturing is flared. At a 50% conversion rate to fuel cell-grade hydrogen, this biogas resource could produce 420 MW of electricity.
renewableenergyfocus
Human history becomes more and more a race between education and catastrophe. H. G. Wells.
Fatih Birol's motto: leave oil before it leaves us.