July 2012 UPDATE: Since the end of June, and as planned, two units are back to normal operation at Tilbury. The rest of units are expected to be working in one month time. More importantly, RWE officials have now confirmed to the press that the fire was caused by self-heating of biomass pellets leading to a smouldering fire: "it is likely that the increased levels of oxygen caused the ignition of the smouldering dust" [Utility Week].
Nov 2012 UPDATE: The largest power station in the UK, Drax, is ready to burn biomass too. They are building four giant domes to store the fuel, about 30 m tall each. I am not familiar with the internal divisions of these domes, but I note that it seems well above the critical self-heating size, specially during summer time. See the domes in this video of the BBC.
|Panoramic of Tilbury Power Plant before the fire. Photo from www.rwe.com|
|Tilbury Power Plant during the fire (2012). Photo from East News/www.mirror.co.uk|
Tilbury was a ~1100 MW coal-fired power plant buitl in 1969. Now it is one of the biggest and most environmentally-friendly combustion power plants in the world after having gone a partial reconversion to biomass burning (750 MW, biomass shipped from the US [The Guardian]). The conversion aimed to "prove that sustainable biomass can play a role in long term carbon reduction, it is crucial to test the technology on large-scale" [RWE]. It was just about to star operations of these new facilities when the fire took place.
I look forward the results of the ongoing fire investigation to identify the cause and origin, but I could not avoid jumping into some some early conjetures.
The fire started in the new biomass storage units where fresh loads of biomass had been stored for the first time (~6,000 tons of biomass pellets). This strongly hints to self-heating as the most probable cause. Self-heating refers to the tendency of certain materials, like biomass pellets and coal, to spontaneously heat up and smoulder at ambient temperatures. This can result in a spreading fire without intervention of any external heat source. The topic is one of my fields of expertise. Power companies know well how to avoid self-heating of coal piles (small stockpiles, ventialtion, quick turn overs) but when a new reactive solid is stored (in this case biomass) the problem can go undetected until the accident takes places. This is the price of innovation. Several types of biomass pellets are known to be more reactive at low temperatures than coal. And this would not the first time that the hazard has been underestimated by applying coal self-heating standards to biomass storage.
Unfortunately, all the biomass involved in the fire was burnt and none of the heat could be used for power or human comfort. The associated pollution (CO, VOC, PAH) and CO2 reached the atmoshpere wihtout giving us any of the potential benefits. Thin favour to sustainablility.