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Let’s talk about Biomass. You’ve asked all the questions to ensure a “sustainable source”. It’s allegedly “carbon-free”. Well it’s not! Let’s ignore for the moment the energy used to cut down the tree, mash it up into chips or pellets and then transport it (apparently from Poland to Durham for example); first from the forest to be processed and then to the end-user (that unless it’s all done by renewably generated electricity (or man and horse power) isn’t emission free). The burning of wood (or alfalfa or whatever biomass we choose) emits carbon to the atmosphere by definition. And it emits more carbon than obtaining the same amount of energy from natural gas would have done! That’s simple chemistry; all cellulose (which is the basis of all biomass) has more Carbon in relation to Hydrogen in its molecules (it varies according to type so I can’t be more specific[1]) than natural gas (mostly Methane CH4), so when burnt more of the energy is released from the generation of Carbon Dioxide than from the production of water.

“OK I emit more carbon dioxide, but that was fixed from the air anyway so it is circular and I’m not increasing the concentration” Unfortunately NO! The carbon WAS fixed from the air, but over the course of the years the tree was growing (OK this argument may not work as well for short rotation crops but…) but you’re releasing ALL of it NOW! That HAS to increase the concentration in the atmosphere and the balance will only be restored when a similar tree has reached the same growth state.

Now let’s consider the efficiency of the boiler. Gas boilers can now have claimed efficiencies of over 95% (in reality it will be rather lower say 85% seasonally) can Biomass boilers claim that? (most are lucky to get peak efficiencies of 80% and seasonally they are MUCH lower -some of the reasons are below). Do they condense to retrieve the latent heat from the flue gas? (if they do they won’t last very long! Phosphoric Acid (found in Biomass Flue gas) for example is much more corrosive than the weak carbonic acid in gas boiler flues), can they be controlled very accurately, turned off immediately the heat demand is satisfied? Unfortunately, because the fuel delivered is a solid, it (well really the heat within it) can’t be delivered immediately on demand or turned off immediately, so it will often be “smouldering” releasing carbon dioxide and generating heat with no purpose. Obviously if you size the boiler to be always running this problem goes away but how often does that happen[2] ?

Combustion is also less efficient, it being much harder to mix solids with air, some of that means that the ash still contains unburnt fuel (not an environmental problem the carbon just stays locked in it!) and evidence of sooting in flues suggests Carbon Monoxide (poisonous!) and particulate carbon are being released (particulate carbon is why you shouldn’t drive diesels in city centres[3]) more waste and pollution.

Now consider the attitude of the consumer. They know that the biomass prevents them from adding to climate change so they can control for comfort, can’t they? The biomass plant doesn’t respond as quickly as people would like, so they are likely to compensate. They may well start it earlier so as its slower (perceived) heat up time won’t be an issue. They may well also note a greater drop in temperature occurring before the system can respond to decreasing internal temperatures (good control and design can sort that out but…) and respond by increasing the set temperature “so we don’t get cold” -so now we use even more energy (let alone release more CO2!).

So your “Carbon- free” biomass will (if not properly controlled) use more energy and increase atmospheric carbon dioxide by more than gas (and a number of other fuels!) – should you get rid of it?+

My Answer is NO! just stop being smug accept that you are not completely blameless and do what you can to minimise wastage and use it properly ( limit hours of operation, keep temperatures under control and maintain insulation standards). And insist that more trees/alfalfa or whatever is planted than you consume fuel. Now let’s abuse electric cars….

[1] If cellulose were an infinite polymer it would tend to a ratio of 2 Hydrogen to 1 Carbon (it must be less because of other elements involved) compared with Methane’s 4:1

[2] My Blog “Big is Better?”


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