10.2: New Solid Biofuels

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However, firewood is now “returning with vengeance”, as wood pellets. Single- home heating installations using firewood in such form are fully automatic and require little maintenance. The wood-pellet industry in the US is growing fast. Advantages: wood pellet heating systems emit no nitrous oxides (NO_x), no sulfur dioxide SO₂. The only product of combustion is CO₂ – but it does not add “new” CO₂ to the atmosphere, it only – as has been discussed earlier – “recycles” the natural CO₂. Moreover, there is much wood available for making pellets. There is one problem, though – it is called the “pollution by particulate matter”. The term particulate matter refers to microscopic solid or liquid particles suspended in the air. Until recently, the pollution by particulate matter was not the principal concern of institutions responsible for the cleanliness of air. But more and more results of studies pointed out to the odd effects of particulates on human lungs.

What first raised the awareness of public opinion to the seriousness of particulate matter pollution were diesel cars. Until recently believed to be the most environmentally friendly of all automobiles, they have been recenly found to emit too much particulate matter (and too much NO_x, either). Some big cities in Europe (where diesel cars are much more popular than in the US) plan in the near future to forbid diesel cars to enter the city centers. Some countries even consider banning sales of new diesel cars altogether in not-so-distant a future.

Figure \(\PageIndex{1}\): Wood pellets in someone’s hands, in order to show what the actual pellets’ size is (source: Wikimedia Commons).

Also, the wood pellet stoves, considered to be “the most green” of all house- hold heating technologies, started attracting attention. Even though they emit no NO_x, there is a growing concern about particulate matter in their exhaust gases. Fortunately, removing the particulates from the gases is tech- nically feasible – so there is no fear that pellet stoves may be banned altogether. But if new laws requires that all new stoves be equipped with filters efficiently removing the particulate matter from the gases, the prices of such heating installations my raise considerably. At the moment this text is writ- ten (2018) it’s not yet clear what may happen – at the moment, we can only “wait and see”.

There are still other possible applications for solid biofuels – we will return to this issue later, after discussing possible applications of liquid biofuels and methods of their production.