Sunday, 12 December 2010

Torrefaction - True or False?

It never ceases to amaze me how much misinformation there is about Torrefied Biomass.
Below are a number of claims that have been published – and I thought it would be fun to look at a few of them – and test your knowledge;
1) By using torrefied biomass, utility companies avoid additional capital expenditure in existing power plants T? F?
2) It is carbon neutral, as all renewable biomass sequesters an equal amount of CO during growth as is released upon its burning T? F?
3) An increase of the heating value per weight unit (9,500 to 11,000 Btu/lb) T? F?
4) Achievement of a hydrophobic property, with a moisture content of less than 3% T? F?
5) Improved grinding, crushing, or pulverizing properties (40 on the Hardgrove Grindability Index, comparable to coal) T? F?
6) Increased uniformity and durability T? F?
7) Torrefaction involves the removal of volatiles, most acids and smoke-producing agents T? F?
8) Each ton of torrefied wood burned in the facility reduces their carbon output by up to 2.4 tons, earning them an estimated $72 in carbon credits. T? F?
9) Torrefied wood can be handled just like coal. T? F?
10) It does not take on water so it can be left uncovered like coal. T? F?
11) During the torrefaction process, as most volatiles are burned off, eliminating the concerns over slagging in the boiler. T? F?

In fact – 9 of them are false
So . . . how did you do?
1) This one is TRUE, but only to a point. Many people are promoting and pumping the value of torrefied Biomass because it “offsets” high CapEx costs associated with handling; grinding storing and burning whitewood pellets. In fact – this ONLY applies to pellets, as most other biomass feedstocks do NOT need special storage and handling systems. It is also TRUE however – that ALL power stations put little to no “value” on these “avoided” costs. They simply pay the Climate Change Levy – and don’t burn biomass.
2) FALSE – ABSOLUTELY FALSE! True carbon neutrality could ONLY be achieved if the CO2 footprint left on the entire supply chain was zero (and this is HIGHLY unlikely). Certainly – biomass absorbs CO2 during its lifetime, and emits it during combustion – however – there are a lot of processes that embed energy into the harvesting; transport, manufacturing and handling of biomass. In the case of forest residues - It is also true that only 30% to 40% of the entire volume of feedstock is converted into fuel. The other 60% to 70% is effectively sequestered carbon (in the form of furniture, building materials, etc.) that could ultimately be converted into fuel. So – it is the FOREST that is carbon neutral – NOT the feedstock.

IF the entire supply chain were carbon neutral, EVERY piece of field equipment, truck and train would need to run on Bio-Diesel; delivered in trucks that run on bio-diesel; derived from a plant that is solar powered. The manufacturing facility would need to be powered by geothermal energy (heat) and solar PV powered (electric); the ships would need to be Gas turbine powered, from Syn-gas, derived from torrefied pellets. Having said that – let’s look at the RELATIVE Carbon neutrality to coal. On average, a ton of coal takes approximately 25 Gj of energy to mine, extract, process and transport. For that – you get 24-26 Gj of Derived energy – after imparting even further energy into handling, conveying, grinding and injecting. Torrefied Biomass, on the other hand, will have an embedded energy of about 2 Gj per tonne.

3) This one is also TRUE – kilo for kilo – torrefied biomass has a higher heating value than its non torrefied counterpart. This however – is predominantly a function of the removal of moisture from the feedstock.

4) FALSE – Most promoters extol the “hydrophobic” properties of torrefied wood. While it is true that it does resist water uptake, it is FAR from being hydrophobic. In fact – some of the “torrefied wood” we have tested actually absorbed MORE water than its untreated counterpart (Bamboo – for example). So – like most generalities – this one doesn’t hold true.

5) FALSE – Again, you need to define “improved”. Certainly – torrefied biomass is more friable – but it comes with a price. That price is explosivity of the dust (when it is kept dry) and the development of “sludge” when it is ground wet. Anyone who has undertaken any testing of torrefied material in a ball-grinder when the material was stored outside will tell you that this is a significant hurdle to overcome.

6) FALSE – Uniformity, and I’m defining that by the term homogeneous, has nothing to do with the process of torrefaction – and everything to do with the feedstock. A wide variety of feedstocks will produce a wide variety of finished products. After all – the old expression “Garbage IN – Garbage OUT” applies. Durability is the antithesis of Friability – so it CAN’T be both. Like most things – this is an area of compromise – where you trade off the durability of the pellets for CV, or Grindability, or particle size and shape. Sweeping generalities like this are commonplace, and simply not true.

7) FALSE, ABSOLUTELY, UNEQUIVOCALY FALSE. I think that this myth was initiated and perpetuated by Ahava Amen from New Earth Renewable Energy. He had a Wonderful U-Tube video that showed him holding a “standard pellet below a smoke detector after lighting it. Guess what happened? Give up? The smoke detector went off! THEN – he held a lit piece of torrefied wood below the same smoke detector – and Surprise . . . Surprise. . Surprise! The smoke detector DIDN’T go off! His explanation was that ALL of the volatiles had been removed from the Torrefied wood – and therefore no smoke could be emitted. (What UTTER Nonsense!) The reality is – that torrefied wood, on average, is about 70% volatiles. At least – ever test we have done – and every credible study I have read indicated the same thing. SO – how did the smoke detector remain silent? Simple breath of air blowing across the top of the pellet – to keep it “glowing” (and provide more complete combustion), while blowing the invisible smoke from the detector’s surface. You heard it here first.

8) FALSE – burning 1 tonne of coal and 1 tonne of torrefied wood release about the same amount of CO2. Actually – the coal does emit more (simply because it has a higher Carbon Content to begin with) but neither of them emits 2.4 tonnes of CO2 per tonne of fuel burned.
Coal with a heating value of 6.67 kWh per kilogram as quoted above has a carbon content of roughly 80%, which is where 1 mol equals to NA (Avogadro Number) atoms.
Carbon combines with oxygen in the atmosphere during combustion, producing carbon dioxide, with an atomic weight of (12 + 16 × 2 = 44 kg/kmol). The CO2released to air for each kilogram of incinerated coal is therefore 2.93 kg

9) FALSE – Torrefied wood has many specific handling requirements that make it significantly different from coal. Firstly – it contains much lower moisture than most coals, and produces a much more hazardous dust, both in terms of explosivity and health & safety. (Coal dust is certainly bad enough – but look up an MSDS on most biomass dusts and you will find that they are MUCH worse.) Many of the “torrefied” biomass products offered on the market today with high CV’s, are virtually charcoal – and if you research the MSDS and COSSH on charcoal dust – you will find that most jurisdictions classify it as “explosive” and “hazardous”. These characteristics necessitate very special handling protocols.

10) FALSE (see #4 above)

11) FALSE – COMPLETELY, UTTERLY, TOTALLY AND ABSOLUTELY FALSE!!!! Torrefaction has NOTHING to do with slagging characteristics of boilers. This is ALWAYS a function of the chemistry of the fuel; and is determined by the presence or absence of K and Cl mostly. It is the ASH MELTING temperature that is the critical determination. Certainly – torrefaction DOES remove a lot of the Acids from the raw feedstock, thereby improving its utility and reducing the tendency to corrode boiler pipes, but that’s about as far as it goes.

The lesson learned here is that, in spite of an ENORMOUS amount of factual Data available; hundreds of scientific papers; and untold thousands of tests – the Fallacies about torrefied biomass still run rampant.
Perhaps is it because people want to “appear” to know what they are talking about?
Perhaps it is a “belief”, based on “wishful thinking”?
Whatever the reason – now you know . . . the rest of the story. . .


  1. True or False: When biomass is subjected to Thermal depolymerization, torrefation takes place equally in ALL biomass?

  2. And this all means??????? There are no real experts, just scientific opinion. If all those involved don't understand this is all revenue driven, then maybe they should read the "Emperors' new clothes". Maybe everyone should start addressing torrefaction as a biomass fuel that is almost ready for the market, if the market is ready to accept it.