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AN OVERVIEW OF A RELATIVELY SIMPLE METHOD TO DETERMINE THE BIOGENIC VERSUS FOSSIL FUEL COMPONENT OF A SOURCE EMISSION: BS ISO 13833: 2013
In this world, the origin of waste is becoming increasingly important to operators who dispose of waste. Often, taxation on the disposal of waste is based on its biogenic credentials. Rebates are sometimes given where energy is produced from sustainable renewable biomass or biogenic material. For waste sites, biogenic materials may be taxed very differently from non-biogenic materials.
As producers of goods get more adept at producing products either wholly from biogenic sources or from a mixture of biogenic and renewable sources, the diffi culty in distinguishing between material that is fossil fuel based or biogenic based is becoming increasingly diffi cult; and yet there are fi scal reasons to distinguish the biogenic make up of waste materials.
The standard methods are: 1. All the material is CO2
Neutral; this is ideal where the waste
stream all arises from a single known sources such as biomass e.g. straw, willow etc.
2. Selective Dissolution Method (SDM); a small fraction of the waste is treated with an oxidising agent, typically a mixture of hydrogen peroxide and sulphuric acid. The biomass fraction is oxidised faster than non-biomass fractions and hence the amount of biomass can be calculated after correcting for moisture, inert materials (such as ash) and the amount of carbonates present.
3. The Reductionist Method; this can be applied where the biomass content is in the range 20-80%. It doesn’t work well where there are high calorifi c contents in the waste (such as fats). The calorifi c value (CV) of the fuel is determined along with the ash content, and moisture content. Then, knowing the CV of individual constituents of the waste, the percentage biomass can be calculated. Unsurprisingly this works well where the contents of the waste stream are well defi ned/characterised.
Based on the 14C values measured in the summer of 2011 at measurement site Lutjewad (NL), a pmC value of 104 % for biomass grown and harvested in the period of 2010-2012 is obtained (oral communication with S. Palstra dated 2011-11-07).
4. The Manual Sorting Method; the waste is sorted into sub- fractions and categorised. It is then sorted into material that is bigger than 1 cm, dried and weighed. The precision of this method can be assessed using the SDM method discussed earlier. This should be carried out in triplicate. Any signifi cant differences in the SDM results suggest that either the sorting method is poor or that the waste is highly heterogenous.
If we consider the incineration of refuse, the tax associated with the disposal of waste is becoming crucial. Furthermore, there are tax benefi ts from the energy regulators where it can be proven that the waste was biogenically derived. Traditionally how was this achieved?
It hasn’t been a pleasant process, as anyone involved will tell you. Ideally, fi rst take 50 tonnes of waste, then split it into a smaller amount and attempt to classify the material visually (remember this is the contents of your dustbin/wheelie bin etc.). Then aim to obtain a 10-20g sample which is representative of that waste! Once you’ve got the “representative sample” what next? Analyse it using the methods discussed above! Clearly, although there are Standards to help do this, the process is hugely manual and subjective. Now add to this the fact that manufacturers of plastics are aiming to make a recyclable or bioplastic which is indistinguishable from a fossil fuel-based product, and the process becomes even worse.
However, there are better ways to do this that are far more elegant. The Carbon-14 (14
C) method is one such alternative.
Is it diffi cult, dangerous, or not very good? Well, the answer to all these is no, it works really well. It relies on the fact that the naturally occurring isotope of 14
C. It is routinely used to C has a half-life of 5730 years. It
is formed from cosmic neutrons interacting with nitrogen in the atmosphere. Plants then absorb the 14
carbon date archaeological artefacts. In addition, anything over 60,000 years old has no detectable 14 devoid essentially of 14
14
C relatively speaking. Is there anything that makes the determination of 14
C more
diffi cult. Well of course there is, this is real life! In the 1950s & 1960s the nuclear weapon tests changed the natural background levels. The levels increased dramatically and have been decreasing since. The graph below shows how 14
Cbio has changed since the
1960s. Other notable events which have affected the levels have included further nuclear weapon trials in the 1980s and the Chernobyl disaster.
It has subsequently been decided that the current level is 104- 105% pmC (percentage of modern Carbon) of the 14 1950. This is accepted to be our datum.
C levels of C present. So, fossil fuels are C, whilst more recent biomass has a lot of
Key Figure 1 - Decrease in 14 Cbio value in the atmospheric air CO2 (in pmC),
measured at high Alpine stations Vermunt (Austria) and Jungfraujoch (Switzerland) (see Reference [1]; for data 2004- 2008: personal communication
S.Palstra with I. Levin)
[1] Levin I. & Kromer B.: Radiocarbon 2004, 46, pp1261-1272
1 fl ue gas 2 probe 3 heater 4 primary fi lter 5 heated sample line 6 dehumidifi er unit
7 water discharge 8 secondary fi lter 9 sampling pump 10 bypass valve 11 to analyser(s) 12 manifold 13 fl ow meter (optional)
Figure 2 - Example of sampling train for proportional sampling
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14 exhaust 15 mass fl ow controller 16 CO2
absorber (LS)
17 velocity measurement 18 fl ow rate meter
CO2
Absorber can be:
• Liquid Impinger with 1mol/l NaOH or KOH • A Caustic Solid Absorber (Ascarite II) • TedlarTM
Gas Bag Collector
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