03.08.2015   Technologies for Converting Biomass to Useful Energy

CO and CO2 emissions

Figure 3.23 and Figure 3.24 present the CO2 and CO exhaust concentrations for TXL andTXL:DB blended fuels, respectively. Very little CO was formed in the lean regime. In lean combustion, there

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Figure 3.21. Equivalence ratio based on air flow rates (^a:F is same as ^flow) and the calibrated fuel flow rate vs. equivalence ratio based on O2% in exhaust for TXL and TXL:DB blended fuels (adopted from Lawrence, 2007).

A:F ф vs. Exhaust Ф

♦ WYO 19M WYOIA PC DB-SspS 490-‘0 WYOiAPC 08 SspS «80-20 WYO lA-PC-Oe-SspS 1.1 ————————

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1 Exhaust

Figure 3.22. Equivalence ratio based on air flow rates (^a:f is same as ^flow) and calibrated fuel flow rate vs. equivalence ratio based on O2% in exhaust for WYO and WYO:DB blended fuels (adopted from Lawrence, 2007).

is sufficient oxygen for all the carbon to fully oxidize to CO2. However, once combustion became oxygen deficient CO begins to be formed. In general, the blended fuels produced more CO because the DB fuels contained more oxygen and they release more CO during pyrolysis.

The equivalence ratio was based upon measured air and calibrated fuel flow rates. It is apparent that CO2 peaked at approximately the stoichiometric condition. As air flow was increased from

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the stoichiometric point, the excess air diluted the flue gas concentrations. This dilution effect decreased the CO2 percentage. On the other hand, if air flow was decreased below the stoichio­metric air flow rate, less CO2 was formed due to insufficient O2 to oxidize fuel-bound carbon. This explains why the peak in CO2 was at approximately stoichiometric.

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WYO presented trends similar to those ofTXL:DB blends. Figure 3.25 and Figure 3.26 present the CO2 and CO concentrations for WYO and WYO:DB blended fuels. The wider uncertainty bands for CO were due to the uncertainty in CO measurements being a percentage of the reading. The uncertainty bands overlap too much to draw any conclusions about the effect of blending coal with DB on CO production. The equivalence ratio was based upon air and fuel flow rates.

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Figure 3.27. Effect of fuel on BF forTXL andTXL:DB blended fuels. Note that in the rich regime, the BF overlaps for all fuels. This indicates that the same percentage of all fuels was burnt (adopted from Lawrence, 2007).