Evaluation Of The Fuel Properties And Thermal Efficiency Of Sub-Bituminous Coal-Biomass Blends

ABSTRACT

The improvement of the combustion properties of coal and biomass by blending and

carbonization was investigated. Proximate and ultimate analysis of coal, sawdust, corn cob

and their blends were carried out using ASTM methods. The proximate and ultimate analyses

were repeated on the five blends after carbonization at 500oC for one hour. Ten mixtures of

coal-sawdust and coal-corn cob blends were made into briquettes using starch binder. The

calorific values of the samples were determined using a bomb calorimeter, while the thermal

efficiency of the briquettes was obtained using the water boiling test analysis. Pollution

potential of the fuel samples were derived using a hypothetical power plant simulation. The

quantity of CO2, NO2 and SO2 that would be emitted per hour in a 20MW power plant were

calculated. The result of the proximate analysis of the raw samples (coal, sawdust and corn

cob) showed that coal had the highest fixed carbon (42.38%) and the lowest moisture content

(4.28%). Sawdust had the lowest fixed carbon (12.35%) while corn cob had a fixed carbon

content of 15.65%. The results obtained showed considerable correlation between the

uncarbonized coal-sawdust and coal-corn cob blends. The carbonized blends of both the coalsawdust

and coal-corn cob blends showed an improved fixed carbon content and volatile

matter, relative to the uncarbonized. The calorific values and other fuel properties were of

similar trends. The results of the ultimate analysis for coal were 70.04% carbon, 5.32%

hydrogen, 2.03% nitrogen and 1.02% sulphur. Corn cob had 48% carbon, 5.79% hydrogen

and 0.89% nitrogen while sawdust had 48.78% carbon, 5.79% hydrogen and 0.89% nitrogen.

Corn cob and sawdust had no sulphur content, while the uncarbonized coal-sawdust and coalcorn

cob blends showed decreasing carbon content. This study revealed that the fuel

properties of coal and biomass can be improved by blending and carbonization. The

simulated power plant analysis of the fuel showed that blending of coal with biomass reduced

the SO2 and NO2 emissions to an extent. For NO2, the value of coal-sawdust blends ranged

from 82.8-190.8 kg/hr, reduced from 198 kg/hr in coal, while the SO2 content was reduced

from 60.5 kg/hr in coal to 5.6 – 50.4 kg/hr in different blends. Therefore, blending of coal

with either sawdust or corn cob should be encouraged in coal fired power plants to reduce

environmental pollution.