Determination of hardness of briquettes
The hardness of the briquettes was determined with a Kiya hardness tester (Fujirara Seisakusho, Ltd., Tokyo, Japan).
The hardness of a briquette was the force required to break a briquette that was 20 mm thick using a 5 mm diameter plunger.
The hardness of the briquettes was determined at a moisture content of 20%, usually after 7 days for samples dried in the oven and 21 days for samples dried under ambient conditions.