Table 10. Experimental Designs of Four Factors and Three Levels.

			–6 + 3 mm lignite		–3 + 1 mm lignite
code	factor	unit	max.	min.	max.	min.	level
A	inlet temperature	°C	60	100	90	110	3
B	pulsating frequency	Hz	3.49	4.36	3.06	3.93	3
C	air velocity	m/s	1.02	1.16	0.48	0.61	3
D	bed height	mm	100	140	60	100	3