Tar evolution in heated-grid apparatus

Inspection of tar evolution data from heated-grid investigations indicates nearly a 600 o C discrepancy in reported temperatures of tar evolution from HV (high-volatile) bituminous coal samples. For reportedly equivalent heating conditions―1000 o C/s heating to peak temperatures in 1 atm of helium and zero hold time―some investigators report half the tar evolved at temperatures from 550 to 600 K while others report peak temperatures of nearly 1100 K are necessary to achieve the same extent of tar evolution. The temperature dependences of tar yields for long-hold-time conditions in the different investigations are in much closer agreement, indicating that given enough time, the thermocouple and sample temperatures reach equilibrium in the various systems