The development of caking propensity in a non-caking coal under hydrot
hermal conditions has been studied, using water up to 400 degrees C un
der autogenous pressure. Although it was not possible to obtain unifor
m development of caking propensity or to isolate a product with upgrad
ed caking capacity without in situ agglomeration, hydrothermal treatme
nt promoted the formation of a coke-like mass. The role of water near
its critical temperature in incipient hydrogenation was observed. Comp
arison with the normal coalification track provided apparent reasons f
or the observed limited development of caking propensity in the coal u
sed. The overall effect appears to be the resultant of deoxygenation o
r dehydroxylation, hydrogenation and polymerization reactions that may
be coal-specific.