There is disclosed a process for dehydrating organic porous material such as brown coal. The process comprises steps of charging the material to a plurality of pressure vessels and filling at least one of the pressure vessels with water, carrying out a dehydration step by supplying steam to the vessel which is filled with water to heat the material therein while exhausting water from that vessel to thereby lower the water surface in the vessel so that the material therein is gradually exposed to the steam and water in the material is removed and mixed with condensed steam to form hot water, transferring the hot water from said first vessel to a substantially top portion of a second vessel while continuously supplying the steam to the first vessel until the second vessel is substantially filled with the hot water, and then expelling the hot water from a substantially bottom portion of the second vessel by the hot water which is transferred from the first vessel to the second vessel. As soon as the water in the first vessel is exhausted, the first vessel is separated from the other vessels and depressurized. An apparatus for carrying out such process is also disclosed.