Abstract: The invention relates to a liquid to solids heat exchanger and to a process for retorting carbon-containing solids (e.g. oil shale) using such heat exchanger. The heat exchanger contains a liquid pool reservoir, heat source or heat sink for heating or cooling the liquid pool, a support for the solids such that there is heat exchange between the solids and the liquid pool without direct contact of the solids and the liquid pool, and oscillators or vibrators to cause the solids to be conveyed while exchanging heat with the liquid pool.