The Geology of coal in the Netherlands IV - New production methods - 4. Underground coal gasification with heat recuperation

Abstract

Gasification of coal occurs at high temperatures. The energy present in the coal, as far as it is not converted into the chemical energy of the gas produced, is liberated in the form of sensible heat. This heat will be carried along by the gases and is partly lost to the cap and base rock of the thin coal layer; the rest of this heat is carried off through a production well. During the cooling process, part of the combustible gas will be reconverted into non-combustible components. This generates further heat. All this heat represents an important part of the energy originally present in the coal. This part can approach values of 100% under unfavourable process conditions or even more than 100% if steam is injected. Because coal in The Netherlands occurs in thin layers and at great depth only small amounts of this sensible heat can be recuperated at the surface. By adapting a heat recuperation method from the oil technology we aim to transfer the heat left upstream of the reaction zone back to this process zone, to accomplish a more efficient gasification process and to avoid excessive temperatures in the production well.