A process for obtaining heat from combustion of a fuel, wherein the process takes place in a single vessel, wherein the process comprises the steps of: i) providing a combustion chamber comprising a fluidized bed material and means for transferring heat out of the combustion chamber; ii) introducing the fuel and a gas into the combustion chamber; iii) introducing a sorbent into the combustion chamber wherein said sorbent is capable of adsorbing sulphur containing compounds; iv) producing a gas stream comprising primarily of CO 2 and H 2 O by combustion of the fuel; and v) transferring the heat produced by the combustion of the fuel out of the combustion chamber; wherein the bed material comprises at least a first material comprising particles having a first minimum transport velocity and a second material comprising particles having a second minimum transport velocity, and wherein the minimum transport velocity of the particles of the first material is greater than the minimum transport velocity of the particles of the second material; wherein the first material comprises an oxygen carrier capable of transferring oxygen to and from the gases in the combustion chamber generated by the localized or distributed partial oxidation of the fuel; wherein the second material comprises the sorbent; wherein the oxygen carrier is selected from the group consisting of ilmenite, and synthetic materials composed of Ni, Cu, Mg, Fe, or Mn; wherein the gas introduced into the combustion chamber comprises oxygen and a moderating gas; and wherein introduction of the gas into the combustion chambers fluidizes the bed material and elutriates a portion of the sorbent. i) providing a combustion chamber comprising a fluidized bed material and means for transferring heat out of the combustion chamber; ii) introducing the fuel and a gas into the combustion chamber; iii) introducing a sorbent into the combustion chamber wherein said sorbent is capable of adsorbing sulphur containing compounds; iv) producing a gas stream comprising primarily of CO 2 and H 2 O by combustion of the fuel; and v) transferring the heat produced by the combustion of the fuel out of the combustion chamber; wherein the bed material comprises at least a first material comprising particles having a first minimum transport velocity and a second material comprising particles having a second minimum transport velocity, and wherein the minimum transport velocity of the particles of the first material is greater than the minimum transport velocity of the particles of the second material; wherein the first material comprises an oxygen carrier capable of transferring oxygen to and from the gases in the combustion chamber generated by the localized or distributed partial oxidation of the fuel; wherein the second material comprises the sorbent; wherein the oxygen carrier is selected from the group consisting of ilmenite, and synthetic materials composed of Ni, Cu, Mg, Fe, or Mn; wherein the gas introduced into the combustion chamber comprises oxygen and a moderating gas; and wherein introduction of the gas into the combustion chambers fluidizes the bed material and elutriates a portion of the sorbent. <EOS>