Method and apparatus for heating the bed material in a PFBC plant

A method of heating of bed material in a PFBC plant including a combustor and wherein bed level adjustment due to a load change is accomplished by injecting bed material into or discharging it from the combustor through feeding devices, said method including the steps of:

• arranging at least two storage vessels in communication with the combustor, each adapted for injecting bed material therefrom to the combustor and for storing therein bed material discharged from the combustor;
• heating and maintaining temperature of the bed material in the storage vessels at a temperature substantially corresponding to the bed temperature by:
• a) injecting bed material into the bed from one of the storage vessels while simultaneously discharging equal amounts of bed material from the combustor into the other storage vessel;
• b) reversing the direction of the bed material flow when the amount of bed material in one of the storage vessels reaches minimum or maximum volume limitation;
• and
• c) controlling simultaneous injection and discharge of the equal amount of bed material between the storage vessels and the combustor to ensure constant bed level in the combustor.