Method of operating a fluid bed reactor

A method of operating a three-phase slurry reactor, the method including

• feeding at a low level at least one gaseous reactant into a vertically extending slurry body of solid particles suspended in a suspension liquid, the slurry body being contained in at least two vertically extending shafts housed side by side within a common reactor shell, each shaft being divided into a plurality of vertically extending channels at least some of which are in slurry flow communication and the slurry body being present in at least some of the channels, at least some of the shafts and/or channels being at least partially defined by heat exchange surfaces;
• allowing the gaseous reactant to react as it passes upwardly through the slurry body present in at least some of the channels of the shafts, thereby to form a non-gaseous and/or a gaseous product;
• allowing any gaseous product and/or unreacted gaseous reactant to disengage from the slurry body in a head space above the slurry body;
• withdrawing any gaseous product and/or unreacted gaseous reactant from the head space;
• and
• maintaining the slurry body at a desired level by withdrawing slurry or suspension liquid or by adding slurry or suspension liquid.