Abstract: In flue and water tube boilers provided with water tubes arranged in a combustion reaction zone or a convective heating zone, the values of L/D or H/D satisfy the following relationships:1.8.ltoreq.L/D.ltoreq.2.5 and1.2.ltoreq.H/D.ltoreq.1.7and the water tubes are disposed in an (aligned) in-line arrangement. L(mm) is the longitudinal pitch of the water tubes taken in the direction of gas flow, D(mm) is the outer diameter of the water tubes and H(mm) is the transverse pitch of the water tubes taken at right angles to the direction of gas flow.

Abstract: A watertube boiler for all types of boilers including natural circulation, forced circulation and one-through types. The boiler includes a plurality of heat absorption water tubes forming a heat absorption watertube unit in the furnace. The heat absorption watertube unit comprises a relatively dense arrangement of heat absorption water tubes disposed in the combustion path of the burner, such that the flame of the burner impinges on the unit. The heat absorption watertube unit can be arranged in the first stage of a watertube boiler having at least one additional furnace stage receiving exhaust gas from the first stage. The additional stage can be disposed either perpendicularly and horizontally, and the air/fuel mixture in each stage is maintained at a specificied ratio to optimize combustion of the fuel. A method of operating a watertube boiler having three stages is also provided.

Abstract: A heat exchanger for flue gas in which water tubes are inserted through the flue wall into the flue from the exterior thereof so as to be adjustable in the depth of insertion. Each of the water tubes has a structure comprising an inner water feed tube and an outer recovering tube for recovery of the waste heat by returning the water from the water feed tube to generate steam by heat transferring from the waste gas passing through the flue. Headers are provided at each exterior top of the feed water tubes and recovering tubes and are connected respectively to a water-steam drum through movable connecting tubes. The headers are movable in co-operation with driving means provided at the exterior of the flue so as to adjust the heating surface of the water tubes inserted into the flue by the action of the driving means.