Requirement design of economizer is made to ensure that steam boiler can be performed efficiently. The requirement design of economizer should describe the provisions for preventing thermal fatigue damage to the economizer inlet manifolds, headers and tubing due to feed temperature cycling during hot banked conditions and start up. The economizer and its circulating system should be designed so as to avoid any serious water hammer caused due to steaming in the economizer tubes.
The economizer tubes can be seamless material. The economizer should be of a continuous loop drainable type and arranged for the upward flow of water and downward flow of flue gas. Staggered spacing and extended fins or studs will not be accepted. The minimum tube spacing should be not less than the spacing of the horizontal tubes which are located above economizer.
The economizer heating surface should be of effective heat transfer design, consistent with the minimum cross sectional free flow area in the tube bundle. The entire tube arrangement should be drainable.
Thermocouples with protection wells should be provided in the requirement design of economizer. Where required for access and inspection, doors should be provided with tight gasket joints.
All headers should be external to the gas stream except economizer inlet and junction headers which are located at low gas temperature area, and should be provided with welded inspection hole covers as required for inspection. The header in the gas stream should be shielded to avoid header damage caused by the flue gas. Inlet and outlet headers and/or lead pipes should have thermo wells with thermocouples and connections for pressure gauge and test gauge furnished in the requirement design of economizer.
Feedwater connection at the terminal point should be welded type and material to match Power piping. Double drain valves should be provided in the requirement design of economizer. In the case of extended surface type finned tube, a special consideration should be made in order to avoid undue fouling or plugging with ash.
The economizer tubes should be arranged to permit the installation and easy replacement of soot blowers and to permit future installation of additional soot blowers. The economizer support should be designed to permit free expansion of all pressure parts and to prevent excessive expansion stresses on the boiler.
The tube spacing of the economizer should be designed to minimize bridging and to avoid tube erosion. Sufficient numbers of baffle plates should be installed at convection zone, including economizer. Manholes installed on the baffle plates of economizer should be of the sliding door type. The casing should be gas tight, and sufficient access door for entrance should be provided at each section of the requirement design of economizer.