The requirement design of superheater will be better to establish before manufacturing process will be performed. The design superheater should provide uniform distribution of steam and temperature at all loads, and provides thermal expansion of headers, tubes, spacers and supports, and should be accessible for cleaning, examination and removal of elements.
The designer of steam boiler should arrange the superheater tube banks as conveniently as possible to perform maintenance and periodic inspection. The requirement should describe what programs are being undertaken, if any, to resolve problems of gas side corrosion and erosion of superheater tube materials at elevated temperatures.
Horizontal tube sections of superheater should be arranged with sufficient clear spacing between tubes in the gas flow at least equal to tube diameter and such as to avoid slag formation. Tubes should be arranged in parallel rows. Horizontal tube banks in the convective pass may have minimum baffles installed for the prevention of acoustical standing wave formation.
The wall thickness for superheater tubes, at least, should have a corrosion and/or erosion allowance of not less than 0.5 mm. All superheater tube joints including connection to headers should be of welded construction in accordance with ASME BPV Section l.
Superheater tubes should be arranged and terminated in outlet headers in a manner which will yield through mixing of the steam, thereby resulting in the same temperature at each of the main steam outlets. The superheater arrangements should be provided so that by the arrangement of the connecting tubes and by the mixing points a uniform flow admission and sufficient temperature balance are insured.
Tube connections should be shop-welded stub ends on headers. Stub ends should be prepared for field welding of superheater tubes. Any welding of ferritic to austenitic stainless metals should be done in work shop.
Spacers and hangers for superheater tubes should be designed to provide for appropriate sliding expansion, and should be of material suitable for temperature encountered. All headers should be external to the gas stream and should be provided with welded inspection hole covers as required for inspection. The header in the gas stream should be shield 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, lest gauge and transmitter should be furnished. The design superheater must be equipped also with desuperheater and safety valve to control pressure and temperature.
Based on description above, requirement design of superheater is a must to be performed prior to begin manufacturing process to get high performance and efficiency.