6.9 Alternative designs of heater construction
A brief description of older heater designs is included to indicate how other approaches to provide cost effective HP heaters have been tried.
The most expensive component in the construction of a conventional hemispherical water header type of HP heater is the water header. To reduce its cost and also its thermal inertia, designs incorporating a drum-type water header have been constructed.
Figure 3.55 (a) and (b) shows two different solutions for constructing an HP heater without a conventional water head. The heater shown on Fig 3.55 (a) was constructed for Thorpe Marsh power station and employed a central header with the mild steel tubes radially disposed, the tubes being welded to the header by the Foster-Wheeler method. The length of the tubes was such that they had to be constructed from several lengths of pipe butt-welded together. This length of tube was difficult to handle and adequate provisions had to be made within the shell to support the tubes. The only drawback to this design was its high cost of construction.
The heater illustrated in Fig 3.55 (b) was constructed by GEC and used mild steel tubes manually-welded to bifurcation pieces which were, in turn, welded to boiler superheater type headers. The bifurcation pieces were used to allow a smaller number of attachments to be made to the header to gain access for the attachment weld to the headers.
These heaters suffer from some tube erosion in the region of the bifurcations but, in general, have been a successful design. Because of the high cost of construction, the development of this design was not pursued.