portion of header at tube connection shall not be insulated. Method of
tube attachment to headers shall be by strength welding or by rolling, seal
welding, and rerolling in accordance with ASME BPVC SEC I. Rolling of
tubes into headers only is not acceptable.
2.2.1.2
Tubes
Tubes shall be electric welded or seamless steel. Boilers shall have
water-cooled furnace walls of a design suitable for the application. Tubes
located in the primary furnace shall be designed for horizontal or upflow
of water. The water shall be distributed to the heating surface in
proportion to the heat absorbing capacities of these surfaces. Tube heat
absorbing surfaces shall be located so that radiant and convection sections
provide for series flow of water, from generator inlet to outlet, to ensure
uniform water distribution and uniform temperature rise from inlet to
outlet. Where required, flow orifices shall be provided. Each orifice
shall be protected from clogging by individual strainers or by the master
strainer located in the HTW generator return line. If individual strainers
are utilized, individual access openings for each strainer shall be
provided. Access plugs, if used, shall be of the shoulder type with
machined surface. The individual access openings shall be provided with
stainless steel filled gaskets. All header gasket surfaces shall be
machined to provide proper seating of gasket.
2.2.1.3
Baffles
Baffles shall be arranged to bring the products of combustion into contact
with the heating surfaces. Baffles shall be either water-cooled or a
refractory material or metal suitable for temperatures encountered. Steel
plate or refractory baffles, if used, shall be provided with water cooling
on the radiant heat (furnace) side. The generator's convection section
shall have counterflow, water-to-gas, to provide an integral economizer
arrangement for optimum heat absorption, gas-to-water. Draft loss shall be
held to a minimum.
2.2.1.4
Furnace
Furnace shall be water-cooled and the combustion space shall be provided
with water cooling on sidewalls, rear wall, roof, and front, except the
portion of the front wall section required for [stoker installation] [and]
[burner installation]. For stoker-fired generators, furnace side walls and
rear wall shall be water-cooled by vertical tubes with center-to-center
spacing not to exceed twice the tube diameter, and shall be furnished with
cast-iron, water-cooled armor block at the grate line to a height of not
less than 380 mm 15 inches above the grate line. The armor block shall be
keyed and held in place without the use of bolts, pins, or mastic. The
armor block shall be readily replaceable without the use of special tools.
2.2.1.5
Supports
HTW generators and firing equipment shall be supported from the foundations
with structural steel independent of all brickwork. HTW generator supports
shall permit free expansion and contraction of each portion of the HTW
generator without placing undue stress on any part of the HTW generator or
setting.
2.2.1.6
Access Doors
Access doors in sufficient number, of adequate size, and properly located
SECTION 15555A
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