One embodiment of the invention consists of a vertical cylindrical process heater with an overhead
convection section, a radiant section containing a contiguous,
helical, down flow, tubular radiant coil, and one or more top, downward fired, pulverized
coal burners. A second embodiment consists of a cabin type heater having a radiant section of rectangular cross section, a contiguous
vertical tube serpentine coil, an overhead
convection section, and one or more bottom, horizontally fired, pulverized
coal, end wall burners. A third embodiment consists of a process heater with a radiant section and overhead
convection section, the radiant section having a vertical cylindrical, contiguous,
helical, down-flow tubular coil, contained in a
refractory lined
enclosure of square cross-section. A continuous chain grate
coal stoker is provided at the base of the radiant section. A coarse coal feed with a minimum of fines is fed thru a hopper located at one end of the traveling chain grate and essentially coal free ash is removed at the opposite end of the chain grate, thru a
nozzle provided with a water seal. One or more centrifugal solids-gas separators are provided at the radiant section
flue gas outlets in the case of all three embodiments, for the purpose of removing ash
particulates from the
flue gas streams, before the latter enter the overhead convection sections. Since the
flue gas enters the convection sections very nearly devoid of
particulates, the convection sections may be of conventional design utilizing bare and / or finned tubes on closely spaced equilateral or
quadrilateral centers.