A boiler for making super heated steam by indirect heat exchange of water
against a hot gas, said boiler being a vertically oriented vessel
comprising a spirally formed conduit around the vertical axis of the
vessel, which vessel is provided with an inlet for hot gas fluidly
connected to the lower end of the conduit for upwardly passage of hot gas
through the spirally formed conduit, an outlet for cooled gas fluidly
connected to the upper end of the conduit, an inlet for fresh water and a
vessel outlet for super heated steam,said vessel further provided with a
water bath space in the lower end of the vessel and a saturated steam
collection space above said water bath space,said spirally formed conduit
comprising of a spirally formed evaporating section located in the water
bath space and a spirally formed super heater section at the upper end of
the vessel, wherein the conduit of the super heater section is surrounded
by a second conduit forming an annular space between said super heater
conduit and said second conduit, said annular space being provided with
an inlet for saturated steam fluidly connected to the saturated steam
collection space and an outlet for super heated steam located at the
opposite end of said annular space and fluidly connected to the vessel
outlet for super heated steam, wherein outlet or inlet are positioned in
water bath space.