Abstract: A steam generating system including an upright furnace section formed by a plurality of tubes, a portion of which have upper and lower tube ends and extend at an acute angle with respect to a horizontal plane, a portion of which extend vertically downwards from the lower tube ends, and a portion of which extend vertically upwards from the upper tube ends. Additional lower and upper vertical tubes are provided which are coplanar with, parallel to, and evenly distributed and interlaced among the tubes extending vertically from the respective lower and upper ends. Means is provided to pass fluid through the length of the furnace section to convert a portion of the fluid to steam or to heat the fluid, the fluid passing upwards first through the additional lower vertical tubes, then through the length of the angularly extending tubes including the vertical extensions thereof, and then through the additional upper vertical tubes.

Abstract: A system and method are disclosed for lowering NO.sub.x levels in flue gases of a fluidized bed reactor using selective non-catalytic reduction. A reactor is connected to a separator by a duct, and a reactant is introduced into the duct for decreasing NO.sub.x levels in the flue gases passing from the reactor, through the duct, and into the separator. The reactant, such as ammonia or urea, is selectively injected into a gaseous-rich region of the duct, near an upper, inner portion of the duct, so that a high degree of mixing of the reactant with flue gases is achieved while maintaining a low degree of mixing of the reactant with the particulate materials. The point of injection of the reactant into the duct is also at a location nearer to the reactor than to the separator to provide for increased residence time. In this manner, the reactant is used efficiently while obtaining the desired lowering of NO.sub.x levels in the flue gases.