6. A supercritical once-through steam generator, comprising:a radiant section comprising a cylindrical horizontal housing having a burner end and an exhaust end opposite the burner end, a burner located at the burner end, at least one furnace coil running in a serpentine path between the burner end and the exhaust end circumferentially and evenly spaced along an internal circumference of the horizontal housing, and an outlet port at the exhaust end that leads to a convection flue, wherein a perimeter of the outlet port is formed by an arc and a chord; and
a convection section comprising a vertical housing that is located above the convection flue;
wherein the once-through steam generator is devoid of a steam separator;
wherein the convection section includes a superheater in fluid communication with the at least one furnace coil and an economizer above the superheater, the economizer being in fluid communication with the at least one furnace coil;
wherein the economizer is tapered, with a greater surface area adjacent the superheater; and
wherein flue gas generated by the burner travels horizontally through the radiant section and travels vertically through the vertical housing.