Patent ID: 9696027
Date: 2017-07-04
CPC Classifications: F22B,F22D

Claim:
1. A fluid recirculation system of a boiler, the fluid recirculation system comprising: an economizer for transferring heat between a mixed water stream provided to a waterwall of a furnace and the flue gas exiting the furnace, the economizer configured to receive flue gas from a superheater and emit the flue gas into a selective catalyst reduction (SCR) system; an arrangement of flow control valves located to receive a recirculation fluid stream, including steam, from the waterwall of the furnace; a fluid stream path in direct fluid communication with the waterwall of the furnace and the superheater; a recirculation flow path in fluid communication with the fluid stream path to provide the recirculation fluid stream to the arrangement of flow control valves; an economizer inlet mixing device including an inlet to receive a feedwater stream, and a sparger assembly located within the economizer inlet mixing device to receive the recirculation fluid stream from the arrangement of flow control valves and the feedwater stream from the inlet, wherein the inlet is offset by less than ninety degrees from a central axis that extends through the economizer inlet mixing device defining an offset angle of the inlet; an outlet to provide the mixed water stream to the economizer controlling a temperature of a flow of fluid entering the economizer; and a temperature of the flue gas is increased in the economizer to exit at an optimum value for operation of the SCR system at less than full load, with the outlet flow of fluid from the economizer recirculated to the waterwall; wherein the sparger assembly and the offset angle of the inlet allow for optimum mixing of the recirculation fluid stream and the feedwater stream so that the temperature of the flow of fluid entering the economizer is precisely controlled to thereby control the temperature of the flue gas exiting the economizer to the optimum value to ensure catalyst reactiveness in the SCR system.