Patent ID: 7637233
Filing Date: 2009-12-29
Classification: F22D

Abstract:
1. A system for sourcing a heated flue gas stream, directing the gas stream through a downstream device and maintain the gas stream entering the device within a desired temperature range or at a desired temperature, comprising: a heat exchanger located upstream gas flow-wise of the device, the heat exchanger having a flue gas inlet and a flue gas outlet and at least two tubular configurations disposed in a cross and/or counter-current heat exchange relationship with the flow path of the flue gas stream, the heated flue gas source being located upstream gas flow-wise of the heat exchanger, each tubular configuration having a feedwater inlet and a feedwater outlet, the outlet of both tubular configurations being attached to a separate or common outlet header and the inlet of each tubular configuration being attached to a separate inlet header, a control system configured to independently control the flow of feedwater through each tubular configuration while maintaining a substantially constant total flow of feedwater through the heat exchanger, a demand signal generator means for generating a proportioned or biased flow rate demand signal as a function of measured feedwater flow to the heat exchanger and fuel type used in the heated flue gas source, means for comparing a measured flow rate in at least one of the tubular configurations to the proportioned or biased flow rate demand signal, means for determining if there is a difference between the demand signal flow rate and the measured flow rate, and control valve means being responsive to said difference for modulating the flow of feedwater through at least one of the tubular configurations, and wherein the flow of feedwater through each tubular configuration is adjusted in a manner that transfers an appropriate amount of heat from the flue gas stream to maintain the flue gas stream entering the device within the desired temperature range or at the desired temperature.