Patent ID: 7578265

Claim:
A system for sourcing a heated flue gas stream, directing the gas stream through a downstream device and maintaining the gas stream entering the device within a desired temperature range or at a desired temperature, comprising: an economizer located upstream gas flow-wise of the device, the economizer 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 economizer, 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 economizer, and wherein the flow of feedwater through each tubular configuration is adjusted in a manner that transfers an appropriate amount of heat from the gas stream to maintain the gas stream entering the device within the desired temperature range or at the desired temperature.