Economizer water recirculation system for boiler exit gas temperature control in supercritical pressure boilers

Patent metadata

Field	Value
Publication number	US-9696027-B2
Application number	US-73153910-A
Country	US
Kind code	B2
Filing date	Mar 25, 2010
Priority date	Dec 21, 2009
Publication date	Jul 4, 2017
Grant date	Jul 4, 2017

Abstract

A fluid recirculation system includes an arrangement of a flow control valve located to receive a flow of fluid from an inlet. The system further comprises an economizer inlet mixing device located to receive the flow of hotter fluid from the arrangement of the flow control valve and from a cooler feedwater stream. An economizer inlet mixing device located upstream of an economizer in a supercritical pressure boiler includes a sparger assembly through which a flow of fluid from the waterwall outlet is received, an inlet through which a flow of fluid from a feed stream is received, and a wave breaker assembly through which an outlet stream from the economizer inlet mixing device is directed.

First claim

What is claimed is:

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.

2. The fluid recirculation system of claim 1 , further comprising a recirculation valve arrangement located at the outlet from the economizer inlet mixing device upstream of the economizer.

3. The fluid recirculation system of claim 2 , further comprising a bypass line to direct at least a portion of a flow of fluid around the recirculation valve arrangement to the economizer.

4. The fluid recirculation system of claim 1 , further comprising a check valve located upstream of the arrangement of flow control valves.

5. The fluid recirculation system of claim 1 , wherein the arrangement of flow control valves comprises at least one of a pneumatic- and a motor-actuated temperature-controlled valve to control the amount of recirculation water stream to the economizer inlet mixing device in accordance to a desired temperature of the mixed water stream.

6. The fluid recirculation system of claim 5 , wherein the arrangement of the flow control valves further comprises a bypass line located to allow a flow of water around the respective pneumatic- or motor-actuated temperature-controlled valve.

7. The fluid recirculation system of claim 1 , wherein the economizer inlet mixing device comprises a sparger assembly disposed within the housing and a wave breaker assembly disposed at the outlet wherein the wave breaker assembly comprises a plurality of baffles.

8. The fluid recirculation system of claim 7 , wherein within the economizer inlet mixing device is the sparger assembly comprising a cylindrical member having a plurality of openings located therein through which the recirculation fluid stream from the arrangement of the flow control valves is received.

9. The fluid recirculation system of claim 2 wherein the recirculation valve arrangement includes at least two valves.

10. An economizer inlet mixing device located upstream of an economizer in a supercritical pressure boiler having at least one waterwall disposed within a furnace to produce a recirculation fluid stream, the economizer inlet mixing device comprising:
a housing to mix a feedwater stream and the recirculation fluid stream, including steam, to provide a mixture water stream;
a first inlet to receive the recirculation fluid stream from the waterwall of the furnace;
a second inlet to receive the feedwater stream and offset by less than ninety degrees from a central axis that extends vertically through the housing, defining an offset angle of the inlet;
an outlet to provide the mixed water stream to an economizer;
a sparger assembly disposed in the housing through which at least a portion of the recirculation fluid stream from the waterwall passes through a plurality of holes to mix the recirculation fluid stream with the feedwater stream; and
a wave breaker assembly disposed at the outlet and comprising a plurality of baffles through which is received the mixed water stream, wherein the plurality of baffles minimize fluid vibration and the mixed water stream comprises a combination of the flow of the recirculation fluid stream through the sparger assembly and the flow of the feedwater stream, with the mixed water stream being of a first temperature sufficient to raise a second temperature of a flue gas exiting the economizer to an optimum value for less than full load operation of a selective catalyst reduction (SCR) system located downstream of and in communication with the economizer
wherein the offset angle of the inlet, the sparger assembly and the wave breaker assembly allow for optimum mixing of the recirculation fluid stream and the feedwater stream so that the first temperature of the mixed water stream entering the economizer can be precisely controlled to thereby control the second temperature of the flue gas exiting the economizer to the optimum value to ensure catalyst reactiveness in the SCR system.

11. The economizer inlet mixing device of claim 10 , wherein the sparger assembly comprises a cylindrical member having a plurality of openings located therein such that the flow of fluid thereto is received into an end of the cylindrical member and directed through the openings and outside the cylindrical member.

12. The economizer inlet mixing device of claim 10 , further includes a pump protection strainer located at the outlet.

13. The economizer inlet mixing device of claim 10 , wherein the wave breaker assembly is located at a downcomer nozzle.

14. The economizer inlet mixing device of claim 10 , wherein the plurality of baffles are longitudinally arranged in a conduit.

Assignees

• Hargrove Michael J
• Navitsky Gary J
• Wailgum Jason J
• Walsh Bernard H
• General Electric Technology Gmbh

Inventors

• Hargrove Michael J
• Navitsky Gary J
• Wailgum Jason J
• Walsh Bernard H

Classifications

• F22D1/28

  for direct heat transfer, e.g. by mixing water and steam · CPC title

• F22D1/003

  Feed-water heater systems (F22D1/325, F22D1/36 and F22D1/40 take precedence) · CPC title

• F22D7/00

  Auxiliary devices for promoting water circulation · CPC title

• F22B29/026

  operating at critical or supercritical pressure · CPC title

• F22B35/06

  for steam boilers of forced-flow type · CPC title