US3818872A - Economizer bypass for increased furnace wall protection - Google Patents

Economizer bypass for increased furnace wall protection Download PDF

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Publication number
US3818872A
US3818872A US00375219A US37521973A US3818872A US 3818872 A US3818872 A US 3818872A US 00375219 A US00375219 A US 00375219A US 37521973 A US37521973 A US 37521973A US 3818872 A US3818872 A US 3818872A
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United States
Prior art keywords
conduit
flow
furnace
working fluid
furnace wall
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US00375219A
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English (en)
Inventor
W Clayton
W Schuetzenduebel
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Combustion Engineering Inc
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Combustion Engineering Inc
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Filing date
Publication date
Application filed by Combustion Engineering Inc filed Critical Combustion Engineering Inc
Priority to US00375219A priority Critical patent/US3818872A/en
Priority to CA192,353A priority patent/CA988794A/en
Priority to DE2428381A priority patent/DE2428381C3/de
Application granted granted Critical
Publication of US3818872A publication Critical patent/US3818872A/en
Priority to CH878574A priority patent/CH571685A5/xx
Priority to JP49072414A priority patent/JPS5138841B2/ja
Priority to NL7408792A priority patent/NL7408792A/xx
Priority to IT24567/74A priority patent/IT1015510B/it
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B29/00—Steam boilers of forced-flow type
    • F22B29/06—Steam boilers of forced-flow type of once-through type, i.e. built-up from tubes receiving water at one end and delivering superheated steam at the other end of the tubes
    • F22B29/12—Steam boilers of forced-flow type of once-through type, i.e. built-up from tubes receiving water at one end and delivering superheated steam at the other end of the tubes operating with superimposed recirculation during starting and low-load periods, e.g. composite boilers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22D—PREHEATING, OR ACCUMULATING PREHEATED, FEED-WATER FOR STEAM GENERATION; FEED-WATER SUPPLY FOR STEAM GENERATION; CONTROLLING WATER LEVEL FOR STEAM GENERATION; AUXILIARY DEVICES FOR PROMOTING WATER CIRCULATION WITHIN STEAM BOILERS
    • F22D1/00—Feed-water heaters, i.e. economisers or like preheaters
    • F22D1/02—Feed-water heaters, i.e. economisers or like preheaters with water tubes arranged in the boiler furnace, fire tubes or flue ways

Definitions

  • ABSTRACT An arrangement for protecting, at low loads, the furnace walls of a once-through steam generator system, having a recirculation loop, by increasing the mass flow of the working fluid flowing through the furnace wall tubes.
  • a bypass for incoming feedwater is provided around the economizer allowing a lower temperature fluid to be delivered to and mixed with the fluid from the recirculation loop lowering the temperature of the fluid mixture.
  • This invention relates to once-through steam generator systems with recirculation through the furnace wall tubes, and more particularly to protection of the furnace wall tubes by increasing the mass flow therethrough.
  • the fluid passed through the furnace walls of a once-through steam generator with recirculation consists of a mixture of heated feedwater from the economizer and recirculated working fluid from the furnace wall outlet. Little control of the temperature of this mixed fluid is possible due to the fact that the furnace wall outlet temperature is maintained close to design conditions and the economizer outlet temperature is a function of combustion gas temperature. Since, at start-up and low load, only a small degree of cooling is obtained by the above-noted mixing (due to high economizer temperatures and low percent through-flow), recirculation does not provide a sufficient heat transfer relationship between the circulating mixed fluid and the furnace wall tubes for the adequate protection thereof.
  • Our invention provides an arrangement for improving furnace wall protection including a bypass for at least a portion of the incoming feedwater around the economizer whereby the temperature of the mixture of the furnace wall outlet fluid and the feedwater from the economizer outlet plus the bypassed feedwater, as delivered to a recirculation pump, is reduced.
  • This fluid temperature reduction permits the amount of fluid mass flow in the furnace wall tubes (and thus the heat transfer characteristics thereof) to be increased.
  • the reduction in temperature of the fluid mixture delivered to the recirculation pumps reduces the specific volume thereof.
  • the volumetric flow of the pumps is substantially the same under any load condition, so that a lower specific volume results in a higher mass flow to be delivered to the furnace walls. Since higher mass flow creates better heat transfer characteristics, the furnace wall tubes are more able to stand the heat of fuel tiring and are thus more adequately protected.
  • FIG. 1 is a diagrammatic representation of the flow arrangement of this invention.
  • FIG. 2 is a graphical representation of the increase in furnace wall mass flow with the increase in economizer bypass line flow.
  • FIG. 3 is a graphical representation showing the decrease in mixed flow temperature with increase in economizer bypass line flow.
  • feedwater is supplied through a conduit 12 to a feedwater supply valve 14.
  • a flow meter 16 provides a signal for an operator 18 which controls the flow through the feedwater supply valve 14.
  • This water is passed serially through an economizer 20 to a mixing vessel 20, and thence through recirculation pump 24 to the furnace wall tubes 26 where it is heated by combustion within the furnace to form steam.
  • the steam leaving the fumace tubes passes through conduit 28 to a superheater 30 from where it is taken through conduit 32 to do useful work such as to operate a turbine (not shown).
  • a feedwater valve bypass portion 34 having a bypass valve 36 is provided for controlling feedwater flow at very low loads.
  • the economizer bypass portion 38 In parallel with the feedwater supply valve 14 and feedwater valve bypass portion 34 is the economizer bypass portion 38, of our novel arrangement.
  • Economizer bypass portion 38 has an economizer bypass valve 40 which enables a portion of the feedwater to be bypassed-around the economizer 20 and flow directly into the mixing vessel 22 at low loads as described hereinbelow. It is pointed out that economizer bypass valve 40 must beparalllel to feedwater bypass valve 36 in order to equalize the pressure drop across the economizer 20 and bypass portion 38 to achieve the bypass flow.
  • cold water is recirculated through conduit 42 from the furnace wall tube outlet 44 to the mixing vessel 22 where it is mixed with incoming feedwater when a nominal through-flow of cold water is established.
  • Nominal through-flow (usually about 5 percent of designed full load through-flow) is used to provided improved pressure control and uniform heating of various tubing and headers outside of the recirculating flow path.
  • the temperature of the fluid in the furnace wall tubes 26 and in the economizer 20 increases.
  • the temperature of the substantially recirculated flow will then increase to a relatively high temperature (approximately 760 to 800F).
  • the mixed flow (consisting of fluid from the recirculating conduit and from the economizer) entering the furnace walls 26 from the mixing vessel 22 will then be at a high temperature and a low density, the density varying inversely with the temperature. For example, at 3,500 psi and 200F, the density is 61.5 lb/ft? while at 800F it is 7 lb/ft.
  • the mass flow rate during this start-up and low load operation is substantial, the mass flow rate is low due to the low density of the mixed fluid.
  • the metal temperature of the furnace side of the furnace wall tubes is dependent not only on the rate of heat transfer from the furnace gases to the tubes but also the thermal resistance of the tubes and the inside film between each tube and the fluid therein. Since this inside film is a function of mass flow rate rather than velocity or volumetric flow rate, poor heat transfer between the tubes andthe fluid is obtaineddu'ring this period of operation. Therefore, while the furnace is operated at low loads and relatively low heat adsorption rates (as compared to full load), high local heating rates still may exist in the general area of the burners which can cause damage to the tubes located in this area.
  • a portion of the feedwater is bypassed through economizer bypass portion 38 around the economizer 20 and directly into the mixing vessel 22.
  • the temperature of the bypassed feedwater is approximately 220F as compared to feedwater passed through the economizer which is at a temperature of approximately 500F. This lower temperature bypassed feedwater reduces the temperature of the mixed fluid which increases its density and mass flow to be deliv ered to the furnace wall tubes 26.
  • a temperature sensing device 46 is located between the mixing vessel 22 and the recirculation pump 24 to sense the temperature of the mixed fluid delivered to the recirculation pump 24.
  • the sensed temperature is compared in a controller 48 to a Set Point temperature (desired optimum working fluid temperature) to control an operator 50 according to the difference, or error, signal generated for regulating the amount of feedwater bypassed around the economizer 20 at the above-mentioned loads.
  • a Set Point temperature desired optimum working fluid temperature
  • the amount of fluid bypassing the economizer is increased. This increased temperature increased bypass association is continued up to about 30 percent load where substantial through-flow will provide sufficient tube wall protection. Therefore, above this point (about 30 percent load) economizer bypass is no longer necessary for tube protection and is discontinued.
  • the mass flow through the furnace wall tubes can be increased up to a maximum of about 123 percent of normal mass flow by the bypassing of the feedwater around the economizer.
  • the temperature of mixed fluid can be lowered from 718 to 715F. While a three degree drop in temperature does not appear large, the specific volume change associated therewith is substantial as reflected in the increased mass flow shown in the graph of FIG. 2.
  • the temperature of the mixed fluid circulating in the furnace walls can be reduced.
  • the reduction in temperature results in increase in mass flow which has the effect of promoting better heat transfer characteristics between the tube walls and fluid therein for improved furnace wall protection during the period of low loads when other protective methods, valid at higher loads, have been found insufficient.
  • a once-through steam generator system comprising a furnace with fuel being burned therein establishing the flow of combustion gases therefrom, furnace wall tubes lining the walls of said furnace for radiant heat absorption from the burning fuel within said fur nace, heat exchange means in the flow of combustion gases, a first conduit for conveying incoming working fluid into said heat exchange means, a control valve in said first conduit for controlling the flow of incoming working fluid, a second conduit for conveying said working fluid to said furnace wall tubes from within said heat exchange means, a third conduit for conveying the working fluid from said furnace wall tubes after passage therethrough, a fourth conduit providing a recirculation path for the working medium from said third conduit to said second conduit and pump means for recirculating at least a portion of the working fluid through said fourth conduit; an arrangement for protecting said furnace wall tubes comprising:
  • bypass means for selectively bypassing at least a portion of the incoming working fluid around said heat exchange means so that said working fluid enters said furnace walls without being heated in said heat exchange means, said bypass means comprising a fifth conduit connected between said first conduit and said second conduit, a selectively operable valve means in said fifth conduit for regulating the flow therein, said pump means being located in said second conduit downstream of the connection of said fourth and fifth conduits with said second conduit.
  • said automatic control means comprise a temperature sensing means sensing the temperature of the working fluid entering said furnace wall tubes, said means located downstream of the junction of said fourth conduit with said second conduit and said fifth conduit with said second conduit and upstream of said pump means, controller means receiving a signal from said temperature sensing means indicating temperature of the working fluid, said controller means also receiving a Set Point signal indicating the desired working fluid operating temperature, said controller means operative in response to the difference between said received signal to control the regulative position of said selectively operable valve means over at least a portion of the steam generator operating load range.
  • a method of operating a once-through steam generator system having a furnace, furnace wall tubes lin- 6 ing the walls of the furnace for radiant heat absorption, omizer is substantial at low loads and discontinued and an economizer, the steps comprising: at high loads.
  • the step of regulatthrough said economizer and said furnace wall ing said bypassed portion comprises the steps: sensing tubes, recirculating a portion of the flow from the 5 the temperature of the mixed working fluid flow as it outlet of the furnace wall tubes to the entrance of enters the furnace wall tubes, comparing the sensed the furnace wall tubes, mixing the recirculated flow temperature to an optimum desired temperature, con and the through-flow upstream of the furnace walls trolling the bypassed flow portion during load operaand downstream of the economizer, firing fuel in tion up to 30 percent of full load according to the difsaid furnace thereby increasing the temperature of 0 ference between the sensed temperature and the dethe mixed working fluid passing through said fursired temperature so that the flow around said econonace wall tubes, bypassing at least a portion of the mizer may be increased, and discontinuing said byincoming working fluid through-flow around said passed flow portion during operating load conditions economizer, regulating

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Control Of Steam Boilers And Waste-Gas Boilers (AREA)
US00375219A 1973-06-29 1973-06-29 Economizer bypass for increased furnace wall protection Expired - Lifetime US3818872A (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
US00375219A US3818872A (en) 1973-06-29 1973-06-29 Economizer bypass for increased furnace wall protection
CA192,353A CA988794A (en) 1973-06-29 1974-02-13 Economizer bypass for increased furnace wall protection
DE2428381A DE2428381C3 (de) 1973-06-29 1974-06-12 Verfahren zum Betreiben eines Durchlaufdampferzeugers
CH878574A CH571685A5 (enrdf_load_stackoverflow) 1973-06-29 1974-06-26
JP49072414A JPS5138841B2 (enrdf_load_stackoverflow) 1973-06-29 1974-06-26
NL7408792A NL7408792A (enrdf_load_stackoverflow) 1973-06-29 1974-06-28
IT24567/74A IT1015510B (it) 1973-06-29 1974-06-28 Generatore di vapore ad attraver samento diretto

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US00375219A US3818872A (en) 1973-06-29 1973-06-29 Economizer bypass for increased furnace wall protection

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US3818872A true US3818872A (en) 1974-06-25

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US00375219A Expired - Lifetime US3818872A (en) 1973-06-29 1973-06-29 Economizer bypass for increased furnace wall protection

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US (1) US3818872A (enrdf_load_stackoverflow)
JP (1) JPS5138841B2 (enrdf_load_stackoverflow)
CA (1) CA988794A (enrdf_load_stackoverflow)
CH (1) CH571685A5 (enrdf_load_stackoverflow)
DE (1) DE2428381C3 (enrdf_load_stackoverflow)
IT (1) IT1015510B (enrdf_load_stackoverflow)
NL (1) NL7408792A (enrdf_load_stackoverflow)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2325879A1 (fr) * 1975-09-26 1977-04-22 Sulzer Ag Generateur de vapeur a foyer ou a chauffage par un gaz
FR2402154A1 (fr) * 1977-09-02 1979-03-30 Sulzer Ag Chaudiere a circulation forcee
US4403571A (en) * 1981-12-09 1983-09-13 Combustion Engineering, Inc. Boiler with economizer heat absorption reduction
US5555849A (en) * 1994-12-22 1996-09-17 Combustion Engineering, Inc. Gas temperature control system for catalytic reduction of nitrogen oxide emissions
US7504260B1 (en) * 2000-05-16 2009-03-17 Lang Fred D Method and apparatus for controlling gas temperatures associated with pollution reduction processes
EP2224164A1 (de) * 2008-11-13 2010-09-01 Siemens Aktiengesellschaft Verfahren zum Betreiben eines Abhitzedampferzeugers
EP2423587A2 (en) 2009-03-10 2012-02-29 Babcock & Wilcox Power Generation Group, Inc. Integrated split stream water coil air heater and economizer (IWE)
WO2011048520A3 (en) * 2009-10-22 2013-08-01 Foster Wheeler Energy Corporation A method of increasing the performance of a carbonaceous fuel combusting boiler system
US20140060459A1 (en) * 2012-09-06 2014-03-06 Mitsubishi Heavy Industries, Ltd. Heat recovery system and heat recovery method
US9574766B2 (en) 2013-08-06 2017-02-21 Siemens Aktiengesellschaft Once-through steam generator
US9927117B2 (en) * 2013-05-23 2018-03-27 Electric Power Development Co., Ltd. Fossil-fuel power plant and fossil-fuel power plant operation method
US20190338944A1 (en) * 2016-08-05 2019-11-07 Siemens Aktiengesellschaft Method for operating a waste heat steam generator

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2413653A1 (fr) * 1977-12-29 1979-07-27 Creusot Loire Dispositif pour mesure de temperature et prise d'echantillon d'un bain d'acier
DE2807152C2 (de) * 1978-02-20 1984-11-22 Fried. Krupp Gmbh, 4300 Essen Einrichtung zur Handhabung von Meß- und Probenahmesonden mittels Meßlanzen in Schmelzen
JPH019008Y2 (enrdf_load_stackoverflow) * 1981-02-24 1989-03-10
JPS59959U (ja) * 1982-06-26 1984-01-06 川崎製鉄株式会社 測温・サンプリング装置
JPS61201123A (ja) * 1985-03-05 1986-09-05 Chino Works Ltd 温度測定装置
DK154731C (da) * 1985-05-21 1989-05-08 Burmeister & Wains Energi Dampkedel med katalytisk roeggasbehandling samt fremgangsmaade ved drift af kedelen

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3164134A (en) * 1962-11-20 1965-01-05 Combustion Eng Apparatus and method for operating a forced flow once-through vapor generator
US3240188A (en) * 1961-10-06 1966-03-15 Sulzer Ag Method of and apparatus for distributing a fluid into at least two heated tubes arranged in parallel relation with respect to the flow of fluid therethrough
US3331202A (en) * 1965-02-15 1967-07-18 Sulzer Ag Steam power plant

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3240188A (en) * 1961-10-06 1966-03-15 Sulzer Ag Method of and apparatus for distributing a fluid into at least two heated tubes arranged in parallel relation with respect to the flow of fluid therethrough
US3164134A (en) * 1962-11-20 1965-01-05 Combustion Eng Apparatus and method for operating a forced flow once-through vapor generator
US3331202A (en) * 1965-02-15 1967-07-18 Sulzer Ag Steam power plant

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2325879A1 (fr) * 1975-09-26 1977-04-22 Sulzer Ag Generateur de vapeur a foyer ou a chauffage par un gaz
FR2402154A1 (fr) * 1977-09-02 1979-03-30 Sulzer Ag Chaudiere a circulation forcee
US4403571A (en) * 1981-12-09 1983-09-13 Combustion Engineering, Inc. Boiler with economizer heat absorption reduction
US5555849A (en) * 1994-12-22 1996-09-17 Combustion Engineering, Inc. Gas temperature control system for catalytic reduction of nitrogen oxide emissions
US7504260B1 (en) * 2000-05-16 2009-03-17 Lang Fred D Method and apparatus for controlling gas temperatures associated with pollution reduction processes
CN102239363B (zh) * 2008-11-13 2015-02-04 西门子公司 用于运行废热蒸汽发生器的方法
WO2010054934A3 (de) * 2008-11-13 2010-10-07 Siemens Aktiengesellschaft Verfahren zum betreiben eines abhitzedampferzeugers
US20110225972A1 (en) * 2008-11-13 2011-09-22 Siemens Aktiengesellschaft Method for Operating a Waste Heat Steam Generator
AU2009315819B2 (en) * 2008-11-13 2014-04-17 Siemens Aktiengesellschaft Method for operating a waste heat steam generator
EP2224164A1 (de) * 2008-11-13 2010-09-01 Siemens Aktiengesellschaft Verfahren zum Betreiben eines Abhitzedampferzeugers
US9593844B2 (en) * 2008-11-13 2017-03-14 Siemens Aktiengesellschaft Method for operating a waste heat steam generator
EP2423587A2 (en) 2009-03-10 2012-02-29 Babcock & Wilcox Power Generation Group, Inc. Integrated split stream water coil air heater and economizer (IWE)
WO2011048520A3 (en) * 2009-10-22 2013-08-01 Foster Wheeler Energy Corporation A method of increasing the performance of a carbonaceous fuel combusting boiler system
US20140060459A1 (en) * 2012-09-06 2014-03-06 Mitsubishi Heavy Industries, Ltd. Heat recovery system and heat recovery method
US9927117B2 (en) * 2013-05-23 2018-03-27 Electric Power Development Co., Ltd. Fossil-fuel power plant and fossil-fuel power plant operation method
US9574766B2 (en) 2013-08-06 2017-02-21 Siemens Aktiengesellschaft Once-through steam generator
US20190338944A1 (en) * 2016-08-05 2019-11-07 Siemens Aktiengesellschaft Method for operating a waste heat steam generator
US10948178B2 (en) * 2016-08-05 2021-03-16 Siemens Energy Global GmbH & Co. KG Method for operating a waste heat steam generator

Also Published As

Publication number Publication date
JPS5036802A (enrdf_load_stackoverflow) 1975-04-07
JPS5138841B2 (enrdf_load_stackoverflow) 1976-10-25
NL7408792A (enrdf_load_stackoverflow) 1974-12-31
CA988794A (en) 1976-05-11
DE2428381C3 (de) 1980-01-10
DE2428381B2 (de) 1979-05-03
IT1015510B (it) 1977-05-20
DE2428381A1 (de) 1975-01-23
CH571685A5 (enrdf_load_stackoverflow) 1976-01-15

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