US20210041100A1 - Premixing apparatus - Google Patents

Premixing apparatus Download PDF

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Publication number
US20210041100A1
US20210041100A1 US16/890,323 US202016890323A US2021041100A1 US 20210041100 A1 US20210041100 A1 US 20210041100A1 US 202016890323 A US202016890323 A US 202016890323A US 2021041100 A1 US2021041100 A1 US 2021041100A1
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US
United States
Prior art keywords
air
supply passage
gas
fuel mixture
flow control
Prior art date
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.)
Abandoned
Application number
US16/890,323
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English (en)
Inventor
Katsuya Noritake
Masaru Takeuchi
Kimihiro Yoshimura
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rinnai Corp
Original Assignee
Rinnai Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Rinnai Corp filed Critical Rinnai Corp
Assigned to RINNAI CORPORATION reassignment RINNAI CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: YOSHIMURA, KIMIHIRO, NORITAKE, Katsuya, TAKEUCHI, MASARU
Publication of US20210041100A1 publication Critical patent/US20210041100A1/en
Abandoned legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/02—Premix gas burners, i.e. in which gaseous fuel is mixed with combustion air upstream of the combustion zone
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N1/00—Regulating fuel supply
    • F23N1/02—Regulating fuel supply conjointly with air supply
    • F23N1/022—Regulating fuel supply conjointly with air supply using electronic means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/46—Details, e.g. noise reduction means
    • F23D14/60—Devices for simultaneous control of gas and combustion air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/46—Details, e.g. noise reduction means
    • F23D14/62—Mixing devices; Mixing tubes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N5/00—Systems for controlling combustion
    • F23N5/02—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium
    • F23N5/12—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium using ionisation-sensitive elements, i.e. flame rods
    • F23N5/123—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium using ionisation-sensitive elements, i.e. flame rods using electronic means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D2200/00—Burners for fluid fuel

Definitions

  • the present invention relates to a premixing apparatus for mixing air with a fuel gas in order to supply a burner with an air-fuel mixture through a fan.
  • the supply amount of the fuel gas varies with the rotational speed of the fan, i.e., with the supply amount of the air. Therefore, by controlling the rotational speed of the fan depending on the required combustion amount, the amount of the air-fuel mixture according to the required combustion amount is supplied to the burner and, as a result, the excess air ratio (amount of primary air/amount of air in theoretical air-fuel ratio) becomes constant.
  • the calorific value (Wobbe Index) of the fuel gas may fluctuate with the time of the day even if the same kind of gas is being used as the fuel gas.
  • the calorific value of the fuel gas may fluctuate, the ratio of the supply amount of air to the supply amount of the fuel gas remains constant. Therefore, accompanied by the fluctuation of the calorific value of the fuel gas, the excess air ratio of the air-fuel mixture may fluctuate, thereby giving rise to the combustion failure.
  • this invention has a problem of providing a premixing apparatus which is arranged to keep constant the excess air ratio of the air-fuel mixture even if the calorific value of the fuel gas may fluctuate, thereby preventing the combustion failure from taking place.
  • this invention is a premixing apparatus for mixing air with a fuel gas in order to supply a burner with an air-fuel mixture through a fan, wherein a downstream end of a gas supply passage is connected to a gas suction part disposed in a portion, on an upstream side of the fan, of an air supply passage.
  • the gas supply passage has interposed therein a zero governor for adjusting a secondary gas pressure to an atmospheric pressure.
  • the premixing apparatus includes: an excess air ratio detection device for detecting an excess air ratio of the air-fuel mixture; and a flow control valve interposed in a portion, on a downstream side of the zero governor, of the gas supply passage. The flow control valve is controlled such that the excess air ratio of the air-fuel mixture detected by the excess air ratio detection device becomes constant.
  • the excess air ratio of the air-fuel mixture can be kept constant by the control of the flow control valve, thereby preventing the combustion failure from taking place.
  • the lower-limit rotational speed of the fan will have to be set relatively high.
  • this arrangement brings about also a relatively higher minimum combustion amount that is the combustion amount obtainable at the time when the rotational speed of the fan is reduced to the lower-limit rotational speed. As a result, a turndown ratio will become small.
  • the premixing apparatus preferably further comprises a swing valve provided in an air-fuel mixture supply passage between the burner and the fan.
  • the swing valve is capable of swinging from a closed posture of being hung down with an upper end shaft serving as a fulcrum to a bottom-up open side against a self-weight thereof.
  • the swing valve may be swung to the bottom-up open side, into a fully-opened state against the self-weight of the swing valve due to a wind pressure from the fan.
  • the swing valve will gradually be swung downward from the fully-opened state.
  • the passage area of the air-fuel mixture supply passage will gradually be reduced. Accordingly, even if the lower-limit rotational speed is relatively high, the supply amount of the air-fuel mixture becomes relatively small due to a decrease in the passage area of the air-fuel mixture supply passage, i.e., the minimum combustion amount becomes relatively lower. As a consequence, the turndown ratio can be made large.
  • the excess air ratio of the air-fuel mixture can be made constant by the control of the flow control valve.
  • such an arrangement will deteriorate the controllability of the flow control valve.
  • the premixing apparatus preferably further comprises a bypass passage having interposed therein an on-off valve, the bypass passage being disposed in parallel with the flow control valve and in a portion, on the downstream side of the zero governor, of the gas supply passage.
  • the flow resistance in a portion, on the downstream side of the zero governor, of the gas supply passage can be varied over a wide range: by the change in opening degree of the flow control valve in a state in which the on-off valve is closed so that the fuel gas does not flow into the bypass passage; and by the change in opening degree of the flow control valve in a state in which the on-off valve is opened so that the fuel gas can flow into the bypass passage. Accordingly, there can be evaded deterioration in controllability as a result of enlarging the opening degree of the flow control valve.
  • FIG. 1 is an explanation diagram showing the premixing apparatus according to a first embodiment of this invention.
  • FIG. 2 is an explanation diagram showing the premixing apparatus according to a second embodiment of this invention.
  • FIG. 3 is a graph showing the relationship between the rotational speed of the fan and the supply amount of the air-fuel mixture.
  • the combustion apparatus represented in FIG. 1 is a heat source apparatus comprising: a totally aerated combustion burner 1 ; a combustion box 2 enclosing a combustion space of an air-fuel mixture to be ejected from a combustion surface 1 a of the burner 1 ; and a heat exchanger 3 disposed inside the combustion box 2 .
  • the combustion gas generated by the combustion of the air-fuel mixture is exhausted outside, after having heated the heat exchanger 3 , through an exhaust tube 4 that is connected to an end part of the combustion tube 2 .
  • the premixing apparatus A according to an embodiment of this invention, air is mixed with a fuel gas, and the resultant air-fuel mixture is supplied to the burner 1 through a fan 5 .
  • the premixing apparatus A is provided with: an air supply passage 6 on an upstream side of the fan 5 ; a gas supply passage 7 for supplying the fuel gas; and an air-fuel mixture supply passage 8 between the burner 1 on the downstream side of the fan 5 .
  • the downstream end of the gas supply passage 7 is connected to a gas suction part 61 which is disposed in the air supply passage 6 .
  • a venturi part 63 of a smaller diameter than the portion in which is disposed a butterfly valve 62 which will be described in detail hereinafter.
  • the downstream end of the venturi part 63 is thus inserted, while leaving an annular clearance, into the upstream end of the tubular part 64 , thereby constituting a gas suction part 61 by this clearance.
  • the downstream end of the gas supply passage 7 is provided with a gas chamber 71 which is in communication with the gas suction part 61 in a manner to enclose the tubular part 64 .
  • the gas supply passage 7 has interposed therein, from the upstream side downward in sequence, a main valve 72 , a zero governor 73 which adjusts the secondary gas pressure to atmospheric pressure, and a flow control valve 74 .
  • the amount of the fuel gas to be supplied through the gas suction part 61 varies with the differential pressure between the atmospheric pressure that is the secondary pressure and the negative pressure in the air supply passage 6 . It is to be noted here that the negative pressure in the air supply passage 6 varies with the rotational speed of the fan 5 . Therefore, the supply amount of the fuel gas varies in proportion to the rotational speed of the fan 5 , i.e., in proportion to the supply amount of air. Further, the ratio of supply amount of the fuel gas to the supply amount of air varies with the opening degree of the flow control valve 74 .
  • the excess air ratio of the air-fuel mixture will become an appropriate value (e.g., 1.3). Then, by controlling the rotational speed of the fan 5 according to the required combustion amount (the amount of combustion required to supply hot water at a set hot water temperature), the air-fuel mixture can be supplied to the burner 1 in an amount according to the required combustion amount at the appropriate value in the excess air ratio.
  • the required combustion amount the amount of combustion required to supply hot water at a set hot water temperature
  • the lower-limit rotational speed of the fan 5 cannot be set to a considerably lower value.
  • the air corresponding to the required combustion amount can no longer be supplied.
  • a butterfly valve 62 that can be switched, by a motor (not illustrated), between a closed posture as illustrated in solid lines in FIG. 1 and an open posture as illustrated in imaginary lines.
  • the butterfly valve 62 is made into the closed posture in order to increase the flow resistance in the air supply passage 6 .
  • the butterfly valve 62 is made into the closed posture in order to make the flow resistance in the air supply passage 6 larger and, at the same time, the flow control valve 74 is throttled by an amount corresponding to the predetermined opening degree from the standard opening degree, thereby attaining a small-capacity state in which the flow resistance in a portion, on the downstream side of the zero governor 73 , of the gas supply passage 7 is made larger.
  • the air-fuel mixture can be supplied to the burner 1 in an amount that corresponds to a relatively small required combustion amount at the appropriate value in the excess air ratio.
  • the butterfly valve 62 is made into an open posture in order to make the flow resistance in the air supply passage 6 smaller and, at the same time, the flow control valve 74 is opened up to the standard opening degree in order to attain a large-capacity state in which the flow resistance in a portion, on the downstream side of the zero governor 73 , of the gas supply passage 7 is made small.
  • the burner 1 can be supplied with the air-fuel mixture in an amount that corresponds to a relatively large required combustion amount at the appropriate value in the excess air ratio.
  • a swing valve 81 that is capable of swinging from a closed posture (the posture illustrated in imaginary lines in FIG. 1 ) of being hung down with an upper end shaft 81 a serving as a fulcrum to a bottom-up open side against a self-weight thereof.
  • a closed posture the posture illustrated in imaginary lines in FIG. 1
  • the swing valve 81 will be swung upward by the wind pressure from the fan 5 against its self-weight, thereby attaining a fully-opened state.
  • the swing valve 81 comes to be swung gradually downward from the fully-opened state accompanied by the lowering of the rotational speed of the fan 5 and, as a result, the passage area of the air-fuel mixture supply passage 8 gradually decreases.
  • the relationship between the rotational speed of the fan 5 and the supply amount of the air-fuel mixture is as illustrated by a characteristic line L in FIG. 3 in the small-capacity state, and is as illustrated by a characteristic line H in FIG. 3 in the large-capacity state.
  • these characteristic curves L, H will become those in which the supply amounts of the air-fuel mixture are made smaller than those of the proportional lines illustrated in FIG. 3 by dotted lines.
  • a large turndown ratio (maximum amount of combustion/minimum amount of combustion) that is the ratio between: the amount Qmax of supply of the air-fuel mixture at the time when the rotational speed of the fan 5 is made the upper limit rotational speed Nmax in the state of large capacity, i.e., the maximum amount of combustion by the burner 1 ; and the amount Qmin of supply of the air-fuel mixture at the time when the rotational speed of the fan 5 is made the lower limit rotational speed Nmin in the state of small capacity, i.e., the minimum amount of combustion by the burner 1 .
  • an excess air ratio detection means 9 for detecting the excess air ratio of the air-fuel mixture.
  • a flame rod provided in a manner to face the combustion surface 1 a of the burner 1 constitutes the excess air ratio detection means 9 so that the excess air ratio of the air-fuel mixture can be detected by flame current that flows through the flame rod.
  • the flow control valve 74 is feed-back controlled so that the excess air ratio of the air-fuel mixture to be detected by the excess air ratio detection means 9 becomes constant, i.e., in order to keep the excess air ratio to a predetermined appropriate value. Specifically, when the excess air ratio in the air-fuel mixture is reduced by an increase in the calorific value of the fuel gas, the opening degree of the flow control valve 74 is reduced so that the ratio of the supply amount of the fuel gas relative to the supply amount of air is decreased so as to attain the appropriate value in the excess air ratio.
  • the opening degree of the flow control valve 74 is increased so that the ratio of the supply amount of the fuel gas relative to the supply amount of air is increased so as to attain the appropriate value in the excess air ratio. According to this arrangement, even if the calorific value of the fuel gas fluctuates, the excess air ratio of the air-fuel mixture can be maintained at the appropriate value, thereby preventing the combustion failure from taking place.
  • FIG. 2 The basic construction of the second embodiment is not particularly different from that of the above-mentioned first embodiment.
  • the members and parts that are the same as those of the first embodiment have been assigned thereto the same reference marks.
  • the difference of the second embodiment from the first embodiment is that a bypass passage 75 is provided in parallel with the flow control valve 74 in a portion, on a downstream side of the zero governor 73 , of the gas supply passage 7 , and that an on-off valve 76 is interposed in this bypass passage 75 .
  • the flow resistance in a portion, on the downstream side of the zero governor 73 , of the gas supply passage 7 can be varied over a wide range: by the opening degree change in the state in which the fuel gas does not flow through the bypass passage 75 as a result of closing the on-off valve 76 ; and by the opening degree change of the flow control valve 74 in a state in which the fuel gas flows through the bypass passage 75 as a result of opening the on-off valve 76 . Therefore, the deterioration in the controllability of the flow control valve 74 due to enlargement of the range in opening degree change can be avoided.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Regulation And Control Of Combustion (AREA)
  • Gas Burners (AREA)
US16/890,323 2019-08-07 2020-06-02 Premixing apparatus Abandoned US20210041100A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2019-145279 2019-08-07
JP2019145279A JP2021025722A (ja) 2019-08-07 2019-08-07 予混合装置

Publications (1)

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US20210041100A1 true US20210041100A1 (en) 2021-02-11

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Application Number Title Priority Date Filing Date
US16/890,323 Abandoned US20210041100A1 (en) 2019-08-07 2020-06-02 Premixing apparatus

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US (1) US20210041100A1 (ja)
EP (1) EP3772614B1 (ja)
JP (1) JP2021025722A (ja)

Family Cites Families (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS56147974A (en) * 1980-04-14 1981-11-17 Youei Seisakusho:Kk Proportional gas control apparatus
US4585161A (en) * 1984-04-27 1986-04-29 Tokyo Gas Company Ltd. Air fuel ratio control system for furnace
JP2644415B2 (ja) * 1992-05-14 1997-08-25 リンナイ株式会社 強制送風式燃焼装置
JP2000146163A (ja) * 1998-11-02 2000-05-26 Harman Co Ltd 燃焼装置
JP2003148725A (ja) * 2001-11-08 2003-05-21 Paloma Ind Ltd 強制燃焼装置
JP6529364B2 (ja) * 2015-07-09 2019-06-12 リンナイ株式会社 給湯器
JP6625925B2 (ja) * 2016-04-06 2019-12-25 リンナイ株式会社 予混合装置
JP6831285B2 (ja) 2017-04-19 2021-02-17 リンナイ株式会社 予混合装置
DE102017222437A1 (de) * 2017-12-12 2019-06-13 Robert Bosch Gmbh Heizgerätkomponente und Verfahren zur Einstellung eines Brennstoffvolumenstroms

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JP2021025722A (ja) 2021-02-22
EP3772614B1 (en) 2023-08-30
EP3772614A1 (en) 2021-02-10

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