JP5428265B2 - Tubular flame burner design method - Google Patents

Description

  The present invention relates to a method for designing a tubular flame burner, and more particularly to a method for designing a combustion flame having a large combustion capacity of 10 to 40 MW and excellent combustion stability and low NOx.

  Conventional gas burners used industrially are roughly divided into those of diffusion combustion method (mixing after nozzle discharge) and those of premixing combustion method (mixing before nozzle), depending on the mixing method of fuel gas and oxygen-containing gas. However, both have a structure in which a flame is formed on the downstream side in front of the tip of the burner.

  The diffusion combustion type is one in which both of the above gases are mixed and burned after the burner tip is discharged, and a high-temperature flame can be obtained and is widely used. The premixed combustion type has the advantage that a relatively short flame can be formed.

  However, in the conventional burner, a flame is formed on the downstream side in front of the tip of the burner. Therefore, a large space for combustion must be secured on the downstream side in front of the burner, and the combustion equipment becomes large. .

  The gas burner is a burner with a relatively wide range of adjustment of the combustion amount. However, if it is necessary to change the combustion amount more drastically, a plurality of burners must be installed, and the combustion facility becomes larger. .

Also, depending on the combustion conditions, or increased production of harmful substances such as NO _X, unburned content or discharge of hydrocarbons, soot or generated, concerns can become a source of environmental pollution Is done.

  For this reason, a tubular flame burner has been developed that can burn fuels with various calorific values, has a very wide range of adjustment of the combustion amount, is miniaturized, and is less susceptible to environmental pollution.

For example, in Patent Document 1, a tubular flame burner has a tubular combustion chamber that is open at one end and from which a combustion flame is ejected. The other closed end of the combustion chamber includes a fuel gas and an oxygen-containing gas. A nozzle for blowing a premixed gas or a nozzle for blowing a fuel gas and a nozzle for blowing an oxygen-containing gas are provided in a direction tangential to the inner wall surface thereof.
JP-A-11-281015

  By the way, in the steelworks, the combustion capacity is as large as about 10 to 40 MW, and the low-calorie ironworks byproduct gases (coke oven gas COG, blast furnace gas BFG, converter gas LDG) are low NOx in the combustion exhaust gas after combustion. A gas burner for a boiler to be burned is required, and application of a tubular flame burner is expected.

  In order to form and hold a tubular flame with a tubular flame burner, it is necessary that the temperature of the combustion field exceeds the self-ignition temperature of the combustion gas used. Compared to a burner, it is characterized by being able to ignite and burn even low-calorie gas.

  However, a specific design method for producing a conventional tubular flame burner having a combustion capacity of about 2 MW and a large combustion capacity has not been clarified.

  Accordingly, the present invention provides a burner design method that has a large combustion capacity of about 10 to 40 MW, can form and hold a flame with a low calorie gas such as an ironworks by-product gas, and achieves both combustibility and low NOx performance. The purpose is to provide.

In addition, the low calorie gas as used in the field of this invention refers to the thing whose low calorific value is 20000 (kJ / Nm < ³ >) or less.

  The inventors of the present invention have obtained knowledge about the generation of NOx from combustion experiments, prevent the rise of the flame, ensure the formation of a stable tubular flame, and increase the combustion chamber inner diameter D. Various knowledge was obtained about the design principle of the slit shape Ls × B and the tube length Lx.

２．燃焼炎が形成される管状の燃焼室と、前記燃焼室に燃料ガスと酸素含有ガスよりなる予混合気を吹き込むノズル、または燃料ガスを吹き込むノズルと酸素含有ガスを吹き込むノズルがその内壁面の接線方向に向けて設けられたノズルがスリットノズルで、燃焼容量が１０〜４０ＭＷの管状火炎バーナの設計方法であって、
初期条件として最大燃焼量、ガス性状（理論空気量、低位発熱量）、空気比、炉内圧、供給圧、上限ＮＯｘ量、燃焼室の内径、スリットノズルのギャップ、および前記スリットノズルのギャップから求まるノズル部助走距離を設定する際、前記燃焼室の内径と、前記スリットノズルのギャップは、１記載の設計方法で求めた値に設定して、前記ノズル部助走距離は、燃焼実験より求められる式（５）を満足するように設定して、
前記ノズル部の圧力損失制約から上限Ｓｗ数を求め、
前記上限ＮＯｘ量および前記上限Ｓｗ数を満足させるバーナ寸法制約と、
管状火炎を保炎するためのバーナ寸法制約からバーナレイアウトを決定することを特徴とするノズルがスリットノズルで、燃焼容量が１０〜４０ＭＷの管状火炎バーナの設計方法。

The present invention has been made by further studying the obtained knowledge. A tubular combustion chamber in which a combustion flame is formed, and a slit nozzle for injecting fuel gas and oxygen-containing gas into the combustion chamber respectively or in a premixed manner are provided toward the tangential direction of the inner wall surface, and the combustion capacity is 10 A method of designing a ~ 40 MW tubular flame burner,
The maximum combustion amount and the upper limit NOx amount are given as initial conditions,
The inner diameter D (m) of the combustion chamber is defined so as to satisfy Equation (3) that defines the relationship between the maximum combustion amount Q (MW) and the inner diameter D (m) of the combustion chamber, which is obtained from a combustion experiment.
The slit nozzle gap B (m) is defined so as to satisfy Equation (4) that defines the relationship between the inner diameter D (m) of the combustion chamber and the gap B (m) of the slit nozzle, which is obtained from a combustion experiment.
The nozzle center to burner tip distance Lx is obtained from the restriction of the pressure loss ΔP (mmAq) of the nozzle part to obtain the upper limit of the Sw number that is a dimensionless number indicating the swirling strength in the flow accompanying swirling, and Sw number−NOx amount−Lx / A method for designing a tubular flame burner, wherein the nozzle is a slit nozzle and the combustion capacity is 10 to 40 MW, which is obtained from an experimental correlation between D.

2. A tubular combustion chamber in which a combustion flame is formed, and a nozzle for blowing a premixed gas composed of fuel gas and oxygen-containing gas into the combustion chamber, or a nozzle for blowing fuel gas and a nozzle for blowing oxygen-containing gas are tangent to the inner wall surface The nozzle provided in the direction is a slit nozzle, and is a method for designing a tubular flame burner with a combustion capacity of 10 to 40 MW ,
The initial conditions are determined from the maximum combustion amount, gas properties (theoretical air amount, lower heating value), air ratio, furnace pressure, supply pressure, upper limit NOx amount, combustion chamber inner diameter, slit nozzle gap, and slit nozzle gap. When setting the nozzle run-up distance, the inner diameter of the combustion chamber and the gap of the slit nozzle are set to the values obtained by the design method according to 1, and the nozzle run-up distance is an expression obtained from a combustion experiment. Set to satisfy (5),
Obtain the upper limit Sw number from the pressure loss constraint of the nozzle part,
Burner dimensional constraints satisfying the upper limit NOx amount and the upper limit Sw number;
A design method of a tubular flame burner in which a nozzle is a slit nozzle and a combustion capacity is 10 to 40 MW, wherein a burner layout is determined from burner dimensional constraints for holding a tubular flame.

  According to the present invention, even when the combustion capacity is as large as about 10 to 40 MW, a tubular flame burner having both combustibility and low NOx property can be obtained, which is extremely useful industrially.

  Hereinafter, a procedure for producing a tubular flame burner having a combustion capacity of about 10 to 40 MW according to the present invention will be described in detail. 5A and 5B are schematic cross-sectional views for explaining the names of the respective parts of the tubular flame burner used for description. FIG. 5A is a side cross-sectional view, and FIG. 5B is a front view.

  In the drawing, B is a slit nozzle gap (nozzle opening height (m)), L is the length (m) of the combustion chamber 2, D is the inner diameter (m) of the combustion chamber 2, Ls is the nozzle width (m), Lb is a back space (m) which is the distance from the nozzle 3 to the closed end 2b of the combustion chamber 2, and Lx is a distance (m) from the open end 2a to the center in the width direction of the nozzle 3 (hereinafter, nozzle center to burner tip distance). (M)).

  1 is a tubular flame burner, 2 is a combustion chamber, 2a is an open end of the combustion chamber 2, 2b is a closed end of the combustion chamber 2, 3 is a nozzle, 4 is a combustion gas or oxygen-containing gas, or a premixed gas thereof. Reference numeral 5 denotes a frame on which the tubular flame burner 1 is attached. FIG. 1 shows a flowchart of a design method according to an embodiment of the present invention.

1. Step 1: Setting of target performance First, the maximum combustion amount Q (MW) and the upper limit NOx amount are set as the target performance, and the gas properties are defined as initial conditions in the design.

Since the lower heating value HL (kJ / Nm ³ ) and the theoretical air amount Ao are determined from the gas properties, the air ratio μ ([the amount of air per 1 Nm ^{3 of the} actually burned fuel] / [theoretical air amount Ao]) The maximum fuel gas flow rate Vf (Nm ³ / s) is obtained from equation (1) and the maximum air flow rate Va (Nm ³ / s) is obtained from equation (2). Use.

2. Step 2: Defining burner dimensions When defining the burner dimensions, first, it is assumed that the combustion experiment results (experimental formulas) investigating the influence of the dimensions of each part of the burner on the increase in combustion volume are satisfied (combustion constraint 1). The inner diameter D of the combustion chamber, the gap B of the slit nozzle, the nozzle portion running distance Lr determined from the gap B of the slit nozzle, and (nozzle center to burner tip distance) Lx are defined (S21).

  The inner diameter D (m) of the combustion chamber satisfies an empirical formula (formula (3)) that defines the relationship between the maximum combustion amount Q (MW) and the inner diameter D (m) of the combustion chamber, which is obtained from a combustion experiment. Stipulate.

  This empirical formula is based on the knowledge that the inner diameter D of the combustion chamber should be increased in proportion to the 0.5th power of the combustion capacity as a design guideline for increasing the combustion chamber, and the maximum combustion amount is 0.3 MW. This is based on the fact that a good combustion state was obtained when the inner diameter D of the burner was 100 mm, the maximum combustion amount was 2 MW, and the inner diameter D was 300 mm.

  The slit nozzle gap B (m) satisfies the empirical formula (equation (4)) that defines the relationship between the inner diameter D (m) of the combustion chamber and the gap B (m) of the slit nozzle, which is obtained from a combustion experiment. Stipulate.

  In this empirical formula, a tubular flame is formed when the square ratio of the inner diameter (D-2 × B) of the combustion chamber excluding the gap of the slit nozzle with respect to the inner diameter D of the combustion chamber is in the range of 0.6 to 0.92. Based on the results of experiments that are easy to do.

  The nozzle part run-up distance Lr is set so as to satisfy the empirical formula (formula (5)) obtained from the combustion experiment in order to rectify the nozzle outlet, but should be shortened in order to reduce the pressure loss in the nozzle part. Is preferred.

  The nozzle center to burner tip distance Lx is obtained from the restriction of the pressure loss ΔP (mmAq) of the nozzle part to obtain the upper limit of the Sw number that is a dimensionless number indicating the swirling strength in the flow accompanying swirling, and Sw number−NOx amount−Lx / Obtained from experimental correlation between D.

  The pressure loss ΔP (mmAq) of the nozzle part is converted to a hydraulic diameter of the nozzle part, and a theoretical formula (“Mechanical Engineering Handbook” (Japan Society of Mechanical Engineers), etc. that takes into account the run-up distance, sudden contraction, and sudden expansion is used. It is possible to calculate using a formula described in the literature.

On the other hand, the swirl number (Sw number) serving as an index of the turning strength is calculated using the equation (8). In the equation (8), the air discharge flow velocity Wa (m / s) is the maximum flow velocity Wa (m / s) calculated by using Ls × B (m ² ) of the equation (6) as the minimum cross-sectional area. The fuel gas flow velocity Wf (m / s) is the maximum flow velocity Wf (m / s) calculated using Ls × B (m ² ) in the equation (7) as the minimum cross-sectional area. As a result, the Sw number calculated by Expression (8) is the upper limit Sw number determined from the pressure loss constraint.

However, in formula (6), Ta: preheated air temperature (° C.), in formula (7), Tf: fuel gas temperature (° C.), in formula (8), G _a : circumferential angular momentum (kg · m ² / s ), G _t : axial translational momentum (kg · m / s), R _b : burner exit radius (m), ρ _a : air density (kg / m ³ ), ρ _f : fuel gas density (kg / m) ^3), _{w a:} air discharge flow rate _{(m / s), w f} : fuel gas discharging flow rate _{(m / s), V a} : air flow rate _{^{(m 3 / s), V}} f: fuel gas flow rate ^(m 3 / s), A _b : Burner cross-sectional area (m ² ). Here, the values under the temperature and pressure conditions of the respective fluids are used as the density and the flow rate.

  FIG. 2 is a correlation diagram for explaining the relationship of Sw number−slit cross-sectional area (Ls × B) −pressure loss ΔP calculated in this manner, and the dotted line in the figure indicates the pressure loss ΔP and the slit cross-sectional area (Ls). XB), the solid line in the figure is the correlation between the Sw number and the slit cross-sectional area (Ls × B).

Here, when the pressure loss constraint (upper limit value) of the nozzle portion based on the supply pressure and the exhaust pressure (furnace pressure) is ΔPa (mmAq), the minimum cross-sectional area allowed from the constraint condition of pressure loss ΔP ≦ ΔPa Ls × B (m ² ) is determined.

  Since the slit gap B has already been determined by equation (5), the allowable slit length Ls is determined. ΔPa is a value determined by the specification conditions of the gaseous fuel and the oxygen-containing gas supply blower.

  Therefore, when the pressure loss constraint (upper limit value) ΔPa (mmAq) of the nozzle portion is determined from the correlation between the pressure loss ΔP and the slit cross-sectional area (Ls × B) in FIG. The area (Ls × B) is obtained.

  Next, the Sw number in the minimum slit cross-sectional area (Ls × B), that is, the upper limit determined from the pressure loss constraint, from the correlation of Sw number-slit cross-sectional area (Ls × B) in FIG. The swirl number SwU is obtained.

  The influence of the Sw number on the NOx amount is shown by a linear relationship organized by Lx / D (FIG. 3). For example, the number of Sws that satisfies the upper limit NOx amount set as the target performance is Sw1 when Lx / D = a and Sw2 when Lx / D = b. Therefore, the relationship between Lx / D and Sw number satisfying the upper limit NOx amount is arranged in a straight line on the XY coordinate axis where Lx / D is the Y axis and Sw number is the X axis (FIG. 4), and is determined by the pressure loss constraint. An upper limit value c of Lx / D corresponding to the upper limit swirl number SwU is obtained. Note that the correlation diagram of FIG. 3 may be experimentally obtained in advance using a small model.

  In the design of the tubular flame burner, the size of each part is restricted from the viewpoint of flame holding for maintaining stable combustion (combustion restriction 2).

  The nozzle center-burner tip distance Lx needs a certain length for flame holding, and is obtained as follows. The time α (sec) required for the fuel gas and the air to pass through the burner can be obtained by equation (9) assuming that it is cold and unreacted.

  Further, the time β required for the fluid discharged from the nozzle at the flow velocity Wa (m / s) to make one rotation of the burner having the inner diameter of the diameter D is obtained by the equation (10).

  From the experimental findings that a minimum of 5 revolutions are required until the fuel gas and air injected from the nozzle reach the tip of the burner as a necessary condition for flame holding from the combustion experiment, α / β ≧ 5 (rotation ) Is defined. Substituting the right sides of Equation (8) and Equation (9) gives 1.25 × (Vf + Va) / (D × Wa) ≦ Lx, and the lower limit of Lx is determined.

  Since the upper limit value of Lx / D is C, Lx is defined as 1.25 × (Vf + Va) / (D × Wa) ≦ Lx ≦ c × D.

  Finally, the backspace length Lb (m) is assumed to have a small value obtained by either Lb = 0.3 × D or Lb = 0.01 × (Vf + Va). From the experimental results so far, the backspace length Lb may be designed to be about 30% of the inner diameter D of the combustion chamber, and the backspace capacity is set to a unit time (1 second) at the maximum load. Based on the knowledge that the amount of gas to be supplied should be 1% or less.

  With the above procedure, all the numerical values for determining the burner layout can be determined.

  In addition, the design method of the tubular flame burner which concerns on this invention mentioned above is applicable also to the shape where the nozzle cross-sectional shape was circular or the shape which connected multiple circles.

  Using the tubular flame burner design method according to the present invention, a large tubular flame burner using LDG as a combustion gas having an upper limit NOx amount of 75 ppm (converted to 5% O2) and a maximum combustion amount Q of 34 (MW) was tested. Produced and confirmed flammability and low NOx. It should be noted that the equations (1) to (7) are already described.

First, the gas properties (maximum fuel gas flow rate Vf and maximum air flow rate Va) used to define the burner dimensions are determined. Than using the LDG as a combustion gas, lower heating value HL is 8600 (kJ / Nm ³⁾ in the air ratio mu ([air amount per fuel 1 Nm ³ to actually burn: 1.94] / [theoretical air quantity Ao : 1.62]) is 1.2, and the air preheating temperature is 400 ° C.

The maximum fuel gas flow rate Vf is Vf: 3.95 (Nm ³ / s) from equation (1), and the maximum air flow rate Va is Va: 7.69 (Nm ³ / s) from equation (2).

  The inner diameter D of the combustion chamber is 1.065 ≦ D ≦ 1.237 from Equation (3), so the inner diameter D of the combustion chamber is 1.2 (m). Next, since the gap B of the slit nozzle is 0.0245 ≦ B ≦ 0.135 from the equation (4), it is set to 0.08 (m).

  Since the nozzle portion running distance Lr is Lr ≧ 0.4 from Equation (5), it is set to 0.4 (m) which is the shortest distance in this embodiment.

  Next, the correlation between the pressure loss ΔP and the slit cross-sectional area (Ls × B) is obtained as indicated by the dotted line in FIG. 6 using a theoretical formula representing the pressure loss ΔP (mmAq) of the nozzle portion.

On the other hand, when the pressure loss constraint (upper limit) ΔPa (mmAq) is set to 1200 mmAq according to the specification conditions of the gaseous fuel and the oxygen-containing gas supply blower, the minimum cross-sectional area Ls × allowable of the slit nozzle from the dotted line in FIG. B: 0.048 (m ² ) is determined. B: Since 0.08 (m), the allowable slit length Ls is 0.6 (m).

  On the other hand, the swirl number Sw is calculated from the equation (6), the air discharge flow rate Wa: 198 (m / s), and from the equation (7), the fuel gas discharge flow rate Wf: 4.4 (m / s). From (8), the correlation between the Sw number and the slit cross-sectional area (Ls × B) is obtained as shown by the solid line in FIG.

However, in the equation (8), the burner outlet radius R _b : 0.6 (m), the preheated air density ρ _a : 0.523 (kg / m ³ ), the air discharge flow rate w _a : 198 (m / s), air flow rate V _a : 19.0 (m ³ / s), fuel gas density ρ _f : 1.13 [30 ° C.] (kg / m ³ ), fuel gas discharge flow rate w _f : 4.4 (m / S), fuel gas flow rate V _f : 4.40 (m ³ / s), and burner cross-sectional area A _b : 1.13 (m ² ).

Then, from the correlation of the Sw number-slit cross-sectional area (Ls × B) in FIG. 6, the upper limit swirl number SwU at the minimum slit cross-sectional area (Ls × B): 0.048 (m ² ) obtained previously: 7. 0 is obtained.

  Next, from FIG. 7 showing the influence of the Sw number on the NOx amount obtained in advance, the Sw number satisfying the upper limit NOx amount: 75 ppm (converted to 5% O 2) set as the target performance is Lx / D = 2. .14 is 14 and Lx / D = 4.25 is 22. Therefore, the upper limit value of Lx / D corresponding to the upper limit swirl number SwU is obtained from FIG. 8 obtained from FIG. 6 and FIG. c: 1.3 is obtained.

  Nozzle center to burner tip distance Lx is 1.25 × (Vg + Va) / (D × Wa) ≦ Lx ≦ c × D, Lx: 1.5 (m), and the back space length Lb (m) is Lb = The value is between 0.3 × D = 0.36 and Lb = 0.01 × (Vg + Vair) = 0.234, and the backspace length Lb is 0.3 (m).

  When the tubular flame burner having the above dimensions was burned, the combustion state (ignitability, flame holding property) was good, and NOx: 73 ppm (converted to 5% O 2) and a low NOx property with a target value of 75 ppm or less were confirmed.

The figure which shows the flowchart of the design method which concerns on one Example of this invention. The figure explaining the relationship of Sw number-slit cross-sectional area (LsxB)-pressure loss (DELTA) P. The figure which arranged the influence of Sw number on NOx amount by Lx / D. The figure which shows the relationship between Lx / D and the number of Sw. It is a cross-sectional schematic diagram explaining the name of each part of a tubular flame burner, (a) is a side cross-sectional view, (b) is a front view. The figure explaining the relationship of Sw number-slit cross-sectional area (LsxB)-pressure loss (DELTA) P in an Example. The figure which arranged the influence of the number of Sw on the amount of NOx in an Example by Lx / D. The figure which shows the relationship between Lx / D and the number of Sw in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tubular flame burner 2 Tubular combustion chamber 2a Open end 2b Closed end 3 Nozzle 4 Oxygen or combustion gas 5 Base B Nozzle opening height L Combustion chamber length D Combustion chamber inner diameter Ls Nozzle width Lb Back space Lx Open end Distance from the center of the nozzle in the width direction

Claims (2)

A tubular combustion chamber in which a combustion flame is formed, and a slit nozzle for injecting fuel gas and oxygen-containing gas into the combustion chamber respectively or in a premixed manner are provided toward the tangential direction of the inner wall surface, and the combustion capacity is 10 A method of designing a ~ 40 MW tubular flame burner,
The maximum combustion amount and the upper limit NOx amount are given as initial conditions,
The inner diameter D (m) of the combustion chamber is defined so as to satisfy Equation (3) that defines the relationship between the maximum combustion amount Q (MW) and the inner diameter D (m) of the combustion chamber, which is obtained from a combustion experiment.
The slit nozzle gap B (m) satisfies Expression (4) that defines the relationship between the inner diameter D (m) of the combustion chamber and the gap B (m) of the slit nozzle, which is obtained from a combustion experiment.
And so that
The nozzle center to burner tip distance Lx is obtained from the restriction of the pressure loss ΔP (mmAq) of the nozzle part to obtain the upper limit of the Sw number that is a dimensionless number indicating the swirling strength in the flow accompanying swirling, and Sw number−NOx amount−Lx / A method for designing a tubular flame burner, wherein the nozzle is a slit nozzle and the combustion capacity is 10 to 40 MW, which is obtained from an experimental correlation between D.

A tubular combustion chamber in which a combustion flame is formed, and a nozzle for blowing a premixed gas composed of fuel gas and oxygen-containing gas into the combustion chamber, or a nozzle for blowing fuel gas and a nozzle for blowing oxygen-containing gas are tangent to the inner wall surface The nozzle provided in the direction is a slit nozzle, and is a method for designing a tubular flame burner with a combustion capacity of 10 to 40 MW ,
The initial conditions are determined from the maximum combustion amount, gas properties (theoretical air amount, lower heating value), air ratio, furnace pressure, supply pressure, upper limit NOx amount, combustion chamber inner diameter, slit nozzle gap, and slit nozzle gap. When setting the nozzle part running distance, the inner diameter of the combustion chamber and the gap of the slit nozzle are set to the values obtained by the design method according to claim 1, and the nozzle part running distance is obtained from a combustion experiment. To satisfy the following formula (5)
Obtain the upper limit Sw number from the pressure loss constraint of the nozzle part,
Burner dimensional constraints satisfying the upper limit NOx amount and the upper limit Sw number;
A design method of a tubular flame burner in which a nozzle is a slit nozzle and a combustion capacity is 10 to 40 MW, wherein a burner layout is determined from burner dimensional constraints for holding a tubular flame.

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