EP0035153B1 - Process and device for minimizing the sound emission of a premix burner - Google Patents

Abstract

1. A process of minimizing the radiation of sound from a premixing burner, which is fed with a gas-air mixture, comprising at least one gas nozzle, which is associated with an injector, and combustion slots, characterized in that the gas is defined (Wobbe number) and the minimum sound radiation is defined as well as the heat output (which is determinable from the total flow area and the gas velocity in the nozzle or nozzles and the total flow area of the injector is defined by the relation see diagramm : EP0035153,P8,F1 wherein V is the sum of the entire gas and air flow, P is a proportionality factor, N is the predetermined maximum sound radiation and K is a constant, which is determined by the Wobbe member, the sound velocity, the load per unit of nozzle area, and the total nozzle area, and the load per unit of combustion area is determined by the relation see diagramm : EP0035153,P8,F2

Description

The present invention relates to a method for minimizing the sound radiation of a premix burner fed with a gas-air mixture according to the preamble of the main claim. The invention further relates to an apparatus for performing this method.

DE-A-2 207 888 discloses a premix burner fed with a gas / air mixture with at least one gas nozzle and combustion slots assigned to an injector. With this burner, no considerations have been made with regard to minimizing sound radiation.

• 1. Das Geräusch, das durch die Verbrennung entsteht.
• 2. Das Geräusch, das am Injektor auftritt.
• 3. Das Geräusch, das sich bei der Strömung von Gasen aus Düsen bildet.

With premix gas burners, there is an overall noise that can essentially be divided into three individual noises:

• 1. The noise caused by the combustion.
• 2. The noise that occurs at the injector.
• 3. The noise that occurs when gases flow from nozzles.

Other sources of noise may include the noise in the Gaz feed pipe and the exit noise of the gas-air mixture from the burner slots. Compared to the noises mentioned under one to three, these two noise sources are, however, easily negligible.

To 1 - combustion noise

Measurements, such as those shown in Figure four, show that the combustion noise produces the greatest sound pressure. The maximum sound level is around 500 Hz, see also GWF 115 (1974, Issue 2, page 50). As this reference also states, the sound pressure depends on the heat output and the degree of air admixture to the gas. The more air that is mixed in with the same gas throughput, the higher the sound pressure.

To 2 - injector noise

This noise prevails in a range between 1 and 8 kHz. It depends on the primary air supply and forms typical resonance frequencies when the gas-air mixture flows in the injector.

To 3 - nozzle outflow noise.

The frequency analysis shows peak values of the sound pressure in the range greater than 8 kHz.

Based on the comparisons of the three noise sources, it can be said that the nozzle outflow noise is small compared to the combustion and injector noise.

In the course of the previous efforts to determine the individual noise sources of premix burners, to weight them and to remedy them, it has become known according to GWF 108 (1967) 47, pages 1325 to 1336 that the individual sound pressures refer to the noise Sources behave as shown in Figure four. However, no instructions can be found in the prior art as to which measures are to be taken in particular in order to reduce the different noise sources in their sound pressure levels and how to proceed in the construction of burners in order to achieve these goals. From the literature it has become known that multi-hole nozzles produce a lower sound pressure level than single-hole nozzles with the same overall cross-section. This statement can also be applied with sufficient accuracy to burners in which an injector is assigned to each nozzle.

On the basis of general considerations, one could influence the combustion noise to the extent that the combustion mixture gas outlet slots in individual burner tubes are made larger in order to achieve a quieter outlet of the combustion gas / air mixture. This measure has its limit, however, where the flame strikes the nozzle through the increasing shooting bronzes. However, this happens when the size of the burner slots is large if the escaping flow is not yet significantly calmed down.

The problem of injector noise has already been attempted by so-called Heimholtz resonators. For example, DE-A-21 17 337 has disclosed a burner for gas-fired devices provided with a Heimholtz resonator, a sound-absorbing device having a resonance frequency of at least 600 Hz being provided at the inlet opening of the primary air suction chamber. It was specifically provided that the Helmholtz resonator had a resonance frequency of 1 to 1.5 kHz.

However, Helmholtz resonators can only extinguish a certain frequency or only a very narrow frequency range over the bandwidth. Accordingly, in order to be able to cancel out the entire injector noise in a frequency range of about 1 to 8 kHz, about five Helmholtz resonators per nozzle were necessary. It can be seen from this that with a multi-nozzle burner the effort is prohibitive, not to mention the size.

wobei p_o die Dichte des Mediums bedeutet, u_o die Düsenaustritts-Geschwindigkeit, d_o der Düsendurchmesser und a die Schallgeschwindigkeit bedeuten.Theoretically, the nozzle outflow noise from Lighthill (Proceeding Royal Society A 221 (1952) and A 222 (1954)) have been examined and described. It states that the sound power of a turbulent flow, and this is why the burners described here and their nozzle flows are always proportional to the 8th power of the nozzle outlet speed and the square of the nozzle diameter.

where p _{o is} the density of the medium, u _{o is} the nozzle outlet speed, d _{o is} the nozzle diameter and a is the speed of sound.

From Lighthill's law it can be deduced that the sound radiation due to the flow from the nozzle is reduced primarily by lower flow velocities.

The present invention has for its object to provide a method in which the sound levels for the combustion and injector noise can be minimized while keeping the heat output constant and with a fixed gas and a predetermined maximum sound radiation. This object is achieved by the method according to claim 1.

From a large number of measurements on premix gas burners of various designs, in which the relationship between the sound pressure or sound power level and the specific burner surface load, the specific nozzle load, the Wobbe index of the gas concerned, the flow conditions in the injector and the The following relationship was found:

Here N means the theoretical sound power in [W], Q _D the specific nozzle surface load in [W / _M ² ), Q _AB the specific nozzle surface load in [W / m ² ], Q _AB the specific focal surface load [W / m ² ], W the Wobbe number in [Ws / m ³ ], a the speed of sound in [m / s], V _{; N} the average velocity of the gas-air mixture in the injector in [m / s], Σ A _D the total area of the nozzle openings in [m ² ]. The further explanations about the method according to the invention relate to the natural gas family because burners are the most widespread in this family. However, it is not difficult to transfer the knowledge gained for natural gas to other gases or gas-air mixtures.

In the natural gas sector, the Wobbe number can be assumed as follows:

For the determination of the exponents, equation (2) was treated in such a way that one of the multipliers is set variably and the others are regarded as constants. A large number of burners could then be measured, the exponents also being regarded as approximately the same in the different burner designs. The exponents result from these measurements as follows:

Taking into account the now fixed exponents, it can be seen from equation (2) that the sound power of an atmospheric burner is directly proportional to the nozzle area and burner area loading, further proportional to the average velocity of the gas-air mixture in the injector and the total area of all nozzles and inversely proportional to the Wobbe number. In equation (2), only Q _AB and V _IN are independent of each other. Furthermore, the following values are either to be assumed as constants or to be used as constants in the noise optimization to be carried out. These are essentially the speed of sound a as well as the specific nozzle surface load and the sum of all nozzle surfaces. The product of Q _D and LAD corresponds to the heat output of the burner. The speed of sound relates once to the air flowing in from a room and the gas flowing into the injector via the gas feed pipe, the mean temperatures of which can be assumed to be constant in the range of 100 ° C.

The burning gas-air mixture has a temperature of approximately 1,400 ° C., which can essentially also be assumed to be constant. Only the absolute temperature levels would be decisive for the variation of a.

Within the natural gas family or another gas family, an atmospheric burner should therefore be optimized so that the theoretical sound power N is not reached at a certain heat output.

Taking the above premises into account, equation (2) is simplified to the following equation (5) or equation (6).

• Die beiden den Wert N durch K ergebenen Faktoren sollen so gewählt werden, daß ihre Summe möglichst klein ist.

The approach for minimization is now:

• The two factors resulting from the value N by K should be chosen so that their sum is as small as possible.

Als Randbedingung wird Gleichung (6) gemäß Gleichung (8) verwendet.

Aufgrund des Lagrange'schen-Ansatzes ergibt sich somit folgende Lösung :

The requirement just described corresponds to the following mathematical approach:

Equation (6) according to equation (8) is used as a boundary condition.

Based on the Lagrangian approach, the following solution results:

In words, this means that the amount of the average gas-air mixture speed up to 4.5 in numerical terms must correspond to the specific focal surface load in order to meet the requirement mentioned at the beginning. This results in equations (10) and (11).

It makes physical sense that the values of Q _AB and V _{IN are} not exceeded, but may, however, fall below them to a certain extent.

On the generally valid basis according to equations (10) and (11), however, measurements have shown that V _IN can be significantly reduced without the perfect combustion suffering. Flawless combustion is understood to mean that the flame which arises at the focal surface slots neither lifts off from the focal surface slots nor burns with the formation of CO. Under this condition, equation (11) can be continued as follows:

In equation (12), 1: P means the reduction factor. The measurements have shown that P is to be narrowed down according to equation (13). If the value falls below the lower value of P, the flame will tend to lift off; exceeding the higher value would mean incomplete combustion. For purely practical reasons, the range of P is narrowed according to equation (14).

A component that can be found on every gas premix burner is the sum of all injector passage areas. If a single injector is used, this is the cross section of the injector at its narrowest point; for multi-nozzle burners with a correspondingly larger number of injector tubes, this is the sum of the smallest passage points of all injectors. This total area is equal to Equation 15.

Setzt man aus Gleichung (12) den Wert für V_IN in Gleichung (15) ein, so ergibt sich Gleichung (17).

Here V is composed according to equation (16), the air flow rate being understood to mean only the primary air flow rate, that is to say the flow rate which is blown through the injector tubes by means of the gas nozzles.

Substituting the value for V _IN in equation (15) from equation (12) yields equation (17).

Thus, the total area of the injector (or the injectors) is determined numerically, whereby the value, according to which an injector is determined according to equation (17), must not be undercut, because this would lead to an immediate increase in the sound radiation while exceeding the Value initially only leads to a deterioration of the combustion.

It can be seen from this that the optimization of the sound radiation and the achievement of an optimal combustion partially contradict each other.

According to equation (17), the total injector passage area of the burner can thus be calculated for a given gas family, a given maximum sound radiation and a given heat output. If this injector area is observed, you can be sure that the sound radiation that will result in practice will be less than the theoretical predetermined value.

The calculated value for the specific focal surface load Q _AB results directly from equation (10). The practical values determined from this form can be exceeded or fallen below in the operational tolerances, falling below leads to an increase in the noise emission, while exceeding leads to the flames fighting back.

und

gearbeitet.This specifies the two most important data of a burner. Before the construction of a burner is shown from equations (17) and (10) using a calculation example, the speed of sound should be limited. For purely practical considerations, values of

and

worked.

The specific nozzle area load Q _D is the throughput of gas-air mixture at a given calorific value based on the individual passage cross-section. This value is assumed to be purely practical

According to FIG. Four, a higher value leads to a higher sound radiation with regard to the nozzle noise, a reduction in the value leads to a lower gas throughput through the nozzles, thus to a low pulse and thus to a lower air intake and thus to a lower burner output or incomplete combustion .

When designing the burner, the maximum sound power that is emitted is specified. Today's burners on the market have an average sound power of over 60 dB (A). The lowest known limit is 52 dB (A).

With the method according to the invention, sound powers of the order of 40 dB (A) are aimed for. This value must therefore be assumed as a premise.

It would also be possible to set a different sound power level and to take this as a premise.

Based on the specified values for the desired sound power, the speed of sound, the Wobbe number, the specific nozzle load and the proportionality factor, an example for an atmospheric gas burner with a power of 30 kW, which is operated with natural gas and which has a sound power of should not produce more than 40 dB (A). The specific nozzle load is not greater than

Die zugrundeliegende Wobbe-Zahl sei

The underlying Wobbe number is

The speed of sound is A = 1 100 or 400 m / s. The proportionality factor p is 3.5. A sound power level of 40 dB (A) corresponds to a sound power of

Dann sind :

und

First, the sum of all nozzle areas must be determined. It is determined from the specified heat output, based on the nozzle area load Q _o . This results in a total nozzle area of 3.75 x 10- ⁵ m ^2. It does not matter whether this area is distributed over one or a large number of individual nozzles. So K can be calculated next. From equation (2) it follows that K comprises the following terms:

Than are :

and

The equations (10), (19) and 21 thus result in Q _AB ≤ 2.3. 10 ⁶ W / m ² . V _IN can be calculated from equations (12), (19) and (22), which results in 3.8 m / s.

From this, the totality of the injector passage areas can be calculated using equation (17).

AN = 1.21 · 10 ^-3 m ² , where for practical reasons V is fixed at 4.6 · 10 ^-3 m ³ / s according to equation (16) for a power of 30 kW.

This means that the design data for the burner are fixed when it comes to minimizing sound radiation.

While the values for the speed of sound and for the Wobbe number represent variables that the burner designer cannot use in the variation, the values for the nozzle surface load and the proportional value p can be changed. When the ranges or values for Q _D and p were checked, it was found that the ranges of Q _D and p should not leave the values mentioned earlier. In the further practical examination of the sizes found by the formulas for Q _AB and A _IN , it turned out that the product of Q _AB and AN can be regarded as a size which must not be exceeded. For the practical dimensioning of the burner, a falling value of Q _AB must therefore be assigned a rising value of A _IN and not vice versa. It goes without saying that the value for the product of Q _AB x A _IN can be changed with the value of the prescribed sound radiation that should not be exceeded.

• Figur eins eine Ansichtsdarstellung einer Brennerhälfte eines Brenners für einen Umlauf-Gas-Wasserheizer,
• Figur zwei eine Schnittansicht auf die Brennerhälfte mit Düsenrohr senkrecht in Ebene II-II zur Ansicht gemäß Figur eins geschnitten und
• Figur drei eine abgebrochene Ansicht auf die Brennerrohre gemäß Figur zwei von oben zur Darstellung der einzelnen Brennflächenschlitze.

An exemplary embodiment of a burner calculated acoustically according to the design rules according to the invention is shown with reference to FIGS. One to three of the drawing:
Mean it

• FIG. 1 shows a view of a burner half of a burner for a circulating gas water heater,
• Figure two is a sectional view of the burner half with nozzle tube cut vertically in plane II-II to the view according to Figure one and
• Figure three is a broken view of the burner tubes according to figure two from above to show the individual focal plane slots.

In all three figures, the same reference numerals denote the same details.

A natural gas burner for a gas-heated device, be it a continuous-flow heater or circulating water heater as well as a boiler or air heating oven, has a gas supply pipe 1 which is supplied with gas by a natural gas network, not shown. The gas supply pipe 1 feeds a nozzle pipe 2, which has at least one gas nozzle 4 in the present example but seven gas nozzles 4 per fuel element 3. The individual gas nozzles 4 each have a passage channel for the gas, the total area of the individual nozzle channels thus giving the total nozzle passage area.

All gas nozzles 4 blow into injector tubes 5, which are formed in half by two sheet metal parts 6 and 7. The injector tubes - one injector tube is provided for each nozzle - have an 8 conical frustum shape at their gas nozzle 4 facing mouth, the cone 9 is arranged so that the cone tapers in the direction of the gas flowing out of the nozzle 4. At the end of the cone there is an almost cylindrical constriction 10, which is followed by a further cone 11 which opens again in the direction of the flowing gas. All added cross-sectional areas of the individual constrictions 10 of each injector tube 5 thus result in the total injector area. The individual cones 11 open into a gas distribution chamber 12, on the top of which individual burner tubes 13 are mounted. The number of burner tubes 13 may differ from the number of nozzles. A plurality of burner tubes 13 are preferably provided as nozzles 4 or injector tubes 5 are provided. The burner tubes 13 have upright rectangular shape, on its upper narrow surface 14 burn slots 15 or openings 15 are provided, which can in principle have any shape, as shown in Figure three in detail. The sum of the individual areas of all burning slots 15 or openings 15 results in the total burning area.

• Dem Gaszufuhrrohr 1 zugeführtes reines Erdgas - gegebenenfalls auch Flüssiggas oder Kokereigas - wird dem Düsenrohr oder den Düsenrohren 2 zugeführt, wo es zu der Vielzahl parallelliegender Gasdüsen 4 gelangt. Jede Gasdüse bläste zentrisch und ohne Versatz in das zugehörigen Injektorrohr 5 ein und reißt aus dem Spalt 16 zwischen Düsenende und Mündung 8 sämtlicher Injektorrohre Primärluft mit sich. Jedes Injektorrohr 5 wird somit von einem Gas-Luftgemisch durchströmt, welches im Bereich des Injektors intensiv verwirbelt und vermischt wird. Das Gas-Luftgemisch tritt in die Gasverteilerkammer 12 ein, die zu einer Vergleichmäßigung der einzelnen Gas-Luftgemische aus den einzelnen Injektoren beiträgt. Aus der Gasverteilerkammer werden die einzelnen Brennerrohre 13 gespeist, aus denen Gas-Luftgemisch jeweils an der Oberseite durch die Brennflächenschlitze 15 austritt, wo es durch eine nicht dargestellte Zündvorrichtung entzündet wird und verbrennt. Die Erfindung hat es sich zum Ziel gesetzt, das Ansaugegeräusch, also das Geräusch, das im Spalt 16 aufgrund der Ansaugung der Primärluft durch den Gasstrom entsteht, und das Verbrennungsgeräusch, das beim Durchtritt des Gas-Luftgemisches durch die Brennflächenschlitze 15 auftritt, zu minimieren, und zwar durch entsprechende Bemessung der Injektorenflächen und der Brennschlitze.

The function of the burner shown in Figures one to three is as follows:

• Pure natural gas supplied to the gas supply pipe 1 - possibly also liquefied gas or coke oven gas - is supplied to the nozzle pipe or the nozzle pipes 2, where it comes to the large number of gas nozzles 4 located in parallel. Each gas nozzle blows centrically and without offset into the associated injector tube 5 and pulls primary air with it from the gap 16 between the nozzle end and mouth 8 of all injector tubes. Each injector tube 5 is thus flowed through by a gas-air mixture, which is swirled and mixed intensively in the area of the injector. The gas-air mixture enters the gas distribution chamber 12, which contributes to an equalization of the individual gas-air mixtures from the individual injectors. The individual burner tubes 13 are fed from the gas distribution chamber, from which gas-air mixture emerges at the top through the focal surface slots 15, where it is ignited and burned by an ignition device (not shown). The invention has set itself the goal of minimizing the suction noise, that is to say the noise which occurs in the gap 16 due to the suction of the primary air by the gas stream, and the combustion noise which occurs when the gas-air mixture passes through the focal plane slots 15. by appropriate dimensioning of the injector surfaces and the burn slots.

With the invention, the largest Q _AB and AN have so far been used to minimize noise. The specific burner ^f lächen-load Q _AB is composed of the thermal power generated to the burner, and the sum of the areas of all the burner outlet slots A _B. The relationship is as follows:

Since a thermal output of 30 kW was assumed and a Q _AB value of = 2.3 10 ⁶ [W / m ² ] was determined in the calculated example, this results in

In the example dealt with, the sum of all focal surface exit slots must therefore be 130 cm ² . This value would be directly measurable on the associated burner.

Based on these considerations, it was found to be included in the considerations in addition to Q _AB and A _IN A _B. The sound power level in dB (A) according to FIG. 5 then relates to the ratio of A _B / A _{IN in} accordance with a hyperbolic curve. The ratio of A _B to A _IN is independent of the burner heat output while maintaining the values for Q _L , Q _D , W, p and the sound velocities a ₁ and a ₂ .

From the observation of the curve according to FIG. 5 it follows that the sound radiation level decreases continuously when the ratio of A _B to AN is increased. Thus, the curve of FIG five serve as a verification of the theory of the invention: Taking the values for Q _L, Q _D, W, p, to a ₁ + a _2, according to the premises to carry out the example calculation, it is clear at a predetermined maximum sound radiation level of 40 dB (A) each a certain fixed and reproducible value for the ratio of A _B to A _IN . This results in the curve when assigning the values from A _B to A _IN for the various different sound radiation levels deviating from 40 dB (A). It follows that the practical value for the ratio of A _B to A _IN must be greater than 10 in order to be guaranteed to be below a maximum sound radiation of 40 dB (A). The ratio of A _B to AN on the finished burner must of course be different if a maximum sound radiation level other than 40 dB (A) is required.

In any case, for a desired sound radiation level equal to or less than 40 dB (A), the ratio of A _B to A _{IN must be} equal to or greater than 10.

The factor K can now be expressed by starting from equations 2 and 5.

The two equations can then be equated, since the value for the power N must be the same in each case. This results in equation (25).

Equation (25) can now be converted to K as equation (26) and solved for K according to Equation (27).

Claims (8)

1. A process of minimizing the radiation of sound from a premixing burner, which is fed with a gas-air mixture, comprising at least one gas nozzle, which is associated with an injector, and combustion slots, characterized in that the gas is defined (Wobbe number) and the minimum sound radiation is defined as well as the heat output (which is determinable from the total flow area and the gas velocity in the nozzle or nozzles and the total flow area of the injector is defined by the relation

wherein V is the sum of the entire gas and air flow, P is a proportionality factor, N is the predetermined maximum sound radiation and K is a constant, which is determined by the Wobbe number, the sound velocity, the load per unit of nozzle area, and the total nozzle area, and the load per unit of combustion area is determined by the relation

2. A process according to claim 1, characterized in that the maximum sound radiation is predetermined, the product of the lowest possible load Q_AB per unit of combustion area and the largest possible total injector area AN is held constant, and the constant is variable with the variation of the predetermined maximum sound radiation.

3. A process according to claim 1 or 2, characterized in that a decrease of the load Q_AB per unit of combustion area has associated with it an increase of the total injector area AN rather than inversely in dependence on the predetermined maximum sound radiation.

4. A process according to any of claims 1 to 3, characterized in that the load per unit of nozzle area is held in the following range

5. A process according to any of claims 1 to 3, characterized in that the proportionality factor P is selected in the following range

6. A process according to any of claims 1 to 3, characterized in that the constant K is selected in dependence on the following relation

7. A premixing burner which is fed by a gas-air nozzle, comprising at least one gaz nozzle, which is associated with an injector, and combustion slots, for carrying out a process according to any of claims 1 to 5, characterized in that for a maximum sound radiation level which is equal to or lower than 40 dB (A) the ratio of the total area A_B of all burner slots to the total of all injector flow areas is equal to or higher than 10.

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