EP0896191B1 - Fuel gas admission device for a premix burner - Google Patents

Abstract

The fuel feed assembly (10), to deliver mixed gas and air to a burner, passes the fuel gas (12) through openings (23) into an inflow chamber (18) for the air (11). The air is diverted into a spiral path (20) within the inflow chamber. The gas feed openings (23) are arranged round the rotating axis (22) of the spiral flow path (20).

Description

The invention relates to a device for initiating Fuel gas in an air stream, especially for a gas premix burner, with an inflow chamber for the air, with a leading into the inflow chamber for the Fuel gas and with a (first) swirl generating device, by means of the air flowing through the inflow chamber Swirl is impressed, the inflow opening in the Axis of the (first) swirl generating device is arranged.

Such a device is for example by DE 33 45 611 A1 has become known.

In the so-called "atmospheric burner" it breaks through an inflow chamber flowing air according to the jet pump principle a corresponding amount of fuel gas. Corresponding the flow velocity of the air or that in the inflow chamber prevailing air pressure becomes more or less Fuel gas metered, although considerable inaccuracies may occur.

Introductory devices are also known in which the fuel gas metering after a pressure loss Throttle point is aimed. In the so-called "mechanical gas-air network" in order to change the performance, the flow cross-sections of air and fuel gas alike. However, this requires a great technical Expenditure. To change the performance, the so-called "Pneumatic compound" is the pressure of one fluid the pressure loss at the throttle point changed to the to achieve the same mixing ratio. Here too is a high technical effort required and the usable performance range remains relatively small. With the so-called "Zero pressure control" is the pressure loss of the throttle point in the one fluid stream chosen approximately the same as the pressure loss of the throttle point in the other fluid flow, which makes the mixing ratio independent of the throughput becomes. The usable performance range is also here small because of precise pressure control with small pressure differences is very difficult.

From the publication "Flame Special ISH Edition" by Honeywell, No. 2, 1997 is still an induction device known, in which the fuel gas in a Venturi tube is initiated in which a negative air pressure prevails. The fuel gas is introduced into the air flow around the narrowest cross section of the Venturi tube via a coaxial to the tube axis of the venturi tube arranged annular inflow opening. That from this ring-shaped inflow opening shaped like a jacket around the air flow fuel gas escaping around flows essentially without Mixing with the air flow on the diffuser wall of the Venturi tube along. The actual mixing between Fuel gas and air only take place in a downstream of the Inflow opening or the venturi arranged fan. The fuel gas metering depends on the negative pressure of the Air in the Venturi tube, however, the vacuum in the Venturi tube still too low to cover large performance ranges to be able to.

In the known from DE 33 45 611 A1 mentioned The fuel gas is introduced via a fuel lance axially in the axis of rotation of one generated with blades Swirls, i.e. introduced into the "eye" of a vortex of air. There is a high one in this eye of the air vortex Negative pressure, which causes the pressure control of the to be initiated Fuel gas simplifies and therefore the metering accuracy is increased.

In contrast, the present invention has the object based on an introductory device of the aforementioned Art in such a way that even better metering accuracy can be achieved.

According to the invention, this object is achieved by a further one (Second) swirl generating device, which through the inflow opening flowing fuel gas or one through the inflow opening already flowing mixture of air and fuel gas imbues a twist.

By the further swirl generating device, which by the the inflow fuel gas flowing through the Inflow opening flowing mixture of air and fuel gas Swirl imprints can already be upstream of the inflow opening a swirl is imparted to the fuel gas or the mixture be the downstream swirl of air reinforced. This is preferably a further swirl generating device upstream of the inflow opening for generation of a swirl only in the air of through the Inflow opening flowing mixture arranged.

Furthermore, it can be advantageous if the inflow opening is designed as a Venturi nozzle. To detach the flowing through Flow from the diffuser wall of the Venturi nozzle delay as long as possible or even prevent it completely, can cause a swirl to flow through it his. When fuel gas and air come together through the Venturi nozzle flow, this leads already upstream of the Inflow chamber for improved mixing.

Due to the swirl of the rotating air flow is in the Inflow center arranged for the center of the swirl Fuel gas generates a high negative pressure, which regulates the pressure of the fuel gas to be introduced is significantly simplified and thus increasing the metering accuracy. This can already with a low pressure drop in the air a precise, adjustable Mixing ratio with the fuel gas in one large performance range can be achieved. The generation of the Swirls in the air also have the advantage that the flow with changes of direction not so easily detachment shows and thereby space is saved can.

The swirl generating device preferably has at least one, in particular several evenly distributed around its circumference swirl-generating guide vanes. Via adjustable Guide blades can also be the metering of Fuel gas or the mixing ratio between air and Influence fuel gas particularly easily.

In preferred embodiments of the invention Swirl generating device designed as a cyclone. It turns out turns out to be advantageous, a larger amount of fuel gas to flow in the center of the cyclone to avoid flow losses to reduce.

Particular advantages arise when downstream of the inflow chamber a radial fan is arranged. The twist of the mixture flowing out of the inflow chamber can be used for inflow of the radial fan can be used advantageously. At Counter-swirl flow can be a particularly high fan output can be achieved while a constant swirl flow particularly low-loss entry of the mixture into the radial fan is possible.

To the negative pressure and also the mixing of fuel gas and To increase air still further, several such induction devices, cascaded as described above become. Should e.g. a relatively small amount of fuel gas can be admixed, it can be advantageous again connect a Venturi nozzle or a cyclone with the air (Cascading).

Further advantages of the invention result from the description and the drawing. The shown and The embodiments described are not intended to be final Understand enumeration, but rather have exemplary Character for the description of the invention.

Fig. 1

eine schematische Darstellung eines Ausführungsbeispiels einer erfindungsgemäßen Einleitungsvorrichtung; und

Fig. 2

einen Querschnitt durch die Einleitungsvorrichtung der Fig. 1, dargestellt in drei unterschiedlichen Schnittsegmenten entsprechend A, B, C in Fig. 1.

It shows:

Fig. 1

a schematic representation of an embodiment of an introduction device according to the invention; and

Fig. 2

2 shows a cross section through the introduction device of FIG. 1, shown in three different sectional segments corresponding to A, B, C in FIG. 1.

The figures of the drawing show the subject matter of the invention some are highly schematic and are not necessarily to understand to scale.

In Fig. 1, 10 'shows an introduction device for a gas premix burner (not shown) in which air 11, 11' and fuel gas 12 are mixed together and then fed to the gas premix burner as a mixture 13 . For this purpose, the air 11 is sucked in via a peripheral opening 17 into an inflow chamber 18 via a radial fan 14 , which is driven by the motor 15 in the direction of rotation 16 . In the inflow chamber 18, guide vanes 19 (FIG. 2) are arranged, which form a cyclone and which impart a swirl 20 to the air 11 flowing through the inflow chamber 18, as is also indicated by the flow arrows 21 in FIG. 2.

In the center of the swirl 20, ie in the region of its axis of rotation 22 , an inflow opening 23 ' in the form of a Venturi nozzle 29 is provided, through which the fuel gas 12 and further air 11' are jointly introduced into the inflow chamber 18 in the direction of the axis of rotation 22. The air 11 'is sucked in via the radial fan 14 via an air duct 31 and into the Venturi nozzle 29, the air 11' entraining the fuel gas 12 via a nozzle-shaped inflow opening 32 arranged in the region of the axis of rotation 22. Already in the air duct 31, a swirl 34 is impressed on the air 11 'upstream of the inflow opening 23' via guide plates 33 (FIG. 2), which continues as a swirl 34 ' in the Venturi nozzle 19 and increases the swirl 20 of the air 11, as by the arrow 35 is indicated. The swirl 35 generates a very high negative pressure at the inflow opening 23, which decisively simplifies the pressure control of the fuel gas 12 to be introduced and thus increases the metering accuracy.

As the sectional segment C in FIG. 2 shows, the mixture 25 of air 11, 11 'and fuel gas 12 in the radial fan 14 flows radially outward into an outer flow channel 24 and then out via an outlet opening 26 in the direction of the gas premix burner.

In the exemplary embodiment shown, the swirl 35 and the direction of rotation 16 of the radial blower 14 are directed in the same direction, whereby a particularly low-loss entry of the mixture into the radial blower 14 is possible if the impeller 27 of the radial blower 14 is equipped with corresponding guide vanes 28 .

mit A₁:

Düsenquerschnitt für die Luft 11, der näherungsweise durch den Querschnitt in der Einströmkammer 18 und, falls vorhanden, durch den Austrittsquerschnitt der Venturidüse 19, abzüglich des Düsenquerschnitts für das Brenngas 12, multipliziert mit dem Flächenverhältnis der Venturidüse 19 gegeben ist,

mit σ1:

Dichte der Luft,

mit p₁:

Eintrittsdruck der Luft 11, und

mit p_G:

gemeinsamer Austrittsdruck von Luft 11 und Brenngas 12 vor dem Radialgebläse 14.

The mixing ratio of air 11 and fuel gas 12 - idealized - is calculated as follows if the volume flow V through a nozzle: V = A * α * ρ * [2Δp / σ] ½ for simplification with α = 1 and ρ = 1 is assumed. For the volume flow V _{1 of} the air 12 follows: V 1 = A 1 * [2 * (p 1 -p G ) / σ1] ½ ,

with A ₁ :

Nozzle cross section for the air 11, which is approximately given by the cross section in the inflow chamber 18 and, if present, by the outlet cross section of the Venturi nozzle 19, minus the nozzle cross section for the fuel gas 12, multiplied by the area ratio of the Venturi nozzle 19,

with σ1:

Density of air,

with p ₁ :

Air inlet pressure 11, and

with p _G :

common outlet pressure of air 11 and fuel gas 12 in front of the radial fan 14.

mit A₂:

Düsenquerschnitt für das Brenngas 12,

mit p₂:

Eintrittsdruck Brenngas, normalerweise gleich p₁, und

mit v:

Gerätekonstante, z.B. 4, d.h., ein bestimmtes Druckgefälle am Düsenquerschnitt für die Luft 11 erzeugt das 4-fache Druckgefälle am Düsenquerschnitt für das Brenngas 12.

The volume flow V _{2 of} the fuel gas 12 is given by: V 2 = A 2 * [2 * (p 2 -p G + (v-1) * (p 1 -p G ) / σ2] ½

with A ₂ :

Nozzle cross section for the fuel gas 12,

with p ₂ :

Fuel gas inlet pressure, normally equal to p ₁ , and

with V:

Device constant, for example 4, ie a certain pressure drop across the nozzle cross section for the air 11 generates 4 times the pressure drop across the nozzle cross section for the fuel gas 12.

By reducing the pressure p ₂ , a smaller proportion of the fuel gas 12 is admixed. This enables a performance-dependent change in the mixing ratio to be achieved. With a constant change in pressure, for example by a different setting on the pressure regulator for the fuel gas 12, the mixing ratio is changed more at low throughputs, with throttling the mixing ratio is increasingly changed at high throughputs.

Claims (8)

1. An admission device (10, 10') for introducing combustible gas (12) into an air stream, particularly for a gas pre-mix burner, with an inflow chamber (18) for the air (11), with an inflow port (23, 23') leading into the inflow chamber (18) and provided for the combustible gas (12) and with a first swirl-generating means by means of which the air (11) flowing through the inflow chamber (18) has a twist (20) imposed upon it, the inflow port (23, 23') being disposed in the axis (22) of the first swirl-generating means (20), characterised by a further second swirl- generating means which already imposes a swirl (34, 34') upon the combustible gas (12) flowing through the inflow port (23) or on a mixture (30) of air (11') and combustible gas (12) which flows through the inflow port (23').
2. An admission device according to claim 1, characterised in that the second swirl-generating means is disposed upstream of the inflow port (23') for generating a twist (34) in the air (11') of the mixture (30) flowing through the inflow port (23').
3. An admission device according to claim 1 or 2, characterised in that the inflow port (23') is constructed as a Venturi jet (29).
4. An admission device according to one of the preceding claims, characterised in that the first swirl-generating means comprises at least one swirl-generating baffle (19).
5. An admission device according to claim 4, characterised in that the at least one baffle (19) is adjustable.
6. An admission device according to one of the preceding claims, characterised in that the first swirl-generating means is constructed as a cyclone.
7. An admission device according to one of the preceding claims, characterised by a radial fan (14) disposed downstream of the inflow chamber (18).
8. An admission device characterised by a cascading of a plurality of admission devices (10, 10') according to one of the preceding claims.

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