Burner for Particulate Fuel

Abstract

Disclosed is a burner for particulate fuel, in particular made of biomass, with a primary tube and a core tube arranged in the primary tube. The primary tube and the core tube form a primary tube gap and the primary tube gap is configured to guide a flow of particulate fuel and gaseous combustion means from an inlet-side end to an outlet-side opening of the primary tube. In order to prevent the drawbacks occurring when using coarse-grain particles, preferably biomass, as a fuel for dust firing, or at least to reduce them without having to accept an increased outlay for equipment and / or additional energy losses, at least one device is provided for centring the flow within the primary tube in the region of the outlet-side end of the primary tube.

Description

BACKGROUND OF THE INVENTION[0001]1) Field of the Invention[0002]The invention relates to a burner for particulate fuel, in particular made of biomass, with a primary tube and a core tube arranged in the primary tube, the primary tube and the core tube forming a primary tube gap and the primary tube gap being configured to guide a flow of particulate fuel and gaseous combustion means from an inlet-side end to an outlet-side opening of the primary tube.[0003]2) Description of Prior Art[0004]Burners for the combustion of particulate fuels, such as, in particular, coal, in a combustion chamber have been known for some time. Dust firing is also referred to in this connection.[0005]A burner of this type is described, for example, in EP 0 571 704 A2. The burner has a core tube, which has air flowing through it, and has a burner gun for igniting the particulate fuel. Arranged concentrically with respect to the core tube is a primary tube, which, with the core tube, forms an annular gap, whi...

AI Technical Summary

Benefits of technology

[0012]The invention recognised that the drawback of an increased carrying air quantity and larger particle diameters in the combustion of coarse-grain fuels, such as biomass, can be in any case partially compensated by a fluidic deflection of a part of the primary air in the direction of the core zone of the burner mouth. The deflection makes it possible to guide a part of the primary air around the flame-holder or to guide it centrally through the latter, without this part of the primary air arriving in the turbulent particle flow zone adjoining the flame-holder. This only takes place at a later point in time, at which the turbulent particle flow zone has widened and the volatile components of the fuel particles have escaped to a greater extent. The particle concentration is consequently high in the particle flow downstream of the flame-holder. Consequently, the flame of the burner can be stabilised despite a delayed escape of volatile components. In addition, the oxygen concentration in the particle flow downstream of the flame-holder is clearly sub-stoichiometric, which counteracts the formation of nitrogen oxides.

[0018]Alternatively or in addition, the core tube may taper toward its outlet-side end. The tapering of the end of the tube, compared to an abrupt end of the core tube, has the advantage that the flow can be guided more uniformly. Stalling and turbulences can thus be avoided in the region of the inner part of the primary air flow. It is particularly preferred if a tapering of the core tube is accompanied by a longitudinal-side spacing of the flame-holder or opening of the primary tube, on the one hand, and the outlet-side end of the core tube, on the other hand.

[0023]Provided between the core tube and the deflection device is preferably a flow channel, through which the deflected primary air flow is guided. In this case, it is particularly preferred from the technical flow point of view if the free flow cross section in the flow channel of the deflection device remains constant. An unfavourable variation with respect to energy of the flow speed can thus be avoided.

[0026]The at least one flow director may, as an alternative thereto, also be oriented transverse to the longitudinal direction, i.e. partially in the peripheral direction, of the primary tube. In this case, the orientation of the at least one flow director may differ from an orientation in the longitudinal direction of the primary tube in such a way that the swirl of the primary air flow is intensified by the at least one flow director, at least for a part of the primary air flow close to the core tube. The at least one flow director may, however, also reduce the swirl of the primary air flow in an also possible orientation pointing more in the longitudinal direction of the primary tube. The at least one flow director may, however, also be oriented in the opposite direction to the swirl direction of the primary air flow. This may, for example, lead to the fact that the swirl direction of the primary air flow is reversed at least for a part of the primary air flow close to the core tube. In order to intensify the swirl of the primary air flow in regions, it may be expedient to incline the at least one flow director by 35° to 45° relative to the longitudinal direction of the primary tube. In order to weaken the swirl of the primary air flow in regions, it may be favourable to incline the at least one flow director by less than 25°, in particular less than 15°, relative to the longitudinal direction of the primary tube.

[0027]Depending on the boundary conditions in terms of flow technology, each of these orientations of the at least one flow director may entail positive effects. Basically, by means of a swirl, which has a different strength or is differently directed, of parts of the primary air flow, a separation in terms of flow technology of these parts can be achieved, as the latter have different properties in terms of flow technology. To enable a control of the burner, the at least one flow director may be variable with regard to its orientation, i.e. incline compared to the core tube.

[0029]Moreover, it can easily be achieved that the swirl of the outer flow in the primary tube gap remains uninfluenced by the at least one flow director in order to not impair the flame stability. For this purpose, the flow director is not provided in the last outer 20% of the primary tube gap. If the outer 30% or even 40% of the primary tube gap can be kept free of flow directors, this is favoured in terms of flow technology. The outer flow director-free region may, for example, be increased in that the number of flow directors arranged on the peripheral side is increased.

Problems solved by technology

Thus, a flow is produced, which is directed into the combustion chamber, with a high degree of turbulence and coal particle concentration.

For this purpose, the biomass has to be very finely ground, however, which, because of the usually fibrous and tough structure of conventional biomasses, is linked with an increased outlay for equipment and energy.

In particular, the fine grinding of biomass often entails a high degree of wear of the equipment used for this.

The volatile components of the biomass particles are already expelled more slowly because of their size, which can impair stable combustion of the biomass.

The larger carrying air quantity flowing through the annular gap between the primary tube and the core tube can, together with a delayed release of volatile components, lead to a local air excess during the combustion.

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