EP3364105B1

EP3364105B1 - Burner for low calorific fuels

Info

Publication number: EP3364105B1
Application number: EP17156516.1A
Authority: EP
Inventors: Pavel Skryja; Igor Hudak; Petr Belohradsky; Petr Stehlik
Original assignee: Vysoke Uceni Technicke V Brne
Current assignee: Vysoke Uceni Technicke V Brne
Priority date: 2017-02-16
Filing date: 2017-02-16
Publication date: 2019-11-27
Anticipated expiration: 2037-02-16
Also published as: EP3364105A1

Description

Technical field

The invention relates to combustion of low calorific fuels from alternative sources and also from standardised sources.

State of the art

Burners for combustion of low calorific fuels has to be designed to be able to cope with variable parameters of fuel. Composition of fuel varies according to the process from which it comes and how it was obtained. In fuel various incombustible components can occur, most often these are carbon dioxide especially by biofuels or nitrogen, which gets into fuel generally during fuelification of solids by the air. Except the instable concentration of inert substances also the composition of combustible components can fluctuate, mostly methane, hydrogen, carbon monoxide. The properties of methane, hydrogen, and carbon monoxide are significantly different. They have different weight, calorific value, and also combustion velocity.
The combustion velocity is absolutely crucial and has to be considered by designing of the burner. Simultaneously, the construction has to be designed so, that it is possible to satisfy various operating conditions. For ignition of the burner natural fuel is often used, which has significantly higher calorific value than low calorific fuels. One of the requirements of the operator used to be also the possibility of power regulation within certain range. Therefore, the designer has to take into consideration the fuel flow rate and air velocity and suggest a solution to avoid disruption of flame and its flashback. It is difficult to keep these parameters.
There exist many solutions, which approach the matter in different ways. Usually, the fuel is supplied by central tube, to which further technical elements are attached. These may be various types of whirlers or parts which ensure mixing of individual components, it means fuel and combustion air. The solutions according to prior art utilise the in steps supply of the fuel or air and solve the distribution and mixing of individual flows in different ways.
In the document EP 0 487 700 B1 , so called matrix burner with a burner head specially designed for combustion of low calorific fuels, is described. In the middle of the assembly a fuel supply tube on which the entire head is fixed, is located. The head is composed of two steel sheets which are compressed together. The burner head is on the sheets provided with matrix arrangement openings, where each opening acts as an individual small burner. The fuel is then directly mixed with combustion air to form a turbulent flow.
The burner described in the document US2016238241 (A1 ) is intended to combustion of lean fuel, it means low calorific fuel (for example synthetic fuel resulting from the fuelification of biomass). The construction of the burner utilizes two-stage air supply to achieve enlargement of the flame and a favourable distribution of temperature field. The burner is provided with central fuel supply, into which quality fuel through four openings can be mixed in order to increase calorific value or for support of the stability. With the expanding burner on the output, the combustion air is gradually blended into the flame.
In the document WO2014204333 (A1 ) a burner for flaring which is intended to thermal liquidation of waste fuels (e.g. methane with a high amount of carbon dioxide) without utilization of their energy, is described. The supply pipe is extended twice and on the output from the flare, a whirler is disposed, in order to set the fuel into motion and to achieve turbulent flow. At the end, in the center a cone is inserted, which directs the fuel towards the whirler. Behind the cone the fuel circulates toward the axis of the burner and due to this better mixing is achieved.
The device described in US2008299506 (A1 ) is a metallurgical burner primarily designed for burning of low calorific fuels. The burner has a central pipe for air supply, around which a fuel supply pipe is arranged. From outer direction secondary air is fed, so that all the fuel is burnt out. Into the fuel flow a whirler creating turbulant flow is placed. It is possible to modify the whirler according to used fuel, especially according to its calorific value.
The document WO2007012755 (A1 ) describes symmetric burner. Along the central axis individual flows of substances are gradually fed. Through the central tube fuel is supplied, from which a part is separated, and before burning is mixed with the air in a special chamber. A perforated whirler which has conical shape is placed at the end of the central tube, in order to put the fuel into direction. Premixed mixture flows from the chamber through nozzles directly to burning flame. Secondary air is fed from the outside end using whirling element is directed to achieve its rotation and mixing,
The document EP 1 436 546 discloses a burner which utilises the co-stream arrangement of the fuel and the air. The feature of the burner is a conical extension ending with circular array of nozzles which are directed to the central surface. Several types of assembly geometry with different mixing ratios and different influence on turbulent flow are proposed. The document US2013036741 (A1 ) discloses a burner according to the preamble of claim 1.
The aim of the invention is to present a burner for low calorific fuels which would ensure sufficient stability of the flame and which would also eliminate undesired critical conditions arising during its operation when disruption of the flame or fire penetration into the burner body occurrs.

Summary of the invention

The above mentioned deficiencies are eliminated by a burner according to claim 1.
In a preferred embodiment the openings on the whirler are arranged in three concentric circular rows.
In another preferred embodiment the fuel supply pipe is provided on its wall with a weld-on sleeve for connection of a pressure gauge or other measuring device.
In another preferred embodiment screws for aretation of an atomiser are located on a free end of the support tube.

Brief description of drawings

The invention will be further described using drawings, where Fig.1 is a longitudinal cross-section of a burner according to the invention with arrangement of individual parts, Fig 2 represents side view of the burner according to the invention in the direction of media flow, Fig. 3 represents a detail of the burner head in a perspective view and Fig. 4 represents a detail of the whirler of combustion air according to the invention in a perspective view.

Preferred embodiments of the invention

In Fig.1 a longitudinal section of a burner can be seen, which consists of a fuel supply pipe 8 provided with connecting flange 10, through which the fuel F enters in the direction of the arrow. Further is the fuel supply pipe 8 attached to a central burner tube 5 which has a front face 6 on the side of the supply pipe 8, which has an opening in the middle to allow insertion of a support tube 7. The whole burner is not displayed, only its built-in assembly. Around it there are situated other standard parts of the burner, which are known to skilled persons. To the central burner tube 5, at its output end is, via weld-on reduction 3, with its inner perimeter 15 a whirler 2 attached. The central burner tube 5 and the weld-on reduction 3, which terminates the central burner tube 5, form together with the support tube 7 an assembly, which defines the flow of combustion fuel F. Thus, the fuel F flows in the direction of the arrow into space, which has a shape of a hollow cylinder, formed by the central burner tube 5 and the support tube 7. This cylindrical space has such a specific length, so that the previous turbulent flow is maximally stabilised. The stabilisation contributes to the uniform distribution of the fuel inside the cylindrical space and the fuel is then uniformly burnt out. The support tube 7 can be used for addition of an atomiser (not shown) for liquid fuel. At the free end of the support tube 7, screws 12 for aretation of such atomiser are situated. At the opposite inner end of the support tube 7 a groove on the burner output is milled into which a burner head 4 is inserted and welded-on, through which the fuel is distributed into combustion space.
On the wall of the fuel supply pipe 8 a weld-on sleeve 11 is located for connection of pressure gauge or other measuring device, which can be seen in Fig. 2. On the connecting flange 10 a shutter is possible to insert in order to regulate pressure on the desired level.
In Fig.3 the burner head 4 in perspective view is shown. The fuel F flowing through the burner head 4 via nozzles 13, which are spaced in a circle at the inner perimeter forming the primary stage of the burner 1, is distributed uniformly along the central axis of the burner 1. This flow is important especially for the flame core stabilisation. In a stable situation in the flame core the flame envelope can be provided in a high rotational mode without disruption of the flame or unstable combustion. Burner head 4 is at its outer perimeter further provided with angled grooves 14, which change the momentum direction of flowing fuel and form the secondary stage of the burner 1. The fuel gets after passing through the angled grooves 14 into tangential rotation along the central axis of the burner 1. Rotational flow causes better mixing of the fuel with the combustion air A, which arrives to the end of central burner tube 5 and simultaneously the flame is partially attached to the burner head 4.
In Fig. 4 whirler 2 in perspective view is shown, its wall 16 has conical geometry extending outwardly from the burner, which has a positive effect on the flow. In the illustrated embodiment, there are openings 9 spaced in three concentric circular rows on the wall 16 of the whirler 2, through which the combustion air flows. It is evident, that the circle with openings may be only one or there can be another number of concentric circles. After passage through the individual openings 9 there is a change in the air flow, namely the strong turbulent flow is created, due to which is the fuel brought into a tangential rotation and mixed with the combustion air even better. The angle of inclination of the wall 16 of the whirler 2 has an important role, since due to this inclination it is possible to direct partially the airflow, to direct it towards the centre of the flame, and causing a complete combustion.
The burner head 4 has defined number of nozzles 13 arranged in a circle, whereas the number and size of nozzles 13 is determined based on the requirements for maximum performance, according to which the dimensions are determined so, that the requested amount of fuel flows through the primary stage created in this way. The number, width, and depth of angled grooves 14 are determined as to allow the remaining fuel to flow through these grooves at maximum power and the groove 14 inclination angle is determined relative to the plane of the burner head 4 in such a way, to ensure optimal turbulent flow in a tangential direction.

Industrial applicability.

The burner is intended for combustion of different types of low calorific fuels, also from other alternative devices, such as fuelifiers. The burner is applicable in plants, where waste fuels occurs, whose energy is let unused in burners with flaring and flue gases are emitted without use into the atmosphere. Another area where it is possible to use the burner, are biogas plants and heat sources connected thereto.

Claims

A burner (1) comprising an air supply pipe, a central burner tube (5), a fuel supply pipe (8) attached to the central burner tube (5), which is terminated by a front face (6) on the side of the fuel supply pipe (8), the burner (1) further comprising a support tube (7) fixed to said front face (6), and a burner head (4) mounted to said support tube (7) at the burner outlet, the burner head (4) being provided with nozzles (13) arranged in a circle near to the inner perimeter of the burner head (4) and forming the primary stage of the burner (1), the burner (1) further comprising a whirler (2) with its inner perimeter (15) arranged onto the central burner tube (5) at its outlet end, wherein the whirler's surface (16) has a conical shape extending outwardly and openings (9), arranged in a circle, are provided in the whirler's surface (16), characterized in that the burner head (4) is provided with angled grooves (14) on the outer perimeter, which form the secondary stage of the burner (1).
The burner according to claim 1, characterized in, that the openings (9) on the whirler (2) are arranged in three concentric circular rows.
The burner according to claim 1, characterized in, that the fuel supply pipe (8) is provided on its wall with a weld-on sleeve (11) for connection of a pressure gauge or other measuring device.
The burner according to claim 1 characterized in, that screws (12) for aretation of an atomiser are located on a free end of the support tube (7).