EP0952398B1 - Air supply method and device for burning particulate fuel - Google Patents

Abstract

The grid is formed of radial, hollow support arms (5) evenly spaced out over the grid and possessing blowing-holes pointed towards the fuel-supporting surface of the grid. An air source is pneumatically connected with the support arms, by means of a movable coupling arrangement (7,8). A post-combustion chamber (15) removes the flame gases, which are mixed with combustion air The solid fuel rests on a grid that has one surface area covered and one not covered by the fuel. Draught is introduced from underneath to the fuel in the combustion area. The flame gases emerging from the combustion zone are mixed with a top draught.

Description

The invention relates to a method and an apparatus to feed the wind for the combustion of lumpy 3. The method according to the preamble of claim 1 and 3, respectively and device of this type are from the essay "The development of the fuel cone for incineration of waste "by the inventor in the magazine "Fuel-Heat-Power", 19 (1967), No. 10, Pages 469 to 473 known.

This essay largely describes an incinerator for the automatic, universal and inexpensive waste incineration for municipalities and small and medium-sized industrial companies. she includes a firing cone that is about an inclined axis rotates, and an afterburner that is vertically above the opening the firing cone is arranged. The firing cone has a frustoconical shape Section, one located at the top larger diameter adjoining cylindrical section and a frustoconical one adjoining its free end Attachment whose small diameter is the free end of the Firing cone and its opening forms.

The frustoconical section consists of itself radial / axial extending, mutually spaced bars, the of several outer circumferential rings of different diameters are mutually supported. The frustoconical section of the fuel cone is blown from below by the downwind, which is the Gaps between the bars must pass to the firing material to reach, which is in the firing cone and due to this its orbital movement is circulated. The one above the The afterburner arranged in the opening of the firing cone attachment has one Afterburning chamber which is frusto-conical in the upper section narrowed and provided with a facility there the upper wind leads tangentially into the afterburning chamber so that a turbulent flow forms in it, which the Exhaust gases emerging from the firing cone and burns out.

For a specific firing cone design with a largest diameter of 1870 mm, a smallest diameter of 530 mm and a length of 460 mm of the frustoconical Section of the fuel cone, which according to the article cited for the incineration of 1.2 to 1.4 t / h municipal waste is determined - the at the time of publication of the essay in Germany had a calorific value of around 1.7 to 1.9 MWh / t a combustion output of 3.58 MW. For achieving bigger ones Achievements is because of the mechanical difficulties which result from an increase in the diameter of the firing cone, in the article a parallel connection of several systems of the described type recommended.

A firing cone firing system of this type is. also in US 3,599,581 A.

EP 0 754 907 A2 describes a method for influencing combustion known in a boiler with shaking grate, in which the Supply of primary air and / or fuel during and briefly after shaking the grate is reduced to one by the Shaking causes the burn rate to increase suddenly to avoid. A sudden drop in oxygen levels in the exhaust gas, which would otherwise occur because of the overall control of the Fuel supply too slow due to sudden changes in combustion conditions is avoided. In the The combustion system shown is the primary air from below blown against the rust and the gaps between the Grate bars pass to the firing material lying on the grate to get to the firing material while secondary air from above is blown, which is fed through nozzles, which at least one of the boiler walls arranged and directed against the grate are. The air volumes supplied depend on the result ongoing measurements of the boiler state variables, the excess air and heat absorption.

GB 1,141,562 A describes a domestic or industrial waste incinerator, consisting of a lying, rotating Grid drum made of axially extending and circular tubes trending rings is formed. Inside the drum are on small tubes attached to the tubes, which are radial into the drum protrude and are connected to the interior of the tube to which they are attached. The tubes are on one arranged helically and through plates connected to each other to form a screw conveyor for the firing material to form, which is attached to the drum by a front Pilot burner can be ignited. The tubes are on the face open to allow the entry of air through the Tubes can escape into the interior of the drum. The drum is surrounded by a double-walled jacket, the outer wall is open at the top. Below in the area of one under the drum Ash box are the jacket and its interior completely open.

In operation, air is introduced into the interior of the jacket from above, that flows through the coat and cools its walls, exits in the ash box at the bottom and from there the bottom Gaps between the tubes of the drum and as primary air in the combustion chamber enclosed by the drum arrives. An external suction fan in the combustion chamber Vacuum generated by this primary air and by the Tubes and secondary air supplied through the tubes, which at the same time cools the pipes, sucks them in.

All known incinerators of the aforementioned type is common that with them the underwind upwards towards the bottom the combustion grate is blown. The combustion grate has openings between the grate bars or tubes forming it, through which the underwind flows only to a small extent can, because the fuel lying on the combustion grate these openings partially blocked. The greater part of the downwind is therefore usually deflected sideways and downwards. This gives the fuel lying on the combustion grate not enough combustion air.

A significant disadvantage is also that in the above Way deflected underwind entrained gas and it contains dusty fuel that burns. The the resulting flame rays overheat and corrode the metallic material of the combustion grate, in particular its consisting of radial arms and circular rings Supporting structure. As the heating value of the fuel increases such overheating and corrosion are more serious.

For post-combustion of the ascending from the combustion grate Flame gases are known to supply this upper air. at known method, this was done in such a way that the flame gas flow the upper air sucked in by itself.

A disadvantage of such grate furnaces was that they were still incomplete Burning out of the fuel, resulting in a corresponding expressed a high proportion of CO in the combustion exhaust gases. Finally, they also contained a significant proportion entrained solid particles, especially fly ash, the separation by means of filter systems and the like is required made. Grate firing of the type described, especially with Cones, therefore, have not become established in practice can.

The invention has for its object a method in The preamble of claim 1 to specify the outlined type sufficient for the complete burnout of the fuel Air supply ensures overheating of the combustion grate avoids and without dust filtering of the combustion exhaust gases gets along. In addition, one is said to carry out the procedure suitable device can be specified.

This task is carried out with regard to the procedure by the Claim 1, with respect to the device by the in claim 2 specified features solved. Advantageous embodiments of the Invention are the subject of the dependent claims.

On the one hand, the invention achieves the desired success apparatus in that the support arms of the combustion grate are hollow are executed and flowed through by the downwind, making them be cooled. The downwind is forced on the top the combustion grate, i.e. directly on the fuel, so that the possibility of deflecting the underwind under the combustion grate is greatly reduced.

On the other hand, to achieve what is sought by the invention The aim of the post-combustion of the flame gases generated by that on the Burn out burning rust burning fuel, special attention given. According to the invention, the flame gases the upper air is supplied in the form of a high-speed flow, which surrounds the flame gases helically and itself propagates towards the combustion grate, the Increased diameter of this vortex. The headwind current describes, for example, the surface of a truncated cone, whose larger diameter faces the combustion grate.

The headwind is due to the smaller diameter of this truncated cone blown. This results in a negative pressure in the center, the sucks in the flame gases. Between the center of the towards this vacuum point flowing flame gas flow and this A zone is formed around the toroidal headwind current intense turbulence from where the flame gases with the headwind be mixed thoroughly. This zone of turbulence is outside of surrounded by a cold air flow of fresh head wind.

The head wind is at a speed of 40 to 100 m / s, preferably 60 to 80 m / s, which is thus so high, that the thereby acting on the particles in the flame gases Centrifugal force the particles into the cold air flow mentioned ejected, where they are cooled so far that they dry fail. In this way, not only the afterburner becomes escaping exhaust gas flow without the use of filters of particles exempt, but is also a slagging of the incinerator avoided.

In fact, there is such a large amount of hot dedusting Flame gases that the exhaust gases emerging from the afterburner - e.g. when blowing out into the open - clear and visual to the eye appear dust-free, what with the current state of hot dedusting technology has so far been considered impossible.

Experiments with waste wood in the form of wood chips as fuel have shown that the above results with a Air flow can be achieved in which about 30 to 40% of the complete combustion of the fuel required air quantity be fed as a downwind while the necessary Remaining portion of 70 to 60% of the air volume supplied as head wind becomes. It can be seen from this that the afterburning also under an essential one from the point of view of fuel efficiency Importance.

In terms of apparatus, the air duct described in the afterburner is achieved with the help of a truncated cone-shaped afterburner into which the upper wind at the smaller end facing away from the combustion grate The same diameter is blown in via an introducer which is the upper wind tangential to the wall of the afterburner leads into this, where it is inclined at an angle to the Axis of the afterburning chamber spreads out in this. At the introduction of the headwind into the afterburning chamber can also be from a flow direction obliquely from the outset by means of guide devices to the axis of the afterburning chamber.

Advantageously, only those support arms of the Combustion grate fed under air on which fuel lies, and preferably in accordance with the thickness of the fuel layer. The other brackets not covered by fuel get no air. You can also give them a small amount of air lead to the penetration of corrosive fuel gases and to prevent fuel or ash particles. A minor one Flow through the support arms not covered by fuel improved also cooling them.

According to a development of the invention, each hollow support arm at least one further opening on the side facing away from the fuel Side so that it has fallen through the combustion grate Ash or fine amounts of fuel in the combustion air ashes get to burn out completely. Through these openings can also penetrate into the pipes fuel or Ash particles are blown out.

The combustion grate is advantageously covered by a jacket hollow (burning) cone, which rotates around a executes an inclined axis. The afterburner is in this Most conveniently arranged coaxially to the axis of rotation of the cone. As a result, the flame gases emerging from the firing cone particularly well directed to the center of the afterburner, where a reduced compared to the pressure prevailing in the firing cone Pressure prevails, which is the conduction of those emerging from the firing cone Flame gases favored in the post-combustion and one uncontrolled escape of these flame gases to the outside or in a the incinerator from the fuel cone and afterburner enclosing housing prevented.

The coaxial arrangement of the afterburning chamber just above the firing cone also has the consequence that the heat radiation in the Afterburning chamber burning flame gases on the in the burning cone located fuel acts advantageously and the taking place there Smoldering and combustion process supported.

The lower diameter of the afterburning chamber should expediently be used slightly larger than the diameter of the top edge of the fuel cone. This will close the afterburner wall downward blown dust from the afterburner past the firing cone into the ash room below blown.

Fig. 1 eine teilweise geschnittene Seitenansicht eines kegelförmigen Brenners mit daran angesetztem Nachbrenner;

Fig. 2 einen Schnitt durch den konischen Teil des kegelförmigen Verbrennungsrostes des Brenners von Fig. 1, und

Fig. 3 einen vergrößerten Schnitt durch einen hohlen Tragarm des Verbrennungsrostes von Fig. 2.

The invention is explained in more detail below with reference to the embodiment shown in the drawings. It shows:

Figure 1 is a partially sectioned side view of a conical burner with an afterburner attached.

Fig. 2 shows a section through the conical part of the conical combustion grate of the burner of Fig. 1, and

3 shows an enlarged section through a hollow support arm of the combustion grate from FIG. 2.

Fig. 1 shows a complete incinerator consisting of a firing cone K rotating about an inclined axis O and one coaxial to the exit end of the firing cone K. subsequent afterburner N, which is enclosed by a housing G. are.

The fuel cone K has a frustoconical section 1, a cylindrical one adjoining it towards the open end Section 2 and an adjoining one section 3 narrowing in diameter. The combustion grate this fuel cone K consists of grate bars 4 made of heat-resistant cast and from hollow, radial support arms 5 and ring carriers (not shown), that connect the support arms 5 to each other. The firing cone K is smaller in diameter at the end of several hollow axially parallel legs 6 held with an air collection box 7 are connected, which has radial partitions, that each close one air collection chamber per support arm 5. The Air collection box 7 is firmly connected to a race 8, the of several stationary rollers (not shown) is stored. The race 8 has one opening per support arm 5 on.

Against the side of the race 8 facing away from the firing cone K. springs pressed a slide ring 9, the several connecting pieces carries that over hose lines 10 with a common air supply chamber 11 are connected. The number of connectors is preferably as large as the number of hollow support arms 5th

With the race 8, a shaft 12 is rigidly connected on the side of the race 8 facing away from the firing cone K of this extends away and in its free end area by means of a spherical roller bearing 13 is mounted. One also recognizes a drive motor 14 which has a spur gear Race 8 and thus the burning cone K in rotation on the axis O added.

At a distance above the end of the larger diameter of the firing cone K is the truncated cone-shaped afterburner N, the coaxial is arranged to the firing cone K. Afterburner N has one frustoconical afterburner 15, which is in the direction of the firing cone K extends and the lower edge 16 one has a larger diameter than the free edge of the narrowing Section 3 of the firing cone K. At the end of smaller diameter the afterburning chamber 15 closes an air collection space 17, arranged in the radially adjustable guide vanes 18 are. By adjusting the guide vanes 18, the effective one Opening cross section of the air plenum 17 changeable. The Air collecting space 17 has an opening (not shown), through the upper air tangentially into the air collecting space 17 can be blown. To the outside, that is to say that of the afterburner 15 opposite side connects to the air collection space 17 a narrowed collar 19 with an outlet cross section 20 leaves free.

The frustoconical wall 21 of the afterburning chamber 15 is from surrounded by a jacket 22 with the wall 21 one of coolant flowed through chamber and can be part of the housing G. Through this jacket 22 and the wall 21 extends Feed shaft 23, which is vertically above the opening of the firing cone K lies and the supply of fuel into the fuel cone K serves. Suitable closing flaps (not shown) arranged.

It can also be seen in FIG. 1 in the housing G below the firing cone K is a screw conveyor arrangement 24 which is responsible for the transport of ash accumulating in the housing G into an ash outlet 25 serves.

It should be noted that the axis of the afterburning chamber 15 against the Axis of the firing cone K can be inclined, especially after above, but the edge 16 of the afterburning chamber 15 should be parallel to the opposite edge of the firing cone K, to avoid the uncontrolled escape of flame gases or at least to decrease.

Fig. 2 shows a section through the conical section of the Brennkegels K. You can see the support arms 5, which are hollow are and are arranged at uniform angular intervals. The Reference numerals of the individual support arms 5 are here for later Provide an explanation of the operational sequence with suffixes a to 1. Between the support arms 5 there are the grate bars 4 made of heat-resistant Greetings, which are essentially T-shaped in cross-section, the wide leg of the T being the bearing surface for the fuel B forms while the protruding rib not only stiffening, but also dissipating heat. The Grate bars 4 have a mutual distance, which is chosen is that ash, but not too large pieces of fuel through the the space formed by the distance can fall through. The The distance is expediently of the order of 4 mm.

In Fig. 3 one of the support arms 5 is enlarged in cross section shown. It can be seen that the same from the hollow interior openings 26 inclined at the top in the from the firing cone K lead enclosed combustion chamber. Another opening 27 can open be formed on the opposite side. Their purpose is still explained.

In operation, the firing cone K rotates about its axis O. This Orbital movement is shown in Fig. 2 with the arrow. The one in Fuel cone K located fuel B is thereby from the fuel cone entrained so that there is an inclined slope results, as Fig. 2 indicates. This embankment is in circulation around the Brennkegels K ever steeper and then collapses, resulting in The consequence is that the fuel B circulates continuously in the fuel cone becomes.

The fuel B is ignited at the beginning of the combustion process by an ignition flame which is supplied by a lance (not shown). If the fuel B burns sufficiently, the combustion flame can be dispensed with. With constant circulation due to the movement of the fuel cone, the fuel B burns in the fuel cone K. Fuel can be added through the shaft 23 at the appropriate time. The metering of the fuel per unit of time is expediently carried out by monitoring the O ₂ content contained in the combustion exhaust gases.

The flame gases emanating from the firing cone K are replaced by the the negative pressure caused by the upstream flow into the afterburning chamber 15 sucked in, being intense with that there swirling headwind. Flammable components the flame gases are completely burned out. Ash particles are thrown out in the direction of the wall 21 and fall down at the edge 16 into the housing G.

For operation it is useful if only those in the combustion zone support arms 5 are supplied with downwind.

These are the support arms 5k, 5l and 5a to 5d in Fig. 2. This can be controlled in such a way that only those connecting pieces with Air supply can be supplied, which are arranged at the positions are who are currently taking the aforementioned arms. Upon further rotation of the firing cone in Fig. 2 counterclockwise the support arm 5j then enters the combustion zone a while the support arm 5d leaves it. Then the later arrives Support arm 5i in the combustion zone, while the support arm 5c them leaves, etc. The rest, not in the combustion zone located support arms, that are shown in Fig. 2 Situation the support arms 5d to 5h, do not become weak or only supplied with air, for example via appropriate throttling points. On the one hand, this weak supply serves one certain cooling, but mainly the prevention of particles penetrate through openings 26.

Through the design and arrangement of the firing cone shown K shows that the layer thickness of the fuel over the Combustion grate is different. For example, it is on Transition between the conical section 1 and the cylindrical Section 2 largest and near the center of the tapered Section 1, i.e. smallest at its smallest diameter. To take this into account during the combustion process, you can the openings 26, which are arranged along each support arm 5, in Diameter and / or longitudinal distribution can be designed such that the sum of the opening cross sections per unit length each Support arm approximately proportional to the layer thickness of the the respective length unit of the support arm Amount of fuel. Which is in the different Height of the support arms during the rotation of the firing cone resulting different coverage of the support arms can by appropriately throttling the downwind supply to the something higher connecting pieces are taken into account.

The openings 26 and 27 in the support arms 5 are preferably so dimensioned that at full load the speed of the exiting from them Underwind between 20 and 60 m / s, preferably at 40 m / s lies.

The latter openings 27 in the support arms 5 serve to on the one hand blow out particles that have penetrated into the support arms 5, and on the other hand, which in the ash receiving room in Housing G particles that may have fallen are not completely burned out, to supply them with combustion air. Therefore, the openings 27 are on the outside of the firing cone K. formed in the support arms 5, expediently on the point at the lowest surface line of the Firing cone is lowest. In the example shown would be that in the area of the transition between the tapered section 1 and the cylindrical section 2 of the firing cone K.

Claims (8)

1. A method of supplying a blast for the combustion of a particulate fuel resting on a surface of a rotational-symmetrical combustion grate comprising a surface portion located in a combustion zone and covered by the fuel and a surface portion not covered by the fuel, said grate performing a rotary movement around its axis, causing a rolling movement of the fuel across the entire surface of the combustion grate, wherein a blast is supplied to the fuel in the combustion zone from below (under blast), and flame gases emerging from the combustion zone are mixed at a distance to the combustion zone with an overfire air, which is routed in a rotating flow in a helically extending path having an expaning diameter and enclosing the flame gases emerging from the combustion zone, towards the combustion zone,
   characterized in that
   the under blast is blown above the combustion grate below the fuel, and
   the overfire air is supplied in a path surrounding the rotational axis of the combustion grate at a speed of 40 to 100 m/s,
   wherein for the complete combustion of waste wood, in particular wood chips, as the fuel to be burnt, an air quantity proportion supplied along with the under blast is approximately 30 to 40 % and an air quantity proportion supplied with the overfire air is approximately 70 to 60%.
2. The method as claimed in claim 1, characterized in that the under blast is supplied to the fuel resting on the combustion grate at a speed of 20 to 60 m/s.
3. An apparatus for carrying out the method as set forth in one of claims 1 and 2, comprising
   a movable, rotational-symmetrical combustion grate (K) having partially radially extending arms (4,5), a combustion zone covering a partial region of the combustion grate (K), and a drive means (14) which sets the combustion grate (K) into a rotary movement around its axis (O), said rotary movement successively routing all partial regions of the combustion grate (K) through the combustion zone,
   an air source which supplies an under blast to the combustion zone,
   and an afterburner chamber (N) arranged above the combustion grate (K) and receiving the flame gases rising from the combustion grate (K) and mixing said flame gases with combustion air freshly supplied as overfire air and burning them out,
   characterized in that
   some of the arms of the combustion grate are hollow supporting arms (5) regularly distributed over the combustion grate (K) and each comprising a plurality of blow openings (26) disposed at the surface of the combustion grate (K) bearing the fuel and directed towards said fuel,
   a movable coupling means (7,8) is provided through which the air source is pneumatically connected at least to the supporting arms located in the combustion zone for supplying under blast, and
   the afterburner chamber (15) is formed rotational-symmetrical and is arranged coaxial with respect to the combustion grate (K).
4. The apparatus as set forth in claim 3, in which the hollow supporting arms (5) not located in the combustion zone are pneumatically connected to the air source via a throttling means.
5. The apparatus as set forth in one of claims 3 and 4, in which the blow openings (26) directed against the fuel are distributed at the hollow supporting arms (5) and are dimensioned in a manner that the sum of the opening cross sections per length unit of each supporting arm (5) is approximately proportional to the nominal layer thickness of the fuel quantity resting on the respective length section of the supporting arm (5).
6. The apparatus as set forth in one of claims 3 to 5, in which the combustion grate is a shell of a truncated cone (K) which comprises an axis of rotation (O) extending obliquely with respect to a horizontal, and in which the supporting arms (5) extend radially, characterized in that at least one blow opening (27) directed away from the fuel supporting surface of the combustion grate is formed at a position of each supporting arm (5) that is located the deepest when the shell line, in which the supporting arm is located, takes a lowermost position during the rotation of the truncated cone (K).
7. The apparatus as set forth in claim 6, characterized in that a rotationally-symmetrically formed afterburner chamber (N) confronts the opening of the cone (K) at the base thereof as an afterburner chamber (15), which has an inlet opening (16) facing the cone (K) which has a diameter larger than the opening of the cone (K), and which comprises means (17,18) for tangentially supplying an overfire air disposed in the area of the outlet end distal to the cone (K), and wherein a collar (19) is connected to this means (17,18) in the direction towards the outlet end, said collar encompassing an opening that has a smaller diameter than the smallest cross section of the afterburner chamber (15).
8. The apparatus as set forth in claim 7, characterized in that said means (17,18) for tangentially supplying the overfire air has a variable opening cross section.

Images