WO1999026022A1

WO1999026022A1 - Combustion furnace particularly for wastes

Info

Publication number: WO1999026022A1
Application number: PCT/IT1998/000311
Authority: WO
Inventors: Andrea Giust; Fabrizio Giust
Original assignee: G.E.M. S.R.L.
Priority date: 1997-11-13
Filing date: 1998-11-09
Publication date: 1999-05-27
Also published as: ATE230091T1; ITUD970212A1; EP1030999A1; ES2190118T3; IT1296716B1; DE69810348T2; DE69810348D1; EP1030999B1; AU1258099A

Abstract

A combustion furnace particularly for wastes, of the type provided with a structure for the advancement of waste material (1-12) in the combustion chamber (2), having a floor with stair-down sectors (21, 22, 23, 24, 25) overlapped by retractable advancement elements (32, 33, 34) with a to-and-fro reciprocating movement (3) having a pusher function for advancing the combustion material towards a downstream area for the ashes discharge (25), characterised in that, just at the material entry and under it, in the respective combustion chamber, an air-jet area (51) able to separate the dust to be burnt with respect to the biggest sized dust is provided, throwing it in the air of the combustion chamber.

Description

DESCRIPTION COMBUSTION FURNACE PARTICULARLY FOR WASTES Technical Field The present invention has for object a waste combustion furnace, also for the wood manufacturing and plastic material scrapes. Background Art In prior art the waste combustion furnaces are already known. Clear reference to the patents IT-83433A/90 and IT-91A000161 is hereby made. Both these patents disclose a waste combustion furnace, characterised in the presence of an entry step structure with reciprocating pusher means for the material advancement during the combustion, towards a discharge area. These solutions even if advantageous allow to easily burn also wet and of the most different type waste materials. For what concerns instead the wood industries waste material combustion, the problem is more difficult, considering that the wood manufacturing waste material contains substances with a high combustion level in a dry state, such as for instance the materials coming from the chip and MD = "Medium Density" panels manufacturing. These are therefore materials which contain both wood and resins and highly combustible plastic and with a high calorific power materials. Furthermore, the material has a rather large size, or is in dust, in chips and in small pieces and in more or less large pieces. The consequence is that such a type of material is very difficult to be burnt homogeneously and with a low level of unburnt gases, which notoriously pollute the environment, because of the presence of dusts which mainly derive from the sawing. Thus the material contains saw-dust, chips and small pieces of wood, resinous substances and plastic materials. The plastic materials derive from the laminated panels coating such as for instance the ones used for the furniture manufacturing. The resinous substances derive from the glues and from the binding plastic materials forming chips and thickened products such as the MD. These resins and plastic materials have the most different origins, such as for instance phenolic resins, epoxidic resins, ureic resins and melamine resins . All these resins and plastic materials together with dry wood, are more or less combustible and with a high calorific power, but are also very polluting because of the unburnt smokes high rate emission (particularly for the resins and plastic materials). This caused the need of being able to control the combustion temperature level and of reducing at the minimum the unburnt smokes and the still unburnt smokes, also by means of a post-combustion action. The combustion temperature may considerably increase, and it is difficult to be controlled, and it is dangerous for the combustion control. The furnace life is limited, the maintenance is frequent. In particular, the high temperature presence may especially compromise the system of pushers which move in a reciprocating way for the material advancement, because of the high temperature which makes the metal material little resistant, which when in presence of obstacles may also be deformed. For such reason some systems for decreasing or at least for limiting the combustion temperature by using heat exchange known means were studied, but this brings the drawback of worsening the combustion performance, so the solution does not find an easy way out, either the temperature decreases and a furnace structures long life is obtained but there is a polluting combustion, or the combustion temperature increases with a good yield, but in this case the furnace life is considerably reduced. The presently existing solutions are not yet able to supply a suitable performance to the plant for the treatment of these materials and even to make it suitable to the combustion both of damp or wet materials with a low calorific power and or alternatively of the highly combustible ones with a high calorific power where a suitable combustion control or restraint or at least a suitable heat regeneration is needed. Purpose of the present invention Purpose of the present invention is that of obviating the above mentioned drawbacks and allowing to realise a universal furnace able to treat the most different materials: - also the ones containing powdery material, and - also the ones with a high calorific power and thus of being able to provide the combustion chamber with very high temperatures, but without endangering the same furnace structure (e.g. also combustibles deriving from the urban solid wastes). Essence of the invention The problem is solved as claimed by means of a combustion furnace particularly for wastes, of the type provided with a structure for the material advancement in the combustion chamber, having a floor with sloping sectors overlapped by retractable advancement elements with a to- and-fro reciprocating movement having a pusher function for advancing the combustion material towards a downstream area for the ashes discharge, characterised in that, just upstream of the material entry in the respective combustion chamber, and under the material entry mouth, an air-jet area substantially towards the combustion chamber centre and having such a range to separate by means of said air-jet the dust with respect to the biggest size which proceeds in its advancement and combustion on the furnace floor. Advantages of the new solution In this way there is the advantage of having a considerable combustion improvement with a higher yield and performance and a plant universality of use, reaching rather high temperatures and allowing a complete combustion of the material with a smaller amount of polluting residuals. In fact with this type of plant it will be possible to burn both non-powdery heterogeneous materials and powdery materials (in this latter case by activating said air-jet). Preferential variations Advantageously for improving the device efficacy a transversal piping in said step structure and in the side walls for the temperature decrease in these areas and at the same time for obtaining a heat regeneration by heat exchange fluid (preferably hot or overheated water) is provided. As much advantageously two ventilation systems will be obtained, the first one as said for the separation and throwing of said dusts and the second one for a ventilation from the whole furnace walls, both from underneath, and by side and above the entry mouth of the materials to be burnt. Thus, controlling and decreasing the excessive temperature in the furnace structural and functional parts is possible, in addition to supplying a suitable contribution of comburant and oxidising air. Substantially this furnace is suitable to treat different types of wastes and therefore : high calorific power and powdery wastes deriving from the wood manufacturing and with the function of obtaining a combustion high yield which is fundamental in the adiabatic and non-adiabatic chambers, an d high humidity degree wastes (30-35%) such as biological mud, barks, but also wastes. By this solution the furnace is able also to carry out the combustion of high calorific power dry residuals such as plastic laminates, varnishing smudges, melamine, phenolic papers and other industrial wastes in general . Description of at least one form of invention embodiment. These and other advantages will appear from the following description of a preferential embodiment solution, with the aid of the enclosed drawings, whose execution details are not to be considered as limitative but are only given as examples. Figure 1 is a longitudinal section schematic view of the furnace on the vertical plane. Figure 2 is a front schematic view of the combustion chamber, with a particular view of the heat regeneration system with fluid side piping. Figure 2A is a partial view of the heat exchange side piping with the thermal regeneration fluid (advantageously water). figures 3,4,5 show the side, plan, and front view of the pusher combs or teeth or grate pusher elements, which move in a reciprocating motion for making the material advance in the various steps and which make up the combustion grate plane. Figures 6,7,8,9 show in view: 6 from the bottom, 7 in longitudinal section and 8 and 9 transversal section, of a comb tooth of the previous figures. From the figures it may be understood that: The furnace function is that of obtaining the thermodistruction of the material which is made advance at first on the tilted plane 21 and then on the steps 22, 23, 24 by movable sectors 32, 33, 34 which ensure the wastes advancement during the combustion process. These are therefore reciprocating movable grate sectors "reciprocating grate" . The furnace is made up of a fixed part in refractory casting and a movable part in refractory steel (movable step structure 3), is particularly suitable to the treating of manufacturing residuals and high calorific power wastes (p.c.i. kcal/kg. 4000-8000). This furnace is characterised in: - wastes feeding (1) with checking door (11) and following advancement inside of the combustion chamber (2) by means of an Archimedean screw or pusher with oleodynamical functioning (12) which push the wastes, at first on the tilted plane (21). - said tilted plane (21) is fixed and it has an inclination of about 30-35% such to allow en easy entry and downflow of the wastes in the combustion chamber; the other steps (22, 23, 24) are also fixed in refractory or grate metal material with water cooled piping, and are horizontally placed on line and the wastes movement from one step to the other is ensured by the mechanical action of the cast or refractory steel pushers (32, 33, 34) on a bearing frame (31), mounted on trolley wheels moved by an oleodynamical cylinder with gear motor (3); - the series of fixed steps (22,23,24) has at least the corner of each step made up of a rectangular section pipe, fixed on the heads of the steps (62), in which the hot water or other secondary fluid such as overheated water passes. The fluid passage in the pipes allows a cooling of the fixed steps head when high calorific power wastes are burnt, avoiding the fast wear and the subsequent continuous maintenance. The secondary fluid, contained in the pipes placed on the grate fixed steps, is conveyed through the suitable pipe bundle along the refractory side walls (61) for allowing a high and better energy regeneration respect to traditional solutions, and subsequently conveyed to the overhanging side collectors (62). Such a solution ensures a better efficiency of the total thermal regeneration because the recovered heat may be conveyed in the heat regenerator (8-81) primary circuit or in a separate circuit. As claimed, the primary and secondary combustion air is distributed in a separate and autonomously controlled way: - by a first plant (4) both under the grate, thus under the steps (4-41), and on the grate side, that is from the furnace side walls (43), and on the furnace head above the entry mouth (42); - by a second plant (5) under the entry mouth (5-51) for separating and throwing in the air the advancing material dust so that it will burn better, at the same time easing the combustion of the underlying heavier size now freed from the dust presence which would otherwise choke the combustion. The two air plants are activated by means of respective centrifugal fans (6, 5) which supply the amount of air necessary for the combustion process whose delivery is controlled by an inverter. The inventive essence thus derives from that together with the previous characteristics and what already said, on the furnace head next to and underneath the feeding Archimedean screw (12), a series of air nozzles (51) are positioned, with the function of making the waste inserted as dust advance (e.g. smoothing dust, polyester dust) thus easing the combustion of this material in suspension and at the same time allowing the combustion on the grate of the waste having a rougher and heavier size. The thus designed furnace allows a first drying of the wastes in the upper steps by means of the surrounding hot smokes and the complete combustion of the wastes along the whole grate also eased by the wastes mixing movement carried out by the toothed pushers (30) (32,33,34) which move in a reciprocating way above said steps (22,23,24). The movement speed and frequency of the pushers are determined each time according to the physical-chemical characteristics of the treated wastes and residuals, in order to ensure at the advancement end and before the discharge area, provided with a manhole 25, by an opening control (251), the complete combustion of the wastes into ash. The ashes fall, at the timed opening of the discharge refractory door (25) with oleodynamical drive (251), into an underlying collection system, which may be made up of a palletizable trolley placed on rail (7) or of a "redler" belt for conveying the ashes outside of the incinerator room. In an alternative variation the manholes are two and a discharge intermediate pre-chamber is formed, so that for the ash discharge: - the first one opens discharging the ashes in an intermediate underlying chamber (25'); - subsequently, the first one closes and the second one of the intermediate underlying chamber opens, discharging the ashes into said underlying trolley. Thus the advantage of preventing the air passage into the combustion chamber is obtained, a fact which may endanger the normal optimal plant functioning . The operational advantages which derive from adopting the piped heat exchange structure in the steps and side walls (6,61,62) are: - combustion temperature reduction avoiding formation of ash melting on grate and along the refractory side walls. - smoke delivery reduction because of the air excess decrease in the combustion chamber. - reduction of the maintenance interventions on the corners and on the steps and on the side walls. - optimisation of energy regeneration by exploiting the direct radiancy principle, in addition to the convection one, during the thermal exchange process. - the pipe bundle on the grate allows to keep the same grate cooled, reducing the excessive air contribution. - it is particularly useful also for the specific treatment of high calorific power wastes. Advantageously the access to said post-combustion or post-treatment chamber (8) is obtained by means of an upper opening opposed to a baffle plate projecting into the combustion chamber (9). Thus a plant yield increase is obtained. The post-combustion furnace (8) may alternatively be used also for a complete oxidising in a single chamber of a large surface and/or volume also having a decantation function and comprising single-block heat exchange piping.

Claims

Claims 1. Combustion furnace particularly for wastes, of the type provided with a structure for the advancement of waste material (1-12) in the combustion chamber (2), having a floor with stair-down sectors (21 , 22, 23, 24, 25) overlapped by retractable advancement elements (32, 33, 34) with a to-and- fro reciprocating movement (3) having a pusher function for advancing the combustion material towards a downstream area for the ashes discharge (25), characterised in that, just at the material entry and under it, in the respective combustion chamber, an air-jet area (51 ) able to separate the dust to be burnt with respect to the biggest sized dust is provided, throwing it in the air of the combustion chamber.

2. A furnace, according to the previous claim, characterised in that said separation and dust throwing air-jet is also provided during the advancement (41) from underneath the material advancement grate or steps (21,22,23,24).

3. A furnace, according to the previous claims, characterised in that a fluid piping system for the cooling of said floor with sloping down sectors (61 ) and on the side (6) with a heat regeneration conveyance (62) is provided.

4. A furnace, according to the previous claims, characterised in that second means for the independent forced conveyance of the air (4) which is let inside the combustion chamber (2) are provided: - under said floor with sloping down sectors (41); - above said material entry (42), and -laterally to the respective side walls (43).

5. A furnace, according to the previous claims, characterised in that downstream of said combustion chamber (2) there is a post-treatment chamber having the function of smoke (8) post-combustion and/or decantation and heat exchange with heat regeneration piping bundle (81).

6. A furnace, according to the previous claims, characterised in that the access to said post-combustion chamber (8) is obtained by an upper opening opposed to a baffle plate projecting into the combustion chamber (9).