DE4225033A1 - Heat treatment system for powdered or granular waste material - uses vertical induction oven for radiation heating of introduced material in free flow - Google Patents

Abstract

The system uses a vertical induction oven with a dia./height ratio of between 1:5 and 1:30 through which the powdered or granular material passes in free fall for radiation heating. The material is cooled after leaving the oven. Pref. the treatment temp. lies between 200 and 3000 deg.C, the material pref. being pre-heated e.g. to a temp. of about 900 deg.C before being fed into the induction oven. The free space between the outer mantle (7) and the inner lining (2) of the oven can be rinsed with an inert gas stream, to prevent O2 penetration.

Description

Today's attack of slightly to moderately contaminated sludges or Dusts which have to be considered as special waste are strong too taking and causing high cost. The deposit of these substances is often impossible due to the lack of suitable landfills without this waste substances rendered inert d. H. in a condition that is harmless to the environment to be brought. Fortunately, the time of waste tourism is also good finally over. It is one of the priority tasks of our time treat the waste near its origin in such a way that a further environmental pollution (be it through the substances themselves, or just by transport kilometers) can be avoided. Treated like this, well harmless waste, should then be disposed of regionally become, or can even be used for a useful purpose. However, the psychological barriers are in a useful application to consider. It will hardly be possible to use such substances e.g. B. in residential construction use, even if this is absolutely technically and health-wise would be safe.

There are already processes for the disposal of waste materials (primarily Heavy metals) in the form that these are built into a ceramic structure or be glazed. The known methods work so that the to inert substances of a longer heat treatment, primarily in Rotary kiln, are exposed and thereby the known disadvantages of all have ceramics or foam glasses treated in such an oven (Open porosity, damaged surfaces, water absorption, heat transfer by convection and thereby large amounts of polluted air and very complex flue gas cleaning, etc.).  

EP 134 584 describes a method and apparatus which are used for thermal treatment of granules from possibly contaminated sludges is not. However, this method is based on countercurrent heating with hot gas, which on the one hand swirls and thus increases Risk of sticking of the melted particles and on the other hand to the Pro production of larger quantities of possibly contaminated exhaust gases.

It has now been found that by using induction heat this after parts can be avoided and a targeted thermal treatment of Powder and granules become possible. The object of the invention is therefore a Process for the thermal treatment of powder and granules, thereby characterized in that the powder or granules in a vertical Induction furnace with a diameter / height ratio of 1: 5 to 1: 30 is heated in free fall by radiant heat and after leaving the oven is cooled again. Another object of the invention is the corresponding induction furnace, consisting of an outer furnace jacket, which is provided with induction coils, a furnace inner tube ceramic or metallic material, graphite susceptors between Outer jacket and inner tube as well as a device for loading with the powder or granules.

The function of this furnace can be explained as follows:

The material to be treated, in the form of powder or granules, with a Grain size smaller than 10 mm is added to the furnace, this falls through in the quasi free fall. The following measure can control the fall time were influenced: Ascending or descending air flow; Furnace length; Initial speed of the feed material; Granule shape and size (air resistance). The furnace is closed at the top, apart from the material task and the air supply / discharge. The oven is open at the bottom.

The graphite susceptor is inductively coupled via the induction coils pelt and heated. This in turn gives the heat as radiant heat to the inner tube of the furnace and makes it shine. The radiation heat from the inner tube of the furnace will fall through if it falls through the furnace Treated goods transferred and warmed this. To burn the To avoid graphite susceptor, the space between the furnace  The jacket and inner tube of the furnace are flushed with an inert gas and the access from Prevents oxygen.

For an explanation, reference is made to FIG. 1, in which an induction furnace according to the invention is shown schematically. The furnace usable space ( 1 ) is limited by the furnace inner tube ( 2 ) and the loading device ( 3 ). The graphite susceptors ( 4 ) are separated from the furnace inner tube and the insulation ( 6 ) by inert gas layers ( 5 ). The induction coils ( 8 ) are attached outside the furnace jacket ( 7 ).

The oven described in this way is in a temperature range of approx. 700 ° C up to approx. 1700 ° C, but can be used with suitable materials for the Furnace insulation and the furnace inner pipe even at temperatures up to 2000 ° C be used. Graphite can be used as a susceptor up to 3000 ° C.

Due to the described construction and dimensioning of the furnace, the Induction heating can be operated at mains frequency (50/60 Hz). Depending on Number of heating circuits and to be controlled with different temperatures The control loops of the induction furnace are operated with three-phase current or with Advantage powered by alternating current. With three-phase supply the ver different induction coils there can be mutual at the coil boundaries strong influences come up that lead to a very irregular field distribution over the entire furnace height. To an uneven network The use of alternating current is an advantage in avoiding exposure to AC from the three-phase network with a mechanical or electronic converter group generated.

The atmosphere in the inner tube of the furnace (heat treatment room) may vary Inner furnace tube and according to the material to be treated, oxidizing to reduced be driven adorningly. Through a certain air exchange (process gas) in the furnace inner tube the furnace atmosphere becomes clear, d. H. kept clear (important for radiant heat transfer).

The advantage of the furnace is the introduction of large amounts of heat in one continuous process to a larger quantity of process material without a large amount of air is contaminated and needs to be cleaned as it is in the case of heat transfer by convection. Likewise, the heat Treatment process take place in a controlled process gas atmosphere.  

In addition, the heat treatment time can be kept short and by the fall time done in a controlled period of time, what certain processes (Fine pores, crystal lattice conversions etc.) of great importance is.

In a particular embodiment of the furnace according to the invention this with a special dosing device for the Introducing powder and granules is particularly suitable. This one Direction is structured as follows:

• - furnace head neck, d. H. Opening in the furnace head of the furnace inner lining in Ceramic material
• - Air duct in ceramic material
• - Material feed pipe in ceramic material
• - Ceramic tappet.

The furnace head neck is the built-in upper opening of the furnace interior lining made of the same material as the rest of the inside Furnace lining. The air duct is inserted into the furnace head neck. In this in turn the material feed pipe. Inner finish of the mate Rial feed and at the same time the furnace end is the furnace pestle. Air pipe, Material feed pipe and furnace pestle are all made of ceramic material provides, tailored to the purpose.

In Fig. 2, a typical embodiment of such a Dosierein direction is shown. The furnace usable space ( 1 ) is closed at the top by the furnace head neck ( 9 ), in which the material is supplied via line ( 10 ) and is regulated by the slide ( 11 ). The material feed pipe ( 12 ) is limited on the one hand by cooling air in the air guide pipe ( 14 ) supplied via line ( 13 ) and on the other hand by the furnace tappet ( 15 ), which is also cooled with a cooling air pipe ( 16 ).

The special requirements and tasks of furnace head dosing are like solved as follows:

Closure against rising gases:

The material feed is possible by opening the pestle. This requires an overlying rel. dense dosing element like a cellular wheel  or double flaps. Without the material supply, the furnace tappet moves down driven and closes the material feed. The air or process gas supply must either be constant or must be completed, so that no gases can rise.

Feeding and dosing of powders and granules:

As described above, powder and granules can be fed through a metering device (cell lenrad, flaps, etc.) are fed when the furnace lifter is raised. The amount and type of material to be fed determines the size and Formation of air duct, material feed pipe and furnace tappet.

Prevention of sticking:

Through a continuous supply of air through the annular gap between the air duct and the material feed pipe, the entire furnace head metering is cooled down so far, that the adhesive temperature of the load is not reached. The The amount of air required depends on the furnace temperature and thus after the radiant heat absorbed by the furnace head dosing. By the outer ribbing of the material feed pipe is an improved one Heat dissipation possible. By additional air or process gas supply via the central hole of the tappet is additionally under this cooling supports.

Fresh air / process gas supply:

The cooling air described above also makes fresh air Furnace fed. The amount can be varied, but may be the required Do not fall below the cooling quantity. Air can also come through the furnace pestle or process gas (oxygen / nitrogen or the like) are supplied.

Blowing out the dosage:

If the dosage is glued by material, a targeted Blast of compressed air through the central hole in the furnace tappet Material to be blown out. The furnace head metering is "blown".

Manufacturing the dosage in ceramic material:

Due to the high temperature range of the furnace head dosing, its on set temperature is mostly above the melting temperature of steel,  it is necessary to manufacture the dosage in ceramic materials. This is possible due to the selected construction and the ceramic specific properties (high pressure, low tension and bending tension strength) are taken into account. Ver come as ceramic materials different in question, e.g. B. silicon carbide and the like.

Quick interchangeability:

The slide ( 11 ) can be closed by pulling the furnace tappet all the way up and air can be blown into the dosing chamber via a valve. So it is possible to change the furnace tappet at the operating temperature of the furnace. The air guide tube and the material feed tube can also be changed if little effort is required, but the furnace temperature must be reduced. An adjustment and a change of the furnace head dosing as a result of different feed material or feed quantity is thus given in a simple manner.

Material distribution in the oven:

Since the heat in the furnace is supplied by radiation from the inner wall of the furnace, it is important that the added material to be treated does not covers itself optically and thus hinders the flow of heat. For this Basically, the distribution of the material after the furnace head is very large Importance. A compact stream of material would only appear after a fall height of a few meters so that the heat supply is unimpeded is possible. Due to the annular material feed of the furnace head dosing there is in principle an improved material release. Depending on that too The fresh air supply and the ram air can achieve this effect Supply or process gas supply, the distribution of the material flow strong be influenced and optimized.

If desired, the furnace according to the invention can also be equipped with a preheater can be combined with a heater that heats up the powder or granulate to a desired temperature and optimal treatment in the actual oven allowed. The preheater becomes multi-stage (2-6 stages) designed to achieve controlled heating and is based on following principle:

Hot air flows through the preheater from bottom to top. in the  Pre-heaters are fitted with air-permeable floors, similar to sieve plates have a certain flow cross-section. The flow cross section is designed so that the air speed in the sieve opening is higher is than the drag speed of the granules. This will make it Granules kept in suspension (floating bed). Through the several Levels arranged one above the other is the controlled pass of the granules, d. H. it is not possible for unheated granu lat leaves the heater, as is a control and monitoring of the Heater better possible.

The one for overcoming the pressure drops in the various heaters air pressure of the hot air, is mainly determined by Fans or blowers that are switched before or after the preheater are generated. Because fans in a hot air flow of 500-900 ° C are technically very difficult, mainly with suction fans the output side of the heater worked there because of the heat of the air Electricity is largely processed. Advantage is in front of the fan a dust collector to arrange a high wear of the ventila prevent tors.

The granulate flows from top to bottom. The Be The heater is sent via a loading device such as cells wheel lock, double flaps or the like. The remaining moisture of the granules expelled and a first heating up a low temperature level. The control of the middle ver time of the granules on the different heating levels takes place over the height of the individual fluid bed fillings, d. H. at higher fill levels (Fluid bed thickness) the mean residence time increases. The fluid bed height is controlled by flaps. There are primarily two flap systems The following can be considered: First, self-regulating heavyweight flaps Counterweight opened by the weight of the fluid bed. The second flap system in question are externally operated flaps that can be opened and closed via a control system. As a control parameter a level measurement of the respective fluid bed height can be used or it can be the pressure difference of the respective fluid bed stage that is roughly proportional to the level of the fluid bed, as a rule  serve parameters. After passing through the granules to be treated this in turn via a high-temperature discharge device such as a cellular wheel / Flaps etc. carried out.

The sketch shown in Fig. 3 illustrates this description. While the exhaust air can escape via line ( 17 ), the material is admitted via line ( 18 ). The material is heated in a first floating bed ( 19 ) on a sieve tray ( 20 ) and falls on the first flap ( 21 ), is further heated up in a second floating bed ( 19 ) and falls on the second flap ( 21 ) before it in the third floating bed ( 19 ) is brought to the desired temperature with fresh air supplied via line ( 22 ). The material outlet takes place via line ( 23 ) and a last flap ( 21 ).

The heater so described gives a very efficient and the same moderate heating of the granules to be treated and can depend on the because of the exact requirements. An additional benefit is that dust that is in the granules or fresh through Abrasion forms, each with the air stream is discharged directly and so in principle a wind sifting takes place.

The method according to the invention can be in various embodiments be performed. The preferred embodiment is manufacturing of light sand based on the method of EP 134 584, whereby mineral raw materials granulated together with a blowing agent, dried and ceramized in a vertical oven. If desired, waste materials can also be added to the mineral raw materials are that can be safely disposed of in this way, ent neither without (to get the most compact powder for landfill or with blowing agent (for the production of light sand, which is used as concrete aggregate, road / rail substructure, etc. can be used) is proceeded.

By using blowing agents, the end product can be in bulk and bulk weight can be set to the desired weight properties. This is particularly important if the final granules are re-used  valuation with market-conforming prices. Comes one Recycling is out of the question, so there is no use of blowing agents Sense, since the end product should be as compact as possible around landfill save space.

In the preparation process of the raw granulate, it is possible to mix in special reaction auxiliaries that not only enable physical inertization in the ceramic final granulate, but also chemical inertization in addition to the physical one. Depending on the waste material and base material, this effect is already available from the base materials even without reaction aids. In addition, certain reactions can be supported in the vertical furnace with a controlled furnace atmosphere (e.g. increased O ₂ content or similar).

The raw materials for the process according to the invention are divided up into in ceramic-compatible base material, in waste material, in reaction aids, in blowing agents and in binders.

Base material: a ceramic-compatible material is normally used as the base material mineral sludge like that in gravel pits as washing sludge, as river and sea deposits, etc. Stone can also be used as the basic material coal fly ash can be used. The base material should be in as possible fine form (grain size below 60 my) are available to suffice To have reaction surface. The chemical and mineralogical Zu The composition of the basic material must be examined more closely, especially in Relation to chemical reactivity to waste. That too is Consistency in the composition of the base material over the delivery period monitor.

Waste: The material to be rendered inert is the waste draws. These are mainly powders and sludges containing heavy metals, but it can also be other chemical compounds to be disposed of, which are converted by a thermal treatment or by ceramics be rendered inert. The exact composition and the expected Reactions must be known. Here too there is a demand for material as fine as possible, which may, if not fine enough, still must be ground beforehand (grinding fineness 10-20 my). The waste  substances are in a ratio to be determined depending on the concentration nis to mix with the basic material. It can be in the finished material from one Pure waste compound content of 10-30% by weight of the base material than to be run out. The waste must be contrary to the reason material is stored closed (silos) and with suitable dosing methods are added to and added to the basic material. By Ab Any dust leakage must be prevented.

Reaction aids: If necessary, a additional components are added to a certain chemical Achieve or improve reaction with the waste. Coming Depending on the base and waste material, a wide variety of reaction aids in Question. For cost reasons, the use of reaction aids as limited as possible. Here too there is a demand for delicacy.

Blowing agent: When the end product is recycled at the hardware store the end product can be inflated with a blowing agent and to be provided with a lighter volume and bulk weight. It these are primarily economic and application-related reasons lead to this demand. Naturally, the mechanical strengthening properties of these light granules are worse than one Compact granules. The respective advantages and disadvantages are exactly what he is average and weigh against each other. Inorganic blowing agents are used Compounds in question which release gases at the ceramic temperature and so lead to a porous ceramic structure. Again there is again the demand for delicacy.

Binder: In the case of poor granulation and binding ability of the Base material / waste material mixture (e.g. when using hard coal fly ash possible as the basic material) must the raw with a binder granulate strength can be improved. Chemicals come as binders Binder, but with advantage physical binders in question. Such one is z. B. the admixture of clay-like substances (similar to the mud like basic materials) which leads to capillary force bonds.

All of the above materials, except for the base material, are closed  stored in silos or tanks. You will have suitable dosing device metered to a mixer or a mixing granulator. There the substances are mixed intimately and then in the same, or granulated on a downstream machine. Depending on the moisture content of the Water is added to materials or while warm is added air water removed (dried).

All dust from the system (from Filters, cyclones, sieve, etc.) returned and the other material beige mixes. It is advantageous for the granulation process if a certain Part of the dust can be added (faster granulation). That so The raw granulate formed should have a grain size of approximately 0.3-3 mm Diameter.

After the granulation, which is still carried out in batch operation, this becomes Raw granulate fed to the dryer via a stacking belt and a coarse sieve leads from which the process is carried out continuously. In the coarse sieve all coarser tubers, glue etc. that are not finely granulated sieved and can be fed back into the process via the base material become.

In the dryer, either a tumble dryer or a floating bed dryer, the raw granulate is largely heated with hot air from the system dried up. The expelled water becomes over with the drying air the filter system fed to the environment. Should it be necessary, it can in the case of a drum dryer, the dryer is also heated indirectly the condensed moisture condenses and from possible Pollutants are cleaned.

After the dryer has been discharged, the dry raw granulate is passed over a small one Roller crusher in which the desired maximum grain is limited, d. H. Any oversize is crushed in the crusher and loads the Process not. After the crusher, the granulate is pneumatic Lift or bucket elevator fed to the fine sieve and above all that Undersize (dust) sieved, which like all other process dusts in the Mixer is fed back to the raw material.  

After the sieve, the remaining grain is dosed into the preheater and there as described above in a multi-stage float heater preheated. Depending on the waste material to be treated, the temperature in the Preheaters can be reduced to pollute the hot air avoid. If the preheating must be done without air flow, so can instead of a preheater on the floating principle, an indirect heated rotary tube heater can be used.

In extreme cases, the preheating stage can also be dispensed with. That has but a significantly smaller grain of the finished ceramic product Consequence, because the time in the vertical furnace limited by the fall time allows only a limited supply of heat and thus only a smaller one Grain can be supplied with sufficient heat. The disadvantage of a smaller one Grain is its larger surface area and thus increased attack area for chemical attacks and a possibly increased binding agent required when used in concrete.

The heat to be supplied in the preheater depends on the product and waste fabric and permissible preheating temperature. This is usually between 400-900 ° C. After the preheater, the granulate is turned vertically oven dosed.

The preheated granulate is metered into the vertical furnace falls through this like a raindrop. During diarrhea takes the granulate due to the very intense radiant heat of the furnace and reaches the ceramic temperature of the base material. This is always according to its composition in the range of 1150-1350 ° C. Depending on the tempe temperature of the preheating is the maximum size of the ceramic that can be ceramized in this way Granules in the range of approx. 1-4 mm in diameter.

The type of radiation heat causes the granules to heat up from the outside in, d. H. the surface of the grain reaches very quickly the ceramic temperature and exceeds it, it reaches you pasty to liquid state. Hikes as the fall time progresses this state inside so that the grain falls out of the oven at the bottom, the grain reaches this state inside. Because of the surfaces  the ceramicized grain becomes circular. Through the flow a mutual touch of the grains is prevented in free fall different. After the end of the oven process, the grain has an even finish ceramized structure in which the waste materials are evenly distributed are installed.

Depending on the basic material and type of waste, these are not just in the ceramic structure built firmly and insoluble, but it form also chemical connections between the base material (possibly with Re action aid) and the waste material. These can be the waste material in addition to physical inerting (integration into the ceramic structure) also chemically inert. Due to the high surface temperature The grain of the grain forms a liquid film over the grain Evaporation of the waste material outside the grain at least partially prevented.

In contrast to all processes taking place in the rotary kiln, they have Grains in the oven do not touch each other. Because of this and through the short Heat treatment time, is the danger of gases escaping from the grain and thereby caused oven porosity, as well as the injury to the upper area of the grain by rolling on each other, only very limited and the environmental resistance of the end product is significantly improved.

Grains that come into contact with the furnace wall in the furnace are first stick to it, there through those on the radiation wall liquefied at high temperatures and run off as drops of the furnace wall long down, drip off there and become like normal grains cooled and discharged.

If blowing agents are also added to the mixture of materials, these form the above temperatures in turn gases to a fine-pored expand the grain to 2 to 10 times the volume. Through the due to the above, very fast running processes, it is very important that all materials to be reacted have the greatest possible fineness (large reaction surface = fast reaction). Through the furnace use room atmosphere that can be partially adapted in the system,  these reactions can still be promoted. Be natural on the grain surface and also by gases escaping from the grain, ge knowing reactions take place with the furnace atmosphere (burns etc.) which makes it necessary to continuously replace the furnace atmosphere. This Oven atmosphere can be extracted at the bottom or top of the oven and ent speaking substitute can be supplied.

Due to the inductive-electric radiation heating in the invention Processes are the amounts of air passed through the furnace, as opposed to all fired and convection heating based procedures, only minimal and are only about 5-10% of the other methods. This minor Exhaust gas quantities can be processed using a multi-stage exhaust gas cleaning system become. Due to the small amounts of exhaust gas, the necessary In Investment and operating costs are clear and the process ent speaking more economical.

After the hot liquid granulate has fallen out of the oven, it becomes through a floating bed cooler with cold air immediately and still during the fall time, cooled under the oven. By cooling it is within seconds fractions of the surface of the grain cooled so far that this solidified. Due to the cold air, the grain becomes inner in a floating bed largely cooled down within half a second and the heat content to the Pass cooling air. This in turn is called hot and drying air in the Preheater and dryer used.

In contrast to conventional, large-sized ceramics, this is very quick Cooling of the ceramic structure of the product according to the invention possible Lich, because on the one hand due to the round shape of the grain an even Heat emission is given and on the other hand by the small size of the grain the heat is given off very quickly.

The cooled, ceramicized granulate is discharged from the cooler and blown into a silo. At this point the whole process is complete and the waste material is embedded inertly in the ceramic grain. This can then be installed or deposited.

Claims (10)

1. A method for the thermal treatment of powder and granules, characterized in that the powder or the granules is heated in a vertical induction furnace with a diameter / height ratio of 1: 5 to 1: 30 in free fall by radiant heat and after Ver Oven is cooled again. 2. The method according to claim 1, characterized in that the treatment at a temperature of approx. 700 ° C to 3000 ° C. 3. The method according to claim 1 or 2, characterized in that the Powder or the granules in a preheater to a temperature up to 900 ° C before being placed in the induction furnace. 4. The method according to any one of claims 1 to 3, characterized in that the raw materials from a ceramic-compatible base material and if desired, waste materials, reaction aids, blowing agents and / or binders exist. 5. The method according to any one of claims 1 to 4, characterized in that the raw materials in the form of annular material Induction furnace can be dosed. 6. Device for the thermal treatment of powder and granules in an induction furnace, consisting of an outer jacket, which with Induction coils is provided, an inner tube made of ceramic or metallic material, graphite susceptors between the outer jacket and inner tube and a device for loading with the powder or granules. 7. The device according to claim 6, characterized in that the Gap between the furnace shell and the furnace inner tube with an inert gas flow is flushed and thus prevents the entry of oxygen becomes.   8. The device according to claim 6 or 7, characterized in that the Device for loading from a furnace head neck, an air duct pipe, a material feed pipe and a furnace pestle. 9. Device according to one of claims 6 to 8, characterized in that the induction furnace with a preheater to heat the Material is combined. 10. Ceramized powder or granules, which by means of a method of claims 1 to 5 in a device according to one of claims 6 until 9 was treated.