NO300864B1 - Method and apparatus used for converting problem waste into harmless aggregate - Google Patents

Abstract

Problem waste is formed into a harmless, non-washable aggregate by introducing the material into a rotary kiln (10) where the large solid particles are at least partially incinerated to form a primary aggregate. Gaseous combustion products and fine particulate waste from the waste materials are introduced into at least one oxidizer (26) operated at a temperature in the range of 982 ° C to 1371 ° C. Under such conditions, some of the fine particles are melted to form a slag-like material which is cooled to form the harmless aggregate. The part of the material in the oxidizer (21) that does not. is melted, cooled and neutralized, and undergoes a solid / gas separation. The solids are reintroduced into the oxidizer with the primary aggregate, where they are either melted or trapped in the molten material and become an integral part of the harmless aggregate.

Description

The present invention relates to a method and an apparatus for converting problematic waste into a harmless aggregate by thermally induced oxidation.

Many industrial processes produce by-products and waste materials that cannot legally be disposed of without some type of container or treatment. Previous efforts to dispose of such materials within containers have proven insufficient, since lack of attention to the manufacture of such containers and their degradation results in leakage or spillage of the problem waste. Other devices for treating problem waste include injecting such materials into wells, but the materials may not stay still in the strata into which they are injected, and may find their way into subterranean water-bearing strata.

In addition to the technical problems associated with such disposal techniques, there is potential liability for those who use such facilities. Several years after the materials have been placed on site, claims for liability can be generated based on the knowledge that someone has been responsible for the placement of hazardous materials within an approved dumping site, only to later find that the dumping site cannot prevent the spread of the waste material. Such problems have generated a search for means of using problem waste in a manufacturing process to eliminate the hazardous nature of the material and to produce a product suitable for sale to and for use by the general public. One of the devices that has been tried has been to oxidize the material by passing it through different types of burners under oxidizing conditions. A variation of such a process is described by W.R. Duffett in "Slagging Kiln 'Fired Up' to meet PCB Disposal Needs", found in the November-December 1987 issue of Hazardous Materials and Waste Management on pages 15-17. This process uses a counter-current rotary drying oven to induce combustion of the combustible components of the problem waste, and to form the non-combustible material into an aggregate that could be sold as a commercially valuable and useful product.

Efforts in this particular method of using waste have been partially successful in producing a

product that can be approved by the current EPA regulations associated with the treatment of waste. However, the processes have significant shortcomings. The most significant shortcoming associated with the use of hazardous waste in a rotary drying oven or similar is

that additional non-combustible materials are generated which cannot be formed into an aggregate, and which must be treated as problematic waste. Although the amount of problem waste is thus

significantly reduced by the process, the problem thus remains of getting rid of part of the treated material as problem waste. In addition, most conventional processes generate large quantities of contaminated water that must be treated

and is emptied.

It is therefore an aim of the present invention to overcome this deficiency in the prior art and to produce a method and an apparatus for converting problem material as a recyclable material in a manufacturing process so that all the products of the process are harmless, and can sold to the public regardless of the type of input material that was processed.

Another purpose of the invention is to convert dangerous solid materials into a harmless, inert aggregate that can be sold without restrictions.

Another purpose of the invention is to make use of liquid problem waste such as fuel and fuel additives. Instead of natural gas or coal, in an economical way, where any solid products resulting from the process can be sold to the public regardless of the type of hazardous input material.

A further object of the invention is to produce a system for the use of problematic waste on a large scale, which can be operated economically without significant risk for the staff operating the system. These and other purposes of the invention shall be explained in more detail in the present specification, or they will be obvious when practicing the invention.

With the method in claims 1-10 and the apparatus in claims 11-18, the objectives of the invention are achieved, and the disadvantages as stated in the prior art are overcome by providing a method and an apparatus for converting problem waste into harmless aggregates without the production of contaminated waste streams that must be treated and taken care of. The specified method generally comprises the step of producing a source of solid waste material consisting of large solid waste and fine particles of waste. These materials are separated and the larger waste is introduced into a rotary drying oven having an entrance area, a combustion area and an exit area. The operating conditions in the drying kiln are controlled so that the large waste is incinerated to form a solid particle-shaped primary aggregate, clinker and gaseous combustion products. A large proportion of volatile combustible products in the solid waste are evaporated in the entrance area of the drying oven. The gaseous combustion by-products from the drying oven are removed from it by means of an induced draft. The fine particles of the waste that are separated from the solid material are introduced into an oxidation device together with the combustible material. Combustion in the oxidizer is induced to transform the fine particulate waste into non-combustible fine particles, liquid slag and exhaust gas. The temperature in the oxidation device is controlled. The non-combustible fine particles and exhaust gas from the oxidizing device are led away from there by means of an added draft. The non-combustible fine particles, the gaseous combustion products and the exhaust gas are cooled, and the non-combustible fine particles are separated from the combustible products and the exhaust gas. The solid particulate primary aggregate and non-combustible fine particles are returned to the oxidation device. Heat from the oxidizing device falls on the non-combustible fine particles and the primary aggregate so that a liquid slag is formed. The liquid slag is cooled to form the harmless aggregate. It is preferred that the primary aggregate and the non-combustible fine particles are introduced into the oxidation device in divided portions. It is further preferred that these materials, when they are introduced into the oxidation device, are introduced in the form of a pile where heat from the oxidation device falls on the surface of the pile.

A preferred apparatus for carrying out the method according to the invention for converting problematic waste into a non-hazardous aggregate comprises a rotary drying oven having an entrance area and an exit end. The oxidizing device is close to the entrance area of the drying oven. A source for solid waste material has also been arranged, where the solid waste material includes large solid waste and fine particulate waste.

A device for separating the large solid waste from the fine particles is included as a device for introducing the large solid waste to the dryer's entrance area. The device further comprises a device for inducing combustion in the drying oven to transform the large solid waste into solid particulate primary aggregate, clinker, volatile gases and gaseous combustion products. The device is used to separate clinker from the solid particulate primary aggregate. The device further comprises a device for conveying the gaseous combustion products from the drying oven and from the oxidation device. It is a device for inducing combustion in the oxidizer to convert the fine particulate waste material, the volatile gases and the gaseous combustion products into non-combustible fine particles, liquid slag and waste gas. A cooling device cools the non-combustible fine particles in the exhaust gas, and a separator device separates the non-combustible fine particles from the exhaust gas. The device further comprises a device for introducing the solid particulate primary aggregate and reintroducing the solid non-combustible fine particles to the liquid slag to form an essentially liquid mixture. The device comprises a device for cooling the mainly liquid mixture to form a harmless slag aggregate. The oxidation device preferably comprises a plurality of adapted containers in flow connection with the drying oven's entrance area.

A preferred embodiment of the invention shall be described in more detail below with reference to the drawings, where: Fig. 1 shows a schematic representation of an embodiment of the present invention. Fig. 2 shows a schematic, partial cross-section of the oxidation device in the embodiment of fig. 1. Fig. 3 is a schematic representation of an embodiment for collecting particulate material introduced into the oxidizing device in the embodiments of fig. 1 and 2.

The embodiment of the present invention is shown schematically in fig. 1.

The present invention is an apparatus for converting problem material into a harmless aggregate, and a process for operating the apparatus to perform this function. According to the invention, a rotary drying oven is arranged which has an entrance area and an exit area. As executed and depicted in fig. 1, the rotary drying oven 10 comprises an entrance area 12 and an exit area 14. Between the entrance area and the exit area is the combustion area 16. Although in the shown embodiment where the different areas border each other, the three areas in the rotary drying oven are only illustrative and can overlap. That is, some combustion may take place in the entrance area 12 or the exit area 14, but combustion primarily takes place in the combustion area 16 of the root drying oven 10.

The drying oven shown schematically in fig. 1 is a standard countercurrent rotary drying kiln designed for treating limestone or oyster shell to form lime. It consists of an outer metal shell lined with refractory stone. The composition of the refractory is determined by the operating temperature and the materials passed through the rotary kiln. In the present embodiment, where the rotary drying oven is designed to operate at a temperature in the range from 871°C to 1260°C, a stone consisting of 70% alumina has been used. This is a product of the National Refractory Company of Oakland, California, and has been used without degradation of the refractory stone. The rotary drying oven is supported on conventional bearings (not shown), and driven at rotational speeds in the range of 1 to 75 revolutions per hour by a conventional drying oven drive device (not shown).

As will be discussed in more detail below, solids are introduced into the entrance region 12 of the rotary dryer 10. As it rotates, material larger than about 50 microns will move through the combustion zone 16 toward the exit region 14, while smaller material will enter the trapped in the gas flowing against the flow of larger solid materials. In the embodiment shown, the rotary drying oven 10 comprises cooling chambers 18 in the outlet area of the drying oven. The cooling chambers receive the solid materials through ports which are connected to the rotary drying oven. The chambers receive the larger solid materials which are transferred by rotation to an output chute 20 where the solid materials from the rotary drying oven come out. Connected to the rotary drying oven 10 is also a source of fuel 22, as well as a source of air 24, to provide combustion inside the rotary drying oven 10. The fuel used can be a combustible liquid or gas, including combustible waste liquids , liquid fuel or flammable natural gas. Oxygen or water in combination is used to control the temperature and combustion. The air/fuel mixture is introduced into the rotary drying oven 10 in an exit area 14, where gases in the drying oven 10 pass in the direction of the entrance area 12 against the flow of the larger solids that are transported by rotation of the drying oven towards the exit area 14. As mentioned earlier, the smaller particles are captured by the gas passing through the drying oven, and are thus separated from the larger solids and transported out of the drying oven.

According to the invention, the apparatus comprises an oxidation device near the entrance area of the drying oven. As implemented here, the apparatus comprises a first oxidizing device 26. As shown in fig. 1, the first oxidizing device 26 is near the entrance area 12 of the rotary drying oven. The oxidizing device 26 is in flow communication with the entrance area 12 of the rotary drying oven 10, and receives volatile gases that are driven from the material introduced into the rotary drying oven, as well as combustion products from the combustion that takes place in the rotary drying oven. A source of waste material introduces the material to the entrance area 12 of the drying oven 10, where the counterflow gas causes a separation of larger particles (solid waste material) and the smaller particles (fine waste particles). According to the invention, the solid waste material consists of larger solid waste and fine particulate waste. For the purposes of the invention, larger solid waste has a particle size of more than about 50 microns, while fine-particle waste is defined as all material with a particle size of less than 50 microns. Although the apparatus can be operated with materials that are separated to a different size, the purpose of the separation is to produce materials for the first oxidizer 26 that can be easily oxidized or melted in their physical state, while larger materials are introduced into the drying oven to be broken down during its transport through the rotary drying oven, either to non-combustible material, volatile gas or combustion by-products.

According to the invention, there is a device for separating the larger waste from the fine-particle waste. As carried out here and shown in fig. 1, the apparatus comprises a passive conveyor 30 which receives materials from the waste source 28 and introduces the waste-derived fuel into the exit area 12 of the rotary drying oven 10. Classification of the larger solid waste from the fine-particle waste takes place throughout the rotating drying oven 10. It should also be noted that the solid waste could also be separated according to size before introduction into the drying oven, and that the fine particles could then be introduced directly into the oxidation device.

According to the invention, the apparatus includes a device for inducing combustion in the drying oven, to convert the larger waste particles into solid particulate primary aggregate, clinker, volatile gases and gaseous combustion products. As carried out here and shown in fig. 1, the combustion device comprises a fuel source 22, an oxygen source 24 and the rotary drying oven 10. As will be explained later, the operating conditions in the drying oven are such that the larger solid particles are preferably converted into particulate primary aggregate, volatile gases and gaseous combustion products, while the amount of clinker produced by the rotary kiln will be minimal. Operation of the rotary drying oven 10 allows the solid particles to pass to the exit area 14 from the rotary drying oven through the cooling chambers 18 to the exit chute 20. As performed here, the solid materials exiting the exit chute 20 are sent to the drying kiln's classification device 34. The classification device 34 can be any conventional mechanism for separating larger solid particles from fine solid particles. In this embodiment, any solid material that has a diameter of more than 9.5 mm is classified as clinker, while anything smaller is placed as primary aggregate. The clinker and particle materials are passed over a magnetic separator 32. The primary aggregate is passed over another magnetic separator (not shown). The ferrous materials are removed and sent to a metal bin for sale as scrap iron.

According to the invention, there is a device for inducing combustion in the oxidation device to convert fine particulate waste, volatile gases and gaseous combustion products into non-combustible fine particles, molten slag and exhaust gas. In this embodiment, the means for inducing combustion in the oxidizer comprises the oxidation fuel source 36 and an oxygen source. The first oxidation device 26 thus receives fine particulate waste and volatile gases from the rotary drying oven 10 which may or may not be flammable, combustion products from the rotary drying oven 10, fuel from the fuel source 36 and oxygen from the oxygen source 38. In the present embodiment, the first oxidation device 26 is operated at a temperature in the range from 980°C to 1650°C. In an oxidizing environment, combustible materials inside the first oxidizing device 26 are converted into exhaust gas and non-combustible fine particles. The non-combustible fine particles may or may not be melted, depending on their composition. As shown schematically in fig. 2, part of the non-combustible fine particles are melted and collected on the bottom of the first oxidizing device 26 in the form of liquid slag 40. Although fig. 2 shows that liquid slag is removed from the apparatus by means of a slag port 42, such a slag port can optionally be placed along the bottom of the first oxidizing device 26. As shown in fig. 2, the slag port 42 is connected to a burner 44 to keep the material near the slag port 42 molten. The apparatus can optionally comprise a burner which is directed into the first oxidizing device 26 for the purpose of raising the temperature at various places inside the first oxidizing device 26.

As shown schematically in fig. 2, a first oxidizing device 26 is a refractory-lined container in electrical connection with the entrance area 12 of the rotary drying oven 10. The first oxidizing device 26 in this embodiment has a square cross-section, and comprises a metal shell 46 with an internal refractory lining. The refractory lining in the embodiment shown comprises refractory rock 48 and a monolithic refractory lining 50. In the embodiment shown, the refractory rock is 70% alumina, made by National Refractory Company, Oakland, California. The monolithic liner is JadePak, made by A.P. Green Company, Mexico, Missouri. In this version, the refractory rock in the bottom of the first oxidizing device 26 is significantly thicker than the refractory rock in the wall section of the first oxidizing device 26. This is a result of the operating temperature in this area of the first oxidizing device 26, caused by the flowing liquid slag 40 which transfers heat from the hot gases flowing through the inner region 52 of the first oxidizer 26. Another preferred embodiment of the first oxidizer 26 could have a water-cooled roof, water-cooled metal walls and a refractory floor. Such a construction allows a higher operating temperature.

In the embodiment in fig. 2, the hot gases are turned 90 degrees towards the pipe 54 which connects the first oxidizing device 26 with another oxidizing device 56. The construction of the second oxidizing device 56 is to a certain extent similar to the construction of the first oxidizing device 26. In the embodiment shown, however, the second oxidation device 56 cylindrical, with an inner area 58 which is also cylindrical. The hot gases and fine particles pass from the first oxidizing device 26, through the pipe 54, to the second oxidizing device 56. The construction of the pipe 54 and the second oxidizing device 56 is similar to the shown embodiment of the first oxidizing device 26, in that they are refractory lined steel constructions. The refractory material used in the tube 54 is JadePak, and the refractory material used in the second oxidizer 56 is also JadePak. Like the first oxidation device 26, the second oxidation device 56 also comprises several layers of refractory stone in the bottom part. The function of these multiple layers of refractory material is discussed above.

In the embodiment shown, not all combustion of the waste material takes place in the first oxidation device 26. A significant part also takes place in the second oxidation device 56. In the operation of the embodiment in fig. 1 thus pass non-combustible fine particles from the inner area 52 of the first oxidizing device 26 through the pipe 54 and into the inner area 58 of the second oxidizing device 56.

In a preferred embodiment, liquids are injected into the second oxidizer 56 as shown here, through the liquid inlet 60. The source of the liquid-to-liquid inlet 60 in the present embodiment comprises a sump system (not shown) which surrounds the entire apparatus. Any liquid, including waste-derived fuels, rainwater or polluted water can be collected in a sump system and injected into the second oxidizer 56 through the liquid inlet 60. The whole apparatus thus has a means of using waste-derived fuel and polluted water from the environment -ne, inside the device itself. Those skilled in the art to which the invention relates can easily construct a drainage and sump system which can work together with the present invention, without particular description of such a system.

According to the invention, there is a device for cooling the non-combustible fine particles and exhaust gas. As carried out and shown schematically in fig. 1, a cooling vessel 62 is included. The cooling vessel 62 comprises a water inlet 64. In the present embodiment, the water inlet 64 has a nozzle (not shown) which introduces water and air at supersonic speed. In the present invention, the spray nozzle is a "supersonic" model SC CNR-03-F-02, made by the company Sonic in New Jersey. In electrical connection with the water inlet is a water source 66. In the present embodiment, the water source 66 is supplied with water that does not contain waste. The function of the water from the water source 66 is to cool the exhaust gas and the non-combustible fine particles down to a temperature of between 175°C and 200°C, so that the gas and the particulate material can be separated in a conventional manner, which will be described below. As shown schematically in fig. 1 there is a source for a caustic material which is in current connection with a spray nozzle 70 for introducing caustic liquid as a spray into the dry spray reactor vessel 62. The injection of caustic material is to neutralize any acids in the exhaust gas.

The apparatus according to the invention comprises a device for transferring the gaseous combustion products from the drying oven and the exhaust gas from the oxidation device. As implemented here, a coupling 72 is included which flow connection between the second oxidizer 56 and the dry spray reactor 62. The coupling is constructed similarly to the second oxidizer 56, namely a refractory lined metal shell. Similarly, the dry spray reactor 62 is also a refractory lined metal vessel.

When connecting the various elements of the present invention, the effect of differential thermal expansion must be taken into account due to the high temperatures of the materials inside the oxidizers 26 and 56, the pipe 54 and the coupling 72. In addition, there are significant temperature differences in different areas of the apparatus, so that the interface between such areas must be arranged for expansion and contraction.

As will be described below, the system operates at a pressure lower than atmospheric pressure. Any leakage at the interface between areas of the apparatus is thus not harmful to the performance of the apparatus as long as the amount of leakage is not so great that it affects the combustion of materials inside the oxidation devices. This requirement is not so critical in other areas of the device that operate at lower temperatures.

The apparatus according to the invention comprises a device for separating the non-combustible fine particles and the exhaust gas. As shown schematically in fig. 1, the apparatus comprises two filter systems which operate in parallel, each comprising a filter 74 and a fan 76. The exhaust gas and fine particles are introduced into the filter at a temperature which is preferably above 176°C and less than 204°C, so that conventional filter chambers can be used. Operation of the present embodiment has shown that conventional Teflon polytetrafluoroethylene filter elements can be used in conjunction with this operation. The exhaust gas is separated from the non-combustible fine particles, and the exhaust gas is then transferred by the monitoring device 78 which monitors the composition and temperature of the exhaust gas. The exhaust gas is then transferred to the atmosphere through the chimney 80. The fan 76 induces a draft throughout the apparatus, which draws the volatile gases and combustion products from the rotary drying oven. , The products of combustion from the rotary drying oven, the products of combustion from the oxidizers and all the gases passing through the system pass through the fan 76, so that the whole apparatus runs under atmospheric pressure. The finer particles that are collected in the filter 74 are transferred by means of a pump device 82 to the accumulator 84. In a similar way, the primary aggregate is transferred through a pump 86 into the accumulator 84. The preferred embodiment of the accumulator 84 is shown in fig. 3.

According to the invention, there is a device for introducing the solid particulate primary aggregate and re-introducing the non-combustible fine particles to the apparatus to form an essentially liquid mixture. As shown in fig. 1 and 2, the apparatus comprises a device for introducing the non-combustible fine particles and primary aggregates into the oxidizing device, in particular the second oxidizing device 56. As shown in fig. 3, the accumulator 84 comprises a first inlet 88 positioned so that it receives fine particles from the pump 82. The accumulator 84 further comprises another inlet 90 arranged so that it receives primary aggregate through the pump 86. In connection with the preferred embodiment of the accumulator 84, there is a first sensor 92 to detect the desired maximum level of particulate material inside the accumulator 84. Another sensor 94 detects the level of particulate material inside the accumulator 84 and, by means of a sensor-flushing mechanism, operates a valve 98 through a valve control device 100. During operation of apparatus, the inlets 88 and 100 carry particulate material into the accumulator 84 where it accumulates to a predetermined level so that an upper sensor 92 is activated through the sensor control device 96 and the valve control device 100 opens the valve 98, thereby allowing a particulate material to pass through the pipe 102 into the second oxidizing device 56 as shown t in fig. 2. When the level of particulate material inside the accumulator 84 reaches the level of the lower sensor 94, the sensor control and valve control 100 will close the valve 98, thereby interrupting the flow of particulate material through the pipe 102.

Although it is shown that the tube 102 introduces solid particulate material into the second oxidizing device 56, solid particulate material can also be introduced into the first oxidizing device 26 or both the first and the second oxidizing device. As shown in fig. 2, the solid particulate material introduced into the second oxidizing device 56 through the tube 102 falls into the central area 58 of the second oxidizing device 56, and forms a pile on the bottom. Heat from the gas passing through the second oxidizing device 56 falls on the surface of the pile of particulate material and melts that portion of the particulate material which has a melting point below the gas impinging on the surface. The material flows from the pile 104 containing any particulate material that is not melted, and flows together with the molten slag 40 and flows out of the slag port 42.

The apparatus according to the invention comprises a device for cooling the essentially molten mixture, in order to form the harmless aggregate. As implemented here, the device comprises a cooling device 106 as shown schematically in fig. 1. In the preferred embodiment, the cooling device simply consists of water into which the essentially molten mixture is emptied. The cooling device extracts the heat from the molten mixture, forming the harmless aggregate.

Operation of the apparatus described above shall now be described as expressed by a process for using problem waste in a manufacturing process to design a non-hazardous

aggregate. The first step of the process according to the invention is to arrange a source for solid waste material which includes large and small particles of the material. In the embodiment according to the present invention, the waste is transported to devices in different forms. The waste can be in the form of solid particles such as contaminated topsoil, contaminated construction waste, semi-solid sludge from a sewage treatment plant, metal drums with liquid waste, fiber drums (often called lab packs) that contain liquids or solids. When the waste is a liquid-containing sludge, the waste is first passed over a grate where the liquid is removed, and fed into the device according to the invention, separated from the solids. When the waste is stored in two-hundred liter metal drums, the drums are shredded and introduced into the rotary drying oven as part of the bulk solid waste, thereby eliminating

the need for cleaning or inspection of the barrels. It may also be necessary to shred the input materials several times in order to obtain an input material that is effectively consumed in the process.

In order to control the process and the operating temperatures of the various components that carry out the process, it is advantageous to know certain characteristics of the input materials, so that the feed quantity of waste materials and other input materials introduced into the apparatus can be controlled to achieve the desired operating conditions. The waste material is preferably delivered with a description that would include a BTU (heat energy quantity) content and moisture content. However, it may also be necessary to check the BTU content and other characteristics of the input materials to facilitate the operation of the appliance. It should be noted that if a load of the waste material can have a total BTU content of one value, it is often that the waste materials are non-homogeneous, and therefore the operation of the device and the control of the process will require some intervention to prevent the operating parameters from to deviate from what is necessary for complete oxidation of the combustible components in the waste material and to produce the desired harmless aggregates. In addition to the BTU and moisture content, it is also advantageous to know the acid content, the amount of ash and the halogen concentration. The acid content of the waste material gives the operator a means of judging how much caustic material would be consumed in the process, which has an effect on both the operation of the process and its economics. The amount of ash in the waste determines how much aggregate will be produced. The halogen content determines how much aggregate will be produced. The halogen content affects the operation of the process, and should preferably be in the range of 10 to 15%. By using these characteristics of the waste material, and by suitable management of the supply of water, fuel, oxygen, caustic material, coolant and the like, to achieve the desired operating conditions, the desired unit can be economically produced.

According to the invention, the process includes a step to separate the larger solid waste particles from the fine particles as described above. This separation can take place in the rotary drying oven 10, or can be achieved by simply directing the appropriate sizes of waste particles to different positions in the apparatus. If e.g. the fine particles consist of contaminated topsoil, they can be introduced directly to the oxidation device.

The process according to the invention comprises the step of feeding the larger solid particles to a rotary drying oven with an entrance area, a combustion area and an exit area. The operating conditions in the drying kiln are controlled so that the larger waste particles are incinerated to form a solid particle-shaped primary aggregate, clinker and gaseous combustion products, where a large part of the volatile combustible substances in the solid waste material are evaporated in the entrance area of the drying kiln. The rotary drying oven is preferably operated at an average internal temperature in the range of 871°C to 1260°C.

It should be noted that there are significant temperature gradients inside the drying oven, both longitudinally and radially. Areas in the drying oven can therefore deviate significantly from the range from 871°C to 1260°C.

The large solid waste particles are introduced into the rotary drying oven at a rate that depends on the BTU content of the waste, but normally at a rate of around 20 tonnes per hour. The drying oven rotates at a speed in the range from 1 to 75 revolutions per hour, so that the total residence time for solid material coming out of the drying oven at the exit area 14 is in the range from about 90 to 120 minutes.

With these operating parameters, the rotary kiln produces a solid output consisting mainly of solid particulate primary aggregate, with small amounts of material that can be classified as clinker. For the purposes of the invention, bricks are usually larger solid objects, e.g. construction bricks that pass through the rotary kiln without reacting, or aggregates of low melting point material that have melted and accumulated at the relatively low temperature of the rotary kiln. The operating conditions in the rotary drying oven are controlled to facilitate two conditions.

Firstly, to convert the majority of the larger solid waste into solid particulate primary aggregate, and secondly to evaporate the majority of the volatile combustible substances in the solid waste in the entrance area of the rotary drying oven. As will be discussed below, the primary aggregate is recycled in the process, where it is melted and introduced to the liquid slag in the oxidizer. Since this slag is formed into the harmless aggregate, it is desired to convert as much of the treated material as possible into this form. The material that forms the clinker output from the drying kiln is tested to determine if it contains problem material that can be washed out. Any material that has leachable hazardous materials is reintroduced into the rotary dryer at the entry area. Operation of the present apparatus and process results in a very small portion of the output from the rotary drying kiln being classified as clinker material.

The second objective of operation of the rotary drying oven is to vaporize a large part of the volatile combustible substances in the entrance area of the rotary drying oven. This reduces the BTU content of the solid material passing through the rotary dryer and into the combustion area 16 of the rotary dryer. If the BTU content of the solid material reaching the combustion area 16 of the rotary drying oven 10 is too high, uncontrolled combustion may occur within the combustion area of the drying oven. The operating conditions in the rotary drying oven should thus include a temperature in the entrance area that is high enough to evaporate most of the volatile components in the large solid waste particles that are introduced into the drying oven.

As shown schematically in fig. 1, the solid material exiting the exit chute 20 is sent to the drying oven classifier 34. The classifier 34 may be any conventional mechanism for separating larger solid particles from finer solid particles. In this embodiment, all solid particles with a diameter of more than 9.5 mm are classified as clinker, while all particles that are smaller are classified as primary aggregate. The clinker and particle material is passed over a magnetic separator (not shown). The primary unit is passed over another magnetic separator 32A. Ferrous metals are removed and sent to a metal bin for sale as scrap metal.

According to the invention, the gaseous combustion products from the drying oven are carried from there by means of induced draft. As mentioned above, the fans 76 maintain the entire apparatus at a sub-atmospheric pressure and draw the gas from the rotary dryer as well as the oxidizers throughout the system.

According to the invention, the process includes the introduction of finely divided waste materials to the oxidation devices. In this embodiment, fine particles from the rotary drying oven 10 are captured in the gas stream and carried into the first oxidizing device 26.

According to the invention, combustible materials are oxidized in the oxidation devices. In this embodiment, there is a source of liquid fuel 36 connected to the first oxidizer 26. The input of fuel, particulate waste, and volatile gases from the solid waste material in the drying oven as well as oxygen injection are all used to control the temperature of the first oxidizer, which should lie in the range from 980°C to 1650°C. The temperature is determined by the BTU content of the input materials, including any auxiliary fuel that is introduced. The auxiliary fuel from the fuel source 36 preferably comprises combustible liquid waste materials. It is further preferred that combustible liquid waste materials comprise a liquid consisting of either organic solvents, liquid drilling waste or paint.

According to the invention, the process includes a step to induce combustion in the oxidizing devices, to convert the fine particulate waste into non-combustible fine particles, liquid slag and exhaust gas. In this embodiment, there are two oxidizing devices, the first oxidizing device 26 and the second oxidizing device 56. In the first oxidizing device 26, a large part of the combustible material is oxidized to form gaseous combustion products. These are drawn through the interior 52 of the first oxidizer 26, through the tube 54 and into the interior 58 of the second oxidizer 56. At the operating temperature, preferably 980°C to 1650°C, some of the solid materials will melt. These materials collect in the bottom region of the first oxidizing device, as shown in fig. 2, as liquid slag 40, which then flows towards the slag port 42. The unmelted solid particulate material passes together with the gaseous combustion products through the pipe 54 and into the interior of the second oxidizing device 56, where a part may be melted in the second oxidizing device 56 or it may remain unmelted and pass through the device as solid fine particles.

According to the invention, solid particulate primary aggregate and non-combustible fine particles are introduced into the oxidation devices. In this embodiment, as shown clearly in fig. 2, there is a pipe 102 which leads the primary aggregate and the solid fine particles to the interior of the second oxidizing device 56. The primary aggregate and the solid fine particles are preferably introduced in separate portions. Continuous introduction of these materials into the second oxidizing device 56 cools the surfaces of the pile of particulate material inside the oxidizing device, and prevents melting on the surface. This delays the melting of the particulate material which is fed into the second oxidizing device 56, and thus slows down the production of the liquid slag which forms the harmless aggregate.

As shown schematically in fig. 2, it is preferred that the separate portions of primary aggregate and non-combustible fines are fed to the second oxidizer 56 to form a pile in the oxidizer. Heat from the oxidizer falls on the surface of the pile, after which materials with a relatively low melting point are melted so that they flow to the bottom of the oxidizer, towards the pipe 54, where the molten material flows out through the slag port 42. The process can generate either a slag-like aggregate or a non- combustible fine particles that have a higher melting point than the temperature in the second oxidizing device 56. Such particulate materials would thus not melt. However, they are trapped into the molten material being formed in the second oxidizer 56, and into the slag to form a substantially liquid mixture. By melting the surface of the heap and allowing the molten material together with the accompanying particulate material to flow towards the pipe 54, a new surface is exposed to the particulate material which is then melted and flows out of the apparatus through the slag port. Although the embodiment shown here illustrates introduction of the primary aggregate and non-combustible fines into the second oxidizer 56, the process can also work if a portion of that material is introduced into the first oxidizer 26. It is also possible to inject separately, the primary aggregate into the one or the other oxidizing device or the fine particles in the one or the other oxidizing device, but it is preferable to combine the particulate primary aggregate and non-combustible fine particles and to reintroduce them into the process as a combination.

The embodiment in fig. 2 also shows an apparatus for injecting oxygen into the first oxidizer 26. The process also works by injecting oxygen into the second oxidizer 56. During the preferred operation of the device, the average temperature in the first oxidizer 26 is about 1650°C. The temperature in the pipe between the first and the second oxidizing device 56 is 1538°C and the temperature in the second oxidizing device 56 is about 1538°C. It is also preferable that the second oxidizing device 56 is arranged to receive liquid in relatively small quantities, so that any combustible problem waste in the liquid is oxidized inside the oxidizing device. In the embodiment shown, it is the second oxidizing device 56 which comprises an inlet 60. At the operating temperature in the second oxidizing device 56, the water is vaporized and the solid particles are introduced into the hot gas stream to either be burned, melted or carried out together with the other non-combustible fine particles into the downstream section of the device.

It is further preferred that the exhaust gas, the gaseous combustion products and non-combustible fine particles from the oxidizer are cooled by injection of water to form a cooled effluent. In this embodiment, and as shown schematically in fig. 1, there is a dry spray reactor 62 comprising a device for injecting water into the dry spray reactor 62. The water preferably forms a cooled effluent having a temperature of less than about 204°C, and preferably more than 177°C. It is also preferable that any acids in the cooled effluent are neutralized.

In this embodiment, and as shown schematically in fig. 1, the apparatus comprises a device for introducing a caustic solution to form a neutralized effluent consisting of non-combustible fine particles and exhaust gas. The exhaust gas is preferably separated from the non-combustible fine particles by dry filtering. This step can be achieved by passing the non-combustible fine particles and the exhaust gas through a conventional filter chamber. The fans connected to the filter chamber, in this case the fans 76 in fig. 1, induces a draft throughout the apparatus, so that the apparatus is operated at a lower pressure than atmospheric pressure.

According to the invention, the process includes a step for cooling the mixture of molten slag and solid particles to form a harmless aggregate. In the preferred embodiment, the mixture of molten slag and solid particles is introduced into a water-filled conveyor where the quenching effect of the water cools the mixture and forms the solid, harmless and non-washable aggregate. The water used to cool the molten material is then reintroduced into the process, either together with waste water to the second oxidizing device or as cooling water in the extinguishing vessel 62.

The operation of the present invention results in the production of four effluents: ferrous metal, which is passed through the rotary drying oven and is thus free of hazardous substances; clinker that is passed through the rotary drying kiln, where any hazardous materials are either bound to the clinker structure or reintroduced into the process until the clinker composition is harmless. The third effluent is a gaseous effluent from the chimney 80, and consists primarily of carbon dioxide and water. Although the preferred embodiment is not classified as a hazardous waste incinerator, and thus is not subject to hazardous waste incineration requirements, its air quality permit is based on the same considerations as a Part "B" hazardous waste incinerator. The present invention easily meets such criteria. In addition to meeting strict air quality specifications, the aggregate produced by the process, although it contains heavy metals that would be dangerous if removed from the aggregate, has converted the material into a form where the heavy metals are bound in the glass-like aggregate . In particular, the levels of arsenic, barium, cadmium, chromium, lead, mercury, selenium and silver are all well below legal limits. In addition, the concentration of insect poison and plant poison compounds, acidic phenolic compounds, neutral compounds and other volatile compounds is well below the legal limits. Although the input materials may contain hazardous products, the materials are either oxidized or locked within the aggregate structure so that the process does not produce any hazardous effluents.

The present invention is shown in a preferred embodiment. However, the invention is not limited to this. The scope of the invention is determined only by the appended claims and their equivalents.

Claims (18)

1. Method for converting problem waste into a non-hazardous aggregate, comprising: arrangement of a source for solid waste material (28) consisting of large waste particles and fine waste particles; separation of the larger waste particles from the fine particles; introducing said large waste particles into a rotary kiln (10) having an entrance area (12), a combustion area (16) and an exit area (14); controlling the operating conditions of the kiln (10), so that said large waste particles are combusted to form a solid particulate primary aggregate, clinker, and gaseous combustion products; a greater part of the volatile combustible substances in the large solid waste particles are vaporized in the entrance area (12); characterized by introduction of the fine waste particles to an oxidation device (26, 56); introducing combustible materials to said oxidizing device (26); leading said gaseous combustion products from said furnace (10) to said oxidizing device (26) by means of supplied draft (76); inducing combustion at a controlled temperature in said oxidizer (56) to convert said fine waste particles into non-combustible fine particles, molten slag and exhaust gas; guiding the non-combustible fine particles, said gaseous combustion products and said exhaust gas from the oxidizing device (56) by means of the supplied draft; cooling said non-combustible fines, said gaseous combustion products and said exhaust gas to allow their separation; separating said non-combustible fine particles from said gaseous combustion products and exhaust gas; introduction of said solid particulate primary aggregate and re-introduction of said non-combustible fine particles into the oxidation device (56); applying heat from said oxidizing device (56) to non-combustible fines and said primary aggregate to form a mixture of molten slag and solid particles; and cooling said mixture of molten slag and solid particles to form said harmless aggregate. 2. Method according to claim 1, characterized in that the said primary aggregate and the non-combustible fine particles will be introduced into the oxidation device (56) in separate portions. 3. Method according to claim 2, characterized in that said separate portions of primary aggregate and non-combustible fine particles form a pile (104) in the oxidation device (56). 4. Method according to claim 3, characterized in that heat from the oxidation device (56) is transferred to the surface of the said pile (104). 5. Method according to claim 4, characterized in that the pile (104) has an inclined outer surface, and that hot exhaust gases from the aforementioned oxidizing device (56) are led towards said inclined outer surface. 6. Method according to claim 5, characterized in that said slanted outer surface is melted, and melted material on said slanted outer surface flows from said slanted outer surface and exposes a new surface with unmelted material on the pile (104). 7. Method according to claim 1, characterized in that said oxidation device comprises a first and a second oxidation device (26, 56). 8. Method according to claim 7, characterized in that said first oxidation device (26) receives said fine waste particles and additional combustion material in the form of liquid fuel and is operated at an average internal temperature ranging from about 982° to 1649°C. 9. Method according to claim 7, characterized in that said second oxidation device (56) receives combustion by-products and non-combustible fine particles from said first oxidation device (26), and said second oxidation device is operated at an average internal temperature in the range from 982° to 1538 °C. 10. Method according to claim 1, characterized in that said waste gas, gaseous combustion by-products and non-combustible fine particles from said oxidation device are cooled using water to form a cooled effluent. 11. Apparatus for converting problem waste into a non-hazardous material, where the apparatus comprises: a container (28) for solid waste material consisting of large waste particles and fine waste particles; a device (32) for separating said large waste particles from said fine particles; a rotary kiln (10) with an entrance area (12), a combustion area (16) and an exit area (14) for introducing the aforementioned large waste particles; means (22, 24) for inducing combustion in the kiln (10) to convert said large waste particles into a solid particulate primary aggregate, clinker and gaseous combustion products; and device for vaporizing a larger part of the volatile combustible substances in the large solid waste particles at the entrance area (12); characterized in that said entrance area (12) is in flow communication with said oxidizing device (26) for introducing the fine waste particles to an oxidizing device (26, 56); introduction device (36, 38) for introducing combustible materials to said oxidation device (26); device for guiding the aforementioned gaseous combustion products from the aforementioned furnace (10) to the aforementioned oxidizing device (26); means (36, 38) for inducing combustion at a controlled temperature in said oxidizer (56) to convert said fine waste particles into non-combustible fine particles, molten slag and exhaust gas; device for guiding the non-combustible fine particles, said gaseous combustion products and said exhaust gas from the oxidizing device (56) by means of the supplied draft (76); means (62, 66) for cooling said non-combustible fine particles, said gaseous combustion products and said exhaust gas to allow their separation; device (74, 76) for separating said non-combustible fine particles from said gaseous combustion products and exhaust gas: device (84-102) for introducing said solid particulate primary unit for re-introducing said non-combustible fine particles into the oxidation device (56) ; means (106) for cooling said mixture of molten slag and solid particles to form said harmless aggregate; device (88-102) for introducing said primary aggregate and said non-combustible fine particles into the oxidation device (56) in separate portions; and gas passing through means (54) for transferring heat from the oxidizer (56) to the surface of a pile (104) to form a mixture of molten slag and solid particles. 12. Apparatus according to claim 11, characterized in that said oxidation device comprises first and second oxidation devices (26 and 56). 13. Apparatus according to claim 12, characterized in that said first oxidizer (26) includes a device for introducing said non-combustible fine material to the slag in said first oxidizer (82 and 84). 14. Apparatus according to claim 12, characterized in that said second oxidation device comprises a device for introducing said non-combustible fine material to the slag in said second oxidizer (82, 84). 15. Apparatus according to claim 11, characterized in that said apparatus includes a slag removal device (42) in flow communication with said oxidation device. 16. Apparatus according to claim 15, characterized in that said slag removal device (42) includes a device for removing said substantially molten mixture from said oxidizing device. 17. Apparatus according to claim 16, characterized in that said slag removal device includes a burner (44) for heating material therein. 18. Apparatus according to claim 11, characterized in that said device for conveying the exhaust gas and said non-combustible fine material from said oxidizing device includes a device for inducing a sub-atmospheric pressure in said apparatus.