MC1188A1 - METHOD AND APPARATUS FOR PYROLIZING RESIDUES - Google Patents

Description

1.

The shortage of suitable sites as landfill sites and recent incidents relating to beach pollution caused by the dumping of sludge into the sea have made it necessary to develop another process for the disposal of urban and industrial waste, such as sewage sludge.

multi-fuel and fluidized bed incinerators; however, such incinerators require large quantities of supplementary fuel and are unacceptable from an environmental point of view in certain inhabited areas.

to the point of a process for the pyrolysis of residues containing significant proportions of both water and combustible organic matter, a process that does not present the drawbacks of the 15 previously known processes and that is acceptable from an environmental point of view. The present process makes it possible to produce activated carbon from these residues, which can be used to reduce pollution of wastewater discharged from wastewater treatment plants.

20 Although in this descriptive memorandum the invention will be described with particular application to sewage sludge, it is quite evident that it is also applicable to other types of urban and industrial waste containing significant proportions of both water and organic matter. 25 In the present process, the sewage sludge, which is very viscous and sticky due to its high moisture content, is mixed with recycled hot carbonized material from the implementation of the process to produce a dry, free-flowing product, as well as a significant quantity 30 of evaporated water, which is then transformed into dry steam. The quantity of carbonized material to be recycled in the present process depends on the initial state of the sludge and the operating conditions of the equipment used to carry out the process. In the present process, only a first portion of the 35 carbonized material is recycled, while a second portion of this material in the form of activated carbon is removed from the equipment in which the process is carried out. This second part is available to serve to reduce the degree of pollution of the water discharged from the water treatment plant. The present

One known method involves burning the residues in

The present invention is primarily aimed at the implementation

2.

The process has the advantage, from an operational point of view, of minimizing the heating of the ambient air near the pyrolysis zone, since the excess heat from this operation is used to transform water into steam, which is then used to at least partially transform the carbonized material produced during the operation into activated carbon. Similarly, some of the excess heat can be used to preheat the air that is mixed with the pyrolysis gas before it is burned to sustain the pyrolysis reaction. In a preferred embodiment of the process according to the invention, the excess combustible gas produced during the pyrolysis reaction is used as fuel to provide the external heat necessary for the reaction. However, when starting the process, it is necessary to use combustible gas from an external source until the production of pyrolysis gas is sufficient to sustain the reaction. The supply of external gas can then be stopped. If the production of pyrolysis gas exceeds the quantity required for pyrolysis, the excess can be removed and used for another purpose, for example, to produce steam or to power an internal combustion engine. Thus, the excess energy can be used to supplement the energy required by the processing plant.

The invention will be illustrated in more detail in Figure 25 of the attached figures, in which:

- Figure 1 is a schematic view of a device that can be used to carry out the pyrolysis operation of wet sewage sludge, in order to convert it into activated carbon;

- Figure 2 is an enlarged view of the burner included in the apparatus shown in Figure 1.

In a preferred embodiment of the process according to the invention, the process is carried out in a refractory material construction A, in which is placed an elongated cylindrical envelope B, serving as a pvrolysis furnace and

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made of a rigid material with high thermal conductivity, for example steel. The casing B has a front end 10 and a rear end 12, as well as an annular transmission 14 fixed to the casing B, near its front end. The casing B is slightly inclined, so that

when the envelope is rotated, the material contained within it moves by gravity all along the cylinder. The annular transmission 14 is engaged with a drive transmission 16 which is rotated by an energy source, for example an electric motor 18.

The two ends 10 and 12 are respectively fixed to sealed rotating joints 20 and 22. The apparatus also includes a firebox C which has an elongated part 24 and a gas evacuation chimney 26 extending upwards. The furnace is connected to a fire compartment 28. The pyrolysis furnace B is fed by a hopper 32, which is connected to the furnace by a tubular discharge 30 in which is housed a conveyor screw 34 driven by a power source 36. The pyrolysis furnace is connected to the discharge unit by means of a sealed rotary joint 20 which allows the furnace B to rotate. The furnace B is supported in the furnace C so as to be able to rotate around its axis by means of two bearings 38 and 40. The sealed rotary joint 22 is connected to a cage 42 extended downwards by a tubular section 44 which divides in its lower part into two discharge pipes, 46 and 48 respectively. A pipe 50 extends upwards from the cage 42, in which the combustible gas with the volatile liquid vapors is separated from the hot carbonized material. A valve 52 is located at the junction of the tubular part 44 with the pipes 46 and 48 to allow the desired quantity of material to flow into one or the other of the two pipes.■A valve 53 is mounted in the pipe 48 to regulate the flow of material in this pipe.

Pipe 46 is connected to the inside of a cylindrical mixing vessel 54, which houses a screw conveyor 56 powered by a power source 58. The end of the cylindrical vessel 54 extends into two pipes 60 and 62. A hopper 64, or other suitable container, for receiving wet sewage sludge is connected to a pipe 68 that connects it to the inside of the cylindrical vessel 54. At least a portion of the pipe 68 is equipped with a screw conveyor 70 powered by a power source 72.

The apparatus also includes a burner 74 which enters the fire compartment 28 and is connected to three pipes 78, 80 and 82. Pipe 78, which is fitted with a valve 84, serves

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to supply the burner 74 with hot compressed air from the blower 94 and the preheater 92u. Pipe 82, which is fitted with a valve 9G, is used to recycle to the burner 74 the combustible gas formed in the pyrolysis zone and separated from the hot carbonized material 5 in the cage 42. A lateral pipe 98, also connected to pipe 82 and fitted with a valve 100, serves to evacuate excess combustible gas and volatile liquid vapors from the device.

Pipe 60 is used to transport granular dry material 10 from cylindrical container 54 to hopper 32. Pipe 62 is used to transport the evaporated water in container 54 to heat exchanger 102, located in chimney 26. The evaporated water transported by pipe 62 and heated in heat exchanger 102 to be transformed into dry steam which is then injected into cylindrical jacket B.

The process according to the present invention is carried out using apparatus A, in the following manner:

During start-up, valve 84 is opened to allow fuel to flow through pipes 86 and 78 to burner 74, which is then ignited. Simultaneously, blower 94 is started to supply compressed air to burner 74 when valve 88 is open. The combustion of combustible gas and compressed air in compartment 28 heats the interior of furnace C, as well as that of furnace B 25, and the released gases are vented upwards through chimney 26 to heat heat exchangers 92 and 102. The first motor 18 is started to rotate furnace B. Dry sewage sludge is then introduced into hopper 32 to form a quantity of carbonized material which is discharged into cage 42 after being exposed to the heat of furnace C as it travels the length of furnace B. The discharge of the sludge into hopper 32 is now complete, and wet sewage sludge is introduced into the second hopper 64. Motor 72 is started to rotate the screw conveyor 70.

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conveying the wet sewage sludge into the cylindrical container 54 to mix it with the hot carbonized material discharged into the cylindrical container 54 via the pipe 46 when the valve 52 is in the appropriate position. The motor 58 is started to cause the screw conveyor 56 to rotate. The mixture of

5.

Hot carbonized material mixed with wet sewage sludge in container 54 produces a substantially dry mixture, and the water evaporated during this operation escapes through pipe 62 to the heat exchanger 102, where it is transformed into dry steam 5, which is injected into furnace B near its front end 10. Motor 36 is started to drive screw conveyor 34, which pushes the dry sludge, introduced into the first hopper 32 via pipe 60, into the rotating furnace B near its front end 10. The dry sludge is heated in furnace 10B as it moves towards the rear end 12. When the dry sludge is heated, it is converted into carbonized material and pyrolysis gas, which pyrolysis gas is a mixture of gaseous hydrocarbons and volatile liquid hydrocarbons. When a sufficient quantity of pyrolysis gas has been formed, valve 1596 is opened, and the gas pyrolysis can be switched to burner 74

to supply gas to heat the interior of the firebox C. Valve 84 can then be closed and the supply of combustible gas from an auxiliary source external to the equipment is finished.

If pyrolysis gas is produced in a quantity greater than that required to heat the interior of furnace C to the temperature necessary to pyrolyze the dry sewage sludge, valve 100 can be opened to allow the pyrolysis gas to be vented to a location outside the apparatus where it can be used to produce energy. The volatile liquid present in the excess pyrolysis gas can be recovered by cooling the gas vented via pipe 98 to a temperature below the liquid's condensation point. The heat of combustion provided by the combustion of the fuel in furnace C is not only used to transform the evaporated water passing through heat exchanger 102 into steam, but also to heat the air compressed by the blower 94 as it passes through heat exchanger 92 before being supplied to the burner 74. Valve 52 is used to regulate the flow rate of the carbonized material stream. flowing through pipe 46 to container 54 to be mixed with the wet sewage sludge 35. If, during operation, the apparatus produces more hot carbonized material than necessary for mixing with the wet sewage sludge in container 54, valve 52 can be used to divert the excess hot carbonized material through pipe 48. The flow of hot carbonized material through pipe 48 is regulated by valve 53.

6.

The steam passing from vessel 54 to the furnace is used to transform the carbonized material produced in the furnace into activated carbon. This activated carbon can be withdrawn in desired quantities via pipe 48. The remaining hot activated carbon 5 is used to transform the wet sewage sludge into a substantially dry material, which is subsequently introduced into the first hopper 32.

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7.

Claims (1)

CLAIMS 1 “A process for the pyrolytic treatment of residues containing significant amounts of both water and combustible organic matter, to produce a carbonized solid, a combustible gas and a volatile liquid, by continuously introducing the residue into an externally heated pyrolysis zone, in which the residue is subjected to a pyrolysis temperature in the absence of substantial amounts of free oxygen and by continuously removing the carbonized matter, gas and volatile liquid from this zone, characterized in that the wet residue is mixed with a portion of the hot carbonized matter removed from the pyrolysis zone to form a substantially dry granular product which is then introduced into the pyrolysis zone” 15 2. Method according to claim 1, characterized in that a portion of the combustible gas produced in the pyrolysis zone is mixed with preheated air and burned to provide the heat required for pyrolysis. 3. A process according to claim 1, characterized in that the mixing of the wet residue and the hot carbonized material is carried out in an enclosure and that the water vapor produced during the mixing operation is heated to form dry steam which is then introduced into the pyrolysis zone to transform at least a portion of the carbonized material into activated carbon. 4. Apparatus for the treatment of residues containing significant quantities of both water and combustible organic matter, characterized in that it is composed of: a) a furnace including a chimney; 30 b) a burner, equipped with gas and compressed air inlets, for heating the inside of the firebox; c) a rotating cylindrical pyrolysis oven, made of a rigid material with high thermal conductivity and housed in an inclined position in the firebox; 35 d) means for separating the pyrolysis gas and the hot carbonized material produced in the pyrolysis furnace and means for transporting said hot carbonized material from the furnace into a mixing container; e) means to receive the wet residue and mix it in 8. the mixing container with the hot carbonized material coming from the pyrolysis oven to produce a substantially soc mixture of water vapor; (f) means for transporting said substantially dry mixture 5 to a reservoir and means for transferring said substantially dry mixture from the reservoir into the pyrolysis oven; g) means for heating the water vapor produced in the mixing vessel and transforming it into dry vapor and for introducing this dry vapor into the pyrolysis oven; 10 h) energy sources and rotary joints necessary for the mechanical operation of the equipment; i) pipes and valves for passing residue, combustible gas, air and products resulting from the operation to, into and through the apparatus as required. 15.5. Apparatus according to claim 4, characterized raised in that it includes means for passing the pyrolysis gas produced in the pyrolysis furnace, from that furnace to the burner. rise in that it includes means for compressing a stream of air, means for preheating the compressed air and means for directing the preheated compressed air to the burner. 6. Apparatus according to claim 4, characterized 25