IE46544B1

IE46544B1 - Sewage sludge pyrolysis

Info

Publication number: IE46544B1
Application number: IE42/78A
Authority: IE
Original assignee: Arcalon Gen Petroleum
Priority date: 1977-01-07
Filing date: 1978-01-06
Publication date: 1983-07-13
Also published as: IE780042L; AU3228578A; FR2376894A1; JPS53111301A; NL7800162A; DK6478A; BE862701A; GB1597517A; IT7847547A0; DE2800030A1; CH621318A5; FI780046A; MC1188A1; IT1104151B; DE2800030B2; PT67495A; SE7800143L; NO780047L; DE2800030C3; LU78830A1

Abstract

The apparatus serves for the conversion of sewage sludge by pyrolysis into a solid material, which is at least partially composed of activated charcoal, and pyrolysis gas, in which process the moist sludge, with exclusion of air, is conducted through a rotary tube (B) which is indirectly heated by a combustion chamber (C) and brought to pyrolysis temperature. At least a part (46) of the carbon-containing material exiting from the rotary tube (B) is continuously mixed with the wet sludge (66). The vapour formed in the mixing of the wet sludge with the carbon-containing material is heated (102) and fed as superheated steam (104) to the rotary tube (B). The essential parts of the apparatus are the inclined rotary tube (B), the combustion chamber (C) surrounding this and a burner (14) connected to it having an associated blower (94) and a hopper (61) provided upstream of the rotary tube (B). The delivery opening (12) of the rotary tube (B) is connected air-tightly via a seal (22) to a housing (42) having a rising pipe (50) and a descending pipe (44).

Description

This Invention relates to,a process and apparatus for the pyrolysis of refuse The scarcity of acceptable land fill sites and recent incidents of beacli pollution caused by ocean dumping of sludge has greatly increased the need to develop a different method for the disposal of municipal and industrial refuse, such as sewage sludge.

One current method is to burn refuse in multiple hearth and fluid bed incinerators. However, such incinerators require large quantities of auxiliary fuel .and are environmentally unacceptable in some communities.

A primary purpose in devising the present invention is to supply a process of pyrolyzing refuse containing substantial proportions of both water and combustible organic material that is substantially free of the operational disadvantages of prior art methods, and one that is environmentally acceptable. The present process produces activated carbon from the refuse that may be used to reduce pollution in the water discharged from waste water treatment plants.

Although in the following paragraphs the invention will be described with particular reference to wet sewage sludge it will be clear that it is equally useful for other types of municipal and industrial refuse containing substantial quantities of both water and organic material.

In the present process the sewage sludge, which is very viscous and sticky because of its high moisture content, is mixed with recycled hot carbonaceous material resulting from the process to produce a dry, free-flowing product, as well as the discharge of a substantial quantity of water vapor that is subsequently transformed to dry steam. The quantity of the CEsybonaceous material that must be recycled in the process, depends on the initial sludge condition and operating condition of the apparatus used in carrying out the process.

In the present process, only a first portion of the carbonaceous material is recycled, with a second portion of this material in the form of activated carbon being removed from the apparatus. This second portion is then available for use in reducing the pollution in the water discharged from the waste water treatment plant. The present process lias the operational advantage that heating of the - 2 - 3 4G344 ambient atmosphere adjacent to the pyrolyzing operation is minimized by surplus heat from the operation being utilized to transform water to steam that is used to at least partially transform carbonaceous material from the operation to activated carbon. Also,’ a portion of the surplus heat may be used to preheat the air which is used to burn the pyrogas to provide the heat required to sustain the pyrolysis reaction.

In a preferred embodiment Of the process excess combustible gas produced in the pyrolysis reaction is used as fuel to supply the external heat required for the reaction. However, when the process is being started up, it is necessary to use fuel gas from an external source until the production of pyrogas is sufficient to sustain the reaction. The supply of external fuel gas can then be discontinued. If the production of pyrogas is in excess of the amount required for the pyrolysis the surplus can be withdrawn and used for another purpose such as, for instance, to raise steam or as fuel for an internal combustion engine. Thus, the surplus energy can be used to supplement the energy required for the treatment plant.

The process of the invention may be carried out by use of an apparatus as illustrated in FIG. 1. The apparatus includes a housing A constructed from refractory material in which an elongated cylindrical shell B is placed that serves as a pyrolysis kiln and is constructed from a rigid material that has good heat conductivity, such as steel. The shell B includes a front end 10 and rear end 12 with a ring gear being secured to the shell B, adjacent to the front end. The shell β is in a slightly inclined position, so that when the shell is rotated, material in the shell will move by gravity downward through the cylinder. The ring gear 14 is engaged by a driven gear 16, which is rotated by a power source, such as an electric motor 18.

Both ends 10 and 12 are secured to rotatable seals 20 and 22. A fire box C is provided that has an elongated portion 24 and a flue gas exhaust stack 26 extending upwardly therefrom. The fire box is in communication with a flamechamber 28. The pyrolysis kiln B is fed from hopper 32 which is connected lo the kiln by means of . 4 . 465 44 a tubular discharge unit 30 provided with a screw conveyor 34 which is driven by a power source 36. The pyrolysis kiln is connected to the discharge unit by means of a rotatable seal 20 which allows the kiln B to rotate. The kiln B is rotatably supported in the fire box C by two bearing assemblies 38 and 40. The rotatable seal 22 is connected to a housing 42 that has a downwardly extending tubular portion 44 that develops on the' lower end into the discharge tubes 46 and 48. A tube 50 extends upwardly from the stationary disengaging chamber 42, in which the combustible gas with the vapors of the volatile liquid are separated from the hot carbonaceous material. A valve 52 is situated at the junction of the discharge outlet 44 with the tubes 46 and 48, to permit desired quantities of material to flow into either tube. A valve 53 is mounted in the tube 48 to control the flow of material from this tube.

The tube 46 is connected to the interior of a mixing vessel 54 that has a screw conveyor 56 which is driven by a power source 58.

The end of the cylindrical vessel 54 develops into two tubes 60 and 62.

A hopper 64 or other suitable receiving container is provided into which wet sewage sludge may be sequentially deposited, which hopper is connected to a tubular housing 68 that is in communication with the cylindrical vessel 54. At least a portion of the tubular housing 68 is provided with screw conveyor 70 driven by a power source 72. Protruding into the flame chamber 28 a burner assembly 74 is provided, which has connections with three tubes 78, 80 and 82. The tube 78, which is provided with a valve 84, serves to feed fuel gas to the burner 74. The tube 80 serves to feed compressed hot air from blower 94 and preheater 92 to the burner 74. The tube 82, provided with a valve 96 is used to recycle combustible gas formed in the pyrolysis zone, and separated from the hot carbonaceous material in the disengaging chamber 42, to the burner 74. Also connected to tube 82 is the lateral tube 98 provided with valve 100 which is used to withdraw the surplus combustible gas and vapors of the volatile liquid from the apparatus.

Tube 60 serves to pass dry granular material from the vessel 54 to the hopper 32. Tube 62 is used for passing water vapor from the vessel 54 to heat exchanger 102, situated within the stack 26. Water vapor from tube 62 that has been heated to form dry steam in heat exchanger 102 is introduced into the cylindrical shell B. -5 When the process is initiated the valve 81 opened to permit fuel to flow through the tubing 78 to the burner assembly 74 while it is ignited. Com urrenl ly, the blowei 94 is actuated to supply compressed air to the burner 74 when the valve 88 is open. The combustion of the fuel gas and compressed air in the compartment 28 results in the interior of the fire box C being heated, together with the kiln B, and the flue gases flowing upwardly through the stack 26 to heat the heat exchangers 92 and. 102. The first power source 18 is actuated to cause rotation of the kiln B. Dry sewage sludge is then deposited in the hopper 32 to obtain a quantity of carbonaceous material that discharges into the housing 42 after it has been exposed to the heat of the fire box C in traversing the length of the kiln B. The discharge of sludge into the hopper 32 is now terminated and wet sewage sludge is discharged into the second hopper 64. The power source 72 is actuated to cause rotation of the screw conveyor 70, with the wet sewage sludge being discharged into the cylindrical vessel 54 to mix with hot carbonaceous material that discharges into the vessel 54 through the tube 46 when the valve 52 is moved in appropriate position. The power source 58 is actuated to cause rotation of the screw conveyor 56. The mixture of hot carbonaceous material and wet sewage sludge in the vessel 54 results in the mixture being transformed to a substantially dry mixture, with the water vapor resulting from this transformation flowing through the tube 62 to the heat exchangerl02 where it is transformed into dry steam that is discharged into the kiln B adjacent to the front end 10. The power source 36 is actuated to driv^ the screw conveyor 34 to move dry sludge delivered to the hopper 32 from the tube 60 into the rotating kiln B adjacent to the front end 10. The dry sludge is heated in the kiln B as it moves downward towards the rear end 12. As the dry sludge is heated, it is transformed into carbonaceous material and pyrogas, which pyrogas is a mixture of hydrocarbon gases and volatile liquid hydrocarbon. When the pyrogas is being generated in sufficient volume, the valve 96 is opened, and the pyrogas allowed to flow to the burner - 6 _ assembly 74 to supply gas to heat the interior of the fire box C. Subsequently, the valve 84 is closed and'the supply of fuel gas from an auxiliary source apart from the apparatus is terminated.

Should pyrogas be generated in quantities greater than that necessary to heat the inferior of the fire box C to the temperature necessary to pyrolyze the ary sewage sludge, the valve 100 may be opened to permit pyrogas to be withdrawn from the apparatus where it may be used for energy, generating purposes. The . volatile liquid present in the excess pyrogas may be recovered by cooling the gas withdrawn through tube 98 to a temperature below the condensation point of the liquid. Heat of combustion from, the burning of the fuel in the fire box C is utilized not only to transform water vapor flowing through the heat exchanger 102 to steam, but also to heat the compressed air from the blower 94 as it passes through the heat exchanger 92 prior to the air being delivered to the burner assembly 74. The valve 52 is utilized to regulate the rate of flow of hot carbonaceous material through the tube 46 through the vessel 54 to mix with the wet sewage sludge.

If the operation of the apparatus results in the production of more hot carbonaceous material that is necessary to mix with the wet sewage sludge in the vessel 54, the valve 52 may be used to divert the excess hot carbonaceous material to the second tube 48. Flow of hot carbonaceous material from second tube 48 is controlled by valve 53.

The steam passing frojn the vessel 54 into the kiln serves to transform the carbonaceous material produced in the kiln into activated carbon. This activated carbon may be recovered from the tube 48 in desired amounts. The balance of the activated carbon in the hot state is used to transform the wet sewage sludge into substantially dry material that is subsequently delivered to the first hopper 32.

Claims

1. A process for the treatment of refuse containing substantial quantities of both water and combustible organic material by means of pyrolysis to produce a solid carbonaceous material, a combustible gas and a volatile liquid by continuously feeding the refuse into an externally heated pyrolysis zone, in which the refuse in the absence of substantial quantities of free oxygen is subjected to a pyrolyzing temperature, and continuously·,withdrawing the carbonaceous vapour of the liquid . material, the gas and the/liqiiid from that zone, characterized in that the wet refuse is mixed with part of the hot carbonaceous material withdrawn from the pyrolysis zone to form a substantially dry granular product, which is subsequently introduced into the pyrolysis zone.

2. A process as defined in Claim 1. characterized in that part of the combustible gas produced in the pyrolysis zone is mixed with preheated air and burnt to provide the heat required for the pyrolysis.

3. A process as defined in Claim 1., in which the mixing of the wet refuse and the hot carbonaceous material is performed in a confined space and the water vapor produced in the mixing operation is heated to form dry steam which is subsequently introduced in the pyrolysis zone to transform at least part of the carbonaceous material into activated carbon.

4. Apparatus for the treatment of refuse containing substantial quantities of both water and combustible organic material comprising:a. a fire box provided with a stack; b. a burner assembly provided with inlets for gas and pressurized air for heating the interior of the fire box; c. a rotatable cylindrical pyrolysis kiln constructed from a rigid material having substantial heat conducting characteristics located in an inclined position within the fire box; d. means for separating the pyrogas and the hot carbonaceous material produced in the pyrolysis kiln and means for transporting said hot carbonaceous material from the kiln into a mixing vessel; -8ε. means for receiving wet refuse and mixing the same in the said mixing vessel with hot carbonaceous material leaving the pyrolysis kiln to produce a substantially dry mixture and water vapor; f. means for transporting said substantially dry mixture to a container, and means for introducing said substantially dry mixture from the container into the pyrolysis kiln g. means for heating the water vapor generated in the mixing vessel to dry steam and'for introducing the same into the pyrolysis kiln; h. power sources and rotatable seals as required for the mechanical operation of the apparatus; i. tubes and valves for passing the refuse, fuel gas, air and the products resulting from the operation to, from and through the apparatus as required.

5. Apparatus as defined in Claim 4,, comprising means for passing the pyrogas produced in the pyrolysis kiln to the burner assembly.

6. Apparatus as defined in Claim 5., comprising means for pressurizing a stream of air, means for preheating the pressurized air and means for directing the preheated pressurized air to the burner assembly.