GB2277527A - Organic waste treatment method and apparatus - Google Patents

Abstract

A method and apparatus for the treatment of organic waste especially dewatered sewerage comprises heating the sludge to a temperature at which the waste breaks down into a combustible gas and a solid residue. The temperature can be at least 400 DEG C. Conveniently the waste is provided in the form of dried pellets and fed through a tube by a screw conveyor 30. The residues can be cleaned of residual carbon by exposing them whilst hot to an oxidising atmosphere. The gases can be cleaned possibly by distilling out impurities, and/or utilised as fuel for the process after optional mixing with air. The ash may be used to form tiles. <IMAGE>

Description

ORGANIC WASTE TREATMENT METHOD AND APPARATUS FIELD CF THE INVENTION The present invention concerns the treatment of organic waste especially sewerage sludge.

BACKGROUND OF THE INVENTION There is a problem in disposing of sewerage sludge of which there is a vast quantity. Present disposal tends to be dumping at sea but this is environmentally unacceptable. Burning of the waste is possible but not really perfect. The sludge is centrifuged to remove as much water as possible which water is purified for re-use leaving the sludge. If this sludge is dried 0 further by heating to say 150 C so sterilising it, the end product can be produced in the form of fuel granules. This fuel can then be burnt in conventional furnaces and the resulting heat used for electricity generation. However the sludge has a high ash content which becomes entrained in the air used for combustion and in addition it must be admitted that the combustion results in smells.

SUMMARY OF THE PRESENT INVENTION One aspect of the present invention provides a method of treating organic waste,especially sewerage sludge after dewatering, comprising heating said waste to a temperature at which it breaks down into a combustible gas and residues.

Such a temperature would be decided by experiment depending on the waste but tests on sundry wastes at above 4000 C have been satisfactory. Such a temperature is a combustion temperature and air, if any, in the sste ust be insufficient to support combustion. Usually, the combustible gas could be burnt efficiently and tends not to give smelly combustion products.

Another aspect of the present invention provides apparatus for treating organic waste, especially sewerage sludge after dewatering, comprising a furnace for heating the waste to a temperature at which it breaks down into a combustible gas and residues and means for collecting the residues and the gas.

In sone specific crises, the combustible gas can, at least in part, be -used in the furnace. However there nay be a need to purify the gas before burning it.

The residues from sewerage sludge will be in the form of an ash but has special properties somewhat similar to calcined clay.

Therefore a third aspect of the present invention provides a residue from sewerage waste for use as a building product for making tiles and bricks and the like resulting from heating the sewe1g:e sludge to 3. temperature sufficient to break it down into combustible gas and the residue.

Such a product can be used alone as a clay substitute or in admixtures.

When the residue is produced at lowish temperatures such as 4000C, the residue tends to be white with a black core, if at 6000C it tends to be pinkandasthetemperature is increased it becomes a darker pink and at about 11000C becomes brown. These are attractive cclours and make attractive end products.

A process for using these residues and an apparatus has been developed but is capable of use with other building product.

A further aspect of the present invention provides a process for making bricks and tiles and the like especially roofing tiles comprising calcining a raw material, mixing the calcined material with a limited amount of waterjinto a paste, pressing the paste into a desired shape, and firing the shape at a high temperaturs for a shortish time.

A yet further aspect provides apparatus for making bricks, tiles and especially roofing tiles, comprising means for calcining a raw material, means for mixing the calcired material with water to form a paste, a press for the paste te form the desired shape, and a high temperature kiln so the shapes can be fired at high temperature for a short time.

It has beil found that a two hour firing time coldto-cold can be achieved without excessive breakage.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of an apparatus for treating organic waste, Figure 2 is a similar schematic view of a second apparatus for treating organic waste, Figure 3 is a schematic view of apparatus for processing combustible gas produced in the embodiments of Figures 1 and 2, and Figure 4 is a schematic flow diagram for using the residue produced from the embodiments of Figures 1 and 2 using sewerage waste as the organic waste and for using other building products.

DESCRIPTION OF EXEMPLARY EEBODIMEWDS The embodiment of Figure 1 is especially suitable for treating wood waste and animal waste or other materials having a low calorific value. The waste is delivered by a first conveyor 11 in the form of an endless belt to a first hopper 12 from which it is extracted at a controlled rate by a second conveyor 14 such as an augur into a main sealed hopper 15; the rate is set by a motor 16 with an associated speed control (not shown). A tube 18 leads from this main hopper and is surrounded by a jacket 19 forming a furnace.

Fuel gas and air is supplied by a compressor 18 into the jacket to burn at a temperature of say 10000C thus heating the waste to about 6000 C at which temperature it evolves a combustible gas some of which is allowed to pass through holes 21 along the top of the tube into the sleeve where it burns. Other gas is removed from the tube by a take-off pipe 22 and returned to the compressor. Any excess combustible gas would be drawn off into a main 23 which is shown blanked off.

Products of combustion from the jacket are drawn out to an exhaust 24 by an aspirator 25,and a pump 26 establishes a below-atmospheric pressure at a discharge end z7 of the tube. Alternatively or additionally, this pressure can be established by the compressor 18. This pressure is transmitted along the tube into a space 27 defined by a baffle 28 keeping this space clear of the waste. This space communicates with the jacket through holes 29 so tending to trap the combustion at the hopper end of the jacket; it must be pointed out that the holes 21 are at this end of the tube. The waste is driven along the central tube by an augur 30 driven by a motor 3-l or by other means such as gravity (depending on the size of the tube and other factors). It will be apparent that the waste filling the hopper owl5, the second conveyor and the first hopper will impede air being drawn by the below-atmospheric pressure into the tube. On reaching the end of the tube, the treated waste now in the form of a residue is extracted by a further conveyor 32 such a worm and delivered into an outlet 33. This embodiment is especially suitable for treating wood waste and animal waste and in effect chars them into charcoal producing a relatively agreeable combustible gas.

In the embodiment of Figure 1 at least some of the gas is burnt and the combustion products exhausted to the atmosphere. Whilst gas, being more intimately mixed with combustion air than solid fuels could ever be, burns more cleanly than solid fuels, such burning may not be environmentally acceptable whether this is logical or nere prejudice if sewerage is involved.

The embodiment of Figure 2 avoids burning the gas evolved from the waste and exhausting its combustion products to atmosphere. It is very sinilar to the embodiment of Figure 1 so the same reference numerals will be used. The differences are that there are no holes 21 and 29 nor a takewoff pipe 22, and there is no space 27 or baffle needed. The gas main 23 feeds into a purification and storage facility 35 shown in greater detail in Figure 3.

In Figure 3, gas passing through the main 23 is first passed through a condenser 36 which is possibly a multi-stage condenser to remove any condensible components of the gas such as oils which are valuable and smelly if burnt. After the condenser there can be a filter 37 possibly of an activated charcoal. After filter, the gas would be received and stored in a reservoir 38 for subsequent burning possibly after more purification. It might be advantageous to use a water jacket in place of the insulation shown surrounding the jacket of Figures 1 and 2. This would not only recover heat but might establish temperature conditions wherein some undesirable components in the gas could recombine chemically with the residue.

Figure 3 also illustrates a valve arrangement, 39-41.

Either the gas can be directed fully into the reservoir or merely recirculated from and back into the reservoir.

In Figure 4, the residue from the plant of Figure 2 when used to treat sewerage sludge or a similar material of a calcined nature is mixed with 4 to 5% water into a dry paste in a mixer40 fed by a hopper 39, this paste is then formed into a desired shape in a press 41 and then fired in a furnace 42. With a low carbon content resulting from calcining and with a low water content the furnace can operate at high temperatures leading to a rapid treatment time so saving fuel which is the most expensive component in the cost of making roofing tiles and bricks.

If the residue from sewerage sludge contains undesirable carbon, it would be possible to introduce some oxygen into the waste so that the carbon would convert to carbon mon-oxide preferably when the residue -was still hot but after most of the treatment is completed either in the tube or in the product outlet.

It will be seen that the present invention provides a method of treating sewerage sludge amongst other wastes. Sewerage sludge is a pest of the modern age which is normally dumped at sea against environmental objections and at great expense. Sometimes the sludge is compressed before dumping at even greater expense.

It not only disposes of the sludge but yields gas which can be convertedinto electricity and a useful residue. In addition as bye-products it can produce heat and valuable oils.

Claims (17)

1. A method of treating organic waste, especially sewerage sludge after dewatering, comprising heating the waste to a temperature at which it breaks down into a combustible gas and residues.

2. A method according to claim 1 wherein the temperature is at least 4000C and any air present in the waste is insufficient to support combustion.

3. A method according to claim 1 or claim 2 wherein a gas containing oxygen is passed through the residues whilst still hot to remove any carbon from the residues.

4. A method according to any one of claims 1 to 3 wherein the residues are mixed with a limited amount of water to form a paste which is then pressed into a desired shape and fired at a high temperature for a shortish time.

5. A method according to any one of claims 1 to 4 wherein all the combustible gas is purified.

6. A method according to claim 5 wherein the gas is passed through a distillation assembly wherein various substances are separated out by condensing in various stages of the assembly.

7 An apparatus for treating organic waste, especially a sewerage sludge after dewatering, comprising a furnace for heating the waste to a temperature at which it breaks down into a combustible gas and residues and means for collecting the residues and the gas.

8. An apparatus according to claim 7 wherein the furnace comprises a tube through which the waste in pellet form is passed by a screw conveyor, the tube being surrounded by a heated suction jacket into which the gas escapes through perforations in the jacket and from which the gas is drawn off.

9. An apparatus according to claim 8 having a pump for taking some gas from the jacket and mixing it with air and then reintroducing the air-gas mixture into the jacket.

10. An apparatus according to claim 7 wherein the furnace comprises a tube through which the waste in pellet form is passed by a screw conveyor, the tube being externally heated with the combustible gas and residues being taken from the tube.

11. An apparatus according to any one of claims 7 to 10 wherein the waste is introduced into the furnace through a series of hoppers and conveyors at least one of the hoppers being sealed so that any air has to pasts through a considerable path within the waste so minimising air entry into the furnace.

12. An apparatus according to claim 11 wherein the waste is introduced into an open hopper from which it is removed by a screw conveyor into a sealed hopper from which it enters the furnace.

13. An apparatus wherein the residues are allowed to drop into a screw conveyor forming a hindrance to air entering the furnace.

14. An apparatus according to any one of claims 7 to 13 wherein the gas is drawn off into a distillation assembly wherein impurities are condensed out.

15. An apparatus according to any one of claims 7 to 14 wherein a duct for introducing a gas containing oxygen into the residues whilst still hot ensures that any carbon in the residues is burnt off.

16. An apparatus according to any one of claims 7 to 15 wherein the outlet for the residues leads to a mixer wherein the residue is mixed with water into a paste, the mixer feeding the paste into a press, and the pressed articles are then moved into a high temperature furnace.

17. A method of treating organic waste such as sewerage substantially as herein described.

18 An apparatus for treating sewerage sludge or other organic waste substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.