GB2356195A

GB2356195A - Organic waste treatment

Info

Publication number: GB2356195A
Application number: GB9926713A
Authority: GB
Inventors: Yves Guibert
Original assignee: SMS SA; HOPPAL Ltd
Current assignee: SMS SA; HOPPAL Ltd
Priority date: 1999-11-12
Filing date: 1999-11-12
Publication date: 2001-05-16
Anticipated expiration: 2019-11-12
Also published as: GB9926713D0; GB2356195B

Abstract

The invention relates to a method of controlled aerobic treatment in an enclosed environment for organic waste. This waste is mixed with quicklime in granulate form and at least one mineral absorbent, whilst maintaining hydration in order to develop the exothermic reaction. At least one binding material is added to the mixture before, during and after the exothermic reaction. The mixture is then left to age without mixing, whilst being ventilated. The quicklime comprises anhydrous calcium oxide made up of 4-10% of particles having an average size of less than 2mm, the rest of the particles having sizes between 2-90mm. An installation suitable for implementing the method is also described.

Description

2356195 A METHOD OF CONTROLLED AEROBIC TREATMENT FOR ORGANIC WASTE IN AN

ENCLOSED ENVIRONMENT AND A PLANT The present invention relates to a method of controlled aerobic treatment in an enclosed environment for essentially organic waste or residues and an installation designed to implement the method. The method proposed by the invention is a process of heat treatment at low temperature (approximately 3000C) by endogenic heat.

An open-air method of treating waste or hydrocarbon residues using anhydrous calcium oxide is already known from European patent application EP 0 306 430. This method consists in mixing the waste with the calcium oxide in the form of granulate, covering this mixture with an aggregate material such as sand, ash, earth or the product of incineration plants, mixing it and then leaving it for the exothermic reaction to develop. Of the granulate used, 3% is of a grain size of less than 3 mm and it contains particles of a size that may be up to 140 mm. The exothermic reaction lasts for between quarter of an hour and three hours, without the need for any subsequent ageing step.

At the end of this exothermic reaction, the product obtained is additionally heat-treated until the fumes have disappeared, in order to remove the hydrocarbons.

The drawback of this method is that it does not allow the gases given off by the chemical reactions, or the dust or amphoteric heavy metals (lead, zinc) present in the waste to be captured, thereby polluting the atmosphere.

In effect, the fact that a cover is provided by the aggregate materials as defined in this earlier 2 patent does not mean that all the volatile organic compounds given of f by the chemical reaction between the waste and the lime are captured.

Furthermore, the product resulting from this process is divided and contains a quantity of uncontrolled fines. Finally, this method does not enable all types of organic waste f rom hydrocarbons to be treated.

Accordingly, the objective of the invention is to propose a new method of controlled aerobic treatment for essentially organic waste and residues, in an enclosed environment, which comprises:

a) producing a mixture comprising waste, at least one mineral absorbent, at least one mineral binder and quicklime in granulate form, the lime essentially comprising anhydrous calcium oxide made up of 4 to 100-. of grains of an average grain size of less than 2 mm, the rest being made up of grains of an average grain size ranging between 2 and 90 mm, b) homogenising said mixture by mixing whilst hydrating it using at least one hydrating agent in order to initiate and then accelerate the exothermic reaction and recovering the gases given off by this reaction, c) then leaving the homogenised mixture comprising the 25 waste and all the reagents to age, without mixing, for a period ranging from 5 to 48 hours, whilst ventilating it by means of a ventilation agent so as to obtain a divided end product that can be put to a subsequent use.

Another objective of the invention is to propose a method of controlled aerobic treatment, in an enclosed environment, for essentially organic waste or residue, comprising:

a) producing a mixture comprising waste, at least one mineral absorbent and quicklime in granulate form, the 3 lime essentially comprising anhydrous calcium oxide made up of 4 to 100i of grains of an average grain size of less than 2 mm, the rest being made up of grains of an average grain size ranging between 2 and 90 mm, b) homogenising said mixture by mixing whilst hydrating it using at least one hydrating agent in order to initiate and then accelerate the exothermic reaction and recovering the gases given off by this reaction, the homogenisation process being effected by simultaneously adding at least one mineral binder, c) then leaving the homogenised mixture comprising the waste and all the reagents to age, without mixing it, for a period ranging from 5 to 48 hours, whilst ventilating it by means of a ventilation agent so as to obtain a divided final product that can be put to subsequent use.

A third objective of the invention is a method of controlled aerobic treatment, in an enclosed environment, for essentially organic waste and residue, comprising: a) producing a mixture comprising waste, at least one mineral absorbent and quicklime in granulate form, the lime essentially comprising anhydrous calcium oxide made up of 4 to 10-06 of grains of an average grain size of less than 2 mm, the rest being made up of grains of an average grain size ranging between 2 and 90 mm, b) homogenising said mixture by mixing whilst hydrating it using at least a f irst hydrating agent in order to initiate and then accelerate the exothermic reaction and recovering the gases given off by this reaction, c) then leaving the homo. genised mixture comprising the waste, all the reagents and a second hydrating agent to age for a period ranging from 5 to 48 hours, without mixing it, ventilating it by means of a ventilation agent, d) then adding whilst mixing at least. one mineral binder to the aged mixture, the exothermic reaction of which has terminated, so as to obtain a solid end product that can be put to subsequent use. 5 The lime grains of a grain size of less than 2 mm. also contain the fines, the average size of which is approximately ten microns. The end product, as obtained by each of the processes described above, complies with specific standards allowing it either to be stored in a landfill site, or used as a material for embankments, as coated f iller for roads or to be used as an ingredient in cement-making.

The binder may be added at different stages of the treatment process. The choice as to which stage will depend on the physical -chemical nature of the waste to be treated as well as the type and storage place of the end product. Adding the binder after the exothermic reaction, as outlined under the third objective of the invention, produces a solid end product. This embodiment can be used in particular if the end product is to be used for earthworks or for storage at landfill sites. The choice between the first and second embodiment will depend on the consistency and moisture content of the waste.

The advantage of the invention is that it avoids open-air processing with all its drawbacks, such as the dissemination of gases in the atmosphere which smell unpleasant or are harmful to the surrounding population, as well as dust. This new treatment also allows the heavy metals present in the waste to be trapped. Finally, the end product resulting from this process is in a divided form and has a controlled quantity of fines or may be in aggregate form exhibiting excellent mechanical strength. This aggregate form avoids the problem inherent in the heavy metals contained in the end product, which would otherwise be leached into the environment where it is stored. The method proposed by the invention has another advantage since it allows the operating parameters of the plant to be more efficiently controlled (residence time in the mixer, in the ageing tank, ventilation flow rate, flow rate of the water and reagent charges, temperature) during the course of treatment whereas the method proposed by the earlier document produces an end product of the "congealed" type, i.e. it is not possible to carry out treatment operations before the mixing temperature has reached ambient temperature.

is In effect, the various adjustments and measurements in terms of ingredients, selected at the start, can be applied during the treatment method depending on the consistency of the product after mixing, the temperature of the mixture in the ageing tank, the nature of the end product or alternatively the chemical nature of the gases released by the exothermic reaction.

In accordance with the method proposed by the invention, the grains of quicklime that are of a size of less than 2 mm allow the exothermic reaction hydrating the mixture to start homogeneously and rapidly and the grains of a larger size allow this exothermic reaction initiated by the more finely-sized grains to be prolonged in time. This extended timing means that the waste is treated to a higher quality.

After the reaction has progressed for one or two hours, the lime which is of a grain size of less than 2 mm no longer reacts as quicklime distributing the hydration heat but continues to act only in its capacity as an alkaline and pozzuolanic agent.

6 The waste that may treated. by the method proposed by the invention includes petroleum waste, oils and/or fats from hydrocarbons or mixtures thereof. The waste may also contain heavy metals. In particular, the method proposed by the invention allows amphoteric heavy metals to be treated, such as lead or zinc. The waste may be in liquid, pasty or solid form. The waste may be made up of solid petroleum residues, waste from evaporation lagoons for industrial effluents, hydrocarbon sludges which can not be excavated.

The binder may be chosen from among pozzuolanic reagents, natural or synthetic, hydraulic binders and mixtures thereof. The mineral absorbent may be selected from among alumino- silicates, calcium salts, natural or synthetic, and mixtures thereof. For the purposes of the invention, the presence of the hydraulic binder, the mineral absorbent and the lime enable leaching of the noxious products present in the waste to be better controlled than would be the case if only lime were used.

The end product resulting from the method may be partially recycled to fulfil the function of an absorbent. The hydrating agent may be water, clean or soiled, from a supply network or from a treatment process and/or provided by the waste if the waste contains f ree water, in which case it can be used f or the purposes of the hydration reactions. The ventilation agent may be selected f rom external air, gaseous emissions f rom. the various chemical reactions between the waste and the reagents and mixtures thereof.

The reagents are present in the waste in def ined proportions. By preference, the ratio by volume of quicklime to waste ranges between 0.05 and 1.5, the ratio by volume of mineral binder to waste being 7 between 0. 01 and 1 and the ratio by volume of mineral absorbent to waste being between 0.01 and 1.

If treating solid petroleum residues, the quicklime will be present in the greater proportion in order to treat the hydrocarbons. When treating waste from evaporation lagoons for industrial effluents, a hydraulic binder will form the majority proportion so as to ensure that the metals and soluble salts are retained. Finally, hydrocarbon sludges which can not be excavated will be treated by a process using mineral absorbent as the majority proportion so as to give the waste a minimum mechanical strength before subjecting it to subsequent treatment to render it capable of excavation.

Another object of the invention is a plant designed to implement the method as defined above and having a mixer designed to contain the mixture comprising the waste, mineral absorbent, quicklime, mineral binder and water. The mixer has at least three separate inlets for reagents and is connected by means of a conveyor device to an ageing tank designed to contain this mixture.

The plant will preferably also have a means for recovering heat, arranged on the ageing tank. The heat recovered can be used to heat waste present in solid form to a temperature of about 200C and that present in liquid f orm. to ap proximately 350C, such as bitumens or tars.

The plant will now be described in more detail in conjunction with the illustrative diagram of the plant.

The description below is not restrictive in any respect.

The single drawing is a schematic lateral view of the plant proposed by the invention.

8 The drawing illustrates. the plant, generally indicated by reference 1. This plant comprises a mixer 2 provided with a helical screw 3 designed to mix the contents of the mixer 2. The mixer 2 may be a vertical shaft mixer (of the central concrete type), a horizontal shaft mixer (of the fired earthenware plant type), or a mobile shaft mixer (of the concrete mixer type). The mixer, substantially cylindrical in shape, is made from protected steel. The helical screw used for mixing purposes rotates at approximately 20 revolutions/minute. The input of the mixer 2 has an inlet hopper 4 for the waste to be treated, arranged on one of the vertical sides of the mixer 2. Arranged at the upper part 2a of the mixer 2 are three inlets 5, 6 and 7 for reagents. These inlets 5, 6 and 7 correspond respectively to the absorbent mixture, granulated quicklime, on the one hand, the mineral binder on the other and finally water. Each of the inlets 5, 6 and 7 is connected to inlet hoppers (not illustrated in the drawing).

The quicklime contains 60-o of grains of a size of less than 2mm and 4011 of grains of a size of 50 mm. The mineral binder added consists of fly ash. The absorbent is anhydrous calcium sulphate. If mixing is applied continuously, the reagents are added all at once. If mixing is intermittent, they are incorporated gradually.

If the waste to be treated needs an external hydrating agent, the reagents are preferably added -in the following order, binder followed by quicklime and finally the hydrating agent. The absorbent agent is the first reagent to be added for the purposes of the method proposed by the invention. In the case of the third embodiment of the invention, the binder along with a top-up of hydrating agent are added at the end 9 of the exothermic reaction. In this embodiment, the partially treated waste is therefore returned to the mixer 2 after ageing.

This mixture is mashed in the mixer f or a maximum for 15 minutes. During this step, the exothermic reaction enters the waste and the quicklime causes gases to be released, which are recovered at the top part of the mixer by means of a duct 8. These gases are then fed to a processing device 9. The gases given off by the exothermic reaction may also be introduced singly or mixed with outside air into the tank 11 by means of an injection device 13. The mixer 2 operates at a throughput rate ranging between 5 and 10 Te/hour.

The mixer 2 is also connected via a conveyor device 10, such as conveyor belts, arranged in the bottom part of the mixer, to an ageing tank 11. This tank 11 also has an inlet for outside air 12 at its upper part. The residence time in the reaction tank ranges between 5 and 48 hours, depending on how quickly the exothermic reaction progresses.

The plant I proposed by the invention operates in the following manner.

The waste to be treated is f ed on a conveyor into the mixer 2, where it is mixed with the various reagents. The mineral absorbent is introduced f irstly into this mixer, its main function being to thicken any waste present in liquid or pasty form. The quicklime is added next, which initiates and maintains the exothermic reaction within the enclosure of the mixer 2. Finally, only water is added during mixing in order to hydrate this mixture and thus accelerate the kinetic action of the exothermic reaction. The mixture comprising the waste and reagents is mixed for a maximum of 15 minutes. 35 Simultaneously with this mashing process, the gases released by the various chemical reactions are drawn of f f rom the mixer 2 and f ed to a processing device 9. Some of these gases are recycled to the ageing tank 11 in order to ventilate the mixture 5 comprising the waste and reagents.

Having been mashed, this mixture is then fed to an ageing tank 11, where it is left to age. This mixture remains in the tank for 24 hours. During this ageing step, the mixture is regularly and constantly ventilated by an intake of air from outside mixed with the recycled gases.

The moisture is incorporated in the mixture in the mixer only and ventilation takes place in the reaction tank only.

When this step of ageing the waste has been completed, the waste is removed f rom the tank 11 to be stored in a storage zone. The noxious components are trapped in the internal structure of the end product resulting from this treatment.

The examples of mixtures comprising waste and reagents described below are given solely by way of illustration.

EXAMPLE 1: Waste from an evaDoration lacTuna for several industrial effluents These effluents, which are of a liquid consistency, have a moisture content in excess of 60-0 In particular, these effluents contain organo halogenated compounds and heavy metals, including some which are amphoteric (lead and zinc).

The soluble fraction of the dry waste is very high; it is greater than 300-..

The mixture of waste and reagents is present in the following proportions, expressed as a percentage by volume relative to the raw waste:

- Anhydrous calcium sulphate (absorbent) 10 - Quicklime 30 - Aluminous cement (binder) 30 - Water 0 The method is implemented in the following manner.

The waste is mixed with the mineral sponge in a buffer lagoon. This mixing process thickens the waste.

The thickened waste is then loaded into a mixer, into which the quicklime and aluminous cement are introduced. This final mixture is then. transferred to an ageing tank where it is left for 36 hours before being drawn off for storage in a conventional storage zone. The end product is then stored in a landfill site.

EXAMPLE 2: Dredged sludges These sludges are of a pasty consistency and have a moisture content in excess of 60-..

In particular, these sludges contain oils and fats in a quantity greater t han 50- of the dry extract, amphoteric heavy metals (lead, zinc) and phenols. The soluble fraction accounts for less than 10% of the dry extract.

The mixture treated by the method of the invention contains the following elements, expressed as a percentage by volume relative to the raw waste:

- Anhydrous calcium sulphate (absorbent) 5 - Quicklime 20 - Active silica (binder) 25 - Water 0 The method consists in thickening the waste by introducing the mineral sponge into a buffer lagoon. The thickened waste is then loaded into a mixer so as to be mixed with the reagents and then conveyed to an ageing tank for 15 hours before being stored with a 12 view to subsequent use.

EXAMPLE 3: Sullphurous tars from oil refinin This waste, of a solid consistency, has a moisture 5 content of less than 20W.

The waste contains oils and f ats in a proportion of approximately 80-. relative to the total weight. It also contains heavy amphoteric metals (lead, zinc). This waste has a high acidity with a pH equal to 2.

The mixture, comprising the waste and the reagents, contains the following compounds, expressed as a percentage by volume relative to the raw waste:

- Recycled product 50 - Quicklime 100 - Aluminous cement 40 - Water 100 The recycled product is defined as being the divided product from waste treated fully or partially by the method proposed by the invention. It enables the waste upstream of the treatment to be neutralised if the waste constitutes sulphurous tars due to its high pH. This high pH value is sought by a brief ageing process or by dispensing with the addition of mineral binder. 25 In the mixer, the waste is mixed with the recycled product, water and quicklime. It is then transferred to a reaction tank where it remains for approximately 24 hours. Finally, it is then mixed with cement and water before being stored with a view to subsequent use.

EXAMPLE 4: Petroleum tank residues The waste from the bottom of petroleum tanks is of a pasty consistency, having a moisture content of 13 approximately 40%.

The waste contains oils and fats in a proportion of approximately 30%.

The waste and the reagents are present in the following proportions, expressed as a percentage by volume relative to the raw waste.

- Recycled product 20 - Quicklime 30 - Active fly ash 20 - Water 0 The waste is firstly thickened in a buffer lagoon by introducing the recycled product. It is then introduced into a mixer where it is mixed with the reagents. The mixture obtained is then fed into an ageing tank where it remains for approximately 24 hours before being rendered inert relative to the environment in which it will be stored.

14

Claims

C L A I X S

1. A method of controlled aerobic treatment in a closed environment for essentially organic waste or residue, comprising:

a) producing a mixture comprising waste, at least one mineral absorbent, at least one mineral binder and quicklime in granulate form, the lime essentially comprising anhydrous calcium oxide made up of 4 to 1001 of grains of an avera ge grain size of less than 2 nun, the rest being made up of grains of an average grain size ranging between 2 and 90 mm, b) homogenising said mixture by mixing whilst hydrating it using at least one hydrating agent in order to initiate and then accelerate the exothermic reaction and recovering the gases given off by this reaction, C) then leaving the homogenised mixture comprising the waste and all the reagents to age, without mixing, ventilating it for a period ranging from 5 to 48 hours by means of a ventilation agent so as to obtain a divided end product that can be put to a subsequent use.

2. A method of controlled aerobic treatment in a closed environment for essentially organic waste and residue, comprising: a) producing a mixture comprising waste, at least one mineral absorbent and quicklime in granulate form, 30 the lime essentially comprising anhydrous calcium oxide made up of 4 to 10t of grains of an average grain size of less than 2 mm, the rest being made up of grains of an average grain size ranging between 2 and 90 nm, b) homogenising said mixture by mixing whilst hydrating it using at least one hydrating agent in order to initiate and then accelerate the exothermic reaction and recovering the gases given of f by this reaction, the homogenisation process being effected by simultaneously adding at least one mineral binder, C) then leaving the homogenised mixture comprising the waste and all the reagents to age, without mixing it, for a period ranging from 5 to 48 hours, whilst ventilating it by means of a ventilation agent so as to obtain a divided f inal product that can be put to subsequent use.

3. A method of controlled aerobic treatment in an enclosed environment for essentially organic waste or residues, comprising: a) producing a mixture comprising waste, at least one mineral absorbent and quicklime in granulate form, the lime essentially comprising anhydrous calcium 20 oxide made up of 4 to 100-. of grains of an average grain size of less than 2 mm, the rest being made up of grains of an average grain size ranging between 2 and 90 mm, b) homogenising said mixture by mixing whilst 25 hydrating it using at least a first hydrating agent in order to initiate and then accelerate the exothermic reaction and recovering the gases given off by this reaction, C) then leaving the homogenised mixture comprising 30 the waste, all the reagents and a second hydrating agent to age for a period ranging f rom 5 to 48 hours, without mixing it, ventilating it by means of a ventilation agent, d) then adding whilst mixing at least one mineral 35 binder to the aged mixture, the exothermic 16 reaction of which has terminated, so as to obtain a solid end product that c an be put to subsequent use.

4. A method as claimed in one of claims 1 to 3, characterised in that the waste may be chosen from petroleum waste, oils and fats produced from hydrocarbons and mixtures thereof, said waste containing heavy metals and optionally being in liquid, pasty or solid form.

5. A method as claimed in one of claims 1 to 3, characterised in that the binder is selected from pozzuolanic reagents, natural or synthetic, hydraulic 15 binders and mixtures thereof.

6. A method as claimed in one of claims 1 to 3, characterised in that the mineral absorbent is selected from alumino-silicates, natural or synthetic calcium 20 salts and mixtures thereof.

7. A method as claimed in one of claims 1 to 3, characterised in that the hydrating agent is chosen from clean or soiled water, or the free water present in the waste.

8. A method as claimed in one of claims 1 to 3, characterised in that the ventilation agent is chosen from among air, the gaseous emissions from the exothermic reaction and mixtures thereof.

9. A method as claimed in one of claims I to 3, characterised in that the ratio by volume of quicklime to waste ranges between 0.05 and 1.5, the ratio by volume of mineral binder to waste being between 0.01 17 and 1 and the ratio by volume of mineral absorbent to waste being between 0.01 and 1.

10. A plant designed to implement the method as claimed in one of the preceding claims, characterised in that it has a mixer designed to contain the mixture comprising the waste, mineral absorbent, quicklime, mineral binder and water, said mixer having at least three inlets for reagents and being connected by means of a conveyor device to an ageing tank designed to contain said mixture.

11. A plant as claimed in claim 10, characterised in that it has a heat recovery means arranged on the ageing tank.

12. A plant as claimed in claim 10, characterised in that the mixture remains in the ageing tank for a period ranging between 5 and 48 hours.

13. A plant as claimed in claim 10, characterised in that the mixer operates at a throughput ranging from 1 to 10 n?hour.

14. A method of controlled aerobic treatment in a closed environment for essentially organic waste or residue substantially as hereinbefore described with reference to the accompanying drawing.

15. A plant for controlled aerobic treatment in a closed environment of essentially organic waste or residue substantially as hereinbefore described with reference to the accompanying drawing.