WO2000046324A1 - Treatment of waste materials - Google Patents

Abstract

The invention relates to reclaimed waste product which has a solid, particulate consistency at ambient temperature and which is the result of the reaction of lime with water carried out in the presence of a blend of carbon-based waste products made up to contain components selected from at least two of the following groups of waste products derived from the production of liquid or gaseous fuel from coal or similar processes, namely: (a) the group consisting of oils, tars, pitches and mixtures thereof; (b) the group consisting of coal dust, spent Funda filter medium and mixtures thereof; and (c) the group consisting of coal ash, underlay and mixtures thereof. The invention further discloses methods for producing such reclaimed waste product and procedures for its utilization as a fuel to produce energy which may in turn be recycled to the industry in which the waste product was produced.

Description

TREATMENT OF WASTE MATERIALS

FIELD OF THE INVENTION

THIS invention relates to a method of converting carbon-based waste products

into stable, utile products. The terms " carbon-based products" or "carbon-based

materials" are herein intended to embrace carbonatious materials, hydrocarbons

and other compounds containing carbon atoms. More particularly, but not

exclusively, this invention is concerned with the treatment of environmentally

hazardous waste materials originating from the production of gaseous or liquid

fuels from coal or gas. One embodiment of the invention is aimed at the

production of solid fuel products. Such manufactured fuel may be adapted to

be suitable for use, inter alia, in the generation of useful forms of energy, such

as steam, electricity or heat, which may, for example, in turn be utilized in the

plant in which the said carbon-based waste products were originally produced.

It may also be adapted to be used as a carbon source for the production of

syngas and hydrocarbons. The product may further find various other

applications such as a landfill site liner or road building component.

BACKGROUND TO THE INVENTION

The production of liquid and/or gaseous fuel from coal gives rise to a large

quantity of waste products of varied composition.

The first stage in such production is the mining, milling and transportation of the

coal to a gasification plant. During this stage coal dust is produced in vast quantities. It has been estimated that about 30% of mined coal converts to coal

dust during this stage. While some of the coal dust may be used as fuel in

certain furnaces, the difficulties associated with its transportation due to its

powdery consistency, and the vast quantities thereof, inevitably leads to a

substantial percentage of coal dust being treated as a waste material requiring

disposal in an environmentally acceptable manner. Such coal dust is one of the

carbon-based products with which this invention is concerned in seeking to find

a solution for the environmental aspect thereof.

The second stage of the production process of gaseous and liquid fuels from

coal involves the gasification of the mined coal to form synthesis gas, also

known as "syngas^'', composed of hydrogen and carbon monoxide. In essence

this stage involves the reaction between carbon, steam and oxygen in a gasifier.

The gaseous and entrained reaction products produced in the gasifier are

passed through a gas scrubber in which the desired syngas component thereof

is separated from by-products which typically include hydrogen sulfide,

ammonia, carbon dioxide, tars and phenols. Some of these by-products may be

utilized in other chemical reactions. A large part thereof is however a waste

product to which further reference is made below. Ash is a further waste

product produced in large quantities during gasification stage, both in the

gasifiers itself and in boilers used for the generation of the large quantities of

steam consumed in the production of syngas. Synthesis gas produced from coal in the manner referred to above may itself be

used as a gaseous fuel, or may be utilised as a starting material for the catalytic

conversion thereof into hydrocarbons useful as fuels. The Fischer-Tropsch

process and the Synthol process as are, for example, utilized in South Africa by

Sasol Limited [hereinafter "Sasol'] in the production of synthetic liquid fuels,

such as gasoline and diesel, waxes and other chemical compounds, are

examples of such synthesis processes. A more detailed outline of the Synthol

process as operated by Sasol at its Sasolburg site in South Africa is contained in

US patents 4111792, 4052477, 4126644, 4049741, 4045505 and 4041094 all

issued to Mobil Oil Corporation. The processes operated at Sasol's other site

located at Secunda, also in South Africa, are similar in nature though not in

detail.

The synthesis processes referred to above likewise give rise to large quantities

of waste products of varied composition which need to be separated from the

desired end product composition. Some of the separated by-products may be

used in other processes. A large part thereof is however waste product for

which no economically feasible use has thusfar been devised. One such waste

product produced at the Sasolburg site of Sasol is known as "Funda" and is a

spent filter medium. Its composition is presently unknown but is believed to be

a spent activated carbon powder saturated with a variety of filtered solids and adsorbed liquids of presently unknown composition. The waste streams from

the synthesis process further comprise waxes, paraffin oils, tars, pitch, process

water sludges (also sometimes called solids), process water commonly referred

to in the case of the Sasol process as RASAMU, fatty acids (e.g. acetic acid),

diesel, benzene, wash water containing a variety of salts and other solutes,

spent catalysts and so-called "synthol gunk'. These streams are collected by a

drainage system into so-called "API dams^'' and are called "API sludges^''.

The waste materials referred to above combined with "tank bottoms", a sludge

removed during cleaning of fuel storage tanks are collectively referred to as

"black products" by Sasol and that meaning is also intended to be applied to the

expression where it is used in this specification.

Such black products have, in the case of the Sasol by-products, not found a

process by which it may be converted into a useful product. The result is that it

has over many years been accumulated in so-called "tar pits". These tar pits

are in the form of large bunded wall reservoirs of which the walls are formed

from coarse coal ash derived from the gasifiers or boilers in which steam is

produced. The contents of these pits are, by their very nature, of heterogeneous

composition. Over the years the large variety of by-products or waste streams

referred to above have been disposed of in these pits. Water is present as a

component of the composition of the pits as a result of rain falling on the surfaces of the pits, and as a result of water being an ingredient of some of the

waste streams and further as a result of ground water seeping into the pits.

Emulsions are consequently also present in the pits. It has been observed by

the present inventor that the water present in the tar pits of Sasol has an

extremely high Chemical Oxygen Demand (COD) which measures as high as 75

000.

Over the years the various components in the pits have tended to separate into

layers. Thus layers of waxes and paraffin oil typically form at the surface of the

pits and layers of progressively denser material are stratified at deeper levels of

the pits. None of these layers are of a homogenous chemical composition.

Over the years the ash layers of the bunded walls, which have periodically been

increased in height and width, have become saturated with at least some of the

components of the waste materials disposed of in the reservoirs. Such

saturated layers of the ash walls and floor of the pits is commonly referred to as

"underlay. For the purpose of this specification the soil surrounding the tar

pits, and which has become contaminated with at least some of the components

present in the tar pit, shall be considered to constitute part of the underlay

despite it not being composed primarily of the ash from which the walls and

floor are constructed. BRIEF DESCRIPTION OF THE PRIOR ART

The manner in which the aforementioned waste products, including the coal

dust, process waste products, ash and underlay have been disposed of in the

past, is no longer considered to be environmentally acceptable.

Various attempts have been made by several people to convert the most

unacceptable component of the aforementioned waste, namely the content of

the tar pits, into a useful product, but with limited success.

The use of such tar as a fuel has been suggested in view of its high

hydrocarbon content which gives it a relatively high calorific value. However, the

conveyance of the tar pit contents to, and into, a furnace at a power station or

steam generator present a major problem due to the sticky consistency thereof.

This property leads to blockages, and furthermore, some components in the tar

pit content are aggressive to the rubber conveyor belts on which it would

preferably be conveyed.

One of the attempts to convert such tar into a more manageable briquette-like

form by mixing and compressing it with fine coal resulted in a product that,

although reasonably acceptable at lower temperatures, is prone to disintegration

and tended to melt while in stockpile, and was hence unacceptable as a

solution. Another approach was to render the tars environmentally inert and suitable as a

landfill material by solidification or fixation of the tar with the aid of lime.

Although that process did render a solid product, it was not considered

acceptable for two reasons. First the resultant product was in the form of a

very fine powder which was poorly compactable and readily airborne and hence

unsuitable from an ecological point of view. Secondly, the manner in which the

process was performed gave rise to a reaction which was highly exothermic with

the concomitant vaporization of components of the volatile components of the

tar thus creating a danger of combustion of the evolved fumes.

The fixation of coal tars with the aid of lime has also been suggested in prior art publications. In the case of the Sasol coal-tar pits it would

appear that its peculiar composition has so far defied the successful application of known lime fixation processes to render its content utile in a manner which is environmentally acceptable, economically feasible

and meets required safety demands.

OBJECTS OF THE INVENTION

It is an object of this invention to provide a novel approach to the long-standing

challenge to deal in a satisfactory manner with the waste materials of the Sasol

coal-to-fuel conversion process. It is however believed that the approach will also find application in other industrial processes generating similar or

comparable carbon-based waste products.

Whereas the aforementioned past approaches seem to have focussed primarily

or even exclusively on the tar content of the tar pits in seeking solutions, the

present invention is based on a more holistic approach. This approach involves

essentially the entire gambit of such waste products and suggests the

integration of the variety of such waste products into a utile product. The end

product is preferably a fuel or gasifiable carbon source for the production of

syngas. The product to be produced by the process of the present invention is

thus intended to be composed largely of a carefully selected blend of a

substantial part of the major components of the aforementioned waste materials.

The invention further has as an object that the product produced according to

the invention shall be in the form of a solid, hard and stable substance from

whence the ingredients will neither be leachable into the environment by the

action of natural water, nor prone to significant evaporation or significant

disintegration into airborne dust particles when the product is stockpiled in the

open or subterraneously while awaiting utilization. The waste management approach of the present invention has as a further

object that the fuel so produced may be used to generate at least part of the

energy requirements of the fuel-from-coal process, such as, for example to

generate electricity, heat or steam required in the gasification process, or could

be applied to desalinate waste water produced in the process and containing

salts or other solutes thereby to be able to recycle such water as clean water to

the plant.

In addition, the solid fuel product to be produced in accordance with the present

invention may be designed to be suitable for gasification to produce syngas, and

hence be available to be converted into hydrocarbons, thereby achieving a

greater degree of optimization of the coal-to-fuel conversion process which is

the primary object for which the coal was mined in the first place.

It is a further object of the invention to suggest alternative uses for the product

produced in accordance with the invention.

DESCRIPTION OF THE INVENTION

This invention stems from the finding that some of the individual waste products

possess desirable properties which may beneficially be combined in the

production of a fuel having the desired properties enunciated above by subjecting a selected blend of such waste products to a fixation process with

lime and water. This finding is surprising in the light of the fact that the

individual waste components to be combined in the manner contemplated by

the present invention have not been shown to be capable of yielding an

acceptable or utile end product by individual treatment according to essentially

the same fixation process.

This invention further relies on a finding that certain properties of water play a

very important role in the reaction by which lime fixates such carbon-based

materials. The chemistry involved in this process is not yet fully understood but

what has become clear is that the stage at which water is made available to the

reagents, i.e. the blend of the content of the tar pit and other waste products

on the one hand, and calcium oxide in the form of quicklime on the other, has a

major effect on the extent of heat generation during the reaction. It also

affects the physical form in which the end product is obtained from the reaction.

It has further been realized that the presence of free water in the waste

material renders the exact initiation time of the reaction with lime added to it

unpredictable, and once initiated, gives rise to an uncontrollable exothermic

reaction which resembles a runaway reaction, with attendant combustion

dangers, and leads to an undesirable fine powdery end product. The quality of

the water used in the reaction, as measured with reference to its Chemical

Oxygen Demand or COD, also plays a role in the reaction and affects the quantity of lime required to fixate a given quantity of carbonatious material. It is

considered to be desirable to use as little lime as possible to fixate the

carbonatious material so as to retain as high as possible calorific value in the

end product, which value is measured in terms of energy per mass. The lime

content in the end product makes no contribution to the energy potential of the

end product but does of course contribute to its mass and is hence preferably

minimized. It is believed that some of the embodiments of the invention will

lead to the detoxification of the tar pits of Sasol and other sites, and that it will

generally offer a feasible solution for the environmental management of a

longstanding problem which needs to be addressed.

According to the present invention there is provided a reclaimed waste product

which has a solid, particulate consistency at ambient temperature and which is

the result of the reaction of lime with water carried out in the presence of a

blend of made up to contain components selected from at least two of the

following groups of waste products derived from the production of liquid or

gaseous fuel from coal or similar processes, namely:

(a) the group consisting of oils, tars, pitches and mixtures thereof;

(b) the group consisting of coal dust, spent Funda filter medium and

mixtures thereof; and

(c) the group consisting of coal ash, underlay and mixtures thereof. Further according to the invention the waste product blend, which includes at

least two components selected from the groups (a), (b) and (c) referred to

above, may be supplemented with other waste products derived from the

aforementioned coal based industrial processes, such as Synthol gunk and

waxes, with the proviso that such additional waste materials should not exceed

15% by mass of the total reaction composition.

It is preferred to incorporate in the waste product blend equal masses of

components selected from at least two of the three groups of components

referred to above. In the more preferred form of the invention at least one

component of each of the three groups of components is incorporated into the

blend. These three components are likewise preferably also present in equal

mass quantities.

The preferred combination for such blends are tar, spent Funda filter medium

and underlay present in equal amounts and is optionally supplemented with one

or more of coal dust, ash, pitch, Synthol gunk and wax.

It has been observed in this regard, and this forms an aspect of the present

invention, that increasing the amount of ash and/or underlay tends to increase

the degree of brittleness of the end product, while increasing the pitch content

tends to increase the hardness of the end product. The reduction of the ash content in the blend in turn reduces the calorific value which value is increased

by the addition of more coal dust or spent Funda filter medium. The

supplementation of the latter two products also contribute to the suitability of

the end product for use as a carbon source in a gasification process to generate

syngas, for which application the product is preferably a hard product, capable

of being broken up into lumps without undue dust generation and adapted

substantially to maintain its lumpy integrity while being heated to the required

temperature for the production of syngas in the presence of steam and oxygen.

According to a particular aspect of the invention the waste product blend is

made up to result in a hard solid or particulate product having a calorific value

of more than 10 KJ/kg.

Further according to the invention the total coal based waste product blend

collectively make up at least 60% by mass of the reaction mixture used for the

production of the particulate product of the invention, the balance being made

up of lime and water. More preferably the waste product blend makes up

between 70% and 90% of the reaction mixture. Most preferably the waste

product blend constitutes between 75% and 85% of the reaction mixture. In all the abovementioned reaction mixtures the mass ratio between the lime

and the water in the reaction mixture may be between 2:1 and 4:1 but is

preferably between 1:1 and 3:1.

The blend of carbon-based compounds may preferably be made up of two or

more compounds selected from the groups referred to earlier and which are

present in the blend in the percentage ranges as indicated:

Coal dust 0 to 66%

Tar 0 to 66%

Underlay 0 to 66%

Spent Funda filter medium 0 to 66%

Wax 0 to 15%

Synthol gunk 0 to 15%

Pitch 0 to 66%

Ash 0 to 66%

provided that coal dust, tar, pitch, underlay, and Funda filter medium

collectively make up at least 60% of the blend.

It has been found that higher percentages of some of the components listed

above may be used in making up the waste product blend to produce a utile

product according to the present invention. Such higher percentages fall within the general scope of the invention defined above. The percentages as are listed

above are aimed at achieving the further object of the invention of providing a

waste product management approach in terms of which a variety of waste

products are simultaneously consumed in the production of the end product.

This aspect of the invention hence approaches the need to clean up the

environment by consuming waste products which are not suited in themselves

for economical environmentally acceptable disposal.

In carrying out the reaction to produce the product of the invention the ratio

between the blend of coal based waste components and lime is preferably

between 4:1 and 30:1. In the most preferred arrangement the ratio is between

20:1 and 6:1.

The lime may be substantially pure lime containing over 90% CaO as quicklime

or it may be dolomitic lime in which the CaO quicklime content is about 50%.

References herein to lime percentages and ratios are intended to refer to

available quicklime. The lime in the product is preferably in finely ground

powder form having an average particle size of less than 500 micron.

It has also been found that a utile fuel product may be produced which

comprises coal dust as the predominant component making up more than 50%

of the fuel product of the fuel product, the balance being made up of the API oil mix, ash, lime and water in combination with a binder which may be starch.

The API oil preferably accounts for more than 70% of such balance, and the ash

and lime being present in a ratio of between 2:1 and 1:2 by mass, and the

starch not exceeding 5%.

More preferably the coal dust comprises between 70% and 90% by mass of the

end product, the API oil between 15% and 25% by mass and the ash and lime

are present in substantially equal amounts collectively making up between 5%

and 15% by mass of the end product which is bound by starch in an amount of

up to 3% by mass into solid composition.

Further according to the present invention there is provided a method for

producing a solid product from a blend of waste materials as defined above

comprising the steps of:

[i] dewatering, if necessary, the waste materials incorporated in the blend to

remove substantially all free water therefrom;

[ii] intimately mixing the waste material blend with calcium oxide;

[iii] adding water with a low COD value to the mixture of dewatered waste

material and calcium oxide with further mixing to obtain a firm slurry;

[iv] allowing the mixture to react and to set; and

[v] optionally, and if required, breaking the set mass into smaller particles. In one form of the invention the waste material may be the oil and tar mixture

obtained by taking a representative sample of the total depth of the tar pits,

including underlay, of Sasol Limited located near Sasolburg. The Sasol oil/tar

fraction is however preferably mixed with other substantially water free carbon-

based materials such as uncontaminated waste streams of carbon-based

materials. Such addition may be aimed at increasing the calorific value of the

end product. The additional carbon-based material is preferably the spent filter

medium derived from the Funda filters of the processes utilized by Sasol. As an

alternative, fine coal dust may be added to the reaction mixture for this

purpose. Such additions of carbon-based materials also has the benefit of

introducing non-hydrocarbon carbon based materials into the reaction product

thereby potentially rendering it suitable to be used as a carbon source in the

production of syngas.

It is also in the contemplation of the present invention to add to the dewatered

tar a quantity of solid material to affect the consistency of the slurry and

thereby to affect the physical^* properties of the set end product. Thus, ash may

be added which ash may, for example, be directly removed from boilers used in

the generation of steam or electricity. Carbonatious solid material, such as coal

powder or coal dust may also be used which will of course also enhance the

calorific value of the end product. The waste material may be dewatered by any suitable process.

The dewatered waste material and lime may be mixed by means of any suitable

mixing device but is preferably mixed by means of a pug-mixer.

Water in the form of ordinary tap water with a low COD value is preferably

introduced by means of water jets directed at the mixture of tar and lime at a

point intermediate the feed and discharge ends of the pug-mixer.

The reaction typically takes between five and thirty days to reach completion and a slow increase in temperature from ambient to between about 40°C and

70°C occurs during the first 8 hours, without unacceptable levels of fume

generation, after which it reduces again to ambient temperature while the

mixture sets into a solid mass. Such solid mass may then be reduced to

particles of a desired size by appropriate means such as milling and screening.

The use of lower percentages lime content lengthens the reaction time but also has the advantage of the reaction temperature remaining well below 50°C and

thus reducing even further the risk of explosion or violent reaction.

In carrying out batchwise testing of the invention it has been found that the

addition of water to the blended lime/waste mixture is advantageously done by producing a stoichiometric slurry of part of the lime in a part of the water added

to the mixture, and adding the slurry with mixing to the lime/waste mixture as

soon as the lime/water reaction has commenced (as evidenced by the

generation of heat) and while it is progressing. It is believed that the addition of

such part of the lime as reacting lime to the bulk of the reaction mixture acts as

a booster for the reaction and contributes, in a manner not yet fully understood,

to the satisfactory product of the invention. This concept of adding a booster

amount of reacting lime and water to the blend of waste material and lime, may

appropriately be adapted for a continuous production process in which a

mechanical pug mixer is used.

It has been found that the process is suitable to produce an acceptable solid

fuel from the Sasol tar pits located at Sasolburg and other waste products. This

fuel is not tacky, has little or at least acceptable odor emission, and is stable

and leach resistant and has a calorific value comparable to that of the fuel coal

used by Sasol.

The product produced in accordance with the present invention has further

been found to have good compactibility features which is desirable for

stockpiling the product should it not immediately be required for use as a fuel. This compactibility feature, coupled with the fact that the product is not prone

to leaching and may be made up to be crushable also renders it suitable for use

in the construction of roads. It is further suitable for the construction of

impermeable barrier layers for waste disposal sites to be used in stead of, or in

conjunction with clays such as bentonite conventionally used in that application.

An approach to the execution of the present invention which has been found to

be particularly useful in consuming, and hence to dispensing of large quantities

of coal dust, involves a slightly modified process and utilisation of API sludges

such as is collected in the API sludge drainage system at Sasol's Secunda site.

Such API sludge contains about 39% water by volume and small, sub-1% solids.

According to this aspect of the invention the API sludge is dewatered to a water

content of less than 10%, the dewatered API sludge is used as a carbon-based

component in making a solid product in the manner disclosed above by mixing it

with between 10% and 20% by mass of a mixture of coal ash and lime in a

ratio of between 2:1 and 1:2. A quantity of water in an amount up to 4% is

added to the mixture, and resultant solid reaction product produced after a

curing time of up to 30 days is then ground and mixed with coal dust in a mass

to mass ratio of between 4:6 and 1:9 and an aqueous slurry of starch in a

quantity to have about 2% starch by mass in the final mixture. The present invention will now be illustrated by means of the following

examples without thereby limiting the scope of the invention to those examples.

EXAMPLE 1

A representative sample of the oil/tar mixture contained in the No. tar pits of

Sasol Limited near Sasolburg was removed. The oil/tar fraction removed from

the pit was dewatered to remove substantially all free water by simply allowing

all free water to run from a mound of the oil/tar under the force of gravity. Such

dewatered oil/tar, which still contained about 30% entrained water, was used in

all further experiments reported herein. It is henceforth simply referred to as

"the oil/tar".

Two forms of lime were used in the experiments, namely unslaked lime

obtained from PPC Lime (Pty.) Limited of which the available lime content is

about 90% (CaO as quicklime), and dolomitic lime, also obtained from PPC Lime

(Pty.) Limited which contains about 50% available lime.

Various blends of waste material and lime/ dolomite were made as set out in Table I below with the aid of a mixer. Ordinary tap water as

supplied by Rand Water was added to the thoroughly mixed material in an amount of between 5 and 35% mass of the mixture as indicated in Table 1. In most instances part of the water was added to the mixture in the form of 3: 1 slurry of CaO in water while the latter was reacting. Such addition seemed to set off the reaction between the remainder of the lime and the waste materials and is considered to have a booster effect. Without the booster the oil/wax or other ingredients of the mixture seems to delay the reaction between the lime and the water. The reactions were allowed to progress to completion over a period of 24 hours. Observations were made with regard to the maximum temperature of the mixture during the reaction time, the emission of fumes, the texture of the mixture after 24 hours, the hardness of the end product, its compactibility and the calorific value of the product.

Table I

Nd - not determined

"cases except sample F and L the end product was a black or brown/black solid

with hardness ranging from brittle to very hard. Sample F rendered a black soft

sandy product and sample L a crumbly product. But for these products, the rest

all had good compactibility and crushability properties. It was found that the

end products were not tacky to the touch and that no leaching of the waste

materials occurred from the product.

The calorific values of the products compare very favourably with the calorific

value of the coal being used in the Sasol gasification plant that has a value of

between 19 and 20 MJ/Kg.

The product of the present invention may thus be used to generate steam or

electricity that may be supplied to the Sasol plant or delivered elsewhere.

Some examples of the end product were crushed to a fine powder and tested

for suitability as a blast furnace fuel. They were found to compare very

favorably with a commercially used coal in terms of igniting temperature,

maximum temperature, burn-out time and ash content.

EXAMPLE 2

A quantity of the API sludge was collected from the API dam at Sasol's Secunda

site in which it had been collected for about 2 years. It was volumetrically analysed and found to contain 61% water, 38% oils and about 1% solids by

volume. With the aid of a bowl-type centrifuge operated at 3000 rpm and Mach

5, the water content was reduced to between 5 and 15% as shown in Table II

below for various samples reported on herein.

The resultant dewatered API sludge, also referred to as the oil in Table II in

Table II was mixed with various quantities of lime and ash in the ratios as

indicated in Table II. A quantity of the lime was premixed in ordinary tap water

and as the exothermic reaction commenced the reacting mixture was introduced

into and thoroughly mixed with the oil/lime/ash mixture. The reaction of the

bulk mixture was also exothermic but the temperatures generally did not raise above 31°C.

The reaction mixture set into a hard solid mass over a period of about 30 days.

The solid mass was ground into a powder and mixed with coal dust and starch

and dried with hot air in a rotating drum for a period of 30 minutes to be

formed into small hard spheres of dimensions between 1 and 5 cm cross

section. The properties of these pellitised spheres in terms of hardness are

reflected in Table II.

The calorific values of these spheres, recrushed into a powder as it would be

introduced into a blast furnace, was found to be between 10 and 20 KJ/Kg. TABLE II PRODUCTION OF SOLID FUEL FROM COAL DUST AND API SLUDGE

Many modifications of the invention may be devised without thereby departing

from the spirit of the invention.

Claims

1. A reclaimed waste product which has a solid, particulate consistency at

ambient temperature and which is the result of the reaction of lime with

water carried out in the presence of a blend of carbon-based waste

products made up to contain components selected from at least two of

the following groups of waste products derived from the production of

liquid or gaseous fuel from coal or similar processes, namely:

(a) the group consisting of oils, tars, pitches and mixtures thereof;

(b) the group consisting of coal dust, spent Funda filter medium and

mixtures thereof; and

(c) the group consisting of coal ash, underlay and mixtures thereof.

2. The reclaimed waste product according to claim 1 wherein the waste

product blend which includes at least two components selected from the

groups (a), (b) and (c) set out in claim 1 is supplemented with other

waste products derived from the aforementioned coal based industrial

processes, such as Synthol gunk and waxes, with the proviso that such

additional waste materials do not exceed 15% by mass of the total

reaction composition.

3. The reclaimed waste product according to claim 1 or 2 wherein the waste

product blend incorporate equal masses of components selected from at

least two of the three, and preferably all three of the groups of

components (a), (b) and (c) as set out in claim 1.

4. The reclaimed product according to claim 4 in which the blend is made

up of a combination of tar, spent Funda filter medium and underlay

present in equal amounts and optionally supplemented with one or more

of coal dust, ash, pitch, Synthol gunk and wax.

5. The reclaimed waste product according to any one of claims 1 to 6

wherein the product blend is made up to result in a reclaimed product

which is a hard, solid or particulate product having a calorific value of

more than 10 KJ/kg.

6. The reclaimed waste product according to claim 1 wherein the total coal

based waste product blend collectively make up at least 60%, more

preferably between 70% and 90%, and most preferably between 75%

and 85% by mass of the reaction mixture used for the production of the

particulate product of the invention, the balance being made up of lime

and water.

7. The reclaimed waste product according to claim 1 wherein the blend of

carbon-based compounds is made up of two or more of the following

compounds selected from the groups (a), (b) and (c) set out in claim 1

and which are present in the blend of waste material in the percentage

ranges as indicated:

Coal dust 0 to 66%

Tar 0 to 66%

Underlay 0 to 66%

Spent Funda filter medium 0 to 66%

Wax 0 to 15%

Synthol gunk 0 to 15%

Pitch 0 to 66%

Ash 0 to 66%

provided that coal dust, tar, pitch, underlay, and Funda filter medium

collectively make up at least 60% of the blend.

8. The waste product according to claim 1 wherein the product results from

a reaction in which the ratio between the blend of coal based waste

components and lime is between 4:1 and 30:1 and preferably between

20:1 and 6:1.

9. The product of claim 1 wherein the lime is substantially pure lime

containing over 90% CaO as quicklime and is preferably in finely ground

powder form having an average particle size of less than 500 micron.

10. The reclaimed waste product according to claim 1 which comprises coal

dust as the predominant carbon based component and making up more

than 50%, and preferably between 70% and 90% by weight of the

reclaimed waste product, the balance being made up of API sludge, ash,

lime and water in combination with a binder which may be starch, the

API sludge accounting for more than 70% of such balance, the ash and

lime being present in a ratio of between 2:1 and 1:2 by mass, and

collectively making up between 5% and 15% by mass of the end product

and the binder being present in a quantity not exceeding 5% by mass of

the end product.

11. A method for producing a solid reclaimed product from a blend of

carbon-based waste products made up to contain components selected

from at least two of the following groups of waste products derived from

the production of liquid or gaseous fuel from coal or similar processes,

namely:

(a) the group consisting of oils, tars, pitches and mixtures

thereof; (b) the group consisting of coal dust, spent Funda filter medium

and mixtures thereof; and

(c) the group consisting of coal ash, underlay and mixtures

thereof.

comprising the steps of:

[i] dewatering, if necessary, the waste materials incorporated in the

blend to remove substantially all free water therefrom;

[ii] intimately mixing the waste material blend with calcium oxide;

[iii] adding water with a low COD value to the mixture of dewatered

waste material and calcium oxide with further mixing to obtain a

firm slurry;

[iv] allowing the mixture to react and to set; and

[v] optionally, and if required, breaking the set mass into smaller

particles.

12. The method according to claim 11 wherein the waste material is a

mixture of carbon based waste materials obtained from the tar pits of

Sasol Limited located near Sasolburg to include material from all the

layers, including the underlay of such tar pit, and is preferably mixed with

other substantially water free carbon-based materials such as

uncontaminated waste streams of carbon-based materials which are added to increase the calorific value of the end product, such additional

waste products, if added, being preferably selected from the group

comprising spent filter medium derived from the Funda filters of the

processes utilized by Sasol, fine coal dust and ash,

13. The method according to claim 11 wherein the dewatered waste material

and lime are mixed by means of a pug-mixer.

14 The method according to claim 13 wherein water in the form of ordinary

tap water with a low COD value is introduced into the mixture by means

of water jets directed at the mixture of tar and lime at a point

intermediate the feed and discharge ends of the pug-mixer.

15. A method for producing a solid reclaimed product from carbon-based

waste products in the form of API sludge and coal dust comprising the

steps of

[i] dewatered the API sludge to a water content of less than 10%,

[ii] intimately mixing the dewatered API sludge with a blend of

calcium oxide and ash in which the ratio of calcium oxide:ash is

between 2:1 and 1:2 by mass and in an amount such that the

blend makes up between 10% and 20% of the mixture ; [iii] adding water with a low COD value to the mixture of dewatered

API sludge, calcium oxide and ash with further mixing to obtain a

firm slurry, such additional water making up not more than 4%,

and preferably about 2%, of the mixture;

[iv] allowing the mixture to react and to set into a solid mass;

[v] breaking the set solid mass into a powdered reaction product;

[vi] mixing the powdered reaction product with coal dust in a ratio of

between 2:3 and 1:9 by mass and binding the mixture with a

suitable binder, preferably starch;

[vii] forming the mixture into solid lumps, which are preferably of

spherical shape.