WO1996037263A1 - Process for producing products from waste material - Google Patents

Abstract

A method of producing useful products from waste material comprising contacting waste material intimately with an exothermic binder in an amount determined to be just sufficient to enable compact products to be made from that waste, mixing said waste and binder by mixing means for a sufficient period of time to permit a substantially uniform cohesive mass to be formed, and before the reaction of the binder is completed, shaping the cohesive mass into a form convenient for an intended use.

Description

Process for producing products from waste material

This invention relates to a process for producing products from waste particulate or comminuted material, particularly wet materials of small particle size typically having a sludge like consistency.

Ever increasing public awareness with regard to pollution and protection of the environment makes the safe disposal of waste products more important. Every industry in the course of its output produces by-products which are regarded as waste material if they cannot be conveniently onward marketed, stock-piled for future recycling or broken down for consumption by other industries. Those waste materials which cannot be dissipated into the environment as gaseous or soluble materials are often buried or dumped at sea but there are natural limits to such methods of disposal. Furthermore, although it is considered that most waste materials could be recycled to some useful purpose the cost of energy input in terms of transport or processing the waste to render it suitable for conversion to another purpose is generally prohibitive, or in some other cases no useful alternative purpose has yet been identified.

Many industrialised nations, especially the developing countries produce waste before considering how it might be disposed of efficiently so that the problem is now of global proportions. The following industries are examples of common and obvious areas of need for waste disposal solutions. Water companies produce waste sludge after purification treatments. Some sludges are raw, digesed and also purified, but many are raw and purification comes later. Such sludge in some regions may contain residual toxins such as traces of Cadmium or Mercury which restricts the possibility of sludge disposal. The coal mining industry produces coal fines and microfines which are fine dusts which are extremely difficult to handle and contain with little known utility. Only a limited proportion of such fines are converted to injectable slurries for furnaces due to the difficulty in forming an acceptable slurry of these microparticles and the associated transport costs . The wood industry in the production of felled and processed timber produces a large amount of waste bark of which only a limited amount can be used in gardens and walkways the rest being stockpiled. Problematic waste disposal also arises in the glass industry which produces glass wastes, fibres and overshot from rockwool . Finally there is the everyday production of commercial and domestic waste including waste plastics.

Generally it is known that it is possible for any dry waste products to be treated with a binder, the most common one being starch cellulose which is an endothermic binder, allowing the waste to be briguetted for easy disposal. In some cases the waste material can be briquetted without the need for the addition of a binder. However when the waste material is in the form of sludge it has to be dried to form briquettes and also to reduce its weight for transport during a disposal procedure. Obviously any treatment process utilising an endothermic binder has an energy demand and quite a high input of thermal energy is required in this type of disposal process thus making the whole process, although necessary, very expensive. Furthermore, in waste water sludges the disposal route is hampered by pathogens generally resident in the sludge which can cause unpleasant odours or present a health risk. Although the sludge is subjected to a large input of thermal energy during treatment and most of the pathogens will be overcome and stabilised it is not possible to ensure that every part of the sludge comes into contact with the heat for the necessary length of time. Therefore the dried bound sludge is usually then formed into briquettes or pellets for burning. This is but one example of the need for a more satisfactory, cost efficient and widely applicable method of disposing of sludge or particulate materials. An aim of the present invention is to provide a process for producing products from waste material, but which obviates or mitigates the aforementioned disadvantages.

According to .one aspect of the invention there is provided a process of producing useful products from waste material comprising contacting waste material intimately with an exothermic binder in an amount determined to be just sufficient to enable compact products to be made from that waste, mixing said waste and binder by mixing means for a sufficient period of time to permit a substantially uniform cohesive mass to be formed, and before the reaction of the binder is completed, shaping the cohesive mass into a form convenient for an intended use.

Preferably the exothermic binder material is applied as a fine spray which may conveniently be derived from discharge of binder-forming materials through at least one nozzle or sparger. Conveniently the binder is formed from two reactants, delivered from separate reservoirs, for mixing at point of use to enable reaction to form a binder essentially in si tu when applied to the waste material.

Preferably the exothermic binder is applied through means causing the binder to acquire a charge in order to enhance the probability of the binder preferentially attaching to the waste particles rather than agglomerating as a mass of binder which would uneconomic and inefficient . The waste material may also be treated with means causing it to acquire a static charge for the same purpose. Chemical reagents to assist application of a charge on the waste material or binder may be used but this would tend to increase the cost of the waste treatment process.

More preferably the exothermic binder comprises a coagulant and a polymeric emulsion. Preferably the polymeric emulsion is naturally occurring e.g. a naturally occurring rubber latex.

Preferably the latex provided is selected from the group consisting of laticifers, wood resins and vegetable oils.

Alternatively the polymeric emulsion is a synthetic product .

Conveniently the polymeric emulsion contains antimicrobial agents and/or bactericides.

Advantageously the polymeric emulsion includes an odour enhancer.

Preferably the polymeric emulsion contains an accelerator such as collagen.

Preferably the coagulant is selected from the group of substances capable of destroying protective soap layers or breaking colloidal systems, dehydrating the particle to which it is applied and/or neutralising the particle charge causing precipitation of the solids from the emulsion.

Preferably the coagulant is selected from the group consisting of weak acids, acid salts or salts of multivalent metals dissolved in water.

In accordance with a second aspect of the invention there is provided a process for producing products from waste material wherein the process comprises the use of an exothermic binder containing a polymeric emulsion, mixing same with the waste product via mixing means, the resultant mixture being moulded into its final form by a moulding means. Advantageously any inorganics and heavy metals are removed from the waste material before processing.

The invention will now be further described below by way of several illustrative examples of applications of the invention.

A process for producing products from waste material is realised by provision of an apparatus which comprises a sprayer of a type which has two separate compartments each with its own spray head. Contained in one compartment of the sprayer is a polymeric emulsion and in the other is contained a coagulant. Each spray head is angled in such a way that when the sprayer is operated the atomised fan of particles from each spray head converges and intermixes in the air to form a fine mist.

The coagulant suitable for the purpose of this invention is generally a substance which when applied to a waste material such as a sludge can disrupt or destroy any protective soap layers on the solids or can break the colloidal systems found in sludges and effectively facilitate release or separation of solids from water to assist dehydration of the sludge by other means. The coagulant may disperse water from the particle to which it is applied and/or neutralises the particle charge causing precipitation of the solids from the emulsion. The most suitable substances to be used as a coagulant are for example weak acids, acid salts or salts of multivalent metals dissolved in water.

The polymeric emulsion can be formed from any suitable compound and can generally be either of a synthetic nature (of which their are many commercially available) or naturally occurring. Examples of suitable polymeric emulsions are polyurethanes, polyols and isocyanates . Some polymeric emulsions are pre-polymers, water based and can react exothermically to create bonding/drying. It is in those that we are particularly interested in this invention.

Creation of the polymeric emulsion from the juices of natural adhesives such as natural gums and resins and in particular from the stems and roots of dandelion and milkweed results in an emulsion which can be used as a natural carbon binder.

Furthermore, the polymeric emulsion can be made up of blends of differing types of substances or a single generic type. Auxiliaries are added, for example, to assist with the destruction of microorganisms such as pathogens. In which case the auxiliaries which would be added would be in the form of antimicrobial and/or bactericides. Odour enhancers can also be added if desired. Further auxiliaries such as latex from laticifers (i.e. birch) , wood resins or vegetable oils are added to assist in increasing the binding power of the polymeric emulsion. The most suitable types are naturally occurring hydrocarbons such as natural rubber latex.

The individual particles in the coagulant and the emulsion receive a charge as they pass through the sprayer thus the resultant mist is full of static charged particles which repel each other but are strongly attracted to the waste products, thus giving maximum dispersion of the exothermic binder.

To accelerate or disperse the binder a collagen can be used as this accelerates and immediates the holding capacity or adhesiveness of the binder and it also negates water in the binder.

The waste material itself is very often made up of a large portion of dried sewage sludge. However, generally some parts of the dried sewage sludge have characteristics undesirable to processing for example the silaceous components of the sands and other inorganics can represent up to 35% or more of the total sludge. These inorganics cause wear when pelleting and the moulds can show high degrees of wear caused by the passage of the dried sludge, under pressure through the mould. This also causes heat build up which further increases the wear. It is therefore necessary to remove these inorganics and some of the heavy metals and metallic parts such as Siθ2, AI2O3, Fe2θ3, Tiθ2, CaO, MgO, Na 0, K₂0, Mn₃0₄, P2O5, SO3 and other such variants before the waster material is placed in a suitable container. In some cases if only the sands/inorganics are separated out than the heavy metals can be caught in filters, or if melted some are melted out.

The waste material or dried sludge is subjected to milling, grinding or micronising, to get a similar size part. In this way the fibres, dried oils, sands/inorganics and heavy metals are air separated. This allows the fibres and some of the oily parts to be used as the part of the binder giving the green strength and to do this more thoroughly as the interstice between molecules/parts being bound are able to be pressed between the thin walls of the fibres causing a greater bond to take place, indeed when pressed at 50bar with the sandy overshott from the manufacture of Rockwool, a strength not before seen in the process was caused, a degree of sodium silicate was mixed also in this process, where the green strength of the instant bond of the fibres allowed the sodium silicate to set, (up to 10% was used in varying trials although the accepted amounts appeared to be between 3 and 5% sodium silicate, 5% fibres and upwards depending on the grain size of the overshott and pressures of 25, 30, 35, 40 and up to 100 bar.

Another test rig gave pressures of up to 500 bar, at this stage the fibre almost disappeared, but the bond - with or without the binder was still strong. It should be noted also that the silaceous inorganic material separated from the waste material or sludge can be recycled for use, in making of cement, roads, or as part of the sand used in Glass making, and the pre-melt for Rockwool .

In the case of road surfacing materials the silaceous parts can be pre-mixed with cement and used for forming paving slabs, blocks etc. The heavy metals can be either recovered by further processing or mixed with cement and binder and landfilled as an inert encapsulated material. At this stage being less than perhaps 1, 2, 3% or parts of 1% AS .03% the bulk has changed and becomes small.

The waste material is held in a suitable mixing means which is generally mechanical and in the form of for example a blade mixer or a continuous screw mixer.

The exothermic binder is sprayed over the waste material held in the mixer which on activation allows intimate mixing of the exothermic binder and the waste material . The binder may be sprayed onto the waste material either before or during the mixing process.

The exothermic binder also confers waterproofing to the mass and provides greater strength to the resultant mixture once in its desired shape and is passed through heat as in gasification, or as a recycle in a cupola, melt zone or enduration in the steel process.

The resultant mixture is then formed into the desired shape for example, beads, boulles, blocks, briquettes, pellets, egg shape or other shape or seed granule by any commonly available press or moulding equipment.

The product is then thermally converted, the ash from which can be used as a fertiliser or as a filler in processes where one is required. In some cases the ash may have to be further processed to make a viable recyclable product, requiring milling, sizing and other additions if required. If traces of contaminants are found to be in the ash then processing can either fully remove them or reduce the level to an environmentally acceptable amount .

In an alternative embodiment the process comprises the use of a polymeric emulsion which is mixed by means of a continuous screw mechanism with the waste sludge at a level of 4 to 8% of the whole. The resultant mixture is then formed into the desired shape by means of a suitable press.

It is envisaged that it will be necessary to use a combination of both methods for some types of waste which do not have any type of inherent mechanical cohesion capacity such as silicon sand from glass manufacture and various glass residues from smelting and steel production.

It is also envisaged that another process of disposing of dried sludges is to mix the dried sludge with some of the ever increasing stream of waste plastics. The use of the waste plastic means that there is a large constant supply of additional energy available to mix with the dried sludge with an increased calorific value. In this case the plastic would be converted either by melting or other treatment to act as part or all of the binder.

In another embodiment of the invention waste paper is shredded or granulated, micronised into micro parts and separated to provide waste of short fibre strands, de-inked parts and also some of the coatings from coated papers, silaceous parts and water. Furthermore micronising enables recovery of metal parts left in the waste paper, card or boards etc. such as pins, drawing pins, tops etc.

When dried and -again micronised or ground up, these parts can be air separated, giving a fibre and a degree of celluloses, lignins, calcium parts etc, these fibres are then able to be used as a binder and the cellulose, lignins etc., also can be added either separately or in suspension (as can the fibres) to a two part binder to provide the strength during the setting of the binder/binders.

The cellulose and also the cellulose salts contained therein can be used for re-cycling and bonding, for example in pelleting ores for the steel industry the pellet has greater enduration, and the cellulose/salts etc., cause less problems than compounds such as Bentonite.

When the cellulose is separated it is found to contain starchy parts, cellulose parts, lignins and derivatives and traces of small fibrous molecules. These fibres and if required part of the cellulose can be mixed in coal briquetting as separate or as in situ in a binder. Furthermore, the fibres and the cellulose can be mixed either separately or as part of the endothermic binder in coal, steel, glass, rockwool, fibreglass, and the holding of various small parts of dolomite, boron, sands, other glass wastes etc, giving a larger and therefore useful briquette, boulld, pellet and form of agglomerate.

In a further embodiment of the invention pressed boards are made from chipped or flaked waste material, for example, building board made from wood flakes. The flakes are generally flaked on a flaker from trunks of trees or parts of trees and are small to medium flakes of about 2" to 3" etc. or parts thereof.

Normally the flakes would be dried and tumbled in a mixer with formaldehyde/urea. This sticks to the flakes and the flakes would then be waxed by mixing in a concentration of heated wax. The flakes would then be formed into pre- pressed boards on the tampan or plate ready for heated pressing. However, this known process rarely gives complete mixing of the flakes with the formaldehyde/urea and an object of this invention is to allow safe storage of the formaldehyde/urea, increased and more even coverage of the flakes and use of smaller amounts of binder. This can be achieved in three ways.

The first comprises a process in which the flakes are fed into the mixer via a static spray which treats the flakes with either a positive or negative charge. The binder is then sprayed over the flakes in the mixer via a sprayer of the type mentioned earlier. This particular type of sprayer is used to provide a two part spray which causes the particles of the spray to be attracted to the flakes rather than themselves. This allows for better coverage of the flakes by the binder and also reduces surplus overspray.

The second comprises a process in which the flakes (this time without being charged) are fed into the mixer where the binder is sprayed through an electrostatic spray or two if desired. The charged particles are again repelled thus keeping them apart to give maximum distribution over the flakes.

The third comprises a process in which the binder is pre-mixed and sprayed through an atomiser spray onto the flakes .

The binder can be in the form of powder or granules and has a better concentrated adhesion to the flakes if treated with electrostatic.

Once the flakes are mixed with the binder they are then pressed into boards in the usual way.

Flaked or shredded paper, sawdust or plastics can also be used in this process. It is envisaged that the flakes could be replaced by dried or milled bark to make blocks or pallet blocks.

Residues from the manufacture of fibreglass can also be included to give strenght to blocks, boards and other products .

In a yet further example the dried sludge is mixed with overshott, glass lumps from a cupola and fibres from the process of making insulation wool. To this mixture is added further amounts of dried sludge which has been heated to over 130°C to partially pyrolise the sludge to save the use of coal or coke in the cupola process for making rockwool. It also has greater significance in that it also saves carbon tax when applied as this is not a fossil fuel.

In the melting process silicates and the like can be used as a useful feedstock for the process . For example in a process in which overshott from the rockwool process is mixed as before with dried partial pyrolisis sludge, ordinary dried sludge, and binder, and any of the mix as before sodium silicate can be added if desired.

This invention has several advantages over prior art methods . The waste material when in the form of sludge would normally have to be dried during treatment with the binder. However use of an exothermic binder naturally dries the waste as it is binding it without the need for any external thermal energy input. This creates a huge saving in the costs and time involved.

The fact that the binder is sprayed with a static charge means that the actual amount of binder used is considerably less because there is less binder wastage due to the binder adhering preferentially only to the sludge particles. This not only reduces the costs concerned with purchasing the binder but also reduces the amount of binder let into the environment and reduces costs in coal briquetting.. The individual particles in the coagulant and the emulsion receive a charge as they pass through the sprayer thus the resultant mist is full of static charged particles which repel each other thus giving maximum dispersion of the exothermic binder, and therefore a larger proportion than normal of the binder sticks to the waste material This fine mist of spray mixture forms the basis of the exothermic binder.

Through the use of the ever increasing stream of Council waste plastics to help dispose of dried sludges it is sought to save millions of tonnes of oil per year. This is highly advantageous as the use of large amounts of oil would be saved by substituting waste package plastic not suitable for recycling which may amount to the largest constant supply of additional energy available to mix with dried sludge with an increased calorific value. This mix could also be used, because of its high energy values, as a substitution for other fossil fuels.

The advantage of using the process of the present invention in the formation of building board from wood flakes or blocks and pallet blocks from dried or milled bark, paper or card is that they have a greater strength due to the increased and more even application of the binder.

The process also acts in treating sludges, dried and sprayed, the static misting keeping the mist drops apart and therefore helping in the prevention of the binder balling. There is also the added advantage of a more even distribution of the binder.

In the case of using pan pelletizers where spray is necessary, the static reduces the amount of binder required and provides an easier and better distributed application of the binder. Therefore reducing the overall costs of the processing. This is also the case in the production of charcoal briquettes or gas barbecue briquettes made in pin mills or by other briquetting applications.

A further advantage of this process is that it can be used in a large number of commercial applications, for example, in recycling of iron ore fines, various smeltings of metals, and recovery of fines in coal processing. Furthermore due to the fact that the dried sludge is fluffy and cellulosistic it acts as a holder for smaller grained materials where normal pressing would not allow the micro fines to stabilise and bind without further treatments.

Spraying of the binder and or using static to save extensive use of a binder can be realised, and mixing and pressing the mixture into a dense shape which can be round, octagonal, etc., enables the product from the process to be recycled in house thus saving raw materials, dumping, energy, and is environmentally safe.

Biomass has been successfully co-fired after first being ground, milled and in some cases micronised to a "wood flour" .

When the inorganics such as the sands and heavy metals are removed the resulting waste product comprises mainly a dry fibre/oil mix. The fibre/oil mix can then be ground, milled and micronised to enable it to be used as a means of co-firing diesel and/or spark ignition engines. If required a gas or oil bleed can be used (to facilitate a better burn) , or the fibre/oil mix can be co injected into the chamber and fired. This saves gasification, burning, and utilises an engine to generate much needed power at the sewage works for the running of pumps, works and can give CHP for power etc.

It is envisaged that a larger ships type slower running diesel and/or gas engine could be used to generate large amounts of power for example to be sold. In a further use of the invention it can be used to generate power from engines, particularly diesel and spark ignition engines in which biomass .

In the drying of this sludge, oil, gas or is some cases methane can be used or dual fuelled to give the energy to dry the wet sludge.

In a dual fire burner the sludge when dry can be separated by micronisation and separation. Again the inorganics are removed thus reducing the wear factor as the inorganics make up 50% plus of the bulk. The remaining fibre/oil mix can be co-fired in a dual fuel special burner where the fibre/oil mix is rotated in an outer tube from the oil, gas partially carbonised or heated and kept for 2 sees at 1,200c so thus falling within the parameter laid down by the EEC legislation for usage of sewage as a f el.

Micronising allows the silicaeous parts to be taken out thereby allowing a burner nozzle to inject or fire the fibre/oil or fibre alone or dried oil alone. Previously the silicaeous material would speed up deterioration of the nozzle.

Alternatively the fibre/oil can be further admixed with oil and fired in a heavy oil burner or co-fired in a gas/fibroil burner. This give great savings over fuel costs, reduces dumping and gives due diligence to the Water company. Furthermore the use of micronisation of dried sewage sludge therefore, greatly enhances the starting materials, increases cost savings, provides a greater environment satisfaction, and also greatly reduces pollution.

The process in totality i.e. drying, (various dryers) , micronising or fine grinding, milling etc., separation of the components and re-use of 95% plus of the components in further processes saves vital natural resources. Taking environment factors into account, it should be noted that odour is now negligible as the dryers has scrubbers or condensers, and part of the waste gas is recycled in the burner and heavy metals are now in extremely limited traces.

The fibre/oil mix can be used in dual fuels or stand alone, in some cases the engines starting on gas and changing to the fibre oil mix when hot. This creates considerable savings and little ash. Prior art burners generally provide 47% or more ash.

Further advantages of this use are that dumping has ceased or become negligible as in encapsulated heavy metals of less than 1% in some cases.

Use of the fibres, fibre oil mixture substances have become useful as in binding or materials etc.

The fibre oil mixture can be further micronised and separated, and the fibres used separately as also the proteinaceous materials and fats as in fuels.

Claims

Claims

1. A method of producing useful products from waste material comprising contacting waste material intimately with an exothermic binder in an amount determined to be just sufficient to enable compact products to be made from that waste, mixing said waste and binder by mixing means for a sufficient period of time to permit a substantially uniform cohesive mass to be formed, and before the reaction of the binder is completed, shaping the cohesive mass into a form convenient for an intended use.

2. A method according to Claim 1 wherein the exothermic binder material is applied as a fine spray which may conveniently be derived from discharge of binder-forming materials through at least one nozzle or sparger. Conveniently the binder is formed from two reactants, delivered from separate reservoirs, for mixing at point of use to enable reaction to form a binder essentially in si tu when applied to the waste material.

3. A method accoring to Claims 1 or 2 wherein the exothermic binder is applied through means causing the binder to acquire a charge in order to enhance the probability of the binder preferentially attaching to the waste particles rather than agglomerating as a mass of binder which would uneconomic and inefficient . The waste material may also be treated with means causing it to acquire a static charge for the same purpose. Chemical reagents to assist application of a charge on the waste material or binder may be used but this would tend to increase the cost of the waste treatment process.

. A method according to any one of the preceeding claims wherein the exothermic binder comprises a coagulant and a polymeric emulsion.

5. A method according to any one of the preceeding claims wherein the polymeric emulsion is naturally occurring e.g. a naturally occurring rubber latex.

6. A method according to Claim 5 wherein the latex provided is selected from the group consisting of laticifers, wood resins and vegetable oils.

7. A method according to Claims 1-4 wherein the polymeric emulsion is a synthetic product.

8. A method according to any one of the preceeding claims wherein the polymeric emulsion contains antimicrobial agents and/or bactericides.

9. A method according to any one of the preceeding claims wherein the polymeric emulsion includes an odour enhancer.

10. A method according to any one of the preceeding claims wherein the polymeric emulsion contains an accelerator such as collagen.

11. A method according to any Claim 4 wherein the coagulant is selected from the group of substances capable of destroying protective soap layers or breaking colloidal systems, dehydrating the particle to which it is applied and/or neutralising the particle charge causing precipitation of the solids from the emulsion.

12. A method according to Claim 11 wherein the coagulant is selected from the group consisting of weak acids, acid salts or salts of multivalent metals dissolved in water.

13. A method of producing products from waste material wherein the process comprises the use of an exothermic binder containing a polymeric emulsion, mixing same with the waste product via mixing means, the resultant mixture being moulded into its final form by a moulding means.

14. A method according to Claim 13 wherein any inorganics and heavy metals contained in the waste material are removed before processing.

15. A shaped product comprising reprocessed waste material intimately mixed with an exothermic binder by a method according, to any one fo the preceding claims.