EP0065259B1 - Process for the preparation of a combustible mixture of coal in water - Google Patents

Description

The present invention relates to a method for producing a combustible mixture of coal and water, it relates in particular to a mixture of finely ground coal, water, a wetting or dispersing agent and a suspending agent.

It has long been known that current oil reserves will run out very quickly. Due to the possible shortage of oil in the world in the future and the ongoing price increases for petroleum products, the use of oil as an energy source has become very expensive, while conversely the oil supply will be uncertain in the future. Those of ordinary skill in the art have tried to reduce the demand for heating oil by replacing it with other fossil fuels. The abundance of coal and its easy accessibility suggest direct replacement of oil with coal in many applications. For this reason, considerable efforts have been made to produce mixtures of oil and finely ground coal in a ratio of 50:50 to 70:30 (see DE-A-28 27 168).

In the cited patent application the suspension of coal dust in heating oil is described, the suspension being stabilized against sedimentation by an additive which makes the mixture viscous at low shear forces, while the viscosity is reduced at high shear forces, so that it easily coexists over longer distances Pumps can be carried on. The additive consists of a suitable surface treatment agent in combination with a gel-forming clay as a suspending agent.

DE-A-29 42 122 describes a suspension of coal dust in heating oil, the suspension also being stabilized using gel-forming clay as a suspension medium.

US Pat. No. 4,062,694 describes the use of attapulgite clay as a suspending agent for coal dust in combustible liquid hydrocarbons for the formation of heating materials which facilitate the removal of fly ash from the combustion device after combustion. U.S. Patent 239,859 also describes an attempt to partially replace oil with coal to create a composite fuel.

A whole series of the mixtures described could be successfully burned in certain types of furnaces.

The problem with the oil-coal mixtures is that they still contain heating oil in as large a proportion as 50 to 70%.

The ideal situation would of course be the complete omission of oil from the fuel mixture. Many of the existing facilities are designed for the combustion of coal dust and have been converted to burn oil for environmental reasons. Many of these plants have no adjoining rooms and options for storing ground coal and therefore it is not possible to switch back to burning coal or powdered coal.

The invention seeks to remedy this. The invention, as characterized in the claims, achieves the object of specifying a method for producing a fuel which enables the use of powdered coal without the addition of heating oil, while at the same time creating a stable and cost-saving fuel composition.

The fuel composition created according to the method according to the present invention consists of a mixture of coal, water, wetting or dispersing agent for the coal and a suspending agent for stabilizing the sludge. The coal is present in the mixture in an amount of 65 to 70%, the wetting or dispersing agent is used in smaller, functional percentages. The suspending agents used are colloidal clays which show gel-forming properties in the water which forms the rest of the composition.

The method according to the invention describes the composition of a new fuel with the above-mentioned components.

• 1. 95 % - 0,15, 80 % - 0,074, 65 % - 0,044
• 2. 90 % - 0,15,75 % - 0,074, 52 % - 0,044
• 3.100 % - 0,044, (44 f.Lm) 55 % - 0,026

Coal such as anthracite coal, semi-anthracite coal, bitumen as well as semi-bitumen or other coal is first crushed and then ground to a fine powder using conventional techniques. Examples of successful grades of paint that can be used in the production of the carbon powder are in clear mesh size (mm),

• 1. 95% - 0.15, 80% - 0.074, 65% - 0.044
• 2. 90% - 0.15.75% - 0.074, 52% - 0.044
• 3,100% - 0.044, (44 f.Lm) 55% - 0.026

The upper limit of the particle size is determined by what burns in the flame (approximately a grain size with a clear mesh size of 0.18). The amount of coal that can be incorporated into a slurry of coal in water depends on the grain size distribution, the structure of the particles and the dispersant used. Grain size distribution and particle shape can be accomplished during dry processing or by post processing the slurry with one of the conventional wet grinders to achieve a change in grain size distribution and grinding of the particle shapes.

It is desirable to incorporate the maximum amount of coal into the slurry while maintaining flow properties that ensure good stability of the mixture and sprayability in the burner nozzle.

The maximum coal content appears to be around 70% and a satisfactory slurry can only be achieved with relatively round particles and a high proportion of fine particles and the addition of a wetting or dispersing agent. A gel-forming agent that imparts gel-forming properties to the water phase is required for any medium or long-term stability.

The dispersing or wetting agents which are effective in the context of the invention foam little or not at all in water, have a structure which consists of an organic half which absorbs the surface of the coal more than water and a charged hydrophilic part which is lyophilic in relation to the water phase is. These agents are used in low concentrations and accumulate at the coal-water interface. They displace air and water, allow the carbon agglomerates to flocculate with gentle stirring and charge the carbon particles so that the viscosities are low.

Many types of coal only produce thick pastes when 70% coal is mixed with 30% water, but as soon as a wetting agent is added, they can be diluted to low viscosity liquids with gentle stirring. The dispersing or wetting agent does not have to interact with the gel formers incorporated to improve the stability. Chemical substances that have a good effect as dispersants or wetting agents for carbon powder are sodium salts of condensed naphthalene-formaldehyde sulfonates (Lomar D and PW from Diamon Shamrock Corp. or Tamol N and SN from Rohm Haas Co. or Darvan 1 and Darvan 2 from RT Vanderbild Co.), further polymerized sodium salts of alkyl naphthalene sulfonic acids and sodium salts of polymerized substituted benzene alkyl sulfonic acids, as well as the first-mentioned types in the composition of similar products from WRGrace Corp. Sodium lignin sulfonates and other lignin sulfonates can also be used.

Stabilizing agents, by means of which the carbon powder is kept in suspension in the water phase, act through the gelation thereof. The water phase transformed into a gel plus the suspended coal should have a gel strength which reversibly breaks up under shear, so that the coal / water mixture, also referred to below as C / WM, can be pressed through a burner nozzle to form a combustible spray . The yellowing agents used are colloidal clays such as bentonite, attapulgite, sepiolite montmorrilonite.

• Wasser 74,25 %
• TSPP 0,75 %
• Attapl. 25,00 %

If clays are used as suspending agents, they can be predispersed with a chemical dispersant such as tetrasodium pyrophosphate (TSPP) before use. Such predispersion with attapulgite has, for. B. The following composition:

• Water 74.25%
• TSPP 0.75%
• Attapl. 25.00%

The resulting predispersion is thin and pourable and can be added to the water of the coal / water mixture before the coal is added. When using 3% TSPP, montmorillonite can be used up to 30% by weight.

Sepiolite can be prepared in a mixture in a similar way to the predispersed attapulgite. Bentonite is predispersed using 0.5% TSPP in an amount of 10% by weight. The coal / water mixtures containing flocculated pre-dispersed clays are very stable and have a higher gel strength than those containing pseudoplastic gels made from dry clays.

If hydrocolloids are used as stabilizers, they are introduced in the conventional manner known to the person skilled in the art.

In order to better understand the compositions and the problems and important data that arise, so that the person skilled in the art is able to produce the mixtures with little effort, examples and technical considerations are discussed in more detail.

• 1. in der Endkonzentration als trockener Ton,
• 2. vorhydratisiert durch Vorquellen in Wasser bei einer hohen Konzentration und Zugabe zu der Aufschlämmung in der gewünschten Menge oder
• 3. vordispergiert bei einer hohen Konzentration in Wasser unter Verwendung eines Dispergiermittels und dann Zugabe zu der Aufschlämmung als Vordispersion.

If clays such as attapulgite, sepiolite and bentonite are used as stabilizers of the coal / water mixture, they can be added to the mixture:

• 1. in the final concentration as a dry clay,
• 2. Pre-hydrated by pre-swelling in water at a high concentration and adding to the slurry in the desired amount or
• 3. Predispersed at a high concentration in water using a dispersant and then added to the slurry as a predispersion.

If one chooses the last route, it may be necessary to add a flocculant or a dispersant neutralizer so that the clay particles interact and form a stabilizing gel structure.

(See table on page 4 f.)

Typical spinning compositions are:

They are made by pouring water into a mixing tank, adding the clay with stirring, and continuing to stir until a gel is formed and there are no more clay lumps. The Pregele are added to the coal / water slurry in the form of the desired aliquot to the water or to the finished mixture.

Typical predispersion approaches are listed below:

The predispersions are prepared by dissolving TSPP in water in a mixing tank, adding the clay while stirring and continuing the stirring process until it is dispersed. The predispersions can be added early or late in the course of the C / WM process, but are generally added before the coal. Common dispersants are tetrasodium pyrophosphate, sodium tripolyphosphate, condensed phosphate-containing dispersants, and other polyanionic organic dispersants that act as dispersants in clays. Aluminum, magnesium and calcium montmorillonites of the non-swelling types can be used as stabilizers in the context of the invention. They cannot be added dry or pre-gelled because they develop a low viscosity, but they form gel structures and therefore a certain viscosity if they are added predispersed. A typical predispersion has the following composition:

This predispersion is prepared and added in the same way as the other predispersions.

All pre-dispersed clay-stabilized coal / water mixtures should be checked whether a neutralizer is required for the dispersant. If very clean coal is used and the viscosity and gel strength of the finished C / WM is low, neutralizers such as hydrated lime, ammonium nitrate, aluminum sulfate etc. can be added to the finished mixture to thicken it by flocculating the clay component. The efficiency of the use of clay for stabilizing the suspension is usually: predispersed> pre-gelled>> dry additive.

The same effect when used is achieved in coal / water mixtures.

• 1-A Diese Mischung war zu dick und voluminös
• 1-B Dick aber gießbar, setzte sich rasch ab
• 1-C Gute Konsistenz, setzte sich aber sofort ab
  
  

Examples of the application of the present invention are shown below, using a finely ground bituminous coal (particle size 80% below 0.074 mm mesh size), processing with medium shear force.

• 1-A This mixture was too thick and bulky
• 1-B thick but pourable, quickly settled
• 1-C Good consistency, but settled immediately
  
  

The results of the composition according to Example 1 show that high coal concentrations (60-70%) give a thick consistency and tend to settle. With a ratio of 55% coal and 45% water, the mixtures are thinner and settle even faster than in the case of 1C.

If attapulgite is added, as shown in Example 2, the slurries become thicker (2A, 2B and 2C), but the clay stabilizes lower coal concentrations in water according to approach 2D.

Since a content of 55% coal in water is less desirable than 70% coal in water for combustion purposes, investigations were carried out with dispersing or wetting agents for coal. Lignin sulfonates and sulfonated condensation products of naphthalene and formaldehyde proved to be suitable agents. They were examined in the batches shown in Example 3, where Raylig 260 LR is a 50% sodium lignisulfonate solution and Lomar D is the sodium salt of a condensed naphthylene sulfonate. As already mentioned, TSPP is tetrasodium pyrophosphate and Calgon is the sodium salt of condensed phosphates (polyphosphates).

Example 3 Water, Coal, Dispersant.

• 1. den großen Kohleteilchen und
• 2. der Tatsache, daß kein stabilisierendes gelbildendes Mittel anwesend war.

Example 3 shows the compositions and evaluation results for the water-carbon dispersant batches. When using Raylig 260 LR or Lomar D, the powdered coal was dispersed in water in an amount of 70% and low viscosities were obtained. The two batches 3A and 3B provided useful viscosities, but after 24 hours of storage there was little settling. This resulted from

• 1. the large coal particles and
• 2. the fact that no stabilizing gelling agent was present.

Note: TSPP and Calgon do not disperse coal in water.

The batches according to Example 4 show the effect of incorporated dry clay in the batches according to Example 3.

Regarding the viscosity results, it should be noted that attapulgite significantly reduces the viscosity of the batch (4A), but stabilizes it against settling. The clay had no opposite effect in batch 4E, so the batch retained its low viscosity while remaining stable. Adding sound to approaches 4C and 4D resulted in very thick compositions. These approaches all had 70% coal. Was the coal concentration reduced to 65%, e.g. For example, in 4B and 4F, much lower viscosities resulted and the batches were stable.

Since usually predispersed attapulgite as a suspending agent is far more effective than dry clay, a 25% predispersion was prepared and examined in conjunction with a 70% coal slurry, shown in Example 5. The amounts of clay are based on predispersed clay and must therefore be divided by 4 to get the dry clay content.

If one looks at the batches and the results according to Example 5, it is found that the amount of predispersed clay required to stabilize a 70% coal slurry is substantially reduced compared to the values shown in Example 4, the 0.75% predispersed clay of the Approach 5A actually corresponds to 0.19% dry clay. Raylig 260 LR plus pre-dispersed clay produce batches that thicken when stored. Batches with Lomar D, Lomar PW and Darvan 1, all sodium sulfonate salts of condensed naphatlin formaldehydes, plus predispersed clay show good viscosities and stabilities.

In order to show the effect of the finishing of these slurries, a larger amount of batch F from example 5 was produced. It was then worked for 5, 10 and 15 minutes in a ball mill as in Example 6.

Shelf life Brookfield Visc. (Pa.s)

Example 6 Effect of treatment in the ball mill, carried out with the aim of changing the Particle shape and particle size distribution

Shelf life Viscosities after treatment in a ball mill (Brookfield Visc. Pa.s)

Treatment of batch 6A in a ball mill of 10 minutes leads to an increase in viscosity compared to the comparison, but also results in a more homogeneous, smooth-looking slurry. It can be seen that the viscosity dropped and became stable.

Montmorillonite of the non-gelling type can also be used to stabilize the coal / water mixture. To show this, a 30% predispersion of montmorillonite was made in the known manner. The predispersion was applied to a 70% coal slurry.

The use of 5% of a 30% predispersion of montmorillonite corresponds to an amount of 1.5% dry clay.

From the batch values and the stability results, it can be concluded that a stable 70% coal in water slurry is used by using dispersants based on lignin sulfonate in the amount of 1 to 5% or sodium salts of sulfonated naphthalene formaldehyde condensates in the amount of 0 , 5 to 2% plus attapulgite in dry, predispersed form or non-gel-forming montmorillonite can be produced as a stabilizer.

Claims (7)

1. Method of preparing a combustible coal/water mixture, characterized in that 65 to 70 % by weight of coal powder, 0.5 to 5 % by weight of a wetting/dispersing agent, 0.19 to 3 % by weight of colloidal clay, and the remaining weight % in the form of water are mixed by stirring.

2. A method as claimed in claim 1, characterized in that the clay, prior to being added, is predispersed by being stirred into water until a gel is formed, with a dispersant being added to the water prior to adding the clay.

3. A method as claimed in claim 2, characterized in that the dispersant is tetrasodium pyrophosphate or sodium tripolyphosphate.

4. A method as claimed in claim 1, characterized in that the clay is attapulgite, sepiolite, bentonite or montmorillonite.

5. A method as claimed in claim 1, characterized in that the particle size of the coal powder is 80 mesh.

6. A method as claimed in claim 1, characterized in that the wetting/dispersing agent is a sodium salt of a sulfonated naphthalene formaldehyde condensate, of lignosulfonic acid, or of alkyl naphthyl sulfonic acid.

7. A method as claimed in any one of claims 1 to 6, characterized in that, after stirring, a neutralizer, such as ammonium nitrate, aluminium sulfate or calcium hydroxide, is added to thicken to final mix.