FR2595711A1 - Coal-based ternary fluid fuel mixture and process for preparing it - Google Patents

Abstract

Preground coal is mixed with water in a tank 1 and is then reduced in a mill 6 to particles smaller than 200 microns, preferably 15 microns, and then a slurry containing 15 % of coal and 85 % of water, prepared in a vessel 8, is mixed in a metering pump 12 with a liquid fuel which agglomerates the coal like domestic heating oil, after which the water, which entrains the inactive matter from the coal is removed through a screen 15 and domestic heating oil and a surface-active agent are again added to obtain a fluid fuel composition with three main components: coal 40 to 60 %, water 16 to 35 %, domestic heating oil 16 to 35 %.

Description

 The invention relates to a fluid combustible mixture with three main components, based on carbon, and a process for preparing it.

 Coal is an abundant fossil fuel that cannot be obtained at the end of coal mines without a non-negligible quantity of various sterile mineral materials, in very variable quantity and composition.

Not only are these mineral materials unproductive of heat but, in addition, they give rise to combustion byproducts considered as pollutants from the surrounding environment, such as ash and various gases, in particular those derived from sulfur.

 Several processes are known, the aim of which is to remove the maximum amount of undesirable mineral matter from coal. This treatment requires a first operation of grinding the coal to a high degree of fineness. The finer the coal is ground, the lower the residual amount of ash after separation of the ground coal and the ground mineral material. For example, for grinding raw coal to a degree of fineness of less than 80 microns (for a fraction of at least 80 X of raw coal), after separation a treated coal is obtained, the ash content of which does not exceed 2 X For a further grinding, up to a range between 0 and 20 microns, the ash content of the treated coal does not exceed 1% in the majority of cases.

 However, when the coal is reduced to such fine particles, its use in this state is not possible.

 The classic technique consists in agglomerating the treated coal, that is to say ash, into larger particles, of the order of a few centimeters in size, which can easily be handled and burned using adapted.

 The separation of coal and mineral materials is carried out after the grinding operation according to various known methods.

 A classic method is to use water with a binder. The latter tends to bind the fine particles of coal together; The water collects with it the sterile mineral matter which is generally hydrophilic.

In practice, a slurry, commonly called a slurry, is produced which is subjected to one or more successive filtration operations to remove the water in which the sterile materials reduced to dust are in suspension.

Then the grains of agglomerated coal are collected and, even, the agglomeration is continued in order to arrive at the final product which is agglomerated coal.

A typical example of this conventional process is found in document US-A-4 248 698. In the latter, provision is made for the use as a binder of petroleum derivatives or fluorochlorinated derivatives of methane or ethane. The raw coal initially reduced to fine particles between
O and 50 microns is transformed into ashed coal agglomerated into particles of 0.5 to 3 cm in size. The binder is removed from the agglomerated ash and recovered. The aforementioned document mentions that the advantage provided by the fluorochlorinated derivatives is that they are more easily eliminated and recoverable from agglomerated ash.

 The invention proceeds from an idea completely opposite to that on which the conventional method of ash ash removal is based.

 According to the invention, after having reduced the raw coal to particles, the fineness of which is related to the residual rate of ash acceptable in the ash, anyway to a maximum dimension of less than 200 microns, a slurry is produced comprising mainly ground coal, water and an agglomerant chosen from petroleum derivatives known as agglomerants and as liquid fuels; after separation of the water and the sterile mineral matter entrained by the water, the quantity of agglomerant is increased to a proportion which can reach 35% by weight, the mixture obtained is vigorously stirred to bring the carbon particles into contact suspension in the divided state in the liquid binder. A dispersing agent is also added which is favorable for keeping the coal in suspension in the binder, in an amount which generally does not need to exceed 1.5% by weight.

 As petroleum derivative, domestic fuel oil is advantageously used, but a lighter fraction (pentane, hexane, heptane, etc.) or a heavier fraction, or mixtures of these derivatives, can be used, depending on the desired viscosity of the final product.

 An advantage of the process of the invention is that it does not oblige to completely eliminate the water which remains contained in the product obtained after separation of the sterile mineral matter entrained by the loaded water, nor to eliminate the agglomerant. , a very expensive operation both in terms of material investment and implementation.

On the contrary, it is advantageous, according to a preferred embodiment of the process of the invention, to keep clean water in the product obtained in order to achieve an essentially ternary mixture, corresponding to the following general formula:
- charred coal 40 to 60% by weight
- water 16 to 35% by weight
- petroleum derivative 16 to 35% by weight
Preferably, a surfactant is incorporated into this mixture in a proportion of 0.5 to 2% by weight of the total weight of the final mixture.

This surfactant is chosen for its property of maintaining the suspension of the carbon and the dispersion of
The water in the petroleum derivative by decreasing the interfacial tension between the two liquids. Examples of suitable surfactants that may be mentioned are nonionic surfactants, such as those which contain polyethylene glycol or polypropylene glycol units, or a combination of these units; for example phenols, alkylphenols, amines,
Diamines, polyethoxylated, polypropoxylated phosphates, as well as polyethylene glycols, Polypropylene glycols, polyalkylene glycols, in general molecules which contain one or more polyalkoxylated units.

 In the spirit of the invention, the agglomerating agent plays an aggregation role only in a limited and momentary manner since it is ultimately desired that the carbon particles remain in suspension in the dispersed, unagglomerated state, in the final mixture.

 During separation, the binder wets and mainly retains the hydrophobic particles of the coal while the hydrophilic particles of the sterile materials are wetted and entrained by water.

 In addition, in the final mixture the binder is a clean fuel with high calorific value which contributes to the calorific value of the mixture.

For example, in a mixture of composition - charred coal at 1 X, type FReyming of
PCI 7800 Kcal / kg (32600 kJ) 50% by weight - domestic fuel oil 20% by weight - water 30% by weight (without taking into account the surfactant) whose PCI is 5900 Kcal / kg (24 662 kJ), we see that Coal contributes to the latter for around 66% and The petroleum derivative for around 34 X.

 In addition, this mixture contains only 0.5% by weight of ash corresponding to a content of 0.203 x 10 g of ash / Joule, content which is lower than the content accepted by French legislation (0.234 x 10 6 g / J .).

These figures are to be compared with those of known coal / water mixtures containing 70% carbon and 30% water. The PCI of such a mixture is only 5145 Kcal / kg (21,506 kJ) and contains approximately 6% ash corresponding to 2,785 x 10 6 9 ash per Joule. On the other hand, in terms of viscosity, the mixtures described by the invention range over a range from 20 Pa> to 150 Depending on the granu
Lometry of the coal used against viscosities of the order of 200 PeA for the conventional 70/30 coal / water mixtures.

 A mixture in accordance with the invention presents no difficulty during combustion. Preheating the combustion chamber is not necessary; ignition is simplified by the presence of liquid fuel, so that intermittent operation is possible without difficulty.

 The process of the invention also has the advantage of not imposing a limit lower than the size of the particles of coal to be treated. It is therefore favorable to the realization of a deep ash removal from the coal.

 Currently, French regulations impose, for the reduction of Atmospheric pollution, an ash content entrained by combustion gases of 1 g per therm (lu / 4180 kJ) produced in generators with a power lower than 3000 therms / hour (12.540 .1û3 kJ). For coal with a PCI of 7500 KcalSkg (31.350 kJ), its ash content must be less than 0.75 x if it is burned pure. Such low contents can only be obtained with a limited quantity of coal and this at a high cost.

 The mixture described by the invention, thanks to the presence of a fraction of liquid hydrocarbon, allows the use of ash coals at a content of about 1%.

To purify a coal to such an ash content of less than 1%, grinding must be carried out until all the particles have an internal size of 20 microns.

 The process of the invention is perfectly compatible with this condition, at an admissible cost from the economic point of view. On the contrary, the finer the particles, the more certain it is that they will remain in suspension in the combustible fluid mixture of the invention and that no sedimentation will be to be feared.

 A description will now be given of an example of implementation of the process of the invention with reference to the single appended figure which is a schematic representation of an installation usable for the use of the process.

 We start from a pulverulent coal of grain size common in industry; for example in particles of maximum dimensions less than about 2 mm; in a grinder, for example a ball mill, the particles are reduced to a size less than 200 microns.

 In a tank 1, the coal thus pre-ground is introduced via a pipe 2 and water through a pipe 3. Using a stirrer 4, a homogeneous suspension is produced at a concentration of 30 to 40% by weight of carbon relative to the weight of the mixture. From this stage, the treated product is pumpable and will remain so until the final mixture which is also pumpable is obtained.

 By a pump 5 the suspension from tank 1 is sent to a ball mill 6 where the particle size is reduced to a maximum size of 20 μm.

 This operation of reducing coal into grains of size less than 200 wm, depending on the desired final ash content, could be carried out using other equivalent means.

 The finely ground water-coal mixture is sent via a pipe 7 to a tank 8 where water is added via a pipe 9.

 A stirrer 10 makes it possible to produce a homogeneous slurry containing 10 to 15% by weight of coal.

 The binder (of domestic fuel oil) contained in a tank 11 is taken up by a metering pump 12 at the same time as The mixture of The tank 8 to produce a homogeneous ternary mixture of coal-water-hydrocarbon. The proportion of the latter depends on the size of the particles of the ground coal; it is between 30% of the weight of the ground coal when it has been reduced to particles with an average size of 10 microns and 5% of the weight of the coal for an average size of around 100 microns.

 In the present example with a slurry composed of 15 X in weight of ground coal at an average size of 15 microns, a quantity of domestic fuel equal to 30% of the weight of the coal is added.

 The output of the metering pump 12 is connected to a pipe 13 on which is mounted an agitator 14.

 Any known online dynamic agitator may be suitable. It is preferable to use an agitator capable of creating a high shear rate to ensure good dispersion of the high hydrocarbon and to promote as much as possible the encounter between the latter and the carbon particles. Small agglomerates are formed, for example several tens of microns, of carbon, while the fine particles of the sterile materials remain dispersed in suspension in water.

The assembly is sent into a vibrating screen 15 to which washing water is added via a pipe 16. The agglomerates of coal which have not passed through the screen are sent into a vacuum filtration device 17 (a filter under pressure could also be used) in order to concentrate the mixture by removing the part of the water which is in excess of its desired final content. At this stage, the quantity of water eliminated is important. It is carried out until the charred ash represents approximately 53% by weight of solid matter relative to the total weight of the mixture which is composed of coal, water and hydrocarbon binder. The composition is typically as follows, in weight of total mixture
. charred coal about 53 x
water about 31.1%
domestic fuel approximately 15.9%
This mixture is then sent to a final preparation tank 18 in which is installed an agitator 19 and where a hydrocarbon pipe 20 and a surfactant pipe 21 terminate.

The amount of domestic fuel added is determined so that the proportion of the latter is approximately 19%, which gives the following final composition, by weight of the total mixture:
- coal approximately 50 X
. water about 29.5 X
- domestic fuel approximately 19%
. surfactant about 1.5%
The mixture thus formulated has a viscosity of less than 100 Ps measured with the DRAGE viscometer.

The surfactant provides an additional guarantee of absence of sedimentation and conservation of
The homogeneity of the mixture obtained during storage until the time of use in a storage tank 22 and during the transfers which will follow, mainly from the point of view of the emulsion of water and of the hydrocarbon.

In another example, using the same installation and grinding the coal to the same average particle size, a mixture having the following composition was prepared before the final preparation tank 21:
- charred coal approximately 60 X
- water about 22 X
- domestic fuel approximately 18 X
Then domestic fuel and a surfactant were added to the tank 21 to arrive at the following final composition, by weight of the total mixture:
. coal about 50%
. water about 18.3 X
. domestic fuel approximately 30%
surfactant about 1.5%
The viscosity of this mixture is 130 Pz 5 measured with the DRAGE viscometer.

 It will be noted that the addition of liquid hydrocarbon, which is ash-free, makes it possible to obtain a fluid ternary mixture with reduced ash rate. It suffices to ash the coal down to a percentage of 0.8% so that, in a final mixture where the hydrocarbon and water enter together for 50%, an ash rate of 0.40% is obtained.

 Crushing the raw coal to a fineness of 0 to 20 µm is very suitable because this value makes it possible to eliminate the ash, as explained above, up to a residual ash rate not exceeding 1%, with most of the coals. Then, after adding water and hydrocarbon in the proportions indicated, the ash content of the fluid ternary mixture is lowered to at least 0.50%.

 One can find certain qualities of coal which do not make it possible to reach an ash content of less than 1% in a single ash removal step as described above in accordance with the process of the invention. It is possible, without departing from the scope of the invention, to apply the two-step process. The first step consists in grinding the coal to be ashed to a medium degree of fineness (for example around 6Q pm, with 80% of the grains of size-less than 80 hum) and to treat it as explained above by adding a reduced quantity agglomerating agent in relation to the size of the ground grains (for example approximately 5% by weight relative to the weight of the coal). This makes it possible to lower the ash rate to a level close to 2% with most coals.

 After filtering, washing and eliminating the water as explained above, this already treated carbon is then subjected to further grinding until a granulometry between 0 and 20ftm (average value 10 /> m) as mentioned above. It is treated again as already described by adding the additional agglomerant to the indicated value (for example up to 30%). The ash content of the coal treated a second time by the process of the invention does not then exceed 1% in most cases. This second treatment is continued until the desired ternary mixture is obtained.

 The invention does not preclude the addition to the mixture defined above of various adjuvants, as is known per se in the field of liquid fuels, without substantial change in the relative proportions of the three main components.

Claims (10)

 1. Fluid mixture with three main components, carbon base, characterized in that these three components are presented in the following relative proportions:  . coal in particles of size does not  not exceeding 200 lin 40 to 60%  . water 16 to 35%  . agglomerating liquid fuel  derived from petroleum 16 to 35% these proportions being understood by weight of the total weight, of these three main components.  2. Fluid mixture according to claim 1, additionally containing a surfactant, characterized in that the components are present in the following relative proportions  . coal 40 to 58%  . water 16 to 35%  . petroleum derivative 16 to 35%  . surfactant 0.5 to 2%, these proportions being by weight of the total weight of these four components.  3. Mixture according to any one of claims 1, 2, characterized in that the charcoal is in particular of a size not exceeding 20 μm with a residual ash content equal to approximately 1%.  4. Mixture according to any one of claims 1 to 3, characterized in that the petroleum derivative is chosen from the following bodies, domestic fuel oil, fraction lighter than domestic fuel oil such as pentane, hexane, heptane, a fraction heavier than domestic fuel oil, a mixture of these bodies.  5. Mixture according to any one of claims 1 to 3, characterized in that the surfactant is chosen from nonionic surfactants containing at least one polyethylene glycol or polypropylene glycol unit, such as Phenols, alkylphenols, amines, diamines, polyethoxylated, polypropoxylated phosphates, bodies containing at least one polyalkoxylated unit such as polyethylene glycols, polypropylene glycols. polyalkyleneglycols.  6. Process for the preparation of a ternary fluid mixture, with three main components, from raw coal containing sterile materials, characterized in that it comprises the following operations:  the carbon is reduced to particles the size of which does not exceed 200 μm,  a homogeneous mixture of the ground coal obtained and of water is prepared,  - Adding to this mixture an agglomerating liquid fuel derived from petroleum and stirring to obtain a homogeneous ternary mixture comprising coal and liquid fuel in a proportion of between approximately 30% by weight of this liquid fuel relative to the weight of coal when that this is in particles of an average size of 10 microns and approximately 5% by weight of this liquid fuel relative to the weight of the coal when the latter is in particles of an average size close to 100 microns,  - the mixture is filtered and washed to remove sterile materials,  - the water is eliminated to a content which corresponds to its desired final content, between 16 and 35% by weight of the final mixture,  - Adding liquid fuel binder derived from petroleum to give it a content of between 16 and 35% by weight of the final mixture.  7. Method according to claim 6, characterized in that a surfactant is added to the mixture in a proportion of between 0.5 X and 2 X by weight of the final mixture.  8. Method according to claim 6, characterized in that the carbon is reduced to particles of average size less than 15 microns, preferably between 5 microns and 20 microns.  9. Method according to claim 6, characterized in that as agglomerating fuel derived from petroleum at least one of the following bodies, domestic fuel oil, is used a fraction lighter than domestic fuel oil such as pentane, hexane, heptane, a fraction heavier than domestic fuel oil.  10. A method of preparing a ternary fluid mixture with three main components, from raw coal containing sterile materials, characterized in that the operations of the process of claim 6 are applied to this coal for the first time. elimination of the water, by grinding this coal to a first average size of 60 lim and using a reduced quantity of agglomerating liquid fuel equal to approximately 5% of the weight relative to the weight of the coal, then a second application is applied to this coal the process of claim 6 until the desired ternary mixture is obtained by subjecting it to a grinding operation which gives it an average size of 10 lim and by using an amount of additional agglomerating liquid fuel up to 30 % by weight relative to the weight of the coal, and then performing the filtering, washing, water removal and final addition of agglomerating liquid fuel operations.