RU2100267C1 - Method of preparation and transportation of concentrated mixtures of coal and water along pipelines - Google Patents

Abstract

FIELD: materials handling. SUBSTANCE: according to proposed method, concentrated mixtures of coal and water are prepared by delivering definite amounts of dispersing addition in preset sequence. EFFECT: enlarged operating capabilities. 6 cl, 6 tbl

Description

 The invention relates to a method for producing concentrated suspensions of coal in water and transporting these suspensions through pipelines.

 Concentrated suspensions of finely ground coal (maximum diameter ≅300 μm) in water (CWM), which can be directly fed to the steam boiler without preliminary dehydration, as disclosed, for example (UK patent N 2099451, class C 10 L 1/32, 1982) , represent an interesting option for producing carbon-containing fuel for steam boilers designed to work with diesel fuel, and which, therefore, can not work with solid fuel.

 The use of such suspensions has particular advantages, both financially and from the point of view of environmental protection, when coal must be transported over long distances from the place of its extraction, where the equipment for receiving the suspension is also installed, to the place of use.

 In an integrated system, in order to compensate for different rhythms of production and consumption, tanks for storing aqueous coal suspensions at the start and end stations of the coal transport pipeline are provided, and the storage time can exceed two months.

 The most important technological properties of CWM are the combustion characteristics together with the stability during pumping and storage. Therefore, the optimal composition should have both of these properties, while minimizing the added amounts of the additive in order to keep its cost limited.

 High concentrations of coal, which define the suspension as fuel (≥60% by weight, preferably ≥70% by weight) can only be obtained through the use of dispersants and the selection of a suitable particle size distribution.

 As dispersing additives, anionic and cationic surfactants are used, nonionic with a high molecular weight (for example: copolymers of alkylene oxide obtained from alkylphenol or alkylene glycols, or alkylene diamines) and polyelectrolytes, in particular, sulfonated surfactants containing multinuclear, alkyl substituted aromatic components and having a higher molecular weight than 300. Among them, salts of monovalent cations of alkyl naphthalenesulfonic acids, c ndensirovannyh with formaldehyde, and among these the compounds known under the trade designation Daxad 15 (W.R. Grace) and Fluidix 05 (Bozzetto).

 Other things being the same, the viscosity of the suspension depends on the amount of dispersant added. Initially, viscosity decreases with increasing added quantities. Since the dispersant additive represents a significant cost (approximately 30% of the production cost of the suspension), the addition of the additive should be accordingly limited until a minimum viscosity is obtained.

 When the level of the additive exceeds this optimal value, then there is no further improvement in yield, on the contrary, in many cases there is a slight increase in viscosity, and the cost of production increases. In the case of an imperfect composition, it is known that the viscosity of the suspension can change over time during long pumping operations, because pumping leads to consumption of the additive, resulting in a decrease in the concentration of free additive in the aqueous solution, which can be separated from the suspension by centrifugation or filtration of the same suspension (11th Int. Conf. On Hydraulic Solid State Transport on Pipes, Stratford-upon-Avon, United Kingdom, 1988).

 If this increase in viscosity resulting from the consumption of the additive during pumping is not controlled, the viscosity of the slurry can reach such high levels that it makes the slurry difficult to pump.

 A known method of preparation and transportation through pipelines of concentrated mixtures of coal in water, including the stage of preparation of the suspension by wet grinding in the presence of one or more dispersing additives and the stage of transportation by one or more pumping stations (application DE, N 3621319, class C 10 L 1 / 32, 1988).

 According to this method, in order to ensure the stability of the pumping process, the dispersing additive is added in excess over the amount of the additive, which was determined as the optimal amount to obtain the minimum viscosity, already at the stage of preparing the suspension during grinding. Due to the fact that the amount of excess additives needed for transport depends on a large number of factors, in particular, on the physical and chemical properties of coal (for example, chemical composition, hydrophilic-lipophilic balance (HLB HLB) of its surface, ability to absorb water, mechanical abrasion resistance, particle size distribution, particle shape, porometric distribution, on the properties of the mixture (e.g., solid concentration, rheological behavior, degree of aggregation or flocculation) and on hydro conditions The speaker during transport, including passage through the pumps, it is obvious that such an excess amount can be estimated only in some approximation.

 Taking into account the significant losses arising from a possible revaluation, conservative criteria are applied in practice, so that the quantity added is in excess of the quantity that is assumed to be strictly necessary for transportation.

 According to the known method, the doses of dispersants add up to 800% of the amount that makes it possible to obtain a minimum viscosity ("amount for a minimum viscosity"). This has, as we have established, undoubtedly negatively affect the static stability of the suspension, even in the presence of stabilizing additives.

 The purpose of the invention is the elimination of the described disadvantages that have occurred in the prior art.

 In particular, in accordance with the method of the present invention, coal-water mixtures can be made pumpable and storage stable without the need for an excess of dispersant.

Accordingly, according to the present invention, at the stage of preparing the suspension, dispersing additives are introduced in an amount minimally necessary to obtain an initial viscosity of the suspension in the range from 0.8 to 1.5 Pa • s at a shear flow rate of 10 s ^-1 , and at the stage of transportation in one or more portions, an additional dispersant is added in an amount that limits the increase in viscosity of the suspension to less than 30% relative to the initial viscosity.

 In addition, at the transportation stage, an additional additive is introduced in an amount that limits the increase in the viscosity of the suspension to a value less than 20% relative to the initial viscosity of the suspension.

 In accordance with the described method, the dispersant or dispersant mixture belongs to the class of alkali metal or ammonium sulfonates.

 Further, in accordance with the described method, the dispersant may belong to the class of alkali metal or ammonium naphthalenesulfonates or alkylnaphthalenesulfonates condensed with formaldehyde.

 In addition, according to the invention, during the transporting stage, the introduction of the dispersing additive is controlled by means of viscometers and dispensers of this additive installed on the pipeline and driven by viscometers when the maximum permissible viscosity is exceeded.

 At the same time, the viscosity and doses of the additive are controlled at the pumping stations of the pipeline line by means of the aforementioned viscometers and dispensers installed on them.

 The term "concentrated mixture of coal in water" refers to aqueous suspensions of finely divided solid fuels, including lignites, bituminous coals, low-grade anthracites, anthracites, coke and other products obtained from coal during heat treatments, petroleum coke, graphite and others high carbon compounds.

 You can also use coal obtained in the process of demineralization and / or desulfurization, in particular, through selective agglomeration, for example (US patent, 4776859).

 According to the present invention, suspensions may contain, for example, from 40 to 85%, preferably from 55 to 80%, of a solid fuel having a particle size distribution characterized by an average diameter of ≅200 μm, preferably ≅50 μm. Particularly preferred are bimodal particle size distributions consisting of two groups of particles with different average sizes, where the first group of particles has an average size within the range of 200-50 microns and the second group of particles has an average size in the range of 1-40 microns.

 In accordance with the present invention, the batchwise addition of the dispersant is achieved, i.e. such a multiple of a portion, its amount, which corresponds to the minimum viscosity for each particular type of solid component and the concentration of the solid component in the suspension, and which is added at the preparation stage. The remaining portions of the additive are added later when the viscosity during transportation exceeds a certain predetermined value, which is in the range of 5-50% of the established viscosity during transportation.

 The amount of dispersant to be added during the transportation step varies in accordance with the parameters mentioned above.

 As dispersing additives, anionic, cationic, nonionic and amphoteric compounds can be used, either as separate compounds or as mixtures. Preferred are anionic sulfonated dispersants used as alkali metal or ammonium salts. Even more preferred are alkali metal or ammonium salts of naphthalenesulfonates or alkylnaphthalenesulfonates condensed with formaldehyde.

 The minimum amount that is necessary in order to have the highest fluidity during the CWM preparation step is a function of many parameters, in particular, the type of coal, its concentration in suspension, the type of additive.

 For illustrative purposes, the minimum concentration of a sulfonated additive, such as a salt of naphthalenesulfonic acid condensed with formaldehyde, necessary to obtain the highest yield at the stage of obtaining a concentrated suspension, lies in the range of 0.4-1.5% with respect to the total weight of the suspension.

 For illustrative purposes, the minimum concentration of Daxad 15 required to obtain the minimum viscosity in a suspension containing 62 wt. coal having the characteristics given in table. 1, turned out to be equal to 1.0 wt. (based on the weight of the suspension).

In addition to water, solid fuel and dispersant, in accordance with the present invention, suspensions may contain: miscible with water organic substances (for example, C ₁ -C ₆ aliphatic alcohols such as methanol, ethanol, etc.), anti-foaming agents, stabilizing additives (for example, bentonite (disclosed Italian patent N 20456 A / 85), polysaccharides, xanthan gums and polyactylamides), biocidal substances and other liquid or semi-liquid fuels, for example: diesel fuel, oil residues, naphtha, petroleum gas, etc.

 In accordance with the present invention, the production of the suspension can be carried out by various procedures, preferably by wet grinding in two stages, as disclosed in the aforementioned patent (UK N 2099451).

 As regards the solution consisting in the sole addition of a dispersant at the stage of preparing the suspension, the method of the present invention has the advantage that, at the same pumping capacity, a higher static stability of the suspension is achieved, followed by storage for longer periods of time as in the initial station, and at the arrival station.

 The following examples are provided to better illustrate the present invention.

Examples
We prepared various aqueous suspensions of Colombian bituminous coal (see Table 1 for its characteristics) by the two-stage wet grinding method (as disclosed in the aforementioned GB, Patent No. 2099451), using Daxad 15 as a dispersing additive (hereinafter “D15”) and in those bentonite as a stabilizing agent. The grinding times were controlled in such a way as to obtain the same particle size distribution for all suspensions, characterized by an average diameter of 20 ± 1 μm and a fraction remaining above a sieve with a mesh size of 200 μm, 7.0 ± 0.5%
The viscosity of the suspensions was measured by a rotational viscometer operating at 10 s ^-1 , a typical value for shear rate during transport over long distances.

The behavior of the suspension during pumping was modeled by a laboratory test (extracted from the Metzner and Otto method, Aiche Journal, 1957, v. 8, No. 1, p. 3 and already described in the past: see the 11th International Conference on Hydraulic Transport of Solids in Pipes), in which the suspension is treated at a constant speed of rotation so that the equivalent shear rate is 10 s ^-1 , and continuously measure the torsional force. By suitable calibrations with liquids of known viscosity, the torsion signal is converted to viscosity.

 The test result was summarized as the time required to reach a viscosity value that is doubled relative to the initial viscosity value, or percentage increase in viscosity, relative to the initial viscosity value, after the set mixing time.

The pumping behavior at low shear rates was simulated as described above, but acting at such rotational speeds that the equivalent shear rate was 1 s ^-1 . The height of the precipitate at the end of the mixing test was assessed by penetration into the specified precipitate of a solid plexiglass rod weighing 15 g ("rod penetration test"), commonly used to evaluate the stability of coal suspensions (e.g., The Chem. Eng. Journal, 1985, v. 31 p. 175).

 The test result was summed as the height of the sediment, which can withstand the weight of the rod.

Stability under static conditions was evaluated by tests on the deposition inside glass tubes (inner diameter 40 mm, useful height 450 mm), thermostated at 20 ^o C. At the end of the shelf life, which was determined in 60 days, the contents of the tube were divided into three parts: , the central and lower parts, and for each of these parts, the concentration of solids was determined by gravimetric measurements. The test result is given as a parameter indicated by “percent deposition”, S, calculated as follows:
S (C _F -C ^average • (C ^max C ^average ),
where C is ^average (C _t + C _M + C _F ) / 3,
C _t , C _M , C _F, respectively, the concentration of solids in the head, central and lower lobes,
C ^max concentration of the maximum solids packing obtained in the lower zone of the test tube by centrifuging the suspension at 20,000 rpm (equivalent to 49,000 times gravitational acceleration) for 20 minutes

With this determination, the deposition percentage S can vary from 0, for a perfectly stable suspension with a homogeneous concentration distribution (C _t = C _M = C _F ), to 100, for a completely unstable suspension, for which C _F C ^max . In the latter case, the sediment behaves like a solid and, obviously, is no longer pumped.

 Characteristics of coal, wt.

Humidity 6.1
Volatiles 36.4
Ash N 6.6
Bound carbon (by difference) 50.9
Carbon 69.9
Hydrogen 5.4
Nitrogen 1.5
Sulfur 0.6
Oxygen (By Difference) 16.0
Heat capacity 28,800 kJ / kg
Example 1. Prepared five aqueous suspensions containing 62.0% of Colombian coal, having the characteristics presented in the above characteristics for coal and various amounts of D 15. It turned out that the optimal level of D 15 to obtain the minimum viscosity is 1.0% (table. 1).

 Example 2. Suspensions NN 2, 3, 4 and 5 were tested for stability during pumping and sedimentation. Pumping stability, presented as the time required to reach a viscosity that is doubled from the initial viscosity, with the same stirring increases with increasing levels of D 15. On the contrary, static stability decreases with increasing levels of D 15 (Table 2).

 Example 3. Suspension No. 3, corresponding to the minimum viscosity value (Table 1), was subjected to a simulated pumping test in which additional dispersing additives were added to the suspension using a burette as soon as the viscosity reached a 5% increase relative to the initial value. The test was carried out for a set time of 270 hours, equal to the test time for the same suspension of N 3 as in example 2 (table 2), in which no dispersing substance was added. The total amount of D 15 (i.e., the amount of D 15 added at the preparation stage, plus the amount of D 15 added during the test) is 1.2 wt. calculated on the suspension.

 The results at the same mixing time, including those obtained in Example 2, in which the entire additive was added at the preparation stage, are presented in table. 3. The third column of this Table shows the percentage increase in viscosity after 270 hours of stirring. With the same total amount of D 15 (1.2 wt.) Received an equivalent characteristic of stability with stirring.

 Example 4. On samples already subjected to a test for simulated 270-hour pumping, as in Example 3, conducted a test for static stability. The results are presented in table. 4.

 With the same total amount of D 15, equivalent static stability values were obtained.

 We recall that, before being subjected to the pumping step, the N 3 suspension showed a higher resistance to precipitation than the N 4 suspension (Table 2).

 Suspension N 5, characterized by a large excess of D 15, was, on the contrary, much less stable than suspension NN 3 and 4.

 Example 5 (Comparative example). On suspensions NN 3, 4 and 5, a simulated pumping test was carried out with a low shear rate for a set time of 270 hours, the results are presented in table. 5.

 Suspension N 5, characterized by a large excess of D 15, shows evidence of precipitation.

Example 6 (Comparative Example). Prepared four suspensions of the same viscosity (1.20 Pa • s at 10 s ^-1 ) and containing the same level of D 15 (1.2 wt.) With different amounts of coal and bentonite, acting as a stabilizing additive. The same indicator of static stability of suspension N 3, i.e. having a minimum viscosity value (table. 2), obtained with a bentonite content of about 1.5% per suspension, but due to a large decrease in the level of coal, which fell from 62 to 57 wt. For a suspension containing only 57 wt. coal, there may be difficulties in combustion due to the low heat capacity of such a suspension.

 The results are presented in table. 6.

Claims (6)

1. The method of preparation and transportation through pipelines of concentrated mixtures of coal in water, including the stage of preparation of the suspension by wet grinding in the presence of one or more dispersing additives and the stage of transportation by one or more pumping stations, characterized in that at the stage of preparation of the suspension dispersing additives are introduced into the amount minimally necessary to obtain the initial viscosity of the suspension in the range of 0.8 1.5 Pa • s at a shear flow rate of 10 s ^{- 1} , and at the stage When transporting one or more portions, an additional dispersant is added in an amount that limits the increase in viscosity of the suspension by an amount less than 30% relative to the initial viscosity.  2. The method according to claim 1, characterized in that one or more portions introduce an additional additive in an amount that limits the increase in viscosity of the suspension by an amount less than 20% relative to the initial viscosity of the suspension.  3. The method according to claim 1 or 2, characterized in that the dispersant or mixture of dispersant additives belongs to the class of sulfates of alkali metals or ammonium.  4. The method according to claim 3, characterized in that the dispersing additive belongs to the class of alkali metal or ammonium naphthalenesulfonates or alkylnaphthalenesulfonates condensed with formaldehyde.  5. The method according to one of claims 1 to 4, characterized in that during the transportation stage the dispersing additive is controlled by means of viscometers and dispensers of this additive installed on the piping line, driven by viscometers when the maximum permissible viscosity is exceeded.  6. The method according to claim 5, characterized in that the viscosity and dosage of the additive are controlled at the pumping stations of the pipeline line by means of the aforementioned viscometers and dispensers installed on them.

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