FR2575489A1 - PROCESS FOR THE PREPARATION OF AQUEOUS SUSPENSIONS OF HIGH-SOLID FUELS BY PERFORMING THE OPTIMAL GRANULOMETRIC DISTRIBUTION - Google Patents

Abstract

A CRUDE COAL MILLED WITH A GRANULOMETRY OF 0-15MM FEEDS A B1 CRUSHER IN THE PRESENCE OF WATER. THE CRUSHED PRODUCT IS SCREENED ON THE C SCREEN AND THE PASSANT IS THE COARSE FRACTION OF THE FINAL MIXTURE. THE REFUSAL USED TO CONSTITUTE THE MEDIUM AND THIN SLICES IS CRUSHED IN B2 AND SCREENED, THEN SUPPLIES A FIRST HYDROCYCLONE HC1 WHOSE OVERVIEW 5 SUPPLIES A SECOND HYDROCYCLONE HC2. THE FINES RECOVERED IN THE SUBVERSE 4 OF THE HC1 AND IN THE OVERVIEW 7 OF THE HC2 CONSTITUTE A SECOND CONSTITUENT OF THE FINAL MIXTURE. THE EXCESS OF THE BIGS FROM THE UNDERVERSE OF THE HC2 IS GRINDED INTO B3 INTO ULTRA-FINE PARTICLES WHICH FORM A THIRD CONSTITUENT OF THE FINAL MIXTURE. SUSPENSIONS OF FUELS WITH A CONTENT OF MORE THAN 45 IN SOLIDS, SUITABLE FOR TRANSPORTATION AND USE.

Description

The present invention relates to the preparation of aqueous suspensions

  of solid fuels with a high solids content by carrying out

  optimum particle size distribution.

  The use of coal as an industrial energy source had

  badly shrunk with the development of cheap petroleum products. The return to this source of energy widely available in the world appeared as the solution for the survival of the activity beyond the oil shocks and in the more or less long term of the exhaustion of

  low-cost oil sources.

  This return of coal and more generally of solid fuels, remained handicapped by the difficulties of handling and implementation of this unsuitable material in the state to simple modern reliable solutions, automatable in good conditions of safety and with little

impact on the environment.

  One of the most suitable ways of using coal in a modern form is represented by coal mixtures with a high solids content, but used for their liquid presentation.

like petroleum products.

  The numerous researches carried out in recent years in this field have shown that one of the conditions to be met in order to obtain

  such mixtures is a good particle size distribution of parti-

  solids. The optimal distribution should result in filling as much as possible of the particle size vacuums

  left by a granulometric slice given by grain size

sion smaller.

  Indeed, the particle size distribution curve of particles

  The result of grinding using a grinder is a bell curve in which most of the crushed material is around average. When two constituents are mixed each from a mill with special characteristics, the particle size distribution curve has two peaks and is a curve called bimodal. Such methods do not make it possible to satisfy perfectly

on the condition mentioned above.

  The work whose results were the subject of US Pat. No. 4,282,006 showed that the optimal distribution can be constituted by a mixture of particles of size less than 1180 μm containing at least 5% by weight of particles smaller than 3. pm, whose particle size distribution is according to the formula of Alfred according to the equation: D. Dn Tamisat% = Mi s DLn Ds n in which DMi is the median size of the particle size range considered in Mm, Ds the size of the most small particles in um, DL the size of the largest particles, n an exponent whose value varies from 0.2 to 1.0. The particle size distribution curve according to this formula is a

  exponential curve with increasing values with the size of parti-

  cules not showing peaks or no pronounced peaks.

  According to the known methods for obtaining such mixtures, one can mix several constituents each from a grinding mode

  different, sometimes by clipping certain fractions.

  Such a method inevitably leads to the elimination and reprocessing of

  several stages of certain fractions and does not appear economical.

  Another method is to carry out a high-density grinding step in a single step by means of periodic sampling to check the conformity of their particle size distribution with that of the Alfred curve. This method has the disadvantage of a high energy consumption because the comminution is not performed according to the conventional law of reduction and a large part of the energy supplied is dissipated as heat. Although close to the ideal curve, however, the distribution needs to be corrected on the bulk side by removing particles larger than 200 μm, for example, and on the fine side by adding very fine particles obtained separately using another. grinding medium. Moreover, it is impossible according to this method to add a deashing technique without diluting the suspension, to which

  case the initial profit of operation in one step is lost.

  The present invention relates to a process for the preparation of suspen-

  high solids content according to the particle size distribution according to the Alfred equation and is based on the use of hydrocyclones in

as a means of classification.

  As with all means of classification, a hydrocyclone is

  tered by its cut-off slice with an

  the percentage of this slice being offset by the underflow. For example, a hydrocyclone designated d90 whose cutoff slice is 70 pm operates a separation in which 90% of the slice of about 90

  flows in underflow and 10% of the same slice in overflow.

  While a sieve produces slices, the hydrocyclones *; - :. _. They believe that they are opting for these imperfections and that they benefit from the present fnvce% to constitute an ideal distribution with a minimum of

  depe-ss energy and the greatest simplicity and efficiency.

  The method according to the invention is characterized in that it feeds a hydrocyclone crushed particles whose particle size most

  is less than X lma X being at most equal to 1180 Mm, the said hydro-

  a cyclone operating in a separation in which 90% of the cutoff slice varying between 1/4 and 1/2 of X flows underflow and 10% of the same slice overflow, the overflow feeding a second hydrocyclone having the same characteristics of cutting than the first, the overflow of the second

  hydrocyclone being combined with the underflow of the first and forming a

  killing the final mixture, the underflow of the second hydrocyclone being milled in a fine mill into a mixture of particles whose size for 80% of the mixture is between 1/10 and 1/20 of X and which forms another constituent of the final mixture, the two drugs being poured into a container of

  mixture in which the solids content is at least 45%.

  One of the important characteristics of the process according to the invention rests on the use of means of compromise such as they correspond to the production of the desired granulometric slices in the best

  conditions of efficiency, while the granulometric slices not retained

  in a given stage are reprocessed in the next step to produce a new granulometric slice according to the needs of the

  granulometric distribution of the final product.

  Thus, according to a preferred embodiment, the raw fuel is ground first in a grinder of the bar-mill type producing relatively coarse grains which, screened on a screen, leave loops constituting the relatively coarse fraction of the final product and refusals. which are subjected to a finer grinding in a mill type

  balls whose screened grinding products leave passersby

  intended to constitute the medium and fine slices of the final product,

  passing fraction feeding the first, then the second hydrocyclone.

  The refusals of the first grinding of the type of bar mill circulate in closed circuit between the mill; ball type and a screen of the same characteristics as the screen used to screen the product from

first bar-type grinder.

  Passersby resulting from the screening of products of the first grinding can

  be poured directly into the mixing tank as a component

  killing final, feed the first and then the second hydrocyclone together with passers-by resulting from the screening of products from the

? 7548 9

  second crusher of the type blets.

  The underflow of the second hydrocyclone is ground into ultrahigh particles

fine in an attrition mill.

  The product from the ball mill is characterized by a distribution

  unimodal concentration centered on the dimensions corresponding to the average slices of the final product. However, the proportion of these slices far exceeds needs. It is the combined hydrocyclone set which allows the extraction of these slices to be adjusted according to the need while cutting the superabundant medium slices which are evacuated at the level of the second hydrocyclone underflow. The fine regrinding of this excess in the attritor crusher finally makes it possible to produce the complement

  fine needed for the final distribution.

  According to an embodiment that is particularly suitable for treating

  coal, the raw coal must have a grain size of 0 to 15 mm.

  Grinding reducing the coal to this particle size can be operated by various means similar to the grinding by means of a bar mill. it can result from a previous treatment or be carried out within the framework of the production facility of the granulometry

  desired according to the invention in which it precedes the group of hydro-

  cyclones. In the latter case, the raw fuel in particles of 0 to 15 mm is milled in a bar mill in water, the grinding product is sorted on a screen whose mesh size is pm, the sieve refusals feeding a ball mill into the water,

  the product of this last grinding is sieved on a sieve whose opening

  mesh size is 200 μm and the recirculated refusals in a closed circuit to the ball mill, the passing fractions of the two sieves

  feed a first, then a second hydrocyclone.

  The screen in this case is common for products from bar and ball mills, the recovery of large particles being entrusted to the first hydrocyclone, under which they are discharged together with the large particles resulting from grinding

using the ball mill.

  Alternatively, the product of the first bar mill is classified into two fractions each of which constitutes 45 to 55% of the ground product, the pass-through fraction is directly poured into the final mixing tank as the final component, while the refusals are

  milled in the ball mill to be reduced

  - by the grain size imposed by the size of the openings of the screen, and the product classified on a sieve whose passers-by

  feed a first, then a second hydrocyclone.

  In particular, the first hydrocyclone operates a separation in which 90% of the 70 m slice slice flows underflow and 10% of this same flowing slice of this first hydrocyclone feed the second hydrocyclone. performing a separation in which 90% of the 70 μm cutting slice flows underflow to feed an attritor mill in which the solids are ground to the maximum size of 15 Mm, while the underflow product of the first hydrocyclone is collected with the overflow product of the second

  hydrocyclone to be mixed in the final mixing tank with the

  lO duit coming out of the attritor mill.

  Other features of the invention will appear in the light of

  the description of an embodiment of the process presented as a

  non-limiting example using drawing, Figure 1 shows a diagram of the process Figure 2 a particle size distribution diagram of the final mixture, and Table 1 showing the distribution of relative weight slices granulometric. The invention is illustrated by a process applied to an American bituminous coal of the Freeport type. This crushed raw coal with a grain size of 0 to 15 mm feeds a mill with bars B1 in the presence of water producing relatively coarse grains of which 80% measures less than 800 pmm The crushed product is driven by 1 on a screen C constituted by a woven fabric passing about 54% of the crushed product of lower particle size

  at 200 pm. This fraction is completely recovered without further treatment.

  to form the coarse fraction of the final product. The refusal of screening is then used to form the medium and fine slices of the final product. To this end, this refusal is first reduced to a total dimension of less than 200 Mm by a ball mill B2 in the presence of water, the treated product circulating by means of the pipe 2 in a closed circuit between the mill B2 and the screen C.

  Screen C is common to mills B1 and B2.

  The product from mill B2 is characterized by a unimodal distribution centered on the dimensions corresponding to the average slices of the final product. However, the proportion of these slices far exceeds needs. It is the combined set of hydrocyclones HC1 and HC2 that allows to adjust the extraction of these slices according to the need, while cutting the superabundant medium slices that are evacuated

  at the level of the underflow of the hydrocyclone HC2.

  The set of passers of the HC1 hydrocyclone sieve C, whose cutting edge is 70 pm and the partition coefficient 90%. of the

  fines are passed under 4 in decreasing quantity with their granulo-

  metry. The large pass in the overflow 5 in decreasing quantities for slices of decreasing grain size. This is taken advantage of

  to separate by the overflow certain slices which would be over-

  in the final granulometric composition as required

of the ideal curve.

  It is the purpose of the second hydrocyclone HC2 of the same cutting characteristics as the first and fed by the overflow 5 to recover underwater these large superabundants to then subject them to fine grinding in the mill B3 working attrition. As the fines do

  are not in excess of the final composition, they are

  pereduced by the underflow 4 of the first hydrocyclone HC1 and finally in the overflow 7 of the second hydrocyclone HC2. The two streams 4 and 7 are combined at 8, drained in a drum filter F1 and poured into a final mixing tank M as a final constituent of the mixture.

  Excess fat recovered in 6 in the underflow of the first hydrocyclic

  lone HC1 feed by 6 a drum filter F2, then are regrinded ultra-fine 80% of which is measured at most 15 pm in attritor mill B3 and the milled product is poured through line 9 into the mixing tank M, in which the water content is adjusted to achieve

  a suspension of 50% or more solids.

  At several points along the route, it is possible to introduce decen-

DC dredging.

  This exemplary embodiment illustrates the application of the Alfred formula

  for the following values: QL = 200 μm, Ds = 0.2 μm, n = 0.37,

  which corresponds to Table 1 of the various granular

  intermediate and final metrics, as well as. the diagram showing

  in percentage by weight the various granulometric slices constituting

  killing the final mix. The origin of the fractions of these slices is indicated as follows: ascending scratches: the passers on screen C direct from the B1 bar mill descending scratches: passers on the screen C from the ball mill B2

  round marks: the fines recovered in the overflow 7 of the second hydro-

  cyclone HC2 crosses: large overflows of hydrocyclones HC1 and HC2 ii :. white on i-a: f. ::.! i - pI oVeIIa; this di er B3o

  The reality and shows a hinge with the optimal theo-

  In the industrial installation, it is possible to adapt the techniques to the control of the feed and to perfect the particle size distribution, in particular by adjusting the grinder-sieve assemblies and the characteristics of the feed. operation of hydrocyclones, such as e. service pressure and openings

outlet nozzles.

  The present process is applicable to all fuels capable of being reduced to fine particles by conventional comminution means, such as coals, lignites, coal cokes, petroleum, hard asphalts, etc. The final mixture can be packaged in a stirred tank where the fluidity and stability reactants are introduced, as well as a possible supply of water to form the fluid mixture ready for transport and use. The additives used are those adapted to the product. basic solid. This mixture can also be made in a ball mill

  paver operating at high density in solids.

  When the water content of the final product resulting from the process exceeds the limits set, the concentration is adjusted by proceeding in the mill

  by attrition to high density solid grinding which allows for

  the granulometry to the optimum particle size of the overall product, but which requires at this point the addition of a surfactant which can go as far as

to 1% by weight of the solid product.

  The process according to the invention does not postulate any particular condition

  as regards the water of the process. The only condition to be met

  the achievement of a fluid mixture and its compatibility with

  additives. In case of necessity and during filtration, it is possible to

  rinse with clear water to correct the salinity and to evacuate

  products initially present, such as flotation reagents.

  Many variants within the reach of those skilled in the art can be made during the implementation of the process according to the invention, which is essentially characterized by a succession of comminution and classification steps leading to reduce the totality of the initial product. to the desired particle size distribution without surpluses or inputs, the adjustment of the granulometric constituents taking place only by

  settings of the means implemented.

  oo0 Distribution of relative weights in% of particle size slices (in Pm) during the preparation process

  tr following the example shown in the diagram for an American bituminous coal.

  Tra nche. E m L r. _ Distribution Distribution of the: -: - - - - Cumulative referencecreferences of the ureolated t o, according to Alfre cdu triques tn, m = M. "o o

_ .. 1 (n .. _-

  triq..uLn -res4-3 0 according to 0 i, m. He U E Alfred process

400,800 14 _ _ _ _

-400 32 - .. _ _.

  -200 19 19 3.7 22.7 22.5 0.2 0.2 - 22.5 - 22.5 25 100 100

  -100 15 15 8.3 23.3 18.4 4.9 3.9 1.0 19.4 19.4 19.6 77.5 75

  -50 9 9 12 21 8.4 12.6 5 7.6 16 - 16 15 58.1 55.4

  12.5; -25 6 6 9.2 '15, 2.2.3 12.9 1.9 11 13.3 0.7 14 11.6 42.1 40.4

  6.2-1235.2 2 5.5 7.5 0.7 6.8 0.6 6.2 6.9 2.7 9.6 9.1 28.1 28.8

  3, s1-622. 2 3.2 5.2 0.4 4.8 0.4 4.4 4.8. 2.5 7.4 7.0 18.5 19.7

  1.6-3.1 1 1 1.4 2.4 0.2 2.2 0.2 2 2.2 2.2 4.4 5.3 11.1 12.7

  0.8-1.6 - - ns 0.9 0.1 0.8 0.1 0.7 0.8 1.7 2.5 4.3 6.7 7.4

  -08 -. - 1.8 1.8 0.2 1.6 0.1 1.5 1.7 2.5 4.2 3.1 4.2.1

TABLE 1,

TABLE 1

  REVE) DCAf ^ 'ITONSc?, The preparation of high strength non-combustible aqueous suspensions and containing particles of baile less than 1180 mim and at least 5% by weight of particles smaller than 3 p, whose granulomeltric repair is according to the formula of Alfred according to the equation: ## EQU1 ## in which Dpi is the median size of the particle size range considered in pm, Ds the size of the smallest particles in pm, DL the size of the largest particles, n an exponent whose value varies from 0.2 to 1.0, characterized in that a hdrocyclone is fed into 0 crushed particles whose largest particle size is less than X im, X being at most equal to 1180 μm, said hydrocyclone performing a separation in which 90% of the cutoff slice varying between 1/4 and 1/2 of X flows underflow and 10% of the same slice overflow, the overflow feeding a second aya hydrocyclone the first of these, the overflow of the second hydrocyclone being united with the underflow of the first and forming a

  first component of the final mixture, the underflow of the second hydrocyclic

  lone being milled in a fine mill into a mixture of particles whose size for 80% is between 1/10 and 1/20 of X and which forms a second constituent of the final mixture, the two constituents being poured into a

  mixing tank in which the solid content is at least 45%.

  2. Process according to claim 1, characterized in that the raw fuel is ground first in a grinder of the type of bar mill producing relatively coarse grains which, screened on a screen, leave loops constituting the relatively coarse fraction of the final product and refusals that are subjected to finer grinding in a grinder of the type

  balls whose sieve grinding products leave passers-by

  intended to constitute the medium and fine slices of the final product,

  passing fraction feeding the first, then the second hydrocyclone.

  3. Method according to claim 1 or 2, characterized in that the refusal of the first grinding of the type of bar mill circulates in a closed circuit between the ball type mill and a screen of the same characteristics as the screen used to screen the product. from the first mill of the

bar type.

  4. Method according to one of claims 1 to 3, characterized in that the

  passers resulting from the screening of products from the first bar-type mill and passers-by resulting from the screening of resulting products

  screening of products from the second ball mill type mill.

  lie the first, then the second hydrocyclone.

  5. Method according to one of claims 1 to 3, characterized in that the

  bystanders resulting from the screening of products of the first grinding are paid

  directly into the mixing tank as the final component.

  6. Method according to one of claims 1 to 5, characterized in that the

  The second hydrocyclone is milled in an attritor mill.

  7. Method according to one of claims 1 to 6, characterized in that the -

  raw fuel particles of 0 to 15 mm is milled in a first bar mill in water, the grinding product is sorted on a sieve whose mesh size is 200 pm, the sieve refuses feeding a second mill in the water, the grinding product is sieved through a screen whose mesh size is 200 μm and the recirculated refusals in a closed circuit to the ball mill, the fractions

  passers of the two sieves feed a first, then a second hydro-

cyclone.

  8. Method according to one of claims i to 7, characterized in that the

  The product of the first mill is classified into two fractions each of which

  45 to 55% of the crushed product, the passing fraction is directly

  poured into the final mixing tank as a definitive constituent

  tif, while the refusals are subjected to grinding in the chopper.

  let and the grinding product classified on a sieve whose passers-by

  feed a first, then a second hydrocyclone.

  9. Method according to one of claims 1 to 8, characterized in that all

  product from a previous treatment and having a granular distribution

  lometrical close to that produced by a crusher-type grinder

  bar can replace the product from the first bar mill.

  10. Method according to one of claims 1 to 9, characterized in that the

  first hydrocyclone operates a separation in which 90% of the cutting slice of 70 pm flows underflow and 10% of this same slice flowing overflow of this first hydrocyclone feed the second hydrocyclone operating a separation in which 90% of the 70 μm cutting slice flows underflow to feed an attritor mill in which the solids are crushed to the maximum size of 15 mm, while

  that the underflow product of the first hydrocyclone is combined with the

  overflow dune of the second hydrocyclone to be mixed in the tank

  final mixing with the product leaving the attritor mill.