WO1989006680A1

WO1989006680A1 - A novel and improved method of producing solid-liquid mixtures with a high concentration of solids

Info

Publication number: WO1989006680A1
Application number: PCT/EP1989/000055
Authority: WO
Inventors: Angela Modugno
Original assignee: Danimar S.R.L.
Priority date: 1988-01-25
Filing date: 1989-01-18
Publication date: 1989-07-27
Also published as: IT1220242B; IT8802104A0; CN1037169A; AU3034889A

Abstract

The invention relates to a novel and improved method of producing suspensions of solids through liquids, and more particularly, of high-concentration coal in water, which comprises conventional pre-crushing of the coal, followed by riddling the pre-crushed to the maximum particle size sought for the end suspension. The pre-crushing operation is performed such that the coarse fraction from said riddling step can account for up to 90% by weight of the overall pre-crushed. That coarse fraction is then passed to wet milling, and the resulting produce of the milling admixed to the fine fraction from the riddling step.

Description

"A novel and improved method of producing solid-liquid mixtures with a high concentration of solids"

TECHNICAL FIELD

This invention relates to an improved method of producing suspensions of solids through liquids, and more particularly, of high-concentration coal in water.

BACKGROUND ART

The relevant literature describes several methods of producing high-concentration coal suspensions in water. Leaving aside those processes which are based on the dry milling of coal, we will focus herein our attention on the wet-type processes.

The latter either include a single-stage milling step leading to a continuous granulometric curve, or a two-stage milling step which expectedly yields a bimodal granulometric curve. Actually, and especially with fine granulometric curves (top size -*> 200 urn), the difference between the granulometric curves from either processes is fairly small, and in some case even negligible.

In principle, however, the two processes are quite different. In the former, milling is performed on the single mill provided for suitable times to yield the required amount of fine for a flowing mixture, and to reduce all the particles to a smaller size than a predetermined top size. Energy-wise, such a process is penalized with an increase of the mixture viscosity within the mill as milling proceeds. In the latter process, which includes a micronization step, a large amount of energy is to be expended for the production of all the fine required to yield the end mixture.

DISCLOSURE OF INVENTION It has now been unexpectedly found, and this forms an object of the present invention, that it is possible to produce mixtures having the same granulometric curves and properties, for an energy input which is significantly lower than that of the aforementioned processes. the aforementioned processes.

The method of this invention comprises an initial pre-crushing step whereby the coal is reduced to a coarse powder having a top size of up to 6-8 mm and a 200-jm segregate in the 60% to 90% range; that pre-crushed is then passed to a successive riddling step and riddled to the maximum size sought for the end mixture. The coarse fraction (60-90% of the total) is then passed to a wet milling step which, while being no micronization step proper because not all the particles are micronized ( < 20 μm), yields all the fine required to obtain a flowing end mixture.

The resulting wet_.mi lied is then admixed to the fine fraction from the riddler to yield the end mixture.

The advantages afforded by the method of this invention are based on actual tests showing that the energy input required to produce a given amount of fine is closely tied to the coal fraction supplied to the micronizer which is actually micronized.

MODES FOR CARRYING OUT THE INVENTION

The Examples set forth herein below will serve to make the foregoing more clearly understood. The Examples are to be regarded as merely illustrative of this invention and in no way limitative thereof. ExamoLe_1_

A high-volatile pre-milled American coal having a top size of up to 6-8 mm and being either riddled or unriddled is assumed. It is assumed that the end mixture sought should have a coal concentration of 69% and a granulometric curve corresponding to a 40% of the coal particles being smaller than 20 jjm.

In accordance with the method disclosed in Italian Patent Application No. 19679A/84, where an hourly mixture output is sought which contains 100 kg/hour of coal, 40 kg/hour of the pre-crushed is passed, along with 44.93 kg/hour of water plus fluidizing additives, into a micronizer mill which reduces all the particles to a size below 20 jjm. In this case, the coal concentration within the micronizer mill is 47.1%, and the coal fraction supplied to the micronizer is evidently 40% of the coal content in the end mixture. The resulting water-plus-micronized mixture is fed into a second mill to which 60 kg/hour of pre-milled coal is also supplied, and which will deliver the end mixture.

Let us put the energy required to icronize the above-noted 40 kg/hour coal equal to 100.

Assume now that that same micronizer mill be supplied a mixture containing water plus fluidizing additives to an amount corresponding to 31% of the end mixture and 50% of the coal content of the end mixture (the mill will then operate at a coal concentration equal to 52.67%).

Assuming that the content in smaller particles than 20 urn of the end mixture is again to be 40% of the coal in the end mixture, it may be appreciated that only 80% of the coal supplied to the micronizer shall have to be reduced to below 20 urn therein.

By operating as just explained, it could be observed experimentally that the amount of energy required to produce an equal amount (40 kg/hour) of micronized decreases from 100 down to 60. If we now supply that same mill with a mixture containing water plus fluidizing additives to an:amount ^"which corresponds to 31% of the end mixture and 60% of the coal content of the end mixture, then the mill will operate at a coal concentration of 57.18%.

Where the content in smaller particles than 20 μm of the end mixture is again to be 40% of the coal in the end mixture, it may be appreciated that in the mill only 66.67% of the coal supplied thereto shall have to be reduced to below 20 urn.

By operating as just explained, it could be observed experimentally that the energy input required to produce an equal amount (40 kg/hour) of micronized decreases from 100 down to 43. If we now supply that same mill with a mixture containing water plus fluidizing additives to an amount corresponding to 31% of the end mixture and 70% of the coal content in the end mixture, the mill will operate at a coal concentration of 60.91%.

Where the content in smaller particles than 20 ₍um of the end mixture is again to be 40% of the coal in the end mixture, it may be appreciated that only 57.14% of the coal supplied into the mill shall have to be reduced to below 20 m therein.

By operating as just explained, it could be observed experimentally that the energy input required to produce an equal amount (40 kg/hour) of micronized decreases from 100 down to 36.

For a given amount of water supplied into the mill, on further increasing the coal fraction supplied to it, it could be observed, for the coal being examined, that the energy input ■ required to micronize 40% of the coal content in the end mixture rises slowly at first and then at an increasingly faster rate.

It should be noted that in all of the cases described above, the granulometric distribution and the mean diameter of the smaller fraction in size than 20 urn are directly comparable with those of the micronized from the first process step which includes two milling steps.

The one just described is not the only advantage to be derived from the method of this invention.

Another advantage resides, in fact, in a considerable increase of the end mixture hourly production.

In relation to the same coal and end mixture types as above, if Q is the hourly end mixture output to be obtained by the process providing for two milling steps, with the method of this invention hourly end mixture outputs equal to 1.68Q, 2.29Q, and 2.78Q, respectively, can be obtained for supplies to the same micronizer mill of 50%, 60%, and 70% of the coal content in the end mixture.

The above advantages are enhanced where the amount of the micronized required is lower than 40% of the dry coal. Examgle_2

100 kg of a high-volatile American coal was pre-milled in a hammer-type pre-crusher to yield a powder having a top size of 2 mm and 70% of 200 μm segregate. The pre-milled is supplied to a riddle and riddled to 200 urn. 70 kg of a coarse fraction and 30 kg of a fine fraction are obtained. The coarse fraction (70 kg) is supplied to a wet mill along with 44.93 kg of a solution containing water plus a fluidizer (0.5% over the end mixture) and milled until 40 kg coal attain a smaller size than 20 μm. The wet milled thus obtained is supplied into a mixer and admixed to the fine fraction from the riddle to yield an end mixture having 69% coal and a viscosity of 980 cps.

That same mixture was then prepared in accordance with the method of Patent Application No. 19679A/84 so as to have the granulometric curve and coal concentration. In this case, the viscosity shows to be 1010 cps.

If the energy input is assigned a value of 100 (referred to each tonne of end mixture) for the method of Patent Application No. 19679A/84, then for the method of this invention the energy input shows to be 46. ExanjBj.e_3

By operating as in Example 2, but micronizing to obtain 35 kg of micronized instead of 40 kg, and thus achieving a coarse-to-fine ratio equal to 65/35 in the end mixture, it could be observed that if_> the energy input to the two-step process is 100, that to the inventive process shows to be 39. ExamgLe_4

100 kg of a petcoke was pre-milled according to a granulometric curve having a top size of 2 mm and 25% of 250

separate. The pre-milled was cut at 250 μm. The coarse fraction (75 kg) is supplied to a wet mill along with 33.70 of a solution containing water plus a fluidizer ⁽0.5% over the end mixture) and milled until 35 kg was reduced to less than 20 μm. The resulting mixture is then admixed to the fine fraction from the riddle to obtain an end mixture at 69% solids and a viscosity of 900 cps.

Also in this case, that same mixture was prepared at a viscosity of 950 cps. If the energy input to the two-step process is assigned a value of 100 (per tonne of end mixture), the process of this invention requires a power input of 49.

Claims

1. A method of preparing solid suspensions in liquids, in particular coal in water, characterized in that the material to be suspended is pre-crushed to yield a pre-milled which is riddled into two fractions; of the two fractions output by the riddle, the coarse one is passed to a wet milling step effective to only icronize a proportion of the supply coal and the output whereof is admixed to the fine fraction from the riddle to yield the end mixture.

2. A method according to Claim 1, characterized in that the pre-milled has a maximum size of up to 6-8 mm and a 200 um segregate in the 60% to 90% range.

3. A method according to Claim 1, characterized in that the pre-milled is riddled to the maximum particle size sought for the end mixture.

4. A method according to Claim 1, characterized in that passed to the wet milling step is the coarse fraction from the riddle which accounts for 50-90% of the pre-crushed coal.

5. A method according to Claim 1, characterized in that of the coarse fraction from the riddle which is passed to the wet milling step, only a fraction in the 30% to 90% range is reduced to a size below 20 um.

6. A method according to Claim 1, characterized in that the fine fraction from the riddle forms the coarse fraction of the end mixture.