DE2458863C2 - Process for making coal extracts - Google Patents

Description

65

The invention relates to the manufacture of coal from

trains or extracts.

Usually coal extracts are made by a process in which coal, tar, pitch or a similar carbonaceous substance is digested or extracted in a solvent at elevated temperature is used to obtain a coal extract in the solvent; then the extract is filtered to remove one substantial amount of undissolved matter, and the filtrate is concentrated to obtain a starting material with low mineral content.

This filtrate is actually a concentrated carbon solution and is useful in a number of processes, viz

1) as a raw material for the manufacture of chemicals and petrochemicals;

2) as starting material for a coking process.

It is known that by heating such a raw material in a coking plant, a coke can be produced in some cases for the production of carbon electrodes for electric arc furnaces Steelmaking and the like are suitable, however, electrodes made in this way must normally be used as well Petrochemical feedstocks are low in mineral content as minerals present can sometimes act as catalysts in later reactions.

Thus, the filtration is of great importance in such a process. Of course all minerals and other solids are from the extract thanks to modern filtration processes removable; however, in the case of processes carried out on an industrial scale, this results in an increase in costs. If all substances are removed from the extract before further processing, of course there is Danger that the very fine particles clog the filter medium or make it impermeable, so that it often needs to be cleaned. In this context, the filter medium can also be a filter kuaifin, i. H. so, that fine particles make the filter medium impermeable and / or result in a filter cake with high filter resistance; in both cases the result is a low filtrate throughput. Conversely, if a filter medium with too wide pores is used, it remains "Too large a proportion of suspended matter in the filtrate before further processing.

The problem of filtering the extract after digestion therefore requires a good balance between a suitable filtrate throughput and a satisfactory mineral content in the resulting filtrate. It was found that one If the coke has a mineral content of more than 1%, satisfactory electrodes cannot be produced from it are; consequently, making a coke suitable for electrodes depends on maintaining one Mineral content of less than 1% by weight, preferably less than 03% by weight, in the coke.

The inventive method for producing coal extracts, in which coal, coal tar, pitch or a similar carbonaceous substance with a solvent at an elevated temperature to obtain of a coal extract digested in the solvent, the extract obtained to remove a considerable Fraction of undissolved matter filtered and the filtrate to form a starting material with low content is concentrated in mineral ash, is characterized by the fact that the digestion of coal, tar,

Pitch or similar carbonaceous substance with a solvent at such a temperature and takes place during such a time interval that the Coal is digested so far that undissolved coal has such a grain size and texture that a Filter cake of low resistivity is formed, and that subsequently the filtration at increased temperature and with such a solvent concentration that the rate of increase the pressure drop & ai filter medium is minimized.

A further development of the invention consists in that the coal with a solvent at a temperature of at least 350 ⁰ C for at least 5 min digested to 1.5 h, the extract thus obtained at a temperature of at least 150 ⁰ C to remove a substantial portion of undissolved and suspended matter is filtered and the filtrate is concentrated to obtain an extract with low mineral matter concentration.

Preferably the digestion time is 20 minutes to 1 hour and the filtration is carried out at a temperature of 250 - 300 ° C carried out

Two factors influence the filtration process according to the invention, namely the viscosity of the to the filtering extract and the filter resistance Filter cake. It can be seen that the filtrate throughput for a given filter cake, bed or media the higher the lower the viscosity; As a result, in the method according to the invention, in which the filter cake itself serves as a filter medium, the viscosity preferably as low as possible be. The viscosity of a given extract changes considerably with temperature, and as it does with as the temperature continues to decrease, the highest possible filtration temperature should be used, to maximize the filtrate throughput. The maximum temperature at which filtration can be performed however, depends on the type of solvent and the pressure at which the filtration is carried out

When the solvent is e.g. B. anthracene oil, which is most commonly used as a solvent for coal, a filter would have to be designed for operating temperatures above 300 ⁰ C with a pressure outlet in order to avoid boiling of the solvent in the filter cake, whereby the pressure difference in the filter cake would be reduced. Consequently, should the filtration preferably in a temperature range of 200 -300 ⁰ C, in particular 250 to 300 "C, are performed.

The solvent is chosen for its ability to extract and then break down the char, and this is important in determining the viscosity of the extract. A large number of tars and tar oils can be used as solvents in the process of the present invention, and therefore preferred solvents are oils produced by tar distillation, these tars being formed in the decomposing distillation of coal; these oils are commonly referred to as anthracenols. The preferred anthracenols contain substantial amounts of phenanthrene, especially alkylated and especially methylated phenanthrene. The solvents preferably have a boiling range of 180-400 ° C., and preferably a solvent with a narrower boiling range is used, e.g. B. the middle 90% of the solvent in the range of 250-350 ° C boil.

The concentration of solvent to coal in the preparation of the extract is preferably in Range from 5 to 2: 1, particularly the oil-coal concentration ratio g - greater than 3: 1. The composition of the filter cake is determined by the oil-carbon ratio not significantly affected during the digestion phase of the process according to the invention and the figures given are the result of commercial considerations.

During digestion there is a possibility that the charcoal will break through the various Crosslinking compounds in the coal itself is broken down and depolymerized. At any given temperature it can be seen that the viscosity of the extract changes with time; in a first stage it takes initially increases, then decreases in a second stage to a low, increases in a third stage a second peak and slowly begins to decrease in a fourth stage.

In the first stage, the viscosity increases during the digestion quickly and reached within a few minutes after the beginning of which a maximum value at the onset of digestion are carbon particles with the digestion ^oil: mixed ji form of slurry and digestion beginning of the ViSkC increased; - ät very quickly..

In the second stage, the viscosity drops ies extract after reaching the maximum value over a period of 20-30 min to a low This period is in the range of 380-450 ⁰ C temperatu substantially independent. The lowest viscosity reached at the end of the second stage is clearly temperature dependent, and it can be seen that the higher the temperature, the lower the viscosity. It is believed that during the viscosity decrease in the second stage, the coal is depolymerized.

After reaching the point of lowest viscosity, this again increases in the third stage Maximum value that is reached within 50 - 70 minutes after the start of digestion. The increase in viscosity is due in part to polymerization reactions that occur in the extract and these begin apparently before reaching the point of lowest viscosity (at the end of the second stage). The rate of viscosity increase does not change greatly with temperature, which indicates a low activation energy for the process indicates what is consistent with the polymerization reaction.

In the fourth stage, the viscosity decreases after the second maximum value has been reached. this could result in part from the coking of the coal extract in the solution.

If the coking reaction can be completed, the extract could have almost the same solids content as the original coal pulp. The higher the temperature and / or the longer the standing time, the more coking has progressed. Normal · ί, the coking is preferably minimized in the inventive process, and therefore is de. best time to stop digestion depending on the type of extraction desired at or before the second maximum viscosity value is reached.

The oil-coal concentration ratio during the Digestion is not critical in its effect on the filter cake, but the oil-carbon ratio is in the filtrate is important; filtration is preferred at a concentration of solvent Coal of more than 3: 1, in particular 4: 1, carried out because this results in a lower viscosity and thus result in easier filtration. Therefore, after digestion, a further solvent addition can be used

can be added to lower the viscosity prior to filtration. Alternatively k; inn a proportion of a lower boiling coal tar light oil, e.g. B. a wash oil, instead of the original digestion solvent can be added. If a lighter oil is added, the filtration can take place at a lower temperature take place.

The type of coal has little effect on the filter cake, provided the digestion is carried out properly carried out. It is preferably used for digestion in fine coal, although the grain size of the coal not critical to the invention and no special treatment of the coal prior to mixing with the Solvent is required. The coal is preferably used in conventional crushing and grinding devices crushed, and the grain size can be chosen so that the coal through a sieve with a clear Mesh size of 15 mm, but preferably 5 mm, is possible. It should be noted that the oil to coal ratio on the temperature to be used in the filtration: i> and the most favorable oil-to-carbon ratio depends on the filtration temperature. In doing so, however, must must be taken into account that the proportion of products remaining in the filter cake (dissolved coal) depends on the Depends on the concentration of the r> solution wetting the filter cake; d. h .. preferably will be a high Oil to coal ratio used. Normally the viscosity increases at low oil-to-carbon ratios, and the level of solutes remaining in the filter cake requires cleaning of the filter cake with further solvent. However, the higher the oil-to-coal ratio, a stronger one occurs Preheating of the filtrate and greater volatilization of the solvent, especially when using filter cake wash oil is added. According to the invention, the oil-carbon ratio for the filtration is therefore preferably in the range from 5: I to 3: I, in particular 4: 1. In a typical embodiment of the Invention can digest digestion with an oil-to-coal ratio of 2: I, and the extract obtained is then adjusted to a ratio before filtration diluted 4: 1.

The temperature at which digestion takes place should, as explained, be as high as possible. Of the However, the time at which the digestion temperature is reached is not critical.

The digestion time is preferably longer than 20 minutes; the highest possible temperature should, however do not cause excessive coking of the extract; i.e. it should be in the range of 400-440 ° C. at continuous digestion, in which some mixing takes place, the mean standing time must be longer than 20 minutes, as short periods of time are very different in terms of viscosity and filter cake resistance adversely affect.

If the digestion conditions used are considerably below the usual 400 ^° C. for 1 hour, the filter cake resistance increases noticeably. This effect was quantitatively determined when using more common coal coffers, and it should be noted that with a viscosity increase of approx. 25% there is a hundredfold increase in the filter cake resistance within a relatively small temperature range, as the following table 1 shows:

Table 1

Effect of digestion temperature on filter coolness

Coal: CRC 702 Oil: Recycled Anthracene Oil

Digestions Time Filtrate Specific temperature <h) viscous Resistance ( ⁰ C) (cP at 250 ⁰ C) capability of the filter cake • (techn. Unit of measurement) 400 1 0.40 3 380 1 0.42 5 360 1 0.49 260

The same effect can be observed with the use of high-quality coals, where with one Digestion of just a few minutes instead of 1 hour, much higher filtration pressures are required to achieve the To maintain throughput. Not all coals have exactly the same relationship between filter cake resistance and digestion temperatures, but a sufficiently high digestion temperature gives for all Types of coal have a relatively low specific filter cake resistance, which is usually more important than viscosity. However, if due to incomplete-1 If an extract is produced with an exceptionally high viscosity after digestion, this can result in very large Filtration difficulties arise. So if a continuously operating system is used ·. will, enables the monitoring of the extraction viscosity to record changes in the digestion conditions, before major filtration problems arise.

Filtrate throughput and filtration efficiency are, in the process according to the invention from the filter cake ^ resistance determined The initial filtration of a pulp is the resistance of the filter medium and its associated Proportional pipelines. However, as soon as a filter cake is formed, the total flow resistance decreases to, and the following applies:

J-

AL

d V

= / TV y, R

~ ⁿ A ² P AP

V A. P. R.

Filtration throughput

Filtrate viscosity

specific cake resistance per unit mass

Mash concentration of the dry cake per mass unit of filtrate

Filtrate mass

Surface of the filter medium

Pressure difference

Resistance value of the filter medium and the associated pipelines

ok

Thus, according to (I), for a filtration at constant r>

df HT

Pressure the curve vorrj "p over V a slope of 'Γ7Π ,.

while for filtration at constant throughput, e.g. B. in an extraction plant, the curve of Püber Veine

wQ

Slope of ~~ y rhat. Since all other parameters

including the viscosity for the system are either permanently specified or for each throughput measurement can be determined, the specific filter cake resistance can be calculated. As already mentioned, limited however, the temperature dependence of the viscosity affects the accuracy of the determination of r.

The initial filtrate throughput before the filter cake has accumulated is determined by the resistance R of the filter medium and the associated pipelines. According to equation (I),

AP

R = ^ £ at V = 0.

In order to maximize the filtrate throughput for a given filter , R must be made as low as possible by using appropriately sized supply lines and as coarse a filter medium or body as is still acceptable to obtain the desired filling quality.

An Ausführungsbeispiei the invention is explained in more detail below with reference to the drawing. It shows

F i g. 1 a filter device suitable for the invention. tung and

F i g. 2 a graphical representation of the filtration at constant pressure, with the reciprocal value of the throughput

Table 2

Specific filter cake resistances

zes is plotted against the total filtrate in kg.

The filter device according to FIG. I has a hollow body 10 with a top wall 11, one Base plate 12 and a substantially cylindrical outer wall, which together form a Fihrataufnahmekammer 14 form. The chamber 14 has an outlet 15 on one side and the top wall 11 has an annular flange 16, the purpose of which will be explained later. The top wall 11 has a pair of spaced apart openings 17, each on Perimeter at 18 are increased to accommodate an upwardly extending filter candle 19, consisting of several stainless steel washers arranged at repetitive intervals of 0.1 mm are; the whole filter candle is with a longitudinal hollow bolt 20 secured. The filter candle formed by the Slahl disc is to form a filter surface 21 with Wrapped in fiberglass; the cloth has a Fothergill and Harvey grade of Y600. The fiberglass cloth is by a wire wrapping 22 made of nichrome wire with a diameter of 30s.w.g. secured. That Filter vessel is completed by an upright cylindrical housing 23, which is on his The lower end has an annular flange 24 which cooperates with the flange 16, and the lower edge of the cylindrical housing 23 is designed so that it is seated on a polytetrafluoroethylene sealing ring 25 can, so that by clamping the flanges 16 and 24, the lower edge of the housing 23 firmly with the Sealing ring 25 is clamped together. The upper part of the housing 23 is by a hemispherical Section 26 closed, which has an upwardly extending outlet 27 which is a branch

28 has. The housing is covered with a heat protection layer

29 and electrical or similar heating elements 30 surrounded.

The extract to be filtered is introduced under pressure through the inlet 27, passes through the filter candles 19, enters the ri'trat passage, flows through the inlet 18 into the chamber 14 and from there out the outlet 15.

A number of coal samples were ground and subjected to digestion using anthracene oil and the in the temperatures and times given in Table 2 were used. The excerpt was made with the Filter device explained above filtered, the specific resistance was recorded. Of the Pressure drop through the filter medium was 2.1-3.5 kp / cm2 (30-

Source material

Digestion conditions

Temperature C ³ C) time
(H)

specific resistance (technical unit)

example

Beynon coal CRC 301a

Union coal CRC 301b

400 1-2 7th 400 1-2 6th 400 1-2 4th 400 1-2 6th 400 1-2 6th 400 1 7th

continuation

10

Source material

Digeslion conditions

Temperature line

( ⁰ C) (h)

spec. Resistance

Annesley Coal CRC 702

Linby Coal CRC 902

3 3 5

260 7

Comparative examples

Phurnacite tar
Phurnacite extract
Dense ball bed

0 10 iim
0 1 am
0 0.1, am

28 100

0.06 6.1 610

1 pressure difference 2.1-3.5 kp / cm ² (30-50 psi)

From Table 2 it can be seen that the type of coal has no particular influence on the specific resistance of the Filter cake had, however, that changes in digestion temperature resulted in a considerable increase in the Caused resistance. Table 2 gives similar numbers for Phurnacite tar for comparative examples, Phurnacite pull-out as well as for tight ball beds.

Examples 1-11 were repeated using different types of coal, the above

J ₀ starting explained filter means was used, the one

Batch capacity of 50 kg and a filter area of

Was 3.7 m ² (4 sq. Ft.); the filtration was carried out at 250 ⁰ C

carried out. From Table 3, in which the results

indicated, it can be seen that the specific

35 filter cake resistance less than 20 in any case

technical units.

Table 3 filter money Mine Anthra- Solids filter Spec. example Type CRC cenoil content of
Excerpt call
pressure resistance
filter Beynon (%) (kp / cm ² ) cake F. 5 3.52 10 12th R. 2.46 10 13th 50 kg 301a R. 5 2.60 8th 14th R. 2.11 9 15th Batch union R. 2.11 9 16 301b Albertillery F. 5 3.87 13th 17th 302 R. 6th 2.11 4th 18th 3.7 m ² R. 2.11 7th 19th Annesley F. 1.76 3 20th 702 R. 2.81 3 21 250 ⁰ C F. 9 1.05 0.6 22nd F. 1.05 0.8 23 Linby F. 0.91 0.5 24 902 F. 10 2.11 6th 25th

F = Fresh from the still.
R = returned.

12th

Table 4 shows the effect of the oil / carbon ratio on the specific filter cake resistance; it can be seen that a decrease in the oil to carbon ratio leads to a rapid increase in the filter cake resistivity causes.

Table 4 example

Nominal oil-to-coal ratio

Filtrate viscosity

oil

Specific filter cake resistance

0.6

0.9 1 1.8 1

fresh or recycled anthracene
recycled anthracene

Filter: batch 50 kg, temperature 250 ° C., pressure 2.1-3.5 kp / cm ³ . Coal: Beynon coal class 301 a.

9 9

17th

For this purpose 2 sheets of drawings

Claims (9)

Patent claims: 1. Process for the production of coal extracts, in the case of coal, coal tar, pitch or a similar carbonaceous substance with a solvent elevated temperature to obtain a coal extract digested in the solvent, the obtained Extract is filtered to remove a significant amount of undissolved matter and the filtrate to form a raw material with a low mineral ash content is concentrated thereby characterized that the digestion of coal, tar, pitch or a similar carbonaceous substance with a solvent at a «soft ι> Temperature and during such a time interval that the coal is digested so far, that undissolved coal has such a grain size and consistency that a filter cake is low Resistivity is formed, and that then the filtration at elevated temperature and with such a solvent concentration that the rate of rise of the pressure drop is minimized on the filter medium. 2. The method according to claim 1, characterized in that the coal ^{digested with a solvent at a temperature of at least 350 0} C for at least 5 min to 1.5 h, the extract thus obtained at a temperature of at least 150 ⁰ C to remove a A considerable proportion of undissolved and suspended matter is filtered and the filtrate is concentrated to obtain an extract with a low concentration of minerals. 3. The method Räch claim 1, characterized in that the Digestior without essential Hydrogenation of the coal is carried out. 4. The method according to claim 1, characterized in that the digestion for 20 minutes to 1 hour at a temperature of 250-300 ⁰ C is performed. 5. The method according to claim 1, characterized in that anthracene oil is used as the solvent and that the digestion is carried out at eii.-er temperature above 300 ⁰ C under pressure. 6. The method according to claim 1, characterized in that the filtration is carried out under pressure, whereby a boiling of the solvent is avoided in the filter cake, so that the pressure difference in the filter cake is reduced. 7. The method according to claim 1, characterized in that when forming the extract a Solvent-carbon concentration in the range of 5 to 2: 1 is used. 8. The method according to claim 1, characterized in that after digesting another Solvent is added to lower the viscosity of the extract prior to filtration. 9. The method according to claim 8, characterized in that to lower the viscosity of the Extract before filtration instead of the original digestive a lower boiling one Coal tar light oil is added.