CS273648B2 - Method of water content and ash forming substances reduction in coal tars - Google Patents

Abstract

1. A process for the reduction of the content of water and ash formers in crude coal tars by means of a three-phase decanting centrifuge with the usual barriers and discharge devices at elevated temperature, characterized in that the crude tar - where appropriate pre-treated - is continously separated into an aqueous phase, a tar phase and a solid phase in the three-phase decanting centrifuge at a centrifuging number of between 1000 and 3000 g, provided with an open one- or two-threaded, preferably armoured worm, at e temperature of between 60 and 105 degrees C, an average dwell period of the tar of between 30 and 80 sec and a differential rotational speed between the worm and the rotor of from 10 to 50 min**-1 , the feed being periodically briefly interrupted during the continous operation.

Description

Method of reducing water and ash-forming substances in crude coal tars (57) We propose a mechanical method of dewatering and ash removal of crude tars by means of a three-phase decanter centrifuge equipped with an open screw. The tar is preheated to 60 to 105 ° C and has a residence time of 30 to 80 s, with a spin number of 1000 g to 3000 g and a differential speed between the screw and the rotor for 10 to 50 min! is continuously separated into the aqueous phase, the tar phase and the solid phase. By periodically interrupting the filling for at least 1 minute after a maximum of 6 hours, a high and long time constant separation step is achieved. The content of the crude tar-quinoline-insoluble parts is practically unchanged.

CS 273 64B B2

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanical method for reducing water and ash-forming substances by means of centrifuges in crude coal tars.

In addition to fuel gases, ammonia and benzene, tars are produced during the coking of coal, which are characterized by the following analysis values:

Q _n η, ,, ~, on „/ __ 3 density at 20 C water content of toluene insoluble part (TI) quinoline insoluble part (QI) of ash-forming substance

1.14 to 1.20 g / cm -1 to 6.5% to 15%

0.5 to 10%

0.05 to 0.30

According to Franck / Collin Steinkohlenteer pp. 25 to 27, the water content of crude tars can be reduced mechanically.

Mechanical dewatering is preferable to dewatering by distillation, since many of the tar substances are passed through with distillation, and therefore oil phase redistillation is required, and water-soluble salts remain in the distillation residue, thereby reducing pitch quality.

Most often, water separation is performed by decanting under gravity at 60 ° C. The water content can be reduced to about 3%. Pressure dewatering at temperatures up to 200 ° C and pressures of about 0.15 MPa under gravity results in a water content reduction of about 1 to 1.5%. However, this requires pressure-resistant retorts. This limits the applicability to small amounts of tar.

Dewatering by centrifugation is particularly effective, but also expensive. Here a water content of 0.5 to 1% is achieved. As an example, plate separators with a nozzle outlet and a centrifugal number of 6000 to 7000 are mentioned. g, at the same time forming a sediment-rich concentrate.

However, the co-drainage and ash removal of crude tars is made more difficult by the fact that at least some of the ash-forming substances act as emulsifiers. This results in a stable emulsion between solids, tar and water, and the achievable degrees of separation and clarification vary between tars. It also depends on the grain size of the solids, the density and the viscosity of the tar. However, the viscosity reduction at elevated processing temperatures has a limit due to the tar content of the boilers which boil below 100 ° C, the azeotropes formed with water and the increasing solubility of tar acids and bases in water. Increased distillation costs have to be expected when using solvents to reduce viscosity.

Disc separators with continuous discharge of solids through nozzles designed for the purification of crude tars are highly solid-oriented. They are therefore used for maximum concentrations of solids. Therefore, as the solids content of the inlet decreases, the concentration in the outlet must also decrease accordingly. Since the solids must be flowable, a solids concentration of only about 60% can be achieved in the effluent. When the concentration in the inflow drops from 5 to 0.5%, it drops in the effluent to about 6%.

The separator plate bundles are provided with riser channels which are to lie in the plane of the separating layer between the lighter phase (water) and the heavier phase (tar), thus allowing optimal separation. Since the position of the separating layer depends on the density ratio between tar and water, it shifts when the tar density changes.

The difficulties caused by the varying solids content and the varying densities of the raw tar are the reasons why the jet separator disc separators have not established themselves. Instead, the raw tars are still dewatered in tanks by sedimentation and are then freed from insoluble matter by batch discharge of solids in self-cleaning plate separators. The ash-forming substances and the soot particles (QI without ash) are separated to the same extent. Ashless QI is very desirable in pitch for many applications, such as for producing electrode binders or hard pitches for coking. For this reason, only tars rich in ash are also freed from solids.

H. Ullrich and C. Loss proposed to heat tar from the gravity separator during the treatment of coke oven gas with a water content of up to 20% to heat with a steam-heated heat exchanger

CS 273 648 B2 and feed it into a three-phase decanter centrifuge to divide it into three phases, water, tar and thick tar (Erdol und Kohle, 1977, pp. 558 to 564). In this case, a residual water content of generally below 5% is achieved. The crude tar thus obtained is stable in storage and in a marketable state. The data on the degree of clarification reached are as little as the reference to the tar content of the aqueous phase. Since the water according to the working scheme returns to the gravity separator for additional clarification, it can be concluded that water contains, in addition to substances soluble from the tar content, also a considerable amount of undissolved substances.

Due to the degree of clarification, it is only possible to prevent sedimentation during storage. In this case, only relatively coarse solids consisting of coke and ash particles can be removed. Thus, the aim of the proposed process using a three-phase decanter centrifuge is to pre-purify the crude tar, in which the variation in composition is equalized in the connected storage tanks.

Mishin et al. I report in detail about the purification of pre-printed crude tar in full-skin centrifuges (Koks and Khimiya, 1978, pp. 47-49). The experiments were carried out at temperatures between 67 and 76 ° C in centrifuges with centrifugal number 445. g. After each cycle, the aqueous phase and then the tar phase were drained after the centrifuge was filled and after a sedimentation time of 8 to 12 minutes. After several cycles, the heavy tar phase containing solids was also removed. Depending on the sedimentation time, the water content decreased from 7.1 to 7.5% to 1.8 to 7.5%

5.5% and an ash content from 0.14 to 0.17% to 0.06 to 0.11%. It has been found that the sedimentation time must not be below 10 minutes if a sufficient degree of separation and clarification is to be achieved. Since the process is carried out batchwise, the variation in the composition of the crude tars plays no role. There is also no mixing of the phases due to the additional flow, as is the case with the continuous processes. The results are therefore not transferable to continuous processes, the results of which are expected to be significantly worse under comparable conditions. Long sedimentation times, however, show that the proposed method is poorly suited for technical implementation.

It is therefore an object of the present invention to provide a continuous method of reducing water and ash-forming substances in precleaned coal tars in which, in addition to a sufficient separation and fining stage, low sedimentation time and low ash-free QI losses are achieved.

The problem is solved by treating the optionally pre-treated raw tar in a three-phase decanter centrifuge with a centrifugal number between 1000 and 3000. g, provided with an open, single or biased, in particular armored worm and conventional weirs and discharge devices, at a temperature between 60 and 105 ° C, a mean tar residence time of between 30 and 80 seconds and a differential speed between screw and rotor of 10 to 50 min ^{. 1} , is continuously separated in the aqueous phase, the tar phase and the solid phase, and during continuous operation, the filling of the periodic, intermittently up to 6 hour intervals, is interrupted for at least 1 minute.

The crude tars may be treated with demulsifiers, flocculants and / or diluents prior to decanting, as is usual in separating techniques to improve the fining or separating step. Decanting may also be preceded by water scrubbing, as is common in the tar industry to reduce the salt content.

In order to facilitate the start-up of the process, it is advantageous to first present the solids phase and then to increase the amount of crude tar up to the rated output. Under no circumstances should the solid phase be stirred up by sudden introduction of large quantities of crude tar.

Decanters are generally used for clarifying liquids whose solids content is so high that they can no longer be processed in disc separators. Typical solids contents are between about 20 and 60%. In the treatment of coke oven gas, such solids contents can be achieved in coke oven gas extraction plants.

It has now surprisingly been found that even for crude tars with a QI content of less than 5 wt. it can effectively reduce the ash content without significantly decreasing the ash-free QI.

CS 273 648 02

The effectiveness of the process according to the invention is illustrated by the following examples.

In Example 1, tar is dewatered and ashed in a conventional three-phase decanter centrifuge as suggested by Ullrich and Lass. The results of this comparative experiment thus represent the state of the art. In Example 2, a decanter modified according to the method of the invention is used without changing the procedure from Example 1. Examples 3 and 4 show two variants of the claimed process according to the invention.

Example 1 (Comparative)

The crude tar deposited at 60 ° C is heated to 80 ° C by means of a temperature-controlled steam heater and fed to a cylindrical three-phase decanter centrifuge with a conical outlet at a rate of 3.8 n n / h. The centrifuge has the following parameters:

drum length 1260 mm drum diameter 355 mm drum speed 3600 min “ ¹ centrifugal number 2550 g differential speed 30 min 1 phase layer thickness water. 41 mm

tar 8 mm solid 2 mm weir height for tar phase 42,5 mm worm, single pass, pitch 114 mm

For the sake of simplicity of the analysis method, only the water content of the feed, in the tar and in the aqueous phase according to DIN 51 582 is determined as a measure of the separation effect. The results are shown in Table 1.

Table 1

Sampling Water content (% vol) Tar phase Aqueous phase after Batch 2 h 4.9 3.2 78 8 h 5.3 '4,1 61 14 h 6.1 5.1 32

As the analysis data shows, sufficient phase separation is not achieved and the degree of separation deteriorates with increasing experiment time.

Example 2 (Comparative)

The crude tar stored at 60 ° C is heated to 85 ° C and fed at 4.0 m ⁵ / h to the same three-phase decanter centrifuge as in Example 1. The centrifuge is equipped with a single, open, screw screw (pitch 114 mm, height 30 mm (corresponding to 11/20 to 16/25 total thickness of all phases). The water contents of the samples are given in Table 2.

Table 2

Sampling Water content (¾ vol.) Tar phase Aqueous phase after Batch 2 h . 5.5 2.6 80 B h 6.0 3.1 78 14 h 5.5. 4.3 77

S 'CS 273 648 B2 4

Similar results are obtained when a single segment screw is used instead of a single-screw screw.

The separation of water is better than that of example 1 by the installation of an open screw, but here too the reduction of the separation power during the duration of the experiment is shown.

Example 3

Example 2 was repeated with a crude tar temperature of 82 [deg.] C., the filling in a three-phase decanter centrifuge being interrupted for 1 minute every 4 hours.

This measure surprisingly succeeds in reducing the separation power loss described in Example 2. In addition to good and uniform water separation, the ash-forming content is also reduced by more than 40%, while at the same time reducing the quinoline-insoluble (Q1) insoluble components adequately.

The light to heavy phase thickness ratio of 4.5 to 5.4, adjusted by the height of the removal throat and the weir height, results in a pure phase separation.

The results are shown in Table 3.

Table 3

Removal sample after Water content (¾ vol.) Ash (% by weight) Ql (% w / w) Batch Dehtová phase Vodná phase Batch Dehtová phase Batch Dehtová phase 2 h 4.6 1.3 83.0 0.21 0.12 2.73 2.63 6 h 5.0 1.7 81.5 0.22 0.13 2.76 2.65 13 h 4.6 1.6 81.5 0.21 0.11 2.71 2.58 21 h 4.6 1.6 83.2 0.22 0.12 2.75 2.64 200 h 6.0 1.5 87.3 0.23 0.12 β 2.74 2.70

Example 4

This example includes 5 test series with different pre-treated crude tars. The raw tar temperatures and the power also change.

To the crude tars in a tank at 60 ° C, 5% by volume of the tar fraction boiling between 200 and 230 ° C, 0.1% by volume of commercial demulsifier and 5% by volume of water (experimental series a to c) or 10% by volume 50% are added. tar / water emulsion. The contents were mixed by pumping throughout the experiment. The charge for the decanting centrifuge is removed approximately in the middle of the tank, at the same time being filled with a corresponding amount of crude tar, tar oil, demulsifier and water or emulsion.

This pre-treatment is intended to achieve the following:

The addition of tar oil is intended to reduce the viscosity of the crude tar and the demulsifier should disrupt the tar / ash / water emulsion to achieve a better separation. Additional water should remove salts from the crude tar and reduce the chlorine content.

The separation of water and solids was carried out in the same manner with the same decanter centrifuge as in Example 3. A sample was taken 22 hours after the start of the experiment.

The complete analysis data are summarized in Table 4. They show that the addition of oils and demulsifiers causes only a small improvement in the separation stage. On the other hand, it is surprising that in tars with such different water and ash contents, such good separation results are achieved without adjusting the workflow or centrifugal geometry, such as the height of the extraction throat for the water phase or the weir height for the tar phase.

CS 273 64B B2

Table 4

Try Temperature (°) Power (m ³ / h) Crude tar Tar phase Vodná phase water (% vol) Phase fixed substances ash (% by weight) water (¾ obj.) ash (% by weight) QI (% by weight) water (% vol) ash (¾ wt.) QI (% w / w and B0 4.0 4.6 0.12 2.8 1.4 0.09 2.8 81 5.1 b 90 4.0 6.5 0.24 2.5 1.9 0.14 2.4 90 6.3 C 93 4.0 6.2 0.09 2.6 1.5 0.07 2.5 80 5.1 d 100 ALIGN! 2.4 17.1 0.24 2.6 1.7 0.09 2.6 90 6.9 E 105 4.0 14.0 0.30 2.7 2,0 0.14 2.7 85 8.0

The solids phase is completely water-free, so that it can, for example, be easily concentrated in a two-phase decanter centrifuge so far that a flowable hydrocarbon concentrate remains, which can be used as an admixture component for lignite.

The performances given in the examples correspond approximately to the following mean tar residence times, calculated on the basis of the total liquid content of the centrifuge.

2.4 m @ 2 / h = 71 s

3.8 m ³ / h = 45 sec

4.0 n? / H = 42 s

The delay times are thus far below the values found by Mischin et al. for fully jacketed centrifuges, at least 10 minutes without impairing the fining or separating performance. This result is surprising since the process of the invention was believed to produce worse results due to the phase mixing caused by the flow. In addition, fluctuations in raw tar composition were expected to have a greater impact on the water content and ash content of the tar phase.

OBJECTS OF THE FINISH

Claims (4)

A method for reducing the water and ash-forming substances by continuously separating heated coal tars in an aqueous phase, a tar phase and a solid phase using a three-phase decanter centrifuge at a temperature between 60 and 105 ° C, a centrifugal number between 1000 and 3000 g, and the rotor 10 to 50 minutes ¹ and ^an average residence time of the tar of between 30 and 80 seconds, wherein the crude tar is divided in the three-phase decanting centrifuge with open jednoohodým or twin- screw extruder, wherein the filling during continuous operation periodically in each case up to six hour intervals interrupts for at least 1 minute. 2. A process according to claim 1, characterized in that water, demulsifiers, flocculants and tar oils are added individually or in combination to the crude tar prior to centrifugation. 3. Method according to claim 1, characterized in that, when starting the process, the solids from the previous separation cycle are first introduced at least in an amount corresponding to the volume of the circular space between the screw and the centrifuge wall and then the raw tar filling is increased to nominal power. 4. The method of claim 4, wherein the ratio of the aqueous phase layer thickness to the tar phase layer thickness in the decanter centrifuge is between 4.5-5.4.