CA1220438A

CA1220438A - Process for cleaning of coke tars with high solids content

Info

Publication number: CA1220438A
Application number: CA000447745A
Authority: CA
Inventors: Dieter Stalherm; Wolfgang A. Hillebrand; Alfred Gwosdz; Ingo Romey
Original assignee: Bergwerksverband GmbH; Carl Still GmbH and Co KG
Current assignee: Bergwerksverband GmbH; Carl Still GmbH and Co KG
Priority date: 1983-02-17
Filing date: 1984-02-17
Publication date: 1987-04-14
Also published as: EP0116956A2; DE3305431A1; EP0116956A3; DE3468121D1; EP0116956B1; CA1221654A; ZA841046B; JPS59157178A

Abstract

PROCESS FOR CLEANING OF COKE TARS
WITH HIGH SOLIDS CONTENT

ABSTRACT OF THE DISCLOSURE

A method of cleaning coke tars having a high content of contaminating solid matter, which are produced in various crude gas separation processes. The high-solids tar is filtered in candle filters, while adding small amounts of, or no, filtering aids and/or diluting substances, to give the tar a consistency suitable for further processing. The tar to be filtered in the candle filters may be either coke tar coming from a coke oven battery operated with preheated coal and having a solid matter content of 10 to 30%, or coke tar having a solids content higher than 30%, or even the usual heavy tar.

Description

WITH HlGH SOLIDS CONTENT

FIELD AND BACKGROUND OF THE INVENTION
-The present invention relates to a process for the cleaning of coke tars which carry a high content of solids. The tars are produced in various cleaning arld cooling processes for crude coke oven gas.

During the high temperature coking o-f coal which has been charged into coke ovens and which has been predried and/or lQ preheated, a tar is formed which camlot be dehydrated by the usual method of tar decantatioll and whose solids content is so high, that it does nQt comply with the required speci-ficatiolls of the tar processillg industry. The sol;ds content or QI
contellt ~considered as a portion of the quinoline insoluble matter) of such tars is between 10 and 30%. The water content of such tars is between 10 aTld 20%. The high solids content is related to the coking conditions (use of predried and pre-heated coal, higher coking temperature) as well as the increased environmental requirements, which necessitate increased ; 20 aspiration during the charging process. This leads to a larger carryover illtO the collecting mains. Experiments for developing improvements ill the design of coke ovens and the of-f-take systems, so far have not achieved the desired results.
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During the coking of fine coal in the coke ovens, a-nd aIso when coal is charged as wet coal, so called heavy tar (approx~
imately 1-2% of the tar) is produced which contains approximately 30-50% solids. With the use of modern high performance coke :

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ovens, operated at increased fl~le temperatures with higher charging gas aspiration to accommodate bigger volumes r an increased amount of carryover is created, which results in a higher transfer of coal flnes from the coking chamber into -the collecting mains. This also decreases the tar quality and leads to an increased yield of heavy tar.

These tars with high solids content cannot be processed in the common tar distillation plants. Only a limited mixing into the coal is possible since homogenization of coal and tar has not yet been achieved because of its high water content.
Furthermore, this method only allows a small portion of the tar which has been produced in preheated coal operations (e.g. precarbon process) to be returned to the coke ovens.
Any further use, like combustion, is hindered by the limited pumping ability and the tendency for sedimentation. Therefore, these tars with high solids content are not only without value, but also present an environmental problem.

It is known from U.S. Patent 4,259,171 that tars with high solids content are separated into two liquid streams using centrifuges.
One product stream has a reduced, and the other one an increased portion of quinoline insoluble matter. However, this is only a partial solution to the problem since the remaining sludge or ~ second product stream i`s still difficult to process. Tests for separation in plate filters are indicated in U.S. Patent 2,956,94~. They were not successful due to the necessary expensive dilution and the remaining unsatisfactory consistency of the residue.
SUMMP,RY OF THE INVENTION
_ It therefore is the purpose of this invention, to provide a process for the separation of coke tars which are unduly ye/~S

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3 ~ 38 contaminated w-ith solids, whereby the residues can be used commercially, or at least can be processed without creating environmental problems.

~his is accomplished by filtering the coke with high solids coll~erlt in candle filters, e.g. according to German Patent P ~ 12 316, with the addi~ion of little or no filtering aids and/or diluting substances. The filtering is achieved to an allowable degree o-f purity for further processing.

In addition, from both German OS 2~ 28 976 and German Patellt 10 P 32 12 316, a candle filter for filtering high viscous liquids :i. s known .

Under this method, the separation of solids is performed by a specially designed bundle of candle filters, whereby the solids are separated at the calldle surface and enter the hollow candle 15 center, therl the solids are discharged from the filter by means of a special device.
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Both above documents and also German OS 27 06 938 only deal with the process alld equipmerlt for filtration of tar, pitch and other consistencies from coal~ which occur durillg coal liquefi-20 cation. These types of tars differ greatly from coke planttar in their composition and their ability to be filtered.

Due to practical experience in the past with the candle filters, which are generally made of ceramic materials, it was thought to be impossible to clean high QI contaminated coke tars in 25 such candle filters. The ceramic filters had the lnherent problem that the pores of the filter always closed up and could only be freed after irksome work with dissolvellts. Surprisingly, it is possible with the new candle filters according to German ` ` P 31 12 316, with the addition of only small amounts of filter-30 ing aids, and/or dilution, to filter high solids content coke ~, ;

~' plant tar.

It was also demonstrated that coke plant tar, especially from preheated coal operating coke oven batteries, having a solids content of approximately 10-30%, can be separated in the candle filters. These tars which include very fine solids which formerly could only be processed with great difficulty, or not at all, can now be sufficiently separated with the candle filter invention, even down to a QI content in the filtrate of approximately 0.1%.

It can also be anticipated to separate coke plant tars with a solids content of more than 30% in candle filters. With the help of these candle filters, it is surprisingly possible to handle this type of coke tars. The application of this new process, does not only result in the production of valuable tar, almost completely free of solid particles, but even more so, resolves the residue problem through the formation of an easily processable filter cake. According to this invention, it is now possihle to separate tars from the coke plants in candle filters. Through this method, a filtrate is produced, which can be processed further in any common tar distillation plant and on the other side, a filter cake remains which allows simple handling.

It has also been demonstrated that the filtration can be accomplished without any type of filtering aids and without any further additives.

Depending upon the actual exact composition of the coke plant tar being recovered, it might be advantageous to use special filtering aids. The invention proposes special filtering aids according to German OS 30 05 246.

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Surprisingly, it was discovered that even tar sludges with a quinoline insoluble content (referred to as Ql-value) of 40%, like the heavy tars mentioned, can be fil~ered with this system.

The invention also suggests the use of coke battery by-products as diluents. Favorable results have been obtained using tar oils as diluents, for instance creosote r in amounts of less than 25%, preferably 15 to 20%. The adding of a diluent almost doubles the absolute filter rate. The utilization of the coke oven by-products, such as primary cooler tar, as diluents, is emphasized. This tar can be added to the mixer without much preheating. Under certain conditions, it is also feasible to usepart of the filtrate as a diluent in a recycle operation.

The invention suggests the grinding of completely dried filter cake and the blending of it back to the wet or preheated coal to be charged to the coke ovens, to insure a meaningful and economical application of the filter cake from the candle filter. The filter cake, especially after grinding, can easily be blended with the coking coal without the formation of nests in the chamber. Also, an efficient energy recovery through filter cake combustion is feasible. Another application ~ould be to use the dried filter material for charging the blast furnace.

Lastly, the filter cake could be prepared and used as binder material for briquettes. The conditioning of the sludge can be of special advantage for a usable consistency.
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The invention also suggests the utilization of the filtrate for the production of special coke, i.e. needle coke, in addition ''''' .~ ~

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back-blending with certain portions of non-filtered i.e. non-prepared high solids content tar is feasible, whereby a product with selected solids content will be provided. This allows the tar manufacturer to be flexible and adapt to the demand of the market situation.

A still further ob~ect of the invention is to provide a method which is simple and effective to purify otherwise useless coke and other tars.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure.

The invention is explained in more detail by the following examples:

Example No. 1 Coke oven tar from a preheated coal operating battery with a water content of 10.1~ and QI-Value of 15.2% by weight and approximately 50C temperature is mixed in the pressure container with a 5% filtering aid without any dilueni, then heated to filtration temperature. The water vapors are exhausted into the atmosphere from the storage container. Subse~uently, -the dehydrated tar is cleaned at approximately 160C-170C in the candle filter. The filtration rate had a QI-Value of only 0.03~ by weight and 0.02~ by weight ash content.

; Example 2 The tar in this test run contained 17~ water and a QI-Value of ' - 6 -~. ~

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17.6%. By adding 5% fil-tering aid and 25% creosote as a solvent, the filtratlon rate was 50 kg/mZh, and the filtrate obtained had a QI-Value of 0.2% by weight. The filter cake had a QI-Value of 53% by weight.

Example 3 In this case the water content of the tar was 20% by weight and the QI content 19.9% by weight. By adding 5.3% by weight filtering aid and 30% by weight (water ~ree tar) of primary cooler tar, the filtration rate amounted to 63 kg/m2h. The filtrate here also had a QI-content of only 0.2% weight at 0.02 weight % ash.

Example 4 A tar obtained at the primary coolers of a coke oven battery and having a QI content of 5.8% by weight and a water content of 3.5% by weight was filtered in the candle filters while adding 3% of filtering aids. The filtering rate was 116 kg/m2h (kg per m2 per hour), and no diluent was added. The obtained filtrate had a QI content of 0.2% by weight.

Example 5 A tar obtained in a coke oven battery operated with wet coal and having a moisture content of 8% and a QI content of 11.6%
by weight was filtered without dilution and at a filtering rate of 37 kg per m2 per hour. The QI content of the filtrate was reduced to 0.5% by weight, and the a content to 0.03%.

The candle filters comprise a housing or a vessel which is divided into two chambers by a partition wall with one of the chambers storing tar to be filtered and the other the filtered ~ ~, 3~
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tar~ The candle Eilters are attached to the partition wall and a riser pipe opens out in the chamber for Eiltered tar and where inlet and outlet lines for tar to be filtered, filtered tar and drying gas as well as an outlet for the filter cake and a beater acting on the partition wall are arranged. An immersion tube serving as an outlet for filtered tar ends immediately near to or at the eleva-tion of the partition wall with the partition wall having a recess for the end of the immersion tube. The beater is arranged concentrically to the immersion tube and the drying gas inlet relative to the candle filters is arranaed in or behind the partition wall level. The filtrate chc~mber is arranged slidable in the housing with the partition wall being used as a cover. Furthermore, flow pipes pass through the chamber for filtered -tar.

In summary, the present invention comprises a method of cleaning coke tars supplied from a container and which were ob-tained from a coking plant and have a high content of solids, comprising filtering the coke tar in candle filters to separate low solid content filtrate from a residue, the filtering being carried out to a degree of purity suitable for further process-~; ing of the filtrate.
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While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
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Claims

WHAT IS CLAIMED IS:

1. A method of cleaning coke tar obtained in a coking plant and having a high content of solids, comprising: filtering the coke tar in candle filters to separate low solid content tar filtrate from a residue in the filters, the filters being carried out to a degree of purity suitable for further process-ing of the filtrate.

2. A method according to claim 1, wherein the coke tar to be filtered comprises coke tar obtained in a crude gas separation process.

3. A method according to claim 1, wherein the coke tar to be filtered comprises coke tar from a crude gas separation process mixed with heavy tar.

4. A method according to claim 1, including admixing small amounts of additives to the coke tar during the filtering of the coke tar.

5. A method according to claim 4, wherein the additives comprise filtering aids.

6. A method according to claim 4, wherein the additives comprise diluents.

7. A method according to claim 1, wherein the coke tar to be filtered is a coke tar having a solid matter content of about 10% to 30%, and being coke tar coming from coke oven batteries operated with preheated coal.

8. A method according to claim 1, wherein the coke tar to be filtered is tar having a solid content of more than 30%.

9. A method according to claim 1, wherein the coke tar to be filtered is heavy tar produced in coke ovens.

10. A method according to claim 5, including admixing the filtering aids in a proportion of up to 5% of the coke tar.

11. A method according to claim 5, wherein heavy tar is admixed with the coke tar and additives.

12. A method according to claim 6, wherein by-products of the coking plant are used as diluents.

13. A method according to claim 6, wherein tar oils chosen from creosote oil and an aromatic, petroleum base distillate having a corresponding boiling range to creosote, are used as diluents, in a proportion of less than 50% of the coke tar.

14. A method according to claim 6, wherein tar obtained in a primary cooler stage of the coke oven is used as diluent.

15. A method according to claim 6, wherein a portion of the filtrate is used as diluent.

16. A method according to claim 1, grinding a completely dry filter cake comprising the residue and adding the ground residue to wet or preheated coal to be charged into a coke oven.

17. A method according to claim 1, wherein completely dry filter cake comprising the residue is burned.

18. A method according to claim 1, including adding a dry filter cake comprising the residue to the charge of a blast furnace.

19. A method according to claim 1, including processing a filter cake comprising the residue to form a binder material for briquettes.

20. A method according to claim 1, wherein the obtained filtrate is used for producing special coke, such as needle coke.

21. A method according to claim 1, wherein the obtained filtrate is mixed with selected amounts of unfiltered or not fully purified solids-free tar, to obtain a product having a selected solids content.