GB1566210A

GB1566210A - Separation of tar containing aqueous mixtures

Info

Publication number: GB1566210A
Application number: GB5075477A
Authority: GB
Original assignee: Krupp Koppers GmbH
Current assignee: Krupp Koppers GmbH
Priority date: 1976-12-06
Filing date: 1977-12-06
Publication date: 1980-04-30
Also published as: ES463639A1; FR2372880A2; BE861254R; DE2655146C2; DE2655146A1; FR2372880B2; MX146617A

Description

(54) SEPARATION OF TAR CONTAINING AQUEOUS MIXTURES (71) We, KRUPP-KoPPERs GESELL SHAFT MIT BESCHRANKTER HAFTUNG, a German Company of 43 Essen 1, Postfach 8, Moltkestrasse 29, West Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the separation of tar from tar containing aqueous mixtures, especially from such aqueous mixtures obtained as a result of the distillation of coal.

In our copending British Patent Application No. 22762/77 (Serial No. 1,566,209) we disclose a two stage process for the separation of a tar containing aqueous mixture into an aqueous fraction, a liquid tar fraction and a heavy tar residue and the plant in which this process is performed. According to the process the tar containing aqueous mixture is fed into a first separation vessel, where it is allowed to separate into a first aqueous fraction, a first liquid tar fraction and a heavy tar residue, which are drawn off the vessel through separate outlets. The first liquid tar fraction, so obtained, is then fed into a pressure separation vessel, in which it is allowed at an elevated temperature, to separate further into a second aqueous fraction, a second liquid tar fraction and a second heavy tar residue.These fractions are drawn off the pressure separation vessel through separate outlets.

According to one aspect of this process, the second heavy tar fraction may then be recycled, being reintroduced into the first separation vessel. Where the construction of the plant allows, that is where the pressure separation vessel is positioned above the first separation vessel, the second heavy tar residue may be fed from the pressure separation vessel to the first separation vessel under -gravity. However, where this is not possible or in Order to assist movement under gravity, it was proposed to use part of'the.first aqueous fraction to dilute and fish the second heavy tar residue into the first separation vessel.

It has subsequently been found that dilution of the second heavy tar residue, in this way, detracts from its separability once it has been returned to the first separation vessel. In order to avoid this problem, it is now proposed that in situations where the second heavy tar residue may not be adequately fed from the pressure separation vessel to the first separation vessel under the influence of gravity alone, a powered conveyor means should be provided for this purpose.

According to one aspect of the invention an industrial plant for the separation of a tar containing aqueous mixture into an aqueous fraction, a liquid tar fraction and a heavy tar residue includes a first separation vessel arranged to permit gravitational settling and having a discharge outlet for a first aqueous fraction, a discharge outlet for a first liquid tar fraction and a discharge outlet for a first heavy tar residue; a pressure separation vessel arranged to operate at elevated temperature and pressure to permit gravitational settling and having a discharge outlet for a second aqueous fraction, a discharge outlet for a second liquid tar fraction and a discharge outlet for a second heavy tar residue; means for transporting the first liquid tar fraction from the first separation vessel to the pressure separation vessel; and powered conveyor means for transporting the second heavy tar residue from the pressure separation vessel to the first separation vessel.

According to a further aspect of the invention in a process for the separation of a tar containing aqueous mixture into an aqueous fraction, a liquid tar fraction and a heavy tar residue the tar containing aqueous mixture is introduced into a first separation vessel in which the aqueous mixture is gravitationally settled and then discharged through separate outlets as a first aqueous fraction, a first liquid tar fraction and a first heavy tar residue; the first liquid tar fraction is then introduced into a pressure separation vessel operated at elevated temperature and pressure, in which the liquid tar fraction is gravitationally settled and then discharged through separate outlets as a second aqueous fraction, a second liquid tar fraction and a second heavy tar residue, the heavy tar residue being returned to the first separation vessel by a powered conveyor means.

An embodiment of the invention is now described by way of example only, with reference to the accompanying drawing, which illustrates schematically an industrial plant for separating the tar containing aqueous mixture obtained from the distillation of coal in a coke oven battery.

The drawing shows a first separation vessel 4 and a pressure separation vessel 12 in longitudinal section.

Crude coke Oven gas coming from a coke oven battery receiver (not shown) is cooled and separated into a gaseous fraction and a tar containing aqueous mixture. This tar containing aqueous mixture is fed into a pipeline 3 leading into a vessel 4 for the purpose of pre-separation. In coking plant technology, vessel 4 is often also called a flushing-water tank or a decant tank. In this first separation vessel or tank 4, separation of the tar-containing aqueous mixture into three factions, water or more correctly liquorhe so called first aqueous fraction, liquid tar and heavy tar residue, takes place by gravitational settling at atmospheric pressure over a period of about half an hour.

For carrying out the process it is an advantage if vessel 4 has the form shown in the figure and has at one end a neck 5 directed upwardly. The liquid tar fraction separates out above the heavy tar residue.

The heavy tar residue collecting at the bot torn of vessel 4 is taken by a scraper chain conveyor 6 arranged just above a base portion of the vessel and transported by this to the top of the neck 5. From there the heavy tar residue falls through a downwardly directed discharge opening 7 into a tank 8 provided for collecting the heavy tar residue. The liquid tar fraction in vessel 4 is drawn off through an outlet by means of a pipeline 9 and is conveyed to a pressure separation vessel 12 through a pump 10 and a pipeline 11 to enter the pressure separation vessel 12 through inlet 20. The first aqueous fraction collecting above the liquid tar fraction in vessel 4 flows over a weir 13 arranged inside the vessel and thence to a discharge outlet and is drawn off through a pipeline 14.By means of a pump 15, this aqueous fraction is returned through a pipeline 16 into a receiver of the coke oven bFy.

In a pressure separation vessel 12, the tar tar fraction introduced through inlet 20 is tread further at elevated pressure and teteratures conditions.

Suitably, the pressure separation vessel is at an absolute pressure of 1.5 to 2.5 atmospheres and a temperature of 60 to 100"C. The pressure separation or "dewatering" is again by gravitational settling assisted by the lowered viscosity of the liquid tar fraction at the higher temperature with the increased pressure inhibiting forthing and vaporisation. hTe settling may be for a longer period than in the first separation vessel ,for example, it may be over a period of 2 to 5 hours, suitably about 3 hours. Valves (not shown) permit the pressure separation vessel 12 to be maintained at a higher pressure than that obtaining in communicating pipelines.The water or liquor separating out under these conditions, the so called second aqueous fraction, is draw noff from the pressure separation vessel 12 throuhg an outlet 21 and goes into a pipe 17, from which it can be removed from the plant through a pipeline 18. At the same time further heavy tar residue separates out fro mthe liquid tar fraction in pressure separation vessel 12, and collects on the bottom of the vessel 12. This second heavy tar residue is taken by a screw conveyor 19 arranged just above the bottom of the pressure separation vessel and is conveyed continuously to an outlet 22. From the outlet 22, the second heavy tar residue is returned to the first separation vessel 4, through pipe 30, the heavy tar residue being forced along the pipe 30 by a screw conveyor 29 which is rotated by drive means, not shown.The second heavy tar ersidue is fed into the veshel 4 in the neighbourhood of the discharge opening 7. Since there is practically no flow in vessel 4 adjacent to outlet 7, the heavy tar residue introduced has ample time to settle. It is then extracted by the scraper chain conveyor 6 together with a first heavy tar residue coming from vessel 4 and is collected in tank 8, from which its further processing can take place. The cleaned and de-watered liquid tar fraction is meanwhile removed from the pressure separation vessel 12 through an outlet 23. This liquid tar fraction goes through a pipeline 26 to a liquid tar reservoir or into a subsequent tar distillation plant.

When the process according to the invention is used, it has been shown that the reservoir to which the liquid tar is discharged needs considerably less frequent cleaning than when the invention is not used.

WHAT WE CLAIM IS:- 1. Industrial plant for the separation of a tar containing aqueous mixture into an aqueous fraction, a liquid tar fraction and a heavy tar fraction including a first separation vessel arranged b permit gravitational settling and having a discharge outlet for a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tar fraction is gravitationally settled and then discharged through separate outlets as a second aqueous fraction, a second liquid tar fraction and a second heavy tar residue, the heavy tar residue being returned to the first separation vessel by a powered conveyor means. An embodiment of the invention is now described by way of example only, with reference to the accompanying drawing, which illustrates schematically an industrial plant for separating the tar containing aqueous mixture obtained from the distillation of coal in a coke oven battery. The drawing shows a first separation vessel 4 and a pressure separation vessel 12 in longitudinal section. Crude coke Oven gas coming from a coke oven battery receiver (not shown) is cooled and separated into a gaseous fraction and a tar containing aqueous mixture. This tar containing aqueous mixture is fed into a pipeline 3 leading into a vessel 4 for the purpose of pre-separation. In coking plant technology, vessel 4 is often also called a flushing-water tank or a decant tank. In this first separation vessel or tank 4, separation of the tar-containing aqueous mixture into three factions, water or more correctly liquorhe so called first aqueous fraction, liquid tar and heavy tar residue, takes place by gravitational settling at atmospheric pressure over a period of about half an hour. For carrying out the process it is an advantage if vessel 4 has the form shown in the figure and has at one end a neck 5 directed upwardly. The liquid tar fraction separates out above the heavy tar residue. The heavy tar residue collecting at the bot torn of vessel 4 is taken by a scraper chain conveyor 6 arranged just above a base portion of the vessel and transported by this to the top of the neck 5. From there the heavy tar residue falls through a downwardly directed discharge opening 7 into a tank 8 provided for collecting the heavy tar residue. The liquid tar fraction in vessel 4 is drawn off through an outlet by means of a pipeline 9 and is conveyed to a pressure separation vessel 12 through a pump 10 and a pipeline 11 to enter the pressure separation vessel 12 through inlet 20. The first aqueous fraction collecting above the liquid tar fraction in vessel 4 flows over a weir 13 arranged inside the vessel and thence to a discharge outlet and is drawn off through a pipeline 14.By means of a pump 15, this aqueous fraction is returned through a pipeline 16 into a receiver of the coke oven bFy. In a pressure separation vessel 12, the tar tar fraction introduced through inlet 20 is tread further at elevated pressure and teteratures conditions. Suitably, the pressure separation vessel is at an absolute pressure of 1.5 to 2.5 atmospheres and a temperature of 60 to 100"C. The pressure separation or "dewatering" is again by gravitational settling assisted by the lowered viscosity of the liquid tar fraction at the higher temperature with the increased pressure inhibiting forthing and vaporisation. hTe settling may be for a longer period than in the first separation vessel ,for example, it may be over a period of 2 to 5 hours, suitably about 3 hours. Valves (not shown) permit the pressure separation vessel 12 to be maintained at a higher pressure than that obtaining in communicating pipelines.The water or liquor separating out under these conditions, the so called second aqueous fraction, is draw noff from the pressure separation vessel 12 throuhg an outlet 21 and goes into a pipe 17, from which it can be removed from the plant through a pipeline 18. At the same time further heavy tar residue separates out fro mthe liquid tar fraction in pressure separation vessel 12, and collects on the bottom of the vessel 12. This second heavy tar residue is taken by a screw conveyor 19 arranged just above the bottom of the pressure separation vessel and is conveyed continuously to an outlet 22. From the outlet 22, the second heavy tar residue is returned to the first separation vessel 4, through pipe 30, the heavy tar residue being forced along the pipe 30 by a screw conveyor 29 which is rotated by drive means, not shown.The second heavy tar ersidue is fed into the veshel 4 in the neighbourhood of the discharge opening 7. Since there is practically no flow in vessel 4 adjacent to outlet 7, the heavy tar residue introduced has ample time to settle. It is then extracted by the scraper chain conveyor 6 together with a first heavy tar residue coming from vessel 4 and is collected in tank 8, from which its further processing can take place. The cleaned and de-watered liquid tar fraction is meanwhile removed from the pressure separation vessel 12 through an outlet 23. This liquid tar fraction goes through a pipeline 26 to a liquid tar reservoir or into a subsequent tar distillation plant. When the process according to the invention is used, it has been shown that the reservoir to which the liquid tar is discharged needs considerably less frequent cleaning than when the invention is not used. WHAT WE CLAIM IS:-

1. Industrial plant for the separation of a tar containing aqueous mixture into an aqueous fraction, a liquid tar fraction and a heavy tar fraction including a first separation vessel arranged b permit gravitational settling and having a discharge outlet for a

first aqueous fraction, a discharge outlet for a first liquid tar fraction and a discharge outlet for a first heavy tar residue; a pressure separation vessel arranged to operate at elevated temperature and pressure to permit gravitational setting and having a discharge outlet for a second aqueous fraction, a discharge outlet for a second liquid tar fraction and a discharge outlet for a second heavy tar residue; means for transporting the first liquid tar fraction from the first separation vessel to the pressure separation vessel; and powered conveyor means for transporting the second heavy tar residue from the pressure separation vessel to the first separation vessel.

2. Industrial plant according to Claim I in which the powered conveyor means includes a screw conveyor disposed within a pipe connecting the pressure separaltion vessel to the first separation vessel.

3. Industrial plant according to Claim 1 or 2 in which the means for transporting the first liquid tar fraction from the first separation vessel to the pressure separation vessel includes a pipe line and pump.

4. Industrial plant according to any pre- ceding claim which is arranged to discharge the second heavy tar residue, into the first separation vessel at a position adjacent to the discharge outlet for the first heavy tar residue.

5. Industrial plant according to any preceding claim wherein the pressure separation vessel includes adjacent to a bottom region thereof a screw conveyor arranged to feed Lhe second heavy tar residue to the heavy tar discharge outlet.

6. Industrial plant according to any preceding claim wherein the first separation vessel includes an upwardly directed neck with the heavy tar residue discharge outlet positioned thereon and a scraper chain conveyor adjacent to a base portion of the vessel and continuing into the upwardly directed neck, arranged to feed the first heavy tar residue to the heavy tar residue discharge outlet.

7. Industrial plant for the separation of a tar containing aqueous mixture, constructed substantially as described herein with reference to and as illustrated in the accompanying drawing.

8. A two stage process for the separation of a tar containing aqueous mixture into an aqueous fraction, a liquid tar fraction and a heavy tar residue in which the tar containing aqueous mixture is introduced into a first separation vessel in which the aqueous mixture is gravitationally settled and then discharged through separate outlets as a first aqueous fraction, a first liquid tar fraction and a first heavy tar residue; the first liquid tar fraction is then introduced into a pressure separation vessel operated at elevated temperature and pressure, in which the liquid tar fraction is gravitationally settled and then discharged through separate outlets as a second aqueous fraction, a second liquid tar fraction and a second heavy tar residue, the second heavy tar residue being returned to the first separation vessel by a powered conveyor means.

9. A two stage process according to Claim 8 in which the second heavy tar residue is introduced into the first separation vessel at a position adjacent to Ithe discharge outlet for the first heavy tar residue.

10. A two stage process according to Claim 8 or 9 in which the pressure separation vessel is operated at an absolute pressure of 1.5 to 2.5 atmospheres and at a temperature of 60 to 100 C.

11. A two stage process for the separation of a tar containing aqueous mixture into an aqueous fraction, a liquid tar fraction and a heavy tar fraction substantially as described herein with reference to the accompanying drawing -.