Process and apparatus for the separation of crude benzol and naphthalene from washing oil

#This invention relates to a process and apparatus for separating crude benzol and naphthalene from washing oil, and more particularly, to regenerating washing oil which has been spent to recover naphthalene and/or benzol from coke oven gas wherein the washing oil is regenerated by using steam to strip it of its volatile constituents to thereby enable resolving the volatile constituents into a number of fractions.

#The crude gas occurring in the process of coking of coal contains, in addition to other substances, naphthalene and various hydrocarbons, particularly benzol, toluene and xylene which are grouped under the general designation of crude benzol. Naphthalene and crude benzol must be removed before the coke oven gas is put to further use. Naphthalene and crude benzol are removed usually by scrubbing the crude gas with washing oil which absorbs the naphthalene and crude benzol. It is known in the art to recover the naphthalene and crude benzol contained in the spent washing oil by distillation to thereby enable the reuse of the washing oil in the washing cycle. Distillation of the readily volatile components is effected with steam in order to avoid excessive oil temperatures and possible thermal damage to the oil during the distillation process.

#The known processes for the regeneration of washing oil by means of steam usually yield two fractions, namely, the crude benzol, which contains all the hydrocarbons and other substances more volatile than naphthalene and naphthalene oil. The naphthalene oil is a mixture of naphthalene and washing oil with crude benzol fractions. Thus, on the one hand, there are considerable washing oil losses; while on the other hand, both fractions contain the required constituents, for example, benzol and naphthalene but in highly contaminated forms so that their sale value is reduced.

#These features and advantages of the present invention as well as others will be more readily understood when the following description is read in light of the accompanying drawing wherein one exemplified embodiment of the apparatus and system is shown for performing the process to regenerate washing oil according to the present invention.

#Spent washing oil which is charged with crude benzol and naphthalene is delivered from a naphthalene or benzol recovery plant, not shown, for regeneration by a line 1 to a heat exchanger 2. Purified oil also flows through the heat exchanger 2. The spent washing oil is then fed from the heat exchanger 2 through a steam heated heat exchanger 3 for heating the spent washing oil to a temperature of about 180.degree. C. The spent washing oil, at this elevated temperature, enters a stripper column 4 which is constructed as a bubble column, and forms an integral part of a main column A. The volatile constituents, i.e., crude benzol and naphthalene, are stripped by steam injected into the stripper column 4 by nozzle tubes 5 that are coupled to a steam supply line 6. The resulting vapor mixture from the stripper column 4 still contains a considerable amount of washing oil. The vapor mixture from the stripper column 4 flows to an exchange column 7 wherein the oil contained in this mixture is exchanged for naphthalene. The vapor mixture passing from the exchange column section 7 still has a temperature of about 165.degree. C. and flows upwardly to a second exchange column section 8 which is arranged in a superimposed relation above the exchange column section 7. The second exchange column 8 is fed with water whereby the vapor mixture is cooled to about 100.degree. C. The liquid mixture conducted away from this second exchange column section consists of a mixture of water and a toluene-xylene-naphthalene mixture. This liquid mixture is collected in a collecting cup 9 and fed to a secondary phase separator 10 wherein the liquid mixture is separated into a water fraction and a toluene-xylene-naphthalene fraction.

#The vapor mixture passing from the second exchange column section 8 being cooled to a temperature of approximately 100.degree. C. flows upwardly to a third exchange column section 11 which is arranged in a superimposed relation above the second exchange column section 8. The third exchange column section 11 is fed with benzol whereby the water, toluene and xylene are exchanged in this section for benzol. The heat product passing from the main column A consists essentially of benzol and water. The head product is condensed in a condenser 12 into which cooling water is fed by line 13. The condensed head product is fed to a phase separator 14. Anhydrous benzol is conducted from the phase separator 14 by a line 14A which is divided so that some of the anhydrous benzol serves as a reflux conducted by the line 14A to the third exchange column section 11. The remaining portion of the anhydrous benzol is passed through a heat exchanger 16 for further cooling and fed therefrom by line 15 as an end product of the process. The accumulating water in the phase separators 10 and 14 is collected in a collecting tank 17. Some of the water in tank 17 is recycled to the second exchange column section 8 through the use of pump 18 coupled to line 18A. The remaining portion of the water in collecting tank 17 is subjected to further cooling in a heat exchanger 19 from which cooled water is discharged from the plant by line 20. The regenerated and stripped washing oil is conducted from the main column A by a line 34. This stripped washing oil is returned, if desired, to the naphthalene or benzol recovery plant.