US3294676A

US3294676A - Process for producing dry hydrocarbon distillates

Info

Publication number: US3294676A
Authority: US
Publication date: 1966-12-27
Anticipated expiration: 1983-12-27

Description

Dec. 27, 1966 P. A. BRUNNER 3,

PROCESS FOR PRODUCING DRY HYDROCARBON DISTILLATES Filed Jan. 29, 1964 WET I 24 FEED W SETTLER STEAM I2 TO SEWER DRY PRODUCT INVENTOR. PAUL A. BRUNNER A TTORN E YS United States Patent 3,294,676 PROCESS FOR PRODUCING DRY HYDROCARBON DISTILLATES Paul A. Brunner, Harvey, Ill., assignor to Sinclair Research, Inc., New York, N.Y., a corporation of Delaware Filed Jan. 29, 1964, Ser. No. 340,970 6 Claims. (Cl. 208-487) This invention relates to the production of dry, petroleum distillates, especially hydrodesulfurized hydrocarbons.

In the refining of petroleum hydrocarbon distillates boiling primarily above the gasoline range, they are commonly subjected to a hydrodesulfurization treatment to remove sulfur contaminants present in these feeds. The hydrodesulfurization treatment is then normally followed by a steam stripping operation to remove hydrogen sulfide and other volatile sulfides that have become entrained in the distillates. As a result of the steam stripping, however, the stripped distillate product contains undesired amounts of water and must be dried, usually to about 40 F. haze point, a specification often prescribed by members of the petroleum industry. Many procedures are employed for the drying of the steam stripped product but most are cumbersome, time-consuming, involve expensive additional equipment, as well as an outside source of heat energy.

A simple and convenient process has now been discovered for producing a substantially dry, steam stripped petroleum distillate without many of the aforementioned attendant disadvantages. In accordance with the process of the present invention, a petroleum hydrocarbon distillate is steam stripped, e.g. after desulfurization, and the bottoms product from said stripping operation, which product is at a temperature of about 125 to 500 F., is flashed in a flash zone at a temperature of about 10 to 50 F. units below the bottoms product temperature. The vapors from the flashing operation are condensed in a condensation zone and the condensate settled in a settling zone to provide a water layer and an oil layer. The oil layer is separated from the water layer, returned, preferably by gravity, to the flash zone and a substantially dry, liquid product recovered from the bottom portion of the flash zone. The flashing, condensation and settling are conducted while applying a vacuum to the settling zone which vacuum also serves to place the flash and condensation zones under a subatmospheric pressure of about 50 to 200 mm. of Hg.

In avoiding the conventional cooling of the stripped liquid product bottoms before flashing, the process of the invention avoids the formation of free water and emulsion difliculties; free water not normally being in the bottoms as produced. Moreover, in flashing a relatively hot, stripped bottoms-liquid product as defined, it has been found that higher absolute pressures can be employed so that excess oil losses to the vacuum means during flashing are reduced and vacuum operating expenses minimized. Since the condensation temperature can be lower than the flash zone temperature, the oil loss in the discarded water is reduced and the concentration of water in the oil condensate is lowered in view of lower solubilities at lower condensation temperatures. Furthermore, inasmuch as the pressure in the flash zone is approximately that of the settling zone, the condensed oil can be returned to the flash zone by gravity thereby eliminating the necessity of pumping means, etc. Thus, it can be seen from these advantages and others which will become apparent from a more detailed description of the invention to follow, that the process provides a highly efiicient means for consistently obtaining a dry petroleum distillate product that meets the 40 F. haze point specification.

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The hydrocarbon feedstocks of the invention are petroleum distillates boiling primarily above the gasoline boiling range. These distillates usually boil primarily in the range of about 370 to 1000 F., and include light dis tillates such as kerosene, middle distillates such as diesel fuels, heavy distillates such as gas oils whether straight run (virgin) or cycle oils (obtained from thermal and catalytic cracking of straight run or cracked gas oils), and other distillates boiling above the gasoline boiling range and obtained from various petroleum processes. Paraffinic and mixed base crudes are the preferred sources.

As previously mentioned the feedstock is often hydrodesulfurized to give a product containing hydrogen sulfide or other sulfur impurities and the resulting material is fed to the steam stripper. The hydrodesulfurization treatment is that conventionally employed in the art and comprises contacting the distillate feedstock and hydrogen in the presence of a sulfur-resistant hydrogenation catalyst under conditions that remove sulfur. The hydro desulfurization conditions will vary depending on the particular feed being treated but in general fall within the following ranges: temperature, about 550 to 800 F.; pressure, about 200 to 800 p.s.i.g.; weight hourly space velocity, about 1 to 8 and hydrogen to hydrocarbon feed rates in standard cubic feet per barrel, of about 500 to 5000/1. Any of the conventional sulfur-resistant, hydrodesulfurization catalysts can be employed as, for instance, cobalt-molybdena-on-alumina, nickel-tungsten oxide-onalumina, nickel-tungsten sulfide-on-alumina, and cobaltmolybdena-on-silica-alumina. Generally, the conditions of the hydrodesulfurization are controlled and regulated to reduce the sulfur content of the feedstocks to no more than about 0.1%.

The steam stripping step of this invention can be performed utilizing any of the well-known steam stripping processes and apparatus of the art for removing, usually as overhead, light materials such as light hydrocarbons, hydrogen sulfide, and other volatile sulfur-containing contaminants from the hydrodesulfurized feed. Generally, the stripping tower is operated under approximately atmospheric pressure say from about 0.5 atmosphere to about 50 p.s.i. and a towers bottom temperature of about 125 F. to 500 F.

The hot stream of stripped bottoms product, which is flashed in accordance with the present invention, usually contains about .01 to 0.25% by weight dissolved water and can be saturated. The process of the invention often reduces the Water content to below about 0.005% by weight. The flashing of the stripped liquid bottoms from the steam stripping can be conducted in a suitable flash zone such as a flash drum or equivalent separating means maintained as aforementioned at a temperature of about 10 to 50 F. units below the temperature of the stripped liquid bottoms product. Conventional condensers can be utilized for the condensation of the flashed vapors and cooling water at temperatures of up to about F. are suitable as a heat transfer fluid to effect condensation. The vacuum applied to the settling zone can be through any suitable vacuum producing means and as aforementioned serves to place the flashing zone and condensation zone under a subatmospheric pressure of about 50 to 200 mm. of Hg and is suflicient to provide the desired dryness.

The following example is presented with reference to the attached drawing in order to further illustrate the present invention.

Kerosene from a hydrodesulfurization zone (not shown) is preheated to 315 F. and introduced into stripper 1 at a rate of 10,000 b/d. Stripping steam is introduced into stripper 1 by way of line 4 and distribution means (not shown) at a rate of 4330 pounds/hr. and at a pressure of about .50 p.s.i.g. Hydrogen sulfide and other volatile sulfur compounds are removed as overhead by means of line 8. 433.7 barrels/hr. of liquid bottoms from the stripper at a temperature of about 313 F. are removed and directed by means of line 12 to flash drum 16 maintained at a temperature of 293 F. and a pressure of about 99 mm. Hg (absolute). The pressure in flash drum 16 as well as condenser 24 and settler 28 was attained by applying a vacuum on settler 28 by way of vacuum means 17. 6,636 pounds/hr. of flashed Vapors from flash drum 16 are taken overhead and directed by line 20 to condenser 24 Where they are condensed at a temperature of 100 F. and a pressure of 89 mm. Hg (absolute). Condensate from condenser 24 is sent to settler 28 and permitted to settle into an upper oil layer (6,400 pounds/hr.) and a lower water layer (235 pounds/hr) Settler 28 is provided with a Weir (not shown) and elevated about feet above flash drum 16 to allow oil accumulating to a level above the weir to flow into the weir and gravitate through line 32 back in flash drum 16. Alternative methods for separating the oil phase from the water phase and returning the former to the flash drum 16, although unnecessary, can be utilized, if desired. The water layer in settler 28 is Withdrawn from the bottom of the settler and pumped through line 36 to a sewer. Substantially dry products (123,267 pounds/hr.) having a haze point of 40 F. are removed from the bottom of flash drum 16.

Having described my invention, it is claimed:

1. A process for the production of dry petroleum hydrocarbon distillates which consists essentially of subjecting a petroleum hydrocarbon distillate boiling above the gasoline range to steam stripping to provide a liquid bottoms product which is at a temperature of about 125 F. to 500 F., flashing the stripped liquid bottoms product at a temperature of about to 50 F. units below the liquid bottoms product temperature, condensing the vapors from said flashing in a condensation zone, settling the resulting condensate in a settling zone to provide a water layer and oil layer, said flashing, condensation and settling being conducted While applying a vacuum to said settling zone which vacuum serves to place the flashing,

4, condensation and settling zones under an absolute pressure of about to 200 milliliters of Hg, separating the water and oil layers,,returning the oil layer to the flashing zone and removing dry liquid product from the flashing zone.

2. The process of claim 1 wherein the oil layer is returned to the flashing zone by gravity.

3. The process of claim 2 wherein the petroleum hydrocarbon distillate is kerosene.

4. A process for the production of dry, hydrodesulfurized petroleum hydrocarbon distillates which consists essentially of subjecting the hydrodesulfurized petroleum hydrocarbon distillate to steam stripping to provide a liquid bottoms product which is at a temperature of about F. to 500 F. and contains about 0.01 to 0.25% by weight of water, flashing the stripped liquid bottoms prodnot at a temperature of about 10 to 50 F. units below the liquid bottoms product temperature, condensing the vapors from said flashing in a condensation zone, settling the resulting condensate in a settling zone to provide a water layer and oil layer, said flashing, condensation and settling being conducted while applying a vacuum to said settling zone which vacuum serves to place the flashing, condensation and settling zones under an absolute pressure of about 50 to 200 milliliters of Hg, separating the water and oil layers, returning the oil layer to the flashing zone and removing dry liquid product from the flashing zone having a water content below about 0.005 weight percent.

5. The process of claim 4 wherein the oil layer is returned to the flashing zone by gravity.

6. The process of claim 5 whereinthe petroleum hydrocar-bon distillate is kerosene.

References Cited by the Examiner UNITED STATES PATENTS 2,983,675 6/1961 Baxter et al. 208212 DELBERT E. GANTZ, Primary Examiner.

SAMUEL P. I ONES, Assistant Examiner.

Claims

1. A PROCESS FOR THE PRODUCTION OF DRY PETROLEUM HYDROCARBON DISTILLATES WHICH CONSISTS ESSENTIALLY OF SUBJECTING A PETROLEUM HYDROCARBON DISTILLATE BOILING ABOVE THE GASOLINE RANGE TO STEAM STRIPPING TO PROVIDE A LIQUID BOTTOMS PRODUCT WHICH IS AT A TEMPERATURE OF ABOUT 125* F. TO 500* F., FLASHING THE STRIPPED LIQUID BOTTOMS PRODUCT AT A TEMPERATURE OF ABOUT 10 TO 50* F. UNITS BELOW THE LIQUID BOTTOMS PRODUCT TEMPERATURE, CONDENSING THE VAPORS FROM SAID FLASHING IN A CONDENSATION ZONE, SETTLING THE RESULTING CONDENSTATE IN A SETTLING ZONE TO PROVIDE A WATER LAYER AND OIL LAYER, SAID FLASHING, CONDENSATION AND SETTLING BEING CONDUCTED WHILE APPLYING A VACUUM TO SAID SETTLING ZONE WHICH VACUUM SERVES TO PLACE THE FLASHING, CONDENSATION AND SETTLING ZONES UNDER AN ABSOLUTE PRESSURE OF ABOUT 50 TO 200 MILITIERS OF HG, SEPARATIHNG THE WATER AND OIL LAYERS, RETURNING THE OIL LAYER TO THE FLASHING ZONE AND REMOVING DRY LIQUID PRODUCT FROM THE FLASHING ZONE.