J W Packie Distillation Equipment In The Oil Refining Industry

Atmospheric Tower Operating Conditions OPERATING PARAMETER UNITS

TEMPERATURES °F

TRANSFER LINE 660

FLASH ZONE 657

TOWER TOP 359

KEROSENE DRAW-OFF 469

PUMPAROUND DRAW OFF 548

PUMP AROUND RETURN 345

LIGHT DIESEL DRAW OFF 603

TOWER BOTTOM 648

PRESSURE psig

REFLUX DRUM 2.0

TOWER TOP 10.3

FLASH ZONE 14.7

REFLUX RATIO, REFLUX/LIQUID DIST. 0.6 STRIPPING STEAM

TO ATMOSPHERIC TOWER lbs/bbl RESID 5.5

TO KEROSENE STRIPPER lbs/bbl RESID 5.9

TO DIESEL STRIPPER lbs/bbl RESID 2.1 ATMOSPHERIC HEATER PROCESS FLUID CONDITIONS

TEMPERATURE IN °F 453

TEMPERATURE OUT °F 660

PRESSURE DROP psi 138

TUBE SKIN TEMPERATURE (AVG) °F 735

STACK GAS TEMPERATURE °F 725 FRACTIONATION EFFICIENCY 95%-5% ASTM DISTRIBUTION GAP

ATMOSPHERIC NAPHTHA-KEROSENE GAP + 10

KEROSENE-LIGHT DIESEL GAP - 36

NOTE: BASIS 154000 BPSD KUWAIT CRUDE RUN.

tanks or tankers, and other contaminants picked up in transit or from processing.

Until recently, the criteria for desalting crude oil was 101b salt/ 1000 bbl (expressed as NaCl), but due to more stringent requirements of some downstream processes, desalting is now done at the much lower level of 1.0 lb/1000 bbl or lower. Reduced equipment fouling and corrosion

Table 1-6

Vacuum Tower Operating Conditions OPERATING PARAMETER UNITS

TEMPERATURES °F

TRANSFER LINE 740

FLASH ZONE 711

TOWER TOP 307

HEAVY DIESEL DRAW-OFF 447

TOP REFLUX TEMPERATURE 121

HVGO DRAW-OFF 613

TOWER BOTTOM 670

PRESSURE mmHg

TOWER TOP 64

FLASH ZONE 125

TOP REFLUX RATIO; REFLUX/FEED 0.15

HOT REFLUX RATIO; REFLUX/FEED 0.97

WASH OIL RATIO; WASH OIL/FEED 0.14

BOTTOM QUENCH OIL RATIO; QUENCH/FEED 0.24 STRIPPING STEAM

TO VACUUM TOWER lbs/bbl RESID 8.0

TO HVGO STRIPPER lbs/bbl RESID 4.6

VACUUM HEATER PROCESS FLUID CONDITIONS

TEMPERATURE IN °F 645

TEMPERATURE OUT °F 736

PRESSURE DROP psi 73

TUBE SKIN TEMPERATURE (AVG) °F 850

STACK GAS TEMPERATURE °F 845

FRACTIONATION EFFICIENCY

95%-5% ASTM DISTRIBUTION GAP

LIGHT DIESEL-HEAVY DIESEL GAP - 145

HEAVY DIESEL-HVGO GAP + 25

NOTE: BASIS 154000 BPSD KUWAIT CRUDE RUN.

Table 1-7

Atmospheric and Vacuum Crude Distillation Utility Consumption

Table 1-7

UTILITY

UNITS

CONSUMPTION

ELECTRICITY

kWhr

8.7

FUEL

mmBtu

0.6

STEAM

mmBtu

0.09

COOLING WATER

MIG*

0.31

DISTILLED WATER

MIG*

0.02

* THOUSAND IMPERIAL GALLONS.

NOTE: THE UTILITY CONSUMPTIONS (PER TON FEED) ARE FOR AN INTEGRATED CRUDE AND VACUUM UNIT.

INJECTION g

FIRST-STAGE DESALTER V-101

ELECTRICAL POWER

STEAM EMULSIFIER MX-101

SECOND-STAGE DESALTER V-102

ELECTRICAL POWER

EMULSIFIER MX-102

DESALTED CRUDE

EFFLUENT ' WATER

Figure 1 -6. Two-stage desalter.

and longer catalyst life in downstream processing units provide justification for this additional treatment.

Desalting is carried out by emulsifying the crude oil with 3 to 10 vol% (volume %) water at a temperature of 200-300°F. Both the ratio of water to oil and the operating temperature are functions of the gravity of the crude oil. Typical operating conditions are given in Table 1-8.

The salts are dissolved in the washwater and oil and water phases are separated in a settling vessel either by adding chemicals to assist in breaking up the emulsion or by the application of an electrostatic field to coalesce the droplets of saltwater more rapidly (see Table 1-9). Either an AC or DC field may be used (see Table 1-10) and potentials of 16,000-35,000 V are used to promote coalescence. Efficiencies up to 90-95% water removal are achieved in a single stage and up to 99% in a two-stage desalting process.

Heavy naphthenic crudes form more stable emulsions than most other crudes, and desalters usually operate at lower efficiency when handling them. The crude oil densities are close to density of water, and temperatures above 280° F are required.

It is necessary to adjust the pH of the brine to obtain a value of 7 or less. If the pH of the brine exceeds 7, emulsions are formed because of the presence of sodium naphthenate and sodium sulfide. For most crude oils, it is desirable to keep the pH below 8. Better dehydration is obtained in electrical desalters when they are operated at a pH of 6. The pH is controlled by the addition of acid to the incoming or recycle water.

Makeup water is added to the second stage of a two-stage desalter. The quantity is 4-5% on crude oil volume. For very heavy crude oil (API <15), gas oil is added as a diluent to the second stage to obtain more efficient separation. The gas oil is recovered in the crude column and recycled to the desalter. Frequently, the washwater used is from the vacuum crude unit barometric condenser or other refinery sources containing phenols. The phenols are preferentially soluble in crude oil, thus reducing the phenol content of the water sent to the refinery wastewater handling system.

Suspended solids are another major cause of water-in-oil emulsions. Wetting agents are frequently added to improve the water wetting of solids and reduce oil carry under in the desalters. Oxyalkylated phenols and sulfates are the most frequently used wetting agents.

Table 1-8

Washwater Requirements of Desalters

CRUDE API WASHWATER, TEMPERATURE, °F

VOL%

Table 1-9 Operating Conditions

PARAMETER UNITS VALUE

CRUDE TO DESALTER* bpsd 98000

WATER TO DESALTER gpm 145

WATER TO CRUDE RATIO % 5

DEMULSIFIER INJECTION ppmw 10-15

PRESSURE

CRUDE TO DESALTER psig 125

DELTA P MIXING VALVE psig 20

TEMPERATURE

CRUDE TO DESALTER °F 270

WATER TO DESALTER °F 265

CRUDE FROM DESALTER °F 260

ANALYSIS RESULTS

CRUDE INLET SALT lb/1000 bbl 3.94

CRUDE INLET SALT ppmw 12.87

CRUDE OUTLET SALT ppmw 1.2

OUTLET BS&W % MASS 0.05

WATER

INLET SALT CONTENT ppm 100

OUTLET SALT CONTENT ppm 310

INLET OIL CONTENT ppm 7

OUTLET OIL CONTENT ppm 10

pH INLET 6.5

OUTLET pH 6.5 OUTLET pH AFTER NH3

INJECTION 7

NOTE: BASIS 98000 BPSD CRUDE.

Table 1-10 Utility Consumption

UTILITY

UNITS

CONSUMPTION

ELECTRICITY

kWhr

0.014-0.070

WATER

GALLONS

10-18

NOTE: PER TON FEED.

NOTES

1. W. L. Nelson. Oil and Gas Journal, (March 2, 1944; July 21, 1945; May 12, 1945).

2. J. W. Packie. "Distillation Equipment in Oil Refining Industry." AIChE Transctions 37(1941), pp. 51-78.

3. Standard Test Method for Distillation of Petroleum Products. ASTM Standards D-86 and IP 123/84.

4. J. B. Maxwell. Data Book on Hydrocarbons. Princeton, NJ: Van Nostrand, 1968. W. C. Edmister. Applied Hydrocarbons Thermodynamics. Houston: Gulf Publishing, 1961. W. L. Nelson. Petroleum Refinery Engineering. New York: McGraw-Hill, 1958.

5. W. C. Edmister. Applied Hydrocarbons Thermodynamics. Houston, Gulf Publishing, 1961.

6. Maxwell, Data Book on Hydrocarbons.

7. Packie, "Distillation Equipment in Oil Refining Industry."

8. R. N. Watkins. Petroleum Refinery Distillation. Houston, Gulf Publishing, 1981.

9. Maxwell, Data Book on Hydrocarbons.

Was this article helpful?

0 0

Post a comment