DR.Hemdan 1

CRUDE OIL DESALTING

DR.Hemdan 2

CRUDE OIL DESALTING

DR.Hemdan 3

• Crude Oil Desalting:-• Salts are distributed in crude oil as brine (Nacl)• Defects of Salts are: -Cause plugging of heat exchangers tubes. -Cause deposits in pipe still tubes (furnaces) and consequently cause . -Decrease in heat transfer coefficient. -Create pressure drop which affects on pumps. • Salts may reach up to 260 PTb each 100 PTb cause

deposits of about 3 ft³/day .• Salts should be removed before distillation tower where

these salts liberate HCL gas which cause many corrosion problems .

DR.Hemdan 4

DR.Hemdan 5

• Problems of oleophobics

-Corrosion due to hydrolysis of salts .

-Increase consumption of NH3 to

neutralize HCL

-Erosion .

-Plugging of Equipment and fouling .

-Trace metals in distillates which acts as

catalyst poisoning

DR.Hemdan 6

Crude desalting is the first processing step in a refinery . The objectives of crude desalting are :

1-the removal of salts and solids

2- the formation water from unrefined crude oil before

the crude is introduced in the crude distillation unit . 3-removal of suspended solids from the crude oil. 4-Reduced equipment fouling and corrosion and 5-longer catalyst life

DR.Hemdan 7

DR.Hemdan 8

DR.Hemdan 9

SINGLE-STAGE DESALTER

..

Mix Valve

Heat Exchangers

Demulsifier

Water

Feed Oil

Desalter

Effluent Water

Desalted Crude

DR.Hemdan 10

1st Stage Crude Outlet(5.0 PTB, 0.2% BS&W)

Two-Stage Desalter Example

2nd Stage Effluent Wateris 1st Stage Wash Water

1st Stage Desalter

Mix Valve

Crude Charge(100 PTB, 1% BS&W)

Desalted Crude(0.5 PTB, 0.2% BS&W)

Wash Water

Effluent Water

2nd Stage Desalter

5.0%5.0%

5.8%

Figure 2

Mix Valve

Counter-current flow

DR.Hemdan 11

SERIES: Maximize Desalting Efficiency

Water

Feed Oil

Heat Exchangers

1st Stage

2nd Stage

Mix Valve

Mix Valve

Effluent Water

Desalted Crude

100ppm salt in

10ppm salt out

1ppm salt out

Overall Efficiency = (100 - 1) / 100 = 99%

MULTI-STAGE DESALTING

DR.Hemdan 12

PARALLEL:

Maximize Throughput

Feed Oil

Heat Exchangers

Mix Valves

Effluent Water

Desalted Crude

Water

MULTI-STAGE DESALTING

DR.Hemdan 13

• Pure water and NaOH is added to the desalter

• Some deemulsifier may be added to break forces between salts and the oil

• In electrostatic precipitator applied voltage up to 30KV

• Salt drops coalesce together and form larger drops which separated down to the bottom of desalter

• Salt removal reach to about 90%

DR.Hemdan 14

• 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.

DR.Hemdan 15

• The trend toward running heavier crude oils has increased the importance of efficient desalting of crudes. Until recently, the criterion for desalting crude oils was 10 lb salt/1000 bbl (expressed as NaCl) or more, but now many companies desalt all crude oils.

DR.Hemdan 16

• Salt in the crude oil is in the form of dissolved or suspended salt crystals in water emulsified with the crude oil.

• The basic process of desalting is to wash the salt from crude oil with water. Problems occur are:

1-inefficient and economical water/oil mixing,

2-water wetting of suspended solids, and

3-separation of oil from wash water

DR.Hemdan 17

• The separation of oil and washwater i.e desalter performance is affected by :

1-the gravity

2-viscosity

3-pH of the crude oil

4-the ratio of water/crude used for washing.

5-temperature

6-pressure drop

7-chemicals additions

DR.Hemdan 18

• Desalting is carried out by emulsifying the crude oil with 3 to 10 vol% water at a temperature of 200-300F. Both the ratio of water to oil and the operating temperature are functions of the gravity of the crude oil. Typical operating conditions are :

DR.Hemdan 19

DR.Hemdan 20

Trouble shooting