Page 191 - Petroleum and Gas Field Processing

Table 1 Properties of Crude Oils Shipped to Refineries

Range Average
Water in crude, % by volume of crude 0.1–2.0 0.3–0.5
Salt content in crude, PTB 10–250 60–130
Salt concentration in brine, wt% 0.4–25 —
Salt concentration in brine, ppm 4,000–250,000 —
Source: Ref. 1.

Table 2 Average Values for the PTB for Some
Typical Crude Oils

Source of oil Avg. salt content (PTB)
Middle East 8
Venezuela 11
United States
Pennsylvania 1
Wyoming 5
East Texas 28
Gulf Coast 35
Oklahoma and Kansas 78
West Texas 261
Canada 200

The method of reducing the PTB by lowering the quantity of remnant
water W R is usually referred to as the treating process of oil dehydration.
This was the main theme of the last chapter. The other alternative of
reducing the PTB is to substantially decrease the dissolved salt content of
the remnant water (i.e., its concentration, S R ). This practice is the one we
are dealing with in this chapter and is known as desalting. Desalting of
crude oil will eliminate or minimize problems resulting from the presence
of mineral salts in crude oil. These salts often deposit chlorides on the heat
transfer equipment of the distillation units and cause fouling effects. In
addition, some chlorides will decompose under high temperature, forming
corrosive hydrochloric acid [3]:
High temp:
MgCl ðaq:Þ ! MgðOHÞ þ HCl ð2Þ
2 2
H 2 0
The removal of these salts is aimed at providing an economical operating
cycle in the refining process of crude oil. The reduction of salt content
down to 5 PTB is feasible. Even with this low salt content, it has been

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