Assay Of Crude Oils (Petroleum Refining)

It is vital to find out the bodily and chemical characterizations of crude oil by means of a crude oil assay, since they’re used in several areas within the petroleum refining business. The most common functions of petroleum assays are:

To offer extensive detailed experimental data for refiners to ascertain the compatibility of a crude oil for a specific petroleum refinery

To anticipate if the crude oil will fulfill the required product yield, quality, and production

To determine if throughout refining the crude oil will meet environmental and different requirements

To help refiners to make choices about changes in plant operation, development of product schedules, and examination of future processing ventures

To produce engineering firms with detailed crude oil analyses for their course of design of petroleum refining plants

To facilitate companiescrude oil pricing and to negotiate possible penalties resulting from impurities and other nondesired properties

A crude oil assay is a compilation of laboratory (physical and chemical properties) and pilot-plant (distillation and product fractionation) knowledge that characterize a specific crude oil. Assay analyses of whole crude oils are carried out by combining atmospheric and vacuum distillation items, which when mixed will present a true boiling-level (TBP) distillation. These batch distillation strategies, though taking between three and 5 days, allow the collection of a enough quantity of distillation fractions for use in additional testing. The values of the distillation ranges of the distilled fractions are often defined on the premise of their refinery product classifications. The commonest distillation ranges utilized in international assays of crude oils are reported in Desk 1.5.

Table 1.5. Typical Distillation Vary of Fractions in Petroleum Assays

TBP Distillation

Range (°C)

Distillate

IBP-71

Mild straight-run naphtha

71-177

Medium straight-run naphtha

177-204

Heavy straight-run naphtha

204-274

274-316

316-343

Straight-run gasoil

343-454

Gentle vacuum gasoil

454-538

Heavy vacuum gasoil

R 538°C+

Vacuum residue

There are numerous forms of assays, which vary significantly in the amount of experimental info decided. Some include yields and properties of the streams used as feed for catalytic reforming (naphtha) and catalytic cracking (gas oils). Others give further details for the potential manufacturing of lubricant oil and/or asphalt. At a minimal, the assay ought to contain a distillation curve (sometimes, TBP distillation) for the crude oil and a selected gravity curve.

Essentially the most complete assay consists of experimental characterization of your complete crude oil fraction and various boiling-range fractions. Curves of TBP, particular gravity, and sulfur content are regular knowledge contained in a properly-produced assay. For example, assays of various Mexican crude oils are introduced in Desk 1.6. The API gravity of those crude oils ranges from 10 to 33°API. API gravity is a measure of the relative density of a petroleum liquid and the density of water (i.e., how heavy or gentle a petroleum liquid is compared to water). Though, mathematically, API gravity has no units, it is at all times known as being in “levels.” The correlation between specific gravity (sg) and degrees API is as follows (the precise gravity and the API gravity are each at 60°F):

Viscosity should be supplied at a minimal of three temperatures in order that one can calculate the sample viscosity at other temperatures. The most typical temperatures used to determine viscosity are 15.5, 21.1, and 25°C. If viscosities of the sample cannot be measured at these temperatures, the sample needs to be heated and higher temperatures are used, comparable to within the case of the ten and 13°API crude oils reported in Desk 1.6. As soon as viscosities at three temperatures can be found, a plot of a double logarithm (log10) of viscosity towards the temperature will be constructed, and viscosities at other temperatures might be obtained easily, as shown in Figure 1.1.

The characterization issue (KUOP or KWatson) of the Mexican crude oils reported in Desk 1.6 ranges from 11.5 to 12.0. The K issue will not be decided experimentally; fairly, it’s calculated using the following equation (for petroleum fractions):

the place MeABP (in degrees Rankine) is the mean common boiling point of the sample calculated with distillation curve data.

Normally, if Ok > 12.5, the sample is predominantly paraffinic in nature, while Okay < 10.0 is indicative of highly aromatic material. The characterization factor thus provides a means for roughly identifying the general origin and nature of petroleum solely on the basis of two observable physical parameters, sg and MeABP. More detailed relationships of the K factor to the nature of the sample are given in Table 1.7 . The characterization factor has also been related to other properties (e.g., viscosity, aniline point, molecular weight, critical temperature, percentage of hydrocarbons), so it can be estimated using a number of petroleum properties.

Table 1.6. Assay of various Mexican Crude Oils

ASTM Method

10 ° API

13 ° API

Maya

Isthmus

Olmeca

Specific gravity, 60°F/60°F

D-1298

1.0008

zero.9801

0.9260

zero.8584

zero.8315

API gravity

D – 287

9.89

12.87

21.31

33.34

38.67

Kinematic viscosity (cSt)

D-445

At 15.5°C

299.2

sixteen.0

5.4

At 21.1°C

221.6

12.5

4.6

At 25.0°C

19,646

181.4

10.3

At 37.8°C

5,102

At fifty four.4°C

7,081

1,235

At 60.0°C

4,426

At 70.0°C

2,068

Characterization factor, ,KUOP

UOP-375

11.50

eleven.60

eleven.71

11.95

12.00

Pour level ( ° C)

D – 97

+ 12

zero

-33

-39

Ramsbottom carbon (wt%)

D-524

20.67

16.06

10.87

four.02

2.10

Conradson carbon (wt%)

D – 189

20.Forty two

Fixed tube plate heat exchanger17.94

eleven.Forty two

4.85

2.76

Water and sediments (vol%)

D – 4007

1.Forty

zero.10

<0.05

< 0.05

Whole sulfur (wt%)

D – 4294

5.Seventy two

5.35

three.57

1.46

0.99

Salt content (PTB)

D – 3230

744.Zero

17.7

15.Zero

4.1

three.9

Hydrogen sulfide (mg/kg)

forty four

fifty nine

Mercaptans (mg/kg)

uOP – 163

sixty five

seventy five

Complete acid number (mg KOH/g)

D-664

zero.Forty eight

0.34

0.30

zero.Sixty one

0.46

Complete nitrogen (wppm)

D4629

5650

4761

3200

1467

737

Primary nitrogen (wppm)

uOP – 313

1275

1779

748

389

a hundred and fifty

nC7 insolubles (wt%)

D-3279

25.06

18.03

11.32

1.65

0.Sixty eight

Toluene insolubles (wt%)

D – 4055

zero.Forty one

zero.20

zero.09

0.Eleven

Metals (wppm)

Atomic absorption

Nickel

94.2

83.4

53.Four

eight.9

1.6

Vanadium

494.Zero

445.Zero

298.1

37.1

8.Zero

Total

588.2

528.4

351.5

forty six.0

9.6

Chloride content material (wppm)

D – 808

86

4

9

Determine 1.1. Kinematic viscosities of a number of Mexican crude oils.

Desk 1.7. Relationship of Kind of Hydrocarbon to the Characterization Factor

K Issue

Type of Hydrocarbon

12.15 – 12.Ninety

Paraffinic

11.50-12.10

Naphthenic-p araffinic

11.00-11.45

Naphthenic

10.50-10.Ninety

Aromatic-naphthenic

10.00-10.Forty five

Aromatic

Figure 1.2. True boiling-level curve of assorted Mexican crude oils.

Asphaltenes, which are generally reported as n- heptane insolubles, are, strictly talking, defined as the load share of n- heptane insolubles (HIs) minus the weight percentage of toluene insolubles (TIs) within the sample (wt% of asphaltenes = wt% of Hi – wt% of TI). For the crude oils given in Table 1.6 , their asphaltene contents are 24.Sixty five, 17.83, eleven.21, 1.Fifty six, and zero.57 wt% for the ten) API, 13°API, Maya, Isthmus, and Olmeca crude oils, respectively.

Figure 1.Three. API gravity of distillates versus average quantity proportion.

Figure 1.Four. Sulfur content of distillates versus average quantity share.

TBP distillations for Mexican crude oils are offered in Figure 1.2 . It is obvious that light crude oils which have excessive API gravity values present also the very best quantities of distillates [e.g., Olmeca crude oil (38.67°API) has 88.1 vol% distillates, whereas the 10° API has solely 46vol% distillates]. Figures 1.3 and 1.4 illustrate plots of API gravity and the sulfur content material of distillates against the average quantity percentage of distillates of the assorted crude Static And Dynamic Seals For Pyrolysis oils. Distillates of heavier crude oils have decrease API gravity and a higher sulfur content than these obtained from light crude oils.

Leave a Reply