Properties Of Liquid Product [

The need for various grades of the product oils separated in the distillation tower is evident. In order to keep the various grades on a uniform basis, the authorities in each country have standardized on a few grades by the properties of the oil produced.

It is necessary to compare reliable properties of the oil produced, as a comparison with those of commercial gasoline, kerosene and diesel. It is essential to determine the physical measurements such as those listed for a variety of the oils, as shown in Table 5.5. Based on these values, the oil produced in the process plant is tested, to determine whether it can be put on the market.

As the density of the oil produced is decreased, the heat value per volume decreases, but the heat value per mass will increase. If the oil is usually purchased and sold on a volume basis, heavy oil is more efficient. Also, if it is necessary to choose the most important specific of the oil produced, viscosity will be selected. Viscosity can aid combustion and can also be the cause of the greatest trouble. For proper and efficient combustion an oil should have a reasonable viscosity at the burner. In the case of too high viscosity, difficulty in pumping in the process and trouble at the burner are encountered and also carbon residue is high due to poor combustion. However, in case of too light oil, incomplete combustion occurs and there will be a loss of economy.

Further sources of trouble with the oil produced is water and sediment present in the oil, when it is used as a fuel oil. Water causes sparking, spitting and flashback of the flame, which result in loss of heat as a result of improper combustion. Sediments such as sand and carbon, etc. cause the erosion of burner tips, pump parts and sensitive control valves, etc. Also, some chemical compounds present in an oil will absorb oxygen from air or water, to form new compounds. Unfortunately, some of these chemical compounds are insoluble in the oil, with the result that they will either remain suspended in the

011 or will drop to the bottom of the tank. They must not reach the suction lines in a storage tank.

When discussing the oil produced, the subject of carbon becomes an issue. Carbon is formed during cracking of hydrocarbons at high temperature and pressure. This carbon is present in heavy oil and will be suspended within the oil. However, oil containing a small amount of carbon is easily combustible without any trouble. The carbon content is

Table 5.5 Properties of the oil product

Items

LO (in KIER)a

Gasoline

HO (in KIER)b

Kerosene

Diesel

Ignition point (°C)

74

>40

>40

Pour point (°C)

<-50

-12.5

<-15

<-15

Copper corrosion (100°C, 3 h)

<1

<1

1

<1

<1

10%carbon residue (wt%)

0.01

0.21

<0.15

Ash (wt%)

0.001

0.003

<0.02

<0.02

Kinematic viscosity (40°C)

<1.0

6.5

1.4-3.0

1.9-5.5

Density (kg/m3,15°C)

757

831

815-855

Distillation (T90)

232

<175

430

285-325

<360

Heat of combustion (kcal/kg)

11,180

10,983

11,020

10,800

Water & sediment (vol%)

<0.01

<0.005

<0.02

measured by the Conradson carbon test, as a relative value of coke formation. This is the amount of carbon remaining after evaporating all the volatile materials in a certain type of apparatus. It is representative of the tendency of the oil to form coke, in many practical uses such as household and industry, etc. But the light oil is very thin and does not have much carbon residue. This oil is distilled until 90% of the sample has been vaporized. The remaining 10%, the heaviest of the entire sample, is used to run the carbon test as 10% carbon residue value measured. For an example, the values for commercial kerosene and diesel would be below about 0.2.

There are certain impurities present in most fuel oils. These organic and inorganic substances are noncombustible and after combustion of the fuel oil they will form a residue called ash. The greatest percentage of ash found in various oils is directly related with the crude oils from which they are refined. The crude oil is usually mixed with water, mud and sand, etc. Most of these contaminants are removed from the crude oil, but very small amounts will still remain suspended in the crude oil. Moreover, the ash-producing materials found in crude oil are concentrated in the heaviest oils such as the residuals. In order to determine the ash amount, the oil in the presence of air is burned. The remaining materials are noncombustible ash, which is computed as the total percentage of ash in the sample. The ash amount measured for kerosene and diesel is below 0.2 wt%, but the oil of two types produced in KIER process is very low.

As the oil is heated, the oil vapors and air will ignite without the application of an external flame or spark at a certain temperature, which is called the ignition point of the oil. Generally the spontaneous ignition temperature reduces with increase in carbon number and is high for the aromatic hydrocarbons, due to the inherent structural stability of the benzene ring [33]. The ignition point of kerosene and diesel is required to be above 40°C. Thus, the oil produced in the pyrolysis process must be blended with a component of high ignition point, which should be watched with great care.

The temperature at which an oil will just flow under standardized conditions is known as the pour point. This test has particular significance in connection with oils that may require heating to liquefy them and also to enable them to be pumped. If an oil of low pour point begins to solidify in the storage tank in cold weather, some other means will be needed to prevent the mass from solidifying completely. For example, when the plant is shut down in cold weather, the oil in the line and tank, etc. will solidify and thus the oil is too viscous to be pumped. So the pour point of the oil produced must be checked during cold weather.

Sulfur is one of most important elements present in an oil, although the sulfur content may be very low. It is usually in combination with carbon, hydrogen, oxygen and nitrogen, forming many different compounds. They have mainly a high boiling point and are therefore concentrated in the residual oils. In the petroleum refinery industry, they break down during the refining processes such as the hydrodesulfurization process, which can lead to low-sulfur residuals. This process brings the residual oil into contact with hydrogen gas and a catalyst. The residual oil is split into low-sulfur oil and hydrogen sulfide gas. The most important trouble for oil containing sulfur is corrosion by its combustion products such as sulfur dioxide and sulfur trioxide. Moreover, the corrosiveness of these sulfur compounds is increased by moisture. But the sulfur has little effect on the handling and storage of the oil and also industrial instruments such as pump and mechanical parts.

Chemical compounds will boil at a certain temperatures. Thus, oil consisting of various compounds is made up of a series of fractions, defining the distillation range of the oil. Distillation range is the difference in degrees between the initial boiling point (IBP) and the end point (EP). Thus distillation range will vary according to the type of oil. The initial boiling point is the temperature at which the first drop of condensed vapor appears in a distillation test. The next temperature point is the 10% boiling point, which is the temperature that 10% of total volume of oil will distill off. The spread between the IBP and the 10% point should be small so that the oil will continue to burn in case of ignition. If the spread is too large, ignition and starting will be difficult. Also, the 90% point and the end point must be watched. If the spread between the 90% point and end point is very great, the oil has been blended or contaminated. This can cause poor combustion. If the end point is high, the 90% point will also be high, these high values may be difficult to burn and can cause carbon trouble. For efficient combustion, the distillation curve should be smooth. A fluctuating distillation curve implies an oil that may give irregular operation due to unstable conditions. Therefore, the distillation test is one of the best methods for detecting the quality of the oil produced such as light or heavy oil fractions.

As an example, the distillation curves of LO and HO obtained in KIER process was compared with those of commercial gasoline, kerosene and diesel are shown in Figure 5.19. The distillation curve of LO product was distributed between commercial

Distillation Graph Diesel Fuel

Figure 5.19 Boiling point distribution of commercial gasoline, kerosene and diesel, and LO and HO products obtained in the KIER process gasoline and kerosene. For LO product, the spread between the 90% point and end point is big, because of the mixing of heavy oil. On the other hand, HO product has a higher boiling point distribution than commercial diesel. Their distillation curves can be changed by experimental variables in the distillation tower, such as temperature gradient, pressure, reflux ratio and reboiler temperature, etc.

Was this article helpful?

0 0
Trash To Cash

Trash To Cash

This book will surely change your life due to the fact that after reading this book and following through with the steps that are laid out for you in a clear and concise form you will be earning as much as several thousand extra dollars a month,  as you can see by the cover of the book we will be discussing how you can make cash for what is considered trash by many people, these are items that have value to many people that can be sold and help people who need these items most.

Get My Free Ebook


Post a comment