Crude Stabilization Process Description

Crude Stabilization Process Description

Pressurized Crude Oil coming out from BUT and HUT oil trunk lines into five streams and preheated by steam up to 45^oC before entering into High Pressure Separators operating at pressure of 3.5 kg/cm²g. The oil flows out under level control and can either be directed towards low pressure separator or can be pumped to the Dehydrator system. High pressure gas letup the HP separators under pressure control and is sent for compression.

If, the oil contains water and/or salt it can be dehydrated in the Dehydrator systems. Before entering the Dehydrators, oil is preheated first by heat exchange with dehydrated oil and then in the crude heaters up to 65°C.

The Dehydrators operate at 2.5 Kg/cm²g and at 65°C. The dehydration is accomplished by injection of demulsifies, heating and application of high voltage electro-static field in the oil-water emulsion. The gas liberated in the Degasser of the dehydrator flows under pressure control to the compressors. 

The dehydrated oil, which came from dehydrator system, flows under level control, exchange heat with feed to dehydrator and is then sent Low Pressure Separators. The produced water flows under interface level control and is sent to the Waste Treatment Plant or EPTP (Effluent Pretreatment Plant) for predisposal treatment.

Series operation of dehydrators A and B is also available. The Low Pressure Separators operate at 0.1 Kg/cm²g and 50/55°C. The oil pumped to HSVR cooler flows under level control into the two Intermediate Surge Tanks by gravity where final separation of gas is achieved.

The stabilized oil is pumped to five Main Storage Tanks. From these tanks oil is pumped into the trunk line dispatch oil to the Trombay Terminal for onward distribution to BPCL Refinery, HPCL storage or (Butcher Island Jetty) Jawahar Deep Island.

The gases from HP separators, Degassers and LP Separators are compressed in the Multi service Gas Compressors and sent to LPG unit combining with associated gas from the trunk line. These are 3 stages reciprocating 

Compressors, operating at suction pressures of0.05 Kg/cm²g, 3.0 Kg/cm²g and 14.0 Kg/cm²g respectively with a final discharge pressure of 51.0 Kg/cm²g. The Degassers and LP separator gases are connected to compressor 1st and HP separator gases are connected to 2nd stage suction.

Solution to Stoichiometric Equation

Solution of Stoichiometric Problem

Hello Everyone, So continuing with the last article ‘Introduction to Stoichiometry’, in this article we will learn the steps to solve a stoichiometric equation.

You should take the following steps in solving stoichiometric problems:

1. Make sure the chemical equation is correctly balanced. How do you tell if the reaction equation is balanced? Make sure the total quantities of each of the element on the left hand side equal to those on the right hand side. For example,

CH₄ + O₂  à  CO₂ + H₂O

Is not a balanced stoichiometric equation because there are four atoms of H on the reaction side (left hand side ) of the equation, but only two on the product side (right hand side) of the equation and also oxygen atom do not balance. The balanced equation is given by

CH₄ + 2O₂  à  CO₂ + 2H₂O

The coefficients in the balanced reaction equation have the unit of moles of a species reacting or produced relative to the other species reacting for the particular reaction equation. If you multiply each term in a chemical reaction equation by the same constant, say two, the absolute stoichiometric coefficient in each term doubles, but the coefficients still exist in the same relative proportions.

2. Use the proper degree of completion for the reaction. If you do not know how much reaction has occurred, you have to assume some amount, such as complete reaction.

3. Use molecular weights to convert mass to moles for the reactants and products and vice versa.

4. Use the coefficient in the chemical equation to obtain the molar amounts of products produced and reactants consumed by the reaction.

Steps 3 and 4 can be applied in a manner similar to that used in carrying out the conversion of units, which I guess you all have already read, due to its basic importance in process industry.

‘Valuable suggestions are required and if u have any question please let me know the comment section given below. ‘

Introduction to Desalting of Crude Oil

Now, in this article we will discuss about a very important topic in crude oil distillation which is 'Desalting of Crude Oil'.  

DESALTING OF CRUDE OIL

If the content in the crude oil of salt is greater than 10 lb/1000 bbl (expressed as NaCl), the crude requires desalting to lower fouling and corrosion happen due to deposition of salt on heat transfer surfaces and acids formed by decomposition of the chloride salts. Afterwards, some metals in inorganic components dissolved in water emulsified with the crude oil, which can cause deactivation of catalyst in catalytic processing units, are partially rejected in the desalting process. 

Until lately, the standard for desalting crude oils was 10 lb salt/1000 bbl (expressed as NaCl) or more, but now many companies desalt all crude oils. Shorten equipment fouling and corrosion and longer catalyst life provide justification for this additional treatment. Two-stage de salting is used if the crude oil salt content is more than 20 lb/1000 bbl and, in the situations where residua are catalytically developed, there are some crudes for which three-stage desalting is used. The salt in the crude is in the form of dissolved or suspended salt crystals in water emulsified with the crude oil. 

The main objective or principle is washing the salt from the crude oil with water. Problems occur in obtaining efficient and economical water/oil mixing, water-wetting of suspended solids, and separation of the wash water from the oil. The pH, gravity, and viscosity of the crude oil, as well as the volume of wash water used per volume of crude, affect the separation comfort and competence.

A secondary but important function of the desalting process is the removal of suspended solids from the crude oil. These are usually very fine sand, clay, and soil particles; iron oxide and iron sulphide particles from pipelines, tanks, or tankers; and other contaminants picked up in transit or production. 

Total suspended solids removal should be 60% or better with 80% removal of particles greater than 0.8 micron in size. Desalting is carried out by mixing the crude oil with from 3 to 10 volume% water at temperatures from 200 to 300°F (90 to 150°C). Both the ratio of the water to oil and the temperature of operation are functions of the density of the oil. The salts are dissolved in the wash water and the oil and water phases separated in a settling vessel either by adding chemicals to see through in breaking the emulsion or by developing a high-potential electrical field across the settling vessel to mobilize the droplets of salty water more rapidly. 

Either AC or DC fields may be used or potentials from 12,000 - 35,000 volts are used to promote mobilization. For single-stage desalting units 90 to 95% efficiencies are obtained and two-stage processes achieve 99% or better efficiency.

Introduction to Stoichiometry

STOICHIOMETRY

As we all know that chemical engineers in practicing their profession are differ from other engineers due to their involvement with chemistry. When chemical reaction occur, in contrast with physical change of material such as evaporation or dissolution, you want to be able to predict the mass or moles required for the reaction(s), and the mass or moles of each species remaining after the reaction has occurred.

Reaction Stoichiometry allows you to accomplish this task. The word Stoichiometry (stoi-ki-om-e-tri) derives from two Greek words: stoicheion (meaning ’element’) and metron (meaning ‘measure’). Stoichiometry provides a quantitative means of relating the amount of products produced by chemical reaction(s) to the amount of reactants.

As you already know, the chemical reaction equation provides both qualitative and quantitative information concerning chemical reactions. Specifically the chemical reaction equation provides you with information of two types:

1. It tells you that what substance are reacting (those being used up) and what substance are being produced (those being made).

2. The coefficients of a balanced equation tell you what the moles ratio are among the substances that react or are produced. (In 1803, John Dalton, an English Chemist, was able to explain much of the experimental results on chemical reactions of the day by assuming that reactions occurred with fixed ratios of element).

A chemical reaction may not occur as rapidly as the combustion of natural gas in the furnace, such as, for example, in the slow oxidation of your food, but if the reaction occurs (or would occur), it takes place as represented by a chemical reaction equation.

‘This is the theory part that we have discussed in this article. If you have any type of problem regarding stoichiometry and its concept, do let me know in the comment section below.’

In the next Article, we will discuss ‘How to solve a Stoichiometry problem.’ 

DISTILLATION- HISTORY& BASIC PRINCIPLE

INTRODUCTION TO DISTILLATION

1. The first clear evidence of distillation comes from Greek alchemists working in Alexandria in the first century AD. 

2. Distilled water has been known since 200 AD, when Alexander The Great described the process. Arabians learned the process from the people Egypt and used it extensively in their chemical experiments.

3. Clear evidence of the distillation of alcohol comes from the School of Salerno in the 12th   century. Fractional distillation was developed by Tadeo Alderotti in the 13th century.

4. In1500, German alchemist Hieronrymus Braunschweig published Liber de arte destillandi (The Book of the Art of Distillation) the first book solely dedicated to the subject of distillation, followed in 1512 by a much expanded version.

5.As Alchemy evolved into the science of chemistry, vessels called retorts became used for distillations. Later, copper alembics were invented. These were called pot stills. Today, those stills have been largely supplanted by more efficient distillation methods in most industrial processes.

6. In the early 19th century the basics of modern techniques including pre-heating and reflux were developed, particularly by the French, and then in 1830 a British Patent was issued to Aeneas Coffey for a whiskey distillation column, which worked thoroughly and may be regarded as the archetype of modern petrochemical units.

7. In 1877, Ernest Solvay was granted a United State Patent for a tray column for ammonia distillation and the same and subsequent years saw developments of this theme for oil and spirits.

With the emergence of chemical engineering as a discipline at the end of the 19th century, scientific rather than posteriori methods could be applied.

The developing industry of petroleum in the early 20th century provided the impetus for the development of accurate design methods such as the McCabe-Thiele method and the Fenske equation.

     

     Basic Principles of Distillation

  Separation of components from a liquid mixture via distillation depends on the         differences in boiling points of the individual components. Also, relying on the             concentrations of the components present, the liquid mixture will have various boiling  point characteristics. Therefore, distillation processes rely on the vapour pressure  characteristics of liquid mixtures.

  

  The vapour pressure of a liquid at a particular temperature is the equilibrium pressure   exerted by molecules leaving and entering the liquid surface.

  

     Below are some important points about vapour pressure:     

1. Energy input raises vapour pressure

2. Vapour pressure is related to boiling

3. A liquid is said to ‘boil’ when its vapour pressure equals the surrounding pressure

4. The ease with which a liquid boils depends on its volatility

5. Liquids with high vapour pressures (volatile liquids) will boil at lower temperatures

6. The vapour pressure and hence the boiling point of a liquid mixture depends on the relative amounts of the components in the mixture

7. Distillation occurs because of the differences in the volatility of the components in the liquid mixture

    

     The distillation equipment to achieve the desired aims will generally consist of:

     1. Heating system to evaporate the solvent;

     2. Condensers and coolers;

     3. Fractionating column

     4. Storage both as part of the plant as a still kettle and to hold residue, products and          feed.

Petrochemical Feed Stocks

Feed stocks for petrochemicals

The petrochemical industry in our country had a strong set back at the time of start as there was no proper coupling with growing petroleum industry. 

Even today, to feed our refineries more oil is produced 34 M²t a from ONGC & OIL fields and 45 M² M³ of gas per day and the accompanying gas has no proper utility thus more than 30% of gas being flared. The realization of saving hydrocarbon, though late, has been resulted in creation of a separate wing, Gas Authority of India, to transport the gas. 

Natural gas being one of the best feed gas for Petrochemicals, the technology is expounded in that direction. Besides the field gases like Natural gas, Associated gas, Lean gas, the other gas comprise of refinery gases. 

The refinery gases are obtained from stabilizers, atmospheric columns, and from process unit like crackers, cokers.

The total raw materials scene as usefully utilized in petrochemical industry is listed below;

1. Gases comprising Associated gas, Lean gas, Refinery off gas, Natural gas LPG, Condensate gases.

2. Light liquid Fractions, Natural gas liquid, Naphtha, wild gasoline, Kerosene (Gas oil ranges), reformates.

3. Heavy Liquids

4. Kerosene, Extracts, Residuum, Low Sulphur Heavy Stocks, Fuel Oil etc.

All the above fractions are used selectively for different chemicals and everyone require certain type of purification. The maximum purification required may be perhaps in the case of gases, as the gases are obtained either from a fields or from a process. 

The gas components in most of the cases may be same, but the concentration are purity vary. The utility of a gas mainly lies in the method of purification and degree of purification.

   

Optimization Algorithms- Bounding & Fibonacci Search

As far as these search are concerned, you can't just have solution of equation so simple than this.

So, here is the Algorithm for two of the best method use in Optimization

Bounding Phase Method

Algorithm

Step 1: Choose an initial guess x ⁽⁰⁾ and an increment Δ. Set k = 0.

Step 2: If f(x ⁽⁰⁾ - IΔI) > f(x ⁽⁰⁾ + IΔI), then Δ is positive;

Else if f (x ⁽⁰⁾ - IΔI) < f(x ⁽⁰⁾) < f(x ⁽⁰⁾ + IΔI), then Δ is negative;

Else go to Step 1.

            Step 3: Set x ^(k+1) = x ^(k) + 2^k Δ.

            Step 4: if f (x ^(k+1)) < f(x ^(k)), set k = k+1 and go to step 3;

Else the minimum lies in the interval (x ^(k-1) , x ^(k+1)) and

Terminate.

Fibonacci search method

Algorithm

Step 1: Choose a lower bound a and an upper bound b. Set L= b – a. Assume the desired number of function evaluations to be n. Set k = 2.

Step 2: Compute L_k^* = (F_n-k+1 / F _n+1) L. Set x₁ = a + L_k^* and x₂ = b - L_k^*.

Step 3: Compute one of f(x₁) or f(x₂), which was not evaluated earlier. Use the fundamental region elimination rule to eliminate a region. Set new a and b.

Step 4: is k = n? If no, set k = k + 1 and go to step 2;

Else Terminate.