Dynamic simulation of caustic regeneration unit and optimization of operational parameters of the third refinery of South Pars gas complex

Number of pages: 142 File Format: word File Code: 31853
Year: 2014 University Degree: Master's degree Category: Chemical - Petrochemical Engineering
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  • Summary of Dynamic simulation of caustic regeneration unit and optimization of operational parameters of the third refinery of South Pars gas complex

    "M.Sc." Thesis for Master's Degree

    Chemical Engineering - Process Engineering

    Abstract

    The removal of mercaptans from hydrocarbon streams is done by various methods. The use of caustic soda solution and mucoli sieve beds are among the most widely used methods. In the oil and gas industries of our country, washing with relatively dilute caustic solution is often used to remove light mercaptans. In this project, caustic regeneration process is described and factors affecting this process are investigated. It is also discussed about the optimal value of the operational parameters of this process. The concentration of the consumed benefit, the operating temperature and the flow rate of oxygen entering the reactor (oxidizer) are the most important operating parameters. The results of this study show that the optimum soda concentration for converting sodium mercaptides to disulfides is around 1.9 mol/liter, but due to the rotation of the soda solution in the system, the optimal soda concentration value should be determined for the entire system. According to the laboratory results, the optimal amount of sodium concentration for mercaptanization from liquefied gas is between 2.75 and 4.25 mol/liter. In addition, the suggested temperature for the oxidizer output is 50 degrees Celsius; Therefore, the temperature profile in the oxidizer will be 10 °C. Also, 1.06 to 1.1 stoichiometric amount of oxygen is suggested for soda which has 8680 ppm of mercaptide by weight at the oxidizer inlet.

    Introduction

    The purpose of this project is to investigate the soda regeneration process and the factors affecting it and to optimize the operational parameters of the mentioned unit. In the first chapter, in order to obtain the necessary basic information, the types of sulfur impurities in liquid gas and the need to separate them are examined, and the different methods of sweetening liquid gas, the applications of each, as well as the respective advantages and disadvantages are given, so that if necessary, according to the design of the South Pars complex and the existing facilities, additional equipment can be used to improve the performance of the process in such a way that the applied changes are justified from an economic point of view.

    In the second chapter, the method used in phases 4 and 5 is discussed and the mercaptanization process of liquefied natural gas by the physical soda solvent is examined in detail.

    In the third chapter, the results of previous research on the sweetening process of liquefied natural gas with physical soda solution are given.

    In the fourth chapter, the simulation is described and the results of The simulation of the process is given and the optimal values ??of the operating parameters for the profit recovery process are analyzed. It should be noted that the simulation of the mentioned unit was done by Plus Aspen and Aspen Dynamic software and based on the laboratory results and experimental relationships presented in the second chapter. Finally, in the fifth chapter, the summary, conclusions and relevant suggestions are given. The first chapter: Types of sulfur impurities in the gas. Liquid and their separation methods

    1-1- Types of sulfur impurities in liquid gas

    Liquid gas is widely used as industrial fuel, household fuel and raw chemical material and often contains impurities of carbon dioxide, hydrogen sulfide, carbonyl sulfide, carbon disulfide, and methyl and ethyl mercaptans.

    According to the harm of sulfur impurities, one of the most important processes of liquid gas purification in the industry is its sweetening process. Today, the permitted amount of sulfur in liquid gas has been greatly reduced. For example, the amount of sulfur allowed in propane and butane used in the production of polypropylene and polybutylene is less than 5 ppm. This has caused the upstream production industries as well as the downstream refining industries to consider lower permitted amounts of sulfur in the design of the processes [1].

     

    1-1-1- Main and major impurities

    Hydrogen sulfide

    Hydrogen sulfide generally results from cracking reactions of sulfur molecules and High concentrations of 2 ppm make the gas highly corrosive. Also, if oil fraction is used as a raw material, hydrogen sulfide causes the formation of free sulfur and mercaptans.

    Hydrogen sulfide is the most destructive impurity that can be present in liquid gas.

    Carbonyl sulfide

    Carbonyl sulfide may be It is present in propane cutting, and although it is not corrosive by itself, it is hydrolyzed in the presence of water and produces hydrogen sulfide, and as a result, it causes the corrosiveness of the product.

    The formation of carbonyl sulfide basically takes place by the following reversible and equilibrium hydrolysis reaction:

    COS + H2O ? H2S + CO2 (1-1)

    Carbonyl sulfide does not form when extracted from the reservoir because natural gas is usually saturated with water. Of course, in some cases, carbonyl sulfide is formed in the absence of water. For example, in molecular sieves for dehydration, carbonyl sulfide is formed due to the reaction of hydrogen sulfide with carbon dioxide. The carbonyl sulfide formed in the molecular sieves located upstream of the LPG unit accumulates in the propane product. Even very small volume amounts of carbonyl sulfide combine with water and produce hydrogen sulfide if proper equilibrium conditions are provided.

    The presence of carbonyl sulfide in the commercial propane product is usually not checked because this compound does not directly affect the corrosion test. If water is present in the propane transmission system, the presence of even very small amounts of carbonyl sulfide and its hydrolysis will lead to the failure of the product received at the destination (in the corrosion test). Carbonyl sulfide formation is accelerated in dewatering units using 4 or 5 angstrom molecular sieves. The mentioned molecular sieves accelerate the formation of carbonyl sulfide for the following reasons:

    High contact surface of zeolite crystals present as catalyst

    Crystal structure

    High concentration of hydrogen sulfide and carbon dioxide in the pores of the sieve due to rapid absorption and lack Water

    The existing technologies for carbonyl sulfide separation include sweetening with amine or adsorbent. If carbonyl sulfide is the only impurity in the propane product, sweetening with an adsorbent is often more economical [2].

    Methyl and ethyl mercaptans (CH3SH and C2H5SH)

    Mercaptans and their combustion products cause the bad smell of light petroleum products such as liquid gas and gasoline, but they do not have corrosive properties. Mercaptans are also the source of gum formation. The concentration of mercaptans in petroleum products varies depending on the reservoir from which the oil was extracted and the way sulfur is distributed in the crude oil. Significant amounts of mercaptans are produced from the decomposition of other sulfur compounds during the distillation and cracking processes of oil [3].

    Propane cut contains only methyl mercaptan and the amount of ethyl mercaptan is very small.

    Butane cut only includes ethyl and methyl mercaptans.

    The chemical formula for all mercaptans is R-SH, where R is a hydrocarbon group, S is a sulfur atom, and H is a hydrogen atom [4].

    1-1-2- secondary and tolerant impurities

    Dialkyl sulfides (RSR)

    Dialkyls are formed by the reaction between mercaptans and olefins. These compounds are not undesirable and are not purified.

    Disulfides

    The origin of disulfides production is the oxidation of mercaptans.

  • Contents & References of Dynamic simulation of caustic regeneration unit and optimization of operational parameters of the third refinery of South Pars gas complex

    List:

    Abstract ..1

    Introduction ..2

    Chapter One: Types of sulfur impurities in liquid gas and their separation methods. 3

    1-1- Types of sulfur impurities in liquid gas. 4

    1-1-1- Main and major impurities. 5

    1-1-2- Secondary and tolerant impurities. 7

    1-2- Reasons for separating the main sulfur impurities in liquid gas. 8

    1-3- Methods for separating sulfur impurities in liquid gas. 9

    1-3-1- Dry processes. 13

    1-3-1-1- Dry renewable processes. 13

    1-3-1-2- Regenerative dry processes. 15

    1-3-1-3- Hybrid dry processes. 17

    1-3-2- Wet processes. 18

    1-3-2- 1- Desulfurization with chemical solvents (amines). 19

    1-3-2-2- Desulfurization with solvents Physical. 20

    1-3-2-2-1- Selexol physical solvent. 21

    1-3-2-2-2- Caustic soda solutions. 23

    1-3-2-3- Desulfurization with hybrid solvents. 24

    1-3-3- Summary of liquid gas sweetening processes. 25

    Chapter Two: Sweetening process Liquid gas with soda physical solution. 28

    2-1- Introduction..29

    2-2- Description of mercaptanization process of liquid gas by soda. 29

    2-2-1- Description of propane extraction unit process. 29

    2-2-2- Description of butane extraction unit process. 30

    2-2-3- Description of caustic reduction unit process. 32

    2-3-Reactions of mercaptanization process by soda.33

    2-3-1- Main reactions.33

    2-3-2- Side reactions.35

    2-4- Catalyst of mercaptanization process by soda.38

    2-5- Investigation of factors affecting mercaptans extraction process and liquid gas purification.40

    2-5-1- The balance of phases and ionization of acids and bases. 40

    2-5-1-1- The balance of acids and bases in the aqueous phase. 41

    2-5-1-2- The balance between hydrocarbon and aqueous phases. 43

    2-5-2- The effect of mercaptan type on the extraction process. 48

    2-5-3- The effect of solution concentration hydroxide on the extraction process and the conversion reaction of mercaptans to sodium mercaptides. Mercaptan from liquefied gas. 60

    2-6- Effective factors on soda reduction process. 61

    2-6-1- Effect of sodium mercaptide concentration on conversion reaction of sodium mercaptides to disulfides. 61

    2-6-2- Effect of soda concentration on catalyst solubility in soda solution. 63

    2-6-3- Effect of soda concentration on mercaptides penetration and Free radicals. 64

    2-6-4- The effect of temperature on the oxidation reaction of sodium mercaptides. 65

    2-6-5- The effect of temperature on the catalyst activity in soda solution. 66

    2-6-6- The effect of the molecular structure of mercaptan on the reaction speed. 68

    2-6-7- The effect of the preparation method of the catalyst solution distributed in soda on the speed Reaction.68

    2-6-8- The effect of gas environment on CoSPc catalyst activity and reaction speed. 70

    2-6-9- The effect of mixing speed of soda catalytic solution and air on sodium mercaptide oxidation reaction speed. 73

    Chapter 4: Description of the simulation and examination of its results. 77

    4-1- Introduction.. 78

    4-2- Description of the simulation. The optimal amount of air entering the oxidizer bed for soda regeneration. 91

    4-4-2- The optimal amount of sodium solution concentration entering the oxidizer bed for soda regeneration. 93

    4-4-3- The optimal value for the oxidizer temperature. 95

    Chapter 5: Summary of contents and conclusions. 96

    List of Persian sources. 100

    List of sources Non-Persian..101

    English abstract..104

    Title page in English.105

     

    Source:

     

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    [12] Mahin Rameshni, P.E., (2000), State of the art in gas processing, Worley Parsons Co., Chief Process Engineer, San Francisco.

    [13] Xiaolin, Q., (2000), Present Status and Development Trends of LPG Desulfurization Technology in Refineries, Chemical Industry and Engineering Progress, Volume 76, Number 9, Page: 49-54, 56, 58-59.

    [14] Suarez, F.J., (1996), Pluses and minuses of caustic treating, Hydrocarbon Processing, Volume 75, Number 10, Page: 117-123.

    [15] Judd, B., (1993), Mercaptan removal rate exceeds 99% at Canadian gas plants, Oil and Gas Journal, Volume 91, Issue 33, Page: 81-83.

    [16] Ruiting, L.; Daohong, X.; Yuzhi, X., (2003), Study on the Stability of CoSPc in LPG Sweetening, American Chemical Society, Division of Petroleum Chemistry, Preprints, Volume 48, Number 4, Page: 338-340.

    [17] Mazgarov, A.M., (2006), A selective treatment of various oils and gas condensates to remove light mercaptans and hydrogen sulfide, Chevron Research and Technology Co. (USA) (1976), Treat propane for COS removal, Hydrocarbon Processing, Page: 137-142.

    [22] Turbeville, W.; Yap, N., (2006), The chemistry of copper-containing sulfur adsorbents in the presence of mercaptans, Catalysis Today, Volume 116, Issue 4, Page: 519-525.

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Dynamic simulation of caustic regeneration unit and optimization of operational parameters of the third refinery of South Pars gas complex