Laboratory investigation of gas dehumidification using triethylene glycol solution in hollow fiber membrane contactors.

Number of pages: 105 File Format: word File Code: 31786
Year: 2014 University Degree: Master's degree Category: Chemical - Petrochemical Engineering
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  • Summary of Laboratory investigation of gas dehumidification using triethylene glycol solution in hollow fiber membrane contactors.

    Master's Thesis in Chemical Engineering (Gas Orientation)

    Abstract

    Laboratory investigation of gas dehumidification using triethylene glycol solution in hollow fiber membrane contactors

    In this In this study, two hollow fiber membrane contactors with different types of polyvinylidene fluoride (PVDF) and polypropylene (PP) fibers have been used in order to dehumidify gas with triethylene glycol (TEG) absorbent solvent. The ambient air as a gas sample, after passing through the humidifier, enters the membrane contactor from the shell part and comes in contact with the triethylene glycol solution that flows inside the fibers. The effect of relative humidity percentage of incoming air, concentration of triethylene glycol solution, different flow rates of gas and liquid, and flow direction on dehumidification efficiency and water vapor mass transfer flux were investigated. In order to simulate membrane contactors, Comsol simulator software was used considering Happel's hypothesis for the gas phase. Also, a mathematical model was used to simulate the membrane contactor by considering the Plug assumption for the gas phase. The differential equations related to the mathematical model were solved by a numerical technique by coding with Matlab software. The simulation results were in good agreement with the laboratory data. The results showed that hollow fiber membrane contactors can be very effective in separating water vapor from gas flow. The flow rate of the gas flow has a significant effect on the efficiency and the dew point temperature of the outlet air flow. It was also observed that changes in the liquid flow rate do not have much effect on the mass transfer efficiency and flux, which indicates that the mass transfer resistance is not in the liquid phase. For membrane contactors, it was observed that the amount of water vapor separation increases for the asymmetric flow mode compared to the parallel flow.

    Key words:

    Dehumidification, triethylene glycol, hollow fiber membrane, polyvinylidene fluoride, polypropylene, Comsol

    Introduction

    1-1- Natural gas and its dehumidification

    Natural gas is one of the most important primary sources of energy. Large gas reservoirs have been discovered in recent decades and the hope of discovering more gas reservoirs is very bright. Natural gas in underground reservoirs is under certain temperature and pressure conditions, next to oil and water. For this reason, natural gas may contain some impurities including carbon dioxide, hydrogen sulfide, water vapor, etc.  carry with you[1].

    In order for natural gas to reach domestic and industrial consumption, it must be refined in several stages in refineries and its impurities must be removed, the amount of these impurities must be within the pipeline or sales standard. One of the most important stages of natural gas purification is the absorption of acid gases from the gas if it contains these compounds and dehumidification[1]. After separating the oil from the gas, there is some free water along with the natural gas. Most of which is separated from the gas by simple separation methods at the wellhead or near it. While the water vapor in the gas solution must be separated from natural gas through a very complex process called dehumidification or dehumidification. 1-2- Problems caused by the presence of water vapor in natural gas. Water is perhaps one of the unwanted impurities common to all natural gases. Usually, water vapor alone does not cause much problem, this liquid or solid substance separates from the gas in the state of condensation or cooling and causes problems.If the temperature of the wall of the transmission pipe or natural gas storage tanks is reduced to below the dew point temperature[2] of the gas, the water vapors in the natural gas will begin to condense on the cold surface of the pipe, which will cause the following problems[2]:

    natural gas next to the water droplets creates the possibility of hydrate formation[3], which causes an increase in pressure drop, obstruction, partial or total clogging of the gas pipeline, and in some cases pipeline explosion

    Carbon dioxide and hydrogen sulfide gases in natural gas dissolve in water droplets and cause the formation of very corrosive compounds that cause damage to the pipeline.

    Water vapor reduces the calorific value [4] of natural gas.

    occupying part of the pipe surface and reducing its useful capacity

    Freezing in absorption units that are associated with gas cooling.

  • Contents & References of Laboratory investigation of gas dehumidification using triethylene glycol solution in hollow fiber membrane contactors.

    List:

    Chapter One: Introduction .. 2

    1-1- Natural gas and its dehumidification. 2

    1-2- Problems caused by the presence of water vapor in natural gas. 3

    1-3- types of natural gas dehumidification methods. 3

    1-3-1- Absorption in liquid by moisture absorbent liquids. 4

    1-3-2- Absorption of water by moisture absorbing solid materials. 7

    1-3-2-1- silica gel. 10

    1-3-2-2- Mobil Sorbid. 10

    1-3-2-3- activated alumina. 11

    1-3-2-4- activated bauxite. 11

    1-3-2-5- molecular sieve. 12

    1-2- Membrane processes. 16

    1-2-1- Introduction of membrane technology. 16

    1-2-2- Membrane separation mechanism. 17

    1-2-3- Division of membranes. 18

    1-2-3-1- Division based on membrane type. 18

    1-2-3-2- Division based on membrane structure. 22

    1-2-3-3- division based on the geometric shape of the membrane. 23

    Chapter Two: An overview of past research. 28

    2-1- History of using common methods for gas dehumidification using absorbent liquids 28

    2-2- History of using hollow fiber membrane for gas dehumidification. 30

    Chapter Three: How to do the work. 33

    3-1- Method of conducting experiments. 33

    3-1-1- moisture absorbent liquid. 33

    3-1-2- Experiments.. 35

    3-1-2-1- Description of the air dehumidification laboratory unit. 35

    3-1-2-2- Description of the test. 42

    3-1-3- extracting the results. 44

    3-2- Simulation method using COMSOL software. 45

    3-2-1- Governing equations. 47

    3-2-1-1- Concentration equations inside membrane fibers (liquid phase). 48

    3-2-1-2- concentration equations in the membrane. 50

    3-2-1-3- concentration equations in the shell (gas phase). 50

    3-2-2- Solubility of water vapor in triethylene glycol solution. 52

    3-2-3- water penetration coefficients. 55

    3-2-3-1- water penetration coefficient in air. 55

    3-2-3-2- water penetration coefficient in triethylene glycol solution. 55

    3-2-3-3- water penetration coefficient in the membrane in a completely dry state. 56

    3-2-3-4- water penetration coefficient in the membrane in the state of complete wetting. 57

    3-2-4- Numerical solution of simulation equations. 58

    3-3- Modeling method using plug assumption. 59

    3-3-1- Governing equations. 59

    3-3-1-1- Concentration equation inside membrane fibers (liquid phase). 59

    3-3-1-2- Concentration equations in the membrane. 61

    3-3-1-3- concentration equations in the shell (gas phase). 61

    3-3-2- Numerical solution of equations. 62

    Chapter four: discussion and results. 65

    4-1- Introducing the investigated parameters in the water vapor absorption process and investigating their effects. 66

    4-1-1- The influence of the relative humidity percentage of the incoming air. 66

    4-1-1-1- The effect of the percentage of relative humidity of the incoming air on the efficiency of water vapor removal and the dew point temperature of the outgoing air 66

    4-1-1-2- The effect of the percentage of relative humidity of the incoming air on the rate of mass transfer of water vapor. 69

    4-1-2- Effect of air flow rate. 71

    4-1-2-1- The effect of air flow rate on water vapor removal efficiency and the dew point temperature of the outlet air 71

    4-1-2-2- The effect of air flow rate on water vapor mass transfer flux. 73

    4-1-3- Effect of liquid flow rate. 75

    4-1-3-1- The effect of liquid flow rate on water vapor removal efficiency and dew point temperature of outlet air 75

    4-1-3-2- The effect of air flow rate on water vapor mass transfer flux. 76

    4-1-4- the effect of triethylene glycol concentration. 78

    4-1-4-1- The effect of triethylene glycol concentration on water vapor removal efficiency and the dew point temperature of the outlet air 78

    4-1-4-2- The effect of triethylene glycol concentration on water vapor mass transfer flux. 80

    4-1-5- Effect of flow direction. 81

    4-1-5-1- Effect of flow direction on water vapor removal efficiency. 82

    4-1-5-2- The effect of flow direction on the dew point temperature of the outlet air. 83

    Chapter five: conclusions and suggestions. 85

    5-1- Conclusion.. 85

    5-2- Recommendations

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Laboratory investigation of gas dehumidification using triethylene glycol solution in hollow fiber membrane contactors.