Study On The Thermodynamic And Kinetic Characteristics Of Hydrate Based Gas Separation For Coal Mine Gas And IGCC Gas

Gas hydrate is a cage shaped crystal structure formed by gas molecules and water molecules at high pressure and low temperature,in which water molecules are bonded into a cage structure by hydrogen bonds.Gas molecules enter a cage structure and combine with water molecules to form a stable gas hydrate by molecular force.Natural gas hydrate,commonly known as "combustible ice",is a common gas hydrate.It is widely found in nature and is considered as a new kind of clean energy in twenty-first Century.In addition,gas hydrate technology has wide application prospects in industrial production,such as oil and gas transportation,gas separation,CO2 capture,and air conditioning cool storage.The research and development of gas hydrate technology has important practical significance for the energy,environmental protection,chemical industry,aerospace and refrigeration of mankind.Low concentration CBM is a coal bed gas with less than 30% methane content.In the process of coal mining,a large number of low concentration CBM gas will be discharged.The coal bed gas resources in China are huge,the main component of which is methane gas.Methane gas has a very high greenhouse effect.It is easy to explode after mixing with air,which brings great safety risks to the safe production of coal mines.Using certain methods to separate and purify low concentration coalbed methane into high concentration coalbed methane which can be directly utilized has become the research hotspot at this stage.The traditional methods of purification of coal bed gas include low temperature distillation,membrane separation and solvent absorption.These methods generally have the disadvantages of high energy consumption,low separation efficiency and high operating cost.In addition,China’s carbon emissions are the highest in the world,mainly from the burning of fossil fuels,exhaust from vehicles and other vehicles,as well as waste gases in industrial production.Carbon dioxide is the main gas in carbon emission,and it is also an important industrial raw material.It can be used to produce dry ice and urea and so on.The control of carbon dioxide emission has great environmental and economic benefits.At present,the commonly used CO2 capture technologies include solution absorption,membrane separation and physical separation.Gas hydrate is a new method of gas separation.It has many advantages,such as high gas storage rate,simple raw material,low operating cost,recyclable and so on.It has been paid more and more attention by scholars from various countries.The problems to be solved urgently in developing hydrate purification technology at present stage include shortening induction time,relieving reaction conditions and raising reaction rate.In view of these key problems,this paper studies the thermodynamic and dynamic characteristics of gas hydrate separation of mixed gas by gas hydrate method,focusing on the influence of the thermodynamic additives on the equilibrium conditions of hydrate phase,and the factors such as additive type,pressure,water to oil ratio and other factors for water,with the study of low concentration coal gas and IGCC gas as the research object.The action rule of the kinetics of complex formation provides a theoretical basis for the development of gas hydrate purification technology.The main research work carried out in this paper includes:(1)Through study,it is found that adding thermodynamic additives to hydrate reaction solution system can effectively improve the phase equilibrium condition of hydrate formation.Starting with the effect of additives on the phase equilibrium conditions of gas hydrates generated by low concentration CBM,the thermodynamic properties of low concentration CBM hydrate formation under different additive systems were studied,and the low concentration CBM was measured under four Butyl Ammonium Bromide(TBAB),cyclopentane(CP)and cyclohexane(CYH)-water system.Phase equilibrium condition.(2)Based on the thermodynamic characteristics of the low concentration CBM under the cyclopentane water system,the experimental study on the dynamic characteristics of the cyclopentane water system was designed to study the effect of pressure on the induction time,gas recovery and gas consumption of hydrate formation.The study found that the higher the pressure,the shorter the induction time,the lower the gas recovery rate,and the higher the gas consumption.On this basis,the effect of twelve alkyl sodium sulfate(SDS)on the kinetics of hydrate formation was studied.The experimental results showed that the effect of SDS on gas recovery was less and the induction time in the reaction was obviously accelerated;and cyclopentane(CP)could better alleviate the hydrate formation conditions.(3)According to the solubility of methane in oil far greater than the solubility of water in the water,the emulsified oil which can be used in the experiment was prepared.The kinetic experiment under the CP-emulsified oil system was designed.The kinetic characteristics of three kinds of water / oil ratio(WOR=10%,30%,70%)were studied.The results show that when the ratio of water to oil is 30%,the recovery rate of methane is the highest,the greater the ratio of water to oil,the longer the induction time;the higher the pressure,the shorter the induction time.According to the phase equilibrium condition of carbon dioxide is lower than the phase equilibrium condition of hydrogen,the experimental study on the separation of IGCC gas(40%CO2+60%H2 simulated gas)by hydrate method under CP-emulsion system was designed.The effects of different water and oil ratio and different pressure on the dynamic characteristics of gas hydrate formation were studied.The study found that the smaller the water / oil ratio,the shorter the induction time,but the gas recovery rate increased with the increase of water / oil ratio.In the experiment.With the increase of pressure,the induction time is shortened and the recovery rate of gas decreases.(4)The reaction solution of THF-nano graphite system was developed and the particle size experiment was carried out.The effect of nano graphite concentration on the recovery rate of CO2 was studied.The results show that the 0.1wt% nano graphite solution has the best CO2 separation efficiency.The experimental research on the separation efficiency of CO2 by pressure driving force is carried out.The results show that the higher the pressure,the worse the CO2 separation effect is.