| Along with the development of the world economy,the deterioration of the earth’s environment has attracted wide attention of the energy industry.Increasing the proportion of natural gas in the structure of disposable energy can reduce air pollution and improve the environment effectively.From the perspective of resource reserves,as of 2016,the remaining proved recoverable reserves of global natural gas are around 186.6 trillion cubic meters,and most of it is sour natural gas reservoirs.With the continuous rise of natural gas in the world energy structure,the status of natural gas purification industry is becoming more and more important.Natural gas desulfurization and decarbonization is the most critical process among all the natural gas purification process with highest energy consumption.Optimizing desulfurization and decarbonization process and reducing energy consumption are the representatives of natural gas purification industry developing towards green and precise direction.After decades of research,some achievements have been made in natural gas desulfurization and decarbonization,such as chemical absorption,physical absorption,membrane separation,low temperature separation and mixed separation.However,for the purification process of highly sour natural gas,especially when the total content of acidic components H2S and CO2 of raw gas exceeds 15%(ⅴ),the conventional chemical absorption method is low efficiency of desulfurization and decarbonization which is caused by pressure conditions and has high energy consumption which is caused by large circulation flow of solvent.The conventional physical absorption method is slightly lower than the chemical absorption method,but it has the problem of hydrocarbon co-absorption.The hydrating separation method studied in recent years has the characteristics of low energy consumption and simple process,but it has the problem of unable to achieve precision removal,and the content of H2S and CO2 in the purified gas cannot meet the requirements of sales natural gas.This paper proposes and studies a new desulfurization decarburization process for high sour natural gas.Selected the five different sour natural gas compositions with high concentration of H2S and CO2 which are CH4 concentration of 85%,79%,73%,67%,60%,H2S concentration of 10%,15%,20%,25%,30%and CO2 concentration of 5%,6%,7%,8%,10%to be studied.The first step is that the water thermodynamic calculation model of legal separation process is set up and the CPA,SRK,PR and Chen-Guo model of hydrate formation conditions is used to calculate the parameters of phase equilibrium and calculate the gas phase components concentration with the hydration reaction process duration.The experimental method of hydrate separation was set up and obtained the experimental data to compare and analyze with calculating data.Based on the dynamic model of the decomposition,the temperature of the system is raised at constant pressure,the decomposition to obtain the relationship between the gas flow and the reaction time for determining the apparent dynamics constant of H2S.Also,selected two groups of high sour natural gas composition to study and compare the new desulfurization and decarbonization process with conventional chemical absorption process and hydrating separation process.The conventional chemical absorption process uses Promax and Amsim software which have been used in the industry to simulate the performance parameters.The hydrating separation process is based on the mathematical model to calculate the performance parameters.The new combined process used the calculating data of hydrating process as the inputs for chemical absorption process to simulate the final performance parameters.Finally,it is compared with product quality,H2S concentration of acid gas which is sent to downstream unit such as sulfur recovery unit,investment and energy consumption.This paper is of great significance to the selection of desulfurization and dehydrocarbon process for high sour natrual gas.The main results are as follows:1.In this paper,an advance process for the desulfurization and decarbonization of highly sour natural gas is proposed,which combines the hydrating separation method with chemical(physical)absorption method to reduce energy consumption and meet the requirements of sales natural gas.2.In this paper,the model of the equilibrium thermodynamic model and the material balance calculation model of the hydating reaction are established based on Gas-liquid equation and hydate model,to calculate the parameters of phase equilibria and concentration variation of gas phase compositions of five groups high sour natural gas respectively,to theoretically approve the feasibility of hydating separation process.3.Through the establishment of the hydrating reaction experimental apparatus,the hydrating reaction experiment was conducted on five groups high sour natural gas compositions.The separation of the mixed gas by hydrating separation process is approved according to the analysis of experimental results and theoretical calculation data,as well as following conclusion:there are two stages during the hydrating reaction of the mixture gas,including the initial growth stage of gas phase dissolution,hydrate nucleation and hydrate crystal as the first stage,and the replacement stage in which the gas phase molecules that are more likely to form hydrates can be replaced by the gas phase molecules that are less likely to form hydrates.In the first stage of hydrating reaction,CH4,H2S and CO2 molecules were partially dissolved in the solvent,and partially hydrated with water to generate CH4,H2S and CO2 hydrate.In the second stage,due to the hydrating driving force of the H2S molecular is stronger than CH4 and CO2 molecule,the H2S hydrates which is formed in the first phase continue to grow in the second stage,and the H2S molecules exist in the gas phase will replace the CH4 moleculars which formed CH4 hydrate with H2O molecules in the first stage already,to form H2S hydrate by entering cavity of hydrates.Meanwhile,the CH4 molecules escaped from cavity of hydrates return to gas phase,resulting that the CH4 concentration of gas phase is altered from high to low in the first stage and oppositely in the second stage.At the same time,the separation efficiency is related to the composition of the mixed gas is concluded.For mixed gases,the hydate separation is the most efficient when the CH4 concentration is between 70%and 80%and H2S concentration is between 15%and 25%.When CO2 concentration is more than 5%,the efficiency of hydrate separation will increase with the CO2 concentration of the mixed gas increase.4.Decomposition activation energy of H2S hydrates of five groups high acid natural gas is achieved,based on the hydates decomposition experiment data obtained by establishment of dynamic model of the hydrates decomposition and the set up of the decomposition experimental apparatus,as well as the continuous of the separation process.5.This paper took composition 2 and composition 4 as examples,and compared the process parameters and energy consumption of the three processes for natural gas desulfurization and decaronization units with flow rate of 800 × 104m3/d and makes simple economic evaluation analysis.Analysis is concluded that the new process can be sure that the H2S concentration of product gas is less than 6 mg/m3,CO2 concentration is less than 2%to meet the requirements of class I sales gas with low energy consumption comparing with conventional MDEA chemical absorption desulfurization process around 48%and 56%.Also,the equipment investment and operation cost are lower than conventional process for high sour natural gas purification,which is an advance desulfurization and decarbonization process with energy-saving and precise. |
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