Study On Prediction Method Of Sulfur Deposition For High Sulfur Natural Gas Gathering Pipeline

With the world’s growing demand for energy, the development of high sulfur gas field can help to relieve the energy shortage situation. High sulfur natural gas in the entire natural gas industry is becoming more and more important. Compared with the conventional natural gas, high sulfur natural gas not only has the intense corrosiveness and violently poisonous, but also has the special PVT characteristic and unique phase behaviors. As the result of decrease in pressure and temperature during the gathering and transportation of high sulfur natural gas, the sulfur dissolving in sour gas maybe dissolve out by solid particle morphology and deposit in pipeline. The sulfur deposition can cause the ground gathering pipeline plugging and the corrosion of steel. Eventually it will affect the normal transportation of gas. Therefore, the research of sulfur deposition in gathering pipeline is very significant for the protection of gathering high sulfur gas safely and effectively. Predicting method of the sulfur deposition in high sulfur gas gathering pipeline will be studied in this paper. The main work is as following.(1) Studying the mechanism of elemental sulfur deposited in pipeline could help understand the nature of the occurrence of sulfur deposition. And it was also the foundation and prerequisite to establish the model of predicting the sulfur deposition. For this reason, the existing form, density, viscosity, specific heat and freezing point of elemental sulfur were researched qualitatively and quantitatively. Then several methods of calculating the physical parameter of high sulfur gas were optimized, finding that DPR with WA correction formula was the best method to calculate Z-factor of high sulfur gas; the state equation of BWRS also had high accuracy to calculate Z-factor of high sulfur gas; Dempsey with Standing correction formula was the best method to calculate viscosity of high sulfur gas. Hydrogen sulfide was a clear source of the material basis of elemental sulfur. According to chemical reaction equilibrium principle, it was proved that there was a small quantity of sulfur dissolved in high sulfur gas through chemical process and the main dissolution mechanism was physical dissolution. Sulfur deposition mainly considered the sulfur solubility changed which was mainly affected by the pressure, temperature and gas composition.(2) On the basis of applicability and limitation evaluation of the model that predicted the sulfur solubility in high sulfur gas, a genetic BP neural network model had been used to predict the sulfur solubility in high sulfur gas. Implementation procedure and parameters setting of this model were introduced in detail. Then the established genetic BP neural network model was tested and verified, the results showed that the accuracy of this model was very satisfactory.(3) According to gas-solid transport characteristic in horizontal pipe and gas-solid two phase flow theory, the stress of the precipitated solid sulfur particles was analyzed. And the model of calculating the critical velocity of solid particle groups was used to analyze the conditions of solid sulfur particles that deposited in pipeline.The migration and settlement law of sulfur particles in straight pipe, horizontal bend and valve had been studied by the RSM model and DPM model of FLUENT software. The deposition rate of sulfur particles in straight pipe would decrease with the increase of velocity and increase with the increase of particle size. The deposition rate of sulfur particles in bend would increase with the increase of velocity, particle size and curvature ratio. The deposition rate of sulfur particles in valve would increase with the increase of velocity, particle size and decrease with the increase of valve opening.(4) Based on the above theoretical achievements and the model of predicting the pressure and temperature distribution of high sulfur natural gas gathering pipeline, the model of predicting the location where sulfur dissolve, determining the sulfur would deposit and calculating the amount of sulfur deposition were established. And these models were used to analyze the sulfur deposition of a domestic high sulfur natural gas gathering pipeline, the results showed that these models were in good agreement with the actual results.