Study On Formation Mechanism And Movement Process Of Black Powder In Natural Gas Pipeline

The black power problem has become a common problem for natural gas pipeline in recent years.Small solid particles will inevitably be produced in transmission pipelines due to many reasons such as gas source or internal corrosion.These particles are known as black powder.The existence of black powder will pollute natural gas products,lead to wear and corrosion of pipelines,destruct equipments,reduce transport efficiency and even cause pipeline blockage.To cope with these problems,a comprehensive and specific understanding of black powder is absolutely essential.This paper focuses on the formation mechanism and movement law of black powder,the following work has been completed:(1)Based on a large number of field data,the macroscopic and microscopic characteristics of black powder in natural gas pipeline are summarized.It is pointed out that the amount of black powder is positively related to the conveying scale(pipe size and medium flow rate),while the particle size under the same condition is negatively correlated with the medium velocity.Based on the analysis of several samples,the formation mechanism of black powder is analyzed.It is emphasized that the large-scale comprehensive corrosion in the gas pipeline is the culprit of a large number of black powder,and the theory of accelerating the corrosion of black powder is put forward.(2)Particle size distribution(PSD)is a key information for black powder description and an important basis for studying the motion law of black powder.In this paper,7 commonly PSD models are selected to describe black powder's PSD information.These models are evaluated from goodness of fit and prediction ability.Although each distribution model has its own advantages and limitations according to the specific application environment,the logarithmic normal model is a relatively superior model to describe black powder particles in natural gas pipeline.(3)According to the characteristics of particle migration and gas-solid flow theory,the force analysis of black powder is carried out.Based on Euler-Lagrange method,the standard k-s model and DPM model are used to simulate the gas-solid flow in horizontal pipe.And the motion law of particles with different size is analyzed.(4)Based on several field data,the black powder cleaning technology for pipeline has been summarized and analyzed.The safety and high efficiency of gel cleaning technology in removing large amounts of black powder are described.A vortex separator which is more suitable for removing black powder from natural gas pipeline is introduced.The cases of pigging and filtration at the scene are analyzed.Based on industrial practice,this paper covers the study of the generation,development,migration and removal process of the black powder in natural pipelines.As the study of black powder problem started late in China,this paper hopes to provide a reference for prevention and treatment of the black powder problem.