Research On Solid Particle Size Distribution And Deposition Law Of Qinnan Coalbed Methane Gathering Pipeline

Coalbed methane usually carrys a large number of solid particles when flowing into ground gathering system.These particles may cause blockage or damage in gathering pipelines and equipment,which will seriously affect the efficiency and safety of gas collection and transportation.To control particle deposition and optimize pipeline operation,this paper has studied theoretical and numerical research about particle deposition in coalbed methane gathering pipelines.The following work has been completed:(1)Qualitative and quantitative analysis for physical properties of coalbed methane and its solid particles.It is clear that the solid particles in coalbed methane gathering pipeline mainly originate from coal and inorganic minerals in the formation;besides,the density range of solid particles in Qinnan is 2600～2800kg/m3.The particle settlement mechanism in coalbed methane gathering pipeline is clarified,and the main factors which may influence particle deposition are summarized:particle size and density,gas flow velocity and pipeline structure.(2)The applicability and limitation of existing methods in obtaining particle size distribution(PSD)in natural gas pipeline is analyzed and evaluated.With reference from other gas-particle flow,the PSD calculation method which is suitable for coalbed methane gathering pipeline is summarized,and calculation process for PSD models is bulit based on classical statistics and Bayesian statistics theory.Based on the particle sample data from two field gathering pipelines,it is found that the calculation result is more accurate when sample size is smaller than 75%using classcical method.Therefore,it is suggested to select Bayesian statistical method when particle sample size is less than 75%.(3)According to gas-solid flow theory as well as characteristics of gas and solid phase in Qinnan coalbed methane gathering pipeline,the standard k-ε turbulence model and DPM model are selected as numerical simulation model.The particles transportation and deposition in straight,elbow and the T-type pipeline segment are simulated using FLUENT software,and the particles with different density and size are simulated under different gas flow velocities.It is found that the particle deposition rate is mainly influenced by air velocity.Besides,when air velocity reaches a critical value,the particle deposition rate tends to be zero.In elbow and T-type section,the particle size is the most important factor that affects particle deposition.(4)Based on the above research results,the relation between critical particle suspension velocity and particle size in coalbed methane gathering pipeline is summarized,and the Weekes model is used for checking the model.In addtion,this paper used a field coalbed methane gathering pipeline for relation model practice.For example,when air velocity is 4.5m/s,particle deposition rate in predicting pipe is 0.0712,deposition mass is 26.97mg/m3,deposited particle size is 46μm and above;thus,it is recommended that gravity separator should be set at the pipeline inlet,and the precision of separation element is 40μm.