含硫站场呼吸管堵塞成因及防控对策

Causes analysis and technical countermeasures of plugging in breathing tube in sulfide-containing natural gas station

关键词:  含硫站场  呼吸管  堵塞  成因  对策 

Key words:  sulfide-containing natural gas station  breathing tube  plugging  cause  countermeasures

摘要:

目的 解决含硫站场气田水罐呼吸管堵塞或腐蚀穿孔问题,保证含硫气田水罐正常运行。方法 通过SEM、EDS和XRD分析测试技术识别TB101-X1井等5个站场呼吸管堵塞物主要成分,根据呼吸管闪蒸气工况特征分析堵塞主要成因。结果 呼吸管闪蒸气常温、微正压、低流速聚集成高含量H₂S气体后,析出单质硫；随呼吸管延伸闪蒸气温度下降冷凝析出的液态水和气田水罐高液位携带的液态水,与H₂S、SO2-₄和Cl-一起与碳钢管道铁离子反应生成硫化铁、硫酸亚铁和氧化铁；气田水罐卸水负压吸氧,增加氧腐蚀,与H₂S水溶液反应析出单质硫。反应产物在低流速下沉积结垢于管道内壁,早中期不易发现,后期快速堵塞呼吸管,造成气田水罐内聚气升压。结论 气田水罐卸水负压补气、优选呼吸管材质、气田水罐上部呼吸口处增设气液分离组件等防控措施,从本质上预防和减少呼吸管堵塞,对保持呼吸管通畅、保障气田水罐安全生产运行具有较强的指导意义。 

Abstract:

Objective The plugging resulting from scale precipitation and perforation due to corrosion easily occurs in breathing tube in sulfide-containing natural gas station, which has big potential risks for the security and environmental protection. Methods The scales obtained from five natural gas stations, such as TB101-X1 well station, were analyzed by SEM, EDS and XRD, the plugging main reasons were discussed according to the flash steam operating conditions of the breathing tube. Results High hydrogen sulfide accumulates in breath tube when the flow of flash steam is low velocity under the normal temperature and slight positive pressure. Accordingly, elemental sulfide is precipitated from high hydrogen sulfide. It is found that liquid water form from flash steam due to condense with the decrease temperature of flash steam with the extension of breath tube, more liquid water is carried by flash steam into breathing tube when the produced water tank keeps high level water. The corrosion of carbon steel tube occurs under the combination of hydrogen sulfide and sulfate and chloride ions to form corrosion scale, such as iron sulfide and ferrous sulfate and iron oxide. When the produced water is discharged from storage tank, negative pressure forms in the tank and oxygen is inhaled into the tank through breathing tube. Therefore, oxygen corrosion and elemental sulfide precipitation occurs through the reaction of oxygen and hydrogen sulfide. Corrosion scales and elemental sulfide are precipitated at the internal tube wall when the flash steam keeps low velocity. At earlier and medium stages, the scales are uneasily found. However, the scales will distinctly plug the breathing tube at the later stage, as resulted in the increase of pressure in the tank due to the accumulation of flash steam. Conclusion sThe technical countermeasures, such as replenishing breathing tube using natural gas when tank is under negative pressure, optimizing the material of breathing tube, adding gas-liquid separation assembly between tank and the inlet of breathing tube, can prevent and reduce the blockage of the breathing tube in essence, and have strong guiding significance for maintaining the unobstructed breathing tube and ensuring the safe production and operation of the gas field water tank.