Effect of Pipe Diameter and Inlet Parameters on Liquid CO₂ Flow in Transportation by Pipeline with Large Height Difference

• Main Authors: Wei Lu, Hao Hu, Guansheng Qi
• Format: Article
• Language: English
• Published: MDPI AG 2019-10-01
• Series: Processes
• Subjects: coal mine; liquid co₂; pipeline with large height difference; safe transportation; limit flow; pipe diameter; optimum inlet temperature and pressure
• Online Access: https://www.mdpi.com/2227-9717/7/10/756

Fire prevention and extinguishing and CO₂ sequestration in coal mine gob require continuous transportation of liquid CO₂ in pipelines with large height difference (from ground to underground). However, the temperature and pressure variation of liquid CO₂ in pipelines with large height difference is still unclear, which hinders the design of a liquid CO₂ pipeline transportation system. The influence of pipe diameter and inlet parameters (temperature and pressure) on the variation of temperature and pressure of liquid CO₂ along the 1000 m vertical pipeline was studied in this paper. The study found that for each pipeline diameter considered there existed a range of flowrates where safe flow conditions could be ensured, at which no phase transition occurs throughout the length of the pipeline. When the transporting flow is larger than the maximum limit flow, phase transition occurs dramatically, which will lead to a sudden drop in temperature and pressure. When the transporting flow rate is lower than the minimum limit flow rate, phase transition of CO₂ occurs slowly along the pipeline. According to the requirement of underground fire prevention and extinguishing for transporting flow rate and the economic cost of the pipeline system, the optimum diameter is 32 mm, and the corresponding safe transporting flow range is 507−13,826 kg/h. In addition, when the inlet pressure is constant, if the inlet temperature is too high, phase transition of CO₂ occurs dramatically at the entrance. For a 1000 m vertical pipe with diameter of 32 mm, when the inlet pressure is 14 bar, 16 bar, 18 bar, 20 bar, 22 bar, 24 bar, the corresponding maximum allowable inlet temperatures are −30 °C, −26 °C, −23 °C, −19 °C, −16 °C and −13 °C, respectively. This research has significant guidance for safety transportation scheme of liquid CO₂ from coal mine surface to underground.