Search

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. [ABSTRACT FROM AUTHOR]

In order to gain a knowledge of the heat emitted from a variety of sources at the blind heading of an underground gold mine, the present study conducts an in situ measurement study in a blind heading within the load haul dumps (LHDs) that are operating. The measurements can provide a reliable data basis for the setting of numerical simulations. The results demonstrate that the distances between the forcing outlet and the mining face (denoted as Zm), as well as the heat generation from LHDs (denoted as QL), has brought significant impacts on the airflow velocity, relative humidity, and temperature distributions in the blind heading. Setting Zm to 5 m could achieve a relative optimal cooling performance, also indicating that when the LHD is fully operating in the mining face, employing the pure forcing system has a limited effect on the temperature decrease of the blind heading. According to the numerical simulations, a better cooling performance can be achieved based on the near-forcing-far-exhausting (NFFE) ventilation system. [ABSTRACT FROM AUTHOR]

In view of the accidents such as rock mass breakage, roof fall and coal slide in coal mines, polyurethane/mesoscopic fly ash (PU/MFA) reinforcement materials were produced from polymethylene polyphenylene isocyanate (PAPI), the polyether polyol, flame retardant, and MFA using stannous octanate as a catalyst. 3-Glycidoxypropyltrimethoxysilane (GPTMS) was grafted on MFA surface, aiming to improve the mechanical properties of PU/MFA composites. The analyses of infrared spectroscopy and compression resistance reveal that the GPTMS can be successfully attached to the surface of MFA, and the optimum modification dosage of GPTMS to MFA is 2.5 wt. % (weight percent). On this basis, the effect of GPTMS on the mechanical properties of PU/MFA reinforcement materials during the curing process was systematically investigated through a compression test, a fracture toughness test, a three-point bending test, a bond property test, and a dynamic mechanics analysis. The results show that the compression property, fracture toughness, maximum flexural strength, and bond strength of PU/MFA composites increase by 21.6%, 10.1%, 8.8%, and 19.3%, respectively, compared with the values before the modification. Furthermore, the analyses of scanning electron microscope and dynamic mechanics suggest that the coupling agent GPTMS can successfully improve the mechanical properties of PU/MFA composites because it eliminates the stress concentration and exerts a positive effect on the crosslink density and hardness of PU/MFA composites. [ABSTRACT FROM AUTHOR]