Anti-Reflection Mechanism of the Coalmass under the Liquid Carbon Dioxide Phase Change Gas Explosion and the Experimental Study

The problems of high efficient coal and gas simultaneous extraction of the low-permeability and high-gas coal seams in deep mines are major problems that restrict the sustainable development of China’s coal industry. In order to solve the scientific permeability problem of the high gassy coal seams with low permeability under deep and complex geological conditions, a technology of liquid carbon dioxide phase change gas explosion for cracking and antireflection is proposed. The formation mechanism of the coalmass fracture circle resulting from liquid carbon dioxide phase change gas cracking coal is analyzed theoretically and a mathematical model within the range of fracture circle is established. Numerical simulation analysis shows that a blasting crushing zone with a radius of 1.0 m formed around the blasting hole. The radius of the secondary expansion zone caused by the explosion gas to promote coalmass formation is 2.0 m, and the limit extension length of the explosion fracture is 2.3 m. The gas phase change gas explosion is determined by the coal roadway driving face based on the gas content index and the analytical index of coal shavings to be able to reduce the pre-drainage time of coal roadway from 30 days to 15 days and 16 days. The comparison experiment also reaches a conclusion that the initial gas emission is increased by 3.7 times from the 100-meter borehole in the original coalmass after coalbed gas explosion anti-reflection. The results of the theoretical analysis are verified by underground experiments in the coal mine.

Combatting lime kiln ringing problems at the Arauco Constitución mill

The lime kiln at the Arauco Constitución mill experienced severe ringing problems requiring it to be shut down for ring removal every 3 to 6 months. The mill controlled the problems by blasting ring deposits off during operation with its existing industrial shotgun and a newly installed Cardox liquid carbon dioxide (CO2) cartridge system. Various ring blasting procedures were tested to determine the optimum ring location and thickness to blast; the optimum depth to insert the CO2 cartridge into the kiln; and the most effective blasting frequency and sequence to employ. The best strategy was found to be the weekly blasting operation that alternated between the liquid CO2 cartridge and the industrial shotgun, with the CO2 cartridge inserted into the ring mass, 20 cm (8 in.) away from the refractory brick surface, and the shotgun aimed at rings at about 28 m (92 ft) from the kiln discharge end. With each blasting event removing considerably more rings than before, it takes a longer time for rings to rebuild, allowing the kiln to run continuously between annual maintenance shutdowns with only a few short (< 4 h) downtimes for ring removal. This substantially reduces the costs associated with ring removal and lime replacement during unscheduled shutdowns.

Development of an Integrated Structure for the Tri-Generation of Power, Liquid Carbon Dioxide, and Medium Pressure Steam Using a Molten Carbonate Fuel Cell, a Dual Pressure Linde-Hampson Liquefaction Plant, and a Heat Recovery Steam Generator

Due to the increase in energy consumption and energy prices, the reduction in fossil fuel resources, and increasing concerns about global warming and environmental issues, it is necessary to develop more efficient energy conversion systems with low environmental impacts. Utilizing fuel cells in the combined process is a method of refrigeration and electricity simultaneous production with a high efficiency and low pollution. In this study, a combined process for the tri-generation of electricity, medium pressure steam, and liquid carbon dioxide by utilizing a molten carbonate fuel cell, a dual pressure Linde-Hampson liquefaction plant and a heat recovery steam generator is developed. This combined process produces 65.53 MW of electricity, 27.8 kg/s of medium pressure steam, and 142.9 kg/s of liquid carbon dioxide. One of the methods of long-term energy storage involves the use of a carbon dioxide liquefaction system. Some of the generated electricity is used in industrial and residential areas and the rest is used for storage as liquid carbon dioxide. Liquid carbon dioxide can be used for peak shavings in buildings. The waste heat from the Linde-Hampson liquefaction plant is used to produce the fuel cell inlet steam. Moreover, the exhaust heat of the fuel cell and gas turbine would be used to produce the medium pressure steam. The total efficiency of this combined process and the coefficient of performance of the refrigeration plant are 82.21% and 1.866, respectively. The exergy analysis of this combined process reveals that the exergy efficiency and the total exergy destruction are 73.18% and 102.7 MW, respectively. The highest rate of exergy destruction in the hybrid process equipment belongs to the fuel cell (37.72%), the HX6 heat exchanger (8.036%), and the HX7 heat exchanger (6.578%). The results of the sensitivity analysis show that an increase in the exit pressure of the V1 valve by 13.33% would result in an increase in the refrigeration energy by 2.151% and a reduction in the refrigeration cycle performance by 9.654%. Moreover, by increasing the inlet fuel to the fuel cell, the thermal efficiency of the whole combined process rises by 18.09%, and the whole exergy efficiency declines by 12.95%.