Production of cryogens using wind energy for use in deep mine cooling and ventilation.

Abstract

This research work, named as ‘CryoVent’, was focused on determining the feasibility of using wind energy, to produce liquefied gases (cryogens) continuously in a safe approach that can be used for the cooling and ventilation of underground mines. The experimental work performed suggested that the continuous production of liquefied gases with variable input work is practical. The average specific power consumption for liquefaction of nitrogen in this work was 7.86 kWh/kg using the refrigeration produced by helium. This is ~20 times higher than that consumed by industrial scale gas liquefaction systems, but is practical for a small scale system. This specific power consumption could probably be lowered if the working fluid itself is liquefied. Analysis on wind speed variability and wind speed data synthesis were also performed which suggested presence of multi-fractal nature in wind speed data that represent the temporal variation. A new method developed to generate high sampling frequency wind speed data from available low sampling frequency wind speed data can have contribution in all sectors when there is a need of higher sampling frequency time series data for simulation/study purposes. The liquid nitrogen mass flow rate (kg/s) increased with increase in compressor motor frequency and also when operating at variable motor input frequency. However, the average compressor power consumption also increased compared to average power consumption during operation at standard motor frequency of 60 Hz. This was in a laboratory scale liquefaction system and needs to be tested in the large scale system experimentally. With 1 kg/s of liquefied nitrogen supplied, ~459 kWr of cooling power is available to cool the deep mine air which is at 30-400C. A volumetric flow rate of 0.062 m3/s of liquefied air can provide a cooling power equivalent to that provided by a volumetric flow rate of 4000 m3/s of atmospheric air, which is the requirement of some of the biggest mines in the world. The hydraulic wind turbine as proposed in this work can eliminate the system start-up issues following the calm period, which are typical concerns with the wind energy integrations. This research work has provided the required modeling and simulation results that are crucial in development of the full scale ‘CryoVent’.