74 / 2023-06-06 12:14:35

Effect of working fluid temperature on energy dissipation characteristics of liquid ring vacuum pump in coal mine gas drainage

Liquid ring vacuum pump; Energy dissipation; Working fluid temperature; Vaporization loss; Suction capacity

Liquid ring vacuum (LRV) pump is safe and reliable in coal mine gas drainage, but its high energy consumption and low efficiency has become an urgent engineering problems to be solved. In this regard, the energy dissipation mechanism of LRV pump is revealed in this paper from the perspective of working fluid temperature variations, elucidating the effect of temperature on pump parameters, such as suction capacity, the loss rate of working fluid vaporization, and the power loss. A new energy dissipation model considering temperature, suction capacity, and working fluid vaporization rate was proposed. The results shows that, as the working fluid temperature increases, the suction capacity rate decreases, and the vaporization rate of the working fluid increases. In addition, the ratio of working fluid vaporization, gas heating, and convective heat transfer of the outer pump wall increases, while the proportion of the energy consumption of working fluid heating decreases. In this study, the 2BV6131 LRV pump operating at a speed of 1500 r/min, a suction pressure of 45 kPa, the heating dissipation and vaporization of the working fluid, gas heating, and the outer wall convective heat transfer significantly changed from 78.8%, 6.6%, 3.9% and 10.7% to 22.1%, 38.7%, 9% and 30.2%, respectively, as the inlet temperature increased from 15℃ to 45℃. For the low fluid inlet temperature, the energy dissipation is primarily due to the rise in working fluid temperature; for the high fluid inlet temperature, the energy dissipation is primarily attributed to the working fluid vaporization. The proportion of wall heat dissipation and heat dissipation of gas heating is relatively small at any temperature.

Furthermore, based on the energy consumption model, a steady-state temperature prediction equation for the LRV pump was established, revealing that the working fluid flow rate and fluid inlet temperature have a significant impact on the working fluid temperature inside the pump. With the increase of the working fluid flow rate, the operating efficiency of the LVR pump first increases and then decreases, and the fluid inlet temperature gradually stabilizes after a significant decrease. This result indicates that the flow rate of the working fluid should be adjusted to its maximum at the same negative pressure during cooling. Further adjustment can be achieved by lowering the inlet temperature of the working fluid. The working fluid temperature in the pump decreases as the inlet temperature decreases. However, the working fluid dissipates more heat at a lower inlet temperature, leading to a higher cooling cost.

Finally, the variation in operating temperature of the 2BEC87 LRV pump was analyzed on site, and the dissipation of useless work was evaluated. When the actual operating power of the pump is 820 kW, with an inlet temperature of 30°C, an inlet flow rate of 10 m³/h, and an operating temperature of 40°C, the energy dissipation components are as follows: isothermal compression, working fluid heating, working fluid vaporization, gas heating, and convective heat transfer of the outer pump wall are 308 kW, 116.7 kW, 308 kW, 76.8 kW, and 10 kW, respectively. If heat pump cooling and waste heat recovery technology is used to cool the pump, with the inlet temperature lowered from 30°C to 5°C and the inlet liquid flow rate increased to 20 m³/h, the operating temperature of the pump will decrease from 40°C to 23.7°C. At the same time, the suction flow rate increases by 5.4%, resulting in an increase of 16.8 kW in useful power. Additionally, it is possible to extract 437.5 kW of thermal energy from the working fluid.

These findings demonstrate that the adoption of heat pump cooling and waste heat recovery technology is an effective approach to cool the LRV pump and improve its efficiency.