In early 2017, Solvay noticed a significantly higher airflow differential between the two intake shafts. Airflow was higher than normal in the #2 Shaft, while the #1 Shaft had a lower than normal airflow. The higher than normal airflow results in an air velocity that could induce the two rope guided skips to be drawn together while passing in the shaft. Solvay approached SRK to provide conclusive evidence of the cause in airflow differential between the two intake shafts and a potential fix for the system.
The suspected cause of the difference was a heater induced ventilation pressure. Fresh air shaft heating at the mine is divided into two separate systems; #1 Shaft (men/materials), and #2 Shaft (materials w/ rope guided skips). Each of the air heating systems uses a forced draft supply fan and an indirect heat exchanger type air heater. The heat exchangers are supplied with hot condensate from the processing plant. The #1 Shaft heat exchanger had recently been replaced increasing the efficiency of the heat transfer between the heater coils and the passing airflow.
The primary concern was the #2 Shaft velocity in excess of 2000 ft/min. This can create a potential condition under which the skips being drawn together because of the venturi effect could collide when passing each other midway in the shaft. While on-site, airflow and psychrometric conditions were measured before and after the condensate flow to the #1 Shaft heater was modified. Before the change, the density of air at the bottom of the #2 Shaft was higher than the #1 Shaft. There was also a significant calculated “natural” ventilation pressure working with the direction of the #2 Shaft airflow and against the #1 Shaft. After the change in condensate flow, airflows were returned to normal conditions and a comparison of densities showed similar densities at the bottom of both shafts. The natural ventilating pressure difference between the shafts was reduced to close to zero.
The goal of the study was to quantify the reason for the imbalance in air velocities between the two parallel fresh air shafts. Because of the rope guided skips, minimizing the air velocity and maintaining it below 2,000 ft/min is critical for safe operation. The “natural” ventilation pressure operating between the two shafts was able to be quantified and a rationale developed to rebalance the condensate flow between the two shaft air heaters without modifying the blade pitch or rotating speed of the forcing fans. Solvay was pleased to have conclusive evidence for the cause of the airflow differential and to bring the #2 Shaft out of a potentially dangerous operating condition.
