Understanding the temperature-viscosity relationship of sulfur is critical to ensuring proper pump operation. Sulfur melts at 119°C (246°F) and experiences a change of phase at a temperature of 158°C (317°F) beyond which its viscosity increases extremely rapidly over a small temperature range. This increase in viscosity or “caramelization” can quickly seize the submerged pump bearings and cause an overload trip of the motor.
Reliable molten sulfur pumping can be achieved by controlling the temperature
below the phase change limit. Maintaining saturated steam in the pump jacketing at a pressure of 35 psi will keep the sulfur at a good pumping temperature in the range of 138°- 148°C (280°- 300°F). This includes an allowance for a small frictional temperature rise that may occur when the sulfur passes through the pump. A steam pressure of 40 psi is recommended for cold weather and outdoor installations. Glycol is also often used as a heating medium in the pump jackets to control temperatures within the ranges specified above.
