Cleaning pipes that have restricted flow due to deposits and other internal buildup can improve flow characteristics and significantly reduce energy costs associated with pumping.
Fort Pierce, Fla., Utilities Authority had two 16-inch diameter wastewater force mains connecting a pumping station on one side of the Indian River with a treatment plant on South Hutchison Island 3,000 feet away. Average flow to the plant is 6 mgd. Both of the mains had been in service continuously for some 20 years and were exhibiting the classic signs of reduced service capacity, including increased discharge head pressures and significantly more pump run time.
Prior to their cleaning, which was done using established poly pigging pipe cleaning procedures, the average discharge head pressure for all four pumps serving the lift station was over 31 psi. Upon completion of the cleaning the average discharge head pressure had been reduced to 22 psi.
The project reduced energy consumption of the system by more than $8,300 a year, yet nothing was done to the system other than clean it. No pumps were upgraded or changed, no modifications to valve or piping were done and no changes in operating procedures were required.
“Our main goal was to carry more flow over to the treatment plant when necessary,” said Vaughn Weaver, Supervising Engineer at Fort Pierce. “The energy savings was just an added benefit.”
When evaluating the current capacity of any pump-oriented piping system, one method is to check the ratio of energy expended, in kilowatt hours, with the volume of gallons pumped. By developing a historical record of pump performance, operators can compare the performance of a system today with its prior capability.
The chart above uses hypothetical figures similar to readings collected from operating systems. It shows how energy usage can climb as a piping system ages. It is also an indicator of energy savings possible if the system were restored to its 1990 productivity levels.
Many factors can contribute to a decline in a systems efficiency. Pumps wear with use, system configurations are modified or expanded and piping systems can suffer infiltration and inflow. However, common to many systems is their propensity for getting dirty with the resulting reduction in their capacity and efficiency. This condition is sometimes not considered when attempting to restore a system to its maximum flow capacity.
A proven method for rehabilitating dirty piping systems is to clean them using poly pigs, which offer a variety of options which can be adapted to the particulars of a given system and its contents.
Available in more than 40 styles, shapes and functions, poly pigs can clean pipes ranging in diameter from a half-inch to 12 feet. At an average inline velocity of three feet per second, they can travel through a mile of piping in approximately 30 minutes. Poly pigs can successfully navigate valves, fittings and multidimensional sections of piping.
A common misconception about the use of poly pigs is that they work as plows, pushing in front of them all the material they are removing from the system. Poly pigs, properly selected and applied, create kinetic energy surges in the pipe which suspend the removed material, incorporate it into the flow and allow the flow in the piping to actually carry and transport the dislodged material out of the pipe.
Another common myth is that if all the adhering material on the pipes interior wall is removed it will increase the leakage rate in the system. There is no evidence to support this thesis. Deposited, adhering or accumulative materials in a piping system are not sealants and their removal does not cause leaks.
Cleaning a piping system with poly pigs is a relatively simple application. Access and egress points are established by modifying, if necessary, the existing piping. A series of pigs are sequentially introduced into the system and then propelled through the piping using the normal flow in the system.
