Prioritization Model for Pipeline Improvements to Limit Increasing Operational Costs

Abstract

Water is needed for all forms of human development and is equally essential to most major industries. Most water today is transported by gravity. However, a growing volume is being conveyed through pumped pipeline systems that are consuming staggering amounts of electricity. Additionally, the cost of electricity is rising in most countries, increasing the cost of operations for municipalities and utilities that operate these water networks. There is significant need to review existing pumped pipeline systems to identify pipelines improvements that can be made to improve energy efficiency. These pipelines can be improved by hydraulic or operational changes to increase their operational efficiency. Decreased energy use will lower operating costs and reduce the environmental effects of electrical production. A pipeline improvement selection and prioritization (PISP) system was developed to evaluate a group of pipelines, determine the appropriate improvement option(s) for each, and prioritize the order in which the improvements should be implemented. The PISP system models hydraulic degradation and energy cost escalation to determine the baseline operating cost of the system over a long term (20 year) analysis period. The system then models the effect of five selected hydraulic improvements (foam swabbing, rigid pigging, intensive cleaning and scraping, rehabilitation, and total replacement) and eight operational improvements (eight different scenarios of limiting and altering the pumping hours to selected time periods) to determine the potential cost savings over the analysis period and the pipelines with the greatest savings are prioritized. The operational and hydraulic characteristics of the prioritized pipelines are then field tested to verify the results of the analysis and make a final recommendation for pipeline system improvements. The PISP system was applied to analyse nine selected pipelines from the City of Tshwane’s bulk water system. • The preliminary evaluation prioritized three pipelines that were in relatively poor hydraulic condition, and three pipelines that were likely to see significant cost savings from operational changes. • The economic evaluation found a potential savings of approximately R100 million for the analyzed pipelines over the twenty year analysis period. • It also determined that the Roodeplaat Raw Water Pipeline – supplying water to the Roodeplaat WTP – and the Roodeplaat to Montana Pipeline – conveying water from the Roodeplaat WTP to the Montana Reservoir – would have the greatest potential cost savings. • The final results suggest that utilizing pump scheduling a 12-15% reduction in yearly electrical cost can be achieved through operational improvements with minimal capital investment. With the addition of a reservoir upstream of the WTP and the expansion of the WTP’s clear water reservoir, the cost savings could be increased to the approximately 25%. • No hydraulic improvements to either pipeline resulted in a long term cost savings for the twenty year analysis period. However, a general inspection found two unnecessary strainers, the removal of which would result in an additional savings of an estimated R100 000 a year. The development of the PISP system highlighted the need to include potential additional reservoir storage to optimize pump system operation. The additional storage allows for the pumps to be operated only when the electrical cost is lowest. Building on these results is an important step in developing a complete system for optimal pumped pipeline operation.