Halcrow has developed an innovative optimization toolkit, aligned with the UKWIR Capital Maintenance Planning Common Framework (CMPCF) approach, for determining the optimal set of intervention options for an inter-dependent system using genetic algorithms based on whole life, cost benefit analysis. The optimal maintenance intervention strategy resulted in a cost saving of 4.85%.
Halcrow were commissioned by Bristol Water to determine an optimal set of intervention options for their water treatment works (WTW).
Optimal interventions are those solutions that maximize the net present value delivered by the asset over its whole life. In this approach, deterioration and failure analysis are used for predicting the performance of non-infrastructure facilities because of their ability to capture the time-dependence and uncertainty of the deterioration process, maintenance operations and initial condition.
The On Target Optimizer toolkit was applied to optimize the maintenance intervention strategy over a 10-year period for a water treatment works which contains 9 asset groups, including Abstraction, Pre Ozone, Coagulation, Clarification, RGFs, Bromate Reduction, Post Ozone, GAC, Chlorination, Phosphoric Acid, High-lift Pumping station as shown below. The required solution to the problem was an optimized mix of investment to ensure the serviceability of the works was maintained at the required level to ensure continuity of supply and acceptable water quality standards.
A spreadsheet tool was developed to carry out whole-life cost-benefit analysis in compliance with the UKWIR Common Framework. The main steps include:
- Application of the linear deterioration model to predict the number of failure events for each of the asset groups and the probability before and after the proposed maintenance intervention actions;
- Calculation of the capital costs for all the proposed maintenance intervention actions during the whole planning (intervention) horizon;
- Calculation of the failure cost (risk) for the loss of headroom (yield), loss of supply to customers, etc in the event of failure;
- Calculation of the difference of the operational costs, including repairs, for before and after the pro-posed maintenance intervention actions;
- Calculation of the net present value of the system cost for all the maintenance costs and failure coats for the entire planning horizon (10 years in this case) and whole life span of the asset (25 years in this case).
The On Target Optimizer has been implemented as a bespoke tool onto the cost-benefit spreadsheet to optimize the capital maintenance planning.
For this application, the optimal maintenance intervention strategy has been indentified which has a total cost of £140.94 million a further saving of £7.2million (4.85%) on the best strategy at £148.14million which was found by other means.