Reliability analysis of Torino Sud district heating system

The system consists of two heat production plants (for a total of 621 MW). a branched closed circuit transportation network, a distribution network and heat exchange substations. AEM wants to modify the district heating system anticipating a growth of user connection; for this reason different system solutions were studied. The object of this study is to evaluate the better solution according to a cost-benefit analysis. The costs are represented by the necessary investments to realise each change; the benefits are represented in terms of reliability growth for Torino Sud district heating system and the decrease of the consequences (user out of service) in case of faults in the system. Then availability and expected number of failures of the system were determined via a fault tree analysis related to the top event "no heat to user for t>1 hour". The consequences of faults for each macro-component of the system were defined as a function of the users out of service and a risk-map of whole system was made. Finally new availability analysis were made analysing four different solutions for the system in order to find the best one. The results of the reliability analysis of the system in the present configuration are satisfactory: the availability is in a range of 97.36% and 99.73%. The mission time is 1 year (8760 hours of continuous operation) and the expected number of failures for a year is in a range of 0.98 and 9.81.