Reliability issues in the design and operation of process utility systems

Abstract

Traditional operation optimization is effective to enhance the energy efficiency of a utility system for given operating scenarios. Total operating cost will be saved, but the penalty cost caused by utility system failures cannot be considered. Optimal operating conditions from traditional optimization might have less flexibility to respond to utility system failures or maintenance and might result in a high penalty cost. In practice, it is not unusual that a unit (boiler, gas turbine, steam turbine) could fail unexpectedly, and lead to an interruption of utility supplies. If an interruption occurs, processes will need to operate at partial load or even to be shut down due to insufficient energy supply. Even though there are standby facilities that could start up in several hours, the penalty cost could still be very high during the response time of utility systems. Safety implications might demand that the system be designed to operate under all possible circumstances. A balance between operating cost and penalty should be achieved for the minimum overall total cost. To obtain the true cost, an analysis of system reliability, availability and maintainability (RAM) is essential. Moreover, not only the operating conditions should be optimized, but also operating strategies should be selected properly, e.g. cold standby, hot standby, load-sharing, etc. A novel optimization methodology has been developed to systematically minimise overall cost by considering utility system failures, maintenance requirements and different operating strategies. Maximum overall site profit will be obtained through advanced optimization with RAM analysis. Copyright ? 2011, AIDIC Servizi S.r.l.