(679g) Optimal Design of Aging Systems: A-Frame Coolers Design Under Fouling
Concentrated solar power (CSP) plants are typically located in regions with high solar incidence but limited water availability (MartÃn and MartÃn, 2013). The large cooling needs, as any other thermal facility, represent the strongest link between water consumption and power production (DOE, 2018). A frames are a special type of air coolers that allows decoupling the water âenergy link in power plants. However, these systems consume up to 10% of the power generated in the facility to power the fans. The design of such units has typically been carried out based on rules (Krogen, 2004). Furthermore, A-frame units are located in open air and fouling, in particular, particle fouling is an important issue for their operation and performance. Fouling does not only affect the heat transfer coefficient, but deposit also block the cross sectional area, generating an additional pressure drop across the system (Pu et al., 2009; Sarfraz and Bach, 2016).
In this work we present a general methodology for the simultaneous optimal design and operation of units or processes whose yield is affected by aging or performance decays. We propose a parametric programming design procedure to determine the design and the cleaning/maintenance schedule. We use it for the design of A-frames under fouling conditions.
A detail equation based model for the units developed including mass and energy balances, design equations for the geometry and pipes layout, , the fan power curves, heat transfer coefficients, etc. and the aging process characterized. A two-stage procedure is proposed. First, the unit is optimally designed for the worst case scenario, just before maintenance. In a second stage, a multiperiod problem is solved for the optimal the operation of the unit over time including cleaning costs. The methodology is applied to A-frame dry cooling systems under fouling conditions, where fouling affects the pressure drop and the global heat transfer coefficient. Due to the sigmoidal deposition profile and assuming cleaning costs, the optimal cycle time is 8 yr. This design allows reducing the energy required to around 4% of the energy produced by the concentrated solar power plant. It is a promising result that can be affected by plant layout and ground availability.
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