Long-Term Degradation-Based Modeling and Optimization Framework

Introduction

Energy engineering systems are degraded over time due to working environment. Degradation mechanism is an inevitable process during system operation that changes the physical and chemical properties of component materials. The degraded materials affect component efficiency and system will operate under less than optimal performance. Figure 1 presents system performance over operating time. As can be seen, performance deteriorates gradually as time passes due to degradation mechanisms (Sánchez-Silva, & Klutke, 2016).

Figure 1.

System performance over time

Performance deterioration affects the economics of energy systems engineering. Figure 2 presents the economic effects of system degradation in long term operation. As performance deteriorates over time, the output power and consequently the income of selling useful heat/power of the system decreases.

Figure 2 shows that the operating cost including fuel cost increases as time passes. System efficiency decreases over time due to degradation mechanisms. As a result, system consume more fuel to have the same output. Therefore, the fuel cost increases over operating time.

In addition, degradation mechanisms can cause system failure over time. The maintenance plans help to prevent system failure and the consequences of failure. As is shown in Figure 2, the maintenance cost is added to systems costs at maintenance intervals.

Figure 2.

The economic effects of system degradation in long term

Ageing is a significant factor in determining the remaining lifetime of components. Studying degradation mechanisms and ageing effects addresses potential problems of a plant and could help to improve plant efficiency and availability (Zhou, Serban, & Gebraeel, 2011).

The worth noting point is that the operating and environmental conditions significantly affects system deterioration rate. Figure 3 illustrates the performance deterioration over time at different operating conditions. As it is clear, performance deterioration rate changes with environmental and operational conditions. In other word, performance deterioration rate can be managed by controlling the environmental and operational conditions (Furtado, & May, 2004).

Figure 3.

Operating conditions effect on performance deterioration over time

Though, the degradation mechanisms are unavoidable, they can be controlled through a comprehensive understanding of operational and environmental effects on degradation and failure mechanisms. Due to a variety of reasons, the influence of operational conditions on performance deterioration process has not received enough attention. However, a two-step model can be proposed to consider the effect of operating and environmental conditions on performance deterioration. At the first step, system degradation mechanism rates are calculated as a function of operational and environmental conditions. The data flow of this step is presented in Figure 4. This step is known as degradation model.

Degradation model tries to model degradation mechanisms that are generally present in the system. Degradation is defined as a gradual and irreversible accumulation of damage that occurs during a system’s life cycle. Some degradation mechanisms can be observed and recorded based on their degradation signals which are condition-based signals from condition monitoring process. The degradation model attempts to characterize the evolution of degradation signals. Analysts by collecting detailed information about the degradation signals over time at different operating modes can obtain system degradation model.