Multiple-resources targeting using water-energy nexus cascade analysis and mathematical modelling

Abstract

Energy and water are two valuable resources that are mainly utilized in all sectors, from residential consumption to industrial processes. As conservation of resources are crucial, optimisation of energy and water system is becoming important. Pinch technology is an outstanding methodology and well known for its simplicity among the various targeting techniques. Previous targeting problems which are solved using the pinch analysis only focused on optimisation of single resource which may lead to under-sizing of system, as systems may rely on one another to operate. The water-energy nexus cascade analysis is introduced with the purpose to concurrently target both water and energy system. A case study involving a residential community comprising of 50,000 household unit with daily electricity demand of 343,750 kWh and water demand of 150,000 m3 is adapted. An integrated gasifier fuel cell is used to meet electricity demand while a water treatment plant is used to meet clean water demand. The results show the highest difference of 9.1% of the system capacities compared to methodology using single resource targeting method such as electric system cascade analysis. Sensitivity analysis is also performed to study the significance of capacity differences if higher water or energy conversion rate is imposed. Nevertheless, water-energy nexus cascade analysis, similar with other pinch and cascade analysis, it lacks the capability to consider other variables such as cost in its analysis. As such, a mathematical model is developed to provide a more holistic approach to the targeting problem. It‘s revealed that using the mathematical modelling, the capacity of the system is larger. The resulting cost of the system is MYR 516.65 million. Apart from identifying the optimal capacity of the system, the study concluded that the higher the interdependency of resources, the differences becomes more significant. Therefore, when analysing system that shows an inter-dependent nature, it is important to consider both resources and target them simultaneously to prevent the system from being under-designed.