A New Targeting Method for Combined Heat, Power and Desalinated Water Production in Total Site

Abstract

Low-grade heat is available in large amounts across process industry from temperatures of 30 °C to 250 °C as gases (e.g. flue gas) and/or liquids (e.g. cooling water). Various technologies are available for generating, distributing, utilizing and disposing of low grade energy. Also, conventional desalination technologies are energy intensive and if the required energy hails from fossil fuel source, then the freshwater production will contribute to carbon dioxide emission and consequently global warming. In this regard, low grade heat source can be very useful to provide energy to the heat sink by upgrading low-grade energy (e.g. low pressure steam). The upgrade of low grade heat can be carried out by desalination technologies by recovering waste heat from various sources. The steam network of site utility system has a suitable potential for production of low grade heat. Estimation of cogeneration potential prior to the design of the central utility system for site utility systems, is vital to set targets on site fuel demand as well as heat and power production. So, a new cogeneration targeting model has been developed for integration of steam desalination systems and site utility of process plant. The new procedure to find optimal integration has been proposed based on new cogeneration targeting. In this paper, evaluation of coupling different desalination systems which includes multi-stage flash (MSF), multiple effect distillation (MED), membrane reverse osmosis (RO), and hybrid (MSF/MED-RO) to steam network of site utility system with have been considered. The integration of desalination systems to a low grade heat source has been performed using proposed cogeneration targeting method. In addition, a modified Site Utility Grand Composite Curve (SUGCC) diagram is proposed and compared to the original SUGCC. A steam network of process utility system has been considered as a case study.