Energy Integration of Multiple Effect Evaporators with Background Process and Appropriate Temperature Selection

Abstract

Multiple effect evaporators (MEEs) are energy intensive equipment. Often the focus is on minimizing the energy consumption of MEEs as a standalone system, rather than that of the entire plant. In this paper, process integration techniques are applied to integrate various stages of a MEE with the background process. To identify various energy conservation opportunities, the MEE is represented as a Grand Composite Curve (GCC) and integrated with the GCC of the background process. Change in utility consumption in the first effect, due to energy shift (in the GCC) between various effects, is determined in this paper. It is proved that for the minimum energy requirement all effects should be pinched. Using these mathematical results, a methodology for optimally integrating the MEE with the background process is developed. Furthermore, additional energy may be conserved by appropriately selecting effect temperatures. A methodology for appropriate selection of effect temperatures is also proposed in this paper. Applicability of the proposed methodologies is demonstrated through a case study. It is observed that 9.8% energy can be conserved by properly integrating an MEE with the background and an additional 25.87% of energy can be conserved by selecting optimal effect temperatures.

Optimal Temperature Selection for Energy Integrated Multiple-Effect Evaporator System

“…For same vapor flow rate and same first effect temperature, the second effect gets shifted away from pinch by a small amount γ, where γ is liquor flashing. At this point, two important propositions are made, as proposed by Sharan and Bandyopadhyay (2016b).…”

“…Higa et al (2009) studied how the number of MEE effects and vapor extraction affects the utility requirement for the integrated system. Sharan and Bandyopadhyay (2016b) proposed a criterion for optimal selection of MEE effect temperature in presence of background process to maximize the energy saving for the integrated system. With optimal temperature selection, additional 25.9% energy saving was observed.…”

Energy optimization in parallel/cross feed multiple-effect evaporator based desalination system

“…5). For the minimum energy consumption, all effects of MEE should be pinched [24]. In order to pinch all the effects a new variable dE nÀ1 is introduced.…”

“…In a recent handbook [23], various applications for process integration are explained. Process integration techniques can also be used for integration of MEE with the background process [24]. Process integration technique came into existence in late 1970s [25].…”

“…It was initially used for targeting the utility requirement for heat exchanger network. Linnhoff and Flower [26] developed an algebraic method, called Problem Table Algorithm [24] represented MEE in the form of GCC and developed mathematical results to minimize the energy consumption of MEE. Recently, Walmsley et al [28] demonstrated that significant energy may be conserved by appropriately integrating vapor compression system with MEE using GCC.…”