A new algebraic tool for simultaneous targeting and design of mass exchanger network

Abstract

Process effluent recovery can be a potential source of revenue as well as an effective way to reduce the environmental footprint for industrial processes. In addition to sustaining business profitability, modern day industries have to fulfil their social responsibility by contributing toward environmental conservation and sustainable development. Mass (or materials) integration is a methodology for systematic and efficient reuse and recycling of materials in a closed loop within a mass exchange network (MEN). The integration of systems and processes promotes manufacturing synergy and minimises waste generation, disposal, and reduces the use of fresh materials and mass separating agents. Methodologies for MEN design and targeting include insight-based graphical and algebraic techniques as well as mathematical programming approaches. This study presents a new algebraic tool for simultaneous targeting and design of mass exchanger network that overcomes the limitations of previously developed mass integration approaches such as composition interval table (CIT), graphical composite curves (CCs) and grid diagram for MEN. The current CIT and CC cannot completely map individual rich and lean process streams, or individual process and utility streams. Hence, the mass separating agent (MSA) targeting results cannot be used to simultaneously design the MEN. Although pinch-based tools have been established for MEN design, the procedure is typically done in two sequential stages. The first stage involves MSA targeting using CIT. Once the targeting stage is completed the MEN design to achieve the MSA target is done using grid diagram. As the CIT cannot be used to visualise the MEN, repetitive stream-wise composition and mass load balance calculations have to be done in order to achieve the minimum MSA and number of mass exchange units. The aforementioned significant limitations of the conventional pinch-based approach have been overcomed by the newly developed segregated composition interval table (SECIT) proposed in this research. SECIT represents mass cascade along composition intervals for lean and rich individual streams. SECIT can help identify pinch point(s), determine utility targets and conduct SECIT mass allocation (SMA). The SMA can be converted to a SECIT network diagram that represents the MEN in terms of mass exchange quality and quantity, on the interval composition scale. Economic analysis study showed that the total capital cost target for MEN based on the newly developed SECIT is USD 752,539. This total capital cost target agrees with those obtained using conventional composite curves. However, sensitivity analysis study carried out using various minimum composition differences showed an optimal total cost of USD 448,945 and was found at minimum composition difference of 0.0001. Furthermore, sensitivity analysis study based on selection of materials of construction showed that 303 stainless steel type is the best material of construction for the newly SECIT network design. Four case studies, including an industrial application had been presented to demonstrate the validity and advantages of the proposed approach. This study shows that the SECIT and segregated network design can be an essential blend of algebraic and graphical visualisation tools for simultaneous MEN targeting and design of simple and complex processes and for retrofit cases involving threshold problems, stream splitting and multiple pinches.