Integration of Thermal Membrane Distillation Networks with Processing Facilities
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Thermal membrane distillation (TMD) is an emerging technology which is gaining an increasing level of interest in the area of high-purity separation especially in water treatment. It is driven primarily by heat which creates a vapor-pressure difference across a porous hydrophobic membrane. The integration of TMD with industrial processes offers several advantages. Excess low-level heat from the process can be used to drive TMD. This transfer of heat also reduces the cooling utility load for the process. Therefore, dual heat-reduction benefits accrue as a result of this heat integration. Additionally, process wastewater and utility water may be treated using TMD then recycle or reused in the process or sold to external users. This paper introduces a process integration framework from the thermal coupling of TMD networks and industrial processes. First, a three-parameter model is developed to quantify the water flux through the membranes as a function of heat and temperature. The model is validated using experimental data for direct-contact membrane distillation (DCMD). Next, the trans-shipment model for heat integration is extended to account for the coupling of the process and the TMD network and the need to optimize the extent of heating for the TMD feed. A discretization approach is used to linearize the thermal-coupling constraints. The mathematical-programming formulation is solved to identify the optimal heat integration strategies within the process and with the TMD network. The program also determines the optimal temperature to which the TMD feed should be heated and the system design and specification. A case study is solved to show the integration between a gas-to-methanol process and an adjacent desalination process. Three scenarios are considered: a standalone TMD network, TMD with thermal and water coupling with a process in an eco-industrial park setting, and TMD as part of the processing facility. 2013 American Chemical Society.