Hydrogen and energy savings using heuristic allocation of mass exchangers in process synthesis: Technical analysis

Abstract

For our works, Mass Exchangers (MEs) are membrane equipment that exchange some component between two streams in a countercurrent arrangement. In previous works these were proposed to use them (with the goal of hydrogen recovery, energy saving and waste minimization) at different stages of the hierarchical decision procedure for process synthesis by Douglas: at an early design stage, when deciding the recycle structure of the process (resulting in considerable changes in the process structure); or at a final design stage, before deciding the mass and energy integrations of process streams (resulting in minor changes in the process structure).The heuristic allocation of MEs was used independently at both design stages in previous works, with the goal of comparing with other design alternatives reported in the literature that use membranes in the conventional configuration (one feed stream and two exit streams; retentate and permeate). In contrast, the present work compares the results of using MEs, when they are used individually at both design stages, and when they are used jointly at both design stages, in different configurations. For the case study example (the HDA Process), the use of a ME at an early design stage reduces the fresh hydrogen consumed by 3.37%, and the recycle compressor power by 4.09%. The use of a ME at a final design stage reduces the fresh hydrogen consumed by 31.64%, but it does not reduce the recycle compressor power. The joint use of the MEs at both design stages reduces the fresh hydrogen consumed by 14.54%, and the recycle compressor power by 2.91%.The joint use of MEs at both design stages retains the principal benefits of its use at early and final design stages (energy saving and hydrogen recovery, principally), so when both a reduction in the fresh hydrogen consumed and in the recycle compressor power is desired, it is the most appropriate option.