Optimal allocations of area margins and spares to accommodate HEN cleaning schedules

Due to fouling in one or more heat-transfer unit, the target temperatures of process streams in a heat exchanger network (HEN) may not be achievable after a sufficiently long period of operation. To circumvent this practical problem, a given HEN design should be modified to accommodate online cleaning operations via proper allocation of area margins and spares. Specifically, the candidate units for incorporating margins can be first identified on the basis of sensitivity analysis. The potential locations of additional auxiliary heaters/coolers and bypasses can then be determined according to the heat-load loops and paths embedded in HEN so as to facilitate compensation of the removed duties during defouling. The optimal design refinements and also the spare-supported cleaning schedule can be generated by solving a mathematical programming model formulated on the basis of a superstructure. A simple example is presented in this paper to illustrate the proposed modeling procedure and to demonstrate the feasibility of this scheduling approach.