Optimal multiperiod planning of utility systems considering discrete/continuous variance in internal energy demand based on decomposition method

Optimal multiperiod planning methodology for utility systems is proposed co nsidering internal energy demand, which is formulated as a mixed integer no nlinear programming (MINLP) problem, The problem is decomposed into two lev els: the energy distribution network level as a mixed integer linear progra mming (MILP) problem, and the steam generation unit as a nonlinear programm ing (NLP) one. The internal steam demand is calculated from the first princ iple model, and the internal electricity demand is obtained from design dat a. For multiperiod operation with varying demand as a series of piecewise c onstant for utilities, the optimal configurations of utility pumps (UP) are determined. The objective function is comprised of the operational costs f or each period, transition costs and switch costs between periods. Total co st obtained from the proposed planning methodology has been reduced by 2.34 % compared with the planning result without considering switch costs betwee n periods and 3.15-9.14% compared with the result by Lee et al, (1998).