Wednesday, October 19, 2011
Exhibit Hall B (Minneapolis Convention Center)
A mathematical programming approach is presented for the optimal planning of biocide dosing and maintenance scheduling in a seawater cooled power/desalination plant. These tasks are used to control the biofouling and consequently the heat losses in the heat exchangers, which are two of the main challenges when using seawater as cooling fluid. The model considers the biocide concentration decay in the network, the biofilm thickness dynamics as a function of the temperature and the biocide concentration, and the heat reduction as a function of the biofilm thickness. It includes constraints over the maximum allowed biofilm thickness and heat reduction. When using biocides (usually chlorine, because of its availability and cost) the residual concentration in the discharge is also an important issue because of its negative environmental impact; therefore, an end of pipe treatment system is considered to meet the environmental constraints over the residual concentration. The resulting model is a mixed integer nonlinear programming problem, which is solved using the GAMS software. A practical case study with a planning span of a year is presented for which several dosing policies were tested. The monthly dosing with a maximum of three treatments per year turned out to be the best option; this policy offers a good compromise between cost and operation flexibility, and reduces the number of plant shutdowns.