Deciphering Refinery Water System Design and Optimization: Superstructure and Generalized Mathematical Model

Abstract

The up-to-date approaches to optimizing water systems only include fresh water, regenerated water and wastewater and ignore other types of water in refinery, i.e., desalted water, deaerated water, circulated cooling water, steam with different pressure levels and condensate water. Therefore, the existing mathematical model for water system optimizaiton is not directly applicable for the optimization of practical refinery water systems. To overcome the limitation and bridge the theory and application, we first presented a generalized model of water-using processes including multiple types of water and a general superstructure for the optimization of refinery water system. The superstructure consists of water-using processes including multiple types of water in the main production units (i.e., crude oil distillation, fluid catalytic cracking), water pretreatment systems (i.e., fresh water station, desalted water station, steam power station) and wastewater treatment system. The flow rate balance equations for those components of a refinery water system and the correlation for all types of water are formulated. The replacement ratio of altered type of water is introduced in the flow rate balance equations for water reuse/recycling and it avoids the imprecise data extraction of limiting water quality for the inlets of water-using processes. We presented two mathematical models with different objective functions (minimum flow rate of water resource (Scenario 1) and minimum partial annualized cost (Scenario 2)). The proposed models are applied for the optimization of the water system of a large-scale refinery in China. Results show that the water system with a minimum flow rate of water source can be obtained in Scenario 1. In Scenario 2, the profit of water conversation for five strategies cannot offset the investment cost of added pipelines, and their actual replacement ratios are zero. It leads to an economic and simpler water system with slightly higher flow rate of water resources.

Optimal Targets of Two Parallel Regeneration Recycling Water Networks

“…Zhang et al 20 optimized the water network in steel plants with a mathematical programming method. Deng et al 21 established a water network superstructure and optimization model applicable to oil refineries. Hansen et al 22 proposed a mathematical method and applied it to water networks in petrochemical enterprises.…”