Data-Driven Robust Optimization for Steam Systems in Ethylene Plants under Uncertainty

Abstract

In an ethylene plant, steam system provides shaft power to compressors and pumps and heats the process streams. Modeling and optimization of a steam system is a powerful tool to bring benefits and save energy for ethylene plants. However, the uncertainty of device efficiencies and the fluctuation of the process demands cause great difficulties to traditional mathematical programming methods, which could result in suboptimal or infeasible solution. The growing data-driven optimization approaches offer new techniques to eliminate uncertainty in the process system engineering community. A data-driven robust optimization (DDRO) methodology is proposed to deal with uncertainty in the optimization of steam system in an ethylene plant. A hybrid model of extraction–exhausting steam turbine is developed, and its coefficients are considered as uncertain parameters. A deterministic mixed integer linear programming model of the steam system is formulated based on the model of the components to minimize the operating cost of the ethylene plant. The uncertain parameter set of the proposed model is derived from the historical data, and the Dirichlet process mixture model is employed to capture the features for the construction of the uncertainty set. In combination with the derived uncertainty set, a data-driven conic quadratic mixed-integer programming model is reformulated for the optimization of the steam system under uncertainty. An actual case study is utilized to validate the performance of the proposed DDRO method.

Energy and Environmental Assessment of Steam Management Optimization in an Ethylene Plant

“…Industrial steam networks are often complicated systems of interconnected pipelines with steam sources and consumers connected to several steam pressure levels [30,31]. Managing such systems requires suitable decision-making tools and sufficient flexibility, which is usually provided by CHP and process steam drives that can be alternated with electrodrives [32,33].…”

“…On the other hand, decentralized steam production in production units is rarely carried out on purpose; residual heat content of material streams or flue gas from refinery furnaces is an almost exclusive heat source for steam production [40]. Among these facilities, ethylene plants (Steam Crackers, SC) are examples of deeply energy-and process-integrated units, combining high-pressure steam production in convection sections of pyrolysis furnaces and dedicated steam boilers [33,41,42]. Produced steam is expanded in large steam turbines driving key process equipment [43].…”

Process Drive Sizing Methodology and Multi-Level Modeling Linking MATLAB® and Aspen Plus® Environment

“…Efficient steam production, and its transport and use for both process heating and polygeneration purposes, has been targeted on various complexity levels in numerous recent studies [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. Starting with techno-economic studies optimizing the efficiency of a single equipment unit [24,27,30,34,35], through steam consumption optimization in a single production unit [25,32,38,39], and cogeneration potential exploitation [19,33,36,40,41] to total site heat and power integration [20][21][22][23]28,33,37,42], the goal is always to reduce operational expenses, improve steam system stability, and decrease fuel consumption in industrial plants. Steam system topology and the impact of pressure and heat losses from steam pipelines on optimal cogeneration system sizing and operation has been addressed in several papers [22,37,...…”

“…Process steam drives are important steam consumers in heavy industry [20,31,34] and play a significant role in the design and operation of complex steam networks. The most common driven equipment includes compressors, pumps, and fans (blowers) [34,38,47]. The steam turbines used can be of simple condensing, backpressure, or of a combined extraction condensing type [36].…”

“…Steam consumption is influenced by several factors that include the actual steam inlet parameters, steam discharge pressure, actual turbine revolutions, as well as the shaft work needed, which varies according to the process requirements. Process compressors driven by steam turbines are standard equipment of ethylene production and gas processing and fractionation plants [38,47], and they are also frequently used in compression heat pump-assisted distillations [48][49][50][51]. Thus, they are deeply integrated in the process.…”