Emission Considered Scheduling for Crude Unloading, Transferring, and Processing

Petroleum refinery is a leading segment of the entire chemical process industry. It uses crude oils to produce various fuels such as gasoline, aviation kerosene, diesel, heavy fuel oil, and chemical raw materials such as naphtha and benzene. Because of the increasingly strict economic competitions and environmental regulations, refineries in one hand are eager to improve production solutions to leverage profitability margins in nowadays volatile market; on the other hand, they have to pursue cost-effective pollution prevention technologies to comply with more stringent environmental mandates, such as air emission requirements. Air emissions from refineries are significant and emission reduction in refineries is a very challenging task. It involves a large-scale complex manufacturing system, which consists of over 17 major facilities with more than 85 main operation units, and thousands of process streams. In such a large industrial system, air emissions could spatially scatter at many reactors, furnaces, and flaring facilities; and temporally occurs at any time. Thus, cost-effective emission-reduction strategies should neither depend on end-of-pipe approaches, nor focus on solutions for single units or subsystems. The major thrusts should focus on the comprehensively study of material, energy, and information exchanges within the entire manufacturing system, so as to identify the best solutions to the entire plant. Therefore, to optimally balance emission source generations and utilizations among the entire system might be the smartest way to reduce refinery emissions.

A concept of profitable emission reduction (PER) is proposed in this research, which has merits of economically attractive, environmentally benign, and technologically viable for air emission reductions in petroleum refineries. To identify PER strategies for refinery plants, a production scheduling model covers both front-end and refinery has to be involved. The key is to optimize the overall material and energy flows to make the plant net profit maximum, meanwhile to ensure emission source generations and utilizations to be smartly balanced. Other manufacturing constraints, such as operation specifications and inventory limits, should also be satisfied as well. Scheduling of front-end and refinery crude oil operations is an important part of petroleum supply-chain management.

In this research, a new methodology framework and a new general scheduling model have been developed for emission-considered crude unloading, transferring, and processing (ECUTP) system to achieve profitable emission reduction. The scope of the scheduling problem includes crude oil unloading from vessels to storage tanks at onshore berths, transfer of crude from these tanks to charging tanks, charging crude distillation units and further processing of crude inside the refinery, which includes crude distillation, cracking, coking, reforming, hydrotreating, product blending and component recovery. It also couples characterization and quantification of major air emissions from refineries, such as CO₂, volatile organic compounds (VOC), nitrogen oxides (NO_X), and particulate matters (PM). A general refinery process with more emphasis on air emission characterization and quantification will be introduced. The scheduling model is a large-scale mixed integer nonlinear programming problem (MINLP). The efficacy of the PER concept and the developed methodology have been demonstrated by different case studies.