optimise the maintenance outage time of process units. The MNLP model is used to optimise the refinery unit shutdown schedule around the separate integrated chemical plant shutdowns. The main analysis steps are: Divide the total shutdown schedule into time periods. Define the units to be shut down for maintenance. Determine unit shutdown durations (times). The problem involved five time periods, each with daily durations of 7, 7, 31, 7, and 7 days, totalling 50 days. A base plan was established, which included process unit outages during each period. Inventory requirements for critical intermediate stocks were also included. The model then optimised the refinery unit shutdown timing relative to the base plan for shutdown and restart. The solution summarised in Table 3 provides a continu- ous shutdown schedule of an optimised schedule for the refinery units, solving for the days required for each unit and shutdown time related to the chemical plant shutdown. Note that the refinery shutdown periods can overlap, with maintenance occurring simultaneously. The optimised case was validated by running five alternate starting point cases. The optimised turnaround schedule improved profits by 5.91 hundred million yuan ($844k) over the scheduled outage. Schedule optimisation of a typical refinery (MINLP model) Case highlights: GROMS can establish a variable-time multi- cycle scheduling optimisation model based on the arrival sequence of crude oil to optimise the schedule-based pro - duction plan. The scheduling optimisation model is a var- iable multi-period scheduling optimisation based on the monthly refinery production plan model, combined with scheduling events such as crude oil receiving, crude oil tank transfer, and crude oil processing. Time variables and dynamic constraints are added to the model, with the time periods divided according to crude oil receipts. The variable multi-cycle scheduling optimisation uses ‘maximum enter - prise’ as the objective function, meeting the processing and tank scheduling requirements. The scheduling optimisation model has two parts: the refinery module and the configuration or scheduling mod - ule. The refinery module is a multi-period model according to the crude receipt timing. The configuration module con - nects crude oil unloading from the ship, crude oil scheduling in the tank farm, and refinery processing. The modules are processed together to determine optimum tank utilisation and maximise process profitability.
Marginal benefit of imported oil
Name
Marginal benefit
Break-even price
(yuan/ton)
(yuan/ton) 5,518.03 5,499.61 5,064.06 4,960.10 4,840.90 4,843.11 4,898.05 5,067.03 5,227.32 4,741.63 4,729.57 5,107.03 4,581.87 4,713.76 4,562.77 4,729.27 4,591.51 4,632.47 4,363.47 4,842.19 4,474.67 4,624.95 4,414.14 4,350.89
Clov Blend (CLV)
547.50 545.95 443.04 201.43 158.78 142.61
Saxi (SAX)
Saturno (STN)
Lula (LUL)
Roncador Light (RCL)
Sururu (SRR) Iracema (IRM) Murban (MEB)
78.34 34.13
Midland WTI Crude Oil (WTI)
0.00 0.00 0.00
Sapinhoa (SPN) Mostarda (MOS)
DSW (WTC) Búzios (BUZ) Kole L (KOL) Atapu (ATP)
-44.81 -118.63 -126.31 -137.73 -145.09 -154.02 -309.92 -323.41 -352.84 -362.19 -424.55 -425.56 -431.80
Sangos Blend (SGB)
Hungo (HNG)
Arabian Light (SAL)
Djeno (JNO) Forties (FOT)
Arabian Medium (SAM)
Nemba (NMB)
Upper Zakum (UZK)
Oman (OMN)
Table 2
This case example uses: Import of five crude oil ships in July. According to ship timing, the refinery model is divided into six periods (planning period 01-06). August is regarded as the planning period 07, and the monthly model in September is regarded as the planning period 08. Intermediate materials and unprocessed crude oils in each period are transferred to the subsequent period through inventory. Note: The length of the planning period 01-06 is a time variable, and only the time range is set in the model. The specific time length is optimised. The optimised schedule reports the start and stop days, and represents optimal operations in each steady-state period. Other events could be added to the problem, but this is a simple example of schedule optimisation for crude oil receipts.
Unit shutdowns – optimised schedule of unit outages
Units 3# CD
Days of shutdown
Explanation
1 2 3 4 5 6
34 35
Stop 6 days later and start 5 days earlier than chemical units Stop 7 days later and start 3 days earlier than chemical units
2# Hydrocracking
2# Coker 1# VRDS
44r
Stop 1 day later than chemical units
35.5 34.5
Stop 5.5 days later and start 4 days earlier than chemical units Stop 5.5 days later and start 5 days earlier than chemical units
4# Dies hydrotreating
Alkylation
45
Synchronise with chemical units
Table 3
91
PTQ Q2 2025
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