PTQ Q1 2023 Issue

Properties of crude oils 1

Crude type API gravity

Light crude

Medium crude

TBP distillation curve

Liquid,

Temperature, ˚C

41.97

34.45

Light end analysis

vol%

Light crude

Heavy crude

Component

Vol%

47.10 84.09

72.26

Methane Ethane Propane

0.0000 0.0005 0.0025 0.0025 0.0075 0.0060 0.0111

0.0000 0.0001 0.0027 0.0020 0.0096 0.0086 0.0138

10 30 40 50 70 90 95

102.13 200.24 245.13 304.88 459.66 660.22 761.67

163.49 206.70 247.68 360.54 492.51 552.53

Iso butane N-Butane Iso-Pentane n-Pentane

Table 1

to obtain the base case LR flow rate value in FD Case 2. All previously mentioned cases were evaluated for lighter and medium heavy crudes. The physical properties are given in Table 1 . All cases were simulated using a well-proven commercial simulator (Aspen HYSY ). The Grayson–Streed thermody- namic model was used in the simulation to predict the prop- erties of the stream. 2 The hardware detail of the ADC and VDC were taken from the commercial refinery database at CSIR-IIP Dehradun. The same hardware details and oper- ating pressure values for the ADC were used in all cases. Similar distillates qualities were ensured by matching their 5% and 95% ASTM D-86 temperatures in all cases. The stripping steam, pumparound duty, and COT were fine-tuned to meet the distillates quality and LR flow rate in the FD and proposed cases. The minimum hot utility requirements to represent the ADC furnace duty were esti- mated using pinch analysis with the help of Aspen Energy Analyzer (AEA) software. The delta T min (DT min ) tempera- ture of 20°C was used to carry out pinch analysis. The steam price of 25$/tonne, furnace fuel price of 7$/MMBtu, furnace efficiency of 85%, and dollar conversion rate of 80 rupees were used for energy cost estimation. Results and discussion The cost of fired furnace fuel and stripping steam were included to estimate the total energy cost for all cases. Study results revealed a significant reduction in ADC fur- nace duty when the COT and stripping steam values are kept the same as in the base case, but at the same time the LR flow rate increases significantly. Therefore, there is a need for a significant increase in stripping steam for FD Case 1 and COT for FD Case 2 to reduce the LR flow rate value close to the base case. This results in an insignificant change in energy cost for existing FD-integrated schemes compared to the base case without compromising the ADC distillates yield. Moreover, there is potential to reduce the ADC bottom stripping steam by 80-100% in the proposed scheme com- pared to the base case, depending on the crude API and excess thermal energy available in the system. Overall, the proposed scheme reduces energy costs by 12-16% com- pared to the base case. This energy cost reduction leads to a monetary saving of ~32-45 Crores per annum for a

typical 10 MMTPA refinery. These savings are over and above the optimisation of HEN, which is typically achieved using pinch analysis. Further, the vapour flow rate in the ADC on the trays above the flash zone is lower than in the base case. This opens up an opportunity to increase the throughput of the ADC. There is a higher vapour rate than the base case in the stripping section trays. However, it is reported in the literature that the ADC stripping section generally suffers from a lower vapour rate, which leads to poor performance of the stripping section and its fouling. 3 Therefore, the higher vapour rate in the proposed scheme seems to be an advantage in improving the performance of the stripping section of the ADC. Moreover, in the pro- posed scheme, the HEN operating pressure and furnace crude volumetric flow rate are lower than the conventional scheme and equal to the existing FD processing scheme. This suggests that the proposed scheme retains the higher ADC distillate yield of the base case and lower HEN operating pressure and furnace crude volumetric flow rate of the existing FD cases. The similar topology of the proposed scheme ensures its implementation in revamp- ing existing CDUs and grassroots CDU designs to reduce operating cost and carbon footprint. References 1 Kumar S, Mhetre A S, Comparative techno-economic evaluation of potential processing schemes for petroleum crude oil distillation. Re- sults in Engineering , 14 (2022) 100480. 2 Errico M, Tola G, Mascia M, Energy saving in a crude distillation unit by a preflash implementation, Appl. Therm. Eng ., vol. 29, no. 8-9, 1642–1647, Jun 2009 18 3 Hartman E, White B, Maximising stripping section, PTQ Q3, 1-7, 2021. Sunil Kumar is Principal Scientist and Head of Modelling and Simula- tion, Separation Processes Division at CSIR-Indian Institute of Petro- leum, Dehradun. He hold M. Tech. in chemical engineering from Indian Institute of Technology, Kanpur and a PhD in chemical engineering from Indian Institute of Technology, Roorkee. Email: sunilk@iip.res.in Avinash Mhetre is Scientist, Modelling and Simulation, Separation Processes Division at CSIR-IIP Dehradun. He holds a M.Tech in chemi- cal engineering from Institute of Chemical Technology, Mumbai. Email: asmhetre@iip.res.in

PTQ Q1 2023