New process arrangements for upgrading heavy oils and residua
Simulation studies reveal increased gasoline and diesel production from extra-heavy oil by means of RFCC and hydrocracking units with a mild hydrogenation process
SEPEHR SADIGHI, REZA SEIF MOHADDECY and KAMAL MASOUDIAN
Research Institute of Petroleum Industry
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In this article, we consider
the results of integrating residue fluid catalytic cracking (RFCC), hydrocracking (HCR) and hydroconversion (HRH). A target refinery was simulated and calibrated, then the HRH unit patented by the Research Institute of Petroleum Industry (RIPI) was added to these units. After validating Hysys-Refinery with actual and design data, four integration strategies were examined to increase the yields of gasoline and diesel. These cases, named simple series, series, parallel and residue upgrading, were compared to the base (designed) one. The results showed that by implementing the mentioned cases, the production yields of gasoline and diesel would increase considerably. For the best case — residue upgrading strategy — the yields of gasoline and diesel would increase to 6.98% and 53.96%, respectively, in comparison to the base case. Moreover, with this integration strategy, and no change in operating conditions, the bottom of barrel could lead to zero, while fresh feed flow rates and their impurities would remain constant.
The market’s demand for heavy petroleum products such as heavy oil is set to decline, while the demand for lighter, more valuable products such as gasoline and diesel is expected to increase. Projections of demand for refined products indicate that middle distillates (diesel fuel and jet fuel) will grow at the highest rate. Demand for diesel fuel is projected to grow by 2% per year worldwide.1 In many countries, the need for gasoline is a crucial subject, so any improvement in the refinery process to increase the yield of this product is welcome.
HCR and RFCC are the major processes to produce diesel and gasoline, respectively. Moreover, recently the HRH unit has been developed by RIPI2 to convert residue and heavy cuts to lighter products.
Hysys-Refinery is a simulation tool commercialised by KBC Advanced Technologies and AEA Technology-Hyprotech. This simulator has made significant advances in detailed representation of reactor sections. Mohaddecy and Sadighi3 have demonstrated the ability of this software to simulate the HCR and catalytic reforming units. Lee4 used Hysys-Refinery software to study the integration of FCC and hydrotreating units. The research was conducted in two steps. First, the simulation and calibration of the two units was carried out, and then the integration was performed. The results revealed that increasing the hydrotreating severity decreased the production of SOx and NOx in the FCC unit.4 Dean, et al, integrated FCC and HCR units to improve the conversion of residue to more valuable products in the gasoline range.5 A FCC unit was assumed as the upstream unit, and products above the gasoline boiling range were sent to the HCR unit. The HCR off-test stream was fed to the FCC unit, and the FCC cycle oil was desulphurised and cracked. The simulated integration scheme that was considered resulted in a 60% reduction in hydrogen consumption. Tallman, et al, integrated the FCC unit with a thermal cracking unit to maximise ethylene and propylene production.6
Initially, the target refinery with HCR and RFCC units was simulated using the HCR-Sim and FCC-Sim reactor modules available in the Hysys-Refinery simulator. For validation purposes, actual data for the HCR unit and design data for the RFCC unit were used. This validated case is termed the base case hereafter. The HRH unit was simulated in the Hysys-Refinery as a yield reactor, to satisfy the yields reported by the licensor. Finally, while keeping constant the feed quality and flow rate to the HCR and RFCC units, these units were integrated by various strategies to increase the yields of diesel and gasoline. The integrated cases that were considered are termed simple series, series, parallel and residue upgrading strategies.
The HRH unit is a liquid phase mild hydrogenation (at 60-100 atm and 400-500°C) process for upgrading extra heavy oil. The HRH process recently developed by RIPI produces higher valued products, which alternatively could be used as feedstock for refineries.7 The main objective of this process is the break-up of high molecular weight hydrocarbons to light and medium molecular weight products. This process is a novel method for upgrading heavy residue to lighter products. In the process, two types of reactions — namely, cracking and mild hydrogenation — occur simultaneously. The hydrogenation and operating conditions allow higher conversion without coking and excess polymerisation. The HRH process has high flexibility with regards to the type of feed and the amounts of sulphur and heavy metal contents in the feed. The process can eliminate all the heavy metals and almost 50% of the sulphur components in the feed. The main products are gasoline, diesel and FCC feedstock, and the designed yields for these cuts are 20, 39.6 and 30 wt%, respectively, on the basis of the fresh feed.
The base case considered in this study takes vacuum gas oil (VGO) from the vacuum distillation tower as the HCR’s fresh feed, combined with the recycle stream from the bottom of the HCR fractionation tower to make the combined HCR feed. The RFCC feed is composed of light vacuum gas oil (LVGO), heavy vacuum slops (HVS), heavy gas oil (HGO) and treated residue (TR). The TR stream is the result of hydrotreatment of vacuum residue, which removes it from the sulphur and metallic impurities, and thus makes it suitable as the RFCC feed. The RFCC unit’s product quality is directly affected by its feedstock quality. In particular, unlike in hydrotreating, RFCC redistributes sulphur into its products. Consequently, in all integration strategies, the quality of RFCC feedstock has been kept the same as in the base case. The block diagram and feed flow rates of the base case are shown in Figure 1 and Table 1, respectively. Both units have been simulated, calibrated and validated using the actual data gathered from the target refinery.8,9
Integration of RFCC, HCR and HRH units
Four case studies for the integration of the RFCC, HCR and HRH units have been surveyed. The main objective of integration is to increase the production yield of gasoline while maintaining the feed specifications of the RFCC and HCR units the same as in the base case. The HRH unit patented by RIPI is flexible towards a variation in feed quality, so the variation in the feed specification is deemed not important for this unit.
Simple series integration
The block diagram and feed flow rates of a simple series integration strategy are shown in Figure 2 and Table 2, respectively. The feed and product properties for HCR were the same as in the base case. The HRH unit takes the HCR off-test stream and the RFCC’s clarified slurry oil (CSO) as feed. The RFCC takes the LVGO, HVS, TR and HGO as feed.
The block diagram, feed and product flow rates of a series integration strategy are shown in Figure 3 and Table 3, respectively. The feed and product properties for HCR were the same as in the base case. The HRH unit takes some TR as well as the CSO, and also the RFCC unit takes the HCR off-test. The advantage of this strategy over the simple series is the direct feeding of the residue treatment unit into the HRH unit. In cases of deep catalyst deactivation or complete shutdown occurring in the residue treatment unit, the flow of untreated residue can be redirected to the HRH unit, and this unit is capable of removing heavy sulphur and metallic contamination.
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