PTQ Q1 2023 Issue






Heavy naphtha



Crude oil

FD vapour







Flash zone





Sour water


Long residue



Figure 2 Schematic of proposed crude oil processing scheme

the PFCI scheme, and to the flash drum in the FDI scheme. Depending on the crude oil processing scheme, the desalted crude oil/PFC bottom/FD bottom streams are routed to an ADC-fired furnace for partial vaporisation. The light naph- tha from the PFC is routed to the naphtha stabiliser column, whereas the FD vapour is routed to the ADC either at the flash zone or near the kerosene draw. The partially vapo- rised crude oil is routed to the ADC's flash zone. The vapour from the flash zone is separated into distillate products, namely light naphtha (LN), heavy naphtha (HN), kerosene, light gas oil (LGO), and heavy gas oil (HGO). The distillate products are processed in their respective side strippers to remove lighter components. The stripping steam is used at the ADC bottom to recover the diesel range material from the liquid falling to the ADC bottom from the flash zone. The long residue (LR) product obtained from the ADC bottom is further heated in a vacuum distillation col- umn (VDC)-fired furnace along with coil steam. The heated crude is processed in the VDC for its fractionation. Products like vacuum diesel (VD), light vacuum gas oil (LVGO), and heavy vacuum gas oil (HVGO) are generated in the upper section of the VDC, and slop and vacuum residue (VR) in the lower portion of the VDC. 1 Proposed common crude oil processing scheme CSIR-IIP has developed a new crude oil processing scheme to increase the ADC distillates yield and reduce energy consumption without compromising product quality (see Figure 2 ). Three main changes were proposed to improve energy and operating cost efficiency compared to existing schemes. 1 Firstly, process water is added to desalted crude to increase the extent of crude vaporisation for lighter and heavy crudes at lower temperatures. Water addition also provides the opportunity to generate process water vapour along with hydrocarbon vapour in the FD using excess thermal process energy. Additional vaporisation of crude oil due to water also reduces the flow of flashed crude to the downstream HEN and ADC-fired furnace. The second change includes FD vapour superheating to reduce the solubility of lighter hydrocarbons with long

residue (LR). The third includes routing of superheated FD vapour to the stripping section of the ADC to exploit its stripping effect to reduce the demand for ADC bottom stripping steam. These changes provide opportunities to maximise the use of available low-level process thermal energy and replace ADC bottom stripping steam to reduce the CDU operating cost. In addition to energy savings, these schemes offer ways to increase the ADC distillate yield without increasing the severity of furnace tempera- ture, which may result in crude oil cracking and furnace tubes fouling, and without increasing the size of the ADC and water dew point in the upper section of the ADC. Techno-economic evaluation of proposed scheme Three cases were conceptualised to make a realistic com- parison and understand the specific benefits of the pro- posed scheme on existing conventional and FD intergraded schemes. The conventional, FD intergraded, and proposed schemes are represented by base case, FD case, and pro- posed case. The quality of distillate products was kept identical in all cases by keeping the same boiling range of products and ASTM (5-95) separation criteria. Since the demand and price of distillate products vary from refinery to refinery and from time to time, energy cost saving was selected as the economic basis. The LR flow rate was maintained close to the conven- tional scheme (base case) in FD integrated and proposed cases to capture the effect of innovative changes made in the crude processing scheme only on operating cost reduction rather than a change in the yield of ADC distillate products. During the study, it was observed that there is an increase in LR flow rate for the FD case compared to the base case for the same furnace coil outlet temperature and ADC bottom stripping steam. Therefore, the FD case was further represented by FD Cases 1 and 2. The ADC bottom stripping steam was increased to a value without changing the coil outlet temperature (COT) to obtain the base case LR flow rate value in FD Case 1. The fired furnace's COT was increased to the required value without changing the ADC bottom stripping steam


PTQ Q1 2023

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