Selection of the precise crude diet is very critical for a hydrocarbon complex as not only Economics, but long term strategy is linked with it. In several ways, this is directly related to the objective function of the project too. In the early days, Refineries were essentially designed for maximization of fuels and distillates. There too, the objective was different from country to country as the requirements of the nations was widely at variation. For instance, some countries preferred to maximize Gasoline and lighters, while others preferred to maximize Middle distillates i.e. ATF and Diesel. In India for several decades, the requirement was essentially to cap Gasoline and ATF, while maximizing LPG and Diesel. This trend of late has also been changing and the Refineries are now addressing maximization of LPG & first generation Petrochemicals, while diesel demand is moderating.  In current times, the requirements seem to be altering further, and while the diesel production continues to be moderate, the demand for Petrochemicals has been a priority and maximization of Olefins and Aromatics is emerging as the key Objective function.

All the above aspects have a direct bearing on the configuration of the plant. It also affects the size and scale of operations. Another important aspect is that the Objective function is required to be flexible, such that swings between light and middle distillates could be addressed appropriately, or alternatively the swing between the refinery products and Petrochemicals could be swung to take advantage of the changing market scenarios and cracks at any given point of time.

All these are subtle and important questions, which invariably contribute towards the formulation and finalization of Design basis of projects. The solutions to address these requirements always is an informed exercise, but one very critical aspect of the Project design lies in the choice of the crude that will have to be processed. This in itself is a challenge as it warrants a thorough deliberation between the type of crude API and the objective function.

In general, if the Intent is to bear flexibility in the plant and maximize LPG and Diesel, as is often the case in India, a sour: sweet mix of crudes can be preferred considering 50:50 or even 70: 30 ratio. More often, such fuel refineries are directionally driven to DCU+ Full conversion HCU configuration. If additional flexibility and swing is required between Diesel and Gasoline, one could consider a DCU+ Once through HCU ( 60% - 70% Conversion) + FCCU. If on the contrary, a Gasoline max Refinery is considered, one could conceive a DCU+ FCCU configuration or a CDU + RFCC or even a CDU+ ARDS + FCCU. However, if the Project favors High Gasoline + First stage Petrochemicals, the configuration may look more like DCU+ VGO HDT + Petro FCCU.

Crude selection for the Dream Project

The Dream Project address the following major objective functions:

1. A single train large Refinery throughput of 20 MMTPA to ensue world scale Aromatics and Olefin production.
2. Capped gasoline and ATF production and a distinct slant towards Petrochemicals.
3. Aromatic production capped in the complex to max capacity of 1.5 MMTPA of PX.
4. Ethylene and Propylene maximized.
5. No Butadiene production and preferably conversion of C₄ mix streams from Olefin and unsaturated LPG from PFCC and DCU to maximize production of Ethylene, Propylene and Aromatics.
6. FCC to be of high severity to ensure upwards of 20% propylene yield.
7. Check case for Zero LPG production.
8. An Alkylation unit capped to 1 MMTPA capacity for ensuring production of high quality gasoline. CCR raffinates routed to gasoline/diesel pools.
9. DHDT designed for cracking up to 35 % to minimize diesel and maximize petrochemical feed.
10. DCU capacity capped to 2.4 -3.0 MMTPA for two-chamber design, and processing of balance Vacuum Residue in Slurry Hydrocracker. VGO from Slurry Hydrocracker routed to PFCCU to maximize its capacity.
11. Aromatic extraction from PFCCU naphtha foreseen.
12. All off gases from DCU, PFCCU, Treated Saturated LPG (SR, PFCCU, DCU etc) to be routed to Olefin complex.
13. Typical feed to Cracker could be Off-gases, LPG, Propane from PFCC, Light naphtha, Heavy naphtha and Light Kerosene after meeting LAB, ATF requirement.
14. Hydrogen plant to be gas integrated.

To meet the above objective certain subtle considerations will have to be adhered to. To start with, since maximization of Petrochemicals close to 45% of the throughput and more, is to be targeted it is imperative, that the bottoms capacity is minimized without losing a very high degree of flexibility to swing the product pattern. This implies that the vacuum residue must be minimized for capped capacity of DCU, and reduced capacity of Slurry Hydrocracker.

One choice of crude that one could be tempted to consider is lighter crudes, which could minimize the bottoms significantly, and produce a lot of lighters for higher capacity of Petrochemical produce. This choice though, could be a little capex friendly, but could lead to loss of a lot of processing flexibility and consequently, swings in product pattern. Additionally this could make the crude sourcing also very restricted and constrained, which will have its own implications.

In view of the same, a more nuanced approach would be processing of AM:AL in 50:50 ratio to help establish a reasonable balance between Capex and Opex, while maximizing the Petrochemicals production to world scale capacities. Total Ethylene of upwards of 2.1 MMTPA, Propylene Upwards of 3.6 MMTPA and PX + Benzene about 2.5 MMTPA are addressed in the configuration, for a crude throughput of 20 MMTPA. Significant benefits of Horizontal integration can also be exploited by exploiting Ammonia production for Urea, Ammonium Nitrate, and Ammonium Sulphate in the complex.

Key Integration/ Design Features conceived

Crude Slate Shift (Sweet/Light Crude Blend):

1. 50: 50 Sour: sweet crude considered for significant impact feedstock economics and design basis across all primary distillation units. Optimizes the Sizes of VDU, DCU and SHCU, as Vacuum Residue would reduce.
2. Additional SR Naphtha Make is ensured with higher paraffin content, which is an excellent cracker feed.
3. Additional SR LPG Make is ensured which can provide additional feed to Cracker.
4. Overall SHCU Load & H₂ Intensity reduces, as the Slurry Hydrocracker is unloaded to heavy bottoms.
5. As overall light sweet naphtha increases as compared to heavy crudes, it requires less hydro treating than heavy sour fractions, overall specific hydrogen consumption per tonne of crude drops.
6. SR Naphtha from relatively sweeter crude offers a higher BMCI (Bureau of Mines Correlation Index) suitability and higher paraffinic ratio, improving single-pass ethylene yields in the Cracking furnaces.
7. Higher Kerosene yield is inherent to lighter 50:50 sweet: sour crude blend and enables higher feed to the Cracker.
8. DHDT conceived to shift to MHC Mode from Max Diesel to Max Naphtha through increased conversion up to 35% Mild Hydrocracker (MHC)  to generate Heavy/Light Naphtha additional feed for Steam Cracker.
9. Because of increased overall feed to Cracker the total Ethylene and Propylene yield increases. C₄ mix and Overall LPG also increases because of which correspondingly K- COT capacity also increases.
10. Light Sweet Crude additions and increased conversion in MHC reduces the overall diesel make in the refinery.

Off gases Integration from PFCC and DCU:

1. Dry Gas Routing: The raw Petro-FCC dry gas (containing methane, ethane, ethylene, and hydrogen) is routed to the olefin complex's shared Cryogenic Cold Box and De-ethanizer train after appropriate NOx treatment rather than being sent directly to the fuel gas header.
2. Hydrogen Co-Recovery: Along with Ethylene, this off-gas stream from PFCCU facilitates internal H₂ recovery in the Cold Box / PSA hydrogen recovery system of Olefin complex.
3. Fuel Gas Loss Control: High-efficiency sponge oil absorption and amine scrubbing are applied to off-gases to limit ethylene losses to the refinery fuel gas system.

Aromatics:

1. The CCR processing the Hydro-treated Heavy naphtha is restricted to a capacity of about 1 MMTPA of PX.
2. The Hydro-treated PGH from the Cracker is integrated downstream of the CCR for maximizing recovery of PX (max 1.5 MMTPA), Benzene and Light and Heavy Raffinates.
3. In addition, the Aromatics extracted from the PFCCU naphtha is also integrated with the Aromatic complex along with the Aromatic cut from K–COT to maximize Aromatic recovery.
4. Light Raffinates are routed to the gasoline blender and the heavier Raffinate is routed to the diesel pool ensure that that the pool specification are adhered to Euro VI levels.

With a proper crude blend and a subtle stream, integration approach the complex can ensure a very high total Petrochemical intermediates, which can be used to produce a variety of Polymers, Niche Petrochemicals, Chemicals and Fertilizer, Ammonium Nitrate /Sulphate.

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