Refining India 2023 Conference Newspaper

refining india 2023

Novel reactor for three-phase hydroprocessing applications

Vinod Kumar, Abdul Quiyoom, Pranab K Rakshit and Ravi Kumar V Corporate R&D Centre, Bharat Petroleum Corporation Ltd

Conclusions Hydroprocessing is typically carried out in a TBR and requires severe operating con- ditions. There are various disadvantages to using TBRs, such as high feed vaporisa- tion, high pressure drop, and high product inhibition. A novel reactor (CFR) has been conceptualised and studied in detail to overcome the drawback of the TBRs. It has been established that the CFR will result in higher conversion without any quench stream. The fruits of the tech- nology can be reaped in many forms per the requirements and concerns of the pro- cess, such as reduction in energy require- ments, reduction in gas-to-oil ratio, reduced pressure, and higher reactor throughput. The CFR is energy efficient, saving 15-20% of energy for hydropro- cessing applications. References 1 Meyers R A, Handbook of Petroleum Refining Processes . McGraw-Hill, 2004. 2 Murali C, Voolapalli R K, Ravichander N, Gokak D T, Choudary N V, Trickle bed reactor model to simulate performance of commercial die- sel hydrotreating unit, Fuel, 86, 1176–1184, 2007. 3 Carbonell R, Multiphase flow models in packed beds, Oil Gas Sci. Technol. 55, 417– 425, 2000. 4 Larachi F, Iliuta I, Al-Dahhan M A, Dudukovic M P, Discriminating trickle-flow hydrodynamic models: Some recommendations. Ind. Eng. Chem. Res . 39, 554–556, 2000. 5 Lappalainen K, Alopaeus V, Manninen M, Aittamaa J, Improved Hydrodynamic Model for Wetting Ef ciency,.PDF. 8436–8444, 2008. 6 Parihar P U, Ravikumar V, Kaalva S, Methods and Apparatus for Three Phase Contacting and Reactions in a Cross Flow Reactor, 33, 2018. 7 Yadav A et al., Corrigendum to Modeling of three-phase radial flow reactor for diesel hydro- treating, Chem. Eng. Sci. 257, 2022, 117713]. Chem. Eng. Sci. 268, 118429, 2023. 8 Yadav A, Roy S, Aijaz T, Modeling of three- phase radial flow reactor for diesel hydrotreat- ing. Chem. Eng. Sci . 257, 117713, 2022.

Hydroprocessing treats heavy hydrocar- bon feedstocks with hydrogen to cre- ate high-quality fuels in a heterogeneous, exothermic process. It involves hydrogen reacting with hydrocarbons to produce desired fuels and lubricants. This typically occurs adiabatically with temperature control through intermediate quenching. The conventional method employs a three- phase packed bed reactor known as trickle bed reactors (TBRs) under high pressure and temperature. This process removes hetero-atoms (S, N, metals), saturates unsaturated hydrocarbons (olefins, aro- matics), and cracks heavier molecules to obtain desired quality products. 1 During hydroprocessing, as reactions progress, hydrogen sulphide (H₂S) and ammonia (NH₃) accumulate, reducing hydrogen partial pressures and also inhib- iting the reactions (see Figure 1 ). Elevated concentrations of these compounds hin- der desulphurisation, denitrogenation, and other saturation reactions, affect- ing catalyst acidity and conversions. This often requires high-severity operation and increased catalyst inventory to meet qual- ity specifications. In the TBRs, a high gas-to-oil ratio is used, which leads to undesired vaporisa- tion of hydrocarbon feed and lighter prod- ucts during the reaction, 2 as shown in Figure 2 . In addition, a higher gas/oil ratio and longer mean flow path for gas leads to increased pressure drop. Further, gas phase hold-up increases along the length as gaseous products are generated. This results in inefficient utilisation, insuffi- cient catalyst wetting, and higher cata- lyst requirements for given throughput and desired product quality and yields. 3,4 Further, the increased residence time of intermediate products such as naphtha and diesel in the reactor leads to more gas production and excessive hydrogen con- sumption. Dry spots are also formed in the catalyst bed in the process, which leads to underutilisation of catalyst in the reactors. To ensure the desired property of treated hydrocarbon, the hydroprocessing con- sists of multiple stages to overcome ther- modynamic equilibrium, increasing the operational cost. 5 Cross Flow Reactor (CFR) The CFR is a three-phase gas-liquid-solid reactor with several advantages over con- ventional TBR.⁶ A schematic representa- tion is shown in Figure 3 . In CFR, liquid feed flows downward through the fixed catalytic bed. Gaseous components such as H₂S and unreacted H₂, from the cata- lytic reactions, flow in the radial direc- tion and are continuously removed from the catalyst bed, which limits the extent of product inhibition. As the gases must travel only the catalyst bed radius, the pressure drop across the bed is signifi-

100

600 Nm/m 400 Nm/m 200 Nm/m

0.8

0.6

0.4

0.2

0.02

0.04

0.06

0.08

0.1

300

320

340

360

380

Mole fraction of HS

Temperature (˚C)

Figure 1 Effect of H₂S concentration on relative desulphurisation rate

Figure 2 Feed vaporisation with temperature and gas-to-oil ratio 2

cantly reduced. Also, introducing H2 uni- formly across the length of the catalyst bed enables maintaining a high partial pressure of H₂ throughout the reactor. It also leads to an increased rate of hydroprocessing reactions and a reduc- tion in both catalyst deactivation and gas-to-oil ratio requirements. A patent US9914104 has been granted on the reactor technology. 6 Diesel Hydrodesulphurisation (DHDS) DHDS is a process in which H₂ is used for removing sulphur from the diesel stream

at high temperature (300-350 º C), high pressure (40–60 bar), and high gas-to-oil ratio (around 400 Nm³/m³). Application of CFR in the DHDS process has been simulated using an in-house-developed 2D mixing cell network (MCN)-based kinetic model 7,8 for an industrial-scale reactor. Figure 4 shows that when CFR is used, it maintains similar temperature profiles across the reactor length with- out using a quench. Moreover, it can pro- vide the same reactor outlet temperature (~370 º C), which is directly linked to the reactor conversions like TBR even when the gas inlet temperature is much lower (26 º C). This saves 15-20% of energy for gas heating, which proves the process is energy efficient.

Recycle gas

Liquid feed

380

370

360

350

CFR, TG = TL = 326 C CFR, TG = 300 C, TL = 326 C TBR, TG = TL = 326 C

340

330

Gas ow

320

Reactor length (m)

Liquid ow

Figure 4 Temperature profile for diesel hydrodesulphurisation process reactor

Figure 3 Schematic representation of CFR

Contact: dlcrdcsupport@bharatpetroleum.in

Decarbonisati n Technolo gy The transition to sustainable fuels & energy

August 2023 Decarbonisati n Technolo gy Powering the Transition to Sustainable Fuels & Energy

GEOTHERMAL ENERGY

RENEWABLE ETHYLENE

Powering the transition to sustainable fuels and energy

FUEL SWITCHING &THE HYDROGEN ECONOMY

CSS - THE VALUE CHAIN

decarb cover.indd 2

31/07/2023 12:41:58