PTQ Q2 2026 Issue

Optimisation of stabiliser column operation at low pressure

Case study on achieving zero-cost energy efficiency by reducing HP steam consumption without bottlenecking downstream sections or compromising product quality

Mohammad Sirajuddin, SK Shabina, Rajasekhar Varchasvi, Manoj Kumar Bhuyan, S Saravanan, and Indranil Roy Choudhury Research & Development Centre, Indian Oil Corporation Limited Srajan Gupta and Bandish Soni Mathura Refinery, Indian Oil Corporation limited

I mproving process energy efficiency is becoming more important as refiners strive to meet net-zero CO₂ emis- sions commitments by optimising fuel and energy con- sumption. This is particularly relevant for energy-intensive units such as the stabiliser column within an isomerisation (ISOM) section. The ISOM process upgrades the octane number of light naphtha fractions while simultaneously reducing benzene content (a hazardous air pollutant and a known carcinogen) by saturation, thereby reducing envi- ronmental pollution. During the isomerisation reaction, minor cracking gener- ates lighter C₁-C₄ components that must be removed from the desired isomerate product in a stabiliser column to meet product specifications. However, this separation requires high-pressure (HP) steam in the reboiler and varies with feed quality, column operating pressure, and temperature. Hence, improper operating conditions lead to inefficient HP steam usage and higher operating costs. Broadly, unit energy efficiency can be improved either by evaluating alternative process flow schemes, including revamp/retrofit options, or by optimising operating param- eters within the existing configuration while maintaining product quality. The latter offers a key advantage because

were conducted at different pressures, which require extra investment. As a final assessment step, a hydrodynamic feasibility was performed for the zero Capex case, which confirmed the feasibility of an optimised (reduced pressure) case. ISOM stabiliser section According to the flowsheet presented in Figure 1 , the feed to the ISOM stabiliser section (C-01) is received from reactor effluent. The stabiliser column separates the components such that the C₅+ fraction is drawn from the bottom of the column and sent to the de-iso hexaniser (DIH) column, while the top section consists primarily of lighter components (H₂S, C₁-C₄). These lighter components pass through the E-03 chiller for the removal of fuel gas (FG) and H₂S. The remaining liquid portion is partially refluxed into the stabi- liser at the top tray, while the rest is sent as feed to the liq- uefied petroleum gas (LPG) stripper column (C-02), which further separates lighter hydrocarbons (C₃-C₄) from fuel gas. The process scheme was configured in the Aspen HYSYS simulation platform using start-of-run (SOR) data as the base case, with the following major steps: • Data collection: Plant feed samples were collected for

it requires no additional capital expenditure (Capex) and can be implemented quickly during normal plant operation. The present work details this second approach to optimise stabiliser column operation without bottlenecking down- stream sections or compromis - ing product quality. To achieve this, a process simulation flow- sheet of the isomerisation sta- biliser section was developed and validated against actual plant operating data. Simulations were performed for optimising column parame- ters, which require zero Capex, and additional case studies

Fuel gas

E-02

AC-01

P top 20.82 P btm 21.29

E-03

Refrigerant

P top 20.72 P btm 21.00

From reactor euent

LPG stripper (C-02)

Stabiliser Feed

Stabiliser (C-01)

E-01

E-04

LPG

To deisohexaniser

Figure 1 Flowsheet of ISOM stabiliser and LPG stripper section

PTQ Q2 2026