Bharat Petroleum Corporation Limited’s (BPCL) Mumbai Refinery is a versatile and productive refinery in India. The refinery processes about 12 million metric tons in 61 different types of crude, making it one of the most flexible refineries in India. In 2011, BPCL embarked on an aggressive refinery modernization project and optimization of the Diesel Hydrodesulfurization Unit and Hydrogen Generation Unit, both of which involved the implementation of Advanced Process Control (APC) strategies. Multiple operating units were part of the modernization project including crude distillation, vacuum distillation, naphtha stabilizer, hydrogen generation, hydrocracker unit (HCU) and lube oil separation.

Benefits

As summarized below, the Honeywell Profit Suite software solution and APC strategies resulted in tangible and intangible benefits for the refinery.

Diesel hydrodesulfurization/hydrogen generation units:

  • Reduced methane slippage variation
  • Higher refinery optimization because of reformer skin temp inferential
  • Less variation in product diesel sulfur resulted in the reduction in the feed heater’s fuel gas requirement
  • Steam reduction in diesel stripper caused by reduction in product diesel flash (inferential) variation
  • BPCL documented an overall reduction in fuel gas and steam usage that resulted in significant financial benefits to the operation

Refinery modernization project

The implementation of APC strategies and software resulted in significant reduction in variations in key parameters.

In addition, BPCL and Honeywell audits showed that cost reductions were realized in the Crude, HGU, HCU and Lubricating Oil Base Stock (LOBS) units.

Challenges

Petroleum refinery processes are interactive in nature, and precise control is needed as product properties and process conditions change. Profitability in terms of feed throughput and preferential product optimization is also subject to multiple constraints. Some of the requirements of BPCL included:

  • Increasing the throughput of the crude unit and hydrocracker unit
  • Improving the stability of column profiles
  • Maintaining reformer steam-to-carbon ratio and temperature profile
  • Maintaining first and second stage reactor temperature profiles
  • Maximizing production of liquefied petroleum gas (LPG) and heavy diesel

Controlling conversion in the hydrocracker was another challenge because LOBS feedstock quality and quantity is dependent on it, and a large dead time exists between the hydrocracker unit’s first stage reactor and final waxy yield in LOBS.

The crude distillation column is designed for hot reflux, and overhead condensation takes place in two phases. This makes the column pressure and reflux drum level control particularly challenging and is a prerequisite for smooth APC functioning. The pressure control becomes critical in the event of water ingress or crude quality change.

The hydrocracking process depends on the quality of the feedstock and the relative rates of two competing reactions – hydrogenation and cracking – which are nonlinear. Preventing hydrogen venting turned out to be another challenging task.

Solution

BPCL used deployed engineering services and software to design, implement and maintain multiple input/output (MIMO) APC applications in various refinery units. These included crude distillation, vacuum distillation, naphtha stabilizer, hydrogen generation, hydrocracker and lube oil separation. The software was based on the patented Robust Multivariable Predictive Control Technology (RMPCT).

In addition to conventional advanced control strategies for maximizing feed throughput and product quality, additional areas of improvement were explored to optimize the processes using RMPCT and inferential technology. Some examples include:

  • Light and heavy kerosene and aviation turbine fuel property inferentials were developed.
  • A crude oil density analyzer feedback was used in crude column control models for better prediction in crude change scenario.
  • An inferential for vacuum residue penetration index was developed for monitoring the same during bituminous crude processing.
  • In the hydrocracker application, viscosity index and percentage unconverted oil predictions were developed to suit the LOBS feed requirements.
  • Viscosity analyzers were used to maximize waxy and dewaxed products.
  • Furnace pass balances were implemented at crude and LOBS units where multiple-pass furnaces are used. The pass balance applications were combined with upstream column level control and furnace outlet temperature optimization strategies.
  • Dynamic product sulfur inferential was done as part of the DHDS APC project for optimization. Based on the high accuracy of the inferential prediction, the same was also used in the blending optimization solution.

The controller and sensor combination provides significant process control and optimization benefits by increasing throughput, product yields and product quality in highly interactive industrial processes. In addition, users benefit from greater flexibility in operations and in meeting their process control needs while maintaining robust and safe control.

Through the APC project at BPCL, Mumbai improved the dynamic control of the DHDS units and achieved monetary benefits. These results were accomplished through the joint efforts of the BPCL and Honeywell project and engineering teams. The inputs and innovations delivered by the BPCL operational and technical teams were instrumental in overcoming the challenges.

Following the engineering and installation of the advanced control systems, comprehensive training, commissioning and startup services resulted in a successful and timely project conclusion.

Perry Nordh, P. Eng., is a senior marketing manager responsible for advanced control, optimization and monitoring at Honeywell Process Solutions. He focuses on delivering advanced solutions that help manufacturers combine workflow and technology, and has implemented advanced process control (APC) projects, designed software, and managed projects and products. Nordh began his career as a process operator while he completed a degree in electrical engineering at the University of Calgary. He is a registered professional engineer in Alberta, Canada.