Sep-2024

Enhanced reliability monitoring of SMRs using advanced data analytics (RI 2024)

Background and Problem Statement: Hydrogen, also termed the ‘Champagne Fuel for the energy transition’, is one of the most important and costly utilities in refineries and petrochemicals.

Sukant Dev, Rohit Kumar, Vikas Sharma, and Kaushalendra Kumar IOCL Mathura Refinery India
IOCL Mathura Refinery India

Article Summary

It is utilised for processes such as hydrocracking, hydrodesulphurisation, and hydrotreating of petroleum intermediates. Most refiners employ steam methane reforming (SMR) for hydrogen production, with the reformer furnace being the central component of the process.

A typical steam methane reformer is a fired furnace with rows of tubes containing catalyst through which feed is passed. The feed is a mixture of steam and methane, which converts to hydrogen in the presence of a catalyst and heat. Steam methane reforming is a highly energy-intensive process. For this, the reformer furnace is operated in the 900-1,000°C range. To endure such severe operation conditions, the tube metallurgy is made of special alloys with excellent creep strength, fatigue strength, oxidation resistance, and structural stability.

IOCL operates steam methane reforming-based hydrogen generation units at its Mathura Refinery (MR). The unit was facing operational bottlenecks and reliability issues. The capacity of the unit was restricted due to tube skin temperatures (TSTs) crossing the design limit above 70% plant load. Also, due to non-uniform firing, the furnace operation was imbalanced. Further, there were incidents of flame impingement on the tube, which resulted in reduced life and poor reliability of the catalyst tubes.

To ensure tube reliability and operational safety, a  TST  measurement is carried out. Unlike other furnaces, the TST measurement of the reformer tube is done manually using non-contact type infrared pyrometers due to the severe operating environment for the skin thermocouples of function. When using IR pyrometers for indirect temperature measurement, factors such as emissivity, sight path effects, and reflected radiation can contribute to errors in temperature measurement.

IR pyrometers capture all the radiation falling on their lens, including radiation emitted by the tube, radiation reflected by the tube surface, radiation reflected by the refractory walls, radiation due to the flames, and they display everything as the tube temperature.

This means that the actual tube temperature would be 900°C, but the pyrometer shows a temperature higher than 900°C. Proprietary technology for real-time thermal imaging of catalyst tubes is available in the industry; however, it might not meet the cost economics of Capex and plant outage for installation for all refiners.

Intelligent use of Tube Skin Temperature Data and Advanced Analytics
Background temperature correction model
IOCL MR has developed a furnace-specific model for background correction and obtaining true temperatures. The background correction model is specific to the constructional geometry of the furnace, has built-in formulae, algorithms, and procedures to generate corrected tube temperatures.

Field trials at varying plant loads were carried out to verify and improve the accuracy of the model. It was discovered that the actual tube temperatures, after background correction, were 25-40° lower than the uncorrected temperatures. Additionally, to validate the accuracy of the model, gold cup pyrometry was used as a benchmark. The results of the gold cup pyrometry confirmed an error in the uncorrected TST of 30-40°C, thereby affirming the accuracy of the background correction model.

With a TST margin of 25-40°C established, the plant capacity was safely increased, and TST was no longer limiting up to 84% plant capacity.

Data visualisation (heat map, burner management, and optimisation)
In the subsequent development, TST data was used to develop an advanced data visualisation tool. The thermal map of the reformer furnace was generated using the TST readings captured by the pyrometer.

With the thermal map, operators were able to see the exact visual profile of the furnace. They could identify areas of localised overfiring, tubes that were exceeding their design limits, burners causing flame impingement, and other crucial information that was previously not visible. Based upon the thermal map, the operators made adjustments to the burners and carried out optimisation.

With regular furnace optimisation, localised overfiring was eliminated, and we could achieve up to 90% production capacity.

Advanced reliability monitoring (utilisation of tst for near real-time creep assessment and fitness for service evaluation)
Utilising the tube skin temperature, stress-strain values from the Larson-Miller Parameter (LMP) curve provided by the tube manufacturer and following the procedures laid down in API 579, which is the API code for Fitness for Service (FFS), the creep damage and fitness for service evaluations for each tube are performed in near real time. The entire evaluation is automated within the tool.

So, the temperature of each tube is utilised to assess the daily health and reliability condition of each tube of the reformer, enhancing the reliability monitoring.

All three functions of background temperature correction, data visualisation, and reliability monitoring have been encapsulated in an in-house developed tool known as REFORM (Reformer Optimisation and Reliability Monitoring) Tool.

TST values are recorded directly using the REFORM Tool loaded on an Intrinsically Safe Tablet. Background correction takes place automatically to provide accurate tube temperatures. A thermal map is generated instantaneously, and the optimisation process is carried out if required.

The data is transferred to server, and reports are available on a dashboard hosted on the local intranet for operators of the next shift or anyone to view.

Benefits
The intelligent use of TST data and data analytics has resulted in the removal of bottlenecks in throughput (achieving 90% plant capacity utilisation without exceeding tube skin limits) with respect to tube skin temperature, more effective reformer furnace management (control of flame impingement and more optimised and balanced thermal profile of the furnace), and enhanced reliability monitoring (better understanding of the impact of everyday TST on tube reliability and enhanced tube life).

This short article originally appeared in the 2024 Refining India Newspaper, which you can VIEW HERE