An energy company’s process furnaces were experiencing excessive coking, leading to wasted energy and frequent downtimes for tube cleaning. After installing WIKA’s Tefracto-Pad® thermocouples, the energy company enjoyed longer run lengths between decoking cycles.
In oil refineries, furnaces play a critical role in several key processes, from the initial distillation of crude to the conversion of different fractions to produce cleaner, higher-quality fuels. The effectiveness of these processes depends on not only the quality and design of the furnaces, but also the quality and design of the temperature sensors in distillation columns and catalyst beds, at coil outlets, on furnace tubeskins, and other key locations.
Importance of Temperature Measurement and Control
There are important reasons for precise temperature control in furnaces, which typically operate at extremely high temperatures to convert and refine the feedstock.
Plant safety: With high temperatures come safety risks. Accurate readings help refineries prevent thermal runaway reactions and ensure that the coils’ temperatures are within safe metallurgical limits.
Energy efficiency: When the temperature is too low, chemical reactions are slower or incomplete. But when the temperature is too high, one result is excess coking. Since the coke layer acts as insulation, operators then must increase the firing rate to maintain adequate process temperatures. Both scenarios waste energy. Thus, precise temperature control optimizes fuel consumption.
Product quality: Temperature has a direct effect on the process media’s physical and chemical characteristics. Keeping the temperature within a specific range minimizes unreacted feedstock and undesirable by-products.
Asset lifecycle: Too-high temperatures reduce the lifespan of furnace tubes, measuring instruments, and even the refinery unit itself.
Regulatory compliance: Regulatory bodies set standards that specify temperature limits for the safe and efficient operation of industrial equipment, including fired heaters. Accurate temperature monitoring helps refineries avoid penalties and downtime.
Problem: Excessive Coking Leading to Excessive Downtime
A multinational energy company based in western Europe was having problems with delayed coker heaters in several of its refineries. Coke was forming too quickly, resulting in short run lengths before having to pause operations to spall and pig the furnace tubes.
Several factors determine the rate in which coke is formed and deposited. Low feedstock quality and uneven feedstock flow are two reasons, but excessive temperature is also a major contributing factor. Accurate temperature sensors would mitigate the issue by allowing the control room to keep temperatures within the optimal range.
The energy company was already familiar with WIKA products, having used them in the past. When our engineers learned that this customer was dissatisfied with its current tubeskin thermocouples’ performance and design, they met with the company’s representatives to fully understand the issue.
Solution: A Comprehensive Package of Custom Sensors and Installation
TC59-T Tefracto-Pad® tubeskin thermocouple assembly
After several more calls and meetings, WIKA recommended a complete solution:
- Tefracto-Pad® thermocouple assemblies made of Hastelloy X
- Engineering and routing (geometry of the loops) mineral-insulated cables in the furnace
- Field service with welders, installers, supervisors, and technicians who can customize the assemblies onsite
Tefracto-Pad offers high accuracy, quick installation
The customer was initially reluctant to adopt the Tefracto-Pad® since it was a new product and had not yet been field tested. However, various teams from the company were intrigued by the thermocouple assembly’s s unique advantages.
First, this patented instrument is highly accurate, proven by repeated testing at WIKA’s research and development facility in Greater Houston. A contributing factor to accuracy is that the Tefracto-Pad® is completely flame-neutral, thanks to a proprietary moldable heat shield and sheathed cable to protect the sensor from flame impingement and severe heat flux.
Second, the assembly is especially easy to install. Most skin points require welding the thermocouple’s hot end directly onto a bare tube or a butter-pad. Then a heat shield has to be aligned over the thermocouple and welded in place. This process is time-consuming, taking at least two hours for 2–3 welding passes and two separate liquid penetrant inspection (LPI) tests.
WIKA purposefully designed the Tefracto-Pad® for quicker installation. This innovative assembly features a large weld-pad already containing the thermocouple’s hot end, which fits precisely into the notch of our proprietary heat shield. Installation time is halved since the Tefracto-Pad® requires only one welding pass and one LPI test.
WIKA engineers made a convincing argument as to why the energy company should try the Tefracto-Pad®, and the customer gave the go-ahead for 60-plus units to be manufactured.
Complete customization and field service
Even the highest-quality sensors will underperform if they are not installed properly. For the customer’s peace of mind, a specialized team from WIKA’s Services division was in charge of the following:
- Job preparation – obtain permits, institute personnel and environmental protections
- Site preparation – clean furnace areas, install platforms and scaffolding, verify safety requirements are met
- Instrument installation – mount brackets, connect pipes and cables, prep tube surfaces, place and weld instruments in specified locations, conduct post-weld liquid penetration tests
Since some of the new connections required specific adjustments, WIKA offered onsite manufacturing of eight assemblies. This level of customization ensured a precision fit and optimal functionality with minimal wait times. Twelve technicians worked in two shifts over three days to complete the project. The customer then integrated the instruments with the control system.
At the time of this publication, more than 60 Tefracto-Pads have been in service for about a year, and the customer is very pleased with the new thermocouples’ performance.
WIKA, Smart in Sensing for Energy Companies
A leading provider of measurement solutions, WIKA designs and manufactures instruments that are found in refineries and chemical/petrochemical plants around the world. What’s more, the Tefracto-Pad® and other models of tubeskin thermocouple are made in our ISO 9001-certified facility near the Houston Ship Channel. Partner with WIKA USA for quality assurance, reliable field service, and quick turnaround times on the instruments your process facility needs to operate more safely and efficiently.
Product mentioned in this article
• TC59-T Tefracto-Pad® tubeskin thermocouple assembly