Hydrogen use is on the rise, fueled by such demands as more stringent motor vehicle emission regulations and an increase in per capita vehicle ownership globally. Energy conservation and renewability provided by hydrogen are also driving the growth of steam methane reformers required for its production. There are, therefore, attempts being made to ensure that the reforming process is as efficient, safe and cost-effective as possible.
While reformers represent a critical asset in terms of operation, safety and reliability, they are also one of the most difficult and challenging assets to maintain and operate. Given that reformers are the single largest consumer of energy within a plant, ensuring that peak reformer performance is mandatory.
Common challenges in a reformer environment range from difficulty in measuring and maintaining tube wall temperatures (TWT) to catastrophic tube failure. There are established TWT upper limits based on tube design temperature and high temperatures in the interior of the box cause tubes to expand. Creep damage, coke formation, tube failure and process flow problems occur when temperatures exceed maximums. When operated at just 20 °C (68 °F) over the design temperature, a tube’s lifetime may be cut in half. If temperatures are too low, production output suffers. It is also very difficult for operators to conduct measurements in extremely harsh environments where flue gas at the outer surface of reformer tubes is 1200 °C (2191 °F) and inner surface process gas ranges from 450 to 900 °C (842 to 1652 °F).
Temperature-related incidents include bulging, cracking, stress cracking, extrusion rupture, overheating and over-temperature operation. Twenty percent of incidents involve tube cracking; however, human error is the primary cause of catastrophic failure. Operators must understand reformer behavior, basic reformer construction, process flow, heat-transfer principles, background radiation, emissivity and cooling effects that occur by merely opening the peep door, and be capable of analyzing data and making rapid decisions in the face of upset within the reformer.
To help offset dangers to the plant and operators, there are standards that govern hazardous environments and atmospheres.
Temperature Measurements in Harsh/Explosion Prone Environments
CSA Group North American Certification Class 1, Division 2, Groups A, B, C, D; T4, the Near Infrared Borescope (NIR-B) 3XR is designed for use as a fixed installation, enabling real-time temperature monitoring and data collection in hazardous atmospheres. Early in 2017, AMETEK Land secured the CSA Certification for NIR-B 3XR, used in hazardous locations in both the United States and Canada.
CSA Class 1 approval covers hazardous locations where flammable gases or vapors in the air are present in sufficient quantities to produce an explosive or ignitable mixture. Division 2 covers locations wherein a classified hazard is not normally present, but is possible under abnormal conditions. The NIR-B 3XR is classified for gas groups A, B, C and D, temperature classification T4 and an ambient temperature range of negative 20 °C (68 °F) to positive 60 °C (140 °F) (CSA Certificate: 70080206).
This certification ensures that the NIR-B 3XR meets regulatory authority requirements at federal, state and local levels. The device had already garnered equipment for potentially explosive atmospheres (ATEX) and international electrotechnical commission explosive (IECEx) certifications, so the certification status indicates that the NIR-B 3XR can be used in nearly every geographic location. This makes it much easier for operators to specify a single technological solution for high-accuracy, safe, non-contact temperature measurement.
The NIR-B 3XR Thermal Imager
To meet the demands for greater reformer safety during hydrogen production, the ability to provide for continuous 24/7 monitoring is necessary. You can also monitor for refractory problems within the reformer: common areas for problems are peepholes, burners, man ways and penthouse roof floorings.
There are several ways to measure temperature in these settings; however, there are two that are the most common. Most plants rely on operators taking TWT readings with handheld pyrometers manually and on a limited schedule. These measurements are only spot readings and the operator might not always find the hottest area of the tube, which can lead to overheating. Many producers also have outlet temperatures that they monitor; the issue here is that once the outlet temperature gives an alarm of rising temperatures, the TWTs are normally above the maximum temperature set by the plant. To operate within an integrity operating window, there is a need for continuous TWT monitoring.
The opening of peep doors to take manual measurement creates enormous stress on the tubes. The door opening and the resulting cooling affect the accuracy of the TWT measurement. In addition, as the tube cools on the side nearest the peep door, the tube will move or bends towards the hotter side, causing stress on the tube wall. This could, potentially, cause damage to the wall.
In comparison, fixed thermal imaging optimizes continuous 24/7 temperature measurement, inserted into the reformer so that the end of the camera is level with the reformer wall refractory. The cameras are water and air-cooled, and yield more accurate and repeatable results.
The AMETEK Land NIR-B 3XR is a short wavelength radiometric infrared borescope imaging camera. It provides a high-resolution thermal image and real-time, highly accurate temperature measurements for steam reformer, cracker tube and furnace optimization and monitoring. It delivers accurate temperature measurements of the tube wall or skin and the refractory wall surface, measuring temperatures in the single range from 600 to 1800 °C (1112 to 3272 °F) based on wide dynamic range imaging technology. With a 90° angle field of view, multiple reformer tubes are imaged and measured simultaneously. Hot and cold areas, uneven heating and even damage can be easily identified, and corrections, when made, are viewable in real time.
Image processing software transfers up to 100 data points via Ethernet transmission control protocol/internet protocol (TCP/IP) to the distributed control system (DCS), recording streams of data in video or frames for additional analysis. Alarms are easily set and operators are provided real-time data necessary to identify issues and take corrective action.
Operator risk is also lower, as continuous remote data monitoring of the reformer allows them to work from a safe control room rather than within the hazardous reformer area.
NIR-B 3XR features include:
- High-performance water cooling system with low water flow requirements for low running costs
- Range of mounting options for simple installation
- NIR-B 3XR tip thermocouple that provides an alarm to remove the instrument to prevent damage if maximum temperatures are exceeded
- 90° viewing angle for thermal view of multiple tubes
- 640 x 480 resolution with 307,200 data points, extending asset life and maximizing efficiency
- Probe length range for proper fit during reformer installations
- Integrated air-purge design provides a clean lens, even in harsh environments while still consuming minimal instrument air
- Hazardous-area certifications
There are many benefits for NIR-B 3XR use. For example, the thermal imager response time of 0.14 seconds is 40 times faster than a traditional tube thermocouple. The speed increase allows the triggering of alarms when there is a sudden temperature rise. Operators can respond almost instantaneously, alleviating catastrophic events. The NIR-B 3XR prolongs reformer tube life, optimizes production throughput and reduces energy consumption.
Ensuring Productivity and Safety
Hydrogen production is a dangerous undertaking that involves extremely harsh environments. Accurate TWT monitoring is crucial to maintaining operations and providing for safety. Unfortunately, TWT is often overlooked until there is an incident. Although there are explosive dangers within this environment, the most common loss is one of productivity. A change of only 10 °C (50 °F) below design temperature, for example, results in a 1 percent productivity efficiency loss. A positive 10 °C (50 °F) error can result in a 25 percent reduction in tube life. Most often, operator errors lead to a temperature reading of 20 to 100 °C (68 to 212 °F) too high, which would have a dramatic impact on tube life. A shut down and tube change post failure can range between $200,000 and $500,000+ a day in production loss. A typical rebuild of a 400-tube reformer can easily exceed $7 million just for material—when you add in labor and lost production, this cost can double.
In comparison, some hydrogen producers are reporting a 2 percent increase in production while operating at a safe condition, within their integrity operating window, by using the AMETEK Land NIR-B 3XR thermal imaging solution. The NIR-B 3XR avoids catastrophic overheating/thermal shock events, provides input for improved temperature uniformity and offers potential for input to tube life consumption calculations.