How to Monitor Temperature in Potentially Explosive Locations

In this report, all three of the cases cited required a safe method to digitally monitor temperature in potentially explosive operational environments. Selecting a certified intrinsically safe (IS) thermometer is therefore critical to safe and efficient operations and to prevent a disastrous fire or explosion. Further, regulatory agencies almost certainly require that all equipment and devices in any such hazardous locations must be IS-certified. Intrinsically Safe means a product used in a potentially explosive atmosphere was designed to be unable to produce sufficient heat or spark to ignite the atmosphere. Many processes in chemical, pharmaceutical, adhesive and other manufacturing facilities use flammable substances that can ignite which would result in devastating fires and explosions. The responsible managers need to assure themselves, their employees, and their companies that their processes are safe.

About Intrinsically Safe Thermometers and Data Collection

The options are limited when it comes to IS rated thermometers and even more so when data analysis is required. The problem is further compounded because wireless transmitters are challenging to certify as intrinsically safe. The energy required to transmit often exceeds the level deemed safe in a hazardous location.

One solution is to run long wires connected to temperature sensors within the hazardous area through an isolation barrier to points outside. This limiting solution requires fixed sensing points, thus restricting the monitoring location. There is also a safety limit on how far cables can be run within a hazardous area.

From a cost perspective, multiple long runs of specialty cable are expensive. From a safety perspective, the longer wire increases the inductance, and therefore, the energy that can be stored just in the wire itself. At some point, this exceeds the safe energy level, which could ignite a flammable vapor or gas. This paper presents three case studies where an industrial handheld IS thermometer with data analysis capabilities is required.

The Advanced Energy's TEGAM 921B IS single input thermocouple thermometer met the operational and safety needs in each case. It is UL/CSA/ATEX/IECEx-compliant, which makes it deployable worldwide. The certified intrinsically safe 921B was designed and approved for use in the continuous presence of flammable gases, vapors, and mists. The 921B features very high accuracy [±(0.04% reading + 0.3°C)] and supports eight (8) thermocouple types. The thermometer also includes built-in data analysis functions as it captures temperature measurements at a rate of three (3) readings per second. Real-time statistics are viewable on demand for MIN/MAX/AVG/RANGE/STDEV (standard deviation) and constantly updated until the user resets the functions by pressing the CLEAR button. This diagnostic information allows the user to analyze critical manufacturing processes on the fly for maximum efficiency and quality.

Case Study 1: Inconsistent Adhesive Application

On an insulation board production line, flammable solvent-based adhesive was not being applied with a consistent thickness causing product defects. Because the viscosity of the adhesive varies with temperature, it must therefore be maintained within certain limits or the application thickness will vary, which was happening. Unfortunately, the problem did not occur consistently, making it difficult to observe the conditions when a failure occurred. To give you an idea of the temperature ranges involved, the list below documents the 10 most common types of flammable adhesives with their temperature ranges. 

Adhesive	Storage Temperature (°F)	Use Temperature (°F)
Contact Cement	40-80	60-85
Neoprene adhesive	50-75	60-85
Natural rubber adhesive	50-75	60-85
Epoxy adhesive	40-75	70-85
Acrylic adhesive	50-75	60-85
Cyanoacrylate adhesive	40-75	60-85
Hot melt adhesive	100-150	250-350
Solvent-based adhesive	40-75	60-85
Water-based adhesive	40-75	60-85
UV-curable adhesive	40-75	60-85

Note that in all examples above, the storage temperature is lower than the production temperature. This led the production team to initially suspect the temperature regulation system in the reservoir that meters the amount of adhesive pumped to the applicator workstation. The production team inserted a TEGAM intrinsically safe immersion probe, connected to a 921B IS thermometer, into a port of the reservoir. The technician pushed the CLEAR button to reset the statistics collected by the thermometer to zero. The thermometer then began monitoring the system, taking temperature readings and updating the statistical data continuously. A technician was assigned to view the thermometer every 15 minutes and record the statistics, then reset the thermometer. Note, as a very low power device, the 921B can run for 2,000 hours on one set of 3AA batteries.

After two days of monitoring, another production fault recurred. The production team reviewed the data gathered by the thermometer to hopefully identify the cause. The specifications for the adhesive required its temperature be maintained within +/- 4°C. At each time check, the technician had recorded that the average temperature at the adhesive reservoir port was within 1°C and the range never exceeded 3°C. This validated the reservoir’s performance but did not identify the root cause of the failure.

The team next investigated the transport piping from the reservoir to the applicator station. As before, the team inserted the IS probe into the port in the piping system and connected it with the 921B. Alternatively, they could have clamped a surface probe to the outside of the pipe and connected to the thermometer. They reset the statistics on the thermometer (a one button press) to begin the monitoring process. After one hour of operation, the technician noticed that the average temperature was 5°C below the target and the minimum point was a full 10°C below the target temperature. This clearly indicated a problem with the transport piping. They addressed the problem in two ways. They installed better insulation on the transport system and moved the temperature regulation point closer to the applicator workstation.

Case Study 2: Liquid Natural Gas Freezer Operations

Operating companies that process and transport liquified natural gas (LNG) need precision temperature measurement and data capture over time. The following operational steps cover the initial intake of feed gas through to the final step of regasification. Each step requires stringent temperature monitoring and data analysis such as that available with the Advanced Energy's TEGAM 921B:

• Pre-cool the feed gas to about -40°C. This reduces the energy required to liquefy the gas. An IS thermometer with data capture capabilities is crucial at this stage. If the temperature falls too low, the gas may freeze and block the pipelines with potentially disastrous results.
• Next, the liquefaction process cools the feed gas further to about -160°C (-256°F) in a series of heat exchangers. Accurate temperature measurement again proves critical. If the temperature is too low, the gas may freeze and block the heat exchangers, again with potentially disastrous results. Once it liquifies, the gas shrinks in volume by about 600 times.
• At this stage, the LNG is pumped into cryogenic tanks at the liquefaction temperature of -160°C which is carefully controlled to prevent the LNG from boiling away. If the temperature rises too high, the LNG may boil off and cause the tank to rupture.
• Now, the cryogenic tanks can be shipped in insulated tankers designed to maintain the optimum temperature of -160°C. As before, this temperature is maintained not only to prevent the LNG from boiling off but also to prevent the tanker from rupturing.
• At the destination, the LNG enters the regasification process which is accomplished by heating it to a temperature of about -40°C.

Two other factors in the LNG process are also crucial to ongoing successful operations: quality control and safety. The temperature of LNG is used to measure its quality. The higher the temperature, the lower the quality of the LNG, thus lowering the price it can command at delivery. Higher temperatures have additional adverse economic and environmental impacts for both the LNG producer and LNG customers. As to safety, monitoring the temperature of the LNG again proves critical to prevent it from boiling off or causing a disastrous rupture to the tanker. For the commercial LNG customer, lower quality gas will result in increased energy costs.

Case Study 3: Calibrating Natural Gas Flow Meters

Industrial maintenance teams must obtain precise temperature measurement with an intrinsically safe (IS) thermometer during all calibration procedures of any natural gas meter. The reason is simple: Gas volume is directly proportional to its temperature. For commercial and industrial applications where natural gas serves as a fuel or feedstock, calibration ensures an accurate measurement of the flow and thus controls raw material costs.

Because natural gas is highly flammable, measuring the temperature with an IS thermometer assures safe operation and prevents overheating which poses the risk of fire or explosion. This point is especially important in confined spaces such as pipelines and processing plants.

Further, most jurisdictions have implemented regulations that require gas flow meters and other measuring devices be regularly calibrated. These regulations often further specify that the temperature of the gas must be measured and recorded during calibration.

In addition to measuring the temperature during calibration, an IS thermometer can be used to detect leaks. For example, a sudden change in the temperature reading can indicate a leak in a pipeline or other piece of equipment. Temperature readings can also monitor the quality of the gas, which can be adversely affected by the presence of impurities, such as water or other hydrocarbons. Continuous temperature monitoring of natural gas equipment allows users to optimize equipment operations in such applications as compressors or turbines. The end result: Increased efficiency and reduced costs.

Measurement technicians who calibrate gas flow meters typically record gas temperatures in the range of 40°F to 120°F (4°C to 49°C). The Advanced Energy's TEGAM 921B thermometer, a certified intrinsically safe thermometer, is an ideal candidate for this use case. For temperature calibration applications, TEGAM will shortly release the 947A Intrinsically Safe Thermocouple Calibrator. This model can calibrate heating and cooling devices, as well as other temperature sensing devices.

Conclusion: The three case studies presented above all included significant potential explosion and/or fire hazards. Fortunately, the Advanced Energy's TEGAM 921B IS-certified thermometer can be used in these environments to deliver highly accurate temperature measurements. It includes real-time statistical data to increase user productivity, process efficiency, and product quality. The on-demand data displays include MIN, MAX, AVG, RANGE, and STDEV (Standard Deviation).

Advanced Energy's TEGAM designed the 921B for high performance, and manufactures it in a durable, handheld, ergonomic case for use in factory-tough conditions. For these three applications, the 921B thermometer delivered critical process control information and diagnostics that allowed safe, efficient, and regulatory compliant operations. For applications that require two temperature inputs, the 922B IS model is also available.

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