From cooking the pulp to drying the final product, paper production is heat-intensive. Thermocouples, RTDs, dial thermometers, thermowells, digital transmitters, and more help ensure the safety and efficiency of many applications in pulp and paper plants.
This article is a continuation of “Flow Metering Solutions for the Pulp and Paper Industry.”
Kraft pulping is filled with high-heat processes, from burners and kilns to recovery boilers and incinerators for biomass and hazardous waste. WIKA offers a wide range of temperature monitoring solutions for these and other high-temperature applications.
A host of special features make them suitable for temperatures up to 2,900°F (~1,600°C):
- Thermowells made of heat-resistant steel or ceramic
- Support tubes made of various steels
- Gas-tight process connections (up to 14.5 psi / 1 bar)
- Options: ceramic inner tubes, armoring, explosion protection (intrinsically safe)
And after the paper or fiber is formed, it needs to be dried at precise temperatures. If too high, the batch is ruined. If too low, the drying is incomplete or takes too long.
TC97 miniature multipoint thermocouple sensor
Electronic Sensors for Temperature Profiling
Miniature multipoint thermocouples like the TC97 are excellent sensors for installing at different heights and positions for complete temperature profiles. Each sensor is protected by a sheath made of stainless steel or another heat-resistant alloy, with mineral insulated (MI) cable or outer tubing also made of a specialty alloy. The sensors may then be combined within a single protection tube for easy mounting. Thanks to their smaller diameter, multipoint thermocouples are ideally suited for applications with limited spaces.
WIKA also manufactures a range of weld-on tubeskin thermocouple assemblies and compact resistance thermometers (RTDs).
Electronic temperature sensors can be paired with a temperature transmitter to facilitate continuous monitoring. Models T32.1S (head mounting version) and T32.3S (railing mounting version)are robust digital transmitters with HART communication. They can be operated in safety applications to SIL 2 when used alone, and to SIL 3 with a redundant configuration. There are connections for one or two sensors, such as resistance thermometers (resistance sensors), thermocouples (mV sensor), or potentiometers. The signaling is per NAMUR NE43, and sensor-break monitoring per NE89 and EMC per NE21.
Another option is to connect the sensors to a controller or digital indicator. WIKA’s portfolio of digital indicators includes various designs for panel mounting or integration with the connection head. Some versions feature HART® communication or additional switching outputs.
Mechanical Thermometers: Simple, smart, cost-effective
TGT73 thermometer with electrical output signal
Not all temperature monitoring devices require a transmitter. The TGT73 is stainless steel gas-actuated thermometer with an onsite display as well as electrical output signal. This two-in-one intelliTHERM® instrument combines the low cost and plug-and-play installation of a mechanical measuring system with electrical signal transmission to the control room or another remote location. Even if the power is cut, operators can still reliably read the process temperature on the dial.
For local temperature indication, use the stainless steel model 73 gas-actuated thermometer. This high-quality instrument offers a fast response time and is available in various configurations for connections and case mounting. In the contact bulb version, temperature measurement does not require any contact with the process medium.
Bimetal thermometers are another excellent choice for general applications. These classic instruments are durable, inexpensive, low maintenance, simple to use, and easily recalibrated onsite. For pulp and paper plants, we recommend the process versions (per EN 13190) of the model 55 or TG54 bimetal thermometers.
Thermowells: Extra protection and peace of mind
There are two main reasons to place an electronic or mechanical temperature probe inside a protective thermowell:
- The process medium is aggressive (corrosive, abrasive), extremely hot, under high pressure, or flows at a fast velocity.
- The measuring point is critical to the safety and efficiency of the application.
Thermowell with ScrutonWell® design
But thermowells, no matter how strong they are, can fail in a fast-flowing process pipe. This is because two rows of vortices form behind the tube in a phenomenon called Kármán vortex street. And when those vortices detach, they create vibrations that cause mechanical fatigue. If the thermowell breaks, not only is the thermometer damaged, but the medium can escape.
To reduce vortex-induced vibrations, operators can shorten the insertion length, increase the root diameter, increase the tip diameter, or add a support collar. However, these measures may not be enough for a thermowell to pass its wake frequency calculation.
That’s why WIKA offers thermowells with a ScrutonWell® design. Its helixes reduce the amplitude of those vibrations by more than 90% without needing to change the thermowell’s dimensions or retrofit it with a support collar.
WIKA USA, Your Partner for Smart Temperature Monitoring
Each process or application calls for a specific temperature measuring solution. To find the ideal instruments and accessories for your pulp and paper facility, contact the product experts at WIKA USA.