Troubleshooting Dryers

When troubleshooting a dryer that has previously operated to specification and is no longer, keep these tips from Drytech Engineering (www.drytecheng.com) in mind.

1. Use logic and common sense. Systematically evaluate the performance of each primary component in your dryer and then break it down to smaller systems to find trouble spots.

2. Don’t be shy, call the supplier. Even if the machine is out of warranty, vendors should provide troubleshooting assistance over the phone.

3. If they are available on your system, use tools such as human-machine interface (HMI) system control and data acquisition (SCADA) systems. These tools make troubleshooting far simpler and quicker to conclude.

4. Becoming familiar with the program or hardwired schematics and the logic of the control system is paramount to successfully troubleshooting poor performance. Familiarizing yourself before you need to pore over the schematics during troubleshooting will eliminate one hurdle to discovering errors.

5. To diagnose a problem, you need to have the correct tools. For troubleshooting a dryer, these would include instruments such as a multimeter, manometer, ammeter and thermometer. Other nice-to-have instruments are a tachometer, anemometer (vaned or hot wire), micro-manometer, pitot tube and infrared thermometer.

6. Understand how the operator can help — and hurt — you. A seasoned operator offers great insights into the process. At the same time, a lot of time is spent troubleshooting issues related to unauthorized changes to operating parameters.

7. Don’t overlook feed changes and contamination. Even if you are certain that nothing has changed in the feed stream, if dryer performance has changed dramatically, check the feed. Be sure that characteristics such as size, moisture level and temperature meet the feed specification.

8. Visually conceptualizing the operation of the system is helpful in troubleshooting transient conditions. As crazy as it sounds, you need to imagine that you are a part of the system and observe what is happening.

9. Confirm electrical components. You might think that electrics are either off or on. This is true when you have single phase but not always when you have three-phase power. Losing a phase may result in dramatically reduced performance but not a fault of the system. This is quite common with electric elements and motors, especially if they are overdesigned. Check all three fuses on fused systems carefully. 

10. Keep records. Rest assured that the problem you just solved will occur again at some time in the future. Think of how nice it would be if the operator could reference a “lessons learned” database, identify that the issue has occurred before and resolve it as part of his normal duties.

Heat Tracing

Electric heat-tracing systems are attached directly to the surface of the pipe. They are especially good at maintaining narrow temperature ranges and have numerous temperature ranges available. Pentair (www.pentairthermal.com) offers 10 tips on industrial heat tracing solutions.

1. Consider an investment study, which looks at total installed costs, total operating costs, expandability, flexibility and accuracy, before specifying new process heating systems. 

2. Because hot water has finite heat capacity and cools continuously as it flows, the pipe temperature varies.

3. A hot water source normally is present in most plants, and the systems have low technology and service requirements for personnel.

4. Water systems require auxiliary equipment such as water pumps, holding tanks and heat exchangers that need mechanical and electrical maintenance.

5. Electric heat-tracing systems can be used for process temperature maintenance for single-walled piping systems and for heating control equipment such as flow meters, pumps and control valves.

6. A temperature sensor or RTD must be utilized with electric heat tracing to maintain a narrow temperature range.

7. Electric heat tracing continuously adjusts its heat output based on the ambient conditions.

8. Self-regulating electric heat tracing can be controlled to a much narrower temperature range than hot water. 

9. With electric heat tracing, the temperature controller can be connected to an Ethernet-capable company intranet system for remote monitoring of the entire system.

10. Because electric heat tracing runs on the outside of the single-wall pipe, there is no potential product contamination.

Temperature Sensors

Temperature measurement accuracy goes beyond just the accuracy of the sensor. Burns Engineering (www.burnsengineering.com) offers 10 things you should know about using platinum resistance thermometers for temperature measurement.

1. Think lifecycle cost. An indicator of the quality of a platinum resistance thermometer is its long-term stability performance. To achieve tight stability performance requires the use of high purity materials and sound manufacturing processes. 

2. Verify that the platinum resistance thermometer is operating properly by performing a calibration at 32°F (0°C) and measuring the insulation resistance (resistance between the lead and the sensor sheath) annually, or as required by your quality system. Tracking the performance is critical.

3. Check the depth. Stem conduction is a source of error that has the potential to cause large errors even if the sensor is working exactly as designed. Make sure the immersion depth is adequate. 

4. The overall system error can be reduced by as much as 85 percent by matching the transmitter to the actual resistance vs. temperature characterization of the platinum resistance thermometer. Periodically recalibrating the thermometer and updating the transmitter to match its new characterization can eliminate sensing errors due to drift and restore accuracy.

5. Long lengths of lead wires can introduce errors when two-wire and three-wire connections are used. Using a transmitter located in the connection head near the thermometer will minimize lead length, and the 4 to 20 mA signal is less susceptible to showing an error from the noise.

6. If a fast response time is desired, select a sensor with minimal mass in the sensing element location.

7. Temperature measurement accuracy goes beyond just the accuracy of the sensor. Contributors to the total measurement error will include components from the transmitter/control system; lead wire connections; readout display; calibration uncertainty of the thermometer and transmitter; and thermal isolation of the PRT from the ambient conditions.

8. Prevent thermowell failures by choosing a thermowell of sufficient stiffness such that the natural frequency of the well will be greater than the wake frequency. Larger diameters and shorter lengths result in higher natural frequencies of the thermowell. 

9. Accurate temperature measurements are necessary for product quality and efficient energy use. Recognizing the errors and accounting for them are critical steps for an accurate measurement system.

10. Respect hazardous areas. Some applications require that the sensor assembly has additional shielding from the environment to avoid igniting explosive gases and dust. 

Valves/Dampers for Oxidizers

This list from Pro-Environmental Inc. (www.pro-env.com) provides an overview of the damper technologies used in the regenerative thermal oxidizer systems.

1. Valve designs should take into account the maximum system pressure, temperature changes and stresses imposed by the connecting ducting so as to prevent distorting and misaligning the sealing surfaces. 

2. The sealing surfaces should be of such material and design that the valve will remain tight over a reasonable service period. 

3. The style of damper used is determined by the canister design. While the odd- and even-canister designs warrant traditional butterfly or poppet dampers, the single-canister design uses the single-can rotary valve.

4. When selecting dampers for regenerative thermal oxidizers, consider the requirements for valve actuation, valve seat design, leakage rate, materials of construction, and resistance to condensable organics and other particulates.

5. The type and size of butterfly damper dictates the torque requirements and, by extension, the actuation requirements.

6. Poppet dampers are used for on-off control only. They are not appropriate for modulating applications.

7. Oxidizer systems that are designed with two-way poppets should have one inlet and one outlet damper to provide fail-safe conditions during power outages and upset operating conditions.

8. Poppet dampers operate best when oriented vertically.

9. The single-canister rotary valve design eliminates the need for separate inlet, outlet and purge valves and replaces them with a single large valve.

10. The single-canister rotary valve utilizes a machined metal-to-metal surface to achieve tight sealing, which makes it more susceptible to wear.

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