In these instances, a little experience and a logical, methodical mind are extremely valuable. The word for it is troubleshooting, and it is aptly descriptive.
There are two types of troubleshooting drying machinery. Troubleshooting a dryer that has never operated to specification from startup is essentially more challenging than troubleshooting a dryer that is no longer operating to specification. The former may result from various issues, including having fundamental design flaws, having been installed incorrectly or having utilities underdesigned. Spending time with these systems and systematically evaluating all of the parameters will enable you to draw conclusions and provide certain fixes to the problems and other enhancements. This conclusion may not always be favorable but frequently will result in an improvement in operation. This article focuses more on the latter -- troubleshooting a dryer that has previously operated to specification and is no longer.
Let's first get rid of the obvious. If your feeder is on fire or if your exhaust fan belts are protruding through the belt guard, get your maintenance man involved. If you are putting material in and nothing is coming out, stop the machine -- there is a serious problem. Obvious mechanical issues that can be assessed visually should be simple enough to identify. It's when there are no obvious signs that the challenge is presented.
Tip 1: Use Logic and Common SenseAs I said, in troubleshooting, a logical and methodical mind is extremely valuable. The systematic approach will lead you to the primary issue and may uncover other hidden retardations. You must systematically evaluate performance of each primary component and then break it down to smaller systems.
Refer back to your piping and instrumentation diagram (P&ID) or control schematic and generate a checklist of obvious functions. Look at the mechanical details and continue to develop a checklist of other inspection points. If thorough, you will only ever need to do this once.
Once you have developed your checklist, analytically inspect and confirm the operation of each item. This action removes any uncertainties and will eventually uncover the principal issue.
Tip 2: Refer to the Operating ManualsMany suppliers will publish a troubleshooting guide or checklist in their manuals. These are invaluable because they often contain a comprehensive list of topics gleaned from the supplier's experience. They can save valuable time by identifying similar issues that others have had with comparable equipment. And, don't be shy: call the supplier. Even if the machine is out of warranty, vendors should provide telephonic troubleshooting assistance.
Tip 3: Use the Available ResourcesShould you be fortunate to have a human-machine interface (HMI) system control and data acquisition (SCADA) system, historical trending package or distributed control system (DCS), and (note that this is a big and) the code has been written with troubleshooting in mind and (another big and) you have invested in field control and motor control input and output (I/O) loops, you should consider yourselves blessed. These tools make troubleshooting far simpler and quicker to conclude.
If you don't, all is not lost. High and low temperature alarms, motor status indicators, pressure and motion switches often are incorporated into relay logic control panels.
Tip 4: Become Familiar with the Program or Hardwired Schematics and the Logic ThereofBecoming familiar with the logic of the control system is paramount to successfully troubleshooting poor performance. Ladder logic or other logic diagrams will illustrate the intended operation. Reducing the time investment in first understanding and then following schematics or logic diagrams to appreciate the intended operation of each condition will absolutely prove to be beneficial. Verifying the logic will remove any uncertainty relating to the control system.
Tip 5: Have the Right ToolsIt goes without saying that in order 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 would include a tachometer, anemometer (vaned or hot wire), micro-manometer, pitot tube and infrared thermometer. And let's not forget the safety equipment, including a flashlight and gloves capable of withstanding reasonably high temperatures. Basic hand tools also are needed.
This may seem mundane, but the amount of time lost because people cannot open a flange or measure current to prove or disprove a theory is immense. Learn how to use the instruments effectively.
Tip 6: Understand How the Operator Can Help You and Hurt YouI cannot overstate enough the value of a talented operator nor emphasize that operators typically know more about the idiosyncrasies of the equipment than anyone else! That being said, the best intentions can have opposite effects. So, verify your setpoints. Check your valve and damper positions. Validate that all control and mechanical variables are as commissioned. Changes to operating parameters can affect the entire system performance.
Tip 7: Don't Overlook Feed Changes and ContaminationSo much can change that will affect the performance of the dryer. For example, in a classifying pre-process, suppose maintenance changes the screen size because the correct spare screen wasn't available. What will making the particle a little bigger do? Well, reducing the surface area of the particles will do lots and can even increase the moisture content.
In a drying process, even if you think that nothing in the feed stream has changed yet the dryer performance has changed dramatically, validate the feed material. Size, moisture, temperature, characteristics, etc., need to be confirmed to be in accordance with the feed specification.
Tip 8: Conceptualize the Operation of the SystemAs crazy as it sounds, you need to imagine that you are a part of the system and observe what is happening. First, imagine you are an air molecule starting from the ambient pool of air -- your first action would be to be induced into the system. Can you get into the burner? Is the inlet filter clogged, making it hard work? Are you mixing with the hot gases? Is there buildup in the combustion chamber? Do you feel hot enough? Are you moving fast enough? Can you sneak by the heat source into the drying chamber without being heated? Can you miss the product and escape? Questions such as these can intuitively lead you to areas that require further investigation.
Now, pretend you are a feed particle. Once again, visualize your path through the machine. Can you enter the dryer easily? Are you leaving some of your friends behind? Are a whole lot of your friends having a get-together in the dryer (buildup)? Are some of your friends getting cremated (burning)? Are you able to escape to the atmosphere (emissions)? Are you being successfully trapped?
As the machine itself, ask yourself questions about vibration, balance, catching or pinching, general wear, valves, bearings, fan wear, insulation breakdown, etc. These all can have unexpected effects on the system performance.
It may sound childish, but visually conceptualizing the operation of the system is very helpful in troubleshooting transient conditions.
Tip 9: Confirm Electrical ComponentsYou would 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.
Motors also may function if one of the windings has failed. The component may seem to operate but with dramatically reduced performance. Checking for rotation of a fan may not tell you that there is a problem because most people presume a fan is functioning if it is turning. But, when variable-frequency drives (VFDs) are being utilized, they will operate at lower power requirements on two phases without any problems.