The dryer is not just a drum, but a whole system designed for the conveyance of product and gases. The product enters and exits the system through conveyors, such as screw conveyors (augers), drag chains or bucket elevators. The gases enter and exit the system through ductwork and are heated by a burner and motivated by fans. The smooth operation of the conveyors and fans ensures consistent drying of the product. Instrumentation relays information that the control system deciphers to keep the dryer running at steady state, which is the safest and most efficient way to run a dryer.
Why is this important? The dryer is a giant furnace being cooled by the water in the product. If the infeed conveyor stops, the cooling disappears and the furnace will get hotter and hotter while the product in the dryer gets dryer and dryer. This could be the perfect recipe for a fire or explosion.
Problems with product and gas conveyance is more likely to lead to a fire or explosion than most other problems. If the dry product is not moved out fast enough, it can provide ample fuel for a fire. Most DDGS dryers have product recycle to get the infeed under the sticky phase moisture content. Startup and shutdown are the most dangerous activities in any dryer, but startup for a DDGS dryer is doubly so. When the product continually recycles, it gets dryer and dryer until the wet infeed is started. This is one of the main causes of fires and explosions in natural gas fired DDGS dryers. Temperature sensors of the product entering the dryer are crucial for the operator to know whether they are getting close to the danger zone.
Another possible cause of a fire or explosion is if the infeed conveyor stops or is plugged during normal operation, because there will be a lack of cooling in the drum due to the cutoff of water to evaporate. To alleviate this possibility, the infeed conveyor must have a zero speed switch or some other device to automatically shut the system down if the conveyor stops. The best solution is to program responses to as many upset conditions as possible for the control system to automatically shut the dryer system down or otherwise return it to a safe operating condition.
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Problems commonly seen in industry
- Blockage/Flow restriction/buildup
- Lack of flow data
- Dirty blades
- Flow issues
- Increased amperage draw
- Lack of data
- Lack of shutdown sensor
- Broken flights/Bent shafts
- Frequent stopping
- drive/motor/gear wear or breakage
- Increased amp draw
Fires and explosions
Dryer System Performance Analysis (DSPA): Increase dryer throughput, capacity and efficiency
- Using pressure gauges, flow meters, thermometers, and combustion analyzer to determine what is happening in your system and how to improve your operations.
- Diagnostic and information about your dryer flows and process
- Fan inspection and diagnostics
- Identifying previously unexploited potential
Mechanical Inspections – Catch problems before it’s too late, to keep costs down
- Duct inspection
- Conveyor inspection and diagnostics
- Recommendations based on results
Capacity Upgrades – because who doesn’t want more product to sell?
- Optimal ductwork cross section
- Reduce buildup in ductwork
- Reduce flow restriction
- Determine bottleneck in process
Instrumentation and Controls – Reduce risk of fires and explosions, ensure smooth operations
- Auto shutdowns
- Temperature sensors
- Fire suppression system