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Common Problems and Solutions for Large-Scale Industrial Dryers

    Common Problems and Solutions for Large-Scale Industrial Rotary Dryers (for Coal Slime, Sludge, Sand, Sawdust, etc.)

    I. Drying Effect Issues (Most Frequent)

    Problem: Unstable moisture content of dried materials (sometimes up to standard, sometimes excessive), especially for high-moisture materials like coal slime and sludge.

    Solution: ① Install an on-line moisture detector to feed back data in real time and link with the control system to automatically adjust temperature/wind speed (recommended temperature 80-120℃ for high-moisture materials, wind speed matched with drum rotation speed).

                   ② Stabilize the feeding volume and initial moisture content to avoid large batch differences of sludge/coal slime (add a homogenization silo before feeding if necessary).

                   ③ Inspect equipment tightness, repair air leakage at both ends of the drum and pipeline joints, and reduce moisture fluctuation caused by heat loss.

    Problem: Uneven drying—local over-drying and caking (e.g., sawdust agglomeration, sand caking) or local under-drying.

    Solution: ① Optimize the material distribution device and install a disperser at the feed inlet (for sawdust and coal slime) to ensure uniform spreading on the drum/conveyor belt (material thickness of belt dryers controlled at 5-8cm).

                  ② Adjust drum rotation speed (0.8-1.5r/min for large equipment) to avoid too long or too short material residence time.

                  ③ Inspect hot air distribution plates, clear blocked air holes, and ensure hot air penetrates the material layer evenly (increase hot air volume for sand drying, reduce wind speed for sawdust to prevent agglomeration).

    Problem: Excessive dust of dried materials (sawdust, coal slime powder) or material adhesion to equipment inner walls leading to unsmooth discharge.

    Solution: ① Excessive dust: Install a pulse dust collector at the discharge port, adjust drying temperature (≤100℃ for sawdust to avoid over-drying and dust generation), and add a spray dust suppression device at the equipment tail if necessary.

                  ② Material adhesion: Clean the drum inner wall regularly (high-pressure water flushing after daily shutdown; install a scraper device for severe adhesion of coal slime/sludge), and add an appropriate amount of flow aid (e.g., fly ash, addition ratio ≤3%) during feeding to reduce viscosity.

    Problem: Sand turns yellow and deteriorates after drying (caused by high temperature); slight carbonization of sawdust during drying.

    Solution: ① Yellow sand: Lower drying temperature (120-150℃), shorten high-temperature residence time, and inspect if the heater is locally overheated (replace aging heating tubes and adjust hot air distribution).

                   ② Sawdust carbonization: Strictly control temperature ≤90℃, increase fresh air supply to reduce oxygen concentration in the equipment, and optimize feeding speed to avoid material accumulation in high-temperature areas.

    II. Equipment Operation Issues

    Problem: Drum/belt dryer deviation, vibration; abnormal noise or excessive wear of transmission components (gears, chains).

    Solution: ① Deviation and vibration: Adjust the angle of drum supporting rollers (parallelism error between supporting rollers and drum axis ≤0.5mm), inspect conveyor belt tension (for belt-type equipment), and replace aging conveyor belts or supporting rollers.

                   ② Abnormal noise of transmission components: Regularly add high-temperature grease (once every 15 days), adjust gear/chain tightness (chain sag ≤2cm), and replace severely worn gear surfaces or chains.

    Problem: Decreased heating efficiency of the heater and slow temperature rise (prone to scaling or blockage when processing high-moisture sludge).

    Solution: ① Scaling treatment: For steam/electric heaters, perform cyclic cleaning with citric acid descaling agent once a month (temperature 60-80℃, soak for 2 hours then rinse).

                   ② Blockage cleaning: Install a filter screen (aperture ≤5mm) at the heater air inlet for sludge/coal slime drying, and clean filter impurities once a week.

                  ③ Inspect the burner (for gas-heated models), clean nozzle carbon deposits, and adjust gas-air ratio (optimal air-fuel ratio 10:1).

    Problem: Insufficient fan air volume, poor heat circulation in the equipment, and excessively high exhaust gas temperature at the tail.

    Solution: ① Clean dust on fan blades (once a week), inspect fan motor speed (frequency conversion control recommended for large equipment, adjust speed according to material moisture).

                   ② Inspect if hot air pipelines are blocked by dust and dredge regularly (once a quarter).

                   ③ Optimize the heat recovery system, introduce tail exhaust gas into the preheater to reduce smoke exhaust temperature (target ≤120℃), and improve feed preheating effect.

    Problem: Control system failure, inaccurate temperature/humidity display, and inability to automatically adjust parameters.

    Solution: ① Calibrate sensors: Calibrate equipment sensors with standard hygrometers and thermometers every 3 months, and replace aging temperature probes (especially those in high-temperature areas).

                   ② Inspect control system wiring, clean dust in the control cabinet (once a month), and repair loose terminals.

                   ③ Back up the control program, restore factory settings and redebug parameters in case of program disorder.

    Problem: Air and material leakage at equipment seals (both ends of the drum, pipeline interfaces) and material scattering or heat loss.

    Solution: ① Replace aging seals (e.g., graphite gaskets, silicone sealing strips); install labyrinth seals for large drum equipment to enhance tightness.

                   ② Adjust drum coaxiality to reduce gaps during operation.

                   ③ Install a receiving trough at the material leakage point to avoid ground pollution and waste caused by material scattering.

    III. Energy Consumption and Cost Issues

    Problem: Sudden increase in gas/electricity consumption when processing the same amount of materials (far exceeding initial operation data).

    Solution: ① Inspect the equipment insulation layer (thickness ≥50mm), repair damaged parts, and add rock wool insulation sleeves to the outer layer if necessary.

                   ② Optimize the drying process and adopt the "low-temperature and high-air-volume" mode (for high-moisture materials) to avoid ineffective high-temperature heating.

                   ③ Regularly clean dust on heat exchanger fins to improve heat exchange efficiency (once a month).

    Problem: Frequent replacement of wearing parts and high maintenance costs.

    Solution: ① Replace with wear-resistant accessories: Install wear-resistant liners on the drum inner wall (for sand and coal slime processing), and select high-temperature and wear-resistant materials for conveyor belts (for belt-type equipment).

                   ② Establish an wearing parts account and stock up in advance according to operation time (e.g., replace seals and bearings every 6 months). 

                   ③ Standardize operating procedures, avoid over-capacity operation (feeding volume not exceeding 110% of the equipment's rated capacity), and reduce component wear due to overload.

    Problem: High frequency of equipment shutdown for cleaning, leading to reduced productivity and increased unit cost.

    Solution: ① Optimize feed pretreatment: Crush sludge and coal slime in advance (particle size ≤5cm) and dehydrate (moisture content reduced to below 60%) to reduce adhesion and blockage.

                   ② Install automatic cleaning devices: Add elastic scrapers inside the drum and automatic cleaners on the conveyor belt to clean residual materials in real time.

                   ③ Formulate a reasonable cleaning cycle (adjust according to material viscosity, e.g., clean sludge dryers once every 8 hours, sand dryers once every 24 hours) to avoid excessive material accumulation.

    IV. Safety and Adaptability Issues

    Problem: Excessively high dust concentration during sawdust and coal slime drying, posing explosion risks.

     Solution: ① Ground the equipment for static electricity prevention (grounding resistance ≤10Ω), and install explosion-proof valves (1 per 2m² of equipment area, installed on the drum top).

                     ② Control drying temperature below the material ignition point (sawdust ignition point 230℃, coal slime ignition point 280℃) to avoid local overheating. ③ Regularly detect dust concentration in the equipment (once per shift), and increase fresh air volume or shut down for cleaning when exceeding the standard.

    Problem: Corrosive components in sludge and coal slime accelerate corrosion and wear of equipment inner walls and liners.

    Solution: ① Select corrosion-resistant materials: Spray anti-corrosion coatings (e.g., polytetrafluoroethylene) on the equipment inner wall, and use high manganese steel or wear-resistant alloy for liners.

      ② Pretreat materials: Neutralize sludge acidity (add lime to adjust pH to 7-8) to reduce corrosive substance content.

      ③ Regularly inspect corrosion conditions (once every 3 months), and repair coatings or replace liners in a timely manner.

     Problem: Fluctuations in material feeding volume and sudden changes in moisture content lead to equipment overload shutdown.

     Solution: ① Install a feed flow control valve and an on-line moisture monitor to adjust feeding speed in real time (reduce feeding volume when moisture content increases).   

       ② Equip the equipment with overload protection devices (e.g., motor thermal relays, torque sensors) that automatically reduce speed or shut down when overloaded to avoid motor damage.

       ③ Establish material pretreatment standards to ensure the fluctuation range of feed moisture content ≤±5%.

     Problem: Substandard drying exhaust gas treatment, facing pressure from environmental inspections.

     Solution: ① Dust treatment: Connect two-stage dust collectors (pulse dust collector + bag filter) in series to ensure dust emission concentration ≤10mg/m³.

       ② Odor treatment: Install activated carbon adsorption devices or biofilters for sludge drying exhaust gas to remove odors such as hydrogen sulfide and ammonia.

                        ③ Wastewater treatment: Collect equipment cleaning wastewater and exhaust gas condensed water, and introduce them into the sewage treatment system for discharge after reaching the standard.

    Would you like me to compile a Standard Operation and Maintenance Manual for Large-Scale Industrial Dryers (Specialized for Coal Slime/Sludge/Sand/Sawdust)? It includes a four-column comparison table of "Problems-Solutions-Inspection Cycles-Emergency Handling" and standardized daily/weekly/monthly operation and maintenance processes for on-site operators to quickly refer to and implement.