What to Do If Your Spray Dryer is Leaking Material?

Spray dryers are crucial equipment in the food, pharmaceutical, and chemical industries for turning liquid materials into powder. Leaks not only waste materials but can also affect product purity, pollute the equipment environment, and even pose safety hazards. Leaks often occur in a few key areas. By following a step-by-step troubleshooting process, you can quickly find the cause and resolve the problem. Below is a detailed explanation of each area.

I. Find the "Source of the Leak": Start with the Material Conveying Process

Leaks in spray dryers often begin before the material even enters the drying tower. Focus on checking the connection between the feed pump and the pipeline, and the seals on the atomizer:

Leaks at the Feed Pump and Pipeline Interface

The feed pump is the core component that transports liquid materials to the atomizer. If the flanges connecting the pump body to the feed and discharge pipes are not sealed properly, or if the seals are aged or damaged, material will leak from the interface.

• Troubleshooting Method: After starting the equipment, observe whether there is liquid leakage at the flange connecting the feed pump and the pipeline. Touch the area around the interface; if it feels sticky or has obvious dampness, it's a leak.
• Solution: First, stop the machine and disconnect the power. Close the feed valve and drain any remaining material from the pipeline. Remove the flange bolts, take out the old sealing ring, and check for cracks or deformation (especially rubber sealing rings, which are prone to aging with long-term use). Replace with a new sealing ring of the same specification (it is recommended to choose a material resistant to material corrosion, such as food-grade silicone rubber or chemical-grade fluororubber). When reinstalling the flange, ensure the bolts are tightened evenly to avoid uneven stress leading to a poor seal.

Atomizer Seal Failure and Leakage

The atomizer is a component that atomizes liquid materials into tiny droplets. Its shaft and housing have a sealing structure (such as a mechanical seal or packing seal). If the seal is worn, insufficiently lubricated, or misaligned, material will leak from the sealing gap, and may even seep into the equipment, damaging the motor.

• Troubleshooting Method: After powering on, observe the bottom or side of the atomizer housing for any material dripping. If leakage is accompanied by abnormal noise (such as a friction sound from the rotating shaft), it is most likely a sealing problem. After powering off, remove the atomizer end cap and check the seals for wear marks (e.g., scratches on the dynamic and static rings of the mechanical seal, or loose or broken asbestos rope in the packing seal).
• Solution: For mechanical seals, check the contact surfaces of the dynamic and static rings. If there are minor scratches, gently sand them smooth with fine sandpaper, reapply special grease, and reinstall. If the scratches are severe or the sealing ring is broken, replace the mechanical seal assembly directly. For packing seals, loosen the gland bolts, remove the old packing, and fill in the new packing (note that the packing should be filled in one ring at a time, with each ring staggered by 90°), then tighten the gland evenly to ensure a seal without affecting the rotation of the shaft.

II. Further Inspect for Leaks Inside the Drying Tower: Focus on Tower Joints and Discharge Valve

After material enters the drying tower, leaks often occur at the tower body welds and the bottom discharge valve. These two areas are in direct contact with the dried powder and are prone to leakage due to wear or seal failure:

Leakage at Drying Tower Welds

Drying towers are mostly stainless steel structures. If there are incomplete welds or gaps during welding, or if the welds crack due to thermal expansion and contraction after long-term use, the powder generated during drying will leak out from the weld gaps. This is especially true when the tower is operating under negative pressure, as outside air may be drawn in, carrying dust outwards.

• Inspection Method: After shutting down the equipment, enter the drying tower (ensuring proper safety precautions such as wearing a dust mask and securing a safety rope). Shine a flashlight on the tower body welds to check for obvious gaps or powder accumulation. Alternatively, apply a layer of transparent tape to the welds on the outside of the tower and observe after starting the machine whether the tape is lifted by dust or whether powder seeps out from the edges of the tape.
• Solution: If the weld gap is small and the material is non-corrosive, apply a high-temperature resistant sealant (such as food-grade silicone sealant) to the outside of the weld. Test the machine after the sealant has cured. If the gap is large or the weld is cracked, stop the machine and have a professional welder repair it using stainless steel welding rods of the same material. After repairing the weld, grind the surface to ensure it is smooth and free of protrusions to avoid scratching the material or accumulating dust.

Bottom Discharge Valve Leakage

The dried powder is discharged from the bottom discharge valve of the tower. Common discharge valves include star-shaped discharge valves and flap valves. If the blades (or valve core) inside the valve body are worn, the sealing gasket is aged, or the flange connecting the valve to the bottom of the tower is not sealing properly, powder will leak out from the valve gap.

• Troubleshooting Method: When starting up and discharging material, observe whether there is dust overflowing from the connection flange between the discharge valve and the bottom of the tower, or whether there is an "air leakage" sound when the valve is running (material leakage is often accompanied by air leakage); after stopping the machine, open the discharge valve for inspection. If there are obvious wear marks on the blade surface or the sealing gasket is damaged, this is the cause of the leakage.
• Solutions: If the flange seal is not tight, replace the sealing ring and retighten the bolts according to the solution for "feed pipeline flange"; if the valve blade is worn, minor wear can be addressed by adjusting the gap between the blade and the valve body (e.g., for a star-shaped discharge valve, adjust the end cap bolts to reduce the gap between the blade and the housing), while severe wear requires replacing the blade; if the sealing gasket is aged, directly replace it with a gasket of the same specification, ensuring the gasket material is suitable for the material (e.g., for powders that easily clump together, choose a smooth PTFE gasket).

III. Finally, check for "leaks in the exhaust gas treatment process": Don't overlook cyclone separators and baghouse dust collectors.

Some leaked material will enter subsequent exhaust gas treatment equipment along with the exhaust gas. If there is a leak at the ash discharge port of the cyclone separator or the seal of the baghouse dust collector, dust will be emitted with the exhaust gas or accumulate outside the equipment:

Cyclone separator ash discharge port leakage

The function of the cyclone separator is to separate most of the powder in the exhaust gas. If the airlock (such as a star valve) at its bottom ash discharge port fails to seal, unseparated powder will leak out from the ash discharge port, or outside air will enter, causing a decrease in separation efficiency and indirectly increasing the amount of leakage.

• Troubleshooting method: Observe the operating status of the airlock at the bottom of the cyclone separator. If there is dust scattered at the outlet of the airlock, or dust accumulation at the connection between the airlock and the separator, this is the leakage point.
• Solutions: Check the seals of the airlock (such as shaft seals and end cover gaskets) and replace worn parts. If the airlock blades are worn, adjust the gap or replace the blades according to the discharge valve's handling method to ensure the airlock can both discharge ash normally and isolate outside air.

Bag Collector Leakage

Bag collectors filter fine dust remaining in the exhaust gas through filter bags. If the filter bags are damaged, the connection between the filter bags and the tube sheet is not tight, or the pressure of the cleaning device is too high, causing the filter bags to fall off, dust will directly leak through the filter bags from the outlet, resulting in "dust emission" (i.e., leakage).

• Troubleshooting Method: After starting the machine, observe whether dust is discharged from the bag collector's outlet (place a piece of white paper at the outlet; if there is obvious dust on the paper, it indicates leakage). After stopping the machine, open the dust collector's inspection door and check whether the filter bags have holes or tears, or whether the clamps at the filter bag openings are loose (loose filter bags will cause dust to leak from the gap between the bag opening and the tube sheet).
• Bag Collector Leakage: Solution: If the filter bag is damaged, replace it with a new filter bag of the same specification (note that the filter bag material should be suitable for the material's temperature and corrosiveness; for example, choose a fiberglass filter bag for high-temperature materials). During installation, ensure the filter bag opening clamps are tightened securely and the filter bag hangs vertically without wrinkles. If the cleaning device (such as a pulse valve) pressure is too high, adjust the cleaning pressure (usually 0.4-0.6 MPa) to prevent excessive pressure from rupturing the filter bag.

IV. Post-Leakage Resolution: Preventive Maintenance to Avoid Recurrence

After resolving leakage issues, proper daily maintenance can significantly reduce the probability of recurrence:

1. Regular Inspection of Seals: Monthly inspection of seals and gaskets in the feed line, atomizer, and discharge valve. Replace any aged or damaged seals promptly to prevent small problems from escalating into major leaks.
2. Standardized Equipment Operation: Before starting the machine, ensure all components are properly installed to prevent loose bolts from causing poor sealing. Control the material concentration and flow rate during feeding to avoid pipe blockage due to excessively thick material or high flow rate, which can indirectly lead to leakage.
3. Cleaning and Maintenance: After each shutdown, promptly clean any residual material inside the equipment (especially easily agglomerated materials such as syrups in the food industry and herbal extracts in the pharmaceutical industry) to prevent material clumping that could wear down seals or clog pipes. Regularly apply grease to the atomizer and discharge valve shafts to reduce wear on seals.

Actually, material leakage in spray dryers is not a big deal. As long as you check the leaks in the order of "from feed to exhaust gas", find the leaks and deal with them accordingly, and do a good job of routine maintenance, you can effectively avoid material leakage problems, ensure stable operation of the equipment, and reduce material waste and production losses.