Feb 14, 2024. Bulkagram 25, Happy Valentine’s Day Everyone!
As a rule, our team of mechanical and chemical engineers must invest hours into reading every imaginable paper on pneumatic conveying of powder.
‘Don’t blame the blow tank’ has distilled this extensive knowledge into 7 factors to consider during dense phase conveying. The list, needless to say, is not exhaustive -the most important step being selecting the right vendor.
What is a blow tank? At Scorpio our trade name is the Dense Flow Vessel. Simply put, this is a pressure vessel that acts as a feeding device for powder materials into downstream, mixing, blending, weighing and batching. It is the heart of the dense phase conveying system. Capable of withstanding pressures from 2-6Bar, they are ideally suited for abrasive and/or high temperature applications.
There are several types:
Bottom Discharge that can handle a wide range of fine, cohesive and coarse materials. (The common Bulk Tanker for cement logistics are also blow tanks)
Top Discharge that is suitable for fine, free flowing powders like poly powder and alumina.
Side discharge that can be seen on ship unloaders
Single slug bottom discharge (without discharge valves, shorter distances upto 100m)
Horizontal blow tanks where there are headroom restrictions
Screw feeding blow tanks for accurate dosage and product contro
Once you have selected dense flow as the mode of conveying your material, keep in mind the 7 Factors that can affect performance, feeding and operational efficiency of the dense flow vessel – the heart of dense phase conveying:
Accurate calculation of capacity: Take cycle overheads including filling time, initial pressurisation time and valve actuation times into consideration before you calculate blow tank capacities
Component selection: the most common complaint us in relation to failure of a certain valve or seal. Don’t blame the entire blow tank conveying system for this problem! Get to the root cause and solve for selection, installation or operation of that particular component.
Material characteristics: Most often different suppliers will supply different grades and qualities of the same material. While this does not affect the integrity of the end product, minute changes in powder characteristics affects the powder conveying system! It is essential that you match the specifications of the component to material characteristics and application requirements.
Air injection method: Depending on the mode of flow, the method of air injection is the most important deciding factor for efficient operation.
Air retention characteristics: the presence of particles are not taken into account during air velocity calculations. Most data for these values, such as minimum conveying air velocity are generally determined experimentally or from operating experience. Air is compressible, so as the material is conveyed along the length of the pipeline. the pressure will decrease and the volumetric flow rate will increase
The bend effect: Acceleration pressure drop occurs at all bends in the pipeline. Slip velocities at exit will be lower than at inlet so the particles will have to be reaccelerated back to their steady state value
Solids loading ratio: for some materials, solid loading ratios well over 100 are common. This parameter is useful in that, unlike conveying velocity or volumetric flow rate, it remains unchanged along the length of the pipeline
Dense Phase flow is truly a beauty to behold!
Look inside your pipeline during dense flow! The material plugs fill the full bore of the pipeline and are separated by short air gaps. As the conveying air velocity is reduced, the air gap between the plugs gradually fills with material along the bottom of the pipeline and the plug ultimately moves as a ripple along the top of an almost static bed of material.
We hope that you too may witness this at your plant and reap the beauty of application physics!
References:
Wypych, P, (Apr-Jun 2002) ‘Blow Tank Technology for Pneumatic Conveying’, Material and Product Handling p.23-28
Mills, D, (Dec 2003) ‘Dilute and Dense Phase Conveying Explained’, Proceedings of BulkIndia 2003 p142-152
FAQs: Troubleshooting Pneumatic Conveying Systems & Blow Tank Issues
1. Why is my pneumatic conveying system underperforming?
While blow tanks are often blamed, most issues stem from:
Improper system design (pipe sizing, air-to-material ratio)
Material characteristics (moisture, particle size)
Upstream/downstream equipment mismatches
2. What are common symptoms of a poorly functioning blow tank?
Inconsistent material flow (pulsing, blockages)
Excessive air consumption
Premature wear of components
3. Why shouldn’t I blame the blow tank first?
Blow tanks are typically victims of larger system issues like:
Incorrect pipe routing (too many bends, vertical lift challenges)
Improper air supply (pressure/volume mismatches)
Material prep problems (degradation, segregation)
4. How can material properties affect blow tank performance?
Abrasive materials erode tanks/pipes faster.
Hygroscopic powders clog systems due to moisture.
Dense particles require higher air velocity.
5. What design flaws cause blow tank failures?
Oversized/undersized tanks for the application
Faulty fluidization systems (poor aeration)
Inadequate venting (pressure buildup)
6. How do I diagnose if the issue is really the blow tank?
Check:
Air pressure/flow consistency
Material feed rate stability
Discharge valve synchronization
7. Can retrofitting fix blow tank problems?
Often, yes! Solutions include:
Upgraded aeration pads
Smart controls for air/material balance
Wear-resistant liners
8. What maintenance prevents blow tank issues?
Regular inspection of seals/valves
Monitoring air filter conditions
Cleaning fluidization components
9. How does Scorpio BMH approach blow tank troubleshooting?
We:
Audit the entire system (not just the tank).
Simulate material flow to identify bottlenecks.
Redesign or modify components for optimal performance.
10. When should I consider a full system redesign?
If you face:
Chronic blockages/unreliable throughput
Frequent downtime for repairs
Spiraling energy costs