• Case Studies
Product Recovery

Chemicals 

Particle separation is required for the production and processing (drying, milling, and classification) of a wide variety of distinct products in the production of organic and inorganic chemical powders. These include pigments and dyes, fertilizers derived from phosphorus and potassium, metal hydroxides and oxides, such as lithium hydroxides and zync oxides, carbides, such as tungsten carbide, plastics, and many others.

Drying presents significant separation issues for chemical powders, especially in fluid bed, spray, rotary, and flash dryers.


Fluid Bed Drying

Fluid bed designs typically include process cyclones with a final dedusting system (Bag Filter, ESP, Wet Scrubber High Efficiency Cyclones).
The function of a process cyclone is to separate fluid bed exhaust stream from the dried products. The fraction of product escaping to the final dedusting system poses a set of operational challenges, such as product cross-contamination when rotating powders and downtime costs to clean filter bags that frequently clog in the presence of high moisture and/or sticky powders. That is the case of several organic compounds, such as sulphanilic acid powder. When the collected product recovered cannot be immediately recovered, waste or side stream management is another problem to tackle.

One of the operational challenges posed by the fraction of product that escapes to the final dedusting system is the potential for product cross-contamination, particularly when dealing with rotating powders. Additionally, the presence of high moisture and/or sticky powders often leads to frequent clogging of filter bags, resulting in downtime costs associated with cleaning. This is especially true for organic compounds like sulphanilic acid powder. Moreover, waste or side stream management becomes another issue when the collected product cannot be immediately recovered.

To address these challenges, cyclone collectors are the preferred method for recovering these very fine powders in the final stage due to their ability to directly and hygienically capture the powder. Unlike bag filters, electrostatic precipitators (ESPs), or wet scrubbers, cyclones offer greater robustness and can be easily and automatically cleaned, minimizing the risk of product cross-contamination and reducing operating costs and downtime.

However, when dealing with powders with a median diameter in volume (MVD) of less than 10µm, losses resulting from low cyclone efficiency can significantly increase, translating into high costs. Even for processes involving less expensive chemicals where losses may not be as financially burdensome, it is crucial to consider the environmental and social responsibility impact.

Strict emission limits for a wide range of substances further necessitate the need for highly efficient end-stage filters to ensure compliance with environmental regulations. When evaluating options for these final dedusting systems, it is important to consider their respective advantages, drawbacks, as well as investment and operational costs.

 
Regular Cyclones and Multicyclones | Problem: Low Efficiency
+ Low cost, easy to operate and clean. Allow for quick stops and product rotation.
- Low efficiency for small particles (<10μm) leading to non-compliance with emission limits. Regular cyclones available on the market are not an option for emission control.
Bag & Ceramic Filters | Problem: O&M costs
+ Bag filters are very efficient (> 99.9 %) and guarantee compliance with a wide range of emission limits. 
- Demanding in terms of temperature and moisture conditions: product can easily stick to the bags if there is condensation.
- Maintenance is labour and time consuming.
- Cross contamination when there is product rotation
ESPs | Problem: High Investment
+ High collection efficiency even for small particles.
+ Absence of filter waste is environmentally responsible.
- Expensive to purchase, install, maintain and operate.
- Risks associated with sparks and explosions due to the power source.
Wet Venturi Scubbers and WESPs | Problem: Secondary Pollution
+ Can work well for a variety of operating conditions.
- No product recovery possible from a wet scrubber.
- Secondary pollution of water is an operational added problem requiring a water treatment facility.

For the first stage separation, clients need the highest possible performance in the process cyclones to minimize carry-over of fines to the end stage. For the final stage dedusting, whenever possible, the fines should be recovered in a high efficiency cyclone system.
 
ACS solutions include very high efficiency process cyclones to maximize yield. ACS final stage cyclones are also a real alternative to other police filters depending on the required emission limits and particle size of the product (<30mg/Nm3 is achievable), thus maximizing yield of the whole production line.

 

Alternative setups of fluid bed drying

Alternative layouts include re-heating and re-injecting the stream under the bed. Even in these cases, the air needs to be clean of fine particles to avoid clogging that leads to expensive non planned maintenance stops. Additionally, the exhaust stream from the fluid bed to the stack needs to be cleaned for emission limit compliance.
 
 
In this setup, ACS can supply high efficiency process cyclones for maximum recovery of product and then also tackle a second stage of separation. In the recirculation line, this may be necessary to further clean the gas and avoid fluidizing of particles below the bed which leads to expensive non planned stops for cleaning. In the bleed off line, an ESP is commonly used but it comes with its usual drawbacks of both high investment cost and also operational and maintenance costs. When possible, the best way to comply with emission limits is through a second set of high efficiency cyclones.
 

Spray Drying

Some fine chemicals such as lithium hydroxide, other valuable metals or metal salts, several kinds of plastics or polymers, ceramic powders, and other products are dried through spray drying, where ACS has a vast experience. Spray drying enables precise control over particle size and morphology, facilitating uniform mixing and improved material properties.
Different set ups include one to three drying stages with the possibility of collecting powder at various points along the line which may include some fine recirculation.
In this setup, ACS can supply high efficiency process cyclones for maximum recovery of product and then also tackle a second stage of separation, depending on emission limits and the characteristics of the powder.
 

Rotary Dryers

For products that can withstand the tumbling action and high temperatures involved, rotary drying may be the ideal process. These include organic and inorganic fertilizers but also pigments, resins, solvents, minerals, catalysts and even metal compounds.
In a standard drum dryer, ACS can provide the process cyclones immediately downstream of the dryer and/or the final stage separation for emission control, depending on emission limits and the characteristics of the powder.