'Wet' Dust Suppression Systems
General Comments
'Wet' dust suppression systems in the past have mainly been:
- Badly designed and applied
- Allowed an excess moisture addition to the product causing screen blinding, Thermal penalties etc
- Poorly maintained and controlled
- Subject to frost damage due to lack of design/client consideration
- Removed to gain access to plant and not re-commissioned
- Not able to achieve the degree of dust control necessary
This has often led to a general 'loss of faith' in standard water only or water + surfactant systems. They however continue to be used as they represent an economical solution to 'dust control'. If not properly designed and maintained this will result in:
- Poor neighbour relationship (and the implications on future planning extensions)
- Poor operator working conditions
- Excess maintenance expenditure
- Availability of high water demand
- Many other adverse factors
Modern properly designed and maintained 'Dustfoam' systems however are a considerable leap forward and in general will totally outperform past systems.
Enviro Wet Dust Suppression Systems - Specific Information
When minerals such as quarry aggregates, metallic ore, coal, iron ore, etc are handled through conveyors, crushing, screening and various dry processes there is dust released - the amount generally depending on the moisture present in the product, the product grading and the degree of disturbance the material is subjected to. If the process is carried out within buildings then this dust is released within the buildings causing serious contamination and producing a hostile environment for other engineering equipment to operate in such as electric motors, gear boxes, compressors etc. The buildings are required to be cleaned out on a frequent basis and in addition to the labour problems involved in cleaning out these buildings, some materials can be hazardous to health as defined by the COSHH regulations. This dust spillage has to be removed by operators wearing protective clothing, masks, breathing apparatus etc (PPE). Enclosing the process reduces the release of dust to the atmosphere but does not eliminate it. (Personnel generally cannot work within buildings during processing).
If the process is not 'contained' and the plant is on an open site then the dust will be released into the atmosphere. This will deposit locally around the process plant but will also blow in the wind and contaminate the surrounding areas. It can however infringe the environmental rules for fugitive dust within and outside the site boundaries.
The addition of moisture for dust control purposes into minerals being processed has been carried out for many years and it is a fact that the addition of water/absorbed moisture can considerably reduce dust nuisance during handling.
In the past water has been added to the process mainly by the use of atomised sprays. This water on some better engineered systems can be automatically shut off to parts of the plant that are not operating by using process signals and solenoid valves. Often, the minerals being handled repel water and it is sometimes difficult using water only systems to allow the water to become absorbed into the finer fraction of the product that is the main contributory mechanism to dust release. This is sometimes overcome by adding more water up to 3% - 5%. This amount of water often cannot be tolerated. To overcome part of this difficulty surfactants are used to reduce the surface tension of the water making it easier to coat the mineral being processed and reduce the water being used. Surfactants can reduce water consumption down to 0.5% - 2%.
'Wet' Dust Suppression Systems have their use in the market place if they are applied properly. They are economical to purchase and operation and chemical costs are relatively low. They however do not as a rule control dust as efficiently as Dustfoam Systems and use more water in the process.
For further information on Enviroflo/Nalco Dustfoam Systems, Click Here