Flow Elements – Orifices, Flow Nozzles, Venturies etc.
Export Performance Award – 2005-2006
What is dust
Dust Solid particles carried by air currents.
It consists of solid particles less than 500 µm.
Median size of 10 µm is inhalable that is trapped in the nose, throat, and upper respiratory tract.
Dust particles smaller than 10 µm are the most dangerous. its known as airborne dust.
A particle of 1,000 µm or larger is no longer considered fugitive dust since it fails to remain airborne.
By a wide range of manufacturing, domestic, and industrial activities.
Construction, agriculture, and mining are contribute most to atmospheric dust levels.
In minerals processing operations. during broking, dumping, crushing, grinding, screening, belt conveying, transferring, stocking, loading and milling materials to a finer size and movement of workers and machinery.
The amount of dust emitted by these activities depends on the physical characteristics of the material and the way in which the material is handled.
Fibrogenic dust is so named because it is a kind of dust that has fibber like tendencies. Fibrogenic dust is biologically toxic and if retained in the lungs can impair the lungs, ability to function properly.
Nuisance dust, or inert dust contains less than 1% quartz, its low content of silicates, having little adverse effect on the lungs. Any reaction that may occur from it is potentially reversible. However, excessive concentrations of it in the workplace may cause invisibility, unpleasant deposits in eyes, ears, and nasal passages and injury to the skin or mucous membranes by chemical or mechanical action.
Respirable dust are small enough to penetrate the nose and upper respiratory system and deep into the lungs, beyond the body's natural clearance mechanisms of cilia and mucous and are more likely to be retained.
Inhalable dust which enters the body, but is trapped in the nose, throat, and upper respiratory tract. The median aerodynamic diameter of this dust is about 10 µm.
Total dust includes all airborne particles, regardless of their size or composition.
Necessity of control
Excessive dust emissions can cause both health and industrial problems.
Reducing health hazard possibilities. -Occupational respiratory diseases. -Irritation to eyes, ears, nose and throat -Irritation to skin.
- Pneumoconiosis known commonly as black lung in this respirable dust collect in lungs and darken tissue, causing breathing difficulties and an increased risk of cancer.
Reducing risk of dust explosion and fire.
Necessity of control
Reducing equipment wear and damage.
Reducing or eliminating unpleasant odours.
Improving relations with neighbours.
Creating safer and more pleasant working conditions, thus improving employee morale and productivity.
Possible product or by-product savings.
To meet threshold limit values of concern pollution control authorities.
How to control
Dust control is the science of reducing harmful dust emissions by applying sound engineering principles. Properly designed, maintained, and operated dust control systems can reduce dust emissions.
How to control
There are four major step to exposure employee.
“ Prevention is better than cure" but prevention of dust in the bulk material handling operation is an impossible task, properly designed bulk material handling components can play an important role in reducing dust generation, emission, and dispersion.
Reduces the dust concentration by the use of uncontaminated fresh air.
How to control
T he worker is placed in an enclosed cab and supplied with fresh, clean, filtered air.
After all prevention the dust still remaining in the workplace can be controlled by one or more of the following techniques.
PREVENTION and control
Simple measures such as providing shrouds, covers, or enclosures around a dust source help to contain dust emissions or allow the existing dust control system to operate more efficiently.
Here we describe some of the commonly used processing and bulk material handling equipment, their major dust emission points, and measures to prevent or reduce dust generation, emission, dispersion and control.
DUST CONTROL SYSTEMS
The three basic types of dust control systems currently used in minerals processing operations.
1 - Dust collection systems
can provide reliable and efficient control however, the capital and operating costs are high and applicable only to sources that tight enclosed.
2 - Wet dust suppression
3 - Airborne dust capture
While somewhat less efficient, are less expensive to install and operate but also require careful selection and planning to b e most effective.
WET DUST SUPPRESSION
Systems wet the entire product stream so that it generates less dust. This also prevents dust from becoming airborne.
Effective wetting of the material can be achieved by Static Spreading and Dynamic Spreading
Water spreading methods depending on the needs of the system. An optimum droplet diameter for maximum material surface coverage must be determined.
Effective spray system performance depend upon such spray characteristics as drop distribution, drop velocity, spray pattern and spray pressure.
WET DUST SUPPRESSION
Surface wetting affected by droplet size and impact velocity. Surface wetting can be increased by reducing the droplet diameter and increasing the number of droplets and by increasing the impact velocity (by increasing the system's operating pressure).
We use nozzles in our system that produce drops in the 200 to 500 µm range to create a light rain effect.
Plain Water Sprays
It is probably the least expensive method of dust control.
The system is simple to design and operate.
A limited carryover effect at subsequent transfer points is possible.
When good mixing of water and material can be achieved, dust generation can be reduced effectively.
Enclosure tightness is not essential.
Water Sprays With Surfactants
This method is used when surfactants are tolerated but excessive moisture is not acceptable.
In some cases, dust control efficiency is higher than with plain water sprays.
Equivalent efficiency is possible with less water.
AIRBORNE DUST CAPTURE
This is a cross between a dust collection system and wet dust suppression system
It works on the principal that small particles of dust and small droplets of water come together, collide, agglomerate are formed larger and heavier particles that settle by gravity.
Droplets and particles that are similar in size have the best chance of colliding.
Nozzles that produce a wet fog consisting of drops in the 10 to 50 µm range are most effective.
Most important among components in a system are the spray nozzles.Following factors must be considered.
1-Droplet size, distribution is the most important variable for proper dust control. The droplet size decreases as the operating pressure increases.
2-Droplet velocity , higher drop velocities are desirable, especially in high-velocity air streams and where the nozzle is not located close to the target. Drop velocity is dependent upon drop size: Small drops may have a higher initial velocity, but the speed diminishes quickly. Larger drops retain velocity longer and can travel further.
3- Spray Pattern, Nozzles produce different types of spray patterns with varying characteristics.
Full cone nozzle product droplets that maintain a high velocity over a distance. They are useful for providing a high velocity spray when the nozzle is located distant from the area where dust control is desired.
FULL CONE NOZZLE
FULL CONE NOAZZLE
Hollow-cone nozzles, produce a circular ring of water. Drops are generally smaller than other nozzle types and are used in locations where dust is widely dispersed. Reduced clogging is an added benefit of hollow-cone nozzles because its orifice is larger than other nozzle types.
HOLLOW CONE NOZZLE
HOLLOW CONE NOZZLE
Flat-spray nozzles, produce relatively large droplets that are delivered at a high pressure and tapered-edge, rectangular or even spray pattern. These nozzles useful for wet dust suppression systems and typically used in narrow or rectangular enclosed spaces.
Hydraulic fine-spray nozzles, produce a fine mist or fog. Hydraulic fine spray nozzles are preferred in most areas because operating costs are lower since compressed air is not required. They are useful for airborne dust control systems.
Air atomizing nozzles , produce finer drops, are effective in locations where dust particles are extremely small and the nozzles can be located in close proximity to the dust source.
Hydraulic fine-spray nozzles
Air atomizing nozzles
4- Spray Angle Each nozzle has a jet spray angle , Spray angle and spray pattern will yield a specific coverage, determining how many nozzles are needed and their relative placement. In most applications, a spray angle between 55° and 70° offers the best coverage .
5-Flow rate of water through the nozzle depends on operating pressure. In order to determine the increase in moisture on materials being sprayed, the flow rate of the spray nozzles must be ascertained.
Water flow rate in Air Borne Capture System
We should know the dust emission rate from the dust source.
We should know the density of dust, where system is required.
We should know the size of emitted dust.
We consider fog density, 10 time of dust density.
It should be accessible for maintenance.
It Should not be in the path of flying material.
It should be upstream of the transfer point where dust emissions are being created.
It should be locate for best mixing.
For airborne dust capture, it should be located to provide maximum time for the water droplets to interact with the airborne dust.
Using more nozzles at lower flow rates can help ensure that nozzles are aimed at the broken material.
Automation of a dust suppression system can result in better performance with less waste and reduced maintenance time.
We use solenoid valves, load sensors, photo sensors, level switch, and etc to oprate system automaticaly.
Pump skid with Pump, Motor, Filter, Pressure gauge, Isolation valves, Water tank, Pressure relief valve, Level switch, D.P.gauge, Pressure switch and etc.
Control panel with MCC, Local push button, Timers, MCB, Volt meters, Ammeters, Indicating lamp etc
It is one of the major pieces of equipment used to transfer ore between processing equipment.
It emit dust from Tail end, Skirting, Return idlers and Head end.
Dust Prevention Measures
1- Belt Loading, The material should be loaded at same speed and same direction onto the centre of the belt
2-Skirting, skirt boards should be sufficiently high and wide, the inclined skirting rubber should be flexible and The top edges of the skirt boards are should be covered and sealed.
3-Impect at loading point, adequately spaced impact idlers should be located at transfer points.
4- Muck shelves, to load the material centrally and protect the inclined skirting rubber.
5- Dust Curtains, installed at the head, tail, and exit ends.
6- Belt Cleaners, should be installed belt scraper or v- plow to dislodge fine dust particles.
7- Conveyor Capacity, The belt conveyor should be designed to operate at 7% of its full rated capacity.
We place a load sensor on feeder belt and solenoid connected nozzles at upstream of discharge and at skirting cover or as required at the site.
Transfer chutes, transport ore from one piece of equipment to another.
Should be big enough to avoid jamming of material and reduce air flow.
Should be designed so the material falls on the sloping bottom of the chute.
Wherever possible, the material should fall on a local rock box or stone box.
Curved, perforated, or grizzly chute bottoms should be used when the product stream consists of fines and lumps.
Different types of chutes are used for controlling dust during bulk material handling like spiral, bin lowering, rock ladder, and telescopic chutes.
Enclosures are used to contain dust emissions around a dust source.
Should be spacious enough to permit internal circulation of the dust-laden air.
should be arranged in removable sections for easy maintenance.
A hinged access door should be provided to aid routine inspection and maintenance.
Dust curtains should be installed at the open ends of the enclosures to contain dust and reduce air flow.
We provide the spray nozzle in side the enclosure or as required at site.
Tow type forces applied to rock fragments, Compression and Impact Force.
All crushers generate dust. Impact crusher produce large amounts of fines and dust.
Dust emits from discharges and feeds.
Usually, no control measures are considered in the design of a crusher.
So shrouds or enclosures and discharge transfer chutes should be properly designed for crushers.
Rubber curtains should be used to minimize dust escape and air flow.
The crusher should be choke fed to reduce air entrainment and dust emission.
We place solenoid operated nozzles at both feed end and discharge end for all crusher or as required at site.
Screens are used to sort material according to size.
Dust is generated in all dry screening processes. However finer material produces more dust.
Screen emit dust from top and discharge.
Dust generated by screens cannot be altered. However, properly enclosed and removable enclosure can reduce dust emissions that consists of a special rubber cloth, rubber moulding, and simple metal hardware.
We recommend water spray system for screen at discharge end only. We place the spray nozzle at discharge end or as required at site.
STORAGE BIN AND HOPPER
These are used to store ore temporarily.
Feed by various equipment, such as conveyors, elevators, and screens and normally discharged through gravity or vibrating feeders .
Emit dust from feed openings, discharge feeder and Inspection doors.
Should be install bin-lowering chute, completely enclosing, telescopic chute and loading spout to minimize dust emission.
We provide spray nozzle at feed opening inside the storage bin and at discharge feeder or as required at site.
Feeders are relatively short conveyors used to deliver a controlled rate of ore to the processing equipment.
All type of feeders emit dust from receiving end and discharge end
Feeder should be oversize or produce less agitation and enclosed as much as possible.
We place nozzle inside the enclosure between receiving end and discharge end or as required at site.
A bucket elevator consists of a series of buckets mounted on a chain or belt that operates over head and foot wheels.
It emit dust from both point, boot end and head end.
The transfer chutes and enclosures between feed equipment and elevator as well as the elevator discharge and the receiving equipment should be proper designed.
We provide spray nozzle at both end to suppress dust or as required at site.
Large volumes of processed material are stored in open or enclosed stockpiles.
It emits dust when format a new pile and from previously formed pile.
Dust can be reduced by minimize the free fall of material and providing wind protection.
We provide a spray header around the discharge chute with hydraulic flat fine spray nozzle or as required at site .
They are used to transport ore from the quarry to the processing plant.
Emission depend upon the condition of the road surface, volume and speed of vehicle traffic.
Reducing traffic volume by replacing small haul vehicles with larger ones.
To reduce the emission Spraying the soil frequently with water or oil.
We manufacture tanker mounted spray system for that purpose.
TRUCK & WAGON DUMPING
Ore is unloaded from trucks or wagon in most minerals processing facilities.
Dumping large volumes of material in a short time, which displaces an equal volume of air carrying fine dust particles and wind spreading the dust.
Enclosures should be used to contain dust during dumping.
We place a overhead spray bar assembly at dump hopper or as required at site.
DESIGN A CONTROL SYSTEM
The following information list is required.
Process flow diagram of the facility indicating items such as the type of material being handled, material flow rates, and the type of equipment.
Major dust emission points and conditions that occur at these points during normal operations.