What is DRY FOG?
It is true fog just like nature makes. Meaning the majority of droplets are between 1 & 10 microns in diameter. The importance of small droplets is there ability to impact and agglomerate airborne dust particles so the process material stays dry.
How EFFECTIVE is it?
Fog systems when properly designed and applied can meet or exceed all air quality standards. The EPA now specifies fogging systems as Best Demonstrated Technology for Sub-bituminous coal. In Wyoming, fogging systems are considered B.A.C.T. (Best Available Control Technology) for conveyors transporting PRB Coal, giving it a Zero Visible Emission Rating. At Rollover Rail Car Dumpers for PRB Coal, DSI has achieved reductions of over 96% as reported in Power Magazine .
Will this WET the material?
Dry Fog is designed to only agglomerate to airborne dust, not wet the material being handled. Typical moisture addition to the material is less than 0.05%. It has been estimated that our nozzle design can create enough fog to cover the area of 1/2 a football field with One Gallon of Water!
Does it work with HYDROPHOBIC materials like COAL DUST?
Yes, Dry Fog is the system of choice and is Best Demonstrated Technology for sub-bituminous western coals like PRB Coal. It used for other hydrophobic materials such as pet coke and fly ash. We make water droplets the same size as the airborne particles overcoming any surface tension issues. The Colorado School of Mines reported their research on the how droplet size effects dust suppression in a 1976 issue of Coal Age Magazine .
Can fog be used on MOISTURE SENSITIVE MATERIALS?
Dry Fog has been used specifically for a variety of moisture sensitive materials such as Clay, Nitrates, Limestone, Clinker, and even Cement. We evaluate site-specific conditions to determine Dry fog applicability with some of these materials. Typically, with moisture sensitive materials, Dry Fog works better on large open areas such as ship holds & dump pockets than it does with enclosed conveyor belts where it is possible for agglomerated material to build up and harden.
Is there a BTU PENALTY for FUEL HANDLING systems?
Dry Fog has the lowest BTU Penalty (chart source Martin Engineering) of any dust suppression system by far. Power Plant Operators report that they have not been able to detect any perceivable increase in moisture to the coal.
How Big Is a MICRON?
For reference, a grain of table salt is around 100 microns in diameter and sand is around 50 microns. The human eye can see an object down to approximately 50 microns. So, an individual fog droplet that is 1- 10 microns is invisible to the human eye, but in mass quantities it appears as fog. Refer to Droplet Size Chart.
Do I need CHEMICALS like SURFACTANTS or BINDERS to make this work?
With Dr Fog, no chemicals are used. Chemical systems can have a Damaging Effect (see article) on conveyor belts. Surfactants are designed to break up the surface tension of the water droplet to increase its distribution into the material. Dry Fog produces microscopic droplets that collide with airborne particles and have very little surface tension. Binders are designed to make the material stick together. Dry Fog agglomerates like size droplets to dust particles and the electrical charges present.
Can fog be used at DUMP POCKETS?
Yes, Dry Fog is often the only practical solution for Dump Pockets. We fill the pocket with fog prior to the dump and continue the fog output through the duration of the dump cycle. At PRB Coal Rollover Rail dumps we have achieved reductions in excess of 96%! DSI can evaluate the feasibility of controlling dust from your dump pocket.
Can Fog be used at STACK OUT conveyors?
There are several issues with using Dry Fog at Stack Out Conveyor Discharge Points. Generally, there are three sources of dust generation: (1) separation of the fines coming off of the belt, (2) separation of the fines as the material freefalls and (3) the impact of the material onto the storage pile. In some cases, the discharge chute can be enclosed with Strip Curtains and positioned close to the pile. In other cases, water sprays must be added at the tail of the conveyor to pre-moisten the material before it stacks out. Typically, we can indicate to our customer's the feasibility of using Dry Fog at Stack Out Conveyors given drawings and photographs. DustTamer Wind Fence Systems are another control measure we use for storage piles.
Will it work with DUST COLLECTION systems?
Dry Fog is designed as a stand-alone dust suppression system and typically replaces the bag-house. Collection can be used upstream or downstream of the fog application point as long as it is far enough away to prevent the fog from being sucked into the collector.
Is there a CARRY OVER effect to prevent dust generation downstream of the fog application point?
Because Dry Fog is designed to treat only the airborne dust using microns sized droplets, very little moisture addition takes place, so there is little if any Carry Over Effect. Dry Fog is injected into each point of dust creation similar to a bag-house collection system.
Do I need source of COMPRESSED AIR, if so how much and what quality is required?
Yes, you need an adequate supply of compressed air at 80 to 90 PSI. The volume of air required is determined by the quantity of nozzles and type of nozzle selected for the application. Instrument air is not required as we are able to filter most air sources within our system.
What WATER PRESSURE does it require?
Dry Fog systems operate between 7 and 15 pounds water pressure. We typically ask for a source that maintains around 50 PSI water pressure.
What keeps the nozzles from PLUGGING?
In addition to our standard two-stage filtration for water and compressed air, the nozzle design itself has many features to prevent plugging:
- There are 4 to 8 water orifices per nozzle, each being .028 inches in diameter or larger.
- Our fine atomization occurs outside of the nozzle via sound waves as opposed to squeezing water through an orifice to atomize.
- The shock wave produced by the nozzle design to shatter the droplets to a micron size, vibrates the nozzle like a sonic cleaner.
- Using low water pressure means the low-pressure drop from 15 lbs maximum delivery pressure reduces the chance for nozzle plugging minerals to come out of suspension (like what happens with high pressure nozzles).
How many TYPES OF NOZZLES do you have?
D.S.I. is unique in that we offer four different flow rated Dry Fog nozzles. These nozzles are interchangeable within our system, so we can adjust the amount of fog output per nozzle to site-specific conditions. Our Nozzle Specification Chart indicates where each nozzle is typically used along with associated air and water Flow Rates.
Note: All Nozzles Are the Same Physical Size & Fit Into the Same Adaptor.
Nozzle Assembly - Dsn 3
Nominal Flow Rate:
3.5 Gal./Hr. (13.25 Liters/Hr.)
Nozzle Assembly - Dsn 6
Nominal Flow Rate:
8 Gal./Hr. (30.25 Liters/Hr.)
Nozzle Assembly - Dsn 10
Nominal Flow Rate:
11 Gal./Hr. (41.6 Liters/Hr.)
What WATER Quality does it require?
We ask for the best available safe water source as volume requirements are low and cleaner water will extend filter life. Water should be free of harmful contaminates and as clean as possible. We realize that all water systems are subject to particulate so DSI provides a permanent media primary filter with an automatic back flush coupled with secondary disposable filters as a standard feature. Dual parallel bypass filters are available for uninterrupted operation.
Does WIND affect the fog?
For open dump pockets we sometimes require a DustTamer Wind Screen to reduce the effects of wind and displaced air caused by the dump. This shields the dump pocket from ambient wind and increases fog and dust retention time.
Will it work in FREEZING Temperatures?
Dry Fog works very well in below freezing conditions. Fog droplets lack sufficient mass to freeze. This phenomenon is known as Cloud Physics. The system components can be protected via insulated enclosures with self-regulating heaters and heat tracing as well as an automatic purge system upon system shutdown.
Will I need a WATER PUMP?
No water pumps are typically required. We ask for a minimum of 30 PSI water at the elevation of fog application. DSI can supply water pumps and storage tanks if required.