Truck Tippers are commonly used at Biomass and Wood Waste to Energy Plants. They are also used at some coal fired steam and power plants. DSI has many years of experience in managing these difficult dust sources.
At the truck tipper, our system is designed to suppress dust using two stages of attack. First, the dump pocket is filled with fog prior to the actual dump from the truck. This “pre-fog” will supply a reservoir of fog-charged air that, when displaced by the falling material, will attach to the airborne dust particles and settle them out in the hopper. To do this, the dump hopper fogging manifolds activate as soon as the tipper platform starts to rise.
Stage two begins when the same foggers operate during the complete dump cycle until the platform rests back on the ground. This stage will attack the creation of additional dust at the dump as the truck continues to dump.
Dry Fog is also used at the hopper discharge to the take-away conveyor and transfer points down-stream.
Rail Car & Truck Dumps can generate a very significant source of dust. Collecting dust from large open dump pockets is very difficult, with costs for collection systems sometimes exceeding $1,000,000. To make matters worse, users are still burdened with what to do with the collected dust once the process is completed. Chemical systems require the use of expensive chemicals and are not effective in removing dust from the air. For power plants, water and chemical sprays create a costly BTU Penalty due to the significant addition of moisture that needs to be driven off. Furthermore, sprays create large water droplets that will freeze, making wintertime operations in many regions impossible. Dry Fog Systems can effectively capture airborne dust, returning it to the dump pocket, without wetting the material. Dry Fog will not freeze and can operate in temperatures as low as –35 F.
One of the first Dry Fog Systems used at a Rollover Rail Car Dumper was for PRB Coal at Basin Electrics Laramie Station (LRS). DSI was able to achieve dust reduction in excess of 95%. This system was featured in Power Magazine in October of 2005. This same dumper is featured in the following video.
Hoppers located near waterways face certain challenges. Regulations often require that no dust or materials from the hopper loading operation enter the water. Areas near waterways often have increased wind conditions that complicate controlling the dust. DSI utilizes it Dry Fog System in conjunction with DustTamer Wind Screen Systems as shown in the photo. The DustTamer fabric screen is installed on the perimeter of the hopper typically on three sides. The fabric serves several purposes:
Conveyor Transfer Points are a great area of concern for Power Plants. The risk of fires, explosions and trouble meeting Fire and Safety Regulations increase significantly with PRB Coal. However, there is a Dry Fog Solution.
DSI pioneered the use of Dry Fog for PRB Coal Fired Plants in the 1990s and still leads this effort today. Dry Fog eliminates the risk of dust explosion associated with dust collection systems. The explosive waste stream is eliminated as we do not collect the dust. Instead, we simply "knock down" the airborne dust at the point of creation. Typically, a secondary waste stream creates a high concentration of explosive dust that re-enters the conveyor belt only to create more issues downstream. Using DSI's system of Dry Fog for PRB Coal Fired Plants prevents the creation of this secondary waste stream.
Dry Fog works by injecting sub-micron water droplets into the air at the point of dust creation. Fog droplets attach to like size airborne dust particles. The slightly wetted particles agglomerate to other particles, adding enough mass to settle the dust back into the conveyed product within the covered transfer point. This is used at crushers, screens, coal yard & plant conveyors, including reclaim, gallery, tripper conveyors and silos.
Controlling dust from Ash Handling can be challenging. Adding enough moisture to the ash to prevent dust is difficult, if not impossible. Mixing the ash with water often creates maintenance issues, including broken paddles and mixing screws. The Hydrophobic nature of ash typically results in some percentage of ash being over-wetted and the balance not wetted at all. Over-wetted ash drys out when spilled onto the ground, creates a secondary source of dust and must be cleaned up. If used for structural landfill, over-wetting can take ash out of specification. Dry Fog Systems use very little water and enables your operation to meet Environmental Compliance while meeting ash compaction specs. It will reduce the mess and increase truck haul capacities. One plant has reduced haul trips by 19%. Big savings!
Dry Fog systems can operate in temperatures well below freezing. At the same time, fog will not freeze in most environments. As the photos show, the fog is injected into the truck bed at the discharge point. The truck bed acts as a reservoir for the fog to attach to the airborne dust particles as they try to escape from the truck bed area. The airborne dust particles become more cohesive and attach to other slightly wetted particles until the increased mass of the larger agglomerated dust particles make them fall back into the truck bed.