Municipal Biosolids Systems
Description
Vulcan® Drying Systems PMRU Portable Mercury Reclamation Unit - The Vulcan PMRU Portable Mercury Reclamation Unit separates mercury from contaminated wastes and then recovers the mercury in our proprietary reclamation system. This proven technology can be witnessed at our on-site commercial demonstration unit. Our dedicated staff has successfully transformed several mercury-contaminated wastes into recyclable feedstock. These wastes include cement kiln dust, activated carbon and bottom ashes from various power plants. The base unit utilizes the following major components to accomplish these tasks:
- Material Feed System: feed storage silo and multiple screw conveyors
- Primary Treatment Unit: indirect fired rotary desorber with combustion chamber, burners and seals
- Dry Material Discharge: screw conveyor and pugmill mixer
- Reclamation System: industrial dust collector and two-stage condensing unit
Process
The Vulcan® Drying Systems PMRU is designed to remediate 5 to 20 tons per hour of mercury-contaminated wastes in a versatile and portable system. All equipment is mounted onto three (3) highway-legal trailers for flexibility of treatment locations. A key design consideration is complete control of operational parameters in each component to tune the system for the most effective operation for a specified contaminate. Once this has been established, the system can be controlled automatically.
The system works on the premises of low-temperature thermal desorption (LTTD), also known as low-temperature thermal volatilization, and thermal stripping, whereby mercury and mercury-containing compounds are vaporized using heat. The temperature must be maintained above the boiling point of elemental mercury but under the auto-ignition temperature of the substrate. In cases where the mercury contained in the substrate is a compound or the substrate is heat-sensitive, special precautions may have to be taken.
Vaporized mercury and the sweep gas draft into an industrial dust collector to separate entrained particulate matter from the vapor stream to adhere to local and federal dust pollution control regulations. Any dust with high mercury content can be reprocessed. After reducing the dust content, the vapors are drafted into the first stage condenser.
Gas enters a shell and tube heat exchanger (gas pre-cooler) where ambient water absorbs excess heat. The purpose of the first stage condenser is to reduce the duty of the second stage condenser, a refrigerated air dryer. Once the gas is cooled, it enters into the second stage condenser, which "dries" the sweep gas by condensing any moisture and mercury.
Materials
Pre-prepped materials (typically cement kiln dust or activated carbon) are stockpiled in a 200 ton capacity storage silo which sits atop an incline screw conveyor. The incline screw conveyor lifts the material to be fed into a high-temperature feed screw. This high-temperature feed screw is bolted to the desorbers breeching, allowing material to drop directly onto the hot shell of the desorber.
Primary Treatment Unit
The primary treatment unit is a 60? diameter x 37? long indirect fired rotary desorber. An external furnace envelops this rotating drum and the flames from 10 industrial burners provide up to 8.5 MMBtu/hour of heat. Heat radiates from the flames to the shell and to the materials travelling the length of the desorber. As the contaminated wastes travel the length of the drum, the temperature increases past the vaporization point of the mercury. Vaporized mercury and sweep gases draft counter-currently to the reclamation system.
Industrial Dust Collector
Exhaust gases carrying entrained solids from the rotary desorber are routed to an industrial dust collector (cyclone, baghouse or multi-clone, depending on the application) to reduce particulate matter emissions and reduce fouling in the downstream condensers.
Two Stage Condensing Unit
Once the gas is separated of particulate matter, the exhaust gases are cooled in the first stage condenser, the gas pre-cooler. This gas pre-cooler consists of a shell and tube heat exchanger and an air-cooled heat exchanger loop. Gases travel counter-currently to a glycol water mix in a shell and tube heat exchanger. Heat exchanged from the hot gases to the water is removed by an ambient air cooler. The now cooler mercury-containing vapors then travel to the second stage condenser.
The second stage condenser is a refrigerated "air dryer". Mercury and water vapor containing gases travel over a bank of mechanically refrigerated coils where they are cooled below ambient conditions. Due to the high vapor pressure of mercury, the cold gases may still contain parts per million of mercury. These are polished off by a traditional activated carbon column. Activated carbon can be re-treated for mercury as the rate of adsorption is much lower than the rate of exhaustion.
Optional Control House
The PLC (programmable logic control) operating system for the entire plant can be operated remotely from stand-alone control panels or in a heated and air-conditioned control house. Both options are NEMA 4 rated for continuous outdoor duty.
About Municipal Biosolids Processing
The BIO-PRILL: Modular Class A Biosolids Dryer
2 Ton
THE CONTAINERIZED BIOSOLIDS DRYING PLANT IS A COMPACT AND COMPLETE SYSTEM DESIGNED TO PRODUCE UNIFORM CLASS "A" PFRP BIOSOLID FERTILIZER PRILLS FROM DEWATERED BIOSOLIDS. THE SYSTEM IS SUPPLIED COMPLETE WITH ALL COMPONENTS TO TURN BIOSOLIDS INTO AN ENVIRONMENTALLY SUSTAINABLE AND SOIL-ENRICHING AGRICULTURAL PRODUCT AS WELL AS A POTENTIAL REVENUE STREAM FOR MUNICIPALITIES.
8 Ton
THE 8-T STATIONARY BIOSOLIDS DRYING PLANT IS A COMPLETE SYSTEM DESIGNED TO PRODUCE UNIFORM CLASS "A" PFRP BIOSOLID FERTILIZER PRILLS FROM DEWATERED BIOSOLIDS. THE SYSTEM IS SUPPLIED COMPLETE WITH ALL COMPONENTS TO TURN BIOSOLIDS INTO AN ENVIRONMENTALLY SUSTAINABLE AND SOIL-ENRICHING AGRICULTURAL PRODUCT AS WELL AS A POTENTIAL REVENUE STREAM FOR MUNICIPALITIES.
Process Description
Dewatered biosolids are introduced through a wet material feed hopper 1 and mixed with dry biosolids in batch mixers 2. A proper ratio of thoroughly mixed materials entering the dryer 3 ensures the consistency required to efficiently reduce moisture and to optimize the formation of Class "A" PFRP dry biosolids. Mixed material is conveyed through the dryer where the heat removes excess moisture and reduces pathogens. Proprietary biosolids dryer technology ensures a uniform and consistent ≥90% dry solids end product. Processed material leaves the dryer through a knock out box 4 and is carried to a screen shaker 5 where it is processed to a uniform size. Any material that is too small is sent back to the dry material hopper 6. Material that is too large is processed through a crusher 7 and used as starter feed for new feed stock. The size-accepted biosolid fertilizer prills are conveyed through a cooling screw 8 and emptied in a client supplied storage container. Particulate and dust from the vapor stream is collected and removed by triple cyclones 9. The captured particulates from the triple cyclones are transferred via a drag conveyor 10 back to the dry material feed hopper 6. The vapor stream from the triple cyclones goes through a venturi scrubber 11 and inertial separator 12 to remove any residual particulate from the vent stream.
Process Capabilities
| % Solids | 14% | 15% | 16% | 17% | 18% | 19% | 20% | 21% | 22% | 24% | 26% | 28% | 30% |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Feed Rate (T/Hr) | 7.6 | 7.7 | 7.8 | 7.9 | 8.0 | 8.1 | 8.2 | 8.3 | 8.5 | 8.7 | 9.0 | 9.2 | 9.5 |
| Fertilizer Produced (T/Hr) | 1.2 | 1.3 | 1.4 | 1.5 | 1.6 | 1.7 | 1.8 | 1.9 | 2.0 | 2.3 | 2.6 | 2.8 | 3.1 |
| ~ Btu/Lb Feed | 1206 | 1190 | 1175 | 1160 | 1144 | 1129 | 1113 | 1098 | 1082 | 1051 | 1020 | 989 | 959 |
LARGE AND INCONSISTENTLY SIZED BIOSOLIDS HAVE LIMITED USE AS FERTILIZER AS THEY ARE IMPOSSIBLE TO APPLY WITH MODERN, PRECISION FERTILIZER APPLICATION EQUIPMENT.
THE PRILL SIZE OF TOP CHOICE ORGANIC (SEE BELOW, FAR RIGHT) IS VERY UNIFORM AND SIMILAR IN SIZE TO COMMON COMMERCIAL FERTILIZERS SO THAT IT CAN BE APPLIED WITH EQUIPMENT THAT FARMERS AND HORTICULTURISTS ALREADY USE. THIS UNIFORMITY ALSO ALLOWS TOP CHOICE ORGANIC TO BE BLENDED IN MIXES WITH OTHER COMMERCIAL FERTILIZERS TO MEET VERY SPECIFIC SOIL FERTILITY REQUIREMENTS.
THE BENEFITS OF DRYING BIOSOLIDS
Working with municipal biosolids is often considered a "dirty job" that few want to dig their hands into. However, each municipality must consider how they will dispose of municipal biosolids created by the population in their area. Due to increasingly changing regulations, rising costs of landfill disposal, and many landfill depositories being landlocked, biosolids disposal is quickly becoming a leech for funds, causing municipalities to begin looking for disposal alternatives. One such solution is found within thermal drying technology, allowing municipal biosolids to be appropriately processed into Class A PFRP biosolids, that can be resold or reutilized.
As the challenge of disposing of Class B biosolids becomes increasingly more complicated, many wastewater treatment plants are searching for cost-effective solutions that will allow them to meet the more stringent EPA regulations being enforced in many areas. Vulcan® Drying Systems has developed the BIO-PRILL, an easy-to-operate, all-in-one solution that will enable municipalities to produce a valuable end-product that can be applied in many different agricultural areas.
Under 40 CFR, part 503, the United States Environmental Protection Agency (EPA) has published regulations for technologies to further reduce pathogens in municipal biosolids. The result of the new regulations is a product classified as Class A biosolids. These biosolids are safe for land application without the negative environmental effects associated with Class B material or the negative publicity received from odors emanating from land application of wet fertilizer slurry.
Vulcan® Drying Systems designed the BIO-PRILL biosolids drying unit with the intent to address the needs of the small to medium-size municipalities. The continuous operation and automated controls ensure that operators can continue to focus on plant operation with minimal interaction with the dryer. All operating parameters are under the control of a PLC system and are capable of being monitored remotely.
The BIO-PRILL is effective in drying a variety of sludges including digested and waste activated sludges. The unique design of the BIO-PRILL includes all the necessary features to produce a consistent and uniform end-product. With the ability to control the feed rate into the dryer, the residence time in the dryer, and the temperature of the air entering the dryer, the BIO-PRILL continually and efficiently produces a valuable 90%+ dry solid material.
The heat energy for drying comes through direct contact with preheated air. By lowering the dew point of the material within the drum, the BIO-PRILL is able to dry at low temperatures (~200°F). Shaker screens separate discharged solids into three sizes: overs, ideals, and fines, with overs and fines being crushed and recirculated back to the front of the system. A cooling screw assures that ideally sized material is cooled to an acceptable temperature for client supplied discharge handling equipment. An integrated cyclone and venturi scrubber remove and capture any particulate prior to vapors being released to the atmosphere.
All this adds up to a cleaner, safer, and more efficient choice for your treatment plant. To find out more about the BIO-PRILL, please download our brochure and contact us HERE.