How Sodimate’s silo Arch Breaker & Feeder ZDM 400 helped the Greenville Utilities Comission Water Treatment Plant achieve 100% efficiency in Powdered Activated Carbon injection
The Water Treatment Plant’s previous discharge system, using vibrating bin activators, caused the PAC to jam the gearbox twice daily, required the replacement of belts and pulleys every 2 weeks and had to be taken offline once a month for dismantling and manual clearing.
Since it became operational in August 2022, Sodimate’s Silo Arch Breaker & Feeder ZDM 400 has been running smoothly for uninterrupted periods of 6 to 8 weeks without any downtime, except to replenish carbon stocks.
Greenville Utilities Commission (GUC)
The Greenville Utilities Commission (GUC) provides electric, water, sewer, and natural gas services to the City of Greenville and 75% of Pitt County.
Its Water Treatment Plant (WTP) serves more than 35,300 people. GUC’s WTP has been honored by the North Carolina Division of Water Resources for “surpassing federal and state drinking water standards” seven years in a row.
To comply with stringent state and federal drinking quality standards, the GUC Water Treatment Plant uses Powdered Activated Carbon (PAC) technology for the removal of organic contaminants in their raw water decontamination process. Their previous PAC discharge system, however, was plagued with reliability and maintenance issues and needed an upgrade.
The maintenance department, led by Robert Veale, an instrument controls specialist with over 35 years’ experience, was in search of a user-friendly and efficient discharge and feed solution that would minimize manual intervention and integrate into their expansion project which aimed to increase the water treatment capacity by an additional 10-million-gallon per day to meet ever-increasing customer base and system demands.
The WTP’s previous system which discharged PAC by means of a vibrating bin activator presented several issues that hindered its effectiveness. First and foremost, the design was not optimized for this application, resulting in frequent conveyor belt breakages and compaction of carbon within the funnel. Not only did its belts and pulleys require replacement every two weeks, but monthly breakdowns also resulted in significant downtime. The PAC would frequently jam and get stuck inside the gearbox – at least twice a day – and the system would have to be taken offline for manual clearing. It would take a 10 hour two-shift effort and a long-winded process, including breaking down the gearbox, into which the PAC had clogged, to restore operation. The feed rate of the system was equally unreliable, and lead to an inconsistent dosing of the PAC. One of the other concerns faced by GUC was retrofitting a new discharge and metering system seamlessly onto their existing application without the need for separate construction or modification of their facility.
Before (left) and after (right) pictures of the installation at GUC’s.
In their quest for an upgrade, Robert Veale and his team conducted online research, leading them to discover Sodimate’s complete PAC discharge and metering system. Through YouTube videos and a comparative analysis with their existing system, they found Sodimate’s all-inclusive Mechanical Arch Breaker to be innovative and unique. “It looked like a really good design, compared to what we had, because of the dual drive system”, explains Robert.
As a matter of fact, the combination of Sodimate’s Arch Breaker and a screw feeder, both employing separate motors, offers distinct advantages overvibrating bin activators when it comes to ensuring a mechanical discharge of a product from a silo. Widely used in the U.S, vibrating bin activators, however, tend to change the density of powder products, leading to arching and clogging issues in silos, a very common effect of powder handling. This, in turn, hampers the proper discharge of the product and negatively impacts dosing accuracy. In contrast, Sodimate’s Arch Breaker features flexible blades which rotate and actively break the arches formed within the silo, thus significantly improving the flow of discharge. The Arch Breaker works in tandem with the screw feeder to ensure a mechanical discharge rather than a vibrating discharge.
Silo Arch Breaker & Feeder ZDM 400 and wetting cone eductor system
A mechanical discharge provides a more controlled and reliable flow of the powder product, ensuring accurate dosing and consistent delivery. A vibrating discharge, on the other hand, relies on vibrations to induce powder flow, which can lead to variations in the amount of powder being discharged and a less precise dosing.
Sodimate’s all-in-one technology thus effectively addresses arching and clogging problems, enabling a very accurate dosing and a consistent product flow.
The PAC is then introduced into a wetting cone. To subsequently ensure a proper blending of the carbon in the water, spraying nozzles are used to pre-wet the PAC – a challenging product to handle effectively due to its thin and volatile nature. This process plays a vital role in making the powder heavier, causing it to drop down instead of floating at the top and prevents issues such as dust, poor handling and floating. As the PAC becomes heavier and drops to the bottom, the Venturi effect generated by the eductor creates a depression that effectively sucks up the slurry. This depression enables the system to achieve high transfer distances, allowing the slurry to be efficiently transported to the desired location. Sodimate’s eductor system guarantees a dust-free operation, maintaining a clean and safe working environment. Additionally, it boasts low energy consumption, promoting cost efficiency. The system can be conveniently mounted on a skid, providing flexibility in installation. Optional instrumentation allows for customized functionality, and the system enables slurry transfer without the need for a mixing tank.
Unlike other systems considered, Sodimate’s all-in- one retrofit solutions can be seamlessly integrated into existing processes, in this case, under the existing silo, with an adapting cone. This was an engineering Holy Grail for Robert’s team, as it implied no new infrastructure building or site layout altering. “We wanted something that could be added to our existing silo,” adds Robert, “our location was good, it was just that our feeder wasn’t the right one. Other systems I had seen had a separate loading system where a forklift or a crane was required to activate the carbon or a cradle had to be used on top of the feeder, which didn’t look as safe for the operator, rather than just having a silo truck offloading the PAC into the silo and at the base of the silo is where the cones are located, as with Sodimate.”
After an initial meeting and analysis of the plant’s layout, process flow, and requirements, Sodimate planned a complete retrofit for a PAC silo with mechanical discharge, feed, and a slurry eductor system. The drawings, determinations, and installation guides were sent for on-site installation. Once the installation was complete, the flow rates and PAC dosages were calibrated and adjusted, the only concern at the time being the long distance coming from the feeder going into the discharge, which they addressed by adding carrying water to the outlet to give an added pressure to the PAC as it goes into the discharge system to break it down even further. At GUC’s request, Sodimate also provided a different gear reducer to account for the feed rate they wanted.
Results & benefits:
The retrofitting of Sodimate’s PAC feeding system, operational since August 2022, in uninterrupted runs of 6 to 8 weeks, has yielded significant improvements for the GUC Water Treatment Plant with a demonstrated 100% reliability rate, in stark contrast to the frequent breakdowns of the previous system.
The maintenance team acknowledges and appreciates the end of operational disruptions caused by clogs and breakdowns while the operation side expresses satisfaction with the feed rate accuracy and dosage
measurement capabilities of the new system. “Working with the old system which never operated as we wanted it to, and putting in this new system, which, from day one, just ran without issues and does what it’s supposed to do, for us, it crosses all the t’s and dots all the i’s. The reliability with this system is up a 100% compared to what we had prior. All we need to do is add PAC when it runs out. It runs until it runs out of PAC. The retrofitting of Sodimate’s PAC feeding system is considered one of the better purchases we have done in the last 10 years!”, concludes Robert.
Sodimate’s solution was integrated into the plant expansion’s new water clarification flow, the new PAC discharger feeding both GUC’s new superpulsator tank which handles the additional 10mgd and the conventional gravity-fed side which continues to handle the 22.5mgd, ultimately ensuring the delivery of high- quality drinking water to the residents of Greenville, as per GUC’s mission statement.
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