Rock Products

JAN 2018

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Page 36 of 73 ROCK products • January 2018 • 33 The original dust control equipment followed that traditional approach, with a goal of wetting the surface of the cargo in order to promote cohesion of particles and prevent them from becoming fugitive airborne emissions. However, Continental Cement discovered issues with this type of solution when applied to its material handling and stockpiling operations. Operators learned that limestone dust was not being ade- quately controlled by the water alone. In addition, the water supply was found to have an excessive sodium content, causing the nozzles, valves and other components to quickly deteriorate and fail, resulting in leaks and insufficient water pressure. A Holistic View Martin Engineering representatives visited the site with a trailer containing a fully functional Martin Dust Control Unit (DCU), allowing a full demonstration of the unit's capabili- ties. Conducting an end-to-end walkthrough of the cargo flow, technicians were able to determine the best course of action. "After inspection, we devised a plan that optimized the dust control at both locations, while using as much common equipment as possible," said Brian Nance, product engineer at Martin Engineering. "Martin's DCU is designed to inde- pendently control dust at several application points, thus allowing for the use of much of the same technology, while employing a different strategy for each of the two emission areas. Using the same additive, we were able to offer treated water suppression close to the hopper's point of emission and then also apply the chemical at the transfer point between Conveyor 0 and Conveyor 1 to mitigate emissions all the way up to the stockpile discharge point." Constructed over two days and scheduled to coincide with mine downtime, three technicians installed the DCU at a location with water and electrical power. A six-nozzle cra- dle-mount system was installed to provide serviceability at the Conveyor 1 discharge, and a manifold system was placed to address the issues at the dump pocket. Material moni- toring sensors were employed at both locations to ensure application only when needed. The pumps in the DCU are powered by variable frequency drive (VFD), allowing independent control over the flow of water and chemicals for each pump. Water application is monitored, and the proprietary Martin MEL-101 chemical binder additive is dosed at the proper ratio to suit the operat- ing conditions. Fail-safe mechanisms are incorporated to shut the unit down and close valves to protect pumps and other equipment from line blockages or breaks. The entire system is integrated with the plant's system, so that it can be mon- itored remotely from the central control room for the plant. Using additives, limestone dust particles are able to agglomer- ate with each other, increasing in size and weight and making them less likely to become airborne, thus preventing fugi- tive emissions. With an approximate 300:1 water-to-additive ratio, the MEL-101 supports the water's role in providing dust suppression using economically concentrated quantities. To control costs, the VFD driven pump regulates chemical flow by only releasing chemical when material is detected. Sprayer Placement is Key "The theory behind how we placed the spray heads is import- ant," said Nance. "It's common practice for companies to spray the top of the material after it's been loaded on the belt as it's exiting the settling zone. But that approach wouldn't work for this application." He went on to explain, "The problem with only spraying the surface is that only surface particles are treated, and the fines tend to ride on the bottom layer near the belt, pre- venting them from being effectively coated. The untreated particles easily become fugitive once the cargo is disrupted or transferred." Due to the difficulty of treating particle emissions at the dis- charge of Conveyor 1, technicians set up the Martin DCU to spray the material in the transfer chute between Conveyor 0 and 1. "By attacking the material from the top and bottom while it's in free fall, we are able to effectively coat more of the dust particles," said Nance. "As cargo continues its transit and is discharged onto the stockpile, the particles are already treated and remain in the material flow." Nozzles were placed at the hopper mouth, so the DCU could spray treated moisture inward toward the impact zone. As the cargo is loaded by haul trucks into the dump pocket, the discharge creates a tremendous amount of airflow, lifting the small particles into the air. Prior to the Martin system's installation, fugitive dust would exit the far end of the hopper This graphic illustrates that the most potentially harm- ful particles are the ones too small to see.

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