High Capacity Dust-Free Barge Loading
by David Beane and Nathan Browe
The Holcim (US) Ste. Genevieve cement facility is one of the industry’s most technologically advanced plants in the world with an immense production capacity. Built over a five year period, the plant opened in 2009 with the potential to produce 4 million tons of cement per year 1 – an amount that makes it one of the world’s largest cement plants and without question, the largest cement plant in North America.
Located in the heart of the Midwest and midway up the Mississippi River, the Ste. Genevieve plant is strategically located to benefit from low-cost, energy efficient barge transportation with easy access to large cities over the river’s 2300 miles. Efficient river transportation is credited with reducing CO2 emissions by 10 to 25 percent when compared to industry averages per ton of cement produced 1.
Ste. Genevieve was selected as an ideal plant location based on abundant limestone reserves along with the opportunity for Holcim to construct its own Mississippi River port and barge loading facilities. In addition, the facility is also well positioned to take advantage of rail and truck transportation.
With lowering emissions and improving air quality a top priority, Holcim considers Ste. Genevieve to be one of the most environmentally efficient cement plants in operation. This was accomplished through the investment in advanced technology to optimize plant productivity in conjunction with barge transportation efficiency. Barges handle 75% of transportation for the plant which translates into 6.6 million tons of combined finished cement product and associated materials shipped on the water per year 1.
In June 2012, Dust Control and Loading, Inc., (DCL, Inc.) was invited to tour the Holcim Ste. Genevieve production facility to review the new system requirements for the barge load-out area. DCL, Inc. is headquartered in Charlevoix, Michigan and has over 30 years of experience designing and manufacturing equipment for a variety of dust-free bulk loading applications.
Holcim specified the following requirements for their barge load-out area:
- Up to 1000 TPH loading rate of type 1 cement for each of the four retractable loading spouts.
- A positioning capability for the four retractable loading spouts that would accommodate a variety of different barge types. The loading spout would need to be lowered through the barge lid into the barge and maintain continuous contact with the product pile.
- Maintain EPA compliance with no visible dust emissions.
- The new barge load-out equipment would need to interface with Holcim’s existing controls system.
Holcim site-specific challenges and possible obstacles:
- Cement is highly aerated and very dusty by nature.
- There would be a long drop from the fluidized conveyor to the loading spout discharge, especially at times when the water level is low. At the river’s lowest level, the high volume of cement within the loading spout would be falling at a very high velocity, creating a significant amount of energy at the spout discharge and the potential for tremendous dust emissions.
- The equipment was to be designed based on 55 ft. water level fluctuations.
Once back in Michigan, the DCL engineering staff designed a system to meet the unique barge load-out requirements for the Holcim facility. Following the bidding process, DCL was awarded the project and in February 2013, the new DCL, Inc. barge-loading equipment was installed and the first barges were loaded mid-way through the month.
To construct the load-out, five types of equipment were custom designed and engineered for the Holcim Ste. Genevieve application – fluidized conveyors (airslide), rotary positioners, dust collectors, retractable loading spouts and motor starter enclosures.
Fluidized Conveyor (Airslide)
DCL provided short sections of fluidized conveying equipment to interface with the existing fluidized conveyor system and the new DCL equipment. The new fluidized conveyor included a hood with an adjustable blast gate for the venting of fluidizing air into the dust collector.
The Dust Collectors (one for each loading point) are reverse-pulse bag house dust collectors. The dust collectors are the top-load design for easy routine maintenance and have Teflon-coated filter bags that have an excellent shedding capability, even when humidity is high. The filter bags have an air to cloth ratio of 4.3:1 and a can velocity of 164 FPM. The exhaust fan is rated for 7500 CFM @ 14” WC and has a sound attenuator to limit noise levels to < 80 db.
The Rotary Positioners, one per bay on the South ends of the load-out, allow the retractable loading spouts to be lowered into the barges without any interference with the barge lids and will accommodate a variety of different style barges. This is accomplished with 359 degrees of rotation combined with a 7 ft. linear travel that is capable of spout placement anywhere within a 7 ft. radius from the center of the pivot. The rotary positioner also features a shallow traveling hopper in order to maximize clearance. A small regenerative blower fluidizes the hopper much like a fluidized conveyor. The traveling hopper has a vent-thru design that allows the cement to flow through the central chamber while the dust laden air is drawn up around the outside of the central chamber. Careful attention was given to the material velocities throughout the cross sections of the vent-thru equipment in order to minimize pressure loss and allow the released dust cake to fall through. To power the unit, a large, stationary, 36-conductor cord reel was used to transfer motor and control voltage to the positioner and loading spout. Wireless transmitters were also used for some of the controls communications between the equipment and the PLC. A maintenance access platform was included and is suspended from the positioner frame. A “GO” switch allows the operator to rotate the positioner until it reaches a specific “home” position where maintenance personnel can then access the positioner maintenance platform from their mobile bridge crane platform. To achieve the positioning flexibility necessary for the size and scale of the Holcim application, DCL built the largest Rotary Positioners in company history.
Retractable Landing Spouts
There are a total of four DCL model OV58HD-85 retractable loading spouts with one per load-out. The OV58HD-85 designation refers to “open vehicle” specific loading with a heavy duty structural steel frame drive assembly. There is 85 feet of vertical travel with an outer sleeve diameter of approximately 58”. The OV58HD-85 features a single continuous cable that runs from one lifting pulley through a series of transfer sheaves and into another lifting pulley. The design ensures that the spout discharge is always level. Safety features of the OV58HD-85 include two over-travel limit switches and a strain pin that is located inside one of the transfer sheaves which provides continuous feedback regarding the loads being placed on the lifting cable. If the safe working load is exceeded, then an alarm will alert the operator and power will be cut from the lifting spout hoist circuit. For example, if the discharge of the spout is caught under a barge lid as it is being retracted, the additional weight of the lid would trigger the alarm. With each of the four retractable loading spouts designed to load 1000 TPH, the internal components that control the flowing column of material were sized to handle the high volume and the outer flexible sleeve was sized to limit the carrying velocities.
To prevent residual material inside the spout from leaking following the loading process, the spout discharge uses a unique shut-off valve with dual semi-circular discs that rotate to open and close. The design of the valve allows the free flow of cement through the center, and the extraction of dust from the perimeter while loading. Redundant safety interlocks within the cement feed system eliminate any cement flow into the spout unless the valve is in the open position.
Motor Starter Enclosures
DCL provided control panels, one per load-out, which simplified the installation of the equipment from an electrical standpoint. Included were starters and variable frequency drives for the motors and terminal strips for the I/O. With the addition of motor starters, Holcim only needed to provide a single point power source for the high voltage motors and label terminal strips to match the corresponding PLC I/O. DCL worked closely with Holcim electrical engineers during the commissioning process to ensure that the PLC programming was optimized.
The Holcim Ste. Genevieve cement plant is an example of the strong commitment to innovation and the fresh thinking necessary to achieve production efficiency while significantly reducing environmental impact at the same time. John Cooper, Manager of Projects and Engineering at Holcim Ste. Genevieve commented that “DCL worked well in conjunction with the Holcim project team, incorporating a number of requested innovations during the design and commissioning process. The net result has achieved all of the specified design requirements with a significant improvement over the original equipment.” Tim English, the President of DCL added, “We enjoyed our collaboration with Holcim on the Ste. Genevieve project and we’re extremely proud of our DCL team of experienced professionals that stepped up to meet the challenges that the project presented.”