A producer serving one of the fastest-growing areas in the U.S. — southern Nevada, where expansion is expected to continue for the next 20 years — Glendora, Calif.-based California Portland Cement Co. constructed a transfer terminal in North Las Vegas to meet rising demand. The terminal, capable of transferring 500,000 tons of cement per year to the Nevada market, is designed to off load 100-ton railcars at a rate of 200 tph into three steel silos using a pneumatic conveyor system. A dedicated double rail spur will accommodate as many as 30 railcars by feeding cars from one spur to the other. Three silos permit handling of more than one product, and three adjustable loading spouts fit a variety of truck configurations.

To mitigate the terminal's visual impact, surrounding landowners, developers, and the city of North Las Vegas required that the terminal height be minimized. In compliance with an established maximum-overall-height limit of 62-ft, the terminal was designed to harmonize with surrounding land use, aesthetically complementing the area in a manner acceptable to the city and local developers.

Triplet storage silos

The total storage capacity of the terminal is 91,000 cu ft. Each of three identical silos has a storage capacity of 1,200 tons. Available for alternate products, the center silo can discharge to either of the loading spouts as well as to the pneumatic conveyor for recirculation of material from one silo to the other.

A 38-ft, 6-in.-diam, fully aerated, 8-degree silo bottom allows the structures to satisfy storage requirements while meeting height restrictions. Covering 90% of the silo-bottom surface, aeration pads are segmented and selectively valve-controlled for directing material to the desired location, thus limiting blower size to 600 cfm. The resultant reclaim capability is 99.6% of stored product.

Cement is conveyed from the silo bin bottoms to the loading spouts by aeration conveyors. The two outboard loading spouts incorporate 2- × 6-ft horizontal positioners on 53-ft centers. Reaching truck hatches from 47 to 59 ft apart, the spouts readily accommodate nearly all trucks using the terminal. A third spout and 2- × 2-ft positioner in the center permit convenient loading of triple-trailer rigs.

Each loading point is provided with an integral dust collector, eliminating the need for ducts and maintenance associated with a remotely mounted dust-collection system. A 130-ft-long, aboveground scale is supplied as two independent platforms, allowing the simultaneous loading of each trailer for reduced loading time. Dual-trailer, 120,000-lb. Nevada rigs are loaded in five minutes.

The loading spouts are fitted with self-sealing cones that close to terminate discharge when not seated in the hatch. By eliminating the dribbling of cement from the spouts upon retraction, self-sealing cones reduce housekeeping requirements.

Low-profile rail unloading

When 100-ton railcars deliver cement to the terminal, product is transferred through two unloading boots that seal against the rail car discharge doors. Accordingly, the cement is discharged into two inclined drag conveyors and carried to a dilute-phase, dual-pod conveying system that delivers the material to one of the three silos. The pneumatic conveyor was selected to maintain a low-elevation profile on top of the silos and to facilitate future expansion of the conveying system.

Push-button control

The terminal is controlled by means of an Allen Bradley PLC SLC 500 with a PC interface. Once the operator aligns the spouts to the hatches with the aid of video cameras, PLC-controlled truck filling is initiated through a start button. A manual override option is available as needed. The silo aeration sequence is also fully automated, as is the twin-platform scale, which permits simultaneous weighing and control of two trailer loads. Inventory and shipping data is transmitted electronically to California Portland offices.

This article was adapted from material supplied by Dust Control and Loading Systems, Inc., Charlevoix, Mich., (+1) 800-748-0563.