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16 / July 2020 powderbulk.com tive block flow diagrams are shown in Figures 1 and 2. Option 1. The mechanical con- veying system consisted of two air-supported belt conveyors that received material from two vibra- tory feeders and one chain bucket elevator that carried the material into a high-pressure grinding roll (HPGR) feed silo, as shown in Fig- ure 1. Air-supported belt conveyors were selected given the material's abrasiveness, the required capacity, and the layout, which was a rela- tively long transport for in-plant equipment. Additionally, this option was a good fit because of the equipment's ability to control on here is the process and not the individual numbers. This case study involves a new process plant that needed a con- veying system that would receive a hot and extremely abrasive mate- rial from two vibratory feeders and carry the material to a silo. The application's process data is broken down in Table I. As you can see, the material was conveyed at 95 short tons per hour (stph), con- tained particles up to 1⁄8 of an inch in size, and contained silica dust, which had to be controlled as silica is hazardous. Two different conveying options were considered and their respec- reviews with plant maintenance personnel. Their input is crucial in this part of the process, as they will bring valuable experience to optimize access to critical parts and input on estimates. Personnel can also help to identify access areas that will need to be reworked for the project implementation costs that will need to be included in the CAPEX estimate. Equipment's annual power con- sumption. Some equipment is more energy intensive than other equip- ment for the same duty. This power consumption obviously impacts OPEX and should be evaluated considering local energy costs. As a side note, make sure your electri- cal room and grid can sustain the additional loads and include the financial cost of necessary upgrades in the project CAPEX. Lost production time. If the spare parts can be changed during a scheduled shutdown, this is less of a problem, but some applications will require frequent changes in spare parts, causing unscheduled downtime that will need to be con- sidered in annual profit loss. Some process equipment needs additional ramp-up time after a shutdown before the equipment becomes pro- ductive again, and this should be considered in the evaluation as well. Technology trade-off case study Now that we've presented the backbone for the OPEX evaluation, we'll present a case study to illus- trate how the determined OPEX can affect the technology selection in a real-life scenario. Note that the numbers presented here are representative of a specific project process, design criteria, and con- ditions. Numbers will be different from project to project, so they need to be studied on a case-by-case basis. The important point to focus FIGURE 1 Option 1 block flow diagram Vent HPGR feed silo Bucket elevator Air-supported belt conveyor Vibratory feeder Air-supported belt conveyor Vibratory feeder FIGURE 2 Option 2 block flow diagram Vibratory feeder Vibratory feeder Vent HPGR feed silo Rotary airlock Rotary airlock Positive- displacement blower