Summary
Highlights
A practical example is solved to determine the diameter and pitch of a horizontal screw conveyor for transporting heavy material, applying the empirical formulas discussed. This demonstrates how to use the provided equations and tables for Cβ and Cfs values based on material type and inclination.
Various types of screw conveyors, such as continuous and band-type (discontinuous) screws, are presented. Advantages of screw conveyors include simple design, easy maintenance, compactness, and convenient intermediate unloading. However, disadvantages include high power consumption, substantial material rubbing/crushing, and high wear on the screw and trough.
The lecture introduces the topic of solid transportation, highlighting its challenges and importance in process industries. It outlines the differences in transporting solids compared to fluids and the necessity of specialized equipment for this purpose. The selection of equipment depends on material characteristics, capacity requirements, and the transport direction (horizontal, vertical, or inclined).
Various methods for in-plant solid transport are discussed, starting from unassisted manpower for short distances, evolving to assisted manpower using hand trucks and trolleys for distances up to 70 meters. For longer distances, portable power-driven machines like electric trucks and power shovels are employed, though power shovels primarily load material onto other transport vehicles.
For very long distances, traditional methods like rail, road, and ship transport are mentioned. However, for distances between 10 to 20 kilometers, mechanical conveyors become more economical than rail or road. The lecture then introduces mechanical conveyors, characterizing them by their use of mechanical drives to move solids, either by carrying them or dragging them through channels.
Different types of mechanical conveyors are listed, including screw conveyors, flight conveyors (scrapers), belt conveyors, apron conveyors, and bucket conveyors (carriers). The distinction between scrapers (which drag material) and carriers (which carry material) is explained. The selection of a conveyor type depends on capacity, travel distance, material shape and size, material characteristics (e.g., sticky, abrasive), and transport inclination.
Screw conveyors are discussed in detail, illustrating their mechanism for transporting pulverized and granular solids over relatively shorter distances (up to 40m horizontally or 30m vertically). They are effective for materials like grain, sand, and coal but are not recommended for sticky or abrasive materials due to the dragging action. The construction, including the semi-cylindrical trough and rotating screw, is explained.
The lecture provides empirical relationships for calculating the throughput capacity (Q) and power consumption (P) of screw conveyors. Factors influencing capacity include screw diameter, lead, rotational speed, material density, and correction factors like Cβ (inclination factor) and Cfs (filling coefficient). Power consumption calculation considers friction, bearing resistance, and ascending motion, using a total resistance coefficient (Kts).