What are Pneumatic and Mechanical Unloading System?Pneumatic transport for unloading from ships uses suction systems and is always in dilute phase.For pneumatic transport by pressure systems, dense phase and dilute phase are both possible. For long distances and high capacities the dilute phase system is preferred, while plugging can be avoided easily.Mechanical unloading is done in various ways, of which the grab-unloader and the screw-unloader are commonly used. The grab-unloader is considered non-continuously, while pneumatic- and screw-unloaders are considered continuously.Features & Benefits of Grab-UnloadersHigh flexibilityAcceptable reach in holdsAcceptable energy consumption per tonClean-up capabilities under normal conditions sufficient.Dust emission caused by leaking grab shellDust emission when opening grab shell by air displacement.Receiving hopper with dust extraction filters around the circumference.Receiving hopper with rain cover when not operating.The hopper can also be filled through a pneumaticConveying pipeline, using the filters for deductingThe convey-air and with closed rain cover.Risk of damage to the shipWearing on rope wires and grabsSubsequent transport also mechanical by means ofBelt conveyors, screw conveyors, trucks, screw feeders, etc.Features & Benefits of Screw-UnloadersLow flexibility.Different types of commodities do mix withRemaining products in dead spaces in the system.Insufficient reach in holds due to rigid constructionLower energy consumption.Clean-up capabilities are poor due to the principle of the vertical screw, whereby the screw section must be completely filled to transport (use of additional devices)System is sensible for blocking in case of overfeeding (use of additional control system)Dust emissions in the holds by avalanches and during cleanup because of product falling back from the screw in case of insufficient filling. Risk of damage to the screw by foreign matter. In such an event the screw can even get stuck.Wearing on screws, screw pipes and shaft sealsSubsequent transport also mechanical by means of belt conveyors, screw conveyors, trucks, etc.A pneumatic subsequent pressure-transport is also an option with the related properties.Features & Benefits of Dilute Phase Pneumatic Transport:High flexibilityEasy reduction of dead spaces in the system internallyMakes the system suitable for handling different types of commodities because of simple and minimum cleaning proceduresReach in holds improved by manoeuvrable nozzle intoTwo perpendicular directions - because of the principle of pneumatic dilute transportA higher energy consumption. (higher velocities)Clean-up capabilities are good, due to the Feeding independent function and movability of the Suction nozzle into two perpendicular directionsVacuum system is not sensible for blocking (or plugging) because of operating principle with application of positive displacement pumps.Pressure system is almost insensible for blocking due to regulating system for continuous maximum performance.Dust emission in the holds is reduced to a minimum by "skimming off" movement of nozzle and downwards flowing covey-air. This also applies for the clean-up situation.Proper operation of shovels is then required.Limited risk of damage to the system by foreign matter. Too big lumps are left behind in the hold. Smaller lumps can pass the system freely.Butterfly valves can be affected by foreign matters. (mainly ropes).Little wearing only on butterfly valves.Subsequent transport is generally also pneumatic, especially where long distances and difficult routing are involved.Combination of mechanical- and pneumatic convey system using screw feeder.A screw-feeder consists of a screw with a reducing pitch along the screw in the transport direction whereby the screw fits exactly into a tube. The feeding of the screw is then higher than the output. This causes the material to be compacted and forming a plug in the tube. This plug can be stable and strong enough to withstand and seal against the high pressure in the pipeline.As the screw feeder in a pneumatic pressure convey system has to push the compacted bulk volume against the pressure underconsiderable friction between the tube wall and the screw flights, this type of feeder consumes a high energy per conveyed ton, depending on backpressure.(i.e. 110 kW for 150 tons/hr at 1.7 bar(o) # 0.73 kWh/ton)Higher pressure requires higher power, also due to increased friction. A to high pressure will cause the drive motor of a screw feeder to stall and choke the screw tube.The screw feeder/pneumatic convey systemSystems using a screw unloading, with the inherit properties, that dump the product into a screw feeder for subsequentpneumatic pressure conveying, will therefore consume this extra amount of energy compared to a double pressure vessel system.This additional energy consumption is a considerable disadvantage.ConclusionAs a terminal design is depending on many parameters, s.a. maximum ship size, annual throughput, local labor cost, dock structure, etc. these variables may influence the decisions.As an unloader has to handle ship unloading through your installation, a failure will stop your operations immediately. Captains Group can provide you a well designed loader-unloader of high quality and maintainability and lowest possible energy demand. To know more details, please contact with us.
Captains Group is a reputed Ship Unloader System Manufacturer in Bangladesh. We manufacture a complete range of mechanical and pneumatic transport for bulk handling of ship loading-unloading. The unloader system manufactured by Captains Group is in operation at different Bulk Cargo Jetty in Bangladesh.