Fig.1: System Concept
The Hong Kong Science & Technology Parks (HKSTP) was the first commercial building which has installed the Automated Refuse Collection System.
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The components of the Automated Refuse Collection System
The Automatic Refuse Collection System (ARCS) consists of the following parts:
1. Central Collection Station
This is where all refuse is collected after pneumatic transport. All equipment, which performs and supports the collection process, are installed here.Fig.2: Diagram of main components of ARCS
2. Refuse Transport Pipes
A Network of underground transport pipes connects the collection station with the building and sites where the refuse originates.
3. Vertical Gravity Refuse Chutes with Loading Doors
The vertical chute run down the length of the building and connects to the refuse transport electronically locked. There is no vacuum in the chute, the
refuse bags fall by gravity down to the discharge valves.
4. Refuse Discharge Valves
These valves are located at the bottom refuse chutes and serve as a barrier between transport pipes and the vertical refuse chutes. Waste is stored on top of the valve ready for collection.
5. Air inlet Valves
These valves, located at the end of each branch of the pipes system, provide the transport air to enter the system.
6. Out Door Loading Stations
These inlet points provide outdoor disposal access to the pipe net work.
The pneumatic refuse collection systems function automatically. Human assistance or supervision is not required during the collection process. A computer, located in the central control panel controls the collection process. During the collection process, the refuse that has been stored on the refuse discharge valves is collected. The collection process is generally repeated two to five times a day. The duration of each process varies between 2 15 minutes, depending on the size of the system. Between the collection times, all machinery of the pneumatic transport system is turned off. The refuse can however be loaded into the chutes at any time when the system rests.
1. The exhausters start and create airflow in the refuse transport pipe system. 2. The central control panel orders the first air inlet valve to open. When the valve is open, a confirmation signal is sent back to the central control panel. 3. A powerful air-steam is created in the refuse transport pipe system from the first air inlet valve to the refuse collection station. The air steam must be powerful enough to transport even the heaviest refuse components. 4. After verifying that a minimum air speed has been established in the transport pipe, the central control issues an order to the first refuse discharge valve on the corresponding pipe branch to open. When the valve opens, the refuse which was stored above the valve falls by gravity/suction into the refuse transport pipe and is transported by the air stream to the collection station. 5. After a period of about 7 seconds, all refuse stored on the first valve is discharged, and the valve is closed.
6. After a short interval, the second refuse discharge valve on the same pipe branch receives an order to open. The same operation described in step 4 is repeated. 7. When all refuse discharge valves connected to the first pipe branch have been discharged, the air inlet valve is closed. 8. After a short interval, an order to open is transmitted to the second air inlet valve in the next pipe branch. The same procedure described previously in step 4 is repeated.
9. The operation is repeated, until the refuse from all discharge valves of all transport pipe branches of the system has been collected. Throughout the collection cycle only one valve is opened at a time and thus each refuse chute is emptied in sequence. 10. When the refuse reached the collection station, the refuse is separated from the transport air steam in the refuse separator. The refuse then falls into the compactor and is compacted into the attached containers. 11. The full containers are then picked up by a standard arm lift truck and transported to suitable sites for emptying. Equipment used in Hong Kong Science and Technology Parks
1. Collection Station
The refuse collection station can be located in a separate building or form part of a another building, e.g. a car Parks. Principle equipment in the collection station consists of:
Fig.3: Collection system in HKSPT
i. Air Exhausters
The exhausters are used to create an appropriate air stream and negative pressure in the underground pipes. In Hong Kong Science and Technology Parks, three exhausters connected in series are installed. Only two will be used, and the other one is used as a stand-by mode.
Fig.4: The Exhauster used by HKSPT
ii. Refuse Containers and Compactor
The size of number of the refuse containers depend on the quantity of refuse collected. Normally, one to five containers are used. In Hong Kong Science & Technology Parks, two refuse containers are used. Each container has the capacity to store ten tonnes to the refuse compactor.
Fig.5: A typical compactor (above); Compactor used in HKSTP (left) iii. Control System
The central control panel controls the automatic refuse collection process. The central control panel consist of the following components: desk top computer with modem for remote control, control board for the general operation, motor control panel, and a panel for the container handling system.
iv. Dust Filters
The transport air requires filtering prior treatment for odour control. The filter installation normally consists of cassette bag type filter for dry filtration installed downstream of the air exhausters.
v. Odour Filters
The exhaust gas passes through an activated carbon filter and a water scrubber to remove odorous gases.
Fig.6: Activated carbon filter
vi. Container Transport
The container transport vehicle does not pertain to the ARCS itself. However, when installing an ARCS, the container transport vehicle always be taken into consideration. The vehicle limits, to a certain degree, the location of the collection station. It is often desirable to locate the collection station at the outer boundary of the installation to minimize local traffic of heavy vehicles.
Fig.7: Container Transport
vii. Diverter Valve
A diverter valve is installed if we are collecting more than one category of waste (i.e. recycling). In Hong Kong Science & Technology Parks, there are two containers, one for non-recycling waste, another one is for recycling waste. So it is used to direct the waste into the correct container.
2. Pipe Network
Fig.8: Pipe Network in HKSTP
Refuse Transport Pipes
The refuse transport pipes are normally manufactured of mild carbon steel. But in the Hong Kong Science & Technology Parks, the pipes are made of stainless steel. In sections where large quantities of refuse are transported or high impact regions (bends and Y-pipes) pipes must be manufactured of material with greater hardness. The wall thickness of the pipe also varies in different parts of the system to cater for different erosion factors. All parts of the transport pipe system are welded together. The transport pipes are usually installed underground. In Hong Kong Science and Technology Parks, however, has use two service tunnel. All the utilities, including the transport pipe, were installed in the service tunnel. Fig.9: The ARCS transport pipe in the service tunnel in HKSTP 3. Refuse Discharge Valves
The refuse discharge valves (DV) separates the vertical refuse chutes form horizontal transport pipe system. The valves are normally installed on the basement level in the buildings. The refuse is stored above the closed valve between emptying cycles. When the valve opens, the refuse falls by gravity/suction into the air stream in the transport pipe. Only one valve can be open at one valve. The operation of the valve is controlled by the computer in the central control panel in the collection panel. Control boxes in the refuse valve rooms verify and execute the orders transmitted from the central control panel. A storage section was installed above the valve, where refuse collects, in HKSTP. A level sensor also has installed which will alert the control centre to start the collection process when full.
4. Air Inlet valves
The air inlet valves are located at the end of each branch of the refuse pipes. The Valves are usually installed on basement level in the buildings near the last refuse discharge emptying cycles.Fig.10: Air inlet valve
5. Refuse Chute and Refuse Inlet Doors
The vertical refuse chutes form part of the building and provide inlet doors for refuse disposal at each level of the building. The refuse chutes are only subjected to a slight negative pressure. The chutes are normally constructed of concrete or steel.
Fig.11: Refuse Inlet Door
In order to prevent blockage of the refuse in the chutes and in the transport pipes, the inlet doors are volume controlled, where the dimensions of the refuse disposed should not exceed the inside diameter of the transport pipes. At the top of the chute, a ventilation fan is provided for exhaust extraction.
Different Configurations for Recycling Purpose
For the first one, there is one main chute, which runs down the building servicing all levels. This main chute will primarily be used to collect non-recyclable waste on a daily basis. The ground level outdoor disposal inlets are provided for the disposal of recyclable materials such as paper or organic refuse. In this configuration, it is necessary to manually carry the recyclable waste from the buildings and out to the specified inlet for collection.
Fig.12: one chute disposal inlet
For the second one, this type of set-up provides the full service of recyclable waste disposal to each level of the building. The collection principle is the same as for the first configuration. However, this arrangement allows disposal of recyclable wastes at the doorstep of each apartment.
Fig.13: Three different refuse chutes are used to transport different categories of wasts Conclusion
At the time being, Since the Hong Kong Science and Technology Parks is still under construction and not yet fully complete. (Phase 1 is 70% finish, Phase 2 & 3 has not start.) Therefore, the ARCS is not fully utilized, and only a few waste was generate per day. However, according to the regulation in Hong Kong, it is not allow to store waste within a long period. It may be not efficiency if transport the waste to landfill with only a few wastes was generated. Therefore, under special arrange, it is allow for HKSTP to store up to 80% of the capacity before a transport the container. It is because only dry waste is allowed to put in this system. Therefore, odour is not problem.
Moreover, the ARCS is possible to collect waste about 1 km far away, it have a big potential to replace the Manual waste handling. Since manual waste handling may bring a lot of hygiene problem.