Some Studies on the Principles and Mechanisms for Loading and Unloading
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There are three common standard lengths, 20 feet (6.1 m), 40 feet (12.2 m) and 45 feet (13.7 m). There are wide varieties of containers that are being used in practice. Most of the containers have standard widths and heights, with standard lengths varying from 20 to 53 feet. After several years of usage, some containers might lose a few inches due to minor accidents and repairs. The dimensions of ISO and non ISO containers are presented in Table ý1. (Source: Kang, 2006). Container capacity of ships and ports is measured in twenty-foot equivalent units (TEU). Figure ý1. shows 1 TEU, and 2 TEU normal, and 2 TEU high cube containers. A twenty foot equivalent unit is a measure of containerized cargo equal to one standard 20 ft (length) × 8ft (width) × 8.5 ft (height) container. Most containers today are of the 40-ft variety and are known as 2 TEU. Two TEU are referred to as one FEU or "Forty foot equivalent unit”. These two terms of measurement are used interchangeably. "High cube" containers have a height of 9.5 ft (2.9 m), and half-height containers used for heavy loads have a height of 4.25 ft (1.3 m). The cost of a 20-feet container is approximately $2,000 to $3,000 (1-1.5 lakh Indian Rupees) and a 40-foot container can be anywhere between $3,100 and $4,500 (1.6-2.25 lakh Indian Rupees). Table ý1. Dimensions f ISO and non- ISO containers 40’ High Cube container 40’ container 20’ container Figure ý1. Forty feet normal, forty feet high cube, and twenty feet containers Containers are also classified on the basis of the type of cargo carried in them. As per this classification, there are four basic types of containers; dry cargos, liquid cargos, bulk commodities, and special cargoes requiring protection from the environment. According to their function containers are classified into general purpose, refrigerated, high cube, open top, flat top, and tank containers, etc. Table ý1. shows these types with their character and applications. Table ý1. Types of containers Container TypeCharacter Application Figures Standard 20' - Max. Payload: 28,23 Tonne(T)
40'HC-Max.Payload: 25,58 TEquipped with a removable steel roof. Especially for heavy loads and over height cargo. Loading through roof opening and doorway by swing outdoor header Open Top20' - Max. Payload: 28,13 T 40' - Max. Payload: 26,63 TWith removable tarpaulin. Used especially for over height cargo. Loading either from top side or door side by swing outdoor header. Flat Rack20' - Max. Payload: 31,26 T 40' - Max. Payload: 26,28 T 40'HC-Max.Payload: 39,30 TEspecially for heavy loads and over width cargo. Platform 20' - Max. Payload: 31,26 T 40' - Max. Payload: 39,30 TEspecially for heavy loads and oversized cargo. Ventilated20' - Max. Payload: 27,99 TEspecially for cargo which needs ventilation. Refrigerated20' - Max. Payload: 27,45 T 40' - Max. Payload: 29,40 T 40' HC - Max. Payload: 29,88 TReefer containers do have their own electrically operated cooling / heating unit. The power supply is provided by ship's electrical plant, by terminal or by "clip-on" diesel generator. Insulated20' - Max. Payload: 21,45 T 40' - Max. Payload: 26,63 TThese containers do not have their own cooling facility. The cooling / heating is supplied by an onboard plant, by terminal or by a "clip-on" reefer unit. Tank24000 Litter /Litter WaterFor the transport of liquid food, e.g.: Alcohols, Juices, Edible Oils, Food Additives Advantages and disadvantages There are many advantages of using containers as a packaging unit, some of which are outlined below: Use of containers reduces loss, pilferage and damage claims significantly. It eliminates a great deal of paper work related to shipments. It expedites door-to-door pick-up and delivery service of cargo by reducing the time for loading and unloading operations. It eliminates multiple handling of cargo because a container is handled as a unit. The consolidation of small loads into a unit load is possible with a container, leading to economy in freight cost Improvement relating to handling, marketing and pattern of packaging is made possible by the container It is possible to reduce the cost of packaging because of possibilities of placing goods without heavy packaging inside the container without any risk of damage in transit. A container combines all the advantages of various mode of transport by rail, road and sea. Containerization has led to improvement in the construction of boxes or containers, and quick turn-round of modes of transport ¨C whether ship, rail, road- which leads to economy in the cost of transport. The main disadvantages of using containers are as follows Containerization increases the fuel costs of transport and reduces the capacity of the transport as the container itself must be shipped around not just the goods. For certain bulk products this makes containerization unattractive. When transporting containers through railways, containers cannot be stacked in layers due to vertical height limitations. As a result transportation through railways sometimes becomes difficult Containers occasionally fall from the ships during storms. It is estimated that over 10,000 containers are lost at sea each year. Identification system Like any vehicle, every container has an identification system based on a unique registration number. The identification system for containers (ID) is based on a series of letters and numbers that represent the owner’s code, the serial number and the code for the country of origin. The registration number is given on all four sides of the container which makes it possible to identify its owner, and to identify the contents of the container. Other important information about the container is also provided by these numbers. All containers are, therefore, required to have these identification numbers and letters. A system also been developed to check this information, and details of the type and dimensions of containers is also expressed in figures. Figure ý1. Example of container ID The container ID is composed of several fields as shown in Figure ý1., including the following fields: 1. The shipping company (e.g., “UXX”) 2. The equipment category (always “U” for freight containers, "Z" or "C" for chassis) 3. The serial number of the container (e.g., “423697”). 4. The check digit of the first 3 fields (e.g.,”0”) 5. The container type (e.g.,”SE4310”) Only the first 3 fields are relevant to the identification of the container, and represent a unique identification number for each shipping container. In the above case, this ID is “UXXU 423687”. The shipping company field ("UXX"in the example) is verified against a pre-defined list of known companies. Additionally, the second field ("U") is always verified. The check digit is used in order to verify the entire 10-character identification number. If the check digit is not identified, only the 10 characters are compared and reported. If it is recognized and tested for correctness, it will also be reported (a "0" in the above case). The container type (in the above example,”SE4310”) is not part of the ID and is not identified or transmitted. Container terminal structure and handling equipment Container terminal is a facility for loading and unloading of containers from ships or another means of transportation. In general terms, a container terminal is an area designated for the stowage (see appendix A) of cargos in container, usually accessible by truck, railroad, or marine transportation. At container terminals, containers are picked up, dropped off, maintained, and housed. Types of container terminals and typical processes are given in the next section. Processes at container terminal Container terminal can be classified mainly into three types: Sea port container terminal Rail container terminal (Dry port) Inland container terminal Containerships as shown in Figure ý1.Figure ý1. are nowadays unloaded and loaded at large sea port container terminals. This loading and unloading of container process can be divided into different sub-processes as shown in Figure ý1.. Figure ý1. view of containership Figure ý1. Process of loading ¨Cunloading containers When a ship arrives at a port, a berth is assigned for unloading. After the ship is positioned under the quay crane(s) (QCs), the containers are unloaded by the QC and are loaded to fleet of trucks and transported to yard area for storage. At the storage area containers are stacked into blocks. Equipments, like cranes or straddle carriers (SCs) serve the blocks .On the berth, a necessary number of quay cranes (QCs) are allocated to unload the containers. A straddle carrier can both transport containers and store them in the stack. It is also possible to use dedicated trucks to transport containers. If a truck arrives at the stack, it puts the load down or the stack crane takes the container off the truck and stores it in the stack. Containers are stored in blocks for certain period until they are claimed by the importer. When containers are claimed, containers are retrieved from the stack by cranes and transported by trucks to transportation modes like barges, deep sea ships, trucks or trains. To load export containers onto a ship, these processes are executed in reverse order. Figure ý1. illustrates a summary of the main operations in a container terminal. Every process is highly dependent on the previous one. Except for arrival and departure of external trucks all the operations are under the control of port’s personnel. A large number of highly dependent operations need continuous coordination and high degree of efficiency. A complete description of various equipment used, and the operations inside the terminal have been described by various researchers with a view to facilitate decision making within the terminal (see Silberholz et al., 1991; Kozen 1997; Nevins et al., 1998; Lee et al., 2003, Linn, et al., 2003, Steenken et al, 2004; Murty et al., 2005a; Murty et al., 2005b; Dekker et al., 2006; Petering, et al., 2006; and Petering 2007). Most of the terminals make use of manned equipments, like straddle carriers, cranes and multi-trailer-systems. However, a few terminals, like terminals in Rotterdam, are semi-automated. At such terminals Automated Guided Vehicles (AGVs) are used for the transport of containers. Furthermore, the stacking process can also be done automatically by Automated Stacking Cranes (ASCs). In practice, the number of containers to be unloaded from or loaded onto a ship is fairly large, ranging from 500 to 2500 containers (Ioannou et al., 2000). Technologies for movement of containers Since containers are large and heavy, specialized material handling equipment are required for transporting them within the terminal. A container terminal provides the location, mechanical devices, space and operating conditions under which the container transfer takes place. Container yard is a materials handling/storage facility used for completely unitized loads in containers and/or empty containers (Dirk, et al., 2004). A great variety of handling equipments are involved in container yard operation (Ioannou et al., 2000). Figure ý1. Different types of handling equipment and their stacking capacity General information as well as particular details of technical equipment for container handling are provided by engineering oriented journals as well as by specialized outlets, brochures, or websites of suppliers of material handling equipment and services in the container sector (e.g., PTI 2006, Kalmar 2006, Noell 2006,and ZPMC 2006) Common equipment such as the chassis-based transporter, straddle carriers (SCs), Reach Stacker (RS), Rubber-Tired Mounted gantries (RTMG) crane, Rail-Mounted Gantries (RMG) crane, are compared in terms of the actual stacking capacity in Figure ý1.. (source:Kalmar, 2006) Over the last decade, technology and automation have been introduced into the container business to improve the efficiency, increase capacity, and meet future demands. Furthermore the explosive growth of freight volume has greatly increased the load on container terminals. Recent advances in electronics, sensors, information technologies and automation have motivated the port authorities to adopt advanced technologies to cope with the booming growth. In the next section, a brief review of some of equipment used for moving the containers within the container terminal as well as details of recent technologies and automation equipment is presented. Container handling equipment Most of the terminals make use of the equipment, like lift truck (front end loader, side loader or reach-stacker), straddle carrier, rail mounted and rubber tyred gantry crane, etc. quay crane at quayside. Straddle Carrier Straddle carriers (SCs) are four wheeled vehicles that are able to pick and drop a container by itself at high speeds. They are available for handling different sizes of containers and with different vehicle-lifting ability. SC as shown in Figure ý1. is often used in medium size multi-modal facilities where speed of operation is important. They are the most common form used for manned inter-terminal transport over short distances say, between the quay side and storage yard. SCs remain popular because of their relatively low purchase cost, smaller yard development cost and their economic and flexible operations (Ioannou et al., 2000). However, SCs are less space efficient, have lower operational capacity and less suited to higher automation and have greater downtime and higher maintenance cost [for more technical information see Siemens, (2007a)]. Figure ý1. Straddle carrier at Singapore port Fork lifts Fork trucks are sometimes used for container handling for small capacity up to 5 tonnes. They are generally considered unsuitable and not recommended for containers because of lack of visibility to the driver, as a result of which there is possibility of damage to containers. Forklifts cannot be used for containers that are not fitted with the pockets for fork truck. Reach Stacker A reach stacker (RS) is a type of fork lift with a telescopic boom and top-lift attachment used for lifting and stacking containers. Its design enables it to reach beyond the first row to pick up a container. Figure ý1. shows a reach-stacker that operates in the container terminal. Its main task is to stack containers and to load them into trucks, tractors or trains. It is a road vehicle, with a high tonnage capacity. Its storage capacity is approximately equal to 500 TEU per hectare. It can stack containers up to 3 containers high and can reach a maximum height equivalent to 5 containers high. The capital cost for a RS is low as compared to other container handling equipment. RS is recommended for small to medium size operations in multi-purpose terminals. Figure ý1. Reach Stacker at ICD, Tughlakabad Multiple trailer system A multiple trailer system (MTS) (also called multi-trailer system) is one where a towing vehicle transports more than one container to and from the container yard. It is also known as elephant trains, and is shown in Figure ý1.. It can move eight trailers loaded with container, which can lead substantial reduction in operation and labour cost (Ioannou et al., 2000). Development of Multi-Trailer System (MTS) has been carried out by the Technical University of Delft, Netherland. The demand for (MTS) is growing rapidly. For example in a Kalmar delivery each MTS will be able to move eight 20ft containers (or an equivalent mix of 20s and 40s) simultaneously, thus providing significant benefit over single trailer systems Figure ý1. Multi-trailers at the port of Rotterdam Stacking cranes Stacking cranes are used for placing and retrieving of containers in stack. These forms of stacking cranes are known as Rail Mounted Gantry Cranes (RMG) or Rubber Tired Gantry Crane (RTGC) [for technical information see Siemens, (2007b) and Siemens (2007c)], and Over-Head Bridge Cranes (OHBC). OHBC requires huge initial investments in erecting columns sustaining crane rail girds and ground breaking works. An RTGC moves on rubber tyres over containers and is able to move among blocks. A RMG runs on rails normally serving a single storage block between the rails. Figure ý1. shows RMGCs at ICD, Tughlakabad terminal The RTGC has the flexibility to change stack but in practice this is time consuming and cannot be done often. Being harder to automate, they are less attractive for the terminals trying to further increase their throughput by automization. As a result yard cranes are space-efficient, fast in operation and more suited for automation. However, they require higher development cost than SCs typically around 3 times the price, because of their heavy body weight and wheel load. RTGs are typically cheaper to install, more expensive to operate and more flexible than RMGs. Comparison of OHBC, RMGC, and RTMC is given in Appendix B. Figure ý1. Rail mounted gantry crane at CONCOR, Tughlakabad, New Delhi. Quay crane Quay crane (QC) is manned equipment; the maximum capacity to load and unload containers from or to the ship is 50 containers per hour (Evers et al., 1996). QC is the most important determinant of the ship operation productivity at the terminal. The number of quay crane µ § required to accomplish the proposed task, can be calculated by µ § Eq ý1. Whereas, Ncontainers is the number of containers to be loaded and unloaded. Cqc is the maximum physical capacity of the quay cranes, Tship is the turnaround time of the ship. Figure ý1. shows Quay cranes (QCs) that have trolleys that can move along the crane arm to transport the container from the ship to the transport vehicle and vice versa. A spreader, a pick up device attached to the trolley, picks the containers Figure ý1.. Quay crane at port of Paranaque, Brazil. The QCs move on rails to the different holds to take/put containers off/on the deck and holds. Technical specifications of quay cranes can be browsed in (Ceres Paragon, (2006); Dubini (2007); Corp, (2007); ZPMC (2007a); ZPMC (2007b); and ZMPC, (2007c).) It can happen that at the same moment one QC is unloading containers while another QC is loading containers. QCs are manned because automation of this process encounters practical problems. For example exact positioning of containers may not be achieved. Recent technologies for container loading -unloading Over the last decade, technology and automation have been introduced into the container business to improve the efficiency of part operations See (Dimitrijevic et al., 2005) and (Asef-Vaziri et al., 2003). Some of these technologies include: Automated guided vehicles (AGV)see (Liu et al. 2002) and (Liu et al., 2004), Automated lifting vehicle (ALV), overhead grid rail system (OHGR), linear motor conveyance system (LMCs), and high rise automated storage and retrieval structure (AS/RS) see (Asef-Vaziri et al. 2000) and (Chen, et al., 2003). Automated guided vehicles Automated guided vehicle (AGV) is driven by an automatic control system that serves the role of the driver, and moves along guide-paths, which can be modified easily. AGVs are considered to be the most flexible type of material handling system (Egbelu, 1984). Their size ranges from small load carriers of a few kilograms to over 125-ton transporters AGV consists of the vehicle, onboard controller management system, communication system and navigation system. AGVs are now becoming popular in automated materials handling systems, flexible manufacturing systems and container handling applications. In this concept the terminal configuration is similar to that of conventional terminals but instead of using manually operated equipment, AGVs are used to transfer containers within the yard and automated cranes are used for loading and unloading. AGVs are very well suited to be deployed for terminal operations due to the repetitive nature of movements within the terminals. The promise of deploying AGVs in container terminals lies in their capability of achieving the following benefits: high container throughput, continuous operation for 24 hours a day, 365 days a year, high controllability and reliability, high safety standards, automated and consistent container handling operation, reduced operational costs, especially labour costs, high position and heading accuracy (Evers et al. 1996). Unlike, straddle carrier, AGVs are not able to load and unload containers themselves. A crane is always needed to perform these operations. However, the system is not cost effective because it does not permit high stacking and requires wide roads to travel through the terminal. The European Container Terminal (ECT) in Rotterdam is the most advanced container terminal in the world. It uses a fleet of AGVs (as shown in Figure ý1. ) between the yard-cranes and ship-cranes at the terminal. The system is considered successful but the rate of success so far has been less than what was expected. Other ports considering this technology are watchful of ECT’s success as they recognize it has been a slow process. In the recent years, there have been substantial improvements in speed of vehicle as well as in the navigation technology and communications systems Figure ý1. Automated guided vehicle used at Rotterdam port. Automated lifting vehicle Automated lifting vehicle (ALV) was launched by Seoho Electric Company and the Korea Maritime Institute (KMI). The design is a hybrid between a passive AGV and a low height straddle carrier (Kim, 2006). It is a vehicle which can both load and unload containers and travel from the ship to the stack during the unloading process and from the stack to the ship during the loading process under its own power. These vehicles are capable of lifting containers from the ground by themselves and that is in fact the main difference from AGV. By using lifting vehicle the loading and unloading process at the crane and the transportation process can be decoupled. A crane places a container on the ground and does not have to wait for a vehicle to place the container on. This last action is required in case when non lifting vehicles are used. Linear motor conveyance system Another technological concept that has demonstrated significant promise for the transfer of containers to and from the yard is based upon linear motor-conveyance system (LMCS). Figure ý1. Linear motor conveyance system Linear induction motor operates on the same basic principles as a conventional, rotary induction motor, except that instead of the coils being wound around a shaft, the entire assembly is “unwound” into a linear configuration. Running current through the unrolled, flattened stator moves a metal flat blank, which is placed above the stator (Ioannou et al. 2000). By controlling an array of linear motors that are placed underneath a platform, one can accurately move the platform given that it is on a sliding or rolling surface. However, the technology is scalable to larger tasks. A system such as this could be ideally suited for port and terminal operations. Prototype of LMCS as shown in Figure ý1. has been constructed and successfully tested in Eurokai Container Terminal in Hamburg, Germany (Patrik et al. 2001).Once the necessary infrastructure is in place and the shuttles to carry the containers are constructed, the system could be operated autonomously without any constraints on the hours of operation, and at a very low cost. Linear motor driven systems could be proven to be more attractive than AGV systems for marine terminal applications in terms of maintenance cost and reliability (Ioannou et al. 2000) However, due to the fixed guide-way associated with linear motor systems, AGV system could be much more flexible in terms of their ability to travel on numerous paths depending on the navigation concept used. Yüklə 423,89 Kb. Dostları ilə paylaş:
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