Simulation-based rescheduling of the stacker–reclaimer operation
Introduction
Dry bulk terminals are essential nodes in the major transportation links for coal and iron ore. These dry bulk materials are used for the worldwide production of electric energy and steel. A dry bulk terminal consists of a quayside where ships are loaded (export terminal) or unloaded (import terminal), a stockyard equipped with machines for the temporary storage of the dry bulk materials and a landside where transport modalities like cargo trains are serviced. Common machines at the stockyard are stacker–reclaimers. These machines combine the two functions of stacking and reclaiming into a single unit. Consequently, one of the two functions can be fulfilled at a time. During stacking, the material is transported through the machine to the end of the machine's boom where the material is discharged and dumped on a pile. During reclaiming, the reclaiming device, which is in most cases a bucket wheel mounted at the end of the machine's boom, digs the material out of the pile. The material is transported in reverse direction through the machine and dumped on a yard conveyor that conveys the material to its new destination.
The terminal operation is complex because both ships and trains have to be served simultaneously and on time to prevent paying demurrage penalties to ship-owners or delivering an unacceptable service to rail operators [1]. Stacker–reclaimers have to handle the incoming as well as the outgoing flow of bulk materials. Consequently, their operation largely determines the terminal's performance. The shiploads and trainloads vary considerably in volume and mass which causes a large variation in operation times. Large bulk ships can contain more than 250,000 t of dry bulk materials but the trainload is significantly smaller. In Western Europe, for example, the trainload is limited with 4000 t while in Australia and South Africa trains loaded with 35,000 t are not exceptional.
Stacker–reclaimers are installed at import terminals as well as export terminals. In this paper the operation at import terminals will be discussed. When during ship unloading a train arrives that requests material that is stored in the reach of an active machine, the train has to wait before being serviced until the stacking operation is finished. The resulting waiting time can lead to an unsatisfactory service to train operators and cargo owners. Rescheduling the stacker–reclaimer's operation by interrupting stacking and handling trains in between is a solution. However, ship unloading cannot be interrupted infinite times because terminal operators have limited time to unload ships.
The paper's objective is to apply simulation for the rescheduling of stacker–reclaimers to decrease the average time that cargo trains have to spend in the port while still guaranteeing the agreed ship port time. This paper is organized as follows. A literature review of stacker–reclaimer scheduling and the related job shop scheduling problem is given in Section 2. In Section 3, the stacker–reclaimers operation is explained and in Section 4, a simulation-based approach for the stacker–reclaimer rescheduling is introduced. An experimental study is included in Section 5 and finally, conclusions are given in Section 6.
Section snippets
Literature review
During the scheduling of the operation at dry bulk terminals many decisions must be made. For example, where to berth the arriving ships, which quay crane must be assigned, where to store the material, which transportation route must be selected and which stacker–reclaimer must be used. Many researchers studied the terminal's seaside operation; see for an extensive literature review [2]. A limited number of papers discussed the allocation of bulk materials at stockyards [3], [4], [5], [6], [7],
Stacker–reclaimers operation
This section provides details about the stacker–reclaimers operation. Fig. 1 shows two typical stockyard layouts for import terminals where only the active belt conveyors are shown. In layout A (Fig. 1A) the stockyard contains four lanes. Both outer lanes (L1 and L4) are accessible by one stacker–reclaimer while the middle lanes (L2 and L3) can be reached by two stacker–reclaimers. In layout B (Fig. 1B) each stacker–reclaimer has exclusively access to two lanes. Usually, at import terminals the
Simulation-based approach
This section introduces the simulation-based approach for supporting decisions whether stacker–reclaimers can be rescheduled or not. Section 4.1 explains this approach, Section 4.2 details the simulation model and the verification of the simulation model is discussed in Section 4.3.
Simulation experimental results
Stacker–reclaimer rescheduling will be investigated for both layouts of Fig. 1 using the input parameters of Table 1. For both layouts it was assumed that the stockyard's areas have sufficient storage capacity to prevent that ships cannot be unloaded because there was no storage area available. Previous research [23] has shown that the ships interarrival times can be modeled using standardized distributions depending on the terminal type. For this case, it was assumed that the terminal acts as
Conclusions
In dry bulk import terminals stacker–reclaimers are occupied for a long time during stacking of materials from ships. When a train arrives at the terminal's landside to pick up material that is stored in the reach of an active stacker–reclaimer, this train has to wait before getting serviced. Waiting of trains may result in an unacceptable service to rail operators. The simulation model presented can be used for supporting decisions whether rescheduling of the stacker–reclaimers operation can
Acknowledgement
The authors acknowledge the terminal operators who provided operational data about the ships arrival process and storage process of bulk materials at their stockyards and gave valuable feedback during the research.
Teus van Vianen received his MSc degree in mechanical engineering at the Delft University of Technology in 2005. After his study, he worked for five years in the machinery industry. In June 2010, he returned to the Delft University and started his Ph.D. project to determine the fundamentals of dry bulk terminal design at the faculty of Mechanical, Marine and Materials Engineering (3ME). His main interests are dry bulk terminals, terminal design, queuing theory, routing & scheduling, storage
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A smart energy scheduling under uncertainties of an iron ore stockyard-port system using a rolling horizon algorithm
2024, Computers and Operations ResearchStockpile scheduling with geometry constraints in dry bulk terminals
2021, Computers and Operations ResearchCitation Excerpt :Sun et al. (2020) considered storage space allocation in bulk material stockyards and developed a MIP model to determine stacking positions. On the topic of scheduling, the following are noteworthy: Van Vianen et al. (2015), Menezes et al. (2017), Burdett et al. (2019), Burdett et al. (2020a), De Paula et al. (2019) and Unsal and Oguz (2019). In Burdett et al. (2019) a proof of concept framework was developed that includes stockpile level profiling, pre-emption handling for reclaim activities, and the development of a meta-heuristic with a priority ordering chromosome.
A flexible job shop scheduling approach with operators for coal export terminals – A mature approach
2020, Computers and Operations ResearchCitation Excerpt :Only a handful of papers address scheduling and resource allocations therein. This observation is made in Vianen et al. (2015) who also comment that although bulk terminal decision problems are similar to job shop scheduling, the prohibition of activity pre-emption in past approaches prohibits their application to the re-scheduling of stacker reclaimers in practice. It is noteworthy to mention that Vianen et al. (2015) applied a simulation approach to support decision making in a bulk import terminal and to reschedule stacker-reclaimers so that the waiting time of cargo trains is reduced.
An exact algorithm for integrated planning of operations in dry bulk terminals
2019, Transportation Research Part E: Logistics and Transportation ReviewCitation Excerpt :However, dynamic structure of YAP largely differentiates it from the strip packing problem. That is, many stockpiles arrive and leave the stockyard during the planning period, and one storage position at the stockyard can be used by many different stockpiles over time. van Vianen et al. (2015) consider a realistic stockyard structure which consists of pads and rail tracks.
Teus van Vianen received his MSc degree in mechanical engineering at the Delft University of Technology in 2005. After his study, he worked for five years in the machinery industry. In June 2010, he returned to the Delft University and started his Ph.D. project to determine the fundamentals of dry bulk terminal design at the faculty of Mechanical, Marine and Materials Engineering (3ME). His main interests are dry bulk terminals, terminal design, queuing theory, routing & scheduling, storage allocation and automation of transport systems.
Jaap Ottjes studied physics at Delft University of Technology and received the MSc degree in 1970. He obtained his Ph.D. degree in the ‘prediction of pressure losses in dilute phase pneumatic transport systems’ at the same university. After his Ph.D. research that he changed subject and specialized, partly as a consultant, on industrial logistics and simulation of transport systems. He was employed as associate professor in transport engineering and logistics at Delft University of Technology within the Department of Marine and Transport Technology at the faculty 3ME. His main research interests are in the field of industrial logistics and transport systems and in the modeling and simulation of these systems in particular.
Professor Gabriel Lodewijks studied Mechanical Engineering at Twente University and Delft University of Technology from which he obtained a master degree (cum laude) in 1992. He specialized in transport technology, material engineering and dynamics. He obtained his Ph.D. degree at Delft University of Technology on the dynamics of belt conveyor systems in 1996. After 5 years of experience in the industry including three years in the USA, he was appointed as professor of transport engineering and logistics at the 3ME faculty of Delft University of Technology. He wrote over 250 papers and contributed to four books. He is frequently commissioned to act as an expert witness and he is further president of Conveyor Experts B.V.