Bulk Engineering, BULKtalk, Logistics, Ports

BULKtalk: Designing a modern bulk port

Steve Davis outlines some key factors for designing a modern bulk commodities port facility.

An engineering group asked if it would be acceptable to base the design of a new bulk materials port facility on the operating history and metrics of the existing operation. The existing operation was designed in the 1960s and has been upgraded several times over its continuous lifecycle. The facility still operates with much of the original equipment, although commodities and configuration have changed over time. The existing operation manages to achieve current targets but has little or no spare capacity. Efficiency is relatively low mostly due to reliability issues. History and metrics for the existing operation are available, however are typically sketchy and unreliable.

The new facility will be required to manage more commodities at higher throughput and will use modern equipment and methods to obtain efficiency and reliability at best practice.

A key aspect of the facility is that it could be considered an intermodal hub for bulk material management. Bulk materials are delivered in large and small packages by ship, train, and truck from various sources, consolidated in storage and transferred in similar large and small packages again by ship, train and truck to users or other hubs. 

Larger ships may be used in addition to the existing mix. A new approach channel will be used for accessing the berth. Trains and trucks will remain as current, limited by regulation and existing access and infrastructure. 

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The facility is part of a large and relatively complex logistics operation. As such, this mandates design around the external impacts that the logistics chain applies to the bulk handling facility.

Experience of a different facility with one commodity, rail only delivery and defined ship fleet is an indication of the result when the external logistics were ignored. The facility was designed to receive a constant rate annual supply by rail and with the expectation that a ship would always be available for loading when required. No reliability calculations were completed, with the supplier confirming that it would be 97 per cent available overall according to contract. This facility was expected to ramp up from initial throughput to approximately triple this but has always struggled to meet the initial throughput. The basic reasons are that the facility cannot achieve anywhere near 97 per cent availability in current configuration, the two rail supply operations do not provide continuous output so loading trains is erratic, trains do not arrive on schedule due to various reliability issues and delays, and shipping is as always erratic due to market factors, weather, and other external impacts. A major factor was the assumption that all ships can be loaded at maximum rate. As this rate is defined by the ships master and the ship design, many were unable to accept more than 50 per cent design rate, extending loading time by a similar amount.

Factors that must be considered for shipping. First define the ships that will be accommodated. A bland assumption of “panamax” is not acceptable. There are now two sets of locks in the Panama Canal, and our conventional reference refers to the first and much smaller locks. Maximum dimensions are length 289.56 m, beam 32.31 m, height 57.91 m and draft 12.04 m. There is no standard for Panamax ships, and my small list of Panamax ranges from 190 m to 230 m length and between 30 m and 32.29 m beam with tonnage listed from 40,000 DWT to 80,000 DWT and critically for load rates, between 5 and 11 hatches and with several being geared ships. There are other classes of bulk ship, see table, definition is not consistent and there are others that are specific to different ports, e.g. Kamsarmax. Make sure that the port matches the vessels to be used. I often see an assumption that a panamax is 85,000 DWT, this may be correct for some but certainly not all. Some bulkers do not travel the Panama Canal and are larger than Panamax, e.g. “post panamax”. Loading rate is difficult to establish and results from deballasting rates, number of holds, gearing clash, and is individual to each ship. Trimming holds at the end of loading may add five per cent to 10 per cent to the load time.

Ships that are being unloaded have similar concerns relating to size and rate of unloading. Additionally, we must consider hold cleaning which can result in the last five to 10 per cent of the load taking up to 25 per cent or more of the total unload time.

Ship considerations must include time at berth for draft surveys and paperwork, berthing and departure time and other non-productive time. Many wharves have a single channel approach, and this means a delay between one ship departing and another being able to berth. Ships can be delayed by lack of tugs. We must also make allowance for wharf activities such as outage, shift change, or failure, to develop a ‘berth occupancy’ value. Berth occupancy in design should target approximately 65 per cent for ports with smaller and varied ships. Spare occupancy provides margin for ship arrival variability, which can be caused by weather, breakdowns, delays enroute and other issues, and also for irregular longer maintenance outage.

For rail and road, we must understand how frequently they arrive and how quickly they can be unloaded and loaded. Both rail and road are batch operations with similarities and differences. With rail it is reasonable to assume there are not many trains in circulation for each commodity and easier if they cycle between end points. On a large rail network this is not always possible, and trains may have an asymmetric cycle over a long time. 

For example, different number of trains per day at differing times, and even with different numbers of railcars, but adding up to a continuous average rate over time. Some operations may require that many trains deliver in a short period to build up storage for shiploading. This is known as cargo assembly. There may be a requirement to offload a train directly to a ship. Trains may be offline for long periods for bad weather, track repairs and maintenance, potentially several weeks at a time for some rail systems. Others manage with many shorter interruptions.

With trucks, depending on the operation we might have many trucks in circulation or few. Roadworks can generally be circumvented. Truck operations can be established to cycle continuously generating an almost constant delivery or collection rate. Truck operations can also be established to deliver or collect only when necessary to fill or empty storage, or to deliver or collect directly from a ship. 

Both trains and trucks often have secondary time-consuming operations, such as driver changes, refuelling, brake checks, covering, transfer paperwork etc. These all must be rolled into cycle time. It is common for a fleet of trucks to have a range of different vehicles, and these must all be considered.

We must establish a baseline reliability / availability for the proposed bulk facility, as without some knowledge of this, the inbound and outbound ship / train / truck knowledge cannot be integrated into an overall model to establish a design basis. It is common for customers to request high availability without fully understanding the consequences. Unfortunately, there is a high cost associated with attaining high availability for anything beyond a facility with only a few items of equipment. A single conveyor might achieve 99 per cent availability (3.5 days downtime per year). A system with a string of eight conveyors will simplistically achieve (0.99)^8 or 92.3 per cent availability. Add in storage, transfers, stackers, reclaimers etc. and the availability will drop unless redundant and duplicate pathways are added.

Availability data is not readily available unless there is a good maintenance data base for similar equipment in type, age, and usage. Data from the existing plant that initiated this article would be irrelevant as it would likely show low reliability due to age and design. As in the previous example, if we get data from existing operation that results in a conveyor availability of 95 per cent, eight conveyors will have an overall (0.95)^8 or a low and unacceptable 66 per cent. If this data is used for the new plant, we would likely have to upgrade conveyor capacity, add some duplication, and buffer storage to obtain a higher overall availability level.

The best source of reliability data is from computerised maintenance management system (CMMS) software, however if not structured and used correctly it can be difficult or impossible to obtain useful data. A structured failure mode, effects, and criticality analysis (FMECA) is one method of predicting reliability. Once reliability data has been defined, reliability availability maintainability (RAM) software such as Blocksim or Maros or similar is the best way to define the overall reliability of the facility.

We now have sufficient data to set up a discrete event simulation model using Rockwell Arena or similar, which will include the complete logistics chain affecting the facility. These simulation model show the function of all parts of the logistics system and will condense years of prediction into a short animation and summary data that indicates whether the system will function as expected. The model is then used to test ‘what if’ scenarios to indicate improvements for the initial design and for future changes. 

The above process is more involved and expensive at the design phase than using unrepresentative data and ignoring up and down stream logistics. Constructing the project will incur significant expenditure and I believe customers would prefer to get an outcome that achieves the required target than a facility that will be a failure from commissioning onwards. 

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