Modular design can give major advantages when companies are constructing processing plants. E&MJ asks some industry experts in this field for their views and advice.
By Simon Walker, European Editor
A mineral processing plant represents a major capital investment for any new mine, with more capex usually needed from time to time as optimization routes become apparent after operational experience has been gained. And, given that most mines are far enough away from major supply sources to make equipment transport costs a real consideration, there can be significant benefit from having components manufactured off-site and brought in, as the construction schedule requires, as pre-assembled modules.
Add to that the cost of on-site fabrication labor compared to the same work being carried out in dedicated workshops located in areas of established infrastructure; the people involved can live at home rather than in camp accommodation. And as for quality control, there can be no doubt that having complex fabrication undertaken under workshop conditions is almost always better than having the same jobs done in the open in the middle of a construction site. Components tend to fit together better if they are assembled by a workforce that feels comfortable, and where potential fabrication issues can be resolved before they show up in hard steel.
Consequently, for some compelling reasons, the concept of building processing plants from largely pre-assembled modules has been slowly gaining ground within the mining industry. It has to be remembered, of course, that some locations are more suitable for this approach than others: mines located close to deep water are at an advantage in this respect, since large plant modules can be brought in by ship, unloaded and moved to site with relative ease. Teck’s Red Dog mine in Alaska was an early convert to this way of thinking.
By contrast, it would be much more challenging to have to transport modules by train or truck where adequate infrastructure does not already exist—with the need to build it for this purpose maybe offsetting any cost advantages that might be won by using modular construction in the first place.
A QUESTION OF SCALE
Plant modules come in all shapes and sizes, ranging from units that can comfortably be fitted into standard sea containers to those that require the services of specialist heavy-lift contractors to move and install them. In some respects, other industries—such as oil and gas production—are way ahead of mining in terms of their use of modular concepts, especially for off-shore installations. Nonetheless, modular concepts are being used more widely in the design of mineral processing plants, especially where individual plant components can be pre-assembled.
As an example of a container-ready module, at the end of November, Metso announced the award of a contract from the Kazakh company, Saburkhan Technologies, to supply a containerized NW Series wheel-mounted crushing and screening plant. Metso noted that the unit is designed to be dismantled and packed into standard 40-ft (12-m) containers for easier, faster and more cost-efficient transport, cutting delivery times and costs as well as speeding setup on-site.
At the other end of the scale, and as noted in E&MJ’s annual review of the Canadian oil sands industry last August (pp. 32–40), construction of the new bitumen recovery plant at the Fort Hills project is heavily reliant on modules that are being constructed both in Canada and overseas. The main contractor for the extraction plant, the South Korean firm SK E&C, is fabricating smaller modules in South Korea; shipped to Alberta, some of these are being joined in Edmonton to form larger units for delivery to site, while others are being taken directly to Fort Hills for installation.
The project’s engineering, procurement, fabrication and construction contractor for utilities is adopting a similar approach. “Fluor will apply our unique modular design and execution approach,” said Jim Brittain, president of its energy and chemicals business for the Americas region, announcing the contract award in 2014. “We will fabricate a significant number of components off-site in order to deliver both schedule and capital efficiencies to Fort Hills.”
And this is not the first time that Fluor has been involved in delivering a modular solution to a mineral processing project. Located close to tidewater in an otherwise inaccessible location, Vale’s Voisey’s Bay nickel complex ticks all of the boxes as far as being a candidate for modular plant construction is concerned. Its Long Harbour hydrometallurgical processing plant, which came on stream in 2014 and for which Fluor was the EPC contractor, made extensive use of pre-assembled modules.
Weighing between 100 and 1,100 metric tons (mt), the modules were assembled at fabrication yards on the U.S. Gulf Coast, the Great Lakes and St. Lawrence before being delivered to the site by a fleet of nine tug-and-barge units. Once there, they were off loaded onto self-propelled modular transporters (SPMTs) for the 3-km journey to site.
E&MJ asked some of the world’s suppliers of modular plant solutions for their views on the benefits associated with using this concept. Referring to its flagship Python plant, Nigel Grigg, business development manager of the Australian company Gekko, noted that the modular design allows it to build the plant at its manufacturing facilities in Australia and completely factory commission each module before it is packed and sent to the remote site. The factory commissioning stage allows it to ensure that everything is working as it should, and speeds up construction and commissioning on-site, he told E&MJ.
Each module is designed to be transported within shipping containers, which also allows operators to pack and unpack a plant when required. “This is a great benefit when considering exploiting smaller or satellite deposits,” Grigg pointed out. Other advantages of this approach include the ability to expand or upgrade a plant easily, while maintaining a small plant footprint. In financial terms, capital costs are lower in most cases, while residual values can be higher when a project has been completed, he added.
With its background in the oil and gas and chemicals industries, Fluor told E&MJ that it has designed and built thousands of modules over many years and in many locations. The company’s executive director for mining and metals business development, Matthew Cobbett, explained that modular plants have evolved from smaller prefabricated units to macro units where up to 90% of a facility can be pre-assembled and commissioned before transport to site, while pointing out that modular plants require smaller teams of workers on site and can reduce build times by up to 30%. “This approach therefore offers schedule certainty when selected early in the study phase,” he stated.
“Better workforce safety is another major benefit, with work shifted to a controlled shop environment,” Cobbett said. “This also cuts the total overall project hours while reducing work at height and with less need to use cranes. The construction schedule is shortened because the modules are built in a controlled environment, providing better quality control at a lower cost, and greater opportunities for completing the project on time.”
Cobbett added that this approach can also result in significant capital cost savings when at least some of the following project conditions exist:
- Remote location site;
- Site subject to adverse weather conditions;
- Limited local skilled craft labor;
- Short supply of construction equipment and small tools;
- Greater labor efficiency or lower labor rates are available at a fabrication yard; and
- Suitable transport, receiving and handling facilities are available for the modules.
Speaking from the viewpoint of a specialist crushing and conveying plant manufacturer, Spencer Kossl, product application manager for Telsmith, agreed that mechanical installation in the field is typically 30% quicker because modules are pre-assembled and disassembled in the company’s factory before delivery. All modules are bolted together and do not require any field welding, he said, while Telsmith’s stationary conveyors have a bent plate modular design that allows assembly and installation much more quickly than a standard truss/channel section conveyor. Idlers, walkways and other components are preinstalled and containerized.
Kossl told E&MJ that using pre-engineered designs accelerates the structural design engineering process. This in turn cuts engineering costs, and means that individual modular footprints can be released almost immediately. In addition, static and dynamic loadings can be released quickly for foundation design, so that staking arrangements for site work is completed more efficiently.
Using modular concepts also means that relocation and design upgrades are more straight-forward, Kossl said. “Modular structures are designed to accept a range of machine sizes,” he explained. “For example, screen modules are designed to accept 6-, 7- and 8-in. screen sizes and are interchangeable. Cone modules can accept 300-, 400-, 500- and 600-hp cone sizes, and are interchangeable with an adapter plate.
“And, of course, modular plants can be taken down and relocated, while you can both build complete modular plants and add other ‘snap-on’ components,” he added.
E&MJ next asked whether the respondents see limits—in terms of geography, logistics, transport and so on—that might actually restrict the use of modular construction and favor “traditional” on-site plant assembly. Cobbett summed up the situation thus: “The limits are determined by what can be safely, legally and economically built and transported to the job site. It is therefore dependent on available infrastructure to accommodate moving the modules, whether by ship, barge, rail or truck. Other factors include handling equipment and job-site access in remote locations, as well as severe weather conditions,” he said.
Kossl noted that functionality remains constant as modular structures are rarely modified, but are versatile in design to allow for mechanical upgrades, as are improved chute liners or special customer requests.
“More importantly, the modular design allows for easy upgrades to varying safety standards ranging across the globe.
“Logistics is no more of an issue for a modular plant than any other heavy piece of industrial equipment,” he said. “Whether an entire plant or specific modular structures, there will be a combination of permitted and legal loads within the United States, and if shipping off shore there will be both containerized and break-bulk loads.”
Grigg’s view was that really there are no limits in terms of geography, logistics and transport. “In operation, the biggest limit is the tonnage modular plants are designed to handle. Gekko often limits throughputs to 50–100 mt/h as this is often ideal for gold projects, so this might be a limitation in bulk-commodity projects such as iron ore or coal.
“Multiple 50-mt/h parallel circuits have been used in the past, allowing easy expandability,” he went on, before giving the example of Gekko’s recent project in the Canadian Arctic for TMAC Resources, which is designed to have one 50-mt/h modular Python plant that will be expanded to 100 mt/h one year after the initial installation.
Grigg pointed out that other limitations include POX, BIOX, ultra-fine grind and specialized metallurgical processes, which are not suitable for Gekko’s current modular plant design. “However, at Gekko, we believe that these could be incorporated into a modular design in the future by other companies,” he said.
Next, E&MJ asked how capital costs compare between specifying modular or on-site construction for plant items and assemblies. According to Cobbett, Fluor would anticipate that the total installed cost of a modular project would be less than a stick-built execution, up to 20% in some cases, when using Fluor’s 3rd Gen Modular Execution approach. “Modular construction can offer improved productivity, shorter schedules, better quality control at a lower cost, and greater opportunities for completing the project on time. Typical mining-industry modules include process facilities, crusher and conveyor modules and pipe racks,” he stated.
“Given the completion of full factory commissioning, the costs of on-site construction and installation are often significantly reduced for modular plants,” Grigg agreed. “Also, considering the standard design of the modules developed by Gekko, capex is also reduced considerably, while we have modularized the gold room, MCCs, laboratories and so on, making them less capital-intensive than traditional plants.”
Kossl sounded a slightly more cautious note, however. “The initial thought is that structurally modular plants tend to have a higher price tag, but what is commonly overlooked is the benefits of a modular structure,” he explained. “The structure itself is a beam and bent plate design with stairways and large walkways/platforms for easy access to all the machines. The modular plant is tailored toward stability, ease of maintenance and most importantly, safety.
“Capital costs, including installation costs of foundations, erection and electrical are very competitive overall, and include the advantage of complete installation at an accelerated rate,” he went on. “To summarize: comparable capital costs, while modular allows for greater flexibility, substantially lower engineering costs and a reduced installation period.”
E&MJ asked the respondents for their views on whether there are limits in terms of the size and weight of individual components that have a bearing on whether a new processing facility can benefit from having off-site modules built.
Grigg said,“Yes, definitely. Having multiple modular units is not always the answer as it could increase capex and add complexity to the flowsheet. One of Gekko’s key design processes is to compare the economic trade-offs when the plant throughput becomes too large and requires multiple units.”
Cobbett pointed out that mining modules typically weigh up to 600 mt whereas in the oil and gas industry, they can weigh more than 50,000 mt. Modules this size can be accommodated at Fluor’s jointly owned 2-million-m2 Zhuhai fabrication yard in China, with the company having four other fabrication yards around the world.
“While modularization is not new, the level of achievable offsite work has significantly increased using the Edison Awards-winning 3rd Gen Modular Execution strategy—which splits the project into process blocks and moves into designing modules that then drive the plot plan. When fully implemented, this approach can achieve new levels of cost, schedule and execution certainty,” Cobbett claimed. “Clients benefit through reduced procurement quantities, productivity gains for work shifted to shop, and reduced costs for field labor, thereby saving time and money.”
Kossl commented, “Freight costs will vary depending on where a project is to be installed, and there is always a differential in shipping a module vs. building a traditional stick plant on-site. Telsmith does work with local fabricators around the world to build the modular structures more locally to minimize transport costs to customers.”
BECOMING MORE MAINSTREAM
Lastly, we asked whether the respondents see modular plant construction now being “mainstream,” and where the concept is likely to develop going forward.
According to Kossl, Telsmith developed its modular concept in the mid-1990s, and it has become more relevant today. “The modular plant is not a concept any more, it is a reality,” he said. Modular plants are not only competitive in the marketplace, they are easily understood in that a customer will know they are getting a top-of-the-line product, and that it will perform day-in, day-out.”
Kossl also added that Telsmith is developing smaller-scale modular plants that are completely containerized to ship worldwide, thus minimizing shipping costs.
Flexibility is a key consideration, Grigg stated. “I’m not sure if modularization is mainstream yet, but in this economic climate and considering the location of some mine sites, it is important to demonstrate how companies can further reduce capital costs while still having a ‘movable asset.’ Having an asset that can be relocated once a mine is exhausted is one of the main advantages of Gekko’s modular systems,” he said.
Cobbett said, “Modular design has been a mainstream execution method in the oil and gas industry for many years, but large-scale modular design in the mining industry only became typical during the recent commodity super-cycle. It started in the iron ore business in the Pilbara region of Western Australia where, due to manpower shortages, a Fluor-led joint venture—FASTJV—pioneered a large-scale modularization initiative for a major client there.
“Across a number of projects, more than 30,000 mt of pre-assembled and modularized structures were transported over 400 km inland. Fluor self-performed the fabrication and assembly of a large portion of these in China.
“Since those projects, the mining industry has progressed, with the trend now becoming a mainstream initiative,” he said. “The iron-ore industry has led the way for large-scale, long distance haulage modularization in mining, and it should flow seamlessly into the coal industry due to its similarity. Other commodities that have increased their use of modularization are predominantly those situated by open water—a project on the coast with water access is always easier to modularize than those inland.
“The natural progression of the modularization effort is into standardization and replication. The iron-ore industry is leading the way, and initial steps are also being taken for large-scale, more remote mining operations for commodities such as gold and copper.”