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Modular Construction: Choosing the Optimal Module Type

| By Mauricio Villegas

Plant process modules are not a one-size-fits-all solution. These considerations can help determine the best size for your project

With the growing recognition of the advantages of modular construction over traditional field construction [1, 2], it’s no surprise that an increasing number of companies across all chemical markets are maximizing the modularization of their facilities. This shift in methodologies aims to reduce project delivery risks, achieve substantial cost savings, and gain scheduling advantages, while accelerating the commercialization of decarbonization technologies worldwide [3]. This trend isn’t unexpected. As equipment, raw materials, craft labor, and other associated construction costs continue to escalate, coupled with labor shortages and higher project financing interest rates compared to just a few years ago, both owners and investors are turning to modularization as a project delivery model to minimize expenses, limit peak site manpower and worker density, and mitigate overall risks. This strategic move ensures that future projects remain financially viable and can meet investment decision gates. However, while modularization can address many of these challenges and offer substantial benefits, it’s essential to recognize that it’s not a one-size-fits-all solution.

Modules can be categorized into three types: truckable, conventional and mega. Various factors, such as size, weight and site location, are critical in determining the optimal module type for a project. Sometimes, a blended approach with two or more module types can accommodate the requirements of larger, more complex projects. Before discussing the benefits and drawbacks of each module type, understanding what constitutes a module and what does not is pivotal.


What is a module?

Modules, regardless of size, exhibit two distinct characteristics that differentiate them from traditional field-erected construction and other pre-assembled units.

Modular design. Modules comprise a structural steel frame housing all related process equipment, seamlessly integrating into either greenfield or brownfield plants along predefined interfaces. Unlike pre-assembled units (PAUs), such as pre-assembled pipe racks (PARs) and skids (packaged equipment), modules are complete, scalable, and repeatable systems containing all process-related equipment. This equipment includes columns, vessels, reactors, heat exchangers, pumps, vacuum systems, filters, all field instruments, piping, pipe supports, thermal insulation, tracing, electrical wiring, control cabinets or junction boxes, control systems, and ancillary equipment such as lighting, fire safety, and eyewash stations.

Offsite construction. Modular construction takes place at an offsite fabrication yard. Once construction is complete, the modules are transported to the final installation location by land or sea using trucks, rail, barges or ships. Offsite module fabrication yards vary in proximity, from local to international, depending on factors, such as experience, capacity and water access. Relocating construction activities offers several benefits, including reductions in project site congestion, increases in labor availability, enhancements in productivity, and improvements in safety and quality performance.


Different types of modules

As stated earlier, there are three module types: truckable, conventional, and mega. Understanding the varying characteristics of each module type enhances discernment when selecting the most suitable mix of attributes based on a project’s design and delivery requirements.

Truckable modules. As the name suggests, truckable modules (Figure 1) are primarily transported by road from an offsite fabrication shop to the final installation location using heavy haul trucks. Known for their smaller footprint compared to conventional and mega modules, they typically measure 12 ft × 14 ft, have lengths up to 80 ft, and weigh up to 100 tons. Truckable modules are ideal for small to mid-capacity projects or downstream processes without nearby water access, where columns have diameters less than 7 ft and tanks and reactors are less than 10 ft. Depending on the road conditions between the fabrication shop and the installation location, minor adjustments may be made to the modules’ dimensions. They can reach most project locations without specialized trailers or lifting equipment and can also be transported by rail, water, or air if project constraints require it.

modular construction

FIGURE 1. Truckable biochemicals module prepared for transport to the project site for final installation

The design of truckable modules is flexible. Process systems can be consolidated into a single module for smaller projects with minimal unit operations. In larger projects with multiple unit operations and increased throughput, systems can be divided into multiple modules to form a complete unit when interconnected at the project site (Figure 2). Depending on the project’s requirements, modules can be installed horizontally, vertically or stacked. Alternative approaches, such as a hybrid solution or larger conventional modules, should be considered for projects too large for the requirements of truckable modules.

FIGURE 2. This plastics recycling process plant is comprised of twenty-five interconnected truckable modules

Unlike larger conventional modules, truckable modules are usually constructed horizontally (Figure 3) utilizing an assembly-line approach in controlled environments, such as an enclosed fabrication shop — increasing overall project productivity, quality, and safety. Upon delivery to the project site, these modules are erected and installed vertically unless the design dictates a horizontal installation.

FIGURE 3. Shown here is a truckable module fabricated in a horizontal orientation

The advantages of truckable modules are key to decarbonization projects with hub-and-spoke deployments [4]. They allow incremental capacity additions as feedstock availability and off-take agreements expand. They can also replicate and transport seamlessly across diverse site locations, an added benefit for global commercialization. Furthermore, constrained brownfield projects with limited accessibility should consider truckable modules, as they offer easy navigation within the facility and straightforward installation.

Conventional modules. Before the emergence of highly specialized truckable and mega-modules, conventional modules (Figure 4) were considered the industry standard. Falling just short of the threshold for mega-module classification, conventional modules typically measure around 240 ft × 140 ft, can have a height of 120 ft, and weigh up to 6,000 tons. Since they are not constrained by column, vessel, reactor, and tank sizes, conventional modules are an ideal option for large-capacity projects where most equipment sizes exceed the capacity of truckable modules.

FIGURE 4. Self-propelled modular transporters (SPMTs) prepare to transport conventional modules a short distance via land to a nearby port

Constructing a conventional module is similar to traditional field construction with the exception that it is conducted at an offsite fabrication yard. Since construction is vertical in orientation and outdoors, safety, cost, and quality benefits are reduced due to the exposure to natural elements and requirements of additional equipment such as cranes, man-lifts and scaffolding. However, the benefit of less site congestion is apparent since the construction is at an offsite location.

Choosing an optimal location for a fabrication yard is critical for transporting conventional modules. These large-scale modules are designed and constructed to include multiple unit operations, and thus, a single conventional module is of considerable dimension and weight. Due to this, they cannot travel along most public roads and highways and can only travel short distances on land. If the fabrication yard is not adjacent to the project site, water transportation is another option (Figure 5).

FIGURE 5. Conventional modules are transported by water from an overseas fabrication shop to the project site for installation

For longer distances requiring water transport, temporary structural steel is required to secure the modules to barges, adding more than 25% to structural steel costs and labor hours as compared to <5% with truckable modules. Ideally, conventional module construction occurs at large domestic or international fabrication yards with sufficient capacity, material handling equipment, labor and water access or temporary fabrication yards near a project site.

Whether transporting conventional modules from the fabrication shop to a barge for water transport or to the project site location, specialized trailers, such as self-propelled modular transporters (SPMTs), assist in moving them to their destination (Figure 6). These remotely operated multi-axle trailers can carry upwards of 60 tons per axle and can be connected in series to accommodate heavy hauls. While this is an additional expense, it is key to note that tools and options are available to support the transportation of conventional modules.

FIGURE 6. This offshore mega module is being transported by SPMT to prepare for water transport to final destination

Mega modules. Tailored for world-scale projects exceeding $1 billion, mega modules are characterized by their complexity and extremely large size, with units often weighing over 6,000 tons, some reaching up to 25,000 tons. Like conventional modules, mega modules are constructed vertically and subject to transportation and fabrication yard requirements. However, the number of fabrication yards capable of handling mega modules is limited, posing challenges in the availability and cost of specialized transportation vessels, such as roll-on roll-off (RO-RO) vessels, heavy haul trailers, hydraulic jacks and lifting equipment.

Mega modules scale up the strategy of truckable modules, integrating multiple conventional modules into a comprehensive system called a mega module. This integration often eliminates conventional pipe racks, reducing the project footprint and overall piping quantities. Opting for a mega module project capitalizes on economies of scale and access to low-cost labor centers. By constructing a single mega module, the number of shipments and infield inter-module tie-ins is minimized, enabling extensive pre-commissioning and commissioning activities at the fabrication yard and facilitating comprehensive pretesting before shipment.

Typically, mega modules are constructed in world-class fabrication yards located overseas in Southeast Asia, leveraging lower-cost labor, materials and equipment. However, executing a mega-module project requires meticulous planning and flawless execution in various aspects, such as design control, project management, interface and change management, supply chain management and transportation. Therefore, selecting a seasoned and experienced project management team is essential.


Selecting the right module type

Selecting the best modular type for a project is a critical decision that can significantly impact overall project success. While modular construction offers numerous advantages, such as reduced project delivery risks, cost savings, and scheduling benefits, it’s essential to recognize that modules are not a one-size-fits-all solution. Understanding the characteristics and benefits of each modular type will aid in determining the optimal delivery model for a project’s unique requirements.

Regardless of which modular type is selected, the common and most important factor is that the decision to go modular needs to be made as early as possible. A change in strategy post-pre-feed will have a greater impact on the project’s cost and schedule and alter the sequence and early timing of some engineering efforts. Therefore, to ensure the greatest opportunity for success, owner’s should engage internal and/or external modular construction subject matter experts to perform a study as early as FEL-1 (feasibility), if possible, to determine the best modular type for the specific project requirements.


Blended delivery

Another great quality of modular construction is the flexibility in design. A blended modular project delivery can be used for mega or large projects, combining two or more module types to leverage their unique advantages. Project stakeholders should consider project objectives, site conditions, transportation logistics, and budget when selecting the appropriate modular delivery model. By evaluating these factors and understanding each module type’s nuances, stakeholders can maximize the benefits of modular construction and ensure project success.

Edited by Gerald Ondrey



1. Villegas, Mauricio and Loftus, Chris, Modularization: Managing Project Delivery Risk in the Time of COVID, Chem. Eng., June 21, 2021, pp. 35–39.

2. Halford, Susan and Kretzschmar, Tony, Practical Solutions to Modular Project Execution, Chem. Eng., June 2017, pp. 44–50.

3. Villegas, Mauricio and Schafer, Tom,

4. Villegas, Mauricio and Schafer, Tom, Decarbonization is at the Forefront of Environmental Innovation, Hydrocarbon Processing, January 2023.



All figures courtesy of Koch Modular Process Systems, unless otherwise indicated.



Mauricio Villegas is the business development manager at Koch Modular Process Systems, LLC (45 Eisenhower Dr. #350, Paramus, N.J. 07652; Phone: 832-859-0416; Email: mauricio.[email protected]). He has more than 25 years of experience in the engineering and construction industry, delivering projects across industries and technologies ranging from small brownfield projects to greenfield mega-projects. Prior to joining Koch Modular, he held various management roles at Worley, Technip, IHI E&C and Arcadis. Villegas earned a B.S. in business administration and management from Northeastern University.