Modular Skid-Mounted Design in VPSA/PSA Oxygen Generation Equipment

In the engineering industry, equipment integration has increasingly become a standard requirement for newly constructed installations. Modular skid-mounted assembly is one of the various methods to achieve such integration.

1. Concept of Modularizing and Skid-Mounting in VPSA/PSA Oxygen Plant

Skid mounting refers to fixing a set of VPSA （Vacuum Pressure Swing Adsorption）and PSA （Pressure Swing Adsorption）oxygen equipment onto a base made of angle iron or I-beams. The entire oxygen unit can be moved using a lifting device or crane. Skid-mounted oxygen equipment is widely used in industrial fields.

Modularizing, on the other hand, involves the efficient integration of oxygen production process and equipment so that each skid has its own independent function. At the same time, it allows for collaborative operation between different skids, facilitating decentralized design, manufacturing, and transportation, while also reducing the difficulty of lifting. Examples of these modules include adsorber inlet/outlet skids, oxygen compression skids, and venting and metering skids.

The modular skid-mounted design in VPSA/PSA oxygen system offers high integration, detailed design, short construction periods, small footprint, advanced control systems, reliable operation,etc., effectively solving the technical challenges in on-site construction of oxygen units.

In this context, a “module” refers to functional integration, while a “skid” refers to spatial integration. A single module may contain multiple skids, and similarly, a skid may consist of several modules.

2. The Modular Skid-mounted Design of the VPSA/PSA-O2 Plant

(1) Design Approach

A. The Modular Design of the VPSA/PSA Oxygen Plant

a. Based on functional units of the oxygen generation process, the VPSA/PSA oxygen generating system is divided into multiple single-function units to form modular unit series.

b. On the basis of modular oxygen unit as a whole, taking into account the maximum size and weight of components within a single module, along with the practical feasibility of transportation and the ease of on-site installation. The final design integrates pipelines, equipment, electrical instruments, and other components within the modular unit, finalizing the overall layout of the module.

c. The piping components inside the module, especially the instruments, should be incorporated within the module as much as possible during the design.

d. The design focuses on key equipment, with auxiliary components included as well. All pipelines, instruments, and valves are integrated into one unit, facilitating the subsequent skid assembly process.

e. The control wiring, electrical and instrument circuits for the modular unit are pre-wired and orderly connected to the control cabinets of the oxygen generating system. Once the power is supplied on-site, the oxygen generator can be quickly put into operation after simple debugging.

B. Skid-mounted Design of the VPSA/PSA Oxygen Plant

a. Based on the oxygen production process, all equipment, pipelines, instruments, and other components within each module unit are assembled into a skid to form multiple skid units.

b. The base dimensions, weight-bearing beam locations, and steel structure specifications are determined based on the overall layout and weight of the VPSA/PSA oxygen generator.

c. Using the piping layout and process flow, the positions of the pipeline supports are defined on the steel structure base, aiming to minimize the connections between skids.

d. During the overall skid design process, factors such as lifting and transportation, on-site installation, ease of operation and maintenance should be thoroughly considered to ensure practical and efficient usability.

(2) Key Points of VPSA/PSA Oxygen Equipment Layout

The equipment layout follows the technical principle of modular skid design. Based on the predefined modular units, the oxygen equipment components are primarily arranged on a unified platform to meet spacing regulations, ensuring a compact arrangement while satisfying operational, inspection, and maintenance space requirements. Furthermore, all pipelines, instruments, and other components within the oxygen unit are prefabricated and installed, so that upon arrival on-site, only welding the inter-skid pipeline connections is needed to complete the oxygen generating system installation.

The principles for skid piping layout are as follows:

 Complies with the process flow requirements and meets skid size and weight specifications. 

 Facilitates operation and management while ensuring safe production.

 Enables convenient pipeline maintenance and valve operation.

 The overall design should be harmonious and aesthetically pleasing, while minimizing material usage.

When modeling the oxygen plant skids, designers should strictly adhere to the piping principles and focus on equipment arrangement. Relatively tall equipment should be positioned in the center, while shorter ones and valves should be placed around. This allows maintenance personnel and their tools to easily access the components, which is crucial for daily operations, maintenance, repairs, and disassembly of the VPSA/PSA-O2 plant.

To ensure quick and reliable connections on-site in the future, the piping between skids should be connected with flanges whenever possible. If personnel passageways are required within the skid, the width should not be less than 900mm, and the height should not be lower than 2150mm.

（3）VPSA/PSA Oxygen Equipment Selection

Under the premise of reasonable and controllable costs, it is essential to select efficient and multifunctional equipment whenever possible. Modular skid-mounted design should begin with the integration of equipment functions, rather than merely “stacking” oxygen generation processes and equipment.

（4）Skid Pressure Testing and Transportation

Once the skid design drawings are completed, the manufacturing and installation process begins in the factory. After completion, each skid undergoes flaw detection, hydraulic pressure testing, air-tightness testing, purging, and corrosion protection, all in compliance with national standards. These tests ensure the quality and reliability of the skid, ensuring the oxygen plant is ready for use upon delivery.

Given the complexity of sea and land transportation, it is crucial to ensure that the oxygen unit skids are not damaged during transit. Skids and other components should be packaged separately, placed in waterproof containers, and clearly labeled with a packing list that includes their names, numbers, equipment list, and drawing references for easy on-site arrangement and disassembly.

3. Challenges of VPSA/PSA Modular Skid-mounted Technology

Modular skid-mounted technology of the VPSA/PSA oxygen plant divides the production units of large-scale oxygen plants into multiple modules based on functional requirements and transportation constraints. Each module is designed separately, with equipment, piping, instrumentation, and other components completed and installed in a prefabrication factory. After initial integration and simple debugging, the modules are disassembled, transported to the site, and reassembled. Finally, the entire oxygen system undergoes overall debugging and pressure testing before operation. While this technology offers significant advantages in safety, environmental protection, project schedule, cost, and quality, it also faces several challenges and obstacles in practical application.

（1）Technical Challenges

The implementation of modular skid-mounted technology requires overcoming a series of technical challenges, including the precision of modular design of the VPSA/PSA oxygen plant, manufacturing accuracy of VPSA/PSA modular components, and the feasibility of transportation and installation of these VPSA/PSA components.

 Multi-disciplinary Collaborative Design: Modular skid-mounted VPSA/PSA oxygen equipment involves multiple disciplines such as process, equipment, piping, structure, and electrical engineering. Efficient collaborative design and precise construction planning are essential.

 Heavy Workload in 3D Modeling: Due to the complexity of skid-mounted equipment structure, detailed 3D modeling is necessary to ensure rational design and avoid potential conflicts.

 On-site Assembly and Disassembly: Multi-layered skid-mounted units must be assembled in layers at the factory. Considering the need for lifting, transportation, and reassembly on-site, a detailed plan must be developed for these processes.

In addition, modular design must consider physical conditions, qualification requirements, human and organization conditions, as well as the application of intelligent software, all of which are essential for successful modular design implementation of VPSA/PSA plants.

（2）Standardization and Scalability

Currently, both domestically and internationally, modular design is still in its early development stages, and a standardized, scalable modular skid-mounted manufacturing supply chain has not yet been established. This means that when implementing modular skid-mounted technology, there may be a lack of unified standards and specifications, leading to compatibility and interchangeability issues between different projects.

（3）Environmental and Safety Factors

In certain special environments, such as extreme weather conditions or complex terrain, the implementation of modular skid-mounted technology may face additional challenges.

Building on the advantages of modular skid-mounted technology, PKU Pioneer offers highly efficient Modular VPSA/PSA oxygen generators that stand out for their cost-effectiveness, reduced footprint, and shortened delivery time. The oxygen generating system is specially designed and installed in a container, making it ideal for clients with space constraints and low oxygen flow needs (usually <450Nm3/h).

In 2023, PKU Pioneer successfully delivered containerized PSA oxygen plant to users in Italy and Malaysia for sewage treatment and food industry. Since its establishment in 1999, PKU Pioneer has offered adaptable oxygen generation solutions to diverse international needs in over 20 industrial areas, making us a trusted and preferred provider in VPSA and PSA industry all over the globe.