There are many ways to increase the sustainability of industrial processes. Looking beyond energy and resource conservation measures, they include revamping existing plant equipment to increase operational efficiency, repurposing unused assets and turning waste streams into valuable resources. The LINDE PLANTSERV^® team recently demonstrated how successful execution of a modernization and plant relocation project - despite the restrictions related to the coronavirus pandemic - can increase operational sustainability.

The opportunity arose in the city of Rubí, Spain. Since 1996, Linde has been operating an air separation unit (ASU) at Rubí. It separates air into its components, producing liquid nitrogen (LIN) and liquid oxygen (LOX) as well as gaseous nitrogen (GAN) as a by-product. "We wanted to revamp the ASU so we could boost operational efficiency and increase the GAN flow in particular," explains Mirco Koelle, Project Manager at LINDE PLANTSERV^®. The plant supplies LOX to hospitals and LIN to various industries, where it is used as a coolant. However, there is no local market for the gaseous nitrogen by-product, with the result that it typically went to waste as it was not economically viable for the plant to capture and condition it.

To capture and valorize this waste nitrogen gas stream, Rubí needed a nitrogen liquefaction unit (NLU). Fortunately, this crucial unit didn’t have to be built from scratch. About 1,800 kilometers to the northeast, the city of Spreetal in Germany was home to a Linde ASU that had been shut down in 2016, but had been well maintained and regularly upgraded until that point. Most importantly, the Spreetal facility included an NLU that was only about ten years old. "This equipment was a good match for the ASU in Rubí from a technical feasibility perspective, so it made total sense for us to relocate it from the decommissioned plant in Spreetal," says Koelle.

This relocation project was a win-win from a sustainability perspective. "On the one hand, we were revamping the Rubí plant to increase operational and energy efficiency and to capture an otherwise unused gas stream," Koelle continues. "And, on the other, we were at least partially recommissioning an idle plant, and thus indirectly extending its service life."

A team of LINDE PLANTSERV^® experts is responsible for relocating processing plants and components. Their job is to manage the entire disassembly, transport and reassembly process, ensuring that the relocated unit is up and running smoothly at the new site. Customers benefit from this service on multiple fronts. Not only is repurposing generally more cost-effective than new builds, it is also a more sustainable choice as existing resources can now add new value. The two-year relocation project was successfully completed by the LINDE PLANTSERV^® team in September 2020.

Relocations present their own challenges, however. The Spreetal plant could not simply be moved and "plugged" into the Rubí site. "Relocating complex process equipment is never that simple," says Daniel Bumann, Project Construction Manager. The first step for the PLANTSERV^® experts entailed establishing whether the new site was a perfect match for the NLU and whether everything they would need at Rubí was in place. This initial review revealed the first challenge. The capacity of the Spreetal liquid nitrogen plant was too high for the Rubí ASU. "So we first had to increase the "waste" GAN flow at Rubí by replacing part of a column within the existing ASU coldbox and upgrading the cooling water capacity by adding a cooling tower," explains Koelle. "Only then could the existing NLU from Spreetal also be used in Spain.” But this was not the only challenge facing the team. "Work on a column in the ASU coldbox required pinpoint precision," adds Koelle. The coldbox had to be partially opened, part of a column removed and a new one inserted to replace it. "For this procedure, operations in Rubí were shut down for six weeks. Thankfully, this was the only downtime required for the project," he notes. To minimize the interruption, the PLANTSERV^® specialists worked in two shifts, seven days a week over a three-week period while the plant was offline.

The groundwork involved various other preparatory steps. Before the NLU from Spreetal could be moved, the engineers had to measure the entire plant precisely. With the help of multiple laser scans, they created a detailed 3D model. "This doesn't replace an on-site visit, but it's a tremendous support for the engineering work," says Koelle. "It's also very helpful to have colleagues on site who can provide advice and assistance, and take specific measurements." The 3D simulation confirmed another challenge. "The footprint of the nitrogen equipment within the machine house in Spreetal was about 80 square meters larger than the floor space we had available in the Rubí machine house," explains Koelle. So the engineers had to rebuild the entire liquefaction plant in Spain to much more compact dimensions.

On successful completion of the rebuild work in the 3D model, the PLANTSERV^® team started the actual relocation planning process. They began by reviewing all of the necessary pieces of equipment and control systems. “The new nitrogen liquefaction unit had to be connected to the existing system at 25 tie-in points,” continues Bumann. As each relocation project is unique, there is no execution blueprint for the team to follow. Hence the entire process flow has to be customized on a project-specific basis.
This is where PLANTSERV^® specialists excel, drawing on their vast experience with industrial plants to develop tailor-made solutions for each project challenge. “Modifications during live operations was still a challenge,” remembers Koelle. “From August 2019 to September 2020, work was carried out on the entire complex in Spain while it was on stream. During this time, Spain was in complete lockdown, and demand for oxygen had risen dramatically to support the sharp increase in ventilated patients." As a result, it was imperative that revamp work be carried out with minimal disruption to daily operations. In addition, only the smallest possible team was allowed on the construction site to minimize the risk of viral transmission. Other technical challenges included the need to integrate two different process control systems at Rubí. Despite all the coronavirus restrictions, the Linde team overcame all of the technical and logistical hurdles. Thanks to Linde's rigorous COVID management plan, construction and commissioning work was executed safely, on schedule and without any Corona infections among the teams. In addition, the project was managed remotely for the most part due to travel restrictions.

Thanks to the new nitrogen liquefaction unit, the Rubí ASU now produces about 20 percent more liquid oxygen and around 400 percent more liquid nitrogen than before. This uptick in capacity required a final step in the revamp project. "When production increases, the plant must be able to store more product," explains Koelle. To support the increase in production volumes, the storage capacity was increased by creating a new, independent LIN tank farm at Rubí and the energy supply was modernized and upgraded.
These upgrade efforts have clearly paid dividends. Today, the Rubí ASU requires less energy even though it produces more gases. This outcome demonstrates how sustainable industrial practices can also translate into financial benefits. In fact, when an independent energy efficiency audit confirmed the plant’s prospective energy savings, the column exchange within the ASU coldbox qualified for an energy improvement grant by the Spanish government.

Even without the subsidy, relocating the liquid nitrogen plant has paid off for Linde. In the words of Koelle: "The revamp was a triple win if you like - we have a lower ASU energy bill, an increase in capacity and repurposed equipment instead of a new build." Since September 2020, the ASU in Rubí has been fully back on stream. The Rubí reconstruction and upgrade project is an outstanding example of industrial sustainability in action. The Linde engineers had to assemble a mixture of retrofitted, relocated and new components into a perfectly functioning unit. The fact that a complex process like this could be seamlessly managed, not only while the plant was in operation but with the added complexity of the pandemic restrictions, bears clear testimony - yet again - to the efficiency and outstanding skills of LINDE PLANTSERV^® specialists. 

Looking ahead, the benefits of teamwork extend far beyond completion of the project. As José María Declara Merino, Director Bulk Operations Iberia at Linde, explains: "Reflecting Linde's commitment to never stop improving, the gases and engineering experts put their heads together to explore ways of increasing production capacity just by keeping the NLU running around the clock. We jointly developed a new, non-standard load case that is currently running to everyone's satisfaction."