Decentralized I/O system for hazardous areas at H2 fueling stations

Hydrogen is expected to play an important role as an energy carrier in the future, with buses and trucks in particular increasingly using it as a fuel. It also appears likely to gain a long-term foothold in the passenger car market. One company benefiting from this trend is Resato Hydrogen Technology B.V. from Assen in the Netherlands, which develops and builds hydrogen fueling stations. The company's core expertise lies in high-pressure technology. Resato has been known for waterjet cutting systems since the early 1990s and has applied that know-how to hydrogen fueling infrastructure since 2018. To date, the company has produced and commissioned more than 45 of these systems in Europe, including nine in the Netherlands.

Two pressure levels for trucks and passenger cars

Hydrogen fueling stations can obtain their fuel in two ways, either from an electrolyzer that uses electrical power to drive a chemical reaction that splits water into hydrogen and oxygen, or from hydrogen tank trailers known as tube trailers. The hydrogen from a tube trailer is compressed in three stages to 350 bar and cooled. It is then held in buffer storage vessels for fueling trucks or compressed in a fourth stage to 700 bar and stored in a separate buffer. Pre-cooling the hydrogen allows passenger cars to be fueled much faster at the 700 bar dispensers.

A hydrogen fueling station is therefore much more complex than a fueling station for carbon-based fuels, as the system must bring the hydrogen to the required pressure through a series of cooling and compression steps. Since higher pressure leads to higher temperatures, the hydrogen must be cooled down repeatedly.  

Hydrogen requires an explosion protection concept

The complexity of the fueling station systems lies in the control system. Resato developed a patented algorithm that delivers the fastest possible fueling based on temperature and pressure. At the I/O level, explosive hydrogen poses a particular challenge for automation, calling for an explosion protection concept and components with the appropriate approvals. The station also has to run with minimal maintenance because no staff are on site to make adjustments. The system processes primarily temperature and pressure signals, plus switching signals from control valves. It also processes safety-related signals from valves, emergency stop pushbuttons and other safety sensors. 

In the first version, the manufacturer still wired its fueling systems using passive I/O technology. The sensor and actuator signals were landed on passive junction boxes at the buffer storage vessel and from there routed to the control system via multicore cables. While this solution worked reliably, it was not very flexible if the system needed to be expanded with additional buffer storage units. "From an electrical standpoint, it was very labor-intensive to add a unit. We also had to completely revise the software. For that reason, we decided to divide the entire system into modules so we can control each module individually," explains Remco Lagendijk, Electrical and Instrumentation Engineer at Resato, describing the start of the modular fueling station concept.

Modularization for greater flexibility

The second generation of Resato hydrogen fueling stations is therefore designed with a modular structure. Buffer storage units, compressors and cooling units can be added and combined flexibly. To make it easier to add these units, all signals on each unit must be bundled into a single data line. The buffer storage units therefore require an I/O solution with industrial Ethernet, more specifically Profinet. Since Resato wanted to avoid protective enclosures and additional mechanical effort, the experts were looking for IP67-rated I/O modules that are temperature-resistant and suitable for outdoor use. Up to this point, the requirement profile would not challenge any automation specialist. However, the modules also had to be approved for ATEX Zone 2 and suitable for connecting intrinsically safe signals from Zones 1 and 0.

The search for an automation partner capable of supporting this decentralized concept in hazardous areas also led the Resato team to the Hannover Messe. At the exhibition stands, the engineers were presented with many IP67 I/O solutions. However, when asked about IP67 with ATEX approval, many providers had no answer. "Except for TURCK. They were able to offer us different IP67 solutions for ATEX zones. We realized that TURCK knows this field well and already has suitable components on the market," Lagendijk reports, describing the search for a decentralized I/O solution.

In-depth consultation during concept development

As a next step, Resato worked with TURCK experts to develop a decentralized I/O concept for its buffer storage vessels. "The support was excellent. Rather than just handing us a few products and wishing us luck, they worked with us to evaluate different options. TURCK even recommended the exact cable types in the right lengths," explains Niels de Jong, R&D engineer. "Resato's goal is to be the global technology leader in hydrogen fueling stations. To achieve that, we need partners like TURCK."

The I/O concept was implemented completely decentralized, including the intrinsically safe sensor signals from ATEX Zones 0 and 1. With devices from the IMC family, TURCK offers special IP67 interface modules. They are installed between the Ex sensor (or actuator) and the I/O device, provide safe circuit isolation and convert the signal currents. Even the safety-related signals are routed locally to the IP67 I/O module TBPN, which communicates with the safety controller via the Profisafe protocol.  

Modular concept simplifies offline testing and shortens commissioning 

"One of the advantages and the reason we chose the TURCK solution is the ability to perform offline testing," says Lagendijk. "In the past, we had to test in our production facility, then we dismantled everything and rewired everything again on site at the customer's premises. Then of course we had to test again to make sure all inputs and outputs were connected correctly. Today we test the systems here and leave all connectors mated to the remote I/O modules. At the customer site, we only have to connect the power and data lines, saving us several days of commissioning time for the electrical work. That also means we can operate with fewer electrical engineers."

Remco Lagendijk emphasizes this advantage of the modular concept: "Commissioning is a critical phase. If errors occur here, it usually takes much longer to fix them than in production. In our own manufacturing, all experts, the right tools and any required spare parts are readily available, unlike at the customer site."  

Consistently modular and highly scalable 

Resato has fully implemented its modular concept. Remco Lagendijk and his software development team have also built the control software as a modular system, so new modules can be added without reworking the entire code base. "It is almost like copy and paste," says Lagendijk. This consistent modular approach makes Resato's hydrogen fueling stations easy to scale. "If the customer wants to expand storage capacity and needs additional buffer storage, that is no problem for us. Especially from the electrical engineering and controls side, it is very easy," adds Niels de Jong.  

Next stop: series production

Demand for hydrogen fueling stations is rising steadily. It can be assumed that Resato will gradually shift its production from a project-based organization to series production in the near future, at least in part. The modular fueling station concept and modular I/O architecture provide ideal preparation for this, as the concept allows for a move into series production at any time. Individual modules such as compressors or buffer storage units can be pre-produced for inventory and then assembled to customer specifications. These economies of scale will also reduce cost and time to market of the hydrogen fueling stations.

Customer | www.resato-hydrogen.com