ETH Zurich – Automation of a pure steam plant with safety level SIL 3 at the Basel site

Unique in Switzerland

With the new construction of the Laboratory and Research Building for Biosystems in Basel, ETH Zurich is investing in a modern infrastructure that offers optimal conditions for improving cooperation between the natural sciences and medicine.

The building infrastructure also includes a pure steam generation plant which essentially comprises two pure steam generators, a feedwater tank and a heat recovery system. The latter uses the returned condensate to further utilise the heat by means of a shell-and-tube heat exchanger.

STEBATEC was commissioned by Colin Swiss AG to supply the EMSR (electrical measurement and control technology) for the new plant. The general contractor for this demanding project is Klima AG in Basel, a branch of Hälg & Co. AG.

In a first step, a risk analysis was drawn up in collaboration with the Swiss Safety Center, part of the SVTI (Swiss Association for Technical Inspections). The safety performance of the plant is described by so-called Safety Integrity Levels (SIL), which quantify, among other things, the probability of a dangerous failure per operating hour.

Safety PLC and SIL 3 for the pure steam generation plant on the 3rd floor

The boiler inspectorate of the SVTI is responsible for ensuring that stationary pressure equipment and plants meet the safety requirements and thus prevent malfunctions, accidents and damage during operation.

The risk assessment, under the given circumstances of an installation on the third basement level without pressure relief to the outside, resulted in SIL level 3. This reliably prevents a bursting of the boilers and the associated considerable danger to people and the infrastructure.

After successful preparation of the necessary documents, the control cabinets could be planned and manufactured. A separate cabinet was built for the condensate control with heat recovery.  A safety PLC is designed according to the SIL level and implemented accordingly.

The system is supplied with clean water via the feed water tank. The water is supplied to the system already treated. In order not to discharge water unnecessarily into the sewage system, the line condensates and the excess water from the pure steam generators are also fed back into the vessel.

2 x 369kW electrical heating capacity

Each clean steam generator is equipped with five electrical heating elements that can be switched on and off in stages. By increasing the temperature, the desired pure steam is produced, which finally reaches the consumers via the steam distributor.

However, evaporation also produces salts, which increase the conductivity in the boiler. A blowdown control, which is controlled via the conductivity measurement, and a time-controlled blowdown ensure that the quality of the clean steam is guaranteed at all times.

The boiler water from blowdown and desalination is fed to the condensate collector for heat recovery. The thermal energy from the condensate collector is further utilised via two shell-and-tube heat exchangers. This is done to preheat the make-up water in the feed water tank and in the building heating system or for hot water preparation. A mixing cooler is connected downstream of the collection tank, which cools down the temperature of the water if necessary, so that no water that is too hot is fed into the sewage system.


After the final acceptance with the TÜV (Technical Inspection Agency), the project was completed to the full satisfaction of all parties involved. Klima AG was supported and advised by STEBATEC throughout the entire project, so that together a pure steam generation plant was created which will be available for research projects for many years to come.

Terms of reference

  • Supply of the electrical instrumentation and control technology for the new plant
  • Preparation of a risk analysis
  • Planning and creation of the control cabinets –  A separate cabinet was built for the condensate control with heat recovery. In addition, a further cabinet unit had to be manufactured for each clean steam unit, which were equipped with all control technology elements.
  • The safety PLC – The safety PLC represents the core of the entire control system.
  • Parameterisable touch panel – For the operating and control functions, the control cabinets are equipped with a touch panel. Parameters can be set and system messages processed on this panel. The intuitive menu navigation is designed in such a way that the operator can find his way around very quickly


  • Pure steam plant on the 3rd floor
  • Due to the parallel processing of the user program and the constant monitoring of the inputs and outputs, as well as other special features, the highest safety requirements were met for this project. If the control system detects any deviation in the safety processes, then the system is brought into a hazard-free basic position with a controlled process. The complete development of the control software and the HMI was realised by STEBATEC at their headquarters in Brügg.
  • The entire STEBATEC AG safety package was rounded off with safety training for the operator. This means that the operator knows what to do in every operating situation and can operate the system in a relaxed manner with the specialist knowledge he has acquired.

Products in use

Planning, implementation, operational support and security tests
Automation of steam boiler and hot water boiler. Whether in milk processing, food production, the paper industry or even laundry and butchery operations, the generation of steam and hot water is an important component. All the more attention is paid to the safety of automation systems in this area, so that daily operations run smoothly and safely.
Cloud process control system for energy suppliers with high demands on security, function and comfort
Industries such as heat supply, steam and hot water generators, as well as operators of hydropower plants rely on the REbella process control system, which is characterized by its scalable, modular and process-oriented design.
Individual automation for safe and efficient processes.
We support you with risk analyses, electrical, control and energy concepts and individual PLC programming in operation and in the realization of automation projects.
Resistant electrical engineering in wet, corrosive, explosive and aggressive environments
As a licensed electrical installation company, we offer the highest installation quality with special products and equipment for durable and trouble-free installations.