Huge testing system for underground explosion prevention

Jon Lawson

German gas systems specialist Witt-Gasetechnik received a special order for a gas mixing system designed to the highest technological requirements. China's highest Testing Authority for mining technologies ordered one of the world's most powerful gas mixing plants for ignitable gas mixtures.

This testing system will enable underground mining machines and devices to be tested for explosion safety. It was delivered to the Testing technology Research Center of CCTEG-SHC, which is the largest of the country's three state Testing Authorities and comparable to the German TÜV.

With a capacity of 80m3 and a diameter of 3.4m, it is now the country's largest testing tank, which the special mixer will be filling with several norm-defined explosive gas mixtures.

The mixer named MG50-6MFC Ex A SO is based on proven Witt gas mixing technology, and the German gas systems specialist has built many testing systems in the past. But the scale and level of in-built technology are unprecedented. The technology includes efficiency enhancements enabling rapid fill times, plus layers of system protection. "After all, it is about the production of highly ignitable gas mixtures", says Zheng Zhang, regional sales manager for the Chinese market.

The gas mixing system enables the following testing procedure: Prior to the exposure to gas, the testing tank is evacuated within a very short time and then flooded with the ignitable gas mixture consisting of oxygen and gases such as CH4, H2, C3H8, C2H4, and C2H2, which is then ignited. To prevent unwanted ignitions and possible accidents, temperature and pressure wave detection is deployed to trigger emergency shut-down of the mixer, followed by nitrogen purging.

The mixing system itself is controlled by the proprietary Gas Control 50 - a PLC with touch screen, designed to ensure simple human-error-free operation. A simulation mode even allows the user to walk through the entire process before the system starts producing the dangerous explosive atmosphere. In addition, an Ex gas analysis module has been integrated to enable monitoring and logging of the required gas quality.

In recent years, Witt has built several systems for similar tasks. Zheng Zhang: "This is why in terms of technology and safety, this was nothing new to us. However, due to its size, the plant is something very special even to us." 

According to Zhang, for instance, even the gas mixing system which the company delivered to the German Federal Institute for Material Testing (BAM), ‘was significantly smaller’.


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