At around 7:00 a.m. on a non-business day, a fire broke out at the cogeneration plant of a waste storage facility. The on-call technician was informed of a problem with the plant’s flare stack. At the plant, he saw the fire finish off the plant’s turbine system. He disconnected the plant’s other facilities and turned the flare stack back on. The turbine system, in particular three of its six turbines, and the power cables of five turbines were severely damaged by the flames.

After a technical analysis, one of the six turbines was turned back on. In August, three other turbines were put back in service, allowing power to be generated from 75% of the biogas produced. During this transitional phase, the operator set up a mobile leachate treatment plant. The last two turbines were put back in service in January 2018.

The operator asked the turbine system’s supplier and the plant’s installer to determine the causes of the fire. They found that the culprit was a leaky check valve on the gas exhaust duct of one of the turbines. The hot gases from the operating turbines backflowed into the combustion chamber of a turbine that was off and whose isolation valve was leaky. They flowed up the air inlet, ignited the air inlet filter and the insulation of the door, and then spread to the other turbines.

Another fire cause by a leaky valve had occurred at the site in May 2016 (ARIA 49014). Corrective measures were subsequently taken (alarm and shutdown of the turbines’ combustion chambers in the event a specific temperature threshold was exceeded) but they proved to be insufficient (the complete shutdown did not prevent the fire).

The following measures were immediately taken after this latest fire:

• the valves on each turbine’s exhaust duct were replaced by new ones;
• each exhaust duct was tested for leaks;
• the relief valve on each turbine was moved so that the hot gases from the combustion chamber are no longer discharged behind the air filter during a sudden shutdown.

In the medium term, the following actions will be taken:

• fitting valves of different design;
• quarterly preventive leakage tests to confirm the absence of valve deformation;
• redundancy of the abnormal temperature detection system;
• installation of a seventh turbine, separate from the system of six turbines involved in the fire. The installed capacity will be greater than actual demand, making it possible to operate just one-third of the turbines in the system at a time and have a stock of spare parts (greater reactivity).