Durable Temperature Sensor for Waste-to-Energy Plants

Combusting cling wrap, Styrofoam, PVC, and other plastics produces highly corrosive gases that can damage measuring instruments and cause them to fail prematurely. WIKA recently came up with a customized solution that withstands the aggressive flue gases of a waste incinerator’s combustion chamber.

This article is the last of a three-part series on energy recovery plants and measuring solutions for waste-to-energy facilities.

Recycling has diverted much of plastic waste from landfills and waste-to-energy facilities. However, municipal solid waste (MSW) still contains about 15% plastic by weight. When materials like Styrofoam, PVC, and cling film are burned, they produce highly corrosive gases. Chlorides and hydrochloric acid, especially, attack the metals that high-temperature sensors are made of, including stainless steel and Inconel. Even thermowells are often insufficient protection in the extremely harsh environments found in most combustion chambers.

Problem: Frequent sensor replacement meant frequent shutdowns

Corrosion at the tip of a competitor’s protection tube

A waste incineration facility was using thermocouples shielded by protection tubes made of Incoloy 800, a material widely used in combustion zones. But even though this alloy is designed for high-temperature corrosive environments, the operator found that corrosion developed fairly quickly at the tip, measuring 2–3 cm in length, and led to signal loss.

To maintain reliable temperature monitoring, the plant had to shut down at least once every three months to replace not just the protection tubes, but also the thermocouples. This is an expensive, difficult, and time-consuming process. There is not just the expense of new temperature probes or the labor involved in replacing the units, but also the high cost of downtime due to lost production.

The EPC (engineering, procurement, and construction) company involved in this WtE facility asked WIKA to find a solution that would extend the interval between thermowell replacements.

WIKA’s specially engineered protection tube

Solution: Specialty materials and skillful welding

WIKA has extensive experience with high-temperature, high-corrosion applications. After investigating the issue, our temperature specialists identified a special material for the protection tubes. In-house testing showed that this alloy withstood the incineration chamber‘s high temperatures and exhibited greater insensitivity to aggressive flue gas.

We welded together this special alloy with 310 stainless steel to form the tube that protruded into the combustion chamber. The weld seam and stainless steel pipe were placed behind the fireproof wall, protecting them from exposure to the flue gas. Our TC81 thermocouple, specially designed for flue gas temperature measurement, completed the assembly.

The customer was delighted with this assembly, as our engineered solution greatly extended the service life of the temperature measurement system. It has already been in use for 18 months and counting, a significant improvement over the three months that their previous assemblies lasted.

WIKA, a Global Leader in Power Generation and High-Heat Applications

WIKA measurement technology and products are found in WtE plants around the world, helping cities and waste management companies responsibly dispose of MSW while putting the generated heat to good use. Contact WIKA USA for customized, long-lasting measuring instruments – for monitoring and controlling temperature, pressure, level, and flow – as well as calibration services, in your power generation facility.