As per the prevailing practices in power and utility boilers in our industry, we measure the metal temperature of the components working in the creep regime temperature. But thermocouples for such temperature measurements are connected to the header to tube stub joints in the penthouse, which is not actually exposed to the hot gas. These hardly represent the actual metal temperature of the parts of the tube that are exposed to hot gas.

Accurate furnace gas temperature profile is one of the most important feedbacks that tell us ‘Where’ the combustion is taking place. High PA / SA ratio, which is endemic with majority of power & utility boilers I have come across, often leads to delayed combustion. Imbalance in coal-air flow in case of corner fired PF boilers shifts the flame ball location towards one side of the water wall causing highly differential gas temperature profile in the furnace. Again in FBC Boilers, similar problems can be seen due to differential PA velocity through wind box.

Accurate measurement of FEGT (Furnace Exit Gas Temperature) is another very important feedback to assess the combustion condition. In case of slagging coal, this is THE temperature to be closely monitored and controlled.

Reliable and accurate measurement of flue gas temperature within a furnace of a solid fuel boiler is a difficult task due to the harsh conditions like high temperature, often in excess of 1000 ◦C, high dust content, chemically aggressive environment, as well as considerable dimensions of the furnace. Another fundamental difficulty is due to the fact that every temperature sensor introduced into the furnace undergoes a heat transfer with its surroundings not only through convection, but also through radiation, which can considerably distort the measured results.

There are few alternative pyrometric measurement methods that many have opted, the pros and cons of which we want to explore in this forum. Gas suction pyrometer, IR pyrometer and Acoustic pyrometer are some of those technologies. Each has got their own advantages and limitations in various operating conditions.

Gas suction pyrometer has questionable reliability. Infrared (IR) pyrometer presents a convenient contactless method of measuring high temperatures. This technology takes advantage of Planks Law, whereby the wavelength and intensity of the IR radiation emitted from a surface is proportional to its temperature. A pyrometer or thermal imager detects this radiation, converting the signal to a temperature. 

But, Emissivity is always an issue with this technology. Different materials at the same temperature radiate different intensities of IR radiation and the sensor must be calibrated for this.

The Acoustic pyrometer appears to be one of the better technologies amongst these. The acoustic method is based on the thermo-acoustic phenomenon where the speed of acoustic wave propagation in gaseous environment depends on temperature. Acoustic-based measurement is an indirect method, as the directly measured value is time of propagation of an acoustic pulse from the signal emitter to the receiver placed in the furnace.

However, In order to determine temperature accurately, it is necessary to know chemical composition of the environment, i.e., concentration of exhaust gas components and their spatial distribution at the time of measurement, which creates a limitation.

I am interested to find out if anyone connected to this network have used this technology in their system. I am aware that a US based company; Enertechnix Inc. are offering this technology by the name PyroMetrix. Another such product is BOILERWATCH® MMP II-SSX, which is supplied by SEI, Spain. They also have an Indian partner; Lucent Marcons Private Limited, in Noida.

Valmet, Finland is another company that offers this technology and they have their sales offices at Chennai, Gurugram, Mumbai and Vadodara in India.

If you know any vendors offering this technology, then please give their details under ‘Suggest Vendor’