Primary Steel Temperature Measurement

To make steel, iron ore is first mined from the ground. It is then smelted in blast furnaces where the impurities are removed and carbon is added. Iron ore and other iron bearing materials, coke and limestone are charged into the furnace from the top and work their way down, becoming hotter as they sink in the body of the furnace. In the top half of the furnace, gas from burning coke removes a great deal of oxygen from the iron ore. About halfway down, limestone begins to react with impurities in the ore and the coke to form a slag. As the iron is formed, it is periodically extracted by tapping a hole at the bottom of the furnace to allow the molten metal to flow out. Most blast furnaces have multiple tap holes so that one may be opened as soon as another is sealed.

Williamson Wavelength Technologies

Pyrometers are used in all areas of the steelmaking process, including the iron stream, stove dome, and main blast gas temperatures, along with pilot flame monitoring at the blast furnace. Pyrometers are also used in the coke making process to monitor the temperature of the coke guide and hot spot detection for conveyor belt protection.

Iron Stream & Tap Time

Application Overview

In the blast furnace, iron ore is combined at high temperatures with carbon in the form of coke to form iron and carbon dioxide. Limestone is also added as a fluxing agent. As the iron is formed, it is periodically extracted by tapping a hole at the bottom of the furnace to allow the molten metal to flow out. Most blast furnaces have multiple tap holes so that one may be opened as soon as another is sealed.

Williamson Wavelength Advantage

Because the process is completely enclosed, it is difficult to make direct measurements within the blast furnace. Instead, external measurements are used to understand and control the status of the process. Continuous iron stream temperature and tap time are critical process parameters that may be used for the optimization of the process. Able to tolerate significant interference from flames, sparklers, and heavy smoke, the Williamson dual-wavelength sensors are uniquely appropriate for this sort of measurement.

Pyrometer Benefits
  • Continuous iron stream temperature during the length of the tap.
  • Automatic indication of tap time.
  • Available in fiber-optic configuration
Wavelength Technology
  • Tolerates significant optical obstruction from smoke and dust
  • Automatically compensates for emissivity variation
  • ESP filtering prevents measurement errors

Stove Dome Temperature

Application Overview

Blast furnace combustion air is preheated in refractory furnaces called stoves. The blast air is preheated in order to achieve the extreme process temperatures required for efficient production of iron. The stoves are divided into two sides: the combustion chamber and the brick checker work. When the stove is “on gas,” fuel is being burned in the combustion chamber, and the heated gases are flowing through the checker work to heat the bricks. When the stove is “on blast,” the checker bricks are being used as a heat exchanger to preheat the blast air. The hot blast air is delivered to the blast furnace through a large refractory-lined duct called the hot blast main. While the stove is “on gas”, extreme temperatures and turbulent air flow combine to threaten the refractory life and efficiency within the stove dome area. The temperature within the stove dome area is a critical process parameter, indicating temperatures at the entry to the checker brick.

Williamson Wavelength Advantage

A dual-wavelength fiber optic sensor is recommended for this application to allow the sensor electronics to be mounted away from the hot viewport surface. The dual-wavelength technology is able to compensate for optical obstruction as a result of refractory dust that can accumulate on the viewport window. The Williamson dual-wavelength sensor provides a measured signal dilution value which can also be used as a dirty window indicator, eliminating the need for routine cleaning of the viewport. Sensor ambient temperature, signal dilution, and measured emissivity values may be monitored locally or remotely to provide additional process feedback and troubleshooting tools.

Pyrometer Benefits
  • Reliable and continuous measurement of stove dome refractory temperature provides a meaningful process control parameter.
  • Eliminates cost and inconvenience of frequent thermocouple changes.
  • More reliable and faster responding than a thermocouple.
Wavelength Technology
  • Dual-wavelength self-aligns to the hot checker brick
  • Dual-wavelength is able to tolerate a dirty viewport from refractory dust

Main Blast Gas Temperature

Application Overview

Hot combustion gas is delivered from the stoves to the blast furnace through a large, refractory-lined duct called the hot blast main. A consistently high temperature of the blast gas is critical for the efficient operation of the blast furnace. Traditional thermocouple temperature sensors are susceptible to frequent failure and excessive maintenance as a result of exposure to excessively high temperatures and periodic rapid temperature changes. Williamson’s infrared thermometers replace these troublesome thermocouples, effectively eliminating the cost and inconvenience of replacement.

Williamson Wavelength Advantage

By using infrared pyrometers, an immediate and direct measure of the hot blast main gas temperature may be obtained, and troublesome maintenance issues may be eliminated. By carefully selecting narrow-band wavelengths we can measure the temperature of the gas, not the refractory wall.

Pyrometer Benefits
  • Reliable, instantaneous, and continuous measure of hot blast main air temperature allows for optimal process efficiency.
  • Eliminates cost and inconvenience of frequent thermocouple changes.
  • More reliable and faster responding than a thermocouple.
Wavelength Technology
  • Unique wavelength selection measures gas temperature instead of refractory wall

CO Gas Flare Pilot Monitoring

Application Overview

Flammable and hazardous CO gases are produced at the blast furnace and coke oven, and are distributed throughout the plant to augment natural gas as a fuel for a wide range of uses from ladle preheat stations to co-generation plants to steam generation to space heating. A flare is incorporated into the distribution network to incinerate any surplus gases before they are released to the atmosphere during low-usage periods or some distribution line failure. When these process gases are released, they are ignited by a pilot flame atop the flare as a safety requirement. The Williamson CO Flame Monitor is used to confirm that the pilot is continuously lit, to control the size of the pilot flame, and to confirm that the vented process gases have been properly ignited.

Williamson Wavelength Advantage

CO flames are difficult to detect because they emit radiated energy only at specific infrared wavelengths. Traditional UV-based flame detectors and IR-based pilot monitors are not designed to recognize a CO flame, rendering these devices highly ineffective. As a result, CO pilot flames are typically excessively large to permit these traditional flame detection devices to sense them. Even with an excessively large pilot flame, these devices frequently generate false alarms, indicating that the pilot flame has gone out when it has not. Plants with automatic igniters report excessive igniter maintenance and failure as a result of frequent and unnecessary firing. The Williamson CO Flame Monitor is specifically designed to measure CO Flame intensity. This device has been used successfully to conserve CO gas – thereby allowing this surplus gas to be used elsewhere in the plant, and reducing the need for and consumption of natural gas. At least one user has reported a savings of over five hundred thousand dollars per stack per year in recovered energy savings.

Pyrometer Benefits
  • Continuous monitor of pilot flame
  • Confirmation of emission and ignition of flammable gases
  • Eliminates false alarms associated with traditional flame detectors
  • Eliminates cost and inconvenience of frequent thermocouple changes
  • Mounted at grade level for easy access
Wavelength Technology
  • Senses small pilot flame allowing for significant fuel savings
  • Unique wavelength selection for maximum sensitivity

Coke Guide Temperature

Application Overview

Coke ovens are used to convert coal to coke. In this process, coal is heated in a reduced atmosphere for about 18 hours, allowing volatile compounds to burn off, producing a hard, porous, and high-carbon material called coke. Ovens are grouped side-by-side to form a battery. The oven walls are heated by flues embedded within the refractory walls. The coal is inserted in batches through charging holes on the top of the oven. The coke is removed using a pusher on one side, and a coke guide on the other. As it is removed from the oven, the coke is guided into a quench car that carries it into position beneath the quench tower. The hot coke is quenched to near-ambient temperatures, and then carried by conveyor to a docking area near the blast furnace.

Williamson Wavelength Advantage

As the coke is pushed from the oven, it passes through the coke guide. Dual-wavelength fiber-optic infrared thermometers are mounted at various heights along the coke guide to monitor the uniformity of the coke temperature. The coke temperature is correlated with the pusher position, and a thermal profile of the temperature within the coke oven is obtained. A consistently cold spot indicates a clogged flue, and corrective action may be taken. A consistently hot spot indicates excessive local heating of the coke resulting in premature refractory wear and excessive fuel usage. The top-most sensor provides assurances that the coke oven was properly filled when a valid measurement is obtained.

Pyrometer Benefits
  • Automatic thermal management feedback for heat distribution within coke furnace battery.
  • Prevents cold spots.
  • Eliminates cost and excessive refractory wear associated with hot spots.
  • Confirms coke furnace is being fully filled.
  • Fiber-optic sensor configuration protects sensor electronics from hostile environmental conditions.
Wavelength Technology
  • Dual-wavelength technology compensates for dirty optics.
  • Dual-wavelength technology compensates for misalignment

Conveyor Hot Spot Detection

Application Overview

After the coke has been quenched, it is delivered to a docking area near the blast furnace by a conveyor belt. If the coke is not properly quenched, then the conveyor belt may be overheated, and significant damage may result. The coke leaves the coke battery in the 2000°F / 1100°C range, and is cooled to near-ambient temperature using thousands of gallons of water. Occasionally, the quench water misses an area, and glowing-hot coke is placed on the conveyor. Damage to the belt will occur if the coke is not cooled to below 400°F / 200°C.

Williamson Wavelength Advantage

A traditional infrared thermometer measures only the average temperature viewed. The Williamson hot slug detector provides a unique rate of change alarm upon the identification of a hot slug in addition to the average coke temperature. The unique wavelength and Auto Null technology provided by the Williamson sensor provides extra sensitivity to hot spots while minimizing the influence of heavy steam and dirty optics. A large viewing area allows the entire width of the belt to be monitored by only one sensor. When hot coke is identified, a water spray is activated to cool the hot coke. A second Williamson sensor and spray is usually installed to confirm that the first spray adequately cooled the hot spot.

Pyrometer Benefits
  • A wide optical viewing area allows a single sensor to view the entire width of the belt.
  • Able to identify very small hot spots.
  • Temperature and Rate-of-Change parameters may be used to alarm and to quantify the amount of water spray applied
Wavelength Technology
  • Provides exceptional sensitivity to hot spots.
  • Narrow-band short-wavelength views through steam.
  • Short wavelength of operation provides relative insensitivity to heavy steam and dirty optics

Consult With One of Williamson’s Temperature Experts

We would love to discuss your temperature measurement application with you.

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