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Being involved in ever changing industries, there will constantly be new applications and new products that will be solutions for these applications. As such, in the subsequent issues of this newsletter, we will be featuring articles on the applications we have worked on, information on our products and additions to our catalogue.
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In this issue...
[ The BFI flame scanner solution ]
[ FCI Thermal Dispersion Technology ]
[ Canty FuseView and the Tempered Glass ]
The BFI flame scanner solution
Flame scanners are designed to monitor flames and provide signals to the operator should there be no flame present. This allows proper measures (such as cutting a fuel line) to be taken so that a catastrophe can be avoided. There are many different types of flame scanners available, depending on the type of flame that requires monitoring.
More commonly, flame scanners make use of the Ultraviolet radiation, Infrared radiation and Visible radiation properties that a flame produces to detect its presence. While this generally works, it can be a challenge in applications where reliable detection in the Infrared range is not possible due to reflection from the combustion chamber.
The method developed by and patented to BFI Automation detects a flame by sensing the temperature re-circulation of its combustion gases. This makes use of the fact that combustion can only be maintained when there is sufficient energy fed back into the ignition zone. This replaces expensive parallel operations of UV and IR flame scanners and works reliably, independent of fuel with any flame colour.
For the radiation sensors, two rows of thermocouple chains are used. These have linear sensitivity across the complete radiation emitted by the flames and can be fine-tuned for certain wave length ranges through the use of filters (such as Silicon). Additional filters can further reduce the flame spectrum to be evaluated in order to pick up the spectral signals of only certain products.
The two thermocouple chains are aligned very close to each other at an offset. Thus the difference between the outputs are a measurement of the radiation picked up, offsetting the signals produced by the brick lining and other sources that we are not interested in.
A downstream amplifier processes flame signals between 25 Hz and 1000 Hz, focusing on the temperature movement of the flame.
FCI Thermal Dispersion Technology
The thermal dispersion method measure flow rate by introducing heat into the flow and determining how much heat is dissipated by the flow using temperature sensors. As the amount of heat lost is dependent on the thermal properties of the medium, the flow meter should be calibrated to suit a specific application (some flow meters have electronics that can cater for more than one calibration and can be used for mutliple gas compositions).
As liquids tend to absorb more heat, the meter is only able to calibrate for a smaller range of signal. Hence, the thermal dispersion method is best used for gas applications.
There are two different methods for measuring how much heat is dissipated. Both methods involve having a heated resistance temperature detector (RTD) and a reference RTD. The only difference lies in how these respond to changing flow rates.
Constant temperature differential (Constant Voltage)
The current going through the heater at the heated sensor changes to maintain the temperature difference between the reference and heated RTD as the flow changes. A feedback loop is set up to feed information on the voltage difference back to the heater so that any adjustments can be made.
The mass flow rate can be calculated by the amount of current being fed to the heater to keep the temperature differential constant. As a result, the instrument will reflect a reading before it is "verified" by the feedback loop and the readings will jump accordingly to the feedback, giving erratic fast response readings.
The current going through the heater at the heated sensor remains constant throughout the operation.
The mass flow rate can be calculated from the difference in voltage. A change in flow rates in the pipe will take some time to be reflected on the readings as the heat generated by the heater takes time to be dissipated by the flow of the medium. As a result, the instrument will give slow stable readings.
FCI follows the constant current principle and ensure basic temperature compensation is done for all instruments that leave the factory. A more robust extended temperature compensation will be done if the instrument is specified to be used in processes with temperatures far beyond calibration conditions at both extremes.
Canty FuseView and the Tempered GlassSight glasses enable operators to visually observe processes inside vessels and it is important that these are safe products that will be able to handle the process parameters without risk of blowing up in front of an operator or chipping into the vessel.
There are generally two different types of sight glasses being used - A tempered glass disk held between two metal frames secured by bolts and gaskets, or a glass disk that is pre-stressed by a metal frame during manufacture. The former is usually the more economical of the two and there is standard that most manufacturers will follow - DIN 7080 - but does have its share of inconveniences.
The amount of torque allowed during installation between the metal frames is very low and it is easy to overtorque, cracking the glass. Even when done correctly, residual stress being created by the initial installation means that rebolting should be avoided to prevent cracking (i.e. one use).
Impact on the glass can cause catastrophic failure, shattering the glass into a multitude of small fragments. Multiple glass layers are usually laminated to increase the strength of the glass. Temperatures above 450 degrees Farenheit cause rapid delamination and loss of optics. At high temperatures, only one piece of glass can be used, yielding a lower level of safety.
Generally, using a glass disk that is pre-stressed to the metal frame during manufacture is more ideal in terms of safety and reliability since there are no torquing problems. While the DIN 7080 standard is not applicable to these type of sight glasses, the mechanically pre-stressed glass proves to be stronger than their tempered counterparts and are less likely to break and compromise the safety of employees using the sight glass.
Canty's Fuseview line of sight glasses are a variant of such sight glasses, using Hastelloy C and Boro Plus glass. Instead of simply mechanically pre-stressing the glass, the Boro Plus compound fuses together with the Hastelloy metal frame. This proves superior to sight glasses that are only mechanically pre-stressed and not fused. These sight glasses will crack under stress and though they do not pose a safety issue to the operator yet, the breakaway flakes will end up in the vessel, contaminating the product.