Burner Flame Detectors

Flame detectors designed for burner protection are quite different than flame detectors designed for fire and gas systems. Burner flame detectors monitor the flame inside a combustion chamber and look for lack of flame. The dangerous condition is loss of flame. 

Conversely, in detectors designed for fire and gas mitigation systems presence of flame is the dangerous condition. Since the dangerous situation is reversed for these two applications, the overall design of the sensor is different especially the fail-safe characteristics. 

A partial Ust of burner flame detectors that has had some level of safety assessment is shown in Table 9-11. 

Fireye Insight 951R/95UV/95DS FMEDA exida 

It should be noted that several manufacturers of burner flame detectors have had their product assessed per EN298, a European standard. This standard is similar to lEC 61508 but does not require publication of failure rates and failure modes nor does it require publication of safety manual. Instruments assessed to this standard should provide a high level of safety however. 

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Burner Flame Burner Flame Detector Burner Safety Low 0 ... 

Table 9-11. Partial List of Burner Flame Detectors with Assessment...

AH gas-fired power plants require oxygen analy2ers to ensure that air has not been drawn into the piping system. Oxygen intake can lead to the presence of an explosive mixture in the pipeline before the fuel reaches the burner or combustor 2one. When gas-fired units are located in an enclosed area, multiple ultraviolet flame detectors are used to shut down equipment and flood the area with CO2 or a chemical fire suppressant whenever a spark or flame is detected. 

Check that the flame detector is registering the presence of a flame. This is continuous until the burner is shut down. 

After any maintenance work involving replacement or adjustment of components it is essential that the plant be re-commissioned in a safe way, including dry mns with the gas turned off to ensure that flame failure devices operate correctly and pilot turndown tests to ensure that if the pilot can energize the flame detector then it can also smoothly ignite the main burner. 

The main components of an elevated flare system are the flare burner with or without smoke suppression capability, pilot(s), pilot igniter(s), support structure, and piping. A number of optional features are available, such as pilot flame detectors air seals (buoyancy or... 

A peculiar feature of flameless oxidation is that it requires recirculation of flue gases above self-ignition threshold (850°C for safety). Below threshold, a burner stabilized flame must be provided (Figure 23.9) and this is carried out by a system capable of selecting between flame mode (the only possible mode below 850°C) and FLOX mode (above threshold both modes are possible). Below threshold, a flame detector (ionization or UV principle) is required if FLOX is selected above threshold, then the flame detector must be neutralized (because there is steady combustion without flame). Dedicated control units have been developed for this purpose [1] the overall operation of the control system should be carefully checked in operating conditions. 

Turndown may be limited by (a) burner stability range, flammability limits, mixing quality, (b) valve leak or process low-flow limit, either of which raises the denominator in the t/d equation, (c) flow controller range limit, (d) low-pressure air atomizer for liquid fuel, (e) flame detector range, and (f) transmitter turndown (4 to 20 ma 5 1 t/d). 

A flame detector used in a burner management application falsely indicates a flame when there is none. How would that failure mode be classified ... 

What t)q)e of flame detector would be chosen for a burner management system ... 

The high loading of the dense-phase conveying requires compliance with defined conditions to avoid clogging. Problems with particle size distribution (mills), instable fluidization [26], and water condensation [6] are reported. In Puertol-lano, the flame detector used to fail and required increased maintenance and readjustment [25]. A burner can operate without interruption for 2000-8000 h. Typically, it is not the burner tip that fails, but the internal coal feeding system [27]. 

Figure 6.9 Schematic drawing of Siemens combined burner for coai gasification 1 -pulverized coal, 2 - oxygen (and steam if used), 3 - pilot fuel, 4 - pilot oxygen, 5 - ignition device and flame detector, 6 - spiral inlet duct gap, 7 - water-cooled parts, 8 - burner tip [42].

Data for the several flame methods assume an acetylene-nitrous oxide flame residing on a 5- or 10-cm slot burner. The sample is nebulized into a spray chamber placed immediately ahead of the burner. Detection limits are quite dependent on instrument and operating variables, particularly the detector, the fuel and oxidant gases, the slit width, and the method used for background correction and data smoothing. 

Figure 3.14 Dual-flane photometric detector (Varian). A, Schematic diagram of the dual-flame burner B, Schematic diagram showing the relationship between the burner and the photometric viewing components. (Reproduced with permission from ref. 177. Copyright American Chemical Society).

Two improvements to the FPD design have been made in recent years. First, the addition of an oxygen-rich burner upstream of the FPD oxidizes hydrocarbons to CO and C02 and thereby eliminates the hydrocarbon interference within the analytical flame [105, 106], This increases the sensitivity of the detector to approximately 20 pg S s"1 for a nonlinearized FPD [102], In a second improvement, the PFPD was developed to significantly reduce the background and increase the sensitivity to all detectable atoms [107], This detector is now commercially... 

In Chapter 5.4, optical ultraviolet radiation sensors are described, including UV-enhanced silicon-based pn diodes, detectors made from other wide band gap materials in crystalline or polycrystalline form, the latter being a new, less costly alternative. Other domestic applications are personal UV exposure dosimetry, surveillance of sun beds, flame scanning in gas and oil burners, fire alarm monitors and water sterilization equipment surveillance. 

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