Combustion processes are in many cases of primary importance in a broad range of different types of industrial plants, among which refining and petrochemicals, blast furnaces, power plants, boilers, process fire heaters, waste incinerators etc.
Reducing the costs of fuel consumption and increasing environmental demands concerning air pollution forced many companies to take actions, that optimize their burner performances. Accurate and reliable measurements, with low maintenance analyzers, are the key stones in achieving this goal.
Combustion of fuel requires stoichiometric amounts of oxygen to form carbon dioxide and water. Insufficient amount of oxygen results in the formation of toxic carbon monoxide and soot, while too excessive oxygen cools, and by that causes reduces the amount of effective energy produced.
Instabilities in the efficiency of burning processes may be caused by various different parameters, such as changes in fuel composition, fuel types and caloric values, density of the fuel, load variation, atmospheric changes such as humidity, burner conditions and fouling of burners and the general overall condition of the entire combustion system.
Measuring the of carbon monoxide and oxygen contents of the flue gas indicates whether optimized and economic burning processes are conducted. In case of discrapency imidiate corrections must be taken, not only to reduce fuel consumption, but especially in view of local environmental legislation, as well as prevention of carbonmonoxide prevention.
Several different types of analyzer are on the market, which have the capability to measure the oxygen or carbonmonoxide content.
Earlier combustion optimization and control was performed by extractive technologies, such as paramagnetic O2 and non-dispersible infrared (NDIR) analyzers. These analyzers were characterized by their slow response due to sampling time and transportation times, differences in sampling times and instruments responses caused “out of phase “O2 and CO signals, high temperature requirements were required for sample conditioning, and blockage and fouling of transport lines and extractive cells.
Introduction of zirconium oxide analyzers, to measure oxygen, and pellistor based catalytic combustion sensor did overcome these drawbacks. This gave the opportunity of O2 and combustion measurements to be in phase, which made them suitable for use effective combustion optimization. The drawback of the simple combustion sensor is that they are in general with poor specificity towards CO for distinguishing between CO and CO2, and are of are of limited sensitivity and accuracy. Further to that catalyst poisoning reduces the lifetime. Aside from known technical failures that occur in zirconium-based analyzers, these analyzers are based on the diffusion of oxygen through a heated zirconium membrane. Organic volatiles undergo oxidation. Oxygen is consumed which results in a difference between real and measured oxygen, and plugging of the membrane is also a well-known phenomenon. All these reduce drastically the lifetime of the analyzers.
The introduction of TDL, tunable diode lasers gave new dimensions in analytical technologies. TDL is based on laser absorption spectrometry. Absorption bands of specific gasses, such as O2, CO of H2O are very narrow, making them easily being extracted from the other absorption bands. Being a spectroscopic method, non-destructive, free of high temperature processes, as used in catalytic and zirconium based sensors, TDL analyzers are characterized by long lifetimes, and low costs of maintenance. In most applications, no sampling system and sample condition are required, the analyzer is free of wearing moving parts, no frequent and expensive calibration routines are required both reducing the investment in purchase and maintenance. TDL analyzers are installed on that spot that must be monitored and characterized by a high accuracy and quickly responding to any changes in the concentration of the measured gas. Many TDL analyzers are cross stack analyzers where the laser must be installed exactly opposite the receiver to ensure highest performance.
The MOD 500 is an “ all in one” TDL analyzer where the laser beam and the receiver are located on the same sid
e of the analyzer. The laser beam passes through a probe, which is inserted in the furnace or stake, and is returned to the detector. This gives the MOD the benefit of doubling the optical pathway, is easy to install. By that, time consuming alignment of the sensor and the detector are omitted and reducing the amount of wires. Furthermore, the expanded operation temperature as from -40 °C makes the MOD 500 highly effective in measuring combustion gasses in extreme cold areas.
Accurate, fast and reliable measurements of gasses playing part in fuel combustion, such as oxygen, carbon monoxide or water vapor are the fundaments of ongoing being in control of the combustion optimization and fuel efficiency. With the benefit of low cost maintenance and long the long lifetime annual cost in fuel and cost of environmental impact is drastically be reduced, which results in an annual saving of thousands of dollars.