Detector, gas, catalytic

To retard corrosion and to facilitate future maintenance (e.g., allow the non-destructive removal of threaded Junction box covers), all threaded connections should be lubricated with an antiseize compound which will not dry out in the environment. If lubricant is applied to the threaded (or flanged) portion of covers of explosion-proof enclosures, the lubricant must have been tested and approved as suitable for flame path use. It is cautioned that some lubricants contain silicone, which will poison most catalytic gas detector sensors and should not be used near gas detectors. 

The catalytic gas detector was originally developed in 1958 for the mining industry. It has become the standard means of detection worldwide in virtually all oil and gas operations. It is also used extensively in coal extraction and the chemical process industry. 

The three equations (12.7)-(12.9) summarize the most important characteristic of catalytic gas detectors. An instrument calibrated to read, say, 0-100% LEL in a standard fuel will give an immediate estimate of the explosiveness of any unknown vapour or mixture of vapours based on equation (12.9). If the composition of the vapour is known, simple correction factors based on the constants in equations (12.7) and (12.8) may be applied to give more accurate readings. 

The following substances have been known to poison catalytic gas detectors ... 

Gas detection is provided in the petroleum industry to warn of and possibly prevent the formation of a combustible gas or vapor mixture that could cause an explosive overpressure blast of damaging proportions. There are two types of gas detectors used in the oil and gas industry. The most common and widely used is the catalytic detector. More recently, infared (IR) beam detectors have been employed for special "line of sight" applications, such as perimeter, boundary or offsite monitoring, pump alleys, etc. 

They are sensitive to all flammable gases, and they give approximately the same response to the presence of the lower explosive limit (LEL) concentrations of all the common hydrocarbon gases and vapors. However it should be remembered that gas detectors do not respond equally to different combustible gases. The milli-volt signal output of a typical catalytic detector for hexane or xylene is roughly one half the signal output for methane. 

Point Combustible Gas Detectors (IR) are used to indicate the presence of gas at a particular location (e.g., in a congested area of the planter in small ducts.) IR technology has proven to be more reliable than catalytic bead detectors. The point detector functions in the same manner as the open path detector, by comparing absorbed and reference frequencies of IR light. The main difference between these and open path type is that the path length of the point type is short (3 inches) and is kept within the confines of the instrument. 

Catalytic (Pellistor) Flammable gases Air Measures the heat output due to the catalytic oxidation of flammable gas molecules. A stream of the sample is passed over the sensor which is usually a ceramic bead impregnated with Pt or Pd. The temperature variations in the sensor due to reaction are monitored. Dependent on individual design. Flammable gas detector. Usually portable... 

The most common type of combustible gas detectors utilizes the catalytic combustion principle. A platinum wire filament (in a Wheatstone bridge cir-... 

Total Organic Carbon (TOC) is usually released by wet chemical or high temperature catalytic oxidation reactor (WCO or HTCO, respectively), for a complete oxidation of organic carbon into dioxide carbon, coupled with a carbon dioxide gas detector, in order to estimate the carbon content of water samples (Dupuit, 2006). 

Hydrogen gas detectors located in your work area can provide warnings of any system leaks. In-line gas detectors, either hydrogen or oxygen, can provide information on the purity of the gases in the system. The most common gas detection technologies are electrochemical and catalytic. 

Metal clusters may also find applications in catalysis. Here the smaller the particle size, the higher the number of their surface atoms [144,145]. This makes the particles interesting candidates for catalytic applications. Crooks used palladium clusters for hydrogenation and showed an elevated reactivity with the particles, depending on the particle size [146]. Nanoparticles are also used as the sensitive layer in selective gas detectors [147]. 

An instrument designed to detect the presence or concentration of combustible gases or vapors in the atmosphere. It is usually calibrated to indicate the concentration of a gas as a percentage of its Lower Explosive Limit (LEL) so that a reading of 100 percent indicates that the LEL limit has been reached. They use either a solid-state circuit, infrared (IR) beam electrochemical or duel catalytic bead for the detection of gas in an area. Portable monitors are used for personnel protection, and fixed installations are provided for property protection. The Instrument Society of America (ISA) has provided a guideline for combustible gas detector utilization, ISA TR 12.13.03, Guide for Combustible Gas Detection as a Method of Protection. 

A flammable gas detector is designed to measure the amount of flammable gas in the atmosphere and relate it to the upper and lower flammable limits. The gas mixture is drawn over a catalytic surface where oxidation, i.e. combustion, takes place. The combustion causes a rise in temperature of the surface which is measured by a decrease in its electrical resistance. The instruments have to be calibrated for the particular gas of interest but for petrol vapours pentane or heptane are used as the reference gas. The readings are usually displayed in terms of percentage of the lower explosive limit. 

Combustible gas detectors are required whenever there is a possibility of a hazard to life or property caused by the accumulation of combustible gases. There are mainly two types of combustible/flammable gas detectors that are often used in most industries. These are the low-cost catalytic bead sensor and infrared sensor [26,27]. 

Catalytic Reaction. A bead or wire is coated with a catalytic material so that it reacts with atarget gas. As the reaction on the catalyzed surface takes place, the bead or wire heats up, and changes its resistance. This resistance change can be proportionally related to the target gas concentration. An example of a catalytic bead detector is a sensor that consists oftwo beads placed in a wheatstone bridge circuit. One of the beads acts as a... 

Point gas detectors should be IR type. [Catalytic detectors are susceptible to poisoning of the catalyst, can give false readings above 100% LEL, and have a slower response time than equivalent IR point detectors. Also, catalytic detectors have a mean time between failures (MTBFs) of 1—4 years and failures are most often unrevealed, leading to a high maintenance/testing load.]... 

Catalytic activity for the selective oxidation of H2S was tested by a continuous flow reaction in a fixed-bed quartz tube reactor with 0.5 inch inside diameter. Gaseous H2S, O2, H2, CO, CO2 and N2 were used without further purification. Water vapor (H2O) was introduced by passing N2 through a saturator. Reaction test was conducted at a pressure of 101 kPa and in the temperature range of 150 to 300 °C on a 0.6 gram catalyst sample. Gas flow rates were controlled by a mass flow controller (Brooks, 5850 TR) and the gas compositions were analyzed by an on-line gas chromotograph equipped with a chromosil 310 coliunn and a thermal conductivity detector. 

The cracking of diphenylmethane (DPM) was carried out in a continuous-flow tubular reactor. The liquid feed contained 29.5 wt.% of DPM (Fluka, >99%), 70% of n-dodecane (Aldrich, >99% solvent) and 0.5% of benzothiophene (Aldrich, 95% source of H2S, to keep the catalyst sulfided during the reaction). The temperature was 673 K and the total pressure 50 bar. The liquid feed flow rate was 16.5 ml.h and the H2 flow rate 24 l.h (STP). The catalytic bed consisted of 1.0 g of catalyst diluted with enough carborundum (Prolabo, 0.34 mm) to reach a final volume of 4 cm. The effluent of the reactor was condensed at high pressure. Liquid samples were taken at regular intervals and analyzed by gas chromatography, using an Intersmat IGC 120 FL, equipped with a flame ionization detector and a capillary column (Alltech CP-Sil-SCB). 

The catalytic experiments were performed at the stationnary state and at atmospheric pressure, in a gas flow microreactor. The gas composition (NO, CO, O2, C3H, CO2 and H2O diluted with He) is representative of the composition of exhaust gases. The analysis, performed by gas chromatography (TCD detector for CO2, N2O, O2, N2, CO and flame ionisation detector for C3H6) and by on line IR spectrometry (NO and NO2) has been previously described (1). A small amount of the sample (10 mg diluted with 40 mg of inactive a AI2O3 ) was used in order to prevent mass and heat transfer limitations, at least at low conversion. The hourly space velocity varied between 120 000 and 220 000 h T The reaction was studied at increasing and decreasing temperatures (2 K/min) between 423 and 773 K. The redox character of the feedstream is defined by the number "s" equal to 2[02]+[N0] / [C0]+9[C3H6]. ... 

The products resulting from the reaction were injeaed into a Varian 3400 gas phase chromatograph and analyzed with a flame ionization detector. The separation was made in a capillary column BPS (SGE). The catalytic activity of the catalyst was measured after a 5 hour reaction with CF3CH2CI (by the amount of chloroalkene formed CF2=CHC1, CFCl=CHCl(ZandE))... 

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