Screen burners

The use of cracked stocks in No. 2 has meant additional problems for the refiner. Besides having to refine for odor and color, he is also faced with a stability problem. While catalytic cracking as a rule produces a more stable oil than does thermal cracking, there are still compounds present which on aging will form insoluble sludge. This sludge, if permitted to form, clogs burner screens, and eventually results in trouble. 

T)q)ical properties for a SiC/SiC CFCC are Young s modulus 100 GPa, tensile strength 260 MPa, and a strain at failure of 0.4%, making it semiductile. Applications include burners, heat exchangers, hot gas fans and filters, and gas turbine combustion liners and shrouds. They have demonstrated 1,000 h without failure as turbine blades in gas turbine engines and 10,000 thermal cycles as radiant burner screens without failure. 

The steam-distillation is continued for 5 minutes after steam can first be seen entering the condenser the ideal rate of distillation is about 4 -5 ml. of distillate per minute, but this is not critical and may be varied within reasonable limits. The receiver J is then lowered from the lip K of the condenser and the steam-distillation continued for a further two minutes, thus ensuring that no traces of liquid containing ammonia are left on the inside of the condenser. At the end of this time any liquid on the lip K is rinsed with distilled water into J, which is then ready for titration. It is important that the receiver and its contents are kept cold during the distillation and it is advisable to interpose a piece of asbestos board or other screen so that it is not exposed to the heat from the burner under the steam generator. 

Prior to being fed to a pulverized fuel burner, coal is ground to a size generally specified such that at least 70% passes a 200 mesh screen (75 Tm) and less than 2% is retained on a 52 mesh screen (300 Tm). The top size is deterrnined by the classifying component of the cmshing mill, oversize material being retained for further grinding (54,100,101). 

The burn rates of propellants are determined in a strand burner (Crawford bomb/ acoustic emission technique) at various pressures using an inert gas for pressurization. This data, when fitted in the empirical relation r = a.P" provides the pressure index n and the coefficient a. This technique is highly useful as a first approximation and is extensively used for propellant screening and quality control. The bum rates at different pressures are also determined by static testing in a ballistic evaluation motors (BEMs) and burn rates are typically scaled up from 1-5% for full scale motors. 

The combustion of pulverized coal at both atmospheric and higher pressure has been studied by Hazard and Buckley (4G), using three sizes of burners. The coal is pulverized to 93% through a 200-mesh screen. Experiments on burning pulverized coal under pressure have also been described (7G). 

RM - Rod mill BH - Burner hood HL - Hearlh layer SC - Sinier cooler SSH - Sinier screening hot SSC - Sinier screening cold EP - Electrostatic precipitator... 

The flames which have been used in these studies are premixed laminar hydrogen/nitrogen/oxygen flames supported on a Meker burner and screened by a second flame of similar composition. These flames are well characterized, and the temperature and composition are well known. In addition, the transient concentrations of free radicals and other minor... 

The liquid in a pear-shaped flask A (Fig. 2.VIII L) is heated by a ring gas-burner B covered by a metal disc. The vapour passes down a central tube into a glass worm-condenser in the calorimeter. The actual evaporation lasts only 2 to 4 mins., the correction for heat radiated from the burner (which is screened from the calorimeter by a sheet of wood covered with wire gauze) being determined by measuring the rise in temperature in the calorimeter before the liquid boils, and after evaporation is completed. The weight of liquid condensed is determined. 

The catalyst is prepared as follows An amount of screened pumice (about the size of a pea) sufficient to fill the tube is soaked in hot concentrated nitric acid and then washed thoroughly with hot distilled water. In a porcelain dish the pumice is mixed with a solution of 40 g. of thorium nitrate crystals [Th(N03) 4 + 12H2O] in TOO cc. of water and is evaporated to dryness, with frequent stirring to insure uniform deposition of the salt. The impregnated pumice is ignited over a Bunsen burner until decomposition of the nitrate is complete. The pumice carries about 15 g. of thorium oxide. 

The technique of flame atomic absorption spectrophotometry accomplishes this by aspirating the sample solution into a burner chamber, where it is mixed with a fuel gas and an oxidant gas. The mixture is then burned in a specially designed burner head (Fig. 2). The light beam is directed lengthway down the burner, and the absorption of the analyte atoms in the flame is measured. The most commonly used gas mixtures are air with acetylene and nitrous oxide with acetylene. Experimental conditions are well-defined in the literature, and cookbook conditions are available from most instrument manufacturers. In addition, many instruments are computer-controlled, and typical conditions are available directly on the operating screen. 

If a heat lamp is used, the crucible is placed on a clean, nonreactive surface, such as a wire screen covered with aluminum foil. The lamp is then positioned about 1 cm above the rim of the crucible and turned on. Charring takes place without further attention. The process is considerably accelerated if the paper is moistened with no more than one drop of concentrated ammonium nitrate solution. The residual carbon is eliminated with a burner, as described in the next paragraph. 

In clinical analysis, flame AAS is very useful for serum analysis. Ca and Mg can be determined directly in serum samples after a 1 50 dilution, even with microaliquots of 20-50 pL [314]. In the case of Ca, La3+ or Sr2+ are added so as to avoid phosphate interferences. Na and K are usually determined in the flame emission mode, which can be realized with almost any flame AAS instrument. The burner head is often turned to shorten the optical path so as to avoid self-reversal. For the direct determination of Fe, Zn and Cu, flame AAS can also be used but with a lower sample dilution. Determination of trace elements such as Al, Cr, Co, Mo and V with flame AAS often requires a pre-concentration stage, but in serum and other body fluids as well as in various other biological matrices some of these elements can be determined directly with furnace AAS. This also applies to toxic elements such as Ni, Cd and Pb, which often must be determined when screening for work place exposure. When aiming towards the direct determination of the latter elements in blood, urine or serum, matrix modification has found wide acceptance in working practices that are now legally accepted for work place surveillance, etc. This applies e.g. for the determination of Pb in whole blood [315] as well as for the determination of Ni in urine (see e.g. Ref. [316]). 

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