Charcoal bed

The HCl gas is absorbed in water to produce 30—40% HCl solution. If the HCl must meet a very low organic content specification, a charcoal bed is used ahead of the HCl absorber, or the aqueous HCl solution product is treated with charcoal. Alternatively, the reactor gas can be compressed and passed to a distillation column with anhydrous 100% Hquid HCl as the distillate the organic materials are the bottoms and are recirculated to the process. Any noncondensible gas present in the HCl feed stream is vented from the distillation system and scmbbed with water. 

Subjective evaluation of odor emission is made difficult by the phenomenon of odor fatigue, which means that after persons have been initially subjected to an odor, they lose the ability to perceive the continued presence of low concentrations of that odor. Therefore, all systems of subjective odor evaluation rely on preventing olfactory fatigue by letting the observer breathe odor-free air for a sufficient time prior to breathing the odorous air and evaluating its odor content. Usually an activated charcoal bed is... 

The basic mechanism for radon adsorption on charcoal and the effects of competing processes have been well studied. Several treatments of the adsorption of radon (and noble gases in general) on charcoal have appeared in the literature (Adams et al., 1959 Strong and Levins, 1978 Kapitanov et al., 1967 Siegwarth et al., 1972). Consider a charcoal bed consisting of N theoretical stages as... 

F = flow rate through the charcoal bed in cnr/min Y = volume fraction of adsorbate in the gas phase leaving the ith stage at time t M = total mass of the adsorber in grams t = time in minutes. 

The adsorbate concentration in the Nth stage along the charcoal bed can be found by solving the series of N differential equations. These solutions represent the concentration profile in the Nth stage. For a unit pulse of adsorbate at time t = 0, the solution reduces to... 

The dynamic adsorption coefficient can be used to gauge the performance of a charcoal bed under various conditions. 

At about 100 C, the desorption of radon from charcoal is rapid and efficient enough to fully regenerate a charcoal bed in a reasonable amount of time. The desorption concentration profile also features an inflection point (see Figure 3). Equation (4) can therefore also be applied to find an optimal temperature for the desorption process. 

The charcoal beds must be thermally isolated from each other. The air inlets must be positioned far enough apart so as to minimize feedback of clean air back into the system. To prevent the accumulation of radon in the house in the event of a valve failure, all valves should be provided with backups. The volume of air cleaned per unit mass of carbon increases exponentially with decreasing temperature (Kapitanov et al., 1967). Thus greatly increased adsorption capacity can be obtained by cooling the carbon below ambient temperature. Although this process will require additional energy input, it may be worthwhile to consider some form of cooling. 

Contaminants Indoor contaminants are expected to compete for adsorption sites on the charcoal. We will experimentally find the effect that these contaminants have on the dynamic adsorption coefficient and on the life-time of the charcoal bed. Since the number of radon atoms in even the most seriously contaminated houses is very small, decay product buildup is not expected to pose a significant problem. 

Compressed air is passed from the gas cylinder through a charcoal bed to remove any organic material in the gas stream. 

The acid solution, often containing suspended sulfur and filter paper, is clarified by filtration by suction through a moist charcoal bed made by shaking 2 g of the decolorizing carbon with 25 mL of water in a stoppered flask to produce a slurry and pouring this on the paper of an 85-mm Buchner funnel. Pour the water out of the filter flask and then filter the solution of dihydrochloride. Divide the pink or colorless filtrate into approximately two equal parts and at once add the reagents for conversion of one part to 2 and the other part to 4. 

If powdered charcoal is added (widely used in the USA) adsorption can be carried out simultaneously with flocculation, but passing through a bed of granular activated charcoal beds is more widely used in Europe. 

The /z-transf orm method was also applied to the calculation of the breakthrough curve for the separation of a binary mixture on a charcoal bed by Tien et al. [36]. By using the li-transform, the course of the separation can be calculated by transforming the concentration variable via the /i-transform into a coordinate system in which algebraic equations describe the process for any number of components. 

Activated charcoal beds are used to capture volatile materials and delay the discharge of radioactive noble gases. Wet-scrubbers are used to capture acids and entrained liquids. In-line filters and wet-scrubbers should be located in the penthouse of the faeility. Scrubbers should have an average flow of 20-30 L/min and should run continuously in any hood that evaporates mineral acids. The individual hood washdown system should have a separate switch to wash down the entire ductwork at the end of the day or at the end of a process. 

Specific treatment combinations can be designed to match airborne contaminants from the physical or chemical operations, the type of sample (solid, liquid, gas), and the quantity that is processed. For example, sample preparation rooms where soil and vegetation are dried, ashed, ground and sieved require particle filter combinations but not charcoal beds and scrubbers. For treating laboratory air, the multiple stage filter system should be based on the expected maximum radionuclide concentration and airborne fraction of the processed samples. Typical combinations include pre-filters, HEPA filters and charcoal beds. 

Adsorption will also occur in solution. For example, charcoal beds are used to adsorb trace organic compounds (such as pesticides and dyes) from water. 

One of the original disclosures of such catalyst preparation was as follows [308]. A transition metal nitrate solution is used to saturate a charcoal bed, previously leached with nitric acid. The charcoal bed is then heated to temperatures high enough to decompose the nitrate to the oxide. 

The gases released from the primary coolant in the degasification system mainly contain the fission product noble gases which, with the sole exception of Kr, are comparatively short-lived nuclides. In order to prevent release to the environment, therefore, it is sufficient to store them for a certain time until these isotopes have decayed. In most of the US PWR plants as well as in the plants built by Frama-tome, gas decay tanks are used for this purpose. In the plants designed and built by Siemens/KWU, decay lines are employed which are equipped with a series of charcoal beds in which the noble gases are delayed relative to the carrier gas flow by a dynamic adsorption-desorption equilibrium. Under normal operation conditions, delay times on the order of 60 hours for the krypton isotopes and 60 days for the xenon isotopes are obtained, which are sufficiently long for nearly complete... 

Due to the delay times achieved on the charcoal beds, the shorter-lived fission product noble gases are completely retained within the plant. Kr is the only one of the radioactive fission gases which passes the delay line and is released completely to the atmosphere, where it contributes to the gobal Kr inventory of the atmosphere. As this contribution is very small compared to the remainders of nuclear weapons testing and to the releases from spent fuel reprocessing plants (as far as they are not equipped with a noble gas retention system) it can be ignored. 

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