Pyrolysis operation

Pyrolysis In pyrolysis, coal is heated in the absence of oxygen to drive off volatile components, leaving behind a solid residue enriched in carbon and known as char or coke. Most coal pyrolysis operations are for the purpose of producing metallurgical coke, with the liquids... 

Although arsenic is less volatile during low-temperature pyrolysis than combustion, some arsenic still volatilizes during the process. The volatilization of arsenic during pyrolysis chiefly results from the reduction of As(V) to AS4O6 ( AS2O3 ) and other As(III) oxides (Helsen and Van den Bulck, 2003 Hata et al., 2003 Helsen et al., (2003)). To minimize arsenic volatilization, the characteristics of the wood must be known and pyrolysis operations must be carefully controlled at temperatures below 320 °C (Helsen and Van den Bulck, 2003). 

Although pyrolytic oil contains significant quantities of benzene and toluene that have high value in the pure form, removal of these compounds from the pyrolytic oil requires expensive fractional distillation equipment. Pyrolysis operators have been reluctant to make the capital investment in distillation equipment because the risk is too high and the return on investment is too low. As a result, the pyrolytic oil must be sold as a replacement for Number Six (low priced grade) fuel oil. The oils generated at Conrad s Centralia facility contain a maximum of 1.5 percent sulfur, and have a potential market as blender oils for commercial fuel.1... 

Tire pyrolysis operations are currently small scale. Large scale operations would not be economically feasible at present. Economically, pyrolysis is a marginal venture. Unless area tire disposal costs are high, on-site energy savings can be realized, tax advantages are present, and... 

There is no known experimental data on the fate of metal in the coke when the coke is gasified (forming carbon oxides) during decoking. Some of this metal may remain on the coil until pyrolysis operations are resumed. 

Interior of high-temperature furnaces pyrolysis operations production of steels, alloys,... 

Albright, L.F. Yu, Y.C. Neither, K. "Coke Formation During Pyrolysis Operation". 85th National AIChE Meeting. June 4-8, Philadelphia. Paper no 15E. 

Next, the dichloroethane source from the chlorination operation is sent to its sink in the pyrolysis operation, which operates at 500°C. Here only 60% of the dichloroethane is converted to vinyl chloride with a byproduct of HCl, according to reaction (3.4). This conversion is within the 65% conversion claimed in the patent. To satisfy the overall material balance, 158,300 Ib/hr of dichloroethane must produce 100,000 Ib/hr of vinyl chloride and 58,300 Ib/hr of HCl. But a 60% conversion only produces 60,000 Ib/hr of vinyl chloride. The additional dichloroethane needed is computed by mass balance to equal [(1 - 0.6)/0.6] X 158,300 or 105,500 Ib/hr. Its source is a recycle stream from the separation of vinyl chlo-... 

As for the pressure levels in the reaction operations, 1.5 atm is selected for the chlorination reaction to prevent the leakage of air into the reactor to be installed in the task integration step. At atmospheric pressure, air might leak into the reactor and build up in sufficiently large concentrations to exceed the flammability limit. For the pyrolysis operation, 26 atm is recommended by the B.F. Goodrich patent (1963) without any justification. Since the reaction is irreversible, the elevated pressure does not adversely affect the conversion. Most likely, the patent recommends this pressure to increase the rate of reaction and, thus, reduce the size of the pyrolysis furnace, although the tube walls must be thick and many precautions are necessary for operation at elevated pressures. The pressure level is also an important consideration in selecting the separation operations, as will be discussed in the next synthesis step. 

As mentioned earlier, for each distribution of chemicals, the needs for separation become obvious. In Figure 3.5, for example, it is clear that the pure effluent from the chlorination reaction operation needs no separation, but the effluent from the pyrolysis operation is a mixture that needs to be separated into nearly pure species. Here, the source of the three species in the effluent is at a composition far different from the compositions of the three sinks vinyl chloride product, HCl byproduct, and the dichloroethane for recycle. To eliminate these composition differences, one or more separation operations are needed. 

A preferable feed temperature would be 35°C or higher, which could be achieved by completing the cooling and partial condensation of the pyrolysis reactor effluent with cooling water, but the introduction of vapor into the column would increase the refrigeration load of the condenser at —26.2°C. Upon making this specification, key differences (temperature, pressure, and phase) appear between the effluent from the pyrolysis operation and the feed to the distillation column. These are eliminated in the next synthesis step by inserting tempeia-... 

In addition, the hot vapor effluent from the pyrolysis operation (at 500°C and 26 atm) is operated upon as follows ... 

In Section 3.4, as the operations are inserted into alternative flowsheets to manufacture vinyl chloride, rules of thumb or heuristics are utilized. For example, when positioning the direct chlorination operation, it is assumed that because the reaction is nearly complete at 90°C, ethylene and chlorine can be fed in stoichiometric proportions. Furthermore, when positioning the pyrolysis operation, the temperature and pressure are set at 500°C and 26 atm to give a 60% conversion. These assumptions and specifications are based on many factors, not the least of which is experience in the manufacture of vinyl chloride and similar chemicals. In this case, a patent by the B.F. Goodrich Co. [British Patent 938,824 (October 9, 1963)] indicates the high conversion of ethylene and chlorine over a ferric chloride catalyst at 90°C and recommends the temperature and pressure levels of the pyrolysis reaction. The decision not to use ethylene in excess, to be sure of consuming all of the toxic chlorine, is based on the favorable conversions reported experimentally by chemists. In the distillation operations, the choice of the key components, the quality of the feed streams and the distillate products, and the pressure levels of the towers are also based on rules of thumb. In fact, heuristics like these and many others can be organized into an expert system, which can be utilized to synthesize sections of this and similar chemical processes. 

PGC is one of the more valuable techniques available to the forensic scientist for examining paint specimens. Application of forensic PGC of paint samples with a wide range of pyrolysis operating conditions has been reported over the years. Because of this variation in conditions and the difficulties in reproducibility, forensic application of PGC has suffered from a lack of standardization. Despite these difficulties, PGC has been shown to be sufficiently characteristic and reproducible to differentiate different manufacturers of similar paints (245-247). 

Slow pyrolysis of biomass operates at relatively low heating rates (0. l-2°C/s) and longer solid and vapor residence time (2-30 min) to favor biochar yield (Nanda et al., 2014b). Slow pyrolysis operates at temperature lower than that of fast pyrolysis, t q)ically 400 10°C and has a gas residence time usually > 5 s. Slow pyrolysis is similar to carbonization (for low temperatures and long residence times). During conventional pyrolysis, biomass is slowly devolatilized facilitating the formation of chars and some tars as the main products. This process yields different range of products with their properties dependent on temperature, inert gas flow rate and residence time. 

Carrying out secondary processing steps on these three fractions enables them to be converted into value-added products. For example, once purified, the pyro-gas fraction can be used as an energy source to help run the pyrolysis operation. The oil fraction can be turned into carbon black by a furnace process, or into fuel oil, or chemical feedstock by distillation. The char fraction can be treated to yield products such as activated carbon, recovered carbon black and recovered inorganic compounds. 

Figure 14.2 In situ and ex situ catalytic pyrolysis operation modes.

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