Flash rapid heating

Flash Pyrolysis Coal is rapidly heated to elevated temperatures for a brief period of time to produce oil, gas, and char. The increase in hydrogen content in the gases and hquids is the result of removing carbon from the process as a char containing a significantly reduced amount of hydrogen. Several processes have been tested on a rela-... 

Another theory of liquid-liquid explosion comes from Board et al. (1975). They noticed that when an initial disturbance, for example, at the vapor-liquid interface, causes a shock wave, some of the liquid is atomized, thus enhancing rapid heat transfer to the droplets. This action produces further expansion and atomization. When the droplets are heated to a temperature equal to the superheat temperature limit, rapid evaporation (flashing liquid) may cause an explosion. In fact, this theory resembles the theory of Reid (1979), except that only droplets, and not bulk liquid, have to be at the superheat temperature limit of atmospheric pressure (McDevitt et al. 1987). 

Microwave-assisted synthesis in general is likely to have a tremendous impact in the medicinal/combinatorial chemistry communities because it shortens reaction times, improves final yields and purities, and can carry out reactions that previously were thought impossible to do. It should be stressed that in general the rate enhancements seen in microwave-assisted synthesis can be attributed to the very rapid heating of the reaction mixture (flash heating) and the high temperatures that can be reached, rather than to any other specific or nonthermal microwave effect.40... 

Flash hydrogenation is a short residence time (1 to 10 sec) gas-phase, non-catalytic process in which pulverized coal is rapidly heated (20,000-30,000° C/sec) in hydrogen to obtain liquid and gaseous hydrocarbons directly. Experiments were conducted in a 2 lb/hr, 1 ID x 8 ft long downflow tubular reactor in the range of 500° to 900°C and 500 to 3000 psi H2 pressure for North Dakota Lignite and New Mexico subbituminous coal (L). The ultimate analyses of these coals are given in... 

There are several procedures to perform pyrolysis flash pyrolysis (pulse mode), slow gradient heating pyrolysis (continuous mode), step pyrolysis, etc. Commonly, the pyrolysis for analytical purposes is done in pulse mode. This consists of a very rapid heating of the sample from ambient temperature, targeting isothermal conditions at a temperature where the sample is completely pyrolysed. Controlled slow temperature gradients are also possible in pyrolysis, but their use in analytical pyrolysis is limited. Step pyrolysis heats the sample rapidly but in steps, each step following a plateau of constant temperature kept for a limited time period. 

Some MS systems have, besides a temperature controlled probe, a heated-filament probe. This type of probe allows a more direct heating of the sample when it is deposited directly on the filament [48]. However, most of these probes still operate within common values for the current intensity and voltage and have a TRT that is longer than those used for flash pyrolysis. True flash pyrolysis using a resistively heated filament requires boosted current or boosted voltage for achieving a rapid heating (see Section 4.3), and such systems are commercially available. 

This trap is not used in typical flash pyrolysis experiments. However, if the pyrolysate is generated for a longer period of time, and it is not delivered to the chromatographic column similarly to a typical injection, a cryofocusing attachment is necessary. In principle, this consists of a short tube through which passes a capillary transfer line (or part of the column). The cryofocusing tube can be cooled at subambient temperatures for a determined period of time and condenses the sample injected in the GC. At the start of the GC run, the cryofocusing tube can be rapidly heated to evaporate the condensate. 

The fact that most flash pyrolysis studies have used radiant heating suggests solar heat as a natural means for effecting flash pyrolysis of biomass feedstocks. Since solar radiation has a characteristic temperature of almost 6000°K, it can be used to achieve very rapid heating of opaque, solid particles. Earlier studies (2) have shown that the quantity of heat required for biomass gasification is small less than 1 Gj per Mg of dry solid... 

---