Pulse combustion drying

Pulse combustion is an emerging technology of significant potential since it is claimed to increase productivity, maximize utilization of the input fuel, and reduce pollutant emissions (Mujumdar, 1991 Maralidhara and Lokhard, 1985 Kudra and Mujumdar, 1995). 

The term pulse combustion originates from intermittent (pulse) combustion of solid, liquid, or gaseous fuel in contrast to continuous combustion in conventional burners. Such periodic combustion generates intensive pressure, velocity, and to a certain extent, temperature waves propagated from the combustion chamber via a tailpipe (a diffuser) to the process volume (an applicator) such as a dryer, calciner, or incinerator. Because of the oscillatory nature of the momentum transfer, pulse combustion intensifies the rates of heat and mass transfer. 

Intake of air and fuel to form an explosive mixture. Valves open. 

Outflow of flue gas from tailpipe. Intake of new charge of air and fuel. Valves open. 

Back-flow of residual flue gas. tt—2L Valves start to dose. 

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Reverse fiow reactor operation Pulse combustion drying... 

Additionally, there are other benefits associated with the pulse combustion drying technology associated with less degradation, improved surface characteristics, and more uniform particle size distribution. These possible benefits were not explored during the trial run conducted by Encapsys, but may be worth exploring for specific products. 

Ozer, R.W. 1993. Review of operating data from pilot plant and field pulse combustion drying systems. Proceedings of the Powder and Bulk Solids Conference/Exhibition, Chicago, IL. 

Kudra, T., Zbicinski, I., and Benali, M. 2003. Pulse combustion drying aerodynamics, heat transfer and drying kinetics. 

Pulse combustion is a specific form of combustion-driven oscillation. Combustion oscillations can be an inherent problem or a potential benefit in enclosed combustion systems, such as gas turbine combustors, afterburners, furnaces, and rocket engines. Oscillations can produce beneficial increases in heat transfer rates and reduce pollutant formation. In other situations, these instabilities are undesirable because they may reduce the thermodynamic efficiency of a combustor or become a source of system failure if their amplitude is not kept within an acceptable range. Oscillations in the pulse combustion drying systems are desired and useful. Combustion with oscillations may be treated as some regular form of unstable combustion. 

An alternative mode of pulse combustion drying was suggested by Zinn et al. (1990), where pulse combustion is mainly applied to generate a large-amplitude pulsation in the drying chamber and, in this condition, provides small portion of heat for moisture evaporation. This kind of pulse combustion dryer consists of a combustor and a dying chamber where the hydro-dynamic action of pressure and velocity waves enhances drying rates. Under certain conditions, these pressure waves can be favorably amplified by an acoustic resonance. To excite... 

Pulse combustion drying systans can be used to dry a wide range of materials, including low- and high-viscosity liquids, pumpable pastes, aU noncohesive filter cakes (and most cohesive ones), and many powders and granules. No other dryer type offers such a variety of feedstocks to handle (Table 23.3, Chowdhury, 1984). 

Another advantage of pulse combustion drying is the very short contact time of drying agent and drying material. Table 23.5 compares the residence times of the dried material in the pulse combustion dryer with selected convectional dryers. The typical residence time is 0.01-1 s for pulse combustion drying. For this reason, this technique can be applied even to extremely sensitive materials (Swientek, 1989). 

Pulse combustion dryers have been in the market for many years. The pilot test and technical reports of pulse combustion dryers indicate that the pulse combustion drying, as compared to classical (continuous) drying, enables one to (1) increase the drying rate by a factor of 1.2-3, depending on the configuration of PC dryer (2) reduce unit air consumption by up to 30% (3) eliminate distribution of characteristic process parameters (e.g., temperature, concentration, and moisture content) within the dryer, which improves the... 

FIGURE 23.12 Dehydration rate for pulse combustion drying and fluidized bed drying. 

Pulse combustion drying has been known for several decades but has yet to become a mainstream drying technology. PC drying appears to have distinct advantages in handling... 

Kudra, T., Buchkowski, A.G., and Kitchen, J.A., Pulse combustion drying of white pine. Proceedings of the Fourth lUFRO International Wood Drying Conference, Rotorda, New Zealand, August 9-13,1994, pp. 396-403. 

Ozer, R.W., Pulse combustion drying. Proceedings of the International Workshop on Pulsating Combustion, Lund University, Lund, Sweden, 1993b. 

Sonodyne Industries, Inc., Pulse Combustion Drying Case Study, Sonodyne Industries, Inc. Portland, OR, 1984. 

Wu, Z.H. and Mujumdar, A.S., R D needs and opportunities in pulse comhustion and pulse combustion drying. Drying Technology, 24, 2006a, 1521—1523. 

Zbicinski, L, EquipmenL technology, perspectives and modeling of pulse combustion drying. Journal of Chemical Engineering, 2002, 86, 33 6. 

Pulse combustion drying combines high economic of direct fire heating system with high intensity of drying of disperse material. Typical power consumption is 3,000-3,500 kJ/kg H2O evaporated (4,500 to -11,500 for spray dryer and 3,200-6,500 for drum dryer) [53,54]. The main advantages of pulse combustion drying are as follows ... 

Pulse combustion drying—PC developed for propulsion and later for combustion applications... 

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