Page 640 - Dust Explosions in the Process Industries

Research and Development 607

model of the eflect of the inertia of vent covers on the efficiency of the venting process.
Tamanini (1998b, 2002) proposed that this kind of simplified, but still scientifically
based, models be used in future revised vent design guidelines to replace the entirely
empirical statistical correlations used up to now. It seems clear that Tamanini’s approach
represents a great step forward compared to entirely empirical formulas and correlations.
It is regrettable that his important contribution has not been included in the recent
European Union design guidelines for dust explosion venting arrangements, CEN (2002).
On the other hand, the accessibility of user-friendly comprehensive CFD-based com-
puter codes for dust explosion simulation is expected to increase at great pace, and only
time can show how long the need for simplified, intermediate lumped-parameter models,
as proposed by Tamanini, will persist. It must also be pointed out that the lumped-
parameter approach can handle only comparatively simple problems, such as venting
simple, single process units. Only comprehensive computer codes can handle the com-
plex explosion scenarios often encountered in the process industries. There, process units
of varying complexity are interconnected by ducts and conveyor lines, and the propa-
gation of a dust explosion in such an integrated system can be performed only by pow-
erful computer codes. However, development of and confidence in comprehensive
computer codes have to be built on extensive validation against full-scale dust explo-
sion experiments, covering a wide range of dusts, initial dust clouds states, and geo-
metrical configurations.

9.2.4.9
Detonations and ‘Quasi’-Detonations in Dust Clouds

Some work up to 1990 is reviewed in Section 4.5 in Chapter 4. It is now generally
accepted that detonations can occur even in dust clouds. A review of the state of the art
and remaining problems in dust cloud detonation research at that time was given by
Kauffman, Sichel, and Wolanski (1991). The current status on dust cloud detonations was
also summarized by Alexander et al. (1993). Kauffman et al. (1992) and Austin et al.
(1993) summarized their extensive work on how detonations can develop from accel-
erating turbulent combustion in dust clouds in long tubes. Sichel and Kauffmann (1994)
studied the transition from deflagration to detonation (DDT) during dust explosions in
long ducts. The dust was initially deposited as a layer along the duct floor, and the dust
cloud was generated by the entrainment of the dust layer by the blast wave propagating
ahead of the flame.
IKhomik, Gelfand, and Knyazev (1993, 1994) determined experimentally the minimum
critical tube diameter for detonation propagation in suspensions of a fine alumhum
flake dust in air. The critical value found was in the range 0.040-0.055 m. Korobeinikov
(1993) conducted a theoretical study of the propagation of detonation waves in dust
clouds. The problem of establishing adequate scaling rules was given particular atten-
tion. Ivhrkov (1993) presented a new method for numerical simulation of nonsteady det-
onations in dust clouds. Two-dimensional computations yielded a multiwave structure
of the detonation process. Ding and Huang (1994) analyzed the mathematical theory for
the reaction zone in a detonation wave passing through a dust cloud and proposed a new
numerical criterion describing the C-J condition.
Tulis et al. (1993) conducted detailed experimental studies of the structures of deto-
nation processes in clouds of aluminum in air. The influence of particle size and shape