PULSED COMBUSTOR ASSEMBLY FOR DEHYDRATION AND/OR GRANULATION OF A WET FEEDSTOCK

Abstract

The invention relates to a pulsed combustor assembly (A) for dehydration and/or granulation of a wet feedstock, in particular a viscous feedstock such as a feedstock containing natural fibres, sugars and/or vegetable starches, comprising a combustion chamber (16), at least one fuel supply line (23), at least one air supply line (26), and at least one pulsed air generator, wherein the pulsed air generator is connected to the air supply line (26) for generating at least a first pulsed air stream with a pulse frequency f1 entering the combustion chamber (16).

Claims

1-15. (canceled)

16. A pulsed combustor assembly for dehydration and/or granulation of a wet feedstock, in particular a viscous feedstock such as a feedstock containing natural fibres, sugars and/or vegetable starches, comprising a combustion chamber, at least one fuel supply line, at least one air supply line, and at least one pulsed air generator, wherein the pulsed air generator is connected to the air supply line for generating at least a first pulsed air stream with a pulse frequency fl entering the combustion chamber.

17. The pulsed combustor assembly of claim 16, comprising a second air supply line and a second pulsed air generator being connected to the second air supply line and configured to generate a second pulsed air stream with a pulse frequency f2 entering the combustion chamber, wherein f2 is preferably higher or lower than fl.

18. The pulsed combustor assembly of claim 16, comprising a control means for adjusting the frequency fl within a predetermined range and/or for adjusting the frequency f2 within a predetermined range.

19. The pulsed combustor assembly of claim 17, wherein the first and/or second pulsed air generator comprises an, in particular motorized, air interrupter, comprising preferably a rotating disc, lobe and/or valve assembly, and/or wherein the first air supply line and the second air supply line are connected to a common compressed air supply line.

20. The pulsed combustor assembly of claim 16, wherein the frequencies fl and f2 are adjusted or adjustable, in particular by the control means, in order to generate a beat frequency f3 within the combustion chamber.

21. The pulsed combustor assembly of claim 16, wherein the control means is configured to simultaneously vary the frequencies fl and f2 within a pre-determined frequency range, wherein a difference flf2 is preferably at least substantially constant for generating an at least substantially constant beat frequency f3.

22. The pulsed combustor assembly of claim 16, wherein fl and/or f2 is more than 100 Hz and/or less than 600 Hz and/or an average frequency f4=(fl+f2)/2 is more than 200 Hz and/or less than 500 Hz and/or the beat frequency f3 is more than 10 Hz and/or less than 30 Hz.

23. The pulsed combustor assembly of claim 16, wherein the frequencies fl and f2 are adjusted or adjustable, in particular by the control means such that the fundamental frequency and/or odd and/or even harmonics of an/the average frequency f4=(fl+f2)/2 resonate with the combustion chamber.

24. The pulsed combustor assembly of claim 16, wherein the frequencies fl and f2 are adjusted or adjustable, in particular by the control means such that the combustions chamber functions as a low pass filter filtering the average frequency f4=(fl+f2)/2, and preferably odd and even harmonics thereof, wherein the beat frequency f3 passes the combustion chamber.

25. A pulsed combustion dryer for dehydration and/or granulation of a wet feedstock, in particular a viscous feedstock such as a feedstock containing natural fibres, sugars and/or vegetable starches, comprising a pulsed combustor assembly of claim 16.

26. The pulsed combustion dryer of claim 25, comprising an atomizer, in particular shear atomizer and/or a drying chamber, wherein a volume of the drying chamber is preferably larger than a volume of the combustion chamber, further preferably at least 50 times, even further preferably at least 100 times as large, and/or a granulator, in particular spouted bed granulator.

27. The pulsed combustion dryer of claim 25 wherein the beat frequency f3 resonates with the drying chamber.

28. A method for dehydration and/or granulation of a wet feedstock, in particular a viscous feedstock such as a feedstock containing natural fibres, sugars and/or vegetable starches, preferably utilizing the pulsed combustor assembly of claim 16, comprising a supply of fuel via a fuel supply line and a supply of a first pulsed air stream with a pulse frequency fl via a first air supply line to a combustion chamber.

29. The method of claim 28, comprising supplying a second pulsed air stream via a second air supply line with a frequency f2 to the combustion chamber, wherein f2 is preferably higher or lower than fl, preferably comprising the further steps of: adjusting an average frequency f4=(fl+f2)/2 in the combustion chamber so that f4, and optionally odd and even harmonics thereof, resonate within the combustion chamber and/or adjusting a beat frequency f3 of fl and f2 so that it passes through the combustion chamber, wherein the beat frequency preferably resonates within the drying chamber.

30. A use of the pulsed combustor assembly of claim 16 for dehydration and/or granulation of a wet feedstock, in particular a viscous feedstock such as a feedstock containing natural fibres.

Description

[0026] The enclosed FIGURE shows an embodiment and (further) aspects of the invention. The FIGURE shows a schematic of a dehydration and granulation apparatus.

[0027] The apparatus comprises a pulsed combustor assembly A for generating a (continuous) stream of high-temperature sonic pulses. Combustor assembly A is coupled to a shear atomizer B. The shear atomizer B finely divides the wet feedstock before being dehydrated on its way to an (integrated) spouted bed granulator C. The spouted bed granulator C produces and delivers the final product as, in particular powders, granules or melts. The pulsed combustor assembly A and shear atomizer B may require less than 10 milliseconds for removing more than 90% of the product's moisture. The balance may be removed in the spouted bed granulator C.

[0028] The combustor assembly A is externally pulsed using two motorised air interrupters 13 and 14, which are both connected to a common compressed air supply 15 via a first and a second air supply line 26, 27. The compressed air supply provides sufficient energy for generating a stream of (sharp) acoustic pulses (or shockwaves) when the air passes through the air interrupters 13 and 14 in the direction of a combustion chamber 16. In the combustion chamber 16, the air is utilised for combustion and optionally as excess air.

[0029] A fuel supply line 23 provides fuel to the combustion chamber 16. The fuel is ignited by an ignition source 24. An inlet 21 is provided for supplying feedstock to the apparatus. Via an outlet 22, humid air and gas emerges from the drying chamber 17. Inlet 21 provides the spouting air source. The granulated product may emerge from an outlet 20.

[0030] The interrupters 13 and 14 may comprise a (motorised) rotating disk, lobe or valve assembly where a ported or shaped element rotates in (close) proximity to a stationary element. Ports may periodically interact or align with one another, thereby releasing a burst of pulsed air into the combustion chamber 16. Rotating the (motorised) interrupters 13 and 14 at a high speed generates two distinct (high-pitch, siren-like) tones at frequencies f1 and f2 respectively, where frequencies f1 and f2 are directly proportional to the motor speeds of the interrupters 13 and 14. Combining the two frequencies f1 and f2 in the combustion chamber 16 produces a distinct third, low beat frequency at a beat frequency f3 corresponding to (or at least closely approximating) the difference between the frequencies f1 and f2. By simultaneously varying the speeds of air interrupters 13 and 14 with a constant speed difference, corresponding to f3, a band of frequencies may be generated, defined by f1 and f2 without affecting the beat frequency f3. This high band of frequencies may contain both odd and even harmonic components of frequencies f1 and f2, while the low (fundamental) frequency f3 remains effectively unchanged.

[0031] The high-frequency band (between 300 and 500 Hz), as defined by f1 and f2, is adjusted to resonate with the (small volume) combustion chamber 16 while the low-frequency component f3 (at least approximately 30 Hz) passes through the combustion chamber 16 to resonate with a (larger volume) drying chamber 17.

[0032] Continuous pulsed combustion in the combustion chamber 16 generates a stream of high-temperature exhaust gases which exit from chamber 16 at high velocity (above 100 m/s) via a nozzle 18. The mass and inertia of the high-temperature, oscillating exhaust gases form a conduit or waveguide on which both high and low-frequency acoustic shockwaves are super-imposed. This conduit may channel a broadband of harmonic frequencies generated inside the combustion chamber (as well as acoustic energy at screech frequencies), towards an impingement zone 19.

[0033] Energy from the high-frequency (e.g. 300 to 500 Hz) and (optionally) screech frequency components of the hot pulsed gas stream is utilised both to atomise and dehydrate wet feedstock passing through the shear atomizer B into the impingement zone 19, while the low beat frequency component of e.g. 10 to 30 Hz is tuned to resonate with the (large-volume) drying chamber 17. The (acoustic) pulses at the beat frequency f3, generated in the pulsed combustor assembly A are generally too low to excite low acoustic resonance in the cavities of the (small-volume) combustion chamber 16 and pass through both the combustion chamber 16 and the shear atomizer B to find resonance in the (larger volume) drying chamber 17 forming a free board area of the spouted bed granulator C. Therefore, combustion chamber 16 behaves like a low pass filter for the beat frequency f3.

[0034] The following example further illustrates the effects and functions of the apparatus (the values are not necessarily limiting). If f1 is 430 Hz and f2 is 450 Hz, the beat frequency f3 is 20 Hz. The combustion chamber may be tuned to the odd and even half wavelength integers corresponding to the average frequency of 440 Hz falling midway between 430 Hz and 450 Hz. The beat frequency of 20 Hz, however, falls outside this resonance band due to its long acoustic wavelength.

[0035] The harmonics of the average frequency originating from the two high-frequency (shortwave length) shockwaves are used to atomize liquid feedstock while the high temperature component driven by the combustion gases is used to dehydrate the feedstock droplets formed during atomisation. The (low-frequency, long wavelength) beat frequency f3 (derived from f1 and f2) is used to enhance dehydration in the downstream drying chamber 17.

[0036] The apparatus allows the generation of both high temperatures (600 to 800 C.) and high frequency (100 to 500 Hz) acoustic shockwaves for atomizing and partly dehydrating liquid feedstock. The atomization and partial dehydration may require less than 0.1 seconds depending on the thermal efficiency of the pulse combustor. High viscosity slurries (as for example in the fruit and vegetable industries) typically require higher acoustic energy and longer atomization times. According to the prior art, usually a post-atomization thermal energy and comparatively long retention times are required for total dehydration. According to the present invention, thermal drying is partly replaced by acoustic drying which greatly reduces energy and product retention times and improves product quality and taste.

[0037] In particular, the apparatus creates improved sonic conditions inside the drying chamber in order to enhance the removal of residual moisture from the atomized droplets (aerosols) at lower temperatures and shorter product retention times.

[0038] In the prior art, after product atomization and partial dehydration, most or all of the thermal and sonic energy is spent, leaving little or no acoustic energy for further dehydration inside the downstream drying chamber. The present apparatus, however, allows subjecting the aerosols in the drying chamber to (transverse) sonic waves, which may be tuned to resonate with the drying chamber cavity. These high energy pressure and partial vacuum pulses based on the low beat frequency f3 accelerate mass transfer (moisture evaporation), thereby allowing a reduction of both chamber temperature and product retention times.

[0039] Because the two frequencies f1 and f2 are provided, it is possible to have a low fundamental frequency (of 10 to 30 Hz) within the drying chamber which would not be possible with a single frequency provided to the combustion chamber.

[0040] In general, low-frequency acoustic waves have longer wavelengths which are more suited to resonate with the large volume drying chamber.

[0041] Moreover, even if low-frequency (long wavelength) pulses are ineffective when used to atomize feedstock (slurries) they are very efficient in enhancing heat and mass transfer inside the drying chamber 17. Because of the higher efficiency, the drying chamber may be smaller (compared with the prior art). The beat frequency f3 may be varied or tuned to resonate with the drying chamber's physical dimensions (at different temperatures and/or gas density conditions). The exact values of f1 and f2 are (in this regard) not relevant, as long as the difference between f1 and f2 is suitably adjusted. This means, acoustic resonance in a drying chamber can be maintained within a band of any two frequencies.

[0042] A further example may illustrate the advantages of apparatus (the values are not necessarily limiting). With a hypothetical high combustion chamber frequency band defined by f1=350 Hz and f2=330 Hz, the beat frequency or drying chamber frequency f3 will be 20 Hz. Likewise, if f1=450 Hz and f2=430 Hz, a beat frequency f3 is also 20 Hz. Drying chamber efficiency could therefore be optimized tuning the beat frequencies of any band of two frequencies, thereby reducing time and thermal energy required for post-atomization dehydration. According to the prior art, optimization of both the combustion chamber and the drying process (via resonance) is not possible with a single frequency provided to the combustion chamber.

REFERENCE NUMERALS

[0043] A Pulse combustor assembly [0044] B Shear atomizer [0045] C Spouted bed granulator [0046] 13 First air interrupter [0047] 14 Second air interrupter [0048] 15 Compressed air supply [0049] 16 Combustion chamber [0050] 17 Drying chamber [0051] 18 Nozzle [0052] 19 Impingement zone [0053] 20 Outlet for granulated products [0054] 21 Inlet for spouting air [0055] 22 Outlet for humid air and gas [0056] 23 Fuel supply line [0057] 24 Ignition [0058] 25 Inlet for feedstock [0059] 26 First air supply line [0060] 27 Second air supply line