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. 2022 Jun 15;11(12):1757.
doi: 10.3390/foods11121757.

Investigations on Backflush Cleaning of Spent Grain-Contaminated Filter Cloths Using Continuous and Pulsed Jets

Roman Alejandro Werner  1 , Alexander Michael Hummel  1 , Dominik Ulrich Geier  1 , Thomas Becker  1
Affiliations

Investigations on Backflush Cleaning of Spent Grain-Contaminated Filter Cloths Using Continuous and Pulsed Jets

Roman Alejandro Werner et al. Foods. .

Abstract

This study investigated the continuous and pulsed backflush cleaning of woven fabrics that act as filter media in the food and beverage industry. Especially in breweries, they are commonly used in mash filters to separate solid spent grains from liquid wort. After filtration, the removal of such cereal residues via self-discharge is necessary. However, this filter cake discharge is typically incomplete, and various spots remain contaminated. In addition to the reduced filter performance of subsequent batches, cross-contamination risk increases significantly. A reproducible contamination method focusing on the use case of a mash filter was developed for this study. Additionally, a residue analysis based on microscopical image processing helped to assess cleaning efficiency. The experimental part compared two backflushing procedures for mash filters and demonstrated fluid dynamical, procedural, and economic differences in cleaning. Specifically, pulsed jets show higher efficiency in reaching cleanliness faster, with fewer cleaning agents and less time. According to the experimental results, the fluid flow conditions depended highly on cloth geometry and mesh sizes. Larger mesh sizes significantly favored the cloth's cleanability as a larger backflush volume can reach contamination. With these results, cloth cleaning can be improved, enabling the realization of demand-oriented cleaning concepts.

Keywords: backflush cleaning; cleaning; filter cloth; filter media; pulsed wash jets; spent grains.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Microscopic image as top and side view and schematic drawing of the filter cloths: (a) F1-TWL-80/100; (b) F2-STN-20; t = length to the repetition on the chain/shoot thread; dChain/Shoot = diameter of chain/shoot thread; lS = length straight-thread section; lZ = length slanted-thread section.
Figure 2
Figure 2
Illustration of the complete experimental procedure. (A) Prepared congress mash. (B) Aluminum stencil on cloth sample. (C) Cloth sample in the object slide. (D) Digital microscope device. (E) Object slide under microscope lens, identifying contamination. (F) Insertion of object slide into cleaning device. (G) Final vertical positioning of the cleaning device. (H,I) Applied cleaning concept. This illustration concludes Section 2.2, Section 2.3 and Section 2.4.
Figure 3
Figure 3
Original image of the cleaned filter sample (a) and its binarized image (b). The white spots represent the remaining contamination after cleaning, whereas the black areas show the cleaned or contaminated surface. The picture also illustrates the area where the jet streamed through the filter cloth (the black spot in the middle of (b)).
Figure 4
Figure 4
Backflow factor ζBF of a defined water volume streaming through filter cloths. Confidence intervals with α = 0.05.
Figure 5
Figure 5
Comparison of pulsed and continuous cleaning with two different cleaning velocities. Settings for pulsed cleaning: tPulse = tPause = 0.1 s in a logarithmic interval [8:265]. Continuous cleaning settings: unpaused in a logarithmic interval [8:256] s. (a) F1-TWL-80/100 and 2 m/s. (b) F2-STN-20 and 2 m/s. (c) F1-TWL-80/100 and 4 m/s. (d) F2-STN-20 and 4 m/s. n ≥ 5. Confidence intervals with α = 0.05.
Figure 6
Figure 6
Velocity variation of vNozzle regarding the transition area of pulsed and continuous cleaning. (a) Pulsed wash jet with 32 pulses and continuous wash jet with a length of 32 s at F1-TWL-80/100. (b) Pulsed wash jets with a quantity of 128 pulses and continuous wash jet with a length of 128 s at F2-STN-20. tPulse = tPause = 0.1 s. n ≥ 5. Confidence intervals with α = 0.05.
Figure 7
Figure 7
Comparison of both filter cloths using pulsed and continuous cleaning. (a) Pulsed cleaning at an inflow velocity of 1.5 m/s. (b) Continuous cleaning at an inflow velocity of 1.5 m/s. (c) Pulsed cleaning at an inflow velocity of 3.5 m/s. (d) Continuous cleaning at an inflow velocity of 3.5 m/s. n ≥ 5. Confidence intervals with α = 0.05.
Figure 7
Figure 7
Comparison of both filter cloths using pulsed and continuous cleaning. (a) Pulsed cleaning at an inflow velocity of 1.5 m/s. (b) Continuous cleaning at an inflow velocity of 1.5 m/s. (c) Pulsed cleaning at an inflow velocity of 3.5 m/s. (d) Continuous cleaning at an inflow velocity of 3.5 m/s. n ≥ 5. Confidence intervals with α = 0.05.
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