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ADVANTAGES OF SCREENING IMBIBITION JUICES

ADVANTAGES OF SCREENING IMBIBITION JUICES

September 14
12:49 2017

By: Muhammad Iqbal Javiad, Director Technical, Shahtaj Sugar Mills Ltd., Mandi Bahauddin

Abstract

Traditionally, all imbibition juices were screened through perforated sheets and cush cush was conveyed by scraper conveyor cum elevator ahead of mill # 2 in the tandem.  With the introduction of DSM screens for the screening of mixed juice, the screening of imbibition juices was also discontinued and these juices were pumped directly along with cush cush through chockless pumps. At Shahtaj, we started screening of imbibition juices which proved to be a great success. In this case study, the advantages / benefits of new adopted system shall be discussed.

Introduction

Traditionally all the imbibitions juices were screened. It was common to have a single cush cush screen, also referred as cush cush conveyor, consisting of a long drag type slat carrier on top of a horizontally fixed perforated screen deck running along side the mills. The juice from each mill passed through the screen and was collected in the respective receivers of mills installed under the screen and all the strained cush cush was returned ahead of mill # 2 through cush cush conveying and elevating system. The screened juice was free of cush cush and hence was applied smoothly and regularly.  The mill juice trays were washed by re-circulating screened juice back to same mill juice tray. On the other hand due to wet and corrosive nature of the cush cush, the conveying equipment was difficult to maintain and the breakdowns/stoppages were high and because of difficult approach under the screens and pockets in the chain, it was a safe heaven for bacterial growth. Further due to conveying of all cush cush ahead of mill # 2, the fiber loading of the whole tandem except mill # 1 increased substantially. With the introduction of chokeless pumps, the use of cush cush conveyors has nearly eliminated.  Now, the unscreened mixed juice is pumped to DSM Screen and cush cush is dropped on Inter Carrier # 1 either directly or through a screw conveyor and all imbibition juices are pumped with chokeless pumps directly before the preceding mill and re-milling of cush cush present in the juice is being done only by one mill.

Presently, the use of DSM Screen for mixed juice screening is being replaced with rotary screen day by day. Where there are many advantages of direct pumping of imbibition juices, some disadvantages were also found which are discussed hereunder;

 

At SHAHTAJ, we were using cush cush Conveyor on one tandem till season 2002-03, which was replaced with chokeless pumps (without screening), on the other tandem  the same chokeless pumps were already in use.

Under mentioned problems were faced due to direct pumping:

  1. The chokeless pumps usually run under “Snore” conditions, drawing in air with the liquid to prevent fiber agglomeration by maintaining a low level in the suction tank. Due to this pumping condition, the flow of imbibition juice remained gushy; resulting in over imbibition, owing to this phenomenon, sometimes the feedability of mills was badly affected, causing choking of the donnelly chutes or even the pressure chutes. We all know, regular and well spread imbibition is basic requirement of good milling, hence, when there was no imbibition or very poor imbibition, dry bagasse passes into the mill which can be a dangerous phenomenon for the pressure chutes. In both cases excessive / less imbibition is experienced. Due to this irregularity, milling results are affected to quite an extent, which are not easy to quantify.
  1. The overflow weirs of imbibition gutters remained choked regularly with cush cush and small channels were formed in the imbibition juice gutter discharge, resulting in very poor spreading of imbibition juice over the entire width of the bagasse belt. To ensure uniform spreading, one worker was engaged all the time for the cleaning of imbibition gutters.
  1. With the introduction of arcing/beading on mill rollers, the phenomenon of cush cush / bagasse falling in the mill juice trays further aggravated, causing increased choking of pumps and piping.
  1. Water hoses were regularly used for washing down the accumulated bagasse in the juice trays, adding unnecessary water into the system, thus increasing the steam requirement.
  1. To overcome the above mentioned problems, we started screening of all imbibition juices with DSM screens.

 

Methodology

The imbibition juice of each mill i.e. 3, 4 & 5 is pumped with chokeless pump to DSM screen installed over intermediate carrier of preceding mill. The screened juice is transferred to imbibition gutter through a pipe as shown in sketch ‘A’. (If there is any space constraint, the bottom of DSM screen trough can also be used as imbibition gutter as shown in sketch ‘A-1’ & ‘A-2’).

 

From the DSM screen juice trough a portion of juice (as primary consumer) about 25~30 tons/hrs. for 42”x84” Mill is transferred back to the same mill juice tray through a pipe 3 ~ 4 Ø which sprays the juice at the mill delivery side of the juice tray through a perforated pipe installed over the entire width of tray, as shown in Photograph P-1.

P-1

This juice washes down all the accumulated bagasse/cush cush dropped in the juice receiving tray of that mill. Due to addition of juice into the mill tray, the proportion of cush cush is decreased in the imbibition juice and smoothens the pumping. This system is illustrated in sketch ‘B’ schematically and also shown in photograph P-2.

 

 

 

 

Sketch –B

 

P-2

(Imbibition juice screens installed at SHAHTAJ)

 

Advantages

 

  1. The chokeless pumps worked smoothly and no gushes are observed. The flow of imbibition juices remained very smooth and regular, the imbibition gutters remain clean and the imbibition juice is spread all over the width of Bagasse as shown in Photograph P-3.

 

 

 

 

 

 

 

 

 

 

 

 

 

P-3

 

Regular and evenly distributed imbibition juice/water is a basic requirement for good milling, which we achieved by adopting this system.

 

  1. We never faced choking problem of mill juice trays, pumps or piping.

 

  1. The use of water hoses to wash the bagasse accumulated in the juice trays was eliminated.

 

  1. The labour requirement for attending the mill trays and imbibitions gutters was reduced substantially.

 

Installation Cost

 

Rs.140, 000 to Rs.150, 000 are needed to install whole new system for one mill only. With the installation of Rotary screens many mills may have surplus DSM screens which can be used for this purpose and then the cost for remaining parts may be reduced to Rs.30, 000 ~ 40, 000 only. Care should be taken that DSM screen used for this purpose should not be less than 0.78 mm aperture,  one may go up to 1.25 mm comfortably.

 

 

Conclusion

 

At the end, I shall say that this is a very low cost job but plays a vital roll in milling efficiency and working. By the grace of Allah, during season 2015-16, under mentioned Mill extraction results were achieved by SHAHTAJ:

 

Plain                    Reduced                                Whole Reduced

97.19                      97.42                           97.51

96.74                      96.99                           97.13

 

Max. Mill Extraction

Average Mill Extraction for the Season 

 

No doubt, we cannot quantify the actual share of the system discussed above; however, we all know that imbibition system plays an important role in milling.

 

Acknowledgment

 

I am highly thank full to PSST to give me chance to present this paper and my thanks are also being extended  to my senior Management, who allowed me and sponsored this presentation.

 

References:

 

  1. Cane Sugar Engineering by Peter Rein
  2. Hand Book of Cane Sugar Engineering by E.HUGOT

 

 

                                                                                        

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Engineering Horizons

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