CA2064104A1 - Apparatus in hydrocyclones for separating sand and the like coarse particles - Google Patents

Abstract

An apparatus (10) is illustrated in the invention for removing coarse particles, such as sand, metal chips, etc., from a liquid, whereby the apparatus is in the first place aimed at separating coarser particles from the so called reject, which is obtained fromthe cleaning apparatuses for fiber suspensions and thus enabling a particular reutilization of the reject with its eventually remaining fiber material. The apparatus comprises a hydrocyclone (15) installed in a cylinder (20), in which the reject thereof flows out, whereby the entraining heavier particles settle and are gathered to the bottom of the cylinder (20) for discharge. The liquid rising in the cylinder flows through an overflow outlet (25) to a separate side chamber (30) open to the atmosphere, in which chamber further settling takes place. An inwardly extending pipe (40) is arranged to extend in the reject nozzle (22) of the cyclone (15). The vacuum therein extends through the inwards extending pipe, which protrudes into the side chamber (30), wherefrom liquid is redrawn to the cyclone. When desired several side chambers can be combined in series one after another for further intensification of the cleaning process.

Description

2 ~ PCT/F190/00185 AN APPARATUS IN HYDROCYCLONES FOR SEPARATING SAND AND THE
LIKE COARSE PARTICLES

The present invention relates in the first place to means for cleaning liquid suspensions, especially fiber suspensions used ln paper manufacturing. Corresponding presen~ apparatuses are almost solely formed and assembled of hydrocyclones, which due to thelr in principle simple construction and la k of movabl~e parts have proved to be especially suitable for this kind of cleaning.

Cleaning of fiber suspensions by means of hydrocyclones, on a so called centrifugal principle is in many cases a complicated process, since the majority of the particles being separated has a density (specific weight) very close to sach other. On one hand, there are the "useful"
particles, such as cellulose fibers, on the other hand there are the group of fouling particles, plastic particles and other impurities, whereby both groups have a densi~y 20 so close to each other that the separation thereof in one .
stage becomes difficult. Therefore, cyclones are mounted in a combined system (for example, in a so called cascade coupling), whereln fiber suspenslons are ~rought to recirculation through the cyclones and thus subject to multi-stage cleaning.
:
A hydrocyclone operates, as known, by recei~ing the liquid to be cleaned, the so called feed, and by continuing the rapid rota~ion so that the lighter particlss accumulate to the center, whereas the heavier particles approach the periphery. Hereby-the circulating llquid is distributed - and discharged from the cyclone so that the majority thereof escapes through a central discharge opening in the farther ; part of the cyclone forming a so called accept, whereas the portion with the separated particles circulating in the periphery is delivered ~owards the top of the cyclone to b~-discharged as a so called reJect. As described above cleaning can seldom be carried out completely in one stage .
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or cyclone passage, since the reject still includes separable useful partlcles which should not be lost and thus the cleaning continues from apparatus to apparatus in the described manner.

But even if the main problem ln this ~yclone cleaning type concerns separatlon of particles, the density of which are close to each other and thus results in the above described, often mixed cascade connected systems, wherein also coarser and heavier particles occur in the feed and also they must be discharged. This concerns sand, metal particles and other heavier impuritie~, in other words said coarse particles. The probability of these causing any problem is eliminated quickly by slingincg them towards the periphery of the cyclone in order to be discharged with the reject.
These heavy particles are entrained in the subsequent cleaning stages and are concentrated continuously to end up in the final reject. This includes all that is separated from the complately treated fiber suspenslon.

- But this final rejec~ is not yet discharged straicght away because it still includes useful particles, such as coarser fibers and fiber bundles, so called shives, whlch would be worth recovering for a secondary ob~ect. However, there is one condition for that, ~.e. the amounts of coarse particles that occur in the final re~ect, i.e. sand, metal particles and o~her coarser scrap ls firstly discharged, because they have a harmful influence on the means which will - treat f~he reject material, for example on pumps, but ahove all, on grinding means and refiners. It is also important `~; that the coarse separation is carried out without any considerable losses in pressure. In other words, it should `~ no~ cost much to remove the coarse particles in order to collect said rest fibers.
There is as such, of course, no problem to separate coarse particles from a llquid or flber suspension in a cyclone;
as already mentioned the ~eavier par~icles are rapidly ~ f WO 91/01810 ~ PCr/f~190/00185 .. ..

slung out towards the cyclone wall to glide downwards therealong and to be discharged with the re~ect. It ls not desirable to lose some of the liquid with the reject, but only to get rld of the coarse particles, while the rest of the liquid continues lts flow through the system. In the known apparatuses, often calle~l as "sand traps", see, for example, US Patents 3 259 246 or 3 529 724, the reject with the coarse particles is therefore allowed to flow out to a closed chamber, where the particles accumulate while the liquid ls delivered ln one way or another back lnto the cyclone through the central part of the re~ect outlet. A
vacuum prevails there drawing the liquid in again, from where it flows up along the center of the cyclone and is discharged through the accept outlet.
These known apparatuses have in principle two disadvantages.
When installed ln a piping system with flowing liquid so as to form there, for example, "sand traps" they, firs~ly, produce conslderable losses of pressure. Secondly, their separation efficiency ls insufflclent. Particles which 3re definitely "coarse" in that meaning that they have a high ~- denslty, bu~ on the other hand are so small that they pos~ibly pass through, will st~ll exist in the accept. This ~'concerns-especially particles which are very hard, for example, sand/quartz partlcle, whlch can cause a great risk in further processing.
:
Another objective of the invention is to produce an apparatus, whlch ls from now on for short ralled a coarse separator to separate effectively~and at low cost these coarse particles from the reject. It can, of course, be maintained tha~ the use range of the coarse separator in accordance with the present lnvention ls not restricted ~o what is axemplified above, but it can be installed anywhere, where a suspension of llght particles, both cellulose fibers and other light particles, can efficiently ~e removed from sand and other coarser and heavier particles ~ V ~

without encountPring any slgniflcant lo~ses of pressure in the cleanlng system.

The objective is achieved and the disadvan~ages encountered with the previously known apparatuses are eliminated by the invention realizing the characteristics described in claim l.

An embodiment of the coarse separator in accordance with the invQntion ls now described in greater detail, as an example, with reference to the enclosed drawings, in which Fig. l lllustrates a total view of the coarse separator from one side and partially sectional, whereas Fig. 2 illustrates a detail of the separator in a larger scale.
Fig. 3 is a sectional view along line III-III in Fig. 2.
Fig. 4 illustrates an alternative discharge apparatus for the separated materlal. Fig. 5 finally illustrates a coarse separator in accordance with the invention formed with the outer cleaning stage in the form of additional settling chambers.

Fig. l illustrates a coarse separator lO in accordance with the invention, in an embodiment applied for treating reject, in, order to separate coarser and wearing particles, such as sand, metal chips, etc. The coarse separator lO comprises two main parts, namely a combined cyclone and settling part 12 and a separate secondary settling chamber or an auxiliary chamber 14.

The combined cyclone and settling portion 12 comprises a hydrocyclon~ 15 of a known type, coaxially installPd in a cylinder 20, the main cylinder, in which it extends from the top downwards, as shown in Fig. ~. The cyclone l5 has usually a feed lnlet l6 and~an accept outlet 18 and flows downwards, lnto its so called underflow, a cylindrical re~ect nozzle 22, through whlch the reject is discharged to the surrou~ding cylindrical chamber. Its lower part is connected to a discharge apparatus 35 of a sluicP ~ype, .... . ... .. . ... ...
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WO91/01$10 ~ PCT/F190/0018;

which is described below and the cylindeir 20 comprises in its upper part an overflow opening ~5, a so called overflow channel, through which the l~quid flowing from the cyclone 15 to the cylinder ~0 and ascending upwards in it flows 5 over to the secondary settllng chamber 14, as described mor~i closely below.

It should be hereby noted that the coarse separator in accordance with the inventlon forms an open system, in lO other words atmospheric pressure has free access, more precisely to the secondary or auxiliary chamber l4, which - is noted by its cylinder 30 pointing openly upwards and `~' being covered by a lid 32. The feed is pumped in at a rather low pressure, 2 to 3 bar, decreasing practically r 15 speaking to zero in the accept outlet 18.
' ~ The auxiliary chamber 14 compri~es a cylindrical vessel 30, the lower part of which is connected in the same way ; as that of the main cylinder 20 to a discharge apparatus ` ~0 35', whereas the upper part as mentioned is open to the atmosphere and covered by the lid 32. A pipebend 26 runs from the overflow opening 25 of the main cylinder 20 into the auxiliary chamber l4, which thus receLves the liq~id " flowing out from the cyclone 15 into the main cylinder 20.
:~ 25 An inwardly extending pipe 40 has been mounted to the re;ect opening 22 of the cyclone, extending coaxially with the reject opening therethrough to the level s-s where the cylindrical re~ect opening 22 is transferred to 30 the conical part of the cyclone 15, see Fig. 2. The inwardly extending pipe 40 then extends out from the reject opening and bends ~hrough the wall of the main cylinder :20 to continue in the auxiliary cylinder 30 and where it ends to a downwardly p:Lpebend 45, which is all evident fro~ Fig. l.
35 The inwardly extending pipe 40 which thus as a whole gets a trunk-like forim, and a valve 4~ is mounted between both cylinders to r~egulate the flow through the pipe 40.

WO 91/01810 P(~/FI90/00185 The coarse separator in accordance with the invention operates in the following manner. The reject coming from a simultaneously operating cyclone cleaning apparatus, and including the coarse material being separated in the apparatus, but also different kind of valuable residual fibers, now forms the feed material to the coarse separator 10 in accordance with the invention and ls supplied thereinto through the tangentially mounted inlet opening 16. U~ually the liquid is brought into circulation in the cyclone 15 of the separator simultaneously with the downwardly movement towards the bottom outlet, where the rapidly circulating liquid par-tly turns and rlses upwards - alony the center of the cyclone, partly flows out through the re~ect opening 22, between the ln~ide thereof and the previously described inwardly extending pipe 40. The ` out~lowing liquid entrains the coarse particles which are ~,l almost immediately slung out towards the inside of the - cyclone 15 so as to follow lt downwards. ~he movement of the outflowing liquid is dampened rapidly in the main cylinder 20 surrounding the cyclone, and the majority of the separated partlcles fall towards the bottom of the cylinder. As mentioned above the liquld rlses in the cylinder so as to flow over through the overflow pipe 25 and through the pipebend 26 into the cylinder 30 of the secondary or auxiliary chamber 14. The purpose thereof is thus to form a secondary settling chamber complementing the main cylinder 20, in which chamber the liquid ~ transferred through the overflow pipe 25 is gathPred and is `~ brought to settle under smoother conditions, in other words ~he coarse particles that eventually have not settled in the main cylinder 20 are~now given a chance to do so in the auxiliary cylinder 30.
.~ . ...
The circulat:Lng liquid generates a vacuum in the center of the cyc1one 15 in a known manner, which vacuum extends through the inwardly extending pip2 to the auxiliary cylinder 30 so that liquid is drawn from it through the trunk-shaped lnwardly extending pipe back to the cyclone .. ..

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WOgl/0]810 2 ~ PCT/Fl90/00l8 15, as indicated with arrows ln Fig. 1. The liquid drawn back to the cyclone rises upwards in the center of the cyclone, jol~s with the llquid directly turning in the bottom outlet and being dlscharged through the accept outlet 18, free from coarse pa:rticles, but entrained with fine particles which are left ln the original re~ect.

The separated coarse particles are gathered thus to the bottoms of the main cylinder ~0 and the auxiliary cylinder 30. From there they can be transferred out in regular intervals by opening, in case of the main cylinder 20, a slide valve 36 so that the coarse material flows down into a gathering chamber 37. ~hen all the coarse material -gathered uptil that moment has flowed down said valve 36 is closed, and a lower slide valve 38 is opened instead ` and the gathering ~hamber 37 is unloaded threrethrough.
The method is applied to the auxiliary chamber 30 which is provided with a valve apparatus 35' comprising a similar, gathering c~amber located exactly in the middle between the upper and lower valves.
. .
It is possible to install a continuously running apparatus ~-in accordance with Fig. 4 instead of this intermittantly running discharge apparatus. In that case the valve `;25 apparatus 35 or ~5' is replaced by an inlPt chamber for a screw conveyer 39 which continuously feeds out the separated coarse m~terial which is gathered to the bottom of the cylinder in question.

In a continuous drive the coarse separator in-accordance with~the invention is set in the optimal drive conditions by regulating the accept outflow (by adjusting the counter pressure in the accept outlet 18) as well as also by regulating the in1Ow through the trunk pipe 40 by means of the valve 46 mounted therein. Thereby the liquid level H-H in the auxiliary chamber 30 is caused to settle to an optlmal position, which gives a maximal cleaning effect, as can be confirmed by taking a sample of the accept. The ;,. - . . ..,. : . :

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practlcal experlments with the separator in accordance wlth the present invention have proved that the separation effect was very good also with small sand and bark particles which can otherwise be separated only by considerably smaller and more effectlve hydrocyclones. Additionally saw dust and the like heavier wood particles are separated and ga~hered into the se~tllng chambers. A study of the accept from the separator showed that it was practically speaking free of the sand par-ticles and also no saw dust ~;lO was to be found in it; the accept comprised only water and fine fiber particles.

~-~,Certain dimensioning conditions for the coarse separator must be fulfilled. As mentioned the conical part of the cyclone 15 ends up with a re~ect portion comprising a cylindrical reject opening 22 with an inwardly extending pipe 40 arranyed coaxially therPin. It is important that -the inner opening of the pipe is at the same level with ,~`the s-s level between the conical part of the cyclone and the cylindrical part of the reject opening 22. The inwardly extending pipe 40 must thus be either extPnding upwards in the cyclone 15 or downwards in the reject opening 22, see -Fig. 2. As for flow surfaces lt must be looked after that the area SA of the accept outlet is greater than the area 25 SI of the feed inlet, and further the annular area SR f the gap between the outside of the inwards extending pipe 40 and the inside of the reject outlet 22 must be smaller than the inner area ST of the inwards extending pipeO
Finally, the total of both these areas, both the annular gap area SR and the area ST of the lnwards extending pipe, must be smaller than the area of SA of the accept outle~O
The area conditions oan be summarized as follows:

SA > SI
SR < SS
SR S~ ~A

WO91/01810 PCT/F190/0018~
0'~
The coarse separator lO is, as mentioned, in a condition that it can practlcally sp~aking completely separate coarser particles from the flowing liquid, for example, fiber suspension, but in case a hundred per cent separation of these particles, especially very small and hard, such as quartz-type, is desired, the cleaner in accordance with the invention can be "refinPd" and its separation effect ; further improved. This can take place in an almost unrestricted extent, as can be seen in Fig. 5, which -;10 illustrates a coarse separator 50 in accordance with the invention, in which additional, extra auxiliary chambers or cylinders 60 extend inwards between the original 30 and main cylinder ~0 with the cyclone 15.

Fig. 5 illustrates thus how three such additional auxiliary chambers 60 are installed, and every such chamber is provided with a central ~ntermediary plate or wall 65. The overflow from the overflow channel 25 of the main cylinder is supplied to one side of the plate 65 in the first auxiliary chamber 60 and flows downwards along it. The plate ends up at a distance from the bottom of the chamber, and it extends upwards to the level of the open upper end of the chamber. The llquid flows thus downwards on one s~,de of the plate 65, turns by the bottom of the auxiliary chamber 60, flows then upwards to an upper overflow channel 25' at the same level with main cylinder's overflow channel.
A second additional chamber 60 is connected subsequent to the first and relative to the current similarly to the first one so that the llquid flows downwards on one side of the plate and upwards along the opposite side of the plate so as to con~inue further to a third addltional chamber 60, in whlch the flow process is repeated. The liquid then continues to a last chamber 30' which corresponds ~he original single auxiliary chamber 30 in accordance with Fig. l. The inwardly extending pipe 44' from the cyclone 15 extends through - or past - all extra chambers 60 to the final pipebend 45' ln the last chamber 30' in order to : - . , . .. . ~ : : :
- , . . .. :- ::: :~. .. . ,: . : - :

WO9l/01810 PCT/Fl90/00185 receive and further transfer the liquid to be redrawn into the cyclone 15.

The aggregate in accordance wi~h Fig. 5 operates exactly in the same way as the described separator in accordance with Fig. 1 with the exception that a number of additional settling stages are tncluded in the cleaning process. In ~, each of the extra chambers 60 the liquid has the opportunity under its relatively smooth through flow to settle and the separated sedimention is discharged through discharge valves 35', as dascribed above. The number of the additional settling stages is determined by how long it is desired in the particular case to run the cleaning process, and as described there is the opportunity to clean the liquid/fiber suspension in thls way practically : speakin~ 100 %.
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. The described coarse separator is simple and rough in its construction and its lack of constriction in the flow channels decreases the loss of pressure to minimum, and at : the same time a high through flow capacity becomes possible.
Finally it is reminded again that the range of use of a separator in accordance with the invention is not restricted to, the above described example of cleaning fiber suspensions, but the separa~or can be utilized in many cases where heavier particles should be removed from a flowing liquid.

Claims (8)

1. Apparatus for separating sand and the like heavy particles from a flowing liquid, comprising:
(a) a hydrocyclone including a stock inlet, an accept outlet and a reject outlet, the reject outlet being defined by a cylindrical nozzle portion disposed at a lower end of said hydrocyclone, remote from said stock inlet;
(b) a main chamber disposed generally coaxially with said cyclone and adapted to receive reject from the hydrocyclone, said main chamber including a settling section for reject separated in the cyclone;
(c) heavy particle removal means adapted to remove heavy particles settled from the reject in said main chamber;
(d) recirculation means including an overflow opening in the main chamber, said overflow opening communicating with an additional settling chamber;
(e) said additional settling chamber being adapted to further settle heavy particles from the liquid fraction of the reject coming from said main chamber;
(f) said additional settling chamber means including heavy particle discharge means for removal of heavy particles settled in said additional settling chamber;
(g) said apparatus further including an inwards extending pipe having an inlet portion near a lower end of said additional settling chamber and extending through a lower portion of the main chamber into the cylindrical nozzle portion and defining therewith an annular reject passage extending from the hydrocyclone to the main chamber.

2. The apparatus in accordance with claim 1, wherein the additional settling chamber communicates with the atmosphere.

3. The apparatus in accordance with claim 1 or 2, wherein said inwards extending pipe extends upwards in the cylindrical nozzle portion of the cyclone with a discharge end of the pipe being disposed at a level located between a conical portion of the cyclone and the cylindrical nozzle portion.

4. The apparatus in accordance with claim 3, wherein the cross-sectional area of the annular reject passage of the cyclone is greater than the cross-sectional area of the stock inlet of the cyclone, and the cross sectional area of the annular reject passage being smaller than the inner cross sectional area of the inwards extending pipe.

5. The apparatus in accordance with claim 3 wherein the total of the cross-sectional area of the annular reject passage and the inner cross-sectionalarea of the inwards extending pipe is smaller than the cross-sectional area of the accept outlet.

6. The apparatus in accordance with one of claims 1, 2 or 4 characterized in that the inwards extending pipe is provided with a valve for controlling the back flow from the additional settling chamber to the cyclone, the purpose of the valve being optimization of the liquid level in the additional settling chamber which is open to the atmosphere.

7. The apparatus in accordance with one of claims 1 or 2 wherein further additional settling chambers open to the atmosphere are provided, each additional settling chamber being provided with a central intermediary partition wall which extends from an upper end of the respective additional settling chamber toa level spaced from the bottom of the respective additional settling chamber, anupper end of the respective additional settling chamber having a feed opening for feeding into the respective additional settling chamber liquid from the immediately preceding settling chamber, said respective additional settling chamber further including an opposite discharge opening disposed on the other side of the plate,whereby the arrangement of each partition wall and of the respective feed opening and the respective discharge opening being such that the inflowing liquid flows downwards along one surface of the partition wall towards the bottom of the respective additional settling chamber and then upwards along the opposite surface of the partition wall for the discharge through said overflow opening with the purpose of offering the liquid an opportunity to settle during its extended passage caused by the partition wall each additional settling chamber being provided with means for discharge of material settled during the liquid passage through same.

8. The apparatus of claim 4 wherein the total of the cross-sectional area of the annular reject passage and the inner cross-sectional area of the inwards extending pipe is smaller than the cross-sectional area of the accept outlet.