US1947889A - Process and apparatus for the manufacture of pulp - Google Patents

Description

Feb. 20, 1934. c B, THQRNE 1,947,889

PROCESS AND APPARATUS FOR THE MANUFACTURE OF PULP Filed April 27, 1933 \NVENTOR:

CARL B. THORNE' ATTORNEY.

Patented Feb. 20, 1934 *raoosss AND APPARATUS Fon 'imi MANUFACTURE or PULP Carl Busch Thorne, Hawkesbury, ohm-i0, Canada Application April 21, 193:, Serial No. 668,209,

and in Ganada 8'Claims.

This invention relates to the manufacture of pulp and particularlyto an improved process and. apparatus therefor.

The object of the invention is to effect economics in the manufacture of pulp by utilizing in an advantageous and convenient manner the heat contained in the materials discharged from both the digester and-the blow pit.v a

Proposals have heretofore been made for the recovery of heat from the digester relief gases but insofar as applicant is aware there are no previous arrangements whereby full advantage may be taken of "all the heat available in treated pulp as well as in the relief gases and the present invention provides a simple practical method and apparatus therefor} ,The invention will now be described with reference to the accompanying drawing, which illustrates in sectional elevation apparatus for car-.

. Tying out the invention.

l'represents any suitable dige'ster as commonly used for cooln'ng wood chips in the manufacture ofsulphite pulp. 2 indicates any convenient recipient or separator tank into which the relief acid from the digester 1 is discharged through a pipe 3. In this tank the free gases are separated from the liquor and the gases are led off along a pipe 4 while the liquor flows down through a pipe 5.

"6, 7- and 8 are heat exchang'ers consisting of a number of pipes made of acid resisting material,

through which hot liquid or gas flows, these pipes Cold water, or other liquid to being surrounded by a cooler liquid flowing in the opposite direction, thus absorbing the heat from the pipes. The heat exchangers are of ordinary-construction and the'pipes are indicated only on the exchanger 8.

A blowpit 9 is provided and may conveniently be of the type commonly used in pulp mills; that is, of the type comprising a tankhaving a perforatedfalse bottom 10; The pulp at a high temperature is discharged from the idigest'er 1 into the blowpit 9 through the blowpipe 11 controlled by a valve 12. The pulp is retained in theiblowpit 5 while the liquor drains downthrough the perforated false bottom 10 and passes through the pump 14 and pipe 15 to the heat exchanger 8. YA valve 16 is provided in the pipe 15 and a discharge pipe 13' for wash water and the like leads to the sewer. Gases liberated in the blowpit may be conveyed to a desired absorption or recovery? systemthrough pipe 29. l tbe heated, for example cooking liquor, is pumped under pressure into the top of the heat exchanger 8 through a pipe 18 while the hot liquor from the blowpit 9'is April 20, 1932 (01f 92-7) w I pumped through the heat exchanger 8 in the bpposite direction. The cold liquid to be heated flows over the outside of the exchanger pipes while the hot liquor is on the inside in the known manner. The heat fromthe liquor is thus transferred to the cold liquid. The liquid from the heat exchanger 8 passes through a pipe 19 to the heat exchanger 7 where it absorbs more heat fronithe hot liquor which flowing through the heat exchanger f rom' therecipient 2. The liquor from the heat exchanger 7 is allowed to go to the sewer. The water or other liquid from the exchanger '7 is carried through the pipe 20 to-the exchanger 8 where it absorbs more heat from the gases from' the recipient 2 as wellas from the top'relief gases from the digester flowing through a pipe 21. The

liquid, which by this time will have reached a temperature of, say, to 9. or more, as it leaves the heat exchanger 6, is carried through a The gas from the heat exchanger 6 flows along a pipe 23 to any suitable recovery tower or other apparatus as desired.

It may be very important when water is being heated in the heat exchangers, that the water should be free from any trace of acid, and in such instances there must be no leakageof acid or gas out from the pipes into the water. When it is necessary to accomplish this, the pressure outside of the exchanger pipes is always kept 35 at a pressure which is greater-than the pressure insidethepipesu In this way if there should be any break or leak in the pipes carrying thev acid, then the liquid will lead into the acid and not the acid into the water.

is placed in the water line 22 as it leaves the. last heat exchanger 6 and this valve may be regulated so that. the pressm'e on the water in 6 is higher than that of the hat fluids in the s s;

the system is always kept at a pressure which tem. A check valve 18' may be provided in the supp y pipe 184:0 prevent reduction of'pressure in the event of failure of the pump supplying no I I the liquid to be heated. I In addition to a thermostatically con trolled valve 25 may also be provided in,the

waterline 22, a.controlling thermometer 26 being placed in the heat exchanger 6. This valve 196 25 is of known constructionand may be setto' open at any desired temperature, for instance 90 to. 95 C., and will close as soon as the temperature drops below this point.

In this way thepressure'of the water, as well l" i 00 To accomplish this, apressure relief valve 24.

.pipe 22 to a tank, not shown, foruse as required. 75

as the temperature of the water, are controlled as desired.

In mills wherein the hot liquor is not drained .into a blowpit, the heat may be recovered by means of an arrangement such as that indicated in dotted lines to the right of Figure 1. In this case, the gas which is given ofi during cooking is relieved through the pipe 21', and the excess cooking liquor is relieved through the pipe 3, as already described. Now, instead of opening the valve 12 in the blowpipe 11 and dumping the whole charge of the digester into. the blowpit, a valve in the pipe 21 is fully opened and the gas is allowed to escape through the heat exchanger 6 until .the pressure is reduced practically to atmospheric. A valve 15" in pipe 15 is nowopened. and,the liquor in the digester is allowed to drain through a strainer bottom 35, through the pipe 15 and the heat exchanger 8 When all of the liquor has drained. ofi, then a water spray 36 is opened and the water washes the pulp in the digester, the water descends and leaves the digester through the pipe 15 In this way the heat from the liquor is recovered in the heat exchanger 8. After the pulp is washed inside the digester, the valve 15 is closed, and

the valve 12 in the pipe 11 is opened and'the pulp is allowed to discharge into the blowpit 9 or into any other tank for further processing in the mill. The liquid to be heated enters exchanger 8 through a pipe 18 which may be fitted with a check valve 18", and, after, being heated in the exchanger, passes-on through pipe 19 to exchangers '7 and 6 to be further heated as hereinbefore described. When this arrangement is employed the exchanger 8, and pipes 18 and 19 are omitted.

It will be apparent that the heat exchangers 6 and"? may be combined in one unit or that a larger number of heat exchangers may be used to obtain the same result. While the use of the separator 2 is preferred, it may be omitted and the gas and liquor together may pass through the heat exchangers.

I claim: 1. A process of manufacturing pulp, vwhich comprises cooking materials in a digester; passing fluids relieved from theupper part of the digester through heat exchanger means to recover heat therefrom, and, after the cooking operation has been completed, discharging solids and liquids from the bottom of the digester into a blowpit, draining the liquids from said blowpit and passing them through. heat exchanging menses 2. A process of manufacturing pulp, which comprises cooking -materialsin a digester, passing fluids relieved from the upper part of the digester through heat exchanger means to recover heat therefrom, and, after the cooking operation has been completed, discharging solids and liquids from the bottom of the digester into a blowpit draining the liquids from said blowpit and passing them through heat exchanging means, circulating liquid to be, heated through said heat exchanging means in counter-current to the hot fluids from the digester, and automatically maintaining the liquid to be heated at a higher pressure than the fluids from the digester. Y

3. A process as claimed in claim 4, wherein the final temperature of the liquid to be heated is automatically maintained above a predetermined figure.-

e 4. A process of manufacturing pulp, which comprises cooking-materials in a digester, discharging fluid from the upper part of the digester, separating the last mentioned fluids into liquid I and gaseous components, passing said fluid components through separate heat exchangers, and,

after the cooking operation is complete, discharging solids and liquids from the bottom of said digester into a blowpit, draining the liquids from said blowpit and passing them through a heat exchanger, and circulating liquid to be heat ed successively through said heat exchangers.

5. A process as claimed in claim 4, wherein the pressure of the liquid to be heated is automatically maintained above the pressure of the, fluids from the digester.

6. A process as claimed in claim 4, wherein if the final temperature of the liquid to be heated falls below a predetermined figure, the circulation of the liquid to be heated is automatically stopped until said predetermined temperature is again reached.

I 7. Apparatus for manufacturing pulp, comprising a'digester, a blowpit having an outlet and a connection to said digester, heat exchanging means connected to said outlet, further heat ex- 12':-

changing means connected to the upper part of changing means.

8'. Apparatus as claimed in claim 7, wherein an automatic thermostatically controlled valve is provided to stop the circulation of the liquid to be heated when the temperature of said liquid falls below a predetermined limit.

CARL BUSCH THORN'E.

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