US2115835A - Sulphate pulp process - Google Patents

Description

May 3, 1938. D. J. YOUNG SULPHATE PULP PROCESS Filed Sept. 15, 1937 .Puuhno :Quali mtb i. M MM www Mw,

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.. W donqvld 35 steam so that the gas as admitted to the bottom is shown at the top to permit charging of the Patented May 3, 1938 y J UNITED STATES PATENT OFFICE I SULPHATE PULP PROCESS Daniel J. Young, Tacoma, Wash., assignor to Young-.Whitwell Gas Process Company, Tacoma, Wash.

Application September 15, 1937, Serial No. 163,973

3` Claims. (Cl. 92-9) The invention relates to improvements in the would be a distinct asset to the community proprocess of treating wood and like cellulosic matevided the obectionable odors resulting therefrom rial for the formation of pulp, and more particcould be eliminated. ularly to the elimination of objectionable odors The primary object of the present inventio 5 which are especially characteristic of the manuis to withdraw the objectionable gases directly facture of pulp by the sulphate procesjs. It is. from the digester before they have become diluted known that the gases resulting from sulphate with air and to preferably burn them or otherpulp manufacture contain certain non-condenwise dispose of them in a manner which is not sible components having an extremely nauseating objectionable. 'I'he ordinary equipment may be odor and consisting largely of combustible mermaintained practically without change, it-being 10 captans and the like. only necessary to add a condenser communicat- In the ordinary method of manufacture of suling with the top of the digester through a valve phate pulp the cellulosic materials to be treated connection, the condenser being equipped with (usually Wood chips) together with the usual a gas offtake leading to a gas holder or the like chemicals are placed in the digester and steam is to which the non-condensed vapors are conveyed 15 admitted at or near the bottom of the digester and from which they may be withdrawn for until the pressure within the digester reaches burning or other unobjectionable disposal. about 125 to 135 pounds with the consequent tem- The invention will be more readily understood perature within the digester from 350 to 400 F. by reference to the accompanying drawing in This condition may be maintained for a period which there is illustrated somewhat diagramof about one and one-half hours and is known as matically a sulphate pulp digester of conventhe cook. When the pulp has been suiiiciently tional type equipped with the improved conneccooked the steam is turned orf, the bottom of the tions whereby the malodorous gases may be withdigester is opened and the pulp is discharged' into drawn and disposed of without pollution of the a closed. tank generally known as the blow pit, atmosphere. n in which tank the liquor containing the chem- Referring to the drawing the reference nuicals and the pulp are held and the excess steam meral I0 denotes a digester of any desired type and gases resulting from the cook are carried being approximately 10 feet in diameter and 60 away and condensed, the non-condensible gases feet high although obviously not limited to these being then usually discharged at the base of the proportions. The digester is i'llled with wood 30 boiler stack, coming out of the top of the stack chips and chemicals to a level II at approxwith the gases from the boiler. imately two-thirds the height of the digester. As the process is nowv carried outy a large The steam inlet I2 may be provided near'the amount of air is taken in with the gases and bottom of the digester and a removable lcap I3 of the stack is practically all air though condigester and also for the preliminary discharge taining the mercaptans. These mercaptan gases of air prior to the digestion proper. The digester being combustible, many eiorts have been made is provided with a bottom I4 through which the to burn them at this time but due to the extent digested materials may be discharged into a blow of dilution with air such attempts have proved pit I5 of conventional form. The blow pit is 40 unsuccessful. o shown as provided with an offtake I6 for gas and The total amount of mercaptans produced steam leading to a condenser I1 provided with during the process is relatively small, that proa liquid outlet I8 and a gas outlet I9. Ordinarily duced in a digester approximately ten feet in the gases passing from the outlet I9are so diluted diameter and sixty feet high, which was studied with air that it is impossible to burn the mer- 45 in connection with the present invention, being captans contained therein. about 100 to 150 cubic feet each time the digester According to my invention an outlet pipe 20 for is blown, a blow taking place about once an hour. gas and steam is provided at the top of the di- However, when these gases are allowed to pass gester, such outlet being preferably provided unburned into the atmosphere the objectionable with a. valve 2|. The pine 20 is preferably of 50 odor may be observed for a. distance of many relatively small diameter so as not to interfere miles. The nuisance is so great that in many with the pressure which is maintained within the communities sulphate plants are not permitted digester. The pipe 20 leads to a condenser 22 to operate simply on account of the odor alwhich may be of the surface type or of the type though from a business standpoint such a plant commonly used in gas plants and referred to 5'5 as the scrubber. The condenser is equipped with a liquid outlet pipe 23 and with an ofitake pipe. 24 for non-condensible gases.

These gases include the mercaptans in sumcient quantity for combustion. 'I'he pipe 24 communicates with a gas holder 25 which may be of conventional type and which is shown as equipped with an offtake 26 controlled by a valve 21. 'I'he oitake 26 may lead to a suitable burner Where the mercaptans or other malodorous gases are disposed of instead of being discharged directly into the atmosphere.

According to my method after the digester has been charged steam is admitted at the bottom of the digester and the cap I3 is left open for a short time until the air has been swept out of the digester by the steam. The cap I3 is then closed thereby maintaining the digester air-tight. Further steam under pressure is admitted to the digester and continues to ilow in sufiicient amount to maintain the pressure in the digester from 125 to 135 pounds more or less. As this steam ilows upward through the pulp and liquor it will force the steam and gases which are above the liquor out through the pipe 20 into the condenser 22 where the steam and other condensible portions will be separated from the non-condensible gases, which are being conducted to the gas holder from which they may be periodically withdrawn for burning. According to this method no air will be present with the gases and they can be satisfactorily burned. During the cooking process the valve 2| may be opened either intermittently or constantly. If desired two or more digesters may be used in battery, the steam and gases from one digester passing into a second one thus more eillciently utilizing the heat` of the steam.

After the digesting process is completedrthe pulp and liquor from which the malodorous gases have been substantially completely driven will be discharged into the blow pit in the usual manner and any gases remaining n therein will be passed to the condenser I1. Since the mercaptans have been eliminated during the digesting period there is no objection to passage-of the non-condensible gases through the outlet I9 directly to the atmosphere, since such gases-are substantially wholly air.

The invention has been described in detail with reference to a particular form of apparatus but it will be understood that many diierent conibinations of operation may be employed without departing from the spirit of the invention which consists brieiLv in withdrawing the gas and suillcient steam to carry the gas, from the digester during the digesting operation, condensing the steam from the gas and conducting the gas to a place where it may be burned, care being exercised to prevent an excess of dilution byair, the gas being at all times kept in closed containers or pipes until it is burned. thereby preventing malodorous gases from escaping into the atmosphere.

I claimz- 1. The improvement in the process of treating sulphate cellulosic pulp contained in a digester, for the purpose of avoiding contamination of the atmosphere with malodorous sulphur containing gases; which comprises sweeping out substantially all of the air from the digester prior to the commencement of the cooking process, then admitting to the digester steam under pressure to perform the cooking operation, and during the cooking stage withdrawing the resulting gases and vapors from the digester substantially free from air, separating the condensible from the non-condensible portions containing the malodorous constituents without introduction of air, and burning said non-condensible portion.

2. A combined process for treating sulphate cellulosic pulp contained in a digester and disposing of the resulting malodorous sulphur containinggases without contamination of the atmosphere; which comprises sweeping out substantially all the air from the digester prior to lthe cooking process. then cooking the pulp and during the cooking process and prior to discharging the pulp from the digester, withdrawing the gases and vapors resulting from the cooking operation substantially free from air, separating the condensible portions from the noncondensible portions containing the malodorous constituents without introduction of air, and burning saidnon-condensible portion whereby the malodorous gases are destroyed.

3. A. combined process for treating sulphate cellulosic pulp contained in a digester, and for eliminating the resulting malodorous sulphur containing gases without contaminating the atmosphere; which comprises conducting the treatment of the pulp in the digester in two distinct stages, the ilrst of which comprises sweeping out substantially all of the air from the pulp prior to the commencement of the cooking process, and the second of which comprises cookingl the pulp from which air has been driven off while avoiding the admission of further air, and during the cooking process and prior to discharging the pulp from the digester, withdrawing the gases and vapors resulting from the cooking operation from the top of the digester, separating the condensible from the non-condensible portions containing the malodorous constituents without introduction of air, and burning the combustible constituents or said non-condensible portion whereby the malodorous gases are destroyed; the pulp being discharged from the bottom o'f the digester after the gases and vapors have been withdrawn.

DANIEL J. YOUNG.

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