US2406581A

US2406581A - Process of utilizing waste liquors

Info

Publication number: US2406581A
Application number: US488094A
Authority: US
Inventors: Bergstrom Hilding Olof Vidar; Trobeck Karl Gustaf
Original assignee: Individual
Current assignee: Individual
Priority date: 1939-05-20
Filing date: 1943-05-22
Publication date: 1946-08-27
Anticipated expiration: 1963-08-27

Description

il 27, A1946.. H. o. v. BERGSTRM ETAM. 2,406,581

PRocEss oFl UTI'LIzING WASTE mcmomA @uur Waste Li lllg- 27, 1946, H. o. v. BERGSTRM Erm. 2,406,581

` .l PROCESS 0F UTILIZING' "ASTE LIQUOR I 'A Filed Hay 22, A194,25 2 Sheets-Sheet 2 GMW Patented Aug. 2K7, 1946 a l PROCESS OFYUTILIZINGIWAsTEL LIQUoRs Hilding Olof Vidar Bergstrm, Stocksund,Y and Karl Gustaf Trobeck, Stockholm, Sweden i Application May 22, 194aseria1N0; 488,094 In Sweden May 20, 1939 The present invention relates to a process of utilizing wastecellulose liquors and other fluids by means of a particular system of concentration and treatment.

Highly concentrated waste liquors from e. g. the sulfate, sulte or soda pulp processes have a pitch-Iike'consistency, for which reasonthey are unsuitable as a fuel as well as for Atreatments such as dry distillation. i

The present invention, which has for its object to transform liquors of this character into substances suitable rfor combustion, dry distillaition etc., is based on our discovery that highly concentrated liquors, when ejected in a suitable manner, will yielda-more or less porous or finely divided dry product. Y

The ejection, which is made under pressure, is effected by means of nozzles of suitableisize and shape, so th'at a development of steam will take place in the material when thisis released into a room with'lower pressure, e. g. the free airv` or a suitable chamber. f The pressure should thus during the evaporation of the liquid to suitable concentration, e. g. corresponding lto 'l5-95 per cent by Wt. of dry substance, previous to the ejection be kept suiliciently high to produce the effect of flash-heat evaporation or flash drying with steam-expansion within the material when this is ejected.

'I'he ejection may be eifected in various ways and `fromj dilferent depthsrrof the liquor in the evaporatorthe nal evaporator) throughnozzles of 'various types, as this influences upon the structure and consistency of the dry'.V product. The'nozzleor nozzles may thushave a round or oval cross section or may resemble'some other geometrical -gure They may furtheribe of different length andbe made with cut out edges or shaped as la connecting piece, havingy aninward oroutward projecting` conicity, or be provided withV a central core so that the liquor will Ybe ejected in the form of a hollow cylinder, etc. The nozzle may also be shaped vas an injector so that air will be brought into intimate contact with th'e ejected material. Y

As already mentioned, the ejection of the concentrated liquor may be made into the free air vor into a so called cyclone'apparatus or similar chamber, whereby the heat content of the developed steam may, atleast partly, be utilized. In such event it is suitableto operate the cyclone or chamber under a certain elevated pressure. It is not `necessary that the ejection be made directly from the evaporator. The liquor may'instead be conveyed from this into an intermedis Claims. v(o1. 23448) atevcontainer from which it is th'en released in 'some suitable manner for obtaining a product of the desired quality.

If waste sulfate liquor, previous to the evaporation, is treated with air or gases containing oxygen, e. g. smoke stack gases,`the sulfur` containing compounds in the sulfate celluloseV liquor are transformed in such manner that they will not develop hydrogen sulfide during the evaporation, or atleast only minor quantities thereof.

The usual manner in which Waste sulfate cellulose liquor is at present evaporatedcauses great quantities of I-IzS to escape. The kliquor will th'us frequently1 lose from 2 up to as much as 10 kilograms of sulfur calculated on the basis of one ton of cellulose pulp produced, in the form of H2S,

ymercaptanes and organic suliides.. The sulfur loss will partly occur during the evaporation of the `wa'ste'liquo'r to'form so called thick-Ive and partly when .this is Vdried to black stuff. For known reasons losses .of sulfur are, however, notV desired in the process since the regenerated `cooking liquor should contain as much NagS as" possible. If the black liquor (the Wasteliquor from the wood digesting process) is subjected to an oxidizing treatment according to the invention, e. g. by means of air, the sulfur will7 however, become fixed in the liquor whereby the above mentioned losses are reduced to a negligiblev quantity. The oxidation may', of course, take place during some stage of evaporation prior to the final evaporating step if the original waste liquor is not previously treated in this-manner.r

The oxidation may for instance be eiected'by means of air or other oxidizing gases in towers through whichY the liquor ows downwards in contact with the oxidizing medium, or it may take place'in columns with perforated plates or bell bottoms, or in disk evaporators or drums in Wh'ich the Waste liquor is brought into contact with the oxidizing medium. Ifrthe oxidation is carried out in a column the waste liquor should suitably be introduced on one rof the lower places since the liquor will, in general, not flow downy which causes the foam to circulate Within the tank. The foam may also be abated by means of a centrifuge or the like. The oxidation may take place at different-l ternperatures. Increased temperatures will increase the velocity of oxidation. This should, however, not be carried too far since it has been found that a too high degree of oxidation will have an undesired influence upon the organic substance in the liquor.` A certain alkalinity Will also cause the oxidation to take place more rapidly.

By the oxidation of the waste sulfate liquor an increase in the sulfur content of the digesting liquor and a dry product (black stuf) `more suitable for combustion is thus obtained. The consumption of lime in the causticizing process is furthermore reduced, and the condensate and gases formed in the evaporation Will be free or almost free from poisonous substances.r

The oxidation of the Waste liquor may, as alf ready mentioned, be made prior to or during its primary evaporation, i. e. beforeV it is introduced into the nal evaporation step., and may be carried out under ordinary or raised pressure as well as under a vacuum.

Instead of being treated with oxygencontaining gases the Waste liquor may, prior Ato or during the evaporation, be treated with SO2 or .SO2-containing gases, which have a `similar oxidizing effect on the suldic and other reducing sulfur compounds as oxygen, so that evolution of hydrogen sulfide will be prevented.

The dry organic substance obtained in the prevously described manner is suitable for dry-distillation. In the case of organic matter from the sulfate-pulp process, such a dry-distillation will yield oils in an amount corresponding to S-150 kilograms as calculated per ton of cellulose'pulp produced. The dry-distillationr is suitablyr carried out continuously in a stationary retort provided with internal conveying means and may, if desired, be directly combined with a combustion of the residue. The non-condensible gas from the dry-distillation may be ,used as a fuel for the steam boilers or for other purposes, preferably after removal of hydrogen sulfide, mercaptanes etc., for instance by scrubbing with cooking liquor or other liquors usedin thepulping process. The remaining dry-distilled material may be burnt -in .a calcining furnace, or the alkali in the same be extracted by lixiviation or leaching. In the latn ter case the remaining carbonaceous matter may be used as a fuel, if desired after briquetting. The carbonaceous matter as well as the undistilled dry product is suitable for powdered fuel firing.

The evaporation of the Waste liquor'to a very high concentration may be eifected in the following manner. The evaporation is divided into several steps. In the rst step the evaporation is v in a multiple effect evaporating system carried up to for instance Sil-60% dry content. The liquor from this step is introduced in the second step evaporator, in which the concentration may be carried up to for instance 'l0-80%. The temperature in this step is kept at about 110 to 250 C., to permit the liquor to remain suiiiciently easyilowing to ensure an ei'licient heat transfer through theheating surface, whereby the capacity of the equipment will be sufficiently high. 'Ihe evaporation in the second step is suitably made in an evaporator in which the liquor is caused tocirculate over the heating surfaces by means of a pump. From the second step evaporation the liquor is now introduced into the third `step evaporation system which consists of an evaporating apparatus in which superheated steam is brought in direct contact With the liquor, e. g. by being forced directly through the liquor or by being showered with a spray of the same, whereby it is concentrated to such an eX- tent that the product at normal temperature vwill assume a solid state.

In the nal evaporator a constant pressure is automatically maintained and the level of the liquor also automatically regulated by special means.

The concentrating of the liquids coming from the three stages of evaporation may suitably be regulated so that the vapor arising from the third step will as much as possible be adjusted to the steam requirements for the second step, and the vapor from this similarly adjusted to the steam requirements in the first step, or else so that the vapor quantities from the second and third steps Will nearly correspond to the steam requirements in the first step. The vapors from the various steps may, `of course, also be utilized in some other manner. The vapors from the second and third steps may thus, by means ofvheat exchangers, be transformed into pure steam which can be utilized for evaporationV or other purposes.

In certain instances the evaporation in the third step may be carried out at a pressure which is insuificient for permitting an employment of the escaping vapors as a heating medium in the second step evaporation. In such cases the vapors coming from the third step are better utilized in some other way, .steam of sufhciently high pressure, e. g. 8-30 atmospheres, being used in the second step evaporation.

The process may also be carried out in such a manner that the vapors in the third step evaporation are circulated by means of a fan or blower through a superheater and from there back to the liquid. In this case the secondstep evaporation may be entirely dispensed with. That part of the evaporation which is carried out by means of direct steam may be distributedfon several units, the vapor from the first of these being passed through a superheater and vdirectly from there into the liquid in the second unit, and so forth. In this case the above mentioned circulating fan or blower is dispensed with.

The final evaporator, or the apparatus in `which the evaporation is carried out with the vaid of superheated steam, must yloe arranged so that the vapor Will leave thesame saturated .or nearly saturated. The vapor should thus leave at nearly the same temperature as that of the liquor. The ,superheated steam may be introduced into the Yliquid in several Ways. The steam may be injected tangentially or nearly tangentially or in some other` manner whereby the liquid is brought into vigorous motion. The steam introducing means may be placed horizontaly or at an angle with the horizontal. It is important that the superheated steamv be introduced in such a manner that the means of introduction will notA presentany heating surfaces in the liquid, as thisfmay cause decomposition by superheating. The intake for the liquid in the nal evaporator should be arranged at some point higher than the liquid level in the evaporator, so that the fresh liquid ows onto the top level. The pressure in this evaporator should be kept higher than 1.5 atmospheres overpressure (above the atmospheric) e. e. above about 36 lbs/sain. abs. pressure,

is directly obtained by ilash 'drying of the waste l cellulose liquors vrnaliesrit possible to improve and simplify their utilization asa fuel. 'V'Ivhis' may e. g. be -realized in the `following manner. The

' dry product (the so called black' stuff) is burnt in calcining furnaces 'or combustion rooms which may be'built as yvery, large-sized units. 'lhecomI-L bust'ion gases are iirst'brought to act onA av steamjboiler or a tube-system combined with af stearrigenerator and are from there conveyed to as'upere heater for superheating of the steam for'the iinal evaporator. From-*the superheater they pass to the above mentioned steam-generator which'in certaintcases'is combined with the tube-system, and from there to an economizer or similar apparatus. By this arrangement the superheater t will'be exposed vto the stack gases at the most suitable ltemperature (from 900"A C. at the front down to 500 C. near the outletend) V, Itis', namely, very important that the superheater l.is not exposed to excessively -high temperatures, which may cause injuries on the equipment at the Acomparatively low velocities which Ythe steam in the superheater Vsometimes ,vmay assume. r A fairly high temperature'fon the combustion gases at the outlet `end will, on the other hand, make it possible to usea f's'uperheater with a comparatively small heating surface. Special., means should be provided for an automatic injection of steam in the system; inY order to prevent the superheaterffrom being burnt if V the circulating fan`- Vfor the vapor from the final evaporator, which is @conveyed through the, superheater, should break down or stop, v c

Thanks to the fact that thedry product may be easily formed intogbriquets of an evenfsize, it is also possi-ble to use'v this as fuel in a gas-producer in which the combustion may thus me very closely regulated. The briquetting is also of importance when the product is to be dry distilled for the recovery of oils. In this case the calcining furnace may suitably serve for the dry distillation. 1

In the foregoing the invention has chiefly been described as applied for the utilization of waste cellulose liquors, particularly waste sulfate liquor. It should be evident, however that the method may also be applied for the recovery of the dry matter in other liquors, particularly those which by means of evaporation may be brought up to a high content of solids.

Examples of suitable recovery plants operating according to the invention are shown in the accompanying drawings. The evaporators in the rst evaporating step are not shown, as this detail may be arranged according to any known system.V A Y Figure 1 is a plant operating with three evaporating steps, of which the second and third are shown in the drawings. Figure 2 is a plant operating with only two evaporating` steps, of which the last is shown in the drawings. Similar parts carry the same numeral in both gures.

In Figure 1 numeral I denotes the pump by which the partly evaporated liquor coming from the iirst step evaporation is conveyed to the second step evaporator 2, which is provided with a circulating pump 3. Y The iinal evaporation takes place in a container 4 in which superheated steam from superheater 8 is directly forced i 6 through the'- liquor. lThe highly concentrated liquor is ejectedbyy means of the above described nozzles into the chamber in which it is received as adry and porous product. From this chamber the dry product is, by means of the screwconveyer 6, fed into the combustion room 1 in the steam-generating system, comprising the superheater 8, f' d t jThe system 'shown in Figure 1 operates as follows.M Y

The Waste liquor which is to be worked up, is

pre-concentrated in a suitable evaporation syste'mtandby means of pump I conveyed to the tube-evaporator 2 which isiprov'ided with a circulating pump V3. The liquor is further concentrated-inl evaporator 2 and from there'introdu'ced in the final evaporator 4. rator 4 the dry content is brought-upto about 80-95% by means of blowing superheatedsteam directly through the liquor. The highly concentrated liquor is by means of suitable nozzles ejected into the chamber 5 in` which a porous solid is received with a moisture content of about 5%. The vapors from evaporator 4 escape from thisthrough line I I with a temperature of about 18o-220 C., which corresponds substantially to vthe temperature of the liquor in the evaporator,

andare either yled to the boiler system orused as live steam 'a't some suitable point in the plant. The saturated vapors from the catch-all 9 in evaporator 2 are by mean sof line I0 also conveyed to the boiler-system or Vused as lli`ve" steam for other purposes. l'

VYAs already mentioned, the'second ev'aporatingY step may in certain casesv be 'dispensed with. A11 example of this is shown in Figure 2.' The preevaporated liquor is in this case by means vof pump I introduced directly into evaporator 4 in which the final concentration inl directv contact with superheated steam takes place; Part of `the vapors from evaporator 4A are by means ofline I2 conveyed to the superheater'dfrom which they are again returned to evaporator`4 in the form of superheated steam with a temperature of about 300-500 C. The bleeder-line II is conected to the boilers or other apparatus, e. g. the primary step evaporators. The quantity of steam through line II is adjusted to correspond to the evaporation in evaporator 4, so that a constant pressure will be maintained in this, the steam in line I2 being re-circulated as already described.

We claim:

1. A process of utilizing waste cellulose liquors comprising subjecting the liquor to evaporation in at least two steps, the concentration of the liquor in the last step being conducted under superatmospheric pressures and being carried to a solids content of about to 95% so that the liquor will assume a solid state at normal temperature, ejecting said liquor in av iinely divided state from the last step of evaporation, while at a temperature of about to 220 C. and while under superatmospheric pressure, under release of pressure so that flash drying takes place and collecting the resulting dry porous product thus received.

2. A process of utilizing waste cellulose liquors, l

solids content of about 80 to 95% so that the almas@ `terat-ura` ejecting `said concentrated liquor in a finely dividedjstata While'at a temperature Vof about180 to 220 C. and While under superatmospheric pressure, under release of pressure so that flash drying Vtakes place and collecting the dry -porous product thus received.

3. A process according to claim 2' in which part of the vapors from the last evaporation step are circulated through a superheater and again brought `in direct contact with the liquor in said step to serve as a means of evaporation.

`4:. A process of utilizing waste sulfate liquor, comprising subjecting the lliquor to evaporation in at least two steps, concentrating the liquor in the last `step under superat-mospheric pressures to a solids-content of about 80 to 95% so that it Willfassume a solid state when .cooled to normal temperature,-ejecting said concentrated liquor ina finely divided state, while at a temperature ofabout 180 to220 C. and while under superatrnospheric pressure, under Yreduction of pressure so that flash drying takes place, collecting the-dry lporous product received land dry-distilli-ng lthe, same.

5. A process for'the recovery Vof Waste cellulose liquorscomprising concentratingthe Waste liquor by a multi-stageevaporation, the last evaporation stage consisting in4 bringing superheated steam in direct contact with a pre-concentrated liquor containingat least 70 per cent solids, 'bringing the concentration up toA at least 80 per cent solids While maintaining at least 36 lbs. per sq. in. absolute pressure in therevaporator and a temperature of at least 110 C., ejecting the concentrated liquor in a finely divided state Aunder a sudden pressure drop so that flash drying takes place Within the ejected material, and collecting the dry porous product thus obtained.

6. A process of utilizing Waste sulfate liquor which comprises concentrating the liquor while contacting it with an oxidizing gas in quantity sulicient tosubstantially A,eliminate evolutionof hydrogen sulfide during ys ubseqllent evaporation to-dryness, then concentrating the oxidized liquor to a solids content of from about 8,0 to per cent While under'superatniospheric pressures and at a temperature of about Yto 220 C., ejecting said concentrated `liquor in a viinely divided Astate into aspacemaintained at substantially atmospheric pressure, so that flash drying to a porous solid takes place, Withoutsubstantial evolution of hydrogen sulde, `and collecting said solids.

'7. A process of utilizing Waste rsulfate liquor which"V comprises concentrating ther liquor while contacting it with. air in quantity sufficient to substantially eliminate Aevolution of hydrogensulfide during subsequent 4evaporation to dryness, then concentrating the oxidized liquor to asolids content of vfrom about 80 to 95 per cent -While under superatmospheric pressures Vand ,at a temperature of -about180 to 220 C., ejecting said concentrated liquor in a finely divided state into a spacemaintained :at-substantially atmospheric pressure, so that :dash drying to a porous solid takes place, without substantial evolution of hydrogen sulfide, and collecting said solids.

,8. .A .process of utilizing Waste sulfate liquor which .comprisesconcentrating the liquor while contacting it with sulfur dioxide in quantity sufficient to substantially eliminate evolution of hydrogen sulfide during subsequentvevaporation to dryness, then concentrating the oxidized liquor to a `solids content of from about 80 to 95 per cent while under superatmospheric pressures and at atemperature of about 180 to 220 C., ejecting said .concentrated liquor 4in a nely divided state into a Vspace maintained at substantially atmospheric pressure, so that flash drying to a porous solid takes place, Without substantial evolution of hydrogen sulfide, and collecting said solids.

vHI/LDING OLOF VIDAR BERGSTRM. KARLGUSTAF TROBECK.