CA1112817A - Pyrolysis of spent pulping liquors - Google Patents

Abstract

PYROLYSIS OF SPENT PULPING LIQUORS

ABSTRACT OF THE DISCLOSURE
The present invention discloses a process of pretreat-ing a waste black liquor which results from the pulping of vari-ous vegetative fibers and wherein the pulping liquor contains as its active pulping ingredient sodium and sulfur with the pretreatment taking place prior to the subjecting of the waste black liquor to a hydropyrolysis reaction. The method and the materials used in the pretreatment are derived from the reac-tion products resulting from the hydropyrolysis reaction. The pretreatment serves to enable one to regenerate the inorganic chemical values to a pulping liquor in an easy and economical manner and the pretreatment, also, serves to appropriately ad-just the physical and chemical characteristics of the char pro-duced in the hydropyrolysis reaction. This is accomplished primarily by utilizing the products resulting from the hydro-pyrolysis reaction.

Description

1$1;~ '7 1 The hydropyrolysis of spent pulping liquors result-ing from the pulping of various vegetative fibrous structures is known in the art. Hydropyrolysis involves the heating under high temperatures and pressures for various time intervals, the spent or waste pulping liquor which produces a reaction product which includes a char-slurry mixture and various uncondensable organic gases The objective in hydropyrolysis is to separate the organic values from the inorganic values in the waste li-quor. The inorganic values are normally used in the regenera-tion of a pulping liquor and the organic values are used for the generation of energy or the production of other useful pro-ducts. One of the other useful products which may be produced from the organic values is activated carbon In the so-called kraft pulping process, wood of var-ious species is reacted with an aqueous solution of sodium hy-droxide and sodium sulfide, which are the active ingredients, and lesser amounts of sodium carbonate, sodium sulfate and other salts which fail to convert to active ingredients in the chemi-cal preparation steps of the pulping chemicals. In the hydro~
pyrolysis of kra~t waste black liquor the object is to separate the sodium and sulfur rom the organic materia]s derived from the wood and to recover the sodium and sulfur in forms suitable for the regeneration of the pulping chemicals.
The present invention teaches a process of pretreat-ing the incoming waste black liquor ~rom the kraft pulping pro-cess with chemicals derived from the hydropyroloysis reaction, so that the filtrate which is separated from the char produced as a result of the hydrop~rolysis reaction, is more like the so-called green liquor from the conventional process. The pre-treatment of the waste black liquor adjusts the nature of the

-2-'7 1 green liquor so that it can be converted to the so-called white liquor The conversion of the green liquor to the white li-~uor is made primarily by reacting lime (Ca(OH)2) with the green liquor, which includes sodium carbonate and sodium bicarbonate, to produce sodium hydroxide and c~lcium carbonate.
The pretreatment of the waste black liquor prior to its entering the hydropyrolysis reaction, also, affects the physi-: cal characteristic of the final char produced. For the sake of example only, without the pretreatment of the present invention ~he resulting char may be very unmanageable in the sense that it may be quite viscous or sticky, With the pretreatment, theproblems are obviated, In some instances the char, which is produced by the hydropyrolysis reaction, contains too high a percentage of sodium which leaves too much ash in the furnace in the event it is burned as fuel The present invention discloses a method of generating a chemical to wash the sodium from the char which chemical is a product of the hydropyrolysis reaction The present disclosure, by way of pointing out one of the best modes of carrying out the teachings of the present invention, portrays the invention as it ~pecifically relates to the treatment of spent liquors from a kraft pulping process;
however, it will be apparent to those skilled in the art that the invention as equally relates to improvements in those hy-dropyrolysis reactions where waste liquor is treated which uti-lizes sodium and sulfur compounds as pulping agents Such other p~ocesses include, but are not limited to:
1. The polysulfide pulping process, in which a portion of the sulfur is present as polysulfide~ ~a2Sx~

~$~83.'7 1 2. The hydrogen sulfide pretreatment pulping process, in which at least a portion of the sulfur in the form of hydrogen sulfide gas is impregnated into the wood prior to heating with an alkali,

3. The sulfite pulping process, in which the pulping mixture contains sodium sul~ite and free sulfur dioxide. Base elements other than sodium may be ' employed such as calcium, magnesium or ammonia.

4. The bisulfite pulping process, which employs sodium (or calcium, magnesium, ammonium) bisulfite and no excess sulfur dioxide.

5. The neutral sulfi~ semichemical process, which uses sodium (magnesium, ammonium) sulfite buffered with sodium carbonate.
60 The green liquor semichemical process, which uses sodium carbonate and sodium sulfide.
All of the above pulping processes and the many other variants and hybrid processes can be used to pulp materials other than wood. The starting material may be sugar cane ba-gasse, straw, reeds, grasses, flax or any ~egetative fibrous structure. In every case, pulping results in a spent liquor containing dissolved organic matter and the constituents of the pulping solution. Hydropyrolysis is applicable to process-ing all of these spent liquors, and the improvements disclosed .

'7 1 in the present disclosure are applicable in all instances to the waste liquors discussed.
Other objects and a fuller understanding of this inven-tion may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which: -Figure 1 is a flow sheet illustrating the teachings of pretreating the waste black liquor from a kraft pulping pro-cess with a material produced from the hydropyrolysis reaction and includes the acid washing of the char to reduce the sodium content;
Figure 2 is a flow sheet similar to Figure 1, but sh~wing an em~ddiment of the invention which omits the acid washing of the char;
Figure 3 is a flow sheet illustrating a modification of the invention illustrated in Figures l and 2 and shows an improvement in the pressure reduction system reducing the pres-sure of the material leaving the hydropyrolysi~reactor with Figure 3 omitting the acid washing of the char; and Figure 4 is a flow sheet combining the pressure re-duction system shown in Figure 3 and the acid washing of thechar illustrated in Figure 1.
The improvements to which the present invention re-late~ will be specifically described in conjunction with the pretreatment of waste black liquor from the kraft pulping pro-cess prior to the liquor being subjected to a hydropyrolysis reaction. The treatment is made by materials produced from the products of the hydropyrolysis reaction. In the process dis-closed in the f~ow sheet of Figure 1, waste black liquor from a kraft pulping mill at about 25 percent s~lids is treated by '7 1 mixing it with the NaHSO3-Na2SO3 solution leaving the acid wash stage of the filtration and acid washing system. The black liquor is then introduced into a heat exchange system under a pressure of about 3000 psig, heated to a temperature in the range of from 630 F to 640 F, reacted, cooled to about 250 F
and separated into a vapor and a char-slurry product. The char-slurry product is then separated into a char and a liquid (fil-trate) and the char is then washed in two stages with water and in one stage with the acid stream leaving the sulfur recovery system.
The vapor product is separated into a condensate and a gas. The gas is then burned or combusted so that energy and sulfur can be recovered. The liquid (separated from the char product) can then be sent to a clarifier and from it a fil-trate results, essentially free of undissolved carbon, which is then reconstituted to an effective pulping liquor.
Referring specifically to the flow sheet shown in Figure 1, it will be seen that waste black liquor from a kraft pulping process is introduced through 21 into a treatment tank 20, which is mechanically agitated and from there the black liquor (through 25) is introduced into hydropyrolysis reactor 30 by means of a transfer pump 22, a high pressure pump 24 and through a cross heat exchanger 26 and a preheater 28. The conditions and parameters of the hydropyrolysis reaction per se are known to thoseskilled in the art and aredisclosed inUnited StatesPatent No. 3,762,989 issued October 2,1973, in the name of Winfried G. Timpe. The incoming waste black liquor is pretreated ~ 6-rr'7 1 in the treatment tank 20 with chemicals produced from the hydro-pyrolysis reaction. The pretreatment chemicals will be discussed hereinafter.
Under normal circumstances the waste black liquor en-- tering the system from the kraft mill will be that coming from the soap skimmer and normally will have a temperature in the range of from 1800 F to 2000 F. The material is added to pre-treat the waste black liquor in treatment tank 20, It is pre-ferable that the treatment tank be designed to provide a hold-ing time of on the order of thirty minutes for the pretreat-ment of the waste black liquor. The high pressure pump 24 is designed to increase the pressure of the pretreated waste black ; liquor to a pressure in the range of from 1000 to 3500 lbs. per square inch, The operating pressure is controlled higher than the pressure of saturated steam at the chosen operating temper-ature in order to prevent flashing of the liquid. The cross heat exchanger 26 utilizes the product stream from the hydro-pyrolysis reactor 30 to bring the incoming waste black liquor up to an intermediate temperature and a final preheater 28 serves to bring the waste black liquor up to the reaction tem perature, which is in the range of from 490O F to 700O F and to a preferable range of from 6300 to 6400 F.
The reactor 30 has been indicated only generally on the flow sheet and the preferred type of reactor is a tubular-flow reactor; however, by the same token a stirred-tank reactor might be utilized or a plurality of such reactors in series, The feed of the strea~ entering the reactor may be on the order of 610 F and at this temperature, the reaction rate is nor-mally rapid enough to insure a reasonable residence time require-ment, The preferred residence time of the black liquor within `7 1 the reaction zone is on the order of from 3 minutes to 3 hours to obtain the required results.
The reaction product leaving the reactor 30 is passed through the cross heat exahanger 26 by way of 31 to heat the incoming waste black liquor traveling to the hydropyrolysis re-actor 30 and from there it is passed through a slurry cooler 32 and cooled down by co~ling water which is passed through the cooler in heat exchange relationship as indicated. The temp-erature is reduced to in the range of from 150 F to 3000 F at a constant pressure which is about that of the reactor 30. The reaction product includes a char-slurry mixture as well as noncondensable organic gases formed during the hydropyrolsi~s re-action~ The reaction products stream is next passed through a pressure letdown valve 34 and intr~duced into a flash gas se-parator 36. For the sake of example, the reaction;; products stream, in passing through the pressure letdown valve 34, is reduced from about 2800 psig to about 4 psig. The action of the pressure letdown valve 34 is normally controlled by sensing the pressure of the waste black liquor stream between the high pressure pump 24 and the reactor 30. The flash gas separator 36 should operate at atmospheric pressure and as a result when the reaction product enters the separator 36, it is flashed at atmospheric pressure and the char-slurry mixture leaving the bottom of the flash gas separator 36 through line 45 is cooled to on the order of about 212 F. The noncondensable gases formed in the hydropyrolysis reaction and some water vapor leave overhead from the flash gas separator 36 through line 47.
It is desirable, therefore, that there should be interposed some type of flash separator to receive these vapors and con-dense whatever condensable materials (such as water) are car-'7 1 ried overhead by the flashing. Such a flash separator has notbeen shown in Figure 1, but will be appreciated by those skilled in the art.
A portion of the noncondensable organic gases produced in the hydropyrolysis reaction which pass overhead are com-busted at 39 in the preheater 28 and serve the purpose of add-ing extra energy to the waste black liquor to bring it up to the desired reacticn temperature when it enters the reactor 30.
The rest of the gases are combusted in a boiler to produce steam. The burning or combustion of these noncondensable gases produces a mixture of gases which include sulfur dioxide, car-bon dioxide and nitrogen~ The noncondensable organic gases leaving overhead from the flash gas separator 36 and traveling to the preheater 28 include methane, ethylene, ethane, hydro-gen sulfide, propane, CH3SH, C4H12, C2H50H and (CH3)2S.
The gases of combustion which result at 39 in the pre-heater 28 are transported by way of line 42 and are introduced into the bottom of an SO2 absorber 41. These gases include SO2, CO2, and N2. The S02 absorber should be some type of contact tower which is satisfactory to absorb the S02 gas into a con-centrated wash solution emanating from the char-slurry end of the system. In point of theory either a packed or tray tower is satisfactory to accomplish this end result.
The char-slurry mixture which is removed from the bot-tom of the flash gas separator 36 is transported through line 45 to a first vacuum filter 44 where the filtrate is removed from the char through 52. The filtrate from filter 44 includes a concentrated solution comprising Na2C03 and NaHCO3. The char is washed by wash water from line 46 which wash water originates from a fresh water source which washes the char at a second l filter 48. The washing of the char at the first filter 44 produces a weak filtrate having the same chemical components as the filtrate leaving line 52, which is transported through line 49 to the top of the SO2 absorber 41 where it is inter-mixed with the S02 gases from the preheater 28. The intermix-ing of the SO2 gases with the weak filtrate from filter 44 pro-ceeds generally along the line of the following reaction:

Na2C03 ~ S~2 > Na2S03 ~ C2 Ma2SO3 + S2 + H2O >2NaHSO3 This SO2 treated weak filtrate is then taken from the bottom of the SO2 absorber through line 50 and introduced into what is referred to as an acid repulp tank 51 which tank also receives the char from filter 44. The acid repulp tank 51 is -~
mechanically agitated and the purpose of mixing the char with the above described material from the S02 absorber is to remove sodium retained in the char. The reason fo~r removal of the so-dium from the char is that in the eJent of the sodium content of the char is quite high and the char is to be used as a fuel, the removal of the sodium at this point reduces the amount of ash resulting ~rom the burning of the char.
The char-slurry mixture from the acid repulp tank is next ~ansferred through line 53 to the second filter 48 where the filtrate is separated from the char and the char is washed again from the fresh water source and is then passed on for fur-ther processing. The filtrate passing through the second fil-ter 48 is t~ans~erred through line 55 to the treatment tank 20 where it is utilized to pretreat the incoming waste black liquor which is subsequently transported to the reactor 30 where it undergoes the hydropyrolysis reaction. The !mechanism of removal of the sodium from the char in the acid repulp tank 1 51 is thought to be essentially a reaction of the sodium bi-sulfite produced in the S02 absorber with a "sodium" group on the char to convert the "sodium" group on the char to an "OH"
group with a subsequent conversion of the sodium bisulfite to sodium sulfite The reason for the pretreatment of the waste black liquor prior to its entering the hydropyrolysis reaction is to bring the ~a2S concentration of the filtrate leaving the ~ilter 44 through 52 up to an acceptable level so that with the addi-tion of the proper chemicals the filtrate from 44 can be con-verted from a green liquor to a white liquor suitable for thepulping of wood products in accordance with kraft pulping pro-cess technology. The conversion of the filtrate from filter 44 is essential~y effected by reacting lime with the filtrate.
Under normal circumstances only about 85% of the required sulfur for pretreatment is produced by burning the uncondensable or-ganic gases at 39. The additional 15% required ~an be added to ~: the gas stream in line 47 as elemental sulfur which can, also, be burned at 39.
:~ The concept of direct absorption of S02 gas resulting from the combustion of various sulfur bearing gases into the waste black liquor can be utilized in pretreating the liquor but this concept is undesirable because it is also necessary to absorb carbon dioxide in the combustion gases and this is unde-sirable because if carbon dioxide is absorbed it reduces t~ pH
which tends to precipitate lignin from solution When this hap-pens the lignin tends to clog the piping which is undesirbble, In the present disclosure carbon dioxide produced in the combustion in the preheater 28 is avoided in the black li-quor because when the combusted gases are transmitted to the L ;~

1 SO2 absorber, the carbon dioxide simply passes out the stack 43 of the absorber because it is not absorbed in the weak filtrate coming from filter 44 through l.ine 49.
In order to assist those skilled in the art in prac- :
ticing the invention a material balance at various places in the flow sheet of Figure 1 is given below in Table I. This ma-terial balance is given when a pH of 3.1 is present in the li-quid flowing in lines 50 and 55 This materialbalance will change with a change in pH of stream 50. Amounts below are given in weight percent TAB~E I

TOTAL FLOW
LOCATION SOLIDS Na S C(lbs/hr) 21 25.00 5.55 0.79 10.70400.00 11.10 2.96 4.14 0.8365.97 23.03 5.20 1.27 9.31465.97 49 10.03 3,01 1,37 1.2267.78 42 93.41 -- 2.51 2.25101~41 43 91.09 -- 0.0052.45101.41 ; 50 13.49 3.01 5.12 0 9267.78 31 23 03 5.19 1 27 9.31465.97 47 -- -- -- -- 11.97 22.07 5 25 0 78 8 96454 00 It will, thus, be seen from the above discussion of the invention in conjunction with Figure 1 that within the closed system disclosed, a new and novel means has been provid-ed for pretreating the waste black liquor which is to undergo the hydropyrolysis reaction, which pretreatment produces a fil-trate that can be conveniently treated to put it in condition to be used as a pulping chemical and, also, serves to adjust '7 1 the characteristics of the char produced in the hydropyrolysis reaction so that it is in its most convenient form. This con-cept is accomplished by taking the noncondensable organic gases resulting from the hydropyrolysis reaction, burning the same to produce heat which can be used in r,aisin,g the black liquor to the hydropyrolysis reaction temperature, and then conducting the gases of combustion to an absorber where S02 is absorbed into a filtrate resulting from the washing of the char produced in the hydropyrolysis reaction, This absorption produces a mixture of sodium bisulfite and sodium sulfite which is intr~duced di-rectly into the waste black liquor to pretreat the same or be-fore int~roduction into the waste black liquor is utilized by mixing it with the char to reduce the sodium content of the char and is subsequently introduced into the waste black liquor to pretreat.
Figure 2 of the drawings is an illustration of the present invention where the sodium content of the produced char is such that it is at an acceptable level. In this instance it is not necessary to wash the char with the product produced in the S02 absorber and under these circumstances the sodium 20 bisulfite produced in the S02 absorber 41 is directly introduced into the waste black liquor in the treatment tank 20 by way of line 58. Under these circumstances the flow sheet of Figure 2 differs from Figure 1 in that the acid repulp tank 51 and the second filter 48 have been deleted. In other respects, the sys-tem is the same in that the char-slurry product from the bottom of the flash gas separator 36 is passed ~rectly to filter 44 producing a filtrate as indicated. The char as separated from the filtrate is washed with fresh water producing a weak fil-trate which is transported to the S02 absorber 41 by way of line - . . ~

l 49 where it absorbs and reacts with the S02 from preheater 28 to produce the sodium bisulfite.
The flow sheet of Figure 3 illustrates an improve-ment in the processes illustrated in Figures 1 and 2 and is best compared with flow sheet of Figure 2 to aid in an under-standing of the impr~vements made in Figure 3. The improvement of Figure 3 is in the pressure reduction system for reducing to atmospheric pressure the char-slurry reaction product leaving the reactor 30 The system of Figure 3 improves the char-slurry composition which in Figure 2 leaves the flash gas se-parator 36 through line 45. The improvement resulting in theprocess illustrated in Figures 3 and 4 produces advantageous results in that it reduces the organic carbon content in the filtrate which is regenerated to produce a kraft pulping li-quor and, also, reduces the sodium bicarbonate level in the filtrate. Additionally,the sulfur level is reduced in the char which is quite advantageous in that when the char is utilized as a fuel, the amount of S02 resulting from burning is reduced.
Referring specifically to Figure 3, the same identi-fying numbers have been applied to the components in Figure 3 that have been shown in Figures 1 and 2 and which are the same;
however, when variations in the structure have been utilized, new identifying numerals have been utilized.
It will be seen that the reaction product exiting the hydropyrolysis reactor 30 is transferrred by way of line 61 in-to the cross heat exahanger 26 where a portion of its heat is given up to the waste black liquor prior to the liquor being subjected to the hydropyrolysis reaction. The cross heat ex-changer shown herein is slightly different than illustrated in Figures l and 2, but for all intents and purposes it is the sa~e and so, therefore, the same reference numeral has been ~ -14-1 used in identifying this element.
After the reaction product exits the cross heat ex-changer 26 it travels to what has been identified as a first or number one pressure letdown valve 62 from whence it is intro-duced into a flash gas separator 64 sometimes referred to as a flash tank. A reduction in temperature and pressure results when the reaction products pass through the pressure letdown valve number one and are introduced into the flash gas separa-tor 64. The temperature reduction is on the order of from 0 F
to 4000 F and the pressure reduction is on the order of from 500 to 3000 psig depending upon the pressure of the hydropyrol-ysis reaction taking place in the reactor 30. As the reaction products are introduced into the flash gas separator 64 at the high temperatures indicated and under only partial pressure re-duction extensive flashing of the reaction products and a wet calcination reaction of sodium bicarbonate results, The flash-ing and wet calcination reactlon reduce the temperature on the order of those referred to above, The flashing vapor overhead is vented through line 63 to what has been referred to as pressure letdown valve number two 70. It is sometimes desirable to reduce the temperature of the flashing vapor and to the extent that the vapor need be cooled, a cooler 67 has been interposed in line 63. The second pressure letdown valve 70 reduces the vapor pressure to about atmospheric pressure in a condenser 72 and the condenser 72 serves the purpose of separating the noncondensable gases from the condensable liquids which comprise primarily water, The noncondensable gases are then transmitted by way of line 47 to the preheater 28 where they are burned at 39 in the manner in-dicated in the discussion of Figures 1 and 2.

1 The bottoms from the flash gas separator 64 which com-prise primarily the char-slurry mixture are traveled through line 68 and preferably through the cross heat exchanger 26 to assist in heating the incoming waste black liquor prior to its entering the hydropyrolysis reactor 30. After the heat exchang-er the char-slurry mixture is cooled to a desired temperature in the slurry cooler 32 to a temperature of on the order of from 1200 to 2120 F, The char-slurry is then passed through pres-sure letdown valve number three 79 and iintroduced to vacuum filter 44 where the filtrate is separated from the char and the char is washed by a source of fresh water.
The pressure reduction system illustrated in Figure 3 acts at high temperatures (400O to 700O F) and high pressures (1000-6000 psig), These high temperatures and partial pressure reduction cause flashing and a partial wet calcination reaction.
The flashing appears to strip volatile organics and volatile sulfur compounds from the slurry, The wet calcination decom-poses the sodium bicarbonate in the slurry to sodium carbonate.
The hi~h temperature of the initial pressure reduction causes the wet calcination reaction to proceed very quickly. The main decomposition reaction is believed to be:

2NaHC03 ~ Na2CO3 + H2O + C2 As mentioned above, this flashing procedure and wet calcination improves the filtrate and char produced in that the organic c~r~bon and sodium bicarbonate in the filtrate are great-ly reduced and the sulfur level in the char is reduced, These improvements are important to a hydropyrolysis recovery system, because it is desirable to remove as much or-ganic carbon and sodium bicarbonate from the filtered mother li-. .

1 quid (filtrate) as possible. The filtrate is returned to the mill operation for treatment to regenerate it into a pulping liquor and lowering the bicarbonate level reduces the amount of treatment that has to be used to regenerate the filtrate into a pulping liquor. The organics in the filtrate represent an unnecessary recirculation of materials and this the reason ~or reducing the organics. Reduction in the sulfur level of the char is desirable particularly where the char is used by burning as a fuel.
A typical operation utilizing the modified pressure reduction system shown in Figure 3 is illustrated in Table II
below, In this case there was no slurry temperature reduction prior to the initial pressure reduction and the temperature was on the order of 6000 F. The pressure was reduced 1000 psig into the flashing tank from a pressure of about 2500 psig, The flashing and wet calcination reduced the slurry temperature 50 F. The falshing operation concentrated the slurry but the filtrate still enjoyed a 1,7% reduction in organic carbon and a better than 20% decomposition of the sodium bicarbonate to so-dium carbonate. The char produced had its sul~ur level de-creased by 17.9%.

T~BLE II

Without Pressure Reduction of Fiqure 3 Fil~rate - 2,37% organic carbon Filtrate _ 50.88 g/l ~a2Co3 Filtrate - 71.57 g/l ~aHCO3 Unwashed char - 3.13% Sulfur (DW~) With Pressure Reduction of Fiqure 3 Filtrate - 2.33% organic carbon Filtrate _ 76.32 g/l Na2C3 Filtrate - 56.50 g/l NaHC03 Unwashed Char - 2.57% Sulfur (DWB) hP~`7 1 Figure 4 illustrates the pressure reduction system shown in Figure 3; however, it illustrates the incorporation of the pressure reduction system into the system found in Figure 1, namely, the acid washing of the char that is produced in the hydropyrolysis reaction with the acid washing being accomplished by the sodium bisulfite produced in the SO2 absorber 41. In all other respects, the pressure letdown system operates in the same manner as the system shown in Figure 3 and the acid wash-ing of the char is accomplished as illustrated in Figure 1.
It will, therefore, be readily appreciated by those skilled in the art that the present invention discloses a unique process and system i-or pretreating the waste black liquor ema-nating from a process wherein any of various vegetative fibers may be digested by a pulping liquor wherein the pulping liquor's main active ingredients are sodium and sulfur. The waste black liquor is conveniently treated by chemicals produced as products of the hydropyrolysis reaction and by means of the pretreatment pulping chemicals recovered can be more easily and economically regan~rat~ to a pulping liquor and the physical and chemical nature of the char and subsequent products produced from the char can be controlled within meaning$ul bounds While we have illustrated and described a preferred embodiment of our invention, it will be understood that this ; is by way of example only and not to be construed as limiting.

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPER-TY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In the hydropyrolysis reaction of waste liquor resulting from the pulping of a vegetative fibrous structure which hydropyrolysis reaction includes the heating of the li-quor under high temperatures and pressures to produce a re-action product including a char-slurry mixture, the improvement comprising the process of reducing the pressure of the reaction product to a pressure lower than the pressure of the hydropyrol-sis reaction which causes nondondensable organic gases to vapor-ize and separate from the char-slurry mixture, combusting the non-condensable organic gases, separating the char-slurry mix-ture into a first filtrate and a char, washing the char with wash water to produce a second filtrate containing the washable material from the char, mixing the second filtrate with the products of combustion of the noncondensable organic gases to produce a treated second filtrate, and mixing the treated sec-ond filtrate with the gases liquor prior to its subjection to the hydropyrolysis reaction.

2. In the process as claimed in Claim 1, the step of washing the char with the treated second filtrate prior to mix-ing the treated second filtrate with the waste liquor.

3. In the process as claimed in Claim 1, wherein the pressure of the reaction product is reduced to about atmospheric pressure in one stage.

4. In the process as claimed in Claim 1, wherein the pressure of the reaction product is reduced to about atmospheric pressure in a plurality of stages.

5. In the process as claimed in claim 3, wherein heat from the combustion of the noncondensable gases is used to heat the waste liquor prior to its undergoing the hydropy-rolysis reaction.

6. In the process as claimed in Claim 4, wherein heat from the combustion of the noncondensable gases is used to heat the waste liquor prior to its undergoing the hydropyroly-sis reaction.

7. In the process as claimed in Claim 5, the step of washing the char with the treated second filtrate prior to mix-ing the treated second filtrate with the waste liquor.

8. In the process as claimed in Claim 6, the step of washing the char with the treated second filtrate prior to mix-ing the treated second filtrate with the waste liquor.

9. In the process as claimed in Claim 3, the step of washing the char with the treated second filtrate prior to mixing the treated second filtrate with the waste liquor.

10. In the process as claimed in Claim 4, the step of washing the char with the treated second filtrate prior to mix-ing the treated second filtrate with the waste liquor.

11. In the process as claimed in Claim 5, wherein one of the products of combustion is sulfur dioxide and wherein the second filtrate includes sodium carbonate which when mixed with the sulfur dioxide produces sodium bisulfite which is mixed with the waste liquor to pretreat the same prior to the hydropyrolysis reaction.

12. In the process as claimed in Claim 6, wherein one of the products of combustion is sulfur dioxide and wherein the second filtrate includes sodium carbonate which when mixed with the sulfur dioxide produces sodium bisulfite which is mixed with the waste liquor to pretreat the same prior to the hydro-pyrolysis reaction.

13. In the process as claimed in claim 11, wherein the sodium bisulfite is used to wash the char to reduce the so-dium content of the char and to produce sodium sulfite prior to being mixed with the waste liquor to pretreat the same prior to the liquor undergoing the hydropyrolysis reaction.

14. In the process as claimed in Claim 12, wherein the sodium bisulfite is used to wash the char to reduce the so-dium content of the char and to produce sodium sulfite prior to being mixed with waste liquor to pretreat the same prior to the liquor undergoing the hydropyrolysis reaction.

15. In the hydropyrolysis reaction of waste liquor resulting from the pulping of a vegetative fibrous structure which hydropyrolysis reaction includes the heating of the li-quor under high temperatures and pressures to produce a reac-tion product including a char-slurry mixture, the improvement of reducing the organic carbon and sodium bicarbonate content of the liquid component of the char-slurry mixture and reduc-ing the sulfur content of the char including the steps of: intro-ducing the reaction product into a first separation chamber through a first pressure reducing valve to reduce the pressure a first amount and whereat vapors pass overhead and the char-slurry mixture is removed from the the bottom, introducing the vapors which pass overhead from the first separation chamber into a second separation chamber through a second pressure re-ducing valve to reduce the pressure a second amount to about atmospheric pressure and in the second separation chamber non-condensable organic gases pass overhead and condensable materi-als are removed from the bottom, transporting the char-slurry mixture to a first filter through a third pressure reducing valve which reduces the pressure to about atmospheric pressure and at said first filter the char is separated from the slurry to produce a filtrate which is usable in producing a pulping liquor.

16. In the hydropyrolysis of waste black liquor from a kraft pulping process wherein the liquor is passed through a cross heat exchanger under pressure and thereafter to a reactor where it is reacted at a temperature of from about 490° F to 700° F and a pressure of from about 1000 to 3500 psig for a time of from about 3 minutes to 3 hours to produce a reaction product including a char-slurry mixture and the reaction pro-duct is passed through the cross heat exchanger to heat the liquor prior to its introduction into the reactor, the improve-ment comprising introducing the reaction product into a flash gas separation chamber through a pressure reducing valve to re-duce the pressure and whereat noncondensable organic gases pass overhead and the char-slurry mixture is removed from the bottom, burning the noncondensable organic gases to preheat the liquor prior to its entering the reactor which burning produces gases including sulfur dioxide, transporting the sulfur dioxide gas and introducing it into the bottom of an absorber, trans-porting the char-slurry mixture from the bottom of the flash gas separation chamber to a first filter where the char is se-parated from the slurry to produce a filtrate which is usable in producing a kraft pulping liquor, washing the char with wash water to produce a weak filtrate which is transported to the top of the absorber and in the absorber is intermixed with the sulfur dioxide to produce sulfur dioxide absorbed filtrate, washing the char from the first filter with the sulfur dioxide absorbed fil-trate from the absorber, separating the char from the sulfur dioxide absorbed filtrate at a second filter and then mixing the sulfur dioxide absorbed filtrate with the incoming waste black liquor prior to the waste black liquor being introduced into the cross heat exchanger, and washing the char with the wash water prior to the wash water being used to wash the char initially to produce the weak filtrate.

17. In the hydropyrolysis of waste black liquor from a kraft pulping process where the liquor is reacted in a reaction zone under a temperature of from about 490° F to 700° F and a pressure of from about 1000 to 3500 psig for a time of from about 3 minutes to 3 hours to produce a reaction pro-duct including a char-slurry mixture, the improvement of reduc-ing the organic carbon and sodium bicarbonate content of the liquid component of the char-slurry mixture and reducing the sulfur content of the char including the steps of: introducing the reaction product into a first separation chamber through a first pressure reducing valve to reduce the pressure a first amount and whereat vapors pass overhead and the char-slurry mixture is removed from the bottom, introducing the vapors which pass overhead from the first separation chamber into a second separation chamber through a second pressure reducing valve to reduce the pressure a second amount to about atmos-pheric pressure and in the second separation chamber noncon-densable organic gases pass overhead and condensable materials are removed from the bottom, transporting the char-slurry mix-ture to a first filter through a third pressure reducing valve which reduces the pressure to about atmospheric pressure and at said first filter the char is separated from the slurry to produce a filtrate which is usable in producing a kraft pulping liquor.

18. In the hydropyrolysis of waste black liquor from a kraft pulping process where the liquor is reacted in a reac-tion zone under a temperature of from about 490° F to 700° F
and a pressure of from about 1000 to 3500 psig for a time of from about 3 minutes to 3 hours to produce a reaction product including a char-slurry mixture, the improvement comprising in-troducing the reaction product into a first separation chamber through a first pressure reducing valve to reduce the pressure a first amount and whereat vapors pass overhead and the char-slurry mixture is removed from the bottom, introducing the vapors which pass overhead from the first separation chamber into a second separation chamber through a second pressure reduc-ing valve to reduce the pressure a second amount to about at-mospheric pressure and in the second separation chamber non-densable organic gases pass overhead and condensable materials are removed from the bottom, burning the noncondensable organ-ic gases from the second separation chamber to preheat the li-quor prior to its entering the reaction zone which burning pro-duces gases including sulfur dioxide, transporting the sulfur dioxide gas and introducing it into the bottom of an absorber, heating the liquor prior to its introduction into the reaction zone with the char-slurry mixture from the bottom of the first separation chamber, transporting the char-slurry mixture after its use in heating the liquor to a first filter through a third pressure reducing valve which reduces the pressure to about at-mospheric pressure and at the first filter the char is separ-ated from the slurry to produce a filtrate which is usable in producing a kraft pulping liquor, washing the char with wash water to produce a weak filtrate which is transported to the top of the absorber and in the absorber is intermixed with the sul-fur dioxide to produce sulfur dioxide absorbed filtrate, and mixing the sulfur dioxide aborbed filtrate with the incoming waste black liquor prior to the waste black liquor being intro-duced into the reaction zone.

19. In the process as claimed in Claim 18, the step of washing the char with the treated second filtrate prior to mixing the treated second filtrate with the waste liquor.