CA1087130A - Method and apparatus for the recovery of easily evaporable components from hot gases - Google Patents
Method and apparatus for the recovery of easily evaporable components from hot gasesInfo
- Publication number
- CA1087130A CA1087130A CA267,678A CA267678A CA1087130A CA 1087130 A CA1087130 A CA 1087130A CA 267678 A CA267678 A CA 267678A CA 1087130 A CA1087130 A CA 1087130A
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- Prior art keywords
- heat exchanger
- additional
- gas space
- gases
- condensate
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Classifications
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C11/00—Regeneration of pulp liquors or effluent waste waters
- D21C11/06—Treatment of pulp gases; Recovery of the heat content of the gases; Treatment of gases arising from various sources in pulp and paper mills; Regeneration of gaseous SO2, e.g. arising from liquors containing sulfur compounds
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- Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method and apparatus for recovery of easily evaporable components from hot gases, e.g. methanol and turpentine, particularly from the expansion vapors of waste liquor such as sulphate black liquor. Buffer vapors emerging from the heat exchanger are exposed to an indirect heat exchange in one or more successive concurrent or countercurrent evaporators. The liquid to be evaporated flows downwards along the heat exchanger surfaces of the evaporator to effectively use the heat contained in the hot gases for evaporation of the liquid.
The easily evaporable components contained in such gases can be separated from the other condensates. The advance of the invention over prior art is in an increased economy of the recovery process
A method and apparatus for recovery of easily evaporable components from hot gases, e.g. methanol and turpentine, particularly from the expansion vapors of waste liquor such as sulphate black liquor. Buffer vapors emerging from the heat exchanger are exposed to an indirect heat exchange in one or more successive concurrent or countercurrent evaporators. The liquid to be evaporated flows downwards along the heat exchanger surfaces of the evaporator to effectively use the heat contained in the hot gases for evaporation of the liquid.
The easily evaporable components contained in such gases can be separated from the other condensates. The advance of the invention over prior art is in an increased economy of the recovery process
Description
()8713 `
A. AHLSTR~M OSAKEYHTI~, Noormarkku Method and apparatus for the recovery of easily evaporable components from hot gases The present invention relates to a method and apparatus for the recovery of heat and easily evaporable components, such as methanol and turpentine, from hot gases, especially from the expansion vapors of waste liquor. This invention relates especially to a method and apparatus for the fractionation of~
the condensates in connection with the evaporation of liquids, and it is intended mainly for the pre-evaporation of a waste liquor, such as sulfate black liquor, emergin~ from a continuous-workin~ di~ester, whereby the black liquor is concentrated from approx. 15-18% to approx. 23-25% in film-evaporation devices working according to the falling film principle, by using for the evaporation the so-called digestion buffer vapor.
In the continuous-working cellulose digester currently in use, the black liquor passing into the evaporator is taken out at a minimum absolute pressure of approx. 8 atm. and at a temperature of approx. 170C. Thus it contains a considerable amount of thermal energy, which can be utilized in the process.
So far the black liquor has usually been pre-evaporated first by .:
~ 2 -' 108~
lowering the pressure durih~ two successive expansion stages so that a liquor vapor at approx. 120C, suitable for the expansion of digestion chips, is obtained from the first stage, and the vapor at approx. 100C generated during the second stage is used for heating water. At this time the temperature of the liquor is approx. 100C, which is regarded as a suitable inlet temperature for the final evaporation. The final evaporation is performed in a multi-stage evaporator based on the indirect transfer of heat; in this case, fresh vapor which yields the thermal energy required by the process is fed to the first stage. Such a use of heat is not as economic as it could be.
If the digester expansion vapor is used as one source of heat for the black-liquor evaporator, the need for fresh vapor decreases. Advantages are also gained in terms of environmental protection.
The use of black-liquor expansion vapor for the pre-evaporation in the buffer evaporator is known p~r se from, for example, U.S.
Patent 3 286 763, and an evaporator suitable for this purpose has been introduced in Canadian Patent 1,032,465 of the present applicant; thls contains laminae inside which heating vapor is fed and which serve as heat exchangers. The liquid to be evaporated is caused to flow onto the outer surfaces of the laminae, where it flows downwards. The direction of the vapor flow is also downwards and the produced condensate is removed at the lower part of the apparatus. One object of this invention is to make the fractionation of the condensates of such a buffer evaporator more effective.
In the evaporation of black liquor the easily evaporable components are removed along with the vapor flow during the first evaporatin~ stages. If a pre-evaporator, for example, a buffer evaporator, is available, a large proportion of these easily evaporable coMponents is separated from the black liquor in the pre-evaporator and is condensed together with the outlet vapor.
The evaporatin~ components in the evaporator thus pass from the liquor into tho condensate. Because the quantities of these ~3 ~ 1~ 8 713~
components, especially of methanol and turnentine, are large and for environmental reasons must be removed from the condensate before it is released into the watercourse, they must be separated from the condensate water. This separation requires a stripping column into which fresh vapor is fed.
The object of the present invention is to provide a more economic method and apparatus than previous ones for the recovery of heat and easily evaporable components from hot gases and vapors In general terms, the present invention provides, in one aspect thereof a method for the recovery of heat and easily evaporable components from hot gases by means of which a liquid flowing downwards along heat exchanger surfaces is simultaneously heated indirectly, whereby the hot gases are fed into the lower section of a gas space, blast gas containing evaporable components is removed at the upper section of the gas space, and a condensate derived from the hot gases is removed at the bottom of the gas space, comprising further ~ringing the blast gases into one or several indirect heat exchange contacts with the liquid, in successive additional gas spaces, recovering condensate accumulated at the bottoms of these additional spaces, and withdrawing the hlast gases from the last additional gas space.
In another aspect, the present invention provides an apparatus for the recovery of heat and easily evaporable components from hot gases, which comprises an evaporation unit having means for feeding the liquid to be evaporated into the evaporation unit, for removing the concentrated liquid from it, and for recycling part of the li~uid which is at the bottom of ..
-3a ~ 10 871 30 the evaporation unit into its ul)per section onto a substantially vertical heat exchanger in the upper section, the lower section of the heat exchanger having an inlet for feeding the hot gases into the heat exchanger, upwards and countercurrently to the liquid flowing along the outer surfaces of the heat exchanger, and an outlet pipe for condensate, the upper section of the heat exchanger being connected to one or more successive substantially vertical additional heat exchangers operating by indirect heat exchange, at least one of the additional heat exchangers having at its bottom an outlet pipe for the removal of the produced condensate and the last additional heat exchanger having, at the end opposite to its gas inlet, an outlet for blast gaseS.
Thus, the buffer vapors emerging from the heat exchanger are still exposed to an indirect heat exchange in one or several successive evaporators operating according to ¦ -the cocurrent or the countercurrent principle, the liquid to -be evaporated flowing downwards along the heat exchanger surfaces of the evaporator. Thereby the heat contained in the hot gases can be used effectively for the evaporation of the liquid and the easily evaporable components present in these gases can still be separated from the other condensates.
!
The invention is described below in more detail with reference to the enclosed drawings, in which Figs. 1 and 2 depict two known evaporation units as diagrammatic cross sections, Figs.
3-5 depict diagrammatic cross sections of three different embodi-ments of the invention, and Fi~. 6 depicts a schematic coupling dia~ram of a sulfate black~liquor evaporation plant provided with evaporation units accordin~ to the invention.
3b--"` ` 1~87~30 ..
Fig. 1 shows an evaporation unit 1 known from the aforesaid Canadian Patent 1,032,465. Liquor to be evaporated is fed along the pipe 6 into its lower section, liquor concentrated by evaporation is removed along the pipe 7, and part of the liquor to be evaporated present in the evaporation unit 1 is removed along the pipe 13 and refed into the same evaporation unit 1, onto the heat exchanger 2 inside the unit,possibly together with a new liquor batch to be evaporated, so that this new and/or recycled liquor flows along the surfaces of the heat exchanger 2, whereby heat is transferred to the liquor.
Through the heat exchanger 2, heating vapor 5 is fed in through the inlet 14 in the upper section of the heat exchanger 2 in such a manner that the vapor flows in the heat exchanger down-wards cocurrently with the liquor to be evaporated, whereby a part 8 of the vapor is condensed, and this part 8 together with the through-blast vapor 10, i.e., the uncondensed part, is directed out at the lower section of the heat exchanger
A. AHLSTR~M OSAKEYHTI~, Noormarkku Method and apparatus for the recovery of easily evaporable components from hot gases The present invention relates to a method and apparatus for the recovery of heat and easily evaporable components, such as methanol and turpentine, from hot gases, especially from the expansion vapors of waste liquor. This invention relates especially to a method and apparatus for the fractionation of~
the condensates in connection with the evaporation of liquids, and it is intended mainly for the pre-evaporation of a waste liquor, such as sulfate black liquor, emergin~ from a continuous-workin~ di~ester, whereby the black liquor is concentrated from approx. 15-18% to approx. 23-25% in film-evaporation devices working according to the falling film principle, by using for the evaporation the so-called digestion buffer vapor.
In the continuous-working cellulose digester currently in use, the black liquor passing into the evaporator is taken out at a minimum absolute pressure of approx. 8 atm. and at a temperature of approx. 170C. Thus it contains a considerable amount of thermal energy, which can be utilized in the process.
So far the black liquor has usually been pre-evaporated first by .:
~ 2 -' 108~
lowering the pressure durih~ two successive expansion stages so that a liquor vapor at approx. 120C, suitable for the expansion of digestion chips, is obtained from the first stage, and the vapor at approx. 100C generated during the second stage is used for heating water. At this time the temperature of the liquor is approx. 100C, which is regarded as a suitable inlet temperature for the final evaporation. The final evaporation is performed in a multi-stage evaporator based on the indirect transfer of heat; in this case, fresh vapor which yields the thermal energy required by the process is fed to the first stage. Such a use of heat is not as economic as it could be.
If the digester expansion vapor is used as one source of heat for the black-liquor evaporator, the need for fresh vapor decreases. Advantages are also gained in terms of environmental protection.
The use of black-liquor expansion vapor for the pre-evaporation in the buffer evaporator is known p~r se from, for example, U.S.
Patent 3 286 763, and an evaporator suitable for this purpose has been introduced in Canadian Patent 1,032,465 of the present applicant; thls contains laminae inside which heating vapor is fed and which serve as heat exchangers. The liquid to be evaporated is caused to flow onto the outer surfaces of the laminae, where it flows downwards. The direction of the vapor flow is also downwards and the produced condensate is removed at the lower part of the apparatus. One object of this invention is to make the fractionation of the condensates of such a buffer evaporator more effective.
In the evaporation of black liquor the easily evaporable components are removed along with the vapor flow during the first evaporatin~ stages. If a pre-evaporator, for example, a buffer evaporator, is available, a large proportion of these easily evaporable coMponents is separated from the black liquor in the pre-evaporator and is condensed together with the outlet vapor.
The evaporatin~ components in the evaporator thus pass from the liquor into tho condensate. Because the quantities of these ~3 ~ 1~ 8 713~
components, especially of methanol and turnentine, are large and for environmental reasons must be removed from the condensate before it is released into the watercourse, they must be separated from the condensate water. This separation requires a stripping column into which fresh vapor is fed.
The object of the present invention is to provide a more economic method and apparatus than previous ones for the recovery of heat and easily evaporable components from hot gases and vapors In general terms, the present invention provides, in one aspect thereof a method for the recovery of heat and easily evaporable components from hot gases by means of which a liquid flowing downwards along heat exchanger surfaces is simultaneously heated indirectly, whereby the hot gases are fed into the lower section of a gas space, blast gas containing evaporable components is removed at the upper section of the gas space, and a condensate derived from the hot gases is removed at the bottom of the gas space, comprising further ~ringing the blast gases into one or several indirect heat exchange contacts with the liquid, in successive additional gas spaces, recovering condensate accumulated at the bottoms of these additional spaces, and withdrawing the hlast gases from the last additional gas space.
In another aspect, the present invention provides an apparatus for the recovery of heat and easily evaporable components from hot gases, which comprises an evaporation unit having means for feeding the liquid to be evaporated into the evaporation unit, for removing the concentrated liquid from it, and for recycling part of the li~uid which is at the bottom of ..
-3a ~ 10 871 30 the evaporation unit into its ul)per section onto a substantially vertical heat exchanger in the upper section, the lower section of the heat exchanger having an inlet for feeding the hot gases into the heat exchanger, upwards and countercurrently to the liquid flowing along the outer surfaces of the heat exchanger, and an outlet pipe for condensate, the upper section of the heat exchanger being connected to one or more successive substantially vertical additional heat exchangers operating by indirect heat exchange, at least one of the additional heat exchangers having at its bottom an outlet pipe for the removal of the produced condensate and the last additional heat exchanger having, at the end opposite to its gas inlet, an outlet for blast gaseS.
Thus, the buffer vapors emerging from the heat exchanger are still exposed to an indirect heat exchange in one or several successive evaporators operating according to ¦ -the cocurrent or the countercurrent principle, the liquid to -be evaporated flowing downwards along the heat exchanger surfaces of the evaporator. Thereby the heat contained in the hot gases can be used effectively for the evaporation of the liquid and the easily evaporable components present in these gases can still be separated from the other condensates.
!
The invention is described below in more detail with reference to the enclosed drawings, in which Figs. 1 and 2 depict two known evaporation units as diagrammatic cross sections, Figs.
3-5 depict diagrammatic cross sections of three different embodi-ments of the invention, and Fi~. 6 depicts a schematic coupling dia~ram of a sulfate black~liquor evaporation plant provided with evaporation units accordin~ to the invention.
3b--"` ` 1~87~30 ..
Fig. 1 shows an evaporation unit 1 known from the aforesaid Canadian Patent 1,032,465. Liquor to be evaporated is fed along the pipe 6 into its lower section, liquor concentrated by evaporation is removed along the pipe 7, and part of the liquor to be evaporated present in the evaporation unit 1 is removed along the pipe 13 and refed into the same evaporation unit 1, onto the heat exchanger 2 inside the unit,possibly together with a new liquor batch to be evaporated, so that this new and/or recycled liquor flows along the surfaces of the heat exchanger 2, whereby heat is transferred to the liquor.
Through the heat exchanger 2, heating vapor 5 is fed in through the inlet 14 in the upper section of the heat exchanger 2 in such a manner that the vapor flows in the heat exchanger down-wards cocurrently with the liquor to be evaporated, whereby a part 8 of the vapor is condensed, and this part 8 together with the through-blast vapor 10, i.e., the uncondensed part, is directed out at the lower section of the heat exchanger
2.
The vapors generated in the evaporation of the liquor are removed from the evaporation unit through the outlet 11 in its upper section.
A distillation effect is produced on the condensing vapor side by making arrangements for a condensate and vapor flow, and for a through-blast,also in a known manner, as shown in Fig. 2.
The inlet vapor 5 and the outlet condensate 8 flow countercurrent!
in the laminae of the heat exchanger 2. The cutlet condensate 8 is purified because it is in contact with the inlet vapor 5, in which the partial pressures of the easily evaporable components are at their lowest. The evaporating components accumulate in the upper section of the laminae of the heat exchanger 2, from where they are removed by a through-blast. A
heat-exchanger lamina thus serves as a kind of distillation device.
It has been observed that in the apparatus shown in Fig. 2 the methanol present in the inlet vapor 5 is distributed in the following manner, depending on the amount of the through-blast 10:
Through-blast 10 Methanol distribution % of inlet vapor 5 In condensate 8 In through-blast 10 10 % 33 % 67 %
20 % 23 % 77 %
30 % 19 % 81 %
11~87~30 If a recovery of 80% of the methanol is desired, 70% of the condensates of the inlet vapor do not require an additional treatment. In these evaporators, in wich the vapor is fed into the upper section of the laminae and the condensate is removed by means of a through-blast at the lower ends of the laminae, 100~ of the condensates of the inlet vapor require further treatment.
The known solution shown in Fig. 2 has, however, certain dis-advantages, since the thermal energy of the through-blast vapor 10 is not used for the evaporation of the liquor.
The object of the present invention is therefore to provide a method and apparatus in which the good points of the solutions illustrated in Figs. 1 and 2 are combined, i.e., an effective utilization of the condensation energy of the inlet vapor 5 and its distilling effect when the vapor flows counter-currently in relation to the produced condensate 8.
According to the invention (Fig. 3), the heating vapor 5 is fed at the lower section of the first lamina group 2 through the inlet 14. From there it flows upwards countercurrently to the condensate 8, and at the upper section of the lamina group 2, that part of the vapor which has not condensed is removed and directed to the upper section of the second lamina group 3 in the same evaporation unit 1. From there it flows downwards cocurrently with the liquid to be evaporated. Here the condensate of the inlet vapor 5 is divided into two fractions 8 and 9, of which one 9 contains the bulk of the evaporable components.
According to a more advantageous emdobiment (Fig. 4), a third lamina group 4 is added to the same evaporation unit 1. The vapors to be blown through are fed from the second lamina group 3 to the lower section of the third lamina group 4; from there they flow upwards and are removed at the upper section of the lamina group 4 through the outlet 15. In this case the condensate of the inlet vapor 5 can be divided into three fractions, whereby the most important evaporable components .
. ' ' : : , . - ~
1~87130 .
of the black liquor, i.e., methanol and turpentine, are separated from each other.
It is evident that instead the second lamina group 3, a single pipe or parallel coupled pipes can be used for directing the gases emerging from the upper section of the lamina group 2 to the lower section of the lamina group 4. In this case the evaporation unit has two heat exchangers 2 and 4 operating according to the countercurrent principle, coupled in series, although the connecting pipe 3 also serves as a heat exchanger to some extent.
The connecting pipe can also be led outside the evaporation unit from the lamina group 2 to the lamina group 4, as shown in Fig.
6.
In the pre-evaporation of black liquor, a suitable through-blast 10 in the first lamina group 2 is approx. 30% and in the second one 3 approx. 1% of the vapor entering the evaporation unit.
In this case the methanol and turpentine are distributed as follows during the black liquor evaporation:
Pure condensateMethanol condensate Through-8 9 blast 10 Methanol 20 ~ 38 % 42 %
Turpentine1.3 %2.4 % 96.3 %
Water 70 % 29 % 1 The pure condensate 8 does not require any further treatment.
The through-blast 10 is condensed in a turpentine condenser (not shown in the figure) and directed to turpentine separation, in which methanol and turpentine are separated from each other.
The methanol from the turpentine separation is combined with the methanol condensate and fed into the stripper, where the methanol is separated from the water. Normally it would have been necessary to separate first the turpentine and then the methanol from the total condensate quantity.
^`` 1~87130 The distilling effect described above can be made more effective in the manner indicated in Fig. 5. In Fig. 5 there are,below the laminae 2, material-transfer trays i2 where the inlet vapor 5 strips the outlet condensates 8. This further promotes the collection of the easily evaporable gases at the top of the laminae. It has been observed concerning methanol that, if three trays 12 with an efficiency ratio of some 50~ are added, 84% of the methanol can be caused to accumulate in a 10~ through-blast 10.
Fig. 6 depicts a sulfate black liquor evaporation plant provided with buffer evaporators and with evaporation units according to the invention.
The black liquor 101 emerges from the digester at 170C. It is fed into the expansion tank 102. From the expansion tank lG2 the vapor 103 and the black liquor 104 are directed into the evaporator 105, into which fresh vapor 106 is also fed. From the evaporator 105 the turpentine through-blast 107 passes into the turpentine condenser 108. The pure condensate is fed through the expansion tank 109 into the pure-condensate tank 110.
The methanol condensate is fed into the methanol condensate tank 111, where it expands, and the expansion vapors 112 are directed into the turpentine condenser 108. The outlet vapor 113 from the evaporator 105 and the outlet black liquor 115 are fed into the next unit 114. As above, the black liquor then passes further through the units 119 and 120. The products obtained are a product black liquor 116, a pure condensate 117, and a methanol condensate 118. The turpentine vapors are collected in the turpentine condenser 108. It is unnecessary to feed the through-blasts from the units 119 and 120 into the turpentine condenser since their turpentine contents are already quite low. The bulk of the turpentine has been separated from the black liquor during the earlier stages.
Fig. 6 shows the water (t/h), methanol (Mkg/h), and turpentine (Tkg/h) balances of sulfate black liquor evaporation.
' ' ' `
8 ~871~(3 The total condensate rate is 300 t/h when the flow 101 in the buffer and final evaporator is evaporated to a dry-matter content of 65%. In Fig. 6 the flow into the turpentine condenser 108 is approx. 1 t/h. The turpentine is thus obtained in a flow which is approx. 0.3% of the total quantity of condensate.
The turpentine recovery rate is nearly 98%. The methanol is collected from the condenser 111 into a condensate quantity which is 23 t/h, which is only 7.5% of the total condensate quantity. The methanol recovery rate is nearly 60%.
Since the recovery rates of methanol and turpentine are thus already high enough at the buffer evaporator, the condensates emerging from the final evaporator can be left untreated.
The vapors generated in the evaporation of the liquor are removed from the evaporation unit through the outlet 11 in its upper section.
A distillation effect is produced on the condensing vapor side by making arrangements for a condensate and vapor flow, and for a through-blast,also in a known manner, as shown in Fig. 2.
The inlet vapor 5 and the outlet condensate 8 flow countercurrent!
in the laminae of the heat exchanger 2. The cutlet condensate 8 is purified because it is in contact with the inlet vapor 5, in which the partial pressures of the easily evaporable components are at their lowest. The evaporating components accumulate in the upper section of the laminae of the heat exchanger 2, from where they are removed by a through-blast. A
heat-exchanger lamina thus serves as a kind of distillation device.
It has been observed that in the apparatus shown in Fig. 2 the methanol present in the inlet vapor 5 is distributed in the following manner, depending on the amount of the through-blast 10:
Through-blast 10 Methanol distribution % of inlet vapor 5 In condensate 8 In through-blast 10 10 % 33 % 67 %
20 % 23 % 77 %
30 % 19 % 81 %
11~87~30 If a recovery of 80% of the methanol is desired, 70% of the condensates of the inlet vapor do not require an additional treatment. In these evaporators, in wich the vapor is fed into the upper section of the laminae and the condensate is removed by means of a through-blast at the lower ends of the laminae, 100~ of the condensates of the inlet vapor require further treatment.
The known solution shown in Fig. 2 has, however, certain dis-advantages, since the thermal energy of the through-blast vapor 10 is not used for the evaporation of the liquor.
The object of the present invention is therefore to provide a method and apparatus in which the good points of the solutions illustrated in Figs. 1 and 2 are combined, i.e., an effective utilization of the condensation energy of the inlet vapor 5 and its distilling effect when the vapor flows counter-currently in relation to the produced condensate 8.
According to the invention (Fig. 3), the heating vapor 5 is fed at the lower section of the first lamina group 2 through the inlet 14. From there it flows upwards countercurrently to the condensate 8, and at the upper section of the lamina group 2, that part of the vapor which has not condensed is removed and directed to the upper section of the second lamina group 3 in the same evaporation unit 1. From there it flows downwards cocurrently with the liquid to be evaporated. Here the condensate of the inlet vapor 5 is divided into two fractions 8 and 9, of which one 9 contains the bulk of the evaporable components.
According to a more advantageous emdobiment (Fig. 4), a third lamina group 4 is added to the same evaporation unit 1. The vapors to be blown through are fed from the second lamina group 3 to the lower section of the third lamina group 4; from there they flow upwards and are removed at the upper section of the lamina group 4 through the outlet 15. In this case the condensate of the inlet vapor 5 can be divided into three fractions, whereby the most important evaporable components .
. ' ' : : , . - ~
1~87130 .
of the black liquor, i.e., methanol and turpentine, are separated from each other.
It is evident that instead the second lamina group 3, a single pipe or parallel coupled pipes can be used for directing the gases emerging from the upper section of the lamina group 2 to the lower section of the lamina group 4. In this case the evaporation unit has two heat exchangers 2 and 4 operating according to the countercurrent principle, coupled in series, although the connecting pipe 3 also serves as a heat exchanger to some extent.
The connecting pipe can also be led outside the evaporation unit from the lamina group 2 to the lamina group 4, as shown in Fig.
6.
In the pre-evaporation of black liquor, a suitable through-blast 10 in the first lamina group 2 is approx. 30% and in the second one 3 approx. 1% of the vapor entering the evaporation unit.
In this case the methanol and turpentine are distributed as follows during the black liquor evaporation:
Pure condensateMethanol condensate Through-8 9 blast 10 Methanol 20 ~ 38 % 42 %
Turpentine1.3 %2.4 % 96.3 %
Water 70 % 29 % 1 The pure condensate 8 does not require any further treatment.
The through-blast 10 is condensed in a turpentine condenser (not shown in the figure) and directed to turpentine separation, in which methanol and turpentine are separated from each other.
The methanol from the turpentine separation is combined with the methanol condensate and fed into the stripper, where the methanol is separated from the water. Normally it would have been necessary to separate first the turpentine and then the methanol from the total condensate quantity.
^`` 1~87130 The distilling effect described above can be made more effective in the manner indicated in Fig. 5. In Fig. 5 there are,below the laminae 2, material-transfer trays i2 where the inlet vapor 5 strips the outlet condensates 8. This further promotes the collection of the easily evaporable gases at the top of the laminae. It has been observed concerning methanol that, if three trays 12 with an efficiency ratio of some 50~ are added, 84% of the methanol can be caused to accumulate in a 10~ through-blast 10.
Fig. 6 depicts a sulfate black liquor evaporation plant provided with buffer evaporators and with evaporation units according to the invention.
The black liquor 101 emerges from the digester at 170C. It is fed into the expansion tank 102. From the expansion tank lG2 the vapor 103 and the black liquor 104 are directed into the evaporator 105, into which fresh vapor 106 is also fed. From the evaporator 105 the turpentine through-blast 107 passes into the turpentine condenser 108. The pure condensate is fed through the expansion tank 109 into the pure-condensate tank 110.
The methanol condensate is fed into the methanol condensate tank 111, where it expands, and the expansion vapors 112 are directed into the turpentine condenser 108. The outlet vapor 113 from the evaporator 105 and the outlet black liquor 115 are fed into the next unit 114. As above, the black liquor then passes further through the units 119 and 120. The products obtained are a product black liquor 116, a pure condensate 117, and a methanol condensate 118. The turpentine vapors are collected in the turpentine condenser 108. It is unnecessary to feed the through-blasts from the units 119 and 120 into the turpentine condenser since their turpentine contents are already quite low. The bulk of the turpentine has been separated from the black liquor during the earlier stages.
Fig. 6 shows the water (t/h), methanol (Mkg/h), and turpentine (Tkg/h) balances of sulfate black liquor evaporation.
' ' ' `
8 ~871~(3 The total condensate rate is 300 t/h when the flow 101 in the buffer and final evaporator is evaporated to a dry-matter content of 65%. In Fig. 6 the flow into the turpentine condenser 108 is approx. 1 t/h. The turpentine is thus obtained in a flow which is approx. 0.3% of the total quantity of condensate.
The turpentine recovery rate is nearly 98%. The methanol is collected from the condenser 111 into a condensate quantity which is 23 t/h, which is only 7.5% of the total condensate quantity. The methanol recovery rate is nearly 60%.
Since the recovery rates of methanol and turpentine are thus already high enough at the buffer evaporator, the condensates emerging from the final evaporator can be left untreated.
Claims (10)
1. A method for the recovery of heat and easily evaporable components from hot gases by means of which a liquid flowing downwards along heat exchanger surfaces is simultaneously heated indirectly, whereby the hot gases are fed into the lower section of a gas space, blast gas containing evaporable components is removed at the upper section of the gas space, and a condensate derived from the hot gases is removed at the bottom of the gas space, comprising further bringing the blast gases into one or several indirect heat exchange contacts with the liquid, in successive additional gas spaces, recovering condensate accumulated at the bottoms of these additional spaces, and withdrawing the blast gases from the last additional gas space.
2. A method according to Claim 1, in which the blast gases emerging from the gas space are fed into the upper section of the first additional gas space and are there contacted indi-rectly, for the purpose of heat exchange, with the liquid flowing downwards along the outer surfaces of the first addi-tional gas space, blast gas and condensate being withdrawn from the lower section of the first additional gas space.
3. A method according to Claim 1, in which the gases emerging from the gas space or the first additional gas space are fed into the lower section of a second additional gas space, contacted there indirectly, for the purpose of heat exchange, with the liquid flowing downwards along the outer surfaces of the second additional gas space, condensate being withdrawn from the bottom of the second additional gas space and the blast gases being withdrawn from the upper section of the second additional gas space.
4. A method according to Claim 1, in which as the hot gas is used a methanol- and turpentine-bearing vapor which has been obtained from the expansion evaporation of liquor from cellulose digestion and which is used for evaporating the liquor obtained from the same expansion evaporation.
5. An apparatus for the recovery of heat and easily evaporable components from hot gases, which comprises an evaporation unit having means for feeding the liquid to be evaporated into the evaporation unit, for removing the concentrated liquid from it, and for recycling part of the liquid which is at the bottom of the evaporation unit into its upper section onto a substantially vertical heat exchanger in the upper section, the lower section of the heat exchanger having an inlet for feeding the hot gases into the heat exchanger, upwards and countercurrently to the liquid flowing along the outer surfaces of the heat exchanger, and an outlet pipe for condensate, the upper section of the heat exchanger being connected to one or more successive substantially vertical additional heat exchangers operating by indirect heat exchange, at least one of the additional heat exchangers having at its bottom an outlet pipe for the removal of the produced condensate and the last additional heat exchanger having, at the end opposite to its gas inlet, an outlet for blast gases.
6. An apparatus according to Claim 5, in which the upper section of the heat exchanger has been connected to the upper section of the first additional heat exchanger in order to cause the gases to flow downwards cocurrently in relation to the liquid flowing along the outer surfaces of the first additional heat exchanger, which has at its bottom an outlet pipe for the condensates and the blast gases.
7. An apparatus according to Claim 5, comprising two successive countercurrent heat exchangers which have been connected by means of a gas pipe leading from the upper section of the heat exchanger to the lower section of the first additional heat exchanger.
8. An apparatus according to Claim 5, comprising successively a countercurrent, a cocurrent, and a counter-current heat exchanger, in which case the two latter ones share a condensate bottom.
9. An apparatus according to Claim 5, in which the heat exchangers are lamina heat exchangers.
10. An apparatus according to Claim 5, in which at least one countercurrent heat exchanger has been provided with one or more material transfer levels, one on top of the other, for stripping the outlet condensates.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI753523 | 1975-12-12 | ||
| FI753523A FI52601B (en) | 1975-12-12 | 1975-12-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1087130A true CA1087130A (en) | 1980-10-07 |
Family
ID=8509612
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA267,678A Expired CA1087130A (en) | 1975-12-12 | 1976-12-10 | Method and apparatus for the recovery of easily evaporable components from hot gases |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1087130A (en) |
| FI (1) | FI52601B (en) |
| SE (1) | SE457963B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5830314A (en) * | 1994-09-06 | 1998-11-03 | Ahlstrom Machinery Corporation | Cleaning condensates from multi-effect evaporator of cellulose pulp waste liquors |
-
1975
- 1975-12-12 FI FI753523A patent/FI52601B/fi not_active IP Right Cessation
-
1976
- 1976-12-10 CA CA267,678A patent/CA1087130A/en not_active Expired
- 1976-12-10 SE SE7613916A patent/SE457963B/en not_active IP Right Cessation
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5830314A (en) * | 1994-09-06 | 1998-11-03 | Ahlstrom Machinery Corporation | Cleaning condensates from multi-effect evaporator of cellulose pulp waste liquors |
Also Published As
| Publication number | Publication date |
|---|---|
| SE7613916L (en) | 1977-06-13 |
| SE457963B (en) | 1989-02-13 |
| FI52601B (en) | 1977-06-30 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |