DE1937874A1 - Process for compression evaporation - Google Patents

Description

Process for compression evaporation

The invention relates to a method for evaporating liquid, in particular for thickening alkalis.

With a compression evaporator, the entire power supply to the compressor is converted into heat. This energy lifts Pressure and temperature of the steam passed through the compressor, with a power supply of 1000 kW to the compressor 1000 kW of excess heat available. So far, this heat has been viewed as waste heat and is not appropriate been used.

Of particular interest is the evaporation of a liquid which shows a steep rise in the boiling point above the liquid concentration. As will become clear below, the liquor in the Kraft wood pulp industry is one such liquid. At a solids content of kO% in such a liquid, the boiling point rise is 4.4 ⁰ C. Taking into account the fact that for Verdiohtungsverdampfer economic pressure at a pressure rise of about 0.35 kg / om is opposite Atmosphärendruok, representing a temperature increase of 8 , 8 ⁰ C from 100 ⁰ C to 108.8 ⁰ C for boiling water, means a boiling point increase of k, h ° C,

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that such a liquid with hO% solids begins to boil at a temperature of 104.4 C ^0. The exhaust vapors at 0.35 kgf / cm ^{2 G.} Kondensationstem- have a temperature of 108.8 ⁰ C. Instead of a temperature difference of 8.8 C ⁰ is thus only a temperature difference of 4.4 C ⁰ au consist of the heating surface of the evaporator. The concentration of the feed liquid flowing into the evaporator can be assumed to be 18% solids. This liquid has a boiling point increase of 1.1 ⁰ C, at atmospheric pressure means a boiling point at 101.1 ⁰ C and leads to a temperature difference of 7 »7 ⁰ C when using Brüdendämpfen of 0.35 kgf / cm * - heated pressure will. In order to make use of the higher temperature difference at lower concentration, a compressor unit is usually divided into a number of sections which are connected in series on the liquid side and in parallel on the vapor and vapor side.

The specific load, expressed in mass (kg) of released vapor per area (cm ² ) and time (h) decreases with the increase in the liquid concentration, not only due to the decrease in the temperature difference but also with the decrease in the heat transfer coefficient due to the increase in the viscosity of the liquid, If, in the above example, the solids concentration in the liquid increases from $ 18 to 40%, the heat transfer coefficient can decrease by 50% , which means a total decrease in the specific load of about $ 78 if the increase in the boiling point is taken into account. This means that then a 3 _f 5 times larger heating surface per kg of released steam is required.

The further part of the evaporation, during which the solids concentration increases from 40% to 50%, which is usually the case with the Evaporation of liquid according to the present example is required, can not be economically in the Compression level can be achieved. The reason is that

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Liquid with a solids concentration of 50 $ one µm. 7.2 ⁰ C has increased boiling point, whereby an effective temperature difference of only 1.6 ⁰ C remains. This requires a heating surface per kg released steam per hour which is at least ten times larger than that in the section for liquid with food concentration.

The invention is based on the object of specifying a new method, the compression with a single-stage or multi-stage Combined evaporator, such a method is suitable for the treatment of liquids whose boiling point increases with an increase in the solids concentration, and optimally utilizes the heat and power supply to a compression evaporator to achieve the desired degree of thickening of the liquid with the smallest heating surface requirement.

The object is achieved according to the invention in that in one Compression evaporation system only hot exhaust vapors obtained by evaporation of liquid in a first evaporator and withdrawn therefrom, all of these Exhaust vapors are compressed mechanically and these condensed exhaust vapors with an excess of heat as indirect Heating means for the evaporation of further liquid which is introduced into the first evaporator shortly before its boiling point, be fed back to the first evaporator, the excess heat from the heating medium in the evaporator from excess vapor is withdrawn due to the compression and this excess vapor is used as a heating medium outside the Verdi evaporation system separate evaporation thickener is fed, in turn this thickener is fed with the liquid product of the compression evaporation system and this liquid product thickens further by conducting it in a heat-exchanging manner with the excess vapor.

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According to a further embodiment of the invention becomes liquid including a compression stage evaporator and a Thickening stage enverdanipf ers evaporated, taking in the compression evaporator hot Bx steamers exclusively through Evaporation of low concentration liquid obtained and subtracted from this compression stage, all of these Exhaust vapors are mechanically compressed and these condensed Exhaust vapors as an indirect heating medium for the evaporation of others Liquid in this vaporizer just before its boiling point is introduced, are fed back to this evaporator, the excess heat being due as excess vapor the compression is withdrawn and this excess vapor as a heating means is removed from the outside of the compression stage Thickening stage evaporator is fed, in turn Liquid from the compression stage with a strong increase in the Boiling point fed to the thickening stage and in indirect Heat exchange is brought with the excess vapor.

Thus, among other things, evaporation and thickening occur low power requirements possible. Both the vaporizer and the thickener can also be of a single or multiple design.

An embodiment of the invention is shown in the drawing and is described in more detail below. Show it:

1 shows the increase in the boiling point of lye with an increase in concentration the liquid;

Fig. 2 is a schematic representation of a preferred Embodiment of a compression evaporator system according to the invention.

In Fig. 1 the relationship between the boiling point tip: In ⁰ C and the solids concentration in ° /, · a lye at Krnfi-

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ZeI1stoff method shown. The same curve progression also applies to lye in the neutral sulphite pulp process «, see also HO No. 11, 921.

The first evaporator or the pre-evaporator stage - shown here as a single evaporator 10 in FIG. 2 - is an indirect or surface evaporator. The evaporator 10 has a lower main section 11 with channel-forming sheets or tubes (not shown) in its interior, these sheets or tubes forming two separate bundles of flow channels. A line 15 is connected to the first of these channel bundles in order to supply these channels with feed liquid to be evaporated. The housing of section 11 of evaporator 10 has a passage 12 at the upper end for the inlet of heating steam, this steam flowing through the other, second duct bundle in section 11 of evaporator 10. Steam and condensate from the heating steam are discharged from the evaporator 10 through the line 1h.

Breath vapor from the evaporation of feed liquid is released from the upper ends of the first channels of the evaporator 10 to one Vapor space 16, which forms the upper portion of the evaporator, released. The remaining feed liquid continues to flow partial evaporation from the upper ends of the first channels and is on the bottom of the vapor space 16 at a level below the upper ends of the channel-forming parts that protrude into the lower portion of the steam space, collected. These already partially thickened liquid is discharged from the lower end of the vapor space through a line 17 which carries the liquid leads to a thickener 35 to be described.

Exhaust vapor is discharged from the vapor space 16 through a line 19 which leads to the inlet or suction opening 22 of a compressor 2h . A prime mover such as an electric motor 26 drives the compressor as shown. The steam from the steam space 16 is released under high pressure from the outlet 26 of the compressor to a line 27 which connects this outlet and the Heizdampfeinlassiiffming 12 of the evaporator 10.

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The above-mentioned discharge line 14 connects the lower ends of the second bundle of channels with a separation vessel 29. Condensate flowing into the vessel 29 through the line 14 collects at the bottom of the vessel and is drained from there through a line 30 provided with a valve 31. In the embodiment shown, the valve 31 is provided with a level control 32 which responds to the liquid level in the vessel 29 so that the level of this liquid is kept essentially constant.

At the upper end of the vessel 29 and well above the liquid level In the vessel, a line 34 is attached, which the vapor portion of the evaporator through the line 14 leaves Vapor-liquid mixture for heating medium inlet- opening 36 of the thickener 35 leads. The thickener in the illustrated Embodiment belongs to the type of indirectly heated respectively, surface thickener and has separate first and second bundle of channels in its lower section 37. The one above mentioned line 17 is with the lower end of the first channel bundle of the thickener 35 connected. Partially thickened liquid from line 17 flows through this first caustic bundle upwards so that it evaporates or thickens in it will. Vapor vapor given off by this thickened liquid flows out of the upper ends of the first channels and is collected in the vapor space 40 which is the upper portion of the thickener 35 forms. Liquid conveyed into the vapor space 40 is collected at the bottom of the vapor space 40 and from there as desired product drained through line 41.

The heating medium inlet opening 36 of the thickener 35 is connected to the upper ends of the second duct bundle in section 37 of the inlet thickers connected. Condensate of the heating medium is drawn from the lower ends of the second channels of the thickener through a Line 39 drained,

Evaporative vapor is discharged from the vapor space 40 of the thickener through a pipe 42 which is connected to an indirect heat exchanger or

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Surface capacitor Vi is shown connected, and the heat supply to this capacitor is used. The condensate of this vapor is drained from the heat exchanger Vt through a separate hollow * 52. Process fluid such as cold water is fed to the heat exchanger Vi through a pipe h? And this water is heated in the heat exchanger kh and then drained from it through a pipe Vo The exhaust vapors remaining from the vapor heating medium, which was fed to the heat exchanger "Ί-Ί, are discharged from the heat exchanger via a pipe ^; i7 sucked off by a steam jet pump hd. This steam jet pump is supplied with steam via a line jO, and it releases this steam and the evacuated Brüdendanipf through a line 51 as shown.

Although only a single embodiment of the invention in the Has been illustrated in the accompanying drawings and explained in the above description, it is understood that various Changes can be made to it without leaving the scope and scope of the invention, which is now for is obvious to a person skilled in the art.

Claims;

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Claims (3)

Claims Process for the evaporation of liquid, characterized in that hot broth vapors are obtained (i9) exclusively by evaporation of liquid in a first evaporator (10) in a compression evaporation system, all these vapor vapors are mechanically compressed (2k) and these compressed vapor vapors with an excess of heat as an indirect heating medium for the evaporation of further liquid, which is introduced into the first evaporator shortly before its boiling point, is fed back to the first evaporator (iO) (27), the excess heat from the heating medium in the evaporator (lO) as excess Exhaust vapor is withdrawn due to the compression and this excess vapor vapor is fed as a heating medium to an evaporation thickener (35) arranged outside the compression evaporation system (10, 2h) , this thickener (35) in turn being fed with the liquid product of the compression evaporation system (10, 24) will and this it thickens the liquid product further by exchanging heat with the excess bread pot. 2. The method according to claim 1, characterized in that during the further thickening of the liquid product in the thickener (35) resulting vapor vapors are drawn off (k2) to be used as heating means in a heat exchanger (kk) separate from the evaporation system (10, 35) to become. 3. Procedure for evaporation of liquid involving a compression stage evaporator (OK) and a thickening stage evaporator (35) »characterized in that in the compression evaporator (OK) only hot vapor vapors obtained by evaporation of low concentration liquid and from this compression stage 009886/1909 _ Q - are withdrawn, all of these broth vapors are mechanically compressed (2h) and these compressed broth vapors are fed back to this vaporizer (10) as an indirect heating medium for the evaporation of further liquid that is introduced into this vaporizer (10) shortly before its boiling point, with the excess heat is withdrawn as excess vapor due to the compression and this excess vapor is fed as a heating medium to the thickening stage evaporator (35) arranged outside the compression stage, whereby in turn liquid from the compression stage is fed to the thickening stage with a strong increase in the boiling point and in indirect heat exchange with the excess Exhaust steam is brought. Or / kn - 22 022 009886/1909 ΛΟ Blank page