US3179159A - Procedure for evaporating waste lye from pulp - Google Patents

Description

D. v.IAPS

April 20, 1965 PROCEDURE FOR EVAPORATING WASTE LYE FROM PULP Filed oct. 19.1960

2 Sheets-Sheet 1 mln TMQSWQ 200 ul' INVENTOR.

DA N/EL J/-s lll' M23 QMM ATTRNEX April 20, 1965 D- JAFS 3,179,159

PROCEDURE FOR EVAPORATING WASTE LYE FROM PULP Filed Oct. 19. 1960 2 Sheets-Sheet 2 C'O/VDNS 19 TE DA A//EL J F5 INVENTOR.

3,179,159 PRGCEDURE FOR EVAPORATING WASTE LYE FROM PULP Daniel Jfs, Warkaus, Finland, assignor to A. Ahlstrom Osakeyhtio, Warliaus Brnk, Warkaus, Finland, a corporation of Finland Filed Uct. 19, 1960, Ser. No. 63,601 3 Claims. (Cl. 159-47) Evaporators employing indirect heat exchange are used especially for evaporating waste lye from the pulp industry. For the sake of simplicity, the following descrip- `tion is conned to `apparatus designed for this purpose. In the evaporation method envisaged by this invention, at least part of-the lye is conducted in the opposite di- United States Patent rection from the vapour, and it is desirable for the lye .to be warmed up before it is taken on to the following stage in inverse order. For this purpose, indirect heating is provided by one or more heat exchangers, using secondary vapour or condensate as the heating medium. If vapour is used, heating must be in several stages to ensure rational utilization of the vapour. This calls for several heat exchangers and considerably raises the cost of the apparatus.

There is an earlier known system of using condensate and taking advantage of its heat content, by mixing the lcondensate in stages and then pumping it in the opposite direction, from the last stage to the first, after which indirect heat exchange with the lye takes place. Under this system waste gas is removed from the condensate in each mixing vessel, stage by stage. One drawback of this is that prior to the heat exchange between the condensate and the lye, the former is at a pure mixing temperature and thus even the hottest partial condensate has been cooled before any useful heat transfer to the lye can take place.

To overcome this drawback and ensure functional economy with the combined condensate at a temperature equal to or higher than that of the hottest partial condensate, the present invention provides for the rst secondary condensate undergoing expansion and then joining the condensate from the following stage, after which the combined condensate from both sources is expanded again. In this way the vapour from each expansion vessel is constantly utilized in the following stage at lower pressure. The condensate obtained from this process is combined with that from the last stage and the total secondary condensate thus received then undergoes direct heating in successive stages, in each case using vapour from the previous stage at higher pressure. The final product is utilized as the heating medium in a heat exchanger to warm up lye introduced under still higher pressure and flowing through the system from one stage to the preceding stage, in a direction opposite to that of the steam.

Combined secondary condensate can also undergo further indirect preheating or intermediate heating in a heat exchanger, using waste gases from a stage or stages with higher than atmospheric pressure.

The invention is explained in greater detail in the following, reference being made to the accompanying drawings, which show two embodiments of the invention in diagrammatical form.

FIG. 1 shows an arrangement without, and

FIG. 2 one with intermediate heating of condensed liquid by means of waste gases.

1, 2, 3, 4 and 5 in both drawings are indirectly functioning evaporators seen in the direction of flow of the vapour. Vapour enters evaporator 1 via tube 6, yields its heat to the lye in the evaporator and condenses, whereupon the primary condensate obtained is led olf to the boiler via tube 7. The vapours resulting from the evapr: `ICC oration of the lye are conducted through tube 8 to evaporator 2, where further lye is evaporated and the secondary vapouristaken on via tube 9 to the next evaporator 3, the process being repeated in evaporators 4 and 5 with vapour entering them through tubes 10 and 11. Each evaporator can be isolated and by-passed. The vapour from` stage 5 goes to a water-cooled condenser 12 via tube 13. For this purpose the vapour feed tubes 6, 8, 9, 10 `and 11 arel provided with selectively operable shut-off valves 60, Iand the vapour exhaust tubes 8', 9', 10', 11 and 13 are provided with similar valves 61. The vapor conducting conduit is provided with a plurality of anged joints, one of which is Vlocated immediately in advance of each of the tubes 8', 9',` 10', 11 and 13. When all of the evaporators are used, valves 60 and 61 are open and each of the flanged joints in the vapor conducting conduit is provided with an imperforate diaphragm 62.- When one of the evaporators is to be isolated and by-passed, its valves 60 and 61 are closed and the diaphragm 62 in the flanged joint of the vapor conducting conduit between the vapor feed and vapor exhaust tubes of such evaporator is replacedby an annular gasket so that vapor may pass through the anged joint.

The secondary condensate from evaporator 2 is led `olf by tube 14 to an expansion vessel 15, where it is allowed to expand. The resulting vapour is taken via tube 16 into tube, 9 to be condensed at stage 3 at lower pressure; The condensate leaves via tube 17 and joins that from evaporator 3 arriving via tube 181. The condensed liquid from both sources then `enters expansion vessel 20 via tube 19 and expands. The vapour resulting from this is conducted via tube 21 totube 10, which leads to the next evaporator 4. The condensate from expander 20 and from evaporator 4 is collected, via. tubes 22 and 23, in expander 24, from which the resulting vapour is taken to the last evaporator 5 via tubes 25 and 11. The condensate is collected via tube 26, together with that coming from evaporator 5 via tube 27, and pumped (by means of pump 28) into a condensate heater 30 via tube 29. Vapour for direct heating is brought here via tube 31 leading from tube 10. The condensate warmed by this heater 30 is taken on via pump 32 and tube 33 (in FIG. 1 only) to the next heater 34, where it is directly heated by vapour taken from tube 9 via tube 35. Pump 36 takes the condensate on via tube 37 to the following condensate heater 38, where it is directly heated by vapour from tube 8 brought by tube 39. By now all the secondary condensate has reached a temperature corresponding to that of the vapour in evaporator 2 and is thus hotter than the hottest partial condensate. It is then pumped by pump 4t) through tube 41 to a heat exchanger 42, where it warms up the lye from stage 5 before the latter is taken back to evaporator 1 Via tube 43. After being thus cooled, the condensate is removed from the system via tube 41a.

Lye for evaporation is introduced into the system via tube 44, which leads to the bottom of evaporator 3, and after evaporation is taken to the bottom of evaporator 4 via tube 45. From here it goes via tube 46 to the bottom of evaporator 5, and then via pump 47 and tube 48 to heat exchanger 42, from which it is led to the bottom of evaporator 1 via tube 43. Tube 49 then takes the lye from evaporator 1 to the bottomrof evaporator 2. After this, it leaves the system via a tube 50 in the form of thickened lye ready for re-utilization.

Waste gases from evaporators 2, 3, 4 and 5 are removed via a single tube 51, are cooled inheat exchanger 52, and then leave the system. Each of the evaporators 2, 3, 4 and 5 can optionally be furnished with a condensate and gas separator 53.

The system shown in FIG. 2 functions in the same way, with the difference that the waste gases from evaporators 2 and 3 are taken via tube 54 to a separate heat exchanger 55, where they are utilized for the intermediate warming of the condensate from heater 30 arriving via pump 32 and tube 56. After intermediate warming, the condensate proceeds via tube 57 to the next heater 34. After cooling, the waste gases are removed Vfrom the system via tube ,58. A further modication could be envisaged if the temperature of the waste gases and the condensate render it possible and desirable: all

`the secondary condensate could be collected together in one heat exchanger for Warming up by the waste gases from all or any desired number of evaporators, before being taken on to the first condensate heater 30.

The invention can naturally be varied in many different ways Without exceeding the limits of the patent claimed. For instance, the lye warmed in heat exchanger 42 could quite easily be taken lirst to evaporator Z and from there to evaporator 1--i.e. in the opposite direction to the Vapour-before it is removed from the system.

What I claim is:

l. A method of evaporating liquid, especially waste lye from the pulp industry, in an evaporation system comprising a pluralitylof stages, each stage having a heating body and each stage operating at a different evaporating temperature and in Which said liquid is evaporated simultaneously in all of said stages, which method comprises, passing the vapor driven off during the evaporation in a particular heating stage as a heating medium into the heating body of a stage which operates at a lower temperature than said particular stage and in said lower temperature stage condensing the vapors so generated to form a first-condensate, expanding said rst condensate in an expansion vessel, leading the vapors resulting from the expansion of said rst condensate to the heating body of a stage with still lower temperature and joining the expanded condensate with condensate from the said stage with still lower temperature, expanding the condensate from both sources, constantly utilizing this expanded vapor from each expansion vessel in a stage with lower temperature, combining all condensates from successive Cil stages in degrading temperature ow with respect to the ow of vapors released from the successive stages and combining said condensates With the condensate from the stage with lowest temperature, heating the thus obtained total condensate directly in successive stages in direct contact counterow with respect to the heating vapors for the various evaporating stages with the aidof vapor from said evaporating stages and nally using the thus heated total condensate as the heating medium in an indirect'heat exchanger to warm up liquid being introduced `into an evaporating stage which operates at a temperature no lower than the next higher temperature above said particular stage.

2. A method in accordance with claim 1 comprising leading the total condensate to a preheating stage in a heat exchanger and employing as an indirect heating medium in said heat exchanger waste gases from an evaporating stage operating at a pressure corresponding to a temperature higher than that of the combined condensates.

3. A method in accordance with claim l comprising leading the total condensate to an'intermediate heating stage between the successive direct heating stages with regard to temperature, and in said intermediate heating stage heating said condensate in a heat exchanger employing as a heating medium waste gases from an evaporating stage operating at a pressure corresponding toa temperature higher than that of the combined condensates.

References Cited by the Examiner UNITED STATES lPATENTS y2,651,356 `9/53 Sadler 159-46 X 2,734,565 2/56 Lockman 159-20 2,896,705 7/59 Ramen 159-20 X 2,941,590 6/60 Rosenblad 159-20 X 2,979,442 4/61 Badger Q--- 159-47 NORMAN YUDKOFF, Primary Examiner.

GEORG-E D. MITCHELL, CHARLES OCONNELL,

BENJAMIN BENDETT, Examiners.

Claims (1)

1. A METHOD OF EVAPORATING LIQUID, ESPECIALLY WASTE LYE FROM THE PULP INDUSTRY, IN AN EVAPORATIONSYSTEM COMPRISING A PLURALITY OF STAGES, ECH STAGE HAVING AHEATING BODY AND EACH STAGE OPERATING AT A DIFFERENT EVAPORATING TEMPERATURE AND IN WHICH SAID LIQUID IS EVAPORATED SIMULTANEOUSLY IN ALL OF SAID STAGES, WHICH METHOD COMPRISES, PASSING THE VAPOR DRIVEN OFF DURING THE EVAPORATION IN A PARTICULAR HEATING STAGE AS A HEATING MEDIUM INTO THE HEATING BODY OF A STAGE WHICH OPERATES AT A LOWER TEMPERATURE THAN SAID PARTICULAR STAGE AND IN SAID LOWER TEMPERATURE STAGE CONDENSING THE VAPORS SO GENERATED TO FORM A FIRST CONDENSATE, EXPANDING SAID FIRST CONDENSATE IN AN EXPANSION VESSEL, LEADING THE VAPORS RESULTING FROM THE EXPANDION OF SAID FIRST CONDENSATE TO THE HEATING BODY OF A STAGE WITH STILLLOWER TEMPERATURE AND JOINING THE EXPANDED CONDENSATE WITH CONDENSATE FROM THE SAID STAGE WITH STILL LOER TEMPERATURE, EXPANDING THE CONDENSATE FROM BOTH SOURCES, CONSTANTLY UTILIZING THIS EXPANDED VAPOR FROM EACH EXPANSION VESSEL IN A STAGE WITH LOWER TEMPERATURE, COMBINING ALL CONDENSATES FROM SUCCESSIVE STAGES IN DEGRADING TEMPERATURE FLOW WITH RESPECT TO THE FLOW OF VAPORS RELEASED FROM THE SUCCESSIVE STAGES AND COMBINING SAID CONDENSTES WITH THE CONDENSATE FROM THE STAGE WITH LOWEST TEMPERATURE, HEATING THE THUS OBTAINED TOTAL CONDENSATE DIRECTLY IN SUCCESSIVE STAGES IN DIRECT CON-

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