WO1983003042A1

WO1983003042A1 - Method related to drying of fish meal and similar products, and production plant capable of exercising the method

Info

Publication number: WO1983003042A1
Application number: PCT/DK1983/000026
Authority: WO
Inventors: Landssmidjan; Mogens Birkeholm; Sigurdur Danielsson; Haukur Baldursson
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-03-05
Filing date: 1983-03-04
Publication date: 1983-09-15
Anticipated expiration: 1984-09-05
Also published as: EP0103595A1; DK95982A; IS2789A7

Abstract

Un procédé pour fabriquer de la farine de poisson et d'autres produits similaires dans un appareillage qui comprend un sécheur chauffé indirectement, c'est-à-dire, un sécheur conçu pour avoir une paroi non-perméable ou autre surface d'échange de chaleur séparant le milieu de chauffage et les matières destinées à être séchées. Le procédé se caractérise par la conduite de la vapeur générée dans le sécheur vers un compresseur, par la compression de la vapeur jusqu'à atteindre la pression requise pour la condenser à la température minimale de chauffage nécessaire dans le sécheur, et par la conduite de la vapeur comprimée du compresseur au sécheur. L'on décrit diverses variations préférées du procédé. L'on décrit un appareillage pour appliquer le procédé avec des exemples du mode préférentiel de réalisation.A process for making fishmeal and other similar products in apparatus which includes an indirectly heated dryer, i.e., a dryer designed to have a non-permeable wall or other surface for exchange of heat separating the heating medium and the materials intended to be dried. The method is characterized by conducting the steam generated in the dryer to a compressor, by compressing the steam until it reaches the pressure required to condense it to the minimum heating temperature required in the dryer, and by conducting compressed steam from the compressor to the dryer. Various preferred variations of the process are described. An apparatus for applying the method is described with examples of the preferred embodiment.

Description

METHOD RELATED TO DRYING OP PISH MEAL AND SIMILAR PRODUCTS, AND PRODUCTION PLANT CAPABLE OP EXCERCISING THE METHOD.

The invention is related to the drying of fish meal or the like in a plant comprising an indirectly heated drier. The invention also pertains to a plant capable of excercisirg the method.

It is well-known to manufacture products as fish meal, meat- and bonemeal and the like by boiling the raw material, after which process the boiled material, eventually after intermediate treatment in a decanter with separation of certain components, e.g. oil, and/or treatment in a press in order to remove part of the water introduced during the cooking process, is fit to a drier.

The drier may be a directly heated drier in which hot and relatively dry air, is directed through or over the material to be dried. Alternatively the drier may be an indirectly heated apparatus in which the necessary heat (enthalpi) for evaporation of the humidity in the material treated is transferred through a heat exchange surface by heat transmission from a chamber for the heating- means, e.g. steam to a drying chamber for the material to be dried. Plant may be constructed that way, that the drying is carried out by successively passing the material through at least two driers, which each may be directly heated or indirectly heated.

An drying plants for fish meal and the like watery solutions are often separated. These solutions are then concentrated in evaporators and eventually has the concentrate later dried completely. This is well-known from fish meal and meat- and bonemeal factories. This invention is related to a drying plant comprising an indirectly heated drier and eventually an evaporator (a stickwater plant), which are indirectly heated, and in which the heating take place by means of steam.

During many years - also during the span of years, when energy prices were relatively lower than now -great effort was allocated in order to reduce the netto-energy-consumption in/plants of this art. This is due of course to the reason, that evaporation of water is a physical process demanding huge quantities of heat, i.e. evaporation of water absorbes waste quantities of heat or enthalpi. Persons skilled within the art are familiar with the difference between enthalpi and free energy.

Among the published methods aiming to minimising the energy (enthalpi) consumption the plants, the following are cited in order to describe the state of art: Norwegian patents No. 56,326, 78,881, and No. 109,226; DE-AS No. 1,210,666 and No. 1,217,763; and Danish document laid open to public inspection No. 143,635. US patent No. 2,718,710 could be cited as documentation of the art concerning regeneration of heat from aircontaminated steam.

Of all the documents cited, only the US patent No. 2,718,710 recommends compression of steam. The apparatus described transfers enthalpi from a mixture of air and moisture under atmospheric pressure to feed water at well below one bar and a subsequent compression of the vacuum pressured steam.

Especially the Norwegian patent No. 109,226 is listing the methods until now considered applicable in the efforts to obtain savings in the enthalpi comsumption related to production of fish meal and similar products (notice Norwegian patent No. 109,226 page 1, column 1 last lines and column 2). According to our knowledge, no later prints than the above mentioned patent lists any methods for saving enthalpi, which is not listed in said Norwegian patent. All known patents are describing different methods for applying the listed, basic principles.

This invention is distinctive in teaching application of a mainly adiabatic heating of the steam generated in an indirectly heated drier (evaporater) until reaching a temperature which is the minimum temperature requested for the heating medium used in the indirectly heated drier/evaporator, which produced the steam to be compressed, and the use of this steam as the heating medium in the drier/evaporator.

Up to now all literature taught, that steam generated in the drier could exclusively be used as heating medium in such enthalpi consumption places in the plant requiring a maximum temperature equal to or below the temperature, at which the steam leaves the drier, and this temperature of course is lower, than the minimum temperature requested for heating steam in the drier. The reasons for the above mentioned teaching may be numerous, but may - except for conventional thinking - very likely be based on the fact that this steam is not only water vapor. The steam is a gaseous mixture containing water vapor, often, controlled or unintentioned, air or gas(es) and always smaller quantities of gaseous components released from the material treated in the drier. These latter compounds are often the very smelly components, which are causing environmental stress to the surroundings.

We have now surprisingly proved, that it is possible to heat the steam generated in an indirectly heated drier/evaporator by compression (an adiabatic heating) and in a simple and very enthalpi saving way generate steam useful inter alia as heating means in the drier itself.

Because the adiabatic or isentropic heating of the steam is requiring only 162 kJ (39 kcal or abt. 0.045 kWh) for each kg of steam in order to have the temperature and pressure increased sufficiently to make the steam useful as a heating medium in the drier, whereas 1 kg of 10°C water fed to a boiler is requiring almost 2,800 kJ (699 kcal or abt. 0.778 kWh) in order to generate steam of even heating quality, the theoretically obtainable energy saving is obvious. According to the invention the energy saving is not only easily calculable but it is basically possible to carry it into effect. It has furthermore been stated that the odor stress applied to the environment is now dramatically reduced because the steam generated in the drier is condensated and possibly via a sewer treatment plant drained off. It has been proved that the small quantities of gaseous components present in the steam generated in an indirectly heated drier of known design and sealed from air-intake working in a fish meal plant, and not dis solved in the condensate, amounts to less than 0.50 per cent of the steam quantity and usually is less than 0.20 per cent. These gaseous components are during production concentrated in the heating chamber of the drier and possibly in the similar chamber in a stick water evaporator. It is relatively simple to control and demolish these small quantities in equipment of known design.

The pecularity that steam generated in the drier after compression is utilised as heating means in the drier is an advantage especially as the drier is usually a substantial or main enthalpi consumer in the plant. A plant comprising a cooker, a multi-step evaporator and a drier is often allocating about one third of the heat consumption to each of the three units. Furthermore, the drier is requiring the highest temperature, a fact that makes the feeding of this unit with inexpensively generated steam extremely interesting.

Thanks to the invention, it is now possible to prevent loss of enthalpi and creation of environmental problems by releasing substantial quantities of steam or by condensation the steam using huge quantities of cooling water.

The method of the invention may be distinctive in the use of enthalpi in condensate generated from the compressed steam by piping this condensate from the drier to the cooker in which it is in an in itself well-known way used as a heating medium. The advantage is saving of specially heated water otherwise necessary for heating the cooker. A special and in itself well-known embodiment of the cooker is utilising both the condensate as well as the steam as heating medium, and it is designed in order to utilise the steam only in that part of the cooker holding the highest temperature range. It is an advantage, too, if the cooker is designed to apply the counter-current principle in the movement of the heating medium and the material to be heated relatively to one another on each side of the heat exchange surface.

The invention may in an embodiment be distinctive in the cooling of the overheated compressed stem to or slightly above the saturation point at the compression pressure. This cooling is preferably carried out by injection of a controlled quantity of condensate generated in the drier and/or in the evaporator if the plant comprises an evaporator. The advantage is that a larger quantity of steam containing approx. even quantity of enthalpi available has been generated in a well-known, simple, and reliable way.

In another preferred embodiment of the invention the steam is heated by compression in two or more steps, and during at least one intermediate step the overheated steam is cooled to a temperature only slightly above the point of saturation for steam at the pressure reached. The advantage is that the following compression step(s) can be carried out at a lower temperature than otherwise necessary and possibly too high to economically acceptable control and handling. For the processes carried out in plants producing fish meal and similar products it is preferable to use saturated or nearly saturated steam rather than overheated steam. Another advantage in using at least two compression steps is, that an evaporator in a plant should often be supplied with steam inferior in pressure and temperature to the steam required to feed the drier. The above mentioned embodiment in this case makes the saving of unnecessary compression possible by allowing branching off a stream of steam between the steps of compression.

An embodiment of the invention as well steam generated in the drier as steam from somewhere else in the plant, e.g. from an evaporator joins in the steam compressionprocedure . The compression may be carried out in one or more steps, and cooling of steam and/or branching off of steam streams may take place in between two steps of compression and/or after the final compression. The advantage related to such a steam compression design is an increa- sed flexibility and an increase in possibilities regarding the control of the entire heat economy of the plant.

The method according to the invention may finally be distinctive by a starting up procedure comprising gene- ration of steam by means of steamgeneration means located in the means for cooling the overheated, compressed steam, steam piping means for piping the first generated steam back to the steam compression means via pressure reduction means, utilising the first generated steam exceeding the normal steam comsumption of the steam compression means for heating cold condensate or start—up feed water in the plant, and when the apparatus (es) in the plant requesting the relatively lowest temperatures du ring production has reached their production temperatures, then leading steam in excess of this need as a heating medium to the indirectly heated drier(s) /evaporator(s), and finally when the steam generating appara- tus(es) in the plant produces sufficient steam, closing down for the piping of steam from the steam cooling means to the steam compression means, and the steam generation means located in the steam cooling means, are shut down and kept unproductive as long time, as steam is produced in the drier(s)/evaporator(s) in sufficient quantity. The advantage related to this method is, that the plant according to the invention in this way can be started up with a minimum, initial steam supply from other steam generation means than the drier(s)/eva- porator(s) being part(s) of the plant.

The invention is describing a plant for production of fish meal or a similar product, and comprising an indirectly heated drier, the plant being capable of practising the method invented.

The plant is peculiar by comprising at least one compressor, steam piping means connecting the suction side of this compressor with the drying chamber in the drier and steam piping means connecting the pressure side of the compressor with the chamber for heating means in the drier. The advantage related to this plant is, that it can perform the method invented and realize the advantages listed above.

A drying plant according to the invention may be peculiar by comprising a boiler or heater designed with at physical separation between the heating medium and the material to be heated, and too comprising piping means for condensate leading hot, condensated steam produced by compression of drying steam/evaporation steam and utilised as a heating medium in the drier/evaporator from the steam condensing apparatus to the boiler/heater. The advantage gained by this design is, that it makes a specials advantageous reuse of the enthalpi in the dryingsteam possible .

The drier according to the invention and comprising more than one steam producing apparatus (drier/evaporator) may further be peculiar by comprising steam piping means converging the different streams of steam generated in the different drier(s) and/or evaporator(s) to one main stream of steam. The means for uniting two or more minor streams of steam may be placed in upstream direction in relation to a first compressor , or one or more of the different streams of steam may be compressed, before the flow of these streams joins. The advantage related to a plant in which the different streams of steam, which after compression are to be used as heating medium in a plurality of steam consuming appara- tuses, are joined, is, that the possibilities for a flexibel control and maintenance of an economical production are considerably increased, if it is possibel to regulate the steam supply to each of "the steam consuming apparatuses an indipendent by. as possibel of the steamproduction in the apparatus in question.

A plant according to the invention maytoo be peculiar by comprising steam cooling means capable of cooling the steam heated by compression and therefore being an overheated steam to a temperature close to or being the temperature creating saturated steam by the pressure reached by the compression. The steam cooling means may be peculiar by having injection means for injection of a controlled quantity of condensate from the drier or the evaporator in the overheated steam. The advantaged by utilising substantially saturated heat instead of overheated steam is, that the temperature on the heat transfer surfaces to be heated by means of the steam in an easier way can be constant uniform and on the desired level. The advantaged related to the injection means system is, that it's inexpensive, simpel and reliable, and the steam quality is not either changed.

The plant according to the invention may further be peculiar by comprising steam compression means involving more than one compression step and by at least one step in between two compression steps involving steam cooling means and/or steam branching off means preferably placed immediately down-stream in relation to the following compression step. The steam branching off means may be equipped with steam valving means making it possible to control the flow in the branched off stream of steam. The advantages related to the above mentioned design of a plant is an economical advantageous production in plants involving major steam consuming apparatuses requesting different pressures and/or temperatures in the heating steam.

Plant accordingto the invention arid comprising steam cooling means placed down-stream after the steam compression means and up-stream in relation to the drier/ evaporator may finally be peculiar by having the steam cooling means comprising steam generation means e.i. in form of electrical heating elements installed in the lower section of the steam cooling means, where condens water/start-up feed water is collected, steam piping means including pressure reduction means and steam valving means designed to feed steam directly from the steam cooling means to the steam comp ression means after a pressure reduction or to alternatively block such steam passage, and steam piping means including valving means and capable of feeding steam from the steam cooling means to heating means for condenswater/start-up feed water and capable of blocking such steam passage.

The invention is. illustrated in the drawing and further explained in the following, detailed description of preferred embodiments and with reference to the drawing. In the drawing is:

fig. 1 a diagram schematically illustrating a fishmeal plant according to the invention and of very simple structure,

fig. 2 an enthalpi diagram illustrating the content of enthalpi in 1 kilo steam (water) at several locations and different states,

fig. 3 a diagram similar to fig. 1, but a plant according to the invention of more complicated structure,

fig. 4 an enthalpi diagram similar to fig. 2, but illustrating content of enthalpi in 1 kilo steam/water at locations and states of matter related to the plant according to fig. 3. In fig. 1 is illustrated an indirectly heated drier 1, an indirectly heated cooker 2, a decanter 3 , steam compression means 4, steam piping means 13 for drier generated steam and steam piping means 15 for compressed steam. Pig. 1 further illustrates the raw material supply conduit 5, a conduit 6 for boiled rawmaterial leading to the decanter 3 , a conduit 7 for fish-oil a stickwater conduit 9 and a conduit 8 for decanted fish-material. The plant further comprises a pump 22 for fish-material, a conduit 10 for fish material. fish meal outlet means 11, drier steam outlet opening 12, outlet opening 14 for compressed steam leaving the steam compression means 4, an inlet opening 16 in the drier 1 for heating means (steam) and a pipe 17 for auxiliary steam. Condensate piping means 19 is connecting the outlet opening lδ for condensate in the drier 1 and inlet opening 20 for heating means in the cooker 2. The outlet opening 21 for used heating means in the cooker 2 is by means of a conduit 22 connected to the sewer.

The plant described above functions as follows: via the conduit 5 for rawmaterial is cold (normally about 5°C) rawmaterial pumped to the cooker 2. In the cooker 2 is the rawmaterial heated p'referably in a counter-current movement relative to the condensate flowing in the heating means chamber on the opposite side of the heat exchange surface in the cooker 2. The heating normally bringing the rawmaterial to the boiling point. Through the conduit 6 is the boiling hot fish material pumped to the decanter 3, in which the oil and stick- water are separated from the solid and semisolid matters. The oil is pumped through the conduit 7 for fishoil and leaving the plant as "raw fishoil".

The solid and semisolid matters and the stickwater are via the conduits 8 respectively 9 and the pump 22 pumped via the conduit 10 to the drier 1.

In the drier 1 is the water/humidity in the fish material dried out by means of indirectly heating provided by condensating steam. The dried matter is leaving the drier via the fish meal outlet opening 11, whereas the generated steam is taken out via the steam outlet opening 12 and via the conduit 13 fed to the suction side if the steam compressor 4. After compression to the pressure required for condensation at the minimum heating temperature in the drier 1 is the steam via the compressor outlet 14 and the conduit 15 fed to the inlet opening 16 for heating means in the drier 1 in order to function as heating medium.

Auxiliary steam may be supplied via conduit 17 especially during start-up of the plant. The auxiliary steam is generated in the steam generator not shown in the drawing.

The condensate generated in the drier 1 is via the outlet 18 and the conduit 19 fed to the inlet opening 20 in the cooker in order to function as heating means for heating the rawmaterial. After a flow (in counter-current configuration relative to the fish material) in the cooker 2, is the condensate leaving the cooker via the outlet opening 21 and is via the conduit 22 directed towards the sewer.

The plant is a combination of units, all of which are well known except for the piping of the steam produced in the drier 1. We therefore underline,that this steam is piped directly into a conventional compressor, in which it is compressed to the pressure necessary to make the steam useful as feed steam in the drier 1.

The steam is after the compression piped to this drier 1, and the enthalpi content in the steam can thus be reused in the drier in an advantageous way .

The reuse of enthalpi is essential for the production cost in plants of this very simple design, because the drier here is consuming far more than half the enthalpi consumed in the whole plant.

Fig. 2 is an enthalpidiagram indicating the enthalpi content in one kilo of water included in the raw- material supplied to the plant at 5°C This water is heated to the boiling point in the cooker 2 under absorption of 419 kJ. In the drier 1 is further enthalpi supplied and absorbed under generation of 1 kilo of steam at 1 bar pressure and 100°C having an enthalpi content of 2676 kJ. In the compressor 4 is another 162,5 kJ enthalpi (converted free energy) supplied to the 1 kilo of steam. This compressed steam with a content of 2838,5 kJ may now be utilised as heating means in the drier 1, in which the steam is condensated releasing a total of 2838,5 - 529,7 = 2308,8 kJ. The residual enthalpi is to a large extent utilised in the cooker 2, where the condensate is cooled from 126°C to 15°C before flowing to the sewer.

Fig. 3 is illustrating a more complicated plant for production of fishmeal according to the invention. The plant comprises the main components comprised in the plant according to fig. 1. In fig. 3 are the reference figures for the drier 101, the cooker 102 and the decanter 103. The plant further comprises a buffertank 104 for hot condensate and a stickwater evaporator 105. The compressor in the plant according to fig. 1 is in the more sophisticated plant illustrated in fig. 3 replaced by two compressors 106, 108 coupled in serie.

In between the two compressors 106, 108 and downstream relative to the compressor 108 is installed steam cooling means embodied as condensate injectors 107 respectively 109. Except for the above listed components comprises the plant in fig. 3 various conduits establishing required interconnections between the components listed.

The plant illustrated in fig. 3 and the plant illustrated in fig. 1 are according to the invention utilising the very same main principle for the main supply of enthalpi. The following description of how the plant in fig. 3 functions, is therefore mainly mentioning the differences between the two plants. The stickwater is piped from the decanter 103 via the pipe 114 to the evaporator 105, in which it is concentrated to a stickwater concentrate, before its piped via pipe 118 and 116 to the drier 101 joining the non -fluid fish components.

The steam generated in the evaporator 105 is piped via pipe 121 to pipe 120, through which it joining the steam leaving the drier 101 and fed to this point through pipe 119 is piped to the compressor 106. The steam compressed in the compressor 106 is piped through pipe 122 to the cooler 107, in which a controlled amount of condensate is injected transforming the steam to substantially saturated steam. Condensate is fed to the cooler via pipe 132, 134 and 135 from the stickwater evaporator 105.

Before compression of the substantially saturaded steam is a part of the steam branched off at the point between pipe 123 and 125 and via pipe 124 fed to the evaporator 105 as heating medium.

The other part of the steam is piped via pipe 125 to the second compressor 108. Prom this compressor is the steam piped via pipe 126 to cooler 109, in which it by means of condensate fed to the cooler via pipe 132, 134 and 136 is transformed to saturated steam. This steam is via pipe 128 fed to the drier 101.

Surplus df steam may via pipe 129 and controlled by valve 130 be fed to the condenswater tank 104. Condensate from as well the drier as the evaporator is fed to the condenswater tank 104 via pipe 131 respectively 132, 133. The condensate is utilised as heating medium in the cooker 102. The drain pipe 138 for heating medium leaving the boiler 102 is branched off in one pipe 139 feeding the heating medium back to the condens- water tank 104, and another branch 140 leading to the sewersystem.

Fog. 4 is an enthalpi/pressure diagram of state illustrating 1 kilo of water moving its way through the plant .Starting at the inlet to the drier or the evaporator this water is containing 419 kJ enthalpi. During evaporation another 2, 257.1 kJ enthalpi is absorbed,and the steam now containing 2,676.1 kJ is fed to the compressor 106 in which further 162.4 kJ enthalpi is supplied (in the form of free energy). The pressure hereby is increased to 2.4 bar, and the temperature is by now l85.3°C. In the cooler 107 is hot condensate from the evaporator 105 injected (approx. 5.5 per cent), and the steam is cooled to 126.1°C (or slightly higher). The slightly more than 1 kilo of steam now contains abt. 2.715 kJ of enthalpi.

Considering one kilo of this steam is fed to the evaporator 105, 2,715 - 529.7 or 2,185 kJ are supplied to the evaporator. The main part is absorbed in water evaporating in the apparatus, and a small quantity (dependent on the insulation) is lost to the environment .

Considering another one kilo of steam leaving the cooler 107 entering the compressor 108, this steam is compressed from 2.4 to 6.0 bar under absorption of further 183.6 kJ. By now the temperature is 222.4°C. This overheated steam is cooled in the cooler 109 by injection of a controlled quantity of hot condensate. Thus, a slightly larger quantity of mainly saturated steam is leaving the cooler 109 having a temperature of abt. 158.8°C and a, total content of enthalpi of abt. 2,756 kJ/kg. The steam prepared this way is utilised in the drier 101 where it is under condensation releasing 2,756.8 - 670.56 = approx. 2,086 kJ per kilo steam. The condensate is piped from the drier 101 to the buffer tank 104 and is mixed with the condensate from the evaporator 105 and possibly other water supplied to this tank. Prom the tank the condensate is piped to the cooker and the contents of enthalpi utilised whereupon the cooled condensate is piped to the sewer. The temperature in the sewer outlet stream is usually held at 15°C (involving a loss of enthalpi of 60-65 kJ per kilo of dumped condensate).

A preferred start-up procedure for a plant according to the invention and designed according to fig. 3 is following:

Steam from an auxiliary supply-source and at a pressure of e.g. 6 bar is fed to the cooler 109. The auxiliary steam may be generated in a separate steam generator or in the cooler itself provided this is equipped with steam generating means e.g. electrically powered heating elements capable of evaporating water from the lower part of the cooler.

When the requested steam pressure has been reached (the conduits 128, 129 - and 141 are kept closed by means of valves), the conduit 141 is open making a steam passage via pressure reduction means to conduit 120 and compressor 106 available. The steam generating means 106, 107. 108, and 109may now start up yielding a reduced increasing steam generation. When the steam generation is adequate the valve sealing conduit 129 is released and condensate or feed-water in the buffer tank 104 is heated. During the start-up period water to the coolers 107 and 109 is taken from the buffer tank 104. When the buffer tank 104 has reached temperature necessary for production start, the heating of the cooker 102 is the first thing to be done. By the time when hot material is ready for the decanter, the steam production should have reached sufficient volume to feed the evaporator. It may at this point be necessary to have auxiliary steam generating, e.g. by electrically heated heating elements activated in cooler 107 as well as in the cooler 109 dependent on the over all design of the plant. The last apparatus in the plant to be heated during the start-up procedure is the drier. When in production it is not necessary to supply auxiliary steam to the plant except in case of extraordinary steam outlets or irregular heat losses.

The consumption of energy in a plant according to the invention is analysed in the following example calculated based on production of fish meal prepared from 1,000 kilos of raw material which were old fish mainly the small atlantic species "lodde" or capelin (Mallotus villosus).

The production was carried out in a plant as illustrated in fig. 3 and 4. The compressors were working at an efficiency of 67 per cent (not 100 per cent as indicated in fig. 4; we have noticed that compressors performing at efficiencies abt. 75 per cent are commercially available). The heat losses from the evaporator and the drier were 15 kW and 24 kW respectively and realized by only moderately insulated equipment. The performance calculated can therefore easily be improved.

1) Production capacity 1,000 kg fish/h

Steam consumption in drier 242 kg steam/h Steam consumption in evaporator 559 kg steam/h Pish meal production 199 kg/h Total evaporation of water 801 kg/h

2) Isentropic energy consumption by compression from 1 - 2 in fig. 4:

Compressor efficiency: 67 per cent

Total energy consumption during, compression:

36.134 ÷ 0.67 = 53.9 kW

3) Cooling the steam from pt. 2 to pt. 3 in the diagram fig. 4, with the correction, that pt. 3 is placed further to the right due to the efficiency loss in the compressor, the losses are removed from the compressor as increased temperature in the steam.

Compressor loss: 53.9 - 36.1 = 17.8 kW Isentropic compression energy:

Total enthalpi to be absorbed by cooling: 27.5 + 17.8 = 45.3 kW

Cooling water (condensate) injected:

4) Heat consumption in the stickwater evaporator (transformance pt. 3 - pt. 7 in fig. 4)

Theoretically:

Heat loss from the evaporator: 15.0 kW

Total heat consumption in evaporator: 350.5 + 15 = 365.5 kW

Steam supply to the evaporator:

5) Energy consumption for the second compression step (the transformance from pt. 3 to pt. 4 in fig. 4 and with a similar efficiency effect taken into account as the one explained under

3) resulting in a move of pt. 4 towards the right.

Steam to be compressed:

801 + 174.6 + 602.1 = 273.5 kg/h Energy consumption for isentropic compression:

plus correction for efficiency in compressor 67 per cent:

13.9 ÷ 0.67 = 20.7 kW of which the losses amount to 6.8 kW

The total energy consumption in the compressors therefore is

20.7 + 53.9 = 74.6 kW

6) Cooling the steam from pt. 4 to pt. 5 in fig. 4 (cooling in cooler 109) Theoretically requested cooling:

plus compressor losses: 6.8 kW

Total cooling requested: 10.8 + 6.8 kW = 17.6 kW

Requested water (condensate) at 126.1ºC, for cooling:

7) Heat consumption in the drier:

The heat treatment of 1,000 kilos of raw material in this case (treatment of old "lodde") and including the heating in the cooler, which were heated by means of condensate from the drier and the evaporator, called for a total energy supply of 74.6 kWh - which figure it is possible to further reduce.

As a comparison with the technology of today, to our knowledge the most efficient plant is consuming approximately 350 kWh per 1,000 kilos of fish in order to perform a comparative heat treatment. The average energy consumption in plants now in operation in Iceland is approximately 840 kWh per 1,000 kilos of fish.

It is evident to persons skilled within the art that the method and the plant described in the above mentioned examples may be modified in many ways without deviation from the idea and scope of this invention. The legal limits to out invention is for this reason set only by the definitions given in the claims below.

Claims

C L A I M S

1. Method for manufacturing fish meal or similar products in a plant comprising an indirectly heated drier, c h a r a c t e r i z e d i n compressing steam generated by the drying of the substance of fish material or the like in the dryer solely or after mixing with steam generated somewhere else in the plant, or in utilising at least part of the compressed steam as the main or only heating medium in the dryer during production.

2. The method according to claim 1 and used in a plant comprising an indirectly heated pre-treatment apparatus, i.e. a cooker in which the raw material, fish or the like, is pre-heated and/or cooked, c h a r a c t er i z e d i n leading condensate generated in the drier to said cooker, and in utilising said condensate as a heating medium in said cooker.

3. The method according to claim 2, c h a r a c t er i z e d i n leading said condensate over the heat exchange surface in said cooker in counter-current direction relative to the substance of raw material passing over the opposite side of said heat exchange surface.

4. The method according to claims 2 or 3, c h a r a c t e r i z e d i n utilising said condensate and steam as heating mediums in said cooker.

5. The method according to one or more of the claims 1-4 in a plant comprising a stickwater evaporator, c h a r a c t e r i z e d i n leading steam generated in said drier and steam generated in said stickwater evaporator together in one stream of mixed steam, and in utilising at least part of said mixed steam after said compression as heating medium in the dryer and possibly elsewhere in the plan.

6. The method according to one or more of the claims 1-5, c h a r a c t e r i z e d i n cooling the overheated steam generated by said compression in one or more steps preferably by injection of water, e.g. con densate from the said dryer and/or from said stickwater evaporator in order to obtain saturated or slightly overheated steam, which is further compressed and/or used as a heating medium.

7. Plant for manufacturing fish meal or the like by the method according to at least one of the claims 1-6 and comprising at least an indirectly heated dryer i.e. a dryer with an unpermeable wall or heat exchange surface separating a drying chamber and a heating medium chamber, c h a r a c t e r i z e d i n, at least one compressor, steam pipingmeans connecting said drying chamber in said dry.er and the suction side of said compressor, and steam piping means connecting the pressure side of said compressor and said heating medium chamber in said dryer.

8. Plant according to claim 7 and comprising an indirectly heated cooker for pre-heating and/or cooking the raw material, e.g. fish, c h a r a c t e r i z e d i n piping means for condensate connecting said heating means chamber in said dryer and the heating means chamber in said cooker .

9. Plant according to claim 7 or 8 and comprising a stickwater evaporator, c h a r a c t e r i z e d i n steam piping means possibly including pipe(s) valve(s), pressure reduction valve(s), and compressor(s), leading a stream of steam generated in said dryer and a stream of steam generated in said evaporator together to create one stream of mixed steam injected to the suction side of said compressor, and in steam piping means connecting the pressure side of said compressor and at least the heating means chamber in said dryer.

10. Plant according to claim 7, 8, or 8, c h a r a ct e r i z e d i n water injection means for injection of water, i.e. condensate in the stream of compressed steam leaving the compressor(s).