SE456795B - Sepn. method for liq. component from mixt. - Google Patents

Abstract

The method involves driving in a circuit flow a current of a carrier gas from an evaporator to a condenser, and then back to the evaporator. The carrier gas is fed to the evaporater for contact with the mixture, and is accordingly transferred to the condenser together with liq. components of the mixture. One part of the liq. components is pptd. through condensation in the condenser. A flow of a fluid is circulated in a circuit flow from a heat transmission contact to the mixture within the evaporator via a heat transmitting contact to a further heat drop in a cooler, via a heat transmitting contact to the carrier gas in the condenser, via a heat transmitting contact to a further heat source in a heater, and then back to the heat transmitting contact to the mixture in the evaporator.

Description

456 795 A separation process can thus be carried out with a high energy efficiency at any pressure level and within any temperature range below the boiling point of the volatile component, which constitutes a first object of the invention.

In particular, a pressure level equal to atmospheric pressure can be selected and a temperature range adapted to the use of heat exchanger surface of plastic material can be selected. In this way, a process equipment can be built with simple, efficient and corrosion-stable means, the rest being a second object of the invention.

Temperature range for a separation process can further be selected to prevent quality reduction of heat-sensitive mixtures, the rest being a third object of the invention. These objects and others, mentioned below, are achieved by a method further characterized in that a flow of a liquid is circulated in successive heat transfer steps from contact to said mixture, via contact in a cooler with an external heat sink, via contact to said salvaged in said condenser, via contact in a heater with a heat source and back to said contact to said mixture.

A further object is the simplified and highly efficient enthalpy transfer surface by using the volatile component as a heat-carrying liquid. Another object is a method of carrying out a separation process over a wide temperature range with further improved energy efficiency.

Another object is to provide a separation process, which can be operated with a liquid / liquid heat pump for further improved energy efficiency.

The invention is described in more detail below in connection with the drawings. The basic principle of the method is illustrated in Fig. 1 in a temperature / enthalpy diagram and in Fig. 2 in an apparatus section. The method operated within an extended temperature range is illustrated in Fig. 3 in a temperature / enthalpy diagram and in Fig. 4 in an apparatus section. 3 456 795 Figs. 5-12 illustrate the method of different methods of heat transfer to a mixture. Thus, Fig. 5 in section shows direct heat transfer through membranes to a liquid mixture. Fig. 6 illustrates in an apparatus section indirect heat transfer to a liquid or solid mixture by means of a steam-saturated carrier gas and Figs. 7 and 8 detail sections thereof. A method for indirect heat transfer to a granulated solid mixture by means of circulating hot gas is illustrated in Fig. 9 in a temperature / enthalpy diagram and in Figs. 10 and 11 in apparatus sections. Fig. 12 illustrates in a temperature / enthalpy diagram drying of wood.

Referring to Figs. 1 and 2, a flow 3 'of an inert carrier gas 3 is driven along an extended evaporator 4 in evaporative transfer contact to a mixture 2, dispersed in the evaporator 4. From its inlet side to its outlet side of the evaporator, the gas flow 3 changes with a temperature rise + At2 and an enthalpy increase + Ai2, the latter consisting essentially of heat of vapor formation in a flow 1 "of a volatile component 1, in vapor form expelled from the mixture 2.

Heat of formation may to a small extent be supplied by heat content in the mixture, but is substantially supplied to the mixture from a flow 1 'of a liquid 11. Heat can be transferred to the mixture 2 by direct or indirect means in countercurrent to the flow direction of the carrier gas 3 as described below. , whereby the liquid 11 changes with a corresponding enthalpy loss -Aiz and a substantially equal temperature drop -A t2. In a temperature / enthalpy diagram according to Fig. 1, the state of the carrier gas 3 is described by means of a curve C ', which represents a section "k" of a curve C, which describes the enthalpy of a carrier gas 3, saturated with steam of the volatile component 1 The corresponding state of the liquid 11 is described in the diagram by a straight line "A", enthalpy and temperature being proportional.

A reverse process takes place in a condenser 5, in which the liquid flow 1 'and the carrier gas flow 3', both flows transferred from the evaporator 4, are driven in countercurrent enthalpy transfer to each other. In the diagram, Fig. 1, condenser conditions 456 795 -y 4 of the carrier gas 3 are described by a curve CE, with the gas changed in temperature -At4 and in enthalpy -A14 during precipitation of a flow 1 "of condensed volatile component 1.

Conversely, the liquid 11 changes substantially with a temperature rise + A t4 and an enthalpy gain + Åi4 and the condenser state of the liquid is described in the diagram by a straight line "B". For working conditions with the carrier gas 3 fully saturated with vapor of the volatile component 1, the curves C 'and Ci are identical. Preferably, volatile component 1 is used for said liquid 11. Condensation can hereby be carried out in a known manner as direct wet enthalpy transfer and condensation between the carrier gas 3 and the liquid 1 sprinkled over a contact body 55 in a vertically extending condenser 5, said flow 1 "of volatile component continuously separated from a substantially larger circulating flow 1 'at an outlet from the bottom of the condenser_ The straight lines "A" and "B" must in the diagram fig.1, obviously enclose the curved lines CÉ and Ci as well as space for the heat gradient which A closed process cycle and a driving force for the process are achieved with a cooling stage in a cooler 62, in which the liquid 11, transferred from "A" to "B", is cooled against an external heat sink 8. during a change in temperature -At3 and enthalpy fAi3.In a heating step from "B" to "A", the liquid 11 is heated in a heater 61 by an external heat source 7 with the liquid changed in temperature atur + át1 och i entalpi + Ai1.

The driving force for the process is an amount of heat Åi fi approx. equal to you, which is degraded in temperature level from a heat source 7 to a heat sink 8. An essential point of the invention is that the driving force may be significantly less than the enthalpy amounts Åiz É.Åi4, which are engaged in the actual process of separating a volatile component 1. from a mixture 2 in the evaporator 4 and to condense them in the condenser 5. Thus, a first energy efficiency e1 = Ai? / UAi1 can be defined. Obviously, said factor is improved by increasing a temperature range "k" for the process and by shrinking the temperature gap between the straight lines "A" and "B". The latter is achieved through the use of large and efficient exchange surfaces for heat and steam. Since the temperature range "k" can be optionally selected below the boiling point of the volatile component 1, temperature conditions can be adapted to the use of plastic materials for cheap, efficient and large transfer surfaces in the evaporator. Furthermore, the described condensation process over a wetted contact body 55 can be extremely efficient. With a temperature range k É 15 ° a first factor e1 = 2 can be achieved.

A second energy efficiency factor ez can further be achieved by interconnecting the external heat sink 8 and the heat source 7 in a heat pump process. This can be done to advantage, using the distilled, fairly pure volatile component 1 as the heating / cooling medium. Temperature range for a heat pump is in the mentioned range k = 15 ° favorable and a heating factor = e2 3 5 may be achieved. A total energy efficiency = e1x e2 É 10 is the result.

The temperature range "k" can further be selected to suit a heat-sensitive mixture 2. Pressure range for gas can also be selected as desired, but atmospheric pressure may be preferred for low apparatus cost. Enclosed carrier gas 3 can also be selected as desired and especially to satisfy quality requirements in connection with the mixture 2, for example lack of oxygen. A gas with a low molecular weight such as helium may be selected for a high degree of diffusion for steam.

In case of high evaporation rate in the evaporator 4 or vapor pressure reducing forces in the mixture 2, the carrier gas 3 does not achieve full steam saturation in the evaporator 4. Process efficiency can in this case be improved by cooling the flow 3 'to the dew point 3 in a heat exchanger 63 before entering the flow in the condenser, the effluent cooled flow from the condenser constituting a preferred cooling medium. Fig. 2 illustrates the method in an apparatus section, which shows a carrier gas 3 driven in a circuit within and between an evaporator 4, a condenser 5 and a heat exchanger 63 and a liquid flow 1 'driven in successive heat exchanger stages in contact with a mixture2 in the evaporator, with a cooler 62, to carrier gas, with a heater 61 and again to the evaporator 4.

Energy efficiency can be significantly increased by means of a further innovative step, described below in connection with Figs. 3 and 4. A number of partial flows 31 ', 32' ... are thus diverted from the mixture of carrier gas 3 and vapor of volatile component stepwise along the current channel in the evaporator 4, and remixed with the mixture of carrier gas and steam stepwise along the current channel in the condenser 5. Furthermore, the temperature range "k" is substantially increased. Using two substreams 31 'and 32', Fig. 3 illustrates evaporator states of the carrier gas 3, described by three different curves C ', Cå and Cå, which represent gradually decreasing mass flows of carrier gas, increasing temperature levels and substantially equal transport capacity of steam. . Conversely, the state of the carrier gas 3 along its flow in the condenser is described by corresponding curves Go 'C; and C "1, which represent incrementally increasing mass flows of carrier gas 3, decreasing temperature level and substantially equal transportability of steam. The state of the liquid liquid stream 1 'is described by the straight lines" A "and" B ". Described differentiation of the mass flows of the carrier gas 3 by using the appropriate number of substreams, will allow a narrow temperature gap between the lines "A" and "B" in combination with a wide temperature range "k". This results in a significantly increased first energy efficiency factor in comparison with the previously described method. , operating with a uniform mass flow 3 'of carrier gas 3.

A process is exemplified with reference to Fig. 3, wherein volatile component 1 is water, carrier gas 3 is air and the mixture 2 is an aqueous solution to be concentrated. Corresponding mass loads, temperature changes Åt and enthalpy changes Äi are shown in the figure. Driving force is a heat amount Ä i1, degraded from a heat source 7 at approx. + 8S ° C to a heat sink 8 at appr. + 15 ° C. Obtained first energy efficiency factor e1 = Å i2 / 4 i1 = 4.3 Another expression for energy efficiency kwh / kg distilled water = 0.19. degree is e3 - 456 795 It appears that a remarkably high energy efficiency can be achieved in a one-step operation with the use of fairly simple heat exchanger means and atmospheric pressure conditions.

Use of a heat pump in the example training heat source 7 and heat sink 8 with a heat factor ez 3 2.5 results in a total energy efficiency factor § 11. Obviously, the investment cost for a heat pump is reduced compared to the process described in connection with Fig. 1, since the pumped heat output is approx. halved.

Depending on the nature of the mixture 2, heat transfer between the liquid flow 1 'and the mixture can be arranged in different ways with reference to Figs. 5-12.

A direct heat transfer through a membrane is illustrated in Fig. 5, which shows a planar section of pairs of flexible, thin plastic membranes 64 vertically suspended within the evaporator. The liquid 11 is driven between inner surfaces of the membranes by gravity such as thin liquid films which are spread over the surfaces by capillary forces. A liquid mixture 2 is driven as open falling films 21 along outer surfaces of the membranes; Referring to Fig. 2, a continuous mixing stream 2 'may be fed to the top of a vertically extending evaporator as a process stream, with a processed stream 2' continuously discharged from the bottom of the evaporator.

The gear material 64 is inexpensive, efficient and corrosion stable and can be easily extended to surface and height for excellent transfer and process conditions. The process flow 2 'can further be preheated in a known manner before being fed into the evaporator against discharged processed flow 2 "and discharged flow. 1 "of volatile component in a countercurrent liquid heat exchanger.

An indirect heat transfer to the mixture 2, distributed in the evaporator 4 as liquid or solid layers 21, is illustrated with reference to Figs. 6-8. A further flow 9 'of the carrier gas 3 is driven in a closed cycle in evaporative, countercurrent enthalpy exchange with the heated liquid flow 1' of the volatile component 1 along a wetted, additional contact body 99 and subsequently in enthalpy transfer to the mixing layers 21 through tube walls 65. _ '~ n »456 795 An additional flow 1" of volatile component, condensed Along the tube walls, mixed with the flow 1'. The tubes 65 are applied inclined for drainage of condensate. The tubes may be of flexible plastic material, for example extruded polyethylene hose, furthermore, be inflated by means of a small pressure difference between the flows 9 'and 3'.

Fig. 7, which shows a planar section of the evaporator 4, illustrates heat transfer from said flow 9 'to a liquid mixture 2, which is driven as open falling films along the outer surface of vertically extended, inflated tubes 65.

Fig. 8, which shows another plane section of an evaporator, illustrates heat transfer from said flow 9 'to a solid mixture, which is spread in the evaporator as parallel layers 21. Flat tubes 65 are inflated against the layers 21 during the process process, for example a batch dryer. of a damp sheet material. The tubes can be sucked together during loading or unloading to facilitate handling of the solid mixing layers 21.

A further method for indirect heat transfer is described below in connection with Figs. 9-12.

The process relates to a granular, gas-permeable type of mixture 2. The process can be applied, for example, for drying moist cereals, chopped organic material or wood. Such a mixture can in a known manner be alternately charged with heat and discharged with steam against a carrier gas in contact with the mixture, evaporative heat being taken from the heat content of the mixture. The alternating thermal charging of the mixture is effected with gas, circulated in a closed cycle through the mixture and a heater.

However, this procedure does not allow a high temperature gradient along the path of the heating gas through the moist material, due to vapor diffusion from a thus heated, warmer part to a colder part of the mixture.

The process of the invention, directly applied to the heat transfer procedure described above, would exhibit a very poor first energy efficiency factor e1¿I1, and thus be meaningless. However, the method described in connection with Fig. 3 can be used by dividing a mass of a moist, granular mixture 2 into a number of sub-items, which are treated within separate, gradually increasing temperature ranges tr.

Referring to Fig. 11, which shows an apparatus section, an evaporator 4 comprises two separate chambers 4a and 4b, each chamber containing a mass of a mixture 2, divided into a number "r" of sub-items 2r, as exemplified by six vertically arranged sub-posts 2r with index r running upwards by 1 to 6. As can be seen from Fig. 10, which shows a plan section, each pair of sub-posts Zr is connected to a damper system 75r, a circulation fan 76r and a heater 66r, by means of a sub-flow 10r of carrier gas 3 can be driven alternately through either of the sub-items 2r during the transfer of heat to the same from the heater 66r. With sub-flows 10r thus connected for heating sub-posts 2r, included in one of the chambers 4a or 4b, the flow 3 'of carrier gas is controlled by means of another valve system 74 in succession through the sub-posts Zr, entering the other chamber, the index r running from 1 to 6. The liquid flow 1 'is driven through the heaters 66r in reverse order, with index r running from 6 to 1.

Furthermore, the partial flows 31 'and 32' are diverted from the carrier gas 3 stepwise from the stream of the flow 3 'through the evaporator 4 and remixed with the flow 3' in a condenser 5 in the manner described in connection with Fig. 4.

For a granular mixture 2 such as cereals, the exposed area is very large. The heaters 66r can further utilize known plastic membrane technology for enlarged and efficient exchanger surface. The required heat transfer gradients can thus be kept low and the thermodynamics in the process as illustrated in Fig. 9 be very similar to the thermodynamic states described in connection with Fig. 3. From the example illustrated in Fig. 3 it can be deduced that mass flow in the partial flows 10r is of the order of = 8 kg in comparison with said differentiated mass flows 3 'of 1.57, 0.74 and 0.26 kg. While the latter flow 3 'is driven through all six sub-posts in a row, each sub-flow 10r is delimited to penetrate a sub-post Zr. The method of dividing heat supply to the mixture 2 into a number of partial flows 10r is thus also advantageous for fan work.A

Claims (1)

1. 456 795 ¶0 A more evenly distributed drying effect in the sub-items Zr can be achieved by cyclic change of flow direction of the sub-flows 10I. This may be desirable when drying a moist mixture such as wood to avoid stresses and cracks. Fig. 12 illustrates in a temperature / enthalpy diagram a wood drying process which is thermodynamically substantially similar to the process described in connection with Fig. 9 but which differs in that the sub-items 2! are determined at rather distinct and uniform temperature levels due to said occult reversal of the partial flows 10 :. The arrangement together with a less advantageous surface / mass ratio for wood than for a granular mixture increases heat transfer gradients in the evaporation process. Nevertheless, for an acceptably fast drying, an energy efficiency of 0.35 kuh / kg or with the use of a heat pump of 0.15 kuh / kg water can be achieved. This figure can be compared with approx. 1.4 cube / kg, which is required for conventional chamber drying of wood with hot air. A method for separating a volatile component (1) from a mixture (2), comprising said volatile component (1), said method comprising driving in a cycle a flow (3 ') of a carrier gas ( 3) from an evaporator (4) to a condenser (S) and again to said evaporator (4), said carrier gas being fed to the evaporator (4) for contact with said mixture (2) and then transferred to the condenser (5) together with volatile component (1) of the mixture (2), a portion (1 ") of said volatile component (1) being precipitated by condensation in said condenser (S) characterized in that a flow (v) of a liquid (11) is circulated in a circuit from a heat transfer contact to said mixture (2) within said evaporator (4), via a heat transfer contact to an external heat sink (B) in a cooler (52), via a heat transfer contact to said carrier gas (3). ) within said condenser (5), via a heat transfer contact to an external heat source (7) in a heater (61 ) and again to said heat transfer contact to said mixture (2) within said evaporator (4) 2. 456 795 11 A method according to claim 1 characterized in that said liquid (11) is said volatile component (1) and that it is supplied to said condenser (5) by sprinkling over a gas permeable, surface enlarged and falling film-forming filler body (55), housed within said condenser (5) to provide direct contact with said carrier gas (3). Method according to claim 1 or claim 2, characterized in that the number of valley flows (31 ', 32' ...) are diverted from said carrier gas (3) stepwise along the path of said flow (3 ') in said evaporator (4) and are remixed with said carrier gas (3) stepwise along the path of said flow (3 ') in said condenser (5). A method according to claim 3, characterized in that said mixture (2) is distributed in said evaporator (4) as layer (21) on membrane (64), that said flow (1 ') is in heat exchange contact with a surface of said layer. (21) through said membrane (64) and that another surface of said layer (21) is in said evaporative contact with said carrier gas (3) z. The method according to claim 2 characterized in that said mixture (2) is distributed in said evaporator (4) in layers (21), that said volatile component (1) and that circulating, further flow (9 ') of said carrier gas (3) is driven countercurrently in direct contact over a gas permeable, surface enlarged and falling film-forming, additional filling body ( 99), further flow (9 ') is then driven through tubes (65) in heat exchanging contact to said layer (21) and then added again to said contact within said further filling point (99). The said tube according to claim 1, wherein said tube: (65) is formed of flexible plastic membrane material and is inflated by means of a pressure difference between said flows (3 ', 9') of said carrier gas (3). A method according to claim 3, wherein said mixture (2) is arranged as two separate, gas-permeable dry goods. embedded in two separate chambers (da and 4b) in said evaporator, said dryer beds being arranged in intermittent heat transfer contact with a circulating heating flow of said carrier gas (3), which is alternately driven by one or the other of dry goods the beds are characterized in that said dryer beds are divided into a number (s) of sub-items (2r) processed at different, stepwise temperature levels (tr), that each pair of said sub-items (2r) are connected in a separate heat transfer circuit comprising a heater '(66), a fan (76r), a damper system (75r) and a circulating valley surface (1s) of aagda carrier gas (3), that said carrier gas flow (3') is driven through said sub-posts (Zr) in succession ( r = 1,2..6) and that said liquid flow (1 ') is driven through said heater (66r) in the opposite order (r = 6,5..1). B. A method according to claim 1, characterized in that said sub-flows (10I) are periodically reversed to the flow direction. 9. A method according to claim 1, characterized in that said external heat source (7) and heat sink (B) are connected in a heat pump process. A method according to claim 1, characterized in that said flow (s fl) of said carrier gas (3) has a cold supply to said condenser (5) in a heat exchanger (63) against said flow (3 '), cooled in and discharged from said condenser (5).