SE508561C2 - Method and apparatus for separating particles from a gas stream - Google Patents

Abstract

The present invention relates to a process for the separation of melt and preferably also solid particles from a gas flow, wherein the said flow arises from the gasification of spent liquor from pulp production, preferably black liquor, and comprises both gaseous substances (4) and melt and possibly also solid particles (5), which gas flow is conducted to a separating arrangement (2) where at least a certain portion, preferably the major portion, of the said particles (5) is separated from the gas stream (4), wherein the said flow of gaseous substances (4) containing melt and/or solid particles (5) is forced to move in a curved path and at least the outer periphery of the said curved path is delimited by a mobile liquid layer (12), wherein the said particles (5) are separated from the gas stream (4) by being amalgamated with, and preferably also dissolved and cooled in, the said liquid layer (12).

Description

10 15 20 25 30 35 508 561 2 the chemical content is separated for recycling. In the following The invention will be related to black liquor gasification. in order to be able to describe the invention in a more concrete way. which thus does not limit the invention to this specific area.

Black liquor is obtained as a residual product, waste liquor, at pulp action according to the sulphate cellulose method. Black liquor in- contains alkaline chemicals, in the form of various sodium compounds which one wishes to recycle for reuse in the process. The recycling process contains a heating step, a reactor in which the organic molecular chains in the black liquor is broken down into energy-rich gas and the inorganic the contents are mainly found as molten particles that can recycled. This is done by pyrolysis and partial burning of the organic constituents of the black liquor.

The pyrolysis and combustion thus release heat energy, usually the temperature is about 1000 C ° in the reactor, as well as cer a flammable gas. It is desirable to extract it released heat as well as utilize the energy-rich gas that fuel.

SE-B-448 173 describes a method for recycling chemicals. and energy from black liquor. According to SE-B-448 173, one has managed to recover the physical heat in the gas and at the same time avoid deposition problems by directly letting the gases pass a liquid bath. In addition to the melt particles being absorbed of said liquid, which is green liquor, the gas is simultaneously cooled.

The gas released from melt particles leaving the liquid the bath then reaches a temperature as in a non-pressurized systems amount to the order of 80 ° -90 ° C, which also corresponds to the approximate temperature in the green liquor bath.

Thus, in this case, a melt-free gas flow is obtained cza 90 ° C and a liquid bath of cza 90 ° C.

From an energy recovery point of view, these temperatures are too low to be optimal. The reason is that you in it preferred case wishes to transfer the heat at a higher temperature level so that it can, for example, be obtained in the form of 10 15 20 25 30 35 508 561 3 superheated steam, preferably for turbine operation in order to generate electricity. When operating with steam turbines, the maximum is obtained efficiency when the superheated steam is delivered at high pressure and high temperature, eg 150 bar and 600 C ° respectively.

Thus, it is desirable to obtain heat exchange at such a high temperature as possible.

However, in the method described above, the gas is cooled to a temperature around 100 ° C which makes efficient heat recovery. From the above reasoning it appears that it would be desirable to be able to recover the heat at a higher temperature atur, so that it can be recovered in the form of superheated steam. Also known from SE-B-363 651 is a method for recovery from effluent, whereby the gases from the reactor are cooled to too low a level to be optimal from the recycling point.

Solution and benefits: Thus, a first object of the invention is to offer a method and a device by which it is possible to separating and recovering the molten particles from a gas stream, without drastically lowering the temperature level of the gas.

The above objects are achieved by means of a method according to claim 1 and a device according to patent claim 7, i.e. by said flow of gaseous substances containing said particles is forced to move in curvature path and that at least the outer periphery of said curved path is defined by a movable liquid layer, wherein said particles are separated from the gas stream by joining with said liquid layer.

Admittedly, in principle itself is previously known to use of "liquid film cyclones" but not in the present context.

Thus, for example, by US-A-793 110 (Uehlíng), US-A-2 259 034, etc. known cyclones for separating solid particles. However, such known cyclones are not intended for the separation of molten particles such as smudges, especially not those produced by gasification of 10 15 20 25 30 35 508 561 4 cellulose precipitates, and therefore has internal parts as after a period of buildup of solidifying molten particles would result to malfunction. Such malfunction is thus avoided with one device according to the invention.

A further object of the invention is to provide one process by which the carbonate formation in the molten particles withheld in favor of the amount of sodium hydroxide, through a high temperature separation of molten particles, so that the high content of CO before binding to sodium has time.

Furthermore, an object of the invention is to enable production of green liquor with different Na / S ratios (su- lfidity), by enabling the separation of the recovered organic chemicals selectively in at least one sulfur and at least one sulfur-containing stream.

A further object of the invention is to provide one procedure by which it is possible to obtain direct digestion of the melting particles into active cooking chemicals, ie NaOH and Na 2 S.

A further object of the invention is to provide a method making it possible to use alternative methods to recover the physical heat content of the gas, i.a. in in the form of preheated gas, such as air, for gasification the actor alternatively in the form of superheated steam, preferably with a pressure of up to about 150 bar and a temperature up to about 600 ° C and this regardless of the reactor operating jerk.

Figure description: In the following, the invention will be described in more detail in detail to the accompanying figures, in which: Fig. 1 shows a preferred embodiment of a device according to the invention, seen partly in section in perspective from the side, 10 15 20 25 30 35 508 561 Fig. 2 shows a horizontal cross-section through a according to Fig. 1, Pig. 3 shows a slightly modified embodiment of an analogue rescue according to Fig. 1, and Fig. 4 shows a basic process plant with two devices according to the invention.

Fig. 1 shows a reactor 1 which is directly connected to one device according to the invention 2, which hereafter will be called liquid film cyclone. In the example shown, was used the device in connection with the extraction of chemicals and energy in black liquor gasification. Black liquor is a residual product obtained during cooking in connection with the production of pulp in accordance with the sulphate cellulose process.

A first supply line 3A is connected to the reactor 1 intended for black liquor and a second supply line 3B intended for air. Pyrolysis and partial combustion take place in the reactor of black liquor. A gas mixture containing is formed partly a gas part, partly a melting part. The temperature in the reactor is normally between 800 ° C and up to 1,500 ° C. Chemical smelting tan is now found in the form of droplets 5 in the gas 4. Gas and the melt mixture 4, 5 is then allowed to exit the reactor 1 into the liquid cyclone 2. The inflow into the liquid cyclone 2 takes place in this case tangentially (see Fig. 2) in relation to the liquid cyclone 2 cylindrically shaped wall. the liquid cyclone 2 consists of a casing 6, 7, 8 with a discharge the 9 at the bottom. Via a supply line 10 and in addition connected distribution lines ll in the top 8 of the liquid cyclo- 2, the liquid cyclone 2 is supplied with a liquid 12, for example water (H 2 O) or weak liquor with a temperature of about 100 ° C, which temperature is possible to increase if the pressure in cyclone 2 increased. Guide rulers 15 are provided on the inside of the liquid film cyclone 2 for distribution and control of liquid The liquid film cyclone 2 is located with its longitudinal axis 13B extending in the vertical plane. In the top gable 8 there is one 10 15 20 25 30 35 508 561 6 outlet mouth to which a pipe 14 for removing gas is connected.

The principle function of the device according to the invention is as follows. The hot gas 4, 5 containing both gas 4 and melt particles 5 flow out of the reactor 1 with relative ivt high speed. The power is supplied to the liquid film cyclone 2 in a tangential and substantially horizontal direction. Hereby the centripetal acceleration (F = mvz / 2r) will be monitored that separation of the melt particles from the gas stream takes place room, because the melt particles are heavier than the gas. Melting the particles will thus be ejected towards the periphery and thereby being captured by the liquid stream 12. The gas 4, on the other hand will move helically up towards the mouth in the top end 8 and is transported further via the pipe 14. The gas will then be in contact with the liquid film for a very short time. In addition, only one smaller comes part of the gas to be in direct contact with the liquid film.

This results in a relatively small heat transfer can occur from the gas to the liquid film. Thus comes the gas 4 in the tube 14 to have a relatively high temperature, in it In the preferred case, a temperature reduction of only is obtained about 100-500 ° C. Because the gasification takes place at the sub- metric oxygen supply, formed gas obtains a significant proportion of combustible components, such as hydrogen (H2), carbon monoxide (CO) and methane (CHA).

The melt particles 5 collected by the liquid 12 in the liquid the film will, in the preferred case, be cooled first the liquid 12 and in connection therewith also dissolved therein as well due to the movement of the liquid film is co-transported downwards in liquid film cyclone 2. Also insoluble solids respectively molten constituents will be collected by the liquid. The particles thus collected will be gene in dissolved form or in undissolved form to be carried out from the cyclone 2 via an outflow 9 in the mouth at the bottom of cyclone 2.

From Fig. 1 it can be seen that the cyclone 2 in the preferred case lO 15 20 25 30 35 508 561 7 has a middle section 7 which is slightly conical. reason the weak conicity is to provide compensation for liquid evaporation. When the hot gas 4, with its contents of molten chemical particles 5, hits the liquid film 12, which preferably consists of a liquid with a boiling point below the temperature of the gas (eg water) some evaporation will occur. To despite this be able to maintain a certain given thickness in the liquid film 12 made part 7 of the cyclone 2 slightly conical, so that despite the volume decrease of the liquid 12 at its downward movement see, an almost constant thickness of the liquid film obtained.

Furthermore, Figures 1 and 2 show that the liquid film cyclone 2 is equipped with longitudinal guide rulers 15. The purpose of these guide rulers 15 are, as already mentioned, distribution and guiding the liquid layer 12, mainly to ensure the liquid film and withstand the strong gas and melt flow it 4, 5.

In a possible operating example, the reactor temperature is cza 950 ° C and the system pressure cza 30 bar. Such as film liquid 12 weak liquor or water was used, which due to the system pressure gets one boiling point of about 230 ° C. The temperature of the liquid film the cyclone 2 outgoing gases in this example are about 600 ° - 700 ° C, which temperature is favorable for a subsequent the following heat exchange generates superheated steam.

Fig. 3 shows an alternative embodiment of a device according to the invention. The reactor 1 is here as well as the liquid film cyclone 2 positioned so that its longitudinal extent is in the vertical plane. The gasification of the black liquor also takes place here preferably by pyrolysis and understochiometric oxygen supply. The gas 4 and the melt particles 5 are led away reactor 1 to the liquid film cyclone 2 via a connecting line 16 which redirects the flow so that a tangential, horizontal inflow into the liquid cyclone 2 is obtained. IN otherwise, the construction of this device is in principle the same ma as for the previously described. Thus, examples 10 15 20 25 30 35 508 561 8 show that distributors 11 and guide rulers 15 are also used here to ensure that the liquid film is obtained to the desired thickness within each area.

Fig. 4 shows an exemplary principal part of a process plant for recycling the chemical content and the energy content of black liquor, by means of devices according to the invention. The plant consists of a reactor 1 which is supplied with black liquor via a line 3A. The black liquor has one temperature of about 130 ° -190 ° C and a dry content of about 65- 85%. Via a second line 38, a preheated second is supplied. there air having a temperature of about 500 ° -700 ° C.

The plant uses a two-step procedure for separation ring of the melt particles 5 from the gas stream 4, wherein a first liquid film cyclone 2A is provided for a first separator ring at a higher temperature and a second liquid film cyclone 2B for a second separation at a lower temperature, which may be favorable because different separation temperatures temperatures, at least to some extent, may change / determine the content and concentration of the liquid taken out respectively cyclone.

The gas 4 with the molten particles 5 flows out of the reactor 1 into the first liquid film cyclone 2A with a first separator takes place in accordance with what has been previously described.

The gas 4 leaving this first liquid film cyclone 2A is contains a certain amount of gasified sodium compounds and passed through a line 14A to the second liquid film cyclone 2B. Only after this second separation step are they added from the melt particles released the gas a first heat exchanger 18B. In this case, the hot gases 4 emit part of their heat input content, which is extracted, for example, as superheated steam, suitable gene with a temperature of about 600 C ° and a pressure of closer 150 bar. The hot gases have before the heat exchanger 18 a temperature of about 600-800 ° C.

After the passage through the first heat exchanger 18, the gas is conducted 4 first into a venturi scrubber 19 and then into one nozzle scrubber 21 after which the gas 4 is diverted via a line 22.

Thanks to the high-grade purification of the gas as on this 10 15 20 25 30 35 508 561 9 way obtained (<lppm alkali) it can be used as fuel to a gas turbine, eg for efficient electricity production.

As washing liquid in the nozzle scrubber 21, one is preferably used relatively weak alkaline solution and in the venturi scrubber preferably liquid retrieved via a line 35 from nozzle scrubber 21.

The first liquid film cyclone 2A has been provided with two separate outflows 23A, 26A at the bottom. The first of these outflows 23A are intended to collect green liquor for further conversion. to cochlear chemicals. It thus recovered the green liquor is pumped by means of a pump 24 via a line 25 to a collection container (not shown). The other the effluent 26A obtained from the first liquid film cyclone 2A is recycled by means of a pump 27 in a line 28 which for the liquid, i.e. green liquor, to the top of this first liquid film cyclone 2A for continuous filling of liquid 12 in the liquid film. Using a heat exchanger 18A in this circuit 28 some of the heat is recovered in the green liquor.

The liquid taken out of line 23B from the second liquid film cyclone 2B, is circulated in a circuit 28B by means of a pump 32. Also in this circuit 28B there is a heat exchanger 18C for the extraction of heat energy from the green liquor before the recycled. Furthermore, it is connected to this circuit 28C a line 28C for liquid supply. From this circuit 28C runs a line 29 which is connected to the first cyclone 2A circulation circuit 28A, for which line 29 is used liquid supply in the first cyclone 2A. Also from dyssk- rubber 21 is collected (pump 36) green liquor for removal to a collection container (not shown).

The invention is not limited by the above described but may be varied within the scope of the following claims. one. Thus, for example, the above-mentioned implied operating pressure limiting without system pressure can be varied to be from atmospheric pressure up to about 150 bar, b.a. depending on the evaporation temperature of the film liquid desired. 10 15 20 25 30 35 508 561 10 By the expression "that the casing encloses a free space" is meant that there are no details placed inside the casing far from its periphery which is not waterlogged and therefore can not the molten particles that smear accumulate and build up one disability coating, which is an essential feature of the invention.

The gasification temperature, i.e. the temperature in the reactor below which the thermal decomposition takes place can take place within a large temperature range, at a temperature exceeding rising 500 ° C. The most preferred range, however, is time 800 ° -1600 ° C and even more preferably 800 ° -1400 ° C. When the gasification takes place in the range 500 ° -800 ° C is not obtained melting particles in the gas flow without crystals why one procedure within these temperature limits is also referred to as the "dry" method. If the temperature in the reactor is between 800 ° C and 1000 ° C the organic substances will be found in the form of melt droplets then mainly in the form of sodium bonate (Na 2 Co 3) and sodium sulfide (Na 2 S). At higher temperatures luck starting from about 1000 ° C, the carbonate formation will held back and therefore offers a procedure at higher temperatures above about 1000 ° C possibility to recover alkali without causticization.

A basic precondition for this to be possible is that the temperature in the reactor is high and most preferred is in the range 1200 ° -1500 ° C. At high temperatures tours, a green liquor is obtained with greatly reduced carbonate content. This is due to the reaction equilibria Nazs + coz + H20 zNaon + coz H25 + Na3Co3 as well Na2CO3 + H2O are strongly displaced to the left at high temperatures and that the separation takes place at this high temperature level.

In the preferred case, the gasification takes place sub- risk which means that an insufficient amount of oxygen is supplied for the complete combustion of the organic substances in black liquor. This results in the production of combustibles gases such as hydrogen (H2) and carbon monoxide (CO), etc. In it In the preferred case, about 50% of oxygen is added relative to 10 15 20 25 30 35 508 561 ll the theoretical need for stoichiometric combustion. The however, it will be apparent to those skilled in the art that this may vary. race within wide limits.

Furthermore, it is obvious to the person skilled in the art that the conical the design of the liquid film cyclone is a preferred one embodiment and that the method also works with a cylinder risk mantle surface if the liquid film is initially given one sufficient thickness to allow a certain thickness play reduction due to evaporation. Also guide lines the vials show a preferred embodiment. It can compensate for the effect of the gas flow on the liquid film in another way, for example by controlling the flow at the outlet of the liquid the film in such a way that the guide rulers at least to much can be dispensed with. Furthermore, of course, jalernas ev. arrangement respectively size and shape depending on the size and velocity of the gas stream as well as that of the cyclone dimensions. In addition, of course, it is not necessary that the entire inner mantle surface is supplied with a liquid film, without only essential parts thereof.

The temperature of the liquid in the liquid film cyclone can naturally also varies widely. Factors affecting which temperature you choose is: any need for rapid cooling of the particles in the gas stream (if particles to be dissolved in the liquid, the dissolution rate may be temperature-dependent and thus to some extent controlling) the pressure, the size of the mantle surface, the gas flow and its temperature, mm.mm.

Instead of recovering the physical heat content of the gas as overheated steam, it can of course be extracted in others forms, for example as preheated combustion air to reactor 1.

The treatment of the gas in nozzle scrubbers or a scrubber system for the removal of residual chemicals is natural of course also a preferred procedure. The washing is done partly for environmental reasons, ie. in order to release subsequent 10 15 20 25 508 561 12 apples from pollutants, partly for technical reasons.

Those skilled in the art will recognize that it is also possible to the gassing of the black liquor takes place completely without the addition of ärluft ie. completely without external supply of oxygen or oxygen-containing gas, whereby a pure pyrolysis is obtained.

Finally, it should be pointed out again that the use of a device according to the invention for black liquor gasification is exemplary only. A device according to the invention the liquid film cyclone 2 can be used in all areas where a separation of molten particles from a, preferably hot, gas stream is desirable and early wish to affect the temperature of the gas stream below the separation as little as possible. It is further understood that they the constructions shown are also not limiting for the invention.

As a means for distributing the liquid 12 at the inlet 11 refers primarily to the mouth of the inlet 11, ie its design and its focus. However, those skilled in the art will recognize that distributor type fixed vanes is one of several obvious means available.

Instead of taking the gas stream directly from a reactor can it is removed from a hot gas separator (not liquid layer) +> 900 ° C and give off the heat to a heat exchanger before it is allowed to enter a liquid cyclone.

Claims (13)

10 15 20 25 30 35 508 561 13 Patent claims A process for separating melt and preferably also solid particles from a gas stream, said stream originating from gasification of liquor from pulp production, preferably black liquor, and comprising both gaseous substances (4) and melt and optionally also solid particles (5) , which flow is led to a separating device (2) where at least a certain part, preferably the excess part, of the molten particles and possibly solid particles (5) is separated from the gas stream (4), characterized in that said flow of gaseous substances (4) containing said particles (5) are forced to move in a curved path and that at least the outer periphery of said curved path is delimited by a movable liquid layer (12), said particles (5) being separated from the gas stream (4) by joining said liquid layer (12). ). Process for separating molten and / or solid particles from a gas stream according to claim 1, characterized in that the average temperature Tg of the gaseous medium (4,5) substantially exceeds 100 DEG C., more preferably> 200 DEG C., still more preferably> 300 ° C and the temperature TV of the liquid layer, Tg-T V> preferably being in the range 400-1300 ° C. A method for separating molten and / or solid particles from a gas stream according to claim 1, characterized in that the liquid flow from the liquid layer (12) is at least partially collected, mainly for recovering the, preferably dissolved, molten and / or the solid particles (4) and / or the heat content of the liquid. 10 15 20 25 30 35 508 561 / lf A method for separating molten and / or solid particles from a gas stream according to any one of the preceding patent claims, characterized in that at least a part of the liquid stream from the liquid layer (12) is recycled. Process for separating molten and / or solid particles from a gas stream according to claim 1, characterized in that parts of the heat in the purified gas stream (4) are recovered, by heat exchange, preferably as superheated steam and / or as preheated gas. Device for separating melt and preferably also solid particles from a gas stream originating from gasification of effluent from pulp production, preferably black liquor, for carrying out the process according to claim 1, comprising a casing (6,7,8; 41) with a gas inlet, for an inflow of gaseous substances (4) containing melt and optionally solid particles (5), at least a first outlet (14; 42) for gaseous substances and at least a second outlet (9; 40) for liquid substances, k ä characterized in that at least one liquid inlet (11) is arranged at the top of said housing (6,7,8; 4-1), which inlet (11) is intended for a liquid (12) and that means are provided for distributing said liquid at least to certain parts, preferably the majority (7), of the inner mantle surface of said casing (6,7,8; 41), whereby a liquid layer movable at said mantle surface is formed. Device according to claim 6, characterized in that said housing comprises a preferably cylindrical or conical part (7) in which said gas inlet opens, guide means (16; 16) being arranged at said housing for controlling said inlet (4,5) in a direction which is substantially tangential with respect to the inner circumferential surface of said housing part (7). Device according to claim 6, characterized in that said control means (1; 16) is arranged so that the main flow direction of the gas inlet becomes substantially perpendicular to an axis of symmetry (13) of said housing part (7), wherein preferably said housing part (7) has an axis of symmetry (13) which extends substantially vertically and consequently the gas inlet takes place substantially horizontally. Device according to claim 6, characterized in that said casing (6,7; 41) is arranged on the inside with guide rails (15) for guiding the liquid film (12). Device according to claim 6, characterized in that said control means (1) is constituted by the outlet of a reactor (1) which is arranged directly at said housing part (7). ll. Method for separating molten and / or solid particles from a gas flow according to claim 6, characterized in that the temperature of the gas stream (4) exiting the separation device (2) has a temperature exceeding 600 C °, preferably exceeding 800 C °. Method for separating molten and / or solid particles from a gas stream according to claim 6, characterized in that the gas stream (4) exiting the separation device (2) is washed in at least one subsequent gas scrubber device (19,2l), after which the gas (4) is suitably used as fuel. A method for separating molten and / or solid particles from a gas stream according to claim 6, characterized in that the gas stream (4) exiting the separating device (2A) is introduced into a second separating device (28).