Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C11/00—Regeneration of pulp liquors or effluent waste waters
  • D21C11/06—Treatment of pulp gases; Recovery of the heat content of the gases; Treatment of gases arising from various sources in pulp and paper mills; Regeneration of gaseous SO2, e.g. arising from liquors containing sulfur compounds
  • D21C11/063—Treatment of gas streams comprising solid matter, e.g. the ashes resulting from the combustion of black liquor
  • D21C11/066—Separation of solid compounds from these gases; further treatment of recovered products
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D50/00—Combinations of methods or devices for separating particles from gases or vapours
  • B01D50/40—Combinations of devices covered by groups B01D45/00 and B01D47/00
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04C—APPARATUS USING FREE VORTEX FLOW, e.g. CYCLONES
  • B04C5/00—Apparatus in which the axial direction of the vortex is reversed
  • B04C5/08—Vortex chamber constructions
  • B04C5/103—Bodies or members, e.g. bulkheads, guides, in the vortex chamber
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04C—APPARATUS USING FREE VORTEX FLOW, e.g. CYCLONES
  • B04C5/00—Apparatus in which the axial direction of the vortex is reversed
  • B04C5/20—Apparatus in which the axial direction of the vortex is reversed with heating or cooling, e.g. quenching, means

Definitions

• the present invention relates to a process and an arrangement for separation of melt and preferably also solid particles from a gas flow, wherein the said flow arises from the gasification of spent liquor from the production of pulp, especially black liquor, and contains both gaseous substances and melt and possibly also solid particles.
• Black liquor is obtained as a residual product, spent liquor, in the manufacture of pulp according to the sulphate cellulose method.
• the black liquor contains alkaline chemicals in the form of a variety of sodium compounds, which it is desired to recover for reusing in the process.
• the recovery process includes a heating stage, a reactor, in which the organic molecular chains in the black liquor are broken down to energy-rich gas and the inorganic content is mainly present as melt particles which can be recovered. This occurs by pyrolysis and partial incineration of the organic components in the black liquor. The pyrolysis and incineration thus release heat energy, usually the temperature is about 1000°C in the reactor, and produce a flammable gas. It is desirable to recover the liberated heat and utilise the energy-rich gas as a fuel.
• SE-B-448 173 describes a method for recovering chemicals and energy from black liquor. According to SE-B-448 173 it has been possible to recover the sensible heat in the gas and simultaneously avoid deposition problems by allowing the gases to pass directly through a liquid bath. As well as the melt particles being taken up by the said liquid, which is green liquor, the gas is simultaneously cooled. The gas which leaves the fluid bath, having been freed of melt particles, thereby has a temperature which in an unpressurised system amounts to something in the order of 80°-90°C, which in turn also corresponds to the approximate temperature of the green liquor bath. Thus, in this instance a melt-free gas flow at about 90°C and a fluid bath at about 90°C are obtained.
• An initial object of the invention is thus to offer a process and an arrangement with which it is possible to separate and utilise the melt particles from a gas stream, without drastically lowering the temperature of the gas.
• liquid film cyclones can be used, but not, however, in the present context.
• cyclones of this type for separating off solid particles are previously known through US-A-793 110 (Uehling) , US-A-2 259 034, etc.
• Such known cyclones are, however, not intended for the separation of melt particles which produce accretion, particularly not such as have been produced in the gasification of cellulose spent liquors, and therefore have inner components which after a period of accretion of hardening melt particles would cause malfunction. Such malfunction is consequently avoided with an arrangement according to the invention.
• a further object of the invention is to offer a process whereby carbonate formation in the melt particles is retarded, in favour of the amount of sodium hydroxide, by carrying out the separation of the melt particles at an elevated temperature, so that the high content of CO-, is separated off before binding to the sodium has time to take place.
• An additional object of the invention is to facilitate the production of green liquor with different Na/S proportions (sulphidity) by making it possible to separate extracted organic chemicals selectively in at least one sulphur-free and at least one sulphur-containing flow.
• a further object of the invention is to offer a process whereby it is possible to obtain direct conversion of the melt particles into active digestion chemicals, i.e. NaOH and Na 2 S.
• An additional object of the invention is to present a process whereby it is possible to use alternative methods for recovering the sensible heat content of the gas, inter alia in the form of pre-heated gas, for example air, for the gasification reactor alternatively in the form of superheated steam, preferably with a pressure of up to about 150 bar and a temperature of up to about 600°C, this being independent of the operating pressure of the reactor.
• Fig. 1 shows a preferred embodiment of an arrangement according to the invention, seen partly cut away in perspective from the side
• Fig. 2 shows a horizontal cross-section through an arrangement according to
• Fig. l, Fig. 3 shows a somewhat modified embodiment of an arrangement according to Fig. 1, and
• Fig. 4 shows a basic process plant with two arrangements according to the invention.
• Fig. 1 a reactor 1 which is directly connected to an arrangement 2 according to the invention, which hereinafter will be termed liquid film cyclone.
• the arrangement is used in connection with the extraction of chemicals and energy during black liquor gasification.
• Black liquor is a residual product which is obtained during digestion in the production of pulp according to the sulphate cellulose process.
• a first inlet conduit 3A intended for black liquor
• a second inlet conduit 3B intended for air.
• pyrolysis and partial incineration of the black liquor take place.
• a gas mixture is formed containing partly a gas portion and partly a melt portion.
• the temperature in the reactor is normally between 800°C and l,500 o C.
• the chemical melt is now present in the form of drops 5 in the gas 4.
• the gas and melt mixture 4, 5 is allowed subsequently to pass out of the reactor 1 into the liquid cyclone 2.
• the inflow into the liquid cyclone 2 takes place tangentially (see Fig. 2) in relation to the cylindrically-shaped wall of the liquid cyclone 2.
• the liquid cyclone 2 consists of a casing 6, 7, 8 with an outflow 9 at the bottom.
• a liquid 12 for example water (H 2 0) or weak liquor at a temperature of about 100°C, which temperature can be increased if the pressure in the cyclone 2 increases, is conveyed to the liquid cyclone 2 via an inlet conduit 10 and distribution conduits 11 connected thereto in the top 8 of the liquid cyclone 2.
• Guide bars 15 are arranged on the inside of the liquid film cyclone 2 for distribution and guidance of the liquid layer 12.
• the liquid film cyclone 2 is placed with its longitudinal axis 13B running in the vertical plane.
• In the top gable 8 is an outlet opening to which is attached a pipe 14 for removal of gas.
• the basic function of the arrangement according to the invention is as follows.
• the hot gas , 5 containing both gas 4 and melt particles 5 streams out from the reactor 1 at a relatively high velocity.
• the stream is brought to the liquid film cyclone 2 in a tangential and essentially horizontal direction.
• the melt particles will thus be thrown out towards the periphery and thereby be caught up in the liquid stream 12.
• the gas 4 will move spirally upwards towards the opening in the top gable 8 and will be transported onwards via the pipe 14. During this process the gas will be in contact with the liquid film for a very short time.
• the gas 4 in the pipe 14 will have a relatively high temperature, in the preferred case a temperature decrease is obtained of only about 100-500°C. Since the gasification takes place in the presence of a sub-stoichiometric supply of oxygen, the gas that is formed will have a significant proportion of combustible components, such as hydrogen gas (H 2 ) , carbon monoxide (CO) and methane (CH 4 ) .
• H 2 hydrogen gas
• CO carbon monoxide
• CH 4 methane
• the melt particles 5, which have been picked up by the liquid 12 in the liquid film, will, in the preferred case, be first cooled by the liquid 12 and concomitantly also dissolved in it, and then, as a result of the movement of the liquid film, be transported with it downwards in the liquid film cyclone 2. Insoluble solid or melt components will also be picked up by the liquid. The particles picked up in this way will be led out from the cyclone 2, either in dissolved form or in undissolved form, via an outflow 9 in the opening at the bottom of the cyclone 2.
• the cyclone 2 in the preferred case has a central section 7 which is slightly conical.
• the reason for the slight conicity is to bring about a compensation for liquid evaporation.
• the hot gas 4 with its content of melt chemical particles 5 meets the liquid film 12, which preferably consists of a liquid with a boiling point below the temperature of the gas (e.g. water) a certain evaporation will take place.
• the liquid film 12 which preferably consists of a liquid with a boiling point below the temperature of the gas (e.g. water) a certain evaporation will take place.
• a part 7 of the cyclone 2 is made slightly conical, so that, despite the decrease in volume of the liquid 12 during its downward movement, a virtually constant thickness of the liquid film is obtained.
• the reactor temperature is about 950°C and the pressure on the system about 30 bar. Weak liquor or water which because of the pressure on the system has a boiling point of about 230°C, is used as the film liquid 12.
• the temperature of the gases leaving the liquid film cyclone 2 is about 600°-700°C, which temperature favours the production of superheated steam in a subsequent heat exchange.
• FIG 3 is shown an alternative embodiment of an arrangement according to the invention.
• the reactor 1 like the liquid film cyclone 2, is here so placed that its longitudinal axis is orientated in the vertical plane.
• gasification of the black liquor takes place preferably by means of pyrolysis and substoichiometric supply of oxygen.
• the gas 4 and the melt particles 5 are conducted from the reactor 1 to the liquid film cyclone 2 via a connecting conduit 16 which diverts the flow so that a tangential essentially horizontal inflow into the liquid cyclone 2 is obtained.
• the construction of this arrangement is in principle the same as for that described previously.
• distributors 11 and guide bars 15 are used to ensure that the liquid film of the desired thickness is obtained within the relevant areas.
• Fig. 4 is shown an exemplifying basic part of a process plant for the recovery of the content of chemicals and energy in black liquor with the aid of arrangements according to the invention.
• the plant consists of a reactor 1 to which black liquor is conveyed via a conduit 3A.
• the black liquor has a temperature of about 130°-190°C and a dry matter content of about 65-85%.
• Pre-warmed secondary air which has a temperature of about 500°-700°C, is conveyed via a second conduit 3B.
• a two-stage process for the separation of melt particles 5 from the gas stream 4 is used in the plant, wherein a first liquid film cyclone 2A has been arranged for a first separation at a higher temperature and a second liquid film cyclone 2B for a second separation at a lower temperature.
• This can be of advantage, since the content and the concentration in the liquid which is removed from the respective cyclone can, at least to some extent, be varied/determined by different separation temperatures.
• the gas 4 with the melt particles 5 streams out from the reactor 1 into the first liquid filin cyclone 2A at which juncture a first separation takes place in accordance with what has previously been described.
• the gas 4 which leaves this first liquid film cyclone 2A contains a certain quantity of gasified sodium compounds and is conducted via a conduit 14A to the second liquid film cyclone 2B. Only after this second separation stage is the gas freed of melt particles conducted to a first heat exchanger 18B.
• the hot gases 4 give off a portion of their heat content, which for example is extracted as superheated steam, appropriately at a temperature of about 600°C and a pressure of nearly 150 bar. Prior to entering the heat exchanger 18 the hot gases have a temperature of about 600-800°C.
• the gas 4 is first conducted into a venturi scrubber 19 and subsequently into a nozzle scrubber 21 after which the gas 4 is led off via a conduit 22.
• a relatively- weak solution of alkali is preferably used as washing liquid in the nozzle scrubber 21 and liquid which has been obtained from the nozzle scrubber 21 via a conduit 35 is preferably used in the venturi scrubber.
• the first liquid film cyclone 2A has been arranged with two separate outflows 23A, 26A at the bottom.
• the first of these outflows 23A is designed to collect green liquor for subsequent conversion to digester house chemicals.
• the green liquor that has been recovered in this way is pumped with the aid of a pump 24 via a conduit 25 to a collecting receptacle (not shown) .
• the second outflow 26A that is obtained from the first liquid film cyclone 2A is recirculated with the aid of a pump 27 through a conduit 28 which leads the liquid, i.e. the green liquor, to the top of this first liquid film cyclone 2A for continuous replenishment of liquid 12 in the liquid film.
• With the aid of a heat exchanger 18A in this circuit 28 a part of the heat in the green liquor is recovered.
• the liquid which is taken out via the conduit 23B from the second liquid film cyclone 2B is circulated in a circuit 28B with the aid of a pump 32.
• a heat exchanger 18C for recovering heat energy from the green liquor before it is recirculated.
• a conduit 28C for liquid supply is connected to this circuit 28B.
• a conduit 29 leads off from this circuit 28B and is connected to the circulation circuit 28A of the first cyclone 2A. This conduit 29 is used for supplying liquid in the first cyclone 2A.
• Green liquor is also collected (pump 36) from the nozzle scrubber 21 for removal to a collecting receptacle (not shown) .
• the invention is not limited by the above description but can be varied within the limits of the subsequent Patent Claims.
• the exemplified operating pressure indicated above is not limiting, and the system pressure can be varied to be from atmospheric pressure up to about 150 bar, depending, inter alia, on what is the required evaporation tempera ⁇ ture of the film liquid.
• the gasification temperature i.e. the temperature in the reactor at which thermal decomposition occurs, can be within a wide temperature range, at a temperature above 500°C. The most preferred range is however 800°-1600°C and even more preferred 800°-1400°C. When gasification occurs within the range 500°-800°C crystals rather than melt particles are obtained in the gas stream, for which reason a process within these temperature limits is also called the "dry" method. If the temperature in the reactor is between 800°C and 1000°C the inorganic substances will be present in the form of melt drops, mainly in the form of sodium carbonate (Na 2 C0 3 ) and sodium sulphide (Na 2 S) . At higher temperatures starting from about 1000°C carbonate formation will be retarded and for this reason a process at higher temperatures than about 1000°C offers the possibility of recovering alkali without causticisation.
• the temperature in the reactor should be high and most preferably be within the range 1200°- 1500°C. This s because at high temperatures green liquor is obtained with greatly reduced carbonate content. This is because the reaction equilibria Na 2 S + C0 2 + H 2 0 H 2 S + Na,C0 3 and 2NaOH + C0 2 Na 2 C0 3 + H 2 0 are greatly displaced to the left at high temperatures and the separation takes place at this high temperature level.
• the gasification takes place sub-stoichiometrically, by which is meant that an insufficient quantity of oxygen is supplied to commit complete combustion of the organic substances in the black liquor. Because of this, production is obtained of combustible gases such as hydrogen gas (H 2 ) and carbon monoxide (CO), and others.
• combustible gases such as hydrogen gas (H 2 ) and carbon monoxide (CO), and others.
• the possible arrangement, size and form of the guide bars depend on the size and speed of the gas flow as well as the dimensions of the cyclone. Furthermore, it is naturally not necessary that the whole of the inner surface of the casing should be supplied with a liquid film, but only important parts thereof.
• the temperature of the liquid in the liquid film cyclone can naturally also be varied within wide limits. Factors which affect which temperature is chosen are: possible requirement for rapid cooling of the particles in the gas stream (if the particles are to be dissolved in a liquid, the speed of dissolution can depend on the temperature and thereby to a certain extent be the determining factor) , the operating pressure, the size of the casing surface, the gas flow and its temperature, and many others.
• an arrangement according to the invention for gasification of black liquor is simply exemplifying.
• An arrangement according to the invention, the liquid film cyclone 2 can be used within all the areas where a separation of melt particles from a, preferably hot, gas stream is required, and where there should be the least possible effect on the temperature of the gas stream during the separation. Additionally, it is appreciated that the constructions shown are also not limiting for the invention.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Paper (AREA)
• Cyclones (AREA)
• Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)

Applications Claiming Priority (3)

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• 1991
  • 1991-07-16 SE SE9102187A patent/SE508561C2/sv not_active IP Right Cessation
• 1992
  • 1992-07-09 BR BR9206270A patent/BR9206270A/pt not_active Application Discontinuation
  • 1992-07-09 WO PCT/SE1992/000515 patent/WO1993001890A1/en not_active Application Discontinuation
  • 1992-07-09 EP EP92915440A patent/EP0593638A1/de not_active Withdrawn
  • 1992-07-09 CA CA002113559A patent/CA2113559A1/en not_active Abandoned
  • 1992-07-09 JP JP5502441A patent/JPH06511290A/ja active Pending
  • 1992-07-09 AU AU23331/92A patent/AU658660B2/en not_active Ceased
• 1994
  • 1994-01-12 FI FI940146A patent/FI940146A/fi not_active Application Discontinuation
  • 1994-01-14 NO NO940150A patent/NO940150D0/no unknown

Non-Patent Citations (1)

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