JP2013524030A - Gasification of concentrated sulfite solution - Google Patents

Abstract

  A method of recovering chemicals and energy from a sulfite concentrated solution containing organic and inorganic compounds obtained when producing pulp by chemical delignification of fiber raw material using sulfite pulping method; Treating the organic and inorganic compounds at a temperature above, thereby producing at least one phase of a liquid substance in part and at least one phase of a gaseous substance, wherein the treatment is gasified Carried out in the reactor (2) by gasifying the concentrated sulfite solution under substoichiometric conditions and in the presence of an oxidizing medium; the reactor (2) has a chute (5) shape at its bottom Wherein the opening is directly open to the quench section (38).

Description

  The present invention is a method for recovering chemicals and energy from a concentrated sulfite solution containing organic and inorganic compounds, which is obtained when producing pulp for papermaking by chemical delignification of fiber raw materials using a sulfite pulping method. Treating said organic and inorganic compounds at a temperature above 800 ° C., whereby partly producing at least one phase of liquid substance and partly producing at least one phase of gaseous substance , Regarding the method.

  The sulfite pulping method is a chemical pulping method of wood chips when producing pulp. Sulphite pulping was historically the dominant pulping method before the major development of kraft (also called sulfate) pulping method made it more common, but now it is the world's pulp production Of less than 10%. There are various sulfite pulping methods, such as acidic, neutral and alkaline sulfite methods.

In the sulfite pulping process using a mixture of sulfur dioxide, sulfurous acid and / or alkali salts thereof, the lignin in the wood chip is made water-soluble by formation of sulfonic acid functional groups and cleavage of bonds in the lignin structure. Typical counterions for sulfurous acid and / or its alkali salts include Na ⁺ , NH ⁴⁺ , Mg ²⁺ , K ⁺ , and Ca ²⁺ .

  The main difference between the various sulfite pulping processes is the pH of the cooking liquor, which means that delignification takes place in the digester at low, neutral or high pH. Alkaline sulfite pulping may be carried out in the presence of sulfides, which is so-called sulfide-sulfite pulping.

  The sulfite pulping process has some advantages over the kraft pulp process, such as higher yields, pulp color is brighter and easier to bleach, and pulp is more easily purified. May have. The sulfurous acid process can produce special cellulose for the production of cellulose derivatives in addition to paper pulp. There are also some disadvantages compared to the kraft pulp method, such as weak pulp, difficulty in pulping certain types of wood, and more complex chemical recovery.

  The chemical recovery process for pulping chemicals depends on the alkali counterion used, but is generally more complex than the recovery of kraft pulping chemicals. The first step in the sulfite chemical recovery process is the separation of the cooking liquor from the pulp / cellulose and the subsequent concentration of the effluent by evaporating the water. can get. The concentrated sulfite solution can then be combusted in a recovery boiler for energy recovery in most counterions, and pulping chemicals are recovered to varying degrees.

  Recovery boilers used to recover chemicals and energy from concentrated sodium-based sulfite solutions are very similar to those used to recover black liquor from kraft pulping, however, such boilers Combustion of a concentrated sulfite solution at 1 is associated with a number of difficulties compared to kraft black liquor combustion, as discussed further below.

  The flue gas generated when burning a sulfite concentrated solution is more corrosive, which limits the efficiency of energy recovery of the effluent and causes an increase in maintenance costs.

  The loss of pulping chemicals primarily as fly ash, both sodium and sulfur, is much higher when burning sodium-based sulfite concentrates compared to kraft waste combustion, which is a chemical in the factory. It may lead to increased replenishment costs.

  The combustion of concentrated sodium-based sulfite solutions to recover cooking chemicals and energy is a high temperature process, and because of the high melting point of the resulting sulfide / carbonate mixture, the salt melt recovered at the bottom of the boiler Must be kept at a high temperature (approximately 1000 ° C.).

  The reduction of the sulfur component in the recovery of effluent from the kraft process can usually reach 95%. When burning a sodium-based sulfite concentrated solution, the reduction efficiency of sulfur species in the sulfite liquid is relatively low. Typically, 80-85% of the recovered sulfur is reduced to sulfide, which can be converted to active cooking chemicals in a subsequent cooking liquor preparation process. Unreduced sulfur causes disadvantages in the form of wasted throughput of the chemical cycle and the tendency to produce deposits in the chemical cycle processing equipment.

  Unreduced sulfur exists at least in part as polysulfides in the salt melt, which is oxidized to thiosulfate in the green liquor produced by the dissolved salt from the recovery boiler. If thiosulfate is present in the cooking liquor, it reduces the pulping efficiency. In order to avoid such effects, wet oxidation is used to convert thiosulfate to sulfate. Thus, large amounts of inactive sulfur are present during the chemical cycle, causing potential problems due to reduced efficiency and scaling. In addition, thiosulfate is known to cause corrosion problems in processing equipment.

  It is known that the sulfite concentrated solution is less reactive in the recovery boiler compared to the kraft cooking waste liquor, which leads to a reduction in capacity when operating the recovery boiler for the sulfite concentrated solution. The main reason why sulfite liquid behaves differently from kraft liquid is usually due to the fact that sulfite waste liquid droplets exhibit smaller expansion behavior during heating before combustion, which means that Provides greater resistance to mass and energy transfer.

  Thus, complex and relatively insufficient chemical recovery and energy recovery from sulfite waste liquor is one reason why the Kraft method has become the dominant pulping method.

  Furthermore, those skilled in the art may have a preconception about the recovery of sulfite liquid by gasification based on initial experience. For example, tests were already conducted around 1960 by the Swedish pulp and paper company Billerud, and two separate routes were further investigated. A non-slagging (low temperature) gasification process has been developed and several facilities have been provided (“SCA-Billerud process”). The slagging (hot) path was tested at a second facility at Billerud Mill. The trial ended after one year due to the overlap of various factors. This method did not meet the low smelt sulfide content requirement set by the remaining recovery methods available at the time. Furthermore, there is a problem that a smelt layer is formed on the wall of the reactor, and the ceramic material available at that time had very severe wear inside the reactor. Later, the “SCA-Billerud method” was also abandoned because of its low performance.

  Document US 2,285,876 discloses a method for recovering sulfite waste liquor. The waste liquid is sprayed into a so-called Tomlinson recovery furnace chamber and burned at a furnace temperature below the melting temperature of the incombustible components of the waste liquid.

  Document DE 1,517,216 describes a process for pyrolyzing cellulose waste liquors, in particular sodium-based sulfite concentrated solutions. The concentrated waste liquor is divided into very fine particles, the majority of the particles should not exceed 200 μm, which are sprayed into a hot oxygen-containing gas stream and pyrolyzed. This document teaches that the pyrolysis temperature should not exceed 800 ° C. in order to avoid sulfides in the solid residue used to make the green liquor and thus in the cooking liquor. However, pyrolysis at temperatures as low as below 800 ° C. will result in unconverted carbides in the solid residue from the gasification process, requiring a second gasification step performed in a fluidized bed. The hot gas to which the effluent is added comes from the combustion of fuel (eg oil).

  Document US 3,317,292 describes a method of treating waste such as sulfite waste liquor, black liquor to obtain hydrogen and other gases and hydrogen-containing products therefrom. The method includes precipitating lignin-derived components and reacting the precipitate with several hundred degrees of steam in a reaction atmosphere substantially free of free oxygen to favor carbon monoxide and hydrogen gas production. Including.

  Another document SE526435 discloses a method for recovering chemicals from an alkaline sulfite pulping process. The method includes a gasification step, and this document teaches that the gasification will preferably be performed at a temperature of 700-750 ° C. in order to maintain a temperature below the melting point of the salt in the solid phase. ing.

  Yet another document CA 619,686 discloses a method for pyrolyzing waste liquor (preferably sodium based) from pulp production by using a fluidized bed.

  In view of the above, it is necessary to improve the chemical recovery method in sulfite pulping and to increase the efficiency with respect to energy recovery and / or chemical recovery.

US 2,285,876 DE1,517,216 US 3,317,292 SE526435 CA619,686

  The object of the present invention is to overcome or at least minimize at least one of the disadvantages and disadvantages of the above chemical recovery process in sulfite pulping. This can be realized by the method of claim 1.

  Thanks to the present invention, more efficient chemical recovery is realized. The cold gas efficiency obtained with industrial scale gasifiers is estimated to be 65-75%, and if this synthesis gas utilization is chosen, it results in a high yield of automotive fuel produced from the synthesis gas.

  Due to the fact that most of the sulfur can be contained in the feed syngas as hydrogen sulfide, the sulfidity of the green liquor is much lower than in the recovery boiler. This sulfur can be returned to the preparation of the cooking liquor in the concentrated gas stream from the acid gas removal unit that processes the gas from the gasifier, which allows a simpler method of preparing the cooking liquor. The throughput in the cooking liquor preparation part that converts sulfides to sulfur dioxide and sulfurous acid is reduced by the reduction of the sulfur content in the green liquor.

  According to one aspect of the invention, the amount of unburned coal in the green liquor is less than 5%, preferably less than 1%, more preferably less than 0.2% of the carbon in the concentrated sulfite solution, ie carbon. It can be said that the conversion rate is very high, and a high quality green liquor is obtained. Due to the advantageous recirculation flow pattern in the reactor chamber that is forced by the limited size of the outlet at the bottom of the reactor chamber, a high carbon conversion is obtained.

  According to another aspect of the present invention, the green liquor may have unreduced sulfur removed to the extent of at least 90%, preferably at least 95%, more preferably at least 98%. This means that the green liquor produced can have a sulfur reduction efficiency close to 100%. High sulfur reduction efficiency reduces the total amount of sulfur that needs to be circulated by reducing so-called wasted throughput (ie, inert sulfur species such as sulfate). High sulfur reduction efficiency is obtained because of the advantageous recirculation flow pattern in the reactor chamber that is forced by the limited size of the outlet at the bottom of the reactor chamber.

  All these benefits combine to provide a more efficient and cost effective chemical recovery method for cooking chemicals as well as energy. The chemical recovery method is no longer a disadvantage in the sulfite pulping method compared to the kraft (sulfate) pulping method.

  Many of the foregoing aspects and attendant advantages of the present invention will become more readily understood when taken in conjunction with the accompanying drawings, and will be better understood by reference to the following detailed description as well. Become.

FIG. 2 shows a typical chemical recovery cycle flow scheme in acidic sodium sulfite pulping. FIG. 2 shows a modified and more efficient cycle flow scheme involving gasification of a sulfite concentrated solution according to the present invention. It is a figure which shows the general process scheme in the gasification plant of a spouted bed type and a high temperature reactor type.

  The following detailed description, and the examples contained therein, are presented solely for the purpose of describing and illustrating specific embodiments of the invention and are not intended to limit the scope of the invention in any way.

  In FIG. 1, a typical chemical recovery cycle flow scheme for sodium-based sulfite pulping is shown. Since this is common knowledge for those skilled in the art, only a brief description of the drug recovery cycle will be given here. Wood chip A is charged to the digester where delignification / pulping process B is performed at high temperature in a suitable sulfite cooking liquor, thereby releasing cellulose fibers, pulp C. The pulp is separated from the cooking liquor, also called a thin sulfite concentrate D, which is a mixture of spent cooking chemicals and wood residues (eg lignin). In this way, the raw material pulp C is completed, but in many cases, it may be further processed in a bleaching unit and then carried out as wet pulp or dry pulp.

  The cooking liquor is cooled and free sulfur dioxide is removed in the evaporator. The pre-evaporated and cooled waste liquor is fermented to reduce the content of sugars in the waste liquor (not shown). After fermentation, the waste liquor is separated to recover the ethanol produced and evaporated in one or several evaporators E to a sulfite concentrate solution F with about 60-70% dry solids. The waste liquid is then combusted in one or several Tomlinson recovery boilers G to obtain smelt, flue gas H containing ash, and heat for steam generation.

  Smelt generally contains sodium carbonate and sodium sulfide. The smelt is dissolved in recycled water. This solution, the so-called green liquor I, is purified or filtered to remove insoluble inorganic materials and any carbides due to incomplete combustion in the recovery boiler. The green liquor is then separated from its sulfide components by contacting it in countercurrent with carbon dioxide and sulfur dioxide recovered from the Claus plant (this and the following are clearly shown in FIG. 1). Not part of cooking liquor preparation). The resulting gas mixture of hydrogen sulfide and carbon dioxide is directed to a Claus plant where it is contacted with sulfur dioxide to obtain elemental sulfur. Elemental sulfur is burned in a sulfur furnace to obtain sulfur dioxide, which is concentrated by an adsorption / desorption system and then directed to a Claus plant. Smoke from the recovery boiler rich in sulfur dioxide is contacted with the sodium sulfite solution from the sulfide separation column in a flue gas scrubber to obtain a mixture of sulfite and bisulfate. This mixture is then contacted with sulfur dioxide from a sulfur dioxide absorbent to obtain a bisulfate solution. A new cooking liquor L containing sodium bisulfate with sodium sulfite, sodium bisulfate, and / or free sulfur dioxide can then be prepared in cooking liquor preparation step J. Supplemental sodium and sulfur K may be added in Preparation J. The new cooking liquor L is thus ready to be conveyed to the pulping process B.

  In FIG. 2, the flow scheme of a preferred embodiment according to the present invention is shown, wherein the recovery boiler is replaced by one or several gasifier (s) for waste gasification M, whereby Smelt and raw material synthesis gas N are formed. The smelt is dissolved in recirculated water or weak wash liquid, thereby forming a green liquor I, similar to the conventional chemical recovery cycle shown in FIG. The raw synthesis gas N passes through a gas purification plant / process O which may be a so-called acid gas removal plant (AGR) to obtain a purified synthesis gas P and a gas Q rich in hydrogen sulfide, which is rich in hydrogen sulfide. The gas is fed to cooking liquor preparation J. Another stream containing mainly carbon dioxide R and substantially free of sulfur compounds can also be made in plant / process O.

  Adding the sulfite concentrated solution gasification step to the sulfite pulping chemical recovery process may result in a much more efficient recovery process for both cooking chemicals and energy. It will be appreciated that the gasification step may be replaced with a recovery boiler or added as an accelerator to an existing chemical recovery process for sulfite pulping. In many factories, the chemical recovery process is a bottleneck, which limits pulp production and cannot be further expanded.

  Since the gasification process and the gasification plant itself are documented, they will only be described briefly here.

  FIG. 3 shows a general process scheme for a spouted bed gasification plant in gasification under slagging conditions (high temperature) according to the present invention. The plant is part of the sulfite pulping chemical recovery cycle shown in FIG. The plant corresponds to the parts shown in FIG. 2 as I, M, N, O, P, R, and Q.

  In FIG. 3, the gasification plant is shown in more detail and will be described below. This description should be understood as a general description of the gasification plant and will be interpreted as illustrative rather than limiting. It should be understood that many changes and modifications may be made to the following plants as defined in the appended claims without departing from the scope of the present invention.

  Detail number 1 in FIG. 3 indicates a pressure vessel comprising a gasification reactor 2 which is internally covered by ceramic. The reactor is provided with an inlet 3 for concentrated sulfite solution, an inlet 4 for oxygen or oxygen-containing gas, and a burner (not shown). There may also be a spray medium inlet (not shown). The opening at the bottom of the reactor chamber is limited in size to provide a recirculation flow pattern in the reactor, which is necessary to obtain high carbon conversion and sulfur reduction efficiency. Preferably, the horizontal cross-sectional diameter of the opening is less than 40% of the diameter of the maximum cross-sectional area in the horizontal plane of the reactor 2, more preferably 5 to 35%. The opening is in the form of a chute 5 that opens directly into the quench compartment 38 above the liquid surface 35 of the underlying green liquor liquid chamber 6. The quench section 38 is an integral part of the reactor 2. One purpose of the quench section 38 is to cool the gas exiting the reactor to a temperature at which a gas phase chemical reaction does not occur with a high probability.

  Several spray nozzles 7 for cooling the liquid open towards the chute 5 and the quench section 38. The green liquor produced is transported from chamber 6 through conduit 8 by pump 9 and heat exchanger 10 to the next process stage for producing white liquor, or to another process stage where the green liquor is used. Is done. The partial stream of green liquor transported to the conduit 8 may be returned to the green liquor liquid chamber 6 by the pump 91 through the conduit 81. Coolant that has not evaporated may be recovered in volume 36 for reuse.

  The raw synthesis gas from the first vessel is conveyed through conduit 11 to a second pressure vessel 12 for gas processing and sensible heat energy recovery.

  This conduit 11 opens towards the pressure vessel 12 above the liquid surface in the washing chamber 13 at the bottom of the vessel.

  The liquid in the cleaning liquid chamber of the second container may be carried by the pump 15 through the conduit 14 to the first container to serve as a diluent or as a cooling liquid supplied by the spray nozzle 7. Good.

  The pressure vessel 12 may include an indirect capacitor 16 of the counter-flow falling film type capacitor located above the chamber 13. Other types of capacitors may be used without departing from the scope of the present invention, and gas cleaning and gas cooling methods are well known and will not be described in detail here.

The cooled raw material synthesis gas discharge pipe 17 is positioned above the second pressure vessel 12. The exhaust pipe 17 transports the cooled combustion gas to the inlet 31 of the plant 30 for further removing sulfur components and most of the CO ₂ . Plant 30 includes any gas separation technique for acid gas removal (AGR). The conduit 32 of the plant 30 allows purified and cooled synthesis gas (referred to herein as purified synthesis gas) to be used at any site that uses synthesis gas, such as chemical production, fuel production, power generation, and / or steam generation. / It may be transported to the site of heat generation. Hydrogen sulfide and carbon dioxide (shown as Q and R, respectively, in FIG. 2) removed from the cooled feed synthesis gas can exit the plant 30 through conduits 33 and 34, respectively. The removed hydrogen sulfide may then be transported to the preparation of cooking liquor while the carbon dioxide is returned to the factory and used where appropriate, for example, for removal of hydrogen sulfide from green liquor in the recovery process. May be.

  Here, a recovery method based on gasification will be described. A concentrated sulfite concentrated solution is supplied to the gasification reactor along with oxygen or an oxygen-containing gas that may be preheated to 50-400 ° C., the sulfite concentrated solution containing organic and inorganic compounds. Treatment of the solution by gasification in the presence of an oxidizing medium (eg oxygen or air), whereby heat is released by the chemical reaction carried out to about 1.5 to about 150 bar, preferably about 10 to about 80 bar; Most preferably in the reaction zone (so-called high pressure gasification) at an absolute pressure of about 24 to about 40 bar, above 800 ° C, preferably above 900 ° C, more preferably above 950 ° C, but below 1500 ° C, preferably Temperatures below 1300 ° C are obtained. A spray assist medium may be used. The gasification is carried out under reducing conditions, i.e. substoichiometric oxygen conditions, whereby partly at least one phase of a liquid substance is produced and partly a mixture of at least one phase of a gaseous substance. Is done. It may be beneficial for the outlet at the bottom of the reactor to be designed to provide a recycle flow pattern in the reactor to obtain the desired process performance.

  Of raw material syngas, eg gaseous substances including carbon monoxide, hydrogen, carbon dioxide, methane, hydrogen sulfide, and water vapor, and liquid substances including inorganic smelts and ash, such as sodium sulfide, sodium carbonate, and sodium hydroxide. The phase is cooled in the quench region by spraying the coolant through several nozzles for maximum contact with the gas / smelt mixture. The coolant consists primarily of water, and a portion of this water will evaporate upon contact with hot gas and smelt at the reactor temperature. The gas temperature decreases to approximately 100 to 230 ° C. in the quenching region. The smelt droplets are dissolved in the remaining portion of the cooling liquid and fall into a green liquor liquid chamber (so-called quenching bath) that dissolves to produce green liquor. Alternatively, the smelt droplets fall directly into the liquid chamber and then only dissolve in the green liquor already present at this location. The smelt droplets are then optionally cooled by evaporation of water in a green liquor bath.

  The green liquor may exit through a conduit from the bottom of the first pressure vessel quencher and be pumped through a heat exchanger where thermal energy is recovered from the green liquor by cooling the green liquor. Alternatively, the heat energy of the green liquor may be recovered by other means. A screen may be used in front of the pump to capture small particles. The amount of unburnt coal in the smelt and the green liquor is less than 5%, preferably less than 1%, more preferably less than 0.2% of the carbon in the concentrated sulfite solution, ie the conversion of carbon in the reactor is Advantageously, it is at least 95%, preferably at least 99%, more preferably at least 99.8%.

  The green liquor sulfide is similar to the sulfide in the green liquor from the recovery boiler, i.e., preferably in contact with carbon dioxide and sulfur dioxide in the absorption / desorption tower in countercurrent with the green liquor. Recovered by separation from the components and then further converted to the pulping chemical sulfur dioxide and / or sulfite, but if the gasified green liquor has a low sulfidity (due to the sulfur content in the raw syngas) ) The capacity requirement of the equipment used for this purpose is low. Furthermore, if the sulfur reduction efficiency is high, the total amount of sulfur that needs to be circulated is reduced by reducing the so-called wasteful load (sulfate or other inert sulfur species). The green liquor has unreduced sulfur removed to the extent of at least 90%, preferably at least 95%, more preferably at least 98%, ie the sulfur reduction efficiency is at least 90%, preferably at least 95%, more preferably It is beneficial to be 98%.

  A small portion of the green liquor may be used to wet the inside of the chute by returning it to the chute and allowing a thin film to form inside the chute.

  The raw synthesis gas leaving the first quenching dissolution tank (substantially free of smelt droplets) of the reaction vessel is saturated in the second vessel 12, which is a gas cooler for particulate removal and gas cooling. Cool until further. The water vapor in the raw synthesis gas may be agglomerated and the released heat may be used to generate steam.

  Hydrogen sulfide and carbon dioxide are removed from the cooled synthesis gas in a so-called acid gas removal plant AGR. Several known industrial gas purification systems may be used, including units for acid gas absorption and sulfur recovery. The removed hydrogen sulfide is then conveyed to the preparation of cooking liquor.

  It is beneficial that the hydrogen sulfide rich vapor removed from the cooled feed synthesis gas by AGR contains at least 25% hydrogen sulfide, preferably at least 35% hydrogen sulfide of the total vapor content, since then high concentration This is because the hydrogen sulfide promotes the subsequent combustion and cleaning steps.

  The carbon dioxide that is removed from the cooled feedstock synthesis gas at AGR may be returned to the factory and used where appropriate, for example, in the removal of hydrogen sulfide from the green liquor in the recovery process.

  The resulting synthesis gas is a synthesis gas that contains carbon monoxide, hydrogen, and a small amount of carbon dioxide, and contains little sulfur, and may be used as an automobile fuel, chemical product, or raw material for power generation.

  A gasification plant with AGR can make several simplifications of the system for recovering pulping chemicals. The burden in the cooking liquor preparation part that converts sulfides to sulfur dioxide and sulfurous acid is reduced by reducing the sulfur content in the green liquor. The Claus plant will not be required to recover sulfur in the form of hydrogen sulfide, because the hydrogen sulfide rich vapor from AGR can be directly burned with air / oxygen and absorbed by the scrubber from the gas This is because a high concentration of sulfur dioxide can be obtained. AGR replaces the function of the flue gas scrubber of the recovery boiler. A portion of the carbon dioxide stream from the AGR may be used for carbonation in the cooking liquor preparation as needed.

Experiment-Pilot test of gasification of concentrated sulfite solution In the present invention, an experimental test of gasification of concentrated sulfite solution from cellulose production with sodium-based sulfite was conducted, but other sulfite solutions such as magnesium, It will be appreciated that calcium, ammonium or potassium sulfite solutions may also be used without departing from the scope of the present invention.

  In the test, the cooking liquor was a sodium bisulfite-sodium sulfite solution.

  The sulfite concentrated solution was transported from the pulp mill to the pilot plant by a cold car. A 62% dry solids (DS) content was used because long-term stability has not been verified at a concentration of 70% DS. The liquid was filtered through a 2 mm screen and placed in a stirred insulated tank from which the gasified liquid was removed.

The main parameters examined are liquid throughput and reactor temperature. The test procedure used is based on a gradual increase in liquid throughput from a relatively low starting point. The reactor pressure was increased simultaneously to keep the reactor residence time comparable. The change in temperature caused by changing the O ₂ / liquid ratio was used to investigate the effect of this factor.

  Prior to spraying, the liquid to be gasified is preheated to reduce the viscosity and improve the energy efficiency of the reactor. During the experiment, fouling on the surface of the heat exchanger used for this purpose was evident, which limited the throughput that could be obtained. Therefore, maximum reactor capacity testing could not be achieved in this experiment. The problem with surface fouling when using indirect heating is well known in the handling of concentrated sulfite solutions in sodium sulfite plants and is not specific to gasification.

  The operating point according to Table I was tested. The total duration of the study was 27 hours. Start, change of operating point, and stop accounted for approximately 5 hours. Operating parameters not shown in Table I were not systematically changed. The same values for kraft black liquor gasification were used for most parameters. The only significant exception was green liquor circulation in the quench section, which was much higher than normal.

Liquid analysis A liquid sample for analysis was taken at the factory when the liquid was transported. The composition shown in Table II is typical of normal factory operation except for the dry solids content, which is lower than normal as explained above.

Syngas The gas composition was measured with an on-line analyzer and sampling, followed by laboratory analysis by gas chromatography.
Only the results from the laboratory analysis will be discussed here because they are more accurate.

The cooled synthesis gas was sampled at the end of each operating period (Table I). The results are shown in Table III. The high N ₂ content is due to the specific pilot scale solution and will not be present in full scale factories. A high CO ₂ / CO ratio is also a pilot scale effect due to high heat loss, as discussed further below.

Green liquor Green liquor samples were taken for chemical analysis (Table IV) and for visual inspection and concentration measurements. Carbonate and bicarbonate were measured by acid titration, sulfide by silver nitrate titration, and total sulfur by wet oxidation followed by ion chromatography.

  It should be noted that there are some difficulties when trying to relate the characteristics of green liquor to the operating conditions of the gasifier. The long residence time of a rapidly cooled green liquor dose requires more time to reach steady state. Only operating point 7 has sufficient duration to obtain a representative green liquor sample. All other samples are thought to be affected by several operating points.

  Although carbon conversion was not clearly measured, the green liquor appearance appears to be complete or nearly complete at all operating points. Even if a small amount of unconverted carbon (carbide) is present in the green liquor, it usually appears as black fine particles that do not clearly settle.

  The concentration of green liquor is lower than that which is standard in pilot plants during kraft liquor treatment and is lower than that currently used in cellulose plants. This is mainly due to the difficulties associated with controlling total titrated alkali (TTA) and changing operating points during short test times. Operation at higher green liquor concentrations is not believed to have a significant impact on the composition or quality of the green liquor.

The degree of sulfidation of the green liquor measured as the S / Na ₂ ratio (mol / mol) is about 0.5 on average. This corresponds to an HS ^- concentration of 25% TTA. CO ₂ absorption is intentionally high due to the high green liquor circulation flow rate, resulting in an HCO ₃ concentration of about 30% TTA. Quench design and operation allows CO ₂ absorption to be controlled to a significant degree, which can be used to optimize the green liquor for the cooking liquor preparation process. It should be noted that because no causticization is used, CO ₂ absorption is not as disadvantageous as in the Kraft green liquor.

  The reduction efficiency appears to be no more than 100% within the accuracy of the measurement (see Table IV values based on analysis of total and sulfide sulfur). This is a significant difference compared to the 80-85% reduction efficiency currently obtained in factory recovery boilers according to the analysis of green liquor.

Analysis and Discussion Sulfur Splitting Ratio Sulfur splitting between gas and smelt can be a very important parameter in factory integration and downstream gas processing equipment sizing. The sulfur split ratio (defined herein as the percentage of sulfur in the synthesis gas) can be calculated from the sulfur content and the flow rates in different combinations of flows. Alternatively, if it is assumed that all Na exits the green liquor stream system, it may be possible to calculate the sulfur split from the S / Na ₂ ratio in the green liquor present and the concentrated solution entering the system.

The method based on the S / Na ₂ ratio does not rely on flow measurement, which is advantageous. Calculations based on the measured ratio show that 69% of the sulfur is in the gas phase at a reactor pressure of 28 bar.

  The sulfur split ratio in gasification of concentrated sulfite solutions is much higher than the 30-40% obtained in kraft black liquor.

The melting point of the smelt The composition of the smelt determines the physical properties of the liquid phase in the reactor. If the melting point is too high, there is a risk of solidification on the “cold” surface at the reactor outlet. By assuming that sulfur is not lost from the green liquor or absorbed into the green liquor in the quench, the approximate smelt composition can be determined from the analysis of the green liquor. Furthermore, it is approximated that the smelt consists only of Na ₂ S and Na ₂ CO ₃ . Although the content of K and Cl is very low (see Table III), the content of hydroxide at 1000 ° C. can be substantial.

Using the composition of the smelt obtained from the experiment to predict the melting point in the Na ₂ S—Na ₂ CO ₃ phase diagram, it is approximately 850 ° C. compared to the 825 ° C. expected for a typical kraft black liquor gasification smelt. The melting point is expected. The relatively low melting point is a very important and promising conclusion because it appears that the risk of operational problems due to smelt solidification does not seem to exceed that of kraft black liquor for sulfite concentrated solutions. It is because it shows. Evaluated from temperature measurements, pressure drop during reactor and quench, and visual inspection of the reactor after completion of the test, there were no signs of problems associated with deposits caused by high melting point melting.

Energy Efficiency Energy efficiency can be measured by the cold gas efficiency (CGE) defined as the energy of the cooled synthesis gas divided by the energy of the sulfite concentrated solution. This indicator shows how much chemical energy in the liquid has been transferred to the synthesis gas and also indicates the potential biofuel yield. This document uses the higher heating value (HHV) for the calculation.

Table V shows CGE values with and without the synthesis gas flow measurement adjustment. The synthesis gas flow rate measurement is adjusted so that the mass balance of C is established. The deviation is -6% based on actual measurements, possibly explained by the uncertainty of the synthesis gas measurement. From experience, it is known that gas flow metering devices can show measurements that are too low due to clogging of the pressure sensor. This is supported by the continuous decrease in gas flow rate measured at some of the operating points despite the operating conditions being kept constant. The gas flow used for balancing is measured at the end of each operating period and is therefore probably too low. An alternative material balance is calculated when the synthesis gas flow rate is adjusted to establish a C balance, which is referred to as alternative value 2 when discussing energy efficiency below. It should be noted that the reactor temperature (and hence the O ₂ / liquid ratio) is important in CGE and is therefore included in the table.

  Due to the pilot scale effect, the CGE values in Table V are not representative of what can be expected in industrial scale gasifiers. In order to estimate CGE in a full-scale plant, the three adjustment values may be compared with values measured in a pilot test.

  1. Heat loss can be reduced to a level that can be expected in a full scale plant (about 500 kW at 500 tDS / d).

2. Since N ₂ is not necessarily used in an industrial plant, the energy required to heat N ₂ in the reactor to the temperature at the reactor outlet may be subtracted.

  3. The results may be adjusted to account for the higher efficiency obtained at higher DS content (70% compared to 62%).

  Focus on operating point 7 as in the previous analysis. This is because this point has the longest duration and can be expected to best represent the steady state. Adjustment by items 1 and 2 at operating point 7 increases CGE to 61% and 65% for alternative values 1 and 2, respectively.

Adjustments to account for the DS content may not be very easy because it may be necessary to consider that the higher the DS content, the lower the O ₂ / BL ratio obtained. Simulations based on a thermodynamic model of the gasification process show that at a constant reactor temperature, the CGE impact from a change from 62% DS to 70% DS is approximately 5% at the relevant operating point. Yes.

  This results in an industrial scale CGE estimate that is approximately 66% and 70% for each of the two calculation methods, subject to operating point 7. It can be noted that the operating point used was “high” at the reactor temperature and acceptable green liquor quality was also seen at lower temperatures. Since CGE increases with decreasing temperature, this indicates that higher CGE is obtained, but further experimentation with higher reactor throughput is required to support this.

Discovery-Complete carbon conversion can be obtained at temperatures and residence times similar to those used in sulfate solutions. This is surprising because sulfite solutions are usually much less reactive than in recovery boilers.
A sulfur reduction rate of at least 98% or as high as 100%, i.e. a much higher sulfur reduction rate than can be expected with reference to experience from recovery boilers, about 70% of the sulfur produced syngas This is a surprisingly high number.
-The slagging temperature (melting point) of the salt produced in the reactor is kept lower than expected, thus improving the ability of the salt melt to flow out of the gasifier.

With very good results, sulfite plants with sulfite gasification can improve the energy efficiency of the recovery process.
-The liquid cycle can be simplified.
-Wasteful throughput of sulfate in the liquid cycle can be greatly reduced or even avoided.
-Significantly reduce or even avoid the loss of sodium sulfate from the liquid cycle, leading to less purchase of new sulfur and sodium (as NaOH).

  As those skilled in the art will appreciate, many changes and modifications may be made to these and other embodiments of the invention without departing from the scope of the invention as defined in the appended claims. You may do it for. For example, if used in a slagging spouted bed gasification process of a sulfite concentrated solution, different process configurations and equipment designs may be used to achieve the same results. It is understood that the liquid phase produced in the gasification process as defined in claim 1 should also be construed to apply to processes that contain any small amounts of solids and / or aggregates that may be present. The person skilled in the art understands that this concept can also be realized at atmospheric pressure, and that this method also applies to the concept of facilitator operating the gasifier in parallel with the recovery boiler.

Claims (18)

  A method of recovering chemicals and energy from a sulfite concentrated solution (F) obtained by chemical delignification of a fiber raw material using a sulfite pulping method and containing organic and inorganic compounds; Treating said organic and inorganic compounds at a temperature in excess of 800 ° C., whereby partly producing at least one phase of a liquid substance and partly producing at least one phase of a gaseous substance, Is carried out in a gasification reactor (2) by gasifying (M) the concentrated sulfite solution (F) under substoichiometric conditions and in the presence of an oxidizing medium; The method (2) has an opening in the shape of a chute (5) at its bottom, the opening opening directly into the quench section (38).   2. Process according to claim 1, characterized in that the horizontal cross-sectional diameter of the chute (5) is less than 40%, preferably 5-35% of the maximum cross-sectional diameter in the horizontal plane of the reactor (2).   Process according to claim 1 or 2, characterized in that the temperature is at least 900 ° C, preferably at least 950 ° C and less than 1300 ° C.   The method according to claim 1, wherein the gasification is spouted bed gasification.   Any one of claims 1 to 4, characterized in that the absolute pressure of the gasification process is about 1.5 to about 150 bar, preferably about 10 to about 80 bar, most preferably about 24 to about 40 bar in the reaction zone. The method according to one item.   The method according to claim 1, wherein the oxidation medium is oxygen gas or oxygen-containing gas.   7. The sulfite concentrate solution (F) in the form of droplets when in contact with the oxidation medium, the droplets having an average droplet diameter of less than 300 μm, The method according to claim 1.   The liquid substance is in the form of a salt melt, the salt melt is dissolved in a chemical solution, thereby forming a green liquid (I), and the green liquid (I) is discharged from the reactor (2); The process according to any one of claims 1 to 7, characterized in that it is further treated to convert sodium sulfide contained in the green liquor (I) into sulfur dioxide and / or sulfite.   The sodium sulfide is first converted to hydrogen sulfide and then further to sulfur dioxide and / or sulfite by contacting the sodium sulfide, preferably in an absorption / desorption tower, with carbon dioxide and sulfur dioxide in countercurrent. The method according to claim 8, wherein:   The amount of unburned coal in the green liquor is less than 5%, preferably less than 1%, more preferably less than 0.2% of the carbon in the sulfite concentrated solution. Method.   11. A method according to claim 8 or 10, characterized in that the green liquor is freed of unreduced sulfur to the extent of at least 90%, preferably at least 95%, more preferably at least 98%.   The method according to claim 1, wherein the gaseous substance is raw material synthesis gas (N) containing hydrogen sulfide, carbon monoxide, hydrogen and carbon dioxide.   The hydrogen sulfide and the carbon dioxide in the raw syngas are removed from the raw syngas in an acid gas removal plant (30), thereby a hydrogen sulfide rich stream (Q) from the acid gas removal plant (30). 13. A process according to claim 12, characterized in that a stream comprising carbon dioxide (R) and mainly carbon dioxide (R) is formed.   14. Process according to claim 13, characterized in that the hydrogen sulfide rich stream (Q) comprises at least 25% hydrogen sulfide, preferably at least 35% hydrogen sulfide of the total content of the stream.   14. Process according to claim 13, characterized in that the stream (R) mainly comprising carbon dioxide is conveyed from the acid gas removal plant (30) to the recovery process.   The hydrogen sulfide rich stream (Q) from the acid gas removal plant (30) is directly combusted with air or oxygen to obtain a post-combustion gas containing sulfur dioxide, the sulfur dioxide being a gas scrubber from the post-combustion gas. 14. Method according to claim 13, characterized in that it is absorbed in.   The method according to any one of claims 1 to 7, characterized in that the sulfite concentrated solution is a sodium-based sulfite solution.   8. A method according to any one of the preceding claims, characterized in that the sulfite concentrated solution is a potassium based sulfite concentrated solution.

Images