JP2007252992A - Inflammable gas from sludge, recovery process of slag, and gasification melting furnace of sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out the gasification melting treatment of activated sludge mainly generated by the biological treatment of sewage highly efficiently and at a low cost, simultaneously recover phosphorous contained in sludge, and utilizing it as a fertilizer and a phosphorous raw material. <P>SOLUTION: This recovery process comprises blowing the sludge into a gas flow bed gasification melting furnace having a temperature of not less than a melting point of sludge ash from a plurality of raw material supply nozzles by air flow conveyance such that a blowing angle in a direction perpendicular to a furnace wall is 0 to 45 degrees downward and in a tangential direction of a swiveling circle coaxial with a furnace having a diameter smaller than that of 1/5 of the inner furnace of the gasification melting furnace, generating a flammable gas by partially reacting the sludge with oxygen and an oxygen enrichment gas, generating a slag containing phosphorous by melting the ash, and recovering generated flammable gas and the slag. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention gasifies and melts activated sludge generated mainly by biological treatment of sewage to recover organic matter in the sludge as a combustible gas, and incorporates phosphorus contained in the sludge into the slag. It is related with the method of collect | recovering by this and using effectively as a fertilizer or phosphorus raw material, and the gasification melting furnace of the sludge used for it.

  Excess activated sludge (hereinafter abbreviated as sludge) generated when wastewater, especially sewage is purified by biological treatment, is used to disseminate sewage systems and introduce advanced treatment processes (such as nitrogen and phosphorus removal) at sewage treatment plants. It tends to increase more and more with such. Currently, most of these sludges are simply disposed of in landfills after volume reduction treatment. As the form of the sludge at that time, the majority of cases are so-called dehydrated cake after dehydration (water content of about 80% by mass) or the case where the dehydrated cake is reclaimed as incinerated ash after incineration.

  In recent years, some sludge melting treatments have been carried out for the purpose of further reducing sludge volume or effectively using sludge for reasons such as tightness in landfills. Sludge melting treatment is a technology that converts sludge into slag by burning it in a high-temperature atmosphere above the melting point of ash to reduce the bulk density of sludge or effectively use it as a construction material. is there.

  Sludge generally has a calorific value of about 6300 to 21000 kJ / kg-dry in a dry state, but still a large amount of about 80% by mass in the state of a dehydrated cake which is the final form in a normal sewage treatment plant. In consideration of heat loss (heat dissipated from the furnace body, sensible heat brought out by entrained nitrogen in the combustion air, latent heat of water evaporation, etc.) That is, it is difficult to self-combust). Therefore, in a conventional sludge incinerator, it is indispensable to use auxiliary fuel by some method (added directly into the furnace, used as air preheating fuel, etc.). For the purpose of reducing auxiliary fuel, the sensible heat in the high-temperature exhaust gas discharged from the incinerator is generally indirectly recovered by a heat recovery facility such as a heat exchanger and used for preheating combustion air.

  In a normal sludge melting furnace, it is necessary to maintain the inside of the melting furnace at a temperature higher than the melting point of ash (about 1100 to 1600 ° C., and the incinerator is 1000 ° C. or lower than the melting point of ash). Since a large amount of auxiliary fuel is required when it is put into the furnace, it becomes extremely inefficient. Therefore, it is common to dry sludge with a drying facility in advance. However, even if the moisture in the sludge is reduced to prevent heat loss due to latent heat of vaporization, if other heat losses are taken into account, even if the sludge is completely burned, the furnace temperature will exceed the melting point of ash. It is difficult to maintain a high temperature, and it is indispensable to use auxiliary fuel by some method (added directly into the furnace, used as air preheating fuel, etc.) as in the case of a sludge incinerator. Of course, a separate heat source is required for the drying facility in the previous stage, but external fuel (auxiliary fuel, such as heavy oil, kerosene, light oil, LPG, LNG, city gas, digestion gas, etc.) is introduced. In order to suppress the heat as much as possible, the sensible heat in the high-temperature exhaust gas discharged from the melting furnace is indirectly recovered by a heat recovery facility such as a waste heat boiler or heat exchanger, and applied to a part of the necessary heat source in the dryer. Is common.

  On the other hand, it is known that relatively high concentration of phosphorus derived mainly from phosphorus contained in waste water is accumulated in sludge. Since the concentration of phosphorus contained in sludge may reach the same level as the phosphorus ore that is the raw material in the normal phosphorus production process, in recent years there has been technology to recover phosphorus from incineration ash after incineration of sludge and make effective use of it. Proposed.

  For example, in patent document 1 and patent document 2, sludge which uses slag produced by melting incinerated ash after incineration treatment of sludge after mixing with calcium component and magnesium component as phosphorus fertilizer (substitute for molten phosphorus fertilizer) An effective utilization method for medium phosphorus has been proposed.

  Further, Patent Document 3 proposes a method of drying sludge, transporting it in an air stream, blowing it into a melting furnace, partially burning the sludge with oxygen or oxygen-enriched air, and recovering reducing gas and slag. The method enables gasification and melting of sludge without using auxiliary fuel.

JP 2001-80979 A Japanese Patent Laid-Open No. 2003-112988 JP-A-11-159722 Noriaki Senba, Shizuo Yasuda, Susumu Nishikawa, Yoshimasa Kawami, Masayuki Furukaku “Proceedings of the 7th Annual Conference of the Japan Society of Waste Management” The Japan Society of Waste Management, 1996, p464 Ryo Yoshiya, Makoto Nishimura, Hiroshi Moritomi "Proceedings of the 11th Annual Meeting of the Waste Society" Waste Society, 2000, p864

FIG. 1 shows a basic flow of a method of effectively using sludge having phosphorus-containing ash generated by biological treatment of conventional waste water described in Patent Document 1 and Patent Document 2 (using slag as phosphorus fertilizer). In the conventional method, a two-stage process in which an ash melting furnace 9 for producing phosphorus fertilizer is further installed downstream of the sludge incinerator 4 for reducing the volume by burning the sludge (dehydrated cake) 1 with air 2. It has become. In such a process, of course, since two furnaces are installed, the equipment cost increases and a large installation space is required. In particular, in the sludge incinerator 4, a large amount of high-temperature exhaust gas 5 (main components are N ₂ , CO ₂ , H ₂ ) generated by high-temperature combustion of sludge 1 (sometimes together with auxiliary fuel) with excess air _2. A series of exhaust gas treatment equipment 11 (waste heat recovery device, dust removal equipment, desulfurization equipment, etc.) for treating from O) is extremely large, which is a major factor in adding installation cost and equipment space. .

  In addition, as described above, the use of the auxiliary fuel 3 is indispensable in the sludge incinerator 4, and the electric furnace is generally used in the latter ash melting furnace 9, so in the conventional process, There was also a problem that utility costs such as fuel costs and power costs would become extremely high.

  In the ash melting furnace 9, the incineration ash 6 of the sludge must be heated to a temperature higher than the melting point of the ash together with the auxiliary materials 8 (magnesium, calcium, etc.) necessary for fertilization, and in that case contained in the sludge It is known that a portion of the metal component to be volatilized and removed from the slag. When the inside of the furnace is a reducing atmosphere, volatilization is further promoted (for example, see Non-Patent Documents 1 and 2). Patent Document 2 also states that the inside of the furnace is maintained in a reducing atmosphere so that heavy metals are not transferred into the slag 10 as much as possible. For this purpose, coke 7 which is an expensive fuel is used as a carbon source from the outside. It was necessary to add.

  Although Patent Document 3 does not describe the recovery of phosphorus, in order to ensure a long partial oxidation reaction time of sludge, the angle of the burner corresponding to the sludge nozzle is set so that the swirling flow of combustion gas becomes large. Therefore, the phosphorus in the sludge is promoted to volatilize and mostly migrates to the combustion gas side, and it is difficult to take in the phosphorus in the slag and recover it.

  In particular, mercury, arsenic, chromium, lead, cadmium, selenium, etc., which are particularly harmful metal components, are essentially contained in the sludge, so it is practical to use the generated slag effectively. There is almost no problem. However, with respect to zinc, it is general that the content is about 1% at the maximum because various components such as detergents used in general households are discharged into sewage. Zinc is not specified as a hazardous substance for effective use of slag (elution limit when used as construction material, content limit when used as fertilizer). Since there is a restriction on the capacity, there is a big problem that zinc dissolved in the soil of farmland gradually accumulates, especially when the generated slag is used as fertilizer.

  The object of the present invention is to melt sludge with high efficiency and low cost, collect flammable gas, and take in and collect much of phosphorus contained in sludge and use it as fertilizer or phosphorus raw material It is providing the sludge effective utilization method which can obtain the slag for performing, and the gasification melting furnace of sludge for it.

In order to achieve the above object, the gist of the present invention is as follows.
(1) Sludge that is generated by biological treatment of wastewater and contains phosphorus into a gas bed gasification melting furnace having a temperature equal to or higher than the melting point of the ash, and the blowing angle in the direction perpendicular to the furnace wall is downward From a plurality of raw material supply nozzles toward the tangential direction of the swirl circle coaxial with the furnace having a diameter smaller than 1/5 with respect to the diameter in the furnace of the gasification melting furnace so as to be 0 to 45 degrees Blowing by air current conveyance, the sludge is partially oxidized with oxygen or oxygen-enriched air to generate a combustible gas, and the ash is melted to generate phosphorus-containing slag, the generated combustible gas and A method for recovering flammable gas and slag from sludge, characterized by recovering slag.
(2) The method for recovering flammable gas and slag from sludge according to (1), wherein the generated slag is rapidly cooled in water and recovered as granulated slag.
(3) In (1) or (2), at least one of a magnesium component, a calcium component, and a silica component is added to the sludge, and the sludge after the addition is blown into the gasification melting furnace. A method for recovering combustible gas and slag from the described sludge.
(4) A sludge gasification and melting furnace that is generated by biological treatment of wastewater and contains phosphorus, and has a plurality of raw material supply nozzles that blow the sludge into the gasification and melting furnace by airflow conveyance, The nozzle has a downward blowing angle of 0 to 45 degrees with respect to the furnace wall of the gasification melting furnace, and has a diameter smaller than 1/5 with respect to the diameter of the gasification melting furnace in the furnace. It arrange | positions toward the tangent direction of the turning circle | round | yen coaxial with a furnace, or is arrange | positioned in the opposing direction facing each other, It is characterized by the above-mentioned.

  The present invention gasifies and melts excess activated sludge generated mainly by biological treatment of sewage with high efficiency and low cost, collects combustible gas, and contains phosphorus contained in sludge in slag. It can be taken in and collected and used effectively as a fertilizer or phosphorus raw material.

  Hereinafter, the present invention will be described in detail. FIG. 2 shows a flow sheet relating to the present invention.

  The equipment configuration in this flow is that a gasification melting furnace (high-temperature gasification section) 17 having a gas quencher 18 provided in the upper part is installed at the rear stage of the sludge drying equipment 12, and the waste heat recovery unit 23 ( Waste heat boilers, air preheaters, etc.), high temperature filters (metal filters, ceramics filters, etc.), dedusting equipment 24 such as cyclo (registered trademark), and desulfurization equipment 26 are arranged, and further combustible gas (product) Clean) 27 is provided with a circulation line 29 to the sludge drying facility 12.

The dried sludge 13 discharged from the sludge drying facility 12 is in a fine powder state and is fed into an airflow bed type gasification melting furnace (high temperature gasification section) 17 by airflow conveyance. In the gasification melting furnace (high-temperature gasification section) 17, sludge is gasified at a high temperature of 1100 to 1600 ° C. by a partial oxidation reaction (incomplete combustion) using oxygen 16 as a gasifying agent, and a high-temperature combustible gas ( main component is converted to _{H 2, CO, CH 4,} CO 2, H 2 O) and slag.

  In addition, the slag described here means that the ash contained in the sludge is melted at a temperature equal to or higher than its melting point (including one that has been cooled and solidified again). The melting point of ash means the melting point temperature defined in JIS M8801 (ash melt test method).

  The atmosphere in a normal sludge incinerator or sludge melting furnace in which sludge needs to be completely burned by adding excessive air (that is, oxygen contained in the air) is an oxidizing atmosphere. In the gasification and melting furnace (high-temperature gasification section) 17, a reaction occurs under an oxygen-deficient state, so that a reducing atmosphere is formed. It is known that when sludge is melted in such a high-temperature reducing atmosphere, volatilization of heavy metals contained in the sludge is promoted (for example, see Non-Patent Documents 1 and 2).

  In particular, the fine powdery sludge charged into the gasification melting furnace (high temperature gasification section) 17 instantly gasifies the organic component, and at the same time the ash melts and is converted into fine particles of slag. As the slag becomes finer, the specific surface area increases and the timing of contact with the surrounding reducing atmosphere gas also increases, so the volatility of heavy metals contained in sludge, especially zinc with a high content, has jumped. Increase. In this case, the particle size of the fine powdery sludge before being charged into the gasification melting furnace (high-temperature gasification section) 17 is preferably 1 mm or less from the viewpoint of increasing the volatile removal amount of heavy metals. The volatilized heavy metal component is entrained in the high temperature combustible gas and is discharged from the gasification melting furnace (high temperature gasification section) 17.

  Since sludge is originally an aggregate of microorganisms and bacteria, if it is dried to a water content of about 15% by mass or less in the sludge drying facility 12, most of the sludge is in a fine powder state with a particle size of about 1 mm or less. However, depending on the method of the sludge drying facility 12 (for example, the rotary drying method with a stirring crusher) and the properties of the sludge, a small amount of granular sludge having a diameter of 1 mm or more may be mixed. These sludge particles having a particle size larger than 1 mm cause not only the above-mentioned decrease in volatilization of heavy metals from the slag, but also causes troubles such as pipe clogging when conveying fine powder sludge. In this case, it is desirable to install a pulverizer such as a roller mill or a cutter mill at the subsequent stage of the sludge drying facility 12 and adjust all sludge particles to 1 mm or less. Further, instead of a pulverizer, a vibration sieve may be installed to remove sludge having a particle size larger than 1 mm.

  The sludge particles thus adjusted usually have a particle size distribution containing particles having a particle size of 1 mm or less, of which 10 μm or less is about 20%. It is not preferable to make the particle size of the sludge finer than necessary because it not only consumes a lot of power, but also causes troubles such as blockage of pipes when carrying the air current and racking of the supply hopper.

  In addition, the particle diameter of the sludge defined here is measured by a sieving particle size distribution measuring device.

  In the gasification melting furnace (high temperature gasification section) 17, it is known that volatilization occurs not only with respect to heavy metal components in sludge but also with respect to phosphorus. In this air-bed type gasification and melting furnace, the slag component stays in the furnace for a relatively short time. In order to prevent long-term stable operation and to improve the added value of slag (increased phosphorus content contained in slag), It is desirable to suppress volatilized phosphorus as much as possible and transfer it into the slag.

  The inventors converted the time that sludge particles blown into the gasification melting furnace (high-temperature gasification section) 17 stays in the furnace to convert the organic matter in the sludge into a combustible gas by a partial oxidation reaction. It was found that the volatilization of phosphorus in the sludge can be suppressed by controlling within the minimum necessary short time. The sludge particles in this case are the original sludge particles blown into the gasification melting furnace (high temperature gasification section) 17, and most of the organic matter in the sludge particles is converted to gas by the partial oxidation reaction. At the same time, the ash contained in the sludge is melted at a temperature above its melting point, and finally converted into slag particles. Further, the time for which sludge particles stay in the furnace (particle retention time) means that the sludge particles are blown into the gasification melting furnace (high temperature gasification section) 17 to be converted into slag particles, and the slag particles. Means the time to reach the furnace bottom.

  In addition, the carbon conversion rate, which is an index indicating the ratio of the organic matter in the sludge converted to combustible gas, may be slightly reduced by shortening the residence time of the sludge particles in the furnace, but the sludge has a particle residence time. However, there is no particular problem because a high carbon conversion rate of 90% or more can be obtained even in a short time of about 1 second.

  That is, as shown in FIG. 3, the raw material supply nozzle 30 (installed in plural) for feeding the dried sludge adjusted to a fine powder into the furnace by airflow conveyance is provided against the wall of the gasification melting furnace (high temperature gasification section) 17. The vertical sludge is installed at an angle of 0 ° or more downward, and fine powder sludge is blown into the gasification melting furnace (high-temperature gasification section) 17 at the same angle to partially oxidize the organic matter in the sludge. The slag generated by melting the ash at the same time reaches the bottom of the furnace without unnecessarily staying in the furnace while securing the time necessary for conversion to flammable gas by the reaction, and enters the slag pot 20. It becomes possible to discharge.

  Further, from the viewpoint of preventing the sludge particles from being blocked in the sludge transfer pipe in the nozzle and in front of the nozzle, the raw material supply nozzle 30 (installed in plural) is perpendicular to the wall of the gasification melting furnace (high temperature gasification section) 17. It is more desirable to install it at an angle of 15 to 45 degrees downward. When the raw material supply nozzle 30 is installed upward from 0 degree (horizontal), the sludge particles blown in and the slag particles thereafter reach the top of the furnace above the nozzle, and then follow the trajectory of dropping to the furnace bottom. As a result, the residence time in the furnace becomes longer, and the volatilization amount of phosphorus increases. Further, the possibility of occurrence of clogging of sludge particles in the sludge conveying pipe in the nozzle and in front of the nozzle increases. . In addition, when the blowing angle is made larger than 45 degrees, damage to the furnace bottom and the furnace wall caused by the high temperature frame (flame) formed at the nozzle tip coming into contact with the furnace bottom and the furnace wall becomes severe. It is not preferable.

  In addition, when the dried sludge adjusted to fine powder is blown into the gasification melting furnace (high temperature gasification section) 17, the swirling in the circumferential direction in the furnace increases, which increases the residence time of the sludge particles. It is not preferable because it is connected. That is, as shown in FIGS. 4A and 4B, the raw material supply nozzle 30 has a diameter smaller than 1/5 with respect to the in-furnace diameter 34 of the gasification melting furnace (high temperature gasification section) 17. It is preferable to install a plurality of circles in the tangential direction of the turning circle 35 coaxial with the furnace to be formed (FIGS. 4A and 4B are examples of 1/6). Each nozzle 30 is preferably directed in the tangential direction of the same turning circle 35, but may be displaced. Further, as shown in FIGS. 5 (a) and 5 (b), the diameter of the swirl circle may be set to zero, and all the nozzles may face the central axis of the furnace.

  Although the number of the raw material supply nozzles 30 may be two, three or more are preferable from the viewpoint of the stability of the swirling flow, and six or less are preferable from the viewpoint of handling ease and economy.

  In order to appropriately control the residence time of the sludge particles by the sludge blowing means as described above, the inner diameter of the gasification melting furnace (high temperature gasification section) 17 is within 5 m and the height is within 10 m. In addition, it is desirable that the speed (linear flow velocity) when the sludge particles are blown by airflow conveyance is 5 m / s or more and 100 m / s or less. In addition, the lower limit of the inner diameter and height of the gasification melting furnace (high temperature gasification section) 17 is that the inner diameter is 0.3 m or more and the height is 0.3 m or more. It is desirable from the viewpoint of maintaining efficiency.

  In a general gasification melting furnace, the sludge particle residence time is several times to several tens of times the gas residence time. However, by setting the conditions as described above, the sludge particle residence time exhibits a residence time similar to the gas residence time. In addition, since the time required for the organic substance in the sludge particles to be converted into gas by the partial oxidation reaction is 1 to 2 seconds, the particle residence time is desirably in the same range of 1 to 2 seconds.

  Further, as shown in FIG. 6, the position in the height direction of the gasification melting furnace (high temperature gasification section) 17 where the raw material supply nozzle 30 is installed maintains the temperature at the bottom of the furnace at a high temperature so that slag can be easily extracted. Therefore, the lower half of the furnace height (inner) is desirable. In addition, the gasification melting furnace (high temperature gasification part) in this case means only a high temperature gasification part which does not include a gas quencher and a slag pot. If the position of the raw material supply nozzle 30 is set higher than this, it is preferable because the amount of slag that is accompanied with the gas increases without being extracted from the bottom of the gasification melting furnace (high temperature gasification section) 17. Absent.

  The produced molten slag is taken out from an extraction hole (slag tap) installed at the bottom of the furnace and falls into a slag pot 20 filled with water. In water, slag rapidly solidifies by being cooled (water granulated) and converted into a vitreous (amorphous) solidified body (granulated slag). By performing water granulation, the phosphoric acid in the slag forms a glassy eutectic with other components, and most of them are not water-soluble but soluble in water (soluble in 2% citric acid solution). Become. Since soluble phosphoric acid has a property of gradually eluting in soil or water, it is suitable for directly and effectively using the produced slag 21 as a slow-acting fertilizer (molten phosphorus fertilizer). When the generated slag 21 is used as an alternative to the blended fertilizer raw material or the phosphorus ore that is the raw material of the phosphorus production process (when phosphorus is produced using this slag as the raw material), the final form of the slag is granulated slag, slow-cooled slag, etc. Any form is acceptable. In addition, what is necessary is just to naturally cool the molten slag extracted from the slag tap when manufacturing slowly-cooled slag.

  In addition, in order to use the produced | generated slag 21 directly as molten phosphorus fertilizer, the specification based on the present fertilizer control method (Cu-soluble phosphoric acid: 17.0 mass% or more, ku-soluble magnesia (Mg): 12 0.0 mass% or more, alkali content: 40.0 mass% or more, soluble silicic acid: 20.0 mass% or more) must be satisfied. In many cases, the original sludge does not contain components that satisfy this standard, so these components are separately added as auxiliary materials 8 and treated with sludge in the gasification melting furnace (high-temperature gasification section) 17. There is a need to.

  In order to satisfy the above specifications, it is necessary to add a magnesium component, a calcium component, and a silica component. However, when the obtained slag 21 is not directly used as molten phosphorous fertilizer but is used as a nonstandard fertilizer or as a raw material for producing phosphorus (substitute for ore), it is necessary to add these auxiliary materials 8 There is no.

  The form of magnesium added at this time is not particularly limited. That is, it may be in any form such as magnesium oxide, magnesium hydroxide, magnesium hydrogen carbonate, magnesium carbonate, dolomite, calcined dolomite, jamonite, and waste containing a magnesium component (such as waste brick). .

  Regarding the form of calcium added at this time, any form such as calcium oxide, calcium hydroxide, calcium hydrogen carbonate, calcium carbonate, dolomite, calcined dolomite, waste containing calcium components (waste bricks, etc.) It doesn't matter.

  Similarly, regarding the form of silica to be added at this time, any form such as silicon dioxide, silica stone, jamonite, waste containing silica component (waste brick or the like) may be used.

  Moreover, what is necessary is just to adjust suitably the mixing ratio of a magnesium component, a calcium component, and a silica component so that the specification based on the fertilizer control law may be met.

  Regarding the timing of adding these auxiliary materials 8 to the sludge, they may be added to the sludge (dehydrated cake) 1 before the sludge drying facility 12 or may be added to the dried sludge 13 after the sludge drying facility 12. However, when using magnesium oxide or calcium oxide as an auxiliary material, it is desirable to add to the sludge (dehydrated cake) 1 before the sludge drying facility 12. The added magnesium oxide or calcium oxide reacts with water contained in a large amount in the dehydrated cake according to the reaction formula shown by the following formula (1) or (2), and a part of the water in the dehydrated cake is removed. Therefore, the required fuel in the sludge drying facility can be reduced.

MgO + H ₂ O → Mg (OH) ₂ (1)
CaO + H ₂ O → Ca (OH) ₂ (2)
A part of magnesium and calcium added as the auxiliary material 8 also functions as a desulfurizing agent. That is, the sulfur content contained in the sludge is fixed as sulfide (MgS, CaS) or sulfate (MgSO ₄ , CaSO ₄ ) in the slag, so that the sulfur content (H _{2 As} S and COS). The reduction of the sulfur content transferred into the gas has an advantage of reducing the scale of the desulfurization facility 11 which must be installed in the latter stage of the gasification melting furnace.

  On the other hand, the high-temperature combustible gas discharged from the gasification melting furnace (high-temperature gasification section) 17 is cooled to 1000 ° C. or less by blowing spray water or quenching gas 19 in the gas quencher 18, and the upper part together with the gas. After preventing slagging troubles by solidifying the slag scattered to a temperature below the melting point, it is introduced into a waste heat recovery unit 23 such as a waste heat boiler or an air preheater for further effective use of heat. However, since the content of phosphorus entrained in the gas is small, avoid troubles due to precipitation of strong adhesive dust derived from phosphorus on the inner surface (heat transfer surface) of the waste heat recovery unit 23. Is possible.

  The combustible gas discharged from the waste heat recovery unit 23 removes dust contained in the gas in a dust removal facility 24 made of a filter (metal filter, ceramic filter, bag filter, etc.) or cyclo (registered trademark). Is done. The temperature of the gas introduced in the dedusting facility 24 is such that most heavy metal components are condensed so that the heavy metal components volatilized in the gasification melting furnace (high-temperature gasification section) 17 are condensed again and can be recovered together with the dust 25. It is desirable that the temperature be 350 ° C. or less at which condensation occurs.

  The combustible gas discharged from the dedusting facility 24 is refined in the desulfurization facility 26, and then the entire amount or a part thereof is used in the sludge drying facility as sludge drying fuel. The calorific value and generated amount of the combustible gas vary depending on the calorific value of the sludge to be gasified, the gasification conditions, and the quenching conditions. However, even if the entire amount of the combustible gas is used as the drying fuel, If the heat source necessary for drying is insufficient, the auxiliary fuel 3 may be used separately. On the contrary, when surplus combustible gas 28 is generated or when another heat source other than the combustible gas is used for drying, the generated combustible gas 27 is used for purposes other than drying (for example, for power generation). It may be used as a fuel, a chemical synthesis raw material such as methanol, a hydrogen raw material).

  As a method of the sludge drying equipment 12, a direct heating method in which high-temperature hot air and sludge are brought into direct contact can easily obtain fine powder sludge without using a pulverizer or only through a simple and small pulverizer. In addition, it is preferable in that the moisture content in sludge (= water mass / sludge mass−wet × 100) can be reduced to 15% or less. Various types of dryers such as an air dryer, a hot air pulverizer, a fluidized bed dryer, and a rotary drum dryer with a stirrer can be used as specific dryers.

  The moisture content in the sludge after drying is from the viewpoint of achieving high efficiency of the gasification melting furnace (high-temperature gasification section) 17, and as described above, the sludge is originally an aggregate of microorganisms and bacteria. Therefore, if the sludge drying equipment 12 is dried to a moisture content of about 15% by mass or less, most of the powder naturally becomes a fine powder having a particle size of about 1 mm or less, so it is desirable to set it to 15% by mass or less. In addition, although it changes also with the property of sludge, it is not preferable to make water content into 5 mass% or less because energy consumption required in the case of drying becomes large.

  The temperature in the gasification melting furnace (high-temperature gasification section) 17 is set to a temperature corresponding to the melting point of the ash contained in the sludge, and is set to a temperature higher than the melting point of the ash, so that it is 1100 ° C. or higher. The above high temperature is not preferable because the life of the furnace wall in the gasification melting furnace (high temperature gasification section) 17 is extremely shortened and the heat loss due to heat dissipation increases, so it is set to 1600 ° C. or lower.

  The oxygen 16 added as a gasifying agent during gasification is preferably as high as possible from the viewpoint of reducing the sensible heat brought out by the accompanying nitrogen. However, the production of oxygen at a concentration higher than necessary increases not only the disadvantages such as an increase in input energy in the oxygen production facility 15, but also has little influence on the gasification itself. Therefore, oxygen used here is general oxygen. The concentration (80% by volume or more) that can be produced by the production method (adsorption separation method <PSA>, deep cold separation method) may be used. In order to reduce the scale of the oxygen production facility 15, oxygen-enriched air obtained by mixing oxygen produced by the oxygen production facility 15 with air may be used instead of oxygen. At this time, if the oxygen concentration in the oxygen-enriched air is higher than the oxygen concentration normally contained in the air, the efficiency reduction of the gasification melting furnace due to the sensible heat of the accompanying nitrogen can be avoided to some extent. . However, in order to increase the efficiency in the gasification melting furnace and reduce the scale of a series of equipment such as the waste heat recovery unit 23, the dust removal equipment 24, the desulfurization equipment 26 installed after the gasification melting furnace, oxygen is used as a gasifying agent. It is desirable to use 80% or more oxygen by volume rather than enriched air.

  In the example of the present invention, energy (electric power) for producing oxygen is separately required. However, since the scale of gas treatment-related equipment after the furnace outlet can be greatly reduced as compared with the conventional method, The amount of power reduction can be covered sufficiently.

The amount of oxygen added here is less than the amount of oxygen necessary to completely burn the organic matter in the sludge containing moisture (so-called theoretical oxygen amount). The organic matter here means a portion (mainly carbon, hydrogen, nitrogen, sulfur, oxygen) from the ash content in the dry base sludge. The ratio varies depending on how many times the sludge heat generation amount and the gasification melting furnace temperature are set, but the ratio when the theoretical oxygen amount is 1 can be adjusted within the range of 0.2 to 0.8. Is preferred. When the oxygen ratio is less than 0.2, the amount of organic matter that is converted into unburned material without being gasified becomes extremely large. When the oxygen ratio exceeds 0.8, combustible gas components (H ₂ , CH ₄ ) and the like, and almost all of them are converted to combustion gases (CO ₂ , H ₂ O), which is not preferable for the purpose of the present invention. More preferably, the adjustment is made within the range of 0.3 to 0.6. If gasification is performed within this range, the proportion of unburned matter generated with respect to the organic matter contained in the sludge is suppressed to 30% by mass or less, and the proportion of combustible components contained in the combustible gas is 40% by volume or more. (Based on dry gas).

  Further, steam may be used in combination with oxygen 16 as a gasifying agent for the purpose of temperature control in the gasification melting furnace (high temperature gasification section) 17.

  The pressure in the gasification melting furnace (high-temperature gasification section) 17 is not particularly specified. However, when the pressure is lower than atmospheric pressure, there is a risk of explosion due to leakage of air from the outside, which is preferable. Absent. Moreover, when it is set as the pressurization conditions higher than atmospheric pressure, there also exists a merit which can make a gasification melting furnace compact.

  As sludge used in the present invention, in addition to sewage sludge, surplus activated sludge generated from biological wastewater treatment facilities (for example, coke oven wastewater (safe water) treatment equipment, stainless pickling wastewater treatment equipment, various Excess sludge discharged from a wastewater treatment facility in a food factory may be used.

Example 1
According to the flow shown in FIG.

  The analysis values of the sewage sludge used are shown in Table 1 (in terms of the ash composition, it contains components other than those indicated and a loss during the analysis also occurs, so the total does not become 100%). In addition, this sludge is what was discharged | emitted from the dehydrator of the sewage treatment plant (dehydrated cake).

  After drying sewage sludge (dehydrated cake) 1 (100 t / day) in an airflow (hot air) type sludge drying facility 12, the produced dried sludge 13 (water content 7 mass%, average particle size 470 μm) From the sludge supply hopper 14, the gas was supplied to the gasification melting furnace (high-temperature gasification section) 17 by air current conveyance using nitrogen which is a by-product of the oxygen production facility 15. The number of raw material supply nozzles is four, and the gasification melting furnace is connected to each of the gasification melting furnaces (high-temperature gasification section) 17 at an angle of 15 degrees downward at a height of 1/3 from the furnace bottom. The dry sludge 13 in the form of fine powder is blown by air flow (gas flow rate 10 m / s, solid-gas ratio 15) toward the tangential direction of a turning circle coaxial with the furnace having a diameter of 1/6 with respect to the inner diameter of the furnace. It was supposed to be.

  In the gasification melting furnace (high temperature gasification section) 17, the sludge is gasified and melted at a temperature of 1350 ° C. together with oxygen 16, converted into high temperature combustible gas and slag, and at the same time, one of the heavy metals contained in the sludge. Part volatilized into the gas. The generated molten slag was extracted from a slag tap at the bottom of the furnace, and after being crushed in a slag pot, was recovered as a slag 21 for granulation. On the other hand, the generated high-temperature combustible gas is cooled to 900 ° C. by the spray water 36 in the gas quencher 18 at the upper part of the gasification melting furnace (high-temperature gasification section) 17 and then recovered by the air preheater 37. Then, it was introduced into the dedusting facility 24 to remove the dust, and further introduced into the desulfurization facility 26, and recovered as a clean combustible gas 27. The entire amount of the combustible gas 27 was introduced into the sludge drying facility 12 as a fuel gas and burned with air preheated in the air preheater 37 to be used as a drying heat source. For this example, no auxiliary fuel was needed and the process could be thermally independent.

  Table 2 shows the composition of the granulated slag 21 recovered from the slag pot 20. It was possible to transfer 96% of the phosphorus contained in the original sludge into the slag. That is, it was possible to volatilize the heavy metal contained in the sludge and remove it from the slag while largely suppressing the volatilization of phosphorus. In particular, most of the zinc contained in the sludge could be removed.

  In addition, the produced | generated slag 21 was effectively usable as a compound fertilizer raw material.

  Table 3 shows the amount of utility used in the present invention example (Example 1) and the conventional phosphorus recovery process (fluidized bed sludge incinerator + phosphorus recovery electric ash melting furnace). In the example of the present invention, the amount of auxiliary fuel used and the amount of power used can be greatly reduced as compared with the conventional method. In addition, since the equipment configuration is much simpler than that of the conventional method, the equipment cost and equipment installation space can be reduced to about 70%.

Example 2
According to the flow shown in FIG.

  The analysis values of the sewage sludge used are shown in Table 4 (in terms of the ash composition, it contains components other than those indicated and a loss during the analysis also occurs, so the total does not become 100%). In addition, this sludge is what was discharged | emitted from the dehydrator of the sewage treatment plant (dehydrated cake).

  After drying sewage sludge (dehydrated cake) 1 (100 t / day) in an airflow (hot air) type sludge drying facility 12, the produced dried sludge 13 (water content 7 mass%, average particle size 470 μm) is used as an auxiliary material. After mixing with 2.6 t / day of dolomite 8 and 0.5 t / day of silica, the gasification and melting furnace (high-temperature gasification section) 17 is transferred from the sludge supply hopper 14 by air flow using nitrogen as a by-product of the oxygen production facility 15. It was thrown into. The number of raw material supply nozzles is four, and the gasification melting furnace is connected to each of the gasification melting furnaces (high-temperature gasification section) 17 at an angle of 15 degrees downward at a height of 1/3 from the furnace bottom. The fine powder sludge mixed with the auxiliary materials is air-flowed toward the tangential direction of the turning circle coaxial with the furnace having a diameter of 1/6 with respect to the inner diameter of the furnace (gas flow rate 10 m / s, solid-gas ratio 15) To be blown by. In the gasification melting furnace (high-temperature gasification section) 17, sludge is gasified and melted at a temperature of 1400 ° C. together with oxygen to be converted into high-temperature combustible gas and slag, and at the same time, a part of heavy metals contained in the sludge Volatilized into the gas. The produced molten slag was extracted from the slag tap at the bottom of the furnace, and after being granulated in a slag pot, it was recovered as granulated slag (phosphorous fertilizer) 10. On the other hand, the generated high-temperature combustible gas is cooled to 900 ° C. by the spray water 36 in the gas quencher 18 at the upper part of the gasification melting furnace (high-temperature gasification section) 17 and then recovered by the air preheater 37. Then, it was introduced into the dedusting facility 24 to remove the dust, and further introduced into the desulfurization facility 26, and recovered as a clean combustible gas 27. The entire amount of the combustible gas 27 was introduced into the sludge drying facility as a fuel gas and burned with air preheated in an air preheater to be used as a drying heat source. In this example, 3 L / t-dehydrated cake of A heavy oil was used as the auxiliary fuel 3 in the sludge drying facility.

  Table 5 shows the composition of the granulated slag 10 recovered from the slag pot 20. It was possible to transfer 95% of the phosphorus contained in the original sludge into the slag. That is, it was possible to volatilize the heavy metal contained in the sludge and remove it from the slag while largely suppressing the volatilization of phosphorus. In particular, most of the zinc contained in the sludge could be removed.

  In addition, since the produced | generated slag 10 satisfy | filled the specification as molten phosphorus fertilizer, it was effectively usable as direct phosphorus fertilizer.

  Table 6 shows utility usage in the present invention example (Example 1) and the conventional phosphorus recovery process (fluidized bed sludge incinerator + phosphorus recovery electric ash melting furnace). In the example of the present invention, the amount of auxiliary fuel used and the amount of power used can be greatly reduced as compared with the conventional method. In addition, since the equipment configuration is much simpler than that of the conventional method, the equipment cost and equipment installation space can be reduced to about 70%.

Comparative Example The inventive example was carried out according to the flow shown in FIG.

  The analysis values of the sewage sludge used are shown in Table 7 (the composition of ash contains components other than those indicated, and the loss during the analysis also occurs, so the total does not become 100%). In addition, this sludge is what was discharged | emitted from the dehydrator of the sewage treatment plant (dehydrated cake).

  After drying sewage sludge (dehydrated cake) 1 (100 t / day) in an airflow (hot air) type sludge drying facility 12, the produced dried sludge 13 (water content 7 mass%, average particle size 470 μm) From the sludge supply hopper 14, the gas was supplied to the gasification melting furnace (high-temperature gasification section) 17 by air current conveyance using nitrogen which is a by-product of the oxygen production facility 15. It should be noted that there are four raw material supply nozzles, and from each nozzle at an angle of 1/3 from the furnace bottom of the gasification melting furnace (high temperature gasification section) 17, each nozzle is connected to the furnace of the gasification melting furnace. A fine powdery dry sludge 13 is blown by air flow (gas flow rate 10 m / s, solid-gas ratio 15) toward the tangential direction of a turning circle coaxial with the furnace having a diameter of ½ of the inner diameter. did.

  In the gasification melting furnace (high temperature gasification section) 17, the sludge is gasified and melted at a temperature of 1350 ° C. together with oxygen 16, converted into high temperature combustible gas and slag, and at the same time, one of the heavy metals contained in the sludge. Part volatilized into the gas. The generated molten slag was extracted from a slag tap at the bottom of the furnace, and after being crushed in a slag pot, was recovered as a slag 21 for granulation. On the other hand, the generated high-temperature combustible gas is cooled to 900 ° C. by the spray water 36 in the gas quencher 18 at the upper part of the gasification melting furnace (high-temperature gasification section) 17 and then recovered by the air preheater 37. Then, it was introduced into the dedusting facility 24 to remove the dust, and further introduced into the desulfurization facility 26, and recovered as a clean combustible gas 27. The entire amount of the combustible gas 27 was introduced into the sludge drying facility 12 as a fuel gas and burned with air preheated in the air preheater 37 to be used as a drying heat source. For this example, no auxiliary fuel was needed and the process could be thermally independent.

  Table 8 shows the composition of the granulated slag 21 recovered from the slag pot 20. The proportion of the phosphorus contained in the original sludge that could be transferred into the slag was 77%. That is, the volatilization of phosphorus was promoted as compared with Example 1, and the ratio of migration into dust increased. Part of the dust containing phosphorus at a high concentration adhered to the heat transfer surface (inner surface) of the air preheater 37 in the subsequent stage, causing a reduction in heat exchange capacity.

  FIG. 10 shows the relationship between the rate of transfer of phosphorus to slag and the sludge blowing angle under the same gasification conditions as in Example 1. By making the blowing angle upward from 0 degree (indicated by a minus sign in the figure), the ratio of phosphorus to slag was reduced. In addition, by increasing the blowing angle to more than 45 degrees, damage to the gasification furnace bodies such as the furnace wall and the furnace bottom became severe. Furthermore, by making the blowing angle smaller than 15 degrees, the frequency of clogging in the sludge air-flow conveying pipe has increased.

  FIG. 11 shows the relationship between the rate of transfer of phosphorus to slag and the sludge blowing direction (the size of the turning circle diameter relative to the furnace diameter) under the same gasification conditions as in Example 1. By making the turning circle diameter 1/5 or more of the furnace inner diameter, the rate of transfer of phosphorus to slag was reduced.

It is the flow sheet regarding a prior art. It is a flow sheet concerning the present invention. It is a flow sheet regarding the blowing method of dry sludge of the present invention. It is a flow sheet regarding the blowing method of dry sludge of the present invention. It is a flow sheet regarding the blowing method of dry sludge of the present invention. It is a flow sheet regarding the blowing method of dry sludge of the present invention. It is a flow sheet and mass balance in the example of the present invention. It is a flow sheet and mass balance in the example of the present invention. It is a flow sheet and mass balance in a comparative example of the present invention. It is a graph which shows the relationship between the transfer ratio to the slag of phosphorus, and the blowing angle of sludge. It is a graph which shows the relationship between the transfer ratio to the slag of phosphorus, and the blowing direction of sludge (size of the turning circle diameter with respect to the diameter in a furnace).

Explanation of symbols

1 Sludge (dehydrated cake)
2 Air 3 Auxiliary fuel 4 Sludge incinerator 5 Exhaust gas 6 Incinerated ash 7 Coke 8 Secondary material 9 Ash melting furnace 10 Slag (phosphorous fertilizer)
11 Exhaust gas treatment equipment 12 Sludge dryer 13 Dry sludge 14 Sludge supply hopper 15 Oxygen production equipment 16 Oxygen 17 Gasification melting furnace (high temperature gasification section)
18 Gas quencher 19 Spray water or quench gas 20 Slag pot 21 Slag 22 Combustible gas 23 Waste heat recovery device 24 Dedusting equipment technology center 25 Dust 26 Desulfurization equipment 27 Combustible gas (clean)
28 Combustible gas (surplus)
29 Circulation line of flammable gas (clean) to sludge drying equipment 30 Raw material supply nozzle 31 Sludge blowing range 32 Gasification melting furnace height 33 Raw material supply nozzle installation position 34 Inside of gasification melting furnace (high temperature gasification section) Diameter 35 Swirl circle 36 Spray water 37 Air preheater

Claims (4)

  The sludge generated by biological treatment of the wastewater and containing phosphorus is blown into the air bed type gasification melting furnace having a temperature equal to or higher than the melting point of the ash, and the blowing angle in the direction perpendicular to the furnace wall is 0-45 downward. And by air flow from a plurality of raw material supply nozzles in the tangential direction of a swirl circle coaxial with the furnace having a diameter smaller than 1/5 of the diameter in the furnace of the gasification melting furnace. Blowing, and causing the sludge to partially oxidize with oxygen or oxygen-enriched air to produce a combustible gas, melt the ash to produce phosphorus-containing slag, and recover the produced combustible gas and slag A method for recovering flammable gas and slag from sludge.   The method for recovering combustible gas and slag from sludge according to claim 1, wherein the generated slag is rapidly cooled in water and recovered as a granulated slag.   The sludge according to claim 1 or 2, wherein at least one of a magnesium component, a calcium component, and a silica component is added to the sludge, and the sludge after the addition is blown into the gasification melting furnace. How to collect flammable gas and slag.   A gasification and melting furnace for sludge generated by biological treatment of wastewater and containing phosphorus, having a plurality of raw material supply nozzles for blowing the sludge into the gasification and melting furnace by airflow conveyance, The gas injection melting furnace has a vertical blowing angle of 0 to 45 degrees downward and coaxial with a furnace having a diameter smaller than 1/5 of the diameter of the gasification melting furnace in the furnace. A sludge gasification and melting furnace, which is arranged in a tangential direction of the swirl circle of the sludge.

Images