JP2005265273A - Sludge gasifying and melting method and device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sludge gasifying and melting method capable of making a melting process for sludge with high efficiency and at a low cost, and, collecting phosphorus from the sludge. <P>SOLUTION: Active sludge is cast into a sludge drying facility for drying it and turning into fine powder, and the dried sludge is cast into a gasifying melting furnace together with oxygen 0.2-0.8 times as large as the oxygen quantity required to make perfect burn to be oxidized partially at 1100-1600°C and is turned into a combustible gas and a slag while part of the phosphorus contained in the active sludge is volatilized, and after being cooled by a gas cooler to 300-1000°C, the combustible gas is further cooled at a water washing tower by water spraying to a temperature between the ordinary one and 250°C and gets rid of the condensed phosphorus component, and the cooled combustible gas is devulcanized by a devulcanizing facility, and part or the whole of the devulcanized gas is passed through a circulation line and fed as the fuel to the sludge drying facility. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of gasifying and melting excess activated sludge generated mainly from a biological treatment facility of sewage, and simultaneously recovering and effectively utilizing phosphorus contained in the sludge.

  Surplus activated sludge (hereinafter abbreviated as sludge) generated when purifying sewage by biological treatment is accompanied by the spread of sewage and the introduction of advanced treatment processes (such as removal of nitrogen and phosphorus) at sewage treatment plants. It tends to increase more and more. Currently, most of these sludges are simply disposed of in landfills after volume reduction treatment. As the form of the sludge at that time, most cases are so-called dehydrated cake after dehydration (water content of about 80% by mass) or landfilled 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 the dry state, but still a large amount of about 80% by mass in the dehydrated cake state 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. 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 used as part of the necessary heat source in the dryer. It is common to do.

  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 phosphorus has been recovered from incineration ash after incineration of sludge or slag after melting. Technologies for effective use have been proposed.

  For example, in Patent Document 1, phosphorus in incineration ash is reduced by melting the incineration ash after incineration of sludge in a closed electric furnace under a reducing atmosphere condition together with a carbon source, together with exhaust gas. There has been proposed a phosphorus recovery method for recovering scattered phosphorus in the latter stage of the electric furnace.

In Patent Document 2, slag produced by melting sludge or incinerated ash in a melting furnace under an oxidizing atmosphere is introduced into a heating furnace under a reducing atmosphere together with a carbon source, and phosphorus contained in the slag is added. A method of recovering phosphorus has been proposed in which phosphorus discharged together with the high-temperature gas from the heating furnace is recovered at a later stage by reducing the amount of hydrogen.
Japanese Patent Laid-Open No. 9-145038 JP 2000-264611 A JP-A-11-159722 Politics of Tateishi, Norihiro Koide, Takashi Tamura “The 36th Sewerage Research Conference Lecture Collection” Japan Sewerage Association, 1999, p869 Hideki Iwabe, Norihiro Koide, Isao Munemiya “The Journal of the Sewerage Association” Japan Sewerage Association, 1999, Vol. 36, No. 443, p112 Hiroaki Miwa, Shigeru Machida “Symposium of the 36th Sewerage Research Conference” Japan Sewerage Association, 1999, p866

  FIG. 1 shows a basic flow of a conventional method for recovering phosphorus from sludge. In the conventional method for recovering phosphorus in sludge, a heating furnace 2 for recovering phosphorus (incineration ash or slag is heated at a high temperature to the subsequent stage of the sludge incinerator 1 or sludge melting furnace 1 for reducing the volume by burning sludge with air. It is a two-stage process that installs in a reducing atmosphere and volatilizes phosphorus. In such a process, of course, since two furnaces are installed, the equipment cost increases and a large installation space is required. In addition, two exhaust gases discharged from the sludge incinerator 1 (or sludge melting furnace) and the phosphorus recovery heating furnace 2 are separated into separate exhaust gas treatment equipment 3 (heat recovery equipment, dust removal equipment, phosphorus recovery equipment, gas Since the processing is performed in a cooling facility, a desulfurization facility, etc., the facility configuration becomes complicated, and the facility cost and installation space are further increased. Further, as described above, in the sludge incinerator 1 or the sludge melting furnace 1 (process including the sludge dryer), it is indispensable to use an auxiliary fuel. Since an electric furnace is used, the conventional phosphorus recovery process also has a problem that utility costs such as fuel cost and power cost become enormous.

Sensible heat from a large amount of high-temperature exhaust gas (main components are N ₂ , CO ₂ , H ₂ O) generated by high-temperature combustion of sludge (and possibly auxiliary fuel together) in an incinerator or melting furnace with excess air Of course, a series of heat recovery equipment (waste heat boiler, heat exchanger, air preheater, etc.) for recovering the wastewater is extremely large, and it is a matter of course that the installation cost and the equipment space are enormous. Costs related to periodic maintenance work required for equipment maintenance, such as removal of deposits on the heat transfer surface (for example, inside the boiler tube), will increase, and the equipment operation rate will also decline due to an increase in equipment outage period accompanying maintenance. There was a problem that. For example, according to Non-Patent Document 1, when sludge containing phosphorus is melted at a high temperature, large sticky dust due to volatilized phosphorus is generated and firmly adhered to the boiler and the flue. It is stated that a great deal of labor is required for the maintenance. Further, in Non-Patent Document 1, it is stated that the volatilization of phosphorus can be suppressed by adding polyferric sulfate to sludge in advance, but the cost of polyferric sulfate is increased. The problem of endlessness cannot be ignored.

  In Patent Document 3, dry sludge is partially combusted with oxygen or oxygen-enriched air in a swirl-type melting furnace having an air flow layer to generate a high-temperature reducing gas, and the sensible heat of the reducing gas is recovered by a waste heat boiler. A sludge incineration method has been proposed for effective use. However, it is known that the volatilization of phosphorus contained in sludge is promoted when the furnace is in a reducing atmosphere, and oxygen with low nitrogen content or oxygen-enriched air should be used as the oxidizing agent. Although the advantages of downsizing the waste heat boiler associated with the reduction in gas capacity due to the above can be enjoyed, there is still a problem that maintenance due to adhesion of dust to the boiler tube due to phosphorus is overloaded.

  Further, due to the problem of equipment corrosion caused by sulfur compounds contained in the exhaust gas, the sensible heat in the exhaust gas discharged at a high temperature of about 1000 to 1600 ° C. reaches about 300 ° C., which is a temperature above the so-called acid dew point. Can only be recovered. Further, indirect heat exchange type heat recovery equipment usually involves a certain amount of heat dissipation (heat loss) (about 10% of the amount of heat exchanged). Therefore, in the current sludge incinerator or melting furnace, there is a limit to the amount of heat that can be recovered from high-temperature exhaust gas sensible heat (in other words, the amount of heat generated by sludge and auxiliary fuel before the furnace is charged (before combustion)), Only a part of the heat required for the process including sludge drying could be covered, and the shortage had to be supplemented by combustion of auxiliary fuel.

  An object of the present invention is to provide a sludge gasification and melting method capable of melting sludge with high efficiency and low cost and simultaneously recovering phosphorus in the sludge.

In order to achieve the above object, the gist of the present invention is as follows.
(1) Activated sludge is directly contacted with hot air and dried, and the resulting dried sludge is partially oxidized at 1100 to 1600 ° C. with 0.2 to 0.8 times the theoretical oxygen amount necessary for complete combustion, combustible It converts to volatile gas and slag, volatilizes a part of phosphorus contained in the activated sludge, cools the combustible gas to 300 to 1000 ° C, further cools it to normal temperature to 250 ° C by water spray and condenses it. The recovered phosphorus component is recovered, the combustible gas after cooling is desulfurized, and part or all of the combustible gas after the desulfurization is circulated and supplied as fuel for generating hot air for drying the activated sludge. A method for gasifying and melting sludge.
(2) The method for gasifying and melting sludge as set forth in (1), wherein dust contained in the combustible gas is removed and then cooled to room temperature to 250 ° C.
(3) Gasification and melting of sludge according to (1) or (2), wherein the dry sludge is partially oxidized with oxygen at a particle size of 0.1 μm to 3 mm and a water content of 20% by mass or less. Method.
(4) A gasification melting furnace with a gas cooler installed in the upper part is installed after the direct heating type sludge drying equipment, and a water cooling tower and desulfurization equipment are installed in the subsequent stage. A sludge gasification and melting device characterized by installing a circulation line to the drying equipment.
(5) The sludge gasification and melting apparatus according to (4), wherein a metal filter, a ceramics filter, or a cyclone is installed in the front stage of the water cooling tower.

  According to the present invention, surplus activated sludge generated mainly from a biological treatment facility of sewage can be melted at a high efficiency and at a low cost, and at the same time, phosphorus in the sludge can be recovered.

  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 7 with a gas cooler 8 provided in the upper part is installed at the rear stage of the direct heating type sludge drying equipment 4, and a high-temperature filter (metal filter, ceramic filter) is installed at the subsequent stage. Etc.) or a cyclone 9, a water cooling tower 10, and a desulfurization facility 11 are further provided, and a circulation line 15 to an exhaust gas sludge drying facility is further provided.

The dried sludge discharged from the sludge drying equipment 4 is introduced into the gas bed type gasification melting furnace 7 by air flow conveyance. In the gasification melting furnace 7, sludge is gasified at a high temperature of 1100 to 1600 ° C. by a partial oxidation reaction (incomplete combustion) using oxygen as a gasifying agent, and a high-temperature combustible gas (main components are H ₂ , CO , CH ₄ , CO ₂ , H ₂ O) and slag.

  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 chemical melting furnace 7, a reaction occurs in 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 phosphorus contained in the sludge is promoted (for example, non-cited documents 2 and 3).

  Accordingly, most of the phosphorus contained in the sludge charged into the gasification melting furnace 7 is volatilized (partially reduced from phosphoric phosphorus to elemental phosphorus), and into the high-temperature combustible gas. Accompanied and discharged from the gasification melting furnace 7.

In addition, since the volatilization of phosphorus is promoted as the reduction degree in the gasification melting furnace 7 increases, the reduction degree in the furnace may be increased by blowing a carbon source other than sludge into the furnace together with the sludge. The carbon source added at this time is not limited to coal (pulverized coal), coke powder, woody biomass, waste plastic, petroleum residue, etc., but as a factor to increase the degree of reduction in the furnace, the carbon possessed by these carbon sources Not only the reducing effect by (C), but also the reducing effect by reducing gases (CO, H ₂ as main components) generated by gasifying these carbon sources simultaneously with sludge. Therefore, a carbon source that generates more reducing gas than sludge when gasified, that is, a carbon source with a high carbon content and a low oxygen content (a carbon source with a small O / C in elemental analysis values than sludge) It is desirable to add.

  In the sludge, most of phosphorus exists in the form of phosphoric acid, but part of it is reduced in the gasification melting furnace 7 in a reducing atmosphere, and in the form of elemental phosphorus (phosphorus simple substance, yellow phosphorus). It volatilizes and otherwise volatilizes in the form of phosphate phosphorus (phosphorus oxide).

  The type of sludge targeted in the present invention is not particularly limited, but it is known that sludge containing a large amount of calcium or iron suppresses volatilization of phosphorus (for example, Non-Patent Documents 1 and 2). In the treatment step, it is preferable to use sludge to which a chemical derived from calcium or iron is not added.

  The high-temperature combustible gas containing volatilized phosphorus discharged from the gasification melting furnace 7 is cooled to 1000 ° C. or less by blowing spray water or quenching gas in the gas cooler 8 and scattered together with the gas. After preventing slagging (slagging) trouble by solidifying slag at a temperature below the melting point, it is dedusted (separated dust) in a high-temperature filter (metal filter, ceramics filter, etc.) or cyclone 9 that is a dust removal facility. Further, the phosphor component (elemental phosphorus, phosphoric acid phosphorus) contained in the combustible gas is condensed by being cooled in the water cooling tower 10. These are effectively used as recovered phosphorus after separation and recovery.

  The primary purpose of the gas cooler 8 is to avoid troubles caused by solidifying the slag, but when ancillary equipment such as heat recovery equipment or dust removal equipment is installed in the front stage of the water cooling tower 9, It also has the role (protection function) of lowering the gas temperature to below the heat-resistant temperature. Although the outlet temperature of the gas cooler 8 is set according to the specifications (heat-resistant temperature) of these incidental facilities, it is preferable that the temperature is not lower than 300 ° C. at which most phosphorus or phosphoric acid compounds start to condense. .

  In the water cooling tower 9, it is preferable to cool the gas to a temperature of 250 ° C. or less at which yellow phosphorus or white phosphorus having the lowest boiling point (281 ° C.) among phosphorus or phosphoric acid compounds is surely deposited. If it is 250 degrees C or less, you may cool to normal temperature.

  Note that the gas cooler 8 can be omitted when no auxiliary equipment such as heat recovery equipment or dust removal equipment is installed. In this case, however, frequent cleaning of the flue from the gasification melting furnace 7 to the water cooling tower 9 is indispensable as a countermeasure against slag adhesion.

  In the present invention, unlike the conventional sludge incinerator and sludge melting furnace, the latent heat (calorific value) of the generated combustible gas can be used as a heat source necessary for the process. Installation of heat recovery equipment (waste heat boiler, air preheater, etc.) for recovering sensible heat is not essential. Of course, it is possible to install some kind of heat recovery equipment to make more effective use of heat. However, as mentioned above, dust containing volatilized phosphorus components is deposited on the heat transfer surface of the heat recovery unit. Need frequent maintenance. However, even when heat recovery equipment is installed, in conventional incinerators and melting furnaces, the amount of exhaust gas discharged from the furnace is extremely large (because it performs complete combustion with air). In the invention, since the amount of combustible gas discharged from the furnace is greatly reduced, the scale of the heat exchanger can be reduced, and the labor related to maintenance is also greatly reduced.

  In the present invention, the high temperature filter or cyclone 9 may be reduced, and the water cooling tower 10 may have a dust removing function. In this case, the purity of recovered phosphorus decreases due to dust contamination, so it is necessary to purify it in a separate process. However, the phosphorus content in recovered phosphorus is the same as that of general phosphorus ore, sludge incineration ash, and sludge slag. Since it is larger than the content, the energy and cost required for purification can also be reduced.

  The combustible gas discharged from the water cooling tower 10 is refined in the desulfurization facility 11 and then used in the sludge drying facility 4 as a sludge drying fuel in whole or in part. The calorific value and generation amount of the combustible gas vary depending on the calorific value of the sludge to be gasified and the gasification conditions. However, even if the combustible gas is used as a drying fuel, it is still necessary for drying. If the heat source is insufficient, auxiliary fuel may be used in combination. On the contrary, when surplus combustible gas is generated or when another heat source other than the combustible gas is used for drying, the generated combustible gas is used for purposes other than drying (for example, fuel for power generation, Chemical raw materials such as methanol, hydrogen raw materials).

  As a method of the sludge drying equipment 4 at this time, a direct heating method in which high-temperature hot air and sludge are brought into direct contact with each other can easily remove fine sludge without using a pulverizer or only through a simple and small pulverizer. It is suitable in that it can be obtained and the water content in the sludge can be reduced to 10% or less. Specifically, various types such as an airflow dryer, a hot-air pulverizing dryer, a fluidized bed dryer, and a rotary drum dryer with a stirrer can be used. In addition, as shown in FIG. 3 as an example of the drying equipment, when the hot air generated by burning the combustible gas in the combustion furnace 12 is introduced directly into the heating dryer 13, it is discharged from the direct heating dryer 13. By circulating part of the exhaust gas for dilution (for temperature adjustment and prevention of ignition) and reducing the amount of exhaust gas released outside the system, the load on the exhaust gas treatment equipment (deodorization, dust removal, etc.) is reduced. It is also desirable to reduce the amount of heat that the exhaust gas carries out.

  In addition, as shown in FIG. 4 as an example of another drying facility, hot air that is in direct contact with sludge is used as a circulation system, and combustion heat generated by burning combustible gas and air in a heat exchange type heating furnace 14 is used. It is also possible to heat the hot air in the circulation system indirectly. The exhaust gas from the heating furnace 14 can be directly diffused into the atmosphere in order to burn clean combustible gas (containing no sulfur content). At this time, it is necessary to extract a part of the hot air (excess gas) that has passed through the direct heating dryer 13 out of the system. Although this surplus gas contains almost no sulfur, it contains an odor component, so it is desirable to introduce it into the heating furnace 14 for combustion deodorization. Of course, a dedicated deodorization facility may be provided separately, but it is not desirable from the viewpoint of increasing the facility cost and the operation cost.

  Note that it is also possible to use a so-called indirect heating type dryer that uses a heat medium such as steam as a heat source and dries the sludge by conduction heat transfer through the heating wall. However, the indirect heating type dryer, due to its characteristics, cannot easily make sludge after drying into a fine powder suitable for airflow conveyance, and is also suitable for preventing heat loss in the melting furnace due to latent heat of evaporation. In order to obtain dry sludge with a moisture content of 20% by mass or less, a huge dryer with a very large heat transfer area is required, and furthermore, the installation of a steam production boiler leads to an increase in equipment costs. Not realistic.

  Thus, the calorific value of the dried sludge discharged from the sludge drying equipment 4 is about 6300 to 21000 kJ / kg-dry, the particle size is preferably about 0.1 μm to 3 mm, and the water content is 0 to It is about 20%. Even when the particle size is larger than 3 mm, it is possible to perform gasification, but as the gasification rate decreases, the amount of unburned substances increases and the gas conversion rate of sludge decreases. On the other hand, in order to reduce the particle size of dried sludge or carbonized sludge to less than 0.1 μm, a special pulverizer that consumes a lot of power is separately required. The particle size is preferably in the above-mentioned range because it causes troubles such as blockage of the pipe during transportation or shelves of the supply hopper. By using a direct-heating sludge drying facility, the particle size can usually be reduced to 3 mm or less, and even if 3 mm or more occurs, it can be easily reduced to 3 mm or less simply by using a small general-purpose pulverizer. It is possible.

  In order to prevent a reduction in efficiency due to latent heat of vaporization in the gasification melting furnace 7 and to make the particle size of the sludge 3 mm or less, the water content in the sludge is desirably 20% or less as much as possible.

  The temperature in the gasification melting furnace 7 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. Is not preferable because it extremely shortens the life of the furnace wall in the gasification melting furnace 7 and increases heat loss due to heat dissipation.

  From the viewpoint of reducing the sensible heat brought out by entrained nitrogen, oxygen added as a gasifying agent at the time of gasification is preferably used as high concentration oxygen as possible. However, producing oxygen at a higher concentration than necessary not only increases demerits such as an increase in input energy, but has little effect on gasification itself, so oxygen used here is a general oxygen production method (pressure swing). The concentration (80% or more) that can be produced by the adsorption method (PSA) or the cryogenic separation method) may be used.

  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 set to an amount of oxygen smaller than the amount of oxygen necessary to completely burn the sludge (so-called theoretical oxygen amount). 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. If the oxygen ratio is less than 0.2, the amount of carbon and hydrogen that are converted into unburned materials without being gasified becomes extremely large, and if the oxygen ratio exceeds 0.8, combustible gases (CO, H ₂₎ , CH _4, etc.) is reduced, and most of it is converted to combustion gas (CO ₂ , H ₂ O), which is not preferable for the purpose of the present invention.

  Further, steam may be used in combination with oxygen as a gasifying agent for the purpose of temperature control in the gasification melting furnace 7.

  The pressure in the gasification melting furnace 7 is not particularly specified, but if the pressure is lower than the atmospheric pressure, there is a risk of explosion due to air leakage from the outside, which is not preferable. Further, when the pressurization condition is higher than the atmospheric pressure, there is an advantage that the gasification melting furnace 7 can be made 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.

  According to the flow shown in FIG. FIG. 5 shows the process mass balance (test results).

  The analysis value of the used sewage sludge is shown in Table 1. 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) 100 t / day in the direct heating type rotary drum type sludge drying equipment 4, the generated fine sludge (water content 5 mass%, average particle size 220 μm) is obtained from the sludge supply hopper 5. The gasification melting furnace 7 was charged by air current conveyance using nitrogen which is a by-product of the oxygen production apparatus 6. In the gasification melting furnace 7, the sludge is gasified and melted at a temperature of 1400 ° C. together with oxygen, and is converted into a high-temperature combustible gas and slag. At the same time, a part of phosphorus contained in the sludge is volatilized into the gas. . The generated high-temperature combustible gas is cooled to 700 ° C. by water spraying in the gas cooler 8 at the upper part of the gasification melting furnace 7, then introduced into the high-temperature filter 9, dust is removed, and further a water cooling tower. 10 was introduced. In the water cooling tower 10, the high-temperature combustible gas is cooled to a room temperature of 40 ° C. or lower. At this time, phosphorus contained in the gas is condensed and separated from the gas, and is extracted out of the system as recovered phosphorus. It was. The phosphorus recovered in the solid state or liquid state here was 405 kg / day in terms of P ₂ O ₅ , and 41% of the phosphorus contained in the natural sludge could be recovered. The discharged combustible gas discharged from the water cooling tower 10 was processed in the desulfurization facility 11, and then the entire amount was introduced into the sludge drying facility 4 as a clean fuel gas and used as a drying heat source. In this example, no auxiliary fuel was required in the gasification melting furnace. However, in the sludge drying facility 4, the amount of necessary heat was insufficient with only the combustible gas generated in the gasification melting furnace. Was added.

  Table 2 shows utility usage in the present invention example (Example 1) and the conventional phosphorus recovery process (fluidized bed sludge incinerator + phosphorus recovery electric heating 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, equipment cost and equipment installation space can be greatly reduced.

  According to the flow shown in FIG. FIG. 6 shows the process mass balance (test results).

  The analysis value of the used sewage sludge is shown in Table 3, and the analysis value of coal char added to the gasification melting furnace 7 as a carbon source together with the sewage sludge is shown in Table 4. This sludge is discharged from a dewatering machine at a sewage treatment plant (dehydrated cake), and the coal char is obtained by rapid pyrolysis of pulverized coal with air at 800 ° C. blocked. .

After drying 100t / day of sewage sludge (dehydrated cake) in the direct heating-type sludge drying equipment 4, the generated fine powder sludge (water content 5 mass%, average particle size 220 μm) is used as a carbon char (2. 4t / day) and mixed with the sludge supply hopper 5 into the gasification and melting furnace 7 by air current transportation using nitrogen which is a by-product of the oxygen production apparatus 6. In the gasification melting furnace 7, the sludge and carbon source are gasified and melted at a temperature of 1400 ° C. together with oxygen, and are converted into a high-temperature combustible gas and slag. At the same time, a part of phosphorus contained in the sludge is contained in the gas. Volatilized. The generated high-temperature combustible gas is cooled to 700 ° C. by water spray in the gas cooler 8 at the upper part of the gasification melting furnace 7, and then introduced into the water cooling tower 10 and cooled to a room temperature of 40 ° C. or less. At this time, phosphorus contained in the gas was condensed and separated from the gas, and extracted with the dust as recovered phosphorus. The phosphorus recovered in the solid state or liquid state here was 550 kg / day in terms of P ₂ O ₅ , and 56% of the phosphorus contained in the natural sludge could be recovered. The discharged combustible gas discharged from the water cooling tower 10 was processed in the desulfurization facility 11, and then the entire amount was introduced into the sludge drying facility 4 as a clean fuel gas and used as a drying heat source. In this example, no auxiliary fuel was required in the entire process including the gasification melting furnace 7 and the sludge drying facility 4.

  Table 5 shows utility usage in the present invention example (Example 2) and the conventional phosphorus recovery process (fluidized bed sludge incinerator + phosphorus recovery electric heating 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, equipment cost and equipment installation space can be greatly 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 drying equipment of the present invention. It is a flow sheet regarding the drying equipment of the present invention. It is the mass balance (test result) of the process in the Example of this invention. It is the mass balance (test result) of the process in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sludge incinerator or sludge melting furnace 2 Phosphorus recovery heating furnace 3 Exhaust gas treatment equipment 4 Sludge drying equipment 5 Sludge supply hopper 6 Oxygen production equipment 7 Gasification melting furnace 8 Gas cooler 9 High temperature filter or cyclone 10 Water cooling tower 11 Desulfurization equipment 12 Combustion furnace 13 Direct heating dryer 14 Heating furnace 15 Circulation line of exhaust gas to sludge drying equipment

Claims (5)

  The activated sludge is directly contacted with hot air and dried, and the resulting dried sludge is partially oxidized at 1100 to 1600 ° C. with 0.2 to 0.8 times the theoretical oxygen amount necessary for complete combustion, and combustible gas. Converted to slag, volatilized part of phosphorus contained in the activated sludge, cooled the combustible gas to 300 to 1000 ° C, and then cooled to normal temperature to 250 ° C by water spraying and condensed phosphorus component And desulfurizing the combustible gas after cooling, circulating part or all of the combustible gas after desulfurization, and supplying the fuel as a hot air generating fuel for drying the activated sludge. A method for gasifying and melting sludge, which is characterized.   The method for gasifying and melting sludge according to claim 1, wherein dust contained in the combustible gas is removed and then cooled to room temperature to 250 ° C.   The method for gasifying and melting sludge according to claim 1 or 2, wherein the dry sludge is partially oxidized together with oxygen at a particle size of 0.1 µm to 3 mm and a water content of 20 mass% or less.   A gasification melting furnace with a gas cooler at the top is installed after the direct heating sludge drying equipment, a water cooling tower and a desulfurization equipment are installed at the subsequent stage, and further to the sludge drying equipment for exhaust gas. The sludge gasification and melting equipment is characterized by installing a circulation line.   The sludge gasification and melting apparatus according to claim 4, wherein a metal filter, a ceramics filter, or a cyclone is installed in a front stage of the water cooling tower.

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