JP2007010309A - Method for recovering flammable gas from sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recovery method of inflammable gas that volume-reduces sewerage sludge with melting treatment of ash component without using auxiliary fuel and can recover useful combustion gas from the sludge. <P>SOLUTION: In the recovery method of inflammable gas from the sludge, sewerage sludge or the like is dried and is blown into an air flow layer melting furnace by air flow conveyance, then the sludge is partially combusted with oxygen, molten slag and inflammable gas are generated, and the inflammable gas is recovered. Especially, in generating molten slag from the sludge, it is preferable to utilize partial combustion heat with the oxygen of the sludge. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for partially combusting sludge generated mainly in sewage treatment to recover a combustible gas.

  Sewage sludge is dehydrated or further dried, using the combustion heat of organic matter in the sludge, and if it is insufficient, using auxiliary fuel, incineration using a fluidized bed, and the ash in the sludge is fly ash In general, the incinerated ash is collected and processed by a dust collector, but it is difficult to process the incinerated ash in the form of fly ash in terms of transportation and use.

In order to facilitate the treatment of incineration ash, Patent Document 1 proposes a method in which incineration ash collected by a dust collector is heated in a melting furnace using auxiliary fuel and processed into a slag. However, in this method, the incineration ash can be effectively used as a civil engineering construction material, but there is a problem that a melting furnace is required in addition to the incinerator and further auxiliary fuel is required. As a method for performing incineration and melting in a single stage, Patent Document 2 proposes a method in which sludge is supplied in layers and a burner is disposed on the upper surface of the sludge to burn and melt the sludge from the surface. This method is advantageous in that it can be incinerated and melted at the same time, but auxiliary fuel is required and it burns at a high temperature of 1300-1500 ° C. in order to melt the ash, so it contains 4-6% in the sludge. There is a problem that the nitrogen to be converted into NOx increases the NOx in the exhaust gas. Moreover, since the sludge combustion reaction burns only on the surface, there is a drawback that the melting furnace becomes large.
JP-A-1-84014 JP-A-5-296425

  The present invention does not use auxiliary fuel, which is essential in conventional methods, and burns and melts sludge in a single stage, and generates and recovers combustible gas that can be used as beneficial fuel gas from sludge. The purpose is to do.

Means of the present invention for solving the above-mentioned problems are as follows.
(1) Drying sewage sludge, etc., blowing it into the airflow layer melting furnace by airflow conveyance, partially burning the sludge with oxygen, generating molten slag and flammable gas, and recovering the flammable gas A method for recovering combustible gas from sludge.
(2) The method for recovering combustible gas from sludge according to (1), wherein molten slag is generated from the sludge by partial combustion heat of oxygen in the sludge.
(3) The molten slag discharge port is provided at the bottom of the melting furnace, and a water pot is further provided at the bottom thereof, and the molten slag is dropped, cooled, solidified and recovered. Or the collection | recovery method of the combustible gas from the sludge of 2.
(4) The slag contained in the generated combustible gas is collected by collecting dust, and then mixed with the dried sludge and recycled. A method for recovering combustible gas from sludge as described in 1.

  In the present invention, paying attention to the heat balance of the sludge combustion furnace, most of the heat generated by the combustion exhaust gas occupies, so that combustion with oxygen makes it possible to reduce the amount of combustion exhaust gas, To find the conditions that can obtain the combustion temperature that melts the ash in the sludge to become slag without using the fuel and without completely burning the organic matter in the sludge, and recovering useful fuel gas from the sludge Is possible.

That is, the gas containing the combustible components of CO and H _{2 in} addition to CO ₂ and H ₂ O can be recovered from the gasified sludge gas. Oxygen is more than the amount necessary to gasify the organic matter in the sludge (the amount of C in the sludge is changed to CO), and the gasification gas temperature is discharged from the lower part of the melting furnace by melting the ash in the sludge. To be above the temperature (melting point of ash). Furthermore, in order to promote the combustion reaction of the melting furnace, it is burned in a state where fine sludge is dispersed by gasifying it in the air flow layer, and the reaction area is larger than that of the surface melting method, and it takes less time. It becomes possible to react, and processing becomes possible in a compact melting furnace. Further, the melted fly ash-like ash collides with the side wall by the force of the combustion gas swirling in the melting furnace, travels along the side wall of the melting furnace, and discharges slag from the slag discharge port at the bottom of the melting furnace. It becomes possible.

  According to the present invention, dry sludge is gasified with oxygen, so that it is possible to incinerate and slag in one stage without using auxiliary fuel, and to recover a gas that can be effectively used as fuel. It becomes possible.

  FIG. 1 is an example of an apparatus for carrying out the method of the present invention. This apparatus comprises a dryer 1, a supply device 2, a melting furnace 3, a cooling furnace 4, a cyclone 5, a boiler 6, and a dust collector 7 which are arranged in association with each other as shown in the figure.

  The dryer 1 is a device that reduces the water content of the dewatered sludge, and a steam heating type, airflow type drying machine, or the like can be used. The supply device 2 is composed of a hopper and a quantitative cut-out device, pressurizes dry sludge with a lock hopper system, conveys the air, and supplies it to the next melting furnace 3. The melting furnace 3 is an apparatus that converts the sludge dried by the dryer 1 into combustion gas and simultaneously melts ash. The melting furnace 3 has two or more burners 8 on the side wall, and discharges the generated gas above the melting furnace 3. A throat 9 is provided. A slag discharge port 10 is provided at the lower part of the melting furnace 3, and a water pot 11 is installed further below.

  As shown in FIG. 2, the burner 8 is arranged with a certain angle in a plane with respect to the furnace wall so that the combustion gas swirls in the melting furnace 3. In this embodiment, an example of four burners is shown, but if there are two or more burners 8, a swirling flow can be obtained. The cooling furnace 4 is provided with a cooling nozzle 12 that blows water or the like on its side surface, and a cyclone 5, a boiler 6, and a dust collector 7 are sequentially connected to the rear stage of the cooling furnace 4.

  The dewatered sludge is dried by the dryer 1 until it has fluidity and can be transported by airflow. The dried sludge is quantitatively cut out from the supply device 2, air-flowed to the burner 8 with air or nitrogen gas, and sent into the melting furnace 3. In the burner 8, dry sludge and oxygen are blown to gasify the sludge. This gasification gas enters the cooling furnace 4 from the throat 9 at the top of the melting furnace 3. The molten fine powder slag collides with the side wall of the melting furnace 3 by the turning force of the burner 8 and becomes liquid, falls from the slag discharge port 10 at the bottom to the water pot 11, and is discharged after cooling and solidification. In the cooling furnace 4, the high-pressure gas is cooled by blowing water or generated gas after cooling from the cooling nozzle 12 to cool the high-temperature gas, and the molten slag accompanied by the gas from the melting furnace 3 is cooled and solidified. In the present embodiment, a method of cooling with a water spray nozzle is shown, but there is also a method of circulating and cooling the cooled product gas, and the amount of heat recovery of the boiler 6 increases, but the facility becomes complicated. The cooling furnace 4 can be used in combination with a method of cooling with a radiant boiler.

The cooled gas removes slag by the cyclone 5, recovers heat by the boiler 6, and removes the slag that could not be collected by the cyclone by the dust collector 7. Since the slag removed by the cyclone 5 and the dust collector 7 is in the form of fine powder, it is preferable that it is mixed with dry sludge, melted again, and recovered as granular slag because the ash can be recovered as granular slag. The cyclone 5 can be omitted, but it is preferable to install it in consideration of wear of the heat transfer tube of the boiler 6. The dust collector 7 is preferably a system with high dust collection efficiency such as a bag filter. The steam recovered by the boiler 6 can be used as a heat source for the dryer, and the recovered gas is a combustible gas mainly composed of CO and H ₂ and can be effectively used as fuel.

  The oxidizer used in the melting furnace 3 can use oxygen-enriched air in addition to oxygen gas, but it can recover high-calorie gas and reduce the amount of recovered gas to reduce exhaust gas treatment equipment. It is preferable to use oxygen that can reduce the size.

Next, the Example which processed the sewage sludge using this invention apparatus shown in FIG. 1 is shown. The sludge was subjected to 20 T / D treatment of the composition shown in Table 1 in a dry amount. A sludge having a moisture content of 80% was dried with a dryer to a moisture content of 20% and gasified in a melting furnace. In the melting furnace, oxygen of 450 Nm ³ / H with a purity of 95% was used, and sludge was gasified at about 1400 ° C. to slag the ash. The amount of oxygen necessary to gasify the organic matter in the sludge is 180 Nm ³ / H, but 450 Nm ³ / H was used to melt and discharge the ash at a temperature of about 1400 ° C. As for slag, about 90% of the ash charged in the melting furnace can be recovered from the slag discharge port, and the remaining 10% was accompanied by gas. However, by collecting and recycling with a cyclone and dust collector, 100% could be recovered in the form of slag.

In the cooling furnace, water was sprayed at 575 kg / H and cooled to 800 ° C., and then 1.2 T / H of steam could be recovered with a boiler. As for the amount of generated gas, 1195 Nm ³ / H of the composition shown in Table 2 as a dry amount could be recovered, and 59% of the sludge calorific value could be recovered as a combustible gas. The recovered gas does not contain NOx, and ammonia that causes NOx is also about 20 ppm. Most of the nitrogen contained in the sludge is converted into nitrogen gas and rendered harmless.

It is a figure which shows an example of the apparatus for enforcing the combustible gas recovery method from the sludge which concerns on this invention. It is explanatory drawing of the burner arrangement | positioning of the airflow layer melting furnace which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dryer 2 Supply apparatus 3 Melting furnace 4 Cooling furnace 5 Cyclone 6 Boiler 7 Dust collector 8 Burner 9 Throat 10 Slag discharge port 11 Water pot 12 Cooling nozzle

Claims (4)

  It is characterized by drying sewage sludge, etc., blowing it into an airflow layer melting furnace by airflow conveyance, partially burning the sludge with oxygen, generating molten slag and flammable gas, and collecting the flammable gas To recover combustible gas from sludge.   The method for recovering combustible gas from sludge according to claim 1, wherein molten slag is generated from the sludge by partial combustion heat due to oxygen of the sludge.   3. The molten slag discharge port is provided at the bottom of the melting furnace, and a water pot is further provided at the bottom thereof, and the molten slag is dropped, cooled, solidified and recovered. To recover flammable gas from sewage sludge.   The slag contained in the generated combustible gas is collected by collecting dust, and then mixed with the dried sludge and recycled. How to recover flammable gas from sludge.

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