JP2004307326A - Method for recovering energy from organic waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for additionally recovering energy from ammonia which is transferred to waste water, in a process to recover a combustible gas by gasifying and reforming an organic waste. <P>SOLUTION: When the combustible gas is recovered from the organic waste by using a gasifying and reforming furnace 4, ammonia is contained in the waste water discharged at a pretreatment step, namely a dewatering and drying process, and in the waste water discharged in a dust eliminating and washing process for the gas generated by gasifying and reforming the dewatered and dried organic waste. The ammonia in the both waste water is recovered and decomposed into hydrogen and nitrogen using a catalyst. The hydrogen is used as an energy resource for an electric power generator. The catalyst for decomposing ammonia prepared by carrying nickel or nickel oxide as a first component on a metal oxide carrier such as alumina, silica, titania, and zirconia and adding at least one of alkaline earth metals and lanthanoid elements as a form of a metal or an oxide as a second component is preferable. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for recovering energy from organic waste such as sewage sludge and biomass.

  Conventionally, organic wastes such as sewage sludge and biomass have generally been dehydrated or incinerated and landfilled as dehydrated sludge or incinerated ash. However, it has become increasingly difficult to secure new disposal sites. In addition, carbon dioxide generated during incineration is considered to be a cause of global warming, and reduction of emissions is required. For this reason, recently, as shown in Patent Document 1, an organic waste gasification and reforming technology for thermally decomposing and gasifying organic waste and reforming the same to recover organic components as combustible gas has been developed. Is being developed.

  In order to obtain flammable gas from organic waste by this method, there is a method in which organic waste is first subjected to pretreatment for dehydration and drying, and then gasification and reforming treatment is performed in a gasification and reforming furnace. Taken. In the dehydration and drying steps performed as this pretreatment, a part of the nitrogen contained in the organic waste is transferred to wastewater (drain water) as ammonia.

The dewatered and dried organic waste reacts with oxygen, water vapor, air, etc. (partial combustion) in a gasification reforming furnace to form a flammable fuel composed of H ₂ , CO, CO ₂ , and H ₂ O. Reformed into gas. At this time, the nitrogen content contained in the combustible gas is transferred to the gas as ammonia, and is transferred to wastewater in a gas cleaning step at the latter stage of the gasification and reforming furnace.

Ammonia that has migrated into the wastewater in the organic waste dehydration / drying process and gas cleaning process is decomposed and discharged by biological treatment, discontinuous chlorination, ozone treatment, etc. The ammonia is released from the wastewater by the stripping method, and the released ammonia is decomposed by combustion or removed by adsorption. As a method of treating the released ammonia, there is a method of re-introducing the gas into a gasification reforming furnace to decompose the ammonia. However, the decomposition rate is low, and the introduced ammonia is transferred to wastewater again in the gas cleaning step. In any of the methods, the ammonia transferred to the wastewater in the pretreatment or the gas cleaning step and the ammonia transferred to the wastewater in the gas cleaning step are not used at all as energy.
Japanese Patent No. 3054595

  The present invention solves the above-mentioned conventional problems, and in the step of gasifying and reforming organic waste to recover flammable gas, an organic material capable of further recovering energy from ammonia transferred to wastewater. This was done to provide a method of recovering energy from waste.

  The present invention made in order to solve the above-mentioned problems is intended to convert wastewater generated in a dehydration / drying step in a pretreatment step of gasifying and reforming organic waste and gasification and reforming of dehydrated / dried organic waste. Ammonia contained in wastewater generated in the dust removal / cleaning process of the generated gas is recovered, and the recovered ammonia is decomposed into hydrogen and nitrogen by a decomposition catalyst to recover hydrogen. It is characterized in that it is used as an energy source.

As a catalyst for decomposing ammonia, nickel or a nickel oxide is supported as a first component on a metal oxide carrier such as alumina, silica, titania, and zirconia, and at least one of an alkaline earth metal and a lanthanoid element is used as a metal or a metal. Those added as the second component in the form of an oxide can be used. In particular, it is preferable to use an ammonia decomposition catalyst in which the weight ratio of the first component / carrier is 1 to 40% and the weight ratio of the second component / carrier is 1 to 15%.
Preferably, the power generation device is a gas engine or a fuel cell driven by hydrogen gas.

  According to the present invention, not only can combustible gas be recovered by gasifying and reforming organic waste, but also hydrogen can be recovered from ammonia transferred to wastewater in this step, and the energy of the power generator can be improved. Can be used as a source. This increases the energy recovery rate from organic waste and reduces the burden on the environment. In particular, when the above-described ammonia decomposition catalyst is used, the catalytic activity does not decrease even in the presence of water vapor, and ammonia can be almost completely decomposed to efficiently obtain hydrogen.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a block diagram showing an embodiment of the present invention. Reference numeral 1 denotes an organic waste containing nitrogen such as sewage sludge and biomass. Since these organic wastes 1 often contain a large amount of water and cannot usually be directly introduced into the high-temperature gasification reforming furnace 4, the dewatering machine 2 and the drying machine 3 And the pretreatment of dehydration and drying is performed. As the dehydrator 2, various types known in the art such as a belt press, a filter press, and a rotary press can be used. The type of the dryer 3 is also arbitrary. For example, a paddle dryer using an external heat source can be used.

  However, no matter what type of dehydrator 2 or drier 3 is used, the organic waste 1 containing water is heated, so that a large amount of steam is always generated and the organic waste 1 is thermally decomposed. This produces ammonia. This ammonia always migrates into waste water (dry drain) in which steam condenses. In the present invention, the drain water containing ammonia is sent to the wastewater treatment step 5.

On the other hand, the organic waste subjected to the pretreatment of dehydration and drying is sent to the gasification and reforming furnace 4. The inside of the gasification reforming furnace 4 is maintained at a high temperature of 600 to 1400 ° C., and oxygen, air, and steam are supplied from the outside. Organic waste is partially oxidized within the gasifier reforming furnace 4, H min C content is converted CO, the fuel gas such as H _2. Note that the gasification furnace and the reforming furnace may be separate furnaces. The gasification reforming process itself is known as shown in Patent Document 1 mentioned above.

  In the dust removal / cleaning step 6, impurities such as dust and sulfur are removed from the fuel gas discharged from the gasification reforming furnace 4. At this time, the ammonia derived from the N content in the organic waste moves to the cleaning drainage side. In the present invention, the washing wastewater containing the ammonia at a high concentration is also sent to the wastewater treatment step 5.

In the present embodiment, the wastewater containing these ammonia is sent to a stripping tower, and ammonia is released into the gas by a known ammonia stripping method. The inside of the stripping tower is filled with a lattice or a corrugated sheet, and air or steam is blown from the lower part of the tower. The pH of the ammonia-containing wastewater is adjusted to an alkaline side by slaked lime or the like, and sprayed from the top of the stripping tower. As a result, NH ₄ OH in the waste water is decomposed into NH ₃ and H ₂ O, and only ammonia gas is recovered from the upper part of the tower. Thus, only the ammonia gas can be recovered from the wastewater. However, in the present invention, the method for recovering ammonia is not limited to the stripping method, and any means such as using an adsorbent can be employed.

This high-concentration ammonia gas is decomposed by a nickel-based ammonia decomposition catalyst to become N ₂ and H ₂ . The ammonia decomposition catalyst used here supports nickel or a nickel oxide as a first component on a metal oxide carrier such as alumina, silica, titania, and zirconia, and further contains at least one of an alkaline earth metal and a lanthanoid element as a metal or Those added as a second component in the form of an oxide are preferred. If this ammonia decomposition catalyst is filled into the inside of the catalytic reactor and ammonia gas is supplied, pure hydrogen gas can be efficiently extracted. This ammonia decomposition catalyst will be described later in detail.

  This hydrogen can be used as an energy source of the power generator 8. The power generation device 8 is, for example, a fuel cell, and according to the present invention, hydrogen gas containing no harmful CO to the fuel cell can be obtained, which is advantageous. However, it is also possible to drive a gas engine using hydrogen as fuel and run a generator. In this case, the exhaust heat of the gas engine can be recovered by a boiler and used as a heat source of the dryer 3. It can also be used as heating water for heating.

(Details of ammonia decomposition catalyst)
The ammonia decomposition catalyst used in the present invention is obtained by supporting nickel or nickel oxide as a first component on a metal oxide carrier such as alumina, silica, titania, and zirconia, and further converting at least one of an alkaline earth metal and a lanthanoid element into a metal. Or those added as the second component in the form of an oxide are preferred. As the alkaline earth metal, magnesium, calcium, strontium, barium and the like are used, and as the lanthanoid element, lanthanum, cerium and the like are used. Such an ammonia decomposition catalyst is produced by, for example, producing a nickel / alumina catalyst by a well-known coprecipitation method, drying the nickel / alumina catalyst, and then dissolving and impregnating a second component such as barium in ethanol or water. Can be.

Here, the weight ratio of the first component / carrier is 1 to 40%, more preferably 5 to 25%, and most preferably 10 to 20%. The weight ratio of the second component / carrier is 1 to 15%, more preferably 5 to 10%, and most preferably 5 to 10%. In the preferred embodiment, nickel is 15.7%, barium is 7.36%, and the balance is alumina. The specific surface area of the ammonia decomposition catalyst is 10 to 1000 m ² / g, more preferably 50 to 500 m ² / g, and most preferably 100 to 300 m ² / g. The catalyst particle size is 10 to 1000 μm, more preferably 200 to 700 μm, and most preferably 300 to 500 μm.

Hereinafter, the results of confirming the characteristics of the ammonia decomposition catalyst by experiments will be described. Preliminary experiments have confirmed that the activity of the ammonia decomposition catalyst is reduced in the presence of steam, but it is not easy to use the ammonia decomposition catalyst in the absence of steam. Therefore, the following graphs all show the conversion of ammonia in the presence of steam. The ammonia flow rate was 9.1 × 10 ⁻³ mol / h, and the ratio of steam / ammonia was 5.5 × 10 ⁻² kg · h / mol.

  The graph in FIG. 2 shows the ammonia conversion of the catalyst in which only nickel is supported on the alumina carrier and the various catalysts in which the second component is further added. The horizontal axis indicates the reaction temperature. The upper graph in FIG. 2 is a graph in which an alkaline earth metal is added as a second component, and the lower graph is a graph in which a lanthanoid element is added as a second component. In each case, the molar ratio of the added metal to nickel was set to 0.3. As shown in these graphs, it can be seen that the addition of the second component improves the catalytic activity. In particular, the best results are shown when barium is added.

  The graph of FIG. 3 shows the effect of the molar ratio of barium to nickel on the conversion of ammonia. If the reaction temperature is 450 ° C., it can be seen that when this molar ratio is in the range of 0.1 to 0.3, the ammonia conversion reaches almost 100% even in the presence of steam. Further, the graph of FIG. 4 shows the change with time of the ammonia decomposition catalyst having the highest activity in which the molar ratio of barium to nickel is 0.2. It can be seen that even if the use is continued, the ammonia conversion rate hardly decreases.

  In the above experiment, alumina was used as the catalyst carrier, but silica, titania, zirconia, or the like may be used. The graph of FIG. 5 is a graph showing the respective ammonia conversion rates when the first component is nickel, the second component is barium, and the carrier is changed to three types of alumina, zirconia, and titania. The carrier is zirconia or titania. It is shown that almost the same result can be obtained by changing to. Although not shown in FIG. 5, the same applies to the case of silica.

  As described above, nickel or nickel oxide is supported as a first component on a metal oxide carrier selected from alumina, silica, titania, and zirconia, and at least one of an alkaline earth metal and a lanthanoid element is metal or oxidized. It was confirmed that when the ammonia decomposition catalyst added as the second component in the form of a product was used, it was possible to almost completely decompose ammonia and efficiently obtain hydrogen.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
The sewage sludge having a water content of 80% was sent to the reduced-pressure evaporative dryer 10 at a flow rate of 12,500 kg / h and dehydrated and dried. The water in the sewage sludge was 10,000 kg / h, the DS (dry solid content) was 2500 kg / h, and the reduced-pressure evaporative dryer 10 produced 9870 kg / h of dry drain water containing 29.6 kg / h of ammonia. The ammonia concentration in the dried drain water is 3000 mg / L. The dried drain water was sent to a wastewater treatment step 5.

The dewatered and dried sewage sludge is sent to a gasification furnace and a reforming furnace to be gasified and reformed, and the generated gas is removed by a filter 11 and further washed to be a fuel gas of 5995 m ³ / h. . This fuel gas was sent to the boiler 12 and the gas engine 13 and used for power generation.

The gas washing wastewater contained 16.1 kg / h of ammonia, and this washing wastewater was also sent to the wastewater treatment step 5. In the wastewater treatment step 5, the dried drain water and the washing wastewater were collected, and the ammonia contained in the water was released into the gas by the ammonia stripping method. The amount of ammonia released is 45.7 kg / h. This ammonia was decomposed into hydrogen and nitrogen by the above-mentioned decomposition catalyst comprising 15.7% of nickel, 7.36% of barium, and the remainder being alumina, and hydrogen gas of 90 m ³ / h was recovered. The calorific value was 275 Mcal / h, and this hydrogen was sent to the boiler 12 and the gas engine 13 and used for power generation. Thus, according to the present invention, the amount of energy recovered from sewage sludge, which is an organic waste, is increased by 275 Mcal / h.

It is a block diagram showing an embodiment of the present invention. It is a graph which shows the ammonia conversion of various catalysts which changed the 2nd component. 5 is a graph showing the effect of the molar ratio of barium to nickel on the conversion of ammonia. It is a graph which shows a time-dependent change of an ammonia decomposition catalyst. It is a graph which shows the ammonia conversion of three types of catalysts which changed the support. FIG. 2 is a block diagram showing an embodiment of the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Organic waste 2 Dehydrator 3 Dryer 4 Gasification reformer 5 Drainage treatment process 6 Dust removal / washing process 7 Decomposition catalyst 8 Power generator 10 Reduced pressure evaporative dryer 11 Filter 12 Boiler 13 Gas engine

Claims (4)

  Wastewater generated in the dewatering / drying process in the pretreatment stage of gasification and reforming of organic waste, and dust removal / cleaning process of gas generated by gasification and reforming of dewatered and dried organic waste Organic waste characterized by recovering ammonia contained in wastewater, decomposing the recovered ammonia into hydrogen and nitrogen with a decomposition catalyst, and recovering hydrogen, and using this hydrogen as an energy source for power generation equipment How to recover energy from things.   As an ammonia decomposition catalyst, nickel or a nickel oxide is supported as a first component on a metal oxide carrier such as alumina, silica, titania, and zirconia, and at least one of an alkaline earth metal and a lanthanoid element is a metal or oxide. 2. The method for recovering energy from organic waste according to claim 1, wherein the second component is added as a second component.   The method for recovering energy from organic waste according to claim 2, wherein the weight ratio of the first component / carrier is 1 to 40%, and the weight ratio of the second component / carrier is 1 to 15%.   3. The method for recovering energy from organic waste according to claim 1, wherein the power generation device is a gas engine or a fuel cell driven by hydrogen gas.

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