JP4364022B2 - Energy recovery method from organic waste - Google Patents

Description

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

  Conventionally, organic waste such as sewage sludge and biomass has been dehydrated or incinerated and disposed of in landfill as dehydrated sludge or incinerated ash, but securing new disposal sites is becoming increasingly difficult. In addition, carbon dioxide generated during incineration is a cause of global warming and reduction of emissions is required. For this reason, recently, as shown in Patent Document 1, organic waste gasification reforming technology that thermally decomposes organic waste and gasifies and reforms, and recovers organic components as a combustible gas has been developed. Has been developed.

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

In addition, dehydrated and dried organic waste is combustible composed of H ₂ , CO, CO ₂ , and H ₂ O by reacting with oxygen, water vapor, air, etc. (partial combustion) in a gasification reforming furnace. It is reformed to gas. At this time, the nitrogen content contained in the combustible gas is transferred into the gas as ammonia, and is transferred into the waste water in the gas cleaning step after the gasification reforming furnace.

As described above, the ammonia transferred into the waste water in the dehydration / drying process and the gas washing process of organic waste can be decomposed and discharged by a biological treatment method, a discontinuous chlorination method, an ozone treatment method, or the like. It is diffused from the wastewater by the stripping method, and the emitted ammonia is burned, decomposed or removed by adsorption. In addition, as a method for treating the diffused ammonia, there is a method of re-introducing it into the gasification reforming furnace and decomposing it. However, the decomposition rate is poor, and the introduced ammonia is transferred again into the waste water in the gas cleaning step. In any method, ammonia transferred into the waste water in the pretreatment or gas cleaning process and ammonia transferred into the waste water in the gas cleaning process are not used at all as energy.
Japanese Patent No. 3054595

  The present invention solves the above-mentioned conventional problems, and in the process of recovering combustible gas by gasifying and reforming organic waste, it is possible to recover further energy from ammonia transferred into waste water. It was made to provide a method for recovering energy from waste.

  In order to solve the above-mentioned problems, the present invention is directed to gasifying and reforming wastewater generated in a dehydration / drying process in a pretreatment stage for gasifying and reforming organic waste, and dehydrated / dried organic waste. The ammonia contained in the wastewater generated in the dust removal and cleaning process of the gas generated by the gas is recovered, the recovered ammonia is decomposed into hydrogen and nitrogen by the decomposition catalyst, and hydrogen is recovered, and this hydrogen is recovered as a power generator. It is characterized by being used as an energy source.

As an ammonia decomposition catalyst, nickel or nickel oxide is supported as a first component on a metal oxide carrier such as alumina, silica, titania, zirconia, and at least one of an alkaline earth metal and a lanthanoid element is a metal or What was added as a 2nd 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 / support is 1 to 40% and the weight ratio of the second component / support is 1 to 15%.
The power generation device is preferably a gas engine or a fuel cell driven by hydrogen gas.

  According to the present invention, not only the organic waste can be gasified and reformed to recover the combustible gas, but hydrogen is also recovered from the ammonia transferred into the wastewater in this process, and the energy of the power generation apparatus is recovered. 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 ammonia decomposition catalyst is used, the catalytic activity does not decrease even in the presence of water vapor, and ammonia can be decomposed almost completely and hydrogen can be obtained efficiently.

Embodiments of the present invention will be described below.
FIG. 1 is a block diagram showing an embodiment of the present invention, where 1 is an organic waste containing nitrogen such as sewage sludge and biomass. In many cases, these organic wastes 1 contain a large amount of moisture and cannot be put into the high-temperature gasification reforming furnace 4 as they are. Therefore, the dehydrator 2 and the dryer 3 Pre-treatment for dehydration and drying is performed. As the dehydrator 2, various conventionally known types such as a belt press, a filter press, and a rotary press can be used. Also, the type of the dryer 3 is arbitrary, but for example, a paddle dryer using an external heat source can be used.

  However, no matter what type of dehydrator 2 or dryer 3 is used, since the organic waste 1 containing water is heated, a large amount of water vapor is always generated, and at the same time, the organic waste 1 is thermally decomposed. As a result, ammonia is generated. This ammonia always moves into the waste water (dry drain) condensed with water vapor. In the present invention, this drain water containing ammonia is sent to the waste water treatment step 5.

On the other hand, the organic waste that has undergone dehydration / drying pretreatment is sent to the gasification reforming furnace 4. The inside of the gasification reforming furnace 4 is kept 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 separated from each other. This gasification reforming process itself is known as shown in the above-mentioned Patent Document 1.

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

In this embodiment, the wastewater containing ammonia is sent to a stripping tower, and ammonia is diffused into the gas by a known ammonia stripping method. The stripping tower is filled with lattices, corrugated plates, etc., and air or water vapor is blown from the bottom of the tower. The ammonia-containing wastewater is adjusted to the alkali side by slaked lime and sprayed from the upper part 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 top of the tower. In this way, only ammonia gas can be recovered from the waste water. However, in the present invention, the ammonia recovery method is not limited to the stripping method, and any means such as using an adsorbent can be adopted.

This high-concentration ammonia gas is decomposed by a nickel-based ammonia decomposition catalyst into N ₂ and H ₂ . The ammonia decomposition catalyst used here has nickel or nickel oxide supported as a first component on a metal oxide carrier such as alumina, silica, titania, zirconia, etc., and at least one of an alkaline earth metal and a lanthanoid element is a metal or What was added as a 2nd component in the form of an oxide is preferable. If this ammonia decomposition catalyst is filled in the catalyst reactor and ammonia gas is supplied, pure hydrogen gas can be taken out efficiently. This ammonia decomposition catalyst will be described in detail later.

  This hydrogen can be used as an energy source of the power generation device 8. As the power generation device 8, for example, there is a fuel cell, and according to the present invention, hydrogen gas containing no CO harmful to the fuel cell can be obtained, which is advantageous. However, the gas engine can be driven using hydrogen as a fuel to move the generator. In this case, the exhaust heat of the gas engine can be recovered by a boiler and used as a heat source for 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 has nickel or nickel oxide supported as a first component on a metal oxide support such as alumina, silica, titania, zirconia, etc., and at least one of an alkaline earth metal and a lanthanoid element is a metal. Or what was added as a 2nd component in the form of an oxide is preferable. Magnesium, calcium, strontium, barium and the like are used as the alkaline earth metal, and lanthanum and cerium are used as the lanthanoid element. Such an ammonia decomposition catalyst is manufactured by, for example, manufacturing a nickel / alumina catalyst by a well-known coprecipitation method, and drying and impregnating a second component such as barium in ethanol or water. Can do.

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 best embodiment, nickel 15.7%, barium 7.36%, balance 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 diameter is 10 to 1000 μm, more preferably 200 to 700 μm, and most preferably 300 to 500 μm.

Below, the result of having confirmed the characteristic of this ammonia decomposition catalyst by experiment is shown. Although it has been confirmed by preliminary experiments that the activity of the ammonia decomposition catalyst decreases in the presence of water vapor, it is not easy to actually use the ammonia decomposition catalyst under conditions where water vapor does not exist. Thus, the following graphs all show ammonia conversion in the presence of water vapor. The ammonia flow rate was 9.1 × 10 ⁻³ mol / h, and the water vapor / ammonia ratio was 5.5 × 10 ⁻² kg · h / mol.

  The graph of FIG. 2 shows the ammonia conversion rate of a catalyst in which only nickel is supported on an alumina support and various catalysts to which a second component is further added, and the horizontal axis represents the reaction temperature. The upper graph in FIG. 2 is obtained by adding an alkaline earth metal as the second component, and the lower graph is obtained by adding a lanthanoid element as the second component. In all cases, 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 catalytic activity is improved by adding the second component. In particular, the best results are shown when barium is added.

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

  In the above experiments, alumina was used as the catalyst carrier, but silica, titania, zirconia, or the like can also be used. The graph of FIG. 5 is a graph showing the 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. This shows that almost the same result can be obtained even when changed 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 support 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 if ammonia decomposition catalyst added as a second component in the form of a product is used, ammonia can be decomposed almost completely and hydrogen can be obtained efficiently.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
Sewage sludge having a water content of 80% was sent to the vacuum evaporation dryer 10 at a flow rate of 12500 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 9870 kg / h of dry drain water containing 29.6 kg / h of ammonia was generated from the vacuum evaporator 10. The ammonia concentration in the dry drain water is 3000 mg / L. This dry drain water was sent to the waste water treatment step 5.

The dewatered and dried sewage sludge is sent to a gasification furnace and a reforming furnace to be gasified and reformed. The generated gas is removed by a filter 11 and further washed to become 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 cleaning wastewater contained 16.1 kg / h of ammonia, and this cleaning wastewater was also sent to the wastewater treatment step 5. In the waste water treatment process 5, the dry drain water and the washing waste water were collected, and ammonia contained in the water was diffused into the gas by the ammonia stripping method. The amount of ammonia diffused is 45.7 kg / h. This ammonia was decomposed into hydrogen and nitrogen by a decomposition catalyst comprising 15.7% nickel, 7.36% barium, and the remainder alumina, and 90 m ³ / h hydrogen gas 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 organic waste, is increased by 275 Mcal / h.

It is a block diagram which shows embodiment of this invention. It is a graph which shows the ammonia conversion rate of the various catalysts which changed the 2nd component. It is a graph which shows the influence which the molar ratio of barium with respect to nickel has on the ammonia conversion rate. It is a graph which shows a time-dependent change of an ammonia decomposition catalyst. It is a graph which shows the ammonia conversion rate of three types of catalysts which changed the support | carrier. It is a block diagram which shows the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic waste 2 Dehydrator 3 Dryer 4 Gasification reformer 5 Waste water treatment process 6 Dust removal and washing process 7 Decomposition catalyst 8 Power generation device 10 Vacuum evaporation dryer 11 Filter 12 Boiler 13 Gas engine

Claims (4)

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

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