JPH0461709B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for wet-processing petroleum-based combustion ash to recover most of the components of the combustion ash as valuable materials. [Conventional technology] Traditionally, combustion ash has been often incinerated and landfilled as industrial waste, which poses environmental and cost problems. Vanadium has been recovered industrially in some cases, but It is insufficient and most of the other ingredients are not utilized effectively. If a method to economically recover vanadium and other components from combustion ash can be established, combustion ash will become a valuable resource. [Problems to be Solved by the Invention] The present inventors have conducted extensive research in order to establish a method for economically recovering each component of petroleum-based combustion ash as valuable materials. [Means for Solving the Problems] As a result, an extremely rational and effective wet treatment method for combustion ash was developed, and the present invention was achieved. That is, the present invention provides a method for recovering carbon, heavy metals, etc. by wet processing of combustion ash collected from a dust collector installed in an exhaust gas flue of a boiler using petroleum-based fuel, etc. )～(11)
This is a method for treating petroleum-based combustion ash, which is characterized by subjecting it to the following treatments. (1) Mix combustion ash and water, add sulfuric acid as necessary to adjust the pH to 3 or less to form a slurry. (2) Separate solid content (carbon). (3) Heat the liquid part to 70°C or higher, supply ammonia and an oxidizing agent, and oxidize the metal while adjusting the pH to 7-9. (4) Separate the precipitate (iron sludge). (5) Cool the liquid part to 40°C or less to precipitate a vanadium compound (ammonium metavanadate). (6) Separate the precipitated vanadium compound. (7) Add sulfuric acid to the liquid part and adjust the pH to 3 to 5.
Nickel compound (nickel ammonium sulfate)
is precipitated. (8) Separate the precipitated nickel compound. (9) Add calcium hydroxide or calcium oxide to the liquid part to precipitate gypsum and liberate ammonia. (10) Separate ammonia and gypsum from the gypsum slurry in which ammonia is dissolved. (11) Water after gypsum separation is recycled into the system for use. Petroleum-based combustion ash in the present invention refers to dust generated when petroleum-based fuel such as heavy oil, asphalt, petroleum pitch, or petroleum coke is burned in a boiler, etc., and some of it adheres and accumulates inside the boiler. Most of it is captured by dust collectors. The composition of petroleum-based combustion ash varies depending on the type of fuel, combustion conditions, whether or not additives are injected into the boiler and/or dust collector, etc., but it is roughly as shown in Table 1.

[Effect]

Hereinafter, the present invention will be explained in detail with reference to the flow sheet shown in FIG. 1 Combustion ash A is thoroughly mixed with circulating water K using a stirrer or the like in dissolving tank 1 to form a slurry, and ammonium sulfate, metals, etc. in the combustion ash are dissolved. PH is approximately 3
However, compared to SO ₄ , NH ₄ and/or
The PH may be higher than 3 due to a large amount of Mg, etc. In this case, the metal will not be sufficiently dissolved, so sulfuric acid G is added to adjust the PH to 3 or less. If the pH is lowered too much, a large amount of alkali for adjusting the pH will be required in the part where the metal is recovered, which is uneconomical, so the pH is preferably about 1.5 to 3. A high temperature is preferred in order to increase the dissolution rate, but 40 to 70°C is usually appropriate. The stirring time is
About 30 minutes or more is required. 2 The slurry of combustion ash is sent to carbon separator 2
, the undissolved carbon B is separated and the liquid part (
liquid) is transferred to the carbon liquid tank 3. The water content of carbon is usually on the order of several percent, and it contains many dissolved components (ammonium sulfate and metals) in the liquid part, so it is preferable to wash carbon with water. As the water for cleaning, circulating water K or industrial water can be used as long as the required quality of the carbon product can be maintained. If the amount of water (cleaning liquid) obtained by washing the carbon and separating it from the carbon is small and/or the concentration of dissolved components is high, it is appropriate to mix it with the liquid. The cleaning liquid is preferably transferred to the circulating water tank 15 because this reduces the concentration of dissolved components in the liquid and reduces the efficiency of separating metals and the like. 3. Transfer the liquid part (carbon liquid) to the metal oxidation tank 4, heat it to 70°C or higher, supply ammonia and an oxidizing agent, and oxidize the metal while adjusting the pH to 7 to 9. In the metal oxidation tank, tetravalent vanadium is
The purpose of this oxidation is to oxidize divalent iron to trivalent iron to facilitate the precipitation of each metal salt.
easily done. If the pH is too high, a large amount of sulfuric acid will be required in the subsequent neutralization step, which is not a good idea, and the pH is preferably 7 to 9, more preferably 8 to 9. As a neutralizer for the carbon liquid, NH ₄ ⁺ is used to precipitate ammonium metavanadate later.
is essential, but if ammonium sulfate is sufficiently present, an alkali such as caustic soda can be used instead of ammonia. However, it is preferable to use only ammonia rather than introducing new species into the system. As the oxidizing agent, air, oxygen, ozone, hydrogen peroxide, etc. can be used, but it is preferable to use air from the viewpoint of the process. In other words, when ammonia is used as a neutralizing agent and air is used as an oxidizing agent, as will be described later, when aeration with air is used to separate ammonia from the gypsum slurry in the ammonia aeration tower (11), Aeration gas (mixture of ammonia and air) can be used directly to oxidize metals. When the pH is set to 7 to 9 and the metal is oxidized, solids (iron sludge) will precipitate. Iron is almost completely precipitated, and vanadium is mostly dissolved in the liquid part as ammonium metavanadate. Iron sludge consists of iron, vanadium, silica, etc., and the higher the temperature, the lower the vanadium content. Therefore, in order to increase the subsequent recovery rate of vanadium, it is preferable to precipitate the iron sludge at a high temperature, preferably 70°C or higher, more preferably 85 to 95°C. 4 The liquid coming out of the metal oxidation tank 4 is transferred to the iron sludge separator 5.
to separate iron sludge C. By separating the iron sludge before precipitation of vanadium compound D, not only iron but also silica can be removed at the same time, and the purity of vanadium compound D can be significantly increased. If the iron sludge C is not separated, iron and silica will be mixed into the vanadium compound D, reducing the purity of the vanadium compound. In order to suppress mixing of vanadium compound D into iron sludge C as much as possible and to increase the recovery rate of vanadium, it is preferable to suppress a decrease in temperature and separate into iron sludge C while maintaining a high temperature. Various conventional methods can be used to separate iron sludge C, but the iron in iron sludge can be separated into hydroxides,
Since the sludge is an oxide and is quite fine, it is preferable to add a polymer flocculant or the like if necessary, sediment and concentrate the sludge, and then separate it using a decanter or the like. 5 Next, the liquid part is transferred to a vanadium compound crystallizer 6 and cooled to 40° C. or lower to precipitate vanadium compound (ammonium metavanadate) D.
The lower the temperature, the lower the temperature of ammonium metavanadate.
The higher the ammonium sulfate concentration, the easier it is to precipitate. Therefore, it is necessary to lower the temperature when the ammonium sulfate concentration is low. When the ammonium sulfate concentration is about 10 to 30 wt%, the temperature is below 40℃,
Preferably, the temperature is 20 to 30°C or lower. 6 Vanadium compound D is separated by vanadium separator 7. Although various methods can be used for separation, a method of sedimentation, concentration, and filtration is preferred.
High purity (about 98-99%) ammonium metavanadate can be obtained by washing the separated vanadium compound with cold water. 7. Transfer the liquid part to the nickel compound crystallizer 8, add sulfuric acid G to adjust the pH to 3 to 5, and precipitate the nickel compound E. The precipitated nickel compound is nickel ammonium sulfate [ _NiSO4 .
(NH ₄ ) ₂ SO ₄ .6H ₂ O] and contains a magnesium compound precipitated at the same time. The lower the temperature and the higher the concentration of ammonium sulfate, the easier the nickel compound will precipitate, but it has a higher solubility than the vanadium compound and is less likely to precipitate, so it is necessary to increase the nickel concentration in the liquid part. Therefore, the concentration of nickel can be increased by recycling the resulting water within the system as circulating water K, which is used for dissolving the combustion ash A, as described above. A nickel compound with a higher solubility will precipitate. 8 The precipitated nickel compound E is separated in a nickel compound separator 9. Although various methods can be used for separation, a method of sedimentation, concentration, and filtration is preferred. 9. The liquid part is transferred to the gypsum reactor 10, and calcium hydroxide or calcium oxide, preferably calcium hydroxide in powder or slurry form for handling reasons, is added to precipitate gypsum F and liberate ammonia. The main reactions in the gypsum reactor are:
(NH ₄ ) ₂ SO ₄ +Ca(OH) ₂ = CaSO ₄・2H ₂ O+
2NH ₃ H ₂ SO ₄ + Ca(OH) ₂ = CaSO ₄・2H ₂ O, the generated gypsum (CaSO ₄・2H ₂ O) becomes a slurry, and most of the ammonia (NH ₃ ) remains in the liquid as free ammonia. It is dissolved. The amount of calcium hydroxide (calcium oxide) to be added is stoichiometric or slightly excessive. At this time, the pH of the gypsum slurry is 9 to 9 due to free ammonia, unreacted calcium hydroxide, etc.
The pH is around 12, but in most cases the pH is between 10 and 11. As mentioned above, it is better to have a high ammonium sulfate concentration in order to precipitate vanadium compounds and nickel compounds well, but some combustion ash has a low ammonium sulfate content. In such cases, by reducing the amount of calcium hydroxide or calcium oxide added and leaving unreacted ammonium sulfate, the concentration of ammonium sulfate in circulating water K can be increased, and this can be recycled to dissolve combustion ash A, thereby increasing the vanadium compound. Crystallizer 6
Also, the ammonium sulfate concentration in the liquid part of the nickel compound crystallizer 8 can be increased. 10 Next, ammonia and gypsum are separated from the gypsum slurry in which ammonia is dissolved. Any order of separation of ammonia and gypsum is possible. Ammonia can be separated by a distillation method or a conventional method for separating dissolved gases, such as an aeration method in which the temperature of the liquid is increased and an inert gas such as air H is supplied to separate the ammonia. The form of ammonia can also be recovered as aqueous ammonia by absorbing gaseous or separated ammonia gas into water. FIG. 1 shows a method in which ammonia is first separated by an aeration method, which is preferable because there is almost no problem with the ammonia odor during operation. In Figure 1, ammonia separation is performed in metal oxidation tank 4.
Two ammonia separators are provided: an ammonia aeration tower 11 for obtaining ammonia aeration gas to be supplied to the reactor and an ammonia aeration tower 12 for recovering ammonia, but of course either one may be used. In the latter case, the required amount of ammonia aeration gas to be supplied to the metal oxidation tank 4 can be obtained by a method such as branching the aeration gas. Gypsum slurry from which ammonia has been separated is
It is preferable that ammonia and unreacted calcium hydroxide remaining without being separated in the gypsum PH adjustment tank 13 be neutralized with sulfuric acid G. At this time the PH
By adjusting the value to 7 or less, preferably 3 to 5, residual ammonia can be converted to ammonium sulfate, and unreacted calcium hydroxide can be converted to gypsum. In this way, the properties of gypsum can be improved by adjusting the pH. If residual ammonia and unreacted calcium hydroxide are extremely small, it is not necessary to adjust the pH. The gypsum slurry is transferred from the gypsum PH adjustment tank 13 to the gypsum separator 14. Although various separators can be used for this purpose, a centrifugal separator is preferred. 11 The water obtained by separating the gypsum is sent to the circulating water tank 15.
Transfer to. Since unprecipitated parts such as nickel and vanadium are dissolved in the circulating water K, a combustion ash dissolving tank 1 and a slaked lime slurry tank 16 are used as water for slurrying calcium hydroxide or calcium oxide I. Recycle the waste and use it internally, eliminate wastewater from outside the system, and keep it to a minimum if any. By recycling the circulating water, the concentration of vanadium and nickel in the vanadium compound crystallizer 6 and the nickel crystallizer 8 can be increased and eventually recovered as precipitate. [Examples] Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Example 1 Combustion ash captured by an electrostatic precipitator installed in the flue of a boiler burning heavy oil C was collected in the first
Continuous processing was carried out according to the flow sheet shown in the figure. The results were as follows. (1) The amount of combustion ash processed was 5500 kg/day, and the composition and content of each component were as follows.

〔Effect of the invention〕

As mentioned before, the present invention has the following excellent effects (1) to (4). (1) Most of the components of combustion ash can be recovered as valuable materials. In other words, carbon is carbon with a high fixed carbon content, NH ₄ is converted into ammonia (NH ₃ ), SO ₄ is converted into gypsum (CaSO ₄ 2H ₂ O) by reacting with calcium hydroxide or calcium oxide, and vanadium is converted into metavanadate. As ammonium (NH ₄ VO ₃ ),
Nickel can be recovered as ammonium nickel sulfate [(NH ₄ ) ₂ SO ₄ ·NiSO ₄ ·6H ₂ O], and iron can be recovered as iron sludge. (2) High purity ammonium metavanadate and gypsum can be obtained without special treatment. (3) There is virtually no waste (effluent, etc.), and if there is, it can be kept to a very small amount. (4) Ammonia needed within the system can be processed at low cost by recycling recovered ammonia.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing an example of implementing the treatment method of the present invention. 1...Dissolution tank, 2...Carbon separator, 3...
Carbon liquid tank, 4...Metal oxidation tank, 5...
Iron sludge separator, 6... Vanadium compound crystallizer, 7... Vanadium compound separator, 8... Nickel compound crystallizer, 9... Nickel compound separator, 10... Gypsum reactor, 11... Ammonia Aeration tower〓, 12... Ammonia aeration tower〓, 13...
...Gypsum PH adjustment tank, 14...Gypsum separator, 15
... Circulating water tank, 16 ... Slaked lime slurry tank, A ... Combustion ash, B ... Carbon, C ... Iron sludge, D ... Vanadium compound, E ... Nickel compound, F ... Gypsum, G ... Sulfuric acid, H...air, I...calcium hydroxide or calcium oxide, J...ammonia, K...circulating water.

Claims (1)

[Claims] 1. A method for recovering carbon, heavy metals, etc. by wet processing combustion ash collected by a dust collector installed in an exhaust gas flue of a boiler using petroleum-based fuel, etc. A method for treating petroleum-based combustion ash, characterized by carrying out the following (1) to (11). (1) Mix combustion ash and water, add sulfuric acid as necessary to adjust the pH to 3 or less to make a slurry. (2) Separate solid content (carbon). (3) Heat the liquid part to 70°C or higher, supply ammonia and an oxidizing agent, and oxidize the metal while adjusting the pH to 7-9. (4) Separate the precipitate (iron sludge). (5) Cool the liquid part to 40°C or less to precipitate a vanadium compound (ammonium metavanadate). (6) Separate the precipitated vanadium compound. (7) Add sulfuric acid to the liquid part and adjust the pH to 3 to 5.
Nickel compound (nickel ammonium sulfate)
is precipitated. (8) Separate the precipitated nickel compound. (9) Add calcium hydroxide or calcium oxide to the liquid part to precipitate gypsum and liberate ammonia. (10) Separate ammonia and gypsum from the gypsum slurry in which ammonia is dissolved. (11) Water after gypsum separation is recycled into the system for use.