JPH0533089B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION The present invention provides a method for purifying flue gases resulting from the combustion of waste materials, which contain solids of various compositions as well as harmful gases and heavy metals in gaseous form. Removed from the gas and collected as smoke ash,
The flue gas is then cleaned in a condensation/cleaning system to combine harmful gases and residual solid components, separating the water vapor and heavy metals contained in the flue gas and separating the condensates from the ash. The present invention relates to a method for purifying said flue gas which is utilized to extract heavy metals and which comprises precipitating and removing soluble heavy metals from the process. BACKGROUND OF THE INVENTION Flue gas purification involves the separation of solid, liquid or gaseous harmful substances from the flue gas in order to reduce environmental damage to an acceptable level. As a rule, the separation of harmful dusts from gases takes place by mechanical and electrical methods and, in the case of wet dedusting, by absorption, adsorption or chemisorption. The basic methods for the separation of harmful gases are absorption, adsorption, condensation and chemical reactions. In the case of wet cleaning, waste mud, salt and waste water are produced. In salt road gas purification equipment, a collective method is often obtained by combining several basic methods. One of the most used waste combustion methods is the purification of waste gases from dust by electric filters or mesh filters on the flue gas side and the harmful gases in the exhaust by acid or alkali treatment methods before or after the filter device. HCl,
Also consider the partial removal of SO ₂ , HF [Abfallwirtschaft an der TU Berlin, Vol.
Vol. 1-41]. Heavy metals present in gaseous form, such as Hg, can conventionally only be removed by means of filters in a wet process. A significant drawback of the conventional method is that approximately 30 kg of halogen-containing dust is produced per ton of burned waste, in which a portion of the heavy metals is present in an easily mobile manner. Therefore, the utilization of dust from the removal of dust from the flue gas is no longer carried out, but rather the dust is still deposited under special conditions. Safe removal of heavy metal toxic substances from ecosystems is therefore not guaranteed, especially over long periods of time. Hazardous substances Hg in smoke ash or hazardous gases and/or waste combustion equipment,
There are problems with Cd, Pb, Sb, Sn, Zn and others. In addition to this, various chemical reactions occur in the waste combustion method due to the composition of the waste. On the one hand, many products decompose or evaporate at a combustion temperature of 800 °C, and on the other hand, the products liberated in the gas phase undergo a long journey under cooling to about 200 °C, and anticombinatorial reactions occur. or new products are formed. Thus, for example, chlorinated organic compounds (aliphatic as well as aromatic) owe their existence to this mechanism. The organic compounds that occur generally adhere to dust or soot particles present in the crude gas.
The smoke discharged into a filter, for example an electric filter, therefore contains different compositions and different concentrations of organic chemicals. The problem is that this organic compound in smoke ash is
This is the case with toxic substances, such as chlorinated dibenzodioxins or dibenzofurans, which complicate or prevent the final removal of the smoke ash. Acid solutions of smoke ash have been found to be particularly favorable in conjunction with the separation of mobile heavy metals. The acid solution does not change the organic content of the harmful substances, but the reflux of the treated smoke ash leads to a combustion chamber for the reduced heavy metal content, where the residual heavy metals are further fixed in the high temperature process. The purpose of the present invention is to remove gaseous heavy metal hazardous substances and, above all, heavy metal hazardous substances dissolved in dust from the flue gas purification process in the honeyiest form possible. ,
The object of the present invention is to obtain a method in which sufficient purification of HCl, SO ₂ and NO _x can be obtained at the same time, and can even be improved. All other residues can be sent for reuse. However, in addition, the organic hazardous substances contained in the residual substance must still be able to be decomposed or at least converted into non-hazardous components. According to the invention, this purpose is to send the remaining solids to the combustion chamber and decompose the organic harmful substances contained therein by high temperature treatment or to decompose the organic harmful substances contained therein or in the acid condensate/wash water. The solution is to separate the dissolved mercury present from the solution phase by reaction with the smoke ash and bind it in insoluble form to the smoke ash. Therefore, in the method of the invention, in order to protect the environment, gaseous harmful substances such as HCl, SO ₂ , NO _x ,
Dust, gaseous metals, especially Hg, and soluble heavy metal hazardous substances that occur in dust and combustion chamber embers are removed by only immobile components remaining.
Consideration must be given to removing this component together with the combustion embers in such a way that long-term immobility and with this a risk-free reuse or removal is guaranteed. By means of the process of the invention, the mercury present dissolved in the acid condensate/wash water is separated in large quantities from the liquid phase by reaction with the precipitated filter dust and is present in insoluble form, i.e. immobile, in the smoke ashes. A combination is achieved. This smoke ash can be combined directly with the cinders. If the ash is returned to the combustion chamber for further high temperature reactions, the mercury is preferably separated and recovered by a further thermal pretreatment. The important novelty of the present invention is that, instead of producing from one tonne of waste approximately 30 Kg of difficult-to-remove smoke residue, for example in conventional deposits, this amount can be reduced to approximately 1 Kg, i.e. for the purpose of the process. Extracting actual heavy metal hazardous substances,
In particular, it is important to obtain the basics of methods for reducing Hg and Cd. For example, when recovering mercury, lead, cadmium from the resulting sulphides, a completely residue-free removal is possible. Handling with salt depends on location. Normally salt can be discharged into drains without any problem. This is because it liberates heavy metals. If suitable drainage channels are not used, salt ash as well as other advantageous salt-containing removal products are obtained, for example by bitium treatment. In method 2 of combustion of this waste, solid residues are present, namely cinders and smoke, but in the second case still a cinder is obtained which no longer contains organic harmful substances due to its high temperature treatment (separated heavy metals supply for reuse). Furthermore, the new process results in a recycled product of trapped organic pollutants, which, together with the formation of this organic pollutant, also contains its thermal decomposition products. In this way, the discharge of organic hazardous substances into the environment is largely prevented. Example In Fig. 1, garbage 1 is sent to combustion material 2 and incinerated.
Heat and embers 3 with flue gases are produced in the process. A portion of the heat is removed from the flue gas in heat exchanger 4 and used elsewhere. After this heat recovery, the flue gas is optionally subjected to a dry prepurification using a cyclone or an electric filter at approximately 180°C, with the dew point of the gas, water vapor, etc. Care must be taken not to fall below. A condensing/cleaning section 6 is connected to the drying and purifying section 5 for the gas and steam passing through a filter or cyclone, where water vapor is produced simultaneously with the removal of HCl and Hg. Subsequently, the residual flue gas containing harmful gas components SO ₂ and NO _X is passed through an alkaline cleaning section 7 and the cleaning gas is sent to a chimney 8 . The washed condensate from the coagulation stage 6 is sent together with the smoke ash 9 to a dissolution reactor 10 in order to partially dissolve the heavy metals from the smoke ash 9. A mechanical mixing step may be considered in this case; the acid-washed condensate (containing HCl) reacts with the alkaline smoke and adjusts the final pH of about 3. In this case, the Hg present completely enters the smoke. A solid/liquid separation device (eg settling or centrifugation) is connected to this dissolution reactor 10. A fixed residue 11 and a solution 12 are formed, which solution mainly consists of the washing condensate (in particular HCl) and the heavy metals removed from the smoke ash 9. However, the solid residue 11 also contains Hg and can be fed directly into the cinders 3. In the case of large amounts of smoke ash 9, one portion of the amount already produced is sufficient to completely bind the Hg. The solid residue 11 of the solid/liquid separation can be sent to a special heat treatment section 27 for recovering the Hg, for example at the temperature of the flue gas, where the Hg is desorbed and the 2
Gather at 8. The solid residue from the special treatment section 27 can be sent further to the combustion chamber 2 or to the cinders 3. The acid solution 12 is preferably subjected to sulfide precipitation in a heavy metal precipitation section 13. After a new solid/liquid separation, a heavy metal honey substance 14 is obtained, which is optionally sent to a recirculation section 16. Note that in order to neutralize the acid solution 15 (neutralization device 17), it is combined with the substance of the alkaline cleaning section 7. The purified sludge formed in the neutralizer 17 is preferably sent to the combustion chamber 2 where it is bonded to the cinders 3 by means of high temperatures. This cinders 3 are recycled into the recycling section 21.
For example, it is used for road construction. If the cinders 3 contain heavy metal components which are still unbound despite suitable assumptions in the temperature treatment and can be washed out, a post-treatment is carried out. Post-treatment considers mild acid treatment of the embers 3, which can be carried out at a pH of about 4. For post-treatment, in a preferred method a bath 21 is suitable,
Therein, the cinders 3 are generally slaked or cooled after being discharged from the combustion chamber 2. Bath 21 consists of water. However, it is also possible to spray the cinders 3 with a mist of weak acids and collect the resulting slaked liquid to liberate the heavy metals. The neutralized re-purified sludge is liberated (purified) and a solution 19 purified of heavy metal hazardous substances is discharged into a drainage channel 20. Example of Hg adsorption Ratio of smoke ash/cleaning condensate = 37.6Kg/1000 = 100
% Smoke ash (%) Hg in solution (ppm) 0 7.8 5 5.1 10 2.4 15 0.97 20 0.45 25 <0.1 Example of thermal desorption of Hg Temperature (℃) Desorption (%) 50 0 200 2 250 86 300 98 The following table is , shows experimental results of the dioxin content of the smoke ash and especially the residual solids before and after treatment.

[Table] The process shown in FIG. 2 corresponds to the process in FIG. This is a process in which the disconnected portion has a characteristic, and this is the second embodiment. In the process from the combustion chamber 2 via the heat exchanger 4 to the electric filter 5, the formation of organic harmful substances takes place.
In the electric filter 5, the main amount of the organic pollutants formed is separated from the crude gas together with the smoke ash 9. In the acid leaching step 10, organic hazardous substances are adsorbed onto the resulting residual solids 11. The residual solids 11 containing organic hazardous substances are then returned - optionally mixed with fresh waste - to the combustion chamber 2, where the organic hazardous substances in the residual solids 11 are decomposed.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an apparatus for carrying out the method of the invention, and FIG. 2 is a system diagram of another apparatus.

Claims (1)

[Scope of Claims] 1. In order to purify flue gas generated from the combustion of waste materials and containing solids of various compositions as well as harmful gases and heavy metals in gaseous form, the main components of solids are removed from the flue gas in a separator. The flue gas is then cleaned in a condensing/cleaning system to remove it, collect it as smoke, and then combine the harmful gases and residual solid components, removing the water vapor and heavy metals contained in the flue gas. said method for purifying flue gas comprising separating and utilizing the condensate to extract soluble heavy metals from the smoke ash and precipitating the soluble heavy metals for removal from the process, comprising: (a) in the acid condensate/wash water; The dissolved mercury contained is separated from the solution phase by reaction with the smoke ashes and bound to the smoke ashes in insoluble form, (b) the mercury is then desorbed and recovered by thermal post-treatment of the leached smoke ashes, and (c ) A process for cleaning flue gases, characterized in that the mercury-free smoke ash is then sent back to the combustion chamber or combined with the ash to be discharged.