EP0239598A1

EP0239598A1 - Process for reducing the content of noxious matter in dust-containing flue or process gases

Info

Publication number: EP0239598A1
Application number: EP19860905801
Authority: EP
Inventors: Jürgen RITTER; Hans Reye
Original assignee: Perfluktiv Technik AG
Current assignee: Perfluktiv Technik AG
Priority date: 1985-10-05
Filing date: 1986-10-04
Publication date: 1987-10-07
Also published as: DE3535600C1; DD249857A5; AU6400486A; WO1987001963A1

Abstract

Procédé pour diminuer la teneur en matières délétères de gaz de fumées ou de traitements contenant des poussières au moyen d'un système de refroidissement à injection et en utilisant un adsorbeur coopérant avec un régénérateur et de charges de coke activé passant sur ces derniers, dans lequel les gaz chargés de poussières avant le filtrage sont envoyés à travers au moins un système de refroidissement à injection avec addition simultanée de l'ammoniac comme additif pour réaliser la liaison chimique de la majeure partie sinon la totalité du SO3 et des halogènes, ainsi que pour séparer et précipiter les sels ainsi formés et les métaux lourds sur la poussière. La poussière chargée de sels précipités est retirée par filtrage et préparée pour récupération de l'ammoniac. Après filtrage des matières solides qu'ils contiennent les gas de fumées sont envoyés par la ou les charges de coke activé de l'adsorbeur, de sorte qu'on sépare dans l'adsorbeur essentiellement seulement du SO2, qui est récupéré du coke activé par le traitement de ce dernier dans le régénérateur et est envoyé pour traitement ultérieur.Method for reducing the content of deleterious matters in flue gases or dust-containing treatments by means of an injection cooling system and by using an adsorber cooperating with a regenerator and with charges of activated coke passing over them, in which the dust-laden gases before filtering are sent through at least one injection cooling system with simultaneous addition of ammonia as an additive to achieve the chemical bonding of most if not all of the SO3 and halogens, as well as for separating and precipitating the salts thus formed and the heavy metals on the dust. The dust laden with precipitated salts is removed by filtration and prepared for recovery of the ammonia. After filtering the solids they contain, the flue gases are sent by the charge (s) of activated coke from the adsorber, so that essentially only SO2 is separated in the adsorber, which is recovered from the coke activated by processing of the latter in the regenerator and is sent for further processing.

Description

Process for reducing the pollutant content of dusty smoke or process gases

The invention relates to a method for reducing the pollutant content of dust-containing smoke or process gases, in which the gases are filtered for dust separation, are cooled by means of an injection cooler by injection and evaporation of water, are fed to an adsorber with an activated coke bed, and for loading the activated coke with pollutants , in particular sulfur dioxide, are conveyed through the activated coke bed, and sulfur dioxide is desorbed from the activated coke bed in the regenerator and fed to further processing.

In particular in connection with the flue gas cleaning for power plants, there are methods of the aforementioned Type known in which the flue gases flowing out of the boiler and through a subsequent heat exchanger are first fed to an electrostatic precipitator for dust separation before the flue gases enter an injection cooler in which the temperature of the flue gases is reduced to approximately 120 ° C. before the gases are passed through the activated coke bed or bed of an adsorber for loading the activated coke with pollutants, in particular sulfur dioxide. Any excessively high amounts of dust are then separated in downstream dust filters and the flue gases cleaned in this way are fed to the chimney.

It has also already been proposed to add ammonia gas to the flue gases in the course of the method in order to at least partially catalytically decompose the nitrogen oxides contained in the flue gas and also to partially remove these pollutants from the flue gas.

A problem with the treatment of the gases involves their SC content. This essentially determines the acid dew point of the gases and causes signs of corrosion, which practically cannot be avoided in the known method.

Another problem is caused by the halogens contained in the flue gas, which can also lead to corrosion damage, and the heavy metals, which are often not or only insufficiently separated.

Finally, problems arise when ammonia gas is added to the flue gas to reduce the pollutant content, which leads to the formation of ammonium salts which accumulate on the activated coke and an increase in the flow resistance of the flue gas in the Cause activated coke bed. In addition, the crystal formation of the ammonium salts in the treatment cycle of the activated coke can cause an explosive effect by which the activated coke particles are destroyed, which leads to increased activated coke consumption in the course of the process.

The object of the invention is to develop a method of the type mentioned in the introduction in such a way that the disadvantages described are largely avoided and the dew point of the flue gases is reduced when they are transferred to the adsorber, and corrosion-free operation of the adsorber is made possible and the activates before Destruction can be protected by ammonium salts.

To solve the above problem, the method mentioned at the outset is characterized in that the gases with their dust content are conveyed through an at least one injection cooler before filtering, with the simultaneous addition of ammonia as an additive for chemical bonding of the predominant to almost complete proportion of the SO ,, and the halogens the gases as well as for the separation and attachment of the ammonium salts and heavy metals thus formed to the dust, and that the gases are transferred to the adsorber after filtering and the dust loaded with the salts deposited is processed after its discharge to recover the ammonia.

The invention is based on the knowledge that the dust particles contained in the flue gas are used as carrier particles before they are discharged through the filtering, to which the ammonium salts formed by the addition of the ammonia can accumulate, so that these together with the dust of the following filters be carried out. The addition of the ammonia as an additive to the injection cooler results in a uniform distribution in the gas volume, and indeed also. when the ammonia is introduced into the injection cooler as a liquid solution, because evaporation takes place in the injection cooler and thus ammonia gas is released, which reacts very quickly with the halogens and the SOn and forms ammonium salts, which are formed by the aforementioned addition to the Allow dust particles to be discharged including the heavy metal dust particles during the filtering process, along with the removal of the gas from the dust. The dust thus discharged and provided with the attached ammonium salts can be processed in a known manner after the separation in order to achieve a recovery of the ammonia, which is then used again in the process, so that the process is used until the first use of ammonia, only the loss amounts of ammonia need to be supplemented.

Due to the recovery of the ammonia, an easy-to-deposit solid is only obtained in small quantities.

The further advantage is achieved that practically only S0 _? is separated by means of the activated coke, which facilitates the cleaning and further processing of the so-called rich gas after the regeneration of the activated coke, since traces of halogens are at most contained in the rich gas.

By withdrawing SC and the halogens from the flue gas or process gas before introducing this gas into the adsorber, the acid dew point and the corrosion potential of the gas are considerably reduced, so that the adsorber is operated at lower temperatures than previously can. This in turn leads to the great advantage that the conditions for improve the deposition of S0 "in the adsorber. The absorption capacity of activated coke for SC is temperature-dependent and becomes cheaper at lower temperatures. The new process can either reduce the need for activated coke, or it can reduce the residence time of the flue gases as they flow through the adsorber.

By adding the ammonia into the injection cooler and the rapid described above taking place there

Distribution of the ammonia over the entire gas volume in the injection cooler makes it practically possible to provide a stoichiometric addition of the ammonia.

As already described above, ammonia can be introduced into the injection cooler in the form of an aqueous solution, since the evaporation produces the ammonia gas which is rapidly distributed in the mixing chamber.

A particularly favorable and faster reaction is achieved if the additive is added at least partially in the form of ammonia gas.

Since the flue dust loaded with ammonium salts has an increased electrical conductivity in the flue gas emerging from the injection cooler compared to unloaded flue dust, an improvement in the separation efficiency can be achieved when an electrostatic filter is used to separate the flue dust loaded with the ammonium salts. A better degree of separation of the fine dust is achieved, on which the heavy metals are preferentially attached. Due to the reduction in the gas temperature previously carried out in the injection cooler, the electrostatic filter can either be smaller than the previous arrangement in front of the injection cooler. measure or be operated with the same dimensioning with longer dwell time of the gas or reduced gas speed and thus lower pressure losses. Depending on the expediency, filter systems of various types, possibly also in combination, can be used for the discharge of the dust with the deposits.

In the preparation of the fly dust loaded with the deposited ammonium salts, the easy solubility of the ammonium salts in water is used in a known manner, so that after the separation of the ammonium salts, the fly dust is present as a moist mass, which makes it easy to handle and transport Airborne dust results.

The method described is not only suitable for flue gases from power plants or the like, but can also be used in the same way for gases from other processes, such as for example in glass production and also in waste incineration.

In the treatment of process gases from waste incineration plants, further difficulties often arise from the fact that the halogen content in these gases is relatively high. This significantly increases the risk of corrosion from the flue gas. The separation of the halogens from process gases from waste incineration plants therefore presents particular difficulties.

According to the invention, the above-mentioned difficulties can be overcome, however, in that the gases are passed through an upstream injection cooler or an upstream injection stage before being introduced into the injection cooler, in which ammonia is added, and thereby by addition of lime milk the SO ,, -, and halogen content of the gases is reduced.

The first injection cooler or the upstream injection stage must have good corrosion protection. In this first injection cooler or in the first injection stage, the exhaust gas temperature is reduced from about 200 to 180 ° C. to about 160 ° C. and not only a reduction in the halogen content is achieved by adding the milk of lime, but at the same time also a part the lime necessary for the subsequent chemical bonding during the preparation is fed to the process gas and thereby partially covers the lime requirement later required for the treatment of the flying dust loaded with the ammonium salts.

The salts which form in the first injection cooler or the upstream injection stage increase the dust in the gas. This is advantageous for smoke or press gases with low dust content.

The residual separation of the halogens except for traces takes place in the manner described in the second injection cooler or the second stage of the injection cooler using ammonia at temperatures between 160 ° and 120 ° C. or possibly even lower temperatures. A temperature reduction noticeably below 120 ° C is possible. It offers advantages for better deposition of heavy metals, especially mercury.

The described pre-separation of the pollutants and the multi-stage injection cooling result in a treatment of the gases in a wide temperature range, which has a favorable effect on the degree of separation which affects pollutants.

In a number of flue or process gases, for example in the case of oil burning, only small amounts of dust accumulate in the gases, so that when these gases are treated in the injection cooler with the addition of ammonia there is a risk that the finest will be increased Ammonium salt particles are formed which are extremely difficult to filter out of the gas.

To remedy this, it is provided in a preferred embodiment of the method that low-dust gases with a dust content which is not sufficient for the addition of the salts formed by the addition of the ammonia, before being fed to the injection cooler, in which the addition of ammonia, lime dust is added in an amount that allows sufficient accumulation of the salts.

The invention is explained below using some examples in conjunction with the drawings.

1 shows a flow diagram for the treatment of flue gases from power plants with a flow diagram for the processing of the fly dust for the recovery of the ammonia, FIG. 2 shows a flow diagram for the treatment of process gases from a glass tank,

3 shows a flow diagram for the treatment of process gases from a waste incineration plant.

In Fig. 1, 1 denotes a boiler of a power plant, from which the flue gas is fed to an injection cooler 3 via the flue gas line 2. The flue gas emerging from the boiler 1 with a

Temperature of 180 ° to 160 ° C is brought to a process temperature of about 120 ° C or below in the injection cooler 3 by the simultaneous addition of water and ammonia. In the drawing, 4 is the

Feeding the water and indicated by the dashed arrow 5, the addition of ammonia in the injection cooler 3.

In the injection cooler 3 the chemical bonding of the halogens and SO, contained in the flue gas, to ammonium salts and their accumulation as well as the accumulation of the heavy metals on the dust particles of the flue gas takes place. The flue gas with the pollutant-laden dust particles is fed via line 6 to an electric filter 7, in which the fly dust is separated, which is transferred to a bunker 8, while the gas freed from dust and ammonium salts via the further feed line 9 into the an active coke bed receiving adsorber 10 is transferred. The adsorber 10 is preferably equipped as a shaft with planar piles of activated coke which are arranged one above the other and which are conveyed through the adsorber from floor to floor and through which the flue gas flows in countercurrent. In the adsorber there is a further reduction in pollutants in the flue gas, the S0 “being substantially completely removed from the flue gas before the flue gas is passed via line 11 and a blower 12 into the chimney 13.

The adsorber works together with an activated coke regenerator, which is not shown in the drawing and which serves to process the activated coke, which is essentially loaded with the SO, by evaporating the sulfur dioxide, the sulfur dioxide in turn can be processed.

Due to the selective reaction of the ammonia in the injection cooler 3 with the halogens and the SO ,, - of the flue gas to the corresponding ammonium salts, which accumulate on the particles of the dust, the removal of the ammonium salts from the flue gas does not pose any great difficulties and also offers them Possibility of recovering the ammonia, as is shown schematically in FIG. 1, for example.

The dust collected in the electrostatic filter 7 and transferred to the bunker 8 and loaded with ammonium salts is transferred from the bunker 8 into a stirring mixer 14, in which the flying dust is mixed with water which comes from the centrifuge 15 arranged after the stirring mixer 14 and is introduced into the agitating mixer 14 via the return line 16.

In the centrifuge 15, the pasty moist mass supplied via the line 17 from the stirring mixer 14 is spun off with the addition of water and the moist solid part originating from the centrifuge 15 is fed via line 18 to a spray dryer 19, to which a filter 20 is connected, in which the solids are separated from the gaseous drying medium fed into the spray dryer 19. The solids separated in the filter 20 are passed into the bunker 21 and later deposited there. The gaseous drying medium from the filter 20 is fed via line 22 to the power plant exhaust gases upstream of the injection cooler 3.

The return line 16 between the centrifuge 15 and the agitator 14 becomes part of the water and salt existing mixture is transferred via line 23 into a mixer 24, in which the water / salt mixture is mixed with hydrated lime. In the subsequent centrifuge 25, the liquid portion consisting of water and ammonia is separated, which is fed via line 26 to the water supply 4 to the injection cooler 3.

The moist from the centrifuge 25 separated

Solids are transferred via a line 27 to a dryer 28- and dried there by means of heated gases at temperatures of approximately 30 ° C. and separated in the downstream filter 29 and transferred via line 30 to the bunker 21, in order later to Landfill.

The gaseous heating medium separated from the solids in the filter 29 is in turn admixed via line 31 to the power plant exhaust gases upstream of the injection cooler 3.

In connection with the processing of the dust containing the ammonium salts, it can be seen that, according to the invention, a high return rate of the ammonia into the injection cooler 3 is possible, since the ammonium salts together with the ammonium salts are combined with the electrolyte 7 after the injection cooler 3 Fly dust can be discharged practically completely and can be separated from the fly dust again in a simple manner.

In the flow diagram shown in FIG. 2, the preparation of the fly dust has not been shown.

The flow diagram shown in Fig. 2 shows the i 12 Reduction of the pollutant content according to the invention for process gases from a Glaswaππe.

The flow diagram essentially corresponds to the flow diagram for the flue gases of a power plant, as shown in FIG. 1. Instead of the boiler

1 according to FIG. 1 is in the flow diagram according to FIG.

2 shows a glass tank 33, from which the dust-containing process gas is removed and treated with a slight variation in order to be freed from the pollutants therein, as described earlier in connection with FIG. 1 for the flue gas from a power plant is. In FIG. 2, the elements corresponding to FIG. 1 are provided with the same reference numbers. An explanation of the path of the flue gases according to FIG. 2 and their treatment should be superfluous with regard to the explanations for FIG. 1.

Since the process gases from glass walls have a significantly higher temperature than the flue gases from the boilers of power plants, the flow diagram according to FIG.

2 between the Glaswanπe 33 and the desuperheater

3, an additional heat exchanger 34 is provided, in which the process gas flowing out of the glass wall is passed through at a temperature of approximately 450 ° C. and cooled to a temperature of approximately 250 ° C. In the heat exchanger, the pollutant-free exhaust gases conveyed into the chimney 13 by the blower 12 are raised to a temperature of approximately 300 ° C., at which they enter the chimney 13.

3 corresponds, however, without the processing of the dust loaded with the ammonium salts of FIG. 1, so that in FIG. 3 the same parts are again provided with the same reference numerals are as in Fig. l.

3 is the treatment of process gases from a waste incinerator.

For the treatment of these process gases, the injection cooler 3 is designed differently from the flow diagram according to FIG. 1. It is designed for the treatment of the process gases from the garbage disposal in the example shown as a two-stage injection cooler. In the upper part of the desuperheater. is carried out by the arrow 35 a-n indicated the supply of water and indicated by the arrow 32 the supply of lime milk in order to reduce the relatively high proportion of halogens contained in the waste combustion gases by 50% before the process gases treated in this way into the lower stage of the Injection cooler 3 enter, in which the supply of water and ammonia takes place in the same manner as has been described in connection with FIG. 1. In this case, even with the flow chart of FIG. 3 is a recirculation of the water with ammonia is carried out of the fly ash treatment, so that only needs to be in the ^process' ends ammonia losses by adding fresh ammonia auftrete according to the dashed arrow 5 is added in the second stage of the injection cooler 3.

The treatment of the gases after they emerge from the injection cooler and the separation and processing of the dust laden with the ammonium salts is carried out in the same way as has already been described in connection with FIG. 1.

Claims

Expectations

1. A method for reducing the pollutant content of dust-containing smoke or process gases, in which the gases are filtered for dust separation, cooled by means of an injection cooler by injecting and evaporating water, fed to an adsorber with an activated coke bed, and for loading the activated coke with pollutants, in particular Sulfur dioxide, through which the activated coke bed is conveyed, and sulfur dioxide is disinfected from the activated coke bed in the regenerator and fed to further processing, characterized in that the gases with their dust content are conveyed through an at least one injection cooler prior to filtering, with the simultaneous addition of ammonia as an additive for the chemical bonding of the predominant to almost complete portion of the SO ,, and the halogens of the gases as well as for the separation and deposition of the ammonium salts and heavy metals thus formed on the dust, and that the gas e are transferred to the adsorber after filtering and the dust laden with the deposited salts is processed to recover the ammonia after it has been discharged.

2. The method according to claim 1, dadurchge ¬ indicates that the additive is at least partially added in the form of ammonia gas.

3. Procedure for reducing the pollutant content of

Process gases from waste incineration plants according to claim 1, characterized in that the gases are passed through a pre-arranged injection cooler or an upstream injection stage prior to their introduction into the injection cooler, in which ammonia is added, and thereby by adding lime milk to the SO ,, - and Halogen content of the gases is reduced.

4. The method according to any one of the preceding claims, characterized in that low-dust gases with a dust content which is insufficient for the addition of the salts formed by the addition of ammonia, before being fed to the injection cooler in which the addition of ammonia takes place, lime dust up to is added to an amount which allows a sufficient accumulation of the salts.