WO1995012448A1

WO1995012448A1 - Method, device and plant for processing sulphur and nitrogen oxide-containing waste gases

Info

Publication number: WO1995012448A1
Application number: PCT/FR1994/001265
Authority: WO
Inventors: Roger Leloup
Original assignee: Roger Leloup
Priority date: 1993-11-05
Filing date: 1994-10-31
Publication date: 1995-05-11
Also published as: PL300960A1

Abstract

A method and a device for removing sulphur and nitrogen oxides from waste gases produced in industrial boilers or the like or coal-fired boilers for burning bituminous coal, lignite and other materials, particularly sulphur-containing petroleum products, by means of a dry process using a solid to retain the acid compounds in said waste gases by means of a chemical reaction. The sulphur oxides, particularly sulphur dioxide, and nitrogen oxides contained in said waste gases are converted in the presence of steam into the corresponding acids, whereafter the low-temperature waste gases are contacted with carbonate blocks (14) in a reactor (12) to retain the previously formed acids by means of a chemical reaction.

Description

PROCESS, DEVICE AND PLANT FOR THE TREATMENT OF FUMES CONTAINING SULFUR AND NITROGEN OXIDES.

Process for the treatment of fumes, in particular for the elimination of oxides of sulfur and nitrogen, device for its implementation and corresponding installation.

The invention relates to a process for the treatment of fumes originating in particular from the combustion of coals containing sulfur such as coal, lignite or other petroleum products. This type of combustion is, for example, carried out in industrial boilers. The gaseous effluents considered according to the invention come from the combustion of coals generally with a high sulfur content, containing substantial quantities of sulfur in the form of sulphides, sometimes from 8 to 10%. This sulfur is at the origin of the formation of sulfur oxides and in particular sulfur dioxide, generators of serious atmospheric pollution.

The invention therefore more particularly relates to the elimination of sulfur oxides, in particular of sulfur (S0 ₂ ) which is formed in large quantities during the aforementioned combustions.

The invention also relates to a device as well as an installation comprising at least one such device, for implementing this method.

The treatment of effluent for the elimination of the acidic pollutants which they contain, is generally carried out using a neutralizing reagent consisting of a basic product in solid form such as lime, intended to react chemically with the acidic compounds present.

There are known, for example, so-called dry processes as described in documents FR-2,572,659 and FR-2,587,238, according to which the effluents to be treated and the neutralizing reagent are brought into contact simultaneously in a reactor. , for example a reaction column. In this case, the neutralizing reagent consists of calcium hydroxide (CaiOH) or lime, in powder form. The solid particles of this reagent then react with the gaseous effluent during the upward movement of the suspension obtained, to lead to the formation of water and calcium salts, CaSO, in the case of S0 ₂ and CaSO, in the case of S0- ,. The purified fumes are finally separated from the resulting pulverulent products by means of separators, before being discharged into the atmosphere.

The implementation of these methods has the drawback of involving the manufacture of lime from limestone and the grinding of the latter in order to obtain a suitable pulverulent product. It is also necessary to provide a final separation step for the gases and the product. powder used for treatment.

Furthermore, for the more specific elimination of sulfur dioxide, the document FR-2 572 951 describes a semi-dry process, of the aforementioned type, but the essential difference of which lies in the addition of a certain amount of powdered lime water before suspending it in the upward flow of smoke in a reaction and drying column.

According to this document, the addition of water to the neutralization reagent makes it possible to improve the chemical reactions between the latter and the fumes during their joint ascent in the column, without excessive cooling of the fumes.

However, a large amount of sludge and plaster is formed, the disposal of which poses many problems.

In addition, the loss of calories by adding water is not negligible.

More recently, there has been described in document FR-2 657 272, a process for the treatment of fumes originating in particular from household waste incineration ovens, according to which the fumes at high temperature, that is to say substantially at oven temperature, are brought into contact with limestone blocks in a reactor.

This process makes it possible to avoid the use of a pulverulent material but is applicable to very different fumes, namely fumes at high temperature (850 ^β C or more) and containing few sulfur pollutants, unlike the fumes considered in the present invention and which are at low temperature (approximately 160 ^β C) and contain large quantities of sulfur oxides, and in particular sulfur dioxide.

Finally, document FR-2,586,204 describes another technique which does not call for neutralization with lime, nor for neutralization by the wet method, implemented for example in a multi-stage reactor successively comprising a spray boom and a heat exchanger.

According to the process described, the fumes resulting from the combustion or incineration of industrial waste, coals, hydrocarbons, household waste, etc. are cooled to a relatively low temperature of around 20 ° C and are treated simultaneously by mechanical and physicochemical action, by spraying with a washing liquid. In this case, the washing liquid consists of an acidic aqueous solution resulting from the condensation of acids and water vapor on a cold wall.

The fumes are then reheated and released into the atmosphere. This process is very complex and consumes a lot of energy to cool the fumes and then heat them, and can therefore only be applied to small pollution control installations.

In addition, the elimination of acid liquors resulting from the at least partial dissolution of sulfur oxides is complex.

The invention therefore aims to provide a process for effective treatment of fumes containing sulfur pollutants in large quantities by overcoming the drawbacks of the above processes.

The object of the invention is a method particularly suitable for the elimination of sulfur oxides, in particular sulfur dioxide as well as for the elimination of nitrogen oxides also contained in the type of fumes considered here. It further aims to provide a dry process, static in nature, easy to implement and not requiring the use of a powdery material to treat the fumes.

The invention also aims to provide an inexpensive process.

Another objective of the invention is also to provide a device and an installation comprising it allowing a simple and effective elimination of the oxides of sulfur and nitrogen. To this end, the subject of the invention is a process for the elimination of oxides of sulfur and nitrogen, in particular sulfur dioxide, contained in the fumes from industrial boilers or the like, from the combustion of coals such as coal, lignite and other products, especially petroleum containing sulfur, of the dry type in which a solid material is used to retain by chemical reaction the acid compounds contained in said fumes, characterized in that it is transformed in the presence of steam of water, the sulfur oxides, in particular sulfur dioxide, and the nitrogen oxides contained in the said fumes in corresponding acids, then, in a reactor, the said fumes are brought to low temperature in contact with carbonate blocks to retain by chemical reaction the acids previously formed.

Preferably, the carbonate blocks are consist of, or mainly include calcium carbonate, such as limestones, dolomites, marbles.

Another subject of the invention is a device for the dry removal of oxides of sulfur and nitrogen, in particular sulfur dioxide, contained in the fumes from industrial boilers or the like, from the combustion of coals such as coal, lignite or other petroleum products containing sulfur, characterized in that it comprises: - a processing chamber which is intended to be connected to the outlet of an industrial boiler or the like and which is provided with means of steam supply, and

- a reactor which is intended to be connected to the transformation chamber and which contains carbonate blocks.

The invention will now be described in more detail with the aid of an exemplary embodiment of a device according to the invention given by way of illustration and not limitation as well as the appended drawings in which:

FIG. 1 is a schematic sectional view of a device according to the invention,

FIG. 2 is a comparative diagram representing the residual sulfur contents of the combustion gases as a function of the temperature after treatment according to the invention with the addition of water (curve A) or with the same filter but without the addition of water ( curve B).

Referring to Figure 1, we see that a device 1 according to the invention comprises a duct 2, through which the combustion gases arrive in the direction of arrow E, connected to an industrial boiler or the like used to burn coal, coal or lignite or other petroleum products containing sulfur.

The conduit 2 opens into a transformation chamber 4 in which the sulfur oxides, essentially sulfur dioxide, and the nitrogen oxides which are formed during combustion by reaction with oxygen, are converted into corresponding acids, essentially in sulfuric acid.

To this end, the transformation chamber 4 is provided with a water vapor supply system 6 making it possible to supply the quantity of water vapor necessary to transform the oxides of sulfur and nitrogen into corresponding acids, in particular sulfur dioxide to sulfuric acid. The supply 6 can be carried out by injecting steam or by spraying water under conditions allowing its transformation into steam.

Blocks 8 made of material resistant to acids derived from oxides of sulfur and nitrogen, in particular to sulfuric and nitric acids, are advantageously placed in chamber 4 to form baffles and promote the mixing of water vapor and fumes. It can be blocks of silicon or silicate rocks, bricks, etc.

The device comprises a conduit 10 intended to bring the gases charged with acids coming from the transformation chamber 4 to the reactor 12 serving as a filter proper.

According to the embodiment shown here, the reactor 12 consists of a reaction column but other types of reactor can also be used.

Column 12 is filled with carbonate blocks 14. They can be blocks of natural carbonates such as limestones, dolomites or marbles. These blocks advantageously have dimensions of between approximately 20 and 250 mm and preferably between 50 and 100 mm. To introduce the carbonate blocks 14 into the reaction column 12, the device comprises a hopper 16 connected to transport means 18 consisting for example of a bucket conveyor, known per se, and opening at the upper end of the column 12. Means 20 of any known type for controlling the filling level of the column 12 can be provided.

Column 12 is also provided at its lower part with means 22 for extracting carbonate blocks, associated with screening means 24. These means 22 and 24 are intended to allow, during use, to remove the fines. resulting from the degradation of the carbonate blocks following their reaction with the acid vapors. These fines can clog the filter column and reduce the contact surface of the carbonate blocks and therefore disadvantage this reaction. Blocks of carbonates are thus extracted at times determined in particular by the operating conditions of the boiler, the pressure drops, the filling level of the filtration reactor, the analysis of the fumes, etc. After screening, the fines are evacuated through line 26 to a container 28 and the reusable carbonate blocks 14 are conveyed through line 30 to the transport means 18 as far as column 12. Blocks of fresh carbonates, that is to say say that have not yet been used for the treatment according to the invention, are also introduced through the hopper 16.

Column 12 therefore contains a mixture of blocks of fresh carbonates and blocks of recycled carbonates. This has an economic advantage and also makes it possible to maintain a large contact surface, suitable for efficient removal.

According to the invention, another solution to avoid the possible risks of clogging consists in filling the filtration reactor 12 with a mixture of carbonate blocks 14 and inert blocks such as granite, silicate, sandstone blocks, etc.

Column 12 advantageously contains, at its center, among the carbonate blocks 14, sheets 32, preferably inclined and intended to direct downward the flow of gas arriving through the conduit 10 and to increase their path through the stack of carbonate blocks. This makes it possible to use all the carbonate blocks present, even those located at the bottom of the column, and to increase the residence time of the gases in contact with them. Advantageously, these sheets 32 are arranged in the column, so as to preserve, in the stack of blocks, an empty space of blocks 14 increasing the dispersion of the gas flow towards said blocks.

Finally, the device is provided at its upper part with a duct 34 for the evacuation of the purified gases according to arrow S.

Of course, the components of the device according to the invention are made of material resistant to attack by acid compounds and in particular sulfuric acid.

The device can be combined with means of measurement of the sulfur and nitrogen content, these means being available at the inlet E and at the outlet S in order to control the supply of water vapor by the means 6 into the transformation chamber 4. This is advantageous d 'From an economic point of view because this makes it possible to provide only the quantity of water vapor necessary and sufficient as a function of the content of oxides of sulfur and nitrogen in the gases and to obtain maximum treatment efficiency.

Although the filter 12 also makes it possible to retain the dust present in the fumes, the device can include means, of any known type, making it possible to eliminate the dust up to the standards i posed, these means being arranged at the outlet of the boiler and before entering E. It is most often multicyclones.

According to the invention, an installation can be provided comprising two filtration reactors arranged in parallel and intended to operate alternately, in order to allow optimal continuous purification.

The smoke treatment according to the invention will now be described:

Considering the device described above, the combustion gases from the boiler, preferably dusted for example in a multicyclone, arrive in the device 1 through the conduit 2, at a temperature which corresponds substantially to the outlet temperature of the boiler, namely about 160 ^β C.

In chamber 4, these gases are retained by the blocks 8 and the sulfur dioxide, formed with oxygen during combustion, is transformed into sulfuric acid by reaction with oxygen in the air in the presence of water vapor.

The nitrogen compounds present also lead to the formation of acids. The conditions for transforming these oxides into corresponding acids, in particular the temperature conditions and the supply of water vapor to chamber 4, either by direct injection of water vapor or by transformation of the water sprayed into steam d are such that the dew point is not reached. There is therefore no condensation of the gas mixture.

The gases charged with acids are then brought, via the conduit 10, to the lower part of the filtration column 12 in which they are _rS subjected to an upward movement through the blocks of carbonates 14. When deε orientation sheets 32 εont provided, the gases first have a downward movement through the carbonate blocks and then an upward movement through said blocks around said sheets. The acids and in particular sulfuric acid, present in the fumes are then absorbed by the carbonate blocks with which they react to lead to water and to sulfates and nitrates. Calcium sulfate is formed in particular in the case of calcium carbonate blocks.

The calcium sulphate recovered can be used for other purposes or be transformed into sulfuric acid.

As an indication, a column 12 of approximately 10 meters in height and approximately 7 meters in diameter and a conduit 2 of approximately 1.5 meters in diameter makes it possible to treat approximately 100,000 πr of gas per hour. For a boiler with an hourly consumption of approximately 7.5 tonnes of coal containing 1.4% sulfur, the water consumption is approximately 2.52 tonnes per day and the consumption in blocks of calcium carbonates is 7.56 tonnes per day.

According to the invention, at least 70% of the sulfur present in the combustion gases can be eliminated.

Figure 2 highlights the effectiveness of the treatment according to the invention. Curve A illustrates the residual sulfur content in the gases after treatment according to the invention, while curve B illustrates the sulfur content after passing through the carbonate block filter but without prior transformation of the sulfur dioxide in the presence of water. .

We see that after treatment εelon the invention at the outlet temperature of the boiler (about 160 ^β C), the residual sulfur content is less than 10% while using column 12 only, εanε water supply for the transformation into sulfuric acid, the sulfur content is of the order of 90%. This illustrates the ineffectiveness of known filters for removing sulfur at low temperatures.

According to another embodiment of the invention, the supply of water vapor allowing the transformation, at least in part _/ of sulfur and nitrogen oxides into corresponding acids, is carried out in situ σ'eεt-à- say during the combustion in the boiler.

In this case, organic matter comprising constituents is mixed with coals, in a suitable proportion according to the content of subsoiled and nitrogenous compounds. hydrogenated. It can be for example household waste, wood, paper, peat, etc.

During combustion, these materials produce water vapor which will allow the transformation into acid of some or all of the sulfur and nitrogen oxides formed.

According to another alternative, the amount of water necessary for the transformation into acid can be provided, at least in part, by sprinkling the coal in the boiler.

The fumes charged with acids at the outlet of the boiler are then directly brought into a filtration reactor containing blocks of carbonates, of the type described above, in order to trap, by chemical reaction, the acids formed during combustion. The treatment of gases in the filtration reactor is identical to the process previously described.

Of course, if the quantity of water supplied during combustion was not sufficient to allow the transformation of all of the oxides present, the smoke is first of all brought into a transformation chamber of the aforementioned type with, advantageously, a controlled water vapor supply, prior to the actual filtration step in the carbonate block reactor.

Claims

1. Process for the elimination of sulfur and nitrogen oxides, in particular sulfur dioxide, contained in fumes from industrial boilers or the like, from the combustion of coals such as coal, lignite and other products, in particular petroleum containing sulfur, of the dry type in which a solid material is used to retain by chemical reaction the acid compound contained in the said smoke, characterized in that it is transformed in the presence of water vapor, the sulfur oxides, in particular the sulphurous anhydride, and the nitrogen oxides contained in the said smoke with corresponding acids, then in a reactor, said fumes are brought to low temperature in contact with carbonate blocks to retain by chemical reaction the acids previously formed .

2. Method according to claim 1, caractériεé in that the fumes are substantially at the outlet temperature of the boiler or the like.

3. Method according to claim 1, characterized in that the combustion of coal is carried out in the presence of a certain amount of organic matter comprising hydrogenated compounds, intended to produce, at least in part, the necessary water vapor to the transformation of oxides of sulfur and nitrogen into corresponding acids.

4. Method according to claim 1, characterized in that the combustion of coals is carried out in the presence of a certain quantity of water intended to allow the transformation, at least in part, of sulfur and nitrogen oxides into corresponding acids.

5. Method according to any one of preceding claims, characterized in that, in a transformation chamber, the smoke is made to pass through blocks forming chiane, these blocks being made of material resistant to acids derived from oxides of sulfur and nitrogen and in that the said smoke is simultaneously subjected to an injection of water vapor or to a spraying of water forming water vapor.

6. A method according to claim 5, characterized in that the sulfur and nitrogen content of the smoke is measured at the outlet of the boiler or the like and at the outlet of the reactor in order to control the supply of water vapor. in the transformation chamber.

7. Method according to any one of the preceding claims, characterized in that the carbonate blocks are made up of or comprise natural carbonates such as limestone, dolomite or tree.

8. Method according to any one of the preceding claims, characterized in that the blocks of carbonate have dimensions between approximately 20 and 250 mm, preferably between 50 and 100 mm.

9. Process according to any one of the preceding claims, characterized in that carbonate blocks which have reacted with the smoke are extracted, they are separated from the fines formed by the reaction, and they are recycled.

10. Process according to any one of the preceding claims, characterized in that a mixture of carbonate blocks and inert blocks is used.

11. Process according to any one of previous claims, characterized in that the reactor consists of a column and in that the fumes charged with acids are passed from bottom to top in said column.

12. Method according to any one of the preceding claims, characterized in that the fumes are filtered beforehand to remove the dust.

13. Device for the dry removal of oxides of sulfur and nitrogen, in particular sulfur dioxide, contained in the fumes from industrial boilers or the like, from the combustion of coals such as coal, lignite or other petroleum products containing sulfur, characterized in that it comprises: - a transformation chamber (4) which is intended to be connected to the outlet of an industrial boiler or the like and which is provided with means for supplying steam water (6), and

- a reactor (12) which is intended to be connected to the transformation chamber (4) and which contains blocks of carbonates (14).

14. Device according to claim 13, characterized in that the water supply means (6) are made up of water vapor injectors or water sprayers.

15. Device according to one of claims 13 and 14, characterized in that the transformation chamber (4) contains blocks (8) of material resistant to acids derived from sulfur and nitrogen oxides, these blocks being intended to form baffles.

16. Device according to one of Claims 13 to 15, characterized in that the carbonate blocks (14) consist of or include natural carbonates such as limestone, dolomites or marble.

17. Device according to any one of Claims 13 to 16, characterized in that the reactor

(12) contains a mixture of carbonate blocks and inert blocks.

18. Device according to any one of Claims 13 to 17, characterized in that the carbonate blocks (14) have dimensions between approximately 50 and 250 mm, preferably 50 to 100 mm.

19. Diεpoεitif εelon one of claims 13 to 18, characterized in that the reactor is formed of a column (12) which eεt connected, at its lower part, to the transformation chamber (4).

20. Device according to claim 19, characterized in that the reactor (12) is provided at its lower part with extraction means (22) of carbonate blocks and of screening means (24) of blocks, intended to allow elimination of fine.

21. Device according to claim 20, characterized in that the reactor (12) is also provided with means (30,18) for recycling carbonate blocks.

22. Device according to any one of Claims 13 to 21, characterized in that it comprises means for controlling the supply of water vapor into the transformation chamber, as a function of the sulfur and nitrogen content. smoke.

23. Device according to any one of claims 13 to 22, characterized in that it is connected to means for eliminating leε pouεεièreε. 18

24. Device according to any one of claims 13 to 23, characterized in that it comprises orientation sheets (32) for orienting the smoke towards the base of a column.

25. Installation for the treatment of fumes from industrial boilers or the like, for burning coal such as coal, lignite or other petroleum products containing sulfur, characterized in that it comprises at least one device according to any one of claims 13 to 24.