FR2722112A1 - Desulphurisation of gases - Google Patents

Abstract

Gases contg. at least one oxide of sulphur are desulphurised by treatment with a synthesised prod. comprising a majority of CaCO3 which is at least partly made by a chemical reaction carried out in the presence of a carbonate, bicarbonate and/or CO2. Also claimed is the CaCO3.contg. compsn..

Description

The present invention relates to a synthetic product used

  especially in processes for desulfurization of products.

  It finds in particular its application for the desulfurization of gaseous compounds, such as gaseous effluents, comprising, for example

  sulfur or nitrogen compounds such as oxides of sulfur and nitrogen.

  In protected areas, strict regulations limit the emission of sulfur oxides by gaseous effluents, notably from heat generators, and prohibit the use of fuels with a high sulfur content, which, moreover, can have certain economic advantages. . Various technological solutions described in the applications and patent of the applicant FR-2. 609.150, FR-2.636.720 use installations in which absorbents are used in the form of a circulating bed or entrained bed, the function of which is to desulfurize the gaseous effluents passing through these installations. The absorbents used are in most cases powdered calcium absorbents in the form of a suspension or in the form of a dry powder capable of capturing the sulfur oxides. It is also possible to use, for example as described in the French application

  FR-2,671,855 so-called regenerable absorbents of the magnesian type.

  In general, the absorbents most frequently used in this type of process are limestones (CaCO3), dolomites (CaMg (CO3) 2) or compounds (Ca xMg 1-x CO3), and all come from deposits

natural.

  Obtaining such compounds, in particular their extraction leads to non-negligible costs which contribute to an increase in production costs

  such desulfurization processes.

  In addition, this extraction contributes to the depletion of natural deposits

  forming the source of these compounds or absorbents.

  In the remainder of the text, the term absorbent is used to designate

  synthetic products used for the desulfurization of compounds.

  The invention, which is the subject of the patent, consists of a synthetic product mainly comprising calcium carbonate and its use, for example, as an absorbent for desulfurizing gaseous compounds, especially

  gaseous effluents containing sulfur or nitrogen compounds.

  The use of synthetic products from, for example, discharges from certain industries have zero or even negative cost, which makes it possible to reduce the costs of the desulfurization processes and therefore has an economic advantage.

  compared to the use of natural absorbents.

  The use, for example, of these absorbents in devices such as combustion boilers eliminates, in addition, the step of prior grinding of limestone rocks carried out to obtain a fine absorbent allowing

  to increase the performance of these operations.

  In addition, the principle consisting in using rejects eliminates any problem relating to the problem of congestion of these rejects requiring for example a

  recycling, or storage, these two operations are not always easy.

  In addition, the exploitation of these "deposits" from industries,

  allows better preservation of natural resources.

  The present invention relates to a process for desulfurization of at least one gaseous compound containing at least one sulfur compound such as sulfur oxides. It is characterized in that said gaseous compound is brought into contact with at least one synthetic product containing predominantly calcium carbonate and in that at least part of said synthetic product results from a chemical reaction carried out in presence of a reagent derived from carbonic acid chosen from the following group: carbon dioxide, carbonate or

hydrogencarbonate of an element.

  The gaseous compound is, for example, in the form of a gaseous effluent in an enclosure and said synthetic product is injected in the form of

dough in the enclosure.

  It can also be in the form of a gaseous effluent in an enclosure

  and said synthetic product is injected in suspension in the enclosure.

  During the process, it is possible to carry out a preliminary drying step of the synthesis product before it is brought into contact with the gaseous compound to be desulfurized and said dried synthesis product is conditioned to avoid agglomeration of the grains of said synthesis product obtained after operation of

drying.

  Mixing, for example, the synthetic product presented under

  paste form to a drying element such as lime.

  One can use a synthetic product from the sugar industry such

than candy scum.

  One can also use a synthetic product from the paper industry. The use of the synthetic product applies particularly well to the desulfurization of a gaseous compound which is in the form of a gaseous effluent. The present invention also relates to a synthetic product used to desulfurize at least one gaseous compound. It is characterized in that it contains mainly calcium carbonate and in that at least a part of said synthetic product results from a chemical reaction carried out in the presence of a reagent derived from carbonic acid chosen from next group: gas

  carbonic, carbonate or hydrogen carbonate of an element.

  The synthetic product can comprise at least 50% and preferably at

  minus 80% calcium carbonate by mass on a dry basis.

  It may result from a chemical reaction such as precipitation of milk from

lime with carbon dioxide.

  The synthetic product results, for example, from a chemical reaction

  having calcium carbonate as a co-product.

  The product can be a sugar scum and / or a reject from the paper industry. The synthetic product contains, for example, impurities such as hydrocarbonaceous materials or nitrogen compounds such as ammonium salts. The synthetic product is, for example, in the form of a paste comprising at least one aqueous part and calcium carbonate under

grain form.

  The use of the synthetic products obtained according to the invention notably offers the advantages of reducing the cost of desulphurization processes by using industrial waste and of preserving the natural deposits of the products usually used in the prior art. In addition, such use makes it possible in certain cases to optimize the yield of these operations. The characteristics and advantages of the invention will appear better after

  the description which follows, given by way of explanation and in no way limiting, in relation

  to the plates showing the structure of the products used.

  Certain basic elements making it possible to implement the method according to the invention are known to those skilled in the art. They will therefore not

  described in detail in the description, only their specific function and / or their

  relationship with other elements will be stated. It is the same for certain devices described in patent applications and the aforementioned and cited patents

  in the description given below.

  The process, in order to better understand the invention, will be described for its application to the desulfurization of gaseous compounds in the form of gaseous effluents comprising at least sulfur compounds, in particular

  sulfur oxides. This description is in no way limited to the desulfurization of

  these effluents but of course extends to the desulfurization of all compounds

  gaseous comprising, in particular sulfur compounds.

  The synthetic product comes, for example, from rejections from certain industries, such as the sugar or paper industries. It mainly contains calcium carbonate and can be in the form of a paste

  consisting mainly of water and fine grains of calcium carbonate.

  The grains of calcium carbonate are, for example, of the order of

a few microns.

  It is possible to widen the field of industries which constitute the source of discharges to the agro-food industries or possibly fertilizers,

for example.

  Discharges or synthetic products from these industries and used to desulfurize compounds, are distinguished, for example, by their

genesis process.

  Thus, synthetic products result in the majority of cases from a chemical reaction involving compounds reacting with each other in the presence of a reagent derived from carbonic acid. This reagent can be chosen from one of the compounds of the following group: carbon dioxide, carbonate or a hydrogen carbonate of an element. The chemical reaction takes place from

  preferably in the liquid phase, for example in the aqueous phase, such as water.

  The synthetic product results, for example from precipitation of milk from

lime with carbon dioxide.

  It can also be the result of a chemical reaction having carbonate

calcium as a co-product.

  The synthetic product obtained by one of the previously mentioned chemical reactions is, for example, in the form of a paste comprising an aqueous phase, such as water, and fine grains of calcium carbonate. The carbonate grains are found in a proportion at least equal to 50% of the whole by mass on a dry basis, this proportion

  being, preferably at least equal to 80%.

  The conditions under which the synthesis reaction of the aforementioned products is carried out can be chosen so as to promote the development of their crystalline structure, in particular to obtain a product

  synthetic with a large internal free surface and high porosity.

  These two parameters are involved in particular in optimizing the performance of gaseous effluent desulphurization processes comprising

sulfur compounds.

  An advantageous application of the invention consists in using synthetic products from the sugar industry, such as sugar scum, in particular for desulfurizing gaseous effluents from, for example, heat generators, such as the devices described. in the requests and

Applicant's patents cited above.

  Thus, the use of sugar scum comprising fine grains of calcium carbonate with an average particle size of approximately 5 microns makes it possible to obtain a desulfurization yield of 80% with a Ca / S molar ratio of 2. Under conditions substantially identical operating limestones of grain size with characteristics substantially

  similar, lead to a yield of around 70%.

  The desulfurization process described in detail in the applications for

  patents and the above-mentioned patents is briefly recalled below.

  The principle of desulphurization consists in bringing into contact, for example, in an enclosure or desulphurization chamber, a gaseous effluent comprising sulfur compounds such as sulfur oxides, and a synthetic product also called absorbent. In this exemplary embodiment, candy scum is used, for example, as absorbent under operating conditions.

  defined temperatures, controlled atmosphere.

  Operating conditions temperatures are in the range

  varying from 400 and 1300 C and preferably between 750 and 1200 C.

  When it is brought into contact with the gaseous effluent to be desulfurized, the sugar scum at least partially absorbs the sulfur compounds contained in the gaseous effluent, the aim sought of course being to absorb the majority and even all of these sulfur compounds. The degree of absorption of the sulfur-containing compounds depends in particular on the nature and the properties of the synthetic product. Various ways of proceeding to inject the absorbent can be envisaged. Thus, in the specific case of the use of sugar scum, these scum can be injected into a desulphurization chamber, for example, in the form of a paste or a suspension having a dryness at least equal to 30% and preferably greater than 50%. The dispersion of the paste or of the suspension is carried out with conventional injectors, known to those skilled in the art, which ensure good distribution of the product over the entire effluent.

gaseous to be treated.

  This injection mode is particularly well suited for injection

  absorbent comprising a certain amount of water.

  When it is desired to use the candy or absorbent scum in dry form, it is possible to subject these scum to a preliminary drying step, which can be carried out by conventional devices known to specialists, which make it possible to eliminate practically all of them. the aqueous part enclosed by the sugar scum. The dried foam can then be packaged to avoid agglomeration of the carbonate grains.

calcium.

  The dried and conditioned products are then sent to the desulphurization chamber in which they are brought into contact with gaseous effluents containing sulfur compounds and where they play their role of absorbent. Another possibility offered by the dry process use of synthetic products, consists in mixing the sugar scum in the form of a paste, with a product, such as lime whose function is in particular to increase the value of dryness of the synthetic product. The use of lime under defined conditions makes it possible to obtain, for example, a synthetic product whose dryness value is at least equal to 80% and which have characteristics allowing it to be used in equipment.

  conventional for natural limestones or powdered lime.

  The use of sugar scum in the form of a paste or pulp contributes to optimizing their dispersion in the gaseous effluent, this compound

  which may be in the form of fumes to be desulfurized.

  Thus, the distribution of the sugar scum used as absorbent in the fumes to be desulfurized is in this way more homogeneous, this homogenization making it possible, in particular, to optimize the yields of the desulfurization processes, for absorbent-gaseous effluent contact times.

identical desulphurizers.

  This description applies of course to all synthetic products

  having characteristics suitable for trapping sulfur compounds

contained in products.

  It has also been noted that synthetic products from the sugar or other industries may include impurities which act as a reducing agent. In this case, the impurities act in particular on the effluents also comprising nitrogen compounds, such as nitrogen oxides. The role of reducing agent of such impurities contributes to optimizing the desulphurization yield processes by adding a process

denitrification.

  These impurities can be hydrocarbonaceous materials or nitrogen compounds, such as ammonium salts which contribute to a reduction

additional nitrogen oxides.

  The table below groups together examples of synthetic products from the sugar and paper industries, the crystal structure of which appears in particular in FIGS. 1 and 2, as well as the yields obtained on a device such as that described in application FR.2.636. 720 of the applicant and for the following operating conditions Desulfurization temperature: 750 C to 1000 C, residence time of the fumes to be desulfurized from 1 to 3 seconds, by

example.

  Specific surface Nature of the Composition of the product Yield of the initial synthesis products of the device m2 / g Limestone CaC03 2.0 70% with recycling Pulp of CaC03 16 80% without sugar recycling

Claims (11)

  1) Process for desulfurization of at least one gaseous compound containing at least one sulfur compound such as sulfur oxides, characterized in that said gaseous compound is brought into contact with at least one synthetic product containing predominantly calcium carbonate and in that at least part of said synthesis product results from a chemical reaction carried out in the presence of a reagent derived from carbonic acid chosen from the following group: gas   carbonic, carbonate or hydrogen carbonate of an element.   2) Desulfurization process according to claim 1, characterized in that the gaseous compound is in the form of gaseous effluent in an enclosure and   Said synthetic product is injected in the form of a paste into the enclosure.   3) Desulfurization process according to claim 1, characterized in that the gaseous compound is in the form of gaseous effluent in an enclosure and   said synthetic product is injected in suspension in the enclosure.   4) Desulfurization process according to one of the preceding claims,   characterized in that a preliminary drying step of the synthesis product is carried out before it is brought into contact with the gaseous compound to be desulfurized and said dried synthesis product is conditioned to avoid agglomeration of the   grains of said synthetic product obtained after the drying operation.   ) Desulfurization process according to claim 4, characterized in that said synthesis product in the form of a paste is mixed with a   desiccant such as lime.   6) Desulfurization process according to one of the preceding claims,   characterized in that a synthetic product from the industry is used   sugar such as candy scum.   7) Desulfurization process according to one of the preceding claims,   characterized in that a synthetic product from the paper industry is used. 1 ()   8) Application of the method and use of the product according to one of the claims   preceding the desulfurization of a gaseous compound having the form of a gaseous effluent.   9) Synthetic product for desulfurizing at least one gaseous compound containing at least one sulfur compound such as sulfur oxides, characterized in that it contains predominantly calcium carbonate and in that at least part of said synthetic product results from a chemical reaction carried out in the presence of a reagent derived from carbonic acid chosen from the following group: gas   carbonic, carbonate or hydrogen carbonate of an element.   ) Synthetic product according to claim 9, characterized in that it comprises at least 50% and preferably at least 80% of carbonate mass calcium on a dry basis.   11) Synthetic product according to claim 9, characterized in that it results from a chemical reaction such as precipitation of a lime milk with carbon dioxide. 12) Synthetic product according to claim 9, characterized in that it results   of a chemical reaction having calcium carbonate as a co-product.   13) Synthetic product according to claim 9, characterized in that the product is a foam of candy.   14) Synthetic product according to one of claims 9 to 13, characterized in that   that it contains impurities such as hydrocarbon materials.   ) Synthetic product according to one of claims 9 to 13, characterized in that   that it contains nitrogen compounds such as ammonium salts.