PROCEDURE FOR SEPARATING BURNED GAS BURN SULFUR. - uescr i pe on The invention is retained by a process for separating azur dioxide from combusted or combustion gases, in which combusted or combustion gas is passed through seawater in an absorption tower, and then the seawater charged with azurite compounds is extracted from the liquid collector of the absorption tower, to feed seawater tresca in a subsequent reaction tank. The processes of gas purification in which seawater is used as an absorption liquid, to separate azutre dioxide from a burned gas or combustion stream, are known, for example, from patent document DE 23 22 958. Such procedures have found practical application and are carried out in some coastal places (? Ertahrenstechn ik 25 1991) No. 9 pages. 12-14 > . The processes use the bicarbonates contained in the seawater to transform the S02 that is abso into innocuous sulfonates. The amount of washing liquid that is required in the absorption zone is determined by the transition or passage of matter, from the gaseous phase to the liquid phase. Within the scope of the known measures, we work with as little as possible of washing liquid. To minimize the requirement of washing liquid, a column with filling bodies is used, which guarantees a good exchange of substances. ? Seawater is used as washing liquid, then, in the case that the washing liquid requirement is predetermined, the amount of bicarbonate must also be established.
"Available, usually only enough to link
- a traction of the amount of S02 abso, while by far the greater part of the amount of S02, in
The solution, which is free of solids, is removed with the liquid from the liquid collector of the absorption tower. In addition, the liquid - due to the high partial pressure of C02 of the combusted gas or combustion - is saturated with C02. Experience has shown that in
The liquid collector of the absorption tower establishes a pH value in the range of 2 to 3. In the subsequent reaction tank, the liquid extracted from the absorption tower is mixed with fresh seawater. whose quantity is calculated in such a way that the
The bicarbonate content should be sufficient to neutralize the separated azerre dioxide. It is necessary to intensively ventilate the content of the subsequent reaction tank, on the one hand to promote the formation of sulphate, and on the other hand for the purpose of expelling C02.
2b Large amounts of air are required with the corresponding compressor capacities. And this must be added that the rate of oxidation, which depends on the pH, is relatively small in a range above the pH of 5.5 that exists in the subsequent reaction tank. Therefore, it is imperative to work with large reservoirs, in order to guarantee a long enough time for the liquid to stay, for the complete or total sulphate formation. The practice shows that the ventilated rear reaction tank has to be dimensioned for a time of stay of 10 to 15 minutes, in order that the reactions can continue until its total completion. Another problem is represented by a bad smell that occasionally occurs in the region of the subsequent reaction tank. This is due to the escape of unbound S02 from the liquid that flows into the subsequent reaction tank, after having been extracted from the liquid collector of the absorption tower. In addition, it is hardly possible to remove the unbound 302, even resorting to strong ventilation. The invention proposes the task of developing the procedure described at the beginning in such a way that it is possible to work with a smaller subsequent reaction tank, and the discomfort due to the bad odors due to the S02 released is avoided with full certainty. It is also intended to reduce the amount of oxidation air that is required. The object of the invention, which in turn represents the solution of this task, is a procedure for separating sulfur dioxide from burned or combustion gases, in which burnt or combustion gas is passed through seawater in an absorption tower, in which the liquid collector of the absorption tower is ventilated, whereby the bisulfites contained in the liquid are transformed into biofoules, in which the liquid is extracted from the liquid collector of the absorption tower and, in order to form sulphates and achieve neutralization, is mixed with fresh seawater in a subsequent reaction tank, in which the pH value of the liquid extracted from the liquid collector of the absorption tower is measured, and the deviations of the values are determined measured with respect to a nominal value of pH established in the range of pH 4.0 to pH 5, and in which, according to the deviations of the measured values, it is regulated, or else an additional torrent of seawater is added. imenta directly e to the wash liquid collector, or a liquid flow that is returned from the liquid collector, to the absorption zone of the tower. Preferably, the nominal value of the pH in the liquid collector is established in the range between pH 4.15 and pH 4.5. Additionally, by addition of fresh seawater, a pH value of at least 6 is preferably set in the subsequent reaction tank. In the process according to the invention, the oxidation of the desulfurization products is carried in the liquid collector of the absorption tower, being that the total amount of water that is added to the absorption tower is calculated in such a way, that the bicarbonate content is sufficient for a trans of sulfur dioxide absorbed, in bisulfites. The amount of washing liquid that is added to the absorption zone of the loft tower is calculated independently of the chemical reactions described, so that the absorption tower achieves a scrubbing performance that is defined as the ratio between concentration to the salt and the concentration at the entrance, of the 302 of the flue gas or of combustion. It is preferable to work with an absorption tower having an absorption zone 1 of internal structures, and dimensioned for a large specific flow rate of liquid per unit area. If the amount of washing liquid required in the absorption zone is so small, that the amount of the bicarbonate contained in the seawater is not sufficient to chemically absorb the absorbed sulfur dioxide, then
- it will be necessary to resort to the regulation according to the invention, of the additional torrent of sea water that is directly immersed in the washing liquid collector. If, on the other hand, the amount of liquid required to wash the gas is already so great that with the addition of seawater bicarbonate amounts are in excess of the stoichiometry, then, according to the invention, a current is returned of liquid from the liquid collector to the absorption zone of the tower, regulating the quantity of this current so that in the liquid collector of the absorption tower a pH value corresponding to the pre-established nominal value is established. By means of the return of the washing liquid it is possible to determine the amount of bicarbonate available in the absorption tower and the hydraulic load of the absorption zone of the tower independently of each other. It is understood that in the case of operating in this manner, the direct sending of the additional torrent of seawater to the liquid collector of 1 avado is suppressed. With the process according to the invention, by virtue of the pH management in the liquid collector of the absorption tower, it is guaranteed that in the liquid extracted from the liquid collector, it is not dissolved 302, without equal, that it could escape during the subsequent treatment in the subsequent reaction tank, causing discomfort due to bad odors. Sulfur dioxide separated in the absorption zone is converted into bisulfites in the liquid collector, or into bisulfates through the collector ventilation. The adjustment of the pH value according to the invention, in the range between pH 4.0 and pH 5, preferably between pH 4.15 and pH 4.5, guarantees a maximum concentration of bisulfite in the relatively small partial liquid stream of the absorption tower, and It creates the preconditions for a rapid trans-formation in bisulfates. By virtue of the highly acidic environment, a high reaction rate is guaranteed, which results in a short period of time for the liquid in the liquid collector of the absorption tower. Depending on the type of combustion or combustion gases and the quality of the seawater, the necessary time of stay fluctuates between 1 and 2 -5 minutes approximately. By virtue of the optimal conditions that are adjusted according to the invention (small liquid stream, higher oxidation rate), the oxidation in the tower washing liquid or absorption column can be carried out with a relatively low investment in equipment for the plant. Due to the reduced volume of liquid, it is also possible,
- work with relatively small amounts of oxygen air. 10 With the oxidation air, the liquid in the liquid collector of the absorption tower is effectively freed from carbon dioxide. We continue with the expulsion of C02 from an almost saturated solution of C02. The liquid collector of the absorption tower is extracted with partially neutralized residual water with the intermediate product bisulfate, and mixed in the subsequent reaction tank with fresh seawater in order to complete the neutralization and the formation of sulphates. . In general, a
ventilation of the subsequent reaction tank, since on the one hand the oxidation of the bisulphites to form bisulfates was carried out in its entirety, in the liquid collector of the absorption tower, and on the other hand important quantities were already expelled. of C02 of
2b l l liquid due to the ventilation of the Tiquido collector. In comparison with the state of the art mentioned at the beginning, it is possible to work with a considerably smaller subsequent reaction tank. The amount of air required and the energy requirements to compress the oxidation air are also lower. It is convenient to cool the air current used to ventilate the liquid collector by injecting water, before it enters the wash liquid collector. The invention will now be explained in more detail on the basis of a drawing that cynically illustrates an embodiment example. A plant for separating sulfur dioxide from burned or combustion gases is shown schematically in Fig. 1 in Figs. 2 and 3 the chemical reactions that take place in the plant, depending on the amount of seawater with respect to the burned gas stream, in Fig. 4 The distribution of the equimolar balance of dissolved sulfur dioxide, bisulfite and ions of sulfite in seawater, depending on the - pH value. The fundamental structure of the plant illustrated in Ftg. 1 consists of an absorption tower 1 connected to a combustion or combustion gas system 2, a seawater pumping station 3, a subsequent reaction tank 4, seawater supply pipes 5 absorption tower 1 and the subsequent reaction tank 4, as well as also a ventilation installation 7 connected to the liquid collector 6 of the absorption tower 1, and having a compressor 8 of air and air lances 9 arranged in the 6 liquid collector. In the exemplary embodiment, the absorption tower 1 is designed as a countercurrent scrubber, where seawater is fed to the absorption zone 10 of the tower through one or more nozzle planes. The absorption zone 10 of the tower does not present internal structures. The liquid from the liquid collector 6 of the absorption tower 1 reaches the subsequent reaction tank 4 through a pipe 11. From the subsequent reaction tank 4 the treated slops 12 are returned to the sea. The alkalinity of seawater, which is usually = and indicated as HC03, is used to bind and neutralize the amount of S02 absorbed from the burned or combustion gas. Normal seawater, with a uniformity of 19 g / kg, has a HC03 content of 0.14 g / kg. Depending on the origin of the seawater, the bicarbonate content can be up to 0.32 g / kg (Gulf of Arabia), where the values indicated represent average values or subject to local differences is considerable, for example in bays. i as or in the vicinity
- from the mouths of the rivers < ULLMANN, Volume 24, pages. 213/214). lü To the lost or exhaust gas seawater is passed into the absorption tower, whereby the sulfur dioxide in the form of gas containing the burned gas, is physically absorbed by the seawater used as a washing liquid : iS + H20 S02 (gas) > S02 (L) di loose
The total amount of seawater fed to the absorption tower is calculated in such a way that the
The bicarbonate contained in seawater is only sufficient for a trans steaming of absorbed sulfur dioxide in bisulfites. The liquid collector 6 of the absorption tower 1 is vented, whereby the bisulfites are converted into bisulfates. Inside
of the liquid collector 6 a p-arial reaction and an oxidation takes place, which is reproduced in a simplified manner by means of the following equation of sums:
S02 < L) + 0 < L > + HC03 > HS04 + C02 (L)
The liquid containing bisulfates is extracted from the collector or liquid of the absorption tower 1, and
- Fresh seawater is supplied to the subsequent reaction tank 4, in order to form sulfates and to grade the pH. The formation of sulphates in the subsequent reaction tank 4 can be reproduced in a simplified manner by the following equation of sums:
HS04 + HC03 > S04 + H20 + C02 < L > 0 The chemical reactions that take place in the plant are illustrated as a model in Fig. 2. On the abscissa is graphically represented the amount of sea water that = e feeds the plant, with respect to 0 the volumetric current of the plant. burnt or combustion gas, L / G in l / m3. In the ordinate, the molar amounts of the starting and reaction products, in each case with respect to the molar amount of the S02 of the gas or combustion or combustion, are graphically represented in percentage of moles. The degree n of washing effectiveness is also represented graphically. They are graphically represented: as curve trace QABC ** D **, the amount of S02 separated < S02, Sep./S02, int.), As curve trace OBCD, the quantity of bicarbonate metered (HC03, int./S02, int.), Being that the trace of line 0BCD2 represents the total amount of bicarbonate transformed < HC03, reacc oned / S02, int.), And the trace of the OB line repersens the cynically transformed amount in the absorption tower. as curve trace OMA ** B **, the pro rata of free S02 in the solution < S02, dis./S02, int.), Which corresponds to the difference between separated S02 and transformed bicarbonate, as line trace C1D1, the remaining bicarbonate, untransformed (HC03, sob./S02, int.) In the tank of subsequent reaction, as line trace 0BC1, the increase and decrease of the bisulfates (HS04 / S02 int.) in the liquid collector of the absorption tower, and in the subsequent reaction tank, as line trace B * * C **, the corresponding increase of the sulfates'. S04 / S02, int.) In the subsequent reaction tank, such as lines OA *, A * B *, B * C *, the content of C02 dissolved in the liquid (C02, d? s./S02, int.) In the absorption zone 10 of absorption tower 1 a saturation with C02 of the water of
O mar (line OA *). In the liquid collector, the
C02 by oxidation air (l ine A * B *). Due to the subsequent reaction, in the reaction tank 4
- Subsequently, an enrichment takes place again with regard to the dissolved carbon dioxide in the 10 washings (line B * C *). The pH value of the washings 12 extracted from the subsequent reaction tank 4 is determined by the concentrations of C02 l ibre (point D ') and the excess bicarbonate (point DI). The best way to influence them is through a
increase in the total amount of seawater that is used. Additionally, there is also the possibility of exerting an influence imitated by the expulsion of C02 in the deposit 4 of subsequent reaction. Fig. 2 refers to a form of operation
0 of the plant, in which the seawater is added to the absorption tower 1 in partial torrents. A first partial torrent is imbedded as a washing liquid to one or more nozzle planes of the absorption zone 10 of the tower. The amount of bicarbonate of liquid
Washing is not enough to chemically completely remove the amount of S02 absorbed. To compensate for the bicarbonate requirement, an additional stream of sea water is fed through a pipe 13 directly to the liquid collector 6. 5 It can also be presented that the amount of liquid to wash the gas in the absorption zone is so great that, when using seawater
As the washing liquid, amounts of bicarbonate in excess of the stoichiometry are fed to the absorption tower 1 with the influx 5 of liquid. This case occurs especially when the concentration of S02 in the burned gas or combustion is low, and seawater is available with a high portion of bicarbonates. In a case like this, the invention teaches that from the
liquid collector or return a stream of liquid through the return pipe 14, to the absorption zone 10, to reduce the amount of bicarbonate in excess of the stoichiometry. By the return of the washing liquid can be regulated independently
of each other, the amount of bicarbonate available in the absorption tower 1 and the hydraulic load of the absorption zone 10 of the tower. Fig. 3 illustrates the chemical processes of the plant corresponding to this case. The dosage of fresh water through pipe 13 to
• 25 liquid collector 6 of absorption tower 1
suppresses The sulphate formation reaction is already carried out partially in the liquid collector 6 of the absorption tower, as can be seen in Fig. 3. With the help of the stream 14 of liquid returned from the liquid collector 6 to the absorption zone 10, the amount of bicarbonate available for chemical reactions can be regulated. Both the additional stream of seawater 13, as well as the stream 14 of liquid returned to the absorption zone 10, can be regulated. The regulation of the quantity operates depending on the pH value of the liquid extracted from the liquid collector 6. For this purpose, the plant illustrated in Fig. 1 is equipped with a measuring and control device 15, with a sensor 16 for capturing the actual pH value, as well as control devices 17 for regulating the amount of the additional water stream of sea, as well as that of the stream 14 of liquid that is returned from the collector or liquid to the absorption zone 10. The pH value of the liquid extracted from the liquid collector 6 of the absorption tower 1 is measured, and the deviations of the measured values are determined, with respect to a pre-established nominal value in the range of pH 4.15 to pH 4.5. According to these deviations from the measured values, the quantity of the additional stream of seawater 13 that is fed to the liquid collector 6 or that of the liquid stream 14 that is returned from the liquid collector 6 is regulated. the absorption zone 10. By means of the volumetric regulation depending on the pH, the pH of the liquid collector 6 remains constant within very narrow tolerance limits, between pH 4.15 and pH 4.5. The regulation according to the invention is comprehensible on the basis of the distribution of the equimolar represented in FIG. 4, of the unbound dissolved S02, of the bisulfite and of the sulphite ions in the seawater. For the Ftg. 4 it is deduced that with the sea water used, the maximum concentration of bisulfite is to be expected with a pH of 4.15. In the case of a lower pH value, dissolved solids, not dissolved, are still in solution, while smaller amounts of sulphite ions are found at higher pH values. Through the procedure according to the invention, which provides for accurate dosing and regulation of seawater, it is guaranteed that the 302 separated in the washing liquid will be completely leaked, and will not be present in solution, as S02 is not stated. By adjusting the pH according to =. The invention, and in the range of pH comprised between pH 4.15 and pH 4.5, is further ensured that the pH value of the liquid extracted from 1 to absorption tower 1, and that im- posed to the subsequent reaction tank 4, is located very close to the optimum point for sulfite formation. The measures according to the invention have the consequence that the liquid which is introduced into the subsequent reaction tank is odor-free, since S02 can not be released in the form of a gas, and that the desired oxidation in the collector 6 of liquid develops very fast, under
- of the high concentration of bisulfite at 1 rein reignant.
Due to the high oxidation speed, it is possible to work with very short periods of time of the liquid in the collector or liquid. Depending on the type of gas burned or combusted, and depending on the quality of the seawater, a period of time between 1 and 2.5 minutes is sufficient. In the subsequent reaction tank 4, a pH value is adjusted between pH, O. and pH 7, by the addition of fresh seawater. Of the total seawater that is fed to the plant, approximately 1/3 correspond to the washing tower 1 and approximately 2/3 to the subsequent reaction tank 4. Since the oxidation has been transferred to the washing liquid collector 6, it is possible to work with quantities of air which are significantly lower than those required by the current state of the art, in which the oxidation takes place in the tank 4. of subsequent reaction. It is convenient to make a cooling of the air flow used for ventilation, by water injection. For this purpose, the ventilation installation 7 comprises a mixing chamber 18 for cooling water, and seawater can be used as water for cooling.