CZ287720B6 - Oxidation process of bottom product in absorption tower for desulfurizing combustion products and oxidation system for making the same - Google Patents

Abstract

The invented oxidation process is characterized in that bottom product (20) is recycled inside an absorption tower (10), whereby a portion thereof is caught and removed into a separate oxidation tank (32) next to the absorption tower (10). Liquid level inside this separate oxidation tank (32) is higher than liquid level (18) of the bottom product (20) in a recycling tank (16) of the absorption tower (10). Subsequently after oxidation in the oxidation tank (32) the oxidized bottom product (50) is returned back to the recycling tank (16), for instance through a line (40). In the present invention there is also claimed an oxidation system (48) intended for making the process and comprising the absorption tower (10) with a bottom recycling tank (16), collecting means (34), oxidation tank (32) and an injection means (22) for injecting oxidation air, whereby between the recycling tank (16) and the oxidation tank (32) there is arranged a connecting means such as a line (40) for keeping the level in the oxidation tank (32) higher than in the recycling tank (16) and for conveying the oxidized product from the oxidation tank (32) back in the recycling tank (16).

Description

A process for oxidizing a bottom product from a flue gas desulfurization absorption tower and an oxidation assembly for carrying out the process

Technical field

The invention relates to a process for the oxidation of wet flue gases of desulfurization absorption towers and in particular to a separate oxidation system for oxidizing a recycled bottom product before it is conveyed to a subsequent dewatering device.

BACKGROUND OF THE INVENTION

Oxidation of the wet flue gas bottom product in a FGD scrubber system is well known. Generally, oxidizing air is blown into the lower region of the absorption module recycling tank so as to provide enough oxygen to convert the sulfite ion (SCV) to the sulfate ion (SO ₄ ⁼ ). The purpose of this forced oxidation is to produce a final or waste product, such as gypsum or calcium sulfate dihydrate (CaSO ₄ 2ΗΌ), which can be easily drained and can later be sold and / or used in another way. In addition, the recirculation and oxidation tank can generally be integrated into the absorption tower to form a bottom thereof.

The oxidation can be carried out in a separate tank which is not part of the absorption tower, but this generally requires the addition of buffers and / or acid additives to assist the desired reaction and facilitate its progress. As a rule, the oxidation discussed above, which takes place outside the absorption tower in a separate tank, due to the chemistry changes therein, is too complex. Generally, sulfite (SO ⁼⁾ reacts with calcium (Ca ⁺⁺⁾ and precipitates as calcium sulfite hemihydrate (CaSO3 _^half Η Ο ₂₎ and thus is not due to the use of buffers and / or acidic additives for long term oxidation achievable.

Despite these difficulties, efforts have been made in the past to oxidize the bottom product or absorbent sludge in a smaller tank separated from the absorption tower. Typically, a portion of the bottom product is transferred from the absorption tower to a separate oxidation tank, the operation taking place in that smaller tank being part of the absorption cycle. The purpose of this conversion was to reduce the pH of the sludge for oxidation, since it is believed that this reduced pH will facilitate sludge oxidation. In addition, a smaller oxidation tank is more suitable for easier addition or mixing of additives and entrapped bottom product. In addition, this smaller tank provides a more even air distribution, meaning the cross-section of the tank. The separate oxidation tank and the absorption tower were essentially joined, allowing the bottom product to flow freely between the oxidation product and the absorption tower. Thus, the liquid level in both the oxidation tower and the absorption tower was and remained the same.

When designing the oxidation system for the bottom product, it is important to maintain the oxygen retention time in the sludge required to carry out the respective reactions, and it is therefore important to correctly select the oxygen injection level or position. If this retention time, or oxygen retention time, is too short, there will be no 100% conversion of sulfite to sulfate, resulting in reduced efficiency of the oxidation system. Therefore, it is envisaged that the oxidation air injection area of said tank should be located at least at a location at least 5.5 m below the operating level of the bottom product in said tank. Of course, the actual injection area may vary depending on the injection system selection and may range from about 4.88 m to 9.15 m below the bottom product level.

While for larger absorption towers that include larger recirculation tanks, meeting this requirement, ie the oxidation air injection area is approximately 4.88 m to 9.15 m below the bottom product, is easy, for smaller towers with smaller recirculation tanks so

- 1 CL 287720 B6 is not easy. In addition to the aforementioned requirement, the size of the tank is further dependent on the chemical reactions taking place, the SO ₂ evacuated, the availability of excess reagent, the level of contamination, etc., and a much smaller tank is sufficient to ensure the chemical reaction itself. Thus, it appears that the design of the much larger tank that is required to meet the oxidation air injection requirement is totally oversized in terms of the reaction itself. In smaller units that process smaller amounts of sulfur dioxide, the liquid height often does not reach 5.49 m and an increase in the unit as a whole to meet the requirement for the oxidation air injection position will result in a significant increase in the cost of the unit.

It is therefore an object of the invention to provide a means for achieving the desired level of oxidation injection without the need to construct a larger absorption tower. It is a further object of the invention to provide a separate tank adjacent to the absorption tower, such that the liquid level of the bottom product in said absorption tower and the liquid level of the bottom product in the 15 separate tank will not be the same. It is a further object of the present invention to provide a means for retaining the recycled bottom product and transferring it to this separate tank without the need for the same level in both the absorption tower and the tank. It is a further object of the invention to provide means for sizing an absorption tower without the need to increase its height in order to meet the requirement regarding the level of oxidation air injection. These and other objects and advantages of the invention will become clearer after studying the following part of the application.

SUMMARY OF THE INVENTION

As already mentioned, the invention provides a method of oxidizing a bottom product from a flue gas desulfurization absorption tower comprising at the bottom a recirculation tank to recirculate the bottom product in an absorption tower, and a separate oxidation tank for oxidation of the bottom product, wherein carrying out a portion of the recirculated bottom product The process is characterized in that the level of the bottom product in the oxidation tank is maintained at a higher level than the level of the bottom product in the recirculation tank and the oxidized bottom product is leads from the oxidation tank back to the recirculation tank.

According to one aspect of the invention, the level of the bottom product in the oxidation tank is maintained at 35 mid-height of the flue gas inlet to the absorption tower, and guiding the oxidized bottom product from the oxidation tank back to the recirculation tank by gravity.

According to a further aspect of the invention, air is injected into the bottom product in the oxidation tank at a location located between 4.88 m and 9.15 m below the level of the bottom product in the oxidation tank.

The invention further provides an oxidation assembly for carrying out the method of the invention, comprising an absorption tower for flue gas desulfurization, with a bottom recirculation tank to recirculate the bottom product in the absorption tower, collecting means located in the absorption tower above the recirculation tank to retain part of the recirculated bottom product. a recirculating tank adapted to receive a bottom product trapped by the collecting means and injection means opening into the bottom of the oxidation tank to inject air needed to oxidize the bottom product, the oxidation assembly further comprising coupling means disposed between the recirculation tank and the oxidation tank to maintain level in the oxidation tank the tank at a higher level than the level in the recirculation tank, and to direct the oxidized bottom product from the oxidation tank back to the recirculation tank.

In one embodiment of the invention, the coupling means is formed by an overflow into the recirculation tank.

-2 CZ 287720 B6

In another embodiment of the invention, the coupling means is a control system comprising at least one valve.

According to a further aspect of the invention, the oxidizing air injection means is located approximately 4.88 m to 9.15 m below the level of the bottom product in the oxidation tank, and the volume of the oxidation tank is less than the volume of the recirculation tank.

Overview of the drawings

Giant. 1 shows a typical absorption tower for flue gas desulfurization;

Fig. 2 shows an alternative embodiment of a typical absorption tower for flue gas desulfurization;

Fig. 3 shows a typical absorption tower for flue gas desulfurization by a pump means and a separate oxidation tank;

Fig. 4 shows the operation of an absorption tower with different levels of liquid levels in the absorption tower and in a separate oxidation tank;

Fig. 5 is a partial cross-sectional view of an alternative pumping device that may be used in the present invention;

Fig. 6 is a cross-sectional view taken along line 6-6 of Fig. 5 of an alternative pumping arrangement that may be used in the present invention.

Examples

Giant. 1 shows a typical absorption tower 10 for flue gas desulfurization. Said absorption tower 10 includes a flue gas inlet 12, a flue gas outlet 14 and an integrated recirculation tank 16. As can be seen from this figure, the liquid level 18 of the bottom product 20 is located just below the flue gas inlet 12. Also, the oxidizing air is injected directly via the injection means 22 into the recirculation tank 16 at an appropriate height. The bottom product 20 is conveyed from this recirculation tank to a subsequent dewatering device (not shown).

Giant. 2 shows an alternative embodiment of the absorption tower 10. In this embodiment, the recirculation tank 16 is not a direct part of the absorption tower 10, but is instead connected to it via a downcomer 24. Thus, in this embodiment the recirculation product 20 also accumulates in the recirculation tank 16 due to attraction and / or by pump (not shown). The oxidizing air is also injected directly into the separate recirculation tank 16 at the appropriate height by the injection means 22. In addition, the bottom product 20 from this separate recirculation tank 16 is conveyed to a downstream dewatering device.

Giant. 3 shows yet another embodiment of a typical absorption tower that is part of the prior art. As shown in this figure, the bottom product 20 is recirculated within the tower by recirculating pumps 26 and recirculating manifolds 28 incorporating spray nozzles 30. In this embodiment, a separate oxidation tank 32 is located adjacent the absorption tower 10. Pumping or other collecting means 34, arranged inside the tower, capture a portion of the spray 36 falling within the absorption tower 10 from the spray nozzles 30 and transfer the captured spray 36 to the oxidation tank 32 by means of a pump tube. In addition, the bottom product 20 from the tower is conveyed to the oxidation tank 32 by overflow, generally 40 (see the downstream product transfer direction 42), causing the liquid level 18 in the absorption tower 10 to be either equal to or higher than the liquid level 44 in the oxidation tank 32. Any levy

The bottom product to the downstream apparatus leading from the oxidation tank 32 is then directed to a downstream dewatering apparatus (not shown) for further processing of the gypsum or final product. The oxidizing air is injected by the injection means 22 into the oxidation tank 32 at the desired height.

The purpose of the collecting means 34 is to trap the sludge from the lower pH tower before it can be mixed with the already consumed "neutralized" bottom product 20 in the recirculation tank 16. FIG. 3 illustrates a typical overflow type of desulfurization system which causes the liquid level 18 in the absorption tower 10 to be generally at the same height as the liquid level 44 in the separate oxidation tank 32 or above. Although it can be said that the system works well, the advantages of the technology of the invention now make it possible to carry out adequate and more economical oxidation in the main recirculation tank 16.

Giant. 4 illustrates the assembly 48 and a new mode of operation of the pumping means and the separate tank, which are designed for flue gas desulfurization. The main difference between existing technologies and the new method of the present invention is the different liquid levels in the recirculation tank 16 and the oxidation tank 32. The new assembly 48 includes a separate oxidation tank 32. wherein the liquid level 44 in that tank is higher than the liquid level 18 in the absorption As a result, the oxidized bottom product 50 flows rather from the oxidation tank 32 to the recirculation tank 16 in the direction of the oxidized underflow current transfer 52 and not in the opposite direction as in Figure 3 and in the prior art types. Thus, there is no longer supply of the bottom product 20 from the oxidation tank 32 to the recirculation tank 16. Instead, the trapped spray 36, sprayed through the nozzles 30, is transferred by the collecting means 34 from the absorption tower 10 to the oxidation tank 32 and transferred directly after oxidation. from this oxidation tank 32 to the recirculation tank 16. In order to do this, a connection 40 is incorporated into the assembly 48 to help transfer the oxidized bottom product 50 back to the recirculation tank 16.

As a result, there is no need to meet the above discussed requirement that the oxidation air injection site should be located approximately 4.88 m to 9.15 m below the level 18 of the liquid in the recirculation tank 16. Of course, the device shown in Fig. 3 , since it is a type of overflow device, it must meet this requirement. Thus, in Fig. 3, even though oxidation air was injected by injection means 22 into the flue gas inlet region 54 of the separate oxidation tank 32, the level 18 of the liquid in the recirculation tank 16 should be maintained at approximately 4 in order to allow flow into the separate oxidation tank 32. 88 m to 9.15 m above the oxidizer air injection means 22.

The assembly 48 of the present invention makes it possible to substantially reduce the height of the absorption tower 10, since the requirement for locating the injection of oxidation air approximately 4.88m to 9.15m below the liquid level satisfies a separate oxidation system 32. This considerable reduction in the absorption tower 10 (the height is reduced by approximately one to three floors) will substantially reduce the cost of the absorption tower 10.

An increase in the oxidation tank 32 is achieved by utilizing the flue gas inlet space 12 in the absorption tower

10. This flue gas inlet region 54 could not previously be used to raise liquid levels due to the fact that the liquid level 18 could not extend beyond the lower edge of the flue gas inlet 12. However, since this liquid level increase is now realized in a separate oxidation tank 32, its height is by no means limited by said flue gas inlet 12. By utilizing this previously prohibited flue gas inlet region 54, the liquid level in the oxidation tank is increased, thereby providing the retention time required for the oxidation air injected by the injection means 22. In addition, the liquid level 44 in the oxidation tank 32 is generally above the liquid level 18 in the recirculation tank 16, which is made possible by the collecting means 34 withdrawing the spray 36 from the flue gas inlet region 54. The new assembly 48 of the present invention does not rely on lower conveyance

The product 20 from the recirculation tank 16, which was necessary in previous known systems, such as the system shown in Figure 3, was necessary.

The spray 36 discharged by the collecting means 34 to the oxidation tank 32 is oxidized as previously indicated and may be returned to the absorption tower 10 via an overflow or other overflow device similar to the connection 40 shown here. Or the oxidized bottom product 50 may be returned from the oxidation tank. 32 to the absorption tower 10 by a control system 56 that uses a control device such as a valve 58. For the assembly 48, either or both of the above systems may be used, or other methods for returning the oxidized bottom product 50 to the absorption tower 10.

In addition, depending on the reactions in progress, the waste sludge product may be removed as required either from the recirculation tank 16 or from the oxidation tank 32 and the subsequent dewatering device (not shown).

An apparent success of the new method and use of the new assembly 48 is the ability to keep the air injection point below the liquid level 44 at a necessary level without having to increase the height of the recirculation tank 16 (and hence the height of the absorption tower 10). In addition, the volume of the oxidation tank 32 can be much smaller than the volume of the recirculation tank 16, which facilitates oxidation of the trapped spray 36 by mixing the additives with the spray 36 in the oxidation tank 32. In addition, by oxidizing the bottom product 50 returning to the recirculation tank 16 due to the attraction, there is no need for additional pumps, engines or other drive devices.

It is to be understood that the foregoing exemplary embodiment is illustrative only and is not intended to limit the scope of the invention as set forth in the appended claims. Thus, for example, in a further embodiment of the invention, instead of and / or with the collecting means 34 already described, for example, a channel around the perimeter of the absorption tower 10 can be used to divert the trapped spray 36 into the pump tube 38 (FIGS. 5 and 6).

Claims (11)

PATENT CLAIMS A method of oxidizing a bottom product from a flue gas desulfurization absorption tower comprising a bottom product recirculation tank for the bottom product recirculation in an absorption tower and a separate bottom product oxidation tank for capturing a portion of the recirculated bottom product and the portion of the bottom product is introduced into an oxidation tank in which oxidation air is injected into the bottom product, characterized in that the level of the bottom product in the oxidation tank is maintained at a level higher than that of the bottom product in the recirculation tank and the oxidized bottom product is returned from the oxidation tank recirculation tank. Method according to claim 1, characterized in that the level of the bottom product in the oxidation tank is maintained at the center of the height of the flue gas inlet to the absorption tower. Method according to claim 2, characterized in that the oxidized bottom product from the oxidation tank is returned to the recirculation tank by gravity. 4. The method of claim 1, wherein air is injected into the bottom product in the oxidation tank at a location located from 4.88 m to 9.15 m below the level of the bottom product in the oxidation tank. -5 CZ 287720 B6 An oxidation assembly for carrying out the method of claim 1 comprising an absorption tower (10) for desulfurization of flue gas with a bottom recirculation tank (16) for recirculating the bottom product in the absorption tower (10), collecting means (34) disposed in the absorption tower (10) above a recirculation tank (16) for retaining a portion of the recirculated bottom product, an oxidation tank (32) separate from the recirculation tank (16) and adapted to receive the bottom product captured by the collection means (34), and an injection means (22) opening into the bottom of the oxidation tank ( 32) for injecting the air needed to co-oxidize a bottom product, characterized in that it comprises coupling means arranged between the recirculation tank (16) and the oxidation tank (32) to maintain the level in the oxidation tank (32) higher than the level in the recirculation tank (32). 16) and for conducting the oxidized bottom product from the oxidation tank (32) back to the recirculation tank (16). Oxidation assembly according to claim 5, characterized in that the absorption tower (10) comprises a flue gas inlet (12) located above the recirculation tank (16), wherein the level of the bottom product in the oxidation tank (32) is at the center of the inlet height (12). ) flue gas. Oxidation assembly according to claim 6, characterized in that the coupling means is adapted to direct the bottom product from the oxidation tank (32) back to the recirculation tank (16) by gravity. Oxidation assembly according to claim 7, characterized in that the coupling means is formed by a connection (40) to the recirculation tank (16). Oxidation assembly according to claim 7, characterized in that the coupling means is formed by a control system (56) comprising at least one valve (58). The oxidation assembly of claim 5, wherein the oxidizing air injection means (22) is located approximately 4.88 m to 9.15 m below the bottom product level in the oxidation tank (32). The oxidation assembly of claim 10, wherein the volume of the oxidation tank (32) is less than the volume of the recirculation tank (16).