WO1998032523A1

WO1998032523A1 - Flue gas scrubber

Info

Publication number: WO1998032523A1
Application number: PCT/FI1997/000036
Authority: WO
Inventors: Heikki Airikkala
Original assignee: Kvaerner Pulping Oy
Priority date: 1997-01-24
Filing date: 1997-01-24
Publication date: 1998-07-30
Also published as: AU1547697A

Abstract

A flue gas scrubber is intended for scrubbing flue gases from an energy production unit. The flue gas scrubber comprises a scrubber housing (1) forming in its interior a scrubber chamber (2), into which a flue gas inlet and equipment for supplying washing solution are brought. The scrubber chamber is divided with a partition wall (3) into two or more scrubber sections (2a, 2b) each with its own flue gas duct (4a, 4b) and its own devices for supplying washing solution (5a, 5b).

Description

Flue gas scrubber

The invention relates to a flue gas scrubber of the type presented in the introductory part of the appended Claim 1.

Flue gas scrubbers are used in processes producing flue gases to remove undesirable gaseous and/or solid substances, such as sulphur compounds, heavy metals and dust, from the flue gases of the process by means of a washing solution before discharging the flue gases into the environment. Flue gas scrubbers intended for the removal of sulphur compounds utilize an alkaline washing solution, wherein they are called either lime scrubbers or caustic scrubbers, depending on the active agent in the washing solution.

Irrespective of the composition of the washing solution, the most common flue gas scrubbers in use are characterized by certain structural features: A vertical, so-called spray tower containing a scrubber chamber, into which the flue gases to be purified and the washing solution are supplied to have contact with each other, an outlet pipe for washed flue gases on the top of the tower, and an outlet in the lower part of the chamber for the washing solutions accumulated in the bottom of the chamber. An example of a scrubber with these structural features is presented in Finnish Patent No. 58443.

At present, scrubbers play an essential role in energy production plants, in which sulphur-containing fuels are used for the production of electricity and/or heat. These power plants, e.g. diesel power plants or package boiler power plants, can comprise several energy production units (diesel engines, boilers etc.) coupled in parallel. For increasing the operational reliability of the power plant, flue gases coming from different units are no longer conveyed to one joint scrubber but to several different scrubbers. For example, a separate scrubber is arranged for each energy production unit producing flue gases, or the units are grouped in such a way that one scrubber receives the flue gases from a group of two or several units. The units can thus operate better in energy production independently of each other. The scrubbers can have a joint stack, to which the outlet pipes from the upper part of the scrubber are introduced via an outlet duct on top of the scrubber, or each scrubber can have a stack of its own. In such a system of several scrubbers it is also possible to arrange scrubber groups where the scrubbers have a joint stack.

The scrubbers naturally take a certain space in the power plant. Thus they can be allocated a separate section in the power plant area, a scrubber plant, which is provided with the equipment and chemicals required for their use and to which the flue gases coming from the energy production units are led.

A problem with present scrubber arrangements is that if each energy production unit is provided with a separate scrubber, the scrubbers occupy an unreasonably large part of the area of the power plant. On the other hand, if the flue gases from several energy production units are led to one scrubber and there is an operational break in the scrubber, all energy production units must be stopped.

The aim of the invention is to present a new type of scrubber with which it is possible to reduce the space requirement of multi-scrubber systems by reducing the number of apparatuses. Further the invention can be utilized to ensure the continuity of energy production at least partly irrespective of malfunction of one scrubber section. For achieving this aim, the scrubber of the invention is primarily characterized in what will be presented in the characterizing part of the appended Claim 1. The scrubber chamber is thus divided by a partition wall into two or more sections provided with flue gas ducts from different energy production units as well as their respective devices for supplying washing solution.

By virtue of the structure according to the invention, the scrubber chamber inside the scrubber housing can be provided with two or more functional scrubbers. The operating devices, such as circulating pumps, maintenance routes, etc. required by the different scrubbers can be arranged more practically around the same scrubber housing without dis- tributing them around the multi-scrubber system, wherein more space is saved and the multi-scrubber system can operate even better. Concerning advantageous embodiments of the invention, reference is made to the appended dependent Claims and the description below.

In the following, the invention will be described in more detail with ref- erence to the appended drawings. In the drawings,

Fig. 1 is a side view illustrating the principle of the scrubber according to the invention,

Fig. 2 shows the same seen from above,

Fig. 3 shows the whole scrubber plant seen from the side, and

Fig. 4 shows the same seen from above.

Figure 1 shows the scrubber in a schematic view from the side, and it also discloses the principle of operation of the scrubber. The scrubber comprises a vertical cylindrical wall which simultaneously constitutes the structural support housing 1 of the tower scrubber and in its interior forms a scrubber chamber 2 in which the flue gases and the washing solution are brought into contact with each other. The foundation of the housing is indicated with the reference numeral 15. The chamber 2 is divided by a vertical partition wall 3 into two separate scrubber chambers or scrubber sections 2a and 2b, each being provided with an inlet flue gas duct 4a and 4b, respectively, coming from different energy production units. In the scrubber sections, above the corresponding flue gas inlet, there are washing solution supply devices 5a and 5b, respectively, which effect the falling down of the liquor against the flow direction of the flue gas, and they usually have the structure of suitable washing sprays distributing the liquor as evenly as possible in the area of the horizontal cross-section of the scrubber chamber. The liquor that has been in contact with the flue gases and accumulated in the lower part of the scrubber chamber is removed via a discharge pipe 6a and 6b, respectively, and it can be recirculated into the washing solution supply devices via a circulating pump 13a and 13b, respectively. The figure shows the principle in a simplified manner, and in practice the scrubber comprises several circulating pumps and correspondingly several circulations for each scrubber section, as well as connections for adding fresh washing solution and for removing the washing solution containing impurities to further processing (shown by broken lines).

The cylindrical side wall has a conically tapered top which ends in a stack 7 extending directly above the housing 1 for conveying the gases discharged from the scrubber directly up from its upper end into the air.

Thus a joint stack can be used for both scrubber chambers 2a and 2b, which is an advantage over a conventional multi-scrubber system, in which the aim is also to build a joint high stack e.g. for two different scrubbers, but in which it would be necessary to arrange a space requiring particular foundation for the stack and to lead separate flue gas ducts from each scrubber to the stack.

The scrubber housing 1 can be sufficient for supporting the stack 7, or it can be supported on the ground with a separate support frame outside the housing, as indicated by broken lines 8 in Fig. 1 , supported on the foundation 15.

In the conical part underneath the stack, in the upper part of the re- spective scrubber section 2a, 2b, droplet separators 9a and 9b, respectively, are arranged. From the droplet separator, the droplets can fall into the scrubber section directly underneath it. Underneath the droplet separator in the conical part or the upper end of the cylindrical part, one or each scrubber chamber can be provided with a packed bed with its own washing solution circulation. In the scrubber sections 2a and 2b, it is also possible to use all arrangements known from gas scrubbers for making the scrubbing action more effective.

Figure 1 shows the extension of the partition wall 3 up to the lower part of the stack 7. The partition wall 3 can also terminate at a lower point for example in such a way that a joint droplet separator is provided for both scrubber sections 2a and 2b. Thus, the purpose of the partition wall 3 is primarily to separate the flue gases coming from different units and their washing solutions from each other.

Figure 2 shows the geometry of the scrubber seen from above. The housing of the scrubber has a circular horizontal cross-section, and it is divided by the partition wall 3 into two sectors of 180°. However, the in- vention is not limited to a scrubber comprising two scrubber sections, but the division of the interior of the housing into three or four separate scrubber sections is feasible, wherein the sectors in the horizontal section of Fig. 2 would be 120° and 90°, respectively.

Further, Fig. 2 illustrates how the circulating pumps 13a and 13b can be arranged next to the scrubber housing in parallel on the same side thereof.

Because the washing solution circulations are close to each other, they can also be connected in such a way that the same circulation solution is used in both scrubber sections. This kind of a connection is intended to be optional, and the scrubber should always comprise the option of completely separate circulations.

Figures 3 and 4 show a scrubber plant comprising the scrubber according to the invention. The structure of the scrubber is the same as shown in Figs. 1 and 2. In this case, the scrubber is a lime scrubber, wherein the plant comprises also a limestone silo for preparing the washing solution, i.e. lime slurry, in a dosage tank underneath the same. The equipment for treatment of the waste removed from the process, in this case the equipment for treatment of calcium sulphate, is indicated with the reference numeral 11. Figure 4 illustrates the grouping of different parts in the scrubber plant into a compact entity. The scrubber housing 1 , the equipment 10 for preparing the washing solution (limestone silo and dosage tank), and the equipment 11 for processing the washing solution removed as waste (calcium sulphate processing equipment) are arranged in a triangle, wherein a staircase tower 12 is arranged in the middle for maintenance and control, having horizontal entrances 14 to all said three parts, i.e. one staircase tower will suffice. The staircase tower can be arranged to have the structure of spiral stairs.

Figure 4 shows also the placement of the circulating pumps 13 in one group on the opposite side of the scrubber housing 1 as seen from the staircase tower 12. Both flue gas ducts 4a, 4b enter the scrubber on opposite sides in the area left between the staircase tower and the group of the circulating pumps. Different energy production units, from which said flue gas ducts 4a, 4b are led into the scrubber plant, are denoted schematically by blocks A and B. Figure 4 shows only one advantageous layout for the scrubber plant, and it is naturally possible to use other layouts as well for the different equipment without deviating from the basic idea of the invention.

The invention is not limited to scrubber plants with only one scrubber housing either. If the large number of energy production units necessitates several separate scrubbing processes which for practical reasons cannot be incorporated within the same scrubber housing, it is possible to provide the plant with more than one scrubber housing having scrubber chambers or scrubber sections, separated from each other with a partition wall according to the invention, and these can be of the type shown in Figs. 1 and 2. From such scrubber housings, exhaust gas ducts can be led to a joint stack.

The invention is intended particularly for scrubbing flue gases from such power plants in which the separate energy production units have a relatively small capacity. Power plants of this kind include particularly diesel power plants, in which several engines are coupled in parallel and the flue gases produced by each engine or a group of several engines can thus be purified in a process of its own, or power plants comprising several boilers with small capacities, such as package boilers or fire-tube boilers. The same power plant can also comprise different types of energy production units.

The invention also covers an arrangement in which flue gases from more than one energy production unit are led to the same scrubber section, but in that case, too, the flue gas ducts come to each scrubber section from a unit or group of units allotted to it.

The scrubber structure shown in Figs. 1 and 2 has the following advantages over two separate scrubbers, in addition to the fact that the structure itself is more compact:

The foundation work is substantially reduced when one scrubber and the stack foundation is eliminated. The scrubber is a part of the stack, wherein the stack becomes shorter in length.

As droplet separators, more advantageous horizontal droplet separators can be used instead of vertical droplet sepa- rators.

Further, the following savings on costs are made, by virtue of the reduction of the quantity of manufacturing materials:

- The roof of the scrubber is eliminated, because it is replaced by the inlet opening of the stack. The horizontal flue gas exhaust duct between the scrubber and the stack is eliminated, because the stack begins directly from the top of the scrubber, and no connector bel- lows between the exhaust ducts and the stack are needed.

The number of chloride-resistant special coatings is reduced by virtue of the omission of said roofs and horizontal exhaust ducts, i.e. there are less walls. By virtue of the smaller need of space, the length of tubing and electric and instrument cables is shorter than in a plant of two separate scrubbers.

Claims

Claims:

1. Flue gas scrubber intended to scrub flue gases originating from an energy production unit, wherein it comprises a scrubber housing (1) forming in its interior a scrubber chamber (2), into which a flue gas inlet duct and equipment for supplying washing solution are brought, characterized in that the scrubber chamber is divided with a partition wall (3) into two or more scrubber sections (2a, 2b) with their own flue gas ducts (4a, 4b) and their own devices for supplying washing solution (5a, 5b).

2. Scrubber according to claim 1 , characterized in that the feeding pumps (13a, 13b) for supplying washing solution into different scrubber sections are arranged in a group on the same side of the scrubber housing (1).

3. Scrubber according to claim 1 or 2, characterized in that the stack (7) for removing the scrubbed flue gases is situated on top of the scrubber housing (1) as its extension and is common to all scrubber sections (2a, 2b).

4. Scrubber according to any of the preceding claims, characterized in that the scrubber housing (1) has a circular horizontal cross-section and the scrubber sections (2a, 2b) are formed by partition walls (3) into sectors of a circle.

5. Scrubber according to any of the preceding claims, characterized in that a flue gas duct (4a, 4b) is connected to each scrubber section (2a, 2b) from at least one energy production unit (A, B), and flue gas ducts are connected to different scrubber sections (2a, 2b) from different energy production units (A, B).

6. Scrubber according to any of the preceding claims, characterized in that the energy production unit is a diesel engine.

7. Scrubber according to any of the claims 1 to 5, characterized in that the energy production unit is a package boiler or a fire-tube boiler.