Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Reexamination Certificate
1999-04-16
2003-05-13
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
C422S170000, C422S172000, C422S205000, C096S366000, C096S367000
Reexamination Certificate
active
06562303
ABSTRACT:
The present invention relates to a method and an apparatus for treating flue gas, and more specifically to the treatment of a flue gas in a wet-cleaning apparatus, which comprises a so-called quencher or cooler.
Flue gases forming in the incineration of materials such as refuse, coal, oil etc, contain impurities which must be removed before the flue gases are released into the atmosphere. Thus, for instance flue gases from refuse incineration contain, among other things, hydrogen chloride and sulphur dioxide which are removed by wet cleaning in a wet-cleaning apparatus. The wet-cleaning apparatus, also referred to as a scrubber, operates in one or more steps with liquid as separating medium. In order to achieve a high degree of efficiency in the wet cleaning, it is preferred to finely divide the liquid. Furthermore, the liquid is often water-based and may contain an agent to improve the absorption of impurities in the gas.
When treating flue gases containing both hydrogen chloride and sulphur dioxide, such as flue gases from refuse incineration, the scrubber comprises one step for removing hydrogen chloride and a subsequent step for removing sulphur dioxide. Adjacent to the inlet of the scrubber and before the hydrogen chloride step a so-called quencher or cooler is arranged, into which finely-divided liquid is injected for cooling the hot flue gas. During cooling, part of the liquid is evaporated such that the flue gas is saturated with liquid. After this saturation quenching of the hot flue gas in the quencher, the flue gas is passed onto an absorption tower for removing hydrogen chloride and, optionally, also sulphur dioxide.
In a frequent design of a scrubber, the quencher or cooler consists of a vertical tower, which has an inlet for flue gas at the upper end, nozzles for injecting finely-divided liquid, and a horizontal outlet arranged at the bottom and connected to an absorption tower with a step for absorption of hydrogen chloride and usually also a subsequent step for absorption of sulphur dioxide. In the outlet of the quencher there is a so-called droplet separator for separation of remaining liquid droplets from the flue gas. This droplet separator may consist of e.g. lamellae, between which the flue gas must pass, whereby the remaining liquid droplets are deposited on the lamellae. The droplet separator may be provided with e.g. a netting instead of lamellae.
A great drawback of such vertically arranged droplet separators is that a thick coating builds up gradually on the droplet separator. This coating originates from disolved and suspended material in the liquid droplets that are separated in the droplet separator. When the liquid in the separated droplets is evaporated, the dissolved and suspended material is deposited as a coating on the droplet separator. In order to counteract the formation of such coating, nozzles are arranged adjacent to the droplet separator for spraying it with liquid, but it is difficult for these nozzles to wet the entire surface of the droplet separator and besides they are operated only intermittently, which results in the surface of the droplet separator not being continuously wetted, but having alternating wet and dry portions. This results, in turn, in the above-mentioned undesired build-up of a coating. When the coating has attained a certain thickness, the droplet separator must be removed and cleaned, thus causing service interruption. Although this service interruption can be minimised by replacing the coated droplet separator with a new, uncoated droplet separator, the labour-consuming cleaning of the coated droplet separator remains.
Theoretically it would be possible to reduce or eliminate the coating on the droplet separator by using clean water when injecting liquid into the quencher and when spraying the droplet separator. In actual practice, this is however not possible since it would result in the formation of a very large volume of waste water having a low concentration of impurities. Such low-concentrated waste water is very labour-consuming and expensive to clean and also cannot be directly discharged into a water course. In the operation of a quencher of the above-described type, one therefore endeavours to use as concentrated an aqueous solution as possible for cooling and spraying of the droplet separator, thereby keeping the liquid volume and, thus, the need of cleaning at a minimum. The higher concentration of the dissolved and suspended substances contained in the aqueous solution, the greater the risk of a coating being built up on the droplet separator, especially if this is not completely wetted but has alternating dry and wet portions.
A further drawback of scrubbers of the above-described type, provided with a quencher, is that they require a large space and are difficult to manufacture. Thus, the cooling tower for a conventional scrubber, which is designed for a gas flow rate of 100,000 Nm
3
/h, has a diameter of about 3.5 m and a height of about 13 m. The quencher and the absorption tower of the scrubber, which are usually made of glass-fibre reinforced plastic, certainly have a cylindrical cross-section, but in the transition between the cooling tower and the absorption tower there are a number of alternating straight and curved surfaces which are difficult to form.
When treating flue gases in a scrubber with a so-called quencher or cooler, there is thus a need of reducing or eliminating the above-described formation of a coating. There is a also a need of a scrubber, which is easy to manufacture and requires but a small space.
In the present invention, it has been discovered that if, instead of a conventional, vertically arranged droplet separator, the liquid injected into the flue gas is used to form a liquid film, through which the flue gas then passes, the formation of a coating, which takes place according to prior-art, will be reduced or eliminated.
More specifically, the invention provides a method for treating flue gas, in which an aqueous liquid is injected in the form of droplets into the flue gas, whereupon flue gas and liquid droplets are separated, said method being characterised in that the flue gas and the droplets are conducted towards a baffle means, on which droplets are deposited and form a liquid film, and that the flue gas is made to pass through the liquid film.
The invention also provides an apparatus for treating flue gas by injection of an aqueous liquid in the form of droplets and subsequent separation thereof, said apparatus comprising a quencher having an inlet for the flue gas, nozzles for injecting an aqueous liquid in the form of droplets into the flue gas, and an outlet for the flue gas, said apparatus being characterised in that a baffle means is arranged in the path of flow of the flue gas for depositing droplets and forming a liquid film, and that deflection means are arranged under the baffle means.
Further distinctive features and advantages of the invention will appear from the following specification and the appended claims.
The baffle means, on which the liquid film forms, may be of varying design, but suitably consists of a surface which is arranged essentially horizontally or transversely of the direction of the flow of the flue gas. Preferably, this surface is curved upwards and has the shape of a cylinder jacket, such as e.g. half of a cylinder jacket, the cylinder jacket being essentially horizontally arranged in the quencher, the convex surface being directed upwards. Alternatively, but at present less preferred, the baffle means may consist of two flat surfaces which are interconnected along a lateral edge and which together form an upwardly acute angle, corresponding to the angle of the roof of a house.
The liquid film formed on the baffle means flows along the surface of the baffle means and falls as a liquid film from the lateral edges of the baffle means. The flue gas passes through this falling liquid film, whereby remaining liquid droplets in the flue gas are separated. For the flue gas to pass through the falling liquid film, the flue gas which orig
Alstom Power Sweden Holding AB
Tran Hien
LandOfFree
Method and apparatus for treating flue gas does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for treating flue gas, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for treating flue gas will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3008078