DD264859A1 - PROCESS FOR DISPERSING DAMAGED GASES - Google Patents

Abstract

Process for the separation of noxious gases from dust-laden gas streams on particulate adsorbents in the dust cake of filtering separators, wherein the dust or additive particles contained in the exhaust gas stream are deposited by corona charging unipolar electrical charges before their deposition in the filtering separator, so that a dust cake with high Volumenporositaet and larger specific surface and low pressure loss arises.

Description

Field of application of the invention

The process for the separation of noxious gases can be used in all industrial areas, in which gaseous pollutants and dust-like impurities must simultaneously be removed by means of filtering separators from the gas stream.

Characteristic of the known technical solutions'

j For the separation of noxious gases from industrial waste gases, a number of physical or physico-chemical

j processes used.

Wet processes are based on the absorption or chemosorption of gases in a washing liquid. Dieoe methods usually require a high expenditure on equipment, due to the required regeneration or aftertreatment of the washing liquids or the residue sludge. The washing process ^s st associated with a strong cooling of the gas, so ι that in many cases a very expensive energy reheating of the exhaust stream is required.

In the known oil-dry processes for the separation of noxious gases, the chomosorption in the absorption suspension which is dispersed in fine droplets is accompanied by the drying of the droplets. The dry reaction products, often together with process-related airborne dust, in a downstream En '' ^ 'iber from the gas stream;

away. Due to the relatively short residence time of the Abtorbensmaterialien in the reactor remains their chemical _;

Implementation degree, however, insufficient, so that a partial recirculation of a mixture of reaction products and unused additives required (DE-OS 3429221). If no dust separation takes place before the removal of harmful gas, Thus, the separated dust mixture contains außeidem considerable amounts of Rugstäuben that, due to their often ι

abrasive properties, considerable difficulty in the treatment of prepared with the addition of these dust mixtures prepares> additive suspensions. In any case, the recirculation increases the load on the downstream dedusting system. Even after-adsorption of unreacted additive particles to downstream fabric filters can not eliminate the disadvantages described, since only a degree of conversion of about 30% is to be expected here,

(DE-AS 2331156).

Dry processes to eliminate νοη harmful gases from industrial waste gases are based on the adsorption of these gases on solid surfaces. The use of Adsobenzien example, or the use of molecular sieves different '

Structure, preferably in apparatuses with fixed and fluidized bed, have long been known (DE-OS 2556388, DF-PS 2732204;

DE-PS 3344571). However, these methods fail when additionally solid particles are in the gas stream. An additional '

upstream dust separation is then required. Also makes a cyclic regeneration of the adsorbent;

necessary, which considerably increases the size of the system. !

Furthermore, solutions are known in which the Adsorptionsvermögon of the process in anyway ant jüenden dust or / and: of the additionally introduced into the process adsorbent to be exploited (DE-PS 3227553; DE-OS 3429332; j

: DE-OS 3511759). Difficulties occur in particular by low residence times, poor dispersion of the j

  Adsorbent and irch changed chemical-physical dust properties in the following ι

! Dust separation on. The amount of pollutant ad- sorbed on the solid is u. a. depending on the total obor area of the '

'Solid in the gas-dust system. Because of the very high specific surface area of fine dusts, the additive is _:

laden gas stream sometimes by means of refinement of the additive particles, such. B. ball mills, passed j

(DE-PS 2908003). The disadvantage of this method is a high additional equipment and energy costs. The fine dust produced in this way or before the addition of additive into the gas stream also causes difficulties in subsequent dust collectors. j

The combination of a simultaneous separation of dust and adsorption of gaseous constituents on the dust filter cake j of a fabric separator, which consists of the process-related dust contained in the exhaust gas and possibly from additionally entered additives, is a technically sensible solution (UE-AS 2331156; US-PS, 3505008 US-PS-3589863). Here, however, occur

serious defects: The filter layer thickness of the dust cake is limited by the permissible maximum pressure loss for the required gas volume flow for the system. As a result, only short residence times of the gas are achieved in the filter cake. Furthermore, the thin filter layer for gas adsorption does not provide sufficient surface area. To increase the contact time, therefore, additional contacting units are frequently introduced into the gas flow (DE-AS 2321881, DE-AS 2539500, DE-OS 2729298). However, these measures require increased plant engineering effort and are often associated with unwanted Flugstaubablagerungen and consequently with a reduction in the technological availability of the facilities.

A variety of inventions deals with ways to increase the contact time between dust or additive particles and exhaust gas by multiple recycling of the solid particles, possibly after prior mechanical processing, e.g. by grinding or classification (DD-PS 215244, DD-PS 239949, DE-AS 2327020, DE-OS 3428502, DE-OS 3526857, US-PS 3933978). However, this increases the dust concentration, which, in particular with very fine dusts or adsorbents, the pressure loss of the filtering dust collector increases inadmissible. The high operating pressure loss requires high Abreinigungsfrequenzen, which in turn lead to disproportionately large filter wear.

Object of the invention

The aim of the invention is to intensify the adsorption of noxious gas components from dust-laden technical exhaust gases on the particles J. of the dust cake of filtering separators.

Explanation of the essence of the invention The invention has for its object to provide such a structure of the dust cake of filtering dust collectors, ]

the intimate contacting of the reactive solid particles contained in the dust cake with the flowing through '

Exhaust gas allows. The object is achieved in that the dust or additive contained in the exhaust stream before their Deposition in a filtering separator by corona charging unipolar electrical charges are imprinted. The charging of the solid particles should take place as far as possible from the filter element in order to avoid charge losses of the Particles, e.g. B. by touching the wall, to avoid. The mutual repulsion of the unipolar electrically charged particles acts on the binding forces between them, which in the Dust cake are effective (especially Van der Waals-Krätte and Flüssigkeitsbrückenbindungon) contrary, so that the

increase the mean distances between the particles in the dust cake and prevent the formation of compact agglomerates. This results in an increase in the volume porosity of the dust cake and thus a significant increase in its accessible specific surface area, i. H. the surfaces of the solid particles suitable as adsorbents become more accessible to the gas molecules. At the same time increases, with the same solids loading of the filter material, the thickness of the

Dust cake and thus the residence time of the gas flowing through in the adsorbent layer. Dio caused by the application of the method according to the invention loosening of the dust cake continues with

a considerable reduction of the pressure loss over the dust cake accompanied. At the same mean pressure loss can:

Consequently, the Abreinigungsfrequenz the filter elements are reduced. In addition to increasing the life of the

Filiergewebes is characterized the residence time of the adsorbent effective solid particles in the dust cake and thus their Contact time with the exhaust gas increased. The effects shown lead to an improvement in the material utilization of the adsorbents, so that an otherwise

necessary recirculation of incomplete converted adsorbent materials omitted or at least significantly reduced. This also makes it possible, with the same pressure drop over the separator additional additives in the

Enter exhaust stream upstream of the separator and thus oine further increase the pollutant gas to achieve. The ancestor requires as additional technical facilities only a corona discharge path, the z. Tie Abgaskenal immediately before the filtering separator or directly into the separator can be easily installed,

and facilities for high voltage generation and control. For the otherwise necessary, much more elaborate

Facilities for the treatment and / or recirculation of solids and additional Kontaktierungselnrichtungen

omitted. Such as B. from the operation of electrical gas cleaning systems is known, are also the energetic

Costs for the corona discharge relatively low. The inventive method is suitable both as a self-sufficient gas purification process, but also offers for Retrofitting already existing filtering dust collector, z. B. behind dry or semi-dry systems for Schadgasentfernung, for the purpose of intensifying the Arbeitswelse of Gasreinigungssyetems. Embodiment 1 '< An advantageous application of the method according to the invention bestem in its use for after-adsorption

of sulfur dioxide in semi-dry flue gas desulphurization process. In a variant of this

Desulphurization process is loaded with fly ash from the combustion process of fossil, solid fuels Flue gas passed through an absorber, in which an intimate contact with an aqueous, hydrated lime particles containing Absorbent suspension by spraying it into fine droplets that completely during the absorption process

dry, is realized.

Due to the relatively short contact time in the absorber, the metabolic rate of the hydrated lime remains incomplete. The now with Fly ash and solid reaction products as well as unreacted Kalkhydratteilchen laden flue gas stream gelengt in one

filtering dust collector, in which, immediately before the deposition of the solid particles on the filter elements whose ^.

Unipolar electrical charging is carried out by corona discharge.

The now formed, highly porous dust cake ensures the usual for the operation of dedusting ί

Operating conditions a nearly complete implementation of both the not trshortzrm hydrated lime particles as well as reactive basic constituents of the fly ash with the residual SO ₂ molecules in the flue gas. The usual Rezierkulation part of the deposited dust mixture, ie its renewed use in the Adsorbenssuspension, which, due to the highly abrasive properties of the fly ash particles, leads to severe signs of wear on conveying and Versprüheinrichtungen can be omitted.

Embodiment 2

Another advantageous application of the method according to the invention consists in the combination with dry flue gas desulfurization., As the flue gas desulfurization in the stationary fluidized bed combustion.

In this method, fine-grained lime hydrate is added to the solid fuel dispersed in the combustion and carrier air.

Because of incomplete implementation of this additive with SO ₂ , a multiple circulation of the Gomisches fly ash, reaction products and unused additives, respectively after the deposition of solid particles from the flue gas, eg in filtering separators, be realized

When the process according to the invention is applied in filtering filters which are present anyway, these act as a second desulfurization stage. Consequently, the return of the dust mixture in the combustion chamber can be significantly reduced, which also reduce the mass of the granular material to be held in the fluidized bed and the dust concentration in the exhaust stream before the dedusting considerably.

With the reduction of the solids flows both the size of the plant with the same power and the energy consumption for their operation, for. B. for the provision of the carrier air to maintain the fluidized bed, be significantly reduced.

Claims (5)

J Claims: '1st method r.ur deposition of noxious gases ous dust-laden Abpasströmen the particles 'of the dust cake filtering dust, characterized in that the exhaust gas flow Particulate adsorbents contained before their deposition in the filtering separator ^: Corona charging unipolar electrical charges are imprinted. ! 2. The method according to claim 1, characterized in that the corona charging of particulate adsorbents in the exhaust pipe directly from the filtering separator
or in the separator itself, at a short distance in front of the filter elements occurs. 3. Process according to claims 1 and 2, characterized in that as adsorbents
Process-related accumulating dusts and / or additionally the exhaust gas flow supplied additives
Find use. 4. Process according to claims 1 to 3, characterized in that the method as self-sufficient
Gas cleaning process or in conjunction with other processes for the removal of gaseous
Pollutants is used. 5. Process according to claims 1 to 4, characterized in that the
Average pressure loss over the deduster at the usual values is maintained.