EP1771254B1 - Structural principle of an exhaust gas purification installation, and associated method for purifying an exhaust gas - Google Patents

Abstract

The structure has a zone (10) for ionization of the particles/aerosols carried in the gas, a connecting zone (7), a collector zone (8) for separating the particles/aerosols electrically neutralized therein and a spraying system for flushing the collector zone. The section for exhaust cleaning has the structure of an upright U with the ionization zone in one leg through which the gas to be cleaned flows down under gravity. The connecting zone has at least one outlet for liquid enriched with particles at its lowest point. The second leg contains the collector zone with at least one collector through which the gas flows up against gravity. A spraying device is mounted above the collector zone or between each two collector zones : An independent claim is also included for a method of cleaning exhaust gas in an exhaust gas cleaning system.

Description

The invention relates to the construction principle of an exhaust gas purification system and a method for cleaning an exhaust gas so.

It is difficult to separate submicron particles from exhaust gases through cyclones, scrubbers and bag filters. The electrostatic precipitator is one of the most effective means / assembly of an exhaust gas purification system for fine particulate separation (see, for example, US Pat DE 101 32 582 ).

• einer Zone zur Ionisation der im Gas mitgeführten Partikel/Aerosole, dem Ionisatorone, gefolgt von einer Verbindungs- oder Übergangszone, wiederum gefolgt von einer Kollektorzone zur Abscheidung der darin elektrisch neutralisierten Partikel/Aerosole und schließlich einer Sprüheinrichtung, die den Kollektor mit einer Spülflüssigkeit besprüht.

An emission control system usually forms a built-in section in a flow channel for gas routing. It consists of the following modules, which follow one another in the flow direction:

• a zone for ionization of the entrained particles / aerosols in the gas, the ionizer zone, followed by a junction or transition zone, again followed by a collector zone for separating the electrically neutralized particles / aerosols therein and finally a sprayer which sprays the collector with a flushing liquid.

Electrostatic precipitation is a physical process by which particles are electrically charged and subsequently separated / separated from the gas under the action of an external electric field. In single-stage electrostatic precipitators, the electric field generates a corona discharge to charge the particles and attract them toward the wall, eventually removing them. In a two-stage electrostatic precipitator, the charging and deposition of the particles generally occurs in two spatially distinct external electric fields.

Procedures and facilities have been designed to ensure the effective separation of particulate matter, reduce the cost of ownership and operating costs of the electrostatic precipitator, and reduce the design to simplify (see DE 102 44 051 ). The particles are charged by a corona discharge and then removed in an external, field-free collector. The separator includes the charging device, the housing connection and the separator. The charger consists of a grounded nozzle plate and high voltage needle electrodes positioned centrally in the nozzles. The particles are charged in the DC corona discharge. The separation device consists for example of a grounded tube bundle collector. The method and the separator differ from the conventional two-stage electrostatic precipitator by the absence of the separate depositing electric field in the collecting zone, which makes it possible to compactly construct the separator.

• Mit Partikeln beladenes Gas strömt zur Reinigung durch den Eingang der Abgasreinigungsanlage, das Abgas tritt in die Düsen ein, die in der elektrisch geerdeten Platte vorhanden sind. Diese Platte steht senkrecht zu Strömungsachse. Das Abgas strömt durch den Ionisator, wo die Partikel in der Koronaentladung elektrisch geladen werden. Der Ionisator sitzt zwischen den Hochspannungselektroden und der inneren Oberfläche der geerdeten Düsen. Die Hochspannungselektroden sitzen ausgerichtet auf einem Hochspannungsgitter, welches stromabwärts von der Düsenplatte elektrisch isoliert am Anlagengehäuse eingebaut ist. Danach passiert das Gas mit den elektrisch geladenen Partikeln den Anschlussbereich der Anlage, der den Ionisator und die Abscheidezone verbindet, um schließlich durch den Ausgang der Anlage in dem angeschlossenen Gaskanal weiterzuströmen.

The procedure consists of the following steps:

• Particulate-laden gas flows through the inlet of the exhaust gas purifier for purification, the exhaust gas enters the nozzles present in the electrically grounded plate. This plate is perpendicular to the flow axis. The exhaust gas flows through the ionizer, where the particles are electrically charged in the corona discharge. The ionizer sits between the high voltage electrodes and the inner surface of the grounded nozzles. The high voltage electrodes sit aligned on a high voltage grid, which is electrically isolated downstream of the nozzle plate mounted on the system housing. Thereafter, the gas with the electrically charged particles passes through the connection region of the system, which connects the ionizer and the separation zone, in order finally to continue through the outlet of the system in the connected gas channel.

According to the known method, the gas flows in the same direction through the charging unit / zone, the connecting piece and the separation zone. In the in the DE 101 32 582 C1 described exhaust gas purification system flows the exhaust gas to be cleaned in the direction of gravity, in the DE 102 44 051 C1 described emission control system against gravity.

Although the process and the exhaust gas purification systems effectively clean the gas flowing through, there are some problems. In the in the DE 101 32 582 described system, the charged particles are deposited in the tube bundle collector by forming a liquid film. At higher aerosol concentration, the film flows on the surface of the tubes in the direction of gravity. When leaving the tubes, droplets form, which are again in the actually purified gas stream. This reduces the degree of separation of the system.

In the in the DE 102 44 015 C1 described exhaust gas cleaning system drips at high particle concentration, a portion of the liquid film from the tube collector to the charging unit and provokes there spark discharge, which reduces the degree of separation. Likewise, a portion of the particles are deposited on the surface of the high voltage grid and the high voltage electrodes mounted thereon. Small droplets form on the electrode tips. This crucially changes the intended corona discharge, provokes flashovers, worsens the process of particle loading and thus reduces the degree of separation.

The invention has for its object to provide an exhaust gas purification system and to be able to operate long term so that their predetermined degree of separation does not, or at most does not change appreciably.

The object is achieved by the construction principle described in claim 1 for the existing of an electrostatic charging device, a transition zone and a Partikelabscheideeinrichtung emission control system and by the method described in claim 4 for operating the same.

The exhaust gas purification system as a section in a flow channel for gas guidance has the shape of an upright U's. In one leg is the zone for ionization of entrained in the gas Particles / aerosols, the electrostatic charging zone or just the ionizer housed. The transition from one leg to the other, the junction zone, forms the sump / vessel for the particles precipitated from the gas stream and dripping from the collector. At its lowest point is at least one spout for discharging the particulate-enriched liquid. Higher-level spouts may be further attached to the sump if needed. In the second leg sits the collector zone in which the particles are separated from the gas stream and are electrically neutralized, with drainage liquid down / - to be washed away.

The collector zone consists of at least one collector or of a plurality of successive collectors in the flow direction, wherein a collector consists of a tube bundle group of at least one tube bundle.

Decisive is the introduction of the particulate, to be cleaned gas in the direction of gravity from top to bottom in the leg of the system in which the ionizer is located. A corona discharge electrically charges the particles as they pass through. The polarity is selectable, but is often negatively charged. The ionizer consists of the well on a defined electrical reference potential, usually ground potential, lying nozzle plate and the high-voltage grid usually at a negative potential with mounted and aligned electrodes. Important for the intended ionization is that the electrodes protrude with their free ends from below into the respective associated nozzle (claim 2). This is the only way to ensure that no droplets are formed at the electrodes, in particular at the electrode tips, which could delicately deprive the corona discharge. Any drop formation at the electrodes immediately flows down to the high-voltage grid and drips there, supported by the gas flow, from, to finally be collected and discharged in the reservoir. To avoid electrical charging, the reservoir is electrically also at a reference potential. In order not to have to take additional structural protection measures (contact protection, for example), the reference potential is simply earth potential.

The exiting from the ionizer, now with charged particles offset exhaust gas is introduced into the connection zone, in which the exhaust gas on the one hand deflected and flows when leaving against gravity vertically upwards from below into the second leg. On the other hand, the dripping part of the still electrically charged particles / aerosols in the connection zone is collected by the sump.

The exhaust gas is, as already mentioned, flows through in the collector for cleaning, or for separating the particles against gravity from bottom to top. The particles / aerosols are all deposited, at least largely, on the walls of the collector, where they are electrically neutralized and flow off in the direction of gravity by means of a flushing liquid sprayed onto the collector, at least from above, against the gas flow as particle-displaced liquid film in the direction of gravity Connection zone, the reservoir, drain. The collector consists of at least one tube bundle, which stands on a also on electric reference potential grid sitting (claim 3). Of course, these grates can be sprayed from below, if such a measure is useful. The spraying of the collector from above is standard.

The gas thus processed leaves the collector free of particles and now flows on as clean gas in the connected flow channel.

The objective of effectively cleaning an exhaust gas of fine, mainly submicron, solid or liquid particles is achieved with the exhaust gas purification system and the method operated therewith.

The exhaust gas cleaning system is characterized by its construction in the form of an upright U's. With her, the cleaning process can be performed highly effective and long-term stable, because the exhaust system avoids the formation of droplets at the free electrode ends in the nozzle and therefore the ionization of the particles in the corona discharge between the free end of the electrode and the inner wall of the nozzle always as intended, ie stable, runs. The effectiveness of the particle / aerosol separation is therefore complete, at least almost complete. The system as part of the flow channel guide is compact and technically robust, due to the three or with spray four modules clearly arranged, easy to assemble and easy to maintain. The flow direction of the exhaust gas in the ionization zone is opposite to that in the collector zone.

The building materials of the exhaust gas purification system are selected based on the process to be performed. Whether dielectrically or electrically conductive depends on the nature of the exhaust gas and the entrained particles. The electrical conditions must be able to be adjusted and the cleaning process can be carried out long-term without corrosion phenomena inside the plant.

The cleaning system can be adapted to purify exhaust gases in the form of ambient air, flue gases, wet gas, dry gas and hot gas. The particles entrained in the exhaust stream, whether liquid or solid, need only be ionized, i. be electrically charged. Such an emission control system is particularly suitable for the separation of submicron spatters in the diameter range D <1 .mu.m, which are otherwise difficult to deposit.

• Figur 1 zeigt das Anlagenschema,
• Figur 2 die Ionisierungszone vergrößert.

Based on the drawing on the schematic exhaust gas purification system the same and the process operated with it will be explained in more detail.

• FIG. 1 shows the plant scheme,
• FIG. 2 the ionization zone increases.

In FIG. 1 enters the exhaust gas to be purified from above into the inlet 2 of the emission control system 1 and flows in the direction of gravity down further through the ionizer 10 therethrough. In it, the particles / aerosols are ionized by corona discharge with a predetermined polarity - usually negatively charged.

FIG. 2 shows the ionizer 10 in sections. Two nozzles 3 in the grounded metal plate, the nozzle plate 4, made of stainless steel or copper or an electrically conductive composite material made of carbon, but in any case inert to the process environment, are shown in section. An electrode tip 5 projects into each of them. All electrode tips are mounted aligned on the high-voltage grid 6. The high-voltage grid 6 itself is electrically insulated mounted on the housing wall of the system. About a passage in the housing wall, the high-voltage grid 6 is connected to the high voltage potential generated in a power supply (see, for example DE 101 32 528 C1 or DE 102 44 051 C1 ). The high voltage potential is generally adjustable on the power supply unit and its polarity depends on the process to be run.

After passage of the exhaust gas through the ionizer 10, the particles / aerosols are now electrically charged. The exhaust gas flow now passes under deflection into the horizontal in the connection zone 7, ie by the foot of the U, flows there horizontally and occurs under renewed deflection against gravity from below into the other leg 8 a. The connecting piece 7 serves as a catch for precipitating out of the gas stream particles and for the running in the collector 8, loaded with particles / aerosols liquid film.

The exhaust gas with the electrically charged particles enters the grounded collector 8. When flowing upward, the electrically charged particles are attracted to the tube walls, which indeed attract attraction due to the electrical connection of the collector 8 to the ground potential, and deposited thereon. In this case, the electrical charge is removed and thereby electrically neutralizes the particles.

The collector 8 is usually sprayed for flushing from above (not shown in FIG FIG. 1 ), so that the particles deposited on the collector walls are washed off downwards and collected in the connection zone 7 constructed for the collecting trough 7 and discharged via a pipe connection.

After emerging from the collector 8, the now purified exhaust gas flows upward, exits at the leg outlet 9 from the exhaust gas purification system 1 and in the cultivated, continuing flow channel or is immediately discharged to the environment.

The effectiveness of the exhaust gas purification system 1 and of the method was tested experimentally on a pilot plant. The pilot plant contained a nozzle plate with 61 nozzles and a tube bundle collector. It was operated with 9.5 - 10.5 kV DC for the corona discharge. The corona current was between 4.5 and 5.5 mA. The ionizer had a hollow cylindrical housing, as well as the collector. The mass concentration of the particles in the exhaust gas was 70-110 mg / Nm ³ .

When the direction of exhaust flow in the ionizer and collector zone was against gravity, the efficiency of the separation was 82-86%.

When the direction of exhaust flow in the ionizer and collector zone was equal to gravity, the efficiency of the deposition was 79-83%.

If the direction of the exhaust flow in the ionizer was the same as that in the ionizer and in the collector zone against gravity, the efficiency of the deposition was 95-97%.

The considerable improvement in the degree of separation is due to the U-shaped construction principle and the stability of the corona discharge in the ionizer.

LIST OF REFERENCE NUMBERS

1

section

2

entrance

3

jet

4

nozzle plate

5

High-voltage electrode

6

High-voltage grid

7

Connection zone, reservoir

8th

Collector zone, particle separator

9

output

10

ionizer

Claims (4)

1. Structural principle of an exhaust gas purification system in the form of a built-in section in a gas flow channel,
   in which, in the flow direction of the gas to be purified, there follow in sequence:

   - a zone for ionisation of the particles/aerosols carried in the gas, the ioniser,

   - a connecting zone,

   - a collector zone for precipitation of the particles/aerosols electrically neutralised therein,

   - a spraying device to flush out the collector zone,

   characterised in that:

   the section (1) for exhaust gas purification is in the shape of an upright U, in one leg of which are located the ionisation zone (10), the ioniser, for the particles/aerosols carried in the gas,
   while the gas to be purified flows in at the top of this leg and downwards in the direction of gravity through the ioniser (10),

   the transition from one leg to the other, the connecting zone (7) which is a collection container/vessel (7) for the particles precipitated out or separated out from the gas flow, at the lowest point of which is at least one discharge pipe to discharge the liquid loaded with the particles,

   the collector zone (8) which consists of at least one collector or of several collectors in sequence in the direction of flow, is located in the second leg (8),
   whereby the gas flows from below into the leg (8) and upwards against the force of gravity through the collector zone (8), a spray device being mounted above the collector zone (8) and, if there is a plurality of collectors, a spray device being mounted between each of the collectors.
2. Structural principle of an exhaust gas purification system according to claim 1, characterised in that in the ionising zone (10), which consists of an injector plate (4) connected to an electrical reference potential and a high-voltage grid (6) with high-voltage electrodes (5) mounted and aligned thereon, each of which projects into an injector (3) and the high-voltage electrodes project into their respectively associated injector (3) from below.
3. Structural principle of an exhaust gas purification system according to claim 2, characterised in that the collector zone (8) comprises at least one group of tube bundles (8).
4. Method for purifying an exhaust gas in an exhaust gas purification system according to claims 1 to 3,
   characterised by the steps:

   the exhaust gas is introduced from a channel from above in the direction of gravity into the leg with the ionising zone (10) and flows downwards through it in the direction of gravity,

   the exhaust gas leaving the ionising zone (10) is introduced into the connecting zone (7), in which the gas is firstly diverted in order to flow counter to the direction of gravity and perpendicular from the bottom upwards into the second leg (8), and secondly a first portion of the particles/aerosols which trickles out is collected in the connecting zone (7),

   the exhaust gas flows through the collector (8), counter to the direction of gravity from the bottom upwards, for purification and precipitation of the particles, in order to deposit its particles/aerosols on the walls of the collector (8), where they are electrically neutralised and where, with the aid of a flushing liquid sprayed onto the collector (8) at least from above, they can flow off counter to the gas flow, in the form of a liquid film loaded with particles in the direction of gravity and can trickle off in the connecting zone (7) into the collection container (7),

   the gas flows out as purified gas at the top of the second leg (8) and is passed on into the attached flow channel.

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