CA2126073A1

CA2126073A1 - Method to purify gases

Info

Publication number: CA2126073A1
Application number: CA 2126073
Authority: CA
Inventors: Pertti Puumalainen
Original assignee: Fabretti Holdings Ltd
Current assignee: Fabretti Holdings Ltd
Priority date: 1991-12-17
Filing date: 1992-12-16
Publication date: 1993-06-24
Also published as: FI942834A0; FI942834A; AU3160393A; JPH07506759A; FI915921A0; EP0642379A1; WO1993011855A1

Abstract

The object of the invention is a method to purify gases, such as combustion gases, in which method oxides of nitrogen and sulphur are converted into solid particles by an electron beam coming from an electron source (1) with the aid of added base. By the present methods oxides of nitrogen and sulphur cannot be removed effectively. In the method of the invention particles charged in the electron beam are guided with an external electric field to gather on a collection sheet (5) into a layer (7) which can be cleaned at desired time periods.

Description

~ 093/118~5 21 2 6 0 7 3 PCT/F192/00343 ~ETHOD T0 PURIFY GASES

The object of the invention is a method to purify gases, such as combu~tion gases, in which method oxides of nikrogen 5 and sulphur are converted into solid particles by an electron beam coming from an electron source, with the aid of added alkaline.

The mostly used method to purify combustion gases these days is a method, in which an electric filter i5 used to remove the solid particles, and slaked lime, which binds to itself part of the sulphur oxide formed during the burning process, is fed into the furnace of the boiler. This slaked lime dust is then filtered off in the electric filter with all the other solid particles. Usually nitrogen oxides are not even attemp~ed to be remo~ed, but the burning prQcess is designed such that the t mperature is low all the time, which reduces the amount of nitrogen oxides produced. In principle the lowered temperature does not reduce the amount ~f heath ~produced, but, because power plants generally produce ele~tricity, according to the theoretical Carnot/s machine ; the efficiency of electricity production is reduced as the te~mperature difference~used by the machine is reduced. The eff:icien~y of the~Carnot'~ machine is (T2 - T~)~T2 (T2> Tl~, 25: ~that is, ~the~tempèrature of the boiler can not be lowered ~ery much without a significant reduction in efficiency.
: Power~ plants: :have~ also been designed, in whlch the : combustion gases~ would be in such a high temperature that they~would already be so strongly ionized, that electricity 3~ I ~ould be:,formed ~directly fro~ ~hese charge carriers by . separating them into collection surfaces of opposite charge with the aid:of a magnetic field. The~, if there is nitrogen present, it certainly burns into oxide. By adding washing ;~ methods ~of combustion gases, of which wet washing is most general, to the above described primary purification methods, 80 % of sulphur can usually be removed. Even with these washing methods nitrogen oxides can not be removed :~

W093/llg5~ PCT/FI92/00 ~
21'~6073 `~

without expensive special chemicals. A great disadvantage of the wet washing methods i5 also a huge amount of dirty water which is usually cleaned and recycled.

Today electric filters are good in removing solid material sufficiently. Perhaps their greatest disadvantages are the duration age of the wires used in the corona discharge, and keeping the corona discharge voltage at the breakdown level.

The aim of the invention is to achieve a method to purify gases, which in addition to removing solid material also efficiently removes S02 and most of N0.

The aim of the invéntion is achieved by a method which is : 15 characterized in the claims.

~s~ - In the method of this invention, particles in the gas, that have ~een ch~rged by an~electron beam, are guided to gather on a collection surface with the aid of an external : : : :
: 20~ electromagnetic field, and this collection surface is cleaned at desired~time intervals. In this m~thod dust-like lime~or some similar material, which removes part of the sulphur~oxides~ dire~tly and, together with ~he moisture in the combustion~gases or~added water, neutralizes nitrog~n ;25~ aGid~and~sulphur~ic~acid~formed in the ~lectron beam of N0 :and S2~ (~ N0 +~ el~ectron-~eam -> N02 + H20 -> HN03; S02 +
n~ ~ electron-b~am:~ S~3~ + H20 -> H2So, ), is added int~ th furnace~of th~boiler~ In addi~tion to lime, also ammonium :added in~o the~combus~ion:gases can:act as a neutralizer. In u ~ 30 'o~her words,-~the:electron beam converts the weakly reacting :N0 and~; S2 ~0, ~:effectively~ reacting nitrogen acid and sulphuric:acid~,~ which are neutralized with ha~es into salts that ~form solid~particles. This is known techn~logy, which has not yet been use~d, mainly because inexpensive, effective electron~beam devices with a:good efficiency have not been available. According;to earlier methods, burned nitrogen and sulphur~:after~they have been converted into solid material, .~YO 93/118~5 212 6 ~ 7 ~ PCT/Fl92/00343 have been removed with electric filters. In this invention the charge of the particles is exploited, because immediately after the electron beam all solid particles have been charged with a strong negative charge by the electron beam. With the charge and an external electroma~netic field the particles can be guided to wanted positions. The currents of the electron beams are very high~ for example in ;~: a 100 MW power plant with electron energy of 330 keV~ the electron beam current is 300 A. In a coal power plant of :lo equal size, the current needed by the elec~ric filter is ~the amount of combustion gases pQr second : 200 m3) 100 m2/m3 0,1 mA = 2 A. That is, when calculated wi~hout the ionization effect the current in the electron beam is more than hundredfold. In other words, it can be shown that ;ionization is apparently much more effective in the'electron beam than in the gas discharge, taking into account also the fact:that the voltage in the electron beam is about fiv~
tim~es higher than in the gas discharge. So the power put to the i:onization in the electron beam device is about 1000 ~ times greater when compared to the power in the electric ilter based on~ g~s dis~harge. This means that distances between~the:~Gollection sheets can be longer and collection :areas~can~be~smal1er. ~

25 ~In:the: fo1lowing the:invention is explained in more detail with~r~ference :to the ~ppended drawings, where figure 1 : presents~;one~e ~ ~diment the method, and figure 2 presents ;another~embodiment of~the method.

lIn :figure~ l~the~ electron ~eam source I has been installed beside~ the;com~ustion channel 9 in such a way that t~e : electron~beam 3~is injected by it into the ga~ flow 2 in t ~
:combustion channel 9.~fter g~in~ through the electron bea.n the :ga~s is ionized~:and the previously m~ntioned r~actions : 3~ take:~place so t~a~: most of the nitrogen and sulphur oxides : are converted into solid particles in the area 4, which : partlcles are~charged negatively by the electron beam. When ~,:

WO93/11855 PCT/F1~2/00.~
s~ , 2~26~ ~
.. 4 the gases have gone a little further, the negative particles are guided between the collection ~heets 5 by the electro-magnetic field 8. In this embodiment the electromagnetic field is produced economically by an organ shaped like a ring. Between the collection sheets 5 there is a separate electric field 6 from one sheet to the other perpendicular to the gas flow. The electromagnetic field which acts as a collection field 6 forces the solid material into the surface of the other collection sheet 7, from where it is removed for example with a mechanical impact or with a fast electrical counter impulse.

In figure 2~ the charged particles are collected into successive c~llection sheets 5 with collection guidance electric fields lO, ll. The collection sheets are in a positive potential referred to the body. There is also a separate collection field 6 in the collection sheets. There ~: can be two or more~&ucce~siv~ sets of collection sheets and :; th collection ~uidance electric ~ield ll can be controlled with separate: con~rollers 12, which are in different potentials, and ~or example shaped like a ring. The , ~
collection sh~ets can al~o be in several layers, in which case each of them is charged to a higher potential than the previous one, or every other sheet is charged to a higher po~:ential. The figures are~ schematic diagrams which can in reality~of oourse b~ ;more:~complicated and for example in di~ferent:positions for ths:removal of solid material.

: ~ The: invention is not restricted to the presented ~ 30~ lembodiments, but it can be altered according to the claims , ~ ~~ and applied also to purify other than combustion gases.

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Claims

1. Method to purify gases, such as combustion gases, in which method oxides of nitrogen and sulphur are converted into solid particles by an electron beam (3) coming from an electron source (1) with the aid of added base, c h a r a c-t e r i z e d in that particles charged in the electron beam are guided with an external electric field to gather on a collection sheet (5) into a layer (7) which can be cleaned at desired time periods.

2. Method in accordance with claim 1, c h a r a c t e r i -z e d in that the particles charged by the electron beam (3) are guided with a spesific collection guidance field (10, 11) between the collection sheets (5) which there can be two or more successive sets.

3. Method in accordance with claim 2, c h a r a c t e r i -z e d in that, for shaping the collection field, organs (12) which are in different potential than the collection sheets are used between the collection sheets and the wall of the combustion channel.

4. Method in accordance to some of claims 1-3, c h a r a c-t e r i z e d in that there are several collection sheets (5) in layers so that every other layer has a higher potential.

5. Method in accordance to some of claims 1-3, c h a r a c-t e r i z e d in that the solid material collected on the collection sheets (5) is removed with a fast electric impulse which has opposite polarity than the voltage of the collection field.