WO1997041959A1 - Procede de regulation d'un precipitateur electrostatique - Google Patents

Procede de regulation d'un precipitateur electrostatique Download PDF

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Publication number
WO1997041959A1
WO1997041959A1 PCT/SE1997/000730 SE9700730W WO9741959A1 WO 1997041959 A1 WO1997041959 A1 WO 1997041959A1 SE 9700730 W SE9700730 W SE 9700730W WO 9741959 A1 WO9741959 A1 WO 9741959A1
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WO
WIPO (PCT)
Prior art keywords
rapping
during
electrodes
voltage
interval
Prior art date
Application number
PCT/SE1997/000730
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English (en)
Inventor
Hans Jacobsson
Original Assignee
ABB Fläkt Aktiebolag
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by ABB Fläkt Aktiebolag filed Critical ABB Fläkt Aktiebolag
Priority to AU27974/97A priority Critical patent/AU2797497A/en
Publication of WO1997041959A1 publication Critical patent/WO1997041959A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/34—Constructional details or accessories or operation thereof
    • B03C3/74—Cleaning the electrodes
    • B03C3/76—Cleaning the electrodes by using a mechanical vibrator, e.g. rapping gear ; by using impact
    • B03C3/763—Electricity supply or control systems therefor

Definitions

  • the present invention relates to a method for controlling an electrostatic precipitator unit, comprising discharge electrodes and collecting electrodes, between which a high voltage is maintained, by a constant or pulsating direct current supplied to the electrodes. Dust deposited on the collecting electrodes is removed by mechanical rapping of the collecting electrodes by one or more mechanical impuls ⁇ es being supplied to the electrodes individually or in groups, in a predetermined manner. All the collecting electrodes of the precipitator unit are cleaned during recurrent, relatively short, rapping periods separated by rapping intervals of considerably longer duration. The duration of the rapping intervals and/or other rapping parameters are controlled.
  • Electrostatic precipitators are suitable in many contexts, especially in flue gas cleaning. Their design is robust and they are highly reliable. Moreover, they are most effici- ent. Degrees of separation above 99.9% are not unusual.
  • a procedure that is central to the function of an electrostatic precipitator is the rapping of the collecting electrodes.
  • the rapping frequency i.e. how often the rapping is effected per unit of time, is controlled mainly by two opposite requirements. Since the dust cake on the collecting electrode by its growth gradually deteriorates the function of the filter, rapping is desirable before the dust cake becomes too thick.
  • rapping in each rapping, a considerable amount of dust is released and reentrained to the flue gas, resulting in a momentarily reduced degree of separation. Besides, a too high rapping frequency results in the formation of a hard coating that adheres to the collecting electrode and is very difficult to remove by rapping.
  • the selected rapping frequency will be a compromise which should, for instance, maximise the average degree of separation.
  • Other rapping parameters that may be varied are the number of raps during each rapping period and the force thereof. The electric voltage between discharge electrodes and collecting electrodes may be reduced, disconnected or even reversed during the rapping in order to facilitate the release of the dust during rapping.
  • An electrostatic precipitator usually consists of a number of precipitator units which are connected in series. Since the amount of dust separated, in a given unit, per unit of time decreases strongly with the increasing number of precipitator units passed by the flue gas, the rapping must be controlled separately for each precipitator unit.
  • the rapping should, however, be co ⁇ ordinated so as not to be carried out at the same time in several precipitator units.
  • the rapping sequence in a precipitator unit containing a plurality of collecting electrodes, to be rapped is selected carefully, such that all electrodes usually are rapped once during a so-called rapping cycle, in a sequence selected for the purpose of minimising the reentrainment of dust to the flue gas.
  • US 4,432,062 discloses an automatic optimisation of the rapping frequency in terms of the average value of the remaining dust content in the flue gas after the precipi- tator.
  • the drawbacks of this method are a dependence on the measuring of the remaining dust content in the flue gas and the fact that the rapping frequency varies over several orders of magnitude between the precipitator units.
  • this leads to simultaneous optimisation of many parameters, which easily results in sub-optimisation or the absence of convergence of the optimising algorithm.
  • predetermined functional relations between the rapping frequencies are selected, e.g. constant relative proportions, the number of degrees of freedom is restricted too much, involving a risk of sub-optimisation.
  • the corresponding conditions apply to other rapping parameters, such as the voltage or current during rapping.
  • the main object of the invention is to maximise the dust separation, in an electrostatic precipitator unit, in order to minimise the dust emission of a plant comprising the electrostatic precipitator.
  • a second object of the invention is to maximise an average degree of dust separation, in an electrostatic precipitator unit, during the rapping intervals.
  • a third object of the invention is to maximise an average degree of dust separation, in one electrostatic precipitator unit, during the rapping intervals without any essential risk of influence from the performance in down ⁇ stream or upstream units.
  • a fourth object of the invention is to maximise an average degree of dust separation, in one electrostatic precipitator unit, during the rapping intervals by purely electrical measurements, in the same unit.
  • the present invention relates to a method for optimisation of the performance of an electrostatic precipitator unit, comprising discharge electrodes and collecting electrodes, between which a high voltage is maintained by a constant or pulsating direct current supplied to the electrodes. Under the action of the electric field between the electrodes, the particles, charged by the current therebetween, are moved towards the collecting electrodes and are deposited thereon. Dust deposited on the collecting electrodes is removed by mechanical rapping of the collecting electrodes by one or more mechanical impulses being supplied to the electrodes individually or in groups, in a predetermined manner. All the collecting electrodes of the precipitator unit are cleaned during recurrent, relatively short, rapp ⁇ ing periods separated by rapping intervals of considerably longer duration. The duration of the rapping intervals and/or other rapping parameters are controlled.
  • a strategy of controlling the electrical parameters is selected and this strategy is maintained during the optimisation.
  • the length of the interval between the rapping periods and possibly also other rapping parameters such as number of raps, rapping force and current or voltage between the electrodes during the rapping period are varied.
  • the cur ⁇ rent and voltage during the interval between the rapping periods are measured.
  • the average of the current, voltage, or a quantity derived from the current and/or voltage, during the interval between the rapping periods is calcul ⁇ ated. This calculated average is used for controlling the length of the rapping intervals and/or other rapping para- meters.
  • the derivative of the voltage should, in this case, be essentially proportional to the amount of separated dust per unit of time.
  • the decreasing efficiency is shown by the fact that, when operating with a constant current, the derivative of the voltage decreases in course of time, as shown in Fig. 3, see the description below.
  • the decreasing degree of separation during the inter ⁇ val between the rapping periods could apparently be met by making the rapping intervals as short as possible. This would, at first sight, make it possible to avoid the grad ⁇ ual deterioration of the efficiency.
  • a strategy of controlling the electrical parameters, for each precipi ⁇ tator unit is selected and this strategy is maintained during the optimisation.
  • the length of the interval between the rapping periods and possibly also other rapping para ⁇ meters are varied.
  • the average of the current, voltage, or a quantity derived from the current and/or voltage, during the interval between the rapping periods is calculated and used for controlling the length of the rapping intervals and/or other rapping parameters.
  • One suggested mode of operation comprises measuring of the average of the current during the interval between the rapping periods.
  • the length of the rapping intervals and/or other rapping parameters are controlled so as to obtain as high an average as possible.
  • Another suggested mode of operation comprises measuring of the average of the voltage during the interval between the rapping periods.
  • the length of the rapping intervals and/or other rapping parameters are controlled so as to obtain as low an average as possi ⁇ ble.
  • modes of operation comprises measur- ing of the average of the product of current and voltage or measuring the average of the time derivative of the voltage during the interval between the rapping periods, and by controlling the length of the rapping intervals and/or other rapping parameters so as to obtain as high an average as possible.
  • the current is kept constant, it may be convenient to try to get the minimum average voltage or the maximum average increase (voltage derivative) . If the voltage is kept constant, it may be convenient to try to get the maxi ⁇ mum average current. If the current must be limited owing to so-called back corona from the dust layer, resulting in a decrease of the voltage when the current increases above a given value, it may be convenient to try to maximise the average power. If the precipitator unit is controlled so as to try to operate close to the limit of electric flashover, this corresponds basically to operation with constant cur- rent. It is the field strength in the gas, rather than the voltage between the electrodes, that decides the flashover level, and the principle of controlling can be selected to be about the same as if the current is kept constant.
  • the main parameter of rapping to be controlled is the length of the interval between the rapping periods.
  • rapping parameters such as, but not limited to, number of raps per rapping period, rapping force and current or voltage during the rapping period.
  • rapping period it is also possible to apply to each collecting electrode a number of consecutive raps and, between the consecutive raps, successively decrease the voltage between the elec ⁇ trodes or the current to the electrodes.
  • Fig. 1 illustrates schematically a precipitator for carry ⁇ ing out the inventive method.
  • Fig. 2 shows schematically the current as a function of the time during some rapping intervals when keeping the voltage constant for two different durations of the rapping inter ⁇ vals, Figs 2a and 2b.
  • Fig. 3 shows schematically the voltage as a function of the time during some rapping intervals when keeping the current constant for two different durations of the rapping inter ⁇ vals, Figs 3a and 3b.
  • Fig. 1 illustrates schematically a precipitator for carry ⁇ ing out the inventive method.
  • the precipitator has an inlet duct 41 and an outlet duct 42, and comprises three precipi- tator units 1, 2, 3 each having a dust hopper 11, 12, 13.
  • the precipitator units are supplied with direct current from three rectifiers 21, 22, 23.
  • the rectifiers 21-23 are controlled and monitored by a control unit 30.
  • the control unit 30 also communicates with devices 51, 52 and 53 for rapping of the collecting electrodes in the precipitator units 1, 2 and 3.
  • Fig. 2 shows schematically how tiie current I in a precipi ⁇ tator unit varies in time during a rapping interval T if the voltage U between the electrodes is kept constant.
  • the maximum current immedi ⁇ ately after a rapping period S is higher after a long rapping interval (I a max' Fig- 2a ) than after a short one ( ⁇ bmax' Fi 9- 2b ) •
  • Fig. 3 shows schematically how the voltage U between the electrodes in a precipitator unit varies in time during a rapping interval T if the current I in the precipitator unit is kept constant. Owing to the increase of the thick ⁇ ness of the dust layer, the voltage increases in time.
  • the minimum voltage immediately after a rapping period S is lower after a long rapping interval (U am i n , Fig. 3a) than after a short one (Uj-jmi j -,, Fig. 3b) .
  • FIG. 3 A starting value for the length of the rapping interval for the precipitator unit 1 is chosen.
  • the voltage curve is assumed to be like in Fig. 3a.
  • the average of the time derivative of the voltage is calculated and the value is stored in the control unit 30.
  • the rapping interval is shortened and the voltage curve is assumed to be like in Fig. 3b.
  • the new average of the time derivative of the vol ⁇ tage is calculated and the value is stored in the control unit 30.
  • the two average values of the voltage time deriva ⁇ tive are compared and if the second value is higher a new test is made with an even shorter length of the rapping interval.

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  • Engineering & Computer Science (AREA)
  • Automation & Control Theory (AREA)
  • Mechanical Engineering (AREA)
  • Electrostatic Separation (AREA)

Abstract

La présente invention concerne un procédé de régulation d'un précipitateur électrostatique constitué d'électrodes de décharge et d'électrodes collectrices entre lesquelles on maintient une différence élevée de potentiel en appliquant aux électrodes un courant continu. On ôte la poussière déposée sur les électrodes collectrices en déclenchant des ébranlements mécaniques des électrodes collectrices en appliquant des impulsions mécaniques aux électrodes prises isolément ou en groupes. Les électrodes collectrices du précipitateur se nettoient à l'occasion de périodes d'ébranlement récurrentes et relativement brèves, séparées par des intervalles entre ébranlements durant considérablement plus longtemps. Une fois qu'une stratégie de régulation des paramètres électriques est définie, on conserve cette stratégie pendant toute la phase d'optimisation. En l'occurrence, on fait varier la durée des intervalles entre ébranlements ainsi qu'éventuellement d'autres paramètres concernant les ébranlements. Pendant l'intervalle entre deux ébranlements, on calcule l'intensité moyenne, la tension moyenne ou une grandeur dérivée de l'intensité et/ou de la tension. Cette moyenne calculée sert à déterminer la durée des intervalles entre ébranlements et/ou d'autres paramètres concernant les ébranlements.
PCT/SE1997/000730 1996-05-09 1997-04-30 Procede de regulation d'un precipitateur electrostatique WO1997041959A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU27974/97A AU2797497A (en) 1996-05-09 1997-04-30 Method for controlling an electrostatic precipitator

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9601763A SE506423C2 (sv) 1996-05-09 1996-05-09 Förfarande för att vid en elektrostatisk stoftavskiljare styra slagningsintervallens längd och övriga slagningsparametrar
SE9601763-7 1996-05-09

Publications (1)

Publication Number Publication Date
WO1997041959A1 true WO1997041959A1 (fr) 1997-11-13

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SE (1) SE506423C2 (fr)
WO (1) WO1997041959A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1967277A1 (fr) * 2007-03-05 2008-09-10 Alstom Technology Ltd Procédé de contrôle de l'ordre d'ébranlage pour la collecte des plaques à électrodes d'un filtre électrostatique
EP1967275A1 (fr) * 2007-03-05 2008-09-10 Alstom Technology Ltd Procédé et système de contrôle des opérations du dernier champ d'un sélecteur électrostatique
EP1967276A1 (fr) * 2007-03-05 2008-09-10 Alstom Technology Ltd Procédé d'évaluation du chargement de poussières d'un filtre électrostatique, et procédé et dispositif de contrôle de l'ébranlage d'un filtre électrostatique
CN114904658A (zh) * 2022-05-06 2022-08-16 浙江菲达环保科技股份有限公司 一种积灰厚度在线测量装置及电除尘器控制方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3469371A (en) * 1967-05-02 1969-09-30 Buell Eng Co Apparatus for controlling the removal of particle accumulations from the electrodes of an electric precipitator
EP0132660A2 (fr) * 1983-07-20 1985-02-13 Siemens Aktiengesellschaft Méthode pour la détection, pendant le fonctionnement, de l'occurence d'un temps de frappe optimale, pour le battage des électrodes d'un électrofiltre

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3469371A (en) * 1967-05-02 1969-09-30 Buell Eng Co Apparatus for controlling the removal of particle accumulations from the electrodes of an electric precipitator
EP0132660A2 (fr) * 1983-07-20 1985-02-13 Siemens Aktiengesellschaft Méthode pour la détection, pendant le fonctionnement, de l'occurence d'un temps de frappe optimale, pour le battage des électrodes d'un électrofiltre

Non-Patent Citations (3)

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Title
PATENT ABSTRACTS OF JAPAN, Vol. 14, No. 475, C-770; & JP,A,02 194 869 (MITSUBISHI HEAVY IND LTD), 1 August 1990. *
PATENT ABSTRACTS OF JAPAN, Vol. 14, No. 526, C-779; & JP,A,02 218 455 (MITSUBISHI HEAVY IND LTD), 31 August 1990. *
PATENT ABSTRACTS OF JAPAN, Vol. 7, No. 122, C-168; & JP,A,58 040 162 (GADELIUS K.K.), 9 March 1983. *

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1967277A1 (fr) * 2007-03-05 2008-09-10 Alstom Technology Ltd Procédé de contrôle de l'ordre d'ébranlage pour la collecte des plaques à électrodes d'un filtre électrostatique
EP1967275A1 (fr) * 2007-03-05 2008-09-10 Alstom Technology Ltd Procédé et système de contrôle des opérations du dernier champ d'un sélecteur électrostatique
EP1967276A1 (fr) * 2007-03-05 2008-09-10 Alstom Technology Ltd Procédé d'évaluation du chargement de poussières d'un filtre électrostatique, et procédé et dispositif de contrôle de l'ébranlage d'un filtre électrostatique
US8268040B2 (en) 2007-03-05 2012-09-18 Alstom Technology Ltd Method of controlling the order of rapping the collecting electrode plates of an ESP
US8328902B2 (en) 2007-03-05 2012-12-11 Alstom Technology Ltd Method of estimating the dust load of an ESP, and a method and a device of controlling the rapping of an ESP
KR101220943B1 (ko) * 2007-03-05 2013-01-11 알스톰 테크놀러지 리미티드 Ｅｓｐ의 수집 전극판들에서 랩핑의 순서를 제어하는 방법
CN114904658A (zh) * 2022-05-06 2022-08-16 浙江菲达环保科技股份有限公司 一种积灰厚度在线测量装置及电除尘器控制方法

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Publication number Publication date
SE9601763D0 (sv) 1996-05-09
SE506423C2 (sv) 1997-12-15
SE9601763L (sv) 1997-11-10
AU2797497A (en) 1997-11-26

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