CA1320686C - Electrostatic precipitator - Google Patents
Electrostatic precipitatorInfo
- Publication number
- CA1320686C CA1320686C CA000545165A CA545165A CA1320686C CA 1320686 C CA1320686 C CA 1320686C CA 000545165 A CA000545165 A CA 000545165A CA 545165 A CA545165 A CA 545165A CA 1320686 C CA1320686 C CA 1320686C
- Authority
- CA
- Canada
- Prior art keywords
- gas
- distribution
- treatment zone
- flow
- precipitator
- Prior art date
- Legal status (The legal status 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 status listed.)
- Expired - Fee Related
Links
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
- B03C3/01—Pretreatment of the gases prior to electrostatic precipitation
- B03C3/011—Prefiltering; Flow controlling
-
- 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
- B03C3/019—Post-treatment of gases
Abstract
ABSTRACT OF THE DISCLOSURE
A dry horizontal flow electrostatic precipitator for removing suspended particles from the gas flow. The precipitator has a casing, a treatment zone consisting of high voltage and collecting electrodes, rapping means to dislodge the particles from the electrodes, an inlet opening at one end of the casing for admitting the untreated gas and an outlet opening at the other end for discharging the treated gas stream. The precipitator has gas distribution means near the inlet face of the treatment zone to ensure non-uniform gas flow distribution so that more than one-half of the gas stream flows into the lower half of the treatment zone. In a further aspect there are gas distribution means at the outlet arranged to produce non-uniform gas flow distribution such that more than one-half of the gas stream flows out of the upper half of the treatment zone.
A dry horizontal flow electrostatic precipitator for removing suspended particles from the gas flow. The precipitator has a casing, a treatment zone consisting of high voltage and collecting electrodes, rapping means to dislodge the particles from the electrodes, an inlet opening at one end of the casing for admitting the untreated gas and an outlet opening at the other end for discharging the treated gas stream. The precipitator has gas distribution means near the inlet face of the treatment zone to ensure non-uniform gas flow distribution so that more than one-half of the gas stream flows into the lower half of the treatment zone. In a further aspect there are gas distribution means at the outlet arranged to produce non-uniform gas flow distribution such that more than one-half of the gas stream flows out of the upper half of the treatment zone.
Description
t NON-UNIFORM ~AS ~ISTRIBUTION
FOR ELECTROSTATIC PF~ECIPITATORS
FIELD OF THE INVENTION
This invention relates generally to dry horizontal flow electrsstatic precipitators, and more particularly to the gas flow distribution at the precipitator inlet and outl0t faces.
DESCRIPTION OF THE PRIOR ART
.
Th0 use of electrostatic precipitatsrs ta remove susp~nded particles trom 3as streams is a well known art and dry horizontal flow precipitators ar~ in s~rvlce on many applications.
The trea!ment zone of a common dry horizontal flow pracipitator cons~s~s o~ highvoltage electrodes and collecting electrodes arranged to form gas passages parallel to the gas flow. The electrode systems ars enclosed in a casing to contain the gas flow.
Rapping systerns are used to dislodge the dust from the electrodes which then falls by gravity to the bottom ot the collector. The bottom of the casing is equipped with a dust removal syst0rn to discharge the collected dust.
Th~ gas is supplied to the precipitator thru an inlet nozzle that connects the inlet -1- ~
~ 1 3206P~h ~ ~
~"ct to th~ predpitator casin~. ~3as ~low ~listribution at th~ Inlot has b~en r~c~nizcd to affect precipitator performanc~ and dis~ribution doviG~s are ~mploycd ~o spread ~h0 ~as flow uniformly across the full fac6 of th0 precipitator treatment zone. Thc details of ~ha devices vary with thc configuration of the inlet duct and nozzls, and with the pr~fsranc~s of tho dssign~r. ~ho gas distribution d~vic~s ar~ typicaliy van~s in ~hq inlet nozzle and diffus~r plates at or near th~ inlet face.
Although flow distribution at the inlet has b~n the primary concern, distribution at the outlst has also been rcco~nized to affect performance, and devices similar to gho~e at tho inlet arc oRen us~d to control the outlet distribution.
Early precipitator installations were often designed with little regard to duct arrangement or gas flow distribution. U.S. pat3nt 1,344,330 to Bradley issued in 1920 dascribss an unusual orific0-precipitator with electrod~ surfaces p0rpendicular to the flow, howev~r H is the attention paid to gas distribution that is of interest. The inlet duc~
is connccted to th~ pr~cipitator casing without an inlet nozzle. Ths entire duct enters below ths horizontal c~ntarline of th~ casing. doss not extond across the full width, and is offs0t from tho v~rtical c~nterline of the casing. The openin~ to th~ treatmeng zone is tnto a small part of ths trsatmsnt zone face and there ar~ no flow distrlbution davi~s.
The patcnt mak~s no m~ntion of gas flow distribution. The collection effici~ncies rsquirsd during tha early stages of precipitator development were achievable without addr~ssing gas flow and th0 importanc~ of flow distribution to performance had not yet bsen rocognizad.
Th~ sciontifis investigation of th~ ~ffscts of flow distribution on el~ctrostatic pracipitator parformancc began about 194~ (H. J. WtlITE, "industrial Elactrostatic Precipitation," Addison-W~sl~y Publishin~ Company, Inc (1963) p. 238). This has 320686 ~- I
V,~ . , ~., - ~ulte~l in pro~resstowardsthe dcsi~n of flowcontrol means that will ~olve the ~luid m~chanics probl~m of taking tha gas stroam from ~he flow diraction and tlow valoci~y of inlet duct and delivering it to tha inle~ of ~he pracipitator treatment zone with uniform distribution. Examplas of this ar0 I).S. patents 3,425,189 to Has~lmayer and 3,831,350 to Gilles. Attention has also been given to achieving flow distribution with devices that ar0 not advers~iy aff~cted by dust cleposits, for ~xampl~ U.S. patsnt 4,026,683 to Snader.
Optimum precipitator p~rformance is associat~d with uniform ~as flow, and uniform gas flow distribution at the precipitator inlet is the recommendation by precipitator manufacturers and other authorities on precipitators. The Industrial Gas Claaning Institute (IGCI) first published a standard EP-7, Gas Flow Model Studies, in 196g.
Since completely uniform gas distribu~ion is not achievable, the IGCI standard for flow distribution ~ives tol~rances on uniformity which are considcred acceptable.
Progressively high0r efficiency requirements, lhe incraasin~ awareness Ihat gas distribution affects partormance, improvements in measuring and control devices, and a mathsmatical analysis that shows uniform gas flow di~tribution ~ives b~st performancs hava led to raising thc standards for flow uniformity. Tho r~visad standard for flow distribution issued by the IGCI in 1981 calls for a high degree of uniformity. Precipita~or manufacturers try to achievs uniform flow and often perform mod~l studies to help in th~ dosign of flow correcting devices.
Th~ rnathematical analysis on which th~ principle that uniform ~as flow distribution givss bost performanca is based assumes uniform dust concentration ovsr a section acrosstheflowat any point within the precipitator. This assumption means eithar no re-sntrainment takes place or that re-entrainment, if it does occur, does not change ' 1 3~0686 ~::
9 dust concentratlon trorrl the ~op to the bottom.
Re-entrainm~nt chan~0s thc dust concantration from th~ top to th0 bottom of a ~ry horizontal flow precipitator. An el0ctrostatic pracipilator removes particles from a ~as stream by char~in~ them el~ctrically and attracting them to an sl~ctrods. Whsn a laysr of dust has accumulated and a rapper is activatecl, tha dust layer is dislodg~d and falls down due to the force of ~ravity. However, not all the dust reaches the bottom of the precipitator. The layer may begin to slid~ down as a sheet, but as it ~athers spoed, it breaks up and some o~ the dust is re-entraincd on its way down. In a high efficiency pr~cipitator most of th0 r~-0ntrained dust is recoll~ctad furthcr back and low~r down within the treatment zona. The cycle of collection and re-entrainment may repeat itself sevsral times before dust which ~ntered the prscipitator near the top falls below th0 bottom of the tr~atment zone and is truly collected. Ths oumulative effcct of this re-sntrainmsnt incraas3s tho dust concentration in th0 low~r zone of the precipitator compared with the upp~r zone as the flow travels thru the precipita~or.
The action of ~ravi~y on uncoll~cted particles passin~ thru th~ pr~cipita~or is also a factor that chan~as the dust conccntration from thc top to th0 bottom.
C)bservations made into ;he outlet nozzles of operating pr0cipitators indicate th~t most of ths IOSSQS occur towards the bottom of the ou~let face.
This was recognized by Gallaer, lJ.S. patent 3,733,785. This patent recommends uniform inlet gas flow distribution and devic~s within the precipitator to direct th~ flow upward as it travels thru the unit to arrive at a skewed distribution at the outlet with the gas flow favoring the top. Precipitator performance depends on treatment time and this distribution slows down the flow in the lower zone toward the outlet giving mors treatment time where th~ dust concentration is higher.
SUMMARY OF THE INVENTION
The presen~ invention involves a significant departure from the accapted theory and practice of providing uniform gas flow at the inlet of a dry horizontal flow electrostatic precipitator.
A oomputer rnodel was used to study how re-3ntrainment and ~as flow distribution affeot parformance. The model is a two dimensional side view section of a precipitator from inlet to ou~let and top to bottom with a vertical and a horizontal grid. Conditions across the width of the precipitator are assumed to be substantially constant. Tha grid breaks the precipitator treatment zone into a number of small elem~nts. The same basic relationships that are commonly applied to predict the p~rformance of large precipitators are ussd by the mod~l to predict the p~rformance of eaoh element.
Tosting th~ mod~l involves assignin~ a ~-entrainment function which specifles how a ~islodged dust laysr is dispersed as it falls down. Ths psrformance with this re-entrainment function and with uniform ~as flow distribution is detarminsd as a reference. Ths inlet and outlet gas flow profiles are then adjusted to skewed distributions and the model is tested again to cornpute the performance which may then b~ compared with that for uniform flow.
The results show that a controllad non-uniform gas distribution may ba used to improvs the performance over uniform flow. Admitting more than half of the gas flow into the lower half and the remaining smaller proportion into the upper half of the inlet to the treatment zone and then discharging more than half the flow from tha upper half ~ 1 3~0686 ,i . . .
-~d the rem~inin~ small~r proportion from the lower half of the outlet from ths tr~atm~nt zona is the pr~fsrr~d non-uniform ~as distribution.
The computer modcl was tested usin~ inlet and outlet skews that varied in a linear way from th0 top ~o th~ bottom. The shape of th~ sk~w for best perforrnance may not be linear, and in practise will be rounded at the top and the bottom boundaries to avoid ~low discontinuity.
With a gas flow distribution at the inlet different from the outlet, the flow profile changes within the precipitator and tha four quarters of a precipitator side view operate generally as follows.
Upper Inlet - This section admits a small flow and a correspondingly srnall dust load.
Becaus~ af th~ low v~locity, tha collection 0fficiency is high and rslativaly littla dust leaYes this section to enter the upper outlet. Losses due to re-entraiment of the dust falling from noar the top ar~ high, but apply to only a small amount of dust.
IJpper Outlot - This sec~ion operates at high velocity and therefora low offici0ncy.
Since tha inlqt load is small, the low afficisncy and high rappin3 losses apply to only a ve~ small fraction of the ~otal dust.
Low~r Inlet - This saction admits a lar~e flow and traats much more ~as and receives correspondingly mor~ dust than the section above it. The efficiency is lower because of the hi~her velocity but tha total dust collected is more. The collected dust is nearer the bottom so the rapping losses are low. Considerable dust escapas to the lower outlat.
Low~r Outlet - This section has a low velocity and therefore operates at high efficiency. The dust load from the lower inlet is collected efficiently near the bottom and is subject ~o low rapping losses.
1 32~)686 BRIEF DESCRIPTION OF THE DRAWiNGS
The drawin~s are all simplified illustrations of typical precipitators and ~as distribution devic~s. In the drawings like parts ar~ marked alike:
FIG. 1 is a side view cross s0ction of a dry horizontal flow precipitator showing the major components.
FIG. 2 is a side vi~w showing an inlst gas distribution means dssigned to give uniform distribution according to prior art.
FIG. 3 is an end view of the inlet distribution deYice in FIG. 2 showing typical means clesigned to ~ive uniform distribution according to prior art.
FIG. 4 is a side view showing an inlet gas distribution means dasignsd to ~ive non-uniform distribution according to a praforred embodimant of the invention.
FIG. 5 is an end vi~w of the inlet distribution device in FIG. 4 showing typical maans designed to giv~ the pr~ferred distribution.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a cross-sectional side view of a dry horizontal flow precipitator. The casing 1 ancloses the 01~ctrod~ systems. Collecting ~l~ctrodes 7 are spaced to form gas passages parallel to ths gas flow. High voltaga electrodes 9 are spaced in the gas passages botwsen the collecting alectrodes and ars supported from insulators.
1 3206~6 ~--f ~e zone ~ormed by th~ ~as passa~es in which tha ~as tlow is ~xposed to ~h~
influenoe o7 the hi~h volta~e and eollectin~ electrodes Is the trea~ment zone. The treatmant ~on~ in this llus~ration consists of two 010ctrod0 fialcts in th~ direction of gas flow. The number of fields in a precipitator may vary from a singlQ field to a larger numbar. The bottom of the casiny is equipped with a dust removal system, which may ba a hopper systam 2 as shown or another system such as drag conveyor or wet sluicing. Collected dust is dislodged from tha electrodes by collecting elsctrode rappers 8 and high voltage 61ectrods rapp~rs 10 which may b~ external to the casing as shown, or inside the casing. Thess systams are all conventional.
Dust laden gas flows from an inlet duct 4 thru an inlat nozzle 3 to the inlet of the precipitator treatment zone. Turning vanes 5 and an inle~ gas distribution davice 6 are us0d to distribute th~ gas flow across the inlet face of the tr0atm~nt zone. The inlet gas disribution davice 6 may be a single diffuser plate as shown, or several diffusers in seri~s. Th~ h~îght of the opening into the treatmsnt zons is givan by dimension 11i1.
The gas flows thnJ the treatment zone, an outlet distribution davice 11, an ou~let nozzle ~2, and Isaves thnJ an outl~t duct 13. Ths height of tho opening from th~ treatmsnt zone is given by dimansion 112.
FIG. 2 shows ideal inlet gas tlow distribution according to prior art. The inlet nozzle 3 is equipped with vanes 5 and distribution devices 6 designed to give uniforrn gas flow as the gas enters a treatmant zone 14. The relative flow volume entaring the treatm~nt zone from top to bottom is dspicted by the length of the arrows 15. For uniform gas flow distribution all tha arrows are the same length resulting in a flow distribution profile 16 with hatf the flow entering the upper half, and half th0 flow entering the lower half of the height of the opening to the treatment zone~
FIG. 3 shows typic~lly ~h~ patterns ot somo distribution cl~vic0s ~ that ar~ d~si~ned to give uniforrn flow. They commonly hav~ equal open araa across the entire face.
FIG. 4 shows tha pr~ferrcd ~as distribution accordin~ to the inv0ntion. Th0 inlst nozzle 3 is equipped with vanes 17 and a distribution device 18 designed to spread ths gas flow across ~hs width and ths height of the oponin~ to the tr~atmsnt zone to give a controllad non-uniform gas flow distribution as the gas flow enters the treatment zone 14. The relative flow volums entering the height of the opening to the treatment ~one is d~picted by ~ha length of the arrows 19. The arrows are of unequal 10ngth. Tha longer arrows toward the bottom result in a gas distribution profile 20 such ~ha~ more than half the total flow enters the lower half of ths height of the opening ~o the treatment zone. The outlat gas distribution device 22 is designed in a reverse manner to the inlet devic~ ~o that mor~ than half the total flow leaves thru the upper half of tha height of the openin~ from th~ treatment zone. This gas flow distribution results in a small upward component of flow as the gas flows thru the treatm~nt zone as indicated by the slopa of the arrow ~1.
FIG. 5 shows typically the pattern of some distribution devices 18 desi~ned to give the preferred non-uniform gas distribution at ths inl~t. A distribution device with mora opan area in ths lower half than the upper half may be used to achieve ths prefarred gas distribution.
FIG.1, FIG. 2, and FIG. 4 show horizontal flow inlet and outlet ducts with symmetric nozzlss. Many other conn~cting duct and nozzle configurations ars possible. In tha nnanner that the design of the distribution devices required to give uniform flow is influenced by tha configuration, so the design of the devices to give non-uniform flow will also be influenced by the configuration. Non-symmetricly shaped nozzles may be f - 1 3Z06~
' qlpful in achleving the preferred non-uniform inlat and outlet ~as distfibutions.
FIG. 3 and FIG. 5 show that th~ pref~rr~d gas distribution may b~ obtain~d by usin~
vanes and distribution devices which except for the size or spacin~ of the openin~s are similar to those conventionally ussd to giva uniform flow.
This inv~ntion is for the flow control means required to ~ivs controlled non-uniform gas distributions at th~ inlet and outlet fac~s of dry horizontal flow precipitators. The duct and nozzle configurations and the vanes and distribution devices at the inlet and outlet of the precipitator are the flow control mearls used to achieve a desired gas flow distribution. Tha details of ths flow control means, whether they ar~ of a type pr~sently in use or of a type to bs developed in the futur~, are not the issue of the invention. The issu~ is the use of th~se means to give ~he prefGrr~d non-uniform gas flow distribution.
~ 10-.
FOR ELECTROSTATIC PF~ECIPITATORS
FIELD OF THE INVENTION
This invention relates generally to dry horizontal flow electrsstatic precipitators, and more particularly to the gas flow distribution at the precipitator inlet and outl0t faces.
DESCRIPTION OF THE PRIOR ART
.
Th0 use of electrostatic precipitatsrs ta remove susp~nded particles trom 3as streams is a well known art and dry horizontal flow precipitators ar~ in s~rvlce on many applications.
The trea!ment zone of a common dry horizontal flow pracipitator cons~s~s o~ highvoltage electrodes and collecting electrodes arranged to form gas passages parallel to the gas flow. The electrode systems ars enclosed in a casing to contain the gas flow.
Rapping systerns are used to dislodge the dust from the electrodes which then falls by gravity to the bottom ot the collector. The bottom of the casing is equipped with a dust removal syst0rn to discharge the collected dust.
Th~ gas is supplied to the precipitator thru an inlet nozzle that connects the inlet -1- ~
~ 1 3206P~h ~ ~
~"ct to th~ predpitator casin~. ~3as ~low ~listribution at th~ Inlot has b~en r~c~nizcd to affect precipitator performanc~ and dis~ribution doviG~s are ~mploycd ~o spread ~h0 ~as flow uniformly across the full fac6 of th0 precipitator treatment zone. Thc details of ~ha devices vary with thc configuration of the inlet duct and nozzls, and with the pr~fsranc~s of tho dssign~r. ~ho gas distribution d~vic~s ar~ typicaliy van~s in ~hq inlet nozzle and diffus~r plates at or near th~ inlet face.
Although flow distribution at the inlet has b~n the primary concern, distribution at the outlst has also been rcco~nized to affect performance, and devices similar to gho~e at tho inlet arc oRen us~d to control the outlet distribution.
Early precipitator installations were often designed with little regard to duct arrangement or gas flow distribution. U.S. pat3nt 1,344,330 to Bradley issued in 1920 dascribss an unusual orific0-precipitator with electrod~ surfaces p0rpendicular to the flow, howev~r H is the attention paid to gas distribution that is of interest. The inlet duc~
is connccted to th~ pr~cipitator casing without an inlet nozzle. Ths entire duct enters below ths horizontal c~ntarline of th~ casing. doss not extond across the full width, and is offs0t from tho v~rtical c~nterline of the casing. The openin~ to th~ treatmeng zone is tnto a small part of ths trsatmsnt zone face and there ar~ no flow distrlbution davi~s.
The patcnt mak~s no m~ntion of gas flow distribution. The collection effici~ncies rsquirsd during tha early stages of precipitator development were achievable without addr~ssing gas flow and th0 importanc~ of flow distribution to performance had not yet bsen rocognizad.
Th~ sciontifis investigation of th~ ~ffscts of flow distribution on el~ctrostatic pracipitator parformancc began about 194~ (H. J. WtlITE, "industrial Elactrostatic Precipitation," Addison-W~sl~y Publishin~ Company, Inc (1963) p. 238). This has 320686 ~- I
V,~ . , ~., - ~ulte~l in pro~resstowardsthe dcsi~n of flowcontrol means that will ~olve the ~luid m~chanics probl~m of taking tha gas stroam from ~he flow diraction and tlow valoci~y of inlet duct and delivering it to tha inle~ of ~he pracipitator treatment zone with uniform distribution. Examplas of this ar0 I).S. patents 3,425,189 to Has~lmayer and 3,831,350 to Gilles. Attention has also been given to achieving flow distribution with devices that ar0 not advers~iy aff~cted by dust cleposits, for ~xampl~ U.S. patsnt 4,026,683 to Snader.
Optimum precipitator p~rformance is associat~d with uniform ~as flow, and uniform gas flow distribution at the precipitator inlet is the recommendation by precipitator manufacturers and other authorities on precipitators. The Industrial Gas Claaning Institute (IGCI) first published a standard EP-7, Gas Flow Model Studies, in 196g.
Since completely uniform gas distribu~ion is not achievable, the IGCI standard for flow distribution ~ives tol~rances on uniformity which are considcred acceptable.
Progressively high0r efficiency requirements, lhe incraasin~ awareness Ihat gas distribution affects partormance, improvements in measuring and control devices, and a mathsmatical analysis that shows uniform gas flow di~tribution ~ives b~st performancs hava led to raising thc standards for flow uniformity. Tho r~visad standard for flow distribution issued by the IGCI in 1981 calls for a high degree of uniformity. Precipita~or manufacturers try to achievs uniform flow and often perform mod~l studies to help in th~ dosign of flow correcting devices.
Th~ rnathematical analysis on which th~ principle that uniform ~as flow distribution givss bost performanca is based assumes uniform dust concentration ovsr a section acrosstheflowat any point within the precipitator. This assumption means eithar no re-sntrainment takes place or that re-entrainment, if it does occur, does not change ' 1 3~0686 ~::
9 dust concentratlon trorrl the ~op to the bottom.
Re-entrainm~nt chan~0s thc dust concantration from th~ top to th0 bottom of a ~ry horizontal flow precipitator. An el0ctrostatic pracipilator removes particles from a ~as stream by char~in~ them el~ctrically and attracting them to an sl~ctrods. Whsn a laysr of dust has accumulated and a rapper is activatecl, tha dust layer is dislodg~d and falls down due to the force of ~ravity. However, not all the dust reaches the bottom of the precipitator. The layer may begin to slid~ down as a sheet, but as it ~athers spoed, it breaks up and some o~ the dust is re-entraincd on its way down. In a high efficiency pr~cipitator most of th0 r~-0ntrained dust is recoll~ctad furthcr back and low~r down within the treatment zona. The cycle of collection and re-entrainment may repeat itself sevsral times before dust which ~ntered the prscipitator near the top falls below th0 bottom of the tr~atment zone and is truly collected. Ths oumulative effcct of this re-sntrainmsnt incraas3s tho dust concentration in th0 low~r zone of the precipitator compared with the upp~r zone as the flow travels thru the precipita~or.
The action of ~ravi~y on uncoll~cted particles passin~ thru th~ pr~cipita~or is also a factor that chan~as the dust conccntration from thc top to th0 bottom.
C)bservations made into ;he outlet nozzles of operating pr0cipitators indicate th~t most of ths IOSSQS occur towards the bottom of the ou~let face.
This was recognized by Gallaer, lJ.S. patent 3,733,785. This patent recommends uniform inlet gas flow distribution and devic~s within the precipitator to direct th~ flow upward as it travels thru the unit to arrive at a skewed distribution at the outlet with the gas flow favoring the top. Precipitator performance depends on treatment time and this distribution slows down the flow in the lower zone toward the outlet giving mors treatment time where th~ dust concentration is higher.
SUMMARY OF THE INVENTION
The presen~ invention involves a significant departure from the accapted theory and practice of providing uniform gas flow at the inlet of a dry horizontal flow electrostatic precipitator.
A oomputer rnodel was used to study how re-3ntrainment and ~as flow distribution affeot parformance. The model is a two dimensional side view section of a precipitator from inlet to ou~let and top to bottom with a vertical and a horizontal grid. Conditions across the width of the precipitator are assumed to be substantially constant. Tha grid breaks the precipitator treatment zone into a number of small elem~nts. The same basic relationships that are commonly applied to predict the p~rformance of large precipitators are ussd by the mod~l to predict the p~rformance of eaoh element.
Tosting th~ mod~l involves assignin~ a ~-entrainment function which specifles how a ~islodged dust laysr is dispersed as it falls down. Ths psrformance with this re-entrainment function and with uniform ~as flow distribution is detarminsd as a reference. Ths inlet and outlet gas flow profiles are then adjusted to skewed distributions and the model is tested again to cornpute the performance which may then b~ compared with that for uniform flow.
The results show that a controllad non-uniform gas distribution may ba used to improvs the performance over uniform flow. Admitting more than half of the gas flow into the lower half and the remaining smaller proportion into the upper half of the inlet to the treatment zone and then discharging more than half the flow from tha upper half ~ 1 3~0686 ,i . . .
-~d the rem~inin~ small~r proportion from the lower half of the outlet from ths tr~atm~nt zona is the pr~fsrr~d non-uniform ~as distribution.
The computer modcl was tested usin~ inlet and outlet skews that varied in a linear way from th0 top ~o th~ bottom. The shape of th~ sk~w for best perforrnance may not be linear, and in practise will be rounded at the top and the bottom boundaries to avoid ~low discontinuity.
With a gas flow distribution at the inlet different from the outlet, the flow profile changes within the precipitator and tha four quarters of a precipitator side view operate generally as follows.
Upper Inlet - This section admits a small flow and a correspondingly srnall dust load.
Becaus~ af th~ low v~locity, tha collection 0fficiency is high and rslativaly littla dust leaYes this section to enter the upper outlet. Losses due to re-entraiment of the dust falling from noar the top ar~ high, but apply to only a small amount of dust.
IJpper Outlot - This sec~ion operates at high velocity and therefora low offici0ncy.
Since tha inlqt load is small, the low afficisncy and high rappin3 losses apply to only a ve~ small fraction of the ~otal dust.
Low~r Inlet - This saction admits a lar~e flow and traats much more ~as and receives correspondingly mor~ dust than the section above it. The efficiency is lower because of the hi~her velocity but tha total dust collected is more. The collected dust is nearer the bottom so the rapping losses are low. Considerable dust escapas to the lower outlat.
Low~r Outlet - This section has a low velocity and therefore operates at high efficiency. The dust load from the lower inlet is collected efficiently near the bottom and is subject ~o low rapping losses.
1 32~)686 BRIEF DESCRIPTION OF THE DRAWiNGS
The drawin~s are all simplified illustrations of typical precipitators and ~as distribution devic~s. In the drawings like parts ar~ marked alike:
FIG. 1 is a side view cross s0ction of a dry horizontal flow precipitator showing the major components.
FIG. 2 is a side vi~w showing an inlst gas distribution means dssigned to give uniform distribution according to prior art.
FIG. 3 is an end view of the inlet distribution deYice in FIG. 2 showing typical means clesigned to ~ive uniform distribution according to prior art.
FIG. 4 is a side view showing an inlet gas distribution means dasignsd to ~ive non-uniform distribution according to a praforred embodimant of the invention.
FIG. 5 is an end vi~w of the inlet distribution device in FIG. 4 showing typical maans designed to giv~ the pr~ferred distribution.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a cross-sectional side view of a dry horizontal flow precipitator. The casing 1 ancloses the 01~ctrod~ systems. Collecting ~l~ctrodes 7 are spaced to form gas passages parallel to ths gas flow. High voltaga electrodes 9 are spaced in the gas passages botwsen the collecting alectrodes and ars supported from insulators.
1 3206~6 ~--f ~e zone ~ormed by th~ ~as passa~es in which tha ~as tlow is ~xposed to ~h~
influenoe o7 the hi~h volta~e and eollectin~ electrodes Is the trea~ment zone. The treatmant ~on~ in this llus~ration consists of two 010ctrod0 fialcts in th~ direction of gas flow. The number of fields in a precipitator may vary from a singlQ field to a larger numbar. The bottom of the casiny is equipped with a dust removal system, which may ba a hopper systam 2 as shown or another system such as drag conveyor or wet sluicing. Collected dust is dislodged from tha electrodes by collecting elsctrode rappers 8 and high voltage 61ectrods rapp~rs 10 which may b~ external to the casing as shown, or inside the casing. Thess systams are all conventional.
Dust laden gas flows from an inlet duct 4 thru an inlat nozzle 3 to the inlet of the precipitator treatment zone. Turning vanes 5 and an inle~ gas distribution davice 6 are us0d to distribute th~ gas flow across the inlet face of the tr0atm~nt zone. The inlet gas disribution davice 6 may be a single diffuser plate as shown, or several diffusers in seri~s. Th~ h~îght of the opening into the treatmsnt zons is givan by dimension 11i1.
The gas flows thnJ the treatment zone, an outlet distribution davice 11, an ou~let nozzle ~2, and Isaves thnJ an outl~t duct 13. Ths height of tho opening from th~ treatmsnt zone is given by dimansion 112.
FIG. 2 shows ideal inlet gas tlow distribution according to prior art. The inlet nozzle 3 is equipped with vanes 5 and distribution devices 6 designed to give uniforrn gas flow as the gas enters a treatmant zone 14. The relative flow volume entaring the treatm~nt zone from top to bottom is dspicted by the length of the arrows 15. For uniform gas flow distribution all tha arrows are the same length resulting in a flow distribution profile 16 with hatf the flow entering the upper half, and half th0 flow entering the lower half of the height of the opening to the treatment zone~
FIG. 3 shows typic~lly ~h~ patterns ot somo distribution cl~vic0s ~ that ar~ d~si~ned to give uniforrn flow. They commonly hav~ equal open araa across the entire face.
FIG. 4 shows tha pr~ferrcd ~as distribution accordin~ to the inv0ntion. Th0 inlst nozzle 3 is equipped with vanes 17 and a distribution device 18 designed to spread ths gas flow across ~hs width and ths height of the oponin~ to the tr~atmsnt zone to give a controllad non-uniform gas flow distribution as the gas flow enters the treatment zone 14. The relative flow volums entering the height of the opening to the treatment ~one is d~picted by ~ha length of the arrows 19. The arrows are of unequal 10ngth. Tha longer arrows toward the bottom result in a gas distribution profile 20 such ~ha~ more than half the total flow enters the lower half of ths height of the opening ~o the treatment zone. The outlat gas distribution device 22 is designed in a reverse manner to the inlet devic~ ~o that mor~ than half the total flow leaves thru the upper half of tha height of the openin~ from th~ treatment zone. This gas flow distribution results in a small upward component of flow as the gas flows thru the treatm~nt zone as indicated by the slopa of the arrow ~1.
FIG. 5 shows typically the pattern of some distribution devices 18 desi~ned to give the preferred non-uniform gas distribution at ths inl~t. A distribution device with mora opan area in ths lower half than the upper half may be used to achieve ths prefarred gas distribution.
FIG.1, FIG. 2, and FIG. 4 show horizontal flow inlet and outlet ducts with symmetric nozzlss. Many other conn~cting duct and nozzle configurations ars possible. In tha nnanner that the design of the distribution devices required to give uniform flow is influenced by tha configuration, so the design of the devices to give non-uniform flow will also be influenced by the configuration. Non-symmetricly shaped nozzles may be f - 1 3Z06~
' qlpful in achleving the preferred non-uniform inlat and outlet ~as distfibutions.
FIG. 3 and FIG. 5 show that th~ pref~rr~d gas distribution may b~ obtain~d by usin~
vanes and distribution devices which except for the size or spacin~ of the openin~s are similar to those conventionally ussd to giva uniform flow.
This inv~ntion is for the flow control means required to ~ivs controlled non-uniform gas distributions at th~ inlet and outlet fac~s of dry horizontal flow precipitators. The duct and nozzle configurations and the vanes and distribution devices at the inlet and outlet of the precipitator are the flow control mearls used to achieve a desired gas flow distribution. Tha details of ths flow control means, whether they ar~ of a type pr~sently in use or of a type to bs developed in the futur~, are not the issue of the invention. The issu~ is the use of th~se means to give ~he prefGrr~d non-uniform gas flow distribution.
~ 10-.
Claims (2)
1. In a dry horizontal flow electrostatic precipitator for removing suspended particles from a gas stream, the precipitator having a casing, a treatment zone consisting of collecting and high voltage electrodes, rapping means to dislodge the collected dust, an inlet opening at one end of the treatment zone for admitting the untreated gas stream and an outlet opening at the other end of the treatment zone for discharging the treated gas stream, the improvement comprising gas flow control means at or near the inlet opening designed for non-uniform gas distribution, such that more than half the gas flow entering the treatment zone enters the lower half of the height of the opening to the treatment zone.
2. A precipitator as claimed in claim 1 further including gas flow control means at or near the outlet opening designed for non-uniform gas distribution such that more than half the gas flow leaving the treatment zone leaves the upper half of the height of the opening from the treatment zone.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US71446985A | 1985-03-26 | 1985-03-26 | |
| US714,469 | 1985-03-26 | ||
| US06/943,855 US4695297A (en) | 1985-03-26 | 1986-12-22 | Electrostatic precipitator |
| US943,855 | 1986-12-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1320686C true CA1320686C (en) | 1993-07-27 |
Family
ID=27109163
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000545165A Expired - Fee Related CA1320686C (en) | 1985-03-26 | 1987-08-24 | Electrostatic precipitator |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4695297A (en) |
| CA (1) | CA1320686C (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4968330A (en) * | 1989-09-01 | 1990-11-06 | Fmc Corporation | Apparatus for separating particulates in an electrostatic precipitator |
| DE4112455A1 (en) * | 1991-04-12 | 1992-10-15 | Ver Energiewerke Ag | Dust removal from flue gas - by gas flow diversion and electrostatic pptn. |
| US5156658A (en) * | 1991-05-01 | 1992-10-20 | Research-Cottrell, Inc. | Electrostatic precipitator gas inlet plenum having a corrugated perforated plate |
| US5223008A (en) * | 1992-08-24 | 1993-06-29 | Flex-Kleen Corp. | Horizontally mounted filter cartridge dust collector |
| US6736878B2 (en) | 2001-03-09 | 2004-05-18 | Arthur G. Hein | Precipitator extraction method and system |
| SE527104C2 (en) * | 2004-05-21 | 2005-12-20 | Alstom Technology Ltd | Method and apparatus for separating dust particles |
| KR100769285B1 (en) | 2007-04-16 | 2007-10-24 | 한국캠브리지필터 주식회사 | Multiple automatic air cleaner |
| DE102008007099B4 (en) * | 2008-02-01 | 2014-03-13 | Munters Euroform Gmbh | The droplet |
| EP2433712A1 (en) * | 2010-09-27 | 2012-03-28 | Alstom Technology Ltd | Duct transition arrangement |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1344330A (en) * | 1918-10-31 | 1920-06-22 | Research Corp | Orifice-precipitator |
| DE520710C (en) * | 1925-01-14 | 1931-03-13 | Siemens Schuckertwerke Akt Ges | Device for dividing the gas flow entering an electrical cleaning chamber |
| US1953082A (en) * | 1932-08-31 | 1934-04-03 | Research Corp | Electrical precipitation |
| GB598928A (en) * | 1943-01-20 | 1948-03-01 | Purification Ind Des Gaz Soc D | Improvement in installations for the treatment of gaseous fluids containing particles in suspension |
| US3425189A (en) * | 1965-08-27 | 1969-02-04 | Metallgesellschaft Ag | Diffuser-like inlet connection for electrical dust separators |
| US3733785A (en) * | 1971-02-04 | 1973-05-22 | Envirotech Corp | Gas flow regulation for electric precipitators |
| DE2130826A1 (en) * | 1971-06-22 | 1973-01-11 | Metallgesellschaft Ag | DEVICE FOR REDUCING AND EQUALIZATION |
| US3892546A (en) * | 1974-05-31 | 1975-07-01 | Rust Eng Co | Electrostatic precipitator |
| US4026683A (en) * | 1975-11-20 | 1977-05-31 | Environmental Elements Corporation | Inlet duct and hopper apparatus for electrostatic precipitators |
| US4251234A (en) * | 1979-09-21 | 1981-02-17 | Union Carbide Corporation | High intensity ionization-electrostatic precipitation system for particle removal |
-
1986
- 1986-12-22 US US06/943,855 patent/US4695297A/en not_active Expired - Lifetime
-
1987
- 1987-08-24 CA CA000545165A patent/CA1320686C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US4695297A (en) | 1987-09-22 |
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