-
recovery boilers
D evelopment of low-pres sures o o tblo'wing te chn olo gyBv H.
TnaN, D. Taxona aNo A.K. JoNEs
Abstract: Sootblowers in a kraft recovery boiler consume a large
amount of high-pressure superheatedsteam. With properly designed
nozzles ar,d increased sootblowing steam flow rates, sootblowers
can operateat a steam pressure as low as 10 bars (150 psig),
without significantly compromising the deposit removal effi-ciency
ofthe sootblowerjet. Since low-pressure steam can be much less
valuable than high-pressure steam, theincrease in steam usage can
be readily justified. The economic benefits of low-pressure
sootblowing mayvaryfrom mill to mill, depending on the differential
cost between high-pressure steam and low-pressure steam.
N RECOVERY BOILER OPERATION, soot-
blowers are used to remove firesidedeposits from tube surfaces
by blastingthe deposits with high-pressure steam
jets [1,2]. An effective sootblowing operation isvitally
important for ensuring continuous boileroperation, and for
achieving high boiler thermalefficienry.
Depending on boiler design and operation,sootblowers typically
consume 3 to 72o/o of thetotal high-pressure superheated steam
producedby the boiler. \A/hile sootblowing is an importantintegral
part ofrecovery boiler operation, it can becosdy due to the
consumption of a large amount ofvaluable high-pressure steam. Thus,
if sootblow-ers can operate at a lower pressure, for instance,10-17
bars (150-250 psig) without compromisingtheir deposit removal
capability, there will be asignificant economic advantage to kraft
pulp mills.This is because low-pressure steam can be muchless
valuable than high-pressure sream, as it canbe taken from the steam
turbine exit after thesteam has been used to generate electricity.
Thechallenge for low-pressure sootblowing operation,however, is to
provide a deposit cleaning powerthat is comparable to that of the
conventionalhigh -pressure sootblowi ng operation.
This paper discusses the concept of low-pressure sootblowing
technology, the key resultsobtained from laboratory experiments and
fromthe two mill trials conducted to date, and thefuture prospects
of the technology.
THE CONCEPTDepending on mill needs, recovery boilers mayoperate
at a superheated steam pressure rangingfrom 41, to 103 bars (600 to
1500 psi) and a steamtemperature from 400 to 515"C (750 to
960"F).In the conventional high-pressure sootblowing
operation, high-pressure steam from the finalsuperheater steam
oudet is passed through a steamturbine to generate electricity,
Fig. 1. The "waste"steam from the turbine exit has a lower
pressure.typically 10 to 17 bars (150 to 250 psi), ani is usedin
various processes in the mill. The sootblowingsteam is tlpically
taken directly from the finalsuperheater steam outlet. It is passed
through apoppet valve to reduce the steam pressure to 27to 24bar
(300-350 psi) before entering the soot-blower feed tube.
In a low-pressure sootblowing arrangement,Fig. 2, instead of
high-pressure steam, exhauststeam from the steam turbine may be
used directlyfor sootblowing. Due to low pressure, the peakimpact
pressure (PIP), and hence, the depositcleaning power of
low-pressure sootblowers, isinevitably lower than that of the
conventionalhigh-pressure sootblowers. In order to make up forthe
low PIP and to produce sootblower jets com-parable to those
produced by high-pressure soot-blowers, low-pressure sootblowers
must operateat a higher steam flow rate. This can be achievedwith
larger nozzles modified for optimum perfor-mance at a lower
Dressure.
Studies have been conducted at the Universityof Toronto over the
past six years to examine thefeasibility of using 10 to 77 bar (150
to 250 psig)low-pressure steam for sootblowing [3,4]. Thesestudies
include theoretical analysis of steam jetcharacteristics;
evaluation of low-pressure soot-blower performance through
laboratory experi-ments; numerical simulations; and mill
trials.
Results of laboratory experiments and numer-ical modeling
suggested that, with properlydesigned fully-expanded nozzles and a
15 to 20o/oincrease in steam flow rate, it is possible to oper-ate
sootblowers at a lance pressure of 200 psig(14 bar) and achieve a
deposit removal capability
H. TRAN.University of TorontoToronto, 0Ntran h
[email protected]. ed u
D. TANDRA,Clyde-Bergemann, IncAtlanta, GA
A.K. JONES,International PaperCincinnat i , 0H
O s2.10s..12/110:1 (2008/200e) . pur-p & pApER CANADA
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peer reviewed
comparable to conventional high-pressuresootblowers [3].
There are several disadvantages associ-ated with low-pressure
sootblowing opera-tion. As the steam jet passes through
thesootblower nozz\e, it adiabatically expandsand cools. Since the
used steam from thesteam turbine is not only at a lower pres-sure,
but also at a lower temperature, theexpansion may lower the
sootblower jettemperature below the steam dew pointand cause a
small portion, about 4o/o of thesteamjet to condense [3]. The
presence ofcondensed water droplets in the sootblow-er jet is
undesirable as it may result in tubeerosion. The problem of
condensation,however, can be minimized by mixingthe low-pressure
steam with a measuredamount of high-pressure steam, althoughthis
will decrease the savings compared tousing only the low-pressure
steam, Fig. 3.
Results oftheoretical analysis also sug-gested that with the
existing sootblowerequipment, the required pressure at theturbine
exit should be at least 1.4.5-76bar(210-230 psig), and that lower
pressuresteam requires at least a 7.63 cm (3) IDpipe to deiiver
steam to the sootblowers, aswell as larger feed and lance
tubes.
MILL TRIALSIn order to evaluate the feasibility of lowerpressure
sootblowing technology, two milltrials have been conducted to
date.
First TrialThe first trial was performed at IrvingPulp and
Paper, Saint John. NB, Canada
[4] in May 2004, on a 1.970 Babcock &
Wilcox UK recovery boiler. The boiler wasdesigned originally to
burn 1087 t/day (2.4million lb/day) of black liquor dry
solids(BLDS) and to produce 163,000 kg/h(360,000 \blh) steam at
440"C (825'F)and 62 bars (900 psig). The liquor fir-ing capacity of
the boiler, however, hasincreased substantially over the
yearsthrough several major upgrades. The boileris presently firing
1,680 metric tlday (3.7million lb/day) of BLDS and producing250,000
kg/hr (550,000 lbs/h) steam.
The steam for sootblowing in thisboiler is taken from the
superheater outletat62bar (900 psig). It is passed through apoppet
valve to reduce the pressure to 20.7bar (300 psig) before entering
the soot-blower lance equipped with two nozzleswtth 25.4 mm (1")
throat diameter atthe tip, Fig. 4,A'. The steam flow rate
andpressure at the nozzles are about 8,1.60 kglhr (18,000 lb/hr)
and 17.9 bN (260 psig),respectively.
Only one low-pressure sootblower wastested during this trial.
The assembly wasinstalled on a sootblower in the uppersuperheater
region between the primarysuperheater and the secondary
superheater.The lance tube of the conventional soot-blowerwas
replacedwith a new one, whichhad two specially-designed nozzles
witha 31.8 mm (1-1/4") throat diameter, toprovide a higher steam
flow rate to com-pensate for the lower steam pressure, Fig.48. The
62bar (900 psig) steam from theboiler was routed through a globe
valve toreduce its pressure to 20.7 bar (300 psig)and then through
a new low-pressurepoppet valve resulting in a blowing pres-
sure of 14.5 bat (210 psig) downstreamofthe poppet valve. The
steam flow ratesand nozzle pressures were calculated to be9,570
kglhr (21,000 lblhr) and 12.1. bar(176 psig), respectively.
The performance of the low-pressuresootblower was evaluated
using an inspec-tion camera to monitor deposit buildupnear the
trial area, and by comparing thedrop in flue gas temperatures at
loca-tions upstream and downstream of lowand high-pressure
sootblowers. Unfort'.r-nately, the use of the camera was
hinderedbecause ofsevere deposit buildup near thetriaJ. area. The
interpretation ofthe resultsobtained was further complicated by
occa-sional thermal shock events that affectedthe deposit buildup
as well as the flue gastemperature in the vicinity of the low
pres-sure sootblowing [4].
\A4rile the results were inconclusive,boiler operating data over
the past threeyears showed no significant difference indeposit
removal effectiveness between thelow-pressure sootblower and the
original,300 psi pressure sootblower in place beforethe trial.
The low-oressure sootblower is current-ly still in opeiation.
The recovery boiler hasbeen running well with no forced outagedue
to plugging since the installation ofthe low-pressure sootblower
inMay 2004.\A4rile this good performance of the boilerwas probably
coincidental and had nothingto do with the operation of only one
low-pressure sootblower, the trial suggests thatthis low-pressure
sootblower has at leastthe same cleaning power as the
originalhigh-pressure sootblower.
PULP & PAPER CANADA. 109:12l110:1 (2008/2009).8 6D
Electricity
4'1-103 bars(600-1500 psi)steam
1G17 bars(15G250 psi)steam tomill processes
PoppetValve
21-24 bars(300-350 psi)Steam to sootblowers
Electricity
41-103 bars(600-1500 psi)steam
10-17 bars(150-250 psDsteam tomill processes
10-17 bars(150-250 psi)steam to sootblowers
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recovery boilers
Second trialThe second trial was carried out at Inter-national
Paper, Vicksburg mill in Missis-sippi, USA. The recovery boiler is
a 1967Babcock & Wilcox unit rated at 231,000lglhr (510,000
lb/hr) steam with oudetconditions of 427"C (800"F) and 70 bar(1020
psig). The boiler tJpically pro-duces between 204,000 and 227,000
kg/hr(450,000 and 500,000lb/hr) of steam flow,and the mjll is not
recovery boiler limited.
The boiler has a fouling monitor systeminstalled that relies on
the use of straingauges to measure the elongation of thehanger rods
supporting each section oftheboiler [5], shown in Fig. 5. The
elongationincreases as the weight of the superheaterplaten
increases due to deposit buildup,
and this information can be related directlyto the total weight
ofdeposits on each sec-tion of the superheater.
Four low-pressure sootblowers wereinstalled in this trial,
replacing four existingsootblowers #904, #804, and #906,
#806located respectively upstream and down-stream of the secondary
superheater, RowC, Fig. 6. The low-pressure sootblowers#904 and
#804were equipped with 31.8mm(7-1./4") nozzles,while #906 and #806
wereequipped with smaller, 28.6mm (7-1./8")nozzles, compared to
their original high-pressure 2.22 mm (7 / 8") nozzles. They wereall
on the right side of the boiler.
The performance of these low-pressuresootblowers was evaluated
against that oftheir high-pressure counterparts, #903,
#803 and #905, #805 on the opposite side(left side) of the
boiler.
Figure 7 shows the steam flow arange-ment in this trial. In the
high-pressuresootblowing arrangement, the steam istaken from the
steam header at 27.6 bat(400 psig), and is passed through a
vari-able flow control valve and then a poppetvalve to reduce the
pressure to 21.4 bar(310 psig) before entering the sootblowerlance
equipped with two nozzleswithT/8"throat diameter at the tip, Fig.
7A. Thesteam flow rate ^t the nozzle was about7,700kgfu
(17,000lb/hr) and steam pres-snre estimated to be 20.1 bar (292
psig).
The low-pressure sootblowing arrange-ment is shown in Fig. 78
for sootblowers#806 and #906 and in Fie. 7C for soot-
O sq.1oe:12/1r0:1 (2008/200e) . pulp & pApER CANADA
Electricity
41-103 bars(600-1500 ps)steam
10-17 bars(15G250 psi)steam tomill processes
10-17 bars(150-250 psi)steam to sootblowers
(A)H P
(B)LP
900 psig
Globe Control Valve
At Nozzle
21 ,OOO lb/hr*'176 psig
703
602
601
a s02
a sol
a 80?
a €or
a 702
t 701
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blowers #804 and #904. No change wasmade to the poppet valve.
Low-pressuresteam was supplied to these sootblowersby regulating
the steam flow rate using avariable flow control valve. The
operatingsootblowing steam pressure was changedby changing the
control set point.
The trial was initially conducted at8,610 lg/hr (19,000 lbs/hr)
steam flow tothe low-pressure sootblowers, 1170 morethan that to
the high-pressure sootblow-ers, 7,700 kg/hr (17,000 lbs/hr). Overan
S-month period, the steam flow tothe low-pressure sootblowers was
reducedstepwise in order to evaluate the perfor-mance of these
sootblowers at differentsteam pressures. Table I summarizes
thesteam flow rates and nozzle oressures ofthe low-pressure
sootblowerc u, they *.r.changed over this period.
The deaning efficiency of the low-pres-sure sootblowers dwing
the trial was deter-mined using a fouling index, which was cal-
culated based on the dlfference in the weightbetween the side of
the boiler deaned withthe low-pressure sootblowers and the sideof
the boiler deaned with the high-pressuresootblowers, recorded on
strain gauges forRow B and Row C, Eg. 6. If this factortrended down
with time, it indicates thatthe side of the superheater deaned by
thelow-pressure sootblowers was cleaner (lessweight) than the side
deaned by the high-pressure sootblowers, a positive outcome. Ifthis
fouling factor trended up with time, itindicates that the
superheater platens on thelow-pressure sootblower side is heavier
(moredeposits), a negative outcome. If the foulingfactor was
unchanged, it indicates that thelow-pressure sootblowers were
comparableto the high-presst.re sootblowers in terms ofdeaning
power.
Figure 8 shows the results of the8-month trial. At flow rates of
18,000 to19,000 lbs/hr (8,150 to 8,610 l1g/hr), thelow-pressure
sootblowers were more efFec-
peer reviewed
tive than the high-pressure sootblowersoperating at 17,000
lbs/hr (7700 kC/hr).This is clearly shown, since the
relativefouling index has a monotonic decreasewhen the low-pressure
sootblowers wereoperating at 18,000 to 19,000 lb/hr.
Note that there were two steep increas-es of the fouling index
in Row C. Theseincreases were associated with shut downsof the
boiler. At these times, the weightremoved from each side of the
boiler maynot have been equal and a new steady stateregime was
established. At 17,500 lbs/hr(7930kglhr), the effectiveness of the
low-pressure sootblowers was about the same asthe high-pressure
sootblowers. The relativefouling factors are flat in this case.
The four low-pressure sootblowershave been operated at a flow
rate of77,500 Lb/hr (7930 kglhr) for about 11months without
affecting the boiler per-formance. No forced outage has occurreddue
to plugging since the installation of
PULP & PAPER CANADA. 109:12l110:1 (2008/2009).35 G?
(A) HP, 7/8" Nozzles, #803, 805, 903, and 905
310 psig
(B) LP ,1-1t8" Nozzles, #806 and 906
Control Valve
(C) LP ,1-114" Nozzles, #804 and 904
168 psigFeed lube
Control Valve
17500 lb/hr140 psig
z
1 . 5
1
0 .5
0-0.5
-1
- 1 . 5
-210/1/05
1200
1000
800
600
400
200
0
-2002 3 4
Differential Cost (US$/1000 lb)
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these low-pressure sootblowers.Grerall, the low-pressure
sootblowers
performed slighdy better than expected,since only3% additional
steamwas required.Before the trial, it was thought that at
least1070 more steam would be required.
ECONOMIC ANALYSISThe economic benefits of using low-pres-sure
steam for sootblowing mainly resultfrom the differential cost
bet'uveen thehigh-pressure steam and the low-pressuresteam. Other
benefits may include a lowermaintenance cost for the
low-pressuresootblowers. Sootblower components,such as seal and
packing, operated withlow-pressure steam are expected to
requireless maintenance and last longer.
The most common parameter that isused to justi{' an investment
is the paybacktime (PT), which is defined as the mini-mum number of
years needed to recoverthe fixed capital investment for
convertinghigh-pressure sootblowers into low-pres-sure sootblowers.
PT is essentially equalthe capital investment, in $, divided by
thevalue ofenergy savings (ES), in $/year.
The capital investment for convert-ing high-pressure sootblowers
into low-pressure sootblowers in existing recoveryboilers is
mill-specific, depending on howmany existing components need to
bereplaced or modified. However, for newrecovery boilers, since the
installation costsof high and low-pressure sootblowing sys-tems are
about the same, there will be nopayback time.
Without taking into account the fixedcosts (labor, capital,
maintenance, etc.), theenergy savings resulting from
implementa-tion of low-pressure sootblowing technol-ogy can be
calculated as follows:
ES = 8520(Cr,rFn, - CLpFHp) (1)
where Cn, and C,_o are, respectively, high-pressure and
low-pressure steam costs in$US/1000ib, F*r, and F.o are,
respectively,
high-pressure and low-pressure sootblow-ing steam flow rates in
1000 lblhr, and8520 is the number of hours/year (355days) the
sootblowers are in operation.Rearranging equation 1 gives:
/ F , , . \ES = 8s2o Fn, (C*o - ,_
C, , ) (2)H T
For a given boiler, the energr savingsdepend mainly on two main
factors:* the amount of additional low-pressuresteam required to
make up for the lowpressure and to attain the same depositcleaning
power as high-pressure sootblow-ers. This factor is embedded in the
FLP/FHP ratio in the above equation;* the differential cost between
high-pres-sure steam and low-pressure steam.
Thus, low-pressure sootblowing canbe attractive for pulp mills
where recoveryboilers consume a large amount of high-pressure
sootblowing steam, andlor wherethe cost (or value) of high-pressure
steamis significantly higher than that of low-pressure steam.
Recovery boilers which have a largenumber of sootblowers,
particularly thosewith inefficient, old HI-PIP rype nozzles,tend to
consume more high-pressure steam(i.e. high Fnr). In pulp mills
where powercosts are high, the differential cost
betvveenhigh-pressure steam and low- pressuresteam is also high. In
these cases, theenergy savings resulting from
low-pressuresootblowing operation can be substantial.On the other
hand, the energy savings maybecome negative if the differential
cost ofthe steam (CHp-CLp) is small and/or if theF.1F"o ratio is
high.
The cost of steam at a pulp mill dependson the mill location,
the quality and quan-tity of the steam, as well as the qpe offuel
used to produce the steam at themill. High-pressure steam presently
costsbetween US $6 per 1000 lbs (US $2.7 permetric ton) and US $12
per 1000 lbs (US
$5.4 per metric ton), whereas low-pressure
steam g?ically costs about $3 US per 1000lbs (US $L.4 per metric
ton), but it can behigh as US $8 per 1000lbs (US $3.6 permetric
ton).
For a 1000 adtld (air-dried short tonsper day) pulp mill, the
recovery boilerqpically burns about 1360 tld (3 milJionslbs) of
black liquor dry solids and pro-duces about 199,000 kglhr (440,000
lbs/hr) high-pressure steam. Assuming 50lo ofthe total steam
produced is used for soot-blowing, the high-pressure
sootbiowingsteam flow rate would be about 10,000 kglhr
(22,000Lb/hr).
Figure 9 shows the annual energJ sav-ings calculated for such a
pulp mill, as afunction of differential steam cost (Crrr-Crr) and
Fr1F"o ratio. The calculationwas based on a high-pressure
sootblowingsteam flow rate (\n,,) of 10,000 kg/hr(22,000lb/hr), and
cost (Crrr) of $US 4.5per metric ton ($US 10 per 1000 lbs).
Thus, if we conservatively assume thatlow-pressure sootblowers
need 10% moresteam to achieve a deaning power compa-rable to that
of high-pressure sootblowers,the Fr'/Fnn ratio would be 1.1. The
annualenergr savings for a 1000 adt pulp millcould then range from
$US 225,000 at adifferential cost of $US 2 per 1000 lbs to$US
637,000 at a differential cost of $US4 per 1000 lbs.
FUTURE PROSPECTSDue to little or no additional cost
forimplementing low-pressure sootblowingin new recovery boilers,
several pulp millshave considered adopting the technol-ogr for
their new recovery boilers. Therisk associated with utilizing
low-pressuresteam for sootblowing is low, since thesootblowing
steam pressure can alwaysbe increased, by mixing the
low-pressuresteam with high-pressure steam, if thedeaning power of
the low-pressure soot-blowers is deemed insufficient.
A p"lp mill in south cenffal USA wasthe first in the world to
fully implementthe low-pressure sootblowing technologyfor its new
recovery boiler. The boiler hasa firing capacity of 2,860 ton/day
(6.3
million Ib/day) of black liquor dry solidsand is equipped with
88 low-pressuresootblowers. Another new recovery boiler(scheduled
to start up in 2008 at a pulpmill in southern USA) with a similar
firingcapacity will also firlly implement low-pressure sootblowing
technology.
Flow Rote, I OOO lblhr Pressure,#804 & #904
Psig#806 & #906
Before triol (HP)During triol (LP)e / 1 / o s - 1 1 / 1 4 / 0
511 /1 5/05 - 1 /18/061/1e/06 - 3/3/063/ 4/06 - 6/1 /06
17.0
r 9 . 01 8 . 51 8 . 017 .5
292
1541 1 4
140
292
r 9 31 8 8182177
O so. 109:12/11 0:1 (2008/200e) . pulp & pApER cANADA
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SUMMARYWhile sootblowing is essential in recoveryboiler
operation, it is a cosdy operation dueto the high consumption of
high-pressuresuperheated steam taken direcdy from thefinal
superheated steam header before theturbine generator. Ifsootblowers
can oper-^te at ^ lower pressure, 1,0-1.4 bars (150-
200 psig), without compromising theirdeposit removal capabiJity,
there can bea significant economic advantage to kraftpulp mills.
This is because low-pressuresteam can be much less valuable than
high-pressure steam, as it can be taken from thesteam turbine after
the steam has beenused to generate electricity.
Results of laboratory studies and twomill trials show that
low-pressure soot-blowing is technically and practically fea-sible.
Economic benefits of implement-ing low-pressure sootblowing
technologydepend mainly on the amount of addi-tional low-pressure
steam required to makeup for the low pressure in order to attainthe
same deposit cleaning power as high-pressure sootblowers, and the
differentialcost between high-pressure steam andlow-pressure
steam.
The technologr can be attractive forpulp mills where recovery
boilers consumea large amount of high-pressure soot-blowing steam,
and/or where the cost ofhigh-pressure steam is significandy
higherthan that of low-oressure steam. Thetechnologlr may be
diffi.ult to implement
on existing recovery boilers due to the needfor re-piping the
sootblowing steam line toaccommodate the low pressure and highflow
rate. It can be easily implementedon new recovery boilers with
litde or noadditional costs.
ACKNOWLEDGEMENTSThis work was conducted as part of theresearch
program on "Increasing Ener-gr and Chemical Recovery Efficiency
inthe Kraft Process", joindy supported bythe Natural Sciences and
EngineeringResearch Council of Canada (NSERC)
and a consortium of the following compa-nies: Abitibi-Bowater
Inc., Alstom Power,Andritz, Aracnv Celulose, Babcock &Wilcox,
Boise Paper Solutions, CarterHolt Harvey, Celulose
Nipo-Brasileira,Clyde-Bergemann, Diamond Power
peet reviewed
International, Domtar, DMI Peace RiverPulp, Georgia Pacific,
International Paper,Irving Rrlp &Paper, Metso Power,
Mead-Westvaco, Stora Enso Research, Tembec,and Votorantim Celulose
e Paoel.
LITERATURE1. BARSIN,J. Recovery Boiler Sootbkrwers. Proc.
o{'Tappi Krafi Recovery Short Course, p.219-227, TappiPress (1992)
.2. TRAN, H.N. Chapter 9: Upper Frrrnace Depositionanrl Plrrgging
in Kraft Rreour.ry 8ollrzr, edited by T.N.Adams et al, p.247-282,
Tappi Press (1997).3. KALTAZINE, A., CORMACK, D. E., TRAN, H.,
JAMEEL, 1.. Feasibil iry of using Low Pressure Steamfor
Sootblowing. Proc. lnternational (lhcmical Recov-ery Conference.
TAPPI/PACTAC, Oharleston, SC(2004) .4. TANDRA, D., KALIAZINE, A.,
CORMACK D.E.,TMN, H.N. Mill Trial on Low Pressure
SootblowerPerlbrmance in a Recovery Boiler. Proc. Tappi
Engi-ncering, Pulping and Environmental (lonfi:rcnce(2005) .
5. .IONES, A.K. System and Method fbr Measur-ing Wcight of
Deposits on Boilcr Superheaters.United States Patent, No. 6,323,442
Bl, November27 (200 ' l ) .
R6sum6: Les souffleurs de suie d'une chaudi6re de r6cup6ration
kraft consomment une grandequantit6 de vapeur haute pression
surchauffde. Si les tuybres sont bien congues et que l'on accroitle
d6bit de vapeur, les souffleurs de suie peuvent fonctionner i une
pression de vapeur aussibasse que 10 bars (150 psig) sans
compromettre l'efficacit6 du jet du souffleur. La vapeur
bassepression co0tant moins cher e obtenir que la vapeur haute
pression, opt imiser l 'u t i l isat ion dela vapeur peut
facilement se justifier. Les retomb6es 6conomiques du soufflage
basse pressionpeuvent varier d'une usine d l'autre selon la
diff6rence de co0t entre la vapeur haute pression etla vapeur basse
pression.
Reference: TRAN, H., TANDRA, D., JONES, A.K. Development of
low-pressure soorblowingtechnology. Pulp €l Papn Canada
109(12)/ll0(l):T121-128 (December 20084anuary 2009).Paper presented
at the 2007 International Chemical Recovery Conference in Quebec,
QC, May 29-June l, 2007. Not to be reproduced without permission of
PAPTAC. Manuscript received March14,2007. Revised manuscript
approved for publication by the Review Panel on October 8,
2008.
Keywords: RECO\T,RY BorLER, soorBlowER, LOW-PRESSURE, FIRESIDE
DEposITS,FOULING. MILL TRIALS. STEAM SAVINGS. THERMAL
EFFICIENCY.
NO WASTING PAPER MILL WASTEA recent study by Agricultural
Research Service (ARS)soil scientist Martin J. Shipitalo in Ohio
found thatmore may be better when it comes to applying paper
millsludge to reclaim soils of surface-coal mined areas.
Over a 10-week period, Shipitalo and his colleaguesapplied paper
mill sludge to recendy surface-mined plotslocated on steep slopes
in southeast Ohio at two rates:the standard 100 tonne Der acre rate
and at 300 tonnesper acre. Grass was planted on the slopes
following the10-week application period.
\A4rile the application of the sludge at both ratesreduced
runoff and erosion, especially before the grasswas planted, the
higher 300 tonne per acre rate reducedsoil loss eight-fold after
the grass was planted and thesoil had stabilised. Both application
rates reduced runoff
from three- to six-fold in the same Deriod afterwas olanted.
The 300 tonne per acre rate also increased soil carbonlevels,
soil pH and calcium more than the lower sludgeapplication rate did.
There were other positive results theresearch supported: the
improved soil quality could helpplant growth and continue reducing
runoff and erosion.Less runoff and erosion could also lead to a
reductionin sediment pond sizes, resulting in lower
reclamationcosts.
There was one negative effect, though: oxygen levelsin the
runoff water were reduced temporarily - for about10 weeks - but
total runoffwas reduced.Source : Uni te d S tates Department
ofAgriculturlAgricultureResearcb Seruice
PULP & PAPER CANADA. 10e:12l110:1 (2008/2009) 37 GD