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 n@chem-eng.toronto. 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

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

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

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

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(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

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- 1 . 5

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0

-2002 3 4

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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

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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

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