steam savings in recovery boilers

7/27/2019 Steam Savings in Recovery Boilers

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Steam Saving in Recovery Boilers

M. I. JameelBergemann USA, Inc.4015 Presidential ParkwayAtlanta, GA 31141

ABSTRACT

Under typical recovery boiler sootblower operatingconditions, the emerging steam jet is severely underexpanded, i.e. the nozzle exit pressure is substantially greaterthan that of the surrounding atmosphere. This results in ashock wave being set up downstream of the nozzle whichdeprives the jet of valuable mechanical energy for depositremoval. New nozzle designs provide full expansion undercurrent operating conditions in recovery boilers.

Energy delivered by jets emerging from full expansionnozzles are substantially greater than those obtained fromconventional nozzles. Alternately, it is possible to achieveenergy levels comparable to what can be achieved by aconventional nozzle while consuming less steam. The latterfeature of the full expansion nozzle has been utilized in tworecovery boilers leading to steam savings of $30 to$40k/month.

1. INTRODUCTION

The burning of black liquor in a recovery furnace ,isone of many stages associated with the regeneration of spent

pulping chemicals. By burning "black liquor" a by productof pulping, "green liquor" and steam are produced. Since

pulp is the valued product, economical advantage fromchemical recovery exceeds that of the energy produced. As afuel, black liquor is the sixth most important fuel in industry.However, it has a low heating value when compared toconventional fuel. Typically this value is around 14MJ/kg(6000 Btu/lb) of dry solids and, the corresponding steam

production is about 3 to 4t steam/t dry solids (3 to 4 lbsteam/lb dry solids) [1]. The steam produced from the boileris used as both process steam, as well as for the generation ofelectricity. Most mills today have to supplement their steamand power requirements by burning alternate fuel in a power

boiler as well as purchasing power from the grid.

As a result of burning liquor, a significant quantityof ash is released. A significant fraction of this ash isdeposited in the convective pass while the remainder iscaptured in the hoppers and the electro static precipitator. Theaccumulation of fireside deposits in a recovery boilerdrastically reduces its heat transfer efficiency. This results inhigher flue gas temperatures which accelerate fouling,

leading to plugging of the downstream flue gas passages [2].As a consequence of the plugging, the boiler has to be shutdown and water washed [3]. The unscheduled shutdown ofa boiler interrupts production and incurs severe financialcosts to the mill. In order to maintain the uninterruptedoperation of the boiler, it is vital to operate sootblowers on acontinuous basis to prevent excessive fouling. Removal ofdeposits depend to a great extent on the type of deposit andthe ability of the sootblower to transmit forces to thedeposit, that exceed its mechanical strength.

For a given boiler, the deposit strength varies fromlocation to location in the boiler and is directly related to theflue gas temperature [2,4]. In the superheater, deposits

primarily consist of carryover type particles that for mostpart consist of smelt and/or partially burned black liquorparticles. On the other hand, in the generating bank andeconomizer the type of deposit consists primarily of fumewhich is formed by condensed volatile material. This typeof deposit is very light and easily removed. Typically,

sootblowers in a recovery boiler use high pressuresuperheated steam as a cleaning medium. This steam isdelivered to nozzles at the end of a lance tube as shown inFigure 1. The steam expands through the nozzle to producea high speed jet which is then directed at the deposits inorder to remove them from the boiler tubes.

Figure 1: Schematic of a Sootblower Jet

Recent studies on sootblower optimization haveshown that for typical sootblower operating pressures in arecovery boiler, the steam reaches the speed of sound at the

nozzle throat while the jet emerging from the nozzles isseverely underexpanded, i.e. the steam pressure at thenozzle exit pe is substantially greater than that of the

surrounding atmosphere p[5]. This results in a normalshock wave being setup just downstream of the nozzlewhich deprives the jet of valuable energy for depositremoval. This drawback can be overcome by extending thecurrent nozzle to provide sufficient expansion so that thenozzle exit pressure is in equilibrium with the surroundingatmosphere.


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However, physical dimensions of the boiler wall openingsand sootblower lanes limit the length to which a nozzle can

be extended.

This limitation has been overcome through a noveldesign in the Contoured Full Expansion or "CFE" nozzle.The wall of this nozzle is uniquely contoured to rapidlyexpand the gas beyond the throat followed by a secondcontour that redirects the gas towards the nozzle axis. Across sectional view through the lance tip for both aconventional (High Impact) and new nozzle of fixed throatdiameter is shown here in Figure 2. In order to fit the newnozzle in a conventional lance tube, the nozzles are offset bythe helix of the sootblower.

Figure 2: Illustration of a Lance Tip Fitted with a

Conventional and Full Expansion Nozzle

Experience has shown that the cleaning potential fora sootblower correlates with its jet Peak Impact Pressure"PIP". This is the centerline stagnation pressure for the jetand is measured by a pitot tube at various distancesdownstream of the nozzle exit. Through dimensional analysisfor the flow in the lance, nozzle and jet, PIP can besummarized as a function of,

l

d&

1U1

p,

p

p,,M,

r

xF=PIP

2oo

e

e

e

e

where the dimension d & l are indicated here in Figure 3.

Figure 3:Characteristic Lengths for Modelling the Flow atthe Lance Tip

It has been estimated that the North American kraft pulpindustry could save about $100 million/year in energy costs

by making modest improvements to the thermal efficiencyof recovery furnaces. One of the main tools used inmaintaining this efficiency is the sootblower. Sootblowersteam consumption in a recovery boiler generally rangesfrom 6 to 10% of the steam produced. Past attempts toreduce this quantity while maintaining thermal efficiencyhas been associated with elaborate control strategies. This

has been tied to monitoring and maintaining the heattransfer rates of the various convective sections of the

boiler. Recent developments in sootblower nozzletechnology [6,7] has shown that steam consumption can bereduced with no significant impact on the thermal efficiencyof the boiler[8].

2 NOZZLE PERFORMANCE

A comparison of the PIP response for the quarterscale conventional as well as for the new full and quarterscale nozzles as a function of lance pressure is shown inFigure 4.


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Figure 4: Comparison of PIP for a Conventional andFull Expansion Nozzle (both full & scale).

The above result also shows that for a conventional

nozzle, an increase in lance pressure produces a PIP thateventually levels off at about 303kPa(44psig). In fact for thisnozzle increasing the lance pressure by 17%, from 2068kPa(300psig) to 2413kPa(350psig)only results in a 10%change of PIP. Alternatively for the new nozzle, a similarincrease in lance pressure means a 37% increase in PIP.Therefore, for a conventional nozzle, increasing the blowing

pressure does not significantly improve the PIP for the jet,while for the new nozzle, the increase in PIP is substantial.The deficiency at high operating pressures seen in aconventional nozzle has been shown to be attributed to thenormal shock wave that is setup downstream of the nozzleexit [5]. Increasing the blowing pressure, results in anincrease in the mass flow through the nozzle as well as the

degree of underexpansion (pe/p1) The latter causes theshock wave to grow in size and strength resulting indiminished returns. Hence, it can be concluded that duringsevere plugging of the boiler, increasing the blowing pressurefor a conventional nozzle will not improve it's cleaning

potential.

The PIP advantage from the new nozzle over that ofa conventional nozzle is realized, for blowing pressure inexcess of about 1379kPa(200psig) as indicated in Figure 4.For a conventional nozzle operating at 2413kPa(350psig) thePIP delivered at a location 76cm(30") from the nozzle isabout 303kPa(44psig). To deliver this amount of PIP with the

new nozzle the required blowing pressure is only about1724kPA(250psig). This amounts to a 29% reduction in

blowing pressure for the new nozzle. The mass flux for achocked nozzle, i.e. nozzle with sonic velocities at the throatis

According to equation (2), the 29% reduction in pressuremeans a 29% less flow of gas through the nozzle.Therefore, for a sootblower operating with a conventionalnozzle at high blowing pressures, the new nozzle provides ameans for better cleaning with no increase in mass flow orequivalent cleaning and a saving of the blowing mediumthrough reduced nozzle pressure.

3. CASE I

3.1 BOILER PARAMETERS

The concept of improved cleaning for the sameblowing pressure or equivalent cleaning while saving steamwas adopted as a new sootblowing strategy by the BoiseCascade Wallula Mill, Wallula, Washington. Theopportunity for sootblower steam savings was originallyidentified by the mill Operations and Maintenance groups.Once identified, a multi-phase implementation strategy wasdeveloped to limit financial risk. The initial phase was to

install 28 new lance tube assemblies in the No. 3 RecoveryBoiler, followed by a nozzle performance evaluation period.Once acceptable performance was verified, the second andthird phases were to proceed with retrofit of spare lanceswith new nozzles for the remainder of the boiler.

The No. 3 Recovery Boiler used for this test is atwo drum C-E unit with tangentially fired air system, a twostage superheater and a long flow economizer. A schematicof the convective pass for this boiler is given here in Figure5. The swirl created by tangential firing leads to non-uniform fouling at the screen tube area of the superheater.

Figure 5:Schematic of the Upper Furnace. New Nozzle &Conventional Nozzle Locations

1T

2p

A o

o

T


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In the past, the boiler had to be shut down every six monthsfor a water wash, to clear the deposit accumulation at thislocation which leads to a loss of final steam temperatures.

Of the 28 lance tubes replaced with the new nozzle,eight were replaced at the screen tube area of the superheaterto achieve better cleaning and twenty were replaced in theeconomizer for steam savings (see Figure 5). The impact ofthis soot blowing strategy on the boiler operation has beenmonitored over two cycles; cycle 1(10/93 to 4/94) where thesootblowers operated as usual with the conventional nozzles,and cycle 2(4/94 to 10/94) with the adjusted poppet valve

pressures and the new sootblower nozzles.

Figure 6: Feedwater and Liquor Flow rates for Cycles 1and 2. For cycle 2, 28 sootblowers were fitted with Full

Expansion Nozzles.

Figure 7: Comparison of final Steam Temperature forCycles 1 and 2.

The liquor flow rate for the No. 3 Recovery Boileris shown above in Figure 6. The unshaded area representscycle 1 that lasted 169 days from water wash to water washwhile, the shaded area represents cycle 2 that lasted 173days. The final steam temperature over this period is givenin Figure 7. During these two cycles, the liquor wasreduced to


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Figure 8: Normalized Heat Absorption Rate for theEconomizer and Superheater

Comparing the superheater results shown in Figure8 for cycles 1& 2, it is seen that a greater fraction of the heatis being absorbed during cycle 2. Since the input heat load tothe boiler is practically unchanged, this increase can beattributed to the performance of the new nozzles at theentrance to the superheater. This is illustrated by the higherand more stable final steam temperature seen in Figure 7, forcycle 2. Since the final steam comes off the 2nd stagesuperheater, the eight new nozzles in its vicinity,significantly affects this temperature. The better heat transferin the superheater given by the higher QSH/QTOTAL, lowers theflue gas temperature entering the generating bank and theeconomizer. This lowers the heat load to the economizerindicated by the lower ratio of QECON/QTOTAL for cycle 2 in

Figure 8.

The availability of both steam and gas sidetemperature measurements for the economizer inlet and exitenables one to compute an overall heat transfer coefficient?ECON, as follows

where [LMTD]ECON is the Logarithmic Mean Temperature,

AECON the surface area and F a factor based on the tubearrangement for the economizer [10]. The thermal resistanceis the reciprocal of the overall heat transfer coefficient(?). Afouling index R, that uses the thermal resistance has been

proposed[10], where

Since AECON and F are constant, a plot of the simplifiedfouling index FI, based on the above principle and definedas

has been calculated for the two cycles and plotted here inFigure 9.

Figure 9:Economizer Fouling Index

The aim here is that in the economizer the newnozzles would save steam, while maintaining the effectivecleaning from the past. Figure 9 indicates that the foulingindex, used in this case as a measure of effective cleaning inthe economizer, shows no significant changes betweencycles 1 & 2. A visual inspection of the economizershowed, that after 66 days (6/94) of operating with the newnozzles and using less steam per sootblower, the tubes were

bare. At this point the steam flow was further reduced andthe boiler was operated until the annual outage and waterwash in October 1994. Once again, visual inspectionsshowed practically no significant change in the fouling ofthe economizer. Due to the unavailability of gas sidetemperatures in the superheater region it was not possible todevelop a fouling index similar to that described for theeconomizer.

The ID fan speed over the period of time corresponding tothis test has been plotted in Figure 10.

[LMTD]FA

Q=

ECONECON

ECONECON

cleanfouled

1-

1=R

Q

[LMTD]-

Q

[LMTD]=FI

ECON

ECON

cleanECON

ECON

fouled

ECON


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The unrestricted flue gas passages following a water washoffers minimum resistance to the flue gas path, hence the IDfan speed required for a fixed mass of gas in the boiler isminimal. As time progressed, the fouling of the boiler posesgreater restrictions for the movement of the flue gas, resultingin increased power consumption (RPM) by the fan. For cycle1, Figure 10 shows that once full load was established, thefan RPM steadily rose from about 550 to 630 RPM over a

period of about 120 days. With the new nozzles(cycle 2), thefan had a more stable speed averaging around 580 RPM overa similar length of time. This implies that the overall flowrestriction to the flue gas or fouling of the boiler, should have

been lower during cycle 2 in comparison to cycle 1.

Figure 10:ID Fan Speed. Lower ID Fan Speed for cycle 2indicates Clear Fuel Gas Passage in the Boiler

3.2 STEAM SAVINGS

In April, 1994, eight screen tube sootblower nozzlesand twenty economizer sootblower nozzles were upgraded.The steam flow was then reduced to 9.5 t/hr (20.5 klb/hr) fora 20% steam savings. After two months of operation, the

boiler was taken off liquor for a visual inspection. Increasedcleaning was observed in both the screen tube area andeconomizer. The economizer sootblowers were then reset to8.4 t/hr (18.5 klb/hr) for an additional 10% steam reduction.The screen tube sootblowers were left as previously set.

The boiler was then operated through October,1995, and taken down for an annual outage. After six monthsof operation with the new sootblower nozzles, visualinspection indicated increased cleaning in the screen tubearea and equivalent cleaning in the economizer. As discussedearlier, the visual indications are quantitatively supported.Both of the original project goals were met concludingnozzle performance verification. Based on these savings, themill is currently upgrading the remaining nozzles in the No. 3Recovery boiler and all the nozzles in No. 2 Recovery Boiler.

Figure 11 shows two sets of data for sootblowersteam consumption on the No. 3 Recovery boiler. In one setof data, 32 sootblowers (24 in the generating bank and 8 inthe superheater screen tube area, GB & SH) are represented.The other data set shows 20 economizer sootblowers(ECON). The base line consumption was 11.4 t/hr (25.1klb/hr) for GB & SH, and 11.5 t/hr (25.4 klb/hr) for ECON.The base line consists of a two-year average from 1/93 to3/94. In October/95 the header pressure was dropped from4Mpa(580 psi) to 3.3MPa(480psi). While this was done, the

poppet valves remain unchanged. This resulted in a flowrate around 7t/hr(15klb/hr). The boiler ran for the usual 6months with this reduced flow and with no change in the

boiler load. Subsequently the header pressure was put backto it's original value of 4Mpa(580 psi) in 6/96.

Figure 11:Sootblower Steam Consumptio

n

Steam savings were calculated by determining theamount of natural gas saved by reducing the load on one ofthe power boilers.

Figure 12:Financial Impact of Steam Saving over TenMonths of Operating with Full Expansion Nozzles.


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The following assumptions were made: (1)$0.25/MJ ($2.72/MMBTU) natural gas, (2) 70% boilerthermal efficiency, (3) enthalpy change of 2814 kJ/kg (1210BTU/lb), which leads to (4) $10.36/1000 kg ($4.70/1000 lbs)of steam. Measured savings from 4/94 to 2/95 are $300,000as shown by the cumulative value in Figure 12. The monthlysavings are all about $30,000/month. When the project iscomplete, estimated annual savings are $700,000/yr for both

boilers.

4. CASE II

4.1 BOILER PARAMETERS

The boiler discussed in case I is not a severelyplugging unit. The run times between water washes istypically 6 months at a firing rate of about 1298t/day(3Mlb/day) dry solids. In order to determine if thesteam savings seen here is applicable to a heavily loaded unit,

a second site was selected. The boiler selected was the unitat the Georgia-Pacific mill, Leaf River, Mississippi. Aschematic of the recovery boiler is shown in Figure 13. Thisunit is a single drum, Gortaverken unit operating at about2802 t/day dry solids (6Mlb/day).

Figure 13: Schematic of Upper Furnace. 52 New NozzleLocation at the end of the Phase I.

The run time on this unit is about 90 to 100 days. Atthis time the boiler is taken off line to be water washed.

Today, 92 sootblowers operate 4 at a time. Saturated steamenters the primary superheater at the beginning of theconvective pass and then passes on to the secondarysuperheater (closest to the generating bank). Sootblowingsteam is extracted at the inlet to this superheater. Followingthis the steam makes a final pass through the tertiarysuperheater before exiting the boiler at 8.6Mpa(1250 psi).Sootblower steam consumption accounted for 18% of thesteam produced.

Due to additional steam demand in themill, a steam savings program was proposed. The mill waswilling to accept the proposal on the condition that the runtime was not compromised and that 100% of the risk betaken by Bergemann. Based on the fact that the fullexpansion nozzle could deliver the same PIP as aconventional nozzle while using less steam, the challengewas accepted. The project was broken into two phases.Phase I: 52 of 92 blowers in the most critical areas based onmaximum usage were identified and replaced with newlance tubes fitted with the full expansion nozzle. The oldlances (52) were sent back to the shop to be retrofitted withthe new nozzles and returned to the mill. Phase II: Theretrofitted lances were now installed in the remaininglocations and the balance 12 lances were put in stock. PhaseI was done during an outage and Phase II was done on therun. The installation was all completed by middle of 12/95.Following this the boiler was water washed and put backonline on 12/15/96.

Historical records for this boiler show that foulingof the secondary superheater leads to an increase in flue gastemperatures in the generating section which eventuallyresults in a pluggage of this section. Therefore, when theheat transfer rate reaches a critical value, the boiler is waterwashed. At present loads the cycle runs for about 90 daysfrom water wash to water wash.

Figure 14: Decay of heat transfer Rate-SecondarySuperheater

Figure 14 above shows the heat transfer coefficient for thesecondary superheater as a % of the rate for a cleansuperheater.


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The initial values >100% are a result of the rampingup of the boiler during startup. The thick line indicates thesame ratio after the nozzles were changed. This periodcorresponds to the time of 12/95 to 3/96. In both these cases,the degradation of the heat transfer rate, i.e. increase offouling is similar. The boiler ran for about 100 days before itwas water washed in 4/96. This entire run was done with lesssteam consumption at all sootblowers. A set of curves for thetertiary superheater during the same period is shown inFigure 15. Once again, the pre and post CFE nozzle erashows no change in the cleaning efficiency as measured bythe thermal efficiency of this surface.

Figure 15: Decay of Heat Transfer Rate-TertiarySperheater

4.2 STEAM SAVINGS

The poppet valve at all sootblower locations were fully open,giving pressure readings of 2068kPa (300 psig).

Figure 16:Sootblower Steam Consumption

The nozzle size was 28mm (11/8 "). Steam flow for 4blowers was measured at 51t/hr (112klb/hr). A daily averagefor 30 days is shown here in Figure 16. Also shown here isthe new flow rate after the nozzles were changed out withthe 25mm(1") full expansion nozzles. At this time the

poppet valves were not turned down. Due to the smallernozzle size the valve pressure increased to 2413kPa (350

psig). The mean flow is now around 40 t/hr (89klb/hr).This is ~21% reduction from the previous value of 51t/hr(112klb/hr).

The dollar value of steam was determined by thecost to generate steam in the power boiler. Based on thefuel cost of $11.5/ton of bark, the steam cost was estimatedat $2.36/klb of steam. At this cost the savings as a %reduction of sootblower steam is shown here in Figure 18.

Figure 17: Financial Impact on Steam Savings/Year.Monthly savings are estimated at around 40,000$.

To date with a 21% reduction, the annual savings isestimated at about $480,000.00. At this reduced flow rate tothe sootblowers the boiler ran its entire 90 day cycle whichended at the end of 3/95.

Since then a second cycle of similar length wascompleted between 4/96 through 6/96. Visual inspectionshowed that the flue gas passages looked no different fromthe past. Further, the economizer was reasonably clean.The heat transfer coefficient ratio for the economizer isshown here in Figure 18. These results are for the monthsof 12/95 through 3/96.


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Figure 18: Decay of heat Transfer Rate-Economizers

During the period of 12/95, the economizer sectionstill had conventional 28mm (1 1/8") nozzles installed. Theheat transfer rate was around 98% of the value at the

beginning of the cycle. Comparing this with the values from

1/96 through 3/96 where the new nozzles were in use, thereappears to be no significant difference in it's thermalefficiency. This is very similar to the observations from caseI (Figure 9). Therefore, the mill has agreed to make a furtherreduction of 10% in the economizer sootblower steamconsumption. Due to the less frequent use of these blowersin comparison to the remainder of the boiler, the net effectwould be less than 30%. It is expected that the total savingswould be around 25%, leading to an annual savings of$571,000.00.

5. IMPLICATIONS

The increased PIP delivering capability of the newnozzle suggests, the potential for improved cleaning oversootblowers using conventional nozzles in a recovery boiler.For a 2.5cm(1") nozzle, this benefit can be realized atoperating pressures exceeding about 1379kPa(200psig).

Laboratory measurements for PIP suggest that thecleaning equivalent of a conventional nozzle can be reachedwith reduced consumption of the cleaning fluid. Once again,for the nozzles tested here, a savings of about 30% isexpected at blowing pressures of 2413kPa(350psig).Measurements of PIP indicate, that there may be little meritin operating at pressures in excess of about2068kPa(300psig) with a conventional nozzle.

Boiler parameters, indicate that the cleanersuperheater in cycle 2, improves the overall boiler

performance. This evidence strongly supports the view that aclean superheater can reduce the cleaning demand in the restof the boiler. Further reduction in cleaning load andimprovements in boiler thermal efficiency are expected oncethe complete change out of all sootblower nozzles are made.

For case I, it turns out that the boiler was able tooperate for it's normal 6 month run time with over 50%reduction in sootblower steam flow. Therefore, it is

probable that in reality sootblower steam usage in recoveryboilers are in excess of what is required.

In addition to the present savings and projectedsavings based on the cost to generate steam, a furthersavings will be realized through reduced wear and tear ofthe sootblowers and associated maintenance costs. Theincrease in sootblower motor amps at high blowing

pressures during the retraction of the lance, is indicative ofthe extra work/load done by/on the sooblower.

6. CONCLUSIONS

The dimensional analysis for the flow in the lance,nozzle and jet provided the key parameters required to scalethis problem. The good agreement between the quarter andfull scale results have been obtained. The increased PIP

measurements for the new nozzle have verified the gain tobe achieved by fully expanding the gas prior to leaving thenozzle.

Both visual inspection and improved boilerperformance parameters have confirmed that the increase inPIP delivered by the full expansion nozzle, does improve thecleaning capability of the sootblower. In this case theimproved cleaning was achieved, with at least 20% lesssteam consumption. The steam saving potential for the newnozzle, together with the lower flue gas temperature due tothe cleaner superheater has enabled a 30% reduction of theeconomizer blowing pressure while the boiler operated at

full load.

It has been shown that steam savings is possible forrecovery boilers operating at both modest and heavy loads.These studies show that there is a fair amount of latitude fortrying to optimize the operating costs and thermal efficiencyof present recovery boilers.

In both Case I where there is high fuel costs butmoderate to low steam usage and, in Case II where there islow fuel costs but high steam usage the net result was asavings of about $30k to 40k per month. Naturally, in alocation where both fuel costs and steam usage are high,

tremendous savings could be realized by taking advantageof recent developments in sootblower technology.

The present study has looked at steam from thepoint of view of fuel cost. An opportunity lies in makinggains in areas where fuel costs are low but electricity is at a

premium. This will come by having to make lesser amountsof extraction form turbines. The author is not aware of sucha study having been done to date.


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The new nozzle together with judicious operatingconditions, provide an excellent opportunity for optimizingthe sootblower operation to achieve both better thermalefficiency while realizing financial savings through reducedsteam consumption and a potential for lower maintenancecosts.

7. ACKNOWLEDGEMENT

The author likes to thank Mark Easterwood, AlanUmemoto, Bill Gallacher & Jim Hanson from the Wallulamill and John Lacher & Ken Petrie from the Leaf River Millfor their efforts in gathering data for this study.

8. NOMENCLATURE

d Diameter l Distance from nozzle entrance to

inner wall of lance tube(Figure 3)p Pressure

r Radiusx Axial distance along the jet center lineA AreaF Shape factor based on tube orientationFI Fouling index, equation (12)LMTD Log-mean temperature differenceM Mach number PIP Peak Impact PressureQ Heat absorbedR Fouling index, equation (11)T TemperatureU Axial velocity of the gas

Greek? Gas density? Overall heat transfer coefficient? Mass flow rate of gas? p Lance-nozzle pressure

Subscripto1 Upstream of Nozzle (in lance)o2 At nozzlee Exit of the nozzlex Center line location in the jetECON EconomizerGB Generating bank

SH Superheater T Throat

Ambient conditions

9. REFERENCES

1. Green, R.P., and G. Hough, Chemical Recovery in theAlkaline Pulping Process, 3rd Edition, TAPPI Press,Atlanta, 1992.

2. Tran, H.N., "Kraft Recovery Boiler Plugging andPrevention", TAPPI Kraft Recovery Operations ShortCourse, TAPPI Press, pp. 209-217, 1992.

3. Hayman, J.R. and V.U. Martin, "Using WaterThrough Retractable Sootblowers for Cleaning Out ofService Recovery Boilers", Proceedings of the TAPPIEngineering Conference, November 1979.

4. Tran, H.N., D. Barham and D. Reeve, "Sintering ofFireside Deposits and its Impact on Plugging in KraftRecovery Boilers", TAPPI Journal, 70 (4), pp. 109-113. 1988.

5. Jameel, M.I., D.E. Cormack , H.N. Tran, and T.Moskal, "Sootblower Optimization Part 1:

Fundamental Hydrodynamics of a Sootblower Nozzleand Jet", TAPPI Journal, 77 (5), pp. 135-142, 1994.

6. Jameel, M.I., H. Tran and D.E. Cormack, "US Patent5,375,771", 1994.

7. Jameel, M.I., "US Patent 5,505,163", 1996.8. Jameel, M.I., H. Schwade and M. Easterwood, "A

Field Study on the Operational Impact of ImprovedSootblower Nozzles on Recovery Boilers", Proc.TAPPI Engineering Conference", Vol. 2, Dallas,1995.

9. Tran, H.N., M. Martinez, D.W. Reeve, T. Cole, R.A.Damon and D.T. Clay, "Removal of Recovery BoilerFireside Deposits by Thermal Shedding", Pulp &Paper Canada, 93 (11), pp. 358-364, 1993.

10. Holman, J.P., Heat Transfer, McGraw-Hill, NewYork, 1986.

(10th Latin American Recovery Congress,Concepcin, Chile, August 26-30, 1996)

steam savings in recovery boilers

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