18

could get more sugar through dilution.Mr. Godfrey replied that there were other ways of

getting every ounce out of the' cane and that wasby extra milling plant,increasing the crushing unitsand so' on. . .

The Chairman asked if the extra mills ,"vould besufficient without a due proportion of maceration.

Mr. Godfrey replied that they would have to havea certain amount of maceration. <

Mr. Truscott stated that in a certain mill it waseasy to get 97% extraction from dilution, so it provedthat by proper methods they could not help gettinga higher extraction. The more water they put onthe more sugar they got, there was no disputingthat.

Mr. Pnllar replied that a similar contention hadbeen considered by better men than himself, and theresult had been that one of the sugar firms had de­cided to sell bye-product power. Why had theydone that? For the reason that they had to burncoal to get heat to evaporate water that they addedto the sugar, Why had they power to sell? Because

instead of wasting it in reducing valves they gener­ated steam at high pressures and superheat.ed andgenerated electricity. That power was. ali asset tothem, so much so that they decided to sell it to theMunicipality. That surely was proof of. what, hesaid, that if they burned their bagasse more efficientlythey should have power available for other purposes.That question had been considerednot only by localexperts but by experts in London. He thought thatought to be sufficient.

At this stage (1 p.m.) the Congress was adjournedfor lunch.

. On resuming at 2.30 p.m. the following paper on"Types and Designs of Bagasse Furnaces" was read.by Mr. John Murray at the request of Mr. P. Murraywho was unavoidably absent, the paper having beenprepared by a Sub-Committee of the Sugar Technol­ogists' Association consisting of Messrs. L. F. deFroberville, J. R. Simpson, John Murray and P.Murray..

TYPES AND DESIGNS OF BAGASSE FURNACE.-------

(Paper prepared' by Sub - Committee of Natal Sugar Technologists Association.)

ltl@I@I~&l\lflTIimIWlltlili'Rilmi1ltiitmilt&lti\'j~If&b1\'i~&'iWRitmili"&IWli"&Iiffi1lX'i\mtlmilmtlr&It&IMi~

Foreword.

When 0111' old ancestral engineers first built a firewith dried sticks of mor.e or less bruised cane withwhich they evaporated the moisture from their canejuice did they ever visualise that the outcome oftheir intelligent efforts would be the modern BagasseFurnace 7 A detailed account of this wonderfulevolution would fill a volume, and can only be re­called in our limited space with fervent thankfulnessthat their repeated and determined efforts have ledthe way to progressive success; and finally buildingon these successes and a better understanding of thepeculiarities of this fuel we have now been able toso design our furnaces and accessories in such a wayas to reduce to a minimum the great losses that havepreviously been unavoidable. So much so indeedis this the case that no modern factory requires touse extraneous fuel except in such countries wherethe cane contains so much moisture that the quantityof fuel available is small. These very valuable andimportant results are only obtained by unremitting'care and team work of attendants as well as a liberaland broad minded .administr-ativenolicv. Thus withthe idea of assisting or interesting <those morecloselvconnected with or r-esponsihla for the erertinn »nddesign of furnaces we are publishing the followingas appendices i-c-

1. The. Theory of Combustion as applied toBagasse.

2. The Composition of Natal Bagasse as a fuel;and economies attendant upon modern im­provements and care in design.

3. Typical Drawings and Settings of Boilers andfurnaces from various parts of the world.

It is now our intention to try and interest youwith the following report in which reference willbe made to several of the numbered drawings.

Burning of Bagasse.In considering the burning of Bagasse it must be

understood that the fibre or combustible portion ofthe sugar cane forms, on an average in Natal 16.2%on weight of cane as compared with an average of12% in the other important sugar growing countries.Also that it contains from 47 to 50% of moisturewhen entering the furnaces.

Quality of Bagasse.It must not be considered that Natal Bagasse is of

inferior quality for steaming purposes to that ofother countries. This is shown in Appendix (1)Page ;) in which a list has been made of practicaltests carried out by such authorities as Messrs. L.Blacklock, E. W. Kerr and R. S. Norj-is of the calori­fic value of bagasse in Louisiana, Hawaii and Natal.There is nothing therefore to prevent our Sugar In­dustry from obtaining just as good furnace resultsas these of other i)arts of the world, . I

19

Quantity of Bagasse.

Also owing to the fact that the fibre content ofour sugar cane is, as pointed out, above the' averagewe are able to afford the steam for the treatment ofjuices from the Uba cane which are of a far morerefractorv nature than any other known. This im­portant feature of the Db~i. cane is most appreciatedj n those factories where white sugar is made, and

• where a large supply of steam is essential.With a properly designed and constructed. boiler,

and given that the result of the plant is modern andefficient no extra fuelshould be necessary even forthe week end purposes of stopping and starting up.'I'his subject of steam balance we hope will be dealtwith at a later date by other Committees.

Furnace Combustion.

vVe now come to the combustion of the bagasse inthe furnace which is ~f the step grate type speciallydesigned for the purpose (see Fig. 1). Thebagasse with its large content of moisture is fed con­tinuously into an 'opening at the top of the furnacevertically above the top of the step grate; and theprinciple of. combustion is as fnllows . In zone A ofthe diagram the moisture in the Bagasse Js evapor­ated by .the heat reflected from the roof of thefurnace, and if the furnace is not properly con­structed this does not occur, and we know this is thecase in many of the Natal furnaces. In the nextLower zone B the bagasse being dry. the volatilematters are now distiller] off andradiate heat to theroof which is reflected back to zone A to dry. '(hebagasse. The design of the roof is of great practicalimportance for this duty. The next stage is thelowest zone C where the fuel now mostly consistsof carbon; and where combustion' is completed andonly .ashes left. Great stress must be 'laid on thenecessity to have the furnace roof of correct shapeas it is 'realized that this has been the cause offailure of many otherwise well designed settings:

\

Design of Furnaces.

The design of the Furnace should be such that thegaseous 'products from the three zon es should firstlybe intimately mixed by passing through a constrictedpnssage shown at D iu diagram, and impinged on theopposite wall of a relatively Iarge 'interual chamberE where the gases are thoroughly mixed; and' byreverberation the walls' of this chamber become in­candescent thus completing combustion before com­ing in contact with the comparatively cool boilershell. Ash is deposited in this chamber, owing tothe velocity of the gases bring greatly decreased;and arrangements have. to be made to. relieve thisash at stated periods through a conveniently placedopening. A spy hole . for observation purposes.should be pierced in a side of this chamber.

Furnace Temperatures.

The following is a list of furnace temperatureswith their corresponding colours.of the fire:-

Appearance of Fire . Temp. deg. F.Red just visible 977Red Dull .. 1290Red Cherry dull 1470Red full .. ., ., 1650Red clear .. .. 1830Orange deep .. .. 2010Orange clear·.. .. 2190White heat .. .. 2370 .White bright .... .. 2550White dazzling .. .. 2730

vVe wish here to draw your attention to Fig No.2which shows a furnace that does not fulfil the ideasof an idea] design, firstly the roof in this furnaceis so constructed that there can be practically noheat radiation from zones B to A or from zones C toB. Also the products of zones A. B. and G are notmixed properly this resulting in incomplete com­bustion.

Having dealt hitherto with step grate furnaces wemust now consider the Flat Grate 'I'ype. There aremany adherents' of this type who hotly contest itsmerits as against the Step Grate and it is unquestion­able that good results are obtainable from it. Theproportions and design are different to the step gratefurnace as may be noted in Fig. Nos. 3 and 4 (appen­dix 3), but they are essentially alike in one mainfeature viz the roof of both types must be as flatas possible, or of. the. segmental arch type ratherthem the semi-circular, so that efficient radiationmay result in order to evaporate the moisture in theentering bagasse.

Boiler Heating Surfaces. 0

We shall next draw your attention to the amountof boiler heating surface required for a sugar factorywith their corresponding areas and volume of flues,all of which have to be carefully proportioned forthe proper working of the boiler plant. The usualheating surface required in boilers of a factory ofpredetermined capacity is given by various' authori­ties as 500 sq. ft. per ton of cane per hour. Fromfigures gathered from. twelve of our Natal factoriesan average of 461 sq. ft. per ton of cane per hour,varyine from 338 to 620 has been obtained; put itmust be noted that those factories showinz thesmaller heating surfaces are in every case adding totheir boiler plant. On Page 5 of appendix 2 you willnote that it is calculated that a boiler requires 1.12lbs. of bagasse per square foot of heating surface.'I'aking the ';"eight of bagasse as being one third thatof cane 595 sq. ft. heating surface will be requiredfor one ton of cane.

Grate Areas.With regard to Furnace Grate Area this is gener­

ally calculated proportionately to the heating sur­f~ce, and for modern mills with finely crushed

20

bl'l,gasse a ration of 100 of heating surface to 1 ofg;rate area is considered a good practice.

The figures of twelve. Natal factories show anaverage ration of 78.2 to 1; varying from 57.9 to 120to 1;. the reason for this great variation being thatfactories whose heating surfaces are small have pro­portionately "large grate' areas or vice versa.

. In Natal 80 to 163 lbs. of bagasse is consumed persquare ft. of grate area, and it will be noted that inAppendix 2 ideal conditions give the figures as be­ing 112.

The problem of the size of grates for burningbagasse is one that is of great importance, and isworthy of more attention. Our local results mightbe carefully tabulated, in order that a definite un­derstanding of the correct size to instal can bearrived at.

It has been found in Hawaii-the country of highextractions and fine crushing-that the finer thebagasse is crushed the smaller the grates should bein proportion to the heating surface. It is also asine qua non that the grate area be well coveredcontinuously with a bed of fuel; and it would addconsiderably to our knowledge if local results ofalteration in grate areas were carefully noted withthe object of tabulating same for future reference.

Furnace Volume.. The volnme of our furnaces next claims our atten­

tion. The combustion chamber sh ould not be of lesscapacity than a quarter cubic. foot per square footof heating surface though in Natal this rule is notadhered to, many being too small. In observing thisrule care must be taken that the furnace roof be notraised too high above- the grate to spoil the radiat­ing or drying action on the bagasse.

Flue Areas.Let us next regard the area of flues or passages

that lead from the feed' hopper to the chimney". Thearea of passage between furnace and heating surfaceof boiler should be in the case of water tube boilersone square inch per square foot of heating surface;and in the case of smoke tube boilers 5/6 square inchper square foot of heating surface; and for thepassage after leaving the boiler this area should be3/5 square inch per square foot of heating snrface.(Appendix 2).

Chimney Draught.With regard to the subject of chimney draught

this is quite an involved subject and each particularboiler plant must be studied for their own distinctivefeatures which may include atmospheric humidity,altitude !' bove sea level, use of waste gases in pre­heaters or economizers, total length of horizontalflues, etc.

Furnace Air Supply.Air supply to the furnace for combustion pur­

poses is most important, as the use of either too muchor too little air means a loss of heat either by dilu­tion or else by incomplete combustion; and in either

case the loss of heat may be. serious. Under present.conditions air may be admitted into a furnace ineither of the following Ways:-

FIHST.-Natural draught conditions in which casethe bagasse should be fed into an enclosed or mech­anical hopper to exclude air entering with bagasse.

SECOND.-Cold air mav be blown in below thegrates at a pressure to red';;'ce the vacuum above thegrate to zero, commonly known as balanced draught.'

THIHD.-Hot air may be blown in in a similarmanner to No.2 the heating of this air being brought

·about by transference of the heat of the waste gases· in a pre-heater to the air to be used in the furnace.

Great stress must be laid On the discreet use of airfor furnace purposes; an example in point may herebe given. It was found at a certain factory that onopening the flue dampers the furnace temperaturewas greatly reduced, am). by calculation thisoccasioned 100% increase in losses in flue gases by

·excess air being drawn in which loss would require17% 111 ore bagasse for fuel. This instance 'wouldpoint to a defective furnace design. Every factoryshould aim at satisfactory fuel combustion and test·their flue gases systematically; and with this in viewthe engineer and chemist should collaborate closelyin order to obtain the utmost efficiency in this im­portant subject.

Pre-Heaters.Recently pre-heaters have been tried in this coun­

try. 'I'hese machines are designed for the purposeof utilizing the heat out of the waste gases to raisethe temperature of the air that is being supplied to­the boiler furnace. The unavoidable heat lost in­the waste gases from the boiler is approximately 30%of the total heat in the bagasse, and by the efficientreturn of this heat into the furnace in the form' ofhot air an inc-rease of 22% in steam may be obtained...(Appendices land 2).

If the greater part of the moisture in the bagasse­is driven off by the waste gases by a process origin­ally used in Mauritius the saving in heat would be­about 17%. We wish to draw your particular at­tention to the important fact of the superior efficiencyof the pre-heated air system.

Another important point about pre-heating is thatit increases the furnace temperatures considerably,thereby greatly increasing the ratio of heat trans-­ference to the boiler, thus increasing evaporation.

Economizers.The economy of feed water heaters by "waste gas

economizers" as supplied by the Greens Economizer.Co., should next be considered. With properly de-­signed' and proportioned economizers say of Ilktimes boiler heating surface an increase in steamproduction' of from 10% to 20% may be expected.

Feed water heating to at least 200 deg. F. is essen­tial to the life of a boiler besides adding to its.efficiency, and should on no account be omitted infavour of air pre-heating, although a judicious com-

21.~''e!,"",---,...~_._--, .-- .. ------ .._.~.,- .-_ .•_-

.Q

I

bination of ~he two should he worth the capital out­lay and mamtenance and also give great efficiency.

Feed Water.

Factories often have to use river water contain­ing mud and other dissolved impurities. and it isvery injurious to boilers to use this as feed waterbesides considerably lowering the steaming efficiency.Some kind of purification system should be under­taken. This is not a costly installation, and onaccount of the benefits derived should not be omitted',Should quick lime and alumina ferric be used as thechemical reagent for settling, a good rule for thesize of the reservoir is a capacity of 250 gallons perton of cane crushed per 24 hours.

Purification Tanks.

Reservoirs of this type are in use at Colenso, Mt.Edgecombe. Umbogintwini and Umfolosi,

Mr. H. H, Dodds has also drawn our attention tothis matter in his paper read before the S..A. Associa­tion of .Analytical Chemists in 1919.

Soot Deposits.

The loss due to carbon and ash deposits on and inboiler tubes and other heating surfaces is often morethan is estimated, and as the conductivity of theheating surfaces varies conversely as the thickness ofthifl deposit great care should be taken that surfaces

Boiler Plants.

Heat is motion. When heat is applied to' a body,a change takes place in its molecular arrangement,the molecules are displaced, they move, and by thisdisplacement or movement, cause the different phen­omena of heat, light and electricity. 'I'he applicationof heat causes an increase in the temperature as wellas in the volume of the body and in the case of aliquid, the temperature rises until it reaches the boil­ing point, whence it remains, stationary until thewhole of the liquid is converted into vapour or steam.If the liquid is in a closed vessel, a further applica­tion of heat will cause the temperature to rise and apressure will be exerted in the vessel; the more heatbeing applied, the higher will be the temperature andthe greater will be the pressure.

'I'he atmosphere exerts a pressure on the surfaceof the earth, which has been found to be 14.7 lbs. persquare inch and the absolute pressure is the sum ofthe atmospheric pressure and of that marked by thegauge or in other words, a 100 lbs, pressure eorres­ponds to an absolute pressure of 100 gauge pressureand 14.7 lbs, atmospheric or 114.7 lbs. absolute persquare inch.

When heat is applied to water at 32 deg. F., thetemperature rises until it reaches the boiling pointor 212 degs., F. and the number of units of heatabsorbed are 212-32-180 per pound of water. '

These units are called British 'I'herrna] Units or

be regularly and properly cleaned; and when clean­i~g boiler tubes that .a stiff brush of the properSIze be used at stated intervals during the week aswell as at week vends. .As an example-of this lossdUA to denosit consider a clean boiler surface asgiving no loss of heat transference, then with 1/16 in.deposit there would be ~ loss of 26%, and with a 3/16in, deposit a loss of 69% would be incurred.

Desian and Appendix.

Weare putting forward certain designs of furn­aces that have been found useful in this and othernnrts of the world, which we hope may be of useto those interested. Nos. 1 and 2 .Appendices havealso been printed with the hope that they may be ofuse to the engineer in his attempts to solve this mostdifficult problem of bagasse furnace design.

In conclusion the Committee have to thank thevarious factory managements for their' courtesy insupply particulars of their plants and a'so draw­ings of boiler settings. .Also they are indebted tovarious other firms and, friends who hvve assisted.It is 'to be regretted that shortness of time has nre­vented the further development of this paper. Butif it should be even merely the means of raisinrr adebate or other constructive criticism on the subject,the obiect, of the Committee will have been amplyachieved.

B.T.U. and' the heat unit is the quantity of heat neces­sary to raise the temperature of water One degreeFahrenheit from 39 degs. to 40 degs. F.

'The quantity of heat necessary to, convert onepound of water at 212 degs. F. into steam at 2-12dogs. F. is called Latent Heat. It is this heat which"is absorbed by the liquid for its conversion into steamat the same temperature and pressure. In the caseof water the Latent Heat is 965.7 at 212 degs. F. andatmospheric pressure and the total heat necessaryfor the conversion of lIb. of water at 32 degs. F. tosteam at 212 degs. F. is 180 + 965.71145.7 B.T.U.and the absolute pressure will be 14.7 lbs, per squareinch. If the pressure in the closed vessel or boilerrises to 100 Ib s, gauge the absolute pressure will be114.7 lbs., the Vl"mperoture will be 337.6 degs. F., theLatent Heat will be 875.6 and the total heat units willbe 1185 B.T.D., as recorded in the Steam Tables inEng-ineer's Manuals.

If the Steam is meant to be "Superheated," thatis, to have a temperature superior to that recordedin Steam Tables for the same pressure. m or« heatmust be applied. In the calculations then, the numberof degrees of superheat must' be multiplied by theSpecific Heat of superheated steam, which is .47!and which may be taken in round figures as .5. Inthe example above, if the steam is to be superheatedto 4000 F., the calculation is:- .337.6=32+875.6+.5 (400--':'337.6)=1212.4 B.T.U.

22

Average composition, of Bagasse i- '

.0371 x 7120 + .0014 x 6748 + 1.012 x7533 + .4552 X 7533 = 3793.01 B.T.U.

In this ease, the non sugar or organic matter hasbeen considered, giving the same B.T.U. as cellulose.'I'hereis already a difference between the value 0 b-

Non sugar includes about 0.14" glucose and 1.20.wax, other organic substances and also-a little sand.'I'aking the composition of the bagasse, the theoreticalheat value as calculated above for each constituent.pel' pound will be i-

1"

3.71% .1.34%

45.52%49.43%

SUCROSE .. : .... , ....NON SUGAR.. .. .. .. .. , ..,FIBRE , .-WATER .

.0371 x 6146' + .0014 x 5840 + .012.x 6488.2+ .4552 x 6488.2 = 3267.5 B.T.U.

per pound of Bagasse at .4943 Moisture.

In the valuable !' Experimental Study of Bagasseand Bagasse Furnaces" by Prof.. E.vV. Kerr, M. E.published in the Louisiana Experiment StationBulletin of August 1909, some interesting figures aregiven concerning the heat values per pound of Fibre,Sucrose, Glucose, etc. These figures hav.e been pro­duced. by Stahlman and Langbein before the BritishInstitution-of Civil Engineers and they obtained 7533B.T.U. per pound of cellulose, 7120 per pound' ofsucrose ancl6748 B.T.D. per pound of 'glucose:

Calculating on. these data, the B.T.U. obtained perpound of'bagasse will he ;-

It will be noticed in the calculations that thequantity between brackets when worked out amountsto nothing.

FIBRE B,.T.U. - 14600 x .4444 + 62000.4939

(.0617- -, )8

6488.24 + 6200 x.4936-.4939C-'---)

8 '

= 6488.24 B.T.U. per pound.SUCROSE = 6146.60 andGlriUCOSE = 5840 B.'l'.U. per pound.

As the Organic matter in the bagasse is usuallytaken as having the same heat units as Fibre thecalculation of heat value can be worked out.

"I'he analyses of bagasse of several mills have been:condensed and' an average composition has beenobtained for the calculation. Bagasse per; cent cane­works out at 36.68%.

Similarly, SUCROSE, C12H22

On represents42.10% of Carbon 6.43% of Hydrogen and 51.47%of oxygen.

, GI.JUCOSE,C 6 HJ 2

0(; represents 40.00% carbon,6.67% Hydrogen and 53.33% Oxygen.

By the simple inspection of. these' formulae, it canbe seen that the ratio H to 0 corresponds to thatforming water, 'or in 'othe'r words, the proportionof hydrogen to oxygen in these three organic bodiesis exactly that 'which produces wat8r.The hydrogenwill combine with the Oxygen present in' the bodyitself to form 'water without the interference of oxy­gen from the air and therefore produces no heat.

Using' Dulong's formula for the calculation of thetheoretical heat values of fibre; sucrose and glucose,the B.T.U. in one pound of the substance is 14,600 C+ 62000 (H-1/s0).

G

BAGASSE AND COMBUSTION.• '. • .• ' <.' •

0+0;2=CO 2

Combustion therefor~ needs Oxygen or Ail' to becomplete. When the quantity of, air is insufficient,the combustion is incomplete and one atom of Carbonis united to one of oxygen to form Carbon Monoxideor CO. Whilst, when air' is supplied in .sufficientquantity, the -whols of the' Carbon is burnt intoCarbon Di-oxide and the number of B.T.U. evolvedis 3.17 times more than that produced by the com­bustioninto CO, where it is' only 4600 B.T.U. per' lb.cubon. ' ,

Bagasse is the residue left after the cane has beencrushed by the mills. It is a complex mixture ofwoody fibre, sugar, glucose, wax, sand, other organicsohds and water; the proportion of these differentconstituents depending on the pressure of the millson the water spread over the bagasse and on theqilality'of the cane. Water forms generally nearlyhalf of the weightof the bagasse, varying between45. and 51 or 52%, the balance being fibre .which'ranges between 43 and 48% and the solids from 4 to7% of the bagasse.

Fibre or Cellulose has the formula C H "0' mean- .6 10 5

ing that 6 parts of carbon (Atomic weight 12), unitewith 10 parts of Hydrogen (at weight.L) and 5 partsof oxygen (at 'weight 16) to f'orm the organic com­pound Cellulose. The percentage of these elementsare: CELLULOSE-C He.

, ,'6)0 5

6 of Carbon or 6 by 12 equals72,- 44.44%., 10 of Hydrogen, 10' by 1 equals 10, ~ 6.17%.

5 of Oxygen or 5 by 16 equals 18, ' 49.39%.

, .When a substance is burnt, the oxygen of the aircombines with the rsubstance, oxidises it, producesheat and givesoffCarbon Di-Oxide as the final resultof combustion.

23

•

tained by the Calorimetric 'rest of the individualbodies constituting the bagasse and the calculatedtheoretical heat values of these bodies.

Mr. L. Blacklock, Chemist of the Hulett's Refinery,has made several tests to detect the heat value ofthe bagasse of several of our mills .and veryoblig.ingly communicated the results of his tests.

Moisture of Nett Heat Value DryBagasse' per pound Bagasse

48.72 3774B.T.D. 8330 RT.U.48.32 3785 823148.36 3894 835049.74 3738 839650.60 3665 .8414B2.96 3318 8300

. 56.54 3024 840059.24 ·2739 8330

Avg. 51.75 3452 B.T.D. 8344B.T.D.

Working on these figures, the total solids in thebagasse being" .5057, the Gross Heat Value perpound of dry bagasse '8344 B.'l'.U.,'\then for a mois­ture of .4943, the B.T.U. 4219.56 arid the differencebetween this figure and. the previous one is-

4219.56-3793.02

4219.56

'"equals 10.1%, indicating that the calculated value is10.1% less than the actual calculated calorimetricvalue.

Prinsen Geerligs rmentions the following formulafor the calculation of the Heat value of bagasse bytaking the calorific values of its constituents.

Calorific value = 8550 Fibre +' 7119 Sucrose,+ 6750 Glucose-972 water and divided by, 100.Working out this formula the' nett calorific valueequals 8550 x .4552 + 7119 x .0371,+ 6750 x .0014minus 972 x.4943 ~ 3665.06 B.'P.D. which is nearlythe same figure from actual tests made 'here.

Referring to the tests carried on by Prof. E. W,Kerr in Louisiana and by Mr. R S. Norris in Hawaii,the nett heat value of bagasse with varying mois­tures from these two regions is recorded togetherwith the results obtained by Mr. L. Blacklock inNatal. .

To establish a comparison between the results'obtained in Louisiana and Hawaii and those in Natal,the nett heat value per pound' of bagasse of variousmoistures has been calculated on the same basis ashas been done for the two other countries, that is,the temperature of the ail' during combustion andthat of the stack which has been taken forLhe twoothers at 500 degs.' F.have been considered and theresults are shown in the following table. Hawaiifigures are lower than those of Louisiana and Natalprobably on account of the nature of the cane there.

Moisture of Bagasse. " Nett Heat Value per Th.Lousiana. Hawaii. Natal. Louisiana. Hawaii. Natal.

48 48 48' 3750 3615 374:148 49 49 3654 '. .'3522 364650 50 50 3558 3428 355051, 51. 51 3462 3335 3455,52 52. 52 . 3366 . 3241' 33'5853 53 53 3270 3148 326354 54 54 3174 3054 316655 55 55 3078 2961 307156 56 .56 2981 2867 297457. 57 57 ' 2886 2774 287958 58 58 2789 2680 278259 59 ·59 2694 2587 268760 60 60 2598 '2494 2592

.The average heat value of bagasse from Calorime­tric tests in Louisiana is 8360 B.T.D. 'per pound ofdry bagasse, in 'Hawaii, the heat value is 8100 B.T.D.per pound and in Natal, the average has been foundto be 8344 B.T.U. 'which is. very nearly the same asthe Louisiana bagasse. '.

The gross heat produced by the combustion of theNatal bagasse at .4943 moisture will be 8344 x ,5057 ,equals '4219.56 B.T.U. per pound , but part of thisheat will be consumed for the evaporation of thewater contained into steam from and at 212 degs.F:, and if it be assumed that the temperature of theair be: 70 degs. F. and that of the- flue 500 degs, F.the number of B.T.D. lost will be .4943 (212-70 +965.9 + .5 (500-212)) equals 618.76. Deductingthis quantity from the total of 4219.56 there remains3600.80 which is the nett thermal. value-of-one pQUJ?-d,of this bagasse and the' percentage 'of .Ioss <is

4219.56-3600.80

4219.56equals 14.7% therefore 14.7% of the heat generatedwill be taken to convert the moisture into steam from.each pound of bagasse. But again, the nett heatvalue obtained will not be utilized in totality by theboiler, a certain part will be lost through rad~ationand other causes and will be delivered to the chimneyby the flues. The EFFICIENCY -of a boiler is therati.o between the heat absorbed by the water in theboiler ancf that supplied to the boiler and is safelytaken as 60% or 60% of the heat supplied are takenand 40% are lost.

Total heat supplied by one pound' of bagasse. = 3600 B.T.D.

Heat absorbed by:boilei',60% = 2160·B.T.D.Radiation and other losses 10% = 360 B.T.U. p

Heat lost in the flues 30% . = 1080 B.T.D..

Total' .. ., 3600 B.T.U.·As the heat lost to dry the bagasse amounts to

(i18.76 B.T.D. there is nearly double the quantity lostin the flues or in other words all the bagasse can bethoroughly ·dried. by the heat which' is lost and theefficiency of a dry machine needs only be

618.76equals 57% to dry the bazasse

1080

24

WEIGHT AND VOLUME OF AIR FOR

COMBUSTION.

The calculation of air excess from flue gas analysisis done thus. In air, Nitrogen occupies a volume3.76 times greater than that of oxygen and if N re­presents the proportion of nitrogen found and 0 thatof oxygen, then volume of air employed . N

'rhe atomic weights' of carbon and oxygen beingrespectively 12 and 16, the molecular weight ofcarbonic acid is 44 and 2.67 parts of oxygen arerequired for 1 part of earb on. As there are 23 partsof oxygen in air, the quantity of this latter will be11.61 parts for 1 of Carbon. Similarly to burn Hy­drogen and produce water, 8 parts of oxygen or 34.78parts of air are required. Assuming the temperatureof air to be 80 degs. P., 1 part of air will occupy 13.6cubic feet and 1.61 lbs. = 157.89 cubic feet per'-pound of carbon and 472 cubic feet per pound ofHydrogen. If there is an excess of air of 50% thevolume will become 157.89 + 78.94 = 236.83 cf.,and if 100% excess, 2 x 157.39 equals' 315.78 cubicfeet;

theoretical quantity

A.ppendlx No.2

N-3.760

If the analysis gave 8 for oxygen and 79 for Nitro­gen, the excess will be-

79 79--- equals 1.612 equals 61.2%

79-3.760 79-30.08Water evaporated per pound of fuel and evaporationper square foot of heating surface.

The evaporative tests on boilers made by Prof. E.W,. Kerr show an evaporation from and at 212 degs.F. of 4.27 lbs. per square foot of heating surface perhour. Tests made here showed an evaporation of3.27 lbs, per sq. foot .per hour; other results fromeleven mills in Natal and recorded by Mr. P. Murray,show an evaporation of from 2.98 to 4.38 lbs., givingan average of 3.64 lbs, for the Natal mills per squarefoot per hour.

The evaporation .f'rom and at 212 degs..F. perpound of dry bagasse was found to be 4.7 lbs. and2.26 lbs. per. pound of bagasse containing 52.1%moisture in Louisiana. The average of pounds ofbagasse burnt per square foot of grate area perhour has been given by Mr. P. Murray as 92.5. Asthe ratio heating surface to grate area works out anaverage of 64.5 to,l, therefore, the average weightof water evaporated per pound of bagasse per houris 2.54 lbs., which is not' far from the figure 2.26obtained above. .

Bag- 'se % on cane 32.13 32.33

Take an average bagasse as:-

Sugar. 4%; Fibre 47%; Moisture 49%and 32% bagasse oncane ..

The usual fuel value of dry bagasse is' taken as8300 B.T.Usper lb. so a bagasse having 49% moisturewould have a fuel value of:-

100=49( ) x 8300-.49

100

x [(2120-900 ) + 970 + .48 (5500-2120) ]

=4233-614.=3619 B.. T.Us per lb. of wet Bagasse;

12.1

1614

Sugar ....Fibre ..MoistureUndetermined

Natal Estates.

3.3746.3349.51

;79

100.00

. Ottawa Estate.

4.3447.2947.151.22

100.00

Babcock and Wilcox formula gives­8550 x .47 + 7119 x .04-972 x .49.-4018.5 + 284.76-476.28.~3826.9 B.T.Us. .

Fuel Value from Theory.

The average composition of dry bagasse is takenby Deerr as 46.5% carbon, 6.5% hydrogen and 46%oxygen;

The atomic weight of:-

Carbon isHydrogen "Oxygen "Nitrogen "

Carb on burns to CO'J

. C + 0 =CO ~,2 2

12 + 32 = 44.

'So for combustion 12 lbs. of carbon requires 32 Ibs.of oxygen.'

Hydrogen burns H 0. 2

H2

+ 0 H20

2 + 16=18.

So 16 lbs. of oxygen requires 2 lbs. of hydrogen, - Specific Heat of gases at 6000 F and 19000 F Averagetherefore :~

100i.s x 23 =5.65 lbs, per lb. of bagasse.

The products of combustion will then be:---:-

Due to carbon .465 + 1.24 - 1. 7050 CO2

Due to Hydrogen .. .065 + .52 - . 5~50 H20

Introduced with air 5.65 x .01 - .0565 H20

5.65 x .76 - 4.2940 N

but there is already .46 lb s, of 0 present so

1.76"':"-.46=1.3 lbs, oxygen is required.

The air has 23% oxygen, 1% water and 76%

nitrogen so' the amount of air required for combus­

tion is:~

32.465 lb s, C requires .465 x 12 tbs. oxygen.

=1.24 Ib s. oxygen.16

.065, Ths.. H requires .065 x '2 Ths. oxygen.

=.520 lbs. oxygen.Oxygen required to burn C in 1Th of bagl!sse=1.24Ths

" ".",,' H """ = .52tbs

2.2661588°F

36003600

1.9051889°F

3600

1.5472326°F

3600

1.1863035

GO .. .215 .. 258 .2362H

2O.. .475 .561 .518

N .248 .263 .2550 ,.217 .23 .223

To raise the products of combustion of Llbs. ofbaaasse 10 F.

Net. 50% 100% 150%

CO 5' x .236 .205 .205 .205 .205H

20 x .518 .423 .431 .437 .445,

N x .255 .558 .837 1.116 1.3950' x . .223 .074 .147 .221

1.186 1.547 1.905 2.266 B.T.Us.

The heat taken away by the exhaust gases in eachcase are at 600° F.

but the full value of bagasse is about 3600 B.T.Usper lb. so the temperature increase reached in com­bustion in each case is :-

showing the reduction in temperature caused throughexcess air.

.. 1.76ThsTotal

100% 150%

.1868 .1868

.4041 .40851.0857 1.3571.1438 .2157

-----1.8204 2.16810092 (1300

B.T.Us) B.T.Us)

50%Net

.1868

.3952.8144.0718

1.0969x600 1.4682(=658 (=881

B.T.Us) B.T.Us)

CO?x .215 = .1868H,p x .475 = .3670N x .248 = .5431o x 217

but as bagasse has 51% dry matter and 49% water,the above results must 'be multiplied by .51 & .49added to the water giving :-

CO2 ' 1. 705 x .51 - .86955

H20= .6415 x .51 +.49 - .'81716

N = 4.294 x .51 o =2.18994

Total .. .. .. .. 6.6405 tbs,

3.87665 tbs.

With 50%, 100% and 150% excess air these

figures would be;-

showing the increase in heat lost by having too muchair admitted to the furnace.

So the heat available for evaporation in the boiler3600 3600· 3600 3600

is less 658 881 . 1092 1300

29.42 B.T.Us. 2719 B.T.Us. 2508 B.T.Us.2300 B.T.Us.

but Llb , of steam at 100 lb s, pressure requires1066.5 B.T.Us. to raise it from 150° F. so each tb.

. of bagasse will evaporate

1065.56.755tbs 8.195tOs = 2.76

Net 50%.

CO2

.869 .869

H2O

.817 , .832

N 2.190 3.284

° 2.190 .331

I' 3.876tbs 5.316tbs--'-

100% 150%

.869 .869

.845 .860

4.378 5.472

.663 .9942942 Ths. 2719 Ths:' 2508 Ths.

1065.5 ' 10f>5.52.55 2.35

2300 lbs,

1065.52.16 tbs.

water

26

Since the heat lost by radiationis ~bout '5% th'es~figures will reduce to:-

= 2.522 2.423 2.233 2.052Ths.

S'o that plants' using large excess of air ~jilfindgreat advantage in using preheaters by saving alarge amount .of fuel, varying from 15% with 50%excess air, to 30% with 150% excess air. ,

of water evaporated pe! tt). of fuel (bagasse).

The usual amount of air admitted to :Zurnaces 'isusually 100% in excess so that if another 50% isadmitted III excess the fuel 'value would. be reducedroughly 8%. .

By preheating' the air 'with exhaust gases a COIl-

siderable saving of heat is affected, as follows:-

Pounds of air per lb of fuel (for ordinary bagasse) :

Net. 50% 100% 150%5.65 x .51 8.475 x .51 11.3 x .51 .14.125 x .51

= 2.88. = 4.32 = 5.76 = 7.2

SUPI)osing air is raised frOI11 80° F to 480° which

means that air would be raised 400° from exhaustgases.

So B.T.Us required to do thiswould be400x speci­fic heat x weight of air per lb. bagasse.

If bagasse was totally dried each lb. of bagassewould give: 8300 x 51 B.T.Us.

100.." 4233 B.T.Us.

but bagasse with 49% moisture has a ealorifie valueof 3600 B.1.'.Us., sc the saving in drying is:

4233-3600---x 100%

360062300

360017.3%.

So heating the air gives much more efficienc'y 'thandrying bagasse. Drying bagasse is more difficult'to control owing to liability to fire, also the air heat­ing usually includes balanced draught which withthe increased temperature in the furnace increasesthe boiler rating greatly.

Volume of Gases.

Volume of 1Th. of gas at 32° Fat atmospheric

400 x .24 x 2.88= 276.5

400 x .24 x 5.76= 553

400 x .24 x4;32.= 415

400 x ,24 x 7.2= (]91.0 pressure -:-

At 600° F At 19l)00:p°

Tl1iS will mean a saving of fuel of:-~76 x 100 415 x 100 553 x100 691 x 100

This means that heat available for evaporationwillbe increased as fcllows i-i-

% heat. regained from exhaust gases by preheating

276 x 100. 415 x 100 . 553 x 100 691 x 100

39.0495.59

61.21

53.72

184.51 cu. ft.

. 15.23 cu. ft.= 36.24 cu. ft.

= 115.97 cu. ft.= 17.07 cu. ft.

17.5342.8926.49

25.750

Ths .869 x .17.53.845 x 42.89

4.378 x 26.49

: 663 x 25.75

CO2

' 8.14

H2

0 19.91

N 12.76

o 11.2

gas expands 1/492 for every 1°F rise in temperature.So the volume of gases with '100% excess air at600° F will be:-

and at 1900° F.CO2 .869 x 39.04 = 33.92 cu. ft.H

20 .845 x 95.59 = 80.77 cu. ft..

N 4.378 x 61. 21 = 267.97 cu. ft.o .663 x 53.72 = 35 .62 cu. ft. .

418.28 cu. ft.So that the volume of gases in the furnace is

. 2.26 times as much as when they emerge from theboiler.

The usualvevaooration for a multitibular boilerburning bagasse is '2l!z lbs, per square foot per hour,but it was already seen that fuel burned -with 100%

130053%

2300. '30%

881 - 415= 466

·1300 - 691.G09 B.T.Us.

250822%

109250.5%

271915.3%

881o 47%

02942.9.4%

65842%

Available heat with-out preheating 2942 2719 2508 2300

.Extra heat gained' 'by preheating 276 415 553 691

-- --Total , . . , 3218 3134 3061 2991

So that B.T.Us to exhaust after preheating air 'upto 480° F would be:-.

658 - 276= 382

,1092- 553,= 539

exces,s air eva?_~rates rOi:~hly 2.23 to s. per PJ. of

fuel so a boiler requires 2.23 .Ths. ~1iel per square foot= 1.12 tos. bagasse. ' --

An 8 ft. x 16 ft, boiler has' a 'heating surface of2144 square foot, so it' will require:-

. . .

2144 x 1.12,ibs. .bagasse per hour ~ 24-01 .lbs.

The grate area is usual 1/100 of the heating sur­fac.e=21.44 sq. ft. So the grate will burn:-

2401 lb s. per hour per square foot.

.21.44: = 112, tos.

The gases. go along _the bottom and sides and outthe tubes' and the' 8 ft. x-16 ft. h6it"er'hai 118 tubes4 in. bore giving a total area through the tubes of10.29 square feet, so the exhaust gases leaving the

-boiler at 6000 F will have a velocity :6f:~

Appendix No.3.

27

184.5 x 2401feet per second.

10.29 x 60 x 60

=. Toughly 12 ft. per second.

Deerr says exhaust gases going to the chimney,the velocity allowed is 20 to 30 feet per second.

If the gases at 19000 are taken going through thetubes the velocity would be roughly 27 ft. per second.

In working out the area of thefl.ues, these shouldbe slightly more, than .the area of-the tubes after thefurnace and slightly less than the tubes after theboiler,

It is u~u~l't~ allo,,~;' 10 square inches fQrevery 12square foot of boiler heatingsudac-e-.before theboiler' and 6 square inches after the boiler; Thiswouldigive 12.4 square ft. and 7.4 square ft·. r,espec­tivelyfor the 8' ft. x 16 'ft. boiler and comparing with10.29 square Ieet through the tubes.

Ill.lMIM:MI\YllMJM[\...v)IMllV)I!.Ql!MID~IMIMIMlMIMl.Q.lIl.Q.lI!Y1IMIl.Q.lIMI!P.~.IIMJIQ1IMlJMlMIMIMIMIMIMIWA!-I':I ~I .. .. ... _. ... .'. --- ...'. Ii '~\I Typical Drawings and Settings of Furnaces from Various, Parts otlheWorid. i

I. . .. - - .

11 .~ ..~ti~_n&::=::;:::=~=:='M;mimrn~n~L- ,

=To..>..>.>~t-- - •. - '.-', - - - - - - - - -

I

%ON' 8 - "7'8'"• 0 - VOLsm' Mort,s

'I.. C - CRAftON;)

Q'" 'gNITR/ettQ' PAGM"

.. - [ltBG88M87"!C

Bf/GB~§£ FURI'IBC£. Fig. 1

28

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,

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o:(·)@O ~.." lD'". _.L_I__.i.. ~

-- _.J: ("::='J

Fig 1. .

Fig. 3. '", .' "...............

//. '/ '. ' '//// '/

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~/

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'r;;j.J .r/'-'/////7///.'//7/ //// '// / //77/

u .U'"'

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1111~.

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II;'" ", : ' ", ~ ~

~:I, ',II .J

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"ul

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.111,

,'" I II" ~-

~'ig, 2.

._-- ... _.__._-_. _.-'2' q.' ,,'

~I,1 '".1

NATAL.

'~ .r.:::::::t

t\ :~~~'S'\.-,"'~.

~ lQ] ~"'~~"''''"""" ..-.._..-

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~

~

0..'

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<,: """"",' "",,'c-: ''\.)..~----- - :-...."''''""-_.:._--

_.. ~--_._.__ ..- -.-

~-.

(g) ~ []. .. -- ------- . ----

... ...

~ ~//,/..... " ....... "",.~v:

~'. .. " ~

~ ~

-'660 g'H.5 N8rRL

Fig,5,

4I

csI

29

r T-' • TT~-:l' 'I II I II I:: :: :L _L •• • • I-I",.J ;

I" .' .'~',',III

Fig. 7,

~ C I 1

r\

IJ

-

• Fig, 6,,lAva PHRE'9recc0C'e

';0'0 a' H s.

Fig. 8.

4 .:, I

30

a'I

Fig. 10.

..~, I 16'"a',.--

~~l .. L. -. - -. --

a fI, WAQtLI!R

.1764 Q' MrS.

~I

-----1-+-­I II L 4

I !. _, ,I II I

L.,.....;.-'-----,:-L-- - t- I---__--Lll./I...-:--------I ,l. ._1

Fig. 9.

II I _

-~ ~.:~Jr;t~~:~~~;:-::!::~-=--::-:-Y :b==========1 L ..J !.: ~-n t-4

. ~-.'

Fig. 11.

31

"DISCUSSION ON TYPES AND DESIGNS OF BAGASSE FURNACES.

I

The Chairman in thanking Mr. Murray, stated thatthey were all very grateful to' Mr. Murray and thecommittee Of the Technologists' Association f01' pro­ducing such an able paper. It was one 'which sho111dbe of great value to the various milling staffs. ..' .

Mr. Dodds asked if Mr. Murray had any informa­tion regarding the composition of the typical fluegases in sugar factories in Natal. It would be veryinteresting information to have.

Mr. J. Murray replied that he regretted they werenot 'supplied with any of these figures. A few ofthe factories had given . some information but notin that connection.

Mr. Townsend stated that although he was a sugarplanter at present he had also had some experiencein mill work and no doubt Mr. Mnrray would re­collect the conditions under which the old boilerswere set, with the boiler overhanging the centre ofthe grate area and a 9 inch space running round theboiler up to about two-thirds of the boiler heightinto tubes and up the chimney.. In those days themills suffered under greater disabilities than to-dayon account of fuel because they had to dry all the fuelbefore they COUld use it. When he took over theSea Cow. Lake Estate the first thing he did was to'purchase an up-to-date boiler-very much largerthan was considered necessary for the mill require­ments at that time, and he also put in what was con­sidered to be an np-to-date furnace. The furnacewas a step grate and there was a distance of 20feet from the grate to the face of the boiler. Fromthere there was a 4 ft. flue and there "vas a wall be­tween the front grate and the cavity under the .boiler. This wall ran up to within a foot of theboiler- which allowed the gases to run over thechamber under, the boiler. All the gases which werepassed into the grate came under. and had to passthrough a set of tubes which caused the air' tobe heated from- the exhaust gases from the boiler. 'I'hegrate area was about' 5 ft. by 9 ft., and the feed wasfrom an opening at the top where the fuel wasdropped in small quantities almost continuously. Thesaving in fuel on that was enormous. The evapora­tors were not up-to-date, however, they had openevaporators, and that meant an enormous amount ofwaste steam. With the new conditions the boilersupplied more steam than was required and it wasnecessary to hold back the fire, with the result thatthe accumulation of fuel was enormous. The condi­tions with that boiler· had' proved to him that thedesign was not far off efficiency. The chimney wasabout 70 feet high and it was hardly possible to tellfrom the chimney whether the mill was working ornot as there was simply a vapour, which to his mindproved that the conbustion was complete. Whenthe tubes were cleaned out there would not be morethan a quarter of a bucketful of dirt and there was

practically no deposit in the tubes.. They had toburn trash' occasionally and had to water it to obtainefficient combustion: He would like to know if Mr.Murray had seen this particular class of boiler andwhy it had gone out of date. It was adopted in the'early days andgave very efficient work. It seemedto him that at the present time a large number ofmillswere working with very inefficient boilers. 1£he saw a chimney 'belching forth black smoke hewould put it down to inefficient boiler installation.The grate area was hadlycalculated or they werenot getting proper combustion: 0

Mr. J. Murray stated that the furnace described byMr. Townsend was a fairly good one,so far as he couldsee, as there was a space 0{20 feet from the firebarsto the underside of the boiler, and with the wall upto within a foot of the boiler surface it would' givea verv efficient combustion. The fact of the smokeissuing from a chimney being white did not neces­sarily mean that there was efficient combustion. Withregard to the use of trash, this being a carbon fuelwith a short flame it could be burnt under the boiler.The poorer the fuel the longer the flame. By addingwetter to the trash it made the flame longer. So' faras he could see Mr. Townsend had struck somethinggood.

Mr. Pullar in referring to what was termed anideal furnace illustrated on page 1 of the paper,stated he would like Mr. Murray to explain what thevolatiles were that were distilled off the bagasse inzone B. This particular type was shown as one ofthe most efficient. If he might venture to say so hethough the efficiency depended on the method ofburning the bagasse. He had had the opportunity ofwatching this matter very closely, especially duringthe last season, and one thing which was very obviouswas that the fluctuations in steam nressures in asugar factory were due as much as anything else toirregular feed of bagasse and irregular boiler feed.The irregular boiler feed could be looked after withapparatus designed .£01' the purpose, and even' byhand if reasonable care was exercised, but the regu­lation of the feeding of bagasse has not yet been

. satisfactorily arrived' at to his mind. On looking atthe diagram it was seen that the bagasse was droppedin to zone "A" where it lost some of its moistureby the radiation from the arch, then it gravitated tozone" B" where the volatiles were driven off, then itgravitated to zone '.'C" where the carbon was burntefficiently. To start off, where the carbon is burnt iswhere they need the air. If they had a furnace ofthat design in his opinion the man who could get thebagasse to flow as described was an artist. In hisopinion it did not flow in that manner. It banked up'in another way' and the heat was under -the hopper,and then suddenly it would slither down and, thedamp bagasse damped the fire. It a meter was in­stalled the variations could -be seen as the bagasse

was fed in, Tha't had' been observed in more thanone place. , 'I'he first thing to do, ~as to design abetter way of feeding the bagasse. If they droppedwet baaasse through a hopper on to a heap. of ~aga~sein' a grate they were continually smothering It Withthe wet bagasse. He would like to know if Mr.Murray could tell them of any design of furnace org'rate that had been designed to g~v~ a feed of drybagasse in proper process without giving those fluctu-ations.

Mr. J. Murray replied that the modern method ofcrushing with shredders and double c~ushers andfinely dividing the bagasse UP was solvmg the pro­blem' enormously. Formerly when they had a jam inthe mill it was found to interfere with ,thequality of the bagasse, but with the moreefficient machinery to-day the product was verymuch better and easier to deal with. He could notsay that he had noticed that particular point Mr.Pullar mentioned, but he thought some of the factor­ies, here 'were p:etttin!! on very well in that respect.,However. he admitted' it was a very difficult problem,pnd the drawing submitted had only been shown toillustrate what thev thought was the best method.If they had a flat grate it was naturally worse.That was why he considered the step grate wasthe best. It. was not. however, imnossible to designsomething provided they could get the product fineenough to deal with conveniently. He thought theyhad just as much brains in this eountry as in Cuba.With regard to volatiles he was not a chemist andno doubt Mr. de FroberviJle would' be able to answerths t rmestion better. '

Mr. Pullar referred to the question of nre-heatersand asked if it W;:lS possible to obtain any availabledat~' regarding the-increased efficiency actuallyohtl'li~lr!'l, 'I'h« fizures g:iven in the panel' were moreor less theoretical and they had yet to learn that thebagasse was being weighed in connection with theseinstruments as against the steam measured from theboiler. 'I'hose.figures should be of some value other­wise thev were still on the theoretical side. Therewas another point he wished to mention. Claimswere made for pre-heaters but some claims werealso made for economizers. He took it that theclaims for the pre-heaters were discounted by theclaims for the economizers. They could not have itboth ways, and he thought that was covered by theremark that a combination of the two was Fldvis'Jble,There was also one thing which he thought hail not'been' clearly explained and that was under the, head­ing of "Furnace Air Supplv" the merits of thet.hree systems were not very clearly defined. Naturaldraught conditions were all right and there 'were cer­tain advantages in having the cold' air blowing inbelow the grates as balanced draught. There wasno mention made, however, of induced draught whichwas a very important thing indeed. Any gains that.were made by installing pre-heaters must embodybalanced draught, so that some of the gains the pre­heaters claimed to give could be obtained withoutpre-heating. The figures given were difficult to fol­low and rather misleading, unless it was very clearlydefined how much of the' gain was due to balanced

draught and how much to pre-heating of ai~. Oneadvantage was that excess air was cut down and ifthat was done they had less air to' absorb heat froma pre-heater. It was not such a very big figureafter all according to reports from various parts ofthe world. It was common practice nowadays to in­stal nre-heaters. The sugar estate 'was not lookingfor the l-st 5% efficiency in burning bagasse. The

, cost of air pre-heating must be very high. The costof economizers was less. With an economizer therewas a great advantage which was not mentioned inthe naper, and that was practically increased' boilersurface. It was always equivalent to a boiler of thesame square feet heating surface, and under varyingsteam conditions, there was a system of thermal stor­age which was a very great advantage in a factory.He had considered another factor in increasing theefficiency of boilers and the method of firing'. Experi­ments had been made by withdrawing a small proper­tion (15 to 20%) of the gases of combustion from thecombustion chamber and returning that nroportionunder the furnace by means of a fan and adding to it,before it was put under the bagasse, sufficient air tosupport combustion. 'The result had been that thevcould reduce still further the surplus air required fo~combustion, They obtained a portion of the benefitfrom a pre-heater and they obtained all the advant­ages of balanced draught 'by taking the air throughthe fuel bed. That was a development which costvery little as compared with the pre-heater. Itwould be very interesting' if they could obtain fromMr. Murray the actual gain per cent by using pre­heated air so that comparison could be made. Itwas not altogether a new system as delayed combus­tion was used in a number of industries; the differ­ence being that he took a small proportion of veryhot gases.

Mr. J. Murray in referring to the question of pre­heaters. He was interested' to hear that Mr. Pullarin in Natal but it was onlv one boiler and he under­stood they could' not get aiw correct figures. So faras he knew there was one firm only who made pre­heaters. He was interested to hear that Mr. PUnaI'had come into the field as competition would makethings cheaper. He had heard about Mr. Pullar'sscheme but understood that it was in the develop­ment stage and it was not desirable to mention itat present otherwise the sub-committee would havebeen onlv to pleased to have included it in the re­port. If they looked at the appendix NO.2 attachedto the paper they would' find it went thoroughly intothe question from a theoretical point of view, andthere was no doubt that there was very 'great valuein pre-heating air.

Mr. Pullar stated he wished to correct Mr. Murravwith regard to the manufacture of pre-heaters. Heknew of at least five, probably six manufacturers.But there was only one pre-heater claiming such anenormously high efficiency as the one Mr. Murrayhad in mind.

Mr. ,J. Murray stated that with regard to economiz­ers very few factories had them. The trouble was thatif they had dirty water they scaled up ranidly and thesoot was rather troublesome to take off.If they had a

33

fairly good water and the people .ooking after the that it was probably one of the most importantplant kept it clean no doubt it was an' excellent things in a sugar factory, he was surprised that ap­thing, He did not remember 'seeing one in Cuba or parently no experiments had been made with a viewHawaii when he was there last, He had been read- to finding a grate which would evaporate the great­ing some papers from America and at some of the est quantity of water with a given quantity of fuel.superpower stations they were getting as high as He considered that in the interests of the Industry92% efficiency without the aid of pre-heaters, He that should be done. .thought one was as good as the other. Probably a Mr. Murray replied that the engineers had theirjudicious use of the two would be the best. o"':n ideas. The object of the paper was to give

Mr. Pullar stated the question of pre-heaters pos- fairly well the volume and areas right through thesibly was considered quite separately in a sugar boilers. In some cases the boiler might have beenfactory. In a big power plant they were used be- designed right but they had not the cross section orcause they could not use the economizer to the same volume in the grate to carry the gases and he thoughtextent as in the past because they had to take some the information given in the paper ought to help inof the steam from the turbine to heat the feed water. that direction. He had no doubt that in time toThe most efficient power station in the world, in come the Technologists' Association which h~d just.America, was equipped half with pre-heaters and been formed would do a lot of good in connectionhalf without, and he believed that the efficiency of with these matters.nre-heaters was considerable and they had decided Mr. Pullar stated that he considered if the Tech­to instal them right through. He understood the nologists ' Association was to be of real value to theimprovement in efficiency was within 5%. Five per Industry there should be some means of recordingcent on a big power station in the coal bill was quite ideas and co-ordinating views on these matters. Hea big thing. At Colenso they were using Babcock had spent a lot of time and it seem to him that thepre-heaters and had no economizers. At the new industry benefitted more than he could possiblyJ:>owerstation to be erected at Durban, Babcocks benefit, and unless some co-ordination took placewere to be fitted. The use of pre-heaters in sugar actively they would never get down to the bottom offactories was more valuable in connection with the things. This was one of the most important things.wet fuel. Bearing on-this he asked Mr. Murray if he could tell

Mr. Townsend stated that he took it Mr. Murray them what ideas he had of the bagasse furnace of thewas fairly well acquainted with the types of furnaces future when they would probably have big steamin Natal, how many types there were in existence generating units to deal with. They would thenand how many were efficient. He wished to know if have problems of handling a bigger volume of fuelthe type described on the first page of the paper and it would no doubt limit the size of boiler to bewas in use at all.. installed. Without knowledge of what size boiier to

Mr. J. Murray replied that that was simply a dia· instal they would not be able to get ahead with thegram and was not an actual type of furnace in use in electrification of mills. So that without co-ordina­Natal, but if they would look at page 5 of the typical tion he did not think they would get very far. Coaldrawings and settings of furnaces they would see one fire boilers had been developed considerably butwhich he knew worked excellently. In that they there were certain difficulties which had not yet beenhad the effects they had just been speaking about. overcome and he thought they would be faced with'I'hey had the various zones and the chambers for the the same difficulties in the burning of bagasse.expansion of the gases. He believed there were 25 Mr. Murray refered to the designs of some of thefactories in Natal and Zululand and he felt sure plants now in use where the boilers were about 15there must be 25 different types of furnaces. He feet in the air which gave plenty of room underneaththought the ones put down in Natal were fairly good. to work. In America in some of the large plantsThere was, however, orie bad one shown in illustra- there were something like 40 feet above. So far astion No. 10. Some of the others might be modified bagasse was concerned he did not think they wouldto the diagram they recommended. have much difficulty with it.

Mr. Townsend stated that he took it all these types Mr. de Froberville in referring to Mr. Puliar'swere more or less in the experimental stage; there question with regard to volatiles, stated that he hadwas not one which could be laid down as an abso- not gone very deeply into the subject. He couldIutely efficient type 0 Efurnace. only mention the gases that were produced by the

Mr. Murray replied that he thought No.5 would combustion. He could not give exact particularstake a lot of beating. as he had not considered the matter sufficiently.

Mr. Wickes in referring to the questionnaire which Mr. Townsend referred to the efficiency of boilershvd been sent round asked how many estates knew and asked-if it was not possible for experiments to bewhat their figures were. to which Mr. Murray replied made to obtain an efficient boiler. At present therethat so far as he could remember there were about was an enormous loss in the boilers and he wonderedsix. Some of the answers received they thought. if by increasing the size or reducing the number ofindicated better results than the average for those boilers it would not tend to more efficient workingparticular f..<tctories. and economy in fuel.

Mr. Townsend stated that in view of the fact that Mr. Murray in reply stated that with the multi-there were at least fifteen different types of furnaces tubular boiler if it was made more than 7 ft. 6 ins.

• present under operation, and in view of the fact it would have to be made of thicker plates" and

34

if that was done the heat would not go through itquickly. With a smaller boiler the plate was thinner.The thickness of the plate and the diameter affectedthe heating efficiency of the boiler. With regard tothe length of the boiler, the length of tube availablegoverned that and 20 feet was the limit so far as heknew. So far as water tube boilers were concernedhe did not know what the limit was but they werevery large. One water tube boiler may equal tenmultitubular boilers.

Mr. Pullar mentioned' that in Germany they werefaced with a difficult combustion question through us­ing lignite coal, etc., and he had seen designs offurnaces where the fuel was fed in through a hopperand before it got On the step grate the fuel had aportion of the actual product of combustion with­drawn from the furnace. By so doing it saved' thetrouble of evaporating the water and, raising it to

the temperature of the furnace, gases .and fluegases. He would like to see that tried with bagasseexperimentally; That would probably be a simplemethod of increasing output and efficienecy.

Mr. J. Murray stated that if they would look at thediagram number 4 they would see that at the top ofthe step grate there was a chamber with a fire barin it. That could be used either with the gases fromthe chimney or coal or wood or anything else. Thatparticular furnace was to dry the bagasse at the 'top of the step grate.

Mr. Pullar pointed out that there was no with­drawing of the vapour or gases.

The Chairman in thanking Mr. Pullar and Mr.Murray remarked on the very good work whichthe Sugar Technologists' Association had alreadydone, and hoped that they would continue the goodwork. (Applause).

THE, USE OF BAGASSE" AS A RAW MATERIALFOR IWANUFACTURED GOODS~

By A. T,. SCURR.

The 'war of 1914-18 stimulated research into theutilisation of by-products or waste of industries, andindeed, waste of any kind to previously unknownlengths, particularly on the part of the Central Euro­pean Powers, who were at times hard pressed for,feeding stuffs for their animals, as well as rawmaterials for their munitions of war. The Alliesthemselves, though not having to find substitutes fortheir usual feedin g-stuffs had to utilise materialsother than those previously used for some of the pro­cluctsneeded for the carrying on of'warfare, as in­stance the use of horse-chestnuts for the productionof alcohol. Since that time economic conditions havedemanded, that industry make use to the fullest ex­tent of any possible' economies, and the exploitationof its waste material.

This note, then is merely to put forward, the pos­sible uses of one of the waste materials of the canesugar industry, i.e., Bagasse: They are not all newand some, like the manufacture of paper from thismaterial was suggested many years ago. Confiningourselves to Natal and Zululand all the bagasse is atpresent used as fuel for steam generation and' assuch has a low-monetary value. The preparation ormanufacture from it of a' fertiliser-an artificial oreynthetio manure, paper, and latterly' "celotex"products seem 'to be the best uses to which bagassecould be put, though to a limited extent it may andhas been used in a ration for feeding stock 'and alsoin the composition of magnesium chloride cementsfor floorings, its incorporation in these latter makingthem more resilient. '

The conversion of bagasse, or indeed almost anyvegetable matter of a similar nature, into an organicnitrogenous fertiliser is accomplished by its fermen­tation in heans in contact with an insoluble or diffi­culty soluble;' but hydrolisable compound of nitro­gen, whereby new insoluble organic compounds ofnitrogen are formed, by the action of the organismsin the fermented mass. The finished manure is adamp soft mass which is comparable in nitrogen fer­tilisingproperties with well matured farmyardmanure and which it resembles in appearance. Itcannot be said, however, that the bagasse will makeas good a manure by this method as -cane trash. forinstance, owing to its more woody nature. '

The most promising uses 'of bagasse, however, areon lines where its fibrous nature is utilised, namely,as a raw material for the manufacture of paper orstraw-board and similar materials. Unfortunatelyit does not seem an easy matter to treat bagassesatisfactorily for paper making as owing to the dis­tribution of the fibres in the cane they are not allof equal strength when the cane is ripe for cuttingand so they respond differently to the chemical treat­ment necessary for their conversion into paper. Thefibres in the outer part of the cane, are of goodstrength and firm, while those inside are weak, andas they, all must receive the same treatment, eithersuch treatment must be severe enough to reduce theouter fibres completely and this will destroy the

, inner fibres with consequent reduction of yield, or itmust be more gentle, a proceeding which will resultin no loss of fibre, but which will only partially re-: