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Title A Theory on the Mechanism of an Outbreak of Spontaneous Combustion of Coal I

Author(s) Hashimoto, Kiyoshi

Citation Memoirs of the Faculty of Engineering, Hokkaido University = 北海道大学工学部紀要, 11(3): 249-268

Issue Date 1962-03

Doc URL http://hdl.handle.net/2115/37828

Type bulletin (article)

Additional Information There are other files related to this item in HUSCAP. Check the above URL.

File Information 11(3)_249-268.pdf

Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP

A Theory on the Meehanism of an Outbreak of

Spontaneous Combustion of Coal I

Kiyoshi HAsHIMOTO

Contents

I. Preface ......:....................... 249 II. Low-Temperature Oxldation Tests .....,.'. ......... 250 (1) Experimental Apparatus and Procedure . . . . . . . . , . . . 250

<2) The Coal Samples ...................,., 251 (3) Experimental Procedure.................... 251 (4) Results of the Experiment.........,......,.. 252 III. The Induction of a Theory of Occurrence of Spontaneous Combustion

of Coal... .,.....,...............,.. 253 (1) Curves of Perfect Dissipation of Heat ............, 253 (2) Curves of Perfect Accumulation of Heat . . . . . . . . . . , . 254

(3)TheInitialOxidationRate([:tl)OandValuesofk......257 '

(4) The Establishment of a Theory of the Outbreak of Spontaneous

Combustion of Coal......,....,.......... 258 IV. The Expansion of the Theory to the 9uantities not used in Experiment 263

(1) Expansion to the Larger Particles ....,.......... 263 (2) Expansion to Low-Temperature ...........,..,, 264 V. Application to Underground Conditions . . . . . . . . . . . . . . . 265

VI. Conclusion .......................,..,.267 Bibliography .......................,.... 268

L Preface

There have been few published reports which treat quantitively the phe-

nomenon of generation of heat in oxidation in the early period of spontaneous

combustion, though many experiments and studies concerning it have been

undertaken hitherto. Insofar as the present writer knows, only G. S. Scott')

discussed it in his paper. ･ In this paper, it is proposed to give quantitative evidence of the phenomenon

of generation of heat in oxidadon in the early period based on experiments on

oxidation under constant low-temperature of coal from the Mitsubishi Oyubari

co}liery in Hokkaido, the results of which have suggested a theory on the out-

break of spontaneous combustion of coal. In other words, a theory has been

formulated concerning its outbreak based upon the results of laboratory ex-

penments.

250 Kiyoshi HAsHIMoTO

The error of oxidating test on coal materials is very great at low-temperature

in the use of rough panicles which are the true conditions in coal mines. The

writer expands his experimental results with his theory, so that he is able

quantitatively to measure the conditions. Consequently this theory is believed

to be applicable to other kinds of coal from other mines through similar

experlments.

II. Low.Temperature Oxidat,ion Tests

Up to this time the oxidation rate and the relationship between the gases

produced by oxidation and its temperature at various temperatures have been

obtained by experiments on low-temperature oxidation, so as to get some solution

of the problem of spontaneous combustion of coal. The results of a number of similar studies on the subje6t have been pub-

lished; isome of them are as fol!ows: Parr and Miiner2), Parr and Hobart3),

Tideswell and Wheeler`), Winmill5)6)7)8) and Graham9), etc.

In the present experiments the apparatuses are basically the same as those

of above mentioned investigators. The consequent oxidation rate is utilized to

design the general formula of the heat generation.

(1)' Experimental Apparatus and Procedure

The appar4tus. for determining the rate of oxidation coal is shown in

Figure 1.

First the quantity .of dried air is measured, and then it is dried up through

drying agent and soda lime. Carbon dioxide (CO,) is drawn off from dried

"Soda lime

1

-

.1tt--

Drying agent

Air ventilator

,

.t l' '

.n

ca

8.gT"k

'..-' ".F"

Soda DryingIine agent

Electric furnace1oo Velt tathermogtat Illiil]

Fig. 1. Low-temperature oxidation

)ryingagent

Temperatum recorder

apparatus

Flevmeter

:

A Theory on the Mechanism of an Outbfeak of Spontaneous Combustion of Coal I 251

air and then the dried air minus CO, is Ied'into the coal to be tested within

the glass tube in the furnace.

The oxidized gases are taken with sampling tubes at random intervals.

The eMuent gases which have completed oxidation are sucked into ventilator

through the air pipe. The volume, temperature and pressure of the residual

gas in the ventilator bottle were measured, and the gas was analyzed.

When necessary, the ecauent gases are led through drying agent and soda

Iime, the resulting out water and the C02 of eMuent gases are measured.

The air ventilator is so prepared as to admit a certain amount of air con-

stantly and to enable exact measurement of the gas.

(2) The Coal Samples

The samples used for the test, were from Oyubari colliery. After they

were taken in the pit, the samples were put into contalners filled with methane

gas as soon as possible. After some of the samples were crushed into needed

size, they were kept cool in air-tight glass vessel, and the experiment was carried

out as, soon as possible.

The sizes of the particles were 20--28 rnesh, 28-35 mesh, 35-48 mesh, 48-

65 mesh, 65-100 mesh and under 100 mesh. When the air current wentthrough the coal under 100 mesh, the finely crushed coal was unstal]le and

accurate results could not be expected. When the particles were big, the

experimental error was big, although the amount of the air current was decreased.

Consequently most of the present experiments were carried out with particles

between 20 mesh and 100 mesh in size.

(3) Experimental Procedure

One hundred grams of the dried sample was carefully put into a g}ass pipe,

which was inserted into the electric furnace.

To get a high degree of correctness of the result of the oxidation of the

coal in an air under a certain temperature, the following methods were adopted.

i) The air pipe containing a certain size of the particles was prepared

so that constant temperature could be mantained; through it the air

at required velocity was passed by means of the ventilator.

ii) Care was taken to gather the eMuent gases without changing the

velocity of the current.

iii) The gas analysis was carried out by means of the Orsats method.

The concentration of 02, CO, and CO was measured. Then the volume of 02 consumed in a given time, and the produced C02, CO

and H20 were measured.

252 ･ KiyoshiHAsmMoTo iv) The quantity of 02 absorbed into the coal was measured under natural

temperature and pressure of OOC and 760 mm after its oxidation rate

had been estimated was corrected by the concentration of 02 and N2

derived from the analysis. The average quantity of 02 could be

decided by calculation based upon the relation between the oxidation

rate per hour and the time.

First the average quantity of al)sorbed O, was obtained by replacing the

air in the air ventilator bottle with water and analyzing the gas. In this pro-

cedure, however, the experiment was interrupted and was complicated by the

double gas analysis. To avoid this complication, the above mentioned methods

were adopted, which have led to more correct results.

(4) Results of the Experiment tt An example of the result of the experiment is shown in Figure 2･

2oo ts g2n ggs Ck lv ta

ooo ` $:1.R'. 150"

:g2 . ;= " [k . :a o oec - u ee R

Ea･:ioo '･ ssb. ot .-E] 8 ts :

ti E2 .', L-H e 22soe ' "' Rtsfi so

Zg.o. . , IOoec ' z･g:･

, 75oe 50oc

Io 2o so'40 50 60 7o 80 9o loo no DXJDATJONTI:{EFRO:･ISTART,llOIMS ･

Fig. Z. Oxidation of Oyubari coal, size 20--28 mesh;

temperature, 1500C, 1250C, 1000C. 75DC, 5oOC

. In the early period of the experiment, particular}y at the high temperatures

of 1500C, 1250C etc., the temperature of the coal was apt to rise because of

rapid 02 absorption, but the heat was wholly dissipated by the air and through

the glass pipe. An experiment of oxidation under a constant temperature is

a method to get curves of the decreasing oxidation rate when the heat liberated

by oxidization is wholly dissipated.

Figure 3 shows the relationship among the quantity of the absorbed oxygen,

the oxidation rate and the temperature, attributed to the relationship shown

above. (Fig. 2)

A Theory on the Mechanism of an Outbreak of Spontaneous Combustion ofCoalI 253

ge

di

g:gHx

o

ccAr.1oog

2oo

1oo

50

20

10

5

2

ee

e

15oec

.

e l25ec

e

e

e 20ooc

'

e

2See

e

Soeo

o 5oo IOOO 15oo 1800

Fig.

oxyGEN coNsuMED (21ge, cuB!c cE)ny[rlMETERs

(N. T. P. ) PER 1oo GRAMS OF COAL

3. 0xidation of Oyubari coal, size 20-28 mesh;

temperature, 1500C, 1250C, 1000C, 75eC, 500C

IIL The Induction of a Theory of Occurrence of Spontaneous Combustion of Coal

(1) Curves of Perfeet Dissipatiom of Heat

The relationship between the oxidation rate and the quantity of the absorbed

oxygen-the curves of perfect dissipation of heat-obtained through the experi-

ment of oxidation of coal under constant low-temperature is shown by the

following general formula.

d`leS2 =f( `dMo )Oe""O (1)

where CIQ:oxidationrate de

(ddoP)e:initialoxidationrate '' '

254 Kiyoshi HAsmMoTo '

k : exponential constant

f : size factor 9 : the quantity of previously consumed oxygen

(2) Curves of Perfect Aecumulation of Heat

The subject of this section is the change of oxidation rate when the heat

!iberated is perfectly accumulated. It is necessary for one to know how many

calories are produced when the coal absorbs 1 cc of oxygen and to know the

specificheatofthecoal. ' The direct determination of the heat liberated by low-temperature oxidation

has been made by Lamplough and HiiliO), who found a mean value of 3.3calories per cubic centimeter of oxygen consumed for a minus 30 mesh coal

at normal temperatures, and by Scott'), who found 4.7 calories for fresh an-

thracite･ The latter's method was adopted for this study. Consequently for

the theoretical basis one should refer to his paper. For the mean specific heat

cc!hr.IOOg

2oo

1oo

so

g E m 20 OH ts g R o 10

5

2 142 284 4265oo568 710 1000 OXYGENCONSVMED CC

Fig. 4. 0xidation rate vs. quantity of oxygen

consumed; size 20-28 mesh

'llIllllllddn4･!sKe'eJIPoae7a

;

15ooc

1 '

1

q ,. l ,

ll 7 I 125ec

sl : ,

, l l

it

, : l

lltlil11'-?fkoelo,oooR"ti,

27e"qo4-dE

20oeo

'

1 '

tl ,

7s.oo

' , ,

t 1 l 1

ISo. :l :

lO,l 4ais1 ,-d.

e,lITtl

TABLE 1. Heat liberated in

of Oyubari coal

]ow-temperature oxidation

Sample No.

1

Lowerseam

s)

tt

ll

20-28

28-35

20-･28

35--48

Tempera- ture ofoxidation eC

150

150

150

150

'rimefromstart

hr

70

100

50

75

Coal

1oo ×cal!g

812,900

807,700

812.900

803,400

Residue

Weight g

101.840

103.820

101.645

104.305

cal!g

7,739

7,405

7,792

7,345

Calories

788,101

768,789

792,O17

766,120

H,Or

Weight g

3.751

4.857

3.603

4.213

Calories

2,187

2,832

2,100

2,456

coWeight g

O.18

O.37

O.125

O.45

Calories

435

894

302

1,087

Calories

22,177

37,I85

18 481 )

29,984

Oxygen con-sumed cc

5,258

8 253 '

4,263

7,770

Mean value

Upperseam

)l

ll

el

20-28

28-35

35-48

20-28

150

150

150

150

120

71

48

70

787,OOO

788,200

792,800

787,OOO

102.113

103.578

103.028

102.127

7,376

7,335

7,464

7,529

753,185

759,744

769,OOO

768,914

4.805

5.126

2.413

2.932

2,801

2,603

1,407

1,709

O.275

O.50

O.30

O.18

664

1,208

725

435

30,350

24p645

21,668

16,942

8 400 '

6,773

6,240

4,550

Mean value

call02 cc

4.2

4.6

4.3

4.3

4.4

3.6

3.6

3.5

3.7

3.6

>H=ooHtc

oprtig-

Kg:i"

:.

H

gg

9-..

.8x

fl

mvop"pt:oo:m

Ooscr=R5i:oH-,

oopt

-Hbooren

256 Kiyoshi HAsHIMOTO

of the coal, O.25 cal was used.

Table 1 was compiled by making use of Scott's method.

The calories of Oyubari coal emitted when 1 cc of oxygen is absorbed in

low-temperature oxidation were found to have a mean value of 4.4 cal!cc.

When 100 grams of the coal is taken,

x×4A =1 O.25 × IOO

x == 5.7 cc!OC. coal 100g

In every absorption of 5.7 cc of oxygen, the temperature for 100 grams

coal rises by 10C. Consequently in every absorption of 142 cc of oxygen, the

increase is 250C. Therefore in Figure 4 when one draws a line passing the

crossing of the lines of every 142 cc and the curves of the perfect dissipation

of heat of every 250C, one can get the curves of the perfect accumulation of

heat, the changing curve of the rising heat and the oxidation rate in the curves.

2oo

1oo

ts ts :

tsgg sog, :s.

Bil - ou

REts 2ogeAEo al ee

t!]' its

E. eoE･g logS:HPHts gg

HMOggm 5AU es

: za pt

::2ft ts8

2

!

tt

qgopa

esxx

P 9o

O,02

O.Ol

O.oo5

O,oo2

O.oo1

O.OO05

O.O{X)2

O,OOO1

- di'

-l,e

7."

o 25

Fig. 5. Values

50 75 TEMPERIXrPVRE,

of k and ( [lltl

1oo 125

eC

)O; size 20-28 mesh

150

ts

eg

A Theory on the Mechanism of an Outbreak of Spontaneous Combustlon of Coal I 257

(3) The Initlal Oxidation Rate ( ddQb )O and Values of k

The initial oxidation rates at different temperatures are shown in Figure 5.

For comparison, the samples were brought to the same initial condition

with respect to the quantity of oxygen consumed and were as fresh as possible.

The related formula may be as foilows:

' (`,l,ISe2 )O=ce"t (2)where (ddee)O:initialoxidationrate

t : temperature OC

a :coeficient C :aconstant e:baseoftheNapierianlogarithms ,

For the 20-28 mesh Oyubari coal shown in Figure 5, the equation is

cclhr.loOg

5oo

2oo p th : g ioo

E

S 50

E 6s-.loo mesh 48o65

55-48 20

28-35

20-28 250 250 270 290 510 -1oo OOO vALUE

Fig. 6. Variatlon of initial oxidation rate with the

reciprocal of the absolute temperature

voous

riHUUOUoeeo..us

258 ･ KiyoshiHAsmMoTo

(C,llSe2 )O =2･5 e-"'02'9` (3)

Values of k plotted against temperature are aiso shown in Figure 5,

k=.e-O,02eSt-4,17 ' (4) Many investigators p!ot the logarithm of the rate against the reciprocal of

the absolute temperature in conformity with the theoretical equation of Arrhenius.

For the samples tested by the present author, the relationship over the range

shown agrees better with the above equation than with the Arrhenius equation.

The results are plotted in Figure 6; they agree with Porter-Ralston'si') and

Scott'si) conclusions.

(4) The Establishment of a Theory of the Outbreak of Spontaneous

Combustion of Coal When the logarithmic mean of initial oxidation rates ( dd9o )O and valges

eclhr.1oog

2oo

1500c

100

50

eaZR 2o:Rg

10

5

2

:lllII,'la17-H-isoe'q･ooo2s"2

'

1 ,

I )a1 d

1 , e･' ' 11 1

: : 1111 1

l : llItII{ dits")<,*oeh4Iopiq

IlltII11iXIlaooc

iP ts :, ,

't-R= '

,:

le-･:2creT"len,T:-eeLk?

1l

1 1

ed,

i2S'oo

V7o li--l :

l ,Soei,itvk,2l

l LO ilII `tt

Fig.

142 284 426500568 710 OXYCEN CON5emED

7. The theory of an outbreak of

combustion of coal, size 20-28

l.2sqc

.t

1OOO

cc

spontaneous

mesh

A Theory on the Mechanism of an Outhreak of Spontaneous Combustlon of Coal I 259

of k are obtained, Figure 4 transforms itself into Figure 7, and the theoretical

chart is established.

In Figure 7 the line PX is drawn parallel to the axis of abscissa from an

optional point 2 At P; 284 cc of oxygen is absorbed up to the given time,

the oxidation rate at the point is 11.8 cclhr. 100 g, and the temperature is 750C.

When the oxidation at P produces no rising of heat, one must draw a straight

line PR. When the heat is perfectly accumulated, the temperature rises and

the oxidation goes along the curve P9. In other words the reaction at an

optional point P is the oxidation and the heat generation progressing rightward

within 2PR.

As the progression of the rate of oxidation in XPR gradually diminishes

even when the temperature rises slightly, there is little danger of the onset of

spontaneous combustion of coal. In 2PLX) however, the oxidation rate rises

in accordance with rising of the temperature. Thus, the temperature rises slowiy

at first, but later on it rises so rapidly that spontaneous combustion results.

cclhr.lo(ig

5oo

2oo

1oo

Z 50Eg:8Hg 2o

10-

5

3･

,1

tIIafie=22oe'-o･ooo27Q,;llpltLltge2:is'

LL

' 1 1

,1 !

1. , 11 l

: II ,

: :4l: leNN Islaje

l

11 lsl

'

: :4£Ie 2oooe

Itsr:

l

lINNI'sEIJN 06e"o]'l･'IOO-SdlTt11

2soo'

,

Ft

t t IO )

l t) ,

I , sl :

:OolOIII

:

: llIi :

15oeo

125OC

142284'426soos6s710 1000 oxycENcoNswuED ceFig. 8. 0xidation rate vs. quantity of oxygen

consumed, size 35-48 mesh

260 ' KiyoshiHAsmMoTo cclhr.1oog

soo

2oo

1co

pe .N so lg

ft" ,o

5-

2･ ,25 '50 75 1co 125 150 TEMPERATURE, OC

, Fig. 9. Valties of k and ([9t )O; size 35-48 mesh

(It is desireable to mention cases in which supplies of heat are received from

other high-temperature coal,)

In Figures 8, 9 and 10 the theoretical charts are drawn on the results of

experiments with 35-48 mesh.

The general formula of the perfect heat accumulation curve is as follows:

dd9o =a( dde9 )OepD (s)

d9 : oxidation ratewhere do ( dcta9 )e: initial bxidation rate

cr : coeflicient about the initial temperature

P : coefficient

xSbC

o7

O.05

･O.02

O.Ol

O.Ocr5'

iO.O02

O.co1

'

,tfr..eNgo

x

e'O.co05

O.OO02

A Theory on the Mechanism of an Outbreak of Spontaneous Combustion of Coal I 261

ccAr.1oog

5oo

2oo 1500C

1oo

1250C

N 50 E it R. ioooc :t

g 2o

{･

10

,

5

5 142 2s4 426soo568 710 looo- OXYGENCONSUI(E) ca

Fig. 10. The theory of an outbreak of spontaneous combustion of coal, size 35-48 mesh

The relationship between the initial temperature and the' coefllcient cr in

the perfect heat aceumulation curve of the Oyubari lower coal is shown in

Figure 11. The numerical value of P is O.O04-O.O063.

Formula (5) is adaptable to change during oxidation at high temperature

over 750C. In the cases of lower temperature, one must depend upon the chart

calculation.

In the chart calculation, as is shown in Figure 12, the crossing point of

the ini£ial oxidation rate, which is the quantity of O, absorbed in the first onehour, and the perfect, heat accumulation curve is named A, and then the oxidation

rate at A is to be regarded as the subsequent oxidation rate; then the crossing

point of this oxidation rate, which is the quantity of O, absorbed in two hours,

and the perfect heat accumulation curve is named B, and then this oxidation

rate at B is regarded as the following oxidation rate; this is repeated again and

thus the oxidation rate and the time needed are calculated.

In Figure 12 the perfect heat accumulation curve was followed from the

I If{･(L' iI-'-'e7oeFe･ooode2

ttItlllil4`Xtlevel

7sce

lil'M,

l it s

･I ' ltt le t

t ,)"ajl :

l 1t

?2eNape.

: llll:

lttIi

lF?>LSs,:2...,l

g/eNOoe}o.?1

,

t s l

, Vl ,7so0

1 t il 1

t : tl ,

f 1Soo : :

l l

ll1

262 Kiyoshi HASHIMOTO

1.0

O.9

O.8

O.740

lv

o O.6g ,.,

g

O.4

O.5

O.2

O.l

o.oo 25 50 75 Xoo 125

INITIAL TEMPERATURE, OC

Fig. 11. Initial temperature vs. tke coecacient in the

perfect heat accumulation curves

150

'

case

ture

'

m.

IS

which750C.

the

In

initial oxidation rate

six hours of oxidation

is 20 cclhr･ico g and

, 1000C was reached.

the first tempera-

cclhr.1oog

100

Nz

Egg

50

40

30

20

1020 64 U6' 182 41.5 88,8 Z46

OXYCEN CONSUMI]D

225 cc

10ooc

7Soe.

Fig. IZ. An example of chart calculation

i

A Theory on the Mechanism of an Outbreak of Spontaneous Combustion ef Coal I 263

IV. The Expansion of the Theory to the Quantities not Used in Experiment

The above discussed theory can be expanded to cases in which no actual

experimental temperature and grain size were used.

(1) Expansion to the Larger Particles

Figure 13 shows a plot of the initial oxidation rates plotted against mean

particle diameter for 500C, 750C, 1000C, 1250C. and l500C.

From Figure 13 it is apparent that a definite reiationship exists between

particle size and initial oxidation rate. The reiationship is shown more

clear!y, if the logaritlmic averages of the rates for each size are plotted

against perticie size, as in Figure14. The relationship becomes much smoother

when the particle s!zes are bigger than 20-28 mesh (O.076cm). The curves

intersect at an angle of 450. This shows that in the low-temperature oxidation

cclhr.ioog

5oo

P 1ooEz9:fl 5Pgx:H,z

H

10

5P,1

150oc

125eC

1cogc

750C

50ee

N

8ai$igts.NEgk"di.s

Fig. 13.

O.05HEAN EIARTCLE DJAMETER,

Initial oxidation rates

em

of

O.Ol

coal

264 Kiyoshi HAsHIMOTO

cclhr.1cog

t. .ss.･-.-.

' ia･

xNmOH::gAfixft

].o

5

5 O.s O.2 O.1 O.05 o.o2 O.OI HEAN PARTICLE DIANETER, cm

Fig. 14. Logarithmic averages of initial oxidation rates

below 1500C, the initial oxidation rates are in direct proportion to the surface

area of the particles.

Thus, if 100 grams of fresh coal is taken for the basis of calculation, the

initial oxidation rate of 20-28 mesh coal is 40cc!hr at 1000C, and when the

diameter of particles is O.1 cm, it is 30 cclhr.

If the coeMcient of the partlcle size is L

f= 30 =o.75 L 40

When the diameter is O.2 cm, it is 15 cclhr.

15 f== 4o "=O-375

(2) Expansion to Low-Temperature In Figure 5, one can regard that the tnitial oxidation rate ( ddPo )O and value

L--h----.--.--.--1500c

r-1--T---1----

l'lt-----------------

125eCF--------------------

1ooOC

t::-----:----=:J.'rtt:::

75ec

b---------X---t/p-------y-----X

F-･---v-----2-/500c

lt-----･------pt

t/il/lt1

l.-i'--;-1-'-J.7

r------f-!-----f/---

L./'..-i/r--H-1-L-!---r---

F---/------V---E : " t t

L-----HH--1-.------IHf------7-!-----"-r(}------t/-----i/--1- 8-ut

.-Douoooveg.zaH8.'

"-e-A6ou wo

/Ei/--'IL-I-/t,Jiiii,-

'

A Theory on the Mechanism of an Outbreak of Spontaneous Combustion of Coal I 265

k are strictly functions of the temperature t. Consequently this theory can be

expanded to the low-temperature, the natural temperature, at which determinations

cannot be made experimentally.

When the size of particle is 20-28 mesh and the temperature is 250C at

the beginning the prefect dissipation curve is

( ad9e ) ==: se-o,oosg

When this equation is integrated, one obtalns

.eo･oosn---1 =so

O.O08

By substituting 142cc for 9 (see Figure 4) and solving for 0,

e= 2･114 -- s2.8 hr･

This shows it takes 52.8 hours for the al]ove mentioned coal to al)sorb

142cc of 02 for the first time. Moreover one can find the quantity of the '

absorbed oxygen in a given time assignlng a number instead of e.

V. Application to Underground Conditions

Figure 15 shows the relationship among the oxidation time, its rate, the

quantity of the absorbed oxygen, rate of temperature rise, etc., when the tempera-

ture of the early period is 250C, the diameter of panicles is 20-28 mesh, O.l cm

or O.2cm. Further, the conditions are altered in the perfect heat dissipation,

in the prefect heat accumulation or in case of keeping up the initial oxidation

rate.

TABLE 2. Relation among the oxidation time, the quantity of

oxygen consumed and the rise of temperature

Oxygen consumedEvery

Total

given volume

volume cc

142

142

142

284

142

426

142 l 142

568 710

Perfect heatdissipation

Temp. ec

Time hr 25

52.8

25

164.8

25

510

25 25

Initial oxidationrate maintained

Temp. oc

Time hr 45

28.4

58

28.4

65

28.4

70

28.4

74

28.4

Perfecth･eataccumulation

Temp.ecTimehr

50

28

75

20

100

9

125

4

150

1.5

266 Kiyoshi HAsHIMoTo These are the temperature and the diameter of particles found in the under-

ground condition, which is fully applicable to out-burst, fallen coal in gob or

crushed coal rib.

Table 2 explains approxirnately the same things as Figure 15. The table

shows the relation among the oxidation time, the quantity of oxygen consumed

and the rise of temperature, of the prefect heat dissipation, of the perfect heat

accumlation or of maintenance of the initial oxidation rate, when the tempera-

ture at the beginning is 250C, and the size of particles is 20-28 mesh.

INITIALTEMPETVLTURE250C .20-28meBh m-.sm"toO.letu .-stn-oprpO.2cm

,eelhr.1oog NUTosERS ILRE OXIDATION TXME

t'

:gta

9$ag

hinthk--la"--ehem"'im'laqm-"""--b.op..

eagge."tu.ig.heajts.eqts..--Nubh"'

tuhlj-...28

'V-----"inh--m-i-"-q.---m-ib--in.

ng

20..t`'b.'.6.-'if..-apt'

m.mu..in- ppta;

.t'75ec''"tulny-･-gsth75oc

50

20

10

52LOD.5

.--. 'in--laqh-alata-ny75OC,didi-.-h.-n."bytu.::kli-tstsop.4rk!

O.2

O.1

-wwewu--ww--in"............

2;r41ilT:';:"KO":hh""-.....,.e"-.k#--e--Wltam-fiee:-ww-="p-la-hme'tanyhnq.Nk----.e#...-e--...NxhN"N?64.etN...,<3&.e3tip'r?Nsx.NsN.NN×Ns×N×.SNtu"-mew-ew-l-mp

O 1co 142 2oo 2843oo , OXYGEN CONSUPED

Fig. 15. The theory of an outbreak of spontaneous combustion of coal, initial temperature 250C, size 20-28 mesh, O.1 cm, O.2.cm. .

sab

A Theory on the Mechanism of an Outbreak of Spontaneous Combustion of Coal I 267

Most oxidation phenomena on the surface or in the underground without

spontaneous combustion of coal show reaction similar to the perfect heat dis-

sipation. The time necessary to absorb a given quantity of oxygen increases

rapidly, while there appears only a slight rise of temperature.

This theory not only explains the problem of spontaneous combustion of

coal, but also has made it possible for one to compare the freshness of coal

quantitatively at the usual temperatufe.

It is technically impossible to maintain the oxidation rate in the early period

for a long time, through it should be possible theoretically. In this case the

velocity of the rising of temperature in every given period, here in 28.4 hours,

gradually decreases. Therefore in this kind of reaction, it is impossible for the

oxidation to proceed toward spontaneous combustion. Consequently the reaction

toward spontaneous combustion is always found in the range between perfect

heat accumulation and the maintainance of the inltial oxidation rate. In the

case of perfect heat accumulation, the time required for the temperature to rise

every 250C decreases along an exponential curve as the temperature rises, which

has been shown as a result of the experiments by J. D. Davis and J. F. Byrnei2)

and Miyakawa etali3). Till now there has been no suthcient explanationabout the abnormal rising ternperature of a sma}1 pile of coal diust produced in

mine levels. Some of the investigators tried to explain it as the working of

some catalyzer, upon which they did not touch. The present writer attempts

to explain it as the oxidation phenomenon close to the perfect heat accumulation.

VI. Conclusion

Experiments have been conducted on oxidation in the constant low-

temperature using Oyubari coa! in Hokkaido. It has been shown as a result

that it is possible to explain the early heat generation phenomenon in the

oxidation of coal quantitatively. The basic difference between this theory and

the information in Scott's report is that in this theory the oxidation of coal

is taken to proceed between the prefect heat accumulation curve and the perfect

dissipation curve unless there is supply or withdrawai of heat by other materials.

To make the problem simple no consideration is taken, in this theory, of

the quantity of coal. The size of a pile of coal greatly influences the change

in oxidation by lowering the oxygen contents, the cooling due to the effects of

the outside air, the spread of heat in a pile of coal and so on. These points,

however, have little importance in the explanation of the rise of the initial

temperature in instances of the spontaneous combustion of coal.

e

268 Kiyoshi HAsHINoTO

Bibliography

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455, 1944.

2) Parr and Milner: The Oxidation of Coal at Storage Temperature. Ind, Eng. Chem.,

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ts