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4.5.1. Estimation of gas emission into development excavationsA. Bozko method

V CH 4

=αwdlW 

0γ 

43200

Where:V CH 

4 = methane emission, m3/minute

α  = factor depending upon the excavation development for a

single excavation, α   = !, for t"o headings, α   = ! # $/l

%&4' "here $ = length of cut(throughl = depth of fracture $one %) m'

d = thic*ness of seam, m

w = rate of advance, m/month

W 0 = methane content of seam, m3/t

γ  = densit+ of coal %1.4 ton/m3'

B. Oriechowa methodV CH 

4

=25αdwV  P ć k w

Where:

V CH 4 = methane emission, m3/minuteα  = ! for a single road"a+,

= ! # .5l1 %&4' for t"o road"a+s "here l1 = distance

-et"een parallel road"a+s, m

d = thic*ness of seam, m

w = rate of advance, m/da+

V  P = uantit+ of gas li-erated from a unit surface area of the

exposed

road"a+, m3/minute/m! %determine experimentall+'

ć = coecient de0ning the increase in gas emission determined

-+ the

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relationship ć  = .!4 ln %1.5!t # 1' 2 .1t, "here t = time,

month

k w = constant given -+ the euation k w=V CH 

4+V CH 

4max

V CH 4

C. Barbara experimental mine methodd w

∑ ¿ γ (W 0−W k )¿

wb¿V 

1CH 4

=¿

dw

∑ ¿V  P¿

V 2CH 4

=b¿

dw

30k +n' 0.5

t −1

¿

∑ ¿w V  P¿V 

3CH 4

=n¿

nd the total gas emitted isV t CH 

4

=V 1CH 

4

+V 2CH 

4

+V 3CH 

4

Where:

dw = total thic*ness of the coal -ed exposed

b = "idth of the excavation, m

γ  = densit+ of coal, ton/m3

V  P = gas li-erated from a unit area of exposed surface

%m3/minute/m!'n = num-er of surfaces in a road"a+ %for full thic*ness

excavation n=!'W 

0 = gas content of the coal, m3/t

W k  = rest gas, m3/t

k  = permea-ilit+

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n '  = seuential num-er of the da+ after the start of drivae of the

excavation.t  = time of drivage of excavation, months %t = n/3'

D. Pawinski method

V CH 4

=2dw(√   mk  μπ ρa )( pa

2− p0

2

 p0

)t 0.5Where:

d = thic*ness of seam, m

w = rate of advance, m/s

 Pa = in(situ gas pressure in the seam, 15 a

 Pv = air pressure in the excavation, 15 a

m = porosit+

µ = viscosit+ of methane, 6s/m!

k  = permea-ilit+

t = time elapsed after start of driving the heanding, s.E. Experimental techniques

V CH 4

= A t α 

and if a heading has -een stopped, gas emission is given -+

V CH 4= A t α − A (t − Lw )

α 

Where:

 V CH 

4 = volume of gas emitted, m3/minute

t  = time elapsed, da+s

α    and = constants for a given area and depend upon local

conditions

w = rate of advance, m/da+, and

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 L = length of the heading.

7f o-servations are made over a period of time for gas emission from

a heading advancing at a 0xed rate, then the value of α   can -e

calculated from the relationship

α =

lnV 

2

V 1

lnt 2

t 1

 8he value of can -e calculated from the relationship

 A=V t 

α 

 8he euations can modi0ed as follo"s:

α =

ln( V i−V 0V n−V 0 )ln( t it n )