Institut za rudarstvo i metalurgiju Bor

Figure 1. Schematic diagram of generator
1 – Coal seam, 2 – roof, 3 – gas inlet, 4 –channels with holes for air supply
DETERMINATION OF GAS
CONCENTRATION IN THE UCG
By development of combustion processes,
the gasification zone is moved and
extended along the coal seam, and CO,
CO2, H2, and CH4 are generated in the reaction
zone. In addition to those, nitrogen is
also present, that is inert, then water vapour
that disappeared at high temperatures as
well as carbon remaining in a form of slag,
so these components are not counted into
the final component balancing.
Oxygen, in the finished gasification
product, is usually manifested in a bound
form of CO and CO2 and in very small
quantities as free O2, but it appears in the
mathematical model. In the combustion, a
part of chemical reactions is exothermic, a
part is endothermic and a part of heat is
carried over to the massif.
Figure 2. Heat balance
For the purposes of analysis of these processes,
the Darcy’s continuity equation is used,
that is applied to the diffusion of oxygen being
the gasification medium in this case.
The equation of oxygen diffusion regarding
to the coal wall of pre-positioned
cylindrical channel may be represented as
follows:
⎡ 2
∂C
r ∂ C 1 ∂ ∂C
⎤
+ ( v∇C
) ' = D⎢
+ r ⎥ + ρ′
(1)
∂τ
2
⎣ ∂z
r ∂r
∂r
⎦
Where:
v r r r r
- velocity of flow: v = u + v′
u r - mean velocity of flow at section in
the channel
v′
r - pulse velocity of flow
D – coefficient of molecular diffusion
No 1, 2010. 132
MINING ENGINEERING