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Table I: Relevant turbine information.
Turbine
number
Maximum
Steam Limit
[ton/h]
Minimum
Steam Limit
[ton/h]]
Conversion
Factor C
ƒ
T
1
(10,0 MW)
55,0
16,5
10/55
T
2
(25,0 MW)
137,5
33,0
10/55
Simulation results
A number of simulations were performed on the power co-generation
capabilities of the engineering plant that utilises residual off-gas for
steam productions. The aim was not to simulate what capacity size
turbine or combination thereof will yield the best power genera-
tion, but to demonstrate the effect that off-gas flaring control could
potentially have on the outcome of a plant’s power co-generation.
The excess steam that was available by the plant during the time of
investigation is plotted in
Figure 4.
Fluctuations with low steam flow intervals are clearly evident
in
Figure 4.
To determine the total power generation potential if
all of the steam could be utilised, (1) is used. All the relevant
turbine information used for the simulations can be found
in
Table 1
, i.e. turbine capacities, steam flow limits and
the conversion factor. For simplicity the conversion
factor is chosen to be equal for both turbines and
constant for all of the operating points. The first
set of power co-generation results are that of the
plant for the initial steam flow profile that will be
used as basis for comparison purposes.
Figure 4: Available steam flow for power co-generation.
Simulations for initial available steam flow
The numerical integral was determined for the initial steam flow as
depicted in
Figure 4
and the maximum average rate of power co-
generation was calculated at
.
W
max
= 21,4 MW. The combined power
co-generation from turbines T
1
and T
2
equals 35,0 MW and will be
used for all steamflow scenario simulations with the combined boiler
houses’ capacity of 260 ton/h. Power co-generation results obtained
for T
1
and T
2
are plotted in
Figures 5
and
6
respectively. Turbine trips
due to steam shortages are evident in these two figures and, further-
more, that both T
1
and T
2
operate mostly below the maximum limits.
T
1
only operates at maximum capacity for 5,1% and T
2
for 21,7% of
the time. The total combined average rate of power co-generation is
20,5 MW out of a potential of 21,4 MW and simulation results show
18 combined trips for the turbines during the time period.
250
200
150
100
50
0
PRESSURE + LEVEL MEASUREMENT
Figure 5: Simulated power co-generation for 10,0 MW under initial
available steam flow.
Investigating the flaring of off-gases
Flared off-gas measurements were obtained for the time period and
the total potential flared steam were calculated and plotted in
Fig-
ure 7
. When
Figure 7
is compared with
Figure 4
it can be seen that a
significant amount of potential steam is flared into the atmosphere
where the energy potential is wasted. Calculations showed that 55,2%
of all energy potential in the residual off-gases were flared, resulting
in only 44,8% usage of this energy resource. The 55,2% correlates to
a 46,9% combined off-gas volume flow that was flared. Take
note that the low off-gas flaring instances correspond to
low steam flow production occurrences and even if
all available off-gases were to be used to generate
steam, low steam availability periods would still
have existed. However, even though it is evident
from
Figure 7
and these percentages that significant
quantities of potential steam generation does not
take place, it is not yet possible to comment on how
this could potentially affect the power co-generation.
Figure 6: Simulated power co-generation for 25,0 MW under initial
available steam flow.
In order to investigate how power co-generation could have been
improved due to less off-gas flaring, the potential steam that could
have realistically been generated must be calculated, i.e. taking into
account the total steam generated as well as the combined boiler
houses’ capacity. The potential steam that could additionally have
been generated during this time can be seen in
Figure 8. Figures 7
and
8
have been plotted on the same y-axis intervals to demonstrate
the difference between the potential steam flow that was flared
against the maximum additional steam flow that could potentially
have been produced. These plotted results further indicate that
significant steam flow productions cannot take place due to boiler
house capacity restrictions.
30
25
20
15
10
5
0
0 500 1000 1500 2000
0 500 1000 1500 2000 2500
Time (h)
Power generation (MW)
Time (h)
12
10
8
6
4
2
0
0 500 1000 1500 2000 2500
Power generation (MW)
Time (h)
2500
Electricity+Control
June ‘17
6