9 / 52
Figure 7: Total potential steam productions flared to atmosphere.
As mentioned, the boiler houses consist of a maximum steamproduc-
tion capacity of 260 ton/h. Furthermore, for line pressure control to
ensure that air does not enter the off-gas pipelines, which are open to
atmosphere, a certain quantity must always be flared. It is therefore
never possible to utilise all the energy potential from the off-gases.
Figure 8: Potential steam productions flared to atmosphere that could
have been realised.
Influence of regulating off-gas flaring percentage
It was mentioned earlier that management was under the impres-
sion that off-gas flaring was regulated to be 10% of the volume flow,
whereas in the previous section it was reported that on a volume
basis 46,9% of the off-gases were flared. Five different off-gas flaring
scenarios are chosen that range from 40,0% down to an optimistic
5,0%. For each scenario the potential steam that could have been avail-
able are calculated and simulations are performed by means of the
mathematical model. The power co-generations are given in
Table 2
.
Table 2: Turbine simulation results for various off-gas flaring percentages.
Flare %
Max Potential
Power
Generation
[MW]
Combined
Power
Generation
[MW]
Trips
46,9
21,4
20,5
18
40,0
25,2
23,1
25
30,0
30,1
27,0
20
20,0
33,4
29,7
15
10,0
35,0
30,8
13
5,0
35,5
31,4
11
From the results in
Table 2
it can be seen that if off-gas flaring was
controlled, significant increases in power co-generation could poten-
tially have taken place. Allowing for only 10,0% of flaring, the potential
power co-generation could increase with up to 50,0% with a reduced
PRESSURE + LEVEL MEASUREMENT
number of combined turbine trips. Even though sufficient steam
is mostly available to operate both turbines at maximum capacity,
turbine trips cannot be eliminated, due to instances of low off-gas
productions as seen in
Figure 7.
In
Table 3
the time percentages are displayed for both T
1
and T
2
,
for all of the different steam flow scenarios, where power co-gener-
ation occurs at maximum capacity and for when the turbines are in
trip. The results show, as expected, that when the flaring percentage
reduces, turbines will operate more frequently at maximum capac-
ity with less time in a tripped state. The reported values in
Tables 2
3
do not show significant changes when the flaring percentage is
lowered from 10,0% to 5,0%. The conclusion to be drawn is not that
there exists a flare percentage where after improved flaring control
does not increase energy utilisation, but that the combined boiler
houses’ capacity is the limiting factor. This correlates with what was
seen in
Figures 7 and 8.
Table 3: Time percentages for turbines operating at full capacity or be-
ing in trip.
Time % for
Maximum Operating
Capacity
Time % for
Turbine in
Trip
Flare % T1
T3
T1
T3
46,9
5,1
21,7
20,0
14,0
40,0
18,0
38,4
15,2
17,0
30,0
37,0
63,4
7,7
15,1
20,0
52,4
78,0
8,2
9,7
10,0
60,2
82,7
7,0
6,4
5,0
62,0
84,4
8,2
3,7
Taking this information into account, it will make sense to simulate
scenarios where the combined boiler houses’ capacity is increased
to further investigate the effect on power co-generation for this
engineering plant.
With an increase in steam production capabilities additional tur-
bines will have to be added for the simulation model or the operating
limits of T
1
and T
2
should be increased.
Conclusion
An engineering works that produces and utilises fluctuating burn-
able off-gases during normal plant operations was investigated.
The residual off-gases that are not used for plant process purposes
are used to generate steam, in boiler houses, and the remaining off-
gases are flared to atmosphere, nullifying the energy potential. Steam
flow productions are necessary for a variety of plant processes and
these usages may fluctuate over time. Once all plant steam demands
are met, excess available steam is utilised for power co-generation
through the use of steam turbines.
References
[1] E. Vine (2008). Breaking down the silos: the integration of energy
efficiency, renewable energy, demand response and climate
change. Energy Efficiency 1, pp 49 – 63.
350
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50
0
350
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150
100
50
0
0 500 1000 1500 2000 2500
0 500 1000 1500 2000 2500
Steam flow (ton/h)
Steam flow (ton/h)
Time (h)
Time (h)
7
June ‘17
Electricity+Control