Electricity + Control June 2017

PRESSURE + LEVEL MEASUREMENT

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Table I: Relevant turbine information. Turbine number Maximum Steam Limit [ton/h]

Figure 5: Simulated power co-generation for 10,0 MW under initial available steam flow. 8 6 4 2 0 0 500 1000 1500 2000 2500 Power generation (MW) Time (h) 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

Minimum Steam Limit [ton/h]]

Conversion Factor C ƒ

T T

(10,0 MW) (25,0 MW)

55,0

16,5 33,0

10/55 10/55

1

137,5

2

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.

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.

250

200

30

150

25

100

20

50

15

0

10

2500

0 500 1000 1500 2000

5

Time (h)

Power generation (MW)

0

Figure 4: Available steam flow for power co-generation.

0 500 1000 1500 2000 2500

Time (h)

Figure 6: Simulated power co-generation for 25,0 MW under initial available steam flow.

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.

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.

Electricity+Control June ‘17

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