The Optimization of Suralaya Steam Power Plant Operation With Equal Incremental Rates and Priority Method

Hartono1*

1 University of Sultan Ageng Tirtayasa, Jalan Raya Jakarta kM.04 Pakupatan, Serang, Indonesia

Currently, the largest cost to produce electricity at Suralaya Steam Power Plant is the cost of coal consumption, which affects the

selling price of electricity per kWh. Saving coal consumption is the strong motivation for Suralaya steam power plantto achieve maximum operational efficiency. Suralaya Steam Power Plant have 7 units of coal fired power plants, connect in parallel order and operate at maximum capacity, to ensure reliability to supply electricity to consumer as the main priority rather than efficiency. An optimal combination in operating the plants and loading operation scheduling in the most economic fashion using equal incremental rates method will save coal consumption significantly. The method will use second-order polynomial equations, and linear approach by deriving the second-order polynomial equation. The solution from equal incremental rates method will yield the most economical operation schedule of Suralaya steam power plantin order to save coal consumption. In this study, we utilize the highest load at 3197 MW generated from 7,561,479,246 kcal/hour coal consumption. After optimization using the equal incremental rates method, we found that coal consumption can be reduced to 7,486,155,768 kcal/hour, which means we save 75,323,478 kcal/hour of coal consumption. Since average coal energy is 5100 kcal/kg, the optimization using equal incremental rates saves us 14.77 ton of coal per hour if compared to the real operation system of Suralaya steam power plant at the same time.

1. Introduction Operating cost of the system is the largest portion of planning cost, at nearly 70% of total cost. To optimize Suralaya steam power plant efficiency in coal consumption, the author will look for a combination of Unit 1, Unit 2, Unit 3, Unit 4, Unit 5, Unit 6, and Unit 7 of the seven units of coal-fired plants so that we obtained 128 possible combinations, in order to achieve the most economic operating combination at Suralaya steam power plant. We will implement the equal incremental rates method, an increment in heat value over coal consumption cost. Using this approach, energy cost for several loading levels at one plant unit will be linear segments.(8) 2. Basic Theory 2.1 Characteristics of Power Generation Units

Fig. 1. Incremental heat rate characteristic.(9) .

Fig. 2. Incremental fuel cost characteristic .(9)

2.2 Calculation Approach Using Linear Equation Maximum output is achieved at the point where the slope of the straight line starting from origin to another point on the curve is minimum, which is where the straight line touches the curve. (13)

PHΔΔ

PC

ΔΔ

Fig. 3. The straight-line approach graph. (7) (13)

PHΔΔ → the incremental of heat rate (MBTU/MWh)

PC

ΔΔ → the incremental of fuel cost (Rp/MWh)

dPidCi

= λ ...............................................................(1)

Where λ is fuel cost incremental or equal incremental rates (Rp/MWh).(9)

∑=

N

iPi

1

= Pload ..........................................................(2)

2.3 The constraints of generation unit Minimum and maximum limits, from operational capactiy can be expressed as (11)

dPidCi = λ , for Pi min < Pi < Pi max.............................(3)

dPidCi ≤ λ ,for Pi = Pi max.......................................(4)

dPidCi ≥ λ ,for Pi = Pi min.........................................(5)

* E-mail: artonid@yahoo.com

Proceedings of the International Conference onElectrical Engineering and InformaticsInstitut Teknologi Bandung, Indonesia June 17-19, 2007

F-51

ISBN 978-979-16338-0-2 846

3. Plant Optimization Problem Solving Methods 3.1 Equal Incremental Rates Method The Consumption of fuel in unit generation production can be state in Eq. 6 - Eq. 8 (1) (9)

2iiiiii PPC γβα ++= ....................................(6)

CCn

iit ∑

=

=1

..........................................................(7)

∑=

++=n

iiiiiit PPC

1

2** γβα ...........................(8)

Where : Ct = Total coal consumption (MBTU/h). Ci = Plant unit coal consumption (MBTU/h).

iii γβα ,, = Constants

PPn

iloadi∑

=

=1

.....................................................(9)

To obtain Equal Incremental Rates, we have to derive equation (3 - 6). (9)

dPidCi = λ............................................................(10)

From equation (6) we derive. (1) (9) iii Pγβλ 2+= ....................................................(11)

The power to be supplied for each plant unit is calculated using the following equation. (1) (9)

i

iiP

γβλ

2−

= .........................................................(12)

If we have more than one generating plant units, we can substitute equation (12) into equation (9) so that. (1) (9)

Pn

iload

i

i∑=

=−

1 2γβλ .............................................(13)

Hence the coal consumption can be calculated for each running plant unit as follows. (1) (9)

∑

∑

=

=

+= n

i i

n

i i

iloadP

1

1

21

2

γ

γβ

λ ...........................................(14)

Since generating unit has limitations. (9)

∑Δ

=Δ

i

kk P

γ

λ

21

)()( ...............................................(15)

then actual coal consumption in MBTU/MWh is the sum of equation (14) and equation (15). (9)

)()()1( kkk λλλ Δ+=+ ...........................................(16) Where:

=+ k )1(λ Actual coal consumption )(kλ = Coal consumption from initial calculation

)(kλΔ = Coal consumption when power generated exceeds or is less than the generating unit capacity. Accuracy of calculation.(11)

∑=

−=Δng

i

kiload

k PPP1

)()( ......................................(17)

Error process ( )(kPΔ ) needs to be iteratively calculated until the desired output becomes more accurate and the difference

( )(kPΔ ) between turbine’s output power and load power is zero. 3.2 Priority Method Priority method is a method of operating generator plant unit based on priority order, started with prioritized generating unit followed by other units.(5) 3.3 Data and Result of Computing Suralaya Steam Power Plant. 1. Maximum and minimum operating limits allowed without constraints.

2. Second-order polynomial equation data for Suralaya steam power plant units

C1 = 1225.98235528122 + 3.79786663310P1

+ 0.01028572890P12

MBTU/hours. C2 = 1353.93776992769 + 0.88284394409P2 + 0.01645659697P2

2 MBTU/hours C3 = 1139.72097160743+ 3.94933262469P3

+ 0.00980239080P32 MBTU/hours

C4 = 1201.37807947711 + 3.74302205963P4 + 0.00778457458P4

2 MBTU/hours C5 = 1873.08742378295 + 1.06373865407P5 + 0.00666016875P5

2 MBTU/hours C6 = 1809.47153156598 + 2.93282769127P6 + 0.00433233514P6

2 MBTU/hours C7 = 739.176241056230 + 4.512480873186 P7 + 0.004702796368P7

2 MBTU/hours From the 127 possible operating combinations, we obtain the most optimal steam power plant operating point.

Fig. 4. Suralaya steam power plant Characteristic curve

Color definitions: Unit 1 = ■ Unit 3 = ■ Unit 5 = ■ Unit 7 = ■ Unit 2 = ■ Unit 4 = ■ Unit 6 = ■

Proceedings of the International Conference onElectrical Engineering and InformaticsInstitut Teknologi Bandung, Indonesia June 17-19, 2007

F-51

ISBN 978-979-16338-0-2 847

From Figure 4 above we can see that the priority which yields maximum saving on coal consumption cost is in the following order: Unit 7, Unit 5, Unit 6, and Units 1, 2, 3, 4. 4. Results and Discussion 4.1 Optimization result analysis

From Table 2 above, we can see that when Suralaya steam power plants supplies 2500 MW power, we have 13 possible operating combinations. Then from the calculation presented at Table 2, we found that the most optimal and economical operating point when Suralaya steam power plants supplies 2500 MW was when Unit 1 and Unit 3 were not operated, meanwhile Unit 2 supplies 282 MW, Unit 4 supplies 400 MW, Unit 5 supplies 608 MW, Unit 6 supplies 608 MW, and Unit 7 supplies 602 MW, produced from 22,192 MBTU/hour of coal consumption. This is the most efficient coal consumption compared to the other 12 possible combinations.

If we compare this result to the combinations when all the 7 units are operating to supply 2500 MW of power, i.e. where the units supply 217 MW, 224 MW, 220 MW, 291 MW, 541 MW, 608 MW, and 399 MW respectively, we’ll find that the previous combination (where Units 1 and 3 are not operating) was consuming less coal. Analysis result proves that operating combination of Suralaya steam power plant units is very influential to its efficency. If we do not choose to run the optimal combination, for example by operating all the 7 units at 2500 MW load, we will have over consumption of coal as much as 1033 MBTU/hour. If the equivalent energy by coal consumed is 5100 kcal/kg then the excessive coal consumed will be 51 ton/hour.

Using the similar operating combination, where Units 1 and 3 are not operating and annual power supplied by each of the other units without optimization techniques (for example when Unit 2 supplies 380 MW, Unit 4 supplies 370 MW, Unit 5 supplies 582 MW, Unit 6 supplies 560 MW and Unit 7 supplies 608 MW), then the coal consumed by Suralaya steam power plant which is supplied by Units 2, 4, 5, 6, 7 can be calculated using the following second-order polynomial equation: C2 = 1353.937 + 0.882P2 + 0.016P2

2 MBTU/hours = 1353.937 + (0.882 x 380) + (0.016 x 3802 ) = 4.065.8 MBTU/hours C4 = 1201.378 + 3.743P4 + 0.007P4

2 MBTU/hours

= 1201.378 + (3.743 x 370) + (0.007 x 3702 ) = 3652 MBTU/hours C5 = 1873.087 + 1.063P5 + 0.0065P5

2 MBTU/hours = 1873.087 + (1.063 x 582) + (0.0065 x 5822 ) = 4748.1 MBTU/hours C6 = 1809.471 + 2.932P6 + 0.004P6

2 MBTU/hours = 1809.471 + (2.932 x 560) + (0.004 x 5602 ) = 4810.5 MBTU/hours C7 = 739.176 + 4.512P7 + 0.004P7

2 MBTU/hours = 739.176 + (4.512 x 608) + (0.004 x 6082 ) = 5221.2 MBTU/hours Total coal consumption for Surayala steam power plant is CTotal = C2 + C4 + C5 + C6 + C7 = 3999.5 + 3544.6 + 4693.5 + 4705.8 + 4961.1 = 22498 MBTU/hours

From Table 3 above we can see significant difference between coal consumption calculated using equal incremental rates and without optimization technique. This means that if we didn’t use the optimization technique, we would waste as much as 306 MBTU/hour of coal. 4.2. Comparing Optimization to Actual Results

Table 4 above shows that in order to supply 2500 MW – 3197 MW power, we need to operate all the 7 units. Priority to operate generating plant unit continuously when required falls to Units 4 and 3. On the other hand, priority not to operate when only low supply required are Units 1, 2, and

Proceedings of the International Conference onElectrical Engineering and InformaticsInstitut Teknologi Bandung, Indonesia June 17-19, 2007

F-51

ISBN 978-979-16338-0-2 848

5. Actual data on Table 4 can be considered when comparing to results from optimization calculation.

Table 5 shows that the most optimal results for supplies over 3000 MW up to 3197 MW can be achieved when Units 1-7 are operated. Priority of continuously operating units after optimization are Units 7, 5, and 6. On the other hand, the priority not to operate units when supplying low powers are in the following order: Units 1, 3, 2, and 5.

Priority by Table 4 is different from priority by Table 5. Priority of operating units according to Table 4 is in the following order: 4 and 3, while according to Table 5 is 7, 5, 6. In order to save coal consumption, priority of operating units is in the following order: 7, 5, 6. Actual operating condition from Table 4 will be compared to the optimized condition from Table 4 and will be presented in Table 6.

Table 6. compares actual data of coal consumption to

equal incremental rates optimization method at the same amount of supply. The largest difference in coal consumption is 1,258,835,595 kcal/hour, achieved when supplying 2447 MW of power.

Table 6. proves that supply of 1402 MW up to 3197 MW using equal incremental rates optimization results in significant reduction in coal consumption, compared to currently operating combination at Suralaya steam power plant. 5. Conclusion

Operating the Suralaya steam power plant unit using equal incremental rates method can significantly reduce coal consumption, compared to actual condition, from 1,142,406 kcal/hour up to 1,258,835,595 kcal/hour.

The priority to operate Suralaya steam power plant units in determining the combination of operation will result in the efficiency of coal consumption. Operating higher capacity plant units (units 5, 6, 7) will reduce coal consumption, compared to when operating small capacities unit (units 1, 2, 3, 4). In condition where low power supply, units with large capacity (unit 5,6,7) should be operated continously to maxsimum capacity meanwhile units with small capacity (unit 1,2,3,4) should be not operated.

The most optimal operation schedule of Suralaya steam power plant using equal incremental rates method at 3197 MW peak load supply, is to run all the 7 plant units with each unit supplies 334 MW, 297 MW, 342 MW, 400 MW, 608 MW, 608 MW, 608 MW respectively. The total coal consumption will be 7,486,155,768 kcal/hour, which yields a reduced coal consumption by 75,323,478 kcal/hour, or equivalent with 14.77 ton coal per hour.

Proceedings of the International Conference onElectrical Engineering and InformaticsInstitut Teknologi Bandung, Indonesia June 17-19, 2007

F-51

ISBN 978-979-16338-0-2 849

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Proceedings of the International Conference onElectrical Engineering and InformaticsInstitut Teknologi Bandung, Indonesia June 17-19, 2007

F-51

ISBN 978-979-16338-0-2 850