Proceedings of the International Conference on Electrical Engineering and Informatics Institut Teknologi Bandung, Indonesia June 17-19, 2007
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The Optimization of Suralaya Steam Power Plant Operation With Equal Incremental Rates and Priority Method 1*
Hartono 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 un its of coal fired power pl ants, 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
2.2 Calculation Approach Using Linear Equation
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)
Maximum output is achieved at the point where the slope of the straight line starting from or igin to another point on the curve is minimum, which is where the straight line touches the curve. (13)
2. Basic Theory 2.1 Characteristics of Power Generation Units
Δ H ΔP ΔC ΔP
Fig. 3. The straight-line straight-line approach graph. (7) (13) Δ H → the incremental of heat rate (MBTU/MWh) ΔP ΔC → the incremental of fuel cost (Rp/MWh) ΔP
dCi dPi
= λ ....................... .................................. ....................... ....................... .................(1) ......(1)
Where λ is fuel cost incremental or equal incremental rates (Rp/MWh).(9) Fig. 1. Incremental heat heat rate characteristic. characteristic.(9) .
N
∑ Pi
= Pload ...................... .................................. ....................... ....................... .............(2) .(2)
i =1
2.3 The constraints of generation unit Minimum and maximum limits, from operational capactiy can be expressed as (11) dCi
= λ , for Pi min < Pi < Pi max.............................(3)
dPi
dCi
Fig. 2. Incremental fuel cost characteristic characteristic .(9) * E-mail:
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ISBN 978-979-16338-0-2
dPi dCi
≤
λ ,for Pi = Pi max........................ ................................... ...............(4) ....(4)
≥ λ ,for Pi = Pi min...................... ................................. ...................(5) ........(5)
dPi
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Proceedings of the International Conference on Electrical Engineering and Informatics Institut Teknologi Bandung, Indonesia June 17-19, 2007
F-51
3. Plant Optimization Problem Solving Methods 3.1 Equal Incremental Rates Method
( ΔP zero.
The Consumption of fuel in unit generation production can be state in Eq. 6 - Eq. 8 (1) (9) 2 C i = α i + β i Pi + γ i Pi ....................................(6)
3.2 Priority Method
n
................................... ....................... ....................... ............(7) (7) C t = ∑ C i .......................
( k )
) between turbine’s output power and load power is
Priority method is a method of operating generator plant unit based on priority order, started with prioritized (5) generating unit followed by other units.
i =1 n
C t =
∑ α i
2 + β i * Pi + γ i * Pi ...........................(8)
i =1
Where : Ct = Total coal consumption (MBTU/h). coal consumption consumption (MBTU/h). (MBTU/h). Ci = Plant unit coal = Constants α i , β i , γ i
3.3 Data and Result of Computing Suralaya Steam Power Plant. 1. Maximum and minimum operating operatin g limits allowed without constraints.
n
∑ Pi = Pload
...................... ................................... ........................ ..................(9) .......(9)
i =1
To obtain Equal Incremental Rates, we have to derive equation (3 - 6). (9) dCi = λ ............................................................(10) ............................................................(10) dPi (1) (9)
From equation (6) we derive. .................................. ........................ ..................(11) .....(11) λ = β i + 2γ i Pi ....................... The power to be supplied for each plant unit is calculated using the following equation. (1) (9) λ − β i ...................... ................................. ...................... ........................ .............(12) (12) Pi = 2γ i If we have more than one generating plant units, we can (1) (9) substitute equation (12) into equation (9) so that. n λ − β .................................. ....................... ...........(13) (13) ∑ 2γ i = Pload ...................... i =1 i Hence the coal consumption can be calculated for each running plant unit as follows. (1) (9) n β Pload + ∑ i ................................. .....................(14) ..........(14) i =1 2γ i ...................... λ = n 1 ∑ 2γ i =1 i Since generating unit has limitations. limitations. (9) ( k ) ΔP ...................... .................................. ....................... .............(15) ..(15) ( k ) Δ λ = 1
∑
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 + 0.01645659697P22 MBTU/hours C3 = 1139.72097160743+ 3.94933262469P3 2 + 0.00980239080P3 MBTU/hours C4 = 1201.37807947711 + 3.74302205963P4 + 0.00778457458P42 MBTU/hours C5 = 1873.08742378295 + 1.06373865407P5 + 0.00666016875P52 MBTU/hours C6 = 1809.47153156598 + 2.93282769127P6 + 0.00433233514P62 MBTU/hours C7 = 739.176241056230 + 4.512480873186 P7 + 0.004702796368P72 MBTU/hours
From the 127 possible operating combinations, we obtain the most optimal steam power plant operating point.
2 γ i
then actual coal consumption in MBTU/MWh is the sum of equation (14) and equation (15). (9) ................................. .....................(16) ..........(16) λ ( k +1) = λ ( k ) + Δλ ( k ) ...................... Where:
λ ( k +1) = Actual coal consumption λ ( k ) ( k ) Δλ
= Coal consumption consumption from initial calculation calculation = Coal consumption consumption when power generated exceeds or is less than the generating unit capacity. Accuracy of calculation.(11) ng
ΔP
( k )
= Pload − ∑ Pi
( k )
....................... .................................. ...............(17) ....(17)
Fig. 4. Suralaya steam steam power power plant Characteristic curve
i =1
( k )
Error process ( ΔP ) needs to be iteratively calculated calculated until the desired output becomes more accurate and the difference
ISBN 978-979-16338-0-2
Color definitions: Unit 1 = ■ Unit 3 = ■ Unit 5 = ■ Unit 7 = ■ Unit 2 = ■ Unit 4 = ■ Unit 6 = ■
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Proceedings of the International Conference on Electrical Engineering and Informatics Institut Teknologi Bandung, Indonesia June 17-19, 2007
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 + 0.882P 2 + 0.016P22 MBTU/hours 2 = 1353.937 + (0.882 x 380) + (0.016 x 380 ) = 4.065.8 MBTU/hours 2 C4 = 1201.378 + 3.743P 4 + 0.007P4 MBTU/hours
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= 1201.378 + (3.743 x 370) + (0.007 x 370 2 ) = 3652 MBTU/hours 2 C5 = 1873.087 + 1.063P 5 + 0.0065P5 MBTU/hours = 1873.087 + (1.063 x 582) + (0.0065 x 582 2 ) = 4748.1 MBTU/hours C6 = 1809.471 + 2.932P 6 + 0.004P62 MBTU/hours = 1809.471 + (2.932 x 560) + (0.004 x 560 2 ) = 4810.5 MBTU/hours C7 = 739.176 + 4.512P 7 + 0.004P72 MBTU/hours = 739.176 + (4.512 x 608) + (0.004 x 608 2 ) = 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 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
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Proceedings of the International Conference on Electrical Engineering and Informatics Institut Teknologi Bandung, Indonesia June 17-19, 2007
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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 s ave 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.
ISBN 978-979-16338-0-2
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.
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Proceedings of the International Conference on Electrical Engineering and Informatics Institut Teknologi Bandung, Indonesia June 17-19, 2007
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References (1) (2)
(3) (4) (5) (6) (7) (8) (9)
A.Momoh, James. 2001. Electric Power System Applications of Optimization, Marcel Dekker, New York Jeremy A.Bloom, Lawrence gallant; Modeling dispatch constraints in production cost simulations based on the equivalent load method ; IEEE Transactions on power systems; Vol.9,No.2, May 1994. P.S.R. Murty; Power System And Control; Tata Mc Graw-Hill Publishing Company Limited, 1984. I.J.Nagrath, D.P.Kothari; Modern Power System Analysis; Tata McGraw-Hill Publishing Company Limited, 1980. Djiteng Marsudi, Marsudi, Ir; Operasi Sistem Sistem Tenaga Listrik ; Balai penerbit & humas ISTN; Jakarta;1990. Robert H Miller, Miller, James James H Malinowski; Power System Operation Third Edition, 1993. J.wood Allen. 1984. Power Generatoion operaton & control, Tata Mc Graw-Hill. Stevenson,Jr, William D. 983. Analisis Sistem Tenaga Listrik. Erlangga, Jakarta. Saadat Hadi. 1999. Power System Analysis,WCB/McGraw-Hill, Singapore.
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