Performance Assessment of Single Flash PLTP LMB 1 After First Year Inspection Using ASME PTC 46:1996 Method
Joni Welman Simatupang1*, Asep Mamat Rahmat Solihat2
1Electrical Engineering Study Program, Faculty of Engineering, President University, Indonesia
2Mechanical Engineering Study Program, Faculty of Engineering, President University, Indonesia
*Corresponding author: [email protected]
Received: May 5, 2023 Approved : May 12, 2023
Abstract
PLTP LMB 1 performs a First-Year Inspection after operating for one year to inspect and repair equipment after the operation. After these activities, a performance test needs to be carried out to determine the effectiveness and success of these activities. ASME PTC 46: 1996 is a widely-used standard for analyzing the performance test of thermal power plant systems, which includes plant heat rate, power output, specific mass consumption, and more. The purpose of the testing is to evaluate the results of system improvements.
Calculation and comparative analysis are performed to determine the system's condition during warranty, commissioning, and testing, as well as after one year of operation and post-first year inspection. After testing, the thermal performance of PLTP LMB 1 was obtained as follows: The corrected net plant heat rate (NPRH) was 18923 kJ/kWh, the corrected net power output was 56,417 MW, and the net specific mass consumption (NSMC) was 6,881 tons/MW. Based on the data guarantee, the thermal performance value of PLTP LMB1 is still below the required value, so it can be concluded that the thermal performance value of PLTP LMB1 is in good condition. The isentropic turbine efficiency value decreased by 2.1% from its design value of 85% to 82.9%, which was caused by suboptimal heat energy absorption by the turbine above the design pressure of 5 bar.
Keywords: first year inspection, performance of thermal power plant, ASME PTC 46:1996, net plant heat rate, net specific mass consumption, isentropic turbine efficiency
Abstrak
First Year Inspection dilakukan oleh PLTP LMB 1 pasca beroperasi selama 1 (satu) tahun penuh dengan tujuan inspeksi dan koreksi peralatan setelah dioperasikan. Pasca dilakukannya kegiatan tersebut, uji kinerja PLTP perlu dilakukan untuk mengetahui efektifitas dan keberhasilan kegiatan tersebut. ASME PTC 46 : 1996 standar yang secara luas digunakan untuk menganalisa uji kinerja sistem thermal power plant yang meliputi plant heat rate, power ouput, spesific mass consumption. Tujuan dari pengujian ini adalah untuk mengetahui hasil dari pekerjaan perbaikan. Perhitungan dan analisa perbandingan dilakukan untuk mengetahui pada kondisi garansi, commissioning dan pengujian untuk mengetahui kondisi sistem setelah dioperasikan selama satu tahun dan pasca first year inspection. Setelah dilakukan pengujian, didapat data kinerja termal PLTP LMB 1 sebagai berikut; net plant heat rate (NPRH) terkoreksi 18923kJ/kWh, net power ouput terkoreksi 56.417 MW, dan net specific mass consumption (NSMC) 6.881 ton/MW.
Berdasarkan garansi data, nilai kinerja termal PLTP LMB1 masih dibawah nilai yang dipersyaratkan sehingga dapat disimpulkan bahwa nilai kinerja termal PLTP LMB 1 dalam kondisi baik . Adapun nilai efisiensi isentropic turbine mengalami penurunan sebesar 2,1% dari desain 85% menjadi 82,9% yang diakibatkan kurang optimalnya penyerapaan energi kalor oleh turbin diatas desain tekanan 5 bar.
Kata Kunci: first year inspection, Kinerja PLTP, ASME PTC 46:1996, net plant heat rate, net specific mass consumption, efisiensi isentropic turbine
1. Introduction
PLTP LMB 1 is a geothermal power plant located in Muara Enim Regency, South Sumatra Province, Indonesia. It supplies electricity of 55 MW to the Sumbagsel grid owned by PT PLN (Persero). Throughout
power plant unit/system/equipment after operating for one (1) full year, compared to the agreed design. The main activity of first-year inspection is to inspect and correct all the main and supporting equipment that has been agreed upon in the contract between the main contractor and the asset owner.
PLTP LMB 1 carried out first-year inspection activities on the main equipment system, namely the steam turbine generator (STG) and supporting balance-of-plant (BOP) equipment systems such as the gas removal system (GRS), water circulating system which includes cooling tower, and other supporting systems, in February-March 2022. The purpose of conducting the first-year inspection at PLTP LMB 1 is to determine the condition of the main and supporting equipment after being operated for one full year and to correct any issues found in the PLTP LMB 1 system equipment. Thus, it is expected that these activities can restore or maintain the performance of the PLTP LMB 1 system.
n the performance testing process, special standards are needed to regulate the procedures for testing power plant performance, which include data collection, data processing, and data representation.
Generally, the performance testing method for power plant units refers to the ASME PTC 46 'Overall Plant Performance' standard. This code provides explicit procedures for determination of power plant thermal performance and electrical output [2]. ASME PTC 46 was developed primarily to address the needs of contract acceptance or compliance testing [2]. By referring to that standard, it is expected that the real condition of PLTP LMB 1's performance after the overhaul activity can be demonstrated. (contract).
However, the test result can be used by a power plant owner, for either comparison to a design number or to trend performance changes over time of the overall plant [2].
Based on data, PLTP LMB 1 has undergone power plant performance testing conducted by the manufacturer during the commissioning phase. The data demonstrates that the performance of PLTP is in accordance with the design specified in the agreed contract, as shown in Table 1.
Table 1. PLTP LMB 1’s guarantee
No. Condition of Parameter Dimension Value
1. Output at the HV delivery point MW 55
2. Spesific Net Mass Consumption for the unit in operation in the same operating conditions as declared by Contractor for the guaranteed value.
kg(steam+gas)/kWh 7.059
3. Spesific Gross Mass Consumption for the unit in operation in the same operating conditions as declared by Contractor for the guaranteed value.
kg(steam+gas)/kWh
4. Cooling Tower Fans Power consumption kW 1.007
5. Hot Water Pump Powe consumption kW 1.445
In order to fulfill the performance requirements according to ASME PTC 46, additional parameters need to be calculated beyond those listed in Table 1, which were the minimum requirements specified in the contract. The Code explicitly requires the calculation of corrected net power, corrected heat rate (including net plant heat rate (NPHR) and gross plant heat rate (GPHR)), and corrected heat input (fuel) [2]. To complete the missing parameters from the commissioning and design phases, a calculation approach is required using data from both phases so that any trends of improvement or decline after the overhaul can be determined to assess the success of the maintenance activity.
2. Material and Methods Methodology
Figure 1 describes the methodology of performance testing and research of PLTP LMB 1, outlining the testing and performance research process. In general, the methodology focuses on the planning process, which includes mapping and isolating the system to be tested, the preparation process, which includes the readiness and completeness of instrumentation according to the isolated system, the system testing process, which includes data collection and stabilization, and the data processing and calculation process at each condition (testing, commissioning, and design).
Fig. 1. Research methodology Source: Personal (Private Document) Isolation and boundary model test PLTP LMB 1
In conducting testing and analysis on complex systems, a simplification is needed by formulating a model that includes the system and its boundaries. This simplification process plays an important role in research. The simplification must be able to meet the process of identifying energy flow that must be measured to calculate accurate results. This concept is used to determine certain flows that must be measured to determine performance [2]. Figure 2 illustrates the isolation and simplification model of the PLTP LMB 1 system that will be tested.
Fig. 2. Isolation and boundary model Source: Personal (Private Document)
Based on Figure 2, the simplification and isolation of the system focus on the energy conversion process, which includes the extraction of heat energy contained in the steam by the turbine as input and the generation of electrical energy by the generator as output.
Instrument mapping and sampling
the testing. To meet the depiction of the measurement process on the isolated system in Figure 2, the appropriate system and instrumentation are determined as listed in Table 2.
Table 2. System and Instrumentation
No. System Name of Instruments/Facilities Type of Instruments Accuracy 1. Steam supply 1. Turbine inlet pressure
2. Turbine inlet temperature 3. Turbine steam flow rate 4. Non – condensable gas flow rate
1. Pressure gauge 2. Temperature gauge 3. Flow transmitter 4. Gas sample analysis
1. 0.3%
2. 0.3%
3. 1%
2. Vacuum and circulating water
1. Condenser pressure 2. Condenser temperature 3. Water flow rate 4. Condensate flow rate
1. Pressure gauge 2. Temperature gauge 3. Flow transmitter 4. Flow transmitter
1. 0.3%
2. 0.3%
3. 1%
4. 1%
3. Power distribution
1. Gross power 2. Net power 3. Power factor
1. kWh meter 2. kWh meter
1. 0.2%
2. 0.2%
4. Environment 1. Amibient temperture 2. Relative humidity 3. Ambient pressure
1. Psychrometer 2. Digital meter 3. Barometer
-
Source: Personal Compiling (Private Document)
Table 2 explains the mandatory systems and instruments to be used during testing. The process read by the instruments in each system is recorded and collected, then processed to determine the performance of the power plant unit. ASME PTC 46 requires a minimum number of data samples to be met and a stabilization time for the power plant unit. Table 3 explains the stabilization time and minimum testing time required by the Code.
Table 3. Stabilitazation and Test run
Type of Power Plant Stabilization Test Run
Gas fired boiler 1 hour 2 hours
Oil fired boiler 1 hour 2 hours
Pulverized coal-fired boiler 1 hour 2 hours Fluidized bed combustor 24 hours* 4 hours Simple cycle with heat recovery 1 hour 1 hour
Combined cycle 1 hour 1 hour
Reciprocating engines 1 hour 4 hours
*If chemical stability has been satisfied, then testing may commence one (1) hour following the achievement.
Source: Personal Compiling (Private Document)
Based on Table 3, PLTP LMB 1 belongs to the simple cycle with heat recovery type of power unit, which requires a minimum test duration after stabilization of not less than 2 hours. The minimum number of data samples for each instrument during the test is at least 30 data samples from the total test duration after stabilization. To obtain good and compliant sample data, a recording period of 1 data reading per 4 minutes per instrument sensor is determined.
3. Results and Discussion Turbine performance
Based on the results of the study and data processing, the performance trend condition of the turbine of PLTP LMB 1 was obtained as shown in Figure 3.
Fig3. Trend of turbine isentropic efficiency Source: Personal Graph (Private Document)
Figure 3 shows a trend of decreasing isentropic efficiency of the PLTP LMB 1 turbine when compared to the design or commissioning represented by the blue line. However, the decrease in efficiency contrasts with the isentropic power, which tends to increase when compared to commissioning or design.
Further investigation and analysis were carried out to determine the conditions using data from Table 4.
Table 4. Entalphy and Entrophy conditions
Parameter Condition Current Guarantee Commissioning
Steam flow rate 404.052 388.224 397.8
Pressure (bara)
2 (inlet turbin)
5.20 5 5.15
Enthalpy (kJ/kg) 2749.83 2748.11 2749.16
Entrophy (kJ/kg.K) 6.81 7.00 6.87
Pressure (bara) 3
(outlet turbin)
0.0659 0.0673 0.0673
Isentropic Enthalpy (kJ/kg) 2106.28 2089.93 2102.27
Delta enthalpy (2 – 3s) (kJ/kg) 643.56 658.18 646.89
Source: Personal (Private Document)
Based on the Table 4, it is known that the decrease in turbine efficiency is caused by a decrease in isentropic enthalpy delta (2-3s). This change is due to a change in the operating pattern of the inlet steam pressure of the power plant unit. This change in pattern cannot be optimally compensated by the turbine, resulting in a decrease in turbine isentropic work.
Correction faktor and thermal performance parameter
Correction factors such as steam pressure correction factor, non-condensable gas percentage, wet bulb temperature, and power factor are required. The correction factor data and compliance with the requirements are presented in Table 5.
Table 5. Correction factor
Correction factor Value Threshold Result
Gross 1.0004387% ± 1.5% Accepted
Net 1.0002639% ± 1.5% Accepted
Source: Personal (Private Document)
Based on the data, the correction factors can be used to correct the values of the power plant's thermal performance, which include gross power, net power, gross plant heat rate, and net plant heat rate as shown in Tables 6 and 7.
Table 6. Corrected power 85
84
83,81 83
82,73 81,9
70,32
71,48
72
69 69,5 70 70,5 71 71,5 72 72,5
80 81 82 83 84 85 86
G U A R A N T E E C O M M I S S I O N I N G T E S T isen turbin Overall
Isent power
Based on Table 6, it can be inferred that the correction value for net power is higher compared to the value during commissioning with the same electrical generation setting. This indicates an increase in electricity production after the first year inspection was carried out.
Table 7: Plant heat rate and specific mass consumption
Parameter Calculation Values Guaranteed Values Commissioning Values Corrected gross heat rate GPHR 18,041kJ/kWh 18,112kJ/kWh 18,768kJ/kWh Corrected net heat rate NPHR 18,923kJ/kWh 19,009kJ/kWh 19,141kJ/kWh Gross spesific mass consumption
GSMC
6.56 ton/MW 6.85 ton/MW 6.992 ton/MW Net spesific mass consumption
NSMC
6.881 ton/MW 7.059 ton/MW 7.016 ton/MW
Table 7 shows that the gross plant heat rate and net plant heat rate values after first-year inspection have decreased. In concept, this indicates a decrease in the amount of heat energy (kJ) needed to generate 1 kWh of electrical energy. Therefore, due to the decrease, it is concluded that there has been an increase in the effectiveness of the absorption of heat energy generated into electrical energy by the power generation unit. The analysis of the decrease is very likely due to the first-year inspection activity which focused on vacuum system correction. With the improvement in the vacuum system, the process of generating electrical energy became more optimal, as evidenced by the decrease in NPHR values.
Based on Table 7, it is known that the values of gross specific mass consumption and net specific mass consumption during the testing period were smaller than the warranty values and values during commissioning. The smaller values compared to commissioning values may indicate an improvement in the working system of PLTP LMB 1 after the first year inspection. With a smaller ratio of steam usage per 1 MW of electricity generated, it indicates that the fuel absorption and utilization system is becoming more efficient. Based on the calculation and analysis of the thermal performance of the PLTP LMB 1 power plant, it can be concluded that the first year inspection activities carried out can maintain and improve the effectiveness of the absorption and utilization of thermal energy by the PLTP LMB 1 power plant.
4. Conclusion
The first year inspection conducted by PLTP LMB 1 effectively maintains the thermal performance of the plant compared to commissioning data. Based on calculation and assessment data, it is concluded that PLTP LMB 1 can generate an output power above 55 MW with net plant heat rate, gross heat rate, and specific net consumption values lower than the commissioning or warranty conditions. This indicates that the performance of PLTP LMB 1 is in good condition with net plant heat rate, gross heat rate, and specific net consumption values of 19,009 kJ/KWh, 18,112 kJ/KWh, and 7.059 ton/MW respectively, at a net power output of 56.417 MW. However, the isentropic turbine efficiency value of PLTP LMB 1 has decreased compared to the design and commissioning values by 1.9% and 0.83% respectively. This value due to the sub-optimal turbine system in absorbing thermal energy contained in steam at pressures above 5 bar a.
5. Acknowledgment
Authors thank PT Pertamina Geothermal Energy Area Lumut Balai, Sumatera Selatan, Indonesia for providing the research equipments and facilities and also to Research Institute and Community Service (RICS) of President University, Cikarang, Indonesia for the incentive scheme of research publication.
6. Abbreviations
ASME PTC 46: 1996 The performance test code for thermal power plants published by the American Society of Mechanical Engineers in 1996.
Correction factor The correction factor is a value used to adjust a calculation or measurement so that the corrected value is as close as possible to the design value.
Fisrt year inspection The first-year overhaul activity on the power generation unit.
Gross Plant Heat Rate (GPRH)
The thermal energy (in kJ) required to generate 1 kWh of electrical energy.
Nett Plant Heat Rate (GPRH)
The thermal energy (in kJ) required to generate 1 kWh of electricity measured at the main transformer after deducting own use.
Non – Condensable Gas Gas that cannot be condensed at the operating pressure of the condenser.
Specific Mass Consumption
The steam mass (in tons/kg) required to generate 1 MWh of electrical power.
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