A Study Analysis of Micro-Hydro Powerplant (MHPP) Potential from Cooling of Steam Turbine
Yayak Triasdian
PLN Unit Pelaksana Pembangkitan Timor, PT PLN (Persero) Unit Induk
Wilayah Nusa Tenggara Timur Kupang, Indonesia [email protected]
Rachmat Sriwijaya Departement of Mechanical and Industrial Engineering, Faculty of Engineering, Gadjah Mada University
Yogyakarta, Indonesia [email protected]
Halomoan Parningotan PLN Unit Pelaksana Pembangkitan Timor, PT PLN (Persero) Unit Induk
Wilayah Nusa Tenggara Timur Kupang, Indonesia [email protected]
Muslim Mahardika Departement of Mechanical and Industrial Engineering, Faculty of Engineering, Gadjah Mada University
Yogyakarta, Indonesia [email protected]
Bambang Triatmodjo Departement of Civil and Environmental Engineering, Faculty of
Engineering, Gadjah Mada University Yogyakarta, Indonesia [email protected]
Muhammad Akhsin Muflikhun Departement of Mechanical and Industrial Engineering, Faculty of Engineering, Gadjah Mada University
Yogyakarta, Indonesia [email protected]
Abstract— Recently, the design of renewable energy power plants have been developed worldwide due to its better offering than conventional fossil fuels to meet the green and environmentally-friendly goal. Consideration in the improvement of micro-hydro as one of several types of renewable energy will take part in the decrease of greenhouse gas emissions. In this study investigation of micro-hydro potential at selected locations in coal-fired power plant, Kupang-Indonesia. The design of a potential head and water discharge to be converted into a micro-hydro system. The water discharge that comes from-outlet of a condenser of the steam turbine will be used to generate of micro-hydro powerplant. The water that to be used in MHPP may be one of the major weaknesses due to its characteristic could affect corrosion.
Compared to MHPP common systems, that shown inefficient operation in the feasibility overview due to several issues like sediment problem, instability grid, water availability, uneconomic grid, and high cost of construction. The study revealed that the turbine type at water discharge 1.91 m³/s and head 10 meter was crossflow. Consideration of the micro-hydro scenario, a minimum required diameter of the penstock pipe to transfer outlet cooling from the steam turbine in place of 1 m.
Besides, the configuration turbine design includes the outside diameter of the turbine, and a total of turbine blades are 0.775 m and 18 to generate 112 kW of electricity. Based on the literature study, calculation, and simulations, all the designs proposed could lead to lower emission gas, the power consumption of coal-fired power plants, and cost production.
Keywords—micro-hydro, power, electricity, environment I. INTRODUCTION
Electricity is an essential public need in this era, as population growth is the main cause of increasing electrical energy needs. The electricity can be generated with several types of power generation based on their main source of fuel.
In remote areas, such as Indonesia which is a country that consists of many islands caused limited electricity. To solve this problem, consideration of developing renewable power plants should be higher than a conventional power plant to generate environmentally and low-cost electricity. One of several types of renewable power plants is hydropower.
Besides, the oldest version of renewable energy sources used to generate electricity, whereby it has well-known itself as the
commonly available one around the world, offering 19% of the earth's electricity. Furthermore, it is the most effective one with minimal impact [1]. In worldwide, around 150-200 GWe of small hydropower potential is estimated, and lastly, only 20% of them have been developed [2].
In micro-hydro development, the consideration of water flow availability and the terrain is one of the most priority- steps in planning [3]. In such condition areas, micro-hydro powerplant systems are the best solutions [4] in which wastewater from the cooling of the steam turbine at a reservoir is directed into penstock pipe and rotate the hydro turbine where the potential head of dam converts into kinetic energy and changed becomes the electrical power. Haidar study [5] has classified hydro turbine concerning capacity as follows in Table I.
The potential of micro-hydro powerplants (MHPP) as a source of renewable energy has been explored in this current work. Where the potential source comes from water cooling of the steam turbine of coal-fired power plants that still have potential head and high water discharge to be converted to other kinetic energy. This development system is a unique configuration in micro-hydro powerplant (MHPP) that enables the cooling of a steam turbine to become its prime mover instead of the commonly generated, such as waterfall [6], river [7]–[9] as the kinetic energy. It is also a gold possibility for improving efficiency in coal-fired power plant itself by reducing power consumption in the entire system cause of lower coal consumption. On the other hand, based on RUPTL 2019-2028, the minimum renewable energy mix target of 23% in 2025 has been encouraged to achieve by the ministry of energy and mineral resources. This research proposal was planned to build a renewable powerplant in Bolok coal-fired steam turbine area at Kupang, which has a potential head and water discharge. The proposed location is shown in Fig. 1 as a solution for reducing emission problems.
2020 International Conference on Technology and Policy in Electric Power & Energy (ICT-PEP)
TABLE I. CLASSIFICATION OF HYDRO TURBINE’S CAPACITY
No Capacity Type of hydro
1 >100 MW Large
2 25001 kW - 100 MW Medium
3 2001 kW - 25 MW Small
4 0.101 MW – 2 MW Mini
5 5 kW – 0.1 MW Micro
6 <5 kW Pico
Fig. 1. Map of micro-hydro proposed location
The integration of several interconnection technologies into an MHPP system required a role from top stakeholder to take priority economic with important trade-offs between operating cost and capital [10]. In such a case, renewable components mostly have higher capital but lower operating cost, rather than conventional energy has lower capital but a higher operating cost and technically have maintenance costs periodically. By combining conventional and renewable energy can create a new hybrid system that brings friendly environmental impact and lower cost in energy production.
Thus, the most significant emissions such as CO2, NOx, and CO that affect the greenhouse gasses and global warming impact, decreased [11]. Micro-hydro production is sensitive enough to short- and long- term climatic variability [12].
The main objective of this study was to evaluate the potential of the MHPP system to gain efficiency in the entire system of the coal-fired power plant and to predict a decrease in power consumption that affect environmental impacts.
TABLE II. NOMENCLATURE
II. MATERIAL AND METHODS
According to the available potential energy at the site, analyzing and optimizing the work of an MHPP divided into some steps to be conducted, includes (1) study literature (2) data collection (3) data analysis (4) processing and planning of an MHPP. The water discharge data, taken from a distributed control system (DCS) datasheet based on daily operation. The length of the pipe and head Netto of the reservoir to tailrace was measured by GPS calculation and manual measurement using the Bosch GLM 250 VF tool.
III. ANALYSIS AND DISCUSSION A. Data Collection
Water Discharge
To determine the energy potential at the site, water discharge data are required. The water discharge data were collected between March 2017 till March 2019 in daily operation. The flow graphic which depicted the variation of time has been plotted and shown in Fig 2. From these data, it looks at data number 14 is the highest rate of water discharge of 6,883 ton/hour.
Head Netto
The head Netto value was obtained by 2 different approaches. The height of the tailrace and water level in the reservoir was defined by map altitude observation compared to manual measurement using the Bosch GLM 250 VF tool and Garmin GPS about 10 meters of the head Netto for both measurements. As shown in Fig. 3 [13], the type of micro- hydro turbine recommended was crossflow.
Fig. 2. Graphic of Water Discharge
Fig. 3. Turbine application chart Nomenclature
Q Water discharge ρ Water density D Diameter of penstock
D₂ The outside diameter of the turbine blades
g Gravity
D₃ Inside diameter of the turbine blades
H Head
r The radius of curvature of the turbine N Total of turbine blade
𝑡𝑝 Penstock thickness P Power of electricity
n Manning pipe coefficient for HDPE L Pipe length
K The distance of each turbine blade
B. Data analysis
Power output
The efficiency of the turbine-generator in the range from 80-95 percent respectively depends on the turbine-generator type [14]. In this study, the generation of electrical energy has been determined, using the total efficiency value that was obtained by referring to Nasir study in 2014 and assumptions for the penstock, gearbox, and transmission efficiency of about 0.6. Based on Table III that water discharge of 1.91 m³/s with the Head Netto of 10 meters can produce with the optimum result of 112 kW, refer to the equation (1). The experience after installation of MHPP considered, that Head Netto would decrease and affected the generated power lower than theoretical calculation [15].
TABLE III. PARAMETER OF POWER OUTPUT
Parameters Symbol Value Unit
Water density ρ 1000 kg/m³
Head Netto H 10 meter
Water discharge Q 1.91 m³/s
Total efficiency ƞ 0.6 -
Gravity g 9.8 m²/s
𝑃 = 𝜌 𝑄 𝑔 ℎ ƞ
𝑃 = 1000kg
m3𝑥 1.91m3
s 𝑥 9.8𝑚²
𝑠 𝑥 10 𝑚 𝑥 0.6
𝑃 = 112,308 𝑤𝑎𝑡𝑡 = 112 𝑘𝑊
Penstock
To determine the penstock pipe diameter, several parameters used were shown in Table IV. Using equation (2) and the parameters in Table IV, the pipe diameter was then calculated. The result of the penstock pipe diameter is 0.868 m or 1 m.
𝐷 = 2,69 [𝑛2𝑥 𝑄2𝑥𝐿
𝐻 ]⁰·¹⁸⁷⁵ (2) 𝐷 = 2,69 [0.0112𝑥 1.912𝑥 54.5
10 ]
0.1875
= 0.868 or 1 m The wall thickness of the penstock depends on the pipe material, its tensile strength, pipe diameter, and the operating pressure. High-Density Polyethylene (HDPE) would be more recommended material of the penstock pipe, due to its corrosion resistance ability [16] also lower cost than stainless steel type. The minimum wall thickness is recommended as :
𝑡𝑝 = [𝐷+508
400 ] + 1.2 (3)
𝑡𝑝 = [868 𝑚𝑚 + 508
400 ] + 1.2 = 4.64 𝑚𝑚
TABLE IV. PARAMETER OF PENSTOCK PIPE
Parameters Symbol Value Unit
Pipe length L 54.5 Meter
Head Netto H 10 Meter
Water discharge Q 1.91 m³/s
Manning pipe coefficient HDPE n 0.011 -
Crossflow turbine design
Crossflow turbine is a type of impulse turbine, that allows water entering the turbine blade from one side, crosses through the middle and out from the other side [17]. This turbine has several main advantages includes easy maintenance, a better efficiency curve than two other types (Kaplan and Francis), and low price [18]. By using equation (4), where outside diameter (D₂) and width of the turbine blade (L) was obtained 0.775 m.
𝐿𝐷₂ = 2.62 𝑥 𝑄
√𝐻 (4) 𝐿𝐷₂ = 2.62 𝑥 1.91
√10 = 1.55 𝑚² 𝐿 = 𝐷₂ = 1.55
2 = 0.775 𝑚
with the outside diameter of 0.775 m, inside diameter of runner turbine was 51.67 cm based on equation (5) below:
𝐷₃ = 2
3𝑥 𝐷₂ (5)
𝐷₃ = 2
3𝑥 77.5 𝑐𝑚 = 51.67 𝑐𝑚
The distance of each turbine blade (K) was then calculated using equation (6) obtained 13.49 cm.
𝐾 = 0.174 𝐷₂ (6)
𝐾 = 0.174 𝑥 77.5 𝑐𝑚 = 13.49 𝑐𝑚
The total of the turbine blade (N) was calculated using the equation (7) obtained 18.
𝑁 = 𝜋 𝑥 𝐷₂
𝐾 (7)
𝑁 = 3.14 𝑥 77.5 𝑐𝑚 13.49 𝑐𝑚 = 18
To determine for the radius of curvature of the turbine blade using equation (8) was 12.6 cm.
𝑟 = 0.163 𝑥 𝐷₂ (8)
𝑟 = 0.163 𝑥 0.775 𝑚 = 0.126 𝑚 = 12.6 𝑐𝑚 All data analysis above is converted into the below design scheme of an MHPP as shown in Fig 4.
Fig. 4. Micro-hydro scheme
Analysis of power consumption and coal consumption for coal-fired power plant
Utilization of micro-hydro powerplant output with estimation factor capacity 60% in a year, could decrease power consumption, and coal consumption in generating electric power also reduces the cost of production simultaneously as shown in Fig. 5 illustration.
The bar graph in Fig. 5 shows that it enables efficiency can be beneficial for generating gross production of electricity.
The bar graph in Fig. 5 show that the power consumption can be reduced by about 5.6%. Increasing efficiency in power consumption would lead to lower fuel consumption inside the furnace of coal-fired power plants and lower emission also cost of production in the illustration as shown in Fig. 6.
Based on the data as shown in Fig. 6, we can estimate that even electricity production is set to be stable (same), the SCC can be reduced as same as the emission. This reduction is directly related to the cost efficiency and gain a huge difference in the supply-demand of the company. Moreover, the reduction of the emission is also related to the environmental issue that we also show in the present study.
Efficiency can push the pollution issue into its minimize.
The performance of the steam turbine cooling system is determined by one of the parameters, it is called cooling water flow. The steam turbine cooling water has a significant role in generating total capacity for this MHPP system due to its velocity and differential height. The higher performance of the turbine cooling system, the higher efficiency in the MHPP system. On the other hand, the steam turbine cooling system performance may decrease due to the height of the reservoir to affect the cooling flow of the steam turbine becomes slower.
Fig. 5. Power consumption simulation effect
Fig. 6. Coal consumption simulation effect
The differences between this project and the general system in micro-hydro powerplant were discussed. The cooling of the steam turbine is being used taken from seawater. Based on several studies, seawater could affect corrosion on metal [19], it may probably the major weakness of this paper. Compared to MHPP common systems, that have several issues such as uneconomic grid, water level [20], high cost of construction [21], unavailable of grid power [22], grid instability [23], sediment problem [24] revealed that micro- hydro potential from the cooling of steam turbine is less of the problem which can bring the further issue and higher capital cost than common MHPP.
IV. CONCLUSION
Based on literature studies, data collection, and data analysis, a pre-feasibility study was conducted by converting water discharge of 1.91 m³/s and potential head of 10 m could generate micro-hydro powerplant (MHPP) at Kupang is up to 112 kW to decrease coal consumption, cost of production and lower environmental impact. With configuration parameters including the outside diameter of the turbine, a total of the turbine blades and penstock pipe diameter are 0.775 m, 18, and 1 m respectively.
ACKNOWLEDGMENT
The authors wish to express special thanks to PT PLN (Persero) Unit Induk Wilayah Nusa Tenggara Timur, Departement of Mechanical and Industrial Engineering and Departement of Civil Environmental Engineering, Faculty of Engineering, Gadjah Mada University for funding this work and technical discussion.
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