Redesign of Hydraulic Cylinder for Muara-Karang Combined-Cycle Power Plant to Improve Admission Control Valve’s Reliability Amalia Fathia, Antonio Febrianta Maha, Indra Surya Dinata, Ngapuli I. Sinisuka School of Electrical Engineering and Informatics Institut Teknologi Bandung Bandung, Indonesia [email protected], [email protected], [email protected], [email protected] Mujiyono, Winarko, Subroto Muliar W. Fauzi Leilan, Tania Revina, Iman Dimassetya PT. Pembangkitan Jawa Bali Muara Karang, Jakarta, Indonesia Abstract—Admission control valve (ACV), as one of the crucial component in steam generator, requires reliable control and high efficiency to assure system’s production operation in a combinedcycle power plant. Muara Karang power plant utilizes such device to control steam supply to the steam turbine generator (STG). Field data have shown that the performance of the existing ACV device is unsatisfactory and uses up too much hydraulic oil for its operation caused by oil leakeage from one of the broken seal component. Doing corrective maintenace for this device will cause steam turbine derating up to 25 MW. Thus, studies on increasing valve’s reliability and eliminating unwanted products affecting the environment due to oil leakage is required. This paper presents a modified ACV design, considering the valve’s structure and its component’s material. Discussions in this paper are based on the impact towards operation’s financial benefit, or decreasing spending in oil supply, and the environmental benefit. The impact of the new design was studied to gradually get the optimal design, hence was tested and proven more robust, reliable and suited for Muara Karang combined-cycle plant. steam flow produced in the Heat Recovery Steam Generator (HRSG) to the LP steam turbine in PLTGU Blok 1 Muara Karang. The ACV itself is a throttling valve that is required to operate and maneuver continuously to increase or decrease load for as long as the steam generator unit is online. With the rapid development of technology and industries, the demand for electricity is inevitably increasing, thus, reliability from generation units as the main electricity producers and suppliers is needed. One problem found in the Muara Karang Plant is the ACV operation, resulting decrement of electricity supply, are caused by: (1) breakdown in rod seal piston; and (2) oil leakage in the rod seal. This paper is organized as follows: in section II and III, a background on Muara Karang plant and ACV operation is given. Section IV describes the proposed method and section V gives the obtained results by the applying the proposed method. The paper is concluded in section VI. Keywords—admission control valve (ACV), combined-cycle power plant, valve design, hydraulic valve II. MUARA KARANG COMBINED-CYCLE NOMENCLATURE ACV CCPP HPU HRSG MCV STG admission control valve combined cycle power plant hydraulic power unit heat recovery steam generator main control valve steam turbine generator I. INTRODUCTION Muara Karang Power Plant is the most important electricity supplier to Indonesia’s capital, Jakarta, and its capital buildings such as Istana Negara, MPR/DPR building and Soekarno Hatta Airport. Operated by the Indonesia’s state owned electricity company PLN, sub division Jawa-Bali Generation aka Pembangkit Jawa-Bali (PJB), Muara Karang owns two steam power plants and a combined-cycle plant consisting of 5 gas turbines and 4 steam turbines with total capacity of 1200 MW. The operation of the CCPP is inseparable to the use of the admission control valve (ACV), which functions to control Muara Karang is a combined-cycle power plant consisting of two main units: gas turbine generator (GTG) and steam turbine generator (STG). In the Block 1 CCPP, the GTG consists of 3 units, each having a capacity of 105 MW. The STG have a capacity of 185 MW, totaling to 500 MW total capacity in the Block 1 CPP. Additionally, Muara Karang has a HRSG unit to maximize the efficiency in a CCPP. The process begins in the GTG, where the GTG is supplied with gas with very high temperature that spins the gas turbine. The fast-spinning turbine drives the generator that converts the spinning energy to electricity. Excess heat from the process is sent to the HRSG through the exhaust plenum to be further utilized. The HRSG contains fin tubes where water is circulated with a pump and absorbs heat from the gas exhaust through several levels including economizer, evaporator, and super heater. The steam generated is then sent to the STG. The STG consists of 2 level turbine, which are high pressure (HP) turbine and low pressure (LP) turbine. The steam that goes into the turbine is regulated by a valve, namely the main control valve (MCV) that regulates steam to the HP turbine and ACV that regulates the LP turbine. These valves are a hydraulic-type valve that receives hydraulic power from the Hydraulic Power Unit. of the ACV, while the closing of the ACV relies on the spring pressure that is designed with the valve in the normally closed position. The valve is initially in the closed position so that when interruptions occur (STG tripping or even blackout), the ACV can immediately secure the turbine by quickly closing and blocking the steam flow without relying on the hydraulic supply from the HPU unit. Fig. 1. Steam turbine gas flow diagram Fig. 3. Admission control valve Hydraulic Power Unit (HPU) is a unit that produces hydraulic power as a driving force for MCV or ACV. It has a main tank that holds hydraulic oil, synthetic phosphate ethyl ester, which have a very corrosive property. HPU has two pump-type pistons installed redundantly to increase reliability and for easier maintenance. Each pump has its own filter in both on the suction and the discharge side of the pump. HPU pump is a rotary type pump with 9 pistons and can produce hydraulic oil pressure up to 136 kg / cm2. The hydraulic pressure required to drive MCV and ACV is only 105 kg/cm 2. The HPU pump will continue to operate continuously to maintain the opening position of MCV and ACV. Currently, steam flow to STG due to ACV opening can only produce maximum of 135 MW of STG load, as shown in Fig. 2. This indicates low availability factor caused by the hydraulic oil leakage. IV. MODIFICATION METHOD The target of the company’s reliability and efficiency management is to ensure that equipment are able to work automatically, reliably, safely, efficiently, and does not experience derating. Using analytical method based on the Pareto Chart show in Fig. 4, modification was focused based on the problem with the piston seal and rod seal leakage since it causes the most frequent damage in ACV. Other problems such as valve jamming, line leakage or servo damage occurs less frequently and less dominant compared to the seal leakage, thus was not further analyzed in this paper. Fig. 4. Pareto chart Fig. 2. STG load vs. ACV opening before modified III. ADMISSION CONTROL VALVE Fig. 3 shows the construction of the existing design of the ACV. ACV regulates LP steam produced by the HRSG unit to the LP steam turbine in the STG Blok 1 Muara Karang. The hydraulic actuator utilizes hydraulic power, facilitated by the HPU, to control the opening of the butterfly-type valve. The servo valve works by regulating the flow of hydraulic oil entering the cylindrical chamber on the hydraulic actuator. Hydraulic supply is only required during the opening operation To further inspect the root cause of damage in ACV, the Fishbone Diagram, shown in Fig. 5, breaks down the main category that details the causes that contribute to the damage. These categories include machine, workforce, operational, materials and methods that played major role in the ACV operation and assembly. The first root of ACV damage was due to the location of hydraulic supply. The located hydraulic supply was prone to heat exposure that impacted the hydraulic component’s material, such as the seal kit. Furthermore, the steam unit operated as a peaker generation and must require all components to be compatible with the system’s operation. From Fig. 5, it is concluded that the ACV becomes unreliable due to the leakage in the seal due to the material that cannot withstand heat exposure and incompatibility with the hydraulic oil composition. Fig. 5. Problem definition fishbone diagram Preliminary data: Admission Control Valve(ACV) life time & performance Problem : Hydraulic oil leak due to damage in seal rod and seal piston in cylinder actuator 1. 2. Field data : Damage in seal rod and seal piston due to heat exposure from steam that flows through valve s stem and body. Design of cylinder actuator positions hydraulic supply inside and near stem valve. Field study : Analyze the cylinder actuator design & seal rod and seal piston material Choose appropriate seal rod and seal piston material Redesign of cylinder actuator Assemble ACV with new cylinder actuator design and seal rod & seal piston material Verification : ACV Operation Implementation : Employment of redesigned cylinder actuator with new seal rod dan seal piston material Fig. 6. Admission control valve design process The flow diagram of determining the design can be seen in Fig. 6. The limitations to be considered in the design of the system is not to alter the whole existing system, but to increase the reliability of the ACV operation by minimizing all the effects of its operation failures, including: 1. Maintaining spring design in normaly close position. It is intended that when STG trips or even blackout, the ACV can immediately secure the turbine quickly by closing and blocking the steam flow to the turbine without the hydraulic supply from the HPU unit. 2. Replace the seal kit material with material that is more resistant to chemical exposure. The hydraulic oil used is very specific and derived from highly reactive phosphate ethyl ester oil. The oil is not only reactive to iron or rubber material. 3. Changing the design of the hydraulic actuator cylinder. This aims at the hydraulic supply manifold to avoid being exposed to heat from steam propagating through the valve stem when a gland-packing leak occurs at the ACV valve. A. Material Selection Materials used for the valve components have to withstand many stress cycles of steam flow, pressure, and temperature changes. Material used in the existing design consist of Fluorocarbon type A. With the problem in oil leakage and rod seal damage, the material chosen as a substitute in the initial design is Perfluoroelastomer due to its following characteristics : High temperature resistance Excellent chemical resistance Low out gassing Chlorine wet/dry Petroleum oil Chlorinated hydrocarbons B. Actuator Design Analysis Modification is done by relocating the hydraulic actuator part, where in the initial design the hydraulic supply manifold is in the inner position and adjacent to the stem valve. This has a risk of heat exposure from steam in the event of a glandpacking leak in the ACV valve. Since the supply position is on the inner side, piston rod requires a seal so that hydraulic oil does not leak through the piston rod. To avoid rod seal damage, modifications was done by moving the position of the supply manifold on the outer side of the cylinder actuator. This design has several advantages: • Damage to the seal kit due to heat exposure can be minimized. • The rod seal in the new design no longer functions as a pressurized hydraulic oil seal but is installed for safety. In case of leakage in piston seal, hydraulic oil will not flow to the drive module but is drained directly to the allocated drain hole. V. RESULT AND DISCUSSION The hydraulic supply manifold in the initial design of the ACV is on the inside of the cylinder actuator, therefore hydraulic oil is in the inboard position of the cylinder and adjacent to the body valve and stem. This design depends on the quality of rod seal and piston seal so that hydraulic oil does not leak out of the cylinder. However, the position of the manifold adjacent to the stem has risk to heat propagation exposure and is exposed directly to steam if the gland packing of the ACV leaks. The initial design of the ACV can be seen in Fig. 6. (a) (a) (b) Fig. 8. Admission control valve after redesign(a) cross section (b) actual (b) Fig. 7. Admission control valve before redesign (a) cross section (b) actual After modification, the hydraulic supply manifold of the ACV is located on the outside of the cylinder actuator; therefore the hydraulic oil is in the outboard position of the cylinder and away from the body valve and stem. This design is highly dependent on the quality of the piston seal to prevent hydraulic oil leakage out of the cylinder. In this modified design, the rod seal's role is no longer the main seal for hydraulic oil leakage, but only as a safety in the event of piston seal damage, hydraulic oil will not flow into the valve body area. The new design of the ACV can be seen in Fig. 7. With the new, modified ACV, the STG does not experience derating and have higher load as high as 161 MW; reaching the desired equivalent availability factor (EAF). Shown in Fig. 8, the opening of the valve is identical to that of the STG load. This concludes that there is no more hydraulic leakage in the process of opening and closing the ACV. STG Load vs Admission Opening STG Load Admission Opening Fig. 9. STG load vs. valve opening after modified As previously mentioned, this paper discusses the financial and environmental benefit after modifying the root cause of the problem resulting in operation derating. The financial and environmental benefits are discussed in the following subchapter A and B. A. Financial Benefit The total innovation cost consisting of: (1) constructing the manifold, (2) creating tension rod and piston rod, (3) relocating stopper spring, and (4) equipment assembly, totaled Rp. 91,000,000 (ninety-one million Rupiah). If the steam turbine generator was to operate without ACV, the operation unit will experience derating up to 25 MW within 24 hours. Therefore, potential loss can be calculated: 𝑃𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑙𝑜𝑠𝑠 = 𝑑𝑒𝑟𝑎𝑡𝑖𝑛𝑔 𝑝𝑜𝑤𝑒𝑟 × 𝑡𝑖𝑚𝑒 𝑜𝑓 𝑙𝑜𝑠𝑠 × 𝑐𝑜𝑠𝑡 𝑜𝑓 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑖𝑡𝑦 = 25.000kw × 24 hours × Rp. 830,27 = Rp. 498.162.000,-/ day = Rp. 498.162.000× 30 days = Rp14.944.860.000,-/month (1) REFERENCES      B. Environmental Impact After modifying the ACV design, potential hazard that may affect working environment was greatly minimized. Previously, hydraulic oil leakage spreading throughout the valve body and insulation blanket increases the risk of fire hazard, which may cause disturbance in the STG operation. This was solved by relocating the hydraulic supply, which in case of any oil leakage occurrence are drained in the allocated drain hole. This also reduced contamination effect of hydraulic oil leakage to the environment; where hydraulic oil leakage is categorized as toxic and hazardous waste. Additionally, due to improved operation performance from minimizing hazardous/toxic waste to the environment, company engages in the PROPER (Program Penilaian Peringkat Kinerja Perusahaan)  program or Company Assessment Performance Rating Program. PROPER encourages companies to improve their environmental management. From the PROPER evaluation, the company will acquire the reputation according to how the environment is managed. VI. CONCLUSION The location of the hydraulic manifold plays an important role in maintaining the lifetime of the ACV rod seal and piston seal. Locating the hydraulic supply manifold outside of the cylinder actuator reduces the risk of heat exposure to the piston and rod seal. The proposed material, Perfluoroelastomer, for rod seal and piston seal was proven more suitable with the temperature and characteristic of the hydraulic oil. The proposed solution increased the operation reliability of the environmental The research data was provided by PJB PLN Muara Karang.  (2) and ACKNOWLEDGMENT  The total cost saving for maintenance: Cost of seal kit = Rp. 5,000,000 / set/ month Cost of hydraulic oil = Rp. 60,000,000 / drum/ month Thus, total saving after the ACV modification is: 𝑠𝑎𝑣𝑖𝑛𝑔 = (𝑙𝑜𝑠𝑠 𝑐𝑜𝑠𝑡 + 𝑚𝑎𝑖𝑛𝑡𝑒𝑛𝑎𝑛𝑐𝑒 𝑠𝑎𝑣𝑖𝑛𝑔) − 𝑖𝑛𝑛𝑜𝑣𝑎𝑡𝑖𝑜𝑛 𝑐𝑜𝑠𝑡 =(14.944.860.000 + 65.000.000) – 91.000.000 = Rp. 14.918.860.000,-/month ACV, therefore prevents derating contamination due to oil leakage. “UNIT PEMBANGKITAN.” PT Pembangkitan Jawa Bali, www.ptpjb.com/unit-pembangkitan/. “O-Ring Material Quick Reference Guide - Rubber Sealing Materials.” Marco Rubber, www.marcorubber.com/materialguide.htm. Sors F, Holm P, Eriksson B, Ölvander J. Development of Steam Turbine Inlet Control Valve for Supercritical Pressure at Siemens Industrial Turbomachinery AB. Linköpings Univ, Maskinkonstruktion 2010 Pondini, M., et al. “Steam Turbine Control Valve and Actuation System Modeling for Dynamics Analysis.” Energy Procedia, vol. 105, 2017, pp. 1651–1656. General Electric, 1995, “Steam Turbine Operation Training Manual volume I”, Muara Karang Combine Cycle Power Plant Mutama KR. Some Aspects of Steam Turbine Valves: Materials, Operations and Maintenance. ASME. ASME Power Conference, Volume 1: Fuels and Combustion, Material Handling, Emissions; Steam Generators; Heat Exchangers and Cooling Systems; Turbines, Generators and Auxiliaries; Plant Operations and Maintenance ():V001T04A009. PROPER, proper.menlhk.go.id/portal/.