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180531 ACV

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
admission control valve
combined cycle power plant
hydraulic power unit
heat recovery steam generator
main control valve
steam turbine generator
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
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
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
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.
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
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
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
• 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.
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.
Fig. 8. Admission control valve after redesign(a) cross section (b)
Fig. 7. Admission control valve before redesign (a) cross section (b)
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
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) [7] 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
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
The research data was provided by PJB PLN Muara Karang.
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,
“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.
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/.
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