Control Valve
Sourcebook —
Chemical Unit
Operations
Turbine
TopicPage
I
How It Operates . . . . . . . . . . . . . . . . . . . . . 2
II
Where Turbines are Used . . . . . . . . . . . . . . . 2
III Gas Turbine Application Review . . . . . . . . . . . 2
Photo credit: lowsun / Shutterstock.com
IV Steam Turbine Application Review . . . . . . . . . 3
Turbine
Turbine
expanding the gas at high temperature and high velocity.
Turbine section converts the thermal energy into shaft
energy and two-thirds of the energy is used to drive the
compressor. At the final stage exhaust gas can be used to
generate steam for power.
I. How It Operates
A turbine is a complex rotary mechanical device equipped
with a series of stationary and rotating blades. Mostly,
turbines are divided into three stages and an exhaust section.
Pressure drop of a high pressure gas or vapor occurs through
nozzles, diaphragms, or stationary blades. This pressure
drop creates high velocity gas or vapor that is directed at a
row of blades connected to a rotor, converting the energy
to mechanical work. There are several different types of
turbines commonly used in the chemical industry. The most
common turbines are gas and steam turbines.
1. Air Extraction Valve
The air extraction valve is used to release excess air to the
atmosphere during startup and shutdown procedures to
protect the compressor. Typically, there are up to four of
these valves.
„„ Typical Process Conditions:
—— Pressure, temperature, and flow are dependent on
process design
II. Where Turbines are Used
„„ Typical Valve Construction:
—— NPS 6 to 30 Fisher® A81, A31A, A41, A11, or 8532
valve
—— Materials of construction: dependent on process
design, typically WCC
Typical plants that use turbines include:
„„ Chemical
„„ Power
„„ Oil and gas
2. Inlet Bleed Heat Valve (IBHV)
III. Gas Turbine Application
Review
The IBHV utilizes compressed air to heat inlet air to prevent
icing during cold and humid condition. Typically the inlet
bleed heat system consists of three valves: IBHV, drain valve,
and manual stop valve. The drain and manual valves are onoff applications and the IBHV is a throttling application.
The gas turbine shown in Figure 1 is made up of several
components and systems, including: turbine, compressor,
combustor, generator, air supply, fuel skid, and lube oil skid.
„„ Typical Process Conditions:
Air is compressed in the compressor section then fuel (gas
or oil) is injected into the combustion section and fired,
—— Pressure, temperature, and flow are dependent on
process design
4
3
COMBUSTOR
FUEL SUPPLY
5
1
COMPRESSOR
TURBINE
GENERATOR
7
2
HEAT
EXCHANGER
WATER
AIR SUPPLY
6
OIL
WATER
E1173
Figure 1. Process Diagram of Gas Turbine
2
Turbine
„„ Typical Valve Construction:
—— IBHV: NPS 6x4 to 12 Fisher EW valve with
Whisper Trim™ I or equal percentage trim
—— Drain valve: NPS 2 Fisher A41 valve
—— Manual stop valve: Fisher 8560 or A11 valve
—— Materials of construction: dependent on process
design, typically Alloy 6 Whisper Trim I is used for the
IBHV, and SST material is used for the drain valve
3. Fuel Gas Control Valve
The purpose of the fuel gas control valve is to simply control
the flow of fuel to combustor. It requires a precise, linearly
characterized valve with the ability to choke very quickly at a
low pressure drop, which results in no change of Cv during a
sudden change in pressure drop.
„„ Typical Process Conditions:
—— Pressure, temperature, and flow are dependent on
process design
„„ Typical Valve Construction:
—— NPS 2 to 6 Fisher ED or ES valve with Class IV shutoff
—— Materials of construction: dependent on process
design, typically WCC with a 17-4 cage is used
4. Stop Ratio Valve (SRV)
The purpose of a SRV valve, also known as the pressure
ratio valve, is to control and supply fuel gas with a constant
upstream pressure based on various turbine loads. Failure
to maintain a constant pressure can lead to excess noise,
exhaust gas temperature variation and excess nitrogen oxide
(NOx) pollutant.
„„ Typical Process Conditions:
—— Pressure, temperature, and flow are dependent on
process design
„„ Typical Valve Construction:
—— NPS 3 to 8 Fisher V300, V200, or SS-260 valve with HD
metal or TCM metal seal, Fisher ED or ES valve with
ENVIRO-SEAL™ packing system to prevent fugitive
emission, and Class VI shutoff
—— Materials of construction: dependent on process
design, chromium carbide coated ball provides better
wear resistance
5. Purge Valve
The two main functions of a purge valve is to protect the fuel
nozzles and flush the fuel lines with air. It requires a design
that allows a small Cv when barely open and develops into a
modified equal percentage as the valve opens. Purge valves
operate in pairs in a double block-and-bleed arrangement to
prevent the hot air from interacting with the natural gas.
„„ Typical Process Conditions:
—— Pressure, temperature, and flow are dependent on
process design
„„ Typical Valve Construction:
—— Fisher CV500 valve with Class V shutoff
—— Materials of construction: dependent on process
design, typically SST body is recommended, chrome
carbide coating on the ball, nitronic 50 shaft (NACE
option) or 17-4PH shaft (High H2S concentration
could cause corrosion with 17-4PH), Alloy 6 bearing
and seal ring
6. 3-Way Temperature Regulator Valve
Purpose of 3-way temperature regulator valve is to
maintain the appropriate temperature of the oil lubricant
by controlling flow of cooling water to the lube oil heat
exchanger. Failure of this valve can affect the bearing system
reliability.
„„ Typical Process Conditions:
—— Pressure, temperature, and flow are dependent on
process design
„„ Typical Valve Construction:
—— 3-way Fisher YD valve
—— Materials of construction: dependent on process
design, typically WCC
7. Lube Oil Pressure Valve
The lube oil pressure valve is used to maintain the pressure of
the lube oil that is pumped to the bearing. A lube oil pressure
valve regulates the flow based on a control signal coming
from a downstream pressure transmitter. It provides high
lubricant pressure at low turbine speed and low lubricant
pressure at high turbine speed.
„„ Typical Process Conditions:
—— Pressure, temperature, and flow are dependent on
process design
„„ Typical Valve Construction:
—— NPS 3 to 4 Fisher easy-e™ valve, Fisher GX valve
—— Materials of construction: dependent on process
design, typically WCC
IV. Steam Turbine Application
Review
Steam turbines are utilized in a variety of industries to
capture energy associated with the expansion of process
generated steam. Turbines convert thermal energy from
steam and use it to do mechanical work on a rotating shaft.
Steam turbines are commonly classified by the condition of
the exhaust, for example non-condensing or extraction.
Non-condensing or backpressure turbines are most widely
used for process steam applications. The exhaust pressure
is controlled by a regulating valve to suit the needs of the
process steam pressure. As shown in Figure 2, high pressure
steam enters the turbine and does the work in front of
turbine and exits the turbine at the low pressure side.
3
Turbine
HIGH PRESSURE
STEAM
HIGH PRESSURE
STEAM
POWER
POWER
LOW PRESSURE
STEAM TO
PROCESS
E1174
LOW PRESSURE
STEAM TO
PROCESS
Figure 2. Non-Condensing Turbine
STEAM TO CONDENSER
E1175
Figure 3. Extraction Turbine
Extracting type turbines are also used in process steam
applications. As shown in Figure 3, high pressure steam
enters the extracting type turbine and steam is released from
various stages of the turbine. Steam from each section is
used for industrial process needs or sent to boiler feedwater
heaters to improve overall cycle efficiency. In commercial
power plants the remainder of steam is directed to the
condenser, turning the steam into water that is then recycled.
Main Steam Turbine
A steam turbine package has several components and
systems including: a steam turbine, generator, gland steam
seal system, lube oil system, shaft seal oil system, hydraulic
system, and a control system. The three areas covered in
this document are the main steam turbine, the steam seal
system, and the lube oil system.
The purpose of main steam control valve is to control the
amount of steam from the boiler or heat recovery steam
generator (HRSG) to high pressure (HP) turbine. These valves
are usually part of the turbine casing itself and are designed
and manufactured by steam turbine original equipment
manufacturer.
As shown in Figure 4, a main steam turbine consists
of several control systems and valve applications. The
valve applications for the main steam turbine section are
numbered from one to five.
1. Main Steam Control Valve
2
1
2
SHAFT
IP
PACKING
GLAND
5
5
CONDENSER
4
3
E1176
STEAM FROM HRSG
Figure 4. Process Diagram of Main Steam Turbine
4
LP
HP
LP
Turbine
2. Low Pressure (LP) Induction Admission Steam
Valves
The LP induction admission steam valve typically consists
of two valves in series. One controls the amount of steam
entering the LP turbine and the other quickly shuts off steam
to the turbine through an on-off application.
„„ Typical Process Conditions:
—— Fluid = steam
—— P1 = 50 to 150 psig (3.45 to 10.34 bar)
—— T = 500 to 700°F (260 to 371°C)
—— Q = 0 to 120,000 lb/hr or higher ( 0 to 54.3 ton/hr)
„„ Typical Valve Construction:
—— NPS 16 to 24 Fisher butterfly valve construction
—— Materials of construction: dependent on process
design, typical construction includes WCC or SST
3. Combined Reheat Intercept Valve
The combined reheat intercept valve is used to control the
hot reheat admission steam from a boiler or heat recovery
steam generator (HRSG) to the intermediate pressure section
of turbine.
„„ Typical Process Conditions:
—— Fluid = steam
—— P1 = 485 to 586 psia (33.44 to 40.40 bar)
—— T = 950 to 1050°F (510 to 565°C)
„„ Typical Valve Construction:
—— NPS 16 to 20 Fisher Large easy-e valve
—— Materials of construction: dependent on process
design, typical construction C12A and Class V shutoff
4. Packing Blowdown Valve
The packing blowdown valve slows down the turbine or
quickly discharges the turbine during a turbine trip. During
a turbine trip the main steam valve, LP induction admission
steam valve, and intercept valve will shut off, trapping
high pressure steam in the boiler and HP turbine. The high
pressure steam will flow from the HP turbine through the
packing into the IP turbine causing the turbine to spin to the
point of overspeed. In order to avoid this overspeed, flow is
diverted with the reverse flow valve.
„„ Typical Process Conditions:
—— Fluid = steam
—— P1 = 400 to 700 psig (27.57 to 48.26 bar)
—— T = 650 to 950°F (343 to 510°C)
„„ Typical Valve Construction:
—— NPS 3 to 6 Fisher HPD valve with butt weld end
—— Materials of construction: dependent on process
design, typical material construction includes WC9,
linear cage, and Class V shutoff
5. Drain Valves
The purpose of the drain valve is to collect any water from
the turbine or steam system. Drain valves will be located
throughout the system.
„„ Typical Process Conditions:
—— Fluid = water/ condensate
—— P1 = 486 to 5000 psi (33.5 to 345 bar)
—— P2 = condenser pressure
—— T = 300 to 1150°F (148.8 to 621°C)
„„ Typical Valve Construction:
—— NPS 1 to 2 metal seated valve
—— Materials of construction: dependent on process
design, typically includes a WCC, WC9, or C12 body,
316 SST/CoCr-A trim
Steam Seal Turbine
Steam seal turbine section as shown in Figure 5 consists of
the valve applications numbered from six to nine.
6. Steam Seal Regulator (SSR) Valve
The purpose of this valve is to adjust the flow of steam into
the steam seal system. It is mainly used during startup and it
is closed during normal operation.
„„ Typical Process Conditions:
—— Fluid = steam
—— P1 = main steam pressure
—— P2 = 3 to 5 psig (0.207 to 0.344 bar)
—— T = 650 to 1050°F (343 to 565.5°C)
—— Q = 0 to 50,000 lb/hr (0 to 22.68 ton/hr)
„„ Typical Valve Construction:
—— NPS 1 to 6 Fisher HP valve that may require a diffuser
or Whisper Trim due to the high pressure drop
—— Materials of construction: dependent on process
design, typically WCC, WC9, C12A, 316SST/CoCr-A
trim
7. Auxiliary Steam Seal Feed (ASSF) Valve
The ASSF valve is used to adjust the flow of steam into the
steam seal system. Supply steam for ASSF is from a secondary
source, usually the cold reheat header. If available this is used
instead of main header steam. This valve is only open during
startup.
„„ Typical Process Conditions:
—— Fluid = steam
—— P1 = 600 to 700 psig (41.37 to 48.26 bar)
—— P2 = 3 to 5 psig (0.207 to 0.344 bar)
—— T = 400 to 700°F (204 to 371°C)
5
Turbine
SPRAY WATER FROM
CONDENSATE SYSTEM
8
7
AUXILIARY STEAM
6
DS
MAIN STEAM
9
10
STEAM TO CONDENSER
OR FEEDWATER HEATER
DS
E1177
HP
IP
LP
LP
Figure 5. Process Diagram of Steam Seal Turbine
„„ Typical Valve Construction:
—— NPS 4 to 8 Fisher easy-e valve with Class IV or V shutoff
—— Materials of construction: dependent on process
design, typically WCC, WC9, C12A, 316SST/CoCr-A
trim
8 & 9. Steam Seal HP/LP Desuperheater
The purpose of this valve is to reduce and regulate the
temperature of steam entering the steam seal system. Water
from condensate system is typically used.
„„ Typical Spray Water Process Conditions:
—— P1 = 150 to 400 psig (10.34 to 27.58 bar)
—— P2 = 75 psig (5.17 bar)
—— T = 100°F (37.7°C)
„„ Typical Valve Construction:
—— NPS 1 Fisher easy-e valve with MicroForm trim and
Class V shutoff
—— Materials of construction: dependent on process
design, typically WCC, 17-4SST cage, 416 SST plug
„„ Typical Desuperheater Selection:
—— Fisher DVI/DMA desuperheater, WCC construction
10. Steam Seal Regulator Dump Valve or Steam Seal
Diverter Valve
In this application either a steam seal regulator dump valve
or steam seal diverter valve is used. The benefit of using
the steam seal diverter valve is to maintain efficiency by
recapturing heat.
Steam Seal Regulator Dump Valve
The steam seal regulator dump valve is used to maintain the
pressure of the steam steal system by regulating the flow of
excess steam that is discharged to the condenser. This valve is
typically closed throughout startup. As turbine load increases
6
and steam leakage from the HP packing increases, this valve
is opened to allow excess seal steam to exit to the condenser.
„„ Typical Process Conditions:
—— Fluid = steam
—— P1= 3 to 5 psig (0.207 to 0.344 bar)
—— P2 = condenser pressure
—— T = 500 to 600°F (260 to 315.5°C)
—— Q = 0 to 50,000 lb/hr (0 to 22.68 ton/hr)
„„ Typical Valve Construction:
—— Fisher Vee-Ball™ valve, Class II shutoff
—— Materials of construction: dependent on process
design, typically WCC or SST
Steam Seal Diverter Valve
Steam Seal Diverter Valve is used to maintain the pressure of
the steam steal system by diverting the flow of excess steam
to the condenser or feedwater heater. Diverting the flow
to feedwater heater helps to recapture the heat and hence
increase efficiency of the turbine.
„„ Typical Process Conditions:
—— Fluid = steam
—— P1 = 3 to 5 psig (0.207 to 0.344 bar)
—— P2 = condenser pressure
—— T = 500 to 600°F (260 to 315.5°C)
—— Q = 0 to 50,000 lb/hr (0 to 22.68 ton/hr)
„„ Typical Valve Construction:
—— 3-way valve
—— Materials of Construction: dependent on process
design, typically WCC
Turbine
RESERVOIR
13
11
12
E1178
HP
IP
LP
LP
Figure 6. Process Diagram of Lube Oil System
Lube Oil System
Lube oil system valve application as shown in Figure 6 is
numbered from eleven to thirteen.
11. Back Pressure Valve
The back pressure valve is used to control amount of lube oil
that is being sent to oil reservoir.
„„ Typical Process Conditions:
—— Fluid = oil
—— P1 = 100 to 400 psig (6.89 to 27.58 bar)
—— P2 = 25 to 30 psig (1.72 to 2.07 bar)
—— T = 70 to 160°F (21 to 71°C)
—— Q = 60 to 700 lb/hr (0.027 to 0.317ton/hr)
„„ Typical Valve Construction:
—— NPS 3 Fisher easy-e valve or Fisher GX valve
—— Materials of construction: dependent on process
design, typically WCC
12. Lube Oil Pressure Valve
The lube oil pressure control valve is self-operating and
regulates the flow of lube oil based on a control signal
coming from a downstream pressure transmitter.
„„ Typical Process Conditions:
—— Fluid = oil
—— P1 = 100 to 400 psig (6.89 to 27.58 bar)
—— P2 = 25 to 30 psig (1.72 to 2.07 bar)
—— T = 50 to 160 °F (10 to 71°C)
—— Q = 60 to 700 lb/hr (0.027 to 0.317 ton/hr)
„„ Typical Valve Construction:
—— NPS 2 to 4 Fisher easy-e valve or Fisher GX valve
—— Materials of construction: dependent on process
design, typically WCC
13. Temperature Control Valve
The purpose of this valve is to control the temperature of the
lubricant as it can affect bearing system reliability.
„„ Typical Process Conditions:
—— Fluid = cooling water
—— P1 = 150 psig (10.34 bar)
—— P2 = 135 psig (9.31 bar)
—— T = 70 to 150°F (21 to 65.5°C)
„„ Typical Valve Construction:
—— Fisher GX 3-way valve or Fisher YD valve
—— Materials of construction: dependent on process
design, typically WCC
7
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D352317X012 / MBB55 / Jul15
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