41-183 Level Instrumentation for Steam Generation

LEVEL INSTRUMENTATION FOR STEAM GENERATION
Level
L1
L2
ACTUATED
S p e c i a l A p p l i cat i o n S e r i e s
2
The Power of Steam
Steam is today’s utility player in the industrial
Steam is ubiquitous because it’s industry-friendly. It’s
energy arena. It cleans and sterilizes, dries and
intrinsically safe, flexible, economical, aseptic, and
concentrates, separates and evaporates. In cookery,
environmentally benign. Steam can arise from fossil
it preserves flavor, texture, and retains nutrients. In
fuels, biomass or biogas. Its high efficiency is due to its
chemistry, it fosters reactions by controlling process
ability to return a significant portion of condensate to
pressure and temperature. In biotechnology, it’s essen-
the generation cycle. With proper maintenance, a
tial for growing production organisms. Steam ranges in
steam plant can last for decades.
purity from boiler grade for
routine tasks, to culinary
This brochure focuses
grade “Clean Steam” for
on the industrial steam
food and dairy, and gradu-
boiler (the massive elec-
ates up to super pure,
tricity-generating utility
pyrogen-free steam for
boilers are addressed in
biopharmaceutical use.
our Power Gen and
Nuclear brochures). The
Steam can drive a simple
Magnetrol® relationship
pump or generate hun-
with steam systems
dreds of megawatts of
dates back to the 1930s,
electricity. It cures rubber,
when, as a new
and puts the corrugated
Chicago-based manu-
furrows in cardboard. It
facturer of boiler sys-
adds heat, humidity and
tems, we needed a boil-
air conditioning to build-
er level controller. Rather
ings and is a fire suppres-
than acquiring one, we
sant, too. In frigid oil & gas
invented one, and the
fields, steam heat-traces
success of that initiative
tanks and pipelines to keep processes moving. Steam
put our young company on a path toward becoming
is so essential to industry that 83% of the total
the level and flow specialist that we are today.
energy used by the pulp and paper segment is for
generating it (57% for chemicals and 42% for refining).
From massive petrochemical complexes to the local
Steam: With all its versatility, is it any wonder that
steam is essential to so many industries? I
microbrewery, steam is the tool for getting things done.
THE STEAM LOOP:
Make-up Water Treatment
|
Feed Water Deaeration
|
Boiler Water Treatment
|
Boiler Steam Generation
|
Condensate Return System
3
STEAM LOOP: 1. Make-up Water Treatment
It all begins with water, the essential medium
for steam generation. Conditioning water properly can
increase boiler efficiency and extend the boiler’s operating life. Improper or nonexistent feed water treatment
is the major cause of boiler failure.
All natural sources of fresh water require varying
degrees of treatment prior to boiler use. Boiler feed
water treatment prevents scale and deposits, removes
dissolved gases, protects against corrosion, eliminates
water and steam carry-over, and optimizes boiler efficiency and minimizes maintenance costs.
Water Source
1
2
Clarification
Filtration
Feed water is treated and conditioned in three
phases: (1) Raw make-up water is treated before
entering the deaerator; (2) Treated make-up water and
return condensate merge in the deaerator for removal
of dissolved gases; and (3) De-oxygenated and heated
feed water enters the boiler where it is further treated
with chemicals.
Feed water treatment requirements vary greatly. In
rare cases, raw make-up water only needs filtering.
More commonly, some form of external treatment is
needed, as in the typical process units shown below.
3
4
Water Softening Demineralization
5
Water Header Tank
Fig. 1. Make-up Water Treatment Applications
‚ Clarification Raw water with sediments may require a settling tank with the addition of chemicals to
foster precipitation of the suspended matter. Clarified water is then drawn off at a surface outlet.
Continuous Level: Eclipse® Enhanced 705 Guided Wave Radar (GWR); Echotel® Model 355 Noncontact Ultrasonic Transmitter; Kotron® Models 82CE, 804 or 805 RF Capacitance Transmitters.
ƒ Coarse and Fine Filtration Suspended solid impurities are reduced or eliminated by passing make-up
water through a filter. If the suspended solids are very fine, a flocculation step may be required.
Continuous Level: ECHOTEL Model 355 Non-contact Ultrasonic Transmitter; Pulsar ® R95 Thru-air Radar
Transmitter; Model R82 Thru-air Radar Transmitter; ECHOTEL 344/345 Non-Contact Ultrasonic Transmitter.
„ Water Softening Calcium and magnesium are hard scale forming minerals that build up on boilers and
steam-related equipment resulting in costly repairs, increased energy consumption, and plugged equipment. Softening occurs as hardness minerals attach to the softening resin and “exchange” for sodium.
Continuous Level: PULSAR R95 Thru-Air Radar Transmitter; ECLIPSE Enhanced 705 Guided Wave Radar;
Atlas™ or Aurora® Magnetic Level Indicators (MLIs).
Point Level: ECHOTEL 961 Ultrasonic Level Switch; Model T20 Single Stage Float Level Switch.
… Demineralization Demineralization is typically an ion exchange process whereby minerals or mineral
salts are removed from water. Chemical treatment or a Feed Water Evaporator can be used as alternative
methods, the latter using extraction steam to remove impurities in raw water.
Continuous Level: ECLIPSE Enhanced 705 GWR; Digital E3 Modulevel® Electronic Transmitter.
Point Level: Models T5x and T6x Float-based Level Switches.
† Header Tank The treated make-up water is routed for storage in a Cold Water Header Tank. From there
the water passes on demand through a flash tank for heating and on to the deaerator for degassing.
Continuous Level: Model R82 Non-contact Radar Transmitter; ECLIPSE Enhanced 705 GWR; ECHOTEL
Model 344/345 Non-contact Ultrasonic Transmitter; PULSAR R95 Thru-air Radar Transmitter.
4
STEAM LOOP: 2. Feed Water Deaeration
Because boiler and steam systems are made
primarily of steel and the heat transfer medium is
water, the potential for corrosion is very high. Dissolved
oxygen is the major cause of boiler system corrosion.
Oxygen and other gases are removed from both
feed water streams—treated make-up water and return
condensate feed water—when they merge in the
deaerator. Deaerators remove non-condensable gases
from feed water streams by steam heating and by
aggressively agitating incoming water. The deaerator’s
storage section is typically designed to hold enough
water for ten minutes of boiler operation at full load.
Steam In
Return Condensate In
Make-up Water In
Make-up Water in
1
Feed Water out
Feed Water to Boiler
Fig. 2. Tray-type Deaerator
‚ Deaerator Level control on a deaerator typically measures the level in the storage tank and modulates a
control valve on feed water streams to maintain tank level at the desired set points.
Continuous Level: ECLIPSE Enhanced 705 Guided Wave Radar; ATLAS or AURORA Magnetic Level Indicators.
Point Level: Series 3 ASME B31.1 External Caged Liquid Level Switch.
STEAM LOOP: 3. Boiler Feed Water Treatment
For higher boiler efficiencies, the feed water is further
conditioned prior to and upon entering the boiler.
First, the water is preheated by an economizer (Figure 3)
using the boiler’s hot exhaust gas streams. Next,
water treatment inside the boiler reduces foaming,
eliminates adherence of suspended matter to boiler
internals, further prevents corrosion and scaling by
eliminating residual oxygen. Chemical feed systems
are employed for both Internal Boiler Treatment and in
the Make-up Water Treatment unit.
‚ Chemical Feed Systems Liquid treatment chemicals in storage tanks, day tanks, or injection skids
require stringent level monitoring to ensure ongoing chemical treatment of make-up and feed water.
Continuous Level: ECLIPSE Enhanced 705 Guided Wave Radar; ATLAS or AURORA Magnetic Level
Indicators; PULSAR R95 Thru-air Radar Transmitter; Model R82 Thru-air Radar Transmitter.
Point Level: ECHOTEL 910, 961/962 Ultrasonic Level Switches; Tuffy® II Side-mounted Float Level Control.
5
STEAM LOOP: 4. Boiler Steam Generation
Feed water routed to the boiler is heated in an
economizer before being chemically treated upon
entering the boiler. After heat converts the water into
steam, the steam is routed to its applications.
Boiler drum level control must maintain water
level within critical set points. Ancillary boiler systems
requiring level control include fuel storage, flash tanks
and the boiler’s blowdown tank.
Steam Out
Feed Water In
1
4
Fuel Storage
Flash Tank
Feed Water in
2
Steam out
3
Fig. 3. Fire Tube Boiler
Blowdown Tank
‚ Fuel Storage A boiler can be fueled by natural gas, propane, fuel oil, coal, biomass or biogas. Storage of
liquid fuel oils with low flash points requires safety-certified controls due to the hazardous location.
Continuous Level: ECLIPSE Enhanced 705 Guided Wave Radar; PULSAR R95 Thru-air Radar Transmitter;
Model R82 Thru-air Radar Transmitter; ECHOTEL Model 355 Non-contact Ultrasonic Transmitter.
Point Level: Model B10/B15 Dual Stage Displacer Level Switch.
Granulated Biomass: Solitel® Vibrating Rod Level Switches detect ground biomass levels in hoppers and silos.
ƒ Boiler Drum Low water level can cause severe, even catastrophic, damage. If necessary, level controls
add feed water or shut-down the burner operation. Excessive high level can cause damaging carryover
and priming in which a large, rapidly applied load results in a sudden reduction in steam pressure that pulls
boiler water into piping. In this event, the level control actuates a valve to throttle down feed water supply.
Continuous Level: ECLIPSE Enhanced 705 Guided Wave Radar; Digital E3 MODULEVEL Electronic Transmitter;
APM MODULEVEL Pneumatic Transmitter; ATLAS or AURORA Magnetic Level Indicators.
Point Level: Series 3 ASME 31.1 External Caged Level Switch; Model B40 HT/HP External Caged Level Switch.
„ Blowdown Tank Undesirable solids in boiler water can be reduced through a continuous purge or blow
down system. Blowdown tanks allow the blowdown to cool before it is discharged into the sewer system.
Continuous Level: ECLIPSE Enhanced 705 Guided Wave Radar; Digital E3 MODULEVEL Electronic Transmitter.
… Flash Tank Boiler water blowdown can be used to heat process streams. Boiler water blowdown heat
recovery systems use flash steam from the flash tank for deaeration. The blowdown from the flash tank is
passed through an exchanger and used to preheat the boiler make-up water.
Continuous Level: ECLIPSE Enhanced 705 Guided Wave Radar; ATLAS or AURORA Magnetic Level Indicators.
Point Level: Model B40 HT/HP External Caged Liquid Level Switch.
6
STEAM LOOP: 5. Condensate Return System
After steam does its work it condenses to water
and is collected in the Condensate Return System for
reuse in the boiler plant. Since condensate has
already been treated with chemicals and has been
through the steam system, it will take far less
resources to turn it back into steam than it would to
make steam from an equal quantity of cold water.
A condensate return unit thus provides a significant
savings in make-up and the associated water treatment chemicals.
Start
Raw Water to Make-up Water
Raw water becomes make-up
water as a result of treatment.
The Boiler Water Cycle
1
Steam to Condensate
Once steam has done its
work it is collected as
condensate and returned
to the deaerator.
Make-up water to Feed water
Make-up water and Return
Condensate merge in the
deaerator to make feed water.
Feed water to Steam
Heat added to feed water
in the boiler changes
the water into steam.
‚ Condensate Receiver Tank Level controls in receiver tanks ensure that water is returned to the boiler
house for reuse. When the control senses the upper level in the receiver tank it will actuate a pump to
route the condensate to the deaerator. Typically, these tanks range from 65 to 1,800 gal. (250 to 7,000 L).
Continuous Level: ECLIPSE Enhanced 705 GWR; Digital E3 MODULEVEL Electronic Transmitter; ATLAS MLI.
Point Level: Thermatel® TD1/TD2 Flow/Level/Interface Switch; ECHOTEL Model 961 Single Point Ultrasonic
Level Switch; Sealed External Caged Level Switch; Model B40 External Caged Liquid Level Switch.
ALL STEAM LOOPS: Flow Control Applications
‚ Pump Protection A flow switch positioned along the pump’s discharge piping will actuate an alarm and
shut down the pump when liquid flow drops below the minimum flow rate.
Flow Alarm: THERMATEL TD1/TD2 Level/Flow/Interface Switch for High/Low Alarm.
ƒ Burner Fuel Gas Flow. Natural gas and biogas are the most common gaseous forms of boiler fuel. Natural
gas is primarily methane, and biogas is typically 65% methane and 35% carbon dioxide. Flaring and
venting biogas is giving way to energy harvesting technologies with the economic advantage of creating
heat, electricity, fuel or feed stocks while also reducing carbon emissions.
Continuous Flow: THERMATEL TA2 Mass Flow Transmitter.
Flow Alarm: THERMATEL TD1/TD2 Level/Flow/Interface Switch for High/Low Alarm.
MAGNETROL Instrumentation for Boiler Drum Level Measurement and Control
7
Perhaps the single most critical level control in the
steam loop is boiler drum measurement and control.
This application requires a high degree of accuracy,
reliability and temperature tolerance—attributes the
instruments below have been engineered to provide.
ECLIPSE Guided Wave Radar
PULSAR Thru-Air Radar
ECLIPSE is a two-wire, loop-powered,
24 VDC level transmitter based on
Guided Wave Radar (GWR) technology.
Available in coaxial, twin rod and single
rod probes, ECLIPSE is offered with HART®,
PROFIBUS® and FOUNDATION fieldbus™
outputs. Of special note is the Model 7xS
Coaxial Steam Probe optimized to effectively measure levels in saturated steam
applications. The 7xS withstands the high
temperature, high pressure and corrosive
nature of steam applications. A patented
steam compensation feature of the probe
protects against measurement errors that
are common to this application.
PULSAR Pulse Burst Radar
Level Transmitters are the latest
generation of loop-powered,
24 VDC, liquid level transmitters.
Offering lower power consumption, faster response time and
simplified operation, PULSAR
performance is not process
dependent (changing specific
gravity and dielectric have no
effect). Its operating frequency
offers superior performance in
the tougher applications that
include turbulence, foam, and
heavy vapors.
Eclipse®
with 7xS
Steam
Probe
Pulsar®
with
Horn
Antenna
Pulsar®
with
Dielectric
Rod
Antenna
TUFFY and MODULEVEL
Float & Displacer Controls
AURORA and ATLAS
Visual Indicators
Float-actuated switches are
ideal for level alarm, interface,
and pump control applications.
Top-mounting displacer
switches offer a wide choice of
alarm and control configurations.
MODULEVEL displacer transmitters offer digital 4-20 mA or
APM
HART output. Specifically
Pneumatic
designed for boiler service, the Modulevel
Model APM MODULEVEL
Pneumatic Transmitter provides
output signals in direct proportion
Tuffy
to changes in liquid level.
Orion Instruments® Magnetic Level
Indicators (MLIs) are robust visual
indicators offering single or redundant
level measurement. ATLAS is the
basic MLI with float-based visual
indication. AURORA provides
redundant control with both float
and ECLIPSE Guided Wave Radar.
ORION INSTRUMENTS MLIs are
ideal for water treatment systems,
deaerators, chemical feed systems,
steam boiler drums, flash tanks and
condensate tanks.
®
®
Digital
E3
Modulevel®
II
Atlas™
Aurora®
KOTRON RF Capacitance
Enhanced JUPITER® Magnetostriction
KOTRON RF Capacitance level
switches and transmitters are
available in nine different models
to provide a wide range of features suitable to a broad range of
applications and process media.
KOTRON RF Capacitance probes
are offered in many different
configurations to suit the user’s
unique application conditions.
The JUPITER Magnetostrictive level
transmitter provides 4-20 mA output,
proportional to the level being measured, or FOUNDATION fieldbus output.
It is designed to attach quickly to
ORION INSTRUMENTS MLIs or to
be directly inserted into a process
vessel. JUPITER offers precision
accuracy and high linearity at a reasonable price.
MODEL
MODEL
804
805
Jupiter®
S p e c i a l A p p l i cat i o n S e r i e s
Other industry and special application brochures from MAGNETROL include:
•
•
•
•
•
•
•
•
•
Chemical
Crude Oil Processing
Flue Gas Desulfurization
Food & Beverage
Interface Level Measurement
Life Science
Mass Flow Measurement
Modular Skid Systems
Natural Gas Processing
•
•
•
•
•
•
•
•
•
Nuclear Power
Petroleum Refining
Power Generation
Pulp & Paper Mills
Renewable Energy
Tank Bridle Level Measurement
Tank Overfill Prevention
Understanding Safety Integrity Level (SIL)
Water & Wastewater
PLEASE NOTE: The instruments recommended in these brochures are based on field experience with
similar applications and are included as a general guide to level and flow control selection. Because
all applications differ, however, customers should determine suitability for their own purposes.
CORPORATE HEADQUARTERS
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Phone: 630-969-4000 • Fax: 630-969-9489
magnetrol.com • [email protected]
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UNITED KINGDOM: Regent Business Centre • Jubilee Road • Burgess Hill, West Sussex RH15 9TL
Magnetrol & Magnetrol logotype, Orion Instruments & Orion Instruments logotype, Aurora, Echotel, Eclipse, Jupiter, Kotron,
Modulevel, Pulsar, Solitel, Thermatel and Tuffy are registered trademarks of Magnetrol International, Incorporated.
FOUNDATION fieldbus is a trademark of the Fieldbus Foundation. HART is a registered trademark of the HART Communication Foundation.
PROFIBUS is a registered trademark of PROFIBUS International.
Copyright © 2012 Magnetrol International, Incorporated. All rights reserved. Printed in the USA.
Bulletin: 41-183.0 • Effective: January 2010
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