Whether you are a mechanical engineering student preparing for competitive exams or a working engineer seeking a comprehensive technical reference, this guide covers everything about the Lamont Boiler: its construction, working principle, components, thermodynamic cycle, comparison with other boilers, applications, advantages, disadvantages, and much more.
What Is a Lamont Boiler?
A Lamont
Boiler is a forced circulation, high-pressure water tube boiler in
which water is pumped through the boiler tubes using a centrifugal pump rather
than relying on natural convection. This forced circulation ensures a
continuous, controlled, and uniform flow of water through the evaporator tubes,
even at supercritical pressures where natural circulation would be insufficient
or impossible.
The
distinguishing feature of the Lamont Boiler is the use of a circulating pump
driven externally, which pumps the water-steam mixture through the boiler
circuit. This forced movement ensures excellent heat transfer, compact design,
and fast steam generation — qualities that made it a preferred choice for
large-scale industrial and marine power plants throughout the 20th century.
Key Fact: The Lamont Boiler can operate at
pressures ranging from 40 bar to over 120 bar and can generate steam at
temperatures exceeding 500°C, making it a true high-pressure boiler.
If you
want to understand where the Lamont Boiler fits in the broader family of steam
generators, check out our complete guide on High-Pressure Boilers and the Ultimate Guide to Boilers.
History and Background of the Lamont Boiler
The
Lamont Boiler was patented by Walter Douglas La Mont in 1925,
during an era when conventional natural circulation boilers were approaching
their physical limits. As the demand for higher steam pressures and
temperatures grew alongside industrial expansion, engineers realized that
relying on density differences between hot and cold water to drive circulation
became increasingly unreliable.
At
elevated pressures, the density difference between water and steam diminishes
significantly. This weakens the driving force for natural circulation, leading
to uneven flow distribution, film boiling, and even tube burnout. La Mont's
innovation — pumping water mechanically — solved this problem decisively.
The
Lamont Boiler found rapid adoption in:
- Marine propulsion systems — where compact,
high-output steam generators were needed
- Industrial power plants — especially in Europe,
during the interwar period
- Chemical process industries — requiring precise,
high-pressure steam
The
boiler's design philosophy also influenced later innovations such as the Benson Boiler and other supercritical once-through
steam generators.
Construction of the Lamont Boiler
The
Lamont Boiler's construction is characterized by a modular, compact layout with
several interconnected circuits. Below is a detailed description of each major
structural component.
1. Steam and Water Drum (Separator Drum)
The steam
and water drum is the central pressure vessel of the Lamont Boiler. It is a
horizontal cylindrical drum that serves multiple purposes:
- Acts as a steam-water
separator, allowing dry steam to rise and exit while water remains
- Provides a water storage
reservoir to buffer feed water supply fluctuations
- Houses baffles and steam
separators (cyclone separators or chevron driers) to produce dry,
saturated steam
The drum
is fabricated from high-strength alloy steel capable of withstanding pressures
above 100 bar. Its size is kept relatively small compared to natural
circulation boilers because the forced circulation reduces the need for large
water storage volumes.
2. Feed Water Pump
The feed
water pump supplies demineralized water to the boiler at high pressure,
typically matching or slightly exceeding the drum pressure. This pump ensures
that the boiler receives a steady supply of make-up water to compensate for
steam output.
3. Centrifugal Circulating Pump
The most
distinctive component of the Lamont Boiler is the centrifugal circulating
pump. This pump:
- Draws water from the
steam-water drum
- Forces it through the
distribution headers and into the evaporator tubes
- Operates continuously to
maintain a high circulation ratio (typically 6–8 times the steam output)
The pump
is driven electrically (or in some designs by a steam turbine) and must be
highly reliable since any failure stops water circulation and risks tube
burnout. Modern Lamont installations use redundant pump systems for safety.
4. Distribution Headers
Water
from the circulating pump enters distribution headers (also called inlet
headers or manifolds). These are horizontal or vertical pipe assemblies that
distribute the hot pressurized water evenly to multiple rows of evaporator
tubes.
Uniform
distribution is critical to prevent hot spots and thermal stresses
in individual tubes.
5. Evaporator Tubes (Riser Tubes)
The evaporator
tubes are the heat-absorbing elements of the boiler. They are arranged in
the radiant zone of the furnace and receive intense heat from the
combustion gases.
- Tubes are typically made of low-alloy
steel (e.g., T11 or T22 grade)
- Their diameter is relatively
small (25–50 mm), which maximizes the surface-area-to-volume ratio for
efficient heat transfer
- Water enters at the bottom
headers and exits as a steam-water mixture at the top headers
Because
circulation is forced, the steam quality at the tube exit can be carefully
controlled, preventing excessive steam blanketing or dry-out.
6. Mixing Device / Orifice Plates
At the
entry of each tube or group of tubes, orifice plates (restrictor
orifices) are installed. These control the flow distribution among the various
parallel tube circuits, ensuring each tube receives its correct share of water
regardless of local heat flux variations.
This is a
subtle but critical design feature that distinguishes the Lamont Boiler from
simpler forced circulation boilers.
7. Furnace and Combustion System
The furnace
is the combustion chamber where the fuel (coal, oil, gas, or biomass) is
burned. The furnace walls are lined with the evaporator tubes (membrane wall
construction in modern units), maximizing heat absorption from the radiant
flame.
The
combustion system includes:
- Burners (wall-fired or tangentially
fired)
- Air preheater — recovers heat from flue
gases to preheat combustion air
- Economizer — preheats feed water using
exit flue gas energy
8. Superheater
Saturated
steam from the drum passes through the superheater, where it is further
heated above the saturation temperature to produce superheated steam
ready for use in turbines or industrial processes.
The
superheater is located in the convection zone of the boiler, where flue
gas temperatures are high but radiant flux is lower, providing controlled
superheat.
9. Economizer
The economizer
is a heat recovery device positioned in the flue gas path after the
superheater. It preheats the feed water using the residual heat of the flue
gases, significantly improving the overall thermal efficiency of the boiler.
For a
deeper understanding of thermodynamic heat recovery concepts, explore our
article on How Does a Heat Exchanger Work.
10. Air Preheater
Located
after the economizer, the air preheater extracts further heat from the
flue gases to warm the incoming combustion air. This reduces fuel consumption
and raises the combustion temperature, improving efficiency.
11. Safety Valves and Boiler Mountings
Like all
boilers, the Lamont Boiler is equipped with essential Boiler Mountings and Accessories including:
- Safety valves — release excess pressure
automatically
- Steam stop valve — controls steam output to
the mains
- Pressure gauges — monitor drum and
superheater pressure
- Water level indicators — monitor drum water level
- Blowdown valves — remove dissolved solids
Working Principle of the Lamont Boiler
The
operation of the Lamont Boiler follows a well-defined forced circulation
steam generation cycle. Here is a step-by-step explanation:
Step 1: Feed Water Supply
Demineralized
feed water is supplied to the steam-water drum by the feed water pump
at high pressure. The water level in the drum is maintained automatically using
a level controller.
Step 2: Forced Circulation
The centrifugal
circulating pump draws water from the bottom of the steam-water drum
and forces it through the distribution headers and into the evaporator
tubes at a flow rate several times higher than the steam output. This high
circulation ratio is the defining characteristic of the Lamont system.
Step 3: Heat Absorption and Steam Generation
As water
flows through the evaporator tubes positioned in the furnace walls:
- The furnace flame and hot
combustion gases transfer heat to the tubes
- Water absorbs this heat and
partially converts to steam
- The resulting steam-water
mixture rises through the tubes back to the steam-water drum
Because
the flow is forced (not gravity-driven), the process is stable even at
pressures where density differences between water and steam are minimal.
Step 4: Steam-Water Separation
Inside
the steam-water drum, the mixture passes through cyclone separators or baffle
plates. Steam rises to the top of the drum while water falls to the bottom,
where it is recirculated by the pump again.
Step 5: Superheating
Dry
saturated steam from the drum passes into the superheater, where flue
gases further heat it to the desired superheat temperature. Superheated steam
has higher energy content and is used directly in steam turbines for power
generation.
Step 6: Flue Gas Heat Recovery
As
combustion gases travel from the furnace toward the stack, they pass through
the superheater, economizer, and air preheater
sequentially, surrendering heat to useful purposes. This multi-stage heat
recovery maximizes thermal efficiency.
Step 7: Steam Delivery
Superheated
steam exits the boiler at the specified pressure and temperature and is
delivered to steam turbines, process heaters, or other steam-consuming
equipment.
Understanding
thermodynamic cycles like this is greatly aided by knowing the foundations —
see our guide on Applications of Thermodynamics and Types of Thermodynamic Systems.
Thermodynamic Cycle of the Lamont Boiler
The
Lamont Boiler operates on the Rankine cycle, which is the standard
thermodynamic cycle for steam power plants. The modified Rankine cycle in a
forced circulation boiler involves:
Key Technical Specifications
Lamont Boiler vs. Other High-Pressure Boilers
Understanding
how the Lamont Boiler compares with other high-pressure designs helps clarify
its strengths and the contexts where it is most appropriate.
Lamont Boiler vs. Benson Boiler
|
Feature |
Lamont Boiler |
Benson Boiler |
|
Circulation
Type |
Forced
(pump-assisted) |
Once-through
(no drum) |
|
Steam-Water
Drum |
Present |
Absent |
|
Circulation
Ratio |
6:1 to
8:1 |
1:1
(once-through) |
|
Operating
Pressure |
Up to
~120 bar |
Above
critical pressure (>221 bar) |
|
Startup
Time |
Moderate |
Fast |
|
Scale
Formation Risk |
Moderate
(drum acts as reservoir) |
High
(treated water essential) |
|
Complexity |
Moderate |
High |
The Benson Boiler eliminates the steam-water drum
entirely, operating as a true once-through system at supercritical pressures.
The Lamont Boiler, by contrast, retains the drum as a phase separator and
operates in the subcritical regime.
Lamont Boiler vs. Babcock and Wilcox Boiler
|
Feature |
Lamont Boiler |
Babcock and Wilcox Boiler |
|
Circulation
Type |
Forced |
Natural |
|
Operating
Pressure |
High
(40–120 bar) |
Moderate
to high |
|
Circulation
Reliability |
High
(pump-controlled) |
Dependent
on density difference |
|
Startup
Time |
Fast
(forced flow) |
Slower |
|
Maintenance |
Pump
maintenance required |
Simpler
(no moving parts in circuit) |
The Babcock and Wilcox Boiler uses natural
circulation, making it simpler but less effective at very high pressures where
density differences become negligible.
Lamont Boiler vs. Cochran Boiler
|
Feature |
Lamont Boiler |
Cochran Boiler |
|
Type |
Water
tube |
Fire
tube (multi-tubular) |
|
Pressure
Capability |
Very
high (100+ bar) |
Low to
medium (up to ~17 bar) |
|
Steam
Output |
Very
high |
Limited |
|
Footprint |
Compact
for output |
Compact |
|
Application |
Power
plants, industrial |
Small
industries, workshops |
The Cochran Boiler is a fire tube boiler suited to
small-scale applications. The Lamont's water tube design allows far higher
pressures, temperatures, and steam outputs.
Advantages of the Lamont Boiler
The
Lamont Boiler's forced circulation design delivers several compelling
advantages over natural circulation alternatives:
1. High
Operating Pressure Capability Forced circulation works effectively at pressures
where natural circulation becomes unreliable (above ~70 bar). This makes the
Lamont Boiler ideal for high-efficiency, high-pressure steam cycles.
2.
Compact Design Because
circulation is not limited by buoyancy forces, tubes can be arranged more
freely and densely. This results in a more compact boiler for a given steam
output.
3. Fast
Startup Forced
circulation allows rapid heating of the water circuit. The boiler can reach
full operating pressure significantly faster than natural circulation boilers —
an important advantage in industrial settings where demand varies.
4.
Uniform Heat Distribution Orifice plates and controlled pump flow ensure each tube circuit
receives the correct water flow, preventing local overheating and tube burnout.
5. High
Thermal Efficiency The
combination of economizer, air preheater, and superheater — made practical by
forced circulation — achieves thermal efficiencies of 85–92%.
6.
Flexible Fuel Use The
Lamont Boiler can be adapted for coal, oil, natural gas, or biomass combustion,
giving it versatility across industries.
7.
Reduced Drum Size Compared
to natural circulation boilers, the steam-water drum is smaller because the
pump handles circulation rather than buoyancy, reducing material costs and
weight.
8. Better
Response to Load Changes The circulating pump can be adjusted to match varying steam demand, making
the boiler more responsive to load fluctuations compared to natural circulation
designs.
Disadvantages of the Lamont Boiler
Despite
its many strengths, the Lamont Boiler has some limitations that engineers must
consider:
1.
Circulating Pump Dependency The boiler depends entirely on the circulating pump. Any pump failure
causes immediate loss of circulation, risking overheating and tube burnout
unless protective shutdown systems activate.
2. Pump
Maintenance The centrifugal
circulating pump operates under extreme pressure and temperature conditions,
requiring regular maintenance and periodic replacement of seals, bearings, and
impellers.
3. Higher
Initial Cost The
pump, its drive system, redundant backup pumps, and associated instrumentation
increase the capital cost compared to natural circulation boilers.
4. Salts
and Deposits The high
circulation ratio means dissolved salts concentrate in the drum water more
rapidly. Rigorous water treatment and periodic blowdown are essential to
prevent scaling and corrosion.
5.
Complexity The
overall system — with pump controls, flow distribution headers, orifice plates,
and automatic safety systems — is more complex to design, commission, and
operate than simpler natural circulation boilers.
6.
Limited Supercritical Application Unlike the Benson Boiler, the Lamont Boiler is not
well-suited for supercritical pressures (above 221 bar), limiting its
application in the most advanced ultra-supercritical power plants.
Applications of the Lamont Boiler
The
Lamont Boiler's combination of high pressure, high efficiency, and compact size
makes it suitable for a wide range of industrial applications:
1. Thermal Power Plants
Large-scale
electricity generation plants use Lamont Boilers (or derivatives) to produce
high-pressure superheated steam for driving steam turbines. The boiler's
ability to operate at high pressures directly improves the Rankine cycle
efficiency.
To understand
how this fits into the broader energy landscape, see our guide on Steam Power Plants.
2. Marine Propulsion
Historically,
Lamont-type boilers were used in naval vessels and merchant ships requiring
compact, high-output steam generators for propulsion and onboard power.
3. Chemical and Petrochemical Industries
Process
industries require high-pressure steam for distillation, cracking, reforming,
and other thermally intensive operations. The Lamont Boiler provides reliable,
controllable steam at the required conditions.
4. Sugar and Paper Industries
These
process industries require large quantities of steam for evaporation and drying
operations. Forced circulation boilers provide the high throughput needed
efficiently.
5. District Heating
In
combined heat and power (CHP) plants, Lamont-type boilers generate steam for
both electricity and district heating networks.
6. Waste Heat Recovery
Modified
Lamont Boiler configurations are used as heat recovery steam generators
(HRSGs), extracting heat from industrial flue gases or gas turbine exhaust to
generate steam.
Lamont Boiler: Numerical Example
Let us
work through a basic thermal calculation to illustrate the Lamont Boiler's
performance.
Given:
- Steam output: 50 tonnes/hour
= 50,000 kg/h
- Steam pressure: 80 bar
- Steam temperature
(superheated): 480°C
- Feed water temperature:
120°C
- Fuel: Natural gas, calorific
value = 47,000 kJ/kg
- Boiler efficiency: 88%
Find: Fuel consumption rate
Solution:
From
steam tables at 80 bar and 480°C:
- Enthalpy of superheated
steam (h₁) ≈ 3,349 kJ/kg
From
steam tables for feed water at 120°C:
- Enthalpy of feed water (h₂)
≈ 503.7 kJ/kg
Heat
absorbed by steam per kg:
Q = h₁ – h₂ = 3,349 – 503.7 = 2,845.3 kJ/kg
Total
heat absorbed by boiler:
Q_total = 50,000 × 2,845.3 = 142,265,000 kJ/h
Heat
supplied by fuel (accounting for efficiency):
Q_fuel = Q_total / η = 142,265,000 / 0.88 = 161,664,773 kJ/h
Fuel
consumption:
ṁ_fuel = Q_fuel / CV = 161,664,773 / 47,000 = 3,440 kg/h ≈ 3.44
tonnes/hour
Result: The Lamont Boiler producing 50
tonnes of steam per hour consumes approximately 3.44 tonnes of natural gas
per hour at 88% efficiency.
Key Differences: Fire Tube vs. Water Tube Boilers
The
Lamont Boiler is a water tube boiler, meaning hot gases flow outside the tubes
while water flows inside. Understanding this fundamental distinction is
important for exam and interview questions.
|
Feature |
Water Tube (Lamont) |
Fire Tube (Cochran, Lancashire) |
|
Hot
gases flow |
Outside
the tubes |
Inside
the tubes |
|
Water
flow |
Inside
the tubes |
In the
shell around tubes |
|
Operating
pressure |
Very
high (up to 250+ bar for advanced types) |
Low to
medium (up to ~25 bar) |
|
Steam
generation rate |
High |
Low to
moderate |
|
Explosion
risk |
Lower
(small tube diameter) |
Higher
(large pressure shell) |
|
Startup
time |
Fast |
Slow |
|
Suitable
for |
Large
power plants |
Small
industries |
Did You Know? Interesting Facts About the Lamont
Boiler
- The name "La Mont"
comes from its inventor Walter Douglas La Mont, and is sometimes
written as "La Mont" or "Lamont" (one word) in
different engineering texts.
- Early Lamont Boilers were
tested and refined extensively in Germany and Switzerland during
the late 1920s and 1930s.
- The Lamont Boiler was among
the first practical demonstrations that forced circulation was a
viable solution for industrial-scale high-pressure steam generation.
- Some Lamont Boiler
installations achieve circulation ratios as high as 10:1, meaning
10 kg of water circulates through the tubes for every 1 kg of steam
produced — this dramatically reduces tube wall temperatures.
- The boiler's design directly
influenced supercritical and ultra-supercritical boiler development,
which uses forced (once-through) flow at pressures above the critical
point of water (221.2 bar).
Internal Insights: Related Topics Worth Exploring
If you
are studying thermal engineering comprehensively, the Lamont Boiler fits into a
wider context of thermodynamic systems and heat transfer:
- Boiler Mountings and Accessories — Understand the safety and control devices fitted to all boilers including the Lamont.
- Steam Power Plant Working Principle — See how the Lamont Boiler integrates into the complete power generation cycle.
- High-Pressure Boilers: Types and Working — Compare the Lamont alongside other high-pressure boiler designs.
- Benson Boiler: Construction and Working — Study the once-through forced circulation evolution of the Lamont concept.
- Babcock and Wilcox Boiler — Compare natural vs. forced circulation water tube boilers.
- Cochran Boiler: Construction and Working — Understand fire tube boiler basics for contrast.
- Applications of Thermodynamics — Broaden your understanding of thermodynamic principles underlying boiler operation.
- How Does a Heat Exchanger Work — Understand the economizer and air preheater used in the Lamont Boiler.
- Types of Thermodynamic Systems — Classify the Lamont Boiler within thermodynamic system types.
- The Ultimate Guide to Boilers — Your one-stop reference for all boiler types and classifications.
Key Takeaways
Here is a
quick-reference summary of the most important facts about the Lamont Boiler:
|
Topic |
Summary |
|
Type |
High-pressure,
forced circulation, water tube boiler |
|
Inventor |
Walter
Douglas La Mont (1925) |
|
Operating
Pressure |
40 –
120+ bar |
|
Circulation
Method |
Centrifugal
pump (forced) |
|
Circulation
Ratio |
6:1 to
8:1 |
|
Steam
Temperature |
Up to
550°C |
|
Thermal
Efficiency |
85 –
92% |
|
Key
Advantage |
Reliable
circulation at high pressures |
|
Key
Disadvantage |
Pump
dependency and maintenance |
|
Main
Applications |
Power
plants, marine, chemical industry |
|
Thermodynamic
Cycle |
Rankine
cycle |
Frequently Asked Questions (FAQs)
1. What is a Lamont Boiler used for?
A Lamont
Boiler is primarily used in large-scale thermal power plants, chemical
process industries, marine propulsion systems, and anywhere
high-pressure, high-temperature steam is required at high output rates. Its
forced circulation design makes it particularly suitable for pressures above 70
bar where natural circulation becomes unreliable.
2. How does a Lamont Boiler differ from a Benson
Boiler?
The key
difference is that the Lamont Boiler uses a steam-water drum and
operates on a recirculation principle (water circulates multiple times before
fully converting to steam), while the Benson Boiler is a once-through system
with no drum, designed for supercritical pressures. The Lamont works at
subcritical pressures (up to ~120 bar), while the Benson operates above the
critical point of water (221.2 bar).
3. What is the circulation ratio of a Lamont
Boiler?
The
circulation ratio of a Lamont Boiler is typically 6:1 to 8:1, meaning 6
to 8 kg of water circulates through the evaporator tubes for every 1 kg of
steam produced. In some high-heat-flux applications, the ratio may be as high
as 10:1.
4. Why is forced circulation used in a Lamont
Boiler?
Forced
circulation is used because at high pressures (above ~70 bar), the density
difference between water and steam shrinks significantly, making natural
circulation insufficient and unreliable. A centrifugal pump ensures
adequate, controlled water flow through the evaporator tubes at all operating
conditions, preventing hot spots, tube burnout, and flow instability.
5. What is the function of orifice plates in a
Lamont Boiler?
Orifice
plates
(restrictors) are installed at the inlet of each evaporator tube circuit to distribute
flow uniformly among all parallel tube circuits. They ensure that each tube
receives the correct flow rate regardless of local heat flux variations,
preventing some tubes from starving (receiving too little water) and others
from flooding (receiving too much).
6. What are the main components of a Lamont Boiler?
The main
components of a Lamont Boiler are: (1) Steam-water drum, (2) Feed
water pump, (3) Centrifugal circulating pump, (4) Distribution
headers, (5) Evaporator tubes with orifice plates, (6) Furnace
and burner system, (7) Superheater, (8) Economizer, (9)
Air preheater, and (10) Boiler mountings and safety devices.
7. Is the Lamont Boiler a fire tube or water tube
boiler?
The
Lamont Boiler is a water tube boiler. This means water and the steam-water
mixture flow through the tubes, while the hot combustion gases flow outside the
tubes in the furnace chamber. This design allows the use of small-diameter
tubes that can withstand very high pressures without excessive wall thickness.
8. What is the thermal efficiency of a Lamont
Boiler?
A
well-maintained Lamont Boiler achieves thermal efficiencies of 85 to 92%,
depending on the fuel type, steam pressure, feed water temperature, and the
effectiveness of heat recovery devices (economizer and air preheater).
9. Can the Lamont Boiler run on multiple fuel
types?
Yes. The
Lamont Boiler's furnace can be configured for coal (pulverized or
stoker-fired), fuel oil, natural gas, or biomass, making it versatile for
different industrial settings and fuel availability scenarios.
10. What happens if the circulating pump fails in a
Lamont Boiler?
If the
circulating pump fails, forced flow through the evaporator tubes stops
immediately. Without cooling water flow, the tube metal temperature rises
rapidly, potentially leading to tube overheating or burnout. Modern
Lamont Boiler installations have automatic safety systems that detect
pump failure, cut fuel supply, and initiate emergency shutdown. Redundant
standby pumps are also provided to allow switchover without boiler trip.
Conclusion
The Lamont
Boiler stands as a landmark achievement in boiler engineering — a design
that solved the fundamental limitations of natural circulation by introducing a
mechanically driven water circuit. Its ability to operate reliably at pressures
and temperatures that would defeat natural circulation boilers made it a
cornerstone technology in 20th-century power engineering, and its principles
continue to influence modern high-pressure steam generator design.
From its
compact, modular construction to its high thermal efficiency and versatile fuel
compatibility, the Lamont Boiler remains a critical topic for mechanical
engineering students, thermal engineers, and power plant operators alike. Its
forced circulation principle — water pumped through tubes at many times the
rate of steam output — ensures reliable performance under demanding conditions
that challenge all other boiler types.
Understanding
the Lamont Boiler thoroughly, including its construction, working principle,
thermodynamic cycle, comparative performance, and applications, is essential
for mastering thermal engineering and performing well in university
examinations and technical interviews.
Explore the full spectrum of boiler technology and thermodynamic systems through our related articles, and build the foundational knowledge that transforms classroom theory into real-world engineering competence.