Steam Boiler Simulator
Fire-tube & water-tube boilers — cut open and animated in 2D & 3D • Explore • Practice • Quiz
Display Controls
Log
Boiler performance problems
Answers within 1 % are marked correct. Every steam-table value you need is printed in the question.
1 Overview
The Steam Boiler Simulator shows how boilers work rather than only how to calculate them. It contains thirteen boilers plus a fire-tube versus water-tube comparison, grouped in teaching order: the principle; five fire-tube boilers (Cochran, Cornish, Lancashire, locomotive and the Scotch marine / three-pass packaged boiler); three natural-circulation water-tube boilers (Babcock & Wilcox, Stirling and the modern D-type); and four high-pressure boilers (La Mont, Benson, Loeffler and Velox).
Each boiler is drawn twice from one geometry: an animated 2D section with an end view and a trend chart, and an operable 3D cutaway you can turn, zoom and click. Hot gas, water, the steam–water mixture, steam and feed water move through the boiler as coloured particles, and a live model of the drum or shell gives pressure, water level, safety-valve and low-water behaviour.
2 Choosing a boiler
Above the canvas, the four numbered buttons are the families. Start with 1 — Start here, which puts a fire tube and a water tube side by side. Then pick a family and a boiler from the row of names under it. The page address remembers the boiler (for example #lancashire), so a link opens straight to it.
3 The 2D section
The 2D view is a longitudinal section, cut where it shows the most. Hot gas glows from yellow-white at the fire to dull grey at the chimney, with temperature tags along its path; gas passages that lie behind the cut are drawn dashed. Blue particles are water, pale blue with white specks is the steam–water mixture, white is steam and green is feed water. Bubbles form on heated surfaces and rise to the water surface.
Boilers with brickwork flues (Cornish, Lancashire), the Scotch boiler and the Babcock & Wilcox boiler also show Section A–A, an end view where ⊙ is gas coming towards you and ⊗ is gas going away. The trend chart plots pressure and water level (or outlet temperature for the once-through Benson boiler) over the last simulated minutes.
Click any label, part or mounting to read what it does. Right-click the canvas to save an image, copy the readings, start the tour or reset. Use Display Controls (top left) to hide flows, labels, mountings, temperatures, the chart or the grid.
4 The 3D view
On a computer or tablet the boiler opens in 3D; on a phone it opens in 2D, and the 2D section | 3D switch changes it at any time (the page remembers your choice). Drag to turn the boiler, scroll with Ctrl or pinch to zoom, right-drag or two-finger drag to pan. The Cutaway button removes the near half so you can see inside; Exterior shows the boiler as it stands. Click any part for its card. The flows are drawn over the cutaway as glowing particles.
5 How it works — the guided tour
Press 🎓 How it works for a step-by-step walk through the boiler on screen. Each step lights up the parts it is talking about and the flow it describes, and dims the rest. The tour plays by itself; use ⏮ ⏭ (or the arrow keys) to step, ❙❙ to pause and ✕ or Esc to close. It works in both 2D and 3D.
6 Running the boiler
Firing rate sets the heat released by the fire; steam demand sets how far the plant opens the steam main. When they match, pressure is steady. Fire harder than the demand and pressure rises until the safety valve lifts (at 8 % above the working pressure); demand more than you fire and pressure falls. Feed water on Auto holds the normal water level; Manual lets you set it yourself; Pump off stops it.
Boilers are slow, so the clock runs faster than real time (×60 by default; the Time speed control goes from ×1 to ×600). The scenarios set up classic lessons: raising steam from cold, a sudden demand (pressure sags; water-tube boilers show swell), feed pump failure (the fusible plug melts on shell boilers; a low-water cut-out trips the burner on modern ones), the safety valve test, and high water (priming). After a trip, restore the feed and press Reset trip.
7 Readouts and performance
The tiles show steam pressure (absolute in SI, gauge in psig in Imperial), saturation temperature, water level relative to the normal water level (NWL), steam output, feed flow, heat input from the fuel, the boiler’s typical efficiency, equivalent evaporation from and at 100 °C (boiler horsepower in Imperial) and the factor of evaporation, all from the embedded saturated steam table. The specification card lists the class, firing, circulation, typical pressure, output and efficiency, with advantages and limitations.
8 Explore
Seven topic tabs: Basics (how steam is made, classification, natural circulation, a fire-tube vs water-tube table), Fire-tube, Water-tube, High-pressure, Mountings & accessories, Performance (equivalent evaporation, factor of evaporation, efficiency, losses, boiler horsepower, each with a worked example) and Safety & codes.
9 Practice and Quiz
Practice gives endless boiler-performance problems — equivalent evaporation, factor of evaporation, efficiency, fuel consumption, wet-steam enthalpy, boiler horsepower, circulation ratio and natural-circulation head. Every steam-table value is printed in the question; answers within 1 % are correct, and the worked solution is shown. Quiz asks five questions drawn at random from a pool of thirty on boiler types, mountings, accessories and principles, with the options shuffled each time, and gives a star rating.
10 SI and Imperial
The Units switch changes pressure (bar abs ↔ psig), temperature (°C ↔ °F), flows (kg/h ↔ lb/h), heat (kW ↔ MBH, thousands of Btu/h), level (mm ↔ in) and the specification card. In Imperial the equivalent-evaporation tile shows boiler horsepower (1 BHP = 34.5 lb/h from and at 212 °F). Your choice is remembered across the site.
11 Tips
Compare response: run Sudden steam demand on the Lancashire boiler, then on the D-type. The shell boiler’s big water store holds the pressure up far longer. Try Feed pump failure on the Cochran and watch the fusible plug in the furnace crown. On the Benson boiler, raise the firing without raising the demand and watch the outlet temperature climb — the firing-to-feed ratio is everything in a once-through boiler.
How a Steam Boiler Works — Interactive 2D and 3D Boiler Simulator
A steam boiler is a closed pressure vessel that turns water into steam using the heat of burning fuel. Fuel burns in a furnace; the hot gases give their heat to water through the metal of the heating surface; the water first warms to its boiling point and then boils; the steam collects in the steam space and leaves through the stop valve. Everything else — flues, tubes, drums, headers, baffles, pumps — is about getting the heat into the water efficiently and holding the pressure safely. This simulator shows all of it moving, for every classic boiler taught in thermal engineering, in a 2D section and in a 3D cutaway you can turn and click.
Fire Tube vs Water Tube Boilers
The first question about any boiler is which side of the tube the fire is on. In a fire tube boiler the hot gases pass inside the tubes, which run through a shell full of water. In a water tube boiler the water flows inside the tubes and the hot gases pass around them. The difference decides almost everything else, because the hoop stress in a cylinder is σ = p·d / 2t: a 2.5 m shell needs about 20 mm of plate at 16 bar, while a 63.5 mm tube needs only half a millimetre for the same stress.
| Fire tube boiler | Water tube boiler | |
|---|---|---|
| Inside the tubes | Hot flue gas | Water / steam–water mixture |
| Typical pressure | Up to about 25 bar | Up to 250 bar and above |
| Typical output | Up to about 25–30 t/h | Up to 2000 t/h and more |
| Water content | Large — steady pressure, slow start | Small — fast start, quick response |
| If a part fails | Large release of stored hot water | One tube fails — far less violent |
| Water quality needed | Tolerant | Must be treated |
| Examples | Cochran, Cornish, Lancashire, locomotive, Scotch marine | Babcock & Wilcox, Stirling, D-type, La Mont, Benson |
Types of Boilers — How They Are Classified
Boilers are classified by what flows in the tubes (fire tube or water tube), by where the furnace is (internally fired, with the furnace inside the shell, or externally fired), by the axis of the shell (vertical or horizontal), by how the water circulates (natural, forced, or once-through), by pressure (low, medium, high, supercritical) and by use (stationary, mobile, marine, packaged). The table lists every boiler in the simulator with its typical textbook rating.
| Boiler | Class | Firing & circulation | Typical pressure | Typical output |
|---|---|---|---|---|
| Cochran | Fire tube, vertical, multi-tubular | Internal, natural | 6.5–10.5 bar | up to 3.5 t/h |
| Cornish | Fire tube, horizontal, one flue | Internal, natural | 7–10.5 bar | up to 6.5 t/h |
| Lancashire | Fire tube, horizontal, two flues | Internal, natural | 10–16 bar | up to 9 t/h |
| Locomotive | Fire tube, horizontal, multi-tubular | Internal, natural; blast-pipe draught | 10–20 bar | 7–9 t/h |
| Scotch marine / 3-pass packaged | Fire tube, horizontal, three-pass | Internal, natural; burner & fan | 10–25 bar | 1–25 t/h |
| Babcock & Wilcox | Water tube, straight inclined tubes | External, natural | 10–40 bar | 20–40 t/h |
| Stirling | Water tube, bent tubes, four drums | External, natural | 20–60 bar | 20–50 t/h |
| D-type (bi-drum) | Water tube, membrane walls | Burner, natural | 10–110 bar | 10–200 t/h |
| La Mont | Water tube, drum | External, forced (pump) | 100–170 bar | 45–50 t/h |
| Benson | Water tube, no drum | External, once-through | 200–300 bar | 100 t/h and far above |
| Loeffler | Water tube, evaporating drum | External, steam circulation | 100–140 bar | up to 100 t/h |
| Velox | Water tube, pressurised furnace | Pressure-fired, forced | 60–100 bar | up to 100 t/h |
Fire Tube Boilers: Cochran, Cornish, Lancashire, Locomotive and Scotch Marine
The Cochran boiler is a vertical, multi-tubular, internally fired boiler: a hemispherical furnace at the bottom of a vertical shell, a flue pipe to a fire-brick combustion chamber, and horizontal fire tubes across the shell to a smoke box and chimney. It needs very little floor space. The Cornish boiler is a horizontal shell with one large flue tube; the Lancashire boiler has two. Both sit in brickwork that forms more flues: in the Lancashire boiler the gases go along the flues, forward through the bottom flue and back through the two side flues to the chimney. The locomotive boiler adds a water-jacketed firebox and a barrel full of small tubes; with no tall chimney, its draught comes from exhaust steam blasted up the chimney. The Scotch marine boiler became today’s three-pass packaged boiler: a corrugated furnace, a wet-back reversal chamber and two banks of tubes in one shell, delivered complete with burner and controls.
Water Tube Boilers: Babcock and Wilcox, Stirling and D-Type
The Babcock and Wilcox boiler has a horizontal steam drum over a bank of straight tubes inclined at about 15°, joined to sinuous front and rear headers. The furnace is under the high end of the tubes (externally fired), and two baffles make the gas cross the tubes three times. Water falls from the drum through the downcomer to the rear header, rises through the tubes as a steam–water mixture and returns through the front header: natural circulation, driven by the density difference Δp = (ρdowncomer − ρriser)·g·H. The Stirling boiler uses bent tubes between three steam drums and a mud drum, so every tube can expand freely. The modern D-type package boiler uses gas-tight membrane water walls and two drums and is shipped complete from the factory.
High Pressure Boilers: La Mont, Benson, Loeffler and Velox
As pressure rises, water and steam densities approach each other and natural circulation weakens, vanishing at the critical pressure of 220.6 bar. High-pressure boilers solve this in four ways. The La Mont boiler uses a pump to force 8 to 10 times the evaporation through the evaporator tubes. The Benson boiler works above the critical pressure with no drum at all: a feed pump drives water once through the whole circuit, which is why it is called a once-through boiler. The Loeffler boiler carries only steam in its heated tubes and evaporates the feed water in a separate drum with superheated steam, about two-thirds of which is recirculated. The Velox boiler burns its fuel at about 2.5 bar, supplied by a compressor driven by a gas turbine, so the gas flows at very high velocity and transfers heat many times faster.
Boiler Mountings and Accessories
Mountings are fitted for safety and control and are required by law; accessories raise efficiency or capacity, and the boiler can run without them. In the simulator every mounting is drawn on the boiler and works: the safety valve blows, the pressure gauge needle moves, the water gauge shows the level, the fusible plug melts if the furnace crown is uncovered and the low-water alarm trips the burner.
| Mounting | Purpose | Accessory | Purpose |
|---|---|---|---|
| Safety valve | Releases steam at the set pressure | Economiser | Pre-heats feed water with flue gas |
| Water level gauge | Shows the water level | Superheater | Raises steam above saturation temperature |
| Pressure gauge | Shows the steam pressure | Air pre-heater | Heats combustion air with flue gas |
| Steam stop valve | Lets steam out to the main | Feed pump / injector | Pushes feed water in against boiler pressure |
| Feed check valve | Non-return valve on the feed | Steam separator | Removes water droplets from the steam |
| Fusible plug | Puts the fire out on low water | Soot blowers | Keep heating surfaces clean |
| Blow-off cock | Removes sludge, empties the boiler | Deaerator | Removes dissolved oxygen from feed |
Equivalent Evaporation and Boiler Efficiency — Worked Example
Boilers working at different pressures and feed temperatures are compared by their equivalent evaporation from and at 100 °C: me = ms(h − hfw) / 2257. A boiler making 2000 kg/h of dry saturated steam at 10 bar (h = 2777.1 kJ/kg) from feed water at 40 °C (hfw = 167.5 kJ/kg) has a factor of evaporation F = 2609.6 / 2257 = 1.156 and an equivalent evaporation of 2312 kg/h. If it burns 250 kg/h of coal with a calorific value of 30 000 kJ/kg, its efficiency is η = 2000 × 2609.6 / (250 × 30 000) = 69.6 %. In US practice the same boiler is rated at 2312 / 15.65 ≈ 148 boiler horsepower (1 BHP = 34.5 lb/h from and at 212 °F).
Boiler Safety: Low Water, Safety Valves and Priming
The simulator’s scenarios reproduce the classic operating lessons. Cut the feed and the water level falls; on a shell boiler the furnace crown is uncovered and the fusible plug melts, letting steam put the fire out, while a modern boiler’s low-water cut-out trips the burner first. Close the stop valve while still firing and the pressure climbs until the safety valve lifts. Over-feed and the water rises into the steam space, carrying water over with the steam (priming). Raise steam from cold and you see why a big shell boiler takes so long, and why water expands as it heats — a boiler is filled low in the glass when cold.
Frequently Asked Questions
What is the difference between a fire tube and a water tube boiler?
In a fire tube boiler the hot flue gases flow inside the tubes and the water surrounds them inside a large shell. In a water tube boiler the water flows inside the tubes and the hot gases flow around the outside. Because small tubes can withstand far higher pressure than a large shell, water tube boilers reach 100 to 250 bar and very large outputs, while fire tube boilers are limited to about 25 bar and 25 to 30 tonnes of steam per hour.
What are the main types of boilers?
Boilers are classified as fire tube or water tube. Well-known fire tube boilers are the Cochran (vertical), Cornish, Lancashire, locomotive and Scotch marine or three-pass packaged boilers. Well-known water tube boilers are the Babcock and Wilcox, Stirling and modern D-type boilers. High pressure boilers include the La Mont (forced circulation), Benson (once-through, supercritical), Loeffler (steam circulation) and Velox (pressurised combustion).
How does a Babcock and Wilcox boiler work?
A Babcock and Wilcox boiler has a horizontal steam drum above a bank of straight water tubes inclined at about 15 degrees, joined to front and rear headers. The furnace burns under the high end of the tubes, and baffles make the hot gas cross the tubes three times. Water falls from the drum down the downcomer to the rear header, rises through the heated tubes as a steam and water mixture, and returns to the drum, where the steam separates and is taken through the superheater.
What is the difference between boiler mountings and accessories?
Boiler mountings are fittings needed for safe operation and control, such as the safety valve, water level gauge, pressure gauge, steam stop valve, feed check valve, fusible plug and blow-off cock. Accessories such as the economiser, superheater, air preheater and feed pump are added to improve efficiency or capacity, and the boiler can run without them.
Why does a Benson boiler not need a steam drum?
A Benson boiler works above the critical pressure of water, 220.6 bar, where water turns into steam without boiling and there are no bubbles to separate. A high pressure feed pump drives the water once through the economiser, furnace tubes and superheater, so no drum is needed. It is called a once-through boiler.
Who Uses This Simulator?
Mechanical and power-plant engineering students working through thermal engineering and steam-generation units; diploma, ITI and vocational learners preparing for boiler-operator and boiler-attendant examinations; teachers who need a projected, animated boiler for the classroom; and anyone who has wondered what actually happens inside a boiler.
Selected References
R. K. Rajput, Thermal Engineering; P. K. Nag, Power Plant Engineering; Y. A. Çengel and M. A. Boles, Thermodynamics: An Engineering Approach (steam tables); Babcock & Wilcox, Steam: Its Generation and Use; ASME Boiler and Pressure Vessel Code, Sections I and IV; EN 12952 and EN 12953.
Explore Related Simulators
Follow the steam on into the Rankine Cycle Simulator, where the boiler is one process of the power cycle, or into the cylinder of a reciprocating engine in the Steam Engine Simulator, and see boiling itself in the Phase Change simulator. For a power station with no fuel at all, compare the Hydroelectric Power Plant Simulator. Size the shell with the Thin-Walled Pressure Vessel calculator, study the economiser and air heater as a Heat Exchanger, revise the laws behind it all in the Thermodynamics simulator, and see the feed pump at work in the Centrifugal Pump simulator.
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