Climax boiler

The large industrial boiler known as the Climax was one of the first of this overall type. It was invented by Thomas F. Morrin and Walter W. Scott of New Jersey and was patented in 1884. The water-tubes were single-turn loops aligned diagonally and arranged into horizontal tiers. The upper tube entry is vertically above the lower entry of the adjacent tube. In the original patent, tubes are hairpin-shaped with radial straight sections. Later designs used a larger outer radius and "pear-shaped" tubes,finally a tube shape that was almost the radius of the outer casing. Reducing the curvature of tubes like this reduces the effects of expansion due to heating and the risk of leakage at the tube entries. The water level of these boilers was around 3/4 of the height of the tube tiers, so that the upper tubes were filled with steam rather than water. Above the tube banks a single flat spiral tube was used as an economiser or feedwater heater.

The furnace used to fire these large boilers was annular, often with four or more separate firedoors. The boiler was also successfully fired with bagasse, plant waste or refuse. Where they were used for continual high-power production, such as for electricity generation, some were also used with early automatic stokers. One advantage of these boilers was the rapidity with which they could be constructed. A factor in this was their pre-fabricated steel casings that were bolted together in sections. Although their potential for high pressure was not made use of, they did gain a reputation for reliability and long service between overhaul.

These boilers were developed by Morrin & Scott at the "Clonbrook Steam-Boiler Works" and have no connection with either the Climax Locomotive Works or their logging locomotives. They were licensed for production to the "Clonbrook Steam-Boiler Co.", but in 1896, their previous manager Thomas J. Lawler began production of a competing boiler at the "Columbian Steam-Boiler Works" and Morrin & Scott successfully sued them for infringement of the Climax patents.

Flued boiler

An early proponent of the cylindrical form, was the American engineer, Oliver Evans who rightly recognised that the cylindrical form was the best from the point of view of mechanical resistance and towards the end of the 18th Century began to incorporate it into his projects. Probably inspired by the writings on Leupold’s “high-pressure” engine scheme that appeared in encyclopaedic works from 1725, Evans favoured “strong steam” i.e. non condensing engines in which the steam pressure alone drove the piston and was then exhausted to atmosphere. The advantage of strong steam as he saw it was that more work could be done by smaller volumes of steam; this enabled all the components to be reduced in size and engines could be adapted to transport and small installations. To this end he developed a long cylindrical wrought iron horizontal boiler into which was incorporated a single fire tube, at one end of which was placed the fire grate. The gas flow was then reversed into a passage or flue beneath the boiler barrel, then divided to return through side flues to join again at the chimney (Columbian engine boiler). Evans incorporated his cylindrical boiler into several engines, both stationary and mobile. Due to space and weight considerations the latter were one-pass exhausting directly from fire tube to chimney. Another proponent of “strong steam” at that time was the Cornishman, Richard Trevithick. His boilers worked at 40–50 psi (276–345 kPa) and were at first of hemispherical then cylindrical form. From 1804 onwards Trevithick produced a small two-pass or return flue boiler for semi-portable and locomotive engines. The Cornish boiler developed around 1812 by Richard Trevithick was both stronger and more efficient than the simple boilers which preceded it. It consisted of a cylindrical water tank around 27 feet (8.2 m) long and 7 feet (2.1 m) in diameter, and had a coal fire grate placed at one end of a single cylindrical tube about three feet wide which passed longitudinally inside the tank. The fire was tended from one end and the hot gases from it travelled along the tube and out of the other end, to be circulated back along flues running along the outside then a third time beneath the boiler barrel before being expelled into a chimney. This was later improved upon by another 3-pass boiler, the Lancashire boiler which had a pair of furnaces in separate tubes side-by-side. This was an important improvement since each furnace could be stoked at different times, allowing one to be cleaned while the other was operating.

Multi Tube Boilers

A significant step forward came in France in 1828 when Marc Seguin devised a two-pass boiler of which the second pass was formed by a bundle of multiple tubes. A similar design with natural induction used for marine purposes was the popular “Scotch” marine boiler.

Prior to the Rainhill trials of 1829 Henry Booth, treasurer of the Liverpool and Manchester Railway suggested to George Stephenson, a scheme for a multi-tube one-pass horizontal boiler made up of two units: a firebox surrounded by water spaces and a boiler barrel consisting of two telescopic rings inside which were mounted 25 copper tubes; the tube bundle occupied much of the water space in the barrel and vastly improved heat transfer. Old George immediately communicated the scheme to his son Robert and this was the boiler used on Stephenson's Rocket, outright winner of the trial. The design was and formed the basis for all subsequent Stephensonian-built locomotives, being immediately taken up by other constructors; this pattern of fire-tube boiler has been built ever since.

steam generator

A boiler or steam generator is a device used to create steam by applying heat energy to water. Although the definitions are somewhat flexible, it can be said that older steam generators were commonly termed boilers and worked at low to medium pressure, but at pressures above this it is more usual to speak of a steam generator

A boiler or steam generator is used wherever a source of steam is required. The form and size depends on the application: mobile steam engines such as steam locomotives, portable engines and steam-powered road vehicles typically use a smaller boiler that forms an integral part of the vehicle; stationary steam engines, industrial installations and power stations will usually have a larger separate steam generating facility connected to the point-of-use by piping. A notable exception is the steam-powered fireless locomotive, where separately-generated steam is transferred to a receiver (tank) on the locomotive.

Solar water heaters

Increasingly, solar powered water heaters are being used. Their solar collectors are installed outside dwellings, typically on the roof or walls or nearby. Many models are the direct-gain type, consisting of flat panels in which water circulates. Heating water itself directly is inherently more efficient than heating it indirectly via antifreeze and heat exchangers. However with hard water supplies, direct solar heaters may need limescale control.

Another type of solar collector is the evacuated tube. It has a row of glass tubes containing heat conducting rods, typically copper which as heating elements in a circulating loop of antifreeze. The captured heat is transferred into the domestic hot water system via a heat exchanger. Usefully, this design is smaller and more efficient than traditional flat plate collectors, and works well in very cold climates. The evacuated description refers to air having been removed from the glass tubes to create a vacuum. This results in very low heat loss, once the inside coating has absorbed solar radiation. So the antifreeze, if pressurised, can be heated to well over 100C if required. Vacuum tubes can be deployed successfully in homes where suitable roof space is a limiting factor: where there is typically less than 1 sqm of sunny roof per person. Other types of solar collector may use solar concentrator dish or trough mirrors to concentrate sunlight on a collector tube filled with water, brine or other heat transfer fluid.

A storage vessel/container is placed indoors or out. Circulation is ideally zero carbon, caused by either natural convection thermosyphon or by a small solar electric pump. However it can also be low carbon circulation, typically, when higher power mains electric powered pumps are used, for example to cope with viscous antifreeze based circuits in cold climates. At night, or when insufficient sunlight is present, circulation through the panel can be stopped by closing a motorised valve and/or stopping the circulating pump, to keep hot water in the storage tank from cooling. Depending on local climate, freeze protection (e.g. via freeze-tolerant silicone rubber water channels, draining the system down or the use of antifreeze), as well as prevention of overheating, must be addressed in their design, installation, and operation.

Combination boilers

Combination or combi boilers, combine the central heating (CH) with (tankless) domestic hot water (DHW) in one box. They are not merely infinitely continuous water heaters having the ability to heat a hydronic heating system in a large house. When DHW is run off, the combi stops pumping water to the hydronic circuit and diverts all the boiler's power to instantly heating DHW. Some combis have small internal water storage vessels combining the energy of the stored water and the gas or oil burner to give faster DHW at the taps or increase the DHW flowrate.

Combi boilers are rated by the DHW flowrate. The kW ratings for domestic units are 24 kW to 54 kW, giving approximate flowrates of 9 to 23 litres (2.4 to 6.1 USgal) per minute. There are larger commercial units available. High flowrate models will simultaneously supply two showers. A further advantage is that more than one combi unit may be used to supply separate heating zones, giving greater time and temperature control, and multiple bathrooms. An example is one combi supplying the downstairs heating system and another the upstairs. One unit may supply one bathroom and one another. Having two units gives backup in case one combi is down, provided the 2 systems are connected with valves that are normally closed.

Installation cost is significantly lower and less space is required as water tanks and associated pipes and controls are not required. Combi boilers are highly popular in Europe, where in some countries market share is 70%. Combination boilers have disadvantages. The water flow rate is likely to be less good than from a storage cylinder, particularly in winter. The power rating needs to be matched to heating requirements; heating water ‘on demand’ improves energy efficiency but limits the volume of water available at any moment. The water supply pressure must not be too low. A combination boiler has more moving parts that can break down, so can be less reliable than a tank system.

Water heating

Water heating is a thermodynamic process using an energy source to heat water above its initial temperature. Typical domestic uses of hot water are for cooking, cleaning, bathing, and space heating. In industry, both hot water and water heated to steam have many uses. Domestically, water is traditionally heated in vessels known as water heaters, kettles, cauldrons, pots, or coppers. These metal vessels heat a batch of water but do not produce a continual supply of heated water at a preset temperature. The temperature will vary based on the consumption rate of hot water, use more and the water becomes cooler. Appliances for providing a more-or-less constant supply of hot water are variously known as water heaters, boilers, heat exchangers, calorifiers, or geysers depending on whether they are heating potable or non-potable water, in domestic or industrial use, their energy source, and in which part of the world they are found. In domestic installations, potable water heated for uses other than space heating is sometimes known as domestic hot water (DHW).

In many countries the most common energy sources for heating water are fossil fuels: natural gas, liquefied petroleum gas, oil, or sometimes solid fuels. These fuels may be consumed directly or by the use of electricity (which may derive from any of the above fuels or from nuclear or renewable sources). Alternative energy such as solar energy, heat pumps, hot water heat recycling, and sometimes geothermal heating, may also be used as available, usually in combination with backup systems supplied by gas, oil or electricity.

In some countries district heating is a major source of water heating. This is especially the case in Scandinavia. District heating systems make it possible to supply all of the energy for water heating as well as space heating from waste heat from industries, power plants, incinerators, geothermal heating, and central solar heating. The actual heating of the tap water is performed in heat exchangers at the consumers' premises. Generally the consumer needs no backup system due to the very high availability of district heating systems.

Stirling boiler

The Stirling boiler has near-vertical, almost-straight watertubes that zig-zag between a number of steam and water drums. Usually there are three banks of tubes in a "four drum" layout, but certain applications use variations designed with a different number of drums and banks. They are mainly used as stationary boilers, owing to their large size, although the large grate area does also encourage their ability to burn a wide range of fuels. Originally coal-fired in power stations, they also became widespread in industries that produced combustible waste and required process steam. Paper pulp mills could burn waste bark, sugar refineries their bagasse waste.

Water Tube boiler

A water tube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Water tube boilers are used for high-pressure boilers. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes. In smaller boilers, additional generating tubes are separate in the furnace, while larger utility boilers rely on the water-filled tubes that make up the walls of the furnace to generate steam.

The heated water then rises into the steam drum. Here, saturated steam is drawn off the top of the drum. In some services, the steam will reenter the furnace through a superheater to become superheated. Superheated steam is defined as steam that is heated above the boiling point at a given pressure. Superheated steam is a dry gas and therefore used to drive turbines, since water droplets can severely damage turbine blades.

Cool water at the bottom of the steam drum returns to the feedwater drum via large-bore 'downcomer tubes', where it pre-heats the feedwater supply. (In 'large utility boilers', the feedwater is supplied to the steam drum and the downcomers supply water to the bottom of the waterwalls). To increase economy of the boiler, exhaust gases are also used to pre-heat the air blown into the furnace and warm the feedwater supply. Such water tube boilers in thermal power station are also called steam generating units.

Shell and tube heat exchanger

A shell and tube heat exchanger is a class of heat exchanger designs.It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. As its name implies, this type of heat exchanger consists of a shell (a large pressure vessel) with a bundle of tubes inside it. One fluid runs through the tubes, and another fluid flows over the tubes (through the shell) to transfer heat between the two fluids. The set of tubes is called a tube bundle, and may be composed by several types of tubes: plain, longitudinally finned.

Locomotive boiler

A locomotive boiler has three main components: a double-walled firebox; a horizontal, cylindrical "boiler barrel" containing a large number of small flue-tubes; and a smokebox with chimney, for the exhaust gases. The boiler barrel contains larger flue-tubes to carry the superheater elements, where present. Forced draught is provided in the locomotive boiler by injecting exhausted steam back into the exhaust via a blast pipe in the smokebox.

Locomotive-type boilers are also used in traction engines, steam rollers, portable engines and some other steam road vehicles. The inherent strength of the boiler means it is used as the basis for the vehicle: all the other components, including the wheels, are mounted on brackets attached to the boiler. It is rare to find superheaters designed into this type of boiler, and they are generally much smaller (and simpler) than railway locomotive types.

The locomotive-type boiler is also a characteristic of the overtype steam wagon, the steam-powered fore-runner of the truck. In this case, however, heavy girder frames make up the load-bearing chassis of the vehicle, and the boiler is attached to this.

Cornish boiler

The earliest form of fire-tube boiler was Richard Trevithick's "high-pressure" Cornish boiler. This is a long horizontal cylinder with a single large flue containing the fire. The fire itself was on an iron grating placed across this flue, with a shallow ashpan beneath to collect the non-combustible residue. Although considered as low-pressure (perhaps 25 psi) today, the use of a cylindrical boiler shell permitted a higher pressure than the earlier "haystack" boilers of Newcomen's day. As the furnace relied on natural draught (air flow), a tall chimney was required at the far end of the flue to encourage a good supply of air (oxygen) to the fire.

For efficiency, the boiler was commonly encased beneath by a brick-built chamber. Flue gases were routed through this, outside the iron boiler shell, after passing through the fire-tube and so to a chimney that was now placed at the front face of the boiler.

Fire-tube boiler

A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water. The heat of the gases is transferred through the walls of the tubes by thermal conduction, heating the water and ultimately creating steam. The fire-tube boiler developed as the third of the four major historical types of boilers: low-pressure tank or "haystack" boilers, flued boilers with one or two large flues, fire-tube boilers with many small tubes, and high-pressure water-tube boilers. Their advantage over flued boilers with a single large flue is that the many small tubes offer far greater heating surface area for the same overall boiler volume. The general construction is as a tank of water perforated by tubes that carry the hot flue gases from the fire. The tank is usually cylindrical for the most part – being the strongest practical shape for a pressurized container – and this cylindrical tank may be either horizontal or vertical.

This type of boiler was used on virtually all steam locomotives in the horizontal "locomotive" form. This has a cylindrical barrel containing the fire tubes, but also has an extension at one end to house the "firebox". This firebox has an open base to provide a large grate area and often extends beyond the cylindrical barrel to form a rectangular or tapered enclosure. The horizontal fire-tube boiler is also typical of marine applications, using the Scotch boiler. Vertical boilers have also been built of the multiple fire-tube type, although these are comparatively rare: most vertical boilers were either flued, or with cross water-tubes.

Puddling process

A number of processes for making wrought iron without charcoal were devised as the Industrial Revolution began during the latter half of the 18th century. The most successful of these was puddling, using a puddling furnace (a variety of the reverberatory furnace). This was invented by Henry Cort in 1784. It was later improved by others including Joseph Hall. In this type of furnace, the metal does not come into contact with the fuel, and so is not contaminated by impurities in it. The flame from the fire is reverberated or sent back down onto the metal on the fire bridge of the furnace.

Unless the raw material used is white cast iron, the pig iron or other raw material first had to be refined into refined iron or finers metal. This would be done in a refinery where raw coal is used to remove silicon and convert carbon from a graphitic form to a combined form. This metal was placed into the hearth of the puddling furnace where it was melted. The hearth was lined with oxidizing agents such as haematite and iron oxide. This mixture is subjected to a strong current of air and stirred with long bars, called puddling bars or rabbles,through working doors. The air, stirring, and "boiling" action of the metal help the oxidizing agents to oxidize the impurities and carbon out of the pig iron to their maximum capability. As the impurities oxidize, the retaining material solidifies into spongy wrought iron balls, called puddle balls.

Wrought iron

Wrought iron is an iron alloy with a very low carbon content, in comparison to steel, and has fibrous inclusions, known as slag. This is what gives it a "grain" resembling wood, which is visible when it is etched or bent to the point of failure. Wrought iron is tough, malleable, ductile and easily welded. Historically, it was known as "commercially pure iron", however it no longer qualifies because current standards for commercially pure iron require a carbon content of less than 0.008 wt%.

Before the development of effective methods of steelmaking and the availability of large quantities of steel, wrought iron was the most common form of malleable iron. A modest amount of wrought iron was used as a raw material for manufacturing of steel, which was mainly to produce swords, cutlery and other blades. Demand for wrought iron reached its peak in the 1860s with the adaptation of ironclad warships and railways, but then declined as mild steel became more available.

Before they came to be made of mild steel, items produced from wrought iron included rivets, nails,wire, chains, railway couplings, water and steam pipes, nuts, bolts, horseshoes, handrails, straps for timber roof trusses, and ornamental ironwork.

Stainless steel

In metallurgy stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass. Stainless steel does not stain, corrode, or rust as easily as ordinary steel, but it is not stain-proof. It is also called corrosion-resistant steel or CRES when the alloy type and grade are not detailed, particularly in the aviation industry. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and resistance to corrosion are required.

Stainless steel differs from carbon steel by the amount of chromium present. Carbon steel rusts when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion and blocks corrosion from spreading into the metal's internal structure.

Superheated steam boilers

Most boilers produce steam to be used at saturation temperature; that is, saturated steam. Superheated steam boilers vaporize the water and then further heat the steam in a superheater. This provides steam at much higher temperature, but can decrease the overall thermal efficiency of the steam generating plant because the higher steam temperature requires a higher flue gas exhaust temperature. There are several ways to circumvent this problem, typically by providing an economizer that heats the feed water, a combustion air heater in the hot flue gas exhaust path, or both. There are advantages to superheated steam that may, and often will, increase overall efficiency of both steam generation and its utilisation: gains in input temperature to a turbine should outweigh any cost in additional boiler complication and expense. There may also be practical limitations in using wet steam, as entrained condensation droplets will damage turbine blades.

Superheated steam presents unique safety concerns because, if any system component fails and allows steam to escape, the high pressure and temperature can cause serious, instantaneous harm to anyone in its path. Since the escaping steam will initially be completely superheated vapor, detection can be difficult, although the intense heat and sound from such a leak clearly indicates its presence.

Scaling of stress in walls of vessel

Pressure vessels are held together against the gas pressure due to tensile forces within the walls of the container. The normal (tensile) stress in the walls of the container is proportional to the pressure and radius of the vessel and inversely proportional to the thickness of the walls.Therefore pressure vessels are designed to have a thickness proportional to the radius of tank and the pressure of the tank and inversely proportional to the maximum allowed normal stress of the particular material used in the walls of the container.

Because (for a given pressure) the thickness of the walls scales with the radius of the tank, the mass of a tank (which scales as the length times radius times thickness of the wall for a cylindrical tank) scales with the volume of the gas held (which scales as length times radius squared). The exact formula varies with the tank shape but depends on the density, ρ, and maximum allowable stress σ of the material in addition to the pressure P and volume V of the vessel.

Shape of a pressure vessel

Pressure vessels may theoretically be almost any shape, but shapes made of sections of spheres, cylinders, and cones are usually employed. A common design is a cylinder with end caps called heads. Head shapes are frequently either hemispherical or dished (torispherical). More complicated shapes have historically been much harder to analyze for safe operation and are usually far tougher to construct.

Theoretically, a sphere would be the best shape of a pressure vessel. Unhappily, a spherical shape is tough to manufacture, therefore more expensive, so most pressure vessels are cylindrical with 2:1 semi-elliptical heads or end caps on each end. Smaller pressure vessels are assembled from a pipe and two covers. A disadvantage of these vessels is that greater breadths are more expensive, so that for example the most economic shape of a 1,000 litres (35 cu ft), 250 bars (3,600 psi) pressure vessel might be a breadth of 914.4 millimetres (36 in) and a width of 1,701.8 millimetres (67 in) including the 2:1 semi-elliptical domed end caps.