Package boiler

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Typical gas-fired package boiler
The burner and centrifugal blower is at the left. Two vertical water level gauges can also be seen. History of lff2.jpg
Typical gas-fired package boiler
The burner and centrifugal blower is at the left. Two vertical water level gauges can also be seen.

A package boiler is a factory-made boiler. Package boilers are available in a range of standard designs. Package boilers are used for heating and act as a steam generator for small power purposes such as self-powered industrial plants. Package boilers are low pressure designs. A low pressure means low temperature water in the heat exchanger. The large difference between the flame temperature and the heat exchanger discards most of the available entropy. Discarding most of the entropy caps the thermodynamic efficiency below the range needed to make a low pressure boiler suitable for a co-generation plants even when the available capacity is adequate for the application. Advantages of package boilers are that they can be delivered and installed as a complete insulated assembly that doesn’t require a large exclusion zone around itself. The required steam, water, fuel, and electrical connections can be made rapidly. These boilers are inexpensive to operate because their automatic burner management system doesn’t require continuous supervision and they have low scheduled maintenance costs. [1]

Contents

A great cost-saving for package boilers is their reduced need for draughting. In operation the stack gasses are cooler and less corrosive than solid fuels. They may be vented using an existing masonry chimney, or an insulated coaxial steel tube chimney. Because the burner’s blower delivers combustion air, the over-fire draught negative pressure required is nearly nil. Stack height need only be sufficient for structure safety and to clear the nuisance of the exhaust fumes. The tall chimney needed to provide a large negative pressure to draw combustion air through a bed of solid fuel is not required. In most installations a barometric damper is used to maintain a constant over-fire draught so that the air to fuel ratio remains constant instead of increasing with the increasing draught available at the stack as the outdoor temperature falls.

Internal arrangement

Internal layout of a three-pass fire-tube boiler Flammrohrrauchrohrkessel 7.jpg
Internal layout of a three-pass fire-tube boiler

Package boilers are commonly called water or fire tube Boilers. Water tube boilers use convection heating, which draws the heat from the fire source, and passes against the generating tubes of the boiler, causing water inside those tubes to boil off into steam. The fire tube boiler arrangement utilizes conduction heating which transfers heat from physical contact. Fire tube boilers are not commonly used due to their method of conduction heating because pipes in direct contact with fire and cold water could damage the pipes. The package boiler is usually a two or three-pass fire-tube boiler with an internal furnace tube. This is similar to the much earlier Scotch boiler.

Generating tubes filled with water are in direct contact with the heat source inside the boiler, causing damage to the pipes as well as scaling. These boilers however are great with steam production due to the large volume inside the boiler and the surface area of the steam output. In order for these boilers to operate properly, they require a long warm-up process, and are prone to thermal shock of the boiler. These boilers can be rated up to 500,000 lb/hr. [2] The wall membrane of the boiler are dual welded, (welded on either side of the wall membrane) to provide extra reinforcement for high loads.

A-type, D-type and O-type are all water tube package boilers.

Combustion

Package boilers are fired from fuel oil in the form of liquid or gas. Fuel is ignited in the burners which creates an explosion within the boiler. Such package boiler do not require purifiers (filters) because they burn consistently removing all contaminants within the fuel. To create constant combustion within the boiler, the forced draft fan forces air into the burner, causing a tornado effect creating turbulence to keep the flame ignited and the furnace pressurized. Other essentials such as Burner electronics provide auto-ignition and on-demand lighting feature that monitors the flame and pressure within the boiler. tube boiler Package boilers are commonly called water or fire tube Boilers. Water tube boilers use convection heating, which draws the heat from the fire source, and passes against the generating tubes of the boiler, causing water inside those tubes to boil off into steam. The fire tube boiler arrangement utilizes conduction heating which transfers heat from physical contact. The package boiler is usually a two or three-pass fire-tube boiler with an internal furnace tube. This is similar to the much earlier Scotch boiler.

Pros and Cons

Pros [1]

Cons

Types of Package Boilers

The D-type Package Boiler

The D-type boiler has a water drum, steam drum, and generating tubes. Water flows into the steam drum, flows down the downcomers and into the water drum. Water is then sent from the water drum through the generating tubes, where the fire is located around causing water molecules to boil off into steam. Steam rises up more generating tubes and finally back into the steam drum where the dry pipe is located then into the plant. This configuration shaped the package boiler into a D-shape, hence the name D-type package boiler. These boilers are mostly used for plants that allow greater clearances.

The A-type Package Boiler

The A-type package boiler has two water drums and one steam drum compared to the D-type package boiler. Water boils off in the water drums shared by a common header, then sent up the generating tubes, into the steam drum and up the dry pipe. Just like the D-type package boiler, fire heats the tubes surroundings causing the tubes to increase in temperature thus boiling off water molecules to steam. A-type package boilers were designed to improve package boiler reliability and reduce tube replacements. A-type package boilers are smaller than D-type therefore will fit smaller plants, but does not have the same power output as D-type package boilers.

The O-type Package Boiler

O-Type Package boiler. The boiler has two drums, one water drum and one steam drum. The combustion chamber is in the middle surrounded by downcomers and generating tubes. Boiler Type O.jpg
O-Type Package boiler. The boiler has two drums, one water drum and one steam drum. The combustion chamber is in the middle surrounded by downcomers and generating tubes.

The O-type boilers are a little simpler compared to D-type and A-type. They consist of one water drum and one steam drum. Generating tubes are lined up from either sides of the steam and water drums. When water boils due to convection heating, steam rises up through the tubes and into the steam drum. This is a symmetrical design for restrictive plant layouts. O-type boilers are mainly used for their fast steam production and reduced maintenance cost. [3]

Related Research Articles

Boiler Closed vessel in which fluid is heated

A boiler is a closed vessel in which fluid is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.

Furnace (central heating) Device used for heating buildings

A furnace, referred to as a heater or boiler in British English, is an appliance used to generate heat for all or part of a building. Furnaces are mostly used as a major component of a central heating system. Furnaces are permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water. Heating appliances that use steam or hot water as the fluid are normally referred to as a residential steam boilers or residential hot water boilers. The most common fuel source for modern furnaces in North America and much of Europe is natural gas; other common fuel sources include LPG, fuel oil, wood and in rare cases coal. In some areas electrical resistance heating is used, especially where the cost of electricity is low or the primary purpose is for air conditioning. Modern high-efficiency furnaces can be up to 98% efficient and operate without a chimney, with a typical gas furnace being about 80% efficient. Waste gas and heat are mechanically ventilated through either metal flue pipes or polyvinyl chloride (PVC) pipes that can be vented through the side or roof of the structure. Fuel efficiency in a gas furnace is measured in AFUE.

Fluidized bed combustion Technology used to burn solid fuels

Fluidized bed combustion (FBC) is a combustion technology used to burn solid fuels.

Fire-tube boiler Type of boiler

A fire-tube boiler is a type of boiler in which hot gases pass from a fire 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.

Water-tube boiler Type of furnace generating steam

A high pressure watertube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which boils 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.

Steam explosion Explosion created from a violent boiling of water

A steam explosion is an explosion caused by violent boiling or flashing of water or ice into steam, occurring when water or ice is either superheated, rapidly heated by fine hot debris produced within it, or heated by the interaction of molten metals. Pressure vessels, such as pressurized water (nuclear) reactors, that operate above atmospheric pressure can also provide the conditions for a steam explosion. The water changes from a solid or liquid to a gas with extreme speed, increasing dramatically in volume. A steam explosion sprays steam and boiling-hot water and the hot medium that heated it in all directions, creating a danger of scalding and burning.

Heat recovery steam generator

A heat recovery steam generator (HRSG) is an energy recovery heat exchanger that recovers heat from a hot gas stream, such as a combustion turbine or other waste gas stream. It produces steam that can be used in a process (cogeneration) or used to drive a steam turbine.

Thermal power station Power plant that generates electricity from heat energy

A thermal power station is a type of power station in which heat energy is converted to electrical energy. In a steam-generating cycle heat is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a steam turbine connected to an electrical generator. The low-pressure exhaust from the turbine enters a steam condenser where it is cooled to produce hot condensate which is recycled to the heating process to generate more high pressure steam. This is known as a Rankine cycle.

Pellet stove

A pellet stove is a stove that burns compressed wood or biomass pellets to create a source of heat for residential and sometimes industrial spaces. By steadily feeding fuel from a storage container (hopper) into a burn pot area, it produces a constant flame that requires little to no physical adjustments. Today's central heating systems operated with wood pellets as a renewable energy source can reach an efficiency factor of more than 90%.

Boiler (power generation) High pressure 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.

Flued boiler

A shell or flued boiler is an early and relatively simple form of boiler used to make steam, usually for the purpose of driving a steam engine. The design marked a transitional stage in boiler development, between the early haystack boilers and the later multi-tube fire-tube boilers. A flued boiler is characterized by a large cylindrical boiler shell forming a tank of water, traversed by one or more large flues containing the furnace. These boilers appeared around the start of the 19th century and some forms remain in service today. Although mostly used for static steam plants, some were used in early steam vehicles, railway locomotives and ships.

High Marnham Power Station Former coal-fired power station in England

High Marnham Power Station was a coal-fired power station in Nottinghamshire, to the west of the River Trent, approximately 0.5 miles (0.8 km) north of the village of Marnham. Construction began in 1954, power generation commenced in 1959, and the station became fully operational in 1962. The plant operated until 2003 when it was decommissioned, though the cooling towers weren't demolished until 2012.

Boilers for generating steam or hot water have been designed in countless shapes, sizes and configurations. An extensive terminology has evolved to describe their common features. This glossary provides definitions for these terms.

A Field-tube boiler is a form of water-tube boiler where the water tubes are single-ended. The tubes are closed at one end, and they contain a concentric inner tube. Flow is thus separated into the colder inner flow down the tube and the heated flow upwards through the outer sleeve. As Field tubes are thus dependent on thermo-syphon flow within the tube, they must thus always have some vertical height to encourage the flow. In most designs they are mounted near-vertically, to encourage this.

Three-drum boiler Compact furnace with two side water drums and one steam drum above

Three-drum boilers are a class of water-tube boiler used to generate steam, typically to power ships. They are compact and of high evaporative power, factors that encourage this use. Other boiler designs may be more efficient, although bulkier, and so the three-drum pattern was rare as a land-based stationary boiler.

Soot blower

A sootblower is a device for removing the soot that is deposited on the internal furnace tubes of a boiler during combustion to prevent plugging of the gas passes and maintain boiler efficiency.

Johnson boiler

The Johnson boiler is a water-tube boiler used for ship propulsion.

Computational fluid dynamics (CFD) are used to understand complex thermal flow regimes in power plants. The thermal power plant may be divided into different subsectors and the CFD analysis applied to critical equipment/components - mainly different types of heat exchangers - which are of crucial significance for efficient and trouble free long-term operation of the plant.

O-type boiler

An O-type boiler is a form of water-tube boiler. It is named, like the D-type and A-type boilers, from the approximate shape of its tubes.

Industrial furnace Device used for providing heat in industrial applications

An industrial furnace, also known as a direct heater or a direct fired heater, is a device used to provide heat for an industrial process, typically higher than 400 degrees Celsius. They are used to provide heat for a process or can serve as reactor which provides heats of reaction. Furnace designs vary as to its function, heating duty, type of fuel and method of introducing combustion air. Heat is generated by an industrial furnace by mixing fuel with air or oxygen, or from electrical energy. The residual heat will exit the furnace as flue gas. These are designed as per international codes and standards the most common of which are ISO 13705 / American Petroleum Institute (API) Standard 560. Types of industrial furnaces include batch ovens, vacuum furnaces, and solar furnaces. Industrial furnaces are used in applications such as chemical reactions, cremation, oil refining, and glasswork.

References

  1. 1 2 Punte, S. "Type of boilers". www.energyefficiencyasia.org. Retrieved 2016-04-14.
  2. Funk, Jason R. "Boilers Basics" (PDF). dol.ks. Hughes Machinery. Archived from the original (PDF) on 21 April 2016. Retrieved 14 April 2016.
  3. Bases, G. "Techs & Specs - National Insulation Association". www.insulation.org. Archived from the original on 2016-05-30. Retrieved 2016-04-14.