Boilers, Steam Generators - Definitions, Types & Terminology - Engineering - http://maxpages.com/jpchemical/Chemical_Cleaning

Boiler

DEFINITIONS
A boiler is a closed vessel in which water or another liquid is heated under pressure. The steam or hot liquid is then circulated out of the boiler for use in various process or heating applications. A safety valve is required to prevent over pressurisation and possible explosion of a boiler.
Construction of boilers is mainly limited to steel and cast iron.
Sources of heat for the boiler can be the combustion of fuels such as wood, coal, oil or natural gas. Electric boilers use resistance-type heating elements. Waste-heat boilers use the heat rejected from other processes such as gas turbines.
A Boiler can be classified into firetube or watertube boilers depending on whether the fire is inside or outside. For example, old steam train locomotives are firetube boilers, where the fire is inside the tube and the water on the outside. Watertube boilers are where the water flows in the tube around the fire.

Basic Boiler Designs

Fire Tube Boilers.
In firetube boilers, the combustion gases pass inside boiler tubes, and heat is transferred to water on the shell side. Scotch marine boilers are the most common type of industrial firetube boiler. The Scotch marine boiler is an industry workhorse due to low initial cost, and advantages in efficiency and durability. Scotch marine boilers are typically cylindrical shells with horizontal tubes configured such that the exhaust gases pass through these tubes, transferring energy to boiler water on the shell side.

Scotch Marine - The Classic Firetube Boiler

The Scotch Marine style of boiler has become so popular in the last 40 years that it frequently is referred to simply as "a firetube boiler." Firetube boilers are available for low or high pressure steam, or for hot water applications. Firetube boilers are typically used for applications ranging from 15 to 1500 horsepower. A firetube boiler is a cylindrical vessel, with the flame in the furnace and the combustion gases inside the tubes. The furnace and tubes are within a larger vessel, which contains the water and steam.

The firetube construction provides some characteristics that differentiate it from other boiler types. Because of its vessel size, the firetube contains a large amount of water, allowing it to respond to load changes with minimum variation in steam pressure.

Steam pressure in a firetube boiler is generally limited to approximately 350 psig. To achieve higher pressure, it would be necessary to use very thick shell and tube sheet material. For this reason, a watertube boiler is generally used if pressure above 350 psig design is needed. Firetube boilers are usually built similar to a shell and tube heat exchanger. A large quantity of tubes results in more heating surface per boiler horsepower, which greatly improves heat transfer and efficiency.

Firetube boilers are rated in boiler horsepower (BHP), which should not be confused with other horsepower measurements. The furnace and the banks of tubes are used to transfer heat to the water. Combustion occurs within the furnace and the flue gases are routed through the tubes to the stack outlet. Firetube boilers are available in two, three and four pass designs. A single "pass" is defined as the area where combustion gases travel the length of the boiler. Generally, boiler efficiencies increase with the number of passes.

Water-tube boiler

From Wikipedia, the free encyclopedia.
A Water-tube boiler is a type of boiler in which water circulates in tubes which are 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 up 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 rises then rises to the steam drum. Steam then comes off the top of the steam drum where it is saturated steam. In some services, the steam will reenter the furnace in order to become superheated. Superheated steam is used in driving turbines. Since any particulate of water will severely damage turbine blades, steam is superheated to 730 F or higher to ensure that there is no water entrained in the steam. Such type of Water-tube boilers in thermal power station are also called Steam Generating units.

Image of a typical Water Tube Boiler

D-type Boiler
A D-type boiler is the most common type of small-medium sized boiler and it is used in both stationary and marine applications. It consists of a large steam drum vertically connected to a smaller water (or mud) drum via multiple steam-generating tubes. These are surrounded by walls made up of larger water filled tubes, which create the furnace.
Other types of water-tube boiler
Stirling boiler has three upper drums connected to two lower drums by water tubes. This type is mainly used as stationary boilers.
Yarrow boiler has three drums in delta formation connected by water tubes. This is mainly of Fuel_oil fired type. Being of three drum type this has greater water capacity. Hence this type is usually used in older marine boiler applications. In view of its compact size it was also used in transportable Power_generation units during the World war. To make it transportable the Boiler and its auxiliaries such as Fuel_oil heating and pumping units, fans etc., and related small sized Turbines and Condenser units were all mounted on Railway wagons for movement on Railway tracks. The electrical panels and Chimney parts etc. were supplied separately.
After the war over some unused transportable sets, as reparation units, were given given to some Indian States for augmenting their Power generating capacities.
Retrieved from "http://en.wikipedia.org/wiki/Water-tube_boiler"

Commercial Watertube Boilers
Commercial watertube boilers typically produce steam or hot water for commercial, or modest-size applications. There are a wide variety of types, sizes, capacities, and design pressures available. Commercial watertube boilers can be membrane type, straight tube, modular, etc. They can be either atmospherically fired or utilize power burners.

Industrial Watertube Boilers

The industrial watertube boiler typically produces steam or hot water primarily for industrial process applications, and is used less frequently for heating applications. In the watertube design, tubes contain steam and/or water and the products of combustion pass around the tubes. Typically, watertube designs consist of multiple drums. A steam drum (upper) and mud drums (lower) are connected by the tubes, which form both the convection section and the furnace area. Packaged industrial watertube boilers are typically rated in pounds of steam per hour output at operating conditions and range from 10,000 to 150,000 lbs/hr. Industrial watertube boilers are noted for their fast steaming capability and high steam quality. Steam is generated very rapidly because of the relatively low water content, thus allowing quick response to changing load demands.
The industrial watertube boiler design makes it capable of generating either saturated or superheated steam. When applications dictate superheated steam, large or fluctuating steam loads, high pressures or high steam quality, an industrial watertube boiler should be considered.

Cast Iron Boilers
Cast iron boilers are limited to low-pressure steam or hot water applications, and typically range in size from 25 to 200 horsepower. One advantage of the cast iron boiler is its modular design, which includes sections for field erection

Steam Information.

Steam is an invisible gas that's generated by heating water to a temperature that brings it to the boiling point. When this happens, water changes its physical state and vaporizes, turning from a liquid into a gas. Conversely, when heat energy is removed from steam, it loses its ability to retain a gaseous state and condenses back into a liquid. The resulting liquid is called condensate. The temperature at which condensation takes place is known as the dew point.When water is heated at atmospheric pressure, its temperature rises until it reaches 212°F (100°C), the highest temperature at which water can exist at this pressure. Additional heat does not raise the temperature, but converts the water to steam.One pound of water takes 1 BTU per Degree of Temperature rise up to 212°F; to form steam, an additional 970 BTUs is required for the "Latent Heat of Vaporization". Therefore, steam has (970 + (212 - Condensate Temperature)) BTUs per pound.
EXAMPLE: If the condensate temperature is 160°F, (970 + (212 - 160)) = 1,022 BTUs per pound. This clearly shows why steam has more energy content than hot water.
NOTE: These are BTUs delivered to the water; efficiency must also be factored in to determine INPUT BTU requirements.

Superheat.
Superheat refers to the process of increasing the temperature of steam above about 400°F and 100 psi to produce a very "dry" steam with absolutely no water vapor. This feature is most common in very large power plant boilers of watertube construction. An additional heat exchanger capable of the high temperatures and pressures is required.

Economizer.
Flue gases from large boilers are typically 450 - 650°F. Stack Economizers recover some of this heat for pre-heating water. The water is most often used for boiler make-up water or some other need that coincides with boiler operation. Stack Economizers should be considered as an efficiency measure when large amounts of make-up water are used (ie: not all condensate is returned to the boiler or large amounts of live steam are used in the process so there is no condensate to return.)The savings potential is based on the existing stack temperature, the volume of make-up water needed, and the hours of operation. Economizers are available in a wide range of sizes, from small coil-like units to very large waste heat recovery boilers.

UNITS OF MEASURE-TERMINOLOGY

Boiler Horsepower (BHP)- The amount of energy needed to produce 34.5 pounds of steam, per hour, at a pressure and temperature of 0 Psig and 212 ?F, with feedwater at 0 Psig and 212 ?F. This is equivalent to 33,475 BTU/Hr or 8430 Kcal/Hr.

Calorie (C) - The amount of heat required, at a pressure of one atmosphere, to raise the temperature of one gram of water one degree Celsius.

Enthalpy (H or h) - Thermodynamically, Enthalpy is defined as the sum of the internal energy of a body and the product of its volume multiplied by its pressure. For the sake of boiler calculations, Enthalpy can be defined as the amount of heat in a fluid, usually expressed as BTU/Lb or Kcal/Gram. In these cases, Enthalpy is considered to be zero at 32 ?F (0 ?C).

From and at 212 degrees F - A term used to qualify the amount of steam produced by a boiler (see the article on Steaming Rate). The qualification indicates that the amount of steam produced is at a pressure of 0 Psig and 212 ?F, with feedwater at 0 Psig and 212 ?F.

Gross Steaming Rate - the amount of steam produced by a boiler at the outlet flange of the boiler. This is the amount of steam produced before steam is removed to heat the water in the feedwater receiver (deaerator or hotwell).

Heat of Vaporization - (for boiler calculation purposes) the amount of heat required to convert water, at saturated conditions, to vapor (steam) at the same saturated conditions. Same as Latent Heat.

Latent Heat - See Heat of Vaporization.

Net Steaming Rate - The amount of steam produced, by a boiler, after blow-down and after steam is used for heating the water in the feedwater receiver (dearator or hotwell).

Saturated Liquid - Liquid that is at a Saturated Pressure at Temperature.

Saturated Steam - Steam (Vapor) that is at a Saturated Pressure and Temperature.

Saturated Vapor - Vapor that is at a Saturated Pressure and Temperature.Saturated Water - See Saturated Liquid.

Saturation Pressure - The pressure at which saturation takes place at a given temperature.

Saturation Temperature

Sensible Heat - The heat (Enthalpy), usually expressed as BTU/Lb or Cal/G, in a liquid.

Specific Heat - The amount of heat (Enthalpy) required to raise the temperature of one unit of mass, one degree. Usually expressed as BTU/LB/?F or Cal/Kg/?C.

Steaming Rate - The rate, usually expressed in Lbs/Hr or KG/Hr, at which a boiler produces steam. (See the Steaming Rate article.)

Sub-cooled Liquid - A liquid that is at a temperature or pressure below the saturation temperature and pressure.

Superheat - The extra heat imparted to a vapor (steam)in heating it from a dry saturated condition. Also the corresponding rise in temperature.

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