All Topics  
Economizer

 

 
   Email Print
   Bookmark   Link
 

 

Economizer
 
 
  Topics Economizer Topic Home

Economizers, or in British English economisers, are mechanical devices intended to reduce energy consumption, or to perform another useful function like preheating a fluid
Fluid

A fluid is defined as a substance that continually deforms under an applied shear stress. All liquids and all gases are fluids. Fluids are a subset of the Phase and include liquids, gas, Plasma physics and, to some extent, plasticity ....
. The term economizer is used for other purposes as well. Boiler
Boiler

A boiler is a closed Pressure vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications....
, powerplant, and heating, ventilating, and air-conditioning (HVAC
HVAC

HVAC is an initialism or acronym that stands for "heating, Ventilation , and air conditioning". HVAC is sometimes referred to as climate control and is particularly important in the design of medium to large industrial and office buildings such as skyscrapers and in marine environments such as aquariums, where humidity and tem...
) uses are discussed in this article. In simple terms, an economizer is a heat exchanger.

lass="link1" onMouseover='showByLink("m6747336",this)' onMouseout='hide("m6747336")'href="http://www.absoluteastronomy.com/topics/Robert_Stirling">Robert Stirling
Robert Stirling

The Reverend Dr Robert Stirling was a Scotland clergyman, and inventor of the stirling engine....
's innovative contribution to the design of hot air engine
Hot air engine

Hot air engine is a catch-all term for any heat engine which uses the expansion and contraction of air under the influence of a temperature change to convert thermal energy into mechanical work....
s of 1816 was what he called the 'Economiser'.






Discussion
Ask a question about 'Economizer'
Start a new discussion about 'Economizer'
Answer questions from other users
Full Discussion Forum



Encyclopedia


Economizers, or in British English economisers, are mechanical devices intended to reduce energy consumption, or to perform another useful function like preheating a fluid
Fluid

A fluid is defined as a substance that continually deforms under an applied shear stress. All liquids and all gases are fluids. Fluids are a subset of the Phase and include liquids, gas, Plasma physics and, to some extent, plasticity ....
. The term economizer is used for other purposes as well. Boiler
Boiler

A boiler is a closed Pressure vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications....
, powerplant, and heating, ventilating, and air-conditioning (HVAC
HVAC

HVAC is an initialism or acronym that stands for "heating, Ventilation , and air conditioning". HVAC is sometimes referred to as climate control and is particularly important in the design of medium to large industrial and office buildings such as skyscrapers and in marine environments such as aquariums, where humidity and tem...
) uses are discussed in this article. In simple terms, an economizer is a heat exchanger.

Stirling engine

Robert Stirling
Robert Stirling

The Reverend Dr Robert Stirling was a Scotland clergyman, and inventor of the stirling engine....
's innovative contribution to the design of hot air engine
Hot air engine

Hot air engine is a catch-all term for any heat engine which uses the expansion and contraction of air under the influence of a temperature change to convert thermal energy into mechanical work....
s of 1816 was what he called the 'Economiser'. Now known as the regenerator, it stored heat from the hot portion of the engine as the air passed to the cold side, and released heat to the cooled air as it returned to the hot side. This innovation improved the efficiency of Stirling's engine
Stirling engine

A Stirling engine is a device that converts heat energy into mechanical power by alternately compressing and expanding a fixed quantity of air or other gas at different temperatures....
 enough to make it commercially successful in particular applications, and has since been a component of every air engine that is called a Stirling engine.

Boilers

In boilers, economizers are heat exchange devices that heat fluids, usually water, up to but not normally beyond the boiling
Boiling

Boiling, a type of phase transition, is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure....
 point of that fluid. Economizers are so named because they can make use of the enthalpy
Enthalpy

In thermodynamics and chemistry, the enthalpy is a quotient or description of thermodynamic potential of a system, which can be used to calculate the heat transfer during a quasistatic process taking place in a closed system thermodynamic system under constant pressure....
 in fluid streams that are hot, but not hot enough to be used in a boiler, thereby recovering more useful enthalpy and improving the boiler's efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water used to fill it (the feed water
Boiler feedwater

Boiler feedwater is water used to supply a boiler to generate steam or hot water. At thermal power stations the feedwater is usually stored, pre-heated and conditioned in a feedwater tank and forwarded into the boiler by a boiler feedwater pump....
).

History

The first successful design of economizer was used to increase the steam-raising efficiency
Thermal efficiency

In thermodynamics, the thermal efficiency is a Dimensionless quantity performance measure of a thermal device such as an internal combustion engine, a boiler, or a furnace, for example....
 of the boilers of stationary steam engine
Stationary steam engine

Stationary steam engines are fixed steam engines used for pumping or driving mills and factories, and for power generation. They are distinct from locomotive engines used on Rail transport, traction engines for heavy steam haulage on roads, steam cars , agricultural engines used for ploughing or threshing, and marine engines....
s. It was patented by Edward Green
Edward Green

Edward Green may refer to:* Edward Green , Edward "Eddie" L. Green, former head football coach at NC State and UNC Chapel Hill* Edward Howland Robinson Green, known as Colonel Green, American philatelist and numismatist...
 in 1845, and since then has been known as Green's economizer. It consisted of an array of vertical cast iron
Cast iron

Cast iron usually refers to Gray iron, but also identifies a large group of ferrous alloys, which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy....
 tubes connected to a tank of water above and below, between which the boiler's exhaust gases passed. This is the reverse arrangement to that of fire tubes in a boiler itself; there the hot gases pass through tubes immersed in water, whereas in an economizer the water passes through tubes surrounded by hot gases. The most successful feature of Green's design of economizer was its mechanical scraping apparatus, which was needed to keep the tubes free of deposits of soot
Soot

Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres, charred wood, petroleum coke, etc....
.

Economizers were eventually fitted to virtually all stationary steam engines in the decades following Green's invention. Some preserved stationary steam engine sites still have their Green's economizers although usually they are not used. One such preserved site is the Claymills Pumping Engines Trust
Claymills pumping station

Claymills Pumping Station is a restored Victorian era sewage pumping station on the north side of Burton upon Trent, Staffordshire, England. It was designed by James Mansergh and used to pump sewage to the sewage farm at Etwall....
 in Staffordshire, England, which is in the process of restoring one set of economizers and the associated steam engine which drove them.

Powerplants


Modern-day boilers, such as those in coal
Coal

Coal is a readily combustion black or brownish-black sedimentary rock. The harder forms, such as anthracite, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure....
-fired power station
Power station

A power station is an industrial facility for the Electricity generation of electric power.Power plant is also used to refer to the engine in ships, aircraft and other large vehicles....
s, are still fitted with economizers which are descendants of Green's original design. In this context they are often referred to as feedwater heater
Feedwater heater

A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system....
s and heat the condensate from turbines
Steam turbine

A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Charles Algernon Parsons in 1884....
 before it is pumped to the boilers.

Economizers are commonly used as part of a heat recovery steam generator in a combined cycle
Combined cycle

A combined cycle is characteristic of a power producing engine or plant that employs more than one thermodynamic cycle. Heat engines are only able to use a portion of the energy their fuel generates ....
 power plant. In an HRSG, water passes through an economizer, then a boiler
Boiler

A boiler is a closed Pressure vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications....
 and then a superheater
Superheater

A superheater is a device in a steam engine that heats the steam generated by the boiler again, increasing its thermal energy and decreasing the likelihood that it will condense inside the engine ....
. The economizer also prevents flooding of the boiler with liquid water that is too cold to be boiled given the flow rates and design of the boiler.

A common application of economizers in steam powerplants is to capture the waste heat from boiler
Boiler

A boiler is a closed Pressure vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications....
 stack gases (flue gas
Flue gas

Flue gas is gas that exits to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator....
) and transfer it to the boiler feedwater. This raises the temperature of the boiler feedwater thus lowering the needed energy input, in turn reducing the firing rates to accomplish the rated boiler output. Economizers lower stack temperatures which may cause condensation of acidic combustion gases and serious equipment corrosion damage if care is not taken in their design and material selection.

HVAC


Air-side economizers can save energy in buildings by using cool outside air as a means of cooling the indoor space. When the enthalpy
Enthalpy

In thermodynamics and chemistry, the enthalpy is a quotient or description of thermodynamic potential of a system, which can be used to calculate the heat transfer during a quasistatic process taking place in a closed system thermodynamic system under constant pressure....
 of the outside air is less than the enthalpy of the recirculated air, conditioning the outside air is more energy efficient than conditioning recirculated air. When the outside air is both sufficiently cool and (depending on the climate) the amount of enthalpy in the air is acceptable to the control, no additional conditioning of it is needed; this portion of the air-side economizer control scheme is called free cooling.

Air-side economizers can reduce HVAC
HVAC

HVAC is an initialism or acronym that stands for "heating, Ventilation , and air conditioning". HVAC is sometimes referred to as climate control and is particularly important in the design of medium to large industrial and office buildings such as skyscrapers and in marine environments such as aquariums, where humidity and tem...
 energy costs in cold and temperate climates while also potentially improving indoor air quality
Indoor air quality

Indoor air quality is a term referring to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants....
, but are most often not appropriate in hot and humid climates. With the appropriate controls economizers can be used climates which experience various weather systems. For information on how economizers and other controls can affect energy efficiency and indoor air quality in buildings, see the U.S. Environmental Protection Agency report, "Energy Cost and IAQ Performance of Ventilation Systems and Controls"

When the outside air's dry- and wet-bulb temperatures are low enough, water-side economizers use water cooled by a wet cooling tower
Cooling tower

Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the Wet-bulb temperature or rely solely on air to cool the working fluid to near the Dry-bulb temperature....
 to cool buildings without operating a chiller
Chiller

A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. A vapor-compression water chiller comprises the 4 major components of the vapor-compression refrigeration cycle ....
. They are historically know as the strainer cycle, but the water-side economizer is not a true thermodynamic cycle. Also, instead of passing the cooling tower water through a strainer and then to the cooling coils, which causes their fouling, more often a plate-and-frame heat exchanger is inserted between the cooling tower and chilled water loops.

Good controls, and valves or dampers, as well as maintenance, are needed to ensure proper operation of the air- and water-side economizers.

Examples of economizers in chiller
Chiller

A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. A vapor-compression water chiller comprises the 4 major components of the vapor-compression refrigeration cycle ....
s would be Flasc Economizers, Flash Economizers, and Flash Flasc Economizers.

See also

  • Countercurrent exchange
    Countercurrent exchange

    Countercurrent exchange along with Concurrent exchange comprise the mechanisms used to transfer some property of a fluid from one flowing current of fluid to another across a semipermeable membrane or thermally-conductive material between them....
  • Regenerator
  • Regenerative heat exchanger
    Regenerative heat exchanger

    A regenerative heat exchanger, or more commonly a regenerator, is a type of heat exchanger where the flow through the heat exchanger is cyclical and periodically changes direction....


  • Feedwater heater
    Feedwater heater

    A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system....
  • Thermal efficiency
    Thermal efficiency

    In thermodynamics, the thermal efficiency is a Dimensionless quantity performance measure of a thermal device such as an internal combustion engine, a boiler, or a furnace, for example....