Economizers (spelled US and Oxford), or economisers (UK), are mechanical devices intended to reduce energy consumption, or to perform useful functions such as preheating fluid. The term economizer is used for other purposes as well. Boilers, power plants, heaters, cooling, ventilation, and AC (HVAC) use are discussed in this article. Simply put, the economizer is a heat exchanger.
Video Economizer
Mesin stirling
Robert Stirling's innovative contribution to hot air engine design in 1816 was what he called 'Economiser'. Now known as a regenerator, it stores heat from the engine's heat section when air is passed to the cold side, and releases heat into the cooled air as it returns to the hot side. This innovation improves the efficiency of the Stirling engine enough to make it commercially successful in certain applications, and has since become a component of every air machine called the Stirling engine.
Maps Economizer
Boiler
In boilers, economizers are heat exchangers of hot liquids, usually water, up but not usually outside the boiling point of the liquid. Economizers are so named because they can take advantage of enthalpy in a hot fluid stream, but not hot enough to be used in a boiler, thus restoring a more useful enthalpy and improving boiler efficiency. They are devices installed in boilers that conserve energy by using exhaust gases from the boiler to heat the cold water used to fill it (feed water ).
Recovery of energy heat by condensing economizer.
The boiler room is a great energy guzzler. It consists of a thermal liquid boiler or steam boiler, with exhaust gases through a common chimney. Indirect contact or direct contact of condensing economizer will recover the residual heat from the combustion product. A series of dampers, an efficient control system, as well as a ventilator, allowing all or part of the combustion product to pass through the economizer, depending on the demand for make-up water and/or process water. The gas temperature can be lowered from 200 ° C to 10 ° C, while preheating the water process from 8 ° C to 80 ° C. On average over the years, the boiler combustion efficiency has increased from 80% to more than 95%. The resulting heat efficiency is directly related to the boiler efficiency. Percentage of excess air and combustion product temperature are two key variables in evaluating this efficiency.
Natural gas combustion requires a certain amount of air to be complete, so the burner requires excess airflow to operate. Burning produces moisture, and its quantity depends on the amount of natural gas being burned. Also, the evaluation of the dew point depends on the excess air. Natural gas has different combustion efficiency curves associated with excess gas and air temperatures. For example, if the gas is cooled to 38 ° C and there is 15% of excess air, the efficiency will be 94%. The condensation economizer can thus recover the sensible and latent heat in the vapor condensate contained in the exhaust for the process. The Economizer is made of aluminum alloy and stainless steel. The gases pass through the cylinder and water through a finned tube. It condenses about 11% of the water contained in the gas.
History
The first successful economizer design was used to improve the steam enhancement efficiency of a stationary steam engine boiler. It was patented by Edward Green in 1845, and has since been known as Green's economizer . It consists of an array of vertical cast iron tubes connected to the water tank above and below, where the boiler's exhaust gas is passed. This is an inverse setting which is usually but not always visible in the flame boiler tube; there is a hot gas usually passes through a tube immersed in water, while in the economizer the water passes through the tube surrounded by hot gas. While both are heat exchangers, in a boiler the combustion gases heat the water to produce steam to drive the engine, whether piston or turbine, while in the economizer, some of the heat energy that would otherwise lost into the atmosphere instead used to heat water and/or air that will enter the boiler, thus saving fuel. The most successful feature of Green's economizer economizer is its mechanical scraper, which is necessary to keep the tube free from soot deposition.
Economizers were finally suited for virtually all stationary steam engines within decades after Green discovery. Some stationary steam engine sites still have their Green savings even though they are usually not used. One of the preserved sites is Claymills Pumping Engines Trust in Staffordshire, England, which is in the process of restoring a set of economisers and associated steam engines that drive them. Another example is the British Engineerium at Brighton & amp; Hove, where the economiser associated with the boiler for the Number 2 Engine is in use, complete with a small stationary-related machine. The third site is the Coldharbour Mill Working Wool Museum, where the Green gauge works in the framework of work, complete with the driving shaft of the Pollit and Wigzell steam engines.
Power plant
Modern boilers, such as those in coal-fired power stations, are still equipped with economizers that are derived from the original Green design. In this context they are often referred to as bait water heaters and heat the condensate from the turbine before being pumped into the boiler.
Economizers are generally used as part of a steam recovery steam generator at a combined cycle power plant. In HRSG, water passes through economizer, then boiler and then superheater. The Economizer also prevents flooding of boilers with liquid water that is too cold to boil given the flow rate and boiler design.
A common application of economizers in a steam power plant is to capture waste heat from a gas stack boiler (flue gas) and transfer it to a feedwater boiler. This increases the boiler feed water temperature, lowering the required energy input, which in turn reduces the required combustion rate for the rated boiler output. Economizers lower the pile temperature which can lead to condensation of acid burning gases and serious equipment corrosion damage if care is not taken in the design and selection of materials.
HVAC
HVAC systems (heating, ventilation and air conditioning) of a building can use air side movers to conserve energy in buildings using cold outside air as a means of cooling indoor space. When outside air temperature is less than recirculated air temperature, conditioning with outside air is more energy efficient than conditioning with recirculated air. When the outside air is cool enough and quite dry (depending on climate) the amount of enthalpy in the air is acceptable and no additional conditioning is required; part of the air side's economizer control scheme is called free cooling.
Economical side air can reduce the cost of HVAC energy in cold and temperate climates while also potentially improving indoor air quality, but which is most often not appropriate in hot and humid climates. With precise controls, economizers can be used in a climate that experiences various weather systems. For information on how economizers and other controls can affect the energy efficiency and indoor air quality in buildings, see the US Environmental Protection Agency report, "IAQ Energy Cost and Performance of Ventilation and Control Studies Systems." [4]
When the air-dry and wet-sphere temperature is low enough, the water side economizer can use water cooled by a wet cooling tower or a cooling cooler (also called liquid cooling) to cool the building without operating the chiller. They are historically known as the filter cycles, but the water-side economizer is not a true thermodynamic cycle. Also, instead of passing the cooling tower water through the filter and then to the cooling coil, which causes fouling, more often the plate-and-frame heat exchanger is inserted between the cooling tower and the cold water loop.
Good control, and valves or dampers, as well as maintenance, are required to ensure proper operation of the air and water side economizers.
Cooling
Cooler Economizer
A common form of economizer refrigeration is the "walk-in cooler economizer" or "outdoor air conditioning system". In systems outside the air which are colder than the air in the cooled chamber is brought into the chamber and the same amount of heat in the air is channeled out. The cooling supplement produced or replaced the operation of the compressor-based cooling system. If the air in the cooled chamber is only about 5 Â ° F warmer than the outside air that replaces it (ie, T & gt; 5 Â ° F) this cooling effect is achieved more efficiently than the same amount of cooling generated from the compressor-based system. If the outside air is not cool enough to overcome the cooling loads the compressor system space should also operate, or the indoor temperature will rise.
Steam Compression Refrigeration
Another use of this term occurs in industrial cooling, particularly the cooling of vapor compression. Typically, the economizer concept is applied when a particular design or feature on the cooling cycle, allowing a good reduction in the amount of energy used from the power grid; in component size (essentially the nominal capacity of the gas compressor) used to produce cooling, or both. For example, for a freezer running stored at -20 ° F (-29 ° C), the main cooling component will include: an evaporator coil (a compact fluid-filled pipe arrangement and a thin metal fin used to remove heat from the freezer ), a fan to blow air on the coil and around the box, air-cooled condensing units placed outdoors, and valves and pipes. The condensing unit will include a compressor and a coil and a fan to exchange heat with ambient air.
The economizer screen takes advantage of the fact that the cooling system has increased efficiency at increased pressure and temperature. The required power of the gas compressor is strongly correlated with ratios and differences, between discharge and suction pressure (as well as other features such as refrigerant heat capacity and compressor type). Low temperature systems such as freezers move less fluid in the same volume. That means pumping less efficient compressors at low temperature systems. This phenomenon is notable when taking into account that the evaporation temperature for freezers running at -20 ° F (-29 ° C) may be around -35 ° F (-37 ° C). Systems with economizers aim to produce part of the cooling work at high pressure, a condition in which the gas compressor is usually more efficient. Depending on the application, this technology enables smaller compression capacity to provide enough pressure and flow for systems that typically require a larger compressor; increasing the capacity of the system without the economizer will produce less cooling, or allow the system to produce the same amount of cooling by using less power.
The economizer concept is related to subcooling because the condensed viscous channel temperature is usually higher than the evaporator, making it a good place to apply the idea of ​​increased efficiency. Given the freezer example indoors, the normal temperature of the liquid ducts in the system is about 60 ° F (16 ° C) or even higher (it varies depending on the condensing temperature). The condition was far less hostile to produce a coolant, than the evaporator at -35 ° F (-37 ° C).
Economizer settings in cooler
Some displays allow the cooling cycle to work as economizers, and benefit from this idea. The design of such a system demands a certain skill on this issue, and the manufacture of certain tools, sophistication and endurance. Decrease in pressure, control of electric valves and oil retardants, should all be attended with special attention.
Two systems and boosters are staged
A system is said to be in two prepared stages if two separate gas compressors in a serial display work together to produce compression. A normal booster installation is a two-stage system that receives a liquid cooling the first compressor discharge, before reaching the second compressor input. The liquid coming to the second interstage of the compressor comes from the liquid line and is usually controlled by the expansion valve, pressure and solenoid.
A standard two-step staged cycle of this kind will have expansion valves that expand and modulate the number of incoming refrigerants in the interstage. When the fluid arriving at the interstage expands, it will tend to evaporate, resulting in overall temperature drop and cooling the suction of the second compressor when mixed with the liquid released by the first compressor. Such arrangements may have a heat exchanger between expansion and interstage, a situation in which the second evaporator can serve to produce cooling as well, though not as cool as the main evaporator (eg to produce air conditioning or to keep it fresh). product). The two-stage system is said to be arranged in a booster view with subcooling, if the refrigerant arriving at the interstage passes through a subclass heat exchanger cooling the main liquid duct that arrives to the main evaporator of the same system.
Economizer gas compressor
The need to use two compressors when considering booster settings tends to increase the cost of the cooling system. In addition to the price of the gear, two gradual systems require special attention to synchronization, pressure control and lubrication. To reduce this cost, special equipment has been described.
Economizer screw compressors are being built by several manufacturers such as Refcomp, Mycom, Bitzer and York. These machines combine the two compressors from the two-stage system into one screw compressor and have two inputs: the main suction and the interstage entrance for the higher-pressure gas. This means no need to install two compressors and still benefit from the booster concept.
There are two types of economizer settings for this compressor, flash and subcooling. The latter works under the same principle as the two booster displays staged with subcooling. Flash drive is different because it does not use heat exchanger to produce sub-cooling. Instead, it has a flash space or tank, where flash gas is produced to lower the liquid temperature before expansion. The flash gas produced in this tank leaves the liquid line and enters the screw compressor economizer entrance.
Optimization of recycling and cooling cycle
All previous systems produce economizer effects by using compressors, meters, valves and heat exchangers in the cooling cycle. Depending on the system, in some cooling cycles it may be easier to produce an economizer using an independent cooling mechanism. Such is the case of subcooling the liquid line in another way that draws heat out of the main system. For example, heat exchangers that preheat cold water required for other processes or human use, can draw heat from the liquid channel, effectively unifying channels and increasing system capacity.
Recently, machines designed specifically for this purpose have been developed. In Chile, EcoPac Systems manufacturers develop cycle optimizers that can stabilize liquid line temperatures and enable increased system cooling capacity, or reduced power consumption. Such a system has the advantage of not disrupting the original design of the cooling system into an attractive alternative to expanding a single staged system that has no economizer compressor.
Internal heat exchanger
Sub-cooling can also be produced by heating the heat of the gas leaving the evaporator and leading to the gas compressor. This system draws heat from the liquid line but heats the suction of the gas compressor. This is a very common solution to ensure that the gas reaches the compressor and the liquid reaches the valve. It also allows the use of a maximum heat exchanger as minimizing the portion of the heat exchanger used to alter the temperature of the liquid, and maximizes the volume at which the refrigerant alters the phase (a phenomenon involving more heat flow, the basic principle of cooling vapor compression).
An internal heat exchanger is simply a type of heat exchanger that uses cold gas leaving the evaporator coil to cool the high pressure fluid leading to the beginning of the evaporator coil through an expansion device. The gas is used to cool the space that usually has a series of pipes for the fluid that flows through it. Super hot gas then continues to the compressor. The term subcooling refers to cooling the liquid below its boiling point. 10Ã, Â ° F (5.6Ã, Â ° C) sub-cooling means 10Ã, Â ° F cooler than boiling at a certain pressure. Since this represents a temperature difference, the sub-cooling value will not change when measured on an absolute scale, or relative scale (10 Â ° F sub-cooling equals 10 Â ° R (5.6 Â ° K) of sub-cooling).
See also
- Backflow exchange
- Regenerative heat exchanger
- Feed water heater
- Thermal efficiency
References
- Hills, Richard L. (1989). Strength of Steam . Cambridge University Press. ISBN: 0-521-45834-X.
Source of the article : Wikipedia
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