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Wednesday 27 November 2013

Cooling Tower:TYPED BY METHOD OF HEAT TRANSFER

TYPED BY METHOD OF HEAT TRANSFER

All of the cooling towers described here are evaporative type towers, in that they derive their primary cooling effect from the evaporation that takes place when air and water are brought into the direct contact. At the other end os the spectrum is the Dry tower, where by full utilization of dry surface coil sections, no direct contact (and no evaporation) occurs between air and water. Hence sensible heat transfer cools the water totally.
IN between these extremes are the plume abatement and water conservation towers, wherein progressively greater portions of dry surface coil sections are introduced into the overall heat transfer system to alleviate specific problems or to accomplish specific requirements

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Cooling Tower:TYPES BY SHAPE

TYPES BY SHAPE

There are two different types:
RECTILINEAR:
These towers are constructed in cellular fashion, increasing linearly to the length and numbers of cells necessary to accomplish a special thermal performance.

ROUND MECHANICAL DRAFT:

Are towers as the name implies, are essentially round in plan configuration, with fans clustered as close practicable around the center point of the tower. Multi-faceted towers, such as the octagonal mechanical draft (OMD) also fall in the general classification of “round” towers.

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Cooling Tower:SPRAY – FILLED

SPRAY – FILLED

This kind of towers has not a heat transfer surface, depending only upon the water break-up af-forded by the distribution system to promote maximum water-to-air

characterization by construction

we can see two different kinds of cooling towers by construction:

Field-erected
Factory-assembled

Field-erected:
The field-erected cooling towers are those on which the primary construction activity takes place at the site of ultimate use. All large towers, and many of the smaller towers, are prefabricated, piece-market and shipped to the site for the cooling towers manufacturer usually provides final assembly.
FACTORY-ASSEMBLED:
The factory-assembled cooling towers undergo virtually complete assembly at their point of manufacture, whereupon there are shipped to the site in as a few sections as mode of transportation will permit.

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Cooling Tower:CHARACTERIZATION BY AIR FLOW

CHARACTERIZATION BY AIR FLOW
The cooling towers by the relative flow are divided in several groups :
COUNTERFLOW:
IN the counterflow towers, the air moves vertically upward through the fill, counter to the downward fall of water. Because of the need for extended intake and discharge plenums; the use of high pressure spray systems; and the typically higher air pressure losses, some of the smaller counter flow towers are physically higher; require more pump head; and utilize more fan power than their cross flow counterparts. In a larger counter flow towers, however, the us of low pressure grativity-related distribution systems, plus the availability of generous intake areas and plenum spaces for the air management, is tending to equalize, or even reverse, this situation. The enclosed nature of a counterflow tower also restricts exposure of the water to direct sunlight, thereby retarding the growth of the algae.

CROSSFLOW:
The crossflow towers have a fill configuration throught, which the air flows horizontally, across the downward fall of water. Water to be cooled is delivered to hot water inlet basins located atop the fill areas, and is distributed to the fill by gravity throught metering orifices in the floor of those basins.

The crossflow towers can be divided in:

DOUBLE-FLOW:

In this kind of towers the fan is inducting air through two inlets and across two banks of fill.

SINGLE-FLOW:
This kind of towers only has one air inlet and one fill bank, the remaining three sides of the towers being cased. Single-flow towers are customarily used in locations where are unrestricted air path to the tower is available from only one direction.

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Cooling Tower:HYBRID DRAFT

HYBRID DRAFT
Tgey are equiped with mechanical draft fans to augment airflow. Consequenly, they are also referred to us fan-assisted natural draft towers. The intent of their desing is to minimize the horsepower required for the air movement, but to do so with the least possible stack cost impact. Properly desogned the fans may need to be operated only during pereiods ao high ambientsand peak loads.

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Cooling Tower:MECHANICAL DRAFT

MECHANICAL DRAFT
Mechanical draft towers uses fans (one or more) to move large quantities of air through the tower. They are two different classes:

Forced draft cooling towers
Induced draft cooling towers

The air flow in either class may be crossflow or counterflow with respect to the falling water. Crossflow indicates that the airflow is horizontal in the filled portion of the tower while counterflow means the air flow is in the opposite direction of the falling water.
The counterflow tower occupies less floor space than a crossflow tower but is taller for a given capacity. The principle advantages of the crossflow tower are the low pressure drop in relation to its capacity and lower fan power requirement leading to lower energy costs.
All mechanical towers must be located so that the discharge air diffuses freely without recirculation through the tower, and so that air intakes are not restricted. Cooling towers should be located as near as possible to the refrigeration systems they serve, but should never be located below them so as to allow the condenser water to drain out of the system through the tower basin when the system is shut down.
FORCED DRAFT
The forced draft tower, shown in the picture, has the fan, basin, and piping located within the tower structure. In this model, the fan is located at the base. There are no louvered exterior walls. Instead, the structural steel or wood framing is covered with paneling made of aluminum, galvanized steel, or asbestos cement boards.

During operation, the fan forces air at a low velocity horizontally through the packing and then vertically against the downward flow of the water that occurs on either side of the fan. The drift eliminators located at the top of the tower remove water entrained in the air. Vibration and noise are minimal since the rotating equipment is built on a solid foundation. The fans handle mostly dry air, greatly reducing erosion and water condensation problems.
INDUCED DRAFT
The induced draft tower show in the following picture has one or more fans, located at the top of the tower, that draw air upwards against the downward flow of water passing around the wooden decking or packing. Since the airflow is counter to the water flow, the coolest water at the bottom is in contact with the driest air while the warmest water at the top is in contact with the moist air, resulting in increased heat transfer efficiency.

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Cooling Tower: ATMOSPHERIC

ATMOSPHERIC
The atmospheric cooling towers utilize no mechanical fan to create air flow through the tower, its air is derived from a natural induction flow provided by a pressure spray.
We can see it in the following picture:

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TYPES OF COOLING TOWERS

TYPES OF COOLING TOWERS
Cooling towers are designed and manufactured in several types:

ATMOSPHERIC
MECHANICAL DRAFT

a. FORCED DRAFT
b. INDUCED DRAFT

HYBRID DRAFT
TYPED BY AIR FLOW

a. COUNTERFLOW
b. CROSSFLOW
a.1 DOUBLE-FLOW
a.2 SINGLE-FLOW
c. SPRAY-FILLED

TYPED BY CONSTRUCTION

a. FIELD-ERECTED
b. FACTORY-ASSEMBLED

TYPED BY SHAPE

a. RECTILINEAR
b. ROUND MECHANICAL DRAFT (RMD)

TYPED BY METHOD OF HEAT TRANSFER

a. EVAPORATIVE
b. DRY TOWER
c. PLUME ABATEMENT
d. WATER CONSERVATION

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COOLING TOWERS

COOLING TOWERS

The machines and processes of industry, as well as those devoted to human comfort and well being generated tremendous amounts of heat, which must be continuously, dissipated if those machines and processes are to continue to operate efficiency. Although this heat is usually transferred to a cool, flowing volume of water, final rejection is always to the atmosphere and, invariably, is accomplished by some form of heat exchanger.
The natural process of evaporation makes them very effective heat transfer mediums, although somewhat inefficient due to their limited surface area and their total dependence upon random winds.

Friday 22 November 2013

Evaporative Condensers

The vapor to be condensed is circulated through a condensing coil, which is continually wetted on the outside by a recirculating water system. Air is pulled over the coil, causing a small portion of the recirculating water to evaporate. The evaporation removes heat from the vapor in the coil, causing it to condense.

The evaporative condenser has a cabinet with a water-sprayed condenser, and it usually has one or more fans. The excess heat is removed by evaporating water. In an evaporative condenser the primary coolant of the cooling system is cooled, which is the opposite of a cooling tower. Evaporator condensers are more expensive than dry coolers and are primarily used in large cooling systems or systems where the outdoor temperature is high. In many locations around the world, regulations limit the physical size of a cooling system and this in turn limits the use of evaporative condensers.

Spraying a condenser with water exploits the fact that the dew point temperature is lower than the air temperature and that a wet surface transfers heat more efficiently.

1 Hot primary coolant

2 Cold primary coolant

3 Cold water

4 Water sprinklers

5 Centrifugal fan

Key benefits of Evaporative Condensers

Low system operating costs: lower condensing temperatures for a more compact compressor using less power
Low refrigerant charge, costs and environmental impact minimised
Space-saving: up to 50% area savings compared to comparable air-cooled installations

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Water-Cooled Condensers

Three main types of water-cooled condensers are pipe in a Pipe", " shell and Coil and plate. Each type performs the same task, approximately in the same conditions using different designs for ships, which contain water and refrigerant in the condenser. Consider every type, from the smallest to the largest capacity.

Pipe-in-pipe", sometimes called the double pipe or coaxial capacitor. Its name reflects its design. One tube is placed in a big pipe, and the ends of large tubes are sealed. Water circulates through one of the tubes, while the refrigerant passes through the other. In this figure, the refrigerant passes through the space between the inner and outer tube. This is the normal arrangement.

These capacitors are flexible in their location and because they are long, as a rule, they are in different forms to fit the space limitations of the application. Product shown here, a boxed product, designed for installation indoors. The compact nature of pipe-in-Pipe " capacitor makes it ideal for this product.

Tube-in-tube condensers most often are used for air conditioning products up to 5 tons of cooling capacity. They are also used, however, the commercial products through approximately 20 tons, as this vertical air conditioning (VAC). This design is ideal for adding air conditioning to old buildings being renovated...

Types of Condenser

1.Air Cooled
2.Water Cooled
3.Evaporative

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Condenser

The functions of the condenser are to desuperheat the high pressure gas, condense
it and also sub-cool the liquid.
Heat from the hot refrigerant gas is rejected in the condenser to the condensing
medium-air or water. Air and water are chosen because they are naturally
available. Their normal temperature range is satisfactory for condensing
refrigerants.
Like the evaporator, the condenser is also heat exchange equipment

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Superheater

A superheater is a device found in steam boilers that is used to convert wet, saturated steam into dry steam. Superheaters are a very beneficial part of the steam cycle, because dry steam contains more thermal energy and increases the overall efficiency of the cycle. Not only that, dry steam also is less likely to condense within the cylinders of a reciprocating engine or the casing of a steam turbine. Boiler superheaters can be found in three varieties:

1.Radiant superheaters
2.Convection superheaters
3.Seperately fired superheaters.

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Atmospheric Fluidized Bed Combustion (AFBC) Boiler

Atmospheric Fluidized Bed Combustion (AFBC) Boiler

Most operational boiler of this type is of the Atmospheric Fluidized Bed Combustion. (AFBC). This involves little more than adding a fluidized bed combustor to a conventional shell boiler. Such systems have similarly being installed in conjunction with conventional water tube boiler.

Coal is crushed to a size of 1 – 10 mm depending on the rank of coal, type of fuel fed to the combustion chamber. The atmospheric air, which acts as both the fluidization and combustion air, is delivered at a pressure, after being preheated by the exhaust fuel gases. The in-bed tubes carrying water generally act as the evaporator. The gaseous products of combustion pass over the super heater sections of the boiler flow past the economizer, the dust collectors and the air preheater before being exhausted to atmosphere.

Pressurized Fluidized Bed Combustion (PFBC) Boiler

Pressurized Fluidized Bed Combustion (PFBC) Boiler

In Pressurized Fluidized Bed Combustion (PFBC) type, a compressor supplies the Forced Draft (FD) air and the combustor is a pressure vessel. The heat release rate in the bed is proportional to the bed pressure and hence a deep bed is used to extract large amount of heat. This will improve the combustion efficiency and sulphur dioxide absorption in the bed. The steam is generated in the two tube bundles, one in the bed and one above it. Hot flue gases drive a power generating gas turbine. The PFBC system can be used for cogeneration (steam and electricity) or combined cycle power
generation. The combined cycle operation (gas turbine &
steam turbine) improves the overall conversion efficiency by
5 to 8%.

Atmospheric Circulating Fluidized Bed Combustion Boilers (CFBC)

Atmospheric Circulating Fluidized Bed Combustion Boilers (CFBC)

In a circulating system the bed parameters are so maintained as to promote solids elutriation from the bed. They are lifted in a relatively dilute phase in a solids riser, and a down-comer with a cyclone provides a return path for the solids. There are no steam generation tubes immersed in the bed. Generation and super heating of steam takes place in the convection section, water walls, at the exit of the riser.

CFBC boilers are generally more economical than AFBC boilers for industrial application requiring more than 75 – 100 T/hr of steam. For large units, the taller furnace characteristics of CFBC boilers offers better space utilization, greater fuel particle and sorbent residence time for efficient combustion and SO2 capture, and easier application of staged combustion techniques for NOx control than AFBC steam generators.

Stoker Fired Boilers

Stoker Fired Boilers

Stokers are classified according to the method of feeding fuel to the furnace and by the type of grate. The main classifications are spreader stoker and chain-gate or traveling-gate stoker.

Spreader Stokers

Spreader stokers utilize a combination of suspension burning and grate burning. The coal is continually fed into the furnace above a burning bed of coal. The coal fines are burned in suspension; the larger particles fall to the grate, where they are burned in a thin, fast-burning coal bed. This method of firing provides good flexibility to meet load fluctuations, since ignition is almost instantaneous when firing rate is increased. Due to this, the spreader stoker is favored over other types of stokers in many industrial applications.

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Chain-grate or Traveling-grate Stoker

Chain-grate or Traveling-grate Stoker

Coal is fed onto one end of a moving steel grate. As grate moves along the length of the furnace, the coal burns before dropping off at the end as ash. Some degree of skill is required, particularly when setting up the grate, air dampers and baffles, to ensure clean combustion leaving the minimum of unburnt carbon in the ash.

The coal-feed hopper runs along the entire coal-feed end of the furnace. A coal gate is used to control the rate at which coal is fed into the furnace by controlling the thickness of the fuel bed. Coal must be uniform in size as large lumps will not burn out completely by the time they reach the end of the grate.

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Waste Heat Boiler

Waste Heat Boiler

Wherever the waste heat is available at medium or high temperatures, a waste heat boiler can be installed economically. Wherever the steam demand is more than the steam generated during waste heat, auxiliary fuel burners are also used. If there is no direct use of steam, the steam may be let down in a steam turbine-generator set and power produced from it. It is widely used in the heat recovery from exhaust gases from gas turbines and diesel engines.

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MECHANICAL,CSS,HTML

Wednesday 27 November 2013

Cooling Tower:TYPED BY METHOD OF HEAT TRANSFER

Cooling Tower:TYPES BY SHAPE

Cooling Tower:SPRAY – FILLED

Cooling Tower:CHARACTERIZATION BY AIR FLOW

DOUBLE-FLOW:

Cooling Tower:HYBRID DRAFT

Cooling Tower:MECHANICAL DRAFT

Cooling Tower: ATMOSPHERIC

TYPES OF COOLING TOWERS

COOLING TOWERS

Friday 22 November 2013

Evaporative Condensers

Evaporative Condensers

Key benefits of Evaporative Condensers

Water-Cooled Condensers

Water-Cooled Condensers

Types of Condenser

Condenser

Superheater

Atmospheric Fluidized Bed Combustion (AFBC) Boiler

Pressurized Fluidized Bed Combustion (PFBC) Boiler

Atmospheric Circulating Fluidized Bed Combustion Boilers (CFBC)

Stoker Fired Boilers

Chain-grate or Traveling-grate Stoker

Waste Heat Boiler

Physics basic inventions and inventors

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