Index

Serial no Topic name

1. Introduction of Air Preheter

2. Advantage of Air Preheater

3. Types of Air Preheater

- Recupererative Air Preheater

- Regenerative Air preheater

4. Recupererative Air preheater

-Tubular Air Preheater

-Plate type Air Preheater

5. Regenerative Air Preheater

-Ljungstrom Type Air Preheater

-Rothemahle Type Air Preheater

6. Ljungstrom Type Air Preheater

-Heat Recovery Cycle

-The Energy converser

7. Ljungstrom Air Preheater Arrengement

-Vertical Heaters

-Horizontal Heaters

-Bisectors

-Trisectors

8. Conclusion

9. Referense

1. INTRODUCTION : -

Air preheater

- Air Preheater is a heat exchanger in which air temperature is raised by transferring heat from other fluid such as flue gas. Since air preheater can be successfully employed to reclaim heat from flue gas at lower temperature levels than is possible with economizer, the heat rejected to chimney can be reduced to a great extent thus increasing the efficiency of the boiler. For every 20 ?C drop in flue gas exit temperature, the boiler efficiency increases by about 1%.Further the air preheater may also be used for heating the air to dry the coal in the pulverizing plant.

2. Advantages of Air Preheaters : -

In addition to increase in boiler efficiency the other advantages that may result in are listed below:

- Stability of combustion is improved by use of hot air.

- Intensified and improved combustion.

- Burning poor quality fuel efficiently.

- High heat transfer rate in the furnace and hence lesser heat transfer area requirement.

- Less unburnt fuel particle in flue gas thus complete combustion is achieved.

- Intensified combustion permits faster load variation.

- In the case of pulverized coal combustion, hot air can be used for drying the coal as well as for transporting the pulverized coal to burners.

- This being a non-pressure part will not warrant shut-down of units due to corrosion of heat transfer surface which is inherent with lowering of flue gas temperature.

- Lower grades of coals can be burnt efficiently with hot air.

- Faster load variations are possible.

3. TYPES OF AIR PREHEATERS : -

- Air preheaters can be classified as Recuperative and Regenerative types based on their operating principle.

- Recuperative Air Preheater :

- In Recuperative type heating medium i.e. flue gas is on one side and air is on the other side of tube or plate and the heat transfer is by conduction through the material which separates the media. These are of static construction and hence there is only nominal leakage through expansion.

- Regenerative Air Preheater :

- In Regenerative type the heating medium flows through a closely packed matrix to raise its temperature and then air is passed through the matrix to pick-up the heat. Either the matrix or the hoods are rotated to achieve this and hence there is slight leakage through sealing arrangements at the moving surfaces.

4. Recupreative Air Preheater : -

-Tubular Air preheater (Recuperative) :

This usually consists of large number of steel tubes of 40 to 65 mm dia. either welded or expanded into the tube plates at the end. Either gas or air may be allowed to flow through the tube. Gas through the tube normally requires higher size tube and vertical flow to reduce fouling. Single or more passes on the gas side and multipass cross flow on the air side usually fits in with the overall plant design. The portion of airheater at low temperature zone is designed normally with a shorter tube length so as to facilitate maintenance of surfaces due to corrosion and fouling. In some cases instead of using boiler flue gases, separate external firing is used particularly during starting.

-Plate Type Air preheater (Recuperative) :

These comprise of parallel plates which provide alternate passage for gas and air. This type is simple and compact compared to that of tubular type. The narrow passes between plates make the cleaning tedious but with shot cleaning method it is improved. But replacement is a major task.

5.Regeneration Air Preheater : -

- Ljungstrom Type (Regenerative) :

The heat transfer elements are rotated at a constant speed and they pass alternately through gas and air passes. The axis of rotation may be horizontal or vertical. The drive is normally electrical operated through reduction gear with compressed air motor as stand-by the plates forming the elements (matrix) may be varied in spacing and thickness and cold ends are made of special corrosion resistance alloy such as corten or enameled to achieve corrosion resistance. This type is very compact and lends easily for ducting

arrangement Effective cleaning of heat-transfer surface by soot blowing is possible.

Rothemuhle Type (Regenerative) :

This type is the same as the Ljungstrom type -except that the matrix element is stationary and the air gas hoods rotate. Again axis of rotation may be horizontal or vertica

6. The Ljungstrom Air Preheater : -

The Ljungstrom Air Preheater is more widely used than any other type of heat exchanger for comparable service.

Proven performance and reliability, effective leakage control, and its adaptability to most any fuel-burning process, are the bases for the It is both designed and built to operate over extended periods with durable, uninterrupted service.Simplicity of design also makes it easy and economical to maintain while in operation and at scheduled

- Application Versatility :

Available in a broad range of sizes arrangements, and materials Ljungström Air Preheaters are custom-engineered to meet specific requirements and operating conditions of a variety of applications.

° Electric power generating plants° Fluidized bed and marine boilers° Pack age & large industrial boilers° Hydrocarbon & chemical processes° Waste incinerators & drying systems° Flue gas & other reheating systems

-Heat Recovery Cycle :

The basic component of the continuously rotating cylinder, called the rotor, that is packed with thousands of square feet of specially formed sheets of heat transfer surfaces.

As the rotor revolves, waste heat is absorbed from the hot exhaust gas passing through one half of the surface.

This accumulated heat is released to the incoming air as the same surfaces pass through the other half of the structure. The heat transfer cycle is continuous as the surfaces are alternately expos ed to the outgoing gas and incoming air streams.

- The Energy Conserver :

For fossil fuel-fired power generators and industrial processes, the recovery of waste heat energy has proven to be one of the most effective ways to conserve fuel and lower operating costs.

Fuel savings with the Ljungström Air Preheater are about 1-1½% for every40°F to 50°F increase in combustion air temperature, depending on the application

They not only provide the highest fuel saving efficiency that is available, but their simplified design and operating integrity assure continuous reliable service throughout the life of the plant.

Heat energy is captured and transferred to incoming air for combustion before it is lost to the stack The result is a substantial saving in fuel that would otherwise be required to bring the air up to combustion temperature

7. Ljungstrom Air Preheater Arrangements : -

Vertical Heaters :

These are the most common air preheaters, with the rotor mounted on a vertical shaft. There is a further naming convention depending on the direction of the gas flow. A Ljungström Air Preheater where the gas flows from the

bottom to the top is referred to as vertical (V). One where the gas flows from the top to the bottom is called “vertical inverted” (VI). Vertical Inverted arrangements are the most common type of Ljungström Air Preheater because gravity

aids in clearing any as h or particulate from the rotor.

Horizontal Heaters

These air preheaters are less common and have a horizontal shaft.

- Bisector :

The majority of Ljungström Air Preheaters supplied are in the Bi- Sector design. These heaters have two basic streams, one of gas and one of air.

- Trisector :

Designed for coal-fired applications the Tri-sector air preheater permits a single heat exchanger to perform two functions: coal drying and combustion air heating.

Because only one gas duct is required, the need for ductwork expansion Joints, and insulation is greatly reduced when compared with a separate air heating system.

Equipment layout is simplified, less Structural steel is needed to install the System and less cleaning equipment is required.

The duct arrangement of a Tri-Sector shows the air and gas flows through the unit. The size and location of the primary air duct can vary, depending on the flow and temperature requirements

The design has three sectors - onefor the flue gas, one for the primary air that dries the coal in the pulverizer, and one for secondary air that goes to

the boiler for combustion

- Quadsector :

The Quad-Sector takes the family one step further, with four flow streams through the rotor The four sectors compromise one gas and one primary air as in the Tri- Sector, but there are two separate secondary air sectors

The design has the primary air sector’ flanked' on either side by secondary air, and this has a benefit on the total air-to-gas leakage of the unit.

This method of leakage reduction is ideal for applications where the pressure differential between the air and gas sides are high, such as CFB applications.

8. Conclusion : -

By this study of air preheater I know about the different types of air pre heaters , advantages of air preheater.

9. Reference : -

www.bigalop.com.on

www.engineering.indiabizclub.com

www.ask.com

www.freepatentsonline.com

www.google.co.in/images

www.weh.mantime.edu

www.arb.traning.com

www.airpreheatercompany.com