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Fin tube for boiler economizer

H type fin tube waste heat recovery device (also called economizer)

The concept of economizer

The economizer  is the heating surface in the tail flue of the boiler that heats the boiler feed water into saturated water under the pressure of the steam drum. Because it absorbs relatively low temperature flue gas, it reduces the flue gas exhaust temperature and saves It improves energy and efficiency, so it is called an economizer.

Working principle of economizer

1. The economizer greatly saves fuel. The economizer absorbs the heat of the low-temperature flue gas, reduces the temperature of the flue gas, reduces the flue gas loss, and saves fuel.

Since the feed water is heated in the economizer before entering the steam drum, the heat absorption of the feed water on the heating surface is reduced, and the economizer can be used to replace part of the expensive evaporation heating surface.

2. The economizer can reduce the temperature of the flue gas, recover the heat of the flue gas, improve the thermal efficiency of the boiler, and save fuel. The temperature of the flue gas at the outlet of the superheater is about 700℃. 

Even if a large number of convection tube bundles are arranged behind the superheater, the temperature of the flue gas leaving the convection tube bundle is still as high as 250-350℃, even if a large number of convection tube bundles are arranged after the superheater. Contain a lot of calories.

3. The economizer can be combined with the circulating water pump to superimpose the water temperature over and over again to increase the boiler feed water temperature from 20 degrees Celsius to about 80 degrees Celsius to ensure that the boiler does not lose pressure or cavitation when replenishing water, and maintain the average water supply , to achieve the purpose of energy saving.

The role of economizer:

1. Absorb the heat of low-temperature flue gas, lower the exhaust temperature, reduce exhaust loss, and save fuel.

2. Since the feed water is heated in the economizer before entering the steam drum, the heat absorption of the feed water on the heating surface is reduced, and the economizer can be used to replace part of the expensive evaporation heating surface.

3. When the feed water temperature is increased, the wall temperature difference will be reduced when entering the steam drum, and the thermal stress will be correspondingly reduced, thereby prolonging the service life of the steam drum.

Classification of economizers:

1. According to materials, there are cast iron economizers and steel economizers;

2. According to the relative flow direction of flue gas and feed water, there are forward economizer and reverse economizer;

3. According to heating conditions, there are boiling economizers and non-boiling economizers;

4. According to the device, there are vertical economizer and horizontal economizer.

H-shaped finned tube economizer technology is a high-efficiency heat exchange economizer assembled with H-shaped fin tubes (also known as H-shaped fin tubes, fin tubes, and butterfly tubes).

Structure type:

The basic form is “H” type and double “H” type, arranged in series.

Performance characteristics

1) The economizer uses the H-shaped finned tube economizer to replace the bare tube economizer, which can increase the heat exchange area and reduce the number of pipe arrangements, thereby increasing the flue gas flow section, reducing the smoke velocity and reducing wear. 

Since the wear rate of the pipe is proportional to the 3.33 power of the flue gas flow rate, if the flue gas velocity is reduced from 9m/s to 7m/s, the wear rate will be reduced to 43% of the original. At the same time, the experiment shows that the finned tube itself has the function of making fly ash concentrate in the middle of the tube row, so the use of finned tube economizer can reduce the abrasion in the structure.

2) The H-shaped finned tube can be made into a double-tube “double H”-shaped finned tube. The rigidity of the structure is good and it can be applied to the occasions with long tube rows.

3) The H-shaped finned tube economizer is arranged in line. The H-shaped fin divides the space into several small areas, which has a flow equalizing effect on the airflow, and greatly reduces wear.

4) H-shaped fins can achieve the best soot blowing effect because of the straight passages formed on both sides.

5) The space is compact, the overall weight is greatly reduced, and the cost is reduced.

6) Energy saving and low power consumption: The economizer used in the generator set can reduce the heat loss of the generator exhaust by at least two-thirds, and consumes only 2 to 4 kW per ton of steam.

7) Simple operation and maintenance; labor saving: the economizer is assembled and shipped as a whole, with few moving parts, simple structure and easy installation. High level of automation, simple operation and maintenance, can reduce operating personnel.

Murphy fin tube high frequency welded aluminum fin tube for Boiler

Parameter

Steam pressure: 0.5~4.0 MPa
Steam form: saturated steam/superheated steam
4. Loop mode
Natural circulation/forced circulation
5. Scope of adaptation
It is suitable for various types of generator sets with a power range of 600kW to 15000kW and various waste heat resources with a temperature greater than 300°C.

Types of boiler economizer corrosion

1. Corrosion of boiler economizer includes internal corrosion and external corrosion. Corrosion in the pipe belongs to oxygen corrosion, also called oxygen absorption corrosion. It means that the boiler feed water still contains a certain amount of oxygen even though it has been treated. The chemical nature of oxygen is very active and can react with the iron element of steel equipment, causing damage to steel equipment. Corrosion produces iron oxides Fe2O3 and Fe3O4, which is called rust.

2. The boiler economizer is based on the above oxygen corrosion principle. When the feed water flows through the economizer tube, oxygen corrosion in the economizer tube is prone to occur due to the high temperature, and ulcer-like corrosion pits are formed on the inner wall of the tube, which endangers the boiler economy. Safe use of coal loader. Oxygen corrosion in boiler economizer tubes is usually lighter in the high temperature section than in the low temperature section, which is the result of the gradual consumption of oxygen in the feedwater.

3. The steel tube economizer is not limited by pressure and can be used as a boiling type. It is generally made of carbon steel pipes with an outer diameter of 32 to 51 mm. Sometimes fins and ribs are added to the tube to improve the heat transfer effect. The steel tube economizer consists of horizontally arranged parallel elbow tubes (usually called serpentine tubes).

The role of economizer recycling:

During the start-up process of the boiler (drum boiler), because the circulation of its steam and water pipes is not established, that is, the boiler feed water is in a stagnant state. At this time, the water in the economizer is in a non-flowing state. 

As the combustion of the boiler increases, the smoke With the increase of gas temperature, the water in the economizer is likely to vaporize, which makes the part of the economizer in an over-temperature state. 

In order to avoid this situation, connect a pipeline from the centralized downpipe of the steam drum to the inlet of the economizer , As a recirculation pipe, keep the water in the economizer in a flowing state. Avoid its vaporization.

Use effect and requirements of economizer

1. Economizer is an indispensable part of modern boilers. Its function is to use the heat of the flue gas at the tail of the boiler to heat the boiler feed water and reduce the heat loss of exhaust gas. The boiler economizer has been adopted in large boilers and has received good results.

2. The economizer can reduce the temperature of the flue gas, recover the heat of the flue gas, improve the thermal efficiency of the boiler, and save fuel. The temperature of the flue gas at the outlet of the superheater is about 700℃. 

Even if a large number of convection tube bundles are arranged behind the superheater, the temperature of the flue gas leaving the convection tube bundle is still as high as 250-350℃, even if a large number of convection tube bundles are arranged after the superheater. Contain a lot of calories.

3. The economizer can also generate a small amount of steam. The feed water entering the boiler economizer comes from the deaerator. The water temperature of the low-pressure deaerator is generally 104°C, and the water temperature of the high-pressure deaerator is about 158°C. 

The saturation temperature of the medium-pressure furnace (4.4Mpa) is about 256°C, and the saturation temperature of the high-pressure furnace (11 Mpa) is 317°C, which is much higher than the temperature of deoxygenated water.

4. The staff of the economizer must pass the medical examination, have enough lighting for night work, turn off the electric welder when leaving the scene after work, protect welding, and save electricity. 

Wear work clothes, wear glasses when welding insulated shoes, and wear glasses. When entering the site, wear a helmet and fasten your seat belt when working at heights.

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