Carbon Steel Flue Gas Economiser With Manifold Header For Pulverized Coal Boiler

Finned Tube Economizer for Pulverized Coal Boilers in Thermal Power Plant

Functions

The origin to use economizers is to heat the feed water using flue gas waster heat so as to decrease the exhaust temperature and increase boiler efficiency, save fuel consumption, which is how economizer is named. If use boiler economizers, the feed water is already heated here before coming to evaporation heating surface, thus the heat absorted on evaporation heating surface as well as the heating area is definitely decreased. Boiler economizers are countercurrent placed. The working fluid average temperature is lower than that of surnatured water, and apply mandatory flow to create conditions for application of thin wall and small diameter tubes. The whole structure is also very tight. Thus, the heat transfer temperature difference and heat transfer co-efficient is higher than that of convection evaporation tube bundle who has the same smoke temperature range. That boiler economizers to replace convection evaporation tube bundles can decrease metal consumption by a large extend. Further more, the heated feed water comes to steam drum, this way can decrease the temperature difference between the water and the steam drum wall, and ultimately decrease the thermal stress of the steam drum. Due to reasons above, now economizer are the crutial parts of boilers. So we can summerize the functions of economizers as below:

1. fuel saving: the economizers are placed at the rear part of boilers. This way can decrease the smoke and gas temperatures, thus to save fuels.

2.improve the working conditions of steam drums: due to economizers, the feed water temperature is increased when entering the steam drum. It reduces the temperature difference between the feed water and steam drum wall as well as steam drum thermal stress, so that it improve the working conditions of steam drums and increase the service life.

3.reduce the boiler manufacturing cost: for the feed water is heated in the boiler economizers. The use of low temperature spare parts as boiler economizers to replace some of high-priced high temperature water wall panels reduces the cost to manufacture boilers.

Types

If according to materials, economizers can be divided into steel tube economizers and iron economizers. At present, most large and medium volume boilers widely use steel tube made economizers, because they have high strength and reliable working ability, and are able to withstand impacts, meanwhile they have good performance of heat transfer, small structure and low cost. One weak point is bad corrusion resistance, but now the modern boiler feed water are strictly treated, so the problem is almost solved.

If according to heating extension of the working fluid, economizers can be divided into non-boiling and boiling types.

1. Boiling economizers: the outlet water temperature not only can reach the surnatured temperature, but also can make some water vapourized, the proportion is about 10-15% of total feed water, not more than 20% in case of much flow resistance caused to the working fluid.

2. Non-boiling economizers: the outlet temperature is 20-25 degrees lower than the boiling point under pressure given.

Most of medium-presssure boilers use boiling type economizers. This is because the latent heat of vaporization of water in medium-pressure boilers is high, and the heat of the heated water is smal. Thus it is necessary to send some water to be vaporized in boiler economizer so as to prevent unstable combusion in funaces and prevent increased consumption of metal in the heating surfaces as superheaters caused by too low outlet flue gas temperature. In addition, it can help to play the role of economizers.

Superhigh pressure boilers mostly use non-boiling type economizers. This is because when the pressure is higher, the latent heat of vaporization is decreased, while heat of the heated water is getting more, so it is necessary to send some water to be heated in water wall panels so as to prevent the slagging on the heating surfaces of the furnace outlets and the furnace inside caused by too high temperatures in furnaces and of outlet flue gas. So usually superhigh pressure boilers use non-boiling type economizers.

The main factor to consider which type of economizers is boiler's parameters. When the boiler parameters differ, the ratio of heat absorption needed in three stages to heat the working fluid make differences. So the corresponding arrangements of three heating surfaces need to change, too. To large units with high parameters, their evaporative heat absorption is less, while the heat absorption of water by heating, the heat absorption of steam by superheating, the heat absorption by reheating are quite big. Thus, non-boiling type economizers are the main type for superhigh pressure unit boilers.

Specifications

Quality Control

1. Impact test and Strength calculation report with applied materials information.

2. 100%NDT(non-destructive inspection) report of steel plate, tube and electrode

3. X-ray, γ-ray and liquid penetrant test inspection report (welding seam): to ensure the quality of the entire boiler

4. Hydraulic test report: ensure the standard working pressure and safety