Abstract: Faced with the shortage of energy and water resources and worsening of environment in China, it is one of the main measures to save energy in the design and reconstruction of thermal power plants that the waste heat of flue gas from power plants should be rationally used to increase the unit efficiency and reduce the coal consumption. The research shows that setting the pre-air pre-heater and bypass economizer system can increase the thermal efficiency of the whole plant, reduce the coal consumption and increase the power generation, which has certain economic and social benefits.
In order to further utilize the exhaust heat of power station boiler, a new bypass economizer is proposed. Bypass economizer can effectively use flue gas waste heat, eliminate the use of front air preheater caused by the original air preheater exhaust gas temperature increases this adverse impact.
Keywords: energy saving; waste heat utilization; pre-air pre-heater; bypass economizer
1 Introduction
March 22, the five ministries jointly issued the "cogeneration management approach," the notice made it clear that "the principle of heat and electricity" to promote the rapid and healthy development of cogeneration, coal-fired boilers energy-saving emission reduction work is imminent. All along, energy-saving emission reduction are the top priority of national work, the state have introduced a series of stringent environmental standards and major energy-saving emission reduction preferential policies. As energy consumption, large pollution, thermal power plant energy conservation is imperative.
2 energy-saving technology
Boiler exhaust loss is the largest one of the power plant boiler heat loss, accounting for about 70% ~ 80% of the boiler heat loss, the effective use of plant boiler exhaust heat, can significantly save coal consumption and reduce emissions. How to effectively use the waste heat of flue gas and develop the corresponding technical means is a hot topic for scholars today.
(1) front air preheater
Front air preheater set in the rear of the boiler, the main air preheater. The inlet air temperature of the front air preheater is about 150 ° C, a portion of the heat is gained by further reducing the exhaust air temperature to heat the low temperature air entering the main air preheater, raising the temperature of the low temperature air so that the main air preheater Avoid acid dew point temperature, to solve the main air preheater corrosion, wear, fouling and other issues, stable boiler combustion, can effectively improve the boiler efficiency.
Because the location of the front air preheater is arranged at the tail of the flue, the temperature difference of the heat exchange is small and the heat exchange area is larger. The problems of corrosion, abrasion and fouling are prominent, and the maintenance cost is high. Moreover, the new front air preheater heating area, greatly increased the flue resistance, affecting the stability of primary and secondary air. The above problems put forward higher requirements for the design and use of the front air preheater. At present, the front air preheater is mainly divided into four types of shell and tube, rotary, heat pipe, compound phase change, this article will introduce the advantages and disadvantages of four types of pre-air preheater in the work of thermal power plant in turn.
Shell and rotary pre-air pre-heater Â
As a traditional air preheater, shell and rotary air preheaters are widely used and mature in technology. However, as a pre-air preheater, there are also obvious defects.
The shell-and-tube type pre-air preheater is mainly composed of heat-exchange bundle bundles, which are fixed on the tube plates at both ends and are sealed into the sealed shell. Flue gas and low temperature air through the tube bundle for heat transfer, in order to achieve the purpose of heating low temperature air.
Tube air preheater has the advantage of good sealing, high heat transfer efficiency, easy to manufacture and process. The disadvantage is bulky, easy to plug the pipe gray, not easy to clean and easy to wear the entrance to the flue gas.
Rotary air preheaters are the most common form of regenerative air preheaters that use air and flue gas alternately to heat the air through metal heating surfaces. Rotary air preheater by movement can be divided into heated surface rotation and hood rotation two. Rotary air preheater relies on the heat transfer surface to achieve the heat exchange between the hot and cold fluids.
Rotary air preheater compact structure, small footprint, easy to layout, and good corrosion resistance to abrasion, allowing greater wear and tear. However, the rotary air preheater has a complicated structure and requires high manufacturing processes. Air leakage, serious and even affect the boiler output.
Heat pipe type pre-air pre-heater Â
As a new type of front air preheater, the heat pipe type pre-air preheater is mainly composed of a heat pipe as a heat transfer element. Heat pipe is the use of closed tube refrigerant phase transition to transfer heat efficient heat transfer components. Heat pipe heat exchanger flue gas, low-temperature air are horizontal erosion, pure countercurrent heat exchange, improve the heat transfer efficiency, making the heat transfer area, the amount of metal are greatly reduced, compact structure. At the same time, the heat pipe type pre-air preheater closed a good performance, air leakage rate is almost zero.
Although the heat pipe type pre-air pre-heater has many advantages, but its shortcomings can not be ignored. Heat pipe type pre-air pre-high cost, low operational flexibility, short life expectancy, and there is over-temperature, explosion pipe and other safety issues.
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