Air Pre heater
Air Pre heater
- Air Pre heater Functions Reduce exhaust temperature, enhance boiler efficiency, save fuel consumption. Air preheater could extract heat from…
- Increase air temperature, enhance combustion condition, reduce incomplete combustion loss. Combustion air at elevated…
- Increase furnace temperature to intensify heat transfer by radiation. Under certain boiler capacity, air at higher…
- Lower flue gas inlet temperature creates better working condition for induced draft fan.
For coal fired power plant, hot air is also medium for drying and conveying of pulverized coal.
Types of air preheater
APH could be classified into basically two types: recuperative air preheater and regenerative air preheater. Recuperative air preheater includes tubular air preheater, plate type air preheater, heat pipe air preheater. Regenerative air preheater is also called rotary air preheater.
Tubular air preheater uses thin wall tubes as heat transfer element, including acid-resistant steel tube (Corten steel, ND steel), enamel coated steel tube, borosilicate glass tube. To improve heat transfer efficiency, turbulator would be used if necessary.
For acid-resistant steel tube air preheater, parallel tubes are welded to tube sheet at two ends. Flue gas passes through tubes vertically, while combustion air passes crosswise.
For enameled tube air preheater, combustion air passes through tubes, while flue gas passes crosswise. And it is featured with smooth surface, erosion & corrosion resistant.
Glass tube air preheater has some unparallel advantages, except all the features mentioned above as enameled tube APH. For a metal tube/plate APH, metal temperature should be higher than flue gas dew point. Thermal recovery is limited considering dew point corrosion. But glass tube air preheater could work safety under 100℃ for a long term due to its excellent resistance to acid. Moreover, it has good thermal ability and resistance to thermal shock at 400℃. Although glass tube is fragile, borosilicate glass gives tubes a high elasticity. And online washing could take away soot deposit to keep its heat transfer efficiency.
Although tubular air preheater has advantages like simple structure, easy fabrication, but it is no more suitable for units with large capacity because of its large size. Following APHs will give you more options.
Flue gas from fired heaters in refinery and petrochemical plant at 250-400℃ is a huge potential for heat recovery.
Due to heat transfer by evaporation and condensation, heat pipe has high thermal efficiency. And fins on heat pipe could spread heating surface. So, heat pipe air preheater is compact in size. If certain heat pipes are broken, partition plate in the middle could avoid flue gas or combustion air leakage into the other side, operation of whole APH is not influenced. By changing heat transfer area in hot/cold end, we can get controllable temperature to avoid dew point corrosion.