Ash cooling & Post-combustion

Q: How high is the temperature of the bottom ash at the FAC^TM (Futong Ash Cooler) discharging point?

A: The temperature at the discharging point depends on many parameters: such as the bottom ash rate, the ash grain size distribution, the length and speed of the FAC^TM extractor etc. Furthermore, each FAC^TM system is designed according to specific requirements. Therefore, it is difficult to define a general value.

Nevertheless, it can be said that in most cases the average ash temperature at the discharging point of the FAC^TM extractor is in the range of 80 - 150 °C in normal, continuous operating conditions of boiler.

Q: Does the post-combustion effect in the ash damage the Futong Super Steel Belt?

A: No. First of all, for most ashes the post-combustion in the FAC^TM system takes place mainly during the downfall of the ash through the boiler throat and hopper (if any) onto Futong Super Steel Belt, where it encounters the heated air flowing up from the FAC^TM into the boiler. Once deposited on the belt, the ash starts to cool down quickly.

If, on the other hand, the unburned carbon content in the ash is high or the post-combustion effect is slow, the ash can also continue to burn during conveying on Futong Super Steel Belt. Even if the burning ash is very hot and sometimes flames may hit the belt, this does not cause any damage, because the belt is kept relatively cool however, thanks to the cooling air flowing underneath it. The stainless steel from which Futong Super Steel Belt is made up, can operate without any problems in these conditions.

Q: What about cooling downstream of the FAC^TM?

A: By including Post-cooling Conveyors (PCC^TM) in the FAC^TM system, an effective further cooling after the FAC^TM extractor can be obtained. Just as the FAC^TM extractor, the Post-cooling Conveyor (PCC^TM) is operated with a slightly negative pressure inside the casing, so cooling air is drafted into the casing from the ambient. This cooling air is subsequently sent back to the FAC^TM via a connecting duct.

Also if a pneumatic conveying system is used, further cooling takes place. As a result, at the final discharge point of the FAC^TM system the ash temperature is generally close to  the temperature 80 - 150 °C.

Q: What is the actual temperature of the casing of the FAC^TM extractor?

A: The ambient air flowing into the FAC^TM extractor, not only cools the ash but also keeps the extractor’s casing at a low temperature. During normal operation, any part of the casing that is accessible to personnel, is at the temperature under 60°C. Any parts of the casing that may be at a higher temperature, are made inaccessible or adequately shielded by protection covers.

Q: How effective is the cooling of large clinkers?

A: Large clinkers are difficult to cool with traditional technology: even if the outer surface gets cooled rapidly, the core usually remains hot. However, with Futong patented PCBD^TM  (Pre-crushing Bottom Doors) technology, the cooling of large clinkers is more easy. Futong patented PCBD^TM is much different to the conventional flap bottom doors. Futong’s PCBD^TM can pre-crush the big ash clinkers less than 350mm, So as to improve cooling effect of the bottom ash on the steel belt dramatically. Meanwhile, it can greatly reduce the wear and load of the crusher, and effectively avoid the backflow the bottom ash to the bottom of the extractor.

Q: Ash clinkers falling from boilers can be as big as 1 x 1 x 2 m. Will the FAC^TM extractor not fail if such an impact occurs?

A: No. With Futong patented PCBD^TM (Pre-crushing Bottom Doors) technology, the big ash clinkers will fall on the impact bars firstly. The operator can monitor the real-time situation on the impact bars through video cameras in the control room. Then the big ash clinkers will be pre-cooled and pre-crushed into the size lower than 300 mm by the operators through the operation of horizontal-moved pre-crushing bottom doors and then

transported by Futong Super Steel Belt extractor.

Q: Is it necessary to avoid direct falling of large clinkers onto the Futong Super Steel Belt? If so, how is it done?

A: No. By its special design, the large ash clinkers will drop the impact bars firstly. Moreover, the Futong Super Steel Belt has a fine characteristic to absorb huge impact loads. Furthermore, under the boiler throat the supporting idlers are closely spaced in order to spread the impact over a large area.

Nevertheless, if the fall of large ash clinkers is very frequent, it may be preferable to avoid the direct impact of such lumps onto the Futong Super Steel Belt. This can be obtained by an asymmetric design of the bottom ash hopper, whereby the FAC^TM extractor and the boiler throat axes are offset. In that case, large clinkers would first fall on the sloped hopper walls.

Q: How can large ash clinkers be handled by the FAC^TM system?

A: The FAC^TM extractor is designed to ensure that anything that passes through the boiler throat, also passes through the FAC^TM extractor. Normally the width of Futong Super Steel Belt is 1200 mm [4 ft] whereas the height of the casing above the belt is typically 1000 mm [3’3”], whereas the boiler throat opening width is usually not more than 900 mm [3 ft]. This means that any big ash clinker falling from the boiler can be conveyed through the FAC^TM extractor to the primary crusher. The outlet size from the crusher is sufficiently low to enable further ash processing in downstream equipment.