Furnaces – Ash receiving and handling devices – Fly ash disposers
Patent
1991-12-19
1995-01-03
Yuen, Henry C.
Furnaces
Ash receiving and handling devices
Fly ash disposers
414327, 198850, 110259, F23J 100
Patent
active
RE0348147
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for continuous dry removal of bottom ash as well as to the relevant apparatus for carrying out said process.
Coal used in steam production [contain] contains inert matter in a percentage varying from 8 to 20% by weight.
In the steam producing boilers of thermoelectric power plants, fed with solid fuels, the combustion produces an ash residue of two fractions, namely fly ash carried by smoke and mainly picked up by the electrostatic filters provided for protecting the environment and bottom ash gathering on the boiler bottom, which must be removed.
Bottom ash contents [is of] are about 20% [on] of the total ash amount and they have a granule size from 0.03 to 300 mm while in the biggest pieces they may have a temperature up to 1200.degree. C.
A percentage of unburnt coal in the ashes, varying from 4 to 16% according to the design and age of the boiler, must be removed with the ash.
The presently used boilers at their bottom have a water tank adapted to cool ash so as to allow the required removal with mechanical or hydraulic systems and also to give tightness so as to prevent false air [to enter] from entering the boiler.
The mixture consisting of water, ash and unburnt coal is sent to a plant for separating and recovering water, while the dry residue, not having an economical industrial use, is sent to a dump and creates considerable environmental problems.
The present invention removes these drawbacks and provides for a dry removal of bottom ash, being based on the novel principle of using a conveyor belt to remove said ash. In order to carry out this system it was therefore necessary to study a particular conveyor belt, adapted to withstand high temperature and provided with means adapted to confer tightness around the boiler bottom.
These problems are perfectly solved by the continuous dry removal apparatus of the present invention, consisting of a [steal] steel belt conveyor made so as to withstand high temperatures, inserted in a tight steel box, which is applied to the boiler bottom so that the conveyor belt contained in the box, receives and removes continuously said ash.
The steel belt conveyor is made so as to withstand mechanical stress due to ash impact and thermal stress due to burner radiation and high temperature of the removed ash.
In said belt the load bearing function and the driving function are assigned to two different but joined elements; the load bearing function to a set of steel plates suitably shaped and partially overlapped so as to form a continuous trough; and the driving function to a net-like wired belt made of high tensile steel. Each plate is individually fixed to the belt by a set of rivets or bolts which are connected with crosspieces inserted in the links of said belt.
This system allows free expansion of the plates in every direction according to temperature variations in order to avoid permanent set.
The steel wired belt is friction actuated by a cylindrical driving drum and it is stretched by a jockey drum on which a tensioning system is acting.
The driving system, based on friction and tension, allows [that also] the wired belt [may] to have free expansion in any direction avoiding permanent set.
Therefore the values of resistances to high temperature of this system are equal to the values of heat resistance of the type of alloy steel used. Refractory steel with high chrome and nickel contents are normally used, but other alloys may be used as well.
Tension induced in the belt by the tensioning system acting on the jockey drum[,] causes a pressure between plates in their overlapping areas, such a pressure between plates for the whole belt length prevents passage [even] of even the smallest particles.
The load bearing run of the belt is supported by smooth rollers while the return run is supported by cast iron or steel wheels.
Roller shafts protrude outside the container box, so that they can be supported by bearings arranged in a cool area. Between the shafts and the corresponding holes made in the box there are heat resistan
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