CA1145617A - Pretreatment to dewater bottom ash from a stem generator firing solid fuels - Google Patents

Abstract

PRETREATMENT TO DEWATER BOTTOM ASH
FROM A STEAM GENERATOR FIRING SOLID FUELS

Abstract of the Invention Apparatus for handling ash produced in the combustion of coal in the furnace (10) of a steam generator, including an ash hopper (14) beneath the furnace (10), a water transport system (26) for carrying the ash away from the hopper (14), a screen arrangement (32) for separating most of the water from the ash, and a relatively small settling bin (40) or tank for separating the ash from the remainder of the water. The separated water can be recycled in a closed loop (44), to be used again as the transport water.

Description

In coal-firecL steam generators, the manner in which the ash is disposed of is a matter of considerable importance. The equipment for handling the ash is costly and can require much maintenance. In prior systems, the ash is usually removed from an asl~ hopper beneath the steam generator furnace along with a considerable amount of water and allowed to settle out in dewatering bins over a long period of time, such as 18 hours. ThusJ large amounts of water have to be stored and held in reserve, not only requiring much water but also a huge storage facility. Also, in colder climates, the dewatering bins are subject to freezing and plugging during the lengthy dewatering period.
In accordanee witll the invention, an ash disposal system for ash dlscharged from a eoal-fired eombustion ehamber is provided, ineluding an ash llopper positioned beneath the eombustion ehamber into whieh tlle ash falls, means Eor maintaining a given water level in the ash hopper, a diseharge opening in the bottom of the ash hopper, through whieh the ash is diseharged, sereen means Eor separating ash from water, pipe means eonnecting the ash hopper diseharge opening with the screen means, means for adding transport water to the pipe at a point adjacent the ash hopper diseharge opening, moalls for reeyeling the water separated in the screoll means baek to tho point acljaeent tlle ash hopper discharge opening, and mealls by whicll the seplrltecl ash ean be clisehar~ed Erom the screon means.
rhe figure is a seetionZIl sicle view ot an asll clis})osll systom Eor the furnaee of a stellll gonerator.
I.ooking now to the clrawing, numeral 10 clesigllltes the furnaee of a steam generator in wh;ieh eoal is burned as 1 Euel. Slag and ash fall through the bottom opening 12 into an ash hopper 14, whieh is kept filled with water to a level 16 by means of pipe 18, _ ~5~

which continuously admits water to the hopper. An overf]ow pipe 20 keeps the water level constant.
~ valve 22 is periodically opened to discharge the ash. A clinker grinder 24 breaks up the large ash particles so that they will not become jammed in the discharge opening, and so that they may be easily transported in a stream of water away from the hopper 14. Generally, the material discharged from the hopper 14 contains 75% solids, and 25% water. Water is added to the transport pipe 26, by means of valved line 25, so that the mix transported therein is 20% ash and 80% water. This mixture is transported to a holding or surge tank 28.
A gate valve 30 in the bottom of tank 28 can be opened at short intervals, or be maintained in an opened position except when the equipment downstream thereof is being repaired, to discharge the ash and water into a vibrating dewatering screen arrangement 32. A pair of screens, 34 and 36, are continuously vibrated in any well-known manner, to separate the ash from a ma~ority of the water. The first screen 34 can separate out the more coarse particles, and screen 36 can remove the fines.
The screens are preferably slightly lnclinecl so that the solids gravi-tate towards and are dLschar~ed througll outlet 38. Some wnter will still be carried over wLth the ash The mlxturc bcLng ~ chnrged througll outlet 38 wlll be approxLmately 25% wnter nnd 75% ash, nnd Ls dlscharged Lnto holdLng tank 40. From here, Lt can be discllarged Lnto n truck, storage pond, etc.
The water f:lowing thro-l~t- the screens ls dlscharged through openlng 42, and flows througtl pipe 44 and pump 46 back to the hopper discharge to be used again as transport water.
From the above, it can be seen that a system is provided which elimi-

- 2 ~5~'7 nates the need for large settling tanks. The majority of the water can be quickly recycled, thus reducing the requirement for large quantities of water. Also, because very little time is involved, there are no freezing or plugging problems in the system. The majority of the water is constantly flowing.

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Claims (4)

Claims:

1. An ash disposal system for ash discharged from a coal-fired combustion chamber, including an ash hopper positioned beneath the combustion chamber into which the ash falls, means for maintaining a given water level in the ash hopper, a discharge opening in the bottom of the ash hopper, through which the ash is discharged, screen means for separating ash from water, pipe means connecting the ash hopper discharge opening with the screen means, means for adding transport water to the pipe at a point adjacent the ash hopper discharge opening, means for recycling the water separated in the screen means back to the point adjacent the ash hopper discharge opening, and means by which the separated ash can be discharged from the screen means.

2. An ash disposal system as set forth in Claim 1, including a holding tank in the pipe means upstream of the screen means.

3. An ash disposal system set forth in Claim 2, whrein the screen means includes a pair of screens, the first of which separates coarse ash particles from the water, and the second of which separates fine ash particles from the water.

4. An ash disposal system as set forth in Claim 3, including a settling tank downstream of the screen means ash dis-charge opening.