Ash melting furnace and ash melting method thereof

Details Ash melting furnace and ash melting method thereof Ash melting furnace and ash melting method thereof

2000-03-28

2001-02-27

Ferensic, Denise L. (Department: 3749)

Heating

Processes of heating or heater operation

Including melting, vaporizing, sintering, expanding...

C432S161000, C373S022000, C266S230000, C266S236000

Reexamination Certificate

active

06193503

ABSTRACT:

FIELD OF THE INVENTION
This invention concerns an ash-melting furnace and a method used to melt the ash. The furnace uses a burner to heat and melt the surface of ash, which may be the fly ash or the ash exhausted from an incinerator such as that which burns municipal garbage or industrial waste, or from a coal-fired boiler. This melted ash is then discharged as liquified slugs.
DESCRIPTION OF THE RELATED ART
The material exhausted from an incinerator which burns municipal garbage or industrial waste contains ash and exhaust gases. The ash is treated with a water-sealing process; the resultant wet ash is collected, and dry ash is collected in the dry state. The two types of collected ash are preprocessed by crushing them and magnetically separating and removing their iron component which has a high melting point. The wet ash is then put through a drier and mixed with the dry ash to form primary ash.
The fly ash is captured when the gases exhausted from the incinerator pass through a dust chamber, such as a bag filter, before being released into the atmosphere.
The fly ash contains a considerable volume of heavy metals and salts with a low boiling point, and most of the components will volatilize and disperse among the gases when the ash is subjected to thermal processing at high temperatures. However, the salts will damage the heat resistant portions of the furnace. This is why it is uncommon to melt the fly ash by itself. Rather, most ash processors mix the fly ash with the primary ash and melt them together.
To melt and solidify the ash mixture described above, a burner-style ash-melting furnace is used. This is a furnace which applies heat to the surface of the ash to melt it and discharges the melted ash as slugs. There are two types of burner-style ash-melting furnaces: a furnace with a round, rotating surface, and a furnace with a fixed surface, which is an inclined reflecting furnace. Then following discussion of burner-style ash-melting furnaces, the primary application for this invention, will be based on the latter type of furnace, a fixed-surface ash-melting furnace, the operation of which will now be briefly explained.
FIG. 19
shows a fixed-surface melting furnace. In this drawing, ash-melting furnace
51
is comprised of floor
55
, which inclines downward; ash supply unit
53
, which is above one end of the main body of the furnace; discharge port
57
, which is on the other end of the furnace; fixed burner
52
, which is installed on ceiling
56
; and pusher
58
, which is a means to propel the ash forward in the furnace.
The supply unit
53
comprises ash stack
60
and its supply port
54
. Ash stack
60
contains ash mixture
50
, a combination of primary ash and fly ash. The ash is fed by gravity to the highest surface of the floor of the furnace, directly below supply port
54
. The ash mixture which drops to this surface is intermittently forced along floor
55
towards the interior of the furnace by the action of pusher
58
. This forms a layer of ash
59
all along the inclined surface of floor
55
.
The burner
52
is placed along the central axis of ceiling
56
. Liquid fuel which is forced into the burner is atomized by compressed air or steam from a waste heat boiler and sprayed into the chamber, where it is mixed with hot air supplied at the same time, causing it to combust. The flames from the fixed burner
52
heat and melt the surface of ash layer
59
.
The end of floor
55
at the port
57
leads to the region where the flames from the burner
52
radiate. The exterior surface of ash layer
59
, which continues to move towards the discharge port
57
, is heated and liquified, forming molten ash
25
, which collects in slug reservoir
65
. This ash passes through drain port
20
in dike
23
as molten slugs
25
a
, which drip out of discharge port
57
. These slugs are carried on a water-sealed conveyor (not shown) and discharged to the exterior.
Related art designs for such an ash-melting furnace have the following shortcomings.
The first problem has to do with the use of a burner relying on air.
If an air-fed burner is used in the related art apparatus described above, a preheater is needed to heat the air to be used for combustion in order to boost the temperature of the flame. Further, a dust separator is needed because a large volume of the exhaust gas will consist of substances with low boiling points. And NOx will be generated from the nitrogen in the considerable quantity of air used for combustion. For these reasons a recent trend is to substitute oxygen-enriched air (with an oxygen concentration of around 30%) for ambient air (with an oxygen concentration of around 21%).
However, the ash to be melted in this sort of furnace consists of various materials with different characteristics due to their different compositions. Insofar as incinerator ash is used, there is no way to avoid fluctuations of the load. The current demand is for appropriate countermeasures for these load fluctuations to assure stable and efficient operation and to produce high-quality molten slugs.
The second problem is associated with slug reservoir
65
, in which the molten ash
25
accumulates, and drain port
20
, which extends through dike
23
on the outlet side of the reservoir.
Dike
23
, which creates the slug reservoir
65
, and drain port
20
in dike
23
are shown in FIG.
21
. Slug reservoir
65
is a more or less rectangular cistern. The molten ash
25
which accumulates in rectangular reservoir
65
is evacuated via drain port
20
in the center of the dike. However, the molten ash
25
which finds its way into the corners where dike
23
meets the walls of the reservoir stagnates there. The stagnant portions of the ash experience a drop in temperature and become larger, thus narrowing the channel. This has an adverse effect on the fluidity of the slug.
The third problem concerns the configuration of pusher
58
, which moves along floor
55
.
Either the ash layer
59
falls naturally from supply port
54
of the ash stack
60
and immediately forms a layer of ash with an angle of repose &ggr;, or the ash
50
from stack
60
is pushed towards the discharge port
57
on the far end of the furnace by pusher
58
, which moves along the floor
55
at the entrance to the chamber.
Burner
52
, which heats and melts the ash, is located along the central axis of ceiling
56
. As can be seen in
FIG. 22
(A), this burner creates a more or less round region of radiated flame
35
on the central axis of the surface of ash layer
59
. The ash in heated region
35
a
on the periphery of region
35
is heated and melts, forming a well of molten ash. From the well, the molten ash
25
drips out of discharge port
57
. However, as can be seen in FIG.
22
(A) and FIG.
22
(B), the pusher
58
used in the related art has a pushing element made as a square form
58
a
of thickness t with a rectangular cross section. When the related art pusher
58
is used, the ash is pushed across the entire width of floor
55
equally and uniformly.
Thus the ash is supplied to the region outside heated area
35
a
in the same quantity as it is to area
35
a
. The ash supplied to the region outside heated area
35
a
is pushed from supply port
54
towards discharge port
57
in an unmelted state. This unmelted ash will be mixed in with the melted ash
25
which drips out of discharge port
57
, degrading the quality of slugs
25
a.
The fourth problem concerns the kinds of incinerator ash to be processed.
In addition to the aforesaid problem, related art ash-melting furnaces experience the following problems concerning the supply of ash even when only a single sort of ash is to be melted.
1) When the ash is supplied to the entrance of the chamber on the near end of floor
55
from stack
60
of ash supply unit
53
, it is allowed to fall by its own weight. However, as the ash falls, it frequently develops cross-linkages, making it impossible to produce an even supply.
2) The ash which falls onto the near end of floor
55
is pushed along the inclined surface of the floor towards disc

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