Process and apparatus for the treatment of dust or like material which is capable of trickle flow

In a process for the treatment of dust or the like containing organic constituents, in particular filter dust from foundry sands containing binding agent, the dust is introduced into a fluidizable heat carrier of refractory material, heated and burnt, wherein the heat carrier is preferably preheated to receive the dust. An apparatus for carrying out that process, a loose material bed comprising a fluidizable refractory material is arranged as a heat carrier in a combustion chamber of a furnace on a fluidization plate, and provided in the heat carrier are a heating means and at least one feed means for the dust.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for the treatment of dust or 
like material which is capable of trickle flow, said dust containing 
organic constituents, more especially filter dust from foundry sands 
containing binding agents or the like. In addition the invention concerns 
an apparatus for carrying out that process. 
For decades the practice has been simply to dispose of filter dust from dry 
filter installations of foundry works, with the foundry waste sand, on 
dumps. Now, when the new law governing the dumping of waste has come into 
force, filter dust must be deposited on special dumps if it cannot be put 
to another use. 
In recognition of that mode of disposal, the invention set himself the aim 
of improving the disposal of dust or like material which is capable of 
trickle flow of the kind referred to above. 
SUMMARY OF THE INVENTION 
The foregoing object is achieved by way of the present invention wherein 
the dust is introduced into a fluidisable heat carrier of refractory 
material, heated and burnt, wherein the heat carrier is preferably 
preheated to receive the dust; the procedure involved makes use of the 
fact that filter dust generally includes an enrichment of high-energy, 
organic and therefore burnable noxious substances and in accordance with 
the invention an inerting operation is carried out by a thermal procedure. 
Admittedly, so-called fluidised bed firing installations are known as an 
effective combustion procedure, but such processes are not suitable for 
burning dusts for the purposes of inerting thereof; due to the fact that 
the individual dust particles have low and different speeds of sinking 
movement, it was hitherto not possible to guarantee a defined residence 
time for the dust, as is required for inerting thereof, at a high 
temperature. 
In carrying the process according to the invention into effect, the dust is 
preferably introduced in the lower region of the heat carrier and the 
starting energy is taken from a heat source which is provided at that 
location and which in particular can comprise electrical heating bars; it 
is also possible however to use heating devices, more especially in bar or 
tube form, which are heated by gas, oil, steam or the like. 
In accordance with a further feature of the invention, in the refractory, 
fluidisable and heated heat carrier, the dust which is introduced is 
increased in temperature to the combustion temperature, the heat carrier 
having a speed of sinking movement which is higher than that of the dust. 
The neat carrier therefore acts as a thermal mass which on the one hand 
quickly heats the dust to ignition temperature but which on the other hand 
prevents the dust from moving upwardly excessively quickly. The heat 
carrier is circulated by a fluidisation air which is introduced in a 
pulsating manner, while an air flow which is dependent on the flow for 
combustion of the organic substances in the dust also flows through the 
heat carrier. The residence time of the dust is controlled by the height 
of the bulk material bed of the heat carrier material and by the 
fluidisation air which is introduced in a pulsating mode. It is so 
selected that the dust is made completely free of combustible substances. 
After the combustion temperature is reached in a starting phase, the 
production of heat of the preferably electrical heating means is reduced 
or at least partially switched off, depending on the respective energy 
content of the dust to be treated. Combustion then takes place 
substantially or entirely autarkically. The residence time of the dust in 
the heat carrier is advantageously determined by the supply of dust and/or 
by fluidisation air which is superimposed on the steady flow of 
fluidisation air required for fluidisation purposes. In addition the flow 
speed above the fill of heat carrier material is to be so controlled that 
it is greater than the speed of sinking movement of the dust; that causes 
the dust to be discharged. 
An apparatus which is suitable for that process for thermal inerting of the 
dust and for removal of its combustible components is distinguished in 
that disposed in a combustion chamber of a furnace on a fluidisation plate 
is a loose material bed comprising a fluidisable refractory material as a 
heat carrier, and provided in same is a heating means and over the heating 
means at least one feed means for dust. 
Preferably, extending above the fluidisation plate is at least one heating 
bar which is or are provided with the feed means at a small distance above 
the fluidisation plate. In accordance with a further feature of the 
invention, disposed in the head or top region of the loose material bed is 
at least one air feed which helps to regulate the flow speed in the 
above-mentioned fashion. Likewise, an outlet for dust particles with a 
high speed of sinking movement may be provided in the head or top region 
of the heat carrier or bed of material. 
Connected to the combustion chamber is a flow path which is defined by 
deflection surfaces or the like fitments, possibly being in the form of a 
meander-like flue gas duct, which is followed by at least one separator, 
in particular a cyclone apparatus; the non-combustible constituents of the 
dust are separated off in the separator; the gases from which the 
non-combustible constituents have been removed then pass into a 
recuperative heat exchanger which is part of the fluid flow feed and 
preheats same. The dust through-put rate can be regulated in accordance 
with the energy content of the dusts. When dealing with dusts with a very 
high energy content, the recuperator can be by-passed.

DETAILED DESCRIPTION 
The interior 10 of a furnace 12 is divided by partitions 14 and 16 into a 
furnace chamber with a flue gas chamber 18 disposed thereabove, and two 
further flue gas chambers 19 and 20 adjoining the latter, the partition 14 
which defines the furnace chamber terminates at a spacing relative to a 
furnace top 24, forming an upper flue gas passage 22, while the other 
partition 16 extends from the furnace top 24 to a lower flue gas passage 
26 which is formed with a furnace bottom portion 26. 
Extending across the furnace chamber is a porous, preferably grid-like 
fluidisation plate 30, below which is an air feed indicated at 32. 
Disposed on the fluidisation plate 30 is a loose material bed comprising a 
refractory fluidisable heat carrier 34 with a high speed of sinking 
movement. Above the fluidisation plate 30, preferably electrical heating 
bars which are indicated at 36 pass through the bed of heat carrier 
material. 
An injection nozzle 38 extends through an outside wall 11 of the furnace 12 
over at least a part of the heating bars 36. Dust which is to be rendered 
inert is introduced through the injection nozzle 38 into the loose 
material bed formed by the heat carrier 34. 
In order to guarantee a defined residence time in respect of the flue gases 
produced, in the furnace 12, provided in the furnace 12 are the three 
series-connected flue gas chambers 18, 19 and 20 which in the illustrated 
embodiment extend in side-by-side relationship, to reduce the structural 
height of the assembly. 
Arranged downstream of the last flue gas chamber 20 is a cyclone separator 
40 in which dust in the flue gas is substantially separated off. 
Downstream of the clean gas side of the cyclone separator 40 and connected 
thereto by a conduit 42 is a recuperator 44, possibly with the 
interposition of a post-combustion apparatus for noxious chemical 
substances such as dioxines or the like. 
Combustion air which comes from a blower 46 and which is required for the 
furnace 12 is passed through the recuperator 44, in a conduit 48. The 
blower 46 if necessary also supplies cooling air for the outlet 45 of the 
recuperator 44, through a branch conduit 50. 
For starting the installation, the heating bars 36 are heated to between 
about 800.degree. and 1000.degree. C., with a greatly reduced fluidisation 
air flow. The heat carrier 34 which is thereby heated in the lower region, 
as well as the heated air, transmit the temperature, by virtue of the 
fluidisation effect and the resulting circulatory movement, to the entire 
bed of material formed by the heat carrier 34 until the latter has reached 
its desired temperature of between 750.degree. and 800.degree. C. A dust 
which is to be rendered inert and which is charged with organic substances 
is now injected into the heat carrier 34 in a controlled fashion, and 
heated in the heat carrier 34. 
The steady amount of fluidisation air which is introduced into the interior 
10 of the furnace beneath the fluidisation plate 30 by way of an air feed 
device 32 from the recuperator conduit 48 is controlled in dependence on 
the CO-value of the flue gas. In the illustrated embodiment, the pulsating 
fluidisation air passes through the recuperator conduit 48 by way of a 
branch conduit 49 to an air nozzle 47; a pulse valve 47.sub.a is disposed 
upstream of the air nozzle 47. 
By virtue of its large surface area, the heat carrier 34 which is moved in 
the clockwise direction (arrow x) due to the flow of air from the lateral 
air nozzle 47 gives off its heat to the dust which burns when the ignition 
or firing temperature is reached, and in turn returns to the heat carrier 
34 the energy produced by combustion of the dust, especially in the head 
or top region of the loose material bed of heat carrier material. 
After the initial or start-up phase, the heating effect, which in the 
illustrated embodiment is produced by the electrical heating bars 34, can 
be reduced or switched off, depending on the respective energy content of 
the dust, and substantially autarkical combustion takes place. 
Above the level of the bed of heat carrier material 34, as indicated at 35, 
an outlet 56 for inerted particles with a high speed of sinking movement 
opens into the furnace, the outlet 56 preferably being provided with a 
charging valve or lock device (not shown). At that location the flow speed 
is also to be selectively increased by the provision of a feed of fresh 
air as indicated at 54, in order to promote the discharge or dust. A 
quantitative regulating valve 52 is disposed in a conduit 49.sub.a which 
is disposed upstream of the fresh air feed 54. 
The furnace interior 10 and the flue gas chambers 18, 19 and 20 are 
insulated for safety reasons and for reasons of saving energy, although 
that is not shown in detail in the drawing for the sake of clarity thereof 
.