Installation for heating starting materials for glass melting

An installation for heating starting materials intended for the melting of glass includes a melting furnace and a preheater for the starting materials which is arranged downstream of the melting furnace and to which a pipe is connected for from the melting furnace introducing the hot residual gases from the furnace.

BACKGROUND OF THE INVENTION 
In the glass industry, a relatively large amount of thermal energy is 
consumed in the melting of the starting materials of the glass in the 
melting furnace. Unfortunately, the efficiency of the melting furnaces is 
relatively poor because the temperature of the residual gases from these 
furnaces is determined by the melting temperature of the glass or its 
starting materials. Accordingly, various attempts have been made to 
improve the overall efficiency of these melting installations. 
In practice, therefore, recuperators for example are connected to the 
melting furnaces, these recuperators generally comprising two chambers 
which are lined with bricks accumulating the heat and, hence, stacked and 
which operate in an alternately periodic manner so that one of the 
chambers is traversed for a predetermined period of time by the residual 
gases from the furnaces (which thus heat the bricks) to be removed through 
the chimney, whilst cold fresh air simultaneously flows through the second 
chamber and is heated to act as combustion air for the melting furnace. 
Under these conditions, therefore, one of the recovery chambers is on each 
occasion heated in an alternately periodic manner by the residual gases 
from the furnace at the same time as these residual gases give off some of 
their thermal energy (to the bricks) and are slightly cooled, whilst 
cooling of the heated bricks and simultaneous reheating of the combustion 
air take place in the second chamber conjointly with the operations 
mentioned in the first place. Apart from the fact that a constant cyclic 
inversion of the chambers of the recuperator modifies the combustion 
temperature of the melting furnace, it has been found that efficiency 
cannot reach the required level. 
In other known installations, the melting furnace is preceded by a vessel 
which is intended for preheating the starting materials and into which the 
residual gases emanating from the melting furnace are introduced and 
utilised to the maximum for preheating the starting materials. 
Unfortunately, it has been found that, in this case, too, the thermal 
efficiency is still inadequate because, in addition to this deficiency, 
there is a further disadvantage that these preheaters operate inadequately 
in the event of a different grain size distribution of the particles in 
the sense that the fine particles of dust are partly drawn off, and the 
starting materials leaving the preheater frequently have a composition 
entirely different from that which they have on entering the preheater. 
Accordingly, these known heating installations are relatively expensive 
with regard to the required efficiency level which is still relatively 
low. 
SUMMARY OF THE INVENTION 
Under these conditions, the problem which the present invention seeks to 
solve is to provide an installation of the type described above which, by 
comparison with known installations, is characterised in particular by its 
improved utilisation of the thermal energy of the residual gases of the 
furnace and by favourable overall dimensions, the composition of the 
starting materials leaving the preheater largely corresponding to that of 
the starting materials entering the preheater in regard to the particle 
size distribution of their constituent particles. 
According to the invention, this problem is solved by virtue of the fact 
that a fluidised-bed preheater provided with a discharge lock is used as 
the preheater for the starting materials and by virtue of the fact that a 
high-performance dust remover, of which the dust extraction pipe is 
connected to the discharge lock of the fluidised bed, is connected to the 
residual gas pipe of the fluidised-bed preheater. 
By virtue of the use of the fluidised-bed preheater, it is possible to heat 
the starting material introduced into the preheater in an extremely 
uniform manner by favourably utilising the thermal energy of the residual 
gases recovered from the furnace. The fine particles of dust entrained by 
the residual gases of the fluidised-bed preheater may be almost completely 
collected by means of a high-performance dust remover, these fine 
particles of dust separated from the residual gases intended for the 
preheater subsequently being directly introduced, by virtue of the 
embodiment of the invention, into the discharge lock of the fluidised bed 
which reliably isolates the fluidised bed from the discharge of the 
starting materials. Accordingly, in the installation according to the 
invention, there is virtually no loss of particles from the composition of 
the starting materials such as is present on entry into the fluidised bed 
and, on leaving the preheater, the starting materials have substantially 
the same composition of particle sizes as that with which they enter the 
fluidised-bed preheater. 
It should also be mentioned here that the starting materials to be 
introduced into the preheater are preferably subjected to an extracting 
operation beforehand to separate for example the relatively coarse 
fragments of glass and other constituents which do not have to be 
preheated, and to introduce them separately into the melting furnace, as 
is already the case in practice. 
In a heating installation comprising a recuperator traversed by the 
residual gases from the furnace and preheating the combustion air intended 
for the melting furnace, it is of particular advantage in accordance with 
the invention for the pipe carrying the residual gases from the furnace to 
connect the fluidised-bed preheater to the recuperator. By virtue of this 
arrangement, the hot residual gases emanating from the melting furnace 
which, in general, are too hot for preheating the starting materials, are 
also utilised first of all in the recuperator for preheating the 
combustion air intended for the melting furnace and are only delivered 
thereafter to the fluidised-bed preheater, thereby resulting in 
particularly *utilisation of the thermal *high energy of the residual 
gases of the furnace and, hence, in a considerable improvement in the 
efficiency of the installation according to the invention in relation to 
conventional installations.

DETAILED DESCRIPTION 
The first example of embodiment of the heating installation according to 
the invention, which is illustrated in FIG. 1, comprises a furnace 1 used 
for melting starting materials suitable for the production of glass, a 
recuperator 2 traversed by the residual gases from the furnace and 
preheating the combustion air of the melting furnace, a fluidised-bed 
preheater 3 connected to a pipe 4 for introducing the residual gases from 
the furnace and a high-performance dust remover 5 which is connected to 
the fluidised-bed preheater by the residual gas pipe 6 thereof. For the 
cold starting materials to be introduced into the fluidised-bed preheater 
3, there is provided a feed hopper 7 below which is a suitable metering 
unit 8 (in this case a feed regulating conveyor for example) which is 
connected to the entrance lock 9 for the starting materials (for example a 
double-valve lock) of the fluidised-bed preheater 3. 
According to the invention, the starting materials leave the fluidised-bed 
preheater 3 through a discharge lock 10 of the fluidised bed which is 
connected by a branch pipe 11 to an intermediate reservoir 12 receiving 
the preheated starting materials and below the outlet of which there is a 
tapping unit 13 which is preferably designed for metering the starting 
materials and which is connected to the melting furnace 1 by an overflow, 
a spout or similar element 14. 
The high-performance dust remover 5 is formed by a bag filter or by any 
other suitable filter which reliably guarantees substantially complete 
separation of the fine particles entrained from the residual preheating 
gases. For the fine particles separated, the filter 5 comprises and 
endless collecting screw 15 of which the discharge nozzle 15a is connected 
by a junction pipe 16 to the discharge lock 10 of the fluidised bed. The 
residual gas pipe 6 of the fluidised-bed preheater 3 is provided with and 
adjustable cold air intake 16a. 
In this first example of embodiment (FIG. 1), the recuperator 2 which is 
arranged immediately downstream of the melting furnace 1 is a conventional 
recuperator comprising two chambers 2a and 2b of which each is traversed 
in an alternately periodic manner by the hot residual gases of the furnace 
and by the combustion air which is introduced as cold air through an inlet 
tube 17 and which is preheated in each of the corresponding chambers 2a 
and 2b before being released to the furnace or to its burner. For 
periodically inverting the flows of combustion air and residual gases of 
the furnace, there is provided in the branch pipe, between the two 
chambers 2a and 2b of the recuperator, a multiple-way valve 18 to which 
are additionally connected the inlet tube 17 and the end 4a of the pipe 4 
for introducing the residual gases from the furnace. 
In addition, a branch pipe 19 connected to a chimmney 20 opening into the 
atmosphere is preferably provided at the end 4a of the pipe 4 for 
introducing the residual gases of the furnace. In order to be able if 
necessary to discharge into the atmosphere a controllable quantity of 
residual gases from the furnace, throttle valves 21, 21a are incorporated 
at suitable places in the branch pipe 19 and in the conduit 4 for 
introducing the residual gases from the furnace. 
In view of the fact that, in the embodiment shown in FIG. 1, the residual 
gases from the furnace have already undergone cooling to a certain extent 
in the recuperator 2, a fan 22 may be incorporation in the pipe 4 for 
introducing the residual gases from the furnace, by means of which the 
residual gases may arrive under the necessary pressure at the grid 23 of 
the fluidised-bed preheater 3 and at the discharge lock 10 of the 
fluidised bed. 
With regard to the construction of the fluidised-bed preheater 3, it is 
also pointed out that, to be complete, the preheater preferably has only 
one chamber 3a for the fluidised bed and is in the form of a chute by 
which the starting materials to be preheated are uniformly transferred 
from the entrance to the exit in an adequately fluidised state. It is of 
course also possible in accordance with the invention to use suitable 
fluidised-bed preheaters having different constructions, and constructions 
comprising several fluidised-bed chambers may optionally be used. 
The mode of operation of the example of embodiment of the heating 
installation described above is explained in detail in the following. The 
starting materials intended for the melting of glass leave the feed hopper 
7 in metered form to arrive at the fluidised-bed preheater and flow in a 
uniformly fluidised state from the entrance to the exit, as already 
mentioned above, during their preheating at the same time as they are 
discharged from the preheater through the discharge lock 10 of the 
fluidised bed without any stray air being able to enter the fluidised-bed 
preheater 3 at this point. In this discharge lock of the fluidised bed, 
the fine particles entrained by the residual gases from the preheater and 
separated in the filter 5 are also mixed simultaneously and uniformly with 
the remaining starting materials so that the preheated starting materials 
arriving at the intermediate reservoir 12 have substantially the same 
composition of particle sizes as that which they had on entering the 
fluidised-bed preheater 3. From this intermediate reservoir 12, the 
preheated starting materials may arrive in uniformly metered form at the 
melting furnace 1 by way of the tapping unit 13. 
As already mentioned, the residual gases emanating from the melting furnace 
1 are delivered in an alternately periodic manner towards one of the two 
chambers 2a and 2b of the recuperator 2 where they give off a first part 
of their thermal energy for preheating the combustion air of the melting 
furnace. The residual gases required for preheating the starting materials 
are delivered through the pipe 4 (their delivery being assisted by the fan 
22) to the fluidised-bed preheater 3, i.e., into its pressure chamber 3b 
situated below the grid 23 in order to impart a fluidised state to the 
starting materials deposited onto the grid 23, to transfer them to the 
exit 10 and thus to reheat them in the desired manner. The residual gases 
flowing upwards in the chamber 3a of the fluidised bed then arrive at the 
filter 5 in the described manner. Cold air may optionally be introduced 
into the air issuing from the preheater through the connecting pipe 6a (in 
particular when the components of the filter 5 are in danger of 
deteriorating under the effects of the temperature of this issuing air). 
In conventional embodiments equipped with recuperators having two chambers, 
necessarily cyclic variations in the temperature of the combustion air of 
the melting furnace are observed on account of the periodic inversion of 
the two chambers, corresponding variations in temperature of the residual 
gases leaving the chambers thus occurring at the same time. If the 
operation of the fan 22 incorporated in the pipe 4 for introducing the 
residual gases from the furnace remains unchanged, the heating temperature 
of the starting materials is thus adapted to that of the residual gases 
introduced and the result is that, for example, the starting materials 
entering the melting furnace are proportionally hotter when the combustion 
temperature is relatively low, which means that a temporarily lower 
preheating of the combustion air to be introduced into the melting furnace 
(and thus a temorarily lower combustion) is compensated by intense 
preheating of the starting materials so that the operation of the melting 
furnace is thus regulated in a predominantly automatic manner. 
FIG. 2 shows a second example of embodiment of the heating installation 
according to the invention of which some points are slightly modified in 
relation to the first example of embodiment (FIG. 1). In FIG. 2, 
components identical with those of FIG. 1 are denoted by the same 
reference numerals so that there is no need for them to be described in 
order to avoid repetitions. 
The main difference of this second example of embodiment lies in the fact 
that the recuperator 30, traversed by the residual gases from the furnace 
and preheating the combustion air of the melting furnace 1, is designed in 
the form of an indirect-action tubular heat exchanger through which the 
hot residual gases emanating from the melting furnace 1 pass in a 
constant, uniform manner (without any inversion) and are then delivered to 
a tubular system 31 which is traversed by the fresh or cold combustion air 
which is indirectly heated therein by the residual gases from the furnace 
before being introduced through a pipe 32 into the melting furnace or its 
burners (not shown in detail). the recuperator 30 is also directly 
connected by a pipe 33 for introducing the residual gases from the furnace 
(without the interposition of a fan) to the fluidised-bed preheater 3 or 
to its pressure chamber 3b' (below the grid 23). Since the residual gases 
from the furnace may still be relatively hot in this case in relation to 
those of the example of embodiment shown in FIG. 1, it is generally 
recommended to line the pipe 33 for introducing the residual gases in such 
a way that it is heat-resistent, as partly indicated by the partly 
sectional illustration in FIG. 2. 
In addition, to avoid overheating in the fluidised-bed preheater 3 and 
hence an undesirable reaction of the starting materials by the action of 
the excessively hot residual gases from the furnace, a corresponding 
fraction of these residual gases may be discharged into the atmosphere 
(optionally by way of a chimmney), passing through a branch pipe 34 
connected to the introduction pipe 33, a fresh air intake 35 being 
connected to the pipe for introducing the residual gases 33 in the zone 
situated upstream of the fluidised-bed preheater 3 (in any case in the 
zone situated between the preheater 3 and the branch pipe 34), so that the 
residual gases from the furnace flowing towards the starting materials 
contained in the fluidised-bed preheater 3 may be brought to the necessary 
temperature by the addition and admixture of cold air. 
In this case, the necessary pressure under which the residual gases from 
the furnace are delivered to the fluidised-bed preheater is produced by a 
corresponding design of the fan 36 arranged downstream of the 
high-performance dust remover 5. 
Similarly, in this second example of embodiment, the exit of the 
fluidised-bed preheater 3 is formed by a discharge lock 37 which, in the 
same way as in the example of embodiment described above, is connected on 
the one hand by a connecting pipe 16 to the endless dust-collecting screw 
15 of the filter 5 and, on the other hand, by the connecting pipe 11 to 
the intermediate reservoir 12. Since, in this example of embodiment 
illustrated in FIG. 2, the fluidised state of the starting materials 
contained in the chamber 3a of the fluidised bed is maintained by the 
reduced pressure generated by the fan 36, it is necessary to connect the 
discharge lock 37 of the fluidised bed to a separate source of compressed 
air. To this end, a compressed-air connecting pipe 38 is used for the 
discharge lock 37 of the fluidised bed and may be connected to a 
compressed-air source not shown in detail (for example to an existing 
compressed-air system or to a small additional fan). 
In this example of embodiment of the invention, which is somewhat 
simplified in regard to its construction, there are preferably provided 
control instruments (not shown in detail) which act on the throttle valves 
39, 39a, 39b incorporated in the pipe 33 for introducing the residual 
gases, in the connecting pipe 34 and in the fresh air intake 35 so that it 
is possible to adjust any optimum temperature of the residual gases for 
heating the starting materials of the preheater 3. In this way, a 
substantially constant temperature also prevails in the melting furnace. 
While this invention has been described in detail with particular reference 
to preferred embodiments thereof, it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention as described hereinbefore and as defined in the appended claims.