Abstrict The present invention relates to a rotation crusher which treats
refuse and seeks to prevent explosions by controlling the volume
of steam fed into the crusher to keep the temperature inside a main
body of the crusher between about 70.degree. C. to 100.degree. C.
so that the steam content may be regulated to exceed a certain value
to keep the oxygen content below an explosion preventive critical
value, thereby preventing completely explosions inside the crusher.
Claims We claim:
1. In a crushing process at a temperature, absent the injection
of steam, below 100.degree. C., for crushing materials including
combustible substances in which steam is injected to limit the amount
of oxygen in said crushing process to thereby eliminate the possibility
of explosions, the additional improvement steps comprising:
(a) determining the amount of steam necessary to prevent an explosion
in accordance with the graphs illustrated in FIGS. 1 through 3;
(b) deriving from the determination made in step (a) a corresponding
minimum amount of oxygen below which none of the combustible substances
could tend, together with any oxygen in said crushing process, to
cause an explosion;
(c) measuring the temperature of said crushing process at a plurality
of locations to establish by the measured temperature the amount
of steam present in said crushing process and thereby also establishing
the amount of oxygen present in said crushing process; and
(d) injecting, in response to the temperature as measured, no more
steam than is required to keep the temperature of the crushing process
at a level that assures that the oxygen content, illustrated as
a function of temperature in FIG. 4 does not exceed the value necessary
to sustain an explosion.
2. The method of claim 1 in which the injection of steam is performed
at a plurality of locations within said crushing process.
3. The method of claim 1 further comprising the additional step
of performing the crushing process at atmospheric pressure.
4. The method according to claim 1 in which the steam content necessary
to prevent explosions when only propane gas is the combustible substance
in the crushing process is determined in accordance with the graph
illustrated in FIG. 1.
5. The method according to claim 1 in which the steam content necessary
to prevent explosions when only gasoline vapor is the combustible
substance in the crushing process is determined in accordance with
the graph illustrated in FIG. 2.
6. The method according to claim 1 in which the steam content necessary
to prevent explosions when only methane gas is the combustible substance
in the crushing process is determined in accordance with the graph
illustrated in FIG. 3.
Description BACKGROUND OF THE INVENTION
The present invention relates to an explosion preventive rotation
crusher which crushes into small pieces big-size disused articles
such as furniture and the like and non-combustible garbage such
as empty cans and bottles and the like.
With development of industries and economies, people have changed
their ways of life and refuse from homes and factories has become
various in kind and increased in quantity. In big cities home garbage
such as left-over foods, waste paper and the like and big-size disused
articles (such as furniture) and non-combustible garbage are collected
separately. The home garbage is burned in an incinerator. On the
other hand, the big-size disused articles and the non-combustible
garbage are crushed into small pieces by horizontal axis type or
vertical axis type rotation crushers and then are grouped into combustible
refuse, metal, glass, and others. The combustible refuse is burned
and metal is put to reuse.
Both the horizontal axis type and the vertical axis type rotation
crushers which crush big-size disused articles and non-combustible
refuse, are so structured that hammers rotate at high speed inside
the crushers to strike, sear and grind the big-size articles and
non-combustible refuse.
Consequently, in the event that combustible refuse happens to have
been mixed in the refuse to be crushed, such as big-size articles
and incombustible refuse, a danger of explosions and fires occurs.
In fact, explosions frequently occur at refuse treating facilities
which dispose of such big-size articles in disused and incombustible
refuse.
A known explosion preventive rotation crusher treating big-size
disused articles and incombustible refuse is filled with steam,
nitrogen gas, CO.sub.2 and the like to keep pressure inside the
crusher within a predetermined range, thereby making oxygen content
almost nil inside the crusher to prevent explosions. Since the crusher
is kept pressurized and filled with steam or the like, explosions
are prevented even if combustible refuse is mixed in the refuse
to be crushed.
But, the above stated rotation crusher still has many disadvantages
and problems to be dealt with. For instance, it is very uneconomical
that so much steam or the like must be fed into the crusher to keep
the crusher at a certain pressurized state. Consequently, in order
to solve the problem, it is very important to know exactly the critical
oxygen content which can prevent explosions (the explosion preventive
critical oxygen content) and further it is also imperative to measure
speedily, exactly and easily the distribution of oxygen in the crusher.
SUMMARY OF THE INVENTION
Against the above stated background the present invention is provided
on the basis of the results of research on causes of explosions,
data analysis, fundamental experiments, experiments using a real
apparatus and others, and is concerned with a practical system which
prevents explosions efficiently and surely.
It is a first objective of the present invention to provide a rotation
crusher which prevents explosions by feeding steam into the crusher
wherein consumption of the steam is held at a minimum without undermining
the safety of the crusher.
It is a second objective of the present invention to provide a
rotation crusher which further improves safety by measuring exactly
the explosion preventive critical oxygen contents, oxygen being
mixed with the steam or the like and combustibles, and also by measuring
quickly, exactly and easily the distribution of oxygen contained
in the crusher.
It is necessary for achieving the above stated objectives to check
the critical oxygen contents which can prevent explosions, with
oxygen being mixed with steam (or the like) and combustibles, and
next to study relations between temperatures and oxygen contents
inside the crusher. Also, it is necessary to learn a range of the
temperatures inside the crusher in operation in which the oxygen
contents inside the crusher are below the explosion preventive value.
The crusher according to the present invention is structured so
that steam fed into the crusher is controlled so that temperatures
inside the crusher are kept within the aforegoing range. That is,
the present invention which crushes in the steam the refuse such
as big-size disused articles, incombustibles and other endeavors
to control the volume of the steam fed into the crusher so that
the temperatures inside the crusher are kept at about 70.degree.
C. to 100.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a critical range resulting in explosions (or non-explosions),
with propane gas being mixed with air and steam;
FIG. 2 shows a critical range resulting in explosions (or non-explosions),
with gasoline being mixed with air and steam;
FIG. 3 shows a critical range resulting in explosion (or non-explosions)
with methane gas being mixed with air and steam;
FIG. 4 shows relations between temperatures, relative humidity
and oxygen content;
FIG. 5 shows a flow-sheet illustrating an embodiment of an explosion
preventive rotation crusher according to the present invention;
and,
FIG. 6 shows a sample of the oxygen content measured inside a crusher
in operation.
DETAILED DESCRIPTION OF THE INVENTION
Generally speaking, an explosion is a kind of combustion reaction
accompanied by production (generation) of gases. Once it starts,
it tends to be accelerated in speed as long as there exists something
combustible. There are various causes of explosions occurring at
facilities treating big-size disused articles and incombustibles.
The explosions resulting from petroleum group combustibles (such
as petroleum, gasoline, benzine, thinner and others) account for
more than 90 of all the explosion accidents. Table 1 shows an example
of the causes of explosion accidents at facilities treating big-size
articles and incombustibles.
TABLE 1 ______________________________________ An Example of Explosion
Accidents: Substances Which Caused Explosions Ratio (%) ______________________________________
Propane gas containers (Bombe) 45.5 Petroleum, benzine & thinner
18.2 Alminium powder 9.1 Chemicals 9.1 Agricultural medicine 9.1
Others 9.1 ______________________________________
Judging from circumstances surrounding explosion accidents, explosions
are inferred to break out as explained below.
When containers such as propane gas containers, petroleum cans,
thinner cans, containers holding chemicals and agricultural medicines
therein and the like are mixed with big-size disused articles and
incombustibles are fed into a crusher, the containers are crushed
and destroyed by hammers of the crusher, thereby inducing liquid
propane, gasoline and the like to evaporate and further causing
the chemicals, the agricultural medicines and the like to turn into
mists. The evaporated gasoline, the turned-into-mist chemicals and
the like are mixed with air to reach explodable content ratio and
are lit by sparks inside the crusher, thereby resulting in explosions.
The present invention is in principle structured for prevention
of explosions so that steam fed into the crusher is controlled to
regulate temperatures inside the crusher so that the steam content
inside the crusher is kept above a predetermined value, thereby
keeping oxygen content below the explosion preventive critical value.
FIGS. 1 to 3 show explosion preventive critical values of the combustibles
mixed with air and steam. FIG. 1 shows the explosion preventive
critical value of propane gas which was learned through experiments,
with the propane gas being mixed with air and steam. If the steam
content exceeds the point A (which means a reduced oxygen content),
explosions do not occur irrespective of the content of propane gas.
Consequently, it is necessary for prevention of explosions that
a value of oxygen content at point A be calculated so that the oxygen
content inside the crusher might be kept below the value as calculated
above.
The oxygen content at the point A is calculated according to the
following formula:
Note:
O.sub.2 (A): the oxygen content at point A
B: the steam content at point A=29.5
C: the propane gas content at point A=3.5%
Hence, O.sub.2 (A)=0.21.times.[100-(29.5+3.5)]=14 (Vol %)
This shows that propane gas explosions are completely prevented
if the oxygen content is kept below 14 Vol % by feeding steam into
the crusher.
Further, FIGS. 2 and 3 illustrated on the basis of the experiments
show the explosion-preventive critical range (scope) gained when
there exist mixtures of gasoline, air and steam, and methane, air
and steam, respectively. The critical oxygen content to prevent
explosions as calculated in the same manner as in FIG. 1 are 13.9
Vol% and 13.8 Vol% with respect to gasoline (FIG. 2) and methane
(FIG. 3), respectively. As a result, gasoline and methane explosions
are prevented completely if the oxygen content inside the crusher
is controlled below the respective values.
In the same manner, experiments show that explosions of isobutane
and benzene are prevented if oxygen content is controlled below
14 Vol% and 13 Vol%, respectively.
Next, turning to a method for controlling the quantity of steam
fed into the crusher, widely known is a method in which the oxygen
content in the crusher is measured and then a control valve is opened
or closed depending upon the oxygen content measured. But, employing
the above stated method makes it necessary to measure the oxygen
content at many places inside the crusher since the capacity of
the crusher is very big and further it is unpredictable where explosions
will occur. Consequently, many gauges for measuring the oxygen content
are necessary according to the aforegoing method. Since pipes leading
to the gauges are easily clogged with crushed articles (refuse),
the method has the disadvantage that it is difficult to measure
continually and exactly.
The present invention employs a new method in which the steam fed
into the crusher is controlled on the basis of temperatures measured
inside the crusher so that the steam content at various places in
the crusher are kept above a certain value, thereby keeping the
oxygen content below the explosion-preventive critical value. In
comparison with the above stated method widely used which directly
measures the oxygen content, this new method is economical, and
superior in that this method can measure the oxygen content minutely
and simultaneously at desired places and can increase easily the
number of the places where the oxygen contents are measured. As
for the method of measuring the temperatures, thermometers can possibly
be inserted inside the crusher. But, the thermometer inserting method
has a disadvantage that the thermometers inserted into the crusher
might be hit and broken by articles crushed in the crusher. Another
method which might be employed instead is one in which the temperatures
inside the crusher are estimated on the basis of temperatures of
the surface of the casing of the crusher.
FIG. 4 shows relations between temperatures, the relative humidity
and oxygen contents, in which the horizontal axis indicates ambient
temperatures, the vertical axis indicates the oxygen content in
the ambient air and H indicates a curve showing the relative humidity
of 100%. It is known that the steam content in atmosphere is kept
at a certain value by the saturation vapor pressure under conditions
of perfect mixing, atmospheric pressure and steam saturation. It
is noted that gases inside the crusher always stay mixed by rotation
of the hammers and that steam saturation or steam supersaturation
can be maintained inside the crusher if atmospheric pressure is
maintained inside the crusher by feeding into the crusher a required
volume of the low-pressurized steam. Consequently, if the temperature
is kept at 70.degree. C. to 100.degree. C. inside the crusher, the
oxygen content remains below 14 Vol% as shown in FIG. 4 thereby
preventing propane gas explosions. The temperatures should be maintained
at 75.degree. C. inside the crusher if it is planned to prevent
also explosions of gasoline, methane, isobutane and benzene so that
oxygen content might be maintained below 13 Vo.%, thereby preventing
explosions with more certainty.
As explained above, unnecessary steam consumption is saved by measuring
the temperatures inside the crusher with the result that it becomes
possible to control the quantity of the fed steam in accordance
with heat loss caused by radiation, steam exhaustion and discharging
the crushed articles, thereby lessening substantially the steam
consumption in comparison with the conventional crusher.
Fundamental experiments and experiments using a real apparatus
show that the steam is preferably fed into the crusher at the windward
side of ventilation for improved explosion preventive effect, that
is, a better effect to lower oxygen content. Consequently, it is
advised that the capacity and the number of steam injecting nozzles
be increased at the windward side and lessened at the leeward side.
Next, the structure of the crusher according to the present invention
is explained with reference to FIG. 5.
FIG. 5 illustrates a flow sheet of an embodiment of the explosion
preventive rotation crusher. A main body C of the crusher has a
rotation type crushing apparatus 10 inside a box C'. The refuse
B such as big-size disused articles, incombustibles and others is
conveyed into the main body C by an apron conveyor 1. A curtain(s)
2 and a steam blowing nozzle 3 are positioned over the conveyor
1 to prevent air current. The refuse B is conveyed under the curtain(s)
2. The curtain 2 helps in blocking substantial leakage of the steam.
Steam blowing nozzles may be provided at places 3 4 and 5 as the
case may require. The steam blown from the nozzles fills the main
body C of the crusher, thereby lowering the oxygen contents.
The crushing apparatus 10 may be of the horizontal axis type or
of the vertical axis type. The hammer of the crushing apparatus
10 rotates to crush the refuse by striking, searing and grinding
force in cooperation with a fixed blade. A discharging apparatus
11 is provided under the main body C and conveys the crushed refuse
to an exit a.
The discharging apparatus 11 may be a vibrating feeder, an apron
conveyor or the like. A curtain(s) 7 and, if necessary, the steam
blowing nozzles 6 are provided to block air current, thereby allowing
the main body to be filled with the steam by preventing steam leakage.
The steam is supplied by a steam generating apparatus 12 to the
steam blowing nozzles 3 to 6 through a valve 13. It is noted that
since ventilation flows in a direction indicated by an arrow b,
the number of the nozzles 3 are more at the windward than at the
leeward, as stated above (FIG. 5). The quantity of the steam to
be supplied is controlled by opening or closing the valve 13 activated
by signals transmitted from temperature regulating apparatus 14
and is so regulated that the temperature inside the main body C
of the crusher stands at within a predetermined range (about 70.degree.
C. to 100.degree. C.). That is, the temperatures inside the main
body are measured by therometers 8 9 19 and others. On the basis
of the temperatures as measured above, the oxygen content inside
the main body C are measured by means of the relationship between
the temperatures, the relative humidity and the oxygen content as
shown in FIG. 4. The oxygen content as measured above are watched
and so regulated that the oxygen content may be maintained below
the explosion preventive critical value. All the steam blowing nozzles
3 4 5 and 6 are not necessarily open together. Some might be
open while the others might be closed, depending upon the situations
of the main body C of the crusher.
Part of the steam insdie the main body C of the crusher is exhausted
through a gas outlet 15 (and, if necessary, through a dust collecting
apparatus 16) to the atmosphere by an exhaust fan 17. The volume
of the exhaust steam is controlled, depending upon the oxygen content,
dust and others inside the main body C, by regulating a damper 18
activated by signals transmitted from the temperature regulating
apparatus 14. Also, the gas outlet may be positioned instead, when
necessary, at a place designated 15' over the apron conveyor 1.
The position and the number of the current preventive curtains
2 and 7 are determined according to the situation of the crusher.
The curtains 2 and 7 may be made, in inseparable (integral) body,
of bendable materials such as synthetic resin, rubber and the like,
or verticaly long plates (made of stainless steel, aluminum, steel
and the like) stitched together in series (just like a blinder).
It is noted that anything can be employed instead of the curtains
2 and 7 as far as it can function to substantially block the gas
current but allow the refuse to pass.
FIG. 6 shows an example indicating data relating to oxygen content
inside the main body of the crusher, said data being obtained through
experiments using a real crusher. The inventors confirmed at the
time of the experiments, by employing oxygen content gauges at the
same time, that it is possible to regulate exactly the oxygen content
inside the crusher by means of temperatures.
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