Process for the preparation of micro inorganic foamed granules

A process for the preparation of micro inorganic foamed granules chracterized in that amorphous particles having particle size of not greater than 150 .mu.m recovered from particles of an amorphous residue produced by partial oxidation of coal is heated by introducing the same into a flame or gas at a high temperature, whereby foaming the amorphous particles.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process for the preparation of micro inorganic 
foamed granules. 
2. Description of Prior Arts 
Inorganic foamed granules are lightweight, and have been accordingly used 
widely as lightweight aggregates for construction of buildings, extenders 
for fertilizer, detergent or paint, absorbents, soil improvers, etc. 
Particularly, the micro inorganic foamed granules having a mean particle 
size of not larger than 500 .mu.m are employed as fillers for imparting 
heat insulating properties to buildings and adjustors for adjusting 
specific gravity of cement used for an oil well or geothermal well, in 
addition to the above usage. 
Particularly, the use as adjustor for adjusting specific gravity of cement 
used for an oil well or geothermal well is one of the quite important 
uses. 
It is required that the micro inorganic foamed granules for employing as 
specific gravity adjustor should have apparent specific gravity in the 
range of 0.6 to 0.9 and particle size of not larger than 500 .mu.m 
(preferably not larger than 200 .mu.m). Further, high strength is 
required, and the micro inorganic foamed granules having hydrostatic 
pressure strength of not lower than 300 kgf/cm.sup.2 at 70% of 
indestructibility are generally employed for the above purpose. 
The known micro inorganic foamed granules are classified into three groups, 
that is, granules manufactured from natural volcanic glassy materials, 
those manufactured from artificial glassy materials and those contained in 
coal ash. 
The micro inorganic foamed granules of natural volcanic glassy materials 
are produced by the steps of pulverizing materials such as obsidian, 
pearlite and volcanic ash to make the particle size not larger than 100 
.mu.m, removing a portion of fine powder, adding thereto additives such as 
SiO.sub.2 powder and Al.sub.2 O.sub.3 powder in an appropriate amount and 
firing the mixture at a temperature not lower than 1,000.degree. C. 
The micro inorganic foamed granules of natural volcanic glassy materials 
prepared in the above method generally has a low apparent specific gravity 
and can be manufactured at relatively low cost. However, hydrostatic 
pressure strength thereof is extremely low. Therefore, the micro inorganic 
foamed granules of natural volcanic glassy materials cannot be employed as 
adjustor for adjusting the specific gravity of cement used for an oil well 
or geothermal well. The foamed granules are used exclusively as heat 
insulating materials or lightweight aggregates for construction of 
buildings, which do not require mechanical strength. 
The micro inorganic foamed granules of artificaial glassy materials are 
produced by steps of adding a foaming compound such as carbon to 
artificially prepared glassy materials, fusing the mixture and spraying. 
The above micro inorganic foamed granules are easily manufactured so as to 
have the particle size of not larger than 100 .mu.m. The apparent specific 
gravity and hydrostatic pressure strength of the obtained micro inorganic 
foamed granules are satisfactory enough to employ as adjustors for 
adjusting specific gravity of cement used for an oil well or geothermal 
well. However, manufacturing cost thereof is high. 
Inorganic foamed granules contained in coal ash in a very small amount are 
known. The inorganic foamed granules show favorable properties such as 0.6 
to 0.7 of apparent specific gravity and 400 kgf/cm.sup.2 of hydrostatic 
pressure strength (measured at 70% of indestructibility) for employment as 
adjustor for adjusting specific gravity of cement used for an oil well or 
geothermal well. However, the foamed granules are generally contained in 
coal ash in the amount of not more than 0.5 wt.%. For this reason, the 
foamed granules are not collected industrially in Japan, which makes the 
granules very expensive. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a process for the 
preparation of micro inorganic foamed granules having favorable properties 
such as small particle size, satisfactory strength and low apparent 
specific gravity at relatively low cost. 
Another object of the invention is to provide a new use of residue produced 
in a coal gasification process, which has not find advantageous use until 
now. 
There is provided by the present invention a process for the preparation of 
micro inorganic foamed granules which is characterized in that an 
amorphous residue having a particle size of not larger than 150 .mu.m 
obtained by partial oxidation of coal is introduced into flame or gas of 
high temperature, thereby foaming the amorphous residue. 
The amorphous residue employed generally contains not more than 65 wt.% of 
SiO.sub.2, not less than 15 wt.% of Al.sub.2 O.sub.3 and not less than 5 
wt.% of CaO. 
The micro inorganic foamed granules obtained generally have a particle size 
of not larger than 200 .mu.m. 
By the process for the preparation of micro inorganic foamed granules 
according to the present invention, micro inorganic foamed granules having 
properties as satisfactory as those of micro inorganic foamed granules of 
natural volcanic glassy materials micro inorganic foamed granules of 
artificial glassy materials and micro inorganic foamed granules contained 
in coal ash, which have been already known, can be produced at a low cost. 
The micro inorganic foamed granules prepared by the process of the present 
invention are strong and light enough to employ as adjustor for adjusting 
specific gravity of cement used for an oil well or geothermal well. 
Further, the process of the invention effectively utilizes amorphous 
residue produced in a partial oxidation of coal, which has not find 
advantageous use.

DETAILED DESCRIPTION OF INVENTION 
The process for the preparation of micro inorganic foamed granules 
according to the invention is characterized in that amorphous residue 
having a specific particle size obtained in partial oxidation of coal is 
introduced into flame or gas of high temperature, thereby foaming the 
particulate residue. 
The amorphous residue is obtained by partial oxidation of coal. An ash 
obtained upon completely firing a particulate coal does not effectively 
foam and is not be used for the preparation of the micro inorganic foamed 
granules of the invention. 
The amorphous residue is available as a residue produced by a process of a 
synthetic gas through partial oxidation of coal. Examples of the process 
of the preparation of synthetic gas from coal include Lurgi process, 
Winkler process, Koppers-Totzek process, Otto-Rummel process, KDV process, 
Lurgi slagging process, Synthane process, WH process, Ugas process, HYGAS 
process, Japan Coal Technology Institute process, Pressure-fuidizing 
hydrogenatic gasification process, Hybrid process, HTW process, BIGAS 
process, Shell(Shell-Koppers) process, Saarberg-Otto process, Sumitomo 
process, and Texaco process. In the process of the invention, residues 
obtained in coal oxidation processs such as Koppers-Totzek process, 
Otto-Rummel process, Lurgi slagging process, Shell(Shell-Koppers) process, 
and Texaco process in which the partial oxidation of coal is performed at 
a temperature of not lower than the softening temperature of the employed 
coal within a gasification furnace are preferably used. 
For instance, Texaco process includes the following procedure: coal is 
charged into a coal gasification furnace in the form of an aqueous slurry 
and heated under pressure at a temperature of not lower than the softening 
temperature of ash of the coal, generally, in the range of 1,300.degree. 
to 1,500.degree. C., whereby partial oxidation of the coal is done. In 
this procedure, a melted or half-melted residue is obtained, and this 
residue is generally cooled with water and exhausted from the coal 
gasification furnace, if necessary, upon being crushed. 
More details of the coal gasification process utilizing Texaco process, 
etc. are described in Chemical Economy (of Japan), 1981, August and 
September. 
The composition of the residue obtained upon partial oxidation of coal 
varies with nature of the coal employed in the coal gasification process 
within certain ranges. However, most of residues obtained upon partial 
oxidation of coal can be employed as the raw material, regardless of 
nature of the coal used. 
The above-described amorphous residue generally contains not more than 60 
wt.% of SiO.sub.2 (usually in the range of 30 to 65 wt.%), not less than 
15 wt.% of Al.sub.2 O.sub.3 (usually in the range of 15 to 40 wt.%), and 
not less than 5 wt.% of CaO (usually in the range of 5-30 wt.%), as well 
as small amounts of sulfides, other sulfur compounds and unburnt carbon. 
It is preferred that the amorphous residue contains sulfur in the form of 
sulfides and unburnt carbon in a total amount of not less than 1 wt.%. In 
the case that the amorphous residue contains sulfur in the form of 
sulfides and unburnt carbon in a total amount of less than 1 wt.%, the 
residue sometimes does not effectively foam. 
The residue obtained by partial oxidation of coal is amorphous and shows 
substantially no specific peak in X ray diffraction pattern. 
The particle size of the amorphous residue employed in the invention is not 
larger than 150 .mu.m. 
The adjustment of the particle size of the amorphous residue collected from 
a coal gasification furnace can be done by sieving or crushing so as to 
have a size of not larger than 150 .mu.m. Crushing is carried out in the 
usual manner by means of usually employed crushing devices such as a bowl 
mill. It is not required to remove the residue having extremely small 
particle size (e.g. smaller than 5 .mu.m.) contained in the residue which 
has been sieved or crushed. In order to obtain micro inorganic foamed 
granules having a particle size within a specific range, the residue 
having the desired particle size is exclusively employed. 
In the case that the residue having a particle size larger than 150 .mu.m., 
retention time in the flame or gas of high temperature should be extremely 
short and thus the amorphous residue does not effectively foam. 
The amorphous residue which is thus adjusted with respect to the particle 
size is then heated by introducing the residue into a flame or gas of high 
temperature. 
The heating process can be performed by, for example, a gas-stream firing 
method. According to the gas-stream firing method, the fine powder to be 
fired is introduced together with carrier gas into a flame or gas of high 
temperature generated in a hot-air oven and fired while the fine powder 
stays in a flame or gas of a high temperature. 
In the process for the preparation of micro inorganic foamed granules 
according to the invention, the amorphous residue is heated and foamed by 
the gas-stream firing method. 
The amorphous residue having particle size of smaller than 150 .mu.m. is 
sent with air into a heating device and passed through a flame generated 
by a burner or gas of high temperature generated in a hot-air oven so as 
to be melted or softened. Simultaneously, easily-foaming materials such as 
unburnt carbon and sulfides contained in the amorphous residue are 
converted into gas to produce a great number of voids. 
Generally, the flame is hot enough to fuse or soften the amorphous residue 
and to gasify the foaming materials such as sulfide-sulfur and carbon. The 
amorphous residue, accordingly, can be foamed effectively. The amorphous 
residue effectively foam by introducing it into a flame of not lower than 
900.degree. C. It is preferred to introduce the residue into a flame of 
not lower than 1,000.degree. C. 
The amorphous residue can be also effectively foamed by introducing into a 
gas of high temperature not lower than 900.degree. C. It is preferred to 
foam the amorphous residue by introducing it into a gas having a 
temperature of not lower than 1000.degree. C. 
The retention time of the amorphous residue in a flame or gas of high 
temperature is generally in the range of 1/1,000 to 1 sec. 
Conventionally used carrier air and firing air can be also employed. 
Devices generally used in gas-stream firing method can be used. A burner 
comprising two tubes of different diameters which are arranged 
concentrically (double-tube burner). 
The generated materials foamed and collected from the flame or gas of high 
temperature are introduced into a water, and a portion floating on the 
surface of the water is collected as micro inorganic foamed granules. By 
carrying out this procedure, the residue which does not sufficiently foam 
and has a specific gravity greater than 1 can be removed. 
The micro inorganic foamed granules collected from water are generally 
dried at a temperature in the range of a room temperature to 100.degree. 
C. 
FIG. 1 is an electron microscopic photograph showing one example of the 
obtained micro inorganic foamed granules. 
As shown in FIG. 1, the micro inorganic foamed granules respectively take a 
form of sphere having a particle size of not greater than 200 .mu.m. More 
than 90% of granules (in terms of number of granules) have particle size 
in the range of 5 to 200 .mu.m. Generally, approximately 20 to 80% (in 
terms of number of granules) of the micro inorganic foamed granules have a 
foam (void) which is open to the outside. The remaining micro inorganic 
foamed granules have an independent foam (void) having no opening 
connected to the outside. 
The micro inorganic foamed granules prepared by the process of the 
invention comprise not more than 65 wt.% (preferably in the range of 63 to 
30 wt.%) of SiO.sub.2, not less than 15 wt.% (preferably in the range of 
17 to 40 wt.%) of Al.sub.2 O.sub.3, and not less than 5 wt.% (preferably 
in the range of 5 to 30 wt.%) of CaO. 
The above three components are comprised in the micro inorganic foamed 
granules in a total amount of, generally, not less than 60 wt.%, 
preferably 70-95 wt.%, and most preferably 75-95 wt.%. 
The micro inorganic foamed granules obtained by the process of the 
invention have particle size not larger than 200 .mu.m, generally in the 
range of 5-150 .mu.m. 
In addition to the above three components, the micro inorganic foamed 
granules obtained by the process of the invention possibly contain iron 
oxide, MgO, Na.sub.2 O and K.sub.2 O in a total amount of, generally, not 
more than 40 wt.%, preferably 5-30 wt.%, and most preferably 5 to 25 wt.%. 
Preferably, iron oxide is contained in an amount of 2-15 wt.% (as Fe.sub.2 
O.sub.3), MgO is contained in an amount of 1-7 wt.%, Na.sub.2 O is 
contained in an amount of 1-6 wt.%, and K.sub.2 O is contained in an 
amount of 0-2 wt.%. Further, the micro inorganic foamed granules may 
contain a very small amount of TiO.sub.2, SO.sub.3, sulfide, other 
sulfur-containing compounds and carbon components. 
The hydrostatic pressure strength of the micro inorganic foamed granules is 
generally more than 300 kgf/cm.sup.2 measured at 70% of indestructibility 
ratio. 
The apparent specific gravity thereof is generally in the range of 0.2 to 
1.0. Apparent specific gravity can be adjusted by changing the content of 
the foaming component contained in the amorphous residue, the temperature 
of the flame or gas, and the retention time in the flame or gas. 
Since the micro inorganic foamed granules prepared by the process of the 
invention have small particle size and high hydrostatic pressure strength, 
they are employable as adjustor for adjusting the specific gravity of 
cement used for an oil well or geothermal well. The apparent specific 
gravity thereof is within the suitable range for the above purpose. As the 
process of the invention employs the amorphous residue produced in a 
partial oxidation of coal, which has not find advantageous use until now, 
the micro inorganic foamed granules can be prepared at a lower cost by the 
process of the present invention compared with the conventional process. 
The micro inorganic foamed granules obtained by the process of the 
invention can be also employed for other purposes such as heat insulating 
materials, lightweight aggregates for construction of buildings, extenders 
for fertilizer, detergent or paint, absorbents, soil improvers, etc. 
The invention will be further described with reference to the following 
examples. 
EXAMPLE 1 
A residue collected from a coal gasification furnace according to a Texaco 
process was crushed in a bowl mill of small size so as to give particles 
having the largest granular size of not larger than 150 .mu.m. 
The X-ray diffraction analysis indicated that the employed residue was 
amorphous. 
The crushed materials obtained in the above were then subjected to 
gas-stream firing by introducing together with air the materials into a 
flame of 1,200.degree. C. prepared by a burner of a gas-stream firing 
device so as to be expanded. 
The fired materials were put in water, and floating portion thereof was 
collected to dry at a room temperature. 
FIG. 1 is an electron microscopic photograph showing a portion of the 
obtained micro inorganic foamed granules. 
The mean particle size of the micro inorganic foamed granules was 60 
.mu.m., the smallest one was approx. 10 .mu.m. and the largest one was 
approx. 200 .mu.m. 
The resulting micro inorganic foamed granules had an apparent specific 
gravity of 0.66 and hydrostatic pressure strength of 340 kgf/cm.sup.2 
(measured at 70% of indestructibility ratio). The chemical composition of 
the amorphous residue and that of the obtained micro inorganic foamed 
granules are set forth in Table 1. 
The above measurements were made using the following process. The same 
measuring process were also utilized in the measurements in other examples 
of the invention. 
MEASUREMENT METHODS 
Apparent specific gravity: measured according to JIS-A-1134 and JIS-A-1135. 
Analysis: made according to JIS-M-8852. 
Hydrostatic pressure strength: measured according to a method for measuring 
a floatation ratio of hydrostatic pressure strength disclosed in pages 
84-91 of 80th vol. of the bulletin edited by the Ceramic Industry 
Association (February, 1972). 
TABLE 1 
______________________________________ 
Amorphous Micro Inorganic 
Component Residue (wt. %) 
Foamed Granules (wt. %) 
______________________________________ 
ig. loss 0.3 0.0 
SiO.sub.2 59.1 59.4 
Al.sub.2 O.sub.3 
21.8 21.9 
Fe.sub.2 O.sub.3 
4.5 4.5 
CaO 11.1 11.2 
MgO 1.2 1.2 
Na.sub.2 O 1.3 1.3 
K.sub.2 O 0.5 0.5 
Unburnt carbon 
1.1 0.1 
Sulfide sulfur 
0.2 0.0 
______________________________________ 
EXAMPLE 2 
Micro inorganic foamed granules were prepared in the same manner as in 
Example 1 except that the amorphous residue was so crushed as to give 
particles having the largest particle size of 74 .mu.m. 
The mean particle size of the micro inorganic foamed granules was 40 .mu.m, 
the smallest one was approx. 10 .mu.m, and the largest one was 60 .mu.m. 
The apparent specific gravity of the obtained micro inorganic foamed 
granules was 0.71 and the hydrostatic pressure strength thereof was 370 
kgf/cm.sup.2 measured at 70% of indestructibility ratio. 
EXAMPLE 3 
Micro inorganic foamed granules were prepared in the same manner as in 
Example 1 except that the temperature of the flame of a burner of the 
gas-stream firing device was made 1,600.degree. C. 
The mean particle size of the micro inorganic foamed granules was 65 .mu.m, 
the smallest one was approx. 10 .mu.m, and the largest one was approx. 100 
.mu.m. 
The apparent specific gravity of the obtained micro inorganic foamed 
granules was 0.87 and the hydrostatic pressure strength thereof was 360 
kgf/cm.sup.2 measured at 70% of indestructibility ratio.