FIELD OF THE INVENTION
The present invention relates to containment of inflammable and combustible liquids,
more particularly to a fire resistant storage tank for containment of inflammable and
combustible liquids and methods of using the same.
BACKGROUND OF THE INVENTION
Underground storage tanks have been used for the storage of fuels and other
inflammable liquids for a long time. However, due to the long-term effects of
groundwater and soil contamination from undetected leakage, the costs of remedial
measures, and the related costs of removing underground tanks, underground storage is
being avoided. Leakage from these tanks can lead to loss of several gallons of liquid
each day. Thus, above ground storage tanks for fuels and inflammable liquids have
been gaining in popularity.
High rise buildings provide uninterrupted power supply to their occupants. However,
they have to rely upon a plurality of generators to ensure uninterrupted power supply,
especially in developing countries where power outages are frequent. The generators
usually run on a fuel like diesel, so a large amount of fuel is consumed in operating the
generators. Thus, there is a need for storage of fuel within the building premises,
proximate to the generators in order to ensure a constant supply of fuel. Thus, these
buildings also have aboveground storage tanks (ASTs) for storage of diesel. Usually
one AST is provided for each generator, and all the ASTs receive diesel from a large
reservoir or diesel supply line.
In v1ew of the large number of storage tanks being installed in buildings, it is
imperative to provide means for prevention and suppression of fire in these tanks in
order to avoid accidents. Several attempts have been made in the prior arts to minimize
the fire hazard in these tanks. However, these methods suffer from one deficiency or
the other.
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For instance, US Patent No. 4,826,644 discloses a steel inner tank for fuels surrounded
by both a polyurethane spacer layer and a polyurethane liner for secondary containment
and, finally, completely entombed in concrete for protection from external hazards. The
document does not provide ways of actively preventing or suppressing fire. Moreover,
since the inner tank is completely entombed in concrete, it isn't possible to access the
inner tank or carry out repairs whenever necessary.
US Patent No. 4,993,497 discloses a deluge funnel tank jacket. A funnel shaped jacket
is attached to a rib framing system that is strapped around the storage tank. In the event
of fire, water is introduced at the top of the tank by the funnel and is then fed by gravity
through the waterway formed between the funnel jacket and the tank shell. However,
this tank suffers from the drawback that feeding water can lead to spreading of the fire
because the inflammable liquid that has caught fire floats on water and is transported
away from the tank along with the water.
Thus, there is a need for a fire resistant storage tank for safe storage of inflammable
liquids. There is a need for a storage tank which has means to prevent fire and also has
means for automatic suppression of fire. There is also a need for methods of providing
such storage tanks for generators so as to reduce the fire hazard in a building.
SUMMARY OF THE INVENTION
In accordance with an embodiment of the invention, is provided a fire resistant storage
tank for containment of inflammable and combustible liquids, comprising:
- an Inner Tank for storing inflammable and combustible liquids;
- an Outer Tank separated from and enclosing the inner tank;
- a vapor detection means for measuring the concentration of one or more types
of gases;
- a temperature sensing means for detecting fire; and,
- a fire extinguishing means for suppressing fire;
wherein, the vapor detection means comprises a plurality of Vapor Detectors provided
in the space between the outer tank and inner tank, and means for displaying the
concentration of one or more types of gases; and,
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wherein, the temperature sensing means comprises at least a Resistance Temperature
Detector for detecting the temperature at at least one location inside the tanks; and, a
Temperature Indicator-cum-Controller for displaying the temperature and comparing it
with predefined limits.
In accordance with another embodiment of the invention, is provided a fire resistant
storage tank, wherein the outer tank comprises a Floor, a Lid and a plurality of walls;
each of them being made of the same or different materials having high fire resistance
rating.
In accordance with yet another embodiment of the invention, is provided a fire resistant
storage tank, wherein the outer tank comprises a floor made of a material like concrete,
four walls made from materials like concrete, plastered bricks, etc. erected on the floor,
and a lid made of a material like Promat board provided above the walls; the lid being
partially or fully removable.
In accordance with yet another embodiment of the invention, is provided a fire resistant
storage tank, wherein the fire extinguishing means comprises a Modular Cylinder for
automatically releasing a fire retardant material upon detection of fire.
In accordance with yet another embodiment of the invention, is provided a fire resistant
storage tank, further comprising a level control means for regulating the level of the
liquid stored inside the inner tank; the level control means comprising a float wall for
detecting the liquid level, a Solenoid Valve for controlling the flow of liquid into the
inner tank in accordance with the liquid level inside the tank.
In accordance with yet another embodiment of the invention, is provided a fire resistant
storage tank, further comprising an Alarm System for generating an audio and/or visual
alarm in case the value detected by at least one of the vapor detection means,
temperature sensing means or level control means is outside predefined limits.
In accordance with yet another embodiment of the invention, is provided a fire resistant
storage tank, further comprising a Vent for removal of air and/or prevention of pressure
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build-up inside the inner tank; optionally wherein a Drain Valve is provided at the
bottom of the inner tank for draining out the liquid, whenever required.
In accordance with yet another embodiment of the invention, is provided a fire resistant
storage tank, optionally comprising an adsorbent and/or absorbent material in the space
between the outer tank and inner tank for adsorbing and/or absorbing any leakage of
liquid.
In accordance with an embodiment of the invention, is provided a method of
containment of inflammable and combustible liquids using a fire resistant storage tank
in accordance with any of the aforementioned embodiments, characterized in that the
fire resistant storage tank is connected to two or more generators.
In accordance with an embodiment of the invention, is provided a method of
containment of inflammable and combustible liquids, wherein a fire resistant storage
tank is connected to three generators.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram showing an aboveground storage tank in accordance with
an embodiment of the invention.
It is to be noted that the above mentioned figure is with reference to an aboveground
storage tank. However, the teachings of the invention can be readily applied to other
types of storage tanks also, with or without some minor modifications.
DESCRIPTION
Discussed below are some representative embodiments of the present invention. The
invention in its broader aspects is not limited to the specific details, representative
devices and methods, and illustrative examples shown and described in this section in
connection with the embodiments and methods. The invention according to its various
aspects is particularly pointed out and distinctly claimed in the appended claims read in
view of this specification, and appropriate equivalents.
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It is to be noted that, as used in the specification and the appended claims, the singular
forms "a," "an," and "the" include plural referents unless the context clearly dictates
otherwise.
Fig. 1 is a schematic diagram showing an aboveground storage tank in accordance with
an embodiment ofthe invention. The AST/Aboveground Storage Tank (100) comprises
an inner tank (200) enclosed by an outer tank (150). The outer tank consists of a floor
(1 05), a lid (135) and four brick walls substantially perpendicular to both the floor and
lid. The floor is preferably made of concrete. The lid (135) is provided substantially
parallel to the floor (1 05) and is preferably made from a material like Promat board
having at least 2 hours fire resistance rating. The lid is partially or completely
removable so as to provide easy access to the inside of the AST (1 00) for servicing,
repairs, inspection, etc. The walls are arranged in the shape of a rectangle, and together
with the floor and lid define a substantially cuboidal enclosure. The cross-sections of
two of the walls (125 and 125') are visible in the figure. The walls are plastered on both
sides for increasing their fire resistance rating. Since concrete is inherently fire
resistant, and the walls and lid also have good fire resistance, the outer tank (150)
prevents any fire inside the AST from spreading out for a several hours.
The inflammable liquid is stored in the inner tank (200) which is placed inside the outer
tank (150). The inner tank (200) is substantially cuboidal in shape and has faces spaced
apart and substantially parallel to the walls (125), floor (105) and lid (135). This tank is
made from a material like mild steel and is completely sealed off from the surroundings
so as to avoid any leakage. The inner tank does not rest on the floor to avoid any
percolation or corrosion due to ground water. A plurality of angle supports (145, 155) is
provided for supporting the inner tank above the floor and maintaining its position
relative to the outer tank. The angle supports may be provided at any suitable locations
so as to bear the weight of the inner tank and also to prevent it from being displaced
relative to the outer tank. The angle supports (145) in the given figure provide support
to the lid (135). Several different arrangements for providing the angle supports would
be apparent to a person skilled in the art. The floor ( 1 05) has a layer of sand so that in
case of leakage, the liquid gets absorbed and does not spread easily on the floor. A
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drain valve (180) has also been provided at the bottom of the inner tank (200) for
draining out some or all of the liquid whenever required.
One aspect of reducing the fire hazard is to monitor the temperature inside the inner
tank (200). This is done using an RTD/Resistance Temperature Detector (11 0) close to
the bottom of the tank. The temperature is determined by the change in resistance of the
RTD material, and the same is displayed by a Temperature Indicator-cum-Controller
(120) connected to the RTD (110). The temperature indicator-cum-controller (120)
compares the temperature detected with predefined limits. When the temperature is
high due to fire or otherwise, an audio and/or video alarm is raised. The AST (1 00) has
means for automatically extinguishing a fire in case it does break out. This is done
using a modular cylinder with sprinkler type fire extinguisher which is designed to be
operated automatically. The modular cylinder (130) has a mixture of ABC dry powder
and dry nitrogen stored under pressure. It has a glass bulb which shatters as soon as the
temperature reaches a predefined value, thereby allowing the contents to be released as
a mist which spreads throughout the inner tank (200). This helps cut off the oxygen
supply to the fire so as to extinguish it. This type of fire extinguisher is much more
effective than the conventional fire extinguishers that sprinkle water or other coolants,
inadvertently spreading the fire in the process.
Another aspect of reducing the fire hazard is to monitor and control the amount of
volatile vapors in and around the inner tank (200). A pair of vapor detectors is provided
180° apart in the gap between the inner tank (200) and the walls (125) for detecting the
amount of vapors present in their proximity. This vapor level is constantly monitored
for early detection of leakage of the contents of the inner tank (200). When the vapor
concentration crosses a predefined value, an audio and/or video alarm may be raised. A
vent ( 140) has been provided for removal of air during filling/refilling of the inner tank
(200) and it also prevents pressure build-up inside the tank. The vent also serves to vent
out volatile vapors, in case they are present in the inner tank.
In another aspect, the level of diesel or other inflammable liquid inside the tank is also
carefully regulated. In the given figure, diesel is supplied to the inner tank (200) via
diesel line (175) coming from a diesel reservoir. The level of diesel inside the tank is
determined using a float valve (160) and the flow of diesel from the reservoir to the
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tank is controlled by a solenoid valve (170). In the present case, three diesel levels R1,
R2 and R3 have been defined. In the present embodiment, the total volume of the tank is
1000 liters. R1 is a low level (say 300 liters) at which an alarm will be raised to show
that diesel level in the tank is low. R3 is a high level (say 800 liters) at which the
solenoid valve (170) will get closed thereby stopping diesel supply to the tank and an
alarm is raised to show that diesel level is high. R2 is an intermediate level (say 500
liters) at which the solenoid valve gets opened and diesel starts filling the tank. A
bypass valve (165) may also be provided in the diesel line. The various alarms
mentioned in the aforementioned paragraphs are raised using an audio-video alarm
system (115). The alarm system typically has a predefined Low level (LI) and High
level (L2) for each of the parameters measured by the RTD ( 11 0), vapor detector ( 190),
float valve ( 160), etc. It generates an alarm if the measured value of the temperature or
vapor concentration or liquid level in the AST is outside the predefined limits.
In another aspect, the invention reduces the fire hazard by reducing the number of
storage tanks that are required in each building. As seen from the figure, three supply
lines emanate from the bottom of the inner tank (200) to supply diesel to three
generators DG1, DG2 and DG3. Likewise, three return lines are provided at the top the
inner tank (200) for return of any residual diesel coming from the three generators DG1,
DG2 and DG3. In the known methods, each generator is provided with a dedicated
storage tank. This means that if nine generators are present in the building, nine storage
tanks must also be installed. However, in the present invention only three storage tanks
are required to run nine generators. This modification can approximately reduce the fire
hazard by 66%. In making this modification, the storage tank capacity and inlet flow
rate from the reservoir is decided on the basis of the consumption of the three
generators.
Thus, the present invention provides an apparatus and methods for passively and
actively providing fire safety for storage tanks containing inflammable liquids. The
number of storage tanks is reduced to one-third, thereby reducing the number of storage
tanks that need to be made fire proof or fire resistant. The vapor detectors, temperature
indicator and alarm system provide an early indication to the operator(s) about
conditions that could cause fire, thus allowing them to take preemptive action. In case a
fire does erupt, it is not allowed to spread to the outside because the inner tank is
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surrounded by the outer tank comprising four walls, a lid and a floor, each of which has
a fire resistance rating of at least two hours. The modular cylinder automatically sprays
fire retardant material throughout the tank once the fire is detected by it. The high fire
resistance of the tank allows the modular cylinder to suppress the fire and prevents
spread of fire and damage around the storage tank.
Several variations are possible within the scope of the invention. For instance, the inner
tank and/or outer tank may be cylindrical instead of cuboidal. The space between the
tanks may also be filled with a fire retardant material. Various materials can be used for
the walls, lid, floor and the inner tank. If a removable lid is not required, then the lid of
the outer tank can be replaced by a roof made of concrete, plastered bricks, etc. A
double-walled inner tank can be used in place of the single-walled inner tank of Fig. 1.
A fire resistant coating may also be provided on one or more sides of the inner and/or
outer tank to increase their fire resistance rating.
Different devices can be used in place of the RTD, float valve, vapor detector, etc. The
number and spatial distribution of the vapor detectors can also be varied as per
requirements. For instance, additional vapor detector may be provided proximate to
locations inside the tank which have been found to be more susceptible to leaks.
Similarly, one could uniformly arrange four or eight vapor detectors instead of two, for
more accurate measurement of the vapor concentration inside the tank. It would be
apparent to a skilled person that the levels like L1, L2, R1, R2, R3, etc. can be set as per
the requirements of the user. Likewise, the number of generators connected to each
storage tank can also be increased or decreased depending upon the requirements. The
predefined limits mentioned in the description can be determined in accordance with
the fire safety guidelines provided by governmental agencies for different types of tank
and building constructions.
The invention is not limited to the embodiments which have been described and
illustrated by way of example and numerous modifications and variations would be
apparent to a person skilled in the art, without departing from the scope of the appended
claims.
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REFERENCE NUMERALS
100. Aboveground Storage Tank
150. Outer Tank
200. Inner Tank
105. Floor of outer tank
110. Resistance Temperature Detector
115. Alarm System
120. Temperature Indicator-cum-Controller
125. Walls of outer tank
130. Modular Cylinder
135. Lid of Outer Tank
140. Vent
145, 155. Angle Supports
160. Float Valve
165. Bypass Valve
170. Solenoid Valve
175. Diesel Line
180. Drain Valve
190. Vapor Detector
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We Claim:
1. A fire resistant storage tank for containment of inflammable and combustible
liquids, comprising:
a) an Inner Tank (200) for storing inflammable and combustible liquids;
b) an Outer Tank ( 150) separated from and enclosing the inner tank (200);
c) a vapor detection means for measuring the concentration of one or more
types of gases;
d) a temperature sensing means for detecting fire; and,
e) a fire extinguishing means for suppressing fire;
wherein, the vapor detection means comprises a plurality of Vapor Detectors
(190) provided in the space between the outer tank (150) and inner tank (200),
and means for displaying the concentration of one or more types of gases; and,
wherein, the temperature sensmg means compnses at least a Resistance
Temperature Detector (11 0) for detecting the temperature at at least one
location inside the tanks ( 150, 200); and, a Temperature Indicator-cumController
(120) for displaying the temperature and comparing it with
predefined limits.
2. The fire resistant storage tank as claimed in claim 1, wherein the outer tank
comprises a Floor (105), a Lid (135) and a plurality of walls; each ofthem being
made of the same or different materials having high fire resistance rating.
3. The fire resistant storage tank as claimed in claim 2, wherein the outer tank
comprises a floor (1 05) made of a material like concrete, four walls (125) made
from materials like concrete, plastered bricks, etc. erected on the floor ( 1 05),
and a lid (135) made of a material like Promat board provided above the walls;
the lid being partially or fully removable.
4. The fire resistant storage tank as claimed in any of the preceding claims,
wherein the fire extinguishing means comprises a Modular Cylinder (130) for
automatically releasing a fire retardant material upon detection of fire.
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5. The fire resistant storage tank as claimed in any of the preceding claims, further
comprising a level control means for regulating the level of the liquid stored
inside the inner tank (200); the level control means comprising a float wall for
detecting the liquid level, a Solenoid Valve (170) for controlling the flow of
liquid into the inner tank in accordance with the liquid level inside the tank.
6. The fire resistant storage tank as claimed in any of the preceding claims, further
comprising an Alarm System (115) for generating an audio and/or visual alarm
in case the value detected by at least one of the vapor detection means,
temperature sensing means or level control means is outside predefined limits.
7. The fire resistant storage tank as claimed in any of the preceding claims, further
comprising a Vent (140) for removal of air and/or prevention of pressure buildup
inside the inner tank (200); optionally wherein a Drain Valve (180) is
provided at the bottom of the inner tank (200) for draining out the liquid,
whenever required.
8. The fire resistant storage tank as claimed in any of the preceding claims,
optionally comprising an adsorbent and/or absorbent material in the space
between the outer tank (150) and inner tank (200) for adsorbing and/or
absorbing any leakage of liquid.
9. A method of containment of inflammable and combustible liquids using a fire
resistant storage tank as claimed in any of the preceding claims, characterized in
that the fire resistant storage tank is connected to two or more generators.
10. The method of containment of inflammable and combustible liquids as claimed
in claim 9, wherein the fire resistant storage tank is connected to three
generators.