Fire extinguishers – Processes
Reexamination Certificate
1999-03-18
2001-05-29
Scherbel, David A. (Department: 3752)
Fire extinguishers
Processes
C169S045000, C169S048000, C169S066000
Reexamination Certificate
active
06237694
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
This invention involves explosion-protecting and extinguishing safety devices for flammable liquid storage tanks under high temperature.
TECHNICAL BACKGROUND
Recovering, refining, storing and transporting of petroleum and flammable liquids requires the use of oil depots, fuel tank cars (including oil trains) and fuel tanks. All of these involve tanks and the tanks are sealed for protection by an outer covering. There is a rare chance for flammable liquid in the tank to touch a tinder directly and cause firing. This is caused by the intrinsic nature of flammable liquids. When there is an external heat conduction, e.g. a lightning strike outside, high temperature is generated on the outer covering of the tank and causes the flammable liquid in the tank to evaporate causing the pressure inside the tank to increase sharply. The explosion will occur right away and cause a firing when the bearing strength of the tank cannot withstand the vapor pressure. The explosion becomes a new tinder and heat source which will threaten other tanks. The intensity of firing will expand and spread continuously. The situation can be harmful to humans, property and the environment. Furthermore, once the burning oil is extinguished, the remaining oil will become waste product because the fire-extinguishing chemicals are often absorbed by the oil. Also a great quantity of manpower and material resources are consumed in the course of rescue.
Cooling methods are a common technique requiring a great quantity of coolant to prevent fire expansion and spreading. Chemical foam fire-extinguishing agents are less effective for oil firing in large areas. Explosion extinguishing methods and water spray methods using jet engines are also impractical for large-area oil firing in the tank. Up to now, there is no effective extinguishing method for the large area firing of flammable liquid in the tank.
An existing technique described in Su787046 generally describes an extinguishing device including a chamber with pipes parallel with the chamber side surface walls. The device is placed in a trough under the liquid storage tank. In an embodiment of this device used for extinguishing a flaming liquid, there is a very large volume under the pipes, i.e. the length of the pipe is shorter than the height of the holder. In an alternate embodiment, the length of the pipe is equal to the height of the receiver and holes are drilled on part of the pipe's wall. Thus, Su787046 generally describes a device which can make the burning liquid flow into the receiver of the device wherein the extinguishing is carried out.
Su1463317 also generally describes an extinguishing device including column shaped pipes having large bores therein. Additionally, the pipes have deflectors with angles calculated to be the ratio of the pipe diameter to the pipe top section length. However, the fire prevention and extinguishing of flammable liquid in the system described suffers from a number of deficiencies.
First, no explosion-protecting measures are described. As the tank of flammable liquid is a sealed type tank, explosion is likely to occur when subjected to heat. If the safety device is installed in the tank, the safety device will be destroyed and lose its function of fire prevention and extinguishing when explosion occurs.
Second, as the pipes must be spread over the entire cross section of the tank, a great quantity of space in the tank is occupied by the device itself.
Furthermore, the functions of fire prevention and extinguishing can be effective only under the condition of normal atmospheric temperatures. If the outer covering is elevated to a high temperature or the liquid's temperature is elevated to its boiling point, the device will lose its effective function.
Therefore, the challenge of liquid explosion-protection of a flammable liquid tank is the first technical difficulty to be solved. When the flammable liquid in the sealed tank is under the influence of an external heat source, explosion does not occur immediately but rather the flammable liquid temperature will go up continuously and a corresponding vapor will be produced unceasingly. The vapor is accumulated continuously and thus the pressure of the tank is increased unceasingly. Explosion and combustion may then occur when the mechanical strength of the tank can no longer withstand the pressure of the vapor. Therefore, controlling the vapor pressure and venting the vapor are the key to the explosion-protection. If there is an aperture or many apertures on the tank and these apertures are shut normally, these apertures may be opened to vent the accumulation of vapor in the tank when the vapor pressure exceeds the working pressure of the tank. Alternatively, the apertures may be opened when the wall of the tank reaches a certain temperature thereby preventing an explosion.
SUMMARY OF THE INVENTION
A main object of the invention is to provide an explosion-protection and extinguishing safety device for a flammable liquid storage tank. After eliminating the influence of an external heat source, the flame above the flameout device can be automatically extinguished so that it does not itself become new tinder. An aperture, or multi-apertures, is opened on the top of a flammable liquid storage tank. The size of the aperture is stipulated so that the aperture is opened automatically at a specified temperature and the vapor is let out continuously to avoid explosion when there is an external heat source causing the pressure inside the tank to increase or elevating the temperature of the tank's wall. This is a suitable method of explosion-protection for a flammable liquid tank. However, the flammable liquid in the tank may burn when the tank apertures are open. Metal net or corrugated metal is an effective fire obstructor. If these fire obstructors are installed at the apertures of the top of the tank, a flame can be blocked from reaching the liquid surface by way of the venting apertures. After the external heat source's influence has been eliminated, the flame above the obstructor still burns continuously until the liquid in the tank has vaporized completely. In fact, if a metal net or a corrugated metal fire obstructor is installed in the aperture above the tank, the fire obstructor impedes the flow of vapor. The obstructor may even impede the vapor from venting to the extent that the accumulated vapor will reach a high enough pressure to expel the obstructor. The present invention improves on the prior art by providing a flameout device installed above the vapor-vent of the tank thereby providing less resistance to vapor flow.
REFERENCES:
patent: 2912054 (1959-11-01), Mathisen
patent: 5415233 (1995-05-01), Roussakis et al.
patent: 5794707 (1998-08-01), Alhamad
Hwu Davis
Jenkens & Gilchrist P.C.
Scherbel David A.
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