EP0421166A2

EP0421166A2 - A process for operating in safety conditions in the maintenance and reclamation of containers of flammable substances

Info

Publication number: EP0421166A2
Application number: EP90117626A
Authority: EP
Inventors: Giuseppe Natta
Original assignee: ECODECO SpA
Current assignee: ECODECO SpA
Priority date: 1989-09-25
Filing date: 1990-09-13
Publication date: 1991-04-10
Also published as: IT8921821A0; EP0421166A3; IT1231037B

Abstract

Process for operating in safety conditions in the maintenance or reclamation of containers of flammable substances comprising the steps of: generating fire-fighting foam; filling with the fire-fighting foam a container on which intervention is required; cutting the container defoaming the foam for its subsequent disposal.

Description

The present invention relates to a process for operating in safety conditions in the maintenance and reclamation of containers of flammable substances.
Several processes are known for dismantling and reclaiming tanks and industrial containers for liquids, sludges or solid products which produce flammable gases or which are flammable products themselves.
Also in the operations of maintenance or repair of industrial containers, the problem to be solved is that of being able to proceed with the various operations of cutting or welding the structures in such a manner that the residual substances or the gases generated inside them cannot ignite.
One of the most commonly used processes currently is that of filling the containers with substances capable of replacing the O₂, and lowering therefore its content to such concentrations as to prevent the forming of explosive mixtures or below the lower flammability limit.
Said substances are generally water and/or sand. The container is then flame-cut and is then opened and reclaimed with any method for the mechanical removal of its contents.
The products of this operation must be disposed.
This method has considerable disadvantages: in particular, difficulty in performing a precise filling of high-volume containers with sand, operational difficulties in cutting in the presence of water, large amounts of products to be handled and most of all high costs for the disposal of the resulting products.
Another system which is used entails the reclamation of the container by means of human intervention inside it, subsequent flame-cutting, and disposal of the products resulting from the reclamation.
This is for all purposes the most economical method, but it entails high risks both for the personnel working inside the tanks during the reclamation step and in the cutting step, since the complete removal of the flammable gases, despite the necessary gas-free certifications, cannot be ensured.
Another known process entails the cold-cutting of the structure with mechanical means.
Several techniques are available for this process, and range from the use of oleodynamic shears mounted on heavy vehicles with an outreach which generally does not exceed approximately 5 m or with nibblers or nibbling machines which perform percussion cutting on thicknesses generally not in excess of 6 mm.
The disadvantages of the use of this process can be summarized as follows:
The means always require simple structural situations, the subjects of the operation must be easily accessible and have few structural limitations in the immediate surrounding area, and furthermore always require the creation of a starting point for the cut which is generally performed with methods which produce sparks, with a consequent high risk of triggering explosions or fires.
The cutting operation is also not free from this risk, through its extent is more limited.
The reclamation operation is performed after cutting; in the case of cutting with shears, this operation is complicated by the irregular profile of the cut.
In the case of high flammability risk, gas-free certification is in any case required.
A process which entails the cold-cutting of tanks, by means of the use of a jet of high-pressure water mined or not with an abrasive substance, is also known.
Among the above described methods, this one is undoubtedly the safest both for the personnel, who works remotely after positioning the devices, and for the risks of flammability or explosion.
The greatest disadvantages of this method consist of the high operation costs, of the large quantity of products requiring subsequent disposal (water and abrasive contaminated by the content of the tanks) and in the installation times of the devices, which are long.
In some cases it is possible to use a process which comprises the initial reclamation of the tanks or containers by stripping the flammable products by steam-current distillation.
This method entails the preparation of a piping system connected directly to a line of steam which has pressure and temperature characteristics adapted to provide practical and efficient operations.
The steam entering the container must follow a path adapted to provide the stripping action. In output, the steam must be condensed, collected and sent to disposal.
The evident disadvantages of this method are first of all the necessary presence of an adapted line of industrial steam in the immediate vicinity.
All the "distillation" line must furthermore be sealed tight and the container must have an optimum configuration in the location of the openings.
This process is necessary and functional only in the case of containers or devices filled with materials (e.g. catalysts or rings).
The aim of the present invention is to provide a process for the reclamation of containers of flammable products which solves the above described problems of the known art and in particular allows to perform all operations in absolute safety and with extremely low costs.
Within the scope of this aim, an object of the invention is to provide a versatile process which may be adapted to any type of container or tank.
Not least object of the invention is to significantly limit the problems related to the disposal of the polluting substances.
This aim, these objects and others which will become apparent hereinafter are achieved by a process for operating in safety conditions in the maintenance and reclamation of containers of flammable substances, characterized
in that it comprises the steps of:
generating fire-fighting foam;
filling a container to be treated with said fire-fighting foam;
cutting said container;
defoaming said foam for its subsequent disposal.
Further characteristics and advantages will become apparent from the description of some preferred but not exclusive embodiments of the invention, described only by way of non-limitative example.
The process according to the invention substantially comprises the steps of:

a) filling the container with fire-fighting foam generated with an inert gas instead of air; the inert gas can generally be nitrogen, but air, too, can be used if the flammability characteristics of tile tanks or containers are such as to not justify the use of inert gas and in any case if the physical-mechanical characteristics of the foam comply with certain requirements, as described hereinafter.
b) flame-cutting the container.
c) temporarily closing the cut being produced by means of any plastic sealant of the silicone or paraffin kind or of another kind.
d) controllably topping-up the foam lost during cutting.

If the operation being performed is maintenance, repair and/or modification of the container, it is performed as in the above described conditions. If instead the operation is dismantling, the complete opening of the container is necessary, whereas the subsequent reclamation is performed by using any mechanical means.
The foam can be defoamed with anti-foaming systems or by sprinkling finely divided water or with any system having a mechanical action on said foam.
Advantageously, the foam can be generated by a modular system which can be carried by a motor vehicle in the immeidate vicinity of the container to be dismantled or on which maintenance is to be performed, and constitutes an autonomous pre-assembled skid unit.
The foam production system is configured so as to have a capacity 50% in excess of the average volume of the containers to be treated, and is in any case designed so as to allow the partial or total use of the available mixture reserve.
The design of the foam-generating system ensures the production of foam with inert gas with absolutely no mixing with the surrounding air and with flow-rates of foam-generating liquid of around 5-10 1/min, sufficient to perform a rapid filling of the containers while simultaneously checking the quality of the filling.
The adopted foaming ratio of the foam is a function of the type of container to be filled. In any case it is possible to use low-foaming, medium-foaming or high-foaming foams.
The type of foam to be used depends on the content of the tanks; universal foams are in any case suitable for all the tested cases.
The on-site generated foam performs in summary two types of action:
it segregates, in a cellular fashion, the gas trapped in said foam with liquid membranes, constituting an obstacle to the propagation of flames and smothering a flame which has already formed;
by means of its liquid fraction, according to the density of said foam, it removes thermal power (heat) with its heat capacity on one hand and with its latent vaporization heat on the other.
These positive effects are present both when the foam is generated with air and when it is generated with gases which are inert with respect to combustion, for example nitrogen.
Undoubtedly, the foam generated with nitrogen, from a conceptual viewpoint, leaves no misgivings as to the validity of its use, since besides the already mentioned actions it also adds a further action related to its chemical inertness in combustion reactions.
A foam generated with air is in any case equally usable with no reduction in effectiveness, except for the psychological tranquility of the cutting personnel.
The cellular structure in the air bubbles which constitute the foam, at least when they are not only stable and consistent but also fine-grained, seems indeed to be adequate for removing from the reacting environment a considerable fraction of the free radicals which form in the flames, leading to the extinguishing of said flame; in other words, the specific surface of the bubbles, above certain values, would make the propagation of radical chains sub-critical, extinguishing the flame.
By way of example, the apparatus for the execution of the process can be constituted by:
- 4 mixture containment tanks having the following characteristics:
- 700 liter capacity
- AISI 304 construction
- A.N.C.C. accepted
- horizontal cylindrical shape.
Each tank is complete with:
- drawing syphon with valve
- gas inlet valve
- pressure gauge
- safety valve
- discharge valve
- 12 nitrogen cylinders connected by means of a manifold in sets of three cylinders, having the following characteristics:
- 50-liter capacity for each cylinder
- 200 bar loading pressure
- A.N.C.C. (ISPESL) accepted
- handwheel-controlled cutoff valve on each cylinder
- connection couplings in output
- three-point gas manifold with cutoff valve
- cylinder assembly framework with possibility of individual disassembly of each cylinder;
the cylinder pack can have different dimensions and reach a maximum capacity of 200 N/m³ nitrogen for each individual pack.
- 1 pressure reducer for feeding the tanks, complete with upstream and downstream pressure gauges.
- 1 pressure reducer for feeding the foam generator, complete with upstream and downstream pressure gauges.
- 1 foam generator for emulsifying the mixture with nitrogen
- foam production 2500/3000 l/min
- mixture and nitrogen adjustment valves
- pressure gauges
The apparatus is provided with a quick coupling in output, to which the foam delivery hose can be connected.
- 1 hose made of rubber-covered synthetic material, 20 m long, complete with quick couplings.
- 1 foam dispenser to be applied to the end of the hose with driving handles.
- 1 pre-mixer for drawing the product to be mixed with the water, complete with, UNI 45 water feed coupling, drawing from drums by direct suction.
- minimum water feed pressure of 5 bar, optionally supplied by means of a self-priming pump.
The apparatus is connected to the tanks to be filled.
- Assembly skid, made of steel profiled elements, complete with lifting and handling hooks.
- Full loading weight of the apparatus: approximately 7000 kg.
Some examples of embodiment of the process according to the invention are now described.

Example 1

Container:
- 50 m³ buried horizontal tank, maximum height 2.2 m
- upper and laterally offset 500-mm flange
Contents:
- fluid but non-pumpable sludge derived from the deposition of mixtures of various non-chlorinated organic solvents
- average high heating value in excess of 8.500 Kcal/Kg
- amount: approximately 10 m³
- analysis performed by means of an extendable-probe explosimeter has detected the presence of flammable gases such as to reach 100% of the L.I.E.
Purpose:
After determining its thicknesses, the tank was found to have a reduction in the thickness of the plating on the side opposite to its flanging; a reinforcement in this point was thus constituted experimentally.
Operation:
After exposing the upper part of the plating of the tank by excavation, the plating reinforcement operation was performed by welding an iron plate at the indicated point. The operation was performed by filling the tank with fire-fighting foaming liquid for hydrocarbons and polar solvents, the foam/N₂ foaming ratio being approximately 1/30. The filling was completed in 30′. The fluidodynamic behavior of the foam allowed its escape from the cut, preventing any backfiring. The foam was not defoamed but was allowed to decay without intervention; 8 hours after the beginning of operations, an approximately 50% decrease in the volume of the foam was observed.

Example 2

Container:
- as in example 1
Contents:
- as in example 1
Purpose:
After determining its thicknesses, the tank was found to have a considerable reduction in the thickness of the upper plating along its entire length: the tank was thus completely dismantled, reclaiming the iron and performing the disposal of the residual substances contained therein.
Operation:
The operation was performed by filling the tank with fire-fighting foaming liquid for hydrocarbons and polar solvents, with a foam/N₂ foaming ratio of approximately 1/50.
Filling was completed in 20′. Once the filling was complete, flame-cutting was performed along the entire length of the tank, creating an approximately 1-meter-long opening in the upper part. The foam lost due to leakage was restored during cutting with one-minute feeds every 10 minutes of work. The cut was temporarily sealed with silicon rubber. After cutting, the top of the tank was removed and the deposited substances were removed after eliminating the foam by sprinkling sand, which was in any case necessary to optimally dry the present deposited substances.

Example 3

Container:
- 20 m³ vertical tank inserted in a set of tubes of a chemical plant during a special production stop.
Contents:
- ethyl ether and pumpable sludge which could not be reached by suction hoses due to the internal configuration of the tank
- by means of analysis performed with an extendable-probe explosimeter, the exceeding of the lower flammability limit, equal to 1.9% in air volume, was detected.
Purpose:
A flanged output was coupled to the base of the tank by welding.
Operation:
Filling with foam was completed in 20′ with fire-fighting foaming liquid for hydrocarbons and polar solvents, with a 1:20 foaming ratio. The operations of cutting the hole and of welding the flanged tube were performed with an oxyhydrogen flame at the level of the surface of the ethyl ether. The leakage of the foam was contained by sealing the cuts with silicone rubber. The operational restoring of the tank was obtained by leaving the foam to deposit, drawing the fluid from the newly-made flange and washing several times with ethyl ether.

Example 4

Container:
- 200-l wide-mouth drum
Contents:
- 10 l kerosene
Operation:
The drum was filled with fire-fighting foaming liquid for hydrocarbons and polar solvents, with a foaming ratio of 1/100. A series of cuts was performed or, the closed drum with an oxyhydrogen flame starting from the top until the kerosene was reached. The operation was completed with no flame ignited.

Example 5

Container:
- as in example 4
Contents:
- 10 l isobutylketone
Operation:
- as in example 4.
Example 6
Container:
- as in example 4
Contents:
- 10 l methyl alcohol
Operation:
- as in example 4.
In practice it has been observed that the invention achieves the intended aim and objects by providing a process which allows to reclaim containers for flammable products with absolute safety and at the same time with extremely low costs.
An important advantage provided by the use of the foam is that of sensibly limiting the amount of polluting product to be disposed of: once it has defoamed, the foam in fact has an extremely small volume.
An advantage of the invention is the versatility of the system, which can be adapted to containers of different types containing different materials.
Another advantage is the rapidity of intervention with respect to conventional systems.
The process according to the invention, is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept; all the details may furthermore be replaced with technically equivalent elements.
Naturally, the materials employed, as well as the dimensions, may be according to the requirements and to the state of the art.

Claims

1. Process for operating in safety conditions in the maintenance and reclamation of containers of flammable substances, characterized in that it comprises the steps of:
generating fire-fighting foam;
filling a container to be treated with said fire-fighting foam;
cutting said container;
defoaming said foam for its subsequent disposal.

2. Process according to claim 1, characterized in that said foam is generated by means of inert gas.

3. Process according to claim 1 or 2, characterized in that said cut is produced by means of an oxyhydrogen flame.

4. Process according to one or more of the preceding claims, characterized in that said cut being produced is temporarily closed by means of plastic sealant.

5. Process according to one or more of the preceding claims, characterized in that it comprises the topping-up of said foam while cutting.

6. Process according to one or more of the preceding claims, characterized in that said foam is defoamed by means of a finely divided water jet.

7. Process according to one or more of the preceding claims, characterized in that said foam is generated by means of a modular device which can be transported by a motor vehicle.

8. Device for generating fire-fighting foam, according to the process of claim 1,characterized in that it comprises: mixture containment tanks, nitrogen cylinders, a pressure reducer for feeding said tanks, a foam generator for emulsifying the mixture with nitrogen, a second pressure reducer for feeding said foam generator, a foam dispenser applied to the end of a hose, a pre-mixer for drawing the product to be mixed with water.