Liquid heaters and vaporizers – Water tube – Tube structure
Reexamination Certificate
1998-01-21
2001-06-12
Ferensic, Denise L. (Department: 3749)
Liquid heaters and vaporizers
Water tube
Tube structure
C122S015100, C165S056000, C126S378100
Reexamination Certificate
active
06244224
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to improved heating for liquid products, particularly petroleum and its derivatives, and aims to facilitate the draining-off of undesirable materials (dense residues, sludges, water, sand, etc.) which normally accumulate in the bottom of liquid storage tanks.
BACKGROUND OF THE INVENTION
It is known to provide a floating roof on a tank for containing relatively volatile liquids, in order to avoid the formation of a gas space in the tank. When the floating roof of such a tank for storing liquid products is low, it is not possible to use the customary systems normally used for heating liquid products in general; these basically depend on a variety of factors, such as the type of product, the amount stored, the temperature to be reached, and the heating time.
The present invention aims to provide tanks with low floating roofs, such as those described in International Application PCT/BR97/00022, with an individual heating system which can be used for such low operating heights, but which can also be used for conventional tanks.
PRIOR ART
Storage tanks are widely used in the petroleum industry and are essential to the functioning of an operational facility. They may be intended, for example, for storing crude oil, intermediate products and final products.
The sources of heat used include heated liquids, pressurized vapours, electrical energy or other less conventional sources.
Coils through which hot fluid passes are amongst the most common ways in which to heat tanks. In normal use, they are generally at a distance of 0.80 m from the level of the tank floor. There is considerable wasted space. Use is also made of laterally mounted heat exchangers.
Our International Application PCT/BR97/00022 relates to a new type of tank floor for which the present heating system is particularly suitable. It proposes the use of a floor whose centre is located at a level which is below the level of the edges. The residues which are to be drained off concentrate in the central region of the bottom of the tank.
With the installation of this new type of floor, because of the better draining-off of the undesirable liquids, the floating roof of the tank is able to descend to a position which is much closer to the floor than was previously attained. Consequently, a new problem arises in that, if the product has to be heated in a tank with a configuration of this type, it is necessary to have a heating system which can be contained in a small space (minimum operational height), which may be as little as 10 cm in height. A heating system of this type is not known from the prior art, however.
The minimum operational height is the minimum height above the floor of the tank, which the floating roof has to maintain during operation. In current storage tanks, particularly those of larger capacity, this minimum operational height may be as much as approximately one meter forty centimeters.
The maintenance height is the height at which the floating roof has to be held when in maintenance mode, in order to enable workmen to enter inside the tank to carry out maintenance operations. This is higher than the minimum operational height.
SUMMARY OF THE INVENTION
The present invention provides an improvement for product-storage tanks which solves the problems described above, saves time and reduces operating costs.
The heating system of the invention is defined in claim
1
. The invention also provides a liquid storage tank including such a heating system.
Use is made of a system of principally radial tubes along which the flow of a heating fluid, preferably steam, may be convergent (towards the centre) or divergent (towards the periphery). All the tubes carry heating-fluids and connect a central, inner arc to an outer arc. Each arc may itself form a ring, or there may be a succession of arcs which may or may not form a complete ring. An analogy may be made between the assembly and a wheel, in which the wheel rim corresponds to the outer ring (periphery) and the wheel hub corresponds to the inner ring. The wheel spokes correspond to the radial tubes. In this way, the system comprises a first tube which is substantially in the form of an outer arc and second tube which is substantially in the form of an inner arc, both interconnected by principal radial tubes from which emerge a plurality of branches which then also assume a radial geometry, forming secondary radial tubes which extend as far as the said outer arc. The system is supported by means of supports which are fastened to the tubes and only rest without being fastened, for example, welded, on the floor of the tank. Most of the tubes of the system slope downwards, which prevents the formation of water hammer and which (as will be described below) may save energy.
The floor of the tank preferably has its centre at a level which is below the level of the edges. In this way, the residues which it is desired to drain off concentrate in a central region of the bottom. Use is also made in this case of a ramp-type drainage channel which starts from the centre of the bottom of the tank and runs towards the edges. This ramp slopes sufficiently to enhance the draining-off of the undesirable materials to the outside of the tank.
However, the present invention may instead be used in tank floors with drainage at the periphery of the tank, in order to provide this type of tank with a heating system.
REFERENCES:
patent: 3685508 (1972-08-01), Heilmann
patent: 3858861 (1975-01-01), Jernigan
patent: 3944113 (1976-03-01), Heisterberg
patent: 4480370 (1984-11-01), Loevinger
patent: 5265651 (1993-11-01), Perkins et al.
patent: 5676039 (1997-10-01), Wedding et al.
patent: 5788152 (1998-08-01), Alsberg
patent: 25 34 380 (1977-02-01), None
Witter Aldyr
Witter Roger Vieira
Ferensic Denise L.
Nixon & Vanderhye PC
Petroleo Brasileiro S.A.
Wilson Gregory A.
Witter Roger Vieira
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