Process For Vaporizing Fuel Oil

Abstract

A process for vaporising fuel oil employs a cylindrical porous heating element through which the oil is passed from the axis, radially outwards. The element is of polycrystalline metal whiskers. The oil feed is in excess of that which the element is capable of vaporising, the excess being returned to the oil source, and the vapour being used for combustion.

Description

The invention relates to a process and a devise for vaporising fuel oil. It employs a porous cylindrical body that is traversed by the fuel oil. The body consists of polycrystalline metal whiskers connected metallically with one another at the points of contact, and heated directly or indirectly, for preference by electric power.

In a known heating element of this type, as described in German Pat. No. 1,288,705, the medium being heated is passed through the porous body in its longitudinal direction. The medium becomes progressively heated as it flows through the porous body until it emerges at one end, heated to the desired temperature or possibly in the form of vapour. Although this known heating element has a very large inner surface and thereby makes possible considerable and instantaneous heating of the medium flowing through, it can give rise to problems with the heating or the vaporisation of hydrocarbons with greatly differing vaporisation temperatures between 60.degree. and 320.degree.C. These often have impurities or additives with high temperatures of vaporisation or decomposition, and it may happen that outbreaks of vapour will occur in the heating element prematurely and in an uncontrolled manner. Residues will remain and choke the pores. Since the vapour has a very much larger volume than the liquid, the pores of the porous body may become filled with vapour inadmissibly far from the outlet end, and this can lead to overheating, since the vapour in the pores has a lower heat capacity than the liquid. Overheating can lead to the local destruction of the porous body and further the formation of residues.

The object of this invention is to provide a process for vaporising fuel oil by means of a heated porous body of this type, but to reduce as far as possible the risk of the formation of residues from the fuel oil.

According to one aspect of the present invention there is provided a process for vaporising fuel oil by passing liquid oil through a heated, porous, substantially cylindrical body consisting of polycrystalline metal whiskers connected with one another metallically at their points of contact, whereby the improvement comprises passing the oil radially, from inside to outside, through the body and supplying more fuel oil to the porous body than is vaporised.

Assuming that the pore size of the porous body is largely uniform, owing to the radial flow from inside to outside, a pore volume that becomes progressively larger is made available, which is in agreement with the increase in volume of the fuel oil which is being transformed into vapour during its passage. As oil emerges as vapour from the outer peripheral surface of the porous body, it has the maximum number of pores to pass through. If just sufficient fuel oil is supplied to the porous body that can be evaporated by the electric power or other form of heat supplied, in the oils vapour will form only in a relatively thin layer or zone on the outer peripheral surface of the porous body where the maximum pore volume is available, although this is hardly attainable in practice. If, however, less fuel oil is supplied vapour can continue to penetrate into the interior of the porous body where a smaller volume of pores is available. This can lead to local overheating, with formation of residues which may choke the pores. Therefore, in the present process excess fuel oil is supplied than can be vaporised, so that the layer of vapour remains confined to the extreme outer zone of the porous body, i.e. the zone in which the largest volume of pores is available, and any deposits forming there can be tolerated.

According to another aspect of the invention there is provided a device comprising a substantially cylindrical porous body consisting of polycrystalline metal whiskers connected with one another metalically at their points of contact, and formed with a central longitudinal duct, means for heating said body, an oil supply pipe communicating with said duct, a housing surrounding said body with a space therebetween for receiving the oil vapour, means placing said housing in communication with a mixing chamber for mixing the oil vapour with air for combustion, and a discharge pipe from a low point of the housing for discharging fuel oil that has not evaporated.

For a better understanding of the present invention, one constructional form thereof will now be described, by way of example, with reference to the accompanying drawing, in which the single FIGURE is a diagram of a device for vaporising fuel oil.

The main component of this device is a porous, cylindrical body 1, which consists of polycrystalline metal whiskers connected metallically with one another at their points of contact. Polycrystalline metal whiskers (vide for instance "Zeitschrift fur Metallkunde" Volume 59 (1968) No. 1, pages 18 to 22 ) can be made with exactly determined diameters from about 0.1.mu.m in likewise predetermined lengths of up to several centimetres. These whiskers are distinguished by their extremely high strength so that they can stand up to high liquid and vapour pressures. Owing to the metallic connection of these whiskers at their points of contact, for instance by deposition of metal through thermal decomposition of a metal compound, by currentless metal separation, by electric beam or ultrasonic welding, or similar well known processes, a rigid, highly porous skeleton can be produced, which can have a pore volume of over 90 percent and possesses good heat conductivity.

The porous body 1 is formed in this example as an electrical resistance heating element, and it is provided at its ends with contact plates 2 and 3 for connection to a voltage source. It has a central longitudinal duct 4 which can be formed for instance by a perforated metal tube. This is sealed at one end 5 and at its other end 6 is connected with an oil supply pipe 7. The supply pipe 7 is connected via an oil pump 8 with an oil supply tank 9.

The porous body 1 is arranged in a housing 10 in such a way that an annular space 11 remains for receiving the oil vapour. The inner space of the housing 10 is connected via a tube 12 with a mixing chamber 13, which communicates with a pipe 14 for the supply of air for combustion. In the mixing chamber 13 the oil vapour passes out radially through openings 12a in the side of the tube 12 and mixes with the combustion air supplied through holes 13a. The mixing chamber 13 connects with the combustion chamber of the heating boiler.

At the lower end of the housing 10 is arranged a discharge pipe 15, which communicates via a second pump 16 with the supply tank 9.

The fuel oil is delivered from the oil tank 9 by the oil pump 8, at a pressure of a few atmospheres excess, into the central duct 4 of the porous body 1, and it flows from there radially through the body 1 outwards to the outer surface 17 of the porous body 1. At the same time the fuel oil is heated so strongly by the electric power supplied to the porous body 1 that it emerges into the annular space 11 principally in the form of vapour. From there, the oil vapour flows through the pipe 12 into the mixing chamber 13, where it mixes with the combustion air. The mixture emerges through a filter 18 and is ignited by an ignition device (not shown). A blue, non-sooting flame is produced.

The oil which has not vaporised collects in the bottom of the tank 10 and is returned by the pump 16 to the oil supply tank 9.

In a modification of the example described, fuel oil can be supplied to the central longitudinal duct 4 from both ends, i.e., also from the end 5. The porous body 1 can also have a diameter which is equal to or greater than the length.

In the example described the heating of the porous body 1 takes place by direct passage of current. However, this heating can also be provided by an insulated electrical heating coil arranged on the inner peripheral surface, i.e., around the central longitudinal duct 4, or on the outer peripheral surface 17 or even inside the porous body 1. In these cases heating takes place by heat convection. The same effect is obtained if, instead of an electrical heating coil, a heating coil traversed by a liquid or gaseous heating medium is provided.

Claims

I claim:

1. A process for vaporising fuel oil by passing liquid oil through a heated, porous, substantially cylindrical body consisting of polycrystalline metal whiskers connected with one another metallically at their points of contact, whereby the improvement comprises passing the oil radially, from inside to outside, through the body and supplying more fuel oil to the porous body than is vaporised.

2. A process as claimed in claim 1, wherein the body is electrically heated.

3. A process as claimed in claim 2, wherein the body is directly heated by electric current passing therethrough.

4. A process as claimed in claim 1, wherein the body is indirectly heated by a heating element in contact therewith.

5. A device for vaporising fuel oil, comprising a substantially cylindrical porous body of polycrystalline metal whiskers connected with one another metallically at their points of contact, and formed with a central longitudinal duct, means for heating said body, an oil supply pipe communicating with said duct, the oil adapted to pass radially from the duct through the heated body to vaporize the oil, means for supplying more fuel oil to the body than is vaporised, a housing surrounding said body with a space therebetween for receiving the oil vapour, means placing said housing in communication with a mixing chamber for mixing the oil vapour with air for combustion, and a discharge pipe from a low point of the housing for discharging fuel oil that has not evaporated.