EP0654138B1

EP0654138B1 - Heating apparatus

Info

Publication number: EP0654138B1
Application number: EP93918026A
Authority: EP
Inventors: John Graham Hart
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-08-13
Filing date: 1993-08-13
Publication date: 1996-12-04
Anticipated expiration: 2013-08-13
Also published as: DE69306395D1; EP0654138A1; GB9217176D0; JPH08500895A; CA2142291A1; ES2094559T3; DE69306395T2; AU4726293A; WO1994004876A1

Abstract

A method of heating a liquid which comprises providing a mandrel (12) within a heating element (14) having at least one surface, and passing the liquid down the mandrel in the form of a thin film (22) in such a manner that it does not contact the heating surface (14). This may be carried out in apparatus which comprises a heating element (14) within which is located a mandrel (12), not in contact with the element, a source of liquid (18), and means (20) for allowing the liquid from the source to flow over the mandrel (12) in the form of a thin film (22). The mandrel (12) will normally be maintained in a vertical orientation and the source of liquid (18) may be at the top thereof. The liquid is allowed to run as a film (22) down the surface of the mandrel (12). The mandrel (12) is surrounded by the hot surface of the heating element (14) and heat passes principally by radiant heat across the gap (16) between the hot surface of the heating element (14) to the liquid passing down the mandrel (12). Thus there is no direct contact between the liquid to be heated and any heated surface of the heating element (14). The mandrel (12) itself will normally not be heated and, indeed, it may be made from materials having good corrosion and release properties but a thermal conductivity so poor that they would not normally be used in heat exchanger manufacture. It need not be made from metal, and may, for example, be made from materials such as ceramics or glass, optionally with release coatings of, for instance, PTFE.

Description

This invention relates to a method and apparatus for heating liquids, and in particular to a method of apparatus for heating liquids in an indirect manner.
Liquids are commonly heated by allowing them to flow over a hot surface but some fluids are very difficult to heat in this way. For example, many (such as some biological fluids) deposit layers of solid material on the heat transfer surface which then act as insulation impeding the further flow of heat to the liquid. This tendency, referred to as fouling, may be reduced to some extent by various stratagems but nevertheless remains a considerable problem.
The invention seeks to provide a method and apparatus of heating liquid improved in the above respects.
US-A-4,164,441 describes an apparatus for heating and separating a corrosive liquid using two spaced concentric tubes. The liquid is made to flow over the inner surface of the inner tube and hot flue gases contact the outside of the outer tube. In this arrangement, the heat is transmitted through the walls of the tubes from the hot gases to the liquid. French patent 2129118 describes a water heater in which hot gases are made to flow in a turbulent manner over the outer surface of a cylinder whilst giving up its heat across a reservoir wall to water contained in a reservoir surrounding the inner cylinder.
According to the present invention there is provided a method of heating a liquid which comprises providing an unheated mandrel within a heating element having at least one heating surface such that there is a gap between the mandrel and the heating element, characterised in that the liquid passes down the surface of the mandrel in the form of thin film and in such a manner that it does not contact any heated surface of the heating element but is heated by heat passing across the gap from the heating surface of the heating element to the liquid.
The invention also provides an apparatus which comprises having at least one heating surface within which is located an unheated mandrel such as to define a gap between the mandrel and the heating element and a source of liquid, characterised in that there is provided means for allowing the liquid from the source to flow over the surface of the mandrel in the form of a thin film and in such a manner that it does not contact any heated surface of the heating element but is heated by heat passing across the gap from the heating surface of the heating element to the liquid.
The mandrel will normally be maintained in a vertical orientation and the source of liquid may be at the top thereof. The liquid is allowed to run as a film down the surface of the mandrel. The mandrel is surrounded by the hot surface of the heating element and heat passes principally by radiant heat across the gap between the hot surface of the heating element to the liquid passing down the mandrel, or by convection in the gas or vapour in the gap, or by a combination of both processes. Thus there is no direct contact between the liquid to be heated and any heated surface of the heating element. The mandrel will itself will normally not be heated and, indeed, it may be made from materials having good corrosion and release properties but a thermal conductivity so poor that they would not normally be used in heat exchanger manufacture. It need not be made from metal, and may, for example, be made from materials such as ceramics or glass, optionally with release coatings of, for instance, PTFE.
The indirect heating of the liquid has various advantages. Firstly heat transferred to the liquid continues even if a layer of solid material builds up on the mandrel over which it flows. Secondly it is envisaged that in most cases solids will not bond to the unheated mandrel in the same way that they would to a heated surface. This will result in a large proportion of any solids formed simply washing down the mandrel with the liquid and not permanently fouling the mandrel surface. The apparatus can be arranged so that mandrels can be removed easily for cleaning in contrast to the tubes or plates of a conventional process heat exchanger.
The heating elements may be of any suitable design and will preferably be a cylindrical element surrounding the mandrel but not touching it. Heating may be, for example, by hot oil or high pressure steam, although in certain circumstances an electrical heating element may be employed. The gap between the heating element and the mandrel will be adjusted to suit the requirements of the process being carried out and may contain air or some other gas or may be evacuated.
The heat supplied to the fluid can simply be to increase its temperature but it is envisaged that the apparatus will be used most frequently for the purpose of evaporating some or all of the liquid. In this case vapour will be produced which will pass through the gap between the mandrel and the heating element and may leave the apparatus from the top, or with unvapourised liquid from the bottom.
The invention will be described further, by way of example, with reference to the accompanying drawing in which the sole figure is a diagrammatic sectional view of an apparatus in accordance with the invention.
Referring to the drawing, an apparatus for heating liquids generally designated (10) comprises a central vertical mandrel (12) surrounded by a cylindrical heating element (14), which may be an electrical heating element. A gap (16) exists between the mandrel (12) and the element (14) and the element (14). A fluid reservoir (18) is provided at the top of the vertical mandrel (12). Means, such as a narrow annular gap (20), are arranged between the reservoir (18) and the mandrel (12) such that a film (22) of liquid flows downwardly over the surface of the mandrel (12).
In use, the element (14) is activated so that heat is radiated and/or convected towards the mandrel (12). The means (20) is activated to allow the film (22) to flow down the surface of the mandrel (12). The film (22) receives heat indirectly from the element (14), that is the liquid is not in contact with any heated surface of the element (14) but receives the heat by radiation, convection or a combination of the two. Hot liquid (24) is removed from the bottom of the apparatus (10).
Should it be required to vaporise some or all of the liquid then the rate of flow of the liquid and/or the amount of heat provided by the element (14) is adjusted so that the necessary evaporation takes place. Vapour may be removed either from the top of the element (14) or from the bottom together with the heated liquid.
For the majority of applications a typical mandrel diameter may be in the range of from 40 to 100 mm with a gap size in the range of from 2mm to 20 mm, but dimensions outside these ranges may be employed where appropriate.
The apparatus and method of the invention are particularly used with liquids which are difficult to heat without fouling, such as oils, aqueous solutions of salts, and biological fluids. The apparatus of the invention may be used singly, in multiple applications, either parallel or series, or with other conventional apparatus.
The apparatus and method of the invention provides an improved method of heating liquids prone to fouling.

Claims

A method of heating a liquid which comprises providing an unheated mandrel (12) within a heating element (14) having at least one heating surface such that there is a gap (16) between the mandrel (12) and the heating element (14), characterised in that the liquid (22) passes down the surface of the mandrel in the form of a thin film and in such a manner that it does not contact any heated surface of the heating element (14) but is heated by heat passing across the gap (16) from the heating surface of the heating element to the liquid (22).
An apparatus which comprises a heating element (14) having at least one heating surface within which is located an unheated mandrel (12) such as to define a gap (16) between the mandrel (12) and the heating element (14) and a source of liquid (18), characterised in that there is provided means (20) for allowing the liquid (22) from the source to flow over the surface of the mandrel (12) in the form of a thin film and in such a manner that it does not contact any heated surface of the heating element (14) but is heated by heat passing across the gap (16) from the heating surface of the heating element (14) to the liquid (22).
An apparatus as claimed in claim 2 further characterised in that the mandrel (12) is maintained in a vertical orientation and the source of liquid (18) is at the top thereof.
An apparatus as claimed in claim 3 further characterised in that the hot surface of the heating element (14) surrounds the mandrel (12) and heat passes principally by radiant heat across the gap (16) between the hot surface of the heating element (14) to the liquid (22) passing down the mandrel (12).
An apparatus as claimed in claim 3 further characterised in that the hot surface of the heating element (14) surrounds the mandrel (12) and heat passes principally by convection in the gas or vapour in the gap (16) between the hot surface of the heating element (14) to the liquid (22) passing down the mandrel (14).
An apparatus as claimed in any of claims 2 to 5 further characterised in that the mandrel (12) is made from a material having good corrosion and release properties but of low thermal conductivity.
An apparatus as claimed in claim 6 further characterised in that the mandrel (12) is made from a ceramic or glass.
An apparatus as claimed in claim 7 further characterised in that the mandrel (12) is coated with a release coating.
An apparatus as claimed in any of claims 2 to 8 further characterised in that the mandrel (12) is easily removable for cleaning.
An apparatus as claimed in any of claims 2 to 9 further characterised in that the heating element (14) is a cylindrical element surrounding the mandrel (12) but not touching it.
An apparatus as claimed in claim 10 further characterised in that the heating element (14) is heated by hot oil, high pressure steam, or an electrical heating element.
An apparatus as claimed in any of claims 2 to 10 further characterised in that the gap between the heating element (14) and the mandrel (12) is from 2 mm to 20 mm.