GB2174017A - Improvements in operation of burners - Google Patents

Abstract

Air is pumped at 7 through diffuser head 8 to rise as small bubbles 10 through water layer 3 and pass through a minor layer portion 4a of disturbed oil/water composition into a major oil layer portion 4. From this it escapes with low water content, and, it is surmised, a content of a catalyst species, probably .OH free radical. The escaping air passes from the convergent vessel top through an outlet 6 to the turbulent root of a burner flame. A small amount of such additive makes a large difference in flame shape and size, leading to a better performance of the boiler. <IMAGE>

Description

SPECIFICATION Improvements in operation of burners This invention relates to the operation of burners for a carbonaceous gas, fuel oil, or solid fuel, and more particularly to equipment which can be connected to such burners, e.g. in a steam-raising or space-heating boiler, to reduce fuel consumption at a predetermined operating temperature.

The invention is related to that described and claimed in Patent No. 2 063 701.

The flame of an oil or gas burner is a complex and turbulent environment of energetic chemical reactions, themselves interdependent in a complicated chain or network until, in theory, all the energy present in the various C-C and C-H bonds (and of any traces of other compounds e.g. the sulphur compounds) is given up with the formation of CO2, H2O and SO2 etc.

Although the theoretical end result, in terms of total energy liberation, is fixed, the dynamic situation within the furnace can vary. If, by suitable feed of air, fuel or a flame-affecting substance the shape, temperature or nature of the flame is caused to change, different results can be obtained for boiler efficiency, probably having their roots in different heat-exchange and heat take-up characteristics. The geometry of that part of the furnace utilised by the modified flame may give different results from that of the part of the furnace using the original flame. Moreover, the take-up of heat after periods of intermittent non-use, is also apparently more effective.

Whether or not the above hypothesis is true, the earlier Patent 2 063 701 of the same inventor describes and claims such a situation, in the light of successful experiment and operation.

It is believed that the flame-affecting species added according to that earlier invention is the free radical .OH, which is nowadays known to be strongly autocatalytic in the turbulent part of a flame. Figures of a growth of .OH concentration of 1013-fold in a few seconds have been claimed when such a free radical is introduced into the turbulent root of a burner flame, and this, the inventor believes, has a marked effect on the path taken to full combustion and thus upon energy liberated in different parts of the path, i.e. in different parts of the flame and furnace geometry, with consequent improvement in boiler performance. In that earlier invention, the catalytic substance, believed to be the .OH free radical, is produced by bubbling air through water.Possibly the surface energies at the bubble surfaces can create a small amount of .OH radical. Further according to that earlier invention, steps are taken to dry the emerging air in a space over the water surface. This space is separated from the water by a barrier layer of an oil. The air is dried by the pressure conditions in this space, which are such as to reduce water-vapour content. Moreover, the vessel is then generally convergently shaped so that the dried air within is swept readily outwards eventually to reach the furnace at the turbulent root of the flame.

Neither the earlier invention nor the present invention should be taken as limited by any of the above theory, although the inventor believes it to be generally true. What is, however, demonstrable is the alteration in furnace performance as described in numerical detail below, and its improvement by the refinements introduced by the present invention.

From a consideration of the device and procedure of the earlier invention it now appears to the inventor that the drying of the air, the converging vessel shape and the consequent prompt onward flow of gas all act to minimise undesired delay time of any active catalytic species (e.g. .OH) and thus minimise interactions of such species with itself, or with water molecules or with the vessel wall. Thus, some of the species always arrives at the furnace.

Probably, with such active species present in such small amounts, the amount arriving varies considerably. The marked autocatalytic growth in the flame may magnify this variation. The inventor has thus sought out a procedure for maximising the amount of such active species initially present and for thus ensuring more uniform performance.

The present invention modifies the nature of the oil layer, and, as a much preferred but optional feature, controls the bubble formation in the base of the vessel.

Hitherto, the inventor has seen the function of the oil layer as a physical barrier between the air and the water. In other words, as long as the integrity of that barrier was not breached, i.e. as long as no water surface was accessible from the air space, the requirements of the earlier invention were met.

Now the inventor has realised that the characteristics of the interface between the oil and water also affect the operation of the invention, even if the barrier is at all times integral at the top layer.

In one aspect, the invention consists in a method of reducing fuel consumption of a burner for carbonaceous gas, fuel oil, or finely divided solid fuel, operating at a predetermined temperature, comprising pumping gas by an externally connected gas pump other than a primary air blower into a container partly filled with water covered with a barrier layer of oil at an inlet below the water level, the container having a convergent top defining with the oil layer a space within which the gas and combustion catalyst formed by the bubbling of gas through the water and oil is held at the pressure exerted by the gas pump and thereby contains only an equilibrium amount of water vapour for that'pressure; allowing the said gas and catalyst to pass out of the container through an outlet in the crown of the convergent top;; introducing the gas and catalyst turbulently to the burner flame, in a steam of primary air for combustion; and reducing the carbonaceous gas or fuel throughput to a level adequate to restore the predetermined temperature; in which method the oil layer is such that under operating conditions it exhibits a major proportion of the oil layer thickness, measured from the top surface as an undisturbed integral layer, and only a minor proportion of the thickness, measured from the effective water interface as a continuously disturbed oil/water combination.

The gas may be any, whether inert or active in combustion, which can generate the catalyst species; it is usually, however, air or possibly oxygen, and for convenience will be described below as air.

The man skilled in the art can readily examine known oils for their interface properties in this regard, although is is not a property the inventor has found widely discussed in textbooks. The inventor has found that if water and oil are shaken in a text-tube the unstable emulsion immediately starts to float to the top and coalesce. However, different oils display extremely different and unpredictable bulk interface behaviour, some settling to a clean separation line forthwith and others giving a long-term oil-water structure over most of the top layer thickness, being neither an emulsion nor a clear separation. The relative solubilities, viscosities, specific gravity, surface tensions or additive or impurity contents probably all play a part.

The inventor has found moreover that upon further simple experimentation, giving continuous disturbance of the effective interface e.g. by bubbles or vibrations only a few of the commercially available oils tested give a layer with only a minor proportion continuously disturbed.

The oil preferred is a poly-alpha-olefin synthetic oil.

It is not known why such an oil layer should be an improvement, although a discussion of a possible reason is given below.

Preferably, the method is carried out in such a way that the bubbles formed in the water are sufficiently small to be essentially spherical by the time they encounter the interface region of the oil and water. It has been found distinctly less valuable to force air through at such a rate that elongated bubbles rush up to the interface; both the formation of the catalytic species and the integrity of the interface are adversely affected.

Small bubbles can be formed by a porous ceramic or foamed polymeric diffuser head if necessary.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is a diagram of a vessel containing a layer of oil separating a body of water (in the base of which air bubbles are being formed) from an air space, and Figure 2 shows a graph of test results using equipment as claimed above.

Figure 1 shows a brass or copper vessel 1 with a converging top portion 2 containing two layers of liquid 3 and 4.

The vessel 1 has a sealably closed inlet 5 for initiai filling with liquids 3 and 4, a top air outlet 6 in the crown of the convergent top portion 2 and a bottom air inlet 7 closed off by a porous ceramic diffuser 8. As shown, the convergent top portion 2 is domed. It could be pyramidal, or conical, but it appears to be important that it does not define "dead spaces" in relation to the airflow.

Liquid layer 2 is basically water; conveniently, it contains some biocidal material to kill bacteria or algae introduced in the current of air.

This inhibitor or biocidal material is typically used as a sodium salt. There are indications that the use of any soluble sodium or like salt in liquid layer 3 in itself improves the operation of the invention; it is thus preferred to incorporate such materials. The use of the sodium salt of the biocidal material or inhibitor is a convenient way of achieving this end and of ensuring that build-up of algae, fungi or bacteria does not affect the interface characteristics between layer 3 and layer 4.

Layer 4 is preferably the poly-alpha-olefin oil described above. Such an oil appears to give only a small amount of interface disturbance 4a between layers 3 and 4, even under the continuously disturbed conditions caused by air bubble flow and vibration.

In use, air is pumped at a positive pumping pressure through inlet 7 and diffuser 8, so as to give a large number of fine spherical bubbles 10.

These increase in diameter as they rise, and eventually encounter the water-oil interface between layers 3 and 4. Obviously, their passage will disturb this interface to some extent, but with the material specified this disturbance is minimised and/or soon corrected, even in conditions (such as use with marine boilers, or mechanical linkage of the container to the boiler structure) where additional vibrations are encountered.

The bubbles thus pass through this shallow "disturbed" zone with as little delay and deformation as possible, and conversely take a longer time to pass through the clear oil region 4b essentially free from films and incursions of water.

The inventor suspects that this passage of the bubble (containing water-vapour and catalyst species believed to be .OH) through the undisturbed region 4b, and its emergence at the upper face of this into a pressure environment which effectively dries the arriving air prior to, or as, it is swept onwards through top air outlet 6.

Possibly, therefore, the undisturbed water-free large portion 4b assists in modifying the watercontent and/or catalyst content of the traversing bubbles, away from contact with films and incursions of water (as at 4a) in a manner which the inventor's previous work did not appreciate.

Some indication of this is given in Figure 2. This is a nominal nomograph showing approximate evaporation ratio in a boiler before and after fitting a device as shown, at different loads, measured as a percentage of the theoretical maximum combustion (MCR) rate against actual MCR at different MCR values.

Two populations of points, marked with an and with a circle respectively are shown, correspondingly respectively to a "before" and "after" fitment of a device according to the invention.

It will be observed that not only are those points on Figure 2 marked with a circle farther to the right, showing an improved MCR, with other things being equal, but also they have an improved tendency, especially at higher MCR values and percentages to relate closely to the notional average line.

The preferred absolute and relative dimensions of the layers and sublayers are still to be fully established, but the inventor believes that layer 4 should preferably be not more than 5cm thick, (e.g.

1 to 3 cms). The lower limit is only adequate to give a layer of mostly undisturbed nature; the upper limits are governed by residence time and cost of the specialised oil. Preferably, it is from one fiftieth to one half the thickness of the layer 5 of water (e.g.

one tenth) which can be up to one metre but is usually 10 to 30 cms, depending on bubble size and expansion during vertical travel. The thickness of ratio of sublayer 4b to sublayer 4a must be greater than 1:1, and is often as great as 10:1.

Claims (14)

1. A method of reducing fuel consumption of a burner for carbonaceous gas, fuel oil, or finely divided solid fuel, operating at a predetermined temperature, comprising pumping gas by an externally connected gas pump other than a primary air blower into a container partly filled with water covered with a barrier layer of oil at an inlet below the water level, the container having a convergent top defining with the oil layer a space within which the gas and combustion catalyst formed by the bubbling of gas through the water and oil is held at the pressure exerted by the gas pump and thereby contains only an equilibrium amount of water vapour for that pressure; allowing the said gas and catalyst to pass out of the container through an outlet in the crown of the convergent top; introducing the gas and catalyst turbulently to the burner flame, in a steam of primary airfor combustion;; and reducing the carbonaceous gas or fuel throughput to a level adequate to restore the predetermined temperature; in which method the oil layer is such that under operating conditions it exhibits a major proportion of the oil layer thickness measured from the top surface as an undisturbed integral layer, and only a minor proportion of the thickness, measured from the effective water interface as a continuously disturbed oil/water combination.

2. A method as claimed in Claim 1 in which the pumped gas is air.

3. A method as claimed in Claim 1 or 2 in which the oil is a poly-alpha-olefin synthetic oil.

4. A method as claimed in any one preceding Claim in which the gas flow is such that the bubbles in the water are sufficiently small to be essentially spherical by the time they encounter the interface region.

5. A method as claimed in Claim 5 utilising a porous ceramic or polymeric diffuser head to produce the bubbles.

6. A method as claimed in any preceding claim in which the water layer contains a biocidal material to kill introduced bacteria or algae.

7. A method as claimed in any one preceding Claim in which the water layer contains a watersoluble sodium salt.

8. A method as claimed in any one preceding Claim in which the oil layer is not more than 5 cm in thickness.

9. A method as claimed in Claim 8 in which the oil layer is from 1 to 3 cin in thickness.

10. A method as claimed in any one preceding Claim in which the water layer is up to 1 metre in thickness.

11. A method as claimed in Claim 10 in which the water layer is from 10 to 30 cms in thickness.

12. A method as claimed in any one preceding Claim in which the ratio of thickness between (a) the undisturbed oil sublayer and (b) the interface region is between 1:1 and 10:1.

13.method as claimed in Claim 1 and substantially as herein described with reference to and as illustrated in the accompanying drawings.

14. A boiler installation operated according to the method as claimed in any one preceding Claim.