NO773920L - PROCEDURES FOR CREATING HOEY COMBUSTION EFFICIENCY - Google Patents

Description

The present invention relates to a method for increasing the combustion efficiency of a liquid hydrocarbon fuel in order to improve the heat yield during combustion.

Liquid hydrocarbon fuels are not flammable as such. They must first vaporize and mix with air or oxygen to burn. As fractions of middle distillates or heavier petroleum fuel have low vapor pressures, effective atomization is a critical factor in the atomization combustion of such fuels. Atomization produces finely divided particles of liquid fuel whose large surface area leads to rapid evaporation and thus rapid and efficient combustion.

Even with efficient atomization, stoichiometric combustion cannot be achieved. A limitation in this regard is the inability to reach a state of perfect mixing in terms of time and size of the combustion process and equipment. In order to produce complete combustion, it is therefore necessary to add an excess of air to the system. Excess air to the extent that it produces complete combustion serves to increase combustion efficiency. But too much air can lead to a reduction in heat output. All the oxygen that is not involved in the combustion process as well as all the nitrogen in the air is heated and thus conducts heat out through the chimney. The greater the air surplus, the greater the mass flow through the system and the shorter the time for heat transfer. Consequently, achieving efficient combustion and heat yield requires a fine balance between atomization and excess air coupled with optimized combustion chamber and heat yield system design.

Due to the limitations caused by the design of the overall equipment, over the years there has also been considerable interest in chemical modification of the combustion. There are at least two ways of approaching the problem chemically, the first by modifying the atomization process and the second by catalytic effects on the combustion process itself. Both seem to be used.

Fluid properties that have an impact on mist particle size in an atomization process are density, surface tension and viscosity. Of these, density and viscosity do not seem to be promising ways to achieve improvements. The density will not be able to be changed significantly by means of an additive. Viscosity, on the other hand, is easily increased using small amounts of polymers, but increased viscosity will lead to larger fog particles, obviously the wrong direction for improved combustion. Surface tension is easily affected by small amounts of additives, and this may seem to be the most profitable way. Various claims for improving combustion efficiency have been made which apparently include this, although not necessarily

it appears that everyone who has worked on it has understood this. E.g. polar substances, such as alcohols, esters, have been described

and ketones, amines, organic phosphates and nitrates, as well as alkali or alkaline earth metals or (alkyl) ammonium sulphonates or carboxylates. Such solutions are not particularly effective and are not usually used commercially.

Improvements in combustion efficiency via catalytic action have also been widely claimed. Most described are transition metal salts of carboxylic acids, especially naphthenates or sulfonates, chelates of transition metals, carbonyl, cyclopentadienyl or other coordination compounds of the transition elements and also lead tetraethyl. Although it is generally accepted that these are effective at least to a certain extent, they all contain ash and thus leave deposits in the combustion system. The balance between the improved combustion and increased maintenance due to the deposits is usually unfavorable and has prevented extensive use of these additives.

Consequently, progress in the chemical modification of combustion has been modest at best, and significant advances will still be of great value.

The work on the present invention has given new interest in the possibility of using "viscosity" to influence the fog particle size and/or distribution. As pointed out above, the addition of polymers to fuels seems to be the wrong direction for a beneficial effect on combustion. But this sees the use of polymers only as a means of increasing viscosity, and does not take into account that polymers impart non-Newtonian characteristics to fluids, which sometimes result in strange and unexpected properties. At least three such applications have been investigated in recent years.

Various polymers have been described that reduce the amount of atomization mist formed in mist lubrication systems. These include polymethacrylates, polyisobutylene, polystyrene and olefin copolymers, particularly of the ethylene propylene type.

The nature of this suggests that the general phenomenon which

is involved may well be a common property for oil-soluble polymers, as one is of course aware that details of the polymer structure are important when it comes to optimization. Although the mechanism for the effect is not defined, it is apparently not a viscosity phenomenon, but rather involves the fluid's viscoelastic properties. It is also believed that these polymers function due to their effect on aerosol particle size and size distribution.

At about the same time, it was observed that polymers can exert a very large effect on fuel particle dispersion when the fluid is subjected to a severe shock. Such a phenomenon is of interest when attempting to regulate the formation of the combustible mist that forms upon impact when an aircraft crashes. Polymers which are claimed to be effective in this area include polyisobutylene, ethylene propylene copolymers, polymers and copolymers of alkylstyrene, olefinic sulfur dioxide polymers, poly(a-olefin) of cg_2o as well as hydrogenated styrene isoprene copolymers and polar polymers in general which can form associative, intermolecular bonds. Again, the activity appears to be common to all high molecular weight polymers. The phenomenon also involves more than just viscosity and is apparently linked to the viscoelastic properties of the fuels.

Later, a third related area has been described. It has been claimed that high molecular weight polybutenes reduce atomization mists that form during industrial metal cutting operations. It is claimed in this case that several other types of polymers do not function. But these others have a lower molecular weight than the effective polybutenes and it will thus not necessarily be expected that these will give the same high degree of viscoelasticity as the above-mentioned polymers.

Each of these three phenomena, and especially the three in their entirety, indicate that a polymer dissolved in a fluid can affect the fluid's fog-forming properties. Polymers can exert an influence on the fog particle size and possibly also the size distribution. It has been observed that with atomization combustion, both aerosol size and size distribution can have an impact on flame speed. The use of polymers to regulate the fuel mist particle size can thus provide new opportunities for improving combustion efficiency. According to the invention, it has been shown that fuels containing high molecular weight polymers provide improved combustion efficiency and a higher heat yield than is possible with ordinary, unmodified fuels. Although it is assumed that this is due to the viscoelastic properties of these fuels, it is not intended that the invention be limited to such a mechanism.

According to the invention, a method has been developed for improving the heat yield during the combustion of a liquid hydrocarbon fuel, and the method is characterized by the fact that a liquid hydrocarbon fuel in which at least one high-molecular polymer is dissolved or dispersed is burned in a heating device under atomization conditions.

Many different polymers can effect improvements

of combustion efficiency and heat yield by the process of the invention, and indeed any hydrocarbon soluble polymer will effect improvement in combustion efficiency. Important parameters for the polymer are its solubility properties, molecular weight and concentration in the fuel.

The polymer can be used in the fuel in a concentration of from 10 to 5000 ppm, preferably from 100 to 1000 ppm, calculated by weight.

The molecular weight of the polymer can be from 10,000 to 15,000,000, but is preferably greater than 50,000, e.g. from 50,000 to 10,000,000.

Suitable polymers include polyisobutylene, poly(1-butene), poly(α-olefins), ethylene propylene copolymers or ethylene propylene diene terpolymers, styrene butadiene or styrene isoprene copolymers or their hydrogenated analogues, polybutadiene, polyisoprene, alkyl polystyrenes such as tert-butylstyrene or copolymers of these, atactic polypropylene, LD polyethylene, polymethacrylates and copolymers thereof, as well as fumarate polymers or copolymers. Other hydrocarbon fuel soluble polymers that can be prepared with sufficiently high molecular weight will be apparent to those skilled in the art.

The polymer is preferably a hydrocarbon polymer, in particular polyisobutylene or an ethylene propylene copolymer with a weight average molecular weight of from 10,000 to 10,000,000, preferably from 50,000 to 1,000,000.

Polyisobutylene, LD polyethylene, atactic polypropylene and other high molecular weight polya-olefins can be used and are readily available with sufficiently high molecular weight from acid or Ziegler catalysis. The production of such polymers is well known to those skilled in the art, and polymers with weight average molecular weights of from 20,000 to 10,000,000 are readily available.

Ethylene propylene polymers are also readily available and can cover a wide range of ethylene propylene ratios. In general, the most useful copolymers are those that have a high ethylene content, more precisely approx. 5-80 mole percent ethylene units. However, copolymers outside this range may also be useful. E.g. can lower ethylene content bring about economic benefits without serious deterioration of the properties, while higher ethylene content, up to approx. 95 mole percent, can be useful provided the polymer microstructure is carefully regulated so that fuel solubility is maintained.

Ethylene propylene polymers may also contain small amounts, generally less than about 10%, of a non-conjugated diene, such as 1,4-hexadiene, dicyclopentadiene or ethylidene norbornene. The effects and ratios of the ethylene and propylene units described above also apply to these polymers. Styrene butadiene and styrene isoprene copolymers can be

either random copolymers or block copolymers. In the case of random copolymers, the products may contain from 30 to 50 percent by weight of diene units. The weight average molecular weight should be high and may be from 30,000 to 10,000,000. If the copolymers are blocks, they may contain two or more blocks. In general, the molecular weight of the styrene blocks can be from 5,000 to 50,000, while that of the diene can be from 10,000

to 1,000,000. Any of the styrene diene copolymers may be fully or partially hydrogenated.

Polymers of conjugated dienes, such as butadiene or isoprene, which cover a wide range of structures are also generally useful. The polymers can be either of the 1,4- or 1,2-type, and the 1,4-polymers can be of either the cis- or trans-configuration. However, polymers with a high cis-1,4 content are preferred. These polymers can also be fully or partially hydrogenated.

Polymethacrylates or other esters such as fumarates that cover a wide range of structures are also effective. Any combination of ester groups in the C-^_2 Jj range can be used, and these alkyl groups can be either linear or branched.

The average carbon chain length when a mixture is used must have at least 6 carbon atoms, and preferably has from 8 to 10 carbon atoms. The weight average molecular weights can be from 50,000 to 15,000,000.

It has been found that when the polymer-modified fuel is burned in a conventional atomization combustor, heat yield improvements over the polymer-free base fuel of from 1 to 6%, typically from 3 to 5%, can be achieved.

The liquid hydrocarbon fuel is a fuel that can be used for atomization combustion. Suitable fuels include petrol, methanol, petroleum, diesel fuel, fuel oil of type No. 1, No. 2, No. 4, No. 5 or No. 6, as well as turbine fuel. It has become common practice to mix used lubricating oil with fuels, and fuels of this type can also be used according to the invention.

The fuels according to the invention can also include all other additives that are in common use. Examples are pour point depressants, antioxidants, rust inhibitors, stabilizers, metal deactivators, injector cleaners, additives for regulating deposits in induction systems, carburettor cleaners, rust inhibitors, sludge dispersants, demulsifiers, as well as slag modifiers and other types of combustion modifiers.

Two samples were used to investigate the combustion efficiency. The first and simpler is a smoke reduction test, while the second, more comprehensive is a product yield test.

In each case investigated, an additive's ability to

to reduce the smoke inevitably associated with an improvement in heat yield. Accordingly, the former sample was generally used for a screening purpose, while the latter was used to produce quantitative results.

In the smoke reduction test, the effect of additives in reducing the smoke produced by burning No. 2 fuel oil in a conventional oil heater was determined using a modification of the method described in ASTM-D-2156-65 (1975 Yearbook of ASTM Standards, part 24, Petroleum Products and Lubricants(II), published by the American Society for Testing and Materials, Philadelphia, Pa.). The furnace used for this work was a New Yorker Unipac oil-fired boiler with flame arrester, model S-165-AP. The boiler temperature was maintained by circulating water through a shell and tube heat exchanger.

Before any smoke measurements were taken, the boiler was brought up to at least 60°C by burning unmodified fuel. Draft over the fire was regulated to from approx. 0.25 to approx. 0.50 mm of water. A smoke sample was taken using a smoke sampling apparatus of the type described in ASTM-D-2156-65. The air was regulated so that a smoke point number of 2-3 was achieved. The burner was then switched off and switched on for fuel testing. The burner was re-ignited and a circulation device started to remove excess heat. Smoke readings were taken at 10, 20 and 30 minutes to ensure that equilibrium conditions had been achieved. The base fuel was examined periodically for reference purposes.

The equipment for the heat yield test was the same as that

which is described in connection with the smoke reduction tests. Before firing the burner, approx. 22.7 1 test fuel weighed up. The burner and fuel switch were started simultaneously. During this cold start, the boiler water circulation pump was out of order. The draft over the fire was kept on from approx. 0.25 to approx. 0.50 mm of water. After 5 minutes of firing, a smoke reading was taken as above. The circulation pump was activated and allowed to run continuously after the water in the boiler had reached a temperature of approx. 93°C.

During a two hour test, data was taken according to Table I. At the end of the test, the fuel switch was stopped and the burner was turned off. The remaining fuel was weighed and the average fuel flow rate was calculated. The average heat yield was then calculated using data for heat recovered in the heat exchanger cooling water and the boiler's total firing rate. A base fuel reference was determined either before or after each test fuel.

Some preferred embodiments of the invention will be described in more detail in subsequent examples where all parts and percentages are by weight unless otherwise stated.

Example 1

Triplicate tests were carried out in the heat recovery test using fuel oil No. 2 treated with 1000 ppm of an ethylene propylene copolymer with a composition of 62/38 by weight and a weight average molecular weight of approx. 80,000. The results given below show an increase of the average

heat yield in relation to the base fuel of approx. 1.6%.

Smoke was also reduced in the presence of the polymer from a smoke point number of 2.5 to 1, while excess oxygen was lowered from 4.5 to 3.9%. Both confirm improved combustion.

Example 2

An ethylene propylene terpolymer with a weight ratio between ethylene and propylene of approx. 55:45, but which also contained approx. 4 weight percent 1,4-hexadiene, and which had a weight average molecular weight of approx. 850,000 were examined in fuel oil No. 2 at a concentration of 200 ppm. The heat yield improvement was 3.3%. Smoke was reduced from 3.5 in the control sample to 1.5 in the polymer-treated fuel, and excess oxygen was reduced from 4.4% to 4.0%.

Example 3

A polyisobutylene with a weight average molecular weight of 1.750,000 was examined in double heat yield samples at a concentration of 150 ppm. An improvement in heat yield from 5.7 to 6.1% was achieved.

Example 4

The polymer of Example 1 was evaluated again using a flame atomizer whose opening was approx. 4.8 mm larger than standard. The relative improvement compared to base fuel was 4.8%. Reducing excess air to match the base smoke level resulted in a further improvement to a net heat yield improvement of 6.1%.

Example 5

A polyisobutylene with a weight average molecular weight of 5,500,000 at a concentration of 25 ppm gave relative heat yield improvements of 2.5% using the standard atomizer cone and 4.1% using the modified cone in Example 4.

Example 6

The ethylene propylene copolymer in Example 1 was evaluated at a concentration of 125 ppm in the heat yield test. Relative heat yield improvements compared to the base fuel of 2.5%

and 2.9% was obtained in duplicates.

Example 7

An ethylene propylene copolymer with an ethylene content of 59 percent by weight and a weight average molecular weight of 150,000 was examined in fuel oil No. 2 in the smoke reduction test at 300 ppm. The base fuel gave a smoke point number of 2.5, while the polymer-modified fuel gave a value of less than 1 in the smoke reduction test.

Example 8

A polymethacrylate with mixed acrylic groups in the form of C4 12 14 16 18 ""■ s^ike conditions that the average was

Cg, where the polymer had a viscosity average molecular weight

of 1,650,000 was examined in a concentration of 2000 ppm in the smoke reduction test. The base fuel gave a smoke point number of 3, while the polymer-treated fuel gave 1-1.5.

Example 9

A polymethacrylate which contained mixed acrylic groups in the form of ^21<3>1415 in such proportions that the average was C^q, where the polymer had a weight average molecular weight of approx. 60,000 gave a smoke reduction of 1.5 units below the base fuel when it was used in a concentration of approx. 4,000 ppm.

Example 10

A polyisobutylene with a viscosity average molecular weight of 10,000 used at a concentration of 1800 ppm gave a smoke point number of 1.5 compared to the base fuel of 4.

Example 11

A polybutadiene with a cis-1,4 structure was investigated at a concentration of 300 ppm in the smoke reduction test. The base fuel gave a smoke point number of 4-5, while the polymer-treated fuel gave a smoke point number of 1-2.

Example 12

A styrene fumarate copolymer used at a concentration of 3300 ppm gave a smoke point number of 1-2 compared to a base fuel f value of 4 in terms of smoke point number.

Example 13

An ethylene propylene copolymer which had a weight ratio between ethylene and propylene of approx. 10:90 and a viscosity average molecular weight of approx. 225,000 were examined in the smoke reduction test at a concentration of 500 ppm. A smoke point number of 3-3.5 for the control sample was lowered to 0.5-1 by burning the polymer-modified fuel. q

Claims (10)

1. Method for producing a particularly high heat yield by burning a liquid hydrocarbon fuel, characterized in that a liquid hydrocarbon fuel in which a high molecular polymer is dissolved or dispersed is burned in a heating device under atomization conditions. 2. Method in accordance with claim 1, characterized in that the fuel contains from 10 to 5000 ppm of the polymer, calculated by weight. 3. Method in accordance with claim 2, characterized in that the fuel contains from 100 to 1000 ppm of the polymer. 4. Process in accordance with one of claims 1-3, characterized in that the polymer has a molecular weight of from 10,000 to 15,000,000. 5. Method in accordance with claim 4, characterized in that the polymer has a molecular weight of from 50,000 to 10,000,000. 6. Method in accordance with one of the preceding claims, characterized in that the fuel comprises at least one of the following: petrol, methanol, petroleum, diesel fuel, heating oil and turbine fuel. 7. Method in accordance with claim 6, characterized in that the fuel is a distillate No. 2 or No. 6 of residual fuel. 8. Method in accordance with one of the preceding claims, characterized in that the polymer is at least one of the polymers polyisobutylene, poly(1-butene), poly(a-olefin), ethylene propylene copolymers or ethylene propylene diene copolymers, styrene butadiene or styrene isoprene copolymers or their hydrogenated analogues, polybutadiene, polyisoprene, alkylated polystyrenes or copolymers thereof, atactic polypropylene, LD polyethylene, polymethacrylates and copolymers thereof as well as fumarate polymers or copolymers. 9. Method in accordance with claim 8, characterized in that the polymer is an ethylene propylene copolymer having a molecular weight of from 50,000 to 1,000,000. 10. Method in accordance with claim 8, characterized in that the polymer is a polymethacrylate having from 1 to 24 carbon atoms in the ester group.