GB1569344A - Combustion efficiency - Google Patents

Description

(54) METHOD OF IMPROVING COMBUSTION EFFICIENCY (71) We, ROHM AND HAAS COMPANY, a corporation organized under the laws of the State of Delaware, United States of America. of Independence Mall West, Philadelphia, Pennsylvania 19105, United States of America. do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention is concerned with a method of increasing the combustion efficiency of a liquid fuel so as to improve the head recovery of the combustion.

Liquid hydrocarbon fuels as such are not combustible. Rather. they must first be vaporized and mixed with air, or oxygen, to burn. As middle distillate or heavier petroleum fuel fractions have low vapor pressures, efficient atomization is a critical aspect of spray combustion of such fuels. Atomization produces fine liquid fuel particles. whose large surface area leads to fast evaporation and thus rapid and efficient combustion.

Even with efficient atomization stoichimetric combustion cannot be achieved. Limitation is imposed in this respect by the inability to reach a condition of perfect mixing in the time and size scale of the combustion process and equipment. In order to get complete combustion, therefore, it is necessary to supply excess air to the system. Excess air. to the extent it provides complete combustion, serves to increase combustion efficiency.

However, too much air can lead to a decrease in heat recovery. All of the oxygen not involved in the combustion process as well as all of the nitrogen in the air is heated and thus carries heat out of the stack. Further, the greater the excess air the greater the mass flow through the system and the shorter the time scale for heat transfer. Hence. achieving efficient combustion and heat recovery requires a delicate balance of atomization and excess air coupled with optimized combustion chamber and heat recovery system designs.

Because of the restrictions imposed by the overall equipment design. there has also been considerable interest over the years in chemical modification of combustion. There are at least two ways to approach the problem chemically - the first through modification of the atomization process and the second through catalytic effects on the combustion process itself. Indeed both appear to have been employed.

Fluid properties which influence mist particle size in an atomization process include density, surface tension and viscositv. Of these. densitv and viscosity do not seem to be promising approaches. Density could not be altered significantly by an additive. Viscosity, on the other hand, is easily increased by low levels of polymers but increased viscosity would lead to larger mist particles, apparently the wrong direction for improved combustion. Surface tension is readily influenced by low levels of additives and this would seem to be the most rewarding route. A variety of claims to combustion efficiency improvement have been made which apparently involve this concept. although it is not necessarily apparent that all workers understood this.For example. polar materials such as alcohols, esters or ketones, amines. organic phosphates and nitrates. and alkali or alkaline earth metal or (alkyl) ammonium sulfonates or carboxylates have been described. Such approaches are not particularly effective and are not generally practiced commercially.

Combustion efficiency improvements via catalytic effects are also widelv claimed. Most widely described are the transition metal salts of carboxvlic acids. in particular. napthenates or sulfonates, chelates of the transition metals. carbonyl. cyclopentadienyl or other coordination compounds of the transition element and even tetraethyl lead. While these are generally accepted to be effective to at least some degree. they are all ashcontaining and thus leave deposits in the combustion system. The balance of improved combustion against increased maintenance caused by the deposits is generally unfavorable and has prevented widespread use of these additives.

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

Our recent work raises new interest in the possibility of using "viscosity" to influence mist particle size and/or size distribution. As pointed out earlier. addition of polymers to fuels would appear to be in the wrong direction to favorably influence combustion.

However, this looks on use of polymers merely as a means to increase viscosity. and fails to recognize that polymers impart non-Newtonian characteristics to fluids which sometimes result in strange and unexpected properties. At least three such applications have received attention in recent years.

A variety of polymers have been described which decrease the amount of stray mist generated in mist lubrication systems. Included are poly(meth)acrylates, polyisobutylene and polystyrenes and olefin copolymers. in particular the ethylene-propylene type.

In fact the nature of this limited art suggests that the general phenomenon involved may well be a common characteristic of oil-soluble polymers. recognising of course that details of polymer structure are important to optimization. While the mechanism of action has not been defined, it is apparently not viscosity phenomenon but rather involves viscoelastic properties of the fluids. Further, it is believed that these polymers function because they influence aerosol particle size and size distribution.

About this same time it was discovered that polymers can exert verv dramatic effects on fuel particulate dissemination when that fluid is subjected to a severe shock. Such a phenomenon is of interest in trying to control the generation of the combustible mist cloud which is generated upon impact during an airplane crash. Polymers claimed to have activity in this area include polyisobutylene, ethylene-propylene copolymers. polymers and copolymers of alkyl-styrene, olefin-sulfur dioxide polymers. poly(a-olefins) of C"~2 ) and hydrogenated styrene-isoprene copolymers and polar polymers in general which are capable of forming associative intermolecular bonds. Again. activity appears to be common to all high molecular weight polymers.Also. the phenomenon involves more than just viscosity and is apparently tied to the viscoelastic properties of the fuels.

More recently a third related area has been disclosed. High molecular weight polybutenes have been claimed to reduce spray mist generated in industrial metal cutting operations. In this case several other types of polymers are claimed not to work. However, these others are lower molecular weight than the effective polybutenes and thus would not necessarily be expected to impart the same high degree of viscoelasticity as the claimed polymers.

Any of these three phenomena and particularly the three taken as a whole indicate that a polymer dissolved in a fluid can affect the misting characteristics of the fluid. Polymers can exert an influence on mist particle size and possiblv even size distribution. It is recognized that in spray combustion both aerosol size and size distribution influence flame speed. The use of polymers to control fuel mist particle size may thus provide new possibilities in improving combustion efficiency. We have now found that fuels containing high molecular weight polymers provide improved combustion efficiencv and higher heat recovery than is possible with conventional. unmodified fuels. While it is believed that this results from the viscoelastic properties of such fuels. it is not intended that this invention be restricted to any such mechanism.

According to the invention there is provided a method of improving heat recovery in the combustion of a liquid alcohol or hydrocarbon fuel which comprises burning under spray conditions in a heating unit a liquid alcohol or hydrocarbon fuel having dissolved or dispersed therein high molecular weight polymer.

A variety of polymers, as described herein. can effect combustion efficiency and heat recovery improvements in the method of the invention. and virtually any hydrocarbon soluble polymer will provide the combustion efficiencv improvements. Important parameters of the polymer are its solubility characteristics, molecular weight and its concentration in the fuel.

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

The molecular weight of the polymer may range from 10.000 to 15.000.000 but is preferably greater than 50,000 for example 50.000 to 10.000.000.

Suitable polymers include polyisobutylene. poly (l-butene), poly(a-olefins). ethylenepropylene copolymers or ethylene-propvlene-diene terpolymers. styrene-butadiene or styrene-isoprene copolymers or their hydrogenated analogs. poly-butadience, polyisoprene, alkylated polystyrenes such as poly-t-butylstvrene or copolymers thereof. atactic polypropylene, low density polyethylene. polv(meth)acrvlates and copolymers thereof, and fumarate polymers or copolymers. Other hydrocarbon fuel soluble polymers which can be prepared in sufficiently high molecular weight will be readily apparent to those skilled in the art.

The polymer is preferably a hydrocarbon polymer, in particular, polyisobutylene or an ethylene-propylene copolymers of weight average molecular weight of 10.000 to 10.000,000 preferably 50,000 to 1,000,000.

High molecular weight polyisobutylene. low density polyethylene. atactic polypropylene and other poly(a-olefins) may be used and are readily available in sufficiently high molecular weight from acid or Ziegler catalysis. Preparation of such polymers is well known to those skilled in the art, and polymers with weight average molecular weights of 20,000 to 10,000,000 are easily obtainable.

Ethylene-propylene copolymers are also readily available and may cover a wide range of ethylene-propylene ratios. Generally the most useful are copolymers which are high in ethylene content, specifically 50 to 80 mole percent of ethylene units. However, copolymers outside of this range may also be useful. For example. lower ethylene contents may provide economic advantages without serious deterioration of properties while higher ethylene contents, up to about 95 mole percent, may be useful provided polymer microstructure is carefully controlled so as to maintain fuel solubility.

The ethylene-propylene polymers may also contain low levels. generally less than 10% of a non-conjugated diene such as 1,4-hexadiene. dicyclopentadiene. or ethylidenenorbornene. The effects and ratios of the ethylene and propylene units described above apply equally to these polymers.

The styrene-butadiene and styrene-isoprene copolymers may be either random or block copolymers. In the case of the random copolymers. the products may contain from 30 to 50 weight percent of diene units. Weight average molecular weight should be high and may range 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 may range from 5000 to 50,000 while that of the diene may range from 10.000 to 1.000.000. Any of the styrene diene copolymers may be partially or completely hydrogenated.

Polymers of conjugated dienes, such as butadiene or isoprene. covering a wide range of structures are also generally useful. Polymers may be either of the 1.4 or 1.2 type and the 1,4 may be in either the cis or trans-configuration. However. polymers high in cis-1.4 are preferred. These polymers may also be partially or completely hydrogenated.

Poly(meth)acrylate alkyl esters or polymers of other alkyl esters such as alkyl fumarates covenng a range of structures are also effective. Any combination of alkyl groups in the C1--24 range may be included in the ester groups and these alkyl groups may be either linear or branched. The average carbon chain length of the alkyl groups where a mixture is used must be at least 6 carbon atoms and is preferably X to 10 carbon atoms. Weight average molecular weights may be from 50,000 to 15.000.000.

We have found that when the polymer-modified fuel is burned in a conventional spray combustion apparatus heat recovery improvements over that of the polvmer-free vase fuel of from 1 to 6%, or more commonly 3 to 5%. may be observed.

The liquid fuel is one which can be employed in spray combustion. Suitable fuels include gasoline, methanol, kerosene, diesel fuel. fuel oils of the No. 1. No. 2. No. 4. No. 5. or No.

6 types, and turbine fuels. It has become frequent practice to blend used lubricating oil into fuels and fuels of this type are included in the scope of this invention.

Preferably, the polymer in the polymer treated fuel is capable of providing a smoke reduction compared to the untreated fuel equivalent to at least 1.5 smoke spot number units as measured by ASTM Standard Test Method D2156-65.

The fuels of this invention may also include any of the other additives commonly used.

Examples include pour point depressants. anti-oxidants. rust inhibitors. stabilizers. metal deactivators, injectors detergents, induction system deposit control additives. carburetor detergents, corrosion inhibitors. sludge dispersants. demulsifiers. and slag modifiers as well as other types of combustion modifiers.

Description of combustion efficiency test procedure Two tests were employed in this work. The first and simpler is the Smoke Reduction Test while the second, more comprehensive test, is the Heat Recovery Test. In every case evaluated the ability of an additive to reduce smoke was invariably accompanied by an improvement in heat recovery. Hence the first test was generally used for screening purposes while the latter was used to quantify results.

A. Smoke reduction test The effect of additives in reducing smoke produced from burning No. 2 fuel oil in a conventional home heating unit was determined using the procedure described in ASTM-D-2156-65 (1975 Annual Book of ASTM Standard, Part 24, Petroleum Products and lubricants (II), Published by American Society for Testing and Materials, Philadelphia, Pa;). The furnace employed in this work was a New Yorker Unipac oil fired boiler with flame retention, Model S-l/s3/45/s-AP. Boiler Temperature was maintained by circulating the water through a shell and tube heat exchanger.

Prior to making any smoke measurements, the boiler was brought up to at least 1400F.

burning unmodified fuel. Draft over the fire was adjusted to 0.01 to 0.02 inches of water. A smoke sample was taken using a smoke tester of the type described in ASTM D-2156-65.

Air was adjusted so as to give a Smoke Spot Number of 2-3. The burner was then turned off and switched to test fuel. The boiler was re-fired and the circulator started in order to dump excess heat. Smoke readings were taken at 10, 20 and 30 minutes in order to assure that equilibrium conditions were reached. Base fuel was run periodically for reference purposes.

B. Heat recovery test Equipment for this test is the same as that described in the Smoke Reduction Tests. Prior to firing the burner approximatey six gallons of test fuel was weighed.

The burner and fuel timer were started simultaneously. During this cold start the boiler water circulating pump was inoperative. Draft over the fire was maintained at 0.01 to 0.02 inches of water. After five minutes of firing, a smoke reading was taken as above. The circulating pump was activated and allowed to run continuously once the bulk boiler water temperature reached 200"F.

During the two-hour test, data were taken according to the Schedule in Table I. At the end of the test the fuel timer was stopped and the burner was turned off. The remaining fuel was weighed and the average fuel flow rate was calculated. The average heat recovery efficiency was then calculated using the data for the heat recovered in the heat exchanger cooling water and the gross firing rate of the boiler. A base fuel reference was run either before or after every test fuel.

Some preferred embodiments of the invention will now be more particularly decribed in and by the following examples, in which all parts and percentages are by weight unless other-wise stated.

Example 1 Triplicate tests were run in the Heat Recovery Test using No. 2 fuel oil treated with 1000 ppm of an ethylene-propylene copolymer of composition 62/38 by weight and a weight average molecular weight of about 80,000. Results shown below show an average heat recovery improvement relative to base fuel of about 1.6C/c.

Example 1 Fuel Flow Theoretical Heat Recovered Efficiency Relative Rate Gal/hr BTU/hr Heat BTU/hr % Improvement Base 1.265 174.900 120.300 68.8 Treated 1.268 175.400 121.900 69.5 1.0% Base 1.263 174.700 119.900 68.6 Treated 1.252 173.200 120.300 69.7 1.6% Base 1.267 175.200 118.100 67.4 Treated 1.276 176.500 121.400 68.8 2.1% Smoke was also reduced in the presence of the polymer from a Smoke Spot No.

of 2.5 to 1 while excess oxygen was reduced from 4.5 to 3.9%. Both confirm improved combustion.

TABLE Schedule for taking data during heat recovery test Test Time - Min. 30 50 60 70 80 90 100 110 120 Barometric Pressure X X X X Room Temperature X X X X Stack Draft X X X X X X X X X Over-Fire Draft X X X X X X X X X Stack Temperature X X X X X X X X X Temperature Water Entering Boiler Water Leaving Boiler X X X X X X X X X Cooling Water to Heat Exchanger X X X X X X X X X Cooling Water from Heat Exchanger X X X X X X X X X Bulk Boiler Water Temperature X X X X X X X X X Smoke Level X X X X Cooling Water Flow Rate X X X X X X X X X Stack Gas Analyses - CO2 X X X O2 X X X CO X X X Example 2 An ethylene-propylene terpolymer with a weight ratio of ethylene/propylene of about 55/45 but also containing about 4 weight percent 1.4-hexadiene and weight average molecular weight of about 850,000 was evaluated in No. 2 fuel oil at a concentration of 200 ppm.Heat recovery improvement was 3.3%. Smoke was reduced from 3.5 in the control to 1.5 for the polymer-treated fuel and excess oxygen decreased from 4.4% to 4.0%.

Example 3 A polyisobutylene of weight average molecular weight of 1,750,000 was evaluated in duplicate heat recovery tests at 150 ppm. Heat recovery gains of 5.7 to 6.1% were obtained. Example 3 Fuel Flow Theoretical Heat Recovered Heat Efficiency Relative Rate gal/hr BTU/hr BTU/hr % Improvement Base 1.264 174.800 123.500 70.6 Treated 1.232 170.400 127.200 74.6 5.7% Base 1.249 172.700 121.400 70.3 Treated 1.225 169.400 126.400 74.6 6.1% Example 4 The polymer in Example 1 was re-evaluated using a flame diffuser end cone the opening of which was larger than standard by 3/16". The relative improvement over base fuel was 4.8%.Reduction of excess air to match the base case smoke level resulted in further improvement to a net heat recovery improvement of 6.1% Example 5 A polyisobutylene of weight average molecular weight of 5,500,000 used at 25 ppm gave relative heat recovery improvements of 2.5% using the standard diffuser cone and 4.1% using the modified cone of Example 4.

Example 6 The ethylene-propylene copolymer of Example 1 was evaluated at 125 ppm in the Heat Recovery Test. Relative heat recovery gains over the base case of 2.5cue and 2.9% were made in duplicate tests.

Example 7 An ethylene propylene copolymer with an ethylene content of 59 weight percent and a weight average molecular weight of 150,000 was evaluated in No. 2 fuel oil in the Smoke Reduction Test at 300 ppm. Base fuel gave a Smoke Spot No. of 2.5 while the polymer-modified fuel gave a rating of < 1 in the Smoke Reduction Test.

Example 8 A polymethacrylate with mixed alkyl groups including C4.12.14.i6.ixin such proportions to give an average of C9, said polymer having a viscosity average molecular weight of 1,650,000 was evaluated at 2000 ppm in the Smoke Reduction Test. Base fuel gave a Smoke Spot No. of 3 while the polymer-treated fuel gave 1 to 1.5.

Example 9 A polymethacrylate containing mixed alkyl groups of C, ,2 ,3,,4 ,5 in such proportions as to give an average of C1() said polymer having a weight average molecular weight of about 60,000 provided smoke reduction of 1.5 numbers under base fuel when used at about 4000 ppm.

Example 10 A polyisobutylene of viscosity average molecular weight of 10.000 used at 1800 ppm gave a Smoke Spot No. of 1.5 as compared to a basic fuel rating of 4.

Example 11 A polybutadiene with a cis-1.4 structure was evaluated at 300 ppm in the Smoke Reduction Test. Base fuel gave a Smoke Spot No. of 4 to 5 while the polymer-treated fuel gave a 1 to 2 smoke No.

Example 12 A styrene-fumarate copolymer used at 3300 ppm gave a Smoke Spot No. of 1 to 2 compared to a base fuel value of a 4 Smoke Spot No.

Example 13 An ethylene-propylene copolymer having a weight ratio of ethylene/propylene of about 10/90 and viscosity average molecular weight of about 225.000 was evaluated in the Smoke Reduction Test at a concentration of 500 ppm. A Smoke Spot No. of 3 to 3.5 for the control was reduced to 0.5 to 1 when combusting the polymer modified fuel.

WHAT WE CLAIM IS: 1. A method of improving heat recovery in the combustion of a liquid alcohol or hydrocarbon fuel which comprises burning under spray conditions in a heating unit a liquid alcohol or hydrocarbon fuel having dissolved or dispersed therein high molecular weight polymer.

2. A method as claimed in Claim 1 wherein the fuel contains from 10 ppm to 5000 ppm on a weight basis of said polymer.

3. A method as claimed in Claim 2 wherein the fuel contains from 100 to 1000 ppm of said polymer.

4. A method as claimed in any of Claims 1 to 3 wherein the polymer has a molecular weight of from 10.000 in 15,000,000.

5. A method as claimed in Claim 4 wherein the polymer has a molecular weight of from 50,000 to 10,000.000.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. Example 4 The polymer in Example 1 was re-evaluated using a flame diffuser end cone the opening of which was larger than standard by 3/16". The relative improvement over base fuel was 4.8%. Reduction of excess air to match the base case smoke level resulted in further improvement to a net heat recovery improvement of 6.1% Example 5 A polyisobutylene of weight average molecular weight of 5,500,000 used at 25 ppm gave relative heat recovery improvements of 2.5% using the standard diffuser cone and 4.1% using the modified cone of Example 4. Example 6 The ethylene-propylene copolymer of Example 1 was evaluated at 125 ppm in the Heat Recovery Test. Relative heat recovery gains over the base case of 2.5cue and 2.9% were made in duplicate tests. Example 7 An ethylene propylene copolymer with an ethylene content of 59 weight percent and a weight average molecular weight of 150,000 was evaluated in No. 2 fuel oil in the Smoke Reduction Test at 300 ppm. Base fuel gave a Smoke Spot No. of 2.5 while the polymer-modified fuel gave a rating of < 1 in the Smoke Reduction Test. Example 8 A polymethacrylate with mixed alkyl groups including C4.12.14.i6.ixin such proportions to give an average of C9, said polymer having a viscosity average molecular weight of 1,650,000 was evaluated at 2000 ppm in the Smoke Reduction Test. Base fuel gave a Smoke Spot No. of 3 while the polymer-treated fuel gave 1 to 1.5. Example 9 A polymethacrylate containing mixed alkyl groups of C, ,2 ,3,,4 ,5 in such proportions as to give an average of C1() said polymer having a weight average molecular weight of about 60,000 provided smoke reduction of 1.5 numbers under base fuel when used at about 4000 ppm. Example 10 A polyisobutylene of viscosity average molecular weight of 10.000 used at 1800 ppm gave a Smoke Spot No. of 1.5 as compared to a basic fuel rating of 4. Example 11 A polybutadiene with a cis-1.4 structure was evaluated at 300 ppm in the Smoke Reduction Test. Base fuel gave a Smoke Spot No. of 4 to 5 while the polymer-treated fuel gave a 1 to 2 smoke No. Example 12 A styrene-fumarate copolymer used at 3300 ppm gave a Smoke Spot No. of 1 to 2 compared to a base fuel value of a 4 Smoke Spot No. Example 13 An ethylene-propylene copolymer having a weight ratio of ethylene/propylene of about 10/90 and viscosity average molecular weight of about 225.000 was evaluated in the Smoke Reduction Test at a concentration of 500 ppm. A Smoke Spot No. of 3 to 3.5 for the control was reduced to 0.5 to 1 when combusting the polymer modified fuel. WHAT WE CLAIM IS:

1. A method of improving heat recovery in the combustion of a liquid alcohol or hydrocarbon fuel which comprises burning under spray conditions in a heating unit a liquid alcohol or hydrocarbon fuel having dissolved or dispersed therein high molecular weight polymer.

2. A method as claimed in Claim 1 wherein the fuel contains from 10 ppm to 5000 ppm on a weight basis of said polymer.

3. A method as claimed in Claim 2 wherein the fuel contains from 100 to 1000 ppm of said polymer.

4. A method as claimed in any of Claims 1 to 3 wherein the polymer has a molecular weight of from 10.000 in 15,000,000.

5. A method as claimed in Claim 4 wherein the polymer has a molecular weight of from 50,000 to 10,000.000.

6. A method as claimed in any preceding claim wherein the fuel comprises at least one

of: gasoline, methanol, kerosene, diesel fuel. fuel oil and turbine fuel.

7. A method as claimed in Claim 6 wherein the fuel comprises a No. 2 distillate or a No.

6 residual fuel.

8. A method as claimed in any preceding claim wherein the polymer is at least one of polyisobutylene, poly( 1-butene), poly( a-olefins), ethylene-propylene copolymers or ethylene-propylene diene ter-polymers, styrene butadiene or styrene-isoprene copolymers or their hydrogenated analogs, polybutadiene, polyisoprene, alkylated polystyrenes or copolymers thereof, atactic polypropylene, low density polyethylene. poly(meth)acrylates and copolymers thereof, and fumarate polymers or copolymers thereof.

9. A method as claimed in Claim 8 wherein the polymer is an ethylene-propylene copolymer having a molecular weight of from 50,000 to 1.000,000.

10. A method as claimed in Claim 8, wherein the polymer is a polymethacrylate altyl ester having from 1 to 24 carbon atoms in the alkyl part of the ester group.

11. A method as claimed in any preceding claim wherein the polymer is the polymer treated fuel is capable of providing a smoke reduction compared to the untreated fuel equivalent to at least 1.5 smoke spot number units as measured by ASTM Standard Test Method D2156-65.

12. A method as claimed in Claim 1 substantially as described in any of the foregoing examples.