WO1999001645A1

WO1999001645A1 - Method for combustion of sulphur in an internal combustion engine

Info

Publication number: WO1999001645A1
Application number: PCT/SE1998/001253
Authority: WO
Inventors: Lars-Ola Olsson
Original assignee: Kemira Kemi Ab
Priority date: 1997-07-03
Filing date: 1998-06-26
Publication date: 1999-01-14
Also published as: SE9702574D0; AU8250598A; WO1999001645A8

Abstract

A method for combustion of sulphur in an internal combustion engine, especially a diesel engine, is described. According to the method, the combustion takes place in the presence of a catalyst, which is selected among platinum-group metals and alloys thereof, preferably platinum or an alloy thereof. The use of polymerised sulphur as lubricant in a sulphur combustion engine is described. Furthermore, the combustion suitably takes place in an engine, the crankcase of which is sealed against the piston, preferably in a crosshead engine. Finally, also a method is described for removing solidified sulphur from metal surfaces, sulphur being dissolved in an oil, preferably diesel oil.

Description

METHOD FOR COMBUSTION OF SULPHUR IN AN INTERNAL

COMBUSTION ENGINE

Field of the Invention

The present invention relates to combustion of sulphur, more specifically to combustion of sulphur in an internal combustion engine. Background Art

Combustion of elementary sulphur into sulphur dioxide in an internal combustion engine is disclosed in, for instance, European Patent Application 95850031.6. The sulphur dioxide formed in the combustion can, when needed, be converted further into other sulphur-containing products, such as sulphur trioxide, oleum, sulphuric acid, sulphites, bisulphites, sulphates etc. In contrast to combustion of sulphur or sulphur-containing compounds, such as ferrous sulphide, in roasting furnaces, energy is generated in the combustion of elementary sulphur as fuel in an internal combustion engine, which can be directly converted into electricity, for instance, via an electric generator connected to the output shaft of the engine. As a result, the efficiency of the process increases. More- over, in the combustion of sulphur in an internal combustion engine, exhaust gases are obtained, that are free from carbon dioxide and carbon black, which in this respect means an environmental advantage. When using air as oxygen source in the combustion, the sulphur dioxide content of the exhaust gas normally amounts to 14-16% by volume. Theoretically, the exhaust gas can in stoichiome- tric combustion of sulphur in air maximally contain 20.8% by volume sulphur dioxide. In addition to air, also other oxygen-containing gases, as well as pure oxygen, can be used in the combustion.

Apart from the use of elementary sulphur as fuel in internal combustion engines, the above-mentioned European Patent Application 95850031.6 describes the use of ele- mentary sulphur as lubricant in an internal combustion engine and the use of elementary sulphur for cooling the engine block in an internal combustion engine.

This prior-art technique using elementary sulphur as fuel, lubricant and cooling agent in internal combustion engines, however, has not gained any extended industrial application owing to various problems. Thus, high pressures are required for ignition and combustion of sulphur in an internal combustion engine of a conventional type, such as a diesel engine. This results in incomplete combustion and the formation of high levels of nitric oxides, N0χ, in the exhaust gases. The use of elementary sulphur as lubricant further causes problems owing to unsatisfactory wetting of the metal parts that are to be lubricated. The unsatisfactory wetting results in poorer lubrication compared with the use of a lubricating oil. It has also been found that the problem with the inferior properties of sulphur as lubricant cannot be solved by mixing sulphur with a lubricating oil since sulphur is not sufficiently miscible with lubricating oil but separates therefrom. A further problem when using sulphur as fuel in internal combustion engines is that sulphur- dioxide-containing combustion gases tend to pass the piston ring seals and, when contacting the lubricant oil in the crankcase, to contaminate this and affect in a corrosive manner parts of the engine such as bearings and the like. A further problem is that sulphur is not liquid at normal ambient temperature ( room temperature ) , and when shutting off an internal combustion engine using sulphur as fuel and/or lubricant, such as when servicing the engine, it may be difficult to remove solidified sulphur from the components of the engine.

The above-mentioned problems are partly connected with the nature and properties of sulphur. Elementary sulphur is available with different structures, ortho- rhombic sulphur (Sα), and monoclinic sulphur (Sβ), both consisting of rings with 8 sulphur atoms. When heating orthorhombic sulphur (S_α), this is converted at a temperature of 96.5°C into monoclinic sulphur (Sβ) and during continued heating, the monoclinic sulphur (Sβ) melts at 119 °C and forms a yellow low-viscosity mass of molten sulphur (Sλ). During continued heating to 159°C, the colour of the molten mass changes to red and the viscosity thereof increases strongly. The reason is that the ring structure of the sulphur breaks up and the linear sulphur fragments are polymerised to sulphur polymers which may contain up to about 100,000 sulphur atoms. This type of sulphur is called catena sulphur and is also designated S_μ. During further heating to 200°C, this type of sulphur (S_μ) achieves maximum viscosity which decreases during continued heating above 200 °C, and the sulphur turns black. The boiling point of sulphur is 444.7 °C. Summary of the Invention

The present invention intends to obviate or reduce the above-mentioned drawbacks of prior-art technique. According to one aspect, the invention provides a method for combustion of sulphur in an internal combustion engine, in which ignition and combustion of the sulphur take place at a lower maximum pressure than before, thereby permitting the ignition delay to be smaller and the combustion of sulphur to become more complete, while forming a smaller amount of N0_X in the exhaust gases. More specifically, the invention provides according to this aspect a method for combustion of sulphur in an internal combustion engine, which is characterised in that the combustion takes place in the presence of a catalyst, which is selected among platinum-group metals and alloys thereof.

According to another aspect, the invention provides a method for combustion of sulphur in an internal combus- tion engine, in which the engine is lubricated with sulphur in a more efficient manner than before. More specifically, the invention provides according to this aspect a method for combustion of sulphur in an internal combustion engine, which is characterised in that the engine is lubricated with polymerised sulphur.

According to one more aspect, the invention provides a method for combustion of sulphur in an internal combustion engine, in which the lubricating oil in the engine is protected from being detrimentally affected by sulphur-containing combustion gases from the combustion chamber and in which besides the sulphur-dioxide-contain- ing combustion gases are free from oil and other contaminants which can be derived from the lubricating oil . More specifically, the invention provides according to this aspect a method for combustion of sulphur in an internal combustion engine, which is characterised in that the combustion takes place in an engine, the crankcase of which is sealed against the piston.

According to a further aspect, the invention provides a method for cleaning solidified sulphur from metal surfaces, such as surfaces of engine components. More specifically, the invention provides according to this aspect a method for removing solidified sulphur from metal surfaces, which is characterised in that the sulphur is contacted with an oil at a temperature above the sulphur melting point, the sulphur being dissolved in the oil, that the oil and the sulphur dissolved therein are removed from the metal surface and cooled, such that the sulphur precipitates, that the precipitated sulphur is removed from the oil, that the oil is heated to a temperature above the sulphur melting point, and that the oil is used for renewed removal of solidified sulphur from a metal surface.

Further characteristic features and advantages of the invention will appear from the following description and the appended claims. Detailed Description of the Invention.

According to the first aspect of the invention, combustion of sulphur in an internal combustion engine is carried out in the presence of a catalyst, which is selected among platinum-group metals and alloys thereof. By platinum-group metals are in this context meant Ru, Rh, Pd, Os, Ir and Pt. It is particularly preferred to use Pt or an alloy thereof as catalyst. By carrying out the combustion of sulphur in the presence of said catalyst, the ignition and combustion of sulphur are facilitated, such that the mixture of sulphur and oxygen-containing gas in the combustion chamber need not be com- pressed to the same high degree as would otherwise be the case. This also results in a smaller ignition delay of the sulphur and less strain affecting the engine construction. The combustion of sulphur will also be more complete, which means that undesired N0_X forms to a smaller extent. The formation of N0_X can also be reduced by carrying out the combustion with an excess of sulphur, i.e. in the form of a substoichiometric combustion, whereby the combustion temperature can be lowered. The internal combustion engine used in the inventive method can be selected among diesel engines, Otto engines or gas turbine engines. It is especially preferred to use diesel engines. It is advantageous that existing engines, such as, for instance, old marine diesel engines, can be used in the invention. Before the sulphur is used as fuel in combustion according to the invention, contaminants, such as sand, acids and hydrogen sulphide, are cleaned in conventional manner from the sulphur. The cleaning operation suitably takes place by filtration of the sulphur in molten state. In the combustion of sulphur in the presence of the inventive catalyst, it is preferred that the catalyst is arranged in the combustion chamber of the engine, such as on the top of the piston of the internal combustion engine or up in the top of the combustion chamber, i.e. on the cylinder head of the combustion chamber. The catalyst can be arranged in the combustion chamber in any suitable fashion that secures it safely in the desired position, for instance by screwing, welding, casting or in some other suitable manner. In the most preferred embodiment of this aspect of the invention, a platinum metal plate is fixed to the piston top in the internal combustion engine.

As mentioned before, the sulphur dioxide content of the exhaust gas normally amounts to about 14-16% by volume in the combustion of sulphur in air. In the invention, the sulphur dioxide content of the exhaust gas can be increased to about 19-20% by volume, i.e. close to the theoretical maximum, by recirculation of at least a partial flow of the exhaust gas to the suction side of the internal combustion engine.

According to the second aspect of the present inven- tion, use is made of sulphur for lubricating a sulphur combustion engine, and more specifically use is made of polymerised sulphur for the lubrication. It is preferred that the lubrication takes place at a temperature of about 160-200 °C, i.e. that the sulphur used for the lubrication has this temperature. As mentioned before, sulphur melts at a temperature of 119 °C, whereas the boiling point is 444.7 °C. Even if, theoretically seen, sulphur could be used as lubricant in the entire temperature range, this is not the case in actual practice. As mentioned above, ordinary molten sulphur (Sx) has in fact poor wetting of metal surfaces, resulting in its lubricating capacity being unsatisfactory. Attempts have been made to eliminate this deficiency by mixing sulphur and lubricating oil, but nor has this resulted in acceptable lubrication owing to the sulphur separating from the lubricating oil. According to the present invention, it has surprisingly been discovered that the problem with unsatisfactory wetting of metal surfaces and thus the problem with unsatisfactory lubrication can be solved by using a certain type of molten sulphur as lubricant, more specifically polymerised sulphur, i.e. so-called catena sulphur (S_μ). This type of molten sulphur has good wet- ting and adhesiveness in respect of metal surfaces and has a lubricating function which is almost equivalent to that of lubricating oil. A possible explanation of this phenomenon can be that catena sulphur (S_μ) contains long linear polymer molecules of up to about 100,000 sulphur atoms instead of ring-shaped sulphur molecules, and that the lubricating and wetting capacity of these linear sulphur polymers is better than in the ring-shaped sulphur molecules. According to the third aspect of the invention, the lubricating oil in a sulphur combustion engine is protected from being detrimentally affected by sulphur-containing combustion gases from the combustion chamber by the crankcase being sealed against the piston. In fact, it has been found that the seal between the combustion chamber and the crankcase which is provided by the piston rings is not sufficient to prevent sulphur-containing combustion gases, such as sulphur dioxide, from passing the piston rings and entering the crankcase of the engine and there contacting and contaminating the lubricating oil and corroding bearings and other parts of the engine. To obviate this problem, the combustion of sulphur takes place in an engine, the crankcase of which is sealed against the piston. This implies that, in addition to the piston rings, there is a further seal between the crankcase and the combustion chamber. According to a particularly preferred embodiment, this sealing of the crankcase against the piston is provided by using a so-called crosshead engine. In crosshead engines, the connecting rod is fixed to a piston rod, which is guided by a crosshead in guide means. In this manner, the piston and the cylinder are also relieved of normal forces acting on the cylinder wall. Big engines, such as marine engines, are often built in crosshead design. According to the invention, it is particularly preferred to combine the second and the third aspect, i.e. to use an internal combustion engine, whose crankcase is sealed against the piston, such as a crosshead engine, molten, polymerised sulphur being used for lubricating the cylinder only, whereas the rest of the engine sealed against the piston and the cylinder is lubricated with oil in conventional manner. If conventional lubricating oil is used as lubricant in the cylinder bore of the engine, residues of burnt oil will in fact be mixed with the sulphur-dioxide-containing combustion gases, and these oil residues may cause problems in the further pro- cessing of the combustion gases. On the other hand, in the combustion of sulphur in an internal combustion engine, which is lubricated with lubricating oil, it is important to protect the lubricating oil from being detrimentally affected by the sulphur-containing combus- tion gases. The combination of an engine, the crankcase of which is sealed against the piston, such as a crosshead engine, and lubrication of the cylinder bore with molten, polymerised sulphur, while the rest of the engine is lubricated with motor oil, therefore offers an excel- lent solution to these problems, i.e. the combustion gases are not affected detrimentally by oil residues from the lubricating oil, and on the other hand the lubricating oil is not at all affected or not detrimentally affected by the sulphur-containing combustion gases. According to the fourth aspect of the invention, solidified sulphur is removed from metal surfaces, such as surfaces of an internal combustion engine as stated above, by washing with hot oil. Such removal of solidified sulphur can be of interest after shutting off an internal combustion engine, which is driven with sulphur as fuel and/or lubricated with sulphur as lubricant, especially when shutting off the engine for service, in which case the engine is to be wholly or partly taken apart. According to the invention, the solidified sulphur is contacted with an oil, preferably a mineral oil, and most preferred diesel oil, at a temperature above the melting point of sulphur, preferably a temperature of 120-160°C. The sulphur is then dissolved in the oil, which normally dissolves about 7-8% by weight of sulphur, based on the weight of oil. The hot oil with dissolved sulphur is then removed from the metal surface and cooled to a temperature below the melting point of sulphur, such that the sulphur precipitates. Subsequently, the precipitated sulphur is separated from the oil, for instance by filtration, whereupon the oil after heating to a temperature above the melting point of sulphur is again prepared for renewed use to remove solidified sulphur from a metal surface. In this method involving simple circulation with heating and cooling and subsequent dissolution and precipitation of sulphur, the used solvent for the solidified sulphur (oil) can be used a great number of times for the removal of solidified sulphur.

According to the invention and the special aspects thereof which have been described above, specific problems in the use of sulphur as fuel and lubricant in internal combustion engines are solved, and the invention contributes actively to permitting industrial utilisation of sulphur as fuel and lubricant in internal combustion engines .

The invention will now be described by means of some nonrestricting Examples . Example 1 ( comparative )

Combustion by using sulphur as fuel in an internal combustion engine was effected in a used 11 1 lorry engine of type Scania, RB82A model. To be able to test the engine under working conditions, it was connected to a water brake. The supercharger (turbo) of the engine and also the charge air cooler were removed. Instead, dried, somewhat pressurised air from a sulphuric acid tower was supplied to the engine. The use of dried air was necessary to avoid acidification (sulphurous acid/sulphuric acid) in and after combustion in the engine. To keep the sulphur fuel liquid, the surroundings of the engine were heated to 130 °C. When testing the engine, a period of operation of about 250 h was obtained under full working conditions. During testing, sulphur passed the pistons, entered the crankcase and was mixed with the lubricating oil . This sulphur caused the formation of sulphide on the bearing surfaces of the crankshaft, and after 250 h operation, the layer of sulphide had grown and the bearing play between crankshaft and bearing had decreased such that there was a risk of the bearings seizing. Example 2

In order to counteract the problems in combustion of sulphur in the internal combustion engine according to Example 1, tests were carried out, using sulphur as fuel in a 3-cylinder (cylinder diameter 160 mm) 2-stroke crosshead engine, manufactured by Bolnes and designated L-Type. In this type of engine, the crankcase is separated from the combustion chamber in the cylinder, and a crosshead produces a linear movement of the rod connecting the piston with the connecting rod. This linear movement reduces the transverse forces of the piston against the cylinder wall, and besides the construction permits a sealing between the combustion part and the crankcase. This type of engine has two lubricating systems, one for the crankcase and the crankshaft bearings and one for the cylinder bores. When testing the Bolnes engine, the components in the fuel system containing sulphur were heated to about 130°C. The test run of the engine was carried out without problems . After about 50 h, the test run was interrupted, and in the subsequent inspection of the engine, there were no problems similar to those of sulphide formation on the bearing surfaces that appeared in Example 1. Example 3

With a view to illustrating the advantage of carry- ing out the combustion of sulphur in the presence of a catalyst, the following test was made. Molten sulphur having a temperature of about 140°C was dropped onto a thermostat-controlled electrically heated hot plate, and any ignition of the sulphur on the hot plate in the ambient air was observed. Only when the hot plate had been heated to a temperature of about 260°C, an ignition of the sulphur was observed. This temperature thus corresponds to the ignition temperature of sulphur in conventional combustion in an internal combustion engine.

Subsequently, a platinum crucible having a diameter of 60 mm was arranged on the hot plate and the test was repeated, dropping molten sulphur having a temperature of 140 °C. With the aid of the hot plate, the platinum crucible was heated successively, and when the crucible had a temperature of 160 °C, an ignition of the added sulphur was observed. This temperature corresponds to the igni- tion temperature of sulphur when using it as fuel in an internal combustion engine with a platinum catalyst.

It is thus established that the ignition temperature of sulphur is reduced quite considerably in the presence of a platinum catalyst, and this reduction of the igni- tion temperature permits combustion of sulphur in an internal combustion engine with a platinum catalyst at a lower maximum pressure, along with complete combustion and reduced formation of N0_X. Example 4 In order to illustrate the lubricating capacity when using polymerised sulphur as lubricant according to the invention, the following test was effected.

An apparatus that was intended to resemble and simulate the conditions in a cylinder of an internal combus- tion engine, was provided. The apparatus consisted of a compressed-air cylinder, which was connected to a lever mounted on a shaft and being able to move back and forth along an arcuate path over a metal surface. At the far end of the lever, a rectangular piece of steel having the dimensions 5 mm x 3 mm was arranged in engagement with the metal surface. On top of the piece of steel, a 750 g weight was arranged for the purpose of increasing the contact pressure between the metal surface and the piece of steel . The metal surface was produced of a material corresponding to that of cylinder linings, while the piece of steel was made of a material corresponding to that of piston rings. In order to obtain the same surface as a cylinder lining, the metal surface was finished by honing. The metal surface was further arranged on a thermostat-controlled electrically heated hot plate to be able to heat the metal surface to the temperatures pre- vailing in an engine.

The substance whose lubricating properties were to be tested was applied to the metal surface, and the feed pressure to the compressed-air cylinder was set at a constant value by means of a pressure regulator. Then the piece of steel was allowed to perform 600 reciprocating movements against the metal surface, driven by the compressed-air cylinder. The time for performing these 600 reciprocating movements was measured and the number of reciprocating movements per second (number of strokes per second) was calculated. The better the lubricating properties of the tested substance, the shorter time was required to perform 600 reciprocating movements, i.e. the greater the number of strokes per second. The number of stroke per second is consequently a direct measure of the friction between the piece of steel and the metal surface. The test was carried out at different air pressures in the compressed-air cylinder.

The following lubricating substances were tested:

A. Motor oil Mobil 10-50, especially intended for diesel engines. The test was carried out at room temperature.

B. The same oil as in A, but the test was carried out at 185°C.

C. Sulphur at a temperature of about 130°C. D. Sulphur at a temperature of 180 °C, i.e. polymerised sulphur according to the invention. The test results are shown in Table 1. Table 1

As is evident from Table 1, the motor oil had the best properties. However, pure sulphur at a temperature of 130°C presented so high values of the friction that the compressed-air cylinder could hardly perform any movement at all and therefore no values of the number of strokes per second could be calculated. On the other hand, polymerised sulphur according to the invention (Test D) presented surprisingly low friction values which are very close to those of the conventional motor oil according to Tests A and B.

Claims

1. A method for combustion of sulphur in an internal combustion engine, cha r a c t e r i s e d in that the engine is lubricated with polymerised sulphur.

2. A method as claimed in claim 1, ch a r ac t e r i s e d in that the lubrication takes place at a temperature of about 160-200┬░C.

3. A method for combustion of sulphur in an internal combustion engine, c h a r a c t e r i s e d in that the combustion takes place in an engine, the crankcase of which is sealed against the piston.

4. A method as claimed in claim 3, c h a r a c - t e r i s e d in that the combustion takes place in a crosshead engine.

5. A method for combustion of sulphur in an internal combustion engine, char ac t er i s e d in that the combustion takes place in the presence of a catalyst, which is selected among platinum-group metals and alloys thereof .

6. A method as claimed in claim 5, ch a r a c t e r i s e d in that the combustion takes place in an engine, whose combustion chamber comprises the catalytic metal.

7. A method as claimed in claim 6, c h a r a c t e r i s e d in that the catalytic metal is arranged on the piston top of the internal combustion engine.

8. A method as claimed in claim 6, c h a r a c - t e r i s e d in that the catalytic metal is arranged on the cylinder head of the combustion chamber.

9. A method as claimed in any one of claims 5-8, ch a r a c t e r i s e d in that the combustion takes place in a diesel engine.

10. A method for removing solidified sulphur from metal surfaces, cha r a cter i s e d in that the sulphur is contacted with an oil at a temperature above the sulphur melting point, the sulphur being dissolved in the oil, that the oil and the sulphur dissolved therein are removed from the metal surface and cooled, such that the sulphur precipitates, that the precipitated sulphur is removed from the oil, that the oil is heated to a temperature above the sulphur melting point, and that the oil is used for renewed removal of solidified sulphur from a metal surface.

11. A method as claimed in claim 10, c h a r a c - t e r i s e d in that the oil has a temperature of

120-160┬░C.

12. A method as claimed in claim 10 or 11, c h a r a c t e r i s e d in that the oil is diesel oil.