GB2358434A - Disposal of waste mineral oils by combustion in a compression ignition engine in an oxygen-enriched atmosphere - Google Patents

Abstract

The invention relates to a method of disposing of waste mineral oils, such as used engine oil, gearbox oil, lubricating oil, hydraulic oil and transformer oil, by means of combustion in a standard high-speed compression ignition engine. In particular, the invention provides a method of disposing of waste mineral oil by means of combustion in a compression ignition engine, wherein an enriched oxygen atmosphere is provided in the combustion chamber of the engine. The combustion atmosphere may be enriched with oxygen to a level, which may depend on an analysis of the exhaust gases, of between 3% and 6% above normal. The enrichment oxygen may be supplied by gas separation membranes or by diluting pure oxygen with air. The exhaust gases may be treated to reduce NOx by catalytic reduction with ammonia, neutralise acid gases with powdered alkaline reagent and collect the products of the neutralising reactions and any other solid or particulate matter in a bag filter.

Description

1 2358434 71018.607 Disposal of Waste Mineral Oils by Means of Combustion

S The present invention relates to a method of disposing of waste mineral oils, such as used engine oil, gearbox oil, lubricating oil, hydraulic oil and transformer oil, by means of combustion in a standard high-speed compression ignition engine. In particular, the invention extends to waste oils that are at risk of being contaminated by hazardous pollutants, such as polycyclic organic chemicals. The heat and power produced by the engine is preferably used to generate electricity.

Waste mineral oils are usually very dirty and tend to be polluted with a variety of contaminants. For example, waste oils can contain varying concentrations of metals, heavy metals, metallic compounds, sulphur, chlorine, carbon and ash. Some waste mineral oils can be contaminated with toxic, carcinogenic polycyclic organic chemicals, including dioxins, furans and polychlorinated biphenyls (PCBs). Many waste oils contain high levels of water.

Waste mineral oils therefore have to be disposed of in a carefully controlled manner to avoid potential environmental pollution and risks to human health.

Although some waste mineral oils are recycled, the most common current method of disposal is to burn the waste oil in either boilers or furnaces.

Before waste mineral oils are suitable for combustion, they normally have to be thoroughly cleaned to remove excessive amounts of contaminants, not only to improve the combustion properties of the oil but also to 3S reduce the risk of releasing harmful substances into the atmosphere when the oil is burned. Excessive water in the oil, which can have a detrimental effect on the combustion characteristics of the oil, is also normally removed before combustion.

The degree of processing required to the waste mineral oil, prior to combustion, is dependent on the type and the concentration of the contaminants present in the oil. The treatment processes, which may include filtration, centrifuging, washing, solvent extraction, distillation, cracking and blending, can be complex anJ costly.

Even after the waste oil has been cleaned, the eventual combustion process still has to be carefully controlled and is subject to strict regulation. Releaspto the atmosphere of prescribed substances produced during combustion, such as carbon monoxide, nitrogen is oxides, acid gases, heavy metals, particulates and polycyclic organic chemicals, are of particular environmental concern.

It can be difficult to deal with the waste oil fro some industrial processes. For example, in the marine shipping industry it is becoming increasingly difficult and costly to dispose of the used lubricating oil taker from the diesel engines that power ships. The waste lubricating oil cannot be dumped at sea because of the risk of marine pollution. It is also no longer acceptable to mix the used lubricating oil with the ship's fuel, for combustion in the marine diesel engines, because of the risk of atmospheric air pollution. The only alternative is to store the waste lubricating oil on board ship, for subsequent disposal at an approved land based facility when the ship docks.

Attempts have been made before to combust waste mineral oils in internal combustion engines. For example, UK patent application 2264304A describes the use of a large low-speed internal combustion diesel engine to burn waste oil. However, the method describE: is dependent on the waste oil being processed substantially prior to combustion, to remove water ancil solids, in order to provide a hydrocarbon oil that is virtually free of contaminants before it can be used as fuel in an engine.

The present invention seeks to provide a method whereby mineral oils that still contain a relatively high level of contaminants can be disposed of in a safe manner by means of combustion in a standard high-speed compression ignition diesel engine. In this context, high-speed signifies engines that operate at say between 1500 rpm and 2500 rpm. In contrast, low-speed engines, such as marine diesel engines, tend to operate at about 600 rpm or even lower.

High-speed compression ignition engines are very fuel specific and will normally only operate efficiently on the petrochemical oils that have been developed as fuel for this type of engine.

From a first broad aspect therefore, the present invention provides a method of combusting waste mineral oils in a compression ignition engine wherein the atmosphere in the combustion chamber of the engine is enriched with oxygen.

Highly contaminated waste mineral oils are difficult, if not impossible, to burn in a high-speed diesel engine under naturally aspirated conditions.

Surprisingly, it has been found that increasing the oxygen concentration in the combustion atmosphere enables contaminated waste oils to be effectively combusted.

With oxygen enriched combustion, the main processing required to the waste mineral oil, prior to combustion, is to pass the oil through a coarse filter or a centrifugal separator or both, primarily to remove large sized particulate matter that would block the fuel injector nozzles in the engine. Filtration and centrifuging are well established techniques to clean poor quality petrochemical oils such as, for example, heavy fuel oils, and a suitable commercially available 4 centrifugal separating system, which has the capability of being able to remove water as well as solids, is manufactured by Alfa-Laval Ltd.

In a preferred embodiment therefore, the inventicn provides a method of combusting contaminated waste mineral oil in a compression ignition engine, which has an enriched oxygen combustion atmosphere, and where the oil is subjected to minimal processing prior to combustion, that is, the oil is pre-treated by filtering and/or centrifuging prior to combustion, without the need for other more rigorous processing procedures such as distillation of the oil or inconvenient techniques such as allowing the oil to settle out in a settling tank.

Viewed from a further broad aspect, the invention thus provides a disposal system for waste mineral oil comprising a compression ignition engine, means for cleaning the wasLe oil prior to combustion, means for heating and agitating the oil prior to its supply to t.

engine; oxygen enrichment apparatus to supply an enriched oxygen atmosphere to the combustion chamber cf the engine, and means for cleaning engine exhaust gases.

Some waste oils contain certain additives and impurities, such as calcium, zinc and phosphorus compounds, which can inhibit sustained, efficient combustion, even with oxygen enrichment, because these materials can form deposits around the valves in the combustion chamber of the engine.

These types of impurity can be reduced in the waE oil by gently washing the oil, under carefully controlled temperature conditions, with dilute diaminoethanetetra-acetic acid. Washing the oil with diaminoethanetetra-acetic acid has been found to have the surprising advantage of emulsifying the oil such that some water (e.g. up to about 10% by volume) can he allowed to remain in the oil during combustion. As a result, further pre-treatment steps to lower the water content of the oil have been found to be unnecessary.

After washing, the dilute acidic solution containing the impurities may be separated from the mineral oil by means of an Alfa-Laval centrifugal separator, and the acid may be recirculated for further use as a washing agent.

The ability of the washing acid, i.e.

diaminoethanetetra-acetic acid to aid emulsification is surprising since this compound is primarily known for its ability to clean oils by virtue of its affinity for calcium, zinc and phosphorus compounds. Thus viewed from a different aspect, the invention also provides the use of diaminoethanetetra-acetic acid as an emulsifying agent, preferably for emulsifying waste mineral oils, but which may also be useful for emulsifying other oils and fats that have a high water content.

Increasing the oxygen concentration in the combustion chamber of a diesel engine encourages early fuel ignition and a more complete burn of the fuel. In the preferred embodiment, no adjustment is made to the normal mechanical timing of the engine to compensate for the early ignition of the fuel, thus providing a longer and more complete fuel burn. This ensures the complete incineration of both the oil itself and any combustible contaminants that may be present in the oil. In this context normal, refers to the conditions or engine settings that would customarily be used to run the regular petrochemical fuel, i.e. diesel fuel oil, usually specified for this type of engine.

Enriched oxygen combustion also enables waste mineral oils that contain water to be effectively combusted. Water can affect both the ignition and combustion properties of mineral oils, and at high levels may even prevent combustion completely. Providing the water is well emulsified with the waste oil, it has been found that oils containing up to 20% water can be combusted with the aid of oxygen enrichment.

6 Excessive water in the oil may be removed by the centrifugal separating treatment. After centrifuging, the waste oil would be highly agitated at its lowest mobile temperature before being injected into the engine, to ensure that water remaining in the oil becE.rTe emulsified with the oil. If necessary, a small amount of emulsifying agent could be added to the oil to aid emulsification. Diaminoethanetetra-acetic acid may b( suitable in some cases, but many other known emulsifyjrg agents are available for use with oil products.

In some cases, depending on the viscosity of the oil, it may be necessary or desirable to heat the oil prior to entering the combustion engine, e.g. to its minimum mobile temperature or above.

Following the basic level of treatment proposed, the waste oil will still contain various contaminants, some of which may not be combustible. After the oil hEs been combusted with the aid of increased oxygen, unburned contaminants, such as ash and metals, and undesirable by-products of combustion, such as carbon monoxide and nitrogen oxides, will be carried over froa the combustion chamber of the engine through to the engine exhaust.

Prescribed substances in the exhaust may be abatE!d down to environmentally acceptable levels by means of well established techniques, before the exhaust gas i,,:i released to the atmosphere. For example, particulates cf ash, carbon, metals and metallic compounds can be collected in bag filters; acid gases, such as sulphur dioxide and hydrogen chloride, can be abated by means cf alkaline treatment e.g. conveniently a powdered alkalire reagent may be used; nitrogen oxides can be reduced by catalytic reduction with ammonia.

Therefore in a further aspect of the invention, a method is provided to dispose of waste mineral oils by means of combustion in a compression ignition engine, which includes an enriched oxygen combustion atmosphel.-E, and where minimal processing (e.g. simple filtering and/or centrifuging) of the oil is carried out prior to combustion but the exhaust gas from the engine, after combustion, is cleaned to abate prescribed substances down to acceptable environmental levels.

A compression ignition engine works by injecting fuel, under pressure, into air that has been compressed by a piston travelling up a cylinder. The fuel and air mixture is further compressed until it becomes hot enough to ignite the fuel. This results in a rapid increase in temperature and pressure inside the cylinder and the piston is forced back down the cylinder. Peak cylinder pressures inside the combustion chamber can be over 140 bar and the combustion temperature in an is enriched oxygen atmosphere can reach over 20000C.

Polycyclid organic chemicals are thermally stable and can only be effectively destroyed by high temperature incineration. Oxygen enrichment provides efficient combustion at temperatures high enough to ensure the effective destruction of polycyclic chemicals, or indeed any other organic based contaminants, which may be present in the waste oil.

The heat and power produced by combusting the waste mineral oil in the manner described can be used to generate electricity.

From a further aspect therefore, there is provided a method of generating electrical power comprising of combusting waste mineral oils in an enriched oxygen combustion atmosphere in a compression ignition engine, and coupling said engine to an electrical power generator. The hot exhaust gas from the engine can also be used to raise steam in a boiler, and the steam utilised to drive a turbine that can generate more electricity.

Heat that has been generated during combustion, in the engine and the exhaust, can also be utilised in the waste oil disposal process itself, for example to raise the temperature of the waste oil to provide adequate mobility to the oil for the processing systems and for injection into the engine.

In order to achieve combustion of waste mineral ot in a high-speed compression ignition engine, the level of oxygen enrichment required will be dependent on the composition of the oil and its combustion properties, and the amount. and type of contaminants remaining in tti oil after processing.

Some waste oils may combust effectively with an enhanced oxygen level as low as 2% above normal (i.e. 23% oxygen).

However, to achieve efficient combustion that woul destroy any organic pollutants in the waste oil, the level of oxygen enrichment supplied to the engine is more likely to be between 3 and 6% above normal (i.e. between 24 and 27% oxygen) and more preferably between P and 5% above normal (i.e. between 25 and 26% oxygen).

At these low levels of oxygen concentration, the oxygen rich air is safe to handle, would not cause oxidation damage to the engine components and would be. reasonably economic to produce and supply to the engiii.

The enriched oxygen air can be supplied by either gas separation membranes or by diluting pure, or almoE--,!,,.-- pure, oxygen produced by commercially available method.., such as pressure swing adsorption, vacuum swing adsorption and cryogenic systems, with normal air.

In addition to the normal management systems buil,-into the engine, a sensor that monitors the temperatur'._ and composition of the exhaust gas stream coming from the engine can, in part, control the combustion proces-3 For example, carbon monoxide in the exhaust gas:L3 an indication of incomplete combustion. It is therefoi--,desirable that the carbon monoxide level in the exhau.--,.-- gas is monitored continually and maintained at a predetermined low level to ensure optimum efficiency ofthe combustion process, as well as to comply with - 9 environmental legislation.

The sensor in the exhaust gas stream would be linked to a valve in the air supply to the engine and said valve would be able to adjust the oxygen concentration in the intake air to ensure efficient combustion, based on the concentration of carbon monoxide in the exhaust.

Waste mineral oils from different sources may require different levels of oxygen enrichment to ensure effective combustion. once established, the overall oxygen concentration for any particular waste oil would generally remain steady but minor adjustments may be made, within say a limited range of e.g. 0.5%, in order to maintain an approximately constant level of carbon monoxide in the exhaust.

Some preferred embodiments of the present invention will now be described by reference to the following illustrations. Used lubricating oil from marine diesel engines was selected as being a typical example of waste mineral oil for the research tests.

Figure 1 illustrates graphically the concentration of carbon monoxide in the exhaust gas from the research test engine when using diesel oil as fuel under naturally aspirated conditions (21% oxygen) and processed waste lubricating oil under enriched oxygen conditions (26% oxygen), at the higher engine power outputs.

Figure 2 illustrates smoke density filter papers taken from the exhaust gas stream when running the test engine with diesel oil naturally aspirated (21% oxygen) at 9-kWe power output, processed waste lubricating oil naturally aspirated (21% oxygen) at 9-kWe, and the waste oil under enriched oxygen conditions (26% oxygen) at 9-kWe.

Figure 3 is a schematic illustration of a waste oil disposal system embodying the invention, which includes oil processing, oxygen enriched combustion in an engine, electricity generation and abatement of pollutants in the exhaust gas stream.

Figure 4 is a schematic illustration of the cylinder head of a compression ignition engine.

The waste marine lubricating oil selected for purposes has properties that differ considerably from conventional diesel oil, as illustrated in Table 1.

The values given in Table 1 are for the waste lubricating oil in the condition as received for testing, and they reflect t he quality of the oil as it was taken from a large marine diesel engine during a routine oil change. The different properties of the waste mineral oil can significantly affect the combustion characteristics of the waste oil compared is with regular diesel fuel oil. This is particularly relevant when the waste oil is to be used as fuel in high-speed engines, as these engines tend to be more critical with regard to the specification and performance of the fuel.

Table 1 Typical Properties of Waste Marine Lubricating Oil Diesel Fuel Oil Property Waste Marine Lube Oil Diesel Fuel Oil Calorific Value MJ/kg 44.8 43.0 Specific Gravity 0.90 0.83 Viscosity cSt at 4TC 133.9 2.15 Pour Point 'C -24 -30 Flash Point 'C 240 61 Conradson Residue mass % 1.90 0 Sediment mass % 0.08 0 Ash Content mass % 2.31 <0.01 Sulphur Content mass % 1.24 Trace Water Content %,wt 0.10 0 The waste marine lubricating oil also contained additives and contaminants that,are not present in diesel fuel oil. In particular, the waste oil supplied for test contained high levels of calcium, zinc and phosphorus, as well as having high ash and sulphur contents. An analysis of the contaminants in the waste lubricating oil is given in Table 2; firstly in the condition as received for laboratory testing; secondly after the waste oil had been processed by means of 10 coarse filtration, washing with dilute diaminoethanetetra-acetic acid and then centrifuging.

In addition to the contaminants described in Table 2, the waste lubricating oil may well have contained various organic chemical pollutants. is Table 2 Contaminants in Waste Marine Lubricating Oil Contaminant Concentration Level In Concentration Level Oil As Received After Oil Treatment Calcium ppm 3312 754 Zinc PPM 849 18 Phosphorus ppm 719 488 Magnesium ppm 19 3 Boron ppm 25 5 Other Metals (Total) PPM 20 37 Combustion trials were carried out in the laboratory using a high speed Lister-Petter two cylinder, four stroke diesel engine, with direct fuel injection and a nominal capacity of one litre. The engine was run at its optimum speed, 2300 rpm, as recommended by the engine manufacturer for continuous running when using diesel oil as fuel.

The engine was operated in a special test rig where the mechanical load consisted of a high power direct current motor with a variable field voltage. The engine could be operated at different power increments, under continuous running conditions, from a minimum power output of 5-kWe to the maximum sustainable load based the exhaust temperature, exhaust smoke and carbon monoxide emission level.

The engine manufacturer recommended that the most favourable power output for continuous running, at 2303 rpm, when using regular diesel oil as fuel, was 9-kWe.

The maximum smoke limited continuous power output was recommended to be 11-kWe.

To confirm the normal engine operating parameters, the engine was initially run naturally aspirated (21% oxygen, 79% nitrogen) at different power outputs using is regular diesel oil as fuel.

The exhaust emissions of carbon monoxide and nitrogen oxides, exhaust temperature and smoke density were recorded at each power increment.

Carbon monoxide in the exhaust gas is an indicatii of incomplete combustion. The level of carbon monoxide in the exhaust therefore provides a good indication of the efficiency of the combustion process.

Figure 1 graphically illustrates the concentratici of carbon monoxide in the exhaust gas, at higher power outputs, when combusting diesel oil under naturally aspirated conditions.

The test runs confirmed the recommendations made the engine manufacturer when running the engine with diesel oil as fuel.

The minimum level of carbon monoxide, around 340 ppm, was achieved at a power output of 9-kWe. Above 9-kWe, the level of carbon monoxide in the exhaust increased until, at a power output of llkWe, the concentration of carbon monoxide was over 4000 ppm and black smoke was coming from the exhaust.

It was then attempted to use waste marine lubricating oil as fuel, whilst operating the engine 13 - under naturally aspirated conditions (21% oxygen, 79% nitrogen).

The waste oil was processed by being heated and coarse filtered, followed by washing with dilute diaminoethanetetra-acetic acid and then centrifuged to remove excessive acid and water. It was established that after being centrifuged, the oil still contained over 10% water. The processed oil was stored in a tank, which was heated to the minimum temperature that provided adequate mobility of the oil. The oil was agitated in the tank, by means of a high speed propeller-stirrer, to ensure that,-the oil was well emulsified with water and dilute acid remaining in the oil, before the oil was injected into the engine.

is It was established that under naturally aspirated conditions it was possible to initiate combustion of the processed waste lubricating oil in the test engine, but difficult to sustain combustion because the power tended to fall off rapidly.

At the recommended optimum power output of 9-kWe, the carbon monoxide concentration in the exhaust was higher than with diesel oil, at about 800 ppm. The exhaust smoke appeared to contain a similar level of particulates as when burning diesel oil. This is illustrated visually in Figure 2, which shows the smoke density filter papers taken from the exhaust gas stream when burning the waste mineral oil and diesel oil under naturally aspirated conditions at a power output of 9-kWe.

Beyond 9-kWe power the carbon monoxide level in the exhaust increased rapidly until at 11-kWe it reached over 14,000 ppm. At this power output the exhaust smoke was very black and extremely high in particulates.

The processed waste marine lubricating oil was then run in the engine at different power increments under enriched oxygen levels starting at 2% above normal (23% oxygen, 77% nitrogen) and increasing in 1% steps to an enriched oxygen level of 6% above normal (27% oxygen, 73% nitrogen).

Again the Exhaust emission levels, exhaust temperature and smoke density were recorded at each operating step.

The results showed that the processed waste lubricating oil could be combusted, in a sustainable manner, at oxygen enrichment levels of between 3 and C,:5 above normal (i.e. between 24 and 27% oxygen) and most efficiently at oxygen levels of between 4 and 5% above normal (i.e. between 25 and 26% oxygen).

Figure 1 graphically illustrates the concentratio,:-. of carbon monoxide in the exhaust gas coming from the engine at higher power outputs, when using the waste lubricating oil as fuel and an enr_-Lched oxygen atmosphere 5% above normal (26% oxygen, 74% nitrogen).

At a power output of 9-kWe, the carbon monoxide level in the exhaust following 5% enriched oxygen combustion of the waste oil, 250 ppm, was lower than that of naturally aspirated diesel oil, and significantly lower than when the waste oil was combusted under naturally aspirated conditions.

Surprisingly, however, when the power output was increased beyond 9-kWe, with 5% oxygen enrichment of tr waste oil, the carbon monoxide level in the exhaust gas increased at a much slower rate than with naturally aspirated diesel oil, as shown in Figure 1. Even at a power output of ll-kWe, the concentration of carbon monoxide in the exhaust only reached 1070 ppm.

The lower carbon monoxide concentration in the exhaust when coTr,Dusting the waste oil with 5% oxygen enrichment, compared with naturally aspirated diesel oil, was accompanied by much cleaner smoke coming fron the engine. The smoke contained a significantly reduce., level of particulates, as illustrated by the smoke density filter paper shown in Figure 2.

Table 3 compares the results of running naturallli P 1 is aspirated diesel oil and oxygen enriched waste oil at a power output of 9-kWe, the optimum continuous power recommended by the engine manufacturer when running diesel oil. For ease of comparison, most of the results in Table 3 are given as figures relative to the naturally aspirated engine running on diesel oil.

Table 3 Results of Continuous Engine Trials Using Waste Oil and Diesel Oil Measured Values Diesel 011 Waste Oil 21% Oxygen 26% Oxygen Actual Power Output kWe 9.0 9.0 Power Output Relative 1.0 1.0 Carbon Monoxide Emission Relative 1.0 0.74 Nitrogen Oxides Emission Relative 1.0 2.8 Actual Exhaust Temperature 'C 440 430 The results of the combustion trials indicated that the processed waste mineral oil could be efficiently combusted with the aid of oxygen enrichment, even when running the engine at higher than normal power outputs.

At higher power outputs, the thermal energy in the combustion chamber is increased, thus raising the combustion temperature, which helps to ensure that any thermally stable organic chemical contaminants present in the waste oil would be incinerated.

The optimum engine power output for continuous operation, when using oxygen enrichment, will be a balance between a power output that produces efficient combustion with a low level of carbon monoxide, and a higher power output having an increased level of carbon monoxide emission, but with a higher mean combustion temperature to ensure the destruction of any thermally stable organic chemicals present in the oil.

The power output would be set at a level so as tc ensure that the carbon monoxide concentration in the exhaust would he below specified environmental limits, For example, the TA Luft European limit for carbon monoxide emissions from diesel engines with a power output less than 3MW is 520 ppm.

As illustrated in Figure 1, to be below this limi with naturally aspirated conventional diesel fuel oil, the test engine would have to be operated at a maximui-r power output of about 9.8-kWe. With 5% oxygen enriched combustion using waste lubricating oil as fuel, the engine could be operated at a power output of 10.5-kWe and still be within the TA Luft carbon monoxide emiss. 3. -:D..-i limit, as illustrated in Figure 1. This represents a potential 7% increase in power compared with naturall), aspirated diesel oil.

Prescribed substances that are present in the exhaust gas stream after combustion, such as nitrogen oxides, acid gases, heavy metals and particulates, ca:ii all be abated down to environmentally acceptable levels by means of well established techniques.

Having discussed the mechanism of the oxygen enriched combustion system, a waste oil disposal syste,-n, which includes combustion in an engine and an electrica power generation system, is now described with refere:ricA to the illustrations in Figures 3 and 4.

The waste mineral oil, such as lubricating oil fron marine diesel engines, is stored in a storage tank 1.When sufficient oil has been collected, the oil is heated to provide mobility and the oil is pumped from tank 1 through a coarse filter 2 to remove large particulate matter.

If the waste oil contains high levels of calcium, zinc and phosphorus contaminants, the oil will be gentlr washed with dilute diaminoethanetetra-acetic acid in Ei rotating drum 25, under carefully controlled temperati--re conditions. After washing, the oil will be treated in a centrifugal separator 3 to

remove more particulate material and excessive water and/or dilute acid.

The processed oil is contained in a holding tank 4, which could be heated if necessary. Oil 5 from tank 4 is passed to a small heated work-in-progress tank 23 where the oil is agitated, by means of, for example, a high speed propeller stirrer 24, to ensure that water remaining in the oil is emulsified with the oil. The -temperature in tank 23 is maintained at as low a level as possible to preserve the stability of the oil and water emulsion, whilst providing adequate mobility to the oil for injection into the engine.

For some waste oils, it may be necessary to add a small amount of a suitable emulsifying agent to the oil in tank 23, to ensure a stable emulsion of oil and water.

A pump 6 pumps the oil from tank 23 to a fuel injection valve 21 in the cylinder head 22 of a high speed compression ignition engine 7.

Air rich in oxygen is pumped from a gas separation module (not shown) to a valve 8 that controls the concentration of oxygen in the air supplied to the engine 7, by selectively admitting atmospheric air to the oxygen rich air.

The control valve 8 adjusts the oxygen concentration in the air supply to the engine, to provide the desired running conditions, in response to sensor 10, which analyses the exhaust gas stream, and in particular the concentration of carbon monoxide, coming from the engine 7.

The supply of oxygen rich air can be by any suitable means, including gas separation membranes, pressure swing adsorption, vacuum swing adsorption or cryogenic systems.

The outlet of the control valve 8 is connected to the air intake manifold of the engine 7 and the oxygen rich air (typically having an Oxygen concentration of ',2 to 26%) is introduced to the combustion chamber 16 of, cylinder 18 via t-he air inlet valve 17. At this time L exhaust valve 20 is closed.

A piston 19 moving up cylinder 18 compresses the air and a small amount of the processed waste mineral oil is sprayed into the combustion chamber 16 by the fuel injection valve 21.

on further compression the oil ignites and the increase in pressure in the combustion chamber forces the piston 19 back down the cylinder 18. This movemen[-, is transmitted to a power take off shaft that drives:-I generator 9 to produce electricity., When the piston 19 returns back up the cylinder 1_8 on its exhaust stroke, the hot exhaust gas is emitted through the exhaust valve 20.

The sensor -1-0 in the exhaust monitors the levels carbon monoxide, nitrogen oxides, sulphur dioxide and any other prescribed emissions in the exhaust gas stream, as well as the exhaust gas temperature. Once Ll system is set up and the engine is running at its optimum continuous power output and speed, any deviati_ from the predetermined desired level of carbon monoxid.

in the exhaust gas can be compensated for by a slight adjustment of the concentration of oxygen to the air intake of the engine.

The engine operation will therefore be controlleci in part by the carbon monoxide measurement from senso:i- 10, and in part by the in-built engine management systems. Sensor 10 is linked to control valve 8, whic1i is able to adjust the level of oxygen enrichment as required to provide efficient engine operation.

The exhaust gas passes to a catalytic reduction unit 11 that utilises ammonia to rEduce the concentration of nitrogen oxides down to an environmentally acceptable level.

Although not illustrated in Figure 3, it is accepted practise that on leaving the catalytic reduction unit, the hot exhaust gas can be used to raise steam in a boiler, in order to drive a turbine to generate extra electricity.

The hot exhaust gas is cooled down by a heat exchanger 12 to about 1500C. Coolant from the engine cooling system also passes through the heat exchanger 12. Heat from the heat exchanger can be used within the waste oil processing system, for example to heat the oil in tanks 1, 4 and 23 to provide adequate mobility.

The cooled exhaust gas passes through a bag filter 13 to remove particulate matter including particles of carbon, soot, ash, metals and metallic compounds.

Prior to entering the bag filter, powdered alkaline is reagent can be injected into the exhaust gas stream, to neutralise any acid gases, such as hydrogen chloride and sulphur dioxide, if these are present in the exhaust gas. Solid products from these neutralising reactions are also captured in the bag filter.

The exhaust gas is then monitored by a further sensor 14 to check that all prescribed substances have been abated down to acceptable environmental limits. The exhaust gas is then released to the atmosphere through flue 15.

Although used marine lubricating oil was used as a typical example of a waste mineral oil in the research tests, the method of the invention would be applicable to other types of waste mineral oil, as well as to blends of different waste mineral oils or even to waste mineral oils blended with diesel fuel oil. Preferred types of waste mineral oil include for example engine oil, gearbox oil, lubricating oil, hydraulic oil, transformer oil or any other form of used mineral oil and mixtures and blends thereof. In general, any waste mineral oil which is contaminated with polycyclic organic chemicals and/or other hazardous pollutants may usefully be combusted according to the method of the invention.

From the above, it will be seen. that the present invention provides an effective method of disposing ol: waste mineral oils. For industrial processes that produce significant quantities of waste lubricating oj-l such as industries that use large diesel engines, for example in power generation or marine propulsion, the method of the invention provides an effective means to, dispose of the waste oil on-site, adjacent to where tl.-i-:

waste oil is being produced. The invention uses oil processing methods and abatement techniques that are well understood by industries that already use large diesel engines operating on petrochemical fuels. An advantage of using small highspeed engines to combusl--.

is the waste oil is that it is relatively easy and cost effective to maintain and overhaul this type of engin(- on a frequent basis. This is an important considerati(:) when combusting,\7aste lubricating oils, which can contain abrasive contaminants that may cause increase(A wear to engine components.

The method of the invention could also be used a-. dedicated waste oil disposal system. It is estimated that in the UK a-lone about 400,000 tonnes of waste mineral oil, f-rc)r,,i various sources, are processed each year into clean oil that is then sold as fuel for boilers, furnaces, etc. The present. invention would allow different.[--ypes of waste mineral oil to be processed and then used as fuel on---site in high-speed engine generator sets. After processing, the waste oi']-:

could be blended together or, if necessary, blended w.j'-commercial diesel fuel oil, before being used as fuel. The electricity generated would be supplied to the lo(--,,,s grid. The hot exhaust gases from different engines could be combined and used to raise steam in a boiler, in order to drive a steam turbine to generate extra electricity. Posl-- cleaning of the combined exhaust ga:-s; stream from the engines would be carefully controlled 21 - ensure the abatement of prescribed substances to below specified environmental limits.

Although the method of the invention, as described, has been applied to high-speed compression ignition engines, it is a known fact that large, low-speed, wide bore engines operate in a similar manner to small high-speed engines. The method of the invention could therefore also be applicable to low-speed, wide bore diesel engines. It may also be applied to land-based or 10 ship-based engines.

Claims (24)

1. Claims:

   A method of disposing of waste mineral oil by meiz-i,-i of combustion in a compression ignition engine, where.j-:- an enriched oxygen atmosphere is provided in the combustion chamber of the engine.
2. 2. A method as claimed in claim -1, wherein the engiri,, is a standard high-speed compression ignition engine. 10
3. 3. A method as claimed in claim -L or 2, wherein the waste mineral oil is used engine oil, gearbox oil, lubricating oil, hydraulic oil, transformer oil or anI other form of used mineral oil.

   is
4. 4. A method as claimed in claim -L or 2, wherein the waste mineral oil is a blend of different types of useA mineral oil.
5. 5. A method as claimed in claim I or 2, wherein the waste mineral oil is a blend of used mineral oils and standard diesel fuel oil.
6. 6. A method as claimed in any preceding claim, whereii the waste mineral oil is contaminated with polycyclic organic chemicals and/or other hazardous pollutants.
7. 7. A method as claimed in any preceding claim, wherEi.-i the waste mineral oil is processed by means of coarse filtration and centrifuging prior to combustion.
8. 8. A method as claimed in claim 7, wherein the waste mineral oil is washed with dilute diaminoethanetetraacetic acid before being centrifuged. 35
9. 9. A method as claimed in any preceding claim, wherein the processed waste mineral oil is heated to its minirium 23 - mobile temperature and the oil is agitated, to emulsify water in the oil, before injection into the engine.
10. 10. A method as claimed in claim 9, wherein an emulsifying agent is added to the oil during agitation.
11. 11. A method as claimed in any preceding claim, wherein the exhaust gas coming from the engine after combustion is treated to:

    - reduce the level of nitrogen oxides by means of catalytic reduction with ammonia.

    - neutralise acid gases in the exhaust with powdered alkaline reagent.

    - collect the products of the neutralising reactions and any other solid or particulate matter in a bag filter.
12. 12. A method as claimed in any preceding claim, wherein the combustion atmosphere is enriched with oxygen to at least 2% above normal (23% oxygen, 77% nitrogen).
13. 13. A method as claimed in claim 12, wherein the combustion atmosphere is enriched with oxygen to between 3 and 6% above normal (24%oxygen, 76% nitrogen and 27% oxygen, 73% nitrogen).
14. 14. A method as claimed in claim 13, wherein the combustion atmosphere is enriched with oxygen to between 4 and 5% above normal (25% oxygen, 75% nitrogen and 26% oxygen, 74% nitrogen).
15. 15. A method as claimed in any preceding claim, wherein the level of oxygen enrichment is controlled in dependence on an analysis of the exhaust gases.
16. 16. A method as claimed in claim 15, wherein the level of oxygen enrichment is controlled in dependence on the 24 level of carbon monoxide in the exhaust gas.
17. 17. A method as claimed in claim -16, wherein said le-s7c of oxygen enrichment is controlled so as to maintain carbon monoxide concentration in the exhaust gas at a predetermined level.
18. 18. A method as claimed in any preceding claim, whereL the engine is operated at a constant optimum speed giving maximum 1--]..-iermal efficiency.
19. 19. A method as claimed in any preceding claim, where-L the engine is operated at a power output that is highEz,than the optimum continuous power output normally recommended by the engine manufacturer for operation with standard diesel fuel oil.
20. 20. A method as claimed in any preceding claim, wherCL the engine is used to generate electricity by couplinc the engine to an electrical generator.
21. 21. A method as claimed in any preceding claim, where-L the hot exhaust gas is used to raise steam in a boilei:, and the steam is used to drive a steam turbine to generate electricity.
22. 22. A disposal system for waste mineral oil comprisiri,j a compression ignition engine, means for cleaning the waste oil prior to combustion, means for heating and agitating the oil- prior to its supply to the engine; oxygen enrichment- apparatus to supply an enriched oxyg.

    atmosphere to the combustion chamber of the engine, ar,.1 means for cleaning engine exhaust cases.
23. 23. A combustion system comprising a compression ignition engine, oxygen enrichment apparatus for supplying an enriched oxygen atmosphere to the 1 combustion chamber of the engine and a supply of suitably processed waste mineral oil as fuel for the engine.
24. 24. An electrical power generating system comprising a generator coupled to a compression ignition engine, said engine burning suitably processed waste mineral oil in an enriched oxygen atmosphere.