Description

This invention relates to. the generation of power using 5 recyclable plant-based fuels, to internal combustion engines, and to a method of scrubbing carbon dioxide and oxides of nitrogen from gaseous products, particularly exhaust gases.

10 Currently large scale generation of power is accomplished mainly by fossil fuel power plants, supplemented by nuclear power stations. Projects have been carried out to investigate the use of renewable sources, such as wind, solar and tidal power but they are limited in scope at

15 present. In general, mobile engines, such as automobile engines are exclusively internal combustion engines.

However, all these energy sources have disadvantages as long term power providers.

20

Fossil fuel is the most widely used source of fuel for power generation and it is probably the most harmful to the environment . Burning fossil fuels allows power to be generated at the time and place which it is required, thus

25 making it useful in transportation applications, and in handling peaks in electricity demand. However, the main

disadvantage of such a widespread use of fossil fuel energy sources is the emission of carbon dioxide into the atmosphere, which may lead to an enlarged greenhouse effect. Further harmful emissions from the burning of fossil fuel include the oxides of nitrogen (NOX) which, when released into the atmosphere, can contribute to the phenomenon known as "acid rain" .

Carbon dioxide is always formed when organic material is burned in a sufficiency of air and this is therefore a fundamental problem.

Nuclear power and conventional renewable sources of energy, e.g. wind, tide and solar, are possible alternatives, but they have their own disadvantages. The major difficulty with these renewal sources, is that they are not able to deliver power when required or to respond to peaks in demand.

Thus it may be seen that none of the present methods of generating power, either at a power station of for mobile transport, is very satisfactory when a combination of economic and environmental factors are taken into consideration.

In our published British patent application No. 2254858, it

is proposed to address these difficulties by employing algae as a fuel for power generation, preferably in a method comprising a cycle of the steps of:

(i) separating fuel algae from nutrient solution; (ii) drying and milling the algae;

(iii) utilising the powdered algae fuel directly in a thermodynamic process resulting in useful work, waste heat and carbon dioxide, for example, burning the algae in an internal combustion engine; and (iv) supplying the waste heat and carbon dioxide to the nutrient solution to promote algae growth.

Apparatus for cultivating algae, known as photobioreactors and sold under the Trade Mark BIOCOIL by Biothecna Limited of London, England, are described in GB-A-2205581; EP-A- 0239272; EP-A-0261872 and; EP-A-0304177. Suc photobioreactors each comprise an upstanding core structure, a substantially transparent tube wound on the core structure so that, in use, the exterior of the wound tube is expose to natural light, means for causing a synthesis mixture to flow through the wound tube and means for withdrawing the grown product. The synthesis mixture, which can comprise algae together with a solution of nutrients essential fo its growth, is caused to flow through the tube, while the

latter is exposed to sun light. The algae, which grows as the synthesis mixture passes along the tube, is then harvested from the tube.

An object of the present invention is to provide improvements to the system disclosed in British patent application No. 2254858 and to internal combustion engines run on powdered fuel stocks in general. Another object of the invention is to provide a method of scrubbing carbon dioxide and/or NOX from gaseous products, preferably from exhaust gases produced by combustion processes.

In accordance with a first aspect of the present invention, there is provided an internal combustion engine comprising combustion chamber means, inlet tract means, for directing air into the combustion chamber means, and fuel induction means, for supplying powdered fuel to be burned in the combustion chamber means, characterised in that the fuel induction means are arranged for supplying the powdered fuel into the inlet track means, and the so supplied powdered fuel forms a substantially homogenous fuel/air mixture for ignition in the combustion chamber means during the engine's operation. Preferably, a substantially homogenous fuel/air mixture is formed in the inlet tract means, prior to entering the combustion chamber means.

The powdered fuel/air mixture, employed in an interna combustion engine in accordance with this aspect of th invention, will burn in a homogenous manner (similar t gasoline) and the engine, .therefore, can be controlled b throttling, as well as by metering the quantity of powdere fuel supplied to the combustion chamber means by the fue induction means. Thus, an engine in accordance with th present invention, can be controlled with greater precisio than previously known powdered fuel fired interna combustion engines, such as coal fired diesel pisto engines, in which the powdered fuel is injected into eac cylinder (under high pressure) immediately before th associated piston reaches top dead centre and the onl control over the engine's speed is through metering the fue supply.

In an embodiment of this aspect of the invention, the fue induction means are arranged to supply the powdered fuel a a fuel in air suspension of greater density than th fuel/air mixture formed for ignition in the combustio chamber means. The preferred powdered fuel is powdere algae, preferably of the chlorella family and mor preferably chlorella pyreniodosa. One advantage o employing powdered algae as a fuel is that, because it i substantially non abrasive, the powdered algae will no accelerate the rate of wear experienced by engin

components, such as piston rings, cylinder bores and turbo- charger bearings, which come into contact with the fuel. This contrasts with coal dust fired diesel engines where the coal dust must be injected.directly into each cylinder, in order to avoid otherwise unacceptable rates of wear.

Additional liquid or gaseous fuel can be required in order to ignite the powdered fuel and, preferably, the inventive engine further comprises secondary fuel induction means for introducing a liquid or gaseous fuel into the combustion chamber means or inlet track means . Suitable secondary fuel induction means include conventional diesel injection equipment and gas values. Thus, a liquid or gaseous fuel can be injected into the engine in substitution for some or all of the powdered fuel. Where the powdered fuel is algae and the engine is a diesel, it is preferred that a quantity of diesel oil should be injected into the combustion chamber means, in order to ignite the algae. Where secondary fuel induction means are employed, the engine can be run on concentrations up to 100% liquid or gaseous fuel but, preferably, such fuel should be used in concentrations of up to 25% and more preferably in the order of 10-20%. The liquid or gaseous fuel can be injected directly into the combustion chamber means just before, in the case of a piston engine, its associated piston reaches top dead centre. In a preferred embodiment, means are provided for

regulating the relative quantities of liquid or gaseous fuel and powdered fuel, in order to achieve a desired total fuel quantity/air ratio in the combustion chamber means, prior to ignition.

In preferred embodiments, the internal combustion engine is based upon a gas turbine, is a spark ignition reciprocating (piston) engine, or a diesel reciprocation (piston) engine. Preferably, the engine is a diesel.

In accordance with a second aspect of the present invention, there is provided a method of scrubbing carbon dioxide from a gas, comprising passing the gas through an aqueous solution containing carbonate ions, to form aqueous bicarbonate ions, and then converting the bicarbonate ions back ^' into carbonate ions by exposing the aqueous solution to a photosynthesising organism, under conditions which enable the organism to extract carbon dioxide from the bicarbonate ions. Thus, this aspect of the invention provides a method whereby carbon dioxide can be removed from a gaseous product and fixed into a non-gaseous organic form, where it cannot contribute to the green house effect .

In a further aspect of the invention, there is provided a method of scrubbing carbon dioxide and NOX from a gas, comprising passing the gas through an aqueous solution

containing carbonate ions, under conditions wherein carbon dioxide and NOX are scrubbed from the gas to produce an aqueous solution containing bicarbonate, nitrate and/or nitrite ions. Preferably, the aqueous solution of bicarbonate, nitrate and nitrite ions is exposed to a photosynthesising organism, under conditions which enable the organism to extract carbon dioxide and nitrogen from the solution. An advantage of this aspect of the invention is that it can be employed to eliminate, or reduce the amounts of the pollutant gases, carbon dioxide and NOX, released into the atmosphere from a combustion process .

Preferably, the gas scrubbed in the methods in accordance with the aforementioned two aspects of the invention is an exhaust gas from a combustion process.

In an embodiment, the gas is contacted with the aqueous carbonate solution in a packed absorption column and, preferably, the conditions in the column facilitate a reaction between nitrogen dioxide in the gas with the dissolved carbonate ions to produce bicarbonate, nitrate and nitrite ions. More preferably, the gas includes oxygen and the conditions within the column are arranged to cause nitrogen oxide in the gas to be oxidised into nitrogen dioxide which, in turn, can react with the dissolved carbonate ions in the aforementioned manner.

In preferred embodiments of the method, in accordance wit the aforementioned aspects of this invention, th photosynthesising organism. is an algae, preferably of th chlorella family and more preferably, chlorella pyrenoidosa. Preferably the aqueous solution exposed to the alga includes further nutrients useful for feeding the algae. I a preferred embodiment, the algae are exposed to the aqueou solution of bicarbonate and, optionally, nitrate and nitrit ions in cultivating means which, preferably, is photobioreactor of the aforementioned type.

In a further aspect of the invention, there is provided method of operating an internal combustion engine, comprising fuelling an internal combustion engine i accordance with the first aspect of the invention wit powdered algae, preferably of the chlorella family, mos preferably, chlorella pyrenoidosa. In a preferred form o the inventive method of scrubbing carbon dioxide and/or NO from a gas, the gas is an exhaust gas from an interna combustion engine in accordance with the first aspect of th invention, or it is derived from a method of operating a internal combustion engine in accordance with the previousl described aspect of the invention.

The invention also provides a method of power generatio

comprising operating an internal combustion engine in accordance with the aforementioned method and scrubbing carbon dioxide and/or NOX from the engine's exhaust, in accordance with one of the aforementioned methods for so doing. In an embodiment of this aspect of the invention, the aqueous bicarbonate and, optionally, nitrate and nitrite solution is passed into algae cultivating means as a nutrient solution and algae are harvested from said cultivating means and used by the internal combustion engine as the powdered fuel. Preferably, the algae are dried after being harvested and, more preferably, the dried algae are milled or otherwise comminuted. The means employed to comminute the algae must be selected to avoid the possibility of causing the dry algae to explode as it is being processed. Most preferably, the comminuted algae are metered into the engine's inlet tract means, by the fuel induction means, as a suspension of algae in air and, optionally, a liquid or gaseous fuel can be metered into the combustion chamber means, or inlet tract means, in addition to the powdered algae.

Apparatus for carrying out methods in accordance with the invention can comprise an internal combustion engine, an absorption column, algae cultivating means, algae harvesting means and means for drying the harvested algae.

In a preferred embodiment, the present invention provides power generation system comprising a diesel (or spar ignition) internal combustion engine, utilising powdere algae as a fuel, wherein, the fuelling system involve "carburetting" the algae into the engine. The algae can b dried, comminuted (if required) , and suspended, at hig density, in air and this suspension can then be treated a if it were a gaseous, or liquid fuel in a gas or gasolin powered engine. The dense algae in air suspension can b injected, or actually carburetted, into the air strea flowing through the engine's inlet tract, so as to form homogenous, but less concentrated, suspension of algae i air (similar to the homogenous mixture of gas or gasolin and air which is drawn into a gasoline engine) which, whe drawn into a cylinder within the engine burns in sufficiently homogenous manner to allow the engine to b controlled by throttling. Thus, the dense suspension o algae and air can enter the inlet tract before the engine' inlet valve, in contrast to the situation in the direc injection diesel, where the fuel enters the cylinde directly.

In a preferred form, when diesel oil is injected into th engine in order to ignite the algae, the oil is injecte directly into the cylinder, just before its associε.te piston reaches top dead centre. Where the engine is bein

used in conjunction with algae cultivating means fed with a nutrient solution derived from scrubbing carbon dioxide and NOX from the engine's exhaust, the amount of "ignition" oil can be altered, so as to .balance the engine's output of carbon dioxide with the growing algae's demand for carbon. Also, the ignition timing may be varied, by adjusting the timing of any injection of ignition oil, or igniting sparks, in order to vary the NOX output, to suit the growing algae's requirements for nitrogen.

The inventive methods of scrubbing carbon dioxide and/or NOX from a gaseous product involves the ability of, preferably, metal carbonates and bicarbonates (exemplified herein by the potassium salts) to provide a buffer "storage" of carbon dioxide. The carbon dioxide is absorbed by a potassium carbonate solution which, preferably, is moved through the packed absorption column, in counterflow to the flow of carbon dioxide containing exhaust gases, and then passed on to the algae. The reaction is as follows : -

K ₂ C0 ₃ +H,0+C0 ₂ →2KHC0 ₃ (I)

In daylight, when the algae are growing and can absorb carbon dioxide from this aqueous nutrient solution then, providing the pH is held at the correct level to ensure equilibrium, this reaction will reverse, releasing carbon

dioxide to the solution. From a consideration of simpl stoichiometry, it can be seen that a concentration of 10k of potassium carbonate per tonne of aqueous solution wil give a "storage" capacity of approximately 3.2kg of carbo dioxide - effectively increasing its solubility by ove 150%.

A major advantage of the use of a packed absorption colum in this aspect of the invention is that the mass transfe coefficient for C0 ₂ absorption in a packed column is 2- times higher than if water was used alone. This results i a proportionate reduction in the packed column volum necessary to absorb the same quantity of carbon dioxide.

Algae contains between 6 and 11% nitrogen and, when used a a fuel for an internal combustion engine, as preferred i the various aspects of this invention, its exhaust gases ar rich in nitrogen oxides . Most of these oxides will be i the form of insoluble nitric oxide (NO) . However, as th gases are rapidly cooled in the absorption column, th reaction: 2NO + 0 ₂ →2N0 ₂ (II) will occur as excess oxygen i present in the atmosphere in the column. Since N0 ₂ i removed, as it dissolves in the aqueous carbonate solution this reaction will proceed to the right in accordance wit its equilibrium constant. The reaction is facilitated b the fact that the residence time in the absorption column i

relatively long due to the low mass transfer coefficients associated with carbon dioxide absorption. Where such a column is not used, this reaction can be facilitated by other means which provide appropriate conditions, similar to those in an absorption column.

The reaction of N0 ₂ in solution favours reaction with the carbonate content as the more alkali ingredient than the bicarbonate, as follows:

2NO ₂ +2K _? C0 ₃ +H ₂ O→2KHC0 ₃ +KN0,+KNO, (III)

or, if the solution is fully saturated with carbon dioxide:

2N0 ₂ +2KHC0 ₃ →KN0 ₃ +KN0 ₂ +2C0 ₂ +H ₂ 0 (IV)

Both nitrate and nitrite are assimilable by the algae as a nitrogen source, thus enhancing the economics of the process by reducing or eliminating the necessity of providing a soluble nitrogen source.

There are several techniques available to present micro- algae for consumption as a solid fuel in an internal combustion engine. Common to most is a double vessel with lock hopper between them (as in a blast furnace) . This

provides continuous output with intermittent charging. The algae is fed from the lower vessel into an air stream provided by a fan or a compressor, depending on the pressure requirements (see below) . The vessel, for preference, must be capable of continuously weighing, in order to accurately meter the algae flow. This can be achieved by the use of suitably located load cells. Such machines include the batch injectors with 'rotofeed' sold under the Trade Mark RO'iOFEED by Simon Macawber Ltd., of Shaw Lane Industrial Estate, Doncaster, South Yorkshire DN2 4SE, England.

The resultant algae/air mixture may be at a concentration of between 0.5 and 3.0kg of algae per normal cubic meter of air. The size distribution requirement of algae is dependent upon the speed of the engine in reciprocating engines, and the volume and configuration of the combustion chamber(s) in a gas turbine. Algae of 100% less than 45 micron particle size has been found to give adequate performance in a 1500 rpm reciprocating engine, and larger particle sizes may be used in slower engines whilst giving adequate combustion performance.

In super-charged or turbo-charged reciprocating engines and gas turbines, the algae can be added after the rotary compression stage and, therefore, the algae/air suspension must be at the inlet manifold pressure in a reciprocating

engine or at the combustion chamber pressure in a ga turbine. Some strains of algae can agglomerate in th feeding process, and it is then desirable to carry out th process in reciprocating .super-charged or turbo-charge engines by introducing the algae/air stream at the centre o the compressor intake, at or near ambient atmospheri pressure. This has the effect of disagglomerating th algae.

In gas reciprocating engines, normally burning natural liquid petroleum gas ignited by an electrical spark, the gas is normally metered into the air stream and mixed therewit in a venturi and the resulting mixture is subsequentl throttled before induction into the engine via an inlet manifold and valves. Such an engine may be directly use for algae firing, with a high concentration (approximatel 1.2-2. Okg/m ³ ) of algae in air, directly substituting for the gas and with a similar apparent calorific value on a volume basis. Since gas engines normally exhibit near-homogenous combustion, control is implemented through throttling. Wit algae firing, combustion can be treated as if it is essentially heterogeneous and, therefore, control can be exerted, down to below 60% power by means of fuel qualit control, as in a diesel engine, - i.e. by passing the same quantity of unthrottled, normal combustion air and reducing the quantity of highly-loaded air/algae mixture. This can

result in a more favourable part-load fuel consumption whe compared with throttling. However, because, in accordanc with the invention, the algae/air mixture flowing into th combustion chamber is homogenous, further control can b exerted by throttling, enabling both the engine's output t be more finely controlled and dual fuel, i.e. algae/gas, operation of the engine.

In an oil/gas dual-fuel engine, the machine is a diese based higher compression machine than a gas engine. The ga is normally, but not exclusively, delivered by supplementary gas inlet valve which opens only when th exhaust valve is shut. Ignition is achieved by injection o oil through a diesel injection system. This machine, wit modifications to the oil injection events, to ensure correc combustion of the algae, is suitable without significan further modification; the algae again being supplied a approximately 1.2-2.0kg/m ³ concentration to the gas inle valve, and at or about air inlet manifold pressure. Th point, flow and duration of injection for optimu performance is a function of engine speed, combustio chamber configuration, algae size distribution and strain. It is best determined empirically.

An oil fired diesel engine may be readily modified for alga fuelling. As with the gas/oil dual-fuel engine, th

injection system must be modified. Again, the point, flow and duration of injection required for optimum performance is a function of engine speed, combustion chamber configuration, algae size .distribution and strain, and is best determined empirically. Diesel engines require one further simple modification; that of reprofiling the cams or otherwise modifying the valve actuating means to eliminate inlet and exhaust valve overlap. This is advisable because the algae is generally introduced with the air, either at or near atmospheric pressure (i.e. before or after any turbo- charger as discussed above) . Elimination of valve overlap prevents potential algae loss directly to the exhaust valve. Providing the algae stays within the flammability limits on introduction via the inlet valve, there are no restrictions on the algae/air ratio from the supply system, as simulation of gaseous fuel is not required. In order words, any extra air used in carrying the algae can substitute for normal air intake.

A small scale power generation plant, employing various aspects of the present invention will now be described, by way of example only and with reference to Figure 1.

Figure 1 is a schematic diagram of a power generation plant

The system uses algae, or biomass, as a fuel to generate

electricity. The plant comprises a settling tank 1, a peristaltic pump 2, a continuous centrifuge 3, a first screw conveyer 4, a screw feed drum drier 5, second screw conveyor 6, a storage silo 7, a shear mill 8, a third screw conveyor 9, a continuous output powder feeder 10, an exhaust gas turbo-charger 11, an air intake filter 12, a 150kw six cylinder 1500 rpm diesel engine 13 and a generator 14. Further components of the plant, which are not shown in Figure 1, include absorption columns and photobioreactors (Biocoils) . The various components of the plant and their function with the plant in operation will now be described in detail. Unless otherwise stated all flow rates etc. are for full load, with the diesel engine 13 running at 1500 rpm and producing 150kw. The arrows used in figure 1 show the flow directions when the plant is in operation.

Chlorella microalgae are cultivated in a farm of photobioreactors, of the aforementioned type. A slurry of chlorella microalgae, suspended in water (6gm/l) is pumped into the settling tank 1 at a rate of 1.66 litres per second, via an inlet conduit 15. The flocculated algae are drawn from the bottom of the settling tank 1 by the peristaltic pump 2 and fed by the latter into the continuous centrifuge 3. The nutrient solution, from which the algae have been separated, is drawn of: ^* : from the settling tank 1 and fed to the absorption columns, via conduit 16. The

peristaltic pump 2 is of a type manufactured by Lowara (UK) of Millwey Rise Industrial Estate, Axminster, Devon EX13 5HU, England, under the model No.A 1CD. The flocculated algae are pumped into the continuous centrifuge 3 at a rate of 360 litres per hour and the centrifuge 3 reduces the moisture content of the algae from 6:1 to 4:1. The water removed by the centrifuge 3, is returned to the settling tank via conduit 17. The centrifuge 3 cannot remove any more water from the algae because a large proportion of the water in the algae is contained within this cell walls.

The algae are fed from the centrifuge 3 by the screw conveyor 4, in the form of a soft cake and at a rate of 50g per second, into the screw feed drum drier 5. The algae cake fed into the drum drier 5 has a viscosity of approximately 2 POIS and a moisture content of approximately 59% wwb. The particle size is between 15 and 80 microns and the cake is slightly sticky. The screw feed drum drier 5 is of a type available from APV Pasilac Limited of Denton Holme, Carlisle, Cumbria CA2 5DU, England (Mitchell Drier) of approximately 5m in length and is of a directly heated rotary type. The drier 5 uses cooling water from the diesel engine 13, at approximately 106°C and exhaust gas at approximately 600°C, via suitable heat exchangers, as its heating medium.

The dried algae are transferred from the screw feed drum drier 5, via the screw feed conveyor 6, at a rate of lOgms per second and at a moisture content of less than 8%, into the silo 5. Water vapour escapes from the drum drier 5 at a rate of approximately 0.04kg/seconds from outlet 18. The algae feed into the silo 7 can have a moisture content between 1 and 10%. Above 10% moisture, the algae cannot be stored without agglomeration and below 10% moisture, the algae can be stored for up to four years .

The algae are fed under gravity from the silo 7 into the shear mill 8, where they are milled. The shear mill 8, is a classifier mill of a type manufactured by Condux and available from Vanward, Kynance House, The Vale, Chalfont St. Peter, Buckinghamshire SL9 9SD, England, under model No. CSM165. The algae are milled because, during the drying process, polysacharides migrate to the cells' surfaces and they are caused to stick together. The shear mill 8 separates the cells and provides a fine powdered output in a size range appropriate for combustion. Appropriate particle size ranges for various engine operating speeds are as follows:

ENGINE SPEED PARTICLE SIZE

RPM min. mean max. 1500 5 20 40 (All values

900 40 45 65 are in

375 65 70 100 Microns)

80 15 120 140

Thus, the preferred mean particle size for the engine 13, when operating at 1500 rpm, is 20, +20, -15 microns.

The milled algae are conveyed, via the screw conveyor 9 into the continuous output powder feeder 10. This unit is a controlled delivery system for supplying the algae into the engine. It consists of two chambers or hoppers 19 and 20 with shut-off valves 21 and 22 and a "rotofeed" unit 40. Material is transferred from the first hopper 19 to the second 20, via the valves 21 and 22 and finally dispensed from the base of the second hopper 20, via the rotofeed unit 40. The algae are fed into the first hopper 19 in 50 kg batches every 85 minutes. The algae are fed as a high density suspension in air at a rate of lOgms per second from the feeder 10, into the eye of the compressor within the turbo-charger 11, via a 10mm diameter steel conduit 23, where the algae are suspended in the air being drawn through

the turbo-charger 11. The rate at which the feeder 10 dispenses the algae can be varied, in order to impart a control over the engine 13. The high density suspension of algae in air, fed from the feeder 10, into the turbo-charger 11, has a density of approximately 1.5 kg/m ³ and a calorific value of approximately 24MJ/kg. The turbo-charger 11 draws in air through the air filter 12 and pumps algae suspended in the air into the engine 13 through the inlet manifold 24, past the inlet valves (not shown) and into the cylinders (not shown) .

The exhaust gas from the engine 13 flows through the exhaust manifold 25 to the turbo-charger 11 and drives the turbine, within the latter. The exhaust gases leave the turbo- charger 11, via conduit 26 and is fed into a heat exchanger, (not shown) from which heated water is pumped to the drum drier 5. The exhaust gases are then passed through packed absorption columns (not shown) through which nutrient solution, for supplying the photobioreactors, is passed. The nutrient solution includes carbonate ions and the conditions within the packed absorption columns are selected in order to scrub carbon dioxide and NOX from the exhaust gas, into the nutrient solution.

The absorption columns comprise two cylinders; of approximately 8m in height and 0.8m in diameter, with a grid

at the bottom. Packing material is placed on the grid to fill the entire space within the cylinders. The packing material may be washed coke or similar, preferably 50mm interlocking berl saddles,, ceramic for the bottom lm and plastic for the remainder. The gas inlet temperature is approximately 150°C and the flow rate is 0.47kg per second. On a dry weight basis, the gas entering the absorption columns comprises 79% nitrogen, 12% carbon dioxide, 1% carbon monoxide and NOX and 8% oxygen.

The engine 13 is a Perkins model 1306 TAG, six cylinder in line turbo-charged and after-cooled diesel capable of producing approximately 150kw of electrical power. The engine 13 is of standard construction with standard injection equipment and mechanical governor. The turbo- charger 11 operates in a conventional manner.

To start the plant, the engine 13 is firstly started and run at 1500 rpm on diesel oil, employing the standard diesel injection equipment. Algae are then introduced into the turbo-charger 11, at an initial rate of approximately 2.5gms per second. The effect of the algae entering the engine's cylinders and combusting causes the engine 13 to overspeed. The governor then pulls back the diesel injector rack and reduces tre amount of diesel injected into the engine 13. As more algae are introduced into the engine 13 ,

overspeeding is controlled by the governor and the amount of diesel injected is further cut back. Thus, by experiment, a direct relation of weight of algae to load and diesel reduction can be deduced .and the feeder 10, calibrated accordingly. Continuous control of the quantity of algae can be carried out by analysing the carbon monoxide content of the exhaust gas, with a feed back loop set up to control the feeder 10. 50% of the power of the engine may be controlled by algae introduction, the other 50% controlled by throttling the air entering the turbo-charger 11, using a throttle control valve (not shown) , in order to keep the critical air fuel ratio correct.

At full load the 150kw engine uses approximately 56 kg of algae per hour, which constitutes 90% of the fuel used, the remaining 10% being diesel oil.

The carbon dioxide and nitrogen dioxide taken up into the algae nutrient solution raises the algae productivity and the exit gases, from the photobioreactors and absorption columns have virtually the same composition as the air used in the engine 13, because oxygen is produced by the photosynthesis occurring in the photobioreactors. In overall terms, the system can provide 90% of its output "free of charge" as it effectively converts sunlight into electricity. The plant can be run on a 24 hour basis, with

night-time running (when no algae are produced) on stored algae. The number of photobioreactors used (40) allows over production during daylight hours and sufficient algae may be stored for night time running.