FR2720566A1 - Gas-fired power station connected to mains network - Google Patents

Abstract

A gas-fired power station connected to a mains network is claimed. The power station has several gas engines. Heat generated by the engines is recovered from the water cooling circuit and/or the flue gas circuit. The flue gas is evacuated into a condensation tower, where it is cooled by a low-temp. primary water circuit which condenses steam from the flue gas, facilitating the recovery of latent heat and the dissolution of CO2. CO2 is used in the prodn. of inorganic carbonates, in organic chemistry(e.g. in the synthesis of hydrocarbons or urea), in photochemistry, biochemistry or biotechnology (e.g in photosynthetic or fermentation processes). The heat recovered is used to generate additional electricity or is used to supply a heating or air-conditioning network.

Description

BACK-UP POWER PLANT OPERATING ON GAS AND
ITS USE IN COGENERATION
The present invention relates to a back-up power station operating on gas, as well as to the use of such a power station for the cogeneration of electrical energy and of other energy, for example thermal, chemical, physical energy. -chemical...

 Currently, in most industrialized countries, most of the electrical energy is produced by three types of power plants, namely traditional thermal power plants operating on coal or oil, hydroelectric power stations and nuclear power stations.

 We know all the problems that nuclear power plants can pose, in their operational safety first and in the problem of radioactive waste storage afterwards. This is why this type of power plant is increasingly provoking, rightly or wrongly, the hostility of the public and sometimes of certain scientists. In addition, for the profitability to be suitable, the nuclear power stations must be of the greatest possible power, which leads to concentrate the production of electricity in a minimum of sites which, for safety reasons always, must be the as far as possible from the places of dense population and, consequently, very often far from the places of industrial consumption where this population works.

 The result is that the ground is covered with unsightly high-voltage lines, which are all the more enormous as the electrical energy to be transported is high (notably in the case of nuclear power plants), arousing more and more opposition from the large public who complains at the same time of the disfigurement of the landscapes and of the little known and suspected consequences that they could have on the health of those who live nearby, even if it is only suspicion.

 There is therefore an imperative need to produce electrical energy as close as possible to the places of consumption, which amounts to multiplying the places of production by correlatively reducing the powers involved. It is better to have a lot of power plants, of the mini-central type, of little power than few very large power plants each.

 There already exist mini-power stations and back-up power stations, so called when they are connected to the main electrical network, which generally run on coal or fuel oil, like conventional thermal power stations, or which are installed on secondary rivers on small dams or on the water.

 Coal-fired or oil-fired back-up plants, polluting fuels often rich in sulfur derivatives for example, pose problems of profitability, due to their low power, compared to large power plants. They pose exactly the same pollution problems, in particular atmospheric pollution as large thermal power plants, especially since their low capacity does not generally make it possible to amortize the costs of a pollution control installation. As for hydroelectric back-up plants, they are also criticized by nature conservationists, accused of distorting the landscapes, and by fishermen, who see their fishing sites seriously disturbed.

 The present invention aims to solve these problems by proposing an auxiliary power plant, the main characteristic of which is to operate with abundant and non-polluting energy, gas, it being understood that it will preferably be, whenever this is possible, natural gas.

 Natural gas is a promising product with the world's largest reserves among fossil fuels (oil, coal). It is a clean, ecological product whose molecular components (carbon and hydrogen) form the basis of organic chemistry. It is found in its natural state, associated with few polluting elements: sulfur, chlorine, vanadium, nickel, chromium. Its combustion releases significant energy which can be used in mechanical or electrical form, as well as natural elements, water vapor, carbon dioxide which are perfectly usable or recyclable.

 It should also be known that the demand for electricity is often high in winter because of the heating and lighting services which are added to the usual needs linked to economic activities. Up to now, it has been hydraulic, thermal and nuclear power stations which have filled this role with the hazards linked to the transport of energy by high voltage line.

 Peak energy is not transported or is difficult to transport because at this time the networks are saturated, hence the inevitable risks of network cuts or malfunctions. It is therefore necessary to produce either near the places of consumption, or in the vicinity of the interconnections for reasons of securing the switchable network.

 In addition, the natural gas network through buried conduits is already distributed in a star in areas of high energy demand. There is therefore a correlation between the demand for electrical energy and the presence of gas. We thus have the assurance of production and flow "on site" by overcoming the constraints of overhead lines damaging to the environment, aesthetics or saturation.

 The electrical energy produced by the auxiliary plant according to the invention is coupled to the main network, and the plant can be equipped with devices making it possible to recover also and in particular the thermal energy produced, for example for district heating, since it will be installed where the need arises, that is to say in urbanized and densely populated areas. The backup plant can also be equipped with devices for recovering combustion gases, essentially carbon dioxide, since the combustion of natural gas does not lead to the formation of highly polluting products, at least not in the proportions associated with combustion fuel oil or coal. This carbon dioxide can be recovered in the form of chemical or physicochemical energy to supply industrial consumers located nearby.

 It will be understood that the auxiliary power station according to the invention is intended to be installed on sites where the need for electrical energy is greater than normal and can be difficult to supply by the main electrical network, on pain of low profitability. or risks to the main network. As already indicated above, these sites will mainly be urbanized and industrialized sites, precisely where the need for other types of energy, thermal or chemical, is also felt.

Such a power plant can be considered as an "energy point" located near the source substation installations of the main electrical network and gas expansion stations supplied by gas pipelines.

 Another advantage of such a back-up unit is that it is easily controllable, due to its low power and that it can therefore be fully automated and switched remotely, requiring a minimum of surveillance personnel and not involving more than low insurance costs.

The present invention will be better understood with reference to the accompanying drawings, given by way of nonlimiting examples. In these drawings
FIG. 1 is a plan view of a natural gas backup plant according to the present invention,
FIG. 2 is a block diagram explaining how to recover the heat generated by the power station, for district heating for example,
FIG. 3 is a block diagram explaining how to also recover the energy contained in the carbon dioxide produced, for industrial use in chemistry,
FIG. 4 explains a principle of cogeneration in which the thermal energy recovered at the end of the production of electricity by a steam turbine is used to also produce electricity, and
- Figure 5 explains a principle of cogeneration in which the energy recovered after the production of electricity is used both to produce electricity, but also to supply a heating network and an air conditioning network.

 As can be seen in FIG. 1, the natural gas backup plant comprises a plurality of gas engines, in this case eight, of the conventional piston type.

The gas engine is first of all a powerful tool for transforming the methane molecule through its thermodynamic cycle with high energy efficiency. It is a thermal machine that is both clean and economical, with great reliability and longevity.

 The air-gas mixture is compressed during the compression stroke of the piston and the ignition of the mixture is carried out by a spark produced by a spark plug or by a pilot injection of a fuel which self-ignites before top dead center . For engines that use spark ignition, this is generated by a low voltage magneto and electronic contactless switch. A Ruhmhoff cylinder type transformer transforms the low voltage pulse into high voltage. One coil per spark plug and one spark plug per cylinder is used.

 The gas engines of the plant, advantageously with a unit power of 1 MW, are each connected to a 50 Hertz / 400 volt alternator.

 Alternatively, the gas engines are gas turbines.

 The electrical power output from the alternator is then raised to a voltage of 20 kV by a three-phase transformer to be delivered to the distribution network (high-voltage interconnection and distribution service).

 As can be seen schematically in FIG. 1, the auxiliary power station is located in a building represented by the general reference 1, in which there is an electrical room 2 allowing the electrical control of the various installations present in building 1, as well as connection to the main electrical network. There is also a gas room 3 comprising a regulator.

 Another room 4 includes a waste oil tank 5 and a new oil tank 6 for supplying the members to be lubricated, in particular the 8 gas engines 8 placed in a main room 7. This main room is provided of soundproof doors 9 and equipped with sound traps 10 8 in number, that is to say in a number equal to that of gas engines. Finally, there is in building 1 a room 11 serving as a maintenance room and a room for staff. It should be specified here that the references 8 each represent a heat engine provided with its generator.

 It will have been checked beforehand that the power called on the 20 kV distribution network is always higher than the power delivered by the backup power plant.

This is indeed the basic condition for good economic functioning in the winter period (from November 1 to March 31).

 The total power of 8 MW delivered during periods of high consumption at the places of use makes it possible to significantly mitigate the phenomena of "blackouts" detrimental to the quality of the network, particularly in industrial, tertiary or technological hubs.

The operating cycle of the 24-hour continuous electric power plant throughout the winter period is particularly suitable for the implementation of all thermal energy recovery projects, as we will see. Two main sources are captured
- the engine water circuit ensuring the evacuation of calories from the combustion chambers, cylinder head, pistons, etc.
- the engine heating gas circuit.

 A suitable arrangement is shown in Figure 2. It includes for each group of four engines first a primary plate heat exchanger having the dual function of preheating the steam production water to 15/80 0C and feeding a 70 / 750C district heating network.

 It then includes a steam production circuit, the essential component of which is a boiler with smoke tubes or water tubes with integrated circulation pump.

 Different installation circuits are shown to ensure the safe operation of the motors.

 Thus, as can be seen in this FIG. 2, the motors 8 are grouped in groups of four and are each connected by outward and return lines 13 via a thermostatic valve (VT) 14 to an air cooler 15.

 From the thermostatic valve (VT) 14 go the outward lines 16 and return 16 'which, past another valve 17, continue by outward lines 19 and return 18, through a valve 20, and outward lines 22 and return 21 passing by an interconnection valve of the remote heating and heating network (CAD) 23 and entering via outward and return lines 24 into a plate exchanger 26 supplied with cold water 27. From this plate exchanger 26 also leaves the hot circuit, serving preheating with water at 70 / 800C and feeding a tank 29 of hot water for domestic use. From this tank 29 leaves a line 30 which enters a boiler with smoke tubes 31, which makes it possible to generate and deliver by a line 32 steam under pressure, for example at 1950C at 13 bars, as well as combustion gases at 2300C by a line 33,34,35 going to a diffuser 45.

 On the valve 17 are connected outward 37 and return 36 lines which allow all the motors 8 to be connected by the same circuit. Each motor is moreover provided with a non-return valve 38, which by a line 40, leads to a thermally insulated expansion pot 40 at around 5000C from which a line 41 leading to the smoke tube boiler 31 leaves on the one hand and a line 42 passing through a motorized valve serving as a bypass valve 43 on the other hand line 44 joining line 33,34,35 towards the diffuser 45.

 It will thus be understood that, by this circuit, it is possible to produce both hot water for domestic use (tank 29), hot water under pressure for industrial use (CAD circuit) and steam under pressure for industrial use (circuit 32).

Advantageously, the exhaust gases from the heat engine are evacuated to a condensation tower cooled by a primary water circuit at low temperature and making it possible at the same time to recover the latent heat of vaporization of the water vapor contained in the exhaust gas according to basic reaction
CH4 + 202 = CO2 + 2H2O and at least partially dissolve the carbon dioxide CO2.

In this way, the carbon dioxide present in the exhaust gases is not released into the atmosphere, which contributes to reducing the greenhouse effect.

This recovery can be associated with the use of the CO2 molecule. Three channels are described in Figure 3, where for the sake of simplification in order to facilitate understanding, no reference figure has been assigned to the connection lines which explain themselves
- mineral chemistry sector with production of carbonated products CaCO3, NaCO3, usable in particular in the treatment of acidic soils,
- organic chemistry sector, with production of heavy CH lines, urea, etc.,
- biochemistry sector.

 The gas engine 8, supplied with energy E in the form of natural gas, directly supplies the electrical transformation energy 46 to the network, the heat released being exploited in a recuperator 31, already mentioned, for the production of industrial steam 47. A steam turbine 48 coupled to the recuperator 31 makes it possible to recover an additional electrical energy 49. The gas engine 8 also allows the generation of domestic hot water in the tank 29 intended for example for district heating at a distance.

 The energy thus recovered is essentially thermal or caloric energy. The combustion of natural gas (CH4 hydrocarbon and higher counterparts) produces carbon dioxide CO2 and water H2O which can be directed to a condensation tower 50 which makes it possible to recover a solution of carbon dioxide in water, usable as it is. .

However, the carbon dioxide CO2 can also be recovered in a mineral chemistry sector, using reactors 51 for the manufacture, for example, of calcium carbonates or sodium carbonates. It can also be used in an organic chemistry sector, in particular in reactors 52 of a process allowing the production of urea. It can finally be directed to a biochemical sector using reactors 53 in which, by supplying oxygen, and where appropriate, photochemical energy, it is possible to carry out various operations
- cultivation of algae in a marine environment or in fish farming,
- treatment of waste water or water loaded with organic products such as slurry.

It will be observed that these different channels can be combined with one another or one or the combination of these makes it possible to consume all or part of the carbon dioxide produced, which means that in any event, the gas dissolved carbon dioxide which could be discharged into the water at the outlet of the condensation tower 50 is very diluted, enough to be eliminated without causing environmental problems
As seen in Figures 4 and 5, the base plant described above, with the same set of eight 8 kVA (Po) reciprocating motors (only one of which is shown) powered by natural gas E for the production of electricity delivered to the distribution network, can be used for combined cycle cogeneration, allowing the supply of a force electrical network (figure 4), which can be associated with a heat or air conditioning network by using the Carnot cycle (figure 5) .

In these two figures, which take up elements from FIG. 3, a so-called condensing steam turbine 54 working in closed loop allows, after the main electric power production 46, the production of complementary electric energy 49, thus improving the efficiency. overall installation. This turbine 54 is supplied with high pressure steam by a boiler for recovering energy from the exhaust gases, which can be a single or double recovery stage, for example a stage 55 for producing steam, recovering energy P2, and a stage 56 for producing superheated water, recovering energy P3
For supplying the heat network, a main exchanger 57 recovers the heat energy P1 from the engine water, T1 and T2 being the outlet temperatures of the exchanger 57 and Tg the inlet temperature.

 The water is superheated through stage 56 of the recovery boiler and stores energy P3 which brings it to a temperature T3.

 Depending on the climatic conditions, an auxiliary boiler 58 brings the heat transfer fluid from the heat network to temperature T4, the heat output of which is then P6, sum P1 + P2 + P3.

The air conditioning network is supplied by two energy sources depending on the system used - absorption system: thermal energy P7 from the auxiliary boiler 58 powered by natural gas, - refrigeration compressor system: electrical energy
P4 of the steam turbine 54, all of the parameters being able to be controlled separately according to the conditions of use (variable heat or cold demand).

 It will be noted in FIG. 4 that the transition from temperature T2 to T3 is carried out using a condenser / air cooler, the circuit being closed on stage 56 by means of a water tank 60 and d '' a lift pump 61.

In summary, the balance of the installation of Figure 5 for example is as follows
cogeneration: mechanical energy Po + P4
heat P1 + P3
rate of return: E / (Po + P1 + P3 + P4)
heat network: P6 = P1 + P3 + P5
air conditioning network: P8 = P4 + P7
electrical network: Po + P4
This leads to installations that can reach energy yields of 80 to 90%, which is the best response to environmental protection with regard to the use of energy.

Claims (10)

1. Power station, characterized in that it is a back-up power station coupled to the main electricity network and that it operates on gas. 2. Auxiliary power plant according to claim 1, characterized in that it operates on natural gas. 3. Auxiliary power plant according to claim 1 or 2, characterized in that it consists of a plurality of gas engines. 4. Auxiliary power plant according to one of claims 1 to 3, characterized in that it comprises means for recovering the thermal energy generated. 5. Auxiliary power plant according to claim 4, characterized in that the means for recovering thermal energy are placed on the water circuit of the motor or motors which ensures the evacuation of calories. 6. Auxiliary power station according to claim 4, characterized in that the means for recovering thermal energy are placed on the engine exhaust gas circuit. 7. Auxiliary power plant according to claim 6, characterized in that the exhaust gases from the heat engine (s) are evacuated to a condensation tower cooled by a low temperature primary water circuit, which allows everything to times to recover the latent heat of vaporization of the water vapor contained in the exhaust gases and to at least partially dissolve the carbon dioxide. 8. Auxiliary power plant according to claim 7, characterized in that it comprises means for the transformation of the recovered carbon dioxide for its use in mineral chemistry for the production of carbonate products, in organic chemistry for the production of heavy CH lines, urea lines, etc ..., in photochemistry, and in biochemistry or biotechnology by photosynthesis or fermentation. 9. Use of the auxiliary power plant according to one of claims 4 to 8, in the cogeneration of electrical and / or thermal and / or chemical and / or biochemical energy. 10. Use according to claim 9, characterized in that the energy recovered after the main electrical production is used for additional electrical production and / or for supplying a heating or air conditioning network.