METHOD FOR SECURING A COMBUSTION OR GASING PLANT AGAINST FIRES

Abstract

The invention relates to a method for fire-resistant protection of a solid fuel combustion or gasification plant (2) (3) comprising a combustion chamber (1) for the solid fuel (3), said chamber (1) being supplied with solid fuel (3) by a fuel supply system (4). The invention is characterized in that it comprises the following steps: injecting a non-flammable liquid into the fuel (3) contained in the fuel supply system (4); forming a plug (7) of fuel (3) in the fuel supply system (4); and creating a fuel-free space (8) in the fuel supply system.

Description

FIELD OF INVENTION

[0001] The present invention relates to the field of energy, and, more specifically, to installations operating on the basis of combustion, gasification, or any other thermochemical process involving solid fuels.

[0002] It relates more specifically to a method of securing a solid fuel combustion or gasification plant against fires, said plant comprising a solid fuel combustion chamber, this chamber being supplied with solid fuel by a feeding system.

[0003] It also concerns a solid fuel combustion or gasification plant equipped with means for implementing the aforementioned safety process. EARLIER ART

[0004] Industrial solid fuel combustion or gasification plants, such as those using biomass, present fire risks, just like gas or oil-fired power plants. Even though the risk of explosion is minimal in solid fuel combustion or gasification plants, it still exists due to the presence of dust and the possibility of combustible gas leaks from the pyrolysis of the solid fuel.

[0005] Furthermore, one of the highest-risk areas in solid fuel combustion or gasification plants is the fuel supply. Fire can spread in this area, travel up the supply system to the fuel reserve, and cause significant damage to the plant.

[0006] It is therefore necessary to prevent and combat the risks of fire in these power plants.

[0007] For this purpose, prior art has shown that there are power plants equipped with fire protection systems using flaps or guillotines, rotary systems, or systems that directly use conveying means to prevent a fire from rising again.

[0008] Damper systems are the most widespread and certainly the oldest type of fire suppression system. They employ a damper, pivoting around an axis, which, when necessary, blocks the passage between the fire and the fuel supply. US patent document 2873703 illustrates this technology for a coal-fired power plant.

[0009] Guillotine systems are quite similar to damper systems. A major difference between guillotine and damper systems lies in the movement of the damper. In guillotine systems, the damper is guided in translation, allowing the feed system to be separated into two distinct zones. It is essential to couple this type of system with a device that clears biomass to avoid obstructing the damper's movement. Patent document FR2615931 describes such a system. It should be noted that, in a guillotine system, the damper is raised above the rest of the feed to prevent the firestop system from being blocked by excess material. Ultimately, this is an "intelligent" system that automatically restarts when the temperature drops below a certain threshold.

[0010] Rotary systems consist of an assembly that rotates around an axis within the feeding system. Unlike the two previous systems, rotary systems are sealed even during normal operation. They are valve-airlock type systems that ensure material distribution and system sealing. Patent document CN178166860 illustrates this technology. It describes a system composed of an airlock valve located above a hopper to prevent backfires.

[0011] Some technologies directly utilize their feeding device in a mode specifically designed to prevent backdrafts. This is the case, for example, with the system described in patent document RU2287474. This system consists of a feed screw, a thermocouple, and a water injection system. When the thermocouple measures a temperature above the programmed threshold, the screw automatically starts, and the system injects water until the temperature becomes too high. The system thus delivers moistened biomass to the boiler.

[0012] Furthermore, patent document EP3015136 describes a solution for detecting fires in biomass storage using a continuous air humidity analyzer. When biomass burns, the water it contains evaporates, increasing the air humidity level.

[0013] Patent document CN106056824 concerns a redundant and intelligent solution for fire detection and suppression in biomass power plants. It comprises two different sensors: a first set of thermocouples in contact with the biomass and an infrared camera that also detects the start of a fire. The two sensors are connected to an intelligent system that controls a fire suppression device. This device can be used in three configurations, depending on the operator's preference: fully automatic, remotely controlled, or manual.

[0014] Finally, patent document CN202554782 presents a fire suppression device integrated into a biomass feed system. This system consists of three thermocouples installed directly in the biomass feed and connected to regulating valves, which are themselves located on a water injection system. When the thermocouples exceed a set value, the valves open, injecting water into the biomass feed.

[0015] The aforementioned systems, as well as their implementation methods, present numerous drawbacks.

[0016] Solid fuels are highly irregular. Mechanical systems with flaps or guillotines are very often clogged, preventing proper biomass isolation. Furthermore, installing mechanical systems and adapting the feed accordingly is often very expensive. Mechanical systems of the flap and guillotine type require regular maintenance and are prone to failure. Rotary systems disrupt the proper biomass feed and are frequently responsible for blockages and bridging. They are not suitable for irregular fuels. Moreover, a fire suppression system should interact with the combustion chamber as little as possible. It is essential not to inject soggy biomass into the combustion chamber to avoid damaging it or rendering it unavailable for an extended period. SUMMARY OF THE INVENTION

[0017] In view of the above, one problem that this invention proposes to solve is to implement a method for securing a solid fuel combustion or gasification plant comprising a solid fuel combustion chamber, said chamber being supplied with solid fuel by a feeding system, which overcomes the aforementioned drawbacks of the prior art.

[0018] The proposed solution of the invention to this problem has as its primary object a method for securing, against fires, a solid fuel combustion or gasification plant comprising a solid fuel combustion chamber, said chamber being supplied with solid fuel by a feeding system, characterized in that it comprises the following steps according to which: a non-flammable liquid is injected into the fuel contained in the fuel supply system; a fuel plug is formed in the fuel supply system; and a fuel void is created in the fuel supply system.

[0019] Advantageously, - the solid fuel comprises biomass, recovered solid fuels and / or waste - the solid fuel feeding system comprises at least one screw conveyor, the solid fuel being brought to the combustion chamber by said at least one screw conveyor; - the feeding system comprises a first screw conveyor positioned substantially horizontally relative to the ground and a second screw conveyor positioned at the terminal end of the first screw conveyor, and the solid fuel is conveyed, from a fuel storage bin located upstream of the first screw conveyor to the combustion chamber located downstream of the second screw conveyor, by means of the first and then the second screw conveyor;- for the formation of the fuel plug and for the creation of the fuel void in the fuel supply system, said at least one auger is operated in reverse after injecting the liquid into the fuel contained in the supply system; - the solid fuel supply system of the plant further includes one or more sensors, and the process further includes a step in which a flare-up in the fuel supply system is detected by means of said sensors; - the sensors are temperature sensors, CO2 sensors, infrared sensors and / or humidity sensors;- the combustion plant is equipped with an automated system, the sensors communicate with said automated system, and the automated system controls the injection of non-flammable liquid into the fuel contained in the fuel supply system and / or the formation of the fuel plug in the fuel supply system and / or the creation of a fuel void in the fuel supply system; and - the plant further includes a general fire-fighting system comprising sensors arranged throughout the plant, a means of extinguishing fires by spraying the plant with liquid and / or non-flammable gas, and a safety automated system.

[0020] The proposed solution of the invention to the aforementioned problem has as its second object a fire-safe solid fuel combustion or gasification plant for the implementation of the process as described above, comprising a solid fuel combustion chamber, said chamber being supplied with solid fuel by a feeding system, characterized in that it further comprises means for injecting a non-flammable liquid into the feeding system, means for forming a fuel plug in the fuel feeding system, and means for creating a fuel void in the fuel feeding system.

[0021] Advantageously, the feeding system includes at least one auger and at least one non-flammable liquid injector.

[0022] The highest-risk phases in solid fuel combustion or gasification plants are the fire suppression phases. Therefore, to prevent fires during these phases, it is necessary to deprive the system of one of three elements: the fuel, the oxidizer, or the heat source, also known as the triggering element. In solid fuel plants and, more generally, in all thermal power plants, the heat source is present from the start-up phase of the installation until the plant has completely cooled down, which can occur several hours after it has been shut down. Solid fuel is extremely difficult to isolate from air; separating the oxidizer and the fuel under these conditions is not a feasible solution. One objective achieved by the invention is therefore to isolate the fuel from the heat source to prevent any fire from starting.In the event of a fire, the energy released by the reaction between oxygen and fuel sustains combustion. To combat the fire, the invention makes it possible to deprive the reaction of one of these reactants by installing a fire-stopping system. BRIEF DESCRIPTION OF THE FIGURES

[0023] The invention will be better understood upon reading the following non-limiting description, drawn up with reference to the accompanying drawings, in which: there figure 1 illustrates, schematically, a secure control center according to the process of the invention; the figure 2A illustrates, schematically, the conventional operation of a secure power plant according to the process of the invention, detailing the progression of the solid fuel in the feed system; the figure 2B illustrates, schematically, the formation of the plug and the creation of the empty space during the implementation of the process according to the invention; the figure 3is a schematic representation of a possible configuration of an installation for implementing the process according to the invention; and the figure 4 is a flowchart representing the steps implemented in the process according to the invention, following a shutdown of a solid fuel combustion or gasification plant. DETAILED DESCRIPTION OF THE INVENTION

[0024] The method according to the invention is a complete method for preventing and combating fire risk, the main source of this risk being the ignition of fire in a solid fuel supply system in a thermal power plant. This risk exists in several situations, namely, during a shutdown of the power plant during normal operation, or during a malfunction of the power plant which may be due to: - a technical problem with the flue gas extraction system, - the use of fuel unsuitable for the thermal power plant, - human error during the operation of the power plant, or - a failure of the control system which leads to a system shutdown, for example, the shutdown of the fuel supply or the draft fan.

[0025] The invention relates in particular to a method of securing or protecting a thermal power plant for combustion or gasification of solid fuel against fires.

[0026] The solid fuel used in such power plants is, for example, biomass, solid recovered fuels (SRF), and / or waste such as household waste. These are fuels whose structure and nature are not homogeneous. However, they can also be other fuels, for example, fossil fuels such as coal.

[0027] Combustion plants are thermal power plants, which produce electrical and / or thermal energy from a heat source, produced by the combustion of solid fuel in a combustion chamber.

[0028] As illustrated in figure 1 , the combustion chamber 1 of a combustion plant 2, is supplied with solid fuel 3, by a feeding system 4.

[0029] In one example, the solid fuel feeding system 4 comprises at least one screw conveyor 4-1, 4-2, and the biomass 3 is conveyed to the combustion chamber 1 by said at least one screw conveyor 4-1, 4-2. In a preferred example, the feeding system 4 comprises a first screw conveyor 4-1 positioned substantially horizontally relative to the ground and a second screw conveyor 4-2 positioned, at the end of the first screw conveyor 4-1, substantially vertically. The solid fuel 3 is conveyed from a storage bin 5 located upstream of the first screw conveyor 4-1 to the combustion chamber 1 located downstream of the second screw conveyor 4-2 by means of the first screw conveyor 4-1 and then the second screw conveyor 4-2.

[0030] The method according to the invention is characterized in that it comprises the following steps.

[0031] In the first step, a non-flammable liquid is injected into the fuel contained in the fuel supply system. In one example, this is water.

[0032] Injection is carried out by means of one or more injectors 6-1, 6-2, 6-3 distributed along the feed system and, in particular, along the first worm gear 4.1, namely the horizontal worm gear. These injectors are schematically represented by arrows at the figure 1 . These injectors 6-1, 6-2, 6-3 form an extinguishing device installed on the independent supply of the extinguishing means of the general fire-fighting system, which is generally present for all power plants.

[0033] The injected non-flammable liquid wets the fuel 3 contained in the fuel system and forms agglomerates of wet fuel at the point of liquid injections.

[0034] In another step of the process according to the invention, a plug 7 of fuel 3 is formed in the fuel supply system 4. Such a plug 7 is schematically shown in the figure 2B .

[0035] To form this plug 7, the auger 4-1 is operated in reverse, that is, in the opposite direction to its normal operation. When the auger operates in reverse, the agglomerate of wet fuel does not move at the same speed within the auger as the unwet fuel. The unwet fuel, located downstream of the wet fuel, will compact onto the agglomerate, and the agglomerate itself will undergo compaction. The plug 7 results from the compaction of the agglomerate under the action of the auger's reverse rotation and the compaction of the fuel downstream of the agglomerate. In practice, when the solid fuel is biomass, the hardness of the plug 7 formed in the auger is on the order of that of a champagne cork. It is therefore extremely hard.

[0036] In another step of the process according to the invention, a fuel-free space 8 is created in the fuel supply system. This empty space 8 results partly from the compaction of the unwet biomass forming the plug 7, but also from the fact that the auger operates in reverse and no fuel source is supplied to the auger inlet.

[0037] As illustrated in the figure 3 The solid fuel supply system of the power plant further includes one or more sensors. According to the invention, a flare-up in the fuel supply system is detected by means of said sensors. The sensors are advantageously temperature sensors, designated TC on the figure 3 , for thermocouples, CO2 sensors, IR infrared sensors and / or humidity sensors.

[0038] Furthermore, the power plant is advantageously equipped with a programmable logic controller (PLC). The aforementioned sensors then communicate with said PLC. The PLC controls the steps of the process according to the invention, namely the injection of the non-flammable liquid into the fuel contained in the fuel supply system and / or the formation of the fuel plug in the fuel supply system and / or the creation of a fuel void in the fuel supply system.

[0039] The aforementioned automaton is, in one example of an implementation of the invention, the automaton that ensures the control and command of the power plant. It is denoted the Main Control-Command Automaton. figure 3One function of this automated system is to enable communication between the sensors and the fuel feed fire suppression system. It also allows alarms to be sent to the operator via the human-machine interface. When the sensor system detects a fire in the conveyor, the automated system triggers the biomass feed system's fire suppression system. This system includes the means to supply water to the injectors from the water reservoir and / or the public water supply, and the means to control the rotation of the augers, particularly the horizontal auger that reverses direction.

[0040] Of course, the safety method according to the invention, as well as the means of implementing this method, does not preclude the presence of a general fire suppression system designed to extinguish fires throughout the entire plant. Such a general system operates on a power supply separate from the specific fire suppression system according to the invention described above and, preferably, on a backup power supply in case of a power outage. It also comprises three interconnected parts.

[0041] Firstly, this involves a system of sensors distributed throughout the power plant, for example, UV or IR sensors for detecting battery fires, or sensors for temperature, CO2, or humidity. These sensors are placed at various locations within the plant where a fire risk has been identified, such as the fuel storage area, conveyors, the fume filtration system, and the power electronics. As with the system for implementing the method according to the invention, the sensors are at least duplicated.

[0042] Secondly, it consists of a fire suppression system independent of that used by the specific firefighting device according to the invention, comprising a water network for spraying all areas where a fire risk is identified. One branch of the system connects directly to the power plant's electrical supply. It is activated by a backup power source, ideally one that is completely independent of the electrical grid.

[0043] Thirdly, there is a safety controller, separate from the controller used for the control system of the central unit. This controller has a backup power supply and / or is independent of the electrical grid. This controller autonomously manages the fire sensors and the triggering of alarm and fire suppression actions. It also communicates alarms to the control controller that manages the central unit.

[0044] Ultimately, the method according to the invention constitutes an effective fire suppression system, which makes it possible both to prevent the risk of fire and to fight it if a fire breaks out. In combustion plants, the risk of fire is very real, but combustion is also the core business and, consequently, the source of revenue. Given such a high stake, it is inconceivable that a technical or mechanical problem should jeopardize the entire installation. The method according to the invention makes it possible to prevent this risk.

[0045] Fire prevention consists of a series of actions carried out automatically during the shutdown of the plant, which is the most risky phase, this shutdown being able to occur following a normal shutdown requested by an operator, or following a sudden and / or unforeseen incident due to human error or technical failures.

[0046] To limit the risk of fire during plant shutdown, a two-phase preventative routine is implemented. The first phase renders the fuel in the feed system non-flammable. This may involve injecting water, which saturates the fuel and makes it incombustible. The fuel in the conveyor cannot then ignite. The second phase creates a fuel plug while simultaneously creating a "fuel void." This limits the risk of fire or smoke rising back up the feed system thanks to the resulting damp fuel plug. This also serves as a double safety measure in case the first step fails. The void reduces the risk of fire rising, and the fuel plug slows the fire and reduces the air supply to the ongoing combustion.The resulting plug is thus advantageously permanent until the power plant has completely cooled down. It will be cleared when the plant restarts.

[0047] The aforementioned phases can be carried out manually but, in a preferred embodiment of the invention, it will be a sequence programmed in the control system of the power plant.

[0048] Furthermore, in the event of a technical or human failure causing a malfunction in the power plant, the plant can automatically enter a so-called safety shutdown position to limit risks to personnel, equipment, and fire. In the present invention, the two preventative phases described above are implemented: the injection of a liquid to render the fuel non-flammable and the implementation of an automatic conveyor sequence that creates a fuel void and a fuel plug.

[0049] These two phases do not necessarily take place under the same conditions as in the case of a normal shutdown.

[0050] The quantities of non-flammable liquid injected may vary, and the sequence of plug formation may also differ. Only the principle remains the same.

[0051] The method according to the invention therefore offers numerous advantages that address the problems posed by the prior art. In the invention, the entire corrective system is redundant. This redundancy prevents the entire installation from being jeopardized by a simple technical problem or a sensor malfunction. The energy systems enabling the operation of both the preventive and corrective components are completely separate. This ensures continued protection in the event of a power failure in either system. The preventive system, particularly the fire suppression system of the fuel supply, is a simple device adapted to solid fuels. Due to the absence of any additional mechanical components dedicated to the fire suppression device, this system is very inexpensive and robust.Due to the system's configuration and the precautions taken in the preventative measures of the invention, the risk of a flashback during normal plant operation is very limited and virtually nonexistent. The flashback prevention system is spatially limited to the fuel supply area, thus protecting the plant's combustion chamber.

[0052] It should be noted that, in the preferred embodiment of the invention, namely the embodiment presented in the Figures 1, 2A, 2B And 3 The power plant can be shut down for two reasons: either the operator decides to turn off the plant and does so via a Human-Machine Interface; or an incident occurs and triggers the plant's safety shutdown. In these cases, an accelerated shutdown procedure is initiated to quickly cool the plant and cut off all fuel supply.

[0053] To limit the risk of flare-ups due to the presence of stationary biomass near the combustion chamber, a series of automatically sequential steps are implemented, involving water injection and the formation of a fuel plug. The vertical screw is stopped to halt the fuel supply to the reactor. A solenoid valve opens to inject mains water into the screw to moisten the fuel. The horizontal screw retracts to create a plug of wet fuel while simultaneously creating a biomass void. Water is injected regularly to ensure that no flare-up occurs.

[0054] An example of a control sequence for performing fuel spraying and fuel plug formation during a normal shutdown is given in the logic diagram shown in the figure 4The sequence during an accidental shutdown will be similar in terms of the flowchart. The timings, the quantities of water injected, and the screw recoil speeds will differ and depend on the fuel and the plant configuration.

[0055] The power plant according to the invention therefore comprises two completely independent and redundant corrective systems. These are the specific fire suppression system relating to the fuel supply and the general fire suppression system. EXAMPLE : SPECIFIC FIRE SUPPLY CONTROL SYSTEM

[0056] Since the fuel supply is the most critical point, it is important to ensure redundancy in the fire suppression system at this point. In this example, the specific fire suppression system of the present invention is as described in this application. Its features are summarized below. The entire system operates on the electrical grid and has a battery backup system in case of power outages. Detection system

[0057] It consists of three TC thermocouples (see Fig. 3 These thermocouples measure the temperature at three different points in the feed system. They are mounted on the conveyor screw chute. These thermocouples act as transmitters, sending their information to the power plant's control system. Programmable logic controller

[0058] This is the industrial programmable logic controller (PLC) for the plant's control system. In the event of a fault detected by the thermocouples (TC), different levels are reached. Level 1: alarm for the operator, no specific action required. Level 2: opening of the solenoid valve used in the preventative system, which is connected to the water network. Level 3: transmission of the alarm to the main fire safety PLC. This last level provides redundancy for water injection because the system triggered by the main fire safety PLC uses another water source, namely an independent reservoir. When an alarm originates from the main fire safety PLC (fire detected elsewhere in the plant), the specific fire suppression system is activated as a safety precaution. Fire extinguishing system

[0059] This system comprises three parts. First, there is piping supplied with pressurized water from the potable water network. Second, there is a solenoid valve communicating with the control system, as well as a manual bypass valve. This bypass valve allows an operator to directly intervene and spray the biomass even without electricity or an automated system if a fire is detected. Finally, there is an injection nozzle located directly inside the fuel supply system. EXAMPLE : GENERAL FIRE FIGHTING SYSTEM

[0060] The general fire suppression system is part of a larger system for combating industrial risks such as the production of CO, CH4, or H2. In this example, according to the invention, it comprises three redundant and independent parts of the specific fire suppression system related to fuel supply. These three parts are described below. Detection system

[0061] It consists of two UV / IR flame detectors to ensure measurement redundancy and detect any flames. These sensors use two technologies, UV and IR, to increase the accuracy of the measurement. They transmit their information to an independent safety controller. They operate using an internal battery. Independent programmable logic controller

[0062] This is the independent safety controller responsible for the entire fire and gas risk suppression system across the entire plant. If the flame detectors detect an anomaly, this controller activates the plant's main fire suppression system, alerts the operator and personnel with audible and visual signals, and transmits the alarm to the programmable logic controller (PLC). The controller operates using an internal battery. Fire extinguishing system

[0063] This system is composed of different parts: - a 10 m³ water reserve, the volume depending on the size of the power plant and the storage areas; - a Diesel pump allowing the water from the reservoir to be sent to the entire fire network; - a fire water network independent of the public water network and totally dedicated to this system, connected to the tank and the pump; and - a set of water injection nozzles positioned above each biomass reserve, fuel conveying system or other area with an identified fire risk.

[0064] In practice, when the main fire suppression system is activated, the pump starts automatically and sends water from the reservoir through the fire suppression network. The water is then sprayed to all areas likely to be on fire. This ensures that water is delivered to the fire's location and also prevents the fire from spreading. Thus, if the fire is not contained where it started because it is too intense or for any other reason, all other areas that could contribute to the fire are moistened and the fire suppressed.

Claims

1. A method for securing against fires a solid fuel combustion or gasification plant (2) (3) comprising a combustion chamber (1) of the solid fuel (3), said chamber (1) being supplied with solid fuel (3) by a feeding system (4), characterized in that It includes the following steps whereby: a non-flammable liquid is injected into the fuel (3) contained in the fuel supply system (4); a plug (7) of fuel (3) is formed in the fuel supply system (4); and a space (8) free of fuel is created in the fuel supply system.

2. Method according to claim 1, characterized in that solid fuel (3) includes biomass, solid recovered fuels and / or waste.

3. A method according to any one of claims 1 or 2, wherein the solid fuel supply system (4) comprises at least one screw, the fuel being brought to the combustion chamber (1) by said at least one screw.

4. Method according to claim 3, characterized in that the feeding system (4) comprises a first worm screw (4-1) positioned substantially horizontally relative to the ground and a second worm screw (4-2) positioned at the terminal end of the first worm screw (4-1), and in that The solid fuel (3) is conveyed from a fuel storage bin (5) located upstream of the first screw (4-1) to the combustion chamber (1) located downstream of the second screw, by means of the first (4-1) and then the second (4-2) screw.

5. A method according to claim 3 or 4, characterized in that, for the formation of the fuel plug (7) and for the creation of the empty fuel space (8) in the fuel supply system (4), said at least one auger (4-1) is operated in reverse after injecting the liquid into the fuel (3) contained in the supply system (4).

6. A method according to any one of the preceding claims, characterized in that the solid fuel (3) supply system (4) of the power plant further includes one or more sensors, and in that It further includes a step in which a flare-up in the fuel supply system (4) is detected by means of said sensor(s).

7. Method according to claim 6, characterized in that The sensor(s) are temperature sensors, CO2 sensors, infrared sensors and / or humidity sensors.

8. A method according to claim 6 or 7, characterized in thatThe combustion plant (2) is equipped with an automated system, in that the sensor(s) communicate with the said automated system, and in that The controller controls the injection of the non-flammable liquid into the fuel (3) contained in the fuel supply system (4) and / or the formation of the fuel plug (7) in the fuel supply system and / or the creation of the empty space (8) of fuel in the fuel supply system (4).

9. A method according to any one of the preceding claims, characterized in that The plant also includes a general fire-fighting system comprising sensors arranged throughout the plant, a means of extinguishing fires by spraying the plant with liquid and / or non-flammable gas, and a safety automation system.

10. Fire-protected solid fuel (3) combustion or gasification plant (2) for carrying out the process according to any one of claims 1 to 8, comprising a solid fuel (3) combustion chamber (1), said chamber (1) being supplied with solid fuel (3) by a feeding system (4), characterized in that It further includes means for injecting a non-flammable liquid into the fuel supply system (4), means for forming a plug (7) of fuel (3) in the fuel supply system (4), and means for creating a fuel-free space (8) in the fuel supply system.

11. Central (2) according to claim 10, characterized in that the feeding system (4) includes at least one screw (4-1, 4-2) and at least one injector (6-1, 6-2, 6-3) of non-flammable liquid.