DE102017205642A1 - Process for the disposal of fuel and motor vehicle with fuel converter - Google Patents

Abstract

The technology disclosed herein relates to a method of disposing of fuel. The fuel to be disposed escapes due to permeation and / or leakage from a fuel-carrying component of a motor vehicle. Alternatively or additionally escapes to be disposed of fuel from a pressure vessel of the motor vehicle for pressure relief of the pressure vessel. Alternately or at least partially simultaneously the following steps are carried out:
- Reacting the fuel to be disposed by a chemical reaction of the fuel; and
- Draining the fuel to be disposed of without conversion of the fuel into the environment.
Further, a fuel converter and a motor vehicle are disclosed.

Description

The technology disclosed herein relates to a fuel disposal method and a fuel converter. Furthermore, the technology disclosed herein relates to a motor vehicle, in particular a motor vehicle, which is operated with gaseous fuel under ambient conditions. If such a motor vehicle is parked in a small and, in addition, fuel-tight garage, leaking fuel from the motor vehicle can change the concentration of fuel in the garage. It is known to react the fuel before exiting into the garage by a chemical reaction. However, this chemical reaction leads to a reduction of the oxygen content in the closed garage. Depletion of oxygen in a confined space may also be undesirable.

It is a preferred object of the technology disclosed herein to reduce or eliminate at least one disadvantage of the previously known solutions. In particular, it is a preferred object to provide a fuel disposal method and / or a motor vehicle or fuel converter that is improved in both fuel emissions and oxygen depletion. Other preferred objects may result from the beneficial effects of the technology disclosed herein. At least one of these objects is / are solved by the subject matter of the independent claims. The dependent claims are preferred embodiments.

The technology disclosed herein relates to a motor vehicle. The motor vehicle comprises at least one pressure vessel for storing fuel and i.d.R. at least one fuel converter for the chemical conversion of fuel, in particular a fuel converter as disclosed herein. The at least one pressure vessel may be fluidly connected to the fuel converter for pressure relief.

The motor vehicle can be, for example, a motor vehicle which is operated with gaseous fuel under ambient conditions, in particular with compressed ("compressed natural gas" = CNG) or liquefied (LNG) natural gas or with hydrogen.

Such a motor vehicle may comprise at least one pressure vessel. The pressure vessel may be, for example, a cryogenic pressure vessel (= CcH2) or a high-pressure gas vessel (= CGH2). But it would also be conceivable other fuel storage such as metal hydride storage

High pressure gas containers are configured to store fuel substantially at ambient temperatures at a nominal operating pressure (also called nominal working pressure or NWP) of about 350 bar (= overpressure to atmospheric pressure), more preferably about 700 barg or more. A cryogenic pressure vessel is suitable to store the fuel at the aforementioned operating pressures even at temperatures well below the operating temperature of the motor vehicle.

The cryogenic pressure vessel system (= CcH2 system) comprises a cryogenic pressure vessel. The cryogenic pressure vessel may store fuel in the liquid or supercritical state. A supercritical state of aggregation is a thermodynamic state of a substance which has a higher temperature and a higher pressure than the critical point. The critical point denotes the thermodynamic state in which the densities of gas and liquid of the substance coincide, that is, it is single-phase. While one end of the vapor pressure curve in a pT diagram is marked by the triple point, the critical point represents the other end. For hydrogen, the critical point is 33.18 K and 13.0 bar. A cryogenic pressure vessel is particularly suitable for storing the fuel at temperatures significantly below the operating temperature (meaning the temperature range of the vehicle environment in which the vehicle is to be operated) of the motor vehicle, for example at least 50 Kelvin, preferably at least 100 Kelvin or At least 150 Kelvin below the operating temperature of the motor vehicle (usually about - 40 ° C to about +85 ° C). The fuel may be, for example, hydrogen, which is stored at temperatures of about 34 K to 360 K in the cryogenic pressure vessel. The cryogenic pressure vessel may in particular comprise an inner container which is designed for a nominal operating pressure (also called nominal working pressure or NWP) of about 350 bar (= overpressure relative to the atmospheric pressure), preferably of about 500 barü, and particularly preferably of approx 700 bar or more. The fuel is stored in the inner container. The outer container preferably closes off the pressure vessel to the outside. Preferably, the cryogenic pressure vessel comprises a vacuum with an absolute pressure in the range of 10 ^-9 mbar to 10 ^-1 mbar, further preferably from 10 ^-7 mbar to 10 ^-3 mbar and particularly preferably from about 10 ^-5 mbar that at least partially between the inner container and the outer container in an evacuated (intermediate) space or vacuum V is arranged. Storage at temperatures (just) above the critical point has the advantage over storage at temperatures below the critical point that the storage medium is present in a single phase. There is So, for example, no interface between liquid and gaseous.

Despite good thermal insulation, the fuel stored in a cryogenic pressure vessel heats up slowly. At the same time, the pressure in the pressure vessel rises slowly. If a limit pressure is exceeded, the fuel can escape here via suitable safety devices in order to avoid bursting of the cryogenic pressure vessel. For this purpose, pressure-operated pressure relief valves can be used, which allow gradual escape of the fuel. Downstream of the pressure relief valves, a so-called blow-off management system or boil-off management system or fuel converter is used here.

The technology disclosed here furthermore also comprises a fuel converter which is fluid-connected or fluid-connectable to the at least one overpressure valve. The fuel converter may, for example, be a catalytic converter which converts the fuel (for example hydrogen) with the oxygen from the ambient air (in the case of hydrogen, the reaction product is water).

In particular, the technology disclosed herein relates to a fuel converter for the chemical conversion of fuel; wherein the fuel converter comprises a jet pump whose driving medium is the fuel; wherein air can be sucked in by means of the jet pump; wherein the air and the fuel are introduced on at least one catalyst surface for the at least partial oxidation of the fuel; and wherein the fuel converter is designed and set up such that air and fuel can be supplied to the fuel converter with an air ratio that is at least temporarily below 1.0. The air ratio λ (also called combustion air ratio or air ratio) indicates by what factor more air is provided than is actually necessary for the reaction. The air ratio λ sets the actually available for the chemical reaction in the at least one fuel converter air mass mL-tats in relation to the minimum necessary stoichiometric air mass mL-st, which is required for a complete reaction in the fuel converter. It therefore applies: $$\mathrm{\lambda }=\frac{\text{mL}-\text{tats}}{\text{mL}-\text{st}}$$

According to the technology disclosed herein, the air ratio λ is at least temporarily changed from the stoichiometric value (λ = 1) and in particular brought to values below 1.0.

The exact values for the air ratio depend on the stoichiometry of the reaction, the lower ignitability limit of the fuel or the targeted maximum concentration limit of the fuel in the garage, and the targeted minimum concentration limit of the oxygen in the garage. It also plays a role, whether the substances involved in the reaction occur as a liquid or gas and thus whether by the reaction, a pressure difference in the garage against the garage environment may arise, the favorable case of a backflow of air into the garage or a discharge of Schadatmosphäre could force the garage. Neglecting air exchange effects, for example, for a target maximum concentration of hydrogen of 2% by volume and an aspired minimum concentration limit of oxygen of 19% by volume (compared to an initial state of 21% by volume), the time-averaged air ratio λ would then be between 0.4 and 0, 6 and ideally should be at 0.5. For other reactants and other assumptions for the limit concentrations, corresponding other values result for the then ideal time-averaged air ratio. The fuel mass flow that can be achieved in this way is considerably higher than if only one of the two mechanisms (complete reaction, unreacted release) were used alone. By using the two mechanisms alternately over time, pressure differences between the garage atmosphere and the environment can sometimes be forced. Ideally, this creates a kind of inhalation and exhalation of the garage: overpressure, in the unreacted release (only mixing with air) and negative pressure in the chemical reaction, for example, if water condenses out as the reaction product. So here is a synergy effect available.

A jet pump is a pump in which the pumping action is generated by a fluid jet (= driving medium, in this case the fuel), which by pulse exchange sucks, accelerates and compresses / conveys another medium (= suction medium, here the air). In particular, in this case, the jet pump be designed so that it is designed for the fuel pressure downstream of the pressure relief valve (corresponds approximately to the trigger pressure) and downstream of a diaphragm (if provided). The jet pump is fluidly connected to the at least one catalyst surface and causes the air and fuel to be introduced to the catalyst surface.

The at least one catalyst surface may comprise, for example, a noble metal, for example platinum, palladium, iridium and / or rhodium. In particular, the catalyst surface may be configured to effect at least partial oxidation of the fuel.

The pressure vessel system disclosed herein includes at least one pressure relief valve for venting fuel. The pressure relief valve may be an activated by the pressure in the pressure vessel and re-closable device. The pressure relief valve allows in particular a gradual escape of the fuel into the environment. Downstream of the pressure relief valve, the fuel converter can be arranged. Preferably, the pressure relief valve opens as soon as the pressure in the pressure vessel system slightly above the max. Operating pressure is, for example, 10% above the max. Operating pressure. This pressure is also referred to as release pressure from the pressure relief valve.

The technology disclosed herein further relates to a tank shut-off valve (= TAV; shut-off valve). The tank shut-off valve is in particular a controllable or controllable and in particular normally closed valve. The tank shut-off valve provides a fuel consumer, e.g. a fuel cell, fuel ready. The tank shut-off valve is i.d.R. integrated into an on-tank valve (= OTV). The on-tank valve is the valve unit mounted directly at one end of the pressure vessel and directly fluidly connected to the interior of the pressure vessel. The tank shut-off valve is i.d.R. fluidly connected in parallel to the pressure relief valve with the pressure vessel interior.

The technology disclosed here can be used in particular in a fuel cell system with at least one fuel cell. The fuel cell system is intended, for example, for mobile applications such as motor vehicles, in particular for providing the energy for at least one drive machine for locomotion of the motor vehicle. In its simplest form, a fuel cell is an electrochemical energy converter that converts fuel (e.g., hydrogen) and oxidants (e.g., air, oxygen, and peroxides) into reaction products, thereby producing electricity and heat. A fuel cell system comprises, in addition to the at least one fuel cell, peripheral system components (BOP components) which can be used during operation of the at least one fuel cell. As a rule, several fuel cells are combined to form a fuel cell stack or stack.

The fuel cell system includes an anode subsystem formed by the fuel-bearing components of the fuel cell system. An anode subsystem may include at least one pressure vessel, at least one pressure reducer, at least one anode inlet leading to the anode inlet, an anode space in the fuel cell stack, at least one anode exhaust line leading away from the anode outlet, at least one water separator, at least one anode purge valve, at least one active or passive fuel recirculation conveyor, and / or at least one have a recirculation line and other elements. The main task of the Anodensubsystems is the introduction and distribution of fuel to the electrochemically active surfaces of the anode compartment and the removal of anode exhaust gas.

• - Umsetzen des zu entsorgenden Brennstoffs durch eine chemische Reaktion, insbesondere Oxidationsreaktion, vom Brennstoff mit einem Oxidationsmittel, insbesondere Luft; und
• - direktes oder indirektes und insbesondere zumindest teilweises Ablassen des zu entsorgenden Brennstoffs aus dem Anodensubsystem ohne Umsetzung des Brennstoffs in die Umgebung, wobei das Ablassen zweckmäßig derart erfolgt, dass insbesondere zumindest in der Umgebung der Ablassstelle kein zündfähiges Gemisch entsteht.

The technology disclosed herein further relates to a method of disposing of fuel wherein the fuel to be disposed of escapes from a leakage site due to permeation and / or leakage from a fuel-bearing component of the motor vehicle, particularly the fuel cell system anode subsystem disclosed herein, and / or wherein Fuel escapes from the pressure vessel of the motor vehicle for pressure relief of the pressure vessel; wherein alternately or at least partially simultaneously the following steps are carried out:

• - Reacting the fuel to be disposed by a chemical reaction, in particular oxidation reaction of the fuel with an oxidizing agent, in particular air; and
• - Direct or indirect and in particular at least partially draining the fuel to be disposed of from the anode subsystem without conversion of the fuel into the environment, wherein the expediently carried out such that in particular at least in the vicinity of the drain point no ignitable mixture is formed.

The fuel to be disposed of, for example, by the wall of the fuel-carrying component, eg. B. the pressure vessel wall to be permeated. Further, the fuel may be leaking through a leak, e.g. from a connection point of a line or a leaky sealing point in the fuel cell stack, leaked. In particular, it is therefore fuel that is not deliberately flushed out of the fuel-carrying components during an active phase of the fuel cell system. It is rather leakage. Furthermore, fuel can be discharged from the pressure vessel for pressure relief.

• - indem der Brennstoff an einem Katalysator, insbesondere der Katalysatorfläche vom Brennstoffkonverter, oxidiert wird und/oder
• - indem der Brennstoff verbrannt wird.

The fuel to be disposed can preferably be supplied in a catalytic fuel converter, in which the fuel is reacted. The fuel to be disposed of can be converted by a chemical reaction,

• - By the fuel is oxidized on a catalyst, in particular the catalyst surface of the fuel converter, and / or
• - by burning the fuel.

This chemical oxidation reaction may alternatively or additionally also take place in a cathode of the fuel cell stack.

The method disclosed herein may include the step of disposing of the fuel to be disposed of, at least during an inactive phase of a fuel cell system. An inactive phase is in particular a phase in which the fuel cell system does not provide electrical energy by means of an electrochemical reaction in the fuel cell stack of an external (useful) load or is not configured for this purpose. The external load can form, for example, the electrical consumers and electrical energy storage of a motor vehicle, which do not belong to the fuel cell system. Likewise, an active phase of the fuel cell system is a phase in which the fuel cell system provides or is set up electrical energy by an electrochemical reaction in the fuel cell stack of an external (useful) load. For this purpose, the fuel cells are supplied with fuel and oxidizing agent during the active phase. Thus, the idle mode or standby mode also belongs to the active phase of the fuel cell system, since electric power can also be provided here in response to a corresponding control signal.

• - Brennstoff unter Sauerstoffverbrauch durch eine chemische Oxidationsreaktion umgesetzt; und
• - die Luft in der unmittelbaren Fahrzeugumgebung mit Brennstoff angereichert.

According to the technology disclosed here, the step may be provided, according to which, at least at times, a fuel-containing mixture of air and fuel flows out of the fuel converter. This is usually the case when the air ratio is less than 1. In this case, at the same time:

• - Fuel reacted under oxygen consumption by a chemical oxidation reaction; and
• - enriched the air in the immediate vehicle environment with fuel.

If the fuel converter with a particular time-averaged air ratio of 0.2 to 1.0, or operated with an air ratio of 0.25 to 0.75, or with an air ratio of 0.4 to 0.6, so comparatively large amounts be disposed of fuel in a relatively small and relatively fuel-tight garage without the concentration of fuel in the air rises too high or the oxygen concentration in the vehicle environment drops too much.

The direct or indirect discharge takes place in such a way that at least in the vicinity of the discharge point or in the surroundings of the motor vehicle no ignitable mixture is formed, and preferably not in a garage in which the motor vehicle is parked. For this purpose, corresponding mixing elements can be provided. Alternatively or additionally, the outflow openings (in particular from the fuel converter into the environment) can be dimensioned and spaced in such a way that no ignitable mixture is produced at the outflow openings to the ambient air. Such outflow openings are for example in the German patent application with the application number 102015222778 discloses, the contents of which are hereby incorporated by reference.

The solution disclosed here with the jet pump has the advantage that very fail-safe mechanical components are used. Likewise, an electronically controlled solution is conceivable. For example, a controller may be configured to control the fuel to be disposed of herein by reacting fuel to be disposed of, and discharging the fuel to be disposed without dissociation of the fuel, such that, during the parking period, the oxygen content of the ambient air decreases and the fuel concentration in the ambient air increases. For this purpose, both process steps can be carried out simultaneously or alternately. In one embodiment, the reaction and / or discharge depending on the actual oxygen concentration and / or the actual fuel concentration in the ambient air of the motor vehicle can take place, which can be detected for this purpose by a corresponding sensor. Furthermore, it can be provided that a warning is output, for example to a vehicle owner or a third party, if the fuel concentration and / or the oxygen concentration have reached a limit value. Alternatively or additionally, it can be provided that a conversion is prevented if an oxygen concentration limit value is reached, and / or that a discharge of fuel without conversion is prevented if a limit value for the fuel concentration is reached.

In other words, the technology disclosed herein relates to the symbiotic combination of deflating fuel without reacting and reacting fuel. It increases thereby the disposable mass flow significantly. Advantageously, the limits for oxygen depletion and for hydrogen enrichment can thus be exploited. The technical implementation can be done in a single fuel converter, which is deliberately driven "fat", ie with a lambda less than 1, for example lambda = 0.5. Exactly considered, there is still a surprising synergy effect: Because the oxygen depletion even increases the lower limit of ignitability of hydrogen. The combination of both technologies thus produces an effect that is greater than the sum of the individual effects

The technology disclosed here will now be explained in more detail with reference to FIG. 1.

The 1 schematically shows a system with a cryogenic pressure vessel 100. The cryogenic pressure vessel 100 comprises an inner container 102, which is enclosed by an outer container 101. At the periphery of the inner container 102, a fiber layer 103 is applied, which increases the pressure resistance of the inner container 102. The fiber layer 103 may comprise a plurality of wound and / or braided fiber layers. At the end 110 of the inner container 102, an outlet for a main fuel line 220 is provided, which supplies the fuel consumer, here a fuel cell stack 200, with fuel. In the supply path to the fuel consumer, a pressure reducer 210 is also provided here.

Further, the pressure relief valve 310 is fluidly connected directly to the end 110 of the pressure vessel 100. In the end 110 and upstream of the pressure reducer 210 in the main fuel line 220, a tank shut-off valve is integrated here fluidly parallel to the overpressure valve 310. Downstream of the pressure relief valve 310 is a throttle 330 which limits the fuel mass flow. If the triggering pressure is reached, a fuel mass flow m converter limited by the throttle 330 flows, max of fuel into the fuel converter 300. However, such a throttle does not have to be provided. Further, a check valve 340 may be provided. The fuel converter 300 is set up here to suck in air through its jet pump. When the release pressure is reached by the overpressure valve 310, the fuel to be disposed of for pressure relief flows through the throttle 330 into the fuel converter 300. The pressure and the amount of fuel are substantially constant. The jet pump uses this fuel as the driving medium and is designed so that then here in the fuel converter 300 sets an air ratio of 0.4 to 0.6. Part of the fuel is then catalytically reacted at the catalyst surfaces, whereby oxygen is consumed. The remainder of the fuel which is not reacted reaches the ambient air. With the air ratio selected here, the ambient air can advantageously be changed so that neither the fuel concentration is too high, nor is the oxygen content of the air in the garage too low. There is also a symbiotic effect, because with the decreasing oxygen content increases the maximum allowable fuel concentration in the ambient air of the garage.

The solution disclosed herein is equally applicable to fuel of a CGH2 pressure vessel permeated in an intermediate layer (between fiber reinforced reinforcement and liner). Such an intermediate layer may be fluidly connected to a fuel converter. Again, there may be a shockous ejection of the fuel to be disposed of from the intermediate layer. This shockingly escaping fuel in turn can serve as a propellant for the air. According to the same principle, leakage fuel escaping from a fuel cell stack can be supplied to a fuel converter. For this purpose, a fuel-tight housing may be provided, which is fluid-connected to a fuel converter (shown in dashed lines). The latter solution can be used in particular for CGH2 pressure vessels.

The foregoing description of the present invention is for illustrative purposes only, and not for the purpose of limiting the invention. Various changes and modifications are possible within the scope of the invention without departing from the scope of the invention and its equivalents.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102015222778 [0026]

Claims (9)

A method for disposing of fuel, wherein the fuel to be disposed escapes due to permeation and / or leakage from a fuel-carrying component of a motor vehicle and / or wherein the fuel escapes from a pressure vessel of the motor vehicle for pressure relief of the pressure vessel; wherein alternately or at least partially simultaneously the following steps are carried out: - Reacting the fuel to be disposed by a chemical reaction of the fuel; and - Draining the fuel to be disposed of without conversion of the fuel into the environment. Method according to Claim 1 wherein the fuel to be disposed of is supplied to a catalytic fuel converter in which the fuel is reacted. Method according to Claim 2 wherein the fuel converter is supplied with air and fuel with an air ratio of 0.2 to 1.0, or with an air ratio of 0.25 to 0.75, or with an air ratio of 0.4 to 0.6. Method according to Claim 2 or 3 , wherein at least at times a fuel-containing mixture flows out of the fuel converter. Method according to one of the preceding claims, wherein the discharge takes place such that at least in the vicinity of the drain point no ignitable mixture is formed. Method according to one of the preceding claims, further comprising the step of disposing of the fuel to be disposed of, at least during an inactive phase of a fuel cell system. Method according to one of the preceding claims, wherein the fuel to be disposed of by a chemical reaction is implemented by the fuel is oxidized on a catalyst and / or by the fuel is burned. Fuel converter (300) for the chemical conversion of fuel; - wherein the fuel converter comprises a jet pump whose driving medium is the fuel; - By means of the jet pump air can be sucked; - Wherein the air and the fuel are introduced at least one catalyst surface for at least partial oxidation of the fuel; and wherein the fuel converter is designed and set up such that air and fuel can be supplied to the fuel converter with an air ratio of 0.2 to 1.0, or with an air ratio of 0.25 to 0.75, or with an air ratio of 0, 4 to 0.6. A motor vehicle comprising: - at least one pressure vessel (100) for storing fuel; - At least one fuel converter (300) for the chemical conversion of fuel after Claim 8 ; - Wherein the at least one pressure vessel (100) for pressure relief with the fuel converter (300) is fluidly connected.

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