GB2607633A

GB2607633A - Fuel gas mixture and use thereof

Info

Publication number: GB2607633A
Application number: GB2108340.7A
Authority: GB
Inventors: Collins Tom; Keyworth Andrew
Original assignee: Bosch Thermotechnology Ltd
Current assignee: Bosch Thermotechnology Ltd
Priority date: 2021-06-10
Filing date: 2021-06-10
Publication date: 2022-12-14
Also published as: GB202108340D0

Abstract

The invention relates to a fuel gas mixture and use thereof for a gas burner, in particular to generate heat for heating a space and/or supplying hot water. The fuel gas mixture comprises a methane gas substitute, in particular propane or butane, and hydrogen in pre-definable proportions and use thereof. The fuel gas mixture has properties relevant to combustion that are substantially like those of methane, including a Wobbe index, flame temperature or minimum air requirement substantially like that of methane.

Description

Fuel gas mixture and use thereof

Background of the invention

Using a fuel gas mixture for a gas burner, in particular to generate heat for heating a space and/or supplying hot water, where the gas burner is designed to generate and/or burn a fuel gas-air mixture from the fuel gas mixture and air is already known.

Disclosure of the invention

The invention relates to the use of a fuel gas mixture, in particular for a gas burner, in particular to generate heat for heating a space and/or supplying hot water, where the gas burner is designed to generate and/or burn a fuel gas-air mixture from the fuel gas mixture and air.

Proposed is the use of a fuel gas mixture comprising a methane gas substitute, in particular propane, and hydrogen in predefinable proportions, the fuel gas mixture having properties relevant to combustion that are substantially like those of methane.

In this context, a "fuel gas mixture" should generally be understood as meaning a mixture comprising at least two fuel gases, in particular a mixture comprising a methane gas substitute and hydrogen. In this context, a "gas burner" should be understood in particular as meaning a device for burning the fuel gas and/or fuel gas mixture, in particular substantially continuously, to create a flame that in particular is substantially continuous and/or locally stable. To this end, the gas burner may comprise in particular components or units such as a fuel gas intake and a fuel gas pipe for supplying and conveying the fuel gas mixture, a fuel gas valve for controlling and/or regulating a volume flow of the fuel gas mixture, an air -2 -intake and/or an air pipe for supplying and/or conveying the air, a fan for conveying air and/or the fuel gas-air mixture, an outlet orifice for discharging the fuel gas-air mixture to a combustion chamber, an ignition device for igniting the flame and/or a monitoring device for monitoring the flame. Heat is generated by means of the flame and/or hot combustion products (combustion exhaust gases). This heat may be transferred to a heat transfer fluid or useful fluid such as heating water or drinking water, for example. To this end, the gas burner may be disposed in particular on a heating device having a heating water and/or drinking water heat exchanger. Alternatively, the fuel gas mixture may also be used for another burner device, for example a gas motor. In this context, "air" should be understood in particular as meaning air from an ambient environment of the burner or air fed in by means of an air pipe. In particular, the air is fed into the burner. In particular, the air serves as a means of carrying the oxygen needed for the combustion process. In this context, a "fuel gas-air mixture" should be understood in particular as meaning a combustible mixture of air and fuel gas mixture. For the fuel gas-air mixture to be combustible, the proportion of fuel gas mixture must lie within a range between the lower flammability limit and the upper flammability limit of the specific fuel gas. To enable complete combustion -which is desirable for reasons of efficiency and environmental protection -the proportion of air must be at least the minimum air requirement of the specific fuel gas. In this context, the statement "the gas burner is designed to generate and/or burn a fuel gas-air mixture from the fuel gas mixture and air" should be understood in particular as meaning that the burner or its components and units are configured and/or operated so that a volume flow of the fuel gas mixture and a volume flow of air can be mixed with one another as homogeneously as possible in the requisite proportions, reliably ignited -3 -and/or burned to create a flame that in particular is continuous and/or locally stable.

Generally speaking, the most frequently used fuel gas is 5 natural gas. Natural gas essentially consists of methane. Natural gas is usually distributed to the domestic or commercial natural gas consumption points via fuel gas pipelines of a national or supranational natural gas distribution network. Most standard gas burners are 10 designed to burn natural gas or methane.

In regions without a natural gas distribution network where no natural gas or methane is available from a distribution network, a methane gas substitute may be used as a substitute for natural gas or methane. The methane gas substitute is supplied in storage containers, for example. For example, the methane gas substitute for applications that are not dependent on distribution networks should have better storage properties than methane.

Propane is known as a methane gas substitute. Alternatively, butane or propane-butane mixtures are also known as methane gas substitutes. Alternatively, LPG (Liquefied Petroleum Gas) and/or optionally other 25 hydrocarbon gases are also known as methane gas substitutes. Methane gas substitutes may be obtained either as fossil fuel gas or as biogas by fermenting biomass.

These methane gas substitutes have combustion properties that are significantly different from those of methane. Standard gas burners that are optimised for methane are not suitable for use with methane gas substitutes. These gas burners need to be at least structurally adapted to enable use with methane gas substitutes. Adaptation involves resources and incurs costs. Additional logistical resources are needed to rule out any mix-up between methane burners and methane gas substitute burners. A mix-up could lead to -4 -system failure, malfunction, unsafe or dangerous operating states such as misfiring or overheating. Dual fuel burners or multi-fuel burners may be susceptible to faults and expensive.

In order to save on resources and costs, it is of advantage if all gas burners -both those for applications dependent on a distribution network and those not dependent on a distribution network -are based on a standard design, in particular a design for methane, and are capable of burning methane safely, efficiently and cleanly. It is therefore of particular advantage to provide a fuel gas or fuel gas mixture that may be used for applications using gas burners based on the standard design, at least in regions where no natural gas distribution network is available. As explained above, methane gas substitute is not suitable for this purpose or at least not directly.

In addition or alternatively, such a fuel gas or fuel gas 20 mixture may also be distributed as an admixture to natural gas or also as a sole component via the natural gas distribution network.

It is proposed that a fuel gas mixture which burns substantially like methane be used. The fuel gas mixture proposed for such use comprises the methane gas substitute as one component and this is mixed with hydrogen as a second component in set predefinable proportions. The resultant fuel gas mixture has properties relevant to combustion that are substantially like those of methane. The fuel gas mixture is suitable as a direct replacement for natural gas or methane in the gas burner. Gas burners based on the standard design may be deployed both for use with natural gas or methane and for use with the proposed fuel gas mixture. -5 -

The fuel gas mixture may be kept in reserve in domestic or communal storage containers, for example. Alternaively or in addition, such a fuel gas mixture may also be produced from its components at domestic or community level, in 5 particular mixed. For example, two storage tanks may be provided for separately storing methane gas substitute and hydrogen, which are mixed in predefinable proportions to obtain a flow of fuel gas mixture and fed to the gas burner when heat is required -optionally via an interconnected 10 standby tank for the fuel gas mixture.

In this context, the statement that "the fuel gas mixture has properties relevant to combustion that are substantially like those of methane" should be understood in particular as meaning that important properties, in particular characteristic values, of the fuel gas mixture which are relevant to combustion are similar to those of methane. In this context, "substantially" or "similar" should be understood in particular as meaning a variance of the fuel gas mixture property from the methane property of at most 15 %, preferably at most 5 %, particularly preferably at most 2 %. The gas burner based on the standard design burns the fuel gas mixture substantially like methane. In this context, "substantially" should be understood in particular as meaning substantially as efficiently, as cleanly, as safely.

A preferred embodiment is the use of a fuel gas mixture having a Wobbe index substantially like that of methane. 30 The Wobbe index is one example of a property of the fuel gas mixture relevant to combustion.

The Wobbe index is a measure of the energy output of a burner and is a key characteristic used to assess the interchangeability of fuel gases. In this context, the upper Wobbe index and/or the lower Wobbe index may be applied. The Wobbe index is a function of a fuel gas' -6 -calorific value and density, and it describes how the calorific energy of a fuel gas flows through dynamic flow restrictions such as nozzles or flow regulating valves. To suit existing burners without requiring adaptation, the fuel gas mixture has a Wobbe index similar to methane. A similar Wobbe index will provide that a burner produces a similar heat output for the fuel gas mixture supplied at a given pressure.

Another preferred embodiment is the use of a fuel gas mixture having a minimum air requirement substantially like that of methane. The minimum air requirement is one example of a property of the fuel gas mixture relevant to combustion.

To suit an existing burner, the fuel gas mixture has an air requirement compatible to methane. The air requirement (for example the volumetric air requirement) is the minimum amount of air (by volume) required to completely burn a unit of (volume of) fuel gas. If the air requirement of the fuel gas mixture is too high compared to methane, then it would not burn completely due to a lack of oxygen. This could produce dangerous products of incomplete combustion such as carbon monoxide, and also would not release all of the available energy of the fuel gas mixture. If the air requirement of the fuel gas mixture is too low compared to methane, then the flame would receive too much air, and could become unstable or again burn incompletely. Preferably the air requirement of the fuel gas mixture is similar to or slightly lower than the original fuel gas methane. If hydrogen makes up a significant proportion of the fuel gas mixture, then the air requirement can be lower still, as hydrogen has a high flame speed and low ignition energy, and is resilient to instability.

Another preferred embodiment is the use of a fuel gas mixture having a flame temperature substantially like that -7 -of methane. The flame temperature is one example of a property of the fuel gas mixture relevant to combustion.

The flame temperature is a temperature which can be 5 measured in the interior of the flame during combustion. In order to maintain the lifetime of a burner and/or adjacent installations (such as for example a combustion chamber and/or a heat exchanger), the fuel gas mixture produces a similar flame temperature. If the flame temperature is 10 higher compared to methane, then the lifetime of the burner and adjacent installations could be reduced. If the flame temperature is significantly lower compared to methane, then the operating thermal efficiency of the burner would be lower.

A fuel gas mixture that can be used in substantially the same way as methane in terms of flow and/or air ratio and/or heat generation is therefore obtained.

Another preferred embodiment is the use of a fuel gas mixture where the methane gas substitute is propane and where the proportions of hydrogen and propane in the fuel gas mixture have a volumetric ratio of hydrogen to propane within a range of 2.13: 1 to 3.00: 1.

Propane is a suitable methane gas substitute due to its characteristic values and combustion properties and due to its availability. A fuel gas mixture of propane with hydrogen in the proportions specified above may be used in substantially the same way as methane.

One particularly advantageous embodiment is the use of a fuel gas mixture where the proportions of hydrogen and propane in the fuel gas mixture have a volumetric ratio of 35 hydrogen to propane of 2.39: 1. -8 -

Another preferred embodiment is the use of a fuel gas mixture where the methane gas substitute is butane and where the proportions of hydrogen and butane in the fuel gas mixture have a volumetric ratio of hydrogen to butane within a range of 3.75: 1 to 4.60: 1.

Butane is a suitable methane gas substitute due to its characteristic values and combustion properties and due to its availability. A fuel gas mixture of butane with hydrogen in the proportions specified above may be used in substantially the same way as methane.

One particularly advantageous embodiment is the use of a fuel gas mixture where the proportions of hydrogen and 15 butane in the fuel gas mixture have a volumetric ratio of hydrogen to butane of 4.00: 1.

The invention also relates to a fuel gas mixture, in particular for use with a gas burner to generate heat for 20 heating a space and/or for supplying hot water.

It is proposed that the fuel gas mixture should comprise a methane gas substitute, in particular propane, and hydrogen in predefinable proportions and the fuel gas mixture has properties relevant to combustion that are substantially like those of methane.

The proposed fuel gas mixture comprises the methane gas substitute as one component and this is mixed with hydrogen as a second component in fixed predefinable proportions so that it has properties relevant to combustion that are substantially like those of methane. The fuel gas mixture is advantageously suitable as a direct replacement for natural gas or methane in the gas burner. Gas burners based on the standard design may be deployed both for use with natural gas or methane and for use with the proposed fuel gas mixture. In this context, "substantially like those of -9 -methane" should be understood in particular as meaning a variance of the fuel gas mixture property from the methane property of at most 15 5, preferably at most 5 5, particularly preferably at most 2 5.

A preferred embodiment of the fuel gas mixture has a Wobbe index substantially like that of methane. The Wobbe index is one example of a property of the fuel gas mixture relevant to combustion.

Another preferred embodiment of the fuel gas mixture has a minimum air requirement substantially like that of methane. The minimum air requirement is one example of a property of the fuel gas mixture relevant to combustion.

Another preferred embodiment of the fuel gas mixture has a flame temperature substantially like that of methane. The flame temperature is one example of a property of the fuel gas mixture relevant to combustion.

A fuel gas mixture is therefore proposed that has substantially the same or similar properties to those of methane in terms of flow and/or air ratio and/or heat generation.

A preferred embodiment of the fuel gas mixture has a methane gas substitute comprising at least one of the components propane and/or butane. In particular, propane may be the methane gas substitute. Alternatively or in addition, butane may be the methane gas substitute.

Based on another preferred embodiment of the fuel gas mixture, propane is the methane gas substitute where the proportions of hydrogen and propane in the fuel gas mixture have a volumetric ratio of hydrogen to propane within a range of 2.13: 1 to 3.00: 1.

10 15 20 -10 -Propane is a suitable methane gas substitute due to its characteristic values and combustion properties and due to its availability. Used in the mixture with hydrogen in the specified proportions, a fuel gas mixture can be obtained which burns in substantially the same way as methane.

In this context, a "volumetric ratio of hydrogen to propane of 2.13: 1" should be understood in particular as meaning that there are 2.13 units by volume of hydrogen in the fuel gas mixture per one unit by volume of propane. In this context, a "volumetric ratio within a range of 2.13: 1 to 3.00: 1" should be understood in particular as meaning that there are 2.13 to 3.00 units by volume of hydrogen in the fuel gas mixture per one unit by volume of propane. Fuel gas mixtures with components in volumetric ratios within this range have properties relevant to combustion that are substantially like those of methane.

Based on one particularly preferred embodiment of the fuel gas mixture, propane is the methane gas substitute and the proportions of hydrogen and propane in the fuel gas mixture have a volumetric ratio of hydrogen to propane within a range of 2.39: 1. A fuel gas mixture with components in this volumetric ratio has properties relevant to combustion that are substantially like those of methane.

Based on another preferred embodiment of the fuel gas mixture, butane is the methane gas substitute and the proportions of hydrogen and butane in the fuel gas mixture have a volumetric ratio of hydrogen to butane within a range of 3.75: 1 to 4.60: 1. Fuel gas mixtures with components in volumetric ratios within this range have properties relevant to combustion that are substantially like those of methane.

Butane is a suitable methane gas substitute due to its characteristic values and combustion properties and due to its availability. Used in the mixture with hydrogen in the proportions specified above, a fuel gas mixture can be obtained which burns in substantially the same way as methane.

Based on one particularly preferred embodiment of the fuel gas mixture, butane is the methane gas substitute and the proportions of hydrogen and butane in the fuel gas mixture have a volumetric ratio of hydrogen to butane within a range of 4.00: 1. A fuel gas mixture with components in this volumetric ratio has properties relevant to combustion that are substantially like those of methane.

A preferred fuel gas mixture consists at least up to 90 % 15 by volume, preferably at least up to 95 5 by volume, particularly preferably at least up to 98 % by volume, of methane gas substitute and hydrogen.

Another preferred fuel gas mixture contains small 20 proportions of inert gases and/or methane and/or other hydrocarbons. Inert gases may be nitrogen and/or carbon dioxide in particular.

The proposed fuel gas mixture represents an energy source which offers major advantages, in particular also in regions where no connection to a natural gas distribution network is available. Furthermore, the components can be produced at least partially on a renewable basis, for example by means of biomass fermentation or electrolysis using green power, thereby promoting the removal of fossil fuel sources from the heating market.

In order to decarbonize heating, it is desirable to replace fossil fuel gases with low-carbon or zero-carbon alternatives. Currently, liquid propane is used in off-grid applications due to its high volumetric energy density (24.1 MJ/d1443). Hydrogen can easily be manufactured as a -12 -low-carbon fuel gas from renewable energy including electricity, but has extremely low density and boiling point, as such it is usually stored as compressed gas. Most industrial applications operate at just under 200 bar (e.g. 178 bar) and at this pressure, hydrogen has a very low energy density (2.2 MJ/dm3). Meanwhile, most burners are designed to operate using natural gas. Natural gas has a moderate energy density as a compressed gas (6.8 MJ/dm= at 178 bar). Both methane and propane can be produced as bio-gas by digesting organic matter. This produces a low-netcarbon hydrocarbon fuel gas, but requires a feedstock which can compete with food supplied for farmland. It is therefore attractive to have a low-carbon fuel gas mixture for example, but not only, for off-gas-grid applications that combine the benefits of hydrogen (that can be manufactured in large quantities) with propane, preferably bio-propane (that has high energy density). Furthermore, it is attractive to have a fuel gas mixture that is compatible with existing appliances, and does not require constructional adaptions or new technology to utilise.

Claims

-13 -Claims 1. Use of a fuel gas mixture for a gas burner, in particular to generate heat for heating a space and/or supplying hot water, where the gas burner is designed to generate and/or burn a fuel gas-air mixture from the fuel gas mixture and air, characterised in that the fuel gas mixture comprises a methane gas substitute, in particular propane, and hydrogen in predefinable proportions, the fuel gas mixture having properties relevant to combustion that are substantially like those of methane.
2. Use of a fuel gas mixture as claimed in claim 1, characterised in that the fuel gas mixture has a Wobbe index substantially like that of methane.
3. Use of a fuel gas mixture as claimed in claim 1 or 2, characterised in that the fuel gas mixture has a minimum air requirement substantially like that of methane.
4. Use of a fuel gas mixture as claimed in any of the preceding claims, characterised in that the fuel gas mixture has a flame temperature substantially like that of methane.
5. Use of a fuel gas mixture as claimed in any of the preceding claims, characterised in that the meThane gas substitute is propane, the proportions of hydrogen and propane in the fuel gas mixture having a volumetric ratio of hydrogen to propane within a range of 2.13: 1 to 3.00: 1.
6. Use of a fuel gas mixture as claimed in claim 5, the proportions of hydrogen and propane in the fuel gas mixture having a volumetric ratio of hydrogen to propane of 2.39: 1.
7. Use of a fuel gas mixture as claimed in any of claims 1 to 4, characterised in that the methane gas substitute is butane, the proportions of hydrogen and butane in the fuel gas mixture having a volumetric ratio of hydrogen to butane within a range of 3.75: 1 to 4.60: 1.
-14 - 8. Use of a fuel gas mixture as claimed in claim 7, where the proportions of hydrogen and butane in the fuel gas mixture have a volumetric ratio of hydrogen to butane of 4.00: 1.
9. Fuel gas mixture, in particular for use with a gas burner to generate heat for heating a space and/or supplying hot water, in particular as claimed dn any of the preceding claims, characterised in that the fuel gas mixture contains a methane gas substitute, in particular propane, and hydrogen in predefinable proportions, the fuel gas mixture having properties relevant to combustion that are substantially like those of methane.
10. Fuel gas mixture as claimed in claim 9, characterised in that the fuel gas mixture has a Wobbe index substantially like that of methane.
11. Fuel gas mixture as claimed in claim 9 or 10, characterised in that the fuel gas mixture has a minimum air requirement substantially like that of methane.
12. Fuel gas mixture as claimed in any of claims 9 to 11, characterised in that the fuel gas mixture has a flame temperature substantially like that of methane.
13. Fuel gas mixture as claimed in any of claims 9 to 12, where the methane gas substitute comprises at least one of the components propane and/or butane.
14. Fuel gas mixture as claimed in any of claims 9 to 13, characterised in that the methane gas substitute is propane, the proportions of hydrogen and propane in the fuel gas mixture having a volumetric ratio of hydrogen to propane within a range of 2.13: 1 to 3.00: 1.
15. Fuel gas mixture as claimed in claim 14, where the proportions of hydrogen and propane in the fuel gas mixture have a volumetric ratio of hydrogen to propane of 2.39: 1.
16. Fuel gas mixture as claimed in any of claims 9 to 13, characterised in that the methane gas substitute is butane, the proportions of hydrogen and butane in the -15 -fuel gas mixture having a volumetric ratio of hydrogen to butane within a range of 3.75: 1 to 4.60: 1.
17. Fuel gas mixture as claimed in claim 16, where the proportions of hydrogen and butane in the fuel gas mixture have a volumetric ratio of hydrogen to butane of 4.00: 1.
18. Fuel gas mixture as claimed in any of claims 9 to 17, characterised in that the fuel gas mixture consists at least up to 90 c by volume, preferably at least up to 95 10; by volume, particularly preferably at least up to 98 by volume, of methane gas substitute and hydrogen.
19. Fuel gas mixture as claimed in claim 18, characterised in that the fuel gas mixture contains small proportions of inert gases and/or methane and/or other hydrocarbons. 15