Field of the Invention The invention relates to the separation of hydrogen gas, and concentration of methane from a feed gas mixture (FGM) such as for residential/commercial gas sources having hydrogen and methane as the major components.

Background

A hydrogen rich feed gas mixture, whilst readily available, lacks the energy rating that a higher methane component may provide. Hydrogen itself is a valuable resource and so its efficient extraction may allow for applications requiring high purity hydrogen including energy generation.

The generation of town gas (coal gas) represents a low cost alternative to natural gas but lacks sufficient high methane composition as compared to natural gas, it would therefore be useful to be able to generate both a high purity hydrogen stream and a methane rich gas stream using an efficient process. Summary of Invention

In a first aspect, the invention provides a method for generating hydrogen gas, the method comprising the steps of: injecting a feed gas mixture comprising methane and hydrogen to a first chamber of a membrane unit, said membrane unit having a membrane separating the first chamber from a second chamber; passing hydrogen through the membrane and so separating from the feed gas mixture; venting the separated hydrogen through a second outlet in the second chamber; venting the separated feed gas mixture through the first outlet in the first chamber.

In a second aspect, the invention provides a hydrogen gas generation system comprising; a gas membrane unit, said gas membrane unit having a first chamber arranged to receive a feed gas mixture comprising methane and hydrogen, and a membrane separating the first chamber from a second chamber; the membrane arranged to allow hydrogen to pass through, whilst retaining the remaining feed gas mixture; the second chamber including a second outlet in for venting the separated hydrogen; the first chamber including a first outlet for venting the separated feed gas mixture.

The invention relates to a means of separating a hydrogen rich feed gas mixture (e.g. town gas) so as to produce a methane rich feed stock for power generation normally associated with natural gas. The high-purity hydrogen separated from the feed gas mixture can then be used for other power generation uses such as fuel cells, or for other industrial applications.

The system according to the present invention may be implemented as a compact and modular gas concentrating system coupled with a power generating system. Part of the power generated from the system according to the present invention may be used to power axillary equipment for the separation process so as to achieve a self-sustaining operation.

The present invention may provide the following advantages:

• Onsite Hydrogen Generation - The system is capable of generating high-purity hydrogen gas using FGM at the site of hydrogen utilisation. This may reduce hydrogen transportation problems.

• Efficiency improvement - by using the gas concentrating system, a substantial part of hydrogen gas is separated from the original FGM, essentially boosting up the methane number count and hence heating value of the FGM. In doing so, the efficiency of electrical power generation using resulting methane-rich gas improves.

• Compactness and Scalability - The gas concentrating system in the invented system may be implemented in a compact and scalable way which makes the deployment relatively flexible. · Reduced CO2 emission - Should the separated hydrogen gas be used for electrical power generation, a system according to the present invention may emit less CO2 compared to a natural gas feed with the same amount of power generated since the carbon content in FGM is lower than that of natural gas.

Brief Description of Drawings

It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

Figure 1 is a flow chart for the separation process according to one embodiment of the present invention;

Figure 2 is a flow chart for the pre-filter and compression of the FGM according to one embodiment of the present invention; Figure 3 is a flow chart for the membrane separation process according to a further embodiment of the present invention;

Figure 4 is a flow chart for a pressure swing absorption system according to a further embodiment of the present invention;

Figure 5 is a flow chart for a power generating system according to a further embodiment of the present invention; Figure 6 is a flow chart for a separation and delivery system according to a further embodiment of the present invention, and;

Figure 7 is separation process according to an alternative embodiment of the present invention.

Detailed Description

Figure 1 shows an overview of the system 5 according to the present invention. A feed gas mixture 10 is introduced into a gas concentrating system 15 which is arranged to concentrate methane 25 while separating hydrogen 30. The process may produce high- purity hydrogen 30 at concentrations up to 99.99%. The methane rich gas 25 is then delivered to a power generating system 20 normally associated with natural gas, which consequently generates electricity 35. Figure 2 shows the initialising process 40 whereby the unfiltered FGM 45 is introduced to a pre-filter so as to remove entrained solids within the gas. It will appreciated that the filter 50 may also separate moisture prior to compression 55 to produce a filtered pressurized FGM 60 prior to introduction into the separation/concentration process 65. It will be appreciated that the process 65 of Figure 3 may considered a separate component from the overall system, whereby it is arranged to receive any incoming hydrogen/methane rich gas 60 into a first chamber of a gas membrane system 70. In the present embodiment the filtered FGM 60 is compressed by, for example, up to 15 bar prior to entering the gas membrane system 70. The membrane is arranged to allow the hydrogen to pass through into a second chamber when under sufficient pressure, whilst retaining the remaining feed gas mixture. The separated hydrogen, at a now lower dissipated pressure, is vented from the second chamber through a second outlet and subsequently passed through a second compressor 75 for delivery 80 to a downstream application for the high-purity hydrogen.

The separated feed gas mixed, being methane rich, is vented through a first outlet of the first chamber, and then delivered 85 to subsequent power generation system.

Figure 4 shows one embodiment for the further concentration of hydrogen. Here a secondary separation device 100 within the concentration system 95 removes residual methane 115 to produce a much higher purity hydrogen 110. The secondary separation device may be one of a pressure swing adsorption, cryogenic separation and thermal reforming system. This may be used for downstream applications, particularly where high purity is beneficial, such as fuel cells. It will noted that, for the use in fuel cells which may not react well to the introduction of methane, therefore a particularly useful application to the system of the present invention.

The residual separated methane 115 may then be combined with the separated methane and from the previous concentration process for subsequent use in power generating systems. Figure 5 shows one power generating system 120 arranged to receive the methane rich gas 85, 115. It will be noted that, following the gas concentration and pressure swing adsorption processes, that the gas 85, 115 entering the power generating system 120 may have a methane volume percentage of about 45% as compared to a typical 26% found in town gas. It will be appreciated that these proportions may vary depending upon the source of the feed gas mixture first entering the overall system.

This greater concentration of methane substantially improves power generation efficiency within the power generation system 120, with the de-rating value dropping to about 28% as compared to 40% observed with various sources of FGM. When combined with the potential power generation from the high purity hydrogen 110, the power generation capacity and overall efficiency of the system is therefore greatly enhanced. It will noted that in this embodiment the power generating system 120 comprises a natural gas engine 130 including an engine 135 in communication with a radiator 140 with the system 120 producing electricity 145.

As mentioned, each of the embodiments shown in figures 2, 3, 4 and 5 may be used separately, subject to the feed stock being received and subsequent application of the resulting gas concentrations. In a still further embodiment, the system 150 may comprise each of the aforementioned processes such that a feed gas mixture 165 passes through a filter 170 and compression unit 175, to be separated 180 into a hydrogen stream 190 and a methane stream 185. The hydrogen stream 190 is further compressed 195 before passing through a pressure swing adsorption device 200 to produce a high purity hydrogen stream 205 for use in a fuel cell 210 or other industrial applications 215. This represents a first step of a gas concentration 160.

The separated methane rich gas 185 is combined with the residual methane 220 to enter the power generating system 155 which is directed to a natural gas engine 225, for subsequent generation of electricity 240.

Figure 7 shows a further embodiment of the gas membrane system 245.

In this particular example, the key parameters include:

Feed Gas Mixture 250 Compressed FGM 255

Pressure = 16 bar

Pressure = 1.5 bar Volume = 700 Nm3/h

Volume = 700 Nm3/h Energy = 3075 kWh

Energy = 3075 kWh

Composition

H ₂ vol% = 50%

Methane vol% = 27% H2-rich Gas 260 Pure Pb Gas 265

Pressure = 11 bar Pressure = Customer requirement

Volume = 400 Nm ³ /h Volume = 281 NmVh

Energy = 1137 kWh Energy = 805 kWh

Composition Composition

H 2 vol% = 80% H ₂ vol% = 99.99%

Methane vol% = 5%

Methane-rich Gas 270

Pressure = 1.5 bar

Volume = 419 NmVh

Energy = 2270 kWh

Composition

H 2 vol% = 16%

Methane vol% = 45%

The gas membrane system, comprising a membrane unit 275, includes a membrane 280 dividing the unit into two chambers 285, 290. As the compressed FGM 255 enters the first chamber, the elevated pressure combined with the membrane 280 separates the hydrogen from the FGM 255. Typical materials for hydrogen separation membrane may include polymers with a thin coating of palladium alloy composite. A number of hydrogen separation membrane products are known in the industry, and available from various gas processing. According to one embodiment, the rotary PSA 295 may be arranged such that only process gas temperatures of up to 60°C may be allowed. As such the preferred temperature range allowed for the invention system may up to 60°C. As both the membrane systems 275 and the PSA system 295 are non-heat exchanging unit thus temperature drop across both systems are negligible, i.e. if the feed 255 to the membrane system 275 is 35°C, then the hydrogen gas and methane-rich gas will be

35°C.