NL1010288C2 - Method for the conversion of hydrogen into substitute natural gas. - Google Patents

Description

Method for the conversion of hydrogen into substitute natural gas

The invention relates to a process for the production of methane-rich product gas (SNG, Synthetic Natural Gas) comprising the supply of 5 biomass and / or fossil fuels to a first reactor for the formation of gaseous reaction products and the supply of the gaseous reaction products from the first reactor on a methanation reactor in which the products fed thereto are converted into the methane-rich product gas.

Hydrogen will play an important role in the future sustainable energy supply 10. The transport and storage of hydrogen in free form (¾) is more complicated and is likely to require much more energy than the transport and storage of hydrogen stored chemically in the form of, for example, methane. An additional advantage of the indirect use of hydrogen as an energy carrier is that in the future (sustainable) energy supply, use can still be made of (parts of) the existing large-scale energy infrastructure, such as the natural gas network. One of the possible processes for the storage of hydrogen in chemically bound form is the hydro-gasification of carbonaceous compounds such as, for example, biomass and waste. By pyrolysing these compounds in an H2 atmosphere, green natural gas can be produced.

It is known from EP-A-0 699 651 that biomass, organic waste or fossil fuels can be converted into a gas mixture with a high methane content and small amounts of carbon dioxide in a hydro-gasification reactor with the addition of hydrogen. The gas mixture is converted into synthesis gas in a second process step in a steam reformer, which is converted into methanol in a third process step in the presence of a known Cu / Zn-based catalyst. The hydrogen remaining in the last step, after removal of the methanol, is fed to the hydro-gasification reactor. This process is only suitable for methanol production.

Furthermore, US-A-3,922,148 discloses a process according to the preamble of claim 1, wherein oil is converted into synthesis gas with the addition of steam and oxygen, which is converted in a three-stage methanation process into a product gas with 99 mol% methane and 0, 8 mol% hydrogen. Due to the high CO / CO2 concentrations of the synthesis gas, a number of relatively large methanation reactors are required to convert the synthesis gas into methane. Furthermore, in the synthesis gas reactor combustion of the oil takes place to provide heat for the synthesis gas formation. Due to the relatively large heat loss in the methanation reactors, the efficiency of the known process is low.

It is an object of the present invention to provide a method with which hydrogen can be stored in chemically bound form in an efficient and economically viable manner, wherein relatively little carbon monoxide is present in the synthesis gas formed and in which a simple and relatively small methanation reactor can be used. will suffice. To this end, the method according to the invention is characterized in that the hydrogen comes from an external source and that the product gas has a Wobbe index between 40 and 45 MJ / Nm3, preferably between 42 and 45 MJ / Nm3, and a mole percentage of methane of at least 75%, preferably at least 80%.

By "external" source herein is meant a source which is not formed by the methanation reactor, but which supplies hydrogen to the hydro-gasification reactor independently of the methane production process of the present invention, such as hydrogen formed by the electrolysis of water, steam reforming of light hydrocarbons , hydrogen formed by partial oxidation of heavy hydrocarbons, such as oil or coal, with steam, or from industrial processes such as chlorine production from membrane or diaphragm cells, methanol production, actetone, isopropanol, or methyl ethyl ketone production, or from blast furnaces.

The addition of external hydrogen to the hydro-gasification reactor has shown that a product gas can be obtained with a Wobbe index, a mole of 25% CH4 and a calorific value very close to the Wobbe index, the CH4 percentage and the calorific value of natural natural gas (for example Groningen natural gas), so that the product gas formed can be transported without problems through the existing gas network to customers and used in existing establishments. The method according to the invention can also be operated with a very compact methanation reactor with a small number of parts, while reduction of tar formation (in comparison with other gasification concepts) is also possible.

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In the long term, where hydrogen from electrolysis processes from sustainable sources becomes important, this process is a suitable way of upgrading biomass and organic waste with hydrogen to SNG. In the short term, however, hydrogen can be obtained from fossil sources. An elaboration of this is given by the example below.

In an advantageous embodiment of the process of the present invention, the hydrogen is generated by pyrolysis in a plasma reactor, for example, via the CB&H process as described in S. Lynum, R. Hildrum, K. Hox, J. Hugdahl: Kvaemer Based Technologies for Environmetntally 10 Friendly Energy and Hydrogen Production, Proceedings of the 12th World Hydrogen Energy Conference, vol I, pp.637-645, 1998. The plasma process produces hydrogen and pure carbon from natural gas.

The invention will be further elucidated with reference to the annexed drawing. In the drawing: Fig. 1 shows a schematic representation of the process for the production of a methane-rich product gas (SNG) according to the present invention, and fig. 2 shows a schematic representation of the process according to the invention, wherein the hydrogen is used for the hydro-gasification comes from a plasma process.

Figure 1 schematically shows the process flow for forming substitute natural gas (SNG) according to the invention. Biomass is fed to a dryer 2 via an inlet 1. This biomass can contain wood chips, green waste, or other organic hydrocarbon sources. Instead of biomass, it is also possible to supply fossil fuels to the hydro-gasification installation 3 without the need for a drying step in that case. CO2 is supplied to the supply line 4 of the biomass 25 via an injection line 4 'to inject the biomass at the prevailing operating pressure (for example 30 bar) into the hydro-gasification device 3. Hydrogen coming from an external hydrogen source is supplied to the hydro-gasification device via a supply line 5. The hydrogen source can comprise an electrolysis process of water or it can come from industrial processes in which hydrogen is formed as a by-product.

From the outlet 6 of the hydro-gasification plant 3, gaseous reaction products are withdrawn from the hydro-gasification plant with the main constituent CR »and with CO, H2, CO2 and H2O. The gas mixture is fed via a 1010288 4 heat exchanger 9 to a high temperature gas purifier 7 for the removal of solid residue and gaseous impurities from the synthesis gas such as H 2 S, HCl, HF, NH 3. The solid residue from the hydro-gasification plant 3 is removed via a discharge pipe 8. The purified methane-rich gas mixture is fed via line 10 and heat exchanger 11 to a methanation reactor 12 in which the methane-rich gas mixture is converted into substitute natural gas (SNG), which is led via a heat exchanger 14 and a water separator 15 to a discharge pipe 16. Substitute natural gas can be injected from there into the existing gas network for transport to the final consumer.

The heat extracted from the methane-rich gas mixture at outlet 6 and in line 10, as well as the heat extracted from the product gas at outlet 13, is supplied via the heat exchangers 9, 11 and 14 to a steam generator 19, the steam of which is generated to a steam turbine 20 which drives generator 17 for electricity production. The condensed steam is returned from the steam turbine 20 via 15 a return line 22 to the entrance of the steam generator 19. Part of the low-pressure steam from the steam turbine 20 is heated via a heat exchanger 18 in the dryer 2. The condensed low-pressure steam is after passing the heat exchanger 18 supplied to the steam generator 19.

In the hydro-gasification plant 3, the following reactions take place, inter alia: C + 2 H2 <- »CH4 (1) CO + 3 H2 o CH4 + H20 (2) 2 CO <-> C + C02 (3) C0 + H20oC02 + H2 (4)

At a constant temperature (T = 800 ° C), in the absence of the supply of hydrogen at a thermodynamic equilibrium, an increase in pressure in the reactor would lead to: a decrease in the CO and H2 concentration and an increase in the concentrations of CH4, CO2 and H20 in the synthesis gas discharged via the discharge pipe 6; a decrease in the conversion of carbon from the biomass, and a decrease in the heat required in the reactor 3.

The above mentioned reaction number (4), the watergas shift equilibrium, is independent of the pressure, while the other reactions shift to the right with increasing pressure and are all exothermic in this direction.

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At higher operating temperatures, at a pressure P = 30 bar, in the absence of hydrogen supply and at thermodynamic equilibrium, the above four equilibrium reactions shift to the left, resulting in: an increase in CO and H2 concentrations, and a decrease in CFL , CO2 and 5 F 2 O concentration in the synthesis gas discharged via discharge pipe 6, an increase in the carbon conversion of the biomass and an increase in the heat demand of the reactor.

The process only becomes autothermic at temperatures below 550 ° C.

The supply of hydrogen at T = 800 ° C, P = 30bar and at thermodynamic equilibrium causes the following effects in the hydro-gasification process in the hydro-gasification plant 3: an increase in the methane concentration and a decrease in the heat demand according to reactions (1) and (2 ), a decrease in the CO concentration according to reaction (2) and 15 - an increase in the carbon conversion according to reaction (1).

At a supply of hydrogen via the supply line 5 of 75 mol / kg of biomass (moisture-free), the synthesis gas formed in the hydro-gasification plant 3 comprises 29% by volume of methane and 7% by volume of CO and with a carbon conversion of the biomass of 78% at a heat demand. of 1.2 MWth / kg biomass (moisture-free). When further discussing biomass, this means anhydrous biomass. An increase in the working pressure at T = 800 ° C, at a hydrogen feed of 75 mol / kg of biomass, results in an increase in the carbon conversion since reaction (1) becomes dominant in this case.

The process parameters in the hydro gasifier 3, the high temperature gas cleaner 7, and the methanation reactor 12, which have formed the basis for calculating the composition of the substitute natural gas (SNG) discharged through the discharge line 16, will be further explained below. The calculation is based on biomass in the form of poplar sawdust with the composition as given in table 1: 1010288 6

Table 1 Specification of the biomass (Poplar sawdust)

Unit Value

Composition C wt% 51.32 H wt% 6.16 N wt% 1.18 S wt% 0.13 O wt% 34.57

Ash wt% 6.64

Total wt% 100.00

Lower calorific value (LHV) anhydrous MJ / kg 21.57

Lower calorific value (LHV), 30 wt. % moisture MJ / kg 14.53

The hydro gasifier 3 was operated in the calculation model at a temperature of 800 ° C and a pressure of 30 bar. At this setting, under a certain deviation from the thermodynamic equilibrium, a carbon conversion of the biomass of 89% can be obtained, with a hydrogen feed of 75 mol / kg of biomass, and the process is autothermic. However, since the supplied biomass is not free of moisture and additional CO2 is supplied to the hydrofluidizer 3, to make the process autothermal, the hydrogen feed in the model was increased from 75 to 100 mol / kg of biomass. At this setting, a conversion of carbon from the biomass of 83% is predicted.

The gaseous products from the hydro-gasification reactor 3 are cooled in two steps from 850 ° C to the inlet temperature of the first methanation reactor at 400 ° C via heat exchangers 9 and 11. In this temperature range, a high temperature gas purifier 7 can be used to remove solid residue and gaseous impurities such as H 2 S, HCl, HF, NH 3 from the synthesis gas.

The methanation reactor 12 is based on the ICI high temperature single pass process as described in the Catalyst Handbook, second 20 Edition, Edited by M.V. Twigg, ISBN 1874545359, 1996. It employs a series of reactors operating at successively lower starting temperatures.

Superheated steam is generated in the steam generator 19 at a pressure of 40 bar. The heat from the methanation reactor 12 as well as from cooling the methane-rich synthesis gas via heat exchangers 9 and 11 was used in the model to generate steam while the remainder of the heat released during the cooling of the methane-rich gas mixture in lines 6 and 10 was used for steam superheat. The steam formed was expanded in two steps to 0.038 5 bar. (The first step from 40 to 10 bar and the second step from 10 to 0.038 bar.)

Based on the above process settings, the mass and energy balance of the system of Figure 1 has been calculated using the ASPEN PLUS process simulation program. Table 2 shows the properties of Groningen natural gas (NG) and synthetic natural gas (SNG) formed in the hydro-gasification process according to figure 1. It is very important to see that the calorific value in MJ / kg and the Wobbe index of synthetic natural gas are virtually the same as that of natural natural gas. It is hereby possible to inject the product gas formed in the hydro-gasification process according to figure 1 directly into the natural gas network and burn it with existing installations.

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Table 2 Properties of piling product gas (SNG) and Groningen natural gas (NG)

NG SNG composition

CH4 mol% 81.30 81.55 H2 mol% 0.00 8.70 CO2 mol% 0.89 8.54 C2 + mol% 3.49 <1 N2 mol% 14.31 0.77 02 mol% 0.01 0.00 molecular weight kg / kmol 18.64 17.33 lower combustion value (LHV) MJ / kg 38.00 39.00

Lower calorific value (LHV) MJ / kmol 708.32 676.08

Wobbe index MJ / Nm2 44.20 43.87

The Wobbe index, based on normal cubic meters (Nm3) at 0 ° C and 1 atmosphere (MJ / Nm3), is the ratio of the gross calorific value and the square root of the relative density of the gas. The Wobbe index is defined according to the following formula: 1010288 8

w- HHV

yj (Pg tPlucht)

In this, HHV is the upper calorific value in MJ / Nm3 and pg and piUCht are the densities of gas and air in kg / Nm3 respectively. The Wobbe index is a measure of the amount of energy that is delivered to a burner via an injection. Two gases of different composition but with the same Wobbe index provide the same amount of energy for a predetermined injection device at the same injection pressure.

Figure 2 shows an embodiment of a method according to the present device in which the hydrogen is formed via a CB&H process as described in R.A. Wijbrans, J.M. van Zutphen, D.H. Recter: "Adding New Hydrogen to the Existing Gas Infrastructure in the Netherlands, Using the Carbon Black & Hydrogen Process, Proceedings of the 12th World Hydrogen Energy Conference", vol. Pp, pp 963-968, 1998. Herein natural gas is supplied via a supply line 23 to a plasma reactor 24, in which a plasma is generated by supplying electric energy and in which hydrogen and carbon are formed. After passing through a heat exchanger 25 and a separator 26, in the known CB&H process, the carbon for blasting and packaging is discharged and the hydrogen is sent to a compression and injection device 27 and subsequently injected into the natural gas network. According to the invention, the hydrogen is supplied to the hydro-gasification process via the feed line 5 instead of to compression and injection device 27. The use of the high-temperature plasma process for production of hydrogen from natural gas in combination with the hydro-gasification process has the advantage that the The CB&H process involves pure carbon, whereby the reduction in calorific value by conversion of natural gas into hydrogen is more than 100% compensated by the reaction of the hydrogen back to SNG. This means that the fossil carbon disappears from the chain while sustainable carbon is supplied from the biomass with a net energy gain by introducing biomass of roughly 60%.

1010288

Claims (9)

1. Process for the production of methane-rich product gas (SNG, Synthetic Natural Gas) comprising the supply of biomass and / or fossil fuels to a first reactor for the formation of gaseous reaction products and supply of the reaction products from the first reactor to a methanation reactor in which the gaseous reaction products fed thereto are converted into the methane-rich product gas, characterized in that the first reactor comprises a hydro-gasification reactor to which hydrogen is supplied, which hydrogen comes from an external source and the product gas (SNG) has a Wobbe index between 40 and 45 MJ / Nm3, preferably between 42 and 45 MJ / Nm3, and with a mole percentage of methane of at least 75%, preferably of at least 80%. Method according to claim 1, characterized in that the product gas (SNG) 15 has a calorific value corresponding to the calorific value of natural natural gas. Method according to claim 1 or 2, characterized in that the product gas is injected into a natural gas pipeline system and transported to consumers. 20 Process according to claim 1, 2 or 3, characterized in that the hydro-gasification reactor is operated at a temperature between 500 ° C and 1500 ° C, preferably between 750 ° C and 850 ° C, at a pressure between 15 bar and 200 bar, preferably between 20 bar and 40 bar. 25 Method according to claim 4, characterized in that CO2 is supplied as transport gas to the biomass or fossil fuels for injection thereof into the hydro-gasification reactor. Process according to any one of claims 1 to 5, characterized in that the amount of hydrogen supplied to the hydro-gasification reactor is regulated such that the hydro-gasification in the hydro-gasification reactor proceeds at least substantially autothermally. 1010288 Process according to claim 6, characterized in that between 50 and 125 moles of hydrogen per kg of moisture-free biomass is fed to the hydro-gasification reactor. Process according to any one of the further claims, characterized in that the heat produced in the methanation reactor is supplied to a steam generator. Process according to any one of the further claims, characterized in that the hydrogen from natural gas is formed by pyrolysis in a plasma reactor. iOlül65