Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
  • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
  • C10L3/10—Working-up natural gas or synthetic natural gas
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
  • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
  • C10L3/08—Production of synthetic natural gas

Definitions

• Biomass such as wood and other vegetable material and other hydrocarbon-containing materials, can be combusted directly, whether or not after admixing fossil fuels.
• the heat released can be used to generate heat and power, for instance in the form of electricity.
• the gasses which are released in such biological degradation can then be combusted, likewise yielding heat and/or power.
• US-A-3 854895 describes the gasification of coal in the presence of steam and oxygen for obtaining fuel gas.
• This fuel gas is converted in three methanization steps to a methane-containing gas.
• An essential step in this process is converting a part of the CO to CO2 and hydrogen gas, followed by washing out of the CO2. for obtaining a proper ratio of hydrogen, carbon monoxide and carbon dioxide.
• US-A-3 642 460 describes a process for making methane from a paraffin flow. To this end, the hydrocarbons are subjected to a steam reforming step, followed by a methanization step. During both steps, water cooling takes place. The thus obtained steam is recirculated.
• SNG is made from biomass and/or fossil fuel by first gasifying and then carrying out a methanization step.
• hydrogen gas By feeding hydrogen gas to the gasification step, it is intended in this reactor to already produce a considerable amount of methane,
• a typical fuel gas obtained by gasification of biomass contains 1 - 5 % by volume of unsaturated hydrocarbons, among which approximately 0.5 vol.% of aromatic compounds, in particular so-called BTX'cs (i.e. benzene, toluene, xylene and naphthalene compounds).
• BTX'cs i.e. benzene, toluene, xylene and naphthalene compounds.
• the object of the present invention is to provide for a method for making a methane-rich product from hydrocarbon-containing material, such as biomass, which at least partly eliminates the above-mentioned disadvantages. It has been found that if at least a part of the hydrogen of the methane- containing gas flow, obtained by methanization of a fuel gas, is separated and is used in the methanization, this object can be achieved. Therefore, the present invention relates to a method for producing a methane-rich gas, comprising the following steps:
• Fuel gas is understood to mean a gas which consists for an important part of CO and Ho, for instance of more than 30 vol.% CO and more than 10 vol.% H2.
• a typical fuel gas composition comprises 40-55 vol. % CO and 20-40 vol.% H2.
• the method according to the invention can be very well used with both economic and environmental advantage, starting from a feed flow which comprises hydrocarbon-containing waste such as plastic.
• a practical embodiment of the invention preferably comprises the following steps: a) converting hydrocarbon-containing material to a fuel gas in a gasifier; bl) cleaning the fuel gas in a cleaner for removal of contaminants; b2) passing the cleaned fuel gas through a guard bed; c) methanizing the product of the preceding step in a methanization reactor; whereby heat is released; d) removing water and drying the methanized gas; e) separating hydrogen from the methane-rich product of the preceding step, wherein this hydrogen is used in the methanization reaction or the preceding process; £) reprocessing the product of the preceding step in a reprocessing unit into a methane-rich product.
• a gas Due to the conversion of fuel gas to a methane-rich product according to the invention, a gas can be obtained which can be converted very effectively to useful energy via existing infrastructures, such as the gas network, in existing and new high efficiency apparatuses, such as central heating installations, combined heat and energy plants, gas engines, etc. Moreover, by preparing the fuel gas from renewable sources (such as biomass), the gas obtained is durable. Methane has a higher energy density or calorific value (indicated in J/m 3 ) than fuel gas.
• the methane-rich product produced according to the method of the invention can be reprocessed to a product with a Wobbe-index and calorific value comparable to that of natural gas of a particular origin (the composition of natural gas varies per country and/or per location).
• the Wobbe- index is a measure for the amount of enthalpy which can be added with a particular gas composition per unit of time to a system, for instance an engine or a stove.
• the efficiency obtained per unit of hydrocarbon-containing material is much higher than when the fuel gas is used directly for the production of electricity, or higher than when the hydrocarbon-containing material is directly converted to electricity, not via gasification but via conventional routes.
• the methane- rich product can be used directly for, for instance, heating, or as a fuel for WK -units with, for instance, gas engines.
• hydrocarbon-containing material such as biomass (vegetable or animal) is gasified, i.e. converted to a gas mixture containing substantially CO and H2.
• gasification medium air, oxygen or steam. Combinations thereof are also possible.
• air gasifier has as a drawback that, with it, nitrogen from the air is introduced into the process. This nitrogen needs to be removed so that, generally, the costs of operation of the installation according to the invention will prove to be higher than when one of the gasifiers of the other type is used.
• oxygen gasifiers, steam gasifiers and combinations thereof are preferred.
• Another great advantage of oxygen gasifiers, steam gasifiers and combinations thereof is that the temperature in the gasifier and at the end of the gasifier can be considerably higher than in an air gasifier. As a result, the amount of tar present in the fuel gas decreases strongly. The gasification process with oxygen is exothermic, hence, heat is released.
• the gasification process with steam is endothermic, hence, it requires heat.
• the gasification process with oxygen can produce the heat for the gasification process with steam.
• the heat can, at least partly, be added to the feed flow (biomass, waste, etc. and/or the oxygen and steam to be used) by heating this with the heat released elsewhere in the process or by using it to cool the fuel gas coming from the gasifier.
• the combination of oxygen and steam gasification and the use of residual heat for the steam gasification process more CO and H can be produced from the same amount of biomass, waste or other organic flow, because less of the feed flow (or fossil fuel) needs to be combusted to CO2 and H2O and the steam is also an extra source of hydrogen.
• a sufficient amount of energy from residual sources is fed into the gasification process, even with use of biomass, a part of the CO 2 formation as a result of the presence of oxygen in the biomass can be prevented.
• the fuel gas After the gasifier, the fuel gas can be cooled with the oxygen and/or steam feed flows by heat exchange before the gasifier. As a result, a large part of the heat of the fuel gas after the gasifier can effectively be returned to the gasification process to improve the total efficiency of the process. Also, the fuel gas can be cooled down while forming high pressure steam, which can be converted with a steam turbine to useful work, for instance into electricity or compression work.
• the contaminating components in the fuel gas are reduced to an acceptable level for the methanization step.
• concentrations of sulfur compounds, halogen compounds and nitrogen compounds need to havo an acceptable level.
• other contaminating components such as tars, ammonia, (heavy) metals and dust also have to be reduced to an acceptable level.
• cleaning gasses such as processes based on washing, adsorption and/or particle separation.
• mercury Hg
• Cd cadmium
• Se the volatile metals
• HCN and COS are converted via hydrolysis in the washing liquid to, inter alia, NHa and HgS.
• An alternative is simultaneous catalytic hydrolysis of HCN and COS at temperatures above 200*C.
• H 2 S it can be desirable, in particular for H 2 S, to use regenerative washing processes and to reprocess the released H 2 S in a Claus- unit (suitable for > 20 tons S/day) to sulfur.
• a Claus- unit suitable for > 20 tons S/day
• washing processes exist which oxidize H2S in the washing liquid to sulfur.
• the through-put speed of the gas through the guard bed is bound to a maximum. This results in a minimal size of the adsorbent volume in the guard bed.
• the amount of adsorbent and the through-put speed through the guard bed depend, inter alia, on the desired degree of purity, the frequency with which the beds are replaced and the degree of contamination in the preceding cleaning step.
• One of the current materials for adsorbing H2S is, inter alia, activated alumina.
• a very suitable chemical adsorbent for H 2 S is zinc oxide (ZnO).
• ZnO zinc oxide
• This adsorbent acts optimally at approximately 200-350°C. This is advantageous as such temperatures are well in line with the required temperatures for the shift reaction and the methanization reaction. As a result, it is possible to omit a cooling or heating step between the guard bed and the methanization step.
• the guard bed based on ZnO makes it possible to reduce the content of sulfur compounds to less than 100 ppb (mol/mol).
• Halogen compounds in the gas can react with ZnO to volatile and corrosive zinc halogenides, which are transported with the process gas to the methanization reactor, where they precipitate on the catalyst and deactivate it.
• an adsorption bed on the basis of ZnO can be combined with a layer of an adsorbent which adsorbs the halogen compounds before the process gas reaches the ZnO adsorbent.
• the layer can consist of, for instance, activated alumina or sodium aluminate on an alumina carrier material.
• the guard bed can be designed in a so-called two-bed system. Then, two beds with adsorbent are arranged next to each other and the feed can be circuited thus, that it is guided over one of the two beds. The bed which is not in operation can then be replaced or regenerated, without the processing needing to be interrupted. After replacement or regeneration, the flow can be diverted for flowing through the regenerated bed so that the other bed can be replaced or regenerated. Particularly effective is the so-called "lead/lag" configuration, which comprises at least two beds, and wherein a ("lag") bed contains the regenerated or fresh adsorption material. The lag-bed is serially connected with a partly loaded (“lead”) bed, which is the first to be flowed through.
• the lead-bed When the lead-bed has been loaded to a particular value, it is regenerated or renewed, while, temporarily, only the lag-bed provides for the adsorption. After regeneration, the regenerated bed is deployed as lag-bed and the cycle can be repeated. This configuration can easily be obtained by switching the flows. In this manner, a maximum loading of the adsorbent is obtained.
• a typical fuel gas composition such as it can be obtained by gasification of hydrocarbon-containing materials and after cleaning and passage through the guard bed, is represented in Table 1.
• Air or oxygen gasifiers and gasification feeds with a relatively low moisture content give a fuel gas with a H2 CO ratio of typically 0.5 - 1. Otherwise comparable feeds with a high moisture content (30 - 40%) and/or steam gasification yield a H2/CO ratio of >1.
• the use of O2 and steam in the gasifier under the conditions wherein the water-gas-shift reaction occurs can increase the Hs CO ratio. In this manner, a H2/CO ratio of 2 to 3 can be achieved.
• Methanization reaction Methanization of the cleaned fuel gas takes place in a methanization reactor.
• the methanization of fuel gas can proceed according to reaction (ID. and/or (III).
• the methanization step upstream of the methanization step, for instance in one of the preceding purification or separation steps. It is also possible to pass the hydrogen- rich gas flow to the fuel gas production step. Also if the fuel gas production step is carried out in the presence of oxygen (for instance from air), the recycling of the hydrogen-rich gas flow can be advantageously used.
• oxygen gasifier two zones can be distinguished. In the first zone, combustion of the hydrocarbons takes place, whereby water, CO2 and heat are produced. In the second zone, all oxygen has been used up and the hydrogen can be safely, i.e. without an explosive mixture being formed, be recycled.
• the heat which is recovered from the product gas after the methanization reactor can be used for operating a heat pump.
• a heat pump known in the art, elsewhere in the process, for instance in the reprocessing, cooling can take place.
• the hydrogen-rich gas flow is recirculated and can, for instance, be fed to the fuel gas at a suitable location.
• the hydrogen-rich gas flow can be supplied at any suitable point before the methanization step.
• the above-mentioned considerations should be taken into account if the hydrogen-rich gas flow is guided to a fuel gas production step operated with oxygen.
• polyimide-membrane systems are utilized. These have a relatively high chemical resistance and, in comparison to other polymer membranes, can be used to a relatively high temperature (up to 150°C).
• This pre-separation has as an advantage, that the volume flows can be smaller and therefore the equipment too.
• Another advantage is that less steam needs to be added to the reactor, since the risk of carbonization has considerably decreased due to the removal of CO2, while the final SNG production remains guaranteed.
• the separation of CO2 before the methanization step therefore not only leads to an extra reduction of the total volume flows (and a corresponding reduction of the equipment), but also increases the efficiency of the total plant.
• a fuel gas which has been obtained by gasifying hydrocarbons in a gasification step (not represented) and largely cleaning in the cleaning step bl (not represented) is raised in pressure with the aid of a compressor to 13 bara.
• the temperature of the gas increases considerably. This is favorable since the successive guard beds operate at a temperature of 200 - 350"C.
• step (b2) the sulfur compounds and halogen compounds are virtually completely removed (sulfur compounds ⁇ 150 ppb (mol/mol) and halogen compounds ⁇ 30 ppb (mol/mol).
• the cleaned gas is passed to the methanization reactor (c), together with an amount of steam. In the methanization reactor, the conversion of CO and hydrogen to methane takes place.
• the thus obtained product gas consists mainly of CO2, CH 4 , and H2.
• the hydrogen is separated from the product gas. In Fig. 1, this i& done by means of membrane separation.
• the hydrogen-rich gas is returned to the feed of the reactor by adding this to the fuel gas before the compression step.

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• 2001
  • 2001-05-28 NL NL1018159A patent/NL1018159C2/nl not_active IP Right Cessation
• 2002
  • 2002-05-27 EP EP02736279A patent/EP1390456A1/de not_active Withdrawn
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