ITRM20130367A1 - GROUP FOR THE PRODUCTION OF GAS METHANE ISSUED BY THE SOIL - Google Patents

Description

DESCRIPTION

of the patent for industrial invention entitled:

â € œ GROUP FOR THE PRODUCTION OF METHANE FROM GAS EMITTED FROM THE SOILâ €

The present invention relates to a group for the production of methane from gas emitted from the ground.

As is known, some quiescent volcanic areas are characterized by a more or less continuous release of gas from the soil, consisting mainly (from 95 to 99% vol) of carbon dioxide (CO2). In areas where the phenomenon of natural degassing from the soil occurs, the gas emitted includes, in addition to CO2, also nitrogen, water vapor, hydrogen sulphide, methane and to a lesser extent radon.

The gaseous manifestations are associated with faults that cut structural highs of buried carbonate rocks that host underlying aquifers. The CO2 content in these areas can reach values of the order of 10-50,000 g / m2 / day.

The need was therefore felt to use the large quantity of CO2 emitted from the soil in a productive manner, at the same time limiting its environmental hazard.

For a correct understanding of the present invention, a few words must be spent on the problem of the storage of energy from renewable sources.

The incidence of production from renewable sources in the global electricity market is greater year after year, both in Italy and in Europe. A typical feature of these renewable sources (wind, solar, biomass, etc) is that they are not programmable over time. The consequent uncertainty of injecting energy into the grid determines the need to identify solutions that allow the stabilization of the national electricity system.

This includes the accumulation systems that store the surplus of energy if the transmission grid is not suitable for safely disposing of all the power generated by non-programmable renewable sources. Generally, electrical storage systems can be defined as systems that store electrical energy by converting it into another form of energy (chemical, mechanical, electrostatic, electromagnetic).

The most common energy storage systems are electrochemical accumulators, also known as batteries, these systems allow medium-term storage (<1 day) with limited use due to their low energy, power density and duration. Other systems include pumping and hydroelectric production plants.

For the long-term conservation and seasonal balancing of renewable energy sources, chemical storage systems that convert electricity into energy carriers such as hydrogen or methane may be the most suitable candidates.

The purpose of the present invention is to provide a solution whose technical characteristics are such as to satisfy the needs relating to both CO2 emissions from the soil and the storage of energy from renewable sources.

The object of the present invention is a unit for the production of methane from gas emitted from the ground, the essential characteristics of which are reported in claim 1, and whose preferred and / or auxiliary characteristics are reported in claims 2-6.

A further object of the present invention is a method for the production of methane whose essential characteristics are reported in claim 7, and whose preferred and / or auxiliary characteristics are reported in claims 8-10.

An embodiment is shown below for illustrative and non-limiting purposes with the aid of the figure in the attached drawing, which illustrates in schematic form the group object of the present invention.

In the figure, 1 indicates as a whole an embodiment of the group object of the present invention.

Group 1 comprises means for capturing the gas from the ground 2, a gas treatment device 3, means for generating electricity from renewable sources 4, an electrolyser device 5, a methanation reactor 6 and a methane treatment device product 7.

The means for capturing the gas from the ground 2 are made with systems which provide for the containment of the gaseous flow coming from natural degassing phenomena from the soils in a confined environment. Generally, these collection means are marketed to collect the biogas produced by landfills. Preferably, the capturing means 2 comprise a natural filling material (such as gravel and clay) or polypropylene or stainless steel frames supporting a layer of sheath and / or covering sheets designed to prevent gas leaks from the captation system, and a gas suction system consisting of a centrifugal extractor.

The gas thus withdrawn is conveyed into the gas treatment device 3, whose main task is to remove the sulfur compounds from the gas itself in order not to jeopardize the subsequent methanation phase by deactivating the catalyst.

The removal of sulfur compounds can be achieved through technologies that provide for absorption through wet or adsorption on high temperature sorbents. Wet desulphurization involves washing with water or with selective solvents against H2S based on soda or amines, which remove the sulfur compounds through absorption in the liquid medium. Generally, absorption takes place in filled towers or columns and is favored by low temperatures of the order of that of the environment and pressures which, depending on the type of absorption, of a chemical or physical nature, can range from ambient pressure to pressures higher. The wet absorption involves a regeneration section of the solvent with the consequent waste of energy and the recirculation of the regenerated solvent to the absorber. This technology is commercially widespread and lends itself in industrial practice to rather large plant sizes given the complexity and costs of the system.

Preferably, the gas treatment device 3 performs a high temperature desulphurization, presenting the advantages connected with the possibility of treating solids and non-liquids with an obvious simplification in management and costs.

High temperature desulphurization is based on the adsorption of H2S on metal oxides of alkaline and transition origin, capable of removing sulphides up to parts per million, and regenerable through oxidation with oxygen or air.

The main distinction between the two types of oxides is the possibility or not of regenerating the sulphate that is formed. Non-regenerable adsorbents contain alkali metals (Ca, Ba, Sr) and these include limestone and dolomite. Conversely, regenerable adsorbents contain transition metals (Fe, Zn, Mn, Cu, Ni, etc.) and can be based on single oxides, combinations of different oxides and combinations of oxide and inert. Generally, the pure oxide phase is confined to supports which increase the surface area and decrease its tendency to sinter.

Indicating with Me the generic metal used, the rations involved can be summarized as follows:

MeO + H2S â † 'MeS + H2O adsorption ∠† H <0 The reaction takes place above 250 ° C while the regeneration takes place in an atmosphere of air diluted in nitrogen or in a vapor stream and develops in the temperature range of 500 ° C -900 ° C with the following reaction:

MeS + 3 / 2O2â † 'MeO + SO2 regeneration ∠† H> 0 The presence of means of generating electricity from renewable sources 4 is an option that may not even be envisaged if a direct interface of group 1 with the grid is considered electric. The production of electricity from renewable sources has the function of covering the electricity needs of group 1 as a whole. In particular, we mainly refer to the electrical needs of the electrolyser and, secondarily, of the auxiliary electrical users, such as eg. water recirculation pumps, compressors, aspirators and instrumentation. The means of generating electricity from renewable sources 4 may preferably comprise a photovoltaic system of the size necessary to cover internal users or of a larger size in the event that surplus electricity is to be transferred to the grid. This type of implant is immediately available on the market.

Small and medium-sized wind power plants could also find their use in this system.

Alternatively and as previously mentioned, it is possible to foresee that group 1 is connected directly to the electricity grid in order to absorb the production surplus at reasonable costs (application as energy storage).

The electrolyser device 5 can be of the alkaline type which uses an aqueous solution of an alkaline hydroxide-based electrolyte with a concentration between 25% and 35%. Conventional alkaline electrolysers work with a pressure close to that of the environment and with operating temperatures ranging between 70 ° C and 90 ° C and a cell voltage ranging from 1.8 to 2.25 V. production of 1 Nm <3> of hydrogen are around 4-6 kwh / Nm <3> H2 with efficiencies between 60 and 70%. Generally this type of electrolyzers can work from 1 to 30 bar.

Alternatively, the electrolyser device 5 can be of the polymeric membrane cell type (PEM). This type of electrolyzer allows to reach, with the same efficiency, much higher energy density and power but requires platinum group catalysts, thus presenting higher costs than alkaline electrolysers. The values of the energy required in kwh by the process to produce a Nm <3> of H2 in the case of electrolysers with PEM technology are 4-5 kwh / Nm <3> H2.

The presence of the electrolyser device 5 in the group 1 allows the system to be able to receive the variable electric power in supply. The hydrogen produced (with a degree of purity of 99%) is sent to an accumulation tank that allows the decoupling of the discontinuous operation of the electrolyser from the continuous operation of the plant.

For a correct analysis of the economic advantages of the group 1 object of the present invention, it must be considered that the oxygen produced by the electrolyser device, having a high degree of purity (99.5% vol), can be exploited by the market.

The methanation reactor 6 carries out the catalytic conversion of CO2 into CH4. The main reactions involved in the process are listed below.

CO2 (g) 4 H2 (g) â † ’CH4 (g) 2 H2O (g) [1] ∠† G ° 298 ° K = - 27150.4 cal; ∠† H ° 298 ° K = - 37531 cal. CO (g) + 3 H2 (g) â † ’CH4 (g) H2O (g) [2] ∠† G ° = -53806 60.34 T cal / mole for T between 600 and 1500 ° K

∠† G ° 298 ° K = -33967 cal; ∠† H ° 298 ° K = - 49271 cal.

If even small amounts of O2 are present, it also has the following reaction:

O2 (g) 2 H2 (g) â † ’2 H2O (g) [3] ∠† G ° 298 ° K = - 115596 cal; ∠† H ° 298 ° K = - 109270 cal. Given the exothermic nature of the reaction, in order to have high conversions, it is necessary to operate at modest temperatures.

Catalysts are used to obtain acceptable reaction rates. Many catalysts have been tested (Ni, Cu, Ir, Co, Fe, Pt, Pd, Mo, W, Ru and Rh, all with different supports such as Al2O3, TiO2, CeO2, -MgO-, -MgAl2O4-, -K2O- MgAl2O4-, SiO2, -Cr2O3, ksr, -MgO-ksr, ZrO2, Al2O3-CaO, La2O3) but the most active are those based on nickel and nickel oxides (70 ± 80%) and Al2O3 (30 ± 20%).

The nickel and nickel oxide catalysts are poisoned by sulfur compounds and arsenic and it is therefore necessary to previously treat the gases to remove the sulfur compounds.

The reaction temperature is kept around 300 ° C and, given the exothermicity of the reactions, it is necessary to check that the temperature in the reactor does not rise above 430 ° C, otherwise there is a lowering of the catalytic activity.

Since the reaction occurs with a decrease in the number of moles, it is possible to operate at a pressure ranging from some atmosphere up to 60 atm.

In particular, the methanation reactor uses the fixed bed technology (catalyst bed shaped into cylinders or tablets) equipped with pressure, temperature and composition controls. The feed gas is preheated to about 250 ° C and sent into the reactor by adjusting the flow rate so that the temperature does not rise beyond the desired values.

The water produced during the methanation phase is subsequently conveyed to the electrolyser 5 by means of a dedicated transport line 8. The methane produced is cooled and sent to the treatment device 7 arranged to purify it of its water content. The methane will then be compressed to the pressure required by the network specifications in which it will be introduced or to the storage specifications in the case of local consumption.

As can appear evident from the above description, the group and the method object of the present invention offer the great advantage of converting the CO2 emitted from the soil into methane through a process that uses the hydrogen produced by electrolysis which is fed energetically from renewable sources. In this way, a production of a natural gas substitute is achieved with zero emissions. The particular advantage of the solution of the present invention is the generation of a standardized product, such as methane, which can be fed into the network or stored for local use.

It should be considered, in fact, that the group and the proposed method could respond, by integrating other storage systems, to the disposal of the surplus of energy production that cannot otherwise be absorbed by the transmission grid.

Claims (10)

CLAIMS 1. Group for the production of methane comprising a methanation reactor (6) suitable for the conversion of carbon dioxide into methane by catalytic hydrogenation and an electrolyser device (5) suitable for producing the necessary hydrogen to be introduced into the methanation reactor (6); the said unit being characterized by the fact that it comprises means for capturing a gas comprising carbon dioxide from the ground (2) and a treatment device (3) for its desulphurization of the gas coming from said capturing means from the ground (2) and act to purify the carbon dioxide to be introduced into the methanation reactor (6), and by the fact that at least said electrolyser device (5) is powered by electricity from renewable sources. 2. Group for the production of methane according to claim 1, characterized in that it comprises means for generating electricity from renewable sources (4). 3. Group for the production of methane according to claim 1 or 2, characterized in that it comprises a treatment device (7) suitable for dehydration of the methane produced. 4. Group for the production of methane according to claim 3, characterized in that it comprises a water transport line (8) suitable for transporting the water produced by the methanation reactor (6) to the electrolyser device (5) . 5. Group for the production of methane according to one of the preceding claims, characterized in that said means for capturing the gas from the ground (2) comprise a natural filling material. Methane production unit according to one of the preceding claims, characterized in that the gas treatment device (3) uses an adsorption technique on high temperature sorbents (5). 7. Method for the production of methane comprising a methanation phase in which carbon dioxide is converted into methane by catalytic hydrogenation and an electrolysis phase in which the water is decomposed into oxygen and hydrogen prepared to feed the said phase of methanation; said method being characterized in that it comprises a phase of capturing a gas comprising carbon dioxide from the ground and a phase of desulphurization of the gas coming from the previous capturing phase; the gas coming from said desulfurization step being disposed to feed said methanation step. 8. Method for the production of methane according to claim 7, characterized in that it comprises a phase of production of energy from renewable sources able to feed at least said electrolysis phase. Method for the production of methane according to claim 7 or 8, characterized in that it comprises a dehydration step of the methane produced. Method for the production of methane according to one of claims 7 to 9, characterized by the fact of integrating with the energy storage systems suitable for the disposal of the surplus of electric energy.