RU2806323C1 - Carbon-neutral energy system with liquid energy carrier - Google Patents

Abstract

FIELD: energy.

SUBSTANCE: invention is related to alternative energy, and can be used in the production of energy from biomass, in particular to a carbon-neutral energy system. The system includes a process of two-stage thermal conversion of biomass into synthesis gas, combining pyrolysis with high-temperature cracking of volatile products on the coke residue of the processed raw materials and a methanol synthesis unit. Moreover, a two-stage purification is used, where in the first stage the reduction of sulphur-containing compounds to hydrogen sulphide is carried out, and in the second stage the adsorption of hydrogen sulphide is carried out.

EFFECT: increase of accuracy of the composition of the resulting synthesis gas.

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Description

The invention relates to the field of energy, namely to the field of alternative energy, and can be used in the production of energy from biomass

The main direction of development of modern energy is the transition to low-carbon technologies for energy production. Priority in this direction is given to hydrogen energy. Carbon-neutral energy systems based on the use of hydrogen are known. Such systems are protected by blocks of patents for inventions. In principle, the energy system described in [A. Kochetov. Russia is about to implement the largest project in the history of world energy / Energy and Industry of Russia. - 08/09/2021]. This system contains a generator that produces energy, devices for its accumulation, devices for transporting energy to consumers, and devices for generating electrical and thermal energy from energy on the territory of consumers.

The advantage of the known system is its high environmental efficiency: hydrogen, used as fuel for heat engines, does not produce harmful emissions into the atmosphere when generating electrical and thermal energy.

Known (RU, patent 2596605, publ. 01/10/2016) is a hydrogen generator of electrical energy containing a series-connected converter of water into hydrogen, a hydrogen combustion chamber and a converter of thermal energy of hydrogen combustion products into electrical energy, and the hydrogen combustion chamber is made in the form of a plasma torch, equipped with air intake slots, and the converter of thermal energy of hydrogen combustion products into electrical energy is made in the form of a magnetic converter containing a dielectric pipe of rectangular cross-section, inside of which plates of an electric capacitor of opposite charge are installed on two opposite sides, and on the outside of the pipe on two other opposite sides - magnets that are oriented to each other with opposite poles, and the plasma torch is connected coaxially and end-to-end with the dielectric tube of the magnetic converter, the electrical capacitor of which is connected through the potential outputs to the electrical outputs of the hydrogen generator.

Also known (RU, patent 2510876, publ. April 10, 2014) is an autonomous hydrogen generator that operates through the reaction of hydrogen reduction from water with aluminum, having a reaction vessel, a supply line for an aqueous solution of sodium metasilicate crystalline hydrate, and a hydrogen supply line. It consists of two articulated chambers, the lower chamber is a reaction vessel with a hydroreaction heterogeneous composition, the upper chamber contains an aqueous solution of sodium metasilicate crystalline hydrate, which is fed into the reaction vessel using a threaded regulator.

The use of hydrogen produced using existing technologies has a number of limitations. First of all, these are price indicators. The cost of electricity produced using hydrogen produced using existing technologies will be higher than the prices at which electricity is currently supplied to consumers. Producing hydrogen from natural gas, oil or coal involves significant carbon dioxide emissions. There are no environmentally friendly technologies for recycling these gases. The idea of underground disposal of CO ₂ cannot be considered legitimate. CO ₂ emissions into the atmosphere are considered harmful to the ecological balance. At the same time, underground burial of this gas is considered harmless and is considered as a solution to the problem of utilization of this gas. Obviously, this procedure cannot be harmless from the point of view of the initial natural balance for the internal layers of the earth. In principle, the explanation of the processes leading to changes in the natural equilibrium in the earth's thickness during the injection of carbon dioxide in the literature is set out in [. V.M. Batenin, L.A. Vytnova, V.M. Zaichenko et al. Integrated processing of natural gas: new approaches and application prospects. Preprint JIHT RAS No. 8-455, M. 2001. Pp. 18-22]. A significant limitation to the use of hydrogen as fuel in electrical generating equipment is the occurrence of detonation phenomena. This is typical, in particular, for gas piston units (GPU), which are the basis of distributed energy [V.M. Zaichenko, A.A. Chernyavsky. Creation of guaranteed energy supply systems using combined energy sources / Energy Policy. - 2020. - No. 10, p. 90-103]. An equally serious limitation to the use of hydrogen as a fuel is the phenomenon of so-called hydrogen embrittlement, the destruction of elements of metal structures when interacting with hydrogen at elevated temperatures.

In the technical solution under consideration, it is proposed to replace hydrogen with methanol, which is produced from synthesis gas obtained using the technology of two-stage thermal conversion of biomass (DTCB) [Batenin V.M., Bessmertny A.V., Zaichenko V.M. et al., Thermal methods for processing wood and peat for energy purposes. // Thermal power engineering. 2010. No. 11. pp. 36-42; Batenin V.M., Zaichenko V.M., Kosov V.F. and others. Pyrolytic conversion of biomass into gaseous fuel // Reports of the Academy of Sciences. 2012. T. 446. No. 2. P. 179; Larina O.M., Sinelshchikov V.A., Sitchev G.A. Comparison of Thermal Conversion Methods of Different Biomass Types into Gaseous Fuel // Journal of Physics Conference Series. T 774, No. 1, 2016], proposed by the Joint Institute of High Temperatures of the Russian Academy of Sciences (JIHT RAS) and PJSC Tatneft, which is an analogue of the proposed technical solution.

Biomass is used as a feedstock for the production of synthesis gas, mainly in the form of waste from various industries: forestry, wood processing, agricultural processing, food industry, organic part of municipal solid waste, cattle waste, poultry, etc. raw materials are either practically free, or for their removal as waste (garbage), enterprises pay according to the tariffs established for each region. In accordance with this, the cost of synthesis gas obtained using the DTKB technology is significantly less than the cost of synthesis gas obtained in a traditional way, for example, from natural gas.

The closest analogue of the developed technical solution can be recognized (RU, patent 2674158, published 12/05/2018), which characterizes an installation for the production of liquid hydrocarbons from biomass, containing series-connected blocks: a synthesis gas (SG) production block, a SG purification and drying block and a synthesis of hydrocarbons, and in the SG production block a process of two-stage thermal conversion of biomass into synthesis gas is implemented, combining pyrolysis with high-temperature cracking of volatile products on the coke residue of the processed raw materials, and the hydrocarbon synthesis block includes two series-connected reactors - a reactor for the synthesis of oxygenates (methanol, DME) and light gasoline hydrocarbons (P1) and a reactor for the synthesis of aromatic hydrocarbons (P2) from oxygenates formed in the first reactor, after their separation from the hydrocarbon part of the product, while the aromatic hydrocarbons formed in P2 are mixed in various proportions with gasoline hydrocarbons series formed in the first reactor, with the formation of a hydrocarbon (h/c) mixture, which is subsequently used as the initial component of aviation gasoline.

A well-known patent proposes a design for a plant for converting biomass into liquid fuels. DTCB technology is considered as a conversion method. The installation includes a synthesis gas production unit, a synthesis gas purification and drying unit and a hydrocarbon synthesis unit. The installation implements a process of two-stage thermal conversion of biomass into synthesis gas, combining pyrolysis with high-temperature cracking of volatile products on the coke residue of the processed raw materials, and a hydrocarbon synthesis unit.

Synthesis gas produced using DTKB technology includes two main flammable components - hydrogen (H ₂ ) and carbon monoxide (CO). The operating mode of synthesis gas production reactors (type of biomass being processed, temperature, pressure, biomass feed rate) is set in such a way as to obtain a ratio of components by volume of the order of 2.0 to 1.0. Experiments to study the operating parameters of this technology have shown that for some types of biomass, this ratio can be obtained, in particular when processing sewage sludge and some types of wood waste.

From the synthesis gas produced using the DTKB technology, methanol is synthesized in an energy carrier generator in the presence of a catalyst, which can be stored in appropriate containers.

Methanol is further used as liquid fuel to operate diesel generator sets (DGS). Such diesel generator sets are widely used as part of low-power autonomous power plants in remote areas not provided with a centralized energy supply. At the same time, the delivery of diesel fuel to the areas where they are located often turns out to be more expensive than the cost of the fuel itself, and the cost of the generated electricity becomes very high, reaching 40-100 rubles/kWh [Fortov V.E., Popel O.S. Energy in the modern world. - Dolgoprudny: Publishing house "Intelligence". - 2011. 168 p., ill.]. At the same time, in each of these remote areas there are always certain types of biomass and its waste suitable for producing synthesis gas and synthesizing methanol from it.

Biomass is a carbon-neutral product; the amount of carbon dioxide that is released when burning biomass or biofuels obtained from it is equal to the amount of carbon dioxide absorbed from the atmosphere during plant growth. The use of biomass in energy does not violate the natural ecological balance on Earth, unlike the use of fossil hydrocarbon fuels extracted from the deep layers of the earth. So, when methanol burns, water vapor and carbon dioxide are formed. But, since the latter is based on carbon-neutral biomass, the process of combustion of methanol (more precisely, biomethanol) is also carbon-neutral.

A disadvantage of the known technical solution is the production of a product contaminated with sulfur compounds.

The technical problem solved using the developed system is to obtain pure synthesis gas.

The technical result achieved by implementing the developed energy system is to increase the accuracy of the composition of the resulting synthesis gas.

To achieve the specified technical result, it is proposed to use the developed carbon neutral energy system. The system includes a process of two-stage thermal conversion of biomass into synthesis gas, combining pyrolysis with high-temperature cracking of volatile products on the coke residue of the processed raw materials and a methanol synthesis unit, while two-stage purification is used, and at the first stage the reduction of sulfur-containing compounds to hydrogen sulfide is carried out, and at the second stage carry out the adsorption of hydrogen sulfide.

In some embodiments of the developed system, low-temperature steam reforming of carbon monoxide is used to adjust the composition of the synthesis gas obtained by two-stage conversion of biomass and purified from sulfur compounds

The use of methanol obtained from biomass in the energy sector is an environmentally friendly process: methanol synthesized using DTKB technology can replace hydrogen used as fuel in hydrogen energy. At the same time, systems using methanol will be more cost-effective than systems using hydrogen in hydrogen energy processes and apparatus.

The DTKB technology for producing combustible gas from biomass is much more effective than the known technologies of pyrolysis and gasification. This technology is carried out as follows. At the first stage, biomass is pyrolyzed at temperatures up to 900°C with the formation of gaseous, liquid and solid reaction products. Liquid pyrolysis products consist of a set of high molecular weight hydrocarbon compounds C _n H _m and pyrogenetic water. These products are in the vapor phase.

At the second technological stage, gaseous products of the pyrolysis reaction, consisting of condensable and non-condensable parts, are blown at a temperature of about 1000°C through the solid carbon phase obtained in this process. At the same time, pyrogenetic water, located in the vapor phase, interacts with carbon to form hydrogen and carbon monoxide:

C+H ₂ O=CO+H ₂ .

High-molecular compounds included in the condensed part are pyrolyzed when passing through the backfill of high-temperature carbon to form hydrogen and carbon monoxide:

C _n H _m +H ₂ O=СО+H ₂ .

Thus, the conversion of liquid and solid products of the pyrolysis reaction into hydrogen and carbon monoxide is carried out. This ensures waste-free processing of biomass to produce high-calorie energy gases. The properties of these gases change depending on the temperature of the processes, as shown in table. 1.

The main advantage of the DTKB technology is the high degree of conversion of the processed biomass into energy gas - an intermediate energy carrier. In existing technologies, for example pyrolysis, this value does not exceed 18%, in DTKB technology it is about 80%. The total yield of combustible gases is 1.4 m ³ per 1 kg of biomass, and the average heat of combustion is about 11.5 MJ/nm ³ .

The subsequent synthesis of methanol from synthesis gas occurs according to the reaction (simplified):

CO+2H ₂ →CH ₃ OH.

Methanol, as an energy carrier, has a number of positive properties in comparison with hydrogen. The fuel use of methanol is not associated with the occurrence of detonation phenomena; the use of methanol does not lead to corrosion of metal structures. Methanol can be stored in large capacity tanks (up to 10-20 thousand cubic meters) with virtually no weight loss. Methanol, like hydrogen, can be transported via pipelines, by road and rail, and by water. The volumetric calorific values of fuel-air combustible stoichiometric mixtures of methanol and hydrogen have approximately equal values - about 7-8 MJ/kg. Methanol can be produced directly at the point of consumption using many common types of biomass or biomass waste. The disadvantage of existing technical solutions for producing methanol from biomass is that during the processing of various types of biomass, nitrogen and sulfur-containing impurities are formed, while the ratio of hydrogen and carbon monoxide in the reaction products may be different. The difference between the proposed technical solution and the known ones is that in order to remove sulfur-containing compounds, a two-stage purification is used. At the first stage, the reduction of sulfur-containing compounds to hydrogen sulfide is carried out. At the second stage, hydrogen sulfide is adsorbed. It is possible to combine the stages of hydrogenation and adsorption in one apparatus with layer-by-layer loading of catalysts. The ratio of volumes of layer-by-layer loading in one apparatus is determined by the concentration of sulfur compounds in the resulting synthesis gas.

In the claimed technical solution, in contrast to the known ones, in order to adjust the composition of the resulting synthesis gas obtained by two-stage conversion of biomass, low-temperature steam conversion of carbon monoxide CO+H ₂ O→H ₂ +CO ₂ is used.

Using this process, the hydrogen content in the resulting mixture of gases is changed in order to obtain the optimal ratio of hydrogen and carbon monoxide for the synthesis of methanol. For steam reforming of carbon monoxide in this case, low-temperature catalysts can be used, which are used to remove residual carbon monoxide content in flue gases. The synthesis gas/water vapor ratio is the determining parameter for regulating the conversion of carbon monoxide and obtaining a reaction gas of the required composition. The composition of synthesis gas for various initial ratios of CO and H ₂ according to the results of experiments carried out to adjust the composition is given in Table 2.

There are significant prospects for the fuel use of methanol in our country. Methanol, according to the technologies being developed, can be obtained by economically viable methods directly from local fuel and energy resources, which include various types of biomass. For many regions of our country, this is much more profitable than using grid electricity and diesel power plants.

Claims (2)

1. Carbon-neutral energy system, including a process of two-stage thermal conversion of biomass into synthesis gas, combining pyrolysis with high-temperature cracking of volatile products on the coke residue of processed raw materials and a methanol synthesis unit, characterized in that a two-stage purification is used, and at the first stage the reduction of sulfur-containing compounds is carried out to hydrogen sulfide, and in the second stage hydrogen sulfide is adsorbed. 2. Carbon-neutral energy system according to claim 1, characterized in that low-temperature steam reforming of carbon monoxide is used to adjust the composition of the synthesis gas obtained by two-stage conversion of biomass and purified from sulfur compounds.