RU2664526C2 - Energy-saving unified method for generating synthesis gas from hydrocarbons - Google Patents

Abstract

FIELD: petrochemical industry.SUBSTANCE: invention relates to a method for producing synthesis gas and can be used in chemical and petrochemical industry in the production of hydrogen, ammonia, synthetic liquid hydrocarbons, aldehydes and alcohols. Method comprises a step of combusting fuel into flue gas, used as a heat carrier, and a step of catalytic reforming of hydrocarbons with water vapor, whose catalytic reactors are in heat-exchange association with flue gas. At least in one of the stages of the catalytic reforming, heat is supplied to the reaction zone mainly due to radiative heat exchange, and at subsequent stages – mainly due to convective heat exchange.EFFECT: technical result is enhanced efficiency of heat exchanger energy use for carrying out endothermic processes of catalytic reforming of hydrocarbons proceeding at high temperature, as well as in the unification of technical solutions and technological methods that allow diversifying the composition of the resultatn synthesis gas as well a heat carrier.6 cl, 1 dwg, 4 ex, 3 tbl

Description

The invention relates to the field of chemistry and chemical technology and can be used in the chemical and petrochemical industries in the production of ammonia, methanol, hydrogen, aldehydes and alcohols.

Known methods for producing synthesis gas (nH ₂ + CO), including catalytic heat exchange and autothermal reforming of hydrocarbons, as well as their partial oxidation. These methods can be combined in various combinations depending on the use of synthesis gas to obtain the target product. (Nitrogen Guide, Moscow, Chemistry 1986, 2nd edition, pp. 76-110, 126-137).

Since the main component of the synthesis gas is hydrogen, which is formed from water molecules, the production of synthesis gas is always accompanied by the consumption of energy, the unit costs of which are a measure of the thermodynamic perfection of the process.

The known method and installation for heating and partial oxidation of a mixture of water vapor and natural gas after primary reforming [RF №2394766, 07.20.2010]. The method includes heating and partial oxidation of an unheated previously subjected to primary reforming mixture of water vapor and natural gas to produce synthesis gas, moreover, thermal energy flows through several porous burners into the gas synthesis gas stream in the direction of flow after the primary reformer.

A known method of producing synthesis gas containing hydrogen and carbon monoxide by combining catalytic partial oxidation, further autothermal catalytic reforming, including:

a) the use in specified proportions of hydrocarbon streams containing oxygen-containing media and process steam;

b) the introduction of these streams in the zone of catalytic partial oxidation to obtain a preliminary product;

c) feeding this pre-product and a second stream containing oxygen to the partial oxidation step by carrying out a reaction in a flame;

d) conducting a further process of partial oxidation in the reaction zone of steam reforming in order to obtain a stream of synthesis gas;

d) separation of the resulting synthesis gas stream in order to prevent partial oxidation, thereby establishing a two-stage process of autothermal reforming [US 6,730,285 05/04/2004].

Closest to the proposed invention is a method for the joint production of synthesis gas and electricity, including at least the stage of producing synthesis gas by burning a second stream of fuel with air into the flue gas, passing it in a heat exchange reactor, and generating electric energy by burning the first the flow of fuel with combustion air in the combustion chamber of the gas turbine into the flue gas with the expansion of the flue gas in the gas turbine; however, the flue gas of one stage is used as combustion air for another [US Patent 5,937,631, 08/17/1999 g].

The disadvantages of the described inventions are:

- Incomplete use of the energy of the coolant flows resulting from the combustion of hydrocarbons with oxygen-containing media;

- The lack of unification of the process, allowing on the basis of a single technology to obtain synthesis gas for the synthesis of ammonia, hydrogen, alcohols and aldehydes, as well as synthetic liquid hydrocarbons.

The technical result to which the invention is directed is to increase the efficiency of the use of heat carrier energy for carrying out endothermic processes of catalytic reforming of hydrocarbons occurring at high temperature, as well as the unification of technical solutions and technological methods allowing to diversify the composition of the resulting synthesis gas, as well as the heat carrier.

Ways to achieve the specified technical result are illustrated by the descriptions of technological schemes for producing synthesis gas for various applications.

The proposed technical solution is based on the fact that the flue gas obtained from burning fuel with an oxidizing agent is used as a heat carrier to supply energy to the stages of catalytic reforming of hydrocarbons, directing it first to the first reactor, in which heat exchange occurs mainly due to the radiation component, and then in the second and subsequent reactors, in which heat transfer occurs mainly due to the convective component of the heat transfer coefficient.

Flue gas is used mainly under pressure, which can significantly increase the intensity of radiation heat transfer in the first reactor and convective heat transfer in the second. The pressure of the flue gas in this case is chosen lower in relation to the pressure of the process by an amount ensuring the safety of its conduct.

Tables 1 and 2 show the values of the radiative heat transfer coefficients a _p and their sum with convective coefficients α _k . in relation to the diagram shown in the drawing. The data presented characterize the ratio of the intensities of both types of heat transfer in the first catalytic partial oxidation reactor 1 with mainly radiation supply of heat to the reaction zone at flue gas pressures of 1 and 28 atmospheres. Table 3 shows similar data for the second catalytic partial oxidation reactor 2 with a predominantly convective supply of heat to the reaction zone at a flue gas pressure of 28 atmospheres.

Example 1. The description of a unified technological scheme for producing synthesis gas is given in the drawing.

Natural gas is mixed with the hydrogen fraction and sent for preliminary heat exchange to heat exchangers 3 and 4. In the heat exchanger 3, the gas mixture is heated by the exhaust flue gas expanded in a gas turbine (expander) 5, and in 4 by a portion of the converted gas and sent to desulfurization apparatus 6, in which exempt from sulfur compounds. The purified gas enters the collector - divider, in which the technological fraction "1" (used for the process) and the fuel fraction "2" (burned in the burners) are separated from it. To the fuel fraction in order to reduce the consumption of the main fuel it is allowed to add any kind of additional fuel heated by the heat exchanger 8. The fuel flow can be divided into several parts. The main part is burned in the main burners of the first reactor 7, the remaining parts are used to control the process and during start-up operations, burning them in auxiliary burners of the turbine and the second reactor 2. Steam is added to the cleaned process fraction in mixer 7. The steam-gas mixture after heating in heat exchangers 9 and 10, depending on the heat transfer rate in reactors 1 and 2, is divided into two parts: the first part enters the reactor 1, and the second into the reactor 2. In both reactors, endothermic reforming reactions with water vapor and / or with carbon dioxide. The heat source that ensures the occurrence of endothermic reactions is flue gas, obtained in the main G1 and auxiliary burners G2 and G3 by burning the fuel part of natural gas with air. Flue gas from the main burners enters the annulus of the first reactor /, gives off part of the heat, and then enters the annulus of the second reactor 2. The second reactor is equipped with an auxiliary start-up burner, which, if necessary, is used to control the process in it. The first and second reactors are distinguished by the fact that in the first of them heat transfer is mainly carried out by radiation heat transfer (80-97%), and in the second, convective heat transfer is the determining factor. The share of radiation heat transfer in the second reactor accounts for 5-20% of the transferred heat. The second reactor may contain one or more stages in order to increase the degree of conversion and use of flue gas heat.

To reduce the temperature of the resulting synthesis gas, if necessary, its flow is passed through a heat exchanger 11.

The described method allows more than two times to increase the use of heat of flue gas (coolant) for the occurrence of endothermic reactions.

Flue gas is obtained as follows. Compressed in the air compressor 12, the air is divided into several parts. The first part is the process air. This air is used, for example, if the described unified synthesis gas generation method is part of the ammonia production flow chart. The other two parts are used to burn fuel in the main burners G1 of the first reactor 7 and in the auxiliary burners of the turbine G2 and burners G3 of the second reactor 2. Thus, all the objects using it are connected in series and in parallel so that any part of the stream bypasses any from the stages. The flue gas produced at all stages of fuel combustion after using heat in reactors with a temperature of ~ 540 ° C enters the turbine manifold, from which part of the flue gas can, if necessary, be taken for technological use.

Work from the expansion of the flue gas in the expander 5 is used to drive an air compressor or for other purposes. The residual heat of the expanded flue gas expanded in the expander is used to preheat the process gas in the heat exchanger 8. The flue gas leaving the heat exchanger 8 has a temperature of 151 ° C. and is released into the atmosphere.

Example 2. Description of the technological scheme for producing synthesis gas for the production of ammonia.

To obtain synthesis gas in the production of ammonia, a unified technological scheme is supplemented by an autothermal reforming (secondary reforming) reactor. Converted gas from reactors 1 and 2 of the unified circuit, as well as process air from compressor 12, are supplied to this reactor. Additionally, a portion of the flue gas taken from the expander manifold 5 is fed to the reactor.

The heat of the converted gas leaving the secondary reforming reactor is used in waste heat boilers to produce steam, and the remaining heat is used to heat the process streams. Then, the converted gas is subjected to processing according to a standard scheme, including medium and low temperature conversion of CO, methyldiethanolamine purification, methanation, a heat and cooling system, until a nitrogen-hydrogen mixture of stoichiometric composition for the synthesis of ammonia is obtained. In addition, the technological scheme constructed by this method allows balancing the ammonia and carbon dioxide productivity to create a complex of ammonia-urea production by extracting carbon dioxide from part of the flue gas under the pressure of the technological process.

A mixture of gases from reactors 7 and 2 is supplied to the secondary reforming reactor as described in Example 1. In addition, a mixture of part of the flue gas leaving one of the catalytic partial oxidation stages and compressed air in a ratio of 0.773 / 1, i.e. providing a stoichiometric ratio of nitrogen and hydrogen for the ammonia synthesis reaction and a predetermined temperature at the exit from the autothermal reforming stage.

The result is a synthesis gas with a stoichiometric ratio for the synthesis of ammonia composition,% vol: H ₂ - 74.00, N ₂ - 24.64, Ar - 0.353, CH ₄ - 0.673.

The implementation of the method of producing synthesis gas according to this invention makes it possible to create the production of ammonia with the following indicators:

1. Energy consumption. Natural gas: nm3 / hour: fuel (23%), for technology 77%, total 798 nm ³ (856.46 st. M ³ , 760 mm Hg., 20 ° C) per ton of ammonia.

At the lowest calorific value (for methane) of 7969.29 kcal / st.m3, the energy consumption for natural gas will be 6.825 Gcal / t of NH ₃ .

The world's best technology provides energy consumption for natural gas of 881.12 ÷ 918 nm ³ or 7.1 ÷ 7.4 Gcal per ton of ammonia.

2. Ecological tolerance. Flue gas emissions into the atmosphere 2420 nm ³ per tonne of NH ₃ . In the best known technology with a temperature of heating the combustion air to 440-600 ° С - 2660 nm ³ per tonne of NH ₃ , in the most common standard scheme - 4470 nm ³ per tonne of NH ₃ or 1.847 times more.

Example 3. Description of the technological scheme for producing synthesis gas for the production of hydrogen.

The technological scheme for producing synthesis gas for hydrogen production differs from the described scheme for producing synthesis gas in Example 2 in that only air or an oxidizing agent (for example, pure oxygen) is fed into the autothermal secondary reforming reactor instead of a mixture of air and flue gas.

The implementation of the method of producing synthesis gas according to this invention makes it possible to create hydrogen production with the following indicators:

1. Energy consumption. Natural gas (in terms of methane) 388.3 nm ³ per 1000 nm ³ H ₂ . The energy equivalent is 3.153 Gcal / 1000 nm ³ H ₂ . World famous technologies - 484.3 ÷ 496.4 nm ³ per 1000 nm ³ Н ₂ .

2. Ecological tolerance. Flue gas emissions into the atmosphere - 1254 nm ³ per 1000 nm ^{3 of} natural gas.

Example 4. Description of the technological scheme for producing synthesis gas for the production of alcohols, aldehydes, and synthetic liquid hydrocarbons.

To obtain synthesis gas suitable for the production of alcohols and aldehydes, as well as synthetic liquid hydrocarbons, gas from reactors 1 and 2 as described in example 1, as well as a mixture of carbon dioxide and oxygen, and the stage of conversion of carbon monoxide with water vapor are fed into the autothermal reactor used to maintain the desired ratio of H ₂ / WITH. Thus, the described method for producing synthesis gas for the described applications becomes unified at the stage of heat exchange reforming of hydrocarbons.

Claims (6)

1. An energy-saving method for producing synthesis gas containing hydrogen and carbon monoxide for the production of hydrogen, alcohols and aldehydes, synthetic liquid hydrocarbons and ammonia, comprising the step of burning fuel into flue gas used as a coolant, and the stage of catalytic reforming of hydrocarbons with steam catalytic reactors which are in heat exchange connection with flue gas, characterized in that at least in one of the stages of the catalytic reforming stage, heat is supplied to the reaction zone carried out mainly due to radiative heat transfer, and in subsequent steps - mainly due to convective heat transfer. 2. The method of producing synthesis gas according to claim 1, characterized in that the pressure of the flue gas is chosen lower in relation to the pressure of the process by an amount that ensures its safety. 3. The method of producing synthesis gas according to claim 1, characterized in that in order to optimize the control of the technological mode, the heat exchange stages of the catalytic reforming are connected in series and parallel along the process and flue gas, so that any part of the stream bypasses any of the stages. 4. The method of producing synthesis gas according to claim 1, characterized in that its unification for producing synthesis gas suitable for the production of ammonia, alcohols, aldehydes and synthetic liquid fuel is achieved by the fact that an autothermal reforming stage is introduced into the technological scheme. 5. The method of producing synthesis gas according to claim 4, characterized in that for the production of synthesis gas in the production of ammonia, a mixture of a portion of the flue gas leaving one of the stages of the catalytic partial oxidation and compressed air in proportions providing a stoichiometric ratio of nitrogen and hydrogen for the ammonia synthesis reaction and a predetermined temperature at the exit from the autothermal reforming stage. 6. The method of producing synthesis gas according to claim 1, characterized in that in order to obtain synthesis gas suitable for the production of alcohols and aldehydes, as well as synthetic liquid hydrocarbons, gas from both reactors with a mixture of carbon dioxide and oxygen is supplied to the autothermal reactor, and a carbon monoxide vapor conversion step is used to maintain the desired H ₂ / CO ratio.

Images