WO2015183122A1 - Furnace pipe unit for pyrolysis of light alkanes - Google Patents

Abstract

The utility model relates to the chemical industry, and specifically to devices for the pyrolysis of light alkanes (ethane, propane), producing olefins and hydrogen. Described is a furnace pipe unit for the pyrolysis of light alkanes, said unit containing: a combustion chamber with pipe coils; a coil convection zone; a coil radiant zone; input laser radiation, a laser CO₂ emitter, an optical distributor of laser radiation, at least one optical window, an optical-window insulation system, a quenching-evaporating unit, fittings for inputting raw materials for pyrolysis and fittings for outputting products of pyrolysis, a fitting for inputting an insulating gas, and gas-stream mixing diaphragms; a chamber, which is outside of the combustion chamber, and which is used for inputting laser radiation, and which is provided with thermal insulation, an optical-window insulation system, and an area for the raw-material absorption of laser radiation. The technological system for the process of pyrolysis using laser radiation is significantly simpler and contains fewer units of primary equipment. The technical result consists in decreasing the temperature at which the pyrolysis process is carried out, while maintaining a high output of target products.

Description

 Furnace tube block for pyrolysis of light alkanes

The utility model relates to the chemical industry, namely, devices for the pyrolysis of light alkanes (ethane, propane, butane) to produce olefins and hydrogen.

 A known pyrolysis reactor, comprising a system of parallel pipes connected by returbents and placed in a radiant section of a tubular furnace. A typical traditional process scheme for producing ethylene from ethane is based on high-temperature thermal pyrolysis of ethane [T.N. Mukhina, N.L. Barabanov, S.E. Babash, V.A. Menytsikov, G.L. Avrekh. Pyrolysis of hydrocarbons. M, Chemistry, 1987, '240 s]. The disadvantages of this technology are significant coke formation, which significantly complicates the implementation of the process and requires regular regeneration procedures; a noticeable amount of high molecular weight waste products, as well as waste water containing them; high specific capital costs associated with the complex process of post-reaction separation of reaction products.

 A known method of increasing the reliability and efficiency of the pyrolysis furnace, in which a more uniform heating of the radiating walls of the furnace due to the implementation of acoustic burners in two stages (RF 2231713, F23C1 / 08. 06/27/2004). Burners are installed on the radiating walls of the furnace with a pitch of 48 - 58 diameters of the primary mixing chamber.

 Known pyrolysis furnace, which is made in the form of a solid metal body with a lining (RF 30747, C10B1 / 04, F23G5 / 027. 07/10/2003). The heating elements are uniformly located on the inner surface in the channels of the furnace lining. The device provides a removable pyrolysis chamber with the removal of pyrolysis products.

Known invention, which allows to create the conditions for Combinations of hydrodynamic and thermal degradation of hydrocarbons, providing a high yield of unsaturated hydrocarbons (RF 2369431, B01J7 / 00, С07С11 / 00. 10.10.2009). An oxidizing agent and fuel are supplied to the hot gas generator, after which the resulting mixture is ignited. The output of the hot gas generator narrows toward the reaction chamber to form a nozzle, and the hydrocarbon feed pipes are located in the zone of the critical section of the nozzle and are oriented radially. The feed, driven by the flow from the hot gas generator, enters the reaction chamber, in which high-speed heating of the feed occurs. Further, the pyrolysis products enter the quenching chamber.

 The closest is the device described in T.N. Mukhina, N.L. Barabanov, S.E. Babash, V.A. Menshchikov, G.L. Avrech. Pyrolysis of hydrocarbons. M, Chemistry, 1987, 240 pp.

 Typical characteristics of the known pyrolysis process in table 1.

Table 1.

Actual characteristics of the process on a traditional ethane pyrolysis unit EP-300 at a temperature in the pyrolysis furnace of 830 X1.

Подобная технология используется для современного многотоннажного производства этилена. В то же время ей присущи определенные недостатки, в частности:

A similar technology is used for modern large-tonnage production of ethylene. At the same time, it has certain disadvantages, in particular:

• Significant coke formation, significantly complicating the implementation of the process and requiring regular regenerative procedures; W

• A noticeable amount of high molecular weight waste products, as well as waste water containing them;

 • High unit capital costs associated with the complex process of post-reaction separation of products

5 reactions.

 Overcoming of these drawbacks is possible due to the use of a new pyrolysis process, in which additional CO2 laser radiation with a power density above 10 W / cm2 is introduced into the reaction zone.

 The utility model solves the problem of reducing capital costs for the 10 construction of the furnace block.

 The technical result achieved by the proposed solution is to increase the degree of conversion of hydrocarbon materials at lower temperatures, as well as to reduce the requirements for cryo-heat-resistant materials for the manufacture of pipes of pyrolysis furnaces by reducing the range of operating temperatures; reduction of energy costs for primary fractionation and separation of products due to the elimination of primary fractionation, debutanization and depentanization blocks from the scheme and reduction of heat losses with flue gases due to the fact that by reducing the overall reaction temperature it is possible to lower the temperature of 20 flue gases without a significant decrease in efficiency heat transfer.

 The problem is solved by the following design of the furnace tube unit for pyrolysis of light alkanes.

 The utility model is illustrated Fig.1-2 .:

25 Fig 1. A block diagram of a pyrolysis furnace block with an additional input of laser radiation.

In FIG. 1 is a block diagram of a furnace tube unit with laser control for pyrolysis of light alkanes, where: 1 - a combustion chamber with pipe coils; 2 - raw materials for pyrolysis; 3 - convection zone 30 of the coil; 4 - radiant zone of the coil; 5 - pyrolysis products; 6 - quenching and evaporation apparatus; 7 - optical laser radiation distributor; 8 - C0 ₂ laser emitter; 9 - optical window isolation system; 10 - wall of the combustion chamber; 17 - coil. Fig 2. The area of the coil with external heating and with additional inputs of laser radiation into the pyrolysis pipe.

In FIG. 2 shows a section of the radiant zone of the coil and the insulation system of the optical window, where: 1 1 is the pipe section of the radiant zone of the coil; 12 - pipe supply buffer (insulating) gas (CH ₄ , N ₂ , N ₂ , Ar); 13 - optical window (ZnSe, NaC, KB g); 14 - diaphragm mixing gas flows; 15 - input laser radiation; 16 - out-of-line laser radiation input chamber with thermal insulation and an optical window isolation system; 17 - zone of the absorption of raw laser radiation.

The proposed design of the furnace tube unit for pyrolysis of light alkanes includes, in particular, the following elements: a furnace chamber with coils made of pipes; convection zone of the coil; coil radiant zone; laser emitter C0 ₂ , an optical laser radiation distributor, at least one optical window, an optical window isolation system, a quenching and evaporation apparatus, pipes for introducing raw materials for pyrolysis and output of pyrolysis products, a protective gas supply pipe, gas flow mixing diaphragm; an extra-flow laser radiation input chamber with thermal insulation and an optical window isolation system, a zone of absorption of laser radiation by raw materials.

 As a material for the manufacture of an optical laser input window, materials are used that are optically transparent for IR radiation, for example, ZnSe, KBr, NaCl, and others.

As the laser light emitter used C0 ₂ laser with a power density in the range of 50 - 10,000 W / ^cm2 or radiation is used as radiation pulse - periodic C0 ₂ laser with a power density in the range of 50 - 10,000 watts / cm ² ..

 As a material for the coil, steel of low heat resistance type 12X18H10T is used.

The pyrolysis of light alkanes is carried out in a tubular furnace, in which the reaction tubes of the coils are heated externally by burning hydrocarbon fuel. Inside the pipes, a temperature of about 630-700 ° C is maintained. In the radiant zone of the pyrolysis coil is fed into the pipe further radiation C0 ₂ laser with a power density of 10,000 watts / cm2 through an extra-furnace laser radiation input chamber with an optical window and an optical window thermal insulation system. An optical laser beam distributor is used to distribute the laser radiation over the coil pipe sections.

 The reaction mixture leaving the pyrolysis furnace is cooled in a quenching - evaporation apparatus. The cooled mixture is subjected to separation. Then the gas stream is compressed to a pressure of about 20 atm, after which it is dried and fed to the separation. The expected productivity of the furnace block for processed raw materials is 10 ^ -50 thousand tons per year.

Owing to the emission of C0 ₂ lasers, local high-temperature zones are created in the tubes of the coils, which serve as an additional source of radicals, which leads to a decrease in the threshold reaction temperature and the yield temperature of the target products by approximately 150 ° C (in the wall zone) compared to the prototype. A characteristic feature of this process is a jump in the conversion of ethane at a wall temperature of about 500 + 550 C under the action of axial radiation. In this case, the cross section of the radiation beam is about 2% of the cross section of the pipe coil. The technological scheme of the process of pyrolysis with laser radiation is much simpler. In this scheme, water may not be used to dilute the feed. The scheme contains fewer units of basic equipment, which leads to a noticeable reduction in capital costs (according to preliminary estimates, by up to 20-25%) compared with the prototype scheme.

 An important consequence of the refusal to dilute the reaction mixture with water vapor is a significant (1.7-1.8 times) decrease in the volume of the reaction mixture in the pyrolysis furnace in terms of unit volume of ethane supplied. This allows you to either increase the productivity of existing furnace blocks, or reduce the dimensions of new furnaces while maintaining the same raw material capacity.

An increase in the power density of laser radiation even against the background of a decrease in the input power leads to a shift in the temperature threshold of the reaction to lower values and to an increase in the depth of processing of raw materials. Thus, an ethane conversion level of about 60% is ensured at a wall temperature of about 150 degrees lower than with standard gas heating through the walls.

 According to experiments [V.N. Snytnikov, T.I. Mishchenko, V.N.Snytnikov, S.E. Malykhin, V.I. Avdeev, V.N. Parmon. Autocatalytic gas-phase dehydrogenation of ethane. Res.Chem.Intermed, 201 1, DOI 10.1007 / sl 1164-011-0449-x.], In this process, ethane conversion of about 85% can be achieved at relatively low temperatures (600-700 ° C) and atmospheric pressure. Such a decrease in operating temperature significantly reduces the formation of coke, as well as heavy pyrolysis products. Due to this, the process can be carried out without dilution of the original ethane with water vapor.

 Table 2 shows the characteristics of the process of pyrolysis of ethane with laser stimulation at a temperature in the pyrolysis furnace of 630 ° C.

Table 2.

Characteristics of the process of ethane pyrolysis with laser stimulation at a temperature in the pyrolysis furnace of 630 ° C.

It is seen that in the composition of the reaction products there are practically no medium-molecular and heavy products of C ₄ and C ₅ +, in addition, due to the absence of water vapor, the formation of carbon oxides does not occur.

Given these characteristics, the primary fractionation blocks, as well as the separation blocks of fractions C ₄ and C ₅ can be excluded from the process flow diagram.

As a laser, it is proposed to use continuous and / or pulse-periodic C0 ₂ laser with a power of up to 700-4000 W with a wavelength of 10.6 microns. The system for isolating an optical window from overheating by hot gas is a chamber filled with shielding gas and a -14 diaphragm system that generates gas flows and minimizes mixing of the reaction mixture with shielding gas. The main energy is supplied for pyrolysis by external heating of the reaction zone - 4. Methan, hydrogen and mixtures thereof are used as a protective gas for windows. The estimated temperature range in the reactor volume is 300 + 700 ° C. Operating temperatures on the outer wall of the reaction zone are 500 900 ° C.

 The calculation of the specific energy consumption in the pyrolysis furnace, made under the assumption that the heat of the effluent is effectively recovered to heat the source gas, shows that the theoretical energy consumption per 1 ton of ethylene produced in this process is 5.14 GJ / t, which is slightly lower than the traditional one process (-5.3 GJ / t). This decrease is associated with a decrease in the formation of by-products of ethane pyrolysis.

 In the proposed process, the energy consumption of lasers contributes to the energy consumption of the furnace tube unit during pyrolysis. With the use of CO2 lasers with a power of up to 1 kW of radiation, their consumed power of electrical energy is about 20 kW. Taking into account 40% of the total conversion efficiency of thermal into electrical energy, the energy consumed by the laser is equivalent to 50 kW of thermal energy when burning fuel. Thus, in the process of pyrolysis using laser radiation, the additional energy consumption for laser radiation is about 2% of the energy consumption in the traditional process, which is comparable to the loss of thermal energy in the pyrolysis process. In addition, in the process of pyrolysis using laser radiation, a real reduction in energy consumption is possible as a result of 1. a reduction in energy consumption for primary fractionation and separation of products due to the exclusion of primary fractionation, debutanization and depentanization blocks from the scheme; 2. reduce heat loss with flue gases associated with a decrease in temperature of the exhaust flue gases.

Claims

15/183122 Utility Model Formula 1. The furnace tube block for the pyrolysis of light alkanes, characterized in that it contains a combustion chamber with coils from the pipes; convection zone of the coil; radiant zone of the coil; laser input radiation, C0 ₂ laser emitter, optical laser radiation distributor, at least one optical window, optical window insulation system, quenching-evaporation apparatus, nozzles for introducing raw materials for pyrolysis and output of pyrolysis products, insulating gas supply nozzle, diaphragm gas flow mixing; an extra-flow laser radiation input chamber with thermal insulation and an optical window isolation system, a zone of absorption of laser radiation by raw materials.  2. The furnace block according to claim 1, characterized in that materials optically transparent for IR radiation, for example, ZnSe, KBr, NaCl, and others, are used as a material for manufacturing an optical window for inputting laser radiation. 3. A furnace assembly according to claim 1, characterized in that the laser emitter is used as radiation C0 ₂ laser with a power density in the range of 50 -. 10000 W / ^cm2. 4. The furnace unit according to claim 1, characterized in that the radiation uses radiation from a pulsed-periodic C0 ₂ laser with a radiation power density in the range of 50 - 10,000 W / cm ² .  5. The furnace block according to claim 1, characterized in that as a material for the coil use steel of low heat resistance type 12X18H10T.