RU2206375C1 - Commercial gaseous carbon dioxide production process - Google Patents

Abstract

FIELD: inorganic compounds technology. SUBSTANCE: production of carbon dioxide from smoke fumes involves removal of sulfur dioxide from the latter, adsorption on zeolite sorbent and subsequent desorption of carbon dioxide, drying by silica gel, purification, and regeneration of sorbents. Desorption is accomplished by heating sorbent to desorption temperature. By-product, namely dried nitrogen gas, is obtained during carbon dioxide adsorption stage, for the purpose of which drying of smoke fumes and simultaneous removal of sulfur dioxide therefrom are performed before adsorption of carbon dioxide. Zeolites, prior to be heated for regeneration, are purged with commercial carbon dioxide at ambient temperature until nonadsorbable impurities are completely removed. Regeneration is accomplished by purging sorbent with earlier obtained dried nitrogen gas. EFFECT: reduced power consumption, reduced price cost of carbon dioxide, and prevented pollution of atmosphere. 3 cl, 1 dwg

Description

 The invention relates to the field of producing gaseous marketable carbon dioxide from flue gases.

 Known methods for the separation of carbon dioxide (carbon dioxide) from its mixtures with other gases can be divided into the following: sorption, sorption-compression and low temperature.

A known method of producing gaseous carbon dioxide, in which flue gases are used as raw material for producing CO ₂ . The specified method is carried out using the installation for carbon dioxide [1] (sorption method). The installation contains a boiler, a scrubber, an absorber, a heat exchanger, a stripper and a refrigerator; a prechamber is installed in front of the boiler. The installation is designed to extract carbon dioxide from flue gases, to use it as a raw material, to obtain marketable carbon dioxide.

According to the specified method, the impurities are distilled off with a mixture of desorbed carbon dioxide and water vapor at a temperature of 110 ^° C in the upper part of the regenerator, and the carbon dioxide free of impurities is removed from the lower part of the regenerator below the input for a saturated ethanolamine solution.

 The disadvantages of the method is that the resulting raw material is contaminated with vapors and traces of monoethanolamine, saturated with water vapor, i.e. does not meet the requirements of GOST 8050-85 *, and therefore cannot be used as a protective atmosphere in welding, for drying foundry molds, in industries using food-grade carbon dioxide. In addition, the neutralization of monoethanolamine effluents is difficult and not completely resolved, requires significant capex, and effluents can pollute the environment.

A known method of producing carbon dioxide [2], in which the flue gas is purified from SO ₂ with a solution of soda, and the absorption of CO _{2 is} carried out with a solution of monoethanolamine. The desorbed gas from the MEA solution is purified from CO ₂ vapor and traces MEA solution of potassium permanganate (KMnO _4), is compressed successively, dried on silica and purified by activated carbon and fed to the consumer in a liquid or gaseous state.

 The specified method is carried out using a plant for the production of liquefied carbon dioxide (sorption-compression method), including a cold scrubber, ash collector, exhauster, soda scrubber, absorber, stripper, heat exchange equipment, circulation pumps, a column with a solution of potassium permanganate, compressor equipment, industrial vessels, slipways cylinders.

 The disadvantages of the method are high gas pressure (up to 7.5 MPa), bulkiness, significant capex and, as a result, the high cost of carbon dioxide produced. In addition, wastewater treatment (including the combination of monoethanolamine, soda, sulfur, etc.) is difficult and requires significant capex, environmental pollution is also possible.

Closest to the described invention in technical essence is a method for producing carbon dioxide [3, 4], in which flue gases are purified from SO ₂ with a solution of soda, and the absorption of CO ₂ from flue gases is carried out with a solution of monoethanolamine. Gaseous CO ₂ desorbed from the MEA solution is sequentially compressed, dried on a solid adsorbent-silica gel, purified on activated carbon and sent to the consumer in a liquid or gaseous state.

The specified method is carried out using a carbon dioxide installation for the production of dry ice based on special combustion of fuel. The installation contains a cold scrubber, smoke exhaust, soda scrubber, wash scrubber, absorber, stripper, heat exchange equipment, wash column, circulation pumps, carbon dioxide compression equipment (for example, a UVZhS installation consisting of a compressor, oil and water separators, refrigerators, activated carbon cleaning units and drying with solid adsorbent-silica gel, electric heaters, steam heater, carbon dioxide condenser), slip-on cylinders, cylinders for liquid CO ₂ , intermediate vessels, le generator, carbon dioxide ramp for filling with liquid CO ₂ , isothermal tank, booster vacuum recovery unit, booster, capacitor, tank for MEA, vacuum pump.

The disadvantages of the method are: the bulkiness of the installation and the complexity of the process, a high degree of compression (up to 7.5 MPa), the inability to obtain gaseous CO ₂ without the presence of liquid CO ₂ , the issues of wastewater treatment generated by this method and contaminated with soda, monoethanolamine and KMnO ₄ , which require significant capex, there is the possibility of environmental pollution.

The essence of the claimed invention lies in the fact that in the proposed method for producing gaseous commodity carbon dioxide, which includes purification of flue gases from sulfur dioxide, adsorption of carbon dioxide, its desorption, drying with silica gel and purification, as well as regeneration of sorbents, according to the invention, carbon dioxide is desorbed by heating the zeolite sorbent flue gases before temperature desorption of CO ₂ as a byproduct - dehumidified nitrogen gas is obtained during the adsorption of carbon dioxide, for which drying of the flue gas and their purification from sulfur dioxide is carried out before the adsorption of carbon dioxide, and simultaneously.

 In addition, according to the invention, zeolites before heating during their regeneration purge commodity carbon dioxide at ambient temperature until the complete removal of non-adsorbed impurities.

 Moreover, according to the invention, the regeneration of silica gel is performed by purging obtained by adsorption, dried with nitrogen gas.

 The technical result from the application of the claimed invention is to simplify the method of obtaining gaseous purified and dried carbon dioxide and to prevent environmental pollution due to a new relationship of signs, reducing energy consumption and cost of carbon dioxide produced.

Obtaining pure marketable carbon dioxide is carried out due to the fact that flue gases containing CO ₂ and previously purified from SO ₂ and moisture are sent to zeolites (for adsorption). Carbon dioxide is adsorbed by zeolites, i.e. commodity CO ₂ accumulates in zeolites, which is subsequently extracted from zeolites when they are heated during regeneration after the complete removal of unabsorbed impurities (N ₂ + O ₂ ) from the free space between the zeolite grains.

Thus, through the use of a new set of features, a previously unknown effect has been achieved - the production of flue gases, previously purified from SO ₂ and moisture on silica gel, of pure marketable carbon dioxide accumulated in zeolites during the adsorption of CO ₂ from flue gases, by simultaneously heating zeolites during their regeneration and evacuation.

 In addition, an additional product is obtained - nitrogen gas, which is used for the regeneration of zeolites in other areas, for example, during the heat treatment of metal.

 The drawing shows a diagram for implementing the proposed method for producing carbon dioxide.

According to a specific example, the flue gases using the exhauster 1 through the pipe 2 are sent 1 through the valve 3, the refrigeration unit, consisting of a refrigerator 4 and the evaporator 5 of the refrigeration machine, in which the flue gases are cooled to a temperature of +4 ... + 8 ^o C, valve 6 to the lower part of the adsorber 7, filled with silica gel and operating in the adsorption mode, in which they are dried to the dew point (-35 ...- 40 ^o С) and at the same time completely cleaned of SO ₂ (in the case of burning natural gas with sulfur-containing impurities).

 The adsorbers 7 and 8 operate alternately, when the adsorber 7 is in the adsorption mode, the adsorber 8 is in the adsorbent regeneration mode — heating and cooling.

After that, the purified and dried gas is supplied through the valves 9, 10 to the lower part of the adsorber 11 (one of the adsorbers 12 or 13 at this time is in the CO ₂ desorption mode when the zeolites are heated, and the other in the cooling mode of the adsorbents - zeolites) filled with zeolites .

In the process of absorption of CO ₂ by zeolites, pure nitrogen gas is obtained, dried and purified from CO ₂ and SO ₂ , which is subsequently used to restore the adsorption properties of silica gel.

Nitrogen gas containing up to 7.8% vol. O ₂ , from the upper part of the adsorber 11 through the valve 14 enters through a pipe 15 to the suction side of the gas blower 16.

 To restore the adsorption properties of silica gel (restoration includes two periods - heating and cooling) by gas blowing 16, nitrogen gas is transported through the valve 17, heater 18, valves 19, 20 to the upper part of the adsorber 8.

In the heater 18, the gas is heated to a temperature of 160 ... 200 ^o With, to ensure the temperature of the silica gel 140 ^o With in the upper layer, necessary for the desorption of H ₂ O and SO ₂ . Contaminated nitrogen gas with impurities of H ₂ O and SO ₂ through the valves 21, 22 is discharged from the system into the flue gas burs.

After reaching the temperature of the upper layer of silica gel 140 ^o With the heater 18 is turned off and the dried nitrogen gas is sent through the valves 23, 21 in the lower part of the adsorber 8 for cooling the silica gel. Heated (cooling) gas through valves 20, 24 is removed from the system and discharged into the atmosphere.

After the end of the CO ₂ adsorption period, the adsorber 11 operating in the adsorption mode is transferred to the CO ₂ desorption mode, and the gases dried and purified from SO _{2 are} sent to the adsorber 12 through the valve 25, where a process similar to that described above occurs.

After the adsorption process of CO ₂ in the adsorber 12, it is transferred to the desorption mode, and dried and purified from SO ₂ gases through the valve 26 is fed to the adsorber 13.

In the initial period of CO ₂ production, zeolites are blown with commercial carbon dioxide at ambient temperature before heating during their regeneration until the non-adsorbed impurities are completely removed, CO ₂ with unabsorbed impurities O ₂ and N ₂ remaining in the adsorber volume between the zeolite grains are suctioned off with a vacuum pump 27 from the adsorber 11 through the valve 28, the refrigerator 29 and discharged into the atmosphere through the valve 30.

 Removal of unabsorbed impurities is carried out at ambient temperature.

 At the end of the removal of non-adsorbed gases, simultaneously close the valve 30 on the discharge candle and open the valves 31, 32 before and after the buffer tank 33, turn on the pressure regulator 34 and open the valves 35, 36 on the pipeline 37 of hot flue gases in the annular space of the adsorber 11.

Part of the hot flue gases after the exhauster 1 through the valve 35, the heater 38, where the flue gases are heated to a temperature of 320 ... 350 ^o C, the valve 36 is fed into the annulus 11 of the adsorber to provide a heating temperature of zeolites of 230 ^o C.

 Having passed through the adsorber 11, the flue gases through the valves 39, 40 through the pipe 41 are returned to the flue gas burs.

Gaseous carbon dioxide, freed from impurities and obtained by heating the zeolites and evacuating the system, is taken from the zeolites through a refrigerator 29, in which CO _{2 is} cooled to a temperature of 40 ^° C, by a vacuum pump 27 and fed through a valve 31, a buffer tank 33, a valve 32 and pressure regulator 34 to the consumer or to the installation for the production of liquefied carbon dioxide (UVZhS).

After the desorption of carbon dioxide from the adsorber 11, the flue gases heating the zeolites are sent to the adsorber, which should work in the mode of heating the zeolites (desorption of CO ₂ ). In addition, the adsorber 11, operating in the mode of heating-desorption of CO ₂ , is transferred to the cooling mode of zeolites with atmospheric air.

 Atmospheric air blower 42 through the pipe 43 is sent through the valve 44 to the adsorber 11; Having passed the annular space and cooled the zeolites, air through the valves 39, 45, 46 through the pipeline 47 is discharged into the atmosphere.

After cooling the zeolites to the adsorption temperature, the adsorber 11 is transferred to the mode of adsorption of CO ₂ from flue gases.

 The absorbers 12, 13 operate in a similar manner.

After the adsorption process (H ₂ O and SO ₂ ) on silica gel in the adsorber 7, the adsorber 8 is transferred to the adsorption mode (H ₂ O and SO ₂ ).

 Switching of the adsorbers 7 and 8 from one mode to another (from the adsorption mode to the silica gel regeneration mode) is carried out using valves 48, 49, 50, 51, 20, 9, 21, 6.

When CO _{2 is} absorbed in adsorber 11, adsorber 12 can be in the (zeolite heating) mode of desorption of CO ₂ from zeolites, and adsorber 13 can be in zeolite cooling mode.

 Switching the adsorbers 11, 12, 13 from one mode to another is carried out using valves 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 36, 44, 10, 39, 45, 28, 14, 25, 26.

Thus, the flue gas is first purged of SO ₂ in an adsorber with silica gel and simultaneously dried before CO ₂ absorption. After that, the gases are sent to an adsorber filled with zeolite to absorb CO ₂ , while the nitrogen gas obtained after drying and purification of flue gases is used either in technology or to restore the adsorption properties of silica gel.

After saturation zeolites their regenerated CO ₂ (heated and cooled) - regain their adsorption properties.

 Gaseous marketable carbon dioxide is obtained during the heating of zeolites during their regeneration.

In order to intensify the production of CO _{2, the} regeneration of zeolites is carried out by evacuation at a regeneration temperature.

Before obtaining carbon dioxide that meets the requirements of GOST 8050-85 *, it is necessary to remove from the space between the zeolite grains non-absorbed impurities (O ₂ and N ₂ ) at ambient temperature. At this time, CO _2, together with these impurities, is discharged into the atmosphere.

 In the process of vacuum-thermal regeneration, carbon dioxide is extracted from zeolites, cooled and fed to the consumer.

Thus, pure CO _{2 is} obtained in a simplified manner and pollution is prevented.

Example. Flue gases are taken from the hog of the fuel-consuming unit in an amount of 2400 m ³ / h. Flue gas composition: CO ₂ - 6.07; O ₂ - 7.80; H ₂ O - 11.99; SO ₂ - 0.20; N ₂ - 73.94 vol.%.

The dry part of the flue gas is V _cyx = 2112.24 m ³ / h.

Количество влаги, подаваемое на силикагелевые адсорберы в течение 8 часов, составляет
V_H2O=(8,59-0,097)•10^-3•2112,24/8=143,5 кг,
где 8,59 г/м³ - влагосодержание сухого газа при t=8^oС;
0,097 г/м³ - то же при t=-40^oС.The amount of carbon dioxide V _CO2 = 145.68 m ³ / h (288.0 kg / h); ρ _o = 1.977 kg / m ³ .
The amount of sulfur dioxide V _SO2 = 4.8 m ³ / h (14.05 kg / h);

The amount of moisture supplied to the silica gel adsorbers for 8 hours is
V _H2O = (8.59-0.097) • 10 ^-3 • 2112.24 / 8 = 143.5 kg,
where 8.59 g / m ³ is the moisture content of dry gas at t = 8 ^o C;
0,097 g / m ³ - the same at t = -40 ^o C.

 The dynamic capacity of KSM silica gel by moisture is 5 ... 8 wt.% [5, p. 263, tab. thirty].

Then the required amount of silica gel G _KSM = 143.5 / 0.05 = 2870 kg.

The dynamic capacity of the silica gel KSM on SO ₂ in the presence of moisture is 12.1 wt.% At 20 ^o C [5, table. 24, p. 245]. Taking into account the stock and the drop in dynamic activity over time, an activity of 6 wt.% Is taken. Then the required amount of silica gel (for the absorption of SO ₂ in the presence of moisture) will be 14.05 • 8 / 0.06 = 1873 kg.

Accepted: G _KSM = 3000 kg.

 The adsorbers operating time is taken to be 8 hours, i.e. the duration of one work shift.

 The amount of carbon dioxide that needs to be adsorbed in 8 hours will be 288 • 8 = 2304 kg.

The dynamic capacity of zeolite CaA in carbon dioxide at 25 ^o C and P = 10 mm RT. Art. is 0.13 g / g [6, tab. 8.1b]. Then the required amount of zeolite G _CaA = 2304 / 0.13 = 17723 kg.

Accepted: G _CaA = 18000 kg.

The bulk density of zeolite is ~ 700 kg / m ³ , the apparent density of 1100 kg / m ³ . Thus, the free volume between zeolite grains is V _sv = 18000 / 700-18000 / 1100 = 9.35 m ³ . The plant capacity will be 288 kg / h; of which 220 kg / h can be directed to UVZhS, 20 kg / h - for cold blowing, 20 kg / h - for blowing salable carbon dioxide, 28 kg / h - unaccounted losses and compression losses.

With a 2-hour cold purge duration, gas exchange in the zeolite layer is 20 • 2 / 1.977 • 9.35 = 2.16, i.e. double exchange, which is enough to remove non-adsorbed gases (N ₂ and O ₂ ).

 Thus, the proposed method provides purified and dried gaseous carbon dioxide, simplifying the method and preventing environmental pollution, reducing energy consumption and cost.

 Purified and dried gaseous carbon dioxide can be used as a protective environment for welding, for drying foundry molds and other purposes. Product quality meets the requirements of GOST 8050-85 *.

 In addition, when carbon dioxide is obtained by this method, no wastewater (including compounds of monoethanolamine, soda, sulfur, etc.) is generated, for the treatment of which huge amounts of money are spent, several times the cost of the acid stations themselves.

Sources of information
1. Copyright certificate 242851, cl. B 01 L 19/04, 1966.

 2. S.V. Altundzhi, V.V. Bukharin and others. "Production and use of liquid carbon dioxide", Pishchepromizdat, 1959.

 3. Model project 414-9-8, Giproholod Institute, “Dry ice workshop with a capacity of 2.2 tons per day based on the use of various fuels as a raw material for flue gases with the possibility of producing liquefied carbon dioxide,” approved by the USSR Ministry of Trade, Moscow, 1975.

 4. "Recommendations on the regulation of the technological process for the production of dry ice and liquefied carbon dioxide for workshops operating on the basis of special fuel combustion", VNIIHP, Moscow, 1970, pp. 11-13.

 5. E. N. Serpionova "Industrial adsorption of gases and vapors", M., "Higher School", 1969.

 6. D. Breck "Zeolite molecular sieves", M., Mir, 1976.

Claims (3)

 1. The method of producing gaseous commodity carbon dioxide, including the purification of flue gases from sulfur dioxide, characterized in that the flue gases are purified from sulfur dioxide and dried with silica gel, carbon dioxide is adsorbed, desorbed, and sorbents are regenerated, and carbon dioxide is desorbed by heating the zeolite sorbent with flue gases to the desorption temperature, and the by-product, dried nitrogen gas, is obtained during the adsorption of carbon dioxide, for which the drying of flue gases and their purification t of sulfur dioxide is carried out before adsorption at the same time.  2. The method according to claim 1, characterized in that the zeolites before heating during their regeneration purge commodity carbon dioxide at ambient temperature until the complete removal of non-adsorbed impurities.  3. The method according to claim 1, characterized in that the regeneration of silica gel is carried out by blowing dried nitrogen obtained during adsorption.