JPS63305915A - Separation of carbon dioxide contained in exhaust gas and recovering method thereof - Google Patents

Abstract

PURPOSE:To efficiently recover high-purity carbon dioxide without largely modifying an existing installation by pressurizing exhaust gas subjected to dust removal and thereafter using a membrane for separating gas to selectively separate carbon dioxide and liquefying gaseous carbon dioxide. CONSTITUTION:In the case of installating a recovery equipment of gaseous carbon to a conventional lime kiln installation, both the exhaust gas of combustion gas generated from a rotary kiln 3 and the exhaust gas generated by decomposition of limestone are mixed and this mixture is sent to a dust collector 7 to remove dust and thereafter pressurized with a compressor 8. After subjecting this exhaust gas to temp. control in a cooler 9, gaseous carbon dioxide is selectively separated with a membrane 10 for separating gas. The separated gaseous carbon dioxide is liquefied wit the compressor 8 and a refrigerator 12 via a tank 11 of a crude gaseous carbon dioxide and highly purified in a purification tower 13 of gaseous carbon dioxide and filled into a tank 14 of liquid carbon dioxide.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for separating and recovering carbon dioxide in exhaust gas, and more specifically, after selectively separating carbon dioxide in exhaust gas using a gas separation membrane, carbon dioxide is recovered. This invention relates to a carbon dioxide separation and recovery method that liquefies gas.

Conventional technology Carbon dioxide (hereinafter referred to as carbon dioxide gas) is used as an atmospheric gas for welding, cooling, and for drinking purposes, but it is also used in steel plants as a stirring gas for steel baths such as complex blowing converters, and in blast furnaces. It is used as a protective and cooling gas for tuyeres, and its demand is on the rise.

Industrial carbon dioxide gas is produced by separating and refining exhaust gas that contains over 98% carbon dioxide gas, which is generated in various processes in the petrochemical industry, but the price of crude oil, which is the raw material, fluctuates. At present, carbon dioxide is very expensive, so its use is naturally restricted.

Therefore, proposals have been made to recover carbon dioxide gas from exhaust gas discharged from calcining furnaces for limestone, dolomite, etc.
There are publications such as Publication No. 8.

The former thermally decomposes limestone, etc. using the combustion heat generated by burning fuel in a fluidized bed reactor, and a part of the CO2 gas produced by this decomposition is circulated into a container as a fluidizing gas, and the fuel is The latter is a method of recovering high-concentration 002 gas from a mixed gas with combustion gas of CO2. This is a gas production and recovery method.

Problems to be Solved by the Invention However, these conventional techniques require the use of a dedicated fluidized bed reactor, and the resulting CO2 concentration is 75%.
~90%, and not only cannot it be used as is for various purposes, but also cannot compete in terms of quality and cost compared to petrochemical industry exhaust gas, which contains 98 to 99% carbon dioxide. do not have.

Although it is suitable for constructing a new fluidized bed reactor, it is not applicable to the method shown in Figure 2, which recovers carbon dioxide gas from exhaust gas emitted from lime kilns operating in steel plants, etc. Can not.

Means for Solving the Problems The present invention aims to solve the problems of these conventional techniques. lead to the membrane,
The present invention provides a method for economically recovering carbon dioxide gas by selectively separating carbon dioxide gas and liquefying the carbon dioxide gas.

That is, the present invention focuses on separating and recovering carbon dioxide in exhaust gas, and after increasing the pressure of the dust-removed exhaust gas and introducing it to a gas separation membrane, separating it into gas other than carbon dioxide and gas mainly composed of carbon dioxide. , is a method for separating and recovering carbon dioxide in exhaust gas, which is characterized by liquefying a gas whose main component is carbon dioxide.

Function The present invention is a method of selectively separating carbon dioxide gas in exhaust gas using a gas separation GL membrane, and liquefying the obtained relatively high-purity carbon dioxide gas by cryogenic separation and recovering it as high-purity carbon dioxide gas. Therefore, according to the present invention, exhaust gas that was conventionally released into the atmosphere can be removed without major changes to existing equipment.
By simple modification, the active ingredient carbon dioxide gas can be efficiently recovered, and high purity carbon dioxide gas can be obtained at low cost and in large quantities.

The present invention will be further explained in detail below.

The present invention can be widely used for exhaust gas in general, but is effective when the carbon dioxide concentration in the exhaust gas is as high as 20% or more.
For example, in a steel mill, it is efficient to use exhaust gas from a lime kiln or combustion exhaust gas from a fuel gas containing a large amount of carbon oxide (for example, converter gas).

The invention will now be explained using the example of a lime kiln.

Quicklime is mainly produced in a lime kiln, and quicklime is produced by a thermal decomposition reaction of limestone (CaCO3) as shown in the following formula, and approximately 400 N m'' of carbon dioxide gas is generated from 1 ton of limestone.

CaC03-+CaO+ C02-42500kcal
/ kg-mol This reaction is endothermic, so 90
The inside of the kiln is maintained at a temperature in the range of 0 to 1000°C to decompose limestone. For this purpose, it is necessary to replenish heat by burning fuel.

Examples of this fuel include gaseous fuels such as coke oven gas and converter gas, and solid fuels such as coal.

Among these, gaseous fuels with high carbon monoxide concentration, such as converter gas, are preferred. The reason for this is that when converter gas is exclusively fired, the concentration of carbon dioxide in the exhaust gas is 36%, but even when coke oven gas is exclusively fired, the concentration of carbon dioxide in the exhaust gas is only 8%. This is because exhaust gas cannot be obtained.

The exhaust gas produced when limestone is burned in a lime kiln is mixed with carbon dioxide gas from limestone decomposition and combustion gas from the fuel, and is discharged outside the kiln, so the concentration of carbon dioxide gas is low, and it is not possible to obtain high-purity carbon dioxide gas as it is at a low price. .

Therefore, the present invention aims to improve the temperature of 500°C discharged from a lime kiln.
The exhaust gas is introduced into a dust remover to remove dust, then pressurized by a compressor and cooled by a cooler to a temperature of 50 to 80°C, preferably 60 to 70°C. The carbon dioxide gas is introduced into a separation membrane, where only carbon dioxide gas is selectively separated, and the separated carbon dioxide gas is compressed, cooled, and expanded to liquefy, and then contained using a separation device such as a rectification tower using the boiling point difference. In this method, impurity gas is purified by cryogenic separation, and recovered as highly pure carbon dioxide gas with a purity of about 99.99%.

What is particularly important in the present invention is to selectively concentrate and separate carbon dioxide in exhaust gas using a gas separation membrane to obtain highly concentrated carbon dioxide.

BACKGROUND ART A method using a gas separation membrane is conventionally known as a separation and purification technique for mixed gas, and gas separation membranes include porous membranes and non-porous membranes.

In general, gas separation by porous membranes cannot be expected in the region of viscous flow, but when the pore diameter is sufficiently smaller than the mean free path of the gas, (1) Knudsen flow (molecular flow), (2) surface Separation can be performed by mechanisms such as flow, (3) capillary condensation, and (4) molecular sieving, but in the present invention, this technique has poor separation efficiency and is not practical.

Gas separation using a non-porous membrane uses a rubber-like polymeric membrane and utilizes the difference between the solubility coefficient of each gas in the polymer and the diffusion coefficient in the membrane. This is suitable for efficiently separating mixed gas in one stage.

The reason why debris permeates through a non-porous membrane is because gas dissolves in the membrane from the high-pressure side (the side with high partial pressure), diffuses through the membrane, and moves to the opposite side, but each gas component The ease of permeation through the membrane (permeation rate) differs depending on the polymer material, but
It can be used as long as it is resistant (heat, pressure, chemically stable) under the conditions of use and has a thin film.

As the membrane used in the present invention, known membranes can be used. Specific examples include polyimide polymer compounds, cellulose acetate, polysulfone, and the like.

-For example, the aromatic polyimide represented by the following formula is 50~
It can also be used at temperatures of 150°C.

(However, Ar in the formula represents an aromatic compound.) Also, the structure thereof may be a flat plate, a tube, a hollow fiber, a film, etc., and it may be used as it is or in combination.

Further, as the membrane shape, homogeneous membranes, asymmetric membranes, composite membranes (multilayer structure in which non-porous membranes or a non-porous material and a porous material are composited) can be used.

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a drawing explaining the present invention in detail, and is a flow diagram in which a carbon dioxide recovery device is installed in a conventional lime kiln facility.

As shown in FIG. 1, the lime kiln equipment consists of a preheating furnace 2, a rotary kiln 3, and a cooler 5. The preheating furnace has a raw material supply port 1, and the cooler 5 has a burner 4 that supplies heat to the rotary kiln 3. A blower 6 for secondary combustion air is provided.

In addition, the carbon dioxide recovery device consists of a dust remover 7, a compressor 8, a cooler 9, a gas separation membrane 10, a tank (buffer) 11, a compressor 8, a refrigerator 12, and a carbon dioxide purifier 13, all of which are They are connected in order by piping, and are further connected so that a part of carbon dioxide gas can be returned from the carbon dioxide purifier 13 to the piping between the cooler 9 and the gas separation membrane 10.

Raw material limestone is preheated from a supply port 1 through a preheating furnace 2 and fired in a rotary kiln 3.

The amount of heat required for limestone decomposition is supplied by burning converter gas or the like in the burner 4. The calcined quicklime exchanges heat with secondary combustion air in the cooler 5 and is discharged. Exhaust gas from combustion gas and exhaust gas generated from limestone decomposition (20-50% carbon dioxide)
The remaining gas (mainly nitrogen, temperature 300-500°C) is sent to a dust remover 7 to remove dust. The exhaust gas from which dust has been removed is pressurized to 5 to 30 kg/crrf by the compressor 8, and has a temperature of about 200°C.

The temperature of this exhaust gas is adjusted by a cooler 9 to 80 to 70
After bringing the temperature to 10°C, carbon dioxide is selectively separated by a gas separation membrane, resulting in a carbon dioxide content of 80 to 90%. Note that the higher the concentration of carbon dioxide gas introduced into the gas separation membrane, the smaller the pressure loss, which is advantageous.

In order to further increase the purity and to facilitate transportation, the crude carbon dioxide gas is passed through the crude carbon dioxide tank 11 and liquefied by the compressor 8 and refrigerator 12, and highly purified to a purity of 99.99% in the carbon dioxide gas purification tower 13. circulated before the gas separation membrane 10,
Most of the liquid carbon dioxide tank 14 is filled with the liquid carbon dioxide gas.

Although the present invention has been explained above using the example of a lime kiln, the present invention is not limited to this.
It can be suitably applied to the separation of gas mixtures containing the above, and high purity carbon dioxide can be efficiently obtained with inexpensive equipment.

EXAMPLE An example in which a lime kiln was modified and a carbon dioxide gas recovery device was installed will be described below.

Lime kilns are equipment used to produce quicklime used for scouring within steel mills. Conventionally, coke gas was used as the combustion gas, and the exhaust gas was also removed and released into the atmosphere. Fig. 2 shows a flow diagram of conventional lime kiln equipment. Since the exhaust gas passes through the air cooling tower 15, the pre-duster 16, and the bag filter 17, there is a large leakage along the way, so it is released into the atmosphere as exhaust gas. The carbon dioxide concentration in the previous chimney 19 was approximately 15%, which was quite low.

Therefore, the modification shown in Figure 1 was carried out, and the converter gas with a carbon monoxide concentration of approximately 57% was used as combustion gas at 19 ONm''.
/v1in was used. The amount of secondary air used for cooling was also kept to the minimum required for combustion, preventing a drop in the carbon dioxide concentration in the exhaust gas. Quicklime is fired at a rate of 20t/hr, and the carbon dioxide gas decomposed at that time is approximately 13ONrn'/win.
The combustion exhaust gas is about 40ONrn'/win, while the combustion exhaust gas is about 15ON.
Carbon dioxide gas of rn''/win was generated. That is, when producing limestone 1, carbon dioxide gas of 84 ONm3 was generated.

The carbon dioxide concentration in the exhaust gas discharged from the preheating furnace 2 is approximately 5
3%, the dust concentration is 20g/Nm3, and the temperature is approx.
The temperature was 300°C. The dust remover uses a wet pentillary flapper method, and the dust concentration is reduced to 0.3mg/Nrn'.
It was lowered to. This is 8 kg/crn' with a blower.
The pressure was increased to 98%, and nitrogen was separated by passing through a gas separation membrane to purify it to a carbon dioxide concentration of 98%. Next, it was liquefied using a cryogenic separator, and the purity was increased to 89.99% by utilizing the difference in boiling points.

Effects of the Invention The present invention allows exhaust gas, which was conventionally discarded into the atmosphere, to be removed by simple modification without major changes to existing equipment.
This paper proposes an economical method for producing carbon dioxide gas in which the useful component carbon dioxide gas is selectively separated and recovered using a gas separation membrane.

[Brief explanation of drawings]

FIG. 1 is an overall flow diagram when the present invention is applied to lime kiln equipment, and FIG. 2 is a flow diagram of conventional lime kiln equipment.

Claims (1)

[Claims] In separating and recovering carbon dioxide in exhaust gas, the pressure of the dust-removed exhaust gas is increased and guided to a gas separation membrane, where it is separated into gases other than carbon dioxide and gas whose main component is carbon dioxide. A method for separating and recovering carbon dioxide in exhaust gas, characterized by liquefying the gas.