JP2886644B2 - How to recycle carbon dioxide - Google Patents

Description

The present invention relates to a carbon dioxide gas recycling method capable of efficiently recovering and reusing carbon dioxide gas, a direct-combustible low-cost carbonaceous fuel obtained by the method, and The present invention relates to a method for producing microalgae that forms one component of the fuel.

[Conventional technology]

In recent years, from the viewpoint of environmental conservation such as global warming, the treatment of carbon dioxide in waste gas discharged from a combustion furnace using fossil fuels such as coal and petroleum has become a problem. Although effective recovery methods have been developed for NOx and SOx, satisfactory results have been obtained, but no satisfactory recovery method for carbon dioxide has been obtained yet.

It is a well-known fact that almost all the carbon dioxide fixation performed on the earth is due to photosynthesis of green plants, and most of it is due to phytoplankton existing in seawater. It is also known that the named microalgae are performing. By the way, to produce 1 kg of algal bodies like Chlorella and Senedesmus, about 1.7 kg of carbon dioxide gas
Is required as photosynthetic weight loss, and the utilization rate of
It is also known that about 3.4 kg of carbon dioxide gas is required even at a high rate of 50% (Organic Synthetic Chemistry, Vol. 34 No. 5, No. 20)
P. 1976).

[Problems to be solved by the invention]

Waste gas from fermentation factories, cement factories, steel plants, thermal power plants, etc. contains more than a few percent of carbon dioxide. Moreover, their volume is enormous, and even thermal power plants alone emit about 57 million tons of carbon into the atmosphere annually in Japan alone.

An object of the present invention is to efficiently collect and reuse this huge amount of carbon dioxide gas.

[Means for solving the problem]

As a result of intensive studies on the recovery and reuse of carbon dioxide gas, the present inventors have found a method of effectively using carbon dioxide gas, and have completed the present invention.

That is, the first invention of the present invention is to install a microalgae cultivation pond in a plant such as a thermal power plant that generates carbon dioxide-containing waste gas, and to separate the waste gas from the waste gas by a carbon dioxide separator, Carbon dioxide gas is separated by adsorption to zeolite, the separated carbon dioxide gas is fixed to microalgae using photosynthesis, and the obtained microalgae is pulverized as it is or a carbonaceous fuel such as fine coal water slurry or heavy oil. And recycling it again as a fuel to a plant such as a thermal power plant.

Further, a second invention of the present invention provides a method for preparing a fine algae, wherein the microalgae produced by the recycling method is added to the following components, ie, the following composition (A) or (B) or a mixture of (C): Algae-containing carbonaceous fuel.

(A) (a) carbonaceous solid powder such as coal, oil coke, petroleum pitch, (b) at least one dispersant, (c) at least one stabilizer, and (d) water as a main component. (B) Carbonaceous liquid composition such as heavy oil (C) A mixture of the above (A) carbonaceous solid / water slurry composition and the above (B) carbonaceous liquid composition A third invention of the present invention relates to a method for producing microalgae, which comprises producing microalgae by irradiating light with carbon dioxide gas separated from combustion waste gas.

Examples of the dispersant include a sulfonated product of naphthalene or creosote oil, a salt thereof or an aliphatic aldehyde addition condensate thereof, or a sulfonic acid group-containing aminotriazine condensation product of an aliphatic aldehyde or a salt thereof.

As the stabilizer, clay minerals, in particular, montmorillo and / or xanthan gum are preferable, but kaolin and illite can also be used.

〔Example〕

Hereinafter, the present invention will be described specifically with reference to examples. However, the present invention is not limited by these examples.

Embodiment 1 Hereinafter, a method for recycling carbon dioxide gas according to the present invention will be described with reference to the conceptual diagram of FIG.

A large amount of carbon dioxide-containing waste gas generated from a thermal power plant is supplied to a carbon dioxide separator to be separated into carbon dioxide and other gases. The separated carbon dioxide is directly or once stored as liquefied carbon dioxide and then supplied to the microalga culture tank.
Microalgae are cultured and propagated in this culture tank by carbon dioxide and light irradiation. The obtained microalgae is pulverized into a fuel as it is, or added to a carbonaceous fuel such as pulverized coal / water slurry or heavy oil to convert it into a fuel. This fuel is used as power generation fuel for thermal power generation.

Example 2 Hereinafter, one example of the method for producing microalgae of the present invention will be described.

A coal-fired power plant has a temperature of about 110 that contains 11% carbon dioxide.
The carbon dioxide gas is separated from NOx, SOx and other gases by absorbing waste gas of ° C. into amine or adsorbing to zeolite. As described above, the adsorbent containing only carbon dioxide gas is heated to release carbon dioxide gas using other appropriate means.
Air or liquefied carbon dioxide containing 5% carbon dioxide is obtained.
The air or liquefied carbon dioxide gas is added by aeration, dropping or other appropriate method to a culturing pond of Chlorella or Senedesmus such as a pool with a plastic roof or a circulating water channel system configured such that a culture solution flows with a slight inclination, At the same time, microalgae are propagated by irradiating with sunlight and light from a light bulb for 24 hours. The microalgae produced in this way are added to a carbonaceous fuel to convert it into a fuel.

Embodiment 3 Next, an embodiment of the preparation of the carbonaceous fuel of the present invention will be described in detail with reference to the drawings.

In FIG. 2, reference numeral 1 denotes a hopper, into which the wet microalgae A produced above is put, and an appropriate amount is sent from the hopper 1 to the dehydrator 2 to adjust the water content to about 30%. Next, a necessary additive such as a preservative and a dispersing agent such as a surfactant is added in a kneading machine 3 through a constant-rate feeding machine (not shown), and the mixture is sufficiently mixed in a mill 4. (Both not shown) and stored in the storage tank 5.

11 is an existing storage tank for coal water slurry (CWM) and heavy oil.

B is a powder of microalgae dried by vacuum drying or solar drying.

The carbonaceous fuel of the present invention may be a carbonaceous solid powder, a dispersant, a stabilizer, a carbonaceous solid / water slurry composition (A) containing water as a main component, or a carbonaceous liquid such as heavy oil in the storage tank 11. To the composition (B), i) a wet microalgae having a water content of about 30% in the storage tank 5 is mixed and added in a mixer 6 or into a fuel supply pipe to a combustion burner 12 as shown in FIG. Ii) by adding the dry microalgae shown in B above immediately before the combustion burner 12 or by using a co-firing burner, or iii) by using the above i) and ii) in combination. It is supplied as carbonaceous fuel to the burners of thermal power plants.

Then, the carbon dioxide gas in the waste gas generated by the combustion show is used for culturing the microalgae as described in the second aspect of the invention, and the production of the microalgae from the carbon dioxide gas by photosynthesis and the recycling by conversion to fuel are established. Therefore, the recovery and reuse of carbon dioxide can be effectively performed.

〔The invention's effect〕

As described above, according to the present invention, it is possible to efficiently recover and reuse carbon dioxide in waste gas, which has various environmental problems such as global warming, and establish a method for recycling carbon dioxide. did it.

In addition, since about 3.4 kg of carbon dioxide is required to produce 1 kg of algae with a carbon dioxide utilization rate of 50%, not only a large amount of carbon dioxide is collected, but also the temperature of carbon dioxide is high. Of course, if you use it, you can maintain a suitable temperature of 25 ° C for growing Chlorella and Senedesmus even in winter,
The algal production per unit area can be increased by using an algal strain having an appropriate temperature of 35 to 40 ° C., and the use ratio of fossil fuel can be reduced to further increase resource saving.

In addition, using the cyanobacterium Spirulina, which has a strong carbon dioxide absorption capacity and a strong retention capacity, reduces the carbon dioxide gas utilization rate to about 80%.
Even when it is desired to increase to 90%, the use of air with a carbon dioxide content of 11%, from which NOx and SOx are separated and removed, allows the recovery of carbon dioxide without adversely affecting the optimal pH 9 to 11 for spirulina growth Can be performed more efficiently.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of carbon dioxide gas recycling of the present invention, and FIG. 2 is a process explanatory diagram showing one embodiment of the preparation of a carbonaceous fuel containing microalgae of the present invention.

Claims (5)

(57) [Claims] (1) A microalgae pond is installed in a plant such as a thermal power plant that generates waste gas containing carbon dioxide, and the waste gas is separated from the waste gas by a carbon dioxide separator or by absorption into amine or adsorption to zeolite. , And the separated carbon dioxide gas is fixed to microalgae using photosynthesis, and the obtained microalgae is crushed and added to a carbonaceous fuel to be recycled as fuel again to a plant such as a thermal power plant. A method for recycling carbon dioxide, characterized by the following. 2. A microalgae-containing carbonaceous fuel obtained by adding a microalgae produced by the recycling method according to claim 1 to the following composition (A) or (B) or a mixture of (C). (A) (a) carbonaceous solid powder such as coal, oil coke, petroleum pitch, (b) at least one dispersant, (c) at least one stabilizer, and (d) water as a main component. (B) Carbonaceous liquid composition such as heavy oil (C) A mixture of the above (A) carbonaceous solid / water slurry composition and the above (B) carbonaceous liquid composition 3. The carbonaceous fuel according to claim 2, wherein the microalgae is a slurry to which a surfactant is added. 4. The carbonaceous fuel according to claim 2, wherein the microalgae is a powder. 5. The carbonaceous fuel according to claim 2, wherein the microalgae are a slurry and a powder to which a surfactant is added.