JP2997779B1 - Method for producing gaseous fuel from algae - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To provide a method for producing a gaseous fuel comprising a step of cultivating algae and a step of gasifying the algae having a high water content obtained in the culturing step, the efficiency of by-product water obtained in the gasification step A method for reducing the production cost of gaseous fuel by utilizing it is provided. SOLUTION: The production of gaseous fuel comprising a step of culturing algae and a step of directly gasifying the algae having a high water content obtained in the culturing step at a high temperature and a high pressure in the presence of a hydrogen-activated metal catalyst. A method for producing gaseous fuel from algae, wherein by-product water containing nutrients such as nitrogen compounds obtained in the gasification step is used as a culture solution in the algal culture step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing gaseous fuel from algae, and its field of application is to use the by-product water obtained in a gasification step as a culture solution in an algal culture step in addition to the energy industry. Therefore, it can be used in various fields using algae, such as waste algae treatment and wastewater treatment in the algae utilization industry.

[0002]

2. Description of the Related Art The increase in the concentration of carbon dioxide in the atmosphere due to the large use of fossil fuels and the accompanying problem of global warming have become serious, and biomass, which is a renewable energy, has been attracting attention. Algae are one of the promising biomass resources because of their fast growth rate among biomass. However, since algae are rich in water, conventional thermochemical conversion methods (combustion, pyrolysis, gasification, etc.) using dried raw materials require a large amount of latent heat of vaporization for drying,
There is a problem in terms of energy balance. Also, since algae require a larger amount of nutrients than higher plants, there is a problem of supply of nutrients, that is, a problem of energy consumption during culture. The conversion of algae to energy by methane fermentation is also being studied, but the biochemical conversion method has a problem that the reaction rate is slow, and further, there is a problem of recovering nutrients.

JP-A-5-213778, JP-A-8-5
Issue 9202, United States Pattern
At t5,019,135, the cellulosic biomass was treated with a hydrogen-activated metal catalyst in the presence of an aqueous medium.
A method for gasification by holding at high temperature and high pressure is shown. Such a high-pressure process without water evaporation is preferable from the viewpoint of energy balance because latent heat of water evaporation is unnecessary, and is a method suitable for biomass containing a large amount of water, that is, algae. Further, according to this method, as shown in JP-T 8-501115,
Nitrogen in the raw material is converted to ammonia and dissolved in by-product water. That is, nitrogen, which is one of the nutrients, can be recovered in the form of ammonia. Nevertheless, the by-product water contains organic substances and trace metals, and it is unclear whether algae can grow in the by-product water. As will be described in detail in Examples of the present invention described later, the present inventors have found that algae can be subjected to gasification under high temperature and pressure, and further, by using by-product water containing ammonia obtained by this gasification. It was found that direct cultivation was possible without killing algae. It has also been found that nutrients such as potassium can be recovered in addition to ammonia.

[0004]

Accordingly, the present invention relates to a method for producing gaseous fuel comprising a step of culturing algae and a step of gasifying algae having a high water content obtained in the culturing step. An object of the present invention is to provide a method for reducing the production cost of gaseous fuel by effectively utilizing by-product water obtained in the process.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, the step of culturing algae and the step of culturing the algae having a high water content obtained in the culturing step with hydrogen activity
Metal catalyst (hereinafter also referred to as hydrogen-activated metal catalyst)
At a reaction temperature of 300 to 450 ° C and a reaction pressure in the presence of
A gaseous fuel production method comprising the step of directly gasifying while maintaining the saturated vapor pressure of water at a reaction temperature or higher, wherein the by-product water containing nutrients such as nitrogen compounds obtained in the gasification step is subjected to the algal culture step. A method for producing a gaseous fuel from algae, wherein the method is used as a culture solution in the above.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The algae referred to in the present specification are aqueous plants in general, and include microalgae (chlorella, spirulina, donaliella, botuliococcus, etc.) and macroalgae (kelp, water hyacinth, etc.). Is done. By-product water as used herein refers to liquid components separated from the gasification products of algae. As used herein, gaseous fuel refers to gaseous components separated from gasification products of algae and combustible components (H ₂ , CH _4, etc.) separated from the gaseous components.

The gasification step in the present invention is a step in which algae are reacted at a high temperature and a high pressure in the presence of a hydrogen activating catalyst. In this case, the algae recovered from the culturing step can be used directly, but usually have a water content of 98% by weight or more, so that 90% by weight is dehydrated from the viewpoint of treatment efficiency and energy balance. It is preferable to adjust the water content to the following. Moreover, since it will become solid if dehydrated too much, a water content of 70% by weight or more is preferable from the viewpoint of handling. That is, in the present invention, 70 to 90% by weight,
Algae having a high water content of preferably 75 to 85% by weight are used as a raw material for gasification. Examples of the hydrogen activating catalyst include ordinary industrial nickel, cobalt, iron, platinum, ruthenium,
Various metal catalysts for hydrogen activation such as rhodium can be used. The gasification reaction temperature is 300 to 450 ° C., and the reaction pressure is equal to or higher than the saturated vapor pressure at the reaction temperature in order to suppress evaporation of water. Since water becomes a supercritical fluid at a reaction temperature of 374 ° C. or higher, a reaction pressure of 226 atm or more is adopted as the reaction pressure in this case. The reaction time depends on the reaction temperature, the water content of the algae (organic matter concentration), the treatment amount (ratio to the amount of the hydrogen activation catalyst), and the like, but from the viewpoint of apparatus design and control, it is in the range of 5 to 180 minutes. Is preferred.

[0008] By-product water obtained from the gasification step contains nitrogen and potassium among nitrogen, phosphorus and potassium, which are the three major nutrients of plants. In the present invention, the by-product water is directly, indirectly or diluted and used as a culture solution of algae. The dilution in this case depends on the ammonia concentration in the by-product water, which depends on the algal concentration during the gasification step. For example, when algae obtained by culturing are concentrated 100 times and gasified, it is preferable to dilute by-product water 100 times. Generally, in order to use as a culture solution, the ammonia concentration in the by-product water is 5 to 200 mg / l,
The dilution is preferably made to be 10 to 100 mg / l. As the dilution water, water returned in the algal concentration step can be used. In addition, since phosphorus and trace metals are insufficient, replenish as necessary. The replenishment amount varies depending on the type of algae, and it is preferable to set the optimum N / P ratio.

In the present invention, as described above, by-product water is effectively used as an algal culture solution, so that the production cost of gaseous fuel from algae can be significantly reduced. In the present invention, since a gasification product of high temperature and high pressure is obtained in the gasification step, the gas from algae is effectively used by effectively utilizing the high temperature calorie and the high gas pressure of the gasification product. Fuel production costs can be significantly reduced. For example, a high-pressure gas pressure (expansion energy) held by a gasification product can be converted to electricity through a gas turbine, and the gas pressure is converted to mechanical energy such as stirring energy of a culture solution. be able to. Further, the high-temperature calorie held by the gasification product can be used as a heat source or the like in the culturing step. The hydrogen gas in the gasification product obtained in the present invention can be used as a fuel for a fuel cell. Also, carbon dioxide in the gasification product is dissolved in water and circulated to the cultivation process,
It can be used as nutrients for algae.

Next, an example of an embodiment of the present invention will be specifically described with reference to the drawings. FIG. 1 shows an example of a flow sheet for implementing the present invention. In FIG. 1, reference numeral 1 denotes an algae culture apparatus, in which algae are cultured. The cultured algae are supplied to the algae concentration device 2 through the line 8.
In the case of large algae, crush as necessary. The return water at the time of concentration is returned to the algal culture apparatus 1 via the line 9. The raw material whose concentration is adjusted to a water content of 70 to 90% by weight is sent to a press-in pump 3 through a line 10, where it is pressurized and sent to a gasification reactor 4 through a line 11. Heating of the gasification reactor 4 is performed by a heating medium, and the heating medium
2 is supplied. Further, the heat medium recovered via the line 13 can be used for preheating the gasification reactor 4. The cooled heat carrier is recovered via line 14.
The collected heat medium can be used for keeping the algae culture device 1 warm. The inside of the gasification reaction device 4 is packed with a catalyst, and is gasified by a catalytic action. The gasification product gasified by the gasification reactor 4 is withdrawn via the line 15 and sent to the cooler 5. The cooler 5 is cooled by supplying a heating medium or cooling water from a line 16, and the recovered heating medium or cooling water is recovered via a line 17. The recovered heat medium or hot water is supplied to the gasification
Available for preheating. The cooled gasification product is sent to the pressure reducing valve 6 through the line 18 and the pressure is reduced to the atmospheric pressure. The decompressed gasification product is sent to the gas-liquid separator 7 through the line 19. In this case, the culture liquid can be stirred by transmitting the energy of expansion of the high-pressure gas (gasification product) to the algae culture apparatus 1. In the gas-liquid separation device 7, the gas product and the by-product water are separated, the gas product is recovered through the line 20, and the by-product water is returned to the algae culture device 1 (line 21). Gaseous products are used as gaseous fuels or chemical raw materials. In the algal culture, the nutrients deficient are supplied through line 22.

In this process, an apparatus having a gas-liquid separation function in a gasification reaction apparatus as disclosed in Japanese Patent Application Laid-Open No. 9-241001 can be adopted. In this case, it is expected that gasification efficiency is improved and hydrogen can be selectively produced. In addition, a high-pressure gas-liquid separation device may be employed between the cooler 5 and the pressure reducing valve 6. In this case, high-concentration hydrogen and methane can be recovered from the difference in gas solubility, and at the same time, carbon dioxide can be recovered. It is expected that by-product water with a high concentration of dissolved carbon can be obtained and used for algae culture. Further, as shown in JP-A-9-255303, solar heat can be used for all or a part of the heat required for the process. In any case, the flow sheet of FIG. 1 is an example of an embodiment of the present invention, and the present invention is not limited to this.

[0012]

The present invention has the above-mentioned structure, and can directly produce gaseous fuel from algae having a high water content without drying. In this case, drying of algae is not required, so that energy efficiency is increased. Furthermore, nutrients such as nitrogen and potassium as ammonia can be recovered in the by-product water, and the by-product water can be directly used as a culture solution of algae. By these effects, practical use of energy production from algae can be achieved. In addition, in industries that currently use algae,
By treating the residue after taking out useful substances by this method, energy and nutrient recovery can be simultaneously performed.

[0013]

Next, the present invention will be described in more detail with reference to examples.

Example 1 Raw chlorella commercially available as algae (water content 87% by weight) was used as a hydrogen-activating metal catalyst, and a commercially available industrial nickel catalyst (reduced with hydrogen before use) was used. 33 ml of raw chlorella and 15 g of nickel catalyst are charged into a batch-type pressurized reaction vessel, pressurized to 30 atm with nitrogen gas in advance to suppress water evaporation, and then heated in an electric furnace at about 10 ° C./min. Heated at a rate to 350 ° C. and held at this temperature for 15 minutes. In this case, the reaction pressure was kept above the saturated vapor pressure of water. After cooling, the product gas was collected and analyzed by gas chromatography. Further, the by-product water and the catalyst were separated and collected by filtration. The generated gas (excluding the pre-pressurized nitrogen gas) was a gas containing hydrogen, methane and carbon dioxide as main components, and produced about 3.7 g. The gasification rate on a carbon basis is 70
% Has been reached. The gas composition was 10% by volume of hydrogen, 38% by volume of methane, 49% by volume of carbon dioxide, and 4% by volume of a hydrocarbon gas having 2 or more carbon atoms. By-product water is colorless and transparent, pH 7,
Organic carbon (TOC) 258 ppm, inorganic carbon 6288p
pm, ammonia 8700 ppm, K1050 ppm,
The content of Na was 990 ppm, and the TOC removal rate was 99% or more. In addition, tar and char-like products were slightly precipitated on the recovered catalyst. 300 by-product water
The mixture was diluted by a factor of 2 (corresponding to an algal concentration of 0.5 g / L), chlorella was added, and the cells were cultured at 25 ° C. at a luminous intensity of about 50 μE / sec / square meter for 2 weeks. When the algal concentration was measured with a spectrophotometer (660 nm), it grew about 30 times in 2 weeks. The growth of those cultured in distilled water as a control doubled in one week and then stopped growing. From this result, it can be seen that algae can be cultured using by-product water.

[Brief description of the drawings]

FIG. 1 is an example of a flow sheet for a preferred embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Algae cultivation apparatus 2 Concentration apparatus 3 Injection pump 4 Gasification reaction apparatus 5 Cooler 6 Pressure reducing valve 7 Gas-liquid separation apparatus

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Claims (5)

(57) [Claims] The present invention relates to a step of culturing algae and the step of culturing the algae having a high water content obtained in the culturing step in the presence of a metal catalyst for hydrogen activation at a reaction temperature of 300 to 450 ° C and a reaction pressure of reaction temperature.
A gaseous fuel production method comprising the step of directly gasifying while maintaining the saturated vapor pressure of water or higher, wherein the by-product water containing nutrients such as nitrogen compounds obtained in the gasification step is cultured in the algal culture step. A method for producing gaseous fuel from algae, which is used as a liquid. 2. The method according to claim 1, wherein a part of the energy of the gaseous fuel obtained in the gasification step is converted into electricity and / or heat. 3. The method according to claim 1, wherein part of the expansion energy of the high-pressure gas obtained in the gasification step is used as stirring energy in the algal culture step. 4. The method according to claim 1, wherein a part of the heat energy of the high-temperature gas obtained in the gasification step is used as a heat source in the algal culture step. 5. The method according to claim 1, wherein carbon dioxide obtained as a by-product gas in the gasification step is used as a nutrient in the algal culture step.