WO2010124978A1 - Method and system for utilization of gaseous and/or solid components in exhaust gases - Google Patents

Abstract

The invention relates to a method and to a system for utilizing gaseous and/or solid components in exhaust gases, wherein the exhaust gas is added to at least one bioreactor or incoming and/or outcoming lines thereof and microalgae are raised in a nutrient medium in said bioreactor, characterized by one or more of the following controls: - the size of the microalgae is adjusted by controlling the carbon monoxide content in the exhaust gas and/or - the pH-value of the nutrient medium is controlled by dust contained in the exhaust gas and/or by feeding dust previously separated from the exhaust gas.

Description

 Process and plant for the utilization of gaseous and / or solid substances in exhaust gases

The invention relates to a method and plant for the utilization of gaseous and / or solid ingredients in exhaust gases.

It is already known to use photoautotrophic microorganisms, referred to below as microalgae, for the conversion of carbon dioxide into biomass and oxygen. For example, algae, cyanobacteria and mosses are used as microalgae.

For recovery, the waste gas is introduced into a suitable bioreactor filled with a nutrient medium in which the microalgae are grown. The flue gas flows through the reactor so that the gas constituents contained in the exhaust gas (in particular CO ₂ , NO _x , CO) can dissolve in the aqueous nutrient medium and be absorbed by the microalgae. By irradiating the reactor with sunlight and / or artificial light, the CO ₂ in the microalgae is converted into biomass and oxygen by the so-called photosynthesis mechanism.

DE 198 14 253 C2 and EP 1 801 197 A1 disclose methods and devices for producing biomass by means of photosynthesis, which carry out a conditioning of the exhaust gas as a function of the pH. Furthermore, it is known from US Pat. No. 6,083,740 A that NO _x and SO _x constituents of the exhaust gas can serve for nutrient supply of the algae.

Equipment for carrying out these processes is already known as a prototype for coal and natural gas fired power plants. It has also been proposed to use this recovery in exhaust gases of cement production, although this has not been practically tested. However, experience with power plants has shown that microalgae react very sensitively to gas components. The Reaction of the algae to the specific exhaust gas composition of cement plants with "raw material dust", CO ₂ concentrations of significantly more than 10% and very high sulfur and nitrogen oxide concentrations was hitherto completely unknown.

The invention therefore an object of the invention to make the process for the recovery of gaseous and / or solid ingredients in exhaust gases efficient.

According to the invention, this object is solved by the features of claim 1.

In the method according to the invention for the utilization of gaseous and / or solid ingredients in exhaust gases, the exhaust gas is added to at least one bioreactor or its feed and / or discharges, wherein microalgae are grown in a nutrient medium in the bioreactor. One or more of the following regulations are used: The size of the microalgae is adjusted by regulating the CO content in the exhaust gas and / or the pH of the nutrient medium is carried by in the exhaust gas and / or by supplying previously from the exhaust gas settled dust settled.

In the experiments underlying the invention has been shown that the

Biomass production can be increased with each of the two listed measures. But especially advantageous is a combination of both measures.

Furthermore, a plant for carrying out the method described above for the utilization of gaseous and / or solid ingredients in exhaust gases is provided.

It has, in addition to at least one bioreactor, one or more of the following control devices: a control device for adjusting the size of the microalgae by controlling the CO content in the exhaust gas and / or a control device for regulating the pH of the nutrient medium by sensing in the exhaust gas and / or by supplying previously separated from the exhaust dust.

Further embodiments of the invention are the subject of the dependent claims.

It can be also provided that the NO contained in exhaust gas _x and / or SO ₂ as a gas or as a concentrated condensate of nutrients and pH control is added regulated.

The dust sensed in the exhaust gas and / or supplied to the bioreactor preferably contains carbonates of the alkaline earth metals whose mass concentration is preferably 60-90%.

In the experiments underlying the invention has been shown that the

Microalgae react very sensitively to fluctuating CO ₂ concentrations and it is therefore necessary to accustom microalgal strains over several growth cycles to new CO 2 concentrations. According to the invention, therefore, the CO ₂ concentration in the waste gas or in the nutrient medium is adjusted in a time-variable manner to the requirements of the microalgae. This can be done, for example, that too high

CO ₂ concentrations, the exhaust gas is mixed with a low-CO ₂ gas, which can be formed for example by ambient air or other unused exhaust air amounts. If the CO ₂ concentration is too low, the exhaust gas concentration can be increased by technical measures. Obvious in this case would be an enrichment of the combustion air in an upstream system with

Oxygen, so that by a smaller nitrogen load in the resulting exhaust gas, the proportion of CO _{2 is} increased.

Furthermore, it has been found that CO at a pH of less than 6 can lead to an enlargement of the microalgae cells, a so-called gigantism.

The cell enlargement takes place until reaching a maximum size, which at Chlorella vulgaris can be 5 times the normal size, without resulting in a decrease in the biomass structure. In business management, gigantism should always be promoted if the microalgae are to have a limited capacity for cell division with a consistently high metabolic activity. This is especially the case when certain cell contents are to be synthesized or cells with increased sinking ability are to be produced. The pH value can be regulated very well, in particular in the case of exhaust gases of cement production, by the dust entrained in the exhaust gas and / or the supply of dust previously separated from the exhaust gas. For this purpose, it is expedient to carry out a pH measurement in the nutrient medium. The amount of dust carried in the exhaust gas and / or supply of

Dust, especially filter dust, can also be controlled by measuring NO, NO ₂ , SO ₂ and CO ₂ in the exhaust gas. The concentration of these constituents can be influenced by secondary reduction means such as DeNOx catalysts and sulfur scrubbers. The CO ₂ can be regulated by air quenching or by oxygenation of the combustion air.

The NO _x - in particular the NO ₂ - reacts in the nutrient medium with oxygen to form nitric acid (HNO3), of which the nitrate (NO3 ^" ) is used by the microalgae as a nutrient for the build-up of amino acids.To promote growth, the nutrient medium is preferably continuous or cyclical Fertilizers in the form of rapidly soluble in water salts or metered from manure on precipitation liquid phase to metered.

Depending on the ReSt-CO ₂ concentration, the off-gas exiting the reactor can be discharged into the environment via a chimney or can be conducted wholly or partly back into the same or else in the form of a series connection into further reactors in order to maximize CO ₂ slip minimize and maximize yield.

Due to the large amounts of exhaust gas, it will be necessary in industrial applications usually to operate a variety of bioreactors, with both a Batch as well as a continuous operation are conceivable. In principle, several bioreactors can be arranged in parallel and / or in series.

In continuous operation, subsets of the microalgae suspension are continuously withdrawn, the microalgae are separated from the nutrient medium and the

Bioreactor supplied with new or processed nutrient medium, so that the

Microalgae can be kept in a certain growth phase. In order to achieve the highest biomass production, the setting is preferably in the

Area of transition from exponential to stationary growth phase laid.

In addition to the exhaust gas and the temperature of the aqueous nutrient medium must be regulated. In temperate latitudes, it may be necessary to heat the nutrient medium by means of process waste heat in suitable heat exchangers, while in regions with strong solar radiation it may be necessary to mix the nutrient medium with one

Air cooling or a cooling water circuit to keep low temperatures. Preferably, temperatures between 5 ° C and 40 ⁰ C are desired. Operating experiments have shown that even at outside temperatures of -12 ⁰ C temperatures within plate-shaped bioreactors a temperature of more than 5 ⁰ C can be maintained when the nutrient medium in the

Reactors are recirculated once every 120 minutes via a circulation loop and heated to 14 degrees Celsius. This makes a year-round operation possible even in northern latitudes. For the situation of overheating, the experiments showed that it is sufficient for northern latitudes to turn the bioreactors out of direct sunlight into a shadow position.

For an adapted to the solar radiation, automatic radial and horizontal alignment of the reactors, for example, they are mounted on mobile consoles, as it already is state of the art in the field of power generation with solar cells. In order to increase the natural light output in normal operation, the bioreactors are aligned so that the incident solar radiation in the daytime and The year should always be as perpendicular to the reactor surface as possible. In midsummer, however, the reactor can also be consciously moved into a shadow position or partial shade position in order not to overheat the nutrient medium.

Furthermore, operational tests have shown that the growth of the microalgae can be considerably disturbed by too low or too high pH values. In particular, CO ₂ , SO ₂ and N0 / N0 ₂ , which are contained in the exhaust of combustion processes and easily dissolve in the nutrient medium, easily lead to acidification of the medium. Experiments show that microalgae are severely restricted in their growth at a pH of 4, and below a pH of 2, microalgal growth is completely absent.

Therefore, it is appropriate that the pH of the nutrient medium is regulated. For this, e.g. a buffer solution, preferably a bicarbonate buffer, may be used. However, the dosage of such a buffer is costly in view of the large amounts of gas. Experiments have shown that the filter dust, which is typically contained in the exhaust gases of cement clinker plants and consists essentially of carbonate, can also perform a buffering function for the nutrient solution. According to the invention, therefore, the pH is regulated by the metered addition of such dust into the nutrient medium and kept constant in a range which is ideal for the growth of the microalgae. Alternatively, the dust collector can be controlled so that the dust content in the exhaust gas for the desired pH in the nutrient solution is optimal, so that can be dispensed with a new metered addition of the dust.

Since the CO ₂ in dissolved form as carbonic acid lowers the pH of the medium, it makes sense to regulate the amount of CO ₂ , which is passed into the reactor so that there is only a small excess of CO ₂ . The demand for CO ₂ will vary due to different growth phases and above all due to the fluctuating light supply over the course of the day. A regulation is eg based on a measurement of the CO ₂ concentration possible, which is carried out in the exhaust gas of the bioreactors.

In order to improve the CO ₂ balance, the CO ₂ -rich process exhaust gas can be used in periods of low or nonexistent solar radiation (winter, night-time, strong)

Cloud cover) and then sent to the reactors during periods of high solar irradiation. In particular, gas-tight geological rock formations, such as e.g. Saline aquifers or depleted deposits of natural gas. It is particularly attractive to carry out algae breeding on those plants which have a device for concentration,

Liquefaction and storage of the CO ₂ contained in the combustion exhaust gas (oxyfuel process, post-combustion capture). A partial flow of CO ₂ can be introduced into the bioreactor, and the CO ₂ content can be adjusted without restrictions, resulting in an optimal algae growth.

Alternatively or additionally, the flue gas can be optimally conditioned before being introduced into the bioreactors by the following measures for use as a nutrient in bioreactors: the dust content is regulated by a separation efficiency

Dust separator or by the metered addition of previously separated dust specifically adjusted and continuously adjusted to the pH signal from the bioreactors.

At high raw-sulfur emissions, the exhaust gas is previously subjected to a sulfur scrubbing or by a dry-additive method of his

Sulfur cargo freed.

At high crude gas NO concentrations, measures such as multi-stage combustion and or selective catalytic reduction (SCR), or selective non-catalytic reduction (SNCR) of NO are undertaken. As a result, less water-soluble NO ₂ is formed in the exhaust gas. With regard to the CO ₂ content in the exhaust gas, experiments show that microalgae react sensitively to fluctuating CO ₂ concentrations and that it is therefore necessary to accustom microalgal strains to new CO ₂ concentrations over several growth cycles. In order to be able to set an optimal CO ₂ -implement, the following options result:

If the CO ₂ concentrations are too high, the exhaust gas can be mixed with a low C0 ₂ gas. This may be ambient air or other unused exhaust air volumes, such. For example, the cooler exhaust air in the production of cement clinker If the CO ₂ concentrations are too low, the exhaust gas concentration can be increased by technical measures. In this case, it may be particularly expedient to increase the CO ₂ content by supplying oxygen in the combustion process in which the exhaust gas is produced so that more than 20%, preferably more than 30%, and more CO _{2 are} contained in the exhaust gas.

Furthermore, it may be appropriate that the exhaust, air,

Nitrogen, CO or CO _{2 is} mixed to provide an optimal gas composition. This is particularly useful when starting the plant and may be necessary to prepare the algae gradually for the extreme living conditions.

In order to enable the most efficient utilization of the gaseous and / or solid ingredients in the exhaust gases, it has proven to be advantageous if the exhaust gas is introduced separately and controlled in the nutrient medium and not previously mixed with the gases for mixing the nutrient medium. To ensure the fastest possible transition of the gaseous substances in the

To reach flue gas into the nutrient medium, it is advantageous if the exhaust gas is introduced in the form of finest gas bubbles in the nutrient medium. This can be done for example via porous tubes or tubes (pore size 3-20 microns), which are installed directly in the bioreactor. A further advantageous method for introducing the exhaust gas are static mixer in the pipe feeds. The above-indicated utilization method of the exhaust gas can be due to the ho hen CO ₂ content particularly advantageous link with a process for cement production, preheated cement raw material in a preheater, calcined in a calciner, finished a furnace and finally cooled in a cooler. The resulting exhaust gas already has a relatively high dust content of about 20-100 mg per m ³ (after dedusting). The dust composition is also ideal for adjusting the pH of the nutrient medium.

From time to time a harvest or precipitation of the microalgae is required. This is expediently carried out by lowering the pH of the nutrient medium. For this purpose, for example, the NO _x and / or SO ₂ and / or CO ₂ components of the exhaust gas can be used. A further possibility for lowering the pH value consists in the use of the condensate formed during the cooling of the exhaust gas.

Further advantages and embodiments of the invention will be explained in more detail below with reference to the description and the drawing.

Fig. 1 shows a schematic block diagram of a plant for the production of

Cement with an exhaust gas utilization plant with bioreactors connected in parallel and

Fig. 2 shows a schematic block diagram of a plant for the production of cement with a plant for the utilization of the exhaust gases with series-connected bioreactors.

In the embodiment of FIG. 1, a plant 1 for the utilization of gaseous and / or solid ingredients in exhaust gases is combined with a plant 2 for cement production. In the context of the invention, however, the plant 1 can also be preceded by other plants. The plant 2 for cement production consists essentially of a preheater 21 for preheating cement raw material 22, a calciner 23 for calcining the preheated material, a furnace 24 for pre-calcining the precalcined material, and a cooler 25 for cooling the cement clinker.

The exhaust gas 26 of the preheater is fed in a conventional manner to a dedusting device 28, wherein the separated dust 30 passes in a silo 31. Furthermore, a catalyst 27, in particular an SCR catalyst and / or a desulfurization device 29 may be provided.

The exhaust gases 26 are formed essentially by combustion in the calciner and are used for preheating in the preheater 21. The combustion in the calciner can be done with either air or oxygen enriched air. Even combustion with pure oxygen is conceivable. In this case, an air separation plant 32 may be provided. In the illustrated embodiment, the kiln exhaust gases are not passed into the calciner. However, this could also be provided within the scope of the invention.

The exhaust gas 33 produced at the end of the cement production is supplied to the plant 1 for the utilization of gaseous and / or solid substances in exhaust gases.

The plant 1 consists essentially of several parallel-connected bioreactors 10, 11, 12 and heat exchangers 13, 34 and 35. The exhaust gas 33 is optionally cooled in the heat exchanger 35 so far that the flue gas moisture condenses out together with the sour gas components. The condensate is separated and collected for the harvesting process and stored in a condensate tank 36. The harvest of the microalgae takes place in that a batch or continuously a portion of the nutrient medium 40 is discharged from the bioreactor and a means 14 for lowering the pH and a subsequent separator 15 is supplied. The coverage of the pH can be according to the above

Possibilities are made. In the batch process, the bioreactor is traversed with flue gas until a desired cell density has been established in the bioreactor. After that, the exhaust gas is switched off and directed to other, freshly populated reactors. All or parts of the microalgae suspension are withdrawn from the reactor ready for harvest, in order subsequently to separate water and microalgae from one another in the separator. This separation is preferably carried out by sedimentation after addition of a precipitant. In order to minimize the amount of precipitant, the pH of the suspension is lowered in the device 14, for example by adding condensate from the heat exchanger 35 to a pH of less than 6.

This pH decrease (acidification) significantly affects the negative electrical charge on the surface of the microalgae. Since the amount of precipitant decreases together with the surface charge, a lowering of the charge is aimed to 0 mV.

Since the amount of exhaust gas in comparison to the nutrient solution provides only a small heat capacity flow despite high temperatures, but can also be dispensed with a flue gas cooling and the associated condensation. Thus, the investment can be significantly reduced. In return, the algae precipitation is carried out with acid, which increases the operating costs accordingly.

After harvesting, the reactor is filled with new or processed nutrient medium 40. Fresh microorganisms may be used for the inoculation, or a certain proportion of the previous microalgae suspension may be deliberately retained and added to the new formulation.

For operation of the plant in the winter months, the nutrient medium 40 can be heated via the heat exchanger 34. This is done, for example, the radiator waste heat, or the exhaust heat, or other external heat sources. Flue gas side evt. Resulting condensate is fed to the condensate tank 36. The harvested microalgae usually contain a high level of moisture. It makes sense, therefore, the flue gas heat is used to dry the harvested microalgae or the product obtained from them in the heat exchanger 13. If the thermal residual energy contained in the exhaust gas is insufficient for this purpose, the heat of the cooler exhaust gas can additionally or alternatively be used.

In the embodiment according to FIG. 2, in turn, a plant 2 'for cement production is combined with a plant 1' for the utilization of the exhaust gases. For plant 2 'for cement production, optional equipment such as

Catalyst 27 and desulfurization 29 omitted. The system 1 'for the utilization of the gases from differs from the previous exemplary embodiment essentially only in that the bioreactors 10, 11 and 12 are not connected in parallel, but in series. The exhaust gas 33 thus flows first through the heat exchangers 34, 35 and 13 and then the bioreactors below

10, 11 and 12. In this arrangement, the components, and in particular the CO ₂ content of the exhaust gas, change from bioreactor to bioreactor. It is therefore expedient to adapt the microalgae of the series-connected bioreactors to the respective gas composition. Although a correspondingly higher expenditure on equipment is associated with such a series connection, the CO ₂ slip can be reduced to a minimum for this purpose.

Of course, a combination of parallel and series connection are conceivable within the scope of the invention. The number of reactors to be used depends primarily on the amount of exhaust gas produced and the amount of exhaust gas to be processed per reactor.

In the invention underlying experiments has been shown that in the

Dust contained in a plant for cement production dust is excellent for adjusting the pH of the nutrient medium in reactors is suitable. It is therefore in the dedusting 28, the dust content in the desired height to adjust. But it may also be quite appropriate to feed a portion of the separated dust regardless of the exhaust gases to the bioreactors, as can be seen from the drawing.

Claims

claims 1. A process for the utilization of gaseous and / or solid ingredients in exhaust gases, wherein the exhaust gas (33) at least one bioreactor (10, 11, 12) or its feed and / or discharges is added in the microalgae in one The size of the microalgae is adjusted by controlling the CO content in the exhaust gas and / or - the pH of the nutrient medium (40) is carried by in the exhaust gas and / or by supplying previously separated from the exhaust dust (30) regulated. 2. The method of claim 1, wherein the in the exhaust gas (33) contained NO _x and / or SO _{2 is added} as a gas or concentrated as a condensate for nutrient supply and pH control controlled. 3. The method of claim 1, wherein the entrained in the exhaust gas and / or the bioreactor (10, 11, 12) supplied dust contains carbonates of alkaline earth metals, the mass concentration is preferably 60-90%. 4. The method according to claim 1, wherein the CO ₂ concentration in the exhaust gas or in the nutrient medium (40) is adapted to the needs of the microalgae in a time-variable manner. 5. The method of claim 1, wherein the microalgae use the NO _x in the form of nitrate as a nutrient. 6. The method of claim 1, wherein the temperature in the at least one Bioreactor (10, 11, 12) is kept constant. 7. The method of claim 1, wherein in a previous process in addition to the waste gas to be used also waste heat is obtained, which is used to keep the temperature in the at least one bioreactor (10, 11, 12) constant. 8. The method according to claim 1, wherein the pH of the nutrient medium (40) for Harvest / precipitation of microalgae is lowered. 9. The method of claim 8, wherein NO _x and / or SO _{2 are used} to lower the pH for harvesting / precipitation of the microalgae. 10. The method of claim 8, wherein the exhaust gas is cooled prior to introduction into the at least one bioreactor and the resulting condensation water is used to lower the pH. 11. The method of claim 1, wherein as an additional nutrient source for the Nutrient medium (40) is obtained via precipitation from manure liquid phase. 12. The method of claim 1, wherein the exhaust gas flows through a plurality of series-arranged bioreactors (10, 11, 12). 13. The method of claim 1, wherein a plurality of bioreactors (10, 11, 12) are used, which are flowed through in parallel by the exhaust gas. 14. The method of claim 1, wherein the CO ₂ concentration of the exhaust gas is set within predetermined limits. 15. The method of claim 1, wherein the exhaust gas is formed in an upstream combustion process, wherein the CO ₂ -GeImIt is increased in the exhaust gas of the combustion process by supplying oxygen to about 20%. 16. The method of claim 1, wherein the exhaust gas is stored in suitable storage sites and the exhaust gas is subtracted as a function of the CO ₂ demand of the microalgae and fed to the bioreactor. 17. The method of claim 1, wherein the at least one bioreactor (10, 11, 12) is moved and / or aligned depending on the position of the sun. 18. The method according to claim 1, characterized in that via fittings the exhaust gas (33) air, nitrogen, CO or CO ₂ are admixed. 19. The method according to claim 1, characterized in that in the exhaust gas (33) entrained amount of dust and / or the amount of dust supplied, by a pH measurement in the nutrient medium (40) is regulated. 20. The method according to claim 1, characterized in that in the exhaust gas (33) entrained amount of dust and / or the amount of dust supplied, is regulated by a measurement of NO, NO ₂ , SO ₂ and CO ₂ in the exhaust gas. 21. The method according to claim 1, characterized in that the exhaust gas is introduced separately and controlled in the nutrient medium (40). 22. Use of the exhaust gas of a cement production process, wherein the raw material cement (22) preheated in a preheater (21), a calciner (23) calcined, a furnace (24) finished and finally burned in a cooler (25) is cooled in a method according to one or more of the preceding claims. 23. Plant for carrying out the process for the utilization of gaseous and / or solid ingredients in exhaust gases according to one or more of the preceding claims, comprising at least one bioreactor and a control device for adjusting the size of the microalgae by controlling the CO content in the exhaust gas and / or a control device for controlling the pH of the nutrient medium (40) sensed in the exhaust and / or by supplying previously separated from the exhaust dust.