JPS6222958B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing fertilizer. More specifically, a sulfur oxide-containing gas and water are reacted in a multistage reactor to form a sulfur-containing acid, and the sulfur-containing acid is reacted with a calcium salt that can be solubilized by an acid monobase reaction to form a phosphate fertilizer. Relating to a manufacturing method. Here the calcium is selected from phosphates. The combination of sulfur oxide absorption and basic salt solubilization is carried out at a solution pH of 2.5-5. To further increase the absorption of sulfur oxide,
Use a solution with a pH of 3-8. The method is suitable for utilizing sulfur oxides resulting from the combustion of high sulfur containing fossil fuels and sulfur producing chemical processes.
The method of the present invention can be used to solubilize phosphate rock that has been thermally pretreated with low concentration sulfuric acid using a multistage reactor. To solubilize untreated phosphate rock, it is preferable to oxidize sulfur dioxide to sulfur trioxide and convert it to sulfuric acid, whereas solubilization of phosphate rock that has been thermally pretreated and defluorinated requires This can also be achieved with sulfurous acid produced from sulfur dioxide, thus eliminating the need for oxidation. Low grade phosphate rock is suitable for use in the method of the invention. Phosphate fertilizers have become extremely important in agricultural economies around the world in recent years. The main phosphate source for such fertilizers is natural phosphate rock. However, in its natural form, phosphate is almost insoluble in water. Various acidification methods using sulfuric, phosphoric or nitric acids have been used to utilize phosphate from natural phosphate rock sources. Phosphoric acid is produced by the action of natural phosphate with hydrochloric or nitric acid, but the soluble nature of the salt in the product makes separation of phosphoric acid commercially impractical; The method was not satisfactory. When natural phosphate rock is treated with sulfuric acid, the products are phosphoric acid and gypsum (hydrated calcium sulfate) and other sulfates.
Because sulfate is insoluble, it can be easily separated from phosphoric acid. In conventional fertilizer production methods, sulfuric acid is used in the production of phosphoric acid by a known "wet method". Superphosphate lime is obtained by treating finely ground phosphate rock with sulfuric acid and has an effective content of about 16 to 20%.
A term commonly used for products containing P ₂ O ₅ . In the production of superphosphate lime, a source of concentrated sulfuric acid and a source of high grade phosphate rock must be available. The reaction depends on good liquid-solid reactant mixing. Low grade phosphate rock containing a high proportion of impurities has not been favorable for conventional phosphoric acid or other phosphate fertilizer manufacturing processes.
Many of the impurities contained in natural phosphate rock react with sulfuric acid, resulting in excessive consumption of sulfuric acid. Furthermore,
Due to the slow reaction rate in the two-phase liquid-solid reaction system in phosphoric acid production, curing or tempering for several days is required.
A period of tempering (i.e., ripening) is necessary. In the production of non-granular phosphate fertilizers, in order to complete the reaction to reduce free sulfuric acid to a minimum amount,
A long curing process of several months is required. In the production of granular phosphate fertilizers using phosphate rock, proper liquid-solid reactant mixture levels are important to minimize bag breakage or other corrosive effects due to excess free acid. The hardness of fertilizer granules depends on the avoidance of unreacted sulfuric acid. Triple superphosphate lime, which provides a highly concentrated phosphate _fertilizer containing 44-46 percent _P2O5 , was produced by decomposing phosphate rock with phosphoric acid.
In this case, citric acid-soluble phosphates can only be obtained using expensive phosphoric acid. The aim of the present invention is to overcome many of the drawbacks of conventional methods for the production of phosphate-based fertilizers. Another object of the invention is to provide a method for producing fertilizer from a relatively low grade natural phosphate rock source. Another object of the present invention is to provide a method for producing fertilizers that utilizes calcium present in natural rock phosphate sources. Yet another object of the invention is to provide a method for producing fertilizers which can be in either solid, liquid or suspension form. It is also an object of the present invention to provide a reaction of thermally pretreated defluorinated phosphate rock with sulfite or sulfuric acid. Another object of the present invention is to provide a method for producing fertilizers that utilizes sulfur-containing dilute acids made from sulfur oxides obtained by combustion of sulfur-containing natural fuels. Another object of the present invention is to provide a method for producing fertilizers that utilizes sulfur-containing acids obtained as a by-product of a sulfur-producing process, such as a wood pulp digester. Furthermore, it is an object of the present invention to provide a method for producing fertilizers in which there is an inexpensive source of sulfur oxide and in geographical proximity to the users of the fertilizers. These and other objects will become readily apparent from the detailed description and reference to the drawings showing preferred embodiments. In the present invention, sulfur oxide is obtained from the combustion of sulfur-containing fossil fuels such as coal or heavy oil in conventional boilers, or as flue gas from any industrial plant such as chemical, oil refining, fertilizer, steel or coke industry. Uses sulfur oxide.
Although the preferred embodiment describes sulfur oxide obtained from the combustion of coal, it will be appreciated that the sulfur oxide may be provided from any other suitable source. It is readily apparent that the process of the present invention allows the use of high sulfur content coals, and sulfur contents greater than about 2% are preferred. Nowadays, there is a large amount of coal that is unutilized due to excessive sulfur content. There is an increasing demand for energy sources other than desulfurized oil or gas. Satisfactory utilization of high sulfur content coal and petroleum would most effectively alleviate such demands and allow use of current combustion equipment with slight modification. Techniques for removing polluting sulfur oxides from such flue gases have heretofore proven to be very expensive and unsatisfactory. The present invention provides a method of encouraging the combustion of high sulfur containing fuels which is often significantly more economical to boiler operators due to their high calorific value and low transportation costs. The present invention also provides a method of combustion of high sulfur fuels that utilizes the sulfur oxide produced by the combustion of high sulfur fuels so that the final flue gas is as safe as permitted by appropriate regulations in terms of sulfur oxide content. amount. In fact, it is usually less than the permissible amount of sulfur oxide. Electric utilities and other companies that rely on sulfur-containing coal and oil boilers can utilize the present method of producing fertilizer as a by-product of the combustion of high-sulfur-containing coal or oil and provide other agricultural growers with benefits. It is possible to supply a variety of varieties of fertilizer material that are just suitable for different cultivation practices, thereby reducing the high transportation costs currently common in the fertilizer industry. Some companies have been forced to convert to coal to preserve oil and gaseous fuels. By using the method of the invention, it is possible to use locally sourced fuels and often also to reduce high transportation costs. The investment in equipment used in the present invention provides both a means for removing SOx from the flue effluent and a means for producing fertilizer. This is very important as fertilizer companies are constantly trying to balance fertilizer supply facilities to meet demand. Passing the flue gas containing sulfur oxide and flyash discharged from a conventional coal-fired boiler at about 380-450㎓ (about 193-232℃) through a device for separating the flyash and solids from the gas stream. I can do it. The flyash separator can be a single stage heterogeneous reactor as described in more detail later in the specification. If the practice is to mix phosphate rock with coal before combustion in the boiler, it may be undesirable to use a flyash separator. In one embodiment of the method of the invention, which will be described in detail, SO ₂ from flue gas is converted to sulfite and can be used to solubilize pretreated defluorinated phosphate ore. In another embodiment of the method of the invention using untreated phosphate rock, SO ₂ from the incoming gas stream is oxidized and hydrated to form sulfate ions and are in equilibrium with the solution.
It is desirable to minimize the amount of _SO2 . Maximizing SO ₂ oxidation reduces the possibility of SO ₂ escaping to the atmosphere. Acid or salt solutions _{of H2SO3} with _SO3 ⁼ groups tend to decompose to form _SO2 . Therefore, it is desirable to oxidize the sulfur oxide as completely as possible to form a sulfate that does not decompose. This oxidation can be carried out in various ways, for example by using an oxidation catalyst in direct contact with the flue gas, especially if solids have been removed;
Alternatively, the oxidation is carried out in a separate air-solution absorber using countercurrent air; or in a heterogeneous reactor cocurrent absorber as cited elsewhere in this specification. or it may be carried out in any absorption apparatus in which air is brought into contact with the liquid produced by the absorption of sulfur oxide gas; and oxidizing salts may be added to the above solution to increase the production of sulfuric acid rather than sulfurous acid or sulfurous acid. can be done. The hot gases are sent to a direct contact cooler-absorber reactor where some of the sulfur oxides are absorbed by direct contact of the gases into a cooling fluid that is injected with water or water to accelerate the absorption reaction. by adding chemicals to
It can be water with increased PH. The solution remaining after evaporation of the water resulting from the cooling of the gas can be sent to a settling tank, from where the supernatant liquid can be recycled to the cooler-absorber reactor. Direct contact of the sulfur oxide-containing gas stream with the supernatant liquid evaporates some of the liquid phase, resulting in cooling of the gas stream. Evaporative cooling is performed to approximately the point where the gas is saturated with evaporation, and the gas stream is then sent to the reaction-absorption column in cocurrent or countercurrent flow with respect to the absorbent liquid. The function of the reaction-absorber is to dissolve any sulfur oxide and possibly nitrogen oxide that has not reacted in the contact cooler-absorber. In this reactor-absorber, chemical solutions with high PH values are used. The gas from which the acid anhydride has been removed is then passed through a demister and blower and is exhausted to the atmosphere through the chimney. In some installations, reheating may be installed to raise the temperature above the exhaust gas saturation point prior to evacuation. One of the chemicals utilized to accomplish sulfur oxide removal is calcium found within phosphate rock. The calcium present in the original phosphate rock is not water soluble, so it must be reacted with an acid to make it water soluble. In the present method, sulfuric acid and sulfurous acid produced from sulfur oxide contained in the flue gas are treated with phosphoric acid or various phosphate acids, nitric acid or various acids in order to increase the reactivity of the acid solution toward phosphate rock. It can be used in combination with basic acids to leach phosphate rock and solubilize calcium ions. The chemical reaction between the acid and the ground phosphate rock can be carried out in a suitable heterogeneous reactor. Rock phosphate can be used in unground form and the reaction of acid and rock rock can be carried out in a ball mill. The function of the ball mill is to accelerate the reaction by mechanically breaking up any coating of calcium salts of the phosphate. When mixtures of phosphoric acids or nitrous acids are used in combination with sulfuric acid and sulfurous acid, it is desirable to use mechanical milling when introducing uncrushed phosphate rock into the process. Another method of reacting unground rock phosphate with acid is to dry-mill the rock phosphate-clinker mixture before adding it to the column. Acidification can also be carried out by contacting pre-ground rock phosphate with a mixture of acids. Powdered or ground phosphate rock can be introduced into the swirling phosphoric acid in the cone and reacted before being introduced into the reaction column. If granulation is not desired, the slurry from the acidified cone is sent to curing and cutting moving slats and belt conveyors to form a powdered or unsorted (ROR) product. Another alternative method is to send the acidified phosphate rock to a granulation system. Nitric acid can also be used if desired. Regarding solubilization, the same considerations apply regardless of how the slurry is formed. Ground phosphate rock can also be added to the top of the heterogeneous reactor. Phosphate is at least 90
It is necessary to grind to a commercial grinding degree of 100% mesh or higher. Phosphate rocks suitable for use in the present invention include approximately 50
has a low BPL. Those with a BPL of about 55 to 65 are particularly suitable for use in the present invention. BPL
66 and below are considered to be low grade phosphate rocks, which are not suitable for currently used fertilizer production methods, but are suitable for the method of the present invention.
The low cost of low grade phosphate rock makes the process of the invention very economically attractive.
Phosphate rocks with a BPL of 66 or higher are also suitable for use in the method of the invention. If, by any of the above methods, the calcium in the phosphate rock is made available for neutralization of the sulfur oxide by acid attack, then all the calcium required for the process can be obtained instead of supplying high calcium from an external source. can be supplied in such a way. If more basic ions are needed to remove the acidic ions formed by hydration of sulfur oxides, ammonia can be added to the system or other basic inexpensive plant nutrients can be used. As an example, potassium carbonate is another basic or buffer ion if economically permitted. The slurry obtained by solubilization of rock phosphate contains calcium ions, sulfate ions, sulfite ions, phosphate ions and possibly nitrate ions, other ions introduced from the desired acid, and from the phosphate rock by solubilization. Consists of released ions. Anhydrous ammonia can be added to the slurry to neutralize the acidity of the slurry to an extent that does not cause operational or storage problems.
For example, granules with very high free acid content tend to become soft after drying. When packed in bags, excess acid damages the bags, causing a phenomenon called "bag breakage." When granules containing excess acid are handled and stored in bulk, drying causes the formation of a solution on their surface, which causes the granules to bind and harden. The favorable economics of this neutralization step are due to the fact that nitrogen, which is present in fixed or solid form, has a higher sales value than the original gaseous ammonia. The production of diammonium phosphate using defluorinated phosphate rock by thermal pretreatment provides an excellent buffering agent and provides a solution that maintains a low SO ₂ vapor pressure at equilibrium. The ash retained in the slurry contains minerals originally derived from plants and later petrified to form coal. These chemicals have dual value. They are also slightly basic, as evidenced by the past production of soap by straining these chemicals from the ashes and saponifying the fats. However, the most important contribution is that these minerals, which contributed to the robustness of prehistoric plants, can perform the same effect on modern crops.
That's what it means. These are commonly used in industry as trace nutrients or micro-nutrients.
nutrients). This also gives added value to fertilizer products. The most important economic contribution is that it allows boiler operators to dispose of flyash in an economical manner by returning it to the soil in fertilized form. Otherwise, operators would have to pay for ash disposal in addition to reducing pollution. The present invention uses calcium derived from phosphate rock to react with sulfur acid, which is very economically available. It was previously thought to be impractical to solubilize apatite with the very dilute sulfuric and sulfuric acids made available in conventional scrubbing methods. The use of strong phosphoric acid is advantageous because when it is added to the weak acid of sulfur oxide, the mixture heats up and increases its ability to attack phosphate rock, making calcium ions available. discovered. The use of weak sulfur acids derived from flue gas to dilute strong acids increases the production of fertilizer phosphates compared to the use of strong acids alone. Conventional practice has been to add concentrated sulfuric acid to phosphate rock to produce monocompositional lime superphosphate. The acidified product produced is approximately 20% P ₂ O ₅ when aged and dried.
was analyzed to contain. When a mixture of concentrated phosphoric acid and phosphate rock in a suitable stoichiometric ratio was aged and dried, the analysis result was 46% P ₂ O ₅ . In a third commercial process, one of which is called the Prayon Process, phosphoric acid is produced using appropriate stoichiometric amounts of sulfuric acid and phosphate rock. A sufficient amount of sulfuric acid is used to precipitate all the calcium in the apatite as sulfate and to precipitate other insoluble salts coming from the apatite. The slurry is then sent to a moving pan filter and the liquid is solidified and separated, but the solids are _white or transparent by burning the phosphorus and hydrating the resulting _P2O5 gas in water. It is called black phosphoric acid in contrast to Furness grade phosphoric acid, which is produced by producing phosphoric acid. The production of black phosphoric acid is becoming increasingly difficult due to the decreasing quality of available phosphate rock. The method of the invention avoids this costly separation. The method of the present invention allows the use of lower grades of phosphate rock than existing fertilizer production methods. The present method can use low grade phosphate rock. This is because the sulfate (calcium) does not need to be separated from the acid produced and the amount of phosphoric acid or expensive sulfuric acid required to feed the process is reduced. In a preferred embodiment of the process of the present invention, commercial embodiments of the process obtain 25% of the _P2O5 in the phosphate fertilizer from phosphoric acid and 75% of the _P2O5 in the phosphate fertilizer.
can be obtained from phosphate rock. The amount of phosphate rock used is that amount necessary to provide calcium to neutralize all of the sulfur oxide available from stack gas or other inexpensive sources of sulfur oxide. Therefore, when the resulting slurry is reacted with ammonia, the benefit is that the ammonia is fixed due to the removal of calcium ions from the phosphate. The phosphoric acid used to assist in acidification can then be used to react with ammonia in the same manner as diammonium phosphate was made. The method illustrated schematically in Figure 1 uses untreated phosphate rock. FIG. 1 begins with a single stage dry particulate removal system to separate the flyash. This is optional. Also, if the crushed phosphate rock fluidized by excess air is introduced into the evaporative cooler, it will be introduced into the drying separator and then into the cooling tower as shown. In the cooling tower, the sulfur oxides contained in the flue gas are absorbed by the solution droplets released from the cooling spray, and the acidified droplets react in turn with the fine particles of phosphate rock. This solubilization of the phosphate rock removes calcium from the rock, leaving behind a phosphate slurry and calcium salts of various sulfur oxides.
The cooling tower can be replaced by any effective heterogeneous reactor, such as the one-stage heterogeneous reactor shown in FIG. 1, without the use of impingement plates. Slurry from the cooling tower enters a settling tank. In the settling tank, the solids fall to the bottom and the clear liquid is sucked out the top and recycled to the cooling tower, so that any calcium ions in the solution are further combined with hydrated sulfur oxides. can react. If the degree of sulfur oxidation is not sufficient to absorb more than about 25% of the sulfur oxide in the cooling tower stage, add commercially available strong phosphoric acid to the settling tank as shown in the figure. Acidification of the ore must be promoted. The gas, from which some of the sulfur oxide has been removed and now saturated with its vapor, is sent to a heterogeneous reactor. These gases also contain particles of ground phosphate rock that have not agglomerated or reacted in the cooling tower. Further ground phosphate rock can also be air fluidized and added to these gases. This mixture enters the top of a heterogeneous reactor, which is fed with a solution containing basic ions to react with and remove residual sulfur oxides. Furthermore, any particles of solid ground phosphate rock transported or added will be agglomerated and sent to the settling tank along with the solution. If the concentration of sulfuric acid is not sufficient to solubilize the phosphate rock to a sufficiently high degree, then commercially available strong phosphoric acid will again have to be added to the settling tank. Although the present invention begins with a dilute sulfur-containing gas stream to produce dilute sulfur acid containing less than 60% sulfur acid by weight, such a process has not, to the best of the inventors' knowledge, been previously used commercially. Ta. The solids are allowed to settle to the bottom again and the clear supernatant liquid is recycled to the heterogeneous reactor. The gas, free of sulfur oxides, flyash, and phosphate particles, is drawn by a blower into a demister and vented out the chimney. Some boiler plant operators may require a reheater (not shown) to raise the temperature of the exhaust gas above the dew point. The PH in the heterogeneous reactor is controlled by dissolved calcium from phosphate rock, but can be further controlled by the addition of anhydrous ammonia, potassium carbonate or other economical basic phytonutrients. The pH to be adopted depends on the degree of sulfur oxidation, the pH in the settling tank,
Depending on the supplemented acid and the sulfur content of the coal, the PH can range from 3 to 8. To further increase the efficiency of sulfur oxide collection, some solution from the settling tank can be regulated with valve _VI back into the settling tank to increase the PH in the settling tank or vice versa. The sedimentation tank is high.
If the pH is maintained, it may be possible to maintain the pH in the tank within the range of 2.5 to 5, but the degree of oxidation of sulfur, the pH in the settling tank, the use of supplementary acid, and the coal Depends on sulfur content. the sulfur content in the coal, the permissible amount of SO ₂ loss, the degree of sulfur oxidation or the degree of thermal pretreatment and defluoridation of the phosphate rock, and the supplementary acid, if certain conditions exist, the operation and the selection of construction materials. To simplify the process, the PH in both baths can be kept the same.
In order to control the reaction of the PH and phosphate rock between the settling vessels, both vessels are connected in such a manner that solid or liquid flow occurs between them. When thermally pretreated, defluorinated phosphate rock is used with the oxidation of SO ₂ to SO ₃ as described in more detail below, a high PH solution from the settling tank is added to the settling tank and cooled. The PH of the spray solution in the column can be adjusted. When thermally pretreated, defluorinated phosphate rock is used to absorb sulfur oxides such as those present in boiler exhaust, ammonia is added to control the PH in heterogeneous reactors and cooling towers. For this purpose, the settling tank may be separated to provide another reaction column. The bottoms are removed from both the settling tank and the combined solid-liquid slurry and, depending on the proportion of solids in the liquid, are conveyed to a pre-neutralizer or a granulator, or are divided between the two tanks. The more liquid there is, the more liquid will enter the pre-neutralizer. This is regulated by valve _V2 .
Again, if it is desired to further solubilize the phosphate rock, strong phosphoric acid and, if desired from a blending and evaporation point of view, strong nitric acid can be added to the pre-neutralization device as shown in FIG. solubilization and evaporation. Subsequent solubilization will occur within the granulator. The drying process can then be completed in a dryer if desired. When anhydrous ammonia is further added to the pre-neutralization device together with phosphoric acid, the reaction heat causes the liquid to vaporize and escape. If there is a large amount of solids compared to liquids in the solid-liquid slurry from the settling tank, the slurry is conveyed directly to the granulator where it is treated with anhydrous ammonia without the need for special vaporization in a pre-neutralizer. Reactions will occur with other acids. When it is desired to obtain N-P-K or granulated complete fertilizer, caustic potash is added to the granulator in an amount necessary to obtain the desired analytical results.
In accordance with standard industrial fertilizer manufacturing practices, the material stream flowing from the granulator to the dryer and cooler is sized and oversized particles are added according to the amount of recirculation required for the sized product. , granulated, mixed with "fine" or undersized particles and recycled to the granulator. Here again, if the amount of liquid is not large, the amount of recirculation may be reduced and the sized product may not be ground. The process can be operated to produce a liquid fertilizer product base by adjusting valve _V3 to remove some of the recirculating liquid from the system as shown in FIG. To this is added white caustic potash, uncoated ammonium nitrate, or other water-soluble plant nutrients in a stirred tank (not shown).
It can be formulated into the desired variety according to standard commercial practices. If thermally pretreated, defluorinated phosphate rock is used, it is highly reactive so that if desired a large part of the flow can be taken off as liquid fertilizer. In this case, both capital and operating costs can be reduced, since the pre-neutralization equipment, granulation plant and associated equipment would be eliminated. The suspension fertilizer base is prepared by adding plant nutrients and the necessary agents to stabilize the suspension in a stirred tank (not shown), which can be obtained by appropriate adjustment of valve V ₆ . It can be added with. Some very fine silicic acid-containing substances from the fly ash and solubilized apatite add to this suspension a stabilizing phenomenon. As can be seen from FIG. 1, the method of the invention makes it possible to produce liquid, suspension and solid fertilizers according to the desired end product. The heterogeneous reactor used in the method of the present invention is
It may be any suitable device for rapid chemical reaction of the reactants in the heterogeneous gas-liquid- and/or solid state, such as turbulent bed packed absorbers and blockage prevention devices known in the art. Another reactor designed to One particularly suitable device is US Pat. No. 677,750, Heterogeneous Reactor and Process, LJPircon, (April 1976).
(filed on May 16th) for more details. The heterogeneous reactor is shown in FIG. 1 with an external casing. External casing 1
The cross-sectional shape of 0 is preferably cylindrical, but may also be square, rectangular, triangular, hexagonal or other symmetrical polygonal shape, and other geometric shapes symmetrical about the axis of the device. That's fine.
The primary need for the casing is that the casing generally encapsulates the device in a liquid and gaseous relationship and provides controlled flow of gas into the interior. In order to give maximum flexibility in the use and maintenance of the heterogeneous reactor, a section with flanges indicated at 11 and 13 at each end and an adjacent section having similar flanges 12 and 14 connected thereto. The casing 10 can be manufactured in each section having a casing section. In place of the flange shown in FIG. 1, any suitable coupling means may be employed. These parts can be welded prior to shipping and construction to maximize economy of initial fabrication and large-scale installation. FIG. 1 shows a two-stage heterogeneous system. The heterogeneous reactor is arranged with its axis vertical and has a reactant solid-liquid-gas inlet at the top. The inlet can be in either a vertical or horizontal position. A flow of reactants is supplied to the top of the casing 10 leading to the inlet at a velocity and pressure sufficient to convey the reactants to the apparatus. The pressure at the inlet is negative in most cases with respect to exhaust to the atmosphere. This is to ensure that the blower providing the flow is not subject to wear from solids and chemical damage from corrosive components that may be contained in the incoming gas. The system is a low pressure system and typically the casing speed is between about 200 and about 1200 feet per minute (about 61 feet per minute) prior to introduction into the nozzle 21.
to approximately 366 m). The spray 41 can be placed in the central part of the inlet to the cylinder 10 and introduces liquid or solid reactants, adsorbents, absorbents or liquid coolants in droplets into the reactant stream. Preferably, the droplets are on the order of about 40 to about 1500 microns in diameter. If evaporative conditions exist, relatively large droplets may be desirable to avoid evaporative effects. The spray 41 is preferably a stiff cone-shaped spray, which, alone or in combination, covers the entire cross-section of the contaminant gas stream and introduces droplets of water before the gas enters the cone 21. arranged in form. acceleration of small droplets of different sizes through the device with maximum discrimination;
Desirable for effecting deceleration and speed and increasing reaction. The form of the spray is nozzle 2.
Preferably, the entire area of one inlet 25 is covered, and any suitable form of spray or multiple sprays is satisfactory. The spray 41 can also be used to introduce solid particles of the above-mentioned size into the reactant stream at the inlet 25 of the nozzle 21. The reactant-containing heterogeneous solid-liquid-gas stream enters concentrating nozzle 21 through inlet 25. Preferably, the inlet is round and the nozzle is conical, but other geometries with respect to the axis of the device are sufficient. The cone ratio, defined as the effective cross-sectional area of the inlet divided by the effective cross-sectional area of the outlet, is approximately 2 to
It should be about 64 and about 2 to about 36 is preferred. Effective cross-sectional area means the area at an angle of 90° to the axis of gas flow. The length of the convergence section of the nozzle is determined by the convergence angle shown at A in FIG. 1 and the nozzle ratio defined above. Preferably, the average convergence angle is from about 6° to about 20°, and more preferably from about 10° to about 16°. By average concentration angle is meant the angle measured between a straight line drawn from the inlet to the outlet and the vertical line indicated by A in FIG. Nozzle 2
The side surface of 1 need not be straight, but can be slightly convex or concave. The distance from the exit 21 to the impact surface 31 should be about 1.3 to about 2.5 times immediately after the exit 24;
And about 1.6 to about 2.0 times is preferable. A suitable impingement plate is shown at 31 in FIG. Collision plate 3
1 provides an area between the impingement plate and the cylinder 10 sufficient to impinge substantially the entire amount of particulate matter from the nozzle outlet 24 on the plate and to pass gas around the impingement plate without appreciably reducing pressure. It is of sufficient size to provide Although the impingement plate 31 is shown as a flat plate, a slightly concave plate may be used to facilitate gas passage around the edges and facilitate removal of particulate matter. For reactions that do not require separation of solid and liquid phases from a gas phase, or where there are mass transfer phenomena associated with evaporation processes such as occur in cooling towers, impingement plates may not be required. An additional spray can be suitably positioned on the top of the impingement plate 31, from which the spray washes particulate matter from the impingement plate 31 as it travels through the apparatus and exits from the bottom. Such sprays can be multiple sprays arranged around the edge of the impingement plate 31, or a satisfactory spray can be placed in a central location. If a sufficient amount of fluid is used, the impingement surface will be the fluid itself. The particulate matter will then be taken into the fluid without colliding with or adhering to the collision plate. The essential criterion for spraying on the impingement plate 31 is to provide a sufficient amount of fluid with sufficient force and direction so that the impingement plate 31 is relatively free of particulate matter. It is possible to operate the reactor without an auxiliary spray to clean the impingement plate surface. Due to the integrated structure of the device of the invention, the first
As shown, multiple stages of nozzle-impingement means can be easily installed with one means on top of the other, resulting in a three-unit sequence as shown in FIG. One to about six sequentially coupled stage nozzles are suitable for the heterogeneous reactor used in the present invention. Preferably 2 to 4 stages are used in succession. The number of stages is controlled by the difficulty of reaction of the reactants, and a large number of stages may be necessary for particularly difficult materials. It could also be influenced by the concentration angle or effective cross-sectional area ratio of the nozzle. Below the impingement plate in the bottom stage there is a reservoir 15 for liquid and slurry removal. Also, outlet means for the removal of cleaning gas is located below or adjacent the bottommost impingement plate 33 and is illustrated as conduit 16 in FIG. A de-mistor 17 is provided in the clean gas outlet tube in order to remove any fine droplets of liquid remaining in the gas stream, together with any solids or liquids trapped in the droplets, within the device or outside the device. It is preferable to have the following. It is particularly advantageous to arrange the concentration nozzles vertically. i.e. nozzle ratio 4 and nozzle angle
Using an apparatus with a 12° demister and an inlet velocity of approximately 2100 feet per minute, the pressure drop through a single nozzle is 3.5 inches (8.9
cm), 5.7 inches (14.5 cm) of water column for two nozzles in series, 7.0 inches (17.8 cm) for three nozzles in series, and 8.3 inches (17.8 cm) of water column for four nozzles in series. 21cm). When using the apparatus with two nozzles in series to remove SOx at an inlet velocity of about 400 feet per minute and making fertilizer in accordance with the present invention, a water column of 0.8 inches (2.1 cm) ) Excellent process results were obtained with a pressure drop of . The pressure drop through vertically successive nozzles therefore proves to be smaller and more advantageous than the cumulative method. As shown in FIG. 1, the second stage is geometrically identical to the first stage. However, it will be appreciated that the water or liquid agent supplied both to the nozzle in front of the cone inlet and to the nozzle supplying liquid to the impingement surface of the same or other stages can be individually adjusted. The liquid, solid and gaseous reactants in the stream are
The passage through such a nozzle promotes intimate contact between the liquid, solid and gaseous reactants and provides the desired high reaction rates. The high reaction efficiency of the heterogeneous reactor and process is due to the combination of incompressibles passing with the compressible gas through the nozzle 21, which has the opportunity to expand to a relatively large extent after exiting the nozzle outlet 24. It is believed that this is due to the differential speeds and differential accelerations and decelerations achieved. A range of compressible and incompressible particles exists in the stream containing the reactants. Particles added to the gas stream by adding solids or liquid droplets are primarily incompressible since it is desirable to increase the incompressible component of the gas stream. Spray 41 can be used to introduce liquid or solid particles of a broadly selected particle size into the gas stream. And, along with a relatively wide range of liquid or solid particle sizes in the inlet gas stream, extremely high collision rates and high rates of compressed gas flowing past the incompressible particles and droplets promote very high efficiency reactions. is achieved. To minimize the height of a heterogeneous reactor such as that shown in FIG. 1, multiple cones can be placed at each stage. Liquid fertilizer product base is removed from the recycle stream and flows from the clarifier via valve V ₁₂ to the heterogeneous reactor. This liquid is transferred to an agitated tank (not shown) and is added to a caustic potash (White
potash), uncoated ammonium nitrate and other conventional liquid ingredients are added and blended to the desired quality. Liquid from the clarifier may also pass through valve _V16 to combine with the solid slurry stream downstream of valve _V15 . The resulting mixture is transferred to valve V ₁₇ and can be used as a similar suspension fertilizer base as described in connection with FIG. It is therefore understood that the method of the present invention is a method for producing fertilizer comprising the steps of: reacting a sulfur oxide-containing gas and water in a multistage reactor to produce a sulfur-containing acid; , the sulfur-containing acid is reacted with calcium ions to produce a phosphate fertilizer.
It is particularly suitable to supply calcium ions obtained from phosphate rock. How do the flows of substances in the gaseous, solid and liquid states through the heterogeneous reactors, condensers/absorbers and other flow contacting equipment involved in the process and apparatus of the invention be directed in combination? It may be current or co-current. i.e., the gas flow is co-current for both the fluid and the solid, or co-current for one and counter-current for the other;
or can be countercurrent to the process flow of both liquid and solid materials. If untreated phosphate rock is used in the process of the invention, the sulfur-containing acid is primarily (more than 50%) sulfuric acid in order to achieve a high conversion of phosphate rock and to remove sulfur oxides from the non-smoke. It was found that it must be. Mainly to obtain sulfuric acid, it is necessary to oxidize the sulfur oxides in the flue gas. This becomes a bigger problem as the amount of sulfur in the burned fuel increases. Under these conditions, a solution with a pH of about 2.5 to 4.0 is used to solubilize the phosphate rock and the pH of the solution is about 5 to 4.0.
We have found it preferable to increase the pH to 8, and preferably 5 to 7 to facilitate removal of sulfur oxide from the gas stream. In the process of the invention, a phosphate rock defluorinated by thermal pretreatment is used, so that the sulfur-containing acid can be sulfurous acid, and a high conversion of the phosphate rock is achieved and a high that sulfur oxides can be removed from the flue gas of fuels with a sulfur content;
The present inventors found out. It has been found that such thermally pretreated defluorinated phosphate rock reacts well with sulfur-containing acids, primarily sulfurous acid. In this way, the need to oxidize the sulfur oxide to fully solubilize the phosphate rock is reduced. Under these conditions, the phosphate rock is solubilized using a solution with a pH of about 3-5 and preferably about 3.5-4.5 and the pH of the solution is about 5-7 and preferably 6-4.
We have found it preferable to increase the pH to 7 to facilitate removal of sulfur oxide from the gas stream. The thermally pretreated defluorinated phosphate ore refers to a mixture of crude tricalcium phosphate or calcium heteropolyphosphate (including calcium metaphosphate) produced by thermally defluorinating fluorinated phosphate ore. The conventional production method for defluorinated phosphate ore is
Phosphorous and Compounds, edited by John R. VanWazer, Volume 2, Interscience Publishers, Inc., New York, 1961, pages 1090-1092. Another suitable form of thermally pretreated phosphate rock, which is particularly suitable when the main energy source is electricity, is the simultaneous oxidation of "calmeta" or elemental phosphorus and the resulting P ₂ O ₅ Calcium metaphosphate produced by reacting with phosphate rock ("Phosphorus and Itsutsu Compounds" above)
(described in detail on pages 1095-1097).
Thermal pretreated defluorinated phosphate ores useful in the process of the present invention generally contain less than about 0.2% F and a minimum of about 18% P (41.3% P ₂ O ₅ ). Thermally pretreated, defluorinated phosphate rock can be used to carry out the operations of the present method described above at higher PH levels than would be possible with untreated phosphate rock. PH
is an important factor in both sulfur dioxide removal and phosphate rock conversion. It has been found that thermally pretreated, defluorinated phosphate rock removes more than 90% of the sulfur oxides, mainly SO ₂ , while producing mainly sulfurous acid in the cooling tower stage. A PH in the range of about 3 to 5 is suitable for the cooling tower and vessel 1, with a PH of about 3.5 to 4.5 being preferred. Thermal pretreatment, the conversion of defluorinated phosphate rock into ammonifying fertilizer by solubilizing it with sulfite is greater than 90%. It has also been found advantageous to treat the thermally pretreated defluorinated phosphate rock by soaking it in water before use. It has been found that treatment by soaking for 2-3 days significantly increases the solubilization of phosphate rock. A long period of about 30 to 120 days is appropriate. Extremely high sulfur dioxide removal rates from the flue gas by combustion of high sulfur-containing fuels reduce the PH in the heterogeneous reactor to about 5-8, preferably about 5.5.
~6.5, is increased by increasing the range. FIG. 2 shows an embodiment of the device according to the invention,
A portion of the product is now transferred to column 2 as a liquid spray.
is recirculated to The embodiment shown in Figure 2 has been found to be particularly useful when using defluorinated phosphate rock, where sulfur oxides can be removed from the gas stream with high efficiency without oxidation. ,
The sulfur-containing acids produced, mainly sulfite,
was found to sufficiently solubilize pretreated phosphate rock. As shown in FIG. 2, sulfur-containing coal is fed by feed means 50 to boiler 51 where it is combusted and the flue gases leave the boiler through flue 62. A spray 90 is arranged in the horizontal flue 62 to cool the hot flue gases before entering the tower 1. Flue gas tower 1
We have found it advantageous to cool it to about 130-160°C (about 54-71°C) before entering. Column 1, indicated at 52, is a heterogeneous reactor that provides high liquid-gas contact to improve the reaction, and has the configuration, for example, shown as a cooling tower in FIG. Tower 1
The spray in is provided by nozzles 91, 92 and 93, and spray 90 in feed flue 62, all of which carry solution from column 2 effluent tank to conduit 7.
9. The amount of liquid supplied via pump P-10 and flowing to the spray and column 1 effluent tank 70 is regulated by valve V-32. The gas leaves column 1 and enters the top of column 2 via conduit 53. Column 2 is a heterogeneous reactor suitable for enhancing liquid-gas reactions. A structure that is particularly well suited for the heterogeneous reactor of column 2 is the heterogeneous reactor shown in FIG. 1 and described in more detail with respect to the heterogeneous reactor of FIG. The gas stream descends within column 2 and contacts liquid from sprays 94 and 95. The gas leaves the column 2 via a flue 55 having the desired analytical means, such as an infrared analyzer 56 for SO ₂ measurement and a dust detector 58. A mist suppressor 57 can be installed if necessary to prevent excess water vapor from forming in the flue effluent. A blower 59 can be used to direct gas through flue 60 to the atmosphere and provide the necessary boiler draft. Column 1 effluent tank 70 contains liquid from conduit 81 at the bottom of column 1 and liquid exiting from column 2 effluent tank 77 into conduit 7.
8 and receives liquid regulated by valve V-31. Liquid from tower effluent tank 70 passes to reaction tank 72 by conduit 71 and optionally pump P-11. Fertilizer producing reactants, other than the sulfur-containing acid produced, are added to the system by addition to reactor 72, and the reactants are shown as water, ammonia, and phosphate rock. Solubilization of the phosphate rock occurs in reaction vessel 72, from which the product passes through conduit 73, regulated by valve V-30, to settling vessel 74, from which liquid fertilizer product is transferred via conduit 75. taken out. Liquid product from tank 74 also provides liquid spray to column 2 via nozzles 94 and 95. The liquid exits column 2 through conduit 82 and enters column 2 effluent tank 77. The liquid from the column 2 effluent tank is transferred to column 1.
spray and directly into the column 1 effluent tank. A pilot plant containing the equipment shown in Figures 1 and 2 conveniently has a general pressure drop of about 2 inches of water between the cooling tower gas inlet and the heterogeneous reactor gas outlet. Manipulated. This represents significant energy savings when compared to conventional scrubbers that operate with pressure drops in the range of 40 to 70 inches (102 to 178 cm) of water column. Fertilizer was produced according to the above method, and the residue after coal combustion was crushed and added to the desired fertilizer product, thus eliminating processing problems. The fertilizers so obtained were tested on soybean, chiyahiki and spring wheat. In each case, the plants grew significantly faster and to a significantly larger size than comparison plants grown on topsoil of good agricultural land. The following examples illustrate specific operations utilizing aspects of the invention and are offered by way of illustration and are not intended to limit the invention in any way. Reference Example A liquid fertilizer was produced from fresh untreated phosphate rock using an apparatus similar to that shown in FIG. 1, except for the pre-neutralization device and the equipment for handling solid fertilizer. about
Coal containing 3.37% sulfur is burned in a boiler,
and the flue gas leaving the boiler with a CO ₂ content of 8.8% and an excess of air in an amount of 89.1% to facilitate the achievement of oxidation (even a slight oxidation) are cooled without separating the flyass. Sent to the bottom of the tower. Gas flow rate is 282CFM (7.99
m ³ /min). 82% passed through a 230 mesh American Standard Silly screen and essentially
Untreated rock phosphate having a particle size of 100% passing a 20 mesh screen was added to the settler at a rate of 81 pounds (36.7 Kg) in 5-1/2 hours. Mix the liquid in the settling tank and spray 19.3 gallons/1000CF (0.073 m ³ /
28.3 m ³ ) of gas was recirculated primarily to prevent nozzle clogging under operating conditions at a flow rate of one-fifth of the design flow rate. The pH of the liquid supplied to the cooling tower is 4.2, and the pH of the liquid flowing from the cooling tower to the settling tank is 4.2.
The pH was 3.5. Gas was removed from the top of the cooling tower and introduced into the top of the heterogeneous reactor. The settling tank is divided into a receiving tank for the liquid from the heterogeneous reactor, as shown in Figure 1, which receives the ammonification reaction for processing the solution for recirculation to the heterogeneous reactor. Supply the solution to the device. Add water and ammonia to the ammonification reactor and mix the liquor from the reactor and spray 22 gallons/ml in the heterogeneous reactor.
It was circulated at a rate of 1000 CF gas (0.083 m ³ /28.3 m ³ gas) to prevent blockage again under reduced flow operating conditions. The pH of the liquid supplied to the heterogeneous reactor was 6.3, and the pH of the liquid sent from the heterogeneous reactor to the receiving tank was 5.9. The overall SO ₂ removal rate from flue gas was 84%. The liquid fertilizer product was removed from the collection tank. The fertilizer ingredients were nitrous from ammonia and phosphate from phosphate rock. EXAMPLE The apparatus of FIG. 1 was modified by replacing the sedimentation tank and sedimentation tank shown in FIG. 1 with a continuous receiving tank, plug flow reactor, back mix reactor, and settling tank. Coal containing 3.4% sulfur by weight was burned in a boiler, and the flue gas from the boiler was sent to the bottom of the cooling tower. Thermal pretreated defluorinated phosphate rock containing less than 0.18% F was hydrolyzed in tap water for 11 days before being added to the process. 100% of the phosphate rock that had been hydrolyzed, thermally pretreated, and defluorinated passed through a No. 8 mesh screen, which was then added to the plug flow reactor. In these experiments, coarse phosphate rock particles (100% 8
2% 30 mesh or more) and fine phosphate rock particles (100% 8 mesh or more, 75% 200 mesh or more)
The desired conversion rate and SO ₂ removal rate were obtained even when using both particles (mesh or higher). The liquid in the settling tank was mixed and recycled to each column at a concentration sufficient for the reacting calcium phosphate to absorb sulfur oxides from the combustion gases. In a process operation where the pH of the solution exiting the heterogeneous reactor is 6.35, the SO ₂ removal rate is 90.1.
% and the SO ₂ concentration at the gas outlet was 142 ppm, while in operation at pH 5.70, the SO ₂ removal rate was 85.6% and the SO ₂ concentration at the gas outlet was 207 ppm. When ammonia is added to the process to increase the pH of the solution at the outlet of column 2 or the heterogeneous reactor to 6.4-6.9, the SO ₂ removal rate is greater than 92%, corresponding to an outlet SO ₂ concentration of about 110 ppm. It increased to In each case above, water was added to the reactor to replace the water evaporating from the column. EXAMPLE The apparatus shown in FIG. 2 and described above with respect to FIG. 2 was used to produce a liquid fertilizer from thermally pretreated, defluorinated phosphate rock. Approximately 6.2 in dry weight
Coal containing % sulfur by weight was fed in a drop-down stoker, combusted with excess air in a double-row heated tube boiler, and flue gas was sent from the boiler to the bottom of column 1. Other comparative examples used only 20% excess air. The temperature of the flue gas before entering column 1 was about 150°C (about 65.5°C) due to the liquid spray in the conduit between the boiler and column 1. 130 pounds of defluorinated phosphate rock containing less than approximately 0.18% F (59
Kg) was hydrolyzed in 60 cubic feet (1.7 m ³ ) of tap water for two weeks. Only the thermally pretreated defluorinated phosphate rock hydrolyzed with water is added to the reactor to obtain the indicated PH in the liquid stream and the desired chemical for sulfur oxide removal and fertilizer production. The conditions were maintained. Assuming a PH of 6.90 in the recycled liquid in the spray in column 2 and a PH of 6.50 in the liquid sent from column 2 to the column 2 liquid effluent tank, the removal rate of sulfur dioxide from the flue gas is 92.5%. It was discovered that When a small amount of ammonia is added to the reaction tank in addition to the defluorinated phosphate rock treated with water as described above, the removal rate of sulfur oxide increases as shown in Table 1, and the removal rate of phosphate rock and ammonia increases. The conversion rate was found to reach 90% based on the reaction products of calcium sulfite, calcium sulfate and ammonium phosphate. The removal rate of sulfur dioxide at 15 minute intervals is shown in the table. The flue gas left column 2 at a temperature of 110°C (43.3°C) and a velocity of 460 ft/min (140 m/min).

[Table] The amount of SO ₂ allowed in flue gas by the United States Federal Environmental Protection Agency is 177 ppm, which is 92.5
% total sulfur recovery rate. Therefore,
Combustion of coal containing 6.2% sulfur was found to be superior to EPA standards. Although the invention has been described in connection with certain preferred embodiments and has been described in many particulars for purposes of illustration, those skilled in the art will appreciate that the invention can take still other embodiments and that have been described herein. It will be obvious that certain details may be changed considerably without departing from the basic principles of the invention.

[Brief explanation of the drawing]

FIG. 1 illustrates one embodiment of a method for making a phosphate fertilizer using crushed phosphate rock according to the present invention. FIG. 2 illustrates one embodiment of a process for making a phosphate fertilizer according to the present invention that employs fluid product recirculation. A brief explanation of the symbols in each drawing is as follows: 10...casing (enclosure); 21, 22...
... Nozzle; 11, 12, 13, 14 ... Flange; 41 ... Spray; 31, 33 ... Collision plate;
90, 91, 92, 93, 94, 95... spray; 70, 77... effluent tank; 72... reaction tank;
V...Valve.

Claims (1)

[Claims] 1. A sulfur-containing acid is formed by reacting a sulfur oxide-containing gas and water at pH 3 to 8 in a multistage reactor;
The pH of the solution of the sulfur-containing acid is maintained between 3 and 8 with calcium ions, the calcium being obtained from a mixture of alpha-tricalcium phosphate or heteropolycalcium phosphate obtained from thermally pretreated phosphate rock. Forming a phosphate fertilizer, the calcium ions are dissolved by reacting with the sulfur-containing acid at a pH of 2.5 to 5, and the pH of this solution is raised to a pH of 3 to 8 by adding ammonia, thereby A method for producing fertilizer comprising buffering this solution to promote the reaction of sulfur oxide. 2 The sulfur-containing acid is mainly sulfuric acid, calcium ions are solubilized at pH 2.5 to 4.0, and the pH of the solution is adjusted to 5 to 8 to facilitate the reaction of sulfur oxide.
2. The method according to claim 1, wherein 3. The method according to claim 2, wherein the thermally pretreated phosphate rock is hydrolyzed by immersion in water before use. 4. A method according to claim 2, wherein the sulfur oxide-containing gas is obtained from the combustion of fossil fuels. 5. The method of claim 2, wherein the sulfur oxide-containing gas is obtained from a sulfur-producing chemical reaction. 6. The method of claim 2, wherein the calcium is derived from phosphate rock having a BPL of about 55-65. 7 The sulfur-containing acid is primarily sulfite, calcium ions are solubilized at pH 3-5, and the solution is at pH 5 to facilitate the reaction of sulfur oxides.
8. The method of claim 1, wherein the method is increased to .about.8. 8. The method of claim 7, wherein the calcium ions are solubilized at a pH of 3.5 to 4.5 and the pH of the solution is increased to 6 to 7 to facilitate the reaction of the sulfur oxide. 9. The method of claim 7, wherein the phosphate rock contains less than about 0.2% fluorine by weight. 10. The method according to claim 7, wherein the phosphate rock is used after being hydrolyzed by immersion in water. 11. The method of claim 7, wherein the sulfur oxide-containing gas is obtained from the combustion of fossil fuels. 12. The method of claim 7, wherein the sulfur oxide-containing gas is obtained from a sulfur-producing chemical reaction. 13. The method of claim 7, wherein the calcium is derived from phosphate rock having a BPL of about 55-65.