Lime slurry

Wet/dry process. Lime slurry absorbs SO2 in vertical spray dryer forming CaSO —CaS, H2O evaporated before droplets reach... 

Most carbide acetylene processes are wet processes from which hydrated lime, Ca(OH)2, is a by-product. The hydrated lime slurry is allowed to settle in a pond or tank after which the supernatant lime-water can be decanted and reused in the generator. Federal, state, and local legislation restrict the methods of storage and disposal of carbide lime hydrate and it has become increasingly important to find consumers for the by-product. The thickened hydrated lime is marketed for industrial wastewater treatment, neutrali2ation of spent pickling acids, as a soil conditioner in road constmction, and in the production of sand-lime bricks. 

Tricalcium phosphate, Ca2(P0 2> is formed under high temperatures and is unstable toward reaction with moisture below 100°C. The high temperature mineral whidockite [64418-26-4] although often described as P-tricalcium phosphate, is not pure. Whidockite contains small amounts of iron and magnesium. Commercial tricalcium phosphate prepared by the reaction of phosphoric acid and a hydrated lime slurry consists of amorphous or poody crystalline basic calcium phosphates close to the hydroxyapatite composition and has a Ca/P ratio of approximately 3 2. Because this mole ratio can vary widely (1.3—2.0), free lime, calcium hydroxide, and dicalcium phosphate may be present in variable proportion. The highly insoluble basic calcium phosphates precipitate as fine particles, mosdy less than a few micrometers in diameter. The surface area of precipitated hydroxyapatite is approximately... 

Pre-liming. Lime slurry, 0.25% lime on juice (0.250 g of CaO/100 g juice), is added to bring the pH of the mixture into the alkaline range. Insoluble calcium salts are precipitated as finely dispersed coUoids. Calcium carbonate in the form of recycled first carbonation sludge is added to provide coUoid absorption and stabilization. Temperature may be cool (50°C) or hot (80°C) depending on the temperature of the next step, or occasionally on the type of diffusion equipment. Retention time is 15 to 30 min. 

Hypochlorite solutions are prepared in near quantitative yield by chlorination of dilute caustic or a lime slurry. 

Chlorination of lime slurried in strong NaOCl solution, followed by cooling to — 15°C, precipitates about 80% of the av CI2 as large hexagonal crystals of a triple salt Ca(OCl)2 NaOCl NaCl -12H20 [64147-46-2] (182). The recovered triple salt, free of much of the lime impurities, is treated with chlorinated lime slurry to produce neutral calcium hypochlorite dihydrate crystals [22464-76-2]. 

Lime slurry is chlorinated in the presence of Ca(OCl)2 mother Hquor, NaOH, and NaOCl (185). After concentration, the resulting slurry of Ca(OCl)2 2H20 is filtered and the cake dried. A portion of the filtrate is treated with caustic, the recovered lime is recycled, and the mother Hquor used to prepare the requited NaOCl solution in an evaporator—chlorinator, which after separation of salt, is sent to the main reactor. In a slightly modified version, a lime purification step is added (186). 

Chlorination of thick lime slurry at 40—45°C forms large crystals of hemibasic calcium hypochlorite. The fine crystals obtained under 30°C are difficult to filter and since they invariably contain occluded mother Hquor, they have frequently been incorrectly referred to as monobasic or two-thirds basic (187,188). The isolated hemibasic crystals are suspended in a thin chlorinated lime slurry and chlorinated, producing laminar crystals of Ca(OCl)2 2H20, which are filtered and dried. Mother Hquors are treated with a lime slurry to recover the dibasic crystals, which are then suspended in a Hquor of lower CaCl2 content and chlorinated to form the neutral salt (188—190). 

Other processes also use the dibasic salt as an intermediate. Dibasic calcium hypochlorite can be prepared from filtrates from chlorinated lime slurries in various ways. In one process, the filtrate is returned to the slurry being chlorinated to keep it thin. This is designed to improve crystal growth. The dibasic crystals, together with water, are added to the slurry during chlorination and some dibasic salt is prepared by chlorination in addition to the dibasic salt made from filtrates (188). In another process, dibasic crystals are separated, slurried in water, and chlorinated to obtain a slurry of neutral Ca(OCl)2 2H20 in a mother Hquor of reduced calcium chloride content which is then filtered and air dried (191,192). 

In a process formerly operated by Pennwalt, lime slurry is chlorinated to produce a solution with equimolar amounts of Ca(OCl)2 and CaCl2 that is sent to a crystallizer where dibasic crystals are formed. 

Addition of NaCl decreases the solubiHty of Ca(OCl)2 in equiHbrium with the dibasic salt and lime. The dibasic slurry is sent to a classifier. Finely suspended lime impurities are removed from the overheads yielding a clear Hquor, which is recycled to the lime slurry makeup. The bottoms from the classifier are chlorinated giving a slurry of Ca(OCl)2 2H20, which is centrifuged. The cake is mixed with strong, low salt NaOCl solution in a pug mill and... 

In another process, hypochlorite filtrate is treated with lime slurry to precipitate dibasic crystals that are filtered. The filtrate is mixed with strong caustic, chlorinated, and filtered to remove NaCl crystals. The filtrate containing Na and Ca hypochlorite is mixed with dibasic crystals and chlorinated producing a slurry of Ca(OCl)2 is filtered the cake goes to a dryer and the filtrate to the dibasic crystallizer (195). 

Several modifications of the preparation of neutral Ca(OCl)2 2H20 do not involve intermediates. In a continuous process, lime slurry containing caustic and Ca(OCl)2 mother Hquor is chlorinated under reduced pressure to remove the heat of reaction, and the resulting slurry is separated in a classifier into Ca(OCl)2— and NaCl-rich regions from which slurry is withdrawn to obtain Ca(OCl)2 filter cake and soHd salt (204). 

In a batch process, NaOH is chlorinated in the presence of recycled neutral Ca(OCl)2 mother Hquor. After separation of salt, lime slurry is added and chlorinated (205). The Ca(OCl)2 2H20 crystals are recovered by filtration. In another version, classification of the Ca(OCl)2—NaCl slurry gives a Ca(OCl)2-rich fraction that is filtered and the filtrate recycled along with the NaCl-rich fraction to the first chlorinator (206). Also, 50% NaOH and soHd slaked lime are used in the second chlorination. 

Two solvent processes for preparation of Ca(OCl)2 have been described. In one, a CCl solution of /-C H OCl is allowed to react with a thin lime slurry and the aqueous phase, a solution of Ca(OCl)2, is evaporated to a product with a purity of >95% (217). In the other, a solution of HOCl in methyl ethyl ketone reacts with either CaO or Ca(OH)2 (133). FoUowing filtration, the residual solvent in the product is removed under vacuum. 

Manufacture. Hemibasic calcium hypochlorite is manufactured by chlorination of lime slurry followed by filtration and dryiag of the filter cake. 

Lime-Sulfuric. Recovery of citric acid by calcium salt precipitation is shown in Figure 3. Although the chemistry is straightforward, the engineering principles, separation techniques, and unit operations employed result in a complex commercial process. The fermentation broth, which has been separated from the insoluble biomass, is treated with a calcium hydroxide (lime) slurry to precipitate calcium citrate. After sufficient reaction time, the calcium citrate slurry is filtered and the filter cake washed free of soluble impurities. The clean calcium citrate cake is reslurried and acidified with sulfuric acid, converting the calcium citrate to soluble citric acid and insoluble calcium sulfate. Both the calcium citrate and calcium sulfate reactions are generally performed in agitated reaction vessels made of 316 stainless steel and filtered on commercially available filtration equipment. 

The General Electric in-duct scmbbing (IDS) process involves the atomization of a slaked lime slurry, using a rotary disk atomizer A test at the 12 MWe scale at the Muskingum River Station of Ohio Power, performed in a duct with a 4.3-m cross section, achieved 50% SO2 removal with good lime utilization... 

The lime application and settling process treatment consists of adding a milk of lime slurry to the wastewater to precipitate the hydroxide of the heavy metals and reduce dissolved sulfate concentrations through the formation of gypsum. Sufficient lime is needed to adjust the pH to between 10 and 11.5. Also, settling may have to be aided by adding small quantities of organic polyelectrolytes. 

A rotary drum filter is to be used to filter a lime slurry. The drum rotates at a rate of 0.2 rpm, and 30% of the drum surface is submerged in the slurry. The... 

HALT [Hydrate addition at low temperature] A flue-gas desulfurization process in which lime slurry is injected into the combustion gases after they have been cooled in the heat exchanger. Developed in Canada in the mid-1970s. 

Salsigne A cyanide process for extracting gold from ores containing arsenic or antimony. Pre-treatment with a lime slurry reduces cyanide losses. 

Equipment for reactive absorption is of the same types as for physical absorption, towers of various kinds and stirred tanks. Packed or tray towers are the most common, but spray or bubble towers are used for their mechanical simplicity and when there is a likelihood of clogging. Thus S02 is scrubbed from air with a spray of lime slurry in a tower. Fluorine waste gases form solids on contact with water, so they are scrubbed by bubbling the gas through water in an empty tower. 

Lime slurry, 15 21 Lime soda process, 22 795 Lime-soda sintering process, for alumina, 2 354-355... 

The most popular dry scrubbing systems for incinerators have involved the spray drying of lime slurries, followed by dry collection in electrostatic precipitators or fabric filters. Moller and Christiansen [Air Poll. Cont. Assoc. 84-9.5 (1984)] published data on early European technology. Moller et al. [U.S. Patent no. 4,889,698 (1989)] describe the newer extension of that technology to include both spray-dryer absorption and dry scrubbing with powdered, activated carbon injection. They claim greatly improved removal of mercury, dioxins, and NO,. 

Several power plants have been equipped with dual alkali processes. These are throw-away processes with two liquid loops. In one common process, the scrubbing liquid is a clear solution of sodium sulfite. The absorption of sulfur dioxide converts the sodium sulfite to sodium bisulfite. In the regeneration loop, an alkali such as lime slurry is added the sodium sulfite solution is regenerated and a mixture of calcium sulfite and calcium sulfate is precipitated. The slurry is... 

If the volume of the liquid in the tank is eonstant, the outflow is the sum of all the inflows. The flow rates of caustic and lime slurry are usually negligible. For three feed streams... 

Fqh = total flow rate of OH- ion into the system in the caustic and lime slurry streams... 

The nonfertilizer calcium phosphates are manufactured by the neutralization of phosphoric acid with lime. The processes for different calcium phosphates differ substantially in the amount and type of lime and amount of process water used. Relatively pure, food-grade monocalcium phosphate (MCP), dicalcium phosphate (DCP), and tricalcium phosphate (TCP) are manufactured in a stirred batch reactor from furnace-grade acid and lime slurry, as shown in the process flow diagram of Figure 3. Dicalcium phosphate is also manufacmred for livestock feed supplement use, with much lower specifications on product purity. 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

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