Calcium sulfate cleaning

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. 

Sugar Processing. Dispersants are used in the production of cane and beet sugar to increase the time between evaporator clean outs. Typical scales encountered include calcium sulfate, calcium oxalate, calcium carbonate, and silica. Dispersants are fed at various points in the process to prevent scale buildup, which would interfere with efficient heating of the vessels. Only certain dispersants, conforming to food additive regulations, can be used, since a small amount of the dispersant may be adsorbed on the sugar crystals. 

Sulfuric acid has found limited use in boiler cleaning operations. It is not feasible for removal of hardness scales due to the formation of highly insoluble calcium sulfate. It has found some use in cases where a high-strength, low-chloride solvent is necessary. Use of sulfuric acid requires high water usage in order to rinse the boiler sufficiently. 

The sodium methoxide solution is prepared as follows- 203 g. of methyl alcohol, available from Fisher Scientific Company, is placed in a 500-ml., two-necked flask under an inert atmosphere. The flask is equipped with a magnetic stirring bar and a reflux condenser provided with a calcium sulfate drying tube. Freshly cut, clean sodium (23 g., 1 mole) is added in small pieces at such a rate that reflux is maintained. The mixture is stirred until all the sodium has reacted. 

In distillation the water closest to the heating surface is hottest and it is there that calcium sulfate is least soluble. Thus, calcium sulfate deposits, forming an adhering film that increases the thermal resistance and decreases the heat flux. The scale is continuously deposited until the tubes are cleaned or become plugged. For scale deposition the local concentration must be at least saturated in calcium sulfate. At 100° C. this occurs in concentrated sea water at a concentration 3.1 times that of ordinary sea water. A plant has been successfully operated continuously without calcium sulfate deposition by taking only part of the available water from the sea water, so that the liquid in the evaporator is never more than 1.8 times the concentration of sea water and the wall temperature is below about 250° F. ( ). This imposes technical and economic limitations on distillation plants. Similar considerations hold for plants distilling brackish water containing calcium sulfate. 

In-Service Cleaning Involving the Removal of Calcium Phosphate, Calcium Sulfate, or Silica... 

Some companies are turning the necessity of cleaning up the environment into new opportunities to improve their profitability. Thus Du Pont has found a useful application as a building material for the calcium sulfate that was piling up as a by-product in one of its Texas plants. 

B. Apparatus (See Chromatography, Appendix IIA.) Assemble a suitable apparatus for ascending thin-layer chromatography. Prepare a slurry of chromatographic silica gel containing about 13% of calcium sulfate (1 g to each 2 mL of water) as the binder, apply a uniformly thin layer to glass plates of convenient size, dry in air for 10 min, and activate by drying at 100° for 1 h. Store the cool plates in a clean, dry place until ready for use. 

Atmospheric acidity is responsible for tbe attack in the presence of humidity whereas the SO2 reaction continues to occur in the presence of liquid water as well as water vapours. The calcium sulfate that forms is less preserved when the structures are exposed to direct rainfall. In protected regions SO2 continues its attack almost continuously and the gypsum obtained from this reaction forms crusts on protected surfaces. As a consequence most ancient buildings in the industrialized countries have a black appearance in some areas and a clean aspect in others. The black appearance is due to gypsum crusts, which have incorporated soot in the process of crystallization whereas the areas directly showered with the... 

In one run, sodium sulfate and calcium chloride were added to a 200-gallon batch of sea water to give a sulfate concentration of 5200 p.p.m. and a calcium concentration of 640 p.p.m. An addition was made of 5 p.p.m. of low molecular weight polyacrylic acid and the treated sea water was evaporated under standard conditions. The over-all heat transfer coefficient averaged 3600 B.t.u./sq. ft. hr. ° F. for a 5-hour period, with no detectable falloff during the period, and the tube was found to be clean, except for the plastic film. In contrast, evaporation of a similar batch of calcium sulfate-enriched sea water, with no polyacrylic acid, resulted in a marked decrease in heat transfer coefficient to less than 800 B.t.u./sq. ft. hr. ° F. after 2 hours. 

The calcium tartrate is removed by filtration and treated with dilute sulfuric acid to produce a solution of tartaric acid and a precipitate of calcium sulfate. The tartaric acid is then concentrated by evaporation under reduced pressure and separated by crystallisation. Tartaric acid is widely used in the food and drink industries, in pharmaceutical preparations, as a retarding agent in plaster and gypsum formulations, and in the polishing and cleaning of metals. Food grade slaked lime is generally specified (e.g., [31.30] and Table 31.2). 

The burning of pulverized coal in electric power plants produces sulfur dioxide (SO2) gas emissions. The 1990 Clean Air Act and its subsequent amendments mandated the reduction of power plant SOj emissions [66-70]. The Best Demonstrated Available Technology (BDAT) for reducing SOj emissions is wet scrubber flue gas desulfurization (FGD) systems. These systems are designed to introduce an aUcahne sorbent consisting of lime or limestone in a spray form into the exhaust gas system of a coal-fired boiler. The aUcaU reacts with the SOj gas and is collected in a liquid form as calcium sulfite or calcium sulfate slurry. The calcium sulfite or sulfate is allowed to settle out as most of the water is recycled [66-80]. 

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