Chemical cleaning operation

Sulfamic acid has a unique combination of properties that makes it particularly well suited for scale removal and chemical cleaning operations, the main commercial appHcations. Sulfamic acid is also used in sulfation reactions, pH adjustment, preparation of synthetic sweeteners (qv), and a variety of chemical processing appHcations. Salts of sulfamic acid are used in electroplating (qv) and electroforrning operations as well as for manufacturing flame retardants (qv) and weed and hnish killers (see Herbicides). 

A Chemical Cleaning Operation Kills Sparrows, but Improves Procedures... 

If the vessel is capable of being fired, as is a boiler, the final alkaline solution will probably be boiled for a few hours before being removed. The vessel will eventually be opened for inspection, and any loose, undissolved debris that normally remains following a chemical cleaning operation will be removed. 

Hydrodynamics/shear, operation below critical flux, chemical cleaning Operate below solubility limit, pre-treatment, reduce pH to 4—6 (acid addition), low recovery, additives (anti-sealants)... 

A chemical cleaning operation kills sparrows, but improves procedures... 

Nonstandard operations hint at the need for supplementary corrosion testing. For example, chemical cleaning operations are sometimes more damaging towards the materials of construction than the process itself. Hydrochloric acid is often used for chemical cleaning because of its low cost and rapid dissolution of metal oxides. Hydrochloric acid affects specific materials of construction, such as stainless steels, by means other than general corrosion. 

Mineral acids used in chemical cleaning operations include hydrochloric acid (HCI), hydrofluoric acid (HF), sulfuric acid (H2SO4), phosphoric acid (H3PO4), nitric acid HNO3), and sulfamic acid (H2NSO3H). Most of these acids have very low pKa values (see Table 1) and are completely ionized at the use strength. An exception is HF, which has a pKa value similar to that of formic acid, and phosphoric acid, which is about 10 times as ionized as HF. 

Research into methods to remove iron oxide and copper deposits from powergenerating equipment constitutes a large portion of the activities of laboratories involved in chemical cleaning operations. With the exception of the work on corrosion inhibitor mechanisms, there is more published information on the chemistry of iron and copper removal than other techniques. A separate chapter is devoted to a review of this information. 

As the economic value of coproducts has decreased, it has become more difficult to provide capital for environmental controls on air emissions and wastewater streams such as toxic phenoHc effluents from chemical recovery operations. Some former coke and manufactured gas sites may require remediation to clean up contaminated soil and groundwater. These difficulties will force the shutdown of some operations and discourage recovery of coproducts in future installations. 

Hydrogen chloride and the aqueous solution, muriatic acid, find appHcation in many industries. In general, anhydrous HCl is consumed for its chlorine value, whereas aqueous hydrochloric acid is often utilized as a nonoxidizing acid. The latter is used in metal cleaning operations, chemical manufacturing, petroleum well activation, and in the production of food and synthetic mbber. 

L. M. Brown,. Springer, and M. Bower, Chemical Substitution for 1,1,1 -Trichloroethane and Methanol in an Industrial Cleaning Operation, U.S. EPA, Cincinnati, Ohio National Technical Information Service, Springfield, Va., 1992. 

Principal uses of KOH include chemicals, particularly the production of potassium carbonate and potassium permanganate, pesticides (qv), fertilizers (qv), and other agricultural products soaps and detergents scmbbing and cleaning operations, eg, industrial gases dyes and colorants and mbber chemicals (qv) (10,34). 

AH volatile organic solvents are toxic to some degree. Excessive vapor inhalation of the volatile chloriaated solveats, and the central nervous system depression that results, is the greatest hazard for iadustrial use of these solvents. Proper protective equipment and operating procedures permit safe use of solvents such as methylene chloride, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene ia both cold and hot metal-cleaning operations. The toxicity of a solvent cannot be predicted from its chlorine content or chemical stmcture. For example, 1,1,1-trichloroethane is one of the least toxic metal-cleaning solvents and has a recommended threshold limit value (TLV) of 350 ppm. However, the 1,1,2-trichloroethane isomer is one of the more toxic chloriaated hydrocarboas, with a TLV of only 10 ppm. 

The first use of new plant, or start-up after a shutdown, poses corrosion hazards additional to those encountered in normal operation. New plant such as boilers requires special water treatment, involving boil-out, passivation and possible chemical cleaning. Actual requirements depend on the boiler type, the proposed service, the quality of water available during commissioning and the internal condition of the boiler. The condition of the boiler depends on for how long and in what conditions it has been stored. The presence of any salts, dirt or rust is harmful. An adherent, protective layer of magnetite in normal operation... 

Overall, these features mean that chemical control standards are necessarily high. For example, supplementation of the water treatment plant by condensate polishing plant and periodic chemical cleaning are particularly important. In addition, before each period of operation, a clean-up of the cycle is applied to remove crud. Stringent attention must be paid to the feed-water conditioning. 

Utility boilers generally require waterside chemical cleaning of all boiler surfaces every 300 to 500 days of operation, and this work may be carried out by specialist contractors. It is regarded as a routine function, irrespective of water chemistry, laboratory involvement, or the quality of FW treatment and water management provided. Chemical cleaning of utility boilers is designed to permit the boilers to operate at peak performance and within knife-edge control parameters. 

It should be noted, however, that oxygen corrosion of operational boilers supplied with mechanically deaerated FW, supplemented by the use of an appropriate oxygen scavenger chemical, and under a constant load is relatively rare. This position is not necessarily the same in idle boilers, low-load boilers, or chemically cleaned boilers, and despite all best efforts oxygen corrosion may take place. 

It is important that the tube surfaces be kept clean to avoid the initiation of corrosion. Regular waterside inspections and, if necessary, chemical cleaning of high-pressure equipment is recommended. The level of chloride that may be tolerated in such boilers during steady operation depends on the type of treatment employed. Where all-volatile alkaline treatments (AVT) are used, then the chloride levels should be lower than where nonvolatile alkalis (NVAT), such as sodium hydroxide and sodium phosphate, are used. The value may vary, depending on whether the boiler is coal-fired or oil-fired. 

Flux Decline Plugging, Fouling, Polarization Membranes operated in NFF mode tend to show a steady flux decline while those operated in TFF mode tend to show a more stable flux after a short initial decline. Irreversible flux decline can occur by membrane compression or retentate channel spacers blinding off the membrane. Flux decline by fouling mechanisms (molecular adsorption, precipitation on the membrane surface, entrapment within the membrane structure) are amenable to chemical cleaning between batches. Flux decline amenable to mechanical disturbance (such as TFF operation) includes the formation of a secondary structure on the membrane surface such as a static cake or a fluid region of high component concentration called a polarization layer. 

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