Chemical feeder process

Figure I. Deionized-alkaline system by chemical feeder process Dl is deionized water alkaline earth is a divalent compound, i.e., Ca+2 or Mg+2.

Table I. Water Analyses from Chemical Feeder Process...

The Deionized Water-Alkaline System. The DI—Ca water analyses from the chemical feeder process are shown in Table I. As the amount of calcium ions in the deionized water was increased, the conductivity values became higher. The amounts of calcium in the Dl-Ca water can be measured by conductivity. The pH of the deionized water was 6.3. The pH of saturated calcium hydroxide solution is 12.3. Addition of 9.2 ppm Ca as Ca(OH)2 in the deionized water raised the pH to 9.9. The level of the pH increased with additional amounts of calcium ions in the DI water. The measurement and adjustment of the calcium solution flow was essential, both for washing and for the deacidification efficiency. 

Table II shows the calcium content in paper from the chemical feeder process. With the addition of 9.2 ppm Ca in DI water, the treated newsprint papers calcium content doubled in comparison with the control. The treated Foldur Kraft paper contained three times more calcium than did the unwashed paper. The more calcium that was added in the DI water, the higher the amounts of calcium absorbed in the papers during the washing and deacidification process. However, the absorption of calcium in the paper reached a saturation point. This is the reason why newsprint and Foldur Kraft papers that are treated with 36.4 ppm Ca in the Dl-Ca water imbibed the same amount of calcium as the papers washed with 112.8 ppm Ca in the Dl-Ca water.

Figure 2. Foldur Kraft paper washed for 1 h in chemical feeder process...

Use of a chemical feeder allows the conservator to wash paper with deionized water containing added calcium ions, wash and deacidify simultaneously, or to directly deacidify paper. Examples of these processes are given in which varying ratios of alkali were fed to deionized water. The resultant alkaline reserves produced in two types of papers are shown. 

Process equipment Typical process equipment will include (a) chemical feeders, (b) mixers, and (c) automatic controls. 

Select another chemical feeder setting and repeat the process. 

Dry chemical solution systems use dry chemical feeders to meter the chemical. The solution part of the system is used to predissolve the chemical or to help disperse the chemical more efficiently into the process water stream. The chemical is measured by the dry chemical feeder. The flow of water through the solution part of the system does not affect the amount fed because the entire chemical from the dry feeder is delivered to the application point. The flow of solution water and the size of the dissolving tank do, however, affect the time needed to deliver the chemical from the feeder to the application point. This delay can be problematic for control systems because changes in dosage are not instantaneous. It may take many minutes or hours to see the result of a chemical change. In addition, insoluble dry chemicals, such as activated carbon, may develop clogs in long pipelines from the solution tank to injection point. 

Liquid chemical feed calculations are the subject of chapter 8. This chapter includes the calculations for dry chemical feed either directly into process water or first into dissolving or slurry tanks, and to prepare solution batches. All dry chemical feeders are calibrated as needed to ensure accurate delivery of the chemical. 

Solid (or dry) chemicals are sometimes used to prepare solutions for feeding. Many operators prefer to feed chemicals with metering pumps rather than dry feed equipment. Also, mixing liquid chemicals into the process water stream usually is more efficient. A weighted amount (using a continuous dry chemical feeder or a batch preparation approach) of the dry chemical is mixed with water to prepare the desired solution strength. Then the liquid is metered into the process water in the usual way. 

One of the principal contributions of electronic data processing over the past several years in terms of chemical analysis is the saving of manual effort in interpreting analytical data. Special techniques, such as Fourier transform, have increased speed (as well as sensitivity) by orders of magnitude in connection with infrared, nuclear magnetic resonance, and mass spectroscopy, Of course, for on-line process analyses, essentially instantaneous interpretation is required to provide the proper error signal that is used to position the final control element (valve, feeder, damper, etc.). 

As sediments act as pollutant sinks in aquatic systems, they can be important sources of exposure, and so of the entry of chemicals into aquatic food chains. Sediments are the ultimate residence location for many pollutants released to water. The widespread presence of complex mixtures of contaminants in sediment is thus likely to occur in any location where multiple localized and diffuse contaminant sources contribute to the overall chemical load within natural waters. The role of sediment in the receipt and resupply of the chemical to the water phase means that there is interest in monitoring sediment chemical pollutant load over both different spatial and temporal scales. Because the process of sediment deposition and chemical adsorption on the one hand and solubilization and resuspension on the other link the pollutant loads of the sediment and water column, many of the species that can be used to sample the environment for waterborne pollutants (e.g., filter feeders such as mussels) can also describe the pollutant load present in sediments (Baumard et al. 1998). 

These equipment items are used to store feed and, in some cases, process bulk solids. The design of economical hopper systems is dependent on the physical, chemical, and flow properties of the materials being stored. It is essential to provide bin, hopper, and feeder designs to enhance the flow of the material from the hopper and to minimize potential problems. 

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