Chemical dosing

Fig. 5. Toxic chemical dose—response curves (a) no effect (b) linear effect (c) no effect at low dose and (d) beneficial at low dose.

Piping system Main steam Process steam Feedwater Raw water Treated water Potable water Aux. cooling system Firefighting system Clarified water Filtered water Water-intake system Circulating-water system Chemical dosing Station drains Fuel oil Fuel gas... 

Chemical dosing. This is a connection into the tank with an internal diffuser for any corrective treatment required for the water. 

It thus becomes necessary to preempt the problem by tightly controlling the FW pH, temperature, and residual hardness levels where MU water source contains a high silica level (say, over 20-30 ppm Si02). The location of FW line chemical injection points and the type of chemicals dosed also may influence the risk of silicate sludges and scales developing, and these factors may also need to be considered. 

The consequences of an increase in the cycles of concentration are that as the level of dissolved solids increases, corrosion and deposition tendencies also increase. The result is that, although increasing the cycles of concentration decreases the water requirements of the cooling system, the required amount of chemical dosing also increases. 

Low running cost. The RNDS requires no brine purge and less chemical dosing. As the RNDS uses dechlorinated brine at pH2, additional HC1 is unnecessary, achieving minimal chemical consumption and loss of NaCl. The RNDS consumes a small quantity of caustic soda at desorption. However, compared with former processes, the consumption is almost the same, since the amount of caustic soda needed for neutralising depleted brine is decreased. 

The abatement of chlorine vents and the subsequent destruction of the resulting sodium hypochlorite has been the subject of many studies. There are a variety of approaches to the waste hypochlorite destruction including chemical dosing, homogeneous and slurry catalysis as well as fixed-bed catalysis. For the most part these processes treat the hypochlorite at its natural strength the stoichiometric equivalent strength of the caustic soda fed to the scrubber. 

It should be noted that these considerations apply strictly to the consumables element. In the operation of a chemical dosing unit there is the additional fixed cost of manning the operation which, as noted above, is negligible for the catalytic reactor and process. 

For continuous processes the catalytic reactor, or a hybrid process if satisfactory chemical dosing equipment is already installed, appear to be a near-optimum solution still for many installations. At moderate hypochlorite concentrations, economic benefit does accrue from using the catalyst in-loop rather than end-of-pipe, but these benefits may be offset by any required investment in heat-exchange capability. At concentrations above 10 wt% the integration of decomposition into the scrubbing process is beneficial to the overall cost base of hypochlorite treatment. 

SSDs are being routinely used for the display and interpretation of effects data (Parkhurst et al. 1996 Posthuma et al. 2002). An SSD for atrazine (shown in Figure 7.3) displays the typical S-shaped curve associated with many chemical dose-response relationships. Each point on the curve represents an LC50 for a particular species exposed to atrazine under standard toxicity test protocols. The SSD approach uses only a single statistically derived endpoint from each available toxicity test (e.g., the LC50 or EC50). In contrast, all data collected during any specific toxicity test can be used in a hierarchical model. The ability to use all available data to make inferential decisions is a marked improvement over the standard SSD effects distribution. 

Research is continuing on the main factors that influence oocyst flocculation since variations in chemical dosing, water chemistry or oocyst characteristics could potentially lead to oocyst breakthrough in water treatment plants. In recent years researchers have proposed that the interactions between oocysts and different coagulants may be quite different [Bustamante et al., 2001]. 

Buning, B. C., Noriega, M. T., Sarmiento, Z. F. Malate, R. C. M. 2000. Experimental injection set-up for downhole chemical dosing. In Proceedings World Geothermal Congress 2000, Kyushu-Tohoku, Japan, 28 May-10 June 2000, 3033-3038. 

Water and Effluent Treatment in Nuclear and other chemical plants. Corrosion resistant linings for water treatment vessels and pipelines, pumps, valves, flowmeters, agitators, chemical dosing tanks, effluent tanks etc. Soft natural rubber or ebonite, EPDM, butyl, neoprene or hypalon. 

Variable and often low levels of chemical reserve, leading to a variety of product performance problems. Often as a direct consequence of having no chemical dosing pumps on-site, or inadequate, automatic control systems, or insufficient attention to the quality of makeup water employed, or maintenance of cycles of concentration. 

Knowledge of a competitor s product dose rate and actual chemical consumption may be vital on those occasions when a survey fails to provide even the most basic information required, as can sometimes happen. It should also be remembered that any increase in proposed COC results in a double savings in chemical product consumption, because of a reduced chemical dose rate and less makeup water. 

It is often observed that many operators of the smallest cooling systems (where the rate of change of water quality, chemical reserves, and operating conditions is the most rapid) fail to have adequate chemical dosing... 

Chemical dosing pumps are installed. There is no automatic bleed system installed. 

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