Scale build up

Scale results from crystalline precipitation on metal surfaces with die formation of a hard bonded crust. 

This is the first salt likely to precipitate out in water, according to the following reaction  

The shift in equilibrium to the right with formation and crystallization of calcium carbonate is influenced by  

The solubility of this salt increases as the temperature rises, reaches a maximum at 40°C and then decreases. 

Solubility product SP of calcium sulfate in pure water versus temperature. (Water Treatment Handbook, Degremont, 1989) 

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Control of scale build-up in re-circulating toilet lines... 

This formulation is designed to be used "as is" and is particularly effective in the removal of scale build-up and rust stains. 

Heat-exchanger fouling, or scale build-up, can be a major factor limiting the kind and concentration of solids in feed that can be processed. The plugging problem can be dealt with by periodically flushing the exchanger with warm water or diluted nitric acid, as in conventional processes. 

Sometimes people refer to water as being "hard" or "soft." If someone says water is hard, he means that there are a lot of calcium (Ca2+) or magnesium (Mg2+) ions dissolved in it. Hard water causes several problems. First, it can cause scales to form on the inside of pipes, water heaters, or teakettles. These scales occur when the calcium or magnesium precipitates out of solution and sticks to the insides of pipes. The scales build up and eventually the pipes are completely clogged. Hard water also prevents soap from lathering, and it reacts with soap to leave behind a sticky film commonly called soap scum. 

Polymeric dispersant and protective colloid for yarn and fabric preparation and bleaching. Minimises scale build-up on hot metal surfaces and fabric. Extremely efficient dispersant for cotton linters and particulate soil. Provides a cleaner fabric after washing-off without drainage marks. Improves absorbency and dyeing properties. 

Calculate the heat transferred from the water to the propane (kJ/m propane fed). Hint Do an energy balance on either the water or the propane rather than on the entire heat exchanger.) Over a period of time, scale builds up on the heat transfer surface, resulting in a lower rate of heat transfer between the propane and the steam. What changes in the outlet streams would you expect to see as a result of the decreased heat transfer ... 

Figure 5 shows the third possibility for the relative positions of the heat generation and heat removal lines. This represents the critical state. That is, there is only one point of intersection between the two curves, only one point at which the heat removal rate is exactly equal to the heat generation rate. This is a point of equilibrium, but if the rate of heat generation should increase (through an impurity which acts as a catalyst, for example), or the rate of heat removal should decrease (e.g., through scale build-up or an increase in the temperature of the coolant), a runaway situation will occur. This critical point is often referred to as the Temperature of No Return, T r. (5) Note that this is the temperature of the reaction mass and not the temperature of the coolant. 

Sulfite pulping chemical recovery consists of greater amounts of sulfite, hydrogen sulfide, and hydrochloric acid than those used in the Kraft process. Because of these corrosive species, the internal portions of the recovery boilers and the evaporators are generally constructed of reinforced plastics, type 316L stainless steel, type 317L stainless steel, or nickel-based alloys. To prevent pitting and crevice corrosion, scale build-up should be prevented, wet-dry zones should be avoided, and chloride concentration should be kept to a minimum. 

Other problems that limit production rates in either longitudinally fired or side-fired bottom zones are restricted gas passages in the bottom zones, and low-velocity luminous flame burners. Low-velocity luminous flames with their variable temperature profiles (hot at the burner wall at low firing rates, and hotter beyond the T-sensor at high firing rates) cause the melting of scale into the bottom zones. To counter this scale build-up problem, operators are prone to lower the bottom zone temperature by 100 F (56 C) or more. 

When excessive scale build-up occurs, it is often because of a problem with temperature measurement. Scale is oxide on the load surfaces. To melt scale, the temperature must exceed 2490 F (1365 C). If the control thermocouple is reading below this melting point, but scale is a problem, it becomes necessary to check the temperature measurement. Problems that may cause a T-sensor reading lower than the true furnace temperature are ... 

If the protective current induces precipitation of an inorganic scale on the cathode surface, such as in hard waters or in seawater, the total required current, as described earlier, falls off as the scale builds up. However, at exposed areas of metal, the current density remains the same as before scale formation only the total current density per apparent unit area is less. 

Finally, the stainless-steel bipolar plate consists of a separator and current collectors. The plate is exposed to the anodic environment on one side and the cathodic environment on the other. The low oxygen partial pressure on the anodic side of the bipolar plate prevents the formation of a protective oxide coating and, on the cathode side, the contact electrical resistance increases as an oxide scale builds up. Active research is focused on finding alloys for bipolar current-collector materials that function well in both anodic and cathodic environments, have a low cost and ohmic resistance, and have good corrosion resistance [15]. 

Table 1 shows that some inhibitors are active in CO2 corrosion at pH 4 where it is believed that no iron ceirbonate scale builds up, while others are only effective at the higher pH where a certain amount of passivation occurs due to iron carbonate buildup. Indeed, the inhibitors of the first kind are also the most effective ones against flow induced localized corrosion (also cedled Mesa corrosion ), where due to high turbulences the protective iron carbonate is washed away. However, some interesting observations were made when carbon steel was precorroded in a CO2 environment [65]. Figure 9 shows that, at a constant inhibitor... 

In fact, the practical balance of calcium bicarbonate with carbon dioxide (CO2) is governed by fairly complex relationships. A shift in the balance can cause chemical reactions that either dissolve calcium carbonate (i.e. aggressivity) or precipitate it (i.e. scale build up). These reactions may be compounded by electrochemical corrosion processes that are specific to metals. 

Key areas of use for POMs are industrial and mechanical products that include molded or machined rollers, bearing, gear, conveyor chains, and housings. POMs are widely used in plumbing and irrigation because they resist scale build up, and have excellent... 

The Goodway GDS-C92 removes tough scale build-up quickly, safely and easily. 

The erosion-corrosion behaviour of the aluminized 12% chromium steel changes in the temperature range from 600°C to 650°C. This is due to a shift in the erosion behaviour of the coating from brittle to ductile , and to a more rapid oxide scale build-up at temperatures above 600°C. 

The amplitude of oscillation in torque-time curve or that of the ram movement decreases as the contents becomes more homogeneous. In order to use these or total energy for deciding the endpoint, the dispersion must be examined ahead of time to assure a satisfactory result. The reproducibility in the same type mixer but different machines may be a problem. There may be a difference in the extent of wear of the rotor blades. The cooling surface may have scale build-up such that the cooling efficiency may be different. 

Internal corrosion of the down-comer pipe is a common problem. Build-up of sediment on the walls or bottom of the treater can cause the interface levels to rise and liquid to carry over and/or oil to exit the treater with salt water. Bi-annual inspections should be performed to include internal inspection for corrosion, sediment build-up, and scale build-up. 

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