Boilers water supply

As it turned out, ideas such as injecting catalyst into the beds via feed tubes were never realized because of a forced roast/acid shutdown in July 1999. Failure of the boiler water supply system resulted in a boiler tube rupture necessitating a total stoppage for three days. During this time, the No. 4 catalyst bed was opened. A sample of catalyst taken from the bed was analyzed and was foimd to have close to 100% activity. Some 2,000 liters of new catalyst were added and the plant was restarted. Little or no decrease in emissions was found and, consequently, a study to finally solve the problem was initiated. The options considered included ... 

EC is effective in water treatment for drinking water supply, membrane pre-treatment, marine operation, and boiler water supply for small systems. It is very effective in treating colloids found in natural water by reducing turbidity and colour as well as removing suspended solids, oil and grease, iron, silicates, humus and microorganisms. A comprehensive summary of pollutants removed by EC is given in [24]. 

Abundant supplies of fresh water are essential to the development of industry. Enormous quantities are required for the cooling of products and equipment, for process needs, for boiler feed, and for sanitary and potable water supply. 

Utilities and yard services (boiler plant, refrigeration, compressed air, water supply and treatment, effluents, fire protection, yard piping, yard electrical, yard materials handling, raw and finished-product storage)... 

The centrifugal pump is the type most widely used in the chemical industiy for transferring liquids of aU types—raw materials, materials in manufacture, and finished produc ts—as well as for general services of water supply, boiler feed, condenser circulation, condensate return, etc. These pumps are available through avast range of sizes, in capacities from 0.5 mVh to 2 X 10 mVh (2 gal/min to 10 gaJ/min), and for discharge heads (pressures) from a few meters to approximately 48 MPa (7000 Ibf/iu"). The size and type best suited to a particular apphcation can be determined only by an engineering study of the problem. 

The efficiency of water separation varies considerably from boiler to boiler. The purity of the steam supplied to a steam turbine should be checked. On the basis of the results, the maximum allowable salt concentration in the boiler water can be determined. This concentration may be much lower than the values given in the table. 

In addition to varying in costs, the chemical composition of the water provided from the mains supply also varies between the water companies, as may that between independent supplies within each company s area. The current criterion on potable water quality requires it to be wholesome i.e. it should not create a health hazard, with relatively wide limits on particular constituents. The cost of removing these constituents (e.g. calcium, magnesium, chlorides, iron and silica) increases with concentration and variability. This imposes a cost burden on, for example, the semiconductor and electronic component industries and on the operation of high-pressure boilers. Therefore both the potential cost of metered water supply and the chemical composition of the supply waters may influence future decisions on the water company s area in which an industry may wish to locate. 

Where joints are unavoidable, they should be welded. Steam coils should drain freely from inlet to outlet. Steam traps, usually of the bucket type, should also be provided. Condensate from steam coils should be drained to waste, unless adequate provision is made to drain trace quantities before return to the hotwell. Where hot-water coils are used, the water supply should be heated through a calorifier. These recommendations will avoid any risk of oil reaching the boiler plant. 

This is a condition which occurs when the feedwater pump is unable to deliver feedwater to the boiler although the feed tank has water available. The temperature of the feed-water coupled with the possible suction effect from the feedwater pump in the line between the feed tank and the pump effectively drops the pressure, causing the feed-water to flash to steam. The pump then loses its water supply. 

Boiler feedwater may be from various supplies. If it is from a main water supply, further filtering prior to treatment is unlikely, but for other supplies such as borehole, lakes, rivers and canals, filters may be required. Impurities in water may be classed as dissolved solids, dissolved gases and suspended matter and suitable treatment is required. 

The water supply for boilers is usually treated. Treatment depends on the quality of the water supply, the pressure of the boiler, the heat flux through the tube walls and the steam quality required. Most waters require de-alkalization. The water produced in this process is nonscaling and potentially corrosive (see above). 

For many years the sole method of purification available was by distillation, and distilled water was universally employed for laboratory purposes. The modern water-still is usually made of glass and is heated electrically, and provision is made for interrupting the current in the event of failure of the cooling water, or of the boiler-feed supply the current is also cut off when the receiver is full. 

External to the boiler itself are various pre-boiler and post-boiler water subsystems. These include the MU water pretreatment system, FW supply system, and steam-condensate recovery system, again of varying complexity depending on the design and size of the boiler. 

Apart from the provision of various permutations of (chemical-based) boiler water programs, it is common to find water treatment companies supplying value adding chemicals and services in other boiler plant-related areas where their expertise in applied chemical technology can deliver additional economic benefit. Such areas typically include cleaning services for boiler waterside and fireside and the provision of fuel treatments and combustion additives, dust suppressants (for coal and ash handling), acids, and cleaner products. 

Where the MU water supply to cast-iron boilers does not precisely keep up with steam generation demands, the water level can quickly decrease and the problems become even more acute. Conversely, where MU does precisely keep up with steaming rates and is supplied to a common condensate receiver-FW tank via automatic level control, the tank can easily overfill when condensate finally drains back under on-off operating conditions. This gives rise to a loss of valuable hot, treated water from the system and the start of another chain of cause and effect problems. 

Although the presence of hardness is reported as calcium carbonate, in reality, for most water supplies the most common major contributors to total dissolved solids are calcium and magnesium bicarbonates. These dissolved solids most readily produce crystalline scales and thus predominantly contribute to boiler system deposits unless removed by some form of pre-boiler, external treatment process. 

This summary all but excludes FT boilers of any description from the requirement to have high-quality (i.e., low TDS) MU water. Exceptions are those FT boilers that have very low rates of CR and/or a high alkalinity MU water supply, and some special purpose boilers. 

NOTE As an example, 90% of water supplied to New York City has a total hardness below 15 to 20 ppm CaCOy Pretreatment softeners are not the norm and consequently there are many thousands of nondomestic LP steam boilers (in addition to greater numbers of domestic LP steam boilers) in daily operation, where the FW hardness is 2 to 5 ppm or more as CaCOy The BSI 2486 1978 table for shell boilers remains a valid standard for these commercial and institutional boilers. 

High levels of silica in the raw water supply can lead to serious risks of deposition in boilers, especially if cycles of concentration (COC) also are high. The incoming silica can be reduced by adsorption on magnesium hydroxide [Mg(OH)2] precipitate during lime-softening processes, or by the addition of magnesium hydroxide in a reaction tank, followed by filtration. 

The water supplied to a boiler by the FW pump and consisting of a combination of CR and MU water. 

For a similar reason the powerhouse, boilers, water pumping, and air supply facilities should be located 250 ft (75 m) from the rest of the plant, and on the upwind side. This is to minimize the possibility that these facilities will be damaged in case of a major spill. This is especially important for the first two items, where there are usually open flames. 

In modern high-pressure systems, blowdown water is normally of better quality than the water supply. This is because plant intake water is treated using clarification, filtration, lime/lime soda softening, ion exchange, evaporation, and in a few cases reverse osmosis to produce makeup for the boiler feedwater. The high-quality blowdown water is often reused within the plant for cooling water makeup or it is recycled through the water treatment and used as boiler feedwater. 

Other problems with ion exchangers include coating of the resin beads or zeolite particles with suspended matter from turbid water (pretreatment with a coagulant may be necessary) or algal growths (chlorination of the water may be required). Zeolites may cause significant silica carryover and should not be used to treat boiler water for steam turbines. Finally, although Ca2+ and Mg2+ are objectionable in boiler or laundry operations, they are necessary nutrients in the human diet. Furthermore, excessive consumption of Na+ can contribute to hypertension and other blood circulatory problems. In Canada, for example, the incidence of heart disease and related health problems is lower in areas where the water supply is... 

There is another problem with the barometric condenser that did not become apparent at first. When the British Navy decided to convert from sail to steam, this problem was immediately obvious. While steam can be generated from seawater, it is far better to use freshwater, especially if one wishes to generate high-temperature, high-pressure steam. And as freshwater supplies are limited at sea, it would be great if the condensed steam could be recycled to the boilers. But the cooling-water supply to the barometric condensers was naturally seawater which mixed with the steam condensate. 

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