A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications Boilers can be classified into the following configurations
a."Pot boiler" or "Haycock boiler": a primitive "kettle" where a fire heats a partially-filled water container from below.
b.Fire-tube boiler. Here, water partially fills a boiler barrel with a small volume left above to accommodate the steam
c. Water-tube boiler. In this type,the water tubes are arranged inside a furnace in a number of possible configurations: often the water tubes connect large drums, the lower ones containing water and the upper ones, steam and water; in other cases, such as a monotube boiler, water is circulated by a pump through a succession of coils
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Cooling water treatment :
Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or rely solely on air to cool the working fluid to near the dry-bulb air temperature. Common applications include cooling the circulating water used in oil refineries, chemical plants, power stations and building cooling.
An HVAC cooling tower is a subcategory rejecting heat from a chiller
Industrial cooling towers can be used to remove heat from various sources such as machinery or heated process material. The primary use of large, industrial cooling towers is to remove the heat absorbed in the circulating cooling water systems
With respect to drawing air through the tower, there are three types of cooling towers:
 Natural draft, which utilizes buoyancy via a tall chimney. Warm, moist air naturally rises due to the density differential to the dry, cooler outside air. Warm moist air is less dense than drier air at the same pressure. This moist air buoyancy produces a current of air through the tower.
Mechanical draft, which uses power driven fan motors to force or draw air through the tower.
o Induced draft: A mechanical draft tower with a fan at the discharge which pulls air through tower. The fan induces hot moist air out the discharge. This produces low entering and high exiting air velocities, reducing the possibility of recirculation in which discharged air flows back into the air intake. This fan/fill arrangement is also known as draw-through. (see Image 2, 3)
Forced draft: A mechanical draft tower with a blower type fan at the intake. The fan forces air into the tower, creating high entering and low exiting air velocities. The low exiting velocity is much more susceptible to recirculation. With the fan on the air intake, the fan is more susceptible to complications due to freezing conditions. Another disadvantage is that a forced draft design typically requires more motor horsepower than an equivalent induced draft design. The forced draft benefit is its ability to work with high static pressure. They can be installed in more confined spaces and even in some indoor situations. Fan assisted natural draft. A hybrid type that appears like a natural draft though airflow is assisted by a fan.
Hyperboloid (a.k.a. hyperbolic) cooling towers (Image 1) have become the design standard Hyperbolic structures have a negative Gaussian curvature, meaning they curve inward rather than outward or being straight. As doubly ruled surfaces, they can be made with a lattice of straight beams, hence are easier to build and, all else equal, stronger than curved surfaces that do not have a ruling and must instead be built with curved beams.
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Wastewater treatment :
Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations. In the most common usage, it refers to the municipal wastewater that contains a broad spectrum of contaminants resulting from the mixing of wastewaters from different sources.
The composition of wastewater varies widely. This is a partial list of what it may contain:
Water ( > 95%) which is often added during flushing to carry waste down a drain;
Pathogens such as bacteria, viruses, prions and parasitic worms;
Non-pathogenic bacteria (> 100,000 / ml for sewage);
Organic particles such as faeces, hairs, food, vomit, paper fibers, plant material, humus, etc.;
Soluble organic material such as urea, fruit sugars, soluble proteins, drugs, pharmaceuticals, etc.;
Inorganic particles such as sand, grit, metal particles, ceramics, etc.;
Soluble inorganic material such as ammonia, road-salt, sea-salt, cyanide, hydrogen sulfide, thiocyanates, thiosulfates, etc.;
Animals such as protozoa, insects, arthropods, small fish, etc.;
Macro-solids such as sanitary napkins, nappies/diapers, condoms, needles, children's toys, dead animals or plants, body parts, etc.;
Gases such as hydrogen sulfide, carbon dioxide, methane, etc.;
Emulsions such as paints, adhesives, mayonnaise, hair colorants, emulsified oils, etc.;
Toxins such as pesticides, poisons, herbicides, etc.
Industrial water treatment seeks to manage four main problem areas: scaling, corrosion, microbiological activity and disposal of residual wastewater.
Boilers do not have many problems with microbes as the high temperatures prevents their growth.
Scaling occurs when the chemistry and temperature conditions are such that the dissolved mineral salts in the water are caused to precipitate and form solid deposits. These can be mobile, like a fine silt, or can build up in layers on the metal surfaces of the systems. Scale is a problem because it insulates and heat exchange becomes less efficient as the scale thickens, which wastes energy. Scale also narrows pipe widths and therefore increases the energy used in pumping the water through the pipes.
Corrosion occurs when the parent metal oxidises (as iron rusts, for example) and gradually the integrity of the plant equipment is compromised. The corrosion products can cause similar problems to scale, but corrosion can also lead to leaks, which in a pressurised system can lead to catastrophic failures.
Microbes can thrive in untreated cooling water, which is warm and sometimes full of organic nutrients, as wet cooling towers are very efficient air scrubbers. Dust, flies, grass, fungal spores and so on collect in the water and create a sort of "microbial soup" if not treated with biocides. Most outbreaks of the deadly Legionnaires' Disease have been traced to unmanaged cooling towers, and the UK has had stringent Health & Safety guidelines concerning cooling tower operations for many years as have had governmental agencies in other countries
Disposal of residual wastewaters[1] from an industrial plant is a difficult and costly problem. Most petroleum refineries, chemical and petrochemical plants [2] have onsite facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the local and/or national regulations regarding disposal of wastewaters into community treatment plants or into rivers, lakes or oceans.
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