INTRODUCTION TO INDUSTRIAL CHEMISTRY

CHM 331 INTRODUCTION TO INDUSTRIAL CHEMISTRY LECTURE NOTES WASTEWATER TREATMENT The principal objective of wastewater treatment is generally to allow human and industrial effluents to be disposed of without danger to human health or unacceptable damage to the natural environment. Irrigation with wastewater is both disposal and utilization and indeed is an effective form of wastewater disposal (as in slowrate land treatment). However, some degree of treatment must normally be provided to raw municipal wastewater before it can be used for agricultural or landscape irrigation or for aquaculture. The quality of treated effluent used in agriculture has a great influence on the operation and performance of the wastewatersoil-plant or aquaculture system. Wastewater treatment is the process of converting wastewater – water that is no longer needed or is no longer suitable for use – into bilge water that can be discharged back into the environment. It is formed by a number of activities including bathing, washing, using the toilet, and rainwater runoff. Wastewater is full of contaminants including bacteria, chemicals and other toxins. Its treatment aims at reducing the contaminants to acceptable levels to make the water safe for discharge back into the environment. There are two wastewater treatment plants namely chemical or physical treatment plant, and biological wastewater treatment plant. Biological waste treatment plants use biological matter and bacteria to break down waste matter. Physical waste treatment plants use chemical reactions as well as physical processes to treat wastewater. Biological treatment systems are ideal for treating wastewater from households and business premises. Physical wastewater treatment plants are mostly used to treat wastewater from industries, factories and manufacturing firms. This is because most of the wastewater from these industries contains chemicals and other toxins that can largely harm the environment. Step by Step Wastewater Treatment Process The following is a step by step process of how wastewater is treated: 1. Wastewater Collection This is the first step in waste water treatment process. Collection systems are put in place by municipal administration, home owners as well as business owners to ensure that all the wastewater is collected and directed to a central point. This water is then directed to a treatment plant using underground drainage systems or by exhauster tracks owned and operated by business people. The transportation of wastewater should however be done under hygienic conditions. The pipes or tracks should be leak proof and the people offering the exhausting services should wear protective clothing. 2. Odour Control At the treatment plant, odour control is very important. Wastewater contains a lot of dirty substances that cause a foul smell over time. To ensure that the surrounding areas are free of the foul smell, odour treatment processes are initiated at the treatment plant. All odour sources are contained and treated using chemicals to neutralize the foul smell producing elements. It is the first wastewater treatment plant process and it is very important. 3. Screening This is the next step in wastewater treatment process. Screening involves the removal of large objects for example nappies, cotton buds, plastics, diapers, rags, sanitary items, face wipes, broken bottles or bottle tops that in one way or another may damage the equipment. Failure to observe this step, results in constant machine and equipment problems. Specially designed equipment is used to get rid of grit that is usually washed down into the sewer lines by rainwater. The solid wastes removed from the wastewater are then transported and disposed off in landfills. 4. Primary Treatment This process involves the separation of macrobiotic solid matter from the wastewater. Primary treatment is done by pouring the wastewater into big tanks for the solid matter to settle at the surface of the tanks. The sludge, the solid waste that settles at the surface of the tanks, is removed by large scrappers and is pushed to the center of the cylindrical tanks and later pumped out of the tanks for further treatment. The remaining water is then pumped for secondary treatment. 15. Secondary Treatment Also known as the activated sludge process, the secondary treatment stage involves adding seed sludge to the wastewater to ensure that is broken down further. Air is first pumped into huge aeration tanks which mix the wastewater with the seed sludge which is basically small amount of sludge, which fuels the growth of bacteria that uses oxygen and the growth of other small microorganisms that consume the remaining organic matter. This process leads to the production of large particles that settle down at the bottom of the huge tanks. The wastewater passes through the large tanks for a period of 3-6 hours. 6. Bio-solids handling The solid matter that settle out after the primary and secondary treatment stages are directed to digesters. The digesters are heated at room temperature. The solid wastes are then treated for a month where they undergo anaerobic digestion. During this process, methane gases are produced and there is a formation of nutrient rich bio-solids which are recycled and dewatered into local firms. The methane gas formed is usually used as a source of energy at the treatment plants. It can be used to produce electricity in engines or to simply drive plant equipment. This gas can also be used in boilers to generate heat for digesters. Here, bacteria break down (digest) the material, reducing its volume, odours, and getting rid of organisms that can cause disease. The finished product is mainly sent to landfills, but sometimes can be used as fertilizer. 7. Tertiary treatment This stage is similar to the one used by drinking water treatment plants which clean raw water for drinking purposes. The tertiary treatment stage has the ability to remove up to 99% of the impurities from the wastewater. This produces effluent water that is close to drinking water quality. Unfortunately, this process tends to be a bit expensive as it requires special equipment, well trained and highly skilled equipment operators, chemicals and a steady energy supply. All these are not readily available. 8. Disinfection After the primary treatment stage and the secondary treatment process, there are still some diseases causing organisms in the remaining treated wastewater. To eliminate them, the wastewater must be disinfected. The process of destroying all the bacteria (either harmful or harmless) is known as sterilization. But in a water supply scheme, we require only the removal of harmful bacteria (pathogenic bacteria) which may cause waterborne diseases like cholera, dysentery, typhoid, etc. The process of destroying harmful bacteria from water and making it safe for drinking is known as disinfection. Common methods of disinfection include using ozone, chlorine, iodine or bromine, excess lime, potassium permanganate, silver, or ultraviolet light. Chlorination remains the most common form of wastewater disinfection in some places due to its low , reliability and long-term history of effectiveness. The water is held for at least 20-25 minutes in tanks that contain a mixture of chlorine and sodium hypochlorite. Chlorine contact basins are usually rectangular channels, with baffles to prevent shortcircuiting, designed to provide a contact time of about 30 minutes. However, to meet advanced wastewater treatment requirements, a chlorine contact time of as long as 120 minutes is sometimes required for specific irrigation uses of reclaimed wastewater. The bactericidal effects of chlorine and other disinfectants are dependent upon pH, contact time, organic content, and effluent temperature. One disadvantage is that chlorination of residual organic material can generate chlorinated-organic compounds that may be carcinogenic or harmful to the environment. Residual chlorine or chloramines may also be capable of chlorinating organic material in the natural aquatic environment. Further, because residual chlorine is toxic to aquatic species, the treated effluent must also be chemically dechlorinated, adding to the complexity and cost of treatment. Chloramine, which is used for drinking water, is not used in wastewater treatment because of its persistence. Ultraviolet (UV) light can be used instead of chlorine, iodine, or other chemicals. Because no chemicals are used, the treated water has no adverse effect on organisms that later consume it, as may be the case with other methods. UV radiation causes damage to the genetic structure of bacteria, viruses, and other pathogens, making them incapable of reproduction. The key disadvantages of UV disinfection are the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that the target microorganisms are not shielded from the UV radiation (i.e., any solids present in the treated effluent may protect microorganisms from the UV light). In some countries, light is becoming the most common means of 2disinfection because of the concerns about the impacts of chlorine in chlorinating residual organics in the wastewater and in chlorinating organics in the receiving water. Ozone O3 is generated by passing oxygen O2 through a high voltage potential resulting in a third oxygen atom becoming attached and forming O3. Ozone is very unstable and reactive and oxidizes most organic material it comes in contact with, thereby destroying many pathogenic microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which has to be stored on site (highly poisonous in the event of an accidental release), ozone is generated onsite as needed. Ozonation also produces fewer disinfection byproducts than chlorination. A disadvantage of ozone disinfection is the high cost of the ozone generation equipment and the requirements for special operators. The disinfection process is an integral part of the treatment process because it guards the health of the animals and the local people who use the water for other purposes. The effluent (treated waste water) is later released or discharged into the environment (local river or ocean) through the local water ways. 9. Sludge Treatment The sludge that is produced and collected during the primary and secondary treatment processes requires concentration and thickening to enable further processing. It is put into thickening tanks that allow it to settle down and later separates from the water. This process can take up to 24 hours. The remaining water is collected and sent back to the huge aeration tanks for further treatment. The sludge is then treated and sent back into the environment and can be used for agricultural use. Wastewater treatment has a number of benefits. For example, wastewater treatment ensures that the environment is kept clean, there is no water pollution, makes use of the most important natural resource; water, the treated water can be used for cooling machines in factories and industries, prevents the outbreak of waterborne diseases and most importantly, it ensures that there is adequate water for other purposes like irrigation. Conclusion Wastewater treatment process is one of the most important environmental conservation processes that should be encouraged worldwide. Most wastewater treatment plants treat wastewater from homes and business places. Industrial plant, refineries and manufacturing plants wastewater is usually treated at the onsite facilities. These facilities are designed to ensure that the wastewater is treated before it can be released to the local environment. Some of the water is used for cooling the machines within the plants and treated again. They try to ensure that nothing is lost. It is illegal for disposing untreated wastewater into rivers, lakes, oceans or into the environment and if found culpable one can be prosecuted according to the Laws of all countries including the Gambia. In environmental chemistry, the chemical oxygen demand (COD) test is commonly used to indirectly measure the amount of organic compounds in water. Most applications of COD determine the amount of organic pollutants found in surface water (e.g. lakes and rivers) or wastewater, making COD a useful measure of water quality. It is expressed in milligrams per litre (mg/L) also referred to as ppm (parts per million), which indicates the mass of oxygen consumed per litre of solution. Biochemical oxygen demand is a measure of the quantity of oxygen used by microorganisms (e.g., aerobic bacteria) in the oxidation of organic matter. Natural sources of organic matter include plant decay and leaf fall. Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. 3Process Flow Diagram for a typical large-scale treatment plant PRODUCTION OF IRON The Blast Furnace is used in the extraction of iron from iron ore, and the conversion of the raw iron from the furnace into various kinds of steel. Extracting iron from iron ore using a Blast Furnace The common ores of iron are both iron oxides, and these can be reduced to iron by heating them with carbon in the form of coke. Coke is produced by heating coal in the absence of air. Coke is cheap and provides both the reducing agent for the reaction and also the heat source. Iron ores: The most commonly used iron ores are haematite, Fe2O3, and magnetite, Fe3O4. The Blast Furnace 4The heat source: The air blown into the bottom of the furnace is heated using the hot waste gases from the top. Heat energy is valuable, and it is important not to waste any. The coke (essentially impure carbon) burns in the blast of hot air to form carbon dioxide - a strongly exothermic reaction. This reaction is the main source of heat in the furnace. The reduction of the ore: At the high temperature at the bottom of the furnace, carbon dioxide reacts with carbon to produce carbon monoxide. It is the carbon monoxide which is the main reducing agent in the furnace. In the hotter parts of the furnace, the carbon itself also acts as a reducing agent. Notice that at these temperatures, the other product of the reaction is carbon monoxide, not carbon dioxide. The temperature of the furnace is hot enough to melt the iron which trickles down to the bottom where it can be tapped off. The function of the limestone Iron ore isn't pure iron oxide - it also contains an assortment of rocky material. This wouldn't melt at the temperature of the furnace, and would eventually clog it up. The limestone is added to convert this into slag which melts and runs to the bottom. 5The heat of the furnace decomposes the limestone to give calcium oxide. This is an endothermic reaction, absorbing heat from the furnace. It is therefore important not to add too much limestone because it would otherwise cool the furnace. Calcium oxide is a basic oxide and reacts with acidic oxides such as silicon dioxide present in the rock. Calcium oxide reacts with silicon dioxide to give calcium silicate. The calcium silicate melts and runs down through the furnace to form a layer on top of the molten iron. It can be tapped off from time to time as slag. Slag is used in road making and as "slag cement" - a final ground slag which can be used in cement, often mixed with Portland cement. Cast iron: The molten iron from the bottom of the furnace can be used as cast iron. Cast iron is very runny when it is molten and doesn't shrink much when it solidifies. It is therefore ideal for making castings - hence its name. However, it is very impure, containing about 4% of carbon. This carbon makes it very hard, but also very brittle. If you hit it hard, it tends to shatter rather than bend or dent. Cast iron is used for things like manhole covers, cast iron pipes, valves and pump bodies in the water industry, guttering and drainpipes, cylinder blocks in car engines, Aga-type cookers, and very expensive and very heavy cookware. Steel: Most of the molten iron from a Blast Furnace is used to make one of a number of types of steel. There isn't just one substance called steel - they are a family of alloys of iron with carbon or various metals. Methods for manufacturing steel have evolved significantly since industrial production began in the late 19th century. Modern methods, however, are still based the same premise as the Bessemer Process, namely, how to most efficiently use oxygen to lower the carbon content in iron. Today, steel production comes from both recycled as well as the tradition raw materials, iron ore, coal and limestone. Two processes; basic oxygen steelmaking (BOS) and electric arc furnaces (EAF) account for virtually all steel production. Modern Production Process: Steel production can be broken down into six steps: 1. Iron making: In the first step, the raw inputs iron ore, coke and lime are melted in a blast furnace. The resulting molten iron - also referred to as 'hot metal' - still contains 4-4.5% carbon and other impurities that make it brittle. 2. Primary Steelmaking: Primary steelmaking methods differ between BOS and EAF methods. BOS methods add recycled scrap steel to the molten iron in a converter. At high temperatures, oxygen is blown through the metal, which reduces the carbon content to between 0-1.5%. EAF methods, alternatively, feed recycled steel scrap through use high power electric arcs (temperatures up to 1650 °C) to melt the metal and convert it to high quality steel. 3. Secondary Steelmaking: Secondary steelmaking involves treating the molten steel produced from both BOS and EAF routes to adjust the steel composition. This is done by adding or removing certain elements and/or manipulating the temperature and production environment. 64. Continuous Casting: In this step, the molten steel is cast into a cooled mould causing a thin steel shell to solidify. The shell strand is withdrawn using guided rolls and fully cooled and solidified. The strand is cut into desired lengths depending on application; slabs for flat products (plate and strip), blooms for sections (beams), billets for long products (wires) or thin strips. 5. Primary Forming: The steel that is cast is then formed into various shapes, often by hot rolling, a process that eliminates cast defects and achieves the required shape and surface quality. Hot rolled products are divided into flat products, long products, seamless tubes, and specialty products. 6. Manufacturing, Fabrication, and Finishing: Finally, secondary forming techniques give the steel its final shape and properties. These techniques include:  shaping (e.g. cold rolling)  machining (e.g. drilling)  joining (e.g. welding)  coating (e.g. galvanizing)  heat treatment (e.g. tempering)  surface treatment (e.g. carburizing) Electric Arc Furnace  An electric arc furnace makes new steel from old steel scrap. It is a giant lidded steel kettle lined with heat-resistant ceramic refractory material. Its lid lifts up for loading with scrap. The lid also holds the three graphite electrodes that create the electric arc to melt the scrap into new steel. After loading, the electrodes are lowered into the scrap and power fed to the furnace. Electricity arcs between the electrodes, creating the heat needed to melt the steel scrap. Fluxing compounds remove impurities. To obtain additional heat, steelmakers inject pulverized coal and oxygen to supplement the electrical heat. Roughly a third of the heat in electric arc furnaces comes from the injection of fuel and oxygen. Basic Oxygen Furnace  A basic oxygen furnace, or BOF, creates steel from molten pig iron produced from iron ore in a blast furnace, together with up to 25 percent scrap steel. This furnace works by injecting high-pressure oxygen into the molten iron to burn out excess carbon and other combustible impurities. Fluxing compounds added to the melt remove noncombustible impurities that float to the top of the melt as slag. The BOF gets the energy needed to convert iron into steel from the original heat of the molten iron together with the heat generated by burning off excess carbon and other impurities in the presence of pure oxygen. Arc Pros and Cons  An electric arc furnace provides precise control of the internal atmosphere and temperature. It emits almost no pollution. Because it starts with scrap metal, an electric arc furnace is economical compared to other steelmaking processes for small-batch steelmaking. But, electric arc furnaces require access to excessive electricity and road or rail access to bring in a steady supply of scrap metal. BOF Pros and Cons  The basic oxygen furnace doesn’t burn fuel, so it is cost efficient, but it does require the separate creation of molten iron by burning coke in a blast furnace to melt the iron from its ore. Because a BOF uses the inherent heat of molten iron as an energy source, efficient operation requires batches averaging 250 tons. Unlike the minimal emissions of an electric arc furnace, a basic oxygen furnace emits a relatively great amount of polluting gases and dust that require costly treatment through air scrubbers, electrostatic precipitators and filters before they can be released into the atmosphere. When both types of furnaces are finished, they pour the molten 7steel into a vessel called a “teeming ladle” that carries the melted metal to a nearby mill, where it will be cast or forged into products. Steel-making: the basic oxygen process Impurities in the iron from the Blast Furnace include carbon, sulphur, phosphorus and silicon. These have to be removed. Removal of sulphur: Sulphur has to be removed first in a separate process. Magnesium powder is blown through the molten iron and the sulphur reacts with it to form magnesium sulphide. This forms a slag on top of the iron and can be removed. Removal of carbon etc: The still impure molten iron is mixed with scrap iron (from recycling) and oxygen is blown on to the mixture. The oxygen reacts with the remaining impurities to form various oxides. The carbon forms carbon monoxide. This carbon monoxide can be cleaned and used as a fuel gas. Elements like phosphorus and silicon react with the oxygen to form acidic oxides. These are removed using quicklime (calcium oxide) which is added to the furnace during the oxygen blow. They react to form compounds such as calcium silicate or calcium phosphate which form a slag on top of the iron. Types of iron and steel: Cast iron has already been mentioned above. Wrought iron: If all the carbon is removed from the iron to give high purity iron, it is known as wrought iron. Wrought iron is quite soft and easily worked and has little structural strength. It was once used to make decorative gates and railings, but these days mild steel is normally used instead. Mild steel: Mild steel is iron containing up to about 0.25% of carbon. The presence of the carbon makes the steel stronger and harder than pure iron. The higher the percentage of carbon, the harder the steel becomes. Mild steel is used for lots of things - nails, wire, car bodies, ship building, girders and bridges etc. High carbon steel: High carbon steel contains up to about 1.5% of carbon. The presence of the extra carbon makes it very hard, but it also makes it more brittle. High carbon steel is used for cutting tools and masonry nails (steel nails). You have to be careful with high carbon steel because it tends to fracture rather than bend if you mistreat it. Special steels: These are iron alloyed with other metals. For example: Steel iron mixed with special properties uses include stainless steel chromium and nickel resists corrosion cutlery, cooking utensils, kitchen sinks, industrial equipment for food and drink processing titanium steel Titanium withstands high temperatures gas turbines, spacecraft manganese steel Manganese very hard rock-breaking machinery, some railway track (e.g. points), military helmets 8Environmental problems in mining and transporting the raw materials. These include:  Loss of landscape due to mining, processing and transporting the iron ore, coke and limestone.  Noise and air pollution (greenhouse effect, acid rain) involved in these operations. Extracting iron from the ore. These include:  Loss of landscape due to the size of the chemical plant needed.  Noise.  Atmospheric pollution from the various stages of extraction. For example: carbon dioxide (greenhouse effect); carbon monoxide (poisonous); sulphur dioxide from the sulphur content of the ores (poisonous, acid rain).  Disposal of slag, some of which is just dumped.  Transport of the finished iron. Recycling:-  Saving of raw materials and energy by not having to first extract the iron from the ore.  Avoiding the pollution problems in the extraction of iron from the ore.  Not having to find space to dump the unwanted iron if it wasn't recycled. (Offsetting these to a minor extent) Energy and pollution costs in collecting and transporting the recycled iron to the steel works. PRODUCTION OF ALUMINIUM Aluminium is mainly produced from bauxite. Over 90% of the world’s bauxite resources are concentrated on the tropical and sub-tropical belt in Australia, Guinea, Jamaica, Surinam, Brazil, and India. In Russia there are nepheline ore deposits located on the Kola Peninsula and in the Kemerovo Region. As a result of nepheline processing, significant volumes of by-products are generated including calcined soda, potash, fertilizers, and cement. Alumina — or aluminium oxide (Al2O3), is produced from extracted ore. Despite its name, it has nothing to do with clay or black soil but resembles a flour or very white sand. Alumina is then transformed into aluminium through electrolytic reduction. One tonne of aluminium is produced from every two tonnes of alumina. Bauxite consists of 40-60% alumina, as well as earth silicon, ferrous oxide, and titanium dioxide. To separate pure alumina, the Bayer process is applied. Purifiying the aluminium oxide - the Bayer Process Crushed bauxite is treated with moderately concentrated sodium hydroxide solution. The concentration, temperature and pressure used depend on the source of the bauxite and exactly what form of aluminium oxide it contains. Temperatures are typically from 140°C to 240°C; pressures can be up to about 35 atmospheres. High pressures are necessary to keep the water in the sodium hydroxide solution liquid at temperatures above 100°C. The higher the temperature, the higher the pressure needed. 9With hot concentrated sodium hydroxide solution, aluminium oxide reacts to give a solution of sodium tetrahydroxoaluminate. The impurities in the bauxite remain as solids. For example, the other metal oxides present tend not to react with the sodium hydroxide solution and so remain unchanged. Some of the silicon dioxide reacts, but goes on to form a sodium aluminosilicate which precipitates out. All of these solids are separated from the sodium tetrahydroxoaluminate solution by filtration. They form a "red mud" which is just stored in huge lagoons Precipitation of aluminium hydroxide The sodium tetrahydroxoaluminate solution is cooled, and "seeded" with some previously produced aluminium hydroxide. This provides something for the new aluminium hydroxide to precipitate around. Formation of pure aluminium oxide Aluminium oxide (sometimes known as alumina) is made by heating the aluminium hydroxide to a temperature of about °C. Conversion of the aluminium oxide into aluminium by electrolysis: the Hall-Heroult process. The electrolysis or reduction of alumina is carried out in a steel tank lined inside with graphite. The graphite lining serves as cathode. Anode is also made of graphite rods hanging in the molten mass. The electrolyte consists of alumina dissolved in fused molten Cryolite(Na3AlF6) and Fluorspar(CaF2). Cryolite is another aluminium ore, but is rare and expensive, and most is now made chemically. Cryolite lowers the melting point of alumina to 9500C and fluorspar increases the fluidity of the mass so that the liberated aluminum metal may sink at the bottom of the cell. Note! Alumina melts at 2015°C. When electric current is passed through this mixture, the aluminum is collected at the cathode in molten state and sinks at the bottom and is tapped off. The molten aluminium is deposited under a cryolite solution with 3- 5% alumina. During this process, temperatures reach 950°C (working temperature), considerably higher than the melting point of the metal itself, which is 660°C. In the Hall-Heroult reduction process, coal anodes are consumed very quickly and should be replaced with new ones. This problem can be solved with the renewable Soderberg electrode. It is formed in a special restoration chamber of coke and tar paste, which is fitted into a steel sheet cover which lies open at both ends. The paste is filled into the upper opening when necessary. It is heated before it reaches the cell with melt. Aluminium production technology applies pre-baked anodes, a method used at many European and American aluminium smelters, and characterised by less power consumption and a negative impact on the environment. The anodes are baked in huge gas furnaces and then, having been fixed into holders, are lowered into a furnace. Consumed electrodes are replaced with new ones and remaining ‘butts’ are sent away for recycling. Due to higher ecological requirements established in recent years, mitigating hazardous emissions is the main challenge which facilities using Soderberg technology face. Now the problem is being actively solved by implementing colloid anodes made of special colloidal paste, which is thermally resistant. In terms of environmental indicators, this method is equal to the pre-baked anodes technology. The metal is removed from reduction cells and poured into moulds every 24 hours or more. Aluminium production is very energyintensive. It is for this reason that the most efficient place to construct aluminium smelters is in remote regions, where there is free access to power sources 10Ionization of Alumina: 2Al2O3 → 6O-2 + 4Al+3 Reaction at Cathode: 4Al+3 + 12e- → 4Al Reaction at Anode: 6O-2 → 3O2 + 12eC + O2 → CO2 Aluminum metal produced by the electrolysis of alumina is 99% pure but contains impurities of Fe, Si and Al2O3. Aluminum is further refined by Hoope’s method. Economic considerations  The high cost of the process because of the huge amounts of electricity it uses. This is so high because to produce 1 mole of aluminium which only weighs 27 g you need 3 moles of electrons. You are having to add a lot of electrons (because of the high charge on the ion) to produce a small mass of aluminium (because of its low relative atomic mass).  Energy and material costs in constantly replacing the anodes.  Energy and material costs in producing the cryolite, some of which gets lost during the electrolysis. Environmental problems in mining and transporting the bauxite  Loss of landscape due to mining, processing and transporting the bauxite.  Noise and air pollution (greenhouse effect, acid rain) involved in these operations. Extracting aluminium from the bauxite  Loss of landscape due to the size of the chemical plant needed, and in the production and transport of the electricity.  Noise. 11 Atmospheric pollution from the various stages of extraction. For example: carbon dioxide from the burning of the anodes (greenhouse effect); carbon monoxide (poisonous); fluorine (and fluorine compounds) lost from the cryolite during the electrolysis process (poisonous).  Pollution caused by power generation (varying depending on how the electricity is generated.)  Disposal of red mud into unsightly lagoons.  Transport of the finished aluminium. Recycling  Saving of raw materials and particularly electrical energy by not having to extract the aluminium from the bauxite. Recycling aluminium uses only about 5% of the energy used to extract it from bauxite.  Avoiding the environmental problems in the extraction of aluminium from the bauxite.  Not having to find space to dump the unwanted aluminium if it wasn't recycled.  (Offsetting these to a minor extent) Energy and pollution costs in collecting and transporting the recycled aluminium. Uses of aluminium: Aluminium is usually alloyed with other elements such as silicon, copper or magnesium. Pure aluminium isn't very strong, and alloying it adds to it strength. Aluminium is especially useful because it  has a low density;  is strong when alloyed;  is a good conductor of electricity;  has a good appearance;  resists corrosion because of the strong thin layer of aluminium oxide on its surface. This layer can be strengthened further by anodising the aluminium. Anodising essentially involves etching the aluminium with sodium hydroxide solution to remove the existing oxide layer, and then making the aluminium article the anode in an electrolysis of dilute sulphuric acid. The oxygen given of at the anode reacts with the aluminium surface, to build up a film of oxide up to about 0.02 mm thick. As well as increasing the corrosion resistance of the aluminium, this film is porous at this stage and will also take up dyes. (It is further treated to make it completely non-porous afterwards.) That means that you can make aluminium articles with the colour built into the surface Some uses include: aluminium is used for because Aircraft construction light, strong, resists corrosion other transport such as ships' superstructures, container vehicle bodies, tube trains (metro trains) light, strong, resists corrosion 12overhead power cables (with a steel core to strengthen them) light, resists corrosion, good conductor of electricity Saucepans light, resists corrosion, good appearance, good conductor of heat PRODUCTION OF CEMENT Definition: Cement is a fine powder which sets after a few hours when mixed with water, and then hardens in a few days into a solid, strong material. Cement is mainly used to bind fine sand and coarse aggregates together in concrete. It is a hydraulic binder, i.e. it hardens when water is added. There are 27 types of common cement which can be grouped into 5 general categories and 3 strength classes: ordinary, high and very high. In addition, some special cements exist like sulphate resisting cement, low heat cement and calcium aluminate cement. The quarry is the starting point Cement plants are usually located closely either to hot spots in the market or to areas with sufficient quantities of raw materials. The aim is to keep transportation costs low. Basic constituents for cement (limestone and clay) are taken from quarries in these areas. A two-step process Basically, cement is produced in two steps: first, clinker is produced from raw materials. In the second step cement is produced from cement clinker. The first step can be a dry, wet, semi-dry or semi-wet process according to the state of the raw material. 13Making clinker The raw materials are delivered in bulk, crushed and homogenized into a mixture which is fed into a rotary kiln. This is an enormous rotating pipe of 60 to 90 m long and up to 6 m in diameter. This huge kiln is heated by a 2000°C flame inside of it. The kiln is slightly inclined to allow for the materials to slowly reach the other end, where it is quickly cooled to 100-200°C. Four basic oxides in the correct proportions make cement clinker: calcium oxide (65%), silicon oxide (20%), alumina oxide (10%) and iron oxide (5%). These elements mixed homogeneously (called “raw meal” or slurry) will combine when heated by the flame at a temperature of approximately 1450°C. New compounds are formed: silicates, aluminates and ferrites of calcium. Hydraulic hardening of cement is due to the hydration of these compounds. The final product of this phase is called “clinker”. These solid grains are then stored in huge silos. End of phase one. From clinker to cement The second phase is handled in a cement grinding mill, which may be located in a different place to the clinker plant. Gypsum (calcium sulphates) and possibly additional cementitious (such as blast furnace slag, coal fly ash, natural pozzolanas, etc.) or inert materials (limestone) are added to the clinker. All constituents are ground leading to a fine and homogenous powder. End of phase two. The cement is then stored in silos before being dispatched either in bulk or bagged. What is concrete? Concrete is a solid material made of cement, water, aggregates and often with admixtures. When fresh, it has a certain workability and takes the form of the mould into which it is put. When set and hardened, it is as strong as natural stone and resists time, water, frost, mechanical constraints and fire. Typically, concrete is the essential material used in all types of construction [residential (housing), non-residential (offices) and civil engineering (roads, bridges, etc.)]. Cement Manufacturing Process The raw materials needed to produce cement (calcium carbonate, silica, alumina, and iron ore) are generally extracted from limestone rock, chalk, shale, or clay. These raw materials are won from the quarry by either extraction or blasting. These naturally occurring minerals are then crushed through a milling process. At this stage, additional minerals are added to ensure the correct chemical composition for making cement. These minerals can be obtained from the waste or by-products of other industries, such as paper ash. Milling produces a fine powder, known as raw meal, which is preheated and then sent to the kiln for further processing. The kiln is at the heart of the manufacturing process. Once inside the kiln, the raw meal is heated to around 1,500°C - a similar temperature to that of molten lava. At this temperature, chemical reactions take place to form cement clinker, which contains hydraulic calcium silicates. In order to heat the materials to this very high temperature, a 2,000°C flame is required, which can be produced through the use of fossil and waste-derived fuels. The kiln itself is angled by 3° (degrees) to the horizontal to allow the material to pass through it, over a period of 20 to 30 minutes. Upon exiting the kiln, the clinker is cooled and stored, ready for grinding, to produce cement. A small amount of gypsum (3 percent to 5 percent) is added to the clinker to regulate how the cement will set. The mixture is then very finely ground to obtain "pure cement." During this phase, different mineral materials, called "additions," may be added alongside the gypsum. Used in varying proportions, these additions, which are of natural or industrial origin, give the cement specific properties, such as reduced permeability, greater resistance to sulfates and aggressive environments, improved workability, or higher-quality finishes. 14Finally, the cement is stored in silos before being shipped in bulk or in bags to the sites where it will be used. PRODUCTION OF ETHANOL, SOAPS & DETERGENTS PRODUCTION OF ETHANOL BY FERMENTATION Slow decomposition of organic compounds is called fermentation. This is the principle behind souring of milk, butter, putrefaction of meat, and preparation of wine and vinegar. Fermentation was the earliest method used for preparing alcohol in industries. This is still used for the manufacture of alcohol and alcoholic drinks like beer, wine, brandy, etc. Raw materials: Cheap starchy materials like cassava, potatoes, maize, barley, rice etc. OR Molasses, a byproduct of sugar industry. From Molasses:The syrup left after the separation of cane sugar or beet sugar crystals from the concentrated sugar cane juice is called molasses. It is a dark coloured syrupy mass and contains about 30% of uncrystallizable sucrose and about 32% of invert sugar (a mixture of glucose and fructose). The different steps in the manufacture of ethanol by fermentation of molasses are: Dilution: The molasses is diluted with water until a concentration of 8-10% sugar is obtained in solution. To discourage bacterial growth, this is acidified with a little sulphuric acid. If sufficient yeast (food for the ferment) is not present, a nutritive solution of ammonium salts is added. Alcoholic Fermentation: The dilute solution obtained as above is taken in big fermentation tanks and some yeast is added (5% by volume). The temperature is maintained at 330K and the mixture is allowed to stand for a few days. Fermentation sets in and the enzyme (organic catalyst) invertase present in yeast, converts sucrose into glucose and fructose. Zymase, another enzyme present in yeast converts glucose and fructose into ethanol and carbon dioxide. The carbon dioxide formed is allowed to escape but air is not allowed to enter. In presence of air ethanol formed would be oxidised to ethanal and ethanoic acid. The fermentation is complete in 3 days. The carbon dioxide obtained as byproduct is recovered and can be sold. Distillation: The fermented liquor contains 9-10% of ethanol and is called wash or wort. It is distilled in a Coffey still to remove water and other impurities present in wash. The Coffey still consists of two tall fractionating columns with perforated plates. These columns are called the analyser and the rectifier. This works on the counter-current principle as the steam and alcohol travel in opposite directions through the still. Steam passes up the analyzer and takes away the alcohol vapors from the dilute alcohol that is coming down. The mixture leaves the analyzer at the top. It then enters the rectifier at the base. The mixture heats the wash or wort flowing through the pipes on its way to the analyzer. The steam condenses and the alcohol vapors escaping near the top are condensed in the condenser. The distillate contains about 90% alcohol and the residue left in the still is used as cattle feed. Rectification: The alcohol obtained contains other impurities besides water. These impurities are further removed by fractional distillation. Low boiling impurities like ethanol and methanol distil over as the first 15fractions. The middle fraction contains about 93-95% alcohol and is called rectified spirit. Often, distillation and rectification is carried out in the same operation. From Starch: Starchy raw materials such as wheat, barley, rice, maize or corn and potatoes. Conversion of starch into maltose:- Conversion of starch into maltose or saccharification is carried out as follows: Malting: Moist barley is allowed to germinate in dark at 290K (about 25 - 30°C). Germinated barley is called Malt and this is heated to 330K ( up to 60°C to stop further germination). It is then crushed and extracted with water. This Malt extract contains the enzyme diastase. Mashing: To break the cell walls, starch is reacted with superheated steam. This exposes the starch inside that forms a paste like mass called Mash. Hydrolysis: Mash and malt extract are treated together at 320-330K. In about half an hour to 2 hours, hydrolysis is complete and maltose is formed. Alcoholic Fermentation Maltose obtained from starch is fermented in the presence of yeast. Maltase present in yeast converts maltose into glucose. Another enzyme zymase present in yeast, then converts glucose into ethanol and carbon dioxide. Subsequent distillation and rectification yields rectified spirit. 1617Extra notes on the fermentation process.  The progress of the fermentation can be followed by measuring the density of the fermented liquid with a hydrometer. Ethanol/alcohol is less dense than water/sugar so the density changes as the sugar is converted into alcohol.  When the concentration of alcohol reaches about 10–20% the fermentation reaction stops because the yeast cells are then killed by this high concentration of ethanol.  Pure ethanol is classed as a toxic poison just like cyanide and arsenic!  It is important to have the optimum temperature (30oC – 40oC) otherwise the efficiency of the process is affected. If the temperature is too high the enzymes in the yeast cells are denatured and if the temperature is too low, the reaction is too slow Oil refinery An oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas. Oil refineries are typically large sprawling industrial complexes with extensive piping running throughout, carrying streams of fluids between large chemical processing units. In many ways, oil refineries use much of the technology of, and can be thought of as types of chemical plants. The crude oil 18feedstock has typically been processed by an oil production plant. There is usually an oil depot (tank farm) at or near an oil refinery for storage of bulk liquid products. Crude oil is separated into fractions by fractional distillation. The fractions at the top of the fractionating column have lower boiling points than the fractions at the bottom. The heavy bottom fractions are often cracked into lighter, more useful products. All of the fractions are processed further in other refining units. Raw or unprocessed crude oil is not generally useful. Although "light, sweet" (low viscosity, low sulphur) crude oil has been used directly as a burner fuel for steam vessel propulsion, the lighter elements form explosive vapors in the fuel tanks and are therefore hazardous, especially in warships. Instead, the hundreds of different hydrocarbon molecules in crude oil are separated in a refinery into components which can be used as fuels, lubricants, and as feedstock in petrochemical processes that manufacture such products as plastics, detergents, solvents, elastomers and fibers such as nylon and polyesters. Petroleum fossil fuels are burned in internal combustion engines to provide power for ships, automobiles, aircraft engines, lawn mowers, chainsaws, and other machines. Different boiling points allow the hydrocarbons to be separated by distillation. Since the lighter liquid products are in great demand for use in internal combustion engines, a modern refinery will convert heavy hydrocarbons and lighter gaseous elements into these higher value products. Oil can be used in a variety of ways because it contains hydrocarbons of varying molecular masses, forms and lengths such as paraffins, aromatics, naphthenes (or cycloalkanes), alkenes, dienes, and alkynes. While the molecules in crude oil include different atoms such as sulfur and nitrogen, the hydrocarbons are the most common form of molecules, which are molecules of varying lengths and complexity made of hydrogen and carbon atoms, and a small number of oxygen atoms. The differences in the structure of these molecules account for their varying physical and chemical properties, and it is this variety that makes crude oil useful in a broad range of applications. Once separated and purified of any contaminants and impurities, the fuel or lubricant can be sold without further processing. Smaller molecules such as isobutane and propylene or butylenes can be recombined to meet specific octane requirements by processes such as alkylation, or less commonly, dimerization. Octane grade of gasoline can also be improved by catalytic reforming, which involves removing hydrogen from hydrocarbons producing compounds with higher octane ratings such as aromatics. Intermediate products such as gas oils can even be reprocessed to break a heavy, long-chained oil into a lighter short-chained one, by various forms of cracking such as fluid catalytic cracking, thermal cracking, and hydrocracking. The final step in gasoline production is the blending of fuels with different octane ratings, vapor pressures, and other properties to meet product specifications. 19Oil refineries are large scale plants, processing about a hundred thousand to several hundred thousand barrels of crude oil a day. Because of the high capacity, many of the units operate continuously, as opposed to processing in batches, at steady state or nearly steady state for months to years. The high capacity also makes process optimization and advanced process control very desirable. Major products: Petroleum products are usually grouped into three categories: light distillates (LPG, gasoline, naphtha), middle distillates (kerosene, diesel), heavy distillates and residuum (heavy fuel oil, lubricating oils, wax, asphalt). This classification is based on the way crude oil is distilled and separated into fractions (called distillates and residuum).  Liquified petroleum gas (LPG)  Gasoline (also known as petrol)  Naphtha  Kerosene and related jet aircraft fuels  Diesel fuel  Fuel oils  Lubricating oils  Paraffin wax  Asphalt and tar  Petroleum coke Common process units found in a refinery  Desalter unit washes out salt from the crude oil before it enters the atmospheric distillation unit.  Atmospheric distillation unit distills crude oil into fractions.  Vacuum distillation unit further distills residual bottoms after atmospheric distillation.  Naphtha hydrotreater unit uses hydrogen to desulphurize naphtha from atmospheric distillation. Must hydrotreat the naphtha before sending to a Catalytic Reformer unit.  Catalytic reformer unit is used to convert the naphtha-boiling range molecules into higher octane reformate (reformer product). The reformate has higher content of aromatics and cyclic hydrocarbons). An important byproduct of a reformer is hydrogen released during the catalyst reaction. The hydrogen is used either in the hydrotreaters or the hydrocracker.  Distillate hydrotreater unit desulphurizes distillates (such as diesel) after atmospheric distillation. 20 Fluid catalytic cracker (FCC) unit upgrades heavier fractions into lighter, more valuable products.  Hydrocracker unit uses hydrogen to upgrade heavier fractions into lighter, more valuable products.  Visbreaking unit upgrades heavy residual oils by thermally cracking them into lighter, more valuable reduced viscosity products.  Merox unit treats LPG, kerosene or jet fuel by oxidizing mercaptans to organic disulphides.  Coking units (delayed coking, fluid coker, and flexicoker) process very heavy residual oils into gasoline and diesel fuel, leaving petroleum coke as a residual product.  Alkylation unit produces high-octane component for gasoline blending.  Dimerization unit converts olefins into higher-octane gasoline blending components. For example, butenes can be dimerized into isooctene which may subsequently be hydrogenated to form isooctane. There are also other uses for dimerization.  Isomerization unit converts linear molecules to higher-octane branched molecules for blending into gasoline or feed to alkylation units.  Steam reforming unit produces hydrogen for the hydrotreaters or hydrocracker.  Liquified gas storage units store propane and similar gaseous fuels at pressure sufficient to maintain them in liquid form. These are usually spherical vessels or bullets (horizontal vessels with rounded ends.  Storage tanks store crude oil and finished products, usually cylindrical, with some sort of vapor emission control and surrounded by an earthen berm to contain spills.  Slug catcher used when product (crude oil and gas) that comes from a pipeline with two-phase flow, has to be buffered at the entry of the units.  Amine gas treater, Claus unit, and tail gas treatment convert hydrogen sulphide from hydrodesulphurization into elemental sulfur.  Utility units such as cooling towers circulate cooling water, boiler plants generates steam, and instrument air systems include pneumatically operated control valves and an electrical substation.  Wastewater collection and treating systems consist of API separators, dissolved air flotation (DAF) units and further treatment units such as an activated sludge biotreater to make water suitable for reuse or for disposal.  Solvent refining units use solvent such as cresol or furfural to remove unwanted, mainly asphaltenic materials from lubricating oil stock or diesel stock.  Solvent dewaxing units remove the heavy waxy constituents petrolatum from vacuum distillation products. 21Flow diagram of typical refinery The image below is a schematic flow diagram of a typical oil refinery that depicts the various unit processes and the flow of intermediate product streams that occurs between the inlet crude oil feedstock and the final end products. The diagram depicts only one of the literally hundreds of different oil refinery configurations. The diagram also does not include any of the usual refinery facilities providing utilities such as steam, cooling water, and electric power as well as storage tanks for crude oil feedstock and for intermediate products and end products. Schematic flow diagram of a typical oil refinery 22There are many process configurations other than that depicted above. For example, the vacuum distillation unit may also produce fractions that can be refined into end products such as: spindle oil used in the textile industry, light machinery oil, motor oil, and steam cylinder oil. As another example, the vacuum residue may be processed in a coker unit to produce petroleum coke. Specialty end products These will blend various feedstocks, mix appropriate additives, provide short term storage, and prepare for bulk loading to trucks, barges, product ships, and railcars.  Gaseous fuels such as propane, stored and shipped in liquid form under pressure in specialized railcars to distributors.  Liquid fuels blending (producing automotive and aviation grades of gasoline, kerosene, various aviation turbine fuels, and diesel fuels, adding dyes, detergents, antiknock additives, oxygenates, and anti-fungal compounds as required). Shipped by barge, rail, and tanker ship. May be shipped regionally in dedicated pipelines to point consumers, particularly aviation jet fuel to major airports, or piped to distributors in multi-product pipelines using product separators called pipeline inspection gauges ("pigs").  Lubricants (produces light machine oils, motor oils, and greases, adding viscosity stabilizers as required), usually shipped in bulk to an offsite packaging plant.  Wax (paraffin), used in the packaging of frozen foods, among others. May be shipped in bulk to a site to prepare as packaged blocks.  Sulphur (or sulphuric acid), byproducts of sulfur removal from petroleum which may have up to a couple percent sulfur as organic sulfur-containing compounds. Sulfur and sulfuric acid are useful industrial materials. Sulfuric acid is usually prepared and shipped as the acid precursor oleum.  Bulk tar shipping for offsite unit packaging for use in tar-and-gravel roofing.  Asphalt unit. Prepares bulk asphalt for shipment.  Petroleum coke, used in specialty carbon products or as solid fuel.  Petrochemicals or petrochemical feed stocks, which are often sent to petrochemical plants for further processing in a variety of ways. The petrochemicals may be olefins or their precursors, or various types of aromatic petrochemicals. Siting/locating of petroleum refineries When searching for a site to construct a refinery or a chemical plant the following issues need to be considered:  The site has to be reasonably far from residential areas.  Infrastructure should be available for supply of raw materials and shipment of products to markets.  Energy to operate the plant should be available.  Facilities should be available for waste disposal. 23Refineries which use a large amount of steam and cooling water need to have an abundant source of water. Oil refineries therefore are often located nearby navigable rivers or on a sea shore, nearby a port. Such location also gives access to transportation by river or by sea. The advantages of transporting crude oil by pipeline are evident, and oil companies often transport a large volume of fuel to distribution terminals by pipeline. Pipeline may not be practical for products with small output, and rail cars, road tankers, and barges are used. Petrochemical plants and solvent manufacturing (fine fractionating) plants need spaces for further processing of a large volume of refinery products for further processing, or to mix chemical additives with a product at source rather than at blending terminals. Safety and environmental concerns The refining process releases numerous different chemicals into the atmosphere; consequently, there are substantial air pollution emissions and a notable odor normally accompanies the presence of a refinery. Aside from air pollution impacts there are also wastewater concerns, risks of industrial accidents such as fire and explosion, and noise health effects due to industrial noise. The public has demanded that many governments place restrictions on contaminants that refineries release, and most refineries have installed the equipment needed to comply with the requirements of the pertinent environmental protection regulatory agencies. Environmental and safety concerns mean that oil refineries are sometimes located some distance away from major urban areas. Nevertheless, there are many instances where refinery operations are close to populated areas and pose health risks Corrosion problems and prevention:-Petroleum refineries run as efficiently as possible to reduce costs. One major factor that decreases efficiency is corrosion of the metal components found throughout the process line of the hydrocarbon refining process. Corrosion causes the failure of parts in addition to dictating the cleaning schedule of the refinery, during which the entire production facility must be shut down and cleaned. Corrosion occurs in various forms in the refining process, such as pitting corrosion from water droplets, embrittlement from hydrogen, and stress corrosion cracking from sulfide attack. From a materials standpoint, carbon steel is used for upwards of 80% of refinery components, which is beneficial due to its low cost. Carbon steel is resistant to the most common forms of corrosion, particularly from hydrocarbon impurities at temperatures below 205 °C, but other corrosive chemicals and environments prevent its use everywhere. Common replacement materials are low alloy steels containing chromium and molybdenum, with stainless steels containing more chromium dealing with more corrosive environments. More expensive materials commonly used are nickel, titanium, and copper alloys. These are primarily saved for the most problematic areas where extremely high temperatures or very corrosive chemicals are present. Corrosion is fought by a complex system of monitoring, preventative repairs and careful use of materials. Monitoring methods include both off-line checks taken during maintenance and on-line monitoring. Off-line checks measure corrosion after it has occurred, telling the engineer when equipment must be replaced based on the historical information he has collected. This is referred to as preventative management. SOAP MANUFACTURING Soap and detergent manufacturing consists of a broad range of processing and packaging operations. The size 24and complexity of these operations vary from small plants employing a few people to those with several hundred workers. Products range from large-volume types like laundry detergents that are used on a regular basis to lower-volume specialties for less frequent cleaning needs. Cleaning products come in three principal forms: bars, powders and liquids. Some liquid products are so viscous that they are gels. The first step in manufacturing all three forms is the selection of raw materials. Raw materials are chosen according to many criteria, including their human and environmental safety, cost, compatibility with other ingredients, and the form and performance characteristics of the finished product. While actual production processes may vary from manufacturer to manufacturer, there are steps which are common to all products of a similar form. Traditional bar soaps are made from fats and oils or their fatty acids which are reacted with inorganic watersoluble bases. The main sources of fats are beef and mutton tallow, while palm, coconut and palm kernel oils are the principal oils used in soap-making. The raw materials may be pretreated to remove impurities and to achieve the colour, odour and performance features desired in the finished bar. The chemical processes for making soap are saponification of fats and oils (lard, olive oil, palm oil, coconut oil and other nut oils etc) and neutralization of fatty acids. Soap was made by the batch kettle boiling method until shortly after World War II, when continuous processes were developed. Continuous processes are preferred today because of their flexibility, speed and economics. Both continuous and batch processes produce soap in liquid form, called neat soap, and a valuable by-product, glycerine (1). The glycerine is recovered by chemical treatment, followed by evaporation and refining. Refined 25glycerine is an important industrial material used in foods, cosmetics, drugs and many other products. The next processing step after saponification or neutralization is drying. Vacuum spray drying is used to convert the neat soap into dry soap pellets (2). The moisture content of the pellets will vary depending on the desired properties of the soap bar. In the final processing step, the dry soap pellets pass through a bar soap finishing line. The first unit in the line is a mixer, called an amalgamator, in which the soap pellets are blended together with fragrance, colorants and all other ingredients (3). The mixture is then homogenized and refined through rolling mills and refining plodders to achieve thorough blending and a uniform texture (4). Finally, the mixture is continuously extruded from the plodder, cut into bar-size units and stamped into its final shape in a soap press (5). Some of today's bar soaps are called "combo bars," because they get their cleansing action from a combination of soap and synthetic surfactants. Others, called "syndet bars," feature surfactants as the main cleansing ingredients. The processing methods for manufacturing the synthetic base materials for these bars are very different from those used in traditional soapmaking. However, with some minor modifications, the finishing line equipment is the same. POWDER DETERGENTS Powder detergents are produced by spray drying, agglomeration, dry mixing or combinations of these methods. In the spray drying process, dry and liquid ingredients are first combined into a slurry, or thick suspension, in a tank called a crutcher (1). The slurry is heated and then pumped to the top of a tower where it is sprayed through nozzles under high pressure to produce small droplets. The droplets fall through a current of hot air, forming hollow granules as they dry (2). The dried granules are collected from the bottom of the spray tower where they are screened to achieve a relatively uniform size (3). After the granules have been cooled, heat sensitive ingredients that are not compatible with the spray drying temperatures (such as bleach, enzymes and fragrance) are added (4). Traditional spray drying produces relatively low density powders. New technology has enabled the soap and detergent industry to reduce the air inside the granules during spray 26drying to achieve higher densities. The higher density powders can be packed in much smaller packages than were needed previously. Agglomeration, which leads to higher density powders, consists of blending dry raw materials with liquid ingredients. Helped by the presence of a liquid binder, rolling or shear mixing causes the ingredients to collide and adhere to each other, forming larger particles. Dry mixing or dry blending is used to blend dry raw materials. Small quantities of liquids may also be added. Both batch and continuous blending processes are used to manufacture liquid and gel cleaning products. Stabilizers may be added during manufacturing to ensure the uniformity and stability of the finished product. In a typical continuous process, dry and liquid ingredients are added and blended to a uniform mixture using inline or static mixers. Recently, more concentrated liquid products have been introduced. One method of pr