Bentonite Processing - Assignment Example

 Bentonite Processing Bentonite is an industrial rock that occurs naturally. This rock has the water absorbing property as well asBase Exchange capacity. These two properties are far much better than the propertiespossessed by kaolin and plastic clay. Water absorption by bentonite makes the rock to considerable increase in volume. Besides increase in volume, this rock forms gelatinous mass. Sodium, organo-clay, activate clay and calcium montmorillonite are the products which are obtained when bentonite is processed. These by-products have numerous uses. Some of the areas of application are foundry, palletizing, engineering construction and in agriculture. Bentonite can be used for water-tight sealing due to its water absorption property. Bentonite rocks can be broadly classified into two categories. The first category is the group of rocks with high water absorption property. The absorbed water makes the rocks to swell and be able to remain suspended in water for long. The second category is the group of rocks that absorb water though they do not swell and remain suspended in water (Chegbeleh et al., 1). Drying operation reduces the moisture content in bentonite rock to the required percentage. Different driers can be used in the moisture reduction. Drying effectively vaporizes the liquid level contain in the rocks. The vaporization is achieved through heat supply to the wet bentonite rock feedstock. The heat from the burner is supplied either through convention, radiation or conduction. The convection method is applied when direct driers are used while conduction method is applied when contact or indirect dryers are used. Most of the driers use hot air as the drying medium. This moisture removal process is an energy-intensive operation since the amount of latent heat of vaporization required is depended on the intensity of the heating (Gillson & Bances, 87). Drying curve A representation curve is required so as to describe the various drying properties for different product at different specific temperature, pressure and velocity conditions. The drying curve for bentonite rock has three different phases. These phases are useful in the energy saving process and are independent. The products are passed through these phases in shifts. After passing from one phase, the product is moved to the next phase. First phase This phase is also called initial period. In this phase, there is transfer of heat from the dryer to the products and the contained moisture. Inlet condition from the dryer heats up the products and this condition further enable subsequent processes to occur. This phase can be substituted by pre-processing. Pre-processing is achieved through preheating the bentonite rock with energy from the waste material. The amount of energy from the waste material would be able to cause dislodgement of moisture contents from the bentonite surface. Second phase This phase is also called constant rate period. In this phase, free moisture attaches themselves on the surfaces. Alteration of the rate of evaporation reduces the moisture content. In this period, high drying rates are achieved through increase in the temperature of the inlet air. This phase accords the product with very little temperature increase. However, this little temperature increase is enough to cause some kinetic energy rise within the rock particles. Third phase This phase is also known as the falling rate period. Intrinsically attached moisture evaporates from the product. The product drying rate is limited by the outer surface. The outer surface provides a barrier that prevents successive evaporation rate. The evaporated moisture would be accumulated within the dryer. Moisture content The drying process employed is control by the moisture content of the bentonite rock. The dryer in this case is required to reduce the moisture content from 11% to 4%. The exact moisture content required is measured by the electrical resistance meter. However, this meter is limited to moisture content in grains, woods, food and concrete. Dielectric moisture meter works on the basis of contact surface with an electrode plate. The electrode plate cannot penetrate wood. The preferred meters are the modern balances that incorporate infrared heaters. The infrared heaters directly measure the product moisture content. These heaters have the capacity of giving moisture content profile variations (Gillson & Bances, 87). Rotary dryers These are continuous and the most available high volume dryer. Many industries prefer these dryers because they have more adaptations. The adaptations are have been facilitated by the technology. The feed materials are made to pass through a rotating cylinder. This rotating cylinder is called a drum. The shell of the cylinder is constructed from slightly inclined steel plates. The internal pressure of these drum are at times set at negative value. The negative value aids in prevention of escape of dust particles. The introduced solids at the upper end are able to move to the lower end. These dryers perform their function on the basis of contact between the fired drying gas and the bentonite solids. The rotary dryers can be categorized as direct, indirect, con-current and counter-current. The drum for the dryer is fixed to steel rings which are called riding rings. The riding rings are supported by fixed roller assemblies. Direct drive or chain drive gives the dryer a rotational motion. The rotational motion of the dryer is able to pick the solid bentonite particles. The particles are lifted within a given distance in the drum and the solids are made to be in contact with the fired gas. The movements of the solids within the drum are achieved through the flight action of the rotating drum (Gillson & Bances, 87). Calculations of the quantity of water to be evaporated The given data are as follows; amount of processed bentonite is 100 tons/day, the expected reduced moisture content is 11% bone dry basis to 4 % bone dry basis. The heat requirement of the dryer is therefore given by; If 1 tonne = 1000 kg; 100 tonnes =100 * 1000 = 100,000 kg. 100,000 kg of wet bentonite contains; 100,000 * 11/100 kg moisture =11,000 kg moisture And 100,000 kg * (1-0.11) = 89,000 kg bone dry bentonite product The moisture content of the final bentonite product is 4 %. From the 4 %, the moisture content is given as 89,000/ (100-4) % = 89,000 / (96/100 * 10) = 89,000/9.6 =9,270.83 kg and so the removed moisture is given by; 11,000- 9270.83 = 1,729.17 kg. The latent heat of evaporation is given by 2257 kJ and therefore the necessary heat to supply the dryer is given by 1,729.17 * 2257 =3.903 * 106 kJ Estimation of the drying time Suspension of a particle of the bentonite in a cabinet in the presence of a stream of air is one of the ways of determining the rate of drying of the particle. The drying sample weight can therefore be measured as a function of time. The function of time ranges from the wet product to the bone dry product. During the drying time estimation, the following conditions are observed; The sample should be exposed to same radiant heat transfer conditions. Secondly, the temperature, humidity and the velocity of air should be similar (Johnstone & Johnstone, 69). Reduction of the moisture content from 6% to 5% or 5.5% The plant can effectively reduce the moisture content from 6% bone dry basis to 5 0r 5.5%. This can be achieved through carrying out pre-processing. Pre-processing can be done through heating of the bentonite rocks with energy from the waste materials. The materials that remain as waste during the processing stages are collected and used as the primary source of pre-processing heat. The moisture can also be effectively reduced through crushing of the bentonite rock into smaller particles. Primary crushing of the wet rock using roller crushers is idle since the roller crushers have special designed toothed rollers that are capable of breaking large blocks of bentonite rock into relatively smaller particles. Mass balance for water and bentonite rock particles The moisture content balance for the bentonite rock can be achieved through heating of the rock particles in the radio frequency dryer. Radio frequency dryer has the capacity of purely selecting areas where much heat is needed. This is possible because water is relatively responsive to radio frequency energy compared to other dielectric materials. Wetter areas in the bentonite rock are able to absorb more power from radio frequency than dry areas. A lot of water is easily removed from the wetter areas. This results into a more uniform moisture content distribution within the bentonite rock (Johnstone & Johnstone, 69). Energy usage reduction ideas The dryers should be insulated to prevent heat loss to the surroundings. Many dryers should incorporate radio frequency radiations since these radiations are able to provide an energy-efficient means. Radio frequency radiations are also a direct application of heat and therefore no amount of energy will be wasted. Transition from oil based world economy to an economy driven by alternative energy source The role played by oil in generation of electricity is minimal. The use oil dates back to First World War when it was the only source of energy. The availability of oil at that particular time was limited. Few countries owned it. Practically, oil found application in much energy areas. It was dominant in the transportation sector. Apart from transportation, oil was also used in heating purposes. The use of oil was associated with many environmental problems. A lot of pollution was emitted from the various locomotives that were using oil. The oil crisis in the year 1973 prompted many governments from different countries to look for an alternative energy source. That crisis marked the first transition idea from the use of oil. Exploration into alternative energy sources kicked off. Other sources of energy which were being exploited at that time included wind energy, solar, geothermal, nuclear, waves and tidal energy, and hydroelectric power. The use of these other sources of energy stood out to be beneficial compared to the use of oil (Jean 23). Economic analysis In terms of the economy, the use of other alternative sources of energy is cheap and efficient. These sources of energy are environmental friendly. They therefore reduce the risks associated with pollution. There cost of production is equally cheaper. These other alternative sources of energy are renewable unlike oil. The efficiency derived from using these sources of energy is better compared to the use of oil (Jean 23). Political analysis Few countries have oil. The amount of money that these countries obtained from the sale of oil is relatively much. Rivalry has been developed between different countries due to possession of this rare commodity. The tycoons who are in this business do not want to lose the market share. Therefore, they have empowered themselves to extend where they are almost controlling the world. The World Bank on several occasions has tried to regulate the price per barrel of this rare commodity. However, there efforts have been met with hostility from these tycoons. As much as many developed countries are trying to move from the use of oil to other renewable sources, most developing countries still relies on the use of oil. Different bodies have been set up so as to regulate prices of this commodity. Such bodies are Organization of the Petroleum Exporting Countries (OPEC). This body is a cartel. It is mandated with the powers to control the World oil price (Jean 23). New source transmission of energy Development in energy is a dynamic field that tends to satisfy the society energy needs through integration of both primary sources of energy as well as secondary energy sources. These developments include mass production of alternative, conventional and renewable sources of energy. Besides production, these measures also tend to put in place recovery methods which can be used to eliminate energy wastages. The primary goal of these development measures is to produce energy at low cost as well as to mitigate environmental impact. The new source of energy transmission is the use of powerful power grids. These grids are designed to transmit huge amount of power from the production source. An energy conference hosted in Boston by New England and New York officials suggested that a powerful grid be constructed to transmit hydroelectric power from Quebec to New England. However, New England lacked such a capacity to build a powerful transmission grid. The members of the conference suggested that the matter should be left to the market. The market would determine whether hydroelectricity plant from Canada would assist. This project so far has no been installed. This is due to the huge capital that it requires. This project has not been undertaken by other countries due to the huge investment capital that it requires. Climate variability and change Energy sector from New Zealand is practically sensitive to the influences of climate that will be caused by electricity transmission. This is because a big fraction of electricity in the country is generated from renewable sources of energy which are sensitive to climate. The climate of the country also varies on various time scales. The generation of electricity in this country depends on renewable sources. These sources are dominated by hydro-electric generation. Geothermal source constitute a small percentage. However, this percentage is greater than wind generation sources (Maunder 405). The storage points for water that is used in the hydroelectric generation are dominated by reservoirs such as: Lake Tekapo and Pukaki. These lakes lie along Waitaki River. New Zealand is positioned on the middle latitudes (34o to 47oS). These latitudes are found within southern hemisphere. Mid latitude westerly winds are the determinants of the variation in climate. Subtropical high pressure belt also affects the climate. The circulation features of both pressure belts and the westerly winds affect the seasons in the country. The case of New Zealand is similar to other countries. The utilization of the powerful power grid would greatly affect these countries. Since most of the electricity generation relies on hydro-electric power, proper utilization of this project would affect the climatic conditions in these countries (Maunder 405). A lot of water is also required in the hydro-electric power generation. This huge utilization of water would cause many server rivers to dry up. Drying up would greatly affect hydrological cycle. The interference with the hydrological cycle will in turn affect the climatic condition of a given country. A lot of precipitation would not be able to take place. Lack of precipitation means there would lack of rain. Since the hydro-electric power stations depend on water, these stations would finally collapse. References Chegbeleh, Nishigaki, Akudago, Alim and Komatsu. Concepts Repository of Bentonite in Repository Environments: A State-of-the-art review. Journal of the Faculty of Environmental Science and Technology, OkayamaUniversity.Vol.13 No 1, (2008):1-5 Gillson and Bances. Industrial minerals and rocks. New York: Mudd series (1960): 87-91 Jean, Laherrere. Future of Oil Supply. Zurich: Belles Publishers, (2003): 23-29 Johnstone and Johnstone. Minerals for the chemicals and allied industries London: Chapman and Hall publishers, (1961):69-75 Maunder. The climate of New Zealand-physical and dynamic features. World Survey of Climatology, 13.2 (1971):405-409 Read More