Chapter 2
Review of Related Literature Theoretical Considerations
The review of related literature for this particular study focuses on the different components of a self-sustaining water purification system. The Purification system consists of four stages. The stages consist of pre-filtration, sediment filtration, carbon block filtration and ultra violet light sterilization. The stages will ensure that the water will be fit for human consumption. Filtration is one of the fundamental processes that separate suspended particle matter from another medium. It is done by allowing a solution or mixture to pass through a porous or semi permeable membrane upon which the solid particles will retain. The separated mixture will then be consisting of two parts, the filtrate and the precipitate. In water purification the water has to undergo two filtration processes which are Pre-filtration and Sediment filtration. Pre-filtration The process involves the separation of large debris from water such as leaves, fecal matter, twigs, rust and other possible objects found in roofs. Most pollutants, such as viruses and heavy metals may be accompanied with particles. Heavy metals accumulate in some fauna and flora, so the elimination of the particles improves the quality of the water (Karbassi, et al., 2006). Sediment Filtration Sediments are particulates that are found in any particular fluid that can be transported as the fluid flows. The particulates have the tendency to form deposits at the bottom of containers and form layers when the fluid becomes stagnant. To remove particles, sediment filtration has to be done. Sediment filtration removes the particles stagnant in water. Sediment filters remove suspended matter such as sand, salt, loose scale, clay or organic matter from the water. Untreated water passes through a filter medium which traps suspended matter on the surface or within the filter. (Dvorak and Skipton, 2008) Carbon block filtration Carbon is a highly porous substance that is capable of absorbing different substances. A number of applications of carbon are available in different aspects of domestic and commercial use. Carbon is commonly used in purification and filtration. One particular use is in filtration processes commonly known as carbon filtering which is applied in carbon filtering.
Carbon filtering is a method of filtering that uses a piece of activated carbon to remove contaminants and impurities, utilizing chemical adsorption Carbon filters are effective for removing chlorine, mercury, iodine, and some inorganic compounds as well as many problematic organic contaminants such as hydrogen sulphide (H2S), formaldehyde (HCOH), and volatile orgnanic compounds (VOCs). Activated carbon does not bind well to certain chemicals including lithium, alcohols, glycols, ammonia, strong acids and bases, metals, and most inorganic substances such as sodium, lead, iron, arsenic, nitrates and fluoride. As a general rule, carbon will bind non-polar materials while polar materials will tend to remain in aqueous solution. Most pesticides are organic and strongly non-polar and thus should display an affinity for adsorption onto the carbon surface. (Kearns, 2007) Ultra Violet Light Ultraviolet light with wavelength shorter than 300 nanometers is effective in killing microorganisms. The most effective sterilizing range of UV is within the C bandwidth (UVC 253.7nm). This range - between 200nm and 280nm - is called germicidal UV bandwidth or UVC. UVC has extremely low penetrating ability and does not penetrate past the dead-cell layers of the skin. Ultraviolet Germicidal Irradiation - UVGI - is a common tool in laboratories and health care facilities and is becoming more and more popular with the general public and HVAC engineers. Interest in UVGI is increasing with the growing pandemic concerns and the opportunity to use germicidal UV for reducing energy and maintenance costs. Previous applications of UVGI have focused mainly on control of tuberculosis transmission, but a wide range of airborne respiratory pathogens are susceptible to deactivation by UVGI. UV treatment breaks down or removes some organic contaminants. UV achieves 1-log reduction of Giardia lamblia at an intensity of 80-120 mWs/cm2, and 4-log reduction of viruses at an intensity of 90-140 mWs/cm2. Only recently has the scientific community begun to accept UV as a highly effective tool for Cryptosporidium control. UV light disinfection does not form any significant disinfection byproducts, nor does it cause any significant increase in assimilable organic carbon (AOC). (Lahlou, 2000) 3.1 Photovoltaic System Photovoltaic systems (PV system) use solar panels to convert sunlight into electricity. A system is made up of one or more solar panels, usually a controller or power converter, and the interconnections and mounting for the other components. A small PV system may
provide energy to a single consumer, or to an isolated device like a lamp or a weather instrument. Large grid-connected PV systems can provide the energy needed by many customers. 3.1.2 Photovoltaic Cells Solar cells, also called photovoltaic (PV) cells by scientists, convert sunlight directly into electricity. PV gets its name from the process of converting light (photons) to electricity (voltage), which is called the PV effect. The PV effect was discovered in 1954, when scientists at Bell Telephone discovered that silicon (an element found in sand) created an electric charge when exposed to sunlight. Soon solar cells were being used to power space satellites and smaller items like calculators and watches. Today, thousands of people power their homes and businesses with individual solar PV systems. Utility companies are also using PV technology for large power stations. 3.1.3 Stand-Alone photovoltaic system Stand-alone photovoltaic power systems are electrical power systems energised by photovoltaic panels which are independent of the utility grid. These types of systems may use solar panels only or may be used in conjunction with a diesel generator or a wind turbine. Standalone system does not have a connection to the electricity "mains" (aka "grid"). Standalone systems vary widely in size and application from wristwatches or calculators to remote buildings or spacecraft. If the load is to be supplied independently of solar insolation, the generated power is stored and buffered with a battery. 3.1.4 Stand alone system with batteries In stand-alone photovoltaic power systems, the electrical energy produced by the photovoltaic panels cannot always be used directly. As the demand from the load does not always equal the solar panel capacity, battery banks are generally used. The primary functions of a storage battery in a stand-alone PV system are: Energy Storage Capacity and Autonomy: To store energy when there is an excees is available and to provide it when required. Voltage and Current Stabilization: To provide stable current and voltage by eradicating transients. Supply Surge Currents: to provide surge currents to loads like motors when required.
4.1 Hydroelectric Power Hydropower or water power is power derived from the energy of falling water, which may be harnessed for useful purposes. Since ancient times, hydropower has been used for irrigation and the operation of various mechanical devices, such as watermills, sawmills, textile mills, dock cranes, and domestic lifts. Since the early 20th century, the term is used almost exclusively in conjunction with the modern development of hydro-electric power, which allowed use of distant energy sources. Another method used to transmit energy used a trompe, which produces compressed air from falling water. Compressed air could then be piped to power other machinery at a distance from the waterfall. 4.2 System Components • • • • •
Water conveyance—channel, pipeline, or pressurized pipeline (penstock) that delivers the water Turbine or waterwheel—transforms the energy of flowing water into rotational energy Alternator or generator—transforms the rotational energy into electricity Regulator—controls the generator Wiring—delivers the electricity.
Many systems also use an inverter to convert the low-voltage direct current (DC) electricity produced by the system into 120 or 240 volts of alternating current (AC) electricity. 4.3 Determining Head Head is the vertical distance that water falls. It’s usually measured in feet, meters, or units of pressure. Head also is a function of the characteristics of the channel or pipe through which it flows. Most small hydropower sites are categorized as low or high head. The higher the head the better because you’ll need less water to produce a given amount of power, and you can use smaller, less expensive equipment. Low head refers to a change in elevation of less than 10 feet (3 meters). A vertical drop of less than 2 feet (0.6 meters) will probably make a small-scale hydroelectric system unfeasible. However, for extremely small power generation amounts, a flowing stream with as little as 13 inches of water can support a submersible turbine, like the type used originally to power scientific instruments towed behind oil exploration ships.
4.4 Turbines and Waterwheels The waterwheel is the oldest hydropower system component. Waterwheels are still available, but they aren’t very practical for generating electricity because of their slow speed and bulky structure. Turbines are more commonly used today to power small hydropower systems. The moving water strikes the turbine blades, much like a waterwheel, to spin a shaft. But turbines are more compact in relation to their energy output than waterwheels. They also have fewer gears and require less material for construction. There are two general classes of turbines: impulse and reaction. 4.4.1 Impulse Turbines Impulse turbines, which have the least complex design, are most commonly used for high head microhydro systems. They rely on the velocity of water to move the turbine wheel, which is called the runner. The most common types of impulse turbines include the Pelton wheel and the Turgo wheel. 4.4.1.1 Pelton Turbine The Pelton wheel uses the concept of jet force to create energy. Water is funnelled into a pressurized pipeline with a narrow nozzle at one end. The water sprays out of the nozzle in a jet, striking the doublecupped buckets attached to the wheel. The impact of the jet spray on the curved buckets creates a force that rotates the wheel at high efficiency rates of 70 to 90 percent. Pelton wheel turbines are available in various sizes and operate best under low-flow and high-head conditions. 4.4.1.2 Turgo Impulse Wheel The Turgo impulse wheel is an upgraded version of the Pelton. It uses the same jet spray concept, but the Turgo jet, which is half the size of the Pelton, is angled so that the spray hits three buckets at once. As a result, the Turgo wheel moves twice as fast. It’s also less bulky, needs few or no gears, and has a good reputation for trouble- free operations. The Turgo can operate under low-flow conditions but requires a medium or high head. References http://environment.nationalgeographic.com/environment/global-warming/hydropowerprofile/ http://en.wikipedia.org/wiki/Hydropower
U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL) ―ENERGY EFFICIENCY AND RENEWABLE ENERGY: Small Hydropower Systems‖ 2001
PUMP A pump is a device used to move fluids (liquids or gases) or sometimes slurries by mechanical action. Pumps can be classified into three major groups according to the method they use to move the fluid: direct lift, displacement, and gravity pumps. Pumps must have a mechanism which operates them, and consume energy to perform mechanical work by moving the fluid. The activating mechanism is often reciprocating or rotary. Pumps may be operated in many ways, including manual operation, electricity, a combustion engine of some type, and wind action. JET PUMP A Jet Pump is a type of impeller-diffuser pump that is used to draw water from wells into residences. It can be used for both shallow (25 feet or less) and deep wells (up to about 200 feet.) It can be also use for increasing the flow rate of the water. Shown here is the underwater part of a deep well jet pump. Above the surface is a standard impeller-diffuser type pump. The output of the diffuser is split, and half to three-fourths of the water is sent back down the well through the Pressure Pipe At the end of the pressure pipe the water is accelerated through a cone-shaped nozzle at the end of the pressure pipe, Then the water goes through a Venturi in the Suction The venturi has two parts: the Venturi Throat, which is the pinched section of the suction tube; and above that is the venturi itself which is the part where the tube widens and connects to the suction pipe. The venturi speeds up the water causing a pressure drop which sucks in more water through the intake at the very base of the unit. The water goes up the Suction Pipe and through the impeller most of it for another trip around to the venturi.
2.5.1 Electric Generator Generator is a latin word that means originator or maker. In power industry, this term refers to a device that produces electrical energy. Although electricity does occur naturally, it does not exist in the forms that currently can be practically utilized. For practical use it is produced from other forms of energy. Since energy cannot be created but can only be
transferred from one form to another, any form of electricity generation obviously needs source of fuel. Technically speaking, in electric generators electricity is produced from mechanical energy. The mechanical energy in turn can be generated from so-called primary sources, such as chemical, nuclear or thermal energy contained in various types of fuel. It can also be obtained from renewable resources such as sunlight, wind of falling water. The machine that converts primary energy into mechanical energy is called prime mover. Steam turbines, internal-combustion engines, gas combustions turbines, water and wind turbines are the common types of prime movers. 2.5.2 Permanent Magnet Synchronous Generator A permanent magnet synchronous generator is a generator where the excitation field is provided by a permanent magnet instead of a coil. Synchronous generators are the majority source of commercial electrical energy. They are commonly used to convert the mechanical power output of steam turbines, gas turbines, reciprocating engines, hydro turbines and wind turbines into electrical power for the grid. They are known as synchronous generators because the speed of the rotor must always match the supply frequency. In a permanent magnet generator, the magnetic field of the rotor is produced by permanent magnets. Other types of generator use electromagnets to produce a magnetic field in a rotor winding. The direct current in the rotor field winding is fed through a slip-ring assembly or provided by a brushless exciter on the same shaft. Permanent magnet generators do not require a DC supply for the excitation circuit, nor do they have slip rings and contact brushes. However, large permanent magnets are costly which restricts the economic rating of the machine. The flux density of high performance permanent magnets is limited. The air gap flux is not controllable, so the voltage of the machine cannot be easily regulated. A persistent magnetic field imposes safety issues during assembly, field service or repair. High performance permanent magnets, themselves, have structural and thermal issues. Torque current MMF vectorially combines with the persistent flux of permanent magnets, which leads to higher airgap flux density and eventually, core saturation. 2.6.1 Battery An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery (or "voltaic pile") in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power source for many household and industrial applications. There are two types of batteries: primary batteries (disposable batteries), which
are designed to be used once and discarded, and secondary batteries (rechargeable batteries), which are designed to be recharged and used multiple times. Batteries come in many sizes, from miniature cells used to power hearing aids and wristwatches to battery banks the size of rooms that provide standby power for telephone exchanges and computer data centers. Secondary batteries must be charged before use; they are usually assembled with active materials in the discharged state. Rechargeable batteries or secondary cells can be recharged by applying electric current, which reverses the chemical reactions that occur during its use. Devices to supply the appropriate current are called chargers or rechargers.
2.6.1.2 Secondary Batteries A rechargeable battery, storage battery or accumulator is a group of one or more electrochemical cells. They are known as secondary cells because their electrochemical reactions are electrically reversible. Rechargeable batteries come in many different shapes and sizes, ranging anything from a button cell to megawatt systems connected to stabilize an electrical distribution network. Several different combinations of chemicals are commonly used, including: lead–acid, nickel cadmium (NiCd), nickel metal hydride (NiMH), lithium ion (Li-ion), and lithium ion polymer (Li-ion polymer).Rechargeable batteries have lower total cost of use and environmental impact than disposable batteries. Some rechargeable battery types are available in the same sizes as disposable types. Rechargeable batteries have higher initial cost, but can be recharged very cheaply and used many times. 2.6.1.2.1 Lead Acid Batteries Lead–acid batteries, invented in 1859 by French physicist Gaston Planté, are the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, their ability to supply high surge currents means that the cells maintain a relatively large power-to-weight ratio. These features, along with their low cost, make them attractive for use in motor vehicles to provide the high current required by automobile starter motors.
2.6.1.2.1.1 Discharging In the discharged state both the positive and negative plates become lead(II) sulfate (PbSO4) and the electrolyte loses much of its dissolved sulfuric acid and becomes primarily
water. The discharge process is driven by the conduction of electrons from the positive plate back into the cell at the negative plate. 2.6.1.2.1.2 Charging In the charged state, each cell contains negative plates of elemental lead (Pb) and positive plates of lead(IV) oxide (PbO2) in an electrolyte of approximately 33.5% v/v (4.2 Molar) sulfuric acid (H2SO4). The charging process is driven by the forcible removal of electrons from the negative plate and the forcible introduction of them to the positive plate.
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