Gasification as Thermal Conversion Technology - Report Example

of Sydney Waste Strategy Review Gasification Gasification, which is also referred to as thermal conversion technology makes use of heat in a low oxygen environment to turn waste solid in form into gas. The gas is then used for the production of electricity or harnessed into a variety of renewable energy sources and rendered into an equivalent of natural gas (City of Sydney, 2014). The process of gasification is a four-step procedure; the first step is to heat and dry the moisture content so the thermal front can enter the fuel particles. The second step is the pyrolysis stage, here there is a series of complex chemical reactions which result in decomposition of the organic compound. The third stage is the converting carbon into carbon monoxide and then hydrogen to H2 and forming methane. The last step is the gas-phase reaction state where the final mix of gaseous products is determined. The parameters for production of gas and the nature of the product include the amount of oxygen in the air stream that gets into the reactor as well as the temperature, which for solid carbonaceous fuel should be between 7500 F to 8500 F. At the final stage, the gas composition is dependent on how much oxygen and steam is in the reactors as well as the duration of the entire reaction. Gasification maximizes on renewable energy recovery since it facilitates the conversion of renewable energy and non-fossil fuel into substitute gases that can be injected into the Gas grid of the City’s planned trigeneration network. By creating a “natural” gas from waste, gasification reduces the amount of fossil fuels required to power up the city; this significantly limits the quantity of greenhouse gases released into the atmosphere. More importantly, it provides for storage of a non-intermittent renewable energy source unlike solar and wind power since its supply cannot fall. Material energy resources recovered from landfills minimizes the amount of waste disposed through this method by eliminating approximately 90% of the content of landfills. Therefore, it almost completely serves the purposes of reducing the amount of waste in landfills, which is a major part of the reason it was recommended in the master plan. Gasification can contribute to the increase of reliability because of providing an alternative energy source that is perpetual unlike the fossil fuels with limited supply. In addition, residual waste from landfills is diverted to a more profitable and less pollutant purpose of generating energy. Gasification Flow Chart (City of Sydney, 2014) Mechanical and biological treatment The Mechanical and biological treatment is a combination of two processes using modern technology to separate the organic from inorganic waste so it can be further refined separately. The waste in this case can range from domestic waste, sludge, sewerage, agricultural crops and livestock manure. Since 2007, this has been the main method of waste management in Sydney but it has been proven to be less than effective since over half the components have to be landfilled. Through the mechanical process, organic waste is separated from the recoverable recyclables such as plastic or glass (City of Sydney, 2013). The biological process, on the other hand, degrades the waste by composting using microorganism in an anaerobic environment to digest the organic material. Through composting, bi-products used for mining site rehabilitation are produced, it does not however recover waste as a treatment. The second stage of the biological process is called anaerobic digestion; it generates biogas through a process of treating the organic components in low oxygen concentration so that specific microorganism can dominate the decomposition process. The biogas is then cleaned and burned directly to heat water in a boiler that in turn drives a steam turbine used for the generation of electric power. Like gasification, mechanical and biological treatment requires low levels of oxygen. Conversely, it cannot be possible unless the waste is sorted so the organic waste can be separately digested from the non-organic products. Mechanical biological treatment has proven very useful in the generation of renewable energy, the methane gas that is its final product is used to power electric motors, which in turn produce clean electricity. By replacing the numerous non-renewable sources of energy such as coal and petroleum with man-made gas, the treatment method has significantly reduced the levels of greenhouse emission by proving a cheap and effective source of clean power. This method has been found to be relatively effective in reducing the amount of waste dumped in landfills in as much as such waste would have not have been recycled. However, the method is limited since it can only process some of the household and industrial waste as it lacks the capacity to degrade non-organic matter. These have to be either recycled or disposed in landfills with the latter being more frequent (City of Sydney, 2013). It has also improved the levels of reliability of the power grid since its power supply is constant and virtually unlimited as long as it is harnessed effectively. Although it only takes out about half, the waste it has plays a major role in reducing the amount of recyclables in the system. Mechanical Biological Treatment (City of Sydney, 2014) Mass Burn Incineration (City of Sydney, 2014) Mass Burn Facilities incineration is the least effective of the three processes; it takes place in a mass combustion facility where the waste is placed in a combustion chamber after being sorted. The mass burn combustion units are well aerated to ensure oxygen reaches all the parts of the waste given the inconsistency of solid waste; the units are sloping with a moving grate that vibrates to agitate and mix the waste with air. At the combustion facility, the waste is placed in trash storage bunkers and then it is sorted using a crane, which hoists it up into a chamber for incineration (City of Sydney, 2014). The incinerator consists of a rotary kiln and requires temperatures of above 1800°F, atomized liquid and gas particles are entered into the afterburner and introduced to temperatures of over 2200°F or higher. Heat produced from the process is then used to heat and convert water to steam that is directed to a turbine generator for production of electric power; the residue, ash is the main weakness of the process since around a quarter of the waste remains as ash to be taken to landfills. Although it does not achieve as much as the other two methods in terms of maximizing energy, it is obviously more effective than just having the waste dumped in landfills than Biological Mechanical Treatment. It minimizes greenhouse emissions since the only thing that is released from the process in gaseous form is vapor and flue cleaned gases that have minimum environmental effect. It considerably reduces the amount of waste in landfills and it actually results in less landfill content (25%) than mechanical and biological treatment that leaves 50 to 60 percent non-processed waste. Nevertheless, it does not get close to the 90% combustion levels of gasification that is comparatively higher in terms of waste consumed. To a fair extent, it increases reliability since it injects a lot of power into the power grid; however, since it directly produces heat as opposed to gas, the process is more expensive and does not give out as much energy as the other two. It can be used like the other two to provide backup for the intermittent energy supply of renewable energies feeding the grid. The process does not really have an allowance for recycling since not all facilities sort the waste; therefore, its contribution to recycling is minimal. In conclusion, taking to account the NSW waste policy and CoS 2030 Vision criteria, it is abundantly clear why the gasification technique should be recommended. It produces very high amounts of energy in comparison, to the others, minimal greenhouse emission and takes the most out of landfills. While the others are also effective in those sectors, it is nevertheless, by far cleaner, more productive and in the long run cost effective. References City of Sydney (2013) Advance Treatment Master Plan. 2013-2030 City of Sydney (2014) Advance Treatment Master Plan. 2012-2030 Read More