Design and Thermal Analysis of a Small-scale Municipal Solid Waste-fired Steam Boiler
Chapter One
Objectives of the present study
This project is based specifically on the design and thermal analysis of municipal solid waste steam boiler that will generate saturated steam for heating and industrial purposes using mass burn incineration technology incorporated with waterwall furnace.
CHAPTER TWO
LITERATURE REVIEW
Historical background
Waste-to-energy projects using municipal solid waste has generated global advantage as a result of combustion generated products that reduces the volume of solid waste material by about 90 percent and its weight by 75 percent and in addition useful energy recovered from it. Similar works relating to this project have been done in the past as stated in the (Texas Comptroller of public account, 2009). In 1885, the U.S. Army built the nation’s first garbage incinerator on Governor’s Island in New York City harbour. Also in 1885, Allegheny, Pennsylvania built the first municipal incinerator. According to John et al.,199), Resource-recovery facilities (waste-to-energy facilities) are not a new idea; in the 1890s the city of Hamburg, Germany, incinerated municipal refuse and used the resulting energy to produce steam and electricity. As their populations increased, many cities turned to incinerators as a convenient way to dispose of wastes.
From (Texas Comptroller of public account, 2009), in the early 20th century, some U.S. cities began generating electricity or steam from burning wastes. In 1903 the first solid-waste-fired plant that produced electricity in the United States was installed in New York City. In the1920s, Atlanta sold steam from its incinerators to the Atlanta Gas Light Company and Georgia Power Company.
These incineration facilities usually were located within city limits because transporting garbage to distant locations was impractical. By the end of the 1930s, an estimated 700 incinerators were in use across the nation. This number declined to about 265 by 1966, due to air emissions problems and other limitations of the technology. In addition, the popularity of landfills increased.
Europe, however, developed waste-to energy technologies more thoroughly, in part because these countries had less land available for landfills. After World War II, European cities further developed such facilities as they rebuilt areas ravaged by war. U.S.cities interested in converting waste to energy tended to acquire European technologies when they built or improved their incinerators.
In the 1970s, the Arab oil embargo and increasing energy prices encouraged the development of waste combustion. The U.S. Navy, for instance, built waste-to-energy plants at two Virginia naval stations, one of which is still in use.
The U.S federal laws and policies aided the development of the waste-to-energy industry. The 1970 Clean Air Act authorized the end of open burning at U.S. landfills. City incinerators also were required to install pollution controls or cease operation, and a number of the worst polluters were closed down. Losing incinerators forced cities to consider waste -to- energy plants and look again to Europe for technology. In 1975, the first privately built waste-to-energy plant opened in Massachusetts; it experienced a number of operational problems at first as engineers sought to adapt it to the contents of American waste and made other operational changes.
In the late 1970s, the federal government of USA started to fund feasibility studies for local governments interested in setting up new waste-to-energy plants.
The 1978 Public Utility Regulatory Policies Act (PURPA) of USA, which required the Federal Energy Regulatory Commission to guarantee a market for electricity produced by small power plants, allowed new waste-to-energy projects to find financing. PURPA made waste-to-energy projects financially viable, since projects could find buyers for the electricity they generated.
The 1980 Energy Security Act appropriated funds to support biomass energy projects and required federal agencies to prepare a plan for maximizing its production and use. The act provided insured loans, loan and price guarantees and purchase agreements for biomass projects, including waste to- energy projects using municipal solid waste. It also directed the U.S. Department of Energy to prepare a municipal waste energy development plan and support it with construction loans, and loan guarantees, price support loans and price guarantees. The act also authorized research and development for promoting the commercial viability of energy recovery from municipal waste.
While the majority of this funding was rescinded in the 1980’s, some federal money flowed to businesses and local governments, and about 46 new waste-to-energy facilities were built.
According to (Texas Comptroller of public account, 2009), the 1986 federal Tax Reform Act simultaneously benefited and harmed the development of waste-to-energy facilities. The act extended federal tax credits available for waste-to-energy facilities for ten years, but also repealed the tax-free status of waste-to-energy plants financed with industrial development bonds. In the 1990s, after the tax credits extended in 1986 finally ended, fewer waste-to-energy plants were built.
In the early 2000s, there were 105 waste-to-energy plants in the United States, including seven refuse-derived fuel (RDF) processing only plants .Of this total, 98 are combusting MSW, and these facilities handle over 29 million tonne of MSW annually, which is approximately 13 percent of the over 225 million tonne of MSW generated annually in the United States.
In this report, the design of municipal solid waste boiler incorporated with waste conditioner connected to flue gas exit for removal of moisture from the waste has been introduced. This will increase the boiler efficiency and reduces furnace batch time, hence reduction in fuel consumption rate. Also considered, is the introduction of screw conveyor for efficient transfer of the refuse to the furnace.
Waste Generation, Disposal And Management In Nigeria
The problem of poor waste management has heightened over the years in Nigeria. The country has experienced a rapid rate of urbanization according to (Olotuah et al., 2005) and this has led to severe degradation of the environment in the urban centres. (Filani,1987), have shown that severe insanitary conditions characterize the urban centres, which do not have adequate provision for waste evacuation, and are exposed to hazards of air, and water pollution. The rate of generation of solid wastes increases by the day in Nigeria with increase in urban population. An estimated 20 kg of solid wastes is generated per capital per annum in Nigeria, equivalent to 2.2 million tonne a year from (Olafusi, 2004). The greater percentage of this is collected and dumped on the surface of the ground, thereby posing severe threat to the health of the populace. (Nigeria Environmental Action Study Team, 1989).
The State Waste Management Authority are organ of government responsible for waste management in each State, which involves enhancing effective waste collection, transportation, disposal and management; ridding the state of undesirable refuse pilation; Setting guidelines, and organizing waste scavenging for recycling; erasing environmental blightedness and development of epidemic, proffering waste management strategies and turning the state accumulated wastes into wealth; and ensuring a clean and healthy environment.
The authority provides larger dustbins to the densely populated areas and commercial centres, while smaller dustbins (drums and buckets) are sold to the less populated areas. The authority employs two methods for waste collection.
House – to – house collection
This method is used in the capital cities that have good access road network, which enables easy movement of the waste collection vans. Domestic wastes from the residences are kept in storage containers to await removal by the waste collection agency into their refuse side loaders. The type and capacities of the containers used depend on the characteristics of the solid wastes to be collected, the frequency of collection, and the space available for the placement of the containers.
Communal/designated collection
Solid wastes that are generated in offices, commercial and industrial buildings (such as banks, hotels, schools), and open spaces including market places are usually collected in relatively large containers bins; When the bins are filled, an empty one is brought and left while the filled one is hauled away to a disposal site. The filled containers are removed by means of roll-on roll-off trucks, are pulled to the disposal site, emptied and returned to their original location. Records from the authority show that the bins are collected twice daily in areas where generation is very large. During peak seasons, when waste generation is higher than usual, pay loaders and open tippers are used to compliment the collecting vans.
The big bins are insufficient for most neighbourhoods in the cities. The bins are usually filled to the brim and the immediate vicinity becomes congested with wastes. A major impediment to efficient waste collection is the poor state of the roads in the capital city. In the absence of proper waste evacuation open dumps are found within most neighbourhoods.
CHAPTER THREE
RESEARCH METHODOLOGY
With the following design specifications – Steam pressure of 10 bar; Fuel consumption rate of 500 Kg/h;combustion chamber that utilizes mass burn incineration using waterwall furnace and municipal solid waste as fuel.The methods carried out in this work will cover the following: Estimation of the amount of waste generated in each state of the federation to assess it availability; calculation of amount of air required and the flue gas produced from the elemental composition of waste; calculation of calorific value of MSW using bomb calorimeter and Dulong’s formula; design and thermal analysis of MSW; draught analysis for adequate discharge of flue gas from the furnace to the atmosphere through the chimney.
Estimation of the amount of waste generated in each state of the federation to assess its availability.
Table 3.1 shows the amount of waste produced in each state of the federation including the federal capital territory. This was calculated based on the state population, urbanization and industrialization strengths.
CHAPTER FOUR
RESULTS AND DISCUSION
The Engineering Equation Solver (EES), developed at University of Wisconsin was used to obtain the solution of the equations in chapter three.EES (pronounced ‘ease’) is an acronym for Engineering Equation Solver. The basic function provided by EES is the solution of a set of algebraic equations. EES can also solve differential equations, equations with complex variables, do optimization, provide linear and non-linear regression, generate publication-quality plots, simplify uncertainty analyses and provide animations. (Klein S.A.2008).
parameters for solution of the municipal solid waste-boiler design equations
The results of the calculated parameters for municipal solid waste design equation from chapter three are shown in Table 4.1
CHAPTER FIVE
Conclusions and Recommendations
Conclusions
With the rapid development of national economy, the ever-accelerating urbanization and the continued improvement of living standard, the output of the solid waste, particularly
Municipal solid waste is constantly increasing. This causes environmental pollution and potentially affects people’s health, preventing the sustained development of cities and drawing public concern in all of society. The continuously generated wastes take up limited land resources, pollute water and air, and consequently lead to serious environmental trouble. Proper waste treatment is therefore an urgent and important task for the continued development of cities.
Volume reduction, environmentally benign treatment and reutilization of waste to energy have been the generally recognized principles and targets. The main technologies for the municipal waste treatment that can meet these three requirements are sanitary landfill technology, incineration technology, and compost technology. Due to the specific characteristics of modern urban life, the combustible components in wastes increase continuously, thus making the advantages of incineration technology more obvious. Incineration treatment is widely adopted worldwide, and becomes the main technology, particularly in densely populated cities. Its proportion among the three technologies is rising, owing to such advantages as decomposition and immobilization of hazardous substances, high degree volume reduction, potential for reutilization of a part of the resulting ashes, low space requirement and energy reclamation.
In this work, calculation of calorific value of municipal waste has been carried out from the elemental composition of the waste using Dulong’s formula. The result of 15,101 KJ/kg obtained agrees with (N.T.Engineering, 2005) of (type 1) waste that contains 25 percent moisture contents from waste classifications. With this heating value, maximum temperature of the flue gas of 833.7K was calculated from the heat balance equation in the furnace. Thermal analysis and proper sizing of the municipal solid waste boiler were done with the operational conditions taken into account, and the following conclusions can be drawn from the results.
- The calculated results of calorific value of waste using Dulong’s formula agree well with the heat values from (N.T.Engineering, 2005) of waste classifications provided they contain the same moisture content.
- The municipal solid waste with higher moisture content has a lower heat value, corresponding to a lower temperature in the furnace and a lower O2consumption during combustion, resulting in a higher O2 content at the outlet. In practical operation, the air supply rate and the distribution of the primary air along the grate should be duly adapted for the specific conditions of the wastes. Hence, for an efficient use of municipal solid waste as a fuel for generation of steam in boiler, waste with lower moisture content and adequate excess air supply should be used.
- An appropriate excess air ratio can effectively ensure the burnout of combustibles in the furnace, suppressing the formation and the emission of pollutants.
- Adopting adequate secondary air can intensify the turbulence in furnace, enhance the flue gas mixing, and prolong the residence time, and thereby contributes to the burnout of combustibles so that an optimal combustion effect can be achieved.
Recommendations
Government policies should be used to advance energy strategies such as energy security and environmental quality. In the case of renewable energy, and bioenergy in particular, a variety of policies should be implemented—research, development, and demonstration of new technologies, financial incentives, and regulatory mandates to advance the use of renewable in the energy marketplace and thus realize the benefits of renewable energy. Many of the benefits of renewable energy are not captured in the traditional marketplace economics. Government policies are a means of converting non-economic benefits to an economic basis .This may be accomplished by supporting the research, development, and demonstration of new technologies that cannot be funded by industry or individual because of the projected high costs or long development time lines of constructing waste to energy facility. To facilitate the introduction and market penetration of renewable technologies, government should establish financial incentives such as tax credits for new technology or additional taxes on existing technology to make the product economically competitive.
Accurate data on municipal solid waste production and usage remain poor. In particular, the modernization of biomass energy use requires a good information base. Nigeria has no reasonably good database on municipal solid waste supply. This serious lack of information is preventing policy makers and planners from formulating satisfactory sustainable energy policies. Programmes to tackle this breakdown in the biomass system will require detailed information on the consumption and supply of biomass (e.g. annual yield and growing stock of biomass resources) in order to plan for future. Clearly, some standardized measurements should be required to put biomass energy on a comparable basis with fossil fuels. It is also necessary to know the quantity of, say, municipal solid waste material available in order to estimate the quantity to be used in the generation of steam. For example, if MSW have to be use for energy generation in a boiler, the annual production rate at specific sites is required in order to assess its economic use and physical availability.
Moreover, in order to assist this noble drive of waste to energy production, there is need to establish what can be called Waste Marketing Board in Nigeria. This board will be responsible for management and selling of waste to the people.
Furthermore, it is necessary for the success of these technologies in Nigeria to evolve an Integrated Waste Management system, coupled with necessary legislative and control measures. A detailed feasibility study needs to be conducted in each case, duly taking into account the available waste quantities and characteristics and the local conditions as well as relative assessment of the different waste disposal options. Suitable safeguards and pollution control measures further need to be incorporated in the design of each facility to fully comply with the environmental regulations and safeguard public heath.
Finally, the information provided in this work are enough for the fabrication of a first prototype which will take about 24 months, hence it is recommended that this work will be continued further for PhD programme, which must first fine-tune the analysis made in this work by the development or use of relevant CAD software.
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