The United States leads the world in per capita production of Municipal Solid Waste (MSW), generating approximately 200 million tons per year. By 2000 A.D. the US EPA predicts a 20% rise in these numbers. Currently the major strategies of MSW disposal are (i) landfill and (ii) incineration. The amount of landfill space in the US is on a rapid decline. There are -10,000 landfill sites in the country, of which only 65-70% are still in use. The Office of Technology Assessment (OTA) predicts an 80% landfill closure rate in the next 20 years. The development of a viable energy resource from MSW, in the form of densified Refuse Derived Fuel (dRDF), provides solutions to the problems of MSW generation and fossil fuel depletions. Every 2 tons of MSW yields approximately 1 ton of dRDF. Each ton of dRDF has an energy equivalent of more than two barrels of oil. At current production rates the US is "throwing away" over 200,000,000 barrels of oil a year. In order to be considered a truly viable product dRDF must be extensively studied; in terms of it's cost of production, it's combustion properties, and it's potential for environmental pollution. In 1987 a research team from the University of North Texas, in conjunction with the US DOE and Argonne National Laboratory (ANL), cofired over 550 tons of dRDF and bdRDF with a high sulfur Kentucky coal in a boiler at ANL. This work examines the emission rates of polychlorinated dioxins (PCDDs) and furans (PCDFs) during the combustion of the dRDF, bdRDF, and coal. Even at levels of 50% by Btu content of dRDF in the fuel feedstock, emission rates of PCDDs and PCDFs were below detection limits. The dRDF is shown to be an environmentally acceptable product, which could help resolve one of the major social and environmental problems facing this country today.

There are 150 million tons of Municipal Solid Waste (MSW) annually produced in the United States, which is approximately equivalent to 150 million barrels of oil. MSW production is inexhaustible, and is increasing on an annual per capita basis of approximately three per cent. After controlling the moisture and adding a binder, the combustible portion of MSW was converted to pellets. The objects of this project were to 1) evaluate the binder, 2) prepare the pellets, and 3) evaluate the pellets with regard to density. The manufacture of pellets was conducted at the Naval Air Station, Jacksonville, Florida. The evaluation of the binders and the pellets was done at North Texas State University (NTSU). There were three procedures for measuring the density. The first, using water displacement, was from the American Society for Testing and Material (ASTM). The second, using wax coating, was also from ASTM. The third, using sharply-cut cylindrical pellets, was developed at NTSU.

Waste-to-energy (WTE) is the environmentally preferred method of managing post-recycling wastes. In this process, municipal solid waste is combusted under controlled conditions to generate steam and electricity. Waste is by nature heterogeneous and has a substantially high composition of chlorine (0.47-0.72 wt%) as compared to other solid fuels used for power production. During combustion, chlorine is converted to hydrogen chloride and metal chlorides, which can accelerate the high temperature corrosion of boiler surfaces, especially superheater tubes. This corrosion can significantly affect plant efficiency and profitability by causing unplanned shutdowns or preemptively forcing operators to limit steam temperatures. The following work focuses on the role of chlorine compounds on boiler tube corrosion and investigates approaches for minimizing its effects. The corrosion behavior was studied by conducting laboratory furnace tests on alloys of current and future interest to the WTE industry. Test specimens were coupons machined from boiler tubes to a nominal area of 3.2 cm² (0.5 in²). An chemical environment was introduced in an electrical furnace that replicates the fireside of superheater tube. This included a mixed gas stream with O₂, CO₂, H₂O, HCl, SO₂, and N₂, and temperatures ranging between 400-550°C (752-1022°F). For some experiments, a salt layer was applied to the coupons with a loading of 4.0 ±10% mg/ cm² to understand the behavior of the effects of metal chlorides. Following each experiment, the corrosion rate was determined by taking the mass loss as specified in an American Standard Testing Method (ASTM) protocol, G1-09. Additional insights were obtained by characterizing the coupons via scanning electron microscopy (SEM) and elemental dispersive spectroscopy (EDS). Additionally, the corrosion scale and salt layer were characterized via powder X-ray diffraction (XRD). The addition of 800 ppm of hydrogen chloride (HCl) gas to a mixed gas oxidizing environment accelerated the corrosion rate of SA178A (Fe-0.1C) at 500°C (932°F) as determined by the change in the parabolic rate constant over a period of 72 hours, from 0.18 to 1.7 μm²/h (3.0 E-03 to 2.5 E-02 mil²/h). The findings from the EDS and XRD scale analyses were compared to other literature and thermodynamic calculations that showed that effect that HCl accelerates corrosion via an active oxidation mechanism. A parametric study was performed on the effect of hydrogen chloride on three alloys, SA178A, SA 213-T22 (2.5 Cr-1 Mo-Fe) and NSSER-4 (Fe-17Cr-13Ni). Varying the concentration from 400 ppm to 800 ppm at 500°C increased the mean mass loss by 17.5%, as compared to the 60% increase from 0 to 400 ppm. For each alloy, the mass loss increased sharply with temperature between 450, 500, and 500°C, with corresponding apparent activation energies of Ea NSSER- 4 53 kJ/mol, Ea SA213 T22 110 kJ/mol, and Ea SA178A 111 kJ/mol. The lower apparent activation energy for NSSER-4 demonstrates that effect of hydrogen chloride is mitigated with austenitic alloys versus carbon steel or low alloyed steel. In a comparative study between isothermal and temperature gradient tests, it was also shown that the corrosion of SA178A was not impacted by a temperature gradient up to 250 °C. Another important chlorine compound in WTE boilers are metal chlorides, which are readily contained in fly ash and boiler deposits. Using sodium chloride as a surrogate compound, the corrosion behavior under chloride salts was investigated by applying a salt layer (4.0 mg/cm²) on coupon surfaces. Corrosion under the chloride layer was much more severe than below the HCl-containing atmospheres alone. The mass loss for the commercial steels was increased by more than an order of magnitude. Based on SEM and XRD coupon and corrosion product characterization, this behavior was the result of a second active oxidation mechanism in which sodium chloride reacts with and depletes protective oxides such as chromium (II) oxide. The WTE furnace tests with the sodium chloride layer were executed for six different Ni-Cr coatings, including Inconel 625 (Ni-Cr-Mo), SW1600, SW1641 (Ni-Cr-Mo-B-Si) and Colmonoy 88 and SP 99 (Ni-Cr-B-W). The primary corrosion attack observed was pitting located under the original salt layer. Colmonoy 88, showed superior corrosion resistance with mass losses between 0.3-3.1 mg/cm2 between 450-550°C as compared to the Ni-Cr-Mo, and Ni-Cr-B-So coatings which has mass losses between 10-30 mg/cm². The enhanced corrosion performance of Colmonoy 88 and SP 99 was attributed to the alloying addition of tungsten, which had been previously shown in literature to also improve the pitting resistance for Ni-Cr in aqueous environments. The corrosion behavior under metal chlorides was compared with metal sulfates, which are also prominent in WTE fly ash and boiler deposits. The application of sulfate salts on coupon surfaces was shown to semi-protective on WTE boiler tube surfaces up to temperatures of 550°C. The mass loss for carbon steel and Fe-17Cr-13Ni (NSSER-4) below sodium sulfate was an order of magnitude lower than under sodium chloride. These results motivated experiments aimed at sulfating chloride boiler deposits by increases the sulfur/chlorine gas ratio (SO₂/HCl) in WTE fuel gas. The SO₂/HCl ratio was modified between 0.3 to 0.6 and 1.0 respectively. By increasing the SO₂/HCl ratio, the sodium chloride layer applied on the coupon surface was converted from a chloride rich salt to a sulfate rich and was shown to dramatically reduce the corrosion of tube alloys up to 500°C. The impact of sulfating the alloy was most prominent with alloys with high mass loss under the sodium chloride layer. Tests showed a reduction in the corrosion rates of SA213 T22 (37%), Inconel 625 (23%), and NSSER-4 (27%). At 550 °C, there was no trend with respect to increases of the ratio, which suggests that other corrosion reactions are faster than the rate of sulfation. Finally, the annualized cost factor was defined and proposed as a method for replacing current superheater alloys with alternative materials, such as those tested in this thesis. From this discussion it was calculated that the installation of a colmonoy 88 protected superheater can cost approximately 1.4 times the cost of an Inconel 625 cladded replacement, or as much as 4.3 times the cost of a T22 superheater tube and remain a cost effective option.

Thesis (Doctor of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2017. / The search for alternatives to fossil fuel is necessary with a view to reducing the negative environmental impact of fossil fuel and most importantly, to exploit an affordable and secured fuel source. This study investigated the viability of municipal solid waste gasification for a fuel cell system. Potential solid fuels obtained from the study in the form of refuse-derived fuel (RDF) had high heating value (HHV) between 18.17 MJ/Kg - 28.91 MJ/Kg with energy density increased from 4142.07 MJ/m3 to 10735.80 MJ/m3. The molecular formulas of RDF derived from Ladies Smith drop-off site, Woodstock drop-off site and an average molecular formula of all thirteen municipal solid waste (MSW) disposal facilities were CH1.43O1.02, CH1.49O1.19, and CH1.50O0.86 respectively. The comparative ratios of C/H were in the range of 7.11 to 8.90. The Thermo Gravimetric Analysis showed that the dehydration, thermal decompositions, char combustions were involved in the production of gaseous products but flaming pyrolysis stage was when most tar was converted to syngas mixture. The simulation of RDF gasification allowed a prediction of the RDF gasification behaviour under various operating parameters in an air-blown downdraft gasifier. Optimum SFR (steam flowrate) values for RDF1, RDF2 and RDF3 were determined to be within these values 2.80, 2.50 and 3.50 and Optimum ER values for RDF1, RDF2 and RDF3 were also determined to be within these values 0.15, 0.04 and 0.08. These conditions produced the desired high molar ratio of H2/CO yield in the syngas mixture in the product stream. The molar ratios of H2/CO yield in the syngas mixture in the product stream for all the RDFs were between 18.81 and 20.16. The values of H2/CO satisfy the requirement for fuel cell application. The highest concentration of heavy metal was observed for Al, Fe, Zn and Cr, namely 16627.77 mg/Kg at Coastal Park (CP), 17232.37 mg/Kg at Killarney (KL), 235.01 mg/Kg at Tygerdal (TG), and 564.87 mg/Kg at Kraaifontein (KF) respectively. The results of quantitative economic evaluation measurements were a net return (NR) of $0.20 million, a rate of return on investment (ROI) of 27.88 %, payback time (PBP) of 2.30 years, a net present value (NPV) of $1.11 million and a discounted cash flow rate of return (DCFROR) of 24.80 % and 28.20 % respectively. The results of the economic evaluations revealed that some findings of the economic benefits of this system would be viable if costs of handling MSW were further quantified into the costs analysis. The viability of the costs could depend on government responsibility to accept costs of handling MSW.

The use of municipal refuse (RDF) as fuels has received widespread attention for reason of its energy equivalence and the increasing lack of available landfill sites. The principal obstacle to the construction of combustion facilities is that RDF produces toxic compounds, including heavy metals and such organic compounds as PCDD and PCDF. In this study, the emissions of metal and organic compounds were investigated under oxygen deficient and oxygen surplus conditions for the RDF and such high volume contributors as office papers and magazines. The principal metal emissions of the RDF were Al, Ca, K, Si, and Zn. Magazines significantly contribute B, Mg, Mn, Ti emissions, whereas office papers contributed Ti and Zn emissions. The metal emissions were not significantly different between oxygen deficient and oxygen surplus conditions at a temperature of 750��C. The combustion of RDF produced a full range of PCDFs and PCDFs, the source of which was determined to be RDF, papers, and even untreated wood combustion effluents in the parts-per-billion range. In contrast to metal emissions, emission rates were higher under the oxygen surplus condition than for the oxygen deficient condition and PCDD and PCDF emissions were significant in relation to the chloride contents of fuel, rather than by fuel type as was the case for the large volume contributors. With the exception of Hg, Se, S, Sr, and Pb, the metal emissions were largely derived from the particles in the effluent. / Graduation date: 1993 / Text is slanted on original. Best scan available.

Effective combustion of waste fuels requires an understanding of the fuels characteristics. Gaseous and particulate emissions, ash residues and combustion properties are of interest to many; those that produce and sell heating units, utilities interested in using the fuels for power generation, regulatory agencies, municipalities needing to solve a disposal problem, and environmentally conscious people interested in maximum utilization of resources. A study was conducted at Oregon State University to test and evaluate the use of two types of waste: mixed waste paper (MWP) and refuse derived fuel (RDF). Wood biomass (ponderosa pine) was used as a benchmark and also cofired with MWP. Samples collected from the Pacific Northwest were tested for physical, chemical, combustion, and emission characteristics. Raw fuel samples were tested for moisture content and bulk density. The samples were then shredded and pelletized. Pelletized fuels were tested for ultimate and proximate analyses, ash fusion temperature, elemental ash analysis, higher heating value, moisture content, bulk density, and pellet durability. Using an existing biomass combustion facility, the samples were fired to determine the optimum thermodynamic conversion combustion condition for each fuel. Observations were made of physical problems associated with firing of the samples. Combustion products were continuously monitored for temperature and composition with a combustion analyzer. An EPA Method 5 sampling train was used to determine particulate, heavy metals, chloride, fluoride, and sulfate emissions. Leachate testing was performed on the bottom ash residue to determine heavy metal concentrations. Waste fuels provided a challenge for combustion study in a biomass combustion unit. Modifications were required to alleviate high ash content problems. Observations of corrosion and clinkers provided another comparison for fuel evaluation. Comparison of emissions resulting from different fuel types provided good practical information for industrial purposes. Observed trends indicated possible minimization of emissions corresponding to optimum thermodynamic conversion. Cofiring analysis revealed possible increases and decreases of heavy metal emissions for MWP and wood. / Graduation date: 1992

Waste to energy (WTE) has been used in some Asian and European countries for decades. It has been re-considered in Hong Kong to solve the landfill space shortage problem since 2000. The consideration was planned for over 10 years but still has not been implemented due to political and social problem. Due to all landfills will be reaching their designated capacity before 2020, there is urgent need to explore other means of disposal. Based on international experience in this study, three technologies are identified to have high potentials, moving grate incineration, anaerobic digestion and plasma gasification. Although moving grate incineration are the most widely used as core technology for large scale plant, anaerobic digestion and plasma gasification are more socially acceptable due to its technological difference. Plasma gasification is a newer technology on waste treatment that the government should explore on the integrated waste management facilities project. The use of all technology variants will cause certain social impacts, and the best use of the facilities affects the benefit to society and influences the public’s view. In the study, the IWMF and OWTF are generally support by the public, but the public’s views are dispersed. Currently the public concerns about the site selection and health & safety problem of both government plan, and required the improvement of recycling and source separation system. Also public are lacking the knowledge of waste management option that Hong Kong could take to solve the waste problem, indicating the need of better government-general public communication mechanism. The government has to do better planning for the use of WTE and engage the public on different level to minimise the social opposition voice in order to proceed with the WTE plan. Policy to gain public support and remove obstacle from private sector are the major works required instead of pure technical report on the choice of WTE facilities as the government has done in the last decade. / published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Thesis (M.S.)--Rochester Institute of Technology, 2007. / Typescript. Includes bibliographical references (leaves 84-87).

Mass balance analysis of two-phase AD indicated that off-gas (H2 and CO2) produced in acidogenic reactor represent up to 30% of the consumed substrate and under most circumstances, this part of energy was not utilized leading to low overall energy recovery. Hence, the objective of this study was to enhance overall energy recovery during two-phase AD of food waste through reutilization of acidogenic off-gas and to further optimize the processes through manipulating the metabolic pathways and controlling acidogenic off-gas production. In the first phase, feasibility of reutilizing acidogenic off-gas in methanogenic reactor and contribution of acidogenic off-gas to overall energy recovery was investigated. Acidogenic off-gas diversion increased the methane gas (CH4, 0.28 L/g VSadded) production up to 38.6%, of which ~8% was contributed by acidogenic off-gas. Both higher hydrolysis rate and COD production were also achieved with off-gas diversion. Metabolic pathway determines the distributions of intermediate soluble products, which constitute the quality of acidogenic leachate. Therefore, two experiments focusing on manipulating metabolic pathways were performed. Firstly, the effects of four levels of headspace pressures, 6-12 psi (T1), ~3-6 psi (T2), ~3 psi (T3) and ambient pressure (T4) were investigated. Mixed acids metabolic pathways prevailed in all the treatments with butyrate as the single major component. Then, four different levels of H2 partial pressure (PH2) were set the next experiment, self-generated PH2 (T1, control), 80% of H2 (T2), 60% of H2 (T3) and 0.04% of H2, while the headspace pressure was kept at 3.3 psi. Typical butyrate fermentation pathways dominated in T4 whereas mixed acid fermentation pathways were prevailing in the other three treatments. Because of the improved hydrolysis/acidogenesis and higher quality of acidogenic products, overall CH4 recovery in T4 (301.0 L/kg VSadded) was 44.6% higher than the control. In Phase III, strategies to enhance acidogenic off-gas production were investigated. First, four types of neutralization modes including daily pH adjustment of leachate to 6.0, methanogenic effluent recirculation, and initial addition of NaOH and lime separately at a dosage of 20.0 and 14.0 g/kg food waste, respectively, were investigated. Obviously, a H2 production rate of 3.0 and 2.1 L/d with lime and NaOH addition was much higher than 0.7 and 0.4 L/d with effluent recirculation and daily adjustment, respectively. Also, addition of alkali agents could enhance the COD leaching of food waste, especially with NaOH. A CH4 production of 11.24 L/d could be attributed to both the elevated leachate quality and the acidogenic off-gas with lime addition. Another experiment investigated the effect of different carbohydrate contents in the substrates on acidogenic H2 production. Anaerobic hydrolysis of wastes sourced from bakery (T1), Chinese-style restaurant (T2), western-style restaurant (T3) and wet market were performed in LBRs. Food waste collected from western-style restaurant with a carbohydrate content of 69.5% achieved the highest H2 production of 61.0 L/kg VSadded. The highest specific CH4 production rate at 0.42 L/gVSadded was also achieved with western restaurant food waste. Finally, the possible redirection of fluxes associated with shift of metabolic pathways from the experiment of PH2 was proposed. Significant increase in the production of butyrate in treatment T4 with PH2 of 3.3 psi × 0.04% indicated the channeling of electrons towards the production of butyrate. Dynamics of the microbial community were correlated with the distribution of metabolites. In T1 without external gas flushing, lactic acid fermentation was dominant during the initial 7-days. Accordingly, phylotypes affiliated to the genus Lactobacillus sp. were detected. A heterlatic fermentation pathway was observed in in both T2 and T4 during first four days, and thereafter the fermentation pathways shifted towards acetate and butyrate as dominant products, which were accompanied by changing the microbial community with phylotypes of Clostridium sp. and Bifidobacterium sp. becoming dominant. To conclude, reutilization of acidogenic off-gas by diversion to methanogenic phase is a promising strategy for enhancing overall energy recovery during two-phase AD of food waste. However, improvement of the short-lived acidogenic H2 production and H2/CO2 ratio needs further investigation.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016. / The generation of municipal solid waste has increased significantly due to the exponential population growth and it has become a global issue. Gasification technology, an alternative method for waste treatment is a thermochemical process where carbon-based material are exposed to an environment deprived in oxygen, was used for this project. The aim of this thesis is to study the gasification of plastic waste which is a potential alternative energy source using infrared heaters. To achieve this goal, fundamental studies have been numerically and experimentally conducted for an infrared gasifier and subsequently establishing the temperature profile for gasification using a small scale reactor. A detailed study on low density polyethylene was conducted using Infrared Spectrometry and thermal decomposition techniques such as Thermogravimetry and Differential Scanning Calorimetry were performed to establish the temperature at which plastic pellets sample used for this research gasify. The gasification behaviour of pelletized low density polyethylene (plastic pellets) was tested and three case studies were done to evaluate the most suitable temperature profile for the reactor to gasify the low density polyethylene at high temperature for less amount of time. Subsequently, the reactor model was simulated and results validate the use of reactor at an optimum temperature of 800 °C for a gasification process with less residue content. The reactor designed for this research is fully functional and validates the temperature behaviour predicted during simulation. The experimental results show infrared heaters are suitable for gas production using this gasification process.