Municipal Solid Waste Moisture Research Articles

Development, exergoeconomic assessment and optimization of a novel municipal solid waste-incineration and solar thermal energy based integrated power plant: An effort to improve the performance of the power plant

Due to the growing population rate and increasing social activities, the content of municipal solid waste (MSW) production is increasing. Energy production from MSW is one of the promising ways to dispose of waste and reduce the limitations of fossil energies. However, this technology has a relatively low efficiency due to the high volume of moisture and inert materials in MSW and the lower heating value of waste. The integration of solar thermal collectors is one of the suggested solutions to increase the temperature of inlet steam to the power generation cycle in order to improve the power plant performance. In this regards, the present study develops a comprehensive thermodynamic-conceptual and exergoeconomic investigation of the performance of a MSW-incineration (MSWI) plant integrated with a parabolic trough collector (PTC)-based solar field. Accordingly, the temperature of the steam elevates by the solar field before entering the electric power generation cycle. Additionally, the solar unit is integrated with a phase change material (PCM)-based storage system. The use of storage tank at the delivery line of PTC can improve the power plant’s reliability. A comprehensive comparison of the developed power plant with the conventional MSWI power plant is presented. In addition, the technical and economic behaviors of the considered power plant have been optimized under two different single and multi-objective optimization scenarios. The outcomes indicated that the developed power plant can provide 15.75% and 15.68% higher energetic and exergetic efficiencies compared to MSWI power plant. In addition, the rate of electric power obtained from S-MSWI power plant is almost 16.1% more compared to MSWI power plant. However, the total cost rate of MSWI plant is almost 24.13% lower compared to the developed power plant. But, the value of LCOE in the developed power plant is approximately 8.93% lower than MSWI power plant. It was also found that, the multi-objective optimization can provide better and optimal results to energy engineers and decision makers compared the single-optimization. The conceptual design of the implementation of the solar field is also developed in a specific geographical condition. Additionally, this research comes from the key technology of the National Key Laboratory of Environmental Protection.

Modelling of an Integrated Plasma Gasification Combined Cycle power plant using Aspen Plus

The development of a steady-state model of an Integrated Plasma Gasification Combined Cycle (IPGCC) power plant is presented here. The model includes the plasma gasifier, syngas conditioning units, and the power generation unit. Furthermore, the model of each component implemented in Aspen Plus is described in detail (thermodynamic method, chemical reactions, and operative conditions). The proposed model was validated by comparing the plasma gasification results with experimental and numerical data from the literature; the relative error was 6.23% and 5.24%, respectively. The model was then used to perform a two-part sensitivity analysis. In the first part, simulations with municipal solid waste (MSW) with a moisture content varying from 20% to 60% were performed. The moisture content increment reduced the torch-specific power consumption by 53%. However, because of the increasing specific fuel consumption, the thermal efficiency of the IPGCC power plant also decreased by 28% as the MSW moisture content increased from 20% to 60%. In the second part, it was determined that the IPGCC power plant reached the best performance (32.5%) when a high plasma temperature (5000 °C) and a low gasification temperature (2000 °C) were used. At these highest efficiency conditions, the 1000 t/day IPGGC power plant’s net power generation was 62 MWe.

Exergoeconomic analysis and optimization of an innovative municipal solid waste to energy plant integrated with solar thermal system

Waste to energy technology is the most promising method to deal with municipal solid waste. However, electrical efficiency of conventional waste-to-energy incineration is low due to the limits of steam turbine inlet parameters by the high moisture in municipal solid waste with low heating value. An integration of municipal solid waste incineration plant with solar thermal system was proposed and designed to increase the energy production efficiency. The integration is accomplished by increasing the steam temperature with the secondary heating by solar parabolic dish system, installed between the exit of the incineration boiler and the entrance of steam turbine. Thermodynamic and exergoeconomic performance of the integrated waste-to-energy plant is evaluated using engineering equation solver, while optimization is performed to set the optimal parameters of the system. Thermodynamic results conclude that the thermal and exergetic efficiencies of the integrated plant are 30.57% and 32.42%, while for conventional plant are only 28.35% and 26.74% respectively. Exergoeconomic analysis reveals that the exergetic cost rate of destruction for the integrated plant is 907.3 $/h and 25.61% more than the conventional design whereas, the total cost rate of the proposed system is approximately 1103 $/h. Generally, it can be concluded that the solar integrated waste to energy plant depicts great performance from a thermodynamic, economic, and environmental perspective.

Sustainable optimization of waste management network over extended planning time horizon

AbstractThis study proposes a multiperiod mixed integer linear programming model for the management of a single municipal solid waste (MSW) treatment plant with sustainability as the objective. Discrete and continuous variables define the capacity selections for diverse MSW technologies, and the operation of the MSW network, respectively. The economic target is considered to maximize the net present value. The environmental impact is the minimization of a normalized environmental objective function (NEOF). The social target is the maximization of jobs. An interesting feature about the research work is the requirement of biodrying technologies for MSW moisture content control. Due to the conflicted nature among the sustainability components, a multiobjective optimization (MO) is carried out to find the Pareto optimal solutions. The MO results show that the Pareto optimal solutions vary around profit range of $4.9–8.5 billion, NEOF impact range of 3.2–3.6 units, and social benefit range of 2700–4828 jobs.

Pilot-scale grinding and briquetting studies on variable moisture content municipal solid waste bales – Impact on physical properties, chemical composition, and calorific value

Low bulk density, variable moisture content, and particle size of municipal solid waste (MSW) create feeding, handling, storage, and transportation challenges. In this study, MSW bales were size-reduced in stage-1 and stage-2 hammer mill grinders fitted with 50.8-mm and 6.35-, 12.7-, and 19.05-mm screens. Ground MSW was densified further in a pilot-scale briquette press by varying moisture content in the range of 10–25% wet basis (w.b.). At 40% (w.b.) MSW moisture content, the stage-1 grinder fitted with a 50.4-mm screen took about 136kWh/ton, while the stage-2 grinder fitted with a 19.05-mm screen took about 151kWh/ton. The bulk density of MSW after stage-1 and stage-2 grinding was about 25–50 kg/m3. Unit bulk and tapped density were in the range of 680–850 kg/m3, 478–315 kg/m3, and 346–540 kg/m3 post briquetting, and 591–830 kg/m3, 295–458 kg/m3, and 319–519 kg/m3 post five days of storage at 20 °C. The durability was about 93.40–98.54% post briquetting, and after five days of storage. Increasing the moisture content and screen size decreased density and improved durability. Briquetting energy increased to 120 kWh/ton at a higher moisture content and larger grind size. MSW flow characteristics improved after briquetting. Higher lignin content (≈30%) and calorific value (19–21 MJ/kg) suggest MSW is suitable for thermochemical conversion. Ash content in the MSW was in the 11.9–14.8% range. CT-scan images of the briquettes showed a network of interconnected pores formed due to compression of various MSW fractions.

Seasonal Changes in the Composition and Thermal Properties of Municipal Solid Waste: A Case Study of the City of Perm, Russia

The paper presents experimental studies of municipal solid waste (MSW) composition and its thermal properties (moisture and ash content). Measurements were taken to track seasonal changes in the composition of MSW. For example, in spring, the content of organic waste was 17.0% and, in autumn, it reached 31.5% due to considerable consumption of seasonal vegetables and fruits. The share of paper in MSW changed from 21.4% in spring to 9.7% in autumn. More paper in spring is due to discarded student notebooks at the end of a school year, as well as spring household cleaning. These data indicate significant changes in waste composition during the year, which should be taken into account when planning technologies for waste management.
 Laboratory studies of moisture and ash content by season allowed the range of these changes to be determined. In autumn for instance, the moisture and ash content of organic waste was about 82% and 14%, respectively, while in winter, it was approximately 73% and 22%, respectively. These figures can be explained by the organic waste origin: autumn organic waste often comes from fruit pulp and, for example, watermelon peels, and winter organic waste tends to consist mostly of dry vegetable peels such as potato peelings.
 The low calorific value of certain components is based on their composition and the level of moisture and ash in different seasons. Therefore, it is important to take into account the moisture and ash content of individual components, not average values, in order to calculate the waste calorific value.
 MSW thermal characteristics change significantly over the seasons: the MSW moisture content is the highest in autumn (about 49%) and the lowest in winter (32%). The ash content in MSW ranges from 20% in spring and autumn to 27% in summer. The lowest calorific value per working mass in different seasons varies from 7 to 10 MJ/kg, which must be taken into consideration when developing waste management systems in general and when designing specific energy recovery facilities.

Stochastic economic analysis of coal-alternative fuel production from municipal solid wastes employing hydrothermal carbonization in Zimbabwe.

Hydrothermal carbonization (HTC) is a promising technology for converting high moisture municipal solid waste (MSW) to a safe low-chlorine hydrochar. The key objective is to assess the economic viability of an HTC based MSW management system in Zimbabwe. Previous studies have only used deterministic estimates of hydrochar production costs disregarding uncertainties in their model parameters. Herein, a probabilistic economic analysis is introduced to quantify the uncertainty concerning costs. The goal is to determine factors that will consolidate the venture to achieve a certain level of return. The effectiveness of different investment strategies, namely, a government or private sector-run operation will be tested using Monte Carlo simulations. Results indicate a 55% and 18% probability for a positive Net Present Value (NPV) for a state-run and private operation respectively. A specific investment cost of US$54 - 67 per Mg of MSW treated, a return on investment (ROI) of 5.4-29.0% and internal rate of return (IRR) of 5.2-22.9% can be expected if the project is undertaken by government. The private sector can expect an ROI of -0.8-18.2% at a 90% confidence level and a lower IRR of -2.1-16.2% from US$57 - 71 per Mg of MSW invested. Contingency costs are US$25 per Mg and US$38 per Mg of MSW for the government and private sector respectively at a 100% confidence interval. A 70% rise in collection tariffs or a minimum selling price of US$91/Mg of the hydrochar would ensure a positive NPV for the government-run operation.

Suitability of municipal solid waste in African cities for thermochemical waste-to-energy conversion: The case of Harare Metropolitan City, Zimbabwe.

The recovery of energy from municipal solid waste (MSW) has gained popularity in many industrialized countries, but its adoption in economically developing countries, especially in Africa, has been slow. While capital investments and technical requirements for waste-to-energy (WtE) systems are among the most important causes for this slow adoption, the unavailability of data on the thermochemical quality of MSW as a potential feedstock for energy recovery is also a limiting factor. In this paper, Harare, a typical African city, was selected as a case study. The evaluation was based on the analysis of the MSW's composition, moisture as-discarded, thermochemical properties and energy content. The results show that the quality of the MSW is comparable to that in regions outside Africa where WtE has been a success. The combustible fraction exceeded 75 wt% making it ideal for thermal treatment without requiring supplementary fuel. With an MSW throughput of 421,757 tonnes year-1 (11.1% of which is recycled), and a lower heating value of 10.1 MJ kg-1, the energetic potential was estimated at 3.8 × 106 GJ. MSW thermal treatment via conventional technologies can reduce the waste throughput to landfills by up to 40%, provide up to 112 GWh year-1 of electrical energy, and increase the annual share of electrical energy produced from bio-fuels and wastes from 1.3% to at least 2.2%. These benefits make thermal MSW treatment a suitable option for waste disposal in African cities.

Distribution and modeling of tar compounds produced during downdraft gasification of municipal solid waste

Tar compounds produced during gasification of municipal solid waste (MSW) hinder downstream utilization of syngas. This study investigated the effects of operating conditions (temperature, equivalence air ratio (ER) and MSW moisture content) during gasification using air on tar emissions. Tar was quantified by gravimetric and GC-MS methods, denoted as gravimetric and collected (GC-MS) tar, respectively. Additionally, styrene evolution was studied as it is one of the main tar compounds produced from MSW. By applying the response surface methodology for modeling, it was found that tar contents quantified by the two methods are influenced similarly by ER and MSW moisture content, but differently by temperature. This discrepancy was attributed to the different composition and properties of tar fractions measured by gravimetric and GC-MS methods. Since the selection of analytical method can have impact on the quantification of tar, adoption of different methods for the characterization of tar emissions from MSW gasifiers is essential in order to provide a holistic analysis of the tar evolution process. The content of styrene in collected (GC-MS) tar from MSW gasification was 13–29%. The lower contents of styrene were favored by operating temperature between 850 and 900 °C, higher ER and higher MSW moisture content.

Enhanced power generation through integrated renewable energy plants: Solar chimney and waste-to-energy

In the present paper, a novel method is proposed to enhance the power production and resolve the inconsistent electricity generation of solar chimney power plants (SCPPs) during nighttime. For this purpose, an integrated renewable cycle is proposed by incorporating two technologies: solar chimney and waste-to-energy. The combination is performed by exploiting the warm air of the condensers outlet into the SCPP. The waste-to-energy (WTE) plant in Tehran is thermodynamically analyzed and the mass flow rate of the condensers cooling air is found. Results indicate that by decreasing the humidity of the municipal solid waste (MSW) from 40% to 30% or by increasing MSW feeding rate (0.934–1.146 kg/s), the mass flow rate of the condenser cooling air increases from 190.3 kg/s to 233.7 kg/s. In addition, by increasing the feeding rate or by decreasing the humidity of MSW in the mentioned range, net power output of the WTE plant increases from 1350 kW to 1650 kW. The best injection method is proposed for the warm air of the condensers outlet into the SCPP. Subsequently, the average power increase is examined in different months and parametric study is performed to assess the influence of the effective WTE parameters and meteorological variables on the power output of the SCPP. The final power of the SCPP reaches 20–70 kW (even at the hottest night of the year with 5% relative humidity) and increases 20–1200% and 65–94% (monthly average) compared to the case of without injection. Results demonstrate that in the integrated system, by a 22% increase in the MSW feeding rate (from 0.934 kg/s to 1.146 kg/s) or by decreasing the MSW moisture content (from 40% to 30%), power output of the WTE plant and SCPP increases by 22% and 7%, respectively. Additionally, relative humidity of the surrounding air can increase the SCPP power production by 25%. In addition, the results indicate that wind speeds higher than 12.5 m/s will not affect power production of the SCPP, while relative humidity of the surrounding air, ambient temperature, the MSW feeding rate, and humidity of the MSW have considerable effects on the SCPP power production. In average, total energy and useful exergy efficiency of the proposed system is increased by 0.15% and 0.12% compared to the standalone WTE plant during nighttime. The integration of SCPP with the WTE plant is an applicable method to enhance the power generation and overcome the inconsistent power production of SCPP during nighttime.

Numerical and experimental studies on effects of moisture content on combustion characteristics of simulated municipal solid wastes in a fixed bed

In order to reveal the features of the combustion process in the porous bed of a waste incinerator, a two-dimensional unsteady state model and experimental study were employed to investigate the combustion process in a fixed bed of municipal solid waste (MSW) on the combustion process in a fixed bed reactor. Conservation equations of the waste bed were implemented to describe the incineration process. The gas phase turbulence was modeled using the k–ε turbulent model and the particle phase was modeled using the kinetic theory of granular flow. The rate of moisture evaporation, devolatilization rate, and char burnout was calculated according to the waste property characters. The simulation results were then compared with experimental data for different moisture content of MSW, which shows that the incineration process of waste in the fixed bed is reasonably simulated. The simulation results of solid temperature, gas species and process rate in the bed are accordant with experimental data. Due to the high moisture content of fuel, moisture evaporation consumes a vast amount of heat, and the evaporation takes up most of the combustion time (about 2/3 of the whole combustion process). The whole bed combustion process reduces greatly as MSW moisture content increases. The experimental and simulation results provide direction for design and optimization of the fixed bed of MSW.

Numerical Simulation on Moisture Influence to MSW Combustion

The combustion process of municipal solid waste (MSW) in a operating 750t/d grate furnace in Guangzhou was researched by means of numerical simulation. The influence of MSW moisture content on burning effect was discussed. The results show that: with the moisture content dropped from 50% to 30%, the heat value could be evaluated from 13.72% to 54.91% and the average temperature in the furnace could be promoted 90-248°C. However, the combustible gases and particle in the flue gas of outlet would take up a high proportion since lacking of oxygen would lead to an incomplete combustion. The excess air coefficient should be increased to 2.043~2.593 in order to ensure the flue gas residence time more than 2s and temperature in the furnace higher to 800°C.

Slope stability of bioreactor landfills during leachate injection: Effects of geometric configurations of horizontal trench systems

In bioreactor landfills, different configurations of closely spaced horizontal trench (HT) systems are often considered as leachate recirculation systems to achieve uniform and rapid distribution of moisture in municipal solid waste (MSW). In this study, a numerical two-phase flow modelling was adopted to study the effects of geometric configuration of HT systems on the moisture distribution in MSW, and the stability of a simplified bioreactor landfill slope during continuous and intermittent leachate recirculation. Transient variations in pore water and capillary pressures in MSW were assessed, and slope stability analyses were performed using strength reduction technique. MSW was considered as heterogeneous and anisotropic with varied unit weight and saturated hydraulic conductivity. The results demonstrated that geometric configurations of HT systems significantly affected the moisture distribution, generation and distribution of pore water and capillary pressures in MSW, and considerably influenced the mechanical stability of bioreactor landfill slope. It was concluded that staggered configuration of closely spaced HT systems with intermittent sequences of leachate recirculation and subsequent gravity drainage in alternate shallow and deep HT layers should be adopted as they produce uniform moisture distribution and ensure the mechanical stability of landfill slope due to low induced pore pressures near side slope. Overall, this study presents a significant contribution to the understanding of the basic mechanisms controlling the geotechnical stability of bioreactor landfills during leachate operations. Furthermore, the capability of the adopted commercial code was verified with complexities related to bioreactors behaviour. However, further research is needed to validate the model based on field monitoring data at actual bioreactor landfills.

Moisture Transfer Models and Drying Characteristics of MSW Containing High Moisture

T he effect of high moisture content on drying characteristics of high moisture municipal solid waste (MSW) material, such as carrot peel and pomelo peel was investigated. The experimental data used to fit the selected published mathematical drying models of samples ， were conducted in a thermogravimetric furnace. Weight reduction during drying was measured with a microbalance in the range of 80-140℃. T he variations of moisture content and drying rate at different temperature were considered. The results show that with increasing in drying temperature the drying time decreased and the maximum drying rate increased at the beginning of drying process .The effective diffusivity ranged from 1.49×10 -9 to 1.25×10 -8 m 2 /s with Fick’s diffusion equation. The activation energy value of 17.12kJ/mol and 37.48kJ/mol was determined through Arrhenius equation. The Modified Page model and Weibull distribution model were the most adequate models in describing the drying process of MSW samples . DOI : http://dx.doi.org/10.11591/telkomnika.v12i3.4478 Full Text: PDF

Environmental, Economic, and Energy Assessment of the Ultimate Analysis and Moisture Content of Municipal Solid Waste in a Parallel Co-combustion Process

Use of municipal solid waste (MSW) as fuel for electricity generation reduces landfill disposal and can mitigate air quality degradation associated with combustion of conventional fossil fuels. Co-combustion is a waste-to-energy technology that can use MSW and coal as co-fuels, offering potential energy recovery and reduced air emissions. This research discerns how MSW composition influences the heating value and air pollution for the co-combustion of coal with MSW using five MSW composition scenarios, four of which were derived by a reduction of plastics, organics, paper, or a combination thereof, as compared to the national average MSW composition. Numerous combustion products could be evaluated; this study focused on five high impact air combustion products: SO2, CO, CO2, NO, and NO2. The moisture content was varied from ∼10% (considered dry) to 40% (average MSW moisture). AspenPlus software was used for the deterministic simulation modeling of incineration (MSW only) and parallel co-firing (co-combustion of coal and MSW) to determine theoretical heating values and pollutant effluent concentrations. The United States Environmental Protection Agency (U.S. EPA) models WAR and WARM were used to determine the potential environmental impacts (PEIs) and greenhouse gas emission equivalencies, respectively, for each MSW scenario. For the WAR model, values for each impact category parameter can vary, but each parameter is weighed equally. Of the MSW scenarios studied, the national average held the highest heating value with 8519 MBtu/lb and the lowest occurred for the MSW scenario with recycled paper and composted organics, with 8251 MBtu/lb. Results show that SO2, CO, CO2, NO, and NO2 flue gas concentrations (and therefore PEIs) depend upon the composition and moisture of the MSW, in addition to the MSW/coal ratio. Approximate ranges for the WAR results (PEI/h) are 7410–7663 for NO, 4–8 for NO2, 18–105 for CO, 30–46 for CO2, and 89–2152 for SO2. WARM results show lower net CO2 emission equivalents to landfill MSW with reduced paper and organics, while combustion is preferred for MSW with paper reduction, organics reduction, and plastics reduction. The results for the national average MSW were independent of the disposal processing method. Reduction in pollutant concentrations did not yield overall cost savings for the electricity producer, as profit was reduced by ∼20–30%. There are savings associated with emission costs using MSW in lieu of coal: up to ∼3.3% for NO, ∼20–47% for NO2, and ∼95% for SO2. A hypothetical carbon dioxide tax was also imposed to realize the potential cost savings by reducing CO2 emissions. In summary, the measurable impact MSW composition and moisture had on pollutant concentration, heating value, and economic parameters was important.

Simulation of Syngas Production from Municipal Solid Waste Gasification in a Bubbling Fluidized Bed Using Aspen Plus

A comprehensive process model is developed to simulate municipal solid waste (MSW) gasification in a bubbling fluidized bed using an Aspen Plus simulator. The model is based on a combination of modules that the Aspen Plus simulator provides, representing the three stages of gasification (devolatilization, partial oxidation, and steam reforming). The restricted equilibrium method is used to correct the deviation caused by uncompleted equilibrium of gasification system. Effects of operating parameters, including gasification temperature, equivalence ratio (ER), oxygen percentage in the enriched air (OP), MSW moisture content, and steam/MSW ratio (S/M), on the syngas composition and gasifier efficiency are analyzed. Higher temperature favors the production of H2 and CO and leads to higher gasification efficiency. Increasing ER improves the CO yield and the carbon conversion of MSW at lower ERs. The optimal value of ER for air gasification of MSW in this study is found to be 0.35. The use of enriched air elev...

Leachate generation and biogas energy recovery in the Jebel Chakir municipal solid waste landfill, Tunisia

A survey was conducted between 2006 and 2008 in order to identify municipal solid waste (MSW) composition and its influence on leachate generation and to assess the amount of biogas yield from the Jebel Chakir landfill in Tunis City. The organic fraction was the predominant compound in the MSW, followed by paper, fine, plastic, leather, rubber, metal, textile, glass and ceramic. The average MSW moisture content varies from 60 % in the wet season to 80 % in the dry one. The recognised MSW composition is well representative if compared to that of cities in developing countries. A large leachate quantity is produced in the landfill of Jebel Chakir, despite the negative water balance of the site. Based on the annual MSW landfilled quantities and using the LandGEM model, the expected peak landfill gas (LFG) production is estimated to occur 1 year after the landfill closure with a rate of 3.53 × 107 m3/year. The analysis of the potential conversion of LFG to electric energy shows it at a total LFG-to-electricity energy of around 257 GWh with a heating value of 4,475 kcal/m3 based on an LFG collection efficiency of 33 % and energy efficiency of 33 % giving an economic feasibility for a 10 MW power plant.

Impact assessment of intermediate soil cover on landfill stabilization by characterizing landfilled municipal solid waste

Waste samples at different depths of a covered municipal solid waste (MSW) landfill in Beijing, China, were excavated and characterized to investigate the impact of intermediate soil cover on waste stabilization. A comparatively high amount of unstable organic matter with 83.3 g kg−1 dry weight (dw) total organic carbon was detected in the 6-year-old MSW, where toxic inorganic elements containing As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn of 10.1, 0.98, 85.49, 259.7, 530.4, 30.5, 84.0, and 981.7 mg kg−1 dw, respectively, largely accumulated because of the barrier effect of intermediate soil cover. This accumulation resulted in decreased microbial activities. The intermediate soil cover also caused significant reduction in moisture in MSW under the soil layer, which was as low as 25.9%, and led to inefficient biodegradation of 8- and 10-year-old MSW. Therefore, intermediate soil cover with low permeability seems to act as a barrier that divides a landfill into two landfill cells with different degradation processes by restraining water flow and hazardous matter.

Swift model for a lower heating value prediction based on wet-based physical components of municipal solid waste

To establish an empirical model for predicting a lower heating value (LHV) easily and economically by multiple regression analysis. A wet-based physical components model (WBPCM) was developed and based on physical component analysis without dewatering. Based on 497 samples of municipal solid waste (MSW) gathered from 14 incinerators in western parts of Taiwan from 2002 to 2009. The proposed model was verified by independent samples from other incinerators through parameters multiple correlation coefficients (R), relative percentage deviation (RPD) and mean absolute percentage error (MAPE). Experimental results indicated that R, RPD and MAPE were 0.976, 17.1 and 17.7, respectively. This finding implies that LHV predicted by the WBPCM could well explain the LHV characteristics of MSW. The WBPCM was also compared with existing prediction models of LHV on a dry basis. While more accurately predicting LHV predicting than those models based on proximate analysis, the WBPCM was comparable with models based on physical component analysis in term of RPD and MAPE. Experimental results further indicated that the prediction accuracy of the WBPCM varied with MSW moisture parabolically. No specific relation was observed in the results of the previous prediction model. The accuracy of the WBPCM was almost approached to that of ultimate analysis in moisture ranging from 40% to 55%. The model was applicable within this moisture range. We conclude that the WBPCM is a faster and more economical model for LHV predictions with comparable accuracy than those models based on physical component analysis. The proposed WBPCM is highly promising for use in designing and operating incinerators.

Effect of Moisture on Partitioning of Heavy Metals in Incineration of Municipal Solid Waste

The effect of moisture in municipal solid waste (MSW) on partitioning of lead (Pb), zinc (Zn), copper (Cu) and cadmium (Cd) was studied in a laboratory tubular furnace by using simulated MSW. The moisture in MSW influences heavy metals in following ways, to increase the moisture in flue gas and decrease the combustion temperature, to prolong the combustion time, and to prolong the releasing time of volatiles with the furnace temperature decreased by increasing the moisture. The volatilization of Pb, Zn and Cd was enhanced by increasing the moisture in MSW because of the prolonged combustion time. For Pb and Zn, the combustion time was important at higher temperature, while for Cd, it was important at low temperature. The moisture content showed slight effect on Cu partitioning. When extra chlorine was added to MSW, such as 1%PVC + 0.5%NaCl, the volatilization of Pb, Zn and Cu was enhanced by increasing the moisture because water evaporation reduced the temperature and increased devolatilization time. At higher temperature, NaCl tends to decompose and generates more free chlorine, producing more metal chlorides. Since Cd is a strong volatile heavy metal in MSW, the effect of moisture content on its volatilization is less than that of Pb, Zn or Cu during the MSW incineration.