Simulation of the flue gas cleaning system of an RDF incineration power plant

Because of the stringent pollutant emission standards introduced with the European Union guidelines for waste incineration, it is very important to optimize the flue gas cleaning systems which are able to result in a low environmental impact according to the emission limits. In this paper a thermochemical model has been proposed for the simulation of the flue gas cleaning system of an RDF incineration plant. The model simulates the operation of the flue-gas treatment section and the combustion section by using a simplified approach. The combustion includes the grate incinerator and the post-combustion chamber, while the cleaning section includes the NO(x) reduction process (urea injection) and the scrubbing of SO(2) and HCl (Ca(OH)(2) as sorbent). The modelling has been conducted by means of ASPEN PLUS code. The simulation results have been validated with the operating data. The model proposed by the authors can be a useful tool in both evaluating the efficiency of the gas cleaning system by verifying the environmental pollution of an incinerator power plant in nominal operating conditions and in forecasting the efficiency of the cleaning system in off-design operating conditions.     

Converting moving-grate incineration from combustion to gasification - numerical simulation of the burning characteristics

Waste incineration is a politically sensitive issue in the UK. The major current technology is based on direct combustion of wastes in a moving-grate furnace. However, general public opinion prefers non-direct burning technologies. Waste gasification is one of those nearest technologies available. By reducing the primary air-flow rate through the grate of a packed-bed system, operation of the existing solid-waste incineration equipment can be easily converted from combustion mode to gasification mode without major modification of the hardware. The potential advantages of this are lower dust carry-over in the flue gases, lower bed temperature (and therefore lower NO(x) formation in the bed), simplified gas-treatment procedures and lower running cost, among other benefits. The major disadvantages are, however, reduced throughput of the wastes and possibly higher carbon in the ash at exit. In this study, numerical simulation of both combustion and gasification of municipal solid wastes in a full-scale moving grate furnace is carried out employing advanced mathematical models. Burning characteristics, including burning rate, gas composition, temperature and burning efficiency as a function of operating parameters are investigated. Detailed comparisons between the combustion mode and gasification mode are made. The study helps to explore new incineration technology and optimise furnace operating conditions.     

Effects of flue gas composition on the catalytic destruction of chlorinated aromatic compounds with a V-oxide catalyst

When using catalytic flue gas cleaning, several flue gas compounds may influence oxidation reactions of hazardous volatile organic compounds, possibly leading to lower reaction rates and, thus, to an incomplete destruction. Experimental investigations were performed with regard to the influence of selected flue gas compounds, like hydrogen chloride, sulfur dioxide, oxygen, and water vapour, on the catalytic destruction behavior of chlorobenzenes under flue gas cleaning conditions of an incineration plant. For this purpose, a metal oxide catalyst was operated at different temperatures at a space velocity of 3600 h-1 in a laboratory-scale fixed bed reactor with model flue gases, and with real flue gases generated from the TAMARA waste incineration plant. The results obtained from the studies with model flue gas were analyzed with respect to reaction kinetics. These kinetics were applied for comparison with the experimental data gained in the real flue gas.     

Economic growth and selection of municipal waste treatment options in Bangkok

A reasonable selection of waste treatment options is indispensable to address challenges in waste management. Introduction of incineration plants for municipal waste in Bangkok had been considered in the past, but each time it was dismissed. In 2013, however, the Bangkok Metropolitan Administration (BMA) decided to introduce an incinerator facility with electricity generation. This study examined how changes in socio-economic factors resulting from economic growth affected the BMA’s decision. First, we conducted interviews of key relevant stakeholders (policymakers and other experts) to determine what kinds of changes in socio-economic factors affected their decision. Then, for interpretation and confirmation of the results from interview, we quantitatively estimated changes in environmental factors (e.g., greenhouse gas emissions), financial factors (e.g., construction and operating costs), and social factors (e.g., employment) in 1990, 2000, and 2012. Based on the result of interview and quantitative analysis, we illustrated the complicated structure of the mechanism of how economic growth affected the selection of waste treatment options in Bangkok, particularly those that led to the selection of the incineration. In addition to local conditions, global economic also affected the waste treatment policy in Bangkok even though waste management is usually thought of as a local issue.     

Environmental assessment of waste incineration in a life-cycle-perspective (EASEWASTE).

A model for life-cycle assessment of waste incinerators is described and applied to a case study for illustrative purposes. As life-cycle thinking becomes more integrated into waste management, quantitative tools for assessing waste management technologies are needed. The presented model is a module in the life-cycle assessment model EASEWASTE. The module accounts for all uses of materials and energy and credits the incinerator for electricity and heat recovered. The energy recovered is defined by the user as a percentage of the energy produced, calculated on the lower heating value of the wet waste incinerated. Emissions are either process-specific (related to the amount of waste incinerated) or input-specific (related to the composition of the waste incinerated), while mass transfer to solid outputs are governed by transfer coefficients specified by the user. The waste input is defined by 48 material fractions and their chemical composition. The model was used to quantify the environmental performance of the incineration plant in Aarhus, Denmark before and after its upgrading in terms of improved flue gas cleaning and energy recovery. It demonstrated its usefulness in identifying the various processes and substances that contributed to environmental loadings as well as to environmental savings. The model was instrumental in demonstrating the importance of the energy recovery system not only for electricity but also heat from the incinerator.     

Feasibility of a monitoring system for detecting changes in dioxin concentrations of both in flue gas and fly ash in incineration plants

Surrogate measurements should be low in cost and quick to perform. To examine its feasibility, continuous surrogate monitoring was performed using an organic halogen compound (OHC) analyzer. Surrogates for dioxins (DXNs) from waste incinerators were examined by changing the operating conditions such as the atomized volume of activated carbon added and the temperature at the inlet of the dust collector. OHCs were measured along with DXNs in flue gas at the inlet and the outlet of the dust collector of two waste incinerators over five runs; the fly ash was sampled at the same time. Although the final flue gas concentration of DXNs at the incineration plants was below the regulation criteria, this does not mean complete reduction of DXNs. In addition, the de novo synthesis of DXNs inside the dust collectors was studied by analyzing the mass balance for DXNs concentrations in flue gas and fly ash. Semivolatile chlorinated organic compound concentrations at the outlet of the bag filter were basically well correlated with DXNs levels at the inlet of the bag filter in the test runs. When advanced flue gas treatment is applied by using a bag filter and lime/activated carbon adsorbent, DXNs that may be generated during flue gas cooling processes move to the fly ash, and this amount determines the mass balance of the entire system. It may be useful to monitor surrogate organic halogens for detecting changes in DXN concentrations of both flue gas and fly ash in incineration plants.     

Economic assessment and energy model scenarios of municipal solid waste incineration and gas turbine hybrid dual-fueled cycles in Thailand

Finding environmentally benign methods related to sound municipal solid waste (MSW) management is of highest priority in Southeast Asia. It is very important to study new approaches which can reduce waste generation and simultaneously enhance energy recovery. One concrete example of particular significance is the concept of hybrid dual-fuel power plants featuring MSW and another high-quality fuel like natural gas. The hybrid dual-fuel cycles provide significantly higher electrical efficiencies than a composite of separate single-fuel power plant (standalone gas turbine combined cycle and MSW incineration). Although hybrid versions are of great importance for energy conversion from MSW, an economic assessment of these systems must be addressed for a realistic appraisal of these technologies. This paper aims to further examine an economic assessment and energy model analysis of different conversion technologies. Energy models are developed to further refine the expected potential of MSW incineration with regards to energy recovery and environmental issues. Results show that MSW incineration can play role for greenhouse gas reduction, energy recovery and waste management. In Bangkok, the electric power production via conventional incineration and hybrid power plants can cover 2.5% and 8% of total electricity consumption, respectively. The hybrid power plants have a relative short payback period (5 years) and can further reduce the CO₂ levels by 3% in comparison with current thermal power plants.     

Supervisory control of a selective catalytic reactor for NOx removal in incineration plants

The purpose of this work is to present an industrial application of an optimization tool for the supervisory control of the NO_x reduction section. This work does not pretend to address any new technique of NO_x reduction but rather to show the results obtained when a comprehensive on-line optimization tool has been successfully applied. The optimization procedure consists of the search of the best working conditions that satisfy the operating and legal constraints, in terms of emission amounts and combustion quality. This procedure adopts a simulation algorithm and data reconciliation tool to verify and improve the consistency of the calculated values by experimental data. Using such algorithm it is possible to identify all the updated data necessary to optimize the plant's performance. Specifically, the DeNO_x section optimization, both from an economical and environmental point of view, is strongly related to the estimation of the nitrogen waste mass fraction together with the catalytic reactor efficiency. The results obtained in many case studies show that it is possible to achieve the desired performance and to reduce the operating costs by defining the optimal operating temperature and the corresponding amount of ammonia required for the catalytic reduction of NO_x subject to the emission limits. These tools were successfully tested on a municipal waste incineration plant.     

Behavior of PAHs from sewage sludge incinerators in Korea

Although production of sewage sludge increases every year, its proper treatment has only been recently raised as a new issue, as current landfill and ocean dumping arrangements are expected to become increasingly difficult to manage in the future. The Korean Ministry of Environment plans to diversify its processing facilities and expand its processing systems by 2011, with the purpose of processing all sludge produced in Korea. According to this plan, incineration (including incineration of municipal wastes) will process 30% of the entire sewage sludge throughout the country in 2011. This study reviews the characteristics of PAH, which is one of the organic substances found in sewage sludge during the incinerating process. The total amount of PAH produced from sewage sludge incineration was found to be 6.103 mg/kg on average, and investigation performed on 16 PAHs of inlets and outlets of the air control devices at five full-scale incineration facilities showed that concentrations of the PAHs on the inlet and on the outlet ranged from 3.926 to 925.748 microg/m(3) and from 1.153 to 189.449 microg/m(3), respectively. In the case of the incineration facility fed with municipal waste (95%) and sewage sludge (5%), the total of the PAH emissions concentration was higher than that found at the incineration facilities used exclusively to treat sewage. The combustion of waste vinyl and plastics contained in municipal waste fed into the facility might contribute to the high levels of PAHs in the stack gas. However more investigation is needed on the production mechanism of PAHs at different operating conditions of the incineration facilities, such as the types of waste, and other relevant factors.     

Efficiency of energy recovery from waste incineration,in the light of the new Waste Framework Directive

This paper deals with a key issue related to municipal waste incineration, which is the efficiency of energy recovery. A strong driver for improving the energy performances of waste-to-energy plants is the recent Waste Framework Directive (Directive 2008/98/EC of the European Parliament and of the Council of 19 November 2008 on waste and repealing certain Directives), which allows high efficiency installations to benefit from a status of “recovery” rather than “disposal”. The change in designation means a step up in the waste hierarchy, where the lowest level of priority is now restricted to landfilling and low efficiency wastes incineration. The so-called “R1 formula” reported in the Directive, which counts for both production of power and heat, is critically analyzed and correlated to the more scientific-based approach of exergy efficiency. The results obtained for waste-to-energy plants currently operating in Europe reveal some significant differences in their performance, mainly related to the average size and to the availability of a heat market (district heating).     

Dioxin emissions from thermal waste management in Medellín, Colombia: present regulation status and preliminary results

Preliminary results of a study undertaken to characterize dioxin and furan releases from waste incineration plants operating in Medellín-Colombia are presented. Emission and fly ash samples were collected from representative plants burning medical and industrial residues to characterize PCDD/PCDF levels. Analyses were carried out following European standards for stationary gas emissions EN-1948:1996 and US EPA 1613 (fly ashes). Final extracts were analyzed by both high resolution gas chromatography coupled to high resolution mass spectrometry (HRGC-HRMS) and high resolution gas chromatography coupled to ion trap tandem mass spectrometry (HRGC-ITMS/MS). Preliminary results revealed emission levels of 1-30.3 ng I-TEQ/Nm3 depending on whether or not an air pollution control system (APCS) was installed. Fly ashes contained 8.5-68 ng I-TEQ/g. Critical issues that should be addressed in an assessment and in developing waste management plans in Colombia are discussed.     

On-site remediation of PCB contamination using transportable incineration systems

Many Superfund or hazardous waste sites prove to be excellent candidates for remediation using transportable incineration. Transportable incineration has been selected as the alternative of choice to remediate numerous sites throughout the United States. There are a number of firms that provide mobile and transportable incineration equipment and services. A variety of treatment systems are available, including rotary kilns, fluidized beds, and infrared incinerators. Roy F. Weston, Inc., has been instrumental in the development, design, permitting, construction, performance testing, and operation of hazardous and toxic waste thermal treatment systems. Weston owns and operates two high-temperature transportable incineration systems (TISs). The first system is Weston's seven-ton-per-hour (tph) TIS-5. The second is the TIS-20, with a design capacity of up to 30 tph. These units are typical rotary kiln incinerators, the most flexible, adaptable type of incineration unit. This article discusses Weston's use of these incinerators to remediate soils at sites contaminated with polychlorinated biphenyls (PCBs).     

Thermal conversion behaviors,kinetics, and thermodynamics of wastewater sludge via thermogravimetric analysis,and emission characteristics from a large-scale incinerator

Journal of Material Cycles and Waste Management - This paper concerned the thermal conversion characteristics, kinetics, thermodynamics, and incineration operation parameters and gas emissions of...     

Integrated drying and incineration of wet sewage sludge in combined bubbling and circulating fluidized bed units

An original integrated drying and incineration technique is proposed to dispose of sewage sludge with moisture content of about 80% in a circulating fluidized bed. This system combines a bubbling fluidized bed dryer with a circulating fluidized bed incinerator. After drying, sewage sludge with moisture less than 20% is transported directly and continuously from the fluidized bed dryer into a circulating fluidized bed incinerator. Pilot plant results showed that integrated drying and incineration is feasible in a unique single system. A 100 t/d Sewage Sludge Incineration Demonstration Project was constructed at the Qige sewage treatment plant in Hangzhou City in China. The operational performance showed that the main operation results conformed to the design values, from which it can be concluded that the scale-up of this technique is deemed both feasible and successful.     

Study on optimal energy efficiency of a sludge drying-incineration combined system

Thermal drying is a frequently used technology to further remove the water in dewatered sludge. However, it is an expensive solution due to its highly energy consumption. The combination of sludge drying and incineration system, in which, the energy generated from sludge incineration is reused to sludge drying, can largely save the energy consumption of sludge treatment facilities. A bench-scale paddle sludge dryer was built to study the drying characteristics of sludge. Results show that, a significant fluctuation of sludge drying rate and stirring power emerges at the moisture content of 55–65 %. An energy model was established based on a sludge drying and incineration project. The most reasonable dryness of sludge outlet from sludge dryer and input to sludge incinerator was analyzed, in the purpose of achieving optimal energy efficiency. The mono-incineration of dry sludge can be achieved at 850 °C combustion temperature, when sludge lower heating value (LHV) is about 11213 kJ/kg and moisture content is about 60 % w/w. The effect of operation conditions, including sludge moisture content, LHV, and operation load were analyzed based on the energy model. This energy model could be applied for the improvement of energy efficiency of sludge drying and incineration combined system.     

LCA to choose among alternative design solutions: The case study of a new Italian incineration line

At international level LCA is being increasingly used to objectively evaluate the performances of different Municipal Solid Waste (MSW) management solutions. One of the more important waste management options concerns MSW incineration. LCA is usually applied to existing incineration plants.In this study LCA methodology was applied to a new Italian incineration line, to facilitate the prediction, during the design phase, of its potential environmental impacts in terms of damage to human health, ecosystem quality and consumption of resources. The aim of the study was to analyse three different design alternatives: an incineration system with dry flue gas cleaning (without- and with-energy recovery) and one with wet flue gas cleaning. The last two technological solutions both incorporating facilities for energy recovery were compared. From the results of the study, the system with energy recovery and dry flue gas cleaning revealed lower environmental impacts in relation to the ecosystem quality.As LCA results are greatly affected by uncertainties of different types, the second part of the work provides for an uncertainty analysis aimed at detecting the extent output data from life cycle analysis are influenced by uncertainty of input data, and employs both qualitative (pedigree matrix) and quantitative methods (Monte Carlo analysis).     

Life cycle assessment of four municipal solid waste management scenarios in China

A life cycle assessment was carried out to estimate the environmental impact of municipal solid waste. Four scenarios mostly used in China were compared to assess the influence of various technologies on environment: (1) landfill, (2) incineration, (3) composting plus landfill, and (4) composting plus incineration. In all scenarios, the technologies significantly contribute to global warming and increase the adverse impact of non-carcinogens on the environment. The technologies played only a small role in the impact of carcinogens, respiratory inorganics, terrestrial ecotoxicity, and non-renewable energy. Similarly, the influence of the technologies on the way other elements affect the environment was ignorable. Specifically, the direct emissions from the operation processes involved played an important role in most scenarios except for incineration, while potential impact generated from transport, infrastructure and energy consumption were quite small. In addition, in the global warming category, highest potential impact was observed in landfill because of the direct methane gas emissions. Electricity recovery from methane gas was the key factor for reducing the potential impact of global warming. Therefore, increasing the use of methane gas to recover electricity is highly recommended to reduce the adverse impact of landfills on the environment.     

Life cycle assessment of bagasse waste management options

Bagasse is mostly utilized for steam and power production for domestic sugar mills. There have been a number of alternatives that could well be applied to manage bagasse, such as pulp production, conversion to biogas and electricity production. The selection of proper alternatives depends significantly on the appropriateness of the technology both from the technical and the environmental points of view. This work proposes a simple model based on the application of life cycle assessment (LCA) to evaluate the environmental impacts of various alternatives for dealing with bagasse waste. The environmental aspects of concern included global warming potential, acidification potential, eutrophication potential and photochemical oxidant creation. Four waste management scenarios for bagasse were evaluated: landfilling with utilization of landfill gas, anaerobic digestion with biogas production, incineration for power generation, and pulp production. In landfills, environmental impacts depended significantly on the biogas collection efficiency, whereas incineration of bagasse to electricity in the power plant showed better environmental performance than that of conventional low biogas collection efficiency landfills. Anaerobic digestion of bagasse in a control biogas reactor was superior to the other two energy generation options in all environmental aspects. Although the use of bagasse in pulp mills created relatively high environmental burdens, the results from the LCA revealed that other stages of the life cycle produced relatively small impacts and that this option might be the most environmentally benign alternative.     

Experimental study on flue gas purifying of MSW incineration using in-pipe jet adsorption techniques

This paper presents the experimental research process and results about flue gas purifying of municipal solid wastes (MSW) incineration using in-pipe jet adsorption techniques. MSW incineration was carried out in a fluidized bed test rig, and the flue gas purifying was carried out in an in-pipe jet adsorption test rig. The experimental results are as follows: when the feedstock of activated carbon is 1.6g/Nm(3), the desulfurization efficiency is 83%, the denitrification efficiency is 41%, and the dechlorination efficiency is 27%. The order of purifying effect of the three kinds of adsorbents on acidic gases from MSW incineration is activated carbon>activated bauxite>kaolin. Comparison of adsorption capabilities of the three kinds of adsorbents to heavy metals shows that activated carbon is the best additive to remove Cd, Pb and Cu, kaolin is inferior, and activated bauxite is the worst one. However, activated bauxite is the best additive to remove Hg, and it can remove Cd effectively. PAHs in fly ash are dominated by three-, four-, and five-ringed PAHs, and PAHs in the flue gas mainly include three- and four-ringed PAHs. When the injected quantity of additive is constant, the order of cleaning effect on PAHs is kaolin>activated carbon>activated bauxite. These three kinds of adsorbents have different purifying effects on acidic gases, heavy metals and PAHs in the flue gas from MSW incineration. In general, activated carbon has a better adsorption capability.     

活性污泥焚烧过程中镍的迁移分布特性

采用管式炉对污水厂活性污泥焚烧过程中Ni的迁移分布特性进行研究。实验结果表明：当污泥掺烧量（污泥质量与煤和污泥总质量的比）为25%时，Ni的挥发率（飞灰与气体中Ni质量的总和与污泥中Ni质量的比）几乎为零，且污泥与煤混合试样的综合燃烧效果最好；当污泥焚烧加入硫化物时，各种硫化物对Ni的残留率（炉渣中Ni的质量与污泥中Ni质量的比）提高能力大小顺序为Na₂S>S>Na₂SO₃>Na₂SO₄；当污泥焚烧加入氯化物时，促使Ni向烟气中迁移，且加入无机氯更易使Ni向烟气中迁移。