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Emissions from the Incineration Industry_Luke Martin

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Emissions from the Incineration Industry_Luke Martin

  1. 1. BSEN40110 Advanced Air Pollution Air pollution in the incineration industry Luke Martin 4/27/2015 The incineration of municipal solid waste has become a popular waste disposal method because of the reduction in emissions compared to landfill and the energy recovery associated with this technology. By incorporating a number of modern abatement methods into their design, incinerators can safely come under the emissions limits set out by the E.U. Focusing primarily on the Irish incineration industry; and subsequently European and US examples, the dispersal of pollutants emitted by these facilities are assessed to determine their potential impact on human health. The study shows that all facilities come under the respective emissions limits and that modern gas- cleaning technology can reduce emissions by 65%.
  2. 2. 1 UCD Assessment Submission Form Student Name Luke Martin Student Number 14200324 Assessment Title Air pollution model of an incinerator Module Code BSEN40110 Module Title Advanced Air Pollution Module Co-ordinator Dr. Tom Curran Date Submitted 27 April 2015 Date Received Grade/Mark A SIGNED COPY OF THIS FORM MUST ACCOMPANY ALL SUBMISSIONS FOR ASSESSMENT. STUDENTS SHOULD KEEP A COPY OF ALL WORK SUBMITTED. Procedures for Submission and Late Submission Ensure that you have checked the School’s procedures for the submission of assessments. Note: There are penalties for the late submission of assessments. For further information please see the University’s Policy on Late Submission of Coursework, (http://www.ucd.ie/registrar/) Plagiarism: the unacknowledged inclusion of another person’s writings or ideas or works, in any formally presented work (including essays, examinations, projects, laboratory reports or presentations). The penalties associated with plagiarism designed to impose sanctions that reflect the seriousness of University’s commitment to academic integrity. Ensure that you have read the University’s Briefing for Students on Academic Integrity and Plagiarism and the UCD Plagiarism Statement, Plagiarism Policy and Procedures, (http://www.ucd.ie/registrar/) Declaration of Authorship I declare that all material in this assessment is my own work except where there is clear acknowledgement and appropriate reference to the work of others. Signed…Luke Martin…………………………………… Date ……24/04/2015…………………………………..
  3. 3. 2 Contents 1) Introduction........................................................................................................................4 2) Literature review ................................................................................................................6 Incineration............................................................................................................................6 Pollutants ...............................................................................................................................7 Abatement Techniques to Limit Pollutant Emissions..........................................................10 3) Site Description.................................................................................................................13 Indaver, Carranstown, Co. Meath........................................................................................13 Covanta, Poolbeg, Co. Dublin ..............................................................................................14 Tersa, Montcada, Barcelona................................................................................................15 Babcock & Wilcox, West Palm Beach, Florida .....................................................................16 4) Modelling Methods ..........................................................................................................17 5) Results...............................................................................................................................19 Sulphur Oxide Emissions......................................................................................................19 Nitrogen Oxide Emissions ....................................................................................................20 Dioxin and Furan Emissions .................................................................................................22 Sensitivity Analyses..............................................................................................................24 6) Discussion .........................................................................................................................26 Interpretation ......................................................................................................................26 Limitations............................................................................................................................29 7) Conclusions.......................................................................................................................30 Reference List...........................................................................................................................31
  4. 4. 3 Figure 1: Number of MSW incinerators in various countries across Europe and the US (ISWA, 2012) .4 Figure 2: Typical layout of a modern moving grate incinerator (Murdoch University, 2014)................6 Figure 3: Electrostatic precipitator (Holbert Faculty, 2003) .................................................................11 Figure 4: Chemical Scrubber (intech, 2014)..........................................................................................11 Figure 5: Gas filtration system (Tri-Mer, 2013).....................................................................................11 Figure 6: Indaver panoramic view and map showing the facility location (Indaver)............................13 Figure 7: Poolbeg incinerator speculative image and location (Covanta, 2015) ..................................14 Figure 8: Tersa incinerator birds-eye view and location (Tersa, 2015).................................................15 Figure 9: West Palm Beach incinerator image and location (Tersa, 2015)...........................................16 Figure 10: Terrain profile taken from the alternate transect at the Carranstown site ........................18 Figure 11 (a): Air Dispersion of SOx emissions in the direction of prevailing wind..............................19 Figure 12(a): Air dispersion of NOx emissions according to prevailing wind conditions......................21 Figure 13: Air Dispersion of Dioxins and Furans in the prevailing wind direction................................22 Figure 14 (b): Air dispersal of dioxins and furans in the alternate wind direction ...............................22
  5. 5. 4 1) Introduction In the past few decades, the incineration of municipal solid waste (MSW) has become a popular method for waste disposal. Some studies even go so far to suggest that modern incineration facilities are crucial to sustainable waste management hierarchies to be in adherence with EU DIRECTIVE 2000/76/EC targets (Hjelmar, 1996; Van Gervan et al, 2005). These facilities take preference over the archaic landfill disposal methods due to a significant reduction in the volume of waste as well as overall emissions reductions (Cherubini et al, 2009). Figure.1 taken from ISWA (2012) shows the number of incinerators currently operating in a number of developed countries across Europe and the US. With the successful completion of the Carranstown incinerator in 2011, Ireland is finally beginning to follow European protocol however is still lagging behind its neighbours. Figure 1: Number of MSW incinerators in various countries across Europe and the US (ISWA, 2012) While the scientific evidence is unequivocally in favour of incineration as a waste disposal technique, the potential of detrimental health effects from stack emissions are of major public concern (Meneses et at, 2004). Up until 2011, Ireland has resisted the use of incinerators largely due to the phenomena such as “NIMBYism” and lack of trust in planning authorities (Davies, 2004; Cavazza, 2013). In an attempt to allay or justify the public’s
  6. 6. 5 concerns, this study investigates the true impact these facilities have on human health. This will be achieved by;  Identifying the key pollutants emitted by an incinerator,  Outlining the specific effects these emissions potentially have on human health,  Explaining the concentrations that these pollutants are harmful to human health,  Analysing the dispersion of these pollutants from several incinerators with samples from Ireland, Europe and the USA. This project uses Lakes Environmental’s air dispersion modelling software “Screenview” to assess the dispersion of pollutants from these facilities.
  7. 7. 6 2) Literature review Incineration Incineration, or under its green-washed pseudonym “thermal treatment”, of municipal solid waste involves the destruction of waste by heating it to high temperatures in the range of 850-1100°C. This is carried out in a controlled environment to limit the release of emissions to the environment. The main appeal of this treatment method is that it reduces the volume of waste to one-tenth of its initial size (Sabbas et al, 2003) and the heat from flue gases can be utilized to run a steam turbine to generate electricity or used directly for district heating. Figure 2: Typical layout of a modern moving grate incinerator (Murdoch University, 2014) Figure.2 depicts the typical layout of a modern, state of the art, moving grate incinerator. This type of incinerator is preferred for treating MSW as they are considered most reliable for dealing with mass quantities of non-homogenous waste streams. All four facilities studied in the project utilise this type of mass burn incinerator. Waste is received into a storage bunker (A). A grabber, (B) controlled by an operator in the control room, transfers waste into a hopper (C). This step allows for the extraction of potentially hazardous wastes unsuitable for thermal treatment which is particularly important from an emissions
  8. 8. 7 perspective as an anomalous piece of waste could lead to a higher release of pollutants than expected. The hopper then gradually feeds the waste into a moving grate incinerator (D). This moving grate shifts waste gradually through the drying stage (<100°C), hydrolysis stage (<700°C) and combustion stage (700-1000°C) (E). The combustion stage results in the production of a flue gas which is directed by a combustion chamber chute (F), towards a boiler system. The heat from the flue gas heats water in the boiler creating steam, which is channelled to a turbine to generate electricity. Flue gases then continue on to an economiser (H) where heat is recycled either for on-site usage, or for supplementary heat to the incineration cycle itself. While the quantities of pollutants are significantly reduced using this waste management technique over others, the release of some of these pollutants to the atmosphere is inevitable. This is where the public’s main concern comes in according to Meneses et al (2004). Modern incinerators are legally obliged to incorporate a number of abatement technologies (Best Available Techniques) to restrict the emissions of pollutants to an acceptable level to avoid affecting human health. Figure.3 illustrates the inclusion of a wet scrubber/evaporating spray reactor (I), an electrostatic precipitator and bag filter system (J), and dioxin filtration system (K) consisting of a catalytic fibre to oxidise dioxins. These technologies are elaborated on in the “abatement techniques” section. Finally the stack height (L) is of importance to ensure adequate dispersal rates of pollutants in the atmosphere which in turn, dilutes their respective concentrations. Provided these abatement techniques are properly utilized, the health risks associated with incineration are estimated to be five times lower than those associated with landfill (Moy et al, 2008). Furthermore, Cangialosi et al (2008) has claimed that the health impacts which may arise from inhalation, dermal contact or soil and food ingestion of pollutants emitted from incinerators are well below background levels of these pollutants. Pollutants The principal air pollutants emitted from a municipal solid waste incinerator are acid gases; consisting of sulphur dioxides and nitrogen oxides, organics; such as dioxins and furans and heavy metals; including lead, mercury, cadmium and arsenic. Each of these toxins has their
  9. 9. 8 own inherent detrimental effect on human health when experienced in acute or chronic concentrations. Nitrogen Oxides (NOx) NOx is one of the most abundant pollutants found in incinerator flue gases. These chemicals form during the combustion phase of the incineration process when the waste is heated above 850°C to “crack” the strong molecular bonds of furans and dioxins (DEFRA, 2010). NOx gases can penetrate deep into the lungs causing, or aggravating existing respiratory illnesses while particularly high concentrations can be fatal (EPA (a), 2015). According to WID 2000/76/EC, limits the daily emission of NOx to 200mg/m³ for plants exceeding an input of 6 t/hr. Sulphur Oxides (SOx) These sulphuric compounds form in any process which involves burning. SOx pollutants also affect the respiratory system and aggravate a number of illnesses such as asthma, bronchitis and emphysema (EPA (a), 2015). Modern incineration plants cannot exceed daily emissions of 50mg/m³. Dioxins and Furans These pollutants account for all polychlorinated dibenzo-p-dioxins and dibenzofurans (WID, 2000/76/EC). These compounds form either from incomplete combustion of the feedstock or through de novo synthesis due to an inconsistency in furnace temperature (DEFRA, 2010). Davies (2004) identifies these pollutants as central to most incinerator objections and with good reason. Benzene, the key component of these compounds can cause dizziness, drowsiness, headaches and unconsciousness following acute exposure and chronic exposure has been linked with causing cancer (EPA (a), 2015). Due to their potency these substances are strictly limited to 0.1 ng/m³. Mercury Mercury emissions are associated with combustion of any type. Exposure to humans can occur either directly through inhalation or indirectly through consumption of fish or animals who have in turn incorporated into their system through consumption. Mercury emissions can cause damage to the brain, heart, kidneys and immune system to people of all ages (EPA, 2015). People with chronic exposure to this substance can exhibit psychosocial
  10. 10. 9 symptoms such as shyness, depression, insomnia and irritability. The severity of this toxin means incinerators are limited to daily emissions of 0.05 mg/m³. Cadmium Cadmium can be emitted in a variety of forms from an incinerator in compounds such as CdO, CdCl₂, CdSO₄ or Cd(NO₃)₂. According to the EPA (2015) cadmium is extremely carcinogenic and can also induce a number of other illnesses. This substance is limited to a daily level of 0.05 mg/m³. Lead and Arsenic Lead and arsenic are the most abundant heavy metals emitted from a typical incinerator. Lead in chronic doses is associated the retardation of mental development in children while arsenic can have detrimental effects on the respiratory, cardiovascular and neurological systems (EPA, 2015). This project intends to focus primarily on NOx, SOx, Dioxin and Furan pollutants. Table.1 summarises the emission limits for these pollutants to allow for ease of reference during the interpretation stage. Table 1: Summary of emissions limits for NOx, SOx and Dioxins and Furans NOx SOx Dioxins/Furans Units mg/m³ mg/m³ ng/ m³ EU.Maximum Emission Conc. 200 50 0.01 Annual Average Daily Emission Conc. 180 40 0.05
  11. 11. 10 Abatement Techniques to Limit Pollutant Emissions In Ireland, under the “Protection of the Environment Act”, (2003) operators of any facility which emits pollutants such as those aforementioned above are required to apply best available techniques to their facilities to limit their release into the environment. This means a spare-no-expense approach must be employed when building facilities such as a mass- burn incinerator. There a number of technologies and techniques which minimize the amount of pollutants emitted by these facilities. Each one generally specializes in the abatement of one or a few specific types of pollutants. Incinerator design features The first step in limiting hazardous emissions begins with the operation of the facility itself. This technically begins at the source of the waste assuming polluters are responsible to sort waste appropriately. Operators are obliged to omit certain hazardous wastes prior to feeding the hopper; this is carried out by the operator of the grabber (B) in figure. 2. The next few emission-limiting steps occur in the furnace itself (D). According to DEFRA (2010) temperature must be increased gradually to inhibit the development of cold pockets or gas channelling. Failure to do so results in the incomplete combustion of the waste which facilitates the release of undesirable, harmful emissions further downstream. The temperature of the flue gases (E) must be brought between 850-1100°C to facilitate the cracking of dioxins and furans into nitrogen oxides. At least one after-burner, additional units added depending on the size of the furnace, must be included according to WID 2000/76/EC. This is to prevent the formation of dioxins and furans de novo synthesis due to a temperature drop. Skipping past the downstream gas-cleaning technologies for a moment, there are a number of features at the point of flue gas exit which limit harmful release of emissions. The height of the stack can ensure that fumes are taken efficiently away from the source without affecting any of the immediate population in close proximity to the facility. As a rule of thumb, DEFRA (2010) recommends that the chimney stack (L) should be 70m in height for this plant considering 250,000 tonnes of waste are expected per year (DEFRA (b), 2007). In addition the volumetric flow rate of the exiting gas along with its temperature can also have
  12. 12. 11 a significant impact on pollutant dispersal. These aspects will be discussed in the “sensitivity analysis” section. Electrostatic precipitator The main function of this device is to divert fly-ash out of the flue gas stream and send it into a containment area where it can be disposed of safely. As illustrated in fig.3 the precipitator achieves this goal by using positively charged plates to attract the negatively charged particles as the flue gas passes through. These can come in two types, wet and dry gas models and are popular due to their high efficiencies at removing dust or sludge’s from the flue gas. The downside to this technology is that if the flue gas particles achieve high resistivity, the electrodes become less efficient at extracting them (Holbert Faculty, 2003). This can be overcome by regulating flue gas temperature, increasing its moisture content or adding conditioning agents to it. Chemical Scrubber These devices are extremely useful at removing acids such as HCl, and HF; and acid gases such as NOx and SOx from the flue gas stream (DEFRA, 2010). Typically this technology function by administering a scrubbing liquid to capture particulates and gases as shown in fig.4 (Pollution Systems, 2014) .This technology can facilitate “selective non-catalytic reduction” by injecting in various reagents to react with and nullify hazardous compounds (Zandaryaa et al, 2001). As this technology’s main objective is to remove acidic components from the flue gas a major disadvantage is that it is susceptible to corrosion, leading to costly maintenance and repairs. Filtration systems These units are particularly adept at removing particulate matter from the gas stream by trapping particulates as the flue gas passes through in their mesh-like structure. They can consist of fabric or ceramic filters the former which needs to be replaced every 24-36 months, while the latter can last for 5-10 years (Tri-Mer, 2013). The ceramic filters can be Figure 4: Chemical Scrubber (intech, 2014) Figure 3: Electrostatic precipitator (Holbert Faculty, 2003) Figure 5: Gas filtration system (Tri-Mer, 2013)
  13. 13. 12 deployed in the treatment of high temperature flue gases while the fabric type requires the gases to be cooled first. These filtrations can assist in the limitation of SOx, HCL, NOx and dioxins.
  14. 14. 13 3) Site Description This study will consider four sites to assess the effects of pollutant dispersal associated with incinerators. Each of these incinerators specializes in the thermal processing of non- hazardous municipal solid waste and commercial solid waste. Indaver, Carranstown, Co. Meath The Carranstown facility was completed by Indaver, a predominantly Dutch company in 2011. It is situated in a rural area and surrounded by a relatively flat landscape. Wind data was compiled from 2012-2015 records provided by MetEireann (2015). The prevailing wind for the site was found to be a south westerly and figure.3 illustrates that these winds are likely to carry emissions from the stack over a flat landscape towards Drogheda town some 6 km away. The “alternate wind” path shows the second most frequent wind direction at this site, a south easterly. This transect will carry emissions past a cement factory approximately 700m downwind followed by a sharp rise in terrain, above the stack height in places, approximately 2,300m downwind. Specifications: The facility consists of a moving grate incinerator and has an annual capacity of 200,000 t. Flue gases are emitted through a single stack which is 40m in height. Abatement technologies at this facility consist of an ammonia solution injection, an evaporating spray reactor, a baghouse filter and an electrostatic precipitator with an activated carbon/dry lime injection system. Prevailing wind (SW, 260) Alternate wind (SE, 140) Figure 6: Indaver panoramic view and map showing the facility location (Indaver)
  15. 15. 14 Covanta, Poolbeg, Co. Dublin The Poolbeg incineration project is being built by an American waste management company known as Covanta. It is anticipated that this facility will commence operations in late 2017 (Dublin Waste-to-Energy, 2014). This incinerator is approximately three times larger than the Indaver project treating 600,000 t of waste per annum. The site is located at the eastern periphery of Dublin City on an old brownfield site in the docklands. The surrounding landscape is flat predominantly however there is an abundance of tall buildings with the potential to create turbulent air flow. It was appropriate to use the same meteorological data as the Carranstown facility for this site as it was extrapolated from Dublin Airport. Hence the prevailing and alternate winds at this site are SW and SE. Figure.4 highlights the path of the prevailing wind which would carry emissions across Dublin Bay, towards the elevated peninsula of Howth and Sutton. The alternate wind direction would transport the emissions from stack exhausts across the north side of the city towards Fairview and Santry. Specifications: This facility is expected to consist of a moving grate incinerator with two 100m high stacks to emit flue gases. Air quality infrastructure include an evaporating spray reactor for NOx reduction, fabric filter to limit particulate matter release, a two-stage wet scrubber for the reduction of HCL and SOx and activated carbon and lime are added to bind dioxins out of solution (Dublin Waste To Energy, 2006). Figure 7: Poolbeg incinerator speculative image and location (Covanta, 2015) Prevailing wind (SW, 260) Alternate wind (SE, 140)
  16. 16. 15 Tersa, Montcada, Barcelona This facility was originally opened in 1975 with a capacity for 15 t/hr (ISWA, 2012). The site was then renovated in 1996 to upgrade its gas-cleaning system and bring its emissions more in-line with the various air quality legislation in Europe at the time. The best available technique act (EU Directive 96/61/EC) would have forced the site operators hand in carrying out these works. The site was upgraded and is now currently run by “Tersa”, a European company consisting of a number of stakeholders from a variety of E.U nations. The prevailing wind of SW, 255 at this site conveniently carries emissions away from the densely populated city of Barcelona. The “alternate wind” pattern was modelled to assess the impacts of pollutants if blown across this urban landscape. Specifications: This facility consists of a moving grate incinerator with a total of three stacks enclosed in one point source which stands at 48m high. Up until 1996 the principal gas-cleaning technology consisted of one electrostatic precipitator. The plant upgrade saw the incorporation of a wet scrubber configured for HCl and SO2 as well as metal limit reduction. In addition an active-carbon, fabric filter was included to target dioxin and furan emission reductions (Meneses et al, 2004). Figure 8: Tersa incinerator birds-eye view and location (Tersa, 2015) Prevailing wind (SW, 255) Alternate wind (SEE, 100 )
  17. 17. 16 Babcock & Wilcox, West Palm Beach, Florida This project was commissioned by the solid waste authority of Palm Beach and built by an American engineering firm called Babcock and Wilcox. This Is a 42t/hr facility located in a relatively obscure area surrounded by marshland and forests on its west side where its prevailing wind carries pollutant emissions. The alternate wind would carry wind towards a number of residential areas approximately 4km to the south east of the facility. Specifications: “State-of-the-art emissions control systems” are included in this facility including a selective non-catalytic reducer system, a baghouse filter, a spray-dry absorber and a venturi-style wet scrubber (Babcock & Wilcox, 2012). The facility has 2 94.49 meter high stacks combined together in one point source as shown in figure.9. Figure 9: West Palm Beach incinerator image and location (Tersa, 2015) Prevailing wind (E, 90) Alternate wind (NW, 320)
  18. 18. 17 4) Modelling Methods The first step taken to accurately model the four chosen sites was to obtain the relevant input data required by the modelling software. This was acquired from a number of sources within the literature such as environmental impact statements, journal articles and similar air pollution studies. This was input into “Lakes Environmental” Screenview software in the format outlined in table.2. Table 2: Model Inputs Unit Indaver Poolbeg Florida Montcada (2001) Montcada (1996) Stack height m 40 100 94.49 48 48 Stack Diameter m 2 4.52 4.26 1.77 1.77 Stack exit velocity m/s 20.5 20.3 20.12 8.9 8.0 Stack gas exit temperature K 373 328 413.7 448.15 509.55 Rural/Urban Rural Urban Rural Urban Urban SOx emission rate g/s 1.049 7.6 68 (lb/hr) 1.052 n/a NOx Emission rate g/s 6.459 30.6 173.3 (lb/hr) 3.0702 n/a Dioxin/Furan Emission rate fg/s 0.42 1.53 n/a 0.199 0.592 Capacity t/hr 27 68 42 15 15 Additional data was required for sites surrounded by complex terrain. This data was collected by taking two transects per site and determining the terrain elevation profile in relation to distance from the site. This allowed the creation of ground profiles such as that in figure.3. The elevation data was extracted from Google Earth and the corresponding distances were found using the ruler function in google Earth. The two 5km transects were selected for each site on the basis of:
  19. 19. 18 I. Prevailing Wind II. In order to capture a particularly complex train to consider the worst case scenario of each site. Figure 10: Terrain profile taken from the alternate transect at the Carranstown site The output data was compiled into a spread sheet and the data was expressed as the four sites contribution to a particular emission.
  20. 20. 19 5) Results This study has narrowed its focus onto three significant pollutants released from incinerators. Sulphur Dioxide and Nitrogen oxides were selected on the basis of a gravity analysis in which these two emissions ranked highest among all the pollutants emitted from a MSW incinerator (Indaver, 2015). Dioxins and furans were selected for study in this project on the premise that they have the potential to cause serious damage to human health and are the prime subject of controversy between the public on incinerators. Sulphur Oxide Emissions Figure.11 (a) and (b) shows sulphur dioxide emissions for all four study sites. In both wind direction scenarios the Poolbeg facility releases the highest amount of this pollutant doubling the emissions of the other sites in some cases. Pollutant concentrations all seem to peak between the 800 to 1000 m mark and trail off gradually to lower concentrations as distance increases from the source. The Carranstown site performs particularly well relative to the other sites with the lowest pollutant emissions out of the four sites. -2 0 2 4 6 8 10 12 14 16 18 0 1000 2000 3000 4000 5000 6000 SOxConcentration(μg/m³) Distance From Point Source (m) Prevailing Air Dispersion of SOx emissions Carranstown Poolbeg Montcada (2001) Florida Figure 11 (a): Air Dispersion of SOx emissions in the direction of prevailing wind
  21. 21. 20 Figure.11 (b) illustrates the effects of pollutants taking a different path following release from the stack. The Poolbeg sites peak pollutant emissions are muted slightly in this scenario however instead of gradually trailing off to lower concentrations, this time emissions rise again at ~2700 m away from the source. The Carranstown emissions rise slightly relative to their prevailing wind concentrations while the Montcada emissions also rise slightly relative to their prevailing counterparts. The Florida site appears to be unchanged in both scenarios. Nitrogen Oxide Emissions The Poolbeg facility also comes in as the highest polluter with respect to NOx, registering its highest emissions at approximately 68µg/m³; doubling the average concentrations emitted from the other three facilities (figure. 12 (a)). The Carranstown facility does not perform as well in limiting Nitrogen emissions as it does Sulphur, ranking second highest in this scenario. Interestingly, the Florida site almost mirrors the dispersion profile of the Carranstown site albeit at slightly lower concentrations. The Montcada site performs greatest at limiting NOx in this scenario. -2 0 2 4 6 8 10 12 14 0 1000 2000 3000 4000 5000 6000 SOxConcentration(μg/m³) Distance From Point Source (m) Alternate Air Dispersion of SOx emissions Carranstown Poolbeg Montcada (2001) Florida Figure 11 (b): Air Dispersion of SOx emissions in the alternate direction chosen for each site.
  22. 22. 21 In Figure.11 (b) the slight rise at the end of the NOx emissions profile for the Poolbeg site is witnessed once more. The Carranstown emissions display a delayed peak at ~ 900 m as opposed to ~300m in fig.12 (a). The Montcada profile, on the contrary peaks earlier in the alternate wind scenario than it did in the prevailing wind scenario. The Florida site sees a slight increase in its peak emissions in the alternate wind scenario however its profile remains superficially the same. -10 0 10 20 30 40 50 60 70 80 0 1000 2000 3000 4000 5000 6000 NOxConcentration(μg/m³) Distance From Point Source (m) Prevailing Air Dispersion of NOx emissions Carranstown Poolbeg Montcada (2001) Florida -10 0 10 20 30 40 50 60 0 1000 2000 3000 4000 5000 6000 NOxConcentration(μg/m³) Distance From Point Source (m) Alternate Air Dispersion of NOx emissions Carranstown Poolbeg Montcada (2001) Florida Figure 12(a): Air dispersion of NOx emissions according to prevailing wind conditions. Figure 12 (b): Air dispersion of NOx emissions according to alternative wind conditions.
  23. 23. 22 Dioxin and Furan Emissions These pollutants have gained a particular degree of notoriety due to being linked with causing cancer hence emissions must be strictly limited below emissions limits. Thankfully this was the case at the three facilities studied in this project hence their concentrations are measured in femtograms (1e-15 grams). Notice the change from µg/m³ to fg/m³ on the graphs. The Florida site did not provide data on the emissions of these toxins hence is omitted from this portion of the study. Data could however be found on the Montcada site before it underwent renovations in 1996 (Meneses et al, 2004). This could provide an interesting perspective on quantitative effects the respective gas cleaning methods mentioned in section.2 have on reducing emissions. In figure 13 (a), it seems the Poolbeg facility has finally met its match in terms of big emitters however it is the pre-renovated Montcada, 1996 site which is shadowing the Poolbeg’s giant profile. The Carranstown site peaks early at ~300m as it has done in all other prevailing wind scenarios. The upgrades carried out to the Montcada site have clearly been successful as it has brought the site from the being the highest polluter to the lowest one in comparison to the two Irish sites studied. -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 0 1000 2000 3000 4000 5000 6000 Dioxin/FuranConcentration(fg/m³) Distance From Point Source (m) Prevailing Air Dispersion of Dioxins/Furans Carranstown Poolbeg Montcada (2001) Montcada (1996) Figure 13: Air Dispersion of Dioxins and Furans in the prevailing wind direction
  24. 24. 23 The Montcada (1996) site well and truly takes over the top spot of highest emitters from the Poolbeg site in this scenario (fig 13, b). The Poolbeg site, as with the previous emissions profiles shows an upward inflection at the 2.7km mark. The Indaver site exhibits its “delayed peak emissions” characteristic of the alternate wind direction scenario while the Montcada (2001) maintains its position as lowest Dioxin emitter. -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 0 1000 2000 3000 4000 5000 6000 Dioxin/FuranConcentration(fg/m³) Distance From Point Source (m) Alternate Air Dispersal of Dioxins/Furans Carranstown Poolbeg Montcada (2001) Montcada (1996) Figure 13 (b): Air Dispersion of Dioxins and Furans in the alternate wind direction
  25. 25. 24 Sensitivity Analyses Three sensitivity analyses were carried out to serve a dual function of testing the model consistency and demonstrating the effects that stack height, volumetric flow and exit gas temperature on pollutant dispersal. Figure.14 and tables 3 and 4 all use the prevailing NOx concentration for the Carranstown site as a parameter for the analysis. Figure 14: Stack height variation Figure.14 shows that the lower the stack height, the higher the associated emissions. While an increase in stack height reduces overall emissions concentrations. However the rate of lowering emissions slows once reaching a stack height of 60m. This analysis revealed that the mean peak point for this parameter occurs at approximately 800m from the site source. This point was utilised in the following sensitivity analyses. Table.3 shows the effect of altering the volumetric flow of the model. The NOx emissions steadily decrease from 39.86µm/m³ to 27.08µm/m³ as the flow rate increases in increments of 10m³/s. Table.3 also notes a slight but steady increase in the buoyancy flux and an almost exponential rate of increase of momentum flux mirror an increase in volumetric flow. -10 0 10 20 30 40 50 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 NOxConcentration(µm/m³) Distance from Point Source (m) Senstivity Analysis for Stack Height 20m 40m 60m 80m 100m
  26. 26. 25 Table 3: Volumetric Flow Sensitivity Analysis Volumetric Flow m³/s 30 41.94 50 60 70 NOx Conc. µm/m³ 39.86 38.43 37.64 32.46 27.08 Buoyancy Flux m^4/s³ 20.084 28.073 33.473 40.168 46.863 Momentum Flux N·s·m−2 ·s−1 71.631 139.996 198.975 286.524 389.991 Table.4 shows an increase in exit gas temperature results in a decrease in emission dispersal at 800 m. Gas temperature increases also results in a buoyancy flux increase however momentum flux is lowered with an increase in temperature. Table 4: Gas Temperature Sensitivity Analysis Gas Temp K 300 373 400 500 600 NOx Conc. µm/m³ 73.04 38.43 37.31 22.18 17.7 Buoyancy Flux m^4/s³ 3.055 28.073 35.019 54.197 66.983 Momentum Flux N·s·m−2 ·s−1 174.062 139.996 130.546 104.437 87.013
  27. 27. 26 6) Discussion To reiterate, the main objective of this study was to allay or justify the public’s concerns with regards to the incineration of municipal solid waste. Collectively, the results show that all four sites lie within the emission limits outlined in table.1 by many orders of magnitude. The results were of sufficient resolution to make a number of inferences about the nature of pollution dispersal within the incineration industry. The interpretation will look at each site individually to highlight these. Interpretation Carranstown Site, Indaver Out of the two Irish incinerators, the Indaver facility performs better on an all levels despite having a stack 60% lower than the projected Poolbeg site. This is likely due to the fact is located in a sparsely populated area and is correctly sized. Perhaps these concerns which were reported in the Irish Independent (2014) are justified. Why site an incinerator in the middle of the country’s most densely populated area? Why pay in excess of €600 million to Covanta when Indaver have already successfully built an incinerator on Irish soil and have offered to build a smaller sized plant at Poolbeg for FREE (Irish Independent, 2014). It appears more than public health and air quality are on the agenda for this project. Looking at greater depth at the Indaver plant, it has the best performance in limiting SOx emissions with the exception of one high peak at ~400m. This would indicate that the baghouse filter and evaporating spray reactor is performing particularly well at this facility. This peak appears ain the same location for all 3 pollutants as shown in figures 11,12 and 13 (a). This initial peak is most likely due to a cement factory approximately 400m downdraft of the site. Evidently, the building dimensions may trap pollutant emissions, elevating their concentration briefly. This peak is still with safe limits for all three pollutants. Nitrogen and Dioxin/Furan concentrations are also relatively low highlighting the effectiveness of the ammonia injection and ceramic filters at the facility. It could also be a testament to an efficient incineration of waste, preventing dioxins to reform de novo synthesis.
  28. 28. 27 In the alternate wind scenarios (fig 11,12,13 (b)), the peak emissions have consistently moved on to ~900m downdraft. This is most likely due to the absence of the cement factory on this transect to disrupt pollutant dispersal. The emissions profiles in the alternate scenarios witness a slight rise from 1800m to around 2600m. This is most likely due to the complex terrain to the NE of the site which is higher than the stack in places. Poolbeg Site, Covanta The main reason the Poolbeg site has a higher relative emissions (fig. 11, 12, 13 (a)) profile is because it is has a much larger capacity than the other facilities at 68t/hr according to table.2. However this does not excuse the site from emitting more pollutants. The Florida plant is a similar sized facility but has a considerably lower eco-impact. The similarities don’t stop there; the stacks are also of a similar dimension as well as gas flow velocities and temperatures. The main parameter these two sites differ on is their location. The Florida site is located in a rural area while the Poolbeg facility will sit in a site with sea on one side and a city on the other. This raises the concerns again over why the planning authorities are so insistent in siting the facility here. Another alarming comparison is when this facility is compared to the Montcada (1996) facility in figure.13 (a). The state-of-the-art Poolbeg plant is performing as poorly as an archaic incinerator with only an electrostatic precipitator as a gas cleaning technology in preventing dioxin and furan releases. Although the concentrations are well below the limits, shouldn’t a monstrous incinerator be performing better than a 40 year old treatment plant? In defence of the Poolbeg project, the input values used are based on estimated data while the rest of the studies rely on empirical data. In addition, given that the prevailing wind carries emissions out to sea, the exceptionally high peak of emissions may be down to marine temperature inversions which trap pollutants, hence raising their concentrations. Looking at the alternate scenario for Poolbeg, the wind is now taking emissions across the city instead of out to sea. An upward inflection in all pollutant concentrations from about 2.7 km is most likely due to the presence of a number of residential buildings at Fairview and Santry. These are more likely to trap emissions, increasing their concentrations of
  29. 29. 28 pollutants. The urban heat island could also come into effect here, which can affect the buoyancy of the air, causing emissions to linger for longer. Montcada Site, Tersa The prevailing profile of this facility has a similar shape to the Poolbeg one albeit at much lower concentrations across the board. This is most likely because this facility is also located on the coast and its stack emissions may also be under the influence of a marine temperature inversion. The alternate wind scenario (fig 11,12,13 (b)) also takes this facility’s emissions across the city and this causes the emissions profile to warp considerably. At <200m distance the profile peaks and then troughs again at 500m and then steadily rises up until 2000m before trailing off. This is explained by the presence of particularly high buildings at ~350 m, 1,100m and 1700m which were modelled in Screenview. Moving on to the most interesting part of the Montcada site; Figure.13 (a) and (b) show the Dioxin/Furan emission profiles and include the Montcada facility before and after renovations to upgrade the gas clean-up infrastructure. Taking the peak of both profiles in both prevailing and alternate scenarios, this represents an emissions reduction of 65%. This figure can be directly attributed to the addition of a wet scrubber and active-carbon fabric filter and their effectiveness at preventing the release of these highly problematic emitters (Meneses et al, 2004). Florida Site, Wilcox & Babcock The stand out feature of this site was the complete omission of dioxin and furan concentrations in any of the associated literature. There was not a single mention of these highly hazardous pollutants in the air modelling report for the site (Solid Waste Authority of Palm Beach County, 2010). Interestingly, there is no use of the term “incinerator” in this report either with the 42 tonne per hour plant being referred to as a “renewable energy facility”. It was quite evident this report was guilty of green washing. Nonetheless the facility appears to perform resonably well in minimizing emissions. While an American facility would greenwash their product in a heart-beat in order to secure more sales, one could be sure that the facility will have the most advanced levels of technology.
  30. 30. 29 The facility is surronded by a similar landscape 360° and did not show much variation in emmsions between the two scenerios figures. 11 and 12 (a) and (b). Limitations There are a number of limitations associated with this study yielding lower resolution data for each site and causing higher uncertainty in the results. Input data: The data obtained for the model inputs has, for the most part been sourced from documentation provided by the operators of the respective facilities. Obviously it is within these company’s interests to present emission limits which remain within the legislative limits. Had the activity data been sourced from an unbiased organisation such as the EPA, and was based on empirical measurements, the integrity of the model would be greatly enhanced. Modelling Software: The “Screenview” software offers a very limited range of data-manipulation features which prevents the user from creating a model that is consistent with the real life scenario. The software does not allow simultaneous use of urban terrain and shoreline fumigation which was required for the Poolbeg and Montcada scenarios. Furthermore it is not possible to model the concentration of emissions on terrains higher than the overall stack height. The modelling function has a very linear nature in the sense that it utilises very simple input data on a single transect and outputs extremely simplified results on a graph based on the distance from the source. More advanced models such as “AERMOD” overlay results on a raster file of the given geographical area giving 360° emission concentrations from the source based on variable wind speeds.
  31. 31. 30 7) Conclusions  The results of this study show a strong argument that the incineration of waste is safe for human health.  The concentrations of NOx, SOx and Dioxins/Furans were found to be several orders of magnitude lower than emissions limits illustrated by the waste incineration directive (WID 2000/76/EC).  By comparing the results of a renovated incineration plant in Barcelona, it was shown that modern gas-cleaning technologies can reduce the emission of cancer- causing Dioxin/Furans by 65%.  Despite being intimately located in the heart of Ireland’s largest population centre; the Poolbeg incinerator is appears to be well below the prescribed emissions limits. However an alarming comparison was made between it and a 1975 standard incinerator which performed almost exactly the same with respect to preventing dioxin/furan release.  The major limitation of this study lies on the source of its data; considering most data was sought from the respective companies which built the infrastructure in the first place, they are hardly going to publish data which does not look well for the company’s reputation.
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