HCl and PCDD/Fs emission characteristics from incineration of source-classified combustible solid waste in fluidized bed

Abstract

A fluidized bed incineration experiment was performed by means of refuse-derived fuel (RDF) from source-classified garbage to study the emission characteristics of hydrogen chloride (HCl) pollutants and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCCD/Fs). This study analyzed the influence of the materials ratio, incineration temperature, and additive volume of calcium oxide (CaO) on the emission characteristics of HCl and the dioxins. Results show that plastics in garbage are direct factors for the emission of HCl and PCCD/Fs. The HCl yield significantly increases when the plastic component ratio increases from 35% to 45%. The RDF containing 45% plastics releases the highest toxicity concentration of total dioxins, whereas the RDF of 35% plastics releases the lowest dioxin toxicity concentration. The optimal incineration temperature is 850 °C, the emission concentrations of HCl and PCCD/Fs are significantly reduced at 850 °C. Adding CaO to combustible solid waste can effectively reduce the emission concentrations of HCl and PCDD/Fs in flue gas.

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1. Introduction

At present, the increase in municipal solid waste (MSW) has become a serious challenge for environmental management and pollution control every year. In China, the annual output of municipal solid waste outnumbers 260 million tons and still increases annually with a rate of 8–10%. The accumulated stock of municipal solid waste is about 7 billion tons in China and more than two thirds of the cities are surrounded by garbage nationwide.^1,2 Therefore, it is necessary to explore a lower pollution and higher energy recovery treatment for MSW. The methods of waste treatment currently include landfilling, high temperature composting and incineration.^3–5 Incineration has been developing rapidly because of the significant effects of volume reduction, resource utilization and less environmental pollution. At present, incinerators mainly include grate furnace, fluidized bed and rotary kiln incinerators.^6–8 Compared with other incineration methods, the technology of fluidized bed incineration can avoid rapid cooling and the thermal shock phenomenon for steady continuous burning as a result of its advantageous large heat storage capacity. We can also take comprehensive measures to decrease secondary pollution and dispose of harmful substances generated in fluidized bed incineration. As a consequence, the technology of fluidized bed incineration has been widely used because of its characteristics of high combustion efficiency, wide fuel adaptability, wide range of load regulation and low pollutant emission.^9,10 Waste incineration will cause secondary air pollution. Especially, combustible compontent containing chlorine (such as PVC) and chloride in waste will produce dangerous pollutants such as HCl, polychlorinateddibenzo-p-dioxins and polychlorinated dibenzofuran during incineration which are enormously harmful to the environment and the human body. Therefore, it is very necessary to research the emission characteristics of HCl and dioxins in MSW incineration for oligosaprobic water and resource utilization of MSW.

Numerous scholars have confirmed that incinerating refuse-derived fuel (RDF) manufactured by municipal solid waste can reduce the emission of dioxins and other pollutants.^11,12 Incinerating source-classified combustible solid waste with a low moisture content and high calorific value is the most effective means of waste reduction in a fluidized bed, and is also an excellent method of converting combustible solid waste into efficient energy. Hydrogen chloride (HCl) is generated during incineration. This process directly corrodes flue gas treatment facilities and promotes the generation of toxic dioxin substances because of the huge amounts of chlorine (Cl) and inorganic salts in municipal household garbage.^13,14 Dioxins are considered to be the most hypertoxic organic pollutant among all pollutants generated by waste incineration. Therefore, finding the optimal incineration operating modes and conditions is one of the decisive factors for low pollutant emission in flue gas.

Xie et al.¹⁵ deemed that adding calcium oxide (CaO) decreases the emission of sulfur dioxide (SO₂) and HCl. Partanen et al.¹⁶ studied the influence of the fluidized bed temperature on CaO dechlorination, and the absorption characteristics of CaO toward HCl in flue gas. The aforementioned research found that the absorption to HCl by CaO is in correlation with the humidity of flue gas when the incineration temperature is 850 °C. Stable and sufficient combustion conditions also can decrease the dioxin yield. The United States Environmental Protection Agency proposed that efficient combustion is one of the most effective measures to control the emission of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs).¹⁷ In addition to the above-mentioned factors, there are also many other factors to influence the dioxin yield. For example, the incineration temperature can significantly influence the generation of PCDD/Fs, however there is no obvious effect on the homolog distribution according to the current study.¹⁸ A key method to control the emission of dioxins is to maintain the incineration temperature above 800 °C because dioxins can be decomposed above this temperature. Therefore, the incineration temperature of fluidized bed is an important factor in dioxin generation.^19,20 The dioxin yield can also sometimes be reduced when some additives are added into MSW. Ruokojärvi et al.^21,22 found that injecting chemical inhibitors such as dimethylamine and ammonia into a combustor at 670 °C can effectively decrease the dioxin concentration in flue gas. M. Y. Wey et al.²³ studied thoroughly and comprehensively the effect of adding CaO on the formation of pollutants (HCl, chlorophenols (CPs)/chlorobenzenes (CBs), PAHs, benzene, toluene, ethylbenzene and xylene (BTEX)) by organic chlorides in waste incineration using fluidized beds. The above-mentioned research found that adding CaO inhibited the production of HCl, CBs and CPs, but did not seriously affect that of PAHs and BTEX. Yan et al.²⁴ conducted assessment research on the emission characteristics of dioxins generated in fluidized bed mixed incineration of coal and urban solid refuse.

Currently, most research is aimed at the emission characteristics of HCl, dioxins and other pollutants when source-classified combustible solid wastes are incinerated in a conventional fixed bed reactor. While in this research, combustible solid waste was incinerated in a pilot-scale fluidized bed reactor and the influences of the source-classified materials composition, additives, and incineration temperature on HCl and dioxins emissions were considered. The research results can not only provide fundamental insight into the resource utilization of municipal solid waste, also provide better guidance for optimizing furnaces, achieving zero emission and using energy efficiently.

2. Experimental

2.1. Experimental materials

Combustible solid wastes with high calorific values were sorted by a source-classified technology as experimental materials. The solid wastes were collected from the domestic garbage of Luzhi Town in Jiangsu Province. The typical components of combustible solid waste include waste plastics, waste fabrics, waste paper and wood chips. All the typical components are dried in a drying oven at 100 °C for two hours in order to eliminate the influence of moisture on the experimental study. Then, the materials were easily crushed into 8 mm molded particles using a crushing appliance. Finally, the experimental sample particles were made into RDF by a modeling machine according to the typical component proportion which is studied in this experiment. Ultimate and proximate analysis data of RDF are shown in Table 1.

Table 1 Ultimate and proximate analyses of RDF^a

Sample	Moisture/%	Volatile/%	Fixed carbon/%	Ash content/%	C/%	H/%	O/%	N/%	S/%	Cl/%	Lower calorific value (kJ kg^−1)
a Notes: the ratios for plastics, paper, wood, fabrics, and CaO in RDF are 45%, 15%, 20%, 15%, and 5%, respectively, for 45% plastics; 35%, 15%, 20%, 25%, and 5%, respectively, for 35% plastics; 25%, 15%, 20%, 35%, and 5%, respectively, for 25% plastics; 15%, 15%, 20%, 45%, and 5%, respectively, for 15% plastics; and 10%, 15%, 30%, 40%, and 5%, respectively, for 10% plastics.
45% plastics	1.59	83.05	6.91	3.46	60.88	8.96	18.68	0.941	0.105	1.443	27 465
35% plastics	1.66	81.43	8.48	3.41	58.07	7.99	21.21	1.43	0.108	1.367	24 660
25% plastics	1.74	79.80	10.05	3.40	55.53	7.02	23.73	1.91	0.132	1.111	21 855
15% plastics	1.81	78.18	11.62	3.39	52.98	6.05	26.26	2.40	0.114	0.945	19 050
10% plastics	2.16	76.64	12.31	3.66	50.22	5.62	29.39	2.14	0.10	0.758	17 818

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2.2. Experimental apparatus

The experiments were performed using a small pilot-scale fluidized bed, the structure of the fluidized bed incinerator is shown in Fig. 1. The experimental table includes a fluidized bed body, a feeding system, an ignition system, an air supply system, a temperature and pressure control system, and a flue gas analyzer. The height and diameter of the fluidized bed combustor are 1500 and 60 mm, respectively.

Fig. 1 Schematic diagram of the fluidized bed test bench: (1) intelligent control cabinet, (2) root blower, (3) screw feeder, (4) pressure measuring device, (5) fluidized bed, (6) temperature measuring device, (7) cyclone separator, (8) Gasmet gas analyzer, (9) induced draft fan, (10) chimney, (11) pump, (12) toluene absorbing liquid, and (13) XAD-2 resin.

2.3. Experimental process

In this research, the quartz sands are put into the reactor as bed materials for the small pilot fluidized bed incinerator and the height of the bed materials is about 100 mm in the stable operation state. The ventilation quantity of the entrance is about 4.8 m³ h⁻¹ and the incinerator temperature varies from 700–900 °C during runtime. When fluctuation of the bed temperature is tiny, the reactive materials are put into the incinerator with continuous feeding. The feeding speed is about 500 g h⁻¹. The detailed operating steps are as below:

(1) Open the pilot circulating fluidized bed boiler. When the fluidized bed temperature reaches the reaction temperature, switch on the spiral feeder power and transport the reaction materials from the feed inlet.

(2) Fine-tune the quantity of the primary air and observe the differential pressure gauge. Then, connect the absorption equipment of dioxins.

(3) The Gasmet gas analyzer is blown out with high purity nitrogen before each experiment.

(4) Open the Gasmet gas analyzer sample device valve to measure the instantaneous release concentration of HCl.

(5) The PCDD/Fs are analyzed and measured according to the United States EPA1613 method. 17 poisonous 2,3,7,8-PCDD/Fs are tested using the method of HRGC/HRMS (high resolution chromatography and high resolution mass spectrometry). The testing of dioxins includes pretreatment and analysis processes. Preprocessing steps are Soxhlet extraction, purification and concentration, and then the analysis of the concentrates utilizing the analytical equipment. Finally, the dioxin content is tested by the JMS-800D HRGC and HRMS analyzers manufactured by Japan Electron Optics Laboratory Co., Ltd.

3. Results and discussion

3.1. The emission characteristics of HCl

3.1.1. Influence of the material ratio on the emission characteristics of HCl. Fig. 2 shows the average emission concentrations of HCl when the RDFs containing 45%, 35%, 25%, 15%, and 10% plastics were incinerated at 850 °C, with an oxygen content of the furnace exit at 9%. As shown in Fig. 2, the HCl concentration increases with increasing plastics content. The HCl concentration in the exhaust gas is lowest (2.60 mg m⁻³) when the plastics content accounts for 10%. The HCl concentration is 10.21 mg m⁻³ when the plastics content accounts for 45%. The emission load of HCl significantly increases from 6.58 mg m⁻³ to 10.21 mg m⁻³ when the plastics content increases from 35% to 45%. Compared with the other components of RDF, the chlorine content of the plastics in RDF is the highest. The chlorinity of RDF increases with increasing plastics content, and then HCl emission increases. In the incineration process, the organic chlorides of household refuse, such as polyvinyl chloride (PVC), can also produce HCl by removal of the chloride substituent. The reaction equation is as shown below:

RDF + O₂ → CO₂ + H₂O + HCl + incomplete comburent. (R1)

Fig. 2 HCl average emission concentration with different materials ratios.

3.1.2. Influence of the bed temperature on the emission characteristics of HCl. Fig. 3 indicates the variation trend of the HCl emission concentration when RDF is incinerated at 750, 800, 850 and 900 °C with an oxygen content of the furnace exit at 9%. The RDF is composed of 45% plastics, 15% paper, 20% wood, 15% fiber, and 5% CaO. The generation and inhibition reaction pathways are as follows:

RCl + O₂ → CO₂ + H₂O + HCl, (R2)

HCl + CaO → CaCl₂ + H₂O, (R3)

CaCl₂ + SO₂ + H₂O → CaSO₄ + 2HCl, (R4)

2HCl + 1/2O₂ ⇔ Cl₂ + H₂O. (R5)

Fig. 3 HCl average emission concentration at different bed temperatures.

As shown in Fig. 3, the HCl concentration increases with increasing bed temperature. However, the influence of the bed temperature on the HCl yield is getting less strong with increasing bed temperature. The cause for these results is that HCl is mainly produced at low temperatures. The higher the fluidized bed temperature, the higher the partial pressure of HCl vapor. Thus, the reaction (R2) is more violent toward the right, the more HCl is generated. The removal efficiency of the calcium compound toward chlorine is best between 600 and 700 °C. While when the bed temperature exceeds 650 °C, the removal efficiency of CaO toward chlorine decreases with increasing bed temperature. Thus, the influence of the bed temperature on the HCl yield in exhaust gas is noteworthy in our laboratory study.

In the combustible solid waste incineration process, most chlorine-bearing compounds can be decomposed in the low-temperature section from 200–350 °C to achieve side group elimination reactions, which produce HCl and conjugate and double-bond polyene hydrocarbons. With increasing temperature, the polyene hydrocarbons randomly degrade generating tar and micromolecular gaseous hydrocarbons under aerobic conditions, which diffusively combust with the surrounding O₂. Therefore, most HCl is released during devolatilization when the temperature ranges from 200 to 350 °C. When the temperature ranges from 750 to 900 °C, the conversion rate curve of HCl is gentle.

3.1.3. Influence of the CaO quantity on the emission characteristics of HCl. CaO was used to remove HCl from exhaust gas in this experiment. RDFs containing 3%, 5% and 7% CaO were incinerated at a bed temperature of 850 °C and an oxygen content of the furnace exit of 9% in the fluidized bed. Fig. 4 and 5 show the experimental results of the HCl emission of two RDF groups (Table 2) with different CaO quantities. As shown in Fig. 4 and 5, we can find that the HCl removal efficiency increases, while the HCl concentration decreases with increasing CaO. From Fig. 4 and 5, the HCl yield of the first RDF group is higher than that of the second RDF group added into the biomass. After adding biomass, the ratio of plastics containing the most chlorine is reduced. K and Na existing in the biomass can also react with HCl. In summary, the HCl concentration of RDF containing biomass is significantly lower than that of RDF without biomass.

Fig. 4 HCl average emission concentration with different CaO quantities of two components.

Fig. 5 HCl average emission concentration with different CaO quantities of three components.

Table 2 The experimental results with different CaO quantities

Fuel	Paper 1, plastic 1	Paper 1, plastic 1	Paper 1, plastic 1	Paper 1, plastic 1, biomass 1	Paper 1, plastic 1, biomass 1	Paper 1, plastic 1, biomass 1
CaO	3%	5%	7%	3%	5%	7%
Ca/Cl	1.4	2.4	3.4	2	4	5
HCl concentration (mg m^−3)	4.82	4.02	3.88	4.35	2.57	2.44

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CaO added to RDF can react with the chlorine-bearing compounds in the incineration process and then inhibit the release of HCl. When the amount of CaO is too little, the limited quantity of CaO reacts completely, thus the HCl concentration in Fig. 2 would suddenly increase.

In actual engineering, the molar ratio of Ca/Cl is an important factor for the dechlorination. Thus it is very important to reasonably confirm the range of the Ca/Cl molar ratio. Fig. 6 shows the HCl average emission concentration at different Ca/Cl molar ratios. We can conclude from Fig. 6 that the increase in Ca/Cl can reduce the HCl yield. However, the HCl removal efficiency becomes lower and lower with increasing CaO. Related data reveal that there is no obvious dechlorination when the Ca/Cl ratio is greater than 6. With increasing Ca/Cl molar ratio, the remaining particles of CaO become unevenly distributed. The adsorption between the CaO particles and gas phase HCl or chlorine is reduced, decreasing the effectiveness of the reaction. In addition, the HCl concentration becomes extremely low when Ca/Cl reaches a certain value. In summary, there is no very obvious dechlorination even if the CaO amount continues to increase.

Fig. 6 HCl average emission concentration at different Ca/Cl mole ratios.

3.2. The emission characteristics of dioxins

3.2.1. Influence of the materials ratio on the emission characteristics of dioxins. Fig. 7(a–c) show the changing trends of the dioxin concentration when RDFs containing 25%, 35%, and 45% plastics were incinerated in a fluidized bed at a bed temperature of 850 °C and with an oxygen content of the furnace exit of 9%. The distribution of dioxins and production of homologs vary when the three RDFs with different plastics content are incinerated. In PCDDs, the toxic concentrations of 2,3,7,8-TCDD and 1,2,3,7,8-PeCDD are higher, whereas the yields of 2,3,7,8-TCDF, 1,2,3,7,8-PeCDF, and 2,3,4,7,8-PeCDF are higher than those in PCDFs of the homologous substances. Based on the overall yield of dioxin homologs, the main dioxin contributors are 2,3,7,8-TCD and 2,3,4,7,8-PeCDF. Meanwhile, based on the distribution of the toxic concentration of PCDD homologs generated by RDF with different plastics content by incineration, the toxicity of each product shows a decreasing trend with increasing degree of chlorination. The toxicity concentrations of OCDD and OCDF generated by the RDF containing 35% and 25% plastics are not detectable.

Fig. 7 (a–c) PCDD/F distribution with different plastics proportions.

The toxic concentration of 2,3,7,8-TCDD in PCDDs and those of 2,3,7,8-TCDF, 1,2,3,7,8-PeCDF, and 2,3,4,7,8-PeCDF in PCDFs produced by RDF with 45% plastics are always the highest, while the toxic concentrations of the above-mentioned dioxins generated by RDF with 35% plastics are the lowest. The toxic concentration of the other dioxin homologs increases as the plastics content of RDF increases. Since the toxicities of different dioxins are disparate, the total toxic concentration of dioxins produced by the RDF with 45% plastics is the highest, which is 0.18 ng I-TEQ Nm⁻³; that of the RDF with 25% plastics is second-largest, which is 0.1425 ng I-TEQ Nm⁻³; the total toxic concentration of the RDF with 35% plastics is the lowest, which is only 0.135 ng I-TEQ Nm⁻³. In summary, the yields of dioxins correlate with the chlorine content, and the production of dioxins can be reduced by means of controlling the plastics content of RDF.

3.2.2. Influence of bed temperature on the emission characteristics of dioxins. Fig. 8(a–c) shows the distributions of PCDD and PCDF homologs as well as the change of total toxicity concentration in flue gas when the RDF with 45% plastics content is incinerated at 750 and 850 °C with an oxygen content of the furnace exit of 9%. Previous research has shown that¹⁸ the combustion temperature exerts a significant influence on the PCDD/F generation, however the influence of temperature on the homolog distribution is not obvious. As shown in Fig. 8(a–c), the distribution of dioxins and their homologs and the total toxicity concentration are different when the incineration temperature of the fluidized bed changes. At 750 °C, the toxicity concentration of seven PCDDs homologs accounts for 60% of the total 17 dioxin homolog gross, which is 1.408 ng I-TEQ Nm⁻³. In PCDDs congener, the toxic concentration of 1,2,3,7,8-PeCDD is the highest, which reaches 0.3909 ng I-TEQ Nm⁻³. The second is that of 2,3,7,8-TCDD, which has a toxic concentration of 0.1866 ng I-TEQ Nm⁻³. With increasing number of chlorine atoms, the quantity of OCDD is 0.0023 ng I-TEQ Nm⁻³. For the PCDF homologs, the toxic concentration of 2,3,4,7,8-PeCDF is the highest, which reaches 0.2255 ng I-TEQ Nm⁻³. With increasing number of chlorine atoms, the toxic concentration of the PCDF homologs is gradually reduced after increasing firstly. In summary, when the bed temperature is 750 °C, the total toxic concentration of dioxins in flue gas exceeds 1 ng I-TEQ Nm⁻³, which is the emission standard in China. When the bed temperature is 850 °C, the distribution of dioxin homologs is changed. For the PCDD homologs, the toxic concentration of 2,3,7,8-TCDD with the highest toxicity is the highest, which reaches 0.0300 ng I-TEQ Nm⁻³. This is because the amount of lower-chlorinated dioxin congeners increases and then the amount of total dioxins yielded is less. In summary, the higher temperature is beneficial to the decomposition of higher-chlorinated dioxins. With increasing number of chlorine atoms, the toxic concentration of the PCDD homologs decreases. The lowest is that of OCDD with 0.0002 ng I-TEQ Nm⁻³. Compared with that at 750 °C, the changed trend of the PCDF homolog distribution is tiny at 850 °C. The major dioxin contributor remains 2,3,4,7,8-PeCDF, which reaches 0.034 ng I-TEQ Nm⁻³ and which is also the main toxic dioxin in household refuse. The generation of lower-chlorinated PCDFs is inhibited at 850 °C. According to the dioxin homolog distribution and its total toxicity concentration at different temperatures, the increase in incineration temperature can obviously decrease the dioxin generation. When the incineration temperature is 750 °C, the total dioxin amount generated by RDF incineration is 1.408 ng I-TEQ Nm⁻³. However, when the incineration temperature is 850 °C, the total dioxin amount is lower, which is 0.1469 ng I-TEQ Nm⁻³ and close to the international emission standard of 0.1 ng I-TEQ Nm⁻³. At 750 °C, the emission of dioxins is significantly higher than the international standard of 0.1 ng I-TEQ Nm⁻³ and close to the emission standard of China. As a consequence, dioxin generation is closely related to the fluidized bed incineration temperature, and the increase in fluidized bed temperature can effectively decrease the total dioxin emission.

Fig. 8 (a–c) PCDD/F distribution at different incineration temperatures.

3.2.3. Influence of adding CaO on the emission characteristics of dioxins. The dioxin homolog distribution and its total toxicity concentration in flue gas are shown in Fig. 9(a–c), when RDFs containing 3% and 7% CaO are incinerated at 850 °C and the oxygen content of furnace exit is 9%. The RDF composition ratio of plastics/wood/paper is 1 : 1 : 1.

Fig. 9 (a–c) PCDD/Fs distribution under different CaO quantities.

Fig. 9(a–c) show that there is a very weak influence of adding different amounts of CaO on the distribution of PCDD and PCDF homologs. When adding 3% CaO, the distribution diagram of PCDDs shows that the toxicity concentration distribution of homologs decreases with increasing chlorinated PCDDs. The toxic concentration of low-chlorinated 2,3,7,8-TCDD is the highest, which is 0.0567 ng I-TEQ Nm⁻³, but the higher-chlorinated OCDD is not detectable. For the distribution of PCDF homologs, the toxicity concentration of 2,3,4,7,8-PeCDF is the highest, which reaches 0.0657 ng I-TEQ Nm⁻³. The toxicity concentration of the higher-chlorinated PCDF homologs becomes smaller and smaller until OCDF isn’t detected with increasing number of chlorine atoms. Compared with the addition of 3% CaO, the toxic concentration of PCDD and PCDFs dioxin homologs generated by RDF are significantly decreased when adding 7% CaO. The CaO added in RDF removes some chlorine, as a result the amount of HCl generated by incineration decreases in the flue gas and then reduces the emission of dioxins. In summary, the addition of alkali compound CaO can effectively decrease the dioxin generation in the incineration.

4. Conclusions

(1) The emission of HCl is closely related to the influence factor of normal pollutants. For RDFs with different plastics content, the yield of HCl increases with increasing plastics content. When the plastics content ratio increases from 35% to 45%, the increase in HCl emission load is faster which increases from 6.58 mg m⁻³ to 10.21 mg m⁻³. The yield of HCl also increases with increasing chlorine content. When the chlorine content of RDF is higher than 1.5%, the increase in HCl yield slows down. The influence of the chlorine source on dioxins is studied by means of adjusting the chlorine-containing plastics proportion in RDF. When the plastics content is changes in RDF, the yield of dioxins and the distribution of dioxin homologs also changes in the incineration. For the quantity of every dioxin homologs, the major dioxins produced are 2,3,7,8-TCDD and 2,3,4,7,8-PeCD. The toxic concentration of PCDD homologs produced by RDFs with different plastics contents shows a decreasing trend with increasing degree of chlorination. For the total concentration of dioxins, the amount of dioxins produced by RDF with 45% plastics is highest while the amount of dioxins produced by RDF with 35% plastics is the lowest. In summary, a reasonable plastics content is beneficial to inhibit the emission of dioxins.

(2) When the fluidized bed temperature varies from 750 to 850 °C, most HCl is produced in the low-temperature area in the fluidized bed and no increase in HCl concentration is obvious. When the incineration temperature is 750 °C, the total yield of dioxins reaches 1.408 ng I-TEQ Nm⁻³, which approaches the emission standard of China. However, when the incineration temperature is 850 °C, the total yield of dioxins reaches 0.1469 ng I-TEQ Nm⁻³, which approaches the international emission standard. Therefore, the increase in incineration temperature can dramatically decrease the toxic concentration of dioxins in the fluidized bed incinerator.

(3) When antichlor CaO is added to RDF, with increasing CaO additive amount the HCl yield gradually decreases while the trend of decrease is more and more slow. In other words, the influence of CaO on dechlorination is restricted when the content of CaO reaches a certain value. Adding the alkali compound CaO can decrease the toxic concentration of dioxins. The toxic concentrations of PCDD and PCDF homologs and the dioxins produced by RDF with 7% CaO decrease sharply compared with those of RDF with 3% CaO.

Acknowledgements

This research was funded by the National Basic Research Program of China (Grant No: 2011CB201506).

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