The emission and capture characteristics of HCl during PVC and food waste combustion in CO2/O2 atmospheres were studied. Replacement of N2 by CO2 decreased the dechlorination rate of limestone at ...600–700 °C but increased dechlorination rate at 800–900 °C. The chlorine species and temperature highly influenced the HCl emission and capture efficiency of limestone for HCl in CO2/O2 atmospheres. Compared with inorganic chloride in food waste, organic chlorine in PVC had much greater Cl–HCl conversion percent (75.0–93.9%), and higher dechlorination rate (20.4–44.9%) with 10% limestone in 80CO2/20O2 atmosphere. The increment of O2 partial pressure in CO2/O2 atmospheres promoted Cl–HCl conversion. Sulphur in the fuel suppressed the formation of HCl but decreased the dechlorination rate at 700–1000 °C in CO2/O2 atmospheres. The dechlorination efficiency of limestone was better than magnesium based additive and could be improved by modification with NaOH. This research helps control HCl and manages MSW oxy-fuel incineration.
•Study on HCl capture characteristics during MSW combustion in CO2/O2 is innovative.•Influences of atmosphere, temperature, chlorine and absorbent species were analyzed.•CO2 atmosphere and sulphur content in the fuel decreased the HCl emission.•Modification with NaOH, higher amount and lower temperature improved dichlorination.
Municipal solid waste incineration (MSWI) fly ash constitutes a hazardous waste. Melting disposal has been verified to be prospective for stabilizing heavy metals and dioxins. Release of contaminant ...HCl during MSWI fly ash thermal treatment leads to potential environmental risks. The behavior and transformation of chlorine are critical to the disposal strategy of MSWI fly ash. In this study, the pathway of HCl formation in MSWI fly ash thermal treatment under complex atmosphere was revealed. Results show that CaOHCl in fly ash was first decomposed to CaCl
2
, CaO and H
2
O below 550°C, which provides H for HCl generation. Then, CaCl
2
, NaCl or KCl were reacted with H
2
O to release HCl, during which process H
2
O and O
2
promote HCl formation, CO inhibit HCl production since H
2
O is consumed in water-gas reaction. The initial temperature of HCl generation affected by the concentration of H
2
O in the atmosphere. When temperature up to 1250°C, almost all NaCl or KCl were volatilized, HCl mainly from the reaction of chlorine-containing minerals with H
2
O, such as Ca
19.2
Mg
2.8
(Si
0.75
Al
0.75
)
8
O
36
Cl
2
, Ca
4
(SiO
4
)(SO
4
)Cl
2
and Ca
10
(SiO
4
)
3
Cl
2
in N
2
, CO and air atmosphere separately. Moreover, in a reducing atmosphere, metals are more easily chlorinated by HCl, resulting in further consumption of HCl. The order of atmosphere for reducing HCl emissions should be CO>N
2
>Air>>H
2
O.
In this study, HCl emission during the co-pyrolysis of demolition wood and a small amount of polyvinyl chloride (PVC) film (the Cl content of which ranged from 0.5% to 6% by weight) in an N
2 ...atmosphere at elevated temperatures of up to 600
°C was measured using a laboratory-scale cylindrical batch reactor. In the pyrolysis experiments, HCl emission was reduced by the presence of wood. The effect of the primary constituents of wood (cellulose, hemicellulose, and lignin) on HCl emission was investigated by not only measuring HCl emission and Cl distribution to various phases during the co-pyrolysis of each constituent with PVC film but also by conducting thermogravimetric analysis of the constituents. This investigation first revealed that hemicellulose significantly reduced HCl emission by fixing most of the Cl molecules in a sample into pyrolyzed residue.
The flue gas cleaning system of a MSW incinerator with a capacity of 350
kt/year was changed to improve the HCl elimination efficiency. Instead of the semi-wet operating spray reactor and subsequent ...baghouse, a two-step wet flue gas cleaning was added behind the baghouse.
Elemental composition, X-ray powder diffraction patterns and TGA measurements showed that the resulting APC residue was totally different from the former residue. As a consequence, leaching characteristics of both residues also differed and another treatment was required prior to disposal.
For the former residue, mainly leaching of Pb (>100
mg/l), necessitated treatment prior to landfilling. The lower alkalinity of the new residue resulted in a leachate pH of 9.7 and a Pb concentration of 0.8
mg/l. The leachate pH of the former residue was 12.4. The leaching of Pb and Zn increased above 100
mg/l when immobilising the new residue with cement. Better results were obtained when immobilising with micro silica.
The high CaCl
2·2H
2O content of the new residue brought along clogging of the bag filter system. Adding 1.4% of CaO (or 1.9% of Ca(OH)
2) to the residue already improved these inconveniences but again significantly changed the leaching behaviour of the residue.
Measurements of NH
3, HCl, HNO
3 and HNO
2 gas as well as NH
4
+, NO
3
−, Cl
− and SO
4
2− aerosol are used to investigate their surface exchange fluxes and the potential for gas–particle ...interactions at a clean coastal Scottish site. Mean concentrations of HNO
3 and HCl were small at 0.68 and 0.32
μg
m
−3, respectively. At relative humidities (
h)<85% measured gas concentration products (
K
m) were smaller than the predicted dissociation constants (
K
e), suggesting potential for aerosol evaporation, but at high
h,
K
e of NH
4Cl was exceeded at the mean canopy height. Above the canopy, small aerosol concentrations resulted in estimated chemical time-scales of >3
min. Thus, chemical reactions should not have affected NH
3 flux measurements by aerodynamic gradient methods (AGMs), except for very low turbulence when AGM is not applicable. Within the canopy, however, the diffusive transport provided enough time for NH
4Cl to be generated. This was substantiated by measurements of NH
4
+ emission and high Cl
− aerosol concentrations within the canopy.
Micrometeorological measurements above the canopy indicated that gaseous Cl compounds were emitted for most of the time, and this was supported by the source/sink distributions of gaseous and aerosol Cl compounds calculated from in-canopy profiles as well as high apoplastic Cl
− concentrations. Although emission of CH
3Cl has been reported for other
Brassica species, an unrealistically large emission would be necessary to cause the observed above-canopy gradients. Emission of HCl liberated from unidentified water pools of high Cl
− or leaf surface reactions is a more likely source of gaseous Cl compounds.
The HCl emission characteristics of typical municipal solid waste (MSW) components and their mixtures have been investigated in a phi 150 mm fluidized bed. Some influencing factors of HCl emission in ...MSW fluidized bed incinerator was found in this study. The HCl emission is increasing with the growth of bed temperature, while it is decreasing with the increment of oxygen concentration at furnace exit. When the weight percentage of auxiliary coal is increased, the conversion rate of Cl to HCl is increasing. The HCl emission is decreased, if the sorbent (CaO) is added during the incineration process. Based on these experimental results, a 14 x 6 x 1 three-layer BP neural networks prediction model of HCl emission in MSW/coal co-fired fluidized bed incinerator was built. The numbers of input nodes and hidden nodes were fixed on by canonical correlation analysis technique and dynamic construction method respectively. The prediction results of this model gave good agreement with the experimental results, which indicates that the model has relatively high accuracy and good generalization ability. It was found that BP neural network is an effectual method used to predict the HCl emission of MSW/coal co-fired fluidized bed incinerator.
Incineration of chloridated plastic (PVC) in solid wastes contributes much to HCl pollutant in air environment. The characteristics of HCl emissions and reduction during PVC combustion were conducted ...in a nearly isothermal, externally heated, horizontal quartz-tube reactor. With increasing temperature from 700 to 900 degrees C, the conversion of HCl increased leniently from 82.5% to 88.3%. High excess air factor enhanced a small amount of HCl existing in form of Cl2. The calcium-based sorbents including CaCO3, Ca(OH)2, Ca(CH3COO)2 exhibited high HCl capture efficiencies from 68% to 79%, while magnesium-based sorbent less than that of 3%. Influences of operational variables, i.e., size of sorbent, Ca/Cl molar ratio and combustion fume compositions, on the HCl reduction were discussed. From a point of view of equilibrium constant of dechloridization reaction the experimental results were explained in detail.
•Torrefied biomass was found to have much lower chlorine content than raw biomass.•Torrefaction was found to preferentially reduce the chlorine content of low alkali biomass.•Most of the biomass ...chlorine was released as HCl during torrefaction.•HCl emissions from burning torrefied biomass were significantly lower than those from raw biomass.•HCl emissions from burning low-alkali torrefied biomass were drastically lower than those from raw biomass.
Elevated emissions of hydrogen chloride (HCl) from combustion of biomass in utility boilers is a major issue as it can cause corrosion and, in combination with the high alkali content often encountered in these fuels, it can also deposit molten alkali chloride salts on the boiler’s water tubes. Such deposition can impede heat transfer and cause further corrosion. This work torrefied and then burned herbaceous biomass (corn straw) as well as crop-derived biomass (olive residue and corn-based Distillers Dried Grains with Solubles, DDGS), all pulverized in the size range of 75–150µm. It monitored the HCl emissions from torrefaction of biomass and, subsequently, the comparative HCl emissions from combustion of both raw and torrefied biomass. Results showed that during torrefaction most of the chlorine of biomass was released in the gas phase, predominately as HCl. Consequentially, combustion of torrefied biomass, which contained less chlorine than raw biomass, generated significantly lower HCl emissions than raw biomass, particularly so for biomass of low alkali content. This observation complements previous findings in this laboratory that torrefied biomass also generated lower SO2 emissions than raw biomass, albeit by a smaller factor. Both of these findings enhance the appeal of torrefied biomass as a substitute fuel in utility boilers.
