Chlorine In Coal Research Articles

Chlorine evolution and char characteristics during pyrolysis upgrading of Xinjiang high chlorine coal

Xinjiang ShaErHu (SEH) coal, characterized by a high chlorine concentration exceeding 1 %, can cause severe chlorine corrosion when directly burned. To utilize this high-chlorine coal in an effective and clean way, specific pretreatments such as low-temperature pyrolysis upgrading are required. In this paper, the changes in tar, pyrolysis gas, combustion characteristics, and chlorine evolution features were analyzed during the low-temperature pyrolysis of SEH coal. The effects of increasing temperature (350 °C, 450 °C, and 550 °C) were studied. The results show that the proportion of aromatic compounds released consistently increases with temperature, reaching a peak of 80 % at 550 °C in the tar. It is noteworthy that chlorine is hardly detected in tar. The percentage of chlorine released in the pyrolysis gas remains relatively stable as the temperature rises from 350 °C to 550 °C, accounting for approximately 17.5 % of the total chlorine. The percentages of water-soluble chlorine in raw coal, char-350 °C, char-450 °C and char-550 °C are 74.3 %, 80.4 %, 82.2 %, and 55.1 % respectively. The majority of the chlorine in the char produced at 350 °C and 450 °C is inorganic, making up 68.9 % and 69.4 %, respectively. In contrast, char generated at 550 °C has 58.4 % chlorine that is primarily organic. About 40 % of the inorganic chlorine is converted to organic chlorine when the pyrolysis temperature is raised to 550 °C. This conversion likely occurs as a result of the inorganic chlorine ions combining with carbon to form C-Cl bonds. In order to effectively prevent high temperature corrosion, high-chlorine coal can be treated by pyrolysis at temperatures between 350 and 450 °C, followed by water washing and burning. This research provides a theoretical foundation for the clean and efficient use of high-chlorine coal.

Effect of calcium-based additives on NO release of coals under different combustion modes

The nitrogen oxides and sulfur oxides released from coal combustion pose serious environmental hazards, but there exists a contradiction between low-nitrogen combustion and efficient desulfurization, necessitating a deeper understanding of the impact of calcium-based desulfurization agents on NOx release. Based on one-stage and two-stage horizontal furnaces, the effects of temperature, coal types and CaO on the release of NO were explored under the coupled combustion and the separated combustion. The experimental results indicate that: under both conditions, the NO emissions of coals decrease with the increase of temperature. The reaction time of separated combustion is shorter than that of coupled combustion. Under the coupled combustion, the order of NO emissions is: anthracite (AC) > bituminous coal (BC) > lignite (LC) > high chlorine coal (HC), and the order are mainly affected by the content of N in coal. At 800 °C, the fuel-N conversion rates of BC, AC, LC, and HC are all the highest, and the rates are 20.52 %, 25.93 %, 14.90 %, and 15.34 %, respectively. As the temperature rises, both volatile-N and char-N emissions show a downward trend. The NO emissions in the separated combustion are greater and the fuel-N conversion rates of BC, AC, LC, and HC are 44.11 %, 47.31 %, 40.44 % and 32.21 %, respectively. The reduction reaction between char and NO plays a crucial role. After the addition of CaO, there is a significant increase in NO release, indicating that CaO has a catalytic effect on the release of volatile-N and char-N. Under the separated combustion, the impact of CaO on NO emissions is relatively minor, and sometimes it leads to a reduction in NO emission. The role of CaO on the NO release is multifaceted.

Identification of HCl corrosion mechanism on Cu-based oxygen carriers in chemical looping combustion

In chemical looping combustion (CLC) of coal, HCl has been demonstrated as the primary gaseous products of the chlorine in coal. Therefore, a comprehensive characterization of Cu-based oxygen carriers (OC) by HCl corrosion was meticulously conducted, including the activity retention, composition distribution and apparent morphology. The experiment consisted of three parts: (I) evaluating of the OC performance for 100 redox cycles with 7.8 vol% CH4; (II) investigating HCl-corrosion of OC by adding 50 ppmv HCl with 7.1 vol% CH4 for the subsequent 50 cycles; (III) regenerating of OC without HCl addition during the last 50 cycles. The reactivity of OC was attenuating via the HCl addition during the 101st–150th cycles (part II) due to the competition adsorption between HCl and CH4, especially for the partly reduced OC. While, in part III, the reactivity performance of OC was partially recovered because of the abundant cracks on the surface of OC particles which ensured the sufficient gas–solid contact. It should be noted that the single particle hardness index and service life were irreversibly decreased for the HCl-treated OC. Moreover, OC particles were fragmented and the inside Al2O3 balls were exposed on the surface of the HCl-treated OC in SEM image. This work will contribute to understanding the mechanism of Cl-corrosive OC and designing the Cl-resistant OC.

Chlorine emission characteristics and control status of coal-fired units

Chlorine is a harmful trace element in coal. During coal combustion, the chlorine undergoes complex changes and transfers to the gas, and forms chlorine-containing substances. This paper summarizes the field test data of chlorine emission from domestic coal-fired units, and analyzes the chlorine emission and control characteristics. The results show that during the combustion process, the chlorine in coal is released into flue gas, mainly HCl, and a small amount of Cl2 and particulate Cl. Conventional pollutant control facilities affect the form and concentration of Cl. The impact of dust removal facilities on Cl is mainly reflected in the coordinated removal of particulate Cl. The impact of wet desulfurization facilities on Cl is mainly reflected in the coordinated removal of HCl. The Cl emission concentration in flue gas of coal-fired units is 0.85 mg/m3, which meets the emission requirements. Chlorine is transferred from coal to fly ash, desulfurization wastewater and desulfurization gypsum, so the secondary pollution of chlorine should be paid much attention. HCl in coal-fired flue gas has an adverse effect on wet desulfurization facilities. Based on the material balance of chloride ions in absorption tower slurry, this paper proposes a technical idea for removing HCl from flue gas with alkaline absorbents.

Performance of elemental mercury removal by activated char prepared from high-chlorine Turpan-Hami coal

This paper provides a new thought that a cost-effective chlorine-rich carbon-based sorbent could be prepared by directly pyrolyzing high chlorine coal in order to capture the elemental mercury, simultaneously realizing value-added utilization of the remained char instead of combustion during low rank coal pyrolysis poly-generation. In this work, the concentration and forms of chlorine in one kind of Turpan-Hami coal were determined quantitatively according to the proposed procedures. Then the release behavior of chlorine and the transformation of chlorine from inorganic state to organic were investigated during coal pyrolysis from 400 to 1000 °C. Moreover, the Hg0 removal performance was examined in a lab-scale fixed bed reactor by the char before and after CO2 activation. The results indicate that over 90 % of chlorine in raw coal is inorganic in the forms of ionic Cl and crystal NaCl, and ionic Cl can be transformed to inorganic NaCl and organic C-Cl species during coal pyrolysis, thus providing chlorine active adsorption sites for Hg0 chemisorption based on the results of temperature programmed desorption and adsorption kinetic analysis. Furthermore, CO2 activation can improve the char porosity and specific surface area, thus promoting the external mass transfer of Hg0 by increasing the opportunity of chlorine active sites being exposed to vapor Hg0. 100 % of Hg0 removal efficiency is achieved in the first hour and equilibrium adsorption amount is 400 ug/g for the activated char obtained by pyrolyzing coal at 600 °C combining with CO2 activation at 900 °C, indicating the good Hg0 removal performance of the as-obtained chlorinated activated char.

Effects of temperature and additives on ash transformation and melting of high-alkali-chlorine coal

The high contents of sodium and chlorine in Shaerhu coal aggravate severe slag-ging ash deposition and corrosion in boilers. Adding proper additives is an effec-tive way to reduce slagging ash deposition and corrosion. Based on the experi-mental study, this paper investigated the effect of combustion temperature, types of additives, and its amount on the ash transformation and melting of high sodium chloride Shaerhu coal. The ash melting characteristics, elemental compositions and mineral compositions of the ash produced under different conditions were characterized. Results showed that the contents of calcium, magnesium, and sul-phur in the coal ash varied slightly with the temperature increasing. Chlorine and sodium released rapidly from coal at 550-815?C and 550-700?C, respectively. At 1050?C, calcium silicate was observed as the main component of the ash. The addition of different additives had no significant effect on chlorine and sodium capture. The addition of silicon species lowered the ash fusion temperatures, while the aluminum had an opposite effect. To prevent the furnace from slagging, a high aluminum additive is proposed to be adopted.

Fate of the Chlorine in Coal in the Heating Process

Fate of the Chlorine in Coal in the Heating Process

23.褐炭液化反応の研究(14) : 褐炭中のClの反応挙動

23.褐炭液化反応の研究(14) : 褐炭中のClの反応挙動

石炭の加熱過程における塩素の行方

石炭の加熱過程における塩素の行方

Release of sulfur and chlorine gas species during coal combustion and pyrolysis in an entrained flow reactor

The release of four sulfur and chlorine species (SO2, H2S, COS and HCl) from a US-American high sulfur high volatile bituminous coal under pyrolysis and combustion conditions was experimentally investigated in an entrained flow reactor. The reactor design and measuring techniques are presented. Under pyrolysis conditions, the reactor was operated at four wall temperatures (900, 1000, 1100 and 1300°C). With each reactor temperature increment, the release of sulfur from the coal was increased. Approximately 11% of total coal sulfur volatilized at 1300°C. Under combustion conditions, the same temperature influence already observed during the pyrolysis experiments applied for sulfur release. Under fuel rich conditions, SO2, H2S and COS were detected, with hydrogen sulfide being the major contributor. Under exactly stoichiometric and fuel lean conditions, almost all sulfur in the product gas occurred as sulfur dioxide. While at 1000°C, only 63–78% of coal sulfur was found in the gas phase, all sulfur was released when the reactor temperature was changed to 1300°C. During pyrolysis, hydrogen chloride concentration reached its final value at 1100°C. This temperature was sufficient to transform all volatile chlorine, which amounts to 15% of total coal chlorine, to the gas phase. While up to 50% of coal chlorine was released as hydrogen chloride during fuel rich combustion, no HCl was detected under stoichiometric conditions and with excess air.

Distribution, occurrence and leaching dynamic behavior of sodium in Zhundong coal

The utilization of rich-reserve Zhundong coal is limited due to the high sodium content, which can cause severe fouling and slagging troubles in a traditional boiler. The collected drill data of sodium, chlorine and ash in Zhundong coal, as well as the vertical samples including roof, up seam (US) coal, parting, low seam (LS) coal and floor were characterized and investigated. It is found that the sodium content in Zhundong coal is a magnitude higher than chlorine content and decreased with the increasing depth to roof of the coal seam, which agrees well with the changing trend in vertical samples: roof>US coal>LS coal>parting>floor. The determined Na2O content in ash was lower than the converted content indicated part of sodium volatilized during ashing process. Water soluble sodium (H2O-Na) predominated and accounted for 65.50, 82.49 and 64.35wt% in US coal, parting and LS coal, respectively. H2O-Na content is affected by migration and evaporating of coalbed water. SEM-EDX and XRD results indicated that Na, S, O and Ca are the main elements in sodium-rich minerals of roof. With higher H2O-Na and less specific surface area and microporous volumes, parting has an obviously higher initial leaching rate and leachability. The shrinking core model shows that the diffusion rate constant (Kp) is 0.002 and 0.005h−1 for LS coal and parting, respectively. 88.63wt% of H2O-Na in LS coal was leached out, and final Na2O content is markedly lower than the threshold value of coal-fired boiler.

Qualitative and chemical characteristics of mineral matter in the selected lignite deposits in light of their suitability for clean coal technologies

An analysis of the variability of ash content and chemical composition of coal ash is crucial when assessing the possibility of using this raw material in clean coal technologies (CCS). The paper focuses on chemical, technological and quality characteristics of ash from the combustion of lignite from Polish deposits. Ash content on a dry ash-free basis for the samples from 9 deposits varies from 1 to 50%. The most commonly observed ash content in the studied samples of lignite is in the range between 10–20%. The measured ash melting temperatures from the collected lignite samples have shown that the sintering, softening, melting and flow temperatures, determined in an oxidizing atmosphere (air), are higher than those determined in a reducing atmosphere. In the majority of Polish lignite deposits, the dominant component of ash was SiO2 , followed by CaO. When evaluating the suitability of coal in energy production, with particular emphasis on the combustion and gasification processes, it is also necessary to study the behavior of ash at high temperatures and the impact of ash on the gasification and combustion facilities. Ash fouling and slagging processes, which are heavily dependent on the ash content, composition, melting point and the content of chlorine, phosphorus and sulfur in coal, have a negative effect on the combustion process.

Chloride corrosion in biomass-fired boilers – Fe-O-Cl system thermodynamic analysis

The most common and easiest alternative technologies for conventional fossil fuel combustion are biomass combustion and co-combustion. However, high-chlorine fuels (Clar >0,2%) like: biomass, waste and high chlorine coals generate the risk of intensified corrosion process and a limited steel mechanical strength is observed.The paper presents a thermodynamic analysis of chloride-induced corrosion in the Fe-O-Cl system. The ranges of the metallic, oxide and chloride phase stability are determined within the temperature range T = 750-1000 K. Based on the parametric equations the equilibrium concentration of gaseous phase determined by Deacon reaction are presented. The effect of H2 O concentration in the gaseous phase on high-temperature corrosion process and gaseous NaCl influence on NaFeO2 formation in the passive oxide scale layer (FeO/Fe3 O4 /Fe2 O3 ) are discussed as well. The results are correlated with available in the literature laboratory experimental data and industrial corrosion process observations. Presented thermodynamic analysis is compared with assumptions of “active oxidation” model. The results may be used for experimental research prediction and a corrosion prevention in the industry.

Determination of chlorine in coal via the SrCl molecule using high-resolution graphite furnace molecular absorption spectrometry and direct solid sample analysis

In this study, the determination of chlorine in coal is described via molecular absorption of the strontium mono-chloride (SrCl) molecule at 635.862nm using high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) and direct solid sample analysis. The pyrolysis and vaporization temperatures were optimized and the measurements are accomplished with a platform coated with zirconium as a permanent chemical modifier in order to increase the sensitivity of the gaseous SrCl molecule generated in the graphite furnace. The optimum pyrolysis and vaporization temperatures were 700°C and 2100°C, respectively. Under optimized conditions, the limit of detection and characteristic mass of the method were 0.85 and 0.24ng, respectively. The accuracy of the method has been verified using four certified reference materials and one not certified reference material of coal, and the results were in good agreement with the certified or reference values.

Dioxin emissions from coal combustion in domestic stove: Formation in the chimney and coal chlorine content influence

Combustion experiments conducted in domestic stove burning hard coal demonstrated a predominant influence of the coal chlorine content on the PCDD/F emissions, together with a pronounced effect of the flue gas temperature. PCDD/F concentrations of over 100 ng TEQ/m3, three orders of magnitude higher than in a modern waste incinerator, were measured in the flue gases of a domestic stove when combusting high chlorine coal (0.31 %). The PCDD/F concentrations in the flue gases dropped below 0,5 ng TEQ/m3, when low chlorine coal (0.07 %) was used. When low chlorine coal was impregnated with NaCl to obtain 0.38 % chlorine content, the emission of the PCDD/Fs increased by two orders of magnitude. Pronounced nonlinearity of the PCDD/F concentrations related to chlorine content in the coal was observed. The combustion of the high chlorine coal yielded PCDD/F concentrations in flue gases one order of magnitude lower in a fan cooled chimney when compared to an insulated one, thus indicating formation in the chimney. The influence of flue gas temperature on the PCDD/F emissions was less pronounced when burning low chlorine coal. The predominant pathway of the PCDD/F emissions is via flue gases, 99 % of the TEQ in the case of the high chlorine coal for insulated chimney.

Study on Separation of Chlorine in Coal in Combustion Process of Pulverized Coal Injection into B.F.

In the combustion process of pulverized coal injection into blast furnace, the chlorine goes into the unburned pulverized coal is about 17%, the chlorine in the unburned coal keeps original state; The chlorine goes into the blast furnace gas is about 83%, and these chlorine stay as Hcl gas. Changes in air temperature and oxygen rate had no significant effect on the decomposition of chlorine in coal, resulting the rate of Cl into the blast furnace gas is difficult to increase significantly.

Simultaneous determination of bromine and chlorine in coal using electrothermal vaporization inductively coupled plasma mass spectrometry and direct solid sample analysis

A new method for the direct analysis of coal using electrothermal vaporization inductively coupled plasma mass spectrometry and direct solid sample analysis was developed, aiming at the determination of Br and Cl. The procedure does not require any significant sample pretreatment and allows simultaneous determination of both elements to be carried out, requiring small mass aliquots of sample (about 0.5mg). All operating parameters, including carrier gas flow-rate and RF power, were optimized for maximum sensitivity. The use of modifiers/aerosol carriers (Pd, Pd+Al and Pd+Ca) was evaluated, and the mixture of Pd and Ca was chosen, allowing pyrolysis and vaporization temperatures of 700°C and 1900°C, respectively. Chlorine was accurately determined using calibration against solid standards, whereas Br could also be determined using calibration against aqueous standard solutions. The limits of quantification were 0.03μgg−1 for Br and 7μgg−1 for Cl, and no spectral interferences were observed.

Further Understanding of Furnace Wall Corrosion in Coal-Fired Boilers

A comprehensive low-NOx corrosion study consisting of pilot-scale combustion testing and laboratory retort exposure was performed. From the pilot-scale testing, the gas and deposit compositions in the lower furnace of utility boilers burning eight U.S. coals with a wide range of sulfur and chlorine contents were determined. These combustion conditions were then closely reproduced in a series of 1,000 h laboratory corrosion tests to evaluate the materials performance of different furnace-wall alloys and weld overlays at 399, 454, and 510°C (750, 850, and 950°F). Results of the laboratory study indicate that a typical dual-layered scale was formed on the metal surface from simultaneous oxidation/sulfidation due to the presence of sulfur in coal. A new corrosion mechanism is proposed here as “active sulfidation” to account for the accelerated corrosion attack on furnace walls resulting from the presence of chlorine in coal. The mechanism involves the conversion of iron sulfide (FeS) in the corrosion scale to...

Behavior of chlorine during co-carbonization of coal and chloride compounds in cokemaking process

The behavior of chlorine during co-carbonization of coal and chloride compounds such as PVC in cokemaking process both on a laboratory scale and commercial scale was investigated. On a laboratory scale test, the chlorine residue ratio in coke derived from PVC was only 0.04%, which was much lower than that derived from the coal tested (35.1%) and NaCl (52.9%). The chlorine residue ratio derived from PVC reached near zero at about 400°C and it decreased at lower temperature range than that derived from MgCl2, NaCl and CaCl2. CaO addition helped the chloride derived from coal, PVC and NaCl to be fixed in coke. In the commercial scale coke oven, the addition of PVC to coal hardly affected the chlorine content in coke and COG. Most of the released chlorine was absorbed by the ammonia liquor spray for cooling hot COG. The chlorine in PVC was distributed to the coke, the ammonia liquor and the COG by 7%, 92% and 1% respectively, while the chlorine in coal was distributed by 43%, 56% and 1% respectively. The chlorine residue ratio in coke derived from PVC was much lower than that derived from coal since the decomposition of PVC added to coal was much faster than the release of chlorine from coal during carbonization.

A robust framework to predict mercury speciation in combustion flue gases

Mercury emissions from coal combustion have become a global concern as growing energy demands have increased the consumption of coal. The effective implementation of treatment technologies requires knowledge of mercury speciation in the flue gas, namely concentrations of elemental, oxidized and particulate mercury at the exit of the boiler. A model that can accurately predict mercury species in flue gas would be very useful in that context. Here, a Bayesian regularized artificial neural network (BRANN) that uses five coal properties and combustion temperature was developed to predict mercury speciation in flue gases before treatment technology implementation. The results of the model show that up to 97 percent of the variation in mercury species concentration is captured through the use of BRANNs. The BRANN model was used to conduct a parametric sensitivity which revealed that the coal chlorine content and coal calorific value were the most sensitive parameters, followed by the combustion temperature. The coal sulfur content was the least important parameter. The results demonstrate the applicability of BRANNs for predicting mercury concentration and speciation in combustion flue gas and provide a more efficient and effective technique when compared to other advanced non-mechanistic modeling strategies.