Flue Gas Emissions Research Articles

HEIGHT OF THE CHIMNEY FOR AN INDUSTRIAL BOILER

The quality of the surface and groundwater significantly change with the ash disposal from theflue gas stack. Atmospheric sulphur dioxide (SO2) and nitrogen dioxide (NO2) are caused for acidrain produced from fossil fuel combustion. The height of the flue gas stack is always essential tominimize the environmental impact of industrial flue gas emission. The wrong design of the fluegas stack height leads to ground-level air pollution, directly contributing to ecosystem failures andhealth impacts. The stack height depends on the sulphur content of the fuel or sulphur dioxidecontent, fuel firing rate, and the height of the tallest building within the affected area. Therefore,a new equation is developed to calculate the required minimum chimney height when sulphurcontent of the fuel and fuel consumption rate is known. Moreover, the equation is implementedto calculate the diameter of the flue gas stack. The new calculation steps are crucial for industrialapplications such as for industrial boiler to minimize air pollution.

Design of a Pyroacuotubular (Mixed) Boiler for the Reduction of Flue Gas Emissions through the Simultaneous Generation of Hot Water and Water Steam

Environmental protection is a continuous challenge that requires innovating the combustion process of boilers that emit polluting gases. This research proposes a novel pyroacuotubular (mixed) boiler design that reduces the emission of combustion gases by hot water and steam. The applied methodology considers the dimensioning-construction, modification, and analytical calculation of water volume, metallic masses, heat for hot water and steam generation, and combustion gases. The Ganapaty method of heat transfer is applied to prioritize the velocity of gas displacement, the pressure drop along the pipe, and its application on surfaces. In the parallel generation of hot water and steam, a mass of CO2 (1782.72 kg/h) and CO (5.48 kg/h) was obtained; these masses were compared with the results of the proposed design, obtaining a reduction in the mass of gases emitted to the environment in hot water CO2 (44.35%) and CO (44.27%); steam CO2 (55.65%) and CO (55.66%). A significant reduction was achieved in the simultaneous generation of hot water and steam compared to the individual generation, which shows that the simultaneous generation of the pyroacuotubular (mixed) boiler reduces the emission of combustion gases.

Mechanistic investigation of the enhanced SO2 resistance of Co-modified MnOx catalyst for the selective catalytic reduction of NOx by NH3

For the effectively removal of NOx emissions in the practical flue gas, a highly active NH3-SCR catalyst with remarkable SO2 tolerance is desirable. Herein a novel MnCoOx sphere catalyst has been developed, which not only exhibited high low-temperature activity for the NH3-SCR of NOx but also significantly enhanced SO2 resistance. XPS analysis and in-situ DRIFTs revealed that the formation of abundant bulk MnSO4 species due to the present SO2 led to the irreversible poisoning of pure MnOx catalyst, which could change the Langmuir-Hinshelwood (L-H) mechanism of NH3-SCR reaction into the Eley-Rideal (E-R) mechanism and inhibit the low-temperature activity. While over MnCoOx sphere catalyst the formation of MnSO4 is significantly inhibited in the presence of SO2, so that the reaction over the SO2-poisoned Mn(5)Co(5)Ox catalyst can still proceed by the L-H mechanism and maintain its high catalytic performance. This work unravels the mechanistic promoting effect of Co on the SO2 tolerance of MnCoOx catalyst from sulfates as well as the reaction mechanism perspectives, which would guide an ingenious design of SO2 tolerant Mn-based NH3-SCR catalysts.

Parameterization of a Rising Smoke Plume for a Large Moving Ship Based on CFD

The plume rising height of a ship will directly affect the maximum ground concentration and distance from the source caused by flue gas emission. Ship movement has an important effect on plume rising, but it is often ignored in previous studies. We simulated the weakening effect caused by ship movement by considering the influence of four main parameters (wind speed, ship speed, flue gas exit velocity, and flue gas exit temperature) on the smoke plume rising height, using the computational fluid dynamics (CFD) model (PHOENICS version 6.0 CHAM, London, UK). The main parameters affecting the difference in plume rising height between stationary and moving sources for the same parameter settings are the wind speed and the ship speed. Therefore, we established two simplified calculation methods that corrected the flue gas exit velocity (Vexit′) and the flue gas exit temperature (T′) for approximately simulating the smoke plume rising height of the moving ship using the formula of a stationary ship. Verification cases indicated that the corrected Vexit′ (the average of relative error is 5.48%) and the corrected T′(the average of relative error is 60.07%) not only saved calculation time but also improved the simulation accuracy compared with the uncorrected stationary source scheme (the average of relative error is 135.38%). Of these correction methods, the scheme with corrected Vexit′ is more effective. The intention is to provide some references for the field experimentation of moving ship plume rising in different ports in the future and to further study the mechanism of moving ship plume rising.

Pulverized biomass flame under imposed acoustic oscillations: Flame morphology and emission characteristics

Forced intermittent combustion with periodical variations of pressure, velocity, and air-fuel ratios is a promising method to increase efficiency and reduce emissions from combustion and gasification applications. In this work, flame characteristics and emissions from a pulverized biomass burner are investigated under oscillations induced by an acoustically-driven synthetic jet. Instantaneous images of incandescent light emitted from flame were captured using high-speed cameras. The images were analyzed to identify the liftoff distance, flame length, and shape. The flame liftoff distance decreased under excited conditions, notably at high forcing amplitude applied to small particle size distribution (63-112 μm). In such conditions, acoustic forcing increases particle dispersion as presented in the previous work, providing conditions for earlier ignition due to enhanced fuel-air mixing besides reducing CO emissions. Flue gas emissions were influenced mainly by the particle size distribution, from which the 63-112 μm particle size presented the lowest values of CO and highest levels of NO emissions. The results presented stable flame edge positions for the particle size of 63-112 μm, while wide range particle distributions (0–600, 0-400 μm) had strong fluctuations, indicating high flame instability. The experimental work adds new insights regarding acoustic excitation in swirl burners, which could be used to optimize pulverized fuel combustion.

Study on the necessity and strategy of popularization of "near-zero emission" technology for thermal power generation.

With the increasingly severe environmental problems, cleaner production has become one of the necessary means to alleviate the problem. The "near-zero emission" technology of thermal power generation is an active attempt of traditional power generation enterprises to further improve the level of clean coal utilization and promote the flue gas emission from conventional management to lean management. The analysis and evaluation of "near-zero emission" technology of thermal power generation in China are conducive to enhancing the scientific understanding of the overall situation of air pollution in China and thus further analyzing the current situation and future development path of thermal power emissions. In this paper, the intelligent prediction algorithm is used to predict and evaluate the emission scale of soot, sulfur dioxide, nitrogen oxides, and other air pollutants in China and the thermal power industry in the future, which reflects the urgency of the promotion of "near-zero emission" of thermal power from the macro level. In addition, based on Evolutionary Game Theory (EGT) and coevolutionary algorithm, the strategy selection of several virtual power generation groups under different policy conditions is simulated around the promotion of "near-zero emission" of thermal power. The results show that the policy subsidy plays an important role in promoting technology popularization.

Process design and economic analysis of hydrogen roasting integrated with CCU for a carbon-free spent LIB recycling process

In the lithium-ion battery (LIB) recycling process, the roasting step decomposes the complex cathode material into metal oxides before leaching and precipitation. Hydrogen gas is a potential candidate among various roasting agents because of its rapid roasting time and zero CO2 emission. However, additional flue gas emission is unavoidable on the industrial scale to meet the roasting temperature and further crystallization of the produced LiOH slurry. This study proposed and simulated a carbon-free LIB recycling method via an integrating system of hydrogen roasting and CO2 capture and utilization (CCU) composed of the following processes: hydrogen roasting of cathode material; two-way Li extraction; acid leaching; and selective extraction of remaining metal oxide. In the two-way Li extraction, the LiOH slurry was split and converted into LiOH·H2O(s) and Li2CO3(s) via crystallization and the CCU process, respectively. In the CCU process, the slurry was utilized as a wet CO2 absorbent in the flue gas emitted from the roasting and crystallization process. According to sensitivity analysis, 98.10 % Li recovery with zero CO2 emission was accomplished in a split fraction of 0.26. Furthermore, over 99 % recovery of remaining metal resulted from early Li rejection in the metal oxide mixture. Economic analysis was conducted with a 10,000 ton/year recycling capacity, and the net present value of the proposed system is 2.74E + 09 $, 3.08 % higher than the conventional hydrometallurgy system. The proposed system offers higher Li recovery and feasible economic profit with zero CO2 emission and less chemical waste disposal than the conventional system.

Pollutant emission and attrition performance of low calorific blended coals during co-combustion in fluidized bed

The co-combustion technology in the fluidized bed is usually used for the utilization of low-rank coals. The pollutant emission and attrition of coal particles, which are subject to bed temperature, excess air coefficient, mixture ratio and particle size, cannot be ignored. In this work, a pyrolysis-combustion-fragmentation method was presented to study the attrition and the quantitative fragmentation indexes of different coal blends, followed by the experimental investigation of the blended coal's gaseous pollutant emissions in a fluidized bed combustion reactor. As demonstrated by the experimental results, the emission of N2O decreases with increasing the bed temperature from 800 to 850 °C, while attrition rate increases with the bed temperature. Increasing the excess air coefficient is conducive to reducing CO2 and SO2. Considering the low flue gas emission and the attrition behavior, the mixed ratio of raw coal, coal gangue and coal slime at 20:60:20 may be an appropriate choice for their co-combustion in a fluidized bed reactor. The main reason for the fragmentation of blended-coal particles is the primary fragmentation. This study is useful for optimizing the condition of blended coal’s combustion in CFB boiler.

The concept of modern ecosystem for the Ural Aluminium Smelter

The main requirement for the ecosystem of a modern industrial enterprise is to ensure the reduction of human impact on the environment. Facing the strict environmental policies of today, most production companies are forced to implement additional environmental measures, which can be quite costly. The share of such costs in the cost of production is constantly rising, which is especially critical in the steel industry where the rate of return is traditionally low. An effective way of tackling this problem would be to develop and implement a strategy for a comprehensive environmental modernization of production sites. This paper examines a concept of such strategy drawn up for the Ural Aluminium Smelter. The paper describes the main aspects related to the use and disposal of hazardous production waste – i.e. red muds and flue gas emissions. The concept is aimed at minimizing the negative impact of waste on the environment by waste neutralization and utilization in the production of additional marketable products. Such potential products may include iron-bearing pellets for iron and steel industry, mortars and fertilizers. The main organic additive considered for use in the above products is peat, a natural renewable resource found locally. A special focus of the modernization concept is on the development and implementation of innovative soil material designed as a temporary cover for existing tailings aimed at preventing wind erosion. It is shown that the use of flue gases for neutralization of highly alkaline solid waste will help reduce the impact of harmful emissions.

Landfill gas as a source of anthropogenic antimony and arsenic release

Antimony is used extensively in consumer goods, including single use plastic bottles, electronics, textiles and automobile brakes, which are disposed of in landfills at the end of their service lives. As a result, Sb is a constituent of concern in landfill emissions. Previous research has focused on leachate (liquid) and waste incineration flue gas emissions; however, Sb has the potential to volatilize through chemical and microbial processes within a landfill. In this study, iron-amended granular activated carbon was used to adsorb volatile metals directly from gas in a full-scale landfill gas collection system. Metals were quantified using acid digestion and ICP-AES analysis. Antimony concentrations far exceeded those previously reported, at up to 733 μg m−3 (mean: 254 μg m−3). In addition to Sb, As was also measured at high levels compared to previous research, as high as 740 μg m−3 (mean: 178 μg m−3). Using US EPA landfill and landfill gas databases, total Sb emissions via landfill gas are estimated to be approximately 27.3 kg day−1 in the US. Based on other estimates of national and global Sb emissions, this corresponds to approximately 4.5% of total US atmospheric emissions of Sb and 0.42% of global atmospheric emissions. Sb mass release via landfill gas is approximately 3.9 times higher than via leachate emissions. Although gas emissions are higher than expected, the vast majority (99.9%) of Sb present in landfilled MSW remains within the waste mass indefinitely. In addition to these mass release estimates, this experiment suggests that iron-amended activated carbon may offer significant metals removal from LFG, especially in the first months of new well operation.

Dark stress for improved lipid quantity and quality in bioprospected acid-tolerant green microalgae.

The cost of microalgae cultivation is one of the largest limitations to achieving sustainable, large-scale microalgae production of commercially desirable lipids. Utilizing CO2 as a 'free' carbon source from waste industrial flue gas emissions can offer wide-ranging cost savings. However, these gas streams typically create acidic environments, in which most microalgae cannot survive due to the concentration of CO2 and the presence of other acidic gasses such as NO2 and SO2. To address this situation, we investigated growth of a mixed acid-tolerant green microalgal culture (91% dominated by a single Coccomyxa sp. taxon) bioprospected at pH 2.8 from an acid mine drainage impacted water body. The culture was grown at pH 2.5 and fed with a simulated flue gas containing 6% CO2 and 94% N2. On reaching the end of the exponential growth phase, the culture was exposed to either continued light-dark cycle conditions or continual dark conditions. After three days in the dark, the biomass consisted of 28% of lipids, which was 42% higher than at the end of the exponential phase and 55% higher than the maximum lipid content achieved under light/dark conditions. The stress caused by being continually in the dark also favoured the production of omega-3 and omega-6 polyunsaturated fatty acids (PUFAs; 19.47% and 21.04%, respectively, after 7 days) compared to 7-days of light-dark treatment (1.94% and 9.53%, respectively) and showed an increase in nitrogen content (C:N ratio of 6.4) compared to light-dark treatment (C:N ratio of 11.9). The results of the research indicate that use of acid tolerant microalgae overcomes issues using flue gasses that will create an acidic environment and that applying dark stress is a low-cost stressor stimulates production of desirable dietary lipids.

Enhanced removal of nitric oxide and carbon dioxide from flue gas in a biofilter: Effect of flue gas recirculation and Fe(II)EDTA addition

Flue gas emission from combustion of fossil fuel is a growing environmental concern. In this study the effect of flue gas recirculation and Fe(II)EDTA addition on CO2 and NO removal from flue gas was explored in a biofilter. The effect of SO2 on CO2 and NOx removal efficiencies were also studied herein. The optimal removal efficiencies of CO2 (88.1%) and NO (85.8%) were achieved with the flue gas recirculation of 2:1. The presence of SO2 showed little impact on CO2 or NO removal while induced the decline of NO removal. The addition of Fe(II)EDTA clearly enhanced NO removal (~85%). The Illumina sequencing results showed that abundant sulfur-associated bacteria (Desulfobulbus, Desulfococcus, Sulfurovum, Chlorobium), nitrogen-associated bacteria (Thauera), fermentative bacteria (Longilinea and Anaerovorax), and various iron-reducing bacteria (Geobacter) were detected in the biofilter with Fe(II)EDTA addition. The synergistic effect of denitrifying/iron-reducing bacteria dedicated to the sustainable NO removal.

Flue Gas Composition and Treatment Potential of a Waste Incineration Plant

Waste-to-energy (WtE) incineration is an important technique in waste management systems and waste hierarchy. It is used to treat approximately 63% of the waste in European countries. The flue gas volumetric rate and its composition are essential to determine and monitor the emissions from waste incineration plants. This paper presents two methodologies used to evaluate the emissions from incinerators during the design phase. The first consists of a set of equations applicable in Excel (calculation model), while the second is the built-in components in Ebsilon 13.2 software which simulates the emissions from a furnace. This paper also proposes a comprehensive flue gas cleaning system for a simulated waste incineration plant in Jordan. According to Ebsilon, the results showed that for a 25 kg/s loading rate, there was 258,514 mg/Nm3, 749.90 mg/Nm3, 890.20 mg/Nm3, and 717 mg/Nm3 of CO2, NO2, SO2, and HCL, respectively. It was noted that these values relate to 1.5 of excess air ratio, where the effect of excess air ratio as the main driver for any combustion process was examined. The calculation method (set of equations) evaluated the flue gas volumetric rate, the CO2 emissions, and N2O and SO2 levels. Ebsilon allows for simulation of the treatment stages and calculates the amount of materials required. Selective non-catalytic reduction (SNCR) (a built-in component in the Ebsilon library) was used to treat the NO2 emissions. For 1.5 of excess air ratio, those emissions were reduced from 749 mg/Nm3 to 180 mg/Nm3, while the Ca(OH)2 injector used to treat the SO2 and HCL emissions reduced emissions from 890.20 mg/Nm3 and 717 mg/Nm3 to 44 mg/Nm3 and 7.16 mg/Nm3, respectively. Regarding the reduction in CO2, the spherical carbon absorption concept was simulated using 9.4 kg/s of carbon which was adequate to verify a 91% reduction rate of CO2. Furthermore, the calculation model was validated and approved as a valuable model to predict the flue gas volume, the oxygen required, and flue gas emissions at the design stage.

Daily Emission Patterns of Coal-Fired Power Plants in China Based on Multisource Data Fusion.

Daily emission estimates are essential for tracking the dynamic changes in emission sources. In this work, we estimate daily emissions of coal-fired power plants in China during 2017-2020 by combining information from the unit-based China coal-fired Power plant Emissions Database (CPED) and real-time measurements from continuous emission monitoring systems (CEMS). We develop a step-by-step method to screen outliers and impute missing values for data from CEMS. Then, plant-level daily profiles of flue gas volume and emissions obtained from CEMS are coupled with annual emissions from CPED to derive daily emissions. Reasonable agreement is found between emission variations and available statistics (i.e., monthly power generation and daily coal consumption). Daily power emissions are in the range of 6267-12,994, 0.4-1.3, 6.5-12.0, and 2.5-6.8 Gg for CO2, PM2.5, NO x , and SO2, respectively, with high emissions in winter and summer caused by heating and cooling demand. Our estimates can capture sudden decreases (e.g., those associated with COVID-19 lockdowns and short-term emission controls) or increases (e.g., those related to a drought) in daily power emissions during typical socioeconomic events. We also find that weekly patterns from CEMS exhibit no obvious weekend effect compared to those in previous studies. The daily power emissions will help to improve chemical transport modeling and facilitate policy formulation.

Experimental investigation on utilization of distillery sludge mixed with coal as a Low-grade fuel in brick kiln industry and product analysis

Energy demand has been considerably increasing since the last few decades. This trend is expected to continue in the coming years and hence alternative energy sources look more attractive and practically feasible. Distillery sludge has emerged as an alternative promising renewable energy source due to its high calorific value, carbon content and volatile matter. Distillery sludge after mixing with coal in different proportion (3:1, 3:2, 1:1 and 1:3) was used in the brick kiln industry as a combustion fuel for the different time of baking. The study results showed that 60 % of coal mixed with 40 % sludge i.e. 3:2 ratio with 4 h baking time was found suitable for the operation of brick kiln plant due to optimum compressive strength (5.35 MPa) and water absorption (17.09 %). On analyzing the flue gas emission characteristics during the operation value of PM (482 mg/Nm3) for coal mixed sludge at the ratio of 3:2, the flue gas emission values were within the prescribed limit of regulatory authority. The other mineralogical properties of bottom ash indicated that it is rich in calcium sulphate and aluminates which can further be used in cement and construction industries. It is recommended that coal mixed sludge in the ratio 3:2 may be utilized as a fuel for partial replacement of coal in the brick kiln industry.

Experimental measurements of CO2 solubility, viscosity, density, sound velocity and evaporation rate for 2-(2-aminoethoxy)ethanol (DGA) + 1-methylpyrrolidin-2-one (NMP) / water + ionic liquid systems

Among technologies used to remove carbon dioxide and hydrogen sulfide from natural gas and flue gas emissions, absorption processes based on amine solvents are the most common. This study investigated the potential of new hybrid amine solutions to absorb carbon dioxide compared to conventional solvents. The solubility of carbon dioxide in hybrid solvents with different mixtures of diglycolamine, water, n-methyl-2-pyrrolidone, 1-butyl-3-methylimidazolium trifluoromethanesulfonate and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide was measured at temperatures of (∼298.15 and ∼313.15) K by a static-synthetic method. Furthermore, the viscosity, density, sound velocity and evaporation rate for the mixtures were measured. Although the addition of an ionic liquid to the solvents increased the viscosity of the solution and decreased the solubility with the aqueous diglycolamine solvents, the replacement of water with a mixture of n-methyl-2-pyrrolidone and ionic liquid increased the solubility. The exception however was observed at lower pressures.

CO2 mineralization of carbide slag for the production of light calcium carbonates

The production of polyvinyl chloride by calcium carbide method is a typical chemical process with high coal consumption, leading to massive flue gas and carbide slag emissions. Currently, the carbide slag with high CaO content is usually stacked in residue field, easily draining away with the rain and corroding the soil. In this work, we coupled the treatment of flue gas and carbide slag to propose a facile CO2 mineralization route to prepare light calcium carbonate. And the route feasibility was comprehensively evaluated via experiments and simulation. Through experimental investigation, the Ca2+ leaching and mineralization reaction parameters were determined. Based on the experiment, a process was built and optimized through Aspen Plus, and the energy was integrated to obtain the overall process energy and material consumption. Finally, the net CO2 emission reduction rate of the entire process through the life-cycle assessment method was analyzed. Moreover, the relationship between the parameters and the CO2 emission life-cycle assessment was established. The final optimization results showed that the mineralization process required 1154.69 kW·h·(t CO2)−1 of energy (including heat energy of 979.32 kW·h·(t CO2)−1 and electrical energy of 175.37 kW·h·(t CO2)−1), and the net CO2 emission reduction rate was 35.8%. The light CaCO3 product can be sold as a high value-added product. According to preliminary economic analysis, the profit of mineralizing can reach more than 2,100 CNY·(t CO2)−1.

Mitigating CO2 emission in pulverized coal-fired power plant via co-firing ammonia: A simulation study of flue gas streams and exergy efficiency

Coal-fired power plants are one of the major sources of CO2 emission, and the novel application of directly co-firing the carbon-free fuel ammonia into the coal-fired power plants is emerging as a promising method of CO2 emission reduction. In this study, simulations of the boiler system of a 600 MWe coal-fired power plant unit were performed in both coal-fired condition and ammonia-coal co-firing conditions, and the impacts of ammonia co-firing on the emission and thermal properties of flue gas, exergy loss, and exergy efficiency were analyzed. Two co-firing scenarios (identical adiabatic flame temperature scenario and identical excess air coefficient scenario) were compared, both assuming that the total heating value of the fuel into the furnace kept unchanged with different ammonia co-firing ratios (5%, 10%, 15%, 20% on heating value basis). The results showed that CO2 emission was effectively reduced by 24.08 t/h for every 5% increase in the ammonia co-firing ratio. The amount of total flue gas was also reduced while both the content and the emission rate of H2O were increased with ammonia co-firing. Consequently, the specific heat capacity of flue gas increased and further changed its temperature distribution profile. Compared with the coal-fired base case, the exergy loss in the furnace under the ammonia co-firing conditions increased continuously as the ammonia co-firing ratio increased, suggesting that the irreversible loss of the ammonia combustion process was greater than that of coal. By contrast, the exergy loss of heat exchangers and fans decreased in ammonia co-firing conditions. Finally, the exergy efficiency of the boiler system was only slightly reduced (53.82% vs. 53.27%–53.22%) in ammonia co-firing conditions, showing that co-firing ammonia in coal-fired power plant would not significantly deteriorate the thermal economy.

Experimental investigation of plastic waste pyrolysis fuel and diesel blends combustion and its flue gas emission analysis in a 5 kW heater

Environmental issues have become prominent due to an increase in the plastic wastes, which can be recyclable for an alternative liquid fuel. In this work, the upgraded plastic pyrolysis oil was used to investigate the combustion performance of the 5 kW scale heater. The plastic pyrolysis middle oil (diesel-like fraction, C11–C22) was similar to the properties of the diesel (45.0 MJ/kg and 2.70 cSt). The plastic pyrolysis fuel and diesel blends were prepared. The efficiency of combustion using 10% and 30% pyrolysis fuel blends showed about 58% at a fuel-air equivalence ratio (Ф) of 0.91, which was similar to that of diesel combustion. The highest heater internal temperature was observed to be about 1060 °C (Ф = 0.91). In addition, the flue gas composition of all the blends showed similar concentrations of CO (∼13 ppm) and CO2 (∼13 vol%). However, a higher NOx concentration was observed with pyrolysis fuel blends (80–130 ppm) than that of diesel due to its higher nitrogen content in plastic waste pyrolysis fuel. Exergoeconomic analysis was also conducted to investigate the plastic pyrolysis fuel efficiency for more evaluation. This study suggested that plastic pyrolysis fuel has a good application prospects as an alternative fuel.

Arsenic chemistry in municipal sewage sludge dewatering, thermal drying, and steam gasification: Effects of Fenton-CaO conditioning

In sludge disposal, Arsenic (As) poses serious secondary pollution due to its high toxicity and low stability. This work systematically studied the effects of Fenton-CaO composite conditioning on As chemistry throughout sludge dewatering, thermal drying, and steam gasification processes. The experimental results showed that, for raw sludge, 40.9% of As was released with filtrate discharging and 26.8–57.3% emitted with flue gas emission. When sludge was conditioned by Fenton-CaO, all of the As in the filtrate was fixed in the sludge cake and the releasing rate of gaseous As was reduced by up to 86.0%. Furthermore, the comprehensive results of the model compounds experiment, sequential extraction, and thermodynamic calculations revealed the effects of Fe/Ca conditioners on As species evolution. In the Fenton pre-oxidation, As(V) was reduced to As(III) due to the decreasing Eh caused by the excessive Fe(II). After adding CaO, As(III)/DMA (dimethyl arsenic) was adsorbed onto the surface of amorphous Fe(OH)3 that was introduced by Fenton's reagent, 50% and 43% of which were then oxidized or demethylated to form As(V)/MMA (monomethyl arsenic), respectively. In the following drying process at 120–180 °C, the FeOOH and CaO derived by residual Fe/Ca conditioners could promote the oxidation of 30% of the rest As(III) by the catalytic effect or directly reacting with it. In the final steam gasification process, the very little As(III) left in the dry sludge was released with the gas phase and the proportion of As(V) in gasification ash almost reached 100%. In short, Fenton-CaO composite conditioning could achieve the near-zero emission of As and reduce the toxicity of the products throughout the whole sludge treatment process.