Shiqing Wang

To address the critical challenge of treating high-concentration nitrogen oxide (NOx) regeneration off-gas generated from Cold Oxidation Adsorption Process (COAP), an innovative concept termed ‘NOx reburning–equilibrium disposal’ is proposed. In this approach, concentrated NOx is re-injected into the boiler combustion zone, where it undergoes efficient ammonia-free decomposition under the high-temperature reducing atmosphere inherently present within the furnace. A comprehensive investigation was conducted through chemical kinetic simulations and laboratory-scale tubular furnace experiments. Chemical equilibrium calculations performed using CHEMKIN demonstrated that thermally generated NOx increases exponentially with temperature and that a distinct thermodynamic equilibrium concentration exists at each temperature. For example, the equilibrium NO concentration reaches 4781 mg·m⁻³ at 1500 °C. Within the temperature window of 1250–1450 °C, reducing atmospheres significantly enhanced NO reburning reduction efficiencies exceeded 70–90%, reaching up to 95% under strongly reducing conditions, substantially exceeding the less than 10% reduction achieved through purely thermal decomposition. Among the reducing species examined, CH₄ exhibited the strongest promoting effect by serving as an effective radical initiator. The simulation results were further verified through laboratory-scale tubular furnace experiments operating at temperatures up to 1700 °C. The combined theoretical and experimental findings systematically elucidate the reburning–equilibrium reaction mechanism of high-concentration NOx under high-temperature reducing conditions and establish a complete scientific evidence chain from fundamental theory to engineering validation. The proposed technology provides a novel pathway for deep ammonia-free NOx abatement in industrial flue gas treatment systems, such as those used in coal-fired power stations, gas-fired power stations, nuclear waste treatment facilities, glass furnaces and waste incineration plants.

In order to solve the problems of low calorific value and pipeline corrosion caused by high concentration of CO₂ in oil-associated gas, and promote the resource utilization of associated gas, this study used validated grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation to investigate the adsorption characteristics of 11 different topological structures (straight-channel MFI/BEA, cage-channel LTA/FAU/CHA) and cation types (Ca²⁺, Na⁺, H⁺) of commercial zeolites for CO₂ and alkanes (CH₄, C₂H₆, C₃H₈) at 0%~90% RH. The results showed that the CO₂ adsorption capacity of all zeolites decreased with increasing humidity, but straight-channel zeolites (ZSM5-300, BETA-25) had excellent moisture resistance, with only a 20.8% and 30.6% decrease in capacity at 90% RH, respectively. The performance of cage-channel zeolite drops sharply under high humidity. Topology structure and cation synergistically regulate separation efficiency, maintaining stable diffusion order in straight channels. Ca²⁺ enhances dry state capacity but is prone to hydrophilic failure. The adsorption heat of CO₂ on straight-channel zeolite is 25–38 kJ/mol, resulting in lower regeneration energy consumption. ZSM5-300 is preferred for PSA (CH₄/CO₂ kinetic separation coefficient of 809.52 at 90% RH), and NaFAU is preferred for TSA (CO₂ adsorption capacity of 3.6 mmol/g and selectivity of 502.6 at 90% RH). This study clarifies the core structure-activity relationship and provides key theoretical support for the decarbonization of oil-associated gas.

In this work, a molecular simulation method was used to study the adsorption of seven combustion products (CO₂, H₂O, SO₂, N₂, O₂, NO and NO₂) on three zeolites with different topological structures (4A, MIF and MOR). Adsorption isotherms of pure components and mixtures at a wide range of temperatures (253–333 K) were calculated using the Monte Carlo method, obtaining equilibrium parameters including the adsorption capacity, adsorption heat and energy distribution. The calculation results indicated that 4A zeolite with more micropores has a stronger adsorption performance for CO₂. The presence of water significantly reduced the CO₂ capture efficiency of the three zeolites, and the CO₂ adsorption amount decreased by more than 80%. Adsorption kinetics was studied using the molecular dynamic (MD) method, MFI and MOR, with channel-type pore structures exhibiting stronger gas diffusion performance, though their separation efficiency was not high. A 4A zeolite has the potential for kinetic separation of CO₂.

The adsorption thermodynamics and kinetics of CO₂ and six combustion products (H₂O, SO₂, N₂, O₂, NO and NO₂) of two most commonly used commercial zeolites (13X and 5A) were studied based on validated molecular simulations. Adsorption isotherms at wide range of temperatures (253–333 K) were fitted by a Langmuir model, obtaining equilibrium parameters including the adsorption capacity, strength, heterogeneity and CO₂ selectivity from the mixture. The diffusion coefficients, isosteric adsorption heats and distributions of potential energy were simulated for further explanation. The comprehensive evaluation results suggest that, in actual combustion product mixtures, the presence of H₂O in combustion products has a significant impact on CO₂ capture efficiency. Under the influence of water, the adsorption capacity of CO₂ was reduced by over 80%.

At present, insufficient works have provided insights into the application of adsorption to remove CO₂ in flue gas below room temperatures under ambient pressure. In this work, the effects of temperature, CO₂ partial pressure and moisture on dynamic adsorption characteristics for CO₂ are conducted for various adsorbents. Based on our findings, lower the adsorbing temperature can drastically enhance the adsorption of carbon dioxide over molecular sieves and activated carbon. Among various adsorbents, 13X molecular sieve shows highest adsorption capacity. With a concentration of 10% CO₂ in flue gas, the specific adsorption capacity of CO₂ over 13X molecular sieve is 0.11, 2.54 and 5.38 mmol/g at 80 °C, 0 °C and − 80 °C, respectively. In addition, the partial pressure of CO₂ also has a significant impact on the adsorption capacity. With the increment of the concentration of CO₂ from 1% to 10% under 0 °C, the specific capacity of 13X molecular sieve increases from 1.212 mmol/g to 2.538 mmol/g. Water vapor in flue gas can not only reduce the specific adsorption capacity of CO₂ due to competing adsorption, but also increase the heat penalty of molecular sieve regeneration due to the water adsorption. An overall analysis is conducted on the energy penalty of capture 1 ton CO₂ at various adsorption temperatures between − 80 °C and 80 °C, considering both the heat penalty of molecular sieve regeneration as well as the energy penalty for cooling the adsorber. It is found that the lowest energy penalty is about 2.01 GJ/ton CO₂ when the adsorption is conducted at 0 °C.

An exceptional phenomenon has been observed that SO₂ and NO_x in flue gas can be effectively adsorbed over activated carbon with a surprising capacity at cold temperatures with the presence of oxygen. In this study, the adsorption characteristics of NO and SO₂ over activated carbon at 80, 20, 0, and − 20 is experimentally investigated. Without the presence of oxygen, adsorption of NO is negligible. In the presence of oxygen, NO can be oxidized to NO₂ over activated carbon which leads to the co-adsorption of NO/NO₂ within the adsorption bed. Catalytic oxidation of NO over activated carbon can be significantly enhanced at cold temperatures, leading to an extraordinary increase of adsorption capacity of NO. With an initial concentration of NO = 200 ppmv and a space velocity of 5000 h⁻¹, the average specific capacity increases from 3.8 to 169.1 mg/g when the temperature decreases from 80 to – 20 ℃. For NO–O₂ co-adsorption, the specific capacity increases along the adsorption bed due to the increasing NO₂ concentrations. The adsorption capacity of SO₂ is also significantly enhanced at cold temperatures. With an initial concentration of SO₂ = 1000 ppmv, the specific capacity increases from 12.9 to 123.1 mg/g when the temperature decreases from 80 to – 20 ℃. A novel low-temperature adsorption (LAS) process is developed to simultaneously remove SO₂ and NO_x from flue gas with a target of near-zero emission. A pilot-scale testing platform with a flue gas flowrate of 3600 Nm³/h is developed and tested. Emission of both SO₂ and NO_x is less than 1 ppmv, and the predicted energy penalty is about 3% of the net generation.

An exceptional phenomenon has been observed that nitrogen monoxide can be effectively adsorbed over activated carbon at cold temperatures with the presence of oxygen. Based on this finding, a novel low temperature adsorption process is developed to simultaneously remove SO2 and NOx from flue gas with a target of near-zero emission. In this study, the adsorption characteristics of NO and SO2 over activated carbon at various temperatures (-20, 0, 20 and 80℃) are experimentally investigated. For NO-O2 co-adsorption, NO-NO2 equilibriums with increasing NO2 concentration along the the adsorption bed are established due to the catalytic oxidation of NO over activated carbon. Co-adsorption of NO-NO2 occurs at each cross section of the adsorption bed and the adsorption capability increases along the adsorption bed with increasing NO2 concentrations. The oxidation rate of NO can be significantly enhanced at cold temperatures, which leads to an extraordinary improvement of NO adsorption. At a space velocity of 5000h-1 and an initial NO concentration of 200 ppmv, the breakthrough time increases from 3.49 to 1591.75 minutes when the temperature decreases from 80 to -20℃. In addition, the adsorption capacity of SO2 is also dramatically increased at cold temperatures. At a space velocity of 5000h-1 and an initial SO2 concentration of 1000 ppmv, the breakthrough time increase from 20 to 265 minutes when the temperature decreases from 80 to -20℃. A pilot-scale testing platform with a flue gas flowrate of 3600 Nm3/h is developed to validate this novel adsorption process for simultaneous desulfurization and denitrification. Emission of both SO2 and NOx is less than 1mg/Nm3, and the predicted energy penalty is about 3% of the net generation.