Regenerative Thermal Oxidizer Research Articles

Characteristics of Volatile Organic Compounds Emissions and Odor Impact in the Pharmaceutical Industry

Volatile Organic Compounds (VOCs) are not only essential precursors for the formation of ozone and PM2.5, but also hazardous to human health and responsible for unpleasant odors. The pharmaceutical industry has become an important industrial source of VOCs due to China’s large emissions and complex emission chains. In total, 245 VOCs samples were collected and analyzed from 11 typical pharmaceutical companies in Zibo City of the North China Plain, in order to investigate the VOCs emission characteristics and odor impacts. The emission factor for the pharmaceutical industry was 7.97 ± 8.21 g/kg pharmaceuticals, while the main emission links were chimney emissions, equipment sealing leakage, and so on. Finally, considering both purifying efficiency and economic benefits, the multistage absorption (AB) method is most effective for VOCs concentrations below 100 mg/m3, while UV photo-oxygenation combined with adsorption (UVA) is more suitable for concentrations below 300 mg/m3. The Regenerative Thermal Oxidizer (RTO), Catalytic Oxidizer (CO), and Condensation + Adsorption (CA) technologies demonstrated greater stability and efficiency, particularly in the treatment of complex organic pollutants, highlighting their advantages in both VOCs and odor removal at higher concentrations.

A 4E Analysis of a Solar Organic Rankine Cycle Applied to a Paint Shop in the Automotive Industry

In a conventional automotive manufacturing plant, the paint shop alone can represent 36% of the total energy consumption, making it the most demanding area in terms of electricity and fossil fuel energy consumption. This study explores the possibility of decentralizing the production of electrical power and heat simultaneously, using an Organic Rankine Cycle (ORC) system integrated with a Parabolic Trough Collector (PTC) in a paint shop. To date, no similar system has been explored or implemented by the automotive industry. To increase the efficiency of the integrated system, wasted heat generated during the paint manufacturing process is recovered and used to pre-heat the organic fluid in the ORC system. A 4E analysis (Energy, Exergy, Economic, and Environmental) is conducted to determine the practical viability of the proposed system. When applied to the southern region of the USA, this system’s installed capacity is projected to be 11 times higher than the two unique SORC pieces of equipment currently running in Louisiana and Florida. The goals are to reduce the reliance on external primary energy sources and decrease the carbon emission footprint from production activity. The system is evaluated for a location in Alabama, USA. The designed SORC, using toluene, can produce 712.2 kWel net and 13,132 kg/h of hot water, with an overall energy efficiency of 31.02%; exergy efficiency of 34.23; and ORC efficiency of 27.70%. This leads to an electrical energy saving of 5.9% for the manufacturing plant. The regenerative thermal oxidizer (RTO) heat exchanger, the secondary heat source of the system, has the highest exergy destruction—3583 kW. The system avoids the emission of 4521 tCO2 per year. A payback period of 10.16 years for the proposed system is estimated. Considering a planning horizon of 10 years, the investment in the system is also justified by a benefit–cost analysis.

Overheating fault traceback of Regenerative thermal oxidizer in Multi-Source waste gas treatment system via dynamic cumulative correlation analysis

Regenerative thermal oxidizers (RTO) are commonly used in the pharmaceutical and chemical industries to treat emissions of volatile organic compounds but are prone to overheating risks stemming from variations in the flow and concentration of exhausted gases from diverse workshops. This paper proposes a dynamic analysis method based on correlation between various sensor-point data to determine the cause of the RTO overheating in such a multi-source waste gas treatment system. This method continuously adjusts the length of the data in the correlation analysis to comprehensively capture the dynamic changing characteristics of the data. And a strategy for the accumulation of association degrees is introduced to reveal long-standing potential causal relationships. The effectiveness of proposed method was validated in an industrial exhaust gas treatment system of a pharmaceutical company with over 1000 sensor points. The fault diagnosis results are consistent with those of the actual on-site investigation in 5 real cases. Our proposed method can provide relatively accurate results within 2–3 h, much faster than the manual investigation of the workers (2 days on average). Moreover, compared to traditional static correlation analysis methods, our method can narrow down the investigation scope by more than 5 times. This study provides a practical and effective method for tracing the source of anomalies in complex dynamic systems, and also contributes to the safe and stable operation of chemical engineering systems.

Experimental Study on Ultra-Low Concentration Methane Regenerative Thermal Oxidation

As a major coal country, China faces the issue of significant gas emissions during the coal mining process. This study aims to improve the utilization efficiency of mine gas, reduce greenhouse gas emissions, and promote the low-carbon and green transformation of the coal industry. A 10 kW gas regenerative thermal oxidizer (RTO) experimental system was constructed. The effects of initial methane concentration, low-temperature flue gas proportion, and operating load on combustion temperature, methane oxidation rate, high-temperature flue gas energy, and system thermal efficiency were studied. The results show that when the combustion temperature is below 600 °C, the CH4 combustion reaction cannot proceed effectively, and the system temperature continuously decreases and cannot be maintained stably. The experiment determines the stable operating methane concentration range of the RTO. In this experimental system, the lower limit of the initial methane concentration is 0.28%, corresponding to an 86% methane oxidation rate. As the initial methane concentration decreases, the combustion temperature also decreases, and the methane oxidation rate follows suit. The higher the low-temperature flue gas proportion, the higher the combustion temperature, and the system’s thermal efficiency and output heat decrease with the increase in the low-temperature flue gas proportion. This experiment explores multiple factors affecting regenerative thermal oxidation, providing a basis for ensuring the safe and stable operation of the system and its optimization. Improving the thermal insulation and heat exchange performance of the storage body can expand the lower limit of the initial methane concentration, thereby increasing the stability and thermal efficiency of the system.

Intelligent condition monitoring with CNN and signal enhancement for undersampled signals

High-frequency signals like vibration and acoustic emission are crucial for condition monitoring, but their high sampling rates challenge data acquisition, especially for online monitoring. Our research developed a novel method for condition identification in undersampled signals using a modified convolutional neural network integrated with a signal enhancement approach. A frequency-domain filtering is applied to suppress similar sidebands and obtain more discriminative features of different conditions, followed by an interpolation-based upsampling in the time domain to restore the signal length and strengthen the low-frequency harmonic information. Enhanced signals are converted into two-dimensional grayscale images for neural network analysis. Tested on bearing datasets and real-world data from regenerative thermal oxidizer lift valve leakage, our method effectively extracts features from low-frequency signals, achieving over 95% fault identification accuracy.

Velocity and Temperature Simulation for a Cylindrical Regenerative Thermal Oxidizer.

The cylindrical regenerative thermal oxidizer (CRTO) came into being later than the three-chamber regenerative thermal oxidizer (TRTO). Compared with TRTO, CRTO has a smaller size and a larger regenerator volume for absorbing and releasing heat. There are few studies on CRTO despite its numerous applications. A CRTO was selected in industrial applications for simulation research. The velocity and temperature of the CRTO were investigated after error analysis of industrial and simulated data. It was found that the velocity and temperature in the regenerative chamber had obvious stratification and gradients after homogenization by the regenerator unit. The velocity and temperature distribution in the oxidation chamber were independent of the position of the CRTO inlet and outlet or the structure below the regenerator, and there were identical periodic changes in each period. A TRTO with primary parameters as those of the CRTO was employed for comparison. The time of the intake and exhaust periods of a CRTO regenerative chamber were 30 s longer than those of a TRTO. The regenerator volume of heat storage used by CRTO for heat exchange increased by 1/6 compared to that of TRTO at the same total regenerator volume. Simulation shows that CRTO had a more uniform velocity and temperature in the regenerative chamber compared to those in TRTO, increasing by approximately 2%; the thermal efficiency is higher, with an average increase of about 3%.

Optimization and Simulation Analysis of Furnace Structure for Regenerative Thermal Oxidizer

Volatile Organic Compounds (VOCs) significantly threaten the atmospheric environment. Currently, common methods for the recovery and treatment of VOCs include adsorption, solution absorption, photocatalytic oxidation, and high-temperature oxidation. Among them, the Regenerative Thermal Oxidizer (RTO) is a scheme for high-temperature oxidation treatment of VOCs, which applies aerospace heat transfer and combustion technology to the treatment of VOCs, and the removal efficiency of VOCs can reach over 99%. Considering the high temperature and possible instantaneous overpressure during the combustion process, a three-dimensional flow model of the bottom air distribution chamber and heat storage chamber was established to solve the technical difficulties of the gas flow field in the existing RTO and improve the safety and stability of the overall flow. Simulated the gas flow field and analysed the distribution pattern of the gas flow rate. In response to the uneven distribution of airflow caused by the pipeline layout, orifice plates were installed at the bottom of the furnace, and various orifice plate designs were considered. The results indicate that adding slanted orifice plates can improve flow conditions and enhance safety while meeting practical needs.

Preparation and Performance of Ferric-Rich Bauxite-Tailing-Based Thermal Storage Ceramics.

In recent years, regenerative thermal oxidizer (RTO) has been widely used in the petroleum industry, chemical industry, etc. The massive storage required by solid waste has become a serious problem. Due to their chemical composition, bauxite tailings as raw materials for high-temperature thermal storage ceramics show enormous potential in the fields of research and application. In this study, we propose a method for preparing ferric-rich and high specific storage capacity by adding Fe2O3 powder to bauxite tailings. Based on a 7:3 mass ratio of bauxite tailings to lepidolite, Fe2O3 powder with different mass fractions (7 wt%, 15 wt%, 20 wt%, 30 wt%, and 40 wt%) was added to the ceramic material to improve the physical properties and thermal storage capacity of thermal storage ceramics. The results showed that ferric-rich thermal storage ceramics with optimal performance were obtained by holding them at a sintering temperature of 1000 °C for 2 h. When the Fe2O3 content was 15 wt%, the bulk density of the thermal storage ceramic reached 2.53 g/cm3, the compressive strength was 120.81 MPa, and the specific heat capacity was 1.06 J/(g·K). This study has practical guidance significance in the preparation of high thermal storage ceramics at low temperatures and low costs.

Fault diagnosis of regenerative thermal oxidizer system via dynamic uncertain causality graph integrated with early anomaly detection

Regenerative thermal oxidizers (RTO) serve as pivotal equipment for the treatment of volatile organic compounds (VOCs). However, a diversity of faults of the RTO system may threaten personnel safety and lead to unscheduled downtime. In this work, we develop a traceability inference method based on dynamic uncertain causality graph (DUCG) to identify root fault cause of RTO at early anomaly alarm. A general expert knowledge base for the fault diagnosis of RTO system is constructed. And the anomaly alarm thresholds are modified according to historical data with n-sigma rules to improve the diagnostic accuracy. Results on different cases show advantages in both triggering early anomaly alarms and avoiding invalid alarms, which is crucial to improve the fault inference accuracy. By applying our method to 35 fault cases of a real RTO for pharmaceutical VOCs treatment, the fault detection rate reaches 94.29%, and the fault inference accuracy is 82.86%. The two scores are 3% and 21% higher than those with the conventional DUCG (with fixed alarms), respectively. This remarkable improvement underlines the significance of our proposed method for RTO maintenance, and it is expected to assure the system’s operational stability and reliability.

Optimization of regenerator operating parameters and thermal insulation construction for rotary regenerative thermal oxidizer (r-RTO) based on thermal-fluid coupling method and quadratic regression model

Rotary regenerative oxidiser ( r -RTO), an effective VOCs treatment equipment, needs to be operated for a long time under actual working conditions, resulting in excessive temperatures on the outer wall of the r -RTO furnace, which causes production accidents. In order to avoid production accidents, the heat transfer process of airflow inside r -RTO regenerator should be clarified. Computational Fluid Dynamics (CFD) method is applied to analyse the temperature and pressure distribution in r -RTO regenerator. The temperature distribution of regenerator is analysed in order to find the main thermal dissipation path based on thermal-fluid coupling method. In temperature distribution, the outlet temperature T outlet is decreased with the increase of regenerator height h . However, T outlet is increased with the increase of gas flow rate v gas pore size D p , respectively. In pressure distribution, the pressure drop P drop is increased with the increase of h and v gas . However, P drop is decreased with the increase of D p . The results of the temperature distribution analysis are shown that the main pathway for thermal dissipation is along the partition dividers to insulation material where thermal dissipated through the insulation material. Quadratic regression method is used to design multivariate simulation experiments. Genetic algorithm is used to find optimal operating parameters. In addition, partition divider material and thermal insulation thickness are used as optimization parameters to optimize the thermal insulation construction. The present study reveals that thermal-fluid coupling method and quadratic regression method are satisfactory for the optimization of regenerator operating parameters and thermal insulation construction for r -RTO regenerator.

CFD Modeling of Flame Jump across Air Gap between Evasé and Capture Duct for Ventilation Air Methane Abatement

The ventilation air–methane (VAM) released from underground mines is often transported into regenerative thermal oxidizer (RTO) devices and burnt into heat energy. This study numerically investigates the scenarios where explosion occurs inside the RTO and the flame and pressure waves propagate back quickly towards the VAM discharge duct. Possibilities of secondary explosion in the discharge duct, hence in the downstream underground mines, are examined. The results critically showed that when the methane concentration accumulated in the RTO reached 7.5% or above, the flame generated from the explosion jumped to the evasé of the discharge section (over a distance of 29.4 m) and could induce explosions in underground mines.

Experimental and Numerical Investigations into Temperature Distributions and VOC Conversion Rate of RTO

As regulations for controlling VOCs (Volatile Organic Compounds) emissions have become more and more stringent, RTO (Regenerative Thermal Oxidizer) which involves heat exchange and storage, combustion and reaction processes has to be further optimised for enhancing the VOC treatment efficiency and reducing energy consumption. In this paper, influences of operating temperature distributions and internal flow fields on gas-out VOC concentration have been studied with experimental investigation and CFD numerical simulation. Experimental results shows that combustion temperature (around the combustor) plays more critical role than thermal storage bed temperature for affecting VOC flow-out concentration. By examining the internal flow and temperature distributions, modelling results demonstrate that fast heat transfer takes place in thermal ceramic beds and high temperature areas are formed around the combustor. At about 20 seconds after a bed working for gas-in flow, the heat transfer has demonstrated obvious attenuating. The research suggests that it is very challenging for simultaneously maintaining low gas-out VOC concentration and keeping low fuel consumption and low combustion temperature in RTOs.

Optimization of design variables for rotary regenerative thermal oxidizer high-temperature valve (rto-HTV) based on transient dynamics analysis and multi-objective optimization algorithm

The rotary regenerative thermal oxidizer of a high temperature valve (rto-HTV) is repeatedly opened and closed, which causes deformation of the valve page and leads to shortened durability. To prevent the drawback, analysis of impact stress at the moment of rapid collision between the valve page and valve seat is critical. The analysis is focused on optimization of the design variable based on the multi-objective algorithm under transient conditions. To perform transient dynamics, LS-DYNA software is applied for the dynamic analysis of valve page rapid collisions under different initial angular velocities ω. From the LS-DYNA output, the response surface methodology is combined with multi-objective optimization for determining the optimized design variables of the rto-HTV valve page. As a result, the valve page maximum stress (σpage)max is increased with the increase in ω, from (σpage)max = 134 MPa to (σpage)max = 175 MPa. The maximum velocity (vpage)max is increased with the increase in ω, from (vpage)max = 4472 mm/s to (vpage)max = 7475 mm/s. Based on (σpage)max and (vpage)max, the optimization results show that (σpage)max is reduced by 20% and the valve page mass Mpage is reduced by 5%. Moreover, (σpage)max of the optimized valve page is less than the yield strength of 316S at 800 °C. Therefore, the optimization of the valve page is satisfactory and effective for reducing the impact stress between the valve page and valve seat during collision.

Numerical Study on Heat Transfer Efficiency of Regenerative Thermal Oxidizers with Three Canisters

The heat transfer efficiency of a regenerative thermal oxidizer with three canisters used for volatile organic compounds treatment was studied using numerical simulation methods. A one-dimensional model that took into account the variation of physical parameters with temperature was built. The results show that the preheating temperature and outlet temperature tend to be stable as the operation time is increased. The heat transfer efficiency of equipment was mainly evaluated by heat recovery efficiency and energy recovery ratio under steady state conditions, which was affected by the inlet gas flow and temperature, valve switch time, combustion temperature, materials and porosity of the regenerative medium, and packing height. With the increase in packing cross-sectional area and packing height, the increase in heat transfer efficiency leads to an increase in equipment cost. Simultaneously, the shorter the valve switch time and the higher the density of the regenerative medium battery also help to improve the heat transfer efficiency without blocking equipment. Unless the removal efficiency of volatile organic compound treatment is reduced, it is recommended to reduce the inlet and combustion temperatures.

Key factors in the volatile organic compounds treatment by regenerative thermal oxidizer

ABSTRACT The regenerative thermal oxidizer (RTO) is widely used in the treatment of volatile organic compounds (VOCs). The RTO with three packed beds has a backflushing process, which makes its operation quite different from common regenerative combustion devices with two beds. However, the published research regarding this kind of RTO was far from sufficient. Thus, models based on an industrial RTO with three beds were developed. Temperature distributions for the RTO were simulated based on the standard k-ε model, heat balance model, DO model, and finite chemical-rate/eddy-dissipation model after model validation. Four operating parameters were selected, and these parameters have a significant impact on key factors, such as the oxidation chamber temperature (OCT), outlet temperature, and thermal efficiency. Multi-factor analysis was performed by orthogonal experiment and regression analysis of the key factors, revealing that different parameters imposed various impacts on the key factors. A linear relationship between the OCT and RTO outlet temperature was identified, yielding a useful formula for engineering applications. Implications: A regenerative thermal oxidizer (RTO) used in volatile organic compounds (VOCs) treatment was studied between engineering and simulation. The simulation results showed a few error compared to the engineering ones. Single parameter simulations, orthogonal experiments and regression analysis were applied to study key factors such as oxidation chamber temperature, outlet temperature, and thermal efficiency. The influence and regularity of the four main operating parameters on the key factors were quite different. The best condition for this RTO was got. The linear formula of the oxidation chamber temperature and the outlet temperature are obtained, respectively.

OPTIMIZATION OF THE OPERATIONAL PARAMETERS FOR THE FURNACE OF A THREE BED REGENERATIVE OXIDIZER THAT NEUTRILIZES GASEUS POLLUTANTS

The purpose of this work is to correlate the excess oxidant-air with the percentage of CO2 in the combustion chamber waste gas of a three-bed regenerative thermal oxidizer unit for the elimination of gaseous pollutants in a given capacity.

SUSTAINABLE BIOMETHANE: METHANE SLIP REMOVAL APPLYING REGENERATIVE CATALYTIC OXIDATION (RCO) POST COMBUSTION TECHNOLOGY

Biomethane is incentivized in Italy and in many other European countries as a substitute fuel for transport, in order to reduce fossil fuel and cut CO2 emissions. In Italy, Certificato di Immissione in Consumo (CIC) is actually sustaining biomethane production, charging petrochemical companies who need to cover their obligation quotes. Actually, biomethane production has to fulfil sustainability requirements in order to be entitled to get CIC. Sustainability principles are, among others, the type of feeding, total biogas capture during the fermentation process and last but not least, a very low methane loss associated to the off-gas of the upgrading unit, actually set at < 1 % CH4 in Italy and most probably further reduced in the short. The upgrading unit off-gas, therefore, has to respect the limit, or as an alternative, it has to be treated in a post-combustion unit. There are technical upgrading solutions on the market that can achieve methane loss < 1% CH4, but incremental energy, operating and investment cost have to be considered in a cost-benefit evaluation. Post-combustion on the other hand can be a serious issue, since the flow to be burnt does not contain oxygen at all, just traces of methane (normally 2-3%) and CO2 (97-98%), changing dramatically operating conditions of traditional post-combustor units applied to cogeneration engines off-gas. For the biomethane off-gas combustion, a sustainable cost-effective solution is the Regenerative Catalytic Oxidation (RCO), operating at lower temperature than Thermal Oxidation (TO), therefore reducing energy costs and improving environmental footprint. The purpose of this article is to compare the Regenerative Thermal Oxidizer (RTO) with the Regenerative Catalytic Oxidizer (RCO).

Binary Adsorption Equilibrium and Breakthrough of n-Butyl Acetate and p-Xylene on Granular Activated Carbon

Compared with abatement methods (regenerative thermal oxidizer, regenerative catalytic oxidizer, etc.), the adsorption–desorption combined method has been considered as a sustainable way to treat a...

Methane loss from commercially operating biogas upgrading plants

Biogas technology is one of the widely applied anaerobic digestion approaches to harvest methane from different wastes. Recently, methane loss from biogas plants and its environmental and economic consequences have been underlined, but not thoroughly researched. In this investigation, process related CH4 loss from nine different commercially operating biogas upgrading plants such as water scrubber, amine, and membrane-based plants was examined. The result of the measurements showed an average of 0.81% methane loss with respect to supplied methane to the upgrading plants. A methane loss up to 1.97% was detected in water scrubber methane upgrading technology and up to 0.56% loss from membrane technology, while 0.04% methane loss was detected in amine based upgrading, thus the water scrubber has shown the most detrimental effect as regards methane loss. The regenerative thermal oxidizer was further applied to reduce CH4 emission by 99.5% of the amount of CH4 in the waste gas from the upgrading unit, which ensures the sustainable process of biogas production.

Catalytic Activity of Ceramic Honeycombs in the Exhaust Gas Oxidation of a Waste Treatment Plant

AbstractThe activity of ceramic honeycombs with varying material composition and degree of utilization is compared on a suitable model gas in a test plant. The tested honeycombs are standard products that have not been surface‐treated in any way. A propane‐air mixture was fed to the test plant and then oxidized in a high‐temperature furnace. The analysis of the conversion rate over the reaction temperature showed remarkable differences in activity. The honeycomb with the most promising results was further investigated with the exhaust gas from the drying process of a waste treatment plant. Finally, the activity of this honeycomb was assessed in a large‐scale trial in an existing running regenerative thermal oxidizer.