Quench Tower Research Articles

PCDD/Fs emissions in a large-scale hazardous waste incinerator under different operation conditions: Effective reduction strategies and an applicable correlation

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) emissions from hazardous waste incinerators (HWIs) have emerged as a great threat to environmental safety and human health, resulting in urgent effective control of the high emissions. In this study, the emission characteristics of chlorobenzenes (CBzs), PCDD/Fs from a large-scale HWI in China were studied under different conditions (inhibitor injection; feeding waste component). The total concentrations of CBzs and PCDD/Fs in stack gas from the HWI ranged from 2.18 to 22.94 μg/Nm3 and 0.98–18.53 ng/Nm3, respectively. Increased chlorine content of feeding waste led to increased PCDD/Fs concentrations, especially PCDDs. The inhibition efficiency of NH4H2PO4 with thiourea and Ca(OH)2 is 42.2% and 9.4% respectively. 2,3,4,7,8-PeCDF (30.7%–44.2%) and 1,3-DiCBz (61%–83%) was the dominating congener of I-TEQ values and CBzs concentration under all conditions, respectively. Furthermore, the relationship among PCDD/Fs, CBzs, traditional pollutants (carbon dioxide, sulfur dioxide, nitric oxide, hydrogen chloride, and particulate matter), and operational parameters were analyzed under six conditions to predict PCDD/Fs by indicators. Results indicated that PeCBz (r = 0.764), HCBz (r = 0.814), and quench tower water spray rate (r = −0.796) present strong correlations with I-TEQ values. Considering the effect of multicollinearity, the multiple regression model with PeCBz and water spray rate of quench tower as indicator variables (R2 = 0.801) has the best fitting effect, with an average absolute relative difference between measured and predicted I-TEQ of 34.8%. The study not only reveals the effects of hazardous waste composition and air pollution control devices (APCDs) parameters on PCDD/Fs emission characteristics, but also provided an accurate prediction method for PCDD/Fs emissions.

Inhibition of PCDD/Fs in a full-scale hazardous waste incinerator by the quench tower coupled with inhibitors injection

The control of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from the flue gas in hazardous waste incinerators (HWIs) is an intractable problem. To figure out the formation mechanism of PCDD/Fs and reduce the emission, a field study was carried out in a full-scale HWI. Ca(OH)2 & (NH4)H2PO4 or CH4N2S & (NH4)H2PO4 were injected into the quench tower, and the detailed inhibition effect on PCDD/Fs formation by the inhibitors coupled with quench tower was studied. Gas and ash samples were collected to analyze PCDD/Fs. XPS, EDS characterization and Principal component analysis were adopted to further analyze the de novo and precursors synthesis. The PCDD/Fs emissions reduced from 0.135 ng I-TEQ/Nm3 to 0.062 or 0.025 ng I-TEQ/Nm3 after the injection of Ca(OH)2 & (NH4)H2PO4 or CH4N2S & (NH4)H2PO4, respectively. The quench tower was found mainly hindering de novo synthesis by reducing reaction time. CP-route was the dominant formation pathway of PCDD/Fs in quench tower ash. Ca(OH)2 & (NH4)H2PO4 effectively inhibit precursors synthesis and reduce proportions of organic chlorine from 4.11% to 2.86%. CH4N2S & (NH4)H2PO4 show good control effects on both de novo and precursors synthesis by reducing chlorine content and inhibiting metal-catalysts. Sulfur-containing inhibitors can cooperate well with the quench tower to inhibit PCDD/Fs formation and will be effective to reduce dioxins formation in high chlorine flue gas. The results pave the way for further industrial application of inhibition to reduce PCDD/Fs emissions in the HWIs flue gas.

Formation and control of dioxins during thermal desorption remediation of chlorine and non-chlorine organic contaminated soil

Formation and emission of dioxins is a great concern during thermal desorption remediation of organic contaminated soil. The differential formation of dioxins from chlorine organic contaminated soil (COCS) and non-chlorine organic contaminated soil (NCOCS) is still unclear and the control technique for the dioxins generated is an urgent need. In this study, the formation and distribution characteristics of dioxins were investigated in the thermal desorption unit combined with flue gas purification system during COCS and NCOCS treatments. Although organic contaminates were well desorbed, de-novo formation of dioxins was observed for both COCS and NCOCS, as well as synthesis from precursors for NCOCS. The gas-phase dioxin in the flue gas purification system continuously decreased during NCOCS thermal desorption, while the dioxin concentration in the quench tower sharply increased from 0.46 to 2.13 ng/Nm3 through de-novo synthesis during COCS treatment. Furthermore, the emission of dioxins only slightly reduced (for COCS) or even increased (for NCOCS) at 70% operating load. The catalytic adsorption tower within modified activated carbon and V5-Mo5-Ti catalyst after bag filter can reduce the emission of dioxins up to 91.4% at the condition of secondary combustion chamber closure, demonstrating that the catalytic adsorption tower can replace the secondary combustion chamber for controlling dioxin emission. More importantly, the highly toxic low-chlorinated polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDD/PCDFs) were selectively removed from flue gas by the catalytic adsorption tower. These results reveal the differential formation characteristics of dioxins during COCS and NCOCS thermal treatments and highlight V5-Mo5-Ti/ modified activated carbon as a promising catalytic adsorption material to control the emission of dioxins from the thermal desorption of organic contaminated soil.

Formation and Growth Behavior Analysis of Slagging Rings in Rotary Kiln-Type Hazardous Waste Incineration Systems

Rotary kiln incineration technology has the advantages of strong material adaptability and a simple treatment process and has been widely used in hazardous waste treatment. However, the actual incineration process has caused problems such as ring formation in the treatment system due to the lack of research on the slagging mechanisms. In this paper, slagging phenomena occurring in the second half of the rotary kiln, the exit flue of the secondary combustion chamber, and the wall of the quench tower are analyzed and discussed in detail through characterization methods. The results indicate that the adhesion of low-melting alkali metal salts on the refractory surface in the second half of the rotary kiln is the key factor in forming the initial slagging layer. In the growth process of the slagging ring, the formed liquid phase can bond incineration residues of different sizes together and form a dense embryo body through liquid phase sintering. The deposition and solidification of molten/semi-molten fly ashes cause slagging formation in the exit flue of the secondary combustion chamber. The slagging phenomenon occurring in the inner wall of the quench tower belongs to the “crystalline-coalesce-hardening” process of the inorganic salts precipitating out of the high-salt wastewater.

Numerical simulation study of quench tower in flue gas purification system

By establishing a numerical simulation model of the high-temperature flue gas spray evaporation process, the heat transfer and flow processes in the quench tower using 4 different numbers of atomizing nozzles were simulated. Research and analysis were conducted under specific conditions. Different number of atomizing nozzles, the flow field above the quench tower is different, the greater the number of atomizing nozzles, the smaller the area occupied by the air flow, the smaller the conical volume formed by the droplets, the less time it takes to fully evaporate. A single atomizing nozzle cools down faster within 2m from the top of the tower, have the longest trajectory length of the droplet movement, but the time for the droplet to completely evaporate is the longest.

Failure of water quench tower in an ethylene cracking plant

This paper presents an erosion corrosion failure in Water Quench Tower in an ethylene cracking plant. It investigates a case in which a failure was noticed in the Water Quench Tower, exactly opposite to the feed entry nozzle. The damage occurred due to continuous impingement of cracked gases en-trained with quench water, which is used for the cooling of cracked gases. The mechanism involved was determined by internal inspection, thickness profiling and computational flow dynamics study at the inlet of the tower.

Fracture failure analysis of the pump shaft

The failure reasons of the circulating pump shaft in the upper section of the quench tower were analyzed by means of chemical composition analysis, macroscopic observation, metallographic examination and fracture section analysis. The analysis result shows that the calcium-silicate inclusions in the surface of the pump shaft cause the microcracks and the parallel fatigue sources, which leads to the fatigue cracks propagation under alternating load and finally the shaft is fatigue fractured.

Modelling the Quench Tower in Flue Gas Cleaning of a Waste Fueled Power Plant

To control the emission of pollutants in the flue gas, a separated flue gas quench was added after flue gas desulfurization and before flue gas condensation. A mathematic model was developed to simulate the heat and mass transfer in the flue gas quench. The model was validated through the comparison with measured data. Based on this model, the impacts of inlet flue gas condition and injected recycling water flow rate on the water consumption of the quench and the temperature of exit flue gas (FG) were studied. The results show that the temperature of exit FG and water consumption increased with the increase of flow rate and moisture content of FG. The temperature of exit FG increased and the water consumption decreased with the increase of droplet water diameter. The temperature of exit FG decreased and the water consumption increased with the increase of water flow rate. In order to cooled and humidified the flue gas sufficiently, the droplet diameter should be limited to 1.2 mm and the water to FG flow rate ratio (L/G) higher than 2.

Tower rises at Shell cracker

Shell says it has installed a huge quench tower at the ethylene cracker complex it is building in Monaca, Pa. Water circulating through the 87-meter-tall tower will cool down cracked gas, condense heavy hydrocarbons, and remove coke and tar particles. Using raw materials from the local Marcellus and Utica formation, the complex, set to open early next decade, will produce 1.6 million metric tons of polyethylene per year.

Removal of PCDD/Fs, PCP and mercury from sediments: Thermal oxidation versus pyrolysis

A continuous pilot-scale system (CPS) equipped with effective air pollution control devices (APCDs) is used for remediating the sediments contaminated with PCDD/Fs, PCP and Hg simultaneously. The removal efficiencies of these three pollutants in sediments collected from seawater pond and river, respectively, are evaluated via thermal treatment processes. PAHs and CBz formed during thermal oxidation and pyrolysis are also analyzed for better understanding the behaviors of chlorinated organic compounds. Experimental results indicate that low-molecular-weight PAHs are closely related to the formation of CBz, PCDD/Fs, and CPs, while low chlorinated PCDD/Fs and CBz are predominant in flue gas with thermal oxidation. However, the PM concentration is higher in thermal oxidation than pyrolysis due to the higher air flow rate of thermal oxidation. It may bring more particles out of the furnace and have a greater potential to form PCDD/Fs within APCDs. Besides, the high air flow also dilutes the Hg vapor in flue gas and would require more energy to condense and collect Hg with the quench tower. Furthermore, for removal of total amount of PCDD/Fs, pyrolysis is better than thermal oxidation. Thus, pyrolysis is more suitable for remediating the contaminated sediment. The removal efficiencies of PCDD/Fs, PCP and Hg in sediments achieved with pyrolysis increase with increasing operating temperature and retention time in CPS. Overall, the residual concentrations of PCDD/Fs and PCP in river sediment are higher than that in seawater-pond sediment since significant formation of tar is observed due to higher organic matter content in river sediment.

Dust emission from wet, low-emission coke quenching process

Coke plants, which produce various types of coke (metallurgical, foundry or heating), at temperatures between 600 and 1200°C, with limited access to oxygen, are major emitters of particulates and gaseous pollutants to air, water and soils. Primarily, the process of wet quenching should be mentioned, as one of the most cumbersome. Atmospheric pollutants include particulates, tar substances, organic pollutants including B(a)P and many others. Pollutants are also formed from the decomposition of water used to quench coke (CO, phenol, HCN, H2S, NH3, cresol) and decomposition of hot coke in the first phase of quenching (CO, H2S, SO2) [1]. The development of the coke oven technology has resulted in the changes made to different types of technological installations, such as the use of baffles in quench towers, the removal of nitrogen oxides by selective NOx reduction, and the introduction of fabric filters for particulates removal. The BAT conclusions for coke plants [2] provide a methodology for the measurement of particulate emission from a wet, low-emission technology using Mohrhauer probes. The conclusions define the emission level for wet quenching process as 25 g/Mgcoke. The conducted research was aimed at verification of the presented method. For two of three quench towers (A and C) the requirements included in the BAT conclusions are not met and emissions amount to 87.34 and 61.35 g/Mgcoke respectively. The lowest particulates emission was recorded on the quench tower B and amounted to 22.5 g/Mgcoke, therefore not exceeding the requirements.

A novel perspective on emulsion stabilization in steam crackers

Fouling issues in steam crackers may arise due to a number of reasons, including emulsion formation in the quench water tower. Freeze-drying according to a protocol developed in-house was used to extract species potentially capable of stabilizing emulsions from process water sampled from a quench tower. Such species were subsequently fractionated into solubility classes: water soluble, and soluble in organic solvents (polar and apolar). Liquid chromatography/mass spectrometry analyses indicated differences in the chemical composition of these fractions, with molecules bigger and richer in oxygen in the fraction soluble in polar organic solvents compared to those detected in the water soluble fraction. Bottle tests demonstrated that the interfacial material soluble in polar organic solvents was the most effective in stabilizing water-in-gasoline and gasoline-in-water emulsions. When the water soluble fraction was added to these stable emulsions it acted as demulsifier, with the most marked effects observed at low pH. In the absence of the water soluble fraction emulsion stability was largely pH-independent. The role of electrostatic forces in emulsion stabilization was investigated by conducting zeta potential measurements. With the organic soluble fraction only added to the oil phase and at pH 5.5, emulsions were stable and the zeta potential was close to zero, proving that electrostatic forces did not play a role in stabilizing this system. With the water soluble fraction added to the water phase and at alkaline pH, emulsions were stable and the zeta potential was negative, suggesting that electrostatic stabilization mechanisms cannot be discounted in the presence of the water soluble fraction. Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Spectroscopy (EDX) were used to probe the morphology and elemental composition of the Langmuir-Blodgett films extracted from the gasoline-water interface. SEM images highlighted the presence of particles at the gasoline-water interface, suggesting Pickering stabilization mechanisms. Dynamic interfacial tension measurements showed that the decrease of the interfacial tension measured for gasoline-water interfaces upon addition of interfacial material was relatively low and similar for all fractions, supporting this hypothesis. SEM/EDX data further reveal the strong correlation between interfacial film composition and emulsion stability, with high densities of particles containing sulfur and iron associated with significant emulsion stability. The compressional visco-elastic moduli of interfacial films were determined using a pulsating drop rheometer. Measurements were done at pH 5.5 and 8.5, with the individual solubility fractions added. Film rigidity was similar with all fractions, indicating that it did not dictate the differences in their stabilizing properties.

Catalytic hydrodechlorination of PCDD/Fs from condensed water with Pd/[formula omitted]-Al2O3

A continuous pyrolysis system (CPS) with effective air pollution control devices (APCDs) is designed and constructed to remediate the soil containing high-concentration PCDD/Fs. The quench tower of the APCDs system can capture the pollutants of high boiling points from the flue gas of CPS and produces condensed water of high PCDD/Fs concentration (16–44 ng I-TEQ/L), and needs further treatment. First, the result of activated carbon adsorption test displays the PCDD/Fs toxicity concentration of effluents meet the regulatory standards as the liquid to solid ratio is controlled at 3: 1. However, large amount of activated carbon need to achieve the high removal efficiency leads to high cost, so catalytic hydrodechlorination technology with Pd/Al2O3 as catalyst is applied to treat the condensed water. The PCDD/Fs mass removal efficiency achieved without the reducing agent is 53.21% with the operating time of 180 min. As 5% reducing agent (methanol) is added, the removal efficiency increases to 71.86%. In addition, to better understand the differences between molecular hydrogen and hydrogen donor, the condensed water was pre-aerated with hydrogen and catalytic hydrodechlorination test with palladium as catalyst was conducted. The results show that the PCDD/Fs mass removal efficiency increases to 97.34% with the operating time of 180 min, demonstrating the high PCDD/Fs removal efficiency of catalytic hydrodechlorination.

Industrial hazardous waste treatment featuring a rotary kiln and grate furnace incinerator: a case study in China

As one of the fastest developing countries, China is facing severe problems concerning hazardous waste treatment and disposal. This paper presents a new incineration technology and demonstration project in eastern China. The incineration system includes a rotary kiln, a grate furnace for burning out the kiln residue and a flue gas post-combustion chamber. Flue gas treatment and emission control is based on: a quench tower, followed by dry hydrated lime and activated carbon injection, a dual bag filter system, and a wet scrubber. It demonstrated that this incineration technology can effectively dispose of industrial hazardous waste with variable and complex characteristics. Gas emissions meet the demands of the Chinese Environmental Protection Association standard.

The effects on baghouse filter bags during the incineration of high-fluoride wastes

Fluorides and fluorosilicates have been widely used in many industrial plants. Hence, there are many hazardous wastes which contain high fluoride. Fluoride gases were reacted with fiberglass at high temperature and the reaction studied as a function of percentage of moisture. Keeping the quench tower, in front of baghouse, in a good working condition can efficiently reduce the attack to the filter bags from the fluoride gases. Aptus, wholly owned by Rollins Environmental Services, currently operates several environmental service facilities in the US. One of six high-temperature incinerators in Rollins is located in Aragonite, UT, which burns hazardous and industrial wastes and features a state-of-the-art air pollution control system.

Increasing efficiency in direct contact heat transfer

AbstractRevamping the top section of the water quench tower in an olefins plant provided a 74% reduction in pressure drop. First stage compression ratio was reduced from 2.21 to 2.02. An additional modification of the lower section of such a column with tower packing reduced the heat rejected to the cooling water by 35% with no increase in pressure drop.

Air Quality Effects from Quenching Coke with Fresh versus Process Water

Because of the extreme difficulties in sampling the discharge from coke-quench towers, only limited data have been available on the magnitude and effect of the emissions from this source. To evaluate this process better, U.S. Steel retained TRC Environmental Consultants, Inc., to undertake a test program at Gary Works (1) to conduct the necessary sampling tests to develop particulate emission factors for the coke-quenching operation during quenching with fresh water and with waste process water makeup to the quench system and (2) to estimate the impact of the emissions on ambient air quality for both conditions by means of dispersion modeling. The test results for a new offset quench tower provided with impingement baffles show particulate emissions of 0.35 pound per ton of coal (Ib/ton) for fresh water and 0.45 Ib/ton for process water quenching. The results for an older, straight-through, low-velocity quench tower, also provided with baffles, show 0.32 and 0.64 Ib/ton for fresh and process water quenchi...

Quench Tower Particulate Emissions

Particulate emission sampling was conducted at Dofasco’s No. 2 Coke Want Quench Tower in August 1977. The sampling was performed by York Research Corporation using EPA developed quench tower sampling techniques. Particulate emissions averaged 0.245 lb/ton of coal over 17 tests. The mist eliminator in the tower consists of two rows of zig-zag baffles inclined at 20° from the vertical. Particle size data indicated that the majority of the particulate emissions were less than 10 microns in diameter. A mathematical model was used to predict the effect of particle size and gas velocity on collection efficiency. Pressure drop and re-entrainment are two restrictions which are considered in baffle design. Quench towers are the largest contributor to Dofasco’s allowable off-the-property suspended particulate impingement concentration.