Wet Tower Research Articles

Enhancement of selenium removal in coal-fired flue gas across wet flue gas desulfurization spray tower by internal components-part 1: Demister and wall ring

Wet flue gas desulfurization (WFGD) device is a key piece of equipment used to control selenium, but its removal efficiency is highly variable (13%–95%). Adding internal components into WFGD can alter the gas-liquid flow pattern and is regarded as a promising technology for selenium removal. In this study, the demister and wall ring were adopted as internal components to investigate their feasibility on selenium removal and inherent mechanisms. Compared with the open tower (without internal components), the outlet selenium concentration was reduced by 52.2%–61.7% by installing a demister. This was because a liquid film was formed on the baffle plates of the demister after intercepting mists, which leaded a secondary absorption process for selenium. The lower plates of the demister made a major contribution to selenium removal, and increasing the plate area of the demister was beneficial to this process. The wall ring reduced the selenium emission by up to 56.5%, because it could force the flue gas and liquid column near/on the walls to flow towards the center, and significantly improve the gas-liquid contact. The enhanced method and mechanisms reported in this study can help to develop a low-cost technology to improve the selenium purification efficiency of existing WFGDs.

PM2.5 Collection Enhancement in a Smart Hybrid Wet Scrubber Tower

The removal efficiency of particulate matter of less than 2.5 microns (PM2.5) using an innovative wet scrubber tower with an IoT system for PM2.5 real-time monitoring was investigated. The PM2.5 used in this experiment was obtained from vehicle exhaust, specifically from running the diesel engine of a pickup truck with a range of PM2.5 with a concentration ranging from 50 µg/m3 to 500 µg/m3. Focused parameters related to PM2.5 were analyzed, such as the liquid-to-air ratio (it uses air because this device purifies PM2.5 for the airflow from the polluted ambient air), turbulence techniques enabled by the installation of a deflector and a baffle at the airflow inlet, water level fluctuation above the nozzle, spray nozzle size, and the type of packing material. The average PM2.5 removal efficiency was determined for each parameter relevant to the experiment. The results showed that increasing the liquid-to-air ratio increased the average PM2.5 removal efficiency, while the smaller droplet spraying water resulted in higher efficiency. The spray section achieved its highest efficiency at 58.63%, with a liquid-to-air ratio of 13.21 L/m3 and droplet size of 270 µm. The turbulence technique showed a higher potential for the removal of PM2.5, with an efficiency level of 71.56% at a water level of 150 mm. Moreover, the operation incorporates water spraying and turbulence induction, promoting higher removal efficiency, from 71.56% to 87.59%, at a water level of 150 mm and a liquid-to-air ratio of 9.03 L/m3. This condition resulted in an output concentration of PM2.5 less than 15 µg/m3, which meets the WHO’s guidelines for PM2.5 intensity. This cleverly designed wet scrubber tower can clean up to 13,320 m3 of air daily or remove up to 2,464 g of PM2.5 per day. No enhancement of PM2.5 removal efficiency was observed when two types of packing materials were used due to the formation of bigger droplets as the packing materials were passed through.

Rigorous simulation of geothermal power plants to evaluate environmental performance of alternative configurations

Different studies highlighted the environmental impacts of geothermal power plants (GPPs), especially in the operational phase. Primary data are essential for reliable environmental assessments, but these are not available when considering alternative configurations. Rigorous simulation can offer such a degree of information, representing also a tool for a digital twin technology transition. Considering a GPP in Tuscany, Italy, four alternatives configurations are simulated in UniSim Design®, performing accurate refinements to the thermodynamic model to properly estimate the behavior of different pollutants (Hg, H2S, NH3, and SO2) among the various unit operations. The configurations alternate direct-contact and surface condensers as well as wet and dry towers as cooling systems, while a fifth one adopts an organic Rankine cycle. The actual plant model has been reconciliated with data collected during two different monitoring campaigns. Performance analysis shows a trade-off: the lowest pollutant emissions are obtained using the dry tower generating less net energy (20.17 MWe and 20.83 MWe), instead, adopting surface condenser and wet tower, 22.26 MWe are produced with NH3 emissions almost 3 times the measured ones. The CO2 and CH4 amount in the well fluid is not abated in any configurations and therefore their emissions are the same among them.

Structure Optimization Research Based on Numerical Simulation of Flow Field in Ammonia-Based Wet Sintering Flue Gas Desulfurization

Although more and more desulfurization equipment has been put into use in sintering plants, how to effectively remove sulfur dioxide from sintering flue gas in a desulfurization tower is still a great challenge in China. The desulfurization tower, as a critical part, needs further improvement and optimization. Therefore, based on the numerical simulation of the flow field of the ammonia-based wet desulfurization tower for sintering flue gas, ANSYS CFX is applied to conduct structural optimization research. Comparing the flow field distribution under different structure conditions, the results show that the flue gas distribution of the dual inlet tower is more uniform than that of the single inlet tower. The designed baffle not only effectively blocks the entry of the spray slurry, but also improves the flue gas distribution; the deflector with its simple structure, convenient operation, and stepped distribution installed in the entrance section can improve the uniformity of the flow field distribution. Based on the comprehensive analysis, these optimized structures are recommended in the design of an ammonia-based wet sintering flue gas desulfurization tower. This work not only develops a simulation of the desulfurization tower but also provides practical structures.

The water cost effect of hybrid-parallel condensing systems in the thermo-economical performance of solar tower plants

The importance of considering the water price in the analysis of the impact of dry versus hybrid condensing systems in the thermo economical performance of solar tower plants was demonstrated in this work. The dry condensing system consists of several induced-draft air-cooled condenser cells (ACCs) and the hybrid system consists of a parallel system where the condensing steam is split between the ACCs and a surface steam condenser where circulating water is cooled in a wet mechanical-draft cooling tower. The influence of the operating parameters of either the dry or wet cooling systems on the cooling load and fan power consumption were studied. Then, for a given condensing system (a system with a defined number of installed ACCs units and cooling tower units) and given the dry-air and wet-bulb air temperatures, the operating parameters were optimized to maximize the revenues of the power plant. This optimization depends on the water-to-electricity price ratio R , showing that at low ambient temperature when this ratio increases it is not profitable to turn on the cooling towers since the water cost is not counterbalanced by the higher cycle efficiency obtained with the lower condensation temperature. Finally, the annual operation and the LCOE and NPV of the CSP plant located in Dunhuang were analyzed for both dry and hybrid condensing systems with different number of ACCs and wet towers, showing that the most cost-effective configuration is the 16 ACCs with 3 wet cooling towers for water-to-electricity price ratio R = 4 ($/m 3 )/($/kWh e ) and R = 5 ($/m 3 )/($/kWh e ), but for R = 10 ($/m 3 )/($/kWh e ), the best option is with only 2 wet towers. • The thermo-economical behavior of dry and hybrid condensing systems is compared. • The annual operation analysis of a real solar tower plant is presented. • The condensing systems operation parameters were optimized to maximize the revenues. • The water cost effect in the thermo-economical performance of the solar plant is shown.

Water Balance Test, Analysis and Application of the Wet Cooling Tower

This study aims to conduct a water loss test and analysis of water used in wet cooling towers. The measuring tools and methods of the liquid level in the collecting basin are clearly guided by establishing the water balance equation. The U-type liquidometer measuring system is used to measure the liquid level of specific open container with a large surface area. The minimum resolution of the U-type liquidometer is 1 mm. The collecting basin area is 375 m2, and the detected water volume is 0.375 m3 mm-1 liquid level. The measurement error caused by water surface fluctuation is overcame. The accuracy of the liquid level data is further improved. Under the water balance test condition, the water loss at the outlet of tower is between 26.25 m3 h-1 and 49.36 m3 h-1, and the loss of exceeding standard is 22.62 m3. This work determined the water balance condition of the wet cooling tower equipment and conducted a detailed analysis of water loss and the water conservation of the wet tower. Moreover, this study promote equipment manufacturing related to the mechanical draft cooling tower industry to the direction of water conservation, energy conservation and environmental protection to provide support. This approach is also widely used in the other air and water systems direct mixing heat transfer equipment.

Experimental Study on Simultaneous Desulfurization and Denitrification by DBD Combined with Wet Scrubbing

A dielectric barrier discharge (DBD) reactor combined with a wet scrubbing tower was used to carry out an experimental study on desulfurization and denitrification. The effects of the packing type, packing height, spray density, mass fraction of the NaOH solution, discharge power in the DBD reactor, and simulated flue gas flow rate on the desulfurization and denitrification efficiency were analyzed, along with the influence weight of each factor, using orthogonal testing. The experimental results showed that SO2 was easily absorbed by the scrubbing solution, while the desulfurization efficiency remained at a high level (97–100%) during the experiment. The denitration efficiency was between 12 and 96% under various operating conditions. Denitration is the key problem in this system. The influence weights of the DBD power, simulated flue gas flow rate, mass fraction of the NaOH solution, spray density, packing type, and packing height on the denitration efficiency were 56.96%, 18.02%, 11.52%, 5.02%, 4.33%, and 4.16%, respectively. This paper can provide guidance to optimize the desulfurization and denitrification efficiency of this DBD reactor combined with a wet scrubbing system.

Optimisation and Analysis Based on Bi-Level Reduced-Order Model for Coupled Heat and Mass Transfer Processes Under Uncertainty

This work proposes an integrated framework to build fast and high-fidelity bi-level reduced-order models (ROMs) for heat and mass transfer processes systems. In the proposed framework, the bi-level ROMs including the ROM for output variables (yROM) and the ROM for state variables (zROM) corresponding to its input variables of the systems are developed by integrating principal component analysis (PCA) with artificial neural networks (ANN), which can closely approximate the results of computational fluid dynamics (CFD). In particular, the CPU time is significantly reduced with the fast bi-level ROMs. A case study is used to demonstrate the benefits of using our proposed bi-level ROMs methodology for simulation and optimisation for heat and mass transfer processes systems, where a bi-level ROMs for the closed wet cooling towers (CWCTs) is built with the help of exergy analysis. The design points served for CFD simulations are randomly sampled by stochastic reduced-order modelling (SROM). The developed yROM is used for stochastic optimisation of exergy efficiency ratio and then the corresponding optimal exergy flux fields are then reconstructed and analysed based on zROM.

The DTT secondary cooling water systems

Abstract The new Tokamak machine DTT (Divertor Tokamak Test), planned under construction by Enea Frascati Research Center, is a machine actively cooled by water. Although DTT is an intermittently operating machine, the thermal power that must be cooled is more or less 127 MW emitted within 100 seconds. Geographically the DTT site, at the Enea Frascati center, doesn’t allow the construction of water basins and the cooling wet towers. Furthermore, it doesn’t have enough water supply coming from the municipal aqueduct. Therefore, the best solution is to project a close loop cooling water system, divided into 2 circuits: primary circuits (Divertor, First Wall, ECRH, ICRH, NBI, Electrical Power Supply and Cryoplant) filled with demineralized water and a secondary circuit filled with cooling water designed for working with pressure under 16 Bars. The thermal Power transferred by the primary circuits using dedicated heat exchangers (plates or shell-and-tube) is delivered to a centralized “warm tank” developed in order to store all the energy emitted during the plasma discharge and to prevent the total water temperature in the tank from reaching boiling point. Afterwards, the warm fluid is transferred to another “cold tank” where the chillers are continuously working between two successive machine pulses every 3600 seconds. The two tanks are designed to optimize the minimum power required by the chillers. Moreover, a recovery energy system will be incorporated in order to heat all components (First Wall, Divert or, Vacuum Vessel) which should be maintained warm between the two pulses. The same logic of centralization is applied to the demineralization with reverse osmosis.

Simulation study on novel groove separator in a dual‐loop wet flue gas desulfurization spray tower

AbstractThe dual‐loop wet flue gas desulfurization spray tower (DLST) is particularly suitable for achieving “ultralow” emission of SO2 for high‐sulfur coal‐fired power plants. The separator is the key piece of equipment for the DLST. In this study, to overcome the disadvantages of a traditional bowl separator, novel groove separators are proposed and compared with the traditional separator. The effects of different separators on the flue gas flow characteristic, slurry droplet distribution, mass transfer resistance, and desulfurization efficiency were analyzed through numerical simulation based on the Euler–Lagrange method and two‐film theory. The results show that, compared with the traditional bowl separator, the proposed groove separator can improve the uniformity of the gas–liquid flow field in the upper loop, increase the liquid‐film side mass transfer rate significantly, eliminate the empty spaces caused by the high‐speed bypass flue gas, and avoid the “flooding” phenomenon completely. Therefore, the resistance losses caused by the separator can be reduced, the desulfurization efficiency can also be improved by adopting the novel groove separators, and the lower the liquid‐to‐gas ratio, the more obvious the increase in desulfurization efficiency. In general, the advantages of the novel groove separators over the traditional bowl separator are obvious.

Year-round operation the solar powered hybrid adsorption-compression refrigeration cycle

In our earlier papers a hybrid adsorption-compression refrigeration cycle was presented. The hybrid, two stages cycle is based only on the natural refrigerants: water and carbon dioxide. The main advantage of the hybrid cycle is that the carbon dioxide compression cycle is subcritical because during the year-round operation it is possible to maintain the condensing temperature below 20 oC. During the hot season, this is achieved by adsorption cooling, during cold seasons the wet cooling tower is sufficient. Already several years of experience, allowed to gather a considerable amount of measurement data. The refrigeration system is working in our laboratory constantly since 2013. In 2015 the adsorption system was upgraded by the manufacturer. In 2017 frequency inverter for wet tower fan controlling was introduced. The refrigeration chamber was used for tests with different content and operation of the refrigeration chamber (loading and unloading). The assumed CO2 evaporating temperature was -35 oC. The averaged for HT(High Temperature) part of the cascade (adsorption cycle only) COPHT=0.51 for the whole year 2018. This may be considered a very good performance. 

Thermodynamic evaluation of hybrid cooling towers based on ambient temperature

In this study, due to importance of water saving in plants, thermodynamic evaluation of wet and hybrid cooling towers of Tabriz refinery and Ahwaz Ramin power plant is carried out. In water scarcity countries, plants are considered as the largest water consumers in the industry. In this study in pilot section of Tabriz refinery and Ahwaz Ramin power plant, dry and wet sections of a hybrid cooling tower are modeled and the amount of water losses is estimated. The tower designed for Tabriz refinery includes a wet tower and 12 air-cooled heat exchangers. Cooling towers of the Ahwaz Ramin power plant are two 315 MW units with four cooling rows, each with five fans for cooling circulating water. Due to changes of the temperature in summer and winter and the severe impact of the air temperature on the cooling and water loss, simulation operations are performed separately. In Tabriz refinery the optimal parallel arrangement in summer occurs in 0.23 of hybrid ratio and 11,2500 m2 dry area. In series the ratio is 0.44. In Ramin power plant, hybridization of cooling towers is proposed in 0.44 by using of 85,1921 m2 dry area. Results show using hybrid towers, water consumption decreases by 34% for the cooling system of Ramin power plant and it is 38% for the cooling system of Tabriz refinery. Also, the economical evaluation is demonstrated.

Water footprint of thermal power in China: Implications from the high amount of industrial water use by plant infrastructure of coal-fired generation system

To reflect an important aspect of the water footprint of thermal power in China, this study as an extension of a previous work (Wu et al., 2018a) uncovers the high amount of industrial water use induced by plant infrastructure of a typical coal-fired power generation system. The systems process method is used by combining process analysis and water intensities obtained from systems input-output analysis. Industrial water use induced by plant infrastructure is accounted to be several times greater than previous estimates, and approximate to or much larger than that induced by fuel mining, preparation and transport in total. For per unit of electricity output, the water use by plant infrastructure amounts to 8.4% of the direct freshwater withdrawal for the majority of supercritical thermal power plants equipped with wet tower cooling, and even up to 38% of the freshwater withdrawal for some plants with air tower cooling. The annual water use induced by coal-fired power generation infrastructure in China is estimated to be 0.6%, 7%, and 23% of the annual freshwater withdrawal by China, Japan, and United Kingdom, respectively. The outcome provides a benchmark for policy makers to measure and curb the upstream water use by plant infrastructure.

A superior liquid phase catalyst for enhanced absorption of NO2 together with SO2 after low temperature ozone oxidation for flue gas treatment

NOx and SO2 are the main air pollutants emitted from the coal-fired combustors. Since the typical combination of selective catalytic reduction (SCR) and wet flue gas desulfurization (WFGD) is not suitable for some of industrial flue gas treatment due to their unsuitable temperature window and limited retrofitting space, new technologies must be developed. This paper proposes an effective wet method for simultaneous removal of NOx and SO2. The insoluble NO was first oxidized into NO2 by ozone, and then NO2 together with SO2 were both absorbed in one wet wash tower. To further improve NO2 removal efficiency, a new kind of additive was proposed and tested. Effects of various influence factors, such as additive concentration, residence time in the wash tower, liquid/gas ratios, initial NO/SO2/O2 concentration and slurry pH value, were carefully evaluated in a home-designed experimental platform. Results indicated that the NOx removal efficiency was positively correlated with the increasing the additive concentration, while the maximum denitration and desulfurization efficiency were more than 95% and 86%. The NOx removal efficiency was enhanced with the increasing residence time and liquid/gas ratios. The alkaline environment was verified to be beneficial for the simultaneous absorption process. The exiting O2 in flue gas would not consume additives, and the denitration and desulfurization efficiency were insensitive to the initial NO and SO2 concentration as well. Only 2% decrease of the denitration efficiency was observed after 300 mins stability test, while the desulfurization efficiency kept >98%. With the characterizations of Ion Chromatograph (IC), NO2−, NO3− and SO42− were detected as the main absorption by-products anions, whereas NO2− accumulation would inhibit the overall NOx removal. Finally, the mechanism of simultaneous removal of SO2 and NO using the novel liquid phase catalyst was proposed and discussed.

Wentwood tower and valve refurbishment

The valve and operating system had reached the end of its asset life and the tower was showing signs of structural distress. The wet tower arrangement required a full drawdown of the reservoir basin to allow surveys of the valve, pipework and tower condition. A pro-active silt management system was required to discharge into the downstream watercourse that flows into sinkholes. The paper covers the development of the scheme through to selection of the preferred solution.

Simulation and optimization of cooling water systems with closed wet cooling tower based on reduced order model

This study presents a CFD (computational fluid dynamics)-assistant multi-scale modeling and optimization strategy for synthesizing cooling water systems which incorporates multiple closed wet cooling towers (CWCTs) installed with plain tubes. The utilization of CFD is capable of providing accurate and visual results with respect to complex thermal and fluid flow phenomena that can be used to explore the synergistic mechanism of multi-parameter for CWCTs. Based on CFD results, a systematic reduced order model (ROM) for CWCTs is developed by closely approximating the high-fidelity CWCTs models through integrating principal component analysis (PCA) with Kriging-based surrogate model. This ROM is accessible to the desired result through input data without accounting for the complex geometries and detailed thermal-hydraulics property models. The proposed CFD-assistant ROM for the CWCTs is applied to enhance solution convergence and obtain optimal results of cooling water systems. An industrial case study is used to demonstrate the superiority of the proposed CFD-assistant strategy for the cooling water system synthesis and optimization.

Electrical power generation under policy constrained water-energy nexus

Water-energy nexus refers to the interdependence between water resources and energy conversion, and it encompasses the multiple phases of electric power generation and water processing and distribution. Current policies for the utilization of freshwater resources in electric power generation regulate the thermal discharges and their effect on the aquatic life. Water withdrawals and consumption polices are mainly prescribed at the regional level instead. This paper focuses on the effects of water policy constraints on electric power generation in changing climate conditions. A river basin is simulated, which hosts two hydraulically linked power generating stations, namely an upstream hydropower plant with reservoir and a downstream thermal power plant. Two alternative cooling designs are tested for the thermal power plant, i.e. once-through and wet tower cooling. Severe drought conditions leading to small river flows and high water temperatures are analyzed, and the limitations to the energy conversion at the thermal plant stemming from the water policies are quantified. The results show that some small flexibility in the water policy constraints during extreme droughts can secure a significant amount of energy to the power system, which would have been curtailed otherwise. Remarkably, the relaxation of 1.5°C in the water policy constraints prevents the curtailment of 42% of the generation capacity of a 1000MWe thermal plant during the analyzed 24h drought scenario. In general, the type and the required amount of constraint relaxation depend on the environmental conditions and are to be judged case-by-case. Furthermore, the smart scheduling of water resources grants a 7% increase of the energy converted during droughts in the hydraulically linked hydro and thermal power plants. Finally, the analysis shows that once-through cooling systems are extremely sensitive to changes in water flow and temperature opening space for less sensitive technologies, i.e. wet cooling towers.

Retrofit of a wet cooling tower in order to reduce water and fan power consumption using a wet/dry approach

A Parallel Path Wet/Dry configuration and a high-precision airflow regulation method are implemented in order to retrofit an existing wet cooling tower. The modifications are intended to reduce water requirements and fan power consumption of a 12-cell wet tower. The proposed method of airflow control takes advantage of fans with variable frequency drive to regulate airflow with high accuracy. A number of simulations are carried out to predict different operating factors of the wet and hybrid towers. Experimentally obtained values of water consumption demonstrate the validity of those obtained using the computer simulations. According to the results, the accurate airflow control prevents sudden fluctuations in requisite fan power and water consumption rate and causes up to 64.6% decrease in fan power consumption. The results reveal that using the proposed wet/dry approach results in an average 9.4% decrease in water consumption. Given the relatively low degree of modifications made to the original wet tower and preserving the condenser operating condition, the accomplished amount of water conservation is satisfactory.

PCM in the heat rejection loops of absorption chillers. A feasibility study for the residential sector in Spain

Abstract This study investigates the integration of phase change materials (PCMs) in the heat rejection loops of absorption solar cooling systems for residential applications in Spain. The feasibility of replacing the open wet tower by an alternative air-cooled system based on a combination of dry-coolers and a thermal energy storage (TES) with PCM inside (TESpcm) has been evaluated in terms of the total cooling energy produced and the system efficiency. TRNSYS® parametric simulations of two configurations have been conducted between the months of June and September. Their performance has been characterized and their advantages and disadvantages have been summarized. The results indicate that the alternative heat rejection loop with a TESpcm of 1 m3 can improve the mean overall system performance coefficient in locations with temperate and humid summers by almost one unit, although different degrees of the deterioration of the mean chiller's performance coefficient (values between 7 and 13%) and a reduction in the total cooling energy produced in the evaporator (21–38%) are inevitable. The study concludes with some suggestions for future work.

Medieval Logic Diagrams

This article describes the finding, documentation and significance of the set of medieval logic diagrams and associated text, all in highly abbreviated Latin minuscule, sketched on an inside wall of the Romanesque tower of the parish church in Bro, near Visby. The diagrams depict the Square of Opposition, the basic concept to be mastered in introductory logic as taught at medieval schools and universities. A date c.1200-1225 is suggested by their being executed in the earliest plaster when wet (tower built c.1200), while up to 1350 is suggested by palaeography. Dating by textual content is still in progress. Either way the Bro diagrams are among the earliest logic texts written in Scandinavia, and this is the first time for such texts to be found outside a manuscript. They are also the earliest known physical evidence of a teaching session or a discourse in logic. Furthermore they contribute to a growing body of evidence of the high standard of learning that existed in medieval Gotland.