Scientific Investigation of Corrosion-Perforation in Desulfurized Flue Gas Heat Exchanger Tubes: Numerical and Experimental Studies

A critical review of parameters governing the boiling characteristics of tube bundle on shell side of two-phase shell and tube heat exchangers

Shell and tube heat exchangers play a crucial role in various industries, including chemical processing, oil and gas, power generation, and HVAC systems. These exchangers are widely used for transferring heat between two fluids while maintaining their separation. The design of a shell and tube heat exchanger consists of a bundle of tubes enclosed within a larger shell. The hot fluid flows through the tubes, while the cold fluid circulates around them in the shell, facilitating efficient heat transfer and pressure drop of the system. The performance of a shell and tube heat exchanger is influenced by various factors, including the configuration of the tube bundle. The choice of different tube bundle combinations can significantly impact the overall performance of the heat exchanger. In this paper, a numerical study is conducted to examine the effects of two combination of circular and square tube bundle with the simple arrangement: i) circular, ii) square, on a shell and tube heat exchanger. COMSOL Multiphysics is employed to model and simulate this heat exchanger under various mass flow rates. The result shown that the combined geometry heat exchanger exhibits the highest overall heat transfer coefficient compared to heat exchangers with single arrangements. The pressure drop on the tube and shell side was also studied for all cases of heat exchangers. The placement of circular tubes in the center and near the shell has a significant effect on heat transfer and pressure losses. It has been demonstrated that the tubes located at the ends of the shell have a much greater impact on heat transfer compared to the tubes positioned in the center.

The reliability of the heat exchanger tube bundle not only affects the economic efficiency of production but also relates to the normal development of production safety and health. To study the flow-induced vibration of tube bundles, a three-dimensional finite element model of heat exchange tubes and watersheds inside and outside the tubes was established to explore the flow-induced vibration characteristics of tube bundles and analyze the natural frequencies of single-span and multispan heat exchange tubes. Considering the randomness of the effective support between the tube bundle and the support plate of the heat exchanger, the natural frequency and vibration mode of the four-span tube with failure of the tube bundle support are analyzed. On this basis, the vibration caused by the two-way coupling flow between tube and tube outflow is calculated. Finally, the flow-induced vibration characteristics of the five-tube bundle with two different pitch-diameter ratios are analyzed. The calculation results show that the error between the calculated natural frequencies and the theoretical values is less than 3%, and within the allowable error range, the natural frequencies of the same order decrease with the increase of the number of support failures. The vibration frequencies of single-span and multispan tube bundles are consistent with the lift and drag frequencies, the vibration displacement curves show typical Strouhal modes, and the amplitude increases with the increase of fluid velocity. Vibration displacement curves of symmetrical spans of multispan tube bundles are similar in shape and amplitude. With the increase of tube bundle spacing, the vibration characteristics become more obvious.

Simulation and Computational Fluid Dynamic (CFD) analyses of condensing shell and tube heat exchanger is subjected in this article. The condensing model using a User Defined Function (UDF) through Ansys Fluent 18.2 is developed. Also, the heat transfer between the shell and tube bundles is considered too. The subjected heat exchanger included seven tubes with a length of 600 mm and a shell with a diameter of 90 mm. The effect of different types of baffles and the distance between them is investigated in this article. All the calculations were done in three different mass flow rates. Finally, the distribution of heat flow is depicted for each stage of the considered heat exchanger. Results show that for the specific geometry and constant distance between baffles, increment in the mass flow rate leads to increasing the heat transfer coefficient. In addition, it shows that the formation of dew droplets and condensed water is higher in the first geometry due to the maximum heat transfer by hot flue gas.

Fouling and thermal-hydraulic characteristics of aligned elliptical tube and honeycomb circular tube in flue gas heat exchangers

CONSOL Energy Inc., Research & Development (CONSOL), with support from the U.S. Department of Energy, National Energy Technology Laboratory (DOE) and the Electric Power Research Institute (EPRI), is evaluating the effects of selective catalytic reduction (SCR) on mercury (Hg) capture in coal-fired plants equipped with an electrostatic precipitator (ESP)--wet flue gas desulfurization (FGD) combination or a spray dyer absorber--fabric filter (SDA-FF) combination. In this program CONSOL is determining mercury speciation and removal at 10 coal-fired facilities. The principal purpose of this work is to develop a better understanding of the potential mercury removal ''co-benefits'' achieved by NO{sub x}, and SO{sub 2} control technologies. It is expected that these data will provide the basis for fundamental scientific insights into the nature of mercury chemistry in flue gas, the catalytic effect of SCR systems on mercury speciation and the efficacy of different FGD technologies for mercury capture. Ultimately, this insight could help to design and operate SCR and FGD systems to maximize mercury removal. The objectives are (1) to evaluate the effect of SCR on mercury capture in the ESP-FGD and SDA-FF combinations at coal-fired power plants, (2) evaluate the effect of SCR catalyst degradation on mercury capture; (3) evaluate the effect of low load operation on mercury capture in an SCR-FGD system, and (4) collect data that could provide the basis for fundamental scientific insights into the nature of mercury chemistry in flue gas, the catalytic effect of SCR systems on mercury speciation and the efficacy of different FGD technologies for mercury capture. This document, the ninth in a series of topical reports, describes the results and analysis of mercury sampling performed on Unit 1 at Plant 7, a 566 MW unit burning a bituminous coal containing 3.6% sulfur. The unit is equipped with a SCR, ESP, and wet FGD to control NO{sub x}, particulate, and SO{sub 2} emissions, respectively. Four sampling tests were performed in August 2004 during ozone season with the SCR operating; flue gas mercury speciation and concentrations were determined at the SCR inlet, SCR outlet, air heater outlet (ESP inlet), ESP outlet (FGD inlet), and at the stack (FGD outlet) using the Ontario Hydro method. Three sampling tests were also performed in November 2004 during non-ozone season with the SCR bypassed; flue gas mercury speciation and concentrations were determined at the ESP outlet (FGD inlet), and at the stack (FGD outlet). Process samples for material balances were collected during the flue gas measurements. The results show that, at the point where the flue gas enters the FGD, a greater percentage of the mercury was in the oxidized form when the SCR was operating compared to when the SCR was bypassed (97% vs 91%). This higher level of oxidation resulted in higher mercury removals in the FGD because the FGD removed 90-94% of the oxidized mercury in both cases. Total coal-to-stack mercury removal was 86% with the SCR operating, and 73% with the SCR bypassed. The average mercury mass balance closure was 81% during the ozone season tests and 87% during the non-ozone season tests.

Heat transfer enhancement of different ribbing pitched semi-closed microstructure tube bundles fabricated by deformational cutting method

Two-phase flow on the shell side of a shell and tube heat exchanger is complex. Several studies have produced flow pattern maps that show surprising differences in flow regime boundaries for data sets that contain relatively small variations in fluid and flow properties. Despite this, correlations for void fraction and pressure drop are sufficiently accurate to allow the thermal-fluid design of heat exchangers to be completed. However, these correlations are based on experimental data taken from tube bundles containing tubes with diameters less than 20 mm. This study examines their applicability to tube bundles containing tubes with a diameter of 38 mm. Results for void fraction and pressure drop are presented for air-water flows near atmospheric pressure. The results were obtained for flows through a thin-slice, in-line tube bundle containing 10 rows. The tube bundle contained a central column of tubes with half tubes placed on the shell wall to simulate the presence of other columns. The tubes were 38 mm in diameter and 50 mm long with a pitch to diameter ratio of 1.32. Previous studies have shown that the void fraction in a shell-side, gas-liquid flow becomes constant after only a few rows. Thus, the void fraction was only measured at one location. A single-beam, gamma-ray densitometer was used to measure void fractions near row 7 in the maximum gap between the rows. Corresponding pressure drops were obtained between rows 3 and 10. Data are presented for a mass flux range of 25–688 kg/m2s and a gas mass fraction range of 0.0005–0.6. The measurements are shown to compare reasonably well with predictions from correlations available in the open literature. This shows that these methods can be used for tube-bundles containing larger diameter tubes. Some elements of a heat-exchanger design require a more complex analysis. For example, tube vibration calculations require the distribution of void and phase velocity along the tube length. Such analysis can be provided by multiphase computational fluid dynamic (CFD) simulations. CFD approaches to modelling these flows require empirical inputs for the drag coefficient and the force on the fluid by the tubes. These are deduced from the measured data. The wall forces are shown to scale well with increased tube diameter, however, caution is required when selecting the drag coefficients.

The shell and tube heat exchangers are widely used in many engineering applications. Tubular heat exchangers can be found in the transport, power engineering, food industry and etc. Therefore, the study of the characteristics of heat transfer and hydrodynamics in tubular heat exchangers is important. In this paper, numerical analysis of a heat transfer in a staggered tube bundle with steady and asymmetrical pulsating flow studied. The transverse and streamwise spacing-to-diameter ratios of the tube bundle were 1.3. The Reynolds number Re was 1100. Numerical simulation of the flow past the tube bundle with 7 longitudinal rows was carried out by solving the incompressible Navier-Stokes equations and energy conservation equation with two different modeling strategies. The simulation was carried out with the RNG k-ε turbulence model with enhanced wall treatment and laminar solver. The sensitivity of the Nusselt number to the mesh parameters is noted. The effect of the number of rows of the tube on the heat transfer rate for the tube bundle with the pulsating flow also was discussed. For the pulsating flow enhancement of the heat transfer in the tube bundle dependence from the row of the tube and modeling strategy. When RNG k-ε turbulence model was employed the heat transfer rate of the first row is increasing by 16 %, downstream rows by 6-7 %. When laminar solver was employed the heat transfer rate of the central rows are increasing by 53 %.

On-site experimental study on fouling and heat transfer characteristics of flue gas heat exchanger for waste heat recovery

In industrial production, flue gas heat exchangers are often affected by the low-temperature condensation of industrial flue gas due to the influence of the working environment, resulting in serious ash deposition and corrosion. In order to solve this problem, in this study, we developed an ash deposition and corrosion monitoring system to compare the ash deposition prevention performance and corrosion resistance of different materials, as well as its influence on the heat transfer performance of different materials in the same environment. The following coatings were selected for the experiment (values in parentheses are the concentrations of the added compounds): ND, Q235, 316L, Ni-Cu (0.4 g/L)-P, Ni-P-SiO2 (40 g/L), Ni-Cu (0.4 g/L)-P-SiO2 (20 g/L), Ni-Cu (0.4 g/L)-P-SiO2 (40 g/L), and Ni-Cu (0.4 g/L)-P-SiO2 (60 g/L). The results show that the Ni-Cu (0.4 g/L)-P-SiO2 (40 g/L) coating has excellent corrosion resistance, while the Ni-Cu (0.4 g/L)-P-SiO2 (60 g/L) coating shows excellent antifouling performance. Through the comparative analysis of polarization curves, impedance spectra, and coupled corrosion experiments, the test materials were ranked as follows based on their corrosion resistance: 316L > Ni-Cu-P-SiO2 (40 g/L) > Ni-Cu-P-SiO2 (20 g/L) > Ni-P-SiO2 > Ni-Cu-P-SiO2 (60 g/L) > Ni-Cu-P > ND > Q235. It was also demonstrated that the new coated pipes were able to reduce the exhaust temperature below the dew point and maximize the recovery of energy from the exhaust gas. The acid–ash coupling mechanism of the coating in the flue gas environment was further analyzed, and an acid–ash coupling model based on Cu and SiO2 is proposed. This model analyzes the effect of the coating under the acid–ash coupling mechanism. Using coated tubes in heat exchangers helps to recover waste heat from coal-fired boilers, enhance heat exchange efficiency, extend the service life of heat exchangers, and reduce costs.

The heat exchanger is the key component of an industrial drying system. The present work introduced a novel tube heat exchanger into a corn drying system. To fully understand the heat exchange process and optimize the heat exchange performance of the heat exchanger, numerical simulation, exergy analysis and economic analysis methodologies were adopted to analyze the comprehensive performance of the heat exchanger. The fluid dynamics as well as the exergy performance of the heat exchanger under different flue gas velocities (3, 5 and 7m/s) and different ambient air relative humidities (80%, 85% and 90%) were investigated. The results showed that there are two strong turbulences causing the huge pressure drop at the last two stages of the flue gas duct, while there are two insufficient heat exchange areas on both sides of the heat exchanger; thus, the corresponding improvement recommendations were proposed in the present work. The values of the Re and Nu were found to vary in the range of 1256.275–2210.554 and 21.337–32.415, respectively. The average heat transfer coefficients were ascertained to be above 8.274 kW·m−2·K−1, while the pressure drop of the ambient air was ascertained to be under 16.138 Pa. Moreover, the exergy analysis revealed that the heat exchanger experiences sustainable development (SI < 2), and the exergy efficiency is above 11.461%. The main results may provide some references for further optimizing the heat transfer performance of the heat exchanger.

The micro-channel heat exchanger is extensively employed in the field of heat exchange, including aerospace precooling technology. This paper takes the bowed heat exchange tubes used in the precooler of aerospace vehicles as the research object and has studied and analyzed the flow and heat transfer characteristics of the tubes under different inflow speeds. In addition, the fluid–structure interaction numerical method based on parametric design language programming is proposed, which is verified by the vibration experiment of bowed tubes. Furthermore, by using the methods, the reliability of the micro-tube structure have been analyzed. The conclusions can be gotten as: (1) With operating conditions of the coolant helium unchanged, the heat exchange effect of the heat exchange tube bundle is greatly affected by the air flow rate. As the speed of the inflow hot air increase, the heat transfer coefficient decreases significantly. (2) The losses caused by wall shear stress near the heat exchange tubes account for the main part. After the air flows through the tubes, vortices are formed, causing disturbances to the tubes. (3) Furthermore, the flow–structure coupling analysis for the heat exchange tubes was conducted. As inflow velocity rises, the vibration displacement also decreases by 5.89%, which is predominantly localized at the middle position of tube bundles, gradually decreasing toward both sides. (4) Concurrently, it is evident that the support plate plays a role in concentrating the various rows of tube bundles. If the support plate is fixed, the vibration displacement of the tube bundle can be reduced.

Sulfur recovery unit (SRU) thermal reactors are negatively affected by high temperature operation. In this paper, the effect of the fuel mass fraction on the combustion and fluid flow in a SRU thermal reactor is investigated numerically. Practical operating conditions for a petrochemical corporation in Taiwan are used as the design conditions for the discussion. The simulation results show that the present design condition is a fuel-rich (or air-lean) condition and gives acceptable sulfur recovery, hydrogen sulfide (H2S) destruction, sulfur dioxide (SO2) emissions and thermal reactor temperature for an oxygen-normal operation. However, for an oxygen-rich operation, the local maximum temperature exceeds the suggested maximum service temperature, although the average temperature is acceptable. The high temperature region must be inspected very carefully during the annual maintenance period if there are oxygen-rich operations. If the fuel mass fraction to the zone ahead of the choke ring (zone 1) is 0.0625 or 0.125, the average temperature in the zone behind the choke ring (zone 2) is higher than the zone 1 average temperature, which can damage the downstream heat exchanger tubes. If the zone 1 fuel mass fraction is reduced to ensure a lower zone 1 temperature, the temperature in zone 2 and the heat exchanger section must be monitored closely and the zone 2 wall and heat exchanger tubes must be inspected very carefully during the annual maintenance period. To determine a suitable fuel mass fraction for operation, a detailed numerical simulation should be performed first to find the stoichiometric fuel mass fraction which produces the most complete combustion and the highest temperature. This stoichiometric fuel mass fraction should be avoided because the high temperature could damage the zone 1 corner or the choke ring. A higher fuel mass fraction (i.e., fuel-rich or air-lean condition) is more suitable because it can avoid deteriorations of both zone 1 and heat exchanger tubes. Although a lower fuel mass fraction (i.e., fuel-lean or air-rich condition) can avoid deterioration of zone 1, the heat exchanger tubes may be damaged. This paper provides a guideline for adjusting the fuel mass fraction to reduce the high temperature inside the thermal reactor and to ensure an acceptable sulfur recovery.

Numerical investigation on the aerodynamic noise and heat transfer characteristics of continuous helical channels with tube bundles