Heat Low Pressure Research Articles

Techno-economic analysis on a new conceptual design of waste heat recovery for boiler exhaust flue gas of coal-fired power plants

Recovering waste heat from boiler exhaust flue gas is an effective way to improve energy utilization efficiency and reduce coal burning pollution of coal-fired power plant (CFPP). The low-pressure economizer (LPE) is the most widely employed in waste heat recovery from boiler exhaust flue gas. However, there is a contradiction in LPE between maximizing waste heat recovery rate and maximizing waste heat utilization efficiency. This research improves waste heat utilization efficiency without reducing recovery rate by converting recovery heat. The recovery heat conversion is realized through organic fluid cycle integrating organic Rankine cycle (ORC) with high temperature heat pump (HTHP). The organic fluid cycle acts as a medium between flue gas and feedwater, which makes recovery heat match higher parameter low-pressure heater (LPH) flexibly. Based on exergy analysis, the upper limit for elevating energy-saving effects by converting recovery heat is given. For calculations and analyses, thermodynamic models are built and simulated in MATLAB together with REFPROP software based on a case study. The results show that using the proposed waste heat recovery system could produce 5361.98 kW additional net power output and electricity revenue of $1220.04 k, which are approximately 409.19 kW and $127.2 k greater than LPE respectively. The proposed system could save 5699.36 t standard coal and $854.9 k coal cost per year, which are nearly 595.5 t and $89.32 k larger than LPE. The maximum of recovery heat utilization efficiency of proposed system reaches 17.35% and the maximum efficiency improvement compared to LPE touches 3.48%.

Removal of Scale from Feed-water in Thermal Power Plant by Magnetic Separation -Analysis of Oxygenated Treatment Scale-

One of the reasons of the deterioration of the power generation efficiency of the thermal power generation is the adhesion of the iron scale generated by the corrosion of the pipe to the inner wall of the feed-water system. Focusing on the magnetic property of scale, we studied on the removal of scales in the feed-water system by high gradient magnetic separation (HGMS) using the superconducting magnet. In this study, we targeted the thermal power plants adopting oxygenated treatment (OT). In order to determine the installation site and the magnetic separation condition of the HGMS system, we analyzed the OT scale and then clarified the aggregation/composite states by magnetic separation experiment. It is concluded that low-pressure feed-water heater drain is suitable for installation site of HGMS system. In addition, it was clarified that homogeneous aggregation particles existed in the OT scale.

Full repowering of an existing fossil fuel steam power plant in terms of energy, exergy, and environmen for efficiency improvement and sustainable development

In this study, the feed-water-heating method is studied due to its numerous advantages for the repowering of 320 MW units at Isfahan power plant. In this method, only low-pressure heat exchangers or only high-pressure heat exchangers can be replaced with a new gas–water heat exchanger, or both can be replaced by two high-pressure and low-pressure heat exchangers. It is also possible to do the preheating of boiler feed water in parallel with existing heat exchangers and new heat exchangers. Each of this method has its own characteristics that have advantages and disadvantages. We first analyze the energy and exergy of the existing cycle and then analyze the methods used to feed-water-heating repowering. Various gas turbines are used for this work, and the results are expressed. Energy and exergy efficiencies are considered as objective functions, and finally, while considering other limiting parameters, it is recommended for each method of optimal gas turbine. The characteristics of the new heat exchangers are also described. In the first method, net efficiency of energy and exergy is increased relatively to 8.25% and 8.4%, respectively, and in the second method net efficiency of energy and exergy is increased relatively to 10.96% and 11.56%, respectively.

Numerical investigation on aerodynamic characteristics of exhaust passage with consideration of multi-factor components in a supercritical steam turbine

Heat transfer and vacuum in the condenser are affected by the flow characteristics in the low-pressure steam turbine exhaust passage. In this study, the Eulerian-Eulerian equilibrium two-phase model is applied to investigate the contribution of multi-factor components on aerodynamic performance of twin exhaust passage. Results show that the share of steam phase is reduced in the exhaust passage with consideration of the built-in pipelines. Total-pressure loss in the exhaust hood is about four times of that in the throat. The sensitivity of local loss existing in the exhaust hood on the whole loss is higher than that in the throat. Considering the factors of LSBs and pipelines, both the static-pressure recovery coefficient of 15.44% and effective specific enthalpy-drop of 0.145% are the best performance. By evaluating the steam turbine economic, however, static-pressure recovery coefficient and specific enthalpy drop are 1.25 times and 0.475 times of that without pipelines, respectively, relative to built-in pipelines. Therefore, a recommendation on the consideration of twin exhaust passage, last stage blades, steam extraction pipelines, low-pressure heater, and wet steam can obtain a representative aerodynamic characteristic.

Exergy analysis of the regulating measures of operational flexibility in supercritical coal-fired power plants during transient processes

Operational flexibility improvement of coal-fired power plants has become a priority objective with the high penetration of renewable energy sources. The regulating measures applied frequently in improving the operational flexibility indeed affect the exergy efficiency of coal-fired power units during transient processes. In this study, the exergy efficiency evaluation of operational flexibility measures during primary frequency control processes was focused on, and the exergy analysis methods of the thermal system were used on the basis of the second law of thermodynamics to analyze the mechanisms for improving the flexibility at four regulation measures, and the exergy storage conversion efficiency and exergy destruction accumulation were quantitatively compared. It turns out that: among the throttling extraction steam of high-pressure heaters, feedwater bypass of high-pressure heaters, and condensate water decrease of low-pressure heaters measures, the exergy storage conversion efficiency and the exergy destruction accumulation increase with the regulating time of primary frequency control. The measure of throttling extraction steam of high-pressure heaters is the most potential option for improving operational flexibility, with maximum value of the maximal output power increment and maximal exergy storage change rate of 71.11 MW and −89.84 MW, respectively. With respect to the economy, the measure of throttling extraction steam of low-pressure heaters is the best option due to its smallest exergy destruction accumulation among all the measures. This study provides a detailed guidance for the selection of the optimal regulating measures when considering the enhancement of exergy efficiency and flexibility comprehensively under different conditions and periods.

Analysis on the change of coal consumption of low-pressure (low temperature) economizer unit

This paper discusses the calculation of coal consumption for power generation when the unit uses steam extraction as a low-pressure (low temperature) heat recovery source. The calculation of coal consumption for power generation when the unit uses low-pressure (warm) economizer as a low-pressure (low-temperature) heat source, the heat source is not recovered. At the same time, the coal consumption of power generation was compared, and finally the reduction of the heat rate of the turbine was discussed as a decrease in coal consumption.

Production of high-early-compressive-strength Portland cement paste using low-pressure microwave-accelerated heating and curing: processing characteristics and factors affected

The use of low-pressure microwave (MW)–accelerated heating and curing in the production of high-early-strength Portland cement paste (CP) in relation to the processing characteristics and factors affected is investigated. The effects of the pressure in the MW cavity, the feed direction of the MW, and the number of CP specimens per MW curing batch on the temperature increase and moisture content (i.e., the water-cement ratio (w/c)) of the CP and its compressive strength after MW-curing CP are considered. A double-feed MW-vacuum system is used to generate MW by applying 800 W (1 magnetron) or 1,600 W (2 magnetrons) and to convey MW to the CP specimens. The CP pastes are designed and mixed at specific initial w/c ratios of 0.25, 0.35, and 0.45. The CP specimens are cured using a low-pressure MW cavity at 30 and 50 kPa and fed in symmetrically or asymmetrically perpendicular directions of the CP specimens in batches of 12 (3.95% of the volume of microwave cavity) and 24 specimens (7.90% of the volume of the microwave cavity) per MW-curing batch with the following dimensions: 5 cm long × 5 cm wide × 10 cm thick. The experimental results show that with the maximum MW curing temperature of 70 °C from the initial stage (approximately the first 30 min of applying low-pressure MW curing) until 100 min, the temperature of the CP increases continuously at a high rate; then, the rate at which the temperature increases decreases slightly, which is consistent with the remaining w/c of the CP. The pressure in the MW has a slightly different temperature increase and remaining CP. A perpendicular symmetric magnetron placement in respect to the horizontal position of the specimens can lead to a steady increase in the strength development of all the CP specimens. Further, over the course of 28 days, compared with the water-cured CP, the MW-cured CP develops more compressive strength.

Transesterification of high-acidity spent coffee ground oil and subsequent combustion and emissions characteristics in a compression-ignition engine

Lipids extracted from spent coffee grounds (SCG) are a potentially promising feedstock for biodiesel production if the relatively high free fatty acid (FFA) portion of the oil can be successfully converted into methyl esters, and the resulting biodiesel found to have acceptable combustion and emissions performance. This study presents experimental results obtained from transesterification of SCG-extracted oil with a FFA content of ∼30% w/w through a two-step process, followed by fuel characterization and combustion experiments with SCG-derived biodiesel, pure and blended with fossil diesel, and untreated SCG oil in a single cylinder research compression-ignition engine. The acid-catalyzed pretreatment reduced the FFA content of the oil below 1.5% w/w, with minor losses, and showed the methanol-to-FFA molar ratio to be more significant relative to the quantity of sulphuric acid used as a catalyst within the range of investigated conditions, while the subsequent base-catalyzed step converted ∼87% of the pretreated oil into biodiesel with a higher heating value (HHV) of 39.7 MJ/kg. The combustion and emission characteristics of pure and blended SCG biodiesel revealed similarities with those of commercial rapeseed and soya biodiesel samples tested. While ignition delay decreased with increasing SCG biodiesel content, the comparatively higher CO, total hydrocarbon (THC) and particulate emissions of the SCG biodiesel were attributed to higher fuel kinematic viscosity (KV). Combustion of the untreated SCG oil produced low in-cylinder peak pressure and peak heat release relative to other samples tested despite a longer ignition delay, suggesting that the oil physical properties were more important in determining combustion performance.

An experimental study of CHF and power transients in flow boiling at low-pressure low-flow conditions

ABSTRACTFlow boiling experiments were conducted in an annular channel at very low flow rates and atmospheric pressure varying the inlet subcooling from 20 to 40. critical heat flux occurred during the oscillatory flow pattern transition from slug to churn regime. Comparison of low-pressure and low-flow critical heat flux correlations with the present data has shown that these correlations are not applicable for prediction of critical heat flux under oscillatory flow pattern transition from slug to churn. Power transient experiments were also performed at low-pressure and low-flow conditions. Flow regimes and the sequence of events leading to critical heat flux were visually observed using the high-speed camera.

Three-Dimensional Numerical Simulation of Steam Turbine Exhaust Passage Considering Small Engine Exhaust

Taking a 600 MW steam turbine as the research object, the three-dimensional numerical simulation of the complex internal structure of the exhaust passage is performed using Fluent software. By establishing three models, the influence of low pressure heater, low pressure extraction steam pipe and small machine exhaust on aerodynamic performance of exhaust cylinder is simulated respectively. The results show that the three components of the extraction pipeline, the low-pressure heater, and the exhaust of the small machine have a significant influence on the aerodynamic performance of the throat, causing a low-speed vortex in the flow field and severely destroying the homogeneity of the flow field, resulting in a he reduction of the heat transfer coefficient. Among them, the exhaust of the small machine has the greatest influence on the uniformity of the flow field at the outlet of the condenser, and further analysis and research are needed.

Effect of vapor liquid equilibrium on product quality and yield in oil shale pyrolysis

Separation of the products from the reacting organic matter is necessary to ensure product quality and reduce oil degradation to solid reside (coke) when considering conversion of oil shale to oil by in-situ processes. Many effects on yield and quality due to operational conditions may be explained by considering their role in volatilization. A five-reaction network with vapor–liquid equilibrium has been created in MATLAB to examine the effect of heating rate and pressure on volatilization. The model uses the Peng-Robinson equation of state, phase stability using the Gibbs tangent plane criterion, and Rachford-Rice flash calculations. Component compositions may be changed with automatically adjusting stoichiometry and species properties. A new feature is that dew and bubble point pressure calculations are performed at each calculation-step and plotted to show the phase behavior of the changing product composition with conversion. Product expulsion is represented as a mass fraction of generated vapor. The results indicate that for 10 °C/min and atmospheric pressure, 50% removal is enough to obtain a liquid yield that is 97% (977 mg/g TOC) of the maximum yield with 95% removal. The operational conditions with the lowest oil yield (127 mg/g TOC) are 0.001 °C/min and 500 psi with 5% vapor removed. Additionally, changing from high to low fractions of removed vapor move the maximum light oil yield from low pressure and low heating rate to high pressure and high heating rate.

Increasing operational flexibility of supercritical coal-fired power plants by regulating thermal system configuration during transient processes

The operational flexibility of traditional coal-fired power generators has played crucial parts in many countries given the continuous integration of intermittent and fluctuant renewable power resources in their power system. This study is aimed at improving the short-term operational flexibility of thermal power units. The transient simulation models of a 660 MW supercritical coal-fired power system are developed by using the GSE software, and the six measures of regulating thermal system configuration, which can rapidly activate thermal storages in thermal systems, are introduced and compared. The greatest potential mode in each measure of regulating thermal system configuration is obtained on the basis of the utilization degree of the internal thermal storages. The dynamic characteristics of the thermal parameters of the selected measures are compared, and the results reveal that the measures of regulating extraction steam from low-pressure heaters has less negative effects on the live and reheat steam parameters but greater negative effects on the deaerator and condenser parameters than the measures of regulating extraction steam from high-pressure heaters. Moreover, the performance indexes of operational flexibility are also evaluated for all the measures of regulating thermal system configuration. Among five measures applied in the power-up process, the values of power ramp rate are from 1.26% to 6.31% of rated power per minute, the values of power capacity are from 12.87 to 48.35 MW, and the values of energy capacity during the regulating time of 120 s are 1009.73 to 5048.93 MJ. However, the measure of condensate water increasing of low-pressure heaters is an only way suitable for the power-down regulation process, and the value of power ramp rate is 0.61% of rated power per minute, the power capacity is −5.65 MW, and the energy capacity is −483.84 MJ. The best regulating measures are obtained on the basis of the different perspectives of operational flexibility. The findings of this study can help determine the best operational control strategies in different situations.

An investigation on flashing-induced natural circulation instabilities based on RELAP5 code

In this investigation, flow instability experiments carried out in a natural circulation loop at the low-pressure condition. Based on experiment data, the RELAP5 code was adopted in the analysis. The objective of this investigation is to get insight into the nature of flashing-induced natural circulation instability. Four typical oscillations observed, intermittent and periodical oscillation, double-peak oscillation, periodical sinusoidal oscillation, and staged irregular oscillation. Under low pressure and low heat flux condition, flashing plays a dominated role in natural circulation oscillation. It is suppressed in higher heat flux. The accumulation of bubbles and fluid inertia result in diverse nonlinear relationship between driving head and kinetic energy. The mechanism of flow instabilities is explored from different aspects. The simulation results of RELAP5 are presented and assessed against the experimental results. The deviation between the results for different circulation modes is discussed as well.

Highly Efficient 2D/3D Hybrid Perovskite Solar Cells via Low-Pressure Vapor-Assisted Solution Process.

The fabrication of multidimensional organometallic halide perovskite via a low-pressure vapor-assisted solution process is demonstrated for the first time. Phenyl ethyl-ammonium iodide (PEAI)-doped lead iodide (PbI2 ) is first spin-coated onto the substrate and subsequently reacts with methyl-ammonium iodide (MAI) vapor in a low-pressure heating oven. The doping ratio of PEAI in MAI-vapor-treated perovskite has significant impact on the crystalline structure, surface morphology, grain size, UV-vis absorption and photoluminescence spectra, and the resultant device performance. Multiple photoluminescence spectra are observed in the perovskite film starting with high PEAI/PbI2 ratio, which suggests the coexistence of low-dimensional perovskite (PEA2 MAn-1 Pbn I3n+1 ) with various values of n after vapor reaction. The dimensionality of the as-fabricated perovskite film reveals an evolution from 2D, hybrid 2D/3D to 3D structure when the doping level of PEAI/PbI2 ratio varies from 2 to 0. Scanning electron microscopy images and Kelvin probe force microscopy mapping show that the PEAI-containing perovskite grain is presumably formed around the MAPbI3 perovskite grain to benefit MAPbI3 grain growth. The device employing perovskite with PEAI/PbI2 = 0.05 achieves a champion power conversion efficiency of 19.10% with an open-circuit voltage of 1.08 V, a current density of 21.91 mA cm-2 , and a remarkable fill factor of 80.36%.

Mass-transfer and differential element mobility in metapelites during multistage metamorphism of the Yenisey Ridge, Siberia

Abstract Pelitic gneisses and schists from the Garevka Complex (Yenisey Ridge) at the western margin of the Siberian craton contain zoned garnet porphyroblasts that show clear evidence of multistage growth. The three discrete stages define a counter-clockwise pressure–temperature ( P–T ) path involving initial prograde low pressure heating followed by near-isothermal medium-pressure compression and post-peak retrograde synexhumation decompression and cooling. The combined study of the variations of in-situ major and trace element mineral compositions of coexisting minerals and mineral modes with changing P and T conditions and metamorphic reactions in rocks allowed detailed investigation of metamorphic processes. A significant increase in pressure during prograde collision-related metamorphism correlates with an abrupt increase of Ca in garnets, which in turn is accompanied by a significant decrease in heavy rare earth elements (HREE) and Y contents. Decrease in temperature and pressure during retrograde metamorphism led to an increase in the HREE and Y content in garnets with concomitant decrease of grossular component of garnet. A pronounced systematic negative correlation between HREE including Y content and Ca content in garnet can be attributed to substitution of trivalent rare earth elements (REE) and Y for divalent Ca cations on eightfold sites. The main reasons for the sharp increase in Ca content in garnets during collisional metamorphism are either (1) the redistribution between garnet and plagioclase, which led to less calcium in composition, or (2) consequence of epidote breakdown. A mass balance of major and trace elements between the reactants and products of metamorphic reactions yield very good matches between the measured and reconstructed modal abundances in all cases, indicating that collisional metamorphism was essentially isochemical with respect to most elements, with the exception of HREE. The minimum equilibration volume for the major elements was c. 1 mm 3 . The total HREE balance requires a rather greater reaction volume involved in the redistribution of HREEs, of the order of 3–8 mm 3 which provides evidence for their relatively higher migration mobility during metamorphism in comparison with other REE.

Performance modeling and maintenance priorities decision for the water flow system of a coal-based thermal power plant

PurposeThe purpose of this paper is to deal with the formation of performance modeling and maintenance priorities for the water flow system (WFS) of a coal-based thermal power plant.Design/methodology/approachThe system consists of five subsystems, i.e. condenser, condensate extraction pump, Low Pressure Heater, deaerator and boiler feed pump. The Chapman-Kolmogorov equations are generated on the basis of transition diagram and further solved recursively to obtain the performance modeling with the help of normalizing condition using Markov approach.FindingsAvailability matrices are formed with the help of different combinations of failures and repair rates of all subsystems. The performance of all subsystems is evaluated in terms of availability level achieved in availability matrices and plots of failure rates and repair rates of various subsystems. The maintenance priorities of various subsystems of WFS are decided on the basis of repair rate.Originality/valueThe adoption of both performance modeling and maintenance priorities decision by the management of thermal power plant will result in the enhancement of system availability and reduction in maintenance cost.

Exergy and exergoeconomic analyses with modeling for CO2 allocation of coal-fired CHP plants

The coal-fired power plant is confronted with severe challenges due to increasing coal price and negative impact on climate change. In this study, exergy and exergoeconomic analyses of a 330 MW coal-fired combined heat and power (CHP) plant are performed to determine the unit exergoeconomic cost and specific CO2 emission of the final products. The cycle is simulated by Aspen Plus software and thermodynamic properties under different conditions are extracted. Exergy balance equations are formed based on the exergy flow of coal, water/steam, ash, and flue gases. Cost formation process has been revealed by the exergoeconomic analysis combining the recent development of residue cost allocation. Different from previous studies, cost of flue gas cleaning is taken into account as a part of the unit exergoeconomic cost of the products. Moreover, CO2 allocation is conducted based on the exergoeconomic model and has been compared with other methods. Results show that the largest exergy destruction occurs in the boiler and the lowest exergy efficiency occurs in the low-pressure heater. There is an energy-saving potential of the residue exergy which accounts for 7.5% of the exergoeconomic cost in heating period and 10.4% in non-heating period.

Performance Evaluation and Off Design Analysis of the HP and LP Feed Water Heaters on a 3 × 135 MW Coal Fired Power Plant

System composing of two high pressure heaters (HPH1 and HPH2), one deaerator-feed water tank (DEA) and four low pressure heaters (LPH4, LPH5, LPH6 and LPH7). This study aims to conduct a performance evaluation during full load on each unit’s regenerative feed water heaters, both closed and open type, using ASME PTC 12.1 and an analysis on the heater off design condition at 5% load intervals. Off design conditions on a heater occurred on several occasions, where unit is at low load or derating, and may affect overall efficiency of a plant. The parameters needed such as load, extraction steam pressure, heater drain temperature and inlet and outlet feed water temperature on a heater were collected on the Distributed Control System (DCS) at Central Control Room (CCR) station. Other necessary data like steam and drain enthalpies were collected using CATT 3 software or steam tables. There were five tests collected at random dates on each unit where it is in operation. The data result features like Temperature Terminal Difference (TTD), Drain Cooler Approach (DCA) and Temperature Rise (TR) across heater were indicators used to determine and evaluate each heaters performance. Extraction Steam Flow Requirement was also calculated for additional performance verification. The evaluation results at maximum load shows that Unit No.2 HPH1 and HPH2 has lower TTD (4.35°C and 3.39°C respectively) and DCA (-0.37°C and 14.68°C respectively) and a higher TR (21.97°C and 46.94°C) were remarkably good. The results also showed that as the low-pressure heaters goes to the last stage heater (LPH4 to LPH7), the TTD was increased on all units. A highest TTD (49.86°C) and lowest TR (2.95°C) on Unit 1 were observed which could be quiet alarming and an indication of off design even at full load. The ranges between minimum and maximum load at 5% load intervals showed that HPH1 and HPH2 (TTD and TR) were proportional to the load while LPH4 and LPH5 (TTD) were inversely proportional to load adjustments on all units. The last stage heater, LPH7, on Units 1 and 2 poorly performed during the load adjustments with its TR maintained only around 4°C at any load is an indication of off design condition. A mathematical approach of non-linear regression was also simulated using MATLAB R2013A on each heater’s TTD, DCA, TR and Extraction steam flow requirement to allow other researcher or performance engineer for future framework. Thus, the results of the tests regarding the performance of regenerative feed water heaters proves that last stage heaters mostly encounter off design and high-pressure heaters are the most efficient. Finally, based from the evaluation results, it recommends inspecting or improve the last stage heaters to prevent equipment breakdown and conduct more routine plant performance on regenerative feed water heaters to monitor the heaters degradation or improvement.

Aircraft fuel system energy and exergy analysis under hot day conditions

In this paper, energy and exergy analysis of the fuel system is performed to investigate the variation of flow and heat energies of fuel. Thermal balance, formed by many different components of aircraft systems by means of heat management, has been significantly affected by aircraft performance. For that reason, thermal management of the fuel system in the aircraft has a significant indication concerning energy and exergy flow. The results indicate that the rate of energy transfer, which is occurred in the fuel system components throughout flight is respectively 42% for low-pressure heat exchanger, 23% for high-pressure heat exchanger and 22% for the low-pressure fuel pump and finally 13% for the high-pressure fuel pump. In addition to that; during the flight the exergy destruction rate in the fuel system, in proportion to flight phases, is 51% during the climbing phase, 21% during the acceleration phase, 14% during the idle position and 7% during both cruise and descent phase.

Energy Saving Effect Test and Operational Optimization of Low Pressure Economizer under Multi-variable Factors

The energy saving effect of low-pressure(LP) economizer of a 220MW unit was tested under multi-variable factors. Using the equivalent enthalpy drop method, the energy saving effect of LP economizer at different operational modes and different operating parameters has been calculated. When the higher water flow rate and inlet temperature of LP economizer is necessary, condensate water from NO.6 LP heater outlet should be used priority. Under the condition of 220MW, the optimal flow into LP economizer from NO.6 LP heater outlet is about 250t/h, the thermal efficiency of the unit could be increased 0.645%. If LP economizer inlet temperature is lower, the outlet of LP economizer should be connected to the outlet of NO.6 LP heater. And water temperature at LP economizer outlet should be slightly higher than the temperature of the NO.6 LP heater outlet. Otherwise, the energy saving effect will be decreased. Under the condition of 220MW, the thermal efficiency of unit increases 2.003%. For different LP economizer operation mode, there will be an optimal water returning location and optimal inlet flow rate.