Inlet Steam Temperature Research Articles

Thermally double coupled reactor coupling aqueous phase glycerol reforming and methanol synthesis

This study proposes a novel thermally double coupled reactor (TDCR) coupling endothermic aqueous phase glycerol reforming (APGR) with exothermic methanol synthesis (MS), utilizing heat transfer between both channels. Hydrogen (H2) source and availability are known as barriers to carbon dioxide conversion to methanol via MS reaction. Waste glycerol could be a source of H2 through APGR reaction. The steady state TDCR model consists of two concentric channels: 1) an inner tube to which CO₂ and H₂ are fed as reactants for exothermic MS and 2) an outer annulus channel through which glycerol and steam are supplied for endothermic APGR. The TDCR could operate without external heat supply when two reactions were coupled. A computational fluid dynamic (CFD) model was established to study this TDCR. APGR was assumed to be catalyzed by Pt/Al₂O₃ at 200−250 °C and 20−25 bar. MS was modeled with a Cu/ZnO/Al2O3 catalyst at 200−250 °C and 50−80 bar. Heat transfer from the exothermic channel to the endothermic channel helped increase glycerol conversion while methanol productivity is the same as conventional reactor. Cocurrent and countercurrent feed configurations were compared and it was found that the cocurrent configuration offered more uniform temperature distribution in the channel with a larger temperature difference between the two channels. On the other hand, hot spots and cold spots were observed in the countercurrent configuration. Effects of operating conditions of both channels: H2:CO2 and glycerol:steam ratios, inlet temperature, pressure, and total feed flow rate on reactor performance significantly affected the performance of TDCR.

Analysis on the Performance of Steam Absorption Chiller at Various Operating Conditions

Steam Absorption Chiller (SAC) is the main component of Cogeneration Plant which provides chilled water by utilizing the steam as system input for the cooling purpose. In this paper, the performance of a double effect lithium bromide-water steam absorption chiller was analyzed by conducting the energy and exergy analysis. An excel spreadsheet program was developed to calculate the exergy destructions within the systems and total exergy loss of the system in guiding future improvement of the plant. Various operating conditions like steam inlet temperature, chilled water inlet temperature and load factor were analyzed in detail. The result showed that the highest exergy destruction occurred at the high temperature generator followed by the absorber. Increasing the load factor, steam and chilled water inlet temperature will increase the system performance.

Effect of modification of spiral pipes on mini boiler to steam temperature and boiler efficiency

The purpose of this study is to modify the water pipe in the mini boiler into a spiral pipe, with a pipe length of 196.8 cm. With the aim of increasing the efficiency and temperature produced by mini boilers. In addition, it is also to determine the shape and length of the pipe that is better for use in mini boilers. The results of the test show the temperature rise that passes through the superheater pipe. In the spiral pipe model there is a temperature increase of 10.92 °C, with a steam inlet temperature of 277.62 °C. While the temperature of steam coming out of the superheater pipe is 288.54°C. This shows a temperature increase of 16.6°C, with a superheater pipe steam temperature of 267.4 °C and a steam temperature of 284 °C from the previous pipe model. Testing for heating water, until it becomes steam in the mini boiler is carried out for 90 minutes.The temperature value of the spiral pipe model is better than the previous pipe model. And the efficiency value obtained in the mini boiler using the spiral pipe is 15.055%, while in the previous study only 5.73%.

A numerical simulation of a linear Fresnel solar reflector directed to produce steam for the power plant

The concentrating solar systems of linear Fresnel reflectors offer the ability to generate electricity from solar energy. The main objective of this paper is to perform a transient numerical simulation on a linear Fresnel solar reflector directed to produce superheated water steam for the power plants, in order to determine its efficiencies (optical and thermal), where the heat transfer fluid mass flow inside the copper absorber tube is 0.045 kg/s. The dimensions of the studied linear Fresnel solar collector are the same dimension as the modular system Nova-1 of NOVATEC SOLAR Company. The dimension of the studied model is 1D. For this purpose, El-Oued region has been designated as a study field. The twelve recommended average days for months have been selected for the study. This paper was based on a numerical solution using the finite differences method. MATLAB has been used as a software language. The optical efficiency of the LFR solar receiver has reached 53.7% where the thermal efficiency has reached 37.5%, while the pressure drop within the absorber pipe has reached 02 bars. As for superheated steam temperatures variations, it ranged between 233.35 °C and 263.75 °C, knowing that the water steam inlet temperature when entering the absorber tube is equal to 140 °C. As for the overall coefficient of heat loss, its mean value is 5.84 W/m2.°C. The results obtained are very encouraging to invest in this steam power plant, especially in the desert areas, which are rich in solar energy.

Steam jet mill—a prospective solution to industrial exhaust steam and solid waste

Bulk industrial solid wastes occupy a lot of our resources and release large amounts of toxic and hazardous substances to the surrounding environment, demanding innovative strategies for grinding, classification, collection, and recycling for economically ultrafine powder. A new technology for grinding, classification, collection, and recycling solid waste is proposed, using the superheated steam produced from the industrial exhaust steam to disperse, grind, classify, and collect the industrial solid waste. A large-scale steam jet mill was designed to operate at an inlet steam temperature 230-300°C and an inlet pressure of 0.2-0.6MPa. A kind of industrial solid waste fluidized-bed combustion ashes was used to grinding tests at different steam temperatures and inlet pressures. The total process for grinding, classification, and collection is drying. Two kinds of particle sizes are obtained. One particle size is d50 = 4.785μm, and another particle size is d50 = 8.999μm. For particle size d50 = 8.999μm, the inlet temperature is 296°C and an inlet pressure is 0.54MPa for the grinding chamber. The steam flow is 21.7t/h. The yield of superfine powder is 73t/h. The power consumption is 3.76kWh/t. The obtained superfine powder meets the national standard S95 slag. On the basis of these results, a reproducible and sustainable industrial ecological protocol using steam produced by industrial exhaust heat coupled to solid waste recycling is proposed, providing an efficient, large-scale, low-cost, promising, and green method for both solid waste recovery and industrial exhaust heat reutilization.

Multi-objective optimization of hot steam injection variables to control wetness parameters of steam flow within nozzles

Abstract The formation of liquid droplets in the low pressure steam turbines has devastating impacts on the turbine adiabatic efficiency and also causes the mechanical damage of blades due to the occurrence of severe erosion phenomenon. Previous investigations have shown that the injection of steam can decrease liquid mass fraction as well as the size of the averaged radius of droplets. To exploit the maximum potentials of this method, the optimization of injection variables is necessary. In the present study, the numerical solution of wet steam flow by the injection of hot steam within convergent-divergent nozzles together with a multi-objective genetic algorithm method are used to evaluate the appropriate injection parameters. It is concluded that to reduce liquid droplet size by 66% and liquid mass fraction by 13%, an injection steam flow rate of 4% of the main stream flow rate with a temperature 1.8 times of inlet steam temperature is required. Such a reduction of liquid droplet size has an enormous effect on lowering the erosion damages of blades. Furthermore, the injection drives the liquid droplets away from the solid boundaries, which is also expected to reduce the possible mechanical damages to the blades and the casings of turbine.

Prediction of the windage heating effect in steam turbine labyrinth seals

Abstract Today’s steam turbine power plants are designed for highest steam inlet temperatures up to 620°C to maximize thermal efficiency. This leads to elevated thermal stresses in rotors and casings of the turbines. Hence, temperature distributions of the components have to be predicted with highest accuracy at various load points in the design process to assure reliable operation and long life time. This paper describes the windage heating effect in full labyrinth seals used in steam turbines. An analytical approach is presented, based on CFD simulations, to predict the resulting steam temperatures. A broad application range from very low to highest Reynolds numbers representing different turbine operation conditions from partial to full load is addressed. The effect of varying Reynolds number on the flow friction behaviour is captured by using an analogy to the flow over a flat plate. Additionally, the impact of different labyrinth geometries on the friction coefficient is evaluated with the help of more than 100 CFD simulations. A meta-model is derived from the numerical results. Finally, the analytical windage heating model is validated against measurements. The presented approach is a fast and reliable method to find the best performing labyrinth geometries with lowest windage effects, i.e. lowest steam temperatures.

Modeling of intensified glycerol steam reforming in a heat-exchange integrated microchannel reactor

The aim of this study is to investigate glycerol steam reforming in a heat exchange integrated microchannel reactor involving solid wall separated, rectangular-shaped, parallel reaction and heating channels by means of mathematical modeling techniques. Heat needed for endothermic glycerol steam reforming taking place in Co-Ni/Al2O3 coated channels is supplied by steam flowing in the adjacent channels separated by solid walls. Simultaneous catalytic reaction and heat exchange within the microchannel reactor are modeled by 2D Navier-Stokes equations which were solved by the finite volume method in ANSYS 16.0 platform to study the effects of operational parameters, namely molar inlet steam-to-carbon ratio (S/C) and temperature of the reactive mixture, inlet temperature and velocity of steam, flow configurations of the reactive mixture and steam, and of structural parameters, i.e. reactor wall material and thickness of the wall between the reaction and heating channels on temperature distribution and on glycerol conversion. The results show that increasing S/C from 1 to 6 promotes H2 and CO2 selectivity, having average values of 64.7% and 21.2%, respectively. The same effect, however, suppresses CO selectivity from 12.8% to 10.8% and resulted in CH4 selectivity below 2.7%. Product distribution is found to be in alignment with those of experimental studies reported in the literature. Heating by steam has an obvious contribution to glycerol conversion, which is found to be 73.3% and 63.8% in the presence and absence of steam heating, respectively. Counter- and co-current flow of steam with respect to reactive mixture, however, do not lead to a notable difference in conversion. Increasing steam inlet temperature from 663K to 783K improved conversion by 10.0%, whereas changing steam inlet velocity from 2 to 8m/s did not change reforming channel temperature significantly. Reactor performance is significantly affected by increasing feed temperature of the reactive mixture from 673K to 773K which improved conversion by 11.7%. Higher glycerol conversions are also obtained by using thicker separating walls and thermally conductive wall materials, both of which favor heat flux into the reforming channel. Changing the wall thickness from 4×10−4m to 1.2×10−3m elevates conversion by 1.3%. A similar response is noted upon using silicon carbide instead of AISI steel as the material of construction of the microchannel reactor. In general, selectivity towards H2 is positively correlated with the degree of uniformity of reaction channel temperature, which is also found to dampen undesired CH4 selectivity.

Online optimal control schemes of inlet steam temperature during startup of steam turbines considering low cycle fatigue

Great thermal stresses and fatigue damages will be developed during the startup of steam turbines, which will threaten the safety of operation. To save energy and improve the flexibility of the power unit, inlet steam temperature of steam turbines should be controlled online in an optimal way. A new method to obtain online optimal control schemes of the inlet steam temperature considering low cycle fatigue is presented in this paper using the Green's Function Method and the Pontryagin's Maximum Principle. New analytical models of temperature and thermal stresses are proposed. For a hot startup, constant material properties are used and the steam temperature history that can maintain maximum Von Mises stress close to the permitted value is proved to be the optimal control scheme. For a cold or warm startup, the optimization thermal stress considering temperature dependent material properties is found to be determinated by material properties and Green's functions, which may not be equal to the maximum permitted value. Application of the proposed method to the cold start-up process of a 600 MW steam turbine is introduced. Compared with the conventional start-up scheduling, the proposed optimal control scheme can shorten the time of startup greatly without exceeding permitted fatigue damage.

ANALISIS KINERJA TURBIN UAP BERDASARKAN PERFORMANCE TEST PLTU PT. INDOCEMENT P-12 TARJUN

This study aims to determine the performance of steam turbine PT. Indocement Tarjun Plant 12 by comparing the results of data obtained during each performance test in 1999, 2016, 2017, and 2018. This research data is taken from the control room of PT. Indocement Tarjun, variable data obtained in the form of load, main inlet steam temperature, main inlet steam pressure, HP heater feed outlet temperature, HP heater feed outlet pressure, main steam flow, and turbine by pass flow. The data is processed to get the turbine heat rate and the efficiency per time of each performance test and then averaging the data results over time, then comparing the turbine heat rate and the average efficiency of each performance test. The calculation of turbine heat rate using heat & mass balance method, turbine efficiency is obtained by comparing the energy of 1 kW with turbine heat rate and multiplying 100%. The result of the average heat turbine calculation per performance test ie August 1999 is 2.546, April 2016 2,537, June 2017 2.56, and May 2018 2.67. The average value of turbine efficiency in August 1999 was 39.30%, April 2016 39.43%, June 2017 39.07%, May 2018 37.46%. Turbine power plant performance of PT Indocement Tarjun Plant 12 decreased from 1999 to 2018 by 1.84%.

Optimization of a Turbine Used in Coal Fired Thermal Power Plants Based on Inlet Steam Temperature Using Thermoeconomics

The purpose of current study is to analyze the effect of inlet steam temperature coming from the boiler on thermoeconomic performance of a steam turbine used in a coal fired thermal power plant. Second law of thermodynamics is used to develop the thermoeconomic model for the turbine. Analyses based on exergetic and exergoeconomic criteria are done for the turbine used in a 210 MW power plant. Methodology is explained with the help of an example. Effect of inlet steam temperature on the exergetic efficiency of the turbine, unit product cost of turbine and unit product boiler has been shown. Optimization has been done for the turbine as a trade off between the unit product cost of inlet steam from the boiler and unit product cost of the turbine.

Prediction-based feedforward control of superheated steam temperature of a power plant

Abstract A novel feedforward-feedback control scheme for superheater steam temperature in accordance with industrial requirements is proposed. The novelty lies in the design of the feedforward compensator (FFC), of which the performance relies on accurately predicting the values of disturbance variables. The heat influx from the flue gas and the superheater inlet steam temperature were identified as two major disturbances, in addition to the change in the power load. Two FFCs were designed to accommodate the individual disturbances. Because the flue gas state is difficult to measure, the superheater pipe temperature was chosen as a new variable to represent the flue gas state and estimated using steam temperature measurements. Both FFCs computed the feedforward inputs based on the predicted values of the disturbance variables. The prediction accuracies of the FFCs were assessed separately using field-test data, and the performance of the resulting feedforward-feedback controller was investigated through numerical simulations. As a consequence, the IAE (integrated absolute error) under the proposed control scheme was observed to be decreased by 25–38% for three load change scenarios compared to that under the existing feedback controller.

Cascaded energy plant using ammonia absorption refrigeration system for combined cooling and heating applications

A cascaded energy plant for the pharmaceutical industry has been developed and implemented to generate chilled water at 7°C and hot water at 58°C for the required applications using ammonia absorption refrigeration system making use of low-grade thermal energy, such as steam. The internal heat recovery (Qihr) of an ammonia–water absorption refrigeration system was improved with additional components. The additional components, such as a generator heat exchanger and solution cooled rectifier, significantly improved the system performance compared to the systems using only conventional components (evaporator, generator, condenser, absorber, solution heat exchanger, and economizer). In addition to the conventional components, the condensate cooler has been added to the system for condensate heat recovery. The system delivers the cooling and heating coefficients of performance of 0.6 and 1.53, respectively, for the tested conditions with a steam inlet temperature of 147°C, cooling process water inlet temperature of 30°C, and chilled water inlet temperature of 15°C. The developed system delivers 300–430 kW of cooling load and 700–1100 kW of heating load, depending on the cooling load of the plant requirement since installation.

Performance Modeling of New and Existing Steam Turbines

This work investigates the effect of structural parameters (turbine size and type) and operating parameters (inlet steam temperature and pressure, steam flow rate, single or multistage exhaust rate, and pressures) on turbine performance for power generation. The paper extends the steam turbine performance model based on the Willans line. The model achieves high accuracy for a wide range of steam turbines at full-load and part-load operation, which has been verified against data for commercial turbines and from the available literature. The correlation of turbine efficiencies provides realistic insights from the model. The model can be applied in utility system design, operational optimization, and system retrofit with complex multistage turbines. For existing turbines, adjustment of operating conditions and steam header conditions can be explored. This overcomes problems from previous correlations, which did not account for changes in steam main pressures. Regression of coefficients from existing turbine operating data can be used to give better performance prediction for existing turbines, allowing more effective system optimization.

Superheated Steam Regeneration of a Desiccant Wheel—Experimental Results and Comparison with Air Regeneration

A commercial zeolite desiccant wheel is tested with atmospheric pressure superheated steam regeneration over a range of air inlet conditions, steam inlet temperatures, and wheel rotation speeds. Results are compared with those from high-temperature air regeneration experiments on the same wheel obtained from the literature. For both cases the air stream to be dried was relatively hot and moist with inlet temperature and absolute humidity values of 50°C and 25 g · kg−1 chosen to reduce heat carryover. Using steam at 160°C to regenerate the wheel leads to the same dehumidification as using hot air at approximately 90°C. The benefit of superheated steam drying is that a nearly closed-loop regeneration process can be used with potential energy savings on the order of 30%.

Simulation-Based Study of a Novel Integration: Geothermal–Biomass Power Plant

This work investigates the potential to integrate a biomass combustor with an existing geothermal power plant. The motivation is to identify the most cost-effective approach to boost the geothermal turbine power output using heat from the biomass combustor to superheat the geothermal steam upstream of the turbine inlet. Different alternative integration configurations were identified and simulated using Aspen Plus software to evaluate their performance in terms of incremental power output and efficiency. Of the three different alternatives proposed, only one of them looked promising—this configuration uses the saturated well-steam for partial preheating of the combustion air. The most promising integration options are compared on the basis of their levelized cost of electricity. The key conclusion is that one should use low-grade heat for low-level heating (well-steam for air preheating) and high-grade heat from the flue gas for steam superheating. Also, the quantity and quality of biomass available dictate the hybrid configuration selected. A proper design of the steam turbine (higher efficiency at higher steam inlet temperatures) is also necessary to enhance the performance of the hybrid geothermal–biomass power plant.

Existence form of boron in dissimilar weld metals of low-alloy steel with boron-bearing high-chromium steel during post-weld heat treatment†

Recently, higher steam inlet temperature and pressure has been required for fossil power plants in order to increase the power generation efficiency. Therefore, boron-bearing high-chromium (high-Cr) steels with higher long-term creep strength are applied to structure materials in these plants. Dissimilar (metal) weld joints between a boron-bearing high-Cr steel and a low-alloy steel are applied for various parts of boilers and other equipment in the plants. Caution has to be paid to maintain the quality of these weld joints because boron is diffused to the low-alloy steel weld deposits by dilution from the boron-bearing high-Cr base metal. However, the existing form of boron and the effect of boron on reheat cracking susceptibility during post-weld heat treatment (PWHT) have not been surveyed in the previous literature. Therefore, using Cr–Mo low-alloy steels with varied contents of B and Cr, reheat cracking susceptibility of the weld metal was evaluated, and the precipitation behaviour of the carbides during PWHT was observed. From these results, the existing form of boron in boron-bearing Cr–Mo steel weld metals is discussed in this study. Reheat cracking susceptibility clearly increased with boron addition, whereas it decreased with increasing chromium content. It was shown by thermo-dynamic calculation that possible existing forms of boron were of four types, namely BN, M2B, M23(C, B)6 and dissolved boron. The amount of M23C6-type carbides was increased with increasing chromium content. On the basis of these results, it was presumed that the amount of dissolved boron in boron-bearing low-chromium steel weld metals was larger than in those with high-Cr. It was suggested that the larger amount of dissolved boron enhanced the strength difference between the matrix and the grain boundary in low-chromium steels, hence it led to higher susceptibility to reheat cracking.

Thermal analysis of heat transfer performance in a horizontal tube bundle

The thermal analysis is demonstrated for the case where steam is condensing inside a horizontal tube bundle, while simultaneously thin water films are evaporating outside the tubes generating vapor that flows across the tubes. Three experiments are carried out each coming up with a valid model to predict the impact of the corresponding parameters on the heat transfer performance or flow characteristics. Then, a collective two-dimensional model is established according to the models from those experiments to simulate the thermal and hydrodynamic performance of the evaporator. This model consists of three parts corresponding to the three models obtained from the experiments mentioned above: the water film evaporation model, the inside-tube steam model, and the intertube vapor model. The operating conditions include the water mass rate, saturation temperatures, and overall temperature difference. Calculations are carried out for water mass rate between 0.03 and 0.09 kg/m s, inlet steam temperature between 53 and 73°C, and overall temperature difference between 1.5 and 4°C. Results of the analysis show that the overall heat transfer coefficient and vapor temperatures have uneven distributions within the tube bundle. The variation of vapor temperature affects the distribution of heat transfer rate and the steam inlet velocity. The utilizations of the initial temperature difference with the change of tube bundle column numbers are also analyzed. It shows that the more column numbers the tube bundle includes, the more heat transfer area will lose a certain amount of initial temperature difference.

Experimental study of the effects of temperature variation on droplet size and wetness fraction in a low-pressure model steam turbine

The three-stage low-pressure model steam turbine at the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) was used to study the impact of three different steam inlet temperatures on the homogeneous condensation process and the resulting wetness topology. The droplet spectrum as well as the particle number concentration were measured in front of the last stage using an optical-pneumatic probe. At design load, condensation starts inside the stator of the second stage. A change in the steam inlet temperature is able to shift the location of condensation onset within the blade row up- or downstream and even into adjoining blade passages, which leads to significantly different local droplet sizes and wetness fractions due to different local expansion rates. The measured results are compared to steady three-dimensional computational fluid dynamics calculations. The predicted nucleation zones could be largely confirmed by the measurements. Although the trend of measured and calculated droplet size across the span is satisfactory, there are considerable differences between the measured and computed droplet spectrum and wetness fractions.

Identification of thermal boundary conditions in heat exchangers of fluidized bed boilers

A CFD simulation was carried out for the platen superheater placed in the combustion chamber of the CFB boiler. Velocity, pressure, and temperature of the steam as well as the temperature of the tube wall with the complex cross section were computed using the ANSYS/CFX software. The direct and inverse problems were solved. In the first inverse problem, the heat transfer coefficient on the flue gas side was determined based on the measured steam temperature at the inlet and outlet of the three pass steam superheater. In the second inverse problem, the inlet steam temperature and the heat transfer coefficient on the flue gas side were estimated using measured steam temperatures at selected locations of the superheater. The first inverse problem was solved iteratively using the secant method. The Levenberg-Marquardt method was used to solve the second inverse problem. At every iteration step, a direct conjugate heat transfer problem was solved using the ANSYS/CFX software.