Constant Pressure Operation Research Articles

The critical electric field of gas mixtures over the extended range of cryogenic operating conditions

In this study, we provide the critical electric field and dielectric strength of cryogenic gas mixtures over an extended cryogenic temperature and pressure range that covers most of the operating conditions of superconducting applications. For gas-cooled cryogenic systems, condensation must not occur during operation. To prevent condensation, we determine the maximum allowed mole fractions of gas species consisting cryogenic gas mixtures by accounting for the operating conditions of cryogenic applications. Subsequently, we estimate the dielectric strength of the gas mixtures in terms of the density-reduced critical electric field ((E/N)cr), obtained by solving the Boltzmann equation with the two-term approximation method. Using the values of (E/N)cr, we calculate the critical electric field (Ecr) over the extended cryogenic operation range of 10–100 K at pressures between 1.0 and 2.0 MPa. The results show that the dielectric strength of cryogenic gas mixtures varies as a function of temperature at a constant operating pressure and reaches its minimum at the condensation point of each gas mixture. The results also suggest that (E/N)cr cannot accurately represent the maximum achievable dielectric strength of a gas mixture unless the maximum allowed mole fractions of gas species have been taken into account. Hence, we discuss (E/N)cr values that are derived from the regulated concentration of gas constituents, which will prevent the components of gas mixtures from condensing. This study provides useful recommendations on the suitability of the gas mixtures and useful reference data for the dielectric design of superconducting and cryogenic applications.

Degradation mitigation effects of pressure swing in proton exchange membrane fuel cells with dead-ended anode

Abstract High cost remains to be one of the primary obstacles for the commercialization of proton exchange membrane fuel cells (PEMFCs). To simplify the fuel cell system and reduce cost, dead-ended anode (DEA) is widely used. However, water and nitrogen can accumulate in the dead-ended anode, resulting in cell performance decrease and severe cell degradation. Anode pressure swing supply is a new technology which has been shown to be effective in reducing local water and nitrogen accumulation in the anode channel. In this work, the effects of pressure swing supply on fuel cell degradation have been experimentally studied. Two sets of experiments on the same fuel cell are conducted, one under conventional constant pressure operation and the other under pressure swing operation. Polarization curves show that pressure swing supply can significantly mitigate cell degradation during DEA operations. Electrochemical characterizations are performed to study the mechanisms of mitigations in cell degradation. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results show that pressure swing supply can significantly reduce electrolyte membrane degradation, but has no significant mitigation effect on the cathode catalyst degradation during DEA operation. Further examinations of the membrane-electrode-assembly (MEA) by scanning electron microscope (SEM) confirm the significant difference in membrane degradations since there is a very large difference in average thickness of the membranes after the degradation tests.

Predicting performance of constant flow depth filtration using constant pressure filtration data

Abstract This paper describes a method of predicting constant flow filtration capacities using constant pressure datasets collected during the purification of several monoclonal antibodies through depth filtration. The method required characterisation of the fouling mechanism occurring in constant pressure filtration processes by evaluating the best fit of each of the classic and combined theoretical fouling models. The optimised coefficients of the various models were correlated with the corresponding capacities achieved during constant flow operation at the specific pressures performed during constant pressure operation for each centrate. Of the classic and combined fouling models investigated, the Cake-Adsorption fouling model was found to best describe the fouling mechanisms observed for each centrate at the various different pressures investigated. A linear regression model was generated with these coefficients and was shown to predict accurately the capacities at constant flow operation at each pressure. This model was subsequently validated using an additional centrate and accurately predicted the constant flow capacities at three different pressures (0.69, 1.03 and 1.38 bar). The model used the optimised Cake-Adsorption model coefficients that best described the flux decline during constant pressure operation. The proposed method of predicting depth filtration performance proved to be faster than the traditional approach whilst requiring significantly less material, making it particularly attractive for early process development activities.

Comparative analysis on off-design performance of a gas turbine and ORC combined cycle under different operation approaches

Abstract This paper presents a comparative analysis on the off-design performance of a gas turbine and organic Rankine cycle (GT-ORC) combined cycle under different operation approaches. A new solving procedure for off-design performance evaluation of the GT-ORC combined cycle was proposed and optimal design parameters for this GT-ORC combined cycle were given. Then simulations were conducted based on the mathematical model and assumptions. The inlet guide vane (IGV) control was applied to regulate the topping GT cycle. Results showed that the sliding pressure operation had an optimal sliding condition to make the GT-ORC combined cycle have the best off-design performance. This condition was a fixed superheat degree of 0.1 K for organic vapor, and the operation approach under such condition was named modified sliding pressure operation (MSPO). Simulation results showed the MSPO performed better than the constant pressure operation and bivariate operation under off-design conditions. Therefore, the MSPO might be more suitable for the off-design operation of the GT-ORC combined cycle. Finally, the sensitivity analysis indicated that the MSPO was more favorable for the GT-ORC combined cycle to reduce the influence of ambient temperature.

Nanostructured mesoporous carbon polyethersulfone composite ultrafiltration membrane with significantly low protein adsorption and bacterial adhesion

Abstract A novel polyethersulfone (PES) ultrafiltration membrane containing 0.05–2.00 wt% of synthesized mesoporous carbon nanoparticles (MCNs) was prepared via the phase inversion technique. The structures and properties of MCNs were characterized using a variety of analytic techniques. The MCNs showed the surface area of 1396.8 m2/g and the highest pore size of around 1 nm. The effect of incorporation of MCNs on the composite membrane morphology and performance was investigated through pure water flux, protein adsorption, and bacterial adhesion resistance tests. The membrane's anti-fouling performances were determined under constant-pressure operation at 100 kPa in a dead-end module. The as-prepared nanocomposite membranes were also studied in terms of morphology, structure and surface chemistry. Generally, the incorporation of MCNs into the polymeric membrane improved the pure water flux. The composite membrane containing 0.20 wt% MCNs exhibited the highest antifouling, protein adsorption resistance, and bacterial attachment inhibition property. The incorporation of the MCNs into the membranes introduces a different strategy of inhibiting biomolecule adsorption and bacterial attachment to the membrane surface, instead of killing the bacteria which may lead to more severe membrane fouling by the intracellular substances.

A Feasibility Study on Adopting Sliding Pressure Operation for Drum Type Boiler

In general, drum-type boilers are designed for base load duty and applied under constant pressure operation mode. Recently, however conditions often occur that even drum-type boilers have to operate at partial load conditions. A feasibility study on adopting the sliding pressure operation for drum-type boiler was conducted, and corresponding performance changes and effects on the equipment were analyzed by utilizing a process simulation model. As a result, the conclusion was reached that drum type boilers are able to adopt the sliding pressure operation and can improve of net efficiency at part load operation in spite of the Rankine cycle efficiency reduction due to the decreases in main steam pressure. Because of thank to improvement of high pressure turbine stage-1 internal efficiency and power savings of boiler feed water pump. The sliding pressure operation is advantageous in terms of stress level relief for boiler tube as well as maintaining the rating steam temperature at part load condition. However, cautions are required because the drum boilers have poor dynamic response characteristics which may get worse during the sliding pressure operation.

Oil refinery hazardous effluents minimization by membrane filtration: An on-site pilot plant study

Experiments for treating two different types of hazardous oil refinery effluents were performed in order to avoid/minimize their adverse impacts on the environment. First, refinery wastewater was subjected to ultrafiltration using a ceramic membrane, treatment, which did not provide an adequate reduction of the polar oil and grease content below the maximal contaminant level allowed. Therefore the option of reducing the polar oil and grease contamination at its main emission source point in the refinery - the spent caustic originating from the refinery kerosene caustic washing unit - using an alkaline-resistant nanofiltration polymeric membrane treatment was tested. It was found that at a constant operating pressure and temperature, 99.9% of the oil and grease and 97.7% of the COD content were rejected at this emission point. Moreover, no noticeable membrane fouling or permeate flux decrease were registered until a spent caustic volume concentration factor of 3. These results allow for a reuse of the purified permeate in the refinery operations, instead of a fresh caustic solution, which besides the improved safety and environmentally related benefits, can result in significant savings of 1.5M€ per year at the current prices for the biggest Portuguese oil refinery. The capital investment needed for nanofiltration treatment of the spent caustic is estimated to be less than 10% of that associated with the conventional wet air oxidation treatment of the spent caustic that is greater than 9M€. The payback period was estimated to be 1.1 years. The operating costs for the two treatment options are similar, but the reuse of the nanofiltration spent caustic concentrate for refinery pH control applications can further reduce the operating expenditures. Overall, the pilot plant results obtained and the process economics evaluation data indicate a safer, environmentally friendly and highly competitive solution offered by the proposed nanofiltration treatment, thus representing a promising alternative to the use of conventional spent caustic treatment units.

Operational flexibility options in power plants with integrated post-combustion capture

Abstract Flexibility in power plants with amine based carbon dioxide (CO2) capture is widely recognised as a way of improving power plant revenues. Despite the prior art, its value as a way to improve power plant revenues is still unclear. Most studies are based on simplifying assumptions about the capabilities of power plants to operate at part load and to regenerate additional solvent after interim storage of solvent. This work addresses this gap by examining the operational flexibility of supercritical coal power plants with amine based CO2 capture, using a rigorous fully integrated model. The part-load performance with capture and with additional solvent regeneration, of two coal-fired supercritical power plant configurations designed for base load operation with capture, and with the ability to fully bypass capture, is reported. With advanced integration options configuration, including boiler sliding pressure control, uncontrolled steam extraction with a floating crossover pressure, constant stripper pressure operation and compressor inlet guide vanes, a significant reduction of the electricity output penalty at part load is observed. For instance at 50% fuel input and 90% capture, the electricity output penalty reduces from 458 kWh/tCO2 (with conventional integration options) to 345 kWh/tCO2 (with advanced integration options), compared to a reduction from 361 kWh/tCO2 to 342 kWh/tCO2 at 100% fuel input and 90% capture. However, advanced integration options allow for additional solvent regeneration to a lower magnitude than conventional integration options. The latter can maintain CO2 flow export within 10% of maximum flow across 30–78% of MCR (maximum continuous rating). For this configuration, one hour of interim solvent storage at 100% MCR is evaluated to be optimally regenerated in 4 h at 55% MCR, and 3 h at 30% MCR, providing rigorously validated useful guidelines for the increasing number of techno-economic studies on power plant flexibility, and CO2 flow profiles for further studies on integrated CO2 networks.

Analysis of co-generation combustion chamber inlet line

Purpose The catastrophic failures of these thick-wall cylinders are mainly due to the presence of inherent cracks in the material. The present study aims to deal with the analysis of stress for a given range of inside pressure. The paper deals with the calculation of radial and tangential stresses for various external pressure-to-internal pressure ratios and external radius to internal radius of the thick-walled cylinder. Design/methodology/approach The inlet line to the combustion chamber normally has an internal diameter of 150 mm and has a thickness of 25 mm. Normal temperature of the working fluid is about 80°C and the outside temperature is kept as room temperature. The present work deals with the stress analysis of the inlet line with and without internal crack. Also the stress intensity factors are calculated to check with the fracture toughness. Analysis is done both theoretically and by FEM by using the well-known software ANSYS. Findings Results show that the radial stress is independent of the external radius-to-internal radius ratio, while the tangential stress increases. Practical implications In process industries like nuclear or chemical, etc., structures in the form of thick-walled cylinders play a vital role, as its failure can affect humans and the environment. Because of this, the design and analysis of the above cylinders are of much significance. Originality/value Due to constant or cyclic operating pressure of pressure vessels and its corresponding pipelines usually in the form of thick-walled cylinders, reliability of the materials and structures used is of critical importance, as its failure can be deadly and possess lethal dangers when the cylinder contains flammable, toxic or reactive working fluid. The major ruling factors for the failure are none other than stress-related defects and presence of cracks.

Comparison of energy efficiencies of a small centrifugal pump at constant and variable speed operations

The objective of this study was to compare the energy efficiencies of flow rate valves used in different lines and variable speed drive (VSD) in a small centrifugal pump irrigation system. The tests were done by using an outlet valve, inlet valve, by-pass valve, and VSD. The study included four replications of constant speed and variable speed experiments, and three replications of constant pressure experiments. In each test, power consumption, inlet pressure, and outlet pressure were measured at different flow rates. During the constant speed tests at about the operating point, by-pass valve saved energy up to 66% and 5% compared to the outlet valve and inlet valve, respectively. Reducing the flow rate by 20% resulted in 7% less energy consumption with the use of both the by-pass valve and the inlet valve, and 19% more energy consumption with the outlet valve. The use of VSD showed profound advantage over the valves used in constant speed tests, with 41%, 44%, and 80% less energy demand compared to the by-pass, inlet, and outlet valve, respectively. Also, VSD and by-pass valves were compared in constant pressure operations. VSD offered 2 to 37% less energy consumption at pressures from 4.0 bar to 2.5 bar. The savings were less at high flow rates and quickly increased as the flow rate need decreased. The low system efficiency found in constant speed tests suggested that the pump was not appropriate for the hydraulic system used in low pressure applications. According to constant pressure tests, the system efficiency for VSD (26-29.1%) was greater than that of the by-pass valve (21.3-25.5%). In conclusion, the VSD was the most energy efficient method and suggested significant energy savings in small powered pump systems.

An Iterative Method to Derive the Equivalent Centrifugal Compressor Performance at Various Operating Conditions: Part I: Modelling of Suction Parameters Impact

This paper introduces a new iterative method to predict the equivalent centrifugal compressor performance at various operating conditions. The presented theoretical analysis and empirical correlations provide a novel approach to derive the entire compressor map corresponding to various suction conditions without a prior knowledge of the detailed geometry. The efficiency model was derived to reflect the impact of physical gas properties, Mach number, and flow and work coefficients. One of the main features of the developed technique is the fact that it considers the variation in the gas properties and stage efficiency which makes it appropriate with hydrocarbons. This method has been tested to predict the performance of two multistage centrifugal compressors and the estimated characteristics are compared with the measured data. The carried comparison revealed a good matching with the actual values, including the stable operation region limits. Furthermore, an optimization study was conducted to investigate the influences of suction conditions on the stage efficiency and surge margin. Moreover, a new sort of presentation has been generated to obtain the equivalent performance characteristics for a constant discharge pressure operation at variable suction pressure and temperature working conditions. A further validation is included in part two of this study in order to evaluate the prediction capability of the derived model at various gas compositions.

Off-design performance comparison of an organic Rankine cycle under different control strategies

Abstract This paper presents the off-design performance analysis of an organic Rankine cycle system in the view of control strategies. Variable inlet guide vanes and evaporating pressure are considered as control variables to adapt the system to the variable geothermal fluid mass flow rate and temperature. The optimal control strategy is studied to maximize the net power under the given geothermal source conditions. The constant pressure operation, the sliding pressure operation and the optimal control strategy are compared in order to analyze their differences. The results indicate that the constant pressure operation with variable inlet guide vanes generates more net power than the sliding pressure operation when the geothermal fluid mass flow rate is relative low. The optimal control strategy is determined by the off-design performance of evaporator and turbine. With fixed geothermal fluid temperature and variable geothermal fluid mass flow rate, the potential increase of the net power under the optimal operation can reach 4.7% and 11.0% for the constant and sliding pressure operation, respectively. When the geothermal fluid temperature decreases, the curve of net power tends to shift to the direction of larger geothermal fluid mass flow rate in all control strategies.

Effect of Spray Cone Angle on Flame Stability in an Annular Gas Turbine Combustor

AbstractEffect of fuel spray cone angle in an aerogas turbine combustor has been studied using computational fluid dynamics (CFD) and full-scale combustor testing. For CFD analysis, a 22.5° sector of an annular combustor is modeled and the governing equations are solved using the eddy dissipation combustion model in ANSYS CFX computational package. The analysis has been carried out at 125 kPa and 303 K inlet conditions for spray cone angles from 60° to 140°. The lean blowout limits are established by studying the behavior of combustion zone during transient engine operation from an initial steady-state condition. The computational study has been followed by testing the practical full-scale annular combustor in an aerothermal test facility. The experimental result is in a good agreement with the computational predictions. The lean blowout fuel–air ratio increases as the spray cone angle is decreased at constant operating pressure and temperature. At higher spray cone angle, the flame and high-temperature zone moves upstream close to atomizer face and a uniform flame is sustained over a wide region causing better flame stability.

In situ investigation of combined organic and colloidal fouling for nanofiltration membrane using ultrasonic time domain reflectometry

Abstract Ultrasonic time domain reflectometry (UTDR) was used to monitor the deposition of combined organic–colloidal fouling on a nanofiltration membrane. The fouling experiments were performed with different feed solutions: a mixture of 1000 mg/L silica and 1000 mg/L NaCl, a mixture of 1000 mg/L silica and 250 mg/L BSA, and 250 mg/L BSA alone, respectively. Results showed that the rate of flux decline obtained in the constant-pressure experiment with the mixture of silica + BSA was greater than that with the mixture of silica + NaCl and BSA alone. The acoustic measurements indicated that the fouling layer obtained from the combined organic–colloidal fouling was denser than that obtained from the colloidal fouling layer in the presence of NaCl. Furthermore, the mixed foulants rapidly deposited on the membrane surface in the early fouling phase, and then reached a plateau in the later fouling phase under a constant pressure operation, whereas the mixed foulants gradually deposited on the membrane surface as the fouling progressed under a constant flux operation. The main reason for the rapid foulant deposition during the initial fouling stage under constant pressure operation was because the initial flux was above the critical flux. The off-line AFM analysis and zeta potential measurements corroborated the ultrasonic measurements.

Energy and exergy analysis of a super critical thermal power plant at various load conditions under constant and pure sliding pressure operation

Abstract The objective of this paper is to perform an energetic and exergetic analysis on a 660 MWe coal fired supercritical thermal power plant at 100%, 80% and 60% of normal continuous rating (NCR) conditions under constant pressure as well as pure sliding pressure operation and to highlight the benefits of the latter over the former. The energetic input, energetic output, exergetic input, exergetic output, energetic and exergetic efficiencies of various components of the supercritical thermal power plant are estimated at 660 MWe, 528 MWe and 396 MWe load under both constant pressure as well as pure sliding pressure operation. Also the energy losses and exergy destruction in various components of a power plant i.e. Boiler, high pressure turbine (HPT), intermediate pressure turbine (IPT), low pressure turbine (LPT), condenser, gland steam coolers, condensate extraction pumps, low pressure heaters (LPH), drip pumps (DP), deaerator (D), boiler feed pump (BFP) and high pressure heaters (HPH) have been calculated. The results have shown that the boiler has the maximum rate of exergy destruction than any other component in the power plant. After the boiler, turbine has the maximum rate of exergy destruction than any other component of the power plant. The study reveals that there is a significant reduction in the rate of exergy destruction at part load conditions for the turbine in case of sliding pressure operation in comparison to constant pressure operation. The rate of exergy destruction in the turbine at 100%, 80% and 60% of NCR conditions is 49.16 MW/43.22 MW/43.92 MW for constant pressure operation and 47.66 MW/37.88 MW/28.94 MW respectively. The BFP power input reduces by 9.39%, 21.52% and 42.5% respectively at 100%, 80% and 60% of NCR conditions if the unit runs in sliding pressure mode compared to constant pressure mode.

Volume based vs. time based chromatograms: Reproducibility of data for gradient separations under high and low pressure conditions

A critical aspect in fast gradient separations carried out under constant pressure, in the very high pressure liquid chromatography (VHPLC) mode is that time-based chromatograms may not yield highly reproducible separations. A proposed solution to improve the reproducibility of these separations involves plotting the chromatograms as functions of the volume eluted vs. UV absorbance instead of time vs. UV. To study the consequences of using the volume-based rather than the time-based chromatograms, separations were first performed under low pressures that do not generate significant amounts of heat and for which the variations of the eluent density along the columns are negligible. Secondly, they were performed under very high pressures that do generate heat and measurable variations of the local retention factor and eluent density along the column. Comparison of the results provides estimates of the improvements obtained when volume based chromatograms are used in gradient analyses. Using a column packed with fully porous particles, four different types of methods and several sets for each method were used to perform the gradient elution runs: two sets of constant flow rate operations, four sets of constant pressure operations, two sets of constant pressure operations with programmed flow rate, and one set using the constant heat loss approach. The differences between time-based and volume-based chromatograms are demonstrated by using eight replicates of early, middle, and last eluting peaks. The results show that volume-based chromatograms improve the retention time reproducibility of the four constant pressure methods by a factor of 3.7 on average. If the column is not thermally conditioned prior to performing a long series of separations, flow controlled methods (constant flow rate, programmed constant pressure, and constant wall heat approaches) are more precise. If one gradient run is used to bring the column to a relatively stable temperature, constant pressure separations have a factor of 3 times better reproducibility of retention times with respect to constant flow rate gradient separations.

Very high pressure liquid chromatography using core-shell particles: Quantitative analysis of fast gradient separations without post-run times

Five methods for controlling the mobile phase flow rate for gradient elution analyses using very high pressure liquid chromatography (VHPLC) were tested to determine thermal stability of the column during rapid gradient separations. To obtain rapid separations, instruments are operated at high flow rates and high inlet pressure leading to uneven thermal effects across columns and additional time needed to restore thermal equilibrium between successive analyses. The purpose of this study is to investigate means to minimize thermal instability and obtain reliable results by measuring the reproducibility of the results of six replicate gradient separations of a nine component RPLC standard mixture under various experimental conditions with no post-run times. Gradient separations under different conditions were performed: constant flow rates, two sets of constant pressure operation, programmed flow constant pressure operation, and conditions which theoretically should yield a constant net heat loss at the column's wall. The results show that using constant flow rates, programmed flow constant pressures, and constant heat loss at the column's wall all provide reproducible separations. However, performing separations using a high constant pressure with programmed flow reduces the analysis time by 16% compared to constant flow rate methods. For the constant flow rate, programmed flow constant pressure, and constant wall heat experiments no equilibration time (post-run time) was required to obtain highly reproducible data.

Very high pressure liquid chromatography using fully porous particles: Quantitative analysis of fast gradient separations without post-run times

Using a column packed with fully porous particles, four methods for controlling the flow rates at which gradient elution runs are conducted in very high pressure liquid chromatography (VHPLC) were tested to determine whether reproducible thermal conditions could be achieved, such that subsequent analyses would proceed at nearly the same initial temperature. In VHPLC high flow rates are achieved, producing fast analyses but requiring high inlet pressures. The combination of high flow rates and high inlet pressures generates local heat, leading to temperature changes in the column. Usually in this case a post-run time is input into the analytical method to allow the return of the column temperature to its initial state. An alternative strategy involves operating the column without a post-run equilibration period and maintaining constant temperature variations for subsequent analysis after conducting one or a few separations to bring the column to a reproducible starting temperature. A liquid chromatography instrument equipped with a pressure controller was used to perform constant pressure and constant flow rate VHPLC separations. Six replicate gradient separations of a nine component mixture consisting of acetophenone, propiophenone, butyrophenone, valerophenone, hexanophenone, heptanophenone, octanophenone, benzophenone, and acetanilide dissolved in water/acetonitrile (65:35, v/v) were performed under various experimental conditions: constant flow rate, two sets of constant pressure, and constant pressure operation with a programmed flow rate. The relative standard deviations of the response factors for all the analytes are lower than 5% across the methods. Programming the flow rate to maintain a fairly constant pressure instead of using instrument controlled constant pressure improves the reproducibility of the retention times by a factor of 5, when plotting the chromatograms in time.

Development and testing of a fully adaptable membrane bioreactor fouling model for a sidestream configuration system.

A dead-end filtration model that includes the three main fouling mechanisms mentioned in Hermia (i.e., cake build-up, complete pore blocking, and pore constriction) and that was based on a constant trans-membrane pressure (TMP) operation was extensively modified so it could be used for a sidestream configuration membrane bioreactor (MBR) situation. Modifications and add-ons to this basic model included: alteration so that it could be used for varying flux and varying TMP operations; inclusion of a backwash mode; it described pore constriction (i.e., irreversible fouling) in relation to the concentration of soluble microbial products (SMP) in the liquor; and, it could be used in a cross flow scenario by the addition of scouring terms in the model formulation. The additional terms in this modified model were checked against an already published model to see if they made sense, physically speaking. Next this modified model was calibrated and validated in Matlab© using data collected by carrying out flux stepping tests on both a pilot sidestream MBR plant, and then a pilot membrane filtration unit. The model fit proved good, especially for the pilot filtration unit data. In conclusion, this model formulation is of the right level of complexity to be used for most practical MBR situations.

Quantum efficiency modeling and system scaling-up analysis of water splitting with Cd1−xZnxS solid-solution photocatalyst

In this paper, a comprehensive study, aimed at the development of a semi-empirical predictive model for quantum efficiency of photolysis systems operating with crystalline photocatalysts and S2−/SO32− electron donors which are widely recognized as having good potential for cost effective solar water splitting, is reported. Efficiency prospects are made and cost goal is determined using the validated model for a scaled-up solar energy conversion system which uses the upper solar spectrum for photocatalysis whereas the middle spectrum is used for PV-electrolysis to generate additional hydrogen. The photochemical system uses an engineered photocatalyst of solid-solution type with general formula Cd1−xZnxS (x=0.21). Photocatalysis experiments are performed in a photoreactor illuminated with monochromatic LEDs of 470 nm (2.64 eV) and the photocatalyst is characterized in order to determine certain fitting parameters of the semi-empirical model and for validation purpose. The crystalline structure of the photocatalyst has been elucidated through X-ray diffraction, its elemental composition by energy-dispersive X-ray analysis, and its band gap has been determined from diffuse spectral reflectance measurements, whereas the morphology has been identified by scanning electron microscopy. The band gap of the catalyst semiconductor is found to be 2.48 eV. The photocatalysis reactor can operate at constant volume and accumulates hydrogen in free space above liquid while pressure increases in time, or hydrogen can be drawn continuously out of gas space while maintaining a constant operating pressure. The molecular diffusion rate of species dissolved in the electrolyte and the relevant mass transport processes at liquid–gas interface where hydrogen diffuses and small bubbles burst out of liquid are also accounted for in the predictive model. The model predictions are satisfactory with 7.1% root mean square error against test data and a maximum hydrogen production rate of ~4.1 mmol/h for 86.4 mmol photons per hour. The void fraction in the electrolyte, caused by the presence of gas bubbles, reaches quickly a maximum of ~7% during constant volume mode simulations and then decreases due to increase of pressure. A plateau value of 8% is observed for void fraction during constant pressure mode simulations with no local maximum. The estimations obtained with the model show that, when integrated with PV-electrolysis, the system production is 6.4 kg H2 per sq.m of solar collector and year. If it is mass produced up to a scale of 14.8 Mt hydrogen per day, then the selling price of hydrogen becomes as low as $2/kg with a payback period of 10 years. The semi-empirical modeling method developed herein can be adapted for other photochemical reactions of similar type and it is considered to be useful for system scaling-up and for engineering design.