Non-condensable Gas Content Research Articles

Performance Evaluation of Geothermal Power Production Using EES (Case Study Ulumbu Geothermal Power Production Unit 4 East Nusa Tenggara, Indonesia)

Ulumbu geothermal working area (GWA) is in Ruteng district, East Nusa Tenggara province, Indonesia. Ulumbu GWA is owned by PLN. There are four geothermal power plants (GPP) in Ulumbu, which capacity 4 x 2.5 MW. It has operated since 2013. Steam used to generate electricity comes from ULB-2 production well. Wellhead temperature and pressure were 180-200°C and 11 bar. Ulumbu GPP Unit 4 uses a condensing type turbine. It has specific steam consumption (SSC) during commissioning around 9.8 T/MW. After 6 (six) years of operation, SSC becomes 10.04 T/MW on average. It gives a chance to perform optimization in the GPP’s equipment. Before performing optimization, evaluation for every equipment based on as-built data is done by modeling using EES software. The method of evaluation is performed by thermodynamics analysis in each GPP’s equipment. EES is chosen due to its simplicity to arrange many equations in a single window. EES could communicatively display calculation results through a parametric table, solution window, and diagram window. Operation data give information that turbine inlet pressure is operated under its specification. Turbine inlet pressure is operated under its specification because of the change of operating wellhead pressure. Non-Condensable Gas (NCG) content also decreases based on the last ULB-2 well fluid sampling. Using EES, parameter changes in turbine inlet pressure and NCG content are simulated to get optimum power generation value. The simulation results indicate that optimum turbine inlet pressure is obtained at 9.3 bar with SSC 9.17 T/MW. Ulumbu GPP Unit 4 that operated in that condition could reach cycle efficiency of about 10.39%.

Heat transfer model based on diffusion layer theory for dropwise condensation with high non-condensable gas

A new heat-transfer model for dropwise condensation with non-condensable gas (NCG) is developed, which can be used in the design and calculations of a dehumidifier in humidification–dehumidification technology. A single-droplet heat-transfer model is established via the rounded analysis of all the contributing thermal resistances based on the diffusion-layer theory. Combined with the drop size distribution, the heat flux of dropwise condensation with NCG is determined, and the error between the predicted results and previous experimental data is found to be within ±20%. The effects of different parameters on the heat transfer of dropwise condensation with NCG are investigated, and the results indicate that there is an optimal contact angle to maximize the heat flux, which depends on the NCG content. The thickness of the coating layer has little effect on the heat flux at a given thermal conductivity of the coating layer, indicating that the dropwise condensation effect can be improved by increasing the thickness of the coating layer, neglecting the heat-transfer deterioration due to the additional thermal resistance during dropwise condensation with NCG.

A pseudo two-phase model to study effects of non-condensable gases on the water autonomy of a direct methanol fuel cell system

In a direct methanol fuel cell (DMFC) system, water at the condenser outlet is recirculated into the mixing chamber where it mixes with pure methanol and anode outlet stream. The selection of condenser design and operating conditions plays a key role in the successful operation of the system with water autonomy. In this study, a novel pseudo two-phase computational fluid dynamics (CFD) model is proposed to investigate the condensation capability of the condenser under the operating conditions of a DMFC system. The condenser model is simplified by implementing an iterative multi-domain approach where continuity at the decoupled domain interfaces is satisfied by the convergence of boundary conditions. The proposed thermofluids model is validated with experimental data. Through the model, the performance of the condenser is investigated for DMFC operating conditions. The results show that the amount of non-condensable gases, the velocity and the saturation level of cathode exhaust gas (CEG) are the key parameters in these scenarios. The highest condensation effectiveness is calculated for the saturated CEG flow scenario with lower velocity and lower content of non-condensable gases, while the lowest condensation effectiveness is calculated as for the under saturated CEG flow scenario. Another important result is that the increment of the amount of the non-condensable gases throughout the downstream distance is found as 4% which results in the decrement of the saturation and film temperature by 8 K and 4 K, respectively. In addition, it is found that when the inlet velocity of CEG decreases from 0.82 m•s-1 to 0.18 m•s-1, the overall condensation rate decreases by 55%.

Numerical study of the biomass pyrolysis process in a spouted bed reactor through computational fluid dynamics

Physical and thermochemical characteristics of biomass pyrolysis in a lab-scale spouted bed reactor are studied by means of a reactive multiphase particle-in-cell approach in which gas and solid motions are respectively resolved under the Eulerian and Lagrangian frameworks. Model validation is first conducted, followed by exploring the reactor hydrodynamics and spatial distributions of gas thermochemical properties. The results show that the preferential distribution of biomass particles at the annulus top affects the distribution pattern of gas thermochemical properties. The vertical flux of solid phase in the spout region is at the scale of 100 kg/(m2s), which is nearly one order of magnitude larger than the horizontal one. The turbulent viscosity of gas phase is at the scale of 10−4 m2/s, and the temperature difference within the apparatus is nearly 100 K. The intensively turbulent flow of gas phase exists in the spout region, which will be enhanced as gas inlet velocity and pyrolysis temperature increase. The preferential distribution of biomass particles gives rise to the large content of non-condensable gas and tar in the primary reaction, low temperature, and large density of gas phase in this region. The large content of non-condensable gas in the secondary reaction exists in the upper part of the bed. The results obtained provide a deep understanding of the hydrodynamics and thermochemical properties of gas-solid flows in spouting apparatuses for biomass pyrolysis.

Features of the Water-Chemical Mode of the I Circuit and Problems of Equipment Operation in the Reactor Units of Atomic Icebreakers

Analysis of the experience gained in operating atomic icebreakers, the specifics of operating equipment of the first circuit, and the organization of the water-chemical regime shows the relationship between the high content of gases in the coolant and the problems of ensuring reliable equipment operation. Spatial modeling of vapor-gas bubbles’ mass transfer in the SG-28 steam generator during damping confirmed the possibility of forming a gas cushion in the stagnant zone of the SG. The abrupt increase in the volumetric content of hydrogen during the transition from the liquid to the gas phase of the water coolant explains the anomalous hydrogenation in the area of weld no. 62 on the tubing of the AO SKBK design steam generators. The multiscale, multiphysical approach to conducting calculations was based on the adaptive use of different calculation codes in accordance with the required degree of analysis detail. Four computational models were developed—a common one based on the Relap5 code and three for the CFD code. An offline scheme of combining codes was used. Within its framework, a consistent decomposition of the general problem into computational domains was carried out; appropriate models for them were used, and organization of information exchange between models was based on the initial and boundary conditions. An analysis of the operating conditions and the nature of the mass transfer of vapor-gas bubbles, taking into account the patterns of their fragmentation, confirms the possibility of their entry into the active zone in transient conditions. The presence of oxygen in vapor-gas bubbles dramatically changes the corrosive environment and can cause the nodular corrosion of zirconium shells. To drastically reduce the content of noncondensable gases in the coolant of the first circuit, it was proposed to study the possibility of using a steam volume pressurizer instead of a gas pressurizer in promising projects of transport nuclear power plants (NPPs).

THE CONDENSATION OF WATER VAPOUR IN A MIXTURE CONTAINING A HIGH CONCENTRATION OF NON-CONDENSABLE GAS IN A VERTICAL TUBE

This paper deals with the condensation of water vapour possessing a content of noncondensable gas in vertical tubes. The condensation of pure steam on a vertical surface is introduced by the Nusselt condensation model. However, the condensation of water vapour in a mixture with non-condensable gas differs from pure vapour condensation and is a much more complex process. The differences for the condensation of water vapour in a mixture containing a high concentration were theoretically analysed and evaluated. In order to investigate these effects, an experimental stand was built. Experiments were carried out in regards to the case of pure steam condensation and the condensation of water vapour with a non-condensable gas mixture to evaluate the influence of the variable non-condensable gas content during the process. A non-condensable gas in a mixture with steam decreases the intensity of the condensation and the condensation heat transfer coefficient. A gradual reduction of the volume and partial pressure of steam in the mixture causes a decrease in the condensation temperature of steam, and the temperature difference between steam and cooling water. The increasing non-condensable gas concentration restrains the transportation of steam towards the tube wall and this has a significant effect on the decrease in the condensation rate.

NATURAL STATE MODELLING OF SALAK GEOTHERMAL FIELD

The Awibengkok geothermal field, also known as Salak, is a liquid-dominated field. The commercial Awibengkok reservoir is a moderate-to-high temperature (240–312 ◦C) geothermal resource with high fracture permeability, moderate porosity, and moderate-to-low matrix permeability, and can generate electricity up to 377 MW. This field fracture-controlled reservoir has benign chemistry and low-to-moderate non-condensable gas content. The geothermal reservoir is associated with youngvolcanism and intrusions in a highland area in the west of Salak Mountain and east of the Cianten caldera, a collapsed andesitic stratocone. In this paper, numerical method for calculation is used for modelling and reservoir simulation. A simulator is used to build the model. The model was built until it reached the natural state. The method used for model calibration is through pressure and temperature matching of two wells P-T logging data. One of the well is located on the western region of Salak geothermal field, while the other is located on the eastern region. Salak geothermal field model would reach natural state with simulation time up to millions of years. The model state the field is a liquid-dominated field and has steam caps in western and eastern area. The material on those two areas are different, thus the initial conditions are different. The temperature is higher in the western area. The gas saturation vary between 0.127 to 0.5 and there is a caprock with permeability 9mD.

Optimizing Ni–Ce/HZSM-5 catalysts for ex-situ conversion of pine wood pyrolytic vapours into light aromatics and phenolic compounds

The main objective of the present work is to investigate the influence of nickel to cerium ratio on hydrogen exchanged Zeolite Socony Mobil-5 (HZSM-5) towards the catalytic upgrading of pine derived oxygenated pyrolysis vapours into aromatic hydrocarbon and phenol in pyrolysis oil via ex-situ fixed bed reactor. The presence of CeO2 could change electron density of Ni, promote the reduction of Ni species, accelerate the transfer of carbon species, and suppress the production of carbon deposits (17.53%–25.11%) compared with the parent HZSM-5 catalyst (28.95%); it also improved the hydrodeoxygenation ability of all xNiyCe/HZSM-5(nickel and cerium bimetal modified HZSM-5) catalysts, resulting increases in noncondensable gas content (from 31.46% to 52.99%–65.53%). Ni to Ce ratio of 1:1 and 1:2 produced highest aromatic hydrocarbon (32.14%) and phenols (55.51%) relative peak areas. The acid center of HZSM-5 and the metal acid center of the Ni:Ce = 1:1 catalyst obviously fine-tuned the formation of coke; and promoted hydrocarbon production. Moreover, high Ni content promoted alkylation of benzene at C6–C9 and increased C10+ PAHs relative peak area; high Ce content promoted the formation of olefin and Increasing the cleavage of C–O bonds and promoted hydrogenation or dehydrogenation, reduced polycyclic aromatic hydrocarbons and coke yield, and increased phenols and alkylphenols selectivity.

Investigation on heat transfer performance of corrugated tubes in low-temperature multi-effect falling-film evaporation

ABSTRACT The enhanced heat transfer performance of falling film evaporation during desalination through altering smooth tubes by corrugated tubes was investigated. An experimental research on corrugated and smooth tubes was carried out using a horizontal-tube falling-film evaporation heat transfer experimental apparatus. The changes in heat transfer coefficient with the process parameters (sprinkling density, heat flux, heat transfer temperature difference, and evaporation temperature) were obtained according to the experimental data. The influence of tube type on liquid-film distribution outside the tube was also examined by numerical simulation. Results showed that within a certain scope increasing of any one variable of sprinkling density, heat flux, and evaporation temperature has a positive impact on the heat transfer coefficient. When the sprinkling density exceeded 0.178 kg/(m·s), the heat transfer coefficient tended to be stable. Compared with the simulation results, the liquid film coverage and thickness outside the tube significantly influenced heat transfer efficiency. When the heat flux exceeded 130kW/m2, the growth of the heat transfer coefficient significantly slowed down. Under the same experimental conditions, the heat transfer coefficient of corrugated tubes increased by 30% compared with that of smooth tubes. In addition, the content of non-condensable gas within the seawater affected the heat transfer coefficient significantly.

Dissolved-gas influence on the Francis part-load oscillation

A forced oscillation of system pressure occurs when a Francis turbine operates at partial load, typically between 50-85% of best-efficiency flow. Its cause is the precession of the draft tube vortex; due to cavitation of the vortex, the oscillation may enter in resonance. Predicting such a resonance from reduced-scale model tests is a long-standing goal of hydraulic research. Key parameter controlling the natural frequency of the underlying eigenmode is the compressibility of the cavitation zone. With the vortex cavity at vapor pressure, the natural frequency would scale by the same factor as the runner speed, thus enabling simple resonance prediction based on the model test. Based on experimental evidence, the actual pressure inside the vortex cavity is higher than vapor pressure, and the non-condensable gas content has significant influence. Due to uncontrolled variation of cavity pressure, the natural frequency in model tests may deviate by as much as 30% under nominally identical conditions. A 1D mathematical model can represent the influence of non-condensable gas on the cavity volume and compliance; even quite moderate cavity pressures explain the observed discrepancies.

An overview of the Muara Laboh geothermal system, Sumatra

The Muara Laboh geothermal system is a liquid-dominated, fracture-controlled reservoir showing some characteristics of both intrusion-related and fault circulation systems. The developed reservoir has moderate to high-temperature (230–310 °C) with a long NNW outflow (160–230 °C) extending to the Sapan Malulong boiling chloride springs. Reservoir fluids generally have low salinity (∼400-1600 ppm Cl) with benign chemistry and low non-condensable gas (NCG) content (∼0.5 to 2 wt% in steam). The proven reservoir is divided into distinct SW and NE sectors. The principal deep upflow zone (270 to 310 °C) is located in the SW and is associated with Patah Sembilan volcano and satellite vents (Anak Patah Sembilan). The SW upflow is characterized by relatively low salinity (∼400-600 ppm Cl), whereas fluids in the NE emerge from a second upflow along faults and fractures at 240–250 °C (1200–1600 ppm Cl) and ascend to an initial-state steam cap near the Idung Mancung fumarole. The shallow NE part of the geothermal system is hosted mainly by Quaternary to Miocene Age andesitic to rhyolitic rocks, whereas the deeper SW part of the system occurs in a Mesozoic to Cenozoic Age plutonic complex and its host rocks that are cut by younger dikes. Rock porosity and permeability trends can be related to reservoir age, volcanic deposit type, and alteration history. Fracture permeability is high, whereas matrix porosity (<1-7%) and permeability are moderate to low and decrease with depth. The volcanic sequence is capped by tuffs dated at ∼34,000 to 41,000 years BP, incapsulated in debris flows. This sequence may have formed during and shortly after likely sector collapse episodes of the Patah Sembilan volcano. The shallow clay cap of the system wraps around the crater, suggesting that it was excavated during crater formation.Permeable fracture patterns and their origins differ somewhat between the deep SW and the shallow NE reservoir. In the deep SW reservoir, fluids ascend along fractured margins of stock and dike intrusions. Steeply dipping intrusions and open fractures strike from WNW to NNW, subparallel to the main Great Sumatra Fault trend, with a secondary set of N to NE fractures and intrusions parallel with the inferred maximum horizontal stress direction (SHMax). In the shallower NE steam cap and outflow, N to NE steeply dipping fractures dominate, with bounding N to NNW faults. Bulk rock alteration includes shallow argillic and transitional clay zones overlying phyllic and propylitic zones. High-T propylitic alteration (secondary amphibole) and rare potassic alteration (secondary biotite) are associated with intrusion. Vein paragenesis in the SW reservoir indicates that portions of the initially permeable propylitic zone have been sealed by calcite and quartz ± prehnite. Late calcite veins suggest ingress of steam-heated bicarbonate waters contributed to resealing of the system. These relationships suggest that the SW system underwent extensive boiling, fluid loss, and inflow of dilute bicarbonate waters, possibly related to sector collapse and partial excavation of the topseal of the system (now Patah Sembilan crater).

Influence of Turbulence and Thermophysical Fluid Properties on Cavitation Erosion Predictions in Channel Flow Geometries

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Cavitation and cavitation-induced erosion have been observed in fuel injectors in regions of high acceleration and low pressure. Although these phenomena can have a large influence on the performance and lifetime of injector hardware, questions still remain on how these physics should be accurately and efficiently represented within a computational fluid dynamics model. While several studies have focused on the validation of cavitation predictions within canonical and realistic injector geometries, it is not well documented what influence the numerical and physical parameters selected to represent turbulence and phase change will have on the predictions for cavitation erosion propensity and severity.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;In this work, a range of numerical and physical parameters are evaluated within the mixture modeling approach in CONVERGE to understand their influence on predictions of cavitation, condensation and erosion. Particular attention is paid to grid resolution, turbulence model and near-wall treatment, fuel surrogate properties, and non-condensable gas content. Assessment of cavitation predictions are conducted through comparison of measured and predicted mass flow rates and cavitation probability distributions for flow through a channel with a sharp inlet. Predictions for hydrodynamic impact loading and cavitation erosion are compared with the experimentally measured incubation period and critical site for erosion. Based on these findings, recommendations are provided for modeling turbulent cavitating flows, using the single fluid mixture modeling approach, to improve predictions for cavitation-induced erosion. In particular, to capture the fluid dynamic phenomena characterizing cavitation cloud formation, development and shedding, a Large Eddy simulation with grid resolution as fine as 2.50 μm is recommended. The assumed concentration of non-condensable gas content is observed to have a strong influence on the predicted cavitation erosion severity, which motivates the need for dissolved gas concentration measurements for future cavitation erosion experimental studies. Using the best practices established in this work, good agreement is achieved between the measured and predicted cavitation parameters, as well as the critical site for cavitation-induced erosion.&lt;/div&gt;&lt;/div&gt;

Numerical simulation of three-phase flow in an external gear pump using immersed boundary approach

• Modelling the compressibility of gas is critical for predicting its effects on cavitation . • Effect of increased gas (NCG) content in the fluid is to decrease the cavitation. • More flow fluctuations are observed at the outlet with higher NCG content. • Modelling contact between the gears is critical for accurate cavitation prediction. • Higher gear RPM results in higher rate of cavitation. This paper presents a three-phase fully compressible model applied along with an immersed boundary model for predicting cavitation occurring in a two dimensional gear pump in the presence of non-condensable gas (NCG). Combination of these models is capable of overcoming numerical challenges such as modelling the contact between the gears and simulating the effect of NCG in cavitation. The model accounting for the effect of NCG also has broader applicability, since gas dissolved in liquids can come out of the solution when exposed to low pressures; this plays a significant role in the pump performance and cavitation erosion . Here the simulation results are presented for the gear pump at different operating conditions including the contact between gear, gear RPM and % of NCG; their effects on performance and cavitation is demonstrated. The results suggest that modelling the contact between the gears play a role in the cavitation prediction inside the gear pump. An increase in cavitation is observed when the contact is modelled even for the small pressure difference considered between the inlet and outlet. An increase in the RPM of the gears also results in increased cavitation within the pump, whereas an increase in the percentage of NCG content by a small amount can reduce the cavitation to a greater extent. This reduction is due to the expansion of the gas at a lower pressure which recovers the pressure and prevents or delays the phase-change process of the working fluid. The fluctuations in the outflow rate is also found to increase when the gears are in contact and also with increasing gas content.

Low emission flash-binary and two-phase binary geothermal power plants with water absorption and reinjection of non-condensable gases

The power production from geothermal resources with a high content of non-condensable gases (NCG) is concerning an increasing number of regions and may affect the sustainability relating to geothermal projects. The selection of an emission abatement system based on water absorption and reinjection of NCG back to the reservoir could solve the environmental impact, yet it implies significant power output penalty and water demand, as demonstrated in a recent paper by the authors (Manente et al., 2019) focused on the retrofit of existing flash steam power stations. A reconsideration of the plant design could result in a better integration with the absorption and reinjection section and finally reduce the associated requirements. To address this point, two “greenfield” plant layouts are investigated in this paper for utilization of a high enthalpy liquid dominated reservoir, where the single flash steam generation unit is complemented or even totally replaced by air cooled binary cycle units. The first layout is an “integrated flash-binary” plant based on a backpressure steam turbine and a bottoming ORC system, whereas the second layout consists in a “two-phase binary” plant. The performance of the two novel layouts is compared against that of a brownfield layout, first proposed in Manente et al. (2019), based on an existing single flash plant retrofitted with the absorption and reinjection system, using a consistent set of assumptions. The results show that the net power output remains almost unaltered because in the novel layouts the lower parasitic loads for gas compression counterbalance the lower production dictated by the air-cooled system and the irreversibility in the heat transfer between geothermal fluid and organic fluid. Thus, due to the better integration between power block and emission abatement section the net power output penalty of the novel layouts is contained within 2%. On the other hand, the hydrogen sulfide and carbon dioxide abatement efficiencies markedly increase as the removal of the cooling tower eliminates the secondary gaseous emissions and makes the entire steam condensate available for NCG absorption. In the integrated flash-binary plant design the overall H2S and CO2 abatement efficiencies reach 99% and 90%, respectively, without any external water demand, provided that measures are taken for a controlled precipitation of silica and other minerals from the geothermal brine prior to using it for NCG absorption.

Modeling of laminar filmwise condensation of methane with nitrogen on an isothermal vertical plate

Liquefied natural gas (LNG) is one of the key technologies in the development and utilization of natural gas. To clarify the condensation characteristics at the last stage of natural gas liquification, saturated methane mixed with nitrogen was chosen as the study object. A numerical model was proposed to predict the filmwise condensation characteristics of ultralow temperature (−162 °C) vapor with non-condensable gas on an isothermal vertical plate. The gas-liquid interface was captured using the Volume of Fluid (VOF) method. A user defined function (UDF), which was written using a cell iteration method and based on the mass conservation on the gas-liquid interface, was applied to deal with the mass and energy source term of the condensing process. The subcooled temperature (temperature difference between wall and saturated gas) and the molar content of non-condensable gas were 2-20 K and 2–13%, respectively. The numerical results show that the heat and mass transfer occur mainly near the cool wall in millimeter level, with the change of temperature, viscosity, phase and mole fraction. A small amount of non-condensable gas can reduce heat transfer coefficients significantly. When the mole fraction of non-condensable gas is 2%, the heat transfer coefficient is reduced by about 59%. And the heat and mass transfer resistance are mainly in the vapor-gas boundary layer rather than in the liquid film.

Динамическое взаимодействие потока теплоносителя с тепловыделяющей сборкой

Papers written by Russian researchers on matters concerned with implementing the “Zero Fuel Rod Defect Concept” are reviewed. The results from investigations of structural, technological and operational factors causing loss of fuel rod (FR) leak tightness are considered. The purpose of these studies is to find the root cause affecting the efficiency of a particular fuel assembly (FA) and to make changes for eliminating it. The results of the study aimed at establishing a correlation between the degradation of defective FRs and the fuel operating parameters are presented. The results obtained from testing the models of FRs and FAs for VVER reactors and Kvadrat type FAs for a PWR-900 reactor for fretting-induced wear under the conditions of the PWR reactor water chemistry are analyzed. It is shown that experimental physical modeling of fretting wear for FA fragments with ensuring similarity and possibility of extending the results for the standard FA is an approach based on which fretting wear can be combated. Based on reviewing the results of numerous investigations, conclusions are drawn about the need to refine data on the level of hydrodynamic loads (in particular, when resonances occur) and to refine data on the content of non-condensable gases in the coolant in the operating reactor under different operating conditions. For verifying the design and technological solutions, for substantiating the reliability and operability of new-generation FRs and FAs, for elaborating recommendations on further improvement of the designs and manufacturing technology, and for developing and certifying computer codes, the following must be carried out and used: integrated experimental investigations of the basic regularities pertaining to the dynamic interaction between the coolant flow and fuel, and the changes in the properties and characteristics of fuel for VVER-type reactors; combined application of theoretical and experimental methods for investigating an abnormal growth of the FR and FA vibration levels in order to predict the conditions of their occurrence, and to identify and prevent them. Refinement of these data will make it possible to solve strategic objectives such as increasing the fuel burnup depth, constructing repairable FAs, and substantiating the fuel efficiency in maneuvering modes and under the conditions of increased reactor power.

Geothermal power plant layouts with water absorption and reinjection of H2S and CO2 in fields with a high content of non-condensable gases

The reinjection of non-condensable gases (NCG) back to the geothermal reservoir has recently proved to be an effective emission abatement method in Iceland, yet it would raise new challenges when applied to geothermal fields with a much higher NCG content and different reservoir’s rock composition like the Italian fields. The features of the surface equipment to implement gas reinjection are rarely reported in the literature, being the attention mostly focused on the subsurface reservoir. To fill this gap, this study examines the integration of the water absorption and reinjection equipment in dry steam and flash steam geothermal power plants fed by steam with a high NCG content (8%). Three novel plant layouts are proposed, modelled and analysed which include a packed absorption column where H2S and CO2 are absorbed in water at high pressure. The study searches for those conditions ensuring an overall H2S abatement similar to that achieved by state-of-the-art emission abatement methods (e.g., AMIS) and, at the same time, enabling a significant capture of the CO2 contained in the geothermal steam, which is currently unabated. The results show that, with minimum modifications to the original plant layout, an overall H2S abatement of 86.5% and CO2 abatement of 47% are attainable. This is obtained using a column pressure of 36 bar, a water supply of 100 ton/hr, and coping with a net power output reduction of 6% and a moderate cost of the added equipment estimated equal to 1.0–2.2 M€.

Steam Condensation from a Moving Steam-Gas Mixture

To date, heat exchange has been studied to the greatest extent for the case of the condensation of pure still and moving steam as well as for the case of condensation from a still steam-gas mixture. There are hardly any papers available wherein a moving steam-gas mixture with a substantial content of noncondensable gases is considered. To investigate this process, an experimental workbench of the working section has been developed, which makes it possible to determine the local values of the heat transfer coefficient from the steam-gas mixture to the walls of cooled heat-exchange tubes at different parameters and velocities of the gas-steam mixture. In the first four rows of tubes of the working section, there is no cooling, and their function consists in a hydraulic stabilization of the flow. In the fifth and the sixth row of tubes, the wall temperature of the cooled heat-exchange tubes is measured for determining the heat transfer coefficients from the moving steam to the tube walls. The seventh row of tubes is also not under cooling. Measuring tubes with temperature sensors have been manufactured that make it possible to obtain the wall temperature for determining the heat transfer coefficient. The adopted scheme of steam motion and the measurement system make it possible to obtain correct results of the heat and mass transfer investigation in the course of steam condensation from a gas-steam mixture with a significant content of noncondensing gases. The studies on steam condensation from a moving steam-gas mixture have been carried out in the range of parameter ρw2 = 9.5 − 66 Pa and at a volume concentration of air in the steam amounting up to νair = 0.18. Convective heat transfer coefficient α values for the heat transfer from a moving steam-gas mixture to the wall of a cooling tube were obtained. At small values of parameter ρw2 = 9.5 Pa and the volume fraction of the air content νair = 0.06 in the steam, the average heat transfer coefficient exhibits a decrease by a factor of two as compared with that inherent in the condensation of almost pure steam. At the values of parameter ρw2 = 66 Pa and at νair = 0.06, the average heat transfer coefficient decreases by 1.3 times. The studies on almost pure steam are in good agreement with Berman’s dependence.

Experimental Study on the Condensation of Steam With Air Out of the Vertical Tube Bundles

In this paper, experimental study was carried out in an open natural circulation loop,to figure out the condensation heat transfer characteristic on the outside of the vertical pipe tube bundle and single- tube. Condensation heat transfer coefficients have been obtained under the wall subcooling ranging from 5 to 22◦C, total pressure ranging from 0.3 to 0.6MPa and air mass fraction ranging from 0.05 to 0.65. The influence of mixed gas pressure, condensate depression of walls, and content of non-condensable gas on the condensation heat transfer performance is analyzed. Under the condition of the same air mass fraction, the condensation heat transfer coefficient increases with the increase of pressure. Also, as the air mass fraction is more than 30%, the effect of pressure will be weakened. The heat transfer features of pipe bundle and single tube is compared and studied, and an empirical correlation of the pipe bundle for the heattransfer coefficient is developed, covered all data points within 10%. According to the research results, heat transfer coefficient for pipe bundle decreases with the increase in non-condensable gas quality and wall subcooling, but increases with the increase in pressure.

Experimental study on superheated steam generation by the reaction of high humidity hydrogen and oxygen in a model internal combustion steam generator

ABSTRACTInternal combustion steam cycle (ICSC) is a novel steam power cycle using hydrogen as an energy carrier to produce superheated steam. High humidity hydrogen produced during fast hydrogen production process is directly used to produce superheated steam by combusting with stoichiometric oxygen without hydrogen storage. The ICSC efficiency is greatly affected by the content of non-condensable gas in superheated steam. In the present study, superheated steam generation by high humidity hydrogen was investigated in a model internal combustion steam generator. Effects of H2O/H2 molar ratio of humid hydrogen and velocity ratio of humid hydrogen to oxygen on non-condensable gas content, combustion efficiency, and mixing rate were evaluated. The results showed that the critical H2O/H2 ratio for the humid hydrogen humidity limit was 2.8. With increasing velocity ratio, mixing rate and combustion efficiency increased under the same H2O/H2 ratio. The H2O/H2 reaction rate monotonously decreased as the H2O/H2 ratio increased from 1.0 to 2.5, while the mixing rate increased along with the velocity ratio. The combustion efficiency initially increased and subsequently decreased, and the peak value was reached at a H2O/H2 ratio of 1.75. This result indicated that the humid H2-O2 combustion was controlled by diffusion under H2O/H2 ratios of 1.0 to 1.75, but turned to be controlled by chemical kinetics when the H2O/H2 ratio ranged between 1.75 and 2.5.