Turboexpander Research Articles

Supercritical water gasification of biomass and agro-food residues: Energy assessment from modelling approach

The gasification of biomass in supercritical water is a promising technology for hydrogen production and the paper reports a thermodynamic analysis, based on minimization of Gibbs free energy, of the gasification with supercritical water of different biomass and agro-food residues: almond shells, digestate from wastewater treatment, algae and manure sludge. Numerical simulations were performed in order to assess the effect of temperature, pressure and biomass-to-water ratio on gas-phase yield and composition.A partial energy integration was also discussed, by considering the energy recovery from a turbine expansion of the gas-phase stream leaving the gasifier. The proposed thermodynamic approach allows predicting not only gasification efficiency of gasifier but also energy balance on the entire gasification process. Results showed that the dry substrates (almond shells and algae more than digestate and sludge) tend to form more carbon monoxide. Besides, data comparison revealed that the produced hydrogen comes from biomass and water for high process temperature, while when temperature decreases, the thermodynamic path tends to promote water formation from the hydrogen of the dry biomass.

Analysis of the influence of the input parameters on the efficiency of the operation of the detander generator unit in the gas network system of the republic of Uzbekistan

The article is devoted to the generally recognized dilemma of using secondary energy resources in the transportation and distribution of natural gas. At stations where throttle devices are used, excessive gas pressure as the main component of secondary energy resources for technological processes is practically not used. Currently, the replacement of throttle devices with turbo-expander units is determined by energy and economic efficiency. This is due to the fact that the use of excess gas pressure in the turbo expander both at gas distribution stations and at compressor stations of gas pipelines without preheating has not yet been widely used. Expander-generator technology is probably one of the most effective technologies for reducing the consumption of fuel and energy resources. The combination of expander-generator units with heat pump units contributes to the creation of highly efficient power generating complexes that can generate electricity without burning fuel. Expansion of high-pressure natural gas at gas distribution stations is one of the technologies for generating electricity without combustion. To determine the share of electric energy supplied to the electric network based on the expander-generator set in the gas supply system, an analytical dependence was determined. Based on this, an arithmetic model of the installation with single-stage expander-generator units and steam-compression heat pump units is proposed. All data will be presented in detail in this article.

ИСПОЛЬЗОВАНИЕ ВАКУУМНЫХ МИКРОГАЗОТУРБИННЫХ УСТАНОВОК ДЛЯ ТЕПЛОЭЛЕКТРОСНАБЖЕНИЯ ЛОКАЛЬНЫХ ОБЪЕКТОВ

Consideration subject in article are vacuum cycles of microgas turbine plants (MGTP) for the purpose of studying of their profitability and perspectives of use for heatpower supply of local objects. Vacuum MGTP of a simple cycle and with warmth regeneration is investigated. Optimum parameters of cycles – ratio of turbine expansion and regeneration ratio are found. It is established that profitability of MGTP with regeneration of warmth is higher in comparison with MGTP of a simple cycle almost twice, specific power decreases approximately by 1,35 times. By virtue of profitability and smaller values of compressor pressure ratio increase of the microturbine it is reasonable to apply in MGTP of a vacuum cycle with warmth regeneration.

Cryogenic Cavitation Mitigation in a Liquid Turbine Expander of an Air-Separation Unit through Collaborative Fine-Tuned Optimization of Impeller and Fairing Cone Geometries

An air-separation unit (ASU) uses atmospheric air to produce essential pure gaseous and liquid products for many industrial sectors but requires intensive power consumption. In recent years, cryogenic liquid turbine expanders have been used to replace the traditional J-T valves in air-separation units to save energy. In this paper, an effective design optimization method is proposed to suppress swirling flow and mitigate cavitation in liquid turbines. A flexible tuning of the impeller and fairing cone geometries is simultaneously realized, where the optimization variables are identified via a geometric sensitivity study. A novel objective function is deliberately established by allowing both swirling flow and cavitation characteristics, driving the optimizer to search for deswirling and cavitation-resistant geometries. A kriging surrogate model with an adaptive sampling strategy and a cooperative co-evolution algorithm (CCEA) are incorporated to solve the highly nonlinear optimization problem, where the former reduced the costly evaluations but simultaneously maintained the model prediction accuracy and enabled the aim-oriented global searching (the latter decomposes the problem into several readily solved sub-problems that could be solved in parallel at a high-convergence rate). The optimized impeller and fairing cone geometries were quite favorable for suppressing swirling flow and mitigating cavitation. The impeller cavitation was significantly reduced, with the maximal vapor volume fraction reduced from 0.365 to 0.17 at the blade surface; the diffuser tube high-swirl flow was significantly deswirled and the intensive vapor fraction around the centerline largely reduced, with the maximal vapor volume fraction in the diffuser tube reduced from 0.387 to 0.121. As a result, the isentropic efficiency of the liquid turbine expander was improved from 88.4% to 91.43%.

Performance design of a cryogenic air separation unit for variable working conditions using the lumped parameter model

Large-scale cryogenic air separation units (ASUs), which are widely used in global petrochemical and semiconductor industries, are being developed with high operating elasticity under variable working conditions. Different from discrete processes in traditional machinery manufacturing, the ASU process is continuous and involves the compression, adsorption, cooling, condensation, liquefaction, evaporation, and distillation of multiple streams. This feature indicates that thousands of technical parameters in adsorption, heat transfer, and distillation processes are correlated and merged into a large-scale complex system. A lumped parameter model (LPM) of ASU is proposed by lumping the main factors together and simplifying the secondary ones to achieve accurate and fast performance design. On the basis of material and energy conservation laws, the piecewise-lumped parameters are extracted under variable working conditions by using LPM. Takagi-Sugeno (T-S) fuzzy interval detection is recursively utilized to determine whether the critical point is detected or not by using different thresholds. Compared with the traditional method, LPM is particularly suitable for “rough first then precise” modeling by expanding the feasible domain using fuzzy intervals. With LPM, the performance of the air compressor, molecular sieve adsorber, turbo expander, main plate-fin heat exchangers, and packing column of a 100000 Nm3 O2/h large-scale ASU is enhanced to adapt to variable working conditions. The designed value of net power consumption per unit of oxygen production (kW/(Nm3 O2)) is reduced by 6.45%.

Process optimization and analysis of a novel hydrogen liquefaction cycle

The preliminary designed hydrogen liquefaction plant process based on liquid nitrogen precooling and helium gas turbine expansion refrigeration is firstly modified, simulated and analyzed by Aspen HYSYS. In addition, the multi-parameter optimization of the system is carried out by genetic algorithm (GA) by considering the specific energy consumption (SEC) of the system as the objective function. After optimization, it can be found that the SEC of the system is 7.1329 kWh kgLH2−1, which is 19.65% lower than that of base case and the coefficient of performance (COP) and figure of merit (FOM) are 0.1704 and 0.4941, which are higher than that prior to the process optimization. In addition, sensitivity analysis is conducted to present the effects of different operation conditions of the designed process on the features of the hydrogen liquefaction process. Compared with the other two systems of hydrogen liquefaction, the process in this paper shows the best performance.

A Gas Turbine Cooled-Stage Expansion Model for the Simulation of Blade Cooling Effects on Cycle Performance

Modern gas turbine firing temperatures (1500–2000 K) are well beyond the maximum allowable blade material temperatures. Continuous safe operation is made possible by cooling the HP turbine first stages, nozzle vanes and rotor blades, with a portion of the compressor discharge air, a practice that induces a penalty on the thermal efficiency cycle. Therefore, a current issue is to investigate the real advantage, technical and economical, of raising maximum temperatures much further beyond current values. In this paper, process simulations of a gas turbine are performed to assess HP turbine first-stage cooling effects on cycle performance. A new simplified and properly streamlined model is proposed for the non-adiabatic expansion of the hot gas mixed with the cooling air within the blade passage, which allows for a comparison of several cycle configurations at different turbine inlet temperatures (TIT) and total turbine expansion ratio (PR) with a realistically acceptable degree of approximation. The calculations suggest that, at a given PR, the TIT can be increased in order to reach a higher cycle efficiency up to a limit imposed by the required amount and temperature of the cooling air. Beyond this limit, no significant gains in thermal efficiency are obtained by adopting higher PR and/or increasing the TIT, so that it is convenient in terms of cycle performance to design at a lower rather than higher PR. The small penalty on cycle efficiency is compensated by the lower plant cost. The results of our model agree with those of some previous and much more complex and computationally expensive studies, so that the novelty of this paper lies in the original method adopted on which the proposed model is based, and in the fast, accurate, and low resource intensity of the corresponding numerical procedure, all advantages that can be crucial for industry needs. The presented analysis is purely thermodynamic and it includes no investigation on the effects of the different configurations on plant costs. Therefore, performing a thermo-economic analysis of the air-cooled gas turbine power plant is the next logical step.

Use of a turbine expander to generate electricity for own operation needs of a gas turbine unit at compressor stations of main gas pipelines

In order to save energy at compressor stations, it is proposed to use expander-generating units (EGU) to reduce gas pressure. An analytical justification for replacing a throttle by EGU is given. The results of economic calculation of electricity savings when using EGU are given. The scheme of gas turbine unit with EGU and gas heating before entering the combustion chamber is presented. When using this scheme, the cost savings for electricity purchase is 83%.

Providing Fault Ride-Through Capability of Turbo-Expander in a Thermal Power Plant

This paper aims to make possible the operation of a turbo-expander (TE) as a renewable resource at the Neka power plant in fault condition in the auxiliary service system (ASS), which is considered one of the fundamental problems in network operation. In this paper, the effect of the failure on the performance of the TE is analyzed whilst the performance of a dynamic voltage restorer (DVR) and static synchronous compensator (STATCOM) to compensate the fault in the ASS network is investigated. To improve the performance of DVR, a novel topology is developed; additionally, the compensatory strategies are assessed, simulated, and validated. In order to optimize the performance of the compensators, their possible presence situations on the ASS in various scenarios under the conditions of severe disturbance, synchronization of fault conditions, and starting of TE are tested. The results of PSCAD/EMTDC software simulation demonstrate that by applying the improved topology and selected compensation strategy of DVR, severe voltage sags are compensated, and the fault ride-through (FRT) capability for the TE is provided. Eventually, it is evident that the proposed solution is technically and economically feasible and the TE can supply the total ASS power consumption in all disturbances.

Integration of a turbine expander with a synthesis gas process – Using process gas as a working fluid

Synthesis gas production provides an excellent opportunity for integration of a turbine expander since the heat is available at very high temperatures (900–1400 °C). This case study considers the integration of a turbine expander with a synthesis gas production process that uses auto-thermal reforming for Fischer-Tropsch synthesis. Auto-thermal reforming technology is a commercialised technology that is well suited to large scale synthesis gas production processes. A methodology that was previously developed and published by the same author is applied in this case study, resulting in an improved flow sheet with significantly improved power output and thermal efficiency improvement. The new flow sheet comprises a unique power production system that uses synthesis gas as a working fluid and wherein the sequence of compression and expansion are reversed in position, compared to conventional power production systems. A conventional steam cycle is also coupled to this synthesis gas power production system to render a combined synthesis gas and steam power production arrangement.Simulation models were created of the conventional and new integrated flow sheets and the analysis focussed on pressure ratio variations across the turbine expander. It is shown how such variations affect other parameters in the system. In one of the cases a 37% improvement in net work was obtained from the new integrated flow sheet compared to the conventional flow sheet. The results are also compared to the results obtained in a recent study on integration of a turbine expander with a steam methane reformer, and further options to implement the synthesis gas power production system for a steam methane reformer are explored.

Development and experimental study of a supercritical CO2 axial turbine applied for engine waste heat recovery

CO2-based transcritical power cycle (CTPC) has been proposed as a suitable engine waste heat recovery (E-WHR) technology with the advantage of miniaturization and good recovery capacity. Expander, as the core power conversion device, is of great importance to the overall cycle performances. The main purpose of this paper is to conduct dynamic tests of the proposed turbine expander, with focus on the turbine operational characteristics and performance. In this study, a partial admission axial turbine expander coaxial with a high-speed synchronous generator is designed and manufactured considering the thermodynamic properties of supercritical CO2. The geometry of the turbine is 56 mm rotor diameter, 4 mm blade height, and 39000 rpm of operating speed at the inlet design condition of 10 MPa and 230 °C, outlet condition of 6 MPa and mass flow rate of 0.18 kg/s. The performance of the developed turbine expander and CTPC system with respect to the rotational speed and mass flow rate are investigated experimentally. Based on the experimental data, the maximum rotational speed of the the turbine reaches 41584 rpm and the turbine expander generated maximum power 2.27 kW at 20878 rpm. The power capacity of the turbine increases to the maximum value first and then decreases with the increase of rotational speed as well as the isentropic efficiency. The power generation of the turbine expander is proportional to pressure ratio as well as mass flow rate.

Numerical and experimental investigation to visualize the fluid flow and thermal characteristics of a cryogenic turboexpander

The increasing demand for cryogenic fluids is acquiring the research attention to develop efficient machines to produce cryogenic temperature such as turboexpander based system. The expansion turbine and nozzle of a turboexpander are the critical components of such systems, and its performance has a significant effect on the overall efficiency of the system. In this paper, the effective design methodology of a radial inflow turbine by considering different loss models is presented. The methodology consists of one-dimensional modeling to describe the geometrical parameters of the nozzle and turbine. The optimal range of important non-dimensional variables such as blade speed, pressure ratio, ratio of hub and shroud radius to turbine inlet radius are predicted using artificial intelligence techniques for better performance of the turbine. This approach improves the turbine efficiency and power output by 4% and 18.9% respectively as compared to the existing model. The three-dimensional numerical investigation is carried out to visualize the fluid flow and thermal characteristics of the designed turbine and nozzle. The study also focuses on to identify the flow separation zone, tip leakage flow, vortex formation, secondary losses and its reasons at different spanwise locations of the turbine. Additionally, Sobol sensitivity analysis method is used to distinguish the significance of different assumed constants on the total losses and non-dimensional design variables on total-to-static efficiency. Finally, the numerical results are validated with experimental data of a case study. The study highlights the importance of the design methodology, the prediction capability of artificial intelligence method, Sobol sensitivity analysis, the experimental techniques and benchmarking model for numerical analysis at different cryogenic temperature.

Simulation study on the flow field of guide vane and impeller of turbo expander

AbstractIn the face of the current energy shortage, organic Rankine cycle (ORC) technology is a way to make efficient use of energy, especially geothermal energy. As the core component of an ORC system, a turbo expander can achieve a high conversion efficiency for geothermal energy and has good development prospects. For low temperature geothermal energy such as 95°C water, R245fa could be chosen as the working fluid. Through preliminary thermal calculations and the MATLAB programming method, the main thermal performance parameters and the aerodynamic parameters, structural parameters, and three‐dimensional modeling of the guide vane and impeller were obtained. The design of the turbo expander was modeled and meshed by the Workbench module using the ANSYS software, and the internal flow path of the expander was numerically simulated by the CFX module. The results showed that there was a small range of wake loss at the trailing edge of the vane flow; impact loss and wake loss occurred at the leading and trailing edges of the impeller blades. At the 30% relative chord strength of the impeller, there was excessive expansion, resulting in a local low‐pressure area and a secondary flow from the hub to the rim.

Experiments on a small-scale axial turbine expander used in CO2 transcritical power cycle

As a result of the miniaturization and better temperature matching advantage of CO2-based Transcritical Power Cycle (CTPC) as well as good thermodynamic properties and natural property of CO2, the CTPC system is an appropriate engine waste heat recovery (E-WHR) technology. In the research, a kW-scale partial admission axial turbine expander with conventional carbon ring mechanical seal and angular contact ceramic ball bearings is manufactured specifically and experimental tests of the turbine expander are conducted on the CTPC test bench to investigate the turbine operational characteristics and performance. Based on the experimental data, the rotational speed of turbine ranges from 10,554 rpm to 14,684 rpm with the adjustments of resistance load, and the power generation of the turbine reaches the maximum 692 W at 14,022 rpm. The isentropic efficiency of turbine expander increases with the increase of rotational speed and maximum efficiency 53.43% is achieved at 13,366 rpm, then decreased. The variation of voltage and electric current generated by the turbine expander with rotational speed is also investigated. Test results show that the reason for the low power generation of the turbine expander is the leakage caused by the failure of the dynamic seal.

On the design of heat exchanger equipment for novel-type isobaric expansion engines

The recently proposed idea of displacer-type heat engines with dense working fluids revived the long-known concept of isobaric expansion (IE). Capable of overcoming some of the most severe disadvantages of gas-phase displacer-type heat engines and state-of-the art ORC plants, these engines offer a solution for future heat-to-power conversion and heat driven pumps or compressors. Effective heat regeneration and heat transfer in general are key issues of all types of displacer-type heat engines and thus, compact heat exchangers with minimum internal volume and pressure drop are required. This study is dedicated to the effects of regeneration on efficiency and considers efficiency-abating internal (dead) volumes and pressure drop. Printed Circuit Heat Exchangers (PCHE) are proposed for application in IE engines and a design procedure for these apparatuses is introduced. The results show that efficiencies close to the optimum can be obtained if the channel size is below 1 mm. Along with recently presented theoretical and experimental studies on such IE engines, this affirms the great potential of this heat conversion technology.

Enhancing refrigeration capacity of turbo expander by means of multipoint design optimization

Turbo expander produces cold energy in cryogenic Air Separation Unit (ASU) to meet the requirement of liquefied air fractional distillation. The study is initiated by recent commissioning operation of a single-point designed turbo expander in the 1600 Nm3/h oxygen yield ASU, where the online measured cold energy at an off-design operation point is under the requirement. To enhance the expander refrigeration capacity over a wide-spread condition and support the ASU flexible operations, a novel multipoint design optimization method is proposed. Characterization of the ASU expander condition point is done by allowing for the expander real status in the operational ASU; a 3-factors and 5-levels’ uniform design experimentation scheme is proposed and used to identify the multiple design points in the 3D space (formed by the expander inlet pressure and temperature, and shaft speed) and they are used to establish the multipoint objective function; adaptive surrogate model-based optimization algorithms are incorporated to enable the aim-oriented global optimal searching with considerably reduced CFD computations. The multipoint optimized expander impeller is manufactured and used to replace the original. In the restarted ASU, the expander operates at a new condition point but produces high-level overall performance and sufficient cold energy for liquefied air fractional distillation.

Effects of Blade Fillet Structures on Flow Field and Surface Heat Transfer in a Large Meridional Expansion Turbine

This paper is a continuation of the previous work, aiming to explore the influence of fillet configurations on flow and heat transfer in a large meridional expansion turbine. The endwall of large meridional expansion turbine stator has a large expansion angle, which leads to early separation of the endwall boundary layer, resulting in excessive aerodynamic loss and local thermal load. In order to improve the flow state and reduce the local high thermal load, five typical fillet distribution rules are designed. The three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solver for viscous turbulent flows was used to investigate the different fillet configurations of the second stage stator blades of a 1.5-stage turbine, and which fillet distribution is suitable for large meridional expansion turbines. The influence of fillet structures on the vortex system and loss characteristics was analyzed, and its impact on wall thermal load was studied in detail. The fillet structure mainly affects the formation of horseshoe vortexes at the leading edge of the blade so as to reduce the loss caused by horseshoe vortexes and passage vortexes. The fillet structure suitable for the large meridional expansion turbine was obtained through the research. Reasonable fillet structure distribution can not only improve the flow state but also reduce the high thermal load on the wall surface of the meridional expansion turbine. It has a positive engineering guiding value.

Process Simulation and Optimization of Natural Gas Dehydration Process using Aspen Hysys

Natural Gas is More Efficient than Other Forms of Fossil Fuel. Natural gas produces more energy than any of the fossil fuels. Although the primary use of natural gas is as a fuel, it is also a source of hydrocarbons for petrochemical feedstocks and a major source of elemental sulfur, an important industrial chemical. The process simulation and optimization of natural gas dehydration process including mono ethylene glycol (MEG) injection and its regeneration process is studied in this research work. This study also carried out the operation parameters and optimization. The simulation is carried out using Aspen-HYSYS. The effect of replacement MEG by DEG and influence of replacement of Chiller by a turbo expander refrigeration technique on the DPCU operation was studied. The result obtained for optimum parameters like inlet pressure and temperature of the LTS are studied and comparing chiller and expander to maximize NGL are presented. The study recommends to use the expander instead of the chiller. The the economic evaluation of the proposed modification is presented in this study.

Prediction of natural gas hydrates formation using a combination of thermodynamic and neural network modeling

During the treatment or transport of natural gas, the presence of water, even in very small quantities, can trigger hydrates formation that causes plugging of gas lines and cryogenic exchangers and even irreversible damages to expansion valves, turbo expanders and other key equipment. Hence, the need for a timely control and monitoring of gas hydrate formation conditions is crucial.This work presents a two-legged approach that combines thermodynamics and artificial neural network modeling to enhance the accuracy with which hydrates formation conditions are predicted particularly for gas mixture systems. For the latter, Van der Waals-Platteeuw thermodynamic model proves very inaccurate. To improve the accuracy of its predictions, an additional corrective term has been approximated using a trained network of artificial neurons. The validation of this approach using a database of 4660 data points shows a significant decrease in the overall relative error on the pressure from around 23.75%–3.15%. The approach can be extended for more complicated systems and for the prediction of other thermodynamics properties related to the formation of hydrates.

ELECTRIC ENERGY GENERATION IN AUTONOMOUS ENERGY SUPPLY MODULE HAVING ROTARY EXPANSION ENGINE

The development of autonomous energy supply systems is among the priority ways of scientific and technological growth in the Russian Federation. The autonomous energy supply module providing the consumer with heat, electric power, hot and cold water can contain the different variants of the electric power subsystem. This paper considers three different variants of building the electric power subsystem for the rotary expansion engine used as a driving machine whereas the permanent magnet synchronous machine is used as a generator. Also the designed structure of 30 kW electric power supply subsystem is regarded.