Thermodynamic performance of ammonia in liquefied natural gas precooling cycle

The selection of proper refrigerants for natural gas liquefaction processes play a key role in cycle?s efficiency. Mixed refrigerants have been proven to improve cycle?s exergy efficiency over single pure refrigerant. However, the future of some of these refrigerants with higher global warming potential index (GWPI) are unknown due to the continuous restriction being enforced by the energy and environmental agencies over the past few decades. This study examines the benefits and drawbacks of mixing ammonia, a refrigerant with zero GWPI and a high occupational safety characteristic, with lighter hydrocarbon refrigerants such as methane and ethane as a mixed refrigerant in a natural gas liquefaction?s precooling cycle. Results showed, presence of ammonia in mixed refrigerant not only saved in capital cost due to the smaller footprint of plant and smaller cold box, it also lowers the plants precooling operation expense by reducing the required compression power needed for the precooling cycle up to 16.2%. The results of exergy analyses showed that by reducing the molar concentration of more pollutant refrigerant methane and replacing it with ammonia enhanced the cycle?s efficiency by 4.3% and lowered the heat exchanger total exergy loss up to 47.9 [kW.kgLNG-1].

CALCULATION OF 2-DIMENSIONAL PWR MOX/UO2 CORE BENCHMARK OECD NEA 6048 WITH SRAC CODE

The mixed uranium-plutonium oxide fuel (MOX/UO2) is an interesting fuel for future power reactors. This is due to the large amount of plutonium that can be processed from spent fuel of nuclear plants or from plutonium weapons. MOX/UO2 fuel is very flexible to be applied in thermal reactors such as PWR and it is more economical than UO2 fuel. However, due to the different nature of neutron interactions of MOX in PWR, it will change the reactor core design parameters and also its safety characteristic. The purpose of this study is to determine the accuracy of SRAC2006 code system in generation of cross-sections and calculation of reactor core design parameters such as criticality, reactivity of control rods and radial power distribution. In this study, PWR MOX/UO2 Core Transient Benchmark is used to verify the code that models a MOX/UO2 fueled core. SRAC-CITATION result is different from DeCART by 0.339% from. SRAC-CITATION result of single rod worth in All Rods Out (ARO) conditions are quite good with a maximum difference of 6.34% compared to BARS code and 4.74% compared to PARCS code. In All Rods In (ARI) condition, SRAC-CITATION results compared to the PARCS code is quite good where the maximum difference is 9.72%, but compared to BARS code, it spikes up to 33.24% at maximum difference. In the other case, overall radial power density results are quite good compared to the reference. Its maximum deviation from DeCART code is 5.325% in ARO condition and 6.234% in ARI condition. Based on the results of these calculations, SRAC code system can be used to generate cross-section and to calculate some neutronic parameters. Hence, it can be used to evaluate the neutronic parameters of the MOX/UO2 PWR core design.Keywords: MOX/UO2 fuel, Criticality, Power peaking factor, SRAC2006

Safety Characteristic Evaluation of Cage in Cylindrical Roller Bearing at the Stage of Start-Up and Stop

The dynamics model of cylindrical roller bearing (CRB) in aeroengine main shaft was promoted and solved by Hilber–Hughes–Taylor (HHT) integer algorithm with variable step in combination with symmetric multiprocessing (SMP) parallel solving technology, and a finite element model of roller to cage contact was built. The dynamic characteristics of CRB at the stage of start-up and stop were analyzed firstly, and then, the collision forces between rollers and cage were used as the boundary conditions of the finite element model to discuss the influences of working conditions, structural parameters, and materials on the stress distribution and safety characteristic of cage at the stage of start-up and stop. The findings will provide the theoretical basis for the designing of CRB in aeroengine main shaft.

SYNTHESIS OF SAFE BEHAVIOR ALGORITHMS OF RADIOELECTRONIC SYSTEMS FOR CRITICAL APPLICATIONS

The safety of radio electronic systems for critical applications is traditionally ensured by inducing structural redundancy. This paper shows a developed technique for ensuring a required level of safety of such systems by inducing time and functional redundancy into its behavior algorithm. The defined safety characteristic is proposed for quantitative efficiency estimation of the induced redundancy. Presented in the article is the synthesis technique of safe behavior algorithms on the basis of safety characteristic minimization of increased values. The developed technique was tested through solving the synthesis problem of the behavior algorithm of the target detection radio electronic complex system.

MODELS AND METHODS FOR RISK ANALYSIS OF FIRE-DANGEROUS SITUATIONS AT NUCLEAR POWER PLANTS

The paper presents the review models, methods and approaches to the formalized analysis of data in the fire extinguishing systems and safety characteristic for difficult, explosive and fire-dangerous management objects. A statistical study of temperatures in the system of passive heat removal from the reactor was carried out using a set of approaches and parallel processing tools for specifically structured large amounts of data. A method for calculating, analyzing and monitoring the risk of a fire-hazardous situation in the passive loop of a reactor is proposed. A subsystem for predicting the occurrence of flammable situations has been developed based on methods, models and algorithms of risk analysis, which has the ability to generate management decisions in the form of a complex of fire prevention measures implemented in accordance with the requirements of regulatory and technical documents valid in the Russian Federation.

Investigation of Suspension Ball Joint Pull Out Force Based on FEA Method and Experimental Study

Suspension ball joints are always used to connect the control arms to the knuckle since they are the only joints which allow three degrees of rotational freedom. On the purpose of an sufficient performance of the ball joint, it is very important to prevent the extraction of the ball stud from the ball joint housing. Ball joint’s housing material and shape design must withstand axial loads in the ball stud from axial direction in order to avoid the ball stud pull out keeping the ball stud inside the housing. The ball stud pull out force is a critical and safety characteristic function because it is related to failure mode for front suspension system. These paper investigate how to determine of suspension ball joint pull out force based on FEA method and experimental study. With respect to results of finite element analysis and experimental study, it is possible to monitoring deformation and displacement versus the load. The result of FE analysis and design verifications make it possible to determination of suspension ball joint pull out force.

Performance Analysis of an Intermediate-Temperature-SOFC/Gas Turbine Hybrid System Using Gasified Biomass Fuel in Different Operating Modes

This work used the established mathematic models of an intermediate-temperature solid oxide fuel cell (IT-SOFC) and gas turbine (GT) hybrid system fueled with wood chip gas to investigate the load performance and safe characteristic under off-design conditions. Three different operating modes (mode A: regulating the fuel proportionally, and the air is passively regulated. Mode B: regulating the fuel only. Mode C: simultaneously regulating the fuel and air) were chosen, and the component safety factors (such as fuel cell maximum temperature, compressor surge margin, carbon deposition in reformer) were considered. Results show that when the operation modes A and C are executed, the hybrid system output power can be safely changed from 41% to 104%, and 45% to 103%, respectively. When mode B is executed, the load adjustment range of hybrid system is from 20% to 134%, which is wider than that of two above operation modes. However, the safety characteristic in this case is very complicated. The system will suffer from two potential malfunctions caused by too lower temperature entering turbine and CH4/CO cracking in reforming reactor when it operates in low load conditions. When the system operates in the high load conditions exceeding 130% of relative power, the potential thermal cracking of fuel cell will be occurred.