Advanced Materials Research Vols. 732-733

Abstract: Cryogenic separation method is the main method to recycle NGL (Natural Gas Liquid). Oilfield two-stage expansion NGL cryogenic separation plant is a complex system composed of varieties of material flow, energy flow and equipments, is a typical distributed energy use system composed of three parts, energy supply, energy use and waste heat recovery. In this paper, according to the process characteristics of two-stage expansion cryogenic separation plant, three-box analysis method was used, the system was compartmentalized into six subsystems, represented the exergy analysis model of system—unit—equipment, given the specific analysis process and the assessment rules for the NGL system. Using the practical operational data, the writers conduct the exergy analysis on the operational working condition of Daqing oilfield NGL system. Based on the calculation results, this paper raises some proposals to improve the operational efficiency, and achieved a good energy saving effect in engineering practice.

Abstract: Traditional models of power plant boiler superheater are incapable of simulating the operating conditions under large disturbances with high precision. To resolve this challenging problem, this paper presents a nonlinear lumped-parameter dynamic model of power plant boiler superheater. The present model describes the dynamic processes of the pressure-flowrate and the enthalpy-temperature channels with sufficient consideration of their coupling effect. To better capture the distributed-parameter property of superheater temperature, the multi-segment lumped-parameter modeling method is employed for modeling the enthalpy-temperature channel. Dynamic responses of the last-stage superheater of a 600 MW controlled circulation boiler to disturbances of the spray water flowrate, the superheater inlet enthalpy, and the absorbed heat flux are simulated. Simulation results show that dynamic responses of the present model are reasonable, and the model has high precision, which can meet the requirements for full scale simulation and control system simulation.

Abstract: The lean blowout experiments of the combustion stability device A (multi-vortexes-dome combustor model) have been carried out at atmospheric pressure. In contrast with the experimental data of device B, and the result shows that the lean blowout performance of the device A is superior to the device B at low operating condition. Furthermore, both the devices A and B were modeled, and the combustion numerical simulations were performed with the steady Flamelet model of non-premixed combustion and the simplified mechanism of methane-air reaction with 14 species and 26 step elementary reactions. The numerical results are in agreement with the experimental phenomena.

Abstract: The heat transfer characteristic of steam condensation in a 50mm diameter and 30° inclined tube was experimentally investigated. Based on the experiment and Akhavan-Behabadi correlation, a new correlation has been developed. It is shown that the heat transfer coefficients for the inclined tube are approximately 1.06-2.98 times higher than those for the horizontal tube. The heat transfer coefficients predicted by Shah correlation, Würfel correlation and Akhavan-Behabadi correlation deviate greatly, though Akhavan-Behabadi correlation is better. But by the developed correlation, more accurate heat transfer coefficients are predicted than Shah correlation, Würfel correlation and Akhavan-Behabadi correlation, and the deviation is less than 15%. The developed empirical correlation is a better one to predict heat transfer coefficients for steam condensation in larger diameter inclined tubes.

Abstract: In this paper, the heat transfer enhancement by pulsating laminar flow in rectangular grooved channels was experimentally investigated. Effects of Reynolds number Re, pulsation frequency, groove depth and groove length on the heat transfer enhancement were studied. Experimental results show that Nusselt number increases with Re increases both in steady and pulsating flow cases. Pulsating flow can efficiently enhance heat transfer in the grooved channels and the heat transfer enhancement factor increases with the increase of Re. There exists an optimal pulsation frequency, corresponding to the maximum heat transfer enhancement factor, which is almost the same for different Re, groove depth and groove length.

Abstract: This paper presents an experimental study on total heat transfer coefficient (h_t) in oscillating heat pipe heat exchanger hot air flow tunnels, h_t plays an important role in the oscillating heat pipes design process. In this paper, h_t and the convective heat transfer coefficient (h) was investigated by experimentally and theoretical calculation respectively. From experimental study, the relationship between the ratio of heat transfer coefficient and the relative humidity is obtained. The results show that the ratio of ht to h increases from 5 to 20 as the relative humidity of the hot gas increasing from 19.22% to 60%. According to the experimental data, a matched curve and an empirical equation were presented, which can be described as h_t=h(1.87783+0.09631x+0.0032x²).

Abstract: A numerical integral method to efficiently solve the point kinetics equations with Newtonian temperature feedback is described and investigated, which employs the better basis function (BBF) for the approximation of the neutron density in integral of one time step. The numerical evaluation is performed by the developed BBF code. The code can solve the general non-linear kinetics problems with six groups of delayed neutron. For the application purposes, the developed code and the method are tested by using a variety of problems, including ramp reactivity input with or without temperature feedback. The results are shown that the BBF method is clearly an effective and accurate numerical method for solving the point kinetics equations with Newtonian temperature feedback, and it can be used in real time power reactor forecasting in order to prevent the reactivity accidents.

Abstract: Insufficient output and rising pressure after governing stage of a 630 MW supercritical unit occurred only 18 month after the first outage. Though analysis based on measured parameters, fouling existed in governing stage and the first stage group. By virtue of linearization of formula and decoupling the impacts to thermal characteristic parameters, the quantified deposition degree was obtained. The fouling reason was determined by scale sample analysis, and the solution was proposed by quantitative calculation. The problem was successfully solved with boiler pickling, turbine cascade jet-beading and pulsing minimum oxygen to inhibit flow accelerated corrosion. A steam quality detection method was also proposed as the installation of measurement point after governing stage of supercritical unit. These treatments provided building and operation experience for 1000MW ultra-supercritical turbine and the same type of equipments.

Abstract: In generators operation,the hydrogen purity is an important monitoring indictor. The change of thepurity affects unit safety operation directly. Hydrogen purity of one #10 generator unit dropquickly. Determining how to find the mainfactors is the main objective. Primarily, it was analyzed that the main reason of hydrogenpurity decrease was the air enter the sealingoil system. Though analyzing DCS history curve,as well as temperature detection test, channeling oil test, and checking thesystem pressure, finally there were two reasons, one isfill oil valve leakage fault, the two is the oil pressure difference of hydrogen side and airside in balance valve aretoo large, causing the oil channeling from air side to hydrogen side.

Abstract: The Ground-Coupled or Source Heat Pump (GCHP/GSHP) system is increasingly being considered as an alternative to traditional cooling/heating system because it can reduce the emission of greenhouse gases. The GCHP/GSHP system uses sustainable ground temperature to emit heat during the summer and to extract heat during the winter. It is a ubiquitous system because it can be used at any time or place and semi-permanent energy. The geothermal system is composed of Ground Heat Exchanger (GHE), heat pump and load facilities. The GHE is embedded in a borehole, which is made up of GHE and grout. The borehole thermal resistance is the most important parameter in designing the geothermal system because it shows the quantity of heat transfer in the borehole. There are many methods to estimate the borehole thermal resistance. Thermal Performance Tests (TPTs) were conducted to directly measure the borehole thermal resistance of several kinds of GHEs. Then the experiment results and analytical results were compared in order to select the most accurate methods to evaluate the borehole thermal resistance.