Start-up Duration Research Articles

Combined Cooling and Antisolvent Crystallization in Continuous Mixed Suspension, Mixed Product Removal Cascade Crystallizers: Steady-State and Startup Optimization

A continuous multistage mixed suspension, mixed product removal (MSMPR) cascade crystallization system has been modeled and optimized for both the steady-state and the startup behaviors when both cooling and antisolvent addition are applied as the crystallization driving forces. The optimal steady-state operating profiles of MSMPR cascade crystallizers have been obtained and found to be similar to the optimal batch trajectory. In addition, the minimum startup duration time is used as the objective function to optimize the startup behavior. Methods, including changing the initial solution compositions, applying dynamic antisolvent profiles, applying dynamic temperature profiles, and applying dynamic combined antisolvent and temperature profiles, are discussed and used to formulate the optimization problems. The optimal results indicate that for a cascade of two MSMPR crystallizers, it is possible to achieve a reduction of approximately 50% of the startup duration time and amount of waste. A model-free or d...

Heating Strategies for Steam-Assisted-Gravity-Drainage Startup Phase

The work introduces an analytical model to predict startup duration for steam circulation by electromagnetically heating with either induction (medium) or radio-frquency (RF) ranges. The results obtained reveal that induction slightly decreases startup time (ranging from 3 to several months' time) for frequencies smaller than 10 kHz, and it can reduce startup time to 30% of original steam circulation for 100 kHz frequency.

Modeling of Monolithic Catalyst Washcoated with TS-1 and Reactor for Continuous Cyclohexanone Ammoximation Reaction

The cyclohexanone ammoximation reaction in a monolithic reactor over titanium silicalite-1 (TS-1) was simulated based on our previous experiments. The catalyst powders of TS-1 were wash-coated on the internal surface of each channel in a honeycomb cordierite support, and external circulation was utilized to vary the flow rate of liquids passing through the channels. A one-dimensional model was employed to investigate the influences of temperature from 318.15 K to 343.15 K and external circulation flow rate of 265–765 mL min–1 on the conversion of reactants. The simulation was from startup to steady-state operation after enough iterative circulations, where the outcomes of simulation agreed favorably with experimental data, and the concentration changes in different computing circulation times are helpful to reveal the reaction process, determine the initial concentrations of reactants in the reactor for shortening duration of startup, and illustrate that the microchannels in the monolithic catalyst effect...

Investigation of effect of cyclic fuel delivery on start mode of small-sized diesel engine CH8,5 / 11

The article considers the possibility of improving starting characteristics of small-size diesel engine type CH8,5/11 by replacing vortex combustion chamber by piston combustion chamber. The authors present the formulas for determination of optimum amount of cycle fuel supply in diesel engine start mode, fuel vaporization in start mode in volume and from the wall of a cylindrical combustion chamber. Results of experimental studies show the influence of cycle fuel supply on duration of small-sized diesel start-up.

Experimental characterization of plasma start-up using ECRH in preparation of W7-X operation

The upcoming operation of Wendelstein 7-X (W7-X) will be supported by an Electron Cyclotron Resonance Heating (ECRH) system working at 140 GHz in second harmonic at the nominal magnetic field of 2.5T. Because the optimization of the plasma breakdown is crucial to ensure a successful plasma build-up, dedicated plasma start-up experiments were performed on three stellarator/heliotron devices: Heliotron J, LHD and WEGA. Start-up behavior and dependencies on ECRH injected power, neutral gas pressure and rotational transform were obtained in X2 heating. Plasma start-up delay time decreases with the increase in ECRH input power. However, this behavior saturates when low pre-fill neutral gas pressure conditions are met. Both the delay time and the electron density are an increasing function of the gas pressure. On Heliotron J and WEGA devices, the higher the rotational transform is, the faster the start-up and the higher the plasma density are. Analysis of the temporal evolution of the plasma start-up shows that plasma start-up on stellarators is a two-step process. In addition, off-axis heating experiments are characterized by a longer plasma start-up duration compared to on-axis heating discharges. Third harmonic in X-mode has been attempted on LHD for different neutral gas puffing settings but no plasma breakdown was achieved. This multi-machine study was useful to define ECRH start-up scenarios for W7-X.

An Evaluation of PCDD/Fs Mass Flux from a Hazardous Waste Incinerator: The Need for a Reasonable Start-Up Procedure

The study includes an investigation on the polychlorinated dibenzo-p-dioxins (PCDD/Fs) mass fluxes of a hazardous waste incinerator in the operation conditions, which occurred shortly after two different start-up periods. The samples were taken from seven possible dioxin output points through the incineration and air pollution control units, which include bottom ash, boiler fly ash, electrostatic precipitator (ESP) fly ash, treated wastewaters and filter cake from the physicochemical treatment of dual wet scrubbers and fly ashes, activated carbon (AC) bed, and stack gas, and they were analyzed for the PCDD/Fs. The results were assessed to determine the emission factors and the mass fluxes of PCDD/Fs for all of the outputs. A review of the congener profiles suggested that start-up conditions, such as the start-up duration and the cleaning process, may have an effect on the concentrations and congener profiles of PCDD/Fs, especially observed in the fly ashes and the stack gas. Considerable concentrations of low chlorinated furans in the ash outflows were attributed to the heterogeneous de novo synthesis of PCDD/Fs on the fly ash surfaces. Congener contributions to the mass flux of each outflow showed that the congeners retained in bottom ash are generally highly chlorinated ones, while the congeners retained by AC bed or released to the atmosphere are predominately low chlorinated ones. The results indicated that a short and clean start-up procedure in terms of a reasonable emission factor in the stack may be needed.

Start-up modes of thermoelectric generator based on vehicle exhaust waste heat recovery

Thermoelectric generator (TEG) is a promising energy conversion device for vehicle exhaust waste heat recovery. Although TEG is desired to work under composite modes and operating conditions, the influence of start-up mode on the performance of TEG was rarely paid attention to. In this study, the transient behavior of TEG under different start-up modes is investigated, including constant current, constant voltage, maximum power and constant power modes, and the differences among these modes are analyzed. The heat flow during a start-up process caused by thermoelectric effects including Peltier effect, Joule heat and Thomson heat is investigated in details, as well as the time to achieve the rated power and the influence of vehicle speed and ambient temperature. It is found that for the different start-up modes, the current is the key factor determining the heat flow and generation. With the increment of current, the temperature difference across the hot and cold junctions reduces due to the enhanced Peltier effect, the Joule and Thomson heat production is higher, and the time to reach the rated power becomes longer. With different start-up currents, the durations to reach the steady-state power are similar (the difference is less than 5.2%). However, the durations to reach 40% and 80% of steady-state power are significantly affected by the start-up current, and the differences in start-up durations are up to 70% to reach 40% of steady-state power, and 32% to reach 80% of steady-state power. A higher vehicle speed improves the TEG performance, and accelerates the transient response. Although the effect of decreasing the ambient temperature is similar to increasing the vehicle speed, the ambient temperature effect is less significant.

Dynamic modeling of high temperature PEM fuel cell start-up process

High temperature proton exchange membrane fuel cells (HT-PEMFCs) are considered to be the next generation fuel cells. Compared with standard low temperature proton exchange membrane fuel cells (LT-PEMFCs) the electrochemical kinetics for electrode reactions are enhanced by using a polybenzimidazole based membrane at an operation temperature between 160 °C and 180 °C. However, starting HT-PEMFCs from room temperature to a proper operation temperature is a challenge in application where a fast start of the fuel cell is required such as in uninterruptible power supply systems. There are different methods to start-up HT-PEMFCs. Based on a 3D physical model of a single HT-PEMFC, the start-up process is analyzed by comparing the start-up duration of the different start-up concepts. Furthermore, the temperature distribution in the HT-PEMFC is also analyzed. Finally, an optimal start-up method is proposed for the given cell configuration.

Optimization of operation conditions for the startup of aerobic granular sludge reactors biologically removing carbon, nitrogen, and phosphorous

The transformation of conventional flocculent sludge to aerobic granular sludge (AGS) biologically removing carbon, nitrogen and phosphorus (COD, N, P) is still a main challenge in startup of AGS sequencing batch reactors (AGS-SBRs). On the one hand a rapid granulation is desired, on the other hand good biological nutrient removal capacities have to be maintained. So far, several operation parameters have been studied separately, which makes it difficult to compare their impacts. We investigated seven operation parameters in parallel by applying a Plackett-Burman experimental design approach with the aim to propose an optimized startup strategy. Five out of the seven tested parameters had a significant impact on the startup duration. The conditions identified to allow a rapid startup of AGS-SBRs with good nutrient removal performances were (i) alternation of high and low dissolved oxygen phases during aeration, (ii) a settling strategy avoiding too high biomass washout during the first weeks of reactor operation, (iii) adaptation of the contaminant load in the early stage of the startup in order to ensure that all soluble COD was consumed before the beginning of the aeration phase, (iv) a temperature of 20 °C, and (v) a neutral pH. Under such conditions, it took less than 30 days to produce granular sludge with high removal performances for COD, N, and P. A control run using this optimized startup strategy produced again AGS with good nutrient removal performances within four weeks and the system was stable during the additional operation period of more than 50 days.

Memory Effects of Polychlorinated Dibenzo-p-dioxin and Furan Emissions in a Laboratory Waste Incinerator

Laboratory wastes are discharged from experimental, testing, or analysis processes, and contain various toxic chemical compounds with a high heating-value and a high chlorine content (＞ 9%). Elevated PCDD/F (polychlorinated dibenzo-pdioxin and furan) emissions during start-up stages are caused by combustion of waste with high chlorine contents, incomplete combustion, and so called ”memory effects”. Even though the duration of cold start-up is short compared with the hours of continuous steady operation in a waste incinerator, its negative effects with regard to PCDD/F emissions on both human health and the environment cannot be neglected. A full-scale laboratory-waste incinerator which is operated for 10 days in each run and has 15 to 20 runs annually was investigated in this study. Eleven PCDD/F samples of stack flue gas were collected during the cold start-up periods (for 60.5 hrs). The gas temperature of the primary combustion chamber was above 850°C, and was maintained at between 850 and 900°C by injecting diesel fuel without waste feed. For first 1.5-7.5 hours, the PCDD/F concentration in the stack flue gas was as high as 0.656-1.15 ng I-TEQ/Nm^3. Afterward, during hours 10.5-35.5 and 54.5-60.5, this reduced to 0.159-0.459 and 0.218-0.254 ng I-TEQ/Nm^3, respectively. Based on principal component analysis (PCA) and the L/H ratio, the results revealed a higher L/H ratio (1.23) before hour 32, indicating that less chlorinated PCDD/F homologues (tetra and penta) dominated, while after hour 32 more chlorinated PCDD/F homologues (hexa, hepta and Octa) had a higher mass concentration and the L/H ratio fell to 0.42. These results indicate that the PCDD/F emissions during cold start-up were caused by memory effects and thermal desorption. Therefore, in order to reduce the PCDD/F emissions from the stack flue gas of waste incinerators, is highly recommended that a higher amount of activated carbon injection is used in front of the bag filters.

Influence of the startup and shutdown phases on the viscoplastic structural analysis of the thrust chamber wall

Detailed structural analysis with Robinson's viscoplastic model of the thrust chamber wall has been completed to explain its damage process phase by phase, indicating that under the same level of thermal–structure loadings, the startup and shutdown phases play an important role of the failure. Different startup and shutdown durations were applied to study the phase influence on structural analysis and predicted life. Results reveal that the startup process mainly affects the remaining strain, while the shutdown process contributes more to the remaining stress on the cyclic effect; quick startup and longer shutdown duration conduce to prolong the chamber life and the life can be promoted 22% through reducing start-up duration from 1.5 s to 0.3 s, while 5% through increasing shut-down duration from 0.15 s to 0.9 s.

Scheduling of multiple chemical plant start-ups to minimize regional air quality impacts

Chemical plant concentrated regions may suffer localized and transient air pollution events that violate national ambient air quality standards (NAAQS). Flaring emissions, especially intensive start-up flaring emissions from chemical plants, have potentially significant impacts on local air quality. Thus, when multiple plants in an industrial zone plan to start-up within a same time period, their start-up plans should be evaluated and optimally controlled so as to avoid unexpected air-quality violations in any air-quality concern regions (AQCRs). In this paper, a general systematic methodology for multi-plant start-up emission evaluation and control has been developed. The methodology starts with collecting regional meteorological information such as wind speed and temperature; geographical information of all of the involved chemical plants and AQCRs; as well as plant operation data such as the start-up time window, start-up duration, and estimated emission profile. Next, a regional air-quality evaluation based on Gaussian dispersion model will be conducted. If any air quality violation is predicted to an AQCR, a multi-objective scheduling problem will be generated and solved to optimize the start-up sequence and start-up beginning time for all chemical plants. The scheduling model minimizes the overall air quality impacts to all of the AQCRs as well as minimize the total start-up time mismatch of all plants, subject to the principles of atmospheric pollutant dispersion. This study may provide valuable quantitative decision supports for multiple stake holders, including government environmental agency, regional chemical plants, and local communities.

The start-up performance of modified anaerobic baffled reactor (MABR) for the treatment of recycled paper mill wastewater

The reduction of the duration of start-up and the improvement of process control are important factors in order to increase the competitiveness of anaerobic baffled reactor systems. In this paper, the start-up performance of modified anaerobic baffled reactor (MABR) in treating recycled paper mill (RPM) wastewater at batch and continuous phases was investigated. In batch phase, about 3.5L (10d HRT) of RPM wastewater were added daily to the reactor for 9 days, while 7L/day (5d HRT) was pumped into the reactor during the continuous phase. During batch and continuous phase, it was found that methane yield increased significantly from 0.003 to 0.09 L CH4/g COD day. During the whole start-up operation, the system demonstrated a remarkable performance of high COD removal efficiency (up to 71%) on day 30. Nevertheless, the pH was slightly decreased (from 7.3 to 6.2) during the period of phase 1 (batch) and phase 2 (continuous).

EMI Soft-Sensing and Filter Based on Wavelet Applied in Underground Monitoring System

In order to enhance Electromagnetic Compatibility (EMC) of monitoring system, the EMI distribution should be obtained. But the measurement could not be accomplished perfectly because of underground condition. A novel EMI soft-sensing method was proposed to measure the electromagnetic interference(EMI) indirectly. The wavelet time-frequency analysis was introduced to monitoring system and the EMI source could be ascertained. The startup time, duration and waveform could be detected based on the running records of underground electric equipments. The electrical fast transient/burst (EFT/B), the most outstanding interference, was studied to verify the validity of wavelet analysis. EMI filter was improved in accordance of the EMI gotten from wavelet analysis. Power port immunity was developed obviously. Therefore the EFT/B of data port was restrained markedly with wavelet filtration. Coordinative effect of EMI power and wavelet filter resulted in reduction of false alarms. Results indicate that wavelet analysis and the improved EMI filter have enhanced the EMC of monitoring substations and sensors obviously. It is concluded the wavelet analysis is of guiding significance to measure underground EMI distribution and EMC of the underground monitoring system.

A Ship Design and Deployment Model for Non-Cargo Vessels Using Contract Scenarios

An optimisation model is proposed for the Ship Design and Deployment Problem (SDDP). This model can be used to support the development of the contract specification for non-cargo, service type of ships, facing a set of available contracts or market opportunities with different start-up periods, durations and vessel capability requirements. The proposed model is a binary integer programming (BIP) model, where the problem is to optimally select a design while at the same time considering which future contracts the vessel should be deployed in. Computational study shows that the model is able to solve the SDDP even for large problem sizes. Variants and extensions to the SDDP model are suggested including concurrent selection of multiple vessels (Fleet Design and Deployment Problem), existing initial fleet and forced contract assignment for some of the vessels. Further, generation of contracts and market opportunities for alternative future scenarios can also be considered.

Evaluation of Influent Medium Composition and Concentration in a Batch Reactor for Effective Startup of UASB Reactors

This study demonstrated the use of batch bioreactor experiments as an evaluation tool to determine appropriate influent medium composition and concentration for effective startup of an upflow anaerobic sludge blanket (UASB) reactor. Using seed sludge from a domestic treatment plant, the weight ratio of glucose and volatile fatty acids (VFA) present in the influent synthetic medium was varied and the batch performance was assessed in terms of pH variation during the course of the experiment, chemical oxygen demand (COD) reduction, specific substrate uptake rates, methanogenic activity, and methane yield. The performance was also evaluated by increasing the concentration of influent COD. Medium composition with glucose to VFA weight ratio at or below 2:8 and COD concentration at 11g∕L was determined to be optimum for effective startup of the UASB reactors. Utilization of the optimized influent medium provided a pH variation from 6.5 to 7.8 over the length of the UASB reactor and resulted in granule formation, high methanogenic activity, and methane yield. The evaluation method provided a practical approach to determine the applicability of seed sludge from a particular source and the desired influent characteristics for reduced startup duration in UASB processes.

Improved wavelet analysis in enhancing Electromagnetic Campatibility of underground monitoring system in coal mine

Underground Electro Magnetic Interference (EMI) has become so serious that there were false alarms in monitoring system, which induced troubles of coal mine safety in production. In order to overcome difficulties caused by the explosion-proof enclosure of the equipments and the limitation of multiple startup and stop in transient process during EMI measurement, a novel technique was proposed to measure underground EMI distri- bution indirectly and enhance Electromagnetic Campatibility(EMC) of the monitoring sys- tem. The wavelet time-frequency analysis was introduced to underground monitoring sys- tem. Therefore, the sources, the startup time, duration and waveform of EMI could be as- certained correctly based on running records of underground electric equipments. The electrical fast transient/burst (EFT/B) was studied to verify the validity of wavelet analysis. EMI filter was improved in accordance of the EMI distribution gotten from wavelet analysis. Power port immunity was developed obviously. In addition, the method of setting wavelet thresholds was amended based upon conventional thresholds in the wavelet filter design. Therefore the EFT/B of data port was restrained markedly with the wavelet filtering. Coor- dinative effect of EMI power and wavelet filter makes false alarms of monitoring system reduce evidently. It is concluded that wavelet analysis and the improved EMI filter have enhanced the EMC of monitoring system obviously.

Minimising the startup duration for mass- and heat-integrated two-column distillation systems: A conceptual approach

The startup of a chemical plant is a complex and highly dynamic process. The main source of complexity stems from the simultaneous variation of all process variables until the required operating point is reached. In previous studies, the startup of single columns for conventional and reactive distillation was considered. A two-column system was also analysed, but featuring only heat coupling without mass integration between the columns, which means with no positive feedbacks. In this work, a heat- and mass-integrated two-column system for continuous pressure-swing distillation (PSD) is investigated experimentally and theoretically on the example of the acetonitrile–water mixture. Rigorous models of the individual equipment units such as trays, condensers and heat exchangers have been formulated and integrated in an overall dynamic system model which has been validated against experimental data. Further, a simple qualitative model to guide the minimisation of the startup duration has been derived and applied to the considered distillation system. The results show that, following the derived criteria, it is possible to reduce the startup duration for the example in Case Study 1 by 78% compared to the duration of empirical startup procedure.

On the start-up transient simulation of a turbo fuel cell system

The start-up transient behavior is an important issue in a turbo fuel cell system design. This paper developed a general dynamic model of the hybrid fuel cell/micro-gas turbine (MGT) system to investigate the transient behavior during cold start. The unsteady flow process through components of the turbo fuel cell system, which includes a solid oxide fuel cell (SOFC) stack, an afterburner, a turbo generator and heat exchangers, was modeled using a filling-and-emptying approach. Each major component was treated as a function block in the coded model. Computer simulations were performed on a Matlab/Simulink platform based on the block-diagram concept. The main focus of this study is on the start-up transient behavior of a basic turbo fuel cell system. The simulation results show that the start-up time for the example turbo fuel cell system (200 kW SOFC plus 50 kW MGT) can be up to about a few hours. Preliminary parametric investigations with different operating conditions show that the start-up duration can be reduced to less than 1 h.

Investigation of the Start-up Strategy for a Solid Oxide Fuel Cell Based Auxiliary Power Unit under Transient Conditions

A typical approach to the synthesis/design optimization of energy systems is to only use steady state operation and high efficiency (or low total life cycle cost) at full load as the basis for the synthesis/design. Transient operation as reflected by changes in power demand, shut-down, and start-up are left as secondary tasks to be solved by system and control engineers once the synthesis/design is fixed. However, start-up and shut-down may be events that happen quite often and, thus, may be quite important in the creative process of developing the system. This is especially true for small power units used in transportation applications or for domestic energy supplies, where the load demand changes frequently and peaks in load of short duration are common. The duration of start-up is, of course, a major factor which must be considered since rapid system response is an important factor in determining the feasibility of solid oxide fuel cell (SOFC) based auxiliary power units (APUs). Start-up and shut-down may also significantly affect the life span of the system due to thermal stresses on all system components. Therefore, a proper balance must be struck between a fast response and the costs of owning and operating the system so that start-up or any other transient process can be accomplished in as short a time as possible yet with a minimum in fuel consumption. In this research work we have been studying the effects of control laws and strategies and transients on system performance. The results presented in this paper are based on a set of transient models developed and implemented for the components of a 5 kWe net power SOFC based APU and for the high-fidelity system which results from their integration. The simulation results given below are for two different start-up approaches: one with steam recirculation and component pre-heating and the second without either. These start-up simulations were performed for fixed values of a number of system-level parameters (e.g., fuel utilization, steam-to-methane ratio, etc.) and were used to generate sufficient information to permit the development of appropriate control strategies for this critical operating point. These strategies are based on a balance between fuel consumption and response time. In addition, energy buffering hardware was added to the system configuration in order to minimize the effects of transients on fuel cell stack performance and lifetime.