Primary Cyclone Research Articles

Preconditioning and Intensification of Upstream Extratropical Cyclones through Surface Fluxes

Abstract The influence of the surface latent and surface sensible heat flux on the development and interaction of an idealized extratropical cyclone (termed “primary”) with an upstream cyclone (termed “upstream”) using the Navy’s Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) is analyzed. The primary cyclone develops from an initial perturbation to a baroclinically unstable jet stream, while the upstream cyclone results from Rossby wave dispersion at the surface where a bottom-up style development occurs. The intensity of the upstream cyclone is strongly enhanced by surface latent heat fluxes and, to a lesser degree, by surface sensible heat fluxes. Forward trajectories initiated from the postfrontal sector of the primary cyclone travel south of the upstream anticyclone and feed into the atmospheric river and warm conveyor belt region of the upstream cyclone. Substantial moistening of this airstream is a result of upward surface latent heat flux present in both the primary cyclone’s postfrontal sector and along the southern flank of the anticyclone. Backward trajectories initiated from the same region show that these air parcels originate from a broad area north of both the anticyclone and the primary cyclone in the lower troposphere. The airstream identified represents a new pathway through which dry, descending air that is preconditioned through surface moistening enhances the development of an upstream cyclone through diabatically generated potential vorticity.

Influence of the Interdecadal Pacific Oscillation on Super Cyclone Activities over the Bay of Bengal during the Primary Cyclone Season

An obvious interdecadal change can be measured in the super cyclones (SCs, categories 4 and 5) that occur from October to November over the Bay of Bengal (BoB). This change may be modulated by the interdecadal Pacific oscillation (IPO). A La Niña-like difference between the 1977–1998 (IP1) and 1999–2014 (IP2) periods forced a local Hadley circulation in the eastern tropical Indian Ocean by strengthening the Walker circulation, which caused plummeting upper-level temperatures and ultimately created favorable thermodynamic conditions to enhance the cyclone intensity. Meanwhile, an equatorial downwelling Kelvin wave caused by heating and westerly wind differences entered the BoB rim along the coast and aptly intensified the cyclone, such that the downwelling Kevin wave and Rossby wave generated by its reflection deepened the thermocline in the BoB. The favorable atmospheric and oceanic conditions in IP2 jointly and preferentially cause far more SC activities from October to November over the BoB compared to IP1.

Functional group characteristics and pyrolysis/combustion performance of fly ashes from Karamay oily sludge based on FT-IR and TG-DTG analyses

Three fly ashes, sequentially from the primary cyclone separator (CS1), the secondary cyclone separator (CS2) and the bag-type dust collector (BDC) at the outlet of industrial oily sludge pyrolyzer, were characterized by proximate analysis, ultimate analysis, FT-IR and TG-DTG methods. Molecular structure, pyrolysis and combustion performance of each fly ash were discussed. Results showed that content of volatile matter in BDC was 16.92% (dry base), and the contents in CS1 and CS2 were similar of 11.18% and 12.51%, respectively. Pyrolysis performance of each fly ash was quite different, among which the weight loss of BDC was higher of 44.3%, while the losses of CS1 and CS2 were 8.77% and 9.66%, respectively. Combustion performance showed that the comprehensive combustion characteristic index (SN) and combustion stability index (DW) of BDC were higher of 25.03 %2·min−2·°C−3 and 10.45 %2·min−1·°C−3, respectively, presenting well combustion performance. Pyrolysis kinetics based on Coats-Redfern model presented that the reaction order of three fly ashes could be selected as n = 5. While the order of combustion kinetics for CS1, CS2 and BDC might be assigned to 1 (or 2), 2 (or 3) and 1, respectively.

Commissioning Analysis and Improvement measures for Biomass Circulating Fluidized Bed Gasifier

This paper presents the debugging test of biomass circulating fluidized bed gasifier in a rice mill factory of Jiangsu Province. The main debugging process of the gasifier system is reported. The typical problems of the gasifier system during the debugging period are analyzed, including the blockage of the primary cyclone separator, blockage of loop seal, bed inventory leakage of blast cap on air distribution plate, feeding tube coking, and large fluctuation of bed pressure. Reasonable improvement countermeasures and implementation plan is provided. The operation characteristics of the gasifier are preliminaries mastered through debugging, which provides reference for the operation and adjustment of the biomass circulating fluidized bed gasifier. These results provide certain guiding significance for the scale application of biomass circulating fluidized bed gasifier.

Variability of southwest Pacific tropical cyclone track geometry over the last 70 years

AbstractVariability in tropical cyclone (TC) track morphology, as it evolves post genesis, presents continued challenges in accurately forecasting TC movement. Therefore, an improved understanding of TC track climatology is essential, given that TCs are one of the most critical natural hazards in the southwest Pacific (SWP) region. We examine the historical variability of TC tracks within the SWP over the last 70 years (1948–2017) using 6‐hourly track data obtained from the South Pacific Enhanced Archive of Tropical Cyclones (SPEArTC) database. A probabilistic clustering technique is applied to separate TC tracks into distinct groups in order to assess the primary cyclone trajectories for the region and its relationship with the El Niño–Southern Oscillation (ENSO). TC tracks are also classified into four sinuosity categories: straight, recurving, sinuous and highly sinuous; and their spatial and temporal characteristics subsequently analysed. The results of the cluster analysis identified five optimal groups of TC tracks, four of which exhibited southeast propagation, except for the southwest moving tracks in Cluster 5. Temporally, significant trends were observed over the last seven decades, with Clusters 1, 3 and 4 becoming less frequent with a substantial increase in the occurrence of Cluster 2 tracks (representing TCs east of dateline), a geometry favoured by El Niño conditions. Further, the sinuosity analysis revealed continued dominance of straight TCs within the eastern SWP with a tendency of encountering TCs of other morphology types. Conversely, the western SWP region is typically exposed to highly sinuous tracks. We also observed a significant decrease (increase) in TCs with straight and quasi‐straight (highly sinuous) tracks, particularly during the last decade. These findings suggest that combined cluster analysis and TC track sinuosity analysis is an important tool in generalising the TC track regimes, refining predicted trajectories and understanding impacts on SWP island nations.

The role of secondary cyclones and cyclone families for the North Atlantic storm track and clustering over western Europe

AbstractSecondary cyclones are those that form in association with a pre‐existing primary cyclone, typically along a trailing cold front. In previously studied cases they have been shown to cause extreme damage across Europe, particularly when multiple cyclones track over the same location in rapid succession (known as cyclone clustering). To determine the dynamical relationship between primary and secondary cyclones over the North Atlantic, a frontal identification algorithm is partnered with a cyclone identification method to objectively identify secondary cyclones in 35 extended winter periods using reanalysis data. Cyclones are grouped into “cyclone families” consisting of a single primary cyclone and one or more secondary cyclones. This paper aims to quantify the differences between secondary and primary cyclones over the North Atlantic, and how cyclone families contribute to episodes of cyclone clustering across western Europe. Secondary cyclones are shown to occur most frequently in the central and eastern North Atlantic, whereas primary cyclones are commonly found over the western North Atlantic. Cyclone families have their strongest presence over the North Atlantic Ocean and contribute more than 50% of cyclones over the main North Atlantic storm track. A final category, solo cyclones, which are not associated with cyclogenesis on any connected fronts, are most commonly identified over continental regions as well as the Mediterranean Sea. Primary cyclones are associated with the development of an environment that is favourable for secondary cyclone growth. Enhanced Rossby wave breaking following primary cyclone development leads to an increase in the upper‐level jet speed and a decrease in low‐level stability. Secondary cyclogenesis commonly occurs in this region of anomalously low stability, close to the European continent. During periods of cyclone clustering, secondary cyclones are responsible for approximately 50% of the total number of cyclones. The increase in jet speed and decrease in static stability initiated by the primary cyclones acts to concentrate the genesis region of secondary cyclones and direct the cyclones that form along a similar track. While there is an increase in the secondary cyclogenesis rate near western Europe during periods of European clustering, the basin‐wide secondary cyclogenesis rate decreases during these periods. Thus the large‐scale environment redistributes secondary cyclones during periods of clustering rather than increasing the total number of secondary cyclones.

A Seasonally Recurrent Annular Cyclone in Mars Northern Latitudes and Observations of a Companion Vortex

AbstractWe study a seasonally recurrent cyclone and related cloud phenomena observed on Mars at Ls ~120°, latitude ~60°N, and longitude 90°W from images obtained with cameras in different spacecraft between 1995 and 2018. A remarkable double cyclone formed in 2012 and we present a detailed study of its dynamics using images from Mars Express and Mars Reconnaissance Orbiter obtained between 6 June and 9 July. A double cyclone was also observed in 2006 and 2008. In other Martian years the primary cyclone showed an annular cloud morphology with a large water ice cloud observed eastward of it. The cyclones have a size of ~600–800 km with a cloud‐free core of a radius ~100–300 km. Tangential velocities measured from cloud tracking in 2012 images are ~5–20 m/s−1 at 10‐km altitude and double cyclone moved eastward with a velocity of 4 m/s−1 during its lifetime of one month. The vortices grow in the morning hours, but with the increasing insolation as the sol progresses, a part of the clouds evaporate, the winds weaken, and the vortices lose coherence. This phenomenon forms under high‐temperature gradients in a region with a large north‐south topographic slope and has been recurrent each Martian year between 1995 and 2018. We argue the interest of studying its changing properties each Martian year in order to explore their possible relationship to the state of the Martian atmosphere at Ls ~120°.

Flow dynamics study of catalyst powder in catalytic cracking unit for troubleshooting

Abstract Gamma scanning and radiotracer applications are very effective and inexpensive tools to understand and optimize the process as well as troubleshoot the various types of problems in many chemical, petrochemical industries and refineries. These techniques are non-invasive; hence, the problems can be pinpointed online, which leads to reduce the downtime, schedule the shutdown and maintenance of the plant equipment, rendering huge economic benefits. In a leading refinery of India, the catalytic cracking unit (CCU) was malfunctioning. It was suspected by the refinery engineers that the catalyst powder was being carried over to the fractionator, which could have led to erosion of the fractionator column internals resulting in their rupture, and consequentially, to the fire hazard. To understand the flow behaviour of the catalyst powder and to ensure the mechanical integrity, catalyst accumulation and choking, both radiotracer study and gamma scanning of the CCU reactor was carried out. The reactor consists of a riser, three primary cyclones and three secondary cyclones. Gamma scanning of the reactor was carried out with the help of an automatic gamma scanner using 1.8 GBq of Co-60 sealed source. Results showed that the catalyst powder was accumulated in one of the secondary cyclones and uneven density distribution was observed in another secondary cyclone. The radiotracer study was carried out using the irradiated catalyst powder as a radiotracer, which contains 0.9 GBq of Na-24. The radiotracer was injected in the reactor through the specially fabricated injection system. Radiation measurement was done using the thermally insulated and collimated NaI(Tl) scintillation detectors located at various strategic locations coupled to a multi-detector data acquisition system. The data were mathematically analysed. It was confirmed that the catalyst powder was accumulated in one of the secondary cyclones with no flow downwards. This resulted in excess powder available to travel along with hydrocarbon towards fractionator. Since the quantity of powder released through the hydrocarbon outlet of CCU was higher than the designed value, the catalyst powder was observed in various zones of the fractionator. Mathematical modelling of the radiotracer data obtained at various locations corroborated the scanning results; also, the flow pattern was obtained. Partially blocked secondary cyclone showed plug flow with recirculation; normal working cyclone had plug flow behaviour and the vortex breaker showed parallel flow.

The role of ENSO and MJO on rapid intensification of tropical cyclones in the Bay of Bengal during October–December

The influence of El Nino/Southern Oscillation (ENSO) and Madden–Julian Oscillation (MJO) and their combined effect on the rapid intensification (RI) of tropical cyclones (TCs) in the Bay of Bengal (BoB) during the primary cyclone season (October–December) is investigated. An empirical index, called genesis potential index (GPI), is used to quantify the relative importance of four environmental parameters responsible for the modulation of TCs characteristics. The analysis shows that TC frequency and RI of TC’s is higher in La Nina than El Nino regime during the primary TC season in the BoB. The combined effect of enhancement (reduction) in mid-tropospheric humidity (primary factor) and relative vorticity (secondary factor) played a major role in the enhancement (reduction) of the TC activity under La Nina (El Nino) regime. In addition, when the MJO is active over the BoB (phases 3–4; characterized by enhanced convective activity in the BoB) under La Nina regime, environmental conditions were more conducive for enhancement of TC activity and RI of TCs compared to corresponding MJO phase under El Nino regime. Increase in mid-tropospheric humidity and reduction in vertical wind shear were identified as the primary and secondary factors enhancing the likelihood of RI of TCs in the BoB during phases 3–4 of MJO under La Nina regime. Further, the role of accumulated tropical cyclone heat potential (ATCHP) on the RI of TC during primary TC season is also investigated. Our analysis demonstrates that ATCHP is large for TCs which undergo RI compared to TCs not undergoing RI.

Development of an idealised downstream cyclone: Eulerian and Lagrangian perspective on the kinetic energy

ABSTRACTIn this idealised modelling study, the development of a downstream cyclone, which closely follows the life-cycle of a Shapiro-Keyser cyclone, is addressed from a quasi-geostrophic kinetic energy perspective. To this end a simulation of a dry, highly idealised, dispersive baroclinic wave, developing a primary and a downstream cyclone, is performed. Kinetic energy and processes contributing to its tendency – in particular baroclinic conversion and ageostrophic geopotential fluxes – are investigated in three dimensions both in an Eulerian and a Lagrangian framework from the genesis of the downstream cyclone as an upper-level kinetic energy centre, over frontal fracture to the fully developed cyclone showing the characteristic T-bone surface frontal structure, with a strong low-level jet along the bent-back front. Initially the downstream cyclone grows by the convergence of ageostrophic geopotential fluxes from the primary cyclone, but as vertical motions intensify this process is replaced by baroclinic conversion in the warm sector. We show that kinetic energy released in the warm sector is radiated away at all levels by ageostrophic geopotential fluxes: in the upper troposphere they are directed downstream, while in the lower troposphere they radiate kinetic energy to the rear of the cyclone. Thereby, vertical ageostrophic geopotential fluxes, their location and divergence, are identified to play a major role in the intensification of the cyclone in the lower troposphere and for the formation of the low-level jet. Low-level rearward ageostrophic geopotential fluxes converging along the bent-back front are shown to be a general characteristic of an eastward propagating baroclinic wave.

Response of extratropical cyclone activity to the Kuroshio large meander in northern winter

We examined possible responses of cyclone activities to the bimodal path states of the Kuroshio Current [i.e., large meander (LM) and non‐LM (NLM)] by using the long‐term reanalysis data and the 20th century hindcast experiment of a high‐resolution atmosphere‐ocean coupled model. Compared with a seasonal mean cyclone track frequency for the LM and NLM periods, a primary cyclone track shifts southward in association with the meander of Kuroshio Current. Composite analyses of the hindcast experiment showed remarkable atmospheric responses accompanying the Kuroshio LM. The Kuroshio LM causes a decrease in latent heat flux in the south of Japan and a southward shift of the near‐surface baroclinic zone. Distinctive decreases in thermodynamic fluxes inhibit the rapid development of cyclones in the meander region, eventually inducing positive sea level pressure anomalies downstream from that region.

Warm Conveyor Belts in Idealized Moist Baroclinic Wave Simulations

AbstractThis idealized modeling study of moist baroclinic waves addresses the formation of moist ascending airstreams, so-called warm conveyor belts (WCBs), their characteristics, and their significance for the downstream flow evolution. Baroclinic wave simulations are performed on the f plane, growing from a finite-amplitude upper-level potential vorticity (PV) perturbation on a zonally uniform jet stream. This nonmodal approach allows for dispersive upstream and downstream development and for studying WCBs in the primary cyclone and the downstream cyclone. A saturation adjustment scheme is used as the only difference between the dry and moist simulations, which are systematically compared using a cyclone-tracking algorithm, with an eddy kinetic energy budget analysis, and from a PV perspective. Using trajectories and a selection criterion of maximum ascent, forward- and rearward-sloping WCBs in the moist simulation are identified. No WCB is identified in the dry simulation. Forward-sloping WCBs originate in the warm sector, move into the frontal fracture region, and ascend over the bent-back front, where maximum latent heating occurs in this simulation. The outflow of these WCBs is located at altitudes with prevailing zonal winds; they hence flow anticyclonically (“forward”) into the downstream ridge. In case of a slightly weaker ascent, WCBs curve cyclonically (“rearward”) above the cyclone center. A detailed analysis of the PV evolution along the WCBs reveals PV production in the lower troposphere and destruction in the upper troposphere. Consequently, WCBs transport low-PV air into their outflow region, which contributes to the formation of distinct negative PV anomalies. They, in turn, affect the downstream flow and enhance downstream cyclogenesis.

A Global View of Equatorial Waves and Tropical Cyclogenesis

Abstract This study investigates the number of tropical cyclone formations that can be attributed to the enhanced convection from equatorial waves within each basin. Tropical depression (TD)-type disturbances (i.e., easterly waves) were the primary tropical cyclone precursors over the Northern Hemisphere basins, particularly the eastern North Pacific and the Atlantic. In the Southern Hemisphere, however, the number of storms attributed to TD-type disturbances and equatorial Rossby waves were roughly equivalent. Equatorward of 20°N, tropical cyclones formed without any equatorial wave precursor most often over the eastern North Pacific and least often over the western North Pacific. The Madden–Julian oscillation (MJO) was an important tropical cyclone precursor over the north Indian, south Indian, and western North Pacific basins. The MJO also affected tropical cyclogenesis by modulating the amplitudes of higher-frequency waves. Each wave type reached the attribution threshold 1.5 times more often, and tropical cyclogenesis was 3 times more likely, within positive MJO-filtered rainfall anomalies than within negative anomalies. The greatest MJO modulation was observed for storms attributed to Kelvin waves over the north Indian Ocean. The large rainfall rates associated with tropical cyclones can alter equatorial wave–filtered anomalies. This study quantifies the contamination over each basin. Tropical cyclones contributed more than 20% of the filtered variance for each wave type over large potions of every basin except the South Pacific. The largest contamination, exceeding 60%, occurred for the TD band near the Philippines. To mitigate the contamination, the tropical cyclone–related anomalies were removed before filtering in this study.

Gas flow behavior in industrial FCC disengager vessels with different coupling configurations between two-stage separators

The gas flow behaviors and gas residence time distribution in industrial FCC disengager space are numerically studied with the combined consideration of the product gas, stripping gas and anti-coking steam. Although purge steam is used in the top dome in order to alleviate the coke formation in the refinery plants, its effectiveness is still obscure. In this study, the Reynolds stress model is applied to calculate the gas flow field and the scalar transport equations are used to obtain the gas residence time distribution. The species transport equations are used to get the local mass fractions of steam and oil vapors and further to verify the effectiveness of the anti-coking steam. In view of the wide use of “open” configuration, the optimizing position of the primary cyclone outlet is proposed for an industrial case in Qianguo refinery. Based on the results, suggestions are made for improved operation of the industrial units.

Gas flow behavior and residence time distribution in a FCC disengager vessel with different coupling configurations between two-stage separators

To deeply understand the effect of coupled configuration between two-stage separators on the gas flow behavior in fluid catalytic cracking disengager space, the gas flow field and residence time distribution in a bench-scale disengager is numerically studied on the platform of the commercial computational fluid dynamics software package, Fluent 6.1. Two conventionally used coupling configurations in refineries and a newly-designed configuration are investigated. The Reynolds stress model is applied to simulate the gas flow field and the results agree well with the experimental values measured by a smart five-hole probe. Coupled with the Reynolds stress model, a scalar transport equation is used to obtain the gas residence time distribution. It is shown that the coupling configuration between the primary and secondary cyclones has an apparent effect on the gas flow behavior. The newly-designed configuration is better to quickly discharge the gas into the secondary cyclone inlet with a maximum residence time of 0.38 s, compared to 7.72 s and 2.79 s for the two conventional configurations. The simulation results indicated that the appropriate modification of the coupling configuration can help to improve the gas flow. The knowledge of the gas flow field also help to understand the coke formation process in the disengager space.

Multiobjective optimization of an industrial grinding operation under uncertainty

Abstract Multiobjective optimization of an industrial grinding operation under various parameter uncertainties is carried out in this work. Two sources of uncertainties considered here are related to the (i) parameters that are used inside a model representing the process under consideration and subjected to experimental and regression errors and (ii) parameters that express operators’ choice for assigning bounds in the constraints and operators prefer them to be expressed around some value rather than certain crisp value. Uncertainty propagation of these parameters through nonlinear model equations is reflected in terms of system constraints and objectives that are treated here using chance constrained fuzzy simulation based approach. Such problems are treated in literature using the standard two stage stochastic programming methodology that has a drawback of leading to combinatorial explosion with an increase in the number of uncertain parameters. This problem is overcome here using a combination of fuzzy and chance constrained programming approach that tackles the problem by representing and treating the uncertain parameters in a different manner. Simultaneous maximization of grinding circuit throughput and percent passing mid size fraction are studied here with upper bound constraints for various performance metrics for the grinding circuit, e.g. percent passing of fine and coarse size classes, percent solids in the grinding circuit final outlet stream and circulation load of the grinding circuit. Uncertain parameters considered are grindability indices of rod mill and ball mill, sharpness indices of primary and secondary cyclones and the respective upper bounds for the constraints mentioned above. The deterministic multiobjective grinding optimization model of Mitra and Gopinath [2004. Multiobjective optimization of an industrial grinding operation using elitist nondominated sorting genetic algorithm. Chem. Eng. Sci. 59, 385–396.] forms the basis of this work on which various effects of uncertain parameters are shown and analyzed in a Pareto fashion. Nondominated sorting genetic algorithm, NSGA II, a popular elitist evolutionary multiobjective optimization approach, is used for this purpose.

An event of stratospheric air intrusion and its associated secondary surface cyclogenesis over the South Atlantic Ocean

This work presents an analysis of a lowermost stratospheric air intrusion event over the coast of Brazil, which may have been responsible for a secondary surface cyclogenesis over the southwestern Atlantic Ocean. The surface cyclone initiated at 0600 UTC 17 April 1999 in a cold air mass in the rear of a cold front after a primary cyclone developed over the same region. The analysis of the secondary cyclone revealed the presence of lowermost stratospheric air intrusion characterized by anomalous potential vorticity (PV), dry air, and high concentration of ozone in atmospheric column. The system developed on the eastern side of an upper level core of PV anomaly, which induced a cyclonic wind circulation at lower levels and favored the onset of the secondary cyclone. In midlevels (500 hPa), the cutoff low development contributed to reduce the propagation speed of the wave pattern. This feature seemed to (1) allow the low‐level cold/dry air to heat/moisten associated with sensible and latent fluxes transferred from the ocean to the atmosphere, which intensified a baroclinic zone parallel to the coast, and (2) contribute to the long duration of the system. The present analysis indicates that this secondary cyclone development could be the result of the coupling between the PV anomaly in the upper levels and low‐level air‐sea interaction.

Linear system identification of a cold flow circulating fluidized bed

Knowledge of the solids circulation rate (SCR) is essential to the control and improved performance of a circulating fluidized bed system. In the present work, the noise model is derived using the prediction error method considering process and measurement noises acting on the cold flow circulating fluidized bed (CFCFB) with a cork particulate material. The outputs of the initial model are the total pressure drop across the riser, the pressure drop across the crossover, the pressure drop across the primary cyclone, the total pressure drop across the stand-pipe, the pressure drop across the loop seal, and the SCR. The stochastic estimate of SCR is determined from the noise model using the stochastic pressure drop estimates. The deterministic estimate is obtained through the inputs taken as move air flow, riser aeration, and loop seal fluidization air that are all independent variables of the given setup and under the control of the user. The theory has been developed to convert a complete blackbox model to a grey box model through the output-to-state transformation such that both the models of the CFCFB consists of all these output variables as the states of the system, and only pressure drops across the system as the output measurements. Thus, the final models do not include any fictitious terms and they are defined only in terms of physical parameters of the given system. Both components of SCR are separately analysed. The combined SCR response of both the noise model and deterministic model is compared with the validation data set of this state variable in terms of modelfit, and the results are shown.

Dependence of ensemble spread on model uncertainties for extratropical cyclone simulations

AbstractIn order to examine the dependence of the ensemble forecast spread on model uncertainty, we use the model grid‐point spacing and the index of shallow‐convection top as surrogates for model uncertainty, to construct two groups of ensemble forecasts (‘experiments’). In each ensemble, we use several members that differ only in the size of their model uncertainties. An initial baroclinic‐jet basic state is constructed, with a balanced three‐dimensional perturbation, to trigger development of a baroclinic wave.In terms of the minimum central surface pressure, the spread associated with each ensemble increases with increasing model uncertainty. Similar sensitivity is observed for the maximum ensemble spread and the domain‐averaged spread in terms of surface pressure. In both experiments, the domain‐averaged spread is linearly proportional to the size of the model uncertainty, and varies in time with a power‐law dependence.The ensemble spread is mainly collocated with the primary cyclone during the cyclone development stage, when amplitude error dominates, and is elongated along the regions with strong gradients during the mature stage, when the phase error dominates.Forecast errors also grow in association with the secondary cyclones that develop in the simulation. The maximum ensemble spread associated with secondary cyclones increases with increasing model uncertainty, as for the primary cyclones. It is found that model uncertainties have a larger effect at the surface on the spread associated with the upstream cyclone, compared to the downstream cyclone (at the same integration time), because of the different stages of development of the upstream and downstream cyclones. Copyright © 2007 Royal Meteorological Society

CFB air-blown flash pyrolysis. Part I: Engineering design and cold model performance

Abstract The objective of this work was to design, construct and test a novel circulating fluid bed fast pyrolysis reactor system for production of liquids from biomass. The novelty lies in incorporating an integral char combustor to provide autothermal operation of the reactor. A reactor design methodology was devised which correlated input parameters to process variables, namely temperature, heat transfer and gas/vapor residence time, for both the char combustor and biomass pyrolyser. From this methodology, a CFB reactor was designed with integral char combustion for 10 kg/h biomass throughput. A full-scale cold model of the CFB unit was developed and tested to derive suitable hydrodynamic relationships and performance constraints. The hot CFB reactor was constructed, its operability was tested and appropriate modifications were accomplished prior to the commissioning. A major requirement for the desired dual-mode operation of the reactor system conceived was the close coupling of the two reactor subsystems, namely the pyrolysis riser (medium temperature) and char combustor (high temperature). The basic CFB reactor design was proven effective in providing the high heat transfer rates – expressed as low voidage values in the riser and high solid circulation rates – to biomass particles in the very short vapor residence times (VRTs) required. The understanding of the complicated aspects related to two-phase gas–solids flow in the standpipe resulted in a smooth, stable transfer of solids over a wide range of operating parameters during cold CFB reactor operation. In the hot CFB unit testing, the use of two and three cyclones in series was proved insufficient to capture char and unconverted wood particles, especially during the reactor start-up phase. These problems were partially faced by adopting a configuration of a primary cyclone and inertia impinger in series, but further development is still required. A variety of configurations for the product collection system were built and tested, the most efficient being a combination of a shell-and-tube heat exchanger (condenser) and a cotton wool filter. However, the liquid recovery configuration gave rise to a number of problems, the most important being gradual plugging of the heat exchanger due to the formation of sticky solid–liquid agglomerates.