Research and Application of Airflow Recirculation System in Working Faces with Leaking Airflow

In order to develop the technology of the controlled recircuIation of airflow in the world, some formulas about the airflow recirculation system in the working face with leaking airflow are deduced,which reduces the error between calculating and real values. on the base of the application of the formulas mentioned above, the problem about lack of airflow in the working face 2712 was solved successfully in Xiandewang Coal Mine.

Anoxic gas recirculation system for fouling control in anoxic membrane reactor

Anoxic gas recirculation system was applied to control the membrane fouling in pilot-scale 4- stage anoxic membrane bioreactor （MBR）. In the anaerobic-anoxic-anoxic-aerobic flow scheme, hydrophilic polytetrafluoroethylene （PTFE） membrane （0.2 μm, 7.2 m2/module） was submerged in the second anoxic zone. During 8 months operation, the average flux of the membrane was 21.3 L/（m2.hr）. Chemical cleaning of the membrane was conducted only once with sodium hydroxide and sodium hypochlorite. Dissolved oxygen （DO） concentration in the second anoxic zone was maintained with an average of 0.19 ± 0.05 mg/L. Gas chromatography analysis showed that the headspace gas in the second anoxic reactor was mainly consisted of N2 （93.0% ± 2.5%）, O2 （3.8% ± 0.6%）, and CO2 （3.0% ± 0.5%）, where the saturation DO concentration in liquid phase was 1.57 mg/L. Atmospheric 02 content （20.5% ± 0.8%） was significantly reduced in the anoxic gas. The average pH in the reactor was 7.2 ± 0.4. As a result, the recirculation of the anoxic gas was successfully applied to control the membrane fouling in the anoxic MBR.

The Experimental Investigation of Recirculation of Air-Cooled System for a Large Power Plant

The paper introduces thermal buoyancy effects to experimental investigation of wind tunnel simulation on direct air-cooled condenser for a large power plant. In order to get thermal flow field of air-cooled tower, PIV experiments are carried out and recirculation ratio of each condition is calculated. Results show that the thermal flow field of the cooling tower has great influence on the recirculation under the cooling tower. Ameliorating the thermal flow field of the cooling tower can reduce the recirculation under the cooling tower and improve the efficiency of air-cooled condenser also.

Sexual Reversal with 17α-Methyltestosterone in Oreochromis sp.:Comparison between Recirculation Aquaculture System(RAS)and Biofloc Technology(BFT)

Precocity in tilapia implies the use of several methods of obtaining monosex seed;the most common tends to use masculinizing hormone 17α-methyltestosterone(17αMT),with variable results.Thus the objective of this study was to compare the efficiency of the sexual reversion process using 17αMT,in a recirculation system and in biofloc.In a totally randomized design,three tanks for recirculation(T-RAS)and three tanks for biofloc(T-BIO)with a capacity of 200 L effective volume were taken and filled with 1,056 larvae of Oreochromis sp.,without reversing and with an initial weight of 0.02 g and an initial total length of 1.4 mm.The study was carried out during 65 d,the fish were fed(10%biomass,adjusted every 15 d)by a commercial diet at 45%of crude protein that included 17αMT(60 mg/kg).Water quality,microbiology,zootechnical and gonadal analysis were monitored.Consequently the water quality results showed that just dissolved oxygen(DO),temperature(T-°C)and alkalinity did not show significant differences.Additionally,in the productive parameters there were significant differences in the final length,the gain in length and in K which were better in T-BIO.The microbiological ones did not present significant differences between the treatments.Lastly,the percentage of reversion was significantly better in T-RAS.Then,this study suggests that settleable solids concentrations above 35 cm decrease the efficiency of the sexual reversion for this species.

The dissolution of total suspended solids and treatment strategy of tailwater in a Litopenaeus vannamei recirculating aquaculture system

In recirculating aquaculture systems(RASs),the effective treatment of aquaculture tailwater is essential to maintain the health of the RAS.This study investigated the optimal time and method for tailwater treatment during three periods of the aquaculture of the Litopenaeus vannamei:nursery(0–26 d),middle(27–57 d),and later(57–104 d).The variation of several water parameters during the dissolution of total suspended solid(TSS)in tailwater,applied with the effects of ozone on the microorganism and water quality parameters were investigated.Results showed that the TSS concentrations in tailwater decreased with time,although not significantly(P>0.05),whereas total ammonia nitrogen(TAN),nitrite(NO-2-N),and nitrate(NO_(3)^(-)-N)increased significantly(P<0.05).Therefore,TSS should be removed from the tailwater as early as possible,being most optimal within 4 h.Ozone removed 38.24%–48.95%of TSS,17.78%–90.14%of TAN,and 87.50%–98.90%of NO-2-N after 4 h of treatment.However,it resulted in the significant accumulation of NO_(3)^(-)-N.Moreover,the total number of Vibrio and bacterial counts in aquaculture tailwater was reduced completely by ozone within 4 h.Thus,these results provided technical details and data support for the effective treatment of tailwater from shrimp RAS.

Influence of Leachate Recirculation on Landfill Degradation and Biogas Production

Population growth combined with the rising standard of living of people around the world is the reason for the ever-increasing production of waste which management is costing states a lot of money for its disposal. Among available waste treatment techniques, landfill is one of the most promoted waste management techniques with the emergence of the bioreactor concept. However, the control of biodegradation parameters in order to accelerate waste stabilization is an important issue. For environmental and economic reasons, the technique of leachate recirculation by injection into the waste is increasingly used to improve the degradation of landfilled waste. The injection of leachate is possible using vertical boreholes, horizontal pipes, infiltration ponds or a combination of these. Indeed, moisture is the main factor in waste degradation and biogas production. The migration of leachate to the bottom of the landfill creates low moisture in the upper areas of the landfill reducing the growth of microbial populations. This results in low or no biogas production. The main objective of the present work is to develop a numerical model of leachate recirculation by injection into the waste to rewet the waste and restart biological activity. The analysis of the results shows that the diffusion of the wet front increases with time and depth. The lateral widening of the wet front is slow in relation to the progression of the wet front towards the bottom of the waste cell. This indicates the predominance of gravity effects over diffusion phenomena. The results reveal that the distributed re-injection is the best mode of leachate recirculation because the moisture distribution on the whole waste mass is totally satisfactory and the biogas generation is more important. Leachate recirculation campaigns should be done periodically to rewet the waste, boost microbial activity and hope for a quicker stabilization of the landfill.

Enhancing treatment efficiency of swine wastewater by effluent recirculation in vertical-flow constructed wetland

Livestock wastewater has been a major contributor to Chinese cultural eutrophication of surface waters. Constructed wetlands are under study as a best management practice to treat wastewater from dairy and swine operations, but the removal efficiency of pollutants is relatively low. Enhancing the treatment efficiency of livestock wastewater by effluent recirculation was investigated in a pilot-scale vertical-flow constructed wetland. The wetland system was composed of downflow and upflow stages, on which narrow-leaf Phragmites communis and common reed Phragraites Typhia are planted, respectively; each stage has a dimension of 4 m^2 （2 m × 2 m）. Wastewater from facultative pond was fed into the system intermittently at a flow rate of 0.4 m^3/d. Recirculation rates of 0, 25%, 50%, 100% and 150% were adopted to evaluate the effect of the recirculation rate on pollutants removal. It shows that with effluent recirculation the average removal efficiencies of NH4-N, biological oxygen demand （BOD5） and suspended solids（SS） obviously increase to 61.7%, 81.3%, and 77.1%, respectively, in comparison with the values of 35.6%, 50.2%, and 49.3% without effluent recirculation. But the improvement of TP removal is slight, only from 42.3% to 48.9%. The variations of NH4-N, dissolved oxygen（DO） and oxidation-reduction potential（ORP） of inflow and outflow reveal that the adoption of effluent recirculation is benefi- cial to the formation of oxide environment in wetland. The exponential relationships with excellent correlation coefficients （R2 〉0.93） are found between the removal rates of NH4-N and BOD5 and the recirculation rates. With recirculation the pH value of the outflow decreases as the alkalinity is consumed by gradually enhanced nitrification process. When recirculation rate is kept constant 100%, the ambient temperature appears to affect NH4-N removal, but does not have significant influence on BOD5 removal.

Inlet Recirculation Influence to the Flow Structure of Centrifugal Impeller

Inlet recirculation is proved as an effective way for centrifugal compressor surge margin extension,and is successively used in some engineering applications.Unfortunately its working mechanism is still not being well understood,which leads to redesigning of inlet recirculation mostly by experience.Also,most study about inlet recirculation is steady to date.It is necessary to study surge margin extension mechanism about inlet recirculation.To expose the mechanism in detail,steady and unsteady numerical simulations were performed on a centrifugal compressor with and without inlet recirculation.The results showed that,with inlet recirculation,the inlet axial velocity is augmented,relative Mach number around blade tip leading edge area is significantly reduced and so is the flow angle.As the flow angle decreased,the incidence angle reduced which greatly improves the flow field inside the impeller.Moreover,inlet recirculation changes the blade loading around blade tip and restrains the flow separation on the blade suction side at the leading edge area.The unsteady results of static pressure around blade surface,entropy at inlet crossflow section and vorticity distributions at near tip span surface indicated that,at near stall condition,strong fluctuation exists in the vicinity of tip area due to the interaction between tip leakage flow and core flow.By inlet recirculation these strong flow fluctuations are eliminated so the flow stability is greatly enhanced.All these improvements mentioned above are the reason for inlet recirculation delays compressor stall.This research reveals the surge margin extension reason of inlet recirculation from an unsteady flow viewpoint and provides important reference for inlet recirculation structure design.

Application of CFD Modeling to Hydrodynamics of CycloBio Fluidized Sand Bed in Recirculating Aquaculture Systems

To improve the efficiency of a CycloBio fluidized sand bed(CB FSB) in removal of dissolved wastes in recirculating aquaculture systems, the hydrodynamics of solid-liquid flow was investigated using computational fluid dynamics(CFD) modeling tools. The dynamic characteristics of silica sand within the CB FSB were determined using three-dimensional, unsteady-state simulations with the granular Eulerian multiphase approach and the RNG k-ε turbulence model, and the simulation results were validated using available lab-scale measurements. The bed expansion of CB FSB increased with the increase in water inflow rate in numerical simulations. Upon validation, the simulation involving 0.55 mm particles, the Gidaspow correlation for drag coefficient model and the Syamlal-O'Brien correlation for kinetic granular viscosity showed the closest match to the experimental results. The volume fraction of numerical simulations peaked as the wall was approached. The hydrodynamics of a pilot-scale CB FSB was simulated in order to predict the range of water flow to avoid the silica sand overflowing. The numerical simulations were in agreement with the experimental results qualitatively and quantitatively, and thus can be used to study the hydrodynamics of solid-liquid multiphase flow in CB FSB, which is of importance to the design, optimization, and amplification of CB FSBs.

Tracking Performance of Electric Power Steering System Based on the Mixed H_2/H_∞ Strategy

The tracking performance of motor current is an important factor that affects the assistance torque of electric power steering （EPS） system. Bad tracking performance will cause assistant torque delay, and make road feeling bad, and is influenced by the input steering torque and system measuring noise. However the existing methods have some shortages on system＇s robust dynamic performance and robust stability. The mixed H2/H∞ strategy for recirculating ball-type EPS system in a pure electric bus is proposed, and vehicle dynamic model of the system is established. Due to the existence of system model uncertainty, disturbance signals, sensor noises and the demand of system dynamic performance, the indexes of robust performance and road feeling for drivers are defined as the appraisal control objectives. The H∞ method is introduced to design the H∞ controller, and the H2 method is applied to optimize the H∞ controller, thus the mixed H2/H∞ controller is designed. The response of EPS system to the motor current command with amplitude of 20 A, the road disturbance with amplitude of 500 N and the sensor random noise with the amplitude of 1 A is simulated. The simulation results show that the recirculating ball-type EPS system with the mixed H2/H∞ controller can attenuate the random noises and disturbances and track the boost curve well, so the mixed H2/H∞ controller can improve the system＇s robust performance and dynamic performance. For the purpose of verifying the performance of the designed control strategy, the motor current tracking performance ground tests are conducted with step response input of the steering wheel, double-lane steering test and lemniscate steering test, respectively. The tests show that the mixed H2/H∞ controller for the recirculating ball-type EPS system of pure electric bus is feasible. The designed controller can solve the robust performance and robust stability of the system, thus improve the tracking performance of the EPS system and provide satisfied road feeling for the drivers.

Intestinal microbiota of healthy and unhealthy Atlantic salmon Salmo salar L. in a recirculating aquaculture system

The present study sampled the intestinal content of healthy and unhealthy Atlantic salmon( Salmo salar L.), the ambient water of unhealthy fish, and the biofilter material in the recirculating aquaculture system(RAS) to understand differences in the intestinal microbiota. The V4–V5 regions of the prokaryotic 16 S r RNA genes in the samples were analyzed by Mi Seq high-throughput sequencing. The fish were adults with no differences in body length or weight. Representative members of the intestinal microbiota were identified. The intestinal microbiota of the healthy fishincluded Proteobacteria(44.33%), Actinobacteria(17.89%), Bacteroidetes(15.25%), and Firmicutes(9.11%), among which the families Micrococcaceae and Oxalobacteraceae and genera S phingomonas, Streptomyces, Pedobacter, Janthinobacterium, Burkholderia, and Balneimonas were most abundant. Proteobacteria(70.46%), Bacteroidetes(7.59%), and Firmicutes(7.55%) dominated the microbiota of unhealthy fish, and Chloroflexi(2.71%), and Aliivibrio and Vibrio as well as genera in the family Aeromonadaceae were most strongly represented. Overall, the intestinal hindgut microbiota differed between healthy and unhealthy fish. This study off ers a useful tool for monitoring the health status of fish and for screening the utility of probiotics by studying the intestinal microbiota.

Commercial Production of Tiger Puffer(Takifugu rubripes)in Winter Using a Recirculating Aquaculture System

Tiger puffer(Takifugu rubripes) is a promising species for aquaculture production because of its high value and limited supply. However, in the north of China, using sea cages to culture this species in winter is hampered by the fact that the seawater temperature is extremely low. Here, a large scale commercial production of tiger puffer has been successfully realized using a recirculating aquaculture system(RAS) from 3 October 2012 to 31 May 2013. The RAS was comprised of nine culture tanks(total water volume 200 m3) and stocked with approximately a total of 14400 fish(initial mean weight 160 g). The tiger puffer was hand-fed at a rate of 0.7% of total body weight per day, and the feed conversion rate was(1.21 ± 0.3) kg kg-1. The recycle water in RAS was treated by a sieve bend screen, a foam fractionator, a submerged biofilter, an UV sterilizer and a submersible aerator. During the whole culture period, an excellent water quality control was achieved in RAS. At the end of this experiment, the survival rate of tiger puffer was more than 98%. The final tank densities averaged 31.2 kg m-3, and the final individual mean weight was 440 g.

Effect of Hydraulic Loading Rate on the Efficiency of Effluent Treatment in a Recirculating Puffer Aquaculture System Coupled with Constructed Wetlands

Constructed wetlands(CWs) were integrated into an indoor recirculating aquaculture system of obscure puffer(Takifugu obscurus) for effluent treatment. The effect of hydraulic loading rate(HLR) on the efficiency of effluent treatment by CWs was examined for over a month. The CWs were operated under brackish conditions(salinity 7.4–7.6) at 3 different HLRs(0.762, 0.633, and 0.458 m d–1) 3 times, 10 days each. Overall, the CWs exhibited high efficiency in removal of total ammonium nitrogen(by 81.03–92.81%) and nitrite nitrogen(by 99.40%–99.68%). The efficiency of CWs in removal of total ammonium nitrogen, nitrate nitrogen, total Kjeldahl nitrogen, total phosphorous, and total suspended solids(TSS) increased with the decrease of HLR. The CWs operated at the 3 HLRs in a decreasing trend proves to be effective, providing a useful method for effluent treatment in commercial puffer aquaculture systems.

Landfill leachate production, quality and recirculation treatment in northeast China

Landfill leachate recirculation treatment process is a promising and economic way in northeast China due to the distinct season variation. In order to study the impact of recirculation on leachate production and its quality, two simulated sanitary landfill reactors, one with leachate recirculation and the other without, were placed outdoor in Harbin. The two-year experimental results indicated that leachate production was reduced by 86% with leachate recirculation and less or no facility for leachate treatment required. Recirculation could improve the leachate quality dramatically with lower COD, SS, NF4-N and higher pH level. Recirculation also could enhance waste degradation and stabilization and improve the efficiency of landfill. This study confirmed that leachate recirculation was a very feasible way for on-site landfill leachate treatment in cold areas.

Characterization of Bacterial Community,Ammonia-Oxidizing Bacteria,and Nitrospira During the Operation of a Commercial-Scale Recirculating Aquaculture System for Culturing Pufferfish Takifugu rubripes

We investigated the changes in communities of bacteria,ammonia-oxidizing bacteria,and Nitrospira during the operation of a pufferfish Takifugu rubripes recirculating aquaculture system by using high-throughput DNA sequencing.Differences in bacterial communities were observed at days 1-32,47-62 and 78-93 of biofilm development by using 16S rRNA gene pyrosequencing.The relative abundance of Proteobacteria(Gammaproteobacteria)increased,while that of Bacteroidetes(Flavobacteria)decreased.The proportions of Nitrosomonas and Nitrospina ranged from 0.02%to 0.30%and from 0.02%to 0.83%,respectively.Ammonia monooxygenase gene pyrosequencing revealed that the top three operational taxonomic units were related to Nitrosomonas aestuarii(17.5%-61.1%),uncultured beta proteobacterium clone B67S-54(1.9%-45.2%),and uncultured bacterium clone AZPa8(3.6%-24.7%).Nitrite oxidoreductase gene pyrosequencing revealed that the relative abundance of the dominant strain Nitrospira sp.Ecomares 2.1 increased,but that of the abundant species Nitrospira marina decreased.Our results demonstrated that the communities of bacteria,ammonia-oxidizing bacteria,and Nitrospira were changing during the operation of the pufferfish recirculating aquaculture system.

Characterization of the bacterial communities associated with biofilters in two full-scale recirculating aquaculture systems

Bacteria play a major role in metabolizing ammonia and other metabolites in recirculating aquaculture systems(RASs).To characterize and compare the bacterial communities in the biofilters of two full-scale RASs for the culture of puffer fish,Takifugu rubripes,at different ages and densities were studied.In overall,47807 optimized reads of the 16 S rRNA gene with V4-V5 region were obtained from four biofilm samples collected after biofilm maturation.At 97%cut-off level,these sequences were clustered into 500 operational taxonomic units,and were classified into 19 bacterial phyla and 138 genera.At the phylum level,Proteobacteria and Bacteroidetes were the most abundant,followed by Nitrospirae and Planctomycetes.At the genus level,Colwellia,Marinifilum,Oceanospirillum,Lutibacter,Winogradskyella,Pseudoalteromonas,Arcobacter,and Phaeobacter were the top members.Nitrosomonas and Nitrospira were main ammonia-and nitrite-oxidizing bacteria.Differences in bacterial communities at different sampling dates and similarities of both biofilters were revealed in the Venn diagram and cluster analysis.Maintaining a good water quality and health offarmed fish in RASs depended on the correct management of the bacterial communities.This study provides more accurate information on the bacterial communities associated with the bifilters of both RASs.

Performance of the Full-scale Loop Hybrid Reactor Treating Coal Gasification Wastewater under Different Recirculation Modes

This paper aims to investigate the simultaneous removal efficiencies of both COD and nitrogen in a single reactor treating coal gasification wastewater( CGW). A novel loop hybrid reactor was developed and operated under different recirculation modes in order to achieve simultaneous removal of refractory compounds and total nitrogen( TN) in a full-scale CGW treatment plant. Mid-ditch recirculation was superior to other operational modes in terms of the NH3-N and TN removal,resulting in a TN removal efficiency of 52. 3%.Although the system achieved equal COD removal rates under different recirculation modes,hydrophobic acid( HPO-A) fraction of effluent dissolved organic matter( DOMef) in mid-ditch recirculation mode accounted for35.7%,compared to the proportions of 59. 2%,45. 3% and 39. 4% for the other modes. The ultraviolet absorbance to dissolved organic carbon ratio test revealed that effluent under mid-ditch recirculation mode contained more non-aromatic hydrophilic components. Furthermore,appropriate recirculation and anoxic / oxic( A/O) partitions were also demonstrated to remove some refractory metabolites( phenols,alkanes,aniline,etc.),which reduced the chromaticity and improved the biodegradability.

Artificial liver support molecular adsorbents recirculating system therapy as a bridge to re-transplantation in two cases of long anhepatic duration

BACKGROUND: Molecular adsorbents recirculating sys- tem (MARS) liver support therapy is the development of albumin dialysis. This study was to assess the successful ap- plication of MARS artificial liver support therapy as a bridge to re-transplantation in two cases of long anhepatic duration. METHODS: MARS therapy was given after failure plasma- exchange ( PE) treatment, which resulted in circulatory de- rangement and acute renal dysfunction in a 36-year-old male patient. Finally his uncontrolled anhepatic condition led to a successful re-transplantation. In another 48-year- old man who was diagnosed as having primary nonfunction (PNF) during the liver transplantation, 10-hour MARS treatment contributed to smooth bridging of his anhepatic phase. RESULTS: The two anhepatic patients were bridged for 26 and 17 hours respectively to re-transplantation with MARS therapy. CONCLUSION: Our experience proves that MARS artifi- cial liver can be an effective support for long time bridging PNF until re-transplantation is available.

Effects of Flue Gas Internal Recirculation on NOx and SOx Emissions in a Co-Firing Boiler

Volumetric combustion has been developed to realize a high substitution ratio of biomass in co-firing boilers, which features an intensive flue gas internal recirculation inside furnace. However, the characteristics of NOx and SOx emissions in large-scale boilers with volumetric combustion were not fully clear. In this paper, an Aspen Plus model of volumetric combustion system was built up based on a co-firing boiler. In order to characterize the reductions of NOx and SOx, three biomass substitution ratios were involved, namely, 100% biomass, 45% biomass with 55% coal, and 100% coal. The effects of flue gas recirculation ratio, air preheating temperature, oxygen concentration, and fuel types on pollutants emission in the volumetric combustion system were investigated. According to the results, it was concluded the higher substitution ratio of biomass in a co-firing boiler, the lower emissions of NOx and SOx. Moreover, flue gas internal recirculation is an effective pathway for NOx reduction and an increased recirculation ratio resulted in a significant decreasing of NOx emission;however, the SOx increased slightly. The influences of air preheating temperature and O2 concentration on NOx emission were getting weak with increasing of recirculation ratio. When 10% or even higher of flue gas was recycled, it was observed that almost no NOx formed thermodynamically under all studied conditions. Finally, to reach a low emission level of NOx, less energy would be consumed during biomass combustion than coal combustion process for internal recirculation of flue gas.

EFFECTS OF COOLED EXTERNAL EXHAUST GAS RECIRCULATION ON DIESEL HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE

The effects of cooled external exhaust gas recirculation （EGR） on the combustion and emission performance of diesel fuel homogeneous charge compression ignition （HCCI） are studied. Homogeneous mixture is formed by injecting fuel in-cylinder in the negative valve overlap （NVO） period. So, the HCCI combustion which has low NOx and smoke emission is achieved. Cooled external EGR can delay the start of combustion effectively, which is very useful for high cetane fuel （diesel） HCCI, because these fuels can easily self-ignition, which makes the start of combustion more early. External EGR can avoid the knock combustion of HCCI at high load which means that the EGR can expand the high load limit. HCCI maintains low smoke emission at various EGR rate and various load compared with conventional diesel engine because there is no fuel-rich area in cylinder.