Air Pretreatment Research Articles

Effect of Water Content in Semidry Grinding on the Quality of Glutinous Rice Flour.

The grinding process is one of the key factors affecting the quality of glutinous rice flour (GRF). As an emerging grinding method, semidry grinding aims to solve the problems of the high yield of wastewater in traditional wet grinding and the high content of damaged starch in dry grinding, in which the water content has a great influence on the quality of GRF. However, semidry grinding has not yet been formally put into production due to limitations such as the long time required to adjust the water content of rice grains. Therefore, this work was carried out to shorten the soaking time of glutinous rice (GR) by hot air pretreatment, and to conduct a systematic and in-depth study of the effect of water content on the quality of GRF, including water distribution, water hydration properties, thermal properties, rheological properties, and microstructure. The results showed that the GRF with higher water content had lower water solubility and higher enthalpy of pasting, which were due to the low content of damaged starch and the high degree of crystallization. The particle size of the GRF became smaller as the interaction between water and starch was enhanced and the GR was softened. In addition, the viscosity and elasticity of the GRF were also improved with an increase in water content. This work provides theoretical guidance for the improvement of semidry grinding to a certain extent.

Low-temperature thermocatalytic removal of formaldehyde in air using copper manganite spinels

The removal of formaldehyde (FA) is vital for indoor air quality management in light of its carcinogenic propensity and adverse environmental impact. A series of copper manganite spinel structures (e.g., CuMn2O4) are prepared using the sol-gel combustion method and treated with reduction or oxidation pretreatment at 300 °C condition. Accordingly, CuMn2O4–O (“O” suffix for oxidation pre-treatment in air) is identified as the best performer to achieve 100% conversion (XFA) of FA (50 ppm) at 90 °C; its performance, if assessed in terms of reaction kinetic rate (r) at XFA = 10%, is 5.02E-03 mmol g−1 h−1. The FA removal performance increases systematically with decreases in flow rate, FA concentration, and relative humidity (RH) or with increases in bed mass. The reaction pathways and intermediates of FA catalytic oxidation on CuMn2O4-A are studied with density functional theory simulations, temperature-programmed characterization experiments, and in-situ diffuse reflectance infrared Fourier transform spectroscopy. The synergistic combination of large quantities of adsorbed oxygen (OA) species and oxidized metal species (e.g., Cu2+) contribute to the enhanced catalytic performance of CuMn2O4–O to oxidize FA into CO2 with the reaction intermediates of H2CO2 (DOM), HCOO−, and CO. The present study is expected to provide valuable insights into the thermocatalytic oxidation of FA over spinel CuMn2O4 materials and their catalytic performances in relation to the key process variables.

Dry-air pretreatments effects on physiochemical properties, stability, antioxidants, phytosterol and tocopherol profiles of hemp oil

The study investigated effects of dry air pretreatment (DAP) at varying temperatures (160˚C, 180˚C, and 200˚C) and times (5-, 10-, 15-, and 20-min) on hemp oil (HeO) quality attributes. The total flavonoid (TfC) and phenolic (TpC) content, tocopherols, phytosterols, flavonoids, phenolic acids, oxidative stability index (OSI), colour attributes, Maillard products, fatty acid profile (FAP), physiochemical properties and radical scavenging activity (RsA) of HeO were studied. DAP had increased Maillard products, browning index, p-anisidine value, viscosity and ΔE while decreased peroxide, a* , b* and L* values of HeO. The TpC, TfC, RsA, phenolic acids (protocatechuic, 4-hydroxybenzoic, ellagic, chlorogenic, rosmarinic and trans cinnamic acids), epicatechin, total hydroxycinnamic and hydroxybenzoic acids and total flavonoids were highest in HeO upon DAP at 200 oC for 15 min. The tocopherols and phytosterols were highest upon DAP at 180 oC for 5 and 10 min, respectively. The highest HeO yield (25.85%) and OSI (6.80 h) was attained upon DAP at 180 oC and 200 oC for 10 min, respectively. In conclusion, the DAP had triggered a Maillard reaction, augmented the release of antioxidants, pigments and increased the OSI of HeO. The optimal DAP can be employed for the improvement of HeO quality attributes.

Evaluation of three suction pretreatment systems for the air compressor

Air compressor, as the power source of pneumatic tools, suffers the problems of low efficiency and high failure rate in summer. In this paper, three suction air pretreatment systems are presented, which are characterized by the cold sources: a vapor compression refrigeration unit, a water chilling unit and a combination of water chilling unit with cooling tower. Models for the thermodynamic and economic performance evaluation of the three systems are established and solved. The moisture diffusion coefficient is applied to consider the influence of the moisture condensation and the Marshall and Swift coefficients is introduced to consider the capital change over time. Formula to calculate the efficiency of refrigeration compressor is adopted. Besides, the system total efficiency, percentage of power saving (PPS) and payback period (PBP) are defined as performance indexes. A comparative study with typical meteorological data of hot-dry regions and hot-humid regions is conducted to analyze the superiority of each system under the operation conditions of varied suction air temperature and volume flow. According to the results, optimal spray water flowrate exists for each operation condition and an air–water ratio of 0.8 is recommended. When the suction air temperature decreases, the PBP of each system increases and a sharp increase occurs when the temperature is lower than the air dew point temperature. A suction air temperature of 26 ℃ is suggested. Direct air cooling with an evaporator is preferred when the suction air volume flowrate is smaller than 60 m3/min for hot-humidity regions. The combined system is significantly superior in hot-dry regions. The PBP of the three systems is all longer than 10 months. How to guarantee the usage rate is the key for enterprises to consider the use of suction air pretreatment systems.

Enhanced abundance of oxygen-containing intermediates from pre-oxidation of poplar sawdust facilitates generation of porous structures in activation with phosphoric acid

Pretreatment of biomass in oxidative atmosphere could induce partial oxidation of organic components on surface of biochar, which might affect evolution of pore structures in subsequent activation of biochar. This was investigated herein by pretreatment of sawdust at 150 to 300 °C in an air or nitrogen flow and the followed activation of the resulting biochar with phosphoric acid. The results indicated that the oxidation in the pretreatment in air became substantial at 250 °C, reducing the yield of biochar, crystallinity of cellulose while introducing abundant oxygen-containing functionalities in form of OH, COC, CO, etc. Some of these oxygen-containing species even can be reserved in the activated carbon (AC) formed, making the oxygen-rich AC with high hydrophilicity. More importantly, these abundant oxygen-containing functionalities were beneficial for the subsequent activation with phosphoric acid for creating developed pore structures (1314.3 m2g−1 of AC-250-air versus 1056.5 m2g−1 of AC-250-N2). This resulted in superior adsorption capacity towards tetracycline over AC-250-air. The in-situ IR characterization suggested that abundant oxygen-containing species bearing ester/carboxyl functionalities were generated during activation of the sawdust pretreated in air, which played essential roles in generation of especially micropores. The deficiency of these oxygen-containing species in activation of the sawdust pretreated in nitrogen negatively affected development of pores.

Pretreatment of pine needles via torrefaction, oxidation and hydrothermal carbonization at 250 °C impacts subsequent pyrolysis and activation in distinct ways

Thermal pretreatment of biomass in varied medium (i.e. nitrogen, air or water) might further impact pyrolysis and activation in distinct ways. Herein, hydrothermal carbonization (HTC) or torrefaction of pine needles in nitrogen or air at 250 °C and further pyrolysis/activation of pretreated samples was conducted. The results indicated yield of solid followed the method of pretreatment: torrefaction > oxidation > HTC, due to significant oxidation of aliphatics in the pretreatment in air and structural reconstruction in HTC. Additionally, pretreatment in air remarkably increased overall production of biochar (35.1 %), owing to enhanced resistivity to cracking. HTC released nearly half of organics, leading to remarkably lower overall yields of biochar than that in blank experiment (24.7 % versus 30.6 %), but increased thermal stability of biochar through enhancing aromatic degree. Additionally, pretreatment in air removed some H species via oxidation but not nitrogen species while the HTC was the opposite while induced leaching of inorganics. In-situ IR characterization indicated conversion of aliphatic -OH to phenolic -OH in nitrogen-pretreatment, oxidation of ether bridging bond between benzene rings in air-pretreatment and formation of thermally carbonyls via HTC. During activation, all the pretreatments reduced specific surface area of activated carbon, following the order: blank (1351.1 m2 g−1) > torrefaction in N2 (1314.7 m2 g−1) > oxidation in air (1293.8 m2 g−1) > HTC (1218.2 m2 g−1). Oxidation or aromatization reactions in the pretreatment increased aromatic degree of the feedstock, making pore generation via cracking more difficult. Besides, pretreatments also changed morphologies of resulting biochar or activated carbon in distinct ways.

Comparative study of three hybrid air-conditioning systems based on multiple evaporative coolers and run-around reheating coils

Existing evaporative-cooling hybrid air conditioning systems cannot fully utilize the synergistic energy-saving potential of multiple evaporative-cooling technologies. Moreover, they cannot meet simultaneously the energy-saving requirements of standard mechanical vapor compression (MVC) systems in the terms of fresh air pre-treatment, condenser pre-cooling and supply air reheating. Therefore, in this paper, integrating MVC system with the indirect evaporative cooler, outdoor-air evaporative-cooling unit, and run-around reheating coils, three alternative hybrid systems were proposed to meet the aforementioned three requirements. The three hybrid systems have different outdoor-air unit configurations (single condenser with direct evaporative cooler, dual condenser with direct evaporative cooler, and dual condenser with two-stage evaporative-cooling configuration) and reheat sources (exhaust, outdoor, and mixed air of fresh and return air). Then, the parameter effects and application potentials of the three hybrid systems were analyzed comparatively based on detailed numerical models. The results showed that the third proposed hybrid system (HAC-R3) exhibits the best energy-saving advantages in almost the range of ambient temperature, relative humidity and fresh airflow rate studied. The first proposed hybrid system (HAC-R1) has the simplest outdoor-air side configuration, which is also a good choice in medium–low humidity conditions. In hot-humid summer in southern China, HAC-R3 has the highest average energy-saving rate and seasonal COP of 16.0 % and 7.0 respectively. In addition, HAC-R1 has the lowest static equipment payback period of 3.3 years, slightly lower than that of HAC-R3 (3.4 years).

Dynamic modeling of a mechanically coupled organic Rankine-vapor compression system for compression heat recovery based on an improved lumped parameter model

Compression heat recovery is getting attention in cryogenic air separation units for its high energy saving potential, while the organic Rankine-vapor compression system (ORVC) is considered as an attractive technology for both compression heat recovery and air pretreatment. As the states of the compression heat inevitably change with the ambient environment, dynamic simulation of the ORVC-air compression heat recovery system (ORVC-ACS) is carried out in this paper. An improved lumped parameter model that enables to solve the dynamic model with complex structure and on large-time scale is proposed and validated. The working fluid density in the heat exchanger is treated as phase-based average in this improved model. The average relative deviations between the simulation results and experimental data are less than 6.8%. The annual dynamic characteristics and varying-duty operation performance of the ORVC-ACS are further studied. The results show that the ORVC-ACS could basically work under the design condition, with the maximum temperature fluctuation amplitude of about 6.9 °C, response time of about 4–6 min without varying-duty conditions and 8 min with duty changing. Besides, for a 60,000 Nm3/h scale ORVC-ACS, the annual energy saving reaches about 13.75 GWh, equivalent to CO2 emission reduction of about 9.9 Mt, and heat recovery ratio of about 76.4%, illustrating great energy saving and environmental protection performance. This research may benefit subsequent control scheme design and actual operation.

Carbon capture and utilization: More than hiding CO2 for some time

Carbon capture and utilization: More than hiding CO2 for some time

Indirect treatment of plasma-processed air to decrease decay and microbiota of strawberry fruit caused by mechanical damage

Due to the soft texture of strawberry fruit, it is highly susceptible to mechanical damage during postharvest supply chains, resulting in decay and quality deterioration. Urgent investigation is needed on the treatment techniques to mitigate the impact of postharvest mechanical damage of strawberry fruit. In the present study, the effect of indirect plasma-processed air (PPA) pretreatment to decrease decay and microbiota of strawberry fruit caused by mechanical damage was investigated. The results show PPA pretreatment reduced the total counts of indigenous microbiota on the surface of intact and mechanical damaged strawberry fruit by 4.29 and 3.76 log10CFU/g at day 0, respectively, and reduced the counts of S. aureus and E. coli inoculated on strawberry fruit by 3.05–3.16 and 3.55–3.56 log10CFU/g, respectively. The disease incidence of fruit inoculated with Botrytis cinerea was also decreased by 6.67 %–18.89 % during storage. Besides, PPA pretreatment reduced the decay rate of strawberry fruit by 5.56 %–21.11 % during storage and did not significantly affect the firmness, color index of red grapes (CIRG) and total soluble solids (TSS) content of strawberry fruit. DHHP results indicate that the antioxidant activity of the strawberry fruit was increased. After PPA pretreatment, 39 metabolites were differentially accumulated in strawberry fruits, 37 of which were up-regulated, including flavonoids, phenolic acids and organic acid.

Fault analysis and troubleshooting of nitrogen supply system for a ship’s nitrogen generator

This paper introduces the working principle and system work flow of the marine nitrogen generator. Emphasis is laid on the air pretreatment subsystem, nitrogen membrane separation subsystem and automatic control system of the nitrogen generator. In view of the automatic alarm shutdown fault of a ship’s nitrogen generator in the course of operation, the reason is analyzed, and it is found that the refrigeration device fault of the nitrogen generator leads to the excessive air temperature before the film inlet group, thus causing the failure shutdown. Finally, the fault location and troubleshooting are carried out.

Membrane fouling behavior in membrane bioreactors for nitrogen-deficient wastewater pretreated by ammonium ion exchange

Nitrogen is a critical element closely related to the synthesis of cellular membrane fouling behaviors in membrane bioreactors (MBRs). In this study, a novel pretreatment process by coupling chemically enhanced primary treatment (CEPT) with ammonia nitrogen ion exchange and regeneration (AIR) was proposed to analyze their influences on sludge properties and membrane fouling in MBRs. The MBRs with CEPT and AIR pretreatment obtained the effluent with chemical oxygen demand (COD) and ammonium nitrogen (NH4+-N) levels comparable to the conventional anoxic/aerobic MBR, but with much lower concentrations of total nitrogen (≤3.0 mg/L) and total phosphorous (≤0.15 mg/L). CEPT and AIR remarkably removed particles and soluble proteins from the influent, prohibited EPS secretion by 62.9–79.1% and elevated viscoelasticity of EPS, and thus alleviated membrane fouling. Membrane foulant in the experimental MBRs had unstable EPS structures easily detached, and low biofilm roughness to prevent the adsorption of organic matters. Nitrogen load had significantly positive correlations with EPS contents, viscoelasticity of EPS, and the total filtration resistance. The nitrogen-deficient condition enriched quorum quenching bacteria and microbes surviving retarding EPS production, and inhibited the overgrowth of filamentous bacteria. Therefore, nitrogen separation from wastewater in advance can effectively alleviate membrane fouling and improve pollutant removal in MBRs.

Hydrogen-powered Electrochemically-driven CO2 Removal from Air Containing 400 to 5000 ppm CO2

The performance of a hydrogen-powered, electrochemically-driven CO2 separator (EDCS) was demonstrated at cathode inlet CO2 concentrations from 400 ppm to 5,000 ppm. The impact of current density and CO2 concentration were evaluated to predict operating windows for various applications. The single-cell data was used to scale a 100 cm2, multi-cell stack using a shorted-membrane design for four applications: direct air capture (DAC), hydroxide exchange membrane fuel cell (HEMFC) air pretreatment, submarine life support, and space habitation. For DAC, a 339-cell EDCS stack (7.7 L, 17 kg) was projected to remove 1 tonne CO2 per year. The addition of the EDCS in HEMFC systems would result in nearly a 30% increase in volume, and therefore further improvements in performance would be necessary. A module containing five 338-cell EDCS stacks (38 L, 85 kg) in parallel can support a 150 person crew at 2.1% of the volume of the liquid amine system employed in submarines. For space habitation, a 109-cell EDCS stack (3.2 L, 10 kg) is adequate for 6 crewmembers, and is less than 1% the size and 5% the weight of the current CO2 removal system installed on the International Space Station.

Hot air pretreatment alleviates browning of fresh-cut pitaya fruit by regulating phenylpropanoid pathway and ascorbate-glutathione cycle

The effects of hot air (HA) pretreatment on quality, phenolic accumulation and antioxidant activity of fresh-cut pitaya fruit were investigated. It was found that 42 °C HA pretreatment for 3 h effectively alleviated the browning of fresh-cut pitaya fruit stored at both 4 °C for 14 d and 20 °C for 48 h. To better understand the physiological mechanisms of HA on browning alleviation, higher storage temperature at 20 °C was used to accelerate and amplify the wounding responses. The results demonstrated that HA pretreatment delayed the wound induced biosynthesis of phenolic compounds of fresh-cut pitaya fruit during earlier storage period but enhanced their contents and maintained higher antioxidant activity during the later stage of storage. It retarded but enhanced the activation of key enzymes (PAL, 4CL and C4H) and their relative gene expressions involved in the phenylpropanoid pathway. Moreover, HA pretreatment suppressed the activities of enzymes associated with oxidative browning of phenolics (PPO and POD), activated ascorbate-glutathione (AsA-GSH) cycle and inhibited the wound induced proliferation of ROS production which could cause oxidative damage of fresh-cut pitaya fruit. These findings suggested that pretreatment with HA could be an efficient and feasible approach for the browning alleviation and quality retention of fresh-cut pitaya fruit, and the phenylpropanoid metabolism and AsA-GSH cycle played crucial roles in this process.

Season-oriented mine ventilation modes analysis

The paper presents the results of the data analysis conducted at Bereznyaki Mine-2 of Uralkali in summer and winter (during the air pre-treatment period). The findings show that when mine air heaters are operating thermal drop of ventilation pressure appears in air supply shafts. It causes “airlocks” in the shafts – a phenomenon that nearly stops the airflow in one of the shafts while increasing dramatically the airflow in the other (others) air intake shafts. As a result, mine air heaters in the shafts may stop running which provokes freezing of the mine shaft shoring. The analysis of mine ventilation modes performed in summer and winter determined the factors affecting the occurrence of “airlocks” in the air supply shafts during air pre-treatment. The reported study was supported by the Government of Perm Krai, research project of the International Research Group «Development of a digital model for forecasting and pricedependent demand response for electricity consumed by underground mining enterprises» (contract No. 26/506).

Improvement in Millet Soaking by Way of Bubbled Cold Plasma Processed Air Exposure; Phytic Acid Reduction Cum Nutrient Analysis Concern

Pearl millet is one of the high-grown and underutilized grain crops. It is confined to traditional foods due to its anti-nutritional and functional properties. The present study investigated the influence of plasma processed air bubbling and soaking on phytic acid content, total and HCl extractable iron, physicochemical, techno-functional, and pasting properties of pearl millet. Exposure of pearl millet to plasma processed air bubbling at 180 V with an airflow rate of 10 liters /h for 1 h and 2 h reduced phytic acid content by 60.66 % and 39.27 % respectively. Whereas soaking for 12 h reduced phytic acid by 21.6 % in contrast with the untreated sample. The total iron content reduced from 39.9 to 29.8 mg/100g and HCl extractable iron content increased from 12 % to 69.49 % with the given treatments. Obtained data were noticed with significant changes (p < 0.05) and are in line with its exposure to the selected variable treatments. This work points to the potentiality of plasma processed air pre-treatment in the food industry to improve nutrition and mineral availability accompanied by modifying pasting, techno-functional properties of pearl millet.

High-performance multi-stage internally-cooled liquid desiccant dehumidifier for high gas–liquid flow ratios

Liquid desiccant dehumidification provides a pathway to high-flow air pretreatment of air compressors for energy savings. However, high air-to-solution flow ratios (i.e., over 4.0) may result in an unacceptable decrease in dehumidification effectiveness, and few studies have managed to overcome this challenge. This study aims to experimentally demonstrate that the multi-stage internally-cooled liquid desiccant dehumidifier (MILDD) is capable of improving the effectiveness at extremely high air-to-solution flow ratios over 10.0. A laboratory bench of the MILDD is designed and tested in various operational conditions. Based on the finite difference model, the experimental results of dehumidification effectiveness are analyzed in terms of the heat and mass transfer process such as irreversible loss and driving forces. The specific cooling capacity associated with the energy efficiency is further studied by considering different desiccant regeneration efficiency. In addition, the experimental latent effectiveness from present and previous work is compared and correlated. Results show that the measured latent effectiveness of the MILDD exceeds 0.42 and goes even up to 1.02 at high air-to-solution flow ratios, i.e., 8.6–20.1, while existing liquid desiccant dehumidifiers maintain a comparable effectiveness only at much lower flow ratios, i.e., below 4.0. The proposed model and correlation also have been validated with a considerable accuracy for predicting the performance of internally-cooled dehumidifiers. This work has experimentally demonstrated the ability of the multi-stage internally-cooled liquid desiccant dehumidifier to overcome the low effectiveness at high gas–liquid flow ratios, which advances the potential application of liquid desiccant dehumidification in the air compression process.

The Application of Liquid Circulation Heat Recovery System

This paper analyzes the characteristics of the exhaust heat recovery devices and the air conditioning system of the pharmaceutical factory, and points out that the pharmaceutical factory is more suitable for the liquid circulation heat recovery system. The principle and composition of the liquid circulation heat recovery system are also introduced. The actual engineering case proves that the use of liquid circulation heat recovery system can effectively reduce the fresh air load. Compared with the traditional fresh air pretreatment method, liquid circulation heat recovery system has a short payback period.

Adequacy of the accelerated aging test for soybean seeds

Seed companies use vigor tests in their internal seed quality control procedures. Therefore, it is necessary to choose effective methods to obtain quick responses for making decisions related to the handling, disposal and marketing of seed lots. Thus, the objective of this work was to adapt a methodology for the accelerated aging test in soybean seeds. Sixty-nine lots were used and the experimental design used was completely randomized, with four replications. For the initial characterization of the lots, water content was determined, germination test and field emergence. The soybean seed lots selected based on the initial characterization, were submitted to the standard accelerated aging methodology and twenty-one adapted methodologies. After the physiological characterization of the 69 lots, 24 lots with similar germination with different levels of vigor were selected. For adapted methodologies that used only distilled water inside the gerbox box, there was an increase in the water content of the seeds of all analyzed lots. However, all methodologies with the use of saline solution had alower water content. The adapted methodologies N (pre-treatment in forced air oven at 35-40°C for two hours, BOD 42°C for 24 hours, using saline) and S (pre-treatment in forced air oven at 35-40°C for two hours, BOD 45°C for 12 hours, with the use of distilled water) are the most suitable for use in the accelerated aging test for soybean crops, as they present relevant results in a shorter evaluation period.

Thermal crosslinking membrane with enhanced CO2 separation performance derived from nitrile-containing phenolphthalein-based poly(arylene ether ketone)

Enhancing gas permeabilities of thermal crosslinking membranes while retaining adequate selectivity is of great significance for industrial applications. In this work, a novel and commercial polymer of nitrile-containing phenolphthalein-based poly (arylene ether ketone) (PEK-C(CN)) was introduced to prepare thermal crosslinking membranes via pretreatment in air and subsequent thermal crosslinking treatment in N2, and the high permselectivity for CO2/CH4 and CO2/N2 gas pairs was achieved. The ATR-FTIR and XPS results demonstrated that the nitrile groups might undergo thermal cyclotrimerization reaction with the formation of stable triazine rings across molecular chains during the pretreatment, which is conducive to the preparation of defect-free and highly permeable thermal crosslinking membranes. During thermal crosslinking treatment, the Cardo moieties decomposed and induced crosslinking with forming bulky biphenyl linkages between polymeric chains, accompanied with pyrolysis of some nitrile groups, which resulted in an increase in interchain distance and microvoid size. The CO2 permeability of the resulting thermal crosslinking membrane was increased to around 3 times without sacrificing CO2/CH4 and CO2/N2 selectivities due to the incorporation of nitrile groups, compared to the thermal crosslinking membrane derived from nitrile-free PEK-C. For equimolar binary mixture gases, the fully crosslinked membranes present the CO2 permeability of around 1300 Barrer with CO2/CH4 and CO2/N2 separation factors of 32.6 and 35.8, respectively, which offer a promising alternative in CO2 capture and separation.