Adsorption Dryer Research Articles

On the controllability and energy sensitivity of heat-integrated desiccant adsorption dryers

This work studies the controllability of heat-integrated zeolite adsorption dryers. Mean product moisture content, temperature and vitamin C concentration (representative of product quality) are considered as controlled variables. Set-point tracking and disturbance rejection controllability metrics are considered in addition to energy performance sensitivity. In adsorption dryers, the adsorption system introduces extra degrees of freedom of which some input–output pairs are promising. For corresponding inputs, adsorption dryers are shown to have higher steady-state gains than equivalent conventional dryers due to correlation between dehumidification, adsorption heat and the controlled variables. They also show improved resilience to ambient air disturbances due to adsorbent subsystem-induced self-regulation properties. The encouraging mechanisms of the self-regulation are adsorption heat, kinetic and equilibrium properties of the adsorbent. Due to the high correlation between product moisture content and temperature, improved controllability is observed when vitamin C concentration is used as an output variable instead of product temperature. It is thus proposed that on the availability of reliable soft sensors or state estimators, instead of product temperature, vitamin C or some other temperature-dependent quality measure should be controlled in addition to product moisture in decentralised drying system control. Under perfect rejection of unfavourable disturbances like ambient temperature drop and humidity rise, the energy performance of adsorption dryers is not significantly degraded, whereas, it is for conventional systems.

Improving Adsorption Dryer Energy Efficiency by Simultaneous Optimization and Heat Integration

Conventionally, energy-saving techniques in drying technology are sequential in nature. First, the dryer is optimized without heat recovery and then, based on the obtained process conditions, heat recovery possibilities are explored. This work presents a methodology for energy-efficient adsorption dryer design that considers sensible and latent heat recovery as an integral part of drying system design. A one-step pinch-based optimization problem is formulated to determine the operating conditions for optimal energy performance of such an integrated system subject to product quality. Because the inlet and target stream properties of the heat recovery network are determined by the adsorption drying conditions, they are unknown a priori and thus are determined simultaneously within the overall optimization using the pinch location method. Energy balances are written above and below the various pinch point possibilities and the optimal pinch point is that which minimizes the amount of external heating utility required while satisfying drying and thermodynamic constraints. Results for a single-stage zeolite adsorption drying process with simultaneous heat recovery optimization show a 15% improvement in efficiency compared to a sequentially optimized system. The improvement is traceable to alterations in enthalpy-related variables like temperatures and flow rates. The discrepancy in optimal operating conditions between the sequential and simultaneous cases underscores the need to change system operating conditions when retrofitting for heat recovery because previous optimal conditions become suboptimal when heat recovery is introduced. Also, compared to a conventional dryer (without an adsorption process) operating under similar conditions, energy consumption is reduced by about 55%.

Model‐Based Energy Efficiency Optimization of a Low‐Temperature Adsorption Dryer

AbstractLow‐temperature drying is important for heat‐sensitive products, but at these temperatures conventional convective dryers have low energy efficiencies. To overcome this challenge, an energy efficiency optimization procedure is applied to a zeolite adsorption dryer subject to product quality. The procedure finds a trade‐off between the improved drying capacity due to dehumidification and energy expenditure due to regeneration while incorporating product drying properties. By optimizing the regeneration air inlet temperature, drying air, adsorbent, and regeneration air flow rates as well as sensible and latent heat recovery from the regenerator exhausts, the energy efficiency is improved by up to 45 % compared to the state‐of‐the‐art. The high mass transfer effect of high temperatures is utilized in the regenerator to boost dehumidification while isolating the heat‐sensitive dried product from the quality‐degrading effect.

Optimizing energy efficiency in low temperature drying by zeolite adsorption and process integration

Drying is an energy intensive process, with low efficiencies, particularly at low drying temperatures required for heat-sensitive products. This work presents an energy efficient method for drying heat-sensitive products based on drying air dehumidification by zeolites and process integration. Two optimization approaches are considered: sequential and simultaneous. In the sequential approach, a zeolite adsorption dryer is optimized for energy efficiency, subject to product temperature and final moisture constraints using the zeolite, drying and regeneration air flowrates as well as the regeneration air inlet temperature as decision variables. Heat is then optimally recovered from the process exhaust streams using pinch analysis. In the simultaneous method, heat recovery is considered an integral part of the drying process and the entire system simultaneously optimized. Since the heat recovery stream properties are now unknown a priori, the pinch point is not unique but determined by optimization. The sequential and simultaneous methods reduce energy consumption by about 45 % and 55 % respectively, compared to a conventional convective dryer at the same drying temperature of 50°C. Copyright © 2011, AIDIC Servizi S.r.l.

Assessment of a Two-Stage Zeolite Dryer for Energy-Efficient Drying

Multistage adsorption drying with zeolite is experimentally evaluated for a single- and a two-stage dryer. For a 1:1 ratio between air flows for drying and regeneration, the energy efficiency for a single-stage system 50–54% and for the two-stage system 63%. Calculations with a calibrated model show that the two-stage system achieves a 4:1 ratio between the air flows an efficiency of 85%, 12% above that of a single-stage system. A sensitivity analysis shows the influence of operational conditions on the energy efficiency. Options to realize multistage adsorption dryer systems and to control such systems as well as the economic aspects are discussed.

Design and performance of an automatic regenerating adsorption aerosol dryer for continuous operation at monitoring sites

Abstract. Sizes of aerosol particles depend on the relative humidity of their carrier gas. Most monitoring networks require therefore that the aerosol is dried to a relative humidity below 50% r.H. to ensure comparability of measurements at different sites. Commercially available aerosol dryers are often not suitable for this purpose at remote monitoring sites. Adsorption dryers need to be regenerated frequently and maintenance-free single column Nafion dryers are not designed for high aerosol flow rates. We therefore developed an automatic regenerating adsorption aerosol dryer with a design flow rate of 1 m3/h. Particle transmission efficiency of this dryer has been determined during a 3 week experiment. The lower 50% cut-off was found to be smaller than 3 nm at the design flow rate of the instrument. Measured transmission efficiencies are in good agreement with theoretical calculations. One dryer has been successfully deployed in the Amazon river basin. We present data from this monitoring site for the first 6 months of measurements (February 2008–August 2008). Apart from one unscheduled service, this dryer did not require any maintenance during this time period. The average relative humidity of the dried aerosol was 27.1+/−7.5% r.H. compared to an average ambient relative humidity of nearly 80% and temperatures around 30°C. This initial deployment demonstrated that these dryers are well suitable for continuous operation at remote monitoring sites under adverse ambient conditions.

Energy Efficiency of Multi-Stage Adsorption Drying for Low-Temperature Drying

This work discusses the evaluation of multi-stage adsorption dryers with air dehumidification by zeolite and alumina pillared clay. In a multi-stage dryer, product is dried in succeeding stages while air leaving a stage is fed to the next stage after dehumidification by an adsorbent. Energy efficiency of the drying system is evaluated for low-temperature drying (10–50°C) and compared with conventional condenser drying. Results showed that the efficiency of the multi-stage adsorption dryers increases with the number of stages. For low drying temperatures, zeolite is most favorable; for drying temperatures 40–50°C, alumina pillared clay needs less cooling and deserves preference.

519. Adsorption dryers: Anon, Research and Development Dept, W C Holmes and Co Ltd, Turnbridge, Huddersfield

In this work, the METCO 307 (75 wt.% Ni + 25 wt.% graphite, M307) abradable seal coatings were deposited by conventional atmospheric plasma spraying system (APS) and high efficiency supersonic atmospheric plasma spraying system (SAPS), respectively. Comparative dry reciprocating sliding wear experiments on the as-sprayed coatings against a 440-C stainless steel ball were conducted on the CETR UMT-3 friction and wear tester. The results indicated that the average width and length of lubrication phase (graphite) were 3.54 ± 0.06 and 7.51 ± 0.13 μm in the SAPS-coating, which were lower than 4.15 ± 0.11 and 8.03 ± 0.09 μm in the APS-coating. The fine graphite phase improved the formation of homogeneous and continuous tribofilm during the reciprocating sliding friction process. The track depth of APS-coating increased from 0.093 to 0.161 mm, while that of SAPS-coating increased from 0.087 to 0.151 mm when the test temperature rose from 25 to 400 °C, indicating that the SAPS-coatings had a higher wear resistance.