Two-stage Dryer Research Articles

Experimental evaluation of a two-stage indirect solar dryer with reheating coupled with HDH desalination system for remote areas

In the present study, the performance evaluations of a two-stage indirect solar dryer with reheating coupled with humidification-dehumidification (HDH) water desalination systems are experimentally investigated. The distillate water production, drying the products and energy-saving represents the main objective of the present experimental work. Due to problems in the availability of distillate water and energy sources in remote areas, the proposed system represents a good option for remote areas. The proposed system consists of two sub-systems: (i) two-stage indirect solar dryer with reheating, which can use to remove the moisture contents from the plants and fruit; (ii) the HDH water desalination, which can use to production of distillate water. The experimental results show that, as the air flow increases from 50 to 75m3/h, the distillate water productivity increases from 29.55 to 42.3l/day and the moisture removal from the product increases from 8.33 to 12.37kg/day during the period 8:00am to 7:00pm. Use a two-stage dryer with reheating improved the moisture removal from the product by 71.78% in average as compared only to the first stage of drying unit. Also, the gain output ratio varies over ranges of 1.24–1.79 and 0.97–1.38 for the proposed system and the HDH desalination system only, when the airflow rate increases from 50 to 75m3/h. The gain output ratio of the proposed system improved by 29% in average as compared only to the HDH desalination system.

A Mixed Integer Formulation for Energy-efficient Multistage Adsorption Dryer Design

This work presents a mixed integer nonlinear programming (MINLP) formulation for the design of energy-efficient multistage adsorption dryers within constraints on product temperature and moisture content. Apart from optimizing temperatures and flows, the aim is to select the most efficient adsorbent per stage and product to air flow configuration. Superstructure models consisting of commonly used adsorbents such as zeolite, alumina, and silica-gel are developed and optimized for a two-stage, low-temperature, adsorption drying system. Results show that the optimal configuration is a hybrid system with zeolite as the first-stage adsorbent and silica-gel as the second-stage adsorbent in counter-current flow between drying air and product. A specific energy consumption of 2,275 kJ/kg is achieved, which reduces to 1,730 kJ/kg with heat recovery by a heat exchanger. Compared to a conventional two-stage dryer at the same drying temperature, this represents a 59% reduction in energy consumption. The optimal system ensures the exhaust air temperature of the first-stage regenerator is high enough to regenerate the second-stage adsorbent so no utility energy is spent in the second stage. A higher second-stage adsorbent wheel speed favors energy performance as it becomes optimized for energy recovery while the first is optimized for dehumidification. Although this work considers three candidate adsorbents in a two-stage system, the same reasoning can be applied to systems with more stages and adsorbents. The developed superstructure optimization methodology can, by extension, be applied to optimize multistage hybrid drying systems in general for any objective.

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.

Dynamic Analysis of Drying Energy Consumption#

A concept of instantaneous drying and energy efficiencies has been applied to analyze energy consumption in a through-circulation conveyor dryer and a batch fluid bed dryer for synthetic rubber. It is shown that the energy performance of the conveyor dryer can be improved by leveling of the moisture content distribution across the material layer by mechanical agitation, and sectioning of the air plenum in order to reduce inlet air temperature in the last two sections of the dryer. It is also shown that drying of a synthetic rubber in the fluid bed dryer is more energy-efficient than in the conveyor dryer, especially in the constant-rate period. Thus, the largest energy savings could be obtained in a two-stage dryer comprised of the plug-flow fluid bed dryer, and the belt conveyor dryer for removal of the bulk and residual water, respectively. #© Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2004.

Feasibility Tests for a Two-Stage Batch Dryer for Curing Farmer Stock Peanuts1

Abstract A two-stage batch dryer for farmer stock peanut was developed by a commercial grain dryer manufacturer and tested at a commercial peanut buying point during the 1996 and 1997 harvests. A 7.3-m diameter grain bin provided the superstructure for two peanut curing chambers. Each chamber had an approximate capacity of 18,000 kg of in-shell peanuts. Comparisons between conventional peanut curing wagons and the bin dryer were conducted. Recorded data included temperature and relative humidity in both type dryers, drying time, moisture content throughout curing, farmers stock grades, milling quality, and seed germination. A total of 451,717 kg were cured in the two-stage dryer and 215,460 kg in conventional dryers. The initial moisture content of peanuts averaged 19% wet basis and dried at an average moisture removal rate of 0.45%/hr. The moisture removal rates for the two dryers were not significantly different. The final moisture content averaged 11%. Moisture content at the time of grading averaged 9%. Farmers stock grades and milling quality were not significantly different. The average quota support price, including LSK for peanuts cured in conventional dryers, was $630.47/1000 kg compared to $636.08/1000-kg peanuts cured in the two-stage dryer. Seed germination averaged 75.8 and 76.1% for conventional and bin-dried peanuts, respectively. The twostage batch dryer was comparable to the current wagon-drying system. A single batch in the two-stage dryer was equivalent to three peanut wagons.