Jonas Berghel

Basic design criteria and corresponding results performance of a pilot-scale fluidized superheated atmospheric condition steam dryer

Basic design criteria and corresponding results performance of a pilot-scale fluidized superheated atmospheric condition steam dryer

Drying of sawdust in an atmospheric pressure spouted bed steam dryer

ABSTRACT The results presented in this paper show the possibility to control the outgoing moisture content using the exhaust temperature as a control parameter. A model for heat exchange is used to support visual observations of the spouting quality in the bed. The model is also used in a discussion about the heat and mass transfer coefficients. Two efficiency concepts are defined and experimental results presented. The temperature efficiency is used to present the possibility to integrate a steam dryer into energy systems such as boilers and heat sinks. Energy efficiency is used to show the variation of the recoverable heat and to point out suitable outgoing moisture contents for steam dryers. It is important to keep the temperature after the dryer as low as possible in order to achieve a high temperature efficiency. It is also shown that energy efficiency improves with decreasing outgoing moisture content and increasing inlet steam temperature.

Controllability of Product Moisture Content When Nonscreened Sawdust Is Dried in a Spouted Bed

Abstract The control of the dried products moisture content is of importance in the production of fuel pellets. Tests have been made in air and superheated steam in a spouted bed using the outlet temperature of the drying medium as a control parameter of the dried materials moisture content. For superheated steam different settings for the inlet medium temperature are also used. In the moisture content interval of 8–17% wet base there is a linear correlation between the dried material moisture content and the outlet temperature of the drying medium. When drying nonscreened sawdust in a spouted bed it is recommendable to use the outlet temperature of the drying medium as a control parameter of the dried material moisture content. This is independent of the size of the sawdust, whether superheated steam or air is used as a drying medium.

USEFULNESS AND SIGNIFICANCE OF ENERGY AND MASS BALANCES OF A FLUIDIZED SUPERHEATED STEAM DRYER

The key characteristics of a drying method for biomass are, firstly, its ability to control temperature, steam flow and pressure drop and, secondly, its ability to stabilise the material flows, particularly the outgoing moisture content. This paper presents the usefulness and significance of using energy and mass balances to improve the measurements and control systems of a drying system of industrial size in order to fulfil the moisture content requirements for biomass compression. In order to assess the reliability and accuracy of the measurements a series of tests at four different temperature and pressure levels were conducted. By verifying the plants energy and mass balances the accuracy of the measurements could be determined and the control system was evaluated. The test results are used to determine the energy and mass balances. The control system yields good stability for the pressure drop, the temperature and the gas flow.

Validation of a Mathematical Model by Studying the Effects of Recirculation of Drying Gases

Drying is a costly and energy-consuming process. Consequently, it is of great practical importance to improve its energy efficiency. Our objective, therefore, is to develop and validate a theoretical drying model by studying the recirculation of drying gases. The results show that the amount of recovered energy over the condenser and the dryer efficiency increase with increased recirculation within our test range, implying an energy-efficient operation. The validation shows that the model correlates well with industrial data collected from a full-scale dryer (diameter 3 m, length 9 m, capacity 5 MW) at a Swedish wood fuel pellet plant. Accordingly, it should be possible to use the model industrially to predict capacity changes and recovered energy when changes in drying gas recirculation are made.

The Gas-to-Particle Heat Transfer and Hydrodynamics in Spouted Bed Drying of Sawdust

Abstract This article presents experimental results for spouted bed drying of sawdust, carried out in a full-scale as well as in a laboratory-scale dryer using air as well as steam as drying media. The aim is to present design parameters for a spouted-bed sawdust dryer that can be used by the industry in designing full-scale dryers. A hydrodynamically stable spouted jet spouted bed was obtained. The heat transfer characteristics of the bed were represented in terms of a volumetric heat transfer coefficient (VHC). When sawdust is dried in a spouted bed, the mean VHC is increasing up to fiber saturation level (20–25% wb) from 40 to 110 W/m3 K. The VHC decreases with the residence time and with an increased static bed height. Gas temperature profiles are also presented for the bottom part of the drying chamber.

The Effect of Using a Heating Tube in an Existing Spouted Bed Superheated Steam Dryer

Interest in the use of biofuels, such as pellets and briquettes, has continued to grow in the European market in recent years. In order to manage the increased use of biofuels, the dryer capacity must also increase. One possible way of accomplishing this is to install heating tubes into the already existing dryers. Therefore, industrially relevant and appropriate design data, such as energy efficiency and a possible increase in the capacity of developing drying systems, are needed. This article presents the experimental results obtained from drying sawdust in a continuous spouted bed using a heating tube submerged in the bed; the results are compared with those obtained from a bed without using a heating tube. Superheated steam is used as the drying gas in all tests. The drying test is performed with an almost constant inlet moisture content and at three different inlet and outlet temperatures. The drying efficiency increases when the heating tube is turned on. Some explanations of the relation between inlet and outlet gas temperature and moisture content are presented.

An Experimental Study on the Influence of Using a Draft Tube in a Continuous Spouted Bed Dryer

Further increasing the production of processed biofuel also increases the demands on drying capacity. With the aim of increasing the heat capacity flow, experimental tests have been performed on the process of drying sawdust in a continuous spouted bed dryer with nine different draft tube designs. The results showed that a draft tube with an increased length and an increased disengagement height decreased the dry substances’ flow rate throughout the dryer. The results also showed that the mass of the material in the dryer was approximately the same in all the tests. This means that the draft tubes, no matter their size, do not influence the amount of material in the dryer.

The Potential of Using Two-Step Drying Techniques for Improving Energy Efficiency and Increasing Drying Capacity in Fuel Pellet Industries

The use of wood fuel pellets has increased worldwide in recent years, and pellet producers conclude that the lack of drying capacity is a barrier to increased production. In this study, we develop a concept of two different dryers called the two-step drying technique. The aim is to show the potential for increasing the drying capacity and improving energy efficiency when introducing a second dryer into the pellet plant. The study is theoretical and based on an industrial packed moving bed dryer. It shows that the drying capacity increased by 22% when a pneumatic second dryer was used.

Performance Study of a Closed-Type Heat Pump Tumble Dryer Using A Simulation Model and an Experimental Set-Up

In the interests of competitiveness, manufactures of tumble dryers are seeking to reduce both their electricity use and the drying time. This study examines how the cylinder volume of the compressor and the total heat transfer of the condenser influence the drying time and electricity use in a heat pump tumble dryer. A transient simulation model was developed and compared to an experimental set-up with good similarity. The simulations show that increasing the cylinder volume of the compressor by 50% decreases the drying time by 14% without using more electricity.