Unit with Fluidized Bed for Gas-Vapor Activation of Different Carbonaceous Materials for Various Purposes: Design, Computation, Implementation
© The Author(s). 2017
Received: 24 December 2016
Accepted: 11 January 2017
Published: 16 February 2017
We propose the technology of obtaining the promising material with wide specter of application-activated nanostructured carbon. In terms of technical indicators, it will stand next to the materials produced by complex regulations with the use of costly chemical operations. It can be used for the following needs: as a sorbent for hemosorption and enterosorption, for creation of the newest source of electric current (lithium and zinc air batteries, supercapacitors), and for processes of short-cycle adsorption gas separation.
In this study, the author gives recommendations concerning the design of the apparatus with fluidized bed and examples of calculation of specific devices. The whole given information can be used as guidelines for the design of energy effective aggregates. Calculation and design of the reactor were carried out using modern software complexes (ANSYS and SolidWorks).
KeywordsActivation Activated coal Absorbent Ecology Cleanup Pollution Simulation ANSYS SolidWorks
Activated carbon is a porous material produced from different carbonaceous materials: charcoal, coal and petroleum coke, coconut shell, etc. . The essence of activation consists in the pores’ opening that is in the closed state in the carbon material. It is executed by a thermo-chemical method (the material is impregnated with a solution of zinc chloride, potassium carbonate, or some other compounds and is heated without access of air) or by treatment with superheated steam or carbon dioxide at a temperature of 800–850 °C. The most widespread activation method is simultaneous supply of incomplete combustion of natural gas and steam in certain proportions into the activation apparatus. The specific surface of the pores of the activated carbon is the most important indicator of its quality, which can reach 600 to 2200 m2 per gram, depending on the initial material and activation methods. Thanks to its absorption properties, activated carbon is one of the most common materials which are widely used in various industries: ecology, medicine, civil defense, and military sphere (for example, in the manufacturing of respirators and life-support systems of air-RAID shelters). Recently, the manufacture of rechargeable batteries of a “new generation”  is very important in the production of which activated carbon with high purity and specific surface area is also used.
The Reactor Type and Its Key Elements: Hydrodynamic Characteristics of Particles of the Processed Material [3, 4]
Usually, the source material is crushed and sieved. Different types of coal have different densities and particle size distribution before and after the activation process. For example, the size of the particles prior to activation may be 0.25 to 10 mm and after the process is less than 0.1 mm. The density of the activated carbon of various types is in the range from 300 to 500 g per liter. In this regard, the design and calculation of appropriate reactor zones are necessary to consider as indicators together with the required performance of the unit.
Calculation Methodology of Material Flows and the Main Parameters of the Unit
The calculation of the material flows and basic dimensions of the reactor (and vice versa) has a certain logic and consistency. Based on the performance of the unit, you must specify the diameter of the reaction zone (diameter of the gas distribution grid). Similarly, it is necessary to determine the “flying speed” of the material based on its type. The example of calculation of activation reactor is given below.
Example of Calculating Flows
The rate of fluidization of the feedstock with the particulate composition 1…3 mm in the reaction zone W f = 0.5 m/s (the speed of free fall W f = 1 m/s)
The area of the reaction zone for the apparatus with a capacity of 3 cm3/h S = 0.785 × D2 = 0.785 × of 0.212 = 0.0346 m2
Rate of flue gases (60%) and steam (40%) G = S × W = 0.0346 × 0.5 = 0.0173 m3/s (62.28 m3)
Steam consumption of G steam = G × 0.4 = 0.00692 m3/s (24.9 m3/h) or 14.9 l/h (1 kg water = 1.67 m3 of steam)
Flow flue gas G f.gas = G × 0.6 = 0.01038 m3/s (37.368 m3/h)
Coefficient of thermal expansion K = (273 + t)/293 = (273 + 900)/293 = 4
The consumption of the combustible mixture G comb.mix = G comb.mix/4 = 0.002595 m3/s
Gas consumption G gas = G comb.mix × 0.1 = 0.0002595 m3/s (0.9342 m3/h)
Air flow G air = G comb.mix × 0.9 = 0.0023355 m3/s (8.41 m3/h)
The number of holes in the cap is six pieces to ensure the material fluidizing the “living section” of the grid should be 1–3% of the grid area (reaction zone). The calculation of the gas distribution grid is concluded to determine the number of caps and the diameter of the holes in them.
Example of Calculating Hydrodynamic
Square of grid (reaction zone) S = 0.785 × D2 = 0.785 × of 0.212 = 0.0346 m2
2%, it is 6.92 × 10–4 m2 (21 caps)
The cross-sectional area of one cap is 3.29 mm2 (six holes)
The area of one hole is 5.5 × 10-6 m
The diameter of the hole of the cap is D = (5.5 × 10–6/0.785)0.5 = 2.64 mm, standard diameter of holes of 2.2 mm
The gas flow rate of a single hole cap is G = 0.0173/(21 × 6) = 1.37 × 10–4 m3/s
The cross-sectional area of one hole of the cap is S = 0.785 × 2.22 = 3.8 × 10–6 m2
The calculated average exit speed from the holes of fluidizing agent (flue gas + steam) is W = G/S = 36 m/s (the recommended starting speed is 35…40 m/s).
CFD Simulation of Steam-Gas Mixture Flows in the Key Zones of the Reactor Activation
CFD Simulation of Heat-Gas Mixing of Gas-Vapor Mixture in the Area under the Gas Distribution Grid in order to Align the Temperature Field on Its Surface
3-D designing of the reactor and its individual elements combined with the modeling of physical processes occurring in the reactor manage to avoid the conceptual errors at the initial stage of the manufacturing of the device. Such errors would result to rapid failure of the whole unit and therefore to great financial losses for the enterprise.
Design of the Unit in 3-D (SolidWorks); Strength Calculation of Construction Elements of Activation Unit (ANSYS)
Running and Commissioning of the Activation Reactor for Different Types of Processing Materials
Results and discussion
Additional file 1: Video S1. This video shows the operation of the reactor and stable boiling of the material in it. (mov 157483 kb)
Technical Characteristics of the Activation Unit
Productivity on the finished product—1..0.3 kg/h (depending on the type of raw materials;
The natural gas consumption is 1 m3/h
Steam consumption is 10…15 l/h
The working temperature of the activation process is 900 °C
The density of activated carbon is 0.42…0.5 g/sm2
The specific surface of the coal is 1300…2000 m2/g (depending on the raw material and activation mode)
The device is of periodic action (duration of one cycle 1…2 h)
The Gas Institute of NAS of Ukraine is a leading scientific institution that has many years of experience in the development and implementation of technologies and technological equipment for the production of activated carbon on an industrial level. Modern and energy-saving units of the new generation are the result of many years of experience and CFD technologies. For example, described in this article modern unit which implementation is carried out in the USA (Argonne National Laboratory) in 2013. The Gas Institute of NAS of Ukraine is constantly working on even more sophisticated, resource-saving technologies and equipment to produce high-quality activated carbon from different raw materials.
Computational fluid dynamic
Khovavko O.I. assisted in preparing the final manuscript.
The author is a candidate of Engineering Sciences (Ph.D.) and a Research Officer of the Gas-Thermal Processes Department, Gas Institute, National Academy of Sciences of Ukraine.
The author declares that he has no competing interests.
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