| Radon is the only natural radioactive gas.Radon and its daughter products contribute most to the natural radiation of human beings.Once radon enters the body,the α and β particles produced by radon decay irradiate lung cells.The resulting radiation damage can cause lung cancer.There is a need for the study of environmental radon concentrations and effective measures of radon control.The underground engineering rock masses continuously emit radon gas,so the environment in which people often stay has a high radon concentration,and because it is not suitable to use ventilation to remove radon,the local radon reduction device can be used.Using activated carbon to adsorb radon from the environment is one of the main methods of reducing radon concentrations,The radon adsorption ability of activated carbon is limited,but it has high desorption and regeneration capabilities.At present,the radon reduction devices used at home and abroad,has the disadvantages of uneven heating,high energy consumption,and requiring a long processing time.To address these shortcomings,microwave technology,which represents a new type of heating technology,has been suggested.Compared with traditional thermal regeneration approaches,microwave heating exhibits a good uniformity and a high efficiency and consequently boasts a short regeneration time and a low energy consumption.So in this paper,microwave heating technology is introduced for inducing the desorption of radon from activated carbon.This paper introduces a microwave desorption and regeneration methods for activated carbon with adsorbed radon,introduces the heating characteristics of activated carbon with adsorbed radon in the process of microwave desorption.A comparative experiment of heating and cooling of activated carbon under different heating conditions was carried out,The heating law of activated carbon at different depths and different factors on the temperature rise and loss of activated carbon were investigated.The influencing factors and objectivity in the process of desorption were tested,and the feasibility of the microwave regeneration of activated carbon with adsorbed radon was analyzed.The results showed that activated carbon with adsorbed radon can be heated uniformly by microwave,after 25 min of heating,the temperature range between different depths in the activated carbon were within 2.7 %;When the temperature reaches 150 ℃,the microwave takes 3 minutes,and the electric heating takes 9 minutes,the energy consumption of microwave heating is lower,and the cooling performance after microwave heating was better than that after electric heating.Five factors were discovered to affect the heating and the loss of activated carbon: the microwave power,airflow rate,the moisture content of activated carbon,the mass of the activated carbon and different types and partical sizes of activated carbon.The higher the microwave power,the smaller the airflow rate,the smaller the moisture content,the smaller the mass of activated carbon,and using small particle sizes of wood or coconut shell activated carbon,As a result,the higher the heating rate of activated carbon is,the higher the maximum temperature will be,but the higher the loss rate will be.Moreover,the heating characteristics of activated carbon are simulated and compared by fitting the experimental data with different functions.Accordingly,the heating of activated carbon in a microwave field can be divided into two stages: the first stage is linear,while the second stage is quadratic.A better desorption rate was achieved with a higher microwave power,a constant airflow rate(an airflow rate that is too high or too low will reduce the desorption rate),a higher moisture content and a lower activated carbon packing density.The effect of microwave desorption activated carbon is remarkable,in our experiment,the maximum desorption rate of the activated carbon reached 97.6%;The loss rate of the activated carbon after regeneration was low,and the total loss rate was 2.65% after five cycles of continuous absorption and desorption.The results can provide guidance for the development of key desorption technologies for implementation in radon reduction devices based on activated carbon. |
