Application of Microwave Technology in Mineral Thawing          

1、 Overview

In Northeast, North and Northwest China, from November to April of the next year, the outdoor temperature is generally - 15 ℃~- 40 ℃, and the temperature is low. The surface moisture of mines in the above areas is high in winter, usually above 8%. Mining and transportation areas are easy to freeze in winter due to low temperature, large mineral surface moisture, long transportation distance and long transportation process. Most enterprises' unloading facilities are not suitable for frozen ore unloading, which requires enterprises to set up thawing facilities for ore transport trains. In factories and mines in severe cold areas, it is common to defrost vehicle borne frozen substances in winter by means of steam pipe greenhouse. When there are many frozen ore trucks, they can not be unloaded in time due to the slow thawing speed. In particular, Northeast China is also located in cold mountain areas, and the low temperature lasts for a long time, which makes the frozen ore waiting for unloading more serious, and the thawing time is longer and more difficult. As a result of this vicious cycle, more and more vehicles are overstocked, the factory storage time is long, and the turnover speed is slow, which causes difficulties and economic losses to railway transportation and mineral processing. Often, people are forced to adopt the "sea of people" tactics, and organize human shifts to raid the frozen ore day and night.

2、 Microwave Thawing principle

The permittivity of water is 80, the permittivity of ice is very small, and the permittivity of general minerals is 2-5. Generally speaking, ice has a very small ability to absorb microwave, while the frozen thickness is 500 mm, and microwave can penetrate (the wavelength of microwave is several orders of magnitude longer than that of infrared, and the penetration ability is generally more than 1000 times stronger than that of far-infrared). Under the action of microwave, the minerals to be thawed penetrate the ice layer to rapidly raise the temperature of minerals, and the ice layer on the surface contacting minerals dissolves into water, which then permeates everywhere. Because the microwave absorption capacity of water is more than 20 times that of ordinary minerals, it quickly heats up and dissolves the ice, thus achieving rapid low-temperature thawing.

III Microwave thawing Advantages of

1. Fast heating speed: microwave heating It is an internal heating mode that makes the heated object itself a heating element, without heat conduction process, so the heating is fast;

  2. Uniform heating: when microwave heating, no matter what the shape of each part of the object is, it can usually penetrate evenly to generate heat, so the heating is uniform;

3. Energy saving and high efficiency: during microwave heating, the heated object absorbs microwave and generates heat as a whole, so the thermal efficiency is extremely high;

   4. Selective heating and easy control: microwave has different effects on substances with different properties. For example, the microwave absorption capacity of water is far greater than that of ice, which is just suitable for microwave thawing.

   5. Strong microwave penetration ability: experiments show that it can penetrate dense ceramics up to 700 mm, and the penetration ability is 1000 times stronger than that of far-infrared, which can achieve deep thawing and other functions.

   6. Clean, hygienic, safe and harmless: microwave is fed directly into the metal carriage of the train or car loaded with goods. Shielding safety protection measures are taken at places where microwave leakage is easy to occur to ensure that microwave leakage meets the standard (<2mW/cm2 leakage is far lower than the national standard (GB10436-89)).