Experimental Investigation Of The Form Of Moisture In Ximeng Lignite Based On Low-field ~1H Nuclear Magnetic Resonance

As the consumption of coal resources increases, the supply of high rank coal such as bituminous coal and anthracite coal is in shortage, the low rank coal is getting more and more attention. Lignite resource is huge in our country and the price is low, so it has promising development prospect.High moisture content is one of the main factors that restrict the development of lignite. In recent years, researches on the moisture distribution and dehydration modification methods have become hot area. This paper applies low field of 1H nuclear magnetic resonance (NMR) technology which is developing fast in recent years. According to the signal characteristics of the transverse relaxation time T2 of moisture in samples, this paper conducted a series of experimental studies mainly for Ximeng lignite:This paper conducted studies and discussions on the accuracy, the stability and the influence factors of the measuring technology of moisture in Ximeng lignite with nuclear magnetic resonance, and compared with the traditional drying method, this technology has more advantages. This paper uses nuclear magnetic resonance (NMR) technology and the mercury intrusion method to measure the surface relaxation rate of Ximeng lignite, and according to the surface relaxation rate, the pore structure can be obtained directly.According to the transverse relaxation time T2 distribution map, the distribution of the inner waters, outer water and balanced water in Ximeng lignite was found, and it was found that the ratio of outer water and inner water in Ximeng lignite is about 2.7:1. The concept of movable water and immobile water in petrology is introduced, it was found that the movable fluid saturation is about 37.3% and the limit of the two kinds of water in Ximeng lignite is the size of the pore, the T2 of the water in which is about 1ms.Through the experiments on different ranks, different humidity, different particle sizes of coal samples, it was found that as the ranks of coal gets higher, the size of the pore gets smaller, the proportion of micropore gets higher. As the humidity increases, the moisture content of the coal samples increases, but the change in quantity is small and the T2 stays the same. As the particle size increases, the moisture content of coal samples gets higher, the T2 gets shorter, which means that the moisture goes to the pores which are in smaller size.Through the experiments on coal samples of Ximeng lignite after low temperature modification, hydrothermal modification, and microwave modification respectively, it was found that in low temperature modification, the higher the temperature is, the faster the moisture evaporates. The moisture of long relaxation time evaporates first, and the moisture of short relaxation time evaporates slowly. In the process of hydrothermal modification, the higher the temperature is, the lower the moisture content is, which shows that as one of the common modification method, the performance of hydrothermal modification is affected largely by temperature. But when the temperature comes to 300 ℃, the influence of temperature begins to decrease. The transverse relaxation time T2 gets shorter compared with before, and as the temperature gets higher, the relaxation time gets shorter. In the process of microwave modification, as the microwave heating time increases, the left water in coal samples gets less. The transverse relaxation time T2 stays almost the same after the microwave modification.