摘要
煤矿是我国主要的能源之一,但是每年在采煤过程中会向大气中排放出大量的甲烷。煤矿乏风的主要成分是甲烷,对环境有很大污染,因此有必要采用乏风氧化装置对甲烷加以收集利用。当甲烷浓度较高时,多采用换热器将多余的能量取出用于供暖,本文采用蜂窝陶瓷内置水平蛇形管实现能量的再利用。
本课题首先自行设计和搭建煤矿乏风瓦斯取热实验台,包括换热系统、汽水循环系统、烟风加热系统及数据采集与控制系统。实验选取相关的元件进行采集,对各元器件进行校核,通过反复的调试验证,保证各实验数据的准确性。此外,对水平蛇形管的换热特性进行研究,重点研究壁温及换热系数随外部烟温、质量流速及干度的变化规律。
通过对单相和两相流壁温特性的研究得出:无论在单相还是两相状态下,沿管长的壁温分布在弯头后都略有降低;沿周向分布的壁温特性有所不同,单相流时,内侧壁温低于外侧壁温,上侧壁温最低,下侧壁温最高,而在分层流和环状流状态下,内侧壁温高于外侧壁温。通过对两相流换热系数特性的研究得出:分层流和环状流的换热系数都随质量流速的增加而增大;分层流状态下随着干度的增加,管内换热得到强化,换热系数呈现增加趋势。但当干度增加到0.8~0.9时,由于两相流质量流速较低,壁温飞升出现恶化,换热减弱,换热系数随着干度的增加反而降低。此外,本课题还对各种工况下的实验数据进行了拟合,通过将实验值与计算值的对比,证明拟合情况良好。
China is in rich of coal mines, but a great much of methane is discharged into the atmosphere through coal mining every year. The methane is the main component of VAM (Ventilation Air Methane). However, VAM is harmful to the environment. Therefore, it is necessary to collect and recycle the energy released by VAM oxidation. A heat exchanger is used to recycle the excess energy to heat when methane concentration is high. In this paper, a horizontal serpentine tube placed in honeycomb ceramic regenerators was presented to recycle the energy.
VAM heating experiment platform is firstly designed and built, including heat exchange system, steam-water circulation system, smoke wind system and data acquisition and control system. All of the experimental equipments should be calibrated and adjusted before experimenting. The accuracy of the experiment data is ensured by repeated tests. The research of heat transfer for a horizontal serpentine tube focused on the correlation between wall temperature, heat transfer coefficient and smoke temperature, mass velocity and vapor fraction under about conditions.
Several runs of experiments were conducted to test the wall temperature of both single-phase and two-phase flow, The results show that the wall temperature along the tube's length slightly decreases after the return bend. The circumferential distribution of wall temperature is different in single phase flow, the inter wall temperature is lower than the outer, the top wall temperature is the lowest whereas the bottom is the highest. However, the inner wall temperature is higher than the outer under certain conditions of stratified and annular flow patterns. The results of experiments on characteristics of two-phase flow heat transfer coefficient show that the coefficient increases with the increase of mass flow in stratified or annular flow. The heat transfer coefficient increases with the increase of vapor fraction as the latter improved the convection effect. But the heat transfer coefficient decreases after the vapor fraction increased to 0.8~0.9, because the low two-phase mass flow and anomaly high temperature lead to a low convection efficiency. The experimental data showed great agreement with the calculation.
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