Abnormal fluctuations in the temperature at the syngas outlet of the gasifier and on the brick support plates

Thread Content

This post was last edited by wang06120325 on 2015-11-18 at 11:46. The company uses GE water-coal slurry pressurized gasification; currently, during operation, one of the two gasifiers experiences frequent and significant fluctuations in the temperature of the syngas outlet as well as the temperature of the brick support plates. The maximum temperature of the syngas outlet fluctuates around 260, while the temperature of the backing brick plate is around 280. The duration of each temperature fluctuation varies; it can be as short as one or two minutes, or as long as several minutes. This poses serious risks to the stable operation of the system; the load on the gasification furnace is around 52, the amount of water used for quenching is around 280, the oxygen-to-coal ratio is maintained at around 490, and the pressure difference at the slag outlet ranges from 44 to 56. Observations of the slag on site showed a small amount of coarse slag and stringy formations; the rest was in the form of fine sand. Recently, there have been significant fluctuations in oxygen levels and coal slurry quality. The coal slurry fluctuates around 0.4, while oxygen fluctuates around 300. By comparing the trends, it was found that before each increase in temperature, there was a significant rise in the amount of syngas at the top of the carbon scrubber. As both the syngas outlet temperature and the temperature of the backing plates increased, the liquid level in the gasifier also rose, while the differential pressure at the slag outlet showed a slight downward trend. Currently, the gasifier is suffering from severe water contamination, and it is operating at half capacity. The reasons for this phenomenon are as follows: The temperature of the gasification furnace fluctuates significantly due to variations in oxygen levels, coal slurry conditions, and design flaws in the burners. This is reflected in the trend of methane content. Frequent fluctuations in furnace temperature lead to frequent changes at the slag outlet of the gasification furnace (the outlet is not yet blocked, but slag continues to form clumps), resulting in an unstable flow field as the syngas passes through this outlet, thereby causing flow deviations. As the syngas passes through the downcomer, uneven heat transfer due to flow deviation causes some liquid slag to clog in the annular gaps between the downcomer and the upcomer. A portion of the syngas passes through the downcomer and then escapes directly from the quench chamber, causing an increase in the syngas outlet temperature; since the gaps had not yet been blocked, the thermometers installed on the shelf bricks did not show a significant rise in temperature. I’m not sure if such phenomena have occurred in other units; I hope everyone will actively analyze the reasons behind them, so as to provide a reference for future operations. Personally, it is necessary to maintain high temperatures at this stage in order to avoid frequent fluctuations in the slag outlet. Switching to coal with a lower ash melting point provides flexibility in controlling the temperature of the gasifier. It is also important to manage the quality of the ash water properly, so as to prevent complete blockage of the gaps between the upward and downward tubes, which could otherwise lead to increased water content in the gasifier. If the gasifier is completely blocked, it can only operate at low load, and both the brick support plates and the syngas outlet will see an increase to a certain extent; however, this increase will not be as severe as the fluctuations seen before.