The pressure control valve on the gasifier torch vent line is not operating smoothly.
Thread Content
This post was last edited by wang06120325 on 2015-9-24 at 18:00. The pressure control valve on the flare vent line of the company’s gasification furnace is a sleeve valve; after successful startup, there were several instances where the valve did not respond properly when the control room adjusted its opening degree. Usually, during the pressure increase process in the gasification furnace, if the control valve does not move much and the valve is kept at its open position, it can suddenly move, which easily leads to pressure fluctuations in the gasification furnace and even poses a risk of shutdown. Personal analysis suggests that the inflexible operation of the valve is related to the accumulation of fine ash particles in the syngas, which cause scaling between the valve core and the valve seat; furthermore, since this valve is of the sleeve type, its flow path is complex and results in high flow resistance. During the shutdown phase of the gasifier and after successful startup, the water in the trays of the carbon washing tower is generally not used. This makes it easier for fine ash to be carried by the syngas and to accumulate there. Additionally, some of this fine ash ends up in the flare water seal tank as it enters the flare pipeline; after the system has been operating for a while, it is necessary to open the manhole of the water seal tank to remove the accumulated debris. I wonder what type of pressure control valves are used in the pipelines of other units, and whether such a phenomenon has occurred there as well.
This situation is common; this sleeve valve tends to get stuck and not operate smoothly. It is usually designed with two channels, which can solve the problem. The best solution now is to have analog feedback for this valve. Based on the actual situation, avoid sudden movements after sticking to prevent system fluctuations.
We redesigned a manual valve of the same pressure rating behind that valve, to be used for manual pressure adjustment in emergency situations when the valve gets clogged
If it is indeed fine ash causing the problem, we can resolve it easily by proactively using a mixer to add water, as well as adding water to the trays of the wash tower. However, I think the time during which the valve is open for venting is relatively short; there is high pressure in front of the vent valve and low pressure in the vent pipeline, resulting in a very high gas flow rate. Even with sleeve valves, fine ash generally does not tend to adhere to them. I think it’s the hot process gas that causes the valve core to expand due to heat, increasing the resistance to the movement of the sleeve. It is also related to the pressure difference before and after the valve; a larger pressure difference further increases the resistance to the movement of the sleeve.
Ventricular dust collectors, as well as adding water to the trays, can help address part of the issue with dust in the gas stream. However, due to the low pressure in the gasifier, high volumetric flow rates, and fast flow speeds, the presence of dust in the gas stream is an inherent problem during the initial operation phase. Stuck valves caused by the expansion of the valve core is something that is taken into account during valve design, and the gap between the sleeve and the valve core is sufficient to accommodate such expansion.
Operate this valve before feeding material; keep the pressure increase as short as possible, at a rate of 0.1 MPa/min. Avoid maintaining low pressure for an extended period. Later, Chase modified the valves, and the results were good.
Once, during operation, this valve got stuck; at that time the pressure in the gasification furnace was 5 MPa. By reducing the pressure in the furnace from 5 MPa to 3 MPa, the valve returned to normal function. This seems to indicate that it wasn’t ash buildup that caused the valve to get stuck.
This is definitely not a stuck valve; it’s a typical situation where a large pressure difference before and after the valve affects the actuator’s ability to regulate and move smoothly.
The analyses provided by those upstairs are quite accurate. There are many factors that can lead to this situation; both the valves themselves and the process operations play a role. In practical applications, a comprehensive consideration of all these factors is necessary, and methods such as switching between the two valves alternately can be used as adjustments.