It is not necessary to add a valve position interlock for the lock-hatch programmable control valve

The control mode of the lock hopper is either program mode (timing mode) or manual mode. When program mode is selected, the opening and closing of its valves are controlled by a program; the interlocks in place serve only as time-based checks. For example, the two overflow valves related to the slag tank have a time limit of 25 seconds, while all other valves have a time limit of 15 seconds. If a valve does not open or close within 15 seconds, the program will continue to send signals to it to open or close it. At the same time, the DCS will issue an alarm indicating an abnormality in the timing mode. Moreover, even if the lock hopper system stops functioning, it will not cause the gasification furnace to shut down; the gasification furnace will only stop operating when its liquid level reaches LL Manual mode refers to manual operation; in this mode, the valve can be opened without being subject to interlock protection. For example, when a valve gets stuck and rebounds, it is in manual mode!

Personally, I think it’s best not to add it. If interlocks are installed on the lockhopper valves, the vaporizer will shut down once those valves cannot be opened or closed. Valves that are not important any longer are of no value, increasing the workload. In the process design, the lock hopper is equipped with interlocks; once the conditions are not met, it stops operating and an alarm is triggered. There is no need to add a gasifier shutdown interlock!

It is best to add this to prevent lax supervision by staff, which could lead to other secondary accidents. Adding the interlock that triggers shutdown in case of valve switch timeout will do; just having an alarm is not sufficient, as employees may not see it.

The interlocking is merely a hopper interlocking; when the valve is not opened or not opened fully, the hopper operation stops and an alarm is issued.

The interlocking is merely a hopper interlocking; when the valve is not opened or not opened fully, the hopper operation stops and an alarm is issued.

The valve position switch must be subject to timing control. As mentioned on the second floor, the typical switching time is set at 15 seconds; if the valve fails to open or close properly by that time, it will switch from automatic mode to manual mode, which will not cause the vaporization furnace to stop operating. Strictly speaking, this is not a interlock mechanism, but rather a condition for sequential operation. If the valve position is not taken into account in the timing control, accidents can occur; for example, a valve that should be closed may not close properly, but since there is no signal indicating the valve’s position, the process can proceed to the next step, which is problematic. Additionally, if the valve operates slowly but can still be opened and closed fully, the time taken for these operations can be appropriately increased, for example to 20 seconds.

The lockhopper system should not be equipped with an interlock that shuts down the gasification furnace; this is unreasonable. Under programmed control, the valves in the lockhopper system have time limits, and if they do not operate properly within the specified time, the lockhopper system can simply be stopped.

The interlocks of lockout valves are generally divided into pneumatic interlocks, electrical interlocks, and logical interlocks. Pneumatic interlock and electrical interlock are also known as hard interlocks. Generally, a gas circuit interlock is required; the circuit interlock is one that is installed by the microcomputer team. The gas circuit interlock is a hard interlock added to the field instruments. It is advisable to install electrical interlocks on the high-pressure and low-pressure valves of the lock hopper, and pneumatic interlocks on its inlet and outlet valves.

It is highly necessary to add logical interlocks to a lock-hopper system, in order to prevent operators from making mistakes; this allows the lock-hopper system to operate automatically and ensures the stable operation of the gasification furnace. An example is that valves 2 and 3 cannot be opened simultaneously in interlock – this is a strict safeguard measure