Control scheme for the two flare valves at the inlet of the compressor in the catalytic unit
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There are two flare valves at the inlet of the compressor in the catalytic unit, one large and one small. Based on what do plants currently control them? What did it look like during design? In my plant design, the pressure at the inlet of the air compressor is used to control the large-flame torch valve, while the pressure at the top of the distillation tower is used to control the small-flame torch valve; in some other plants, the shutdown signal from the air compressor is used to control both torch valves. Let’s talk about our own installations and our opinions on them.
Reaction pressure control: 1) During the drying stage in both reactors, the pressure in the settler is controlled via a remote-controlled vent valve located at the top of the settler, with the aim of regulating the heating rate of both reactors. 2) During the fluidization test phase from the steam seal to the two reactors, the butterfly valve on the oil and gas outlet pipeline at the top of the distillation tower is used to control the pressure at that location, thereby maintaining equilibrium in the reaction pressure. 3) From the time the reaction feed is introduced until the rich gas compressor is started, the pressure at the top of the distillation tower is used to control the small valve for venting at the compressor inlet (for fine adjustment), along with the remotely controlled large valve for venting at the compressor inlet (for coarse adjustment), in order to maintain stable reaction pressure. 4) Once the rich gas compressor is operating normally under normal conditions, the speed of the rich gas compressor unit is controlled by using the top pressure of the fractionation column to maintain a stable reaction pressure. At this time, the anti-surge control valve located on the outlet circulation line of the compressor is used to prevent surge in the rich gas compressor unit. 5) Turbine governor failure: If the turbine governor fails, set the governor in a fixed position to keep the unit operating at a constant speed. A control system composed of the top pressure of the fractionation tower and the anti-surge control system of the rich gas compressor is used to regulate the anti-surge control valve on the outlet circuit of the compressor; simultaneously, PIC11201C is activated to control the flare valve and ensure stable reaction pressure. 6) Automatic pressure protection control at the inlet of the rich gas compressor: In the above two operating conditions, an independent automatic pressure protection control circuit is installed at the inlet of the rich gas compressor; its output signal directly controls the large flare valve. The set value of this regulator is 10 KPa higher than the normal operating pressure. When a sudden failure of the compressor causes the inlet pressure to rise sharply, this regulator automatically opens the large flare valve, thereby ensuring that both the inlet pressure of the rich gas compressor and the reaction pressure do not become too high.
The small flare valve at the compressor inlet is controlled by the compressor shutdown interlock signal; it opens once the compressor is shut down urgently, and remains closed under normal conditions. The large flare valve is manually controlled and is used to start and stop the operation of the facility
Control scheme for our three-stage reactor: Reaction pressure control. During the drying phase of the two reactors, the pressure in the settler is controlled via a remote-controlled vent valve located at the top of the settler; this is done to regulate the heating rate of the two reactors. * During the fluidization test phase from the steam seal to the two reactors, the butterfly valve on the oil and gas outlet pipeline at the top of the distillation tower is used to control the pressure at that location, thereby maintaining a stable reaction pressure. *From the time the reaction feed is introduced until the rich gas compressor is started, the pressure at the top of the distillation tower is used to control the small valve for venting at the compressor inlet (for fine tuning), along with the remotely controlled large valve for venting at the compressor inlet (for coarse tuning), in order to maintain stable reaction pressure. *After the rich gas compressor is operating normally, under normal conditions, the pressure at the top of the fractionation tower is used to control the speed of the rich gas compressor unit, thereby ensuring stability in the reaction pressure. At this time, both the large and small valves for venting at the inlet of the rich gas compressor close automatically. Meanwhile, the anti-surge control system of the rich gas compression unit operates the anti-surge control valve on the outlet circulation line of the compressor to prevent surge in the rich gas compression unit. *In the event of a fault in the turbine governor, the governor should be set to a fixed position so that the unit can operate at a constant speed. A control system composed of the pressure at the top of the fractionation tower and the anti-surge control system of the rich gas compressor is used to regulate the anti-surge control valve on the outlet line of the compressor; simultaneously, the control valve for the flare is activated to ensure stable reaction pressure. Automatic protection control for the inlet pressure of the rich gas compressor: Under the above two operating conditions, an independently installed automatic pressure protection control circuit for the inlet of the rich gas compressor is activated; its output signal directly controls the large flare valve. The set value of this regulator is about 10 KPa higher than the normal operating pressure. When a sudden failure of the compressor causes the inlet pressure to rise sharply, this regulator automatically opens the large flare valve, thereby preventing the inlet pressure of the rich gas compressor as well as the reaction pressure from becoming too high.
In our old factory, the small torch is operated automatically, while the large torch is operated manually. However, it also has its disadvantages in daily operation; often, when the flame is turned up to full strength, the excessive opening causes surging in the pressure compressor. What the original poster mentioned – using the pressure at the inlet of the compressor or a signal indicating that the compressor has stopped to control the activation of the flare system – is likely a relatively new design in China; it features a high degree of automation and significantly improved safety levels. However, the extent of the impact on the entire system in practical operation still needs to be determined through experience. It's just my personal opinion; my skills are limited.
The large flare valve at the inlet of our plant’s air compressor is used for emergency flaring in case of accidents; it is usually kept closed； The inlet pressure of the compressor is controlled using a fine-tuning vent valve and a backflow prevention valve.
During normal production, the large flare valve of the DCC unit in our facility is kept closed; it is controlled manually at the unit. When the compressor stops, the large flare valve automatically opens to 30% level, after which control is transferred to the reaction system, while the small flare valve is used very rarely. The large flare of the MIP unit is manually controlled, while the small flare can be operated automatically.
The large flare valve is manually controlled and is used when starting up or shutting down the facility or for self-protection； The small flame valve at the compressor inlet is controlled by the compressor shutdown signal; it opens when the compressor is shut down urgently, and remains closed under normal conditions.
In our plant, the control valves for venting are designated as 600 and 800. Our plant is also connected to the air compressor via a interlock system for self-protection; these valves remain closed under normal conditions, but they automatically open when the air compressor stops operating. Normally, the reaction pressure is controlled by adjusting the speed of the air compressor
At the inlet of my pneumatic compressor, there are two flare control valves of different sizes. During normal operation, these control valves remain closed, and the reaction pressure is controlled by manually adjusting the speed of the compressor. In the event of an accident and the reaction pressure rises above the specified limit, the small flare valve will open automatically, with the operator making further adjustments as appropriate. If the compressor stops operating due to a fault, not only will the small flare valve open fully, but the large flare valve will also open automatically to 25%.
The small valve is operated by automatic control for use during normal compressor operation, while the large valve is controlled manually for use in emergency situations and during shutdowns.