How to control the reaction pressure

1. When the two reactors are started up and their temperatures are raised, the reaction pressure during the drying process is released through the vent at the top of the settler. 2. When fluidization and fractionation in the two reactors are not connected, the pressure is regulated by releasing gas and oil before it enters the fractionation tower, via the spray tower. 3. After the gas and oil blind flanges are removed, before the compressor is started, the pressure is controlled using the gas and oil butterfly valve in the fractionation tower as well as the flare valve at the compressor inlet. 4. During the startup process of the compressor, when the gas and oil butterfly valve is fully open, part of the gas and oil enters the compressor; this gas and oil is then released either through the flare at the inlet or at the outlet. 5. Once the compressor is operating normally, the pressure is regulated using the compressor’s speed or by adjusting the backflow at the compressor outlet. In the actual production process, with the compressor speed remaining constant, we only use the counter-rotation control valve for regulation

Some companies use gas and oil butterfly valves to control the reaction pressure. The gas and oil butterfly valves in our company are in the fully open position; under normal conditions, counter-rotating control valves are used for control, with the turbine speed serving as an auxiliary adjustment mechanism

Controlling the pressure of these two vessels is quite challenging, especially during startup/shutdown operations or in the event of accidents; it requires a dedicated person to monitor their pressure. Generally, newly hired operators are not capable of handling this task. Operators tasked with pressure control need not only to have certain operational experience but also to remain calm and quick-thinking. The reaction pressure is primarily controlled by the compressor system, whose control methods include the compressor speed, the backflow rate, and the two flare systems of different sizes. Of course, there is also a large butterfly valve on the overhead vapor line of the fractionator. It is not used under normal conditions; it comes into use when there is no feed to the settler during shutdowns, startups, or when the feed self-protection system is activated, resulting in too low pressure that prevents equilibrium with the regeneration pressure – at such times, it is used to throttle and maintain pressure. It should be noted here that the function of backflow control is to ensure that the unit has a certain level of load, so as to prevent vibrations caused by too low a load. However, operators often use it to adjust pressure, which is not the correct approach. Excessive backflow can result in energy waste, while too little backflow can affect the stable operation of the unit. There is another interesting question: when the speed of the compressor is under automatic control and the pressure at the compressor inlet remains constant, if the reaction pressure is stable, the relationship between these two pressures is given by the following equation: P1 + ΔP = P2. Here, P1 represents the pressure at the compressor inlet, P2 represents the reaction pressure, and ΔP represents the pressure drop across the distillation column and the subsequent oil and gas pipelines. At this point, if a large backflow occurs, the pressure at the inlet of the compressor remains unchanged due to automatic control, but the reaction pressure increases. Beginners often don’t understand why this happens It’s actually quite simple: as ΔP increases, the backflow occurs from the compressor outlet back to the oil-gas line at the top of the tower, at the inlet of the cooler. The flow rate in this section increases, and as a result, the pressure drop – and thus the spontaneous combustion – also increases. The regeneration pressure is controlled in stages by the flue gas turbine inlet butterfly valve and the flue gas turbine bypass double-acting slide valve. How to control the pressure of the two devices properly? Under normal operating conditions, if the butterfly valve at the flue gas inlet is already fully open, I recommend changing this valve to a manually controlled type, with the regeneration pressure being automatically regulated by a double-acting slide valve in a single circuit. If the speed of the compressor is also automatically controlled, with a slight backflow, and both flare valves are closed, this is an ideal situation that makes operation much easier for the staff. In the event of emergencies such as moisture in the feed material, pump failure in the distillation system, moisture in the cold reflux stream, shutdown of the compressor, or automatic shutdown of the feed system, it is not advisable to switch the double-acting slide valve to manual control. As long as the instruments are functioning properly, the double-acting slide valve should remain under automatic control. The operator should ensure that the regeneration pressure matches the reaction pressure, keeping the pressure difference between the two vessels at a reasonable level. The operator’s main focus remains on controlling the reaction pressure, which makes the operation relatively simple and allows for easier maintenance of stable pressure levels. If the reaction pressure rises suddenly, it may be necessary to open the large flare valve. This valve is used very rarely under normal conditions, and when it needs to be opened, sticking often occurs; sometimes it still doesn’t respond even when opened fully. In such situations, the operator must be extremely careful and keep a close eye on the pressure at the compressor inlet. As soon as there is a response, the valve should be closed partially right away to prevent the compressor from running out of pressure. It is generally stipulated that the large flare valve should be tested once a week; operators must adhere to this requirement. If any problems are detected, they should contact the instrumentation or fitter team as soon as possible to address them, in order to avoid sticking during use. When there are large fluctuations in pressure between the two vessels and operators are busy regulating this pressure, it sometimes seems that the instruments in the double-acting slide valve control circuit do not function properly, or one of the slide valves gets stuck. In such cases, operators switch to manual control. However, manual control presents a problem: since the regeneration pressure needs to adjust in response to the process pressure in order to prevent the pressure difference between the two vessels from exceeding limits, if I want to reduce the regeneration pressure, should I increase or decrease the output value? It seems necessary to consider whether the valve should be set to a signal-on or signal-off mode; if it’s set to signal-off, then the output should be reduced and the valve opened wider, so that the regeneration pressure can drop. Conversely, a similar kind of thinking is also needed. If you think in that way, it becomes too complicated and it’s easy to go astray and make mistakes. The correct way to think about this is to determine whether the circuit operates in a positive or negative manner; it’s better if it’s positive. As long as the pressure increases, my output will increase as well, which simplifies the adjustment process and reduces the chances of errors. If it is a reverse reaction, one can contact the instrumentation team to install an output signal inverter, which is easy to implement in a DCS.

The information on the 2nd and 4th floors is quite comprehensive; after starting the air compressor, the reaction pressure is controlled using the speed； Before starting up, use a flare or the butterfly valve at the top of the distillation tower to control the reaction pressure and maintain pressure balance ； Before blind 201, use the settler top vent to control the reverse force

What was said upstairs covered all aspects in general. Currently, during startup, there are operations that do not involve using torches; dry gas is injected into the fractionation tower to warm up the compressor, or gasoline is sprayed first before injecting fuel in order to accelerate the compressor’s rotation speed