PSA pressure swing adsorption

Our pressure swing adsorption carbon removal unit is not designed this way; the venting consists of a phase of forward venting along with some reverse venting, as well as a second phase of reverse venting, without the use of a pressure equalization tank.

The original poster must be mistaken; the PSA pressure swing adsorption processes vary, but they all follow the same basic principles and are largely similar to each other. There is usually forward and reverse operation; it is not possible to evacuate after entering the equalization tank. The reason why the original poster thinks so might be as follows: 1. The original poster did not carefully examine the process and mistakenly assumed it was the pressure equalization tank being emptied. 2. Under certain specific circumstances, the temporary measures taken by the unit in question, such as overpressure in the pressure equalization tank, are mistaken by the person in charge for regular operational procedures. 3. The sequential discharge tank can be configured to recover the fluid, or it can discharge it directly without recovery; it is possible to mistake the discharge from such a tank for that from a pressure equalization tank.

During forward adsorption in pressure swing adsorption, the gas composition changes over time; in order to recover some hydrogen and nitrogen, the process is divided into two stages.

What was said on the third floor is correct; could the original poster upload the flowchart so that everyone can take a look at it?

This post was last edited by Chemical Gas Purification on 2010-10-20 at 13:55. I’m not sure if the materials compiled earlier are useful: Pressure Swing Adsorption Carbon Removal Process. Chapter 1: Overview. Section 1: Job Responsibilities and Shift Handover. 1. Arrive at the post half an hour in advance to understand the production status and any existing problems, and conduct routine inspections； 2. Attend the pre-shift meeting, listen to the production report from the shift handover supervisor as well as the work plans outlined by the supervisor for the current shift. 3. Conduct a thorough handover of duties; by meeting with the relevant personnel and reviewing records and reports, gain a better understanding of the performance of various process parameters during the shift, as well as the operation and maintenance status of equipment, electrical systems, and instruments. Also, learn about the status of key operating equipment and backup machines, as well as the causes of any failures and how they were addressed ； 4. After both parties have verified everything is correct, they sign the document; once the shift is taken over, all subsequent work is the responsibility of the person who takes over the shift. Shift handover: 1. Make efforts to create favorable production conditions for the incoming shift, keep the work area and equipment clean; under normal circumstances, process parameters must not be changed arbitrarily within 30 minutes before the handover ； 2. Provide a detailed on-site explanation to the successor regarding changes in production load, existing problems, and points of attention ； 3. During the shift handover, production is the responsibility of the person conducting the handover; if the person taking over has not arrived, the current worker should continue to be on duty and report to the shift leader ； 4. In the event of abnormal circumstances due to an accident, shift handover should be postponed proactively, and personnel should be organized to handle the situation; shift handover can take place only after normal conditions are restored, or upon clear communication during the handover and mutual agreement between both parties. 5. After both parties sign to confirm the handover, the person handing over the shift goes to attend the shift meeting; everything thereafter is the responsibility of the person taking over the shift. Section 2: Basic Precautions for Safe Production 1. Operators must follow the procedures outlined in the operation manual. All new employees must receive safety training as well as instruction on operating methods*. During actual operations, those who have not passed the tests related to technical skills and operating methods are not allowed to carry out tasks independently. 2. When returning to work, operators must be properly dressed; they are not allowed to bring any flammable or explosive items into the workplace. They must strictly adhere to labor discipline, carry out proper shift handovers, conduct regular inspections, strictly control process parameters, follow operating procedures meticulously, and comply with all relevant safety regulations. 3. The area within the boundaries of this device must be kept clean; it is not allowed to store flammable or explosive materials there, especially not on traffic routes, in order to ensure smooth traffic flow. 4. Fire-fighting equipment should be installed in the area where this device is located; all operators must be aware of its location and how to use it. It is strictly prohibited to touch this equipment without permission, and it should be inspected regularly on an annual basis. 5. No repairs or welding shall be carried out on the equipment while it is under pressure; screws must be tightened, and it is strictly prohibited to use metal tools to strike the equipment. 6. The pressure gauge used on the equipment must be certified as qualified and sealed with a lead seal; it shall not be used if its pointer does not point to zero or if the error exceeds the allowable range for its grade. The pressure gauge must be checked annually and re-sealed with a lead seal. For pressure gauges that indicate air pressure, the zero point must be adjusted before use. 7. Smoking and hot work are strictly prohibited within the boundary of this equipment. Before performing any hot work on containers and pipelines that may contain explosive or flammable gases, approval from the factory’s safety department must be obtained. The area in question should first be purged with nitrogen, and after on-site analysis confirms that conditions are safe and appropriate safety measures have been taken, a hot work permit can be obtained before proceeding with the work. Hot work is strictly forbidden in the absence of an approved permit, without isolating the area from the production system, without proper cleaning and purging, without removing any flammable materials from the vicinity, without conducting necessary safety analyses, and without fire protection measures or supervision in place. 8. Ensure the airtightness of equipment, pipelines, and valves; check for leaks after maintenance, and operation can only commence once they are found to be leak-free. Be careful at all times during use to prevent any gas leaks ； 9. In the event of a malfunction in the instrumentation system, it should be repaired by the instrumentation technicians. These technicians must work closely with the operators; when restarting the system after shutdown for maintenance, attention must be paid to the pressure in the adsorption tower to prevent high-pressure backflow. Section 3: Job Responsibilities and Scope of Authority. Job responsibilities: Utilize the selective adsorption property of adsorbents to reduce the 29.95% CO2 content in the raw gas obtained through transformation, bringing the CO2 level down to around 3%, so that the resulting gas can be sent on for further desulfurization. Scope of coverage: From the inlet section butterfly valve V02401 to the outlet butterfly valve V02403 ； All equipment within the pressure swing adsorption unit – excluding adsorption towers, gas-liquid separators, purified gas buffer tanks, vacuum pumps, pipelines, valves, instruments, electrical devices, as well as tools, apparatuses, personal protective equipment, fire-fighting equipment, buildings, communication equipment, and utility systems – is used, maintained, and serviced by the operators of this position. Section 4: Process Principle. Pressure swing adsorption technology is based on the physical adsorption of gas molecules by the surface of adsorbents (porous solid materials). Taking advantage of the fact that adsorbents readily adsorb high-boiling-point components at constant pressure while having difficulty adsorbing low-boiling-point components, as well as the increase in adsorption capacity under high pressure (for the components to be adsorbed) and a decrease in adsorption capacity under reduced pressure (for the components to be desorbed), the feed gas is passed through an adsorbent bed under high pressure. Impurity components with higher boiling points than hydrogen are selectively adsorbed, whereas hydrogen along with low-boiling-point components passes through the adsorbent bed, thereby achieving separation of hydrogen from these impurities. Subsequently, the adsorbed impurities are desorbed under reduced pressure, allowing the adsorbent to be regenerated for use in further adsorption and separation processes. This cycle of adsorbing impurities to produce hydrogen under high pressure and desorbing the impurities under reduced pressure to regenerate the adsorbent is the pressure swing adsorption process. During the pressure swing adsorption process, the desorption of the adsorbent in the adsorption bed is achieved by reducing the partial pressure of impurities. Common methods include:  reducing the pressure in the adsorption bed (pressure relief),  flushing with product components, and  pumping using a vacuum pump. Section 5 describes the process flow: The raw gas coming from the pressure swing adsorption unit enters this device under conditions of 2.0 Mpa and 40°C. First, it passes through a gas-liquid separator (V02401) to remove any substances that may be present in the gas. After that, it is measured by a flow meter (FIQ-02401) before entering the pressure swing adsorption system, which consists of 19 adsorbers (T02401A–S) and a set of programmable valves. This PSA system operates with 19 towers, with 3 towers used for feeding, 12 cycles of pressure equalization, and processes such as flushing, evacuation, and desorption. The raw gas passes through three adsorbers that are in the adsorption state; all components other than CO2, CH4, N2, H2S, etc., are removed from the gas through the adsorbent. The purified gas then exits at the top of the tower, passes through a buffer tank (V02402), is measured again by a flow meter (FIQ-02402), and is sent out through pipes. The remaining towers go through sequences of pressure equalization, flushing, reverse discharge, evacuation, pressure equalization again, and final charging. The 19 towers operate in an alternating cycle, one after another, thereby ensuring a continuous supply of raw gas and a continuous output of purified gas. All steps in the pressure swing adsorption process are controlled by a DCS system. The desorbed gas from the PSA system comes from the reverse discharge and evacuation phases of the adsorber; the gas from these phases, along with the flushing gas, is discharged directly into the atmosphere through pipes at high altitudes. Evacuation is carried out using water-ring vacuum pumps (P02401A, B). Section 6: Specific operating steps of the adsorption tower 1. Adsorption: The raw gas coming from the pressure swing adsorption unit is sent to the gas-liquid separator V02401, where free water in the gas is removed. After that, the gas exits the separator and enters the tower via the lower end of the programmable valve KV02401. Under the adsorption pressure, as the gas flows downward through the adsorption bed, CO2 is selectively adsorbed. The gas after CO2 absorption is discharged from the top of the tower through the programmable valve KV02402; part of this gas is used as make-up gas via HV02401, while most of it is sent to the advanced desulfurization unit through the butterfly valve V2423 and PV02403. When the adsorption front approaches the exit end of the adsorption bed, feed intake and product gas output are stopped. At this point, there remains a section between the adsorption front and the exit end that contains unsaturated adsorbent. Chapter 2: Main Process Parameters
I. Components of Raw Gas, Purified Gas, and Desorbed Gas
Components of Raw Gas:
Component | H2 | CO2 | CO | CH4 | N2 | H2O | Σ V%
---|---|---|---|---|---|---|---
Value | 45.47 | 29.95 | 21.00 | 2.29 | 0.92 | 0.37 | 100

Components of Purified Gas:
Component | H2 | CO2 | CO | CH4 | N2 | H2O | Σ V%
---|---|---|---|---|---|---|---
Value | 63.83 | 3.00 | 29.05 | 2.84 | 1.28 | 0.00 | 100

Components of Desorbed Gas:
Component | H2 | CO2 | CO | CH4 | N2 | H2O | Σ V%
---|---|---|---|---|---|---|---
Value | 0.70 | 95.68 | 1.37 | 0.94 | 0.03 | 1.27 | 100

II. Pressure
① Pressure of raw gas ≤ 1.9 Mpa
② Pressure of purified gas ≥ 1.8 Mpa
③ Pressure of desorbed gas ≤ 0.02 Mpa
④ Pressure of nitrogen used for purging: 0.4 Mpa
⑤ Pressure of instrument air: 0.45–0.55 Mpa
⑥ Pressure of water supplied to the system: > 0.4 Mpa
⑦ Pressure of return water: Atmospheric pressure
⑧ Vacuum level of the vacuum pump: > –0.08 Mpa

III. Temperature
① Temperature of raw gas, purified gas, desorbed gas, nitrogen used for purging, and instrument air: ≤ 40°C. ②1. The temperature of the water in use is ≤20°C. ③ The temperature of the return water is around 30°C. ④ The temperature of the bearings in the vacuum pump motor is ≤85°C. ⑤ The temperature of the transmission oil is ≤65°C. ⑥ The dew point temperature of the instrument air is –60°C.
IV. Flow rates: ① The flow rate of the raw gas is 94,000 Nm3/h. ② The flow rate of the purified gas is 66,664.8 Nm3/h. ③ The flow rate of the desorbed gas is 27,335.2 Nm3/h. ④ The flow rate of the N2 used for displacement is 5,000 Nm3/h. ⑤ The flow rate of the instrument air is 300 Nm3/h. ⑥ The flow rate of water is 35 Nm3/h.
V. Recovery rates: CO > 95% (by volume); H2 > 97% (by volume).
VI. Current: The current consumption of the vacuum pump is < …
VII. Switching time of the automatic valves

Pressure swing adsorption involves several tanks: an air balance tank, an adsorption tower, an outlet gas balance tank. The part used for venting is where the gases are released during desorption

OP, the purpose of pressure equalization is to use the depressurized gas to fill other adsorption tanks, thereby achieving maximum utilization of the material. When it becomes impossible to maintain pressure equalization, reverse ventilation of the adsorbers is required, along with vacuum evacuation for desorption, in order to regenerate the adsorbers. Direct venting involves shutting down a single adsorber for treatment in the event of an accident, while the remaining towers simply have their adsorption procedures adjusted, without affecting the stability of production.

Thank you all. I took another close look, and it was my mistake – some of it was actually direct venting under overpressure conditions. I really learned something from this.