For the modification of the absorption analysis system, please leave your comments
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Purpose of modifying the absorption process: To optimize the absorption process and reduce fluctuations in the operation of the absorption and separation system. Approach to the modification: Eliminate the process of feeding the rich absorption oil into the intermediate condensate tank, and improve the cooling efficiency of cooler 1, thereby enhancing the cooling effect without the need for additional cooling equipment. Theoretical feasibility: The condensed oil at the bottom of the absorption tower merges with the compressed rich gas and the desorbed gas to enter cooler 1. The purpose is to use the rich absorption oil at the bottom of the tower to absorb some of the liquid hydrocarbon components present in the compressed rich gas and the desorbed gas. However, due to the large difference in density between gases and liquids, the liquid and gas flow separately during air cooling; this results in a high temperature and a smaller area available for condensation of the gas phase, thereby increasing the cooling load. Some carbon dioxide-containing components dissolve in the liquid, while some light hydrocarbon components circulate within it. As a result, the desorption and absorption loads increase, which in turn affects the operating capacity of the absorption tower, and it is not possible to achieve the goal of absorbing liquid hydrocarbons. Modification point: A pipeline is laid directly from behind the check valve of the oil-rich absorption pump to before the hot feed to the separation tower, allowing the liquid phase to enter the separation tower directly. The gas phase is separated through condensation, thereby enabling the recovery of liquid hydrocarbons. The condensed oil tank serves as a true gas-liquid equilibrium tank, achieving genuine gas-liquid equilibrium. Advantages: Through gas-liquid separation, the following benefits can be achieved: 1. Cooling load is reduced. 2. The hot feed entering the stripping tower lowers the thermal load at the bottom of this tower. 3. The pump load for transporting the rich absorption oil at the bottom of the absorption tower is decreased. 4. With reduced cooling load, less mixed gas enters the absorption tower, thereby avoiding operational fluctuations caused by excessive gas-phase load
The following content is drawn from the topic of Dongfang Zhi Dong: Do you mean the vaporization tank for rich gas as the oil-gas separation tank at the top of the fractionation tower before the compressor? I’d like to ask again ； Our fractionation pressure is 0.13 MPa, and the flash pressure of the rich liquid is 0.19 MPa – will this not have any impact? Would introducing light hydrocarbons affect the pressure at the top of the distillation tower? I replied as follows: The rich gas flash tank is also known as a rich gas buffer tank. In my installation, the distillation pressure is 0.114 MPa, while the pressure of light hydrocarbons is 0.3 MPa; the pipe diameter is 25. This has minimal impact on the compressor. As for the distillation pressure, there are cooling units at the top of the distillation tower, so these pressures have little effect on the distillation tower itself
Do you mean that the rich absorption oil from the reformated absorber is directly pumped into the feed of the desorber? That’s always been how we operate our process – our rich absorption oil is pumped out and then heated in a heat exchanger before being fed into the desorber; there’s no need to cool the rich absorption oil before feeding it in~~~:loveliness:
My unit did not use this feeding method before; the main reason was to facilitate better absorption of liquid hydrocarbons after cooling, while also avoiding the impact of flow fluctuations on the distillation column. Excuse me, up there – is the parsing tower operating stably?
If I understand correctly, in your modification plan, you are suggesting adding another gas-liquid separation tank and a condenser to separate the rich absorbent oil and liquid? So that the highly absorbent oil pump can enable the liquid phase to enter the separation tower directly, while the gas phase is separated through condensation? It doesn’t seem convincing!
Hehe, your understanding is incorrect. The rich absorption oil from the absorption tower is directly pumped into the stripping tower using a pump; no other equipment is added, and existing control valves are reused. Most absorption and separation double-tower processes utilize a condensate oil tank in between, while my approach to modification is to avoid having the rich absorption oil pass through such a tank.
I finally understand. By bypassing the condenser 1 and the intermediate condensate tank, the cost is a reduction of 1 to 2 theoretical equilibrium stages for gas-liquid separation.
Yes, but it also reduces the cooling capacity, adapting to situations where the load that the device can handle is limited; as a result, the size of the device decreases, and the effect is noticeable
Yes, there’s always a trade-off! The required energy and the number of theoretical plates are always a pair of contradictions in separation columns. The original process has been in use both domestically and internationally for over half a century, as it not only facilitates further gas-liquid contact but also offers ease of operation and system stability. I also suggest that you take a look from the HAZOP perspective.
In our system, the rich absorption oil flows automatically from the absorption tower into the condensate oil tank, without mixing with the rich gas or desorbed gas in the subcooler. Then, a pump is used to draw the condensed oil from the tank into the desorption tower~
Hazard and Operability (HAZOP) study is a risk assessment method based on systems engineering that can be used for qualitative analysis or quantitative evaluation. It is employed to identify the hazards in production facilities and processes as well as their causes, with the aim of finding appropriate countermeasures. By analyzing the variations in process parameter values during production, the potential deviations in operation control, as well as the impact of these variations and deviations on the system and the possible consequences they may lead to, the causes of such variations and deviations are identified. The main risks and hazard factors present within the equipment or system as well as during the production process are determined, and measures to address the consequences of these variations and deviations are proposed. Due to the issue with the condensate tank in my unit, an update has now been carried out. The management does not pay much attention to this design; although the problem of pressure surges in the tower has not been resolved, operations are still proceeding according to the original procedures. Once the device starts operating and the temperature after cooling exceeds 38 degrees, it becomes a challenge for us to handle the situation; we have no choice but to follow the instructions of our supervisors
With the temperature of the condensate oil tank at 40 degrees, another severe tower flooding incident occurred, which led to the shutdown of the compressor and the cessation of operation in the backstream section of the plant; it was necessary to re-establish a three-tower cycle, a rather troublesome situation.