133- Special vaned separation collector for droplet capture of steam desalination fluid in the steam tower of the propylene plant catalyst stripping and regeneration process

Here, the steam generated by the process steam tower used for catalyst stripping and regeneration in the propylene unit of a large enterprise in the northwest region is taken as an example to discuss and analyze the problems encountered in catalyst stripping and regeneration. This propylene plant was designed by a renowned domestic engineering company, which also included the design of the process steam tower used for the catalyst stripping and regeneration in the propylene plant.

Let’s first take a look at the operating parameters for this process steam tower, which is used for the catalyst stripping and regeneration in propylene plants, as provided by the process package: I. Normal operating parameters: 1. Gas phase medium: Steam； Liquid medium: deionized water. 2. Operating pressure: 1.8 MPaG. 3. Operating temperature: 210°C. 4. Steam flow rate: 153,500 kg/hr. 5. Estimated droplet carryover rate: 1250 kg/hr. 6. Other physicochemical parameters of the gas-liquid two-phase system were not provided by the design institute, and shall be supplemented by the designer themselves. II. Maximum operating condition parameters: 1. Gas phase medium: Steam ； Liquid medium: deionized water. 2. Operating pressure: 1.8 MPaG. 3. Operating temperature: 210°C. 4. Steam flow rate: 225,500 kg/hr. 5. Estimated droplet carryover: 1750 kg/hr. 6. Other physicochemical parameters of the gas-liquid two-phase system were not provided by the design institute, and shall be supplemented by the designer themselves.

The last edit to this post was made by luoli519 on 2019-12-5 at 21:03. The engineering company responsible for designing the steam tower in accordance with this process simply carried out a conventional design based on the basic operating data provided in the process package, and then handed it over to the equipment manufacturer for production. The following figure shows the steam tower for this process:

As can be seen from the above diagram, aside from being equipped with an internal reboiler and an internal reflux condenser, the steam column of this process has the same structure as conventional columns; no purification treatment is applied to the steam before it exits the column system. From the perspective of gas-liquid separation technology, the steam supplied by the steam tower manufactured according to the drawings will not be of very high quality.

This post was last edited by luoli519 on 2019-6-11 21:55. In actual use, it was found that the activity of the catalyst after stripping and regeneration declined rapidly, and its service life was significantly lower than normal. After conducting a systematic analysis together with the design team, the owner focused their suspicions on steam purity. Therefore, the owner hired a specialized testing agency to examine the steam generated by the process steam tower, and it was found that the levels of Na+ and K+ ions in the steam were above the permissible limits. The process package supplier indicated that steam with excessive metal ions is the reason for the rapid decline in catalyst activity and a significantly shorter service life than normal. The process package supplier requires the installation of gas-liquid separation internals in the process steam tower to remove the liquid droplets and foam carried by the steam, as well as the dissolved metal ions.

This post was last edited by luoli519 on 2019-7-2 at 13:24. Due to the short downtime for equipment maintenance, the owner opted to install conventional, simple mesh foam eliminators that are readily available and low in cost, within the process steam tower. The structural diagram of the steam tower section of this process, which uses a screen defoamer, is as follows:

This post was last edited by luoli519 on 2019-7-2 at 13:25. Here is also a simple installation diagram for a mesh demister provided by a domestic supplier of such demisters:

After installing a wire mesh demister in the process steam tower, fluctuations in the amount of steam used in the process cause the level of metal ions in the steam to fluctuate as well, going up and down from their original values, resulting in instability. When the steam demand for the process is high, the content of metal ions in the steam returns to the excessive levels it had before the installation of the wire mesh demister ； And a low, slightly vibrating noise from the wire foam remover inside the tower can be heard. It is presumed that this was caused by \"flooding\" resulting from the steam volume passing through the wire mesh demister exceeding the processing limit. As is well known, in the use of conventional wire mesh demisters, their maximum processing capacity is usually controlled to not exceed 110% of the design value. Otherwise, \"liquid flooding\" is likely to occur, which not only results in the loss of the defoaming and separation capability but also causes liquid to accumulate on the surface of the screen, leading to equipment vibration or even the overturning of the screen.

This post was last edited by luoli519 on 2023-9-26 at 16:56. At the advice of foreign process package suppliers and foreign experts, we carried out a technical upgrade using a specialized feather separation device. Our technical solution essentially follows the same approach as that adopted in the smoke desulfurization and washing system of our rapid recovery device, where a dedicated vane-type demister is used; similarly, a specialized separation internal component set is added to the inside of the original shell at the air outlet, while the existing internal components within the shell remain unchanged. The advantage of this is that it enables technical upgrades to be achieved with minimal engineering work and renovation costs, while also allowing the renovation projects to be completed in a short time to restore production promptly.