109- Discussion on the upgrade of the flue gas washing system in the heavy oil catalytic cracking unit for flue gas desulfurization and denitrification, using vane-type mist eliminators for mist and dust removal

This post was last edited by luoli519 on 2017-8-2 at 18:47. To focus limited efforts and resources on the critical aspects of foam and dust removal in the flue gas emission control process of catalytic cracking units, the dry denitration stage will not be discussed in detail here.

This post was last edited by luoli519 on 2019-12-18 at 16:48. Regarding Exxon’s WGS process package, it mainly includes a venturi sodium-alkali reaction absorption stage, a liquid-solid-solids swirl pre-separation stage at the direct inlet of the scrubber tower, a secondary liquid-solid capture stage within the scrubber tower for thorough separation from the flue gas, and a flue gas extraction and emission stage. The simple process is shown in the figure below:

In the venturi sodium-alkali reaction absorption stage, appropriately increasing the amount of sodium-alkali spray and the liquid-to-gas ratio can both achieve satisfactory absorption of acidic gases； However, an increase in the amount of sodium-alkali spray and an increase in the liquid-to-gas ratio not only raise operating costs but also pose challenges to the gas-liquid-solid swirl pre-separation stage at the direct inlet of the downstream scrubber tower. In particular, the process focuses on pipeline pressure drops, ignoring the fact that an inappropriate ratio between the diameter of the direct inlet pipe and that of the scrubber tower leads to a decrease in the efficiency of gas-liquid-solid swirl separation. When the ratio of the diameter of the direct inlet pipe to the diameter of the scrubber tower is too large, the efficiency of gas-liquid-solid separation decreases significantly. This results in the liquid and solid particles carried by the flue gas escaping back, posing a major challenge to the subsequent processes aimed at effectively capturing these particles, and may even cause blockages in the subsequent separation components. To this end, at the red-marked point “1#” in the WGS flowchart, we employ a patented flow pattern correction internal component to restore the pre-separation efficiency of the direct inlet of the scrubber for gas, liquid, and solids.

This post was last edited by luoli519 on 2017-8-16 at 18:38. I have discussed in other technical posts the control value for the ratio between the diameter of the direct inlet pipe of the cyclone scrubber and the diameter of the scrubber tower. When the actual value deviates significantly from the control value, a flow pattern correction internal component must be used to restore the efficiency of gas-liquid-solid separation. The following image shows a photo of the relationship between the diameter of the direct inlet of a certain device’s scrubber tower and the diameter of the scrubber tower itself. The diameter of the straight-cut inlet is indicated by the spacing of the yellow lines in the photo; clearly, this diameter exceeds half of the diameter of the washing tower, or even more. Introducing air at the upper edge of the inlet directly will not create a swirl; on the contrary, it will disrupt the swirl field that has already formed in the airflow at the lower edge of the inlet. As a result, the efficiency of gas-liquid-solid separation in the intake air is low, posing severe challenges to the downstream precision separation components and even causing blockages. It should be noted, however, that while using flow pattern correction internals for the originally imbalanced direct inlet can restore the efficiency of gas-liquid-solid separation, it will increase the pressure drop by 1–2 kPa. It is necessary to carefully consider whether the system’s capacity and the headroom available in the downstream fans are sufficient to meet the requirements.

This post was last edited by luoli519 on 2022-11-30 at 17:57. If technical improvements are not made at the direct access point “1#”, then it often becomes necessary to carry out technical upgrades using vane separators at the location marked in red as “2#” in the WGS flowchart. In the secondary separation internals of the wash tower in the WGS process package, EF-25A type packing or the first-generation Chevron simple baffle plates were originally used. For the EF-25A type packing, it is an excellent choice for mass transfer through the mixing of gas and liquid phases ； However, in situations where preventing the mixing of gas and liquid phases is necessary and full separation of the two phases is desired, its effect is counterproductive, resulting in low separation efficiency ； Furthermore, it can easily cause particulate matter to clog the internal components. For the first-generation Chevron simple baffle plates, there are no special channels for capturing and directing the liquid flow; as a result, the separated droplets can easily be carried back by the upward airflow, leading to low separation efficiency ； Moreover, many domestic enterprises and universities often rely on experience for \"rough estimates\" or even arbitrary decisions; they do not use precise dynamic gas-liquid separation and configuration design system platforms to develop accurate design plans. Without core technical documents such as accurate mechanical calculation sheets for dynamic separation, separation efficiency curves, and operating pressure drop curves to support technical reliability, it is impossible to ensure the actual separation efficiency.

This post was last edited by luoli519 on 2023-9-27 at 12:56. To carry out a technical upgrade of the existing washing tower, and in order to reduce the workload associated with the renovation efforts as well as shorten the duration of the modification, it is sufficient to add a vaned separator at the location marked “2#” in red in the WGS flowchart, so that it can be used in series with the existing internal components. For newly installed units, the vane separator internals package can be used directly to replace the original packing or simple baffle internals in the process package.

This post was last edited by luoli519 on 2022-11-30 at 17:58. In some areas, Class 1 emission standards are applied, which impose stricter requirements on factors such as the amount of liquid in the flue gas, dust content, and even the length and shape of the smoke plume. Therefore, a combined device of \"flue gas heat exchange + vane separator\" needs to be added at the position marked \"3#\" in red font on the WGS flowchart. As is well known, the flue gas that has passed through the vane separator at position “2#” contains very little residual liquid droplets. However, the flue gas containing saturated water vapor and residual fine droplets undergoes frictional impacts between these droplets as well as with the inner wall of the chimney as it rises spirally, resulting in the formation of secondary droplets. If the flue gas is highly humid, there is a large temperature difference between the inside and outside of the flue gas, and the length-to-diameter ratio of the chimney is high, then the flue gas discharged into the atmosphere through the chimney will form plumes, or even mist. To avoid mist and plume phenomena, some companies also use GGH plate heat exchangers, utilizing the hot flue gas before it enters the venturi to heat the gas emitted from the chimney. This not only helps the cooled flue gas to react and be absorbed more effectively within the venturi, but also facilitates the heating of the gas emitted from the chimney, enabling it to disperse rapidly into the atmosphere and thus reducing the occurrence of mist and plumes.

This post was last edited by luoli519 on 2017-8-10 15:59. For GGH cold and hot gas flow plate heat exchangers, since the cold gas stream consists of saturated vapor with a high humidity level, while the hot flue gas is nearly dry, the degree of temperature reduction of the hot flue gas is not equal to the degree of temperature increase of the cold gas stream. The greater the difference between dry and wet conditions, the larger the differences in specific heat and mass flow rate; as a result, the losses due to external convection/radiation/heat conduction become greater, and the temperature differences in the flue gas become more pronounced. Furthermore, the greater the difference between the temperature of the heated cold flue gas and the ambient temperature, the greater the flue gas extraction capacity, and the faster the flue gas moves away from the chimney. This leads to a Joule-Thomson effect in which the airflow expands, resulting in a decrease in temperature and pressure within the GGH system; this effect is particularly pronounced when a negative-pressure exhaust fan is also used downstream of the GGH. In fact, we can consider the entire GGH as a throttling fitting for analysis, where the internal energy of the fluid is converted into static pressure energy and kinetic energy. I would like to remind everyone that the T-J effect of GGH must not be ignored. When I have time another day, I will post a technical thread on this issue for a detailed discussion.

This post was last edited by luoli519 on 2017-8-2 at 22:14. The diagram below provides a brief overview of the cooperation process for upgrading the demisting and dust removal technology using Exxon’s WGS process package, as requested by our design institute; it is provided for reference

For the DuPont-Berg Company EDV process package, the cooperation modification plan we propose is similar to that of Exxon Company’s WGS process package. The difference is that the EDV process package of Dupont-Belco uses a \"filtration module + water droplet separator\".