136 - Questions and discussions regarding the technical solutions for eliminating white smoke in peer consultations on FCCU units

This post was last edited by luoli519 on 2019-8-6 at 19:54. Regarding flue gas emissions, **the Environmental Protection Administration’s strict emission standards are being implemented across the country. Stringent numerical requirements exist for harmful substances such as residual chemicals and dust in the exhaust gases. Although the various parameters of the flue gas emitted by many enterprises after technical treatment meet the latest standard requirements set by the **Environmental Protection Administration, there is still a plume of smoke coming from the chimneys. The \"plume\" formed by the flue gases that meet the latest standards set by the Environmental Protection Administration is, in fact, an optical phenomenon resulting from water vapor present in those flue gases – water droplets and mist of various small sizes that appear in a certain area of the temperature-humidity phase diagram; these droplets and mist give rise to light refraction and scattering. Therefore, for the \"plume\" formed by the exhaust gases that meet the latest standards set by the Environmental Protection Administration, such emissions represent a safe level that is acceptable for both the environment and human health. In fact, in Europe and the United States, the \"plumes\" formed by exhaust gases that meet their environmental standards are also considered safe emission practices that are accepted by authorities and the public; there is no requirement for companies to invest heavily in so-called \"whitening\" measures for such plumes. In China, driven by certain factors, some enterprises are making substantial investments in what is known as \"whitening\" processes to address the \"plumes\" formed by the exhaust gases that already meet the latest standards set by the Environmental Protection Administration. In particular, in previous years, when the causes of fog were unclear, such \"whitening\" measures were required for the treatment of exhaust gases from thermal power plants; recently, this practice has gradually spread to oil refining companies as well. Some well-known academicians, experts, and scholars in the fields of petrochemicals and environmental protection recently called for a rational approach to the \"whitening\" projects aimed at treating the smoke plumes generated by emissions that already meet the latest standards set by the Environmental Protection Administration. Of course, this is a different matter when it comes to the \"plumes\" formed by exhaust gases that do not meet the latest standards set by the Environmental Protection Administration.

This post was last edited by luoli519 on 2019-11-18 at 16:40. A colleague from a refining enterprise working with heavy oil cracking units mentioned a solution for eliminating white smoke plumes. Based on the materials he provided, this solution is a technology developed by an environmental protection technology company. However, has it truly achieved flue gas condensation? This is one of the doubts and questions. One can start by analyzing the text and flowcharts provided in its documentation.

This post was last edited by luoli519 on 2019-11-18 at 16:46. This is a process flow diagram of the smoke plume whitening treatment solution provided by an environmental protection company:

The last edit to this post was made by luoli519 on 2019-10-9 at 12:37. As can be seen from its flow diagram, external steam pipelines or electric heaters are used to preheat the mixed air; thereafter, this preheated air undergoes heat exchange with the high-temperature flue gas at the system inlet. The cooled flue gas then enters a Venturi desulfurization scrubber and a scrubbing tower, where it is sprayed and washed, cooled, and subjected to desulfurization reactions； The circulating wash fluid flow is regulated by heat transfer through circulating water, ensuring that the temperature of the gas-liquid washing desulfurization system within the scrubber meets the system temperature requirements specified by the desulfurization process packages (such as Exxon WGS process packages, Berger EDV process packages, etc.) ； The wet flue gas exiting the tower is directly mixed and heated by the heated air before being discharged through the chimney. Essentially, this process involves only \"heat exchange,\" unlike a complete process which includes both \"heat exchange\" and \"separation\" as its core components. In terms of heat exchange methods, direct internal heat exchange between hot and cold flue gases is not employed; instead, the simplest and most primitive method—air blowing for heat transfer—is used both domestically and internationally. However, this method fails to sufficiently cool the hot flue gases. Consequently, it is necessary to utilize a circulating cooling water system to remove heat from the circulating slurry, thereby preventing the heat energy from being used to raise the temperature of the wet flue gases. As a result, the proportion of thermal energy transferred within the system remains low. Additionally, external steam pipelines are required to heat or electrically heat the air, resulting in high demands for thermal energy. Therefore, the technological advancement of this process is questionable.

This post was last edited by luoli519 on 2019-10-9 at 12:42. Furthermore, regarding the process of preheating the mixed air with external steam, its location also needs further optimization to facilitate more efficient heat exchange between the hot flue gas and air, thereby cooling the hot flue gas to a lower temperature. Lower-temperature flue gas is more conducive to the desulfurization reaction, and it also reduces the cooling required by the circulating cooling water system for the circulating slurry. The data provided, namely a flue gas temperature of 56°C upon leaving the scrubber tower and a residual SO2 level of 100 mg/Nm^3 in the flue gas at that point, indicate that the heat exchange efficiency between the gas streams in this process is not satisfactory. As a result, the hot flue gas enters the venturi scrubber and the desulfurization tower at a high temperature, which leads to inadequate desulfurization and hence a residual SO2 level of 100 mg/Nm^3 in the flue gas exiting the towers. The standard of 100 mg/Nm^3 for SO2 residues in these flue gases is likely taken from the emission standards for thermal power plants, or it may be an older environmental emission standard. After 2015, the **Environmental Protection Administration issued new standards, setting an upper limit of 50 mg/Nm^3 for SO2 residues in the flue gas emissions from refining and chemical enterprises; many such companies have already adopted a limit of 30 mg/Nm^3. At CNPC’s Wushan Petrochemical and Dushanzi Petrochemical plants, the residual SO2 level in the flue gas is usually less than 15 mg/Nm^3. It can be seen that the gas-to-gas heat exchange efficiency of this FCH process is not satisfactory, which results in the hot flue gas entering the venturi scrubber at a high temperature and leading to inadequate desulfurization in the desulfurization tower. Please check its performance data:

This post was last edited by luoli519 on 2019-11-18 at 16:42. Regarding the doubts raised by colleagues in the refining industry regarding the term “Smoke Consendation,” I personally believe that this Chinese and English expression is merely a one-sided promotional tactic used by that company. The flue gas from the FCCU comes from the high-temperature catalyst regeneration system; at this stage it is \"dry gas\" that is far from the saturated vapor state. Condensation occurs only when the flue gas is cooled to a very low temperature, bringing the water vapor content in it close to the dew point. Heated air is used to cool the high-temperature flue gas, or \"dry gas\"; the temperature of the cooled flue gas does not drop below the temperature of the \"heated air\", which makes it difficult to achieve a level of \"smoke condensation\". It is recommended that everyone clarify this matter.

This post was last edited by luoli519 on 2019-10-9 at 12:46. So, can the flue gas exiting the tower be truly \"dewhitened\" after being mixed and heated by the forced hot air? Based on the data from the operation of a certain petrochemical I heavy catalyst reactor, the lower limit (design value) of the chimney temperature after heating is only 70°C. As we all know, after passing through a Venturi scrubber and a spray scrubber in the scrubbing tower, the flue gas carries a large number of liquid droplets and mist particles of various sizes. At atmospheric pressure, when the flue gas is heated to 80°C or even 90°C (which requires a larger flow of hot air to heat the flue gas), the water droplets and mist remain in a liquid state. These numerous tiny liquid droplets and bubbles in the flue gas remain in the \"plume\" region of the flue gas temperature and humidity diagram, and thus cannot achieve the effect of \"plume whitening\". Please carefully examine the data on the operation of this whitening process in a certain petrochemical FCC unit, and compare it with the phase diagram data regarding the formation of smoke plumes from flue gas that can be found online.

This post was last edited by luoli519 on 2019-11-18 at 16:45. Based on the so-called \"performance guarantee values\" provided by that environmental protection company, it is necessary to remind the owners of petrochemical enterprises of two points: First, the first condition specified for those \"performance guarantee values\" is that the flue gas temperature at the outlet of the desulfurization tower (under design conditions) should be 45°C. All the technical personnel working on FCCU units are aware of how much water and steam they had to use for circulation and spraying in order to barely keep the flue gas temperature within the range of 55–60°C required by the desulfurization process If it is necessary to meet the first condition specified in its \"performance guarantee values\", which requires keeping the flue gas temperature at the outlet of the desulfurization tower at 45°C, then how much cooling capacity and spray water are required to lower the temperature of the flue gas and the circulating slurry? ? Moreover, the desulfurization reaction also releases heat continuously! For refining and chemical companies, it is difficult to keep the flue gas temperature at the outlet of the desulfurization tower at 45°C.

This post was last edited by luoli519 on 2019-11-18 at 16:44. II. The stated \"performance guarantee values\" are accompanied by additional conditional clauses: \"Under conditions of an ambient temperature above 0°C and a relative humidity below 78%, it is guaranteed that no white smoke will appear at the chimney outlet.\" Technical operators in refining and chemical enterprises all know: in the summer, how many enterprises across the country can ensure that the relative humidity of their ambient air remains below 78%? According to the forecasts from the Central Meteorological Observatory, in many areas the ambient temperature will be in the 30s degrees Celsius range, with relative humidity as high as 95%! In winter, are there any companies in the north where the ambient temperature is above 0°C? Thus, this stated “performance guarantee value” is again accompanied by conditional clauses that are difficult for the owner’s company to meet.

This post was last edited by luoli519 on 2019-12-5 at 20:29. According to certain operational data from a petrochemical plant provided for this technology, it is not capable of eliminating the white plumes throughout the whole year. During the summer (a season when the smoke plumes are not severe), the failure of the smoke plumes to turn white is due to the owner’s failure to meet the design conditions (ambient air humidity must not be higher than 78%, and the temperature of the flue gas at the exit of the desulfurization tower must not be higher than 45°C); this is the owner’s responsibility ； During winter (the season when smoke plumes are particularly severe), the failure of the smoke plumes to become ‘white’ is the responsibility of the owner, as they fail to meet the designed operating conditions (an ambient temperature of not lower than 0°C and a flue gas temperature at the exit of the desulfurization tower of not higher than 45°C). Anyway, the failure of the smoke plume to become “whiteless” is entirely due to the fact that the owner’s operating conditions do not meet the design requirements; it is the owner’s responsibility.