11- Discussion on the use of feather leaf separators for vacuum pumping in distillation systems or for gas discharge and material recovery
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This post was last edited by luoli519 on 2023-10-3 at 17:47. Faced with the dual pressures of stricter environmental emission standards and a sluggish market, many petrochemical companies are focusing on improving their internal capabilities by upgrading their technologies at the source of emissions. Among them, the approach of capturing and recovering materials and finished products from the exhaust gases pumped out by the vacuum pump in the distillation system is particularly noteworthy. The purpose of a business is to achieve at least two goals at once, or even multiple goals. Some companies install deep condensers on their vacuum pipelines in an effort to condense more of the materials and finished products present in the gas stream ； Some companies not only install condensation equipment on the vacuum pipelines, but also add high-efficiency vane separators between the end condensers and the vacuum pumps ； Other companies intend to install the gas-liquid demister on the exhaust pipeline behind the vacuum pump. Different companies have varying processes, and the focus and objectives of technological upgrades also differ. Please discuss the methods for selecting additional equipment based on the actual manufacturing processes of your own companies, in order to gain more insights and improvements.
The approach I am using now is to connect two condensers in series ahead, using the refrigerant to cool down a portion of the residual material. The exhaust gas from the vacuum pump set is directly sent to the waste gas treatment system for neutralization. But there is still a smell of solvent near the vacuum pump set. I am also looking for better solutions now, including replacing the vacuum pump. Experienced experts, please share your insights.
Vacuum needs to be treated in a categorized manner. Generally, the economically viable method is pre-pump condensation, as it allows for the direct recovery of cooling residues and reduces the power requirements of the vacuum pump; however, this approach relies on an existing cooling system； In conditions where vacuum condensation is not available, post-pump recovery can be an option; however, this requires higher investment in pumps, and the recovered material may not be suitable for direct reuse due to the risk of contamination or deterioration. As for vacuum exhaust gases, extremely small amounts of unrecycled material will certainly remain; carrying out further recovery for quality assurance purposes has no economic value. It is recommended to use chemical methods or spray absorption to eliminate these substances.
The use of two-stage series condensation is indeed the method for deep cooling and vacuum pumping to recover materials that plants consider first. I have reviewed a considerable amount of information on the condensation of process media in vacuum systems, and from it I learned that since the temperature drops after evacuation through condensation, the amount of material recovered from the gas flow increases relatively ； However, due to the gas flow condensation mechanism, the primary liquid droplets formed in the gas stream are smaller in size and more numerous; as a result, more material is recovered compared to the uncondensed exhaust gas stream. At the same time, the suspension of droplets in the condensed gas stream is greater in quantity and smaller in size. This is why, even after many companies install condensers, liquid droplets are still carried through the vacuum pump, and the odor of the material remains strong. As everyone knows, the condensation mechanism in which a vacuum stream carrying material vapor passes through a condenser to form liquid droplets – does this produce more and smaller droplets?
That condenser for pre-pump condensation isn’t designed properly; the optimal design approach would be one that utilizes gradient condensation. For example, the condenser would only need to be 30 square meters in size with a cooling temperature of -10 degrees, but in actual engineering designs, a combination of a 20-square-meter condenser at 0 degrees and another 20-square-meter condenser at -10 degrees is usually chosen. A single condenser is prone to a design that leads to sudden cooling, resulting in a large amount of liquid droplets – a phenomenon somewhat similar to oil in water or water in oil.
1) Installing a cryogenic condenser in front of the vacuum system is indeed a good way to recover organic compounds with slightly higher molecular weights; it also reduces the size of the vacuum system downstream, and **lowers the emission and pollution caused by condensable organic compounds. However, low-molecular-weight organic compounds certainly cannot be cooled through ordinary condensation; further treatment is required. 2) Common refrigeration systems using chilled water at -5 to 5 degrees can effectively condense a large amount of substances with slightly higher molecular weights; this is applicable to vacuum systems in the petrochemical industry that operate at pressures ranging from several tens of mbar to over a hundred mbar ； 3) At even lower temperatures, in refrigeration systems operating at -30 to -15 degrees, many substances can be condensed into frost, including water; the pressure that can be maintained is usually in the range of a few mbar ； 4) However, it is necessary to continuously calculate the power consumption of these refrigeration systems as well as that of conventional systems: the reduced energy consumption of the steam ejectors and liquid ring pumps in typical vacuum systems, and the increased power consumption of the refrigeration systems ； 5) At the same time, it is important to design the pre-condenser properly, because a condenser pressure drop of 5 mbar to 10 mbar in normal-pressure systems is not a big issue, but in vacuum systems, a pressure drop of 5 to 10 mbar for the pre-condenser can be a serious problem!
The last edit to this post was made by luoli519 on 2023-10-3 at 17:48. Regarding vacuum pumping systems, it is certain that deep condensation allows for the recovery of more condensed liquid； Additionally, installing an efficient gas-liquid separation and demisting device at the outlet of the terminal condenser has become a necessary requirement in recent years; it ensures that the larger quantities of liquid droplets and mist present in the airflow after deep condensation are captured and recovered, thereby preventing the exhaust port of the vacuum pump from being contaminated by such fine liquid droplets and mist. Regarding the design of deep condensers, as suggested by the aforementioned experts, multi-stage condensation offers advantages over single-stage condensation in terms of operational flexibility, reliability, and the degree of condensation achieved. For high-efficiency gas-liquid separation demisters, the use of vane-type demister technology to replace traditional mesh or filter-type demisters not only prevents the droplets separated by these traditional demisters from mixing back with the upward-flowing air as they settle downward, thereby ensuring efficient separation, but also enables high-efficient and precise separation. In addition, it offers significant advantages such as lower pressure requirements, resistance to clogging, and no need for spare parts. For the technical parameters of the feather-leaf type demister, please visit http://bbs.hcbbs.com/thread-1354813-1-1.html directly on this HCH Chemicals forum to learn more.
The choice of method for recovering exhaust gas components depends entirely on the medium composition of the exhaust gas and its physical and chemical properties!
It’s not possible to simply say which recycling method is the best – that’s an assumption
This post was last edited by luoli519 on 2023-10-3 at 17:49. The recovery of liquid-phase components from exhaust gases involves efficient capture and recovery techniques used internationally; these techniques require consideration not only of the composition and physicochemical properties of the exhaust gas medium； It is also necessary to consider the fluid velocity, compression effects, and corresponding flow patterns associated with hydrodynamic separation under actual operating conditions, and to select the appropriate separation techniques accordingly. Otherwise, effective quantitative and efficient separation cannot be achieved. The gas-liquid separation process is necessarily a kinetic separation process; it requires consideration not only of the static composition and physicochemical properties of the medium, but also of the flow regime parameters under the corresponding operating conditions. Over the past century or so, foreign countries have conducted systematic research and testing on numerous gas-liquid separation techniques, and have consistently recommended vane separation technology as well as multi-factor swirl-based mother-son gas-liquid/solid separation technology for the recovery of components from exhaust gases. The former is suitable for medium pressure and lower pressure conditions, while the latter is mainly applicable to high pressure and ultra-high pressure conditions.
This post was last edited by luoli519 on 2023-9-26 at 15:23. Additionally, the following professional discussion posts published by NOVEL Nuowei Energy Technology Company on the HaiChuan Chemical Forum are listed here for everyone to use as links to join the discussions: 14. Regarding the issues that arise when using swirl tubes/swirl plates demisters for wet flue gas desulfurization in boilers, please visit http://bbs.hcbbs.com/thread-1599605-1-1.html to participate in the discussion. 15. For discussions on the selection of separation internals for the gas-liquid separators in the gas distribution units of natural gas projects, please visit http://bbs.hcbbs.com/thread-1598340-1-1.htmll to participate in the discussion. 16. Regarding the issues of liquid presence at the outlet of the low-temperature separator in the natural gas dehydration unit and excessive dew point, please visit http://bbs.hcbbs.com/thread-1596842-1-1.html to participate in the discussion.