Understand flashing and dispel misconceptions about hydrophobicity
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This post was last edited by Fuleide on 2019-5-30 at 17:25. Understand flash evaporation and dispel misconceptions about traps. For a long time, most steam users have mistakenly believed that no steam should escape when a steam system’s trap is functioning properly; only a trap that does not emit steam is considered a good one, while any steam leakage is seen as a sign of a faulty trap. This misunderstanding leads users to incorrectly choose low-temperature hydrophobic equipment after using steam-based devices, which significantly reduces the production efficiency of such equipment and causes problems such as water hammer. This is mainly due to their lack of understanding of the flashing process, and even less awareness of the difference between secondary steam and leakage steam. Recently, through customer inquiries, we have found that the aforementioned issue remains widespread. In light of this, Fred would like to first share with you some insights on the flashing phenomenon in steam systems. What is flash steam (secondary steam)? When high-temperature and high-pressure condensate is released into a low-pressure area, part of the energy (enthalpy) in the condensate is released, causing some of the condensate to vaporize and generate secondary steam; this results in the temperature of the remaining condensate dropping to the saturation temperature. This phenomenon is known as flashing, and the steam produced is referred to as flash steam or secondary steam. A large amount of flash steam is generated when the high-temperature and high-pressure condensate inside the equipment is drained. The generation of flash steam is a normal phenomenon. When high-temperature condensate moves from a high-pressure area to a low-pressure area, if the saturation temperature in the low-pressure area is lower than that of the condensate in the high-pressure area, secondary steam will definitely be produced. For example, the condensate pressure in front of the device’s outlet steam trap is 2 barg at 133.4°C; when this condensate is discharged outside, where the external pressure is 0 barg at 100°C, approximately 6.3% of the condensate turns into secondary steam. The generation of flash vapor is inevitable and normal, in accordance with the laws of conservation of energy and mass. What factors are related to the flash evaporation volume? The prerequisite for flash evaporation is: pressure difference + temperature difference. Pressure difference refers to the change in pressure before and after the condensate water ； The temperature difference refers to the fact that the saturation temperature corresponding to the low-pressure area is lower than the temperature of the condensed water in the high-pressure area; in other words, the temperature of the condensed water is higher than the saturation temperature corresponding to the low-pressure area where it is released, which is the boiling point at that pressure. For saturated condensate, the greater the pressure change of the condensate, the higher the proportion of flash vapor ； The greater the condensate flow rate, the greater the flash vapor flow rate. The significance of flash vapor generation: In fact, whether flash vapor can be generated and the amount of such vapor are important indicators of the condition of the water separator. If there is little or no flash vapor when draining the condensate from the outlet of the hydrophobic equipment, it usually indicates that water has accumulated inside the equipment that uses steam (except in cases where the drain pipes are too long and have cooling sections). Water accumulation in the equipment inevitably reduces its heating efficiency and production efficiency; it can also lead to water hammer and local deformation of the equipment, thereby shortening its lifespan. Therefore, the condensate drainage condition and operating status of the equipment can be determined through flash steam. How to handle flash vapor? As mentioned above, the generation of flash steam is a normal phenomenon and is common in industrial processes that utilize steam. Equipment efficiency must never be sacrificed in order to eliminate flashing. The proper approach is to ensure the efficient operation of the equipment while effectively recovering and reusing the flash steam, thereby achieving improved efficiency and energy savings. Regarding the drainage in steam systems, steam emission is not necessarily indicative of a leak; sometimes, the absence of steam emission is actually the problem! Understanding flash evaporation and uncovering the truth are key to solving problems, improving efficiency, and saving energy and reducing emissions. (This article is excerpted from the WeChat official account “Fured Steam Energy Saving”)
I’ve learned it, thanks for sharing! Corrected the long-standing misunderstanding!
That’s absolutely right! ! Due to their structural design, most steam traps contain moving parts inside them – such as float-type or inverted bucket types. Frequent operation of these steam traps leads to wear of the sealing surfaces, and over time this results in poor sealing and leakage of fresh steam. Another aspect is the domestic industry standard for steam traps: the leakage rate of qualified products should be ≤3% of fresh steam. From this, it can be seen that even new steam traps have a leakage rate of around 3%, while imported brands of steam traps can achieve a leakage rate of around 1%. Over time, the air leakage rate increases gradually as the sealing surface wears out. Air leakage during the drainage process of a steam trap is an inevitable issue. This imposes requirements on steam energy conservation in enterprises that use steam – how can steam be utilized efficiently? How can flash vapor be recycled? Yantai Yitongda Steam Energy Saving Equipment Co., Ltd. is a leading provider of services for optimizing steam waste heat systems in order to save energy. It is capable of fully recovering the fresh steam that leaks from steam traps, as well as the secondary flash steam generated by condensate water; this recovered steam is then pressurized and heated again before being sent back to the equipment that uses steam. Our equipment also allows users to eliminate the need for steam traps in their equipment, thereby improving the heat exchange efficiency of such equipment and enhancing production efficiency and product quality. Just by saving energy related to steam use, we can help customers reduce their operational costs by 10–25%. If the enterprise has its own boiler, we can keep the high-temperature condensate completely sealed and use it to feed water into the boiler; the temperature of this water can reach 130 degrees, thereby eliminating the costs associated with softening and deoxygenating the water used for boiler feeding. It can also save on the fuel costs required to maintain a water temperature difference of 110 degrees (130 degrees minus 20 degrees, which is the normal temperature) for boiler make-up water. The energy-saving value is extremely significant. Our company has been in operation for over a decade, focusing on the recovery and utilization of waste heat from steam. We serve industries such as petrochemicals, biopharmaceuticals, food and beverages, and fine chemicals, with clients located throughout the country – totaling more than 700 companies. The company has obtained two **invention patents, as well as multiple utility model patents, design patents, software copyright patents, etc. It has been recognized as a high-tech enterprise and has received honors such as \"Yantai City Small and Medium-sized Science and Technology Innovation Enterprise\". Those who are interested in learning about energy savings through steam waste heat can get in touch with me. At the same time, thanks to the original poster for sharing this knowledge.
Freed only wants to engage in technical exchanges with everyone; he doesn’t want anyone to use our articles as a platform for blatant advertising! I also don’t like it when people keep criticizing drain valves all the time! Every product comes in different quality levels; we can’t go back to the outdated drum-type steam traps used years ago, which not only are of poor quality but also cause water accumulation in equipment, just because there are low-quality steam traps available on the market As for all the knowledge, techniques, and experience related to energy savings in steam systems – such as the effective utilization of secondary steam, pressure increase, and the recycling of condensate water – we are well-versed in them. Our 15 years of industry experience is readily verifiable, so there is no need to elaborate on this here! Here, I just want to exchange technical insights with everyone, learning from one another to improve! I hope our communication isn’t disturbed by ads!
The steam or condensate coming out of the steam traps is currently discharged directly into the rainwater drain. There is such a steam trap at regular intervals along the steam pipes. What is the best way to collect this fluid?
This share is good; I indeed had such a misconception before. However, condensate collection behind the steam trap is indeed an issue related to energy conservation and emission reduction!
Under normal circumstances, few steam traps installed on pipelines are used for condensate recovery, as the condensate generated on these pipelines arises mainly from the heat loss of the pipelines themselves; therefore, the amount of condensate is relatively small. Since a steam trap is usually installed every 50 meters along the pipeline, they are spread out over a large distance, and installing a recovery system would require very long pipes, which is not cost-effective. Generally, what is recovered is the condensate water generated by heat exchange equipment, and the volume of this water is considerable. Heat exchange equipment located in the same area can have their waste water collected together. As for whether this condensed water should be subjected to pressure reduction and flash evaporation or used back in the boiler after treatment, that depends on specific requirements and circumstances.