Discussion on the 5 New Urea Technologies Series, Part 4 (Combined with Stripping Method)

By combining this method with stripping, the wastewater is brought into direct contact with water vapor, allowing the volatile toxic and harmful substances in the wastewater to diffuse into the gas phase in a certain proportion, thereby achieving the goal of separating pollutants from the wastewater. The basic principle of the stripping method is the same as that of the blowoff method, except that a different medium is used; stripping is achieved by utilizing water vapor as the medium. The processes for separating pollutants using the stripping method vary depending on the nature of the pollutants, and can generally be classified into the following two types: 1. Simple distillation – For volatile substances that are miscible with water, this method takes advantage of the fact that, under gas-liquid equilibrium conditions, their concentration in the gas phase is higher than that in the liquid phase. It is directly heated by steam, causing it to become enriched in the gas phase at a certain proportion at its boiling point (a temperature between the boiling points of water and the volatiles). 2 Steam distillation for volatile pollutants that are immiscible or practically immiscible with water. By taking advantage of the fact that the boiling point of the mixture is lower than that of its components, high-boiling volatile substances can be separated and removed at lower temperatures. For example, substances such as turpentine, aniline, phenols, and *** in wastewater can be separated using distillation at temperatures below 100°C. The main equipment for stripping is the stripping tower, which falls into two categories: packed towers, in which various types of packing are placed in layers inside the tower; and tray towers, which are further divided based on their tray structure into: (1) bubble cap towers, (2) floating valve towers, and (3) sieve plate towers. Tray towers are more efficient than packed towers. In terms of the application of the stripping method, it was initially used to recover volatile phenols from wastewater containing phenols. The wastewater is preheated to 100°C and then sent downward from the top of the stripping tower, where it meets the rising vapor stream. Mass transfer takes place within the packing layer or on the trays, and the purified wastewater is then discharged through a collection tank. The vapor-phenol mixture is discharged from the top of the tower and forced into the regeneration section by a blower to recover phenol. The phenol-containing steam is fed in from the bottom of the regeneration section, where it first meets the circulating alkali solution that flows downward in counterflow, and then encounters the additional fresh alkali solution (with a concentration of 10%). Phenol is removed through chemical absorption, and the purified steam is sent to the stripping section for reuse. Alkali reacts with phenol to produce sodium phenolate

A few humble opinions: 1 The so-called five world-leading high-tech technologies involve a combination of an isothermal synthesis tower, a stripping tower, carbon dioxide absorption at medium pressure, crystallization and granulation, and the addition of an ammonia cooler. 2 I guess their device is an old type of aqueous solution-based device, a mix of various elements put together. 3 UTI is MEC’s heat cycle process in the United States; it actually makes use of an isothermal design with two synthesis towers, as already explained by the moderator. 4. The air lift process is not available in aqueous solution processes; its inclusion equates to adding high-pressure recovery, which reduces the recovery load on subsequent units and is beneficial for energy savings and cost reduction. 5 Introducing a stream of carbon dioxide from between the compressor stages into the medium-pressure decomposition and recovery system can absorb excess ammonia, as the ammonia-to-carbon ratio in the existing process 4.0 is already at its highest level; using carbon dioxide for absorption can reduce the water-to-carbon ratio in the system. The improved “C” method developed in Japan in the late 1960s already featured this design. 6 Crystal granulation is also one of the features that improve the “C” method, characterized by low levels of biuret and water content. However, this method requires complex equipment and is difficult to operate. 7 As for whether the “evaporative ammonia cooler” is used in the evaporation system, it eliminates the need for an evaporator jet, thereby saving power steam and circulating water. It has been suggested that it be used in medium pressure instead of in front of the ammonia cooler, as its use is not appropriate due to the presence of carbon dioxide. The ammonia gas that is flashed enters the synthetic chiller, or urea itself is used with a small chiller for recycling. This type of evaporative ammonia condenser is widely used in synthetic air separation units. The above are merely my personal guesses; please correct me if there are any inaccuracies. This post was last edited by lxq700918 on 2009-2-13 17:45.]

“The \"combined stripping method\" is most likely to be used in the medium-pressure decomposition tower and the hydrolysis tower. The medium-pressure decomposition tower in UTI is a packed tower, but it must have a sufficient spray density; the recycled ammonia is supplied to this tower using pumps. The \"evaporative ammonia cooler\" appears to be a replacement for the conventional shell-and-tube ammonia condenser, used for condensing the gases from the medium-pressure decomposition process. Regarding the issue of CO2 rising upward, the design of the medium-pressure decomposition tower cannot rely on the traditional bubble column design anymore – a packed tower should be the preferred choice, as it offers greater operational flexibility.

The so-called “combined stripping method” is believed to originate from IDR – “isobaric double stripping”, a technology developed by Mentediason in Italy in the 1970s. “The “five major technologies” each have their own patents; it’s unclear which research institute put together that “Allied Forces of Eight Nations” approach. Fortunately, those patents are quite old now, and no one bothers to pursue them any further. Though it’s a makeshift version, the fact that it was able to run successfully on its first try is worth praising; it can be seen as the first result of successfully integrating this technology after half a century. Whether it’s healthy or not is unknown, and I’m skeptical about how good the actual performance metrics will be. This post was last edited by lxq700918 on 2009-3-16 at 22:41.]