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makes effi cient use of the stripping action of steam to remove the NH3 and High Effi ciency Hydrolyser. CO2 from the treated urea plant waste water condensate in order to maximize the hydrolysis of the urea content. The effi ciency is enhanced by the fact that the hydrolyser is divided into two zones, with a fresh steam re-injection after the fi rst zone, in order to keep the driving force for the NH3 and CO2 removal as high as possible. It is, in fact, very important to eliminate as many products of the hydrolysis reaction (NH3, CO2) from the liquid as possible, since their presence tends to slow down the hydrolysis. Both zones are provided with Casale- Dente HETs, which divide them into compartments. In each compartment the liquid is separated from vapour (containing NH3 and CO2), creating a multiplicity of streams of vapours, which are reinjected into the liquid in the form of a column of small bubbles, maximizing the mass and heat transfer. With Casale HEH and one or two stripping columns, it is possible to completely eliminate NH3 and urea from the process condensatem reaching residual values lower than 3 ppm. Existing hydrolysers of certain types can be also conveniently revamped to the HEH technology just by changing the internals. Currently the Casale high effi ciency hydrolysers are in use in 20 urea plants. HEC (high effi ciency combined) process The development of this process opened the way to very large capacity increases, 50% or more, in conventional total recycle plants. The process is based on the combination of a conventional total recycle reactor (secondary reactor) with a very effi cient “once-through” reactor (primary reactor) having upstream a carbamate condenser to control the heat balance, and a HP decomposer downstream to recycle most of the unreacted NH3 and CO2 directly into the secondary reactor. The HEC has the unique feature of achieving a very high average CO2 conversion, and low energy consumption. The capacity of conventional total recycle plants can be drastically increased, by 50% or more, by applying the HEC concept, with the addition of a HP carbamate condenser, a HP decomposer and a reactor, reutilising the existing one either as primary or as secondary reactor, depending on the required capacity increase, and adding a second one. Due to the much higher conversion obtained, the existing back-end of the plant can be reutilised at higher capacity with only minor modifi cations. Seven plants have been revamped with the HEC process, achieving capacity increases up to 70%-80%, and two more are currently being revamped. VRS (vapour recycle system) process This technology has been developed for the revamping of stripping plants and is used in certain cases to drastically increase the capacity of these plants. The VRS concept envisages a separate circulation of recycle water and recycle NH3 and CO2, i.e.: • the carbamate solution obtained in the downstream process sections, before being sent the HP section, is decomposed in an HP decomposer working in parallel to the existing stripper. • the vapours thus obtained, very rich in NH3 and CO2, are sent to the HP Section, while the remaining solution, enriched in water, is sent back to the back-end of the plant. NH3 CO2 REACTION SECTION Stripping plant revamped according to the VRS concept 5 Vapors rich in NH3 and CO2 NEW DECOMPOSITION SECTION HP DECOMPOSITION & RECYCLING SECTION Conventional total recycle plant revamped with the HEC concept. By adding a new VRS decomposition section in parallel to the existing plant, practically only the NH3 and CO2 contained in the carbamate are sent back to the synthesis section, while the water is almost totally sent back to the recycling and waste water treatment sections. As a consequence, the HP synthesis loop will operate with very low water content, obtaining high CO2 conversion and stripping effi ciencies and having less water throughout the whole plant. Thanks to the increase in effi ciency and the decrease of water content, the existing plant can be reutilized at higher capacity with only minor modifi cations. With this approach, an increase in capacity up to 50% or higher can be obtained. MP and/or LP DECOMPOSITION & RECYCLING SECTIONS Almost pure H2O FINISHING & WASTEWATER TREAT. H2O UREA
REACTOR Split Flow Loop confi guration. NH3 SCRUBBER Split-Flow-Loop process and Full- Condenser design The development of these two technologies is the latest result of Urea Casale’s constant research into improvements in urea plants stemming form the market’s need for more effi cient and economical ways to increase plant capacity. These technologies are, in fact, a powerful tool to increase the capacity of CO2 stripping plants in the most economic way. The Full-Condenser design drastically improves the existing vertical HP carbamate condensers by changing the falling fi lm confi guration to the more effi cient bubble fl ow confi guration. With only few internal modifi cations, the existing HPCC will operate as a much more effi cient submerged condenser with natural circulation. Once transformed to the Full-Condenser design, the HPCC can be operated as a total condenser, allowing the application of the Split-Flow-Loop process which debottlenecks the rest of the HP loop. With this new process the vapours from the stripper are split into two parts: ● one major part goes to the HPCC, where it is totally condensed, except for CARBAMATE HPCC (FULL CONDENSER TM ) 6 STRIPPER CO2 LP. DECOMP. the inerts that are sent to the scrubber, and sent, as carbamate, to the reactor through a new ejector. ● the second part goes straight to the reactor. In this way a major part of the inerts are not sent to the reactor with a positive effect on its effi ciency. Thanks to the additional reaction volume created in the HPCC, operating full of liquid, and to the lower amount of inerts in the reactor, which de-bottleneck the reactor itself and the stripper, and to the higher effi ciency of the HPCC the entire HP loop is de-bottlenecked and capacity increases of up to 50% can be reached. three plants have been revamped with these technologies to reach 50% higher capacity, and three more applications are under implementation. Methanol Casale Methanol Casale was founded in 1994 and, following the trend established by Ammonia Casale, has dedicated a lot of effort to develop technologies for the revamping of methanol plants. With 30 plants revamped since its foundation, Methanol Casale has become a leader in methanol plant revamping. The following Section outlines the most important technologies developed by Methanol Casale. Axial-radial pre-reformer The same technology used for ammonia plants is also used for methanol plant revamping. ARC synthesis converter The ARC synthesis converter is basically an adiabatic, quench cooled, single vessel converter with very effective quench mixing. This design was originally developed to increase the effi ciency of the ICI quench lozenge converter, but it has also been successfully used for brand new converters. The main characteristic of the ARC converter, i.e. the very effi cient mixing zone between the beds, allows for a temperature spread at the inlet of the next bed of only a few degrees. This eliminates hot spots inside the bed, which are responsible for catalyst deterioration, and by-product formation, and allows operating the beds at very low inlet temperatures. Additional features are the simplicity of the design and the high catalyst volume achievable. Thanks to these features, a revamping of an ICI methanol converter with ARC design will bring: a) high carbon effi ciency; b) very low by-product levels; c) longer catalyst life. Due to its simplicity and effi ciency, the ARC design has been used for the revamping of many ICI methanol converters as well as for grass root plants with a single unit capacity exceeding 3,000 t/d. Pseudo-isothermal synthesis converter The ARC is a very simple and effi cient converter, but being an adiabatic converter, it has the intrinsic limitations of this type of design. In order to go beyond these limitations without incurring all of the limitations and mechanical complexity of conventional isothermal converters, Methanol Casale has developed the pseudo-isothermal methanol synthesis converter. This converter, based on direct heat removal from the catalyst bed with plate elements, reaches the maximum converter effi ciency, with the catalyst beds operating always along the maximum reaction rate curve, i.e. obtaining the maximum possible conversion. This is obtained by feeding in different quantities of cooling fl uid at different position in the plates, thus enabling the removal of differential
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