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The task of the catalytic cracking (FCCU) absorption and stabilization system is to process the crude gasoline and rich gas coming from the overhead vapor separator of the distillation tower, to separate out the dry gas (C1, C2), and to recover qualified products in the form of liquefied gas (C3, C4) and stabilized gasoline (>C4). The absorption and stabilization unit is mainly composed of an absorption tower, a desorption tower, a reabsorption tower, and a stabilization tower. 1 Conventional process flow and existing problems: The old units from the 1960s used a single-column process, whose drawback was the high C3 content in the overhead gas and the high C2 content in the bottom stream of deethanized gasoline. In the 1980s, most of these older units switched from a single-column process to a double-column process, thereby avoiding the disadvantages of the single-column process. The feeding methods for the desorption tower in the double-tower process mainly include cold feeding, hot feeding, and combined cold and hot feeding. The characteristic of the cold feed process is that the condensed oil from the equilibrium tank enters the top of the desorption tower without being heated first ； The dry gas in this process contains low levels of C3, resulting in good absorption efficiency and low amounts of gas to be desorbed; however, the load on the desorption tower and the reboiler at the bottom of the desorption tower is high. The hot feed process uses the thermal energy of stabilized gasoline to heat the condensed oil before it enters the top of the desorption tower ； Its advantage is that it reduces the load on the reboiler of the desorption tower; however, with hot feed, the amount of gas released during desorption is high, which leads to a reduced absorption efficiency in the absorption tower and an increased load on the rich gas condenser as well. 2 Introduction of the new process and its advantages 2.1 Introduction of the new process (1) Concept behind the new process For conventional hot feeding and twin-stream feeding, in order to reduce the load on the reboiler in the desorption tower, the condensed oil is heated again after being cooled before entering the top of the desorption tower; this process of cooling first and then heating actually represents an energy loss. The improved solution takes into account the use of the heat generated by the material itself, in order to avoid a process that involves cooling first and then heating. The primary condensation of the material requires only slight cooling; only a portion of the feed is cooled to a lower temperature in the secondary stage. As a result, the cooling load before the equilibrium tank is significantly reduced, and unnecessary energy consumption is avoided, thereby achieving energy savings. (2) Secondary condensation process: The characteristic of this process is that the compressed rich gas is mixed with the rich absorbent oil from the bottom of the absorption tower and the desorbed gas from the top of the desorption tower. After the first cooling step (the temperature is generally maintained between 60°C and 70°C; too low a temperature increases the load on the reboiler at the bottom of the desorption tower), the mixture enters an equilibrium tank. The condensed oil obtained in this step is used as a hot feed to the middle and upper parts of the desorption tower, while the condensed oil obtained after the second cooling step is used as a cold feed to the top of the desorption tower. This process features dual-stream feeding; the difference is that, due to the different composition of the feed to the desorption tower, backmixing is avoided. (3) Two-stage condensation and intermediate reboiler hybrid process: This process combines the advantages of both the two-stage condensation technique and the intermediate reboiler technique. Since the desorption tower in this scheme is equipped with an intermediate reboiler, it is possible to appropriately lower the temperature of the first-stage condenser, thereby reducing the amount of gas released during desorption and the load on the absorption tower; meanwhile, the load on the reboiler at the bottom of the desorption tower remains relatively low. 2.2 Advantages of the improved process flow (1) Reduced energy consumption: The energy consumption in the absorption stabilization system process flow includes both cooling energy consumption and heating energy consumption. The cooling energy consumption mainly consists of two parts: the cooling load before the balance tank and the heat exchange cooling load in the absorption tower, with the former being the dominant factor and the latter being relatively smaller. Thermal energy consumption mainly includes the heat load of the reboiler at the bottom of the desorption tower and the utilization of waste heat from the stabilized gasoline, which comes from the system. In the two-stage condensation process, primary condensation requires only slight cooling – only a portion of the feed is cooled to a lower temperature in the secondary stage – which significantly reduces the cooling load before the equilibrium tank, thereby lowering energy consumption. For the mixed process, the secondary condensation section significantly reduces the load on the condenser before the equilibrium tank, while the intermediate reboiler section can lower the load on the reboiler at the bottom of the desorption tower. The new process combines the advantages of both cold and hot feeding methods, while avoiding backmixing. (2) Reducing the load in the tower: The load in the tower during the absorption stabilization process is mainly reflected in two aspects: the flow rate of the desorbed gas and the gas-phase load on the plates of the desorption tower. Since the materials in the improved process are not condensed to 40°C all at once but in stages, with only a portion being cooled to 40°C, this two-stage condensation process results in a significant reduction of the C2 content in the condensed oil. The purpose of the desorption tower is to desorb the C2 components from the stream. When condensate oil with a low C2 content enters the desorption tower, it significantly reduces the load on the tower trays, the flow rate of the desorbed gas also decreases, resulting in an improved desorption effect. This post was last edited by ali2004 on 2007-12-23 10:11.]