Energy Saving Reconstruction Of Intermediate Cooler In Multistage Compressor

Multi-stage compressor, a main gas supercharging machine, is widely used in air separation, petrochemical, ammonia production and refrigeration processes. During gas compression, the large amount of heat generates, which adversely influence the compression efficiency. So the generated heat must be removed by coolers continuously. It follows that the performance of the cooler plays an important role to enchance the compression efficiency. In recent years, energy saving of industrial process draws more and more attention, which makes the heat-exchanger energy saving reconstruction quite important for some special industrial processes.This study aims to the energy saving task for a three-stage compressor intercooler. Both thermal dynamic analysis and numerical simulaitons of fluid flow are performed to optimize operation parameters and the intercooler structures. An energy cost comparison is also conducted for the optimization.The main conclusions are as follows:(1) The intercooler system of original design was optimized.In the original process, recycled water was used to cool down the compressed gas by the intercooler directly. Due to the poor quality of the recycled water and high tubewall temperature of the coolers, the fouling easily forms on the tube walls of the heat-exchanger. This decreased heat exchanging efficiency. The temperature at the outlets of the three compressors reaches to77.8℃,87.2℃and62.4℃respectively, which are far higher than design temperature of45.0℃. In order to decrease the energy costs and improve productivity, the recycled water was replaced by demineralized water (soft water) to cool down the hot compressed gas in the intercooler. To sovle the problem and save the desalinated water, a new technical scheme was adoped:a recycle water demineralized water heat exchanger, where recycled water flows in tube side, and desalinated water passes in shell side, was newly designed to cool down the demineralized water. The recycle water flow through tubes at low temperarure level can decrease fouling to assure stable operation of the new added heat exchanger.(2) The design of the recycle water/demineralized water. Two tube diameters (Φ19×2mm andΦ25×2.5mm) and three tube passes(one pass, two passes and four passes) are chosen for comparison, ASPEN heat exchanger design and reting software was used to simulate the6designs respectively. After simulation, with the velocity data of inlet/outlet and heat transfer area, the tube numbers can be calculated. The equipment cost is also estimated. Two tube passes with Φ25×2.5mm tubes heat-exchanger shows the best performance. The velocity in the tubes and shell are1.56m/s and1.41m/s respectively, with20kPa pressure drop.(3) The simulation of flow field in the heat-exchanger. FLUENT, a commercial computational fluid dynamics package was used to simulate the flow field distribution in the heat exchanger. The parameters of the added heat-exchanger were reasonable with uniformed flow field distribution, the required heat-exchange performance shouled be achieved.(4) Analyze of energy saving and consumption reduction. According to the calculation of energy consumption by using the intercooler,38000tons of water can be saved annually. The compressor efficiency was also enhanced as respected.