Simulation And Optimization Of Quench System And Compression System In Ethylene Plant

Quench system and compression system are two important parts in ethylene plant. Quench system is the first step of the processing cracking gas to separate gasoline, diesel and fuel oil from the pyrolysis gas. Also it is the key part of the whole plant to recycle heat from hot pyrolysis gas. It is usually the operatic "bottleneck" due to amount of feeding and abominable operation conditions. Quench system, locating between cracking unit and compression unit, has an important impact on the ethylene plant performance. The compression system that contains pyrolysis gas compressor, ethylene compressor and propylene compressor plays a central role in the separation apparatus. It not only determines the level of power consumption of the separation apparatus, but also determines the running stability of the ethylene plant. Notice that the cracking gas compressor limits the apparatus largest single line production capacity. It’s of great significance to establish the production process model and optimize the production process because it can improve the operation level of the unit, recover the heat as much as possible, reduce the energy consumption, and ultimately increase the economic benefits.In this thesis, Aspen HYSYS is used as a developmental platform to develop the steady-state and dynamic model of gasoline fractionator system in ethylene plant. The main problem of the steady-state simulation is that feed components contain many uncertain substance petroleum fractions. Therefore, a few long-chain alkanes are used to substitute those uncertain heavy oil fractions in the simulation. We use n-decane, n-tetradecane and n-Heneicosane respectively substitute pyrolysis gasoline, pyrolysis diesel and cracking fuel oil fraction. Since the boiling points of pyrolysis gas components are different, SRK is selected for thermodynamic calculations. After the convergence of the steady-state model, we then implement the dynamic model which contains following three steps:1) define the dynamic data such as the geometry of the unit operations and liquid volume percent,2) design the control circuit and,3) tune the controller PID parameters. The cascade automatic control scheme that controls the top-tower temperature of the gasoline fractionator and cycle gasoline flow is also tested in the dynamic simulation environment. The simulation results hows that the control system can satisfy the stable requisition that the system can run in10%fluctuation of the feed flow and the load of the circulating quench oil. Lastly, we get the operation parameters by using particle swarm optimization algorithm where the objective function is to maximize recovery of waste heat.