(399g) Integration of EFPS and PROVISION for Hybrid Cracking in Modern Cracking Furnace Design

Cracking furnaces are the heart of the ethylene plant. Ethylene producers purchase various feedstocks ranging from ethane, propane, EP, naphtha and up to heavy condensates and vacuum gas oil (VGO). However, in a modern feed flexible ethylene plant, the quantity of each feedstock received varies. In Co-cracking or blended cracking, each feedstock cannot be cracked at its optimal conversion or severity. Economically, it is also very important to minimize the number of furnaces in the design of an ethylene plant.

Therefore, hybrid cracking (two or more feeds cracked in one single cell or twin cell furnace) with partial decoking capability (cracking in one cell while decoking in another cell in twin cell furnace) becomes important in modern furnace design for achieving feedstock flexibility. However, the biggest challenge in the design of hybrid cracking furnaces is how to properly simulate the furnace performance due to the following reasons:

? Two or more feedstocks enter different passes of process banks in the convection section and two or more mixed feeds (dilution steam plus feed) enter radiant coils in the firebox. However, steam superheater coils and boiler feed water coils are still common in the convection section. Accurate prediction of process and flue gas temperature profiles is a challenge.

? Fired duty in each cell of a twin cell furnace during partial decoking, especially with hybrid cracking, can be significantly different. Challenges in the design are the prediction of flue gas mixing in the transition to the convection section, associated impact on the firebox, and prediction of the performance of the coils and passes of the convection section.

This paper presents a novel cracking furnace model developed by Technip called SPLIT-MIXING to simulate hybrid cracking using an integrated EFPS model and PROVISION software. This program conveniently runs in PROVISION environment.

EFPS (Ethylene Furnace Program Set) is Technip's proprietary ethylene furnace yield prediction and cracking furnace simulation program which is widely used by nearly 80% of worldwide Ethylene Producers for feedstock selection, case studies, trouble shooting and optimal furnace operation. EFPS consist of four sub models:

? SPYRO (Steam Pyrolysis) - Rigorous Radiant Coil Simulation Program

? FIREBOX - Rigorous Firebox Simulation Program

? CONVEC - Rigorous Convection Section Simulation Program

? TES ? Rigorous Transferline Exchange Simulation Program

Provision (PROII) is a well known process engineering software which is also widely applied in the petrochemical industry for process design, simulation and optimization.

Computational Fluid Dynamics (CFD) is also applied to demonstrate furnace flue gas flow distribution in the transition region from firebox to convection section and in the lower banks of the convection section where flue gas is relatively hot.

Several case studies are presented in this paper:

? Gas-Gas hybrid cracking for single cell furnace with ethane/propane segregated cracking

? Gas-Liquid hybrid cracking for twin cell furnaces with ethane/naphtha segregated cracking in the same type of radiant coils.

? Gas-Liquid Hybrid cracking for twin cell furnaces with ethane/naphtha segregated cracking in different types of radiant coils

? Partial decoking for twin cell furnaces with one cell cracking ethane feed while another cell is used for furnace decoking.

This novel model can be used and extended for simulating hybrid cracking with two gas feedstocks, one gas and one liquid feedstock, or two different liquid feedstocks.

The furnace can be single cell or twin cell. For a twin cell furnace, one cell can be on gas or liquid feed cracking while another cell is on decoking.