CBL technology is a state-of-the-art technology with low investment both for grass root and revamping furnaces. CBL furnace with high feed flexibility could be applicable to different feedstock such as ethane, light hydrocarbons, NGL, naphtha, light gasoline oil and Hydrotreated VGO, especially for heavy feedstock; CBL technology has special advantages: long run length and high ethylene/propylene yields. SINOPEC swirling element of radiant tube (SERT) could be installed to the radiant coil as anticoking elements to extend the run length to more than 80 days. The furnace could be double firebox with shared convection section, and separate firebox decoking as well as decoking effluent back to firebox can be adopted in the furnace.
The characteristics of CBL technology are listed
1. Liquid feed
1) Two pass high selective coil configurations (2-1(CBL-Ⅲ)，(4-1(CBL-Ⅳ), modified 2-1 (CBL-V), modified 1-1 (CBL-VI), etc.) can be selected for different cases. The first pass has small diameter with relatively large specific surface area, resulting in a quick temperature increase; the second pass has relatively large diameter, resulting in a lower pressure drop and helping lower the hydrocarbon partial pressure. Appropriate coils are chosen based on different feeds and capacity requirements. The coil configuration combining with higher coil outlet temperature, shorter residence time and lower hydrocarbon partial pressure leads to the advantages of high cracking selectivity, long run length.
2) TLE: 1 or 2-stage TLE can be selected based on different cases. Linear quench cooler is preferred for shorter resident time.
3) Dilution steam injection: 1 stage (for light feed) / 2 stages (for heavy feed). By using such technique, the coke formation of heavy oil in convection section coils can be avoided.
4) Heat supply: combination of hearth and sidewall burners or hearth burner only. The heat distribution along the radiant coil can be optimized to avoid overheat.
5) High thermal efficiency: up to 94-96%.
6) Variable Frequency Speed Control driving motor can be adopted for Induced Draft Fan.
2. Gas feed
For gas feed, four pass coil configuration is adopted. The TLE could be 2 or 3 stages. For the ethane-cracking furnace, the run length could be longer than 80 days.