Cracking, thermal furnaces

M.E. Masoumi, S.M. Sadrameli, J. Towfighi, A. Niaei. Simulation, optimization and control of a thermal cracking furnace. Energy Volume 31, Issue 4 (2006). 

Table 3 Characteristics of modern thermal cracking furnaces...

Cold box and refrigeration system. After the acid gas and water removal, the pyrolysis gas is cooled and condensed to approximately -165°C only hydrogen and some methane remain in the vapor phase. The feed locations are determined via process simulation. Hydrogen and methane are drawn from the lowest temperature stage separator and sent to thermal cracking furnaces as fuel. 

Recent improvements of process controls have resulted in improved operations and higher profits. Real-time optimization of thermal cracking furnaces based on the feedstock and product flow rates, pricing, and fuel cost has become a reality. Implementation of pinch technology, process separation network analysis, and optimization has made significant reductions in energy demands. 

Side and top view of a thermal cracking furnace with straight parallel reactor tubes. 

VERCAMMEN AND FROMENT Thermal Cracking Furnace Simulation 273... 

Disturbance variables (DVs) Process variables that affect the controlled variables but cannot be manipulated. Disturbances generally are related to changes in the operating environment of the process for example, its feed conditions or ambient temperature. Some disturbance variables can be measured on-line, but many cannot such as the crude oil composition for Process (c), a thermal cracking furnace. 

Olefins are produced primarily by thermal cracking of a hydrocarbon feedstock which takes place at low residence time in the presence of steam in the tubes of a furnace. In the United States, natural gas Hquids derived from natural gas processing, primarily ethane [74-84-0] and propane [74-98-6] have been the dominant feedstock for olefins plants, accounting for about 50 to 70% of ethylene production. Most of the remainder has been based on cracking naphtha or gas oil hydrocarbon streams which are derived from cmde oil. Naphtha is a hydrocarbon fraction boiling between 40 and 170°C, whereas the gas oil fraction bods between about 310 and 490°C. These feedstocks, which have been used primarily by producers with refinery affiliations, account for most of the remainder of olefins production. In addition a substantial amount of propylene and a small amount of ethylene ate recovered from waste gases produced in petroleum refineries. 

Thermal Cracking. Thermal chlorination of ethylene yields the two isomers of tetrachloroethane, 1,1,1,2 and 1,1,2,2. Introduction of these tetrachloroethane derivatives into a tubular-type furnace at temperatures of 425—455°C gives good yields of trichloroethylene (33). In the cracking of the tetrachloroethane stream, introduction of ferric chloride into the 460°C vapor-phase reaction zone improves the yield of trichloroethylene product. 

In addition to conventional thermal cracking in tubular furnaces, other thermal methods and catalytic methods to produce ethylene have been developed. None of these are as yet commercialized. 

FIG. 23-3 Temperature and composition profiles, a) Oxidation of SOp with intercooling and two cold shots, (h) Phosgene from GO and Gfi, activated carbon in 2-in tubes, water cooled, (c) Gumene from benzene and propylene, phosphoric acid on < uartz, with four quench zones, 260°G. (d) Mild thermal cracking of a heavy oil in a tubular furnace, hack pressure of 250 psig and sever heat fluxes, Btu/(fr-h), T in °F. (e) Vertical ammonia svi,ithesizer at 300 atm, with five cold shots and an internal exchanger. (/) Vertical methanol svi,ithesizer at 300 atm, Gr O -ZnO catalyst, with six cold shots totaling 10 to 20 percent of the fresh feed. To convert psi to kPa, multiply by 6.895 atm to kPa, multiply by 101.3. 

The main use of residual fuel oil is for power generation. It is burned in direct-fired furnaces and as a process fuel in many petroleum and chemical companies. Due to the low market value of fuel oil, it is used as a feedstock to catalytic and thermal cracking units. 

Industrial furnaces, 12 286, 327-330 fuels for, 12 323, 324t for thermal cracking, 10 601-609... 

Both types of surface oxides are found on technical products. Rubber grade carbon blacks are produced in different processes. Channel blacks are made by cooling a flame on iron plates, the so-called channels. The resulting carbon blacks are acidic in character because an excess of air is present (25). In the production of furnace blacks, the fuel, mostly oil or natural gas, is burned with a limited supply of air. Thermal blacks are obtained by thermal cracking of the gas, which sometimes is diluted with hydrogen. In consequence, both types show weakly basic reaction in aqueous suspension. 

---