Tube Skin Temperature Research Articles

Oxidative Pyrolysis of Ethane

The effects of the addition of oxygen to the feed of an ethane steam cracker for ethylene production were investigated at industrial conditions by means of experiments and computer simulations. The oxidation of a small fraction of ethane feedstock in the cracking coil generates a significant amount of heat which can be used by the endothermic pyrolysis reactions. With this, the heat-transfer limitation in the industrial crackers is released. The addition of oxygen increases the conversion of ethane, while the yield to ethylene decreases slightly. Simulations indicate that the effects of the oxygen addition can be beneficial to industrial crackers in three manners: decreased residence time or increased throughput, higher severity, or reduced tubeskin temperature and longer coil lifetime.

Corrosion of T-11 syngas cooler tubes in IGCC pilot plant

Measurements of wall loss of syngas cooler tubes (T-11) were done in an IGCC pilot plant which was operated 4700 hours for 6.25 years. The corrosion rate is pseudo-linear and the total loss is 3.2 mm max. The scale formed consists of the layers of iron sulfide and oxide. The corrosion loss is too large for high temperature corrosion only at tube skin temperature of 230–250°C. The syngas cooler was opened to air for the shutdown time of about 59000 hours. Therefore, it is concluded that the downtime corrosion strongly contributed to the loss of tube wall in this test plant.

A Pyrolysis Furnace with Reactor Tubes of Elliptical Cross Section

Circular tubes suspended in pyrolysis furnaces suffer from significant nonuniformities in heat flux, tube skin temperature, and coking rate profiles around the tube perimeter, due to the presence of front sides and shadow sides on the tubes. Simulation results for an ethane cracker with cracking tubes of elliptical cross section reveal that smoother circumferential heat flux, tube skin temperature, and coking rate profiles are obtained as the eccentricity of the elliptical tubes increases. The circumferential maximal values in coking rates are reduced by 30%. The more uniform tube skin temperature distributions and coke layers in tubes of elliptical cross section favor the run length of the furnace and the tube metal life.

Circumferential tube skin temperature profiles in thermal cracking coils

AbstractUniform temperature distributions in cracking furnaces favor the run length of the production cycle of the furnace and the tube metal life. The coupled simulation of the furnace and the reactor tubes by means of the zone method is extended to permit the calculation of circumferential nonuniformities under reaction conditions. Circumferential tube skin temperatures were found to vary over 50°C and more, due to “shadow effects.” As a result, nonuniform coking rates and coke layers are obtained. The model and computational scheme presented here can be used as a guide for plant operators and as a tool for designing.

Coke deposition in the thermal cracking of ethane

AbstractA novel experimental setup allowed both the kinetics of the thermal cracking of ethane and of the coke formation to be studied over a temperature range extending from 750 to 870°C. The overall kinetics of ethane disappearance are in excellent agreement with previously reported pilot results. Coking rates are initially high but rapidly decrease to reach an asymptotic value. The initial product distribution also differs from the asymptotic product distribution. A kinetic model for the coking is derived from the experiments and used in conjunction with a set of conservation equations for the simulation of industrial ethane cracking. The predicted run length, thickness of the coke layer and evolution of the tubeskin temperatures are in agreement with industrial observations.

Design and performance prediction of pyrolysis furnaces by flux methods and by the zone method

The major problem of high temperature, high pressure, low residence time operations is the prediction of the heat flux profiles on the pyrolysis furnace tube walls, where the tube skin temperature becomes the limiting factor. Solution of this problem by numerical methods requires high space resolution of the volume and walls of the furnace. This results in large sets of non-linear energy balance equations, to be solved simultaneously with the radiative transport equation. The zone method and the flux methods provide two different treatments of the radiative transport equation; they lead to sparse and tridiagonal matrices, respectively. The theoretical principles of each approach are briefly outlined, the accuracy and computational load discussed, and the application to the case of a typical pyrolysis furnace shown. The effects of space resolution and of improving the model of radiative properties of the combustion products are also examined.