Investigation on Carburization during the Repeated Coking and Decoking Process

Abstract

In this work, stainless steel blank tube and TiN-coated tube obtained by atmospheric-pressure chemical vapor deposition were used to explore the carburization during the repeated coking and decoking process. Various analytical techniques including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy were applied to analyze the morphology, composition, and type of coke. To protect the pipeline, the on-line decoking method was used to determine the amount of coke. During the coking experiment, it was observed that carburization and metal outdiffusion occurred on the inner surface of the microchannel by scanning the cross section of reaction sheets. Moreover, the coke mass of the blank tube in the next coking experiment increased evidently after the previous coking and decoking cycle. However, under the same experimental condition, TiN coatings transforming into TiO2–TiC x N y –TiN multilayer films could still maintain anticoking performance because it alleviated the carburization and metal outdiffusion.

Effect of Methanol Additives on Soot Inhibition during n-Decane Pyrolysis

“…A TiN-coated reaction tube with a length of 1000 mm and an inner diameter of 2 mm was used to carry out the thermal cracking and coking experiments of n- decane with methanol addition, as shown in Figure . Detailed descriptions of the reactor can be found in our previous studies. ,, Because methanol and n- decane cannot dissolve in each other, two high-pressure constant-flow pumps were used to transport methanol and n- decane. n- decane was pumped at a flow rate of 1 g/s, while methanol was pumped at a distance of 40 cm from the inlet of the heating section at a flow rate of 0.05 g/s.…”

“…Hydrocarbon fuel cracking equipment: (I) fuel-feeding system; (II) test system; (III) cooling system; and (IV) analysis system, including (1) storage tank, (2) constant-flow pump, (3) needle valve, (4) mass flow meter, (5) pressure sensor, (6) K-type thermocouple, (7) electric heater, (8) condenser, (9) filter, (10) backpressure valve, (11) liquid/gas separator, (12) Erlenmeyer flask, and (13) wet gas flowmeter.…”

“…Detailed descriptions of the reactor can be found in our previous studies. 7,45,46 Because methanol and n-decane cannot dissolve in each other, two high-pressure constant-flow pumps were used to transport methanol and n-decane. n-decane was pumped at a flow rate of 1 g/s, while methanol was pumped at a distance of 40 cm from the inlet of the heating section at a flow rate of 0.05 g/s.…”

“…Soot formation during pyrolysis or incomplete combustion of hydrocarbon fuels has attracted a lot of attention because of the adverse implications on the human health, environment, and engine fuel efficiency. − To inhibit the soot particles, it is necessary to comprehensively understand their formation mechanism. The mechanism of soot formation is complicated, involving four processes, i.e., the initial ring formation, the polycyclic aromatic hydrocarbon (PAH) growth, the particle nucleation via coalescence of PAH, and the particle growth by coagulation or surface reactions. − Small pyrolysis intermediates such as C 2 H 2 , C 3 H 3 , and cyclopentadienyl (C 5 H 5 ) have been proved as the most important reactants for soot formation .…”