Objectives The on-line sampling device for cracking gas in ethylene cracking furnace was developed, and an on-line sampling device for cracking gas was obtained with compact structure, sufficient gas-liquid separation, and small sampling and analysis error, which can improve the accuracy of cracking gas analysis.

Methods After analyzing the shortcomings of the existing cracking gas sampling devices, it is determined that the newly developed sampling device should have the advantages of full-component sampling, sufficient gas-liquid separation, small sampling and analysis errors, compact structure, easy movement, and convenient assembly and maintenance. It is an on-line sampling device for cracking gas with two-step condensation, sufficient gas-liquid separation, and real and reliable analysis data.

Results The volume of the condensing shell Ⅰ and cryogenic shell Ⅱ of the formed cracking gas on-line sampling device are not less than 140 L and 130 L, respectively, the produced cracked gas flow rate is 15-25 L/min, and the produced cracking gas outlet temperature is not more than 550 ℃, under the above conditions, the temperature of the gas-phase material after gas-liquid separation is not higher than 25 ℃, which can realize the full-component sampling of the cracking gas, and the gas-liquid separation is sufficient.

Conclusions After sampling and analysis of the developed cracking gas on-line sampling device, the water-oil ratio of the cracking furnace deduced is 0.498, which is very close to the actual operation water-oil ratio of 0.50, indicating that the sampling method and data processing algorithm used by the cracking gas online sampling device have high performance scientific rationality. The industrial cracking furnace was calibrated by using the on-line sampling device of cracking gas, and the calibration data were used to guide the optimization and control of the outlet temperature (COT) of industrial cracking furnace. With the gradual increase of COT from 845 ℃ to 855 ℃, the yield of propylene and butadiene did not change much, but the ethylene yield increased from 27.78% to 30.31%, with an increase of 2.53 percentage points, and the effect was remarkable. In general, the yield of diene and triene decreased slightly at first and then increased with the increase of outlet temperature of cracking furnace, the increase range reached 5.83% and 5.42%, respectively, which effectively improved the efficiency of the plant.