Numerical Study of CH4 Generation and Transport in XLPE-Insulated Cables in Continuous Vulcanization

Abstract

<jats:p>In this work, we apply a computational diffusion model based on Fick’s laws to study the generation and transport of methane (CH 4 ) during the production of a cross-linked polyethylene (XLPE) insulated cable. The model takes into account the heating process in a curing tube where most of the cross-linking reaction occurs and the subsequent two-stage cooling process, with water and air as the cooling media. For the calculation of CH 4 generation, the model considers the effect of temperature on the cross-linking reaction selectivity. The cross-linking reaction selectivity is a measure of the preference of cumyloxy to proceed either with a hydrogen abstraction reaction, which produces cumyl alcohol, or with a β -scission reaction, which produces acetophenone and CH 4 . The simulation results show that, during cable production, a significant amount of CH 4 is generated in the XLPE layer, which diffuses out of the cable and into the conductor part of the cable. Therefore, the diffusion pattern becomes a non-uniform radial distribution of CH 4 at the cable take-up point, which corresponds well with existing experimental data. Using the model, we perform a series of parametric studies to determine the effect of the cable production conditions, such as the curing temperature, line speed, and cooling water flow rate, on CH 4 generation and transport during cable production. The results show that the curing temperature has the largest impact on the amount of CH 4 generated and its distribution within the cable. We found that under similar curing and cooling conditions, varying the line speed induces a notable effect on the CH 4 transport within the cable, while the cooling water flow rate had no significant impact.</jats:p>

Numerical Analysis of a Continuous Vulcanization Line to Enhance CH4 Reduction in XLPE-Insulated Cables

“…The generation and transport of the cross-linking byproducts are calculated by the computational model, and the overall procedure was described in our previous paper [ 5 ]. In this section, therefore, we discuss only the main assumptions and equations used to simulate the cross-linking reaction, heat transfer, and the byproduct transport process on top of the additional equations and boundary conditions for the additional features (e.g., conductor pre-heater and online relaxation) implemented in this study.…”

“…The main assumptions on which the model is based are [ 5 ]: (1) the cable layers are homogeneous and isotropic in terms of thermal conductivity and byproduct diffusion; (2) DCP is uniformly distributed along the entire insulation; (3) the heat generated by the cross-linking reaction, i.e., 900 kJ·kg of DCP, is negligible when compared with the heat supplied by the heating zones [ 27 , 28 ]; this cross-linking reaction enthalpy is, therefore, not included in the model; (4) because the cable has no free space between the layers, there is no extra loss of thermal energy and the byproduct concentration along the interfaces.…”

“…Cross-linked polyethylene (XLPE) is one of the most popular insulation materials for producing power cables due to the exceptional electrical properties, production efficiency, and resistance to chemicals, moisture, and temperature [ 1 , 2 , 3 , 4 , 5 ]. To manufacture and apply XLPE for cable insulation, dicumyl peroxide (DCP) is commonly used as a cross-linking initiator of polyethylene (PE) due to its relatively fast decomposition rate at typical cable manufacturing temperatures, especially in the curing tube [ 4 , 6 ].…”

“…Here, we extend the study to investigate the manner in which the cable production line and operating conditions can be enhanced to effectively reduce the concentration of byproducts in an XLPE-insulated cable during production, and therefore to minimize the cost for the byproduct degassing. From the previous CV line study [ 5 ], we figured that the temperature is the key factor for both the creation and transport of the byproducts so that the key elements in the CV line process affecting the temperature of the cable were chosen and customized in this paper such as the conductor pre-heater, curing tube temperature control, transition zone length and insulation, and online relaxation between the cooling sections. The details of the elements are described in Section 2 .…”

“…The details of the elements are described in Section 2 . On top of the governing equations and boundary conditions applied for the basic CV line process in our previous work [ 5 ], additional conditions have to be implemented for the elements tested in this work, and the numerical models and boundary conditions are demonstrated in Section 3 . In Section 4 , we show how the case studies are designed based on the basic CV line configuration to possibly enhance the cable production process to minimize the byproduct remaining in the cable.…”