Improvement of cathodic protection of greenhouse buried heat-supply metal pipeline based on thermoelectric cell

With the development of the global economy and the improvement of people's living standards, the demand for traditional energy is increasing, which has led to serious energy shortage, and increasingly serious environmental pollution. More and more attention has been paid to thermoelectric power generation technology which takes the industrial and automobile waste heat as heat source. In order to plant out-of-season plants and southern plants, the northern greenhouses generally use heating pipeline for heating. Cathodic protection, as the main protective measure for buried pipelines, plays an important role in pipeline protection. In order to alleviate the corrosion rate of heating pipelines, the method of joint use of external anti-corrosion insulation layer and cathodic protection is generally adopted during the deployment of metal pipelines. This is also the most economical and reasonable anti-corrosion measure. Cathodic protection protects the metal from being corroded by the environmental media (such as soil), protect pipeline or equipment by corrosion with auxiliary anode or sacrificial anode materials, thereby achieving the purpose of prolonging the service life of the protected pipeline and improving its safety and economy. However, the cost for conventional external-current cathodic protection method is high with large footprint, and the protection life of the sacrificial anode method is too short. Therefore, in order to provide reliable external-current cathodic protection for greenhouse heating pipelines, this article uses the waste heat from the surface of the underground heating pipelines, through direct conversion of thermal energy into electrical energy by a thermoelectric power plant, to provide the cathodic protection of the external current mode for the buried heating pipeline. The technology has the advantages of green, environmental protection, simple structure, safety and reliability. This article focuses on the research of thermoelectric power generation systems, introduces the basic theory of thermoelectric power generation and derives the relationship of characteristic parameters of the thermoelectric cell. Based on the output characteristics of the thermoelectric cell, this article designs a self-powered system based on BQ25504 chip. The system collects the thermoelectric energy and continuously supplies it in the maximum power point tracking mode during operation. The thermoelectric conversion energy is collected by the BQ25504 chip produced by TI, and then supplied by the step-down regulator chip LM317 to cathodically protect the buried heating pipeline. The design uses the temperature of the pipeline as a heat source, and it has the advantages of almost no land occupation, long-term use, flexible protection and energy saving. Through field tests, the temperature difference between the cold and the hot ends of the device was found to be 33.2 ℃, which proved that the greenhouse heating pipeline was a heat source worthy of utilization. Finally, through the natural corrosion test, it was found that when the horizontal distance of the anode bed was 1.69 m and the protective potential provided by the device was -1 100 mV, the degree of protection to the pipeline could reach 92.79%. This study provides a more feasible solution for the protection of greenhouse heating pipelines, and at the same time, the short-distance pipeline protection technology of external current mode is also explored. © 2018, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.