Why should deep well anode choose low resistivity backfill?

In the design of deep well anode engineering, the selection of backfill is also very important. The main function of backfill is to reduce the grounding resistance of anode. Because the reaction of anode will be transferred to the backfill, the backfill can reduce the consumption of anode itself and maintain the shape of anode well. Therefore, it can be understood that the backfill material must have the characteristics of low resistivity, small particles and high density.

At present, there are mainly two kinds of backfill in the market: one is petroleum coke, the other is metallurgical coke. One of the main recommendations here is petroleum coke, which is fired at high temperature and has excellent conductivity and uniformity. When the coke backfill is filled into the anode well, it is better to pump the coke from the bottom of the anode well into the well.

Current density of backfill

The size of anode well is not determined randomly, it will be affected by a series of factors. One of them is the current density at the interface between the filler and the soil. Experience shows that the current density of backfill should be limited because of the following reasons:

(1) A certain humidity must be maintained between anode and soil. Due to the electroosmosis effect, cathodic protection current tries to evaporate the moisture, and the degree depends on the soil type and current density;

(2) The anode reaction consumes water and produces gas. The accumulation of gas or the drying of anode surface will increase the grounding resistance of anode. The amount of gas generated is directly related to the current density;

(3) In special cases, the temperature of the interface between anode and soil will increase. This will also increase the rate of water evaporation, and the temperature is related to the current density, soil thermal conductivity and anode size.

Previously said that the selection of fillers must choose the low resistivity, mainly because this can reduce the consumption of anode as much as possible. In short, assuming that under the same construction environment and the size of anode well used is the same, the lower the resistivity of the selected backfill, the larger the anode spacing; on the contrary, the smaller the selected resistivity, the smaller the anode spacing.

Now there are more and more manufacturers producing backfill materials. Many manufacturers take resistivity as the selling point and emphasize that the resistivity of backfill they produce is very low. But different construction environment, the actual situation of anode installation and some characteristics of anode selection, such as compactness, and of course, the water content of soil in the surrounding environment are important factors to be considered. Therefore, the most basic requirements for the selection of backfill are as follows: the minimum resistivity is 2.0 ohmnan; the spherical particles are best backfilled and compacted; in order to facilitate the consumption of supplementary filler, the backfill should be 3M lower than the bottom of anode and 3M higher than the top of anode.

The long-term construction experience shows that the current density of the filler should be properly controlled. The main reason is that there must be a certain humidity between the anode and the soil. The amount of gas will directly affect the current density. Under special circumstances, the temperature of the contact surface between the anode and the soil will also increase, which will accelerate the evaporation of the surrounding water. At this time, the temperature is closely related to the current density, the thermal conductivity of the soil and the size of the anode well.

Shandong Linyi Bosi conductive materials Co., Ltd. is a high-tech enterprise specializing in the production of MMO flexible anode, conductive polymer flexible anode and titanium coated anode, mainly providing corrosion protection, cathodic protection, engineering design, installation and technical services.