The so-called Terra Invader systems can penetrate up to 8000 m into the earth in order to tap oil, gas or geothermal resources (Figure 1). The latter are becoming more and more important in times of increasingly scarce fossil resources. This is down to their high availability: there are huge amounts of geothermal energy around the world.
The market leader for tunnel boring machines, Herrenknecht, Schwanau/Germany, entered the deep drilling rig business in 2005. The first systems worked in Germany and Brazil, but the systems are now in operation in many countries around the world. The vertical drilling rigs are developed and manufactured by the subsidiary company Herrenknecht Vertical – and these are made individually for each customer.
When manufacturing the systems, the company works according to the high standards of offshore technology, because the systems are also used offshore. In addition, the systems have a large number of new developments, including an optimised safety concept (hands-off technology). Further features of the state-of-the-art drilling rigs are flexible energy management and integrated noise protection measures. The main advantage of Herrenknecht deep drilling rigs compared to conventional systems, however, is their high degree of automation. This means that users can operate the systems with just four men per shift, which results in significant cost savings.
When designing the drilling rigs, Herrenknecht attaches great importance to optimum explosion protection. The reason for this is that the deep drilling rigs can also tap oil and gas reserves. Their components must therefore be absolutely explosion-proof. The search for a suitable rotary encoder for positioning the top drive and the elevator was difficult under these conditions.
“Very few suppliers have explosion-proof rotary encoders in their product range,” says Jürgen Binder, Herrenknecht Vertical’s technical director. They finally found what they were looking for at the automation technology specialist Hengstler GmbH, Aldingen/Germany.
Fig. 2. The ACURO AX71 absolute encoder from Hengstler ensures the exact positioning of the top drive and the elevator in the deep drilling rigs. Photo: Hengstler
The ACURO AX71 absolute encoder not only meets the high standards in terms of explosion protection (Figure 2). “Of all the rotary encoders tested, it did the best in terms of field suitability,” recalls Binder. Among other things, the ACURO AX71 impressed with its very good EMC and lightning protection, but also withstood temperatures from –40 to +50 °C and contact with salt water best. It was therefore decided that the absolute optical angle encoder will be installed in all Herrenknecht deep drilling rigs with immediate effect.
The task of the ACURO AX71 on the system is to accurately position the top drive and the elevator, the so-called rack and pinion. Since new drill rods are always being connected, the height position at the elevator must be precisely recorded and added up in order to determine the exact chisel depth. The ACURO AX71 from Hengstler is recommended in every respect for this task, because it outputs binary-coded position values and shows the axis position in relation to a reference point. The rotary encoder is not only distinguished due to its resolutions of up to 12 bit in the multiturn and up to 22 bit in the single turn version. With a diameter of only 70 mm and a shaft diameter of only 10 mm (solid shaft), it is also very compact. The numerous interfaces such as SSI/BiSS and SSI (programmable) as well as Profibus, CANopen and DeviceNet ensure comprehensive compatibility of the rotary encoders.
Hengstler developed the rotary encoder with a stainless steel housing specifically for use in potentially explosive areas in accordance with the ATEX and IECEx guidelines (EN 60079). The ACURO AX71 is therefore suitable for the ATEX zones Ex II 2 G Ex d IIC T4 Gb or Ex II 2 D Ex tb IIIC T135°C Db IP6X. Such zones are found, e. g., in painting, filling, mixing or silo systems as well as in the petrochemical industry or in mills.
The ACURO AX71 was also individually adapted for Herrenknecht. The rotary encoder received a scaling, also called residual value calculation or a rotary indexing function. This ensures that the encoder is reset to zero after a certain number of rotations. The residual value is saved and is available again immediately after switching on the encoder.
Herrenknecht has been using the Hengst-ler rotary encoders successfully for over ten years and will also be installing them on a new geothermal system that is currently being designed. “We are very interested in the new ACURO AX73,” says Binder. This is not surprising. The housing of the pressure-resistant encapsulated rotary encoder, in which the user can easily install their own cable using sophisticated locking technology, would even withstand an explosion on the inside. Any sparks that may occur are also extinguished before they can get outside.
Further information:
Hengstler GmbH
www.hengstler.com
Herrenknecht Vertical
www.herrenknecht-vertical.com
