Application of Profibus-DP fieldbus in gas recovery transformation

introduction

The steelmaking plant under Laiwu Steel Group Co., Ltd. is the pillar unit of the company. In response to production requirements, the original gas recovery automatic control system was transformed. The original gas recovery automatic control system was put into operation in 1998 and adopted the S5 PLC system of German Siemens Company. The host computer adopted Advantech IPC-610 (P166), the MMI system adopted FIX DMACS monitoring software, and adopted the Ethernet communication network of SINEC H1 based on TF protocol with coaxial cable as the medium, as shown in Figure 1.

The original system gradually exposed more and more problems, mainly in the following aspects:

(1) It cannot meet the needs of hardware and software expansion;
(2) Spare parts are outdated and difficult to supply;
(3) The network is designed as a ring structure, which is difficult to maintain;
(4) The programming environment is based on DOS and cannot interface with the advanced monitoring platform.

2 System Introduction

In addition to upgrading the PLC, the system transformation also needs to change the ring network to a star structure, using the Profibus-DP fieldbus. The fieldbus control method is suitable for the decentralized control equipment and harsh field environment of the converter gas recovery site.

The PLC uses the S7-300 of Siemens, and the monitoring station uses the Advantech PIII series. The PLC and the host computer use the Ethernet communication method based on the TCP/IP protocol and star topology. The star connection topology makes the network more reliable and expandable; due to the long network routing distance, the communication medium uses optical cable, which can support a maximum communication rate of 100 Mbps, an ultra-long transmission distance of tens of kilometers, strong anti-interference ability and extremely low bit error rate. In order to adapt to the harsh industrial environment, the PDP and SDPb series I/O modules with high functional protection levels of Turk are used as remote stations for signal acquisition of field equipment. The Turk remote module has a high protection level, protection capability and perfect diagnostic function, which is very suitable for use in poor conditions and reduces maintenance costs. The transformation plan is shown in Figure 2.

(1) PLC configuration

1 CPU 315-2 DP supporting Profibus-DP bus protocol, 1 CP 343-1 supporting TCP/IP communication protocol, 1 PS 307 (considering the low backplane current consumption of the main rack module, the power module capacity is selected as 5A), 3 32-point 24V DI templates, 2 32-point 24V DO templates, and 1 8-way AI template.

BL20 is used for furnace control, and PDP and SDPb series I/O modules are used for field control.

(2) The hardware configuration of the TURCK system is:

(a) Field control:
21 4-channel AI modules (SDPB-40A-0007), 11 4-channel RTD modules (SDPB-40A-0009), 3 16-point DI (PDP-IM16-0002), 4 8-point DO (PDP-OM8-0004, 2A).
(b) Furnace front control:

The hardware configuration of the control systems in front of the three converters is the same, which are:
1 Profibus-DP coupler (BL20-GW-PBDP-12MB, 12Mbps), 1 bus power module (BL20-BR-24VDC-D), 1 32-point DI template (BL20-32DI-24VDC-P), 1 output template power supply module (BL20-PF-24VDC-D), 1 16-point DO template (BL20-16DO-24VDC-0.5AP, 0.5A).

(3) The host computers all use high-performance Taiwan Advantech industrial computer IPC-610 (Pⅲ1.0G/256M/40G).

3 Computer system software programming

The process flow chart of the entire gas recovery production process is shown in Figure 3.

The PLC control software of the entire gas recovery production process consists of three parts: ladder diagram, sequence diagram, and statement table, using step7 software. The monitoring station system uses wincc monitoring software.

3.1 Program compilation and structure

Based on the requirements that the control program should be concise, safe, reliable, easy to read, and modifiable, a modular programming structure is adopted to complete the structural function block diagram of the control program. The structural function block diagram of the control program is shown in Figure 4. Hierarchical programming is performed according to the allocated system resources to improve the interface.

The main functional modules of this program are:

(1) Self-diagnosis program

Complete the analysis and identification of system hardware and software faults and make appropriate treatments. Prevent accidental downtime (except serious CPU failure) and complete automatic restart after communication interruption.

(2) Data preprocessing procedure

Complete switching and analog data, secondary processing and some engineering quantity conversion, etc.

(3) Alarm and accident handling procedures

Complete monitoring and alarm of fan current and other important process parameters and emergency handling of accidents.

(4) Gas recovery and release process control procedures

Complete gas recovery during normal production, equipment operation interlocking control and loop regulation control during the release process.

(5) Production data statistics: Statistics on important production activities such as recovery, oxygen blowing, and hood lowering.

(6) Fan operation control: It can complete the automatic control of 4 fans and related negative equipment.

3.2 Operation interface configuration design

The monitoring operation interface adopts the wincc software package based on the windows 2000 platform of siemens company. It is an industrial automation software that provides field data acquisition, process visualization and process monitoring functions. Its own database capacity is large and can be programmed in c language.

According to the process requirements, the process flow chart, real-time trend chart, historical trend chart, alarm chart, etc. are compiled, and then the data information is filled and connected to the compiled various charts and output reports. All these component functions are integrated into one, real-time and comprehensive reflection of the complex dynamic production process. The buttons, signal lights, valve positions, temperature and flow signals are clear at a glance. The system has 1 process flow chart, 5 production monitoring charts, 6 real-time trend charts, 3 historical trend charts, and 2 alarm charts. The representative monitoring charts are shown in Figure 5 and Figure 6.

4 Conclusion

Profibus technology has been officially adopted as an industrial control standard in my country. Its standardization and efficiency are obvious. It is also the first time to be adopted in Laigang Group and has been running stably so far. With the industrial development of the group and the good operating performance of profibus, it will surely be widely adopted and serve the industry efficiently.