Management control of cold
The purpose of this plant automation is “Management of cold.”
This plant consists of a group of nine compressors and a condenser system, coolers and separators. This set of equipments are responsible for the production of cold, needed to manufacture the product, based on the existence of three collectors at different temperatures (0°C, -5°C and -12°C).
In addition to the control also a series of calculations is performed in the PLC in order to analyze the load produced and consumed cold, as well as its energy efficiency, based on data supplied by power meters and flow meters.
Description of the automation system
The automation system is in charge of coordinating the boot and stops of the compressors, condensers, coolers and separators in their automatic operation, in function of the production load at every moment, as well as the operation in manual of each.
This plant is automated based on a central PLC with distributed periphery and a set of nine PLCs to control each individual compressor. At the side of monitoring a Scada system and different field panels have been used.
The monitoring system is based on the In-Touch Wonderware Scada, where the whole plant can be operated in both manual as well as automatic from the station located in the control room. Communication between PLC and SCADA system is performed via central Ethernet with TCP / IP protocol.
In case of failure of the SCADA system there are different operations panels, all based on the OP’s and TP’s Siemens, to perform control from field between them. These screens are part of the distributed periphery of Central PLC protocol (Profibus-DP).
There is a central type SIEMENS PLC S7-400 with 10 stations distributed remote periphery SIEMENS ET200M to control capacitors, coolers and separators. This communication is done via Profibus-DP.
Two touch screens are incorporated to control the installation from field as well as 10 flow and energy meters from Endress-Hauser to perform energy management of the cold produced, in conjunction with power consumption.
Compressors consist of nine PLCs of the type of SIEMENS S7-300, one for each compressor. All these communicate via Profibus (RS-485) with the Central PLC. In normal operation the control of the compressors control is done from Central PLC, leaving the S7-300 automat for the intrinsic protection of its own equipment or for running in case of failure of the Central PLC. Each one has an OP SIEMENS PLC to perform monitoring and for control of the compressor locally.
Communicating with the PLC Central there are 28 items measuring energy consumption rate CVM CIRCUTOR. This communication is done with protocol Modbus / TCP, as these elements have Modbus communication protocol, but they have been integrated into the corporate network and a gateway Modbus / TCP have been added to them, PLC forcing function of this way.
All programs of the different PLCs are based on the programming SIEMENS Step 7. However, to control the input-output compressors to the different process lines, due to its complexity and the process consumption needs so variables, a proogram based on programming language Siemens S7-GRAPH had to be done, which adapts the standard GRAFCET.