Development Of Elastic Load Control Technology For Large Cryogenic Equipment

This paper briefly describes the importance and principle of elastic load technology for large air separation systems, and elaborates on the technical points of elastic load technology and its system software and hardware configuration methods, which ensures the variable demand for production gas in Laigang, reduces the emission, and reduces the energy consumption of the oxygen generator in the whole process at different loads. It has important reference value for the automatic load adjustment of other large air separation systems.
Keywords: distributed control system; advanced process control system; elastic load

Content Menu
1. Introduction
2. Basic principles of implementation
3. Hardware environment
4. Technical solution

1. Introduction

Maintaining cooling balance and logistics balance, reducing the energy consumption of the whole process of the device at different loads, and maintaining economic operation are increasingly valued by the industry, and elastic load technology has also become a key topic of development.
Laigang's 60000m³/h oxygen generator is responsible for most of Laigang's gas supply tasks. At the same time, Laigang's production needs for oxygen and nitrogen vary greatly. Sometimes more oxygen is needed, and sometimes more nitrogen is needed. The elastic load technology can well ensure the variable demand for Laigang's production gas needs, solve the energy consumption of the oxygen generator in the whole process under different loads, and reduce the emission rate.

2. Basic principles of implementation
The control system of Laigang's 60000m³/h oxygen generator is divided into two levels: distributed control system DCS (basic control) and advanced control system (advanced control).
2.1 Distributed Control System DCS (Base Control)
The distributed control system (DCS) performs basic control tasks, including: automatic control of air compressor inlet guide vanes, automatic control of air compressor anti-surge, and interlocking protection of air compressors; automatic control and interlocking of liquid levels of air cooling towers and water cooling towers; automatic adjustment of water flow after water pumps; automatic control and automatic switching of water pumps; automatic control of molecular sieve adsorbers and interlocking protection of molecular sieve heaters; automatic control of air compressor inlet guide vanes, automatic control of air compressor anti-surge/interlocking protection of air compressors; automatic control of turbine expander inlet guide vanes/automatic control of anti-surge at the boosting end/interlocking protection of turbine expanders; control and distribution of air flow in the main heat exchanger; automatic control of oxygen-nitrogen distillation, oxygen-nitrogen product purity and oxygen-nitrogen gas product flow; automatic control, load regulation and automatic switching of liquid oxygen pumps; argon distillation, argon product purity and argon gas Automatic control of product flow; automatic control and load adjustment and automatic switching of argon pump; protection and control of storage tank system; control and protection of electrical system; operation and automatic switching of cryogenic liquid pump during normal operation.
2.2 Advanced control system (advanced control)
Add advanced control system on the basis of DCS. The advanced control system performs the task of remote control and command of DCS. Its main function is to calculate according to the product target value through the process mathematical model of the advanced control system, and read the instantaneous value of the relevant process parameters of DCS at the same time, obtain the change of the automatic control operation point (all relevant process parameters are converted from current value to target value at the same time), transmit it to DCS, and remotely control DCS for adjustment, so as to realize the automatic load change of the product. The advanced control system has a mathematical model of the process parameters of each working condition within the load range of 80%~110% of the oxygen generator, which is the core part of realizing elastic load technology.

3. Hardware environment
The basic control uses 3 sets of FOXBORO I/A Series DCS systems to realize the basic control of air separation; the control system consists of 1 engineer station, 3 operator stations, 1 process control station and communication network. The workstation and control station form a full fiber redundant MESH network. The advanced control station exchanges data with the engineer station through OPC Server communication. As a higher-level control brain, the advanced control station remotely controls the basic control DCS to perform variable load regulation on air separation.

4. Technical solution
4.1Configuration of advanced control station
The advanced control system runs on the advanced control station and uses the English version of Windows XP Professional system. The DCS engineer station acts as an OPC server, and the database of the advanced control system and the DCS engineer station realize OPC communication to transmit and exchange data. The real-time database of the advanced control system stores all data sent to and received by the DCS, as well as supplementary data that must be shared between several software modules. The real-time database is managed in the background, and the operator does not have the right to directly access the database service function. The real-time database is the basic software module, and all other modules are connected to it.
The real-time database consists of three parts:
①The storage area of ​​the real-time database: other modules on this storage area access data through a dedicated interface function, which must be run before all other modules are started; the service program RDB_OPR can be used to monitor and use the data in the database;
②OPC module: This module is responsible for data transmission between the DCS system and the advanced control system real-time database. The main functions are to read the configuration data file, create data points in the real-time database, initialize or start communication from/to the DCS system, and perform timed data transmission according to the request;
③Operator interface: All user interface functions (such as data monitoring and operator control functions) are provided by the operator interface OPI. The data monitored and controlled by OPI is the data obtained in the real-time database.

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