Abstract: This paper introduces the main applications of Zhejiang University Control System (ZJU) DCS in lime kilns in mines, briefly explains its working principle, and details the process and control flow of lime kilns.
Keywords: DCS system lime kiln process and control flow
Abstracts： This paper introduces Zhjiang University SUPCON DCS system's main application in the mine limekiln, a brief description of its working principle; At the same time, a detailed description of the lime kiln process and control flow.
Keywords： SUPCON DCS system the mine limekiln process and control flow
I. Overview
Fujian Sansteel (Group) Co., Ltd.'s Mining Company originally had five 150m³ gas-fired lime vertical kilns. Kilns #1 and #2 were converted from 150m³ mechanical coke vertical kilns and put into operation in April and December 1998, respectively. Kiln #3 went into operation in February 2001. Kilns #4 and #5 went into operation in August 2004. Currently, the economic indicators of these gas-fired kilns rank among the top in China for similar kilns, with an annual production capacity of 20 × 10⁴ tons of metallurgical lime. According to Sansteel's "Eleventh Five-Year Plan," two additional 155m³ gas-fired lime kilns (#6 and #7) need to be built to meet the demand of an annual steel production of 5 million tons. These gas-fired lime vertical kilns mainly use blast furnace gas and some converter gas as fuel. These two kilns were put into operation at the end of 2007.
II. Process Flow
The raw material for lime kilns is mainly limestone, and the finished product is quicklime. Limestone is added to the feed inlet of the vertical kiln, calcined into quicklime through gas combustion, and then discharged into the finished product silo. The system mainly includes limestone screening, feeding, calcination, cooling air circulation, combustion air circulation, exhaust gas dust removal and circulation, finished product discharge, transportation, and supporting systems such as a gas pressurization pump station and a hydraulic station.
1. The entire process flow of a lime kiln is shown in the following diagram:
Limestone is calcined by mixing coal gas and air. Producing lime at a high temperature of around 1000℃ is a complex process.
The factors affecting lime activity are the temperatures of different sections of the gas-fired kiln, primarily the calcination zone temperature, which is generally between 800 and 1100℃. Here, the calcination zone temperature is taken as the control objective, and the inlet gas flow rate is used as the control parameter (the inlet air flow rate is adjusted according to the air/coal ratio based on the gas flow rate). Due to the significant time delay of this object, conventional PID control is ineffective; therefore, a fuzzy control algorithm is adopted. The main principle of the fuzzy control algorithm is as follows: the calcination zone temperature deviation (E), the rate of change of the calcination zone temperature deviation (EC), and the control gas flow rate (U) are set as the three elements of fuzzy control. Based on operating procedures and the experience of operators, a corresponding fuzzy rule table is formulated (as shown in the figure below). The basic control principle is that when the error is large or significant, the control quantity should be selected to eliminate the error as quickly as possible; when the error is small, the control quantity should be selected with care to prevent overshoot to ensure system stability.
The fuzzy rule table of control quantity U under different E and EC conditions uses PID control for air flow. The output value of gas flow is multiplied by the air/coal ratio as the set value of PID control air flow to ensure that the air/coal ratio is constant.
2. The main functions of the lime kiln process control system (DCS system) include:
(1) Real-time acquisition and processing of parameters such as pressure, temperature and flow rate during the production process are achieved through the DCS system.
(2) The entire feeding and discharging process is fully automated through the DCS system, fault diagnosis is performed, and the feeding batch and discharging time are displayed on the monitoring screen.
(3) The control of the gas pressurization station and the air pressurization station is realized through the DCS system. The gas flow rate, gas pressure, air flow rate and air pressure are controlled by hand controller to ensure that the gas and air are mixed in a certain proportion so that the gas in the kiln is more fully burned, and to realize real-time alarm and interlock shutdown control for their faults. The gas pressurizer and the blower are started in sequence.
(4) The DCS system is set to two working modes: automatic and manual. The manual mode is used for single equipment debugging and standby, while the automatic mode is used for normal production. Important parameters such as gas pressure, gas temperature and ore weight are displayed by both CRT and instrument, ensuring the operating conditions under manual mode.
(5) All equipment operating parameters, including fault, stop, run, manual and automatic status, can be observed on the CRT in the control room, which facilitates maintenance and handling. A dynamic flow chart is used to display the overall process overview, and real-time values are displayed on the flow chart.
(6) Accurately accumulate energy consumption indicators of coal gas through the DCS system; correctly record the ash weight and time of lime production.
The system's main screen is shown below:
III. Introduction to SUPCON DCS System
The SUPCON WebField GCS-2 system is an important member of the control system family from Zhejiang University Control System Co., Ltd. It is a multi-functional control system (Mini DCS) designed for small and medium-sized control applications, capable of real-time tasks such as data acquisition, process control, and sequential control. In its functional design, the system retains the powerful analog signal processing and loop control functions of conventional DCS systems while also featuring fast logic control and superior real-time performance. System Overall Structure
The GCS-2 control system is a "networked control system" that adopts a web-based architecture, supports client/server mode, breaks through the hierarchical model of traditional control systems, achieves compatibility with various fieldbus technologies and comprehensive integration with intelligent devices from other manufacturers, and can interconnect with various domestic and foreign DCS, PLC and other control devices.
The first layer network is the process control network, called SCnet II, which uses 10/100Mbps adaptive industrial Ethernet for data communication.
The second layer network is a remote communication network called Rcom I network. It is designed based on industrial Ethernet technology and is used to connect remote I/O racks and remote expansion racks.
The third layer is the rack-mounted I/O bus—the CDM bus. It is a high-speed parallel bus that can provide bus speeds of up to 80Mbps, greatly accelerating the data exchange speed between the I/O modules and the CPU module.
The GCS-2 system uses high-speed redundant industrial Ethernet SCnet II as its process control network. It directly connects the system's CPU, operator stations, engineer stations, communication interface units, etc., serving as the channel for transmitting real-time information and possessing high real-time performance and reliability. The SCnet II network can support up to 16 operator stations, with TCP/IP protocol addresses selectable between 128.128.1.129 and 128.128.1.160, and a subnet mask of 255.255.255.0. The following diagram shows the structure of the operator station network card:
As a node in SCnet II, the CPU module's network communication functions are handled by the communication controller on the backplane. The CPU module has two Ethernet communication ports, with PORT-A used for the SCnet II network. The CPU module's control cycle is selectable from 100 ms to 5 seconds.
IV. Summary
After the new kilns were built, the utilization coefficient of the company's five gas-fired vertical kilns was controlled between 0.8 and 0.9 t/m³.d, and practice has shown that the lime quality is relatively high. The improvement in lime quality has significant indirect economic benefits in converter smelting, such as reducing ash consumption per ton of steel, reducing smelting splashing, increasing metal yield, and extending furnace life.
The gas-fired lime vertical kiln primarily uses blast furnace gas and a portion of converter gas as fuel, fully utilizing our plant's secondary energy resources. With a gas cost of 70.00 yuan per ton of lime, this saves our plant 70.0 yuan/ton × 80,000 tons/year = 5.6 million yuan/year. This system has been in operation for over a year, proving safe, reliable, easy to operate, and highly stable.
References:
[1] Guan Chenxiang. Lime Kiln. Beijing: China Building Industry Press. July 1986.
[2] Sun Xisheng. Factors affecting the quality of active lime for steelmaking, Lime. 1998
[3] SUPCON WebField System Manual, Zhejiang Supcon Technology Co., Ltd.
[4] Automation Control System for Gas-Fired Lime Kiln in Sansteel Mining, Sansteel (Group) Co., Ltd.
