Application of Siemens PLC in waste incineration power plant

Thread Content

Author of the application of Siemens PLC in waste incineration power plants: Huang Weisong This article introduces the characteristics and processing methods of garbage treatment, and details the characteristics of the control system of the waste incineration power plant and the configuration, logic control and PID control loop of the corresponding control system. 1 Introduction Waste incineration treatment technology such as urban domestic waste, industrial waste, hospital sanitary waste, sludge and waste rubber tires, using the waste heat of waste incineration to generate electricity and turning waste into treasure will be an important development direction of environmental protection technology in the future. This kind of waste incineration has a daily waste processing capacity of 1 to 350 tons. The heat capacity of the waste heat boiler is small, and the generator set is small, generally within 20 megawatts. Therefore, the control system of a waste-to-energy plant is much simpler than that of a large power plant. Generally speaking, the host control system of large power plants cannot be controlled by PLC, and only some auxiliary systems can use PLC. However, with the rapid advancement of fieldbus technology and microprocessor performance, high-end PLC distributed control systems have been successfully used in medium-sized and more complex control fields. For example, waste incineration power plants can use high-end PLC control systems, which can * * Reduce control system costs. This article will introduce the PLC control system of the waste incineration power plant in Nanhai City, Guangdong Province. This control system was successfully developed by Zhuhai Guangdong Yafang Technology Co., Ltd. and was successfully put into production and operation at the first time. 2. Introduction to the overall scheme of the control system. The distributed control system uses Siemens S7-400 series PLC. Siemens' S7-400 series PLC is a large model in the S7 series launched in the 1990s. It has complete functions and powerful communication capabilities. Especially Profibus, one of the international bus standards, is supported by many manufacturers and is very conducive to the use of distributed control systems. The communication rate of the Profibus-DP bus can reach 12Mbps. The Profibus-DP bus network composed of the S7-417H dual-machine hot standby system and ET200M distributed I/O forms a switching structure, which realizes disturbance-free automatic switching in the event of a fault and can be used in control systems with extremely high safety performance requirements. However, the S7-417H dual-machine hot standby system is relatively expensive. In order to reduce hardware investment, you can choose software dual redundancy (using 416CPU for dual-machine hot standby), using the Profibus-DP field control bus of distributed I/O. The OSM/ESM ring 100M industrial Ethernet optical network is used for communication between the host computer and the PLC. The host computer uses Intouch7.1 configuration software for system configuration. The plant's waste incineration process introduces the patented technology of the American Basic Company and uses a four-stage pulse grate. All indicators meet international environmental protection requirements. It can incinerate 200 tons of waste per day in one phase. This process technology has practical application value in my country. (1) Working principle: The garbage is fed to the drying bed of the incinerator through the automatic feeding unit for drying, and then sent to the grate. The grate throws the garbage driven by the pulse aerodynamic device. The garbage is mixed and burned with the combustion-supporting air ejected from the uniform pores on the grate piece. The heat generated by the combustion is recovered by the waste heat boiler. The high-temperature and high-pressure water vapor generated by the waste heat boiler drives the turbine to generate electricity. After burning, it enters the ash pit and is discharged by the automatic slag removal device. The flue gas evaporated and cracked from the main combustion chamber enters the second and third-stage combustion chambers for further combustion, causing the temperature of the flue gas to reach as high as 1000°C. The flue gas stays here for no less than 2 seconds, causing the toxic flue gas to rapidly decompose. It is then discharged into the atmosphere after passing the flue gas treatment equipment and dust removal equipment (electrostatic precipitator, bag dust collector). (2) Main equipment of the environmentally friendly power plant ① 2 incinerator boilers, the main technical parameters of each are as follows: Waste processing capacity: 8.33t/h Steam generation: 22.5t/h Superheated steam pressure: 4.0MPa Superheated steam temperature: 400℃ Furnace temperature: 980℃ Feed water temperature: 145℃ ② One set of steam turbine generator set, the main technical parameters are as follows: Main steam pressure: 3.9MPa Main steam temperature: 390℃ ③ The main technical parameters of the generator are as follows: Power: 12000kW Outlet voltage: 10.5kV Frequency: 50Hz Rated speed: 3000r/min Power factor: 0.8 Excitation method: Brushless excitation system ④ Two sets of flue gas treatment systems ⑤ Supporting electrical power supply and distribution system The PLC distributed control system has more than 3,000 I/O points, including more than 300 analog values. The PLC distributed control system diagram of the whole plant is shown in the attached figure. Attached figure: PLC distributed control system of the whole plant. Figure 3: Configuration of the host computer monitoring system. The system has a total of 4 operator stations and 1 engineer station. Two of the operator stations are used to monitor the furnace-side equipment, including the incinerator and boiler systems, the flue gas desulfurization system, and the ash removal system; the other two operator stations are used to monitor the machine-side equipment, including the turbine system, water supply system, wastewater treatment system, electrical and other parts. The two operator stations on the furnace side and the two operator stations on the machine side are dual-machine hot standby. The operator stations on the furnace side and machine side are functionally independent and cannot be operated interchangeably. The engineer workstation is responsible for system software development and configuration and alarm sequence event recording. The engineer station will be able to serve as any operator station to complete related control and monitoring functions. The engineering station, operator station and PLC use OSM/ESM ring 100M industrial Ethernet optical network for interconnection and communication. The operating system adopts Chinese Windows NT window operating system. The host computer uses Intouch7.1 configuration software for system configuration. The main design of the human-machine interface has the following contents: (1) System process flow display: based on the system process flow chart provided by the design institute, divided according to functional group areas; (2) Sequence control system operation guidance display: there is a sequence control step display, that is, the status display of the sequence control program steps, and operation prompts, etc.; (3) Adjustment system and adjustment screen: loop manual operation station, centralized display of adjustment parameters and parameter trends; (4) Important parameter trend display: there are two displays of real-time trends and historical trends; (5) Bar graph display of steam turbine status and other parameters; (6) Global alarm display: The system is divided into several alarm groups according to functions, and the alarm windows of each alarm group are distributed above the corresponding function display window. The global alarm display provides the ability to centrally view all alarms of the system, or filter and view by priority and alarm group, and has global alarm confirmation; (7) Report management: Provides daily and monthly report printing functions, and the printing methods include: scheduled printing, event-driven printing, operator call printing, and historical report data viewing functions; (8) PLC system status display: Provides error checking and maintenance functions for the system hardware network; (9) Multi-level map menu display; (10) System security level definition In order to ensure the safe operation of the system, it is designed with three levels of authority: engineer level, senior operator level, and operator level. Operator level users can perform normal system operations. In addition to operator level functions, advanced operator level users can also modify adjustment parameters, modify time, view historical reports, and call for printing. The engineer level has the highest authority, has all the functions of the advanced operator level, and can also enter the development environment for configuration modifications. 4 PLC control system configuration The entire system is divided into 1# and 2# PLC master stations. The 1#PLC master station controls the 1# and 2# boiler incinerators respectively; the 2#PLC master station controls the turbine system, water supply system, wastewater treatment system, electrical and other parts respectively. Each PLC master station consists of two CPU416-2DP (order number: 6ES74162XL010AB0) to form a dual-machine hot standby. Real-time redundancy software is used to realize non-disturbing switching of the control system to ensure safe and stable operation of the system. The two CPUs monitor each other and back up data through the MPI interface. Each CPU communicates with the host computer through the CP443-1 industrial Ethernet communication module. Siemens' 416CPU forms a dual-machine hot standby, which can only be realized through software, so it is called soft redundancy. In principle, all CPUs above CPU315 can form soft redundancy. Users must write their own redundancy management program and put the data that needs redundancy in specific DBs. In each scan cycle, the main CPU will image the data in these specific DBs to the slave CPU. Software redundancy and hard redundancy have the advantage that developers can customize the redundant database so that * * Reduce the imaging time of redundant data in each scan cycle. The input/output of control signals is completed by the relevant ET200M distributed I/O module, using the "proximity principle" to minimize on-site hard wiring. Each ET200M has two IM153-2 communication modules, which are respectively hung on the DP bus to form a redundant DP bus. ET200M uses Siemens 300 series distributed I/O modules, which are low-priced. Each ET200M can be expanded to 8 I/O modules, with a capacity of up to 128 words of input/128 words of output, and a maximum transmission rate of 12Mbps. This control system is composed of Siemens 400 series CPU416-2 to form a dual-machine hot standby for data redundancy. The 300 series distributed I/O forms a dual redundant DP bus. It is a highly cost-effective distributed control system and has great promotion value in the fields of host control of various environmentally friendly power plants and auxiliary engine control of large generator sets in the future. CPU416 has extraordinary performance, its binary instruction execution time is 0.08μs (CPU417H is 0.12μs), and the maximum digital IO or analog IO is as high as 65536 or 4096 points. This distributed control system has more than 8,000 logic control statements and 30 PID control loops, including: 2 loops with differential feedforward control, 10 loops with conditional switching output, 2 three-impulse adjustment loops, and 26 single-impulse adjustment loops. The system has high real-time reliability requirements. In this distributed control system, PLC completes the logical sequence control of the entire plant and the control of all PID loops. Among them, the logical sequence control is divided into the following parts: (1) 1-2-3 level purge: its purpose is to ensure that the relevant equipment of the 1-2-3 level combustion chamber air and smoke system is normal and the channel is smooth, which is one of the important operations required for furnace protection; (2) fan start; (3) incinerator-boiler purging: its purpose is to ensure that the relevant equipment of the entire air and smoke system of the incinerator-boiler is normal and the channel is smooth, which is one of the important operations required for furnace protection; (4) Second-stage preheating: Its purpose is to increase the second-stage temperature to reach the set value, which is a prerequisite for the first-stage preheating and the first combustion chamber burner input; (5) First-stage preheating: The purpose is to increase the first-stage temperature to reach the set value; (6) Sequential shutdown; (7) Sequential ignition/stop of the burner; (8) Automatic circulation of the feeding system; (9) Automatic circulation of the slag removal system; (10) Slag pit water level interlock control; (11) Soot blowing system sequence control; (12) Boiler protection; (13) Main fuel trip; (14) Feed oil trip; (15) Normal power generation mode; (16) Isolated operation mode; (17) Turbine failure mode; (18) Chemical water treatment control; (19) Sewage treatment control. 5 Main PID control loop (1) Furnace pressure adjustment system This system is a single impulse adjustment loop. According to the system technology, the furnace should maintain a certain negative pressure value (PT101), so the induced draft fan (PV101) needs to be adjusted by PI. In order to prevent the induced draft fan frequency converter from running too large or too small, causing the boiler to stall, high and low limiting modules are introduced in the regulating system. (2) Drying grate temperature control system This system is a single impulse control loop. According to the system technology, the garbage entering the 1# grate of the first combustion chamber of the incinerator contains a certain amount of moisture, which directly affects the temperature of the furnace and increases the burden on the 1#-2# burners. Therefore, the mixed flue gas is introduced from the third combustion chamber for drying. Since the temperature of the mixed flue gas in the third combustion chamber is relatively high, the drying grate temperature (TE108) is maintained within the set working range by adjusting the drying fan (TV108). (3) Recirculation flue gas temperature regulation system This system is a single impulse regulation loop. By adjusting the recirculation fan (TV109), the flue gas temperature of the fourth combustion chamber (TE109) ​​is maintained within the set working range. (4) Furnace temperature regulation system in the first combustion zone. This system is a conditional switching multi-output regulation loop. According to the system technology, the combustion chamber of the incinerator is divided into two stages: starting operation and normal operation. During the start-up operation stage, the furnace temperature (TE101) is mainly controlled by the amount of fuel in the 1#-6# burners. The system requirements for the furnace temperature (TE101) are maintained by adjusting the 1#-6# burner oil return regulating valves (HV107, HV111, HV117, HV121, HV127, HV131). In the normal operation stage, the furnace temperature is mainly maintained by the combustion of garbage on the 1#-4# grate. By adjusting the exhaust air regulating valve (HV104, HV114, HV124, HV134) of the 1#-4# grate (the air supply fan speed is constant, the exhaust air regulating valve can adjust the air supply volume) to control the combustion of the garbage on the 1#-4# grate, so as to meet the system requirements for the furnace temperature (TE101). This adjustment process will directly affect the furnace negative pressure. In order to prevent the reduction of furnace negative pressure from affecting the system, when the furnace negative pressure exceeds a certain value (such as less than 1kpa), the exhaust control valve will be limited. (5) Boiler drum water level adjustment system This system is a three-impulse adjustment loop. By using the main signals of feed water flow (FT101), steam flow (FT103) and drum water level (LT102) to perform PI adjustment on the feed water regulating valve (LV102), the drum water level is maintained within the set range to adapt to the evaporation capacity of the boiler. (6) The superheated steam temperature regulation system introduces the steam temperature after the desuperheater (TE116) as a feedforward signal, and performs PI regulation on the desuperheating water regulating valve (TV119) together with the main signal of the superheated steam temperature (TE119). (7) Turbine front pressure regulation system This system is a conditional switching output regulation loop. During normal power generation, the balanced configuration of the steam turbine and the bypass system is used, and the main steam valve front pressure (PT302) is adjusted through the steam turbine synchronous controller speed valve to stabilize it at the working pressure. When the generator is shedding load, control the bypass steam regulating valve (PV302) to exit the automatic state. (8) The desuperheater and pressure reducer temperature adjustment system has two adjustment tasks for the desuperheater and pressure reducer: adjust the water spray volume to maintain the steam temperature after decompression within the working range; adjust the opening of the pressure reducing valve to maintain the steam pressure after decompression within the working range. This regulation system adjusts the temperature after the desuperheater and pressure reducer (TE327) through the desuperheater water regulating valve (TV327) to stabilize it at the operating temperature. (9) Temperature reducing and pressure reducing device pressure regulating system. This system is a conditional switching output regulating circuit. In the low load state, this regulating system maintains the pressure after the desuperheater and pressure reducer (PT325) by adjusting the steam bypass regulating valve (HV302) to stabilize it within the set working range. When in load shedding state, the system is adjusted to adjust the steam regulating valve (PV325). (10) Low-pressure cylinder pressure regulation system. This system is a dual-regulator conditional switching single output circuit. The steam in the low-pressure cylinder comes from the extraction steam of the steam turbine in normal power generation mode; when the generator is in a load-shedding state or a turbine failure state, it comes from a part of the main steam after passing through the desuperheater and pressure reducer (while the other part of the steam enters the high-pressure condenser). This regulating system distributes these two parts of steam safely and reasonably by adjusting the steam regulating valve according to the system requirements. When the pressure of the high-pressure steam condenser (PT327) is less than 0.2Mpa, the regulating system maintains the low-pressure cylinder pressure (PT326) by adjusting the steam regulating valve (PV326) to stabilize it within the set working range. When the pressure of the high-pressure steam condenser (PT327) is greater than 0.2Mpa, the regulating system maintains the pressure of the high-pressure steam condenser (PT327) by adjusting the steam regulating valve (PV326) to stabilize it within the set working range. (11) Deaerator liquid level adjustment system This system is a conditional switching output adjustment loop. In normal power generation mode, a large amount of condensed water is sent directly from the condenser to the deaerator through the low-pressure pump without passing through the drain tank. The supply water to the deaerator is adjusted through the water inlet regulating valve (LV304)._1), to achieve constant deaerator liquid level (LT404). When the turbine fails, a large amount of condensed water gathers from the high-pressure condenser to the drain tank. The supply water for the deaerator is transported through the drain tank. The liquid level of the deaerator (LT404) is adjusted by the water inlet regulating valve (LV304)._2), to achieve constant liquid level. 6 Conclusion After more than two years of operation, the PLC distributed control system has proven that all technical indicators have reached the international advanced level. The main performances are as follows: (1) High combustion efficiency: the garbage is evenly mixed with air on the grate and burned fully, and the garbage burnout rate is high; (2) High heat recovery efficiency: The waste heat boiler is distributed in the main furnace and flue, which can fully absorb the heat of garbage combustion. The normal combustion thermal efficiency is more than 80%. Even for household garbage with a large moisture content, the combustion thermal efficiency is more than 70%; (3) It has a wide range of waste processing: it can handle industrial waste, domestic waste, hospital waste, discarded rubber tires, etc.; (4) Low operation and maintenance costs: the grate adopts a monolithic design with low maintenance, high automatic control level, and few operating personnel; (5) High reliability: after nearly 2 years of operation, this incinerator has a very low failure rate, with an annual operation of more than 8,000 hours, and a utilization rate of more than 95%; (6) High level of emission control: Due to the use of secondary flue gas re-burning and advanced flue gas treatment equipment, the flue gas is fully treated. After long-term testing, the CO content in flue gas emissions is 1 to 10PPM, the HC content is 2 to 3PPM, and the NOx content is 35PPM, fully complying with European and American emission standards. When the flue gas is burned in the second and third stage combustion chambers, the temperature reaches 1000°C and the residence time is more than 2 seconds, which can basically decompose the dioxin. The dioxin content in the flue gas is 0.04ng/m3, which is far lower than the European and American standard of 0.5ng/m3.