This article outlines the problems and deficiencies of ordinary ignition methods, introduces the structural features of plasma ignition devices at Jinghai Power Plant, and discusses the working principles, combustion mechanisms, and control logic methods of the system and its application in power plants.
The 1# and 2# boilers of Guangdong Yuedian Jinghai Power Generation Co., Ltd. are 600MW supercritical parameters transformer direct current boilers produced by Dongfang Boiler (Group) Co., Ltd., and use the front and back wall hedging arrangement, and the front and back walls are each burned with three layers of coal. Device. The medium-speed mill positive-pressure direct-blown cold primary air-milling system is used, and each furnace is equipped with 6 medium-speed coal mills. In recent years, with the world’s energy shortages and rising crude oil prices, fuel costs for thermal power generation have become higher.
In order to save fuel during the start-up and commissioning phases and to support the combustion-supporting oil during the peaking phase, the DLZ-200 plasma ignition device manufactured by Yantai Longyuan Power Technology Co., Ltd. was selected according to the actual conditions of the 1# and 2# boilers. The six burners were converted to plasma pulverized coal burners. The ignition and stable combustion characteristics of the modified burners are economical, environmentally friendly, efficient, and simple compared to traditional fuels.
1 Plasma Generator Working Principle
1.1 Plasma Ignition Mechanism
The DLZ-200 plasma ignition device uses a DC current to contact the arc at a medium pressure of 0.4 kPa, and obtains a stable power of a DC air plasma under a strong magnetic field. The plasma forms a T> in the primary combustion tube of the burner. In the highly localized high-temperature region with a gradient of 5000K, the pulverized coal particles are exposed to high temperatures through the plasma “fire coreâ€, rapidly releasing volatiles, and pulverized coal particles are broken up and crushed to rapidly burn. In addition, the plasma contains a large amount of chemically active substances. Particles, such as atoms, radicals, ions, and electrons, can accelerate the thermochemical conversion and promote complete combustion of the fuel.
1.2 Plasma Generator Working Principle
The generator is a magnetically stable air carrier plasma generator, which is composed of a coil, a cathode, and an anode as shown in FIG. The cathode material is made of high conductivity metal material or non-metal material. The anodes are made of high conductivity, high thermal conductivity and anti-oxidation metal materials. They are all water-cooled to withstand high temperature arc shocks. The coil has a DC voltage breakdown resistance of 2000V at a high temperature of 250°C. The power supply adopts full-wave rectification and constant current performance.
The ignition principle is: first set the output current, when the cathode 4 advances with the anode 1 contact, the entire system has the ability to resist short-circuit and the current is constant, when the cathode slowly leaves the anode, the arc in the magnetic force of the coil pull out Outside the nozzle. The air with a certain pressure is ionized into a high-temperature plasma under the action of an arc, and its energy density is as high as 105 to 106 W/cm2, which creates favorable conditions for ignition of different types of coal.
Application of Plasma Ignition Technology in Power Plants
Figure 1 plasma generator operating principle
1.3 combustion mechanism
According to the principle that the high temperature plasma finite energy cannot match the infinite coal powder volume and wind speed, a multi-stage burner is designed. Applying the principle of multi-stage amplification, the concentration of the airborne powder and the air flow rate of the system are in a working condition that is very favorable to the ignition, thereby completing a continuous and stable ignition and combustion process.
Using this principle and design method, the output of a single burner can be extended from 2t/h to 10t/h. The plasma film cooling technology of the burner design of the plasma ignition device avoids the adherent flow and hanging of the coal powder, and at the same time solves the burning problem of the burner.
At the same time, the principle of “dense point concentration†is adopted, and a ring-like dense-burning burner applies a thin powder flow to the wall and the heavy powder is mixed into the main ignition burner to burn. The result of this is to both facilitate the ignition of the mixing section and cool the walls of the mixing section. Multi-stage ignition can also be used if the flow conditions are extremely large.
2 Composition of Plasma Ignition System
2.1 Plasma Electric System
The plasma generator electrical system is used to generate a DC power supply device that maintains plasma arc stability. The basic principle is to turn three-phase AC power into a stable DC power supply through a three-phase fully-controlled bridge-type thyristor rectifier circuit. It is composed of two parts: isolation transformer and rectifier cabinet. There are mainly three-phase full-controlled rectifier bridge composed of six groups of high-power thyristors in the rectifier cabinet, and a stable DC power supply high-power DC governor 6RA70 and control PLC.
2.2 Plasma Igniter Maintenance System
In order to protect the plasma igniter itself, the closed cooling water supply main pipe draws water to the igniter for cooling water via a pipeline booster pump and returns the water to the closed water back to the jellyfish pipe. The carrier air of the plasma system is supplied by a high pressure centrifugal fan. In order to achieve a cold and oil-free start of the boiler, a steam heater is installed in the hot air inlet of the coal mill inlet. When the boiler is cold start, steam is used to heat the inlet air temperature of the coal mill to the required temperature for milling, so that the coal mill is equipped with Start conditions and grind qualified coal powder.
3 Control System Structure and Control Implementation
3.1 Control System Network Structure and Control Implementation
The control system of the plasma ignition and stable combustion system is responsible for the control of various equipment inside the plasma system. The S7-200 CPU224 programmable controller in the rectifier cabinet uses the USS protocol to use the free port communication mode programming to exchange data between the communication port PORT0 on the CPU 224 and the communication port X172 on the 6RA70 so as to complete the operation control of the main circuit and each The reading and condition judgment of the class status information realize the control of the DC power supply.
Electrode control signals and signals such as compressed air pressure and cooling water pressure necessary for ignition are directly connected to the CPU's 224 inherent digital input and output, and the internal logic of the CPU 224 is used to realize the automatic control of the ignition device.
CPU224 programmable controller and DCS connection using hard-wired connection, through its I / O expansion module, using the standard 4 ~ 20mA and passive contact signal directly to the DCS I / O module, this method is safe Reliable, only need to increase DCS I/O module and corresponding control module.
Other important signals such as MFT, mill trip, plasma arc cut, etc. are connected directly to DCS with hard wiring, so that the control of the plasma ignition device can be incorporated into the DCS system to complete the signal acquisition and control of the plasma ignition control system of the DCS system. The control operation of the plasma ignition device is integrated into the DCS operator control screen, which facilitates the monitoring operation of the operating personnel and realizes the remote control of the plasma ignition device.
3.2 Realization of Plasma Ignition Control Logic in DCS System
Plasma ignition is an important stage in the ignition of the boiler, so the control logic of the plasma ignition combines the ignition control of the entire boiler, especially the control of the boiler fuel and the FSSS system. In order not to affect the normal control logic of the FSSS system, a normal mode and a plasma ignition mode are set for the coal mill that has newly added a plasma ignition system.
In the normal mode, the pulverizing system maintains the original control logic unchanged. In the plasma mode, the start permission conditions and the grinding protection of the mill have been modified accordingly: (1) One of the allowable conditions for the original grinding start is “coal ignition permissionâ€. Change to "coal ignition allowed" or "plasma igniter arc success and furnace ignition allowed" to meet either. (2) One of the original grinding start permission conditions "Ignition energy is satisfied" is changed to "Plasma arc success". (3) One of the original grinding protection conditions "lost the fire detection tripping" Now change to "lost fire detection tripping" or "plasma mode energy shortage skipping" to meet the requirements for jumping.
4 Application
The plasma ignition system has the characteristics of simple debugging, convenient operation, safe use, reliable operation, high efficiency, and low pollution. Programmable controller and DC drive device can well complete the plasma ignition system's automatic control tasks, and through the DCS system can realize centralized control of each plasma burner centralized control; both software and hardware are modular structure, convenient The installation, commissioning and maintenance of engineering and technical personnel ensure the smooth investment of the plasma ignition system.
Jinghai Power Plant #1 and #2 units used the plasma ignition technology to ignite and stabilize the combustion during the steam flushing, the whole group start-up and the normal operation of the unit, and did not use a drop of auxiliary fuel, which greatly shortened the start-up of the supercritical boiler. At the time, a single unit saved about 20 million yuan, which made a huge contribution to energy conservation and emission reduction.
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