Energy conservation and emission reduction are the two main themes of coal-fired power plants. To optimize combustion, it is necessary and important to add pulverized fuel (PF) flowmeters and flow control and balancing devices for boiler combustion, both to ensure combustion efficiency and to meet the requirements of low NOx emission.
Energy conservation and emission reduction are the two main themes of coal-fired power plants. To optimize combustion, it is necessary and important to add the pulverized fuel (PF) flowmeters and flow control and balancing devices for boiler combustion, both to ensure combustion efficiency and to meet the requirements of low NOx emission. Walsn FMVC is a uniquely developed system to provide an optimal solution. This system can
1) Accurately guide the operator to adjust the coal and air flow, by effectively controlling the primary air speed, the coal powder distribution and the burner air-coal ratio and other important parameters, so as to balance the temperature as well as the dynamic in the furnace and optimize the combustion conditions in the furnace, to achieve the purpose of high-efficiency combustion with low NOx emission.
2) Has a positive impact on the safety and efficiency of the desulfurization and denitrification system, especially to prevent ammonia escape and ensure the efficiency of denitrification.
3) Improve the stability of combustion, reduce the fluctuation of the negative pressure of the furnace, and prevent the occurrence of pipeline blocking or other accidents.
4) Timely prevent safety issues with boiler equipment caused by flame deflection: online diagnosis of the balance of coal powder flow rate and the concentration at each burner outlet, to prevent uneven pulverized fuel distribution caused by the furnace slag, thermal load skew, high temperature corrosion, wear, flue gas temperature deviation at the furnace outlet and other issues.
Measurement of the velocity of coal powder
Atom consist of negatively charged electrons and positively charged protons. When two different objects come into contact with each other, an object loses or gains some charge. For coal-powder particles, they can carry charges and induce a minute electrical response on an electrode nearby. In the pulverised fuel flow, coal powders flow through a sensing unit where an array of electrodes is present (see illustration below of signals from three electrodes). The signals on two electrodes will include a certain time delay which can be determined by a cross-correlation signal processing technique. Since the distance between two electrodes is known, the particle velocity can be determined as distance divided by the time delay T1or T2 from the electrodes.
Flow measurement principle
Measurement of the coal powder concentration and mass flow
In the primary PF flow pipe, due to the different permittivity between air and coal powder, when the concentration of coal powder in the pipe changes, the capacitance value between the corresponding electrodes will change. Using this principle, the mass concentration of coal powder can be calculated by measuring the change of the capacitance value between the electrodes of the relative capacitive sensors.
Calculate the mass flow through the cross-section Qm：
Qm=A ρm Vc
Vc: velocity of the powder flow;
A: Cross-sectional area of pipe;
Measurement of the distribution of coal powder fineness
When coal-powder particles collide with the probe rod, transient elastic stress waves are generated. Based on the piezoelectric effect, the acoustic emission sensor collects the vibration on the tiny surface from the sound emission source. The acquired signal is mathematically calculated to obtain the particle size of the collision particles.
Basic Specifications and System composition
• PF flowmeter measures coal powder flow rate, coal powder concentration and coal powder fineness in the PF pipe.
• Flow rate of coal powder can be measured directly
• Measurement accuracy of the coal powder flow rate ：± 2%
• Measurement accuracy of the coal powder concentration：±5%
Measurement data is transmitted via the RS485 Modbus.
• The central control unit can use flexible combinations of industrial PCs and PLCs to meet different needs.
Execution unit：The flow control valve controls the inside area of the primary PF pipe, thus changing and balancing the resistance inside the pipe to achieve the evenness of flow distribution across different PF pipes.
• Two modes of operation, remote and on-site
• Open signal: 4 to 20mA
• Effective angle of output axis: 90 degrees
• Basic error: .5%
• Section effective area of about 50%, eliminate operational safety hazards
• High resistance to wear
• Partial throttle design
FMVC products provide accurate measurement and control for the primary PF pipes：
1) Real-time measurement of the velocity, concentration and fineness of the coal powder in pipelines;
2) Real-time monitoring of the evenness of the coal powder flow distribution in different pipes;
3) Diagnosis and alarm for the flow condition (e.g. blockage);
4) Display of operating trends, flow ratios, trend charts, bar charts, and back up data.
FMVC is able to：
• Maintain the best air/coal ratio in the PF flow for each burner
• Maintain the coal-powder flow balance of the burners
• Ensure even distribution of coal powder
• Monitor the fineness of the coal powder inside the pipeline
• Achieve balanced combustion of boilers