Flow Instrumentation Solutions for Thermal Power Plants
Application Description
A power plant is divided into three major systems according to the energy conversion process: the combustion system (coal handling, coal pulverizing, boiler and combustion, air and flue gas, ash and slag handling), the thermal system (boiler, steam turbine, condenser, feedwater pump, deaerator, high- and low-pressure heaters) and the power generation system (turbine generator, auxiliary power system, step-up substation). A flue gas desulfurization (FGD) system is added to meet environmental emission requirements. Energy is converted step by step throughout the process: the chemical energy of the fuel is converted into heat in the boiler, the heat is converted into mechanical energy by the steam turbine, and the generator finally converts the mechanical energy into electrical energy.
Application Focus
1. Air flow measurement: flue gas and air ducts have very large cross-sections (equivalent diameter usually above 5 m) and are mostly rectangular, with asymmetric flow distribution and severely limited straight pipe runs. Rotary air preheaters have an ash leakage rate of about 10%, which easily clogs throttling-type sensors. In large-diameter ducts the differential pressure is low at small flow rates, which reduces measurement accuracy.
2. Main steam network, desuperheating water and main feedwater: operating pressure reaches 20–30 MPa at 250–500 °C; safety and reliability are the primary criteria for valve and instrument selection.
3. Low-pressure steam, compressed air, fuel gas and condensate: pressure and temperature are moderate, but stable and accurate measurement and control are required, so selection must be based on the properties of the medium.
4. Water treatment plant: the media are mainly ordinary water and chemical solutions (most of which are conductive). Particular attention must be paid to low-conductivity demineralized water and to corrosion caused by acid and alkaline media.
5. FGD system: sulfur corrosion, ammonia/alkali corrosion and crystallization of spent lye are common concerns. In addition, lime slurry with a solids content of about 50% causes abrasion, and solid particles striking the electrodes introduce noise interference.
Solution Overview
1. Air Flow Measurement
A matrix-type air flow measurement device is used. Multi-point matrix sensors (back-supported and Venturi types) are arranged across the whole duct cross-section to calculate the average flow velocity, giving results much closer to the true velocity than single-point or single-line measurement. Enlarged open pressure taps or built-in ash removal devices relieve clogging, and the smooth inner wall resists ash build-up. The device suits primary air, secondary air and flue gas flow measurement.
2. Main Steam, Desuperheating Water and Main Feedwater
A nozzle flowmeter from the standard throttling devices is selected. The bell-mouth self-guiding nozzle resists deformation under the long-term impact of high-temperature, high-pressure, high-velocity media, maintaining measurement accuracy and stability over time. Welded or flanged mounting is selected according to the operating temperature and pressure, and the material and heat treatment grades meet the process requirements.
3. Low-Pressure Steam, Compressed Air, Fuel Gas and Condensate
A standard orifice or multi-hole orifice flowmeter is selected. Integrating flow conditioning with multi-hole balanced throttling, it minimizes vortex effects and recovers pressure quickly, shortening the required straight pipe run to 1D while reducing the risk of clogging by dirty media.
4. Water Treatment Plant
Electromagnetic flowmeters (MFC/MFES/MFL series) are selected. Based on Faraday's law of electromagnetic induction, they are unaffected by fluctuations in density, viscosity, temperature, pressure or conductivity. With no obstruction inside the pipe, there is no pressure loss and the straight pipe requirement is minimal. Accuracy reaches Class 0.2, sizes cover DN2.5–DN2400, and a wide choice of liners and electrodes is available.
5. FGD System
For sulfur corrosion, ammonia/alkali corrosion and media crystallization, electromagnetic flowmeters are preferred. With a full-bore, non-clogging design and a smooth inner wall, crystallization does not readily adhere or accumulate. A PTFE liner provides corrosion resistance, and the electrodes are selected according to the aggressiveness of the acid or alkaline medium (316L, titanium, Hastelloy HC, tantalum). Accuracy is Class 0.2 and the minimum measurable velocity is 0.2 m/s, allowing small-flow ammonia spray measurement. For even smaller spray flows, a lined, ammonia-resistant metal-tube rotameter (RFC series) is available. To suppress the noise generated when solid particles strike the electrodes in lime slurry with about 50% solids, four core technologies ensure measurement stability: multi-frequency excitation (low frequency for a stable zero, high frequency of 25–100 Hz for noise reduction), DSP digital filtering, high-speed sampling and comprehensive data analysis (rejecting slurry noise spikes).
Customer Value
The solution is precisely tailored to the combustion, thermal, power generation and FGD processes of thermal power plants. For demanding conditions such as large-cross-section dust-laden air and flue gas, high-temperature and high-pressure steam and water, acid and alkaline water treatment media, and highly corrosive high-solids slurry, it applies proven measurement and control technologies and highly reliable products. It effectively solves the industry pain points of conventional flow measurement – ash clogging and drift, deformation under high pressure, corrosive interference and insufficient stability – delivering accurate, stable flow measurement in all operating conditions and providing reliable data support for combustion optimization, stable steam-water system operation and environmental compliance management.
Related Products
1. DFF Series Matrix Air Flow Measurement Device: for primary air, secondary air, flue gas and mill inlet/outlet air flow measurement.
2. DF Series Differential Pressure Flowmeters: including standard orifice, multi-hole balanced orifice, nozzle, wedge, V-cone, Venturi, segmental orifice, averaging pitot tube and rectangular flowmeter, for main steam, desuperheating water, saturated water, main feedwater, condensate and low-pressure steam measurement.
3. VF Series Vortex Flowmeter: for low-pressure steam and compressed air measurement.
4. MF Series Electromagnetic Flowmeter: for water treatment plant feedwater and demineralized water, FGD slurry, circulating water and make-up water measurement.
5. RFC Series Metal-Tube Rotameter: for low-flow FGD ammonia spray, chemical dosing and low-flow condensate measurement.
