Thermal Flow Meter
By Jack Burke30 January 2017
Fluid Components International has released the ST100, an air/gas thermal flow meter designed to enhance close ratio control of natural gas and air feeds in combined cycle gas turbines.
Combined cycle power plants operate with both natural gas and steam turbines to produce up to 50% more electricity from the same fuel as traditional fossil fuel power plants, the company said. The steam turbine is driven by the waste exhaust gases from the natural gas turbine. To operate safely, the gas turbine must receive an exact, controlled air-to-fuel ratio mixture. Such control is achieved by closely monitoring the ratio of the air (oxygen) and the fuel, which is typically natural gas. This ratio is also known as stoichiometric mixture. The company said both the air feed and the flow rate of natural gas must be measured accurately, and even more importantly, repeatably accurate and reliably. The flow meter also must operate over a wide turndown range for safe startups and restarts of the gas turbines.
Installing a direct mass device such as FCI’s ST100 in the process control loop offers a number of advantages, the company said. It allows the operator to achieve a direct ratio of control between the natural gas, the air and waste gas fuels without any corrections for pressure, temperature or density, which requires extra components and possibly extra offsets and failures, the company said.
FCI’s thermal flow meters with their direct mass flow sensors are installed at dozens of CCGT power plants throughout the world. They measure the mass flow rates of both natural gas and air in line sizes from small 1-in. gas pipes to 2000 x 2000 mm air inlet ducts.