An Endress+Hauser client in the power industry presented a challenge – measuring the flow of sulphur trioxide (SO3) into a plant. The sulphur has to remain in a liquid form at 135°C to prevent it from hardening, blocking the feed-tubes and ultimately obstructing the process.
Coal has been the mainstay of electricity generation and therefore plays an important role. The coal is finely ground before being mixed with warm air and burned in huge boilers. The generated steam passes through a turbine making it rotate to generate electricity, which is then fed into the national grid. Waste produced in the form of pulverised fuel ash is removed from the boiler gases by electrostatic precipitators before the gases pass up the chimneys. http://bit.ly/246Ll7e
In the order to reduce harmful emissions, SO3 is injected into the precipitation inlet flow to change the resistivity of the existing particles and enhance the performance of the electrostatic precipitators. Too much SO3 will create a higher acid dewpoint and increased probability of cold-end corrosion and acid emission. If there is too little, the electrostatic precipitator’s performance will suffer and release increased particulate emissions to the atmosphere.
Measuring the flow of SO3 plant is therefore integral to the process, as is retaining the optimum temperature. The sulphur flows at extremely high temperatures and the pipelines need to be trace-heated to maintain its fluid properties.
The Promass 83F Coriolis flowmeter is more than up to the challenge with a process temperature capability of 350°C, performing at pressures up to 350 bar. In order for the application to work effectively, the sulphur has to remain in a liquid form at 135°C, however, if the temperature exceeds 150°C, the viscosity rises and the sulphur does not flow easily. Maintaining the optimum temperature is therefore vital to achieving maximum effectiveness of the process. Heating jackets were recommended as they can be placed over the Promass meter in order to maintain the optimum temperature for sulphur flow.
The process also demanded high accuracy at very low flow rates. Due to Promass 83F zero point accuracy, this was no problem. What’s more, in providing a short-tube Promass 83F, the client can clean the meter in the event of a problem. This was of great benefit as the previous flowmeters had bent tubes, preventing them from cleaning away build-up. The short-tube design of the sensor is instrumental in keeping the plant operation and maintenance costs to a minimum as there is no longer the necessity to buy a replacement meter every time there is a problem. The effect on plant operation has been significant: Promass 83F has improved performance and reduced maintenance costs.
Feedback from the end-user
The client stated that the sensor design of Promass 83F did not block like other designs, and the flow of liquid sulphur to the process has not been impeded either. The heating jackets were designed to be a perfect fit around the flowmeters, making heat transfer excellent. The system is so reliable that downtime has virtually been eliminated and emissions are also controlled as the Promass 83F is part of the SO3 injection system. They were more than happy to recommend Promass 83F for other installations of a similar design.
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