Case Study for Level Sensor selection

Application

Coal fired power station – Holding tanks for boiler water feed treatment plant.

Customer

AES Drax Power station

Challenge

Fluid control systems are a key part of many industrial processes, large and small industry alike require access to a comprehensive range of fluid control products including flow and level controllers, sensors, switches and indicators.

Water quality is critical in any large scale steam generation system. The water used to feed the boilers must be free of impurities, this helps to minimise the chance of corrosion, scaling and sludge formation. The AES Drax power station is the largest coal fired power station in western Europe – water is drawn from a local bore hole and is subject to a three stage de-ionisation process to dissolve minerals. This process requires regular regeneration using concentrated solutions of sulphuric acid and caustic soda.

The 98% acid and 47% caustic solutions are held in five bulk storage tanks: four hold approximately 50t while can the other hold 148t of acid. Replenishment of the tanks comes from road tankers which hold a 25t load.

The tanks must be monitored constantly to ensure that they are never completely empty – if sludge from the bottom of the tanks reached the ion-exchange beds then a costly de-contamination process would need to be performed. When the tanks are re-filled they must be able to take a complete 25t load as spillage is not acceptable and part loads are uneconomical.

Considerations

The choice of level sensor must be suitable for extreme corrosive environments. The sensor must measure fluid level and calculate volumes. The installation should be be quick, efficient and economical and with minimal ongoing maintenance cost.

The Solution

The level of acid and caustic solutions must be monitored to ensure correct level measurement at all times, due to the nature of the liquid the level sensor has to be corrosive resistant. Using Atex approved ultra sonic sensors mounted on each tank provides a low cost installation with low maintenance and reduced downtime. Ultra sonic sensors use echo detection, pulses from the sensor bounce off the liquid solutions and the time of reflection is used to calculate the liquid level in each tank. The sensors will ensure that the tanks are capable of taking a 25t load without the worry of over spill, and also monitor the level continuously to ensure they are never completely empty, thus removing the risk of costly de-contamination processes.

613 2210 Ultra sonic level transmitters were purchased to provide a solution for this application

This is a good example of application, problem, solution, the ultra sonic level transmitters, ensure the tanks are never completely empty and have the capacity to take a 25t load. They are Atex approved and suitable for use in extreme environments. Other benefits include, low cost of installation and commissioning, low maintenance costs and reduced downtime.