FEATURE WATER MONITORING RADAR DELIVERS BIG WATER SAVINGS
Waste-to-energy plant Cory Riverside Energy recently selected a contactless liquid level radar from VEGA Controls to control water levels in its ash quenching system
The water used in the ash quenching process needs a constant level to be maintained through replenishment of either recycled or fresh mains supplies. This is monitored in a small balance tank off the main chamber. The optimum solution is of course to
C
ory Riverside Energy is a waste-to- energy plant to the east of London.
With a population approaching nine million people, London has an incredible appetite for energy. Keeping the lights on in the face of increasing demand is one of the major challenges facing the city today. It produces around 22 million tonnes of waste every year. Or, to put it another way, enough to fill the largest skyscraper at Canary Wharf every eight days. Cory Riverside Energy utilise this waste to help provide London with a safe, secure, affordable and sustainable energy supply, which also makes great environmental sense. The site at Belvedere uses these materials, that would otherwise have gone to landfill, as a feedstock to generate electricity. As one of the largest operations of its kind in the UK, this facility generates around 525,000MWh of electricity each year from processing 750,000 tonnes of waste. Additionally, they use the River Thames as a ‘green highway’ to move the waste from the centre of the city to the facility on their fleet of tugs and barges, removing around 100,000 truck movements a year off the UK capital’s congested roads. Of course creating energy from waste creates a hot ash residue that needs cooling quickly. This is achieved by
34 APRIL 2018 | INSTRUMENTATION
The quench water balance tank (cover removed) shows the typical build up and residue, which coats all surfaces
quenching it in water via an ‘ash expeller’ system before stockpiling for disposal. Each system sits under one of the three main combustion chambers. With moving grates, the waste ash can drop into a water filled hopper below. The quenched ash is then scraped out by a ram and removed to the rear side via a conveyor into a stockpile chamber for loading out and disposal/recycling.
use recycled and recovered plant water, which reduces costs and environmental impact. However, a simple level probe to control the water will not do the job. The water contains many contaminants from the ash, readily adhering and building up on any surface and the ‘ideal water level’ control band is only over a few millimeters. The temperature runs about 50°C, which produces a lot of condensation and sublimation onto the sensor. The total measuring range is only around 15cm, there can also be regular foaming on the surface, carrying ash residue and leaving behind deposits. The site engineer added extra process information: “The ram movement in the ash expeller also plays a part. This ram is used to keep the ash moving through the expeller. One of the main issues we have is that the ram movement causes the water level to fluctuate rapidly and it encourages foaming, the old level device often couldn’t keep up or lost the signal and caused it to overflow.” If the probe is not reading or working correctly, the automatic safe ‘default’ is to keep fresh water continuously running into the ash expeller system.
Diagram of an ash quenching system
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