Chemical dosing in process plant often needs corrosion resistant components
Chemical dosing usually needs great precision, extreme reliability and the components with the ability to withstand hostile environments.
For example, there’s a lot of chemical dosing going on in wastewater processing, either as part of the treatment or as a means of removing existing unwanted components of the process fluid. One of the major problems in UK urban wastewater treatment is the high level of phosphates in the untreated wastewater and, while a significant number of treatment works have phosphorus discharge consents at varying levels, many don’t. Overall, the problem of phosphate control and of staying within phosphorus discharge consents is growing.
Controlling phosphate levels is sometimes achieved by naturally occurring biological or chemical precipitation, but in cases where phosphate monitoring systems show that leaving things to nature just isn’t enough, minutely controlled chemical dosing of iron salts, such as ferric chloride or ferrous sulphate, or a combination of iron salts and aluminium salts usually brings phosphate levels back within limits. The problem is that continuous chemical dosing is expensive and plays havoc with wastewater treatment budgets – but there is also a pH control issue, since variable pH can have a direct effect upon the efficiency of the process and upon the acceptability to planners of the outflow from the plant.
Potential damage to the dosing system
The pH level can also have unfortunate effects when the process fluid comes into contact with, or close proximity to, the dosing system itself, particularly if components of the system are manufactured from materials that will corrode in the presence of wastewater with very high or very low pH. Fortunately, an Australian company, Kelco, whose products are distributed in the UK by Pressure Vacuum Level Ltd, based in Crowborough, Sussex, has come up with a remarkable range of products in which all the wetted parts are made of plastics rather than metals, and which are exceptionally suitable for resolving the corrosion problems that are experienced by instrumentation in wastewater plants.
As an example, the Kelco CR20 Microflow switch is ideal for monitoring precise chemical dosing flows for applications in wastewater processing (you can download a data sheet at http://www.pvl.co.uk/user/datafaxes/CR20.pdf). This microflow switch detects flows, pulsed or continuous, of less that 5ml per minute and can handle continuous flows of up to 4L per minute and up to 16Bar (260 psi) pressure. All wetted parts are made of uPVC, and a PVDF model with Viton seals is also available, so corrosion is not going to be a problem. The CR20 can be supplied as a normally-on or normally-off device.
Of course, chemical dosing is a feature of many other process industry applications, and a version of the CR20, the CR20-B, can be used in hazardous areas, since it is classified as a simple device, provided that it is isolated by an intrinsically safe zener barrier. You can find at www.pvl.co.uk a huge range of products for the process and chemical industries and can discuss your needs and applications with PVL’s team of qualified engineers simply by phoning 01892 664499. At www.pvl.co.uk, click on the parameter you need to measure – flow, pressure, temperature etc – and look for the devices that you require.
To talk to the qualified engineering team at PVL about your application and the corrosion problems that it presents, phone +44 (0)1892 664499. Or email firstname.lastname@example.org.