Dosing pumps critical for process plant

When a dissolved-air filtration plant was selected as one of several measures to update Essex and Suffolk Water's Lound water treatment works, PCM Pumps was called in to provide new chemical dosing equipment.

Essex and Suffolk Water has been updating its Lound water treatment works following the introduction of EC legislation designed to raise potable water quality standards.

The improvements were necessary to cut the risk of formation of trihalomenthanes (THM), which are formed during the treatment process when chlorine mixes with naturally occurring organic material in the water.

To solve the problem, it was decided that a Dissolved Air Filtration (DAF) plant should be installed because of its proven effectiveness where algae-laden, low turbidity and highly coloured water conditions prevail.

Earth Tech Engineering, which was the process designer for the project, called in Corby-based PCM Pumps to supply and install new chemical dosing equipment, which would be critical to the operation of the new process.

PCM, working in conjunction with Earth Tech, engineered and installed complete ferric chloride, caustic soda and sulphuric acid storage and dosing systems for the newly constructed DAF building on the Lound site. Each of the PCM-supplied systems included two chemical storage tanks and a dosing skid incorporating two Alldos KM Series piston diaphragm dosing pumps in a duty/standby arrangement.

The pumps offer low-maintenance leak-free operation, because of the hydraulically actuated diaphragm principle, which also has an internal pressure relief valve as a means of pump overpressure protection.

The dosing skids were pre-wired and fully tested at the PCM factory before delivery to site. Each skid is equipped with clear PVC splash screens for operator protection, enabling maintenance to one pump and associated dose line components, while the other chemical dose line remains operational without compromising the integrity of operator protection, thereby providing a true duty/standby dosing system.

Due to their size, the six chemical storage tanks, which range from 15cu m to 26cu m, were positioned in the new building before the roof was installed. PCM then installed the factory-built chemical dosing skid units and completed the installation of all interconnecting pipework, which was fabricated on site by coded welders. Each system also included the installation of access ladders and platforms, mezzanine floors, chemical splash protection screening, and dual contained tank fill lines.

Road tankers deliver chemicals to the site, where there are three dedicated intake loading points, one for each of the three storage areas. Ferric chloride at a concentration of 40% is pumped to two vertical cylindrical GRP storage tanks to be used as a flocculent while 47% sodium hydroxide (caustic soda) used for pH control is transferred to two carbon steel storage vessels supported on steel cradles.

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