Rand Waters Installs Chlorine and Ammonia Dosing Equipment

Gas dosing upgrades and expansion allow South Africa’s largest water supply utility to continue

Challenge

Klomac, the Southern African agent for Wallace & Tiernan® products, has successfully completed the supply and installation of chlorine and ammonia dosing equipment at Rand Water’s Mapleton Pumping Station as part of that station’s upgrading and expansion programme. The Wallace and Tiernan equipment includes four Model V2000™ automatic chlorinators rated at 40 kg/h each, four ammonium hydroxide dosing pumps and GMS chlorine gas leak detection equipment.

Rand Water is South Africa’s largest water supply utility, supplying an average of more than 3000 Ml/day of potable water to some 10 million people over an area of 18000 square kilometres. Most of this water is consumed in the Johannesburg industrial and urban complex which, uniquely, is not situated near the source of the water but is located some 70 km away at an altitude 375 m above that of the Vaal Dam from which the water comes. To meet these requirements, water is pumped from primary and secondary pumping stations through a network of high pressure, large diameter pipelines. This has required the development of some unique engineering solutions over the years of which Rand Water can be justly proud.

Solution

Water is treated at both the primary and booster pump stations. The treatment process includes chlorination at the primary pump stations followed by further chlorination and ammoniation at the booster pump stations. It is here that Wallace & Tiernan chlorinators and dosing pumps have been used at several pumping stations over the years, the latest of which is the Mapleton booster pump station. In order to meet their stringent water quality standards, Rand Water required the plants to be fully automated, with chlorine and ammonia dosing rates being automatically controlled from water flow and chlorine residual input signals. Klomac’s scope of supply thus included PLC equipment with a local human machine interface in the chlorine building and with a SCADA system in the main pump building control room to allow dosing system monitoring and control to be done from either location.

Because of the hazardous nature of chlorine, the Rand Water specification called for the supply of a safety shut-off system whereby the gas supply valve on each 1 ton drum must be automatically closed in the event of a high level chlorine leak. This was achieved by installing a geared air motor at each drum station, connected to the drum valve by a telescopic shaft. Wallace & Tiernan® GMS leak detectors were supplied for chlorine leak detection and, in the event of a high level leak, the GMS relay triggers the air supply to each motor via the PLC to automatically shut off the gas supply at each drum station.

The Mapleton Pumping Station expansion consists of a new 600 Ml/ day pipeline and booster pumps to complement the existing 600 Ml/day line. The new chemical dosing plant caters for the dosing of chlorine and ammonia into both these lines. To ensure continuity of dosing, the Rand Water specification required the supply of duty/standby chlorinators and dosing pumps for each of these lines. Chlorine gas is supplied from 2 banks of 10 x 1 ton chlorine drums with a change-over facility to automatically change the gas supply from an empty to a full bank. Ammonia is dosed in the form of a 25% ammonium hydroxide solution which is stored in 4 x 14000 l tanks. These also have change-over facilities to automatically change the chemical supply from an empty to a full tank.

 

Results

Rand Water is committed to the ongoing development of it’s water supply network in order to provide it’s consumer base with a reliable, safe and healthy source of water. Klomac, with it’s range of Wallace & Tiernan products, is proud to be a participant in this process.