Rotary valves handle limestone demands

Edited by the Engineeringtalk editorial team Apr 28, 2008

HDG rotary valves are frequently used to provide high levels of discharge control for fine powders which are subject to flooding.

Seeking to cut product waste and improve efficiency, Tarmac's Ballidon site chose Rota Val heavy-duty rotary valves to handle limestone powders and granules.

Limestone, or Calcium Carbonate, is used extensively in foodstuffs such as baking and brewing, dairy products and even digestion aids and in fertilisers, glues, pesticides, toothpaste, pharmaceuticals and sugar refining.

Other uses include construction and building materials such as cement and asphalt, agriculture, abrasives, adhesives, cosmetics, glass manufacture, drinking water treatment, floor covering, carpets, paper, paints, rubber and shower trays.

Tarmac's Ballidon site includes three limestone quarries producing 1.25 million tons of stone per year.

On average, 40% of this output goes to the industrial market, with the remainder being used by the construction industry.

A new processing plant has been built on the site, where limestone is extracted, crushed and then screened into fine powders and small granules.

The new plant has replaced four smaller, less efficient plants.

Materials are blown from drying ovens into seven new silos each holding 250 tons, using Rota Val rotary valves and Rota Val plug diverter valves to control and direct the flow.

From the silos, powder and granules are discharged on to enclosed belt conveyors and then into road tankers through two loading stations.

Originally built with two rotary valves to permit controlled discharge from the silos on to the conveyors, Tarmac decided to upgrade their facilities on the Ballidon site and asked Rota Val to recommend suitable valves for the project.

After detailed consultation about Tarmac's needs, Rota Val recommended five new HDG rotary valves.

These valves are frequently used to provide high levels of discharge control for fine powders which are subject to flooding under certain circumstances, especially when used in applications with anti-bridging systems.

Steve Bottomley, Tarmac's Ballidon Site Construction Manager, said "Tarmac has a very strict and active policy on environmental impact and expends considerable efforts to ensure our activities are acceptable to local people".

"The crushed limestone powder does not represent any danger, but obviously we place great importance on keeping our products where they belong - inside the plant and under control".

"The two silos fitted with Rota Val rotary valves gave no trouble and loaded the conveyor correctly under perfect control".

"We had already standardised on other Rota Val valves in the plant and have about 30 rotary valves from 250 up to 450mm, plus 18 plug diverter valves, so it was no surprise that we called in the company to make recommendations for further plant improvements".

Rota Val suggested the installation of five new HD450 rotary valves to provide the required degree of flow control.

The HD heavy-duty valves are available in 12 standard valve sizes ranging from 50 to 750mm to give capacities up 250m3/h.

Round, rectangular or square-flange options can be provided to meet a wide range of customer application requirements.

The HD series valves are designed and constructed to ensure high sealing efficiency with maximum durability.

They are the "design hub" around which all Rota Val's rotary valves are based, a feature which results in competitive prices without compromising performance.

The valves may be manufactured as standard in cast iron, SG iron, aluminium and stainless steel, with alternative materials such as Monel, Inconel, Titanium and Hastelloy also available.

For the Tarmac application, valves were specified to operate effectively at up to 85C when discharging fluidised powders.

The HD series of valves may be supplied for temperature ranges from -100 to +900C.

Full ATEX certification for explosion and flame containment for S2 dusts may be supplied to order.