Erwin Weber explains how a large salt producer simplified the removal of corrosive sludge with a mobile rotary lobe pump
Salt is still one of the most valuable commodities, but there is a major problem involved in its production: during rock salt production, sodium chloride quickly accumulates in the collecting tanks, along with sand and other degrading materials. It also encourages metal corrosion in the production plants. As a result, one of the largest salt producers in the world continually needed to bring in a cleaning company with vacuum tankers to spend several weeks removing sludge from the tanks.
A Tornado rotary lobe pump from Netzsch has since been used to reduce the effort and costs involved. The self-priming equipment reduces the emptying time of the tanks from two weeks to around five days due to its continuous output.
About 100m³ of pure solids are deposited every year in each of the 10 storage tanks, which each hold 20,000m³ of salt. The mixture comprises sodium chloride, sand, which forms during the mining process, anhydrite and gypsum and its high solid content makes it difficult to clean the tanks. Vacuum tankers had to be brought in once a year to suck the residues out of the tanks using negative pressure created by a vacuum pump.
However, the search for an alternative proved difficult. Because of the corrosiveness of sodium chloride in contact with metal, a number of pump manufacturers only offered models made of special materials, which were resistant but expensive. In the end, this led to the decision to use a system where the protection of the pump body relies on a design that is particularly easy to operate, rather than on special materials. Corrosion clusters are only formed in standing water. It is therefore crucial that the pump can be cleaned quickly and easily when it is out of use for a longer time. Netzsch’s Tornado rotary lobe pump is specially designed to meet this requirement: to clean the system, the user just needs to remove the housing cover and they can then rinse the inside from flange to flange with water. This completely removes the salt, so that the key elements of the device are not attacked by the aggressive medium. In addition, the pump and timing gear areas are physically separated from one another, which means that the corrosive medium cannot get into the gearbox and damage it.
Impressive pumping capacities
The self-priming rotary lobe pump achieves pumping capacities of up to 1,000m³/h with a maximum 6 bar pressure and a suction lift of up to 8 mWS. It is even possible to convey mixtures with solids up to a grain size of 70mm. Thanks to these features, the salt mash can also be sucked out with hardly any thinning, and during the process the pumping capacity lies constantly between 10 and 25m³/h. This means it only took five days to empty the tanks in the first test run, with the result that the use of the Torndao pump had already paid for itself. Overall, costs for the cleaning process are reduced by 50 to 80% by using the rotary lobe pump.
Erwin Weber is with Netzsch
