MATERIALS HANDLING
also results in improved process control, improved system reliability, reduced maintenance costs due to reduced wear, and soft starter capability. For this reason, VSD-driven pumps are becoming increasingly common in the mining industry. T e wear of the impeller and volute case
drop the head and effi ciency of the pump, with an increase in the energy consumption as a result. Unnecessary machine downtime can be minimised by: monitoring the condition of the volute case, impeller and other components of a wear-resistant pump; identifying pump defects at an early stage; and by planning preventive maintenance eff ectively.
Smart pump selection When selecting a slurry pump, the most important thing is to classify the type of the pumped liquid or slurry. T e rough selection of whether to use a wear-resistant (WPP design) pump, an ordinary process pump or a heavier design can be made according to the graph below. T e values may vary depending on how
abrasive the particles in the slurry are and how corrosive the liquid is. T e maximum lifetime can be reached by selecting a pump with the biggest impeller diameter (lower running speed) and with the duty point as close as possible to the best effi ciency point (BEP).
of weeks if the design and material selection are not optimised. If only abrasion needs to be considered (non-corrosive liquid), a hard material should be selected. One solution is chromium iron with a hardness of 600 HB. T is material, A532 Class IIIA, contains about 23-30% of chromium to provide high levels of hardness. If the pumped liquid comes out of the pump to the atmospheric side, there is usually corrosion, especially when the liquid contains sulphuric acid. T e material comes off by corrosion on the atmospheric side when holes have been made in the volute case. T is is the reason why holes for example for draining the pump are not accepted in the volute case. Corrosion is a complicated phenomenon and the result of electric and chemical eff ects. Corrosion is commonly divided into the following categories:
● general ● galvanic ● crevice
● pitting ● stress ● abrasion
T e general rule to increase corrosion resistance is to use higher-alloyed stainless steels. Pitting and crevice corrosion resistance in particular can be improved by adding molybdenum and chromium. Duplex stainless steels are also resistant to stress corrosion. Abrasion corrosion typically appears when pumping liquids that contain corrosive solid particles. It also occurs when pumping clean but corrosive liquids without solids when the velocity of the fl ow within the pump is high enough. High velocity occurs in the impeller and volute case when a pump operates at a high rotational speed.
Pump types according to average particle size and specifi c gravity
When corrosion and abrasion take place at the same time in the pump, a metallic material is usually selected. Sulzer off ers a wide range of metallic materials for wear-resistance pump designs, such as duplex, super duplex and austenitic cast steels. Austenitic cast steels such as 654 SMO can manage simultaneous corrosion and abrasion very well due to their tough features. Also, their corrosion resistance is good when chlorides are present in liquids that contain acidic solid particles, for example in metals leaching plants. ●
T ere are many applications where suspended solids can severely damage the pump in a short period of time. T e pump can be lost in a matter
46
www.engineerlive.com
Merja Pärssinen is with Sulzer Pumps Finland.
www.sulzer.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
