PLANT MANAGEMENT
using traditional methods of controlling the fl ow, such as throttling (forcing a bottleneck) wastes a lot of energy. Improved equipment or control system changes could deliver between 30% and 50% in energy savings. Modern drive and motor technologies
off er far more effi cient control and monitoring of pump operations.
Drives make the diff erence in chemical plants
DRIVING DOWN COSTS
reliability and profi tability. Chemical plants can have hundreds of pumping systems, and the motors and drives running these consume enormous amounts of electricity. Pumps account for 10% of the world’s total electrical energy consumption. Pump systems are responsible for around 20% of industrial
U 28
www.engineerlive.com
pgrading the motors and drives in chemical plants could signifi cantly reduce energy use in pumping systems while improving safety,
Modernised drives and motors make substantial energy savings for chemical plants, explains Petteri Hyytiäinen
electricity use with the chemicals sector being one of the biggest pump users. However, studies show that pumping
effi ciency in manufacturing and processing plants can be less than 40%. Process intensive sectors, such as the chemical industry, have a high base production fl ow that is generally managed by pumps – usually centrifugal pumps – operating at constant speed and there is always a need to control the process fl ow over time. Operating pumps at a constant speed and
VARIABLE SPEEDS FOR EFFICIENCY Traditionally, controlling fl uid fl ow rates in chemical plant pumping systems was a bit like driving a car with the accelerator pedal pushed fl at on the fl oor, while simultaneously using the brake pedal to vary the speed. A control valve is put on the outlet side of a centrifugal pump, which is powered by an electrical direct-on-line (DOL) motor running at full speed and using the valve to throttle or choke the liquid to achieve the desired fl ow. To be on the safe side, pumps and DOL motors selected are often oversized in the engineering phase, but in practice the maximum conceivable fl ow rates are rarely reached. Simply put, the fl uid comes out of an oversized pump run by an oversized motor working at full speed and hits a partially closed fl ow valve. T e fl ow rate is controlled but in a very crude manner, causing severe wear and tear on the system components and wasting energy. T e excess mechanical energy that is expended in the piping system often shows up as unwanted side eff ects – such as vibration, heat and noise. Over time, these negative factors can weaken the integrity of the pumps, pipes, valves, joints and instrumentation, leading to expensive downtime and reduced process reliability. Pumping systems in industrial processes are frequently reported to have the highest overall maintenance costs compared to other motor-driven systems. In addition, pumps and valves are very common sources of process leaks, which can be both costly and dangerous.
A far better alternative for adjusting
fl ow rates and pumping capacity is to use a variable speed drive (VSD) on the motor. Flow control can be more precise and energy savings very large due to the ‘Cube Law’, which describes the relationship between fl ow output and energy input for centrifugal pumps or fans. For instance, a 20% drop in motor speed can reduce its energy consumption by 50%. Recently, an ABB test compared data
from a centrifugal pump with throttle valve control driven by a 37kW direct-on- line motor run at constant speed with an
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 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68
