descale pump systems for energy savings

We drive industryProprietary to TMEIC GE

High Pressure Descale Pump

225 Bar Pump Systems

North of 1000 m3/hr

10 MW power consumption



SMS Siemag Standard Fixed Speed System

M P M P M P M P

3x3000 kW3000 rpm

Active

1x3000 kW3000 rpmStandby



TMEIC Standard Energy Saving Solution

1. Three pumps run up and down together, fourth pump is standby. This is a very effective system.

2. Justify four medium voltage drives

3. Customer wants to save as much energy as possible with as little investment as possible

M P M P M P M P

4x3000 kW3000 rpm

Active



Problems with Standard Solution4-pole motor has radial forces at right angles that balance forces on the shaft

2-pole motor has forces in one axis

This makes lateral vibration not only possible but guarantees a critical frequency at which the motor will shake itself apart, usually somewhere between 30 to 70%



Solution to Critical Speed Problem

1. Use a 4-pole motor and apply a speed increaser

2. Now we need to justify the price of the speed increaser (€150,000)… times four!

M PSpeed

Increaser



SMS Siemag Standard Variable Speed System

1. Biggest 3000 rpm variable speed pump from KSP is 2500 kW

2. Now we need to justify the cost of the speed increaser (€150,000)… times four!

M PSpeed

Increaser M PSpeed

Increaser M PSpeed

Increaser M PSpeed

Increaser M PSpeed

Increaser

4x2500 kW1500 rpm

Active

1x2500 kW1500 rpmStandby



Chinese Standard Variable Speed System

1. Note two-pole solution and 3000 kW variable speed pumps

2. The reason that this works concerns the behavior of pumps with one or more pumps operating at top speed!

M P M P M P

2x3000 kW VS 3000 rpm

Active

M P

1x3000 kWFS 3000 rpm

Active

1x3000 kWFS 3000 rpm

Standby



Types of Descale Pump

1. Reciprocating (piston) pumps like Hoogovens: smaller drives and many pumps all variable speed, simpler.

2. Weir from Scotland: let’s not go there!

3. Multistage Centrifugal pumps like Union Pump USA, or KSB Germany: subject to cavitation damage.



PlumbingAccumulator

BlockingValve

P1 M

Strainer

Booster M

M

Bypass

BlockingValve

P2 M

Strainer

M

Bypass

Primary Descale

Box

RM Descale

FM Descale



Pumps are to Flow as Generators are to Current

A small change in pump speed produces a large change in flow

Pre

ssu

re

FlowQ

2

Pump 1

Pump 2

Q1



For the benefit of EEs:

1. The second pump is running at 92% speed, but only producing half the flow

2. At 10 volts, 83% speed, there is no flow

1Ω2A

12v 10Ω1.2A

1Ω1A

11v 10Ω1.1A

10v



Power available to be saved1. We can adjust the

flow from about 80 to 100 percent, going down to 60% power

2. Below that, no flow, so we reduce speed to 30% speed 3% power where friction tends to increase

3. We end up with a two-speed system and avoid critical frequency

Power

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Speed

Po

wer



How does this help over start-stop?

1. If you have no possibility of operating at critical speed, you don’t need a speed increaser.

2. You can only start and stop machines this big four times per day, and you need a cool-down period of hours between starts.

3. The MV drives can modulate the power according to some control signal



Calculation of energy savings

1. This is a simple example of how the system is rated by the mill builder: add up the time sequence of required flows. Start with the production schedule.

2. Calculate the required speed of the pumps

3. Calculate the power put out at each speed point and integrate over time to get energy.

0

0.5

1

1.5

2

2.5

3

3.5

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106 113 120 127 134 141 148

Slab 1

Slab 2

Slab 3

Total



You are wasting your time!1. The descale sprays go on and off depending on the when the

operator transports the slab to the mill, and the operator often controls the speed of tables and time of pass. No one can predict the future exactly. Duh! (Of course the mill can be completely automatic, in which case we can do a fair job…)

2. It takes 15-20 seconds to slow down, and 4 to 5 seconds to accelerate these pumps which have considerable inertia. Think of your Prius. Check with the pump supplier.

3. Pump cavitation and serious blade damage can result from excessive accel / decel rates. (See Anyang Steckel Mill.)

4. On a big plate mill in full production you cannot practically slow down the pumps! (Conventional Wisdom)



Is there no hope of calculating saved energy?

The only strategy for controlling pump speed has to be to slow down during delays of several minutes or hours. It also has to be a L1 function. For example:

•If the RM or FM is empty and there is no slab waiting you can slow down the MV AS Pumps.

•If the operator enters a delay > 1 hour you can stop the FS pumps.

•You can select some Permissive Diagnostic Alarms which will obviously take some minutes to sort out and agree with Customer that slowdown is OK.

•After a ten-minute delay at the RM use an Alarm to ask the operator “What’s going on? Can I back off on the descale?”

Mainly, you are reminding the operators, who are often busy trying to fix a problem, “Hey… Let’s turn off the lights!”

To estimate energy savings, get the mill delay and production time logs for the last year. On a new mill see what the Mill builder is estimating for actual rolling hours, hours per year and % efficiency.



If only it were that simple…

1.For a HSM the FM descaler pump must be on continuously when you have 10 second gap. But the computer knows when the gap is greater, and you can slow down the pumps between bars. There is a Crop Shear HMD you can use.

2.If you have to use FS motors, you can use one of the MV drives and some Vacuum switches to soft start any and all of the pumps, so you get around the 4 starts per day requirement.

3.Pumps like to run at 5000 rpm, more than they do at 3000-3600 rpm. Some of the cost of the speed increaser can be offset by a lower pump cost (fewer stages) at higher RPM.

4.Energy savings are not the only issue: the biggest single maintenance cost on a mill is probably these pumps. Slowing down the pumps has been known to increase life and reduce maintenance cost by as much as ten to one. You also save water!

5.You need to “sequence” the Standby to equalize wear on the pump.

There are some things you should consider. It is possible to design a system that will save energy, but not easy. Any time you can slow down will help. On a large plate mill, the descale system is actually on only 15% of the time! HSM… 50%!



The Biggest Problems?

1.The cost of the speed increaser adds to their mechanical cost, and they get orders based on their mechanical price.

2.Electrical energy savings are not part of their price evaluation.

3.They have always designed their systems this way unless the User forces them to use variable speed.

4.It is less work, less risk if they do not to have to redesign, or address the complex alternatives TMEIC may have to negotiate with the Customer. There is no “canned” solution.

Mechanical OEMs have an entrenched Fixed-Speed mentality. The Customer has to be serious about thinking this through.

A foolish consistency is the hobgoblin of little minds,Adored by philosophers, statesmen, and devines.



Optimization Starting Point

T M M VI n v e r t e r

6.6 KV LINE


432


4- Pole 3.3 kV or 6.6 kV Motors

GEAR MULTI-PLIER

HI-SPEED PUMP

GEAR MULTI-PLIER

HI-SPEED PUMP

GEAR MULTI-PLIER

HI-SPEED PUMP

RM DESCALE SYSTEM FM DESCALE SYSTEM


5

GEAR MULTI-PLIER

HI-SPEED PUMP


1

GEAR MULTI-PLIER

HI-SPEED PUMP

descale pump systems for energy savings

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