ammoniac Screw Compressor Responce

[gwapa]

Dear friends
How fast a srew compressor could responce to an increse of load?

If you have a system running at 50 % of total load and suddely a proces equipment start up wih an adicional load of 40 % to a total load of 90%
How fast the compressor take the load in orther to garantee the product temperature?

Thanks for your opinon
Regards
Gwapa

[nh3wizard]

I don't think I fully understand the question, if the load has increased the compressor should load, how fast it loads depends on various things, compressor setpoints etc...

[Grizzly]

gwapa.
Most screws have regulation that is either Manually adjustable, Software controlled, or a combination of both.
Also as nh3wizard points out, there are also many other factors that can affect how one loads and unloads.
If you have a specific problem.
Please tell us more!
Grizzly

PS Please spell check ammoniac ( a brilliant word but highly unusual!)

[Segei]

What is the product?

[Tycho]

Depending on the controller, anything from 1 second from the change in suction temperature is registered till the solenoid is activated and from there it's just a matter of how big the oil feed pipe to the capacity piston is :)


The system we use for regulation of RSW temperatures reacts on a 0.1 deg C change on the watertemp on the cooler outlet.


but the loading and unloading of the screw compressor is done slowly.


it's no problem to have the compressor go from 10% load to 100% load in less than 10 seconds, but then you'd have tons of problem with suction pressure, oil being thrown out into the system, liquid not boiling fast enough in the suction accumulator (LP cutout) etc etc etc.



so it all depends on what application, and how fast is it really needed to respond.

the best would be to dimension the other parts of the system so that the compressor can make small steps in capacity to get a much smoother operation.

[gwapa]

These is a commun problem that we face in a brewery or softdrik carbocooler or any food processe industrie when the process operator start up a cooler .Especially after it has been CIP.
In most of the case I have made a combination of piston compressors and screw compressor in order the piston improves the responce of the system
As Tyco have point out , I am trying to evoid the installation of a booffer tank . If the response of the screw compresor to a step load of 50% is 5 second or less the the temperature offset could be handle but longer could be a problem and It drives me to a booffer tank
I appreciate any additional comment
Gwapa

[US Iceman]

These is a common problem that we face in a brewery or softdrink carbocooler or any food process industry when the process operator start up a cooler .Especially after it has been CIP.


You actually have two issues with fast loading rates:

1) faster response can contribute to increased wear of the slide valve and guide. If the slide valve guide wears the slide valve can lift up into the rotors!

2)If the compressors load up to fast the evaporators can boil over leading to flooding of the compressors because the surge drums/accumulators are typically based on steady state operation.

On possibility may be to use a high performance butterfly valve with an actuator as a outlet pressure regulator. After CIP the suction pressure could be very high which could force the compressor to ramp up capacity quickly. This depends on how fast the load rates are adjusted on the pulse signal for the load solenoid and also the oil flow rate to the slide valve piston. If either are too fast the compressors ramps capacity too quickly.

If the outlet pressure regulator is used as a crankcase pressure regulator (I know there is no crankcase on a screw compressor but the function is the same;)) the compressor can only load in response to the slow increase in the outlet pressure as the evaporator pressure pulls down.

Then after the pressure is reduced down to the normal levels the butterfly valve is wide open and offers very little pressure loss that can reduce compressor capacity.

Another factor is the effect of high suction pressure pull down loads on the motor amps. At high suction pressures the motor power input will increase and if the current goes too high the compressor could be forced to unload on amps. This also forces the motor to operate at higher internal winding temperatures which could affect motor life in hot ambient temperatures.

Therefore, if you limit the range of operation of the suction pressure you keep everything under control.