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chemicalENG
12-01-2015, 08:53 PM
I am doing project for refrigeration cycle . I notice that the suction pressure is regulated by speed control of the compressors which are driven by Gas Turbines . Why is that ??

What is the relation between condensing , evaporating temperature and suction pressure because I noticed from data that the speed control increases on afternoon(11 am -12 pm ) but at night or morning it decreases why is that ?

Also , the suction flow rate is higher in the afternoon that at night or morning !

Brian_UK
12-01-2015, 10:14 PM
Perhaps investigation of a temperature / pressure table for a refrigerant will help explain things for you.

Also study a Mollier diagram of the process.

Rob White
13-01-2015, 06:26 PM
I am doing project for refrigeration cycle . I notice that the suction pressure is regulated by speed control of the compressors which are driven by Gas Turbines . Why is that ??



My knowledge of gas turbines is limited but I believe they are fixed speed?
If the gas turbine is fixed speed the compressor duty will be fixed also?





What is the relation between condensing , evaporating temperature and suction pressure because I noticed from data that the speed control increases on afternoon(11 am -12 pm ) but at night or morning it decreases why is that ?


Refrigeration is a relationship between temperatures and pressures
inside a system and they are affected by temperatures outside the
system.

If the ambient is high it will effect the pressure temperature relationship,
if the product around the evaporator changes in temperature that will place
different loads onto the working system and pressure temperatures will change.

Ask yourself what happened in the afternoon for there to be a change?
Did the day warm up and put more load onto the system?




Also , the suction flow rate is higher in the afternoon that at night or morning !


Regards

Rob

.

chemicalENG
13-01-2015, 08:42 PM
My knowledge of gas turbines is limited but I believe they are fixed speed?
If the gas turbine is fixed speed the compressor duty will be fixed also?





Refrigeration is a relationship between temperatures and pressures
inside a system and they are affected by temperatures outside the
system.

If the ambient is high it will effect the pressure temperature relationship,
if the product around the evaporator changes in temperature that will place
different loads onto the working system and pressure temperatures will change.

Ask yourself what happened in the afternoon for there to be a change?
Did the day warm up and put more load onto the system?





Regards

Rob

.


The gas turbine is variable speed . On afternoon the speed increases .

On afternoon there is two problem I guess : The temperature of air in air cooler and temperature of process feed gas in evaporator because it comes from longline pipes .Hence , in summer the temperature of gas entering the evaporator increases.

Different load you means that the required refrigerant flow rate is changining depending on the temperature outside of the system ???

Josip
14-01-2015, 12:33 AM
Hi, chemicalENG :)


I am doing project for refrigeration cycle . I notice that the suction pressure is regulated by speed control of the compressors which are driven by Gas Turbines . Why is that ??

What kind of project are you working on?
I assume you have turbo compressor and speed control is used to control compressor capacity.





What is the relation between condensing , evaporating temperature and suction pressure because I noticed from data that the speed control increases on afternoon(11 am -12 pm ) but at night or morning it decreases why is that ?

Also , the suction flow rate is higher in the afternoon that at night or morning !

Evaporating temperature and suction (evaporating) pressure within evaporator are the same for refrigerant in question expressed in different way ... i.e. at saturated state evaporating temperature corresponds to evaporating pressure and v.v. you can check that in refrigerant charts for your refrigerant or for any other refrigerant ....

Condensing temperature/pressure you can choose according to your system and your needs and of course it will change with changing of compressor capacity and evaporating pressure/temperature.

Flow rate is different, because you have to have higher compressor speed to move more mass due to heat ingress from surrounding (long pipes, not good insulation or maybe just capacity increase within evaporator itself) ... we do not know anything about your system and all this is guessing, agree?


Best regards, Josip :)

chemicalENG
14-01-2015, 09:28 AM
Hi, chemicalENG :)



What kind of project are you working on?
I assume you have turbo compressor and speed control is used to control compressor capacity.





Evaporating temperature and suction (evaporating) pressure within evaporator are the same for refrigerant in question expressed in different way ... i.e. at saturated state evaporating temperature corresponds to evaporating pressure and v.v. you can check that in refrigerant charts for your refrigerant or for any other refrigerant ....

Condensing temperature/pressure you can choose according to your system and your needs and of course it will change with changing of compressor capacity and evaporating pressure/temperature.

Flow rate is different, because you have to have higher compressor speed to move more mass due to heat ingress from surrounding (long pipes, not good insulation or maybe just capacity increase within evaporator itself) ... we do not know anything about your system and all this is guessing, agree?


Best regards, Josip :)


the project is about the relationship between gas turbine power and refrigeration effect in evaporator .

how improving gas turbine power increases the refrigeration effect in summer !!

chemicalENG
14-01-2015, 09:49 AM
the process diagram almost like the attached image11934

Josip
17-01-2015, 09:36 PM
Hi, chemicalENG :)


the process diagram almost like the attached image

11934

Almost like :confused: ... that discrepancy (if) can change a lot at final outcome ....

but let's try to do our best, at least ...

Gas turbine we usually use to drive centrifugal compressors (with reduction gearbox also other compressors and other machines), but still we do not know anything in general about your plant ... is it possible to tell us something more about ... to be able to help you as much as possible.


Best regards, Josip :)