Re: Optimization of the refrigeration plants operation
Quote:
Originally Posted by
AmmoniaMike
Describing the entire system in one sitting will be very difficult but it is essentially three systems with one common high pressure side. The three systems are like this:
Spiral freezer system is run by one RWF II 399 Frick 600 hp compressor set at 12" Hg suction: Glycol and water chiller system is run with a RXF 58 Frick 134 hp compressor set at 24 psig suction: Plant cooling is run using a RXF 68 Frick 165 hp compressor and a RXF 50 Frick 123 hp compressor set at 39 psig.
The condenser for the complete system is a Frigid Coil/Imeco IDC 1200-2S evaporative condenser. Condensing pressure set by PLC based on relative humidity and temperature. I don't think I can go into the entire system at one go so I will break it down by system.
The freezer system's compressor is set up as follows:
suction pressure: 12" Hg
suction temp (typical) -13F
suction superheat (typical) 31F
discharge pressure: between 120 and 160 psig (depending on weather)
discharge temp (typical) 164F
Discharge superheat (typical) 89F
Oil pressure (typical) 114 psig
oil temp (typical) 113F
oil cooled by thermosyphon no pump
compressor capacity (typical) 65%-80% (average about 70%)
Compressor also hooked up to an economizer whose main duty is to cool liquid in a coil from the +25 recirculating vessel to -14F before going to -45F recirculating vessel. The liquid is pumped from the +25F recirculating vessel. The liquid in the economizer vessel is supplied from the HP receiver and the vapour is taken in by the 600 hp compressor. The suction line from the economizer is also supplied with a cross over 1 1/4" HA4AS, 1 1/2" FLGS set at 40 psig which goes to the suction of the +25F recirculating system (compressors for this side are set at suction of 39 psig).
The liquid cooled in the economizer then goes to the -45F recirculating vessel. From there it is pumped to the spiral freezer which has 4 of 62 ton capacity coils. The freezer is maintained at -35F. The coils are set to defrost individually in this order A, C, B and D. Time intervals from start up are set at 90, 120, 150 and 180 minutes respectively and 35 minutes between unit defrosts. The defrost cycle is set to 10 minutes pumpdown, 2 minutes soft HG and 15 minutes HG (at 70 psig for the hot gas) and 5 minutes drying. C and D are the bottom two coils and A and B are the top coils. The freezer is an Aerofreeze 185 ton unit set at 4:1 recirculating ratio at -40F ET. This is getting pretty long so I will leave the rest of the system for another day :)
As an aside the frost on the coil wasn't noticed by the operators because when freezing hot chicken from the oven the bare metal in the freezer tends to get frosted from all the steam comming off the chicken at the infeed of the freezer so it isn't readily noticable at that end. The real give away was the lack of frost on the suction valve on the roof that had no frost on it at all since the liquid valve was closed to that coil. Everyone was too busy looking at the valve assembly for coil B and no one looked at the other valve assemblies :(
The guys were too focused on the problem with temperatures rising when B went into defrost and all assumed the problem was with that coil.
It isn't clear for me how economiser hooked up. Does it have level control or it has TXV?
As far as I understand every coil in spiral freezer defrost every 2 hours. If it is true, you have clear over defrosting. You have 2 coils to freeze the product. One coil on defrost. Second coil(right after defrost) run for 30min to remove the heat of this coil defrost. Typically 90% of defrost heat goes to the freezer and you have to run this coil to remove this heat. Do you have any frost on the coil before defrosting? Probably, very little. That is why you didn't notice the poor operation of one coil.
What is the settings of your condenser? Minimum allowable head pressure, wet bulb approach...
By the way chicken should cooled before going to the spiral freezer, otherwise you waste a lot of energy. Do you have full production? Why compressor load just 70%? Do you have any storage room for the frozen chicken?
Re: Optimization of the refrigeration plants operation
Econimizer is set up this way:
line goes in by pump from +25 recirculating vessel. In economizer this liquid goes into a coil is cooled to -14 then out to -45 recirculating vessel. The economizer is filled to 5% to 15% with HP liquid from HP receiver. The vapour from the vessel is sent to 600 hp compressor at the normal hook up for economizer (part way down screw) also if pressure gets too high in economizer a valve opens up at 40 psig to dump excess vapour into +25 system. The levels in all vessels is controled by solenoid openened and closed by PLC according to need for make up liquid.
The defrost is set up with a point system. The first coil starts to defrost 90 minutes into production (this coil is closest to infeed and get more frost from chicken) after this coil defrosts there is a 35 minute wait before next one will defrost and so on. The way the point system works is that the lower number coils have less points than the higher number coils so the coil at 90 minutes would start timing down after its defrost. The coil that has the lowest number after the 35 minute wait after a coil defrosts gets to defrost next. The nice thing about using this system is that the coil nearest the infeed (it is set to 90 minutes) gets more defrosts and the coil furthest from the infeed gets the fewest defrosts. In an 8 hour shift the closet coil might get 3 defrosts and the coil furthest from the chicken infeed gets only 1 defrost. The coil next closest to the infeed gets 2 defrosts (it is set at 120) and the others gets 1 or 2 defrosts depending on how long the freezer is on. The system works pretty good. We aren't over defrosting.
I agree with you that the chicken should be cooled a bit before going in but the system is continuous feed. The last plant I worked at we used Cryojet blowers to cool the chicken a bit before going in. That cut down on a lot of frost caused by steam from hot chicken. I'm working on getting that done here.
The condenser pressure is set according to outside temperature and relative humidity for energy savings (still haven't had a chance to look at that one very closely). The theory being that on cool days in summer (20C or so) with low humidity the set point is at 120 psig. On a hot humid day (say 35C with 90% relative humidity) the set point goes to 160 psig. To maintain the pressure the condenser works by stages. Stage 1 is one pump on, stage 2 is 2 pumps on, stage 3 2 pump and 1 fan and stage 4 is 2 pump and 2 fan. I suppose we are using a wet bulb approach for determining condensing pressure.
Re: Optimization of the refrigeration plants operation
Quote:
Originally Posted by
AmmoniaMike
Econimizer is set up this way:
line goes in by pump from +25 recirculating vessel. In economizer this liquid goes into a coil is cooled to -14 then out to -45 recirculating vessel. The economizer is filled to 5% to 15% with HP liquid from HP receiver. The vapour from the vessel is sent to 600 hp compressor at the normal hook up for economizer (part way down screw) also if pressure gets too high in economizer a valve opens up at 40 psig to dump excess vapour into +25 system. The levels in all vessels is controled by solenoid openened and closed by PLC according to need for make up liquid.
The defrost is set up with a point system. The first coil starts to defrost 90 minutes into production (this coil is closest to infeed and get more frost from chicken) after this coil defrosts there is a 35 minute wait before next one will defrost and so on. The way the point system works is that the lower number coils have less points than the higher number coils so the coil at 90 minutes would start timing down after its defrost. The coil that has the lowest number after the 35 minute wait after a coil defrosts gets to defrost next. The nice thing about using this system is that the coil nearest the infeed (it is set to 90 minutes) gets more defrosts and the coil furthest from the infeed gets the fewest defrosts. In an 8 hour shift the closet coil might get 3 defrosts and the coil furthest from the chicken infeed gets only 1 defrost. The coil next closest to the infeed gets 2 defrosts (it is set at 120) and the others gets 1 or 2 defrosts depending on how long the freezer is on. The system works pretty good. We aren't over defrosting.
I agree with you that the chicken should be cooled a bit before going in but the system is continuous feed. The last plant I worked at we used Cryojet blowers to cool the chicken a bit before going in. That cut down on a lot of frost caused by steam from hot chicken. I'm working on getting that done here.
The condenser pressure is set according to outside temperature and relative humidity for energy savings (still haven't had a chance to look at that one very closely). The theory being that on cool days in summer (20C or so) with low humidity the set point is at 120 psig. On a hot humid day (say 35C with 90% relative humidity) the set point goes to 160 psig. To maintain the pressure the condenser works by stages. Stage 1 is one pump on, stage 2 is 2 pumps on, stage 3 2 pump and 1 fan and stage 4 is 2 pump and 2 fan. I suppose we are using a wet bulb approach for determining condensing pressure.
Many plants work pretty good but not efficient. It is better to see the picture of the coil before defrosting. I still believe that time between defrosts can be doubled and suction pressure can be increased. Do you have holding freezer? Do you have VFDs for compressors, fans? Your main compressor is loaded 70%. It isn't efficient especially with economizer.
Re: Optimization of the refrigeration plants operation
We are looking at the defrost system. At this point the guys start the auto defrost cycling when the freezer is started. I believe we could hold off on starting the defrost till middle of the shift. I am trying to convince the company to do this but their argument is that this is how it is supposed to run. My argument is that if that was the case than why bother having the auto defrost cycle on a seperate start? It is a big waste of energy to start defrosting too early. A picture is a good idea, I will take one of all the coils just before the first coil goes into defrost. A picture could say plenty, good idea and thanks for that.
We do have a holding freezer, it is in the old section of the plant and that is using R22. I am looking at replacing the R22 system in the old part of the plant but first I have to try and optimize the new NH3 system. It is only a couple of months old and still has some bugs to work out, especially in the DDC programming.
There is no VFD on any of the compressors only capacity and volume valves for the screw. The freezer blowers are single speed. Converting the compressors to VFDs would be very expensive and since electricity if still fairly cheap in Canada the payback would be too long to be able to sell the bean counters on it. I'm sure when the carbon tax comes into effect one day the cost of electricity will be high enough to convince them to do it but at that point so many people will want it that the cost of converting to VFDs will jump up a lot too ;)
Re: Optimization of the refrigeration plants operation
Quote:
Originally Posted by
AmmoniaMike
We are looking at the defrost system. At this point the guys start the auto defrost cycling when the freezer is started. I believe we could hold off on starting the defrost till middle of the shift. I am trying to convince the company to do this but their argument is that this is how it is supposed to run. My argument is that if that was the case than why bother having the auto defrost cycle on a seperate start? It is a big waste of energy to start defrosting too early. A picture is a good idea, I will take one of all the coils just before the first coil goes into defrost. A picture could say plenty, good idea and thanks for that.
We do have a holding freezer, it is in the old section of the plant and that is using R22. I am looking at replacing the R22 system in the old part of the plant but first I have to try and optimize the new NH3 system. It is only a couple of months old and still has some bugs to work out, especially in the DDC programming.
There is no VFD on any of the compressors only capacity and volume valves for the screw. The freezer blowers are single speed. Converting the compressors to VFDs would be very expensive and since electricity if still fairly cheap in Canada the payback would be too long to be able to sell the bean counters on it. I'm sure when the carbon tax comes into effect one day the cost of electricity will be high enough to convince them to do it but at that point so many people will want it that the cost of converting to VFDs will jump up a lot too ;)
This is major misconception in refrigeration that only VFDs can save energy. I estimate that VFDs(compressors, evap. fans, cond. fans) can save 20-30% of total energy savings. Optimization of a refrigeration plant operation can save 70-80%. This is just smart efficient operation.
Re: Optimization of the refrigeration plants operation
The thing i found from experience, the weather changes everyday so does you running temps they change with ambient and humidity, so do the same with refrigeration components CONTROLS, VFD'S and so on its only logic dont you guys think so?
Re: Optimization of the refrigeration plants operation
My biggest problem with any kind of consultant is their unwillingness to put their money where their mouth is...
They're quick to tell you you're going to save 10% on your electricity bill every month, for a small capital outlay of $10000 or $100000...
OK, sounds good, guarantee that. If we don't save 10% per month you refund us the capital outlay.
And they disappear like... I dunno... stuff that disappears ;-P
Re: Optimization of the refrigeration plants operation
Quote:
Originally Posted by
subb-zero
The thing i found from experience, the weather changes everyday so does you running temps they change with ambient and humidity, so do the same with refrigeration components CONTROLS, VFD'S and so on its only logic dont you guys think so?
When the weather change operating of evaporative condensers will change.Optimum set point should be readjusted. For example. Optimum wet bulb approach is 10degF. During the day wet bulb temp. is 75 degF so optimum head pressure will be 75+10=85degF or 150psig. During the night wet bulb drop to 60F and optimum head pressure will be 60+10=70F or 115psig. Capacity of evaporative condensers should be readjusted.
Re: Optimization of the refrigeration plants operation
Quote:
Originally Posted by
RefrigNoob
My biggest problem with any kind of consultant is their unwillingness to put their money where their mouth is...
They're quick to tell you you're going to save 10% on your electricity bill every month, for a small capital outlay of $10000 or $100000...
OK, sounds good, guarantee that. If we don't save 10% per month you refund us the capital outlay.
And they disappear like... I dunno... stuff that disappears ;-P
I know that it isn't easy to find a good consultant. Majority of consultants are professional engineers(designers). To save energy they can redesign the refrigeration plant. Typically their suggestions require capital investment.
I have different approach. Optimization of refrigeration plant operation doesn't require capital investment because it changes operation of existing plant. Right now I do remote tuning up of refrigeration plants. This approach is similar to our forum. People give me information about their plants and I suggest them how to change operation and energy will be saved. Energy can be saved for every refrigeration plant(industrial ammonia refrigeration) around the globe. Initial part of this tuning up is free.:eek: However, many people are sceptical to any new approach. It is easier to buy VFDs then try something new. Recently I saw one plant around 2000HP. It has VFDs for compressors, condenser fans, evaporator fans. Probably, they invested around $200,000 for these VFDs. However, this plant operated at 150psig of condensing pressure all year around. Reduction of this pressure to 120psig will save them more than all VFDs. :D
Re: Optimization of the refrigeration plants operation
Quote:
Originally Posted by
Segei
I know that it isn't easy to find a good consultant.
That is so very true :confused:
But it sounds like what you're doing will catch on, and we might even get some people like you here in the 3rd world eventually :)
Good luck with your endeavors! :D
Re: Optimization of the refrigeration plants operation
Quote:
Originally Posted by
RefrigNoob
That is so very true :confused:
But it sounds like what you're doing will catch on, and we might even get some people like you here in the 3rd world eventually :)
Good luck with your endeavors! :D
Thanks. I hope that one day end users will realise that optimization is the best way to save energy.
Optimization of the refrigeration plants operation
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Re: Optimization of the refrigeration plants operation
As an operator of a NH3 plant there are things that an operator can do to reduce energy costs, I have implemented many items that have small effects on the system as a whole. I have installed VFD's on condenser fans, and written plc code to run these fans on PID loops based on head pressure, also VFD's on evaporator fans in areas that can handle reduced air flow, fans can be set to reduce speed when temp in room is satisfied. Also optimize defrost, temp sensors on suction lines and programming that will trigger defrost when superheat from the evaportor starts to fall because the coil is icing over. There are many things that can help in these systems.
Re: Optimization of the refrigeration plants operation
Quote:
Originally Posted by
jerry68nh3
As an operator of a NH3 plant there are things that an operator can do to reduce energy costs, I have implemented many items that have small effects on the system as a whole. I have installed VFD's on condenser fans, and written plc code to run these fans on PID loops based on head pressure, also VFD's on evaporator fans in areas that can handle reduced air flow, fans can be set to reduce speed when temp in room is satisfied. Also optimize defrost, temp sensors on suction lines and programming that will trigger defrost when superheat from the evaportor starts to fall because the coil is icing over. There are many things that can help in these systems.
Can you give us more information about PID loops? You mentioned about temp sensors on suction lines to initiate defrost. Can you give more information about these coils(feed, air temp, evaporating temp, ...)