Liquid Nitrogen to Cool Condenser Water 1

[Jackson Morgan]

During the extreme hot days of the year, our cooling towers struggle to keep the condenser water cool enough. It was mentioned that we should look into using the liquid nitrogen as well as a heat exchanger to provide additional cooling to the condenser water system. The idea is that it will both vaporize the nitrogen and cool the system. I was curious if this is even possible? I thought the temperature of the liquid nitrogen would be too cold and would cause problems more than anything. Although, I am not exactly sure. This system uses 30 percent glycol. Any help or comments is much appreciated.

Jackson Morgan

 

[pierreick]

Hi,
Consider this paper issued by Praxair,
Pierre

 

[EdStainless]

There are special heat exchangers designed for this. The tubes ice over about 2/3 of the way up (they have to be vertical or inclined).
Both the mechanical design and the thermal design are special for this service.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[georgeverghese]

Can be done provided you use some compact HX (all welded narrow gap plate HX or PCHE or similar) that presents a very high htc on the glycol side so that film temperature on the glycol side plate surface at the cold end of the HX, in the worst case turndown condition, is say some 5degC above the freeze point of the glycol solution. The HX thermal designer should prove this by thermal calculations.
Rather expensive option, using LN2 for this.
Tell us about the current setup. Why not increase the exchanger surface area for the open loop CW - closed loop glycol HX instead to offset the increase fouling on the open loop CW side ?

 

[Rubje]

@Edstainless

What are the name of these exchangers? Haven't heard of them but sounds neat!

 

[EdStainless]

I am not sure what they are called, I have seen them used as shipboard LNG vaporizers.
The tube pitch was fairly large because they were designed to allow significant ice formation at the cold gas inlet end.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[LittleInch]

Sounds like it isn't really feasible and the lack of any other units kind of tells you the full story.

If you're using gaseous Nitrogen from liquid for some other reason then it can make sense to use some of the cold air / liquid to help your condensor, but seems to be far too complex for only a few days a year.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EngrPaper]

I have used these in the past with great success. I wanted the vaporized gas, but they also have the benefit of cooling your water.

https://www.acmecryo.com/products/vaporizers/shell-tube/forced-convection-water-bath-vaporizer/

As others have said, this is a relatively expensive option unless you are already vaporizing some LN2 in your facility and this is just augmenting that.

 

[Jackson Morgan]

@EngrPaper

Thank you I will take a look at those. We are already vaporizing LN2 and figured we could use this to also cool the water. Just have to figure out how much energy it would save if we used it year-round to take load off the chillers and cooling towers.

 

[georgeverghese]

For increased assurance against freezing on the clean non fouling glycol solution side, you may want to consider pure co current flow. Talk to Heatric.

https://www.heatric.com/heat-exchangers/

 

[Caloooomi]

@EdStainless LNG Vaporizer / forcing vaporizer / BOG warm up heater, are all names I've seen for on board LNG heat exchangers. All just different types of shell and tube.

@Jackson Morgan 30% glycol should make this fine. 30%vol of EG / water is around -16C for freezing point. It's about managing tube wall temperatures in the unit over your range of operating cases.
As others have mentioned, the tube pitch and overall shell diameter typically ends up larger compared to a non-cryogenic shell and tube due to allowance of ice growth. Some IG majors specify the minimum gap required (ice thickness + x mm allowance), for instance.
Assuming it is subcritical LIN you are dealing with too!