Steam Jet Refrigeration 1

[butelja]

Does anyone with practical experience relating to steam jet cooling have pro's and con's on how the system performs? This pertains to chilled water systems producing 500 to 1,000 tons of cooling at 45 °F.

 

[TBP]

I've never heard the term "steam jet cooling". Do you mean absorbtion chillers? If you do, then the size range you're talking about is very common. They don't use steam jets, but rather steam in a heat exchanger to re-concentrate the lithium bromide solution. (There are other kinds, but lithium bromide is common.) These machines are used where electric power is expensive or there is waste heat, such as exhaust steam from a process. You can make 45*F chilled water, but not much lower. The refrigerant in absorbers is water (there are three water flows in these machines - cooling water, chilled water, and refrigerant water) and it is lower temp than the chilled water. If you go to chilled water output temps in the low 40s, the refrig water is very close to freezing. Believe me, you DON'T want that to happen.

They are physically large, heavy machines for their output, as compared to screws or centifugals. They also require more cooling tower capacity per ton of chilling.

The biggest electrical motor on a 500 ton absorber will be a solution pump motor that's about 15 HP.

 

[butelja]

TBP,

Steam jet refrigeration uses a steam ejector system to pull vacuum on a flash evaporation tank. In the case of 45 °F temperature, it will operate at 7.63 mmHg (abs). Typically it will require a 3 stage ejector system with intercondensors between the stages to lower steam usage. The return water is circulated through the flash tank, where a portion of it spontaneously boils off due to the low pressure. The ejector system removes this vapor as well as any non-condensible gases.

My question pertains mainly as to how capacity is controlled in this type of system, as well as any common problems.

From what I've gathered, these systems are used primarily in industrial installations where equipment reliability outweighs operating costs. In the past (before 1930) there were some commercial HVAC applications.

 

[TBP]

That's an unusual system, for me anyway. I can't help but think absorbers are far cheaper to operate. I can't think of even reading about any chilled water systems operating like this.

We were having problems with vacuum pumps on some absorbers in a plant where I worked (not the fault of the pumps, but nasty old, poorly maintained absorbers) and I looked into staging ejectors for this function. It was the same kind of vacuum required, and I was going to need 3 stages. The cost was going to be just nuts, so we stuck with the conventional pumps.

 

[butelja]

TBP,

From additional information I've found, these systems appear to be mostly obsolete. The combination of factors that make them economical are cheap steam at 100-150 PSIG, expensive electricity, and cheap and plentiful cooling water supply. Outside of process applications with these conditions, they are not economical. There is 2-3 pages of information on these systems in Perry's Chemical Engineers Handbook.

 

[TBP]

After I posted, it dawned on me that the refrigerant & refrigeration effect are the same in both of these. Make water boil at low temps by pulling a big-time vacuum on it. Absorbers can run on steam at 5 PSIG, or hot water. At 125 PSIG steam, you can run a 2-stage absorber that will need 11#/hr steam per ton of chilling, and at 10 PSIG you have a single stage that needs 20 #/hr of steam per ton of cooling.

I'd never heard of "steam jet cooling" before. I'll check out the write-up in Perry's. Thanks.

 

[UtilityLouie]

A site that I have worked on uses an extensive amount of "Chill-Vactors" for both process chilled water and comfort chilled water. Chill-Vactor is a brand name. These particular units are built by Croll-Reynolds. I would try a search for Chill Vactor or Croll-Reynolds on a search engine. I have found this site but I cannot recall the address and it does have good information on it.

I know that Chill Vactors are very reliable in operation. Maintenance is also very easy, there are effectively no moving parts on the chiller itself and any repairs to the chiller (vacuum leaks primarily) can be performed by a certified welder. There is no refrigerant used, which is a big bonus environmentally. They do require a little larger cooling tower than a comparibly sized absorption chiller and they usually must be free standing outside and have a larger foot print than an absorption chiller.

These units can usually put out chilled water at most any design temperature (I think they can be designed to output at least 40 degree water).

As was said in previous posts, excess steam is required. Usually a power plant or industrial plant with a lot of steam generation can support a chill-vactor. Usually summer time venting of medium pressure steam would indicate a possibility to apply this process. If you have to generate excess steam to support this, it's not worth it.

These chillers are what I would label as "old school". They use proven low maintenance technology to give you quality chilled water supply. They are not for every application. If they are right for your application, there will be many that think they are not the answer because they are not commonly supplied. Stick to your guns. Maintenance has a very high cost especially on absorption chillers.

 

Steam jet chilling is well discussed in older version of the ASHRAE Equipment Handbook. I think you will have to go back to about 1983 or so to find it though, because it was eliminated from later versions.

 

[cheah]

Dear sir,

Kindly please sent me a quotation for the Hot water Venturi Ejector.

Venturi Ejector:
Design Pressure: 15 kg/cm2G
Design Temp: 190 degree
Pressure drop: 0.5 kg/cm2G

Water Inlet:
Flow rate: 120 m3/hr
pressure: 13.5 kg/cm2G
temperature: 84 degree

Water Outlet:
Pressure: 13 kg/cm3G
Temperature: 91 degree

Steam Inlet:
Density: 4.2
Flow rate: 0 - 1, 270 kg/ hr
Pressure: 7 kg/cm2 G
temperature: 170

Material Construction: SUS 304
Insulation: yes
Connection Size:
Water side 6" ANSI 300# RF, Steam side 3" ANSI 300# RF

Thank you and we hope to hear from you by today.

Best regards,

Cheah
socheah@hotmail.com