Solar Evaporation rate 1

[Homayun]

Hi
For our project in Kuwait, we are considering to allow the liquid blowdown of an incinerator, which consists of mainly spent caustic and some solids, to be sent to drying beds where, after water has been evaporated by solar radiaition, the solids can then be separated.

However, in order to be able to determine the size of such a bed, which is essentially comparable to a swiming pool, we need data on solar evaporation rate in Kuwait.

Does any one know where I could get this data?

 

[buzzie]

I would suggest using published pan evaporation rates for an area like Las Vegas as a conservative design indicator of evaporation. Although Kuwait ambient can be 10-15 F higher any US desert numbers which are widely published should be a good place to start.
Keep in mind that your blowdown should be classified as a high TDS brine for purposes of evaporation - this significantly reduces the published pan evaopration rates.
For the Nevada USA desert I have used 3 gpm per acre for brine solutions.
Regards

 

[Homayun]

thanks buzzie.

But do you have any internet link where I could find data on Las Vegas Pan evaporation rates?

 

[buzzie]

Google "pan evaporation rates". This provides a good series of links. Let me know if you can't find what you need.
Regards,

 

[Homayun]

Buzzie,
I have found a theoretical way of calculating the pan-evaporation rate besed on Penmann theory or something. I have also got measured values from Kuwait. But the thing is, they are in mm! So are these values per day? I have an average of 15 mm for kuwait. I assume it is 15 mm/day, can you confirm that?

Thanks

 

[buzzie]

15 mm (per day ??) calculates to about 11-12 gallons per minutes per acre. This seems high especially for high TDS brines. I don't know what other contingencies you have in your estimate but I would not use a number for design more than one-third of 15 mm or about 4 gpm per acre.

Regards,

 

[Homayun]

Buzzie,
1) How do you calculate the 11-12 gallons per minute per acre? If I do this, I get 27 US Gallons per minute per acre? How have you done this?

2) with a design evaporation rate of 15 mm we already are at the maximum land at our disposal for drying bed purposes! So if I take 1/3th of this value, that'll make it worse! What next? I mean, this becomes now too uncertain to base my calculation on!

 

[buzzie]

acre equals 43,560 square feet
325,851 US gallons per acre-foot
15 mm equals 0.0492 foot
1 acre at 15 mm equals 16,032 gallons per day
16,032 / 24 / 60 = 11.1 gpm

I checked with another colleague regarding evaporation rates in US desert. Suggested using "lake evaporation" rate and not "pan" rates which are considered too high for large scale pond evaporation. Highest annual lake rates I could find for US desert was 80 inches per year. This is about 5.5 mm per day. Remember annual rates average summer and winter conditions. Could be your 15 mm number is best case summer evaporation. But unfortunately have no data of Kuwait to compare. In any case, this latest evaporation rate (correcting for brine condition @ 70%) is more conservative than my earlier 3 gpm per acre and would suggest using a number no higher than 1.5 to 2.0 gpm per acre.

If you don't have enough surface area for evaporation you may have to consider an evaporator to preconcentrate the blowdown prior to going to pond. Sorry don't have better news.

Regards,