Examples from design calculation to RO plant
Design for 100m3/day as example:-
* Assume feed water TDS = 40000 ppm, so Osmotic pressure =30
1) Selection for F.F.P.:-
-For sea water recovery (20:40) %, so select 30 %
Recovery = Qp/Qf
0.3= 1000m3/d/ Qf , Qf = 3000 m3/d
Q = A*V From curve η = 75%, P = pghQ/ η
P= 1000*9.8*50*0.0347/0.75=22.68 kw
Assume Head = 50 m , so we already make selection for F.F.P.by deter P ,Q .
* Head > ^P (S.F.)+ ^ P (C.F.) + Suction P of H.P.P. + losses + P (S.F .)
2) Selection for pipeline:-
* Assume water velocity V = 2 m/sec, Q = A*V , 0.0347 = 3.14/4*D²*2
D = 0.148 m, D = 6 inch.
3) Selection for S.F.:-
* Assume No. of S.F.= 2 , V = 0.2 m/sec , Q = 0.0347/2 =0.0174 m3/sec
Q = A*V, 0.0174= D²/4 *# * 0.2/60, D = 2.5.
4) Selection for C.F. :-
* Flow per cart. 10" =5 GPM= 5/4.4033 = 1.13 m3/h
*Assume no. of C.F. = 2 filter, Q1 = 125/2 = 62.5 m3/h=70m3/h.
Q1 = no. of cartridge * qc, no. of cart. = 70/1.13 = 61.6 for cart.10"
For 40 " no. of cart. = 14 cart.
5) Selection for R.O. membrane:-
- Membrane product = 8 m3/ d
- No. of membranes = 1000/8 = 125 membrane
- No. of vessels = 125/6 = 20.8 =21 vessel + 3 vessel standby.
6) Selection for flushing pump:-
*Assume vessel need 8 m3/ h , Q = 8*24=192 m3/ hr
.
7) Selection for cleaning pump:-
*Assume each vessel need 5.5 m3/ h , Q = 5.5*24 = 132 m3/ hr
2- At case 500m3/ d
Q =A*V , 70/3= D²*3.14*V/4 , V = 23.3*4/3.14*2.8*2.8=3.78 m/ hr.
* At case 2x 500m3/ d
Q =A*V , 140/3= D²*3.14*V/4 , V = 4.6.6*4/3.14*2.8*2.8=7.5 m/ hr
*Filtration rate between (10 :25 ) m3/m2.hr.
*B.W.rate (20 : 40 ) m3/m2.hr.
* Air filtration rate (40 : 60 ) m3/m2.hr.
* Q=A*V = 240m3/hr
*Retention time = Raw water tank volume /HPP (Q )m3/hr
* To obtain the power for Pelton wheel
P1 (pelton) = Q*inlet P* 10.2 /367
Consumed power = pump power (without pelton) – P1 (pelton)
*How to calculate cleaning tank volume?
- No. of vessels to be cleaned = 8 vessel
- Volume of each vessel = 200 liter. Empty,
so Min. required tank volume = 2*200 =1600 liter.
- The first 20 % of water is drained = 0.20*1600/10 = 320 liter.
- The total capacity = 1600+320 =~2 m3
- So. for tank retention time with respect to pump 5*60/44 = 6.82 min
.
*How to calculate Raw water tank volume?
- 2x146+2x70+10=442 m3/h
- Assume retention time = 1.5 hr , tank volume = 1.5x442 =663 m3 ~740 m3.
*How to calculate Backwash water tank volume?
- For 500 m3/d unit ,
backwash rate = 25-35 m3/m2.h
Required water for back wash = 3.14*(2.8/2)*30 = 184.7m3/h
The time required for backwash = 15 min
So the max.daily water required for backwash (3 filters) =184.7*15*3/60=138.5m3
For 1000 m3/d unit,
-backwash rate = 25-35 m3/m2.h
Required water for back wash = 3.14*(2.8/2)*30 = 184.7m3/h
The time required for backwash = 15 min -
So the max.daily water required for backwash(5 -
filters ) =184.7*15*5/60=230.8m3
-Backwash tank volume = 231+138=369~400 m3 -
*How to calculate Brine( reject) water tank volume?
Reject water = brine water + Backwash water = (92.5*2 + 49*2) + (185) = 476 m3/h
Retention time = 15 min.
Tank volume = 476/60*18=150m3
*How to calculate flushing water tank volume?
Say 5 min. for RO (500) &(1000) ,
64*15/2/60+128*15*2/60=12+22+91(constant)=150m3
Ahmed Mahmoud
