inlet location to tank
inlet location to tank
(OP)
Hi,
1) We're designing a 1250m3, 2-cell un-baffled rectangular ground level concrete tank, 3.6m is the TWL. We're debating the issues of inlet location with respect to water turnover and chlorine residual. We've currently got our inlet discharging through an elbow downward at TWL. Any comments?
2) This issue concerns the tank's overflow discharge. Ten State Standards wants 1 -2 feet above grade for visibility. We've got Dept of Fisheries to satisfy that we're not putting chlorinated water into the creeks. Similar to item 1), but now we want vaporization, would a splash pad cause enough vaporization of chlorine to occur?
1) We're designing a 1250m3, 2-cell un-baffled rectangular ground level concrete tank, 3.6m is the TWL. We're debating the issues of inlet location with respect to water turnover and chlorine residual. We've currently got our inlet discharging through an elbow downward at TWL. Any comments?
2) This issue concerns the tank's overflow discharge. Ten State Standards wants 1 -2 feet above grade for visibility. We've got Dept of Fisheries to satisfy that we're not putting chlorinated water into the creeks. Similar to item 1), but now we want vaporization, would a splash pad cause enough vaporization of chlorine to occur?





RE: inlet location to tank
RE: inlet location to tank
I'm interested also to know where the doc indicates discharge elevation to be, at the bottom, midway or at the top.
RE: inlet location to tank
Full reference is "Technical Report TR60: Disinfection by chlorination in contact tanks by J.G Naughton and R.Gregory December 1977"
The most important bits follow:
Firstly, introduction of water into the chlorine contact tank:
"the major problem at this stage of treatd water flow is the need to produce a more uniform flow across the channel in as short a distance as possible. This is sualully acheive dby rapid reduction in the excess energy of the incoming floew to small scale turbulence.
An example of poor inlet design is that of a pipe aligned along the longitudinal axis of the first bay of a contact tank. With this arrangement, retention time in the bay can be reduced to one twentieth of the theoretical residence time..Studies..favour an inlet design incorporating a baffle to break up the jetand a further perforated baffle to smooth the flow..one way of acheiving this baffle effect is to introduce the inlet pipe at right angles into the bay.
..studies..favour narrow bays..give better performance in flow distribution."
More generally,they go on to recommend a rectangular channel with width to length ratio of 40:1. This is acheived in a compact space by forming four or more 10:1 ratio channels joined by 180 degree bends. A minimum theoretical hydraulic residence time of 30 minutes is recommended, at a free chlorine dose of 1-2mg/l.
RE: inlet location to tank
RE: inlet location to tank
RE: inlet location to tank
You will not vaporise chlorine with a baffle. You will need to get a dechlorination chamber. These hold tablets which liberate chlorine destroying chemical into any water flowing through. I've used quite a few of these for river discharge of chlorinated stored water in the UK.
RE: inlet location to tank
I also want to promote circulation to minimize dead spots and so am concerned about the location of the tank inlet pipe. Both these concerns affect where the discharge is located: at the top of the tank or somewhere below.
The second issue in my original posting related to dechlorination and also to making the condition of tank overflow physically visible. In the overflow condition, we want dechlorination to occur.
Sorry if it the issues weren't clearly described.
RE: inlet location to tank
What makes you think you can vaporize the chlorine. The reaction to get chlorine out of water by vaporization is very long and therefore not very usefull in normal water engineering applications.
The inlet to the pipe at the top would not be my first choice, but that is based on it being a water storage tank.
BobPE
RE: inlet location to tank
Tank is potable water storage for distribution for a residential development.
RE: inlet location to tank
BobPE
RE: inlet location to tank
RE: inlet location to tank
I dont follow ten states, they are good for wastewater, but I think they are a joke when it comes to water, but that is personal preference.
There was another post here talking about a declorination chamber, that is a good design you will have to put in. The last one I did used a chem feed system with sodium bisulfite into a stilling pool. You will have to consider this seriously since the fish commission carry guns and can place the operator in jail.
BobPE
RE: inlet location to tank
RE: inlet location to tank
BobPE
BobPE
RE: inlet location to tank
You are right in saying they aren't much use if no-one fills the chamber.You can have a simple mechanical system to warn that an overflow has taken place. I am assuming that overflows from this tank are not common occurrences.
I'd need to know how large the maximum overflow rate was to decide between a no moving parts system and the full chemical dosing system you describe. It'll certainly do the job, but as you say, it's a waste of money.
RE: inlet location to tank
RE: inlet location to tank
As BobPE mentions in passing, if you can flow over a decent run of grassland before the watercourse, this will deactivate the chlorine.
Alternatively, you could consider a granular activated carbon bed.
RE: inlet location to tank
RE: inlet location to tank
DOesn't putting the influent pipe towards the top waste the velocity head energy of the fluid entering the tank and reduce mixing? I've modeled the influent and opposite effluent for several tanks and it isn't an efficient mix design when you look at it on paper.
Just some thoughts...
BobPE
RE: inlet location to tank
RE: inlet location to tank
* wind direction on open topped reservoirs dictated the circulation pattern irrespective of the inlets
* outlet location made very little difference in the flow pattern
* inlet location (both in plan & elevation) had the major impact (especially the velocity)
* at one stage in a reservoir, to mix an artesian water (hot) with ground water (nutrients) & dam water (sometimes some algae), we used a 'jet pump' where we directed the hot artesian flow in a pipe down the reservoir slope & into a submerged cone & a short length of (larger) pipe. This appeared to mix very well
* inlet velocity was the major contribution to flow patterns
* an inlet in the centre of one wall (in plan) at top water level, developed two large circular circular flow patterns. Not as effective as a bottom inlet
* an inlet located in a corner, if the flow was directed along a wall, a large circular flow pattern was developed, but if the flow was directed diagonally, two circular patterns developed (some dead spots)
* tests were also done for inlet location on models of tanks (for 1,000 to 5,000 cub m tanks) & the best location of an inlet was just above the top water level & directed circumferentially, causing a slow (but steady) circular pattern that spiralled downwards to the outlet with no dead spots
* this inlet (just above water level) means that there is a constant head on the pumps. If this is not required (lower tank levels mean lower pump head & higher flows) then the inlets are brought up under the footing & directed circumferentially up at an angle. Good circulation develops
regards
barrya
RE: inlet location to tank
RE: inlet location to tank
The hydraulic tests were done for a major water utility in the State of Western Australia.
Regards
barrya