6 replies to this topic

Dear All,

I m writing my diploma thesis, one part is to design a quench. Now i want to calculate the height of a spray tower. I want to cool down the incoming gas from 300°C to 50°C. The quench is a spray tower, the flue gas is directly in contact with the water. The water will be injected with spray nozzles.
The data i have are:
- diameter of the quench
- mass flow rate of the incoming gas (dry and total)
- Enthaphy of Inlet Flue Gas
- Enthaphy of Outlet Flue Gas
- Specific Heat Capacity of Wate Vapor
- Required Outlet Temperature
- Theoretically Quench Water Requirment
- Selected Value
- Enthaphy of Inlet Flue Gas
- Enthaphy of Outlet Flue Gas
and i also have the molar flow rate, molar heat capacity, Enthaly and the pressure of the incoming gas.

Can somebody help me to solve this problem?
Greets Gissy

[siretb]

Quenching is a very rapid phenomena, and the effective heigth for the quench should not exceed one-meter or so.

This will of course depend on the velocity you selected, and also much of the ratio
(amount sprayed)/(amount evaporated)
Many designs are possible, and I like to have high ratio (about 10). I design it that way, and it works well
Since the amount of water sprayed will be much over the theoretical figure, water will be pumped around. The quench is likely to collect some pollutants, and a bleed is needed. Have you made the overall material balance, including possible pollutants?

Often, the quench is followed by a wet scrubber, and the quench can be well integrated. Is this the case?
You say you have the diameter of the quench. This gives the velocity. With typical quench/evaporation times found in litterature you will find H.
Also browse the internet, you will find a lot (you write a thesis, don't you?)

If you need more help, send more a your tentative design. Regards.

Thanks for ur answer,

First we cool down the gas, the second step is to treat it in a scrubber.
Yes i write my thesis, that's why i need some calculations. I don t want to appreciate the height. Do you have a tip for an online book or do you have a calculation. I only can use online books, cause i write my thesis in china. It's impossible to find here english engineering books.

[siretb]

Gissy,
for someone writing a thesis you don't seem to go for a lot of effort in finding either standart quench designs or evaluate the heigth. Do some work, please.
I do not have a readily available ressource. I have rules (L/G, number of banks, ...), I stated some of the most important in my previous reply.
Our designs (I have seen/designed/checked dozens of quenchs in scrubbers) use spray nozzles, we need little heigth, we integrate them in scrubbers, most of the time.

My advice is integrate the quench and the scrubber into a single vessel.

[Andrei]

Gissy,
It is relatively simple and it is not. You can consider your tower similar with a distillation one, with no more than 2 to 3 theoretical trays. Now, you have to determine the hight of your theoretical tray, depending of your specific conditions, and that's your total height.
I guess the scrubber will remove some sulphur (SO2 actually). What siretb is suggesting is common practice: scrubbing and quenching are happening in the same equipment usually. There are proprietory processes available: see MHI (Mitsubishi Heavy Industries), Fluor, CBI and Alstom. You will find some very interesting papers on MHI's webpage:
http://www.mhi.co.jp...ndexe-45-1.html

Good luck

In my case the scruber and the quench are not one unit. The quench is only used for cooling down fluegas with spray nozzles. There are no packings rather trays inside. Till now i haven t found any examples how to calculate the height of a quench as described in my case.
I m thankfull for any help...

[Andrei]

Gissy,

There may be somebody that wants these two processes to occur in different steps, but mother nature is following her ways, and whoever want to bend them, finishes being fried.
There is no way to tell the flue gas: Hey, first you have to quench and only after that you have to scrub yourself.
You will have the two processes happening in the same time either you or anybody else want it or not. And sulphur? It is one of the most reacting chemical species known. You say that you are just quenching first? And who can prevent the sulphur components to disolve/react with your quench water?