5 replies to this topic

[theoneajit]

Hi all,

The pipe reactor used for DAP production in fertileser is common by using ammonia and phosphoric acid. I would like to design the pipe reactor for caustic and phosphoric acid reaction to get disodium phosphate. I would like to know the detailed steps involved in designing the pipe reactor.
I am mainly looking for following details:
1. Whats the time required for the reaction?
2. How to calculate the dimensions (length & dia) of reactor?
3. What steps are considered for ensuring better mixing?
4. Heat liberated during a. Ammonia & Phosphate reaction b.Caustic & Phosphoric acid reaction

I know its too much detailing even if you can guide the related site or books it will be helpful for me to design the reactor.

Thanks

[theoneajit]

waiting for your reply

[kkala]

Having worked in fertilizer industry (1975-81) I saw the preparations for replacing two continuous stirred tank reactors (upstream rotary drum granulator) with a tubular reactor injecting the fertilizer slurry into granulator. Beside space saving, tubular reactor (TR) would be able to produce drier slurry, which saved fuel in the downstream rotary drier. The TR was installed and operated after I had left the company. Main problems were scales (but it is easy to stop the unit every so often for a while to clean the TR) and risk of back flows (a consequence of scales).
The design of TR was undertaken by a foreign fertilizer company, having successfully installed TRs in their own fertilizer plants. I guessed that they had managed it through continuous trials on the field, theoretical design calculations were rather a small part of the whole effort. Since I was not involved in the design, following are only my thoughts, not based on experience.
1. Reaction can be considered very fast (almost instantaneous), time required for it is small.
2. Reaction of NH3 with H3PO4 and H2SO4 creates heat, thus a mixture of vapor, liquid, solids, whose composition can be estimated (mass & heat balance). TR diameter should: (α) cause a high enough velocity of the mixture to result in homogeneous flow (to limit scales). (β) promote smooth flow to TR exit, with a pressure at the point of mixing sufficiently lower than the pressures of any feeding stream (to avoid back flows). The latter affects TR length too.
Valves of high ΔP at normal flow were placed at feeding lines, just upstream TR.
Note: Pressure would be lower and lower (so volume higher) as the mixture goes to TR exit.
3. Better mixing can be obtained by longer TR and higher mixture velocity (but see above).
4. For DAP 2NH3 liq + H3PO4 liq -->(NH4)2HPO4 liq ΔH=?
2NaOH liq + H3PO4 liq --> Na2HPO4 liq + 2H2O liq ΔH=?
Standard heats of formation for all above is not easy to find, e.g. by searching for them in Perry or similar handbooks. Lange's handbook of chemistry may have them, advice where to find them (or values themselves!) would be welcomed.
Other notes on the matter are as follows.
(1) At that time the TR designer operated its plants using NH3 liq. I am not sure, but introduced phosphoric acid probably was of 30% P2O5, not 50% P2O5. Gaseous NH3 or more concentrated acid caused scales and plugging inside TR.
(2) Tennessee Valley Authority (TVA) was considered leader in TR development (1979). They can probably have some preliminary data available.
(3) Books on fertilizers mentioned the TR, without much design details (but I cannot remember them).
(4) Finally the TR produced 16-20-0 without difficulty (N=16%,P2O5=20%, K2O=0%, w/w). Production of DAP or 0-42-0 was unsuccessfully tried using the two stirred tank reactors (atmospheric pressure), so it is reasonable to assume that they were not produced using the TR.
(5) Since design of TR contains a lot of empirical data, the alternative to assign it (probably with installation & commissioning) to a specialized company should be investigated.

Edited by kkala, 30 July 2011 - 02:54 AM.

[theoneajit]

Hi,

Thanks a lot for the reply,

I guess using TR (Tubular reactor) for caustic and phosphoric acid has no history, as I am not getting any of the reference either on net or books. Considering all the factors like pressure drop, velocity & time required for the reaction to complete, we are in the process of taking trials. Since volumetric flow to TR is as low as 5 m3/h the initial designed TR(6 inch dia line at inlet reducing to 4 inch line with static mixer & then expanding to 8 inch line at the discharge) was creating lot of noise. I am planning to reduce the outlet line size to as low as 50mm using a reducer ( to ensure line is always filled with liquor).
Fingers crossed, Need to see the results.

I will share the outcome of trials....
Thanks,
Ajit

[kkala]

Thanks for the info. At that time the tubular reactor consisted of a tube of uniform diameter, slightly bent at one point rather far from exit. Now I can see improvements, like static mixer. Diameter of 2" (50 mm) at the last part of the discharge pipe seems small at first look (risk of plugging); 10 m3/h would result in 1.5 m/s (Sch80), if no vapor were produced. However volume will greatly increase due to flashing steam (but I cannot "feel" conditions for Na2HPO4). It is indicated to estimate flashing steam and volumetric flow rate, then specify TR exit diameter for a smooth flow (acceptable ΔP through the TR). 0-42-0 was unsuccessfully tried using phosphate + H3PO4 in the stirred tank reactors, now Na2HPO4 is another product. May you have patience and good luck!

Edited by kkala, 01 August 2011 - 12:00 AM.

[ramachandran_chem]

Hi,
I would like to know the heat balance around the Ammonia Granulator(AG).Feed composition contains recycle feed(filler+fines&oversize product) of 240MTPH at 79.5 deg.C and 27 M3/hr of slurry(Mono-Ammonium phosphate)(slurry contains 80-85%solids and 20-15% water) at 120-123 deg.C having specific gravity of 1.50 to 1.60 and liquid Ammonia at 0.7kg/cm2g(-4 deg.C) with max flow rate of 1.5 MTPH.
Outlet (solids+partially slurry) goes to the dryer at 85-90 deg.C were it gets dried up and the gases from AG is sucked my the fumes fan.what will be the outlet gas temperature?and also please tell me how to do heat balance around the AG?

Moisture at outlet of AG will be 2.3-2.5%. and also AG(discharge end) will be partially open were Air+Moisture enters.

In AG large amount of heat is generated which helps in evaporating the water.

specific heat of NPK=0.32kcal/kg deg.C
specific heat of slurry = 0.5 kcal/kg.deg.C
latent heat of crystallisation of slurry = 18 kcal/kg.

waiting for your reply.

thanks