7 replies to this topic

[K J]

Hello everybody,

        Normally TSP is injected directly in steam drum and its concentration is maintained around 7 to 10 ppm in boiler blow down (in high pressure 100 bar(g) boiler). Is it not possible to inject TSP in BFW pump suction line as done with morpholene and hydrazine with maintaining same 7 to 10 ppm in BBD.

[mario_1970]

These phosphate values ​​are very high for that pressure.

See Phosphate Continuum Treatment (former EPT) in EPRI guidelines.

Do not inject TSP in feedwater (FW).

The maximum recommended value is 20 ppb hydrazine in FW. It is generally used when copper metallurgy (see document 3).

 

Documents:

 

1) Cycle Chemistry Guidelines for Combined Cycle/Heat Recovery Steam Generators (HRSGs).

EPRI, Palo Alto, CA: 2006. 1010438.

 

2) Cycle Chemistry Guidelines for Fossil Plants: Phosphate Continuum and Caustic Treatment,

EPRI, Palo Alto, CA: 2004. 1004188.

 

3) Guidelines for Controlling Flow-Accelerated Corrosion in Fossil and Combined Cycle Plants,

EPRI, Palo Alto, CA: 2005. 1008082.

Edited by mario_1970, 04 June 2014 - 09:16 AM.

[tarafdar]

  Phosphate precipitates calcium or magnesium into a soft deposit rather than a hard scale.Phosphate forms sludge as it reacts with hardness which remains mostly in suspended form in the boiler water.During operation the sludge must be removed by sufficient blow down.

   Normally you have Heat Exchangers between BFW pump & the Steam Drum.To avoid sludge deposit(afterwards turned to  scale) in these equipments , phosphate is dosed in the Steam Drum directly.

[rychurek]

Tarafdar

 

If in our steam methane reformer plant we have fosphate injection point between BFW pump and heat exchanger, does it mean that it is not according to best practice, standarts...?

[tarafdar]

Hi rychurek,

 

Since residual hardness & phosphate react to form sludge,it is better to remove it as quickly as it is formed.In steam drum you have that facility.

Normally in a heat exchanger the fluid velocity is low & there is a chance of settling of sludge.

Whether it is a best practice or not ,it depends on your water quality & heat exchanger design.

 

Regards

[rychurek]

Hi tarafdar

What you said it seems very logical, so i start to wondering why in our case contractor made it different.

Beside economical reasons ( shorter injection pipeline- from present injection point to steam drum is extra 50 m) i assume there is better trisodium phosphate solution mixing with BFW.

Dosing point is on discharge side of BFW pump, because like you said possibility of sludge forming, so designer protect pump from erosion but didn't care about heat exchanger fouling by phosphate salts ?

 

Regards

[SSWBoy]

Is your BFW used for desuperheating in the steam bank of your reformer?

 

 

Hi tarafdar

What you said it seems very logical, so i start to wondering why in our case contractor made it different.

Beside economical reasons ( shorter injection pipeline- from present injection point to steam drum is extra 50 m) i assume there is better trisodium phosphate solution mixing with BFW.

Dosing point is on discharge side of BFW pump, because like you said possibility of sludge forming, so designer protect pump from erosion but didn't care about heat exchanger fouling by phosphate salts ?

 

Regards

 

 

 

[rychurek]

SSWBoy
Part of BFW from export steam system is use as quench for prereformer, reformer,and export steam heat exchangers. Process steam system is supply mostly from process condensate and balanced by demineralized water