7 replies to this topic

[samayaraj]

Hi all,

 

In my plant we have 90m S type once through type steam generator (Tube side: Feed water) with inlet/outlet temp of 180/440 Deg. C feeding to turbine. We maintaining the water chemistry by a online condensate polishing unit and the silica content inlet/outlet of SG and rest of the steam water system is <20 ppb. But in the last two weeks, silica started increasing gradually and gone more than 50ppb from the SG outlet. Hence, we pulled out the turbine.

 

As suggested by our cheif chemist, we are doing flushing with more amount of feed water (mechanical cleaning) to remove the silica formed in the SG. So far, two weeks gone, the silica content out from the SG outlet is more than 200ppb.

 

Here we cannot use manual cleaning as we can do in condenser. Since, its a enclosed steam generator.

 

My question is, whether this mechanical cleaning is the easiest way to reduce the silica carry over or any chemical cleaning is required?

 

#Samayaraj

Edited by samayaraj, 02 December 2014 - 01:04 PM.

[shan]

It seems to me that there is higher silica content in your feed water than that in your condensate.  Please check the performance of you make-up feed water treating facilities.

[samayaraj]

It seems to me that there is higher silica content in your feed water than that in your condensate.  Please check the performance of you make-up feed water treating facilities.

 

The water quality we making up having silica content <20 ppb. Once it has reached deaerator, silica is raising. Any chemical cleaning is available?

 

 

#Samayaraj

[unchalee]

Information on the chemical and physical properties of silica at Silica or silicon dioxide

[manojkaila]

Dear Samayaraj,

 

1 Check your condensate return silica. 

2 Are you adding any chemical additives( Like Hydrazin)  and yes then what is the water used for making that solution.

3 Check the steam quality because in deaerater normally LP steam is used for heating of feed water to remove the dissolved oxygen.

4 Check you continuous blow down quality from boiler. If your blow down is not sufficient your silica carry over with steam will increase.

5 Keep watch on the DM plant for the time of regeneration, If RO then quantity of reject. This will give you indication of the indirect water quality.

 

I hope this will help.

 

Regards,

 

Manoj

[breizh]

Hi ,

Talk to the company in charge to provide chemicals for your feed  water. They are the specialists .

 

http://www.gewater.c...dbook/index.jsp

 

Breizh

Edited by breizh, 07 February 2016 - 04:16 AM.

[samayaraj]

Dear Samayaraj,

 

1 Check your condensate return silica. 

2 Are you adding any chemical additives( Like Hydrazin)  and yes then what is the water used for making that solution.

3 Check the steam quality because in deaerater normally LP steam is used for heating of feed water to remove the dissolved oxygen.

4 Check you continuous blow down quality from boiler. If your blow down is not sufficient your silica carry over with steam will increase.

5 Keep watch on the DM plant for the time of regeneration, If RO then quantity of reject. This will give you indication of the indirect water quality.

 

I hope this will help.

 

Regards,

 

Manoj

 

Dear Manoj,

 

Silica in feed water before SG is less than 20 ppb. But, silica in the SG outlet went upto 200 ppb. The reason was found to be colloidal silica present in the feed water. Our raw water quality was found to be more in colloidal silica content than normal limit. During operation, colloidal silica converted into reactive silica and thus detected more in the outlet.

 

We opened our deaerator to inspect and it found to be clean. No silica scales were found. We do not have steam supply from other source. It was fed by turbine.

 

As I said, Its a once through type steam generator, there is no blow down. Instead we have "Online Polishing Unit" which comprises of mixed bed resin to remove these silica and other impurities. Now the quality of raw water becomes normal and silica in SG inlet & outlet is within the limit. We are planning to install UF membrane before feeding raw water to DM plant to reduce the colloidal silica.

[samayaraj]

Hi ,

Talk to the company in charge to provide chemicals for your feed  water. They are the specialists .

 

http://www.gewater.c...dbook/index.jsp

 

Breizh

 

Dear Breizh,

 

Thanks for your share.