Poor Boiler Feed Water Quality

[gattwood]

I'd like to know about the operations of boilers with less than ideal feed water (ASME quality). What type of maintenance are you doing? How often are you cleaning? What type of failures do you have? Do you have reliability numbers (ie/ MTTF, MTTR, etc...) I'm really interested in high pressure, 1000+ psig, boiler operation, but i'd still like to know about any operation. What type of design considerations would you do to fix this?

 

[unclesyd]

I personally think your only alternative is get the BFW up to par. Nothing good ever happens with poor BFW quality.

Come back with a description of your boiler.

Just what are your water quality problems?

 

[rmw]

Where I come from we call what you are proposing "putting lipstick on a pig". Any 1000 PSI boiler needs some pretty good quality water or you are asking for trouble.

I have dealt with some low pressure steam boilers (200 PSI) with crappy water and the problems are legion; scale, tube failures, loss of performance, tube pluggage, drum internals fouling to name a few. I would not have wanted to see what all that would have been if the pressure (and temperatures) were associated with 1000 PSI.

rmw

 

[gattwood]

I've also run boiler plants with less than good water and it became about the downtime versus the cost to improve this downtime. I have to qualify that this was for 2 different low pressure boilers (~350 & 600psig). Both ran for a significant period 2+ years before they had to be cleaned. The other thing to note is that they were produced sat'd steam only. They were neither attached to a turbine or running a superheater section on the boilers. But I'm looking for more evidence in the high pressure side. I know that there is a boiler running in Jamaica running this way and there are a number of other's around the world. What I don't know are the details. This is what I'd like to know to provide a more quantitative basis for moving forward in our project. The boilers will only be producing sat'd steam downstream of an evaporator. The only target that couldn't be met from the evaporator would be the silica quality (~2 ppm). But I'd still like to know others experience in operating these systems.

 

[vpl]

It comes down to "pay me now or pay me later". I'm with unclesyd and rmw that poor quality boiler feed water is trouble. The time and money you think you're saving up front is lost many times over on the back end.

You stated that the parameter that is out of spec is silica. Isn't silica corrosive? How many tube replacements (including down time) will it take to exceed the cost of improving your boiler feed water up front?

Granted, I don't define a "significant period" of time as being two plus years. That would be the minimum period of time that I would expect any boiler to run without cleaning.


Patricia Lougheed

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[gattwood]

I'm dealing in the SAGD industry which has to always "pay me later". Our current designs put through water in OTSG "boilers" at 8000ppm of TDS. They are currently cleaned every 6-12 months. They are operated with an understanding that the water quality is always going to be bad. The produced water which comes up from the reservoir is at 3500 ppm. This is a fact which we live with every day. Again, it's about the economics of doing this. The heavy oil industry in Bakersfield also lives with this issue. So what I'm looking for are some current plants, outside of our industries (CSS, SAGD) which operate high pressure boilers (sat'd) at less than ideal conditions. I really could use this help.

 

[NickDubya]

We manufacture OTSG 'Steam Generators' and would typically like to see 2000 ppm TDS max in the feed with a 1:10 concentration as it passes through giving 20,000 ppm in the carry over water, you mention 3500 from the resevoir which you then presumably treat in some fashion to end up with 8000 ppm? What sort of water treatment do you use. Silica forms a scale that is very difficult to remove and will cause problems with heat transfer leading to local overheating of the coil material. If you are using ph balancing chemicals to ensure the water is slightly alkaline, vast quantities of sludge conditioner - to reduce scale build up from the high TDS level, increased over-watering of the boiler - either by de-rating the burner or over running the pumps... fascinating... I've not come across this before - it's not an industry we have in the UK but I'd be interested in hearing what the treatment regime is. Have you considered a Reverse Osmosis plant to sort the water or have you seen this article...

http://www.worldoil.com/Magazine/MAGAZINE_DETAIL.asp?ART_ID=3321&MONTH_YEAR=Oct-2007,

this gives an insight into your industry for those who are not familiar and proposes a water treatment regime appropriate to the industry. Let me know how you get on.

 

[fatgit]

Gattwood

This isn't really something that you can afford to get wrong, the cost of boiler damage is too high. Not to mention the risks of pitting and gouging causing catastrophic failure.
Consult a treatment specialist or three! these guys will often do a survey for free as they will want to sell you their chemical treatments afterwards. Try to get hold of the Spirax Sarco book of water treatment. You won't become an overnight expert but you'll be speaking the right language when these guys arrive. You have got to know what's in the water, the risks posed by this and then take steps as appropriate
Goodluck