Steam Accumulators

ducon,

I having written some information on troubleshooting it basically envolves the food and dairy. on steamloads, traps, injectors and recovery, if you like I can email you this. I do not want to 'bury' you with more information.

After you looked it over you may see some items that you can use.

Phoenix911

Thanks buddy. Will highly appreciate if you mail me at duconems@yahoo.com.

Frankly about 8 years back I had given a dimensions of a steam accumulator on a 1.2 Tph steam generator and instructed the Client to have it made from a boiler manufacturer, duly passed & certified by Lloyd's. The Client picked up one of his old yarn dyeing vessel (since it matched the dimensions) and converted it into an accumulator. He was very happy since he overcame the steam starvation problem. I had repeatedly told him to get it certified. Within just days it "EXPLODED" right when the poor guy was standing there. He died instantly. I still feel bad even today that I am responsible for this. Everything was OK till I gave him the idea of the accumulator.

Had he had it hydraulically tested & certified this would not have happened.

I still pray for his soul since this is the only thing i can do.

The past experience frightens me to go ahead with a new one.

Anyway thanks buddy.

sorry to hear about that experience,

you did what you could,

good luck,

phoenix911

Sorry I can't help with any experience of Steam Accumulators, etc. - but please try not to feel bad. You obviously did your damnedest to get them to do it correctly, but if your client goes off on their own (ignoring your warnings) it's on their head and not your responsibility.

Best regards, John.

(Edit:

"Had he had it hydraulically tested & certified this would not have happened."

- Exactly.)

Thanks buddy.This time I'll have it designed & engineered not by me but an Engineering Company 10 times my size and highly reputable in pressure vessels, ensure the accumulator is fabricated by a reputable boiler maker (making water-tube boilers) & tested/certified. Call Spirax for all the instruments to be extra extra cautious.

Thanks & Rgds.

Thanks umpteen times for emailing me . I've downloaded the pdfs & opened them. Just briefly went thru to go in details in the morning (its 3.51am now).

Every bit helps.

Just let me know if there is anything I can do for you.

Thanks again n Rgds.

Perhaps I'm out of order as I have not had any direct experience with steam accumulators, all I remember of them was that they where used to drive steam driven tractor for moving material around the factory many years ago. But there is a point I would like to mention, I worked in a power station for 19yrs, and a Similar vessel is a boiler drum, and it is temperature sensitive, so an accumulator in a steam range that is undergoing large pressure swings, and in my mind that means temperature swings? this could lead to material failure. I raise the point as it is something you may wish to further investigate.

All the best in your endeavour. JD.

Steam Accumulators

Heat Storage? The best guide available I have found for information on Heat Storage, is to search on Google for Steam Accumulators and find latent heat storage, I think on the third page. I hope this will help you. Conserving thru Efficiency, The Electronic Condensate Controller DonnieH

Thanks. I got that as mentioned earlier. I just want the input from any member actually having & operating a steam accumulator.

I assume you are referring to "wet" accumulators, half full of water just below the flash point. They are great for instantaneous demand situations. They are widely used in situations where the instant demand is often 10 or more times the boiler output, but only lasts for a few seconds per cycle.

We have several in operation in various configurations and pressures. Do you have any specific questions?

"wet" accumulators, half full of water - Yes

instant demand is often 10 or more times the boiler output, but only lasts for a few seconds per cycle - Yes and designed for that peak load of 15/30/45 minutes.

We have several in operation in various configurations and pressures. Do you have any specific questions? Great. I will prepare specefic questions and mail you.

Thank you.

interesting. beriberi has put in great info. must keep reading.

Do you have any specific questions?

My application will be on a boiler 8000 kg/hr at 10 bar with a shortfall of 5000 kg/hr for 30 min at 8 bar. I am aware of the engineering & designing as well as instruments & equipments.

We have several in operation in various configurations and pressures.

What configurations and pressures you are utilizing?

Do they really work with ease as theoretically detailed?

Any problems encountered during operation?

Any tips you can provide to be extra careful prior activation?

Are they worthwhile the expense ?

My application will be on a boiler 8000 kg/hr at 10 bar with a shortfall of 5000 kg/hr for 30 min at 8 bar. I am aware of the engineering & designing as well as instruments & equipments.

Assume you have run the numbers, but this looks very doable. Surface area is the key. We have always used numbers from BASF: Maximum steaming rate = 3 * area * psia.

What configurations and pressures you are utilizing?

These have been installed over a period of years and philosophies have evolved...not necessarily results. All are half full with condensate traps at the half way mark. Different configurations of regulation: before, after, or none. Two units use back pressure valves between boilers and accumulators. Pressures vary depending on the process, but most run at either 6-7 bar or 3-4. Most efficient for us seems to be in line: boiler to backpressure valve to accumulator to prv to system header.

Do they really work with ease as theoretically detailed?

Yes, we tend to forget they are there. We have had experts tell us we should put them parallel to our demand with valves and bells and whistles. Since we like simplicity, we have kept control to a minimum.

Any problems encountered during operation?

The main problem we have had is boiler water carry over. This is not the fault of the tank. In Ohio we have an arcane law that limits us to less than 350 sq. ft. of heat tansfer surface per boiler. This results in a 75 HP shell with enough of a blower to get 225 HP output...theoretically. With this small of a shell there is not enough steaming surface area and carryover is always a potential problem. Hence, the back pressure valve. If it isn't working properly the tds builds up in the accumulator and will occasionally get into the process.

Any tips you can provide to be extra careful prior activation?

1) Start up empty. It will soon fill up with water on its own. Cold water and steam don't mix well. 2) have a nice long well protected sight glass to monitor the water level. 3) The level will "bounce" a little, don't be alarmed.

Are they worthwhile the expense ?

Any time your instant demand is greater than your boiler output you have a potential need. If you suck the water out of your boiler and it shuts down to refill and recycle you have shortened its life and potentially lost production time. I speak from sad experience.

Thank you for your reply. It is really building me the confidence to go ahead if the client agrees. Enclosed my calculation. The Questions are not entirely for you for, this becoming and interesting engineering topic for many CR4 members to put their inputs too.

Steam Accumulator Sizing:

Charging 10 bar : Discharging 7 bar

Boiler rating : 8000 kg/hr

Maximum continuous rating : 7200 kg/hr at 90% efficiency.

Normal working pressure : 10 bar (hf = 781.6 kj/kg)

Maximum instant demand : 12,600 kg/hr (12.6 Tph) 30 minutes

Pressure : 7 bar (hf = 721.4 kj/kg)

Imperial Volume: D² x L x 6.22 = UK gallon

Steam Accumulator : Ø 12' x Length 24'

(12)² x 24 x 6.22 = 22392.0 Gal (UK) = 101,796.1 Litres /Kg = 101.8 m³

Water Capacity 90% = 20152.8 Gal (UK) = 91,616.48 Litres/ Kg = 91.6 m³

Metric Volume: π x D²

------- x height = m² x 1000 kg = m³

4

Steam Accumulator : Ø 4 m x Length 8 m

Metric Volume = 100.5 m³ = 100 m³

Water capacity 90% = 90 m³

Steam Storage Capacity:

= Diff. in enthalpy of water kj/kg x mass of water kg

-------------------------------------------------------------

Enthalpy of evaporation at lower pressure kj/kg

= (781.6 kj/kg – 721.4 kj/kg) x 91616.48 kg

-------------------------------------------------- = 2722.26/ 2700 kg steam flashed in 1 hr

2026

(1) In 30 min = 2700kg x 60 min/30 min = 5400 kg/hr (5.4 Tph) steam

Total Steam: Boiler + Steam Accumulator

= 7200 kg/hr + 5400 kg/hr = 12,600 kg/hr (12.6 Tph) every 30 min.

Steam storage = 12,600 kg – 7,200 kg = 5400 kg/hr/ 5.4 Tph

Steam required 30 min/ hr = 5400 x 30/60 = 2700 kg/cycle

Steam Accumulator charged 10 bar, discharged 7 bar, proportion of flash steam

= (781.6 kj/kg – 721.4 kj/kg)

-------------------------------------------------- = 0.0297 kg / kg water

2026

To produce 2700 kg flash steam = 2700 kg flash steam /0.0297 kg/kg water

= 90909.0 kg water / 90,900 kg water at saturation temperature.

Water 90% of volume of accumulator = 90.9 or 91.0 m³/ 90%

= 101 m² Total Vessel Volume.

101 m² Vessel Volume as calculated above 4m Ø x 8 m length.

I . Please comment on above and how to calculate Area of Flash steam available ?

Do we just take the percentage?

II. Now these are the questions which are bogging my no-good brain:

A. Question : How to calculate Area M² of steam space available & space available for

water ?

B . As per extract Spirax Sarco Module 3.22 which states" There is no theoretical limits to the size of a steam accumulator but of course practical consideration will impose restrictions."

Question:

B.1 When we can size the accumulator why no theoretical limits to the size?

C. As we calculated above:

30 min = 2700 kg x 60 min/30 min = 5400 kg/hr steam (1) Hence,

15 min = 2700 kg x 60 min/15 min =10800 kg/hr steam (2)

So, this then calculates out as:

(1) Boiler + Steam Accumulator Total Steam:

7200 kg/hr + 5400 kg/hr = 12,600 kg/hr (12.6 Tph) every 30 min.

(2) Boiler + Steam Accumulator Total Steam:

7200 kg/hr + 10800 kg/hr = 18000 kg/hr (18.0 Tph) every 15 min.

Questions:

C. 1 Does this then mean that can we get also 18.0 Tph for continuous 15 min

then drop down to 7,200 kg/hr?

C.2 How long it will take to recharge to be ready again?

C.3 How does the Accumulator actually operate based on (1) or (2)?

This is the experience that I want you to share.

Trust you do understand what is actually bothering me?

(Will appreciate answer point-wise)

Note:

You can download Module 3.22 Steam Accumulators by going to Spirax Sacro learning .

Read & work on the formulas then reply. No hurry.

Thanks.

To Do Lists:

1. Designing & Engineering, Plate thickness, Dish depth etc.
2. Fabrication & Certification.
3. Steam Pipeline sizing/connection.
4. Steam Separator outlet Boiler & Accumulator (for carry over).
5. Injector Sizing/selection/location.
6. Air Vent & Vacuum Breaker.
7. Gauges: Pressure, Temperature & Gauge Glass set.
8. Valves: Main outlet Valve, Safety Valve, Disk Check Valve, Drain Valve.
9. Steam Trap Ball Float on over flow sizing & selection.
10. Surplussing Valve boiler 10 bar.
11. Pressure Reducing Valve accumulator 7 bar.
12. Steam Flow Meter.
13. Condensate Power Pump to return Trap condensate to feed tank.
14. Insulation & Cladding.
15. Commissioning & Startup.

Ducon-

Unfortunately, I still am employed and should spend my time on my own projects, so this will be brief.

Question : How to calculate Area M² of steam space available & space available for water?

Spirax is pretty good in their methodology to determine the vessel size, but mentions that in a new process there is still some guessing needed to avoid undersizing.

Our peak demands are measured in seconds rather than minutes. We have up to 15 machines on random cycling so we have taken the approach that we need the maximum surface area, hence the horizontal cylinder half full approach. We have totaled the average demands for the machines and sized the steam supply to be slightly greater, but use the accumulator to smooth out the bumps which can add to 3 to 4 times boiler output at any instant.

When we can size the accumulator why no theoretical limits to the size?

I guess you need to have the theoretical size first, then work out the practical from there. For example, we limit our diameter to 9 feet, since this is largest dimension allowed across the roads without permits.

Ducon-

I didn't review your calculations, but think you need to trust your abilities. Your methods appear solidly thought out. Hope your bad experience didn't shatter your confidence.

BTW, where are you located on this green earth?

Hope your bad experience didn't shatter your confidence.

Honestly speaking beriberi it did. But after what you wrote to me about your personal experience esp. "Yes , we tend to forget they are there" together with complete details to all my questions and the contribution of Mr. Abdel Halim Galala on the fabrication material specification I've regained my confidence.

This is from the core of my heart that, had it not been for you sharing with me your personal experience it would not have been possible. I am born again.

One more request, please send me your e-mail address to keep in touch with you and if you are in Canada/USA I'd love to visit you personallly whever possible to thank you.

The only accumulators that I have dealt with is an accumulator for a steam catapault on an aircraft carrier, it provided steam to the shuttle of the catapault that actually launched the aircraft. These worked very well with not too much trouble. I hope I can expand on this if you require me to; just let me know if it could be ob any help.

That the way I understood an accumulator, Store larger amount of energy during off peak times for release when the boiler is undersized

Yes Phoenix911. You can go to spirax sarco learning and down load M3.22 on Steam Accumalotors Pdf detailing everything you ever want to know.

spirax sarco has had good information for as long as I can remember

Hi phoenix,

The reason the catapault had an accumulator was to ensure that with every launch the steam condition is the same and not relying on boiler pressure which could alter from launch to launch. The boilers were not undersized, however steam requirements could differ for each launch, dependent on sea, wind conditions and speed of the vessel.

As I recall a long time back when I went to a Hevay Foundry Forge Plant, where they had a Steam Forgeing Press requiring 10 T steam from the boiler at 7 bar. The Steam would go to the press, the press come down "bam" and "whoosh" the steam exhausted. There was no accumulator and the Boiler would come down to 0 bar lock out. They would waint a couple of hours for the boiler to restart, gain pressure before they would start the second press cycle. The Steam Accumulator would've made production faster on the time lost at the boiler getting ready. Good application on the catapault.

Was that a fire tube boiler? Certainly sounds like it.

In warships they used to have high forcing rate water tube boilers (Admiralty three drum with superheaters) on the aircraft carrier and a couple of older destroyers, all the smaller vessels had Foster-Wheeler controlled superheat boilers @ 600psi and the DDGs had the "D" type Foster - Wheeler boilers @ 1 200psi. Now all ships (warships) are gas turbine or diesel.

Was that a fire tube boiler? Certainly sounds like it. Unfortunately Yes.

the aircraft carrier

The catapult you were mentioning were for this?

Foster-Wheeler controlled superheat boilers @ 600psi and the DDGs had the "D" type Foster - Wheeler boilers @ 1 200psi.

Boy, these are some boilers. The biggest I've seen here is 1900 psi at a Power plant.

up to 600psi at Sugar Mills.

Mine are Processing Industries(Textiles,Tanneries, Pharmaceuticals, Food etc.) where 98% boilers are packaged fire-tube 10 bar. Maximum 15 Tph.

the aircraft carrier

The catapult you were mentioning were for this?

Yes ducon it was. The catapault actually launches the aircraft from the deck of the carrier. At the bottom of the top illustration you will see a cylinder (under 8), this is the accumulator. The photo just shows an aircraft on the catapault. A little bit of trivia, some of the latest catapaults deliver 75 000 000ft.lbs of energy and can accelerate a mass of 79 000lbs to 140 knots in 302'.

Those monster carriers in the US navy have four steam catapaults.

The boilers that were used in warships were very flexible to cater for manoeuvring at high speeds from full ahead to full astern to stop numerous times in very shot periods of time.

Would you call a Flash Tank a Steam Accumulator? That is what I feel is being discussed. Can Steam Be Stored as a vapor or must it be stored as a liquid under Pressure? If so what is it called? Could Condensate be considered liquid Steam? The answer to these question is determined by the engineered specifications that were required when designing a Steam/Condensate system using a Steam Accumulator to supply a short high energy demand the Boiler is unable to supply.

Would you call a Flash Tank a Steam Accumulator?

No. It just a receiver to vent flash steam from condensate to ease condensate pumping to the boiler lest the pumps are damaged by cavitation.

The only pump that can handle 100C condensate without damage or cavitation are condensate power pumps (as the photograh under may name) and that too has a receiver to collect condensate from various sources and can be connected both with open & closed system with the pump. The flash steam does not affect the pump.

Please read : Flash steam & condensate power pump for further information.

Unless you register as a member I'd abstain from going into technalities.

Somebody can please tell me the cost related to the above mentioned spec of the steam accumulator? Hoping a general value. Just to get an idea...

It has been a while since I purchased one, but I would guess a 9' dia. x 24' long unit would cost in the ballpark of 40,000 USD. This does not include any valving or installation.